bluuebunny/crossref_metadata_2025 huggingface dataset:
Underfloor heating with latent heat storage
Authors: Farid M , Kong W. J.
Published: October 2002

Underfloor heating is known for its comfort due to the low and favourable temperature gradient in the heated space above the large floor area available for heating. This paper addresses the idea of improving the existing underfloor heating system by using an encapsulated phase change material (PCM) that melts and solidifies at about 28 °C, placed in the concrete floor during construction. The objective is to minimize the fluctuation in the floor surface temperature and to have sufficient heat storage so that heating can be done during the off-peak electricity period only. Two concrete slabs (0.5 m × 0.5 m × 0.095 m) were constructed with a hot water pipe embedded in both of them to provide the required heating. Nodules having a diameter of 75 mm and containing CaCl26H2O were placed in one of the concrete slabs prior to its moulding. Unlike the plain concrete slab, the concrete-PCM slab showed a much lower surface temperature fluctuation and maintained an acceptable surface temperature during the whole day even though the heating process was done for only 8 h. A simple one-dimensional model was developed to simulate the underfloor heating system, so that it can be used to optimize its design. Comparison between the measured and predicted performance of the two slabs for 3 days showed a reasonable agreement.
Effects of Reynolds and Mach numbers on the profile losses of a conventional low-pressure turbine rotor cascade with an increasing pitch-chord ratio
Authors: Coton T , Arts T , Lefèbvre M
Published: October 2002

The evolution of the pressure loss coefficient and the exit flow angle has been investigated for a conventional low pressure turbine rotor blade of Snecma-Moteurs mounted in a stationary cascade arrangement at the von Karman Institute. As the boundary layers along those airfoils could exhibit laminar characteristics over a non-negligible distance, the profile losses are directly linked to the occurrence of transition and separation. The main parameters affecting the boundary layer status are taken into account. The exit Reynolds and Mach numbers respectively range between 190000 and 680000 and between 0.6 and 0.9, the inlet free stream turbulence is 0.8 per cent. The pitch-chord ratio has also been varied from its nominal value. Although general tendencies for the loss coefficient variation with respect to each parameter have been found, it has been demonstrated that a better loss estimation needs to consider the conjunction of all these parameters. The present work also points out the weakness of the traditional correlation methods when the aerodynamic load of the blades is increased.
Numerical simulation of the flow in a boiler circulating pump
Authors: Baumgarten S , Fritz J , Knierim C , Müller T
Published: October 2002

The present report outlines the numerical simulation of the flow in a hot water circulating pump. The impeller, diffuser and spherical casing of an existing machine are simulated using different computational fluid dynamics programs. Calculation and analysis of both the individual components and their interaction as a coupled system serve as basis for step-by-step improvement. Further, the newly designed impeller is modelled together with the impeller side gap geometry to compute numerically the internal leakage losses and particularly the axial thrust during operation. The measured pump characteristic shows a significant improvement in efficiency compared with the original hydraulics, and the calculated and measured axial thrust agree well over a wide range of operating points.
Micro-hydropower: Status and prospects
Authors: Paish O
Published: October 2002

Hydropower on a small scale, or micro-hydro, is one of the most cost-effective energy technologies to be considered for rural electrification in less developed countries. It is also the main prospect for future hydro developments in Europe, where the large-scale opportunities either have been exploited already or would now be considered environmentally unacceptable. Whereas large hydro schemes often involve the construction of major dams and the flooding of whole valleys, micro-hydro is one of the most environmentally benign energy technologies available. The technology is extremely robust and systems can last for 50 years or more with little maintenance.
Application of simulated annealing to inverse design of transonic turbomachinery cascades
Authors: Tiow W. T. , Yiu K. F C. , Zangeneh M
Published: October 2002

In turbomachinery blade design, inverse methods and optimization techniques are often applied independently to produce high performance blade shapes. The idea of using an optimization algorithm to seek the optimal target distribution for an inverse design methodology has been explored. However, these efforts have been made mainly in the design of single aerofoils. In this paper, a new inverse design method is coupled with a simulated annealing algorithm to search for the optimum turbomachinery cascade shape. In order to speed up the algorithm, a database of generated designs is set up and the nearest match is selected to initialize subsequent calculation. The proposed computational procedure equips engineers with an automatic design tool with which the inverse method may be applied in isolation or combined with the optimization algorithm to produce the optimum.

The inverse methodology is based on a cell vertex, finite volume time-marching flow solver that gives the viscous cascade flow solution in both the subsonic and the transonic flow regimes. The cascade shape is computed subject to an imposed distribution of the mass-averaged tangential velocity and a specified tangential thickness profile. The solver code is validated using experimental data and the accuracy of the inverse method is verified by regenerating a known cascade geometry starting from a different one using its mass-averaged tangential velocity distribution. In combining the inverse methodology with the optimization algorithm, the mass-averaged tangential velocity distribution is parametrized using a cubic B-spline curve and the proposed simulated annealing algorithm is applied to predict the optimal distribution by minimizing loss. The overall procedure is demonstrated to produce optimum shapes of a transonic axial turbine and an axial compressor rotor.
Experimental investigation of flow and cavitation characteristics of a two-step throttle in water hydraulic valves
Authors: Liu Y. S. , Huang Y , Li Z. Y.
Published: October 2002

In hydraulic power systems with water hydraulic valves, cavitation is more likely to happen than in an oil hydraulic system. A two-step throttle, which consists of two orifices, is an effective way to avoid or reduce cavitation damage. In this research, experiments are conducted to investigate the flow-pressure and cavitation characteristics of throttles of different shapes. The working medium is tap water. A new indicator is introduced to detect cavitation inception, namely that a particular low-frequency component of the outlet pressure fluctuation of valve appears and grows rapidly when cavitation occurs. From the experimental results, it can be concluded that the two-step throttle has different features to a single-step throttle.
Worldwide use of biomass in power generation and combined heat and power schemes
Authors: Arbon I. M.
Published: October 2002

Biomass is a truly renewable, sustainable source of energy; in its firewood form, at least, it has always been humanity's primary fuel. Nevertheless, it is only in the very recent past that it has been regarded as a viable substitute in power generation for the fossil fuels that have caused most of the world's environmental pollution problems. This paper distinguishes between truly renewable, sustainable sources of fuel from agricultural sources, i.e. biomass, and the disposal of domestic, urban and hazardous waste in energy-from-waste (EfW) plants; although these differences may appear to be marginal, and any EfW plant is of value for power generation, there are particular reasons why the generation of power from genuine biomass reaps environmental benefits.

The bulk of the paper discusses the generation of electric power from a variety of different biomass substances, some from purpose-grown ‘energy crops’ but mostly from ‘agricultural residues’. While this is predominantly through conventional combustion systems with steam turbines, more recent experience of both gasification and pyrolysis, with power generation by other prime movers, such as gas turbines and reciprocating engines is also covered. The concluding section of the paper looks briefly at the relative benefits of combustion, gasification and pyrolysis and what the future is likely to hold for each of these technologies.
Off-design flow analysis of low-pressure steam turbines
Authors: Petrovic M , Riess W
Published: October 2002

In this paper, a method for flow calculation in large steam turbines is presented. The method is based on the through-flow theory and the finite element procedure. It includes some extensions and improvements in the form of a new combination of loss correlation, radial distribution of losses and spanwise mixing, a new procedure for density calculation and an extension to encompass reverse meridional flow. The method is applied to the LP (low-pressure) part of a 165 MW steam turbine for which the flow field and performance over a wide range of mass flow and input pressure are calculated. The flow at far off-design loads, at which flow reversal behind the last stage occurs, and the last stage changes to ventilation are especially analysed. The comparison of numerical results with experimental data shows good correspondence.
Diffusion rate influences on inter-turbine diffusers
Authors: Norris G , Dominy R G
Published: October 2002

Inter-turbine diffusers are becoming of increasing importance to the aero gas turbine designer to diffuse the flow between the HP (high-pressure) or IP (intermediate-pressure) turbine and the LP (low-pressure) turbine. Diffusing the flow upstream of the LP turbine and raising the mean passage radius increases stage efficiency. These inter-turbine diffusers, which have high curvature, S-shaped geometry and low-energy wakes created by the upstream turbine, together give rise to secondary flows, making the flow fully three-dimensional. Using both experimental measurements and CFD (computational fluid dynamics) predictions, this paper demonstrates how the secondary flow behaviour is controlled by both the duct diffusion rate and upstream wake intensity.
Experimental and numerical investigation on flow and heat transfer in large-scale, turbine cooling, representative, rib-roughened channels
Authors: Arts T , Rau G , Çakan M , Vialonga J , Fernandez D , Tarnowski F , Laroche E
Published: October 2002

This paper deals with the application of a three-dimensional Navier-Stokes solver for the prediction of steady viscous compressible flow and heat transfer in a square channel with one rib-roughened wall. The computation results are compared with detailed experiments carried out at the von Karman Institute.

The two-dimensional computations agree rather well with the experiments for the prediction of the aerodynamics, even if the recirculation length is overestimated. In this case, a k-l turbulence model seems to be sufficient. However, heat transfer between the ribs is poorly matched except when a thermal ASM (algebraic stress model) turbulence model (GGDH, or generalized gradient diffusion hypothesis), which computes the u iθ (velocity-temperature) correlations by algebraic equations, is used.

The three-dimensional computations capture the correct position of the reattachment point with the k-l turbulence model. It is nevertheless necessary to use the ASM turbulence model to find vortices turning the correct way in the cross-sections. These are indeed secondary flows of the second kind which are mainly due to turbulence anisotropy when the ribs are inclined at 90° to the flow direction.
United States high-level radioactive waste management programme: Current status and plans
Authors: Richardson J A
Published: October 2002

Commercial reactor nuclear power generation in the United States is produced by 107 units and, during 1996, represented over 21 per cent of the nation's electricity generation in 34 of the 50 states and, through electric power wheeling, between states in most of the 48 contiguous states. Spent fuel is stored in fuel pools at 70 sites around the country and the projected rate of spent fuel production indicates that the current pool storage will be exceeded in the out years of 2000, 2010 and 2020 at 40, 67 and 69 of these sites respectively. The total accumulation projected by the end of 1996 at reactor sites is 33 700 metric tons of heavy metal (MTHM), with projections for increasing accumulations at annual rates of between 1800 and 2000 to produce an end of life for all commercial nuclear reactors of about 86 000 MTHM.

There are presently eight facilities in six states with out-of-pool dry storage amounting to 1010 MTHM and this dry storage demand will increase. Based on all current commercial reactors achieving their 40 year licensed operation lifetimes, the dry storage needs will increase to 3128 MTHM at 28 sites and 20 states by 2000 and 11 307 MTHM at 58 sites in 32 states by 2010; the year 2010 is the present scheduled operation date for the federal mined geological disposal repository being characterized by the USDOE at Yucca Mountain, Nevada.

The enabling statute for the federal high-level radioactive waste management programme is the 1982 Nuclear Waste Policy Act (NWPA) which charges the USDOE with the responsibility for the disposal of HLW and spent nuclear fuel. The Act also charges the utilities with the responsibility for managing their spent nuclear fuel until the USDOE can accept it into the federal waste management system. The funding for the federal programme is also stipulated by the Act with the creation of the Nuclear Waste Fund, through which the electric utilities entered into contract with the USDOE by payment of a fee of 1 mill per kilowatt hour sold and for which the USDOE would start collection of spent fuel from the reactor sites starting 31 January 1998.
A critical analysis of the thermodynamic advantages of reheat in gas turbines
Authors: Crane R I
Published: October 2002

Apparently conflicting ideas on the effects of reheat on gas turbine performance can be obtained when comparing thermodynamics textbook treatments with recent literature on the new generation of reheat machines. These are resolved through the use of models with varying degrees of realism. The models are built with ‘live mathematics’ software which makes it straightforward to incorporate additional irreversibilities and less-simplified gas property relationships, and can be more effective than algebraic analyses for demonstrating the effect of cycle parameters. It is shown how the sign of the change in overall efficiency due to reheat depends on pressure and temperature ratios and on compressor and turbine efficiencies, and why a high compressor pressure ratio is beneficial. The trade-off between gains in specific net work and efficiency, by selection of the reheating pressure, is illustrated, the current relevance of the value that maximizes net work, traditionally termed ‘optimum’, is questioned and it is demonstrated that an exhaust temperature suitable for combined cycle operation requires a higher reheating pressure. Further results show how fuel consumption and gross power are divided between high- and low-pressure combustors and turbines respectively.
The research and development of the solar house in China
Authors: Qian S-Y , Ling Z-G
Published: October 2002

A brief recommendation about solar energy resources and the status of solar house research and development in China is introduced. The reasons for the slow development of an active solar house in the past is analysed. By combining with various research achievements, the passive solar house has had good advancement and applications. The demonstration transparent insulation material (TIM) solar house project in Shanghai is described as an example showing that with the development of solar material, absorbing and storage wall and air-conditioning measures, the passive and hybrid solar house has the potential to provide future wider applications in China.
Advances in laboratory tests for predicting coal-related combustion problems
Authors: Gibbins J R , Williamson J
Published: October 2002

Problems in pulverized fuel combustion in steam-raising plant that can be attributed to the nature of the coal being fired include excessive slagging and fouling, poor char burnout, NOx emissions and flame stability. Coal performance in these areas can, to some extent, be related to the results from existing coal characterization tests but, particularly for coals from unfamiliar areas, these correlations may be unreliable and misleading. For example, attempts to relate slagging propensity to the chemical composition of the coal ash have met with only limited success. It now seems clear that empirical indices and viscosity measurements do not reflect the complex mineral interactions that occur during combustion. However, new microanalysis techniques, capable of characterizing the distribution of mineral matter in a pulverized fuel (PF), now appear likely to provide an improved assessment of the slagging propensity of a coal.

Other factors, such as coal volatile yield and nitrogen release, are quite sensitive to the heating conditions. Laboratory tests which match PF combustion conditions much more closely than existing standard methods are now being developed. New approaches to predicting char burnout, by better identification of the small subset of the coal which is actually causing the problem, are also under investigation.

While not a general panacea, the appropriate use of new tests is likely to offer engineers involved in coal procurement, who face an increasingly complex market, improved methods for evaluating coals before embarking on expensive pilot- or full-scale trials.
Numerical simulation of the effect of a moving wall on separation of flow past a symmetrical aerofoil
Authors: Chew Y T , Pan L S , Lee T S
Published: October 2002

This paper applies the numerical simulation technique based on the generalized conservation of circulation (GCC) method to investigate the effects of a leading-edge rotating circular cylinder on the suppression of stall flow past a symmetrical Joukowski aerofoil. The variables investigated were the angle of attack α and the ratio of the surface velocity of the cylinder to freestream velocity, CU. The Reynolds number based on chord length is 1.43 × 105. It was found that the separation point on the upper surface of the aerofoil shifts downstream with increasing CU and stall flow can be significantly suppressed even at α up to 30° when CU = 4. The lift coefficient CL increases and the drag coefficient Cd decreases with increasing CU and the optimum CL/ Cd occurs at α=80°. The maximum CL/ Cd obtained is about 60 at CU = 4.
A new analysis of recuperative gas turbine cycles
Authors: Cai R
Published: October 2002

It is shown that the classical recuperator effectiveness is not an appropriate evaluation criterion for the gas turbine recuperator or a suitable independent thermodynamic parameter of the recuperative gas turbine cycle. Another parameter—the average heat transfer temperature difference in the recuperator—is recommended as the new criterion instead of the recuperator effectiveness. Therefore, the original classical analysis results of the recuperative gas turbine cycle are also inappropriate and it is necessary to give a new analysis. In this paper, the analytical expressions of the simple recuperative cycle efficiency and the optimum pressure ratio based on the new criterion are derived from general simplified assumptions. Some typical calculation results are also presented. With this new criterion, the optimum pressure ratio values for efficiency of a simple recuperative gas turbine cycle do not vary very much with the temperature ratio and are approximately equal to 3, much lower than the figures generally recognized before. A similar analysis for the recuperative gas turbine cycle with intercooler and reheater and an analysis ensuring approximately constant recuperator heat transfer area per unit power output are given also.
Performance and pressure distribution changes in a centrifugal pump under two-phase flow
Authors: Pak E T , Lee J C
Published: October 2002

Pump performance characteristics change drastically under two-phase flow conditions from those of single-phase flow. This is due to a change in flow characteristics in the impeller. Owing to a positive pressure gradient the air bubble moves more slowly than the water in the impeller channel, but in the suction surface region of the impeller inlet, where a negative pressure gradient prevails, the bubbles move more quickly than the water. Thus, in the space just after this region the distributions of the void fraction obtained are considerably higher and uneven. The change in the pressure distribution owing to air admission is also particularly evident in the inlet region of the impeller. These changes bring about an alteration of the whole flow pattern in the impeller and also cause a drop in pump performance. The Reynolds-averaged Navier-Stokes equations for two-phase flow in a centrifugal pump impeller are solved using a finite volume method to obtain the pressure, velocities and void fraction respectively. Good agreement is achieved when the predicted results are compared with those measured experimentally within the range of bubbly flow conditions.
Computer aided study of the transient performances of a highly rated sequentially turbocharged marine diesel engine
Authors: Tauzia X , Hetet J F , Chesse P , Crosshans G , Mouillard L
Published: October 2002

The sequential turbocharging technique described in this paper leads to an improvement in the operations of highly rated diesel engines, in particular at part loads (better air admission). However, transient phases such as a switch from one turbocharger to two turbochargers can be difficult, mainly because of the inertia of the turbochargers. In order to simulate the dynamics of turbocharged diesel engines, the SELENDIA software has been extended. When applied to two different engines (12 and 16 cylinders), the program shows good agreement with the experimental data. Moreover, the compressor surge has been investigated during faulty switch processes. The software has then been used for predictive studies to evaluate the possibility of adapting sequential turbocharging to a 20-cylinder engine and to calibrate the optimum switching conditions (air and gas valve opening timing).
Modelling vehicle emissions using the TEMIS program: Part 2: Case studies
Authors: Saleh W , Nelson J D
Published: October 2002

Many challenges are associated with the ever increasing level of energy consumption and the damage to the environment caused by the pollutants from all sectors, On the local level the problem is associated with matters such as noise and air pollution, while on the global level the problems are associated with acid rain, ozone layer depletion and the greenhouse effect (global warming). The transport sector is a major contributor in this respect. The use of appropriate decision-making tools to assist in the assessment of alternative transport policies is required urgently. One such tool is the TEMIS program which was described in Part 1 of this investigation, where the methodology for the enhancement of TEMIS was reported. The enhanced version of TEMIS has subsequently been used to model the effects of different transport scenarios in order to improve future fuel economy and the adverse effects of air emissions as well as the greenhouse gases. In the present paper, three main case studies have been considered to test the effect of different scenarios (in terms of alternative fuels and technical advances) on energy consumption and emissions: firstly, the switch to alternative fuels, through investigating the effects of switching from petrol to diesel, secondly, the effects of switching from diesel to bio-diesel (for buses) and, finally, the effects of technical advances (three-way catalytic converters) and the effects on fuel consumption and emissions are considered.
Evaluation of the instantaneous unsteady heat transfer in a rapid compression-expansion machine
Authors: Chen K , Karim G A
Published: October 2002

Investigation is made of the instantaneous unsteady heat transfer within a pneumatically driven rapid compression-expansion machine that offers simple, well-controlled and known boundary conditions. Values of the instantaneous apparent overall heat flux from the cylinder gas to the wall surfaces were calculated using a thermodynamic analysis of the experimentally measured pressure and volume temporal development. Corresponding heat flux values were also estimated through the application of a three-dimensional computational fluid dynamics code, KIVA3. Correlation of the derived data using the mean piston speed and cylinder bore diameter as the characteristic parameters for the Reynolds and the Nusselt numbers resulted in Nu = 0.010 × Re1.188 for all compression ratios (8.4–24.3).

Correlation of the derived data when using the instantaneous height between the piston top and the cylinder head, the maximum gas velocity and the kinetic mean gas velocity obtained when using the KIVA3 code as the characteristic parameters for the Reynolds and the Nusselt numbers was found to produce values of the Nusselt number that were almost independent of the corresponding calculated values of the Reynolds number during the major part of the compression and expansion strokes. A power relationship between the cylinder pressure and gas temperature and the apparent heat transfer coefficient was demonstrated.
The effects of the outlet area and the location of the main power supply unit on the cooling capability through naturally air-cooled electronic equipment casings
Authors: Ishizuka M
Published: October 2002

This paper describes a practical thermal design approach to natural air-cooled electronic equipment casings. A set of simplified equations for the thermal design of natural air-cooled electronic equipment casings has been proposed. The proposed set of equations satisfied the demand of practical air-cooling systems, since it takes account of factors such as the stack effect, the air flow resistance and the heat transfer due to natural convection. The effects of the outlet area and the location of the main power supply unit on the natural cooling capability of electronic equipment casings were studied using a set of equations. The results have shown that a uniform temperature distribution could be achieved when the main power supply unit was placed at the bottom of the casing. It has also been suggested that the value of the heat removed from the casing surface could be more significant than that from the outlet vent in the thermal design of natural air-cooled electronic equipment casings.
Fuel cell bus operation at high altitude
Authors: Spiegel R. J. , Gilchrist T , House D. E.
Published: October 2002

In an effort both to address air quality problems relating to vehicle emissions in Mexico City and to ascertain the effects of the environment (air pollution and high altitude) on the operating characteristics of fuel cell powered vehicles, a seminar/exposition and a demonstration on clean vehicles were held in Mexico City in June 1997. The seminar and exposition addressed the state of the art of several clean vehicle technologies, including one of the most promising: the proton exchange membrane (PEM) fuel cell engine. The demonstration consisted of the display and operation of the world's first full-size, zero emission, PEM fuel cell powered transit bus, which was built by Ballard Power Systems. This paper describes the bus performance in the atmospheric environment of Mexico City.
Managing risk—achieving the balance for Magnox reactors
Authors: Freeman R. I. , Taylor R. H. , Gibson G. P. , Bishton J. C.
Published: October 2002

The paper outlines how the safety principles involved in the design of Magnox Electric's nuclear power plants have evolved over 30 years. It is a case study of the development of a reactor type from its initial design through a series of reviews, which led to modifications that had to be considered against the criterion of reasonable practicability. A methodology embodying the Health and Safety Executive's ‘tolerability of risk’ framework is described, which has enabled designers to make judgements regarding the reasonable practicability of practicability of particular safety improvements. The paper also describes improvements made to the human aspects of running plants and considers how the balance between engineered features and reliance upon reactor operators has altered over time.
Dust explosions at elevated pressures and their suppression
Authors: Welford G. B. , Ivatt S , Dennison G
Published: October 2002

Many of the advanced coal-based power generation technologies currently under development involve the pressurized handling and storage of feedstocks and residue. The handling of fine coal at atmospheric pressure has always presented problems associated with the risk of explosion. These problems are exacerbated at higher pressures. This paper presents the results of investigations to characterize explosions at pressure, to investigate preventative measures and to evaluate the potential for explosion suppression.
Operational safety and post-maintenance gas leak detection in GE frame 9001FA gas turbines
Authors: Farthing D. A. , Marley L , Lees J. A.
Published: October 2002

The increased use of a natural-gas-fuelled combined cycle gas turbine and combined heat and power plants in recent years has been accompanied by the practice of constructing acoustic enclosures around the gas turbines for environmental reasons. This can increase the risk of an explosion if, for any reason, there is a build-up of flammable gas within the enclosure, since there can be a range of possible ignition sources. The UK Health and Safety Executive consider gas leaks within such enclosures to be foreseeable, especially following maintenance. The paper presents a review of operational safety and a leak detection method for the inspection and testing of flanged joints within the acoustic enclosures around GE 9001FA gas turbines, providing a practical step towards minimizing the risk of explosion due to fuel leakage.
A tactile sensing surface for artificial neural network based automatic recognition of the contact force position
Authors: Brett P N , Li Z
Published: October 2002

The paper describes a new technique for data entry hardware. It is a high-level interpretation method based on the back-propagation neural network model, in which two aspects of research and development works are illustrated in detail: one is a tactile sensing surface comprising a deformable surface with optical sensing elements; the other is the data acquisition and processing model in which a neural network model, called Tactile Position Recognitron, is programmed to realize the real-time and precise recognition of a contact force position, which enables the contact position of a constant force to be determined within an accuracy less than 4 per cent of full scale in a continuous spatial resolution of 35 zones.

The device described utilizes a simple low-cost and robust mechanical design combined with software to interpret sensory data to measure the contact position of a normal force applied on a planar surface. The high-level interpretation method for this system enables automatic determination of contact position in real time.
Finite-dimensional variable structure control design for systems with a single time delay
Authors: Zheng F , Frank P M
Published: October 2002

A design method for the variable structure control of point time-delay systems is studied in this paper. The proposed switching function and variable structure controller are of finite dimension. The basic idea is to construct a finite-dimensional system which contains all the unstable poles of the original time-delay system and hence those unstable poles of the time delay system will be absorbed by the developed variable structure controller. The proposed method is applied to the stabilization of combustion in a liquid monopropellant rocket motor and satisfactory results are obtained by simulation study. Smooth dependence of the closed-loop system response on the two parameters, the pressure exponent y and time lag ∞, are shown by simulation results.
Stable observer-based controller design for robust state-feedback pole assignment
Authors: Liu G P , Duan G R , Daley S
Published: October 2002

The design of stable observer-based controllers for robust pole assignment is addressed in this paper. The stability problem of these dynamical controllers is investigated, which is often ignored during the controller design. A design formulation of stable observer controllers is presented using state-feedback pole assignment techniques. Although the design formulation is principally aimed at the design of a stable controller, the mixed sensitive function in the frequency domain is also considered to improve the robustness of the closed-loop system. This ensures that the closed-loop system has good robustness and the controller is stable.
Experimental comparison of the performance of different chain conveyor controllers
Authors: Barton A D , Lewin P L
Published: October 2002

Current control methods for chain conveyor systems in manufacturing consist almost exclusively of proportional, integral and differential (PID) control implemented using programmable logic controllers (PLC). The necessity of reducing manufacturing costs requires that the throughput of the conveyor system is increased. As the maximum accelerations allowable are strictly limited, this requires that the control accuracy is improved. This paper investigates the possibility of improving the position control of the conveyor system by replacing the PID controller with a model-based controller. Two types of model-based controller are presented and tested experimentally. By constructing a suitable performance index, the performance of the various controllers is then compared with that achieved using PID control.
The ALSTOM benchmark challenge on gasifier control
Authors: Dixon R , Pike A W , Donne M S
Published: October 2002

Integrated gasification combined cycle power plants are being developed around the world to provide environmentally clean and efficient power generation from coal. As part of the UK's Clean Coal Power Generation Group, ALSTOM (formerly GEC ALSTHOM) has undertaken a detailed feasibility study on the development of a small-scale prototype integrated plant (PIP), based on the air-blown gasification cycle. In pursuit of this goal the ALSTOM Power Technology Centre (formerly the GEC ALSTHOM Mechanical Engineering Centre) has produced a comprehensive dynamic model and control philosophy for the PIP. The gasifier is one component of the model which, being a highly coupled multi-variable system with five inputs (coal, limestone, air, steam and char extraction) and four outputs (pressure, temperature, bed mass and gas quality), has been found to be particularly difficult to control. For this reason the gasifier, together with its associated control specification, operating constraints and various disturbance characteristics, has been selected as the subject for this control challenge. This paper provides a brief background to the problem and describes the control specification and closed-loop tests to be performed.
Proportional-integral-plus (PIP) control of the ALSTOM gasifier problem
Authors: Taylor C J , McCabe A P , Young P C , Chotai A
Published: October 2002

Although it is able to exploit the full power of optimal state variable feedback within a non-minimum state-space (NMSS) setting, the proportional-integral-plus (PIP) controller is simple to implement and provides a logical extension of conventional proportional-integral and proportional-integral-derivative (PI/PID) controllers, with additional dynamic feedback and input compensators introduced automatically by the NMSS formulation of the problem when the process is of greater than first order or has appreciable pure time delays. The present paper applies the PIP methodology to the ALSTOM benchmark challenge, which takes the form of a highly coupled multi-variable linear model, representing the gasifier system of an integrated gasification combined cycle (IGCC) power plant. In particular, a straightforwardly tuned discrete-time PIP control system based on a reduced-order backward-shift model of the gasifier is found to yield good control of the benchmark, meeting most of the specified performance requirements at three different operating points.
Closed-loop neural network controlled accelerometer
Authors: Gaura E I , Rider R J , Steele N
Published: October 2002

The purpose of this paper is to present aspects of an integrated micromachined sensor-neural network transducer development. Micromachined sensors exhibit particular problems such as non-linear characteristics, manufacturing tolerances and the need for complex electronic circuitry. The novel transducer design described here, based on a mathematical model of the micromachined sensor, is aimed at improving in-service performance and facilitating design and manufacture over conventional transducers. The proposed closed-loop transducer structure incorporates two modular artificial neural networks: a compensating neural network, which performs a static mapping, and a feedback neural network, which both linearizes and demodulates the feedback signal. Simulation results to date show an excellent linearity, wide dynamic range and robustness to shocks for the proposed system. The design was approached from a control engineering perspective due to the closed-loop structure of the transducer.
Numerical and experimental investigations on a shock wave related cavitational flow
Authors: Chochia G A , Tilley D G , Nguyen-Schaefer H
Published: October 2002

Shock waves often occur in hydraulic systems, including pipes, valves and pumps due to quickly closing valves. As a result, cavitation and air-release-related bubbles are created due to local pressures in the liquid dropping below the liquid saturation pressure. The developed model, combining fluid dynamics of the flow and a numerical model of cavitation and air release, computes all flow characteristics, including the behaviour of pressure, mass flow and volumetric void fractions of vapour and air in liquid. The occurrence of the shock waves and their relation to cavitation are explained and discussed in detail. To avoid numerical oscillations and to maintain a high numerical accuracy in shock wave flows, the total variation diminishing method is applied to discretize the equation system. Furthermore, various limiters are used to prevent the numerical solutions from overshooting or undershooting. Finally, the computational results are compared with the experimental data measured on a simple pipeline terminated with a valve. This comparison shows very good agreement with the experiment.
Hydraulic locking-in spool-type valves: Tapered clearances analysis
Authors: Borghi M
Published: October 2002

The paper deals with the analysis on the influence of geometrical characteristics on the locking force acting on spools in tapered clearances exposed to decentralizing pressure drops. An estimation is presented of the different results in locking force prediction deriving from the comparison of the ‘classical’ one-dimensional approach of flow and a more complex description represented by the Reynolds equation. A sensitivity analysis on the influence of clearance geometrical parameters is performed, showing the limits of application of the one-dimensional approach. Two non-dimensional geometric variables are identified, which can be adopted to define some polynomial corrective functions correlating one-dimensional results with more reliable two-dimensional solutions. The determination of the locking force can therefore be performed by an analytical process, involving the ‘classical’ one-dimensional solution and a polynomial correction which is a simple two-variable function of the clearance geometry. In comparison with results coming from the direct solution of the Reynolds equation, the process leads to errors confined within the range of a few per cent, considering clearances in a wide dimensional range representing a large amount of couplings actually encountered in hydraulic spool valves.
Fault diagnosis for unknown non-linear systems via neural networks and its comparisons and combinations with recursive least-squares based techniques
Authors: Wang H , Noriega J R
Published: October 2002

In this paper, an algorithm for the detection and diagnosis of faults in sensors and actuators in unknown non-linear systems is presented. Firstly, the normal operation of the non-linear system is modelled via a feedforward neural network in order to produce a healthy model which is used later as a redundant relation. It is assumed that every faulty sensor or actuator can be modelled by a single parameter f. Such a parameter is defined to be f=1 when the system is healthy and 0 < f < 1 otherwise. A residual signal is evaluated from the difference of the output of the healthy model and that of the system. A simple threshold function is used to detect the faulty behaviour of the system. The estimation of f is then computed by minimizing the differences between the output of the system and that of the healthy neuro model with the help of the gradient descent rule. It has been shown that the algorithm is able to estimate the fault with large magnitude accurately. However, if the deviation of f from its healthy value is small, a linearized healthy model, together with the recursive least-squares algorithm, can be used to estimate the fault. As a result, a combination of both methods will provide a powerful technique for accurate fault diagnosis.
Non-linear system identification using an artificial immune system
Authors: Luh G-C , Cheng W-C
Published: October 2002

In this paper, a novel non-linear system identification methodology is developed employing the features of the artificial immune system. A simplified incremental approach integrated with the maximum entropy principle and an instantaneous feedback mechanism is proposed to reorganize the system's parameters simultaneously. To verify and demonstrate the effectiveness of the proposed algorithm, a simulation example on a two-link robot was studied. This algorithm can achieve robustness and efficiency in identifying complex non-linear systems. The simulation results show that the identified immune models are robust to noise and various uncertainties in the robot dynamics.
Analysis of the bond graph model of hybrid physical systems with ideal switches
Authors: Buisson J , Cormerais H , Richard P-Y
Published: October 2002

This paper deals with the modelling of hybrid physical systems. The bond graph technique is used to establish their knowledge model, based upon an ideal representation of the switches. These components are modelled either by flow or by effort sources according to their state and therefore modify the circuit topology at switching times. The paper shows the usefulness of the implicit representation to derive a unique implicit state equation with jumping parameters, to analyse the model properties, to derive an implicit state equation with nilpotency index one for each configuration and to compute the discontinuities. Also, a comparison between the chosen ideal modelling approach and the more common non-ideal approach is carried out using singular perturbations theory. After a presentation of the whole study in the most general context, its results are applied to power converters, which constitute a particular class of hybrid physical systems where switches only commutate in pairs. Finally, an example is developed.
Ideal physical element representation from reduced bond graphs
Authors: Louca L. S. , Stein J. L.
Published: October 2002

Previous research has demonstrated that bond graphs are a natural and convenient representation to implement energy-based metrics that evaluate the relative ‘value’ of energy elements in a dynamic system model. Bond graphs also provide a framework for systematically reformulating a reduced bond graph model (and thus the state equations) of the system that results from eliminating the ‘unimportant’ elements. This paper shows that bond graphs also provide a natural and convenient representation for developing a rigorous approach for interpreting the removal of ideal energy elements from the system model. For example, when a generalized inductance in the mechanical domain is eliminated from a model, the bond graph shows whether the coordinate representing the motion of the body becomes free to move (zero inertia) or fixed to ground (infinite inertia). This systematic interpretation of element removal makes bond graphs an attractive modelling language for automated model reduction techniques. An illustrative example is provided to demonstrate how the developed approach can be applied to provide the physical interpretation of energy element removal from a mechanical system.
Vibration control of a single-link flexible manipulator using command shaping techniques
Authors: Mohamed Z , Tokhi M O
Published: October 2002

This paper presents experimental investigations into the development of feed-forward control strategies for vibration control of a flexible manipulator using command shaping techniques based on input shaping and low-pass and band-stop filtering. A laboratory-scale single-link flexible manipulator is used and various system responses are obtained. Initially, an unshaped bang-bang torque input is used to determine the dynamic response parameters of the system for design and evaluation of the control techniques. Feed-forward controllers are then designed based on the natural frequencies and damping ratios of the system. Experimental results of the response of the manipulator to the shaped and filtered inputs are presented in time and frequency domains. Performances of the techniques are assessed in terms of level of vibration reduction at the natural frequencies, time response specifications, robustness to natural frequency variation and processing time. The effects of the number of impulses and filter order on the performance of the system are investigated. Finally, a comparative assessment of input shaping and filtering techniques is presented.
The identification of engineering system parameters
Authors: Whalley R , Mitchell D
Published: October 2002

A procedure enabling the identification of the mass/inertia, damping and stiffness matrices for mechanical systems or the analogous inductance, resistance and capacitance matrices for electrical, fluid or thermal systems from measured results is developed. Analytical constraints that are mandatory are defined. Illustrative examples are provided.
Analytical solution of distributed-lumped parameter network models
Authors: Whalley R , Bartlett H , Ebrahimi M
Published: October 2002

System models for distributed-lumped parameter processes are derived. Procedures leading to the Smith normal form and thereafter to the admittance matrix of these models are presented. General results for interconnected distributed-lumped parameter models are provided and a typical application study is included.