Learning Forum

[murali]

Is it possible to obtain the frequency response of a cantilever beam to an initial displacement. Or only time domain results are possible?

[Erik Kostson]

Hi
In your initial question you pulled it up (that is what you mean with initial displ. you said) and you release to see the free vibration. That was a transient analysis as it is a transient event (pull and release, followed by free vibration).

Now if you have a harmonic event like say we move the fixed end of the beam up and down with a sinusoidal displacement then we can use a frequency domain harmonic structural response. We have a course on that, so you can see how it is done.

All the best

Erik

 

[murali]

 

Hi Erik,

Yes I meant the same. Can you please share the link of the course? I would like to know the principles behind adjusting the  analysis settings and other parameters in harmonic analysis. Thanks in advance. 

 

[Erik Kostson]

Hi

What do you mean by "I meant the same" - do you mean that you want to excite with a sinusoidal excitation (say displ. or acc., or force)? Please be more clear when describing what you want to do as that will make our feedback back to you better.

 

In that case here is a course:

/courses/index.php/courses/harmonic-analysis-of-structures/

All the best

Erik

[murali]

Yes, i meant introducing a sinusoidal displacement input. Thanks for the link.

On a different note, is there any way to convert the frequency response thus obtained into time domain?

[Erik Kostson]

No - that is not possible.

All the best

Erik

[Erik Kostson]

Another course is the msup harmonic:

/courses/index.php/courses/mode-superposition-method/

This explains how to set up a base excitation like you might need:

/forum/forums/topic/base-excitation-harmonic-analysis/

 

[murali]

Thanks a lot Erik. I have another question, is it possible to obtain an amplitude-frequency and phase-frequency response from the time domain result of the transient problem?? Like we do in matlab??

[Erik Kostson]

 

 

Hi

No that is not possible – you can bring it into CFD Post (create a Chart there and use Fourier Transform option),

or even excel (FFT):

https://www.youtube.com/watch?v=nbj18E4q1uA

All the best

Erik

 

 

[murali]

Ok. Can I use the transient conditions (lifting the free end and releasing it) to conduct a sine sweep in Harmonic analysis? Would it be successfull?

[Erik Kostson]

Lifting and releasing is not a harmonic sinusoidal load, so of course not - please go through the courses in harmonic analysis to understand this type of analysis.

Closing this post as we have changed many different topics/questions - open a new one should you have any other questions please.
Thank you
Erik