bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of non-linear systems using wavelets
Authors: Staszewski W J
Published: October 2002

Analysis of non-linear systems is an essential part of engineering structural dynamics. A number of methods have been developed in recent years. Classical Fourier-based methods have been extended to the use of phase plane, combined time-frequency, time-scale approaches and multidimensional spectra. This paper is an attempt to collate in one place some of the recent advances in wavelet analysis for the study of non-linear systems. This includes methods related to system identification based on wavelet ridges and skeletons, damping estimation procedures, wavelet-based frequency response functions, cross-wavelet analysis, self-similar signals, coherent structures and chaos.
The theoretical development of wavelets in reacting flows
Authors: Prosser R , Cant R S
Published: October 2002

This paper focuses on the simulation of turbulent reacting flows via recent developments in wavelet-based analyses. The unique data compression properties of wavelet methods render them especially attractive for such simulations, in which the length and time-scales of interest originate from both physical and chemical processes and may span several orders of magnitude. The particular difficulties encountered when representing reacting flow problems on non-periodic domains, and how these difficulties have led to the adoption of a biorthogonal wavelet framework, are discussed. This leads to consideration of interpolating wavelet transforms based on second-generation wavelets, for which a fast transform algorithm is presented. Issues raised by the application of wavelet transform methods to the reacting Navier-Stokes equations, including the calculation of differential operators, the extension to two and three dimensions and the evaluation of non-linear terms, are examined. The implications of the wavelet approach for the representation of the turbulent energy cascade are explored briefly. Finally, some future directions for research into the extension of wavelet analysis as an underpinning technology for computational fluid dynamics are indicated.
Regenerator thermal design in a nutshell
Authors: Organ A J
Published: October 2002

For the thermal regenerator having high thermal capacity ratio an intuitive approach defines the fluid temperature envelope with a minimum of algebra. An expression for temperature recovery ratio follows. This is checked against the specification and operating conditions of the MP-1002CA air engine. The new formulation is the basis for an analytical statement of the regenerator operating at the optimum balance between pumping loss and penalty of incomplete temperature recovery.
The dynamics of a vibrating silicon diaphragm microgyroscope
Authors: Burdess J S , Harris A J , Wood D , Cruickshank J L
Published: October 2002

This paper describes the principal features of a microgyroscope bulk machined from a [100] silicon wafer by chemical etching. The equations of motion of the gyroscope are derived and the factors that determine both the mechanical and electrical characteristics of the device are identified. The response to constant and harmonic rates of turn is evaluated for both tuned and untuned gyros. Gyro performance is shown to depend upon the relationship between the mistuning of the primary and secondary modes and the secondary mode damping factor.
Experiments on the prediction of unbalance changes in rotating machines
Authors: Ding J J
Published: October 2002

This paper presents sensitivity analyses of a numerical method for the prediction of multiplane unbalance changes in multibearing rotating machines. Experiments were conducted on a four-bearing rotating machine where the journal-to-bearing displacements were collected for rotational speed of 3000 r/min. These displacements were used to obtain the corresponding velocities. The displacements and velocities were integrated in the time domain by using Reynolds’ generalized equation to obtain the time-dependent hydrodynamic forces. All the signals were processed to study the sensitivities of the proposed method to different noise levels and different experimental data. The results showed promising future practical applicability.
Newtonian and non-Newtonian viscous flows in nozzles
Authors: McNeil D A , Addlesee A J , Stuart A
Published: October 2002

A study of laminar, Newtonian and non-Newtonian fluids in nozzles has been undertaken. A theoretical model, previously deduced for Newtonian flows in expansions, was developed for Newtonian and non-Newtonian flows in nozzles. The model is based on a two-stream approach where the momentum and kinetic energy stored in the velocity profile of the fluid is altered by an area change of one stream relative to the other. The non-Newtonian liquids investigated were shear thinning. The model was used to investigate these non-Newtonian fluids and to justify the use of simpler, more approximate equations developed for the loss and flow coefficients. The model is compared favourably with data available in the open literature.
Heat conduction through irregularly spaced plane strip contacts
Authors: Manners W
Published: October 2002

Solutions are developed for the conductive heat flow in the xy plane where there is a uniform flow at infinite values of y, and where y = 0 represents the interface between two materials. This interface consists of an arbitrary pattern of perfectly conducting strips and non-conducting gaps. It is assumed that thermoelastic effects are negligible. The solution takes the form of an equation with one unknown parameter per gap, and these unknowns can be found by a simple solution process involving numerical integration. The effective resistance of the interface can then be determined by a simple numerical integration.
Impact behaviour of elastoplastic spheres with a rigid wall
Authors: Li L-Y , Thornton C , Wu C-Y
Published: October 2002

The paper presents a numerical study of the normal impact of elastoplastic spheres with a rigid wall. The analysis is performed by employing DYNA2D, a non-linear, explicit, two-dimensional finite element (FE) code for impact mechanics. Deformations, time evolution of the contact force and contact force-displacement relationships during the impact are presented. Influences of material behaviour are discussed and their effect on the coefficient of restitution is also demonstrated.
On axisymmetric free vibrations of a thin disc-rod structure
Authors: Pham D C
Published: October 2002

A simple asymptotic formula for the principal natural frequency of a thin disc-rod structure with variable material and geometric characteristics of the rod is constructed.
Integrated diagnostic/prognostic tools for small cracks in structures
Authors: McDowell D. L. , Clayton J. D. , Bennett V. P.
Published: October 2002

An integrated system for diagnosis of the ‘health’ of a structural component subjected to high-cycle fatigue (HCF) consists of sets of embedded or emplaced sensors at various locations, extracting information related to the generation of material defects, the presence of crack-like discontinuities and their progression and changes in system dynamics that may relate to this progression. Conceptually, signals from these sensors are fed into a processing environment that can project deleterious conditions related to the onset of loss of function or propagation of cracks to critical dimensions. Since the idea is to monitor the gradual changes of component performance and various local related indices before catastrophic failure to enable the operator to respond with a maintenance hold, it is essential to couple the diagnostics with prognostic capability; this facilitates a prediction of how much time remains within the window of viable servicing or repair. In the HCF regime, the dominant fraction of total fatigue life may be spent at crack lengths of the order of 20-500 um. The detection of longer cracks near the end of component life is critical since component failure may lead to failure of the overall structure. This necessitates the identification of (a) algorithms for identifying component ‘hot spots’ where failure is likely to occur, (b) development of appropriate crack growth laws for cracks of different length scales, ranging from the order of grain size to the order of component dimensions, including consideration of contacting components (fretting fatigue) and environmental effects and (c) development of algorithms for identifying the progression of component degradation on the basis of multiple-sensor inputs at different time and length scales, providing feedback to support cause for maintenance shutdown. This paper discusses each of these issues.
Mechanisms of fatigue crack initiation in annealed, quenched and tempered 4340 steel
Authors: Yang F , Saxena A
Published: October 2002

The mechanisms of fatigue crack initiation in annealed and quenched and tempered 4340 steel were characterized. Several axial fatigue specimens were tested at a strain range of 1.5 per cent to various fractions of fatigue life. The tested specimens were thoroughly examined using a scanning electron microscope (SEM) and an atomic force microscope (AFM). The latter technique provides a better resolution and is also capable of providing quantitative surface topographical information.

In annealed 4340 steel, the initial fatigue damage is shown to accumulate in the form of steps between ferrite and cementite laths in the pearlitic microstructure. Subsequent damage accumulation occurs by formation of slip bands which are formed by joining several adjoining steps. Cracks initiate from the slip bands. In quenched and tempered steels, the fatigue damage accumulates at discontinuities at a more rapid rate than in the remaining regions of the specimen, leading to crack initiation and growth emanating primarily from the discontinuities. The roughness of the specimen surface increases with fatigue damage in both microstructures, as demonstrated from the measurements obtained from AFM studies. Such correlations may be useful in predicting the remaining life of cyclically loaded structural components.
Diagnostics and prognostics of a single surface defect on roller bearings
Authors: Li Y , Zhang C , Kurfess T. R. , Danyluk S , Liang S. Y.
Published: October 2002

Bearing condition monitoring has been the focus of a wide range of studies over the past years. Current monitoring techniques that focus on the identification of faults present in a bearing have various limitations. Typically they are applicable only under well-defined, specific and pre-calibrated operating conditions, thereby preventing continuous monitoring of a system operating in a variant environment. They are often limited in damage severityestimation and prognostic capability. This, in turn, prevents the development of optimal maintenance scheduling in favour of overall system safety and productivity. Research presented in this paper has yielded results that have extended bearing diagnostics and prognostics to address these limitations and to achieveoptimal machinery maintenance scheduling. This paper discusses the current research status on the development of a new signal processing method with noise cancellation capability to provide early defect detection, the establishment of a diagnostic model to estimate bearing defect severity under variant conditions and the formulation of an adaptively tuned defect propagation model to track thetime-variant nature of defect growth for the forecasting of bearing remaining utility.
An in situ modal-based method for structural dynamic joint parameter identification
Authors: Shamine D M , Hong S W , Shin Y C
Published: October 2002

The present paper proposes an in situ modal parameter-based method for determining the dynamic joint characteristics of mechanical systems. The proposed method uses the mass, damping and stiffness matrices of the structure, calculated by the finite element method (FEM), along with measured eigenvectors and eigenvalues of the actual system. While the modal parameters at the joint must be known in order to identify the structural joint dynamic characteristics, it is often impossible to measure the response of the system directly at the joint location. To overcome this problem and eliminate the errors associated with using measurements close to the joints, an alternative indirect estimation scheme is used to determine the complete set of eigenvectors, and thus the eigenvector component corresponding to the joint location is extracted. Therefore, the proposed method allows in situ joint parameter identification. The efficiency of this method is validated by simulations with different mechanical systems, and the robustness is also demonstrated with errors introduced into the estimated eigenvectors. Finally, the method is implemented for experimental identification of the joint parameters of an actual spindle system.
Wave transformation by a vertical barrier between a single-layer fluid and a two-layer fluid
Authors: Lee M M , Chwang A T
Published: October 2002

The reflection and transmission of water waves by a vertical barrier between a homogeneous fluid and a two-layer fluid are investigated for two different types of barrier: type I is a surface-piercing barrier and type II a bottom-standing barrier. For a type I barrier, the lower-layer fluid is the same as the homogeneous fluid and has a higher density than that of the upper-layer fluid. For a type II barrier, the upper layer fluid is the same as the homogeneous fluid and has a lower density than that of the lower-layer fluid. For any given finite thickness of the fluid layers, a hydrostatic equilibrium state exists. Incident progressive waves can then be transmitted through the gap beneath or above the barrier. By using the linear wave theory and eigenfunction expansions, these boundary value problems are solved by a suitable application of the least-squares method. The definitions of the corresponding reflection and transmission coefficients are introduced in each case. For the two-layer fluid, there are two different wave modes: the surface (barotropic) and interfacial (baroclinic) wave modes. It is found that water waves, propagating either from the homogeneous or from the two-layer fluid, are partially reflected or transmitted and produce simultaneously both modes of water waves in the two-layer fluid.
Linear and non-linear potential-flow calculations of free-surface waves with lift and induced drag
Authors: Janson C-E
Published: October 2002

A potential-flow panel method is used to compute the waves and the lift force from surface-piercing and submerged bodies. In particular the interaction between the waves and the lift produced close to the free surface is studied. Both linear and non-linear free-surface boundary conditions are considered. The potential-flow method is of Rankine-source type using raised source panels on the free surface and a four-point upwind operator to compute the velocity derivatives and to enforce the radiation condition. The lift force is introduced as a dipole distribution on the lifting surfaces and on the trailing wake, together with a flow tangency condition at the trailing edge of the lifting surface. Different approximations for the spanwise circulation distribution at the free surface were tested for a surface-piercing wing and it was concluded that a double-model approximation should be used for low speeds while a single-model, which allows for a vortex at the free surface, was preferred at higher speeds. The lift force and waves from three surface-piercing wings, a hydrofoil and a sailing yacht were computed and compared with measurements and good agreement was obtained.
Highly oscillatory properties of unsteady ship waves
Authors: Chen X-B
Published: October 2002

The singular and highly oscillatory properties of unsteady ship waves are studied by considering potential flows generated by a point source pulsating and advancing at a uniform forward speed located close to or at the free surface. The wave component of the free-surface potential defined by Noblesse and Chen by a single integral along the dispersion curves defined by the dispersion relation is analysed by developing asymptotic expansions of the open dispersion curves at large wave numbers. The asymptotic analysis of the wave component contributed by the leading asymptotic term of a parabolic form shows that unsteady ship waves are highly oscillatory with infinitely increasing amplitude and infinitely decreasing wavelength, when a field point approaches the track of the source point at the free surface. The highly oscillatory property and complex singular behaviour of unsteady ship waves are further expressed in an original and analytically closed form.
Numerical simulation of internal tides
Authors: Martins H , Santos A , Coelho E F , Neves R , Rosa T
Published: October 2002

This work compares the numerical results of a three-dimensional hydrodynamic baroclinic model and a known analytical solution due to Baines of the baroclinic lunar semidiurnal (M2) tidal propagation over the continental shelf. The simplifying numerical approaches are the Boussinesq and the hydrostatic hypothesis. The hydrostatic pressure restricts the use of this model to every phenomenon associated with major vertical accelerations, as is sometimes the case of internal tides near steep slopes. A comparison between the two models in the area of the continental shelf was performed for 2.5, 5 and 10 per cent shelf slopes. The results obtained are the following: (a) the linear numerical solution approaches the analytical solution for these slopes, (b) the convection terms become significant for slopes greater than 5 per cent and (c) the non-linear numerical model becomes unstable for slopes above 10 per cent, therefore requiring non-hydrostatic pressure.
Hydrodynamic analysis of flow patterns and estimation of retention time for a polluted reservoir
Authors: Yu L , Giorgetti M F
Published: October 2002

This paper presents a numerical prediction of the flow patterns in a polluted reservoir to supply the fire control water and to process water to an oil refinery. A biological treatment for improving water quality started in 1995. Although the treatment was successful in reducing organic load and bad odour, it was suspected that the locations of the inlet and outlets in the reservoir were possible causes for a short cut in the flow, which might greatly reduce the efficiency of the biological treatment. A numerical investigation to simulate and predict the fluid motion was carried out with the aim of providing quantitatively remedial approaches to perfect the biological treatment process, especially for future working conditions of increased pumping flowrate. The numerical analysis predicted the appearance of a flow short cut in the reservoir with the consequential reduction in its retention time; simulation has shown that this negative characteristic can be eliminated if the inlet and the outlets are relocated.
Characteristics of a magnetic fluid heat transport device Part 1: Numerical simulation of flow and heat transport phenomena
Authors: Yamaguchi H , Kobori I , Kobayashi N
Published: October 2002

A numerical analysis is conducted in order to study the flow state and thermal characteristics of a magnetic fluid heat transport device. A simple geometrical model of the device is considered in the present numerical study. The highly simplified marker-and-cell (HSMAC) method is adopted for the numerical analysis, where the transient solutions are obtained in the two-dimensional axisymmetric computational plane. From results of the numerical calculation it can be shown that the vortex zone appears when a magnetic field is applied and the configuration of flow associated with the vortex zone changes for variation in the magnetic field, increasing or decreasing the heat transport capability dependent upon the conditions of the device.
Isentropic recuperative heat exchanger with regenerative work transfer
Authors: Rao H V
Published: October 2002

A counter-flow heat exchanger is considered to be the ideal method for recuperative heat transfer between hot and cold fluid streams. In this paper the concept of an isentropic heat exchanger with regenerative work transfer is developed. The overall effect is a mutual heat transfer between the two fluid streams without any net external heat or work transfers. The effectiveness for an isentropic heat exchanger with regenerative work transfer is derived for the case of fluid streams with constant specific heats and it is shown that it is greater than unity. The ‘isentropic effectiveness’ of a heat exchanger is defined. The relationship between the entropy generation and effectiveness for the traditional heat exchanger is also examined and compared with that of the isentropic heat exchanger. The practical realization of isentropic operation of a heat exchanger and its possible application are briefly considered.
Design of a stabilizing controller for a ten-degree-of-freedom bipedal robot using linear quadratic regulator theory
Authors: Akdas D , Medrano-Cerda G A
Published: October 2002

This paper considers the design and evaluation of stabilizing controllers for a ten-degree-of-freedom (10 DOF) biped robot using linear quadratic optimal control techniques and reduced-order observers. The controllers are designed using approximate planar dynamical models for the sagittal and lateral planes. Experiments were carried out to test the control system when the biped robot was in the double-support phase and the robot was subject to external disturbances. Although the control system is based on single-support models, the experimental results have shown that the robot successfully kept its given posture under disturbances.
On the reverse swing of a cricket ball—modelling and measurements
Authors: Sayers A T
Published: October 2002

The phenomenon of reverse swing of the ball in a game of cricket is achieved by very few bowlers, and then only by those who seem able to bowl at speeds in excess of 85 mile/h. It also seems that reverse swing cannot be achieved at will. Rather, it is obtained perhaps by accident as much as by design, its inception being as much of a surprise to the bowler as to the batsman. This would suggest that the flow conditions pertaining to reverse swing are extremely marginal at best. This paper investigates the flow conditions required for reverse swing to occur and presents data describing the lift and drag on the ball. While some direct measurements are made on a cricket ball for comparison purposes, the flow over the ball is modelled through a 2.7:1 scale ratio sphere. This permitted relatively large lift and drag forces to be measured. The results define the range of Reynolds numbers and seam angles over which reverse swing will occur, as well as the corresponding forces on the cricket ball. Flow visualization is used to indicate the state of the boundary layer.
Design of hammer mills for optimum performance
Authors: Kosse V , Mathew J
Published: October 2002

Hammer mill manufacturers are under increasing pressure to deliver mills of high productivity with a reduced level of vibrations. However, in practice, excessive wear of the rods carrying the hammers takes place, and cracks develop in the vicinity of the holes holding the rods with the hammers, with the possibility of breakaway fracture and disastrous consequences. An increased level of vibrations has been found on many new mills. Existing design approaches have proved to be incapable of explaining this phenomenon. This paper presents a new approach to hammer mill design and enables the prevention of increased vibrations and uneven wear and, finally, provides better performance of hammer mills.
Theoretical modelling of the self-tapping screw fastening process
Authors: Seneviratne L D , Ngemoh F A , Earles S W E , Althoefer K A
Published: October 2002

The results of a theoretical study of the self-tapping screw insertion process are presented. Fundamental concepts of engineering mechanics are employed to analyse the axial torque required to complete a general self-tapping screw insertion operation. Equations for the screw insertion torque as a function of screw, hole and material properties are presented. Experimental results for torque signature signals are compared with the predictions of the theoretical model, confirming the validity of the model. The theoretical model provides a basis for developing automated monitoring and control strategies for self-tapping screw fastenings.
Inverse kinematic analysis for triple-octahedron variable-geometry truss manipulators
Authors: Xu L J , Tian G Y , Duan Y , Yang S X
Published: October 2002

In this paper, a new triple-octahedron variable-geometry truss manipulator is presented. Its inverse kinematic solutions in closed form are studied. An input-output displacement equation in one output variable is derived. The solution procedure is given in detail. A numerical example is illustrated.
Measurement of the stiffness of joints in a graphite brick assembly
Authors: Robinson A M , Drinkwater B W , Dwyer-Joyce R S , Payne J F B
Published: October 2002

Large, dry-contacting assemblies of graphite blocks are a feature of many nuclear reactors, and the seismic response of these structures is dependent on both the bulk and surface properties of the blocks. The nature of the interblockinterface will influence the load-deflection relationship of the blocks, which is important in understanding the response of the structure to seismic loading. The stiffness of this interface is dependent on surface roughness effects.

In this paper, ultrasonic reflection coefficient measurements are used to investigate the stiffness distribution of this interface under various loading conditions. A low-frequency quasi-static spring model of the interface was adopted. This allowed the interfacial stiffness to be determined as a function of applied load, frequency, surface roughness and graphite composition. Cyclical loading of the graphite-graphite interface has also been carried out. This has shown that there is only a slight plastic deformation under normal loading, and also is indicative of a degree of intersurface adhesion at the interface. Direct measurement of the load-deflection relationship of an entire brick was also carried out which, in conjunction with the ultrasonic measurements, suggests that it is the effect of macroscopic surface features rather than microscopic roughness that is the dominant interfacial contribution to brick-tilting stiffness.
Effects of misalignment on the transmission characteristics of magnetic couplings
Authors: Huang S M , Chen W L , Yau C H , Sung C K
Published: October 2002

Magnetic couplings possess no mechanical contact and permit higher assembly tolerance for transmitting torque from a primary driver to a follower by magnetic force. This paper investigates the effects of misalignment on the transmission characteristics of synchronous magnetic couplings. The misalignment can be categorized into the following three types: transverse, angular and a combination of these two misalignments. Without loss of generality, an axial synchronous magnetic coupling is adopted in the present because of its simplicity both in design and fabrication. The phenomenon and influence of shafts with assembly misalignment are described first. The mathematical model for the magnetic coupling with misalignment is then constructed for the purpose of deriving the equations governing the torque transmission and force interaction characteristics. The method of equivalent magnetic charge is employed to calculate the variations in the transmitted torque owing to each type of misalignment. Finally, a test apparatus is constructed for verifying the static and dynamic characteristics of the designed coupling under various misalignment conditions. Good agreement between numerical simulation and experimental results is obtained.
Direct evidence of lubrication in ceramic-on-ceramic total hip replacements
Authors: Smith S L , Dowson D , Goldsmith A A J , Valizadeh R , Colligon J S
Published: October 2002

A study of surface contact and separation of ceramic-on-ceramic joints was undertaken in 25 per cent bovine serum using a hip simulator. An electrical resistivity technique was used to detect the extent of surface separation throughout a complete walking cycle. The femoral and acetabular components were coated in a thin conducting film of titanium nitride to allow application of the resistivity technique to non-conducting ceramic.

Surface separation of the acetabular and femoral components was detected throughout each simulated walking cycle. Fluctuations in the applied voltage across the joint were observed which could not be attributed to elastohydrodynamic or squeeze-film lubrication effects. The probable cause of the voltage fluctuations was brief and occasional contact between the surfaces caused by a combination of asperity contact and subsequent detachment of the conductive coating.
Thermal error measurement and modelling techniques for the five-degree-of-freedom spindle drifts in computer numerically controlled machine tools
Authors: Pahk H J , Lee S W , Kwon H D
Published: October 2002

Thermally induced errors have been significant factors affecting machine tool accuracy. In this paper, the spindle thermal error is examined, where thermal error components with five degrees of freedom (DOFs) are considered. An effective measurement system has been devised for five-DOF thermal errors, consisting of gap sensors and thermocouples around the microcomputer-interfaced environment. Several thermal error modelling techniques are also implemented for the thermal error prediction: multiple linear regression, neural network, system identification methods, etc. The performance of the thermal error modelling techniques is evaluated and compared, giving the system identification method as the optimum model having the least deviation. The developed system for the thermal error measurement and modelling has been practically applied to a computer numerically controlled machining centre, and the spindle thermal errors are effectively compensated using the microcomputer-machine tool interfaced networks. The machine tool accuracy has been improved about four to five times typically.
Circular solid plate supported along an edge arc and deflected by a central transverse force
Authors: Strozzi A , Vaccari P
Published: October 2002

A purely flexural structural analysis is carried out for a thin solid circular plate, deflected by a static central transverse concentrated force, and simply supported along an edge arc, the remaining part of its periphery being free. This problem is modelled in terms of a Fredholm integral equation of the first kind, where the kernel is expressed analytically, and where the unknown function is the reaction force along the support. The initial equation is then modified into a new Fredholm integral equation of the first kind, which implicitly respects the condition imposed on the plate edge deflections by the rigidity of the support, but which has still to be coupled with the translational and rotational equilibrium conditions. By showing that a certain operator is a contraction mapping, it is demonstrated that this new integral equation coupled only with the translational equilibrium condition possesses a unique solution expressed in terms of a smooth function with square root singularities at the support ends. It is also shown that this unique solution, when expressed via Chebyshev polynomials, does not fulfil the rotational equilibrium condition, apart from the limit case when the plate is axisymmetrically supported. It is concluded that, in the framework of the purely flexural plate theory, the title problem does not possess any smooth solution with square root singularities at the ends. An approximate solution is nevertheless computed with the collocation method, by accepting limited undulations of the plate periphery.
Prediction of the forming limit diagram on the basis of the damage criterion under non-proportional loading
Authors: Chow C L , Yang X-J
Published: October 2002

Based on the theory of damage mechanics, a recently developed anisotropic plastic damage model for the prediction of forming limit diagrams (FLDs) is extended to take into account the effect of rotation of the principal damage coordinates on the deformation and damage behaviour. With the aid of the damage plastic potential, the damage evolution equations are established. A damage criterion for localized necking under arbitrary loading history is proposed. The model is employed to predict the FLDs of AL6111-T4 alloy. The predicted results agree well with those determined experimentally.
Analysis of the dynamic contact between rotating spur gears by finite element and multi-body dynamics techniques
Authors: Lee K
Published: October 2002

A numerical method is presented for the dynamic contact analysis of spur gears rotating with very high angular speeds. For each gear an elastic tooth of distributed mass is connected to a rigid disc with kinematic constraints, and finite element formulations are used for the equations of motion of the teeth. The velocity and acceleration as well as the position of the contact point sliding on the mating gear teeth are precisely computed by simultaneously using the motions of a pair of rotating tooth surfaces. The equations of motion subjected to the kinematic constraint and contact condition are solved by enforcing the velocity and acceleration constraints as well as the displacement constraint. In the numerical simulation the importance of the mass effect of gear teeth is demonstrated, and it is shown that the solution is obtained even if gears repeat contact and separation.
A non-Newtonian computational fluid dynamics study of the stencil printing process
Authors: Glinski G P , Bailey C , Pericleous K A
Published: October 2002

This paper describes the application of computational fluid dynamics (CFD) to simulate the macroscopic bulk motion of solder paste ahead of a moving squeegee blade in the stencil printing process during the manufacture of electronic components. The successful outcome of the stencil printing process is dependent on the interaction of numerous process parameters. A better understanding of these parameters is required to determine their relation to print quality and improve guidelines for process optimization. Various modelling techniques have arisen to analyse the flow behaviour of solder paste, including macroscopic studies of the whole mass of paste as well as microstructural analyses of the motion of individual solder particles suspended in the carrier fluid. This work builds on the knowledge gained to date from earlier analytical models and CFD investigations by considering the important non-Newtonian rheological properties of solder pastes which have been neglected in previous macroscopic studies. Pressure and velocity distributions are obtained from both Newtonian and non-Newtonian CFD simulations and evaluated against each other as well as existing established analytical models. Significant differences between the results are observed, which demonstrate the importance of modelling non-Newtonian properties for realistic representation of the flow behaviour of solder paste.
Minimization of transmission error in helical gears
Authors: Rao S S , Yoon K Y
Published: October 2002

A method of minimizing transmission error in helical gears is presented. Using the concept of optimal modification of the plane of action to generate the new tooth profile, the idea of perfect plane of action of helical gears is introduced. The cubic splines are used to determine the optimal helical tooth profile. The method proposed in this work constitutes a general tooth correction method and makes the design, unlike other modification schemes presented in the literature, less complex and less sensitive to dynamic factors and retains the involute characteristics. Also the proposed method permits easier cutting of the tooth profile because of the simplicity of the process.
Dynamic Preisach modelling of hysteresis for the piezoceramic actuator system
Authors: Yu Y , Xiao Z , Naganathan N G , Dukkipati R V
Published: October 2002

A rate-dependent hysteresis property is a common phenomenon in various hysteretic systems including the piezoceramic material system. The dynamic Preisach model is needed to describe the rate-dependent hysteresis. This paper proposes a new dynamic Preisach model by introducing the dependence of the Preisach function on the input variation rate. An input variation rate function was introduced to adjust the relationship of hysteresis loop to the input variation rate for different hysteresis systems. A detailed numerical implementation procedure is also presented. Experiments were conducted to study the hysteresis behaviour of the piezoceramic actuator system and to verify the proposed model.
The angle-resolved velocity measurements in the impeller passages of a model biocentrifugal pump
Authors: Yu S C M , Chua L P , Leo H L
Published: October 2002

Velocity measurements have been obtained in a model of biocentrifugal pump in terms of angle-resolved values in the impeller passages, the volute and the inlet and exit ducts running at the design condition using a laser Doppler anemometer. Water was used as the working fluid. Three impeller geometries have been considered including the 16 forward swept-blade design, 16 straight radial-blade design and 8 backward swept-blade design. The results indicate that all designs showed pockets of recirculating flows and high-shear-stress regions in some passages of the impeller. The splitter plate located along the centre-line of the volute passage was found to be responsible for restricting part of the flows from exiting the impeller to the volute passage. The original intention of the splitter plate was to minimize the imbalance of the radial thrust when the impeller was magnetically suspended. The splitter plate also creates a velocity difference on either side of the splitter plate at the exit duct and may have provided conditions for the formation of spanwise vortices downstream from the exit of the pump. Further development on the biopump should focus on the design integration of the impellers, splitter plate and volute so as to achieve a better pump performance.
Contact between a centrally loaded plate and a rigid or elastic base, with application to pivoted pad bearings
Authors: Kauzlarich J J , Greenwood J A
Published: October 2002

Coker and Filon first introduced the idea that the contact area between a pad and a support may decrease under the application of a load, the process subsequently called a ‘receding contact’ by Keer et al. Filon analysed the contact between two matching slabs under a line load, and showed that, for the two to remain in contact, the mid-plane contact stresses must change from compression to tension beyond a distance from the line load of approximately 1.35 times the slab thickness. Filon argued that, since the tensile stresses are small, in a real contact the two slabs will separate at approximately these locations. A photoelastic study by Frocht of the stress pattern when a line load acts through a pad resting on an elastic base supported Filon's prediction.

It is shown by a three-dimensional finite element (FE) solution for the axisymmetric load problem that the radius of separation on a rigid base is significantly smaller than that calculated using the Filon assumption. When the pad is supported on an elastic base of the same material, the same is true, though both radii are significantly larger than with the rigid base.

The results are applicable to several practical problems. For a rigid base, examples are two slabs pressed together by circular dies, and the initial geometry in resistance spot welding. The case of an elastic base is of wide application in civil engineering, when a pillar is supported on a bearing plate on an elastic base. In tribology it may explain the start-up under load of a centrally pivoted thrust pad bearing, which otherwise must rely on surface tension to retain a residual oil film.
Experimental verification of the autofrettage process for thick-walled tubes
Authors: Ragab A R , Abbas A T , Khorshied S A
Published: October 2002

The success of the autofrettage process applied to thick-walled tubes is determined in industry via a control chart representing the measured permanent diametral expansions versus the yield stress of the material. The widely used acceptance limits are due to Hill's analysis of the problem. An experimental investigation showed that the above limits might lead to refusal of a substantial number of autofrettaged tubes. By considering the separate effects of hardening, the Bauschinger factor, reverse yielding, anisotropy and geometrical eccentricity, the need for a more realistic material model is demonstrated. A model incorporating the first three factors, found in the literature, is used to suggest new acceptance limits. Autofrettage experiments on a relatively large number of tubes indicated that the new control limits might render refusals acceptable.
Analytical formulae for the design of a railway vehicle suspension system
Authors: Mastinu G R M , Gobbi M , Pace G D
Published: October 2002

A simple two-degree-of-freedom (2DOF) model is used to derive a number of analytical formulae describing the dynamic response of railway vehicles to random excitations generated by vertical track irregularities. The dynamic response is given in terms of standard deviations of a number of relevant performance indices such as body-bogie suspension stroke and body acceleration. The derived analytical formulae can be used either during preliminary design or for other special purposes, especially when approximated results are acceptable. An estimation of the degree of approximation offered by analytical formulae is attempted and the results seem satisfactory. By inspection of the analytical formulae a parameter sensitivity analysis may be readily performed.

In the second part of the paper, an optimization method for the improvement of the dynamic behaviour of railway vehicles is introduced. The method, based on multiobjective programming (MOP), is a general one and can be exploited for many engineering purposes. In the paper the method has been applied with the aim of achieving the desired trade-off among conflicting performances such as standard deviation of the body acceleration versus standard deviation of the secondary suspension stroke. As a result, new analytical formulae defining the settings of some relevant vehicle suspension parameters have been derived.
Compensating analysis of a double circular-arc helical gear by computerized simulation of meshing
Authors: Chen C-K , Wang C-Y
Published: October 2002

A mathematical model of a stepped double circular-arc helical tooth profile with two centre offsets is developed. The conditions of gear meshing that reflect manufacturing and assembly errors are simulated. The locations of bearing contact and the contact path pattern of mating tooth surfaces are determined by tooth contact analysis (TCA). By applying the proposed mathematical model and TCA, single error impact can be determined. To compensate for offset and angular misalignment, the authors propose an adjustable bearing whereby transmission errors can be minimized. The investigation is illustrated with several numerical examples.
An experimental method to measure gear tooth stiffness throughout and beyond the path of contact
Authors: Munro1 R. G. , Palmer D , Morrish L
Published: October 2002

A method is presented that allows the accurate measurement of the tooth pair stiffness of a pair of spur gears. The method reveals the stiffness behaviour throughout the full length of the normal path of contact and also into the extended contact region when tooth corner contact occurs. The method makes use of the properties of transmission error plots for mean and alternating components over a range of tooth loads (Harris maps). It avoids the usual problem when measuring tooth deflections that deflections of other test rig components are difficult to eliminate. Also included are predicted Harris maps for a pair of high contact ratio spur gears, showing the effects of various simplifying assumptions, together with a measured map.
An experimental and numerical study of the flow past elliptic cylinder arrays
Authors: Castiglia D , Balabani S , Papadakis G , Yianneskis M
Published: October 2002

The subcritical flow over an array of elliptic cylinders with an axis ratio of 1:2 was studied both experimentally and numerically. The mean velocities, turbulence levels and the vortex dynamics of the array were determined experimentally by flow visualization and using a laser Doppler anemometer (LDA) and the flow was modelled using three-dimensional large eddy simulation (LES). The experimental results were compared with results obtained previously using circular cylinders and with numerical predictions of the flow. The study indicated that the flow past such a widely spaced array is characterized by low turbulence levels and poor lateral mixing compared with conventional circular cylinder arrays, and a weak flow periodicity with a constant Strouhal number of 0.11 was detected in downstream rows. The predicted mean and r.m.s. velocities, as well as the flow periodicity, were in good agreement with the experimental results.
A parsimonious model for the proportional control valve
Authors: Elmer K F , Gentle C R
Published: October 2002

A generic non-linear dynamic model of a direct-acting electrohydraulic proportional solenoid valve is presented. The valve consists of two subsystems—a spool assembly and one or two unidirectional proportional solenoids. These two subsystems are modelled separately. The solenoid is modelled as a non-linear resistor-inductor combination, with inductance parameters that change with current. An innovative modelling method has been used to represent these components. The spool assembly is modelled as a mass-spring-damper system. The inertia and the damping effects of the solenoid armature are incorporated in the spool model. The model accurately and reliably predicts both the dynamic and steady state responses of the valve to voltage inputs. Simulated results are presented, which agree well with experimental results.
Geometric tolerances: A new application for line geometry and screws
Authors: Davidson J K , Shah J J
Published: October 2002

A new mathematical model is introduced for the tolerances of cylindrical surfaces. The model is compatible with the ISO/ANSI/ASME standard for geometric tolerances. Central to the new model is a Tolerance-Map®†, a hypothetical volume of points that corresponds to all possible locations and variations of a segment of a line (the axis) that can arise from tolerances on size, location and orientation of the cylindrical surface. Each axis in a tolerance zone will be represented with the six Plücker coordinates. Cylindrical surfaces in a tolerance zone for the same hole can then be treated by attaching a size tolerance to each of the lines, thereby forming a screw. Relationships for the content of line solids for a tolerance zone are developed to correspond to the variations of locations. These are then used to obtain a measure for the increment in cost when a more refined tolerance is specified. This model is one part of a bilevel model that is under development for geometric tolerances.
Three problems in robotics
Authors: Selig J M
Published: October 2002

Three rather different problems in robotics are studied using the same technique from screw theory. The first problem concerns systems of springs. The potential function is differentiated in the direction of an arbitrary screw to find the equilibrium position. The second problem is almost identical in terms of the computations; the least-squares solution to the problem of finding the rigid motion undergone by a body given only data about points on the body is sought. In the third problem the Jacobian of a Stewart platform is found. Again, this is achieved by differentiating with respect to a screw. Furthermore, second-order properties of the first two problems are studied. The Hessian of second derivatives is computed, and hence the stability properties of the equilibrium positions of the spring system are found.