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Normal Modes frequencies calculation

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03-26-2018 05:30 AM

Hello,

I just faced one problem. Is there any built-in feature in NX/ NX Nastran, for including following phenomenas in analysis of normal modes ?

1. I would like to add some additional mass to the structure (in sim file) that will represent eg. floor coverings, non-modelled equipment etc. For example to add additional 50 kg/m^2 for plates. I can do it via material density, however looking for something more elegant...

2. Second thing is more tricky and maybe more theoretical than software-related. I need to include influence of the presence of the water that is adjusted to the structrure. Let's say I have tank for water that has internal bulkheads and need to check natural frequencies of particular plates.

For bulkheads insidie the tank I need to check then frequencies when tank is full as well, so bulkheads are surrounded by water but outer shell of tank has water from one side only. Do you have any idea or well known theory how to included such pehenomena in the analysis?

Great thanks for any help !

3 REPLIES 3

Re: Normal Modes frequencies calculation

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03-26-2018 05:48 AM

Hello,

Regarding:

1. in the properties definition with non structural mass you can add mass/m2.

2. you want to analze the natural frequnces once the strcuture is loaded. If it is so, then that is prestressed modal analysis. You have to run the static and then with the strcuture loaded modal analysis. I hope it helps

Re: Normal Modes frequencies calculation

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03-26-2018 06:11 AM - edited 03-26-2018 08:05 AM

2. Also you may be interested in using virtual fluid mass:

Nastran has capability to include influence of surrounding water. I dont know how to define this in NX, but this can be easily defined in Femap.

Also check this theme:

Re: Normal Modes frequencies calculation

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03-26-2018 07:59 AM

Will have to try it !

Thanks a lot !

Thanks a lot !

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