# Discussion Forum

## Help for Modal analysis of a nonuniform beam using COMSOL

 Topics: 4.3, Structural Mechanics
RSS feed   |   Turn on email notifications   |   4 Replies   Last post: October 11, 2012 7:22pm UTC

Lin Wang

October 10, 2012 10:30pm UTC

Help for Modal analysis of a nonuniform beam using COMSOL

Hello,everyone. I want to do modal analysis of composite blade using COMSOL. The blade will be represented as a series of beam element. My question is how to use COMSOL to build nonuniform beam, because the properties of each blade section is different.
I am grateful for any help.
Regards

Ivar Kjelberg

October 11, 2012 5:31am UTC in response to Lin Wang

Re: Help for Modal analysis of a nonuniform beam using COMSOL

Hi

can you make a series of adjacent volumes and give properties per layer ? Or do you have any more complex constitutive equations ?

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Good luck
Ivar

Lin Wang

October 11, 2012 12:19pm UTC in response to Ivar Kjelberg

Re: Help for Modal analysis of a nonuniform beam using COMSOL

The blade is divided by 20 cross sections. The cross section properties is show as follows:
mass per unit length EI
90.37 44200000
58.496 27595540
47.192 19615360
49.105 15821054
50.333 12799255
48.912 10427460
45.977 8427317
42.735 6826572
39.243 5550799
36.024 4462882
33.118 3589918
30.272 2821277
27.523 2221759
24.996 1677427
22.991 1264032
20.925 883482
18.628 625509
16.201 382064
12.871 239543
9.536 103000
6.1 103000
I use 20 beam elements in COMSOL to represent the blade. Each beam element is setted different material properties. However, the results for COMSOL do not agree with those from analytical method. I do not understand why.

Nagi Elabbasi
Certified Consultant
Veryst Engineering

October 11, 2012 1:36pm UTC in response to Lin Wang

Re: Help for Modal analysis of a nonuniform beam using COMSOL

Hi Lin,

You have 21 sections, so you need at least 21 elements not 20, right? In general however, you need multiple beam elements per section to accurately calculate the beam’s frequencies and mode shapes.

Nagi Elabbasi
Veryst Engineering

Lin Wang

October 11, 2012 7:22pm UTC in response to Nagi Elabbasi

Re: Help for Modal analysis of a nonuniform beam using COMSOL

Dear Ivar and Nagi, thanks for your help.

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