Learning Forum

[chiheb ben abdallah]

hello,

i want to perform a dynamic analysis where a sinusoidal force is applied on semi-trailer initially subjected to static loads. i did a static structural analysis then a modal analysis to extract mode  shapes and natural frequencies. i modal analysis, i used static structural as pre-stress.

 the purpose of the simulation is to investigate the occurence of resonace . i tried a transient structural analysis but i don't know whether it is the correct choice or not. i have 3 questions:

which type of dynamic analysis should i perform?

how to know wether the dynamic analysis was performed on the deformed structure from static analysis or not?

how to know whether resonant vibrations occur or not?

can anyone help me please. 

  

[Chandra Sekaran]

Since you mention you have a sinusoidal load (specific frequency or a range of freqeuencies) you can probably do a harmonic analysis instead of the transient unless you are interested in transient effects at the beginning of the load or end of the load. The harmonic analysis will give the steady state response of the structure under sinusoidal load at a particular frequency.

The way you have set up the modal analysis will be based on the deformed configuration from the static analysis and will take into account the stress stiffening effects due to the stress in the static analysis. Then the subsequent mode superposition transient/harmonic analysis will use these modes. However the thing to NOTE is that the stresses from the static analysis are not included in the transient or harmonic results. Only the mode shapes are used. So you may need to add the static results to the transient results or harmonic results separately using solution combination.

The resonant conditions occur when the applied force's frequency matches the natural frequencies of the structure and if the mode shape has components in the direction of the applied force. This will be obvious in a harmonic analysis when you plot the structures response vs frequency. In a transient this may not be obvious but is taken into account. You can see it by comparing to a static analysis with that load or with differnet amounts of damping.

[chiheb ben abdallah]

hello chandra sekaran

thank you for answering,

 i did a modal analysis and i set 'static structural' is pre-stress and it worked well. when  i tried to perform harmonic analysis and i set modal in initial conditions , the simulation failed and the warning message 'one or more contact regions has been defined as non linear contact' appeared. can you please tell me how to solve this problem and how to do solution combination?