Tham khảo tài liệu 'underwater vehicles part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Studies on Hydrodynamic Propulsion of a Biomimetic Tuna 469 orientation of each rib section and the tail can be determined. Transformation matrices are computed for each section of the moving tail and fin pre-multiplied together and then multiplied with the respective coordinates of the cross-sections. Fig. 7. The tail components superimposed on the travelling wave Fig. 8. The time step visualization of the tail motion There are three main outputs of the spline motion and strain calculations which can be run for various percentages of the tail period a superimposed image of the tail position on the 470 Underwater Vehicles travelling wave a visualization of the tail at each time step including the SMA wires and graphs of the strain time histories for both side of the fish shown in Figures 7 and 8 respectively. The circles in Figure 7 represent the locations of the axles on the tail. All figures are for at a frequency of 1Hz with Ao equal to amplitude at tip of tail equal to 8cm and k equal to 4. Fig. 9. The SMA wire strain time histories The E1 through 4 time histories illustrated in Figure 9 are the strains from the forward most section 1 through aft section 4 for the wires on both sides of the tail. Notice the SMA strains have a phase angle of 180 between opposing sides of the same section and have the profile of sine waves as would be expected. The pre-strains in section one through four are . The thermomechanical model derivation In order to size the wires and controller power supply a thermodynamic model of the heating and cooling of the wires was developed. The lumped capacitance model was used in a 1-D radial formulation and the accompanying differential equation solved numerically using Matlab. The resistive heating of the wires was modelled based on a supplied current and free convection was used for the heat transfer at the surface of the wires. The coating on the wires was neglected since it was assumed to be a very thin
