bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristic tetrahedron of wrench singularities for parallel manipulators with three legs
Authors: Ebert-Uphoff I , Lee J-K , Lipkin H
Published: October 2002

A new analysis of wrench singularities is presented for spatial parallel platform manipulators consisting of three legs, with up to two actuators each, and connected to the mobile platform by spherical joints. The analysis also applies to some related manipulators with six legs, such as the 6-3 Gough-Stewart platform. The characteristic tetrahedron is introduced to identify wrench singularities, i.e. configurations where the platform can move infinitesimally with all actuators locked. An important theorem is presented that provides a geometric interpretation of wrench singularities: a manipulator is at a wrench singularity if and only if the characteristic tetrahedron is singular. All cases in which the tetrahedron becomes singular are enumerated, which leads to a classification of wrench singularities. This method is easy to visualize and presents an alternative to standard approaches using line geometry.
Numerical analysis of dynamic contact with combined constraint of displacement, velocity and acceleration on the contact surface
Authors: Lee K
Published: October 2002

For an efficient dynamic contact analysis in finite element techniques, a contact error vector is defined on the possible contact surface by combining the displacement, velocity and acceleration, and the contact error vector is monotonically reduced by an iterative scheme similar to the augmented Lagrange multiplier method. The numerical experiments show that, when the time step size is small, the present technique gives more smooth and accurate solution than Abaqus.
Design and analysis of a passive damping device in a head actuator assembly
Authors: Xu L M , Zeng S , Guo N , Lin R M , Du D
Published: October 2002

It is known that a quasi-rigid-body mode (QR mode) exists in hard disk drives (HDDs) in the frequency range from 3 to 5 kHz and that it is caused by the flexibility of the pivot and the mass and structure of the head actuator assembly (HAA). This mode hinders performance improvement of the servo system in this bandwidth and thus limits the area density growth of HDDs. In this paper, a novel tuned damping device is proposed to suppress the QR mode and to reduce the residual vibration in head positioning in order to improve the servo system performance. The damping device is to be installed on the arm and hollow space within the voice coil motor (VCM) on the HDDs. The dynamic characteristics of the HAA with the tuned damping device are measured in both the frequency and the time domain and are analysed by finite element modelling (FEM). It is shown that the tuned damping device can work effectively to suppress quasi-rigid body vibration of the HAA and minimize the residual vibration in head positioning.
Inelastic failure of fully clamped beams and circular plates under impact loading
Authors: Jones N , Jones C
Published: October 2002

An experimental investigation is reported on the impact loading of fully clamped mild steel beams and circular plates struck by relatively heavy masses. The impact energies are sufficient in some tests to cause material failure and, thus, to provide the threshold conditions for cracking and severance for impact velocities up to 6.74m/s for beams and 15.66m/s for plates. The beams were struck at several locations across the span, and a significant reduction in the threshold energy is observed for strikes near to a support. Round-nosed impactors require more energy to induce failures than flat-nosed ones. Furthermore, they cause failure to develop at the supports of both beams and plates rather than initiating rupture at the impact point, which is the case for a blunt striker. Reasonable agreement is obtained between the predictions of an elementary theory, which uses rigid-plastic methods of analysis, and the experimental results for the deflection and failure of beams struck at the mid-span. The experimental data, which include static and dynamic material properties, are suitable for calibrating numerical schemes and for further study on the accuracy of criteria for the dynamic inelastic failure of structures.
Control of diffusing flow at low Reynolds numbers with annular wall jets
Authors: Burgess C P , Lawn C J
Published: October 2002

During the course of experiments to determine the influence of coflowing streams of air on the lift-off height of a methane jet flame, it was necessary to achieve a smooth axial decay of the velocity field in a conical diffuser. It was also crucial that the mean axial velocity profile was flat in the central region of the flow. These criteria proved to be quite difficult to meet, even with diffuser half-angles limited to 12.6°, partly because of the low Reynolds numbers involved, which were in the range 780-3500 based on the inlet pipe diameter.

A satisfactory solution, following Duggins, proved to be the injection of high-velocity air along the wall from a narrow annulus around the inlet. For diffusers with half-angles of 3.5, 7.5 and 12.6°, the optimum rates of injection were found to be independent of the half-angle but dependent on the Reynolds number and on whether a gauze mesh was present at the inlet. The efficiency of diffusion reached an optimum value of 60 per cent at the highest Reynolds numbers, and this was achieved both with and without the mesh.
An engineering model for coupled heat and mass transfer analysis in heated concrete
Authors: Li L y , Purkiss J A , Tenchev R T
Published: October 2002

In this paper an engineering model for coupled heat and mass transfer in heated concrete is proposed. The model considers the heat transfer and mass transport of liquid water and gaseous mixture. The evaporation of liquid water is assumed to be related to the imbalance pressure between liquid water and water vapour controlled by the ideal gaseous mixture pressure and water saturated pressure. Thus, the content of liquid water is determined directly from its mass transport equation rather than through assumed sorption isotherms as in most existing models. Numerical results for temperature, pore pressure and contents of liquid water and gaseous mixture are presented. Some important features are highlighted through the discussion of results.
A method for the solution of the forward position problems of planar mechanisms with prismatic and revolute joints
Authors: Hernández A , Petuya V , Amezua E
Published: October 2002

In this paper, a method to solve the forward position problems of planar linkages with prismatic and revolute joints is presented. These linkages can have any number of degrees of freedom. This method has been named the geometrical iterative method and is based on geometrical concepts. An iteration sequence that corresponds to the system of non-linear equations describing closure of the mechanism loops is defined. This sequence is applied in successive iterations to obtain the position of the mechanism. In order to achieve convergence, the iteration sequence must fulfil two fundamental conditions. A searching algorithm has been developed to obtain a useful iteration sequence. It is based on the use of hierarchical rules and criteria. The method has been implemented in a simulation program developed by the authors. Several illustrative examples are presented using representative linkages.
Flexural wave generation and stress analysis during laser evaporative heating of steel
Authors: Yilbas B S , Hyder S J , Shuja S Z
Published: October 2002

Flexural waves are generated during the laser evaporative heating process. In this case, vapour pressure developed at the workpiece surface generates a pressure force acting normal to the surface. This, in turn, results in waves in the workpiece. Moreover, a stress field arises in the substrate material during the flexural motion. Consequently, investigation into the flexural waves and stress levels developed in the substrate material on account of the laser evaporative heating process becomes necessary. In the present study, laser evaporative heating of steel is considered. The flexural waves generated by teh normal pressure force are formulated and the stress levels inside the substrate material are computed numerically using the finite element method (FEM). To investigate the effect of an additional element, as an impurity in the substrate material, on the stress levels, aluminium is added to the steel substrate. It is found that a displacement of the surface of the order of 2μm occurs, and that the maximum stress level is of the order of 105 Pa during the heating process. The additional aluminium lowers the displacement and stress levels in the substrate material.
Outline of a new evolutionary algorithm for fuzzy systems learning
Authors: Pham D T , Castellani M
Published: October 2002

This paper describes a new evolutionary algorithm for the automatic generation of the knowledge base for fuzzy logic systems. In common with other evolutionary approaches, the approach adopted is to treat the problem of knowledge base generation as that of searching for a solution of an acceptable quality by applying genetic operators to a population of potential solutions. The algorithm presented dynamically adjusts the focus of the genetic search by dividing the population into three subgroups, each concerned with a different level of knowledge base optimization. The algorithm also includes a new adaptive selection routine that aims to keep the selection pressure constant throughout the learning phase.
Evolutionary fuzzy logic system for intelligent fibre optic components assembly
Authors: Pham D T , Castellani M
Published: October 2002

This paper presents a new evolutionary fuzzy logic system for use in the assembly of optical fibre components. The system optimizes the light output from a fibre by applying a gradient-based algorithm enhanced with momentum information. The parameters of the algorithm are adjusted on-line by a fuzzy controller according to the progress of the alignment process. The control knowledge base is automatically generated via a new evolutionary algorithm. The algorithm divides the population into three subgroups, each concerned with a different level of knowledge-base optimization, and employs a new adaptive selection routine that aims to keep the selection pressure constant throughout the learning phase. The resulting fuzzy logic controller demonstrated a robust performance with alignment times and accuracies comparing favourably against those obtained using a manually designed controller. Moreover, the evolved knowledge base was expressed in a transparent format that facilitated the understanding of the control policy.
Unsteady unidirectional flow of a Maxwell fluid in a circular duct with different given volume flowrate conditions
Authors: Chen C-K , Chen C-I , Yang Y-T
Published: October 2002

In this paper, the velocity profile and pressure gradient of the unsteady state unidirectional flow of a Maxwell fluid in a circular duct are considered. The flow motion in the duct is induced by a prescribed arbitrary inlet volume flowrate which varies with time. Based on the flow conditions described, two basic flow situation are solved; these are a suddenly started and a constant acceleration flow respectively. These two results are applied to a practical case that is a trapezoidal motion. In addition, oscillatory flow is also considered. The results show that the effect of the relaxation time, λ, of the viscoelastic fluid is only of importance when the motion is unsteady.
Analysis of damped composite sandwich plates using plate bending elements with substitute shear strain fields based on Reddy's higher-order theory
Authors: Nayak A K , Shenoi R A , Moy S S J
Published: October 2002

Two new C0 assumed strain finite element formulations of Reddy's higher-order theory are used to determine the natural frequencies and loss factors of layered anisotropic composite and sandwich plates. Material properties typical of fibre polyester resins for the skin and HEREX C70 PVC foam damping materials for cores are used to show the parametric effects of plate aspect ratio, length-thickness ratio on natural frequencies and loss factors. A consistent mass matrix is adopted in the present formulation. Both frequency-independent and frequency-dependent damping of viscoelastic materials are considered. The developed elements are free from spurious zero energy modes due to the assumed strain approach.
An optimum synthesis for gripping mechanisms by using natural coordinates
Authors: Ceccarelli M , Cuadrado J , Dopico D
Published: October 2002

In this paper a simple and efficient procedure for optimum dimensional synthesis of gripping mechanisms is presented. The proposed design method is based on a suitable formulation of grasping performance of gripping mechanisms and makes use of a description of mechanisms by means of natural (fully Cartesian) coordinates. The optimization design problem is formulated by an objective function describing the main grasping performance and constraints prescribing practical design requirements and mechanism peculiarities. A numerical example is reported and discussed to illustrate the engineering feasibility of the proposed design procedure.
Car—caravan snaking: Part 2: Active caravan braking
Authors: Sharp R S , Fernández M A Alonso
Published: October 2002

Founded on the review and results of Part 1, Part 2 contains a description of the virtual design of an active braking system for caravans or other types of trailer, to suppress snaking vibrations, while being simple from a practical viewpoint. The design process and the design itself are explained. The performance is examined by simulations and it is concluded that the system is effective, robust and realizable with modest and available components.
A review of vehicular emission models and driving cycles
Authors: Esteves-Booth A , Muneer T , Kubie J , Kirby H
Published: October 2002

This article reviews the latest and relevant work on both vehicular emission models and driving cycles. The three main types of emission models, namely emission factor models, average speed models and modal models, are covered. Each project is analysed regarding its characteristic parameters, such as data collection technique, methodology, statistical analysis and pollutants covered, where appropriate. Other parameters were taken into account, such as the project objectives, results and relevance regarding the wider spectrum of the road traffic situation.
An application of thermal exermal analysis to the development of mine cooling systems
Authors: Twort C T , Lowndes I S , Pickering S J
Published: October 2002

The extraction of minerals and coal at greater depth, employing higher-powered machinery to improve production levels, imposes an increased burden on the ability of a ventilation system to maintain an acceptable mine climate. Hence, mechanical mine cooling systems are often adopted, which can be expensive both in terms of their associated capital and operating costs. Consequently, in order to optimize the costs it is essential to provide the mine operator with a method with which to determine the most cost effective and efficient mine cooling system.

The following paper overviews the development of a novel approach to the energy analysis of mine cooling systems using the concepts of thermal exergy analysis. Generic model mine ventilation networks are constructed and the subsurface environments of these mine networks predicted. Models of various cooling system methods are developed and applied to control the underground climate within these mine networks to within pre-set climatic limits. The exergy transfers that are produced by the application of the different cooling methods are compared using performance indices. Models to represent chilled water distribution networks, used to supply the air coolers within the various cooling systems, are designed and balanced. The results of the exergy analyses applied to the operation of the various chilled water pipe networks are discussed and used to assess the exergetic performance of the application of each cooling system to the mine ventilation network.
On the balancers of any frequency term of the shaking moment of spatial mechanisms
Authors: Chiou S-T , Tzou J-C
Published: October 2002

It is proved in this paper that the hodograph of a frequency term (for example the kth frequency term) of the shaking moment of spatial mechanisms is an ellipse. Furthermore, expressions are provided for the lengths and attitudes of the semi-axes of this ellipse in terms of Fourier coefficients of the shaking moment. Accordingly, two equivalent systems of the kth frequency term of the shaking moment can be found; consequently two types of their balancers are proposed. A 7-R linkage is used as a numerical example for demonstrating the effects of the balancers. Additionally, it is also shown that the result of a previous work by other researchers, concerning the optimum balancing of a frequency term of pitching and yawing components of the shaking moment of high-speed machinery, is a special case of this study; furthermore, additional to the balancer they proposed, another is provided.
Vibrational measurement of the specific damping capacity of 15-5 ph stainless steel
Authors: Allgeier T , Adams R D , Evans W T
Published: October 2002

In order to quantify the phenomenon of mechanical hysteresis in precision force transducers, the specific damping capacity (SDC) of 15-5 ph stainless steel having various heat treatments was measured. Extraneous damping was greatly reduced by testing under vacuum. The results at cyclic stresses of 200 MPa in vibrational bending at room temperature were compared to static tests of force transducers, made from the same material and heat treated to the same specifications, also at 200 MPa maximum stress. This comparison confirms the vibrational test as a quick and reliable method for indicating the hysteresis characteristics of a material/heat treatment combination. However, no proportional relationship between the SDC and force transducer hysteresis was established. An attempt is made to explain the variation of SDC with the heat treatment of the steel.
Surface behaviour testing of phosphate—stearate coated steel parts
Authors: Dubois A , Oudin J , Rigaut J M
Published: October 2002

Two recently developed tests are used in this work in order to simulate contact and friction conditions in metal working processes. The upsetting—sliding test and the indentation—rotation test are able to measure the frictional properties induced by various lubricants or steel surface treatments during the actual forming operation. In this paper, the interest is focused on friction measurement and seizure performance of steel phosphate coatings strengthened by localized high contact pressures.

In the upsetting—sliding test, the indenter slides along the workpiece surface with a given penetration. Depending on the penetration and on the indenter geometry, a more or less strengthened plastic zone appears in the contact surface vicinity. Indenter normal load and tangential force values are related to mean contact pressure and mean friction stress at the contact surface. The experimental surface behaviour is then identified using friction stress—contact pressure curves.

In the indentation—rotation test, the workpiece rotates while in contact with a fixed semi-cylindrical slider. Curves of friction force versus workpiece revolutions are related to an increase in coating damage and to seizure.

The sensitivity of the upsetting—sliding test is illustrated by friction stress—contact pressure curves obtained for different phosphate—stearate coatings, indenter velocities and workpiece initial roughness. Phosphate—stearate coating performance until seizure is finally obtained from the indentation—rotation test and results from both tests are compared and discussed.
Dynamic modelling of planar flexible manipulators: Computational and algorithmic efficiency
Authors: Shyu Y-J , Gill K F
Published: October 2002

Traditionally, many robot arms are very rigid in construction; this was believed to be necessary for accurate placement and repeatability but led to higher material costs and increased energy consumption. Higher operational speeds and the use of lightweight materials cause elastic deformations to occur during the operation of the manipulator. These deformations degrade the path-tracking performance of the end-effector. The dynamic behaviour of a flexible manipulator is described mathematically by non-linear equations which are difficult to solve analytically. Unfortunately, there is currently no experimental information available with which to compare this design of flexible structure. For design and control purposes, it is suggested in this paper that it is more appropriate to employ approximate solutions with the emphasis on the development of a fast computational algorithm. An analytical study was undertaken to investigate the relevant uncertainties that are either inappropriately described or unavailable in the literature. The purpose of the paper is essentially to include the initial deflections in the simulation, to select the size of the time step, to select the models for emulating the end-effector, payload and joint actuator and, finally, to suppress the uncontrollable off-plane vibrations when encountered. When this knowledge has been obtained, the design and development of the simulation process can begin. In order to demonstrate the practicability of the open-loop simulation proposed and test the software, two representative models were investigated.
Effect of induced vortices on liquid outflow from vessels
Authors: Chow K C , Kubie J
Published: October 2002

This paper considers the influence of viscosity and circulation on the effect of vortices on the liquid outflow from open vessels. One of the simplest possible arrangements is investigated: an axisymmetric vertical cylindrical vessel with an outlet in its base with the vortex flow generated by supplying the liquid through pipes located at the perimeter of the vessel. It is shown that for low liquid levels in the vessel the vortex provides a hindrance to the flow, but that for high liquid levels it is the vortex flow which discharges more freely. It is also shown that the liquid level in the vessel is proportional to the liquid flowrate, with the constant of proportionality being a function of viscosity and initial circulation.
An approach to mechanism topology identification with consideration of design processes progression
Authors: Zhang W J , Breteler A J Klein
Published: October 2002

This paper deals with mechanism (including kinematic chain) identification with respect to topology. It is argued in the paper that the meaning of mechanism topology should have certain different abstraction levels in terms of different mechanism design tasks or processes. As such, four abstraction levels of mechanism topology are proposed and described. A new approach to mechanism topology identification with consideration of all these proposed levels is presented and described. One of the main features of this new approach is to extend the existing incident degree code approach. Examples are given to exhibit its effectiveness, compared with some existing methods.
On the performance of a cascade of turbine rotor tip section blading in wet steam Part 2: Surface pressure distributions
Authors: Bakhtar F , Mashmoushy H , Jadayel O C
Published: October 2002

In the course of expansion in turbines steam nucleates to become a two-phase mixture, the liquid consisting of a very large number of extremely small droplets carried by the vapour. Formation and subsequent behaviour of the liquid lowers the performance of turbine wet stages. To produce turbine nucleating and wet flow conditions realistically requires a supply of supercooled steam which can be achieved under blow-down conditions by the equipment employed. To obtain wet steam, the supercooled vapour generated is passed through a venturi before admission to the cascade. To evaluate the influence of droplet size two separate Venturis have been used in the investigation. The performance of a cascade of rotor tip section blading in wet steam has been studied. This paper is the second of a set and describes the results of the surface pressure measurements.
The optimal control problem of profiling the hydro-cannon nozzle to obtain the maximum outlet speed
Authors: Atanov G A
Published: October 2002

The hydro-cannon is, an interesting and a promising installation for producing high-speed pulsed liquid jets (1–3). It uses the inertial principle of fluid acceleration. The key feature of the hydro-cannon is that the dynamic pressure of the jet can be many times higher than the static one inside the installation. Hence, the form of the hydro-cannon nozzle is essential for the acceleration process of the water. The paper deals with calculation of the nozzle profile to obtain the maximum outlet speed.
A general solution to the axisymmetric frictional contact problem of a thin bonded elastic layer
Authors: Jaffar M J
Published: October 2002

The configuration of a thin elastic layer bonded firmly to a rigid substrate and pressed by a spherical punch has been used as a model to many problems arising in the field of biomechanics. This work presents a rigorous analysis of a thin bonded layer indented by a punch of general profile in the presence of the radial tangential traction. The method is based on perturbation theory. Formulae for stresses, strains and deformations are derived in terms of layer thickness, material properties and surface tractions. The results are illustrated by the evaluation of the expressions for several simple punch shapes. The influence of friction on the results is also examined. Good agreement is found between the present solution and the results reported in the literature.
Stress state and modelling of mode I cracks in layered materials suffering normal or near-normal contact loading
Authors: Kelly P A , Hills D A , O'Connor J J
Published: October 2002

Stress intensity factors are found for cracks arising in an elastic layer, perfectly bonded to an elastic substrate and propelled by surface contact loading, in a range of different distributions. In each case the loading is normal or very nearly normal, with only a modest frictional shearing force present. It is shown that the most favoured regions for crack growth, i.e. where tension occurs, are adjacent to the interface (at 45°) and normal to the free surface, based on the assumption that cracks grow mainly in mode I.
Fast modelling of roll stack behaviour for control applications
Authors: Allwood J M , Bryant G F
Published: October 2002

A fast model of roll stack deformation is presented. Appropriate simplified structural models are chosen by careful consideration of the application of general theories. Discretization of continuous variables allows the use of matrix-based weighting functions in describing component deformation and leads to a vectorized solution. All model non-linearities are considered, with particular attention given to the variable region of contact between adjacent rolls in the stack. A novel and efficient ‘binary choice matrix’ method is developed to describe the uncertainty in defining this region. This leads to a more efficient solution than previously published related models. Opportunities for future extensions are discussed.
Integral formulation of balance equations for two-phase flow through a sudden enlargement Part 1: Basic approach
Authors: Attou A , Bolle L
Published: October 2002

A general expression of irreversible losses related to two-phase flows through a sudden enlargement is derived from basic balance equations (mass, momentum and energy). The need to take into account void fraction and quality changes is emphasized for some one-fluid flows. From a comparison with several experimental results, it is concluded that a void fraction decrease downstream of the enlargement must be considered in order to predict satisfactorily pressure variations on the basis of the momentum balance procedure. When expressed in the form of a fraction of reversible pressure recovery, dissipation losses appear to depend strongly on the quality. Their minimum value is observed for a larger quality value when the pressure of the system is increased.
On the calculation of the unsteady compressible flow through an N-branch junction
Authors: William-Louis M J P , Ould-El-Hadrami A , Tournier C
Published: October 2002

This paper presents the generalization of the ‘branch superposition method’ (BSM) for the computation of the unsteady compressible flow through an N-branch junction. In the case of a perfect gas flow in a three-branch junction, a mathematical study of the system of equations resulting from the combination of the characteristic relations and the boundary conditions is investigated. This clearly shows many possible solutions, including non-physical ones. The algorithm of the BSM is then extended to the case of an N-branch junction. The numerical calculation of unsteady compressible flow through three-branch and four-branch junctions by this method is compared with experimental measurements.
Martensite formation and residual stresses around railway wheel flats
Authors: Jergéus J
Published: October 2002

A finite element (FE)-based computational model is developed for the calculation of residual stresses in steel as induced by a local thermal shock. Subroutines to handle phase transformations and constitutive behaviour including volumetric expansion and transformation-induced plasticity are added to a commercial FE code. Sliding contact problems with application to railway technology are studied. Six examples of wheel flat formation are investigated in detail. In all of them rather high tensile stresses are found in the wheel rim in a domain below the top layer of phase transformations. For those combinations of train speed, wheel load and sliding duration, where the brittle martensite phase is found, surface cracks are likely. The predicted tensile stresses may propagate these cracks further into the rim material and thus cause spalling.
The ranking of efficiency of structural layouts using form factors Part 1: Design for stiffness
Authors: Burgess S C
Published: October 2002

This paper presents a method for ranking the mass efficiency of simple structural layouts for stiffness design using form factors. Form factors are derived for three different frameworks and seven different beams for an example load case of a simply supported and centrally loaded structure. The form factors show how structural efficiency is affected by four different design aspects: (a) severity of height constraint, (b) uniformity of stress, (c) utilization of height and (d) principle of load transfer. Form factors can be used as a preliminary design tool to help select and design structural concepts.
Design optimization of a pneumatic-powered drilling tool thrust assembly
Authors: Ferguson G L , Samineni R , Johnson P W
Published: October 2002

The petroleum industry is dependent on developing more efficient means of drilling oil and gas wells. A prototype of a new design has been recently demonstrated which places the drilling power source (a pneumatic turbine) down-hole with the drilling bit. However, the thrust assembly shaft used to connect the power source to the bit was not optimally designed. Because of constraints placed on the geometry of the thrust assembly, severe stress raisers exist and these cannot be predicted by traditional analytical means. The conflicting requirements for increasing air flow through the internal passages in the thrust shaft while maintaining the torque-carrying capacity were studied to develop the guidelines for optimizing the thrust assembly.
Modelling the dynamics of misaligned helical gears with loss of contact
Authors: Smith J D
Published: October 2002

Misaligned helical gears generate vibration, which under light load can cause loss of contact of the teeth. Conventional frequency domain methods are not satisfactory for predicting loads and vibration. A basic approach is described and the corresponding program is given together with some typical results.
Modelling of spur gear mesh stiffness and static transmission error
Authors: Du S , Randall R B , Kelly D W
Published: October 2002

A modified transmission error (TE) model is introduced for analysing the effects on the transmission error of variation of tooth body stiffness with load application point, and a simulation program for transmission error computation with varying stiffness has been developed. In order to obtain the case where the tooth deflection component is the dominant source of the TE, nylon gears were used in this study. All the simulation results have been compared with the measured transmission errors from a single-stage gearbox. Even though carried out on low precision gears, the validity of the model for the more flexible nylon gears indicates that the model can be used for analysing the transmission error of high-precision gear sets.
The influence of rounded edges on indentation by a flat punch
Authors: Ciavarella M , Hills D A , Monno G
Published: October 2002

The contact problem and stress state for indentation by a flat punch with rounded edges is studied. For the contact problem itself analytical solutions are obtained for both surface pressure and interior stress fields. Cases of normal indentation and frictional contact, the latter in both sliding or partial slip conditions, are all treated.

The transition from the Hertzian configuration to the contact between a nominally flat pad and contacting flat surface is discussed, and it is found that the strength of the contact decays surprisingly slowly. Regarding the von Mises yield parameter, there is a range of configurations for which the strength is actually higher than the Hertzian one, and the strength decays only when the corner radii are very small. The present solution is therefore a realistic alternative to the classical rigid-flat punch idealization, and has particular application to fretting fatigue tests.
A feature complexity index
Authors: Little G , Tuttle R , Clark D E R , Corney J
Published: October 2002

An index is presented for quantifying the geometric complexity of a three-dimensional solid model. This provides a measure by which components may be compared one with another in relation to their relative complexity. The index is alphanumeric and readily computable. Such an index can be of use in the field of feature recognition as a means to determine how efficiently one algorithm handles components of varying complexity compared to another such algorithm.

The performance of the authors’ own feature recognition algorithm is tested against components of differing complexity as determined by the index.
Some insights into the dynamics of defective structures
Authors: Brandon J A
Published: October 2002

As a general principle, it should be assumed that defective structures will exhibit nonlinear response behaviour. The primary activity of the Cardiff research group over the last ten years has been the identification of the types of non-linear phenomena encountered in the dynamics of defective structures together with an estimation of their observability, albeit in a qualitative sense. A wide range of classical non-linear effects from subharmonic oscillations to chaotic vibrations has been observed. It is argued that structural integrity assessment can be enhanced by incorporating these non-linear effects into damage assessment criteria.
The effect of swirl on the annular flow past an axisymmetric poppet valve
Authors: Nadarajah S , Balabani S , Tindal M J , Yianneskis M
Published: October 2002

This paper describes an experimental investigation of the swirling flow through an axisymmetric port and poppet valve assembly under steady flow conditions. This work is an extension of the preceding paper, which is a study of the non-swirling flow in the same flow configuration [1]. Three different swirl rates were investigated with the aim to study the effects of swirl on the mean flow and turbulence characteristics of the flow field. The flow structure was studied by means of laser sheet flow visualization and the three velocity components and the associated Reynolds stresses were measured by ensemble-averaged laser Doppler anemometry techniques. The results are compared with those obtained with the non-swirling flow.

The addition of the swirl was found to alter the flow structure, particularly below the valve where a new counter-rotating vortex is formed. A toroidal recirculation zone is also formed in the valve passage. The growth and entrainment of the jet emanating from the valve gap increase and its trajectory angle changes. The flow visualization studies showed evidence of precession of the swirl centre and jet flapping. Swirl increases the Reynolds stresses and the turbulence production rate in most regions of the flow.
The interfacial heat transfer coefficient in hot die forging of titanium alloy
Authors: Hu Z M , Brooks J W , Dean T A
Published: October 2002

An investigation of die temperature changes and the heat transfer coefficient during hot forging of titanium alloy has been carried out using experiments and a thermal-plastic coupled finite element analysis. Hot Ti-6A1–4V rings were forged between two heated flat dies made of Inconel alloy IN718. The bottom die was instrumented with high-response thermocouples on its surface and subsurface. The recorded temperatures were analysed and used to determine the interface heat transfer coefficient between the die and the workpiece in conjunction with the thermal-plastic coupled finite element analysis using a reverse algorithm. The coefficients determined were then used in a finite element model for the analysis of the upsetting process and the results produced were in good agreement with the experimental data.
Theoretical and experimental simulation of accident scenarios of the Joint European Torus cryogenic components Part 1: The in-vessel cryopump
Authors: Ageladarakis P A , Papastergiou S , O'Dowd N P , Webster G A
Published: October 2002

A large cryopump has been operational since 1994 inside the plasma chamber of JET (Joint European Torus), the world's largest thermonuclear fusion facility. In this work, a flexible mathematical model, which analyses the thermal behaviour of the cryopump and associated water-cooled components, under all possible operating conditions, is presented. The system behaviour is simulated for a wide range of fault conditions, e.g. loss of vacuum, loss of cryogen flow, loss of cooling water supply and combinations of these. The model is validated by a series of experiments conducted both in a specially designed test rig and inside the JET vacuum vessel, using real scale components. Based on this analysis, an automatic safety system has been constructed and implemented into the JET operation routines. The system incorporates protective actions (e.g. draining) that prevent the development of excessive stresses in the cryopump components, thus ensuring their mechanical integrity and reliability. The work has been divided into two parts: Part 1 outlines the model used in the analysis and examines the behaviour of the divertor cryopump; Part 2 which follows, deals with a different type of cryopump which operates outside the plasma chamber.
Inelastic finite element analysis of fibre-reinforced composite laminates with damage
Authors: Chow C L , Yang F
Published: October 2002

In this study, a method of finite element analysis is presented to examine the three-dimensional inelastic behaviour of fibre-reinforced composite laminates with damage. The constitutive model for the characterization of mechanical responses of non-linear composite materials to damage that was proposed recently by the authors is employed. The formulation of the elastic damage stress-strain relationship in incremental form is first developed and then incorporated within the context of the displacement-based finite element procedure. Solution of the non-linear equilibrium equations is obtained with the modified Newton—Raphson iteration technique. Numerical implementation of the stress calculation is discussed in detail. Results predicted using the present finite element program for uniaxial off-axis tensile loading of unidirectional graphite/epoxy composite laminates show satisfactory agreement with those obtained from experiments. Other results describing the development of damage zones, the inelastic effect on stress distributions and material property variations due to damage in cross-ply laminated composite structures are also examined and discussed.
An efficient procedure for modelling limited plastic flow
Authors: Blomerus P M , Hills D A
Published: October 2002

A degree of plasticity is often tolerated at stress raising features in severely loaded, nominally elastic, components. Conventionally, the methods available for analysis are the finite element method (FEM) or an approximate notch root plastic strain method. The method introduced here is based on the idea of distributing dislocations to form a perturbation on an elasticity solution to solve the problem for an elastic—perfectly plastic material in transverse plane strain. Specialized kernels are used to satisfy exactly the far field boundary conditions and those at the stress raiser, so that only the small plastic enclave of material need be discretized. The method is seen to follow the incremental nature of the problem and to take into account the stress redistribution in plasticity. The problem of a circular hole under remote tension is solved and good agreement with an FEM analysis of a similar problem is observed.
On gearing of helical screw compressor rotors
Authors: Stošić N
Published: October 2002

Twin-screw compressor rotors are effectively helical gears. When these are formed from a hobbing cutter, the hobbing tool and the rotor together constitute a pair of crossed helical gears. In the present paper, the envelope gearing method is used to derive a meshing condition for crossed helical gears which is then used to create the profile of a hobbing tool. A reverse transformation enables the rotor profile thereby manufactured to be calculated. Simplification of the main gearing condition leads to the meshing expression for helical gears which may be used for the design of screw compressor rotors.
A software environment for conceptual mechanism design
Authors: Kenney L P J , Rentoul A H , Twyman B R , Kerr D R , Mullineux G
Published: October 2002

This paper describes how problems in machine design can be tackled by computer modelling of the constraints that exist due to the design specification and the conceptual solutions themselves. The design strategy proposed is one of identifying the most important constraints first and trying to satisfy these. This provides an acceptable solution. It is then possible to investigate less critical constraints which, in general, will have the effect of improving the performance of the machine. The case study example is taken from the food processing industry and involves the design of a highspeed mechanism to cut extruded dough into uniform blocks.
Aerodynamic design of 50 per cent reaction steam turbines
Authors: Havakechian S , Greim R
Published: October 2002

On the basis of their inherent favourable aerodynamic properties coupled with past progress, 50 per cent reaction stages already achieve a high efficiency level. Developments aimed at further performance enhancement entail employment of advanced design features that require a deep understanding of the flow phenomena involved and their interactions. In addition, substantial on-going efforts are needed to improve the quality of the design tools. This paper focuses on the key design issues, including advanced quasi-three-dimensional and three-dimensional design aspects. It further describes developments by the authors' company during the last decade for the design of modern reaction blading and establishment of state-of-the-art design tools.
Hydraulic turbines—basic principles and state-of-the-art computational fluid dynamics applications
Authors: Drtina P , Sallaberger M
Published: October 2002

The present paper discusses the basic principles of hydraulic turbines, with special emphasis on the use of computational fluid dynamics (CFD) as a tool which is being increasingly applied to gain insight into the complex three-dimensional (3D) phenomena occurring in these types of fluid machinery. The basic fluid mechanics is briefly treated for the three main types of hydraulic turbine: Pelton, Francis and axial turbines. From the vast number of applications where CFD has proven to be an important help to the design engineer, two examples have been chosen for a detailed discussion. The first example gives a comparison of experimental data and 3D Euler and 3D Navier-Stokes results for the flow in a Francis runner. The second example highlights the state-of-the-art of predicting the performance of an entire Francis turbine by means of numerical simulation.
Computational fluid dynamics for turbomachinery design
Authors: Denton J. D. , Dawes W. N.
Published: October 2002

Computational fluid dynamics (CFD) probably plays a greater part in the aerodynamic design of turbomachinery than it does in any other engineering application. For many years the design of a modern turbine or compressor has been unthinkable without the help of CFD and this dependence has increased as more of the flow becomes amenable to numerical prediction. The benefits of CFD range from shorter design cycles to better performance and reduced costs and weight. This paper presents a review of the main CFD methods in use, discusses their advantages and limitations and points out where further developments are required. The paper is concerned with the application of CFD and does not describe the numerical methods or turbulence modelling in any detail.
Centrifugal compressor design
Authors: Came P. M. , Robinson C. J.
Published: October 2002

Centrifugal compressors are used in a wide range of applications in which performance and mechanical integrity are invariably among the paramount design objectives. There is therefore continuing interest in the development of a sound understanding of the relevant physical phenomena and in the systematic application of the knowledge base that is the forerunner of the established design procedures. The paper reviews centrifugal compressor design methods that are commonly used in industry and reviews the underlying engineering science supporting the design practices. The design process, starting with the preliminary design and its reliance on empirical rules through to state-of-the-art aerodynamic design using computational fluid dynamics (CFD), is presented. The essentials of impeller mechanical design are also included in the paper.
Direct simulation of fatigue crack growth for arbitrary-shaped defects in pressure vessels
Authors: Lin X. B. , Smith R. A.
Published: October 2002

An advanced technique has been developed by the authors to predict fatigue crack growth for longitudinal and circumferential planar defects with arbitrary shape in pressure vessels. This is based on the step-by-step integration of an experimental fatigue crack growth law at a set of points along the crack front, enabling the crack shape developed during the fatigue process to be predicted. The stress intensity factors along the crack front are calculated by a three-dimensional finite element method. Automatic regeneration of finite element models for propagating cracks designed for this technique makes the simulation technique highly efficient. In this paper, following a description of the principle of the technique, some typical crack geometries are investigated. These include external and internal surface longitudinal cracks, an embedded longitudinal crack, a twin crack configuration and two circumferential surface cracks. The results obtained are compared with both the widely used ASME XI and BSI PD6493 guidelines, and some discussion on the safe use of the two guidelines is made.