Supercavitating bodies can achieve very high speeds under water by virtue of reduced drag: with proper design, a cavitation bubble is generated at the nose and skin friction drag is drastically reduced. Depending on the type of supercavitating vehicle under consideration, the overall drag coefficient can be an order of magnitude less than that of a fully-wetted vehicle. However, as discussed in this article, control and maneuvering present special challenges. Strategies for meeting those challenges are also presented. The first section describes example vehicle configurations, and discusses the nonlinear forces acting on the cavitator, the fins (if present), and any portions of the hull that penetrate the cavity boundary during excursions from the fully-enveloped condition. The need for a bank-to-turn maneuvering strategy is also discussed. The second section describes simulation of vehicle flight, including system stability and system performance during execution of a banked turn. Without control, some vehicle configurations can be unstable, whereas a feedforward-feedback strategy can control some configurations over a range of turn rates.

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We present a wave transmission line model developed to understand the transmission of energy through fluid-filled piping systems. The piping systems are represented as a sequence of components, e.g. valves, bends, and other components, connected with straight pipe sections. The transmission line model makes use of experimentally- or analytically-determined scattering coefficients to represent component behavior. The coefficients capture important coupling between fluid and structure, and among different structural wave types. The measurement of these coefficients is the subject of a separate paper [1]. The straight pipe segments are modeled analytically using fluid-filled, thick shell theory. Their motion is described in terms of amplitudes of freely traveling, left-and-right propagating waves. Results are presented which compare transfer functions measured on a piping system to predictions from the transmission line model, where each component is modeled with experimentally determined scattering coefficients. Initial results highlight important issues regarding the use of reciprocity, passivity, and causality to improve the quality of coefficients which are difficult to measure (for example, where certain frequency bands had high signal to noise). Algorithms for determining whether measured coefficients meet constraints on passivity, reciprocity, and causality are introduced. Predictions comparing analytical and measured coefficients are shown for a single-component (elbow) piping system.

This paper presents an experimental demonstration of the active control of a novel, modular sound enclosure that is built of panels which are stiffness controlled throughout the frequency range of interest. In this range, traditional passive noise enclosures are difficult to successfully implement. The design of the lightweight, stiff panels permits active control with a manageable number of actuators and sensors. The control technique is the adaptive, feedforward, filtered-x approach. Adaptive control is needed because realistic changes in the enclosure temperature and structural resonances would degrade the performance of fixed feedforward filters. The design of the enclosures makes this adaptive approach computationally feasible. Two performance criteria are evaluated: the minimization of the sum of the squares of the accelerations of the panels, and the minimization of certain supersonic wave-number components of the surface vibration field. Both approaches are straightforward for this enclosure design, where each panel behaves like a piston. [Work supported by the National Science Foundation.]