bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calculation of the Unsteady Flow in Exhaust Pipe Systems: New Algorithm to Fulfil the Conservation Law in Pipes with Gradual Area Changes
Authors: Van Hove W , Sierens R 
Published: February 2007

In this paper a new calculation method is proposed for the gas flow in tapered pipes. The model is adapted to the hybrid method of characteristics. The key idea of the model is to concentrate any area change over one mesh length in the mesh points instead of using an area gradient along the characteristic lines. The model has the disadvantage that the computing time increases, but it has the great advantage that the law of conservation of mass is fulfilled for the whole pipe length, even for important area changes. This allows the other advantages of the method of characteristics to be retained, for example the treatment of discontinuities in temperature or gas composition, without compromising the mass balance of the engine. In a test case it is shown that the new model correctly predicts the mass flowrate at all mesh points, which is not the case for the original hybrid method or other adapted versions. Tests for a real engine situation give results for the conservation of mass that are comparable with the best results of the Lax-Wendroff method.
Metal Fatigue—Past, Current and Future
Authors: Miller K J 
Published: February 2007

Metal fatigue has been a problem for more than 150 years, but because of rapid developments in fracture mechanics analyses, possibly at the expense of the traditional approach based on cyclic deformation processes, afar better understanding of fatigue failure behaviour has recently been achieved. Consequently the engineer now has the basic tools at his/her disposal to make good assessments of the numerous factors that control the fatigue lifetime of engineering materials, components and structures. Additionally, more intensive interdisciplinary research studies involving chemists, materials scientists, mathematicians and physicists—but engineering led—have generated both greater insights into long-known industrial problems and routes to required solutions. This paper traces the growth of recent developments in understanding metal fatigue from the days of our mentors to the present day, and concludes with a brief review of some future research areas that are now available for exploitation.
Power Flow and Ratio Sensitivity in Differential Systems
Authors: Lloyd R A 
Published: February 2007

It has been known for some time that, in single-degree-of-freedom differential systems, the sensitivity of the overall transmission ratio to a change in ratio of one of the differentials is proportional to the fraction of the input power flowing in the relevant differential. A complete and general proof of this theorem is presented, using matrix algebra, determinants and a coherent subscript notation. The theorem provides a direct method for calculating the internal power flows during the synthesis of multi-epicyclic systems, and defines a theoretical limit to the ratio range and efficiency of a split-path continuously variable transmission. Analysis of the Allison WT is used to illustrate application of the theory to a change-speed transmission.
Failures of Liquefied Gas Storage Vessels
Authors: Lihou D A 
Published: February 2007

Pressurized storage tanks are robust structures and catastrophic failures are very rare events. Nevertheless, owing to the rapid rate at which the liquid contents will be released from an open valve or a fractured pipe and the subsequent flashing of the liquefied gas, these types of storage are often the criteria by which a site is classed as a major hazard under the Control of Industrial Major Accident Hazards (CIMAH) Regulations. The listed materials include ammonia, chlorine, ethylene oxide and flammable gases (boiling point <20°C). Methods of predicting leakage rates from various types of breach are presented with tables of physical property parameters for the more common materials, which simplifies the calculation of leakage rates. Brief details are given of some notable accidents involving liquefied gas storage failures to illustrate the following lessons for designers: 1. Continually review the field data concerning chemical attack from contaminants, particularly of the stress corrosion type. 2. Ensure that materials will retain adequate strength at the temperature extremes that may be encountered during abnormal conditions. 3. Design and locate fixtures and fittings so that they are operable and maintainable, paying particular regard to draining facilities. 4. Continually update the codes for passive and active protection against fire and impact, in the light of losses occurring worldwide; for example by abstracting reports from Lloyd's Register. 5. Be alert during hazard and operability study reviews to chance contamination of the tank contents with other process fluids which can cause the tank to become a ‘eactor vessel’ with rapid evolution of heat and pressurized gas.
Theoretical Modelling of Wheel-Rail Noise Generation
Authors: Thompson D J 
Published: February 2007

The major source of noise from railways, particularly at high speeds, emanates from the wheel-rail region. This wheel-rail rolling noise is generally attributed to structural vibrations of the wheels and rails, excited from the contact patch area. The main excitation is caused by the wheel and rail surface roughness (undulations), which introduce a relative vibration between the wheel and rail. A linear mathematical model of wheel-rail interaction has been developed which incorporates detailed predictions of the vibration properties of the wheel, the rail and the contact area. Results of this model give good agreement with experimental results as long as the roughness levels are not too severe. Models of the noise radiation from the wheel and rail vibrations have also been developed, from which it is apparent that the vibrations of both the wheel and rail are significant sources of noise and that the vibrations of both components need to be reduced if a significant reduction in noise is to be achieved.
Vibration Analysis of Gas Turbines by an Intelligent Knowledge-Based System
Authors: Allwood R J , Christie P I 
Published: February 2007

Monitoring the vibrations of a gas turbine during its development tests requires manual inspection and interpretation of thousands of diagrams displaying measurements made by hundreds of strain gauges and other transducers. This paper describes a prototype knowledge-based computer system to assist in this task. The features on each diagram are located by image processing methods and interpreted by stored knowledge which represents the experience of vibration engineers. The objective of the system is to distinguish the relatively few diagrams which have unusual features from the majority which have only expected features, leaving the interpretation of the unusual diagrams to real experts. The paper gives an overall description of the problem of vibration in gas turbines and some details of the image processing and knowledge processing methods used, and shows some examples of typical diagrams handled by the system.
Vibration Analysis of a Blood Processor Centrifuge with Anti-Twister Mechanism
Authors: Herman H , Dastane A , Sofer S 
Published: February 2007

This paper deals with the vibration analysis of a blood processor centrifuge with an anti-twister mechanism. Blood processors that employ anti-twister mechanisms are becoming increasingly popular because they cause relatively less damage to the blood than the conventional ones, which employ rotating seals. Knowledge of the vibration response of the device in its operating regime is important for trouble-free operation. A simple, three-degree-of-freedom, lumped-parameter, torsional-mode model is presented here. This model was used to analyse an existing blood processor. On comparing experimental and analytical values, it was found that the fundamental frequency as predicted analytically is within 19 per cent of the experimental value; the predicted second harmonic is about 28 per cent higher than the experimental one. Thus the proposed model predicts the fundamental frequency with reasonable accuracy. In design, the goal is to keep the operating frequency of the device sufficiently above the fundamental frequency to avoid resonance problems.
Tribology of Human and Artificial Joints
Authors: Unsworth A 
Published: February 2007

Studies of human joint lubrication mechanisms have led to the conclusion that under normal healthy conditions they are fluid film lubricated. The main features responsible for allowing this mechanism to operate are the dynamic nature of the loading and the compliance of the bearing surfaces (articular cartilage). In contrast, artificial joints, being made of much more rigid materials, have been demonstrated to be lubricated by a mixed regime, where some load is carried by the fluid film and some by solid to solid contact. Since some surface contact takes place then wear remains a problem and friction is much higher than in human joints. The use of compliant surface bearings for artificial joints has been explored and shown to be of great advantage, reproducing the effects of natural joints. However, elastomeric materials are known to degrade in aqueous solutions so this aspect has been examined to ensure a reasonable life in the human body. Joints of the lower limb—hip, knee and ankle—have similar load and motion patterns and behave in a similar way in terms of lubrication. Joints of the hand are not in any way similar in their behaviour and so a typical upper limb joint, the finger, has been studied to see if improvements can be made to the design of replacement artificial joints. Novel suggestions like plastic on plastic joints have been shown to be an alternative which is worthy of further consideration.
The Impedance Characteristics of Fluid Power Components: Relief Valves and Accumulators
Authors: Edge K A , Johnston D N 
Published: February 2007

This paper describes an experimental and theoretical investigation of the impedance characteristics of various relief valves and an accumulator. The test programme involved the measurement of pressure ripples at three locations in a specially designed test circuit. From these measurements, the impedance of a component was evaluated as a function of frequency. The experimental results are compared with mathematical models. For a single-stage relief valve, a simple orifice model has been found to be adequate. For two-stage valves, a much more complex model was considered. This was found to predict the basic trends but was not accurate. Tests on an accumulator yielded results which correlated well with a relatively simple mathematical model. However, it is difficult to quantify the model parameters. It is concluded that for the more complex components used in hydraulic systems it is necessary to measure the impedance characteristics rather than predict them. There is a need to adopt a standard test procedure for this purpose.
Improving the Fatigue Resistance Of Cold Forging Tools by Fe Simulation and Computer Aided Die Shape Optimization
Authors: Geiger M , Hänsel M , Rebhan T 
Published: February 2007

It is the intention of the present article to point out a new method for computer aided tool optimization as part of computer integrated tool manufacturing. Based on the results of finite element (FE) analysis and subsequent tool failure simulation, it is possible to optimize the FE model of a tool already at the stage of construction, in order to enhance the service life and process reliability. The permissible degree of freedom for any shape correction, of course, is mainly limited by constructive constraints of the tool and the properties of the material flow during the extrusion process. Thus the resulting optimized geometry has to he considered as a possible constructive alternative. However, analytical as well as practical solutions already show that a parabolical or elliptical curved surface contour, replacing a regular radius, not only improves the fatigue resistance but may have a positive influence on material flow behaviour, friction forces and resulting tool loads as well (1). The influence imposed on the material flow by the geometrical modification of the die shape will be clarified in future by the results of FE process simulation. A renewed simulation run, employing the optimized shape, may be conducted immediately after the optimization process. Along with current material research, the simulation of tool failure based on the finite element method (FEM) analysis of forging techniques (FE process simulation) therefore represents a promising direction for future developments (2–4).
Vibrations of Circular Cylindrical Shells under External Water Pressure
Authors: Ross C T F , Johns T , Stanton R M 
Published: February 2007

A theoretical and an experimental investigation was made on the vibration of three machined circular cylindrical shells under external water pressure. The theoretical investigation was based on the finite element method, where the shell was modelled by a truncated thin-walled conical shell element and the surrounding fluid by an annular element which had a cross-section in the form of an eight-node isoparametric quadrilateral. Comparison between theory and experiment was good and showed that the resonant frequencies decreased with an increase in the externally applied water pressure.
Computer Simulation of a Variable Fill Hydraulic Dynamometer Part 3: Closed-Loop Performance
Authors: Hodgson P G , Raine J K 
Published: February 2007

An engine and hydraulic dynamometer system is dynamically modelled with two different control systems. The closed-loop system behaviour is studied for a hydromechanical back-pressure water outlet valve and for an electrohydraulic servo-controlled water outlet valve. This is an extension of the open-loop dynamic model of Part 2, which incorporates the mathematical model of the torque absorption processes in a variable fill Froude-type hydraulic dynamometer presented in Part 1. The models are based on a system of first-order differential equations which are solved numerically using an Adams predictor corrector method. Both the analogue hack-pressure valve and digital servo-controlled valve are accurately simulated. In both cases the influence of the dynamic dynamometer model on the transient response is apparent. Variation in digital control system parameters across the operating envelope illustrates the non-linearity of dynamometer response. The computer model and experimental results are compared and implications of the closed-loop behaviour discussed.
The Minimum Film Thickness in Lubricated Line Contacts during a Reversal of Entrainment—Isoviscous Behaviour
Authors: Hooke C J 
Published: February 2007

In most line contacts, the film thickness can be adequately determined using a quasi-static analysis. The one exception appears to occur when the direction of entrainment changes. Here, the quasi-static approach predicts that the film will fall to zero while, in practice, there will always be a finite clearance between the surfaces. It was shown in a previous paper that this minimum clearance depends upon the rate of change of entrainment velocity, and limit expressions for the film thicknesses in the four regimes of lubrication were developed. The present paper examines the transition between the rigid-isoviscous and the elastic-isoviscous regimes and determines how the minimum film thickness behaves in this transition zone.
Inspection and Integrity Methodology for Storage Tanks
Authors: Kinnear D M 
Published: February 2007

The integrity of large storage tanks features significantly in the budget of maintenance and inspection departments within the petroleum and petrochemical industries. The unpredicted failure of a storage tank will not only seriously affect the operating flexibility within a company, but may lead to punitive action being taken by the authorities against the company for any pollution that may occur. A great deal of effort, as well as expense, is expended in the monitoring and inspection of storage tanks to ensure their integrity. Techniques used in predicting and assessing the condition of storage tanks are improving steadily and this paper provides an insight into techniques that are currently being used and methods that are being developed. The paper also proposes areas of research which need to be undertaken if economies are to be realized in this expensive process.
Structural Effects of Foundation Tilt on Storage Tanks
Authors: Palmer S C 
Published: February 2007

Vertical cylindrical tanks for bulk storage of oil and liquefied gas are sometimes constructed on soils that are susceptible to settlement. The types of foundation settlement and their structural effects on the tank are reviewed. An arbitrary operational limit of 1 in 200 is sometimes quoted for the foundation tilt of atmospheric storage tanks. This limit is based on aesthetic considerations and on the effects on pipework connections and other attachments. Many tanks reach this limit before the end of their design life, and tank owners face difficulties in assessing the effects of foundation tilt since the current design and inspection codes give no guidance. The purpose of this paper is to present a simple method for calculating the overturning moment, shear force and associated stresses caused by tilt of a tank, and to present a rational design basis. The procedures can be used in the design of new tanks to withstand a specified magnitude of foundation tilt and also to predict the maximum allowable tilt for existing tanks. Similarities with the overturning effects caused by wind and seismic loading are identified. The possibilities of axial buckling and shear buckling are investigated, and allowable stresses are discussed. For anchored tanks, the effects of tilt on the shell hold-down anchors are shown to be significant, and for unanchored tanks the possibility of shell uplift is discussed. A diagrammatic representation of the results is presented which allows stresses caused by tilt to be compared with stresses caused by other tank loads and the prediction of stresses caused by future tilt. Experimental tests on a model open-top tank are reported, and indicate that tilt did not cause significant distortion of the tank.
Integrated Flying Helmets
Authors: Jarrett D N , Karavis A 
Published: February 2007

The addition of vision enhancement, display and control functions to aviator's headgear is operationally attractive. Fast jets and helicopters currently under development call for headgear with a combination of these novel facilities. This paper reviews the recent history of such helmet systems, which demonstrate admirably the inventiveness of the design teams. However, there are attendant perceptual and operational concerns and the addition of extra components invariably compromises basic ergonomic qualities. It is suggested that a new design philosophy, which emphasizes functional integration rather than the incorporation of compatible sub-systems, has become essential. This will be assisted significantly when key optical and electro-optical technologies become mature.
The Function of Bipolar Hip Prostheses—A Laboratory Study Using Cadaveric Acetabula
Authors: Wetherell R G , Unsworth A , Amis A A 
Published: February 2007

Cadaveric acetabula were mounted in a hip simulator and the friction developed in each during articulation with a series of metal femoral head prostheses of differing sizes was measured. In a separate study, assembled Hastings bipolar hip prostheses were subjected to weight-bearing forces in the same acetabula and their self-righting mechanism was observed. The self-righting mechanism was found to function efficiently, in most cases overcoming the combined friction of the inner and outer articulations of the Hastings hip. However, during motion in the hip simulator a wide variation of friction was observed between different acetabula and within the same acetabulum with differing head size. In several cases this acetabular friction was found to be less than the friction in the inner articulation of the Hastings bipolar hip prosthesis, and this may explain some cases of reported failure of biarticular function.
The CADCAM Contribution to Customized Orthopaedic Implants
Authors: Crawford H V , Unwin P S , Walker P S 
Published: February 2007

CADCAM (computer aided design/manufacture) production methods are often associated with mass production; working in the medical field at the Department of Biomedical Engineering, the requirement is for one-off, individualized implants. Using a knowledge-based system, implant designs are produced from X-ray data. Assembly from modular components has greatly reduced the production time of implants for bone tumour cases. CADCAM techniques are also used in the production of custom-made hip replacements using digitized data gathered from radiographs. Femoral canal shape is calculated and the optimal implant designed and manufactured from titanium alloy on the Department's CNC (computer numerically controlled) machines.
A Device for Wear Resistance Tests of Artificial Heart Valves
Authors: Gorshkov Y V , Evdokimov S V , Kombalov V S 
Published: February 2007

According to the International Standard ISO 5840: 1990 the wear resistance test is a necessary step in the development and production of artificial heart valves (AHV). In developing the device, it is important that a reliable prediction is made of AHV longevity, as a number of specific problems appear that are connected with the results of tests, duration of testing, efficiency and reliability of the testing device. In this paper a procedure is outlined of service life testing of mechanical AHV and a description of the device is given. A comparative example of loads acting on AHV, operating in the accelerated wear testing device and in the pulse duplicator of the physiological mode is also described.
Implementation of Minimal Control Synthesis on a Servo-Hydraulic Testing Machine
Authors: Stoten D P 
Published: February 2007

The minimal control synthesis (MCS) algorithm is an adaptive controller that requires no prior knowledge of plant dynamic parameters, and yet is guaranteed to provide global asymptotic stability of the closed-loop system. The algorithm has been implemented on a variety of plant, ranging from laboratory-based rigs to industrial machines. The purpose of this technical note is to present the results of the first known implementation of the algorithm on a servo-hydraulically actuated machine. The results of the MCS implementation will be seen to compare very favourably with those of a conventional (P + I) implementation.
The Design and Development of Modern Lifeboats
Authors: Hudson F D , Hicks I A , Cripps R M 
Published: February 2007

Well-established operational practices have determined the evolution of RNLI lifeboats throughout their history. The RNLI's requirement/or an all-fast offshore fleet of the self-righting type by 1993, however, motivated the need to re-examine basic design parameters of boats and launching equipment. More recent requirements to improve lifeboat performance further have demanded even closer evaluation of design requirements of hull form, machinery installation and construction materials. This paper outlines the history of the development of RNLI craft and describes the procedures for the design and development of its newest classes of lifeboat (FAB 3 and FAB 4), for which extensive model testing of differing hull forms was evaluated, various types of machinery were reviewed and construction, although in composite materials, was carefully designed to accommodate high hydrodynamic and impact loads. Technical trials and operational evaluation procedures are also discussed.