bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal Excitation for Aircraft Flutter Testing
Authors: Burrows A P , Wright J R , Coote J A
Published: February 2007

The choice of excitation signal for flutter testing of a full-scale aircraft or wind tunnel model is crucial if the flutter test clearance is to be performed quickly and with confidence. The use of chirps (that is, sinusoidal signals with varying frequency) is commonplace but has limitations. In this paper the idea of a simple chirp is extended to the development of a multi-sectional variable amplitude/variable power chirp in which the relative signal amplitude and power between sections may be specified over the frequency range of interest. An optimal chirp for a particular application may thus be designed. Sample results from a wind tunnel model flutter test are presented. In addition, the practice of sweeping up and then down in frequency is shown to be inadvisable under certain circumstances.
Design of a Non-Constrained, Non-Cemented, Modular, Metacarpophalangeal Prosthesis
Authors: Beevers D J , Seedhom B B
Published: February 2007

A non-constrained, non-cemented, modular prosthesis for replacement of the metacarpophalangeal joints of the fingers has been developed. The prosthesis is of a surface design which is modular in construction and is implanted into the hones with a press fit. The prosthesis is designed to be implanted into patients with traumatic injuries, post-traumatic osteoarthritis and into patients with rheumatoid arthritis at an early stage in the disease where the muscles and ligaments that surround the joint are still functional and can provide joint stability.
Fuzzy Control of a Mobile Robotic Vehicle
Authors: Baxter J W , Bumby J R
Published: February 2007

This paper presents a fuzzy logic control scheme for the navigation of a mobile robot in the presence of obstacles. A fuzzy navigation controller is described which guides the robot from a start position to a goal, or sub-goal, position assuming that no obstacles are in the path. Obstacles affect the navigation controller according to a set of fuzzy inhibitive rules that take into account the vehicle geometry, the distance of the obstacle from the robot and the probability of the object being at the position indicated. To ensure that all possible collision-free paths are considered, each entry in the fuzzy fit vector is distributed, or spread, across the output universe of discourse before using a sliding window defuzzification technique to produce a crisp output value. The use of the sliding window defuzzification technique helps to remove indecision from the controller. Both simulated and laboratory test results are presented.
Autopilots for Tactical Missiles: An Overview
Authors: Horton M P
Published: February 2007

In recent years, a number of technology and operational features have emerged which have had an impact on the design of control systems for tactical missiles. These have required the closer tuning of autopilots to both the guidance loop and the aerodynamic limits and, at the same time, new design and assessment methods have also been developed for control systems. It is the purpose of this paper to bring these developments together and show how the various aspects contribute to the overall design process which enables a missile autopilot to reach maturity.
Design of Compensators for Actuator Saturation
Authors: Chan C W , Hui K
Published: February 2007

Actuator saturation is a common non-linear control problem; if it is not being compensated properly, the system can become unstable. When the actuator saturates, the control that cannot be implemented can be interpreted as a non-linear disturbance being injected into the closed-loop system. After transformation, the applied set-point is altered by the disturbance, giving the effective set-point. If the effective instead of the applied set-point is used to calculate the control, no actuator saturation occurs. Since the effective set-point always replaces the applied set-point whenever the actuator saturates, a compensator can be designed aiming to produce a more acceptable effective set-point. The conditions for its implementation are given, followed by the properties of the effective set-point. A procedure for selecting the parameter of the compensator is also described. Examples are presented to illustrate the design procedure and to compare the performance of the proposed and the existing compensators.
Decentralized Adaptive Control of a Directly Driven Hydraulic Manipulator: Part 2: Experiment
Authors: de Almeida F Gomes , Edge K A
Published: February 2007

The implementation of a decentralized model reference adaptive control scheme for a two-axis robotic manipulator is described. It is shown, through an extensive series of experiments, that very good model-following performance and axis decoupling is achieved regardless of manipulator payload and working position.
Adaptive Control of Robot Manipulators Including Motor Dynamics
Authors: Yu H , Lloyd S
Published: February 2007

An adaptive control scheme for robot manipulators including motor dynamics is proposed in this paper. The proposed scheme avoids the assumption that the values of motor parameters are known which is required in reference (13). An exponential control law is first developed under the assumption of no uncertainty. This forms a controller structure for the adaptive control. Using this control structure, a full-order adaptive control law is proposed to overcome parameter uncertainty for both robot link and motor. The stability analysis is in the Lyapunov stability sense. The method is further extended to the task space. Extensive simulations are performed to compare the different control schemes.
A Self-Organizing Neural Network Approach to Data-Based Modelling of Fluid Power Systems Dynamics Using the GMDH Algorithm
Authors: Xue Y , Watton J
Published: February 2007

The group method of data handling (GMDH) is used to identify the non-linear transient behaviour of fluid power elements based upon input/output observations. It is shown how a variety of multi-layered perceptron-type feedforward neural networks evolve for each application due to the heuristic self-organization of the approach. Single-input-single-output systems are considered and a modified algorithm is proposed and developed for multi-input-single-output systems. The technique is applied to a pressure relief valve and a variety of servo-valve-controlled motor systems.
Impedance Characteristics of Hydraulic Orifices
Authors: Lau K K , Edge K A , Johnston D N
Published: February 2007

The impedance characteristics of cylindrical and sharp-edged hydraulic orifices under non-zero mean flow conditions have been investigated through experimental measurement and computational fluid dynamics (CFD) simulation studies. Based upon these investigations a generic model of the impedance characteristics of orifices has been developed. This model can be adopted in computer simulations of pressure ripple in hydraulic systems. The results of this investigation also provide the basis for modelling more complex hydraulic components.
Non-linear Transient Analysis of Submerged Oil Journal Bearings Considering Surface Roughness and Thermal Effects
Authors: Ramesh J , Majumdar B C , Rao N S
Published: February 2007

A time-transient non-linear analysis has been carried out to study the influence of surface roughness and viscosity-temperature dependency on stability of a submerged oil journal bearing. The average Reynolds equation has been solved simultaneously along with the energy equation and heat-transfer equation in bush and shaft. The cavitation model, proposed by Kicinski along the lines of Jacobsson-Floberg theory, has been modified to account for the surface roughness effects. The effect of various surface roughness parameters, such as the composite surface roughness, roughness orientation pattern and variance ratio, on the stability has been studied. The non-linear transient analysis of submerged oil journal bearings under (a) a unidirectional constant load, (b) a unidirectional periodic load and (c) a variable rotating load is performed.
Elastohydrodynamic Lubrication of Elastomeric-Coated Surfaces in Line Contact
Authors: Elsharkawy A A , Hamrock B J
Published: February 2007

Elastohydrodynamic lubrication analysis for an elastomeric layer bonded to an elastic substrate and indented by a rotating elastic cylinder is introduced. The surface elastic deformations are computed from full elasticity analysis of layered elastic half-space. The dry-contact problem was solved first, and the iterative Newton-Raphson method was used to solve the elastohydrodynamic lubrication problem. The lubricant rheological equations were considered in the present analysis. The significant effects of the elastomeric layer thickness on the pressure profiles and film shapes at different operating conditions are presented and discussed.
Energy Usage and Environmental Pollution in the United Kingdom: Which Sector Dominates?
Authors: Darkwa K , O'Callaghan P W
Published: February 2007

The trends of energy consumption and the sources of the associated emissions over the past two decades in the United Kingdom have been analysed. There are indications that the levels of emission of CO 2, NOx, CO, VOCs (volatile organic compounds) and black smoke are rising steadily as a result of energy consumption. The road transport sector emerges as the current overall major contributor of these pollutants and the likely candidate to remain as the fastest growing energy consumer and polluter for some years to come. With the current rate of increase in the number of motor cars, that is 3.9 per cent per annum, and the likely environmental consequences, immediate technological solutions to reduce transport pollution are strongly recommended.
Development of the Trilateral Flash Cycle System: Part 3: The Design of High-Efficiency Two-Phase Screw Expanders
Authors: Smith I K , Stošič N , Aldis C A
Published: February 2007

An extensive research and development programme carried out at City University, London, has led to an improved level of understanding of how Lysholm twin screw machines may be used to recover power from two-phase flash expansion processes. The mode of operation of such machines is described together with the various types of rotor shapes used. Details are given of a computer simulation of the expansion process which was used to analyse 636 test results. These were obtained from earlier investigations as well as those of the authors and include three different working fluids, varying rotor profiles and sizes and power outputs of 5–850 kW. Good agreement was obtained between predicted and measured performance parameters and statistical analyses of the results indicate that this is unlikely to be improved without the development of more refined methods of two-phase flow analysis than are currently in use. Included in the tests are a set of measurements of pressure-volume changes within the expander carried out by the authors which confirmed a hitherto unappreciated feature of the expansion process. This is the relatively large pressure drop associated with the initial filling of the volume trapped between the rotors and the casing. The analytical technique thus developed was used both to explain the poor results of earlier studies with water expanders and to estimate optimum design performance. It is shown that, when expanding wet organic fluids, adiabatic efficiencies of over 70 per cent may be obtained at outputs of only 25 kW while multi-megawatt outputs are possible from machines no bigger than large compressors with efficiencies of more than 80 per cent. Two-phase screw expanders may be used not only for large-scale power generation in trilateral flash cycle (TFC) systems, but also in place of throttle valves in vapour compression systems to drive screw compressors in sealed ‘expressor’ units. The coefficient of performance of large refrigeration, air conditioning and heat pump systems may thereby be raised by up to approximately 8 per cent.
A Lean Burn Low Emissions Gas Engine for Co-Generation
Authors: Mendis K J S , Stone C R , Ladommatos N , Daragheh M
Published: February 2007

This paper presents the rationale behind a fast burn high compression ratio (FBHCR) combustion system intended for use in a lean burn natural gas engine. Comparisons are made between the FBHCR combustion system, predictions made by a two-zone combustion model and measurements from the original combustion system, for the brake efficiency, brake mean effective pressure and the brake specific NOx emissions. Experimental measurements of the unburnt hydrocarbon emissions, the burn duration and the cycle-by-cycle variations in combustion are also discussed from the two combustion systems. The results show how the conflicting aims of low emissions and low fuel consumption can be satisfied by using a lean burn combustion system. A comparison is also made between the following ways of expressing the exhaust emissions: volumetric, brake specific, mass per megajoule of fuel and gravimetric referenced to a specified oxygen level.
Optimum Matching of Non-Electrical Loads to Wind Turbines
Authors: Kirke B K
Published: February 2007

Improvements in technology have reduced the unit cost of wind–electric power systems by almost an order of magnitude since 1981, and installed wind power capacity is growing rapidly world-wide. Paradoxically, the use of wind-powered pumping systems, formerly the major application of wind power, is declining and little progress has been made towards the direct application of wind power to drive other mechanical loads such as aerators and compressors for heat pumps, despite huge potential markets in areas remote from electricity grids. A major reason for this failure to apply improved wind turbine technology to non-electrical loads is low system efficiency resulting from poor torque matching between the wind turbine rotor and the load. Methods of improving system efficiency are reviewed, including load-disengaging devices to permit easy starting and a simple mechanical control system for a variable ratio drive which would ensure that any wind turbine driving any load will operate near peak efficiency over the full operating range from cut-in to governing. The latter system could improve average system efficiency by a factor of 3 to 8 and has the further advantage that it can provide starting torque and can actuate overspeed control for Darrieus vertical axis wind turbines and low-solidity horizontal axis wind turbines.
Present Knowledge of the Effects of the Impeller Geometry on the Developed Head
Authors: Yedidiah S
Published: February 2007

This paper discusses the present state of knowledge of the manner in which the impeller geometry affects the developed head. A comparison with test results shows a very impressive agreement between theory and practice.
A Status Update of Westinghouse's Contributions to Clean Coal Technology
Authors: Bannister R L , Newby R A
Published: February 2007

The power generation cycle of choice today is the combined cycle, which uses both the Brayton and Rankine cycles. The combustion turbine in a combined cycle can be used in a repowering mode or in a Greenfield plant installation. Today's fuel of choice for new combined cycle power generation is generally natural gas. Due to an estimated global recoverable reserve of over 200 years of coal that can be used to generate electricity, future power generation systems must be designed to include coal. Working with the US Department of Energy and other organizations, Westinghouse is actively pursuing the development and commercialization of several clean-coal-fuelled technologies to provide high efficiency, high reliability, cost competitive and environmentally superior power generation compared to conventional coal-fuelled technology. This paper reports primarily on the status of advanced clean coal power technologies that Westinghouse is helping to develop.
An Intelligent Planning Aid for the Design of Progressive Dies
Authors: Cheok B T , Foong K Y , Nee A Y C
Published: February 2007

The design of progressive dies is a highly iterative planning process in which the designer attempts to select a die configuration which will produce a part most efficiently by minimizing material, tooling and maintenance costs while achieving the required part specifications. The planning process involves a considerable amount of human cognitive skills such as pattern recognition and matching (as in punch shape recognition) and spatial planning (as in nesting and staging of die processes) based on the geometrical features of the part. This paper describes an intelligent planning aid which can assist the die designer in planning progressive dies. The highly automated and yet flexible planning aid is developed by linking together a CAD (computer aided design) system, a knowledge-based system and a library of numerical routines.
On the Improvement of Tool Life in Self-Piloting Drilling with External Chip Removal
Authors: Astakhov V P , Osman M O M
Published: February 2007

This paper presents both the design and the method of grinding of self-piloting drills (SPDs) with external chip removal. The main advantage of the proposed SPDs over the standard SPDs is brought out using a comprehensive analysis of the SPD auxiliary flank design. The concept of increasing the cutting fluid pressure in the limited space between the tool flanks and the bottom of the hole being drilled by increasing the hydraulic resistance of the channel connecting this space and the chip removal passage is proposed. For the realization of the concept, the mathematical model for the auxiliary flank has been derived on the basis of the obtained condition for a free tool penetration into the workpiece. Using this model, the detailed grinding procedure for the proposed SPDs is explained. The two-stage experimental comparison of the standard and proposed SPDs shows that a significant improvement of tool life is achieved by using the proposed SPDs.
Concurrent Engineering Assessment: A Proposed Framework
Authors: Poolton J , Barclay I
Published: February 2007

There are few studies that have found an adequate means of assessing firms based on their specific needs for a concurrent engineering (CE) approach. Managers interested in introducing CE have little choice but to rely on their past experiences of introducing change. Using data gleaned from a nine month case study, a British-wide survey and a series of in-depth interviews, this paper summarizes the findings of a research study that examines how firms orientate themselves towards change and how they go about introducing CE to their operations. The data show that there are many benefits to introducing CE and that firms differ with respect to their needs for the CE approach. A tentative means to assess CE ‘needs’ is proposed which is based on the level of complexity of goods produced by firms. The method is currently being developed and extended to provide an applications-based framework to assist firms to improve their new product development performance.
The Effectiveness of Quality Management Tools and Techniques: An Examination of the Key Influences in Five Plants
Authors: McQuater R E , Dale B G , Boaden R J , Wilcox M
Published: February 2007

There are a number of critical factors which need to be in place for the effective use and successful application of quality management techniques and tools (QMT&T). These ‘success’ factors may be classified into four categories: the role of the technique or tool in the improvement process, organization and infrastructure, data collection and the use and application of the tool or technique. Each of the categories are subject to influences, defined as experience, management, resources, education and training. It is these influences that create the issues and difficulties associated with the techniques and tools. Their effects may be minimal in isolation, but, when accumulated, may have a profound adverse influence on the successful use and application of QMT&T. Based on the outcome of the investigation described in the paper, guidelines for the effective use of QMT&T have been produced. When used in conjunction with the UMIST Quality Technique and Tool Assessment Method (UMIST QAM), the guidelines will provide organizations with the means of determining how the various influences manifest themselves in their own operating environments and will act as pointers for tackling them. This form of assessment process may also help organizations to realize the potential difficulties and issues that arise in areas such as new product development or strategy development, thereby aiding the continuous improvement process.
An Experimental Study of Resistance Spot Welding in 1 mm Thick Sheet of Low Carbon Steel
Authors: De A , Gupta O P , Dorn L
Published: February 2007

Investigations on the influence of welding parameters such as welding current, electrode force and weld time in resistance spot welding processes have been carried out with the help of a specially developed simulator. The effect of these parameters on dynamic contact resistance as well as on the quality of weld joint in terms of weld joint strength, nugget diameter, etc., was studied and conclusions have been made. Experiments have been carried out on 1 mm thick St1203 (DIN 1623) type of steel. Experimental observations were analysed statistically to obtain an empirical relationship between weld strength and the welding process parameters and subsequently a polynomial relation of second order has been fitted with a satisfactory degree of reliability. From these results welding lobes were also drawn which will provide information on different conditions needed for specified weld strength and also ensure a minimum guaranteed strength at those combinations. The possibility of using dynamic contact resistance as a means of monitoring the quality of spot welds has been explored and certain important observations are reported.
A Three-Dimensional Upper Bound Elemental Technique for Forging Analysis
Authors: Lee R S , Kwan C T
Published: February 2007

In this paper, two kinematically admissible velocity fields are derived for the proposed three-dimensional arbitrarily triangular and trapezoidal prismatic upper bound elemental technique (UBET) elements. These elements are applied to the portions between the circular shaped part and the straight rod part with three-dimensional metal flow in connecting rod forging, and then the capability of the proposed elements are shown. From the derived velocity fields, the upper bound loads on the upper die and the velocity field are determined by minimizing the total energy consumption with respect to some chosen parameters. Experiments with connecting rod forging were carried out with commercial pure lead billets at ambient temperature. The theoretical predictions of the forming load is in good agreement with the experimental results. It is shown that the proposed UBET elements in this work can effectively be used for the prediction of the forming load and velocity field in connecting rod forging.
Automated Design of Progressive Dies
Authors: Huang K , Ismail H S , Hon K K B
Published: February 2007

This paper describes the structure and operation of a prototype intelligent system for progressive die design and manufacturing. The system is developed using X Window ‘C’ programs to create an interface linking the CAD (computer aided design) package, AutoCAD and the expert system shell, Kappa. AutoCAD is used for the input of the piece part geometry, creating the temporary drawings and final design drawings of the tool parts and assembly while Kappa is used to create the knowledge base, the databases of the standard tool parts and the menu system for entering design data. Purpose-built ‘C’ programs are also used for some numerically intensive computations, for example calculating the best material utilization. The system knowledge is based on a structured analysis of present press tool design techniques.
A Strategy for the Verification of Tolerances by Coordinate Measuring Machines
Authors: Medland A J , Mullineux G , Rentoul A H
Published: February 2007

Tolerance definitions and standards have been derived from manual inspection procedures. These interpret manufacturing errors through the use of comparative instruments, such as straight edges and height gauges. These tolerancing forms cannot be applied directly to inspection by coordinate measuring machines, where points on an object are sampled and assembled geometrically to allow features to be calculated.

In this paper an alternative approach is presented in which all tolerance conditions are recast into a series of allowable spherical deviations spread across the features to be measured. The distribution of these spherical zones and their radii are chosen, at the design stage, to provide checks on the various tolerance conditions required and to reflect the degree of confidence in the surface conditions provided by the manufacturing processes.

This approach has been employed within an automated inspection procedure to allow both top-down and bottom-up error checking procedures to be employed.
A New Method of Measuring Involute Profile Deviations of Gear Teeth
Authors: Munro R G , Ling P H K
Published: February 2007

The principle behind all involute profile measuring machines is to arrange for relative movements between the gear and a stylus, so that the stylus measures only the deviations from a perfect involute curve. Over the years a number of different ways have been devised to produce the relative movements, involving discs and levers, and more recently computer numerical controls (CNC). This paper draws attention to the fact that accurate, large displacement optical gratings remove the need for accurate motion generation by using software compensation. The principle is applied to a base disc type of machine, which can be easily converted so that its full diameter range can be covered by a handful of nominal size discs, rather than needing an accurate and unique size of disc for every gear base diameter. In addition the output display can be made similar to that of a modern CNC machine.
A Review of Forced Convective Heat Transfer in Stationary and Rotating Annuli
Authors: Childs P R N , Long C A
Published: February 2007

The study of heat transfer by forced convection in annular passages is of interest across the range of process and aeronautical industries, for example from annular heat exchangers to the various configurations of annuli found in turbomachinery. The aim of this paper is to review relevant experimental, numerical and analytical research of heat transfer in both stationary and rotating annuli, with an emphasis on presenting useful information for designers. The geometries considered are the stationary annulus with superposed axial throughflow and the rotating annulus with rotation of either the inner or outer cylinder (both with and without throughflow). The work presented covers laminar and turbulent flows as well as flow regimes where transition occurs or vortex flows are present.
Compression Processes and Performance Analysis of a High-Pressure Reciprocating Gas Compressor
Authors: Wu T T , Hsieh W H
Published: February 2007

Compression processes and compressor performance in a two-stage 41.34 MPa (6000 lb/in2) reciprocating gas compressor were investigated by transient multi-dimensional and transient global thermodynamic models. The transient multi-dimensional model was adopted to predict the two-dimensional compression processes in the second-stage cylinder of the high-pressure reciprocating gas compressor. Calculated results showed no significant temperature gradients anywhere in the compressor cylinder except near the wall, throughout one complete compressor cycle. On the other hand, the calculated velocity fields and streamline contours showed a convergent flow pattern during the process of compression with discharge and a large recirculation vortex during the process of expansion with suction. A parametric study based on the transient global thermodynamic model was conducted to investigate the effect of various parameters, that is clearance volume, wall temperature of cylinder head and stroke length, on the compressor performance. Among these parameters, it was found that the clearance volume had the strongest effect on the compressor performance. A reduced clearance volume increased volumetric efficiency. Also, it was found that decreasing the stroke length would not degrade the compressor performance, but it could reduce the compressor size and thereby the manufacturing cost significantly.
Numerical Analysis of Fully Penetrated Weld Pools in Gas Tungsten Arc Welding
Authors: Zhang Y M , Cao Z N , Kovacevic R
Published: February 2007

Full penetration welding is widely used in metal joining, but it has been ignored in previous convective numerical models. In addition to the free surface on top of the pool, an additional free surface appears on the bottom of the workpiece. It can be shown that the top surface, temperature distribution and fluid flow field in the weld pool are all coupled with the pool's bottom surface. This complicates the numerical process and therefore no convective models have previously been developed for fully penetrated weld pools. In order to improve the numerical solution for the fully penetrated weld pool, a three-dimensional model is proposed. Free top and bottom pool surfaces have been included. The electromagnetic force, buoyancy force and surface tension gradient (Marangoni) are the three driving forces for weld pool convection. Welding parameters are changed in order to analyse their effects on weld pool geometry. It is found that the depression of the top surface contains abundant information about the full penetration state as specified by the back-side bead width.
Cable Stretch Asymmetries in Multi-Cable Spreader Suspension Systems Undergoing Combined Translations and Rotations
Authors: Morrish L , Cartmell M P , Taylor A J
Published: February 2007

The work presented in this paper proposes that for widely spaced cable reeving configurations in container-handling cranes there is an interesting, and unexpectedly useful, phenomenon defined henceforth as geometrical extension which gives rise to unevenly distributed cable stretch and, hence, uneven tensions across the system. Geometrical extension is entirely caused by the reluctance of the trolley, spreader and cable system to conform, as a whole, to certain overall shapes. Such shapes are developed because of the various translational and rotational motions which can be experienced at the trolley (that is at the attachment point of the cables running down to the spreader). Other cables stretch effects, such as those due to static and dynamic (inertia) loads, are additional to the geometrical extension (which can, in some circumstances, manifest as a compression instead).

The net effect of cable stretch asymmetries is to stiffen up the suspension for certain cases of translation and rotation. This has a direct, and useful, influence for anti-sway control.
Profile Determination of Plate Cams with Oscillating Convex Arbitrary-Shaped Followers
Authors: Hwang G S , Tsay D M , Huang M H
Published: February 2007

A universal form of profile equation for a plate cam whose follower has an oscillating motion and a convex arbitrary shape is derived in this study. The applied concept is the theory of envelopes in a parametric form. The derived results can be used to determine the profile of the cam with any kind of convex shape of the followers. It is also shown that the traditional followers, such as flat-faced and roller followers, are special cases of the universal form.
Mesh Refinement Formulations in Adaptive Finite Element Methods
Authors: Li L-Y , Bettess P , Bull J W , Bond T
Published: February 2007

This paper presents some new ideas for developing adaptive remeshing strategies. It is shown that correct mesh refinement formulations should be defined at an element level rather than a global level. To accomplish this, permissible element errors are required to be defined. This paper describes the methods to determine the permissible element errors. Two mesh refinement formulations are derived according to different accuracy definitions and are compared with the conventional mesh refinement formulation derived at the global level. Numerical examples are shown to explain the features of these mesh refinement formulations. Recommendations are made for use of these mesh refinement formulations.
Vibration Analysis of Helicoidal Plates
Authors: Ko C L
Published: February 2007

Governing equations for free vibrations of thin orthotropic or isotropic helicoidal plates are formulated by expressing displacements in terms of components in a helical orthogonal coordinate system. Equations derived for isotropic helicoidal plates are applied to the vibration problem of twisted rectangular turbine blades without camber. These twisted cantilever rectangular blades are simulated to be isotropic helicoidal plates with their angles of twist approximated to be their centre-line helical angles. Natural frequencies are calculated by solving the eigenvalue problem using the finite difference method and are compared to experimental measurements reported in the literature. Reasonably good agreement has been found for flexural modes; however, some discrepancies have also been observed for higher-order modes due to the inaccuracy of modelling the blade geometry as that of a helicoidal plate and due to the approximation of assuming the angle of twist to be the helical angle.
Mechanical Work at a Boundary and its Associated Exergy Transfer
Authors: McGovern J A , Yantovski E I
Published: February 2007

This paper is a didactic discussion of mechanical work at a boundary from the standpoint of exergy analysis. It is shown that the use of the material velocity vector and the mechanical stress tensor of continuum mechanics allows the magnitude and direction of the energy flux vector at a point to be determined unambiguously. Hence, the amount and direction of the energy transfer at a boundary can be established. This methodology is then extended to the calculation of the associated exergy flux vector and the exergy transfer at the boundary. It is noted that the exergy transfer is not always equal to the energy transfer as mechanical work. In general, the exergy transfer also involves a term consisting of the product of the environmental pressure and a volume displacement or transfer.
Effect of Non-Linear Components on the Performance of a Hydro -Pneumatic Slow-Active Suspension System
Authors: El-Demerdash S M , Crolla D A
Published: February 2007

In this work, the effects of component non-linearities on the ride performance of a hydro-pneumatic slow-active suspension system are studied theoretically. Based on the quarter car linear model, linear optimal control theory is used to calculate the feedback and feedforward gains. These gains are used in both linear and non-linear models with and without preview control. The Pade approximation technique is used to represent the preview time resulting from a preview sensor mounted on the vehicle front bumper to measure the road irregularities ahead of the front wheel. The results on a typical major road showed that at similar r.m.s. values of suspension working space, the non-linear slow-active system with preview provided a 28 per cent improvement in ride comfort and a 17 per cent reduction in dynamic tyre load compared with a passive system. However, the inclusion of non-linear effects of the components increases the ride comfort acceleration by 10 per cent and suspension working space by 12 per cent compared to the equivalent linear model at approximately equal values of r.m.s. dynamic tyre load.
Reduction of Unburnt Hydrocarbon Emissions from Spark Ignition Engines Using In-Cylinder Catalysts
Authors: Hu Z , Ladommatos N
Published: February 2007

Exhaust unburnt hydrocarbons (HC) in spark ignition engines arise from a number of sources, including flame quenching at the entrance of crevice volumes and at the combustion chamber wall, absorption and desorption of fuel vapour into oil layers on the cylinder wall, partial burning and misfiring. All sources other than partial burning and misfiring are in close proximity to the wall surfaces of the combustion chamber. The significance of this observation is that unburnt HC emissions from spark ignition engines may be reduced at their sources of production using in-cylinder catalysts on the surfaces of the combustion chamber wall. This paper examines in detail a novel approach to reduce exhaust HC emissions using an in-cylinder catalyst on the combustion chamber walls, in particular, the surfaces of the crevice volumes. Platinum-rhodium coating on the piston crown led to a reduction of approximately 20 per cent in engine-out HC emissions over a wide range of engine operating conditions.
Control Strategies for Semi-Active Lorry Suspensions
Authors: Cebon D , Besinger F H , Cole D J
Published: February 2007

The optimum level of passive damping for minimizing the root mean square (r.m.s.) dynamic tyre force and r.m.s. body acceleration of a heavy vehicle is determined by testing a damper in a ‘hardware-in-the-loop’ (HiL) test rig. Two different control strategies [‘modified skyhook damping’ (MSD), and linear optimal control with full state feedback (FSF)] are investigated theoretically using linear models, and suspension force control laws are derived. These control laws, along with simple ‘on–off’ control, are then tested experimentally using a prototype semi-active damper which is controlled so as to follow the demanded force, except when power input is required. The achievable performance improvements are compared and differences between the linear theory, computer simulations and experimental performance are discussed. It is found that using FSF control, r.m.s. body acceleration and r.m.s. tyre force can be reduced simultaneously by 28 and 21 per cent of their values for optimal passive damping.
A New Method of Investigating Piston Ring Friction Under Firing Conditions
Authors: Paul G R , Sixsmith I J
Published: February 2007

A new method of investigating piston ring friction in a firing engine is described. Preliminary results are presented for a spark ignition four-stroke 15 cm3 single cylinder engine. Tests were carried out on both a ringed and ringless version of the same engine. From the difference in b.m.e.p. between the engines, the ring friction could be deduced under firing conditions. This friction increased linearly with speed.
New Concept of Automatic Control for a Passenger Car Clutch
Authors: Esenovsky-Lashkov Y , Polyak D
Published: February 2007

This paper highlights the main functions of clutch automatic control systems. These are:

forced clutch disengagement during gear shifting and when the engine falls below its minimum operating speed; forced clutch engagement under conditions of increasing engine speed or vehicle speed at a preset level or at a definite throttle position; adjustment of clutch friction torque, depending on the control parameter used.

To achieve this, a closed-loop automatic control system is required. The system compares control signals with feedback from a selected parameter and generates commands for changing clutch friction torque.

At present some automatic clutch systems use either the position of the accelerator pedal (‘Drivematic’ and ‘Guidosimplex’) or engine speed (ACTS) as the control parameter. The feedback parameter in these systems is the position of the clutch drive element. Comparison of the two systems shows that those using engine speed as the control parameter are more advanced, although their design is more complex. Engine speed is also used in the system of automatic electrovacuum friction clutch control (EPS) designed at the Central Automobile and Automobile Engine Scientific Research Institute (NAMI), but the principle of operation is totally different from existing systems. Particular features of this system are as follows:

all necessary modes of automatic control are provided by only one multi-function electromagnet acting on the vacuum valve in the clutch actuating servo chamber; the feedback is dependent on the position of the clutch actuator and is provided by a spring acting on the armature of the valve drive electromagnet—the force of this spring changes in proportion to the position of the clutch actuator; clutch friction torque control as a function of engine speed is provided by changing the current strength in the electromagnetic winding—these changes are initiated by the electronic control unit of the automatic control system.

To achieve the optimal performance of modern high-speed engines in combination with an automatic clutch system, all elements of the clutch control system must have minimal delay in converting input signals into control signals. This requirement resulted from an investigation of the EPS mathematical model comprising three non-periodic dynamic elements. The same results were experimentally proved when amplitude and phase frequency characteristics of the control system were measured.

It was shown in particular that the time constants of dynamic elements must not exceed 0.04–0.06 s. This required the application of a brand new engineering circuit for designing the EPS electronic unit. The EPS system is now in mass production and is standard equipment for some models of small passenger cars manufactured in the former Soviet Union. The system has been patented in the United States, Japan, Germany, Great Britain, France and Italy.
The Variation of Hydrocarbon Emissions from Different Piston Designs in a Spark Ignition Engine
Authors: Willcock M , Tidmarsh D , Foss P
Published: February 2007

The total hydrocarbon (HC) emissions and the distribution of hydrocarbon species from several different piston and cylinder liner configurations were compared against those from the standard piston for this engine. Reductions in total HC emissions were observed for each design variant, top land crevice volumes and cylinder liner surface finish achieved the most significant reductions. The variations between the relative quantities of a selection of the most significant HC species were investigated for each design and showed considerable differences between each test.
The Effect of Boundary Conditions on the Downstream Penetration of Pulsed Sprays After Impaction on a Flat Surface
Authors: Yule A J , Mirza M R
Published: February 2007

An experimental study has been conducted of the wall sprays produced after impaction on a flat surface by the pulsed spray from a single hole nozzle. The experiments are of relevance to direct injection diesel engines and they extend the range of boundary conditions covered in previous work, with variation of gas density, spray wall angle, gas cross-flow velocity and cross-flow turbulence level. The initial and boundary conditions are documented to provide a database which is suitable for computational fluid dynamics (CFD) model validation of an important aspect of diesel engine in-chamber flow. Previous work in the area is described and published empirical correlations are reviewed. The measurements of wall spray penetration as a function of time are presented and described and a correlation equation is proposed which fits the data with good accuracy.
Substructuring Method and Eigenfunction Representation for a Rolling Tyre Coupled to a Secondary Mechanical System
Authors: Vinesse E P
Published: February 2007

This paper deals with the simulation of a running, vibrating tyre coupled at its spindle to a secondary structure. First a generalized substructuring formulation is derived from the equation of continuum of the rolling tyre projected in the reference frame of the road. It results in the ability to express the coupling problem on the basis of the modal characteristics of the system with fixed interface. This simplified condition is then investigated further. Physical models of the tyre, such as membranes on springs, make it possible to extrapolate rolling conditions eigenfrequencies and mode shapes from quasistatic identifications. New results are provided concerning the direction along which resonances are observed at the spindle as a function of speed. In particular it is shown how the resultant of a mode ‘rotates’ when speed increases. Finally structural and physical models are used jointly for the simulation of the forces at the spindle of a tyre rolling over a small cleat. The input from the cleat is described using a ‘virtual profile’. This technique allows the contact area to be reduced to a single point and eigenvalues are then derived from the membrane analogy. It is found that the model allows for an accurate representation of experimental data at the speeds of interest.
Railhead Corrugation Growth Explained by Dynamic Interaction between Track and Bogie Wheelsets
Authors: Igeland A
Published: February 2007

Short-wave railhead corrugation growth on tangent tracks due to wear from driven locomotive wheels is investigated. A track model with a given initial random railhead irregularity is used. The track parameters and the railhead irregularities are estimated from measurements performed on a newly built track. The corrugation calculations are based on rolling contact mechanics; a semi-empirical relationship between creep, friction force and normal contact force is employed. Only longitudinal creep and creep forces are taken into account. The vertical contact forces between the moving wheels and the rail are calculated using a time-stepping method, allowing for a non-linear Hertzian wheel/rail contact stiffness. Numerical examples are given. It is found that the two wheelsets of a travelling bogie interact and that both of them should be considered in the same calculation. The bogie wheelbase turns out to be an important parameter.
Aerodynamic Drag on Trains in Tunnels Part 1: Synthesis and Definitions
Authors: Vardy A E
Published: February 2007

Aerodynamic drag on trains in tunnels includes friction drag and pressure drag, which are respectively the algebraic sums of the longitudinal components of all shear and normal forces on the train surfaces. The first of these is broadly similar to its counterpart in the open. The second is shown to include two effects that are usually negligible in the open.

It is shown that the overall drag force must be regarded as the sum of individual components, each of which behaves differently from the others. The components can be represented by non-dimensional coefficients whose numerical values are nearly constant for a wide range of train journeys. In contrast, the overall drag coefficient is shown to vary significantly, even during any particular journey.

The principal causes of aerodynamic drag in tunnels are also the principal causes of pressure waves that give rise to potential aural discomfort for passengers. It is argued that a common method of analysis is appropriate for the prediction of both of these effects.

Ill-defined train areas are shown to be a potentially serious source of confusion in the estimation and interpretation of drag coefficients. The relevant train area is shown to be its aerodynamic area, the definition of which is explained.
Optimization of Design of Railway Disc Brake Pads
Authors: Benseddiq N , Weichert D , Seidermann J , Minet M
Published: February 2007

High temperatures are one of the main problems encountered in disc brakes, contributing to rapid wear and poor braking performance. In this paper, a two-dimensional finite element model using a thermomechanical algorithm is used to predict the evolution of the bearing surface and temperature distribution at the interface between the disc and pad. After determination of the temperature of a conventional brake configuration, the behaviour of several modified friction pad designs is simulated numerically in order to improve contact and so to achieve lower surface temperatures.