Simcenter 3D Solutions Simcenter 3D Low Frequency Electromagnetics. MAGNET Solver Errors - Coils: error 149081

Error 149081 - There is no path from the start terminal to the end terminal of at least one of the current sources which does not pass through another current source or no path exists.

Some examples that can cause this error in MAGNET solver are shown below.

A single closed conducting path (e.g. a loop), consisting of one or more conducting geometric components, that has two or more coil objects set on it can lead to this error if two of the coil objects are current driven. 

The error occurs because the conducting path is overdetermined with too many current driven coil objects. This is analogous to a circuit branch that has two or more current sources in series. It only needs one current source and similarly a single closed conducting path only needs one of the coil objects to be current driven.

If the coil object that is current driven is a solid type coil then all the other coil objects must be solid type. In this case, the other coil objects may be placed in the Circuit page and connected to passive circuit components (only in version 2020.1 and later) or the coil objects can be deleted.

If the coil object that is current driven is a stranded type coil then all other coil objects of any type must be deleted.

Another example is this set of conducting paths that form a three leg network or an "eight" shape. Each leg or branch has a current driven solid coil object set on it. Note that for a geometry with multiple conducting paths, the coil objects cannot be stranded. This setup of coil objects may seem okay initially but this will cause the same error as the first example. 

This is because this will result in an overdetermined set of conducting paths. Only two current driven coil objects are needed for two branches. The current in the third branch is simply the sum of the other two branches and therefore does not need to be current driven. This is essentially the same situation as the overdetermined circuit (please, see the Circuits: errors), which gives the same error.

This third coil object can be deleted or placed in the Circuit page and connected to passive circuit components. Note that if all three coil objects were voltage driven, there would be no error and the solve would succeed because the conducting paths are not overdetermined.

A model with a conductor whose ends touch the exterior surfaces of the model (usually the air box) that have Odd Periodic boundary conditions applied will report error 149081. The reason is due to the latter part of the error message, no path exists.

This is caused by odd periodicity. Periodic boundaries are used when the model file only contains the geometry of a partial segment of the whole device, which in real life is itself made of many shifted or rotated copies of the same segment. The periodic boundary condition mimics the field behavior that would occur between adjacent segments but without explicitly modeling them. But these adjacent "unmodeled" segments can have coils and magnets with the same polarity or the opposite polarity of the modeled segment. For odd periodicity, the unmodeled segments have excitations with reverse polarity. This means that the example above is unrealistic because it results in current flowing against each other in the modeled conductor and its two unmodeled adjacent conductors.

This example can only be solved successfully when the boundary condition is even periodic, where the unmodeled copies have excitations with the same polarity as the modeled segment.

A more complicated example that is similar to the example above is shown below. It has two geometrically disjoint conductors (or conducting paths) but they will be connected virtually by the boundary conditions of the exterior surfaces of the model so only one coil object is needed. Odd Periodic boundary conditions are on the left and right exterior surfaces of the air box. The coil terminals of the coil object (made creating a Multi-terminal Coil Simulation Object Type) lie on the symmetry plane (assumed to be flux tangential by default when no boundary condition is explicitly set). However, the reference directions of the coil terminals are in opposite directions. This would be correct if the boundary condition was even periodic but for odd periodic they should both be the same (i.e. either both pointing inwards or outwards). But it is not possible to use the Multi-terminal Coil Simulation Object Type to make both terminals inwards or outwards on the component faces.

The solution is to delete the coil object and make a coil object on only one of the conducting paths. In the image below it was created on the component on the left in the left conducting path (but it would have been equally valid to make it on the right conducting path instead). The solver will correctly handle the current direction in the other conducting path based on the periodic boundary condition. This method works for both even and odd periodic.