Minimum wall pressure coefficient of orifice plate energy dissipater

Orifice plate energy dissipaters have been successfully used in large-scale hydropower projects due to their simple structure, convenient construction procedure, and high energy dissipation ratio. The minimum wall pressure coefficient of an orifice plate can indirectly reflect its cavitation characteristics： the lower the minimum wall pressure coefficient is, the better the ability of the orifice plate to resist cavitation damage is. Thus, it is important to study the minimum wall pressure coefficient of the orifice plate. In this study, this coefficient and related parameters, such as the contraction ratio, defined as the ratio of the orifice plate diameter to the flood-discharging tunnel diameter; the relative thickness, defined as the ratio of the orifice plate thickness to the tunnel diameter; and the Reynolds number of the flow through the orifice plate, were theoretically analyzed, and their relationships were obtained through physical model experiments. It can be concluded that the minimum wall pressure coefficient is mainly dominated by the contraction ratio and relative thickness. The lower the contraction ratio and relative thickness are, the larger the minimum wall pressure coefficient is. The effects of the Reynolds number on the minimum wall pressure coefficient can be neglected when it is larger than 10^5. An emoirical expression was presented to calculate the minimum wall oressure coefficient in this study.

新型震后可修复预制混凝土填充墙板抗震性能研究

为了解决预制混凝土墙板在强震作用下损伤严重、结构功能难以快速恢复的问题,提出了一种带防屈曲耗能杆的柔性连接预制混凝土填充墙板(flexible connected prefabricated concrete wall panel,FCWP)。首先,介绍了新型墙板的概念及工作原理;其次,采用ABAQUS有限元软件对耗能杆及预制混凝土填充墙板进行了有限元模拟;最后,对比分析了FCWP和传统刚性连接预制填充墙板(traditional rigid connected prefabricated wall panels,RCWP)在低周往复荷载下的受力机理及损伤模式。结果表明:RCWP加载初期预制墙板底部出现水平裂缝,墙板右底部出现逐渐向左上部延伸的斜裂缝,随着位移的持续增大,斜裂缝在墙板跨中贯通,结构破坏;FCWP中防屈曲约束耗能杆发挥了优异的耗能能力,预制墙板仅在底部及顶部与耗能杆连接部分出现裂缝,损伤程度较轻。所提新型柔性连接墙板应力及损伤显著低于刚性连接墙板,且损伤主要集中于耗能杆,具有较好的耗能能力和震后可恢复能力。

齿墩长度对齿墩式内消能工水力特性影响的数值分析

为了探究齿墩长度对齿墩式内消能工水力特性的影响,使用Fluent软件中的k–ε数学模型进行数值模拟,并和前期物理模型试验的结果进行比对,验证了模型的准确性,进而对7种不同齿墩相对长度(相对长度η为齿墩长度l与管道内直径D之比)的内消能工的中心轴流速、时均压强、过流能力、消能率、紊动能和流场等进行了分析。结果表明不同相对长度齿墩式内消能工中心轴流速分布规律基本一致,除η等于0.1外,各方案中心轴峰值流速出现的位置相同,不随相对长度的变化而变化,均在齿墩进口后0.38D处;齿墩前后壁面时均压强变化较大,存在低压区;齿墩段后侧旋涡区内紊动能较大,且回流区长度随齿墩相对长度增加逐渐减小;在模拟范围内,流量系数随着齿墩相对长度的增加先增加后减小,η在0.2~0.9范围内流量系数较大,消能率的变化规律则相反;η大于0.9时,突缩突扩段旋涡区分离,此后随着齿墩相对长度增加,多余长度对消能的作用仅由沿程水头损失产生,对消能工消能率的贡献不大,可忽略。综合分析,相对长度为0.2~0.9范围内的齿墩长度较优,给齿墩式内消能工的体型优化提供了依据。

FLOWS THROUGH ENERGY DISSIPATERS WITH SUDDEN REDUCTION AND SUDDEN ENLARGEMENT FORMS

The energy dissipation of flood discharges has been one of important problems that affect directly the safety of hydropower projects. The energy dissipater with sudden reduction and sudden enlargement forms, used widely in large-scale projects has been a kind of effective structure for energy dissipation. The concept of critical thickness was defined, which is related to both the geometric parameters and the hydraulic parameters of the energy dissipater, and the factors affecting the critical thickness, were analzsed by means of dimensional analysis. The empirical expression about the critical thickness was obtained and could be used as the criterion to distinguish the flows through the energy dissipater, i.e., the plug flow and the orifice plate flow. The error analysis showed that the critical thickness calculated by the expression has the errors of smaller than 10% in the estimation of the flows for the energy dissipater mentioned above.

HYDRAULIC CHARACTERISTICS OF PLUG ENERGY DISSIPATER IN FLOOD DISCHARGE TUNNEL

The hydraulic characteristics of three types of plugs, namely, the single plug, the stepped plug and the gradually contracted plug were studied by means of experimental and numerical simulations. Main research findings are as follows. For the single plug, the pressure recovery lengths inside and after the plug range from 0.63-1.05 times and 2.02-2.84 times of the tunnel diameter, respectively. For the stepped plug, the lengths are 0.24-0.32 times and 1.62-2.84 times of the tunnel diameter, respectively. The best ratio of the inlet diameter to the outlet diameter of the gradually contracted plug can be expressed by a linear function. The relationship between the head loss coefficient and the area contraction ratio is obtained. The incipient cavitation numbers of different plugs are experimentally and numerically determined, and the incipient cavitation numbers are expressed by a formula. Model experiment with scale of 1：50 was carried out on a pressure tunnel with three-stage gradually contracted plugs. The results show that this type of energy dissipater is suitable for spill tunnels of high head （nearly 200 m） and large flow rate （nearly 2500 m^3/s）.

Flow choking characteristics of slit-type energy dissipaters

In this paper, the behavior of the flow choking, including the critical and developing states, was experimentally investiga- ted by means of five slit-type outlets, characterized by the outlet width, the contraction angle and the opening of the working gate. The results showed that the approach flow Froude number of the critical choking decreases if the outlet width increases, or the con- traction angle decreases, or the opening increases. There is the hysteresis when the flow choking develops, i.e., the Froude numbers of the appearance and disappearance of the flow choking at the increasing discharge regime are all larger than those at the decreasing discharge regime. For various widths of the outlets, the differences between the critical Froude numbers at small opening are much larger than thoset at large opening. The change range from appearance to disappearance of the flow choking at small opening is smaller than that at large opening.

Local scour by multiple slit-type energy dissipaters

Energy dissipation and scour control are all the key issues for the design of hydraulic structures.On the basis of the high energy dissipation for the multiple slit-type energy dissipaters(M-STED)developed by the authors,in this work,the characteristics of the scour hole for the M-STED were experimentally investigated through three sets of those physical models with five cases and a scour hole form index was proposed.The results show that,the M-STED results in not only the high energy dissipation but also the mild upstream slope of the scour hole thanks to the scour hole form index of larger than 0.5,which is in favor of the safety of the release works.

Shock waves and water wing in slit-type energy dissipaters

The slit-type energy dissipater（STED）is widely used in hydraulic projects of high water head,large discharge,and narrow river valley,thanks to its simple structure and high efficiency.However,the water wing caused by the shock waves in the contraction section of the STED may bring about harmful effects.A coefficient is introduced for the application of Ippen？s theory in the STED.The expression of the coefficient is experimentally obtained.Simplified formulas to calculate the shock wave angle and the water wing scope are theoretically derived,with relative errors within 5%.

洞塞泄洪洞的水力特性研究

本文提出的洞塞式消能工与孔板非常相似 ,充分利用高速水流经过局部突缩突扩断面产生巨大水头损失实现消能 ,但体型简单 ,洞塞内水流相对平稳 ,消能率很高。本文较为详细地介绍了洞塞消能的特点、洞塞泄洪洞的布置型式和水力学计算。

过悬栅、悬板栅水流流场测试及消能分析

用多普勒激光测速系统对悬栅和悬板栅附近流场进行了测试 ,分析了悬栅、悬板栅的消能效果。研究表明 ,悬栅的消能率随流量的增加而增加 ;悬栅和悬板栅的总消能率为 71.89% ;该消能形式能够显著降低弯道凹岸水深 ,减小弯道内横向水面比降 ,可将泄流能力提高 2 .3倍左右 ;经消能后陡坡下游水流平顺 ,避免了水流翻越边墙造成的破坏 ;上述结果表明悬栅、悬板栅“消、导”结合、联合消能是消除陡坡弯道急流冲击波的一种新型消能型式 。

耗能减震技术研究及应用的新进展

本文总结了耗能减震技术近年来的研究与应用情况，主要包括各种新型耗能减震装置的原理、性能及应用。文中介绍了有关国家耗能减震技术标准发展的情况，提出了该项技术今后应加强研究的若干问题，并预测了其发展前景。

洞塞式消能工的数值模拟

针对有压洞内洞塞式消能工附近局部流动,分析研究了水流紊动特点,应用三维RNGk-ε紊流模型,利用物理模型试验资料对其计算结果进行了验证,利用模型对洞塞式消能工引起的水头损失进行计算分析,分析结果表明,当洞塞段相对长度从很小开始增加时,水头损失系数呈现先急剧降低而后明显增加,最后缓慢线性增加的趋势;在有压洞半径一定的情况下,洞塞段过流半径的变化比洞塞段过流长度的变化对水头损失系数影响更为明显,可为洞塞式消能工的设计提供相关参考依据。

渐缩渐扩洞塞消能和空化特性

建立了三维RNG k-ε紊流数学模型和突缩突扩洞塞泄流的物理模型试验,利用实验结果对数学模型进行了验证,利用验证后的数学模型对突缩突扩洞塞和渐缩渐扩洞塞的水头损失系数和空化数进行了计算。结果表明,洞塞渐缩(或渐扩)段相对长度一定时,随着渐扩(或渐缩)段相对长度的增加,水头损失系数减小,最小空化数增加。当渐缩段和渐扩段几何尺寸互换时,水头损失系数和最小空化数的变化不大;其他几何参数一定的情况下,随着横断面半径收缩比的减小,水头损失系数增加,最小空化数降低。圆弧连接情况下,随着圆弧夹角的增加,水头损失系数呈现先降低后增加的趋势;而最小空化数呈现先增加后降低的趋势。其他几何参数一定的情况下,圆弧连接的水头损失系数小于斜线连接的对应值,最小空化数则相反。在水头损失系数和最小空化数权重相等的假定条件下,初步探讨了渐缩渐扩洞塞几何体型参数的优化方法,给出了渐缩渐扩洞塞的最优几何体型参数。

新型耗能(阻尼)减震器的开发与研究

文阐述了耗能减震的概念和原理，提出了耗能减震器设计的新思想，研制开发了多种新型实用耗能（阻尼）减震器，并对其中的圆环耗能器、双环耗能器、加劲圆环耗能器、弹塑性－摩擦复合耗能器等进行了循环荷载试验，考察了耗能器的工作性能和耗能性能。对已装与未装耗能减震器的钢筋混凝土框架模型进行了伪动力对比实验，进一步考察了耗能减震器的减震效果。在试验研究的基础上，对耗能（阻尼）减震结构体系的分析方法进行了研究，并编制了相应的计算软件。试验和分析表明，所研制的耗能减震器工作性能稳定、耗能效率高、减震效果好，构造简单。文章最后对耗能减震技术的前景作了展望。

齿墩状内消能工的消能及压力特性

输水管道或泄洪洞常见的内消能方式为孔板和洞塞,结合明渠水流中的消能工形式提出了齿墩状内消能工,并通过物理模型试验对不同面积收缩比的齿墩状内消能工进行了研究,分析了它们的过流能力、消能率、压强沿程变化及脉动压强特性.结果表明:齿墩状内消能工的过流能力主要是由消能工的体型及尺寸决定的,其面积收缩比越大,消能率越低,过流能力就越强;齿墩状内消能工的时均压强在收缩段骤降,在其后部逐渐上升,而后恢复至稳定,其恢复长度基本相同;齿墩状内消能工的脉动压强最大点均出现在收缩段后1倍圆管直径范围内,随后迅速减小,逐渐趋于平稳;面积收缩比为0.471 2的齿墩状消能工的脉动强度最小,因而其抗空化性能优于其他情况,且脉动压强最大点的压强概率密度分布接近正态分布.

跌坎式底流消能工的消能机理与水力计算

应用平面紊动射流理论,分析淹没射流在跌坎式底流消能工消力池中的运动规律以及跌坎式底流消能工降低临底流速的机理,得出射流扩散中心线上最大流速计算式。通过建立消力池内水流运动的动量方程,推导出跌坎式底流消能工的水力计算公式,通过试验验证,结果表明,公式是合理的,为跌坎式底流消能工的设计提供了依据。

小石峡水电站表孔溢洪道模型试验研究

通过对新疆小石峡水电站表孔溢洪道的模型试验研究,优化了溢洪道进口段,改善了进口流态;提出在溢洪道消力池内布设趾墩—消力墩—尾坎的修改方案,试验结果表明,修改方案有效的改善了池内水流流态,同时缩短了池长、降低了池深,提高了消能效果,并且消力池内各项水力指标满足设计要求。试验成果对于工程设计具有借鉴意义。

减压环耗能性能的静力试验及动力有限元分析

被动柔性防护系统中采用的减压环由钢管及铝管套筒组成,应用中将钢丝绳穿过钢管连接在防护系统的支撑绳及拉锚绳上,起到吸收能量和缓冲冲击荷载的作用。根据被动防护系统中减压环的工作状态,将减压环的受力形式简化为一端固定,另一端受荷载作用,并进行了静力试验和动力有限元分析。在较低的冲击荷载作用下,数值计算结果与试验结果较吻合,随着冲击荷载速度的增大,启动荷载逐渐增大,减压环耗能能力有一定的提高。另外,采用数值计算方法研究了减压环中的铝管套筒长度对耗能性能及启动荷载的影响。结果表明:减压环在动力荷载作用下的耗能能力开始增大比较明显,后期耗能能力无明显增大,而启动荷载随着套筒长度的增大先减小而后增大,当铝管套筒在合适长度范围内时,减压环在动力荷载作用下理想吸能效率与静力试验结果较接近。

高水头船闸闸室明沟消能效果及机理分析

利用ADV等先进的量测仪器,通过船闸局部水工模型试验和三维数值模拟,对高水头船闸闸室明沟的消能效果和消能机理进行研究,分析流速分布、剩余比能、水面波动和紊动能耗散率等参数的结果表明:明沟消能工出流掺混强烈,97%的耗能位于明沟区,扩散均匀,水面波动较小,消能效果较优。明沟型式结构简洁,可在我国高水头船闸中推广应用。

坝身泄水孔窄缝消能工三维水动力特性数值模拟

本文采用双方程紊流模型对中孔窄缝消能工的出流进行了三维紊流数值模拟,给出了侧墙压力分布、流场、挑流水面线等水流特性。计算结果和模型试验数据对比,两者吻合较好,对不同底板挑角的方案进行的比较计算结果,发现底板挑角对水流特性有着明显的影响。