Learning Forum

[ronclaudel]

Hi all,

I am going to perform a Harmonic Acoustics Analysis on a pre-stressed structure using a Static Acoustics Analysis. I first used the Static Acoustics Analysis to calculate the displacement of two masses in a melamine foam under gravity, but the following error occurred during the calculation:

1) Warning: Solver pivot warnings or errors have been encountered during the solution. This is usually a result of an ill conditioned matrix possibly due to unreasonable matertial properties, an under constrained model, or contact related issues. Check results carefully.

2) Error: A solver pivot warnings or errors have been detected in the UZ degree of freedom of node 348048 located in 1(3). This is usually a result of an ill conditioned matrix possibly due to unreasonable matertial properties, an under constrained model, or contact related issues. Check results carefully.

3) Warning: One or more remote boundary condition is scoped to a large number of elements which can adversly affect slover performance. Consider using the pinball setting to reduce the number of elements included in the solver.

4) Warning: Not enough constraints appear to be applied to prevent rigid body motion. This may lead to solution warnings or errors. Check results carefully.

5) Error: Solver pivot warnings or errors have been encountered during the solution. This is usually a result of an ill conditioned matrix possibly due to unreasonable matertial properties, an under constrained model, or contact related issues. Check results carefully.

And here are some material properties and boundary conditions I set:

Melamine foam:

The two masses:

Steel panel:

I use the Remote Displacement to constrain the three translational degree of freedom on the four sides of the model:

Here is a picture of the Melamine foam being hidden:

 

Any suggestions for solving this problem?

Thanks : )

 

[peteroznewman]

What is the acoustic load that you want to apply?

It seems you want a Static Structural analysis to compute the displacement due to gravity of a mass suspended in a foam. 

(a) Is there a mass-shaped cavity in the foam?

(b) Is there Bonded Contact between the mass and the foam cavity faces, or are you using shared topology?

(c) Have you turned on Large Deflection?

Replace the Remote Displacement with Fixed Support to get rid of warning #3.

[ronclaudel]

Hello,

Thanks for your reply.

I actually want to compute the transmission loss of the entire structure under the influence of gravity and the acoustic load I applied is the Diffuse Sound Field.

Here is the Project Schematic I use:

And there is no mass-shaped cavity in the foam. I first built a cuboid to represent the foam, and then subtracted the volume of the two masses from the cuboid. There are only these two masses in the foam, nothing else.

I think I am using shared topology. All geometry is in one part, so the generated meshes are sharing nodes in the position where the foam and the mass block come into contact:

I didn't turn on the Large Deflection option. I will try to turn on this option to see if it can solve this problem.

[peteroznewman]

The website is broken today, no one can Insert Images.

If you first built a cuboid to represent the foam, and then subtracted the volume of the two masses from the cuboid, that means you created mass-shaped cavities in the foam. 

You are using Shared Topology if you put all the bodies into one part. This is the best approach. Make sure you delete any Contacts that are automatically created in the Connections folder. They are redundant if you have Shared Topology.

I'm not an acoustics expert but did do a few models to study transmission loss. Those models were in a duct with an acoustic source at one end and an object in the middle of the duct. The transmission loss was measured between points before and after the object. It's not clear from your description where the two sides of the transmission loss are to be measured.

[ronclaudel]

Hi,

Sorry for the late reply.

After changing some settings, it ran successfully and got the results.

I first turned on Large Deflection as you suggested, but still got the following error:

Ansys Workbench - Error: The solver engine was unable to converge on a solution for the nonlinear problem as constrained. Please see the Troubleshooting section of the Help System for more information.

Then I tried to set the Physics Region of the melamine foam into Structural instead of Acoustics, and no error occurred after running. Although the problem is solved, I'm not sure if it's correct to set the foam's region to Structural for subsequent Harmonic Acoustics Analysis.

Another problem is that I can only see the deformation of the two masses after hiding the foam. Is there a way to see the deformation of the foam caused by the gravity of the two masses?

On how to measure the transmission loss, you can insert a Diffuse Sound Transmission Loss under Solution to output the results directly:

[peteroznewman]

You can pick the faces of the cavity in the foam as the scoping for a deformation plot.  That would give you the same result as the deformation of the masses.

[zulkarnainzakri]

Can you help me on how to combine the explicit dynamic result with your suggested analysis system to obtain the sound pressure level. Actually i want to analyse the sound pressure of moving wheel on rail track. Whether need to analyse at first by using explicit dynamic or static structural ?..n