Test research on the resistance performance of high-speed trimaran planing hull

ABSTRACT In order to identify high-speed navigation ability of trimaran planing hull, as well as investigate the characteristics of its resistance and hull form, ship model tests were conducted to measure resistance, trim and heaving under different displacements and gravity centre locations. The test results were then used to study the influence of spray strips on resistance and sea-keeping qualities. Moreover, different planing surfaces were compared in the model tests which helped to look into influence of steps on hull resistance and its moving position. Also, the resistance features of monohull and trimaran planing hulls, both with and without steps, were compared to each other. From the tests it can be concluded that: the two auxiliary side hulls increase aerodynamic lift at high-speed motion, which improves the hydrodynamic performance; the trimaran planing hull has also excellent longitudinal stability and low wave-making action; when Fr∇ > 8, its motion is still stable and two distinct resistance peaks and two changes of sailing state (the second change is smaller) appear; spray strips are favourable for sea-keeping qualities at high speed. The change trends before the second resistance peak as to the resistance and sailing behaviour of trimaran planing hull without steps are the same as for monohull planing hull without steps. but when steps in both hulls exist the change trends are different; more specifically: trimaran planing hull with steps has only one resistance peak and its resistance increases along with its speed increasing, and the resistance is improved at the increasing speed as the number of steps increases.

ELASTIC MODULI AND SOUND VELOCITY IN La1-xSrxMnO3 (x = 0 to 0.3)

The longitudinal and shear sound velocity in colossal magnetoresistive La 1-x Sr x MnO 3 (x = 0.0, 0.05, 0.15 and 0.3) were measured using the pulse-echo-overlap technique in the temperature range of 80 to 300 K. An abrupt increase in the longitudinal velocity was observed immediately below the insulator-metal transition (T im ) in the x = 0.05 and 0.15 samples. This anomaly shifted towards higher temperature with an increase in Sr content. The absolute velocities (measured at 80 K) increased with Sr content. Hystereses in the longitudinal and shear velocity were observed in the x = 0.05 and 0.15 samples. A step-like longitudinal sound velocity anomaly between 150 K and 220 K during warming and cooling was observed in the x = 0.05 sample. A sudden hardening was observed for longitudinal and shear sound velocity coinciding with second broad resistance peak at temperature below T im in x = 0.15 sample. The characteristic Debye temperature increases as Sr content was increased, indicating a hardening trend. These results indicate the importance of phonons in the transport mechanism of these colossal magnetoresistive materials.

MAGNETIC AND ELECTRONIC TRANSPORT PROPERTIES OF NANOSTRUCTURED La0.67Ca0.33MnO3 FILMS

Nanostructured colossal magnetoresistive (CMR) films of La 0.67 Ca 0.33 MnO 3 (LCMO) were deposited by using pulsed electron deposition technique on anodized aluminum oxide membranes with pores of 50 nm in diameter. The magnetic and electronic transport properties were measured on Quantum Design physics properties measurement system (PPMS) and magnetic properties measurement system (MPMS). The resistance peak temperature ( T P ) is about 165 K and the Curie temperature ( T C ) is about 260 K. Large magnetoresistance was observed near T P in these nanostructured LCMO films. Linear I-V curves at different temperatures indicate no electronic tunneling effect. The large difference between T P and T C suggests that the nature of the resistance peak is different from that of bulk samples. The physics in these nanostructured films should be interesting to explore the mechanism of CMR effect.