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2. A series of process-oriented panels contained within the STAR GUIde window. These represent an additional GUI facility, suitable for building STAR-CD models from scratch. An outline description is given in the section entitled“The STAR GUIde Environment” on page 2-38. Information on how to use this environment is provided by an on-line Help system accessed from within the STAR GUIde window.
Note, however, that:
• In the present release, a number of pro-STAR facilities are not accessible via either of the GUI systems. Where this is the case, the discussion is in terms of commands rather than GUI operations.
• For the convenience of users who prefer to work with commands, the description of every GUI panel and dialog box also includes a list of commands that have equivalent functionality. A summary of all pro-STAR commands is given inAppendix B of the Commands volume. A summary of pro-STAR’s conventions regarding command syntax can be found in this volume,Appendix A. The same information is also available on line by choosing Help > pro-STAR Help from the menu bar in the main pro-STAR window and then selecting item PROGRAM (for command syntax) or COMLIST (for command summary) in the scroll list at the bottom of the Help dialog box.
• Details of all available commands and specific aspects of the command-driven mode of operation are discussed in the Commands volume.
Whichever operating mode is chosen, the same principles of use apply, namely:
• A model is constructed or examined with the aid of numerous functions or
‘tools’, each of them represented by a menu-item choice, a special dialog box, a STAR GUIde panel or a command.
• Tools are selected as necessary, in a sequence that is sensible for modelling purposes. The recommended sequence is described inChapter 1, “The Basic Modelling Process” and is further elaborated in the Tutorials volume.
• A tool always provides instant feedback so the user can tell immediately if it was used properly.
• Users can greatly influence the speed with which certain operations are performed by intelligent use of the available options.
Running a STAR-CD Analysis
A STAR-CD analysis may be performed in one of the following two ways:
• By typing a series of script names in a shell or command prompt, each designed to help you build a CFD model, obtain a solution and then display the analysis results. This is the original method of working with STAR-CD and, for reasonably experienced users, may be the quickest way of getting results.
• By employing a new utility, STAR-Launch, as an aid to navigating through the various STAR-CD functions. This method should be particularly beneficial to novice users.
Running a STAR-CD Analysis
Using the script-based procedure
To perform the analysis using scripts, the procedure described below should be followed in the order indicated:
Step 1
Set up an appropriate environment for your STAR-CD system. The desired pro-STAR setup is defined by a number of environment variables such as:
STARUSR — path to the location of files PRODEFS (for command
abbreviations) and PROINIT (for pro-STAR initialisation) — see Chapter 16, “Set-up Files”
MACRO_LOCAL and MACRO_GLOBAL — paths to the local and global macro locations (seeChapter 16, “Macros”)
PANEL_LOCAL and PANEL_GLOBAL — paths to the local and global
user-defined panel locations (seeChapter 16, “Panel definition files”)
TMPDIR — path to the location of pro-STAR’s temporary (scratch) files Further instructions on how to set the STAR-CD environment variables are given in the Installation and Systems Guide, supplied with the STAR-CD installation CD-ROM. Note that these settings can usually be made once and for all, at the time when STAR-CD is first installed on your computer.
Step 2
Create a separate subdirectory for each case to be analysed and give it a descriptive name. This helps to organise the various files created during a run and makes it much easier to check or repeat previous work.
Step 3
Move to the appropriate subdirectory and start a pre-processing (model building) session by typing:
prostar
The system will respond by prompting you to define the pro-STAR variant you wish to use
Please enter the required graphics driver Available drivers are:
x, xm, glm, mesa [xm]
where the options refer to the various types of graphics libraries commonly used for graphical displays in workstations or X-terminals, i.e.
x — X-windows
xm — X-windows using the Motif interface for pro-STAR’s GUI functions
glm — Motif interface plus the standard OpenGL libraries for pro-STAR’s GUI functions
mesa — As above but using the Mesa OpenGL library (this option is not available in Windows ports)
Running a STAR-CD Analysis
The precise list of options displayed by the prompt depends on how the pro-STAR environment was originally set up on your particular machine. Type in a response that is appropriate to the workstation or terminal you are using.
Note that pro-STAR automatically searches for the highest depth pseudo colour, direct colour or true colour visual that exists for your screen and uses it. This may be overridden by specifying option -c when starting up pro-STAR, as shown below:
prostar -c
This is an 8-bit pseudo colour setting with shared colour map. The setting causes no screen flashing but requires sufficient available colours to work.
Once the desired pro-STAR variant has been chosen, an introductory panel opens up leading you into STAR-CD’s model-building environment, as discussed in the section on“pro-STAR Initialisation”. From that point on, you may provide input for setting up your model according to the descriptions given in the remaining chapters of this manual.
Step 4
When you have finished setting up your STAR-CD model, it is advisable to check the files created so far in your working directory. These should include:
• File .mdl, containing all user-supplied information about the model
• File .ccm, containing a full description of the model geometry. The
STAR-CD solver operates only in SI units and all dimensions must therefore be defined in metres. However, it is possible to scale the mesh dimensions by a scaling factor if non-SI units were used during mesh generation.
• File .prob, containing problem data, such as material properties, boundary conditions, control parameters, etc.
• File .echo, containing a log (echo) of all instructions issued to pro-STAR during the session
Depending on the nature of your problem (e.g. whether it requires a special modelling facility such as Lagrangian multi-phase) additional files may be created.
These are discussed fully in individual chapters of this volume dealing with such topics. A detailed description of all commonly used data files is given inChapter 17, “Commonly used files”.
Step 5
If user-defined subroutines are not required, go toStep 6.
Otherwise, create a subdirectory called ufile and place your subroutine files in it. The most convenient way of doing this is to create both the subdirectory and the files from within the pro-STAR session (seeChapter 14, “Subroutine Usage”).
Note that these files contain default (dummy) code to start with and you should edit them as necessary to insert your own code.
Step 6
Based on the geometrical and physical data of the model just created, you are now in a position to run STAR. This may be done in one of the following ways:
1. Via STAR-GUIde’s“Run Analysis Interactively” panel. Examples of using this panel are provided in the Tutorials volume. This way, the STAR
Running a STAR-CD Analysis
executable will be run automatically and the analysis results (in terms of solution residuals) will be displayed on a separate window;see “The StarWatch Utility” on page 17-15 for more details.
2. By exiting from pro-STAR and then running STAR from your session’s shell or command prompt. For a large number of cases, it will be sufficient to type one command. For a single-precision run, type:
star
whereas for a double-precision run, type:
star -dp
Please note that it is not necessary to provide the case name of the model you are running. However, for better bookkeeping, it is still important to keep every case in its own directory.
In most cases, and based on the model characteristics specified in
pro-STAR, STAR automatically recognises the default run-time requirements and proceeds with the CCM analysis without further user input. Some cases, however, require the specification of additional options related to both run-time resources and/or behaviour. Briefly, the user can control the operational behaviour of STAR in one of the following areas:
• Job precision (single or double precision)
• Job control (to abort, kill or restart a job)
• Environment (to export environment variables)
• User coding (to control the compilation and/or linking of user-supplied code)
• Parallel setup (pertaining to domain decomposition variations, data distribution and parallel communication libraries)
• Resource allocation (to choose which machines to use) A full list of such options can be obtained by typing:
star -h or
star -help
The listing will also contain a short description of each option’s purpose. A more complete description can be found inAppendix F of this manual.
Please note that, in general, one needs to specify the machine (node)
resources for running STAR and this input is automatically used to determine the type of run required. The following examples illustrate this point:
star Runs sequentially on the local node
star origin Runs sequentially on a host called origin star 4 Runs in parallel with 4 processes on the local node
Running a STAR-CD Analysis
star origin,16 Runs in parallel with 16 processes on a host called origin
star cheese,2 pickle,2 curry,2 rice,2
Runs in parallel on a cluster of 4 machines with 2 processes each
Please note that, for parallel cases, the computational domain decomposition is automatically handled by the star front-end script. The output files generated during the course of the run will be merged and placed in the case’s directory. There is then no visible difference between running in sequential and running in parallel.
Extra options exist to cater for special situations which cannot be detected automatically. Please refer toAppendix F for a list of such options, their syntax and their intended purpose.
Step 7
Once the run starts, iteration or time-marching continues until one of the following conditions is met:
• All the iterations or time steps specified for the current run have been completed.
• The normalised residual sum drops below a specified value (steady-state runs only).
• The solution starts to diverge. This occurs when a residual anywhere inside the solution domain reaches a very high value or a numeric overflow
condition. Divergence is automatically detected by STAR, which then stops the calculations and writes a file with extension .div. This is identical in format and content to a normal solution data (.ccm) file and thus enables you to inspect the residuals and identify the mesh location(s) where numerical instability has occurred.
Check the condition under which your run has terminated. The parameters involved in controlling the STAR-CD simulation are set in pro-STAR using the facilities provided by the“Analysis Controls” folder in STAR GUIde. Additional
information, such as printout of input data, boundary conditions, residual histories of the inner iterative loops, etc. can also be generated, as described inChapter 15.
Step 8
At the start of the analysis, STAR will read the following files:
• case.ccm — geometry data (plus solution data for restart runs)
• case.prob — problem data
and, optionally, one or more problem-dependent files such as
• case.vfs — view factors for radiation problems
• case.evn — transient event data
• case.drp — droplet data
On completion of the run, file case.ccm will contain the current analysis results in a form suitable for post-processing or for starting another STAR run. A number of additional files will also be present in your working directory, including:
Running a STAR-CD Analysis
• case.run— summary of input data plus numerical statistics and (optional) printout of solution variables
• case.info — STAR warning messages and (optional) additional numerical statistics
• case.rsi— Solution residuals, in a form that can be displayed graphically.
The above is the minimum number of output files created by a STAR run and you should confirm that they are all present. Additional files may appear depending on the nature of the problem. Such cases are discussed and explained individually in the relevant chapters of this volume. A description of all commonly used output files appears inChapter 17, “Commonly used files”.
Note that, at the beginning of every restart run, all current results files (such as the ones listed above) are automatically saved in a local sub-directory called RESULTS.xxx, where xxx stands for the run number. These sub-directories thus contain results obtained at the end of each successive run and are available for future inspection, or as a backup in case the restart run’s files are corrupted. If the case is subsequently run from initial conditions, the results of the last run performed are stored in sub-directory RESULTS.000 and all other RESULTS directories deleted.
The process then repeats itself with the creation of a new RESULTS directory for each new restart.
Step 9
You should now check the results of the analysis by looking at the run history (.run) file (seeChapter 15 for more information on its contents). The additional information (.info) file should also be examined for any signs of numerical problems. These are normally translated into warning messages. Both these files may be inspected via a suitable text editor or via panel“Run History of a Previous Analysis” in STAR-GUIde.
Satisfactory completion of steady-state STAR runs can usually be judged by observing the following quantities:
• The residual history printed during the run. The sum of the normalised absolute residuals should diminish steadily.
• The monitoring values of the dependent variables at a critical location within the solution domain. These should stabilise to the converged solution.
In transient calculations, completion is defined in terms of the elapsed (simulation) time or establishment of a steady state. In the latter case, information on the global change and monitoring values can be used in the same way as for a steady state analysis.
It is important that checks are made regularly during the initial stages of the analysis to monitor the solution progress. If divergence occurs, the run should be terminated and appropriate adjustments made to the relevant control parameters such as under-relaxation factors. Neglecting this can result in costly and
unproductive runs. Note, however, that increases in residuals and oscillations in the computed variables during the early stages of a run are not uncommon and should disappear after a few iterations. The run should therefore be given sufficient time to stabilise before any judgement is made on its progress.
Step 10
Continue with an evaluation of the simulation results (post-processing) using the
Running a STAR-CD Analysis
relevant facilities in STAR-GUIde. If you have previously exited from pro-STAR and run STAR separately (seeStep 6 above), continue by typing
prostar
to re-enter pro-STAR. Reply as before to the initial prompt Please enter the required graphics driver
Available drivers are:
x, xm, glm, mesa [xm]
and then supply the case name and other input, as described inStep 3.
Using STAR-Launch
STAR-Launch is a graphical interface that provides access to most of the CD-adapco modelling tools, including pro-STAR, several es-tools and the STAR solver.
Using STAR-Launch eliminates the need to enter multiple script names manually, as described in the previous section, and also ensures settings can be saved between sessions and between cases. STAR-Launch is intended to be used with only one case at a time. There is, however, no limit on the number of STAR-Launch windows that can be active simultaneously.
Activating STAR-Launch On Unix/Linux
Either double-click the appropriate icon on your desktop (for systems which support this), or else type
starlaunch &
in an appropriate X-terminal window. This will display the STAR-Launch main window shown below:
On Windows
Double-click the appropriate icon on your desktop.
Window layout
The key parts of the STAR-Launch main window are highlighted below. The
Running a STAR-CD Analysis
Shortcut Buttons provide quick access to the three main functions of STAR-Launch, namely:
• Setting the working directory
• Launching a pre-/post-processing tool
• Running the STAR solver
These functions are also accessible through the Main Menubar running along the top of the window. The current working directory is displayed to the right of the Shortcut Buttons. This is the directory that will be used when launching a pre-/post-processing tool or running the STAR solver.
Setting the working directory
Choose File > Set Working Directory or click the first shortcut button on the main window. This will display a directory browser as follows:
Main Menubar
Shortcut Buttons
Current Working Directory
Workspace for Process Output
Run STAR Interactively Launch Pre-Post Tool Set Working Directory
Running a STAR-CD Analysis
Navigate to the desired directory and click OK. Note that a path can be entered manually in the Look In entry box at the top of the browser window. The directory tree will be updated to reflect any valid path entered here.
The path that will be set on clicking OK is shown along the base of the browser window.
Starting a pre-/post-processing tool
To start a pro-STAR session, or an equivalent pre-/post-processing tool, select the appropriate entry in the Pre-Post menu, or click the second shortcut button on the main window. The tool that will be started from this button is set using the Pre-Post tab of the Preferences dialog. Only tools available in the current installation will be listed in the Pre-Post menu.
STAR-Launch will open a new Process Output window as shown below, which will contain any text generated by the Pre-/Post-processing tool as it starts up.
The STAR-Launch window can be resized as necessary to display more of the text appearing in the Process Output window.
Only one pre-/post-processing tool can be running at any one time. If an attempt is made to start another one, a prompt will appear asking if the existing tool should
Running a STAR-CD Analysis
be closed. Choosing Yes will kill the existing process, which could result in loss of any unsaved data.
When a process is active, the ball appearing in the Process Output window tab will be shaded red. This will change to black when the process is finished.
Running STAR interactively
Selecting Solver > Run Star Interactively, or clicking the third shortcut button, will display the Run Star Interactively dialog shown below. The dialog provides several options for running the STAR solver; detailed information on these options can be found in the STAR-Launch On-line Help, accessed from Help > Online Manual. When all settings have been made, the solver is started by clicking Run.
STAR output will appear in a new Process Output window, similar to the one
STAR output will appear in a new Process Output window, similar to the one