bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experimental Study of the Mean Flow and Turbulence Structure Of Cross-Flow Over Tube Bundles
Authors: Balabani S , Yianneskis M
Published: February 2007

The velocity characteristics of cross-flow over tube bundles were investigated in a water tunnel. Three tube arrays with a transverse pitch ratio of 3.6 were studied: an in-line and two staggered arrays with longitudinal pitch ratios of 2.1, 1.6 and 2.1 respectively. The mean velocities, turbulence levels, spectra, time and length scales and dissipation rates were determined from ensemble-averaged and time-resolved laser Doppler anemometry (LDA) measurements. The pressure drop across the bundles was also measured.

The staggered arrays were found to generate higher levels of turbulence and a higher pressure drop. Turbulence kinetic energy reaches a maximum downstream of the second row in staggered arrays. The wake regions in both geometries are anisotropic with transverse r.m.s. velocities being higher than axial ones. Increasing the longitudinal spacing in the staggered configuration results in lower r.m.s. levels in the wakes and alteration of the recirculation characteristics. A discrete periodicity with a Strouhal number of 0.26 was identified in the 3.6 times 1.6 staggered array which is associated with vortex shedding. Turbulence scales and dissipation rates were estimated and compared with numerical predictions.
Three-Dimensional Shortest Path Planning in the Presence of Polyhedral Obstacles
Authors: Jiang K , Seneviratne L D , Earles S W E
Published: February 2007

A new algorithm is presented for solving the three-dimensional shortest path planning (3DSP) problem for a point object moving among convex polyhedral obstacles. It is the first non-approximate three-dimensional path planing algorithm that can deal with more than two polyhedral obstacles. The algorithm extends the visibility graph concept from two dimensions to three dimensions. The two main problems with 3DSP are identifying the edge sequence the shortest path passes through and the turning points of the shortest path. A technique based on projective relationships is presented for identifying the set of visible boundary edges (VBE) corresponding to a given view point over which the shortest path, from the view point to the goal, will pass. VBE are used to construct an initial reduced visibility graph (RVG). Optimization is used to revise the position of the turning points and hence the three-dimensional RVG (3DRVG) and the global shortest path is then selected from the 3DRVG. The algorithm is of computational complexity O(n3vk), where n is the number of verticles, v is the maximum number of vertices on any one obstacle and k is the number of obstacles. The algorithm is applicable only with polyhedral obstacles, as the theorems developed for searching for the turning points of the three-dimensional shortest path are based on straight edges of the obstacles. It needs to be further developed for dealing with arbitrary-shaped obstacles and this would increase the computational complexity. The algorithm is tested using computer simulations and some results are presented.
Flaw Detection in Composite Materials Using Infra-Red Thermography by the Method of External Heating
Authors: Dutton A G
Published: February 2007

A non-destructive technique for the detection of air-filled voids and foreign bodies within glass/polyester composite material is described. The technique involves the use of infra-red thermography with an external radiative source to excite temperature differences at the surface of the body. A low-intensity heat source is used to avoid large overall temperature rises which might damage the composite and some care is taken to ensure a uniform heat distribution. Results are presented that show the detection of air-filled voids at depths up to 9 mm. A qualitative measure of defect depth can be derived from the test results. A one-dimensional heat conduction model is presented and shown to reproduce the qualitative nature of the measurements in terms of defect depth and type.
Theoretical Analysis of Large Deformation Simultaneous Tearing and Peeling of Elastoplastic Materials
Authors: Liu J H , Atkins A G , Jeronimidis G
Published: February 2007

Simultaneous tearing and peeling of multiple strips is theoretically investigated using the large deflection theory of cantilevers made of elastoplastic material with linear strain hardening. The relationship between the fracture toughness and the curvature at the fracture propagation front is obtained for general cases. It is shown that for the moment loading case, the non-dimensional external moment, m1, during tearing and peeling along straight paths, is a constant and is independent of the initial beam length Lo. With concentrated force loading, the non-dimensional force f will reach a constant value f=fm during propagation. It is shown that fm is almost the same for both initially straight and pre-bent beams, and decreases with an increase in the external force loading angle φ. For initially straight beams, when the non-dimensional fracture toughness, D, is small, fm may be less than the initiation force f1 for fracture. Fm/H does not increase linearly with an increase in the beam width B0 and decreases at large B0 after it passes through a peak value. Comparison is made with experimental results for the tearing of ductile metal sheets along straight paths and the tearing fracture toughness value is found, including a method that uses propagation crack front curvature alone, without additional reference to the tearing force. However, the accuracy of the curvature at the crack propagation front has a large effect on the estimation of fracture toughness. High work-hardening and/or low toughness materials have no rapid change of curvature away from the crack front so that good estimates are possible and vice versa for low work-hardening solids.
Dynamic Instability Characteristics of Plates Subjected to Partially Distributed Follower Edge Loading with Damping
Authors: Datta P K , Deolasi P J
Published: February 2007

The dynamic instability characteristics of rectangular plates with at least one free edge and subjected to non-conservative follower loading at the free edge has been studied by using the finite element formulation. The loading is distributed partially at the centre of the free edge. The modal transformation is applied to the resulting equilibrium equation for subsequent analysis. Structural damping is introduced into the system in terms of equivalent viscous damping. The effects of load bandwidth, plate aspect ratio, direction control parameter, damping, etc., on the stability behaviour of the plates are studied. The results show that the load bandwidth has a significant effect on the dynamic instability characteristics of the plates. The results also show that, under follower loading, the system is susceptible to instability due to flutter alone or due to both flutter and divergence, depending upon the system parameters. Structural damping may significantly reduce the critical flutter loads of the plates.
Evaluation of the Effect of Droplet Collisions on Spray Mixing
Authors: Gavaises M , Theodorakakos A , Bergeles G , Brenn G
Published: February 2007

A spray model, implemented in a three-dimensional computational fluid dynamics (CFD) code has been used to evaluate the effect of droplet collisions on spray mixing resulting from the overlapping of liquid spray cones produced by two parallel hollow-cone nozzles under the influence of a cross-flow. The computations are compared with experimental results from phase Doppler anemometer (PDA) measurements in mixing steady sprays. The results show that the droplet collisions, which mainly occur in the mixing area of the two different sprays, have great influence on the droplet size and, as a consequence, on the predicted droplet velocities, especially at distances far from the spray nozzles. Information about the collision mechanisms as well as about droplet velocities and droplet dispersion due to collisions is also presented.
Application of Domain Decomposition in Modelling Flow and Heat Transfer Problems
Authors: Muralidhar K , Chatterjee A , Rao B V Nagabhushana
Published: February 2007

The present work is concerned with the application of the domain decomposition technique for modelling transient flow and heat transfer problems. The solutions obtained within each subdomain are matched at the interfaces using Uzawa's algorithm. This algorithm has been originally developed in the context of steady heat conduction. The objective of the present study is to test and extend the algorithm to a wider class of problems. Examples considered are non-linear heat conduction in one and two dimensions, simulation of oil recovery from porous formations using water injection, movement of a plane thermal front and heat transfer from a cylinder placed in Darcian flow. The suitability of Uzawa's algorithm for interface treatment with up to nine subdomains has been studied. The method is found to converge to the full-domain solution in all cases considered. Besides this, results show that there are additional advantages which include the generation of small matrices and, in certain cases, a marginal reduction in CPU (central processing unit) time, even on sequential machines.
Profile Determination of Planar and Spatial Cams with Cylindrical Roller-Followers
Authors: Tsay D M , Lin B J
Published: February 2007

A simple and useful procedure that can be used to determine profile surfaces of planar and spatial cams with cylindrical roller-followers is presented. Based on the rigid-body transformation between the cam and the roller-follower, the pitch (curve) surface which is the path of the point of the roller centre can be easily generated. Then the analytical profile surface of the cam can be represented by the offset surface of the pitch surface with a distance equal to the radius of the roller. To illustrate the ease and effectiveness of the approach, analytical expressions of profile surfaces of a disc cam, two cylindrical cams and two globoidal cams are typically given. Furthermore, in order to show the validity of this method, the results are then compared to those derived by an earlier procedure based on the screw theory.
Statistical Mechanics Material Model for the Constitutive Modelling of Elastomeric Compounds
Authors: Allport J M , Day A J
Published: February 2007

Material models for the finite element analysis (FEA) of polymeric and elastomeric compounds are only available in limited form in most commercial finite element (FE) packages. The most common are the phenomenological Mooney-Rivlin and the Ogden models, for which the constants bear no relationship to the physical or chemical characteristics of the rubber and their derivation is difficult. Both models are limited in their accuracy for filled rubbers used in combined states of tensile and compressive deformation, and since these are common operational conditions for engineering components such as drive couplings, engine mounts and torsional vibration dampers, their use in engineering analyses is restricted.

In this paper a statistical mechanics material modelling approach for synthetic, filled elastomeric compounds in FEA is presented. Using styrene-butadiene rubber (SBR) as an example, the theory and its application in the commercially available ABAQUS finite element analysis program is explained. FE models of tensile and compressive specimens in two and three dimensions are used to demonstrate the use of the model, and results are presented, discussed and compared with measured data. Good correlation in both tension and compression is demonstrated. A practical application of the model to the SBR blocks in a Holset torsional drive coupling is presented; this analysis involves complex issues of mesh design and contact modelling. The results show good agreement with measured performance, and clearly demonstrate how this type of material modelling approach can be effectively used in the computer aided engineering and design of engineering rubber components.
Couette Flow Heat Loss Model for the Rotary Combustion Engine
Authors: Gorla R S R , Bartrand T A
Published: February 2007

A novel model for predicting heat transfer in a rotary engine was formulated and implemented in a zero-dimensional engine performance model. Results were compared with a commonly used intermittent combustion engine heat transfer model and with results from a three-dimensional simulation of flow within a rotary engine. When squish effects associated with fluid motion within the chamber were included, the Couette flow model reproduced peak heat transfer rates and timing for the peak heat transfer rate was better than that of the commonly used heat transfer model.

Previously, rotary engine performance models have employed flat plate type heat transfer correlations. These correlations, though useful, do not model the flow physics in the rotary engine faithfully. Rather than flow over a flat plate, flow in the rotary engine was approximated as turbulent Couette flow. The Couette model was altered to account for centre-line velocities higher than half the rotor speed. There are two advantages to using the Couette flow model. Firstly, as noted, the underlying physics of the Couette flow model is closer to conditions in the rotary engine. Secondly, with the Couette flow model it is possible to differentiate between the rotor and housing heat transfer coefficients.
Optimal Roll Control of a Single-Unit Lorry
Authors: Lin R C , Cebon D , Cole D J
Published: February 2007

Lateral acceleration control and linear quadratic regulator (LQR) theory are used to design active roll control systems for heavy goods vehicles. The suspension consists of a limited bandwidth hydraulic actuator in series with an anti-roll bar. The procedure used to determine suitable controller gains is described. The simulation results show that roll control of a single-unit lorry requires an actuator bandwidth of 6 Hz and mean power of approximately 17 kW for a ‘worst case’ random steering input. The static roll-over threshold of this vehicle is increased by 66 per cent when compared with the same vehicle with passive suspensions and the r.m.s. lateral load transfer is reduced by 34 per cent for a typical random steering input.
Particle Image Velocimetry Measurements of In-Cylinder Flow in a Multi-Valve Internal Combustion Engine
Authors: Reeves M , Garner C P , Dent J C , Halliwell N A
Published: February 2007

Particle image velocimetry (PIV) has been used here to characterize the formation and breakdown of barrel swirl or tumble in a production geometry, four-stroke, four-valve motored optical internal combustion (IC) engine. The engine was motored at 1000 r/min at wide open throttle. Double exposed images were recorded from a plane parallel to the cylinder axis which passed through the centre-lines of an inlet and exhaust valve. Particle image velocimetry images from a range of crank angles between inlet valve closure and the ignition point were interrogated by digital autocorrelation to give two-dimensional maps of instantaneous velocity.

The in-cylinder flow is characterized by the formation of an ordered barrel swirl or tumbling vortex, which is shown to persist throughout the majority of the compression stroke with maximum velocities of the order of three times the mean piston speed and a high velocity bulk flow at the time of ignition near the spark plug. With respect to the PIV technique itself, image labelling and cross correlation are considered essential to improve measurement dynamic range, valid data rate and tolerance to velocity gradients in the turbulent flows encountered near top dead centre (TDC).
Study on Independent Effects of Diesel Engine Operating Conditions on Nitric Oxide Formation and Emissions Through Schematical Combustion Simulation
Authors: Desantes J M , Lapuerta M , Salavert J M
Published: February 2007

A mathematical model has been used to evaluate the effect of diesel engine operating conditions on nitric oxide formation and emissions. Although there are several formation pathways during diesel combustion, only the supposed most important one was considered in the present work: the thermal mechanism. The effect of the engine operating conditions was simulated by means of schematical variations of local temperature and fuel–air ratio of the mixture. The evolution of these local variables is described by three characteristic time intervals, which define the timing of the following items: the temperature and pressure peaks; the dilution of burnt products with surrounding air; and the decay of temperature and pressure due to expansion. In addition, the temperature peak was related to the adiabatic flame temperature, which was previously calculated for each mixture condition. A computational parametric study was carried out by varying each of the local mixture parameters and characteristic times, either separately or in combinations. The trends obtained show a qualitative agreement with those obtained by other authors from experimental tests on different diesel engines. The analysis of these trends contributes to a better understanding of the sources of NO diesel emissions and could provide guidelines for cleaner diesel engine design.
Truck Suspension Design to Minimize Road Damage
Authors: Cole D J , Cebon D
Published: February 2007

The objective of the work described in this paper is to establish guidelines for the design of passive suspensions that cause minimum road damage. An efficient procedure for calculating a realistic measure of road damage (the 95th percentile aggregate fourth power force) in the frequency domain is derived. Simple models of truck vibration are then used to examine the influence of suspension parameters on this road damage criterion and to select optimal values.

It is found that to minimize road damage a suspension should have stiffness about one fifth of current air suspensions and damping up to twice that typically provided. The use of an anti-roll bar allows a high roll-over threshold without increasing road damage. It is thought that optimization in the pitch-plane should exclude correlation between the axles, to ensure that the optimized suspension parameters are robust to payload and speed changes.

A three-dimensional ‘whole-vehicle’ model of an air suspended articulated vehicle is validated against measured tyre force histories. Optimizing the suspension stiffness and damping results in a 5.8 per cent reduction in road damage by the whole vehicle (averaged over three speeds). This compares with a 40 per cent reduction if the dynamic components of the tyre forces are eliminated completely.
An Experimental Study of a Fluidic Type Fuel Injector in Comparison With a Solenoid Type Injector
Authors: Huang Q , Sansum D P
Published: February 2007

An experimental study of a fluidic type fuel injector for spark ignition (SI) engines is described in this paper. The fluidic injector unit consists of four monostable fluidic devices controlled by a solenoid interface and air–fuel mixing nozzles for better fuel atomization. The prototype fluidic injector unit was implemented on a research engine. The results of air–fuel ratio (AFR) variations, engine combustion characteristics and exhaust emissions from the fluidic injector were compared with those from a baseline solenoid type injector.

It was demonstrated from single cylinder engine tests that the fluidic system produces 9 to 20 per cent lower hydrocarbon (HC) emissions and 5 to 8 per cent higher indicated mean effective pressure (IMEP) than the baseline injection system. This has confirmed the effectiveness of the use of air-assisted fluidic injectors and the fact that improved mixture preparation and better fuel presentation are obtained by the fluidic injector. However, the lean misfire limit by the fluidic injector is reduced by 1 AFR compared to that of the solenoid injector due to large AFR dispersions caused by cyclic fuel delivery variations of the fluidic device. It is envisaged that the fluidic injector potentially offers cost and emission benefits for SI engines when the cyclic flow stability is improved.
Development and Validation of a Computer Simulation Model for Diesel Fuel Injection Systems
Authors: Arcoumanis C , Fairbrother R J , Gavaises M , Flora H , French B
Published: February 2007

The basic elements of a computer simulation model for a diesel fuel injection system based on a distributor-type rotary pump are summarized followed by details of the experimental set-up used to validate it. The results of parametric studies performed with the validated model on the effect of various geometric parameters on the injection characteristics are presented and discussed.
The Transmission of Vibration to the Occupants of a Car Seat with a Suspended Back-Rest
Authors: Lewis C H , Griffin M J
Published: February 2007

A new type of car seat has been designed in which the back-rest is able to move freely in the vertical direction. The design allows the back-rest to follow the vertical vibration of the back of an occupant of the seat. This is intended to decrease any strain on the lumbar part of the spinal column caused by a different vertical motion at the seat squab and the seat back. The transmission of vertical (z axis) vibration from the base of this seat to the seat surface, to the back-rest and to the backs and heads of seat occupants has been measured. Measurements were made with the seat back fixed, to prevent vertical motion relative to the seat frame, and with the seat back free to move.

Vibration transmissibilities from the seat base to the seat surface were characterized by a resonance at frequencies in the region of 4 Hz. The resonance frequencies were slightly higher with the fixed back-rest than with the moving back-rest. The transmissibilities at frequencies above 4 Hz were generally higher with the fixed back-rest. Measurements with no contact between the seat occupants and the seat back indicated that the dynamic properties of the human body and the seat cushion were less influenced by the moving seat back than by the fixed seat back. Differential motion between the seat surface and seat back was smaller with the moving seat back than with the fixed back.
Road-Damaging Potential of Measured Dynamic Tyre Forces in Mixed Traffic
Authors: Potter T E C , Cebon D , Collop A C , Cole D J
Published: February 2007

A series of tests was conducted on a British trunk road in which the dynamic tyre forces generated by approximately 1500 heavy goods vehicles (HGVs) were measured using a load measuring mat containing 144 capacitive strip sensors. The data were used to investigate the relative road-damaging potential of the various classes of vehicles. Air suspensions were found to be more effective at static load equalization than steel suspensions. Two criteria were used to rank axle groups in terms of road damage: the average dynamic load coefficient and the 95th percentile aggregate fourth-power force. These criteria were found to rank axle groups in different orders, due to spatial correlation between tyre forces. On average, air suspended vehicles were found to generate smaller dynamic loads and hence less road damage than steel suspended vehicles. However, some air suspensions with inadequate suspension damping were found to generate very high dynamic loads and consequently very high levels of road damage.
An Investigation of Combustion Chamber Shapes for Small Automotive Direct Injection Diesel Engines Employing Spray Impaction
Authors: Park K , Watkins A P
Published: February 2007

In modern compact combustion chambers of direct injection diesel engines with high-speed injection spray, the impaction of the spray on the wall is almost inevitable. This may result in high levels of unburnt hydrocarbons. However, a number of combustion systems have been developed which deliberately employ wall impaction as a means of breaking up the fuel spray and/or directing it in a desired direction. These include chambers which employ impaction sites attached to the cylinder head or a cut-off pip in the piston bowl centre.

A further type of geometry, which has been the subject of an earlier investigation by the authors, is presented here, in which cut-off pips are provided for a number of sprays directed not only straight down into the combustion chamber centre but also across and down into the bowl in the normal radial direction. For the current analysis, the sizes of the pips and their positions are based on the previous work. All these cases are investigated using a computation fluid dynamics code employing non-orthogonal grid systems, the k–epsis; turbulence model, the implicit PISO {pressure implicit by splitting of operators) solution scheme, and the discrete droplet model for the sprays.

Comparisons of simulations with relevant experimental data show that the code returns good qualitative and quantitative results. Apparently good qualitative results are also returned for a number of the combustion chambers employing impaction sites attached to the combustion head and in the centre of the piston bowl. Simulations of combustion chambers employing a number of impaction sites around the piston bowl indicate the likely advantages of such a system over a conventional highly swirled one.
Diesel Injector Dynamic Modelling and Estimation of Injection Parameters from Impact Response Part 1: Modelling and Analysis of Injector Impacts
Authors: Gu F , Ball A D
Published: February 2007

Part 1 of this paper presents the development and validation of a detailed dynamic model for the needle motion of a common hole-type dieselfuel injector as used in a direct injection diesel engine. The injector needle motion is described as a two-mass piece-wise linear vibro-impact system, unlike the conventional modelling techniques which use a single-mass approach. The use of two masses permits analysis of both the needle impact behaviour and of the more general dynamics of the fuel injection process.

Model parameters are derived from a combination of measurement and estimation, and the subsequent model is evaluated via direct measurement of the spring seat displacement. The opening and closing needle impact behaviour is shown to exhibit close correlation with key injection parameters, including fuel injection pressure, fuelling rate and timing.

The model revealed that the impact of the needle when opening is found to exhibit lower amplitude but more high-frequency components than the impact associated with the closing. The measurement of the injector body vibration response to these impacts is shown to enable non-intrusive estimation of injection parameters, alleviating the problems associated with conventional intrusive needle-lift measurement.
Experimental Measurements and Theoretical Predictions of the Thermohydraulic Performance of Clean Rooms for the Semi-Conductor Industry
Authors: Quarini G L , Chang Y C
Published: February 2007

There is a need to engineer working areas where air-borne pollution is below specified limits. This need arises from activities as diverse as food processing, semi-conductor manufacture and surgery. In this paper, detailed experimental measurements of flows in a semiconductor manufacturing room are reported. Computational fluid dynamics (CFD) has been used to study the flows within the room. Good agreement was found between the measured and predicted mean flow velocity distributions. Both the experimental measurements and the numerical predictions suggest that the ventilation system used in this room, which is of a common industrial design, does not produce ideal clean room conditions.
Current Issues and Technologies for the Reassessment of Existing Offshore Installations
Authors: Billington C J , Bolt H M
Published: February 2007

The statutory requirement to prepare safety cases for United Kingdom offshore platforms following the Piper Alpha disaster, the extensive damage to offshore platforms in the Gulf of Mexico caused by Hurricane Andrew and the desire to extend the operational life of hydrocarbon production platforms throughout the world has led to several important industry initiatives concerning requalification and reassessment of offshore platforms.

This paper describes the development of a new industry reassessment guideline document, the philosophy within the guidelines and the technologies available for reassessment. In particular, the availability of validated non-linear system ultimate strength collapse analysis computer software is revolutionizing the reassessment process by being able to take advantage of the system reserve and residual strength above the individual component design capacity level.

However, there are problems in the application of these advanced techniques and there are several generic issues concerning acceptable levels of risk, the scope and methodology of reassessment and the development of international standards for reassessment. The paper draws out these issues and describes industry initiatives that are working towards their resolution.
A Fluidic Flowmetering Device for Remote Measurement
Authors: Boucher R F , Beck S B M , Wang H
Published: February 2007

This paper deals with an experimental study of a new fluidic flowmetering device. When fluid flows through this device, it alternates between its two states of high and low resistance, producing pressure pulses in the flow. The frequency of these pulses is directly proportional to the fluid flowrate and can be detected far down-stream of the device. One attraction of this device is that it could be designed with a stand-by mode so that most of its time could be spent in its low-resistance state with little effect on the fluid flowrate. It contains no moving parts, and so in principle is completely maintenance free. This potential very high reliability means that it can be used in extremely hostile environments. Possible uses include measuring oil flowrates under the sea-bed or in any process industry where there is a hot, radioactive, inaccessible or corrosive environment which precludes the installation of a conventional flowmeter. It could also be installed as a meter for measurement where penetration of the pipe wall is to be avoided, with pulses being detected on the pipe external surface.
A Preliminary Study of a Single-Vessel Pharmaceutical Processor
Authors: MacGregor S A , Staniforth J N , Newnes L B , Kay G R
Published: February 2007

A preliminary study of the operation of a single-vessel processor for pharmaceutical products is presented. The results show that it is possible to achieve size reduction and mixing as effectively as conventional methods. The single-vessel processor offers great potential for any batch manufacturing processes in terms of both speed and efficiency.
Recipe Control for Closed-Field Unbalanced Magnetron Sputter Ion-Plating Machines
Authors: Roskilly A P , Barlow M I
Published: February 2007

The requirements, specification and chosen implementation of a secure, reliable and compact process control system on a personal computer is described for automating closed-field unbalanced magnetron sputter ion-plating machines. The made-to-order nature of many such installations has consequences for the design of the control system, necessitating great flexibility and ease of reconfiguration. The system described has been implemented for the deposition of Al2O3, alloy nitride, ‘diamond-like’ carbon and other coatings. Examples are presented of the control script language and a typical mimic display.
Reliability Assessment of Mechanical Systems
Authors: Moss T R , Andrews J D
Published: February 2007

The assessment of mechanical systems is not an exact science and predictions can be subject to considerable uncertainty. In this paper the particular problems of mechanical system reliability assessment are discussed and a general methodology presented based on experience from availability studies carried out on offshore and onshore process plant.
The Effect of Discontinuities on the Long-range Propagation of Lamb Waves in Pipes
Authors: Alleyne D N , Cawley P
Published: February 2007

Laboratory tests and supporting finite element predictions of the interaction of Lamb waves with typical features found in chemical plant pipework are reported. The L(0, 2) mode is an attractive mode to use for long-range (> 15 m) propagation in 2–12 inch (51–305 mm) nominal bore pipes and the behaviour of this mode has been studied using a bonded piezoelectric transducer system. The amplitude of the reflection from butt welds and welded supports was found to be between 5 and 20 per cent of the incident amplitude, while flanges gave almost 100 per cent reflection. It is therefore not possible to test past a flange. It has been shown that wet or dry insulation has little effect on the propagation of the L(0, 2) mode, so inspection under insulation is feasible. Initial work on the reflections from defects is also reported. It has been shown that when the axial extent of the defect is significantly less than a wavelength of the L(0, 2) mode (about 80 mm at 70 kHz), the reflectivity is largely a function of the depth and circumferential extent of the defect. The reflections from notches, troughs and corrosion patches have been detected successfully.
Aerodynamic Drag on Trains in Tunnels Part 2: Prediction and Validation
Authors: Vardy A E
Published: February 2007

The principal sources of aerodynamic drag on simple trains in tunnels are (a) surface skin friction and (b) stagnation pressure losses at the nose and tail. On sufficiently long trains, the first of these is dominant. On shorter trains, local losses can be more important.

This paper seeks to provide a theoretical basis for predictions of the dependence of drag on the train/tunnel blockage ratio, attention being given to tunnel resistance as well as to train resistance. Hitherto, most predictions have relied on empirical formulae.

It is shown that the train skin friction coefficient varies approximately linearly with the blockage ratio, βz. The dependence increases with increasing train roughness. The nose loss coefficient kN is shown to be smaller than 0.1 for reasonably streamlined noses. An approximate relationship between kN and βz is hypothesized. The tail loss coefficient kT is shown to be approximately equal to β2z for poorly streamlined tails. A tail shape coefficient is introduced for use with more streamlined tails.
Validation of Measures to Improve Rail Vehicle Crashworthiness
Authors: Lewis J H , Rasaiah W G , Scholes A
Published: February 2007

The authors describe development work in the area of crashworthiness of railway vehicles carried out during a four year period in the UK. Specific areas of investigation include vehicle overriding and the collision behaviour of complete trains or rakes of vehicles. Developments in crashworthiness by European railways are also discussed.
Mode Tracking During Flutter Testing Using the Modal Assurance Criterion
Authors: Desforges M J , Cooper J E , Wright J R
Published: February 2007

Tracking the aeroelastic modes of an aircraft through changing flight conditions is an essential element of flight flutter testing, which is made difficult by corrupted data and high modal density. The modal assurance criterion (MAC), a method of evaluating the consistency of two modal vectors, is shown to simplify the mode tracking procedure by putting a numerical value on the correlation between pairs of modes identified at consecutive flight conditions. Representation of the resulting MAC values as a colour map gives a clear visual indication of modal consistency. An automated approach to mode tracking is introduced and shown to work on aircraft-type systems, over significant changes in flight condition up to and beyond the flutter speed. Some potential problems of a practical implementation are discussed.
Flight Validation of the Computer Program CBAS (Cable Body Airborne Simulator)
Authors: Henderson J F , Ireland B
Published: February 2007

Flight measurements of the three-dimensional motions of an airborne towed target and the towing aircraft have been compared with the motions calculated by the computer program CBAS (Cable Body Airborne Simulator). The agreement is excellent and is considered to validate the program.
A Geometry Independent Technique for Solid Propellant Grain Design
Authors: Mashayek F , Farzad H , Ashgriz N
Published: February 2007

One of the most important parameters which determines the thrust-time history of a solid propellant rocket is the initial propellant grain shape and its variation with time. An alternative technique to the presently available grain design codes is introduced here which can calculate the time evolution of the grain shape for any given initial geometry. This technique is based on the volume fraction method which has been previously used in the modelling of free surface flows. The new technique does not have any restriction on the shape of the grain and is capable of handling any variation in burning rate with time and position along the burning surface. This technique is applied to several grain types, and the rocket thrust and the internal pressure are calculated with time. A power relationship is used to calculate the burning rate from the internal pressure. Also, the effect of the propellant surface curvature on the shape evolution of the grain is discussed.
Application of Approximate Equations for Waveriders with Multi-Directional Curvature
Authors: Lin S-C , Shen M-C
Published: February 2007

This study thoroughly analyses the parameters affecting aerodynamic performance and the shapes of the multi-directional curvature waverider. This hypersonic vehicle is developed from a hypersonic flowfield of a perturbed cone with longitudinal and transverse curvatures, as derived by combining the hypersonic small disturbance theory (HSDT) with the perturbation method. A range both theoretically and practically sound is also determined to alter the parameters. Numerical methods are then used to find the vehicle's optimal shape having a maximum lift, lift–drag ratio, or volumetric ratio when the viscous effect is considered. Furthermore, the curve fitting method is utilized to establish a set of approximate equations capable of speedily estimating the aerodynamic performance and the volumetric ratio. In addition several samples are presented to illustrate how to use this set of equations to generate the optimal shape under any combination of constraints in the lift–drag ratio, lift, and volumetric ratio. Notably, the viscous effect is approximate and takes no account of displacement corrections. Moreover, the base drag is neglected here.
Control Law Design for a Thrust Vectoring Fighter Aircraft Using Robust Inverse Dynamics Estimation (RIDE)
Authors: Muir E , Bradshaw A
Published: February 2007

Control laws have been designed for a high performance fighter aircraft using robust inverse dynamics estimation (RIDE) with the aim of providing good control at high angles of attack. This necessitates the use of thrust vectoring in flight conditions where aerodynamic control surfaces become ineffective. It is shown that the RIDE controller is able to transfer smoothly from using the aerodynamic surfaces to thrust vectoring during post-stall manoeuvring. The RIDE controller is structured so as to estimate the inverse dynamics of the aircraft and gives the designer freedom to assign the dynamics of the controlled states. Simulation results demonstrate that RIDE provides a simple method for the design of control laws which give specified response characteristics across the flight envelope and are robust to plant variations.
The Effect of Ultrasonically Determined Anisotropy on Longitudinal Fracture of Cortical Bone
Authors: Han S , Medige J , Ziv I
Published: February 2007

This study examines the effects of density and microstructural anisotropy on longitudinal crack propagation in compact bone. Bovine cortical bone samples were demineralized by acid, producing specimens with a wide range of bone density. Ultrasound velocity was measured in the radial and longitudinal directions of each specimen using a pulse transmission technique. A proposed microstructural anisotropy parameter based on these ultrasound velocities was introduced and evaluated. The critical stress intensity factors KIC of these specimens were determined by mechanical fracture toughness tests. A linear regression study demonstrated that assessment of fracture toughness was precisely achieved by the combined effect of density and microstructural anisotropy of compact bone (r2 = 0.951, p < 0.0001).
A Comparison of Finite Element Codes for the Solution of Biphasic Poroelastic Problems
Authors: Prendergast P J , van Driel W D , Kuiper J-H
Published: February 2007

The extent to which three finite element codes can solve problems in biphasic poroelasticity is examined. Both linear and non-linear (that is where the permeability of the material is a function of deformation) formulations are studied using the standard confined compression problem as an example. The results are compared, where possible, to the results of Spilker, Suh and Mow (1) who first presented a solution to this problem for cartilage. The agreement is excellent for the linear case. For the non-linear case, the solutions do differ slightly; however, the difference would not appear to be significant.
The Importance of Multidirectional Motion on the Wear of Polyethylene
Authors: Bragdon C R , O'Connor D O , Lowenstein J D , Jasty M , Syniuta W D
Published: February 2007

The development of a new hip simulator for the study of bearing materials used in total hip replacements has led to several findings which add important new information to the understanding of wear process of ultra-high molecular weight polyethylene, the most commonly used bearing material today for total joint replacements. Using this hip simulator which is capable of applying the physiological motion pathways occurring during gait to total hip components which are held in the correct anatomical position under the complex loading conditions of the hip in gait, the authors have shown that physiological motion pathways produce very different wear rates and morphology of the wear surface than unidirectional reciprocating pathways. Scanning electron microscopy studies show striking differences in the morphology of the wear surfaces of the polyethylene depending upon the relative motions of the components. Wear rates, surface morphology and particle debris generation consistent with clinical and retrieved studies are achieved when physiological conditions are simulated.
The Medical Device Directives and Their Impact on the Development and Manufacturing of Medical Implants
Authors: Crisp S
Published: February 2007

The introduction of a legal framework for the supply of medical implants is discussed with reference to the Active Implantable Medical Device Directive and the Medical Device Directive. The definitions of medical device and manufacturer are discussed. The application of the Directives to device/drug combinations is considered. All implants must meet certain essential requirements to ensure that they do not harm the patient, clinician or any third party. For most implants this will be indicated on the product or its packaging by CE marking involving an independent organization called a Notified Body; the latter are appointed by the Competent Authority of the Member State. Devices are classified in proportion to the risk associated with them. The steps needed to be taken by manufacturers are outlined and the verification options discussed. The role of standards and the new approach to writing them in Europe is presented. After placing a product on the market, the manufacturer must set up a system of post-market surveillance, including a vigilance procedure, in order to monitor product performance. Individual Member States can exercise the safeguard clause when a product appears to have had the CE marking incorrectly applied.
Finite Element Stress Analysis of a New Design of Synthetic Leaflet Heart Valve
Authors: Clift S E , Fisher J
Published: February 2007

This paper presents a parametric finite element analysis of the stresses in the leaflets of a new design of polyurethane heart valve in the closed position. The alpharabola geometry of the valve has previously been reported by heat and Fisher (1) and has been shown to demonstrate good opening characteristics. The effects of variations in leaflet offset parameter, g, length, h, and local thickening have been determined for a valve where the frame is assumed rigid. A spherical leaflet geometry has also been analysed for comparative purposes. Results have shown that the alpharabola leaflet geometry can reduce the maximum principal tensile stress to 60 per cent of that for a spherical valve of the same mesh density.
Blood Flow Measurement Using a Highly Filled Carbon Polymer Sandwich Sensor and an Elasto-Pseudo Compressible Vascular Flow
Authors: Mehdian M , Rahnejat H
Published: February 2007

Vascular grafts are widely employed in clinical practice and still pose significant problems of compatibility and longevity, particularly when the prosthesis is to replace arteries of small diameter. Once a graft has been implanted in the vascular tree, there is no easy way of assessing its interactions with the surrounding tissue. Doppler flow probes or some imaging techniques are commonly used to monitor flow velocity in vascular prostheses. It is, however, difficult to monitor a patient's recovery on a continuous basis. Continuous means of measurement can be quite invaluable. This paper presents a high-carbon filled polymer (HCFP) sensor that is developed for blood flow measurement in vascular grafts. Furthermore, a computational fluid dynamics model of incompressible blood flow in elastic blood vessels is presented.
Control of Flexible Manipulator Systems
Authors: Tokhi M O , Azad A K M
Published: February 2007

This paper presents an investigation into the development of open-loop and closed-loop control strategies for flexible manipulator systems. Shaped torque inputs, including Gaussian-shaped and low-pass (Butter-worth and elliptic) filtered input torque functions, are developed and used in an open-loop configuration and their performance studied in comparison to a bang-bang input torque through experimentation on a single-link flexible manipulator system. Closed-loop control strategies that use both collocated (hub angle and hub velocity) and non-collocated (end-point acceleration) feedback are then proposed. A collocated proportional and derivative (PD) control is first developed and its performance studied through experimentation. The collocated control is then extended to incorporate, additionally, non-collocated feedback through a proportional integral derivative (PID) configuration. The performance of the hybrid collocated and non-collocated control strategy thus developed is studied through experimentation. Experimental results verifying the performance of the developed control strategies are presented and discussed.
On Eigenvectors and Generalized Eigenvectors in Multi-Variable Descriptor Control Systems
Authors: Liu G P , Patton R J
Published: February 2007

This paper is concerned with an eigenvector problem in multi-variable descriptor control systems. It proves that the eigenvectors and generalized eigenvectors premultiplied by the singular matrix E of the descriptor system as well as the eigenvectors and the generalized eigenvectors, which play a very important role in the design of multi-variable descriptor systems via eigenstructure assignment, are linearly independent.
A Riccati Equation Approach to the Design of Memoryless Stabilizing Controllers and Observers for Uncertain Linear Systems with Time-Varying Delay
Authors: Shen J-C
Published: February 2007

In this paper, a procedure for designing the memoryless state estimation feedback controller for uncertain dynamic systems with time-varying delay is presented. The uncertainties are time varying and are bounded. The design procedure involves solving two Riccati equations. If the positive-definite solutions of Riccati equations also satisfy a matrix inequality then the asymptotic stability of the closed-loop system is guaranteed. Furthermore, the state observer and control law can be constructed from these solutions.