Base Motion in Modal Based Frequency Response.

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.

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

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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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.

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.

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.

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.

Unable to find an attachment - read this blog

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. /emoticons/default_sad.png' srcset='/emoticons/sad@2x.png 2x' title=':(' width='20' />

do you need such a big model?

I would suggest you first to get the current optimization ready, and then try to get more complete setup.

Crawl, walk and run approach.