Figure 23: The harmonic structures of horizontal wave loading on the cylinder and the envelops for both focused wave group cases F3 and case F4. From top to bottom: long wave, linear, 2 nd , 3 rd and 4 th harmonic. . Case F3 Numerical long wave Case F3 Numerical 1 st harmonic Case F3 Numerical 2 nd harmonic Case F3 Numerical 3 rd harmonic Case F3 Numerical 4 th harmonic Case F4 Numerical long wave Case F4 Numerical 1 st harmonic Case F4 Numerical 2 nd harmonic Case F4 Numerical 3 rd harmonic Case F4 Numerical 4 th harmonic ×2.0 ×2.0 2 ×2.0 3 ×2.0 4 =
A switched inertance hydraulic system uses a fast switching valve to control flow or pressure and is potentially very efficient as it does not rely on dissipation of power by throttling. This article studies its performance using an analytical method which efficiently describes the system in the time domain and frequency domain. A lumped parameter model and a distributed parameter model have been used for investigation using different parameters and conditions. The analytical models have been validated in experiments and the results on a prototype device show a very promising performance. The proposed analytical models are effective for understanding, analysing and optimizing the characteristics and performance of a switched inertance hydraulic system.
The harmful effects on human performance and health caused by unwanted vibration from vehicle seats are of increasing concern. This paper presents an active seat system to reduce the vibration level transmitted to the seat pan and the occupants' body under low frequency periodic excitation. Firstly, the detail of the mechanical structure is given and the active seat dynamics without external load are characterized by vibration transmissibility and frequency responses under different excitation forces. Owing the non-linear and time-varying behaviour of the proposed system, a Filtered-x least-meansquare (FXLMS) adaptive control algorithm with on-line Fast-block LMS (FBLMS) identification process is employed to manage the system operation for high vibration cancellation performance. The effectiveness of the active seat system is assessed through real-time experimental tests using different excitation profiles. The system identification results show that an accurate estimation of the secondary path is achieved by using the FBLMS on-line technique. Substantial reduction is found for cancelling periodic vibration containing single and multiple frequencies. Additionally, the robustness and stability of the control system are validated through transient switching frequency tests.
The optimization of a wave energy converter (WEC) hydraulic power takeoff (PTO) for sea states of varying wave amplitude, direction, and frequency is a significant problem. Sub-optimal configuration can result in very inefficient energy conversion [1], so understanding the design trade-offs is key to the success of the technology. This work focuses on a generic point absorber type WEC. Previous work by the authors [2] has considered the optimisation of this device for regular waves to gain an understanding of the fundamental issues. This work extends the analysis to the more realistic case of irregular waves. Simulations are performed using an irregular wave input to predict how the PTO will operate in real sea conditions. Work is also presented on a motor speed control strategy to maintain the maximum flow of electrical power to the grid, assuming the use of a doubly fed induction generator (DFIG). Finally, the sizing of key components in the PTO is considered in an attempt to maximise PTO efficiency and generated power.
Wave energy has the potential to be a major provider of renewable energy, especially in the UK. However, there is the major problem of producing efficient devices for a wide variety of sites with different operating conditions. This article addresses the time domain modelling of a heaving point absorber connected to a hydraulic power take-off (PTO) unit in regular waves. Two cases for the hydraulic PTO unit are considered: an ideal model and a model containing losses. Component losses are included to give a more accurate prediction of the maximum power production and to discover if the parameters to optimize the device change when losses are included. The findings show that both cases are optimized by varying the size of the hydraulic motor and the optimal size is only dependent on wave period and the trend is the same for both cases. Results also showed that to maximize the power produced for both cases, there is an optimal force that the unit produces, which can be derived from theory. Finally, power reduction as a result of the hydraulic losses is also observed with efficiencies reducing at larger wave heights.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.