Enlarged Moment

The position of the hydraulic rams and the magnitude of the moment arm dictates the velocity, pressure and stroke length of the power cycle. Clearly, when replacing the power take off for a direct drive system, there are different priorities involved in locating the system parts. Electrical machines benefit from positions of higher velocity as the required reactive force is lower, whilst still extracting the same power from the body. Hydraulic systems can operate at pressures of several hundred bar (107 Pa) and are hence able to react huge forces. They also have a seal-enforced upper limit on permitted velocity. Furthermore, if an electrical machine can be made longer in the direction of travel, the required width will decrease for the same active area and hence rated force. The active chamber of a hydraulic ram, however, should be kept as small as possible to reduce weight and volume of fluid.

These conflicting factors imply that the best place for a hydraulic power take off system is the worst place to consider a direct drive system. The latter would benefit from locating the generators in a position on the Stingray with a larger moment arm and active length.

Referring again to Figure 7.2, the two dimensions which can be most conveniently altered are marked as A and B. The former mainly alters the minimum (active) length whereas the latter greatly affects the moment arm length. For demonstration purposes, both of these dimensions are doubled. The required moment can now be applied by two opposed generators with have an active length of 4.66 metres each reacting a maximum force of 680 kN over a 1.44 m amplitude of oscillation. Two generators of the type detailed in Table 7-4 could provide this function. The total mass added by the direct drive system is now 69 tonnes. To gauge a feeling of how this would sit in the device, Figure 7.7 shows a scale diagram allowing comparison of the linear generator to both an original cylinder and the device itself.

Table 7-4: Linear generator suitable for use with enlarged moment arm

Axial length of phase (m)

1.03

Outer width (m)

1.40

Mass rotor (tonnes)

11

Mass magnets (tonnes)

0.39

Mass copper (tonnes)

5.1

Total mass (tonnes)

35

Figure 7.7: Comparison of proposed generator and existing cylinder Although the generator is clearly larger than its hydraulic equivalent, when compared with the scale of the machine it is not a cumbersome alternative. If the pivot arm, dimension B, could again be doubled, then the total width of the generator would be comparable to the combined width of the two cylinders it would be replacing. Demonstrated is the importance of the location of the generators, with 8 tonnes being saved on the direct drive concept by altering its position.

Figure 7.7: Comparison of proposed generator and existing cylinder Although the generator is clearly larger than its hydraulic equivalent, when compared with the scale of the machine it is not a cumbersome alternative. If the pivot arm, dimension B, could again be doubled, then the total width of the generator would be comparable to the combined width of the two cylinders it would be replacing. Demonstrated is the importance of the location of the generators, with 8 tonnes being saved on the direct drive concept by altering its position.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

Get My Free Ebook


Post a comment