DHI Wasy GmbH

Stuttgart, Germany

DHI Wasy GmbH

Stuttgart, Germany
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Koch H.,Water Resources University | Koch H.,Potsdam Institute for Climate Impact Research | Vogele S.,Jülich Research Center | Kaltofen M.,DHI Wasy GmbH | Grunewald U.,Water Resources University
Climatic Change | Year: 2012

The availability of electric power is an important prerequisite for the development or maintenance of high living standards. Global change, including socio-economic change and climate change, is a challenge for those who have to deal with the long-term management of thermoelectric power plants. Power plants have lifetimes of several decades. Their water demand changes with climate parameters in the short and medium term. In the long term, the water demand will change as old units are retired and new generating units are built. The present paper analyses the effects of global change and options for adapting to water shortages for power plants in the German capital Berlin in the short and long term. The interconnection between power plants, i. e. water demand, and water resources management, i. e. water availability, is described. Using different models, scenarios of socio-economic and climate change are analysed. One finding is that by changing the cooling system of power plants from a once-through system to a closed-circuit cooling system the vulnerability of power plants can be reduced considerably. Such modified cooling systems also are much more robust with respect to the effects of climate change and declining streamflows due to human activities in the basin under study. Notwithstanding the possible adaptations analysed for power plants in Berlin, increased economic costs are expected due to declining streamflows and higher water temperatures. © 2011 Springer Science+Business Media B.V.

Luo J.,DHI Wasy GmbH | Diersch H.-J.G.,DHI Wasy GmbH | Monninkhoff L.M.M.,Hohai University
Mine Water and the Environment | Year: 2012

The abandoned, flooded deep salt mine in Stassfurt, Germany has been extensively studied. The mine causes serious uncontrolled salt leaching and mass displacement effects underground that have led to significant regional-scale subsidence. Collapsing mined areas and further large-scale subsidence pose a potential danger to the city of Stassfurt. Comprehensive modeling of the three dimensional (3-D) variable density flow dynamics is required at both large and local scale to assess the stability of the cap rocks and the potential of subsidence due to salt leaching processes, and to better control (minimize) salt leaching. The impact of different engineering solutions and appropriate remedial strategies (e. g. pumping schemes) on the subsurface spatio-temporal distribution of salinity is of specific concern. Coupled variable density flow and transport simulations were performed using FEFLOW, a finite-element simulator, which is capable of both porous media (Darcy-type) flow computations and lower-dimensional discrete elements for laminar or turbulent flow. The geometry of the mine workings is incorporated in suitable detail and resolution in the developed 3-D model. Computational results were successfully compared with field observations and geophysical measurements. Different model scenarios provide better insight into flow and mass transport processes in the study area, which could provide significant information to quantify subsidence potential of the mine site. © 2012 Springer-Verlag.

Rivera Villarreyes C.A.,University of Potsdam | Rivera Villarreyes C.A.,DHI Wasy GmbH | Baroni G.,University of Potsdam | Oswald S.E.,University of Potsdam
European Journal of Soil Science | Year: 2014

Summary: We used inverse modelling techniques and soil moisture measured by the cosmic-ray neutron sensing (CRS) to estimate root-zone soil hydraulic properties at the field scale. A HYDRUS-1D model was developed for inverse modelling and calibrated with parameter estimation software (PEST) using a global optimizer. Integral CRS measurements recorded from a sunflower farm in Germany comprised the model input. Data were transformed to soil water storage to enable direct model calibration with a HYDRUS soil-water balance. Effective properties at the CRS scale were compared against local measurements and other inversely estimated soil properties from independent soil moisture profiles. Moreover, CRS-scale soil properties were tested on the basis of how field soil moisture (vertical distribution) and soil water storage were reproduced. This framework provided good estimates of effective soil properties at the CRS scale. Simulated soil moisture at different depths at the CRS scale agreed with field observations. Moreover, simulated soil water storage at the CRS scale compared well with calculations from point-scale profiles, despite their different support volumes. The CRS-scale soil properties estimated with the inverse model were within the range of variation of properties identified from all inverse simulations at the local scale. This study demonstrates the potential of CRS for inverse estimation of soil hydraulic properties. © 2014 British Society of Soil Science.

Bauer D.,University of Stuttgart | Heidemann W.,University of Stuttgart | Diersch H.-J.G.,DHI Wasy GmbH
Geothermics | Year: 2011

This paper presents the development and application of a three-dimensional (3D) numerical simulation model for U-tube borehole heat exchangers (BHEs). The proposed model includes the thermal capacities of the borehole components, viz., the fluid inside the tubes, as well as the grouting material, making it possible to consider the transient effects of heat and mass transports inside the borehole. In this approach, the use of simplified thermal resistance and capacity models (TRCMs) provides accurate results while substantially reducing the number of nodes and the computation time compared with fully discretized computations such as finite element (FE) models. The model is compared with a fully discretized FE model which serves as a reference. Furthermore, the model is used to evaluate thermal response test (TRT) data by the parameter estimation technique. Comparison of the model results with the results of an analytical model based on the line-source theory further establishes the advantage of the developed 3D transient model, as the test duration can be shortened and results are more accurate. © 2011 Elsevier Ltd.

Bauer D.,University of Stuttgart | Heidemann W.,University of Stuttgart | Muller-Steinhagen H.,University of Stuttgart | Diersch H.-J.G.,DHI Wasy GmbH
International Journal of Energy Research | Year: 2011

The detailed design and energy analysis of ground source heat pump systems requires the ability to predict the short-term behavior of borehole heat exchangers (BHE). The application of fully discretized models leads to extensive computation times and a substantial effort in terms of pre-processing work. On the contrary, analytical models offer simple, parameter input-based modeling and short computation times, but they usually disregard the transient effects of heat and mass transport in the borehole and hence are not suitable for the prediction of the short-time behavior. In order to combine the advantages of both types of models, the authors developed two-dimensional thermal resistance and capacity models for different types of BHE. These models take the capacity of the grouting material with one capacity per tube into account and, therefore, the range of validity is extended to shorter times. The correct consideration of all thermal resistances between the fluid in the pipes, the grout capacities and the borehole wall is important because of the significant influence on the validity of the models. With the developed models, the modeling work and the computation time can be significantly reduced compared with fully discretized computations while precise results are still achieved. The validation of the suggested models against fully discretized FEM models shows a very good agreement. Copyright © 2010 John Wiley & Sons, Ltd.

Gayer G.,Helmholtz Center Geesthacht | Leschka S.,DHI Wasy GmbH | Nohren I.,Helmholtz Center Geesthacht | Larsen O.,Nanyang Technological University | Ganther H.,Helmholtz Center Geesthacht
Natural Hazards and Earth System Science | Year: 2010

An important part within the German-Indonesian Tsunami Early Warning System (GITEWS) project was the detailed numerical investigation of the impact of tsunamis in densely populated coastal areas of Indonesia. This work, carried out by the German Research Centre Geesthacht (GKSS), in co-operation with DHI-WASY, also provides the basis for the preparation of high resolution hazard and risk maps by the German Aerospace Center (DLR). In this paper a method is described of how to prepare very detailed roughness maps for scenario computations performed with the MIKE 21 Flow Model FM in three highly resolved (∼10 m) priority regions, namely Kuta (Bali), Padang (West-Sumatra), and Cilacap (southern coast of Java). Roughness values are assigned to 43 land use classes, e.g. different types of buildings, rural and urban sub-areas, by using equivalent coefficients found in literature or by performing numerical experiments. Comparisons of simulations using differentiated roughness maps with simulations using constant values (a widely used approach) are presented and it is demonstrated that roughness takes considerable influence on run-up and inundation. Out of all simulations, the results of the worst case scenarios for each of the three priority areas are discussed. Earthquakes with magnitudes of MWCombining double low line8.5 or higher lead to considerable inundation in all study sites. A spatially distinguished consideration of roughness has been found to be necessary for detailed modelling onshore. © Author(s) 2010.

Diersch H.-J.G.,DHI Wasy GmbH | Bauer D.,University of Stuttgart | Heidemann W.,University of Stuttgart | Ruhaak W.,DHI Wasy GmbH | Schatzl P.,DHI Wasy GmbH
Computers and Geosciences | Year: 2011

Single borehole heat exchanger (BHE) and arrays of BHE are modeled by using the finite element method. The first part of the paper derives the fundamental equations for BHE systems and their finite element representations, where the thermal exchange between the borehole components is modeled via thermal transfer relations. For this purpose improved relationships for thermal resistances and capacities of BHE are introduced. Pipe-to-grout thermal transfer possesses multiple grout points for double U-shape and single U-shape BHE to attain a more accurate modeling. The numerical solution of the final 3D problems is performed via a widely non-sequential (essentially non-iterative) coupling strategy for the BHE and porous medium discretization. Four types of vertical BHE are supported: double U-shape (2U) pipe, single U-shape (1U) pipe, coaxial pipe with annular (CXA) and centred (CXC) inlet. Two computational strategies are used: (1) The analytical BHE method based on Eskilson and Claesson's (1988) solution, (2) numerical BHE method based on Al-Khoury et al.'s (2005) solution. The second part of the paper focusses on BHE meshing aspects, the validation of BHE solutions and practical applications for borehole thermal energy store systems. © 2010 Elsevier Ltd.

Diersch H.-J.G.,DHI Wasy GmbH | Bauer D.,University of Stuttgart | Heidemann W.,University of Stuttgart | Ruhaak W.,DHI Wasy GmbH | Schatzl P.,DHI Wasy GmbH
Computers and Geosciences | Year: 2011

Single borehole heat exchanger (BHE) and arrays of BHE are modeled by using the finite element method. Applying BHE in regional discretizations optimal conditions of mesh spacing around singular BHE nodes are derived. Optimal meshes have shown superior to such discretizations which are either too fine or too coarse. The numerical methods are benchmarked against analytical and numerical reference solutions. Practical application to a borehole thermal energy store (BTES) consisting of 80 BHE is given for the real-site BTES Crailsheim, Germany. The simulations are controlled by the specifically developed FEFLOW-TRNSYS coupling module. Scenarios indicate the effect of the groundwater flow regime on efficiency and reliability of the subsurface heat storage system. © 2010 Elsevier Ltd.

Borghi A.,CNRS Georesources lab | Renard P.,University of Neuchatel | Cornaton F.,DHI Wasy GmbH
Advances in Water Resources | Year: 2016

Karst aquifers are characterized by extreme heterogeneity due to the presence of karst conduits embedded in a fractured matrix having a much lower hydraulic conductivity. The resulting contrast in the physical properties of the system implies that the system reacts very rapidly to some changes in the boundary conditions and that numerical models are extremely sensitive to small modifications in properties or positions of the conduits. Furthermore, one major issue in all those models is that the location and size of the conduits is generally unknown. For all those reasons, estimating karst network geometry and their properties by solving an inverse problem is a particularly difficult problem.In this paper, two numerical experiments are described. In the first one, 18,000 flow and transport simulations have been computed and used in a systematic manner to assess statistically if one can retrieve the parameters of a model (geometry and radius of the conduits, hydraulic conductivity of the conduits) from head and tracer data. When two tracer test data sets are available, the solution of the inverse problems indicate with high certainty that there are indeed two conduits and not more. The radius of the conduits are usually well identified but not the properties of the matrix. If more conduits are present in the system, but only two tracer test data sets are available, the inverse problem is still able to identify the true solution as the most probable but it also indicates that the data are insufficient to conclude with high certainty.In the second experiment, a more complex model (including non linear flow equations in conduits) is considered. In this example, gradient-based optimization techniques are proved to be efficient for estimating the radius of the conduits and the hydraulic conductivity of the matrix in a promising and efficient manner.These results suggest that, despite the numerical difficulties, inverse methods should be used to constrain numerical models of karstic systems using flow and transport data. They also suggest that a pragmatic approach for these complex systems could be to generate a large set of karst conduit network realizations using a pseudo-genetic approach such as SKS, and for each karst realization, flow and transport parameters could be optimized using a gradient-based search such as the one implemented in PEST. © 2016 Elsevier Ltd.

Lakdawala Z.,DHI Wasy GmbH | Cornaton F.,DHI Wasy GmbH
Proceedings of IAMG 2015 - 17th Annual Conference of the International Association for Mathematical Geosciences | Year: 2015

Stochastic subsurface hydrology has been an area of intensive research over the past few decades, but there are limited software tools to analyze and model heterogeneous groundwa-Ter systems. The focus of this work is to provide an overview of some stochastic approaches to quantify uncertainty using the Monte Carlo approach. The aim is to work towards a module for uncertainty quantification in the existing FEFLOW software, a development of DHI-WASY GmbH. For the scope of this work, the Monte Carlo (MC) technology is discubed which includes generating the stochastic input (using two-point/multiple-point statistics in FEFLOW), transforming the input into the output (using FEFLOW determin-istic solvers), and analyzing the output. Each of these will be briefly discubed with practical relevance to solve for flows related to groundwater applications. A few numerical results will be presented for a complex spatially heterogeneous model for the Rhone alluvial aquifer in Switzerland.

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