bluuebunny/crossref_metadata_2025_split huggingface dataset:
A model to predict the life of pneumatic conveyor bends
Authors: Hanson R , Allsopp D , Deng T , Smith D , Bradley M S A , Hutchings I M , Patel M K 
Published: October 2002

A new approach to the prediction of bend lifetime in pneumatic conveyors, subject to erosive wear is described. Mathematical modelling is exploited. Commercial Computational Fluid Dynamics (CFD) software is used for the prediction of air flow and particle tracks, and custom code for the modelling of bend erosion and lifetime prediction. The custom code uses a toroidal geometry, and employs a range of empirical data rather than trying to fit classical erosion models to a particular circumstance. The data used was obtained relatively quickly and easily from a gas-blast erosion tester. A full-scale pneumatic conveying rig was used to validate a sample of the bend lifetime predictions, and the results suggest accuracy of within ±65%, using calibration methods. Finally, the work is distilled into user-friendly interactive software that will make erosion lifetime predictions for a wide range of bends under varying conveying conditions. This could be a valuable tool for the pneumatic conveyor design or maintenance engineer.
Solid/liquid separation by sedimentation
Authors: Holdich R G , Butt G 
Published: October 2002

The analysis of batch sedimentation tests performed for the purpose of continuous sedimentation vessel design is described. Conventional design techniques employ the concept of settling flux with, under certain conditions, a constitutive equation linking solid concentration and pressure in a unique and time-independent manner. Experimental studies employing measurement of local concentration and the liquid pressure gradient during sedimentation were used to determine the limits of the conventional design techniques. A 'maximum fluidized concentration' is defined which is the value above which it is difficult to maintain stable flux conditions and is the limit of applicability of conventional design methods based on settling flux. It is shown that the suspended solids contribute towards the liquid pressure gradient and, therefore, to the buoyancy experienced by the settling solids. However, during settlement the liquid pressure gradient reverts to the hydrostatic gradient alone; hence the buoyancy effect is a function of sedimentation time. Additional considerations also suggest that a unique relation between concentration and pressure should only be used as a constituent term in a time-dependent consolidation model. Current research effort includes a suitable method of linking time-dependent consolidation theory, under conditions of extremely low applied pressure, and sedimentation flux analysis.
Some railroad settlement models—A critical review
Authors: Dahlberg T 
Published: October 2002

Mathematical models to simulate railroad track settlements are reviewed and commented upon. There do not seem to be any generally accepted damage and settlement equations describing the long-term behaviour of the track. This also seems to be the case for the ballast material. Most descriptions of the settlement found in the literature are empirical; only different suggestions to describe the track settlement from a phenomenological point of view are available. The track settlement is mostly considered to be a function of number of loading cycles and/or a function of the magnitude of the loading. The settlement should also be a function of the properties of the ballast and subground materials, but very little has been found on this in the literature. By use of the finite element program LS-DYNA, a computer model (very simple) has been created to simulate the long-term behaviour of the track. The model consists of a rail, rigid sleepers, non-linear ballast springs (stiffnesses) and ballast damping. In a solid element beneath each ballast spring, track settlement can be accumulated. Settlement will occur if the stresses in that element exceed a yield limit of the element material. Also ‘hanging sleepers’ may be modelled and obtained as a result of the track settlement.
On the velocity profile of inclined jets in a boundary layer for vorticity production
Authors: Bray T P , Garry K P 
Published: October 2002

The velocity profiles of air-jet vortex generators have been investigated, and the effect of varying velocity profiles on vortex production has been assessed. In the simplest case of a jet generated by fluid effusing through a cylindrical hole drilled into a solid surface, the internal flow in the nozzle is critical to the development of jets to be used for vortex production. A series of Pitot traverses through a range of jet diameters and pitch angles has been made in order to characterize the jet development. In order to produce an axisymmetric jet profile, modifications were made to the jet nozzles, thereby overcoming the critical flow features within the jet nozzle. In order to assess the jets for vortex production, a range of air-jet vortex generator configurations have been used to produce discrete vortices in a turbulent flat plate boundary layer. Velocity vectors were measured over a cross-stream plane through the vortices, from which the vorticity could be derived across the plane. The vorticity at the centre of the vortex (or the peak vorticity) was then used as an indication of the strength of the vortices. It has been shown that the nature of the jet velocity profile is not significant to the strength of the vortex, so long as the average jet velocity is held constant.
Study of the aerodynamics of in-plane motion
Authors: Shaw S T , Qin N 
Published: October 2002

A computational analysis is performed of the unsteady aerodynamics associated with the blade sections of helicopter rotors in forward flight. The unsteady flow is studied through solutions of the two- dimensional Reynolds averaged Navier-Stokes equations together with a strongly coupled two-equation model of turbulence. Two motions are studied. The first motion is that of an aerofoil subjected to harmonic in-plane oscillations. The influence of advance ratio and reduced frequency is investigated. It is shown that, in the absence of shock waves, the flow is periodic with a reduced frequency equal to that of the forcing motion. However, the flow development lags behind the forcing motion. Furthermore, for constant reduced frequency the phase lag is independent of advance ratio. In addition to harmonic motion, the aerodynamic response to a step change in Mach number is investigated. Using an assumed form of the response of lift coefficient to a step change in Mach number, a lift transfer operator for step changes in Mach number is obtained in the Laplace domain. An analytical expression for the response to harmonic Mach number oscillations is then obtained from the transfer operator. The resulting formulation for the aerodynamic response confirms that the lag between the forcing motion and the aerodynamic response is independent of advance ratio.
Helicopter flight around a ship's' superstructure
Authors: Wakefield N H , Newman S J , Wilson P A 
Published: October 2002

A computational fluid dynamics model of a hovering helicopter main rotor is developed to examine air flow in the presence of ship structures and side winds. An illustration of the problem is given. The rotor is modelled by modifying the governing Navier-Stokes equations in the region of the disc. The extra terms added to the governing equations apply a downward force to the fluid; these forces are independent of the flow around the rotor and are equal to the helicopter weight. The helicopter rotor model and the ship model are combined to yield one flow solution, which, due to the severe non-linearities of the problem, cannot be achieved by superposition. The resultant flow yields valuable data about the induced velocities at the rotor, which ultimately determine the control pitch and power required to maintain the hover in a given location. Indeed, the interactions between the rotor downwash and ship air flow are known to produce unexpected and adverse flight dynamic behaviour of the aircraft.
A validation of the three-dimensional finite element contact method for use with Curvic couplings
Authors: Richardson I J , Hyde T H , Becker A A , Taylor J W 
Published: October 2002

Curvic couplings transmit torque between parallel in-line shafts or turbine/compressor discs. They are used extensively within the aero-engine industry but can also be found in industrial gas turbines. The manufacture of Curvic couplings involves the precision cutting and grinding of mating teeth on the adjacent ends of the components; the assembly is then clamped together with bolts. The design objectives for aerospace transmissions, and hence the Curvic coupling, are to reduce manufacturing cost, weight and size. The experimental testing of Curvic couplings within an aero-engine environment is time consuming and expensive. The objective of this paper is to justify confidence in the results from three-dimensional finite element (F E) contact analyses when investigating Curvic couplings. The accuracy of the FE analyses requires a fine mesh in the contact region and the capability to deal with stick-slip behaviour in multiple three-dimensional contact surfaces. A comparison of the results from a photoelastic test with the results from an FE analysis provides a validation of the FE contact method for use with Curvic couplings. The results presented in this paper indicate that the photoelastic results agree reasonably well with results of the FE method analyses.
The internal bevel gear and its applications
Authors: Molyneux W G 
Published: October 2002

Information on bevel gears and their applications is comprehensive where external bevel gears are concerned but proves to be more scarce when related to internal bevel gears, despite the fact that there are isolated practical examples of the use of such gears that have demonstrated their effectiveness in demanding transmission situations. In what follows a unique family of transmissions is examined, based solely on a particular layout of internal and external bevel gear combinations, that aims to demonstrate the wide ranging, largely unexploited, potential of transmission systems of this kind.
Development of artificial articular cartilage
Authors: Oka M , Ushio K , Kumar P , Ikeuchi K , Hyon S H , Nakamura T , Fujita H 
Published: October 2002

Attempts have been made to develop an artificial articular cartilage on the basis of a new viewpoint of joint biomechanics in which the lubrication and load-bearing mechanisms of natural and artificial joints are compared. Polyvinyl alcohol hydrogel (PVA-H), ‘a rubber-like gel’, was investigated as an artificial articular cartilage and the mechanical properties of this gel were improved through a new synthetic process. In this article the biocompatibility and various mechanical properties of the new improved PVA-H is reported from the perspective of its usefulness as an artifical articular cartilage. As regards lubrication, the changes in thickness and fluid pressure of the gap formed between a glass plate and the specimen under loading were measured and it was found that PVA-H had a thicker fluid film under higher pressures than polyethylene (PE) did. The momentary stress transmitted through the specimen revealed that PVA-H had a lower peak stress and a longer duration of sustained stress than PE, suggesting a better damping effect. The wear factor of PVA-H was approximately five times that of PE. Histological studies of the articular cartilage and synovial membranes around PVA-H implanted for 8–52 weeks showed neither inflammation nor degenerative changes. The artificial articular cartilage made from PVA-H could be attached to the underlying bone using a composite osteochondral device made from titanium fibre mesh. In the second phase of this work, the damage to the tibial articular surface after replacement of the femoral surface in dogs was studied. Pairs of implants made of alumina, titanium or PVA-H on titanium fibre mesh were inserted into the femoral condyles. The two hard materials caused marked pathological changes in the articular cartilage and menisci, but the hydrogel composite replacement caused minimal damage. The composite osteochondral device became rapidly attached to host bone by ingrowth into the supporting mesh. The clinical implications of the possible use of this material in articular resurfacing and joint replacement are discussed.
An investigation of three-dimensional scanning of human body surfaces and its use in the design and manufacture of prostheses
Authors: Bibb R , Freeman P , Brown R , Sugar A , Evans P , Bocca A 
Published: October 2002

The capture of highly accurate data describing the complex surfaces of the human body may prove extremely useful in many medical situations. The data provide a method of measuring and recording changes to the surface of a patient's soft tissue. The data may be applied to computer-controlled manufacturing techniques, such as rapid prototyping (RP). This enables accurate physical replicas of the patient topography to be produced. Such models may be used as an aid in the design and manufacture of prostheses. This paper describes an investigation aimed at identifying problems that may be encountered when scanning patients and describes the application of the resulting data in the design and manufacture of facial prostheses. The results of the experiment are presented together with a discussion of the accuracy and potential advantages afforded by this approach.
Development of a computer model to predict pressure generation around hip replacement stems
Authors: Dunne N J , Orr J F 
Published: October 2002

Cemented fixation of hip replacements is the elective choice of many orthopaedic surgeons. The cement is an acrylic polymer which grouts the prostheses into the medullary cavity of the femur. Cement pressure is accepted as a significant parameter in determining the strength of cement/bone interfaces and hence preventing loosening of the prostheses. The aim of this work was to allow optimal design of the intramedullary stem of a hip prosthesis through knowledge of the flow characteristics of curing bone cement which can be used to predict pressures achieved during insertion of the femoral stem. The viscosity of the cement is a vital property determining the cement flow and hence cement interdigitation into bone. The apparent viscosities, ηa, of three commercial bone cements were determined with respect to time by extrusion of the curing cement through a parallel die of known geometry under selected pressures. Theoretical models were developed and implemented in a computer program to describe cement flow in three models each of increasing complexity: (a) a simple parallel cylinder, (b) a tapered conical mandrel and (c) an actual femoral prosthesis, the latter models being complicated by extensional effects as annular areas increase. Predicted pressures were close to those measured experimentally, maximum pressures being in the range 10-160 kPa which may be compared with a threshold of 76 kPa proposed for effective interdigitation with cancellous bone. The theoretical model allows the prosthesis/bone geometry of an individual patient to be evaluated in terms of probable pressure distributions in the medullary cavity during cemented fixation and can guide stem design with reference to preparation of the medullary canal. It is proposed that these models may assist retrospective studies of failed components and contribute to implant selection, or to making informed selection from options in custom hip prosthesis designs to achieve optimum cement pressurization.
The effect on the fatigue strength of bone cement of adding sodium fluoride
Authors: Minari C , Baleanil M , Cristofolini L , Baruffaldi F 
Published: October 2002

New bone cements that include several additives are currently being investigated and tested. One such additive is sodium fluoride (NaF), which promotes bone formation, facilitating implant integration and success. The influence of NaF on the fatigue performance of the cement as used in biomedical applications was tested in this paper. In fact fatigue failure of the cement mantle is a major factor limiting the longevity of a cemented implant. An experimental bone cement with added NaF (12wt%) was investigated. The fatigue strength of the novel bone cement was evaluated in comparison with the cement without additives; fatigue tests were conducted according to current standards. The load levels were arranged based on a validated, statistically based optimization algorithm. The curve of stress against number of load cycles and the endurance limit were obtained and compared for both formulations. The results showed that the addition of NaF (12 wt %) to polymethylmethacrylate (PMMA) bone cement does not affect the fatigue resistance of the material. Sodium fluoride can safely be added to the bone cement without altering the fatigue performance of the PMMA bone cement.
Comparison of wear, wear debris and functional biological activity of moderately crosslinked and non-crosslinked polyethylenes in hip prostheses
Authors: Endo M , Tipper J L , Barton D C , Stone M H , Ingham E , Fisher J 
Published: October 2002

The wear, wear debris and functional biological activity of non-crosslinked and moderately crosslinked ultrahigh molecular weight polyethylene (UHMWPE) acetabular cups have been compared when articulating against smooth and intentionally scratched femoral heads. Volumetric wear rates were determined in a hip joint simulator and the debris was isolated from the lubricant and characterized by the percentage number and volumetric concentration as a function of particle size. The volumetric concentration was integrated with the biological activity function determined from in vitro cell culture studies to predict an index of specific biological activity (SBA). The product of specific biological activity and volumetric wear rate was used to determine the index of functional biological activity (FBA). On smooth femoral heads the crosslinked UHMWPE had a 30 per cent lower wear rate, but it had a greater percentage volume of smaller, more biologically active particles, which resulted in a similar index of FBA compared with the non-crosslinked material. On the scratched femoral heads the volumetric wear rate was three times higher for the moderately crosslinked UHMWPE and two times higher for the non-crosslinked UHMWPE compared with the smooth femoral heads. This resulted in a higher wear rate for the moderately crosslinked material on the scratched femoral heads. All the differences in wear rate were statistically significant. There were only small differences in particle volume concentration distributions, and this resulted in similar indices of FBA which were approximately twice the values of those found on the smooth femoral heads. Both materials showed lower wear and FBA than for previously studied aged and oxidized UHMWPE gamma irradiated in air. However, this study did not reveal any advantage in terms of predicted FBA for moderately crosslinked UHMWPE compared with non-crosslinked UHMWPE.
Effects of the sample preparation temperature on the nanostructure of compression moulded ultrahigh molecular weight polyethylene
Authors: Ho S P , Riester L , Drews M , Boland T , LaBerge M 
Published: October 2002

In this study, the effects of the sample sectioning temperature on the surface nanostructure and mechanical response of compression moulded ultrahigh molecular weight polyethylene (UHMWPE) at a nanometer scale (nanomechanical properties) have been characterized. The primary focus of this work was to determine if the sample sectioning temperature significantly changed the nanostructure of UHMWPE, while the secondary focus was to characterize the effect on the mechanical response due to the changes in the sectioned surface nanostructure. The goals of this study were: to investigate the potential possibility of creating surface artefacts by the sample preparation technique by sectioning at different temperatures relative to the published range of glass transition temperatures, Tg, for PE (−12, −80 and −25°C); to determine the possibility of molecular orientation induced by plastic deformation of the UHMWPE sample during the process of sample preparation; to measure the relative difference in nanomechanical properties owing to evolution of different nanostructures as a function of sample sectioning temperature. Field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and nanoindentation were used to demonstrate that the sectioning temperature caused a change in nanostructure of the compression moulded UHMWPE sectioned surface, explaining the change in mechanical response to indentation at a nanoscale. In this study, it was demonstrated that significant plastic deformation occurs when a shear stress is applied between the glass or diamond blade and the UHMWPE during sample preparation under ambient conditions at a temperature of 22°C. These results also suggest that an optimum sample sectioning temperature should definitely be below the measured Tg of the polymer.
Analysis of contact mechanics for composite cushion knee joint replacements
Authors: Stewart T , Jin Z M , Fisher J 
Published: October 2002

Recent research in the area of cushion form bearings for total joint replacements has primarily used thin, soft, elastomeric layers with similar elastic modulus to articular cartilage, bonded to rigid substrates. These are designed to promote the body's natural lubricants to separate the articulating surfaces and prevent wear. Applications to joint replacements have revealed that the abrupt change in stiffness between the soft layer and the rigid substrate and the relatively low strength of the interface resulted in high shear stresses and debonding of the soft layer from the substrate. The approach adopted in this study is to use components with a graded modulus or composite construction. The composite construction consists of a soft compliant layer of polyurethane and a second stiffer polyurethane layer thought to be rigid enough to mechanically interlock to a metallic tibial tray. In this composite structure the deformation of the more rigid polyurethane underlay may generally influence the stress distribution and deformation in the softer upper layer and at the interface between the two materials. A simple analysis technique is presented in the present study where the composite double layer was approximated as an equivalent modulus single layer. Single layer theory, which is readily available in the literature, can then be used to determine the contact parameters, including the maximum contact pressure and the contact radius, for the composite structure. By varying the layer thicknesses and material properties of both the soft surface layer and the stiffer structural support layer, the magnitudes and locations of stresses can be controlled. Results of a parametric stress analysis are presented to assist in the selection of the most appropriate composite layers for cushion knee designs. A 4 mm thick surface layer with an elastic modulus of 20 MPa and a 4 mm thick structural support layer with an elastic modulus of 1000 MPa were considered suitable for this application.