Design of A Hydraulic Power Take-off System for the Wave Energy Device with An Inverse Pendulum

This paper describes a dual-stroke acting hydraulic power take-off （PTO） system employed in the wave energy converter （WEC） with an inverse pendulum. The hydraulic PTO converts slow irregular reciprocating wave motions to relatively smooth, fast rotation of an electrical generator. The design of the hydraulic PTO system and its control are critical to maximize the generated power. A time domain simulation study and the laboratory experiment of the full-scale beach test are presented. The results of the simulation and laboratory experiments including their comparison at full-scale are also presented, which have validated the rationality of the design and the reliability of some key components of the prototype of the WEC with an inverse pendulum with the dual-stroke acting hydraulic PTO system.

Capture Performance of A Multi-Freedom Wave Energy Converter with Different Power Take-off Systems

Among the wave energy converters (WECs), oscillating buoy is a promising type for wave energy development in offshore area. Conventional single-freedom oscillating buoy WECs with linear power take-off (PTO) system are less efficient under off-resonance conditions and have a narrow power capture bandwidth. Thus, a multi-freedom WEC with a nonlinear PTO system is proposed. This study examines a multi-freedom WEC with 3 degrees of freedom: surge, heave and pitch. Three different PTO systems (velocity-square, snap through, and constant PTO systems) and a traditional linear PTO system are applied to the WEC. A time-domain model is established using linear potential theory and Cummins equation. The kinematic equation is numerically calculated with the fourth-order Runge–Kutta method. The optimal average output power of the PTO systems in all degrees of freedom are obtained and compared. Other parameters of snap through PTO are also discussed in detail. Results show that according to the power capture performance, the order of the PTO systems from the best to worst is snap through PTO, constant PTO, linear PTO and velocity-square PTO. The resonant frequency of the WEC can be adjusted to the incident wave frequency by choosing specific parameters of the snap through PTO. Adding more DOFs can make the WEC get a better power performance in more wave frequencies. Both the above two methods can raise the WEC’s power capture performance significantly.

Research of Power Take-off System for “Sharp Eagle Ⅱ” Wave Energy Converter

The " Sharp Eagle” device is a wave energy converter of a hinged double floating body. The wave-absorbing floating body hinges on the semi-submerged floating body structure. Under the action of wave, the wave-absorbing floating body rotates around the hinge point, and the wave energy can be converted into kinetic energy. In this paper, the power take-off system of " Sharp Eagle Ⅱ” wave energy converter (the second generation of " Sharp Eagle”) was studied, which adopts the hydraulic type power take-off system. The 0-1 power generation mode was applied in this system to make the " Sharp Eagle Ⅱ” operate under various wave conditions. The principle of power generation was introduced in detail, and the power take-off system was simulated. Three groups of different movement period inputs were used to simulate three kinds of wave conditions, and the simulation results were obtained under three different working conditions. In addition, the prototype of " Sharp Eagle Ⅱ” wave energy converter was tested on land and in real sea conditions. The experimental data have been collected, and the experimental data and simulation results were compared and validated. This work has laid a foundation for the design and application of the following " Sharp Eagle” series of devices.

Power Absorption of A Two-Body Heaving Wave Energy Converter Considering Different Control and Power Take-off Systems

This study proposed a wave power system with two coaxial floating cylinders of different diameters and drafts.Wavebob’s conceptual design has been adopted in the wave power system.In this study,a basic analysis of the wave energy extraction by the relative motion between two floats is presented.The maximum power absorption was studied theoretically under regular wave conditions,and the effects of both linear and constant damping forces on the power take-off(PTO)were investigated.A set of dynamic equations describing the floats’displacement under regular waves and different PTOs are established.A time-domain numerical model is developed,considering the PTO parameter and viscous damping,and the optimal PTO damping and output power are obtained.With the analysis of estimating the maximum power absorption,a new estimation method called Power Capture Function(PCF)is proposed and constructed,which can be used to predict the power capture under both linear and constant PTO forces.Based on this,energy extraction is analyzed and optimized.Finally,the performance characteristics of the two-body power system are concluded.

Hydraulic Power Take-off and Buoy Geometries Charac-terisation for a Wave Energy Converter

In the past few decades, world energy consumption grew considerably. Regarding this fact, wave energy should not be discarded as a valid alternative for the production of electricity. Devices suitable to harness this kind of renewable energy source and turn it into electricity are not yet commercially competitive. The work described in this paper aims to contribute to this field of research. It is focused on the design and construction of robust, simple and affordable hydraulic Power Take-Off using hydraulic commercial components.

Application of the Latching Control System on the Power Performance of a Wave Energy Converter Characterized by Gearbox,Flywheel,and Electrical GeneratorGustavor

The latching control represents an attractive alternative to increase the power absorption of wave energy converters(WECs)by tuning the phase of oscillator velocity to the wave excitation phase.However,increasing the amplitude of motion of the floating body is not the only challenge to obtain a good performance of the WEC.It also depends on the efficiency of the power take-off system(PTO).This study aims to address the actual power performance and operation of a heaving point absorber with a direct mechanical drive PTO system controlled by latching.The PTO characteristics,such as the gear ratio,the flywheel inertia,and the electric generator,are analyzed in the WEC performance.Three cylindrical point absorbers are also considered in the present study.A wave-to-wire model is developed to simulate the coupled hydro-electro-mechanical system in regular waves.The wave energy converter(WEC)performance is analyzed using the potential linear theory but considering the viscous damping effect according to the Morison equation to avoid the overestimated responses of the linear theory near resonance when the latching control system is applied.The latching control system increases the mean power.However,the increase is not significant if the parameters that characterize the WEC provide a considerable mean power.The performance of the proposed mechanical power take-off depends on the gear ratio and flywheel.However,the gear ratio shows a more significant influence than the flywheel inertia.The operating range of the generator and the diameter/draft ratio of the buoy also influence the PTO performance.

The Method of Imbedded Lagrangian Element to Estimate Wave Power Absorption by Some Submerged Devices

A simple approach is described to estimate the wave power absorption potential of submerged devices known to cause wave focusing and flow enhancement. In particular, the presence of a flow-through power take-off （PTO） system, such as low-head turbines, can be accounted for. The wave radiation characteristics of an appropriately selected Lagrangian element （LE） in the fluid domain are first determined. In the limit of a vanishing mass, the LE reduces to a patch of distributed normal dipoles. The hydrodynamic coefficients of this virtual object are then input in a standard equation of motion where the effect of the PTO can be represented, for example, as a dashpot damping term. The process is illustrated for a class of devices recently proposed by Carter and Ertekin （2011）, although in a simplified form. Favorable wave power absorption is shown for large ratios of the LE wave radiation coefficient over the LE added mass coefficient. Under optimal conditions, the relative flow reduction from the PTO theoretically lies between 0.50 and 1 2 ≈ 0.71, with lower values corresponding to better configurations. Wave power capture widths, the sensitivity of results to PTO damping and sample spectral calculations at a typical site in Hawaiian waters are proposed to further illustrate the versatility of the method.

上司示意型知识隐藏的双刃剑效应及其边界条件研究

基于压力认知评价理论,构建了有调节的中介模型以探讨上司示意型知识隐藏影响下属知识隐藏的二元效应及其边界条件。基于两个时间点的团队成员配对数据,采用路径分析对假设模型进行检验。研究结果表明:上司示意型知识隐藏一方面会诱发道德推脱,从而促进下属知识隐藏;一方面也会唤醒关系经营,从而抑制下属知识隐藏;且两种效应与道德认同和权力距离导向的联合调节作用相关。

太原电网安全稳定分析及技改规划建议

针对太原电网供电负荷持续增长、电力体制改革深入、电网运行安全裕度下降的现状,通过短路、潮流、稳定分析计算,评估了太原电网安全稳定裕度,提出了存在的问题及主要风险,并结合太原电网的发展趋势及电网分区原则,根据项目的时序性、紧迫性及难易程度,提出合理的电网技改、规划建议,指导太原电网技改规划立项,提高电网投资的精准性,引导太原电网健康发展。

Research on Energy Conversion System of Floating Wave Energy Converter

A wave power device includes an energy harvesting system and a power take-off system. The power take-off system of a floating wave energy device is the key that converts wave energy into other forms. A set of hydraulic power take-off system, which suits for the floating wave energy devices, includes hydraulic system and power generation system. The hydraulic control system uses a special“self-hydraulic control system”to control hydraulic system to release or save energy under the maximum and the minimum pressures. The maximum pressure is enhanced to 23 MPa, the minimum to 9 MPa. Quite a few experiments show that the recent hydraulic system is evidently improved in efficiency and reliability than our previous one, that is expected to be great significant in the research and development of our prototype about wave energy conversion.

Connection Technology of HPTO Type WECs and DC Nano Grid in Island

Wave energy fluctuating a great deal endangers the security of power grid especially micro grid in island. A DC nano grid supported by batteries is proposed to smooth the output power of wave energy converters（WECs）. Thus, renewable energy converters connected to DC grid is a new subject. The characteristics of WECs are very important to the connection technology of HPTO type WECs and DC nano grid. Hydraulic power take-off system（HPTO） is the core unit of the largest category of WECs, with the functions of supplying suitable damping for a WEC to absorb wave energy, and converting captured wave energy to electricity. The HPTO is divided into a hydraulic energy storage system（HESS） and a hydraulic power generation system（HPGS）. A primary numerical model for the HPGS is established in this paper. Three important basic characteristics of the HPGS are deduced, which reveal how the generator load determines the HPGS rotation rate. Therefore, the connector of HPTO type WEC and DC nano grid would be an uncontrollable rectifier with high reliability, also would be a controllable power converter with high efficiency, such as interleaved boost converter-IBC. The research shows that it is very flexible to connect to DC nano grid for WECs, but bypass resistance loads are indispensable for the security of WECs.

Optimization of Bottom-hinged Flap-type Wave Energy Converter for a Specific Wave Rose

In this paper, we conducted a numerical analysis on the bottom-hinged flap-type Wave Energy Convertor (WEC). The basic model, implemented through the study using ANSYS-AQWA, has been validated by a three-dimensional physical model of a pitching vertical cylinder. Then, a systematic parametric assessment has been performed on stiffness, damping, and WEC direction against an incoming wave rose, resulting in an optimized flap-type WEC for a specific spot in the Persian Gulf. Here, stiffness is tuned to have a near-resonance condition considering the wave rose, while damping is modified to capture the highest energy for each device direction. Moreover, such sets of specifications have been checked at different directions to present the best combination of stiffness, damping, and device heading. It has been shown that for a real condition, including different wave heights, periods, and directions, it is very important to implement the methodology introduced here to guarantee device performance.

Theoretical and Experimental Study of A Coaxial Double-Buoy Wave Energy Converter

The double-body heave wave energy converter(WEC)is one of the most conducive devices to absorb the wave energy from relative motion while the law of which is not well understood.This paper makes an in-depth study on this wave energy converter,by means of the combination of theoretical analysis and physical model experiment.The hydrodynamic characteristics and energy capture of the double-buoy under constant and linear Power Take-Off(PTO)damping are investigated.Influences of absolute mass and mass ratio are discussed in the theoretical model.Relative displacement amplitude and average power output are tested in the experiment to analyze the effect of the wave period and outer buoy’s mass,while the capture width ratio(CWR)is also calculated.Results show that the wave period and mass of the buoys have a significant effect on the converter.Different forms of PTO damping have no influence on the optimal wave period and mass ratio of this device.It is recommended to select the double-buoy converter with a mass ratio of 0.80 and to place it in an area with the frequent wave period close to the natural period of the outer buoy to achieve the optimal energy capture.

Power enhancement of pontoon-type wave energy convertor via hydroelastic response and variable power take-off system

Wave energy has gained its popularity in recent decades due to the vast amount of untapped wave energy resources.There are numerous types of wave energy convertor(WEC)being proposed and to be economically viable,various means to enhance the power generation from WECs have been studied and investigated.In this paper,a novel pontoon-type WEC,which is formed by multiple plate-like modules connected by hinges,are considered.The power enhancement of this pontoon-type WEC is achieved by allowing certain level of structural deformation and by utilizing a series of optimal variable power take-off(PTO)system.The wave energy is converted into useful electricity by attaching the PTO systems on the hinge connectors such that the mechanical movements of the hinges could produce electricity.In this paper,various structural rigidity of the interconnected modules are considered by changing the material Young’s modulus in order to investigate its impact on the power enhancement.In addition,the genetic algorithm optimization scheme is utilized to seek for the optimal PTO damping in the variable PTO system.It is observed that under certain condition,the flexible pontoon-type WEC with lesser connection joints is more effective in generating energy as compared to its rigid counterpart with higher connection joints.It is also found that the variable PTO system is able to generate greater energy as compared to the PTO system with constant/uniform PTO damping.

载货汽车AMT不分离离合器换挡技术的研究与应用

根据换挡接合齿轮副的特性和车辆动力学原理,分析载货汽车AMT不分离离合器摘挡、挂挡过程及换挡前后的动力中断与恢复过程,并确定应用此技术的工况及其实现方法。将该技术应用于某重型载货汽车AMT中,得出应用该技术既能保证换挡的舒适性及缩短AMT换挡过程中动力中断时间,又能提高离合器使用寿命的结论。

行星齿轮式离合器可行性研究

离合器主要的功能是实现动力的分离和结合。行星齿轮组的特性是:如果将行星齿轮的三元件(太阳轮、行星架和齿圈)中某一个固定,动力传递固定;将三元件全部松开,动力不能传递,也就是动力分离和结合的过程。本文从设计角度分析采用行星齿轮组作为离合器机构的可行性。

An Assessment of Eco Driving System for Agricultural Tractor

In this study, tractor power output, fuel consumption rate and work performance were indirectly predicted in order to develop an eco driving system. Firstly, equations were developed which could foretell tractor power output and fuel consumption rate using characteristic curves of tractor power output. Secondly, with actual engine revolution per minute （rpm） determined by initial engine rpm and work load, tractor power output and fuel consumption rate were forecasted. Thirdly, it was possible to foresee tractor work performance and fuel consumption rate by the speed signals of Global Positioning System （GPS）. Lastly, precision of the eco driving system was evaluated through tractor Power Take-Off （PTO） test, and effects of the eco driving system were investigated in the plowing and rotary tilling operations. Engine rpm, power output, fuel consumption rate, work performance and fuel consumption rate per plot area were displayed on the eco driving system. Predicted tractor power outputs in the full load curve were well coincided with the actual power output of prototype, but small differences, 1 to 6 kW were found in the part load curve. Error of the fuel consumption rate was 0.5 to 3 L/h at the part load curve. It was shown that 69% and 53% of fuel consumption rates could be reduced in plowing and rotary tilling operations, respectively, when the eco driving system was installed in tractor.

带前副箱的变速器匹配取力器脱挡故障

带前副箱结构的双中间轴变速器在匹配贯通轴取力器时,当取力器工作时,前副箱频繁“脱挡”,分析了产生该故障的原因。以此为基础,提出了一种改变一轴外花键段的局部参数的新结构,使用该结构的新一轴,通过试验验证,“脱挡”故障得以解决。此研究结果对贯通轴取力器在带前副箱结构的双中间轴变速器上匹配有指导意义。

肥西变电站220kV母线短路电流越限解决方案的研究

随着安徽电网规模的不断扩大,500 kV肥西变电站即将出现短路电流越限的问题,应及时研究其解决方案。比较电网解环、在变压器中性点加装小电抗及220 kV母线分裂运行等措施限制短路电流的效果,结合对电网的影响及适应性,推荐采取肥西变电站220 kV母线分裂运行的方案。

Performance analysis of a tuned point absorber using SPH calm water and wave tank simulations

In this paper,two smoothed particle hydrodynamics(SPH)models,namely SPH-W and SPH-C were used to evaluate the motion response of a point absorber wave energy converter(WEC).In the SPH-W model,a long wave flume was constructed and a long simulation was performed to obtain the motion response of the WEC.In the SPH-C model,the SPH method is only used to find the hydrodynamic coefficients of the device by analysing a few seconds of free-decaying motion of WEC in calm water in a much smaller numerical flume.Then,these coefficients were inserted in the equation of motion of a heaving WEC that was solved using a 4th order Runge-Kutta(ODE45)solver in MATLAB.First,the energy conservation property of the WCSPH model was examined through a standing wave benchmark test.Then,the wavepoint absorber interaction was simulated.While the simulation time for SPH-C model is much smaller than that of SPH-W,it gave almost similar results for the motion response of WEC.These two models were used to evaluate the effects of the control force and the draft of a cone-cylinder point absorber on its hydrodynamic responses.The results showed that compared to the effect of the supplementary inertia,changes in the draft of the WEC have a small influence on its hydrodynamic responses.The buoy draft has an inverse relationship with both added mass and damping coefficients.However,increasing the supplementary mass increases the added mass and decreases the hydrodynamic damping coefficients.