vibration amplitiude

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I want to minimize the vibration amplitude at any modes on Optistruct 

is it possible?/ how to perform it

best regards

Adriano Koga_20259

Hüsnü Yalınkılıc said:

intermediate iterations? Also, I need them. how to get them

If you need results for intermediate optimization iterations, you need to add the control card OUTPUT.

This card controls the Output frequency of many different result files. In the case of H3D results, the default is 'FL'>>First and Last. You may want to change this to 'ALL'.

Adriano Koga_20259

Using OptiStruct for optimization you have a few approaches:

- the amplitude should be obtained from a FRF analysis to be more accurate.

Then you can create a FRF displacement response, for example, and select this response as objective. Bear in mind that only 1 point/frequency can be used directly as objective. Ohterwise you will need an objective reference.

 

- there is an alteranative way, using modal analysis only, where you can use the 'mode shape 'response from your modal analysis and ask OS to minimize it. But in this case, the ampllitude is normalized in general, so you need to take care with the meaning of your actual result/response.

create a response 'mode shape', for a particular mode and node in some direction.

then assign it as objective.

Hüsnü Yalınkılıc

Adriano Koga_20259 said:

Using OptiStruct for optimization you have a few approaches:

- the amplitude should be obtained from a FRF analysis to be more accurate.

Then you can create a FRF displacement response, for example, and select this response as objective. Bear in mind that only 1 point/frequency can be used directly as objective. Ohterwise you will need an objective reference.

 

- there is an alteranative way, using modal analysis only, where you can use the 'mode shape 'response from your modal analysis and ask OS to minimize it. But in this case, the ampllitude is normalized in general, so you need to take care with the meaning of your actual result/response.

create a response 'mode shape', for a particular mode and node in some direction.

then assign it as objective.

Then you can create a FRF displacement response, for example, and select this response as objective. Bear in mind that only 1 point/frequency can be used directly as objective. Ohterwise you will need an objective reference.

thank you for reply but how to perform what you said???

I created a FRF acceleration for a single node as in picture 1.

 

then how to select the mode frequency from panel as a response at picture 2.

do we choose from here ????

best regards 

Adriano Koga_20259

Hüsnü Yalınkılıc said:

Then you can create a FRF displacement response, for example, and select this response as objective. Bear in mind that only 1 point/frequency can be used directly as objective. Ohterwise you will need an objective reference.

thank you for reply but how to perform what you said???

I created a FRF acceleration for a single node as in picture 1.

 

then how to select the mode frequency from panel as a response at picture 2.

do we choose from here ????

best regards 

You can choose all freq in the response panel and then in the dconstraint panel, you could select the limit amplitude and select a frequency range by defining a LFREQ and UFREQ. LET'S say that you will have the acceleration amplitude for your upper point as a response and then you want to limit the acceleration to 0.5, from 200 to 300Hz. Create the frf acceleration, selecting the node and all freq. Create the dconstraint and assign an upper bound of 0.5 and selecting your frequency response loadstep. After creating if you can go to the entity editor in the lower left corner and define the LFREQ and UFREQ boundaries as 200 and 300.

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Adriano Koga_20259 said:

You can choose all freq in the response panel and then in the dconstraint panel, you could select the limit amplitude and select a frequency range by defining a LFREQ and UFREQ. LET'S say that you will have the acceleration amplitude for your upper point as a response and then you want to limit the acceleration to 0.5, from 200 to 300Hz. Create the frf acceleration, selecting the node and all freq. Create the dconstraint and assign an upper bound of 0.5 and selecting your frequency response loadstep. After creating if you can go to the entity editor in the lower left corner and define the LFREQ and UFREQ boundaries as 200 and 300.

first of all, thank you for quick reply

I aim to the minimize the amplitude at resonance frequency. That's why I'm looking for something like this.

if I define the max_acc as a constraint how do I define the objective function?

Adriano Koga_20259

Hüsnü Yalınkılıc said:

first of all, thank you for quick reply

I aim to the minimize the amplitude at resonance frequency. That's why I'm looking for something like this.

if I define the max_acc as a constraint how do I define the objective function?

it really depends on your problem, and what are your design variables, but i would try minimize Mass.

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Adriano Koga_20259 said:

it really depends on your problem, and what are your design variables, but i would try minimize Mass.

ok, If we go back to the beginning

is there a way for calculating acceleration (vibration amplitude) at a spesific mode by optistruct

I want to learn only this

I have a more problem,

when I conduct modal frf, I have received error  which is "not enough disc space"

how to deal with this problem 

thank you for reply 

best regards

Adriano Koga_20259

Hüsnü Yalınkılıc said:

ok, If we go back to the beginning

is there a way for calculating acceleration (vibration amplitude) at a spesific mode by optistruct

I want to learn only this

I have a more problem,

when I conduct modal frf, I have received error  which is "not enough disc space"

how to deal with this problem 

thank you for reply 

best regards

Some options:

 

- the amplitude obtained from a FRF analysis to be more accurate.

You can create a FRF acceleration response and and define 1 point/frequency to be monitored. The problem with this is that it takes a specific frequency or a frequency range, so that you would create a constraint for it, for example, limiting the amplitude to some value.

when you define a optimization constraint, you could specify a particular frequency range (if you go to the dconstraint, there will be a UFREQ e LFREQ). You do not guarantee exactly the specific mode, as it can shift a little bit, but you can at least select a range)

 

- there is an alteranative way, using modal analysis only, where you can use the 'mode shape 'response from your modal analysis and ask OS to monitored. But in this case, the ampllitude is normalized in general, so you need to take care with the meaning of your actual result/response.

create a response 'mode shape', for a particular mode and node in some direction.

 

 

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Thanks for the valuable information you gave. my friend

do you have any document about hyperstudy for FRF

Adriano Koga_20259

Hüsnü Yalınkılıc said:

Thanks for the valuable information you gave. my friend

do you have any document about hyperstudy for FRF

You're welcome.

 

HyperStudy is an "external" optimizer that can use OptiStruct as a solver and perform Shape and Parametric optimization. There are a couple tutorials on coupling OptiStruct models with it in HyperStudy Help section. Pelase take a look there or here in the Knowledge Base of Altair Community.

 

Please consider also the usage of DRESP3 in OptiStruct coupled with Compose to create more advanced responses in your case. The attached example is a topology optimization (which is not so efficient to use with DRESP3), but you can use the same approach with Size Optimization.

 

Altair Compose extends even further the optimization capabilities of OptiStruct as you are able to create your own responses. In the attached example, you will see a DRESP3 that call Compose, and the Compose function takes the peak and valley frequencies of an FRF to perform some calculation and give it back to OptiStruct.

OptiStruct calculates sensitivities using Finite Differences in this particular case, so that's why having less design variables (size, shape) is more feasible than topology.

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I can get graphical data (frf curve)  with optistruct optimization, alright?

Adriano Koga_20259

Hüsnü Yalınkılıc said:

I can get graphical data (frf curve)  with optistruct optimization, alright?

The same results you get in your analysis is still available in the optimization run. By deafult you will get the results for iteration 0 and final iteration.

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intermediate iterations? Also, I need them. how to get them

Adriano Koga_20259

Hüsnü Yalınkılıc said:

intermediate iterations? Also, I need them. how to get them

If you need results for intermediate optimization iterations, you need to add the control card OUTPUT.

This card controls the Output frequency of many different result files. In the case of H3D results, the default is 'FL'>>First and Last. You may want to change this to 'ALL'.

Hüsnü Yalınkılıc

hello Mr @Adriano Koga 

I have conducted a gauge optimization procedure and got some results

I created a response whose title "max_acc" and assigned this response objective function (minmax)

but this procedure found the minimum values among the maximum max_acc values for each frequency.

I wished that the software would find the minimum among the calculated maximum values for each design variable/variables (tu and tl )

where am i doing wrong/what is the problem?

 

On the other hand, there is a paper about optimization and this study was performed via Optistruct

in this paper a optimization procedure was conducted and celullar angle and cell thickness were assigned as design variable.

 

 

 

 

how to assign celullar angle optistruct as design variable?

Adriano Koga_20259

Hüsnü Yalınkılıc said:

hello Mr @Adriano Koga 

I have conducted a gauge optimization procedure and got some results

I created a response whose title "max_acc" and assigned this response objective function (minmax)

but this procedure found the minimum values among the maximum max_acc values for each frequency.

I wished that the software would find the minimum among the calculated maximum values for each design variable/variables (tu and tl )

where am i doing wrong/what is the problem?

 

On the other hand, there is a paper about optimization and this study was performed via Optistruct

in this paper a optimization procedure was conducted and celullar angle and cell thickness were assigned as design variable.

 

 

 

 

how to assign celullar angle optistruct as design variable?

MinMax problem will chase after the maximum peaks that you have, and then try to minimize them, wherever they are.

 

For the angle, they probably performed a shape optimization, using HyperMorph feature in HyperMesh. Take a look at the shape optimization tutorials in the OS Help. For help with HyperMorph, please take a look at the HM tutorials in the HyperMorph section.

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@Adriano Koga 

hi I would like to add a constraint static deflection due to gravity load 

how to realize