bluuebunny/crossref_metadata_2025 huggingface dataset:
Dispersion processes in reservoirs and natural streams
Authors: Fares Y R
Published: October 2002

The application of dispersion models in estimating the concentration levels of a solute, or a pollutant constituent, resulting from discharging waste into reservoirs and natural streams is presented. For the reservoir case, the mass balance principle of the aggregated dead zone (ADZ) model is employed, from which a general formulation for the dispersion of a pollutant constituent is derived. A hypothetical case is presented where an accidental spillage of a chemical discharge into a reservoir is considered. The prediction of the transient change in the concentration levels is analytically derived for the general case of reservoirs of arbitrary volumes and of various influx rates and duration.

For the case of natural streams, the classic version of the Fickian diffusion model is modified, from which an expression for quantifying the coefficient of dispersion is proposed. The proposed dispersion model has been applied to a case study carried out on Waikato River, in New Zealand, where a dye is released in the river for the purpose of providing information about flushing rates at low steady flows. It has been demonstrated that the proposed dispersion model gives a more realistic estimation of the concentration profiles than those obtained from other existing models. Reasonably good comparisons were obtained with the measured concentration levels in the river at both the near-field and the far-field locations from the injection site.
Simulations of oil spread on a water surface
Authors: Liu Y , Liu H , Zhang H , Miao G
Published: October 2002

Numerical simulation of an oil slick spreading on still and wavy surfaces is described in this paper. The so-called σ transformation is used to transform the time-varying physical domain into a fixed calculation domain for the water wave motions and, at the same time, the continuity equation is changed into an advection equation of wave elevation. This evolution equation is discretized by the forward time and central space scheme, and the momentum equations by the projection method. A damping zone is set up in front of the outlet boundary coupled with a Sommerfeld-Orlanski condition at that boundary to minimize the wave reflection. The equations for the oil slick are depth-averaged and coupled with the water motions when solving numerically. As examples, sinusoidal and solitary water waves, the oil spread on a smooth plane and on still and wavy water surfaces are calculated to examine the accuracy of simulating water waves by Navier-Stokes equations, the effect of damping zone on wave reflection and the precise structures of oil spread on waves.
Stirling's air engine—a thermodynamic appreciation
Authors: Organ A J
Published: October 2002

Stirling's original engine is remarkable for having been the first application of the thermal regenerator—and an instant technological success. While the patents and their intriguing history are the normal focus of study, this paper shifts attention to the insights afforded by reconstructing the thermodynamic personality of the engine itself. The kinematics of the drive mechanism are recovered, and volume variations determined as a function of crank angle. Recently developed thermodynamic tools are introduced and applied to the construction of the fluid particle trajectory map. The map forms the integration grid for calculation of the temperature response of the regenerator. The claim for 2 bhp from the original engine is explored. Potential is identified for an up-to-date version of Stirling's elegant concept in the form of cheap quiet power units of attractive specific output.
Geometric modelling for cylindrical and helical gear pumps with circular arc teeth
Authors: Chen C-K , Yang S-C
Published: October 2002

This paper describes a simple approach based on the envelope theory for deriving the geometric models of cylindrical and helical gear pumps with circular arc teeth. A gear pump with circular arc teeth can be easily obtained through the envelope theory for a one-parameter family of surfaces. In the process of machining a gear blank, the required rack-cutter teeth can be obtained by using the obtained cylindrical and helical gears, whose forms are easily determined by the envelope theory. Here the authors provide geometric modelling of the designed gear pump meshing when assembly errors are present. To illustrate the effectiveness of the approach, an analytical expression of cylindrical and helical gear pumps with circular arc teeth is given.
Noise generation in vane axial fans due to rotating stall and surge
Authors: Čudina M
Published: October 2002

A characteristic of axial flow fans is instabilities in their performance and noise in partial load operation. These instabilities are a consequence of rotating stall created in the rotor blade and/or in the guide vane cascade. At some operating conditions the rotating stall caused the appearance of a surge representing the lowest region of fan operating stability. The rotating stall and especially surge caused a steep increase in the emitted noise and lowered the performance of the fan. The present paper highlights the rotating stall generation phenomenon and its influence on the emitted total noise level and noise spectra for axial flow fans with inlet and outlet guide vanes.
Mechatronics design for a programmable closed-loop mechanism
Authors: Zhang W J , Chen X B
Published: October 2002

As the demand increases for machines with high accuracy, high speed and high stiffness, programmable closed-loop linkages (PCLL) emerge. This paper presents further results obtained from a study of the mechatronics design approach to PCLL systems proposed by the authors elsewhere. In this approach, the system performances such as motion tracking and torque fluctuation are further improved after a suitable design of mass redistribution. In the present paper it is shown that a scheme called negative mass redistribution, which follows the principle of shaking force/shaking moment balancing, can achieve an excellent improvement in system performance. Furthermore, simultaneous variation in the length of the link and the gain of the PD controller is studied, which shows promise for further improvement in system performance. In general, these studies have shown that complex control algorithms may not achieve a better result than that achieved by a simple PD controller combined with a mass redistribution scheme.
Trends in the drawing of mechanisms since the early Middle Ages
Authors: Ceccarelli M , Cigola M
Published: October 2002

Drawing of mechanisms is a fundamental tool for mechanical design and representation. In this paper a historical study on the evolution of representation of mechanisms has been carried out in order to establish the historic background and identify the progress over time. Investigating several authors has identified basic changes in the evolution of mechanism drawing, and a few examples are reported in this paper to stress the main concepts. The drawing of mechanisms has evolved from an intentionally incomplete representation to a naturalistic and pictorial view, then from concise sketches and kinematic diagrams to modern abstract graphic pictures. The development of mechanism drawing has been strongly linked with and affected by the evolution of knowledge in mechanical sciences and particularly mechanism design.
Gas-assisted laser single-pulse heating: Study of thermal stresses
Authors: Arif A F M , Shuja S Z , Yilbas B S
Published: October 2002

Pulsed laser heating of metals causes an excessive temperature gradient across the heated zone, which in turn results in thermal stresses developing in the heated region. In the present study, gas-assisted pulsed laser heating of steel is simulated. The governing flow, energy and thermal stress equations are solved numerically. The low Reynolds number k-ε model is introduced to account for the turbulence. In the analysis, temporal variation in heating and stress development are considered. In order to examine the material response to the heating pulse, constant and variable properties of the workpiece are taken into account. It is found that the thermal stresses are highly concentrated in the surface region of the substrate. The radial component of the stress is compressive while the axial component is tensile. The maximum equivalent strain is of the order of 10−3. The maximum equivalent stress occurs below the surface along the z axis, where the radial intersection is the centre of the heated spot.
Exact deflection expressions for a thin solid circular plate loaded by periphery couples
Authors: Nobili A , Strozzi A , Vaccari P
Published: October 2002

A mechanical analysis is carried out for a thin, solid, circular plate, deflected by a series of periphery-concentrated couples with a radial or circumferential axis. Although such couples need not be of equal intensity or angularly equispaced, they must constitute a self-equilibrated system of couples. This problem is decomposed into a combination of two basic models, the first of which considers a single periphery couple with a radial axis, and the second addresses an edge couple with a circumferential axis. In both models the concentrated border couple is equilibrated by a sinusoidal boundary line load of proper intensity, whose wavelength equals the plate edge. When such basic configurations are combined, respecting the condition that the system of concentrated couples be self-equilibrated, the effects of the sinusoidal loads cancel out, and the title problem is recovered. A classical series solution in terms of purely flexural plate deflections is achieved for the two basic models, where the series coefficients are computed with the aid of an algebraic manipulator. For both models, the series is summed in analytical form over the whole plate region. Closed-form deflection formulae can thus be easily derived from the two basic models for any combination of self-equilibrated edge couples, where some selected relevant situations are developed in detail.
Uniaxial crushing of constrained tubes
Authors: Singace A A , El-Sobky H
Published: October 2002

By changing the end constraints, the behaviour of mild steel and aluminium alloy tubes of relatively low D/ t ratio, subjected to an axial crushing load, is studied. Many combinations of end constraints were produced by radially constraining one or both ends of the loaded tube outwards, inwards or in both directions. Partially constrained mild steel and aluminium tubes are found to collapse into either a pure concertina mode or a pure diamond mode, depending on the ratio D/ t and the material characteristics. Mixed concertina-diamond modes would generally result by radially constraining the tube at both ends. Constraining the tube radially outwards at one end does not significantly affect the load-displacement characteristics and the mode of collapse. However, constraining the tube radially inwards produces a different mode than that observed under outward, inward or combined outward/inward constraint. New modes of collapse have been observed under different combinations of outward and inward constraints at both ends. Fully constraining the tubes in the radial direction results in the removal of the initial overshoot in the load-displacement curve, which is responsible for the overestimation of the mean crushing load and the energy absorption capacity of tubular elements. The mode of collapse and the energy absorbed could be controlled with the proper choice of the end constraints.
A novel tool for the prediction of earth-contact heat transfer: A multi-room simulation
Authors: Zoras S , Davies M , Adjali M H
Published: October 2002

This paper reports a new simulation method for the prediction of earth-contact heat transfer. The new method claims to be fast, accurate and flexible by means of incorporating elements of the response factor method into a numerical method based on the finite volume technique. More specifically, the development of the method is presented and implemented for a general multi-room structure. Work undertaken so far shows that the current combination of the finite volume and response factor techniques is at its most useful when the new tool is used in a parametric analysis process. Initially, a ‘pre-processing’ procedure is utilized to generate a certain number of simulated hours for use as a time series by the response factor technique in the second stage of the method. Assuming that the earth-contact parameters then remain constant, every subsequent simulation in which the non-earth-contact parameters are varied can incorporate the earth-contact heat transfer efficiently, by the use of the response factor technique, which takes a few seconds. Very good agreement has been achieved between a three-dimensional finite volume model and the present method, for a typical multi-room slab-on-ground floor, coupled with dramatically improved run times which is essential for the rapid parametric analysis of a structure.
Geometric model of a rolling process for multi-wave tubes
Authors: Yang S-C , Chen C-K
Published: October 2002

From a geometric viewpoint, this work considers the process of wavy tubes cross-rolling at the precision rolling section as meshing of a pair of conjugate surfaces. This work applies coordinate transformation and envelope theory to determine the spatial set of points for contacting surfaces that define the roller. The proposed method can be used to derive the roller surfaces for cross-rolling and parallel rolling of wavy tube manufacture. The envelope theory and the analytical procedure for the proposed method are presented. Numerical examples are presented to demonstrate the application of the method developed in this paper. The advantages, limitations and potential applications of cross-rolling are briefly reported.
Contact between a pin and a plate with a hole under interference-fit and clearance-fit conditions
Authors: Hou J P , Hills D A
Published: October 2002

The contact problem of a circular pin journalled in an almost conforming hole in a plate, and subject to a radial force, is considered. Both interference-fit and clearance-fit cases are treated, uniformly, as is the problem when the elements are elastically dissimilar, but the interface frictionless. The strength of the contact is assessed by classical yield criteria, and a calibration is given for the crack tip stress intensity factor for a radial crack, so that the brittle fracture strength may also be assessed.
On the structural configuration synthesis and geometry of machining centres
Authors: Chen F-C
Published: October 2002

The purpose of this paper is to synthesize all possible structural configurations of three-, four- and five-axis machining centres and to investigate the geometrical characteristics of five-axis machining centres. Based on the definition of coordinate systems and the configuration code of machine tools, it was found that there are 24, 96 and 288 feasible configurations for three-, four- and five-axis machining centres respectively. The geometric characteristics of five-axis machining centres were analysed and summarized by using the method of coordinate transformation. The results of this paper are beneficial to engineers in the design and evaluation of machining centres.
Analysis of braking noise and vibration measurements by time—frequency approaches
Authors: Charley J , Bodovillé G , Degallaix G
Published: October 2002

This paper presents an analysis of braking noise and vibration measurements using the short-time Fourier transform (STFT), Morlet wavelet transform (WT) and Wigner—Ville distribution (WVD). These time—frequency analysis tools are described and applied successively to a simulated signal and to experimental measurements performed during a braking test. Particular attention is paid to the dependence on rotational speed, and on the correlation between noise, vibration measurements and other physical parameters.
Flow characteristics and micro—bubble behaviour in a rotating pipe section with an abrupt enlargement
Authors: Yamaguchi H , Matsubara D , Shuchi S
Published: October 2002

The flow characteristics and dynamic behaviour of micro-bubbles were investigated experimentally and numerically for swirling flow within rotating pipe sections. In the present investigation, three types of rotating pipe section were used in order to study the effects of geometric configuration upon the flowfield. Experimental data were obtained for locations of the stagnation point and profiles of the parabolic surface. The results obtained from experiments were examined and verified with the aid of numerical analysis. It was found that the air pocket formed at the stagnation point was moved upstream by the effect of the suddenly expanded part when pipe rotation was increased. The reattachment point did not shift downstream as a result of an increase in the Reynolds number. This is due to the fact that the vortex zone at the expanded corner expands or shrinks, depending on the speed of rotation.
On the geometry of rigid-body motions: The relation between Lie groups and screws
Authors: Stramigioli S , Maschke B , Bidard C
Published: October 2002

This paper gives a synthetic presentation of the geometry of rigid-body motion in a projective geometrical framework. An important issue is the geometric approach to the identification of twists and wrenches in a Lie group approach and their relation to screws. The paper presents a novel formal way to describe the spaces of lines, axials, polars and screws as subsets or subspaces of Lie algebras in order to make clear the relation between screw concepts and Lie group concepts.
Spatial point contact kinematics and parallel transport
Authors: Pfister F
Published: October 2002

A point contact kinematic model is developed, using a non-holonomic parameterization first introduced in 1885 by Neumann and Richter. The model is built with two auxiliary pairs of imaginary bodies. Each body carries a coordinate reference frame. By this, one single point pair becomes a serial composite of three pairs, two Levi-Civita and one revolute pair. Convenient, insightful and computationally attractive algebraic expressions are obtained. The approach is general and applicable to any pair of regular, parametric surfaces. Algebra is simplified by the discovery of an intimate relationship between point-contact kinematics and parallel transport of vector fields in the sense of Levi-Civita. A new special motion, Levi-Civita motion, is defined and discussed. The following first- and second-order kinematic properties of Levi-Civita motion are presented: motion screw, motion pitch, Hamilton cylindroid, Sturm theorem, parallelism, Schieldrop-Johnsen vector of non-holonomic deviation, analogy to a rigid body with a fixed point and a kinematic proof of the Gauss-Bonnet theorem of differential geometry.
Euclidean metrics for motion generation on SE(3)
Authors: Belta C , Kumar V
Published: October 2002

Previous approaches to trajectory generation for rigid bodies have been either based on the so-called invariant screw motions or on ad hoc decompositions into rotations and translations. This paper formulates the trajectory generation problem in the framework of Lie groups and Riemannian geometry. The goal is to determine optimal curves joining given points with appropriate boundary conditions on the Euclidean group. Since this results in a two-point boundary value problem that has to be solved iteratively, a computationally efficient, analytical method that generates near-optimal trajectories is derived. The method consists of two steps. The first step involves generating the optimal trajectory in an ambient space, while the second step is used to project this trajectory onto the Euclidean group. The paper describes the method, its applications and its performance in terms of optimality and efficiency.
Orientation capability of planar serial manipulators using rotatability analysis based on workspace decomposition
Authors: Dai J S , Shah P
Published: October 2002

This paper presents a new approach for analysing and synthesizing the orientation capability of planar serial manipulators. By relating the end-effector to the base joint of a manipulator using a virtual adjustable link, the paper converts the open-chain kinematic problem into that of an equivalent close-chain mechanism, and characterizes the relationship between the orientation capability of a serial manipulator and the rotatability of the equivalent mechanism. The orientation capability of a manipulator can hence be placed in the realm of mechanism rotatability. The approach is taken further by decomposing the reachable workspace of a manipulator into ranges, based on the extreme and singular positions of a manipulator. In each of the workspace ranges, the rotatability of the equivalent mechanism is examined and results are categorized to indicate the orientation capability of the manipulator. The approach produces a direct correlation between the orientation capability and manipulator parameters and generates a way of examining the orientation capabilities of serial manipulators. The approach is extended to n-link serial manipulators.
Formulation of surface temperature for laser evaporative pulse heating: The time exponentially decaying pulse case
Authors: Yilbas B S , Kalyon M
Published: October 2002

Modelling of the laser heating process is fruitful, since it enhances the understanding of the physical processes involved and minimizes the experimental cost. In the present study, an analytical solution for the temperature distribution inside the solid substrate is obtained using a Laplace transform method. A time exponentially decaying laser pulse profile is introduced in the analysis. The phase change process and recession velocity are accommodated to account for the evaporation at the surface. The closed-form solution obtained is compared with the analytical solution obtained previously for a conduction limited heating case. It is found that the closed-form solution obtained from the present study reduces to a previously obtained analytical solution when the pulse parameter, β∗, is set to zero in the closed-form solution. Temperature predictions from simulations agree well with the results obtained from the closed-form solution.
The effect of friction on a receding conformal contact
Authors: Hou J P , Hills D A
Published: October 2002

The influence of interfacial friction on the contact between a pin and an almost conforming hole is considered. The technique is developed from the fundamental two-dimensional solution for a line force in an infinite plane, using distributed strain nuclei to model both separation and slip. This provides a numerically efficient solution for the problem, and enables the local subsurface stress to be found which, in turn, governs the crack initiation environment.
Practical reliability-based analysis of a coil tube spring
Authors: Zhang Y M , Liu Q L
Published: October 2002

The coil tube spring, a new type of spring, has been recently used in engineering. This paper presents a method for reliability-based analysis of a coil tube spring. A technique, using the perturbation method and reliability-based design theory, is employed to present a practical and effective method for the reliability-based analysis of a coil tube spring. Theoretical formulae of the reliability of a coil tube spring are obtained. The given approach can be used to determine the reliability of a coil tube spring accurately and quickly.
Design constraints of five-arc Roots vacuum pumps
Authors: Wang P-Y , Fong Z-H , Fang H S
Published: October 2002

The design constraints for the tooth profile of the five-arc Roots vacuum pump are derived and discussed in this paper. The addendum portion of the five-arc tooth profile comprises five smoothly connected circular arcs, while the dedendum portion consists of conjugate curves of the addendum portion of the mating rotor. The top land of the proposed rotor profile is a circular arc with its centre coinciding with the centre of rotation. Therefore, the gap between the top land of the rotor and the wall of the chamber turns into a long and narrow path, which provides better gas sealing and wider inlet opening. The design constraints of the rotor profile are quite complex owing to the limitations of zero carryover and the condition of non-undercutting. A design procedure is proposed for determining the feasible design region by considering the geometry constraints, zero carryover and non-undercutting. By using the proposed procedure, wider inlet opening and better gas sealing are expected, while the characteristic of zero carryover is maintained. The results of experiment show that the ultimate pressure of the prototype of the five-arc Roots vacuum pump is 2,5 × 10-3 torr, and the maximum pumping speed is 1600L/min. The performance of the prototype is excellent compared with commercially available mechanical dry vacuum pumps.
Effect of a local crack on the dynamic characteristics of a rotating grouped blade disc
Authors: Huang B W , Kuang J H
Published: October 2002

The effects of a local blade crack and the group arrangement on the mode localization in a rotating turbodisc are studied in this paper. Periodically coupled Euler—Bernoulli beams are used to approximate the grouped and shrouded turboblades. A two-span beam with a torsion spring is used to model the cracked blade. The crack depth characterizes the stiffness of the assumed torsion spring. Galerkin's method is applied to formulate the localization equations of the grouped turbodisc system. Numerical results indicate that the crack depth, crack distribution and rotational speed in a rotating grouped blade disc may significantly affect the localization phenomenon.
Air flow in a plate valve with unequal upstream and downstream orifice sizes
Authors: Cabral E L , Hunold M C , Tu C C
Published: October 2002

Pneumatic valves with unequal upstream and downstream orifice sizes make the proportional control of flow easier. It also enables the load to respond faster and increases the energy efficiency of the controlled system. A plate valve is the only type where this difference in orifice sizes can be implemented in a straightforward manner. A four-way, rotary plate valve was designed, constructed and analysed. The advantages of control and energy efficiency that result when this valve is used in a pneumatic system are studied. Experimental results for the case of this valve controlling a pneumatic vane motor confirm the theoretical predictions.
Modelling of the injection of hot liquid sprays into a closed vessel
Authors: Kubie J
Published: October 2002

An experimental and theoretical study recently investigated the transient processes that occur when hot liquid spray droplets are suddenly injected into air contained in a closed chamber [1]. The analysis gathered all important parameters governing droplet heat transfer in a single dimensionless group, denoted by K2. The work has been extended by redefining K2, and introducing a new dimensionless group KN2, and by using helium as the surrounding gas. The dimensionless group KN2 is, to a first approximation, independent of all parameters investigated in the present work, including the properties of the surrounding gas, and approximately equal to 0.12. The dimensionless group KN2 =0.12 should be used instead of the Nusselt number as the primary dimensionless group in analysing the heat transfer performance of spray injection nozzles in closed chambers.
Bearing life prognosis under environmental effects based on accelerated life testing
Authors: Zhang C , Le M T , Seth B B , Liang S Y
Published: October 2002

The reliability of a bearing is typically estabilished by repeated life testing which provides valuable information on the fatigue mechanisms from crack initiation, crack propagation to flake or spall. Under nominal operating conditions, life testing often consumes a significant amount of time and resources, due to the comparatively high bearing mean lifetime before failure (MTBF), rendering the procedures expensive and impractical. Therefore, the technology of accelerated life testing (ALT), which is widely used in manufacturing practice, offers the attractive benefit of requiring relatively less investment in terms of time and resources. Data from tests at high stress levels (e.g. temperature, voltage, pressure, corrosive media, etc.) can be extrapolated, through a physically reasonable statistical model, to obtain life estimates at lower, normal stress levels. In this study, a methodology to predict bearing lifetime under a corrosive environment has been developed based on accelerated life testing data and the application of the inverse power law. Bearing life tests under various corrosion stress levels were performed for model identification followed by additional independent bearing life tests conducted for model verification. The experimental result shows that the accelerated life test model can effectively assess the life probability of a bearing based on accelerated environmental testing, even with extrapolation to untested stress levels.
Junction characteristics of energy wave methods
Authors: Chen T , Boucher R F
Published: October 2002

Physical dynamical systems may be modelled by connecting wave-transmitting elements using junctions that depict the relations of energy transmission. Elements transmit wave energy from one end to the other end and junctions reallocate energy to those attached elements. The scattering coefficients of junctions may be derived by satisfying the continuity constitutive relations and energy conservations. The scattering coefficients expressed in general forms of 13 different junctions demonstrated in this paper permit systems with multiple energy domains to be modelled and are applicable to modelling distributed, lumped and mixed type systems. Careful selection of the correct types of junctions and construction of the system topology are keys to successfully modelling physical systems.
Vibration control using a tunable vibration neutralizer
Authors: Brennan M J
Published: October 2002

The harmonic vibration of a machine at one position can be controlled using a vibration neutralizer whose natural frequency is the same as the excitation frequency. However, a conventional vibration neutralizer is only effective over a narrow frequency band and is unable to track changes in excitation frequency. A way of overcoming this problem is to use a tunable vibration neutralizer which, due its variable stiffness capability, can be tuned to operate at different frequencies. With this system, however, there is an inevitable delay between a change in the excitation frequency and the re-tuning of the neutralizer. This delay is dependent upon the control system, and the way it affects the vibration of the machine depends upon certain design parameters. This paper discusses the behaviour of a machine fitted with a tunable vibration neutralizer during the adaptation process when the system is in a transient state. It is shown that if a neutralizer cannot respond quickly enough to a frequency transient, its contribution can be to increase the vibration level of the machine. A theoretical study is presented which shows that to avoid such an increase in machine vibration a maximum control time delay should be imposed. This delay is dependent upon the rate of change of excitation frequency and the ratio of the mass of the neutralizer to that of the machine. Experiments are conducted to validate the theoretical predictions using a tunable neutralizer which consists of a mass supported by an air mount, whose natural frequency can be adjusted by varying the pressure in the mount.
Heat transfer from a flat plate to a turbulent axisymmetric impinging jet
Authors: Ashforth-Frost S , Jambunathan K , Whitney C F , Ball S J
Published: October 2002

The heat transfer due to a single axisymmetric impinging jet at a Reynolds number of 20 000 and nozzle-to-plate spacings of 1—8 has been determined using a combined constant heat flux/constant temperature electrocaloric test plate. Both unconfined and semi-confined geometries have been considered for a uniform mean exit velocity. The exit conditions and axial development of the jet have been quantified using hot-wire anemometry. Careful design of the composite heater plate has reduced experimental uncertainties in the local Nusselt number to 5 per cent.
Redundancy utilization for obstacle avoidance of planar robot manipulators
Authors: Sezgin U , Seneviratne L D , Earles S W E
Published: October 2002

Two obstacle avoidance criteria are developed, utilizing the kinematic redundancy of serial redundant manipulators having revolute joints and tracking pre-determined end effector paths. The first criterion is based on the instantaneous distances between certain selected points along the manipulator, called configuration control points (CCP), and the vertices of the obstacles. The optimized joint configurations are obtained by maximizing these distances. Thus, the links of the manipulator are configured away from the obstacles. The second criterion uses a different approach, and is based on Voronoi boundaries representing the equidistant paths between two obstacles. The optimized joint configurations are obtained by minimizing the distances between the CCP and control points selected on the Voronoi boundaries. The validities of the criteria are demonstrated through computer simulations.
Analysis of isothermal elastohydrodynamic point contacts lubricated by Newtonian fluids using multigrid methods
Authors: Ehret P , Dowson D , Taylor C M , Wang D
Published: October 2002

A multigrid multi-integration method has been used to solve the elastohydrodynamic lubrication (EHL) point contact problem over a large range of loads. Solutions obtained with the multigrid method are compared with those computed with an effective influence Newton method. Good agreement has been obtained, which validates the results obtained by both of these independent methods. Smooth surface problems have been used to test the multigrid method, but an example that takes into account a wavy surface has demonstrated the robustness and the large potential of the multigrid method to analyse EHL problems with three-dimensional surface roughness.
A generalized elastica-type approach to the analysis of large displacements of spring-strips
Authors: De Bona F , Zelenika S
Published: October 2002

An elastica-type analytical solution to the problem of large deflections of slightly curved spring-strips, fixed at one end and loaded at the other with couples and with forces of various directions, is obtained in this work. The main methods of calculation of elliptic integrals are studied, and the limits of their applicability are established as functions of the required degrees of accuracy and of the loading conditions of the spring-strips.

The results obtained with the proposed method are then compared to particular cases already developed in the literature with different approaches. It is shown that in all the cases considered the method permits accurate results to be obtained.
The use of the split Hopkinson pressure bar techniques in high strain rate materials testing
Authors: Al-Mousawi M M , Reid S R , Deans W F
Published: October 2002

The use of the split Hopkinson pressure bar (SHPB) techniques for materials testing under a high rate of loading is described, including various modifications of the original compression testing set-up for tension testing, torsion testing and dynamic fracture testing. Details of measurement techniques and instrumentation are included together with the calibration of the air gun and strain wave measuring system. The SHPB techniques provide a relatively cheap and simple method for high strain rate materials testing with an acceptable level of accuracy when sufficient care is taken for the proper lubrication of the interfaces and the correct length—radius ratio of the specimen is chosen. The limitations of the method are discussed and possible improvements using FFT (fast Fourier transform) techniques to take into account dispersion effects are considered.
Comparative bending fatigue strength of precision forged spur gears
Authors: Eyercioglu O , Walton D , Dean T A
Published: October 2002

To determine the bending fatigue strength of precision forged spur gears and to compare the results with those obtained from conventional cut gears, single tooth bending fatigue tests were carried out on both through-hardened and induction-hardened gear teeth. The gears were produced from rolled bar cut blanks, disc forged blanks or precision forged teeth blanks. For this purpose, a special test fixture was designed and built for an Amsler high-frequency vibrophore fatigue testing machine. The results show that the endurance limit of precision forged gears is significantly higher than those obtained from cut gears. The bending fatigue strength of forged gears was some 12.5 per cent higher than the cut teeth in a through-hardened condition and 8.4 per cent higher for the induction-hardened teeth. The effect of surface roughness at the tooth root area on the bending fatigue strength of the forged gears is also shown.
A study of non-redirection louvre fin-and-tube heat exchangers
Authors: Wang C-C , Chang Y-P , Chi K-Y , Chang Y-J
Published: October 2002

Extensive experiments on the heat transfer and pressure drop characteristics of louvre finand-tube heat exchangers were carried out. In the present study, 14 samples of non-redirection louvre fin-and-tube heat exchangers with different geometrical parameters, including the number of tube row, fin pitch and tube size, were tested in a wind tunnel. Results are presented as plots of the Fanning friction factor f and the Colburn j factor against Reynolds number based on the tube collar diameter in the range of 300–8000.
An endochronic damage model for three-dimensional ductile failure analysis of double-edge notched thick-tension specimens
Authors: Chow C L , Chen X F
Published: October 2002

A three-dimensional ductile damage model based on the endochronic plastic theory is developed and employed to characterize the failure process of double-edge notched thick-tension specimens. A ductile damage evolution equation is derived with a new intrinsic time-scale specifically defined to characterize damage evolution. Two damage failure criteria are proposed and employed to predict the failure loads and crack initiation sites which correspond well with those measured experimentally.
Notch effect arising from the stud bolt in a 750 MVA turboalternator
Authors: Belloni G , Davoli P , Matteazzi S
Published: October 2002

Strain gauge measurements are described, which were carried out on a rotor of a 750 MVA turboalternator in the notched area arising both from the presence of a radial hole for the passage of the stud bolt that served to connect the conductors running axially with the external ones, as well as the variation in diameter between the slotted central part of the rotor and the cowled end portion. The load conditions were the weight of the rotor and the centrifugal forces acting on the masses of the stud and the conductors connected to it. The centrifugal forces were simulated by means of an external reaction ring. The notch effect resulting from the radial holes and the variation in diameter was assessed.
The ranking of efficiency of structural layouts using form factors Part 2: Design for strength
Authors: Burgess S C
Published: October 2002

This paper presents a method for ranking the mass efficiency of simple structural layouts for strength design using form factors. Form factors are derived for three different frameworks and seven different beams for an example load case of a simply supported and centrally loaded structure. The form factors show how structural efficiency is affected by four different design aspects: (a) severity of height constraint, (b) uniformity of stress, (c) utilization of height and (d) principle of load transfer. Form factors can be used as a preliminary design tool to help select and design structural concepts.
A mechanistic approach to laminar flow through an abrupt enlargement
Authors: McNeil D A
Published: October 2002

The flow of highly viscous fluids in pipeline fittings has previously been of little interest to mechanical engineers. More recently it has become more topical because design methods for emergency pressure relief systems on polymerization reactors need to be improved. The abrupt enlargement is of particular importance in this respect, because it regularly occurs on pipeline systems and is also an integral component part of other pipeline fittings such as orifice plates and valves. The energy loss mechanisms that occur in an abrupt enlargement will therefore occur in many other pipeline fittings. A semi-empirical, mechanistic approach was used to develop a simple, one-dimensional flow model that allowed these energy loss mechanisms to be understood. The energy loss predictions from the model compared well with data available in the open literature. The model was used to generate some simple design equations.
A numerical simulation of steady state metal cutting
Authors: Joyot P , Rakotomalala R , Pantalé O , Touratier M , Hakem N
Published: October 2002

An arbitrary Lagrangian-Eulerian (ALE) approach is used to model the orthogonal metal cutting in a steady state situation. The thermomechanical model includes the effects of elasticity, plasticity, strain rate, large strains and friction with heat generated between the tool and the chip. The ALE formulation can combine the advantages of both the Eulerian and Lagrangian approaches in a single description. Particularly, problems linked to the free surface in a Eulerian description and those linked to severe mesh distortions in a Lagrangian one can be solved by this formulation. The ALE governing equations are briefly reviewed in this paper; finite element and finite volume methods are used for the discretization of the conservation equations and an explicit time integration is adopted. Only the steady state solution is required; the ALE formulation is exploited to update the free and the contact surfaces. The model predicts the thermomechanical quantities, the chip geometry and the cutting forces from the cutting data and the material and friction parameters.

Cutting experiments were performed with 42CD4 steel and comparisons of experimental tool forces and chip geometry with the numerical results are presented.
The twin helical screw compressor Part 1: Development, applications and competitive position
Authors: Fleming J S , Tang Y , Cook G
Published: October 2002

Part 1 of this paper describes the origins, principal developments, characteristics, applications and current competitive position of the twin helical screw compressor. It is now the preferred type in a large range of gas and refrigeration applications previously serviced by the larger piston and smaller centrifugal compressors. Its success has been made possible by two crucial developments: (a) a lubricated variant in which one rotor drives the other without timing gears and (b) the introduction of advanced machine tools capable of mass producing reliably a rotor pair of high efficiency and low maintenance. The technical reasons for its (still growing) success over its rivals are explained, as is the competitive challenge presented by the scroll compressor, which is being produced in ever larger sizes. The paper concludes that if the twin helical screw compressor is to maintain/advance its present dominant position, three things are needed:

A designer-friendly computerized model of the working process which is comprehensive, accurate and of general application. Part 2, which follows, addresses this issue. A designer-friendly computerized profile design system not limited to predefined geometric forms and having an optimization facility. Faster, more accurate and cheaper manufacturing methods for rotors.
Application of periodic time-varying autoregressive models to the detection of bearing faults
Authors: McCormick A C , Nandi A K , Jack L B
Published: October 2002

Model-based approaches to vibration monitoring can provide a means of detecting machine faults even if data are only available from the machine in its normal condition. The cyclostationary nature of rotating machine vibrations can be exploited by using periodic time-varying autoregressive models to model the signal better than time-invariant models. Experimental data collected from a small rotating machine set subjected to several bearing faults were used to compare time-varying and time-invariant models. Comparison is also made with a simple feature-based neural network fault diagnosis system.
The turbulence structure of the annular non-swirling flow past an axisymmetric poppet valve
Authors: Nadarajah S , Balabani S , Tindal M J , Yianneskis M
Published: October 2002

This paper describes an experimental investigation of the non-swirling flow through an axisymmetric port and poppet valve assembly under steady flow conditions using laser Doppler anemometry. The three velocity components and the associated Reynolds stresses were measured by ensemble-averaged techniques and the turbulence kinetic energy and its production rate were determined. Time-resolved measurements were also taken in order to determine turbulence time and length scales and the dissipation rate of the turbulence kinetic energy. The Reynolds number, based on the minimum cross-sectional area of the port, was 25000.

The flow is characterized by an annular jet which forms two vortices, one on either side of the jet. A jet flapping instability is also evident since the skewness and kurtosis of the velocity probability distribution function depart from the Gaussian form. This instability causes an intermittent mixing between eddies in the jet region and the vortices which introduces a non-turbulent contribution to the measured quantities. The production rates of the turbulence kinetic energy were found to be negative in some regions of the flow, indicating counter-gradient transport of momentum by turbulence; according to the coherent structures approach, the distribution of the Reynolds shear stresses and the length scales in these regions imply possible changes in the orientation of eddies.
Applications of probability density estimation to the detection of abnormal conditions in engineering
Authors: Desforges M J , Jacob P J , Cooper J E
Published: October 2002

A method is described for the identification of abnormal or unexpected conditions from measured response data. Such a technique would be useful in a wide range of engineering situations where a clear, early warning of an abnormal condition is required, but where classification of the specific abnormality is only of secondary importance. In this work, occurrences of unexpected operating conditions are indicated by measured data which exhibit a high degree of novelty with respect to that corresponding to normal conditions or responses. The proposed approach is based upon the probability density function (PDF) estimation using a kernel method, the basis of which is described. The need for data compression in practical applications of PDF estimation is highlighted and a method demonstrated which is based on the wavelet transform. The combined data compression and PDF estimation approach for novelty detection is applied to data measured from a gearbox with a progressive fault and to radar data corresponding to six military targets. In both cases, abnormal situations are clearly identified on the basis of novel data inputs.
Temperature stresses in thick circular cylindrical shells used in nuclear reactors with and without uniform internal heat generation within the shell wall thickness
Authors: Guerreri G , Cossa L M
Published: October 2002

In the thick circular cylindrical steel shield of a nuclear reactor, the attenuated radiations generate heat which develops radial temperature profiles and consequent thermal stresses. In this first paper formulae and graphs are furnished which are used to calculate heat flow, temperature and stresses in the shell, away from external constraints, due to uniformly generated heat.

Previous work and formulae [1] for the case where heat is not generated inside the thickness are also recalled. Triangular and exponentially generated heat will be examined in the following paper. Finally, the principle of superposition will be used to solve cases where the generated heat paths are not uniform, triangular or exponential.