Learning Forum

[kamalkrishna]

I am doing response spectrum analysis.i did modal analysis,first natural frequency is 457 Hz.i took sufficent modes so that sum of ratio of effective mass to total mass is 0.9. I gave displacement spectrum input as 2.5 mm up 10Hz,10-20Hz 0.68 mm,20-25Hz 0.45 mm,25-30Hz 0.28 mm,30-33Hz 0.23 mm.I kept on missing mass effect and rigid response.In the result i got stresses like 2000Mpa.My first natural freq is 457Hz.is it possible or i did any mistake.

[peteroznewman]

 

@kamalkrishna

It’s very common to have stress singularities in a model. An example is a sharp interior corner. If an interior corner is the location of the maximum stress, you can modify the geometry and blend that interior corner with a radius. Locally mesh that new blend face with elements small enough to put at least two elements across the new blend face and the stress will be reduced. There are many other ways to create a stress singularity. Please reply with an image of the mesh where the maximum stress occurred.

 

[kamalkrishna]

Thank you sir for your reply.

I work in a company so i can not share any photograph.Ignore my previous query.I am doing RS Analysis for single body looks like cylinder weighing 272 kg,it has 8 holes,i gave fixed support for those.the body contains 182210 nodes,111587 elements,0.81 avg  element quality,0.264 avg skewness and my first 10 natural frequencies are 274.77,432.69,467.98,522.82,621.35,672.53,782.26,820.74,839.13,843.46 and it ranges up to 9050 Hz ,300 modes were extracted,mass participation ratio 0.95 ratio in z direction,same loading condition as above,i got max stress at holes(fixed support) 669 Mpa,avg stress of body 95 Mpa,min stress 15 Mpa,i have continues stresses around 200Mpa over comparable area,i kept rigid response effect to off,i got top of the body directional accerlation min 13515 m/s2 and avg 38887 m/s2,max dir acc 101580 m/s2 in z direction.i used SRSS as mode combination method and i am pretty sure it is not because of stress singularity (due to meshing).

I have doubts that is the simulation is correct and which type of mode combination method i should use,if rigid response effect is on what should be Rigid response effect freq begin and end.

i am using licensed version 2022 R1