Modal analysis problems in Abaqus

r08521221 · February 27, 2021, 01:36

Hello everyone,

I'm doing modal analysis in Abaqus (step type: frequency).

Yet the results seem to have some problems.

The picture below is mode 1 shape.

https://imgur.com/bMzpCTO

The result is wrong, it seems that most elements are not deforming.

Normally, it should be like this:

https://imgur.com/HFOdUEU

Boundary condition at the bottom: (fixed)

https://imgur.com/KM6gx9t

I've checked everything, boundary conditions, interactions,....

Still I couldn't find where the problem is.

Need your kind suggestion and guidance, thank you very much!

karachun · March 3, 2021, 17:14

You have some parts that are not connected to the main structure. These parts can move freely and exhibit rigid body modes.
Carefully check deformed mode shape and determine what part is not connected to structure and fix it.

February 27, 2021, 01:36	Modal analysis problems in Abaqus	#1
r08521221 New Member Chuan-Hsiu Lo Join Date: Feb 2021 Posts: 1 Rep Power: 0	Hello everyone, I'm doing modal analysis in Abaqus (step type: frequency). Yet the results seem to have some problems. The picture below is mode 1 shape. https://imgur.com/bMzpCTO The result is wrong, it seems that most elements are not deforming. Normally, it should be like this: https://imgur.com/HFOdUEU Boundary condition at the bottom: (fixed) https://imgur.com/KM6gx9t I've checked everything, boundary conditions, interactions,.... Still I couldn't find where the problem is. Need your kind suggestion and guidance, thank you very much!

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Modal Analysis in CFX	Aashi171185	CFX	2	January 11, 2019 09:48
Modal Analysis of a MEMS cantilever	hereford_jon	Structural Mechanics	0	March 21, 2018 10:01
ANSYS Workbench - Modal Analysis of Model Floor	zchini	Structural Mechanics	3	March 19, 2018 11:11
Applying mass for modal analysis	gajjar	Structural Mechanics	3	September 25, 2017 02:36
Optimization using modal analysis failing	Miguel_2661	ANSYS	0	May 20, 2013 12:36

March 3, 2021, 17:14		#2
karachun Senior Member Join Date: Nov 2015 Posts: 244 Rep Power: 11	You have some parts that are not connected to the main structure. These parts can move freely and exhibit rigid body modes. Carefully check deformed mode shape and determine what part is not connected to structure and fix it.