Home / Examples / Magnetic Analysis (Luvens, Transient Analysis) / Example 3: Cogging Torque of Axial Gap Type Motor

Example 3: Cogging Torque of Axial Gap Type Motor

General

Axial gap type motor is analyzed.
Axial gap type motor consists of opposing disc type rotor and stator.
Cogging torque is analyzed which is generated by the rotor's rotation while no electricity is applied to the coils.
Analysis function for axial gap motor is applied.
The cogging torque and the magnetic flux density are solved.
Unless specified in the list below, the default conditions will be applied.
Obtain this session's project file. (Right-click and choose 'Save link as')

Results will vary depending on Femtet version and the PC environment.

Analysis Conditions

Item	Settings
Solver	Magnetic Analysis [Luvens]
Analysis Space	3D
Analysis Type	Transient Analysis
Unit	mm
Options	Select Rotating Machinery. [Partial Model (Symmetric Model) Setting] Select Partial Model. Number of Divisions of Full Model: 4 Select Convert results to full model for output.

The Rotating Machinery tab is set as follows.

Tab	Setting Item	Settings
Rotating Machinery	Rotational Movement	Select Constant Velocity Number of Rotations: 1800 [r/min] Rotor’s Initial Rotation Position: 0 [deg]
	Gap Type	Axial Gap
	Number of Sliding Mesh Divisions	Circumferential Division Angle: 1.0 [deg] Rotational Quantity per Step: 1 [mesh] Number of Sliding Mesh Layers: 3
	Location of Sliding Mesh	Deselect Automatic Calculation Rotor Type: Outer Rotor [Gap Radius] Inner: 110×10-3 [m] Outer: 112×10-3 [m] [Gaps' Coordinates in Axial Direction] Top Side of Upper Gap: 52×10-3 [m] Bottom Side of Upper Gap: 50×10-3 [m] Top Side of Lower Gap: -50×10-3 [m] Bottom Side of Lower Gap: -52×10-3 [m]
	Division Size of Sliding Mesh in the Axis Direction	Divide at uniform interval with specified mesh size 10.0 [mm]

Set the Mesh Tab as follows.

Tab

Setting Item

Settings

Mesh

Meshing Setup

Automatically set the general mesh size: Deselect

General Mesh Size: 7 [mm]

Air Domain Creation

Select Create air domain automatically

Air Domain Scale: 1.2

The Transient Analysis tab is set up as follows.

With the settings as below, number of calculation steps is 90, circumferential division angle is 1.0 [deg], and rotational quantity per step is 1[mesh]. The rotation up to 90 degrees (=90*1.0*1) is analyzed.

Tab

Setting Item

Settings

Transient Analysis

Timestep

Automatic

Table

Number	Number of Calculation Steps	Output Interval
1	90	1

Graphical Objects

A rotor core and coils are placed between stator cores and permanent magnets.

By utilizing the symmetry of the analysis model, it is made to be a quarter model.

"Air Domain Creation" is selected.

It is assumed that coil1, 2, and 3 are made of fine copper wires which will have little effect of induced current. So, [No] is selected for the options of Induced Current.
If [Yes] is selected, the loss by induced current will affect the analysis and correct cogging torque will not be obtained.

Body Attributes and Materials

Body Number/Type	Body Attribute Name	Material Name
34/Solid	coil1	Cu
35/Solid	coil2	Cu
36/Solid	coil3	Cu
33,37,38/Solid	st_core	core
20,31/Solid	mag1	mag
19,30/Solid	mag2	mag
23,32/Solid	rt_core	core

The material properties are set up as follows:

Body Attribute Name	Tab	Settings
coil1	Current	Induced Current: Deselect
coil1	Stator/Rotor/Air	Stator
coil2	Current	Induced current: deselect
coil2	Stator/Rotor/Air	Stator
coil3	Current	Induced Current: Deselect
coil3	Stator/Rotor/Air	Stator
mag1	Direction	Vector: X=0, Y=0, Z=1
mag1	Stator/Rotor/Air	Rotor
mag2	Direction	Vector: X=0, Y=0, Z=-1
mag2	Stator/Rotor/Air	Rotor
rt_core	Stator/Rotor/Air	Rotor
st_core	Stator/Rotor/Air	Stator

The material properties are set as follows.

Material Name

Tab

Properties

Conductivity

Conductivity Type: Conductor

Conductivity: 5.977x107 [S/m]

mag

Relative permeability

Material Type: Permanent Magnet

Magnet

Magnetization Characteristic Type: Linear

Magnetization Strength: 0.5 [T]

Relative Permeability: 1.05

core

Permeability

Magnetization Characteristic Type: Select B-H Curve

B-H Curve Table

Magnetic Field [A/m]	Magnetic Flux Density [T]
0	0
58	0.42
90	0.8
180	1.19
380	1.37
1100	1.48
2000	1.55
3000	1.608
11000	1.81
20000	1.91

Boundary Conditions

Symmetric period boundary is set.

Boundary Condition Name/Topology	Tab	Boundary Condition Type	Settings
Symmetry	Symmetry/Continuity	Periodic	Rotation (Periodic)

Results

The distribution of the magnetic flux density at the rotation angle of 0[deg] is shown below.

The waveform of cogging torque is shown as follows. It is output to [Torque [N*m]] of the result table.