# yao

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## Posts posted by yao

1. ### How does AcuSolve compute the residual ratios and solution ratios that are used to check for convergence?

The residual ratios used by AcuSolve are a non-dimensional measure of how "out-of-balance" the governing equations are. The residual ratios are recomputed at each timestep to give an indication of how well the solution is converging.

The solution ratio that is computed by AcuSolve represents the ratio of the change in the solution between timesteps to the solution at the previous timestep. This value indicates the level of unsteadiness present in the solution.

Note that the solution ratios and residual ratios are computed using the contribution of each node in the model. The single value is obtained by taking the appropriate norm of the contribution from each node. The details of this procedure are described in the attached document.

2. ### What differencing scheme does AcuSolve use and how can I change it?

AcuSolve uses the Finite Element Method to discretize the governing equations. By default, AcuSolve uses linear shape functions and Gaussian quadrature to perform the necessary integrations. This results in a numerical method that is second order accurate in space. Although there is no direct comparison to the common diferencing schemes found when using the finite volume method, this approach most resembles central differencing with a small amount of upwinding blended locally when necessary for stability. There is no way to reduce the spatial accuracy of AcuSolve below second order, however, quadratic tetrahedra elements are supported to increase the spatial accuracy above second order.

3. ### Recovering data from corrupted AcuConsole database

If User's are unable to open a database or if it gives an error like "Unable to create path Marker" then we can say that the database is corrupted. In such cases the data from this corrupted database can be extracted by following the below steps,

1. Install HDFview on the machine (http://www.hdfgroup.org/hdf-java-html/hdfview/)
2. Open HDFview GUI
3. Load the database by clicking on File > Open in the menu bar and navigating to the database location. Select the database and click Open
4. All the data in the database will be displayed in hierarchical format
5. Click on first item in the tree, press Shift and select the last item. All the items in the tree will be selected
6. Right click and select Copy
7. Click on File > New > HDF5
8. Provide a filename (eg: test.acs) and save the database
9. Scroll down to the bottom to see the new database created (test.acs.h5)
10. Right-click on the new database and select Paste. Click Yes to copy the selected objects
11. You can see all the objects under the new database
12. Save the database. File > Save, then close the HDFview GUI by clicking on File > Exit
13. Rename the new database (eg: test.acs.h5 to test.acs)
14. Load the new database into AcuConsole

4. ### How do I get rid of the following error that appears when I launch AcuConsole on my Linux system?

python: error while loading shared libraries: libstdc++.so.5: cannot open shared object file: No such file or directory

AcuConsole requires the standard C++ libraries, version 5 to be installed on the system. These libraries can be downloaded from the various rpm repositories on the web.

5. ### Why can't I get AcuConsole to work using a remote display on my Linux system?

If you see an error message such as, "Can't set up a valid OpenGL canvas," "something is seriously wrong with the system!". It might be that you are using VNC for remote display. Unfortunately, OpenGL does not work over VNC, but TurboVNC based on VirtualGL should do the job. Check the following link for more information, https://mailman.coin3d.org/pipermail/coin-discuss/2006-June/006979.html

6. ### Why can't I get AcuConsole to display properly on my Linux machine?

AcuConsole uses Coin3D for visualization. Coin3D ( http://www.coin3d.org )requires OpenGL. There are multiple sources of problems with display. 1. OpenGL is not installed on your machine. Try running "glxgears" application as a test. 2. The graphics driver used. On Linux try running /sbin/lspci to see the drivers for your video controller. 3. On Linux, check the following files ( mail it to our support ), /etc/X11/XF86Config and /usr/X11R6/lib/X11/Cards

7. ### Disabling SELinux

This issue is caused by SELinux. At the current time, the only way to work around this issue is to turn off SELinux. This typically needs to be deactivated by the root user. Using the GNOME desktop environment, this can be done by running system-config-securitylevel and selecting the "SELinux" tab. Disable SELinux and apply the settings.

8. ### Why do I get errors about libstdc++ missing when I try to launch AcuFieldView?

AcuFieldView requires libstdc++.so.5. This library is present on most Linux systems as part of the GNU C compiler collection. However, newer Linux kernels are updating to libstdc++.so.6, which is not compatible with AcuFieldView. To resolve this issue, users need to install the libstdc++.so.5 library. This can typically be found using the package manager, or by doing a google search for libstdc++ and the name of your Linux flavor/version. These libraries can be downloaded from the various repositories on the web.

For 64 bit SuSe Linux, the package may be obtained from the following link:
http://rpm.pbone.net/index.php3/stat/4/idpl/7968158/com/compat-libstdc++-5.0.7-121.1.x86_64.rpm.html

For Ubuntu and other Debian systems, the following link can be used to search for "libstdc++.so.5" in the "Search the contents of packages" field:
http://www.debian.org/distrib/packages

A direct link to the debian package download is shown below (contained in the most recent debian version as of the date this is being posted):
http://packages.debian.org/squeeze/libstdc++5

9. ### My animation/movie frames are all black after going through the sweep. And I get 'Unable to allocate fbo for save image' in the AcuFieldView console w

Create an environment variable called
FV_NO_FBO
and set its value to 1 then re-launch AcuFieldView and re-build the animation.

10. ### Why am I unable to save images on Windows Vista?

Running AcuFieldView while using the Vista "Aero" themes could cause trouble saving images. Changing to a more "classic" appearance usually corrects the problem. Click here to take you to instructions on how to select a non-Aero theme.

11. ### How do I set up AcuFieldview to operate in client-server mode?

AcuFieldview supports client-server operation which allows users to process their data in its original location (i.e. on a compute cluster) while viewing it on their local desktop system. Client-server is supported across platforms (i.e. Windows clients, Linux Servers) and is the fastest and most efficient method of viewing large datasets that reside on remote platforms.

Using AcuFieldview in client-server mode requires a few simple set up steps. These steps are outlined in detail in the FV Reference Manual in Chapter 3 under the "Client-Server Mode" subsection. The FV Reference Manual can be accessed on Windows by selecting Help--->Contents-->Reference Manual. On Linux, the manual can be found in the AcuSolve installation directory under the fv/doc subdirectory.

12. ### Why do I get 'The specified address is already in use' or 'The requested port number is already in use'?

By default when acuFieldView (or FieldView) is launched it tries to make a connection for client/server behavior. The default client port number that is used is 12345. If something else is using that port number, then you will see that error.

Let's assume that on a Linux system, AcuSolve is installed in /home/Acusim/LINUX64/V1.7f/... There are two ways around this - both involving settings in one of the Acusim.cnf files.

1. This will disable client/server mode for acuFieldView:
acufieldview_executable = /home/Acusim/LINUX64/V1.7f/bin/acuFv -port none

2. This will use a different port number from the default:
acufieldview_executable = /home/Acusim/LINUX64/V1.7f/bin/acuFv -port 12344
NOTE - It is good if each user uses a different port number if they are all working on the same machine.

You can see the default setting for acufieldview_executable via
'acuConsole -h'

It is also possible that a firewall is blocking access to that default port 12345.

13. ### Why does 'acuLmg -query' give license expiry date of Dec-31-1969 when my licenses have not expired yet?

If on LINUX try

yCTxePXm3CPElP5oe6bIya AcuConsole 1 0 Dec-31-2010 0xa3be71g5 host1

14. ### How do I fix the following errors on Windows when trying to start the license manager from the command prompt?

or
"rexed.exe: can't establish connection"

This error is related to the permissions associated with the UAC (User Access Control) feature in Windows Vista or 7. Even when users are logged in as Administrator, you don't have administrative privilege by default unless you specifically request it for a given program. To resolve this problem, right click on acuLmd.exe in the "bin" folder of the AcuSolve installation and select "Run as administrator".

15. ### How do I 'point' to a different server for checking out a license?

There are two methods to do this.

One would be to add the parameter
-lmhost server_name
to the command being issued.

The other would be to edit the Acusim.cnf file and change only the lmhost value to the correct license server. The license deamon process acuLmd still needs to run on the local machine.

16. ### What is the mathematical definition of the strain_rate_invariant_2 quantity that AcuSolve exports?

The strain_rate_invariant_2 (I_2) is defined as follows:

I_2 = 2*Delta_s(Velocity):Delta_s(Velocity)

Where:

Delta_s denotes the symmetric gradient operator and ":" is tensor contraction.

To obtain the magnitude of the strain rate, the square root of the strain_rate_invariant_2 should be used.

17. ### What is the difference between Time Average Output and Running Average Output?

TIME_AVERAGE_OUTPUT

This type of output is a simple average. The value that is printed in the output file is computed as follows:UTimeAve = sum( U_n )/n, where n = the step number. The reset_frequency tells AcuSolve to start the time averaging procedure over by deleting the previous time averaged field, setting n=0, then starting the process out with a fresh set of values. Note that these values are not carried forward across restarts. So, every time you restart AcuSolve, the time average output is reinitialized.

RUNNING_AVERAGE_OUTPUT

This type of output uses a weighted average to compute the output value. This is useful for cases where you may want to weight the initial time steps less as the flow field is developing. The value that is printed in the output file is computed as follows: URunAve = 1/N*U_n + (1-1/N)*URunAve_n-1. Where N = min(step,N_max), step= the current time step number, and N_max=running_average_steps. The running_average_steps parameter is set in the EQUATION command. So, setting the running_average_steps essentially defines an averaging "window" over which to compute the output. This value is carried forward across restarts, and may also be initialized using the NODAL_INITIAL_CONDITION command. Note that TIME_AVERAGE_OUTPUT is simply an output quantity, whereas the RUNNING_AVERAGE_OUTPUT field is used in other areas internal to AcuSolve such as the non-reflecting boundary conditions, and running_average_wall_function.

Both types of output can be visualized using Fieldview, Ensight, and Paraview. They are included in the extended output variables when using acuTrans to convert nodal output. Here is an example:

acuTrans -out -to fieldview -extout

If either TIME_AVERAGE_OUTPUT or RUNNING_AVERAGE_OUTPUT are defined, their variables will be written into the output file.

18. ### How can I use if/then statements in a UDF for AcuProbe?

The syntax for conditionals is as follows:

if condition1:
expression
elif condition2:
expression
else:
expression

Depending on the desired function, elif and else are optional. See attached image.

19. ### How do I visualize Lighthill's Stress Tensor?

The Lighthill stress tensor is constructed by taking derivatives of the velocity field. It is possible to build all terms of the Lighthill stress tensor within a post processing package (Fieldview, Ensight, or Paraview) by using the function calculator. To make this calculation efficient, it is suggested that the -extout flag is used on acuTrans when converting the solution to the post-processor format. This writes the velocity gradients to the file. The velocity gradients can then be assembled appropriately in the post processing package to form the Lighthill stress tensor without havin to compute each derivative in the post processor. The divergence of the Lighthill stress tensor is typically used for visualizing the acoustic source strength. Creating and animating isosurfaces of divT can provide insight into the acoustic source characteristics.

20. ### How do I use the latest version of Paraview for AcuSolve results?

http://paraview.org/

http://paraview.org/paraview/resources/plugins.html

Once you have installed Paraview, unpack the plug-in and follow these instructions:

On Windows platforms:
Place the AcuSolveReader.dll file into the /bin/plugins folder of the ParaView installation

On Linux platforms:
Place the file called libAcuSolveReader.so into the lib/paraview-3.6/plugins directory. Note that you may need to create this directory.

21. ### How do I get Ensight 8.x to launch from AcuConsole?

In the /script/Acusim.cnf file of the installation - try adding:

ensight = "absolute path to ensight8.bat"

(You could also add this in your 'user' Acusim.cnf or the project Acusim.cnf.

For example, on Windows:

ensight = C:\Program Files\CEI\bin\ensight8.bat

22. ### How do I get the AcuSolve reader for Ensight 8.2 to work?

With this version of Ensight, you may need to create the environment variable

and set the value to the full path to the /script/ directory of the AcuSolve installation.

23. ### When should the temperature_flow stagger be used?

We typically suggest to use temperature_flow if the properties are strongly dependent on temperature. Treating flow and temperature as one large matrix can aid convergence in these cases. The degree to which it aids convergence will be extremely problem dependent, so it is difficult to make a blanket statement. If the free convection is dominant, temp-flow would have more effect than if the forced convection is dominant.

If the flow equations don't depend on temperature, solving them separately will be faster.

24. ### How does AcuSolve use the relaxation factor, and what is the default value?

The relaxation_factor parameter is available through the AUTO_SOLUTION_STRATEGY command. By default the relaxation factor is 0 (i.e. no relaxation). When relaxation_factor is set to a non-zero value, a number of changes to the solution strategy are made. These changes are primarily made through the LINEAR_SOLVER_PARAMETERS command. It should be noted that these changes typically cause slower non-linear convergence for steady state cases, so relaxation should only be used for cases that are very stiff or difficult to converge. Also, the relaxation factor should always be set to 0 for transient simulations. When relaxation is used, AcuSolve adjusts the number of projection vectors, the regularization factor, and the update factor that is used for each equation. These parameters are automatically adjusted when relaxation is used through the AUTO_SOLUTION_STRATEGY command. This ensures that suitable values are set for each parameter. Although it is not recommended, users can manually adjust the various parameters (i.e. update factor, regularization, number of projection vector) through the LINEAR_SOLVER_PARAMETERS command.

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