V形布局起伏地形上布拉格共振引起的波能聚焦特性研究

基于高阶谱(HOS)方法,文章建立了考虑起伏地形上三维布拉格共振的数值模型。基于该模型探讨了地形为V形空间布局时的波能聚焦特性,对比分析了地形不同夹角(α)下波能聚焦点处的聚焦效果。试验结果表明:V形布局中不同的α有着不同的聚波特性,通过优化α,可以很大程度上提高波能聚焦效果;当145°α180°时,波能聚焦效果较好,波能聚焦点处的振幅可达到初始入射波振幅的1.70倍以上,其中α=162.24°时,波能聚焦效果最优,最大振幅增大2.87倍。     

规则波作用下旋转浮子式波浪能捕获装置水动力试验研究

提出一种旋转浮子式波浪能捕获装置,并进行一系列物理模型试验来研究其在规则波作用下的水动力行为特性。试验研究发现：1）浮子旋转角速度随螺距的增大而减小。2）入射波周期小于2.4 s时,平均角速度随入射波周期的增加呈增大趋势;入射波周期大于2.4 s时,随着入射波周期的增加,平均角速度增幅趋缓,个别工况呈轻微减小的趋势。3）波能捕获宽度比与入射波周期基本呈正相关关系。波能捕获宽度比随螺距的减小而增大;在螺距δ=0.02、入射波周期T=2.4s时,波能捕获宽度比达到最大。最后,利用量纲分析方法,推导旋转浮子的平均角速度方程,并利用试验数据对其进行验证。     

粤东近岸深水区周年波浪特征分析

  目的  根据粤东近岸深水区1a的现场实测海浪资料,主要对该海域周年波浪基本特征进行统计分析。  方法  首先对波高和周期特征值进行逐月统计,得到全年基本分布特征;再对波向进行统计,得到波向季节特征;再对波高-周期联合分布和波高与周期之间的关系进行探讨;最后对典型台风浪的特征进行研究。  结果  结果表明:（1）全年H_s平均值为1.52 m,H_max为15.97 m,全年12月、1月和2月的H_s平均值最大,H_max由台风“山竹”造成;（2）受季风季候和热带气旋影响,全年常浪向和强浪向分别为ENE向和SE向;（3）全年波浪类型主要以风浪成分为主,对波高与周期的相关关系进行拟合;（4）根据“山竹”台风浪实测数据,波高和周期都有显著的升高和降低过程。通过海浪谱分析,台风期间经历了从双峰谱向单峰谱的演变,说明台风期间的波浪类型主要为风涌混合浪,谱峰值于9月16日6时达到最大值96.74 m2/Hz,谱峰频率为0.07 Hz。  结论  研究成果可以为相关海洋工程的设计提供技术参考。     

同轴双浮体波能装置最优获能研究

该文以同轴双浮体波能装置为研究对象,通过理论分析建立运动方程,求解线性能量摄取(PTO)作用下的最优阻尼系数及最大输出功率。同时探究了装置能量捕获的影响因素及控制策略,提出一种具有普遍意义的最优获能估算公式。研究结果表明:双浮体波能装置可通过调节PTO阻尼力使得获能最大化,且较单浮体装置具有更宽的能量俘获频率范围;不同PTO控制策略及水体粘性阻尼均对该类装置获能影响显著。     

基于单摆和拾振弹簧的漂浮式波浪能发电装置研究

针对漂浮式波浪能发电技术,提出一种采用单摆和拾振弹簧结构的新型波浪能发电装置。基于汉密尔顿能量定律建立该装置的两自由度运动模型,通过有限元分析得出单摆的运动规律,再根据单摆的角位移和电磁感应定律建立输出电动势模型。研究结果表明:在正弦振动激励下,通过拾振弹簧结构可有效增大单摆的转动角度,从而提高装置的输出电压;当波高为4.0 cm,频率为1 Hz时,该装置的输出电压为5 V,平均输出功率为0.46 W,可满足小型电子设备的供电需求;该漂浮式波浪能发电装置的设计是可行的。     

垂直轴风力机三维尾流模型的研究

基于流量守恒，提出一种H型VAWT的三维解析尾流模型，该模型考虑了风切变效应，并采用多元高斯分布。首先，通过风洞试验及大涡模拟数据进行模型验证，结果表明在x/D> 3的远尾流区，横向剖面的相对误差小于2%，垂向剖面的相对误差小于3%。然后，从下游4个位置(x/D=3、6、9、12)、3种推力系数(C_T=0.6、0.7、0.8)、4种风切变指数(α=0、0.1、0.15、0.2)、两种湍流强度(I₀=5%、8.3%)下演示了一系列预测结果，结果显示该文模型能有效地描述尾流风速的空间分布。由于考虑了高度影响，该模型可用于风力机轮毂高度的优化及风电场的布局优化，有利于提高风电场的功率输出。     

加热和水处理共同调控PbI2薄膜形貌及其在钙钛矿太阳电池中的应用研究

该文研究加热和水处理共同作用对PbI₂薄膜形貌的调控和对钙钛矿太阳电池性能的影响。使用的钙钛矿体系为（FAPbI₃）_1-x（MAPbBr₃）_x,并在两步法工艺基础上对PbI₂薄膜进行不同时间加热和短时间水处理可将PbI₂薄膜制备成多孔结构。将双重处理后的PbI₂薄膜制备成钙钛矿薄膜后,可发现钙钛矿薄膜质量明显提升,表现在：钙钛矿的晶粒尺寸明显增大、结晶性增强、吸光能力提升、载流子传输更快。且此种方式能有效调控钙钛矿薄膜中的PbI₂残留量。在器件效率方面,只对PbI₂薄膜进行加热处理制备的电池的开路电压、短路电流、填充因子和效率分别为1.05 V、23.12 mA/cm²、73.81%和17.92%,而在最优双重处理工艺下制备的电池的这4个相应的参数分别为1.09 V、24.75 mA/cm²、77.85%和21.10%。     

基于DSSOGI锁频环与改进鲸鱼优化算法的波浪发电系统功率优化控制

为改善波能转换器的能量捕获效率问题,提出基于双自调谐二阶广义积分器(DSSOGI)锁频环与改进鲸鱼算法的优化控制方案.基于水动力模型的频域响应分析,寻求波浪发电系统最优负载,引入DSSOGI锁频环结构实时测量波浪频率,并采用扩展卡尔曼滤波方法,加快动态响应速度,预估波浪主频.当海况发生变化时,通过DSSOGI锁频环结构...     

Al-Y-Zr原位共掺杂提高4.53V钴酸锂正极材料的循环性能

钴酸锂是一种成功实现商业化的锂离子电池正极材料,但其实际的容量远低于其理论容量(274 mAh/g)。提高钴酸锂的充电截止电压能够有效提高其放电容量,但钴酸锂在高压条件下结构不稳定性,导致其循环寿命明显降低。本工作提出一种Al-Y-Zr原位共掺杂的策略,以提高钴酸锂在4.53 V的循环性能。通过将Al-Y-Zr掺杂的Co₃O₄、Li₂CO₃、MgO按一定化学计量比称取并混合均匀后,采用高温固相法合成LiCo₍(1-a-b-c-d))Al_aZr_bY_cMg_dO₂正极材料,并探究了原位共掺杂对高电压钴酸锂循环性能的影响。X射线衍射(XRD)表明掺杂前后晶体均为六方相层状结构,扫描电镜(SEM)说明了掺杂元素对晶体颗粒粒径的调控作用。循环前后的电化学阻抗谱(EIS)表明,Al-Y和Al-Y-Zr共掺杂能有效抑制循环过程中电荷转移阻抗(R_ct)的增长。扣式电...     

基于田口试验方法和CFD相结合的振荡翼捕能性能的优化研究

为了提升振荡翼的捕能性能,该文采用田口试验和CFD相结合的方法,对决定振荡翼捕能性能的5个特征参数进行优化。结果表明：振荡翼的特征参数对其捕能性能具有重要影响,最优和最差参数组合下振荡翼捕能效率相差137.84%。俯仰中心位置对振荡翼捕能效率影响最大,在试验样机设计中应优先考虑;所研究的5个特征参数对振荡翼捕能性能的影响程度依次为：x_p/c>θ₀>翼型相对厚度>h₀/c>f^*。通过对不同参数组合振荡翼的流场分析发现,特征参数优化的振荡翼产生的涡流始终吸附在翼型表面,从而使振荡翼获得较好的升力特性,进而在升沉运动中捕获更多的能量。     

OWC波能转换装置输出控制技术的研究

文中利用实验方法系统研究了负载控制技术对OWC波能转换装置的影响。研究结果表明,当透平完成自起动过程后,在装置输出最佳工况点处,输入波况对平均最佳进气迎角的影响很小,其值基本处于8°~10°之间。因此,为实现变工况下波能装置的最佳性能输出,只需保证透平的平均进气迎角始终处于上述范围。反之,利用文中给出的平均最佳进气迎角也可确定透平的最佳转速,进而确定最佳工况点。     

扁平五边形后弯管模型初级转换效率试验研究

为降低五边形后弯管装置的吃水深度,在保证弯管横截面积不变的条件下对已有的五边形后弯管模型进行改进,使其五边形底部呈扁平状、迎浪面变宽。在造波水槽中对扁平五边形后弯管模型进行规则波和随机波下的初级能量转换效率试验研究,探究不同质量和不同锚泊点下模型的能量转换特性。试验结果表明,在入射波波高0.1 m、周期1.15 s的规则波下,模型最高输出气动功率和俘获宽度比分别为8.551 W和98.59%,JONSWAP谱下模型的俘获宽度比最高达58.45%,优于历史文献值52%。规则波和随机波下扁平后弯管技术均具有较高的初级能量转换特性。     

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。     

Further analysis of change in nearshore wave climate due to an offshore wave farm: An enhanced case study for the Wave Hub site

This paper addresses the use of numerical wave models for assessing the impact of offshore wave farms on the nearshore wave climate. Previous studies have investigated the effect of energy extraction by wave energy devices through the use of spectral models such as SWAN, representing a wave farm as one or more barriers within the model domain and applying a constant wave energy transmission percentage across the whole wave spectrum incident at the barrier. However, this is an unrealistic representation of the behaviour of real wave energy converters. These will exhibit frequency-dependent energy absorption characteristics that will correspond to the spectral response of the device, and may reflect its ability to be tuned to extract energy at particular frequencies. This study describes a modification of the SWAN source code to enable frequency-dependent wave energy transmission through a barrier. A detailed analysis of the wave climate at the Wave Hub wave farm site is also presented, with a particular focus on the occurrence of bimodal sea states. The modified SWAN code is used to assess how impact predictions for typically occurring sea states may differ when using frequency-dependent rather than constant wave energy transmission, with reference to a previous study using the unmodified code (Millar, Smith and Reeve, 2007 [1]). The results illustrate the dependence of the magnitude of the impact on both the response function of the devices and the spectral sea state in which they are operating.     

波能利用型圆筒透空堤水动力特性实验研究

将波能装置与防波堤等海洋结构物相结合,将有助于提升其经济性,促进其应用。以一定间距平行排布多个圆筒振荡水柱装置（OWC）形成波能利用型圆筒透空堤,并基于二维波浪水槽物理模型实验对其水动力特性展开研究,重点关注筒间距、OWC吃水、波高对于波浪防护和波能转换的影响规律。结果表明：圆筒较为紧密排布时,高效波能转换的波频范围显著拓宽;较浅OWC吃水在获得近似波浪防护效果的同时波能转换性能更佳;波浪防护效果及波能转换性能受波高影响较小。波能利用型圆筒透空堤在实际应用时,应采用较小的筒间距和OWC吃水,以同时兼顾较好的波浪防护效果和波能转换性能。     

Effects of the geometry of downstream pipes with different angles on the shock ignition of high-pressure hydrogen during its sudden expansion

To investigate the effects of the geometry of downstream pipes on the shock ignition and the formation of the shock waves during high-pressure hydrogen sudden expansion, a series of bench-mark experiments were designed and high-pressure hydrogen were released into five types of pipes with different angles (60, 90, 120, 150 and 180°). It was found that the geometry of downstream pipes had a significant influence on the shock ignition of hydrogen. The incident shock wave would be reflected at the corner of the pipes with angles of 60, 90, 120 and 150°. The intensity of the reflected shock wave is higher if the angle is smaller. In addition, the average velocity of the leading incident shock wave would decrease when it passed the corner of the pipe. Using a pipe with smaller angle significantly increases the likelihood of shock ignition and lowers the minimal required burst pressure for shock ignition. The overpressure of the incident shock waves inside the exhaust chamber (for the cases with the angles of 60, 90, 120 and 150°) decreases sharply. There are three flame propagation behaviors inside the exhaust chamber: flame quenching, flame separation and no flame separation. The results of this study have implications concerning designs for storage safety of hydrogen energy and may help get better understanding of shock ignition mechanism of high pressure hydrogen and effect of pipeline geometry on ignition.     

On the factorisation of incidence angle modifiers for CPC collectors

It has been suggested earlier that the incidence angle modifier K_τ for low concentrating collectors with tubular absorbers could be factorised according to K_τ(θ_t,θ_l) ∝ K_τ(θ_t,0)K_τ(0,θ_l, where θ_tand θ_l are the projected incidence angles in the transversal and longtitudinal projection planes, respectively. Ray-tracing calculations on low-concentrating CPC collectors with flat absorbers parallel to the cover show that a K_τ factorisation overestimates the annual delivered energy from the collector by about 4–5%, when compared to calculations using the full incidence angle modifier. Data from outdoor testing has been used for characterization of incidence angle behaviour for a truncated CPC with a concentration of C = 1.56. Multiple linear regression analysis was used. This analysis technique makes feasible the determination of angular dependent incident angle modifiers and is an efficient tool to use for all collectors which cannot be characterised by standard equations of the incidence angle dependence.     

Configuration of Shock Waves in Two-Dimensional Overexpanded Jets

An experimental and analytical study has been carried out to obtain the clear understanding of a shock wave transition associated with a steady two-dimensional overexpanded flow. Two-dimensional inviscid theory with respect to a shock wave reflection is used in the present study on the characteristic of shock waves. The results obtained from the flow analysis are compared with those obtained from flow visualizations. It is shown that in the region of regular reflection, the angle of an incident shock wave becomes lower than that calculated by two shock theory with an increment in the ratio pe/pb of the nozzle exit pressure pe to the back pressure pb. It is indicated that the configuration of shock waves in overexpanded jets is influenced by the divergent angle at the nozzle exit. Also it is shown from the flow visualization that a series of shock waves move into the nozzle inside with a decrease in pressure ratio pe/pb, even if the pe/pb is under overexpanded conditions.     

Characterising the wave power potential of the Scottish coastal environment

The study focuses around the energetic waters of Scotland that has expressed high interest in the development of wave energy farms. There are only a few long-term suitable studies characterising coastal locations. A detail coastal resource assessment is provided, focusing on wave energy and site characterisation. Mean nearshore energy content in the Western coasts is ≥50?kW/m and on the East ≈10?kW/m. Monthly and seasonal analyses outline available resource and annual variations. Availability of production is also examined, West coastlines present higher levels, however, depending on resource and wave converters operational range significant differences are shown. Availability levels on the East coastline are low ≈40% due to lower wave heights, while Western locations record consistently over 80% at both scenarios examined. Results discuss the potential applicability of favourable wave converters, and characteristics which achieve maximum utilisation based on the local environment.