Stress in Modal anaysis

raju mandal

Hi,

Can anyone tell me the importance of stress output from the modal analysis??

Thanks in advance for any help

Altair Forum User

I dont know much,but if i were you,i would ignore it.

Altair Forum User

i'm not sure but i think it gives us the peak stresses when in that mode shape an natural frequency. modal analysis means eigenvectors and eigenvalues, so those stresses occurs when in that mode.

Altair Forum User

Hi Raju,

 

           If you are doing normal modal analysis means you can only get displacement as result output, if you are practicing modal transient or modal frequency simulations you should go for stress contour.

     

            In that condition solver will give both frequency and stresses. what you have to do means:

 

#1 - Check at what frequency maximum stresses are occurring ( that can easily predicted by generating graphical curves )

 

#2 - Choose the respective frequency to display the result for that particular frequency and check for the stress region in that frequency

 

#3 - Then import your normal modal analysis results and check for the structural behavior at the frequency ( in which max stress occurred ), in that if local mode shapes are occurring means the design change should your first option.

 

 

I follow this procedure. Is there any better option means share with me. /emoticons/default_dry.png' alt='<_<'>

 

 

Thank you

 

Arun 

Altair Forum User

In a modal analysis the value of the displacements and stress outputs must be ignored. This type of analysis only computes the modal frecuencies and shapes.
Harmonic or random vibration analysis (for example) use the information of a modal analysis to calculate the responce of the system to a certain frequency - responce which includes displacements and stress.

raju mandal

Thank you all for your replies

Altair Forum User

I am having this error while doing a random vibration analysis.. any idea how to resolve this error please ?

Messages for the job:

 
 *** ERROR # 2813 ***
 TABRND1 referenced by RANDPS data returned a negative value for each
 frequency. This is probably due to extrapolation of the TABRND1 data.
 No results can be calculated.
 
 *** PROGRAM STOPPED: FATAL ERROR(s) ENCOUNTERED.

Elangovan T

Altair Forum User said:

I am having this error while doing a random vibration analysis.. any idea how to resolve this error please ?

Messages for the job:

 
 *** ERROR # 2813 ***
 TABRND1 referenced by RANDPS data returned a negative value for each
 frequency. This is probably due to extrapolation of the TABRND1 data.
 No results can be calculated.
 
 *** PROGRAM STOPPED: FATAL ERROR(s) ENCOUNTERED.

hi bro.. Have you got answer for this question?

Please share the answer as i am getting same issue

Arul

Hi Elangovan,

 

Can you share the .fem file ?

 

Regards,

Arul

alper_21686

Hi,

I try to random vibration analysis on hyperworks with optistruct (tool/Freq Resp Process/random PSD). 

It seems to work, but stress levels are extremely low.

I think, this problem is about mass elems, contacts or cards used in the model. 

My model can be seen on this messages. Can you check pls ?