Plastic behavior of superplastic material moving between two coaxial rotating cylinders

A one-dimensional stationary boundary problem is solved and the related plastic behavior is analyzed for a superplastic material moving between two coaxial rotating cylinders. The well-known relationship for a non-linear viscous material is used as a constitutive relation, which reduces the problem to an ordinary differential equation. The effects of the strain-rate sensitivity and geometrical factor on the kinematics and stress-strain distribution are analyzed. From this analysis it is found that as the value of m decreases, the deformation gradient increases, and localization of the deformation in the vicinity of the interior cylinder takes place. It is shown that the solution obtained fully coincides with the known one for the Couette flow of a Newtonian viscous fluid as a special case.     

Multi-objective optimization for turning processes using neural network modeling and dynamic-neighborhood particle swarm optimization

In this paper, we introduce a procedure to formulate and solve optimization problems for multiple and conflicting objectives that may exist in turning processes. Advanced turning processes, such as hard turning, demand the use of advanced tools with specially prepared cutting edges. It is also evident from a large number of experimental works that the tool geometry and selected machining parameters have complex relations with the tool life and the roughness and integrity of the finished surfaces. The non-linear relations between the machining parameters including tool geometry and the performance measure of interest can be obtained by neural networks using experimental data. The neural network models can be used in defining objective functions. In this study, dynamic-neighborhood particle swarm optimization (DN-PSO) methodology is used to handle multi-objective optimization problems existing in turning process planning. The objective is to obtain a group of optimal process parameters for each of three different case studies presented in this paper. The case studies considered in this study are: minimizing surface roughness values and maximizing the productivity, maximizing tool life and material removal rate, and minimizing machining induced stresses on the surface and minimizing surface roughness. The optimum cutting conditions for each case study can be selected from calculated Pareto-optimal fronts by the user according to production planning requirements. The results indicate that the proposed methodology which makes use of dynamic-neighborhood particle swarm approach for solving the multi-objective optimization problems with conflicting objectives is both effective and efficient, and can be utilized in solving complex turning optimization problems and adds intelligence in production planning process.     

逆向工程中二次曲面拟合方法的研究

数据分块和曲面拟合是逆向工程中最关键的部分。主要探讨并实现了一种新的二次曲面拟合算法：首先用一种改进的参数化方法建立球面、圆柱面、圆锥面和圆环面的几何距离函数，然后用非线性最小二乘法拟合曲面。实验证明所采用的拟合方法能够有效避免奇异值问题，具有较好的健壮性和拟合精度较好等优点。     

Intelligent methods for the process parameter determination of plastic injection molding

Injection molding is one of the most widely used material processing methods in producing plastic products with complex geometries and high precision. The determination of process parameters is important in obtaining qualified products and maintaining product quality. This article reviews the recent studies and developments of the intelligent methods applied in the process parameter determination of injection molding. These intelligent methods are classified into three categories: Case-based reasoning methods, expert system- based methods, and data fitting and optimization methods. A framework of process parameter determination is proposed after comprehensive discussions. Finally, the conclusions and future research topics are discussed.     

Damage of plastic cylinders under localized pressure loading

The purpose of this paper is to develop a general methodology of converting a two-dimensional boundary value problem for a cylindrical shell to an equivalent one-dimensional problem of a plastic string on a non-linear plastic foundation. The shell is subjected to a localized pressure loading, thereby producing large plastic displacements and rotations. The equivalence parameter is defined and evaluated by making assumptions about the shape of the displacement and velocity field in the cross-sectional plane of the cylinder. Closed-form solutions for the deformation and velocity profile in the axial direction of the shell are obtained for two types of pressure loading, a rectangular pressure load and a Gaussian pressure load. The strain distribution and the maximum strains are also calculated for each load case and the possibility of predicting shell fracture is briefly discussed.     

Robust component modal synthesis method adapted to the survey of the dynamic behaviour of structures with localised non-linearities

This paper deals with a method to study closely the stationary solution of non-linear dynamic systems at several degrees of freedom (dof) subjected to harmonic excitations with or without parametric modifications. This solution is obtained basically with the utilisation of an iterative algorithm adapted to the first approximation of Newton–Raphson method. This method is based on the exploitation of the eigensolutions of the associated conservative linear system with or without parametric modifications as well as on the characteristics of localised non-linearities and finally on the exploitation of the equivalent linearisation method. With the application of this method at first on linear models initially condensed by modal synthesis, the predictions of non-linear responses can be obtained rapidly. In a second step, this method is adapted to a condensed linear model used in the first optimisation procedure of the non-linear dynamic behaviour. In fact, before the non-linear analysis, the appropriate choice of the basis of reduction, that is referred to as “robust” obtained from the initial linear system is necessary. This robust basis will be used as condensation basis of the modified model local per zone or global by substructure leads to a prediction of vibratory responses of complex structures greatly modified and affected by localised non-linearities.At the end of this article, two examples are given to illustrate the efficiency and the performances of the proposed method.     

Transient free convection flow past an infinite vertical cylinder with thermal stratification

This paper presents an analytical solution of one-dimensional free convection flow past an infinite vertical circular cylinder in a stratified fluid medium. The dimensionless unsteady coupled linear governing equations are solved by Laplace transform technique for the case when the Prandtl number is unity. Due to the effect of thermal stratification, the velocity, temperature, skin-friction and Nusselt number shows oscillatory behavior at smaller times and then reaches steady state at larger times, while this behavior is not seen in the absence of stratification.     

Leaflet geometry extraction and parametric representation of a pericardial artificial heart valve

Reverse engineering technology was used to reconstruct the complex leaflet geometry of a commercial pericardial valve in our study. Results show that the three-dimensional computer-aided design model of the leaflet surface can be rendered by fitting the surface either to cloud points or by a group of B-splines fitted to a set of cloud points that had been obtained by the process of laser-scanning digitizing. However, an acceptable smooth surface is usually not guaranteed and additional manipulation is required. An alternative method is introduced in this paper, which involves the fitting of an equation to the leaflet geometry to create a smooth surface. The geometrical profile of a pericardial artificial heart valve was scanned using a laser digitizing system. The leaflet profile is represented as a set of cloud points. A quadric surface is fitted to a set of unique points, which were located on the set of cloud points. A mathematical equation is obtained by solving a least-squares fit. The geometry of the fitted leaflet surface has been proven to be closely represented by an elliptical hyperboloid. The quadratic equations of the leaflet curvatures, calculated along both the circumferential and the radial directions, resulted in simple hyperbolic curvatures. The advantages of using elliptical hyperboloid geometry for the leaflet surface are discussed and compared with other types of conicoid geometries. The concepts of parametric representation of the leaflet geometry and parametric design for leaflets are discussed. A smooth surface without inflection points and with an adjustable surface area suitable for a series of stent sizes with incremented diameters is created by this method of a single parametric design. Finally, a generic method to apply the geometry extraction and parametric representation to most pericardial heart valve prostheses was discussed. The application to valves with natural shape was introduced, challenges were identified, and a technical solution was proposed.     

Lubricating Grease Shear Flow and Boundary Layers in a Concentric Cylinder Configuration

Grease is extensively used to lubricate various machine elements such as rolling bearings, seals, and gears. Understanding the flow dynamics of grease is relevant for the prediction of grease distribution for optimum lubrication and for the migration of wear and contaminant particles. In this study, grease flow is visualized using microparticle image velocimetry (μPIV). The experimental setup includes a concentric cylinder configuration with a rotating shaft to simulate the grease flow in a double restriction seal geometry with two different grease pocket sizes. It is shown that the grease is partially yielded in the large grease pocket geometry and fully yielded in the small grease pocket. For the small grease pocket, it is shown that three distinct grease flow layers are present: a high shear rate region close to the stationary wall, a bulk flow layer, and a high shear rate boundary region near the rotating shaft. The grease shear thinning behavior and its wall slip effects have been identified. The μPIV experimental results have been compared with a numerical model for both the large and small gap size. It is shown that the flow is close to one-dimensional in the center of the small pocket. A one-dimensional analytical model based on the Herschel-Bulkley rheology model has been developed, showing good agreement with the measured velocity profiles in the small grease pocket. Furthermore, wall slip effects and shear banding are observed, where the latter imply that using the assumption of uniform shear in conventional concentric cylinder rheometers may result in erroneous rheological results.     

Multi-objective optimization of combustion,performance and emission parameters in a jatropha biodiesel engine using Non-dominated sorting genetic algorithm-II

The present work studies and identifies the different variables that affect the output parameters involved in a single cylinder direct injection compression ignition (CI) engine using jatropha biodiesel. Response surface methodology based on Central composite design (CCD) is used to design the experiments. Mathematical models are developed for combustion parameters (Brake specific fuel consumption (BSFC) and peak cylinder pressure (P_max)), performance parameter brake thermal efficiency (BTE) and emission parameters (CO, NO _x , unburnt HC and smoke) using regression techniques. These regression equations are further utilized for simultaneous optimization of combustion (BSFC, P_max), performance (BTE) and emission (CO, NO _x , HC, smoke) parameters. As the objective is to maximize BTE and minimize BSFC, P_max, CO, NO _x , HC, smoke, a multiobjective optimization problem is formulated. Nondominated sorting genetic algorithm-II is used in predicting the Pareto optimal sets of solution. Experiments are performed at suitable optimal solutions for predicting the combustion, performance and emission parameters to check the adequacy of the proposed model. The Pareto optimal sets of solution can be used as guidelines for the end users to select optimal combination of engine output and emission parameters depending upon their own requirements.     

Boundary conditions for axisymmetric piezoelectric cylinder

For axisymmetric piezoelectric cylinder, the reciprocal theorem and the axisymmetric general solution of piezoelasticity are applied in a novel way to obtain the appropriate stress and mixed boundary conditions accurate to all orders for the cylinder of general edge geometry and loadings. A decay analysis technique developed by Gregory and Wan is converted into necessary conditions on the end-data of axisymmetric piezoelectric circular cylinder, and the rapidly decaying solution is established. The prescribed end-data of the circle cylinder must satisfy these conditions in order that they could generate a decaying state within the cylinder. When stress and mixed conditions are imposed on the end of cylinder, these decaying state conditions for the case of axisymmetric deformation of piezoelectric cylinder are derived explicitly. They are then used for the correct formulation of boundary conditions for the theory solution (or the interior solution) of axisymmetric piezoelectric cylinder. The results of the present paper enable us to establish a set of correct boundary conditions, most of which are obtained for the first time.     

Determination of diffusion controlled reaction rates at a solid/liquid interface using scanning electron microscopy

A high‐resolution method has been developed for the determination of localized values of interfacial reaction rate and mass transfer coefficient in aqueous solution. Scanning electron microscopy has been successfully applied to this problem through the measurement of electroplated film thickness formed under limiting current conditions. The method involves the calculation of local values of reaction rate via Faraday's laws and subsequent conversion of the data to absolute values of mass transfer coefficient. The technique has been verified in an undisturbed, turbulent flow regime (rotating cylinder electrode) through the use of Sherwood group dimensionless analysis. The resulting relationship shows comparable accuracy relative to electrochemical measurements. Favourable comparison has also been made with the generally accepted rotating cylinder correlation of Eisenberg, Tobias and Wilke. Differential rates of mass transfer to a single surface under conditions of disturbed flow have also been examined at a high spatial resolution using the stepped rotating cylinder electrode geometry. In this case, reaction rates have been measured as a function of circumferential distance within a recirculation zone situated immediately downstream of a backward‐facing step.     

A non-linear integrated aeroelasticity method for the prediction of turbine forced response with friction dampers

The aim of this paper is to describe an integrated aeroelasticity model for turbine blade forced response predictions. Such an approach requires a successful integration of the unsteady aerodynamics with non-linear structural dynamics, the latter arising from the use of root friction dampers to dissipate energy so that the response levels can be kept as low as possible. The inclusion of friction dampers is known to raise the resonant frequencies by up to 20% from the standard assembly frequencies, a shift that is not known prior to the aeroelasticity calculations because of its possible dependence on the unsteady excitation. An iterative procedure was therefore developed in order to determine the resonance shift under the effects of both unsteady dynamic loading and non-linear friction dampers. The iterative procedure uses a viscous, non-linear time-accurate flow representation for evaluating the aerodynamic forcing, a look-up table for determining the aerodynamic boundary conditions at any speed, and a time-domain friction damping module for resonance tracking. The methodology was applied to a high-pressure turbine rotor test case where the resonances of interest were due to first torsion and second flap blade modes under 40 engine-order excitation. The forced response computations were conducted using a multi-bladerow approach in order to avoid errors associated with “linking” single bladerow computations since the spacing between the bladerows was relatively small. Three friction damper elements, representing one actual friction damper, were used for each rotor blade. The number of rotor blades was decreased by 2–90 to obtain a cyclic sector of 4 stator and 9 stator blades. Such a route allowed the analysis to be conducted on a much smaller domain, hence reducing the computational effort significantly. However, the stator blade geometry was skewed in order to adjust the mass flow rate. Frequency shifts of 3.2% and 20.0% were predicted for the 40 engine-order resonances in torsion and bending modes, respectively. The predicted frequency shifts and the dynamic behaviour of the friction dampers were found to be within the measured range. Furthermore, the measured and predicted blade vibration amplitudes showed a good agreement with available experimental data, indicating that the methodology can be applied to typical industrial problems.     

A semi-analytical approach for the geometrically nonlinear analysis of trapezoidal plates

This paper presents a semi-analytical approach for the geometrically nonlinear analysis of skew and trapezoidal plates subjected to out-of-plane loads. The thin elastic plate theory with nonlinear von Kármán strains is used for the nonlinear large deflection analysis of the plate. The solution of the governing nonlinear partial differential equations with variable coefficients is reduced to an iterative solution of nonlinear ordinary differential equations using the multi-term extended Kantorovich method. The geometry of the trapezoidal plate is mapped into a rectangular computational domain. Parallelogram (skew) plates are considered as a particular case of the general trapezoidal ones. The capabilities and convergence of the method are numerically examined through comparison with other semi-analytical and numerical methods and with finite element analyses. The applicability of the approach to the nonlinear large deflection analysis of skew and trapezoidal plates is demonstrated through various numerical examples. The numerical study focuses on combinations of geometry, loading and boundary conditions that are beyond the applicability of other semi-analytical methods.     

Advanced inelastic analysis of solids by the boundary element method

Two boundary element solution algorithms are used for solving a range of elastoplastic and thermoplastic problems. The first algorithm is the conventional iterative procedure in which the unknown boundary solution and the initial stress (or strain) rates are found together in an incremental iterative fashion. The second algorithm is a new variable stiffness type approach in which the incremental boundary solution is obtained in a direct (non-iterative) manner. This new approach is presented in a general manner for axisymmetric, two- and three-dimensional analyses. The formulation is implemented in a general purpose, multi-region system that utilizes quadratic isoparametric shape functions to model the geometry and field variables of the body and can admit up to 15 substructured regions of different material properties.     

基于 MEMS 的量热式传感器气体流量测量的模型研究

气体流量测量广泛应用于呼吸监测、管道运输等领域。本研究细致分析了MEMS量热式传感器温度一维分布模型中的热边界层参数,进行了相应的经验修正。并且在温度一维分布模型的基础上,针对具有两对上下游测温电阻芯片结构的MEMS量热式传感器,提出了一种新的传感器输出电压关于气体流量的半修正理论模型。该理论模型能够适用于不同类型的单介质气体。同时,开展了N₂、CO₂流量测量实验,与理论模型进行对比,证明所提出的理论模型可以正确预测不同气体介质的流量,其中针对CO₂测量介质的均方根误差为0.15%。此外,结合理论分析,提出了一种高精度,拟合形式简单、针对确定气体适用性更好的测量模型,其中针对CO₂测量介质的均方根误差为0.05%。     

Photogrammetric measurement process capability for metrology assisted robotic machining

This paper documents the findings of experiments done to assess the capability of a photogrammetric measurement process for use in a metrology assisted robotic machining application. Capability is judged from the perspective of uncertainty and error across various part geometries over several days. The influence of operator technique on error and point acquisition ability for challenging geometry is also assessed. The process is found to be resistant to short-term error drift when operating in a controlled environment but systematic and random errors are demonstrated to be highly dependent on geometry. Operator influence on capability is found to be minimal when scanning freeform geometry, although this is unlikely for more complex parts. Acquisition of inspection points on cylindrical pockets is found to be a limitation. Technological development opportunities are highlighted in the context of the metrology assistance application considered. Overall, a thorough assessment of the measurement process capability is made and findings provide a quantification of current state, setting a base case for comparing research progress against.     

Contour Quality Evaluation of the Toroidal Cutter

A toroidal cutter is an effective tool for use in the machining of freeform surfaces. Its contact point on the machined surface creates a second-order continuous curvature, thus the scallop height is decreasing if the cutter axis is inclined at a suitable angle against the machined surface. However, few studies address the evaluation of the contour quality produced by this kind of cutter. The geometry of a toroidal cutter includes a cylindrical shank, cutting body, and a toroidal surface. These components may deviate from the ideal geometry, resulting in contour errors. Therefore, it is very important to evaluate the radius of the cutting body and the toroidal surface based on the axis of the minimal circumscribed cylinder. This paper first presents a reliable model to determine the axis of the minimal circumscribed cylinder (MCC) of the cutter shank, from measured data. Then, based on the determined axis, the radius of the cutting body is calculated, and finally the minimal circumscribed toroidal surface (MCTS) of the revolving surface of the corner arc is investigated. An illustrative example is given to verify the validity of this modelling methodology. This work provides a basis for evaluating the actual contour quality for this kind of rotating cutter. The method illustrated here can also be used for error evaluation for other kinds of cutter with a single shank having multiple cutting edges.     

Reducing the Radial Error Motion of an Aerostatic Journal Bearing to a Nanometre Level: Theoretical Modelling

Ultra-precision air bearings could enable novel and more accurate precision applications. In this paper we report on the design of an ultra-precision air-bearing system, intended to reduce the radial error motion, i.e. the deviation from perfectly centric motion, to a nanometre level (i.e.<10 nm). To this end, the influence of several manufacturing errors, bearing parameters and feeding geometries is analysed on the radial error motion of an aerostatic journal bearing. This finally leads to the formulation of several design guidelines. On this basis, a numerical gas film model is developed and validated. Increasing the number of feedholes proves to be a promising solution as it results in an evenly distributed air film. The latter is confirmed by the fact that the radial error motion of an aerostatic journal bearing with a porous ring feeding geometry, which can be seen as a limiting case of infinite number of feedholes, is only 1 nm.