平面闸门启闭过程中的动水垂直力数值模拟研究

动水垂直力是影响闸门启闭力的重要因素,为准确计算闸门启闭力采用RNGk-ε方程紊流模型与物体移动模型(GMO)相结合的方法,对平面闸门启闭过程中的动水垂直力进行了数值模拟研究,以积石峡水电站泄洪洞闸门为例,分析了闸门不同底缘型式和不同启闭速率在闸门启闭过程中对动水垂直力的影响及动水垂直力在闸门启闭过程中的变化规律。

Hydrodynamic Characteristics of Three Rows of Vertical Slotted Wall Breakwaters

In this study, we examine the hydrodynamic characteristics of three rows of vertical slotted wall breakwaters in which the front and middle walls are permeable and partially immersed in a water channel of constant depth, whereas the third wall is impermeable. The wave–structure interaction and flow behavior of this type of breakwater arrangement are complicated and must be analyzed before breakwaters can be appropriately designed. To study the hydrodynamic breakwater performance, we developed a mathematical model based on the eigenfunction expansion method and a least squares technique for predicting wave interaction with three rows of vertical slotted wall breakwaters. We theoretically examined the wave transmission, reflection, energy loss, wave runup, and wave force under normal regular waves. Comparisons with experimental measurements show that the mathematical model results adequately reproduce most of the important features. The results of this investigation provide a better understanding of the hydrodynamic performance of triple-row vertical slotted wall breakwaters.

The Effect of Netting Solidity Ratio and Inclined Angle on the Hydrodynamic Characteristics of Knotless Polyethylene Netting

Knotless polyethylene(PE) netting has been widely used in aquaculture cages and fishing gears, especially in Japan. In this study, the hydrodynamic coefficient of six knotless PE netting panels with different solidity ratios were assessed in a flume tank under various attack angles of netting from 0?(parallel to flow) to 90?(perpendicular to flow) and current speeds from 40 cm s^(-1) to 130 cm s^(-1). It was found that the drag coefficient was related to Reynolds number, solidity ratio and attack angle of netting. The solidity ratio was positively related with drag coefficient for netting panel perpendicular to flow, whereas when setting the netting panel parallel to the flow the opposite result was obtained. For netting panels placed at an angle to the flow, the lift coefficient reached the maximum at an attack angle of 50? and then decreased as the attack angle further increased. The solidity ratio had a dual influence on drag coefficient of inclined netting panels. Compared to result in the literature, the normal drag coefficient of knotless PE netting measured in this study is larger than that of nylon netting or Dyneema netting.

Experimental Investigation on Critical Heat Flux for Water Flowing in a Vertical Uniformly Heated Rifled Tube under Near-critical Pressures

This study experimentally investigated the critical heat flux(CHF) of departure from nucleate boiling(DNB) of water flowing under near-critical pressures in a 2 m-long vertical upward rifled tube with the size of Φ35 × 5.67 mm. Operating conditions included pressures of 18–21 MPa, mass fluxes of 475–1000 kg·m^(-2)·s^(-1), inlet subcooling temperatures of 3–5°C, and wall heat fluxes of 40–960 kW·m^(-2). Tube wall temperature distribution and heat transfer performance in different test conditions were obtained. The effects of the operating parameters on CHF were analyzed. Four heat transfer coefficient correlations were evaluated against our experimental data for further investigation of the two-phase heat transfer characteristics. A heat transfer correlation based on Martinelli number utilized in two-phase region and two empirical correlations used to predict the CHF in rifled tube at near-critical pressures were proposed. Meanwhile, experimental CHF data in rifled tube were compared with six widely used correlations and a CHF look-up table. The CHF enhancement effect in rifled tube is obvious as compared with the CHF data in smooth tube. Results show that DNB occurs at low vapor quality and subcooled region in the rifled tube at near-critical pressures. The increase in pressure leads to the early occurrence of DNB and the decrease in CHF, whereas the increase in mass flux delays the occurrence of DNB and results in the increase in CHF. DNB presents a tendency to move toward the inlet of the rifled tube. At individual operating conditions, DNB and dryout coexist at different sections of the rifled tube.

Modeling study of residence time and water age in Dahuofang Reservoir in China

Understanding the dynamics of water renewal in a reservoir is essential when the transport and fate of dissolved substances are evaluated.A three-dimensional hydrodynamic model was implemented to compute average residence time and water age in Dahuofang Reservoir in China.The model was verified for a one-year time period in 2006.A simulation reproduced intra-annual variation of mixing represented by the fall/winter mixing and the spring/summer stratification.The simulated variation of vertical thermal structures also matched observation.The spatially varying average residence times and age distribution were investigated through a series of numerical experiments using a passively dissolved and conservative tracer as a surrogate.Residence time estimations yield a broad range of values depending on the position.The average residence time for a tracer placed at the head of the reservoir under high-,mean-,and low flow conditions was found to be about 125,236 and 521 days,respectively.The age simulation reveals that the age distribution is a function of the freshwater discharge.In the vertical direction,the age of the surface layers is larger than that of the bottom layers and the age difference between the surface and bottom layers decreases further downstream.The density-induced circulation plays an important role in the circulation in the reservoir,and can generate vertical age distribution in the reservoir.These findings provide useful information for understanding the transport process in Dahuofang Reservoir that can be used to assist the water quality management of the reservoir.