PROGRAM CODE GERA

CODE FEATURES

Graphical interface

GeRa provides a unified graphical environment for carring out a full cycle of modeling: from creating a model and loading data to visualizing the results of calculations. There is an intuitive panel "Creation new model wizard" to simplify model creation and further work with it, which is designed to guide the user step by step through the process of creating a model.

Multivariant user data uploading

In the GeRa code, various types of data can be loaded for the convenience of creating a geological model. To import maps it is possible to load data in JPG, BMP, PNG and TIFF formats, or to use already built contours in MapInfo (.mif) or AutoCAD (.dxf) formats; it is also possible to load field data to set various features of the model - layer surfaces, heterogeneities, etc.

Geological model creation

To create a geological model in GeRa, a geostatistics module is used, which implements various methods for constructing layers: 

• setting the plane;
• triangulation;
• reverse distances;
• kriging;
• nearest neighbor.

Selection of variograms and its control are available.

Phisycal processes

Nowaday, the following physical processes can be simulated in the GeRa code:

• steady and unsteady groundwater flow in confined and confined-unconfined conditions;
• saturated-unsaturated groundwater flow;
• unsteady advective-dispersive-diffusion mass transport with the ability to take into account chemical interactions in the water-rock system and radioactive decay with accounting decay chains;
• density convection;
• groundwater flow and mass transport in dual porosity media (GeRa/V2);
• thermal processes: heat release during radioactive decay, heat convection (GeRa/V2);
• two-phase water-gas flow (GeRa/V2);
• surface runoff in coupling with groundwater flow (GeRa/V2).

Chemical reactions

GeRa provides the ability of calculating the transport of solutes taking into account the interactions occurring in an aqueous solution (the activity is calculated using the Davis equation), as well as the calculating sorption within the linear sorption model, a model in which the sorption coefficient functionally depends on the concentration of any component of the solution, ion exchange model and model of non-electrostatic complexation on the surface of host rock phases. The software implementation is based on using of the IPhreeqc libraries (https://www.usgs.gov/software/phreeqc-version-3).

Mesh Generators

There are two mesh generators in the GeRa code:

• triangular-prismatic mesh generator;
• hexahedral mesh generator.

The storage of grid data in the GeRa code is carried out using the INMOST software platform (http://inmost.org). This platform allows to perform parallel calculations, providing synchronization of grid data, assembly and solution of linear systems.

Examples of meshes for real objects

Discretization

For spatial discretization of the diffusion operator in the GeRa code, it is possible to use one of three numerical schemes of the finite volume method (FVM): a classical two-point scheme, a multipoint O-scheme, or a nonlinear monotonic two-point scheme. To solve the transport problems, the following numerical schemes are implemented:

• explicit convection - implicit diffusion within the scheme of splitting by physical processes;
• completely implicit nonlinear monotonic scheme FVM;
• completely implicit scheme with piecewise constant flow approximation.

Linear systems solving

Systems of linear equations arising from discretization in GeRa code are also solved using the INMOST platform. This platform allows to use both embedded software and other libraries such as PETSc (https://petsc.org). The platform also provides the ability to use massive parallel computing.

Verification and visualization

GeRa graphical interface has the ability to visualize the results of calculations, as well as check the calculation results and analyze it.

Verification of the created model can be carried out according to monitoring data, but in case if monitoring points were loaded into the model before the calculation start. The GeRa code provides the possibility of numerical verification of the model (calculation of the variance, mean absolute error and root mean square of the error (RMS) separately for each well and for all wells at once) and visual verification of the model (diagonal scatter plot of field monitoring data and calculation data, histogram of the frequency of occurrence of the difference between monitoring and calculated data, visualization of numerical values ​​for wells in the plane of the model).

Visualization of calculations can be made in the plane of the model and in cross-section (isolines of groundwater heads / pollutants halos in model layers, numerical values ​​of the model data and monitoring data ​​in the wells in the plane of the model, the magnitude of the deviation between the calculation and monitoring data ​​for the wells), and in the form of curves for the wells (dynamics of groundwater heads / specific activity of pollutants versus time).

GeRa also has a balance module that allows to display balance characteristics for groundwater flow and mass transfer both for areas, model layers and zones of heterogeneities, and for individual elements of the model - rivers, lakes, etc. Fluxes are displayed for boundary conditions (both separate advective and diffusion fluxes, and the total fluxes), saturation, total content of the components, etc.

Full cycle of NRNF modeling

It is possible to carry out a full cycle of modeling of nuclear radiation-hazardous objects (NRHF) in the GeRa code: from the pollution source (near field model) to the places of groundwater discharge (far field model) and doses calculations on the population. In the near field, it is possible to take into account the degradation of engineering safety barriers, which is possible with a recharge increasing, a decreasing of the sorption coefficients of the barriers in relation to the considered radionuclides, and an increasing of the hydraulic conductivity of the barriers. It is possible to calculate doses on the population under various scenarios of water using (external and internal exposure) with the GeRa-Aqua module. The calculation is made for six age groups.

An example of visualization of calculation results and construction of isolines of a solution