Updates to SLFFEA

Updated 12/31/08

Here is a summary of the updates as of 12/31/08:

Version 1.5 is finally here.

You can get it at the download page. There are major additions in terms of adding non-linear large deformation elements. These new elements are based on the work I did with the brick element. Here is a summary:

Science Code Changes

Expanded the double curved shell to handle triangle elements. The 4 node shell element can now handle 3 nodes. One problem though is the execssive stiffness I encountered with other triangle elements. The 3 node version should therefore be used only to get qualatative results. The data for a 3 node element is essentially the same as a 4 node element except that the element connectivity listing 3 nodes.
Added several non-linear(large deformation) codes and cleaned up the brick and truss non-linear codes. So now it is possible to use the conjugate gradient method as well as dynamic relaxation. The following elements now have non-linear counterparts.
As with most non-linear FEA software, these calculations require a little art in the selection of parameters which will keep the program stable as it iterates toward the solution. Determination of when convergence is reached as well as the choice of time step and damping so that the calculation is stable are considerations for which users will have to carefully decide.
I have changed the format of the non-linear input file files so that the parameters are better labeled as well as some additional features. The input file looks like:
```
dynamic relaxation(DR) or conjugate gradient(CG) method ( 0 = CG, 1 = DR )
1
number of iterations for DR or CG
20000
time step for DR
1.0
damping constant for DR
.02088
stress calculation for CG (Lagrangian = 0, stress updating = 1)
1
```
Most of the above should be clear, except for the "stress calculation for CG" which tells whether the stress should be calculated based on "stress updating" or whether calculated at the end using the final displacements. I compared the results for both with dynamic relaxation which only uses stress updating and neither method matched more than another.

Graphics Code Changes

The graphics codes for the shell has been modified to display the 3 node elements.

I have also added a few new mesh gererators which will also be included in SLFMESH-1.5. They generate meshes for a brick hose element and wedge loop and spring elements.

Go here to see the previous update page listing the modifications leading to Version 1.5.

Go here to see the previous update page listing the modifications leading to Version 1.4.

Go here to see the previous update page listing the modifications leading to Version 1.3.

Go here to see the previous update page listing the modifications leading to Version 1.2.

Go here to see the previous update page listing the modifications leading to Version 1.1.

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