Direct method for surface forces (dFmagS)


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

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 a force density on a face support (Flux mesh or imported mesh) at the interface between two regions with different magnetic permeability defined with a data support as shown in Figure 1. The magnetic force density dFmagS is directly computed on the support and then is integrated with different methods to get the most adapted distribution for mechanics-coupled simulations. Being this approach only able to compute the normal forces to the mesh of the support, tangential and axial forces are not taken into account.

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 (dFmagS)
  • Choose a data support to collect the data
  • 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: In advanced mode, more integration options are available, see this pagefor more details.
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.


  • 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


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