bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-destructive and non-invasive observation of friction and wear of human joints and of fracture initiation by acoustic emission
Authors: Schwalbe H-J , Bamfaste G , Franke R-P
Published: October 2002

Quality control in orthopaedic diagnostics according to DIN EN ISO 9000ff requires methods of non-destructive process control, which do not harm the patient by radiation or by invasive examinations. To obtain an improvement in health economy, quality-controlled and non-destructive measurements have to be introduced into the diagnostics and therapy of human joints and bones. A non-invasive evaluation of the state of wear of human joints and of the cracking tendency of bones is, as of today's point of knowledge, not established.

The analysis of acoustic emission signals allows the prediction of bone rupture far below the fracture load. The evaluation of dry and wet bone samples revealed that it is possible to conclude from crack initiation to the bone strength and thus to predict the probability of bone rupture.
On-line computer system to minimize laser injuries during surgery: Preliminary system layout and proposal of the key features
Authors: Canestri Franco
Published: October 2002

The aim of this paper is to investigate some new user interface ideas and related application packages which aim to improve the degree of safety in an operating room during surgical operations in which an invasive laser beam is deployed. The overall value of the proposition is that a means is provided which ensures the successful completion of the surgical case while minimizing the risk of thermal and mechanical injuries to healthy tissues adjacent to the surgical field.

According to surgeons operating with a variety of CO2 lasers available at both the National Cancer Institute in Milan, Italy, and the Sackler School of Medicine, Tel Aviv University, Israel, each laser device presents different cutting and coagulation properties. In order to identify which ‘ideal’ procedure might corroborate the subjective impression of each surgeon and also to provide one common tool to ensure procedures with a high level of safety, the author has worked for several months with surgeons and technicians of both Institutions to define the general design of a new on-line surgical operation planning and design system to be used during the pre-operative briefing activities and also as a consultation tool during operation. This software package will be developed and tested on both ‘C’ and FORTRAN compilers running on a commercially available PC which is driving a continuous wave (CW) CO2 laser device via its Instrument-Bus interface. The present proposal describes the details of a software package called LCA (Laser-beam Controller and Adviser) which performs several controls in parallel on the key output parameters of a laser beam device during its utilization in delicate surgical operations. The required performances of this device needed during a given surgical operation are pre-simulated and compared against the well-known safety limits, which are stored in the computer's mass storage. If the surgeon's decision about the laser device set-up are considered to be too close to the required physiological safety limits, then the SW alerts the surgeon and proposes alternatives based on other combinations of both HW and SW configurations.

An additional application of LCA uses this SW as a warning tool during the operation itself. If a wrong set-up of the laser device is accidentally used, an alarm will be generated and the laser beam automatically switched-off prior to an ‘incident report’ printout. The operation will continue only when the surgeon validates the choices that the SW suggests for implementation. If necessary, the surgeon can switch off the device and continue to operate it manually. In this case, the surveillance mode will be totally excluded.
Ultrasonic investigation of blood flow
Authors: Fish P J
Published: October 2002

Ultrasound and the Doppler effect are used to measure blood velocity non-invasively in order to diagnose blood vessel disease. Intrusive lesions on arterial walls give rise to an alteration of the time-varying blood velocity waveform and local blood flow disturbance which are detected and measured using the envelope and width of the Doppler signal spectrogram respectively. Flow may also be imaged in colour superimposed on a grey-scale anatomical image allowing vessel narrowing and the accompanying flow disturbance to be visualized. Developments in three-dimensional imaging, angle tolerant velocity measurements and increased sensitivity using second harmonic backscatter from encapsulated-bubble contrast media ensure increasing use of this modality.
Reconstruction of blood flow patterns in human arteries
Authors: Xu X Y , Long Q , Collins M W , Bourne M , Griffith T M
Published: October 2002

Local haemodynamic factors in large arteries are associated with the pathophysiology of cardiovascular diseases such as atherosclerosis and strokes. In search of these factors and their correlation with atheroma formation, quantitative haemodynamic data in realistic arterial geometry become crucial. At present no in vivo non-invasive technique is available that can provide accurate measurement of three-dimensional blood velocities and shear stresses in curved and branching sites of vessels where atherosclerotic plaques are found frequently. This paper presents a computer modelling technique which combines state-of-the-art computational fluid dynamics (CFD) with new non-invasive magnetic resonance imaging techniques to provide the complete haemodynamic data in ‘real’ arterial geometries. Using magnetic resonance angiographic and velocity images acquired from the aortic bifurcation of a healthy human subject, CFD simulations have been carried out and the predicted flow patterns demonstrate the non-planar-type flow characteristics found in experimental studies.
Type of motion and lubricant in wear simulation of polyethylene acetabular cup
Authors: Saikko V , Ahlroos T
Published: October 2002

The wear of ultra-high molecular weight polyethylene, the most commonly used bearing material in prosthetic joints, is often substantial, posing a significant clinical problem. For a long time, there has been a need for simple but still realistic wear test devices for prosthetic joint materials. The wear factors produced by earlier reciprocating and unidirectionally rotating wear test devices for polyethylene are typically two orders of magnitude too low, both in water and in serum lubrication. Wear is negligible even under multidirectional motion in water. A twelve-station, circularly translating pin-on-disc (CTPOD) device and a modification of the established biaxial rocking motion hip joint simulator were built. With these simple and inexpensive devices, and with the established three-axis hip joint simulator, realistic wear simulation was achieved. This was due to serum lubrication and to the fact that the direction of sliding constantly changed relative to the polyethylene specimen. The type and magnitude of load was found to be less important. The CTPOD tests showed that the subsurface brittle region, which results from gamma irradiation sterilization of polyethylene in air, has poor wear resistance. Phospholipid and soy protein lubrication resulted in unrealistic wear. The introduction of devices like CTPOD may boost wear studies, rendering them feasible without heavy investment.
Effect of supplementary firing on the performance of an integrated gasification combined cycle power plant
Authors: De S , Nag P K
Published: October 2002

The effect of supplementary firing on the performance of an integrated gasification combined cycle (IGCC) power plant is studied. The results are presented with respect to a simple ‘unfired’ IGCC power plant with single pressure power generation for both the gas and the steam cycles as reference. The gases are assumed as real with variable specific heats. It is found that the most favourable benefit of supplementary firing can be obtained for a low temperature ratio R T only. For higher R T, only a gain in work output is possible with a reverse effect on the overall efficiency of the plant. The second law analysis reveals that the exergy loss in the heat-recovery steam generator is most significant as the amount of supplementary firing increases. It is also noteworthy that, although the total exergy loss of the plant decreases with higher supplementary firing for a low R T (= 3.0), the reverse is the case for a higher R T (= 6.0).
Combustion characteristics of higher-alcohol/gasoline blends
Authors: Gautam M , Martin D. W.
Published: October 2002

An experimental investigation of combustion characteristics of higher-alcohol/gasoline [unleaded test gas 96 (UTG 96)] blends is presented. Lower alcohols (methanol and ethanol) have been used in the past as fuel extenders by mixing them with gasoline, but relatively little work has been reported on higher alcohols (propanol, butanol and pentanol). All these alcohols can be produced from coal-derived syngas. Given the abundant coal reserves in the United States, use of such higher alcohols offers an attractive alternative to alleviate the country's growing needs for transportation fuels.

Comparisons of knock limits, indicated mean effective pressure (i.m.e.p.), emissions and fuel characteristics between higher-alcohol/gasoline blends and neat gasoline were made to determine the advantages and disadvantages of blending alcohol with gasoline. All tests were conducted on a single-cylinder Waukesha cooperative fuel research (CFR) engine operating at steady state conditions and stoichiometric air-fuel ratio. The data show that higher-alcohol/gasoline blends have a greater resistance to knock than neat gasoline does, as indicated by the knock resistance indicator (KRI) and the (RON+MON)/2 antiknock index (where RON is the research octane number and MON the motor octane number). Ignition delay and combustion interval data show that higher-alcohol/gasoline blends tend to have faster flame speeds.
Application of a semi-empirical approach to the thermal design of electronic equipment
Authors: Ishizuka M , Hayama S
Published: October 2002

A semi-empirical approach to the thermal design of electronic equipment is presented. Although recent progress in computer technology has enabled a complex analysis to be made, it is difficult to carry out numerical studies for practical electronic equipment cabinets, which have extremely complicated boundary conditions due to the various sized components mounted in the cabinets. It has thus become important to establish an analytical model in order to apply computer simulation to the thermal design of electronic equipment. This paper reports the semi-empirical approach based on a lumped model, and experimental data on the flow resistance coefficient and heat transfer coefficient. A simulation was carried out for a photocopy machine model by using a personal computer. The proposed method is confirmed to be capable of serving thermal designers satisfactorily.
Two-dimensional Navier-Stokes analysis of an internally cooled turbine blade
Authors: Sarkar S , Das K , Basu D
Published: October 2002

The flow and thermal fields developed over an internally cooled turbine inlet guide vane have been analysed numerically. For this purpose, a robust and rapid Navier-Stokes flow solver in the finite volume from has been developed that uses an explicit four-stage Runge-Kutta integration technique in the physical space. Local time stepping, variable coefficient implicit residual smoothing and a full multigrid method have been implemented to accelerate the steady state calculations. Turbulence is simulated by the Baldwin-Lomax algebraic model. Results obtained are in good agreement with the experimental data. The main thrust of the paper is to examine the effects of variable wall temperature, which occurs as a result of internal convective cooling, on prediction of blade surface heat transfer.
Pressure recovery in a turbocharger compressor volute
Authors: Eynon P A , Whitfield A
Published: October 2002

The diffusion and pressure recovery in a centrifugal compressor stage is normally accomplished in the diffuser (vaned or vaneless) downstream of the impeller and, at the design flowrate, the volute is designed to collect the gas flow without further diffusion. It is, however, well established that at high flowrates the gas accelerates around the volute and as a consequence the pressure decreases, while at flowrates less than that at design the gas decelerates and a pressure rise occurs. There is little published material with respect to the detailed design of volutes, and the procedure is largely one of experience based on previous designs and tests. This investigation describes the performance of the volute with both a vaneless diffuser and a series of low solidity vaned diffusers upstream. It is shown that the volute provides a significant pressure rise at the best efficiency point and at flowrates down to full surge. It is shown that the volute performance is a function of inlet flow angle and that it plays a significant role in setting both the best efficiency flowrate and the operating range of the compressor.
Techniques for control of splitting ratios of particulate materials at bifurcations in pneumatic conveying pipelines
Authors: Holmess T , Bradley T M S A , Selves T P , Farnish R J , Bridle I , Reed A R
Published: October 2002

In this paper the negative effect on the efficiency of coal-fired power generating stations, caused by unequal split ratios of pulverized fuel in pipeline branches downstream from bifurcations, is identified. Five active techniques for controlling split ratios have been developed and tested on a test-scale rig. Three of the five techniques were deemed to have potential for retrofitting into existing power generating stations and have been tested in detail on a large pilot-scale rig. The observations and the ensuing conclusions are presented.
Mathematical modelling of supermarket refrigeration systems for design, energy prediction and control
Authors: Ge Y T , Tassou S A
Published: October 2002

This paper describes a mathematical model developed to simulate the performance of supermarket refrigeration systems. Such a model can be used for the comparison of different systems and control strategies in terms of their energy and total equivalent warming impact. The model is based on a large number of component models which have been linked together within the TRNSYS environment. Major component models include the compressor, air-cooled condenser, thermostatic expansion valve, display cabinet and control. The overall system model has been validated against monitored data obtained from both a laboratory-based system and a full-scale system in a supermarket in Scotland. The value of the model is illustrated by determining and comparing the effectiveness of head pressure and variable-speed control against fixed head pressure and constant speed control. It is shown that even at summer ambient conditions the system can be operated without problems at much lower head pressures than is done in practice under fixed-pressure control strategies. The use of variable-speed control on one of the compressors can also provide better control of the suction pressure and a substantial (up to 23 per cent) energy savings compared to on-off control.
Modelling of cogeneration systems. Part 2: Development of a quasi-static cogeneration model (steam turbine cogeneration analysis)
Authors: O'Brien J M , Bansal P K
Published: October 2002

Steam turbine cogeneration analysis (STuCA) is a quasi-static cogeneration plant model that has been developed to simulate steam turbine cogeneration plants subject to varying loads. STuCA was developed to provide potential cogeneration plant users with a model that could simulate part-load performance over the expected operating range of the cogeneration plant using fundamental engineering analysis methods. The model was designed to bridge the gap between static design-point models that could not accommodate part-load conditions and complex part-load models which are too expensive for small scale cogeneration proposals. In addition, the model contains economic analysis tools to analyse the thermoeconomic performance of the plant and to conduct a cash flow analysis. These features are an extension to the static and part-load models. The model consists of four submodels: a load, system, plant and economic model. The load submodel drives the cogeneration plant simulation, supplying utility demands to the system models. The system submodels calculate the steam required by the system components to meet the utility demands. The plant submodel then predicts turbine and boiler performance as they meet the steam demand. The primary plant submodel outputs are the electricity generated and quantity of coal consumed by the boiler, which are used by the economic submodel to conduct a thermoeconomic analysis of the site as well as a discounted cash flow analysis. This method of modelling results in a model that can predict plant performance with respect to varying load and then use those data to conduct a meaningful economic performance analysis of the site.
Multi-point optimal design for diffuser cascades of centrifugal compressors
Authors: Fan H-Y , Xi G , Wang S-J
Published: October 2002

The ‘multi-point design’ approach for single airfoils in aeronautical engineering is introduced into the optimal design for diffuser cascades of centrifugal compressors. Genetic algorithms are used to solve the multi-point problem. The proposed approach is applied to a ‘two-point design’ of a real diffuser cascade. The numerical results show that a group of optimal blade profiles can be obtained, from which the designer can select performance compromises for the two given design condition points.
Dynamic modelling of recuperative gas turbines
Authors: Camporeale S M , Fortunato B , Dumas A
Published: October 2002

This paper describes the mathematical model and the computational procedure adopted for the development of a modularly structured computer code able to simulate the dynamic behaviour of recuperative gas turbine power plants. For accurate simulation of the turbine components, the model includes a stage-by-stage procedure for the air-cooled turbine based on the blade geometry and the characteristics of the cooling system. The counter-flow surface heat exchanger, assumed as recuperator, is described by a set of partial differential equations, giving à One-dimensional description of the temperature for air, hot gas and metal. A single-shaft recuperated cycle gas turbine, provided with compressor variable inlet guide vanes, is analysed. The transient cases caused by a step variation in the fuel flow and compressor guide vanes geometry are simulated and a linearized model is obtained, in order to identify the dynamic behaviour of the gas turbine and to design a multivariable controller. Finally, the transient case of a controlled turbine after a sudden variation in the electric load is simulated.
Practical applications of a recently developed method for calculating the head of a rotodynamic impeller
Authors: Yedidiah S
Published: October 2002

This paper discusses the practical significance of the recent finding that the amount of liquid which is directly affected by a blade appears to be of the same order of magnitude as the volume which the blade is displacing. The paper discusses, primarily, cases related to rotodynamic pumps, but it is emphasized that this finding is also applicable to a wide spectrum of additional disciplines.
Film cooling on a turbine guide vane: A numerical analysis with a multigrid technique
Authors: Sarkar S , Das K , Basu D
Published: October 2002

The flow and heat transfer due to film cooling over a turbine nozzle guide vane, which was also cooled by internal convection, were numerically analysed under engine conditions. The time-dependent, two-dimensional, mass-averaged, Navier-Stokes (N-S) equations are solved in the physical plane based on the four-stage Runge-Kutta algorithm in the finite volume formulation. Local time stepping, variable coefficient implicit residual smoothing and a full multigrid technique have been implemented to accelerate the steady state calculations. Turbulence was simulated by the algebraic Baldwin-Lomax (B-L) model. The computed heat transfer distributions with film cooling in conjunction was successful in describing the coolant behavior over the curved suction and pressure surfaces of a turbine blade for varying blowing and temperature ratios.
An insight on intercooling and reheat gas turbine cycles
Authors: da Cunha Alves M. A. , de Franca Mendes Carneiro H. F. , Barbosa J. R. , Travieso L. E. , Pilidis P , Ramsden K. W.
Published: October 2002

The current drive for high efficiencies and low emissions has resulted in the examination and development of advanced power systems based on complex gas turbine cycles. Reheat and intercooling are two such schemes. The basic objective of introducing intercooling and reheat is to sources of loss in a gas turbine engine are those arising from the turbomachinery and the need to cool the turbine blades. In this paper the concepts of intercooling and reheat for gas turbines are assessed, in a systematic way, using a model that includes the above losses in order to evaluate their effects on the engine performance. Also examined is the choice of the position where intercooling or reheat is implemented which can have a large effect on the engine output. A comparison is made with the simple cycle and it is shown that these schemes show much promise. Some of the development difficulties are also outlined. Intercooling promises large improvements in efficiency over the simple cycle, especially at high pressure ratios. Reheat on the other hand is much more suited to combined cycles.
Part load operating strategies for gas turbines in district heating applications
Authors: Carcasci C , Cormacchione N. A Colitto.
Published: October 2002

Centralized heating and cooling systems (i.e. district heating and cooling networks) are becoming increasingly widespread in many countries. At the same time, environmental concerns related to climate change are forcing many countries to consider increased implementing co-generation of heat and power. Gas turbines are well suited to combined heat and power (CHP) applications in district heating systems. Gas turbines can produce electricity at relatively high efficiency, and the hot exhaust gases can be used either directly to provide heat to the district heating network or to generate steam to drive a conventional steam turbine in a combined cycle system. However, the heat load of a district heating network varies considerably over the course of the year, and the gas turbine CHP system must therefore often operate in off-design conditions, particularly at part load. When evaluating the overall performance of a gas turbine CHP system, it is important to account for all operating conditions encountered in the course of a typical heating season. This study examines the performance of gas turbine CHP systems for different operating conditions encountered when they are providing heat to a district heating system. Special emphasis is placed on evaluating part load performance and discussing different operating strategies for part load operation of the CHP plant. The different strategies discussed are compared in terms of fuel usage and overall economy.
The unsteady performance of a centrifugal compressor with different diffusers
Authors: Engeda A
Published: October 2002

Unsteady flow in turbomachinery may be due to turbulence, wakes (rotor-stator interaction), inlet distortion, rotating stall or surge. It is undesired, because it may lead to narrow operation range, poor efficiency and blade failure due to vibration. Four low solidity vaned diffusers (LSVDs) together with one conventional vaned diffuser and two vaneless diffusers were tested downstream of the same impeller for the purpose of understanding the unsteady performance (stall and surge characteristics) of each diffuser and the performance relative to each other. This paper is a complementary paper to previous work where the design and overall and component performances of eight LSVDs have been reported.
Numerical and experimental investigation of a centrifugal compressor with an inducer casing bleed system
Authors: Hunziker R , Dickmann H-P , Emmrich R
Published: October 2002

State-of-the-art centrifugal compressors for turbocharger applications are required to provide broad compressor maps, high pressure ratios and high efficiency levels. Usually these requirements are perceived as contradictory and represent challenging design targets. Various techniques for map width enhancements have been reported since the early 1980s. ABB Turbo Systems Limited has adopted a simple bleed system for internal flow recirculation to a high flowrate, high efficiency, pressure ratio 4.2 centrifugal compressor stage. After initial test runs had proved the effectiveness of the bleed system, computational fluid dynamics (CFD) calculations were performed in order to gain insight into the flow pattern in both the compressor stage and the bleed system. The simulations explain the effectiveness by comparing them with simulations without the bleed channel. Selected streamline and iso-surface plots show the effect of the bleed channel flow on the main flow through the impeller. Four more variants of bleed channels have been modelled and investigated by CFD in order to optimize the bleed slot location and dimension. The most promising configuration, which showed a significant improvement in map width without a loss in efficiency, was subsequently built and tested. This test confirmed the validity of the CFD simulation results.
Rotor-stator interaction in a centrifugal pump equipped with a vaned diffuser
Authors: El Hajem M , Akhras A , Champagne J. Y. , Morel R
Published: October 2002

This paper provides the results of a detailed flow investigation within a centrifugal pump equipped with a vaned diffuser. The measurements made with a laser Doppler velocimeter were carried out at two operating points. Unsteady velocity measurements obtained in phase with the impeller angular position gave access to the relative flow within the impeller channels. Measurements were obtained in the impeller and the diffuser at different measuring planes relative to the diffuser vanes. Results are presented as animations reconstituting a temporal evolution of the flow permitting a better comprehension of the complex flow structure existing between the two interacting blade rows. The analysis of the relative flow field indicates the presence of a jet wake structure. The wake is characterized by low relative velocities localized in the suction side-shroud corner. At the design flowrate, the presence of the vanes seems to have a limited effect on the impeller flow structure, except when the suction side of the blades is facing the diffuser vanes. At the impeller discharge, the time-resolved sequences show that the mixing process of the unsteady and periodic flow leaving the impeller is affected by the presence of the diffuser.
Systematic two-zone modelling for performance prediction of centrifugal compressors
Authors: Oh H. W. , Yoon E. S. , Chung M. K.
Published: October 2002

This paper presents systematic two-zone modelling for reliable performance prediction of centrifugal compressors. In order to improve the predictive capability, a modified jet slip factor is developed and new corrections for the wake flow deviation and mass fraction are suggested on the basis of the comprehensive experimental data of the three Eckardt impellers. The proposed two-zone modelling is tested against nine sets of measured data of centrifugal compressors. The results are also compared with those obtained by mean streamline analysis. It was found that the predictions by the present two-zone modelling agree fairly well with experimental data for a variety of centrifugal compressors over the wide operating conditions.
Sulphur removal from flue gases in the utility sector: Practicalities and economics
Authors: Cooper J R , Collins R , Massey T H , Venkateswaran N , Westaway S
Published: October 2002

Sulphur dioxide control in the utility sector has come of age with established technologies supplied by companies with international reputations and good track records now taking major contracts on a regular basis. Although not employed as extensively as originally anticipated in the United Kingdom, subject to gaining the necessary consents and authorizations, a major contract may be placed for sulphur control on Orimulsion fired plant. World-wide use of desulphurization technologies continues to expand with many installations now under construction or in operation in areas such as the Pacific Rim and Eastern Europe to meet increasingly stringent environmental regulations aimed at controlling unwanted environmental effects.

Previous papers from suppliers and operators have tended to concentrate on the theory of the process or the practical engineering aspects of on-site installation and operation. This paper considers the overall impact and cost of various systems and reviews established and developing systems of flue gas desulphurization processes. It focuses not only on the technology but also on the supply of raw materials, marketing and/or disposal of products, the economics of such systems and some of their potential environmental impacts both on and off site. In this respect the paper reviews all the major areas to be considered in the selection of a process for a particular site.
Simulation of hydraulic power plant transients using neural networks
Authors: Bidini G , Mariani F
Published: October 2002

In this work the efficiency of the artificial neural network technology for evaluating the turbine speed and drain synchronous valve during the turn-off transient phase of an actual hydraulic power plant has been evaluated. These results have been achieved avoiding a detailed time consuming analysis of the power plant. Several net architectures have been set up and verified with regard to their response to this strongly non-linear problem.
Generic design of ram pumps
Authors: Young B W
Published: October 2002

The hydraulic ram pump was invented over 200 years ago but became obsolete with the general availability of mains water. It is used for pumping surface water and is powered by the potential energy of the supply. Ram pumps are particularly appropriate for use in remote regions of the developing world as their construction is basic and robust and they are inexpensive and easy to install and maintain. A rational design procedure applicable to any ram pump is described in this paper. The method is based on the three non-dimensional relationships that have been found to govern ram pump behaviour. The relationships express beat frequency, quantity delivered and source capacity in terms of the independent variables. By assigning upper and lower bounds to the critical velocity in the drive pipe, it is possible to derive three characteristic pump parameters from which the dependent variables may be determined directly. These parameters all take the same numerical values within a feasible design space. The design method has been confirmed using the results of existing experiments. A number of examples are given which illustrate the ease and rapidity of the procedure.
Estimation of extreme mass flowrate in district heating systems
Authors: Jónsson G R , Jónsson V K , Pálsson Ó P , Hrafnkelsson B
Published: October 2002

This paper focuses on how extreme mass flowrate conditions, i.e. T year events, in district heating systems can be estimated by extreme value analysis, namely the method based on annual maximum values and the peaks over threshold (POT) method. Only a few years of mass flowrate data are available, which is far too short a time to be of any practical use for extreme analysis. However, 42 years of climate data are available, which are used to generate daily mass flow data using an autoregressive external (ARX) model. The simulated mass flow contains uncertainty which must be considered in the analysis. This is not possible using a traditional analysis without some modifications. Furthermore, it is also of interest to consider the uncertainty in the climate. A bootstrap technique is applied in order to answer these questions and a comparison is made of the traditional analysis and the bootstrap approach. The results show that when using the bootstrap method the estimated T year events and their uncertainties are always higher compared to traditional methods, whether based on the annual maximum or the POT method. The difference is, however, quite moderate in most cases. The POT method yields somewhat higher estimates than the annual maximum method. It turns out that the predicted load in severe cold spells is not drastically higher compared to, for example, what has been experienced in Reykjavik over the last ten years when the climate has been quite normal. For instance, the 100 year event is estimated to be approximately 20 per cent higher than the average maximum mass flowrate during the last ten years.
Dynamic modelling and simulation of power plant systems
Authors: Lu S
Published: October 2002

This paper gives a brief review of the modelling and simulation techniques and describes basic steady state and dynamic models for power plant components. As an example, a dynamic model for a 677 MW coal- and gas-fired power plant has been built with MATLAB and SIMULINK. Every power plant component was modelled using mainly physical modelling techniques and a whole-plant model can easily be configured by graphically linking the standard components by steam and gas flows, as in physical processes. The simulation results of responses to typical plant disturbances are satisfactory.
Asymmetric line-axis inverted absorber compound parabolic concentrator optical parameter analysis
Authors: Kothdiwala A. F. , Eames P. C. , Norton B
Published: October 2002

A detailed optical analysis of an inverted absorber compound parabolic concentrator, which separates the dissimilar effects of beam and diffuse insolation, gives the effect on the optical efficiency of varying the tertiary cavity height, the reflectance and the acceptance. For the system considered, the optical efficiency decreases with increasing tertiary cavity height and is higher for beam than for diffuse insolation. A high mirror reflectance is essential for an adequate optical performance.
Optimum values of design variables versus specific speed for centrifugal pumps
Authors: Oh H. W. , Chung M. K.
Published: October 2002

An optimal design code for centrifugal pumps has been developed to determine the geometric and fluid dynamic variables under appropriate design constraints. The optimization problem has been formulated with a non-linear objective function to minimize one, two or all of the fluid dynamic losses, the net positive suction head required and the product price of a pump stage depending on the weighting factors selected as the design compromise. The optimal solution is obtained by means of the Hooke-Jeeves direct search method. The performance analysis is based on the mean streamline analysis using the present state-of-the-art loss correlations. The optimized efficiency and design variables of centrifugal pumps are presented in this paper as a function of non-dimensional specific speed in the range, 0.5 ≤ Ns ≤ 1.3. The diagrams presented herein can be used efficiently in the preliminary design phase of centrifugal pumps.
Fire safety engineering for the International Centre for Life, Newcastle-upon-Tyne
Authors: Rhodes N , Hoffmann N
Published: October 2002

This paper describes a study undertaken to determine the fire safety aspects for the International Centre for Life in Newcastle-upon-Tyne, UK. Studies have been carried out to assess the consequences of fires in different areas of the building and to determine their impact on evacuation. Three-dimensional computational fluid dynamics models were developed to represent the complex geometry of the building. During the full analysis, several scenarios of possible fire locations were simulated, providing predictions of temperature and smoke movement. In parallel, an evacuation model was developed to predict the movement of people and studies were carried out on a range of scenarios to assess time-scales for overall evacuation. Using some of the results of one of the scenarios, this paper illustrates how such state-of-the-art computer simulations can be used to demonstrate that the requirements of the relevant safety regulations will be met.
Emission behaviour of a catalytic burner fuelled with mixtures of hydrogen and methanol
Authors: Wiese W , Bröckerhoff P , Emonts B , Riedel E
Published: October 2002

A catalytic radiant burner was chosen as the process heat source in a fuel cell drive system. The advantage of a catalytic burner is the low level of harmful substances in the flue gas. Besides the production of process heat, another task of the burner is to convert different gas mixtures effectively from the system into CO2 and H2O.

The basic burner structure is a ceramic cylinder to which the fuel gas, pre-mixed with air, is internally supplied. On the outer surface of the cylinder, a wire mesh coated with noble metal is provided on which the combustion takes place catalytically.

The emission behaviour of the burner was investigated under different operation conditions concerning the gas mixture and the catalyst. From the results, the mechanisms of the formation of pollutants are discussed and the suitability of the burner concept is checked by comparing the measured emissions with the emission standards. The operation condition ranges are determined under which the burner works in the drive system without exceeding the emission standards.
New stability criteria for a class of systems arising in neural network control and fuzzy systems
Authors: Fang Y , Kincaid T G , Li S
Published: October 2002

In this paper, the stability of a class of systems arising from neural control and fuzzy systems is studied. A new unifying stability criterion is presented using a very simple derivation. This result generalizes some previous results; some easily testable conditions are obtained.
Friction compensation control of an electropneumatic servovalve by using an evolutionary algorithm
Authors: Choi S H , Lee C O , Cho H S
Published: October 2002

A poppet-type electropneumatic servovalve developed in this study utilizes a poppet directly operated by a moving-coil actuator in the metering stage and is controlled by a digital controller. This servovalve is insensitive to air contamination and has no problem of air leakage at null, but it has relatively large friction between the O-rings installed in the peripheral grooves of the balance pistons and the valve sleeve. For friction compensation control, a static friction model that enables simulation of the stick-slip phenomena and a dynamic model that captures the friction behaviour such as presliding displacement and varying break-away force are presented. The parameters for the friction models are identified by utilizing an evolution strategy, one of the evolutionary algorithms, which is a probabilistic global search algorithm based on the model of natural evolution. These friction models are then used in designing a non-linear friction compensation controller. It is found in the experiment that the electropneumatic servovalve has almost no hysteresis and that the friction compensation control significantly improves valve performance. The experimental results of the open loop test on poppet positioning agree well with simulation results of the valve model with identified friction parameters. It is also shown that the experimental results of friction compensation control using a static friction model show a small steady state error but those using a dynamic friction model show almost no such error.
Development of a non-linear force controller using fuzzy logic techniques
Authors: Burn K , Bicker R
Published: October 2002

As the demand for robots to perform complex tasks grows, there is an increasing need to utilize robust and stable force control strategies. Most current schemes can only provide adequate force control with the controller tuned to specific task requirements since, if there is a wide variation in the overall compliance at the robot tool/task interface, the performance is rapidly degraded. This paper describes a method for the design of a fuzzy logic controller to replace a conventional controller in a force control loop. The method combines an analytical approach to controller tuning, with the intuitive properties and self-adjusting gain characteristics associated with fuzzy logic systems. It is demonstrated using a model of a single-axis experimental rig and is shown to perform well over a wide range of stiffnesses. The implementation of the controller on the actual rig is also described. Experimental results compare favourably with those obtained from simulation using an accurate model of the system. Issues relating to the implementation of the controller on multi-axis systems are also addressed.
A new two-degree-of-freedom gain scheduling method applied to the Lynx MK7
Authors: Prempain E , Postlethwaite I
Published: October 2002

This paper considers the design of two-degree-of-freedom gain-scheduled controllers for a helicopter system in a new fashion. By taking advantage of a two-degree-of-freedom decoupling scheme, it is possible to generically split the controller synthesis into two parts. One part is concerned with the synthesis of a regulator and the other aims to achieve the tracking requirements. An important feature of the method is that the feedforward filter can be designed by solving a particular full information problem. A robust linear time-invariant (LTI) regulator will be designed and two methods used to synthesize a gain-scheduled feedforward tracking controller will be investigated. The first method is based on a quadratic gain scheduling technique which makes use of a polytopic description of the plant. The second is simpler and uses the concept of linear interpolation of LTI controllers. Both methods are tested on a Lynx MK7 helicopter in simulation. For this application, the benefits and the shortcomings of the respective methods are discussed. Non-linear simulation results show that the gain-scheduled interpolated controller performs remarkably well over the flight envelope.
Design and implementation of force and position control with anti-windup conditioned transfer compensation
Authors: Tsai M C , Chuang H-S
Published: October 2002

This paper investigates the design and implementation of a force and position servo control system where non-linearities are encountered due to constraint on the torque signal to the motor drive, and switching between position and force controllers. The so-called two-step design paradigm is employed, whereby the velocity, position and force controllers are designed first ignoring control input non-linearities, and then anti-windup and conditioned transfer compensators are added using the Hanus conditioning technique. Both linear position and force controllers are designed using the H∞ loop shaping design procedure, and the H∞ controllers are found such that the Hanus conditioning technique for anti-windup conditioned transfer compensation can be applied. The overall controller is derived and presented in the state space framework, and its performance is evaluated in real time on an experimental set-up using a commercial digital signal processor.
Predictive control of fast output—sampled digital feedback systems via a polynomial approach
Authors: Truman A W , Govan M
Published: October 2002

This paper describes the synthesis of model-based predictive controllers for multivariable digital feedback systems in which the plant output signals are measured at a faster rate than the controls are applied. In contrast with the recent literature devoted to multirate sampled-data system theory, where state-variable system representations are used exclusively, a polynomial modelling approach that exploits the frequency and switch decomposition techniques established in the 1950s is adopted. It is demonstrated that the principal advantage of fast output signal-sampled predictive control algorithms lies in their potential to suppress process and, particularly, measurement noise disturbances.
H∞ control of gasification plant
Authors: Walker D J
Published: October 2002

The design and simulation of an H∞ control system for an experimental 87 MW fluidizedbed coal gasification reactor (‘gasifier’) are described. This is a highly coupled multivariable system that produces fuel gas by reacting coal, air and steam at a high temperature and pressure. H∞ optimization is used to design a robust controller that attenuates the effect of a pressure disturbance on four key outputs. The initial design was fairly robust to changes in load condition and to input non-linearities, but the performance was only moderate; it violated nine out of 48 limits given in a tentative specification, including some at nominal conditions. A redesign led to a 20-state controller that essentially met the specification, bar the transient violation of a lower pressure limit at the extreme operating point. This is shown to be due to the effect of input rate limits.
Automatic design of multi-variable quantitative feedback theory control systems via evolutionary computation
Authors: Tan K C , Lee T H , Khor E F
Published: October 2002

This paper proposes a multi-objective evolutionary automated design methodology for multi-variable quantitative feedback theory (QFT) control systems. Unlike existing analytical and convex optimization-based QFT design approaches, the evolutionary ‘intelligent’ technique is capable of automatically evolving both the nominal controller and the pre-filter simultaneously to meet the usually conflicting multiple performance requirements in QFT, without going through the sequential and conservative design stages for each of the multi-variable subsystems. In addition, it avoids the need of manual QFT bound computation and trial-and-error loop-shaping design procedures, which are particularly useful for multi-variable or unstable plants where stabilizing controllers may be difficult to synthesize. The effectiveness of the proposed QFT design methodology is validated upon a benchmark multi-variable system, which offers a set of low-order Pareto optimal controllers satisfying all closed-loop performances under practical constraints.
Bond graphs and object-oriented modelling—a comparison
Authors: Borutzky W
Published: October 2002

Bond graph modelling was devised by Professor Paynter at the Massachusetts Institute of Technology in 1959 and subsequently developed into a methodology for modelling multidisciplinary systems at a time when nobody was speaking of object-oriented modelling. On the other hand, so-called object-oriented modelling has become increasingly popular during the last few years. By relating the characteristics of both approaches, it is shown that bond graph modelling, although much older, may be viewed as a special form of object-oriented modelling. For that purpose the new object-oriented modelling language Modelica is used as a working language which aims at supporting multiple formalisms. Although it turns out that bond graph models can be described rather easily, it is obvious that Modelica started from generalized networks and was not designed to support bond graphs. The description of bond graph models in Modelica is illustrated by means of a hydraulic drive. Since VHDL-AMS as an important language standardized and supported by IEEE has been extended to support also modelling of non-electrical systems, it is briefly investigated as to whether it can be used for description of bond graphs. It turns out that currently it does not seem to be suitable.