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# Compiling and Loading User Defined Functions (UDFs) for Fluent 14.5 using the Microsoft Visual Studio 2010 compiler

For the complete tutorial on how to compile and load User Defined Functions (UDFs) for Fluent 14.5 please download the attached .pdf document.

# What does it mean when damped imaginary frequency is zero? I am using the QRDAMP modal solver and there is damping in the model.

Development advised that in this case a zero imaginary component of frequency indicates a mode is over damped.<br><br>Mode 3 is a rigid body mode of the structure bouncing vertically...

# Why does HFPORT,MODAL give wrong power excitation? If I run my input with HFPORT,1,Modal,11,1,IMPD,,,,0,1000, I get a power of 2488 on the port after solution. The same model with HFPORT,1,RECT,11,TE10,IMPD,a,b,,0,1000 gives the expected value of 1000.

This is defect 57399, an error in the normalization of the eigenvalue solution. It is fixed in 12.0.

# Why don't my harmonic reaction forces include contribution of damping? This is obvious because the imaginary damping force is zero.

This is defect 57436 and applies to damping specified with DMPRAT or MP,DMPR It is fixed in 11.0 SP1. It is documented in Class 3 2007-1.<br><br>A workaround at 11.0 is to use DMPRAT...

# Why don't my harmonic reaction forces include contribution of damping?

From the deformation plot, you can see there are some spurious displacements in the slender vertical members. This occurs when long slender members are meshed with only one element through the...

# Why is -{TIME}^2 interpreted by function editor as 1-{TIME}^2?

This is defect 57372. The negative sign in front of the primary variable, TIME, cannot be handled properly by the function editor. This will be error trapped in ANSYS 12.0. The workaround is to...

# How is the nonlinear quantity SRAT (PLNSOL,NL,SRAT) computed? After my first load step the value is 7, but after the 2nd load step SRAT is back to 1.0 as would be expected for a converged solution.

As the Theory Manual says, SRAT is the ratio of the trial stress to the yield stress. In the first load step, the trial stress is the 1st computed elastic stress which is above yield, so you get...

# Can you increase the 5000 limit on the number of parameters at ANSYS 11.0?

No, there is no way to increase it. Perhaps using an array in which the individual parameters are replaced by components of the array is a workaround.

# Why doesn't my surface load applied with SF in a *DO-loop that loops through the nodes on the surface get applied?

An SF command is ignored if the selected nodes don't define a face of an element. Applying SF to a single node doesn't work.

# How can I tell the ADAMS macro to write to bigger disk?

This is handled in the MNF library (not ANSYS). Try adding the following to your .cshrc file:<br><br>setenv TMPDIR /where/I/want/it/to/go<br><br>You can verify that it is...

# How should the real constant DIRZ be used in PLANE53? In ANSYS 10.0, for PLANE53 with KEYOPT(1)=2, real constant 4 (DIRZ) is documented as the current? Doesn't ANSYS calculate the current from the voltage and RSVX?

You are right, that real constant is just to indicate the direction, positive or negative. The documentation is misleading. At 11.0 we changed the description to:<br><br>1 for current...

# Why does my cyclic model, which I saved after the solution, have a large number of constraints on it?

This is the normal case when solving harmonic index 0; the 2nd sector is being fully constrained. If a 2nd harmonic index had been solved for, these constraints would have been deleted. The user...

# How to check whether an array parameter is already in existence by APDL? We can achieve this by GUI; however, we need to check it in batch mode. If the array is already in existence, we don't need to define it again.

You can use the following *GET command to test if a parameter name exists.<br><br>*GET,PRM_TYPE,PARM,name,TYPE ! where "name" is the parameter...

# Why does the solution diverge for this circuit-coupled motor?

It is not known why, but changing the transient time step by a small amount, such as 1 nanosecond, completely corrects the problem.<br><br>The time step is being computed as (1/60)/40...

# How does FLUID136 get its displacement DOF? The ANSYS Documentation states that the SETFGAP command updates the real constants according to the displacements in the database. The FLUID136 element has no displacement DOFs. Are the displacements taken from neighboring elements?

Development confirms that the adjacent elements provide the DOF for SETFGAP.

# Why doesn't a single point response spectrum (SPRS) match Multi-Point Response Spectrum (MPRS) with same input? As a test, I created a model and performed an SPRS analysis. Then an MPRS analysis was performed with the same spectrum for all nodes. This analysis matches the SPRS analysis. However, when the same spectrum is applied separately for each node in an MPRS, the results no longer match the SPRS. Is my procedure wrong?

It¿s expected that applying the displacements separately would give a lower value because they are assumed to be uncorrelated in the crude sort of way that is obtained with SRSS. If you...

# Can you use CPCYC on a thermal model? The command documentation only mentions structural DOF.

Yes, you can use CPCYC on TEMP and other non-structural DOF. See example...

# When calculating the covariance between two PSD quantities, should ANSYS be producing a value which is normalized? (i.e., 0 for no correlation and 1 for full correlation)

No, the covariance should not be confused with the coherence function or correlation coefficient. The covariance is output as defined in Equation 19-179 of the Theory...

# Can a fatigue analysis be done based on results from a PSD analysis?

There is no automated way, but there is information from the PSD analysis that could be used to do a fatigue analysis.<br><br>We introduced the Segalman-Reese SEQV value in ANSYS 8.1...

# Are there any special geometry requirements for magnetic analysis in Simulation?

Yes, the geometry must be in the form of a multibody part. There is not magnetic contact capability, so the mesh must be continuous from one body to the next.

# Why is CORIOLIS,ON,,,ON required in the static pass of prestressed rotordynamic modal?

The command CORIOLIS,ON,,,ON needs to be issued in the static analysis so that enough memory is allocated for the emat file to be unsymmetric in the modal. Some additional background information...

# Why is a prestressed modal analysis giving different results in ANSYS at 11.0? The SHELL181 model is of a curved pipe prestressed by internal pressure. In ANSYS 10.0 the first frequency was 199 Hz. At 11.0 the first frequency is 184 Hz. The un-prestressed first frequency is 184 Hz.

ANSYS 11.0 correctly accounts for the follower nature of a pressure load and does not show any stiffening. In 11.0 we began including "pressure load stiffness" automatically in a...

# Is there a way to get participation factors for a PSOLVE PRESTRESS modal?

Based on the test below, you can run a spectrum analysis after the modal to obtain participation factors in the x, y, and z direction. These spectrum runs are very...

# How can I specify my workspace amounts (-m, -db) in Simulation at 11.0? I can't set them in the same way I did in 10.0. Is this capability removed from workbench now?

At 11.0 they are under Tools - Solve Process Settings ¿ Advanced. Do a string search on "workspace" to go to the applicable help section.

# Is it possible to perform a modal cyclic symmetry analysis in Simulation at 11.0? I placed a CYCLIC command in a command snippet, but the results look odd.

No, for several reasons. At 11.0, postprocessing in Simulation is done by reading the ANSYS RST file which contains results for two sectors, only one of which Simulation knows about. Also,...