Direct method for surface forces

Introduction

This chapter discusses the use of the Direct method for surface forces to create force collections in the Import / Export data context: this kind of collection allows to compute forces on a face mesh.

The following topics are covered in this page:
  • Description of the approach
  • Creation of this force collection
  • Limitations
  • Example

Description of the approach

This approach evaluates forces on a face support at the interface between two regions with different magnetic permeability defined with a data support as shown in Figure 1. Two main computation methods are available to compute forces, the first is a direct computation of forces by using the nodal virtual work method and the second is based on a local integration of the magnetic pressuredFmagS. For this last method, several local force integration methods are available, consult method of force integration at nodes for more details.
Figure 1. Simple actuator with a yoke, a coil and a plate with a support described by a line and then extruded with the help of data supports.


Creation of this collection

This approach (and so this kind of collection) is available in all Flux modules (2D, 3D and Skew) for all the magnetic applications. This collection can be created as follows:
  • In the data tree, select the menu Forces data collection
  • In the dedicated GUI for Forces data collection, choose Direct method for surface forces
  • Choose a data support to collect the data
  • Choose the computation method
  • 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: For AC Steady State applications, the user must also choose the type of values to collect: continuous, instantaneous (the phase value is asked) or pulsating values.
Note: When using a dFmagS based method, the force is limited to the normal component.

Once the collection is created and the data collected, forces can be visualized with the Data visualizers and / or exported to OptiStruct with the Data export function.

Limitations

  • Only the forces normal to the support can be evaluated
  • This collection must be defined at the interface between two regions with different magnetic permeability

Example

In this example, the aim is to compute the global force on the plate of the actuator shown in Figure 1.

To do this, we define a support to collect the data: it comes from the Flux mesh and is the same as the one described in Figure 1; it has been created from the line that we choose to extrude during the creation of the support.

Once the collection is correctly defined, the data must be collected by right click and Collect data on the forces data collection; now forces can be visualized with the Data visualizers as shown in the figure below:
Figure 2. Distribution of nodal forces in Newton on the actuator plate.


The analysis of global forces may be achieved with several approaches:
  • The approach described on this page
  • With Computation on physical entity available in the tab Computation > On physical entity
Table 1. Comparison of the results between the global computation in the Import / Export data context and the global computation on the region with the computation on physical entity.
Approach Force value (N)
Direct method for surface forces (dFmagS) 4.53 N
Computation on physical entity (region) 4.73 N