The hydrostatic/hydrodynamic behaviour of an axial piston pump slipper with multiple lands

This study considers an analytical approach towards the understanding of the hydrostatic leakage and lift characteristic of a flat slipper of the type used for piston/slipper units within an axial piston pump or motor. In particular it considers a slipper design incorporating a groove on the slipper face and also includes the effect of motion around its associated swash plate. A new set of equations are developed and in generic form for a slipper with any number of grooves. Experimental comparisons are then undertaken and extended to include the effect of relative motion around the swash plate and slipper tilt. A CFD study of the slipper is also presented. Comparisons between analytical, experimental and CFD results show a very good agreement, validating the equations presented and extending the conclusions when tilt and tangential speed are considered.     

考虑上游泵送效应的滑靴副动压润滑特性

为了改善轴向柱塞泵滑靴副的润滑性能,利用仿生学原理,在斜盘上构建倾斜椭圆形微坑织构. 通过微坑产生的动压效应和上游泵送效应,以期能够优化滑靴副的摩擦性能并减少泄漏量. 基于CFD方法开展了具有椭圆形微坑织构滑靴副的建模与润滑性能研究,揭示了不同润滑介质黏度和转速下柱塞泵滑靴副的承载能力、泄漏量和摩擦系数随微坑倾斜角度的变化规律. 研究结果表明:通过在斜盘面上建立无倾斜椭圆形微坑,能明显提高滑靴副的承载能力,并降低摩擦系数,但会导致泄漏量增大;而在此基础上,通过将椭圆形微坑相对于其滑动方向旋转一定角度,滑靴副的承载能力和摩擦系数不会明显变化,但可以显著减小润滑介质泄漏量.      

Electroerosive wear of the barrel of a coaxial hybrid magnetoplasma accelerator in the acceleration of solids

The main regularities of electroerosive wear of the barrel of a hybrid coaxial magnetoplasma accelerator in the acceleration of solids are studied. In order to significantly reduce the erosive wear of the barrel without changing the dynamics of solid projectiles, a system of discharge shunting in the acceleration channel was used. It is shown that the plasma structure of a high-current arc discharge is fountain-shaped and its bridge consists of numerous discrete conduction channels.     

一种新型结构火炮身管膛线的计算分析

针对传统的火炮身管内弹道结构形式,提出了一种新型结构形式的火炮身管膛线——渐变截面结构膛线。以大口径火炮身管膛线作为研究对象,计算分析传统等截面结构膛线和渐变截面结构膛线的弹丸弹带挤进阻力、导转侧向力、膛线截面面积和膛线摩擦力的变化情况。计算结果表明,新型渐变截面结构膛线有利于增强弹丸弹带的挤入能力,减少膛线根部应力集中,减少弹丸弹带对膛线的冲击和磨损,有效提升弹丸弹带的闭气性能,同时渐变结构膛线可有效减小弹丸在膛内运动时受到的扰动,使得弹丸在膛内运行平稳,减少炮口章动,在保证射击精度的同时,有利于提高身管的使用寿命。     

Stability and stabilization of circular plate parametric vibrations

The stability of parametric vibrations of circular plate subjected to in-plane forces is analyzed by the Liapunov method. Assuming that the compressing forces are physically realizable ergodic processes the plate dynamics is described by stochastic classical partial differential equations. The energy-like functional is proposed; its positiveness is equivalent to the condition in which static buckling does not occur. Taking into account that a plate is compressed radially by time-dependent and uniformly distributed along its edge forces, a dynamic stability of an undeflected state of isotropic elastic circular plate is analyzed. The rate velocity feedback is applied to stabilize the plate parametric vibration. The critical damping coefficient has been expressed by the variance and the mean value of compressing force. The admissible variances of loading strongly depend on the feedback gain factor.     

条状亲油表面的润滑特性试验研究

分别利用疏油薄膜和梳齿形凹槽队列织构,在钢表面的润滑轨道上围成了两类条状亲油区. 试验表明,两类条状亲油区对置于其上的润滑油滴有明显约束作用,限制润滑油向润滑轨道之外的区域铺展. 在有限供油条件下,对两类条状亲油区表面与钢球组成的摩擦副进行了测量,结果表明两类表面在混合润滑区均具有较低的摩擦力和磨损. 将试验结果归因于条状亲油区边界处润滑油所受的表面力不同,从而润滑轨道自集油能力得到增强. 最后,用光弹流试验证实了条状亲油区对摩擦副供油的改善.      

Simultaneous digital image correlation/particle image velocimetry to unfold fluid–structure interaction during air-backed impact

Predicting the response of air-backed panels to impulsive hydrodynamic loading is essential to the design of marine structures operating in extreme conditions. Despite significant effort in this area of research, the lack of full-field measurement techniques of structural dynamics and flow physics hinders our understanding of the fluid–structure interaction. To fill this gap in knowledge, we designed a laboratory-scale experiment to elucidate fluid–structure interaction associated with impulsive hydrodynamic loading on a flexible plate. A combined experimental approach based on digital image correlation (DIC) and particle image velocimetry (PIV) was developed to afford spatially- and temporally-resolved measurements of the plate deflection and fluid velocity. From the velocity field measured through PIV, the hydrodynamic loading on the structure was estimated via a pressure-reconstruction algorithm. Experimental results point at a strong bidirectional coupling between structural dynamics and flow physics, which influence temporal and spatial patterns in counter-intuitive ways. While the plate deflection follows the fundamental in-vacuum mode shape of a clamped plate, the pressure exhibits a complex evolution. Not only does the location of the peak loading on the plate alternates between the clamp and the center as time progresses, but also the time evolution of the peak loading anticipated the peak displacement of the plate. This study contributes a new methodological approach to study fluid–structure interaction in three dimensions, offering insight in the physics of air-backed impact that could inform engineering design and scientific inquiry.     

基于流固耦合的燃气冲刷烧蚀内膛特性分析

火炮发射时,火药燃气与身管间发生剧烈的传热传质作用是导致身管烧蚀的重要因素。为了研究某155 mm火炮中高温高压高速的燃气流对身管的烧蚀特性,采用CFD流固耦合方法,建立了发射过程中的身管非稳态流动传热模型,并根据炮钢在不同温度下的烧蚀特点,将烧蚀过程分为热化学烧蚀和熔化烧蚀,建立了分段烧蚀模型。计算结果表明,身管内壁温度随时间的增加先迅速增大,随后逐渐降低。整体上,内壁温度随身管轴向距离的增大而逐渐降低。身管膛线起始区域的壁面温度最高,其烧蚀是熔化和热化学烧蚀共同导致的,而线膛部的大部分区域仅发生了热化学烧蚀。总烧蚀量随着身管轴向距离的增大而逐渐降低,膛线起始部的烧蚀最为严重,单发总烧蚀量（常温）为5.06μm。同时分析了不同工况对身管烧蚀特性的影响,发现最大烧蚀量与初始壁面温度呈现很强的正相关性,温度的升高会加剧身管的烧蚀。     

Mathematical modeling of brush seals

A computational fluid dynamics (CFD)-based model of brush seals has been developed and tested against other workers' experimental data. In the model, the brush is treated as an axisymmetric, anisotropic porous region with nonlinear resistance coefficients. The resistance coefficients are chosen through calibration against measurements. The CFD model gives predictions of flow rate, pressure distribution, velocity field, and bending forces on the bristles. The bristle forces are used in a separate calculation to estimate bristle bending and reaction forces on the shaft and backing plate. Bending in both the axial direction and the orthogonal plane are considered.     

Numerical and experimental study of the traveling magnetic field effect on the horizontal solidification in a rectangular cavity part 2: Acting forces ratio and solidification parameters

In recent decades, many phase change processes in metals have been optimized using traveling magnetic fields due to a better understanding of their electromagnetic impact in such applications. In this paper, numerical and experimental study of the effect of traveling magnetic field on the solidification process was evaluated. A three-dimensional numerical model based on the multi-domain method was used to analyze the process of gallium horizontal solidification under the electromagnetic impact in a laboratory-size rectangular cavity. A linear inductor creating traveling magnetic field was designed and built for appropriate measurements and validation the calculations. The analysis was focused on the influence of the ratio between the applied electromagnetic forces and natural convective forces on the solidification front location and shape and on the velocity field. Since the overall electromagnetic force impact on the melt reduced during the solidification, when the melt area was converting into a solid, a new approach to control the solidification parameters was analyzed. In this approach, the value of electromagnetic force acting on the remaining melt during the process was maintained. The main result is the development and improvement of an effective tool for the analysis of direct solidification parameters.The experimental setup included an ultrasonic Doppler velocimeter (UDV) for noninvasive measurements of the velocities in the liquid part of the metal and the liquid-solid interface position, its profile and displacement. All important characteristics of the process were measured, and the results of computations agreed well enough with experimentally obtained data.     

Experimental and numerical analysis of nonlinear dynamics of rotor–bearing–seal system

Nonlinear dynamics and stability of the rotor–bearing–seal system are investigated both theoretically and experimentally. An experimental rotor–bearing–seal device is designed and corresponding tests are carried out. The experimental rotor system is simplified as the Jeffcott rotor. The nonlinear oil–film forces are obtained under the short bearing theory and Muszynska nonlinear seal force model is used. Numerical method is utilized to solve the nonlinear governing equations. Bifurcation diagrams, waterfall plots, Poincaré maps, spectrum plots and rotor orbits are drawn to analyze various nonlinear phenomena and system unstable processes. Theoretical results from numerical analysis are in good agreement with results from experiments. Conclusions are drawn and prove that this study will contribute to the further understanding of nonlinear dynamics and stability of the rotor system with the fluid-induced forces from oil–film bearings and the seals.     

冲击载荷下自增强身管残余应力变化规律

基于有限元分析方法,建立速射火炮身管截面的有限元模型,采用直接耦合的方法,模拟了承受热应力和火药燃气压力的自紧身管在先50连发、冷却后再连发10发过程中身管的残余应力,得到并分析了残余应力的变化规律,指出内壁薄层的塑性变形和残余应力的反复变化,不利于内壁的稳定,还提出了减小残余应力变化程度的策略.     

An investigation into the effect of electric field on the performance of Dielectric Barrier Discharge plasma actuators

The influence of the inter-electrode electric field of a single Dielectric Barrier Discharge (DBD) actuator on the performance of the device was investigated. The electric field of the actuator was manipulated through the variation of the angle between the electrodes of the actuators. Response forces generated by the plasma actuators were used as performance indicators for these devices. These forces were measured directly utilizing a highly sensitive balance scale. It was verified that depending on the orientation of the variation of the angle between the electrodes, the performance of the actuator may be decreased or increased when compared to a DBD on a flat dielectric plate more commonly investigated in literature. The manner in which the ionic wind flows over the actuators was also explored in the effort to elucidate the influence of the variation of the angle between the electrodes on the response force generated by the device. Results demonstrated that the response forces generated by the actuators may be improved by up to 50% compared to the actuator configuration on a flat dielectric plate commonly investigated. These results indicate the potential available to advance plasma technology by physically manipulating these devices to increase the performances of the actuators.     

Two-phase flows in gun barrel: Theoretical and experimental studies

In the paper theoretical and numerical model of two-phase flow of solid granular propellant and its products of combustion in the gun barrel during interior ballistic cycle is given. Two cases are considered: base ignition of propellant charge and ignition by igniter. The theoretical model includes the balance equations of mass, momentum and energy for both phases, as well as necessary constitutive laws. The igniter efflux in the propellant chamber is obtained by incorporation in the model the two-phase flow model of igniter function. The convergent, unconditionally stable, numerical procedure is formed to solve the system of equations of the theoretical model. An original procedure of numerical grid adaptation to the flow field increase, caused by the projectile motion down the gun bore, is developed. The TWOPIB code for the computation of whole interior ballistic cycle of ammunition is developed. Four kinds of experimental investigations were carried out:igniter function in open air, flamespreading through propellant charge in the fibreglass tube during base ignition or during ignition by igniter, and firing of 100 mm APFSDS projectile. Verification of the theoretical–numerical approach by the comparison with experimental data is carried out. The great number of computational results is presented for the parameters that can not be measured, but which are necessary for more complete understanding of examined processes. The presented theoretical–numerical access enables, not only the complete optimisation of propellant charges, but more successful solutions of many interior ballistic problems.     

小内力平板弹性波散射问题的摄动方法

基于平板小挠度弯曲波动方程,采用摄动方法具有纵向内力作用下的平板开孔弹性波的散射问题进行了研究,得么了传播稳态波时此种平板弯曲波动问题的分析解,分析了均匀纵向内力对弹性波散射结果的影响,作为算例,本文给出了平板圆形开孔的动应力集中系数的数值结果,并对计算结果进行了讨论。     

Frequency response of primary resonance of electrostatically actuated CNT cantilevers

This paper deals with electrostatically actuated carbon nanotube (CNT) cantilever over a parallel ground plate. Three forces act on the CNTs cantilever, namely electrostatic, van der Waals, and damping. The van der Waals force is significant for values of 50 nm or less of the gap between the CNT and the ground plate. As both forces electrostatic and van der Waals are nonlinear, and the CNTs electrostatic actuation is given by AC voltage, the CNT undergoes nonlinear parametric dynamics. The methods of multiple scales and reduced order model (ROM) are used to investigate the system under soft AC near half natural frequency of the CNT and weak nonlinearities. The frequency–amplitude response and damping, voltage, and van der Waals effects on the response are reported. It is showed that only five terms ROM predicts and accurately predicts the pull-in instability and the saddle-node bifurcation, respectively.     

Estimation of plated-hole barrel stress from thermally induced out-of-plane displacement gradients measured by electro-optic holographic interferometry

Electro-optic holographic interferometry was used to measure the thermally induced out-of-plane displacement field around both sides of a plated hole on a single layer, FR-4 laminate. The unique features of the electro-optic holographic interferometry technique are described as well as a method for estimating the stress in the barrel from the deflections of the pad. The pad deflections were observed to be roughly axisymmetric and were nearly the same on the front and back of the laminate. The stress was observed to increase at a more rapid rate for temperatures above the glass temperature than below and is of sufficient magnitude to cause plastic deformation in the barrel although none was observed.     

An Inertial Reference Frame Method for the Simulation of the Effect of Longitudinal Force to the Dynamics of Railway Wheelsets

In the current practice of wagon dynamics simulation, traction and braking forces are seldom considered although such forces modify the wheel-rail contact parameters and hence the wheelset dynamics. On the other hand, whilst the traction and braking forces are considered in the simulation of train and locomotive systems, their lateral dynamics is predominantly disregarded. Therefore, there exists a gap in the knowledge of the effect of the application of the longitudinal forces to the lateral dynamics of wagons; this paper aims at bridging this gap. An inertia reference frame method available in the literature has been extended for the purpose. This paper reports the formulation and presents numerical examples of a single wheelset contained within a bogie frame subjected to longitudinal forces of varying severity. The results have been validated where possible.     

High Speed Blanking: An Experimental Method to Measure Induced Cutting Forces

A new blanking process that involves punch speed up to 10 ms ^?1 has obvious advantages in increased productivity. However, the inherent dynamics of such a process makes it difficult to develop a practical high speed punch press. The fracture phenomenon governing the blanking process has to be well understood to correctly design the machine support and the tooling. To observe this phenomenon at various controlled blanking speeds a specific experimental device has been developed. The goal is to measure accurately the shear blanking forces imposed on the specimen during blanking. In this paper a new method allowing the blanking forces to be measured and taking into account the proposed test configuration is explained. This technique has been used to determine the blanking forces experienced when forming C40 steel and quantifies the effect of process parameters such as punch die clearance, punch speed, and sheet metal thickness on the blanking force evolution.     

Dynamic behavior of gear pumps: effect of variations in operational and design parameters

This work presents a wide number of results about the influence that variations in terms of operational and design parameters play on the dynamic behavior of external gear pumps. These results are obtained by using a non-linear lumped-parameter kineto-elastodynamic model developed and experimentally assessed with the aim of including all the important dynamic effects. On the one hand, the effects of variations in the operational parameters—namely output pressure, rotational speed and oil viscosity—are analysed; on the other hand, the effects of modifications of some design parameters are shown: clearances and relief groove dimension. The results in terms of gear eccentricity, pressure evolution, pressure forces, gear accelerations and variable forces exciting the pump casing enlighten the dynamic behavior of gear pumps and give useful indications for design improvements and vibration and noise reduction. As regards specifically gear accelerations as well as forces exciting the casing, they strongly increase with both output pressure and rotational speed, but variations in rotational speed in the operational range give lower effects. Conversely, the modifications of the clearances give negligible effects, while the relief groove dimension is very important: the larger the relief grooves are, the higher the gear accelerations and forces exciting the casing become.