# Simcenter MAGNET Suite Setting up a 3D Type C Motion model to start at an unaligned position

2024-01-04T18:40:00.000-0500
MAGNET

## Summary

In previous versions of Simcenter MAGNET there was a limitation with 3D type C motion. The motion component of the partial model with periodic boundary conditions could not start at an unaligned position and would cause an error. This limitation has been removed but requires some careful steps in order for it to solve without error.

## Details

Until Simcenter MAGNET 2212.0003, a partial 3D model with periodic boundary conditions (a Type C motion model) would issue one of a few different errors when solved with the Transient 3D with Motion solver from an unaligned starting position. Since Simcenter MAGNET 2212.0003, this limitation can be overcome by meeting the following conditions:

1. At the zero position, the geometric components that are or will be part of the motion component must be perfectly aligned with the stationary geometry in the model. The sliding interface between the moving and stationary parts should not be exposed. If this is not the case, shift or rotate the geometric components that are part of the motion component as needed to satisfy this condition. The zero position in MAGNET would correspond to the position of the motion component seen in the Solid Model View when Position at startup = 0 or when time = 0 and position = 0 is set in the Position vs Time table (if the Position based definition for a Velocity driven motion component is being used).
2. Then at the model level, set the system parameter MeshAtPositionZero to Yes.

There is one quirk with MeshAtPositionZero = Yes. In the Motion Component's Position page, no matter what value is set for Position at startup or what value is set for t=0 in the Position vs Time table (if the Position based definition for a Velocity driven motion component is being used), the motion component will always appear as if it's at the zero position in the Solid Model view. But there is no need to worry. After you solve with the Transient 3D with Motion solver and look at the solution mesh or field at the first time instant you will see that the motion component was meshed at the desired unaligned position. However, if you solve with a Static or Time-Harmonic solver these solvers will solve at the zero position no matter what value is set for Position at startup since these solvers don't support motion. If one wishes to solve a parameterized set of static or time-harmonic problems where Position at startup is used to simulate different positions via its system parameter PositionAtStartup then one should set MeshAtPositionZero to No or delete its value.

This downloadable model shows a simple model that was set up with MeshAtPositionZero = Yes for Problem 1, which will solve successfully with the Transient 3D with Motion solver for the non-zero Position at startup of the motion component. Problem 2 has MeshAtPositionZero = No which will fail to solve with the 3D Transient with motion solver.

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Simcenter MAGNET