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  • 1
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    Simulating Linear Kinematic Features in Viscous‐Plastic Sea Ice Models on Quadrilateral and Triangular Grids With Different Variable Staggering (2021)
    Details
    Publication Date: 2022-04-04
    Description: Observations in polar regions show that sea ice deformations are often narrow linear features. These long bands of deformations are referred to as Linear Kinematic Features (LKFs). Viscous‐plastic sea ice models have the capability to simulate LKFs and more generally sea ice deformations. Moreover, viscous‐plastic models simulate a larger number and more refined LKFs as the spatial resolution is increased. Besides grid spacing, other aspects of a numerical implementation, such as the placement of velocities and the associated degrees of freedom, may impact the formation of simulated LKFs. To explore these effects this study compares numerical solutions of sea ice models with different velocity staggering in a benchmark problem. Discretizations based on A‐,B‐, and C‐grid systems on quadrilateral meshes have similar resolution properties as an approximation with an A‐grid staggering on triangular grids (with the same total number of vertices). CD‐grid approximations with a given grid spacing have properties, specifically the number and length of simulated LKFs, that are qualitatively similar to approximations on conventional Arakawa A‐grid, B‐grid, and C‐grid approaches with half the grid spacing or less, making the CD‐discretization more efficient with respect to grid resolution. One reason for this behavior is the fact that the CD‐grid approach has a higher number of degrees of freedom to discretize the velocity field. The higher effective resolution of the CD‐discretization makes it an attractive alternative to conventional discretizations.
    Description: Plain Language Summary: Sea ice in the Arctic and Antarctic Oceans plays an important role in the exchange of heat and freshwater between the atmosphere and the ocean and hence in the climate in general. Satellite observations of polar regions show that the ice drift sometimes produces long features that are either cracks (leads) and zones of thicker sea ice (pressure ridges). This phenomenon is called deformation. It is mathematically described by the non‐uniform way in which the ice moves. For numerical models of sea ice motion it is difficult to represent this deformation accurately. Details of the numerics may affect the way these models simulate leads and ridges, their number and length. Specifically, we find by comparing different numerical models, that the way the model variables are ordered on a computational grid to solve the mathematical equations of sea ice motion has an effect of how many deformation features can be represented on a grid with a given spacing between grid points. A new discretization (ordering of model variables) turns out to resolve more details of the approximated field than traditional methods.
    Description: Key Points: The placement of the sea ice velocity has a mayor influence on the number of simulated linear kinematic features (LKFs). The CD‐grid resolves twice as many LKFs compared to A, B, C‐grids. A, B, C‐grids on quadrilateral meshes resolve a similar number of LKFs as A‐grids on triangular meshes (with the same total number of nodes).
    Keywords: ddc:550 ; ddc:551.343
    Language: English
    Type: doc-type:article
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  • 2
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    Spatial variability in river bed porosity determined by nuclear density gauging: A case study from a French gravel‐bed river (2021)
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    Publication Date: 2022-04-01
    Description: Porosity is one of the key properties of fluvial sediments. It is defined as the ratio of pore volume to total volume. In river science, porosity is often assumed to be spatially constant, which might be a gross simplification of reality. Ignoring the spatial variations in porosity can cause errors in morphological, ecological, hydrological, hydrogeological and sedimentological applications. Although detailed information about spatial porosity variations can be obtained from porosity measurements at field sites, such information has never been collected where these variations might be important. In this study, field porosity measurements were carried out to quantify the magnitude of the spatial porosity variation for four different sedimentological environments of a braided river: a confluence, a tributary delta, a braid bar and a secondary channel. A nuclear density gauge was used for the measurement of porosity. The nuclear density gauge proved to be a time‐saving and labour‐saving technique that produces accurate porosity values with a root mean square error of 0.03. The four sedimentological environments showed significant differences in porosity, with mean porosity being lower for confluence and bar than for delta and secondary channel. Semi‐variogram analysis showed the absence of any spatial correlation in porosity for distances beyond 4 m. This shows that distance cannot be used as a parameter for porosity extrapolation in a fluvial system unless the extrapolation distance is less than 4 m. At least eight measurements of porosity are required to obtain a reliable estimate of mean porosity in a sedimentary environment, i.e. with uncertainty 〈0.03. Although grain size characteristics were found to have a significant impact on porosity, the relationships between these parameters and porosity were not very strong in this study. The unique porosity dataset, presented in this article, provides a valuable source of information for researchers and river managers.
    Description: Deutsche Forschungsgemeinschaft
    Keywords: ddc:550
    Language: English
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  • 3
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    Tracking Downstream Variability in Large Grain‐Size Distributions in the South‐Central Andes (2021)
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    Publication Date: 2022-03-31
    Description: Mixed sand‐ and gravel‐bed rivers record erosion, transport, and fining signals in their bedload size distributions. Thus, grain‐size data are imperative for studying these processes. However, collecting hundreds to thousands of pebble measurements in steep and dynamic high‐mountain river settings remains challenging. Using the recently published digital grain‐sizing algorithm PebbleCounts, we were able to survey seven large (≥ 1,000 m2) channel cross‐sections and measure thousands to tens‐of‐thousands of grains per survey along a 100‐km stretch of the trunk stream of the Toro Basin in Northwest Argentina. The study region traverses a steep topographic and environmental gradient on the eastern margin of the Central Andean Plateau. Careful counting and validation allows us to identify measurement errors and constrain percentile uncertainties using large sample sizes. In the coarse ≥2.5 cm fraction of bedload, only the uppermost size percentiles (≥95th) vary significantly downstream, whereas the 50th and 84th percentiles show less variability. We note a relation between increases in these upper percentiles and along‐channel junctions with large, steep tributaries. This signal is strongly influenced by lithology and geologic structures, and mixed with local hillslope input. In steep catchments like the Toro Basin, we suggest nonlinear relationships between geomorphic metrics and grain size, whereby the steepest parts of the landscape exert primary control on the upper grain‐size percentiles. Thus, average or median metrics that do not apply weights or thresholds to steeper topography may be less predictive of grain‐size distributions in such settings.
    Description: Plain Language Summary: Rock fragments on hillsides are transported to rivers, eventually becoming pebbles, sand, and mud as they are carried downstream by flowing water. The initial size of the pebbles, the way the size changes downstream, and the overprinting of the sizes with new pebbles from other hills and tributaries all form a complex process that can be difficult to disentangle. Yet studying the size of the pebbles at a given stream location or in a sedimentary deposit can provide insights into the conditions of their transport in terms of local upstream patterns of erosion, tectonics, and climate. We show that just looking at the size of the large pebbles on a riverbed can be used to infer the sources of material, but, since there are fewer large pebbles, they require more measurements to quantify. This necessitates new methods for pebble measurement using modern image‐processing tools.
    Description: Key Points: Complex grain‐size distributions in dynamic mountain rivers can be computed via thousands of measurements from PebbleCounts. Many measurements allow robust estimation of higher percentiles and we observe the most significant changes in the ≥95th percentile. Downstream grain‐size variation is nonlinearly related to variations in topographic steepness and lithology.
    Description: Deutsches Zentrum für Luft‐ und Raumfahrt (DLR) http://dx.doi.org/10.13039/501100002946
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: Bundesministerium für Bildung und Forschung (BMBF) http://dx.doi.org/10.13039/501100002347
    Description: Brandenburger Staatsministerium für Wissenschaft, Forschung und Kultur (MWFK) http://dx.doi.org/10.13039/501100004581
    Description: https://zenodo.org/record/5089789
    Keywords: ddc:551.3 ; ddc:550
    Language: English
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  • 4
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    Reanalysis in Earth System Science: Toward Terrestrial Ecosystem Reanalysis (2021)
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    Publication Date: 2022-03-29
    Description: A reanalysis is a physically consistent set of optimally merged simulated model states and historical observational data, using data assimilation. High computational costs for modeled processes and assimilation algorithms has led to Earth system specific reanalysis products for the atmosphere, the ocean and the land separately. Recent developments include the advanced uncertainty quantification and the generation of biogeochemical reanalysis for land and ocean. Here, we review atmospheric and oceanic reanalyzes, and more in detail biogeochemical ocean and terrestrial reanalyzes. In particular, we identify land surface, hydrologic and carbon cycle reanalyzes which are nowadays produced in targeted projects for very specific purposes. Although a future joint reanalysis of land surface, hydrologic, and carbon processes represents an analysis of important ecosystem variables, biotic ecosystem variables are assimilated only to a very limited extent. Continuous data sets of ecosystem variables are needed to explore biotic‐abiotic interactions and the response of ecosystems to global change. Based on the review of existing achievements, we identify five major steps required to develop terrestrial ecosystem reanalysis to deliver continuous data streams on ecosystem dynamics.
    Description: Plain Language Summary: A reanalysis is a unique set of continuous variables produced by optimally merging a numerical model and observed data. The data are merged with the model using available uncertainty estimates to generate the best possible estimate of the target variables. The framework for generating a reanalysis consists of the model, the data, and the model‐data‐fusion algorithm. The very specific requirements of reanalysis frameworks have led to the development of Earth‐compartment specific reanalysis for the atmosphere, the ocean and land. Here, we review atmospheric and oceanic reanalyzes, and in more detail biogeochemical ocean and terrestrial reanalyzes. In particular, we identify land surface, hydrologic, and carbon cycle reanalyzes which are nowadays produced in targeted projects for very specific purposes. Based on a review of existing achievements, we identify five major steps required to develop reanalysis for terrestrial ecosystem to shed more light on biotic and abiotic interactions. In the future, terrestrial ecosystem reanalysis will deliver continuous data streams on the state and the development of terrestrial ecosystems.
    Description: Key Points: Reanalyzes provide decades‐long model‐data‐driven harmonized and continuous data sets for new scientific discoveries. Novel global scale reanalyzes quantify the biogeochemical ocean cycle, terrestrial carbon cycle, land surface, and hydrologic processes. New observation technology and modeling capabilities allow in the near future production of advanced terrestrial ecosystem reanalysis.
    Description: European Union's Horizon 2020 research and innovation programme
    Description: Deutsche Forschungsgemeinschaft
    Description: U.S. Department of Energy
    Description: Emory University's Halle Institute for Global Research and the Halle Foundation Collaborative Research
    Description: NSF
    Description: NASA
    Description: Natural Environment Research Council
    Description: European Union'’s Horizon 2020 research and innovation programme
    Description: NSERC Discovery program, the Ocean Frontier Institute, and MEOPAR
    Description: Research Foundation Flanders (FWO)
    Description: Helmholtz Association
    Description: NASA Terrestrial Ecosystems
    Keywords: ddc:550
    Language: English
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  • 5
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    Significance of flow rule for the passive earth pressure problem (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-09-12
    Description: Determination of earth pressures is one of the fundamental tasks in geotechnical engineering. Although many different methods have been utilized to present passive earth pressure coefficients, the influence of non-associated plasticity on the passive earth pressure problem has not been discussed intensively. In this study, finite-element limit analysis and displacement finite-element analysis are applied for frictional materials. Results are compared with selected data from literature in terms of passive earth pressure coefficients, shape of failure mechanism and robustness of the numerical simulation. The results of this study show that passive earth pressure coefficients determined with an associated flow rule are comparable to the Sokolovski solution. However, comparison with a non-associated flow rule reveals that passive earth pressure coefficients are significantly over predicted when following an associated flow rule. Moreover, this study reveals that computational costs for determination of passive earth pressure are considerably larger following a non-associated flow rule. Additionally, the study shows that numerical instabilities arise and failure surfaces become non-unique. It is shown that this problem may be overcome by applying the approach suggested by Davis (Soil Mech 341–354, 1968).
    Description: Ruhr-Universität Bochum (1007)
    Keywords: ddc:550 ; Finite-element limit analysis ; Finite-element analysis ; Non-associated plasticity ; Passive earth pressure
    Language: English
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  • 6
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    Pure cross-anisotropy for geotechnical elastic potentials (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-09-13
    Description: The pure cross-anisotropy is understood as a special scaling of strain (or stress). The scaled tensor is used as an argument in the elastic stiffness (or compliance). Such anisotropy can be overlaid on the top of any elastic stiffness, in particular on one obtained from an elastic potential with its own stress-induced anisotropy. This superposition does not violate the Second Law. The method can be also applied to other functions like plastic potentials or yield surfaces, wherever some cross-anisotropy is desired. The pure cross-anisotropy is described by the sedimentation vector and at most two constants. Scaling with more than two purely anisotropic constants is shown impossible. The formulation was compared with experiments and alternative approaches. Static and dynamic calibration of the pure anisotropy is also discussed. Graphic representation of stiffness with the popular response envelopes requires some enhancement for anisotropy. Several examples are presented. All derivations and examples were accomplished using the algebra program Mathematica.
    Description: Karlsruher Institut für Technologie (KIT) (4220)
    Keywords: ddc:550 ; Cross-anisotropy ; Hyperelasticity ; Inherent anisotropy ; Response envelopes ; Scaling of strain ; Transverse isotropy
    Language: English
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  • 7
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    Bayesian Quantification and Reduction of Uncertainties in 3D Geomechanical‐Numerical Models (2022)
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    Publication Date: 2023-09-13
    Description: The distance to failure of the upper crustal rock in the prevalent stress field is of importance to better understand fault reactivation by natural and induced processes as well as to plan and manage georeservoirs. In particular, the contemporary stress state is one of the key ingredients for this assessment. To provide a continuous description of the 3D absolute stress state geomechanical‐numerical models are used. However, stress magnitude data for model calibration are sparse and incomplete and thus, the resulting model uncertainties are large. In order to reduce the uncertainties, we incorporate additional constraints on stress magnitudes to check the plausibility of different data‐based stress states. We use formation integrity tests, borehole breakouts, drilling induced fractures, and observations of seismicity and distinct seismological quiescence. This information is weighted according to its confidence and the agreement with the different modeled stress states is assessed. The information is introduced to a Bayesian approach to estimate weights of the modeled stress states and thereby identify their plausibility. A case study in southern Germany shows the ability of the approach to identify from a wide range of stress states a small number of plausible ones and reject implausible stress states. This significantly reduces the number of stress states and thus lowers the model uncertainties.
    Description: Plain Language Summary: The upper crust of the Earth (upper few kilometers) is subject to a kind of pressure, referred to as stress. When the stress becomes larger than the strength of the rock, the rock breaks. Sometimes this can be measured or even felt as a seismic event. It happens naturally but may also happen due to human activity. To prevent such induced seismic event, it is important to know the stress state. But there is only few information on the magnitude of the stress so we need computer models to predict the stress state. These models are often not very precise since there is only few information on the stress magnitudes and in addition they are often contradicting. We use all stress magnitude information individually to model various stress states. Then we look at other information that is related to the stress state but does not provide stress magnitude information on its own. We compare this information with the modeled stress states to find out whether a stress state agrees with the additional information or not. This allows us to identify a few realistic stress state models out of a wide range of possible ones. This reduces the uncertainties of the stress predictions.
    Description: Key Points: Bayesian approach to uncertainty quantification and reduction of 3D geomechanical‐numerical models of the undisturbed stress state. Additional constraints on the stress state by formation integrity tests, borehole breakouts, and drilling induced tensile fractures. Constraints on the differential stress by observation of seismicity or distinct seismological quiescence.
    Description: Bundesministerium für Bildung, Wissenschaft und Forschung http://dx.doi.org/10.13039/501100013699
    Description: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Description: Helmholtz Centre Potsdam ‐ Deutsches GeoForschungsZentrum GFZ
    Description: RI Fabrice Cotton
    Description: Federal Company for radioactive waste disposal
    Description: https://github.com/MorZieg/FAST_Calibration
    Keywords: ddc:550 ; geomechanics ; uncertainties ; stress state ; modeling ; Bayes
    Language: English
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  • 8
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    Influence of Inner Surface Roughness on the Spectral Induced Polarization Response—A Numerical Study (2023)
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    Publication Date: 2023-11-23
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Spectral induced polarization (SIP) laboratory measurements on water‐saturated rocks show a strong correlation between the electrical polarization strength and the inner surface area of rocks. We investigate the influence of inner surface roughness on the SIP response by simulating the frequency‐dependent complex conductivity of micro‐scale rock models. Starting with smooth grain models, we introduce surface roughness using two different approaches: increasing the surface roughness in a fractal‐like manner, and creating random surface structures, resulting in more natural‐looking surfaces. We find that surface roughness has two distinct effects on the SIP response: (a) a shift in the position and magnitude of the primary relaxation frequency to lower frequencies and lower magnitudes, respectively, and (b) the formation of secondary polarizations above the polarization frequency of the primary polarization. We also compare the relaxation time and normalized chargeability obtained by Debye decomposition and the imaginary conductivity at 1 Hz of our models with mechanistic models and empirical relations. We point out the congruences and offer explanations for the discrepancies between our models and the empirical observations. We conclude that the results of our study are applicable to real rocks and that the SIP method has the potential to detect inner surface roughness. However, the SIP method it not able to discriminate between signals from rough particles and a distribution of smooth particles.〈/p〉
    Description: Plain Language Summary: The spectral induced polarization method measures the electrical conductivity of the subsurface at depths of investigation ranging from a few dm to several 100 m. The potential of the method to detect mineral resources, contamination, microbial activity, etc. makes it a promising tool for today's environmental challenges. However, due to the complexity of the underlying physical and chemical processes the interpretation of SIP measurements often remains qualitative. Mathematical and mechanistic models used to describe the processes are usually simplified with respect to geometry, chemistry, and physical properties. In this study, we use computer simulations to investigate the surfaces of spherical particles (grains). After simulating the SIP response of models with smooth and rough surfaces, we analyze the influence of surface roughness on the SIP response. We find that surface roughness causes distinct changes in the SIP response compared to the smooth grain. However, we also find that this introduces an ambiguity in the interpretation of SIP data.〈/p〉
    Description: Key Points: 〈list list-type="bullet"〉 〈list-item〉 〈p xml:lang="en"〉Inner surface roughness of rocks has substantial impact on spectral induced polarization response〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Surface roughness shifts the primary polarization peak to lower frequencies〈/p〉〈/list-item〉 〈list-item〉 〈p xml:lang="en"〉Surface roughness causes additional polarizations above the primary peak frequency〈/p〉〈/list-item〉 〈/list〉 〈/p〉
    Description: https://doi.org/10.5281/ZENODO.7049722
    Keywords: ddc:550 ; SIP ; surface ; roughness
    Language: English
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  • 9
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    FID GEO latest: How to cite data publications correctly (2023)
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    Publication Date: 2023-12-07
    Description: Publishing data with a DOI (Digital Object Identifier) is becoming increasingly popular, and many researchers are being asked by journals to publish the data underlying the research results described in the article. Where does the data come from and how do I cite it correctly? […] This publication is a translation of the FID GEO article in 〈a href="http://doi.org/10.23689/fidgeo-5688"〉GMIT 90.〈/a〉
    Description: research
    Keywords: ddc:550 ; GMIT ; Geowissenschaftliche Mitteilungen
    Language: English
    Type: doc-type:article , publishedVersion
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  • 10
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    FID GEO latest: Recommendations for using ORCID iD (2023)
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    Publication Date: 2023-12-07
    Description: The ORCID is an open alphanumeric identifier used to uniquely identify researchers.In an increasingly connected scientific landscape, the growing number of published research outputs (data, text, software) and new open publishing models pose major challenges for scientific publication management. The repositories available to FID GEO, GEO-LEOe-docs (SUB Goettingen) and GFZ Data Services (GFZ), have long been working with PIDs such as the Digital Object Identifier (DOI ) and the Open Researcher and Contributor iD (ORCID iD ), and recommend the use of the ORCID. This publication is a translation of the FID GEO article in 〈a href="http://doi.org/10.23689/fidgeo-5832"〉GMIT 87.〈/a〉
    Description: DFG, SUB Göttingen, GFZ Potsdam
    Description: research
    Keywords: ddc:550 ; GMIT
    Language: English
    Type: doc-type:article , publishedVersion
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