I have a SS beam (Solid C3D8R), I did frequency analysis and obtained each mode. Then I tried to replace the boundary condition with Spring elements (connected to Ground) to replicate the same frequencies. Regardless of No. of DOF and stiffness value I define, I get same frequencies! The model is sound and has no error.
The reason I am Interested in Spring is to find out the fixity of support, because sometimes the full fixity does not match the experimental boundary conditions, which is the case for me. Hence, I need to use Spring Elements in order to find out the approximate fixity of my boundary condition to match with experimental frequencies.
Cheers,
boundary conditions are nothing but grounded springs with infinite stiffness. If your chosen value of stiffness is already very large, further increasing the stiffness will not make any diference as infinity in numerics is relative. Try using very small stiffness for springs and see what happens (or very small stiffness at just one end springs)
Hey Abhimanyu,
Thanks for your input. I did change the stiffness values (up to 0.5 N/m) and strangely I did not get any difference,that's why I am confused.
how are you applying ss bc and springs....what's the bending stiffness of your beam (EI/L^2)
I figured it out, it was due to some issues in the DOF of the spring properties, which I matched with analytical solution to get the changes due to variation in spring stiffness.
Hey,
I'm a beginner to abaqus and myself am trying to do modal analysis of a beam that instead of cantilever, is connected using a spring. but I want the boundary condition to behave as a rotary spring, what should i take the dof if i'm appying the impulse in radial direction at the end of the beam ?
Aditya,
I cannot remember the DOF options on top of my head; but to achieve that you need to release the rotational DOF.
You can experiment that by first doing fully fixed beam and checking the natural frequencies by hand calcs so that your model is sound. Then place the springs at each end and release the required rotational directions.
Cheers,
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