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The application of linear optimal control theory to the design of active automotive suspensions / Nadjib Louam 

Public ISBD Titre : The application of linear optimal control theory to the design of active automotive suspensions Type de document : texte imprimé Auteurs : Nadjib Louam, Auteur ; D. A. Wilson, Directeur de thèse ; R. Sharp, Directeur de thèse Editeur : University of Leeds Année de publication : 1990 Importance : 161 f. Présentation : ill. Format : 27 cm. Note générale : Thèse de Doctorat : Electronique : Angleterre, University of Leeds: 1990 Bibliogr. f. 162 - 165 . Annexe: [20] f Langues : Anglais (eng) Mots-clés : Linear  optimal  control  theory Suspension  systems Automobiles Half-car  model  problem Correlation Optimal  control Discrete  regulator  framework Computer  simulation Index. décimale : D001690 Résumé : In the present work, linear optimal control theory is applied to the design of active supension systems for automobiles. Most of the effort is directed towards the case of the half-car model problem in which the correlation between front and rear wheel inputs is taken into consideration. Particular attention is focussed on the difference between the optimal correlated and uncorrelated cases. To this end, rigorous mathematical developments are considered. An optimal control law for a vehicle suspension is developed using a discrete regulator framework. The time delay between the disturbance due to the road at the leading and trailing wheels is incorporated, without approximation, into the model. The control law derived for the optimal correlated problem requires information gathered at the leading wheel. The superiority of this solution over the suboptimal one, which does not incorporate leading wheel information, is clearly confirmed by the computer simulation. To enhance the performance of active suspension systems, under preview of the road, the application of linear optimal control theory is also considered. The vehicle model with completely général inputs to front and rear wheels is set up as an optimization problem and it is converted to standard form by a state variable transformation. It is shown that the solution for the optimal tracking problem over a finite time interval is not of practical use, because it requires knowledge of the road surface over the whole journey time, whereas for a preview control scheme, a sensor mounted on a car in motion would provide a continuously moving window of road surface data. By combining linear optimal theory with ideas for the overtaking optimality method, control laws for both infinite and finite preview problems are produced. The solution obtained in this framework utilizes road surface data in precisely the format which would be available from a preview sensor. The discrete time version of this solution is also examined. In the absence of limitations on either processing or actuator speeds, the value of preview in enhancing quarter and half-car suspension performances is assessed as a function of preview time and the simulation results show clear benefits are possible when the future road information is included. The application of linear optimal control theory to the design of active automotive suspensions [texte imprimé] / Nadjib Louam, Auteur ; D. A. Wilson, Directeur de thèse ; R. Sharp, Directeur de thèse . - [S.l.] : University of Leeds, 1990 . - 161 f. : ill. ; 27 cm. Thèse de Doctorat : Electronique : Angleterre, University of Leeds: 1990 Bibliogr. f. 162 - 165 . Annexe: [20] f Langues : Anglais (eng) Mots-clés : Linear  optimal  control  theory Suspension  systems Automobiles Half-car  model  problem Correlation Optimal  control Discrete  regulator  framework Computer  simulation Index. décimale : D001690 Résumé : In the present work, linear optimal control theory is applied to the design of active supension systems for automobiles. Most of the effort is directed towards the case of the half-car model problem in which the correlation between front and rear wheel inputs is taken into consideration. Particular attention is focussed on the difference between the optimal correlated and uncorrelated cases. To this end, rigorous mathematical developments are considered. An optimal control law for a vehicle suspension is developed using a discrete regulator framework. The time delay between the disturbance due to the road at the leading and trailing wheels is incorporated, without approximation, into the model. The control law derived for the optimal correlated problem requires information gathered at the leading wheel. The superiority of this solution over the suboptimal one, which does not incorporate leading wheel information, is clearly confirmed by the computer simulation. To enhance the performance of active suspension systems, under preview of the road, the application of linear optimal control theory is also considered. The vehicle model with completely général inputs to front and rear wheels is set up as an optimization problem and it is converted to standard form by a state variable transformation. It is shown that the solution for the optimal tracking problem over a finite time interval is not of practical use, because it requires knowledge of the road surface over the whole journey time, whereas for a preview control scheme, a sensor mounted on a car in motion would provide a continuously moving window of road surface data. By combining linear optimal theory with ideas for the overtaking optimality method, control laws for both infinite and finite preview problems are produced. The solution obtained in this framework utilizes road surface data in precisely the format which would be available from a preview sensor. The discrete time version of this solution is also examined. In the absence of limitations on either processing or actuator speeds, the value of preview in enhancing quarter and half-car suspension performances is assessed as a function of preview time and the simulation results show clear benefits are possible when the future road information is included.

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Design methodologies for broadband voltage-controlled-oscillators / Chawki Ghennai 

Public ISBD Titre : Design methodologies for broadband voltage-controlled-oscillators Type de document : texte imprimé Auteurs : Chawki Ghennai, Auteur ; M. J. Howes, Directeur de thèse Editeur : University of Leeds Année de publication : 1993 Importance : 170 f. Présentation : ill. Format : 27 cm. Note générale : Thèse de Doctorat : Électronique : Angleterre, University of Leeds : 1993 Bibliogr. f. 160 - 164 . Annexe f. 171 - 173 Langues : Anglais (eng) Mots-clés : Broadband  --  voltage-controlled-oscillators Negative  resistance/conductance  technique Transferred-electron-device Computer-aided-design  program Index. décimale : D000793 Résumé : The aim of the work presented in this thesis is to establish a design strategy for broadband Voltage-Controlled-Oscillators (VCOs). The desing methodology is based on a one port negative resistance/conductance technique and an accurated charactérisation of the VCO circuit. The circuit optimisation for maximising the available tuning bandwidth concentrates on the coupling between the active device and the tuning device. Small-signal and large-signal characterisation of the active device (TED) is carried out and presented as a two terminal admittance over the desired frequency range. A suitable topology of the VCO is then chosen, taking into account the fabrication constraints due to the packages of the divices and the microwave medium. An aquivalent circuit model for the VCO is then established and experimental investigations of the tuning circuit, the output circuit and the active device are carried out over the desired frequency range. Finally, a Computer-Aided-Design program is developed for the circuit optimisation process and performance determination at small-and large-signals. Since the use of a two terminal active device is in principle straightforward in oscillator design, the Transferred-Electron-Device (TED) is used as the active device in this work. The nonlinear characterisation of the TED is accomplished by the use of a physical model based on a one-dimensional drift-diffusion description of the intrinsic device. The VCO is built on microstrip using packaged devices for both the varactor and the TED. Apart from the nonlinear admittance of the intrinsic TED, the rest of the equivalent circuit model of the VCO is described in the frequency domain. However, the evaluation of the VCO circuit performance required by the optimisation process requires fast synthesis of the microstrip circuitry and hence approximate empirical expressions are used. Both distributed and lumped elements of the equivalent circuit are treated as multi-ports. The synthesis of the VCO has demonstrated the dependence of the tuning bandwidth of the chosen configuration of the VCO on the parameters and dimensions of the coupling elements between the varactor diode and the TED. An efficient overall Computer-Aided-Design (CAD) program has been developed and the comparison between the experimental and computed results has validated the design strategy. Minor differences are thought to be due to uncertainties in the values of the equivalent circuit elements of the device packages. Design methodologies for broadband voltage-controlled-oscillators [texte imprimé] / Chawki Ghennai, Auteur ; M. J. Howes, Directeur de thèse . - [S.l.] : University of Leeds, 1993 . - 170 f. : ill. ; 27 cm. Thèse de Doctorat : Électronique : Angleterre, University of Leeds : 1993 Bibliogr. f. 160 - 164 . Annexe f. 171 - 173 Langues : Anglais (eng) Mots-clés : Broadband  --  voltage-controlled-oscillators Negative  resistance/conductance  technique Transferred-electron-device Computer-aided-design  program Index. décimale : D000793 Résumé : The aim of the work presented in this thesis is to establish a design strategy for broadband Voltage-Controlled-Oscillators (VCOs). The desing methodology is based on a one port negative resistance/conductance technique and an accurated charactérisation of the VCO circuit. The circuit optimisation for maximising the available tuning bandwidth concentrates on the coupling between the active device and the tuning device. Small-signal and large-signal characterisation of the active device (TED) is carried out and presented as a two terminal admittance over the desired frequency range. A suitable topology of the VCO is then chosen, taking into account the fabrication constraints due to the packages of the divices and the microwave medium. An aquivalent circuit model for the VCO is then established and experimental investigations of the tuning circuit, the output circuit and the active device are carried out over the desired frequency range. Finally, a Computer-Aided-Design program is developed for the circuit optimisation process and performance determination at small-and large-signals. Since the use of a two terminal active device is in principle straightforward in oscillator design, the Transferred-Electron-Device (TED) is used as the active device in this work. The nonlinear characterisation of the TED is accomplished by the use of a physical model based on a one-dimensional drift-diffusion description of the intrinsic device. The VCO is built on microstrip using packaged devices for both the varactor and the TED. Apart from the nonlinear admittance of the intrinsic TED, the rest of the equivalent circuit model of the VCO is described in the frequency domain. However, the evaluation of the VCO circuit performance required by the optimisation process requires fast synthesis of the microstrip circuitry and hence approximate empirical expressions are used. Both distributed and lumped elements of the equivalent circuit are treated as multi-ports. The synthesis of the VCO has demonstrated the dependence of the tuning bandwidth of the chosen configuration of the VCO on the parameters and dimensions of the coupling elements between the varactor diode and the TED. An efficient overall Computer-Aided-Design (CAD) program has been developed and the comparison between the experimental and computed results has validated the design strategy. Minor differences are thought to be due to uncertainties in the values of the equivalent circuit elements of the device packages.

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Beneficiation of Algerian phosphate tailings by electrostatic methods / Ould Hamou, Malek 

Public ISBD Titre : Beneficiation of Algerian phosphate tailings by electrostatic methods Type de document : texte imprimé Auteurs : Ould Hamou, Malek, Auteur ; P. A. Young, Directeur de thèse Editeur : University of Leeds Année de publication : 1990 Importance : 182 f. Présentation : ill. Format : 30 cm. Note générale : Thèse de Doctorat : Génie Minier : Royaume-Uni, University of Leeds : 1990 Bibliogr. f. 183 - 189 . Annexe f. 190 - 193 Langues : Anglais (eng) Mots-clés : Phosphate  tailings Electrodynamic  separator Pneumatic  separation Djebel-onk  tailings Algeria Mineralogical  analysis Index. décimale : D001390 Résumé : With the increased demand for phosphates in fertilizer and other industries and the decreased availability of high grade ores in many parts of the world, beneficiation of low phosphate ores and tailings may be needed. A phosphate tailings sample from Algeria was investigated with the emphasis on beneficiation by dry methods. In the present study, an electrodynamic separator has been used and its working parameters considered. Particular attention has been paid to comminution and to phosphate grade and recovery as a function of size analysis. Initial studies have shown that separation in terms of mineralogical constituents is poor. Adapting the electrodynamic separator to sizing is possible and separation by "electrodynamic size analysis" is compared with pneumatic separation - in terms, that is, of the upgrading - of Djebel-Onk tailings. Mineralogical analysis indicated that undesirable impurities are scattered in the phosphate matrix, therefore, giving a narrow option to any physical process. Relatively good results have been achieved in electrodynamic sizing at low voltages. Two stages of separation with an intermediate recrushing upgraded the feed material from 22.7 to 26.75 % P₂O₅ at 47.1 % recovery, and there is a possibility that this concentrate could be blended into higher grade products. Beneficiation of Algerian phosphate tailings by electrostatic methods [texte imprimé] / Ould Hamou, Malek, Auteur ; P. A. Young, Directeur de thèse . - [S.l.] : University of Leeds, 1990 . - 182 f. : ill. ; 30 cm. Thèse de Doctorat : Génie Minier : Royaume-Uni, University of Leeds : 1990 Bibliogr. f. 183 - 189 . Annexe f. 190 - 193 Langues : Anglais (eng) Mots-clés : Phosphate  tailings Electrodynamic  separator Pneumatic  separation Djebel-onk  tailings Algeria Mineralogical  analysis Index. décimale : D001390 Résumé : With the increased demand for phosphates in fertilizer and other industries and the decreased availability of high grade ores in many parts of the world, beneficiation of low phosphate ores and tailings may be needed. A phosphate tailings sample from Algeria was investigated with the emphasis on beneficiation by dry methods. In the present study, an electrodynamic separator has been used and its working parameters considered. Particular attention has been paid to comminution and to phosphate grade and recovery as a function of size analysis. Initial studies have shown that separation in terms of mineralogical constituents is poor. Adapting the electrodynamic separator to sizing is possible and separation by "electrodynamic size analysis" is compared with pneumatic separation - in terms, that is, of the upgrading - of Djebel-Onk tailings. Mineralogical analysis indicated that undesirable impurities are scattered in the phosphate matrix, therefore, giving a narrow option to any physical process. Relatively good results have been achieved in electrodynamic sizing at low voltages. Two stages of separation with an intermediate recrushing upgraded the feed material from 22.7 to 26.75 % P₂O₅ at 47.1 % recovery, and there is a possibility that this concentrate could be blended into higher grade products.

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Studies of transition in taylor-couette flow using hot wire anemometry and on-line computation / S. Benmansour 

Public ISBD Titre : Studies of transition in taylor-couette flow using hot wire anemometry and on-line computation Type de document : texte imprimé Auteurs : S. Benmansour, Auteur ; F. R. Mobbs, Directeur de thèse Editeur : University of Leeds Année de publication : 1984 Importance : 330 f. Présentation : ill. Format : 30 cm. Note générale : Thèse de Doctorat : Mechanical Engineering : Royaume-Uni, University of Leeds : 1984 Bibliogr. f. 331 - 342 . Annexe f. 343 - 379 Langues : Anglais (eng) Index. décimale : D003584 Résumé : The phenomenon of Taylor vortex flow is particularly suitable for the study of hydrodynamic stability and its relationship to transition to turbulence. It is of considerable academic interest as well as occurring in practical engineering situations. Various techniques have been used to investigate the instability and subsequent behaviour of the flow between rotating concentric cylinders. Hot wire anemometry, in conjunction with on-line computation, was employed in the present work to determine the frequencies and wave numbers associated with wavy Taylor vortex flow using spectral analysis, for the case of a stationary outer cylinder and rotating inner cylinder. As the speed of the inner cylinder was gradually increased, the flow was seen to exhibit various complex transitions in the range of Taylor number covered, which was up to 600 Tc. A literature survey showed extensive research into Taylor vortex flow using many different methods of investigation. The results reveal discrepancies in some cases due partly to the many parameters involved and to the different geometry of the rigs used. In the present work, we have assessed the influence of the aspect ratio and radius ratio on the transitions and compared the results with other workers' findings. The experiments were conducted at three positions in the gap, namely 0.18 d, mid.gap and 0.81 d from the inner cylinder. The aspect ratio was varied from 35 to 20 for the two values of radius ratio considered (i.e. n = 0.713 and 0.497). The general trends of the results revealed similar behaviour in terms of frequency bands for the three probe positions in the gap and for all the aspect ratios considered, but wave number changes were the most outstanding feature of the flow which were reflected in relative wave speed changes. The axial wave length was also seen to play an important role in determining the onset of waviness and the value of the wave frequencies. Studies of transition in taylor-couette flow using hot wire anemometry and on-line computation [texte imprimé] / S. Benmansour, Auteur ; F. R. Mobbs, Directeur de thèse . - [S.l.] : University of Leeds, 1984 . - 330 f. : ill. ; 30 cm. Thèse de Doctorat : Mechanical Engineering : Royaume-Uni, University of Leeds : 1984 Bibliogr. f. 331 - 342 . Annexe f. 343 - 379 Langues : Anglais (eng) Index. décimale : D003584 Résumé : The phenomenon of Taylor vortex flow is particularly suitable for the study of hydrodynamic stability and its relationship to transition to turbulence. It is of considerable academic interest as well as occurring in practical engineering situations. Various techniques have been used to investigate the instability and subsequent behaviour of the flow between rotating concentric cylinders. Hot wire anemometry, in conjunction with on-line computation, was employed in the present work to determine the frequencies and wave numbers associated with wavy Taylor vortex flow using spectral analysis, for the case of a stationary outer cylinder and rotating inner cylinder. As the speed of the inner cylinder was gradually increased, the flow was seen to exhibit various complex transitions in the range of Taylor number covered, which was up to 600 Tc. A literature survey showed extensive research into Taylor vortex flow using many different methods of investigation. The results reveal discrepancies in some cases due partly to the many parameters involved and to the different geometry of the rigs used. In the present work, we have assessed the influence of the aspect ratio and radius ratio on the transitions and compared the results with other workers' findings. The experiments were conducted at three positions in the gap, namely 0.18 d, mid.gap and 0.81 d from the inner cylinder. The aspect ratio was varied from 35 to 20 for the two values of radius ratio considered (i.e. n = 0.713 and 0.497). The general trends of the results revealed similar behaviour in terms of frequency bands for the three probe positions in the gap and for all the aspect ratios considered, but wave number changes were the most outstanding feature of the flow which were reflected in relative wave speed changes. The axial wave length was also seen to play an important role in determining the onset of waviness and the value of the wave frequencies.

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