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Post 1 of 4

Seismic Tank Sloshing

259 Views, 3 Replies
10-07-2014 08:23 AM

I work for a company that do simulations for oil tanks...In the last days we test CFD simualtion because we wanted to do the simulation of sloshing of a tank when a seismic load is applied. A natural frequency study is not enought for this simualtions and we require a more precise simulation.

 

As many people ask in the forum of how to setup free surface simulations and I believe that the tutorial of CFD is not clear enough I'm Going to explain how I did the simulation.

 

My first step was to get the accelerations in X,Y,Z for a specific earthquake. I download the files from http://peer.berkeley.edu/smcat/search.html

I suggest these files http://peer.berkeley.edu/svbin/Detail?id=P1083 you have to download the accelerations of UP,NS,EW they are equal to X,Y,Z.

 

The file are read from left to right  and up to down with a time between measure of 0.005 second and the values are in g. to use this data in CFD it is need to translate the information into a simple column and mm/s3. I am attaching a small xls that i wrote to process the data.(to paste the data use the paste assitant of excel)

 

I create the model in Inventor and exported to autodesk CFD.

 

i set the fluid as diesel.

I set the upper boundary as 0 pressure surface and the low volume as initial heogh of fluid.

Know we can setup the free space model.

Solve/physics/free surface

 

set the gravity in the direction you want in my case is 0,0,-1 and I set the tables of accelerations . The first step to set the tables is to save a blank file . that file is going to be your base *.csv file where you are going to paste the yellow data of my excel after editing that file in excel you can import the file to CFD

 

You have to do the same for all axis. place the files inside of the same folder of the design number in my case design 1 folder.

The time step size has to be less than 0.005 s or the simulations is not going to be good.

 

The only question that i couldt solve is how to obtain a good surface mesh between the volumes i want a inital flat surface.

However the results are good

 

 

If i am doint something wrong please comment and let me know.....This is the first time that i do a simulations of this type and is only a test for future projects. If you know how to obtain a good flat initial surface between the volumens please let me know....

 

 

 

Wilmer Ariza
Researcher Control and SI with AI for autonomous underwater vehicles
PhD student(Australian Maritime College-University of Tasmania)
Master of engineering (Advance Manufacturing Technology- Swinburne University of Technology)
Mechatronic Engineer
Post 2 of 4

Re: Seismic Tank Sloshing

10-07-2014 08:40 AM in reply to: arizawilmer

Thanks for this, nice idea :)

 

Could you try adding more mesh to the simulation? It looks like this might be the answer. Typically we refine just where the free surface is but yours is going to move pretty radically so you may end up needing a good uniform mesh throughout the model.

 

Thanks,

Jon

Post 3 of 4

Re: Seismic Tank Sloshing

10-07-2014 11:36 AM in reply to: Jon.Wilde

 

 

in the test i did that but i continue having spyes in the model and i can not get a flat surface. at the start of the simulation.

 

and if i carry the mesh to a high level(manual 500mm per element-my tanks has 30 m od diameter) i get

 

The spykes only get smaller but they do not disappear.

 

Is there any way of meshing the surface to get a smooth flat surface between the volumes?

 

Wilmer Ariza
Researcher Control and SI with AI for autonomous underwater vehicles
PhD student(Australian Maritime College-University of Tasmania)
Master of engineering (Advance Manufacturing Technology- Swinburne University of Technology)
Mechatronic Engineer
Post 4 of 4

Re: Seismic Tank Sloshing

10-08-2014 07:36 AM in reply to: arizawilmer

Hi,

 

I do not think so, no. All we can do it use the additional mesh to reduce the spikes.

Happy for someone else to comment to prove me wrong but I'm sure that is the case.

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