Turbulent Jet Energy Dissipation at Vertical Drops

The energy loss of the vertical drop with subcritical flow in the upstream channel has been studied experimentally with a physical model of 0.20?m drop height. Experimental data were collected in a range where few data exist. Based on a similarity between a turbulent surface jet and the flow over the drop, a model is developed using the theories of the shear layer and fully developed surface jet to estimate the energy loss. The results were compared with previous and current experimental data and were found to agree well with the proposed model.     

A three-dimensional (3D) numerical study of fatigue crack growth using remeshing techniques

Numerical analyses based on the finite element (FE) method and remeshing techniques have been employed in order to develop a damage tolerance approach to be used for the design of aeroengines shaft components. Preliminary experimental tests have permitted the calculation of fatigue crack growth parameters for the high strength alloy steel adopted in this research. Then, a robust numerical study have been carried out to understand the influence of various factors (such as: crack shape, crack closure) on non-planar crack evolution in solid and hollow shafts under mixed-mode loading. The FE analyses have displayed a satisfactory agreement compared to experimental data on compact specimens (CT) and solid shafts.     

Computational and Experimental Study of Surcharged Flow at a 90° Combining Sewer Junction

Combining sewer junctions with a lateral inflow at 90° angle are commonly used in our sewer systems. A computational fluid dynamics (CFD) model based on Ansys CFX 10.0 was established to simulate fully surcharged flow at a 90° combining sewer junction. The model was carefully assessed by comparing its results with the measurements of detailed physical experiments. Good agreement was obtained between results of the computational model and of the laboratory experiments. The computational model was proved to be capable of simulating surcharged combining junction flow in the aspects of water depth, energy losses, velocity distributions, and turbulence. The verified CFD model was also used to investigate air entrainment and effects of the size of the junction chamber on the flow. Such CFD models can be used to optimize the design of sewer junctions and will also be useful in studying sediment transport at sewer junctions.     

Vortex structure of circular jets in crossflow

This paper presents the results of an experimental study of the properties of the bound vortex system housed in a circular jet issuing perpendicularly into a crossflow for three values of the ratio of the jet to crossflow velocity equal to 2.73, 4.52 and 7.05.     

Discharge Characteristics of Weirs of Finite Crest Length

This technical note presents a critical analysis flow over weirs of finite crest length, with square-edged or rounded entrance, for free-flow conditions. Using the flow equation for the broad-crested weir with parallel flow in the critical state as the basis, we have defined the discharge coefficient Cd, with the head on the weir as the length scale. Based on an extensive analysis of the experimental observations in the literature, we have confirmed the classification of finite crest length weirs into four classes of long-crested, broad-crested, short-crested, and sharp-crested weirs. For the square-edged entrance, we have developed robust correlations for Cd when the Weber number is greater than 1. For weirs with a rounded entrance, for which the data set is not that extensive compared to the square-edged case, we have developed good correlations for Cd.     

TRUST-TECH-based expectation maximization for learning finite mixture models

In spite of the initialization problem, the Expectation-Maximization (EM) algorithm is widely used for estimating the parameters of finite mixture models. Most popular model-based clustering techniques might yield poor clusters if the parameters are not initialized properly. To reduce the sensitivity of initial points, a novel algorithm for learning mixture models from multivariate data is introduced in this paper. The proposed algorithm takes advantage of TRUST-TECH (TRansformation Under STability-reTaining Equilibra CHaracterization) to compute neighborhood local maxima on likelihood surface using stability regions. Basically, our method coalesces the advantages of the traditional EM with that of the dynamic and geometric characteristics of the stability regions of the corresponding nonlinear dynamical system of the log-likelihood function. Two phases namely, the EM phase and the stability region phase, are repeated alternatively in the parameter space to achieve improvements in the maximum likelihood. The EM phase obtains the local maximum of the likelihood function and the stability region phase helps to escape out of the local maximum by moving towards the neighboring stability regions. The algorithm has been tested on both synthetic and real datasets and the improvements in the performance compared to other approaches are demonstrated. The robustness with respect to initialization is also illustrated experimentally.     

Four-Tube Probe for Velocity Measurement in 3D Flows

This paper presents the concept and development of a four-tube probe for the measurement of the three velocity components in 3D flows. The necessary calibration curves have been developed and are presented along with a procedure to use this probe. This probe is more convenient to use than the traditional five-tube probe and is believed to be useful for the measurement of the three components of velocity in 3D flows in the laboratory. It has already been used successfully in the measurement of the velocity field in a vertical slot fishway.     

Observations on Performance of Three-Tube Pitot Probe

This technical note discusses two questions related to three-tube (pitch or yaw) pitot probes, which are used for measuring the velocity vectors in 2D flows. When a pitch probe is used in flows in which the third component of the velocity is small but not zero, it is important to know the error this causes in the measurement of the velocity vector. Calibration experiments on a pitch probe showed that as long as the yaw angle is less than 14°, the relative error in the velocity measured by the pitch probe is less than 3% and the error in the pitch angle is less than 1°. Typically a pitch or yaw probe can only be used when the angle of attack is less than approximately 50°. The second part of this work addresses the practical issues associated with pretilting the probe to measure flows at angles greater than 50°.