The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Ali Haghighi - One of the best experts on this subject based on the ideXlab platform.
-
Uncertainty Analysis of Transient Flow in Water Distribution Networks
Water Resources Management, 2018Co-Authors: Adell Moradi Sabzkouhi, Ali HaghighiAbstract:For transient analysis of a pipe network, the unsteady flow governing equations should be solved to obtain the extreme Pressure Heads in the system, which may be faced with several uncertainties. To evaluate that to what extent the input uncertainties can affect the system responses, a simulation model based on the fuzzy sets theory is introduced. For this purpose, triangular fuzzy numbers are used to represent the input uncertainties. Then, to obtain the extreme Pressure Heads in each location of the network and at each level of uncertainty, four independent optimization problems are solved. In these problems, the nodal maximum and minimum Pressure Heads are the objective functions and the simulation parameters are the decision variables. Accordingly, for fuzzy analysis of a pipe network, a complicated many-objective optimization problem arises. To solve the problem efficiently a many-objective genetic algorithm is coupled to the transient simulation model. To speed up the analysis, a transient simulation model in the frequency domain is used. The proposed model is applied to a pipe network and the results are discussed. The model is found computationally fast and promising for real applications.
-
Analysis of Transient Flow Caused by Fluctuating Consumptions in Pipe Networks: A Many-Objective Genetic Algorithm Approach
Water Resources Management, 2015Co-Authors: Ali HaghighiAbstract:Small, but fast fluctuating consumptions in a pipe network can lead to severe transient flows. Such fluctuations are stochastic in nature and, cannot be explicitly identified and analyzed for the systems in operation. This study introduces a mathematical model for taking into account the fluctuating consumptions in analysis and design of pipe networks. For this purpose, the fluctuations are simulated by two successive triangular pulses with adjustable geometry. A many-objective optimization problem is developed to find the worst maximum and minimum Pressure Heads. A new scheme of genetic algorithms is developed to find the extreme values of all Pressure Heads in only one single simulation run. The proposed model is applied to two water distribution networks. It is found that, the transient flow caused by fast fluctuating consumptions could seriously affect the system’s performance. For instance, analyzing a real pipe network reveals that, when the fluctuations are critically combined, the nodal Pressure Heads averagely change by 29 % (13 to 88 %) and −43 % (−16 to −177 %) with respect to the initial steady state.
Martin Wegehenkel - One of the best experts on this subject based on the ideXlab platform.
-
Simulation of Long-Term Soil Hydrological Conditions at Three Agricultural Experimental Field Plots Compared with Measurements
MDPI AG, 2019Co-Authors: Martin Wegehenkel, Karin Luzi, Dieter Sowa, Dietmar Barkusky, Wilfried MirschelAbstract:Soil hydrological conditions influence crop growth and groundwater recharge and, thus, precise knowledge of such conditions at field scale is important for the investigation of agricultural systems. In our study, we analyzed soil hydrological conditions at three agricultural experimental field plots with sandy soils and different crop rotations using a 22-year period from 1993 to 2014 with daily volumetric soil water contents measured by the Time Domain Reflectometry with Intelligent MicroElements (TRIME)-method and Pressure Heads determined by automatic recording tensiometers. These measured data were compared with soil water contents and Pressure Heads simulated by a process-based agroecosystem model. Within this 22-year period, time spans with a better model performance and periods with a lower goodness of fit between simulations and observations were observed. The lower goodness of fit in the summer periods was attributed to inadequate calculations of root water uptake. Measurement errors of the TRIME-probes and differences between soil water contents measured by TRIME and Pressure Heads observed by tensiometers due to different measurement volumes, precision and measuring principles were identified as further reasons for mismatches between simulated and measured model outputs
-
22-years time series of observed daily soil water contents and Pressure Heads under rain-fed conditions from agricultural field plots at the Experimental Station Muencheberg, Germany
2018Co-Authors: Martin WegehenkelAbstract:22-years period from 1993 to 2014 with time series of daily Pressure Heads measured by automatic recording tensiometers. Continuouslongterm time series of daily soil contents measured for soil compartments 0-30 cm, 30-60 cm, 60-90, 990-120, 120-150 cm and 200 cm depth using Time-Domain-Reflectmetry (TDR)-probes for the timeperiod 1993 to 2014. Quality check of the time series= Field calibrationof the TDR-probes using gravimetric method and consistency check using meteorological time series of measured rainfall and Pressure head and calculated evapotranspiration. This data set consist of continuous longterm time series of daily Pressure Heads measured at 30 cm, 60cm, 90 cm,120 cm , 150 cm and 200 cm depth using automatic recording tensimeters for the time period 1993 to 2014. The quality check of the time series consists of aplausibility check and correction using meteorological time series of measured rainfall and soil water contents, and calculated evapotranspiration.
-
Validation of a soil water balance model using soil water content and Pressure head data
Hydrological Processes, 2005Co-Authors: Martin WegehenkelAbstract:The validation of soil water balance models and the evaluation of the quality of the model predictions at field-scale require time-series of in situ measured model outputs. In our study, we have validated such a model using a 6-year period with time-series of automatically recorded, daily volumetric soil water contents measured with the time-domain reflectometry with intelligent microelements (TRIME) method and daily Pressure Heads measured with tensiometers. The comparisons of simulated with measured soil water contents and Pressure Heads were analysed using the modelling efficiency index (IA) and the square root of the mean square error (RMSE) in order to evaluate the prediction quality of the model. In our study, IA and RMSE, obtained either from the comparison of simulated with measured soil water contents or the comparison of calculated with observed Pressure Heads, in some cases lead to different results regarding the evaluation of the simulation quality of the soil water balance model. For example, a good fit between simulated and observed soil water contents does not necessarily result in a comparably good fit between the corresponding calculated and measured Pressure Heads. Therefore, a combined use of both measurement techniques, which takes into account their respective advantages and disadvantages, gives a more complete overview on the simulation quality of the soil water balance model than the single use of one of those techniques. Copyright © 2004 John Wiley & Sons, Ltd.
Jan Feyen - One of the best experts on this subject based on the ideXlab platform.
-
Sensitivity analysis of soil hydraulic properties on subsurface water flow in furrows
Journal of Irrigation and Drainage Engineering, 2006Co-Authors: David Rocha, Fariborz Abbasi, Jan FeyenAbstract:Knowledge of the sensitivity of various soil hydraulic properties is beneficial for model development and application purposes. It can lead to better estimated values, better understanding, and thus reduced uncertainty. In the present study, an extensive sensitivity analysis was performed to investigate the effects that various soil hydraulic properties have on subsurface water flow below furrows during two successive irrigation events to see which irrigation event was more sensitive and to analyze the effect of spatial variations in the initial soil water contents within the soil profile. Testing the sensitivity of the various soil hydraulic parameters in the van Genuchten-Mualem expression was carried out using the HYDRUS-2D model for two irrigation events 10 days apart. Results showed that the first irrigation event was clearly more sensitive than the second one. The latter event was mainly associated with the nonuniformity of the initial soil water contents within the soil profile. Pressure Heads in t...
-
Cautionary notes on the use of pedotransfer functions for estimating soil hydraulic properties
Agricultural Water Management, 1996Co-Authors: A. Espino, Dirk Mallants, Marnik Vanclooster, Jan FeyenAbstract:Abstract The performance of published pedotransfer functions was evaluated in terms of predicted soil water content, Pressure Heads, and drainage fluxes for a layered profile. The pedotransfer functions developed by Vereecken et al. (1989), Vereecken et al. (1990) were used to determine parameters of the soil hydraulic functions θ(h) and K(h) which were then used as input to SWATRER, a transient one-dimensional finite difference soil water model with root uptake capability. The SWATRER model was used to simulate the hydraulic response of a multi-layered soil profile under natural climatic boundary conditions for a period of one year. The simulations were repeated by replacing the indirectly estimated water retention characteristic by (1) local-scale, and (2) field-scale mean observed θ(h) relationships. Soil moisture contents and Pressure Heads simulated at different depths in the soil profile were compared to measured values using these three different sets of hydraulic functions. Drainage fluxes at one meter below ground surface have also been simulated using the same three sets of hydraulic functions. Results show that simulations based on indirectly estimated moisture retention characteristics (obtained from pedotransfer functions) overpredict the observed moisture contents throughout the whole soil profile, but predict the Pressure Heads at shallow depths reasonably good. The results also show that the predicted drainage fluxes based on estimated retention functions are about four times as high compared to the drainage fluxes simulated using measured retention curves.
Martinus Th Van Genuchten - One of the best experts on this subject based on the ideXlab platform.
-
Estimating unsaturated soil hydraulic properties from laboratory tension disc infiltrometer experiments
Water Resources Research, 1999Co-Authors: Jiři Simůnek, Ole Wendroth, Martinus Th Van GenuchtenAbstract:Four tension disc infiltration experiments were carried out on a loamy soil in the laboratory for the purpose of estimating the unsaturated soil hydraulic properties. Sixteen tensiometers were installed in pairs at the following coordinate (r, z) positions: (10, 2.5), (10, 5), (10, 10), (15, 5), (15, 10), (15, 15), (15, 20), and (15, 30), where r represents the distance from the axis of symmetry and z is the location below the soil surface. A time domain reflectometry (TDR) probe was used to measure water contents at a depth of 2 cm directly below the tension disc. The first three experiments involved supply Pressure Heads at the disc of -20, -10, -5, and -1 cm, with the experiment lasting for -5 hours. The same supply Pressure Heads were also used for the fourth experiment, which lasted 6.25 days so as to reach steady state at each applied tension. The measured data were analyzed using Wooding's [1968] analytical solution and by numerical inversion. The parameter estimation method combined a quasi three-dimensional numerical solution of the Richards equation with the Marquardt-Levenberg optimization scheme. The objective function for the parameter estimation analysis was defined using different combinations of the cumulative infiltrated volume, TDR readings, and tensiometer measurements. The estimated hydraulic properties were compared against results obtained with an evaporation experiment as analyzed with Wind's [1968] method. Water contents in the retention curves were underestimated when both transient and quasi steady state experiments were analyzed by parameter estimation. Unsaturated hydraulic conductivities obtained by parameter estimation and using Wooding's [1968] analysis corresponded well. Drying branches of the hydraulic conductivity function determined by parameter estimation also corresponded well with those obtained with the evaporation method.
-
parameter estimation analysis of the evaporation method for determining soil hydraulic properties
Soil Science Society of America Journal, 1998Co-Authors: Jiři Simůnek, Martinus Th Van Genuchten, Ole WendrothAbstract:Soil hydraulic properties are important parameters affecting water flow in variably saturated soils. We estimated the hydraulic properties from a laboratory evaporation experiment using both a parameter estimation method and the modified Wind method. The parameter estimation method combined a one-dimensional numerical solution of the Richards equation with the Marquardt-Levenberg optimization scheme. In our study we used both numerically generated data and data measured in the laboratory. Two experiments were carried out on 10-cm-high soil cores containing two different soils. Pressure Heads inside the cores were measured with five tensiometers, while evaporative water loss from the top was determined by weighing the soil samples. The objective function for the parameter estimation analysis was defined in terms of the final total water volume in the core and Pressure head readings by one or several tensiometers. An analysis of numerically generated data showed that the optimization method was most sensitive to the shape factor (n) and the saturated water content (θ s ) and least to the residual water content (θ r ). Pressure Heads measured close to the soil surface were found to be more valuable for the parameter estimation technique than those measured at lower locations. The optimized hydraulic parameters corresponded closely with those obtained using Wind's analysis. All optimizations gave similar results for the soil hydraulic properties within the range of measured Pressure Heads (0 to -700 cm). Extrapolation beyond this range involved a high level of uncertainty because of high correlation between parameters θ r and n.
Kevin E Lansey - One of the best experts on this subject based on the ideXlab platform.
-
demand and roughness estimation in water distribution systems
Journal of Water Resources Planning and Management, 2011Co-Authors: Doosun Kang, Kevin E LanseyAbstract:To provide more accurate estimates and account for associated uncertainties, a parameter estimation methodology for water distribution systems (WDSs) that combines demand and parameter estimation processes is proposed. A two-step sequential method for dual estimation of demand and roughness coefficient is presented based on a weighted least-squares scheme using field measurements of pipe flow rates and nodal Pressure Heads under multiple demand conditions. The uncertainties in the estimated variables and resulting nodal Pressure predictions are quantified in terms of confidence limits using the first-order second moment method. The algorithm is applied to two network systems including a midsized real WDS. The two-step sequential model provides accurate and precise estimates while joint estimation provides poor estimates.