Hi

Maybe you want to take a look at this discussion?

https://www.researchgate.net/post/What_should_be_the_correct_boundary_condition_for_soil_when_accl-time_history_analysis_is_attempted_in_ABAQUS

Sincerely

Claes

Hi claes

thanks for your attention. I visit the page but I can't find any to my problem.the advices were  general. I want to know how can I model the soil and it's boundary in ABAQUS, exactly!

Best 

Hi

I believe the answer boils down to using a matrix of dynamic stiffness functions on your boundary.

You

• Use analytical functions for the 'green field'
• Exctract data at the cavity of your dig and/or surface of your interface
• Invert the matrix that is output from the above (one inversion per frequency)
• Insert the inverted result as BC to your Abaqus model
• Analyze the response using direct matrix solution

The above can be rather time consuming, so it may be worth your while to see if you can make some shortcuts, e.g. by the use of reciprocity. It all depends on your analysis purpose.

Sincerely

Claes

Dear Claes. 

thanks alot for your advices.I try to do it..

Hello Azadeh

That's easy first model your parts than for the infinite part assign C3D8 then write input  and in the input file change C3D8 to CIN3D8

Be aware that for the infinite part you have to use sweep mesh and the arrow should be outward

Regards

Hamed

Hello Hamed

Thank you for your sugestions.

As you said I do your procedure for CIN3D8 except the sweep mesh! after I run the sample,It's not seem any problem exist!!

Would you please describe why should I do sweep mesh?                                                  

I await your response in kind

Hello Azadeh

Well you normally use infinite element for seismic affairs so in these cases the wave direction is very important.

By using sweep mesh you let  the seismic wave go freely in that direction.

Regards

Hamed

Thanks alot Hamed

You mean that according to my earthquake direction (X,Y,Z or multicomponent), I should use sweep mesh and then check the arrow of that to be in my earthquake direction?

Hi

Yes exactly. if you are applying the seismic forces in just one direction that would be easy otherwise  it would be a bit difficult.

Regards

Hamed

Thanks for such valuable information sharing with me.

Sincerely

Azadeh

Hi Azadeh

See following link, its can be very useful 

https://www.linkedin.com/groups/Abaqus-Use-3D-Infinite-Elements-3958425.S.194473817

Best Regards

Alireza

Hello Alireza

Thanks for your sugestion.

Hi

I may be wrong here but to the best of my knowledge, infinite ('perfectly' absorbing elements) exist only for acouustic waves (Pressure-waves), while soil involves more wave types.

Aligning the mesh to be normal to the wave direction is good avice but I believe it cannot handle more than some situations as infinite elements handle most situations for the acoustic case.

Therefore, the much more laborious procedure where you use matrices as described above is the general procedure. Than again, if a simple mesh adapations is good enough, then you should use it.

In this spirit, here (see Figure 3) is another approach to model absorbing boundaries. It is simple to make but computationally costly. http://qringtech.com/wp-content/uploads/2014/01/SPIE205933-18.pdf

There exists also the FE code calles Code Aster which uses a 'rubber band mesh' on the boundary to, as best possible, absorb impinging waves. Code Aster has implemented the coupling matrix approach to a French analytical code for layered soils. http://www.code-aster.org/V2/spip.php?rubrique2

Sincerely

Claes

Hello Claes

Thanks for your attention.you mean in the soil problem it's better to use absorbing boundaries than infinite elements?

I really don't know what should I do.

Hi

As far as I understand, a matrix on the boundary is the general method. Physical modelling as shown above using 'absorbing wedges' handle more wave types but leave some reflection. Infinite elements for one wavetype is bettwer than rho*c boundary conditions (rho*c corresponds to diagonal matrix, while the general approach involves a full matrix).  The Code Aster 'rubber band' boundary mesh relects but is easy to work with and allow introduction of impinging waves as loads. 

The 'best' approach is the one that works for you. What works for you depends on what you want to do and how well you have to do it.

Sincerely

Claes

Hi

Code Aster contains a coupling to a code calles MISS3D which implements the matrix method. Here is PhD thesis on the subject http://www.theses.fr/2013ECAP0006/abes

If you are running a very large model, the matrix method probably is your best bet. I was invoved with a project where we used this approach and still had to use a local supercomputer for the analysis.

Feel free to drop me a mail if you want to try Code Aster instead of Abaqus.

Hope this helps

Claes

Dear Claes.

thank you so much for your responses.

would you please give me your email adress ?

You can mail me via Researchgate.

/Claes

Hi

I advice you to see the document. You will find what you need.

Best regards

http://imechanica.org/files/Pichler_TUHH_final_2222012.pdf