How to Model and Simulate Complex Electric Motors

For many years, the best practices to prepare a 3D model for simulation involved first importing 3D geometry, then defining the smallest circumferential symmetry. In the case of radial field design, we would first separate the symmetric 3D design (3D slice) from the rest of the 3D geometry by two radial planar cuts, which would later be used to define the boundary conditions to assign such symmetry. This is still a modern approach, largely used in the simulation industry to narrow down the simulation design space and reduce the total computation time required by already expensive time-stepping analysis. Due to this space reduction, the mesh maker can deploy more symmetric and regular mesh topologies to minimize the numerical method impact (finite element) to the overall prediction of motor performance, which is good.

However, the challenges encountered by designers when 3D geometry becomes more complex have yet to be addressed. 3D designs with skew rotor and/or stator configurations (see below) and their electric motor topologies require a compromise between smallest valid geometric symmetry and the required electromagnetic conditions. Despite the symmetry used to compute the motor performance, any designer would also prefer to get the field solution displayed back onto the entire 3D geometry. 

3D electromagnetic problems become more complex in multiphysics simulations such as noise-vibration and harshness (NVH). Thermal management presents another set of problems where the entire 3D design space solution might be required to satisfy the specific physics conditions.

How Designers Deal With Complex 3D Geometries Today

There are a number of drawbacks associated with how designers typically approach complex 3D geometries.

For instance, importing computer-aided design (CAD) geometries might also bring in details that aren’t necessary for electromagnetic simulation, which would then require time to remove. Creating the geometry from scratch would require CAD skills as well as associated time and costs.

As mentioned previously, defining circumferential symmetry (3D-slice) by creating radial planar cuts do not always capture the correct symmetry in the geometry, especially when the motor shows skew configurations. Planar cuts mandate separation of the 3D-slice model from the rest of the geometry, which makes it difficult to transfer electromagnetic data (losses or forces) onto the full 3D geometry when thermal management or NVH analyses are required as multiphysics coupled designs.

Finally, manually assigning mesh operations to ensure simulation accuracy requires knowledge about the mesh impact on the FEA solution.

Field calculation on a circumferential symmetry using automatic nonplanar boundary conditions

Targeting these challenges, Ansys Maxwell has introduced a best-in-class solution in 2021 R1. It allows engineers to import an entire 3D motor geometry from any CAD tool. Maxwell automatically creates the 3D circumferential slice-based model, applying nonplanar cuts as boundary conditions and corresponding regular and symmetric mesh (clone mesh) on all parts of the geometry.