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  • Articles  (13)
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  • Articles: DFG German National Licenses  (13)
  • simulation  (13)
  • Springer  (13)
  • 1995-1999  (8)
  • 1990-1994  (5)
  • Architecture, Civil Engineering, Surveying  (13)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Stochastic environmental research and risk assessment 10 (1996), S. 167-186 
    ISSN: 1436-3259
    Keywords: Reservoir stochastic theory ; reliability ; mean ; variance ; indicator function ; storage bounds ; nonlinear programming ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A new formulation is presented for the analysis of reservoir systems synthesizing concepts from the traditional stochastic theory of reservoir storage, moments analysis and reliability programming. The analysis is based on the development of the first and second moments for the stochastic storage state variable. These expressions include terms for the failure probabilities (probabilities of spill or deficit) and consider the storage bounds explicitly. Using this analysis, expected values of the storage state, variances of storage, optimal release policies and failure probabilities — useful information in the context of reservoir operations and design, can be obtained from a nonlinear programming solution. The solutions developed from studies of single reservoir operations on both an annual and monthly basis, compare favorably with those obtained from simulation. The presentation herein is directed to both traditional reservoir storage theorists who are interested in the design of a reservoir and modern reservoir analysts who are interested in the long term operation of reservoirs.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Stochastic environmental research and risk assessment 5 (1991), S. 125-134 
    ISSN: 1436-3259
    Keywords: Empirical Orthogonal Function analysis ; random fields ; simulation ; non-homogeneous fields
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract In several fields of Geophysics, such as Hydrology, Meteorology or Oceanography, it is often useful to generate random fields, displaying the same variabilitity as the observed variables. Usually, these synthetic data are used as forcing fields into numerical models, to test the sensitivity of their outputs to the variability of the inputs. Examples can be found in subsurface or surface Hydrology and in Meteorology with General Circulation Models (GCM). Different techniques have already been proposed, often based on the spectral representation of the random process, with, usually, assumptions of stationarity. This paper suggests that Empirical Orthogonal Function (EOF) analysis, which leads to the decomposition of the covariance kernel on the set of its eigen-functions, is a possible answer to this problem. The convergence and accuracy of the method are shown to depend mainly on the number of EOFs retained in the expansion of the covariance kemel. This result is confirmed by a comparison with the turning band method and a matrix technique. Furthermore, a synthetic example of non-homogencous fields shows the interest of EOF analysis in the direct simulation of such fields.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Stochastic environmental research and risk assessment 12 (1998), S. 33-52 
    ISSN: 1436-3259
    Keywords: Keywords: Streamflow ; simulation ; nonparametric
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A new approach for streamflow simulation using nonparametric methods was described in a recent publication (Sharma et al. 1997). Use of nonparametric methods has the advantage that they avoid the issue of selecting a probability distribution and can represent nonlinear features, such as asymmetry and bimodality that hitherto were difficult to represent, in the probability structure of hydrologic variables such as streamflow and precipitation. The nonparametric method used was kernel density estimation, which requires the selection of bandwidth (smoothing) parameters. This study documents some of the tests that were conduced to evaluate the performance of bandwidth estimation methods for kernel density estimation. Issues related to selection of optimal smoothing parameters for kernel density estimation with small samples (200 or fewer data points) are examined. Both reference to a Gaussian density and data based specifications are applied to estimate bandwidths for samples from bivariate normal mixture densities. The three data based methods studied are Maximum Likelihood Cross Validation (MLCV), Least Square Cross Validation (LSCV) and Biased Cross Validation (BCV2). Modifications for estimating optimal local bandwidths using MLCV and LSCV are also examined. We found that the use of local bandwidths does not necessarily improve the density estimate with small samples. Of the global bandwidth estimators compared, we found that MLCV and LSCV are better because they show lower variability and higher accuracy while Biased Cross Validation suffers from multiple optimal bandwidths for samples from strongly bimodal densities. These results, of particular interest in stochastic hydrology where small samples are common, may have importance in other applications of nonparametric density estimation methods with similar sample sizes and distribution shapes.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Stochastic environmental research and risk assessment 4 (1990), S. 255-276 
    ISSN: 1436-3259
    Keywords: Stochastic hydrologic process ; daily discharges ; correlated generation ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A geomorphological study at the confluence of the Danube and the Isar in Bavaria required long series of daily discharges in both rivers. A model that generates simultaneous correlated streamflows in both rivers was developed and tested. The model is a modified shot noise model, first developed by Treiber (1975) for a single river, that was adapted to two rivers. It generates correlated pulses of events that produce flow for each river, and these pulses are then convoluted with a river specific systems function. The model, after being calibrated for the two rivers on the basis of 85 years of records, yields artificial series of discharges, in which the statistical properties of the historical records are reproduced. The performance of the model was tested with 20 generated series each 100 years long.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Transportation 26 (1999), S. 399-416 
    ISSN: 1572-9435
    Keywords: cellular telephones ; incident detection ; simulation ; traffic modeling ; wireless communications
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract This research study was designed to assess by simulation the efficacy of incident detection by cellular phone call-in programs. The assessment was conducted by varying the proportion of drivers with cellular phones on the highway so as to mirror the cellular industry statistics that show a continued growth of ownership of cellular phones in the United States. An analytical model, which combined simulation and the limited field data available in the literature, was used to determine measures of effectiveness of the cellular phone-based detection system. The results showed that a cellular phone detection system offers fast incident detection times and higher detection rates for both shoulder and lane blocking incidents. For example, in moderate traffic flow (i.e. 1,550 vehicles per hour per lane), 90 percent of incidents blocking two lanes were detected in 1.5 minutes when the proportion of drivers with cellular phones was one out of 10 drivers, even with only 20 percent of them willing to report incidents. When the current proportion of cellular ownership, i.e. 1 out of 3, was used in the simulation, the detection time improved to 0.8 minutes. The simulation analysis of incident detection by cellular phones also showed that there is a direct relationship between the probability of detection and the detection time; that is, the specification of a higher detection rate resulted in slower detection times. This is in sharp contrast with the results of field study of automatic incident detection (AID) systems which demonstrated an inverse relationship between probability of detection and detection time.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Water resources management 11 (1997), S. 395-406 
    ISSN: 1573-1650
    Keywords: irrigation reservoirs ; operation ; water deficit ; yield response ; multicrop environment ; stochastic dynamicprogramming ; soil moisture ; water allocation ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract A two-phase stochastic dynamic programming model is developed for optimal operation of irrigation reservoirs under a multicrop environment. Under a multicrop environment, the crops compete for the available water whenever the water available is less than the irrigation demands. The performance of the reservoir depends on how the deficit is allocated among the competing crops. The proposed model integrates reservoir release decisions with water allocation decisions. The water requirements of crops vary from period to period and are determined from the soil moisture balance equation taking into consideration the contribution of soil moisture and rainfall for the water requirements of the crops. The model is demonstrated over an existing reservoir and the performance of the reservoir under the operating policy derived using the model is evaluated through simulation.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Water resources management 11 (1997), S. 437-444 
    ISSN: 1573-1650
    Keywords: water first and second drainage ; layered unsaturated soil ; experiment ; γ-radiation ; simulation ; finite differences ; periodically changing head
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract Experimental results during first and second drainage in a vertical column of saturated layered soil were compared to those predicted from simulation. The sample was composed of a sandyloam soil overlying a fine sand. The soil water content was measured by using γ-ray absorption method (241Am) and the water pressure through tensiometers, arranged vertically along the column and connected to pressure transducers. From the evaluation of moisture and pressure versus time, the characteristic curves Ψ(θ) of the layers were obtained and approximated by van Genuchten's analytical equation. The relationship K(θ) between hydraulic conductivity and moisture was estimated by van Genuchten's prediction model. Ψ(θ) and K(θ) equations were used as inputs in the numerical model. The drainage of water was simulated by Richard's partial differential equation, which was solved with the finite differences computational scheme type Laasonen. The upper and lower boundary conditions were zero flux and a periodically changing head respectively. Numerical results show a good agreement with experimental data, with small deviations for certain hours.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Water resources management 12 (1998), S. 13-30 
    ISSN: 1573-1650
    Keywords: risk ; reliability ; resiliency ; vulnerability ; drought risk index ; drought damage index ; simulation ; water supply ; reservoir operation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract In this study, simulation is used to evaluate the performance of the municipal water system in Fukuoka city. In combination with daily simulation model, a kind of risk model incorporating water demand prediction is presented. This model applies five risk indices: reliability, resiliency, vulnerability, drought risk index (DRI) and drought damage index (DDI). They aid in the identification of operation policies for the municipal water system, and the planning and operational policies obtained are aimed at achieving minimum risk for a given scenario of operation. In this paper, the performance risk of the municipal water system is investigated under three alternatives: (1) the existing system operation when available supply from the Chikugo river is decreased; (2) water restrictions for different percentages of reduction are implemented; and (3) available water supply increases when desalination of sea water is implemented. The results obtained show that savings of between 5 and 12% of water consumption from May 1, or increasing of daily desalination of sea water about 30 000 m3 or more, may efficiently decrease the performance risk of the Fukuoka water supply system. Potentials also exist for further increase of reservoir storage by more rational operation. The measure that more attention should be paid to increasing the water supply from stable sources is recommended as well.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Water resources management 12 (1998), S. 285-293 
    ISSN: 1573-1650
    Keywords: agrometeorological models ; PRZM ; simulation ; SWATRER ; water balance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract Two methods widely used in agrometeorogical simulation models for describing field soil water regimes are compared and evaluated based on their ability to predict experimental data from a single field study. The first method is based on a numerical solution to the Richards' equation for describing water movement in the soil profile, while the second method is based on soil-water capacity terms. The evaluation of the performance of the two methods is based on goodness-of-fit statistics and graphical analysis. Results indicate that the first method is more accurate for both the upper and the lower soil zones; the second method, despite its low performance in the upper soil zone can adequately describe soil moisture conditions in the lower soil zones. Recommendations are made for model use based on comparison results, the intended model use, and the difficulty in the acquisition of required model inputs.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Water resources management 6 (1992), S. 149-159 
    ISSN: 1573-1650
    Keywords: Manning's equation ; vegetated open channels ; submerged aquatic weeds ; simulation ; Egyptian canals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract Modified formulas for Manning's equation are developed for use in the design of earthen open channels with submerged aquatic weeds. The proposed relations have their basis in field and experimental data. A multiple regression analysis was used to develop a relationship between the mean velocity, hydraulic radius, and water surface slope. The new formulas are dependent on the distribution of weeds along the channel's wetted perimeter and the percentage of vegetation density with respect to the cross-section area of the waterway.
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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Water resources management 6 (1992), S. 101-115 
    ISSN: 1573-1650
    Keywords: Staged disaggregation ; parameter estimation ; Mejia-Rousselle model ; moment preservation ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract The problem of moment preservation associated with the use of the Mejia and Rousselle model in a staged disaggregation scheme is addressed in this paper. General parameter estimation equations are derived. Different from the original parameter estimation equations, the equations proposed herein employ two corrected historical moments which are shown to be conditional on the stage and the annual input generation model. With parameters estimated from the proposed equations, the modeling can exactly preserve the historical moments of interest and maintain the linear relationship between the input and output of each disaggregation process.
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Water resources management 11 (1997), S. 165-184 
    ISSN: 1573-1650
    Keywords: optimization ; linear programming ; simulation ; irrigation planning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract A methodology is presented for planning the operation of the Fuerte-Carrizo irrigation system in northwest Mexico. The system has two storage dams, two irrigation districts, and water transfer capabilities between both dams. The methodology uses a combination of linear programming (LP) and simulation. The LP model maximizes the net return of the farmers, subject to restrictions of the system, availability of water and land, and water transfer relationships. The simulation model is programmed as a microcomputer interactive package simulating the performance of the system. The methodology has proven to be a useful tool to assist those responsible for the operation of the irrigation system.
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Water resources management 8 (1994), S. 245-264 
    ISSN: 1573-1650
    Keywords: groundwater ; hydrogeochemical investigation ; simulation ; urban area ; arid climate groundwater management ; conservation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: Abstract The urban area of Greater Dhahran has an extremely arid climate where the average annual rainfail is less than 71 mm. The Umm Er Radhuma (UER) aquifer in that area is the main source of domestic and landscape irrigation demands. Groudwater use has increased drastically during the last 15 years due to extensive developments in the area. Numerical simulation techiques and hydrogeochemical investigations were carried out to assess the effects of increasing pumping rates on the piezometric surface in the UER aquifer and to predict the future levels and quality of water under different pumping scenarios. A groundwater flow model was developed and calibrated for the area. The increase in the water extraction rate between 1967 and 1990 has resulted in a decline in the piezometric surface by about 4 m in the Dhahran area. The results of simulation investigations indicated that if the present trend of the groundwater withdrawal rate continues, the water level is expected to drop by an additional 2 and by the end of the year 2000, by an additional 6 m by the end of 2010. If the present increasing rate in groundwater withdrawal is reduced by 50%, the additional drawdown will also be reduced to about 1 and 2.5 m by the end of years 2000 and 2010, respectively. The average total dissolved solids (TDS) has increased from 2750 to 3545 mg/l between 1967 and 1990 and will continue to rise to 3922 and 4361 by the end of years 2000 and 2010, respectively. These original findings are important because they postulates the negative impacts of increasing groundwater pumping from an aquifer in an arid urban area on future groundwater levels and quality. Therefore, effective groundwater management and conservation schemes should be adopted to maintain the long-term productivity and quality of aquifers in the area.
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