Showing papers in "WIT transactions on engineering sciences in 1970"

MATHEMATICA-aided Study Of Lie AlgebrasAnd Their Cohomology - From Supergravity ToBallbearings And Magnetic Hydrodynamics

Abstract: We describe applications of a MATHEMATICA-based package for the study of Lie algebras and their cohomology such as (1) the possibility to write Supergravity Equations for any TV-extended Minkowski superspace and to find out the possible models for these super spaces; (2) the possibility of studying stability of nonholonomic systems (ballbearings, gyroscopes, electromechanical devices like a rotor collector with a gliding contact; waves in plasma, etc.); (3) description of the analogue of the curvature tensor for nonlinear nonholonomic constraints and the fields of solids or their surfaces, e.g., cones, as in optimal control; (4) a new method for the study of integrability of dynamical systems. The above problems are particular instances of the general problem to compute cohomology or homology of the given Lie algebra or superalgebra with various coefficients. The package SuperLie makes it possible to determine (1) Lie algebras via defining relations, from the Cartan matrix, realized via vector fields, as polynomials with Poisson or contact (Legendre) bracket, etc., (2) various modules over these Lie algebras (tensors, with vacuum vector, etc.), (3) list central extensions and deformations and even (4) back up the Leites conjecture (an analog of Kostrikin-Shafarevich conjecture) classifying simple Lie algebras over the algebraically closed field of characteristic 2 with new examples. For the details see references.

Error Analysis Of A Hexapod Machine Tool

Abstract: This paper describes the measurement and analysis of the quasi-static errors of a prototype hexapod milling machine at the National Institute of Standards and Technology (NIST). Emphasis is placed on a) the identification and definition of the parametric errors, b) the development of an analytical model to describe how these parametric errors affect errors in the position and orientation of the tool, c) identification of the most important parametric errors and their potential impact on performance, d) comparison of hexapod error characteristics to those of conventional machine tools, e) description of the techniques used to measure and estimate the hexapod errors, and f) application of the various concepts to model the geometrical and thermal errors of the NIST hexapod, including measurement results.

Estimation Of The Tangential Stresses In The Stator/Rotor Contact Of Travelling Wave Ultrasonic MotorsUsing Visco-elastic Foundation Models

Abstract: A new stator/rotor contact model of travelling wave ultrasonic motors is developed, in which the stick/slip behavior within the contact area is taken into account. The distributions of displacement and velocity and normal and tangential interface forces between rotor and stator are calculated. The results allow to estimate motor performance like e.g. the torque-speed curves as a function of the motor's parameters. Furthermore, the influence of main material and geometrical parameters and different operating conditions are investigated. The mathematical model developed in this paper can be used as a design tool for optimizing motor performance with the flexibility for a wide variety of geometries and materials.

Application Of Zagarola/Smits Scaling InTurbulent Boundary Layers With PressureGradient

Abstract: The empirical velocity scale determined for zero pressure gradient turbulent boundary layers of Zagarola and Smits [1], t/oo(

Mathematica In Education: Old Wine In NewBottles Or A Whole New Vineyard?

Abstract: On its own, a new piece of technology is not enough to change anything very much. Things change, in any field, not through technology alone but through the way people use it. How people use it depends in turn on how they think about it. In the early history of many technological innovations that went on to shape modern life profoundly there was a period in which the innovation was seen, and therefore used, mainly as a new way of doing old things. The revolutionary potential of new technology lies, however, in our finding new things to do with it. The impact upon educational practice of powerful software like Mathematica has been less profound than optimists hoped or pessimists feared. In many classrooms, I argue, it may be used as an adjunct to a curriculum and pedagogy unaltered in its essence. I here compare some possible approaches to the use of Mathematica with students, and ask of each one how close it comes to realising the potential of the software to transform the experience and nature of mathematical learning. Version 3 presents our community with fresh challenges and fresh temptations. I show how Version 3, at the same time as it opens up new, exciting avenues for educators, also makes it easier than before to "bend" Mathematica to old-fashioned pedagogic strategies that leave much of its potential unexplored. New tools for old jobs? One can't spend much time in technology-in-education circles without running into phrases like "the effects of calculators on children's learning of arithmetic" or "the impact of computer algebra systems on the traditional calculus curriculum". But no technological innovation, on its own, has any "effects", still less any "impact". Things don't have effects: actions do. What matters isn't what technology there is, but the way that technology is used. Transactions on Engineering Sciences vol 15, © 1997 WIT Press, www.witpress.com, ISSN 1743-3533

Investigation Of Axially Compressed Frusta AsImpact Energy Absorbers

Abstract: This paper reports, both experimentally and analytically, two new modes of plastic deformations of frusta when used as collapsible energy absorbers. Deformable energy absorbers are briefly introduced, and their relevance in crash protection systems is stressed. A general review of literature is presented on energy absorption by metallic absorber of various cross sections with special attention to frusta. Experimental results for the two deformation modes of capped spun aluminum frusta under quasi-static testing condition are given. An Explicit version of ABAQUS 5.7-3 FE code is used for computing and describing the deformation modes of the frusta. Good agreement is obtained between the experimental results and the FE predictions.

Residual Stresses Induced By Hole Cold Expansion

Abstract: This paper describes an X-ray diffraction technique for measuring residual stresses. The results of measurements at locations in the vicinity of plain and cold expanded holes in an aluminium alloy are presented. Residual stresses are shown to vary significantly in all three dimensions and two dimensional analyses commonly used for residual stress determination are shown to be inadequate. The results of a fatigue test programme are also presented in which simple aluminium alloy specimens containing plain and cold expanded holes were subjected to constant amplitude fatigue loading. The results show that cracks from plain holes continuously increase in growth rate to failure whilst cracks from cold expanded holes decrease in growth rate and frequently arrest. The arrested crack lengths are different on either face of the cold expanded specimens and this is equated to the different residual stress fields present. Fatigue crack growth rates predicted using a Green's function technique are compared with those measured experimentally.

Significance Of The Characteristic Length ForMicromechanical Modelling Of DuctileFracture

Abstract: The ductile fracture behavior of materials is considerably influenced by the characteristic microstructural length which may be related to the average inclusion spacing. However, it is not easy to introduce this critical parameter into micromechanical modelling. An additional problem met at the simulation with micromechanical models is the sensibility of numerical results to the mesh size. In this work the nonlocal damage concept developed by Bazant was introduced into the modified Gurson model. The ability of the nonlocal micromechanical concept to reduce the mesh-size dependency and the relationship between the localization limiter and the characteristic length have been studied by simulating damage development in shear bands, necking regions and at crack tips.

An Advanced 6-degree-of-freedom Laser SystemFor Quick CNC Machine And CMM ErrorMapping And Compensation

Abstract: It is well understood that if one wants to measure all geometric error components (i.e. linear, straightness, pitch, yaw, roll and squareness) of a 3 axes CNC machine tool using a conventional laser interferometer system [1,2], it may take somewhere between 2 to 3 days to complete. To measure each error component, the laser is required to setup and align with the appropriate optics, and each measurement has to be done independently. The entire process requires some 20+ measurement runs and some of the runs may have to be repeated since the environmental conditions may have changed since the first run. This process is so tedious and time-consuming that very often, component measurements are limited to linear only. Other parameters like straightness, squareness, and angles, although known to be equally important, are generally ignored. Since the successful introduction of the 5-Degree-of-Freedom (5-D) laser measuring system in 1996, and the 6-D laser* [3] in 1998, the generally perception of geometric error measurements and performance evaluation of machine tools has altered significantly. The new 6-D laser offers tremendous time saving by allowing an operator to setup and measure all 6-D errors (i.e. linear, straightness in Y and Z, plus pitch, yaw and roll angles) of a rectilinear axis simultaneously. Squareness measurement is readily achieved with the use of a penta-prism while measuring the perpendicular axis. In addition, alignment of the laser is made easy with the compact, on-machine mounting design and the build-in fine adjustments. * Patent Pending Transactions on Engineering Sciences vol 23, © 1999 WIT Press, www.witpress.com, ISSN 1743-3533

Data Assimilation Schemes For Non-linear Shallow Water Flow Models

Abstract: In theory K aim an filters can be used to solve many on-line data assimilation problems. However, for models resulting from the discretization of partial differential equations the number of state variables is usually very large, leading to a huge computational burden. Therefore approximation of the Kalman filter equations is in general necessary. In this paper two new algorithms are proposed, that extend the idea of the Reduced Rank Square Root filter [15] for use with non-linear models. The algorithms are based on a low rank approximation of the error covariance matrix and use a square root representation of the error covariance. For both algorithms the tangent linear model is not needed. The first algorithm proposed is accurate up to first order terms, which is comparable to the extended Kalman filter. The second, at the cost of twice the number of computations, is second order accurate, which may be important for strongly nonlinear models. Several experiments were performed on a model of the southern part of the North Sea to measure the performance of both algorithms. Both algorithms perform well when the the number of modes, i.e. the rank of the approximation, is set to 30. This corresponds to a computation time of approximately 30 model runs for the first order algorithm and 60 for the second order algorithm.

3-d Axisymmetric Numerical Analysis And Experimental Study Of The Fastener Hole Coldworking Process

Abstract: Most theories developed for the determination of the residual stresses and strains near the edge of a coldworked hole have been based on two-dimensional analysis considerations. They do not reflect faithfully the actual situation because of the three-dimensional nature of the coldworking procedure. In the present work, the ABAQUS finite element computer program was used to simulate the three dimensional behaviour of a cold expanded fastener hole. The through thickness hole profile and the variation in residual stresses and strains on both lateral surfaces and in the centre of the plate are studied and compared with experimental measurements of the residual stresses on both surfaces together with the values obtained from theoretical models proposed in the literature. Since the present analysis takes into account the non-uniformity of the coldworking procedure through the thickness of the hole, the proposed model may effectively be used to study the effect of the coldworking parameters on the residual stress distribution and thereby on fatigue life.

Interaction Of Newly Defined Stress IntensityFactors For Angular Corners In Two Diamond-Shaped Inclusions

Abstract: This paper deals with a row of equally spaced equal diamond-shaped inclusions with angular corners under various loading conditions. The problem is formulated as a system of singular integral equations with Cauchy-type singularities, where the unknown functions are the densities of body forces distributed in infinite plates having the same elastic constants of the matrix and inclusions. In order to analyze the problems accurately, the unknown functions of the body force densities are expressed as a linear combination of two types of fundamental density functions and power series, where the fundamental density functions are chosen to represent the symmetric stress singularity of \(1/r^{1 - \lambda _1 } \) and the skew-symmetric stress singularity of \(1/r^{1 - \lambda _2 } \). Then, newly defined stress intensity factors for angular corners are systematically calculated for various shapes, spacings, elastic constants and numbers of the diamond-shaped inclusions in a plate subjected to uniaxial tension, biaxial tension and in-plane shear. For all types of diamond-shaped inclusions, the stress intensity factor is shown to be linearly related to the reciprocal of the number of diamond-shaped inclusions.

Mass Transfer Analysis Of An Air Curtain System

Abstract: Air curtain systems can be used to prevent smoke propagation in the case of a tunnel fire. To study the performances of such devices, a scaled down model was designed at the Ecole des Mines de Nantes. Using experimental technics like hot wire anemometry or gas tracer detection, investigations on the influences of geometric and dynamic parameters give information about the design of the installations. It also explains how and where the mass transfer occurs through the air curtain.

Combined Mode Matching-integral EquationTechnique For Feeders Optimization

Abstract: The realization of high performances feeders is of fundamental importance for satellite telecommunication antennas. A powerful numerical technique for the analysis of circular corrugated horn is briefly presented and exploited, jointly with an optimization algorithm, to obtain optimized feeders. The code has been successfully used to develop horns currently mounted on telecommunication satellites. A sample of the most significant projects developed with this CAD environment will be also shown.

Measuring And Modelling Thermal Distortion On CNC Machine Tools

Abstract: Heat sources internal and external to a machme tool cause temperature gradients to arise due to resistance to heat flow in and around the machine tool and workpiece This causes linear expansion and distortion of the structural elements from which the machine tool is constructed The connectivity of the structural elements sets the effect of the expansion and distortion on the relative positions of the tool and workpiece, leading to thermal errors on the workpiece Measurement on a wide range of machine tools confirms that temperature gradients are significant in their effect on machining accuracy and that they move and change shape during the machining process An analysis of machine tool structures and connectivity shows that both the position and magnitude of temperature gradients is important in its effect upon the relative movement of the tool and workpiece A bending model that estimates the effects of thermal distortion using knowledge of the position of the temperature gradient is derived The performance of the bending model is compared with a finite element analysis model and a model that has no knowledge of the position of temperature gradients Results obtained from a vertical machining centre show that knowledge of the position and magnitude of temperature gradients is an essential part of predicting thermal distortion accurately

Effect of history on hydrogen assisted cracking

Abstract: In hydrogen assisted cracking, hydrogenation and crack growth are coupled processes. Consequently, particular histories of stress intensity factor K and crack size evolutions influence crack growth rate v that can occur at the same instantaneous K in a given material. Thus, curve v = v(K) in general does not possess uniqueness as a intrinsic material's property. This paper provides an analytical treatment of the problem by stress-strain assisted diffusion.

Fatigue Performance Of Friction Stir Butt Welds In A6000 Series Aluminum Alloy

Abstract: Friction stir welding is a novel solid state joining process for making low cost, energy efficient butt welds in aluminum alloy extrusions. The plate edges are clamped against a backing plate and the material is plastically deformed and stirred by a rotating tool moving along the joint line. The resulting weld bead is flush with the surface and exhibits little distortion. The material in the weld and heat affected zone (HAZ) has a fine-grained microstructure and a high tensile strength compared with welds produced by conventional arc welding methods. The present investigation was undertaken to determine the fatigue properties of friction stir welds in 5 mm thick plates in an AA6082 alloy. Extruded plates in the T4 condition were used in the test program. S-N tests in pulsating tension at R = 0.5 were performed on specimens with the weld transverse to the stress direction. Reference tests were made on the base material. Crack growth data were obtained for material in the weld metal, in the HAZ and base material. S-N tests were also made on conventional MIG butt welds from the same batch material to enable a comparison of the two welding methods. The results indicate that the fatigue strength of transverse friction stir welds is approximately 50 percent higher than the fatigue strength of MIG butt welds. The crack growth rates obtained for the weld material were lower than in the base material, probably due to a more fine grained microstructure in the weld region. INTRODUCTION The friction stir welding process has recently been developed as a cost effective alternative to conventional metal inert gas (MIG) and tungsten inert gas (TIG) Transactions on Engineering Sciences vol 8, © 1995 WIT Press, www.witpress.com, ISSN 1743-3533 226 Surface Treatment Effects II welding in aluminum alloys [1]. A major advantage of friction stir welding is that it is a solid state process involving a much lower heat input than that required in conventional arc welding methods. The weld itself and its adjacent narrow heat affected zone both have a very fine-grained microstructure with high mechanical strength. The high tensile strength of the weld material and the favorable geometry would also indicate that friction stir welds could have high levels of fatigue strength. A testing program was implemented to determine the fatigue properties of transverse butt welds of two alloys in the AA6000 series. The data presented in this paper are results from introductory tests on specimens fabricated from extruded plates in AA6082 material in the T4 temper condition. THE FRICTION STIR WELDING PROCESS In friction stir welding the plates to be joined are clamped on a backing plate to prevent movement A cylindrical shouldered tool with a specially profiled pin is rotated at a high speed, see Fig. la. The pin is slowly brought into contact with the joint line, and the material is heated by friction and plasticised in an annular volume around the pin. As the pin is lowered into the plates, soft material is extruded at the surface. Upon further lowering of the pin and movement along the joint line the shoulder face contacts the plate surface and the plasticised material is compressed against the face of the shoulder. The soft material is mashed by the leading face of the pin profile and transported to the trailing face of the pin where it consolidates and cools to form a solid-phase weld. The generation of a friction stir weld has many similarities with extrusion seam welds that form when material is joined in the weld chamber of an extrusion die [2]. The material flow, however, is somewhat different due to the more extensive mechanical mixing of the material from the two plates in the friction stir process. The properties of the weld are closely related to the tool technology. The tool bit shape and material determines the heating, plastic flow and forging pattern. Development of the friction stir welding process has up to now been concentrated mainly on butt and lap joints, however, introductory tests have shown that friction stir welding is suitable for a wide range of joint configurations [4], as shown in Fig. 2. EXPERIMENTAL PROGRAM The specimens were fabricated from AA6082 alloy plate material, in the T4 (as-extruded) condition. The plate thickness was 5 mm. The mechanical properties are listed in Table 1. Transactions on Engineering Sciences vol 8, © 1995 WIT Press, www.witpress.com, ISSN 1743-3533 Surface Treatment Effects II 227 Table 1. Mechanical properties of the AA6082 alloy in T4 temper.

A Practical System For 5-axis VolumetricCompensation

Abstract: Compensation is a recognised technique for correcting the systematic errors inherent to machine tool positioning systems. It offers a cost effective and flexible solution to the problem of enhancing machine accuracy. In spite of this controller manufacturers provide limited facilities for applying compensation, and in many cases linear positioning compensation only is available. The main reason for this is the potential complexity of a comprehensive compensation system able to cope with the variety of axis combinations and configurations available in the modern machine tool market. This problem is compounded by the demand from industry for precision 5 axis machining. This paper describes a practical geometric error compensation system that can be applied to any machine tool that has up to 5 axes. The system can correct for the effects of all the geometric errors associated with a machine's linear axes, together with the geometric errors associated with a fork type servo head. The system applies compensation dynamically and in real time as the machine moves throughout its working volume.

A general purpose thermal error compensation system for CNC machine tools

Abstract: Thermal effects cause the majority of machining errors on many types of machine tool, with linear expansion and distortion of the structural elements causing unwanted movement between the tool and workpiece. Heat inputs that cause temperature elevation and gradients come from many sources mternal and external to the machine tool and make thermal errors difficult to control without some form of compensation. Many thermal error modelling and compensation systems have been proposed which use neural networks, multi-regression analysis, heat modelling or probing techniques. However, each method suffers from one or more major drawbacks that limits its effectiveness when used in a practical machining environment. One feature of all the thermal error compensation techniques is their lack of flexibility that makes them difficult to apply to more than one machme type in a timely and cost-effective way. This paper describes a combined thermal and geometric error compensation system with a flexible structure that is general purpose in its application to any machine tool. The system can accept input from any number of temperature sensors. Information from the temperature sensors is acted upon by a novel programming language based model that estimates thermal movement and directs error components to a number of outputs for compensation by axis position modification. The entire compensation system can be applied either in a stand-alone computer that accepts a wide range of feedback signal types, or integrated into an open archtecture machine controller. The system allows the management of temporary or permanent input failures and displays every thermal error component as an aid to fault diagnosis. Both position independent and position dependent thermal errors can be reduced through compensation. The system has been applied to several machine tools.

A New Approach To The Modelling AndSimulation Of A CNC Machine Tool Axis Drive

Abstract: The paper presents a new approach to the modelling and simulation of a CNC machine tool axis drive. Modules have been created for different parts of the CNC machine tool. This allows greater flexibility in the construction of the model and an investigation of the interaction between model components. In this way all the shortcomings of the traditional methods are overcome. MATLAB / SIMULINK package has been used to simulate this new model for a CNC machine tool. Simulation results are very good, in accordance with CNC machine tool theory. The described approach allows the easy construction of detailed machine tool drive models. It represents the basis for future incorporation of geometric, non-rigid and thermal models of machine tool behaviour.

Heat Transfer At The Outer Surface Of ARotating Cylinder In The Presence Of AxialFlows

Abstract: A numerical analysis has been made of forced convection heat transfer for axial flow of air along the outer surface of a rotating cylinder. The analysis was two dimensional with an allowance for a swirling component of velocity around the cylinder. The results show that an exponential law correlates the numerical data well with an exponent of 0.8, such as is obtained for turbulent flow past a flat plate. The results were compared with that available for cross flow of air but it is shown that for axial flow, rotation never becomes dominant enough to make the Nusselt number independent of the blowing Reynolds number.

Experimental Design In Determining TheParametric Errors Of CMMS

Abstract: Procedures to determine the parametric error behaviour of co-ordinate measuring machines (CMMs) from measurements of calibrated artefacts such as ball plates are well established in principle. However, since their practical implementation requires significant resources, both in terms of measurement time and computation, it is important that these procedures provide reliable information. In recent modelling and simulation work at NPL, measurement experiments involving ball plates, ring gauges, step gauges and spheres have been analysed. The results show that the design of the experiment has a critical influence on the accuracy of the results obtained and that experiments, at first sight quite similar, can have markedly different degrees of effectiveness. This paper discusses how modelling and numerical simulation can be used to assess and improve effectiveness of different strategies involving a range of artefacts.

Thermal Effects On Solar Radiated Sand SurfacesContaining Landmines — A Heat Transfer Analysis

Abstract: This paper reports on the possibility of modelling thermal effects for detecting mines using infrared imaging systems. Results from experiments made in an indoor test landscape, using a sandbox and a solar panel with measuring instruments, are compared to simulated data from a heat transfer model. The radiation from the panel was varied in order to resemble the solar variation from sunrise to sunset. The different temperatures of the sand surface, the sand at different depths and on the surfaces of the four generic mines were sampled at one-minute intervals throughout the experiments. Infrared cameras working in the 2-5 p.m and 8-12 jam bands were used in order to record images of the sand surface. The camera system calculates the apparent temperature of selected areas of the images based on the detected radiation The simulation was carried out using the Finite Element Method. The sequences of the infrared images show the variation in emitted radiation as the irradiation of the surface is varied. There are two different phenomenon dominating the two wavelength bands In 2-5 p.m region there is a reflecting dominance and in the 8-12 p.m region the radiation originates mainly from emission. The simulation shows good agreement with the experimental result for the depth profile, where the temperatures were studied along a vertical line through the centre of the mine, as well as for the surface temperature

Circular Inclined Punch Problem With Two Corners To Contact With A Half Plane With A Surface Crack

Abstract: A circular rigid punch with two corners coming into contact with an elastic half plane is presented to initiate a surface crack on the boundary of the half plane. The punch is usually inclined by an angle owing to the existence of the crack and the frictional force on the contact region. The problem is solved by three steps; the first step is to map the half plane with a surface vertical crack into a unit circle by a rational mapping function; the second step is to transform the problem into a Riemann-Hilbert problem; the third step is to solve the R-H equation. Then stress components and stress intensity factors of the crack are calculated. The inclination of the punch is decided by the condition that the resultant moment on the contact region about the center of the punch is zero.