bluuebunny/crossref_metadata_2025_split huggingface dataset:
Computer aided modelling of the human spine
Authors: Case K , Xiao D C , Acar B S , Porter J M 
Published: October 2002

The human spine is the main structure to support human body weight and external loads, to allow the torso to reach to a variety of positions and to protect the spinal nervous system. Lumbar back pain and disorders may be related to spinal curvature and disc pressure, and it is an ultimate objective of the work reported here to include consideration of these issues in computer aided ergonomics design systems for evaluating a wide range of situations including manual handling and car seat design. Several methods from structural analysis have previously been used to model the human spine, principally lever and beam structures, but these have frequently shown discrepancies when compared with experimental data. As an alternative, an arch representation for the spine is considered here and allows the establishment of a criterion for the failure of the spine that may be useful in determining absolute maximum loading conditions. However, the main interest is in submaximal loading conditions where damage or discomfort are the concerns rather than fracture. It is proposed that the location of the thrust line in relation to the centre-line of the spine is a useful predictor, and optimization techniques have been developed to find the ‘best-fitting’ thrust line for the statically indeterminate structure. Further work is concerned with adding muscle and ligament forces to the loading system of the model, extension of the two-dimensional model into three dimensions, validation against experimental data and integration with the SAMMIE computer aided ergonomics design system.
A prototype constraint-based system for the automation and optimization of machining processes
Authors: Gayretli A , Abdalla H S 
Published: October 2002

This paper presents an intelligent design system that enables designers to consider at the early stages of the design process all issues associated with the product life cycle. The evaluation and optimization of machining processes are among the most important aspects of these issues, requiring the involvement of various types of information from the different aspects of the product life cycle. The representation of this information in efficient format is very important for carrying out different design tasks. In order effectively to manage information exchange within different design and manufacturing domains, it is necessary to provide an efficient and timely communication network system. Therefore, various critical tasks such as overall coordination, control, consistency and data integrity have to be considered in order to avoid costly design iterations. This research article has focused on the development of a prototype system for machining process optimization. The system uses a combination of both mathematical methods and constraint programming techniques and provides designers with the evaluation and optimization of feasible machining processes in a consistent manner at the early stages of the design process. As a result, unexpected and costly design iterations, which result in wastage of a great amount of engineering time and effort, and in a longer lead time, can be avoided. The development process has passed through four major stages. Firstly, an intelligent constraint- based design system for concurrent product and process design, including a machining process optimization module, has been developed. Secondly, the product features, processes, cost, time and requirements have been represented in the format of constraints, frames, objects and production rules in order to be utilized to accomplish different design tasks. Thirdly, rules for the selection and optimization of feasible processes for complex features have been written, and finally, an information management system, with a conflict resolution mechanism, has been developed to achieve consistency in information exchange and decision-making activities between the different design areas.
Scheduling for just-in-time flexible manufacturing using adaptive fuzzy logic
Authors: Tedford J D , Lowe C 
Published: October 2002

Production scheduling for flexible manufacturing needs to satisfy multiple and often conflicting criteria. The multicriteria problem is generally difficult to solve using existing heuristics without a means of combining rules and adapting them to changing circumstances. A scheduling system incorporating an adaptive fuzzy logic system is proposed which can be tailored to suit the characteristics and objectives of an organization and maintain its performance by constantly adapting to changes in the production environment. The system developed indicates that its application shows benefits in terms of the resulting schedule performance and with respect to the simplicity of the scheduling algorithms required. The computational overhead of the fuzzy system is also shown to be insignificant, thus permitting real-time operation in a manufacturing situation.
Finite element computer investigation of the electrochemical machining process for a parabolically shaped moving tool eroding an arbitrarily shaped workpiece
Authors: Hardisty H , Mileham A R 
Published: October 2002

This paper describes a computational investigation into the electrochemical machining (ECM) process for the case of a tool of fixed parabolic shape, moving at a uniform speed while eroding a stationary work surface initially of arbitrary shape. The numerical simulation of this two-dimensional moving boundary problem is based on the finite element method (FEM). The improved algorithms presented here, which model the erosion process at the work surface, remove certain limitations of the previous square mesh method. In ECM, as time increases, the eroded surface approaches more closely to an equilibrium shape. One-dimensional ECM theory is briefly reviewed in order to provide a background to the physical factors which influence this equilibrium state. A general equilibrium criterion is derived which is first used as part of a check on the test data, and later made the basis of an iterative design method. The present paper is divided into two sections. In the first, the modular computer package, which simulates the continuous erosion process, is described. A parabolically shaped tool was selected to allow the final equilibrium work shape generated after a number of time steps to be checked. These checks demonstrated excellent agreement between computer predictions and theory; they constitute a successful validation of the methodology. In the second part of the paper, the inverse of the above process is considered. Algorithms are described which, starting from the specified work shape, iteratively generate the tool shape required to produce that work shape. This avoids the multiple trial and error runs normally associated with the evolution of a tool shape in practice.
Detection of tooth breakage in end milling using machine tool axis control signals
Authors: Johns C , Prickett P W 
Published: October 2002

This paper considers the feasibility of utilizing existing machine tool axis drive control signals as a mechanism for the early identification of tool breakages. In particular the paper outlines the utilization of axis tachometer feedback signals as a means of monitoring the cutting process of a computer numerical control vertical milling machine. The work describes how a fault signature, corresponding to a tool breakage, can be identified in the axis tachometer signals at varying feed rates. The results of the preliminary testing of a monitoring system utilizing existing axis feed drive signals are presented. The paper then outlines steps being taken to develop the application of the method to an increased range of cutting conditions. This work was based upon a study of the interrelationship between the axis control signals when cutting is proceeding in either the X - or the Y -axis direction, and when both the X axis and the Y axis are feeding simultaneously.
Modelling with gradient information
Authors: Malik Z , Dyck D , Nelder J , Spence R , Lowther D 
Published: October 2002

Response surface models (RSMs) can be used to model expensive simulations or real measurements [1]. An RSM is constructed by simulating solutions at systematic points in a design space and fitting a model to them. The RSM is then employed in subsequent calculations (for instance in optimization) effectively replacing the original expensive simulator, which leads to considerable savings in time and money. A novel technique is presented here which uses the gradient of a function as well as the function itself to construct the RSM. Such an approach is possible because, for many types of simulations, gradient information is simple and cheap to obtain. The design of an electromagnetic speaker assembly is used to illustrate the new approach. The finite element method (FEM), on which the simulation is based, can provide gradient information at little extra cost and hence the benefits of using gradient information are considerable, being especially marked in higher-dimensional spaces.
Precision forging
Authors: Dean T. A. 
Published: October 2002

The manufacture of forgings to precise dimensional form and with specified mechanical and metallurgical properties has been the aim of industry since the industrial revolution. Developments towards this objective have been continual over the years as companies have sought commercial advantage in markets where competition from other industries such as foundry, powder metallurgy, sheet metal and fabrication is increasingly fierce. This paper starts with a brief review of historical milestones in the development of forging up to the first half of the twentieth century. The last 50 years have been a period of great activity in the establishment of a science base for forging technology and the development of cold, warm and hot processes with associated equipment to enable industry to provide components of greater complexity, increasing accuracy and nearer to net shape and research in the present author's laboratory has contributed to the advances in many areas. The major thrusts have dealt largely with improved tool designs and coatings for greater accuracy and longevity, techniques to enable metal to flow into die cavities of complex geometries and methods for complete process control, from raw material to product despatch. This paper attempts to highlight significant aspects of the technological developments which have been the result of world-wide activities. To give a coherent picture the steps of knowledge acquisition which have supported technological advancement are described using mainly the results of work from the present author's laboratory.
Compressor blade leading edges in subsonic compressible flow
Authors: Tain L , Cumpsty N. A. 
Published: October 2002

The flow around the leading edge of a compressor blade is interesting and important because there is such a strong interaction between the viscous boundary layer flow and the inviscid flow around it. As the velocity of the inviscid flow just outside the boundary layer is increased from subsonic to supersonic, the type of viscous-inviscid interaction changes; this has important effects on the boundary layer downstream and thus on the performance of the aerofoil or blade. An investigation has been undertaken of the flow in the immediate vicinity of a simulated compressor blade leading edge for a range of inlet Mach numbers from 0.6 to 0.95. The two-dimensional aerofoil used has a circular leading edge on the front of a flat aerofoil. The incidence, Reynolds number and level of free-stream turbulence have been varied. Measurements include the static pressure around the leading edge and downstream and the boundary layer profile far enough downstream for the leading edge bubble to have reattached. Schlieren pictures were also obtained. The flow around the leading edge becomes supersonic when the inlet Mach number is 0.7 for the zero-incidence case; for an inlet Mach number of 0.95 the peak Mach number was approximately 1.7. The pattern of flow around the leading edge alters as the Mach number is increased, and at the highest Mach number tested here the laminar separation bubble is removed. Positive incidence, raised free-stream turbulence or increased Reynolds number at intermediate inlet Mach numbers tended to promote flow patterns similar to those seen at the highest inlet Mach number. Both increased free-stream turbulence and increased Reynolds number, for the same Mach number and incidence, produced thinner shear layers including a thinner boundary layer well downstream. The measurements were supported by calculations using the MSES code (the single aerofoil version of the MISES code); the calculations were helpful in interpreting the measured results and were demonstrated to be accurate enough to be used for design purposes.
The spring-and-lever balancing mechanism, George Carwardine and the Anglepoise lamp
Authors: French M J , Widden M B 
Published: October 2002

Two short and direct methods of exact analysis of the spring-and-lever balancing mechanism are presented. It is shown that perfect balance can be achieved by the use of a close-coiled spring whose free length is effectively zero and whose stiffness is chosen appropriately. The two-degree-of-freedom balancing mechanism, commonly seen in desk lamps but useful in many other situations, is then analysed. The treatment is extended to allow for the weight of the components of the mechanism itself. The originator of these devices was George Carwardine, whose patents over the period 1931–35 show the evolution of his ideas on this subject. A short biographical note is included as an appendix.
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.
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.
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.
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.
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.
Walking machine leg design: The effect of leg geometry on knee torque
Authors: Howard D , Zhang S J , Sanger D J , Chen J Q 
Published: October 2002

The authors have been studying the fundamental mechanics of legged vehicles with the aim of establishing generic principles for their mechanical design. The approach to date has been to consider overall machine design and leg mechanism design separately. In leg design there is inevitably a trade-off between workspace (reach) and leg weight for given loading conditions. To understand this trade-off, the effects of leg geometry on both kinematic workspace and leg weight must be investigated. Leg weight is largely a function of the hip and knee design torques; the former is determined by the overall machine design which has been discussed elsewhere. This paper considers the effect of leg geometry on the total design torque that the knee must support through both its structure and the knee actuator. The actuator design torque is also considered. The leg geometry varied includes link lengths and knee twist angles. The necessary mathematical analyses are developed and data presented showing the relationship between knee or actuator torque and leg geometry.