bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preliminary investigation of a novel controlled stiffness proximal femoral prosthesis
Authors: Simões J A O , Taylor M , Marques A T , Jeronimidis G 
Published: October 2002

Previous studies have suggested that a controlled stiffness prosthesis is required to address the conflicting requirements of minimizing stress shielding and micromotion. The design for a controlled stiffness prosthesis is proposed and a preliminary analytical investigation performed to assess its predicted performance before fabrication of a prototype component. The novel prosthesis consisted of a cobalt-chrome core and a flexible composite outer layer. Varying the composite layer thickness allowed the prosthesis stiffness to be controlled. Three variants of the controlled stiffness prosthesis were critically assessed using the finite element method and their predicted performance compared with those of conventional prosthesis designs. The potential for stress shielding was assessed by examining the periosteal strain energy and the potential for migration assessed by examining the endosteal minimum principal cancellous bone stresses. Both the conventional and controlled stiffness implants performed poorly as press-fit prostheses. All the press-fit prostheses generated high cancellous bone stresses, suggesting that excessive migration of these implants would be likely. The controlled stiffness implants performed better than the conventional implants when bonded to the surrounding bone. Although the controlled stiffness implants did not eliminate stress shielding of the calcar, they produced higher strain energies than the conventional designs. The findings of this study are that osseointegrated controlled stiffness implants may perform better than current osseointegrated cementless prostheses and therefore it is worth while progressing to the next stage, of prototyping an implant.
Quantitative assessment of anterior cruciate ligament deficiency: Applied load versus applied displacement
Authors: Grimshaw P N , Bowker P 
Published: October 2002

The Salford static knee instrument (SSKI) was developed to determine the quantitative assessment of the human knee joint in vivo by utilizing the technique of applied displacement and measurement of resistive load as proposed by Butler et al. (1). The instrument was used in parallel with the device developed by Al-Turaiki (2) which utilized the opposite method of assessment. The objective of the research was to examine which of the two techniques provided the more reliable and accurate method of knee assessment. Fourteen patients with suspected isolated rupture of the anterior cruciate ligament (ACL) were subjected to anterior-posterior drawer testing on both devices. The results showed that each instrument produced results which confirmed the clinical diagnosis by indicating a significant decrease in anterior stiffness when comparing the injured and uninjured knees. [SSKI device ( p = 0.000) and Al-Turaiki (2) device ( p = 0.002) statistical significant difference testing with Bonferonni Alpha correction p = 0.0125]. The results showed the Salford static knee instrument indicated a 58 per cent decrease in anterior stiffness and the Al-Turaiki (2) device a 35 per cent decrease when comparing the injured and uninjured knees. In conclusion it is suggested that the application of displacement and measurement of load as proposed by Butler et al. (1) may be the most appropriate technique for precise clinical diagnosis of pathological human knee joint instability. load, displacement, knee, anterior, stiffness
Effect of phospholipidic boundary lubrication in rigid and compliant hemiarthroplasty models
Authors: Foy J Rogers , Williams P F , Powell G L , Ishihara K , Nakabayashi N , LaBerge M 
Published: October 2002

Hemiarthroplasty may benefit from materials which produce lower friction and improved boundary lubrication protection during start-up conditions. The purpose of this study was to evaluate the effect of phospholipidic boundary lubrication in both rigid and compliant hemiarthroplasty. An in vitro model was designed to dissociate the relative contribution of implant material compliance and the presence of phospholipid to the overall friction of a hemiarthroplasty contact using bovine articular cartilage. Normal bovine articular cartilage was articulated against four flat materials using reciprocating motion: (a) borosilicate glass; (b) borosilicate glass coated with dipalmitoylphosphatid-ylcholine (DPPC); (c) polyurethane (PU) elastomer (Tecoflex®SG93A, a medical-grade aliphatic thermoplastic PU, Thermedics Incorporated, Woburn, Massachusetts); and (d) surface-coated PU (Tecoflex®SG93A substrate coated with lipid-attracting copolymer poly[methacryloyloxyethyl phosphorylcholine (MPC)-co-butyl methacrylate (BMA)]). Tests were conducted in physiologically simulated tribological conditions for a non-conformal point contact. Friction and lubrication analysis was performed using both static and kinetic coefficients of friction μ measured for each group as a function of time for a sliding distance of up to 60 m. Results showed that the inclusion of supplemental phospholipid, DPPC, on a rigid substrate significantly decreased μ in comparison with the control (cartilage-glass). Additionally, removal of phospholipid components from the articular cartilage surface produced a significantly greater start-up μ in comparison with normal cartilage at the test onset. The use of a material with a lower modulus resulted in lower μ for the entire duration of the test. Polyurethane elastomer coated with the lipid-attracting copolymer, poly(MPC-co-BMA), resulted in the lowest frictional response. As seen in this study, the improvement of low-modulus hemiarthroplasty may involve the optimization of chemical modification and incorporation of lipid-attracting MPC copolymers onto compliant materials. However, further tests are warranted to determine whether lipid-attracting MPC copolymers perform as well during long-time, in vivo wear studies.
An axisymmetric contact model of ultra high molecular weight polyethylene cups against metallic femoral heads for artificial hip joint replacements
Authors: Jin Z M , Heng S M , Ng H W , Auger D D 
Published: October 2002

Contact mechanics of ultra high molecular weight polyethylene (UHMWPE) cups against metallic femoral heads for artificial hip joints is considered in this study. Both the experimental measurement of the contact area and the finite element prediction of the contact radius, maximum contact pressure and maximum Von Mises stress have been carried out for a wide range of contemporary artificial hip joints. Good agreement of the contact radius has been found between the experimental measurements and the finite element predictions based upon an elastic modulus of 1000 MPa and a Poisson's ratio of 0.4 for UHMWPE material under various loads up to 2.5 kN. It has been shown that the half contact angle for all the cup/head combinations considered in this study is between 40° and 50° under a load of 2.5 kN. The importance of this result has been discussed with respect to the anatomical position of the cup when placed in the body and the selection of a simple wear-screening test for artificial hip joints. The predicted contact radius and maximum contact pressure from the finite element model have also been compared with a simple elasticity analysis. It has been shown that the difference in the predicted contact radius between the two methods is reduced for more conforming contacts between the femoral head and the acetabular cup and smaller UHMWPE cup thickness. However, good agreement of the predicted maximum contact pressure has been found for all the combinations of the femoral head and the acetabular cup considered in this study. The importance of contact mechanics on the clinical performance of artificial hip joint replacements has also been discussed.
The thermo-acoustic response of a premixed swirl burner
Authors: Lawn C. J. 
Published: October 2002

Application of the theory of thermo-acoustic excitation of flames requires a detailed knowledge of the flame response to plane-wave velocity fluctuations of a given frequency through the burner. A model of the type of swirl burner used in some designs of industrial gas turbine is investigated, chemiluminescent emission being used as a marker of the hear release from both methane and propane premixed flames. The effects of the equivalence ratio and the withdrawal of the swirler so as to allow an annulus of unswirled premixture are also examined. It is found that there are two distinct modes of self-excitation. The response of different burner configurations in the mode with the higher frequency is analysed in terms of four parameters. These characterize the position and spread of the axial distribution of heat release fluctuations, and the origin and effective velocity of convection of disturbances. From these parameters, the Rayleigh integral can be calculated and this defines the frequency range over which excitation is possible. If the acoustic conditions require that the flame is lengthened, retracting the swirler, reducing the equivalence ratio or changing from propane to methane are all shown to be possible control measures for this particular burner.
Efficiency of a district heating network serving hot water absorption chillers
Authors: Kitanovski A , Poredoš A 
Published: October 2002

In the future, cooling needs will increase during the summer months because of an ever-increasing desire for comfort within buildings. Over the last decade, the use of absorption chillers has increased. These chillers require a heat source for their operation. When compared with conventional electrically driven compressor chillers, the electrical energy requirements for absorption chillers are almost negligible. As a heat source, absorption chillers can use fuel gases, fuel oils, steam and hot water. An analysis was made of the influence of the supply and return temperatures on the efficiency of district heating systems (DHSs), with hot-water-driven absorption chillers (HWACs) as a component of a heat-driven distributed district cooliing system. An optimal configuration of HWACs was proposed. A comparison between the efficiency of a DHS and HWACs for a range of hot water supply and return temperatures was made and an optimal operating temperature of 95/80°C was estimated.
Computation of unsteady flow through steam turbine blade rows at partial admission
Authors: He L 
Published: October 2002

Partial admission in the steam turbine is associated with strong unsteady flow effects on aerodynamic performance. This paper presents a first-of-its-kind computational study of the problem. The unsteady flow field in multiple blade passages and multiple blade rows is governed by the quasi three-dimensional unsteady Navier-Stokes equations, closed by a mixing-length turbulence model. The partial admission is introduced by blocking one segmental arc (or several segmental arcs) of the inlet guide vane of the first stage. The flow equations are solved by using a time-dependent finite volume method. The calculated unsteady force on rotor blades for a turbine stage at partial admission compares well with the corresponding experimental data. The present results show that a cyclic pumping and sucking phenomenon occurs in the rotor blade row of the first stage, resulting in large unsteady loading and marked mixing loss. For a single stage at a given admission rate, a blocking arrangement with two flow segments is shown to be much more detrimental than one arc of admission, because of the extra mixing loss. The results for a two-stage case, however, suggest that the decaying rate of circumferential non-uniformities could be far more important for performance. For this reason, an enhanced mixing loss in the first stage might be beneficial to the overall efficiency of a multistage turbine.
Application of casing treatment to an industrial axial-flow fan
Authors: Hill S D , Elder R L , McKenzie A B 
Published: October 2002

This paper deals with an experimental investigation into the influence of a vaned recess casing treatment on the performance of an industrial-type axial-flow fan with a hub-tip ratio of 0.4. The treatment has been tested in a variety of configurations relative to the fan, with an emphasis on the amount of fan blade tip exposure to the treatment. Two sets of blading, one of which is of the fully reversible type, have been investigated. Detailed flow measurements have been carried out with a slanted hot wire probe to provide an insight into the operation of the device and into the nature of the rotating stall in the solid casing configuration. Strain gauges have been employed to enable blade stresses to be recorded and an in-duct microphone to enable comparative tests on fan noise has also been used.
Low-temperature natural-gas-fired combustors and NOx formation
Authors: Syred N , Mirzae H , O'Doherty T 
Published: October 2002

This paper discusses the characteristics of low-temperature cooled combustors as currently being developed and utilized in situations where very low NOx emissions are required with natural gas firing. Cyclone or swirl-type combustors are commonly used owing to their very wide blow-off which when translated to a cooled situation results in a system with acceptable blow-off limits for flame front temperatures as low as 1000 °C with only 20 per cent excess air. This depends on the careful integration of the heat transfer surface with the flame front region such that the products of combustion are directed away, inwards from the cooled surface, thus permitting complete fuel burn-out to occur. The combustion aerodynamics of a multi-inlet pre-mixed natural gas-air cyclone combustor has been characterized using laser Doppler anemometry together with detailed mapping of NOx, temperature and gas species concentration. This has been undertaken in 32 different operational cases involving five different multi-inlet cyclone combustors operated over the equivalence ratio range 0.45 ≤ φ ≤ 1.25. The NOx emission data has been examined in light of the prompt NO model of De Soete and modified in light of the known combustion temperatures, NO and species concentration levels. A correlation was derived of similar form to that of De Soete and found to give a reasonable data fit over the temperature range from 900 to 1500 °C, especially for lean equivalence ratios. The constants in this correlation are quite different from those of De Soete; this is felt to reflect the much lower temperature levels over which the data were gathered. Conclusions are then drawn as to the configuration of very low NOx emission combustors.
Examination of flow behaviour of electrorheological fluids in the flow mode
Authors: Wolff-Jesse C , Fees G 
Published: October 2002

The use of electrorheological (ER) fluids in hydraulic systems has been demonstrated in detailed investigations at the Institute of Fluid Power Transmission and Control (IFAS) [1]. The flow behaviour of this fluid cannot be described reliably. A detailed knowledge of this flow behaviour would enable better ER component design and produce basic information for simulation models. It is therefore important for the practical applications of ER fluids. A detailed comparison is made between existing rheological models, e.g. the Bingham model, and measured values in flow mode to confirm these models and, if possible, to define a material property constant. In addition, a simple model describing the flow behaviour of an ER fluid in the flow mode with the help of a geometrical dependent variable is presented. This variable is derived from measured values and reflects the influence of the gap height and the gap length. A comparison between this function and real measured values gives a very good agreement within the defined sphere and therefore it is a good tool for the design of electrorheological flow resistors.
Two-dimensional flow of a non-Newtonian lubricant
Authors: Greenwood J. A. 
Published: October 2002

The traction coefficients predicted in an elastohydrodynamic contact with a Newtonian fluid are impossibly large, so that methods of analysing the behaviour of a non-Newtonian fluid are essential. Except for one-dimensional flow, no convenient exact method is known. Two approximate methods of treating the flow of a non-Newtonian lubricant, proposed by Ehret et al. and Hooke respectively, are examined by comparing their predictions for a particular non-Newtonian fluid for which an exact solution may readily be obtained. While there is no reason to believe that any real fluid exhibits this behaviour, it is not too different from Eyring behaviour, so that the conclusions are believed to be applicable to real fluids. A method of obtaining an exact solution for a general non-Newtonian lubricant is investigated, although it appears to involve too much computation for use in an elastohydrodynamic lubrication (EHL) solver. A limited number of full solutions obtained for an Eyring fluid support the conclusions deduced using the model fluid, namely that the approximations will be quite adequate for the analysis of EHL of smooth surfaces and may be good enough for wavy or rough surfaces.
Wear debris and associated wear phenomena—fundamental research and practice
Authors: Roylance B. J. , Williams J. A. , Dwyer-Joyce R 
Published: October 2002

The effect and consequences of wear on the present-day operation and maintenance of industrial machinery are considerable and far reaching in terms of the performance, cost and underlying business environment. One of the ways open to maintenance engineers to keep track of the wear occurring is to monitor the condition, or ‘health’, of critical items of machinery by either measuring or capturing representative samples of wear products, primarily the debris that is generated in the contact which is subsequently released and transported away from the source by the lubricant behaving as a carrier fluid. Commencing with a brief description of some wear-related failures of critical components, such as bearings and gears, the different manifestations of wear debris are reviewed with particular regard to the methods employed to measure or capture the debris and how their characteristics are determined. Of particular importance is the need to establish and single out those morphological features which relate to the underlying wear mechanisms involved which led to their generation. The manifestation of wear phenomena and the causal effects are to be addressed by examining the mechanisms in the light of current fundamental research in which the links between wear and the generation of the associated debris are reviewed and discussed.
Optimum initial axial compression due to preload in an arrangement of two tapered roller bearings Part 2: Application to the transfer shaft of an automobile automatic transaxle
Authors: Bercea I , Nélias D , Cretu S 
Published: October 2002

A method to determine the optimum value of the initial axial compression or preload between two tapered roller bearings has been described in Part 1 of this paper. The optimization consists in maximizing the fatigue life of the bearing arrangement. The method is applied here to the transfer shaft of an automobile automatic transaxle, and the results are analysed. Numerical results show the importance of an adequate axial compression to ensure a maximum bearing arrangement reliability for a complex cycle of operating conditions in terms of load and speed.
Comprehensive design methodology for an engine journal bearing
Authors: Hirani H , Athre K , Biswas S 
Published: October 2002

The trend towards high power output, high speed and low power loss in engines requires a better understanding of bearing behaviour. Research in this area is directed more towards different aspects involved in bearing analyses, rather than providing a comprehensive guideline on design of bearing. This effort compiles the design methodology for selection of diametral clearance and bearing length by limiting the minimum film thickness, maximum pressure and temperature. The design procedure is summarized on the basis of the existing rapid bearing analyses for evaluation of the journal trajectory, minimum film thickness and maximum pressure and simplified thermal analysis. A flow chart is provided for step-by-step bearing design. Finally, two case studies of engine bearings are described: one investigates the VEB bigend connecting-rod bearing for a large industrial reciprocating engine and the other a main crankshaft bearing for an automotive engine. The methodology translates into easy-to-use expressions and the overall procedure is outlined, using practical data to demonstrate how this can be employed effectively by users.
Wear behaviour and surface form evolution of a novel titanium carbide implanted surface under lubricated conditions
Authors: Fletcher D. I. , Kapoor A , Steinhoff K , Schuleit N 
Published: October 2002

Tribological behaviour (friction and wear) of heavily loaded lubricated surfaces is found to be influenced by the presence of very small scale surface textures. The Indirect Structuring process, which is described here, is a new method of surface texture production through implantation of a surface with wear-resistant regions. During use a surface texture is developed and maintained because, at a given wear rate, the wear-resistant regions can sustain higher contact pressures than can the substrate. Indirect Structuring of a tool steel surface was carried out by laser implantation of the surface with titanium carbide implants, and rolling contact experiments were conducted under elastohydrodynamic and mixed-lubrication regimes. It was found that the indirect structuring process produces a surface structure which fulfils the design requirements for textured tool surfaces, and which is insensitive to the load applied to the surface. The mechanisms found to steer the development of the surface texture may be used to develop design methods for application of the Indirect Structuring process.
Implications of cavitation in individual grooves of spiral groove bearings
Authors: Broman G. I. 
Published: October 2002

The pressure distribution in a flat spiral groove thrust bearing obtained from a straightforward solution of the Reynolds equation includes subatmospheric pressure in part of the grooved area. This is masked in the common theory based on the assumption of an infinite number of grooves. Furthermore, the negative contribution to the load capacity from this area is usually small, which may explain why the presence of subatmospheric pressure has not been given much attention in connection with these bearings. Subatmospheric pressure is, however, necessary for liquid-lubricated flat spiral groove thrust bearings of conventional design to work at all at low numbers of grooves, which in turn requires a non-zero cavitation pressure. Cavitation within individual grooves implies non-linearity in, for example, the relation between load capacity and rotational speed of the bearing and limits the obtainable load capacity. This is more pronounced and important to consider at low numbers of grooves (wide grooves) than at high numbers of grooves (narrow grooves), and it is difficult to determine for what number of grooves that reliable prediction of bearing performance can be expected. It depends on the actual value of the cavitation pressure and other parameters that are usually unknown or difficult to account for. To avoid this disadvantage a modified design of liquid-lubricated flat spiral groove thrust bearings is suggested.