Structural Design and Optimization of Herringbone Grooved Journal Bearings Considering Turbulent

In order to improve the performance of the traditional constant-width herringbone grooved journal bearing in a computed tomography tube under a high-temperature environment, the present study designed a convergent herringbone grooved journal bearing (HGJB) structure lubricated by liquid metal. The bearing oil film thickness and the Reynolds equation considering the influence of turbulence are established and solved by using the finite difference method in the oblique coordinate system. The performance of the two bearings was compared, and the static and dynamic performance change trends of the two bearing structures under different eccentricities were systematically studied. The results show that the convergent herringbone grooved journal bearings are superior to the constant-width herringbone grooved journal bearings in terms of bearing capacity and stiffness coefficient. At the same time, the influence of structural parameters, such as the number of grooves, helix angle, groove to ridge ratio, groove depth on the performance of the constant-width herringbone grooved journal bearings, and the convergent herringbone grooved journal bearings was studied. Finally, we conclude that the performance of the convergent herringbone grooved journal bearings is optimal when the number of grooves is 15–20, the helix angle is 30–45°, the ratio of the groove to ridge is 1, and the groove depth is 0.02 mm −0.024 mm. This research has provided the thinking and reference basis for the design of liquid metal bearings for high-performance CT equipment.

Basic Experimental Evaluation of Fresh and Hardened Properties of Mortar Using Additive Manufacturing

Recently, the three-dimensional concrete printing (3DCP) method has been garnering considerable interest owing to its ability to significantly reduce the construction time. In this study, 3D printing or additive manufacturing was applied to mortar using a small gantry type equipment and the performance of the method was evaluated. The mixture proportioning for good mortar printing and deposition was derived. The parameters of printability, buildability, compressive strength, flexural tensile strength, and anti-washout were considered for the performance evaluation. The results showed good printability with a constant width and no surface defects. In the buildability test, the rate of yield stress development increased, and the rate of change in the layer height decreased as the interlayer time interval increased during underwater printing. The flexural tensile strength of the specimen cast into the mold was lower than that of the specimen extracted from the additive parts owing to the longitudinal confinement during printing. The compressive strength in the lateral direction was slightly higher than that in the perpendicular direction, whereas the compressive strength of the specimen extracted from the part printed underwater was higher than that of the specimen cast into the mold.

A Concise Method to Predict the Mean Dynamic Pressure on a Plunge Pool Slab

Hydrodynamic pressure exerted on a plunge pool slab by jet impingement is of high interest in high dam projects. The present study experimentally investigated the characteristics of pressure induced by a jet through a constant width flip bucket (CFB) and a slit flip bucket (SFB). A pressurized plane pipe was employed in the flume experiments to control the inlet velocities in the flip buckets. A concise method is proposed to predict the mean dynamic pressure field. Its implementation is summarized as follows: First, the position of the pressure field is determined by the trajectories of free jets, and to calculate its trajectories, an equation based on parabolic trajectory theory is used; second, the maximum mean dynamic pressure is obtained through dimensional analysis, and then the pressure field is established by applying the law of Gaussian distribution. Those steps are integrated into a concise computing procedure by using some easy-to-obtain parameters. Some key parameters, such as takeoff velocity coefficient, takeoff angle coefficient, and the parameter k2, are also investigated in this paper. The formulas of these coefficients are obtained by fitting the experimental data. Using the proposed method, the easy-to-obtain geometric parameters and initial hydraulic conditions can be used to calculate the maximum mean dynamic pressure on the slab. A comparison between experimental data and calculated results confirmed the practicability of this model. These research results provide a reference for hydraulic applications.

Comparative Evaluation of Crack Width for Reinforced Concrete Bridge Deck

Cracking in reinforced concrete bridge decks is a massively concern in the India. Many concrete bridge decks, inobservant to the age of construction, have shown different levels and patterns of cracking. Not only does cracking of bridge decks weaken the bridge infrastructure, but also allows the inflow of corrosive agents into the reinforcement. In this study, the crack width evaluation of RC bridge deck of span of 5 m. and 9 m. is based on equations given by IRS Concrete Bridge Code 1997 for different cases like- the effect of depth variation, reinforcement diameter, clear cover, variation in live load moment, spacing of tension reinforcement and different no. of tension reinforcement bar to constant width for the same crosssection. This study concluded that crack width increases with increase in clear cover, variation in live load moment and spacing of tension reinforcement while it decreases with increase in reinforcement diameter, depth of the bridge deck and number of reinforced bars and percentage change evaluation of different parameter of 5m and 9m span bridge deck. Keyword: Crack Width, Cracking, Bridge Deck Slab, Crack Spacing.

Diameter, width and thickness in the hyperbolic plane

In hyperbolic geometry there are several concepts to measure the breadth or width of a convex set. In the first part of the paper we collect them and compare their properties. Than we introduce a new concept to measure the width and thickness of a convex body. Correspondingly, we define three classes of bodies, bodies of constant with, bodies of constant diameter and bodies having the constant shadow property, respectively. We prove that the property of constant diameter follows to the fulfilment of constant shadow property, and both of them are stronger as the property of constant width. In the last part of this paper, we introduce the thickness of a constant body and prove a variant of Blaschke’s theorem on the larger circle inscribed to a plane-convex body of given thickness and diameter.

Vehicle-Bridge Interaction System with Non-Uniform Beams

Since the bridge is often treated as the uniform beam for simplicity in most numerical studies of vehicle-bridge interaction, this study proposes a non-uniform vehicle-bridge interaction system by incorporating a three-mass vehicle model in a non-uniform bridge for wider applications, in which non-uniform beam elements of constant width and varying depth are considered. For clarity, the inclined ratios of the entire bridge and one beam element are separately defined in order to describe the non-conformity in computation while both mass and stiffness matrices are re-formulated to comply with the finite element sign convention. As the natural frequencies of a non-uniform bridge cannot be accessed directly, the vehicle scanning method is first adopted to obtain the bridge frequencies. Then, the parametric study is conducted by considering vehicle damping, bridge damping, and pavement irregularity. In addition to the vehicle frequency, the numerical results show that the proposed vehicle-bridge interaction system is able to scan the first four bridge frequencies with desired accuracy subject to pavement irregularity. Concerning the pitching effect of the vehicle, it is shown that the locations for installing sensors are actually affected by both the geometry and the cross-sectional geometry of the bridge in the concern of achieving high resolution of frequency identification.

Numerical Simulation Studies on Stall Suppression of a NACA0015 Airfoil

This study aims to achieve an improved airfoil performance at low Reynolds number, and to determine the optimum position and size of rectangular cross-section burst control plate (BCP) to suppress stall in airfoil. The type of airfoil used in the present study is NACA0015 (National Advisory Committee for Aeronautics) airfoil with 200 mm of chord (c) length. Here, rectangular cross-section burst control plates with different sizes and at different locations are investigated numerically at the low Reynolds number of 1.6×105. Total of three positions (0.05c, 0.1c and 0.2c from the leading edge of airfoil), and four sizes (with heights 0.3 mm, 0.7mm, 1mm and 1.5 mm, and constant width 4 mm) of rectangular BCPs are simulated in ANSYS Fluent software using Transition SST model. The results indicate that the rectangular cross-section burst control plate is an effective device in the suppression of airfoil stall. For 0.7 mm and 1 mm height BCPs, the stall angle is postponed by 2° for all positions, while for 0.3 mm and 1.5 mm height BCPs, the reduction in sudden fall of lift can be observed but at the cost of reduction in maximum lift coefficient. Among various configurations, the 1mm height BCP located at 0.2c position is found to be most effective in the suppression of stall.