MOFAT - 有限元软件

MOFAT是有限元程序，模拟多相（水、油和气）流动和五种非惰性化学物质的运输。MOFAT模拟三种流体相系统中轻质或致密有机液体的流动。MOFAT将动态或被动气体模拟为的三项流动问题。可通过在变饱和的多孔介质中模拟水流，油水流或水 - 油 - 气流。MOFAT通过压力和饱和度超过规定公差的相位求解流动方向，实现了高度的计算效率。因此，如果NAPL不存在或存在残余饱和度，则MOFAT将局部那些流动方程。

MOFAT分析水中的对流 - 分散运输，NAPL，通过假定流体相和固相之间的局部平衡或非平衡分配来确定气相。MOFAT考虑了相间质量传递和相密度的成分依赖性。使用了对土壤毛细按压力关系的简明但的描述，其了单相、两相和三相条件之间的自然连续性。用户可以使用估算土壤性SOILPARA。MOFAT for Windows图形预处理器，网络编辑器和带有在线帮助的后处理器。

MOFAT预处理器旨在写入数据文件并存储数据用于MOFAT数值模型运行。预处理器与网格编辑器和后处理协同工作，可以为美国EPA的多相有机物流动和传输模拟器提供的图形界面。MOFAT中有四个不同的程序：MOFAT数值模型，MOFAT预处理器，网格编辑器和后处理器。彼此依赖于数据输入和输出。

MOFAT功能

• 模拟五个非惰性化学物质的多相传输

• 对三个液相系统中的轻质或稠密有机液体的流动进行建模

• 使用ASD方法求解具有瞬态行为的相的流动方程

• 将动态或被动气体模拟为的三相流问题

• 对饱和压力——渗透率关系使用三相van Genuchten模型

• 处理助焊剂类型，指定扬程，指定浓度或混合类型边界条件

• 考虑由于流体截留的油渗透性的滞后现象

• 对水流，耦合的油水流或水-油气流进行建模

MOFAT is a finite element program that simulates multiphase (water, oil and gas) flow and transport of up to five non-inert chemical species. MOFAT models flow of light or dense organic liquids in three fluid phase systems. MOFAT simulates dynamic or passive gas as a full three-phase flow problem. Model water flow only, oil-water flow, or water-oil-gas flow in variably-saturated porous media. MOFAT achieves a high degree of computational efficiency by solving flow equations only for phases that are undergoing changes in pressures and saturations above specified tolerances. Therefore, if NAPL is absent or exists at a residual saturation, MOFAT will locally eliminate those flow equations. MOFAT analyzes convective-dispersive transport in water, NAPL, and gas phases by assuming local equilibrium or nonequilibrium partitioning among the fluid and solid phases. MOFAT considers interphase mass transfer and compositional dependence of phase densities. A concise but accurate description of soil capillary pressure relations is used which assures natural continuity between single-phase, two-phase and three-phase conditions. The user can estimate soil properties using SOILPARA . MOFAT for Windows includes a graphical preprocessor, mesh editor and postprocessor with on-line help.

MOFAT for Windows includes a graphical pre-processor, Mesh Editor and post-processor with on-line help.

Simulate multiphase (water, oil and gas) flow and transport of up to five non-inert chemical species in MOFAT. Model flow of light or dense organic liquids in three fluid phase systems. Simulate dynamic or passive gas as a full three-phase flow problem. Model water flow only, oil-water flow, or water-oil-gas flow in variably-saturated porous media. MOFAT achieves a high degree of computational efficiency by solving flow equations at each node (on the finite-element mesh) only for phases that are undergoing changes in pressures and saturations above specified tolerances using a new adaptive solution domain method. Therefore, if NAPL is absent or exists at a residual saturation, MOFAT will locally eliminate those flow equations. MOFAT analyzes convective-dispersive transport in water, NAPL, and gas phases by assuming local equilibrium or nonequilibrium partitioning among the fluid and solid phases. MOFAT considers interphase mass transfer and compositional dependence of phase densities. A concise but accurate description of soil capillary pressure relations is used which assures natural continuity between single-phase, two-phase and three-phase conditions. The user can estimate soil properties using SOILPARA.

MOFAT FEATURES

-Simulate multiphase transport of up to five non-inert chemical species.

-Model flow of light or dense organic liquids in three fluid phase systems.

-Solve flow equations for phases exhibiting transient behavior using the ASD method.

-Simulate dynamic or passive gas as a full three-phase flow problem.

-Use a three-phase van Genuchten model for saturation-pressure-permeability relations.

-Handle flux type, specified head, specified concentration or mixed type boundary conditions.

-Consider hysteresis in oil permeability due to fluid entrapment.

-Model water flow only, coupled oil-water flow, or water-oil-gas flow.

MOFAT TECHNICAL INFORMATION

This section is extracted from the EPA Document EPA/600/2-91/020 May 1991:

MOFAT: A TWO-DIMENSIONAL FINITE ELEMENT PROGRAM FOR MULTIPHASE FLOW AND MULTICOMPONENT TRANSPORT

ABSTRACT

This report describes a two-dimensional finite element-model for coupled multiphase flow and multicomponent transport in planar or radially-symmetric vertical sections. Flow and transport of three fluid phases - water, nonaqueous phase liquid (NAPL) and gas - is considered by the program which also handles cases in which gas and/or NAPL phases are absent in part or all of the domain at any given time. The program will simulate flow only or coupled flow and transport. The flow module can be used to analyze two-phase flow of water and NAPL in a system with gas present but at constant pressure or explicit three-phase flow of water, NAPL and gas at variable pressure. The transport module can handle up to five components which partition among water, NAPL, gas and solid phases assuming either local equilibrium interphase mass transfer or first-order kinetically controlled mass transfer. The governing equations are solved using an efficient upstream-weighted finite element scheme. Required input for flow analyses consists of initial conditions, soil hydraulic properties, fluid properties, time integration parameters, boundary condition data and mesh geometry. Three-phase permeability-saturation-capillary pressure relations are defined by an extension of the van Genuchten model which considers effects of oil entrapment during periods of water imbibition. For transport analyses, additional input data are porous media dispersivities, initial water phase concentrations, equilibrium partition coefficients, component densities, diffusion coefficients, first-order decay coefficients, mass transfer coefficients (for nonequilibrium analyses) and boundary condition data. Time-dependent boundary conditions for the flow analysis may involve user-specified phase heads at nodes or phase fluxes along a boundary segment with zero flux as the default condition. For transport analyses, initial conditions are specified in terms of equilibrium water phase concentrations of each partitionable component. Time-dependent boundary conditions may be stipulated as equilibrium water phase concentrations in the porous medium as prescribed fluxes defined in terms of a specified concentration in the influent liquid or with zero dispersive flux specified. Program output consists of basic information on input parameters, mesh details and initial conditions plus pressure heads, saturations and velocities for each phase at every node for specified output intervals. For transport analyses, the phase concentrations at each node are output at each printout interval.

MOFAT WINDOWS INTERFACE

What is the MOFAT Pre-processor?

The MOFAT pre-processor was designed to write data files and store data for MOFAT numerical model runs. The pre-processor works in concert with the Mesh Editor and with the post-processor to make a complete graphical interface to the US EPA's Multiphase Organic Flow and Transport simulator. There are four distinct programs in MOFAT: the MOFAT numerical model, the MOFAT Pre-processor, the Mesh Editor, and the Post-processor. Each rely on one another for data input and output. For instance, the Mesh Editor is a dumb program that doesn't care whether it is working with MOFAT, or with BIOF&T, MOVER or MARS. It simply reads in a template file that lets it know what associations (for example, soil types, boundary conditions, etc.) are legal for MOFAT and what associations have been entered in the pre-processor for that mesh file. This arrangement allows for development of the Mesh Editor to include more features in the future without disturbing the main MOFAT program.

The MOFAT Pre-processor allows for entry of Control Parameters (for example, whether or not transport will be solved for in the run), Initial Conditions (initial heads of water and oil), Species Properties for up to five species, Fluid Properties, Transport Properties, Boundary Conditions, and Material Properties for up to ten soils. Many values entered in the pre-processor are used in the Mesh Editor. Values like non-uniform water heads are defined in the pre-processor, then later assigned to nodes in the Mesh Editor. Material Properties, Boundary Conditions, non-uniform oil heads, and individual node printouts are all assigned to nodes or edges in the Mesh Editor.

The MOFAT Pre-processor also has a run module for writing input data files and executing the MOFAT numerical model. It is important to understand that the pre-processor does not read MOFAT numerical model data files, it only writes them. The pre-processor and Mesh Editor use text files to save project data to disk and to open projects. After a data file for the numerical models has been written, you can change individual control parameters but these changes will not be reflected in the pre-processor.

The MOFAT Pre-processor Interface

After clicking on the MOFAT pre-processor for the first time, a setup notebook will appear on the screen. This notebook acts as a binder for all MOFAT data files, for links to the Mesh Editor and a project mesh, for writing input files and running the numerical model, and for cue cards and additional help. This notebook is available at any time by selecting Tools|Setup from the main menu or Tools|Runner. To prevent this notebook from automatically displaying every time the pre-processor is run, click off the Show Again check box on the Cue Cards page.

Note: all variable names like ITRN are in capital letters and match exactly the names used in the MOFAT FORTRAN source code.

The MOFAT pre-processor runs under Windows 3.X, Windows 95 and Windows NT. Currently all MOFAT programs are 16-bit, so there is no speed or multitasking advantage to running the programs under a 32-bit operating system. For most problems, the pre-processor will run well under 4 MB of RAM. When dealing with large finite element meshes, you will find that reading and writing files, and working with the Mesh Editor will greatly slow down under 4 MB of RAM. Also, the numerical model will not run under 4 MB of RAM for larger problems.

The MOFAT pre-processor uses a commonly-used tabbed notebook interface to allow quick editing of input files. The main program has two sets of tabs, one along the bottom which separates major sections of the interface, and, on some of the large notebook pages, tabs along the  that separate subsections to make the most use of available screen space. For example, clicking on the bottom tab "Boundary Schedules" takes you to the boundary schedule notebook. Here there is a tabbed notebook for editing type 1 and type 2 boundary schedules.

MOFAT for Windows does not have a pre-processor checklist or linear approach for a user to step through each necessary data input value. MOFAT starts up with default values selected for logic switches (for example, ITRN - solve for transport is default set to off), but data values are set to zero (for example, TH - time weighting factor). The MOFAT numerical model will not run if these data values are not input by the user. While the pre-processor will check to be sure that at least one soil type has been entered before running the numerical model, it will not check control parameter data values. While this method may lead to some misunderstanding for the beginning modeler, most who use the preprocessor more than a few times will appreciate not having dialog boxes pop up every time they don't want to enter a value for a variable.

Opening and Saving Projects in MOFAT

A MOFAT project is similar to a multi-table database. Data for the pre-processor is stored in ASCII text files as is data for the Mesh Editor and Post-processor. When a new project is created and saved to file, the pre-processor prompts you for a project name (an .mfp file extension is the default type). The pre-processor will then create sub-data files for species data and materials data.

What is the MOFAT Mesh Editor?

The Mesh Editor in MOFAT was designed to work with these numerical models to create and edit finite element meshes. The Mesh Editor allows designing irregular quadrilateral meshes in two dimensions and hexahedral meshes in three dimensions. MOFAT version 2.2 only uses 2D rectangular elements. Working with a numerical model pre-processor, the Mesh Editor provides a graphical interface for assigning properties to a mesh such as initial concentrations of contaminants, soil properties, boundary conditions, etc.