ISIS 2D Quick Start Guide - Halcrow

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ISIS 2D Quick Start Guide Principles of Working with ISIS 2D There are several phases when working with ISIS 2D models and various parts of the ISIS 2D software are used during the process. The main phases of working with the 2D models are: 1. Pre-processing of the input files for running ISIS 2D simulation; 2. Preparation of the ISIS 2D control XML file; 3. Running the ISIS 2D simulation; 4. Viewing ISIS 2D results files; ISIS Mapper can be used for pre-processing of the input files for running the ISIS 2D simulation and for viewing ISIS 2D results files; ISIS Mapper can be accessed by clicking the ISIS Mapper icon or selecting > Tools > ISIS Mapper in ISIS Network Properties window of ISIS. ISIS Mapper is a GIS tool specially designed for doing the pre & post processing of ISIS 1D, ISIS 2D and TUFLOW 2D models. Other GIS software can also be used to generate input files for ISIS 2D. There are two ways of running the calculations using ISIS 2D models: using the command prompt or the ISIS 2D Interface Tool. ISIS 2D Interface Tool can be accessed by selecting > Run > ISIS 2D in the ISIS Network Properties window. This option is described in more details in ISIS 2D Manual. The ISIS 2D Interface is a special application designed for making the creation of ISIS 2D XML control files easier for the users. Preparation of the ISIS 2D control XML file is done by using both ISIS Mapper and the ISIS 2D Interface. More details about this can be found in ISIS 2D Manual. Basic Concepts ISIS 2D is a shallow water flow model which predicts depths and velocities on a regular square grid, and can link to an ISIS 1D model representing flows in a channel. It has been designed to model flows in coastal, estuary and floodplain environments. At the core of ISIS 2D, there are two numerical schemes that are specifically developed to tackle different types of hydraulic conditions: ADI (Alternating Direction Implicit) and TVD (Total Variation Diminishing). The main differences between these two themes are listed in the Table 1 below: Modelling rapidly varying flows ADI May not represent higher Froude number flows correctly TVD Accurate representation of high Froude number flows, shocks and jumps Computation Times Short run times Longer run times Time steps Long time steps possible Shorter time steps needed for model to run Stability Mass Conservation Some instabilities/oscillations in the solution may become apparent for simulations with Froude numbers approaching or exceeding one, or too large a time step Generates acceptable mass balance errors for well set up 2D and linked 1D-2D models Generates more stable and smoother solutions Can lead to larger (but still acceptable) mass balance errors for linked 1D-2D models 3
ISIS 2D Quick Start Guide Table 1. Differences between the ADI and the TVD schemes used in ISIS 2D. In order to run an ISIS 2D model the following information is needed: 4 • A geographic model domain extent: to represent an extent of the possible flooding; • Topography (ground level data and information of the locations of defences) of the area under consideration; • Hydrological data in the form of the boundary and initial conditions: to represent the flows entering and leaving the model extent and the water levels passed to the model as well as the initial state of the system; • Roughness coefficients: to describe variation of roughness coefficients in different parts of the model (can be represented by one value for all the domain extent); • Such data as duration of a simulation period, time step, grid cell size etc: to represent various run parameters of the model; ISIS 2D uses an XML (Extensible Markup Language) control file to describe the model composition. The locations of the model input and output files and various parameters are described by an XML control file. This control file provides all the necessary information for running ISIS 2D numerical engine. As mentioned earlier, the ISIS 2D Interface Tool helps the user build 2D models and do the pre & post processing work. ISIS Mapper, a GIS tool specially designed for doing the pre & post processing of ISIS 1D, ISIS 2D and TUFLOW 2D models, is supplied together with ISIS 2D Interface Tool as part of ISIS 2D product. Setting up an ISIS 2D model effectively means completing a valid ISIS 2D XML control file (validate against the predefined XML schema) and preparing the associated data files. Files ISIS uses a range of different files to manage model data and results. The data formats that ISIS 2D uses are: XML file (.xml file): this is the format in which ISIS 2D control file is written; Comma Separated Values format (.csv file): The mass balance ISIS 2D output files, and depth, elevation, flow or velocity at user specified points in the domain are saved in this format; ESRI ASCII raster grid file (.asc file): model domain extents, topography, boundary & initial conditions, roughness coefficients can be represented by an ASCII grid. ESRI shapefile (point, polyline, and polygon) (.shp file): active computation area, boundary & initial conditions and topography, link lines are represented by shapefiles. 2D Model Results Data file (.dat file, .2dm and .sup files): ISIS 2D model results are written in such a format that enables them to be viewed, visualised and analysed by ISIS Mapper. The files with the extension .dat contain all the results of ISIS 2D simulation, the files with the extension .2dm contain the geographic information about the 2D mesh. The .sup file, which contains a list of the .2dm and .dat files associated with the model results, is provided for compatibility with other software which reads this file format. Standard text file: the boundary condition file for ISIS 1D simulation (.ied file), ISIS 2D log file are saved in this format (normally .log or as specified by the user in the ISIS 2D Control XML file) and ISIS 1D event file (.ief file). The last file contains the information regarding the parameters and input and results file for ISIS 1D simulation. Example files The "isis" folder of your machine (upon the installation of ISIS) should already contain some example files. Some of them will be used in this Chapter. The default location for your ISIS data is C:\isis\data (if ISIS is installed at a location other than the default folder, it will be xxx\xxx\isis\data where xxx stands for where ISIS is installed). The ISIS 2D related examples are placed into ISIS 2D subfolder (eg C:\isis\data\examples\ISIS 2D). Some of these files are used when describing various operations in this Quick Start Guide.
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ISIS 2D Quick Start Guide - Halcrow

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