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Apply nodal displacement from saved eigevectors

Hi all,

I need to apply a nodal displacement X to my model and evaluate the stress.

The displacement X should be the nodal amplitude at a natural frequency normalized to the largest displacement (I can use NORM=MAX in the eigrl card)

What I can't understand is how I can apply the nodal normalized displacements to the model to evaluate the stress. Maybe using EIGVRETRIEVE as input in 'post>apply results' in Hypermesh?

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Altair Forum User

HI,

EIGVRETRIVE retrieves results of normal modes analysis which are saved using EIGVSAVE

Altair Forum User

In few words I need to apply a static displacement to the nodes of the model.

The displacement should be the normalized eigenvector a the first modal frequency. But I am still trying to understand how.

The only thing that I have understood so far is that with RESVEC i can output the normalized eigenvector (see picture).

<?xml version="1.0" encoding="UTF-8"?>

Altair Forum User

natural frequency normalized to the largest displaceme

Can you explain a little more about this?

From what I understood, I can suggest you to run a Modal frequency analysis with displacement load applied.

Altair Forum User

Hi Prakash,

There is a technique to evaluate the stress on a component at its natural frequency without running a frequency response analysis.

Clearly, it is an approximation since it does not take into account the damping effect. I want to investigate what the error is in terms of percentage.

In order to do so, I need evaluate the normal modes of the component (it can be done by running a modal analysis). For each natural frequency

(eigenvalue) there is a modal shape associated (eigenvector).

I need to apply as 'displacement load' one of the modal shapes found in the modal analysis.

The eigenvector that I need to apply to the part should be normalized to the largest displacement of the eigenvector. Namely, the largest nodal displacement

should be 1 and the other displacements between 0 and 1.

There are 2 things that I am not able to do yet:

1) save the modal shape for a natural frequency (NORM=MAX may normalize the vector the way I need)

2) apply the shape vector obtained in point 1 to the structure

Sorry if I didn't make myself clear in the first post. I can also make a little presentation to explain it better.