natural frequency issue 1

[jc9005]

hi all,

trying to validate a model that has been testing in real life to gain the first natural frequency.
I know what the results should be and for what mode.

but any attempts to create a frequency job in abaqus to output the same results isn't successful.

its an imported igs file, ive followed various tutorials with my own properties bc's etc.

the main problem is the output results in abaqus are very small in terms of Hertz... whereas the real life test was 5kHz which is proven.

Any common issues I should look out for with solid models and natural frequency jobs?

if any pics or further info is require happy to supply!

Thanks in advance.

 

[bkal]

Some pictures and details about material properties used would help. There are so many reasons why your FE model could be wrong,the most obvious ones are:
- have you specified correct boundary conditions,
- are your material properties correct, have you used a consistent set of units (I would recommend kg, m, N and their combinations),
- assuming that your geometry is correct, is the mesh type / density adequate,
- check if ABQUS has given any warning messages for further information.

 

[jc9005]

hi bkal,

im only to the point of asking here now as my lecturers and tutors cannot even help me anymore.

the part is in the image attached with these conditions..

the boundary conditions are encastre in initial step. at either end of the part in the through holes
material props (6082 Aluminium) are entered like below:

density 2700
youngs mod: 70000
poisons: 0.33
yield: 310

meshed at a seed of 4
part drawn in solidworks in MMGS

no error messages from abaqus either.

 

[bkal]

It seems that your stresses and Young's modulus are in N/mm^2 and your density is in kg/m^3 - these are not compatible. What are your dimensions in , mm or m? ABAQUS is not unit aware, so you need to ensure that the units are compatible.

I suggest you use as follows:
- length - m
- density - kg/m^3
- Young's modulus, stress - N/m^2

or, alternatively:
- length - mm
- density - tonne/mm^3, i.e. 2.7E-9
- Young's modulus, stress - N/mm^2

 

[jc9005]

Thanks for your help.

turn out that the density was causing some issues.

some trial and error with the step manager and I have my results!

Thanks Bkal!