bluuebunny/crossref_metadata_2025 huggingface dataset:
A new oscillating saw for robotic aided surgery
Authors: Moctezuma J L , Schuster D , Gossé F , Schulz H-J
Published: October 2002

In this paper a brief description of a computer and robotic aided surgery system is given with a detailed overview of the necessity to develop special tools for robotic surgery. The application range of this robotic system has been specially focused on the orthopaedics field and, more particularly, on the execution of osteotomies. It was therefore necessary to develop a new saw device which would meet medical and—from the robot system point of view—mechanical as well as functional requirements. After describing the device which was developed on the basis of these requirements, a detailed comparative study of off-the-shelf oscillating saws and the new device is given at the end of the paper.
A technique for measuring contact force distribution in minimally invasive surgical procedures
Authors: Brett P N , Stone R S W
Published: October 2002

This paper investigates new methods for measuring forces and tactile sense as a contribution towards relaying the sense of touch to the surgeon. The approach used is to determine a distribution of contact force using a small number of sensory outputs to detect the bending of a surface of known behaviour. Software algorithms have been produced to interpret the contacting force from sensory data, and have achieved a bandwidth of 30 Hz and an accuracy of 2 per cent. The sensor construction is of sufficiently low cost to produce a disposable unit and uses materials that are compatible with the invasive working environment.
The Probot—an active robot for prostate resection
Authors: Harris S J , Arambula-Cosio F , Mei Q , Hibberd R D , Davies B L , Wickham J E A , Nathan M S , Kundu B
Published: October 2002

As men age, their prostates can enlarge, causing urinary difficulty. Surgery to correct this [transurethral resection of the prostate (TURP)] is a skilled and time-consuming operation requiring many repetitive motions of a cutter. A robot has been developed to perform these motions, relieving the surgeon of much of the burden of surgery. This robot has been tried both in the laboratory and later on human subjects and has proved itself capable of performing prostate resection. The Probot system consists of on-line imaging and three-dimensional prostate model construction, an appropriate surgeon-computer interface, a counterbalanced mounting frame and a computer controlled robot.
Simulation of resistance forces acting on surgical needles
Authors: Brett P N , Parker T J , Harrison A J , Thomas T A , Carr A
Published: October 2002

High precision in the manual control of needles and biopsy probes in medical treatment requires high skill and dexterity levels. In anaesthesia, force sensation is an important feedback mechanism, and the practitioner needs to refresh or develop skills to improve on the interpretation of needle progress towards the target site. This paper describes an experimental tactile force simulator for uniaxial needle action for which the force resisting progress of the needle is derived from measured data. As an example, the approach taken to develop the simulation of the insertion of epidural needles is described. Adaptation to other procedures would be possible by adopting new reference models based on appropriate measured force data.
The size and shape of particulate polyethylene wear debris in total joint replacements
Authors: Kobayashi A , Bonfield W , Kadoya Y , Yamac T , Freeman M A R , Scott G , Revell P A
Published: October 2002

Osteolysis induced by wear particles has been recognized as one of the major causes of long-term failure in total joint replacements. However, little is currently known about the exact nature of particles, as the particles are too small to be characterized by light microscopy. In this study, ultra-high molecular weight polyethylene (UHMWPE) particles retrieved from ten cases (six cemented and four uncemented) for Freeman type conforming tibiofemoral total knee replacements (TKRs), three Charnley total hip replacements (THRs) and five Imperial College/London Hospital double cup surface hip replacements for aseptic loosening were extracted using a high-performance method with ultracentrifugation and characterized by scanning electron microscopy. The equivalent circle diameter (ECD) of all 18 cases ranged from 0.40 to 1.15 μm (Mean ± SE = 0.70 ± 0.05 μm, median = 0.67 μm). The aspect ratio was 1.50 to 2.04 (Mean ± SE = 1.75 ± 0.04, median = 1.73), and roundness was 1.24 to 2.34 (Mean ± SE = 1.61 ± 0.07, median = 1.65). The numbers of particles were 5.2 × 108 to 9.17 × 1010/g tissue (Mean ± SE = 1.42 × 1010 ± 5.41 × 109/g tissue, median = 7.04 × 109). The number of polyethylene (PE) particles/g tissue in TKRs was significantly larger than that in THRs (1.04 × 1010/g tissue and 2.16 × 109/g tissue respectively, median. p = 0.03, Mann-Whitney U test). Unstable fixation of the tibial PE component might account for the accumulation of a large number of PE particles in the interface tissue.
Kinematics of the MATCO™ hip simulator and issues related to wear testing of metal-metal implants
Authors: Medley J B , Krygier J J , Bobyn J D , Chan F W , Lippincott A , Tanzer M
Published: October 2002

Metal-metal hip implants have been used clinically in Europe to reduce the risk of wear particle induced osteolysis. Joint simulator devices could provide useful information for design improvement of the modern generation of metal-metal hip implants. Early wear results for metal-metal hip specimens were obtained using a MATCO™ hip simulator. A detailed kinematic analysis was developed for the MATCO™ simulator and applied to two of the wear experiments to predict the starting surface motion, contact zone and lubricant film thickness. It was shown that points on cup surfaces were not subjected to a reciprocating interaction with the head during wear at the beginning of testing but as wear proceeded, it was suggested that, in some cases, reciprocating interaction did occur on the cup surface. Comparison between simulator and in vivo kinematics suggested a more realistic representation for cup than for head wear. In the simulator, the Hertzian contact zone moved in a circular path over the cup surface and changed in size in correspondence with the applied load. Elastohydrodynamic lubrication was considered to be possible in the simulator, with estimated fluid film thickness as great as 0.1 μm. However, such thick films were not likely to have occurred at the start of the two wear tests which were examined in detail, although some mixed film lubrication might have accounted for the relatively low wear of one of the specimens. The inclusion of kinematic details, contact mechanics and elastohydrodynamic lubrication analysis in simulator testing protocols and in design of metal-metal hip implants was recommended.
Frictional heating of bearing materials tested in a hip joint wear simulator
Authors: Lu Z , McKellop H
Published: October 2002

In a hip simulator wear test using bovine serum as a lubricant, the heat generated by ball-cup friction may cause precipitation of the proteins from the lubricant. The resultant accumulation of a solid layer of precipitated protein between the ball and cup could artificially protect the bearing surfaces from wear, in a manner that does not occur in vivo. Alternatively, the gradual depletion of the soluble proteins could interfere with their ability to act as boundary lubricants on the bearing surfaces, thereby artificially increasing the wear rate. Because the rate of protein precipitation may depend on the maximum temperature at the bearing surfaces during sliding, rather than the mean temperature of the bulk lubricant, this study determined the transient surface temperatures using an array of thermocouples embedded in acetabular cups of GUR 415 ultra-high molecular weight polyethylene (UHMWPE) and femoral balls of metal or ceramic, in conjunction with a finite element model of the temperature distribution. The prostheses were tested at one cycle/s under a Paul-type, physiological load profile with 2030 N maximum force, with the load cycle synchronized to the motion cycle. The steady state temperatures of the bulk lubricant were 38°C for the zirconia balls, 36°C for the cobalt-chromium and 33°C for the alumina. However, the corresponding surface temperatures of the polyethylene, calculated with the finite element model, were 99°C with zirconia ceramic, 60°C with cobalt-chromium alloy, and 45°C with alumina ceramic. The rank order of the surface temperatures corresponded to the relative amounts of protein that were precipitated in the test chambers during wear tests with these materials.
Wear of the high-density polyethylene socket in total hip arthroplasty and its role in endosteal cavitation
Authors: Wroblewski B M
Published: October 2002

High-density polyethylene (HDP) has been used in clinical practice in total hip replacement since its introduction by Charnley in November 1962. Fears are being expressed that this may be the weakest link and the ultimate cause of failure of the arthroplasty. Long-term clinical experience suggests that loosening may be the primary cause while the presence of HDP wear particles is secondary. Healing of endosteal cavities can take place in the presence of HDP wear particles.
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.
The yielding of tensioned fine wires in the Ilizarov frame
Authors: Hillard P J , Harrison A J , Atkins R M
Published: October 2002

The Ilizarov frame uses tensioned fine wires to support bone fragments. The objective of this study was to determine whether these wires deformed plastically under functional load bearing and to determine the significance of such deformation on the long-term performance of frames used for treating lower limb conditions. The mechanical characteristics of the wires were determined by means of destructive tensile tests and used in the construction of a series of finite element models replicating typical frame configurations. Each model was then subjected to a single load cycle representing a single step and the residual displacement (i.e. plastic deformation) was determined. In each case a residual displacement of between 0.26 and 0.42 mm was observed giving a corresponding reduction in wire tension of between 8.3 and 32.8 per cent. These reductions in wire tension reduce the frame's overall stiffness and so compromise its ability to inhibit high-amplitude axial and shear motions at the fracture site which are deleterious to the healing outcome.
Current trends in biocompatibility testing
Authors: Kirkpatrick C J , Bittinger F , Wagner M , Köhler H , van Kooten T G , Klein C L , Otto M
Published: October 2002

Biocompatibility remains the central theme for biomaterials applications in medicine. It is generally accepted that this term means not only absence of a cytotoxic effect but also positive effects in the sense of biofunctionality, i.e. promotion of biological processes which further the intended aim of the application of a biomaterial. The national and international standards for testing regimes represent a lowest common denominator for such applications and do not necessarily ensure that optimal function will be achieved. The authors' thesis is that biocompatibility testing has scope for extensive development with respect to biofunctionality. The present paper reviews current trends in the in vitro aspects of biocompatibility testing. As well as a critical appraisal of the recent literature, future trends are also stressed, which the authors regard as essential for a meaningful integration of a modern biological approach into new developments in the material sciences. These include the application of modern techniques of cell and molecular biology, the concepts of tissue remodelling, hybrid organ development and encapsulated cell technology.
Prediction of transient lubricating film thickness in knee prostheses with compliant layers
Authors: Jin Z M , Dowson D , Fisher J , Ohtsuki N , Murakami T , Higaki H , Moriyama S
Published: October 2002

The transient lubricating film thickness in knee prostheses using compliant layers has been predicted under simulated walking conditions based upon the elastohydrodynamic lubrication theory. Qualitative agreement has been found between the present theoretical predictions and the experimental measurements using an electric resistance technique reported earlier. It has been shown that the contact geometry plays an important role in the generation of fluid film lubrication in knee prostheses using compliant layers. The maximum lubricating film thickness is predicted for the maximized contact area of a transverse conjunction where the semi-minor contact radius lies in the direction of entraining. The additional advantage of the transverse contact conjunction is that the possibility of lubricant starvation due to small stroke length can be minimized. All these factors, together with the kinematic requirements in the natural knee joint, should be taken into consideration when designing artificial knee joint replacements.
Investigation into the effect of proteoglycan molecules on the tribological properties of cartilage joint tissues
Authors: Pickard J , Ingham E , Egan J , Fisher J
Published: October 2002

The aim of this research was to investigate the role of the hydrophilic properties of the proteoglycan molecules within the cartilage matrix, on the tribological properties of joint tissues in the mixed and boundary lubricating regime.

Bovine articular cartilage, bovine meniscus and bovine cartilage that had been degraded to remove the chondroitin sulphate from its proteoglycans were studied in order to investigate differences in their friction and compression responses. The tissues were tested on a sliding friction rig under nominal contact stresses of 0.5 and 4 MPa. The compression tests were carried out under a 0.8 MPa contact stress.

The compression tests showed the cartilage and meniscus deforming at the same rates, but the degraded cartilage deformed more quickly to reach its equilibrium position in a shorter period of time. The friction tests carried out at a constant load revealed the friction of the meniscus rising more rapidly with loading time than the cartilage. The degraded cartilage followed an almost identical curve as the untreated cartilage. Although the reduced proteoglycan content of the degraded cartilage substantially altered the biphasic compression response, it did not have an effect on the frictional properties of the tissue.
A new method for accurate measurement of displacement of the knee menisci
Authors: Ikeuchi K , Sakoda H , Sakaue R , Tsuji K , Tomita N
Published: October 2002

It is difficult to measure the displacement of the menisci under external forces by the radiographic method using markers because the movement may be smaller than the detecting limit. A device with a flexible needle attached to a journal of a miniature linear bearing is developed to investigate the meniscal functions which depend on the mobility. The needle tip is fixed to the target point in the meniscus and the axial displacement is measured with a laser sensor. According to the test, the lower limit for detection was 10 μm, the error due to non-linearity was less than 5 per cent and the reactive force was less than 0.15 N in the operating range of ± mm. Displacement vectors were determined at four points in a pair of menisci in a porcine knee subjected to external forces. This accurate method will lead to further investigation into the mechanical function of the menisci.
A two-dimensional model of cyclic strain accumulation in ultra-high molecular weight polyethylene knee replacements
Authors: Reeves E A , Barton D C , FitzPatrick D P , Fisher J
Published: October 2002

As new methods of sterilization of the ultra-high molecular weight polyethylene (UHMWPE) component in knee replacements are introduced, reported incidents of delamination will decrease. The prediction of plastic strain accumulation and associated failure mechanisms will then become more important in knee replacement design. The finite element analysis reported in this paper aims to advance the modelling of strain accumulation in UHMWPE over repeated gait cycles and seeks to determine the effects of the knee replacement design variables of geometry and kinematics. Material testing was performed under cyclic and creep conditions to generate the elastic, viscoplastic material model that has been used in this time-dependent analysis. Non-conforming geometries were found to accumulate plastic strains at higher rates than conforming geometries. The anatomical motion known as rollback initially produced lower strain rates, but predictions of the long-term response indicated that designs which allow rollback may produce higher strains than static designs after only about a week of loading for a knee replacement patient.
The numerical analysis of fluid-solid interactions for blood flow in arterial structures Part 2: Development of coupled fluid-solid algorithms
Authors: Zhao S Z , Xu X Y , Collins M W
Published: October 2002

In this paper, the authors extend their study of wall mechanics given in Part 1 to the overall problem of fluid-solid interactions in arterial flows. Fluid-solid coupling has become a specific topic in computational methods and applied mechanics. In this review, firstly, the effects of elasticity of blood vessels on wave propagation and local flow patterns in large arteries are discussed. Then, numerical techniques are reviewed together with the alternative coupled methods available in fluid—wall models. Finally, a novel numerical algorithm combining two commercial codes for coupled solid/fluid problems is presented. As a consequence of the present studies, wall effects are now able to be included in predictions of haemodynamics in a clinical context.
The compressive strength of articular cartilage
Authors: Kerin A J , Wisnom M R , Adams M A
Published: October 2002

Articular cartilage provides the smooth bearing surfaces in freely moving (synovial) joints. Its mechanical properties are important because structural failure of cartilage is closely associated with joint disorders, including osteoarthritis. Some mechanical properties of cartilage are well characterized, but little is known about its compressive strength. A technique for measuring cartilage compressive strength is evaluated, and an overview of experiments which relate strength to stiffness and tissue hydration is given.

Specimens of bovine articular cartilage-on-bone, approximately 15 mm square, were loaded on a hydraulic materials testing machine using flat impermeable indentors. Linear-ramp loading/unloading cycles of 1 s duration, and of increasing severity, were applied until failure was evident on force-displacement graphs. Some specimens were tested following a 30 min period of creep loading. Inkstaining and histology were used to locate the site of initial damage to each specimen.

Specimen failure occurred first in the cartilage surface layer at a nominal applied stress of 14–59 MPa (mean 35.7 MPa). Mechanical properties were little affected by specimen or indentor size, provided both remained within defined limits, and compressive strength could be measured to an accuracy of approximately ±5 per cent. Compressive stiffness was a significant predictor of strength, but only if it was measured at high levels of stress. Strength increased following creep-induced water loss, and initial mechanical damage could propagate under moderate cyclic loading. This technique for measuring cartilage compressive strength has potential for investigating the causes of cartilage failure in vivo
Osteotransductive bone cements
Authors: Driessens F C M , Planell J A , Boltong M G , Khairoun I , Ginebra M P
Published: October 2002

Calcium phosphate bone cements (CPBCs) are osteotransductive, i.e. after implantation in bone they are transformed into new bone tissue. Furthermore, due to the fact that they are mouldable, their osteointegration is immediate. Their chemistry has been established previously. Some CPBCs contain amorphous calcium phosphate (ACP) and set by a sol-gel transition. The others are crystalline and can give as the reaction product dicalcium phosphate dihydrate (DCPD), calcium-deficient hydroxyapatite (CDHA), carbonated apatite (CA) or hydroxyapatite (HA). Mixed-type gypsum-DCPD cements are also described. In vivo rates of osteotransduction vary as follows: gypsum-DCPD > DCPD > CDHA ≍ CA > HA.

The osteotransduction of CDHA-type cements may be increased by adding dicalcium phosphate anhydrous (DCP) and/or CaCO3 to the cement powder. CPBCs can be used for healing of bone defects, bone augmentation and bone reconstruction. Incorporation of drugs like antibiotics and bone morphogenetic protein is envisaged. Load-bearing applications are allowed for CDHA-type, CA-type and HA-type CPBCs as they have a higher compressive strength than human trabecular bone (10 MPa).
Applications of computer modelling for the design of orthopaedic, dental and cardiovascular biomaterials
Authors: Vander Sloten J , Hobatho M-C , Verdonck P
Published: October 2002

Biomaterials do not escape from the general trend present in all contemporary science and technology towards increasing use of computers and information technology. In this paper the use of computer modelling for the design of biomaterials is discussed. The word 'biomaterials' is interpreted in its broadest sense, i.e. referring to any foreign object brought into the body for temporary or permanent use. Computer modelling will first be discussed as a tool to model biological structures (bones, arteries) or to investigate and simulate biological interactions at implant-host interfaces. It will then be illustrated how computer modelling, using insights gained from the modelling of the biological structures themselves, is used in the design process of dental, orthopaedic and cardiovascular prostheses.

The area of computer modelling for biomaterials applications has become so vast that an exhaustive overview is impossible in the framework of one paper. Rather, some illustrative case studies will be discussed which are, in the opinion of the authors, representative of general trends in this challenging domain of science on the boundary between engineering and medicine.
Three-dimensional surface characterization for orthopaedic joint prostheses
Authors: Jiang X Q , Blunt L , Stout K J
Published: October 2002

This study attempts to investigate a range of ‘better’ methods for the characterization of the three-dimensional (3D) surface topography of orthopaedic joint prostheses. In this paper, a new characterization tool for the comprehensive identification and evaluation of functional features of these surface topographies is presented. For identification, the surface topography is investigated in a space-scale space, by employing wavelet analysis. The roughness, waviness and form involved in surface topography are consequently separated and recovered respectively. The multiscalar topographical features are identified and captured. The errors caused as a consequence of three-dimensional measurement methods can be reduced. After identification, the three-dimensional surface assessment techniques previously reported by Stout and co-workers are used for the quantitative evaluation of various surface roughness features of the or topaedic joint prostheses. Moreover, the functional properties, such as bearing area, material volume and void volume which are significantly effected by large peaks, pits and scratches are studied and the location of isolated peaks, pits and scratches in the different scales is also clearly characterized. In this work, measurement of the femoral heads and acetabular cups is carried out to demonstrate the applicability of the characterization technique for the three-dimensional surface topography of orthopaedic joint prostheses.
Non-invasive measurement of mechanical properties of arteries in health and disease
Authors: Hoeks A P G , Brands P J , Willigers J M , Reneman R S
Published: October 2002

Major conduit arteries should, by their elastic nature, be able to store blood volume temporarily during systole and release it during diastole. This reduces the systolic blood pressure required for the flow of a given volume quantity and gradually suppresses the pulsatile flow pattern. The haemodynamic characteristics of arteries have consequences for the load of the heart but also for the mechanical load of the arterial wall. The repetitive stretching of the wall (strains of up to 10 per cent) may cause fragmentation of the elastic fibres in the wall, modifying wall elasticity. To maintain wall stress the elastic arteries respond with a diameter increase in combination with an increase of arterial wall thickness. A larger diameter for a smaller distension (change in artery diameter from diastole to systole) will restrict the reduction in storage capacity. Alternatively, pulse pressure may go up, increasing the mechanical load on the wall. In recent years various methods have been developed to assess and monitor the above interaction. Most of these methods are based on ultrasound techniques because of its wide availability and its non-invasive and non-traumatic nature. Presently these techniques enable the assessment of wall thickness, diastolic diameter, distension waveform, i.e. the time-dependent change in diameter, the relative pulsatile increase in diameter, and pulse wave velocity, for elastic and muscular arteries in humans but also in small animals such as rats and mice. The present paper discusses the techniques in more detail.
Haemodynamics, wall mechanics and atheroma: A clinician's perspective
Authors: Stanton A V
Published: October 2002

Atherosclerosis, leading to myocardial infarction and stroke, is the major cause of death and morbidity in Western societies. Atheromatous lesions characteristically occur in regions of branching and marked curvature. Low shear stress and increased mural tensile stress may be major determinants underlying atheroma formation at these sites. Furthermore, the distribution of circumferential tensile stresses may play a critical role in where, why and when advanced atheromatous plaques rupture, leading to catastrophic ischaemic events. Recent advances in the application of computational modelling to in vivo vascular ultrasound and magnetic resonance imaging data should further elucidate the roles of haemodynamic factors and vessel wall mechanics in atherosclerosis. In future this is likely to lead to better use of currently available anti-atherosclerosis strategies. It may also facilitate the discovery, evaluation and development of novel treatments.
Local haemodynamics of arterial bypass graft anastomoses
Authors: Rowe C S , Carpenter T K , How T V , Harris P L
Published: October 2002

One of the main causes of failure of expanded polytetrafluoroethylene (PTFE) bypass grafts used in the lower limbs is the development of myointimal hyperplasia (MIH). Clinical studies show that higher patency rates can be obtained with the use of an autologous vein cuff (the Miller cuff) interposed between the graft and artery. The reasons for the improved performance are still unclear, but preliminary studies suggest that the change in local haemodynamics due to the cuff geometry may be the significant factor rather than the presence of autologous material. If this is the case, then PTFE grafts can be produced with an integral cuff, i.e. a precuffed graft, with similar haemodynamic patterns to that of the Miller cuff. In this paper, two different types of precuffed graft are presented and their flow patterns are compared with those recorded in the Miller cuff and the conventional end-to-side anastomosis. The haemodynamic studies were carried out using optically clear silicone rubber models under simulated in vivo pulsatile flow conditions. Flow structures similar to those observed in the Miller cuff were seen in the precuffed grafts.
A review of studies on seated whole body vibration and low back pain
Authors: Pope M H , Wilder D G , Magnusson M L
Published: October 2002

The paper reviews the epidemiologic evidence linking low back pain (LBP) and exposure to whole body vibration (WBV). Particular emphasis is placed on studies where the exposure is quantified. Biomechanical studies show a resonance at 4–5 Hz. At the resonance the transmissibility exceeds 1.0, and is dependent on seat attenuation, posture and seat back inclination. Increased spinal loading is evidenced by increased muscle activity, muscle fatigue, and disc pressure, and by decreased stature. Physiologic changes also occur with WBV. The risk of LBP can be reduced by vibration damping, good ergonomic design, reducing exposure, and reducing other risks such as lifting.
Discriminant analysis of human kinematic data: Application to human lumbar spinal motion
Authors: Barker T M , McCombe P
Published: October 2002

A study was undertaken to determine the applicability of a multivariate discriminant technique in order to analyse human kinematic data, specifically lumbar motion during forward flexion. This method was used in an attempt to allow comparison of time-series data (three joint angles and three linear displacements) between groups of subjects. Results obtained from ten healthy subjects performing simulated abnormal styles of forward flexion indicate the feasibility and potential utility of this method in a clinical environment. Further investigations will be undertaken on clinical subjects to discriminate more effectively between healthy and pathological movements.
Puncture resistance and tensile strength of skin simulants
Authors: Ankersen J , Birkbeck A E , Thomson R D , Vanezis P
Published: October 2002

This study aims ultimately to quantify the force needed to penetrate human tissue. The results will reduce the subjectivity of expert opinion in stabbing incidents. They will also aid clinicians in assessing the severity of injury and help prevent the unnecessary deaths which can occur when this is not fully appreciated. Tensile tests were performed to identify suitable skin simulants with synthetic chamois and pigskin as candidate materials. Quasi-static penetration experiments were also performed in which a knife blade penetrated a skin simulant target. Pigskin was found to be much stronger than chamois under tensile load yet the puncture resistance was almost identical for the two materials.
Improvements in the prediction of performance of centrifugal slurry pumps handling slurries
Authors: Gandhi B. K. , Singh S. N. , Seshadri V
Published: October 2002

A methodology based on a loss analysis procedure has been presented to predict the performance of centrifugal slurry pumps handling solid-liquid mixtures. Various energy-head losses in the pump have been estimated using analytical models based on the pump geometry and the properties of suspended solids. The proposed methodology accounts for the constructional differences of the slurry pump as compared with the conventional pump. The predicted values of head over the operating range of flowrates of the pump have been found to be in reasonable agreement with the measurements made at various rotational speeds and solid concentrations.
The design and performance of axial compressor stages in fully developmed flow
Authors: McKenzie A B
Published: October 2002

A design method for axial compressor stages is presented which is indicated to reduce the tendency for efficiency to diminish as the design work coefficient increases. Three worked examples with different levels of design work coefficient are used to demonstrate the potential advantages of the procedure. If experimentally confirmed, the results would be of value in situations where the blade speed is restricted, as in the case of core compressor stages attached to the fan shaft of turbofan aero engines. Another potential field of application is the compression of such gases as helium and hydrogen, where the speed of sound is high and mechanical limitations to the blade speed restrict the Mach numbers and therefore the stage pressure ratio achievable with conventional levels of work coefficient.
Pollution-cost balance in road tunnel ventilation
Authors: Vardy A E , Ichikawa A
Published: October 2002

The increasing complexity of road tunnels, coupled with increasing demands for cost effective operation, favours automated methods of selecting fan settings for ventilation control. Implications of conflicting demands for pollution control and cost control are discussed and a method of expressing them in a single parameter is introduced. First, two indices are derived, one for pollution and one for cost. Next, the indices are combined to yield a penalty factor whose value defines the level of acceptability of the tunnel conditions, allowing for future conditions as well as instantaneous ones. The method of combining the indices can be influenced by tunnel operators, both off line and on line. Examples are presented to illustrate the consequences of alternative choices of penalty factors.
A neural network approach for centrifugal impeller inverse design
Authors: Fan H-Y
Published: October 2002

In this paper a neural network approach is proposed to solve an inverse design problem of a centrifugal impeller when the basic structure parameter and the hub-shroud contours are known, and the expected blade surface velocity distribution is given. The proposed neural networks have a four-layered feedforward architecture and are trained with finite samples by means of a back-propagation algorithm. The simulations show that the trained networks can yield a blade shape that generates the expected velocity distribution on its surface.
Gas turbine hot section components: The challenge of ‘residual life’ assessment
Authors: Wood M I
Published: October 2002

Gas turbine hot section parts are high-value components which have finite lives. Their durability has an important role in controlling maintenance intervals and the associated costs. This paper reviews the sources of degradation in some components, the technology available to quantify the damage, and publicly available assessment procedures which can be used for component life assessment.
Inlet induced flow in squirrel-cage fans
Authors: Montazerin N , Damangir A , Mirzaie H
Published: October 2002

Energy conversion in squirrel-cage fans is sensitive to the inlet geometry. It occurs at the inlet where a separation zone which occupies a major volume in the rotor and the volute starts. In this research, different inlets of inward and outward types were tested on two fans. First, the inlet diamenter and position were matched with the rotor, which improved the fan characteristic curves. The results of the experiments were sensitive to the width of the blade retaining ring (shroud). Later the tangential and radial components of the velocity out of the rotor were measured. The resulting velocity profiles across the scroll width showed that outward inlets produce a more uniform velocity angle inside the volute than inward inlets did. This was not because of a more aerodynamic flow through the rotor blades by was due to a better match between the inlet and the volute. The axial energy transfer resulted in tangential velocities larger than the rotor velocity, at axial positions across the volute where there was no flow out of the rotor.
Strategy for optimal operation of a biomass-fired cogeneration power plant
Authors: Prasertsan S , Krukanont P , Ngamsritragul P , Kirirat P
Published: October 2002

Biomass-fired cogeneration not only is an environmentally friendly energy production, but also possesses high energy conversion efficiency. Generally, the wood product industry requires both heat and electricity. Combined heat and power generation cogeneration) using wood residue has a three-fold benefit: waste minimization, reduction of an energy-related production cost and additional income from selling the excess electricity to the utility. In reality, the process heat demand fluctuates according to the production activities in the factory. The fluctuation of process heat demand affects the cogeneration efficiency and the electricity output and, consequently, the financial return, since the prices of heat and electricity are different. A study by computer simulation to establish a guideline for optimum operation of a process heat fluctuating cogeneration power plant is presented. The power plant was designed for a sawmill and an adjacent plywood factory using wood wastes from these two processes. The maximum boiler thermal load is 81.9 MW while the electricity output is in the range 19-24 MW and the process heat 10-30 MW. Two modes of operation were studies, namely the full (boiler) load and the partial (boiler) load. In the full load operation, the power plant is operated at a maximum boiler thermal load, while the extracted steam is varied to meet the steam demand of the wood-drying kilns and the plywood production. The partial load operation was designed for the partially fuelled boiler to provide sufficient steam for the process and to generate electricity at a desired capacity ranging from the firmed contract of 19 MW to the turbine maximum capacity of 24 MW. It was found that the steam for process heat has an allowable extracting range, which is limited by the low pressure feed water heater. The optimum operation for both full and partial load occurs at the lower limit of the extracting steam. A guideline for optimum operation at various combinations of electricity output and steam demand is presented. The maximum achievable overall efficiency is 64.6 per cent when the power plant is operated at partial (boiler) load condition for 19 MW electricity and 30 MW process heat. The full load operation, although having lower overall efficiency, is preferable financially because of the higher unit price of electricity in comparison with heat.
Performance prediction of axial flow compressors using stage characteristics and simultaneous calculation of interstage parameters
Authors: Song T. W. , Kim T. S. , Kim J. H. , Ro S. T.
Published: October 2002

A new method for predicting performance of multistage axial flow compressors is proposed that utilizes stage performance curves. The method differs from the conventional sequential stage-stacking method in that it employs simultaneous calculation of all interstage variables (temperature, pressure and flow velocity). A consistent functional formulation of governing equations enables this simultaneous calculation. The method is found to be effective, i.e. fast and stable, in obtaining solutions for compressor inlet and outlet boundary conditions encountered in gas turbine analyses. Another advantage of the method is that the effect of changing the angles of movable stator vanes on the compressor's operating behaviour can be simulated easily. Accordingly, the proposed method is very suitable for complicated gas turbine system analysis. This paper presents the methodology and performance estimation results for various multistage compressors employing both fixed and variable vane setting angles. The effect of interstage air bleeding on compressor performance is also demonstrated.
Performance analysis of industrial gas turbines for engine condition monitoring
Authors: Mathioudakis K , Stamatis A , Tsalavoutas A , Aretakis N
Published: October 2002

This paper presents methods of analysing aerothermodynamic performance measurement data for the purpose of assessing the condition of the components of a gas turbine. Features of the methods are analysed in function of the available measurements and ways of extracting as much information as possible from a given measurement set are discussed. The principles discussed are highlighted by presenting results from application to data from operating industrial gas turbines. Particular applications discussed are the identification of deposits on the blades of a gas turbine used for power generation and the monitoring of compressor fouling on another industrial gas turbine.
Determination of daily volume of pumped water as a function of mechanical energy from a photovoltaic water-pumping system
Authors: Kolhe M , Kolhe S , Joshi J. C.
Published: October 2002

A technique that estimates the output of a photovoltaic (PV) water-pumping system from a database of monthly average daily insolation would be very useful for design studies of PV water-pumping systems. Here a simple algorithm has been presented to estimate the long-term average performance of a directly coupled PV pumping system by using monthly average daily insolation. The mechanical energy available at the shaft of the PV motor pump has been found by using the utilizability concept. Then an analytical relation between mechanical energy, volume of pumped water and water head has been developed.
Different modelling strategies for in situ liquid chillers
Authors: Browne M. W. , Bansal P. K.
Published: October 2002

This paper presents an overview of various simulation models that may be useful for predicting the in situ performance of vapour compression liquid chillers over a wide range of operating conditions. Five models were considered, namely the regression model, the steady state and transient physical models and the steady state and transient neurale network models. Typical real-time operating data taken under various conditions including start-up, quasi-static and modulating operation were used as input to the five models. The predicted performance was then compared with the experimental data to see the conditions under which each may be suitably applied. It was found that steady state models can give fairly accurate results under mildly dynamic conditions (±5 per cent) although, as the operation becomes more strongly transient, inaccuracies can be as high as 25 per cent. However, the dynamic models perform much better under these conditions (such as start-up and during sudden changes in load condition), predicting performance to within ±10 per cent.
Experimental investigations of the externally heated valve engine model
Authors: Brzeski L , Kazimierski Z
Published: October 2002

The experimental investigations of the first model of the externally heated valve engine carried out during 1998-9 are the subject of this paper. The working gas of the engine is air. A detailed description of the engine equipped with two consecutively working heaters is given. Two kinds of heaters were constructed and investigated. The experimental stand and the measurement system are described. In this first stage of the engine investigation, electric radiators were used as the external source of heat. The main aim of the experimental investigations was focused on measurements of time-dependent pressures inside the expander and compressor cylinders. The pressures were measured by means of two kinds of pressure transducers (piezoresistive and piezoelectric) to get confidence in the obtained results. The conducted investigations prove that

The engine model has an operating ability.

Comparisons of the experimental and theoretical pressures inside the expander and compressor show a satisfactory agreement.

It confirms that the engine operates according to the original thermodynamical cycle and exhibits the internal power and efficiency predicted by the computer simulation. The experiences gained during these investigations have been used to modify the engine model, which is outlined in this paper.
Reasons and repair plans for cracks in the regenerator of heavy oil catalytic cracking units
Authors: Meng J-a
Published: October 2002

The crack state in the regenerator of the heavy oil catalytic cracking unit of Daqing Petrochemical Complex is summarized. The reasons for a large number of welding seam cracks in the regenerator-third-stage cyclone system of the heavy oil catalytic cracking unit are analysed. Correlated countermeasures to prevent cracks and several repair plans for the present cracks are proposed. The key technology and measures of repairs are described and could be used as guides for crack repair of similar equipment
Performance improvements of the intercooled reheat regenerative gas turbine cycles using indirect evaporative cooling of the inlet air and evaporative cooling of the compressor discharge
Authors: Bassily A. M.
Published: October 2002

Inlet air cooling and cooling of the compressor discharge using water injection boost both efficiency and power of gas turbine cycles. An innovative method of cooling the inlet air (indirect evaporative cooling) is introduced. Six different layouts of the intercooled reheat regenerative gas turbine cycle are presented. Those layouts include the effect of different methods of inlet cooling and evaporative cooling of the compressor discharge (evaporative aftercooling). A parametric study of the effect of turbine inlet temperature, ambient temperature and relative humidity on the performance of all six layouts is carried out. The results indicate that as the turbine inlet temperature increases the optimum pressure ratio increases by 1.5 per 100 K for the regular intercooled reheat regenerative cycle and by 4.2 per 100 K for the intercooled reheat regenerative cycle with evaporative aftercooling. The cycles with evaporative aftercooling have distinctive patterns of performance curves and higher values of optimum pressure ratios. The results also show that indirect evaporative cooling of the inlet air could boost the efficiency by up to 3 per cent, which is 1 per cent higher than the direct evaporative cooling method and that evaporative aftercooling could increase the efficiency by up to 5 per cent.