## Discovery Import

#### Nonlinear Solution

TAGGED:

• mtruong
Subscriber

Hi,

How do I switch from a linear solver to a nonlinear solver in AIM?

Thanks!

Sincerely,

Michelle Truong

• Brian Bueno
Ansys Employee

mtruong7

This video outlines how to define nonlinear conditions: https://discoveryforum.ansys.com/t/m2p16p/discovery-aim-nonlinear-contacts

# Setting Nonlinear Controls in a Static Structural Simulation

When solving nonlinear simulations, AIM carries out an iterative procedure (equilibrium iterations) at each substep, successfully solving the simulation only when the out-of-balance loads are less than the specified convergence criteria. On the Solution Progression panel, you can define the number of substeps in a solution step. You can then define the convergence controls and other solution progression properties.

For Substepping, you can define a range or a fixed number, or you can leave it up to the solver.

AIM displays the convergence criteria appropriate for each physics type. For a static structural physics solution, the convergence criteria consist of Force convergence, Moment convergence, Displacement convergence, and Rotation convergence. You can set the convergence controls for each of these criteria.

Under  Additional Convergence Controls, you can also specify the number of equilibrium iterations at each substep, activate a predictor on the degree-of-freedom solution for the first equilibrium iteration of each substep, and control the line search program.

For Stabilization, you can specify the key for controlling nonlinear stabilization. Convergence difficulty due to an unstable problem is usually the result of a large displacement for small load increments. Nonlinear stabilization technique can help achieve convergence. Nonlinear stabilization can be thought of as adding artificial dampers to all of the nodes in the system. Any degree of freedom that tends to be unstable has a large displacement causing a large damping/stabilization force. This force reduces displacements at the degree of freedom so stabilization can be achieved.