Scattering of water waves by a wave energy device consisting of a pair of co-axial cylinders in a uniform water having finite channel width

We consider a device which consists of a floating structure over a cylindrical plate placed at a finite height from the impermeable ocean floor.This paper developes the interaction of linear water waves with such a device.The whole fluid domain is divided into a number of sub-domains and boundary value problems are formulated for each identified sub-domain.The channel multipoles,separation of variables and matched eigenfunction expansion methods allow us to solve boundary value problems for the diffracted velocity potentials in each sub-domain.We investigate the wave forces exerted on the proposed device.Consequently,the effects of the various parameters,e.g.,drafts,radii,the gap between the cylinders and mainly channel width of the device on the wave forces exerted by the cylinders are presented graphically.We observe a small oscillation nature near the peak value of the exciting force for the particular value of channel width w=2.4m.The peak value of the exciting forces occurs near the wavenumber kr 1=1.0 for different width of the channel walls.The obtained results are compared with some available results,and it shows a good agreement between the obtained and available results.

Exploration of channel width scaling and edge states in transition metal dichalcogenides

We explore the impact of edge states in three types of transition metal dichalcogenides （TMDs）, namely metallic Td-phase WTe2 and semiconducting 2H-phase MoTe2 and MoS2, by patterning thin flakes into ribbons with varying channel widths. No obvious charge depletion at the edges is observed for any of these three materials, in contrast to observations made for graphene nanoribbon devices. The semiconducting ribbons are characterized in a three-terminal field-effect transistor （FET） geometry. In addition, two ribbon array designs have been carefully investigated and found to exhibit current levels higher than those observed for conventional one-channel devices. Our results suggest that device structures incorporating a high number of edges can improve the performance of TMD FETs. This improvement is attributed to a higher local electric field, resulting from the edges, increasing the effective number of charge carriers, and the absence of any detrimental edge-related scattering.

An Experimental Study on Flow Patterns and Width Adjustment in Self-formed Channels

The distribution of velocity is one of the basic issues in river dynamics.Based on the experimental data measured by ADV in the flume of State Key Hydraulics Laboratory (SKHL),this paper analyzed the ver- tical distribution of point velocity and the varying law of turbulence intensity in straight mobile compound chan- nel with an asymmetric floodplain.Above certain relative height,the streamwise point velocity follows the loga- rithmic distribution.Below the location,the velocity varies linearly approxim...

Investigating the Effect of Relative Width on Momentum Transfer between Main Channel and Floodplain in Rough Rectangular Compound Channel Sunder Varius Relative Depth Condition

Compound section is referred to a section the surface of which is made of several sub-sections with different flow characteristics. The difference in the hydraulic and geometry characteristics causes a complexity in flow hydraulic and creates an interaction between the main channel and floodplains, resulting in an apparent shear stress and a transverse momentum transfer. The amount of such a stress plays an important role in many river engineering measures [1]. Due to the flow complexity, the common approximate analytical methods are not enough to identify the flow profile. The FLOW3D Software with its great features in three-dimensional analysis of flow field is used as a tool to investigate the shear stress in a direct symmetrical compound rectangular channel. After the simulation of models, it is found that an increase in the relative width and relative depth parameters decreases the percentage of apparent shear stress and an increase in the relative roughness causes it to be increased [2].

基于机器视觉的刚性罐道接头缝隙宽度测量算法

针对罐道结构复杂、空间狭小、传统检测系统不便于安装,容易导致接头缝隙测量困难问题,提出一种基于机器视觉的非接触式测量接头缝隙宽度的方法。使用高斯滤波和CLAHE算法,去除噪声并提高图像对比度,经过阈值分割、图像形态学操作提取接头缝隙边缘特征;通过孤立点消除和透视变换去除图像畸变,使用SKE-骨架提取算法减少接头缝隙特征像素宽度,通过霍夫变换和最小二乘法计算接头缝隙宽度。测量了4~12mm接头缝隙宽度,结果表明:该方法测量误差控制在0.8 mm以内,为立井提升系统安全稳定运行提供保障。

U型渠道中直角三角形量水槽体型设计

量水槽体型设计是量水槽应用于灌区的重要环节,目前尚无完善的体型设计标准可依。为解决直角三角形量水槽实际应用中的体型设计问题,提出以淹没度、壅水高度和上游弗劳德数的限制条件为标准的量水槽体型设计准则。在2种型号、3种坡度的U型渠道上,利用钢模板修建5座直角三角形量水槽进行灌区试验;建立了包含渠道坡度的流量公式,拟合了淹没阈值、壅水高度和上游弗劳德数的经验公式。研究表明:含有坡度的流量公式精度较高,平均相对误差仅为1.88%,相对误差的最大值为5.56%,相对误差在±5%范围以内的数据比例为98%;拟合得到的3个经验公式描述了淹没阈值、壅水高度和上游弗劳德数与量水槽喉口宽度之间的定量关系,可用于量水槽体型设计。基于体型设计准则和经验公式,建立了最大流量和最小流量下淹没度小于相应淹没阈值、最大流量下壅水高度小于渠道岸顶超高、最小流量下上游弗劳德数小于0.5的直角三角形量水槽体型设计方法。研究成果可为类似量水槽体型设计提供参考。

PEMFC压差流道构型特征参数对电池性能的影响

针对质子交换膜燃料电池PEMFC(proton exchange membrane fuel cell)压差流道构型尺寸对电池电化学性能影响机理不明的问题,研究流道高度和脊背宽度对压差流道和直流道在氧气浓度、水浓度分布特征和电流密度、功率密度、压降等方面影响规律,并对两者进行了对比分析,结果表明流道高度对压差流道和直流道性能影响较小,压差流道在脊背宽度为1.25 mm和1.50 mm时具有明显优势;进一步研究压差流道变压区对流道性能的影响,结果表明变压区高度为0.05 mm和长度为1.50 mm时,压差流道峰值功率密度最高。综合考虑功率密度和压降的影响,选择压差流道高0.40 mm、宽1.25 mm、脊背宽1.25 mm、变压区长1.50 mm、高0.05 mm,此时压差流道峰值功率密度为0.3661 W/cm^(2),相较于直流道峰值功率密度提升6.3%。

浅埋近煤层群采动“三区”漏风裂隙场时空演化规律数值模拟

浅埋近煤层群采动下,地面采空区工作面“三区”之间易形成连通的漏气通道引发工作面低氧和采空区煤自燃,如何厘清采动效应下浅埋煤层群“三区”漏气通道的时空分布演化规律是有效防控煤自燃和低氧的关键。以陕煤柠条塔煤矿S1232工作面为研究背景,采用理论与数值模拟相结合的方法,研究了单一煤层、复合煤层重复开采下覆岩破坏特征,分析了煤层间距与采厚对裂隙二次发育的影响规律。结果表明:浅埋近煤层群开采下上覆岩层裂隙仅存在垮落带与裂缝带,主关键层破断后裂缝带快速发育至地表,关键层周期破断控制地表裂隙周期生成与下沉;上煤层裂隙密度发育由原始阶段先后经历快速增长、稳定和二次增长3个阶段;随采厚增大,各区间裂隙密度增大,大裂隙发育更充分,裂隙宽度整体增大;随煤层间距增大,小于0.2 m的裂隙宽度随采厚增大,且增加的速度逐渐加快,大于0.2 m的裂隙宽度随采厚增大,但增加速度逐渐变缓;采厚相同时,裂隙宽度大于0.2 m的裂隙密度随着煤层间距的增大逐渐减小。

Downstream Decreasing Channel Capacity of a Monsoon-dominated Bengal Basin River: A Case Study of Dwarkeswar River, Eastern India

Downstream changes in channel morphology and flow over the ephemeral Dwarkeswar River in the western part of the Bengal Basin, eastren India were investigated. The river stretches from the Proterozoic Granite Gneiss Complex to the recent Holocene alluvium, forming three distinctive geomorphological regions across the river basin: the pediplane and upper and lower alluvial areas. Sixty cross-sections from throughout the main trunk stream were surveyed and the bankfull width, depth, cross-sectional area, and maximum depth were measured. Sediment samples from each location were studied and the flow velocity, stream power, Manning’s roughness coefficient, and shear stress were estimated. The results show that the bankfull channel cross-section area, width, width-to-depth ratio, and channel capacity increased between the beginning and middle of the river. Thereafter, the size of the river started to decrease in the lower alluvial area. This was characterized by gentle gradients, cohesive bank materials with grass cover, and channel switching. Within the lower part of the river, the channel capacity was observed to diminish as the drainage area increased. This increased the bankfull flow frequency and accelerated large floodwater losses in the floodplain via overbank flows and floodways.

回撤通道末采期间矿压显现与围岩破坏规律研究

以陕西某矿大采高综采工作面设备回撤通道为工程背景,综合运用现场监测和数值模拟等方法,开展回撤通道末采期间矿压显现与围岩破坏规律研究。研究发现,末采阶段平均来压步距为15.6 m。支架最大动载系数K P为1.76,平均K P为1.53。支承压力峰值位于在工作面前方13.4 m处,应力集中系数K平均为1.67。随工作面持续推进,间隔煤柱上的支承压力曲线是呈明显的“非对称双峰”转“单峰”分布。支承压力峰值P随间隔煤柱宽度的减小其转移路径为:远离回撤通道煤柱帮侧→逐渐靠近煤柱帮侧→跨越通道转移至实体煤侧;回撤通道围岩的塑性区分布形态与围岩变形破坏作用也呈动态变化,当间隔煤柱宽度减小至8 m时,回撤通道围岩塑性区与采动塑性区开始连接,导致间隔煤柱承载性能下降。间隔煤柱由8 m减小至2 m过程中,低于4 m时工作面与回撤通道的塑性区彻底贯通,产生“非对称”围岩大变形,塑性区扩展出现“蝶形”现象。主要原因是超前支承压力造成的高偏应力环境引起回撤通道围岩表现出持续大变形。

Cross-Layer Framework for Fine-Grained Channel Access in Next Generation High-Density Wi Fi Networks

Densely deployed Wi Fi networks will play a crucial role in providing the capacity for next generation mobile internet. However, due to increasing interference, overlapped channels in Wi Fi networks and throughput efficiency degradation, densely deployed Wi Fi networks is not a guarantee to obtain higher throughput. An emergent challenge is how to effi ciently utilize scarce spectrum resources, by matching physical layer resources to traffi c demand. In this aspect, access control allocation strategies play a pivotal role but remain too coarse-grained. As a solution, this research proposes a flexible framework for fine-grained channel width adaptation and multi-channel access in Wi Fi networks. This approach, named SFCA(Subcarrier Fine-grained Channel Access), adopts DOFDM(Discontinuous Orthogonal Frequency Division Multiplexing) at the PHY layer. It allocates the frequency resource with a subcarrier granularity, which facilitates the channel width adaptation for multi-channel access and thus brings more fl exibility and higher frequency efficiency. The MAC layer uses a frequencytime domain backoff scheme, which combines the popular time-domain BEB scheme with a frequency-domain backoff to decrease access collision, resulting in higher access probability for the contending nodes. SFCA is compared with FICA(an established access scheme)showing significant outperformance. Finally we present results for next generation 802.11 ac Wi Fi networks.

基于国内外规范计算兼具航道功能狭长港池宽度设计

合理确定港池水域布置对狭长港池类港口升级改造项目成本控制和保障后期安全运营至关重要。根据欧美规范与中国规范关于兼有航道功能的狭长港池宽度设计影响因素与取值方法的对比分析,归纳不同规范的差异性与适用性,提出了中国规范设计时应增加考虑的因素,并给出了海外类似工程的设计建议。通过典型工程实例对设计计算加以说明,并结合船舶操纵模拟试验对狭长港池设计方案合理性加以论证和优化,对海外港池水域尺度的确定及拓宽国内海港工程港池尺度设计思路具有借鉴意义。

冷弯薄壁型钢纯弯构件截面分类

为研究冷弯薄壁卷边槽钢纯弯构件截面分类,基于试验数据验证后的有限元模型,对不同板件宽厚比下冷弯薄壁卷边槽钢纯弯构件进行了大量的参数分析。结果表明:抗弯承载力随翼缘与腹板宽厚比的减小而增大。在考虑翼缘与腹板相关作用的前提下,基于截面承载力得出板件截面宽厚比限值,提出了冷弯薄壁卷边槽钢纯弯构件截面分类方法。

Effect of asymmetrical channel chirping on field intensity patterns of supermodes and modal discrimination in index guided laser arrays

The effect of channel-width chirping on near- and far-field intensity patterns of the six supermodes was investigated. The supermode discrimination was evaluated in various channel-chirped index guided laser arrays. The results show that the linearly channel-chirped laser array has very good supermode discrimination which is better than that of a uniform laser array, the V channel-chirped laser array has the smallest radiation angle of the fundamental supermode among the calculated arrays, and the asymmetrically V channel-chirped array has a very small radiation angle of the fundamental supermode, which is smaller than that of the uniform array and also allows for very good fundamental supermode discrimination against the higher-order supermodes, which is better than that of the V channel-chirped laser array.

Theoretical analyses on bed topography responses in large depth-to-width ratio river bends with constant curvatures

Bed morphology is the result of a dynamic response to a complex meandering river system. It is an important factor for the further development of river. Based on the meandering river characterized by a large depth-to-width ratio, a theoretical model is established with the coupling of Navier-Stokes （N-S）~ sediment transport, and bed deformation equations. The flow characteristics and bed response of river are obtained with the perturbation method. The research results show that, under the effect of two- dimensional flow disturbance, the bars and pools present the regular response. For a given sinuousness, the amplitude of the bed response can be used as a criterion to judge the bedform stability. The effects of the Reynolds number, disturbance wavenumber, sinuousness, and bed morphology gradient on the bed response development are described.

Lateral Shear Layer and Its Velocity Distribution of Flow in Rectangular Open Channels

The lateral velocity distribution of flow in the shear layer of open channel is required to many problems in river and eco-environment engineering, e.g. distribution of pollutant dispersion, sediment transport and bank erosion, and aquatic habitat. It is not well understood about how the velocity varies laterally in the wall boundary layer. This paper gives an analytical solution of lateral velocity distribution in a rectangular open channel based on the depth-averaged momentum equation proposed by Shiono & Knight. The obtained lateral velocity distributions in the wall shear layer are related to the two hydraulic parameters of lateral eddy viscosity (λ) and depth-averaged secondary flow (Γ) for given roughened channels. Preliminary relationships between the above two parameters and the aspect ratio of channel, B/H, are obtained from two sets of experimental data. The lateral width (δ) of the shear layer was investigated and found to relate to the λ and the bed friction factor (f), as described by Equation (26). This study indicates that the lateral shear layer near the wall can be very wide (δ/H = 14.6) for the extreme case (λ = 0.6 and f = 0.01).

明渠弯道交汇口水动力特性数值模拟

为研究不同宽深比和径宽比对明渠弯道交汇口水动力特性的影响规律,利用体积函数法(VOF)追踪自由表面,采用RNG k-ε模型封闭控制方程,建立明渠弯道交汇水流三维数值模型对3种宽深比和3种径宽比的5种组合工况进行了模拟,分析了交汇口附近的水面形态、流速分布、断面环流和分离区形态等特征。结果表明:随着宽深比的增大或径宽比的减小,交汇口附近水面跌落程度减弱;与径宽比相比,宽深比对弯道交汇口以及下游区域内流速分布的不均匀性影响较大,宽深比增大,纵向流速变幅增大,流速分布更加不均匀,水流偏转效应增强;宽深比或径宽比减小导致弯道处环流强度增大;宽深比或径宽比增大,弯道处回流结构增强,分离区尺寸增大,水平方向上形态更加狭长。

不同缘条宽度复合材料C型柱轴向压缩吸能特性

针对不同缘条宽度的复合材料薄壁C型柱开展准静态轴向压缩实验,通过CT扫描分析其轴向压缩失效模式及破坏机理,利用吸能特性评估参数分析不同缘条宽度对C型柱轴向压缩吸能特性的影响。建立复合材料C型柱单层壳模型与多层壳模型,通过对比轴向压缩仿真与实验获得的失效模式、载荷-位移曲线以及吸能特性评估参数,来验证模型有效性。结果表明:缘条宽度对C型柱轴向压缩失效模式和吸能特性的影响较大,缘条宽度为25 mm和30 mm的C型柱在轴向压缩载荷作用下能够以稳态渐进的形式发生失效,且吸能特性较好;C型柱多层壳模型仿真获得的平均压缩载荷、总吸能及比吸能偏差在5%以内,单层壳模型仿真获得的平均压缩载荷、总吸能及比吸能偏差在8%以内,多层壳模型轴向压缩仿真精度更高。

PEMFC新型压差流道传质与电化学性能研究

双极板是质子交换膜燃料电池PEMFC(proton exchange membrane fuel cell)核心组件,极板的流道形状和尺寸直接影响反应气体的利用率以及电池的排水、散热性能。基于极板工作原理提出一种新型PEMFC压差流道构型,研究流道内阴极氧气浓度、水浓度分布、进出口压降、流速的变化,分析电流密度和极化曲线对燃料电池电化学性能的影响;在50%开孔率时,通过对比8组低压直流道和高压直流道的宽度同时增大的仿真结果发现,低压直流道和高压直流道宽度均由2.25 mm减小到0.5 mm时,功率密度峰值提高了31.9%。进一步探究压差流道中增大或保持一种流道宽度不变而改变另一种流道宽度对燃料电池电化学性能的影响,结果表明低压直流道和高压直流道宽度均为1 mm时,功率密度峰值最高可达0.39 W/cm~2。

多路LLC谐振变换器交错并联均流控制

LLC谐振变换器多路交错并联具有良好的应用前景,然而谐振元件的参数偏差会导致各路LLC谐振变换器电流不均衡的问题。为了解决这一问题,通过将二次侧的同步整流替换为可控整流方式,利用各路输出电流作为控制信号对二次侧进行脉宽调制控制,提供附加的电压增益,形成均流控制环路,保证各路的电压增益相同,从而实现多路LLC谐振变换器在相同开关频率下运行的均流调节。介绍了该控制的原理及实现方法。基于电磁暂态过程进行仿真,得出不同负载率下的电流不平衡度;同时搭建100 W的实验样机,在电流不平衡度最大的工况下,验证了该均流控制方法的可行性和有效性。