This is probably a bit basic, but I feel compelled to ask the question. In the practical use of mechanica, I am having a bit of a problem understanding what practical uses there are for springs in analysis. Can someone give me a practical example? Maybe a short description of the intended use for springs?
We design multiple axis positioning systems (think X-Y stages). I use springs to model the linear bearings. The ProM-springs are a bit flaky in torsion, but with careful set-up, a quad set can model a linear bearing's pitch, yaw, and roll stiffnesses, as well as the lateral Ky & Kz.
By far, springs in FEA have been mostly used to model fasteners. However, there are other novel uses, such as those you have already heard of from other users.
Springs are very efficient (run time) and represent the most basic property of the finite element method, stiffness. They do a very nice job of solving the force and displacement components of a model. You will not have stress output available for springs.
The caveat with springs is that since there is no area at the point of load transfer, stresses are unreliable at the mating parts in the vicinity of the spring attach points. If you are solving for stresses in your analysis, you may consider excluding elements in those vicinities from convergence (MPA convergence algorithm, of course). The run will complete much faster.
Randy Speed President and CEO Speed Consulting, LLC (972) 938-0490 ph (972) 937-2319 fax www.speedconsulting.com