Therefore, for a first estimate, the linear static analysis is often used prior to performing a full nonlinear analysis. A nonlinear analysis is an analysis where a nonlinear relation holds between applied forces and displacements. These effects result in a stiffness matrix which is not constant during the load application. This is opposed to the linear static analysis, where the stiffness matrix remained constant. As a result, a different solving strategy is required for the nonlinear analysis and therefore a different solver. Modern analysis software makes it possible to obtain solutions to nonlinear problems.

However, experienced skill is required to determine their validity and these analyses can easily be inappropriate. Care should be taken to specify appropriate model and solution parameters. Understanding the problem, the role played by these parameters and a planned and logical approach will do much to ensure a successful solution. The source of this nonlinearity can be attributed to multiple system properties, for example, materials, geometry, nonlinear loading and constraints.

Here are some examplesâ€¦.

Geometric Nonlinearity In analyses involving geometric nonlinearity, changes in geometry as the structure deforms are considered in formulating the constitutive and equilibrium equations. Many engineering applications such as metal forming, tire analysis, and medical device analysis require the use of large deformation analysis based on geometric nonlinearity.

Small deformation analysis based on geometric nonlinearity is required for some applications, like analysis involving cables, arches and shells. Material Nonlinearity Material nonlinearity involves the nonlinear behavior of a material based on a current deformation, deformation history, rate of deformation, temperature, pressure, and so on. Examples of nonlinear material models are large strain visco elasto-plasticity and hyperelasticity rubber and plastic materials.

Constraint and Contact Nonlinearity Constraint nonlinearity in a system can occur if kinematic constraints are present in the model. Attaching the archived model prepared in Please help. Here is the screenshot. I have also attached archived model of it. I set the number of steps to 1, since you only have one load, gravity. However, the solver will not converge in 26 iterations with substeps. If you look at the NR Force Residual, all the points are around the brown strap.

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## Non linear analysis- doesn't converge

Here is a better mesh made by putting a Sizing Mesh Control on the 8 edges at the bottom of the strap. While you are in the area, you can also add a Sizing control to the face of the solid part that the strap holds onto. That was too coarsely meshed also. While a better mesh on all four straps and Tee bolts will allow the convergence to continue, it would be ideal to midsurface the straps.

## A non-linear analysis of Turing pattern formation

The next issue that prevents convergence is the interference between the large light grey sidewall and the darker grey strap backer. The solver is trying to resolve that interference. Do you want to resolve it in the geometry editor and get rid of that interference? Then the model should converge.

Thanks, Peter. I will try to resolve the model again by implementing the suggestions above. Just one question, what are the substeps required in this case? How do we decide the number of substeps?

## Log-linear analysis

I see that you did a modal analysis. Remove the Fixed support and perform an unconstrained modal analysis, what do you observe for the first 6 modes? Is something flying away? Try the methods listed here to debug. Regards, Sandeep Guidelines on the Student Community. I tried the modal analysis without any constraint, nothing is flying but still, modes are not coming zero.

You just need to learn to respond to NR Residuals with a mesh refinement and you will be a bit more capable. One idea to save you some time in the Geometry editor fixing the interference. Just remove that one strap face actually 4 faces from the contact definition so that the solver is not checking the faces that penetrate the tank. All the other faces of the strap that wrap around the tank are fine. Why not use a Bonded Contact so that the Tee bolt stays at its current location on that midsurface plate? So I used no-separation to allow the movement along the axis of T bolt. I am not sure if this is the right approach.

So what I did was, I converted the following contact as bonded.

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I am still running the model, so can't comment on the results. I converted the No Separation to Bonded and found the next problem is that there is a large interference of the top of the strap with the tank. It's best to check for interference in the CAD system before you bring the geometry over for modeling.

### Description

Ohh, I didn't really see that. So what will be the best method to fix that? All your geometry is in SpaceClaim, so you could try to use the Move tool to move those faces of that part up, while leaving the faces around the Tee bolt in place.

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This is complicated because there is the strap and the pad under the strap that both have to move. What if you just delete the pad from the model, and just have a strap? You might have more control in the native CAD but then you will break a lot more of the model in Mechanical. Right now what I am doing is applying force at the bottom of T- bolt, I don't know if it is right or wrong?

Ohh, so the image up there is blurry, adding more information the belt inside is steel, outside strap is neoprene and tank is steel.