Set HST3D control parameters using an easy and user-friendly dialog box.

Assign physical properties using GIS and intuitive drawing tools.

Automatically mesh the problem domain and run HST3D.

Visualize HST3D results using 3D visualization tools on top of the problem domain.

HST3D-ANE includes the Argus ONE Grids Module. This Argus ONE Module can also be used with your other models as well.

HST3D enables you to:

- Assess well performance including the type of well bore.
- Analyze pressure flow, heat and solute transport in the saturated zone with variable or constant density and viscosity.
- Model ground-water flow separately.
- Model heat or solute transport coupled with ground-water flow.
- Predict chemical species transport including landfill contaminant movement.
- Predict waste injection into saline aquifers.
- Analyze freshwater storage in saline aquifers and saltwater intrusion in coastal aquifers.
- Analyze liquid-phase geothermal systems and heat storage in aquifers.
- Model brine disposal and movement of connate water.
- Model contaminant (single species) transport in complex 3D aquifer systems.
- Model hydraulic barriers, liners and water-quality protection systems.

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 include specified value, specified flux, leakage, heat conduction, an approximate free surface, and two types of aquifer-influence functions. All boundary conditions can be functions of time.

Two techniques are available for resolution of the finite-difference matrix equations. One technique is a direct elimination solver, using two-line successive over-relaxation.

A restart option is available for storing intermediate results and restarting the simulation at an intermediate time with modified boundary conditions. This feature also can 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-ANE is now connected with the general Pre and Postprocessor Argus Numerical Environments (ANE) that permits it to work under 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.

This new interface allows the user to automatically input all data, run the correct size of HST3D and visualize the results all within one easy-to-use graphical package.

A Help Menu under Windows is also available with the new interface.

HST3D-ANE reformats the classic output file created by HST3D in a format readable by the graphics packages ANE and SURFER.

1. The saturated ground-water flow equation written in the pressure dependent variable. This equation is a combination of the conservation of total-fluid mass and Darcy's Law for porous media.

2. The heat transport equation from the conservation of enthalpy for the fluid and porous medium

. 3. The solute transport equation from the conservation of mass for a single solute species that may decay and also adsorb onto the porous medium. These three equations are coupled through the dependence of advective transport on the interstitial fluid velocity field, the dependence of fluid viscosity on temperature and solute concentration, and the dependence of fluid density on pressure, temperature and solute concentration.

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. Contours maps or scarce data of the initial conditions and the parameters may be interpolated on the grid using the ANE interface. A wide variety of boundary conditions on heat-flow and solute transport may be simulated with HST3D.

HST3D has been compiled using the Lahey-EM32 Compiler. This allows much larger executables than the PC version of HST3D. Because of the 32-bit word size used, execution times are up to three times faster than code generated with other compilers. HST3D-ANE comes with three executables requiring 4, 8 and 16 MB RAM. These files allow the modeling of 2,500, 7,000 and 14,000 nodes respectively.

In addition, specified heat and solute flux boundary conditions are available.

Leakage, aquifer-influence function and river leakage boundary conditions are available.

Porous-media thermal properties, dispersivity and compressibility may have spatial variation defined by zones.

A point-distributed, finite-difference grid is used, rather than a cell or block-centered grid. It allows a better truncation error and an easy incorporation of boundary conditions.

The heat-conduction boundary condition is generalized to apply to any cell face.

Global flow, heat and solute balance calculations are performed including flux calculations through specified pressure, temperature and mass fraction boundaries.

A robust algorithm for the computation of the optimum over-relaxation factor for the two-line, successive over-relaxation, matrix solution method is employed with a convergence criterion that includes the matrix spectral radius estimate.

All arrays with lengths depending on the size of the problem are in two variably-partitioned arrays, integer and real, to facilitate double precision arithmetic.

Arrays required for thermal or solute calculations exclusively are eliminated if only one of these transported quantities is being simulated which results in a considerable decrease in computer storage.

Arrays used for a specific type of boundary condition or source sink condition are dimensioned automatically to the length required.

The allocation of space for the direct equation solver is explicitly determined during array-space allocation rather than estimated.

A system of logical variables presented as questions are used to select the different options and control program execution.

The input file is a free-format ASCII file generated by the Windows interface. The input file may be changed from the DOS prompt or read by the HST3D-ANE interface. When the input file is not completed, the read command distributes the existing values of the incomplete input file at their place.

A read-echo file may be written. It assists the user in locating errors in the data-input file. A complete visualization of the zones is available.

Although the internal calculations of the program are performed in metric units, the input and output can be chosen to be in inch-pound units.

Error tests are included to locate mistakes in data input.

Error messages are printed explicitly rather than as code numbers.

The solute concentration can be chosen to be the mass fraction or a scaled mass fraction that ranges from 0 to 1.

Map contours of any output or input data may be created directly on the screen.

Initial pressure conditions can be specified to be other than hydrostatic. For example, an initial water-table configuration can be used.

Precipitation and replenishment can be specified using the distributed flux-boundary conditions.

The conductive heat loss to overburden and underburden is a general heat transfer calculation, applicable to any cell face in the region.

The well-riser calculation has been formulated to solve the total energy and momentum balance equations simultaneously using the Bulirsh-Stoer algorithms for integration of the ordinary differential equations.

The well bore equations are implicitly coupled to the system equations for cases of cylindrical geometry.

The well-datum pressure and the well flow rate calculations may be performed explicitly or iteratively in conjunction with the solution of the flow equation.

The full nine components or an approximate three-component dispersion coefficient tensor may be used for cross-dispersive flux calculations.

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.

The finite-difference techniques used for spatial and temporal derivative approximations have some limitations:

- 1. Where longitudinal and transverse dispersivities may be small, 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 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 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 groundwater 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 mixed. 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.

The HST3D-ANE package includes:

- A DLL Interface to Argus ONE (Grid Option).
- Two executables for running on PCs with 8 or 16 MB RAM.
- Hard-copy documentation and tutorial examples.
- Technical support by hydrogeologists and software developers.
- Four examples of simulation of flow, heat and chemical transport in an aquifer with pumping and injection wells.

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