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# Difference between FEA modelling with forces, NSM or elements with mass?

## Difference between FEA modelling with forces, NSM or elements with mass?

(OP)
Hello,

We are working in an aerospace project using MSC Nastran, and we have to model external loads acting on our system.

The question arises due to the several possibilities of modelling the external effect in a static analysis.

What is the difference between modelling using a prescribed forces, NSM (non-structural mass), or modelling the external body with elements and associated mass?

Thank you.

### RE: Difference between FEA modelling with forces, NSM or elements with mass?

In static analysis these different approaches should give you the same results if used appropriately. As long as equivalent values (i.e. force corresponding to mass of the object being replaced) are used, of course.

### RE: Difference between FEA modelling with forces, NSM or elements with mass?

you can use discrete forces or load factor (if you've specified the weights). try it out on a small test case.

### RE: Difference between FEA modelling with forces, NSM or elements with mass?

NSM affects both static and normal modes solutions. If you replace some mass with force then you will not account for Normal Modes and dynamics solutions.

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