Analysis of hydrofilm extrusion of three-dimensional shapes from round billets

A new method of die construction is proposed, which enables the exact geometrical control of die shape and ensures the initial sealing between billet and die. Using the modified method of die construction the internal metal deformation is analyzed with the aid of a special transformation combined with the upper-bound method. Based on a concept of equivalent friction factor the energy dissipation in fluid film is calculated approximately for three-dimensional hydrofilm extrusion. Computations are carried out for hydrofilm extrusion of various sections such as squares, rectangles, ellipses and clover shapes and various factors affecting the process are discussed. Experiments are performed for clover and square sections using the dies from NC manufacture based on the suggested theoretical design. A reliable sealing system is developed between punch and container. The experimental results are compared with the theoretical prediction and it is shown that the theory is in reasonable agreement with the experimental observation. Various aspects are discussed from the experiment.     

Further investigation into extrusion of trocoidal gear sections considering three-dimensional plastic flow

In the present study, theoretical development proposed in previous work carried out in extrusion of clover sections in relation to a generalized die design method is presented in the extended scope for three-dimensional extrusion of trocoidal gear sections from round billets with experimental verification. Computations are carried out for clover and trocoidal gear sections. The CAD/CAM of the suggested dies is introduced for the experiments. Experiments are carried out for a clover section and a trocoidal gear section with eight teeth. Al 2024 aluminum billets were used as the working material. Half-cut specimens are used for flow visualization of the extrusion process. The theoretical predictions are in good agreement with the experimental results in extrusion load and metal flow.     

铜合金水表外壳破裂失效检测分析

采用金相显微镜、扫描电子显微镜、能谱分析仪等检测分析方法对铜合金自来水表外壳在使用中发生破断开裂泄露的原因进行了分析。结果认为,铜合金自来水表外壳在使用中发生破裂属于应力腐蚀破裂,导致发生应力腐蚀的原因与使用环境中的硫化物有关。     

Numerical analysis of cavitating flow past an axisymmetric cylinder with comparison to experiments

Simulation of cavitating flow is of practical importance for many engineering systems such as propellers, pump impellers, nozzles, injectors, and torpedoes. In this study, a two-phase flow solver based on a homogeneous mixture model was developed. Computations were carried out for an axisymmetric cylinder, and the present code was validated by comparing the calculation results with experimental results. The results showed that the system is suitable for simulating evaporation and condensation processes in water flow. What’s more, the changes of cavity length with various operational conditions were calculated including the water depth, angle of attack, and free stream velocity. The conditions for cavitation inception were also studied to show the relationship between the operational conditions in multiphase flows.     

Numerical solution for frequencies and mode shapes of elliptical plate half of whose boundary is simply supported and the rest free

Free transverse vibrations of elliptical and circular plates of variable thickness with half of the boundary is simply supported and the rest is completely free have been computed till the first four frequencies converge to at least four significant digits. The thickness of the plate is taken varying linearly with space coordinates. Computations have been carried out by using the famous Rayleigh–Ritz method. Results are reported for various values of the taper parameters. Almost all the results reported here are entirely new. A table has been prepared to indicate the trend of convergence of the results with increasing the order of approximation. Comparison has been made with known results in special cases. For the sake of completeness, results for the cases when the entire boundary is simply supported or completely free are also reported. Three-dimensional mode shapes and the associated contour lines have been plotted in some selected cases using tools of Computer Graphics and Turbo C++.     

Multiagent control of computational systems on the basis of meta-monitoring and imitational simulation

This paper describes the control of computations in a distributed computing environment (DCE) on the basis of its meta-monitoring and simulation modeling. Computations are controlled by a multiagent system with a given organizational structure. Resource allocation is carried out by agents with the use of economic mechanisms for controlling their supply and demand. Controlling actions for agents are formed on the basis of the simulation modeling of functional processes of the DCE. Data about the DCE resources and processes are collected and emergency situations in the DCE nodes are detected and prevented by the meta-monitoring system of this environment. The research results are the techniques for selecting control actions and the methods for intellectual processing and effective storage of data.     

An analysis of axisymmetric hydrostatic bulging by the upper-bound method

An upper-bound solution for the analysis of hydrostatic bulging is found by minimizing the plastic energy consumption rate divided by the fluid volume change rate. The corresponding upper-bound pressure is found through optimization with respect to some parameters given in the assumed velocity field. Computations are carried out for axisymmetric hydrostatic bulging of isotropic work-hardening sheet metal. The computed results are then compared with those by the finite-element method and by the finite-difference method as well as the reported experimental results. The comparison shows that the present method renders excellent predictions in pressure and strain distributions with much reduced computational time, which are still in close agreement with those obtained by the numerical methods.     

三柔索吊床机构设计与运动学分析

研制了一种有重力约束的三索控制的柔索吊床机构来模拟船体海面上的运动。为了解三柔索吊床机构的运动特性 ,对其进行了运动学建模与仿真。仿真结果表明 ,台面倾角在 0°～ 30 0°变化时 ,台面不碰撞立柱 ,且柔索伸缩长度与台面倾斜角度接近于线性变化。本文所做的工作对吊床平台避免撞击立柱、缩小吊床立柱布置空间、提高空间利用率 ,以及为吊床的运动控制提供了理论依据     

Load-carrying capacity of a spherical shell with circular holes

The load-carrying capacity of spherical shells loaded by external pressure with circular holes is investigated. The problem is solved with the use of a numerical variant of the experiment-the-oretic method. Computations were carried out using an ANSYS/LS-DINA 11.0 finite-element package. Semianalytic formulas were obtained for computation of critical loads. The effect of sizes of the circular hole on the load-carrying capacity of shells studied is investigated.     

硬地层单牙轮-PDC钻扩联合钻头破岩特性

提出了新型单牙轮-PDC钻扩联合钻头,先依靠单牙轮破岩钻孔,释放地应力,产生岩石损伤,再助推PDC钻头刮切破岩。运用有限元法,建立钻扩联合钻头、双级PDC和常规PDC钻头破岩的非线性动力学模型。通过对岩石本构关系进行D-P准则描述以及确定岩石破碎的判据,分析钻扩联合钻头钻进硬地层的破岩机理,开展了3种钻头动态破岩过程的对比研究。结果表明：钻扩联合钻头在钻进过程中井底井壁的岩石应力得到明显释放,大大提高了岩层可钻性;在硬地层中钻扩联合钻头钻进速度提高的主要原因是拉应力破岩;钻扩联合钻头在硬地层钻进过程中的扭转振动大大降低,破岩效率更高,钻头寿命更长;由于单牙轮领眼破碎岩石的作用,钻扩联合钻头对井底岩石的冲击破碎能力更强,在硬地层中钻进更快。研究结果为新型单牙轮-PDC钻扩联合钻头的研发提供了参考。     

Extrusion of non-symmetric U- and I-shaped sections through ruled-surface dies: numerical simulations and some experiments

In this paper, previously developed analytical approach (Chitkara NR, Celik KF. Int J Mech Sci 2000; 42:273) based on the upper-bound theory was applied to analyse the mechanics of the extrusion of non-symmetric U- and I-shaped sections and the symmetric ones from initially round billets through the ruled-surface dies. To investigate the optimum shape of the designed extrusion dies, that yield the lowest upper-bound for a given reduction in area, die length, off-centric positioning and frictional conditions a computer program was developed. Computations were carried out for various cases and some of the results compared with the experimental verifications. Curvature of the extruded product and simulated deforming grid patterns were also predicted and compared. A sophisticated CAD/CAM package was used in conjunction with the CNC and EDM processes to design and manufacture the streamlined dies for the extrusion of some non-symmetric U- and I-shaped sections. The theoretical predictions were observed to be in good agreement with the experimental results.     

In-process tool-failure detection by means of AR models

The present paper proposes a cutting tool breaking and chipping detection system for continuous and interrupted cutting, based on the analysis of the cutting force componentsF _x andF _y. A multifactorial experimental design has been carried out, to take account of the variability of the force signal. An adaptive signal processing algorithm is proposed, which detects catastrophic failure when at least one component deviates outside an estimated oscillation band for a time duration longer than a prefixed interval. The algorithm has been implemented on a four-microprocessor transputer board. Several tests confirmed the validity of the approach for detecting breaking and chipping phenomena in a few milliseconds, both in turning and in milling operations.     

On-line cutting state recognition in turning Using a neural network

Tool wear, chatter vibration, chip breaking and built-up edge are the main phenomena to be monitored in modern manufacturing processes. Much work has been carried out in the analysis and detection of these phenomena. However, most work has been mainly concerned with single, isolated detection of such phenomena. The relationships between each fault have so far received very little attention. This paper presents a neural-network-based on-line fault diagnosis scheme which monitors the level of tool wear, chatter vibration and chip breaking in a turning operation. The experimental results show that the neural network has a high prediction success rate.     

材料参数直接反求方法研究

提出直接从仿真分析结果反求材料塑性参数的方法。该方法以仿真分析为基础，根据能量守恒原理建立实测值与待求参数之间的关系并形成多元方程组；应用理想成形理论，即单元的变形遵循最小塑性功原理，使多元方程组成为静定或超静定方程组；将方程两边的计算差值定义为目标函数，用遗传算法来寻找目标函数最小解。对单向拉伸试验和四边简支球头冲压试验进行了算例计算，反求结果表明该方法能够反求得到较精确的参数。该方法拓宽了参数测定的试验途径。     

船体清洗装置的国内外应用与现状分析

目前,国内船体表面的清洗作业均是在船坞内进行,能够成功用于水下作业的自动化清洗设备仍需要潜水员下水进行作业,成本高而且工作效率低下。本文介绍了国内外有关船体清洗的现状及各种设备的优缺点及相关技术,如坞内清洗技术、水下清洗技术等,对今后船体水下清洗装置发展动态进行了分析,为船体清洁装置的发展提供了理论依据。     

Theoretical Analysis of Thermal Stresses in Electro-discharge Diamond Grinding

Excessive heat generated at the machining zone, during Electro-discharge diamond grinding (EDDG), is the major cause of thermal stresses, untempered martensite, overtempered martensite, and cracks. Therefore, the key to achieve good surface integrity in a machined part is to prevent excessive temperature and thermal stresses generated during machining process. A finite element model has been developed to estimate thermal stresses during EDDG when the current is switched-off. First, the developed code calculates the temperature in the workpiece and then the thermal stress field is estimated using this temperature field. Computations were carried out in plane strain condition for different down feeds of the grinding wheel. The effects of time of grinding and feed on thermal stress distribution have been reported. The thermal stresses are found to be higher near top surface at initial time of grinding but shifted away towards bottom after some grinding time.     

Numerical investigation of fluid flow past a square cylinder using upstream,downstream and dual splitter plates

A two-dimensional numerical study is carried out to analyze the drag reduction and vortex shedding suppression behind a square cylinder in presence of splitter plate arranged in upstream, downstream and both upstream and downstream location at low Reynolds number (Re = 160). Computations are performed using a Single relaxation time lattice Boltzmann method (SRT-LBM). Firstly, the code is validated for flow past a single square cylinder. The obtained results are compared to those available in literature and found to be in good agreement. Numerical simulations are performed in the ranges of 1 ≤ L ≤ 4 and 0 ≤ g ≤ 7, where L and g are the length of splitter plate and gap spacing between the splitter plate and main square cylinder, respectively. The effect of these parameters on the vortex shedding frequency, time-trace analysis of drag and lift coefficients, power spectra analysis of lift coefficient, vorticity contours visualization and force exerted on the cylinder are quantified together with the observed flow patterns around the main cylinder and within the gap spacings. The observed results are also compared with a single square cylinder without splitter plate. We found that at some combinations of L and g, the mean drag coefficient and Strouhal number reach either its maximum or minimum value. It is found that the drag is reduced up to 62.2 %, 13.3 % and 70.2 % for upstream, downstream and dual splitter plates, respectively as compared to a single square cylinder (without splitter plate). In addition, in this paper we also discussed the applications of SRT-LBM for suppression of vortex shedding and reduction of the drag coefficients.     

Extrusion of non-symmetric T-shaped sections, an analysis and some experiments

In the present study, previously developed analytical approach (Int. J. Mech. Sci. 42 (2000) 273), based on the upper-bound theory, for the design of three-dimensional off-centric extrusion of arbitrarily shaped dies was applied to the extrusion of T-shaped sections from initially round billets with the experimental verifications. Here, non-symmetric T-shaped sections as well as symmetric ones were considered. A computer program was written to obtain optimum die design which yield the lowest upper-bound for a given reduction in area, die length, its off-centric positioning and the frictional conditions. Computations were carried out both for the converging (ruled-surface) and the smooth curved (advanced-surface) dies. Curvature of the extruded product and simulated deforming grid pattern were also predicted. A sophisticated CAD/CAM package was used in conjunction with the CNC and EDM processes to manufacture the streamlined dies for the extrusion of T-shaped sections. The theoretical predictions were observed to be in good agreement with the experimental results.     

基于改进LRN k-ε模型的汽车气动特性研究

针对由Jones和Launder提出的LRN（低雷诺数）k-ε湍流模型对转捩预测不足等问题,引入全应力限制（TSL）方法及流线曲率因子以改进湍动能耗散率及湍流黏性系数,最终获得了一种改进的低雷诺数湍流模型,并将其应用于汽车外部流场计算仿真中,利用ISIS-CFD求解器实现计算。将计算结果与其他常用于汽车外部流场仿真的湍流模型以及风洞试验得到的结果进行了对比分析,结果表明,在同等计算条件下改进LRN k-ε湍流模型能更加准确且高效地模拟车身表面的气流分离以及尾部流场。     

船体外板水火成型机器人Y轴横梁变形计算和模态分析

对船体外板水火成型智能机器人的重要部件——Y轴横梁进行了有限元静力学分析和模态分析。采用三维十节点四面体结构单元计算Y轴横粱在各种典型工况下的变形，提取变形规律。在此基础上，对Y轴横梁进行模态分析，求解出前5阶的固有频率和相应频率处的振动模态，验证其设计结构的可行性。同时，也为后续的加工精度分析和误差补偿提供了理论依据。