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Xiantao Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Multi-Stable Mechanism of an Oscillating-Body Wave Energy Converter
    IEEE Transactions on Sustainable Energy, 2020
    Co-Authors: Xiantao Zhang, Zhiming Yuan, Yan Gao
    Abstract:

    The present research aims to utilize the multi-stable mechanism to increase the energy conversion of the Oscillating-Body wave energy converter (WEC). Considering that a majority of WEC concepts are linear and single-stable, a nonlinear spring-damper model is proposed to achieve the multi-stable mechanism. The system is either monostable or bistable depending on the initial condition of the springs. The energy conversion of a heaving point-absorber with the nonlinear spring-damper model is investigated in the present research. First, a state-space dynamic model of the heaving point-absorber is developed. Then, the energy conversion at both the monostable mode and the bistable mode is simulated. The present research also illustrates the response feature at the two stable modes. It is found the nonlinear point-absorber behaves like a linear system in the monostable mode. The energy conversion is just increased slightly. Nevertheless, the energy absorption is increased substantially in the bistable mode. It is found that the velocity phase is adjusted in the bistable mode, leading to the enhancement of the energy conversion.

  • effects of wave excitation force prediction deviations on the discrete control performance of an Oscillating wave energy converter
    Ships and Offshore Structures, 2016
    Co-Authors: Xiantao Zhang, Jianmin Yang, Wenhua Zhao, Longfei Xiao
    Abstract:

    Oscillating-Body converters are widely used in offshore engineering, to capture wave energies. In such a case, discrete control including both latching and declutching controls is adopted to improve the power capture performance of Oscillating wave energy converters (WECs). A reliable prediction of wave excitation forces on the WEC is essential for the discrete control strategy. In this study, a time domain model is developed to calculate the hydrodynamic responses of a hemispherical Oscillating WEC with discrete control in regular waves. A state space model is used to deal with the convolution term in the time domain equation, taking into account the memory effects of wave surface. Based on the developed numerical model, the effects of prediction deviations, such as the amplitude and phase of wave excitation force, have been studied. It is observed that the amplitude prediction deviation exhibits very few effects on the control performance. However, the phase prediction deviation performances significant...

  • effects of wave excitation force prediction deviations on the discrete control performance of an Oscillating wave energy converter
    Ships and Offshore Structures, 2016
    Co-Authors: Xiantao Zhang, Jianmin Yang, Wenhua Zhao, Longfei Xiao
    Abstract:

    Oscillating-Body converters are widely used in offshore engineering, to capture wave energies. In such a case, discrete control including both latching and declutching controls is adopted to improve the power capture performance of Oscillating wave energy converters (WECs). A reliable prediction of wave excitation forces on the WEC is essential for the discrete control strategy. In this study, a time domain model is developed to calculate the hydrodynamic responses of a hemispherical Oscillating WEC with discrete control in regular waves. A state space model is used to deal with the convolution term in the time domain equation, taking into account the memory effects of wave surface. Based on the developed numerical model, the effects of prediction deviations, such as the amplitude and phase of wave excitation force, have been studied. It is observed that the amplitude prediction deviation exhibits very few effects on the control performance. However, the phase prediction deviation performances significant...

  • power capture performance of an Oscillating Body wec with nonlinear snap through pto systems in irregular waves
    Applied Ocean Research, 2015
    Co-Authors: Xiantao Zhang, Jianmin Yang
    Abstract:

    Abstract Compared with solar and wind energy, wave energy is a kind of renewable resource which is enormous and still under development. In order to utilize the wave energy, various types of wave energy converters (WECs) have been proposed and studied. And Oscillating-Body WEC is widely used for offshore deployment. For this type of WEC, the Oscillating motion of the floater is converted into electricity by the power take off (PTO) system, which is usually mathematically simplified as a linear spring and a damper. The linear PTO system is characteristic of frequency-dependent response and the energy absorption is less powerful for off resonance conditions. Thus a nonlinear snap through PTO system consisting of two symmetrically oblique springs and a linear damper is applied. A nonlinear parameter γ is defined as the ratio of half of the horizontal distance between the two oblique springs to the original length of both springs. JONSWAP spectrum is utilized to generate the time series of irregular waves. Time domain method is used to establish the motion equation of the Oscillating-Body WEC in irregular waves. And state space model is applied to replace the convolution term in the time domain motion equation. Based on the established motion equation, the motion response of both the linear and nonlinear WEC is numerically calculated using 4th Runge–Kutta method, after which the captured power can be obtained. Then the influences of wave parameters such as peak frequency, significant wave height, damping coefficient of the PTO system and the nonlinear parameter γ on the power capture performance of the nonlinear WEC is discussed in detail. Results show that compared with linear PTO system, the nonlinear snap through PTO system can increase the power captured by the Oscillating Body WEC in irregular waves.

Longfei Xiao - One of the best experts on this subject based on the ideXlab platform.

  • comparative study on power capture performance of Oscillating Body wave energy converters with three novel power take off systems
    Renewable Energy, 2017
    Co-Authors: Xiaolong Xiao, Longfei Xiao, Tao Peng
    Abstract:

    Abstract Converting persistent and renewable wave energy into electricity has been a research focus in recent years. The Oscillating-Body wave energy converter (WEC) is a promising approach, especially for offshore areas. However, conventional Oscillating-Body WECs with linear power take-off (PTO) systems are less efficient under off-resonance conditions and have a narrow power capture bandwidth, which has inhibited the commercial application of wave energy. In order to enhance the power capture performance, this study examined Oscillating-Body WECs with three new types of PTO systems: bistable impulsive PTO, coupled linear PTO, and coupled bistable PTO. Governing equations for the heave motion of a WEC were established based on the linear potential theory by coupling the buoy and PTO systems and were numerically calculated with the fourth-order Runge–Kutta method. The influence of PTO parameters such as the spring constant, stable equilibrium position, and mass ratio on the power capture ratio was investigated. The differences among the WECs with different PTOs were analysed to determine the optimum device. Compared with the linear PTO system, the WEC with the bistable impulse PTO system enhanced the power capture ratio for low-frequency regular waves, and WECs with coupled linear or coupled bistable PTO systems increased the power capture ratio for low-frequency regular waves and expanded the power capture spectrum bandwidth when proper PTO parameters were applied.

  • effects of wave excitation force prediction deviations on the discrete control performance of an Oscillating wave energy converter
    Ships and Offshore Structures, 2016
    Co-Authors: Xiantao Zhang, Jianmin Yang, Wenhua Zhao, Longfei Xiao
    Abstract:

    Oscillating-Body converters are widely used in offshore engineering, to capture wave energies. In such a case, discrete control including both latching and declutching controls is adopted to improve the power capture performance of Oscillating wave energy converters (WECs). A reliable prediction of wave excitation forces on the WEC is essential for the discrete control strategy. In this study, a time domain model is developed to calculate the hydrodynamic responses of a hemispherical Oscillating WEC with discrete control in regular waves. A state space model is used to deal with the convolution term in the time domain equation, taking into account the memory effects of wave surface. Based on the developed numerical model, the effects of prediction deviations, such as the amplitude and phase of wave excitation force, have been studied. It is observed that the amplitude prediction deviation exhibits very few effects on the control performance. However, the phase prediction deviation performances significant...

  • effects of wave excitation force prediction deviations on the discrete control performance of an Oscillating wave energy converter
    Ships and Offshore Structures, 2016
    Co-Authors: Xiantao Zhang, Jianmin Yang, Wenhua Zhao, Longfei Xiao
    Abstract:

    Oscillating-Body converters are widely used in offshore engineering, to capture wave energies. In such a case, discrete control including both latching and declutching controls is adopted to improve the power capture performance of Oscillating wave energy converters (WECs). A reliable prediction of wave excitation forces on the WEC is essential for the discrete control strategy. In this study, a time domain model is developed to calculate the hydrodynamic responses of a hemispherical Oscillating WEC with discrete control in regular waves. A state space model is used to deal with the convolution term in the time domain equation, taking into account the memory effects of wave surface. Based on the developed numerical model, the effects of prediction deviations, such as the amplitude and phase of wave excitation force, have been studied. It is observed that the amplitude prediction deviation exhibits very few effects on the control performance. However, the phase prediction deviation performances significant...

Tao Peng - One of the best experts on this subject based on the ideXlab platform.

  • comparative study on power capture performance of Oscillating Body wave energy converters with three novel power take off systems
    Renewable Energy, 2017
    Co-Authors: Xiaolong Xiao, Longfei Xiao, Tao Peng
    Abstract:

    Abstract Converting persistent and renewable wave energy into electricity has been a research focus in recent years. The Oscillating-Body wave energy converter (WEC) is a promising approach, especially for offshore areas. However, conventional Oscillating-Body WECs with linear power take-off (PTO) systems are less efficient under off-resonance conditions and have a narrow power capture bandwidth, which has inhibited the commercial application of wave energy. In order to enhance the power capture performance, this study examined Oscillating-Body WECs with three new types of PTO systems: bistable impulsive PTO, coupled linear PTO, and coupled bistable PTO. Governing equations for the heave motion of a WEC were established based on the linear potential theory by coupling the buoy and PTO systems and were numerically calculated with the fourth-order Runge–Kutta method. The influence of PTO parameters such as the spring constant, stable equilibrium position, and mass ratio on the power capture ratio was investigated. The differences among the WECs with different PTOs were analysed to determine the optimum device. Compared with the linear PTO system, the WEC with the bistable impulse PTO system enhanced the power capture ratio for low-frequency regular waves, and WECs with coupled linear or coupled bistable PTO systems increased the power capture ratio for low-frequency regular waves and expanded the power capture spectrum bandwidth when proper PTO parameters were applied.

C H K Williamson - One of the best experts on this subject based on the ideXlab platform.

  • the effect of reynolds number on the critical mass phenomenon in vortex induced vibration
    Physics of Fluids, 2009
    Co-Authors: T L Morse, C H K Williamson
    Abstract:

    In this study, we investigate the critical mass phenomenon in vortex-induced vibration over a wide range of Reynolds numbers (Re=4000–30 000). We consider an elastically mounted cylinder that is able to vibrate transverse to a fluid flow. If we remove the restoring spring (k=0), then above a certain critical mass ratio (m∗ is Oscillating Body mass/displaced fluid mass), the cylinder will experience almost no motion, despite its unrestrained freedom to move transverse to the flow. However, when the mass ratio is decreased below a special critical value, without altering anything else in the system, we see a catastrophic increase in amplitude, and the Body settles into a large amplitude periodic vibration. This corresponds to a change from a desynchronized wake to a 2P mode of vortex formation, where two pairs of vortices are formed per cycle of motion. Since a system with no restoring force represents a case of infinite normalized velocity (U∗→∞), the observation of high amplitude motion indicates that the...

Xiaolong Xiao - One of the best experts on this subject based on the ideXlab platform.

  • comparative study on power capture performance of Oscillating Body wave energy converters with three novel power take off systems
    Renewable Energy, 2017
    Co-Authors: Xiaolong Xiao, Longfei Xiao, Tao Peng
    Abstract:

    Abstract Converting persistent and renewable wave energy into electricity has been a research focus in recent years. The Oscillating-Body wave energy converter (WEC) is a promising approach, especially for offshore areas. However, conventional Oscillating-Body WECs with linear power take-off (PTO) systems are less efficient under off-resonance conditions and have a narrow power capture bandwidth, which has inhibited the commercial application of wave energy. In order to enhance the power capture performance, this study examined Oscillating-Body WECs with three new types of PTO systems: bistable impulsive PTO, coupled linear PTO, and coupled bistable PTO. Governing equations for the heave motion of a WEC were established based on the linear potential theory by coupling the buoy and PTO systems and were numerically calculated with the fourth-order Runge–Kutta method. The influence of PTO parameters such as the spring constant, stable equilibrium position, and mass ratio on the power capture ratio was investigated. The differences among the WECs with different PTOs were analysed to determine the optimum device. Compared with the linear PTO system, the WEC with the bistable impulse PTO system enhanced the power capture ratio for low-frequency regular waves, and WECs with coupled linear or coupled bistable PTO systems increased the power capture ratio for low-frequency regular waves and expanded the power capture spectrum bandwidth when proper PTO parameters were applied.