Learning Forum

[Sushant]

Hello, I am performing 2D modal analysis on a assembly of Elliptical cam and ball bearing, bearing is fitted on elliptical cam. I merge two blocks structural and modal analysis, in structural I am using two steps, Step 1: Frictionless contact is used with Add Offset, ramping effects between cam and inner race of bearing, at initial there is interface between two surface along Major axis and there is gap of 0.35mm along minor axis. step 2: Change the contact to Bonded. after these 2 steps I saw that there is small gap of 40 micron between surfaces along minor axis but Bonded contact status is shown closed or successfully bonded contact created between two surfaces.

After that performed modal analysis on this assembly, applied remote displacement at center of cam, only rotation in Z direction is allowed for Cam and restricted in Xand Y direction, I am expecting 1st mode with 0 frequency as just 1 DOF kept free in assembly. But in 1st mode shape, bearing fly off from assembly. I don't know exactly why this happened. Is that because of small gap between contacting surface this happend? If so, is there any way to closed that with any offset settings. Kindly guide me, so that I can correctly simulate problem and get expected results

note: If I take just elliptical cam without bearing and put same boundary condition, I get 1st mode with 0 frequency and rotating in z directio

attaching image of bonded contatct settings

 

[mohan.urs]

Hey,

Are you trying to conduct a pre-stress modal analysis ? If so you can use this link to know more about it here

https://innovationspace.ansys.com/courses/courses/modal-analysis-in-ansys-mechanical/lessons/how-to-perform-prestressed-modal-analysis-lesson-2-2/

If you are indeed using a prestressed modal can you share more info on the contact status before the modal analysis is performed ?

Thanks

 

[Sushant]

Thanks for prompt reply!

Yes, I am performing Pre-stress Modal Analysis. I have gone through that video, and understand that.

Static Structural : In this, as mentioned above using two steps for assembly of Elliptical cam and ball bearing.

                           BC's : Center node of CAM is allowed to rotate in  direction and in plane X-Y motion is fix

                           Contact : In step 1 uses frictionless, to solve interference. Step 2 applied Bonded contact between two edges

In Modal, I am expecting to get 1st natural frequency to be zero i.e rigid body motion about z. but it showing non zero frequency (373 Hz).

Before modal, contact status between CAM and Inner race of bearing is Bonded. (with gap of 40 micron along Minor axis (x-horizontal) and 0 gap along major (y-vertical). Does this gap causes any problem or not.

For more details about model, pleae go through Last msg again.

In pre-stress modal analysis, does modal block consider deformation after load step 2. cause I tried to search pre stress problem which has used 2 or more load steps in structural stage but didn't found any problem with 2 or more load steps on youtube and Ansys forum. Every problem has only 1 Load step in Structural part. Please clarify on this as well.

[Sushant]

Thanks for prompt reply!

Yes, I am performing Pre-stress Modal Analysis. I have gone through that video, and understand that.

Static Structural : In this, as mentioned above using two steps for assembly of Elliptical cam and ball bearing.

                           BC's : Center node of CAM is allowed to rotate in  direction and in plane X-Y motion is fix

                           Contact : In step 1 uses frictionless, to solve interference. Step 2 applied Bonded contact between two edges

In Modal, I am expecting to get 1st natural frequency to be zero i.e rigid body motion about z. but it showing non zero frequency (373 Hz).

Before modal, contact status between CAM and Inner race of bearing is Bonded. (with gap of 40 micron along Minor axis (x-horizontal) and 0 gap along major (y-vertical). Does this gap causes any problem or not.

For more details about model, pleae go through Last msg again.

In pre-stress modal analysis, does modal block consider deformation after load step 2. cause I tried to search pre stress problem which has used 2 or more load steps in structural stage but didn't found any problem with 2 or more load steps on youtube and Ansys forum. Every problem has only 1 Load step in Structural part. Please clarify on this as well.

[Sushant]

Reminder! can anyone help me in this