bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficiency of a district heating network serving hot water absorption chillers
Authors: Kitanovski A , Poredoš A
Published: October 2002

In the future, cooling needs will increase during the summer months because of an ever-increasing desire for comfort within buildings. Over the last decade, the use of absorption chillers has increased. These chillers require a heat source for their operation. When compared with conventional electrically driven compressor chillers, the electrical energy requirements for absorption chillers are almost negligible. As a heat source, absorption chillers can use fuel gases, fuel oils, steam and hot water.

An analysis was made of the influence of the supply and return temperatures on the efficiency of district heating systems (DHSs), with hot-water-driven absorption chillers (HWACs) as a component of a heat-driven distributed district cooliing system. An optimal configuration of HWACs was proposed. A comparison between the efficiency of a DHS and HWACs for a range of hot water supply and return temperatures was made and an optimal operating temperature of 95/80°C was estimated.
Frost formation and defrost control parameters for open multideck refrigerated food display cabinets
Authors: Tassou S. A. , Datta D , Marriott D
Published: October 2002

In order to achieve the required air and product temperatures in refrigerated food display cabinets, the evaporator coils, which are normally located in the base of the cabinets, operate at temperatures below the freezing point of water. The air which is circulated over the evaporator coil is cooled below its dew point and water vapour present in the air condenses and eventually freezes on the coil surface. With continuous operation of the coil, frost will accumulate on the coil surface leading to a decrease both in the air flowrate and in the overall heat transfer coefficient. In order to maintain satisfactory performance, evaporator coils are defrosted periodically. Although different defrost control strategies can be employed, for simplicity and cost considerations, defrosting in supermarket refrigeration systems is usually controlled by a pre-set time cycle. It is widely acknowledged, however, that time-based defrost may cause a number of unnecessary defrost cycles and this reduces the energy efficiency of the refrigeration systems as well as the accuracy of temperature control of the cabinets. Implementing defrost only when it is needed or on ‘demand’ should reduce the number of defrost cycles and lead to savings in energy and improved product quality. This paper reports on field and experimental investigations on the processes of frosting and defrosting of medium-temperature display cabinet evaporator coils. The results show that for medium-temperature refrigeration applications where the environment temperature is kept reasonably constant, the store humidity is the primary parameter influencing the rate of frost formation. Using relative humidity as a control parameter the defrost frequency can be reduced considerably without affecting cabinet performance and product integrity. Alongside the effect of relative humidity, the paper also considers the effects of other performance parameters on the processes of frosting and defrosting such as cooling time and length of previous defrost cycle, and discusses ways in which some of these parameters may be used to implement defrost on demand.
The exploitation of low-head hydropower by pressure interchange with air, using siphons
Authors: French M. J. , Widden M. B.
Published: October 2002

The paper describes and analyses a hydropower system based on siphons in which the pressure of low-head water is converted into air pressure. The analysis suggests that, with careful design of the flow passages to minimize losses, air-pumping efficiencies of 70 per cent or more should be achievable; the overall efficiency of the hydropower system should be better than 60 per cent. Although such values of efficiency are lower than usually found in hydro plant, the economics of the system are likely to be attractive owing to the low capital cost of the system compared with conventional water turbine systems. It is shown that a siphon plant is suitable, in single-stage from, for heads up to about 1.7m. For higher heads the system can be used in two or more stages.
Three-dimensional flow field downstream of an embedded stator in a multistage axial flow compressor: Part 1: Steady and unsteady flow fields
Authors: Prato J , Lakshminarayana B , Suryavamshi N
Published: October 2002

A comprehensive investigation of the three-dimensional unsteady flow and thermal field downstream of an embedded stator in a multistage compressor, acquired with a high-response hot-film probe and aspirating probe, is presented and analysed. Some of the earlier data (from a five-hole probe and a high-response Kulite probe) from the same compressor is used with the present data to provide an integrated interpretation of the flow and thermal fields. Part 1 includes a brief description of the facility, the development of the hot-film technique for the multistage flow field measurement and an interpretation of the various flow field features, such as the hub clearance flow and the suction surface-casing end-wall corner region. Part 2 covers velocity-velocity and velocity-temperature correlations and the assessment of their magnitudes in the average-passage equations. The results presented in this part of the paper (Part 1) indicate that major blockage in the stator hub end wall is caused by leakage flow and its possible subsequent roll-up into a vortex. Similar features exist in the suction surface casing end-wall corner due to secondary flow and its interaction with the upstream rotor end-wall flow. These are also the regions with the highest levels of unsteadiness. The transport of rotor wake towards the pressure side of the stator is confirmed. Both the revolution and the blade periodic velocity fluctuations are found to be significantly greater than the aperiodic fluctuations.
Performance and optimization of gas turbines with real gas effects
Authors: Guha A
Published: October 2002

The influence of various levels of mathematical modelling on gas turbine performance is systematically analysed. It is shown that internal combustion with real gas effects gives rise to an optimum turbine entry temperature which does not arise in a perfect gas analysis and has not been described previously in the literature. At any pressure ratio, the maximum possible efficiency with real gas effects is significantly lower (15-20 per cent) than the maximum possible value predicted by a perfect gas analysis. An explicit equation has been derived for determining the optimum pressure ratio as a function of turbine entry temperature and component efficiencies. It is shown that the optimum design depends very strongly on turbine and compressor efficiencies. It is demonstrated that the optimum relation between pressure ratio and turbine entry temperature depends strongly on whether the optimization is carried out at fixed pressure ratios or at fixed temperatures. All previous references seem to have considered only the latter method.
Particle image velocimetry investigation of the flow characteristics in two-leg internal coolant passages of gas turbine airfoils
Authors: Chanteloup D , Bölcs A
Published: October 2002

A study of flow in a stationary model of a two-pass internal coolant passage is presented which focuses on the flow characteristics in the 180° bend region and downstream of the bend, where the flow is re-developing. A stereoscopic digital particle image velocimetry system measured all three velocity components simultaneously to obtain mean velocity and turbulence quantities of the flow field. The coolant passage model consisted of two square passages, each having a 20 hydraulic diameter length, separated by a web of 0.2 passage widths and connected by a sharp 180° bend with a rectangular outer wall. Ribs were mounted on the bottom and top walls of both legs with a staggered arrangement and at 45° to the flow. The rib height and spacing were 0.1 and 1.0 passage heights respectively. The measurements were obtained for a flow condition with a Reynolds number of 50000. The geometry is similar in the straight sections to a previous configuration but has ribs extending into the bend region. The paper presents new measurements of the flow in the straight legs of the passage, comparison of the flow in the bend region with a previous configuration and details of the flow recovery from the bend in the second leg.
Numerical simulation of wake velocity and wake turbulence effects on unsteady boundary layer transition
Authors: Thurso J , Stoffel B
Published: October 2002

Linear and non-linear low Reynolds number k-ɛ eddy viscosity models are applied to the simulation of unsteady transitional flows pertinent to axial turbomachine aerodynamics. Adequate test cases are selected to allow an individual investigation of wake velocity and wake turbulence effects on unsteady transition induced by separation bubbles and wake passing respectively. Separation bubbles under steady main flow conditions are calculated first, demonstrating the applicability of the numerical scheme and the selected turbulence models. Unsteady simulations show that essential features of the experimental investigation can be reproduced, although oscillation characteristics of the separation bubble, such as phase shifts, can only be partly reproduced. Predictions of wake-induced transition on a flat plate agree with the underlying direct numerical simulation study in many important aspects. However, simulation results show deficiencies with respect to the time-averaged transition length and the spatio-temporal evolution of turbulent flow regions.
Nucleating unsteady flows in low-pressure steam turbine stages
Authors: Winkler G , Schnerr G. H.
Published: October 2002

The present paper deals with the detailed numerical investigation of transonic, turbulent, unsteady two-phase steam flows with internal heat addition after partial condensation of the working fluid. The observed phenomena include homogeneously, homogeneously-heterogeneously and heterogeneously dominated condensation effects. The results concerning the different condensation mechanisms are initially discussed in terms of the turbulent, transonic flow through Laval nozzles. Further, an interesting phenomenon of nucleation and droplet growth inside turbulent boundary layers is presented. Application to transonic turbine flows in the rotor cascade VKI-1 shows the influence of homogeneous nucleation on the turbulent shock-boundary layer interaction. Finally, the different types of condensation models were compared to investigate the two-dimensional transonic two-phase flow in an entire turbine stage including high-frequency rotor-stator interactions.
Aerothermal predictions with transition models for high-pressure turbine blades
Authors: Roux J. M. , Mahé P , Sauthier B , Duboué J. M.
Published: October 2002

Turbine aerothermal analysis is a key issue of the entire engine design as higher performance and longer component life must always be reached. For this purpose, a substantial effort is dedicated to aerothermal methods at Snecma-Moteur. This paper deals with the problem of heat transfer prediction on uncooled turbine blades. The main parameter investigated is the transition process, but consideration is also given to the turbulence model, effect of free stream turbulence on laminar boundary layer and mesh refinement. All the models are implemented in a three-dimensional Navier-Stokes code. Quasi-three-dimensional computations are used to evaluate all models, and then fully three-dimensional computations are performed. Aerothermal predictions are compared with static pressure and heat transfer measurements from the IACA and TATEF Brite-EuRam programmes carried out in the test facilities of DERA, Pyestock and the von Karman Institute.
A performance study of a radial turbine for wave energy conversion
Authors: Setoguchi T , Santhakumar S , Takao M , Kim T. H. , Kaneko K
Published: October 2002

Bidirectional flow air turbines are used in association with oscillating water columns to convert wave energy available in the oceans into mechanical power. Radial turbines, among others, were studied for such an application. The efficiency of radial turbines using reaction blading was found to be extremely low. On the other hand, the efficiency of impulse-type radial turbines was found to be higher. However, detailed performance studies on impulse-type radial turbines are not found in the literature. This paper presents detailed performance characteristics as well as some parametric studies based on laboratory experiments.
Control of visible plumes from cooling towers
Authors: Winter A R
Published: October 2002

Emissions from evaporative cooling towers can have a major impact on the environment and are a potential obstacle to obtaining planning permission for new power stations. This paper discusses how cooling tower selection in the United Kingdom has been influenced by the increasing reluctance of the planning authorities to accept visible plumes in the years since the privatization of the power industry.
Computation of unsteady flow through steam turbine blade rows at partial admission
Authors: He L
Published: October 2002

Partial admission in the steam turbine is associated with strong unsteady flow effects on aerodynamic performance. This paper presents a first-of-its-kind computational study of the problem. The unsteady flow field in multiple blade passages and multiple blade rows is governed by the quasi three-dimensional unsteady Navier-Stokes equations, closed by a mixing-length turbulence model. The partial admission is introduced by blocking one segmental arc (or several segmental arcs) of the inlet guide vane of the first stage. The flow equations are solved by using a time-dependent finite volume method.

The calculated unsteady force on rotor blades for a turbine stage at partial admission compares well with the corresponding experimental data. The present results show that a cyclic pumping and sucking phenomenon occurs in the rotor blade row of the first stage, resulting in large unsteady loading and marked mixing loss. For a single stage at a given admission rate, a blocking arrangement with two flow segments is shown to be much more detrimental than one arc of admission, because of the extra mixing loss. The results for a two-stage case, however, suggest that the decaying rate of circumferential non-uniformities could be far more important for performance. For this reason, an enhanced mixing loss in the first stage might be beneficial to the overall efficiency of a multistage turbine.
Flow around the sections of rotor blading of a turbine stage with relatively long blades at off-design conditions
Authors: Šťastný M , Šafařík P , Hořejší I , Matas R
Published: October 2002

The paper deals with the results of aerodynamic research of flow through blade cascades at off-design conditions. Variations of inlet velocity vectors during the operation of the stage at off-design flow conditions are calculated and compared with experimental results. The detailed measurements provide data on aerodynamic parameters, kinetic energy losses and flow structure. Leading edge flow separation occurs mainly at off-design incidences and is proved to be the reason for the considerable kinetic energy loss increase. The occurrence of unsteady aerodynamic phenomena and forces at off-design performance of blade cascades is shown. The transonic flow structure is studied in detail and experimental data analysis and results of numerical calculations are presented.
Turbine blade heat transfer calculations using two-equation turbulence models
Authors: Larsson J
Published: October 2002

A full Navier-Stokes solver is used to calculate external heat transfer in two linear two-dimensional turbine cascades, one subsonic and one transonic. Heat transfer results obtained with two low-Reynolds k-∊ models (Chien and Launder-Sharma) and two k-ω models (Wilcox standard and transition) are compared with measurements. Good agreement is found in some regions, but the suction side transition and the leading edge are not predicted correctly. Problems with turbulence levels that are too high in the leading edge region are investigated. The numerical quality of the results is investigated and a few general guidelines about the numerics are given. Grid and scheme independence is also demonstrated.
Application of casing treatment to an industrial axial-flow fan
Authors: Hill S D , Elder R L , McKenzie A B
Published: October 2002

This paper deals with an experimental investigation into the influence of a vaned recess casing treatment on the performance of an industrial-type axial-flow fan with a hub-tip ratio of 0.4. The treatment has been tested in a variety of configurations relative to the fan, with an emphasis on the amount of fan blade tip exposure to the treatment. Two sets of blading, one of which is of the fully reversible type, have been investigated.

Detailed flow measurements have been carried out with a slanted hot wire probe to provide an insight into the operation of the device and into the nature of the rotating stall in the solid casing configuration. Strain gauges have been employed to enable blade stresses to be recorded and an in-duct microphone to enable comparative tests on fan noise has also been used.
An inverse design method of diffuser blades by genetic algorithms
Authors: Fan H-Y
Published: October 2002

A genetic algorithm incorporating a neural network technique is proposed to search for a turbo-machinery diffuser blade profile that produces a given velocity distribution on its surface. Such a new inverse design method works through minimizing the error between the surface velocity distribution of candidate blades and the target velocity distribution. For ease of employing the genetic algorithm, the blade profiles to be searched are parameterized by Bezier curves. To fix the surface velocity distribution of a candidate blade, a special type of back propagation (BP) neural network is implemented. The proposed approach is illustrated by a diffuser having two-dimensional blades with constant height and thickness. The simulations show that the new method is not only feasible but also reliable and efficient.
Natural gas exploitation by carbon dioxide from gas hydrate fields—high-pressure phase equilibrium for an ethane hydrate system
Authors: Nakano S , Yamamoto K , Ohgaki K
Published: October 2002

Natural gas hydrate fields, which have a large amount of methane and ethane deposits in the subterranean Arctic and in the bottom of the sea at various places in the world, have become the object of public attention as a potential natural gas resource. Here the idea of natural gas exploitation from natural gas hydrate fields combined with CO2 isolation using CO2 hydrate has been presented. As a fundamental study, high-pressure phase behaviour for the ethane hydrate system was investigated in a high-pressure cell up to a maximum pressure of 100 MPa, following a previous study of CO2 and methane hydrates. Consequently, the phase equilibrium relationship of an ethane hydrate—water—liquid ethane mixture was obtained in the temperature range from 290.4 to 298.4 K and over a pressure range of 19.48 to 83.75 MPa. The observed phase boundary corresponds to the three-phase coexisting line with a non-variant quadruple point of ethane hydrate—water—liquid ethane—gaseous ethane at 288.8 K and 3.50 MPa, similar to the CO2 hydrate—water—liquid CO2 system.
Modelling vehicle emissions using the TEMIS program: Part 1: Enhancement of the TEMIS framework
Authors: Saleh W , Nelson J D , Bell M G H
Published: October 2002

The total emissions model for integrated systems (TEMIS) program was developed at the Institute of Applied Ecology, Darmstadt, to provide an analytical tool for planners and decision-makers involved in formulating energy policy. In this paper, the first of two, the enhancement of the TEMIS framework to accommodate various transport and traffic situations is reported. A number of factors were identified as having an influence on vehicle fuel economy and emission characteristics. Determination of these factors has involved reference to results of published empirical studies where vehicle exhausts have been monitored under a wide range of driving conditions. The life cycle of bio-diesel (UK) as a transport fuel has been created within TEMIS as an example of modelling the complete transport fuel cycle. In addition, the effects of different driving conditions (cruising, acceleration, deceleration and idling) on emissions and fuel consumption have been considered by defining different TEMIS processes for each of these driving modes.
Intelligent computer aided optimization of power and energy systems
Authors: Wu C
Published: October 2002

CyclePad, an intelligent computer aided instruction (ICAI) software package is described. It can be used for design, analysis and improvement of power and energy systems. Performance and sensitivity analysis of a Brayson cycle are discussed in order to illustrate its capabilities.
Energy and exergy balance in a gas turbine combustor
Authors: Datta A , Som S. K.
Published: October 2002

An energy and exergy balance in the process of spray combustion in a model tubular gas turbine combustor has been made to determine the combustion efficiency and second law efficiency of the process at different operating conditions. The velocity, temperature and species concentration fields in the combustor have been evaluated numerically from a two-phase separated flow model of the spray along with suitable reaction kinetics for the gas phase reaction. A theoretical model of exergy analysis, based on availability transfer and flow availability, has been developed to predict the second law efficiency of the combustion process in the gas turbine combustor. A comparative picture of the functional relationships of combustion efficiency and second law efficiency of the process with the operating parameters of the combustor have been made to throw light on the trade-off between the effectiveness of combustion and the lost work due to thermodynamic irreversibility.
Domestic electrical space heating with heat storage
Authors: Farid M. M. , Chen X. D.
Published: October 2002

Electricity consumption varies greatly during the day and the night. Any effort made to shift the use of electricity from the peak period to the off-peak period by applying some heat storage for space heating will be beneficial. In this paper, underfloor electrical heating has been studied using computer simulation. The objective is to investigate the potential of using a phase-change material placed between the heating surface and the floor tiles to increase the thermal mass of the floor. The same principle may be applied to the walls or ceiling of the house. It was found that a 30 mm layer of a phase-change material having a melting point close to 40 °C is sufficient to provide heat storage for 1 day under the ambient condition investigated. The simulation also showed that a compact storage heater, using phase-change materials with higher melting temperatures, could be an alternative to the underfloor heating investigated. In both methods, the heater may be operated for only 8 h during the off-peak load period, while the heat stored in the phase-change material is sufficient to provide reasonably uniform heating throughout the whole day.
Numerical simulation and aerothermal physics of leading edge film cooling
Authors: Chernobrovkin A , Lakshminarayana B
Published: October 2002

A viscous flow solver based on the Runge-Kutta scheme has been modified for the numerical investigation of the aerothermal field due to the leading edge film cooling at a compound angle. An existing code has been modified to incorporate multiblock capabilities. Good agreement with the measured data has been achieved. The results of the numerical investigation have been used to analyse the vortex structure associated with the coolant jet-free-stream interaction to understand the contribution of different vortices on the cooling effectiveness and aerothermal losses. Two counter-rotating vortices generated by the interaction between the main flow and the coolant jet have been found to have a major influence in decreasing the cooling efficiency through strong entrainment of the hot fluid. Numerical simulation was carried out to investigate the influence of the inlet Mach number, the inlet turbulence intensity and the length scale on the aerothermal field due to the leading edge film cooling. Variation in the inlet Mach number leads to a minor modification of the cooling effectiveness, and this is predominantly caused by the modified pressure gradient. An increased turbulence intensity has a profound effect on the cooling near the leading edge. The adiabatic effectiveness downstream of the second row of coolant holes is less sensitive to a change in the turbulence intensity. The results of the numerical simulation indicate that the turbulence length scale has a significant effect on the accuracy of the numerical prediction of film cooling. Not only the inlet turbulence intensity but also the turbulence length scale should be accurately set to achieve a reliable numerical prediction of the heat and mass transfer due to film cooling.
A new thermal engine concept suitable for automobiles
Authors: Kovacs A
Published: October 2002

The historical concept of thermal engines based on four strokes taking place in one single capsulism (volumetric device) is currently reaching the limits of its perfectibility. It is therefore legitimate to begin trying to conceive radical departures from this well-rooted paradigm. This paper describes one of them, based on the use of two volumetric devices linked in a particular way and a continuous combustion which can be internal or external. The theoretical figures for specific power and efficiency are quite compatible with automotive uses as well as other features needed in these applications.
Prediction of wall heat transfer for a gas turbine combustor
Authors: Gosselin P , de Champlain A , Kretschmer D
Published: October 2002

This paper describes an improved method for predicting wall temperatures in gas turbine combustors in terms of critical parameters such as scale and pressure. It is demonstrated that existing prediction techniques are not necessarily applicable to small combustors and that a good part of it is due to an imprecise knowledge of the hot gas temperatures within the recirculation, primary and secondary zones. From the analysis of new experimental data, obtained recently in the Laval Combustion Laboratory, with wall temperature measurements at three different scales of the same combustor, a new volume function was implemented in the formulation to account for scaling effects.
Low-temperature natural-gas-fired combustors and NOx formation
Authors: Syred N , Mirzae H , O'Doherty T
Published: October 2002

This paper discusses the characteristics of low-temperature cooled combustors as currently being developed and utilized in situations where very low NOx emissions are required with natural gas firing. Cyclone or swirl-type combustors are commonly used owing to their very wide blow-off which when translated to a cooled situation results in a system with acceptable blow-off limits for flame front temperatures as low as 1000 °C with only 20 per cent excess air. This depends on the careful integration of the heat transfer surface with the flame front region such that the products of combustion are directed away, inwards from the cooled surface, thus permitting complete fuel burn-out to occur. The combustion aerodynamics of a multi-inlet pre-mixed natural gas-air cyclone combustor has been characterized using laser Doppler anemometry together with detailed mapping of NOx, temperature and gas species concentration. This has been undertaken in 32 different operational cases involving five different multi-inlet cyclone combustors operated over the equivalence ratio range 0.45 ≤ φ ≤ 1.25.

The NOx emission data has been examined in light of the prompt NO model of De Soete and modified in light of the known combustion temperatures, NO and species concentration levels. A correlation was derived of similar form to that of De Soete and found to give a reasonable data fit over the temperature range from 900 to 1500 °C, especially for lean equivalence ratios. The constants in this correlation are quite different from those of De Soete; this is felt to reflect the much lower temperature levels over which the data were gathered. Conclusions are then drawn as to the configuration of very low NOx emission combustors.
Multistage three-dimensional Navier-Stokes computation of off-design operation of a four-stage turbine
Authors: Gerolymos G. A. , Hanisch C
Published: October 2002

In this paper a three-dimensional computational methodology for multistage turbomachinery flows is developed, validated and applied in analysing the reduced mass flowrate operation of a four-stage turbine. The flow is modelled by the three-dimensional Favre-Reynolds-averaged Navier-Stokes equations using the Launder-Sharma near-wall k-ɛ turbulence closure, which are integrated using an implicit third-order upwind solver. The computation models the eight blade rows, including the tip clearance gaps of the rotors, using a 6 × 106 points grid, and computes the time-averaged flow using mixing planes between rows. Computational results are compared with measurements for various operating points. After this validation the method is used in a first attempt to analyse the three-dimensional flow at reduced-mass-flow operation.
Induced flow reciprocating pumps Part 2
Authors: Burton J. D. , Short T. D.
Published: October 2002

The application of the induced flow principle is particularly important for modern high-speed reciprocating diaphragm pumps. Subresonant systems have been available commercially for more than two decades now. After reviewing such systems, the paper evaluates the much more recent development of over-resonant running. A dynamic model is presented together with the electrical analogue, and the paper indicates that over-resonant induced flow pumps seem particularly suited to electrically driven solar (photovoltaic)- and wind-powered applications.
Combustion analysis of coconut oil and its methyl esters in a diesel engine
Authors: Shaheed A , Swain E
Published: October 2002

Renewable diesel fuel substitutes need to be developed to fulfil the future energy demands in regions such as the Maldives where traditional petroleum-based fuels are scarce or non-existent. Therefore, the interest in developing alternative fuels based on locally available raw materials has increased during the past few years. This paper is based mainly on the possible use of coconut-oil-based fuels that can be produced in the Maldives and can be used as a substitute for diesel fuel. The combustion data of coconut oil, coconut oil methyl esters and diesel fuel were compared using a naturally aspirated single-cylinder diesel engine. The engine performed well on the three fuels except for initial engine starting problems with coconut oil. In addition, there was a small reduction in power using coconut oil, consistent with the lower calorific value of the fuel. Comparative combustion analysis data together with the emissions for the three fuels are presented.
Stability and robustness for discrete-time systems with control signal saturation
Authors: Plummer A R , Ling C S
Published: October 2002

All practical control systems exhibit control signal saturation. The effect that this saturation has on the control system performance, especially stability and robustness, can be significant and must be understood at the controller design stage. This paper presents conditions for global asymptotic stability and measures of stability robustness for such systems. These are demonstrated through simulation examples, and it is shown how an understanding of the stability conditions can inform the controller design process. The off-axis circle criterion is used as the basis for a sufficient condition for stability, and it is argued that this is not overly restrictive in practice. The derivations are carried out in discrete time, and servo-system control is envisaged as an important application area for the techniques; however, the results are applicable more widely.
Prognosis of remaining bearing life using neural networks
Authors: Shao Y , Nezu K
Published: October 2002

A new concept referred to as progression-based prediction of remaining life (PPRL) is proposed in the present paper in order to solve the problem of accurately predicting the remaining bearing life. The basic concept behind PPRL is to apply different prediction methods to different bearing running stages. A new prediction procedure which predicts precisely the remaining bearing life is developed on the basis of variables characterizing the state of a deterioration mechanism which are determined from on-line measurements and the application of PPRL via a compound model of neural computation. The procedure consists of on-line modelling of the bearing running state via neural networks and logic rules and not only can solve the boundary problem of remaining life but also can automatically adapt to changes in environmental factors. In addition, multi-step prediction is possible. The proposed technique enhances the traditional prediction methods of remaining bearing life.
Navigation of a sonar-equipped mobile robot with real-time local map building
Authors: Fujimori A , Ogawa Y , Teramoto M
Published: October 2002

This paper presents a navigation technique for a sonar-equipped mobile robot with real-time local map building in unknown environments. Since the map built in this paper represents a local region around the robot, the computation time and the memories required for map building are less than those for a global map, which is obtained after exploring over the entire environment. A navigation algorithm is constructed with the proposed local map building and reactive obstacle avoidance behaviours. In navigation experiments using a commercial mobile robot named Pioneer-1, the local map built was effective for navigation in several environments compared with a reactive navigation technique without map building, especially in complicated environments.
Flexible time-response matching in discrete model reduction
Authors: Lucas T N
Published: October 2002

A simple way to match the time responses of the full- and reduced-order models at arbitrary sampling points is given for discrete-time systems. It is seen to be a natural extension of the Padé methods and is particularly useful in oscillatory systems. An example illustrates the technique.
An advanced predictive control approach to the ALSTOM gasifier problem
Authors: Rice M J , Rossiter J A , Schuurmans J
Published: October 2002

Predictive-optimal control is able to deal with many practical control issues, such as guarantees of nominal stability, nominal performance optimization and constraint handling. It is also particularly easy to apply to a system that is well approximated by a linear model such as with this benchmark problem. Here the aim is to illustrate the efficacy of two novel approaches to predictive control. In the first approach the system is first stabilized with a simple control law. The predictive control is then added as an outer-loop optimization for constraint handling. The second approach is computationally more efficient; here constraints are handled by a systematic mixing of two stabilizing control laws.
Robust control of the gasifier using a mixed-sensitivity H∞ approach
Authors: Prempain E , Postlethwaite I , Sun X D
Published: October 2002

This paper presents a mixed-sensitivity H∞ design for the ALSTOM gasifier benchmark challenge. The controller has been designed with the linearized plant model at the 100 per cent operating point. Performance and robustness specifications were expressed in the frequency domain. The controller has been tested on the 0, 50 and 100 per cent load models. Input and output limits were not exceeded during the tests apart from the gas pressure when testing the controller on the 0 per cent load model. Clearly, this design demonstrates the effectiveness of an H∞ approach in stabilizing the gasifier for different operating points with good robust performance.
A sequential loop closing approach to the ALSTOM gasifier problem
Authors: Munro N , Edmunds J M , Kontogiannis E , Impram S T
Published: October 2002

A sequential loop closing technique combined with high-frequency decoupling was applied to the design of a control scheme for a gasifier unit that forms part of an integrated gasification combined cycle power plant. The data describing the plant were provided by ALSTOM, in the form of three locally linearized state-space models. Although the initial analysis tests were frustrated by the extremely ill-conditioned nature of the model data, which yielded erroneous results when used with standard test procedures, it was possible to design a control system for the gasifier at the 100 per cent load condition by making use of certain scaling and decoupling algorithms. The robustness of this control scheme was then assessed by applying it (unchanged) to the 50 and 0 per cent operating conditions. The resulting closed-loop systems were simulated and the results obtained show that the controlled system performed quite well at all load conditions, albeit with the violation of input constraints in the face of pressure disturbances.
Enhancement of the least-squares Padé method for discrete systems
Authors: Lucas T N
Published: October 2002

The least-squares Padé method for discrete system order reduction is further enhanced. First, it is shown how the method may be extended to produce true least-squares approximations between the time responses of the full and reduced models. Second, it is shown how different stable reduced degree denominator polynomials can be generated from subsets of the system Markov parameters. Examples are given to illustrate these enhancements to the method.
Motion control of constrained systems considering their actuation-related singular configurations
Authors: Özgören M K
Published: October 2002

In this paper, the constrained motion control of a normally unconstrained mechanical system is investigated. As far as its motion control is concerned, such a system will have a redundancy in its actuators due to the reduction caused in its number of degrees of freedom by the presence of the constraints. Four methods are described in order to determine the actuator and constraint forces. The first three of these methods necessitate using all the actuators and the fourth method is applicable in a case where non-redundant (i. e. minimum) number of actuators is used. In such a case, it is shown that there exist actuation-related singular configurations (ASCs), at which the actuator and constraint forces become unboundedly large, unless some special precaution is taken. The fourth method includes an efficient precaution as well. As a case study, computer simulations are made considering a typical constrained system that consists of two cooperating manipulators. Only the fourth method is applied because it is preferable with its minimal operational complexity and also because its application needs extra care due to the troublesome but interesting phenomenon of ASCs.
On the control design of a gyro test table
Authors: He Y , Liew K M , Gu D-W , Postlethwaite I , Wang G
Published: October 2002

An important aspect of linear controller design is to clarify whether the design reaches the performance limit, which is highly significant to the practice of control system design. Based on an industrial project of a high-precision gyro test table (servo system), a paradigm is presented to demonstrate that the performance limit of the disturbance attenuation design of the servo system can be reached in a systematic way by usingμ synthesis. A gyro test table is a servo system employed to measure the drift of a gyro. In contrast with general sensitivity theory, which generally considers the output disturbance rejection, the main concern in gyro test table design is the input disturbance attenuation. The uncertainty caused by the neglected dynamics in this servo design implies a limitation on the bandwidth of the gyro test table, i. e. the bandwidth is limited by the robust stability requirement. Furthermore, it is manifested that the multiplicative uncertainty description plays a leading role in the H∞/μ design. This paper reveals that the performance limit is determined by the bandwidth. This finding will help the designer to judge whether any given performance specification is achievable and illustrates the design idea of giving priority to the bandwidth.
Use of time domain features for the neural network based fault diagnosis of a machine tool coolant system
Authors: Samanta B , Al-Balushi K R
Published: October 2002

A procedure is presented for the fault diagnosis of a machine tool coolant system by the use of artificial neural networks (ANNs). The characteristic features of time domain signals of the system with normal and faulty conditions have been used as inputs to ANNs, consisting of input, hidden and output layers. The input layer consisted of nodes for features extracted from the time domain response of the coolant system with simulated faults and severity levels. The inputs were normalized within the range 0.0 and 1.0. The output layer consisted of nodes indicating the status of the system: normal or defective, with classification of faults and severity levels. Two hidden layers with different numbers of neurons were used. Two schemes were used to develop ANNs for the separate and simultaneous detection of fault type and severity level. The ANNs were trained using a back-propagation algorithm with the normalized set of extracted features for known conditions. The ANNs were tested using the data of simulated test faults of both trained and novel types. The diagnostic system detected the fault type and severity level quite accurately in both schemes. The reduced number of inputs lead to faster training, requiring far fewer iterations compared with the case of using the entire time response curve.
Robust model reference control for multivariable linear systems subject to parameter uncertainties
Authors: Duan G R , Liu W Q , Liu G P
Published: October 2002

Robust model reference control for multivariable linear systems with structural parameter uncertainties is considered. It is shown that the problem can be decomposed into two subproblems: a robust state feedback stabilization problem for multivariable linear systems subject to parameter uncertainties and a robust compensation problem. The latter concerns solution of three coefficient matrices such that four matrix equations are met and, simultaneously, the effect of the uncertainties to the tracking error is minimized. Based on a complete parametric solution to a class of generalized Sylvester matrix equations, the robust compensation problem is turned into a minimization problem with quadratic cost and linear constraints. A set of linear equations is derived that determines the optimal solution to the minimization. An example illustrates the application of the proposed approach.
Non-linear control design for a boost converter using bond graphs
Authors: Lin-Shi X , Retif J-M , Allard B , Morel H
Published: October 2002

The bond graph technique is applied to model a boost converter in order to derive an averaged model. The obtained averaged model is non-ideal as it takes into account most of the converter non-linearities introduced by power semiconductor devices. An ideal averaged model of the converter can be deduced easily for computing a non-linear control law in a real-time control context. The current-mode control of the boost converter is considered. The zero dynamics are studied by both classical theory and the bond graph approach. A modified version of a conventional nonlinear control law is proposed in order to improve the dynamic behaviour and to reduce the sensitivity to control model errors. The non-ideal averaged model is used firstly for simulation analyses of the proposed control law and then for comparison with experimental results.
The static and dynamic characteristics of a pressure relief valve with a proportional solenoid-controlled pilot stage
Authors: Maiti R , Saha R , Watton J
Published: October 2002

The steady state and dynamic characteristics of a two-stage pressure relief valve with proportional solenoid control of the pilot stage is studied theoretically as well as experimentally. The mathematical model is studied within the MATLAB-SIMULINK environment and the non-linearities have been considered via the use of appropriate SIMULINK blocks. The detailed modelling has resulted in a good comparison between simulation and measurement, albeit assumptions had to be made regarding the solenoid dynamic characteristic based upon practical experience. The use of this characteristic combined with additional dynamic terms not previously considered allows new estimations of internal characteristics to be made such as the damping flowrate. The overall dynamic behaviour has been shown to be dominated by the solenoid characteristic relating force to applied voltage.
System identification and predictive control of laser marking of ceramic materials using artificial neural networks
Authors: Peligrad A A , Zhou E , Morton D , Li L
Published: October 2002

Laser marking of ceramic materials is a multivariable non-linear process. Real-time control of the process requires the understanding of system dynamics and parameter interaction. In this work, direct inverse control (DIC) and non-linear predictive control (NPC) based on artificial neural networks were applied. The output variable considered for the laser clay tile-marking process was melt pool temperature. The input quantities investigated were laser power and traverse speed. The results show that the NPC accomplished a better reference tracking than the DIC. It was also found that the beam velocity and laser power could well be used to counteract disturbances.
Robust eigenstructure assignment using the genetic algorithm and constrained state feedback
Authors: Clarke T , Davies R
Published: October 2002

This paper describes a robust eigenstructure assignment methodology for a constrained state feedback problem. The method, which is based upon the linear quadratic regulator and involves the minimization, via the genetic algorithm, of a multiobjective cost function, is applied to L1011 Tristar aircraft lateral dynamics. The design example generates a fixed-gain state feedback solution which shows independent phase margins of 51· in each channel, while exhibiting an eigenstructure close to that desired, lying well within specified handling quality requirements. If two states are made unavailable for feedback, the robustness properties are seriously eroded. When a dynamic feedback compensator is then used, there is a substantial recovery of the robustness. It is concluded that the genetic algorithm approach described here is easy to use and generates good multivariable stability margins.
A comparison of linear discrete-time design methods for servosystem control
Authors: Plummer A R
Published: October 2002

Three linear discrete-time model-based controller design techniques are compared: pole placement, linear quadratic Gaussian (LQG) and H∞ control. It is shown that design choices can be made for all three controllers by considering the effect on the sensitivity functions of the closed-loop system. Also all three controllers can be implemented using an identical controller structure. A comparative study of the application of the techniques to an electromechanical servosystem is made. The controllers are designed from a discrete-time plant model estimated from experimental data, and a polynomial-based solution method is used in each case. It is concluded that acceptable performance can be achieved using any of the controllers if informed design choices are made.