A body of literature quantifying wave attenuation through vegetation has developed within the last few decades and serves as the foundation for growing interest in wetlands for engineering with nature applications. Wave dissipation is shown to be highly variable, influenced by hydrodynamics, plant structure, and the interaction between the two. The current method of predicting wave dissipation often makes use of an empirical drag coefficient, which is given as a function of nondimensional flow parameter. These empirical equations are shown to have limitations, particularly in the transition from the submerged to emergent regime, and are highly variable in nature and in magnitude. Vegetation is shown to preferentially dissipate energy at frequencies higher than the spectral peak for single-and double-peaked wave spectra. Idealized simulations of Jamaica Bay with STeady-state spectral WAVE (STWAVE) demonstrate the potential for vegetation to provide shoreline protection by reducing wave height under severe wind and water level conditions.

This article reports on the design and experimental characterization of an electromagnetic transducer for energy harvesting from large structures (e.g., multistory buildings and bridges), for which the power levels can be above 100 W and disturbance frequencies below 1 Hz. The transducer consists of a back-driven ballscrew coupled to a permanent-magnet synchronous machine with power harvesting regulated via control of a four-quadrant power electronic drive. Design considerations between various subsystems are illustrated and recommendations in terms of minimal values are made for each design metric. Developing control algorithms to take full advantage of the unique features of this type of transducer requires a mechanical model that can adequately characterize the device’s intrinsic nonlinear behavior. A new model is proposed that can effectively capture this behavior. Comparison with experimental results verifies that the model is accurate over a wide range of operating conditions. As such, the model can be used to assess the viability of the technology and to correctly design controllers to maximize power generation. To demonstrate the device’s energy harvesting capability, impedance matching theory is used to optimize the power generated from a base-excited tuned mass damper. Both theoretical and experimental investigations are compared and the results are shown to match closely.

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This article illustrates that certain relatively well-known results from feedback control theory can be used to determine the maximum-attainable power generation for a vibratory energy harvester excited by a stationary broadband stochastic disturbance. For such applications, control techniques based on impedance matching theory cannot be used to optimize power generation, because the dynamic controller they prescribe is always anticausal. However, an optimal causal controller does exist, and can be derived using H 2 /LQG theory. Levels of power generation with this controller are compared to those of the anticausal optimal performance, as well as to traditional 'tuning' techniques which match the anticausal impedance only at the resonant frequency. It is demonstrated that tuning techniques can be significantly sub-optimal in broadband applications, especially when electronic conversion is relatively efficient. In addition to being useful in the design of controllers for energy harvesting applications, these results may also be used to ascertain the insurpassable power generation limits associated with a given combination of transducer and electronic hardware.

Regenerative force actuation networks are groups of electromechanical force actuators that produce significant but constrained control forces, while requiring minimal external power. They differ from semiactive devices by the fact that they are capable of sharing power with one another; i.e. one device may remove energy from one location in a vibrating structure while another injects some of that energy back into the structure at a different location. These devices employ ballscrews and rotational electric machines to facilitate electromechanical power conversion. Excess energy removed from the structure is dissipated electrically in a resistor bank. This paper introduces these concepts, and presents a generalized model for an actuation system with an arbitrarily large network of actuators. The characteristics of this actuation system are discussed, accounting for energy dissipation and dynamics in the electrical network. A numerical example of the use of these devices in a structural control system is presented, in which two devices are used to control a three‐storey scale‐model building under earthquake loading. It is shown that the power coupling between the actuators can be used to improve the overall structural performance. Copyright © 2004 John Wiley & Sons, Ltd.

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