Nonlinear analysis is often decided to be used out of necessity, however there are other benefits to using nonlinear analysis. Incremental control techniques are a massive piece of the puzzle in how nonlinear studies are run and give some awesome benefits that linear static analysis can’t offer. Today we are going to talk about the three control techniques Force, Displacement and Arc Length Control and some benefits they can offer.
For all three methods, the load will be incrementally applied, and this allows the solver to calculate the appropriate response that will satisfy the equilibrium equation. This allows the studies to converge more often and is done by using pseudo time curves.
Allows users to incrementally apply loads according to a user defined time curve. The pseudo time curve is scalar, so imagine I have a 100 N load. At a load factor of .5 the load applied will be 50N, this allows users to create a sequencing of loads or even a loading that is fully reversing in the same analysis. Force control can be defined with any boundary condition such as a force or pressure, or even a fixture moving a block to create an o-ring seal.
What if rather than knowing how much of a load we have, we instead only knew how far a specific location needs to displace? This is where displacement control comes into play. This control method allows us to pick a node and specify a displacement in a particular direction. After we have picked the node, direction of displacement and distance we pick where the load is applied. This load is not actually causing the displacement, but rather we are asking what value this load would need to be to create this displacement.
This has major benefits when trying to determine loads required to create a displacement. As well as aiding in convergence because we now have a very straightforward ask of the software to solve for.
The final control method we will learn about is used for looking at buckling and post buckling behavior of our structures. When doing buckling analysis in SOLIDWORKS we have two options linear buckling with Simulation Professional, and nonlinear analysis using arc-length control method from Simulation Premium.
Three major capabilities differences between the two are: materials, understanding stress values, and snap through points. We will focus on the latter two items.
With arc-length control we can understand the stress, displacement, factor of safety more accurately than in a linear buckling analysis. In linear buckling we are seeing the buckling mode shape amplitudes and factors of safety. With arc-length control method we can also analyze the stress, strain, and displacement results if they are needed.
Snap through points and post buckling behavior are the biggest differentiation. Linear buckling assumes no major changes in shape prior to the buckling occurring, however this is not a safe assumption with all geometry.
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