boundary conditions to absorb waves

[steelix]

I am having model where a wave is traveling. the waves should continue to travel through the body (soil) without coming back . in other softwares this is done by usiing infinite elements or dampers and springs. I know I can add springs in autodesk sim for dynamic analysis but how about dashpot dampers. or if there is any other suggestion please provide with source and reference because this is for a masters research. feel free to ask for any further details.

thanks

[AstroJohnPE]

Hi steelix,

You can define dashpot elements using the analysis type of "Nonlinear > MES". I think that is the best (if not only) option.

[steelix]

thanks for the reply it is really helful and a first step in acheiving what I want. 

I can see that I can specify the element type as a spring and as dashpot. please would you tell me how to add such elements to the surface of cube, instead of the fixed x y z constraints, the spring and dashpot should exist in each node of the mesh at the surface. 

thanks,

[AstroJohnPE]

The main thing to keep in mind is that the FEA Editor just works with lines. It uses some "tricks" to make you think that you are working with elements, but it is really just individual lines. As long as the lines represent the geometry you want, it does not matter how the lines get created (drawn, copied, created by an automatic mesher, etc). Once you run the simulation or do a Check Model, what you see in the Results environment are the elements that are used in the analysis.

So, you need to create some lines for the spring and dashpot elements. How about using the "Draw > Line" command? That is certainly the easier concept to understand but not very efficient if many elements are required.

Otherwise, the commands of the "Draw" menu provide other methods of creating lines. Which command or commands you use depending on what the geometry needs to be. For example, you could:

1. If the mesh were uniform, you could draw one line, and then copy it N times in one direction and M times in the other direction.
2. select the lines on the surface of the cube and copy them some distance. There is an option on the copy command to join the original selection and the copy with lines. These joined lines would then be defined as the dashpot elements. (The copy of the original surface would then be deleted since those lines are not needed.) Of course, the joined lines need to be on a different part number so that you can define the element types.
3. connect the nodes on the surface of the cube to a point or points out in space using the "Contact Elements" command.