Analysis of the velocity field in a large rectangular channel with lateral shockwave

In this work the authors describe the main characteristics of the velocity field of hydraulic jumps in a very large channel where lateral shockwaves occur. Experiments were carried out at the Coastal Engineering Laboratory of the Water Engineering and Chemistry Department of the Technical University of Bari (Italy). Extensive flow velocity measurements were investigated in order to have a clearer understanding of both hydraulic jump development and lateral shockwave formation in a very large channel. Eight experiments were performed in a 4m wide rectangular channel; the experiments differed in the inlet Froude number F ₀ and the jump type. Seven tests were carried out with undular jumps and one with a roller jump. The flow velocity and the flow free surface measurements were taken using a two-dimensional Acoustic Doppler Velocimeter (ADV) and an ultrasonic profiler, respectively. The experimental results can be summarized as follow: (i) the formation of well developed lateral shockwaves similar to those of oblique jumps were observed; (ii) the comparison of the experimental and theoretical data shows that the classic shockwave theory is sufficiently confirmed in the analyzed range of Reynolds number, taking into account the experimental errors and the difference between the theoretical and experimental assumptions; (iii) the transversal flow velocity profiles in the recirculating zone show a good agreement with the numerical simulations presented in literature in the case of a separated turbulent boundary layer over a flat plate. This conclusion enables us to confirm the hypothesis that the lateral shockwaves in the channel are the result of a boundary layer which, as observed, forms on the channel sidewalls.     

Turbulent velocity profile in fully-developed open channel flows

The determination of velocity profile in turbulent narrow open channels is a difficult task due to the significant effects of the anisotropic turbulence that involve the Prandtl’s second type of secondary flow occurring in the cross section. With these currents the maximum velocity appears below the free surface that is called dip phenomenon. The well-known logarithmic law describes the velocity distribution in the inner region of the turbulent boundary layer but it is not adapted to define the velocity profile in the outer region of narrow channels. This paper relies on an analysis of the Navier–Stokes equations and yields a new formulation of the vertical velocity profile in the center region of steady, fully developed turbulent flows in open channels. This formulation is able to predict time averaged primary velocity in the outer region of the turbulent boundary layer for both narrow and wide open channels. The proposed law is based on the knowledge of the aspect ratio and involves a parameter C_Ar depending on the position of the maximum velocity (ξ_dip). ξ_dip may be derived, either from measurements or from an empirical equation given in this paper. A wide range of longitudinal velocity profile data for narrow open channels has been used for validating the model. The agreement between the measured and the computed velocities is rather good, despite the simplification used.     

流速比对反向流动中射流流动特性的影响研究

应用超声多普勒测速技术,对不同流速比下反向流动水体中单圆管排放的射流特性进行了水槽模拟实验。介绍了实验装置和量测技术。分析了反向流动水体中射流的流动特征。获得了不同流速比下射流轴线流速的沿程衰减规律,以及流速比对射流轴线流速、射流扩展半宽度、平均最大射流长度和最大射流宽度等特征参数的影响,并与已有的研究成果进行了对比。实验研究成果对潮汐水域城市污水的水下处置等有着重要的实际意义和参考价值。     

新型结构内循环生物流化床的流体力学特性试验及数值模拟

建立小型试验模型,利用粒子成像测速(PIV)技术对模型4个工况的流场进行测量.然后对其中3个工况进行数值模拟,对数值模拟和试验测量结果进行分析比较,证明用数值计算方法来模拟生物流化床流体力学特性的可行性.     

Effects of Vehicle Impact Velocity and Front-End Structure on Dynamic Responses of Child Pedestrians

To investigate the effects of vehicle impact velocity and front-end structure on the dynamic responses of child pedestrians, an extensive parametric study was carried out using two child mathematical models at 6 and 15 years old. The effect of the vehicle impact velocity was studied at 30, 40, and 50 km/h in terms of the head linear velocity, impact angle, and head angular velocity as well as various injury parameters concerning the head, chest, pelvis, and lower extremities. The variation of vehicle front-end shape was determined according to the shape corridors of modern vehicles, while the stiffness characteristics of the bumper, hood edge, and hood were varied within stiffness corridors obtained from dynamic component tests. The simulation results show that the vehicle impact speed is of great importance on the kinematics and resulting injury severity of child pedestrians. A significant reduction in all injury parameters can be achieved as the vehicle impact speed decreases to 30 km/h. The head and lower extremities of children are at higher injury risks than other body regions. Older children are exposed to higher injury risks to the head and lower leg, whereas younger ones sustain more severe impact loads to the pelvis and upper leg. The results from factorial analysis indicate that the hood-edge height has a significant effect on the kinematics and head impact responses of children. A higher hood edge could reduce the severity of head impact for younger children, but aggravate the risks of head injury for older ones. A significant interaction exists between the bumper height and the hood-edge height on the head impact responses of younger child. Nevertheless, improving the energy absorption performance of the hood seems effective for mitigating the severity of head injuries for children.     

Rockburst hazard determination by using computed tomography technology in deep workface

The rockburst in mines results from the dynamic load coupled with static one in coal seams around workface zones, so it is essential to learn the stress distribution of the coal and surrounding rock for determination of rockburst risk areas. The relationship between the elastic wave velocity and stress applied on coal sample was investigated systematically by laboratory testing, theoretically analysis, as well as on-site observation, and a positive correlation between them under uniaxial compression was put forward. Furthermore, it is drawn that the anomaly of elastic wave velocity reflects the stress changes: the positive anomaly ascertains the stress concentration while the negative anomaly estimates the mining destress and weaken degree, and corresponding assessment criterions and parameters were established respectively. The hazard areas and degree of an island longwall face 16302C were forecasted before coal winning based on the elastic wave anomaly distribution rules using active tremor velocity inversion, monitoring results of mining shocks during exploitation indicate that the consistency between locations of big tremors and where forecasted by computed tomography (CT) exceed 80%. The successful application of this technology achieved remarkable economic and social benefits for disaster control in rockburst mines.     

渠式生化反应器处理城市污水的研究

采用渠式生化反应器、交替好氧缺氧工艺处理城市污水 ,当水力停留时间为 1 0 h,空气阀开闭周期为 3 0 / 3 0 min时 ,COD的去除率达 86.8% ,T-N的去除率达 63 .6%。在相同的反应条件下 ,流速对处理效果的影响不大。试验结果表明利用污水渠处理城市污水在技术上是可行的。     

USE OF DYE TRACERS TO COLLECT HYDROLOGIC DATA IN OREGON1

Dye tracers have been used in Oregon in the Collection of hydrologic data on 2,350 miles of stream channels in the Long Tom, Umpqua, Willmette, and John Day River basins, and in the Carmen-Smith power tunnel. These investigations demonstrated the usefulness, of dye tracers for determining: (1) estimates of traveltimes and travel rates of water, (2) discharge where standard methods of measuring are not applicable, and (3) dispersion characteristics of streams. Illustrations are used to present the results of time-of-travel studies in simple, concise, and readily interpreted form.     

初沉池内速度场数值模拟

采用改进的k-ε两方程模型和SIMPLEC算法,对平流式初沉池内速度场进行了数值模拟,研究发现:池内存在着一个小回流区和一个大回流区,小回流区位于进水区底部,大回流区位于入流挡板后的沉淀池上部,约占整个容积的30%~40%,是初沉池性能下降的重要原因。     

Study on the initial velocity distribution of exhaled air from coughing and speaking

Increasing concerns about the spread of airborne pathogens such as severe acute respiratory syndrome (SARS) and novel swine-origin influenza A (H1N1) have attracted public attention to bioaerosols and protection against them. The airborne pathogens are likely to be expelled from coughing or speaking, so the physical data of the exhaled particles plays a key role in analyzing the pathway of airborne viruses. The objective of this study was to analyze the initial velocity and the angle of the exhaled airflow from coughing and speaking of 17 males and 9 females using Particle Image Velocimetry (PIV) and acrylic indoor chamber. The results showed that the average initial coughing velocity was 15.3 m/s for the males and 10.6 m/s for the females, while the average initial speaking velocity was 4.07 m/s and 2.31 m/s respectively. The angle of the exhaled air from coughing was around 38° for the males and 32° for the females, while that of the exhaled air from speaking was around 49° and 78° respectively. Also, the linear relation between the tested subject’s height and their coughing and speaking velocity was shown in this study.