Is your problem taking 7-8 hours because the iteration is taking long or because it is going into a nonlinear solution? I wasn't sure from your email if you had one or both problems.
If you have KEYOPT(1)=1 and CV2=0, I don't believe that COMBIN14 should behave in a nonlinear manner. You can verify whether it is doing so if the Convergence Monitor graphical tracking is being displayed (L2 norms and CRIT). Checking the jobname.mntr file after a solution will also confirm how many total iterations were performed.
On the other hand, if the solution with COMBIN14 is taking a long time because the iterations is taking long, I would suggest using the sparse direct solver (EQSLV,SPARSE) to speed up your solution. If the COMBIN14 spring stiffness is too small, the matrix may become ill- conditioned. The PCG solver (and other iterative solvers) will have trouble if the matrix is too ill-conditioned. Look in the jobname.PCS file for information on the PCG solver. If you run two cases - with a large and small value for the spring stiffness, compare the number of iterations required by the PCG solver in the jobname.PCS file, and you'll probably see a drastic difference (order of magnitude or so). Hence, for ill-conditioned matrices (i.e., cases where the spring stiffness is very small), use of the sparse direct solver is preferred over the PCG solver, and the jobname.PCS file will help you determine this.
Best regards, Sheldon ANSYS, Inc.
http://www.ansys.com/ (Official Site) http://ansys.net/ansys/ (Cheap imitation) "This email is not being provided in my capacity as an ANSYS employee. I am solely responsible for the content."
--- In xansys@y..., "Asha Rani" wrote: > Hi, > I am conductiing a static structural analysis(only interia load) of > a piping system where I am using combin14 as spring pipe supports > hanging from the roof (ie. tension springs). > Here are the details of the combin14 keyoptions used.
> 1. It is created with I-J nodes in the Z direction of the global > cartesian system. > 2. keyopt 1 = 0 > keyopt 2 = 3 > keyopt 3 = 0 > 3. only k value as real constant, around 360.
> Now the problem is it takes 7 to 8 hours to solve this problem, when > it should not take maximum of 2-3 hours. > If I make the springs very stiff, it solves in an hour.Even when I > have set the keyopt 1 to 0, which means linear analysis, it is going > into non-linear. I do not have any other kinds of non-linearity in > the model.
> I am using Ansys 5.7, PCG solver with 1e-3 tolerance.
> Is there anything which I should be careful about Combin14. Can > anybody suggest a way to come out of it?