Details of the model

Although the tubular machine has a three dimensional flux pattern in Cartesian coordinates, its uniformity around the centre line (x=0) allows it to be modelled using two dimensional analysis in an axisymetric coordinate system. The repetitive behaviour of the translator field could be investigated using a model consisting of one pole only, but the use of a three phase winding means it is beneficial to have a wider scope model. The four magnet, four surface pole model of Figure 5.8 allows a three phase winding spanning a surface pitch to be modelled across two entire surface poles, leaving half a pole width clearance at each end. By terminating the model halfway through the stainless steel support, the boundary condition is set as a flux line, i.e. having zero normal flux. The same is true for terminating the model at the mid point of a translator steel spacer.

r

p=0

c

B

A

stainless steel magnets support

p=100 c

p 50

B

A

c

B

A

I

\ /

/

\

N /

3 phase coil air steel spacer

Figure 5.8: Position of coils

Also shown in Figure 5.8 is the definition used for coil position i.e. at p=0, p=50 and p=100 coil B is exactly aligned above a steel spacer / surface pole.

The model mesh is shown in Figure 5.9. As with the VHM model, the smallest mesh size is 1 mm and is located in the coil / airgap region. In order to avoid computational bias in the coil region, the mesh was made densely throughout the translator / air boundary. The general structure of the mesh remains unaltered as the coil changes position, but this comes at the expense of many more elements in the model than necessary.

Figure 5.9: FEA mesh of tubular machine
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Renewable Energy Eco Friendly

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