Problem in Dynamic Analysis

[Sayan]

Hi Elmer and Team,
I am an amateur in this software. I am trying to solve a problem of forced vibration analysis of a cantilever beam. After constructing my model and generating .sif file I am getting eigenvalues appropriately but the displacement field is not showing good displacement results when opening it with Paraview. Also, I am finding it difficult to apply harmonic boundary force. If anyone please help me in this regard to find the problem in my .sif file, it will be helpful for my research work. Also please guide me how can I apply harmonic load and get displacement results for a given time range.

[kevinarden]

I deleted the results solver and let it write out the default results

displacement mode 1.png

(28.21 KiB) Not downloaded yet

[Sayan]

Thank you so much for your reply...I tried to generate solution after removing result solver..But in my case, it's showing
"ERROR:: LoadInputFile: Unknown specifier: [0.001]
ERROR:: LoadInputFile: In section: [material 1]
ERROR:: LoadInputFile: For property name:[rayleigh beta]"
Is there anything that also I need to change to generate results?

[kevinarden]

Needs to be

Rayleigh beta = real 0.001

case.sif

(2.01 KiB) Downloaded 226 times

[Sayan]

Thanks,,,,it's executing now.. I need little more help regarding the use of tx variable,,,,,as i want to get some displacement results within a time range for this forced vibration problem,will you please suggest me how can I define the time range? And in this case though i have used tx variable, but not defined time range, still results are executing for different harmonic modes,,then what value elmer is using in place of tx variable?

[Sayan]

Hi,
In relation to the previous problem, I just checked by removing assigned forces, the force assigned in boundary condition 2 and body force is not actually participating in the displacement field calculation, as I have got the same results even after removing forces. Is there any suggestion for this? I tried many times to analyze the beam with an applied dynamic force.. But only modal displacement is being evaluated...But I need displacement value against time due to applied sinusoidal force.,,,Please help me with this issue...

[raback]

Hi

If you have applied sinusoidal force of known frequency you should be looking for harmonic analysis. Eigenmode analysis is not related to some specific frequency as eigen frequencies are part of the solution.

When using harmonic analysis the force is not a function of time. It is just the real component of the force. You can solve a harmonic system also as a time-dependent solution but if your solution is purely harmonic that may of course be an overkill.

-Peter

[kevinarden]

In a steady state harmonic analysis there is no time variable so perhaps tx is zero. Force as a function of time would require a transient analysis.
In a forced vibration modal solution, the force is generally applied as a function of frequency.

[Sayan]

Hii,
Thanks to you for helping me with your expert comments..I am learning a lot from you.. Still as I didn't reach my goal, I am willing to learn more from you which will be useful for my work,,,I am explaining the problem statement so that I can clearly state my questions:
One cantilever beam of dimension 0.58x0.02x0.002m is subjected to a dynamic udl 1.5sinwt Newton along vertically downward direction,w=41.88rad/s; My goal is to find out the displacement at midpoint at time 24.6 to 24.8 with a timestep 0.1s considering geometric non-linearity...Beam material is having rayleigh damping factor beta=0.001.... To find out this what modifications are required in the following .sif file which I attached for your kind perusal..I am finding errors and also its not clear how will I get results at a specific time in the output file. so i request your kind help in this regard..I also checked one option that is geometric stifnness ,,Probably it takes into account geometric non-linearity in the calculation....If it's not so please make me correct....

___Sayan

[kevinarden]

Eigen Analysis = False

This is a direct transient approach in the time domain.
Everything you are asking for is in the time domain, so make the Eigen Analysis false, it is not required in this case. The transient analysis will output the solution for each time step interval since you have.

Output Intervals = 1

It is possible to do a modal (eigenvalue) analyses, then use that modal solution to do a time domain transient, but I am not sure Elmer supports that. I believe the eigen value analyses with the harmonic option, keeps everything in the frequency domain.

also there was a typo on this line

Force 2 =Variable time; Real MATC "-129.31*sin(41.88*tx)"

it should be a semi-colon which means the rest is a next line. It could also be written this way

Boundary Condition 2
Target Boundaries(1) = 3
Name = "BoundaryCondition 2"
Force 2 =Variable time
Real MATC "-129.31*sin(41.88*tx)"
End