July 26, 2023 at 6:41 pm
July 27, 2023 at 2:30 pmDave LoomanAnsys Employee
So you are modeling a simply supported beam bending in the yz plane? What is your theoretical mode 2 frequency? What does the mode 2 shape look like?
July 28, 2023 at 3:44 amAbhishek ChauhanSubscriber
This is the Ansys Value
Calculated value analytical
Ms excel is calculated from formula of different mode and i want this frequency
As the model is extruded z-plane and uses remote displacement with y rotation free and the rest are fixed.
Kindly give way to find the correct values of natural frequency and reply asap
July 28, 2023 at 2:30 pmDave LoomanAnsys Employee
The problem is you have a simply supported beam in the XZ plane, but a fixed-fixed beam in the YZ plane. If you display mode 2 you will see that it is in the YZ plane and is the 1st fixed-fixed mode. Mode 3 is the 2nd simply supported mode. The mode 3 frequency may be slightly smaller than an analytical calculation because the analytical formula might not include the rotary inertia of the cross-section (may assume the mass is concentrated at the centerline) and may not consider shear deformation. To get rid of the fixed-fixed modes you could create the cylinder in 4 quadrants so that you end up with a line down the centerline and then constrain that line in the Y direction.
July 29, 2023 at 5:34 amAbhishek ChauhanSubscriber
Sir, then I have to make a cylinder on which plane and which rotation i have to free in remote displacement .
Kindly elaborate please help........
July 29, 2023 at 2:49 pmDave LoomanAnsys Employee
Every thing else would be the same except you would scope the remote displacements to the 4 quarter faces now. Another ideas is to just model half the cylinder cross-section and constrain UY at the two faces at y=0 to zero.
August 2, 2023 at 7:13 amAbhishek ChauhanSubscriber
I do not understand can you give the steps on how to rectify this?
I tried many times but did not get any method can you the way with steps and examples please.
August 2, 2023 at 2:16 pmDave LoomanAnsys Employee
What have you tried? Modeling a half the cross-section? Why didn't that allow you to constrain UY? If the fixed-fixed frequency is bothering you, don't constrain ROTX at the ends. Then you will get duplicate simply supported modes.
August 3, 2023 at 1:57 pmAbhishek ChauhanSubscriber
As i tried half cross-sections by using the named selection mesh node but it is also not working.
As I used avoid rotation x also it is not working.
can you tell me the other method or give any reference?
August 3, 2023 at 2:17 pmAbhishek ChauhanSubscriber
Is the any way to find the required natural frequecy.
August 3, 2023 at 2:18 pmDave LoomanAnsys Employee
If you created a half model there should be 2 faces at y = 0 that you could apply a displacement to. I don't understand why you would need a named selection mesh node. A simpler way to model a beam is with beam elements.
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