How to improve Natural frequency of a System(assembly of more than 20 Parts interconnected)

[damymady]

How to improve Natural frequency of a System(assembly of more than 20 Parts interconnected)

My Problem definition is as below..

a system of 20 parts which are interconnected are given..

Run a Modal analysis...

Identify Some major modes (Bending and Torsion importantly)

Then i have to improve the system frequency..

for this I need to know following things:

1) Which part is major contributor to a particular mode, say BENDING? This i can see the mode shape and identify which components are having displacement..

2) Now i want to know in which part of the component i need to work to improve the natural frequency? Is there any procedure to identify the zone which i should concentrate?

ANY reference link also would be helpful, Where i can see How i can arrive at the critical zones of a component in a system based on natural frequency..

Thanks in advance..
Damodharan B

 

[GregLocock]

Never done it but strain energy contribution used to be one criterion

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[damymady]

Thanks Greg, for the response

I am just looking for an step by step procedure on How to arrive at my critical location for natural frequency improvement..
Some kind of Algorithm based steps..

Let see if someone can help me from here

 

[rstupplebeen]

For algorithm based steps I would suggest optimization strategies. A cost function of maximizing the first natural frequency while minimizing weight. This could be achieved by modifying: parametric geometry, material selection, boundary conditions of connections or many others. I hope this helps.

Rob Stupplebeen

http://www.optimaldevice.com

 

[bkal]

I must be missign something very obvious, but what do you mean by "improving natural frequency"? Do you mean improve the accuracy of your motel, or make sure that some frequencies are in the certain range or ... ?

 

[IRstuff]

Is this for school? Student posting is prohibited

TTFN
faq731-376

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[damymady]

Not for School.. i m working on a system whose global frequency(Bending and torsion) to be improved by optimizing the critical parts which are contributing to the system frequency

 

[damymady]

Improving i mean i want to increase the frequency.. (Say from 42 Hz to 45 or 48 Hz)

 

[IRstuff]

I don't think anyone understands what you're having a problem with. You presumably ran some sort of analysis that determined that the first mode is 42 Hz, which has to correspond to something physically happening in your assembly. Generally, this means that something is too floppy, i.e., not stiff enough. You stiffen it, and iterate the analysis; rinse, repeat.

TTFN
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[SergioP]

Try to:

Decrease the weights
Increase the stiffness of the assembly
Lowering the center of gravity
Add more fixation points

 

[BlasMolero]

Dear Damodharan,
Frequently we are faced with the decision of modifying your structure in order to meet stringent design criteria. In most instances, your objective is to maximize the benefits with minimal changes. The element strain energy output result is an excellent tool for identifying areas of modification that will reap the most benefits for design changes, I used a lot when performing an eigenvalue analysis using FEMAP & NX NASTRAN. The element strain energy is basically the elastic energy stored in the structural element.

For example, a value of 48.8 for the strain energy output for one element means that it contains 48.8% of the total strain energy of the whole FE model. In other words, this element is the MOST effective element to modify if you wish to increase the stiffness of the structure for the same amount of weight increase.

As you can see, the element strain energy output is an extremely useful tool in helping you to identify the most efficient locations for modification.

Best regards,
Blas.



~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48004 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[izax1]

Looking at strain energies and strain energy densities (normalized to element size) are tools to use for optimizing (Increasing or decreasing) natural frequencies