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In MSC Nastran, vibro-acoustics is called fluid-structure analysis. The fluid may be a gas or a liquid but in both cases the linear small displacement theory either allows the modes of the structure to be computed separately from the modes of the fluid or they can be computed as coupled modes...

The eigenvalue table you see at the end of the job is obtained from an analysis which detected a massless mechanism. The one massless mechanism was constrained, and in doing so it looks like it removed a rigid body mode. Lesson 1: Read the messages in the f06 file. Immediately prior to the...

MSC Nastran SOL 400 has the possibility to model a cohesive zone (look for the CIFHEX entry) where you can define the proper dimensions of the bond (one of the element dimensions may be extremely small compared with the other two). The PCOHE entry is used to define the element properties for...

The term Kms.Kss^-1.Ksm is subtracted because it computes reaction forces. Just as an applied load is equal and opposite to a reaction force in linear statics, so the total behaviour must turn the reaction force into internal loads by reversing the sign. For a determinate system, when any one...

Static condensation starts by moving the points in the M set each, one at a time, by a value of 1.0 while all other points in the M set are fixed. The result is M displacements of the sm DOF according to these unit displacements. This computes the result of this action on the S set so that...

Drop back to SOL 103 and SOL 101 to check out the model. If the model won’t run cleanly in these solution sequences, you have little hope of getting a frequency response to function correctly. There are reports of many negative values on the factor diagonal of the dynamic stiffness, which is...

You wrote "Depending on when I run the analysis..." - do you mean when you run the model once, and then again sometime later without changing the input, the quantity of output changes? Which output? The f06 file? The punch file? I don't see any specification of an output file for a post...

Did you run the job more than once? The XDB file is a fully relational database, and if an XDB file exists with the current job name, and you run the job again, the XDB file will be updated with the new results. This might explain the two sets of results. To be sure, either delete the XDB...

When you get to the Hexagon Simcompanion site, go the Adams section and search for Article 000002738 - looks like it got renamed in the migration from MSC.Software to Hexagon. DG

On the original question of inertia relief, under most circumstances, an inertia relief analysis in MSC Nastran does not have any SPC’s defined. Special cases may arise, for example if you want to study a symmetric half model, in which case the acceleration vector must be orthogonal to the...

You can get a whole bunch of good practice ideas from these sources: Acoustic theory, not too heavy reading: Room Acoustics, Heinrich Kuttruff Master Handbook of Acoustics, F. Alton Everest & Ken C. Pohlmann Practical aspects: BBC Engineering, Guide to Acoustic Practice, Keith A. Rose -...

Short version: Do the opposite, remove the stuff you don’t need. Use MATPRN, DO WHILE-ENDDO, PARAML(DTI) and PARAML(TABDEL). Long version: I am assuming you are using MSC Nastran, so I may mention some specificities to this code. The basic method is to make a copy of GEOM2 and remove the...

Elements are not contained in GEOM3 - did you mean GEOM2? If yes, it would be relatively, easy yes. Which shell elements were you considering? The different elements are identified by their type, and shell elements is broad category - do you mean QUAD4, QUAD8, CTRIA3, CTRIA6, etc. - do you...

Which Nastran and which version are you using and from the remarks about colour I infer you are looking at the results in a post processor. Which post processor are you using and does it support complex composite stress results? Do you get any complex composite output in the f06 file? DG

If you get stuck, just let me know. You will need a DMAP license to allow the compiler to work. DG

The 0.5 constant is obtained from the relative location of the GRID points. In the image you posted, the diagram in the upper right corner (labelled finite element model) shows GRID points 2 and 3 at a Y distance of 0.5 from GRID point 1; this is the moment arm to multiply by the rotations...

Using Nastran documentation for a different Nastran may not be a good idea. Can you post the full message - I suspect message 7701, and an aeroelastic bent. DG

That's the pre-post. Am I to infer that you are using Siemens NX Nastran, or do you solve the problem in MSC Nastran?

Which version of Nastran are you using?

By the way, what happens if you have a local coordinate system defined on one of the boundary points? BGPDT is no good for that.