Transient analysis and design of composite structures in multiphase flows.

Composite marine propellers are composed of carbon fiber reinforced plastics (CFRP). They have a number of advantages over conventional propellers, which are typically made of nickel-aluminum-bronze (NAB). A flexible composite propeller will not only bend, but also twist. This is the so-called self-twisting propeller. If properly designed, a self-twisting propeller can lead to significant efficiency improvement over its rigid counterpart. Fundamental mechanisms for the performance enhancement were identified in the current work. A novel design strategy was systematically proposed, formulated, and implemented, to exploit and utilize the two governing mechanisms. A sample design was provided to illustrate the implementation of the design strategy. The feasibility of performance enhancement was demonstrated by comparing the predicted performance of the designed self-twisting propeller and rigid propeller pair under various operation conditions. Results showed significant performance improvement from the self-twisting propeller over its rigid counterpart. Relevant problems, including crash-back operation and static divergence, were addressed. Comprehensive evaluations demonstrate the robustness of the designed self-twisting propeller. Analytical and numerical models are also developed to study the transient interactions between underwater shocks/explosions and composite structures, with the ultimate target being the self-twisting propellers. The newly developed numerical solver was systematically validated against a series of bench-mark problems. It was also exercised to study realistic problems involving composite structures. A number of insights were obtained for the blast mitigation and blast-resistent designs.