Generalized projective method

Introduction

This chapter discusses the use of the Generalized projective method to create force collections in the Import / Export data context : this kind of collection allows to compute forces on a generic mesh (i.e., a set of points) with the aim to be exported towards OptiStruct to setup a NVH analysis of electrical devices, such as rotating machines. This method and then the collection created may be seen as an extension of the simplified projective method dedicated to rotating machines which overcome its limitations.

Description of the approach

This approach is based on two data supports defined by the user: one to collect the data and a set of supports to compute and integrate the magnetic pressure to be projected on the first support. The support to collect the data must be generated by importing a mesh from a .fem file as it is shown in (b) part of Figure 1. To compute the forces, two methods are available: the Maxwell tensor method or the nodal virtual work method. The type of computation supports to be created depends on the chosen method.

In the case of the Maxwell tensor method, the set of supports to compute and integrate the magnetic pressure must be located in air regions and can be defined by an extruded path, a 2D grid as shown in (a) part of Figure 1 or an extruded geometric line. All the components of the magnetic pressure are locally integrated on the computation supports before being projected on the support chosen to collect the data.
In the case of the nodal virtual work method, the set of supports to compute forces must be located on the geometric entities at borders of regions (lines or extruded lines in 2D, faces in 3D). The forces will be directly computed on the nodes of the supports before being projected on the support chosen to collect the data.

Figure 1. Axial flux motor in Flux 3D: (a) the support to compute and integrate magnetic pressure with Maxwell method created from a 2D annular grid, (b) the support to collect the data imported from OptiStruct

Note: With Maxwell method, to have accurate results, the computation support (the grid on the figure above) must have a fine discretization.

Creation of this collection

This type of collection especially dedicated to electrical rotating machines but applicable on any device is available in all Flux modules (2D, 3D and Skew) for static and transient magnetic applications. Its creation is made via the following steps:

In the data tree, select the menu Forces data collection
In the dedicated GUI for Forces data collection, select Generalized projective method
In the Definition tab:
1. Choose an imported data support to collect the data
2. Choose the computation method
3. Choose a list of data supports to compute forces
In the Advanced tab, the user can decompose the computed forces in radial and tangential components. To this aim, he is invited to:
1. Select the rotation axis (X, Y or Z expressed in XYZ1 coordinate system)
2. Choose a pivot point by its coordinates and a coordinate system
Choose the collection interval:
- Collect for all the steps of the scenario
- Collect only for the current step
- Collect for a specified interval
Click OK
Right click on the forces data collection just created in the data tree and run the command Collect data

Note: As a next step, forces can be visualized with the Data visualizers and / or exported towards OptiStruct with the Data export.

Example

In this example, the aim is to compute the global force on each tooth of the 3D axial flux machine described in Figure 1 after solving a scenario in Flux.

To this aim, a support to collect the data is imported from OptiStruct which is the same as part (b) of Figure 1. The Maxwell computation method is chosen then the computation support is defined in the airgap region by a 2D-grid (see (a) of Figure 1).

Once the data collection is correctly defined, the data must be collected with a right click and the command Collect data on the forces data collection; forces can now be visualized with the Data visualizers as shown in the figure below:

Figure 2. Visualization of global forces per tooth for a 3D axial flux machine: (a) the forces normal to the collect support, (b) the forces tangential to the collect support.