Import, export and reuse magnets

Introduction

The stability of the permanent magnets integrating an electromagnetic device is affected by its operation conditions. Changes in their magnetization states may result in performance degradation and thus must be considered in the design of robust, reliable electromechanical apparatus.

Consequently, Flux provides its users with a comprehensive set of tools dedicated to the analysis of permanent magnet demagnetization. More specifically, the hard magnetic material model Magnet (unidirectional): demagnetization curve (HcB, HcJ and Br) available in Flux is well adapted for this context of applications, since it allows the consideration of the demagnetization of a permanent magnet during resolution.

Moreover, Flux also implements data exchange tools that simplify the transfer of magnet characteristics between projects, namely:

Export Br of magnets to a JSON file;
Import magnet material from a JSON file;
Reuse magnets in a new project.

These tools, when used together with the aforementioned hard magnetic material model, allow the user to simulate his device under different magnetization states of the permanent magnets (i.e., before and after being subjected to a demagnetization). The following sections of this chapter discuss each of these tools in detail.

Export Br of magnets to a JSON file

This feature is available in Transient Magnetic and Magneto Static applications (Flux 2D and 3D) and allows exporting to a JSON file the magnetization state of the magnets at a given step of the computation scenario (i.e., their remanent magnetic flux density distribution, represented by the vector quantity BrMagnet).

To perform this export:

Firstly, solve a scenario and select the resolution step containing the magnetization state of the magnets to be exported.
Select Magnets → Export Br of magnets to a JSON file in the Data exchange menu.
Then, in the Export Br of magnets to a JSON file dialog box, in its General tab:
- provide a name for the exported file in the field JSON file and
- in the Material of the magnet to export drop-down menu, select the material associated to the magnets that are going to be exported.
In the Advanced tab, modify, if necessary, the values for the options below:
- Compact format for JSON file: keep this option set to yes (default value) to export the data to an unindented JSON file. Set it to no instead to obtain an indented (and consequently more readable) but larger JSON file.
- Extrude magnet data to 3D (not available in 3D and 2D Axisymmetric projects): set this option to yes to generate 3D magnetization data of the magnets through an extrusion in the JSON file. This option is set to no by default.
- Reconstruct the full device: setting this option to yes will include data from symmetrical and periodical parts of the device in the exported JSON file. This option is set to no by default.
Click OK to generate the JSON file.

Note: The data contained in a JSON file may account for demagnetization effects for a magnet in the project if the material selected is of type Magnet (unidirectional): demagnetization curve (HcB, HcJ and Br). The application of the source project must also be the Transient Magnetic application.

Note: The generated JSON file contains data expressed in the Global coordinate system of the project and in SI units. This file may be imported in a different Flux project, accordingly with the discussion in the next section.

Import magnet material from a JSON file

This feature is available in Transient Magnetic and Magneto Static applications (Flux 2D, Skew and 3D) and recovers in an unsolved project the magnetization state of magnets from a previously exported JSON file.

To perform this import:

In the Physics menu, select Material→Import magnet material from a JSON file.
Then, in the General tab of the Import magnet material from a JSON file dialog box:
- provide the name for a new material in the field Name of the new material (spatial linear magnet);
- provide the path to a previously exported JSON file in the field Spatial remanent flux density (JSON file) containing the spatial remanent flux density data of the magnets to be recovered in the current project;
- provide the relative magnetic permeability of the new material in the Relative magnetic permeability field. This field is pre-filled with the default value of 1.05.
In the Advanced tab, if necessary, select from the drop-down menu the Coordinate system in which the data contained in the JSON file will be positioned. If left empty (the default option), Flux will import the data using the Global coordinate system of the project.
Click OK to complete the import.

Note: Importing a JSON file will generate the following Flux entities:

A new, real, vector spatial quantity called BR_<new material name> containing the remanent magnetic flux density of the exported magnets at the selected time step of the source project (i.e., the built-in quantity BrMagnet). The string <new material name > is the name provided by the user for the new material during the import.
A new material of type Spatial linear magnet, which uses the spatial quantity mentioned above in its definition for Br values.

Note: Once the import is completed, the user still needs to assign the new material of type Spatial linear magnet to the regions representing the magnets in the project.

Reuse magnets in a new project

This feature is available in Transient Magnetic applications (Flux 2D and 3D only). It creates a new project containing one new material of type Spatial linear magnet for each magnet material in the source project. Each new material represents the magnetization state of the original magnets at the resolution step that was selected to be reused.

To use this feature:

Firstly, solve the scenario and select the step containing the magnetization state of the magnets to be reused.
Then, in the Data exchange menu, select Magnets → Reuse magnets in a new project.
Finally, in the Reuse magnets in a new project dialog box:
- provide the New project name and
- click OK to generate the new .FLU project.

Note: The Reuse magnets in a new project feature is useful to "recycle" magnets that suffered demagnetization into a new project (keeping the geometry and the physical description) and thus continue with an investigation on the impact of their degraded magnetization on the performance of the modeled device. Remember that the original magnets must be of type Magnet (unidirectional): demagnetization curve (HcB, HcJ and Br) (i.e., they must support demagnetization during resolution) and that the application must be set to Transient Magnetic for this kind of analysis.

Note: The names of the new materials generated by this tool are the names of their parents in the source project, with an additional "_REUSED" suffix added at their ends to distinguish them. A spatial quantity named BR_REUSED representing the remanent magnetic flux density of the reused materials is also generated. The new materials are also automatically assigned to the regions to which their parent materials were previously assigned.

Note: Remark that the type of magnet material always changes to Spatial linear magnet in the project issued from Reuse magnets in a new project. Moreover, their spatial relative permeabilities are set to 1.05 by default. This parameter may be changed manually if required. The user is also advised to verify if the Spatial linear magnet model remains pertinent in the case of magnets exhibiting a highly non-linear behavior in the source project.

Remarks

The Import magnet material from a JSON file and Reuse magnets in a new project features are based upon resources of the Data import/export context. Consequently, entities generated by these tools, notably the spatial quantities stocking the remanent magnetic flux density of imported and reused magnets, may not be deleted as usual. To destroy them, the user must first go to the Data import/export context and delete the associated Imported Data Collections. This dependency may be verified by right-clicking on the spatial quantity at the Data Tree and executing the Find usages command.