The compliance of a fin affects the thrust of underwater vehicles mimicking the undulatory motion of fish. Determining the optimal compliance of a fin to maximize thrust is an important issue in designing robotic fish using a compliant fin. We present a simple method to identify the condition for maximizing the thrust generated by a compliant fin propulsion system. When a fin oscillates in a sinusoidal manner, it also bends in a sinusoidal manner. We focus on a particular kinematic parameter of this motion: the phase difference between the sinusoidal motion of the driving angle and the fin-bending angle. By observing the relationship between the thrust and phase difference, we conclude that while satisfying the zero velocity condition, the maximum thrust is obtained when a compliance creates a phase difference of approximately π/2 at a certain undulation frequency. This half-pi phase delay condition is supported by thrust measurements from different compliant fins (four caudal-shaped fins with different aspect ratios) and a beam bending model of the compliant fin. This condition can be used as a guideline to select the proper compliance of a fin when designing a robotic fish.

This paper proposes a rapid and accurate evaluation scheme for cycle counts of a pipelined processor using evaluation reuse technique. Since exploration of an optimal processor is a time-consuming task due to large design space, fast evaluation methodology for an architecture is crucial. We introduce the performance simulation model which can evaluate the performance without considering the functional correctness. This model has an FSM-like form and can afford to take all hazard types of pipelined architectures into consideration. The proposed approach is based on the property that an application program, especially multimedia application, has many iterative loops in general. This property invokes many iterative operations in the simulation. Evaluation reuse scheme can alleviate redundantly iterative operations of conventional simulators in the loop. A performance simulator for the pipeline architecture has been developed through which greater speedup has been made compared with other approaches in the evaluation of cycle counts.