Analytical study on water hammer pressure in pressurized conduits with a throttled surge chamber for slow closure

This paper presents an analytical investigation of water hammer in a hydraulic pressurized pipe system with a throttled surge chamber located at the junction between a tunnel and a penstock, and a valve positioned at the downstream end of the penstock. Analytical formulas of maximum water hammer pressures at the downstream end of the tunnel and the valve were derived for a system subjected to linear and slow valve closure. The analytical results were then compared with numerical ones obtained using the method of characteristics. There is agreement between them. The formulas can be applied to estimating water hammer pressure at the valve and transmission of water hammer pressure through the surge chamber at the junction for a hydraulic pipe system with a surge chamber.

INFLUENCE OF SEA LEVEL RISE ON SHANGHAI ASTRONOMICAL TIDE AND STORM SURGE AND ESTIMATION OF PROBABLE WATER LEVEL

A nonlinear two-dimension dynamic model of storm surge (SS) and astronomical tide(AT) was used to investigate the effects of SS and AT on expected sea level rise (SLR) at principalcoastal stations in the Shanghai region and to estimate numerically the probable maximum water lerel for2010 - 2050. Evidence suggests tha SLR causes reduction of SS; that its influence on SS depends on theintensity and path of a tropical cyclone and the station locality; tha the SLR’s effects on AT vary periodi-cally, with the peried being the same as tha of the AT’s: and that as the SLR increment grows, its impactincreases; below mean sea level (MSL) the effect is positive at rising tide and negative at ebb tide, andvice versa for the effect above MSL. Study of the probable maximum water level (by assuming SLR, SSalong favorable tropical cyclone’s path, its possible maximum intensity and effectivee spring AT at a rangeof set paths of Cyclones 5612, 8114, 9417) showed that the probable maximum water level is 740, 745,and 751 cm in the years 2010, 2030, and 2050, respetively, over the target region.

Stochastic Model for Estimating Extreme Water Level in Port and Coastal Engineering Design

Extreme water level is an important consideration when designing coastal protection structures. However, frequency analysis recommended by standard codes only considers the annual maximum water level, whereas water levels should actually be regarded as a combination of astronomical tide and storm surge. The two impacting factors are both random variables, and this paper discusses their dependency structures and proposes a new joint probability method to determine extreme design water levels. The lognormal, Gumbel, Weibull, Pearson type 3, traditional maximum entropy, and modified maximum entropy distributions are applied to fit univariate data of astronomical tides and storm surges separately, and the bivariate normal, Gumbel-Hougaard, Frank and Clayton copulas are then utilized to construct their joint probability distributions. To ensure that the new design method is suitable for use with typhoon data, the annual occurrence frequency of typhoon processes is considered and corresponding bivariate compound probability distributions are proposed. Based on maximum water level data obtained from Hengmen hydrological station in the Pearl River Basin, China, these probability models are applied to obtain designs for extreme water levels using the largest sum of the astronomical tide and storm surge obtained under fixed joint return periods. These design values provide an improved approach for determining the necessary height of coastal and offshore structures.

Characteristics Analysis and Risk Assessment of Extreme Water Levels Based on 60-Year Observation Data in Xiamen, China

Extreme water levels are related to astronomical tides and storm surges.Eleven typhoon systems,which have caused extreme water level rises,were selected based on 60-yr water level data from the Xiamen tide gauge station.In these 11 typhoon systems,the astronomical tide component accounts for 71%-95%of the total water level.The Gumbel distribution of extreme water level rise was estimated,and the impact of typhoon surges on water levels during the return period was analyzed.The ex-treme tide levels caused by typhoons Herb(1996)and Dujuan(2015)are much higher than those of other typhoons and correspond to the return period of 76 yr and 71 yr,respectively.The differences of sea levels in the presence and absence of these two typhoons in the 10-100 yr return period are 5.8-11.1 cm.For the 100-yr return period,the total risks within 10,25,50,and 100 yr increase by 94.3%,85.4%,72.9%,and 54.4%,respectively,if the Herb and Dujuan are not considered.Assuming that typhoon Herb(1996)occurred during the highest astronomical tide,it will produce a water level higher than that of the 1000-yr return period.Sea level rise has an important influence on the water level return period,and the contribution of nonlinear sea level rise in the next 100 yr is estimated to be 10.34%.

Experimental Study of Overtopping on Sea Dikes and Coastal Flooding Under the Coupled Processes of Tides and Waves

Storm surges are cataclysmic natural disasters that occur along the coasts and are usually accompanied by large waves.The effects of coupled storm surges and waves can pose a significant threat to coastal security.Previous labo-ratory studies on the effects of storm surges and waves on coastal structures have typically utilized steady water levels and constant wave elements.An indoor simulation of the coupled processes of tides and waves is developed by adding a tide generation system to an existing laboratory wave basin to model continuous dynamic tide levels so that tide generation and wave-making occur synchronously in the pool.Specific experimental methods are given,which are applied to further study waves overtopping on artificial sea dikes and coastal flooding evolution under the coupled actions of tides and waves.The results of the overtopping discharge obtained by the test with a dynamic water level are compared with those obtained from steady water level tests and the existing empirical formula.In addition,the impacts of ecological coastal shelterbelts and structures on coastal flood processes and distributions are also investi-gated.The proposed simulation methods provide a new approach for studying the effects of storm surges and waves on coastal areas.The study also aims to provide a reference for coastal protective engineering.

THEORETICAL,NUMERICAL AND EXPERIMENTAL STUDY OF WATER HAMMER IN PIPE SYSTEM WITH COLUMN SURGE CHAMBER

A new kind of governing equations for water hammer based on the elasticcolumn theory was proposed and adopted to analyse water hammer phenomenon in the pipe system with avertical column surge chamber and water level fluctuation in the surge chamber during pressuretransient. The wrongness existing in the classical governing equations for water hammer wasanalysed. A typical reservoir-valve pipe system was chosen as an example to verify the new governingequations numerically and experimentally. The finite difference method based on the method ofcharacteristics was used to solve numerically the nonlinear characteristic equations. The temporalevolutions of transient volume flux and head and of water level fluctuation for various surgechamber configurations were worked out, assuming that the air in the surge chamber are compressible.The relevant experiment was conducted to verify the new governing equations and numerical method.The numerical and experimental results show that the new governing equations are valid and theconventional assumption that the pressure head at the base of a surge chamber equals that of thestatic head above it during pressure transient is not always valid. The surge chamber generallyreises the period of transient pressure wave in pipe system, reduces the maximum pressure envelopeand lifts the minimum envelope substantially. The water level fluctuation in the surge chamber wasnumerically and experimentally observed. Increasing the size of the surge chamber and/or decreasingthe initial air pressure in the surge chamber enhance the effectiveness of the surge chamber insuppressing pressure wave.

三峡库区黑石板滑坡的变形特征和涌浪预测

三峡库区水位波动易于导致库岸滑坡失稳进而形成涌浪灾害。以三峡库区黑石板滑坡为研究对象,基于近5年的监测数据分析:三峡库区黑石板滑坡为动水压力型滑坡,降雨只在库水位下降时和低水位波动期对滑坡的变形有一定的助推作用,其他时间对滑坡变形影响并不大。通过分析累积位移曲线中的6次阶跃变形,确定了库水位下降至165 m时为滑坡阶跃变形的启动阈值,并以此作为滑坡最危险情况下所对应的库水位高度,将其设置为数值模拟的初始水位高度。运用FLOW-3D软件进行了涌浪计算及预测:在165 m水位时,滑坡入水的最大速度为19.4 m/s,涌浪产生的最大波高为24.9 m,最大爬高为42.21 m。预测结果表明,黑石板滑坡破坏后引发的涌浪将会淹没水田坝乡沿岸部分区域,毁坏入乡主干道,这将严重影响后续对水田坝乡的救援工作。该研究为三峡库区库岸滑坡涌浪的风险管理提供科学依据,具有一定的工程实践意义。

NUMERICAL STUDY OF WATER LEVEL FLUCTUATION IN BULL-HORN SURGE CHAMBER IN PIPE SYSTEM DURING WATERHAMMER

The method of characteristics was adopted to analyze water level fluctuationexisting in Bull-Horn surge chamber in reservoir-valve pipe system during waterhammer caused byvalve closure operation. The Finite Difference Method (FDM) based on the method of characteristicswas used to solve numerically the nonlinear two-parameter characteristic equations governingwaterhammer. The finite fixed mesh was applied to obtaining the discrete form of the governingequations and discrete flow-field. The temporal trends of the y -directional flow, water level,velocity of water level and head difference for different heights of water in surge chamber,diameters of cylinder, cutting angles of surge chamber, lengths of horizontal cylinder and lengthsof inclined cylinder were obtained under the condition that the air in surge chamber iscompressible. The conclusions on water level fluctuation in Bull-Horn surge chamber were given basedon the analyses of the obtained transient numerical results. These conclusions can play a guidingrole in designing pipe system and executing surge suppression.

1950-2003年中国近海历史风暴潮增水时空特征

风暴潮是中国沿海最严重的自然灾害之一。对1950-2003年中国沿海67个站点的风暴潮增水数据进行了统计和分析,得到了中国沿海风暴潮增水的时空分布。研究发现,无论在频次还是在强度上,东南沿海都是中国沿海风暴潮灾害最严重的区域,风暴潮强度集中在Ⅲ级、Ⅳ级和V级,其中长江口和杭州湾风暴潮增水较大。此外,风场路径和天文潮潮汛对风暴潮增水的影响显著;以定海站点为例,在125°E以西转向的热带气旋对该站点风暴潮增水影响最大,风暴潮增水的极值时刻绝大多数在大潮时刻,潮汐时刻多在天文低潮前后。研究结果可为风暴潮风险评估和防灾减灾提供参考。

长距离负扬程加压泵站调水工程水力控制方式探讨

事故掉电引发的停泵水锤是泵站调水工程安全运行最主要的威胁之一,而对于下游水位低于上游水位的长距离负扬程加压泵站调水工程而言,事故停泵易造成管道拉空,负水锤防护难度较大,因此,针对其停泵工况的水力控制研究十分重要。以某长距离负扬程泵站调水工程为例,模拟计算了事故停泵、阀门拒动这一控制性工况下的水力过渡过程,并对比分析了空气罐、空气阀与空气阀联合空气阀调压室3种水力控制方案的水锤防护效果。结果表明:对于长距离负扬程加压泵站调水系统而言,当采用空气罐的水力控制方式时,所需的空气罐体积较大,投资高昂;当单纯采用空气阀的水力控制方式时,难以有效解决管道局部高点处负压较大的问题,仍可能诱发弥合性水锤;当将部分空气阀附加一根短管组合成空气阀调压室后,能够有效控制管内负压。空气阀与空气阀调压室联合防护是一种十分经济且有效的水锤防护方案,可为这类负扬程加压调水工程的水力控制方式选取提供参考。

渤、黄海天文潮—风暴潮相互作用及其对极值水位的贡献

基于Delft3D模型建立了中国渤、黄海风暴潮数值模型,选取1979—2020年影响该海域的93场风暴过程(包括台风、寒潮和温带气旋),模拟了所产生的风暴增水和风暴潮总水位。采用泊松—皮尔逊复合极值分布理论,推算了渤、黄海对应不同重现期的极值水位;通过数值试验,对天文潮—风暴潮非线性相互作用对极值水位的贡献进行了量化分析。研究结果表明,渤海的莱州湾、渤海湾,以及黄海的江华湾、西朝鲜湾风暴增水最大,其中江华湾北侧和渤海湾西南侧的百年一遇风暴增水可达4 m;天文潮—风暴潮非线性相互作用在潮差较大、水深较浅的河口、湾顶区域更为显著,与耦合模型结果相比,非线性作用使极值水位值偏小,天文潮、风暴潮增水的线性叠加可显著高估极值水位,高估的幅值可达0.5~0.8 m。考虑重现期极值水位是海岸灾害防护工程的关键设计参数之一,对海岸构筑物的安全和建造成本影响极大,应重视天文潮—风暴潮非线性相互作用对重现期水位的影响。

GNSS-IR测量水位的精度评估和站点对比:以中国南海北部和日本南部站点为例

通过南海北部和日本多个实例,量化分析影响近岸全球卫星导航系统干涉反射计(GNSS-IR)反演潮位或风暴潮过程效果的主要影响因素。结果表明:接收机所能接收的卫星信号波段数量、反射信号功率对反演的时间分辨率和精度影响巨大。研究以中国香港HKQT站点为例量化多模多频GNSS-IR监测风暴潮的优势,同时展示日本J425站点在潮位站空缺地区记录完整风暴潮波形的能力。分别针对卫星信号接受波段、硬件配置、台站架设位置和架设高度等因素,对未来架设具有测量海平面能力的近岸GNSS站点提供具体的指导意见。

西藏扎拉水电站引水发电建筑物设计

为解决扎拉水电站引水发电建筑物设计过程中存在引水隧洞穿越活动断裂,引水隧洞Ⅳ类、Ⅴ类围岩洞段占比较大,调压室顶部层间密集剪切带,巨型冲击式机组配水环管充水保压浇筑混凝土等重大技术难点,充分论证引水隧洞过活动断裂洞段增加衬砌混凝土厚度、短分节、上部设置排水洞(兼勘探洞、灌浆洞、监测洞)等措施的有效性。通过优化布置和计算线弹性有限元结构,提出了引水隧洞Ⅲ类、Ⅳ类、Ⅴ类围岩分别选取40,60,80 cm厚度衬砌结构设计,调压室选取1.5,1.0 m厚度衬砌结构设计,配水环管选取5.5 MPa的充水保压埋设方式,配水环管分区配置钢筋来优化结构设计。相关设计成果可供同类工程参考。

基于有限体积法的含无压段泵站水锤模拟及调压井优化

针对含无压段的泵站输水工程水锤模拟常采用特征线法,且往往忽略动态摩阻和有压-无压相互干扰影响的问题,该研究建立了考虑动态摩阻的二阶有限体积法模型,进行有压段-无压段实时联合计算。首先,采用二阶Godunov格式分别对有压流、无压流流动控制方程进行求解,同时考虑了动态摩阻效应以准确模拟水力瞬变过程中的能量耗散,并进行试验验证。进一步地,对有压段、无压段交接处采用变时步法传递数据,结合实际工程对阻抗式调压井的尺寸、位置进行了敏感性分析。结果表明:考虑动态摩阻效应后模型模拟结果与试验结果基本一致,阀门处水锤压力误差最大值仅有4.58%;与特征线法相比,二阶Godunov格式稳定性更高,库朗数小于1.0时水锤压力只有轻微的数值衰减。本文建立的有压段-无压段实时联合计算方法能够充分考虑有压段出水池水位变化以及无压段倒流的影响。针对水泵失电工况,对阻抗式调压井进行的优化研究表明,随连接管直径增大,系统内最大压力水头、调压井最高涌浪水位和水泵最大反转转速增大,调压井最低涌浪水位降低;随调压井直径增大,最高涌浪减小,最低涌浪增高,最大压力在连接管直径较小时一直降低,在连接管直径较大时先减小后增大;当连接管管径3.5 m,调压井直径15 m时,既能满足系统控制参数要求,也能减少工程量。调压井位置离泵站越近,最大压力、反转转速、最高涌浪越大,最低涌浪越小,当调压井布置在泵后1.0 km时,最高涌浪水位会达到172.35 m,不满足控制标准要求。综上,建立的模型具有较高的准确性、稳定性和适用性,研究结果可为含无压段泵站输水工程的水锤模拟提供参考。

气垫调压室联合单向塔的停泵水锤防护研究

针对某长距离、大流量、高扬程泵站加压供水工程,对事故停泵进行模拟。结合工程地形特征,提出采用气垫调压室和单向塔联合防护的方法,并结合管道压力控制要求,对泵后阀门关闭规律及调压室阻抗孔径进行敏感性分析。结果表明,气垫调压室可有效防护停泵水锤及泵后阀快速关闭产生的关阀水锤,单向塔解决了气垫调压室持续补水导致的局部高点低压问题,保护了高点管段安全。联合防护方案可显著减小气垫调压室体积,节约工程成本。另外,泵后阀关闭规律及气垫调压室阻抗孔面积对管道的水锤压力影响较大,关阀过快或阻抗孔口面积过大会导致管道正压超标;关阀过慢或阻抗孔口面积过小会导致管道出现较大负压,具体工程需结合过渡过程模拟进行优化,对于本工程,经过模拟优化,阻抗孔口直径取0.8 m,泵后阀采用5 s直线关闭,结果可满足调保计算要求。

水电站调压室托马临界稳定断面公式再认识

托马临界稳定断面公式通常被认为是含调压室的水电站输水发电系统运行稳定性判别的重要依据。本文首先从理论上论证了刚性水体假设与等出力调节方式下,系统不可能稳定运行;之所以能够得到托马临界稳定断面公式,是由于推导过程中忽略了调压室后压力管道与机组后尾水道的水体惯性,而这恰是导致系统不稳定的关键因素。其次针对实际弹性水体,理论上论证了等出力调节方式下,真实的水力发电系统也不可能稳定运行;同时指出含调压室的水电站输水发电系统稳定性主要取决于水轮机上下游侧的水锤反射系数;无论是调压室前引水道还是调压室后的压力管道与尾水道,管道内的摩阻均有利于稳定,调压室面积大小对稳定影响相对较小;等出力调节模式下,无论是采用刚性水体假设还是针对实际弹性水体,含调压室的水电站输水发电系统一定是不稳定的,一个不稳定的系统不可能存在稳定断面,托马临界稳定断面在理论上是不成立的。

大变幅浮船泵站输水系统停泵水锤防护研究

浮船泵站输水系统的停泵水锤防护除了需保证机组和输水管道安全外,还要考虑水锤压力对活动摇臂和浮船的冲击,保证浮船稳定。对云南省某大变幅浮船泵站输水系统的停泵过渡过程进行数值模拟研究。结果表明,最低进水位工况为水锤防护的最不利工况;泵出口阀拒动条件下,若机组倒转转速超标且在停泵后3s内即达到最大倒泄流量,综合考虑阀门驱动能力需求、机组倒转转速和水锤压力,泵出口阀推荐采用轴流式止回阀;在“泵出口轴流式止回阀+岸上空气罐+中间止回阀+防水锤空气阀”的水锤防护方案中,轴流式止回阀保证机组不倒转,空气罐和防水锤型空气阀降低了输水管道内的最大水锤压力并改善了负压状况,中间止回阀减小了水泵出口和摇臂段的压力振荡幅度和振荡时间,有效解决了该浮船输水系统的停泵水锤防护问题。

长距离有压隧洞引调水工程过渡过程研究

在有压隧洞运行期间,由于流量调节或事故等原因导致长距离输水系统发生非恒定流的现象,需对其水力过渡过程进行研究。过渡过程发生时,输水系统沿线的水力参数随时间变化发生急剧变化,往往超出恒定流的设计范围,从而对输水系统造成不利影响,尤其是在有压输水隧洞中,由于流速的急剧变化会导致水锤产生。针对引江补汉输水沿线补水工程输水流量大、隧洞超长的工程特点,对其水力过渡过程影响性进行分析、研究,并提出相应的处理措施,可为类似工程提供经验。

河口风暴潮极值增水研究进展与展望——以粤港澳大湾区为例

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