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  • 1
  • 2
    Language: English
    In: Journal of Hydrology, January 2016, Vol.532, pp.90-101
    Description: Ground water flow systems of shallow sedimentary basins are studied in general by analyzing the fluid dynamics at the real world example of the Thuringian Basin. The impact of the permeability distribution and density differences on the flow velocity pattern, the salt concentration, and the temperature distribution is quantified by means of transient coupled simulations of fluid flow, heat, and mass transport processes. Simulations are performed with different permeabilities in the sedimentary layering and heterogeneous permeability distributions as well as with a non-constant fluid density. Three characteristic numbers are useful to describe the effects of permeability on the development of flow systems and subsurface transport: the relation of permeability between aquiclude and aquifer, the variance, and the correlation length of the log-normal permeability distribution. Density dependent flow due to temperature or concentration gradients is of minor importance for the distribution of the flow systems, but can lead to increased mixing dissolution of salt. Thermal convection is in general not present. The dominant driver of groundwater flow is the topography in combination with the permeability distribution. The results obtained for the Thuringian Basin give general insights into the dynamics of a small sedimentary basin due to the representative character of the basin structure as well as the transferability of the settings to other small sedimentary basins.
    Keywords: Subsurface Flow and Transport ; Fluid Dynamics in Sedimentary Basins ; Heterogeneity in Permeability ; Density Dependent Flow ; Thuringian Basin ; Opengeosys ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 3
    Language: English
    In: Computers and Geosciences, 2010, Vol.36(10), pp.1268-1275
    Description: Characterization of the earth's subsurface involves the construction of 3D models from sparse data and so leads to simulation results that involve some degree of uncertainty. This uncertainty is often neglected in the subsequent visualization, due to the fact that no established methods or available software exist. We describe a visualization method to render scalar fields with a probability density function at each data point. We render these data as isosurfaces and make use of a colour scheme, which intuitively gives the viewer an idea of which parts of the surface are more reliable than others. We further show how to extract an envelope that indicates within which volume the isosurface will lie with a certain confidence, and augment the isosurfaces with additional geometry in order to show this information. The resulting visualization is easy and intuitive to understand and is suitable for rendering multiple distinguishable isosurfaces at a time. It can moreover be easily used together with other visualized objects, such as the geological context. Finally we show how we have integrated this into a visualization pipeline that is based on the Visualization Toolkit (VTK) and the open source scenegraph OpenSG, allowing us to render the results on a desktop and in different kinds of virtual environments.
    Keywords: Visualization ; Visualisation ; Uncertainty ; Scalar Fields ; Monte Carlo Simulation ; Geology
    ISSN: 0098-3004
    E-ISSN: 1873-7803
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  • 4
    Language: English
    In: Tectonophysics, 15 March 2017, Vol.699, pp.42-60
    Description: The purpose of this study is to use one complex geological 3D model for numerical simulations of various physical processes in process-specific simulation software. To do this, the 3D model has to be discretized according to different cell types, depending on the requirements of the simulation method. We used a salt structure with a diapir and its deformed host rock to produce two 3D models describing the boundary surfaces of the structure: one very simplified model consisting of cuboid surfaces and a realistic model consisting of irregular boundary surfaces. We provide a workflow for how to generate hexahedral, tetrahedral and spherical volume representations of these two geometries. We utilized the volume representations to simulate temperature, displacement and transient electromagnetic fields. We can show that the simulation results closely reflect the input geometry and that it is worth the effort to produce geometric models that are as realistic as possible. Additionally, we provide a workflow for simultaneous visualization and analysis of the simulation results. Scientific visualization is an important tool for deriving knowledge from complex investigations.
    Keywords: Geological 3d Modeling ; Structured Grid ; Tetrahedral Mesh ; Distinct Elements ; Electromagnetic Monitoring ; Displacement and Thermal Fields ; Salt Diapir ; Geology
    ISSN: 0040-1951
    E-ISSN: 1879-3266
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  • 5
    Language: English
    In: Computers and Geosciences, June 2015, Vol.79, pp.105-117
    Description: Subsurface processing numerical simulations require accurate discretization of the modeling domain such that the geological units are represented correctly. Unstructured tetrahedral grids are particularly flexible in adapting to the shape of geo-bodies and are used in many finite element codes. In order to generate a tetrahedral mesh on a 3D geological model, the tetrahedrons have to belong completely to one geological unit and have to describe geological boundaries by connected facets of tetrahedrons. This is especially complicated at the contact points between several units and for irregular sharp-shaped bodies, especially in case of faulted zones. This study develops, tests and validates three workflows to generate a good tetrahedral mesh from a geological basis model. The tessellation of the model needs (i) to be of good quality to guarantee a stable calculation, (ii) to include certain nodes to apply boundary conditions for the numerical solution, and (iii) support local mesh refinement. As a test case we use the simulation of a transient electromagnetic measurement above a salt diapir. We can show that the suggested workflows lead to a tessellation of the structure on which the simulation can be run robustly. All workflows show advantages and disadvantages with respect to the workload, the control the user has over the resulting mesh and the skills in software handling that are required.
    Keywords: Unstructured Tetrahedral Mesh ; Finite Element ; Geomodeler ; Electromagnetics ; Geology
    ISSN: 0098-3004
    E-ISSN: 1873-7803
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  • 6
    Language: English
    In: Computers and Geosciences, January 2016, Vol.86, pp.83-91
    Description: 3D geological underground models are often presented by vector data, such as triangulated networks representing boundaries of geological bodies and geological structures. Since models are to be used for numerical simulations based on the finite difference method, they have to be converted into a representation discretizing the full volume of the model into hexahedral cells. Often the simulations require a high grid resolution and are done using parallel computing. The storage of such a high-resolution raster model would require a large amount of storage space and it is difficult to create such a model using the standard geomodelling packages. Since the raster representation is only required for the calculation, but not for the geometry description, we present an algorithm and concept for rasterizing geological models on the fly for the use in finite difference codes that are parallelized by domain decomposition. As a proof of concept we implemented a rasterizer library and integrated it into seismic simulation software that is run as parallel code on a UNIX cluster using the Message Passing Interface. We can thus run the simulation with realistic and complicated surface-based geological models that are created using 3D geomodelling software, instead of using a simplified representation of the geological subsurface using mathematical functions or geometric primitives. We tested this set-up using an example model that we provide along with the implemented library.
    Keywords: Rasterization ; Voxelization ; Scan Conversion ; Seismic ; Finite Difference Simulation ; Parallel Computation ; Geology
    ISSN: 0098-3004
    E-ISSN: 1873-7803
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  • 7
    Language: English
    In: Environmental Earth Sciences, 2015, Vol.73(5), pp.2269-2285
    Description: In past decades, high performance computing has became a valuable tool in many fields of environmental science and technology to utilize computational power for better characterization of the complexity of environmental systems as well as predicting their evolution in time. In this work, a parallel computing technique is presented for the numerical simulation of two-phase flow processes in porous media. The Galerkin finite element method (FEM) is used to solve the initial boundary value problem arising from the underlying mathematical model. The PETSc package is utilized for parallelization of the computational task in both the global assembly of the system of linear equations and the linear solver. In order to parallelize the global assembly of the linear equation system, the overlapping domain decomposition method is used. The preset parallel FEM approach is realized within the framework of OpenGeoSys, an open source C++ finite element code for numerical simulation of thermal, hydraulic, mechanical and chemical processes in fractured porous media. The computational efficiency of the approach has been tested with three examples of increasing complexity, the five spot benchmark, dense non-aquaeous phase liquid infiltration into a inhomogeneous porous medium and a real-world application to the $$\mathrm {CO}_2$$ CO 2 storage research site: Ketzin, in Germany.
    Keywords: Parallel computing ; Two-phase flow ; Porous medium ; Finite element method ; OpenGeoSys ; PETSc
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 8
    Language: English
    In: Environmental Earth Sciences, 2014, Vol.72(10), pp.3881-3899
    Description: Scientific visualization is an integral part of the modeling workflow, enabling researchers to understand complex or large data sets and simulation results. A high-resolution stereoscopic virtual reality (VR) environment further enhances the possibilities of visualization. Such an environment also allows collaboration in work groups including people of different backgrounds and to present results of research projects to stakeholders or the public. The requirements for the computing equipment driving the VR environment demand specialized software applications which can be run in a parallel fashion on a set of interconnected machines. Another challenge is to devise a useful data workflow from source data sets onto the display system. Therefore, we develop software applications like the OpenGeoSys Data Explorer, custom data conversion tools for established visualization packages such as ParaView and Visualization Toolkit as well as presentation and interaction techniques for 3D applications like Unity. We demonstrate our workflow by presenting visualization results for case studies from a broad range of applications. An outlook on how visualization techniques can be deeply integrated into the simulation process is given and future technical improvements such as a simplified hardware setup are outlined.
    Keywords: Virtual reality ; Visualization ; Computer graphics ; Data exploration ; Hydrological processes ; Geotechnics ; Seismic data ; OpenGeoSys ; VISLAB
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 9
    Language: English
    In: Computers and Geosciences, 2006, Vol.32(1), pp.73-84
    Description: Volume rendering methods enable the user to explore interactively scalar data on regularly spaced three-dimensional grids. This article discusses how to use this method to explore and analyse three-dimensional tensor fields. The proposed visualization makes use of the programmability of modern graphics hardware and of “Line Integral Convolution”, a texture-based technique for the visualization of vector fields. While an example from geomechanics is used for presentation purposes, the rendering methods introduced are generic and would suit other application areas that involve volumetric data with several attributes equally well.
    Keywords: 3d Visualization ; Volume Rendering ; Tensor Fields ; Programmable Graphics Hardware ; Line Integral Convolution ; Geomechanics ; Geology
    ISSN: 0098-3004
    E-ISSN: 1873-7803
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  • 10
    Language: English
    In: Energy Procedia, 2013, Vol.40, pp.418-427
    Description: The available static geological model of the Stuttgart Formation at the Ketzin pilot site was revised based on the re- interpretation of the available 3D seismic data. Using this model three independent modelling groups initiated an intercomparison study using the standard industrial (ECLIPSE 100) and scientific dynamic flow simulations codes (TOUGH2-MP/ECO2N, DuMu and OpenGeoSys) to employ their strategies for matching of downhole pressure and CO arrival times. The current results demonstrate that the introduction of distinct near- and far-well areas with different permeability tensors is required to achieve a reasonable match with the data observed at the Ketzin pilot site.
    Keywords: Co2 Storage ; Numerical Modelling ; Ketzin Pilot Site ; Tough2 ; Eclipse ; Dumux ; Opengeosys ; Engineering ; Economics
    ISSN: 1876-6102
    E-ISSN: 1876-6102
    Source: ScienceDirect Journals (Elsevier)
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