bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of gas jet velocity in laser heating—a moving workpiece case
Authors: Shuja S Z , Yilbas B S
Published: October 2002

In the present study, gas jet-assisted laser heating of a moving steel substrate with finite thickness is considered. Three-dimensional flow and energy equations with variable properties of the gas are introduced in modelling the heating process. The low Reynolds number k-ε model is employed to account for the turbulence. A numerical scheme using a control volume approach is introduced to discretize the governing equations. The simulation is repeated for three assisting gas jet velocities (100, 10, 1 m/s) and a constant workpiece speed (0.3 m/s). It is found that the effect of assisting gas jet velocity on the surface temperature is more pronounced in the cooling cycle than in the heating cycle of the laser heating process. The workpiece movement affects the location of the maximum temperature at the surface, which moves away from the initially irradiated spot centre in the direction of motion of the workpiece.
Dynamic simulation and monitoring of a non-contacting flexibly mounted rotor mechanical face seal
Authors: Zou M , Dayan J , Green I
Published: October 2002

Mechanical face seal rotor dynamics is investigated through both simulation and real-time monitoring of a non-contacting flexibly mounted rotor (FMR) mechanical face seal in a seal test rig. Dynamic simulation is performed to investigate the seal rotor angular response to the stator misalignment, the stator angle, the initial rotor misalignment and clearance. Rotor angular response orbit is introduced and is able to characterize the rotor dynamic response. A real-time monitoring system is constructed in the test rig to monitor the instantaneous dynamic behaviour of the seal rotor, including its angularresponse, precession angle and angular response orbit. Experimental results agree qualitatively well with those of the dynamic simulation. Potential applications of the monitoring system for detecting seal face contact and for seal control are stated.
Some insights into slamming forces: Compressible and incompressible phases
Authors: Campana E F , Carcaterra A , Ciappi E , Iafrati A
Published: October 2002

In the present paper the slamming force occurring in the free-fall impact of cylindrical bodies over the water surface is analysed in both compressible and incompressible stages. In the compressible phase the hydrodynamic analysis is carried out by the acoustic approximation and a closed-form expression for the impact force is recovered. The incompressible stage is approached through an unsteady boundary element method to compute the free surface evolution and the slamming force on the body. In both cases the hydrodynamic force is coupled to the rigid body motion to update the entry velocity of the body. The combined effect of the increasing wetted area and the reducing entry velocity leads to a maximum in the impact force that depends on the body mass. A parametric investigation shows that in the impact of a wedge section, if the maximum is reached either in the compressible or in the incompressible stages, a similar square root trend characterizes the dependence of this maximum on a non-dimensional mass parameter.
The effect of diametral clearance, motion and loading cycles upon lubrication of metal-on-metal total hip replacements
Authors: Smith S L , Dowson D , Goldsmith A A J
Published: October 2002

A study of surface contact and separation of 36mm diameter metal-on-metal joints was undertaken in 25 per cent bovine serum using a hip simulator. A range of diametral clearances from 130 to 170 μm was tested and each joint was subjected to two different dynamic motion and loading walking cycles. One simulation used physiological motion and loading cycles as described by Paul [I], while the other used simplified motion cycles, as described by Barbour et al. [2], and simplified loading. An electrical resistivity technique was used to detect the extent of surface separation throughout a complete walking cycle.

The proportion of surface separation per cycle was generally greater in the simplified than in the physiological walking cycle. The latter cycle thus appears to present a more severe condition than the simplified cycle as far as joint lubrication is concerned.

No surface separation was observed, for either cycle, with the largest diametral clearance of 170 μm. All of the remaining joints, with smaller diametral clearances, showed surface separation for at least a portion of each walking cycle. The proportion of surface separation per simulated walking cycle generally increased as the diametral clearance decreased.
Numerical simulation of the flow and heat transfer around a cylinder with a pulsating approaching flow at a low Reynolds number
Authors: Papadakis G , Bergeles G
Published: October 2002

Two-dimensional numerical simulations of flow and heat transfer around a cylinder at a Reynolds number Re= 100 have been performed in order to investigate the effect of imposed inlet velocity pulsation on the heat transfer and flow fields. First the code is validated against existing results from the literature and then several external frequencies are examined. The numerical results confirm the existence of a vortex shedding lock-on regime where the wake behaves in a very ordered manner (completely periodic). Outside the lock-on region the flow is quasiperiodic. The length and centre of the mean recirculating zone downstream of the cylinder are also affected by the external pulsation. Regarding heat transfer, the results indicate that by imposing an external velocity pulsation, the root mean square (r.m.s.) of the local Nusselt number Nu increases, but the mean value increases only in the area downstream of the separation point. The mechanism responsible for this is identified: hot fluid is engulfed by stronger vortices (compared with the steady approaching flow case) shed from the upper and lower side of the cylinder and returned close to the downstream stagnation point. This mechanism also explains the observed variation in Nu with time. In the front part of the cylinder, the Nu varies almost sinusoidally and closely follows the imposed external velocity pulsation. The results indicate also that there is a range of external frequencies where the time and spatially averaged Nu number is maximized.
Optimal suppression of parametric vibration in discs under rotating frictional loads
Authors: Ouyang H , Mottershead J E
Published: October 2002

This paper investigates the parametric resonances of a stationary disc excited by a rotating frictional load and influenced by a series of mass-spring-damper systems with or without friction. The genetic algorithm is used to find out the right number of mass-spring-damper systems and their optimal positions in order to reduce and even eliminate the dynamic instability caused by the rotating friction as a follower force on the disc surface. It is found that, if these mass-spring-damper systems involve no or low friction, they can reduce or suppress the dynamic instability of friction-induced parametric resonances when correctly located, but they have, at best, no effect when the level of friction is high.
Design evaluation of multiroll mills for small-diameter wire rolling
Authors: Kuroda K , Kuboki T , Imamura Y , Hayashi C
Published: October 2002

A comprehensive study on the evaluation of mill designs was carried out for three types of multiroll mill for wire rolling by using both prototype mills and numerical experiments. The laboratory experiments were carried out in order to examine both the deformation and loading characteristics of two-, three- and four-roll mills using a set of rolls of the same diameter. As a result, the data allow a direct comparison of the rolling characteristics among the three types of mill, which is not found in previous work. The analytical results showed a good matching with the experimental results, and evaluation was then carried out on the three mills. It has been found that the four-roll mill ensures the highest reduction and the two-roll mill the lowest reduction under the restriction that certain dimensional precision of the rolled wire be maintained. This tendency becomes greater as wire diameter decreases and in practice it is recommended that a four-roll mill equipped with small-diameter rolls be used when rolling small-diameter wire. As regarding the loading characteristics, similar conclusions apply. Finally, domains were determined where four-roll mills show their marked superiority.
Consideration of manufacturing parameters in the design of grooved globoidal cam indexing mechanisms
Authors: Tsay D M , Ho H C
Published: October 2002

By considering the manufacturing variables involved in the processes of machining and assembly, analytical expressions for the turret motion and indexing accuracy of intermittent grooved globoidal cam mechanisms have been identified. Based on the kinematic and geometric relationships between the cam and its roller-follower turret, the effects on the output of the cam mechanism owing to clearances in the grooved cam and in the roller bearing, preload between the cam and its turret wheel and the cam taper angle have been investigated. As a result, the roller alternation in the cam-turret system has been analysed. Favourable parameters for the design, machining and assembly can be selected to manufacture such devices with improved turret motion and indexing accuracy. Worked examples are given to demonstrate the usefulness and effectiveness of the approach.
A new practical modal method for rotor balancing
Authors: Bingang Xu , Liangsheng Qu
Published: October 2002

A new practical modal balancing technique, which uses the modal ratio among measurement points (MRMP coefficient), has been developed. This new method is an improvement upon traditional modal balancing when the rotor to be balanced operates at the speed between the first and second critical speeds. The concept of the MRMP coefficient is introduced for the first time in this paper, on the basis of which the rotor-bearing system can be balanced at any one rotational speed between the first and second critical speeds by decomposing the modal components of unbalance and response simultaneously. Moreover, only one test run is required in three of the four balancing schemes provided in this paper to balance the rotor. In the new method, the test weights need not be orthogonal, so prior modal function knowledge is not necessary for calculation of the test weights, as required in the traditional modal balancing method. To verify the validity of the new technique, a balancing experiment using a rotating cantilever rotor is carried out. The results show that the new method can be applied effectively in field balancing.
A study on the link between coupled plasticity and damage and decohesion for multiscale modelling
Authors: Chen Z , Fang H E
Published: October 2002

To predict the transition from continuous to discontinuous failure modes, a bifurcation analysis is performed based on the continuum tangent stiffness tensor of a coupled plasticity and damage model. As a result, continuum damage and decohesion approaches can be combined for multiscale modelling of material failure.
Analysis of the conjugate effect of wall and flow parameters on pipe flow heat transfer
Authors: Arici M E
Published: October 2002

A combined numerical and analytical solution procedure is proposed to examine the conjugate heat transfer for laminar flow in a pipe. This simple and rather general procedure has the capability of handling the constant temperature, the constant heat flux, and the convection heat transfer boundary conditions of the pipe outer surface without detailed program modification. The results of the present work and fully analytical solution are compared to test the proposed solution procedure. The general trend of predicted results is in agreement with the analytical solution, but the quantitative differences between them is considered to be acceptable from the numerical point of view. Variation in the local Nusselt number and in the the wall and local mean fluid temperature across the axial direction is strongly dependent on the pipe wall thermal conductivity and the boundary condition at the outer surface of the pipe wall. Two non-dimensional numbers, the thermal conductivity ratio ks/ kf and the Biot number, are found to be controlling parameters for the effect of wall axial heat conduction on the heat transfer characteristics.
Modelling of the laser surface nitriding of Ti-6Al-4V alloy—analysis of heat transfer and residual stresses
Authors: Labudovic M , Kovacevic R
Published: October 2002

A three-dimensional finite element modelling of the laser surface nitriding of Ti-6A1-4V alloy is presented. Design capabilities of ANSYS parametric design language (APDL) were employed for this purpose. The model calculates transient temperature profiles, the dimensions of fusion zone and residual stresses in the laser surface nitrided Ti-6A1-4V alloy. Model simulations are compared with experimental results, acquired on-line using an ultra-high-speed shutter camera which is able to acquire well-contrasted images of the molten pool, and off-line using metallographical and X-ray diffraction analyses which show very good agreement. The results are further discussed to provide directions for reducing the residual stresses, as well as for feedback and process control.
Mathematical model of curvature analysis for conjugate surfaces with generalized motion in three dimensions
Authors: Chen C-K , Chiou S-T , Fong Z-H , Lee C-K , Chen C-H
Published: October 2002

A general mathematical model is proposed to determine the direct relations between the principal curvatures and directions of two conjugate surfaces in continuous tangency along a line at every instant. Without any assumption regarding the motion of mating surfaces, this model, created on the basis of kinematics, the theory of gearing and differential geometry, is especially suitable for calculating the curvatures of a surface generated on a computer numerically controlled (CNC) machine with surface modifications by non-constant-speed supplemental correcting motions. The model has simplified dramatically the calculation of curvatures by comparison with the differential geometry approach. The principal curvatures of a generated surface and dimensions of contact ellipses can be obtained by the model without the need for complicated equations of the generated surface. For verification of the model, a helical gear set comprising a gear with involuted teeth and a pinion with modified circular arc teeth is investigated. The tooth contact analysis (TCA) technique is also applied to study the shift of bearing contacts and dimensions of contact ellipses under three different kinds of generation setting.
Approach to diameter measurement of optical fibres: Forward near-axis far-field interference
Authors: Wu J
Published: October 2002

A new, simple, fast, accurate and non-destructive method is presented for determining the diameter of optical fibres. The technique is based on the analysis of the forward near-axis far-field interference pattern from an optical fibre illuminated by a laser beam perpendicular to its axis.
Effect of the pivot assembly on the dynamic behaviour of a head actuator in hard disk drives
Authors: Gao P , Xu L , Lin R , Tan H
Published: October 2002

Vibration/dynamics studies have become increasingly important in the mechanical design of hard disk drives (HDDs) owing to the ever-growing demand for greater storage density and access speed. In fact, it is anticipated that it is the vibration/dynamic characteristics of HDD assemblies that will eventually pose a design limit on their performance, not the associated electronics whose designs are far more advanced. In this study, finite element analysis is used to model and investigate the dynamic behaviour of a head actuator with consideration of the effect of pivot assembly. Then, an experimental method for measuring the vibration/dynamics of the head actuator is developed using the Ometron VPI laser sensor system. The representative vibration modes that limit the servo bandwidth are identified and analysed. The effect of pivot assembly on the vibration modes of the head actuator is studied under different conditions. From the results of numerical analysis and experimental demonstration, it is shown that pivot assembly is an important factor that limits the servo bandwidth and access speed of the head actuator. Based on these studies, a new passive damping structure, which is attached to the housing of the pivot assembly, is proposed, and its feasibility for improving the dynamic behaviour of the head actuator is theoretically proved.
Fuzzy control of a three-tank system
Authors: Pham D T , Li D
Published: October 2002

Fuzzy inverse reasoning performed using fuzzy relational equations can be employed to deduce control actions appropriate for a desired process output. The three-tank plant to be controlled has two inputs and hence the fuzzy relational equation describing the dynamics of the plant is a two-decision variable equation. Algorithms are only available for solving equations that have a single decision variable. A method is proposed in this paper to decompose the two-decision-variable fuzzy relational equation into single-decision-variable equations so that existing algorithms can be applied to produce control actions for the plant.
A method to determine the dynamic load distribution in a chain drive
Authors: Troedsson I , Vedmar L
Published: October 2002

This paper presents a method to calculate the forces in a chain and, thus, the resulting load distribution along the sprockets in a chain transmission working at a moderate or high speed. When the chain drive is loaded, the rollers that contact the sprockets will move along the flanks to different height positions. There are mainly two different ways to determine the actual positions: to assume the positions or to use force equilibrium and to calculate the positions. To find the correct solution the geometry and the force equilibrium are used which will give each roller's position, along the flank. This method demands knowledge of all parts of the chain, even the slack part. Therefore it has been necessary to model both the connecting tight and the slack spans in which power between the two sprockets is transmitted. The gravitational force acting at the chain has been included in the complete model so that the position of the rollers and the forces in the links at the slack span can be calculated. The elastic deformation in the chain has also been included. The moment of inertia in the two sprockets and in the outer geometry has been taken into account, but not the inertia forces in the chain.
Exact solution for time exponentially varying pulsed laser heating: Convective boundary condition case
Authors: Kalyon M , Yilbas B S
Published: October 2002

Laser heating offers considerable advantages over conventional methods. The closed-form solution for the temperature rise in the substrate during the laser heating process gives insight into the physical phenomena involving during the heating process and the material response to a laser heating pulse. In the present study, the exact solution for the temperature rise due to a time exponentially varying pulse and convective boundary condition at the surface is obtained. The closed-form solution to the solutions available in the literature for a step input intensity pulse with a convective boundary condition at the surface as well as a time exponentially varying pulse with a non-convective boundary condition at the surface is deduced. A Laplace transformation method is used in the analysis. In order to account for a pulse resembling a typical laser pulse, an intensity function resulting in exponentially increasing and decaying intensity distribution is employed in the source term in the governing transport equation. The effects of the pulse parameters β′, β′/γ′ and Biot number Bi on the resulting temperature profiles are presented and the material response to a pulse profile resembling a typical actual laser pulse is discussed. It is found that the closed-form solution obtained in the present study becomes identical with those presented in the previous studies for different pulse and boundary conditions. Moreover, the coupling effect of pulse parameter β and Bi is significant for the temperature rise at the surface.
New developments in the design and generation of gear drives
Authors: Litvin F. L. , Fuentes A , Demenego A , Vecchiato D , Fan Q
Published: October 2002

Design, generation and simulation of the meshing and contact of gear drives with favourable bearing contact and reduced noise are considered. The proposed approach is based on replacement of the instantaneous line of contact of tooth surfaces by point contact and on application of a predesigned parabolic function of transmission errors that is able to absorb linear discontinuous functions of transmission errors caused by misalignment. Basic algorithms for analysis and synthesis of gear drives are presented. The developed theory is applied for design and generation of the following gear drives with modified geometry:

(a) spur and helical gears,

(b) a new version of Novikov-Wildhaber (N-W) helical gears,

(c) asymmetric face gear drives with a spur pinion,

(d) formate-cut spiral bevel gears.

Generation of the tooth surface of a worm gear is presented as the formation of a two-branch envelope. The discussed topics are illustrated with examples.
Effect of the gear finishing process on bending fatigue crack initiation and propagation in spur gears
Authors: Hidayetoglu T. K.
Published: October 2002

The depth and stress levels of residual stress profiles are a major concern in carburized components such as transmission gears. Residual stress profiles are, among other factors, a function of the gear steel composition, the carburizing process and the gear finishing process. One of the goals of the finishing process in gears is to obtain a certain level of toughness in the gear teeth to reduce and/or eliminate bending and contact fatigue failures. This article presents a comparison of the characteristics of bending fatigue crack initiation in cubic boron nitride (CBN)-ground only and CBN-ground and shot-peened gears during single-tooth bench testing, and also a comparison of the characteristics of bending fatigue crack initiation in shot-cleaned only and CBN-ground only gears during single-tooth bench testing. The gear steel used in this study was SAE 8620/22.
Contact and elastohydrodynamic analysis of worm gears Part 1: Theoretical formulation
Authors: Sharif K. J. , Kong S , Evans H. P. , Snidle R. W.
Published: October 2002

The paper presents the theoretical basis for modelling the contact conditions and elastohydrodynamic lubrication (EHL) of worm gears, the results of which are presented in Part 2. The asymmetric elongated contact that typifies worm gears is non-Hertzian and is treated using a novel three-dimensional elastic contact simulation technique. The kinematic conditions at the EHL contact are such that the surfaces have a slide-roll ratio equal to almost 2, and the sliding direction varies over the contact area. These considerations require a non-Newtonian, thermal analysis, and the appropriate form of a novel Reynolds equation is developed that can incorporate any form of the non-Newtonian relationship between shear stress and strain rate. A form that incorporates both limiting shear stress and Eyring shear thinning is utilized in which the two effects can be included both singly or together.
Central burst defect analysis of the wire-drawing process using an accumulated damage parameter
Authors: Phelan P , Brandon J , Hillery M
Published: October 2002

The paper reviews the theoretical and empirical basis for predicting central burst defects in wire drawing under varying die semi-angle conditions. These are used to develop a numerical modelling approach, which results in an accumulated damage criterion to predict material instability. The predictions from the resulting theoretical model are consistent with previous experimental and theoretical studies in the literature.
Fault detection and tolerance in synchronous vibration control of rotor—magnetic bearing systems
Authors: Sahinkaya M N , Cole M O T , Burrows C R
Published: October 2002

The use of magnetic bearings in rotating machinery provides contact-free rotor support, and allows vibration control using both closed-loop and open-loop strategies. One of the simplest and most effective methods to reduce synchronous lateral vibration when using magnetic bearings is through an open-loop adaptive control technique, in which the amplitude and phase of synchronous magnetic control forces are adjusted automatically to minimize the measured vibrations along the rotor. However, transducer malfunction, or faults in the signal-processing channels, may cause the controller to adapt incorrectly, with unwanted and possibly catastrophic effects. It is shown that an extension to the control strategy, which utilizes the variances of the measured system response and identified parameters, enables the faults to be detected and accounted for so that a modified control action can achieve continued and effective control of the synchronous vibration. The approach is extended further to identify changes in external factors, such as unbalance and rotor dynamics. Various faults and perturbations are examined experimentally, and the ability of the controller to detect and compensate for these changes is demonstrated.
Sir Robert Stawell Ball and methodologies of modern screw theory
Authors: Lipkin H , Duffy J
Published: October 2002

The theory of screws was largely developed by Sir Robert Stawell Ball over 100 years ago to investigate general problems in rigid body mechanics. Nowadays, screw theory is applied in many different but related forms including dual numbers, Plilcker coordinates and Lie algebra. An overview of these methodologies is presented along with a perspective on Ball. Screw theory has re-emerged after a hiatus to become an important tool in robot mechanics, mechanical design, computational geometry and multi-body dynamics.
Application of screw theory to lumped-parameter modelling of elastically coupled rigid bodies
Authors: Fasse E D
Published: October 2002

This work considers the problem of modelling elastically coupled rigid bodies, with application to modelling and computer simulation of spatial, flexural mechanisms. Two modelling methods are presented, both of which use elements of screw theory and dual number calculus. The potential utility of the methods is demonstrated by simulating the behaviour of a complex spatial, flexural mechanism.
An initial investigation into the geometrical meaning of the (pseudo-) inverses of the line matrices for the edges of platonic polyhedra
Authors: Lee J , Duffy J , Rooney J
Published: October 2002

It is well known that there are five regular (Platonic) polyhedra: the tetrahedron, the hexahedron (cube), the octahedron, the icosahedron and the dodecahedron. Each of these polyhedra has an associated dual polyhedron which is also Platonic. By considering the Platonic polyhedra to be constructed from lines, and then representing the lines in terms of both ray and axis coordinates, a further aspect of this duality is exposed. This is the duality of poles and polars associated with projective configurations of points, lines and planes. This paper shows that a line matrix may be constructed for any regular polyhedron, in such a way that its columns represent the normalized ray coordinates of the edges of the polyhedron. The (pseudo-) inverse of this line matrix may then be constructed, the rows of which represent the normalized axis coordinates of the corresponding dual polyhedron.
Equilibrium and diffusion equations using cylindroidal coordinates
Authors: Dooner D B
Published: October 2002

Presented is a system of curvilinear coordinates based on a cylindroid. Cartesian, cylindrical and spherical coordinates are special scenarios that emerge from a system of cylindroidal coordinates. A system of cylindroidal coordinates was originally proposed to parameterize toothed bodies or generalized hyperboloidal gear elements, and consequently certain fundamental relations for conjugate hyperboloidal pitch surfaces in mesh are presented. Two applications of cylindroidal coordinates are presented. The first application addresses the equilibrium equation and the second application addresses the diffusion equation for a differential cylindroidal element. It is demonstrated that the developed diffusion equation degenerates into established diffusion relations for cylindrical, spherical and Cartesian coordinates.
An optimal design of axial-flow fan blades by the machining method and an artificial neural network
Authors: Lin B-J , Hung C-I , Tang E-J
Published: October 2002

The geometry design and machining of blades for axial-flow fans are important issues because the twisted profile and flowfield of blades are complicated. The rapid design of a blade that performs well and satisfies machining requirements is one of the goals in designing fluid machinery blades. In this study, an integrated approach combining computational fluid dynamics (CFD), an artificial neural network, an optimization method and a machining method is proposed to design a three-dimensional blade for an axial-flow fan. From the machining point of view, the three-dimensional surface geometry of a fan blade can be defined as the swept surface of the tool path created by using the generated machining method. By taking advantage of its powerful learning capability, a back-propagation artificial neural network is used to set up the flowfield models and to forecast the flow performance of the axial-flow fan. The desired optimal blade geometry is obtained by using a complex optimization method.
The effect of laser processing parameters on the particulate generated during the cutting of thin mild steel sheet
Authors: Lobo L , Williams K , Tyrer J R
Published: October 2002

Monitoring of the particles formed during carbon dioxide laser cutting of thin (2 mm) mild steel plate was undertaken to investigate the effect of processing parameters and melt removal mechanisms on the cut quality. The airborne particles (< 40 μm) formed during cutting were captured and the particle diameter distribution was measured using a laser diffraction method and examined using scanning electron microscopy (SEM) analysis. The particles formed were spherical and found to range from micrometres to millimetres in diameter with a monomodal distribution for the airborne fraction. It was found that the airborne micrometre particle diameter range had a mean particle diameter that was directly related to the process quality measurands of cut edge surface finish, cut width and heat-affected zone (HAZ) width.
Elasticity solution for thick laminated anisotropic cylindrical panels under dynamic load
Authors: Alibiglu A , Shakeri M , Eslami M R
Published: October 2002

The dynamic response of an axisymmetric arbitrary laminated anisotropic cylindrical panel subjected to asymmetric load is studied on the basis of three-dimensional elasticity equations. The shell panel has a great length and is simply supported at both edges. The highly coupled partial differential equations (PDEs) are reduced to ordinary differential equations (ODEs) with variable coefficients by means of trigonometric function expansion in circumferential directions. The resulting OPEs are solved by Galerkin's finite element method. Numerical examples are presented for 45°/-45° and 45°/-45°/45° laminations under dynamic load. Finally, the results are compared with published results.
A mathematical model of the rotor profile of the single-screw compressor
Authors: Yang S-C
Published: October 2002

This paper presents a method for determining the basic profile of a single-screw compressor including a gate rotor and a screw rotor. The inverse envelope concept for determining the cutting-edge curve of the gate rotor is presented. Based on this concept, the required cutter for machining the screw rotor can be obtained by an envelope of the one-parameter family of obtained screw rotors. The obtained screw rotor is an envelope of the family of gate rotor surfaces. Let the obtained envelope of the one-parameter family of gate rotor surfaces become the generating surface. The inverse envelope can be used to obtain the envelope of the family of generating surfaces. Then, the profile of the gate rotor with the cutting-edge curve can be easily obtained. The proposed method shows that the gate rotor and the screw rotor are engaged along the contact line at every instant. This is essential to reduce the effect of leakage on compressor performance. In this paper, a mathematical model of the meshing principle of the screw rotor with the gate rotor is established. As an example, the single-screw compressor for a compressor ratio of 11:6 is determined with the aid of the proposed mathematical model. Results from these mathematical models should have applications in the design of single-screw compressors.
The effect of a concentrated mass on the modal characteristics of a rotating cantilever beam
Authors: Yoo H H , Seo S , Huh K
Published: October 2002

Modal characteristics of rotating cantilever beams with a concentrated mass located in an arbitrary position are investigated in this paper. Equations of motion are derived by employing hybrid deformation variables. The resulting equations are linear but capture the stiffening effect induced by the rotational motion of the beam. For modelling of the concentrated mass, use is made of the Dirac delta function, which avoids increasing the degrees of freedom of the system. The resulting equations of motion are transformed into dimensionless forms in which four dimensionless parameters are identified. The effects of the dimensionless parameters on the modal characteristics of the rotating beams are examined through numerical study. It is found that the magnitude and the location of the concentrated mass significantly influence the modal characteristics of the rotating beam.
Transient elastohydrodynamic lubrication analysis of ultra-high molecular weight polyethylene hip joint replacements
Authors: Jalali-Vahid D , Jin Z M
Published: October 2002

The cyclic variation in both the load and speed experienced during walking was considered in an elastohydrodynamic lubrication (EHL) analysis for artificial hip joint replacements in this study. A general numerical procedure was developed to take both the entraining and squeeze-film actions into the solution of the Reynolds equation in the spherical ball-in-socket coordinate, simultaneously with the elasticity equation, using the Newton-Raphson method. The numerical procedure developed was then applied to an example of hip joint replacements employing an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup against either a metallic or ceramic femoral head under simplified cyclic load and speed conditions. The predicted minimum film thickness was found to stay remarkably constant, despite a large change in the angular velocity and the load. This was attributed to the combined effect of entraining and squeeze-film actions in generating, replenishing and maintaining the lubricating film in artificial hip joint replacements. Furthermore, it was pointed out that the average transient minimum film thickness predicted throughout one cycle was very close to that under quasi-static conditions based upon the average angular velocity and load.
Large deflection of elastoplastic, non-linear strain-hardening cantilevers
Authors: Huang X , Wang B , Lu G , Yu T X
Published: October 2002

This paper concerns the large deflection of elastoplastic, non-linear strain-hardening cantilevers of rectangular cross-section, for which the stress-strain relationship after yielding is described by σ= K1εq. Both the bending moment and axial force are included in the yielding criterion, and the corresponding strain increments obey the associated normality rule. Comparisons between the experimental data and the theoretical predictions are made for mild steel cantilevers subjected to a tip force with an inclined angle ϕ = 67.5,90 and 157° respectively. Reasonable agreement is obtained. The theoretical analysis has described the large deflection behaviour of the cantilever and is in good agreement with tests.
Analysis of two-phase ejectors with Fabri choking
Authors: Lear W E , Parker G M , Sherif S A
Published: October 2002

A one-dimensional mathematical model was developed using the equations governing the flow and thermodynamics within a jet pump with a mixing region of constant cross-sectional area. The analysis is capable of handling two-phase flows and the resulting flow phenomena such as condensation shocks and the Fabri limit on the secondary mass flowrate. This work presents a technique for quickly achieving first-approximation solutions for two-phase ejectors. The thermodynamic state of the working fluid, R-134a for this analysis, is determined at key locations within the ejector. From these results, performance parameters are calculated and presented for varying inlet conditions. The Fabri limit was found to limit the operational regime of the two-phase ejector because, in the two-phase region, the speed of sound may be orders of magnitude smaller than in a single-phase fluid.
Simplified characteristics of active magnetic bearings
Authors: Peel D J , Bingham C M , Wu Y , Howe D
Published: October 2002

Traditionally, active magnetic bearing (AMB) systems are designed as an integral component of machines having generally complex dynamic characteristics. An AMB supported rotor has been tested over a speed range that included system natural vibration frequencies. A linear stiffness and viscous damping AMB characteristic with constant coefficients was identified which was independent of the overall system characteristics and which can thus provide simple and transferable data for a machine designer.
Electric defrosting analysis of a finned-tube evaporator coil using the enthalpy method
Authors: Alebrahim A M , Sherif S A
Published: October 2002

When moist air comes into contact with a surface maintained at a subfreezing temperature, which is also below the dew-point temperature of water vapour in air, frost will form. Although this frost formation process is associated with a temporary increase in the heat transfer rate in the initial stages of deposition, the overall thermal performance over an extended period of time is degraded due to the insulating effect of the frost and also due to blockage of the coil and the accompanying reduction in air flow. One method of defrosting employs electric heat to melt the frost of the coil. This paper describes how the enthalpy method can be used to calculate the defrosting time and the temperature distribution in the frost layer during the defrosting process of a finned-tube evaporator coil. While the analysis presented applies mainly to electric defrosting, the method can be easily modified to handle different defrosting methods and processes.
Chaotic behaviour identification of a rub-impact rotor using short-term predictability of measured data
Authors: Hu N Q , Wen X S
Published: October 2002

Based on short-term predictability of a chaotic time series, this paper presents a new method for chaotic behaviour identification of a rub-impact rotor from measured data. The method is composed of two steps: in the first step, the phase space was reconstructed from measured data. Local prediction of the time series was performed in the second step with local fitting. Short-term predictability can be used to identify the chaotic property of the time series characterizing dynamic behaviour of the rub-impact rotor. The result of a local prediction is consistent with that of the correlation dimension and largest Lyapunov exponent estimated from measured data. The study shows that short-term predictability via local prediction can effectively identify chaos of a rub-impact rotor. The proposed method is simple, straightforward and suitable for real-time application.
Car—caravan snaking: Part 1: The influence of pintle pin friction
Authors: Sharp R S , Fernández M A Alonso
Published: October 2002

A brief review of knowledge of car-caravan snaking is carried out. Against the background described, a fairly detailed mathematical model of a contemporary car-trailer system is constructed and a baseline set of parameter values is given. In reduced form, the model is shown to give results in accordance with literature. The properties of the baseline combination are explored using both linear and non-linear versions of the model. The influences of damping at the pintle joint and of several other design parameters on the stability of the linear system in the neighbourhood of the critical snaking speed are calculated and discussed. Coulomb friction damping at the pintle pin is then included and simulations are used to indicate the consequent amplitude-dependent behaviour. The friction damping, especially when its level has to be chosen by the user, is shown to give dangerous characteristics, despite having some capacity for stabilization of the snaking motions. It is concluded that pintle pin friction damping does not represent a satisfactory solution to the snaking problem. The paper sets the scene for the development of an improved solution. This involves actively braking the caravan wheels, which is treated in Part 2 of the paper.
A novel robot hand with embedded shape memory alloy actuators
Authors: Yang K , Gu C L
Published: October 2002

This paper describes the development of an active robot hand, which allows smooth and lifelike motions for anthropomorphic grasping and fine manipulations. An active robot finger 10mm in outer diameter with a shape memory alloy (SMA) wire actuator embedded in the finger with a constant distance from the geometric centre of the finger was designed and fabricated. The practical specifications of the SMA wire and the flexible rod were determined on the basis of a series of formulae. The active finger consists of two bending parts, the SMA actuators and a connecting part. The mechanical properties of the bending part are investigated. The control system on the base of resistance feedback is also presented. Finally, a robot hand with three fingers was designed and the grasping experiment was carried out to demonstrate its performance.
Action aggregation and defuzzification in Mamdani-type fuzzy systems
Authors: Pham D T , Castellani M
Published: October 2002

This paper discusses the issues of action aggregation and defuzzification in Mamdani-type fuzzy systems. The paper highlights the shortcomings of defuzzification techniques associated with the customary interpretation of the sentence connective ‘and’ by means of the set union operation. These include loss of smoothness of the output characteristic and inaccurate mapping of the fuzzy response. The most appropriate procedure for aggregating the outputs of different fuzzy rules and converting them into crisp signals is then suggested. The advantages in terms of increased transparency and mapping accuracy of the fuzzy response are demonstrated.
Design optimization of large-scale structures with sequential linear programming
Authors: Lamberti L , Pappalettere C
Published: October 2002

Design optimization of complex structures entails tasks that oppose the usual constraints on time and computational resources. However, using optimization techniques is very useful because it allows engineers to obtain a large set of designs at low computational cost. Among the different optimization methods, sequential linear programming (SLP) is very popular because of its simplicity and because linear solvers (e.g. Simplex) are easily available. In spite of the inherent theoretical simplicity, well-coded SLP algorithms may outperform more sophisticated optimization methods.

This paper describes the experience obtained in the design optimization of large-scale truss structures and beams with SLP-based algorithms. Sizing and configuration problems of structures under multiple loading conditions with up to 1000 design variables and 3500 constraints are considered. The relative performance and merits of some SLP-based algorithms are compared and the efficiency of an advanced SLP-based algorithm called ILEAML (improved linearization error amplitude move limits) is tested. ILEAML is also compared to the sequential quadratic programming (SQP) method, which is considered by theoreticians as probably the best theoretically founded optimization technique.
Theoretical investigation into the modelling of a flexible beam with drive-line compliance
Authors: Purdy D J
Published: October 2002

A comparison is made between the dynamics of three possible models for a flexible link and drive-line as used in some robotic or weapons systems. The three models considered are: model 1, a flexible link with compliance in the drive-line; model 2, flexible link with direct drive; and model 3, rigid link with drive-line compliance (flexible joint). Non-dimensional parameters are suggested for the models and comparisons are made between them, by examining the transfer functions poles (resonances) and zeros (anti-resonances). From the study, recommendations are made as to the suitability of the three models for different applications.
Transient heat transfer modelling in automotive exhaust systems
Authors: Konstantinidis P A , Koltsakis G C , Stamatelos A M
Published: October 2002

Transient heat transfer computations in automotive exhaust systems are increasingly employed in the design and optimization phases. The complex geometry of the exhaust line and the special flow conditions complicate the problem of accurately estimating several important heat transfer parameters. This paper initially summarizes the current status of knowledge regarding heat transfer phenomena in automotive exhaust systems. A comprehensive transient computer model covering all exhaust piping configurations (single wall, double wall with air gap or insulation) is presented. A novel solution procedure is proposed, resulting in significant savings in processing time. Two-dimensional heat transfer in connecting flanges is also accounted for. The model is validated with the help of full-scale measurements on vehicles. Examples are presented, illustrating the application of the model in the comparative assessment of different exhaust configurations. In conjunction with existing models, which simulate the operation of three-way catalytic converters and of other exhaust gas after-treatment devices, the model can be integrated in a CAE (computer aided engineering) package for the support of exhaust system design optimization.
Particle image velocimetry: A review
Authors: Grant I
Published: October 2002

The evolution of particle image velocimetry (PIV) from its various roots is discussed. The importance of these roots and their influence on different trends in the speciality are described. The state-of-the-art of the technique today is overviewed and illustrated by reference to recent, seminal publications describing both the development and application of PIV.
Dynamic deflection of a cracked beam with moving mass
Authors: Parhi D R , Behera A K
Published: October 2002

An analytical method along with the experimental verification have been utilized to investigate the vibrational behaviour of a cracked beam with a moving mass. The local stiffness matrix is taken into account when analysing the cracked beam. The Runge—Kutta method has been used to solve the differential equations involved in analysing the dynamic deflection of a cantilever beam.