How to add mass to Pro/Mechanica Model

[SolidworksFan]

I am a Solidworks Simulation user that must migrate to Pro/Mechanica with the new job.

I am trying to add a 1 lb mass to a model. That is, I want to "smear" 1 lb over the face of the part. Solidworks considers this a distributed mass. I can not find the equivalent in Mechanica. I tried Mass Definition but it is looking for a Geometrical Reference. It will not let me pick any features on the part.

Any ideas?

 

[rb1957]

density (as a material property) and apply a body force ("g")

 

[GenericUser]

Its been a while since I used Mechanica, but what you can do is define a datum point and add a mass element to it. Then define a weighted link between the point and the surface. The point should be located on the centroid of the surface so that you do not alter the desired mass moment of inertia of the model. Will Mechanica let you define a weighted link between two items in the same plane? I am not sure - like I said its been a while.

Altering density would only work if you applied a shell element directly on the surface, but that would introduce shell-solid links - and that would make the model a bit messy.

When I left PTC 3 years ago there was talk of adding a distributed mass feature - so it might be there some where.

Hope this helps.

 

[SolidworksFan]

I found you can add a distributed mass to a surface if you are in FEM Mode. However, as a new user to Mechanica this adds a new level of complexity. The Run Model icon is not present in FEM Mode so I assume you have to use other methods to analyze a model.

Like most FEA software, one needs to learn how to set up models and the PROCOACH lesson on Mechanica does not mention how to drive in FEM Mode.

I guess I need a better tutorial!

 

[GenericUser]

FEM mode is NOT Mechanica, its actually a different PTC product that used to be called Pro/MESH. It is meant only for defining loads/constraints, material props, a mesh, and then exporting to 3rd party solver (Ansys and Nastran but again that might have changed).

So just to be clear, when the FEM mode box is checked you are not actually using Mechanica.

Give the weighted links a try.

 

[rb1957]

do you want to add mass to the model, or model the weight of the part ?

 

[SolidworksFan]

I wanted to add additional mass to the model to simulate parts not included in the base part. To be specific, I am modeling a pcb (printed circuit card). I defined material in the model. The pcb has an additional 1 lb of "components" distributed.

As a work around, I made a new material with an increased density to match the weight of the pcb plus the 1 lb.

I am only looking for the natural freq at this point and the above approach worked but was much more time consuming than just adding a distributed load like I could do in Solidworks.

 

[rb1957]

"the above approach worked but was much more time consuming" ... how much time can it take to change the density on a material card ?

 

[SolidworksFan]

I guess it really does not take any time but I hate "faking" the model to perform this task. If someone else was to use the model,the change in density or reason behind it would not be obvious. This just seems like a dumb way to solve the problem. Of course I am new to the software and I resist change!

 

[rb1957]

accept change ! and accept doing things that make you want to shower ! and (unfortunately) writing up your "quick fixes"