HST3D - simulation of heat and solute transport in three-dimensional ground-water flow systems
HST3D Model Categories: flow models - pathlines/capture zones, flow models - saturated zone, heat
transport, solute transport models - saturated zone, saltwater intrusion models
HST3D GUI - A Windows Preprocessor and Postprocessor for Simulation of Heat and Solute Transport in Three-Dimensional Ground-Water Flow Systems
Save Money - Work with all the models you wish to interface yourself.
Save Time Learning - Use the same modeling environment with all models.
Reuse Your Data - Data for one model can be used for all other models.
The HST3D GUI is a Graphical User Interface for HST3D version 2.0 by Ken Kipp of the U.S. Geological Survey. The HST3D GUI is a Plug-In Extension (PIE) of Argus ONE. HST3D is used for simulation of "Heat and Solute Transport in Three Dimensions." It is suitable for a wide variety of problems including salt water intrusion, density dependent flow and coupled, heat, solute and fluid flow. The HST3D GUI provides a convenient way to set up the input files for HST3D and the related program BCFLOW. Instead of preparing a long file of numbers in a precise format, you can set up your model graphically on the screen. In the illustration above, for example, the permeability of an aquifer has been interpolated from a number of known locations (not shown). For simplicity, a second aquifer below the top one has been assigned a uniform permeability that happens to be much lower than the typical permeability of the upper aquifer. The topography of the surface between the two aquifers has been specified by a series of contour lines shown in color. An Argus ONE expression has been used to compare the elevations of individual elements within a layer to the elevation of the interface between the aquifers and to assign the permeability of individual elements the permeability of the appropriate aquifer. The boundary between the aquifers is between the orange and yellow contour lines. You can see a distinct change in the color of individual grid cells at the change between aquifers. The grid cell colors reflect their permeability.
It would be impractical to create a model of this complexity by hand but with the HST3D Graphical User Interface and Argus ONE, it can be set up easily. In addition, in Argus ONE, the data defining aquifer properties and boundary conditions are independent of the grid. Thus, you can destroy the grid and create a radically different one without needing to re-enter data. Instead of tediously creating the input file for HST3D, you can instead concentrate your time and effort on making your model better.
The HST3D GUI provides extensive on-line Help in the form of a series of linked web pages. For nonspatial data, there are also flyby hints that appear when you position your mouse over an edit box or other control. These direct you to the place in the HST3D manual where the data for that control is described. The online Help also gives a complete description of the spatial data and how it is related to HST3D variables.
The HST3D GUI includes:
Registered users will be eligible to receive up to three free recompilations of HST3D per year to allow them to change the array dimensions in HST3D without needing to purchase a compiler. Additional recompilations are subject to a nominal fee. At the present time, the fee is $20.00.
To use the HST3D GUI, you must have Windows 95/98/2000/NT. You also need at least 16 MB of memory. Full installation requires approximately 7 MB of free disk space. Of this, approximately 6 MB comprises HST3D and related executable programs (HST3D: 5.4 MB, DIMEN: 340 Kb, and BCFLOW: 145 Kb.) To view the online Help for the HST3D GUI, you need a frames-capable web browser. (The more popular web browsers are frames-capable.) The memory requirements of HST3D vary depending on the size of the arrays used in the program. Registered users may have HST3D recompiled to change the memory requirements up to three times per year without charge.
HST3D, "A Computer Code for Simulation of Heat and Solute Transport in Three-Dimensional Ground-Water Flow Systems" is by Kenneth L. Kipp, Jr. of the USGS. HST3D enables you to:
The heat and solute transport program, HST3D, simulates ground-water flow and associated heat and solute transport in three dimensions. The HST3D model may be used for analysis of problems such as those related to subsurface waste injection, landfill leaching, saltwater intrusion, freshwater recharge and recovery, radioactive waste disposal, water geothermal systems, and subsurface energy storage. The three governing equations in HST3D are coupled through the interstitial pore velocity, the dependence of the fluid density on pressure, temperature, and solute-mass fraction. The solute-transport equation in HST3D is for only a single, solute species with possible linear-equilibrium sorption and linear decay. Finite-difference techniques in HST3D are used to discretize the governing equations using a point-distributed grid. The flow, heat, and solute-transport equations in HST3D are solved, in turn, after a partial Gauss-reduction scheme is used to modify them. The modified equations are more tightly coupled and have better stability for the numerical solutions.
The basic source-sink term represents wells. A complex well flow model may be used to simulate specified flow rate and pressure conditions at the land surface or within the aquifer, with or without pressure and flow-rate constraints. Boundary condition types offered in HST3D include specified value, specified flux, leakage, heat conduction, an approximate free surface, evapotranspiration, and two types of aquifer influence functions. All boundary conditions can be functions of time.
Four techniques are available in HST3D for resolution of the finite-difference matrix equations. There are two variations of a generalized conjugate gradient iterative solver, a triangular-factorization direct solver and a two-line successive over-relaxation solver.
A restart option is available in HST3D for storing intermediate results and restarting the simulation at an intermediate time with modified boundary conditions. This feature can also be used as protection against computer failure. HST3D is a descendant of the Survey Waste Injection Program (SWIP) written for the USGS under contract.
HST3D is now connected with the general Pre and Postprocessor Argus Open Numerical Environments (Argus ONE ) that permits it to work in Windows with easy database management. Data input and output may be in metric (IS) units or inch-pounds units. Input and Output may be represented as tables of dependent variables and parameters, zone contour maps, and plots of dependent variables versus time.
The equations that are solved numerically for HST3D using the finite-difference technique are:
Numerical solutions are obtained for each dependent variable: pressure, temperature and mass fraction (solute concentration). Finite-difference techniques are used for spatial and temporal discretization of the equations. The spatial discretization grid is generated and visualized on the screen. Contour maps or scarce data of the initial conditions and the parameters may be interpolated on the grid using the Argus ONE interface. A wide variety of boundary conditions on heat flow and solute transport may be simulated with HST3D.
Two related programs come with HST3D 2.0. BCFLOW is a post-processing program for determining flux within specified regions. DIMEN is used to determine the array sizes required in HST3D to run a particular model. Output of DIMEN can be used to recompile HST3D to a size capable of running the model.
One way to objectively assess the impact of existing or proposed activities on ground-water quantity and quality is through the use of ground-water flow, heat and solute transport models. HST3D allows a quantitative understanding of how the sources and sinks, the boundary conditions and the aquifer parameters interact to cause ground-water flow patterns and consequent thermal and solute concentration movement in a studied area. The magnitude of concentrations and discharges at the boundary of the studied area are of particular interest in the study of a contaminated aquifer. The degree of realism and the accuracy of a given simulation is strongly dependent on the quantity and quality of the parameter distribution, boundary conditions and source sink data.
HST3D is suitable for simulating ground-water flow and the associated solute transport in saturated, three-dimensional flow systems with variable density and viscosity. As such, the code is applicable to the study of waste injection into saline aquifers, landfill contaminant movement, sea-water intrusion in coastal regions, brine disposal, freshwater storage in saline aquifers, heat storage in aquifers, liquid-phase geothermal systems, and similar transport situations. If needed, only the ground-water flow may be solved. Also, after the computation of the ground-water flow, only the heat or the solute transport equation may be solved. Three-dimensional Cartesian or axisymmetric, cylindrical coordinate systems are available. (The GUI only supports cartesian coordinates.)
The finite-difference techniques used for spatial and temporal derivative approximations have some limitations:
1. Where longitudinal and transverse dispersivities may be small in HST3D, cell sizes will need to be small to minimize numerical dispersion or oscillations. Furthermore, if the region of solute is somewhat convoluted and three dimensional, the projection of nodal lines from regions of high nodal density will result with an excessive node number in other regions. These two factors may cause an excessive number of nodes for a given simulation, thus making the simulation prohibitively expensive because of computer storage and computation time requirements. In such cases, a simple model of the system, useful for investigating mechanisms and testing hypothesis, may be the only practical solution.
2. Another limitation of HST3D results from the so-called grid-orientation effect (Aziz and Settary, 1979, p.332). Numerical simulations of miscible displacement converge to two separate solutions as the mesh size is refined depending on whether the major velocity vectors are parallel to one of the coordinate directions or are diagonally oriented. This effect is more pronounced for conditions of little dispersion or piston-like displacement of the solute, and for conditions of small viscosity of the displacing fluid. The effect is almost absent when the two viscosities are nearly equal, or if the dispersion coefficient is large. One of the causes of the grid orientation effect appears to be the use of a seven-point difference formula for the three-dimensional flow and solute transport equations because this formula restricts transport in the diagonal directions. Use of a grid where the major velocity vectors are oriented parallel to one of the coordinate directions has been found to give more realistic results (Aziz and Settari 1979, p. 336). To completely eliminate this problem, a higher-order differencing scheme or curvilinear coordinates need to be used, but these modifications are not implemented in the present version of HST3D.
3. The boundary conditions in HST3D can be used with a tilted coordinate system. The free surface and leakage boundary conditions require that the Z-axis be oriented in the vertical direction.
4. HST3D has difficulty in representing quantitatively viscous fingering instabilities and an abrupt change of fluid density that may occur when a fluid of greater density overlies one of lesser density. For most of ground-water flow and transport modeling these physical phenomena are secondary. Viscous fingering instabilities may occur during the displacement of a resident fluid by an injected fluid with significantly less viscosity. The injected fluid forms channels or fingers through the resident fluid, as described by Saffman and Taylor (1958). When a fluid of greater density overlies one of lesser density, Raleigh-Taylor convective cells are formed. In these cells, the two fluids mix. Numerical simulation tends to predict these transport instabilities later than they occur in laboratory scale experiments. However, laboratory-scale viscous fingering and convective cell formation may be much more unstable than the corresponding field scale. Therefore, at the field scale, numerical simulation may be more valid than at a laboratory scale. Nevertheless, these limitations need to be kept in mind when simulating fluid flow with large viscosity or density contrasts.
A user guide in the form of a series of linked web pages comes with the GUI. The source code is available on request for registered users. In addition, a tutorial in Windows permits the user to easily understand the menus and commands. For more general explanations on the mathematical and physical aspects of the HST3D code and the exact definition of each parameter, the HST3D report/doc is available separately. Two example problems are described in detail with input and output files. The Help Menu and the different documents are intended to be sufficiently complete and easy to use. The user may now easily obtain successful simulations, diagnose computational problems and develop remedies.
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