Optimisation topologique : A propos

Introduction

Since version 2023.1, Flux 2D provides its users with novel topology optimization tools for the design of electromagnetic devices. This new toolset complements the free-shape optimization functions already available in Flux 2D, allowing electromagnetic designers to benefit even further from the state-of-the-art structural optimization methods offered by the Flux-OptiStruct coupling.

In Free-shape optimization, the boundaries of selected parts of an initial design are iteratively displaced and modified by the procedure. The result is an improved shape that satisfies the optimization criteria and that usually resembles the original design. Topological optimization methods, on the other hand, are based upon the addition or removal of the matter composing the parts being optimized. This process is governed by the evolution of the values of a material density function throughout the optimization procedure, and frequently leads to quite innovative shapes that may not have been previously considered. Figure 1 illustrates both approaches in the simple case of the optimization of a beam.

Figure 1. Comparison of free-shape (a) and topology (b) optimization strategies in a simple structural mechanics example (the structural optimization of a beam).

This powerful new feature is now available in Beta mode and may be applied in the optimization of a broad range of electromagnetic devices (including rotating machinery and actuators). Its use is outlined in the next sections of the documents, which cover the following topics

Topology optimization strategies implemented in Flux 2D

Two well-known topology optimization strategies for electromagnetic devices are available in Flux 2D through a coupling with OptiStruct, namely:

the Density method and
the LevelSet method.

For an introduction on these gradient-based methods, please refer to the following open access reference:

F. Lucchini, R. Torchio, V. Cirimele, P. Alotto and P. Bettini, "Topology Optimization for Electromagnetics: A Survey," in IEEE Access, vol. 10, pp. 98593-98611, 2022, doi: 10.1109/ACCESS.2022.3206368.

Software requirements

As already mentioned, the new topological optimization tools delivered with version 2023.1 rely on a coupling between Flux and OptiStruct. Consequently, to use this feature the following software are mandatory:

Altair Flux 2023.1;
Altair OptiStruct 2023 or later.

A faire : After completing the installations, check if the path to OptiStruct is correctly configured in Flux Supervisor. To verify this setting:

In Flux Supervisor, click the Options button.
Then, in Acces paths, select Coupled Software.
Check if the field OptiStruct scripts directory is correctly configured:
- In Windows systems, this field should contain the folder storing the file optistruct.bat. After a standard installation of OptiStruct, that path should be similar to C:\Program Files\Altair\2023\hwsolvers\scripts.
- Similarly, in Linux systems, this field should contain the subfolder of the OptiStruct installation directory containing the file optistruct.sh.

Additionally, and as discussed in the section Comment exploiter les résultats d'un problème d'optimisation topologique ?, the user may want to install the latest version of Altair SimLab to exploit the content of the generated H3d files.

Current limitations

Since Flux 2023.1, this new feature is made available in Beta mode. Consequently certain limitations still apply. Most of them are related to the type of region to which the faces subjected to topology optimization have been assigned, or to the type of material assigned to those regions. The most important cases are listed below:

Unavailable in the following applications:
- Steady State AC Magnetic;
- Non-magnetic or coupled applications.
The faces being optimized need to be finely meshed. Moreover, the following mesh types are forbidden:
- Mesh with first order elements;
- Heterogeneous meshes (i.e., mixing triangles and quadrangles).
Axisymmetric domains are not supported yet.
It is not possible to perform the topology optimization in Transient magnetic applications with the Initialized by file option.
Only faces lying on a Magnetic non conducting regions may be used for topology optimization. Assigning other types of region (such as Air or vacum regions, Regions with current density, Laminated magnetic non conducting regions, Coil conductor regions and Solid conductor regions) to faces make them incompatible with topology optimization in this version.
Only faces on regions characterized by materials with simple B(H) magnetic properties may be used (e.g., Linear isotropic, Isotropic analytic saturation, Isotropic analytic saturation + knee adjustment, isotropic spline). Faces in regions with hysteretic, anisotropic and magnet materials ar not allowed.