不等波长行波运动的能量吸收特性研究

为改善做行波运动的行波板的能量吸收特性,基于计算流体力学方法,分析了波长系数(-0.1～0.3)和无量纲振幅(0.1～0.2)对做不等波长行波运动行波板能量吸收特性的影响。结果表明：相比于做等波长行波运动,做不等波长行波运动行波板的能量吸收效果更好;在较小的无量纲振幅下,沿流向线性增大波长,可以提高能量吸收效率;随着波长系数增大,能量吸收效率先升高再降低,存在最佳波长系数使得能量吸收效率最高达到69%;在较大的无量纲振幅下,随着波长系数的增大,能量吸收效率先降低再升高。     

结合防波堤的振荡摇摆式波浪能装置试验研究

讨论一种结合防波堤的振荡摇摆式波浪能装置的结构和工作原理,并在河海大学河口航道综合试验厅进行物理模型试验。试验以重块和不锈钢板间的摩擦力作为波浪能转换装置的负载阻尼,通过测量不锈钢板两端的拉力及其位移计算波浪能转换输出功率。结果表明,当入射波的周期和浮体的固有周期接近时,浮体的运动接近共振状态,此时波浪能转换平均输出功率和转换效率最高,分别可达0.05 W和17.9%。入射波周期较大时,装置的波浪能转换输出功率较高,但此时其波浪能转换效率低于入射波周期较小时。水深对于浮体的姿态和运动特性起到关键作用,结果表明水深为60 cm时波浪能转换输出功率和转换效率最高。     

转叶孔板螺旋流消能的影响因素试验分析

为解决供水工程中的过剩水头问题,常在有压输水管道中配置合适的消能装置,转叶孔板螺旋流消能是一种新型的内消能方式,通过转叶孔板螺旋流消能装置的水力特性试验,可知影响转叶孔板螺旋流消能效率的主要影响因素有雷诺数Re、转叶孔板开口角度和孔板之间的相互扭转角度,还有试验装置结构的设置。根据试验数据计算分析各个影响因素对消能效率的影响。结果表明,转叶孔板螺旋流消能效率与转叶孔板之间的扭转角成正比,与雷诺数成正比,与转叶板的开口角度成反比。试验装置在进口段和出口段设置管径突变均对消能有利,该装置比与其消能原理类似的孔板消能装置更实用,且消能效率更高,对下游建筑物设施起到良好的保护作用,可推广应用。     

THERMOELASTIC LAMB WAVES IN ELECTRICALLY SHORTED TRANSVERSELY ISOTROPIC PIEZOELECTRIC PLATE

The propagation of Lamb waves in a homogeneous, transversely isotropic, piezothermoelastic plate, which is stress free, electrically shorted, and thermally insulated (or isothermal), is investigated. Secular equations for the plate in closed form and isolated mathematical conditions for symmetric and antisymmetric wave mode propagation are derived in completely separate terms. It is shown that the motion of the purely transverse shear horizontal (SH) mode gets decoupled from the rest of the motion and remains unaffected due to piezoelectric, pyroelectric, and thermal effects. The secular equations for stress-free piezoelectric, thermoelastic, and elastic plates are deduced as special cases in the current analysis. At short wavelength limits the secular equations for symmetric and skew symmetric modes reduce to Rayleigh surface wave frequency equation, because a finite-thickness plate in such a situation behaves like a semi-infinite medium. The amplitudes of dilatation, electrical potential, and temperature change are also computed during the symmetric and skew symmetric motion of the plate. Finally, numerical solutions of various secular equations and other relevant relations are carried out for cadmium selenide (6 mm class) material. The dispersion curves, attenuation coefficients and amplitudes of dilatation, temperature change, and electrical potential for symmetric and antisymmetric wave modes are presented graphically to illustrate and compare the analytical results. The theory and numerical computations are found to be in close agreement. The coupling between the thermal/electric/elastic fields in piezoelectric materials provides a mechanism for sensing thermomechanical disturbances from measurements of induced electric potentials and for altering structural responses via applied electric fields. Therefore, the analysis will be useful in the design and construction of Lamb wave sensors, temperature sensors, and surface acoustic wave filter devices.     

Nontracking solar concentrators

We derive the theoretical upper limit for concentration of direct solar radiation at low latitudes with nontracking concentrators from the projected solid angle sampled by the apparent motion of the sun, for the case where the energy efficiency is referred to the energy incident on the entrance aperture. Based on the fact that the solar radiation is not uniformly distributed within this projected solid angle and that the apparent solar motion is known, we derive the optimal acceptance as a function of direction and time, which means rejecting the lower density radiation and switching off the device when losses would be higher than gains. Just as a device may gain concentration by rejecting radiation from certain directions, it can also gain by not operating at all, thus avoiding losses at certain times. Trough-type systems, which have translational symmetry, cannot be ideal nontracking concentrators, but for low losses they perform only slightly worse than general three-dimensional concentrators.     

行波波长及波速对获能特性的影响

在一定的运动参数条件下,行波运动可以从流水或风中吸取能量。以NACA0012翼型作为行波运动鱼体二维简化模型的原始翼型,采用数值模拟的方法研究波长及波速对行波运动获能特性的影响。结果表明：当波长不变时,随着无量纲波速的增大,行波运动从流水中吸收的能量（无量纲侧向功率）和能量利用率先增大后减小,并存在一个最佳波速使得无量...     

Large deflection analysis of laminated composite plates resting on nonlinear elastic foundations by the method of discrete singular convolution

This paper presents nonlinear static analysis of a rectangular laminated composite thick plate resting on nonlinear two-parameter elastic foundation with cubic nonlinearity. The plate formulation is based on first-order shear deformation theory (FSDT). The governing equation of motion for a rectangular laminated composite thick plate is derived by using the von Karman equation. The nonlinear static deflections of laminated plates on elastic foundation are investigated using the discrete singular convolution method. The effects of foundation and geometric parameters of plates on nonlinear deflections are investigated. The validity of the present method is demonstrated by comparing the present results with those available in the literature.     

Influence of stroke deviation on the power extraction performance of a fully-active flapping foil

The influence of stroke deviation on the power extraction performance of a fully-active flapping foil is numerically investigated in this work. A NACA0015 airfoil placed in a two-dimensional laminar flow is employed to extract power from the flow. It synchronously executes a rotational motion and a translational motion. In the traditional flapping foil based power extraction system, the foil only translates in vertical direction (heaving motion). In the current study, however, the foil can translate in both horizontal direction (surging motion) and vertical direction, which is attributed to the stroke deviation of a flapping wing. At a Reynolds number of 1100 and the position of the rotating axis at one-third chord, the effects of the amplitude of horizontal motion, the phase difference between the horizontal motion and the vertical motion as well as the frequency of horizontal motion on the power extraction performance are examined in detail. It is shown that compared with the traditional flapping foil, the efficiency improvement of power extraction for the flapping foil with additional horizontal motion can be achieved. Based on the numerical analysis, it is found that the enhanced power extraction from the vertical motion, which is induced by the increased lift force under appropriate horizontal motion, directly benefits the efficiency enhancement.     

Natural Convection Heat Transfer of a Rectangular Block within a Vertical Enclosure

A numerical solution of the natural convection heat transfer between two cold and hot isolated vertical plates is presented for different horizontal and vertical location ratios of an enclosure. Results show that: a) flow configurations of cold and hot plates are different; b) the increase of vertical location ratio, toward that corresponding to the enclosure middle value, is considerably diminishing the temperature differences between heating and cooling conditions; c) the effect of vertical location ratio variation is more prominent on heat transfer for cold and hot plates than that of the horizontal location ratio variation; d) the average Nusselt number, obtained from the hot isolated plate, is 20–39% larger than that of the cold plate under the same conditions when the isolated plate varies horizontally; e) for a narrow distance between the inner plate and the bounding wall, the inner plate Nusselt number is enhanced, but aside from this, the plate average Nusselt number is insensitive to the plate position; and f) different trends are found to affect heat transfer for cold and hot plates when the isolated plate varies vertically. The optimal vertical location can be found at specific Rayleigh number for the hot plate and cold plate.     

Experimental investigation and ANN modeling on improved performance of an innovative method of using heave response of a non-floating object for ocean wave energy conversion

To convert wave energy into usable forms of energy by utilizing heaving body, heaving bodies (buoys) which are buoyant in nature and float on the water surface are usually used. The wave exerts excess buoyancy force on the buoy, lifting it during the approach of wave crest while the gravity pulls it down during the wave trough. A hydraulic, direct or mechanical power takeoff is used to convert this up and down motion of the buoy to produce usable forms of energy. Though using a floating buoy for harnessing wave energy is conventional, this device faces many challenges in improving the overall conversion efficiency and survivability in extreme conditions. Up to the present, no studies have been done to harness ocean waves using a non-floating object and to find out the merits and demerits of the system. In the present paper, an innovative heaving body type of wave energy converter with a non-floating object was proposed to harness waves. It was also shown that the conversion efficiency and safety of the proposed device were significantly higher than any other device proposed with floating buoy. To demonstrate the improvements, experiments were conducted with non-floating body for different dimensions and the heave response was noted. Power generation was not considered in the experiment to observe the worst case response of the heaving body. The device was modeled in artificial neural network (ANN), the heave response for various parameters were predicted, and compared with the experimental results. It was found that the ANN model could predict the heave response with an accuracy of 99%.     

一种多浮体铰接式波浪能装置的运动分析与俘获特性研究

基于线性势流理论，利用总模态法对多浮体铰接波浪能装置“海星号”在波浪中的运动开展水动力学系数计算；然后基于矢量力学建立多浮体刚体运动学方程，并结合几何约束条件开展动态响应计算，获得最优俘获效率和最优负载阻尼；最后比较并分析“海星”波浪能装置的多浮体俘获效率，获得“海星”多浮体做功的俘获特性。研究表明：“海星”波浪能装置的多浮体四向迎波设计可拓宽装置最优俘获频带宽度，提高装置整体俘获效率；正向迎波与背向迎波俘获波浪能方式相比，小周期情况下，正向吸波浮体俘获效率较高，随着周期增大，正向吸波浮体俘获效率开始降低，背向吸波浮体俘获效率开始增大，极大周期情况下，正向吸波浮体和背向吸波浮体俘获效率趋于一致且趋近于零。     

Numerical Study of the Forced Convective Condensation on a Short Vertical Plate

Numerical investigation was conducted on the effects of gravity, surface tension, and wall adhesion upon condensation on a short vertical plate. The volume of fluid method was applied to model the interaction between the liquid and vapor phases and to capture the interface. The surface tension was implemented by employing the method of continuum surface force model. A modified phase-change model, derived from basic equations related to the kinetic gas theory, was proposed and verified based on the cases of Nusselt film condensation of water vapor on a vertical flat plate, the forced convection film condensation on a horizontal flat plate, and the capillary blocking due to condensation in a horizontal miniature circular tube. The predicted results showed that a laminar capillary wavy flow regime exists and the waves enhance the heat transfer of condensation on the plate. The mean film thickness increases and the heat transfer performance becomes worse with decrease of gravity. A high value of surface tension or contact angle, representing a large surface free energy difference, leads to an enhancement of heat transfer on the plate with large-amplitude waves.     

A heaving point absorber‐based triboelectric‐electromagnetic wave energy harvester: An efficient approach toward blue energy

This paper presents a hybridized triboelectric‐electromagnetic generator based on heaving point absorbers to harvest the energy of water waves. The device consists of a cylindrical freestanding grating triboelectric generator (TENG) and a 3‐phase tubular electromagnetic generator (EMG). The proposed system incorporates a slider which is capable of moving through a stator under the motion of a floating buoy. The floating component can heave up and down while facing water waves without being affected by the wave direction. The performance of the TENG and EMG units and corresponding electrical outputs are evaluated under various structural, dynamical, and electrical conditions. It is shown that the number of segments in the TENG unit, phase number in the EMG unit, and motion frequency in both harvesters are the key elements in the outputs of the hybridized system. For the first time, the effect of irregular wave motion on the TENG harvester performance is systematically explored using a well‐known wave spectrum. Also, the performance of the hybridized system for charging a storage unit is evaluated in details. The presented energy harvester shows a great potential toward harvesting the energy of water waves as well as hydrodynamic sensing applications. In addition, this research provides a framework for the exploration of irregular wave motion in TENG‐based energy harvesters.     

An experimental study on the efficiency of the submerged plate wave energy converter

Several studies have been made using submerged plates for wave-damping purpose. A pulsating flow occurs opposite to the direction of wave propagation below these wave breakers. This water flow can be used for energy production purposes. In this study, the energy efficiency of the plate wave energy converter is determined experimentally. The length of the plate L=1 m, the water depth d=60 cm, the width of the plate b=60 cm and the thickness t=2 cm were held constant through all the experiments. Each experiment set has a total number of 20 different wave properties composed of T=1.16, 1.50, 1.87 and 2.05 s wave periods and H=2, 4, 6, 8 and 10 cm wave height values. The velocity and the wave length of the water flow occuring below the plate were measured for several conditions such as: 1. the plate only, 2. the plate and a triangular structure below it, with five different heights, 3. The plate and a vertical wall below it, with two different heights. In this manner, the submerged plate wave energy converter efficiency values were determined for 20 different conditions. It is understood that the efficiency of the submerged plate wave energy converters can reach up to 60% and the existence of a vertical wall below the plate rather than a triangular form is more efficient.     

Energy analysis of evaporating thin falling film instability in vertical tube

The Kelvin-Helmholtz instability of evaporating thin falling film flow in vertical tube is studied by method of energy analysis. Based on the rules that the interfacial capillary waves come from the balance of works done by inertial force, surface tension on phase-change interface, and also capillary force on tube wall, the stability behaviors of falling film with different Reynolds number and different perturbation wavelength are explored in detail. The analysis indicates that the main reason of film breakup by increasing tube wall heat flux is that, the stability effect of capillary adsorbability on tube wall is weakened as surface tension waving is enhanced by improving tube wall temperature.     

CIRCULAR CRESTED THERMOELASTIC WAVES IN HOMOGENEOUS ISOTROPIC PLATES

The propagation of circularly crested thermoelastic waves in a homogeneous isotropic cylindrical plate subjected to stressfree and isothermal conditions is investigated in the context of conventional coupled thermoelasticity (CT), Lord-Shulman (LS), Green-Lindsay (GL), and Green-Nagdhi (GN) theories of thermoelasticity. The secular equation for the circular plate in closed form and isolated mathematical conditions for symmetric and skew symmetric wave mode propagation in completely separate terms are derived. It is shown that the motion for SH modes gets decoupled from the rest of the motion and remains unaffected due to thermomechanical coupling and thermal relaxation effects. The phase velocities for SH modes have also been obtained. It is noticed that the rest of the motion for circular crested waves is again governed by Rayleigh-Lamb-type secular equations. The secular equations for these plate and Lamé modes are also obtained and discussed for different regions. The results for coupled and uncoupled theories of thermoelasticity have been obtained as particular cases from the derived secular equations. At short wavelength limits, the secular equations for symmetric and skew symmetric waves in stressfree insulated and isothermal circular plate reduces to Rayleigh surface wave frequency equations. Finally, the numerical solution is carried out for aluminium-epoxy composite material, and dispersion curves for symmetric and skew-symmetric wave modes are presented to illustrate and compare the theoretical results. The theory and numerical computations are found to be in close agreement.     

实海况条件下磁流体波浪发电机的优化设计

以点吸收式波浪发电装置为例,考虑浮体和阻尼板在垂荡方向上的运动响应特性及磁流体发电机的发电特性,利用遗传算法优化不同规则波况下磁流体发电机的结构参数,得到装置投放于南海某岛屿附近时不同平均有效波高下的发电效率.然后,根据该岛屿全年波况的频率分布规律,计算得到全年发电量,年发电量最大时磁流体发电机结构参数最优.与传统按主...     

Optimal design of plate-and-frame heat exchangers for efficient heat recovery in process industries

The developments in design theory of plate heat exchangers, as a tool to increase heat recovery and efficiency of energy usage, are discussed. The optimal design of a multi-pass plate-and-frame heat exchanger with mixed grouping of plates is considered. The optimizing variables include the number of passes for both streams, the numbers of plates with different corrugation geometries in each pass, and the plate type and size. To estimate the value of the objective function in a space of optimizing variables the mathematical model of a plate heat exchanger is developed. To account for the multi-pass arrangement, the heat exchanger is presented as a number of plate packs with co- and counter-current directions of streams, for which the system of algebraic equations in matrix form is readily obtainable. To account for the thermal and hydraulic performance of channels between plates with different geometrical forms of corrugations, the exponents and coefficients in formulas to calculate the heat transfer coefficients and friction factors are used as model parameters. These parameters are reported for a number of industrially manufactured plates. The described approach is implemented in software for plate heat exchangers calculation.     

基于炉控片矫顽磁力测量方法评价PVA压力烧结炉温度场均匀性

根据炉控片的矫顽磁力和温度的关系用拉格朗日插值法建立了温度和炉控片矫顽磁力的关系方程.测量各炉控片的矫顽磁力值得到炉内轴向和垂直方向的温度分布规律,评价了硬质合金(PVA)压力烧结炉内温度场的温度均匀性.     

溶液全热回收装置及其优化分析

分析了制约现有溶液全热回收装置效率的主要因素,以内部驱动势分布均匀一致为原则,对溶液全热回收装置进行了优化分析,并给出了在不增加装置体积投入的前提下,提高热回收装置效率的有效措施。构建了溶液全热回收装置最高可达效率的处理流程,并分析实际装置接近可达效率的程度。