ALBERT

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): Rik Gijsman, Jan Visscher, Torsten Schlurmann〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Migration of nearshore sandbars results from nonlinear interacting hydro- and morphodynamic processes in the surf zone of wave dominated sandy shorelines. To gain new insights in the largely varying temporal effects of shoreface nourishments within these areas, the principle component analysis is applied to sixteen data sets with i) natural sandbar migration on different timescales and ii) interfering shoreface nourishments. The statistical methodology is able to separate the non-stationary effects of shoreface nourishments from the natural stationary migration of the sandbars. Depending on other long-term morphodynamic changes and nourishment interactions in the data, the duration of these interferences (the nourishment lifetimes) can be quantified. Relating these nourishment lifetimes (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈msub〉〈mrow〉〈mi〉L〈/mi〉〈/mrow〉〈mrow〉〈mi〉n〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉) with respect to the bar cycle return periods (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"〉〈mrow〉〈msub〉〈mrow〉〈mi〉T〈/mi〉〈/mrow〉〈mrow〉〈mi〉r〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉) of these areas (e.g. the relative nourishment lifetime) of twenty-one shoreface nourishments with several design parameters, and parameters of the sandbar system in which they were placed, remained inconclusive. A negative exponential fit with the bar cycle return period itself was the most significant (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"〉〈mrow〉〈msup〉〈mrow〉〈mi〉r〈/mi〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉  = 0.41). Assuming a linear system of the parameters increases the predictive capability (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"〉〈mrow〉〈msup〉〈mrow〉〈mi〉r〈/mi〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉  = 0.67). The most influential parameters in this relation are the nourishment concentration (+), the nourishment depth (+), the concentration of the migrating sandbars (−) and the bar cycle return period (−), thereby indicating the prominent roles of both nourishment design and natural sandbar system in the inter-site variability of shoreface nourishment lifetimes.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): G.K. Bullard, R.P. Mulligan, A. Carreira, W.A. Take〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Landslides into water can generate massive tsunamis which are major natural hazards in coastal regions. In this study, waves were generated in a series of 41 laboratory experiments by releasing 4 different slide volumes ranging from 0.1-0.4 m〈sup〉3〈/sup〉 of highly mobile material down a 6.73 m long slope into a reservoir of depth varying from 0.15-0.65 m, to achieve a wide range of dimensionless landslide parameter values. Water is used as the sliding material and with zero internal shear strength it is representative of the upper limit of high landslide mobility. The slide characteristics of thickness and velocity were measured at impact using high speed cameras and the time series of the resulting changes in water surface elevation were measured using nine wave probes along the 33.8 m long flume. The experimental results indicate that in the near-field the maximum wave amplitude is dependent on the landslide thickness and velocity and is relatively independent of the reservoir water depth. As waves propagate to the far-field, the depth-limited breaking reduces the wave amplitude, such that the maximum wave amplitude is highly dependent on the reservoir depth. The wave breaking limit, which differentiates the breaking from the non-breaking waves, is defined by the relationship 〈em〉a〈/em〉〈sub〉〈em〉m〈/em〉〈/sub〉〈em〉/h〈/em〉 = 0.6 that is very closely adhered to for all source volumes and reservoir depths. The time and length over which the waves are generated are determined from the digital imagery, and are used to describe the scales of the momentum transfer. These observations are compared with previously published empirical and theoretical equations for granular landslides and positively buoyant avalanches, indicating that water is a useful source material for simulating highly mobile landslides. Since these parameters are difficult to obtain in field cases, a simplification of the theoretical equation is presented and this yields reasonable results for the maximum wave amplitude generated by slides with high mobility.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): Yuli Liu, Chin H. Wu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A Lifeguarding Operational Camera Kiosk System (LOCKS) is developed and implemented at the North Beach of Port Washington, WI to provide real-time flash rip warnings to beach users for the first time. LOCKS has three components. First, a real-time environmental observation system acquires timely beach view images and local environmental condition data. Second, an integrated nowcast forecast operational system, a high performance and distributed computing infrastructure, digitally detects and assesses flash rip hazards in high, moderate or low risks. Third, an automated kiosk dynamically issues real-time warnings on site by a three-color dynamic lights and a digital display monitor. Results of flash rip detection show that the combined length threshold and HSV-based segmentation method can be used in both sunny and cloudy days with an overall accuracy of 83%. Nonstationary locations and intermittent occurrences of flash rips are observed and characterized. The length of the flash rip ranges between 10 and 50 m. The duration of flash rips varies from 1 to 5 min with 65% of flash rips less than 2 min. A flash rip occurrence checklist by adding two new (storm and visual observation) factors is constructed to reliably assesses the likelihood of hazardous flash rips. Public communication through media mentions, news releases, and website usages show the strong interest and support of the LOCKS as a new approach to issue timely and dynamic flash rip warnings to beach users. LOCKS can be used to issue warnings of other types of rips like bathymetry-controlled and boundary-controlled rip currents in the future.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 22 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Miguel Esteban, Jochem Jan Roubos, Kotaro Iimura, Jorrit Thomas Salet, Bas Hofland, Jeremy Bricker, Hidenori Ishii, Go Hamano, Tomoyuki Takabatake, Tomoya Shibayama〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The accurate modelling of overtopping of coastal defences by tsunami waves is of vital importance for the formulation of disaster management strategies. To improve knowledge of this phenomena the authors conducted experiments on coastal structure overtopping using bores that were generated by a dam-break mechanism. Three types of structures were tested, namely a coastal dyke, a wall, and a wall of infinite height. The results highlight the necessity to consider the energy present in a bore to determine if a structure will be overtopped or not. As a result of these experiments an empirical formula to determine the height of overtopping given the incident bore height and velocity was validated. The study highlights the importance of clearly modelling the velocity and Froude number of a tsunami. Such experiments should be conducted on rough beds, for which a suitable Manning's n seems to be around 0.06 sm〈sup〉-1/3〈/sup〉. The study also contrasted the results obtained to those of the ASCE7 method, and concludes that the Manning's n values recommended in ASCE7 are probably too low.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): Sara Mizar Formentin, Barbara Zanuttigh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper proposes a semi-automatic and customizable procedure for the identification of the overtopping waves based on a threshold-down-crossing analysis of the sea surface elevation signals. The procedure can be applied to 2D experimental and numerical signals, to emerged and submerged structures, with the same accuracy of a human-supervised analysis. The procedure includes an original and innovative algorithm to compare the water level signals at consecutive gauges and couple the waves propagating in between. The coupling algorithm implies a series of original applications of practical relevance, such as: i) the computation of the wave celerity, which is a crucial parameter for the assessment of the structural stability and the hydraulic vulnerability of the landward area; ii) the estimation of the wave overtopping discharge, which can be obtained by integrating the wave celerities with the surface elevations; iii) the description of the wave overtopping characteristics and their evolution over the structure crest; iv) the evaluation of the volumes lost for percolation in permeable structures. The application to new and literature data and the comparison with well-established formulae prove that the results obtained from the identification and coupling procedures are accurate and reliable.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): Eleonora Perugini, Luciano Soldini, Margaret L. Palmsten, Joseph Calantoni, Maurizio Brocchini〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The accuracy of bathymetry estimated by optical implementations of remotely sensed depth inversion algorithms is in part related to the presence of optical wave signal in the images, which depend nonlinearly on the water surface slope. The signal to noise ratio in video images of waves decreases under large azimuthal angles between the camera and wave propagation direction, which can result in poor bathymetry estimation. We quantified errors in depth estimation by analysing the sensitivity of the optical implementation of cBathy v1.1, a widely applied algorithm for depth inversion in coastal regions, to wave viewing angle using synthetic tests. We found relative root mean square errors between 0.02 and 0.08 when the azimuthal angle between the camera look direction and wave approach was less than 75°. However, for higher azimuthal angles, the wave signal was dominated by short wavelengths in the optical images leading to larger depth errors (relative root mean square error = 0.2). We also investigated the sensitivity of the initial guess of the wave direction in the nonlinear solution used by the cBathy v1.1 algorithm to estimate water depth. Observed water depth errors caused by wave viewing angle or initial guess of the wave direction are shown in part to be related to errors in the estimates of frequency and wavenumber. The synthetic methodology and the results of the sensitivity analysis can be generalized to test the accuracy of depth estimation in shore-based video monitoring systems, to design future fixed camera coastal video monitoring stations or to drive the choice of the better viewing angles using small Unmanned Aerial Systems (sUAS) using the Matlab Toolbox we developed.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 143〈/p〉 〈p〉Author(s): Ali Albatal, Heidi Wadman, Nina Stark, Cagdas Bilici, Jesse McNinch〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In order to investigate the effect of wave processes on the geotechnical characteristics of topmost sediments, a Portable Free Fall Penetrometer (PFFP) was deployed in the energetic nearshore zone of the U.S. Army Corps of Engineers' Field Research Facility (FRF) in Duck, NC. A total of 335 deployments were conducted from the FRF's 560 m long pier over six non-consecutive days in September and October of 2016. During the surveying period, significant wave heights varied between 〈em〉H〈/em〉〈sub〉〈em〉s〈/em〉〈/sub〉 = 0.8–2.4 m measured at a water depth of 17.4 m. The results showed that the sediment strength is affected by the wave climate. The derived average maximum quasi-static bearing capacities (〈em〉qsbc〈/em〉), which reflects sediment strength, during low energy wave periods (September 22–24 and 26; 〈em〉H〈/em〉〈sub〉〈em〉s〈/em〉〈/sub〉 = 0.8–1.3 m) ranged between 67 and 73 kPa with maximum 〈em〉qsbc〈/em〉 values of 120–136 kPa, while the average values were 47–59 kPa with a maximum 〈em〉qsbc〈/em〉 of 82–98 kPa during the high energy wave periods (October 5–6; 〈em〉H〈/em〉〈sub〉〈em〉s〈/em〉〈/sub〉 = 2.4 m). Results also showed that the sediment strength decreased in the shallow water depth regions in spite of the increase in the particle size distribution, due to the increasing wave impact on the seabed within the shallow water region. The area where seabed strength variations were affected by the wave action became wider in the cross-shore direction as the wave height increased. Results further showed that the strength of the topmost sediment layers varied spatially along the profile and temporarily with variations in significant wave height. This likely reflects the impact of waves on sediment strength.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 143〈/p〉 〈p〉Author(s): Julia W. Fiedler, Pieter B. Smit, Katherine L. Brodie, Jesse McNinch, R.T. Guza〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Numerical models predicting surfzone waves and shoreline runup in field situations are often initialized with shoreward propagating (sea-swell, and infragravity) waves at an offshore boundary in 10–30 m water depth. We develop an offshore boundary condition, based on Fourier analysis of observations with co-located current and pressure sensors, that accounts for reflection and includes nonlinear phase-coupling. The performance of additional boundary conditions derived with limited or no infragravity observations are explored with the wave resolving, nonlinear model SWASH 1D. In some cases errors in the reduced boundary conditions (applied in 11 m depth) propagate shoreward, whereas in other cases errors are localized near the offshore boundary. Boundary conditions that can be implemented without infragravity observations (e.g. bound waves) do not accurately simulate infragravity waves across the surfzone, and could corrupt predictions of morphologic change. However, the bulk properties of infragravity waves in the inner surfzone and runup are predicted to be largely independent of ig offshore boundary conditions, and dominated by ig generation and dissipation.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 143〈/p〉 〈p〉Author(s): Dawei Guan, Shih-Chun Hsieh, Yee-Meng Chiew, Ying Min Low〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Submarine pipelines are widely used for the conveyance of hydrocarbons, oil or other fluids in the offshore industry. Although much progress has been made on pipeline-seabed interactions in the past decades, an experimental study solely devoted to investigating interactions between the flow fields, scour and forced vibrating pipelines in a quiescent water environment still has not been conducted. In practice, this condition, to a certain extent, resembles a Steel Catenary Riser (SCR) in deep offshore environments in the absence of currents and waves. The present study aims to obtain an improved understanding of the mechanics of scour around a forced vibrating pipeline in quiescent water. Tests with the same initial gap ratio 〈em〉G〈/em〉〈sub〉0〈/sub〉/〈em〉D〈/em〉 = 1 and two different induced frequencies were conducted. A circular cylinder with a diameter of 3.5 cm was used as the pipeline model. With the help of a high-speed camera, the details of flows, pipeline motion and scour process are vividly presented in this paper. The magnitudes of flow velocity, vorticities, and turbulence fluctuations are found to be strongly dependent on the frequency of the vibrating pipeline. The scour mechanism of the two tests is different because of the complex interactions between the flow fields and pipeline motion. For the low-frequency case, the flow field associated with the falling stage of the vibrating pipeline controls the formation of the scour trench. On the other hand, for the high-frequency test, the scour process is controlled by the flow field during the rising stage of the vibrating pipeline.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 143〈/p〉 〈p〉Author(s): Wen-Gang Qi, Yi-Xuan Li, Kai Xu, Fu-Ping Gao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Under the actions of ocean waves and current, severe local scour can be induced around pile groups, significantly compromising the safety of marine structures. A series of flume tests were conducted for physical modelling the local scouring process around twin piles in the cohesionless soils under combined waves and currents, and compared with the pure current case. The effects of non-dimensional pile spacing (〈em〉G/D〈/em〉) and flow skew angle (〈em〉α〈/em〉) on the scour depth and time scale of scour around twin piles are intensively examined. The experimental observations indicate that the influence of pile spacing on the scour depth development is much more significant for the side-by-side (〈em〉α〈/em〉 = 90〈sup〉ο〈/sup〉) arrangement than that for the tandem arrangement (〈em〉α〈/em〉 = 0°). With the increase of flow skew angle 〈em〉α〈/em〉, the maximum scour depth is remarkably enhanced within the examined range 0 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mo〉≤〈/mo〉〈/math〉 G〈em〉/D〈/em〉〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mo〉≤〈/mo〉〈/math〉 3.0. When 〈em〉G〈/em〉/〈em〉D〈/em〉 = 3.0, the pile group effect on the time scale is generally negligible for pure current cases, whereas a prominent pile-group effect can still be observed for combined wave-current cases, especially for the side-by-side arrangement. A parameter of "equivalent pile diameter" is then introduced for evaluating the maximum scour depth at the twin piles with the previous formulas for the single pile. Based on the existing and present experimental data, the empirical formula of dimensionless equivalent pile diameter as the function of 〈em〉G/D〈/em〉 and 〈em〉α〈/em〉 is established to predict the maximum scour depth at the twin piles.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 29 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Tomohiro Suzuki, Zhan Hu, Kenji Kumada, Linh Khanh Phan, Marcel Zijlema〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A new wave-vegetation model is implemented in an open-source code, SWASH (Simulating WAves till SHore). The governing equations are the nonlinear shallow water equations, including non-hydrostatic pressure. Besides the commonly considered drag force induced by vertical vegetation cylinders, drag force induced by horizontal vegetation cylinders in complex mangrove root systems, as well as porosity and inertia effects, are included in the vegetation model, providing a logical supplement to the existing models. The vegetation model is tested against lab measurements and existing models. Good model performance is found in simulating wave height distribution and maximum water level in vegetation fields. The relevance of including the additional effects is demonstrated by illustrative model runs. We show that the difference between vertical and horizontal vegetation cylinders in wave dissipation is larger when exposed to shorter waves, because in these wave conditions the vertical component of orbital velocity is more prominent. Both porosity and inertia effects are more pronounced with higher vegetation density. Porosity effects can cause wave reflection and lead to reduced wave height in and behind vegetation fields, while inertia force leads to negative energy dissipation that reduces the wave-damping capacity of vegetation. Overall, the inclusion of both effects leads to greater wave reduction compared to common modeling practice that ignores these effects, but the maximum water level is increased due to porosity. With good model performance and extended functions, the new vegetation model in SWASH code is a solid advancement toward refined simulation of wave propagation over vegetation fields.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 24 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Nadeem Ahmad, Hans Bihs, Dag Myrhaug, Arun Kamath, Øivind A. Arntsen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Scour is recognised as one of the major causes of seawall failure. This paper presents numerical modelling of seawall scour due to wave impact on a vertical seawall. The modelling of waves hydrodynamics is based on the solution of the Reynolds-Averaged Navier-Stokes equations with the k-〈em〉ω〈/em〉 model. Fifth-order Stokes waves are generated in a numerical wave tank (NWT) using the relaxation method. The free surface under the breaking wave is captured with the level set method. The wave field is coupled with a sediment transport algorithm to simulate seawall scour. The model is validated for an accurate wave field and the seawall scour due to the wave impact. The accuracy of the simulations is assured by comparing the numerical results with the theory and the experimental observations. The numerical results give insight into the seawall scour process through different stages. The results show that the seawall scour is governed by the breaking wave impact on the seawall. The development of the standing wave due to the reflected wave energy from the seawall leads to further sediment transport seawards. Finally, the model is used to simulate seawall scour for different scenarios of seawall locations, incident wave height and seabed slope. The study examines the wave impact on the seawall toe and resulting scour. The maximum seawall scour is observed when the seawall is located at the intersection point of the still water depth and the bed slope. A displacement of the seawall from the intersection point leads to a decrease in the wave impact. The surf similarity parameter 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉ξ〈/mi〉〈/mrow〉〈mrow〉〈mn〉0〈/mn〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 is recognised as an important factor affecting the seawall scour.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 144〈/p〉 〈p〉Author(s): Bingchen Liang, Zhuxiao Shao, Huajun Li, Meng Shao, Dongyoung Lee〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The reasonable estimation of design wave heights is crucial for coastal and offshore engineering practices. To obtain sufficient data for model estimation, the peak over threshold (POT) method with the generalized Pareto distribution (GPD) model is employed. When using this method (i.e., the POT/GPD method), peak excesses over a sufficiently large value (i.e., threshold) are fitted. The extrapolated significant wave heights are highly dependent on the threshold, which must carefully be determined. In this study, significant wave heights from a 40-year (1975–2014) hindcast of tropical cyclone waves in the South China Sea (SCS) are adopted as the initial dataset to study extreme significant wave heights. Based on this initial dataset, the threshold selection is studied by analysing the influence of the excluded samples on the return significant wave heights when the threshold continuously increases. A stable threshold range corresponding to stable return significant wave heights is found, which exhibits a high probability of containing the suitable threshold. To determine the suitable threshold within the stable threshold range, an automated threshold selection method based on the characteristic of extrapolated significant wave heights (ATSME) is proposed. As shown by the reliability (via asymptotic tail approximation and estimation uncertainty) of the POT/GPD method and comparison with other threshold selection methods (i.e., the GPD parameter plot and automated threshold selection method based on the characteristic of the modified scale parameter (ATSMP)), the thresholds obtained by the ATSME are reasonable. Considering that the proposed method is based on the characteristic of extrapolated significant wave heights, data (such as measured, simulated and calculated data) participating in the extrapolation must carefully be processed, which influence the extrapolated results.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 146〈/p〉 〈p〉Author(s): Hassan Akbari, Amir Taherkhani〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The response of a composite breakwater against wave load is numerically investigated using Smoothed Particle Hydrodynamic (SPH) model. Permeability of the stone layer beneath the caisson is implemented in the model and a new scheme free of any tuning parameter is introduced to estimate the dynamic friction forces transitionally applied to the moving caisson. To overcome pressure noises inside the porous medium, a treatment based on δ-SPH scheme is utilized and its performance is verified by modeling a simple hydrostatic condition inside a homogeneous porous medium. The model ability in simulating fluid flow through porous media is approved by modeling dam break flow through a porous block. In addition, a caisson breakwater with an impermeable bed is modeled and the results are compared with experimental and other numerical results to validate the performance of the introduced friction coefficient. Then, the same caisson but with a permeable bed is simulated against the incident waves and the horizontal forces as well as sliding displacements are calculated. Good agreements with the experimental data show the acceptable performance of the developed model as well as the importance level of the permeable bed on the caisson response. Based on the results, neglecting the flow through the porous bed of the caisson may result in an overestimated wave force and an underestimated caisson sliding. Finally, the caisson responses to different wave conditions are studied and it is shown that the peak load on the caisson increases as the wave height or wave period rises.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 145〈/p〉 〈p〉Author(s): Enrico Di Lauro, Javier L. Lara, Maria Maza, Inigo J. Losada, Pasquale Contestabile, Diego Vicinanza〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉This paper presents the stability analysis of a non-conventional breakwater cross-section integrating an overtopping wave energy converter, named OBREC. The device consists of a traditional rubble-mound breakwater in which the upper part of the armour layer is replaced by a smooth ramp and a reservoir.〈/p〉 〈p〉The analysis of the structure is carried out by combining model scale experiments and numerical simulations based on the Volume-Averaged Reynolds Averaged Navier-Stokes (VARANS) equations.〈/p〉 〈p〉The numerical analysis is used to complete and extend the results of the physical model test campaign, providing a deeper understanding of the pressure distribution and resultant force behaviour in locations where laboratory measurements were difficult to obtain or not available. Results show that the maximum vertical and horizontal total forces on the device are not simultaneous. At the time instant of the maximum total horizontal force, the vertical force is zero or directed downward, due to the significant positive contribution of the force acting on the sloping ramp. Additional numerical simulations show the influence of the submerged ramp length on the forces acting on the structure using the global and local stability analysis. The presence of the shaft contributes positively to the global stability against the sliding failure mode by reducing the uplift force exerted on the horizontal base. Moreover, the stability analysis shows that the critical conditions for the global failure modes occur at different time instants.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 145〈/p〉 〈p〉Author(s): Bas Hoonhout, Sierd de Vries〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Mega nourishments are a novel approach to stimulating coastal safety and resilience. Mega nourishments are intended to spread along the coast on a decadal time scale by natural sediment transport processes with a minimum of intrusion into the natural coastal system. The supratidal morphodynamic behaviour of mega nourishments is not well understood due to complexities introduced by limitations in sediment availability to aeolian sediment transport. Consequently, the effectiveness of mega nourishments to stimulate coastal safety and to influence coastal landscape and habitat development remains unknown.〈/p〉 〈p〉In this paper we present a detailed 4-year hindcast of the morphological development of the Sand Motor mega nourishment in The Netherlands. We use the aeolian sediment transport and availability model 〈span〉AeoLiS〈/span〉 that focuses specifically on the simulation of spatiotemporal variations in sediment availability. The model includes the recurrence relation between sediment availability and aeolian sediment transport through self-grading and beach armoring.〈/p〉 〈p〉We show that the model is able to reproduce multi-annual aeolian sediment transport rates in the Sand Motor domain in the four years after its construction. The RMSE is 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mn〉3〈/mn〉〈mo〉⋅〈/mo〉〈msup〉〈mrow〉〈mn〉10〈/mn〉〈/mrow〉〈mrow〉〈mn〉4〈/mn〉〈/mrow〉〈/msup〉〈mspace width="0.25em"〉〈/mspace〉〈msup〉〈mrow〉〈mtext〉m〈/mtext〉〈/mrow〉〈mrow〉〈mn〉3〈/mn〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉 (7% of the total sediment accumulation) and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈msup〉〈mrow〉〈mtext〉R〈/mtext〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉 is 0.93 when comparing timeseries of total sediment accumulation in the dunes, dune lake and lagoon. The combination of spatial and temporal variations in aeolian sediment availability, due to the combined influence of soil moisture, sediment sorting and beach armoring, is essential for an accurate estimate of the total sedimentation volume. The simulated feedback between aeolian sediment availability and transport is required for accurately describing compartmentalization of the beach and locating the aeolian sediment source areas in the Sand Motor domain.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 145〈/p〉 〈p〉Author(s): Krisna A. Pawitan, Aggelos S. Dimakopoulos, Diego Vicinanza, William Allsop, Tom Bruce〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Wave energy is one of the most promising marine energy resources in terms of the scale of the resource, but there remains little technology convergence and costs remain at near-prohibitive levels. Of many wave energy converter (WEC) concepts that have been developed over the years, the oscillating water column (OWC) stands out for its simplicity and low maintenance cost. Quite some experience of actual OWC operation has been gained to date from small, stand-alone pilot schemes. One way to reduce costs is the integration of an OWC-WEC into a breakwater, enabling some degree of cost-sharing between energy and harbour or coastal defence functions. A major problem encountered during the design of an OWC-WEC scheme remains the uncertainty in the wave loads, with their critical influence upon capital cost. A model to estimate forces acting on an OWC chamber in a caisson breakwater is proposed in this paper. Horizontal forces on the front (curtain) wall and the rear (in-chamber) wall are predicted. In addition, and unlike a conventional caisson breakwater, vertical forces acting on the caisson chamber ceiling will have considerable effect on sliding and overturning characteristics of the breakwater structure. The proposed model enables the prediction of chamber pressures which in turn influence the chamber vertical force. The new model has been compared with results from large scale physical model measurements from tests carried out in the very large wave channel, GWK, in Hannover (Germany). Forces under both regular and irregular wave conditions were measured. The comparisons show that the model fits well with the test results to the factor of 1 ± 0.2 for the regular wave cases and to the factor of 0.8 ± 0.2 for irregular wave cases. This model will enable the structural design of caisson breakwater-integrated OWCs to be approached with uncertainties reduced to those comparable with conventional caisson design.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 144〈/p〉 〈p〉Author(s): Alaa Khoury, Armelle Jarno, François Marin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper describes an experimental investigation of runup for intermediate sandy beaches from a physical modelling in a wave flume with tide simulation. Shoreline elevation measurements are acquired over a wide range of conditions using an optical method. Simultaneous morphological and hydrodynamic changes are considered to determine the best parameters to predict the maximum wave runup. The tidal level significantly affects the breaking conditions (position, height and type), and the slopes of the beach. Present data show that the surf zone slope and the wave breaking height should be used to estimate the maximum runup. The results are compared with previous formulations issued from the literature. A new formula is proposed for the runup estimation for intermediate beaches.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 146〈/p〉 〈p〉Author(s): Eranda Perera, Fangfang Zhu, Nicholas Dodd, Riccardo Briganti, Chris Blenkinsopp, Ian L. Turner〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A surface-groundwater flow model is developed for the swash flow on a barrier beach. The non-linear shallow water equations are used to simulate the surface flow. Laplace's equation is used to describe the groundwater flow and is solved using the Boundary Integral Equation Method to provide potential heads and normal potential derivatives at and within the boundaries of the barrier. An exfiltration incorporated bottom boundary layer sub-model is used to obtain bed shear stress. The groundwater model is verified against the numerical test results in Kazemzadeh-Parsi and Daneshmand (2012) for the groundwater flow through a rectangular dam. The coupled surface-groundwater model is validated against the prototype-scale BARDEX II experimental results (Turner et al., 2016). The steady-state groundwater flow comparisons show excellent agreement in phreatic surfaces. The comparisons of groundwater flow under the action of waves show reasonably good agreement with experimental results in phreatic surfaces. The simulated time averaged pore velocities for the runs with and without waves are in satisfactory agreement with experimental results in general, and certain discrepancies are observed near the beach side. The bed shear stress variation due to exfiltration is investigated by incorporating the modified logarithmic bottom boundary layer model of Cheng and Chiew (1998) in the coupled surface-groundwater flow model. The results confirm that as exfiltration increases, bed shear stress decreases as a result of thickening of the bottom boundary layer.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 154〈/p〉 〈p〉Author(s): Shengnan Liu, Inno Gatin, Charlotte Obhrai, Muk Chen Ong, Hrvoje Jasak〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Four different types of breaking wave impacts on a vertical wall are simulated using a two-dimensional two-phase Computational Fluid Dynamic (CFD) model. Air is considered as an isentropic ideal gas without solving an additional energy equation and water is treated as an incompressible liquid. The discontinuity in fluid properties across the free surface is treated using the Ghost Fluid Method, which accounts for the jump in density and compressibility. The numerical results are compared with large-scale experimental data for five cases in terms of surface elevations, total forces and pressure distributions along the wall, and a reasonable agreement is obtained overall. The characteristics of impact pressures under different breaking wave conditions are discussed and compared to each other. The two largest total forces on the wall occur in the ‘flip-through’ and ‘large air pocket’ cases. The peak pressure of the flip-through impact is localized in both time and space. The pressure within the trapped air pocket is nearly uniform with a smaller peak value and a much longer duration than that of the ‘flip-through’ case. The compression and expansion of the air pocket results in pressure oscillations, which are overestimated in frequency and amplitude due to the inaccuracy in capturing the air escape. The broken wave case has the smallest total force, but the largest local pressure among the present numerical cases, which demonstrates the necessity to study all different impact types.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 26 December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): S.I. de Lange, N. Santa, S.P. Pudasaini, M.G. Kleinhans, T. de Haas〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Debris-flow generated tsunamis can be extremely dangerous for lakeside settlements and infrastructure. Debris-flow composition strongly affects debris-flow thickness and velocity, and therefore also the generated tsunami. This interaction is, however, poorly understood. We investigate the effects of debris-flow volume, composition (gravel, sand, clay, water) and subaerial outflow slope on wave celerity and amplitude in a small-scale physical model consisting of an inclined outflow channel which transits into a three-dimensional water reservoir.〈/p〉 〈p〉We find that upon debouching, a debris flow pushes the water forward until wave celerity exceeds subaqueous debris-flow velocity (i.e. Froude number 〈1). The wave then detaches from the debris flow and travels into the far-field. Pushing of the debris-flow oversteepens and accelerates the generated wave beyond the celerity predicted by linear wave theory for shallow waves. It also increases its non-linearity but does not result in wave breaking.〈/p〉 〈p〉Wave celerity has the strongest relation with debris-flow velocity. Debris-flow velocity increases with increasing water and clay content (up to 22%), which both lubricate the flow. Far-field leading wave amplitude has the strongest relation with debris-flow momentum (velocity times effective mass), which is mostly a function of debris-flow thickness, water and clay content.〈/p〉 〈p〉We test the applicability of published (semi-empirical) equations for predicting tsunami amplitude generated by dry landslides, and show that they are to some extent also applicable to debris flow. Potential scale effects, especially considering the smallest waves and water depths, could influence the applicability of these predictors and translation of the results to the field scale. Our results demonstrate the importance of debris-flow composition on tsunami generation and evolution, and thus the necessity of including flow composition in predictive simulation models.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: May 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 147〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 149〈/p〉 〈p〉Author(s): Vera M. van Bergeijk, Jord J. Warmink, Marcel R.A. van Gent, Suzanne J.M.H. Hulscher〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉An accurate description of the maximum flow velocity across flood-protective structures is necessary in order to determine the stability of the landward slope and the amount of cover erosion. In this paper, two new formulas are derived to describe the change in the maximum overtopping flow velocity along the dike crest and the adjacent landward slope. These formulas are coupled in an effort to accurately predict the velocities in wave overtopping events. This analytical model is validated using 244 data points from flume tests and 300 data points from field tests on river dikes in the Netherlands. The modelled flow velocity shows good agreement with the measured flow velocity, with a Nash-Sutcliffe efficiency factor varying from 0.49 to 0.87. Also, the derived formulas are compared with existing formulas for wave overtopping flow velocities and overall showed a better performance for a wide range of geometries and covers.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 148〈/p〉 〈p〉Author(s): Xiaoteng Shen, Erik A. Toorman, Michael Fettweis, Byung Joon Lee, Qing He〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Floc Size Distributions (FSDs) of suspended fine-grained sediment flocs play a prime role to estimate their own fate and the transport of contaminates attached to the flocs. However, developing an efficient flocculation model that is capable of simulating continuous and multimodal FSDs is still a challenge. Recently, the population balance equation solved by the Quadrature-Based Method of Moments (QBMM) with lognormal kernel density functions has been developed to investigate the aggregation and breakage processes. It coincides with some recent observations which describe a measured FSD in coastal waters with a set of constituted lognormal distributions. The newly developed lognormal QBMM was tested with several ideal flocculation kinetic kernels, none of which, however, was used for interpreting cohesive sediment dynamics. Therefore, it raised our interest to evaluate the model performance for fine-grained sediments in shear turbulence dominated environments. In this study, additional validations against two kaolinite laboratory experiments were tested in the framework of the extended QBMM. It is hypothesized that these subordinate lognormal distributions share the same value of standard deviation. Different from the previous methods, the common standard deviation is determined empirically to reduce the number of tracers and better represent the FSDs. With sediment flocculation kinetics, the predicted FSDs reasonably reproduce the FSDs observed in both the mixing chamber and the settling column experiments. Despite the lacking of explicit descriptions of microbial effects at the current stage, this model has the potential to be implemented into large-scale particle transport models and deserves a more in-depth study in the future.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): Xuan Li, Wei Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Low-crested and submerged breakwaters, serving as one of the coastal defensive structures, are usually used to dissipate wave energy and help reduce wave impacts on coastal infrastructures and communities especially during extreme weather events, such as hurricanes or tsunamis. Many recent post disaster surveys indicated that breakwaters did not perform as designed during some extreme weather events. The performance of the breakwaters subjected to strong waves is still not clear especially when the breakwaters turn into the submerged condition. Meanwhile, many researches on the breakwaters are usually carried out in a two-dimensional wave flume either experimentally or numerically. However, the incident wave could impact the breakwaters from any directions instead of only from the head-on direction, which should be a three-dimensional physical process of wave and breakwater interactions. Therefore, it is essential to conduct a three-dimensional numerical study to investigate the breakwater performance in reducing the transmitted wave energy behind it and compare the results with those from a two-dimensional study. This study is to investigate the effect of three-dimensional interactions of obliquely incident waves and breakwaters on wave potential energy reduction based on the proposed energy transmission coefficient. Computational fluid dynamics (CFD) simulations are carried out in OpenFOAM to simulate the interactions between the wave and breakwater using a three-dimensional Reynolds-averaged Navier-Stokes (RANS) model together with the k-ω SST turbulence model. Two validation studies are performed to validate the applicability of the proposed numerical model in two-dimensional and three-dimensional numerical simulations. Sensitivity analyses are performed to investigate the effect of different parameters associated with breakwater geometries and incident wave properties on a two-dimensional submerged breakwater performance in reducing the transmitted wave height. The effects of incident wave angle on the transmitted wave energy reduction for a three-dimensional submerged and surface breakwater are then investigated and compared with the two-dimensional simulation results. The numerical studies indicate that a three-dimensional simulation is more appropriate to describe a breakwater behavior in the real-world scenario.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 18 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): M. Welzel, A. Schendel, A. Hildebrandt, T. Schlurmann〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper presents the results of an experimental study on the scour development of a hydraulic-transparent offshore foundation exposed to combined waves and current. Irregular waves propagating perpendicular to a current were simulated in a wave-current basin. The physical model tests were conducted in a length scale of 1:30 while measurements of the scour development over time were achieved by echo sounding devices placed at several locations at the upstream and downstream side of the jacket structure. Insights were gained on the scour development and time scale of the scouring process around a complex jacket structure for different wave-current conditions. The results were presented with respect to the Keulegan-Carpenter KC number and the relative wave-current velocity. Wave conditions were adjusted so that KC numbers between 6.7 and 23.4 could be tested in a systematic wave-current test program with tests reaching from wave dominated conditions up to current dominated conditions. Measured scour depths were critically assessed by an extrapolation to expected equilibrium scour depths. With respect to the current flow direction, the experiments showed generally larger scour depths at the upstream side and lower scour depths on the downstream side for each pile of the jacket structure. The development of global scour around the structure intensified with increasing relative wave-current velocity. As a result, a practical formulation is proposed for the reliable prediction of local scour depths around a jacket foundation in combined wave-current conditions. Finally, dimensionless time scales and observed as well as predicted scour depths are compared to values for the scour development around monopiles.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 26 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Gioele Ruffini, Valentin Heller, Riccardo Briganti〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Large landslide-tsunamis are caused by mass movements such as landslides or rock falls impacting into a water body. Research of these phenomena is essentially based on the two idealised water body geometries (i) wave flume (2D, laterally confined wave propagation) and (ii) wave basin (3D, unconfined wave propagation). The wave height in 2D and 3D differs by over one order of magnitude in the far field. Further, the wave characteristics in intermediate geometries are currently not well understood. This article focuses on numerical landslide-tsunami propagation in the far field to quantify the effect of the water body geometry. The hydrodynamic numerical model SWASH, based on the non-hydrostatic non-linear shallow water equations, was used to simulate approximate linear, Stokes, cnoidal and solitary waves in 6 different idealised water body geometries. This includes 2D, 3D as well as intermediate geometries consisting of “channels” with diverging side walls. The wavefront length was found to be an excellent parameter to correlate the wave decay along the slide axis in all these geometries in agreement with Green's law and with diffraction theory in 3D. Semi-theoretical equations to predict the wave magnitude of the idealised waves at any desired point of the water bodies are also presented. Further, simulations of experimental landslide-tsunami time series were performed in 2D to quantify the effect of frequency dispersion. This process may be negligible for solitary- and cnoidal-like waves for initial landslide-tsunami hazard assessment but becomes more important for Stokes-like waves in deeper water. The findings herein significantly improve the reliability of initial landslide-tsunami hazard assessment in water body geometries between 2D and 3D, as demonstrated with the 2014 landslide-tsunami event in Lake Askja.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 151〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 148〈/p〉 〈p〉Author(s): Vânia Veloso Lima, Paulo Avilez-Valente, Maria Ana Viana Baptista, Jorge Miguel Miranda〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉In this research work, a novel theoretical first-order formulation for the generation of N-waves in laboratory, by means of a piston-type wave-maker, is presented. The plate's trajectory, velocity and acceleration equations for the generation of tsunami N-waves in a wave flume are deduced. A set of laboratory experiments performed for the generation of leading depression N-waves in a wave basin is described.〈/p〉 〈p〉A Tadepalli–Synolakis N-wave profile is assumed and the equations for the paddle's trajectory, velocity, and acceleration and for the piston stroke and stroke period are derived and discussed in detail. Limits for the initial paddle velocity and acceleration are established.〈/p〉 〈p〉A set of experiments, devised and performed in the 28 m long wave basin of the Laboratory of Hydraulics, at the Faculty of Engineering of the University of Porto, is described. Six leading depression N-waves were selected and classified into three categories, according to their Stokes parameter. The results show that the shorter waves undergo a strong transformation, tending to a solitary wave-like pulse, followed by a trough. The longer waves show a distinct behaviour, tending to a bore-like wave exhibiting a leading trough. The generated longer waves presented the best results when compared with the expected Tadepalli–Synolakis N-wave profiles. Further investigation on the formulation of the wave velocity of the N-waves and on the behaviour of waves with higher order Stokes parameter is necessary.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 24 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Zhipeng Zang, Guoqiang Tang, Yanfei Chen, Liang Cheng, Jinfeng Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper presents experimental results on temporal developments of local scour below a partially buried pipeline under oblique currents/waves. The effects of the flow incident angle (〈em〉α〈/em〉 ≤ 45°, 〈em〉α〈/em〉 = 0° denotes that the currents/waves are perpendicular to the pipeline) and the embedment-to-diameter ratio (〈em〉e〈/em〉/〈em〉D〈/em〉 ≤ 0.5, 〈em〉e〈/em〉/〈em〉D〈/em〉 = 0 denotes no embedment) on the equilibrium depth and time scale of scour were quantitatively investigated. The experimental results indicate that with the increase of the embedment-to-diameter ratio from 0 to 0.5, the equilibrium depth of scour decreases by up to 30 and the time scale increases by approximately 5 times. With the increase of the flow incident angle from 0° to 45°, the equilibrium depth decreases by approximately 25% and the time scale increases by approximately 0.7 times. A uniform empirical relationship between the equilibrium depth for arbitrary conditions (〈em〉S〈/em〉, i.e., for 〈em〉α〈/em〉 〉 0° or 〈em〉e〈/em〉/〈em〉D〈/em〉 〉 0) and that for a conventional case (〈em〉S〈/em〉〈sub〉0〈/sub〉, for 〈em〉α〈/em〉 = 0° and 〈em〉e〈/em〉/〈em〉D〈/em〉 = 0) is newly proposed for both current and wave conditions based on theoretical derivation and curve fitting to the experimental data, where 〈em〉S〈/em〉〈sub〉0〈/sub〉 can be easily predicted from existing empirical formulae. The correlation analysis indicates that the experimental results of the equilibrium depth can be well represented by the newly proposed formula. For predicting the time scale of scour process, a theoretical approach based on the erosion rate of sediment, which was originally proposed for a conventional case, is expanded to arbitrary conditions. It is indicated that the time scales of scour obtained from the theoretical approach are well coincident with the experimental values. Finally, an empirical relationship between the time scale for arbitrary conditions (〈em〉T〈/em〉) and that for a conventional case (〈em〉T〈/em〉〈sub〉0〈/sub〉) was established based on the theoretical derivation. The newly proposed empirical formula is found to provide satisfactory predictions of the time scale compared with the present experimental results and those published.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 23 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Christopher G. Siverd, Scott C. Hagen, Matthew V. Bilskie, DeWitt H. Braud, Shu Gao, R. Hampton Peele, Robert R. Twilley〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The co-evolution of wetland loss and flood risk in the Mississippi River Delta is tested by contrasting the response of storm surge in coastal basins with varying historical riverine sediment inputs. A previously developed method to construct hydrodynamic storm surge models is employed to quantify historical changes in coastal storm surge. Simplified historical landscapes facilitate comparability while storm surge model meshes developed from historical data are incomparable due to the only recent (post-2000) extensive use of lidar for topographic mapping. Storm surge model meshes circa 1930, 1970 and 2010 are constructed via application of land to water (L:W) isopleths, lines that indicate areas of constant land to water ratio across coastal Louisiana. The ADvanced CIRCulation (ADCIRC) code, coupled with the Simulating WAves Nearshore (SWAN) wave model, is used to compute water surface elevations, time of inundation, depth-averaged currents and wave statistics from a suite of 14 hurricane wind and pressure fields for each mesh year. Maximum water surface elevation and inundation time differences correspond with coastal basins featuring historically negligible riverine sediment inputs and wetland loss as well as a coastal basin with historically substantial riverine inputs and wetland gain. The major finding of this analysis is maximum water surface elevations differences from 1970 to 2010 are 0.247 m and 0.282 m within sediment-starved Terrebonne and Barataria coastal basins, respectively. This difference is only 0.096 m across the adjacent sediment-abundant Atchafalaya-Vermilion coastal basin. Hurricane Rita inundation time results from 1970 to 2010 demonstrate an increase of approximately one day across Terrebonne and Barataria while little change occurs across Atchafalaya-Vermilion. The connection between storm surge characteristics and changes in riverine sediment inputs is also demonstrated via a sensitivity analysis which identifies changes in sediment inputs as the greatest contributor to changes in storm surge when compared with historical global mean sea level (GMSL) rise and the excavation of major navigation waterways. Results imply the magnitude of the challenge of preparing this area for future subsidence and GMSL rise.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 149〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: Available online 25 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Mitchell D. Harley, Michael A. Kinsela, Elena Sánchez-García, Kilian Vos〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Shoreline change information is critical for effective management of the coastal zone. This study presents a low-cost method for mapping shoreline change that harnesses smartphone images collected by the community and uploaded to social media platforms. A smartphone camera cradle installed overlooking a coastal region is used to constrain the crowd-sourced camera extrinsic parameters and accompanying signage instructs participants on how to share their image to social media using a site-specific hashtag identifier. Surveyed ground control points solve for the focal length of the smartphone lens and more-accurately resolve the camera extrinsic parameters. Shoreline position is subsequently mapped on georectified images using an edge detection technique based on the red and blue colour channels. A validation of the method was conducted at two sandy beaches in SE Australia and resulted in strong community participation (400 images submitted over 7 months by 198 individual contributors). Concurrent shoreline surveys using RTK-GNSS indicated that shoreline accuracy using this crowd-sourced approach is comparable to that of established coastal imaging systems, with cross-shore shoreline accuracy best for these two elevated validation sites (camera elevation = 17.3 m–27.1 m above MSL) in the camera nearfield (RMSD ≈ 1.4 m) and RMSD ranging between 2.6 and 3.9 m over coastal stretches spanning up to 1 km. Minimal differences in shoreline accuracy were observed between low resolution images characteristic of those uploaded to social media and higher resolution images sourced from the smartphone. The successful application of this low-cost approach, combined with the proliferation of smartphones and social media usage, open up new possibilities for crowd-sourced shoreline change mapping at suitable coastal locations worldwide.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): Ana Matias, Ana Rita Carrasco, Carlos Loureiro, Gerd Masselink, Umberto Andriolo, Robert McCall, Óscar Ferreira, Theocharis A. Plomaritis, André Pacheco, Martha Guerreiro〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Overwash hydrodynamic datasets are mixed in quality and scope, being difficult to obtain due to fieldwork experimental limitations. Nevertheless, these measurements are crucial to develop reliable models to predict overwash. Aiming to overcome such limitations, this work presents accurate fieldwork data on overwash hydrodynamics, further exploring it to model overwash on a low-lying barrier island. Fieldwork was undertaken on Barreta Island (Portugal) in December 2013, during neap tides and under energetic conditions, with significant wave height reaching 2.6 m. During approximately 4 h, more than 120 shallow overwash events were measured with a video-camera, a pressure transducer and a current-meter. This high-frequency fieldwork dataset includes runup, overwash number, depth and velocity. Fieldwork data along with information from literature were used to implement XBeach model in non-hydrostatic mode (wave-resolving). The baseline model was tested for six verification cases; and the model was able to predict overwash in five. Based in performance metrics and the verification cases, it was considered that the Barreta baseline overwash model is a reliable tool for the prediction of overwash hydrodynamics. The baseline model was then forced to simulate overwash under different hydrodynamic conditions (waves and lagoon water level) and morpho-sedimentary settings (nearshore topography and beach grain-size), within the characteristic range of values for the study area. According to the results, the order of importance of factors controlling overwash predictability in the study area are: 1〈sup〉st〈/sup〉) wave height (more than wave period) can promote overwash 3–4 times more intense than the one recorded during fieldwork; 2〈sup〉nd〈/sup〉) nearshore bathymetry, particularly shallow submerged bars, can promote an average decrease of about 30% in overwash; 3〈sup〉rd〈/sup〉) grain-size, finer sediment produced an 11% increase in overwash due to reduced infiltration; and 4〈sup〉th〈/sup〉) lagoon water level, only negligible differences were evidenced by changes in the lagoon level. This implies that for model predictions to be reliable, accurate wave forecasts are necessary and topo-bathymetric configuration needs to be monitored frequently.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 10 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Íñigo Aniel-Quiroga, César Vidal, Javier L. Lara, Mauricio González〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Rubble mound-breakwaters are commonly constructed with a parapet or crown-wall at the crest. The design of these superstructures depends on the expected storm wave load history throughout the service life cycle. In tsunami-prone areas, this design must include tsunami actions since their loads can definitely exceed those of storm waves. However, tsunami loads are rarely accounted for. This study aimed at incorporating tsunami actions in the design of crown-walls of rubble-mound breakwaters for the first time. Within this scope, laboratory experiments on a scaled model of a typical Mediterranean rubble-mound breakwater typology under tsunami actions were conducted. This paper is the continuation of our previous paper, Aniel-Quiroga et al. (2018) [1], in which experiments were presented and a stability analysis of the armor units was conducted. This research paper presents the second part of the analysis focused on understanding the pressures that crown-walls of rubble-mound breakwaters must support due to tsunami-like actions. These pressures were measured and analyzed, providing the horizontal and uplift pressure time series and laws. The magnitude and timing of the maximum pressure peaks were identified. The maximum horizontal pressure is caused by the first impact of the tsunami. By contrast, the maximum uplift pressure is prompted by a pressure wave generated by the overtopped water falling into the leeside. This pressure wave penetrates the structure from the rear slope. As a result of this analysis, pressures were characterized, allowing the presentation of a new complete methodology that provides, for the tested structure, the design procedure of the crown-wall under tsunami actions. A new formulation to calculate the run-up of solitary waves on the tested rubble-mound breakwater slope is presented here.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 9 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Edwin J.F. Drost, Michael V.W. Cuttler, Ryan J. Lowe, Jeff E. Hansen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Tropical Cyclone (TC) Olwyn travelled along the coast of Ningaloo Reef in northwestern Australia as a Category 3 TC during 12-13 March 2015 with sustained wind speeds over 130 km hr〈sup〉-1〈/sup〉 and significant wave heights on the forereef reaching 6 m. Observations from TC Olwyn showed that, contrary to typical wave transformation patterns across a coastal reef-lagoon, under TC conditions there was a substantial shoreward increase of wave height. This unusual pattern was primarily due to strong local wind wave generation under the extreme wind conditions, despite the lagoon itself being relatively small (order 1 km wide) and shallow (order 1 m depth). Two common types of coastal numerical wave models that include either wave growth (i.e. the phase-averaged model SWAN) or infragravity waves (i.e. the surfbeat resolving model XBeach), but not both processes, were used to assess the capabilities of numerical models to predict cyclone-induced hydrodynamics. Model results showed that wave conditions in the lagoon and at the shoreline were dominated by locally-generated wind waves, with the reef efficiently dissipating the large incident waves offshore. The infragravity waves in the lagoon were only of secondary importance during the TC compared to the locally-generated sea-swell waves. Although both the phase-averaged (SWAN) and surfbeat-resolving (XBeach) models were able to predict some of the local hydrodynamic responses, for this specific site and storm, the use of a phase-averaged model yielded the most accurate predictions of the hydrodynamics given that it included wind wave growth. However, because the influence of infragravity waves cannot be neglected in reef environments in general, these results emphasize the need for a more general modeling approach that requires the addition of wind wave growth formulations into surfbeat- or fully-phase resolving classes of numerical wave models and/or the addition of an IG-wave formulation in spectral wave models.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 19 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Mads Røge Eldrup, Thomas Lykke Andersen〈/p〉 〈div xml:lang="en"〉〈div〉〈p〉The present paper presents new formulae for hydraulic stability of the main armour layer on rock armoured conventional rubble mound structures. In the present study, new stability tests were performed covering both mild (1:100) and steep (1:30) foreshores. The tests covered nonbreaking and breaking waves on the foreshore and also waves of very low steepness. The tests with the 1:30 foreshore showed the armour layer to be significantly more stable in the surging domain than predicted with the Van Gent et al. (2004) formulae. This was attributed to nonlinear waves with significantly larger 〈em〉H〈/em〉〈sub〉1/3〈/sub〉 than 〈em〉H〈/em〉〈sub〉m0〈/sub〉. New stability formulae are presented and fitted to existing and present stability data. The new formulae provide a significant increase in the reliability for nonlinear waves compared to the Van Gent et al. (2004) formulae.〈/p〉〈/div〉〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): Nobuki Fukui, Adi Prasetyo, Nobuhito Mori〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study develops and validates a numerical model of tsunami inundation using upscaled urban roughness parameterization and a Drag Force Model (DFM) to simulate the effect of structures as a drag force acting on flow. The DFM can deal with subgrid scale effects of structures using three upscaled parameters: the characteristic height of the structures, and the projected areas of the structures in the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"〉〈mrow〉〈mi〉x〈/mi〉〈mo linebreak="goodbreak" linebreakstyle="after"〉−〈/mo〉〈/mrow〉〈/math〉 and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"〉〈mrow〉〈mi〉y〈/mi〉〈mo linebreak="goodbreak" linebreakstyle="after"〉−〈/mo〉〈/mrow〉〈/math〉 directions. The validation is based on experimental results of the physical modeling of tsunami inundation conducted in the HyTOFU flume targeting the 2011 Tohoku Earthquake Tsunami; the physical model was a 1:250 scale idealization of the town of Onagawa in Japan. This study numerically simulated tsunami inundation by comparing the experimental results with numerical results reproduced by the DFM using roughness parameterizations. The validation of the DFM reveals that it can express the effect of the flow direction and inundation ratio, and it improves the estimation of inundated extent, maximum inundation depth, and arrival time when compared with other roughness parameterizations. This technique requires careful validation of inundation characteristics and mesh size dependency, and future work to improve estimates of the drag coefficient for the prototype scale and incident wave conditions is recommended.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): Erwin W.J. Bergsma, Rafael Almar, Luis Pedro Melo de Almeida, Moussa Sall〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Commercial Unmanned Areal Vehicles (UAV) are taking a flight: it has never been more accessible to own an UAV and as easy to operate one, e.g. a drone. For coastal monitoring these advances open a new world of monitoring such as inter-tidal beach topography through Structure for Motion. This paper aims to 1) show the potential of the UAV-based depth inversion with 2) limited georeferencing resources for rectification, comparing traditional field-based GCPs and fully remote standalone methods (few local GCPs and Google Earth derived GCPs) and a 3) novel automated error reduction inclusion for the breakpoint location. Unlike with shore-based cameras, image stabilisation is key airborne bathymetry estimation. At places that are hard to reach it is not always possible to get ground control points. We discuss the use of Google Earth to obtain ground control points. In all video-derived bathymetries obtained in this work, great overestimation of the depth is found around wave breaking which is often linked to a phase shift in pixel intensity (dark wave front to white foam). A new method to overcome phase shift issues around breaking is presented that results in a significant error reduction of 58% around the break point.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): Claudio Iuppa, Luca Cavallaro, Rosaria Ester Musumeci, Diego Vicinanza, Enrico Foti〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The results of a new experimental campaign on an Overtopping BReakwater for Energy Conversion (OBREC) device are presented. Previous 2D model tests carried out at Aalborg University (DK) made it possible to define new prediction methods that were used to design the first OBREC prototype breakwater which has been operating at Naples Harbor (Italy) since January 2016. The new tests were carried out at the Hydraulic Laboratory of the Catania University aiming to provide reliable methods for evaluating the energy extracted by the device. In particular, the new tests investigate the probability distribution of the individual overtopping volumes which enter the OBREC reservoir. The methods presented and validated here allow for a reliable estimate of the time distribution of the input flow, which along with the characteristics of the device, can be used to predict the energy produced by OBREC devices.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): Yeulwoo Kim, Ryan S. Mieras, Zhen Cheng, Dylan Anderson, Tian-Jian Hsu, Jack A. Puleo, Daniel Cox〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A new methodology capable of concurrently resolving free surface wave field, bottom boundary layer, and sediment transport processes throughout the entire water column was recently developed in the OpenFOAM framework, called SedWaveFoam. In this study, SedWaveFoam is validated with large wave flume data for sheet flow driven by near-breaking waves. Good agreements are obtained for free surface elevation, flow velocity, turbulence kinetic energy, sediment concentration, and sheet flow sediment fluxes. Model results are used to investigate the joint effects of velocity skewness, acceleration skewness, and progressive wave streaming on sheet flow sediment transport. SedWaveFoam results are contrasted with rigid-lid one-dimensional-vertical model results to isolate the effect of the free surface. Onshore directed near-bed flow velocity and sediment flux are enhanced due to the presence of the free surface via progressive wave streaming. However, the enhancement of net onshore sediment transport for the near-breaking condition with both high velocity and acceleration skewness is several factors greater than that found in the nonbreaking condition with only high velocity skewness. Model results suggest that the large horizontal pressure gradient, which has a Sleath parameter exceeding 0.2, may play a key role. Momentary bed failure is identified via near-bed instability of the sheet flow layer, associated with a large bed shear stress and horizontal pressure gradient. Instantaneous near-bed vortices due to the near-bed instability correspond to the increase of horizontal pore pressure gradient during the wave crest, consistent with measured data. Model inter-comparison suggests that a two-dimensional model is crucial to capture the effect of momentary bed failure that increases sediment suspension during wave crest passage and net onshore sediment transport.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 151〈/p〉 〈p〉Author(s): L. Aragonés, J.I. Pagán, M.P. López, J.C. Serra〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Depth of Closure (DoC) calculation has been analysed for engineers and researchers during decades due to its relevant importance on marine works, such as beach nourishments or littoral defense projects. Several methods can be found in the literature related to the evaluation of DoC. However, they just focus on the bottom elevation change, leaving aside the cross-shore sediment transport issue. This work deals with all requests of the DoC definition and presents a new method based on the comparison of repetitive beach profiles. The main contribution of this research is the methodology presented to quantify the cross-shore sediment transport by the calculation of the Net Cross-shore Sediment Transport Parameter (NCSTP〈sub〉C〈/sub〉). Its application to a complex area of the East Spanish coast concludes that NCSTP〈sub〉C〈/sub〉 values less than or equal to 10% can be considered as no significant. The differences between several criteria based on the change of the bottom elevation are also studied in order to evaluate if they are relevant for engineering works. The new methodology developed is a great advance in the knowledge of this imaginary boundary (DoC), since it allows to discriminate between different possible DoC values when applying any method based on profile surveys comparison.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): Peter Nielsen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A reply is offered to the discussion by Baldock, T E, (2018): Bed shear stress, surface shape and velocity field near the tips of dam-breaks, tsunami and wave runup. Discussion, 〈em〉Coastal Eng, Vol 142〈/em〉, pp 77–81, henceforth B18 of the swash tip model by Nielsen, P (2018): Bed shear stress, surface shape and velocity field near the tips of dam-breaks, tsunami and wave runup. 〈em〉Coastal Engineering, Vol 138〈/em〉, pp 126–131, henceforth N18. The point made by B18, that the near uniform velocity profiles predicted by the N18 model close to the contact point are unrealistic, is substantiated via new data with enhanced vertical resolution due to large bed roughness, 〈em〉k〈/em〉〈sub〉s〈/sub〉 ≈ 6.5cm. This data shows that the tip does not actually have a vertical tangent at the contact point. Hence, the main argument for a vertically uniform velocity at a tip, propagating with constant form, falls away. When the N18 model is applied using a measured, non-bullnose, near-tip surface shape it provides realistic velocity profiles and bed shear stress magnitudes. Thus, N18 provides a step towards an integrated explicit 2DV description of swash tips, though not a definitive description.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): M. Bendoni, I.Y. Georgiou, D. Roelvink, H. Oumeraci〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The study describes an improvement of the 1D version of the hydro-morphodynamic model XBeach to simulate the erosion of saltmarsh edges under wave attack. The effects of sand-mud mixture and characteristics of vegetation on the erosive processes are implemented, along with a nonlinear version of the Exner equation to better simulate the horizontal migration of a vertical bank profile due to wave impact. Numerical experiments reveal that the effect of soil composition is crucial for the development of bank morphology where steep scarps are associated with muddier soils while gently smoothed cross-shore profiles are associated with sandier soils. The effect of vegetation in controlling the morphodynamic evolution under wave attack is greater when the sand fraction increases, thus contributing to the development of small steep scarps. The model is further tested against field data of a saltmarsh bank profile and wind conditions collected before and after the passage of Hurricane Isaac in Lake Borgne, Louisiana. After validation of the hydrodynamics, a tuning procedure to match the final profile is carried out on the main model parameters. The results illustrate the potential utility of the model for application to geomorphic settings subjected to wave impact and characterized by high mud content and halophytic vegetation; yet, the model still has limitations and further improvements are needed. Finally, the results demonstrate the ability of saltmarshes to withstand erosion during the peak of large storms when the marsh is submerged, and highlight transient conditions as important drivers of geomorphic change during storms.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 24 May 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Juan Del-Rosal-Salido, Pedro Folgueras, Miguel Ortega-Sánchez, Miguel Á. Losada〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This work develops an integrated method for characterizing the spatiotemporal variability and distribution function of extreme total water level events in a transitional coastal environment forced by multiple simultaneous climatic agents. The approach incorporates the reconstruction of the total and isolated components of the water level, as well as the nonlinear interaction term, via the hybrid downscaling technique. It also analyzes the contribution of both non-extreme and extreme values of each component to the magnitude and variability of the extreme total water level events and their relations of concomitance to characterize the combinations that cause the extreme events. In addition, the method assesses the probability of flooding events along the transitional coastal environment. The outcomes of the method constitute a useful tool for dividing the transitional environment into homogeneous zones based on the probability of flooding, the dominance of the agents and the relationships between water level components. The application of the proposed method to the Guadalete estuary (South West, Spain) enables the identification of three homogeneous sections: the outer section, where there is no significant variability of the extreme total water level events, and they are explained only by the extremes of the astronomical tide; the inner section, with the highest variability and the domination of the extremes of the river discharge over the rest of the agents, and the middle estuary, where a similar contribution between the extreme values of the river discharge and the extreme and non-extreme values of the astronomical tide is found. These zonation maps are key elements to support decision-making for ecosystem management and risk analysis and facilitate the identification of vulnerable areas, quantification of the flooding frequency and identification of the agents responsible for flooding.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 152〈/p〉 〈p〉Author(s): Xuan Zhang, Richard Simons〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper presents insights into the structure of turbulence in combined wave-current boundary layers, based on experiments performed in flumes of different scale using Particle Image Velocimetry and hydrogen bubble visualisation. Flow conditions covered a range of wave frequencies, wave amplitudes and mean flow conditions. Results show that the spacing between turbulent streaks varies periodically with the passage of each wave, increasing when the flow accelerates and decreasing when the flow decelerates. A new formula has been put forward, relating the streak spacing variation and the wave-induced orbital displacements. The near-wall flow structure suggests a rhythmic pattern in terms of the velocity gradients across the flume. Waves with higher frequencies and larger amplitudes lead to a greater reduction of mean streak spacing, together with a greater increase of the maximum Reynolds shear stress induced by ejections. These results can be useful for better predictions of the hydrodynamics and sediment transport in combined wave-current flows.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: January 2020〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 155〈/p〉 〈p〉Author(s): Georgios Th. Klonaris, Anastasios S. Metallinos, Constantine D. Memos, Konstantina A. Galani〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In the present work the evolution of a sandy beach in the lee of a permeable submerged breakwater was studied both experimentally and numerically. Three-dimensional laboratory experiments were performed to investigate regular and irregular wave propagation over a porous submerged structure and the resulting bed morphology evolution down-wave of it. The tests included normal wave incidence of breaking and non-breaking, long and shorter waves. The measurements were also used to validate a compound numerical model. The basic solver relies on enhanced Boussinesq-type equations extended to simulate wave propagation over porous beds. The wave module accounts for the entire nearshore zone, from deep water to the swash zone, and it is coupled with a sediment transport module including both bed and suspended loads. Adequate agreement between measurements and model results was achieved in most cases.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 26 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Dongxu Wang, Jing Yuan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The shape of vortex ripples generated by wave boundary layers determines the local hydrodynamics and sediment motions, and therefore is critical for understanding coastal sediment transport in the rippled-bed regime. In this study, coarse-sand vortex ripples were generated by periodic oscillatory flows mimicking full-scale field conditions in an oscillatory water tunnel. A laser-based bottom profiler was applied for measuring the movable bed's profile. The observed ripple development from a flat bed is in agreement with many previous studies. Small ripple marks appeared within a couple of flow periods, and gradually became 3-dimensional (3-D) transient ripples, which eventually evolved to equilibrium 2-dimensional (2-D) ripples after 〈em〉O〈/em〉(100–1000) flow periods. The shape of equilibrium 2-D ripple was studied based on a representative ripple profile obtained by ensemble averaging a periodic ripple train. The shape of ripples formed under sinusoidal flows become increasingly sinusoidal as the flow becomes stronger (larger Shields parameter) or wave period becomes longer, which is possibly because the influence of coherent vortex becomes more significant. Wave nonlinearities have different effects on the ripple shape. Generally speaking, wave skewness makes ripples onshore-leaning while wave asymmetry makes ripples' crests sharper and troughs flatter. Our measurements also revealed some detailed geometric characteristics, i.e., the roundness of ripple crests and the maximum local slope along ripple flanks.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 16 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Haochen Zhang, Shuxue Liu, Jinxuan Li, Ronglin Zhang, Jian Hao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Pile groups are widely used structures in coastal and ocean engineering, such as in cross-sea bridges and offshore wind turbine foundations. The effect of a pile group must be considered when calculating the wave forces on piles. In addition, real sea waves are multi-directional waves. However, the associated regulations and studies have mainly concentrated on the action of a unidirectional wave on pile groups. Few studies have considered the interactions between multi-directional irregular waves and pile groups. In this study, we experimentally investigated the interactions between multi-directional irregular waves and a small scale, vertical bottom-mounted pile group comprising nine piles in a side-by-side arrangement. We propose a new parameter: 〈em〉KC〈/em〉〈sub〉〈em〉LD〈/em〉1/3〈/sub〉 = 〈em〉KC〈/em〉〈sub〉1/3〈/sub〉 × 〈em〉L〈/em〉/〈em〉D〈/em〉, to comprehensively consider the effects of the relative pile diameter 〈em〉D/L〈/em〉 and 〈em〉KC〈/em〉〈sub〉1/3〈/sub〉 number on the wave inline force and transverse force on piles. The results show that directional spreading has a significant effect on the interaction between multi-directional irregular waves and piles, especially on the transverse force of piles. The relationships between the inline force, transverse force, and resultant force are studied, and the differences in the wave force among different piles are determined. These results may provide a reference to facilitate the design of engineering structures.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: May 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 147〈/p〉 〈p〉Author(s): Xuexue Chen, Bas Hofland, Wilfred Molenaar, Alex Capel, Marcel R.A. Van Gent〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper describes a method of determining the reaction forces of a vertical structure with an overhang to impulsive wave impacts. The aim is to develop a method to design a hydraulic structure exposed to the impulsive wave impact. At present, there is a lack of guidelines on the designing and verification with such a purpose. The impulse of the impact is taken as the primary design variable to estimate the impulsive reaction force instead of peak impact forces. By using extreme value analysis (EVA), the characteristic impulse (e.g., 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉I〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈mi〉m〈/mi〉〈mo〉,〈/mo〉〈mn〉0.1〈/mn〉〈mtext〉%〈/mtext〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉) can be determined. Then a simple structure model is used for obtaining reaction forces to the characteristic impact impulse. The sum of the impulsive reaction force and the quasi-steady wave force could represent the total reaction force, which can be used as a design load on the structure. The advantage of using the impact impulse could give an approach in which several aspects of the impulsive wave impact force can be incorporated better, like determining the exceedance probability of a certain load, incorporating the flexibility of the structure and correcting possible scale effects in small scale hydraulic models. The proposed method based on the characteristic value of the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉I〈/mi〉〈/mrow〉〈mrow〉〈mi〉i〈/mi〉〈mi〉m〈/mi〉〈mo〉,〈/mo〉〈mn〉0.1〈/mn〉〈mtext〉%〈/mtext〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 is applied to forces measured in a small scale model of the Afsluitdijk discharge sluice, and compared well to a full-time domain solution. The results indicate the initial assumption that using the impact impulse of the impact as the primary design variable, it is possible to estimate the dynamic response of the structure.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 7 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): C.E. Stringari, D.L. Harris, H.E. Power〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper describes a novel image processing technique that detects wave breaking and tracks waves in the surf zone using machine learning procedures. Using time-space images (timestacks), the algorithm detects white pixel intensity peaks generated by breaking waves, confirms these peaks as true wave breaking events by learning from the data's true colour representation, clusters individual waves, and obtains optimal wave paths. The method was developed and tested using data from four sandy Australian beaches under different incident wave and light conditions. Results are a representation of the position of the wave front through time, i.e., space-time data, which when shown overlaid on the original timestack shows the high degree of accuracy of the method developed here. The utility of the method is demonstrated in two ways: 1) through a comparison between the instantaneous wave speed calculated from the wave paths with the theoretical shallow water wave speed, and 2) by obtaining optical intensities that could be translated into wave roller lengths. The algorithm developed here has the potential to improve understanding numerous nearshore process such as bore propagation and capture in the surf zone, surf zone energy dissipation, surf beat and infragravity waves, and as a direct speed input for depth inversion methods.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 7 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Dongmei Xie, Qing-Ping Zou, Anthony Mignone, Jean D. MacRae〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In the northeastern United States, flooding arising from wave overtopping poses a constant threat to coastal communities during storm events. The purpose of this study is to construct a novel integrated atmosphere-ocean-coast modeling framework based on the coupled tide, surge and wave model, ADCIRC-SWAN, to assess risk and facilitate coastal adaptation and resilience to flooding in a changing climate in this region. The integrated modeling system was validated against the field observations of water level, wave height and period during the January 2015 North American blizzard. Water level measurements by a sensor in the Avenues Basin behind the Seawall in Scituate, Massachusetts were combined with the basin volume determined by the USGS LIDAR data to verify the model predictions of wave overtopping volume. At the storm peak, the significant wave height was increased by 0.7 m at the coast by tide and surge. The wave setup along the coast varied from 0.1 m to 0.25 m depending on the coastline geometry. The interaction between tide-surge and waves increased the wave overtopping rate by five folds mainly due to increased wave height at the toe of the seawall. The wave overtopping discharge would approximately double in an intermediate sea level rise scenario of 0.36 m by 2050 for a storm like the January 2015 North American blizzard. The wave overtopping discharge would increase by 1.5 times if the seawall crest elevation was raised by the same amount as sea level rise. An increase of 0.9 m in the seawall crest elevation is required to bring the wave overtopping discharge to the current level under a 0.36 m sea level rise scenario, primarily due to larger waves arriving at the seawall without breaking in the presence of larger water depth.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: May 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 147〈/p〉 〈p〉Author(s): P. Camus, A. Tomás, G. Díaz-Hernández, B. Rodríguez, C. Izaguirre, I.J. Losada〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Disruptions in harbor operations have significant implications for local, regional and global economies due to ports strategic role as part of the supply chain. A probabilistic evaluation of port operations considering the influence of climate change is required in order to secure optimal exploitation during their useful life. Here, we propose a hybrid statistic-dynamical framework combining a weather generator and a metamodel. The stochastic generator is based on weather types to project climate variability on hourly multivariate dependent climate drivers outside ports. The metamodel efficiently transforms hourly sea conditions from the entrance of the harbor towards the inside port adding the advantages of a physical process model. Thousands of hourly synthetic time series based on present climate conditions and future ones were transferred inside the port to perform a probabilistic analysis of port operations. Future forcing conditions were defined adding several sea level rise (SLR) scenarios, sampled from their probability distribution, to the synthetic sea level fluctuation time series. Wave amplification due to non-linear interactions between wave and sea level variations and changes in the reflection coefficients inside the port induced by SLR were modelled. Probabilistic future changes of operation downtimes were quantified considering the uncertainty associated with the historical forcing conditions outside the port and likely SLR scenarios. The methodology was applied to a specific case study on a regional port located in the north coast of Spain, were port operability due to wave agitation was assessed.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: May 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 147〈/p〉 〈p〉Author(s): K.L. Phan, M.J.F. Stive, M. Zijlema, H.S. Truong, S.G.J. Aarninkhof〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Wave attenuation through mangrove forests has received more and more attention, especially in the context of increasing coastal erosion and sea-level-rise. Numerous studies have focused on studying the reduction of wave height in a mangrove forest. However, the understanding of this attenuation process is still in its infancy. In order to obtain more insight, a laboratory experiment, mimicking the processes of wave attenuation by coastal mangroves in the Mekong Delta, Vietnam was conducted. The reduction of wave height for different scenarios of mangrove densities and wave conditions was investigated. A new method to quantify vegetation attenuation induced by vegetation is presented. The wave height reduction is presented over a relative length scale (viz. the number of wavelengths), instead of an absolute length scale of the forest (e.g per meter or per 100 m). The effects of wave non-linearity on the wave height attenuation over the mangrove forest were investigated using the Ursell number. It is suggested that the non-linear character of waves has a strong influence on the attenuation of the waves inside the mangrove forest. A numerical model, mimicking the experiment was constructed in SWASH and validated using the experimental data. Finally, the data set was extended through numerical modelling so that a larger ranging relationship between wave attenuation per wave length and the Ursell number could be formulated.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: May 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 147〈/p〉 〈p〉Author(s): Weikai Tan, Jing Yuan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The seabed is sloped in shallow coastal regions, where strong nonlinear shoaling waves can generate sheet-flow sediment transport. Both wave nonlinearity and bottom slope can lead to a wave-averaged (net) sediment transport rate, but the bottom slope effect is often overlooked in existing sediment transport models. A full-scale experimental study of sheet-flow sediment transport under the oscillatory flows with nonlinear features (skewness or asymmetry) was conducted in an inclinable oscillatory water tunnel, so the bottom-slope-induced net transport rate in the context of nonlinear waves was experimentally investigated. The tests cover a variety of nonlinear wave shape, bottom slope (0 to 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msup〉〈mrow〉〈mn〉2〈/mn〉〈mo〉.〈/mo〉〈mn〉5〈/mn〉〈/mrow〉〈mrow〉〈mo〉∘〈/mo〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉) and two sediment diameters (0.24 and 0.51 mm). Since the downslope direction is the “offshore” direction in our tests, it is found that bottom slope reduces the net “onshore” transport rate due to wave nonlinearity. The slope contribution to the net transport rate is evaluated by taking the difference between the measured net transport rate from a sloping-bed experiment and the measured net transport rate from the corresponding horizontal-bed experiment. The results suggest that slope-induced net transport rate is insensitive to wave nonlinearity, and its variation with bottom slope can be considered linear in the context of predicting net transport rate. Comparisons between this study and a preceding sinusoidal-flow study of Yuan et al. (2017b) suggest that nonlinear waves can be approximated as sinusoidal flows for estimating the slope contribution to the net transport rate. Subsequently, an empirical model for predicting net sheet-flow transport rate due to bottom slope is established based on dimensional analysis. This model can be simply added to existing sheet-flow sediment transport models to improve their applicability in coastal regions.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: May 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 147〈/p〉 〈p〉Author(s): Yi Liu, Jennifer L. Irish〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Forerunner surge, a water level rise ahead of tropical cyclone landfall, often strikes coastal communities unexpectedly, stranding people and increasing loss of life. Surge forecasting systems and emergency managers almost exclusively focus on peak surge, while much less attention is given to forerunner surge. To address the need for fast and accurate forecasting of forerunner surge, we analyze high-fidelity surge simulations in Virginia, New York/New Jersey and Texas and extract physical scaling laws between readily available storm track information and forerunner surge magnitude and timing. We demonstrate that a dimensionless relationship between central-pressure scaled surge and wind-duration scaled time may effectively be used for rapid forerunner surge forecasting, where uncertainty is considered. We use our method to predict forerunner surge for Hurricanes Ike (2008)—a significant forerunner surge event—and Harvey (2017). The predicted forerunner surge 24 to 6 h before Hurricane Ike's landfall ranged from 0.4 to 2.8 m, where the observed forerunner surge ranged from 0.4 to 2.6 m. This new method has the potential to be incorporated into real-time surge forecasting systems to aid emergency management and evacuation decisions.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 146〈/p〉 〈p〉Author(s): Joep van der Zanden, Dominic A. van der A, Iván Cáceres, Bjarke Eltard Larsen, Guillaume Fromant, Carmelo Petrotta, Pietro Scandura, Ming Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The present study aims to extend insights of surf zone turbulence dynamics to wave groups. In a large-scale wave flume, bichromatic wave groups were produced with 31.5 s group period, 4.2 s mean wave period, and a 0.58 m maximum wave height near the paddle. This condition resulted in plunging-type wave breaking over a fixed, gravel-bed, barred profile. Optic, acoustic and electromagnetic instruments were used to measure the flow and the spatial and temporal distributions of turbulent kinetic energy (TKE). The measurements showed that turbulence in the shoaling region is primarily bed-generated and decays almost fully within one wave cycle, leading to TKE variations at the short wave frequency. The wave breaking-generated turbulence, in contrast, decays over multiple wave cycles, leading to a gradual increase and decay of TKE during a wave group cycle. In the wave breaking region, TKE dynamics are driven by the production and subsequent downward transport of turbulence under the successive breaking waves in the group. Consequently, the maximum near-bed TKE in the breaking region can lag the highest breaking wave by up to 2.5 wave cycles. The net cross-shore transport of TKE is in the shoaling region primarily driven by short-wave velocities and is shoreward-directed; in the wave breaking region, the TKE transport is seaward-directed by the undertow and the long-wave velocities. Downward transport of TKE is driven by the vertical component of the time-averaged flow. The cross-shore and vertical diffusive transport rates are small relative to the advective transport rates.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 20 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Gopal S.P. Madabhushi, Jad I. Boksmati, Samy G. Torres〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Gravity Wharf Structures are widely used worldwide to form shallow and deep water ports. They are large structures with a height of 25~50 m depending on the water depth. When these structures are to be sited on loose to medium dense sand, earthquake induced liquefaction settlements present a significant risk. This often requires expensive soil replacement or other ground improvement techniques. In this paper, the dynamic behaviour of these large structures that exert very high bearing pressures on the foundation soil was investigated for the first time. The level of settlements they can suffer due to soil liquefaction was investigated using dynamic centrifuge testing. It will be shown that the full liquefaction does not occur below the structure even when the free field soil fully liquefies during strong earthquakes. However there will be some stiffness degradation owing to excess pore pressure generation and consequent structural settlements. The level of these settlements are considered to be acceptable from a Service Limit State (SLS) perspective. In addition to this the hydro-dynamic pressures that act on the Gravity Wharf structure were also investigated.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 26 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Isa Ebtehaj, Hossein Bonakdari, Bahram Gharabaghi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The authors of the paper under discussion predicted the scour depth around pile groups in clear water using the extreme learning machine (ELM) neural network. The ELM model performance results were compared with those obtained with support vector machine (SVM) and artificial neural network (ANN). This discussion highlights Baghbadorani, Ataie-Ashtiani, Beheshti's (2018) incorrect calculations in Table 3 and scatter plots in Fig. 1 presented in their discussion. For example, they indicated the overall performance of R2 is −2.5 and MAPE is 67% for the 27 raw data listed in the table. They reported these statistical indices not only according to erroneous calculations but also for merely 27 samples selected arbitrarily and without valid justification from over 1 100 data available from previous studies. Using 27 out of 1 100 data points is evidently not a sound means of evaluating the overall accuracy of the proposed equation. Subsequently, the authors provide information to further clarify their responses to the comments in the discussion paper.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 19 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Nadeem Ahmad, Hans Bihs, Dag Myrhaug, Arun Kamath, Øivind A. Arntsen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Understanding the pipeline scour processes under the combined action of waves and current is essential for adequate scour protection measures. This paper presents the numerical modelling of pipeline scour under the co-directional combined action of waves and current including the prediction of the unsteady free surface. The numerical modelling is performed with the open-source CFD model REEF3D. The model solves the Reynolds-Averaged Navier-Stokes (RANS) equations together with the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mi〉k〈/mi〉〈mo〉−〈/mo〉〈mi〉ω〈/mi〉〈/mrow〉〈/math〉 turbulence model and a sediment transport algorithm. In order to ensure the accuracy of the flow field, the model is thoroughly validated for the hydrodynamics of co-directional combined waves and current. Results for the velocity profiles show a good agreement with the experimental observations. The model is then applied to simulate the different case scenarios of the scour under waves alone, current alone, and combined waves and current. The numerical results for scour below the pipeline show good agreement with the experimental data which confirms the applicability of the model to study pipeline scour under the combined action of waves and current. A series of simulations are run for different values of the non-dimensional parameter for the combined waves and current 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉U〈/mi〉〈/mrow〉〈mrow〉〈mi〉c〈/mi〉〈mi〉m〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 varying between 0 and 1.0 for the given KC number. The results demonstrate the correlation between values of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉U〈/mi〉〈/mrow〉〈mrow〉〈mi〉c〈/mi〉〈mi〉m〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 and (1) the flow field below the pipeline, (2) the scour depth, and (3) the temporal variation of the scouring process. The findings highlight the variation of the maximum scour depth below the pipeline with 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉U〈/mi〉〈/mrow〉〈mrow〉〈mi〉c〈/mi〉〈mi〉m〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 19 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Jiarui Lei, Heidi Nepf〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Aquatic vegetation provides ecosystem services of great value, including the damping of waves, which protects shorelines and reduces resuspension. This study proposes a physically-based model to predict the wave decay associated with a submerged meadow as a function of plant morphology, flexibility, and shoot density. In particular, the study considers both the rigid (sheath) and flexible (blade) segments of the plant. Flexible plants reconfigure in response to wave orbital velocity, which diminishes wave decay relative to a rigid plant of the same morphology. The impact of reconfiguration on wave decay can be characterized using an effective blade length, 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mspace width="0.25em"〉〈/mspace〉〈msub〉〈mrow〉〈mi〉l〈/mi〉〈/mrow〉〈mrow〉〈mi〉e〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉, which represents the length of a rigid blade that generates the same drag as the flexible blade of length 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mi〉l〈/mi〉〈/mrow〉〈/math〉. The effective blade length depends on the Cauchy number, which defines the ratio of hydrodynamic drag to blade stiffness, and the ratio of blade length to wave orbital excursion. This laboratory study considered how the scaling laws determined for individual blades can be used to predict the wave decay over a meadow of multiple plants, each consisting of multiple blades attached at a rigid stem (sheath). First, the drag force on and motion of individual model blades (made of low-density polyethylene) was studied for a range of wave conditions to provide empirical coefficients for the theoretically determined scaling laws for effective blade length, 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉l〈/mi〉〈/mrow〉〈mrow〉〈mi〉e〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉. Second, the effective blade length predicted for individual blades was incorporated into a meadow-scale model to predict wave decay over a meadow. The meadow-scale model accounts for the contribution from both the rigid and flexible parts of individual plants. Finally, wave decay was measured over meadows of different plant density (shoots per bed area), and the measured decay was used to validate the wave-decay model. Wave decay was shown to be similar over meadows with regular and random arrangements of plants.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: May 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 147〈/p〉 〈p〉Author(s): Wen-Gang Qi, Chang-Fei Li, Dong-Sheng Jeng, Fu-Ping Gao, Zuodong Liang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Waves are coexisting with currents in coastal zones; nevertheless, previous experimental studies for excess pore-pressure responses in a porous seabed were predominantly limited to the wave-only condition. In this study, the combined wave-current induced excess pore-pressures in a sandy seabed were experimentally simulated with a specially-designed flume, which can concurrently generate periodic waves and a following/opposing co-directional current. The effect of a current on the wave profile is firstly examined. The wave steepness is decreased by a following current, but enhanced by an opposing current. Flume observations indicate that, under combined wave-current loading, the wave-induced pore-pressure is increased for the following-current case, but reduced for the opposing-current case. Such wave-current combination effect becomes more significant for shorter wave periods. The variation trend of the excess pore-pressure distribution in the present flume observations is consistent with that of the existing analytical solutions. Nevertheless, due to the existence of wave and/or current boundary layer and non-lineartiy of wave-current interactions as indicated by the flume observations, certain deviations exist between the flume results for excess pore-pressure and the analytical solutions, which can not be ignored especially for the opposing-current case. The effects of the boundary layer on the combined wave-current induced pore-pressures in the seabed are further highlighted by supplementary numerical simulations. A favorable prediction by the analytical solution would be expected for following-current cases and smaller pore-pressure amplitudes would be obtained for opposing-current cases.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: May 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 147〈/p〉 〈p〉Author(s): Clément Bouvier, Yann Balouin, Bruno Castelle, Robert Holman〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Video monitoring the nearshore can provide high-frequency remotely-sensed optical information from which morphological changes and hydrodynamic data can be derived. Although overlooked in most of the studies, it is acknowledged that camera viewing angles can substantially vary in time for a variety of reasons, reducing consistently data accuracy. This paper aims to identify the primary environmental parameters controlling camera shifts at the video monitoring station of Sète (SE France) and develops an empirical model to routinely reduce these deviations. Our model simulates camera movements with an excellent skill (BSS = 0.87) and shows that camera viewing angles’ deviation is primarily controlled by the position of the sun during sunny days, making it predictable. This study opens new perspective to routinely improve camera geometry of video monitoring systems.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 14 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Luc Ponsioen, Myron van Damme, Bas Hofland, Patrik Peeters〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A high quality safety assessment of levee systems requires a good prediction of when the grass cover of levees fail. Current methods relate the onset of failure to the peak in momentum or energy of the flow, instead of the peak in momentum transfer or energy transfer to the grass cover. The critical velocity necessary in the current methods is thereby difficult to quantify. In line with determining the peak in momentum transfer to the grass, here is shown that the onset of damage of the grass cover can be related to the peak normal stresses acting on the grass cover during wave overtopping. The peak in momentum transfer is thereby assumed to be located at the point of reattachment of the flow with the landside slope. The method is validated against the results of two wave overtopping experiments and benchmarked against the cumulative overload method. An advantage of this method is thereby that both the time and location of the onset of damage can be predicted.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: May 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 147〈/p〉 〈p〉Author(s): Mahsa Ghazian Arabi, Deniz Velioglu Sogut, Ali Khosronejad, Ahmet C. Yalciner, Ali Farhadzadeh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A series of experiments and numerical simulations on the interactions between a solitary wave and an impervious structure of square cross-section (block) in relatively shallow water were conducted to shed light on the physical processes of origination and evolution of coherent structures induced during such events. The block was placed at two different positions in a laboratory flume and was exposed to a solitary wave. The flow fields around the block were measured spatially and temporally for the validation of a three-dimensional (3D) computational fluid dynamics (CFD) numerical model results. The numerical model results were, then, used to further understand the generation and propagation of turbulent coherent structures around the block. The results show that two-dimensional (2D) spanwise vortices attributed to surface wave can evolve into coupled 3D turbulent coherent structures that penetrate into the water column at the sharp corners of the block. As the incident wave approaches the block, flow accelerates resulting in positive pressure gradients near the leading and trailing edges of the block. This leads to flow separation and, thus, the formation of vortices near the sharp corners. The vortices are extended through the water column, from the surface to the bottom. This is accompanied by a streamwise return flow that has a velocity of 25–50% of the incident flow velocity at the block. This flow carries the vortex tubes away from the block in the upwave direction. The one-dimensional power spectral density of the streamwise velocity demonstrates the production range and inertial subrange, following slopes of −1 and −5/3, respectively. The production range indicates the production of turbulence kinetic energy as a result of low frequency coherent structures. The inertial subrange marks the transfer of energy from the low to high frequency coherent structures, which correspond to high and low energy eddies, respectively. It is noted that the number of the initial vortices formed at the block corresponds to the number of sharp corners exposed to the incident wave.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 143〈/p〉 〈p〉Author(s): Kim Bastian, Stefan Carstensen, Titi Sui, David R. Fuhrman〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper presents 25 new laboratory experiments involving the wave-induced backfilling of wave-induced scour holes beneath submarine pipelines (so-called wave-to-wave backfilling scenarios). The experiments complement the previous 8 wave-to-wave backfilling experiments of Fredsøe et al., as well as recent current-to-wave backfilling experiments of Bayraktar et al. It is found that the wave-induced backfilling time scale is generally an order of magnitude larger than for scour, and is relatively insensitive to the initial (current- or wave-induced) pre-backfilling scour profile. Based on this, the data sets involving wave-induced backfilling are collectively analyzed, resulting in a new generalized expression for estimating the wave-induced backfilling time scale beneath pipelines in the live-bed regime. This expression accounts for primary dependence on the Shields parameter, as well as secondary dependence based on the difference between the (estimated or known) initial and expected final equilibrium scour depth due to the backfilling wave condition.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 143〈/p〉 〈p〉Author(s): Bo Terp Paulsen, Ben de Sonneville, Michiel van der Meulen, Niels Gjøl Jacobsen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Physical model tests were analyzed with the objective to establish a formulae for the probability of wave slamming on offshore wind turbine foundations and the associated slamming force. Furthermore, the effect of wave slamming is analyzed for a monopile wind turbine foundation using a state-of-the-art aeroelastic model. The laboratory measurements were carried out in Deltares’ Atlantic Basin as part of the joint industry project “wave impacts on fixed turbines”, in short JIP-WiFi. Long crested and irregular waves typical for the North Sea were applied and more than 130 design storms and 500 slamming impacts were analyzed. A simple closed form expression for the probability of wave slamming is presented and a reasonable agreement with the laboratory measurements shown. A criterion for when wave slamming should be included in design computations is formulated based on the sea state steepness. It is observed that wave slamming occurs during tests with a flat seabed, and that seabed features, such as sand waves, significantly increase the probability of wave slamming. Furthermore, a simplified slamming load formulation is proposed based on observations from a subset of the laboratory tests. The magnitude of the slamming load is validated against the remaining part of the laboratory measurements and compared with existing slamming load formulations. The new formulation is in better agreement with the underlying measurements than existing formulations and is of a simpler form which makes it easier to apply. The new slamming load formulation is applied in design computations for a realistic wind turbine with the offshore wind farm Gemini as base case. The computations show that wave slamming, at this specific location, is not governing the structural design. However, wave slamming may introduce high accelerations in the transition piece located in the free surface zone where waves are impacting the structure.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 142〈/p〉 〈p〉Author(s): Riccardo Briganti, Nicholas Dodd, Giorgio Incelli, Gustaaf Kikkert〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper examines the numerical prediction of the sediment transport and bed evolution for a single swash event on a coarse sediment beach. In these conditions bed load is the dominant mode of sediment transport. Laboratory experiments of a single bore-driven swash event are simulated numerically using a fully-coupled model that solves the system of Non Linear Shallow Water Equations and the Exner sediment conservation formula. The analysis focuses on two aspects: the optimal choice of parameters for the Meyer-Peter and Müller sediment transport formula and the model used for computing the shear stress. The methods tested for the bed shear stress are the momentum integral method and the Chezy formulation in which the friction factor is computed using two different formulae. Infiltration into the beach and its effects on the shear stress and sediment transport are also modelled. Results show that the basic Meyer-Peter and Müller sediment transport formula provides good results in the run-up. On the other hand, the sediment transport in the early stage of the backwash is overestimated. A reduction of the sediment mobility constant in the formula in the backwash marginally improves the results. However, the causes of the overestimation of the sediment transport at the early stage of the backwash is the overestimation of the shear stress, while at later stages there are several contributions that are identified, i.e. modelling of the sediment transport and infiltration. It is also suggested that the Meyer-Peter and Müller sediment transport formula might not capture the complexity of the processes involved during the backwash. The comparison of the methods for the estimate of the bed shear stress show that comparable results can be obtained using the momentum integral method and the Chezy formulation with time and space varying friction factor. The resulting bed evolution is also described. In the predicted final profile, deposition is found in the upper part of the beach and erosion in the lower part. A bed step is formed just below the position of the initial shoreline. This feature is determined by the onset of a hydraulic jump during the backwash.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 142〈/p〉 〈p〉Author(s): Tom E. Baldock〈/p〉

Description: 〈p〉Publication date: November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 141〈/p〉 〈p〉Author(s): J. Stolle, C. Derschum, N. Goseberg, I. Nistor, Emil Petriu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Historical tsunami events have resulted in extreme damage to coastal regions worldwide. Among the various loads associated with tsunami waves, debris impact has been shown to cause major damage to nearshore infrastructure. As a result, debris impact loads have been included prominently in existing design guidelines and standards, such as the FEMA P-646 [11] and ASCE7 Chapter 6 [6]. In the present study, single debris impacts on structures was experimentally investigated under tsunami-like wave conditions. Eccentric and oblique impacts of a model shipping container (length scale 1:40) on a non-rigid structure were examined. The experimental results of the non-rigid impacts are discussed in the context of the existing force equations which were derived under the assumption of rigid-body impact theory. As expected, the elasticity of the structure was determined to influence and, specifically, reduce the magnitude of the debris impact forces. Existing impact force equations are herein critically discussed through comparison with the experimental results and, finally, modifications to existing force equations to account for non-rigid collisions are proposed.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 142〈/p〉 〈p〉Author(s): Paula Gomes da Silva, Raúl Medina, Mauricio González, Roland Garnier〈/p〉

Description: 〈p〉Publication date: November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 141〈/p〉 〈p〉Author(s): Matthew Jones, Hans Fabricius Hansen, Allan Rod Zeeberg, David Randell, Philip Jonathan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We estimate uncertainties in ocean engineering design values due to imperfect knowledge of the ocean environment from physical models and observations, using Bayesian uncertainty analysis. Statistical emulators provide computationally efficient approximations to physical wind–wave environment (i.e. “hindcast”) simulators and characterise simulator uncertainty. Discrepancy models describe differences between hindcast simulator outputs and the true wave environment, where the only measurements available are subject to measurement error. System models (consisting of emulator–discrepancy model combinations) are used to estimate storm peak significant wave height (henceforth 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mi〉H〈/mi〉〈mi〉S〈/mi〉〈/msub〉〈/mrow〉〈/math〉), spectral peak period and storm length jointly in the Danish sector of the North Sea. Using non-stationary extreme value analysis of system output 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mi〉H〈/mi〉〈mi〉S〈/mi〉〈/msub〉〈/mrow〉〈/math〉, we estimate its 100-year maximum distribution from two different system models, the first based on 37 years of wind–wave simulation, the second on 1200 years; estimates of distributions of 100-year maxima are found to be in good general agreement, but the influence of different sources of uncertainty is nevertheless clear. We also estimate the distribution of 100-year maximum 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mi〉H〈/mi〉〈mi〉S〈/mi〉〈/msub〉〈/mrow〉〈/math〉 using non-stationary extreme value analysis of storm peak 〈em〉wind speed〈/em〉, propagating simulated extreme winds through a system model for 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mi〉H〈/mi〉〈mi〉S〈/mi〉〈/msub〉〈/mrow〉〈/math〉; we find estimates to be in reasonable agreement with those based on extreme value analysis of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mi〉H〈/mi〉〈mi〉S〈/mi〉〈/msub〉〈/mrow〉〈/math〉 itself.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 141〈/p〉 〈p〉Author(s): Paolo Blondeaux, Giovanna Vittori, Gaetano Porcile〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We investigate the turbulent oscillatory flow generated by propagating surface waves close to the sea bottom focusing our attention on moderate values of the Reynolds number 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈mrow〉〈mi〉δ〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 of the bottom boundary layer. For such moderate values of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈mrow〉〈mi〉δ〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉, turbulent fluctuations appear only during parts of the oscillation cycle and the flow recovers a laminar-like behaviour in the remaining parts. Different roughness sizes are considered and both the smooth and the rough flow regimes are analysed. The aim of the present investigation is to test the performance of different two-equation turbulence models to compute the flow field over both smooth and rough walls and for moderate values of the Reynolds number. The considered models are the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mi〉e〈/mi〉〈mo〉−〈/mo〉〈mi〉ω〈/mi〉〈/mrow〉〈/math〉 model by Saffman and Wilcox (1974), two 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈mi〉k〈/mi〉〈mo〉−〈/mo〉〈mi〉ω〈/mi〉〈/mrow〉〈/math〉 models (Wilcox (1988) and a model derived from Wilcox (1992)), a low-Reynolds number 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"〉〈mrow〉〈mi〉k〈/mi〉〈mo〉−〈/mo〉〈mi〉ε〈/mi〉〈/mrow〉〈/math〉 model (Foti and Scandura, 2004) and the model by Menter et al. (2003). To evaluate the performance of the models, the numerical predictions of the bottom shear stress are compared both with experimental measurements and with results of direct numerical simulations (DNS). All the models are found to provide fair results for high values of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈mrow〉〈mi〉δ〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 and for a smooth wall. For moderate values of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈mrow〉〈mi〉δ〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉, when turbulence is observed only during parts of the oscillating cycle, only one of the low-Reynolds number 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈mi〉k〈/mi〉〈mo〉−〈/mo〉〈mi〉ω〈/mi〉〈/mrow〉〈/math〉 models is able to describe the rapid growth of the wall shear stress due to turbulence appearance. On the other hand, if a rough wall is considered, the performance of the models greatly depends on the size of the roughness.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 149〈/p〉 〈p〉Author(s): Peiwei Xie, Vincent H. Chu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The hydrodynamic forces on coastal structures impacted by tsunami depend on the wave Froude number, the sizes and shapes of the structures and also on whether the structures stand in water or on dry land at the time of the impact. We conducted simulations using shallow-water hydraulic equations and then simulations using full Navier-Stokes equations to determine the wave impact on a vertical wall – i.e., a structure of infinite width – and a structure of finite width. In the case of steep waves on a wet bed, the wave-drag coefficient rose to a peak on impact and then settled to a wave-structure interaction equilibrium. In the case of smooth waves on dry land, the approach to the equilibrium was gradual. The numerical simulations determined the dependence of the wave-drag coefficients on the Froude number and the width-to-depth ratio for waves on wet beds and, separately, for waves on dry land. The simulations also reproduced the wave forces for the range of conditions observed in the laboratory.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 150〈/p〉 〈p〉Author(s): Katherine A. Serafin, Peter Ruggiero, Patrick L. Barnard, Hilary F. Stockdon〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Total water levels (TWLs) at the coast are driven by a combination of deterministic (e.g., tides) and stochastic (e.g., waves, storm surge, and sea level anomalies) processes. The contribution of each process to TWLs varies depending on regional differences in climate and framework geology, as well as local-scale variations in beach morphology, coastal orientation, and shelf bathymetry. Large-scale changes to the climate altering the frequency, direction, and intensity of storms, may therefore propagate to the nearshore differently, amplifying or suppressing local coastal hazards and changing the exposure of coastal communities to extreme TWLs. This study investigates the hydrodynamic and geomorphologic factors controlling local TWLs along high-energy United States coastlines where wave-influences dominate TWLs. Three study sites in the states of Washington, Oregon, and California are chosen to explore how regional and local differences in beach topography and wave transformation over shelf bathymetry drives variations in the magnitude and impacts of extreme TWLs. Results indicate that TWLs are most influenced by wave transformation processes in locations with steep beach slopes and complex offshore bathymetry, while beach topography influences the severity of coastal impacts. Once the relative morphologic controls on TWLs are better understood, hypothetical future climate scenarios are explored to assess how changes to the average deepwater wave climate (height, period, and direction) may alter local TWLs when compared to estimates of likely sea level rise and future coastal management strategies. Changes to the wave climate are found to be as detrimental to the coastline as sea level rise in some locations, where small variations of the TWL drive large, nonlinear changes in hours of impact to the backshore beach. Overall, this study develops an approach for quantifying the range of hydrodynamic and morphologic controls on the magnitude of TWLs which will ultimately better prepare coastal communities for uncertain changes to the global climate.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): N.G. Jacobsen, B.C. McFall, D.A. van der A〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Existing dissipation models (bulk and frequency distributed) describing the wave attenuation in canopies rely on a characteristic shape of the velocity profile and corresponding characteristic frequency, which is integrated analytically over the height of the canopy. This means that all frequencies higher than the characteristic peak frequency are assigned excessive dissipation, while all frequencies lower than the characteristic peak frequency are assigned insufficient dissipation.〈/p〉 〈p〉The present work presents a new dissipation model, which is given in a closed form based on the surface elevation spectrum, 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉S〈/mi〉〈/mrow〉〈mrow〉〈mi〉η〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉. The model calculates the frequency dependent dissipation at a given vertical elevation z, which is numerically integrated over the height of the canopy. A comparison with existing bulk dissipation models shows that there are large differences between the existing models and the present work. These differences are particularly noticeable for realistic peak enhancements factors for the JONSWAP spectrum (1.0–10.0) and submerged canopies.〈/p〉 〈p〉A comparison with the frequency distributed dissipation model in the spectral wave model SWAN is also presented and the present model distinguishes itself by naturally incorporating a cut-off frequency above which the dissipation effectively vanishes. This offers a more realistic frequency distribution of the dissipation. The frequency distribution of the dissipation and the existence of a frequency cut-off is verified with experimental data.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 25 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Kilian Vos, Mitchell D. Harley, Kristen D. Splinter, Joshua A. Simmons, Ian L. Turner〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The ability to repeatedly observe and quantify the changing position of the shoreline is key to present-day coastal management and future coastal planning. This study evaluates the capability of satellite remote sensing to resolve at differing temporal scales the variability and trends in shoreline position along sandy coastlines. Shorelines are extracted from 30 + years of publicly available satellite imagery and compared to long-term in-situ measurements at 5 diverse test sites in Europe, Australia, the USA and New Zealand. These sites span a range of different beach characteristics including wave energy and tide range as well as timescales of observed shoreline variability, from strongly seasonal (e.g., Truc Vert, France), to storm-dominated (e.g., Narrabeen-Collaroy, Australia), to only minor annual to multi-annual signals (e.g., Duck, USA). For the 5 sites, the observed typical horizontal errors varied between a root-mean-squared error (RMSE) of 7.3 m and 12.7 m. An analysis of the typical magnitudes of shoreline variability at temporal scales ranging from a single month up to 10 years indicates that, by the implementation of targeted image pre-processing then the application of a robust sub-pixel shoreline extraction technique, the resulting satellite-derived shorelines are generally able to resolve (signal-to-noise ratio 〉 1) the observed shoreline variance at timescales of 6 months and longer. The only exception to this is along coastlines where minimal annual to multi-annual shoreline variability occurs (e.g. Duck, USA); at these sites decadal-scale variations are successfully captured. The results of this analysis demonstrate that satellite-derived shorelines spanning the past 30 years as well as into the future can be used to explore and quantify intra- and inter-annual shoreline behaviour at a wide range of beaches around the world. Moreover, it is demonstrated that present-day satellite observations are also capable of capturing event-scale shoreline changes (e.g. individual storms) that occur at timescales shorter than 6 months, where this rapid response exceeds the typical magnitude of shoreline variability. Finally, several practical coastal engineering applications are presented, demonstrating the use of freely-available satellite imagery to monitor inter-annual embayed beach rotation, rapid storm-induced shoreline retreat and a major sand nourishment.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 24 April 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Vahid Etminan, Ryan J. Lowe, Marco Ghisalberti〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Aquatic vegetation in the coastal zone dissipates wave energy and provides a form of natural coastal protection against storm waves. The capacity of aquatic vegetation to attenuate incident waves depends on the extent to which wave energy is dissipated by small-scale hydrodynamic interactions within a canopy, which in turn depends on the work done by drag forces exerted by the canopy. Canopy drag forces (and hence rates of wave dissipation) are conventionally parameterised using a drag coefficient 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈mrow〉〈mi〉d〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉. Existing empirical models for predicting 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈mrow〉〈mi〉d〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 are usually dependent solely on either Reynolds number 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mi〉R〈/mi〉〈mi〉e〈/mi〉〈/mrow〉〈/math〉 or Keulegan–Carpenter number 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈mi〉K〈/mi〉〈mi〉C〈/mi〉〈/mrow〉〈/math〉, and hence neglect the potential effect of vegetation canopy density 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"〉〈mrow〉〈mi〉λ〈/mi〉〈/mrow〉〈/math〉 and the interactions between adjacent stems. This study uses high-resolution numerical simulations to investigate the dynamics of wave-driven oscillatory flow through emergent canopies (modelled as arrays of rigid cylinders). The simulations cover a wide range of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈mi〉K〈/mi〉〈mi〉C〈/mi〉〈/mrow〉〈/math〉. The influence of two mechanisms in modifying canopy drag, namely the effects of blockage and sheltering, are evaluated. The blockage effect is found to be the dominant mechanism responsible for increasing the canopy drag coefficients at high 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈mi〉K〈/mi〉〈mi〉C〈/mi〉〈/mrow〉〈/math〉 for medium to high density canopies; however, the sheltering effect plays only a minimal role in reducing the drag coefficient of the very sparse canopies. We show that 〈em〉C〈/em〉〈sub〉〈em〉d〈/em〉〈/sub〉 for canopies at high 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈mi〉K〈/mi〉〈mi〉C〈/mi〉〈/mrow〉〈/math〉 can be robustly estimated using a new modified drag formulation for the same canopies in unidirectional flow. Conversely, in the limit of the low 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈mi〉K〈/mi〉〈mi〉C〈/mi〉〈/mrow〉〈/math〉, 〈em〉C〈/em〉〈sub〉〈em〉d〈/em〉〈/sub〉 is close to that of a single isolated cylinder at the same 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈mi〉K〈/mi〉〈mi〉C〈/mi〉〈/mrow〉〈/math〉. The results of this study can be used as a basis for developing new predictive formulations for specifying bulk canopy drag coefficients, and in turn quantifying wave attenuation by vegetation.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 149〈/p〉 〈p〉Author(s): S. Draycott, A.C. Pillai, D.M. Ingram, L. Johanning〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Complex wave and wave-current conditions exist in the natural world, and are increasingly emulated in advanced experimental facilities to de-risk the deployment, operation and maintenance of offshore structures and renewable energy devices. This can include combinations of ocean swell, multi-directional wind-driven seas, and reflected wave conditions interacting with a current field. It is vital to understand the full nature of these potentially hazardous conditions so they can be properly simulated in numerical models, to contextualize measurements made in field, and experimental programmes. Here, a numerical framework is presented for isolating both the wave systems and the mean current velocities from measured data using an interior point optimizer.〈/p〉 〈p〉A developed frequency domain solver is used to resolve, from experimentally obtained wave gauge measurements, two opposing wave systems on a collinear current, and used to effectively isolate the wave systems and predict the current velocity using only wave gauge measurements. Thirty five test cases are considered; consisting of five wave spectra interacting with seven different current velocities ranging from −0.3m s〈sub〉-1〈/sub〉0.3m s〈sub〉-1〈/sub〉. Comparisons between the theoretical and derived wave numbers and current velocities show good agreement and the performance of the method is similar to that of existing methodologies while requiring no a priori knowledge of the current velocity impacting the wave field required.〈/p〉 〈p〉Although results are presented for the collinear problem, the presented method can be applied to a wide range of wave and current combinations, and provides a useful tool for increasing understanding of both ocean and experimental conditions.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 149〈/p〉 〈p〉Author(s): Jorge Molines, Maria P. Herrera, M. Esther Gómez-Martín, Josep R. Medina〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Conventional mound breakwaters are usually designed to withstand low mean wave overtopping discharges and a low proportion of overtopping waves (P〈sub〉ow〈/sub〉). Existing formulas to estimate P〈sub〉ow〈/sub〉 and maximum individual wave overtopping volume are usually based on tests with high P〈sub〉ow〈/sub〉; this study is focused on mound breakwaters subjected to P〈sub〉ow〈/sub〉 〈 0.2. The performance of the 2-parameter Weibull and Exponential distributions is examined in order to describe individual wave overtopping volumes of mound breakwaters in non-breaking wave conditions. A new methodology is applied to 164 small-scale 2D physical tests to identify the number of overtopping waves, and the corresponding individual wave overtopping volumes. Utility functions are used to consider the relative relevance of the observed data: in this study, a quadratic utility function depending on all the individual wave overtopping volumes and step utility functions with 10%, 30% and 50% of the highest volumes are used to fit the Weibull and Exponential distributions. In this study, a new estimator of P〈sub〉ow〈/sub〉 is proposed to improve the predictions required to estimate the maximum individual wave overtopping volume. Existing estimators of P〈sub〉ow〈/sub〉 underpredict the largest values of P〈sub〉ow〈/sub〉 measured in the physical tests. The parameters fitted to the Weibull and Exponential distributions using the quadratic utility function provide estimations of the dimensionless maximum individual wave overtopping volume with relative mean squared errors rMSE = 10.4% and 10.6%, respectively. When CLASH Neural Network-estimated mean overtopping rates are used to predict the maximum individual wave overtopping with the quadratic utility function, the 2-parameter Weibull and Exponential distributions provide rMSE = 31.6% and rMSE = 33.3%, respectively. The new estimators proposed in this study improve the predictions of P〈sub〉ow〈/sub〉 and maximum individual wave overtopping volumes on conventional mound breakwaters designed for low wave overtopping rates.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 149〈/p〉 〈p〉Author(s): Ling Zhu, Qin Chen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In the recent paper by Garzon, Miesse, and Ferreira (Coastal Engineering, DOI: 〈a href="https://doi.org/10.1016/j.coastaleng.2018.11.001" target="_blank"〉https://doi.org/10.1016/j.coastaleng.2018.11.001〈/a〉), the authors collected field data from Chesapeake Bay, and numerically simulated the wave attenuation by vegetation using five different empirical drag coefficient formulas. The implementation of the formula from Jadhav (2012) was incorrect by Garzon et al. (2018), resulting in considerable under-prediction of wave height in comparison of the field data. This discussion aims to present the correct way to use the drag coefficient formula from Jadhav (2012). Our numerical results show that the drag coefficient formulas of Jadhav (2012) and Jadhav and Chen (2012) are suitable for modeling wave attenuation by salt marshes in Chesapeake Bay.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 23 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Francis C.K. Ting, Deryn A. Beck〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The distribution of suspended sediment in plunging regular waves was measured simultaneously with the three-dimensional (3D) turbulent velocity field on a 1 in 40 plane slope using a volumetric three-component velocimetry (V3V) system. White solid glass spheres (diameter 0.25 mm, specific gravity 2.5) were used as sediment particles. The V3V system was positioned to capture the impingement of the first or second splash-up vortices on the bottom. The measurement volume encompassed the lower 25% of the water column and a bottom area of length and width equal to approximately ½ the local water depth. Phase separation of glass spheres and fluid tracers in the V3V images was performed by varying the settings of four particle processing parameters in the commercial software INSIGHT™ V3V 4G. The measured fluid velocity fields were decomposed into a wave-induced component and a turbulence component by ensemble averaging 28 experiment runs conducted under the same incident wave condition. The two-phase flow measurements were used to delineate the process of sediment entrainment, to determine the turbulent flow properties around the suspended sediment, and to investigate the relationships between sediment pickup rate and the different flow parameters. The two dominant mechanisms of sediment suspension observed were the deflected flow created when breaking wave vortices impinged on the bottom and the up-wash induced by the transverse vortices. The suspension process was associated with large apparent shear stresses and positive vertical velocities greater than or equal to the sediment fall velocity. It was observed that sediment trapping by transverse vortices with horizontal axis and columnar vortices with vertical axis was an important mechanism for keeping sediment in suspension for transport by the organized wave-induced flow (mean flow). It was found that measured sediment pickup rates generally correlated better with total apparent shear stress than bed shear stress or turbulent kinetic energy. The experimental investigation suggests that sediment suspension by breaking-wave-generated vortices cannot be modeled by bed shear stress alone but will also require information on the vertical velocities induced by these vortices over the bed.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 23 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Kai Parker, Peter Ruggiero, Katherine A. Serafin, David F. Hill〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Probabilistic flood hazard assessment is a promising methodology for estuarine risk assessment but currently remains limited by prohibitively long simulation times. This study addresses this problem through the development of an emulator, or surrogate model, which replaces the simulator (in this case the coupled ADCIRC+SWAN model) with a statistical representation that is able to rapidly predict estuarine variables relevant to flooding. Emulation of water levels (WLs), non-tidal residual, and significant wave height, is explored at Grays Harbor, Washington (WA) USA using Gaussian process regression. The effectiveness of the methodology is validated at various model simplification levels to determine where error is being sourced. Emulated WLs are found to be skillful when compared to over a decade of tide gauge observations (root mean square error, RMSE, 〈15 cm). The largest loss of skill in the method originates with ADCIRC+SWAN attempting to reproduce observations, even when the majority of relevant physics are included. Subsequent simplifications to the simulator (input reduction techniques) and the emulator itself are found to introduce a trivial amount of error (average increase in RMSE of 1 cm). Emulated WLs are also compared to spatially varying observations and found to be equally skillful throughout the estuary. An example emulation application is explored by decomposing the relative forcing contributions to extreme WLs across the study site. Results show a compound nature of extreme estuarine WLs in that all forcing dimensions contribute to extremes, with streamflow having the least influence and tides the largest. Overall the approach is shown to be both skillful and efficient at reproducing critical hydrodynamic variables, suggesting that emulation may play a key role in improving our ability to probabilistically assess flood risk in complex environments as well as being promising in a range of other applications.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 149〈/p〉 〈p〉Author(s): David A. Honegger, Merrick C. Haller, Robert A. Holman〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paired study, we apply a recently developed high-resolution bathymetry estimation algorithm (“cBathy”) to X-band marine radar observations at two nearshore field sites. The algorithm exploits observations of the spatial structure of wave phase to attain wavenumber estimates, inverts the linear water wave dispersion relation for depth, and then applies a Kalman filter to objectively update the bathymetry estimates. Previously, performance has only been tested using optical video observations. In this first of two papers, performance of the algorithm using X-band radar image time series is tested at two disparate barred beach environments: Duck, NC, USA, and Benson Beach, WA, USA. Each of the test beaches is either co-located with (Duck, NC) or geographically close to (Benson Beach, WA) those utilized in the original algorithm verification. Concurrent echosounder surveys are used as ground truth. The bulk performance of the radar-derived bathymetry estimate at Duck, NC, achieves 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mn〉0.49〈/mn〉〈mspace width="0.25em"〉〈/mspace〉〈mtext〉m〈/mtext〉〈/mrow〉〈/math〉 root-mean-square error (RMSE) with 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mn〉0.26〈/mn〉〈mspace width="0.25em"〉〈/mspace〉〈mtext〉m〈/mtext〉〈/mrow〉〈/math〉 bias deep. This compares well with the bulk performance of the concurrent estimate derived using optical video (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈mn〉0.44〈/mn〉〈mspace width="0.25em"〉〈/mspace〉〈mtext〉m〈/mtext〉〈/mrow〉〈/math〉 RMSE and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"〉〈mrow〉〈mn〉0.23〈/mn〉〈mspace width="0.25em"〉〈/mspace〉〈mtext〉m〈/mtext〉〈/mrow〉〈/math〉 bias deep). The radar-derived bathymetry estimate performance at Benson Beach, is similar (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.gif" overflow="scroll"〉〈mrow〉〈mn〉0.35〈/mn〉〈mspace width="0.25em"〉〈/mspace〉〈mtext〉m〈/mtext〉〈/mrow〉〈/math〉 RMSE and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si6.gif" overflow="scroll"〉〈mrow〉〈mn〉0.11〈/mn〉〈mspace width="0.25em"〉〈/mspace〉〈mtext〉m〈/mtext〉〈/mrow〉〈/math〉 bias shallow), and is comparable to that of an optical video derived estimate at a similar Pacific Northwest beach (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si7.gif" overflow="scroll"〉〈mrow〉〈mn〉0.56〈/mn〉〈mspace width="0.25em"〉〈/mspace〉〈mtext〉m〈/mtext〉〈/mrow〉〈/math〉 RMSE and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si8.gif" overflow="scroll"〉〈mrow〉〈mn〉0.41〈/mn〉〈mspace width="0.25em"〉〈/mspace〉〈mtext〉m〈/mtext〉〈/mrow〉〈/math〉 bias shallow). At both beaches, significantly higher performance is achieved at locations deeper than 2 m (offshore of the surfzone) than at locations shallower than 2 m (surfzone), where errors are often a large fraction of the total depth. Lastly, several weeks of observations are utilized to assess the sensitivity of algorithm quality control to environmental conditions. Thresholds based on the shoreward component of wind stress and offshore wave steepness are identified and shown to impact the areal coverage of radar-derived bathymetric estimates. Overall, these results demonstrate the viability of marine radar observations as input to the cBathy algorithm and delineate some environmental constraints on algorithm performance. In the companion paper, the algorithm is extended to areas where tidal currents are important, including an ebb tidal shoal and an estuary mouth.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 21 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering〈/p〉 〈p〉Author(s): Alessandro Antonini, Alison Raby, James Mark William Brownjohn, Athanasios Pappas, Dina D'Ayala〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Historic rock lighthouses are unusual structures that are situated in hostile marine environments to provide warning to mariners. Even in an era of satellite navigation their role continues to be an important one, but their survivability into the future is not assured. Out of concern for their ongoing service, the multidisciplinary STORMLAMP project is assessing their survivability under wave loading. This paper presents the various stages of investigations into the structural integrity and stability assessment of the Fastnet lighthouse, situated just off the coast of Ireland. The paper describes: Extreme Bayesian analysis to quantify waves of particular return periods resulting in a 1 in 250 year return period wave with 〈em〉H〈/em〉〈sub〉0.1%〈/sub〉 of 17.6 m and an associated maximum force of 20,765 kN; logistically challenging field modal tests revealing the key modal parameters, like the modal masses of 1822 t and 1 675 t for 4.8 Hz and 5.0 Hz modes respectively, the cantilevered nature of the overall lighthouse and the directional effects due to the asymmetric contact with the granite rock; and details of a discontinuous finite element model that is used to determine the stability of the tower under the 1 in 250 year return period breaking wave condition, which is well within stability and material strength limits, causing maximum horizontal displacements in the order of 1 mm at the top of the tower. The overall assessment is that the sheer mass of the lighthouse and its interconnected joints are able to withstand the worst of the Atlantic storms.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 142〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 144〈/p〉 〈p〉Author(s): Hannah E. Power, Bahram Gharabaghi, Hossein Bonakdari, Bryson Robertson, Alexander L. Atkinson, Tom E. Baldock〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper assesses the accuracy of seven empirical models and an explicit Gene-Expression Programming (GEP) model to predict wave runup against a large dataset of runup observations. Observations consist of field and laboratory measurements and include a wide array of beach types with varying sediment sizes (from fine sand to cobbles) and bed roughness (from smooth steel to asphalt). We show that the best performing models in the literature are prone to significant errors (minimum RMSE of 1.05 m and NMSE of 0.23) when used with unseen data, i.e., uncalibrated models; however, overall error values and correlations are significantly reduced when models are optimised for the dataset. The best performing empirical models use a Hunt type scaling with an additional parameter for wave induced setup. The predictive ability of the explicit GEP model, which better captures the complex nonlinear effects of the key factors on the wave runup length, resulted in a statistically significant improvement in predictive capacity in comparison to all other empirical models assessed here, even on unseen data. Wave height, wavelength, and beach slope are shown to be the three primary factors influencing wave runup, with grain size/bed roughness having a smaller, but still significant influence on the runup. The r〈sup〉2〈/sup〉 of the best optimised existing models (which takes the form of Holman (1986) and Atkinson et al. (2017) their M2 model) was 0.77, with a RMSE of 0.85 m. These were improved to an r〈sup〉2〈/sup〉 of 0.82 (6% increase) and RMSE of 0.75 m (12% decrease) in the GEP-based model. The sensitivity of the proposed GEP-based model to each input variable is assessed via a partial derivative sensitivity analysis. The results demonstrate a higher sensitivity in the model to small values of each input and that wave steepness and beach slope are the primary factors influencing wave runup.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 143〈/p〉 〈p〉Author(s): María L. Jalón, Andrea Lira-Loarca, Asunción Baquerizo, Miguel Ángel Losada〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉An analytical model of the interaction of oblique incident regular waves with a maritime structure is developed and extended to irregular waves. The structure is composed of a semi-submergible vertical impermeable plate enclosing a chamber. Linear wave theory is considered, taking into account the head loss due to the constriction of the flow. The results are compared to those obtained with computational fluid dynamics models, revealing that the proposed model is capable to efficiently describe the performance of these systems for weakly non-linear incident waves. The influence of fundamental design parameters, such as geometric and wave characteristics, on the hydrodynamic behavior and the loadings on the plate is analyzed.〈/p〉 〈p〉When dealing with irregular waves, the spectra at the seaward region and inside the chamber show a nodal and antinodal structure that varies with the distance to the reflector. This structure, as well as the phase lag between the free surface elevations at both sides of the plate, affect the total loads over the plate. The statistical analysis of the free surface elevation, wave heights, and crests and throughs of the forces is also presented to evaluate the effect of the geometry in both regions and over the plate.〈/p〉 〈p〉The results show that the model allows to efficiently test different configurations to control wave reflection at the structure and the oscillation in the chamber. It can therefore be applied e.g. for the optimization of the design towards (i) harbor tranquility in the seaward region, (ii) energy extraction inside the chamber and (iii) loads on the structure.〈/p〉 〈p〉As an application, a failure mode defined as the excess of a critical predefined load over the plate, is analyzed by means of Monte Carlo simulations using known theoretical distributions fitted to the random variables. The results show the importance of the analysis of the performance of the system regarding not only the effect inside the chamber but also on the structure.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Coastal Engineering, Volume 143〈/p〉 〈p〉Author(s): 〈/p〉