bluuebunny/crossref_metadata_2025 huggingface dataset:
The Design and Heat Pipe Tests for a Line Focus Solar Stirling Domestic Generation system
Authors: Trolove H P , Raine J K
Published: February 2007

This paper outlines the methodology used in the design of a line focus solar Stirling power generation system for remote locations. Tests of potential working fluids for the heat pipes, used to transport energy from the solar concentrator focus to the Stirling engine heater heads, are also described. At the optimum achievable solar absorber temperature, very few heat pipe working fluids are available. Those tested were a sulphur iodine system, the organic fluid dioctyl phthalate and mercury These were designed to deliver energy to an already developed compact hermetically sealed Stirling engine battery charger of 200 W electrical power output. The only fluid to show promising performance was mercury, but safety considerations may rule mercury out for application in numerous dispersed small domestic systems.

The line focus system efficiency tends to be low because of the low Stirling engine heater head temperature at optimum system conditions and the greater losses associated with a larger focal area than that used in a point focus system of similar power output. Predicted system efficiency was 4.9 per cent for the prototype 200 W generator and 12.5 per cent for a 3 kW full-scale system on which better insulation of the heat pipe is possible. The size and cost of the 200 W unit in relation to output are likely to be too high to be economically attractive, but development of the 3 kW system may still be viable if alternator efficiency can be maximized and heat pipe thermal losses kept to a minimum.
BRAKINE: A Programming Software for the Performance Simulation of Brayton and Rankine Cycle Plants
Authors: Roy-Aikins J E A
Published: February 2007

BRAKINE is a component-matching thermodynamic analysis computer program designed to simulate both the design point and off-design steady state performance of arbitrary BRAyton or RanKINE cycle plants, or of combined cycles and cogeneration processes. Plant performance can be appraised by simulating either all fluid streams or only those streams that completely describe the working cycle. A power plant is assumed to be constructed in modular form with each component handling a specific thermodynamic process. As a result, flexibility of operation is provided by the use of ‘codewords’, which allow the user to simulate any plant type by stacking in the appropriate sequence the various modules that describe the performances of the components that make up the plant. This paper describes the mechanics of operation of BRAKINE and concludes that the program is a useful tool for power plant performance simulation.
Performance of the Islay Wells Air Turbine
Authors: Raghunathan S , Curran R , Whittaker T J T
Published: February 2007

A comparison of predicted and measured performance of the bi-directional Islay Wells air turbine is presented. Reasonable agreement was evident for pressure, converted power and efficiency, at lower flowrates. For higher flowrates larger discrepancies were evident due to limitations in the theory, inaccuracies in experimental measurement and flow separation at the Islay turbine. It was concluded that improvement could be achieved through streamlining of the flow through the turbine, in order to defer turbine stall at the higher flowrates and to also improve flowrate measurement. Improvements are necessary in the measurement of flowrate and power conversion, and in the prediction technique.
Efficiency Improvement Options for Municipal Waste-Fired Power Generation—Recent Development Activities in Japan: A Review
Authors: Haneda H
Published: February 2007

The development of high-efficiency municipal waste-fired power plants, although not yet developed for practical use because of the technical difficulties involved, has recently come to be considered quite important, reflecting strong public demand for conservation of the global environment and preservation of energy resources. Development of such plants is now being actively promoted in various national projects in Japan.

This paper first reviews the current status and technical issues concerning (a) municipal waste disposal plants and (b) municipal waste-fired power plants in Japan. Then each of the three approaches that are currently being proposed and vigorously promoted as national projects in Japan for realizing high-efficiency municipal waste-fired power plants is discussed.

Although a high percentage of the municipal waste in Japan is incinerated, only a relatively small amount of electricity is generated at present. The paper shows that increasing the proportion of waste used to provide electricity could lead to savings of up to 30 per cent of the annual cost consumption in Japan, with accompanying substantial saving in CO2 emissions. The more effective utilization of municipal waste as an energy source would thus have a significant effect on global environmental conservation and in saving primary energy sources.
Air-Standard Modelling for Closed-Cycle Diesel Engines
Authors: Woodward J B
Published: February 2007

The author posits that a model constructed from ideal processes is the most desirable starting point for analysis of real power machinery, and then presents means of following this concept in the case of a closed-cycle diesel engine. The traditional air-standard limited-pressure cycle is found unsuitable for this application in that it offers only an unrealistic constant-volume cooling as the model for the processes that must occur between cylinder exhaust and cylinder intake. The present paper substitutes isentropic expansion, throttling and constant-pressure cooling as being suitable ideal models for the actual processes. Equations are presented and sample calculations are given for the cylinder-to-cylinder part of an ideal cycle representing a four-stroke naturally aspirated engine. Two alternatives are also discussed via examples: an engine with partial bypassing of untreated exhaust gas to the cylinder intake and a two-stroke engine with blower or compressor driven by an exhaust gas turbine. A closing example is given to demonstrate one way in which the analyses can be used to find the effect of external process states an engine-cycle output.
The Electrical Systems of Five Wind Farms
Authors: Jenkins N , Vaudin A
Published: February 2007

The design, construction and early operating experience of the electrical systems of five wind farms, with a total installed capacity of 35 MW, is described. The design approaches adopted for the wind farm internal electrical systems and the interfaces to the rural public supply networks have been shown to be successful. No significant failures of electrical equipment or disturbances to the public supply network have occurred.
An Integrated Neural Network and Expert System Tool for Statistical Process Control
Authors: Pham D T , Oztemel E
Published: February 2007

Control charts are a basic means for monitoring the quality characteristics of a manufacturing process to ensure the required quality level. They are used to track product and process variations through graphical representation of the quality variable of interest. A control chart shows the state of control of a process and can exhibit different types of patterns which are indicative of long-term trends in it. This paper describes the integration of an expert system and a neural-network-based pattern recognizer for analysing and interpreting control charts. The expert system has an on-line process monitoring package to detect general out-of-control situations and a diagnosis module to suggest corrective actions. The pattern recognizer is an on-line system comprising two neural networks and an heuristics module designed to identify incipient process abnormalities from control chart patterns. The paper also compares neural networks and expert systems and provides the rationale for the integration process.
Change with People
Authors: Dobbs P J
Published: February 2007

The Manufacturing Business Unit of Parsons Power Generation Systems Limited has had to change to sustain its position as a world class manufacturer of heavy engineering products. The change mechanism used was systems engineering applied to a new area of business. Acting as a model for the rest of the business, the facility manufacturing aerospace components is used as an example in this discussion of introducing and managing change.
Engineering Success Using Teamwork
Authors: Price F Christopher
Published: February 2007

The incoming President reviews his career which has primarily been in the development of shoemaking machinery and materials with British United Shoe Machinery Limited, subsequently USM Texon Limited, and also in the automobile components industry with Rearsby Automotive Limited. He focuses on the process of using teamwork in achieving successes in these businesses and describes two recent successes in highly sophisticated shoemaking machinery—a family of computer-controlled machines used in the process of bonding soles to shoes and an automatic stitching machine using an integrated vision system to identify and locate workpieces. He reflects on his involvement in the Institution running almost continuously from student membership to his election as the youngest President for 100 years and recommends active involvement as a good contributor to personal and professional development, especially for younger engineers.

At a time when the new relationship within the engineering profession is being crystallized, Mr Price discusses the opportunities and challenges for the profession in the light of the ongoing need for strengthening of engineering and manufacturing in the United Kingdom. He concludes that progress has to be achieved by effective teamworking, both within the Institution, with other engineering institutions, with government and with other key organizations in the wider community.
Development of a Micro-Positioning Grinding Table Using Piezoelectric Voltage Feedback
Authors: Kim J-D , Nam S-R
Published: February 2007

Micro-positioning systems using piezoelectric actuators have a very wide range of applications including ultra-precision machine tools, optical devices and measurement systems. In order to ensure a high-precision displacement resolution, they use a position sensor and error feedback. From a practical point of view, a high-resolution displacement sensor system is very expensive and it is difficult to guarantee that such sensitive sensors work properly in the harsh operating environments of industry.

In this paper, a micro-positioning grinding table has been developed which does not require a position sensor but instead uses piezoelectric voltage feedback. It is driven by a hysteresis-sensitive reference input voltage calculated by computer using the actuator/sensor characteristics of piezoelectric materials. The experimental results illustrate the fast and stable response of the micro-positioning system, and the paper suggests a more efficient technique for controlling piezoelectric actuators.
Acceleration and Injection Effects on Longitudinal Vortices in Concave Wall Boundary Layers
Authors: Umur H , Crane R I , Whitelaw J H
Published: February 2007

Measurements of longitudinal velocity and wall temperature have been obtained in a wind tunnel with a concave wall, with momentum thickness Görtler numbers from 5 to 10 at the initial station. Vortex generators were used to enhance the vortex structure in flow with zero streamwise pressure gradient. Spanwise variations existed over a limited range which is quantified. It is shown that mild acceleration amplified the vortices and enhanced the regularity of the spanwise variation; strong acceleration, with velocity gradient parameter K near 2 times 10−6, suppressed them and limited the growth in spanwise-averaged Stanton number. The influence of favourable pressure gradients was confirmed in a curved water channel with similar Görtler numbers. Discrete hole wall jets with varying jet-to-free-stream velocity ratios were used in the water channel to examine the response of longitudinal vortices to a spanwise-periodic disturbance of different wavelengths. The wall temperature characteristic of the jets persisted for a considerable streamwise distance with velocity ratios of 0.4 and unity, while a distribution not dissimilar to that without blowing was found at all stations with a velocity ratio of 1.5.
Boundary Singularities in Steady Potential Compressible Flow Through Plane Two-Dimensional Channels: Part 2: Full Solutions
Authors: Streeter C A C
Published: February 2007

A solution is given, in hodograph coordinates, of the subsonic entry flow of a perfect gas in plane-parallel channels, in terms of the stream function. The particular solution and the full solution of the relevant equation are part-analytical and part-numerical. Results correspond to an approach velocity M*e = 0.5 and γ = 1.4. An error analysis is given, the results of which have general application in locating accurately the sonic line between regions of subsonic and supersonic flow. This analysis is applied in determining the steady, transonic choked flow of a perfect gas through a convergent channel. The methods of calculation can be applied in the design of engineering components, where flow structure and flow performance parameters are a basic requirement.
An Energy Error Estimation Method for Improving Analytical Models Using Vibration Modal Test Data
Authors: Guo S , Hemingway N G
Published: February 2007

When improving analytical dynamic models using modal test data, correct localization of the poorly modelled areas in the analytical model is essential for ensuring the accuracy of the model improvement obtained. In this paper, a method referred to as the energy error estimation (EEE) method is proposed. Firstly, this method is capable of effectively distinguishing the correctly modelled mass and stiffness elements from those poorly modelled regions by using a limited number of test modes. This results in an accurate localization of the analytical modelling errors. Secondly, a set of correction factors can be obtained for improving those elements that are identified as having been poorly modelled. The improved analytical model will also retain its original matrix configuration, size and physical explanation, which is desirable.

In order to verify the efficiency and accuracy of this proposed method, beam examples using both simulated and experimental modal test data are demonstrated. Excellent model improvement is shown in these examples.
On the Performance of a Cascade of Turbine Rotor Tip Section Blading in Nucleating Steam: Part 1: Surface Pressure Distributions
Authors: Bakhtar F , Ebrahimi M , Webb R A
Published: February 2007

During the course of expansion in turbines, steam first supercools and then nucleates to become a two-phase mixture. Formation and subsequent behaviour of the liquid lower the performance of turbine wet stages. To reproduce turbine nucleating and wet flow conditions requires a supply of supercooled steam which can be achieved under blow-down conditions by the equipment employed. The performance of a cascade of rotor tip section blading in nucleating steam has been studied. The results of the surface pressure measurements are described in the paper.
Uncoupled Torsion of Thin-Walled Sections
Authors: Grant C
Published: February 2007

Pure bending-free torsion of a prismatic bar requires that the axis of twist be located at the shear centre of the section. However, finding the position of the shear centre in an asymmetric section is not a trivial task and corresponds to a complete bending or torsion analysis. By isolating the contribution from the axis of twist to the warping displacement distribution, the shear centre is determined from the solution to the related problem with the axis of twist at the origin. It is then necessary only to correct this solution for torsion about the shear centre rather than to re-solve the whole problem. Network theory is employed extensively in the solution.
Finite Twist Mapping and its Application to Planar Serial Manipulators with Revolute Joints
Authors: Dai J S , Holland N , Kerr D R
Published: February 2007

This paper reviews a method of representing the finite twist motion of a rigid body, and applies this concept to the problem of describing the motion capabilities of planar serial manipulators. In particular, this finite twist representation describes the position and orientation of the end-effector link relative to a defined reference position and orientation. The transformations associated with the joint motions are used to investigate the range of end-effector motion, including the effects of limits of joint travel. The finite twist representations are then extracted from such transformations and presented in an image space so that the motion of the manipulator is fully characterized. Further, the reachable and dexterous workspaces are predicted by the same general means. Examples of planar serial manipulators with two (RR) and three revolute (RRR) joints are given to illustrate the approach.
Dynamic Constitutive Equations and Behaviour of Brass at High Strain Rates
Authors: Li L-Y , Molyneaux T C K
Published: February 2007

This paper presents an experimental study of the mechanical properties of brass at high strain rates. The brass tested is the copperzinc alpha-beta and beta two-phase alloy in the cold-worked state. Experiments were conducted using an extended tension split Hopkinson bar apparatus. It is found that, at lower strain rates, the stress-strain curve is smooth, exhibiting no well-defined yield stress, but at higher strain rates the stress-strain curve not only shows a well-defined yield stress but also displays a very pronounced drop in stress at yield. The flow stress is found to increase with increasing strain rate, but the increase is more significant for the yield stress than for the flow stress, showing that the yield stress is more sensitive to the strain rate than the flow stress away from the yield point. Based on the experimental results, empirical strain-rate-dependent constitutive equations are recommended. The suggested constitutive equations provide a reasonable estimate of the strain-rate-sensitive behaviour of materials.
Numerical Uncertainty in Heat Conduction Calculations for a Tube Immersed in a Fluidized Bed
Authors: Karamavruc A I , Clark N N , Celik I
Published: February 2007

A numerical code has been evaluated with regard to numerical uncertainties involved in calculating heat flux through the wall of a horizontal tube in a bubbling bed of sand. The two-dimensional unsteady heat conduction equation is solved numerically with a non-linearly varying temperature boundary condition prescribed according to measurements. The finite difference method used is an implicit method with a second-order accurate discretization scheme both in temporal and spatial domains. Previous literature dealing with numerical calculations in heat conduction usually reports any detailed study about numerical errors. In the present analysis, a rigorous grid dependence test is applied, and it is shown that the results, in particular heat flux, are very sensitive to the grid size and distribution. Therefore, to achieve better grid convergence when heat flux is sought, the discretization error in the heat flux rather than in the temperature calculations should be considered. This should be done even in cases where temperature is the primary unknown, because it is usually the derivative of temperature which is of any physical importance. The errors are also strongly dependent on the number of iterations which need to be increased as the grid is refined. The present application showed that a non-uniform grid refinement throughout the calculation domain gives a more efficient (less expensive) solution than uniform grid refinement. Furthermore, for calculation of the temperature gradient at the wall, a parabolic profile assumption gives a faster grid convergence compared to a linear profile assumption. The present study shows that the previously published results concerning calculated heat transfer coefficients should be interpreted with caution, unless the authors have provided some measure of grid dependency of their results.
The Use of Statistical Process Control in the Manufacture of High-Integrity Products
Authors: Bird D , Dale B G
Published: February 2007

A study has been made of the use of statistical process control (SPC) in a company manufacturing high-integrity components for assembly into engines used in automobiles. The findings indicate that there is a lack of clear objectives for its use within the company. Some benefits have been achieved but the technique is being deployed imperfectly. A number of areas have been identified in which improvements are needed to make more effective use of SPC. For example, there is too much resetting of the machine tools, control limits are calculated too frequently, special causes have not been successfully identified and eliminated, teamwork is not widely used and insufficient resources are allocated to resolve problems in the company's manufacturing processes.
Flow Prediction in an Axisymmetric Inlet Valve/Port Assembly Using Variants of k—ε
Authors: Naser J A , Gosman A D
Published: February 2007

The paper describes a computational investigation of steady incompressible air flow through an enlarged-scale version of an axisymmetric intake valve/port assembly. The numerical procedure used for this purpose solves the governing equations using the SIMPLE algorithm. The governing equations are expressed in a general curvilinear coordinate system and are discretized in a finite volume fashion. The time-averaged governing equations are closed using four different variants of the k—ε turbulence model. In addition to the standard model, which is known to be deficient in predicting strongly curved flows with steep pressure gradients, a variant was tried in which the dissipation equation is sensitized to irrotational strains. The third alternative involved a two-layer representation employing a one-equation model in the near-wall viscosity-affected region and the standard k—ε model in the core region. The fourth model employed was developed from the combination of the last two. The predictions are assessed by comparing the available experimental flow field data. The fourth model showed substantially improved qualitative behaviour and good quantitative agreement in comparison to the other alternatives.
Friction Materials—Black Art or Science?
Authors: Smales H
Published: February 2007

This address highlights some of the experiences of the Chairman in his career at Mintex Don Limited, a member of the BBA Group of companies, concerning the development and installation engineering of friction materials.

Work on specific component design to overcome problems in both transmissions and brake systems is described; an outline is given of how testing has developed over the past 40 years; and the influence of regulations on testing is described, as well as how the change from asbestos-based to asbestos-free friction materials was achieved.

Modern analysis techniques, electronic instrumentation and computational methods have increasingly assisted in this work and it is shown that friction materials have ceased to be developed by ‘black art’ and are now a well understood science.
Modification of a Heavy Vehicle Suspension to Reduce Road Damage
Authors: Cole D J , Cebon D
Published: February 2007

A test rig for measuring the quasi-static performance of tandem suspensions in the laboratory is described. Measurements on a standard tandem leaf-spring suspension show it to have high effective stiffness in bounce and poor static load equalization. A method for eliminating the spring-end friction is investigated, and found to improve the performance significantly.

A two-dimensional articulated vehicle simulation is validated with measurements from a test vehicle. The simulation is then used to study the effect on dynamic tyre forces of three modifications to the trailer suspension: softer springs; elimination of spring-end friction; and hydraulic dampers. The r.m.s. dynamic loads generated by the trailer axles are predicted to decrease by approximately 31 per cent and the theoretical road damage is predicted to decrease by about 13 per cent.

The trailer suspension of the test vehicle is adapted to incorporate the three modifications and the measured reductions in dynamic tyre forces are found to be about half those predicted by the simulation.
Simple Technique for Measuring Air Humidity Using an IBM Microcomputer
Authors: Wahab M B Abdul , Badros M Z , Ramli A R
Published: February 2007

A thermocouple consisting of copper and constantant wires has been used as a relative humidity detector and was interfaced to an IBM microcomputer. The temperature differences between the wet and dry junction of the thermocouple were used to calibrate the relative humidity of air. The generated e.m.f. signal was amplified and thus converted to a digital signal using an analogue-to-digital converter (ADC). The digital data output of the ADC was then passed to an IBM microcomputer via a programmable peripheral interface (PPI) chip to process, display and store the relative humidity data. The relative humidity profile in the range 23–32°C of the dry bulb temperatures for a specific day can also be plotted and analysed. The measured relative humidity was compared to a commercial humidity meter and showed good agreement.
Modelling of a Controlled Pneumatic Swing-Plug Train Door
Authors: Post Y W , van Oostveen H J , van der Weiden A J J
Published: February 2007

In this paper, a mathematical description will be given for a controlled pneumatic swing-plug train door. On the basis of the significant dynamics in the door system, a non-linear model is derived and implemented into the simulation package ‘SystemBuild'. Computer simulations of a closing procedure show that this non-linear model closely correlates with measured data of an experimental set-up. Linearization of the model gives rise to a drastic simplification. This linearized model is used to predict the influences of parameters on the door's behaviour.
An Aeronautical Engineering Degree Course Designed For Prospective Pilots
Authors: Duggins R K , Baird J P
Published: February 2007

A new aeronautical engineering degree course has been designed and introduced at the Australian Defence Force Academy for prospective pilots. It is a three-year Bachelor of Technology course leading to engineering technologist status.
Contact Pressure Prediction in Total Knee Joint Replacements Part 2: Application to the Design of Total Knee Joint replacements
Authors: Jin Z M , Stewart T , Auger D D , Dowson D , Fisher J
Published: February 2007

The general elasticity contact theory for elliptical geometry developed in Part 1 (1) has been applied to the design of current total knee joint replacements. A two-step curve-fitting technique using cubic spline interpolation routines has been adopted to represent the full elasticity solutions. The curve fit results of the maximum contact pressure have been compared with the full elasticity solution for a specified elliptical geometry and different polyethylene thicknesses and good agreement has been demonstrated. The computing time required by the curve-fitting technique is very small compared with the full elasticity solution and therefore can readily be applied to the design of knee joint replacements. Furthermore, reasonable agreement has also been found for the contact area for a typical knee joint design between the present theoretical prediction and the experimental measurement using pressure-sensitive film. Predictions of the maximum contact pressure have been made for an existing knee joint replacement in order to illustrate the present analysis in the design cycle. It has been shown that the effect of the thickness of ultra high molecular weight polyethylene is relatively small on contact stress predictions provided a sufficiently large value is chosen. On the other hand, the effect of conformity has a much greater influence on the contact stress distribution, particularly in the direction of the smaller principal radius.
The Effect of the Geometry of the Tibia on Prediction of the Cruciate Ligament Forces: A Theoretical Analysis
Authors: Chan S C N , Seedhom B B
Published: February 2007

This paper attempts to highlight the importance of the tibial geometry in the prediction of forces along the cruciate ligaments. A two-dimensional model of the knee which comprises the femur, the tibia and the cruciates was used. The model was subjected to an external antero-posterior force and an external axial compressive force. The analysis showed that, with aflat tibial plateau the tension arising along either cruciate as a result of the application of an external antero-posterior force is determined solely by the inclination of the ligament to the direction of that force; it is independent of the magnitude of the external axial compressive force. A curved tibial plateau modifies the tension along either cruciate, and in the absence of an axial compressive load on the joint small changes in the geometry of the tibial surface cause slight changes (increase/decrease) in the tension. However, these changes can become considerable when a large axial compressive load is applied on the joint. A concave tibial plateau, where the tangent to the surfaces at the point of contact is inclined to the direction of the same external antero-posterior force by 7.8°, can reduce the tension along either cruciate to zero, if a sufficiently large axial compressive load is applied on the joint. It was shown that the convexity of the lateral tibial plateau can provide an important protective function for the posterior cruciate ligament (PCL) at extreme positions of flexion. The analysis showed that the PCL should experience a larger force than that experienced by the anterior cruciate ligament (ACL) and hence explain why the former should be the stronger of the two. Finally, a hypothesis is proposed suggesting that bone remodelling may occur in the tibiae of the older people, causing them to become more concave with age and as a consequence provides greater protection to the cruciates in the aged, in order to compensate for decreasing strength in the older person.
Axisymmetric Finite Element Analysis of Hip Replacements Possessing an Elastomeric Layer: The Effects of Clearance and Poisson's Ratio
Authors: Unsworth A , Strozzi A
Published: February 2007

A finite element analysis has been performed for a hip replacement incorporating an elastomeric surface layer. The effects of assuming the elastomer as incompressible have been examined for imposed loads, by comparing the incompressible solution to that using accurately measured values for Poisson's ratio, and while deflections were found to be significantly different, the changes in maximum pressure in the contact, maximum shear stress, contact angle and angular position to maximum shear stress were all small (less than 10 per cent). Comparisons have also been made between the finite element results for ABAQUS and an asymptotic solution, land it was found to be important to use the numerical model particularly at small values of clearance.
An Estimation of Fatigue Life for a Carbon Fibre/Poly Ether Ether Ketone Hip Joint Prosthesis
Authors: Akay M , Asian N
Published: February 2007

A fracture mechanics approach was applied to estimate the life of a prosthesis injection moulded from short carbon fibre reinforced poly ether ether ketone. Flexural modulus and strength, fracture toughness, fatigue endurance limit, fatigue crack growth rate and threshold stress intensity factor were determined. The dimensions of the test pieces were selected to yield fibre orientation and fibre length distributions similar to those obtained in the prosthesis. Stress levels generated in the prosthesis under different activities were estimated by conducting three-dimensional finite element analysis. It was shown by a fracture mechanics approach that a fatigue failure due to the propagation of an embedded elliptical slit, under these stresses, would be unlikely for a crack length smaller than 1.85 mm. However, the cement would fail under the same conditions, irrespective of the type of the prosthesis employed.
In Vivo Measurement of Spinal Column Viscoelasticity—An Animal Model
Authors: Hult E , Ekström L , Kaigle A , Holm S , Hansson T
Published: February 2007

The goal of this study was to measure the in vivo viscoelastic response of spinal motion segments loaded in compression using a porcine model. Nine pigs were used in the study. The animals were anaesthetized and, using surgical techniques, four intrapedicular screws were inserted into the vertebrae of the L2-L3 motion segment. A miniaturized servohydraulic exciter capable of compressing the motion segment was mounted on to the screws. In six animals, a loading scheme consisting of 50 N and 100 N of compression, each applied for 10 min, was used. Each loading period was followed by 10 min restitution with zero load. The loading scheme was repeated four times. Three animals were examined for stiffening effects by consecutively repeating eight times 50 N loading for 5 min followed by 5 min restitution with zero load. This loading scheme was repeated using a 100 N load level. The creep-recovery behaviour of the motion segment was recorded continuously. Using non-linear regression techniques, the experimental data were used for evaluating the parameters of a three-parameter standard linear solid model. Correlation coefficients of the order of 0.85 or higher were obtained for the three independent parameters of the model. A survey of the data shows that the viscous deformation rate was a function of the load level. Also, repeated loading at 100 N seemed to induce long-lasting changes in the viscoelastic properties of the porcine lumbar motion segment.
Clamping the Small Intestine During Surgery: Predicted and Measured Sealing Forces
Authors: Frank T , Willetts G J , Carter F , Cuschieri A
Published: February 2007

During bowel surgery it is often necessary to occlude the bowel using clamps. Occlusion occurs in two stages: approximation of bowel internal surfaces followed by sealing which is necessary to prevent seepage. The occlusive force at both stages depends on the luminal pressure, the latter stage requiring greater force than the former. The difference in luminal pressure across the sealing line results in a slipping force which is resisted by friction between the bowel and the clamp jaw surfaces. A theoretical model was developed to describe these forces and the predicted values obtained from this model were compared with direct measurements carried out on porcine bowel samples in a test rig. It was found that the measured approximation force was between 25 and 50 per cent of the maximum theoretical values and that sealing without seepage requires a clamp force of about ten times the approximation force. Using these results and known intraluminal pressures in the human gastrointestinal tract, a bowel clamp must apply around 7 N to prevent seepage and the coefficient of friction between clamp and bowel should be between 0.6 and 0.9.
Detachable Clamps for Minimal Access Surgery
Authors: Frank T , Willetts G J , Cuschieri A
Published: February 2007

A detachable clamp and applicator have been developed for use in minimal access surgical operations involving hollow visceral transection and anastomosis. The clamp has parallel jaws which ensure uniform distribution of the occlusive force. Following application on the bowel, the clamp is released from the applicator, thus freeing the access port. On completion of the anastomosis, the clamp is docked to the applicator, its jaws opened for release from the bowel and then closed prior to removal. The jaws of the clamp are kept closed by a pseudoelastic nickel-titanium (NiTi) alloy spring which imparts advantageous force characteristics when compared to stainless steel. The excellent holding and atraumatic characteristics of the detachable clamp have been confirmed by use in laparoscopic and thoracoscopic surgery on the gastrointestinal tract.
Biomechanics and Design of Shoulder Arthroplasty
Authors: McCullagh P J J
Published: February 2007

Since the introduction by Neer in 1973 of the metal-on-plastic unconstrained total shoulder replacement, unfortunately there have been no long-term clinical follow-up reports. Short- to mid-term information (less than ten years) indicates good to excellent clinical results in approximately 90 per cent of cases. While this early experience is encouraging, much attention has been focused on tucencies of the glenoid componenti which although they may not predispose to failure, have led to considerable design activity. The humeral component has also advanced in design, with modularity of the head in particular providing greater intra-operative flexibility. State-of-the-art instrumentation, borrowing key features found beneficial to hip and knee joint replacement, is an important advancement in contemporary systems. The aim of this paper is to position shoulder arthroplasty in relation to biomechanical considerations and recommendations from clinical experience.
Winging of the Scapula: The Underlying Biomechanics and an Orthotic Solution
Authors: Barnett N D , Mander M , Peacock J C , Bushby K , Gardner-Medwin D , Johnson G R
Published: February 2007

Winging of the scapula occurring in muscular disorders (muscular dystrophy and spinal muscular atrophy) or nerve injury has been investigated, resulting in a thorough understanding and presentation of the underlying biomechanics causing this occurrence. This includes a biomechanical explanation of the characteristic prominence of the medial border of the scapula upon attempted elevation, together with the biomechanical reasons for the rotation of the scapula in a direction contrary to the normal scapulohumeral rhythm. Based on these findings, a non-invasive alternative to the surgical technique for scapular stabilization has been devised, using an inflatable orthosis, placed between the scapula and an external restraint (such as a spinal jacket). The device has been tested on one subject using a 3SPACE™ Isotrak™ electromagnetic source and sensor system, and gave encouraging results. Elevation increased by up to 35° (37 per cent), and functional improvement in the use of the hand around the head and face has been achieved. The technique needs no aftercare or physiotherapy and is therefore both economical and functionally effective.
The Influence of Scratches to Metallic Counterfaces on the Wear of Ultra-High Molecular Weight Polyethylene
Authors: Fisher J , Firkins P , Reeves E A , Hailey J L , Isaac G H
Published: February 2007

A number of studies of explanted metallic femoral heads have shown scratches or damage caused by bone cement, bone or metallic particles. This damage has been cited as a cause of increased wear of ultra-high molecular weight polyethylene (UHMWPE) acetabular cups. In this laboratory study, small scratches 2 μm deep were made on smooth stainless steel surfaces at a spacing of 10 mm. These individual scratches were found to increase the wear rate of UHMWPE by a factor of 30 in unidirectional sliding and a factor of 70 in reciprocating motion. It is of particular concern that a single small scratch, which is not detected by the average surface roughness measurement Ra can cause such a dramatic increase in the wear of ultra-high molecular weight polyethylene.
Multi-Variable Control of an Integrated Propulsion and Airframe System
Authors: Perez R A
Published: February 2007

The development of an integrated control scheme to enhance the performance of a generic interconnected multi-variable dynamical system, consisting of a turbofan engine and an airframe, in the presence of predominantly destructive dynamical interactions over the flight envelope is considered in this paper. The control scheme consists of two components: a simple static forward loop or feedback loop precompensator to improve the interactions followed by a forward or feedback loop controller to improve the performance. The system must be tolerant to soft and hard output sensor failures by means of analytic redundancy only. A control methodology to satisfy the above specifications is presented here. Necessary and sufficient conditions are presented in order to achieve a stable closed-loop performance of the overall system by tuning every loop separately, that is decentralized stability.
Robust Motion Tracking Controllers for Uncertain Robot Manipulators
Authors: You S-S , Hall J L
Published: February 2007

This paper considers the problem of designing a class of robust algorithms for the trajectory tracking control of an uncertain robot manipulator. The general control structure consists of two parts: the primary control law is first introduced to stabilize the nominal system and then a class of robust non-linear control laws are adopted to compensate for the system uncertainties by using the deterministic approach. The uncertainties assumed are bounded by higher-order polynomials in the Euclidean norms of system states with known (or unknown) bounding coefficients. The possible bounds of uncertainties are assumed to be known for the robust non-linear control with less computational burden. If no information on these bounds is available, then the adaptive bound of the robust controller is presented to overcome possible time-varying uncertainties, that is a decentralized adaptive control scheme. With a feasible class of desired trajectories, the proposed control laws guarantee that all possible responses of the corresponding closed-loop systems are at least uniformly ultimately bounded (UVB) by Lyapunov stability theory. The effectiveness of the proposed control algorithms are verified through numerical simulations. Finally, it is shown that the presented controllers are evaluated to be robust with respect to a given class of uncertainties.
Pressure-Induced Torque in Unloaded Hybrid Bearings—A Case Study
Authors: Attar S E , Nicolas D , Lucas V , Frêne J , Constantinescu V N
Published: February 2007

A pressure-induced torque is emphasized in externally pressurized bearings having deep pockets, due to the pressure buildup by shaft rotation on the downstream vertical side of the recess. A standard simplified analysis is presented for both laminar and turbulent operation, with improved values for parameters kx and kx, which intervene in the pressure differential equation, as well as for the Couette turbulent shear stress; the mentioned values are valid for large Reynolds numbers. Comparison with experimental data for a water-lubricated test bearing exhibits the importance of the pressure-induced effect on the torque acting on the stationary member of the bearing.
Modelling of the Behaviour of Dynamical Gas Seals: Calculation with a Finite Element Method Implicitly Assuring the Continuity of Flow
Authors: Hernandez P , Boudet R
Published: February 2007

The objective of this paper is to present a model of the behaviour of dynamical seals and the corresponding numerical results. These seals are used in the mechanism to realize partial sealing when the relative rotating speeds are too high for usual solutions. The studied seals mainly include two discs: one is attached to the shaft and the other to the body, the last one being pushed and the first being attached by springs. During operation, a gaseous film is created between the discs, preventing any contact. The control of the film thickness allows the leakage flow to be controlled.

For the behaviour of such mechanisms, an analytical formulation of the problem is firstly presented. Then a geometrical and kinematical model having one degree of freedom is proposed to model the mechanism having two discs in relative rotation, one of which is spirally grooved. A dynamical model associated with the motion of the disc attached to the body has been developed and the mechanics of thin viscous films is used to study the behaviour of the gaseous film at the interface.

Utilization of the finite element method in the mechanics of thin viscous films is introduced and a description of the elements used is presented. The influence of the groove's angle and the groove's depth is shown through numerical results concerning leakage mass flow through the mechanism and the loading capacity of the fluid film, as well as the coefficients of stiffness and damping associated with the dynamical model.
Investigation of the Working Cycle of a Metal Hydride Heat Transformer for Upgrading Waste Heat
Authors: Kuznetsov A V
Published: February 2007

This paper presents an investigation of the working cycle of a metal hydride heat transformer for upgrading waste heat. A mathematical model for calculation of the heat and mass transfer processes in the metal hydride heat transformer is suggested. The method for balancing the heat and mass exchanges in the thermodynamic cycle is developed. This method essentially takes into account the pressure drop inside a reacting hydride bed.
Criteria for the Choice of Fans for use in Thermal Power Plant Applications
Authors: Godichon A
Published: February 2007

Large fans for the thermal power industry operate more and more on part load. This paper discusses how the total cost of an investment is increasingly based on the inclusion of the operating costs. Today there is still a high demand for conventional thermal power stations. New ones are under construction and existing ones are in the process of conversion with new desulfurization units; more and more emphasis is being concentrated on: Operating efficiency Technical reliability The environment and noise and, of course, Return on investment

Because these priorities are contradictory, the objective of this paper is to guide the reader to the best choice of fan technology given differing circumstances.

The correct choice is important concerning primary air, forced draft, induced draft and booster fans which can represent a total power consumption of 2–4 per cent in a 350–600 MW power plant depending on the quality of coal used and the boiler type. These fans are generally characterized by a large volume flow and a relatively large pressure and can be of the centrifugal or axial type.

Many solutions are possible for controlling the air flow of these fans. The main ones will be examined by looking at their general principles, their performance and characteristics, and then comparing them from an energy consumption point of view.
Theoretical and Experimental Studies of the Steady State Performance of an Orbital Rotor Low-Speed High-Torque Hydraulic Motor
Authors: Dasgupta K , Mukherjee A , Maiti R
Published: February 2007

In this paper the steady state performance of epitrochoid generated orbital ‘rotary piston machine’ (ROPIMA) type ‘low-speed high-torque’ (LSHT) hydrostatic unit has been studied. The complex variation of the volume of a chamber of such a machine with shaft rotation, along with the various flow and torque losses, demand a structured approach to arrive at its mathematical model. In conventional approaches the system morphology becomes obscured as the mathematical model is approached. Bondgraph provides a structured approach to model engineering systems in a simplified manner. A reduced Bondgraph model of the LSHT Orbital motor is made where the various losses are lumped in suitable resistive elements. The variations of the loss coefficients are identified. The predicted performance of the motor has been experimentally verified.
Fuzzy Ratings in Mechanical Engineering Design—Application to Bearing Selection
Authors: Chen Y H
Published: February 2007

In the preliminary stage of engineering design, descriptions of design elements are often imprecise. In this paper, imprecision is represented using fuzzy numbers. Calculation based on fuzzy weighted average is performed to produce the ratings among design alternatives. Alternatives then proceed to the more detailed design stage in the fuzzy rating order. This method provides a tool for design automation at a higher abstract level. This is demonstrated in the bearing selection case study where imprecise linguistic description of a design problem in a manner similar to human language can be accommodated.