Base Motion in Modal Based Frequency Response.
Answers
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By the way, if the vibration mode is well known you might not need to run the frf for the peak frequency, only modal (response: frequency)
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Altair Forum User said:
You could calculate your transmissibility by using advanced dresp2 or dresp3 with Compose.
I can already obtain this curve for my all model. no problem without optimization
I want to improve this curve
for example I want to obtain 0.1 (TR) at Hz 100 Hz
is It possible?
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Altair Forum User said:
Dresp2 allows you to create an equation and use this as objective or constraints.
I know Dresp2 it is used when perform topology optimization
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Hi
In order to perform your optimization, you will need to create your responses.
You can create one response using a dequation, which is the transmissibility, the same way as you did in your graph, but now you will embed this into your optimization model, and then refer this as a constraint and assign a value of 0.1 foe your 100hz.
Just take care and remember that as you change your structure, your mode frequency will change a bit, and maybe the frequency of interest might change as well.
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Altair Forum User said:
Just take care and remember that as you change your structure, your mode frequency will change a bit, and maybe the frequency of interest might change as well.
My frequency range is wide enough therfore I think I experince no problem..
Altair Forum User said:In order to perform your optimization, you will need to create your responses.
I create a response (frfaccelerration)
I select the thickness as the desvar
Altair Forum User said:constraint and assign a value of 0.1 foe your 100hz.
how to perform this /profile/97129-adriano-a-koga/?do=hovercard' data-mentionid='97129' href='<___base_url___>/profile/97129-adriano-a-koga/' rel=''>@Adriano A. Koga
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Can we define an angle as a design variable? in hyperstudy or optistruct
thank you for quickly reply
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Can you be more specific? What kind of angle? A geometric angle in your part, such as your honeycomb?
If is this you can create some shape design variables using HyperMorph.
This is shown in some of the tutorials for OptiStruct i believe.
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Altair Forum User said:
constraint and assign a value of 0.1 foe your 100hz.
how to perform this
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If You'reonly interested in exactly 100Hz.
- create a response for 'FRF acceleration (?)', for a specifoc frequency of 100hz.
- create a DEQUATION, and write your equation as a function of the f100. I.e: F(x) = some_equation_using_x
- create a response of type function (dresp2) and edit it, assigning the freq100hz as the main argument - equivalent to the 'x' in your equation. Activate it in the DRESP1L field and assign it to your frf loadstep.
- using the above response, create your dconstraint and assign a upper bound of 0.1
If you are interested in the peak value, you can change your first response, frf acceleration for some amplitudes, such as 'max'.
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Altair Forum User said:
If You'reonly interested in exactly 100Hz.
No, I interest in range of 10-100 Hz. but I would like to obtain a transmissibility value in range of 0.02-01 at frequency band of 90-100 Hz . it is meaning that the efficiency of my vibration isolators will be range of %80-90 .
Also I dont want to obtain second peak in 10-100 Hz
Do you recommend that I use the optimization software in optistruct? it is meaning that you dont recommend I dont use hyperstudy OK?
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Altair Forum User said:
reate a DEQUATION, and write your equation as a function of the f100. I.e: F(x) = some_equation_using_x
there is a analyticial equation. I'm not sure if it's useful
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for frequency of peak control, you can use directly modal analysis, and create a 'frequecy' response in OptiStruct and assign a dconstraint over it. Let's say, 10Hz <= Mode 2 frequency <= 100Hz.
For controlling your amplitude, you will use something similar to what i've described above:
- create a response for 'FRF acceleration (?)'
- create a DEQUATION, and write your equation as a function of the f100. I.e: F(x) = some_equation_using_x
- create a response of type function (dresp2) and edit it, assigning the 'FRF acceleration' as the main argument - equivalent to the 'x' in your equation. Activate it in the DRESP1VL field and assign it to your frf loadstep.
- using the above response, create your dconstraint and assign a upper bound of 0.1
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Altair Forum User said:
Also I dont want to obtain second peak in 10-100 Hz
I want to obtain the second peak outside range of 10-100 Hz it must be higher than 120 Hz (f2>120)
Altair Forum User said:create a response for 'FRF acceleration (?)
I've done
Altair Forum User said:- create a response of type function (dresp2) and edit it, assigning the 'FRF acceleration' as the main argument - equivalent to the 'x' in your equation.
I cannot this part anytime can you explain a bit more
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for frequency greater than 120, you just need to adapt the dconstraint for the freq2, then.
for function response:
- create a response for 'FRF acceleration', all freqs, selectiong your dof's
- create a DEQUATION (optimization>>dequation), give a name, and write your equation as a function of the f100. I.e: F(x) = some_equation_using_x
- create a response (optimization>>responses), give some name, select type: 'function' (dresp2), select your 'dequation' and click 'edit', assigning the 'FRF acceleration' as the main argument - equivalent to the 'x' in your equation. Activate it in the DRESP1LV field and assign it to your frf accel and respective loadstep. Then, return, and click create.
- using the above response, create your dconstraint and assign a upper bound of 0.1
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thank you for your all supports
I selected the solver as Modalfrf but I received an error as ' it is not compitable for this loadstep
the Modalfrf solver extracts both natural frequency and vibration amplitue, doesn't it?
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Not really..
In an analysis stand point, yes, you can obtain both frequency and amplitude from the frf curves.
But regarding optimization, frequency is only got from modal analysis loadstep, as a response.
The frf amplitude will be extracted from the frf loadstep.
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Altair Forum User said:
Not really..
In an analysis stand point, yes, you can obtain both frequency and amplitude from the frf curves.
But regarding optimization, frequency is only got from modal analysis loadstep, as a response.
The frf amplitude will be extracted from the frf loadstep.
then I have to use two load step, alright?
look, the last question, can I define constraint for spesific amplitude, at a spesific frequency ?
What kind of equation should I enter?
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You will need 2 loadstep. One modal and another frf.
About a specific frequency, that was exactly what i wrote a few posts before.
The equation will be always the same.
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Altair Forum User said:
You will need 2 loadstep. One modal and another frf.
I have two loadstep the first is normal modes and another one is direct frf
Altair Forum User said:The equation will be always the same.
Do you mean the equation on the graph? I added as a post before?
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at this time, I cannot sent rep I'm sorry I accesed daily limit
I added my model file /profile/97129-adriano-a-koga/?do=hovercard' data-mentionid='97129' href='<___base_url___>/profile/97129-adriano-a-koga/' rel=''>@Adriano A. Koga
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can you explain a little better what is going on with your model? what did you try? did an error occured?
i've noticed that you're running FRF direct in your model. This is very expensive.
I would use FRF modal instead.
For this I would change the EIGRL lower bound for frequency back to zero.
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Altair Forum User said:
i've noticed that you're running FRF direct in your model. This is very expensive.
you said that I would create loadstep; the first one is modal frf and normal modes, ok?
Altair Forum User said:For this I would change the EIGRL lower bound for frequency back to zero.
I receive this error
Can amplitude be calculated for a spesific mode? for example, The amplitude obtained at 3 times the mode frequency should not be more than 9 m/s2
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i've made a few modifications for testing.
Still didn't finish, but you might want to take a look at it and check the idea.
We better check how to make your model running more efficiently.
I've changed from direct to modal FRF and adjusted the extracted modes.
Also changed for EIGRA, as it is more efficient for large models.
Can amplitude be calculated for a spesific mode? for example, The amplitude obtained at 3 times the mode frequency should not be more than 9 m/s2
In theory you could. But it would complicate a little further your model.
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Altair Forum User said:
In theory you could. But it would complicate a little further your model.
No Problem, just wondering if we can do this on optistruct
can I do it?/How
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Just like your first function, dresp2 can be used to combine different basic responses.
So just follow the same structure to implement these.
There's another option that is dresp3, which can call excel, compose, fortran..but this needs some coding, although it gives you much more freedom.
Your model is too big..i couldn't run it in my machine.
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do you need such a big model?
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Altair Forum User said:
do you need such a big model?
I want to know how to realize what I wrote above
Altair Forum User said:Your model is too big..i couldn't run it in my machine.
I have big work station no problem
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I would suggest you first to get the current optimization ready, and then try to get more complete setup.
Crawl, walk and run approach.
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Altair Forum User said:
I would suggest you first to get the current optimization ready, and then try to get more complete setup.
then I dont need to dequation or dresp2
but it would be great! if I could what I deserved
There must be a way!!!
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