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random response analysis

hi sir,

these are different load collectoes defined in random response analysis tutorial they have explained about randps and tabrnd1 can u please tell what values are defined in other load collectors and they used two load steps(load1 and load 2) can u pls explain about that also??

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Altair Forum User

@jahnavi

RANDOM takes RANDPS. RANDPS takes loads (excited load and applied load... FRF) and TABRND1 which refer to power spectral data.

Altair Forum User

they have defined total of 10 load collectors FREQ156, R , Rload2 , TABLE , SPC , force , FREQ 257 , DAREA2 what did they define in these load collectors ? why do we need force when we are defining psd??

Altair Forum User

Jahnavi,

Can you share the video link?

Altair Forum User

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=video&cd=1&cad=rja&uact=8&ved=0ahUKEwj83ITh4OTSAhXLRY8KHdO2C7YQuAIIGjAA&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DbNdQFfn1EpQ&usg=AFQjCNF5y8ID-fmWg10UWcCCVIVIXNQWvg

Altair Forum User

in that at 1:16:45 they did random respone analysis

Altair Forum User

Jahnavi,

There are number of loadcollectors to define multiple loads. Load can be in any form, like velocity, load, acceleration etc...

The total PSD will be a sum of PSD responses of individual loads. These loads can be same or different.

Altair Forum User

hi sir ,

In my problem i don't want to constraint my model, i want to give psd at some nodes allowing them single dof i.e base excitation

i have doubts at each step can u pls clarify them

my input is only acceleration psd or displacement psd over a range of frequencies

1. I will give only SPCD not spcs. in spcd what is that displacement mean? i want to change the displacements over a range on frequencies i.e psd.how can we give acclerations in spcd instead of displacement?

2. then a tabrnd1 is created. after that randps is created. what should be specified in J?? is that spcd??

3. what is the difference in acceleration given at spcd and tabrnd1??

Altair Forum User

Jahnavi,

Displacement means enforcing the node to displace by a certain magnitude. In RLOAD you can change to Acceleration.

Since you have only one load specify the same for both J and K

If you have given a value of 5 in SPCD for instance, it will be used as a factor in tabrnd1.

Altair Forum User

I want to accelerate 58 nodes in xyz direction as 1g,1g,1.5g.

I defined this acceleration through spcd card in one load collector only.

However if I changed the starting location of node for defining spcd my results are varying.

I have also used Tabled1 for defining acceleration in xyz direction.