振荡浮子式波能转换装置动力输出系统特性研究

动力输出系统(Power Take-Off, PTO)作为波浪能转换装置(Wave Energy Converter, WEC)的主要构件之一,对系统运动及能量转换至关重要。首先基于势流理论,运用特征函数展开法得到圆柱形浮体所在流域的速度势函数级数表达式,进而通过边界匹配法得到作垂荡运动浮子的附加质量、阻尼系数及波浪激励力的解析表达式。针对阻尼器特性,分别研究线性和非线性PTO阻尼作用下,浮子的运动及波能转换特性,重点研究了线性PTO作用下的过阻尼问题。计算结果表明,低速度指数的PTO系统对装置运动的影响主要体现在PTO阻尼系数上,随着阻尼系数增大,波能装置的共振频率逐渐减小,但减小幅度很小;PTO系统的非线性特性并不能改变浮子的最优转换效率,但是较大的速度指数能有效改善PTO系统的阻尼容量;在较低频和较高频时,通过解析算法得到的最优PTO阻尼系数会使得装置处于过阻尼工作状态,且在低频部分需要进行最优PTO修正的最高频率和在高频部分需要进行修正的最低频率均随着半径和吃水的增大而逐渐减小。     

穿孔式双浮体装置水动力及波能转换特性研究

为进一步解决波能转换装置向深水环境推进过程中存在能量转换效率问题,在现有双浮体点吸式波能装置基础上考虑穿孔阻尼板,提出新的穿孔双浮体带支撑立柱的结构形式.基于线性微幅波假设,通过特征函数展开和边界匹配的势流半解析方法,并结合多自由度振动理论,探索穿孔阻尼板对获能系统水动力、运动响应及俘获宽度比的影响.计算结果表明,阻尼...     

基于Stewart并联机构的直驱式波能转换器能量转换性能研究

为实现对不同方向海洋来流波浪能量的高效俘获,设计了一种基于Stewart并联机构的直接驱动式波浪能量转换器,该转换器的支链单元采用弹簧连接永磁体动子,通过与定子线圈的相对运动实现波浪能与电能的转换。在特定海域波浪环境下对该波能转换器进行动力学分析,并基于弗汝德-克雷洛夫假定法计算了转换器所承受的水平和垂直波浪力;采用ADAMS动力学仿真分析软件对该波能转换器进行动力学建模与能量转换仿真分析,研究了波浪力作用下其弹性支链的变形规律,并分析了支链弹簧刚度系数与动平台质量之比对转换器能量转换率的影响。研究结果表明：在波浪激励下,该波能转换器能够俘获由垂向和横向波浪运动产生的能量;通过优化调整支链弹簧刚度系数与动平台质量的比值,该波能转换器的最大能量转换率可达35.2%。研究结果可为新型高效波能发电装置的设计提供重要的理论依据。     

浸没式参数激励摆波能转换装置能量俘获特性研究

引入参数激励摆的非线性机制,应用于波浪能发电装置,并根据实际波浪低频、低幅值激励特性,提出浸没式单摆波能转换装置,研究其在规则波中的能量俘获情况。基于势流理论,针对垂荡运动,建立非线性运动方程,进行数值求解,分析摆球质量比、激励频率、幅值和系统阻尼对能量俘获效率的影响,并与空气中单摆的能量俘获效率进行对比。结果表明:合理选取质量比,可降低浸没式参数激励摆固有频率;与空气中单摆相比,浸没式参数激励摆在低频、小振幅的波浪激励环境下,俘获能量频谱带宽更宽,发电功率更高。     

A boundary element model for a partially piston-type porous wave energy converter in gravity waves

The present paper applies the multi-domain boundary element method (BEM) to investigate the performance of a partially piston-type porous wave energy converter (WEC), which consists of a solid wall, a vertical porous plate, a transmission bar, a rigid block constrained by rollers, a spring, and a damper. This WEC is subjected to a dynamic loading external source from a wave attack. For this wave-body interaction problem, a single-degree-of-freedom (SDOF) system is developed to describe the response of the present WEC. Linear wave theory governs the entire fluid domain, which is divided into three regions by a pseudo boundary and the vertical porous plate. Darcy's law applies to the porous plate. Examples are shown to illustrate the wave reflection from the WEC, the response to wave loading, and the instantaneous mechanical power from the wave.     

Simplified unipolar, quasisquare wave energy recovery drive circuits for piezoelectric actuators

A simple two-switch circuit for driving piezoelectric actuators with unipolar quasisquare waves is presented. The circuit provides for recovery of the energy stored on the actuator capacitance back to the primary power supply when the actuator is de-energized.     

Hydrodynamic principles of wave power extraction

The hydrodynamic principles common to many wave power converters are reviewed via two representative systems. The first involves one or more floating bodies, and the second water oscillating in a fixed enclosure. It is shown that the prevailing basis is impedance matching and resonance, for which the typical analysis can be illustrated for a single buoy and for an oscillating water column. We then examine the mechanics of a more recent design involving a compact array of small buoys that are not resonated. Its theoretical potential is compared with that of a large buoy of equal volume. A simple theory is also given for a two-dimensional array of small buoys in well-separated rows parallel to a coast. The effects of coastline on a land-based oscillating water column are examined analytically. Possible benefits of moderate to large column sizes are explored. Strategies for broadening the frequency bandwidth of high efficiency by controlling the power-takeoff system are discussed.     

Spiral wave self-organization in a coupled-map lattice: Hydrodynamic scaling

The dimensions of spiral waves reveal a scaling correspondence with the diffusion length, which is a fundamental unit of length in a coupled map lattice. Pis’ma Zh. Tekh. Fiz. 25, 89–94 (February 12, 1999)     

Hydrodynamic modelling of flow over a spillway using a two-dimensional finite volume-based numerical model

Spillway flow, a classical problem of hydraulics, is generally a gravity-driven free surface flow. Spillway flows are essentially rapidly varying flows near the crest with pronounced curvature of the streamlines in the vertical direction. Two processes simultaneously occur in the flow over the crest, that is, formation and gradual thickening of the turbulent boundary layer along the profile, and gradual increase in the velocity and decrease in the depth of main flow. Spillway hydrodynamics can be obtained through physical modelling or numerical modelling. Physical modelling of spillways is expensive, cumbersome and time-consuming. The main difficulties in solving the spillway problem numerically are: rapidly varying flow, existence of both subcritical and supercritical flows, development of turbulent boundary layers, unknown free surface and air entrainment. Numerical simulation of such flows over spillways in all flow regimes is a challenging task. This paper describes a numerical model and its application to a case study to investigate the hydraulic characteristics of flow over spillway crest profiles by simulating the velocity distribution, pressure distribution and discharge characteristics. Results of the numerical modelling are compared with those from the physical modelling and found to be satisfactory.     

Optimum values of energy converter efficiency

Analytical expressions for optimum values of the thermodynamic and thermal efficiency of heat converters to other kinds of energy have been obtained with the use of the methods of nonlinear equilibrium thermodynamics. Their comparison with the data of industrial power plants has been made.     

Fused deposition modelling using direct extrusion

In the present work, a process based on the principle of polymer extrusion is developed: the extruder deposition process (EDP). This system uses a screw extruder to deposit the material on a computer-controlled positioning system to build components. Experiments (Box–Behnken technique is used for experimental design) are carried out to study the influence of three process variables: nozzle temperature, chamber temperature and road gap on bond strength (inter-road and interlayer) and surface finish. Surface roughness and ultimate tensile strength values are measured for test specimens. Analysis of variance (ANOVA) is used to determine the significance of process variables. It is concluded that the developed EDP eliminates many of the shortcomings of the systems developed based on the principles of extrusion and produces components having higher bond strength than that achieved in commercial fused deposition modelling (FDM) systems.     

Fused deposition modelling using direct extrusion

In the present work, a process based on the principle of polymer extrusion is developed: the extruder deposition process (EDP). This system uses a screw extruder to deposit the material on a computer-controlled positioning system to build components. Experiments (Box-Behnken technique is used for experimental design) are carried out to study the influence of three process variables: nozzle temperature, chamber temperature and road gap on bond strength (inter-road and interlayer) and surface finish. Surface roughness and ultimate tensile strength values are measured for test specimens. Analysis of variance (ANOVA) is used to determine the significance of process variables. It is concluded that the developed EDP eliminates many of the shortcomings of the systems developed based on the principles of extrusion and produces components having higher bond strength than that achieved in commercial fused deposition modelling (FDM) systems.     

Continuous optical discharge in a thermionic converter for conversion of laser radiation energy into electrical energy

A model is developed and calculations are made of the characteristics of a continuous optical discharge in the interelectrode gap of a thermionic converter for conversion of laser radiation energy into electrical energy. Pis’ma Zh. Tekh. Fiz. 25, 90–95 (April 12, 1999)     

A nine-level hybrid symmetric cascaded multilevel converter for induction motor drive

A nine-level hybrid symmetric cascaded multilevel converter (MLC) fed induction motor drive is proposed in this paper. The proposed converter is capable of producing nine output voltage levels by using the same number of power cells as that of conventional five-level symmetric cascaded H-bridge converter. Each phase in this configuration consists of one five-level transistor-clamped H-Bridge (TCHB) power cell and one three-level H-bridge power cell with equal dc link voltages, and they are connected in cascade. Due to cascade connection and equal dc link voltage, the power shared by each power cell is nearly equal. Near-equal power sharing enables the feature of improving input current quality by using an appropriate phase-shifting multi-winding transformer at the converter input. In this paper, the operation of the converter is explained using staircase and hybrid multi-carrier sine PWM techniques. Further, a detailed analysis for the variations in the dc link capacitor voltages and the dc link mid-point voltage in TCHB power cell is carried out, and the analytical expressions thus obtained are presented. The performance of proposed system is analysed by simulating a 500 hp induction motor drive system in MATLAB/Simulink environment. A laboratory prototype is also developed to validate the claims experimentally.     

中空45钢棒材摩擦焊接工艺研究

为了改善大直径中空45~#钢棒材的连续驱动摩擦焊接性,采用二级加压方法进行了外径42 mm,内径26 mm的45~#钢连续驱动摩擦焊接.试验结果表明,焊接热输入随着摩擦时间、旋转速度的增大而增大,当摩擦时间较短、旋转速度较低时,采用较大的顶锻力、二级摩擦力不能显著增加焊接热输入,导致无法顶锻,产生严重的焊接缺陷.对于无缺陷接头,接头最大强度系数达到80.9%,接头中未发现熔化现象,焊缝发生动态再结晶,热机影响区和部分正火区出现魏氏体组织.接头冲击试验发现,力学性能优异的接头薄弱区位于部分正火区,而焊接热输入较高的接头薄弱区位于热机影响区.焊接热输入较低难于获得缺陷的焊接接头,焊接热输入过大显著降低接头力学性能.     

Development of a pMOSFET sensor with a Gd converter for low energy neutron dosimetry

A pMOSFET having a 10 microm thick Gadolinium (Gd) layer has been invented as a slow neutron sensor. When slow neutrons are incident to the Gd layer, conversion electrons, which generate electron-hole pairs in the SiO2 layer of the pMOSFET, are generated by a neutron capture process. The holes are easily trapped in the oxide and act as positive-charge centres in the oxide. Due to the induced charges, the threshold turn-on voltage of the pMOSFET is changed. The developed sensors were tested at a neutron beam port of the HANARO research reactor and a 60Co irradiation facility to investigate slow neutron response and gamma ray contamination, respectively. The resultant voltage change was proportional to the accumulated neutron dose and it was very sensitive to slow neutrons. Moreover, ionising radiation contamination was negligible. It can also be used in a mixed radiation field by subtracting the voltage change of a pMOSFET without Gd from that of the Gd-pMOSFET.     

Key features of wave energy

For a weak point source or dipole, or a small body operating as either, we show that the power from a wave energy converter (WEC) is the product of the particle velocity in the waves, and the wave force (suitably defined). There is a thus a strong analogy with a wind or tidal turbine, where the power is the product of the fluid velocity through the turbine, and the force on it. As a first approximation, the cost of a structure is controlled by the force it has to carry, which governs its strength, and the distance it has to be carried, which governs its size. Thus, WECs are at a disadvantage compared with wind and tidal turbines because the fluid velocities are lower, and hence the forces are higher. On the other hand, the distances involved are lower. As with turbines, the implication is also that a WEC must make the most of its force-carrying ability-ideally, to carry its maximum force all the time, the '100% sweating WEC'. It must be able to limit the wave force on it in larger waves, ultimately becoming near-transparent to them in the survival condition-just like a turbine in extreme conditions, which can stop and feather its blades. A turbine of any force rating can achieve its maximum force in low wind speeds, if its diameter is sufficiently large. This is not possible with a simple monopole or dipole WEC, however, because of the 'nλ/2π' capture width limits. To achieve reasonable 'sweating' in typical wave climates, the force is limited to about 1?MN for a monopole device, or 2?MN for a dipole. The conclusion is that the future of wave energy is in devices that are not simple monopoles or dipoles, but multi-body devices or other shapes equivalent to arrays.