水质和空化比尺效应

本文提出了新的空化数和初生空化数的表达式,说明水体抗拉强度在空化中的作用,并且也指出,除抗拉强度外,水中气核半径及其数量也起着相当大的作用,从而可以解释在试验中即使同一个模型在不同的设备中以及不同的情况下可得差别很大的初生空化数。另外,对模型数据引伸到原型提出了一些具体建议。     

初生空化与液体抗拉强度的关系

自1983年开始以液体的抗拉强度作为其空化临界压强研究初生空化的比尺效应以来,该方法已得到进一步的应用和完善。本文就研究中遇到的一些问题,如关于空化灵敏度仪的校正,“零抗拉强度”的概念,试验设备中液体抗拉强度的动态变化以及在空化试验中使用该方法的技术和意义等作详细的阐述。     

ZERO-TENSILE STRENGTH FOR RESULT COMPARISON IN CAVITATION INCEPTION TESTS

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初生空化数公式的优化研究

初生空化数是衡量过流体型是否发生空化的判别标准。传统的托马公式认为液流负压值达到液体饱和蒸汽压时即发生空化。近来研究表明,气核和液体抗拉强度等对初生空化有重要影响。有学者认为把托马公式中的液体饱和蒸汽压替换为临界压强更为合理。本文在已有研究的基础上,对空化初生机理和影响空化初生的因素进行分析。认为空化仅是气核克服表面张力和液体饱和蒸汽压膨胀而形成的,并没有克服液体抗拉强度,且在空化源附近的液体几乎不具有抗拉强度,并基于此提出新的初生空化数公式。     

液体抗拉强度与空化比尺效应

本文讨论了在动水力学法测量液体抗拉强度时小文杜时管中有空化，而喉部却出现了“负抗拉强度”的原因。同时利用小文杜里管作为空化器件，探讨了空化比尺效应，说明液体抗拉强度只是影响了临界空化压力pc，而在产生初生空化时,空泡也同样影响到参考点的压力pu。     

验证用于初生空化数检测的比较法

该文作者在若干年前提出了用于初生空化试验的"比较法"的概念.方法的原理是:当初生空化数和消失空化数之差达到最小时,试验液体的抗拉强度就非常接近于零.由此;可以在不用专业仪器的情况下,检测不受液体抗拉强度影响的初生空化数.近年来的的研究成果证实了该"比较法"与使用检测仪器得到的成果具有相同的效果,进一步地验证和讨论了它的合理性.     

泄水建筑物若干体型初生空化数的合理取值

 在泄水建筑物高速水流防空蚀水力设计中，通常用水流空化数与初生空化数对比，判别该部位(或体型)是否发生空化。关于体型的初生空化数，一般应通过减压试验确定，而在初步设计优选体型过程中，通常就需知其初生空化数。在前人研究成果基础上，通过综合分析，提出若干体型初生空化数，可供当工程不具备进 行减压试验情况下，设计和科研人员参考。     

台阶溢流坝过流掺气减蚀问题的研究

根据大朝山水电站表孔减压模型试验资料,结合原型观测有关资料,对台阶溢流坝掺气减蚀问题进行了分析研究。结果表明,利用表孔宽尾墩+台阶面的过流形式,可以解决台阶面大单宽过流掺气减蚀问题,台阶面水流近底掺气浓度最小在5%以上。高坝试验结果还表明,坝高增加20 m,台阶面水流掺气浓度沿程分布规律不变,即该掺气减蚀方法应用范围可推广至坝高131.0 m的台阶溢流坝。     

高负荷螺旋桨水动力性能试验研究

以某大型集装箱船高负荷螺旋桨为研究对象,分别采用大侧斜、反弯扭叶片和毂帽鳍等技术进行螺旋桨优化设计,以改善螺旋桨的空泡和水动力性能.设计了5型螺旋桨,分别在空泡水筒进行了模拟伴流场中的空泡和激振力试验,并在拖曳水池进行了敞水试验.试验结果表明,采用大侧斜可有效减小螺旋桨诱导船艉激振力;反弯扭叶片螺旋桨空泡性能较好,有较低的螺旋桨诱导船艉激振力水平;桨毂帽鳍可改善毂涡空泡,模型试验状态下可提高推进效率2%左右.     

The effect of water quality on tip vortex cavitation inception

The inception of tip vortex cavitation is very sensitive to water quality. In order to quantify the effect of water quality on the inception of tip vortex cavitation, we develop a motion model to describe the migration and growth of nuclei in water. An analytical solution of migration of nuclei in a vortex flow is obtained so that the capture times of various nuclei can be given out directly. A criterion is built to determine the critical nucleus in a certain nuclei spectra distribution. Tensile strength of the critical nucleus is used to quantify the effect of water quality and correct the tip vortex cavitation inception number. Finally this change of cavitation inception number is compared with experimental results to validate our model.     

JS—18(CPE)防水卷材抗空蚀抗磨蚀性能的试验研究

JS— 18(CPE)防水卷材因具有抗拉强度高、延伸率大、抗渗性能强等优点 ,已用于水工防渗止水工程等 ,其抗空蚀抗磨蚀性能经过试验表明 ,当流速小于 10m/s时 ,完全满足要求。     

EXPERIMENTAL STUDY ON CAVITATION AND WATER-WING FOR MIDDLE-PIERS OF DISCHARGE TUNNELS

1. INTRODUCTION Discharge tunnel ,specially , deep-water one , is a sort of usual flood discharge structure with pressure flows in the inlet section,followed pres- sure flows or free flows ,and is used in flood dis- charge or emptying a reservoir , and/or washing sands .For deep-water tunnels ,the designs were u- sually adopted of the manners of the shaft ,of the inclined sectionin the inlet or in the outlet ,called visually as “Dragon up one’s head”or “Dragon down one’s tail”in Chi…     

EXPERIMENTAL STUDY OF EFFECTS OF AIR CONTENT ON CAVITATION AND PRESSURE FLUCTUATIONS

This article studies the effects of air content on propeller cavitation and pressure fluctuations. The cavitation is observed while the pressure fluctuations on the hull are measured. When adjusting the air content, the sheet cavitation range does not change distinctly, but the pressure fluctuations see obvious differences. The amplitudes of the pressure fluctuations increase with the decrease of the air content. The results indicate that the air content has little effect on the sheet cavitation range but has an important effect on the bubble cavitation and the tip vortex cavitation. When the air content decreases, the water tensile force increases, which results in the instability of the bubble cavitation and the tip vortex cavitation and the increase of the pressure fluctuations. To minimize the scale effects, the experiments should be run at a high Reynolds number with a high nuclei content. The high Reynolds number is often realized by increasing the flow velocity and the propeller rotation speed, and the high nuclei content is often made by increasing the dissolved air content.     

Characteristics of structural loess strength and preliminary framework for joint strength formula

The strength of structural loess consists of the shear strength and tensile strength. In this study, the stress path, the failure envelope of principal stress （ Kf line）, and the strength failure envelope of structurally intact loess and remolded loess were analyzed through three kinds of tests： the tensile strength test, the uniaxial compressive strength test, and the conventional triaxial shear strength test. Then, in order to describe the tensile strength and shear strength of structural loess comprehensively and reasonably, a joint strength formula for structural loess was established. This formula comprehensively considers tensile and shear properties. Studies have shown that the tensile strength exhibits a decreasing trend with increasing water content. When the water content is constant, the tensile strength of the structurally intact soil is greater than that ofremolded soil. In the studies, no loss of the originally cured cohesion in the structurally intact soil samples was observed, given that the soil samples did not experience loading disturbance during the uniaxial compressive strength test, meaning there is a high initial structural strength. The results of the conventional triaxial shear strength test show that the water content is correlated with the strength of the structural loess. When the water content is low, the structural properties are strong, and when the water content is high, the structural properties are weak, which means that the water content and the ambient pressure have significant effects on the stress-strain relationship of structural loess. The established joint strength formula of structural loess effectively avoids overestimating the role of soil tensile strength in the traditional theory of Mohr-Coulomb strength.     

ON CAVITATION TESTS IN VACUUM TANK

In this paper some discussions shown what should be the considerable reasons for difficulty in comparison between results of cavitation tests in vacuum tank and some suggestions are given how to improve the cavitation tests under a condition of vacuum pressure.     

水流初生空化噪声机理分析及试验研究

根据水流的初生空化特性,对其发生发展过程在模型和原型进行系统的试验观测。试验和理论分析表明,水流的初生空化和空蚀可以利用常压水洞来模拟。与减压箱试验结果的比较可知常压水洞更可信和合理。水流的初生空化噪声频率不仅与汽化压力和流体的特性有关,而且还与流体的环境压力分布和速度分布有关,与空化类型关系更为密切。试验和计算表明初生空化噪声频率的分布频段为10kHz—12.5kHz。     

三峡工程表孔体型空化试验研究

根据三峡工程溢流坝表孔设计体型,通过减压试验 ,研究了体型的空化特性。成果表明：WES曲线坝面为免空蚀体型; 挑流鼻坎虽有弱空化现象,但空蚀的可能性不大;工作门槽体现为蒸汽型空化特征,其强度 随工作水头增大而加剧。对两道门槽进行局部体型修改后,两者的空化特性均有明显的改善 。要达到完全免除空化之目的,有待进一步优化。     

构皮滩水电站泄洪中孔体型空化特性试验研究

 构皮滩水电站泄洪中孔出口布置型式分平底式和上弯式两类,其最大运行水头 95.36 m ,事故检修门采用倾向上游的斜门槽,门槽区域流速超过30m/s。由减压模型试验成果知,上弯式中孔门槽区蒸汽型空化强度未超过初生阶段,其体型基本上为免空蚀体型;平底式泄洪中孔门槽区域空化严重,蒸汽型空化达发展阶段,通过体型优化方案比较,采取减小有压段出口面积或扩大有压段断面尺寸的措施都可有效解决上述问题。因此泄洪建筑物有压段内布置斜门槽时,应控制门槽断面平均流速不宜过大,否则其会较直门槽更易产生危害性较大的空化。     

水胶比对掺粉煤灰混凝土强度的试验研究

本试验以C30为设计强度,选定粉煤灰掺量为30%,取水胶比为0.36、0.4和0.5,考核指标为7 d、28 d和90 d混凝土试件的抗压和抗拉强度。研究表明,随着龄期的增长,试件抗压强度和劈拉强度基本上逐渐增大;随着水胶比减小,混凝土试件抗压和劈拉强度随之增加。经本次试验数据分析,粉煤灰掺量为30%的最优水胶比为0.4。     

Regional scale analysis for the design of storage tanks for domestic rainwater harvesting systems

A regional scale analysis for the design of storage tanks for domestic rain water harvesting systems is presented. The analysis is based on the daily water balance simulation of the storage tank by the yield-after-spillage algorithm as tank release rule. Water balances are applied to 17 rainfall gauging stations in Sicily (Italy). Compared with literature existing methods, a novel dimensionless parameter is proposed to better describe the intra-annual character of the rainfall patterns. As a result, easy-to-use regional regressive models to evaluate the water saving performance and the overflow discharges from the tank are provided along with a stepwise procedure for practical application. The regional models demonstrate good fits between model predictions and simulated values of both water savings and overflows from the tank.