In a more electrified world, designing quieter electric motors has become a differentiating factor for manufacturers in industries ranging from transportation to automation. While the focus in designing electric motors has always been on power, efficiency, cost, and volume, designers are now incorporating noise, vibration, and harshness (NVH) in their conception flows. Designers must aim to lower the sound levels of electric machines as much as possible without compromising on efficiency and make the sound more agreeable to our ears.
Some motors emit reasonable sound levels, but the sound quality can be poor and include annoying sounds like humming. Sound engineers try to modify the sounds by trial and error, which can be lengthy and costly. However, simulation can reproduce the measured sound levels. This involves chaining multiple solvers together, as these noises result from electromagnetic (EM) effects and can be amplified by electrical harmonics. It is also possible to use simulation to predict noise levels for designs that have not been prototyped. It enables designers to virtually assess whether noise levels meet mandatory noise thresholds. If those noise levels are too high, a process can be implemented to lower the noise through an optimization engine.
Typical flow for e-motor noise, vibration, and harshness (NVH) analysis. The electromagnetic (EM) force mapper tool helps at the interface of the magnetic and structural domain.
Understanding the Complexity of NVH Simulations
The main source of acoustic noise in electric machines is the vibrations of the stator — the stationary part of the motor — under the influence of the electromagnetic forces in the small air gap between the stator and rotor. The vibrations of the stator teeth propagate through the assembly and create acoustic noise as the external surface of the motor vibrates. When the magnetic force’s harmonic content contains frequencies close to the motor’s vibration modes, resonance can occur and produce high sound levels. Solving this problem requires a multiphysics approach, as engineers must consider the assembly’s electromagnetic, mechanical, and acoustic aspects.
Ansys, through its coupling field technology, can solve this flow and assist customers with NVH analysis. However, using this flow without following a precise methodology can lead to errors. In particular, at the interface of the electric and mechanical domains, the NVH analysis of electric motors requires collaborative work between mechanical and electromechanical engineers. Often those engineers have different backgrounds and are unfamiliar with what it takes to accurately and efficiently calculate forces and apply them in the structural environment in this context. Yet another level of complexity is that transient magnetic data is transformed in frequency data for structural harmonic simulation.
To evaluate the magnetic mesh quality, the tool compares built-in torque with torque calculated from forces. When the two curves match, the mesh quality is optimal.
Guiding Designers to Success With the NVH Force Mapping Workflow
To facilitate the NVH analysis of electric motors, Ansys has developed a guided workflow for the most important simulation step: the coupling between the magnetic and mechanical domains. This application enables engineers to collaborate, calculate, and map the forces in a reliable, robust way, including checking force accuracy.
At the beginning of the workflow, you must provide an existing project from the Ansys Maxwell advanced electromagnetic field solver. After you provide all the relevant inputs for NVH simulation, they will be used to automatically set up the project in Maxwell software, using PyAnsys behind the scenes. The tool will also verify whether the mesh quality is adequate for NVH simulation, as the force calculation accuracy is very mesh-sensitive. Once this process is complete, the forces will be calculated and displayed in the tool, which enables you to visualize the force plots.
Before mapping the forces on the structural model, radial and tangential forces can be visualized.
Next, you can provide the project from Ansys Mechanical structural finite element analysis software, in which the forces will be applied. Every step is enriched with comprehensive documentation. This workflow is an application with a dedicated user interface (UI), automation scripts, and postprocessing capabilities. The application will automatically initiate and manage processes in Maxwell and Mechanical software, but it also offers third-party file support.
By using this workflow, engineers can follow the documented steps in a collaborative way, ensuring that the setup of the Mechanical project has accurate electromagnetic loads. Many configurations are supported, including skewing, symmetries, and importing measured data.
A force mapping demonstration
Learn more about Ansys’ electronics and NVH solutions.
