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1 
A novel feedback design method for mimo QFT with application to the X29 flight control problemLan, ChenYang 15 May 2009 (has links)
Quantitative Feedback Theory (QFT) method employs a two degree of freedom
control configuration that includes a feedback controller and a prefilter in the feedforward
path. When applied to multiinput multioutput (MIMO) systems, the QFT
method calls for a special decomposition of the MIMO system. Specifically, the MIMO
system is decomposed into multiple multiinput singleoutput (MISO) equivalent
systems, and is followed by the singleinput singleoutput (SISO) QFT design of each
equivalent system. Depending on polezero structure of the equivalent SISO plants so
obtained, the QFT design may become unnecessarily difficult/conservative or even
infeasible. This situation is especially true for linear time invariant (LTI) systems with
nonminimum phase (NMP) zero(s) and unstable pole(s).
This unnecessary design difficulty and the challenge of dealing with MIMO
systems that have unstable poles and NMP transmission zeros in undesirable locations,
when MIMO QFT is considered, is investigated and addressed in this research. A new
MIMO QFT design methodology was developed using the generalized formulation. The
key idea of the generalized formulation is to utilize appropriate modifications at the plant input and/or the output to obtain a better conditioned plant that in turn can be used to
execute a standard MIMO QFT design. The formulation is based on a more general
control structure, where input and output transfer function matrices (TFM) are included
to provide additional degrees of freedom in the typical decentralised MIMO QFT
feedback structure, which facilitates the exploitation of directions in MIMO QFT
designs. The formulation captures existing design approaches for a fully populated
MIMO QFT controller design and provides for a directional design logic involving the
plant and controller alignment and the directional properties of their multivariable poles
and zeros. As a case in point Horowitz’s SingularG design methodology is placed in the
context of this generalized formulation, and the SingularG design for the X29 is
analysed and redesigned using both nonsequential and sequential MIMO QFT
demonstrating its utility.
The results highlight a fundamental tradeoff between multivariable controller
directions for stability and performance in classically formulated MIMO QFT design
methodologies, which elucidate the properties of SingularG designed controllers for the
X29 and validate the developed new MIMO QFT design method.

2 
Quantum Spacetime from QM and QFTMuch, Albert 26 July 2013 (has links) (PDF)
The main focus of the work is the construction of a quantum spacetime emerging from theory.

3 
Vertical Control of Unmanned Helicopter During Payload DropRaol, Divyarajsinh 27 February 2015 (has links)
Unmanned helicopters in recent years have gained much attention due to their potential in both civil as well as military applications. Helicopter is an inherently unstable system. As a result there is a growing need of developing a control structure that allows the helicopter to perform various applications while remaining stable throughout the flight.
This thesis presents developments of a robust controller for the vertical channel of an unmanned helicopter while carrying and dropping a payload. In addition, a simulation platform is developed in Simulink that uses a nonlinear six degree of freedom helicopter model.
Quantitative Feedback Theory, a frequency domain technique, is used to design a controller that meets specific performance criteria when uncertainties associated with different payload weights exist in the system. The controller performance is examined in simulation for an Xcell 60 helicopter for effective lifting and dropping of up to 10 lb payload. The performance is then compared with a traditional ProportionalIntegralDerivative controller. Further, the effect of actuator dynamics on the controller performance is also evaluated. Finally, a controller that is robust in minimizing the effect of actuator dynamics and the payload drop while keeping the helicopter stable in flight is designed.

4 
Hadamard subtractions for infrared singularities in quantum field theoryBurton, George Edmund C. January 2011 (has links)
Feynman graphs in perturbative quantum field theory are replete with infrared divergences caused by the presence of massless particles, however these divergences are known to cancel orderbyorder when all virtual and real contributions to a given cross section are summed and smeared against an experimental resolution. In this thesis we treat the infrared problem formally in the language of distribution theory so that we can remove the divergences with local momentum space subtractions using Hadamard's procedure. This is analogous with the BPHZ mechanism for removing UV divergences. Our aim is to show how it is possible to make both the real and virtual subtractions analytically such that we are left with manifestly finite integrands. For the virtual graphs we present a new decomposition of the integrand in momentum space and remove those terms that are divergent. For the real graphs we show how the Taylor expansion of the momentum conserving delta function allows the explicit removal of the divergent part; furthermore we show that the homogeneous properties of the soft structure greatly simplifies this procedure.

5 
Styrlagsdesign för ett instabilt stridsflygplan med hjälp av QFTDahlgren, Joacim, Gustafsson, Daniel January 2005 (has links)
<p>A modern fighter aircraft is exposed to very different flight conditions and must despite that perform infallibly in every single situation. Several variables like center of gravity, speed, altitude and weight vary during a standard mission flight or</p><p>between flights. For the aircraft to be able to perform effectively, superior manoeuvrability is vital. Hence it is of great importance that the flight control system is capable to cope with these different variations.</p><p>In the 1960s professor Isaac Horowitz presented the method Quantitative feedback theory (QFT) which is a method whose aim is to manage system variations. The method can be useful in the construction of the control system for a fighter aircraft. QFT is a frequency based method whose main objective is to shape the</p><p>open loop gain in a Nicholschart to meet the required closed loop demands. A prefilter is then applied to achieve correct reference tracking.</p><p>This thesis is divided into two parts, where the first part presents the method QFT for both the SISOsystems and for the MIMOsystems. For the MIMOsystems several design techniques are presented, the chapter also includes a method on the implementation of state feedback. Furthermore statements of how nonlinear and unstable systems are handled with the QFT is included.</p><p>The second part of the thesis presents the design of a control system for an unstable fighter aircraft. The design is constructed for the SISO longitudinal dynamics as well as for the MIMO lateral dynamics, where the design must be robust against variations in speed, altitude and center of gravity.</p><p>The flight control system that is implemented meets almost all requirements and gives good preformance and this is achieved with only a few regulators. Proposals of possible solutions to those requirements note yet reached are discusssed.</p>

6 
Synthesis of controllers for nonminimum phase and unstable systems using nonsequential MIMO quantitative feedback theoryLan, Chenyang 29 August 2005 (has links)
Considered in this thesis is multiinput multioutput (MIMO) systems with nonminimum phase (NMP) zeros and unstable poles where some of the unstable poles are located to the right of the NMP zeros. In the singleinput singleoutput (SISO) case such systems pose serious difficulties in controller synthesis for performance and stability. In spite of the added degrees of freedom the MIMO case also poses difficulties as has been shown in the stabilization of the X29 aircraft. When using the MIMO QFT technique the synthesis starts by considering a set of equivalent SISO plants derived from the plant transfer function matrix that are used to develop a controller. In effect the design problem is reduced to several MISO designs with the diagonal entries of as the equivalent SISO plants. Developed is a transformation scheme that can be used to condition the resulting equivalent SISO plants so that the difficult problem of NMP zeros lying to the left of unstable poles is avoided. Examples illustrate the use of the proposed transformation.

7 
Styrlagsdesign för ett instabilt stridsflygplan med hjälp av QFTDahlgren, Joacim, Gustafsson, Daniel January 2005 (has links)
A modern fighter aircraft is exposed to very different flight conditions and must despite that perform infallibly in every single situation. Several variables like center of gravity, speed, altitude and weight vary during a standard mission flight or between flights. For the aircraft to be able to perform effectively, superior manoeuvrability is vital. Hence it is of great importance that the flight control system is capable to cope with these different variations. In the 1960s professor Isaac Horowitz presented the method Quantitative feedback theory (QFT) which is a method whose aim is to manage system variations. The method can be useful in the construction of the control system for a fighter aircraft. QFT is a frequency based method whose main objective is to shape the open loop gain in a Nicholschart to meet the required closed loop demands. A prefilter is then applied to achieve correct reference tracking. This thesis is divided into two parts, where the first part presents the method QFT for both the SISOsystems and for the MIMOsystems. For the MIMOsystems several design techniques are presented, the chapter also includes a method on the implementation of state feedback. Furthermore statements of how nonlinear and unstable systems are handled with the QFT is included. The second part of the thesis presents the design of a control system for an unstable fighter aircraft. The design is constructed for the SISO longitudinal dynamics as well as for the MIMO lateral dynamics, where the design must be robust against variations in speed, altitude and center of gravity. The flight control system that is implemented meets almost all requirements and gives good preformance and this is achieved with only a few regulators. Proposals of possible solutions to those requirements note yet reached are discusssed.

8 
Production of bosonic molecules in the nonequilibrium dynamics of a degenerate Fermi gas across a Feshbach resonanceDobrescu, Bogdan E. 02 June 2009 (has links)
In this thesis I present a nonequilibrium quantum field theory that describes the
production of molecular dimers from a twocomponent quantumdegenerate atomic
Fermi gas, via a linear downward sweep of a magnetic field across an swave Feshbach
resonance. This problem raises interest because it is presently unclear as to why
deviations from the universal LandauZener formula for the transition probability at
twolevel crossing are observed in the experimentally measured production efficiencies.
The approach is based on evaluating realtime Green functions within the Keldysh
Schwinger formalism. The effects of quantum statistics associated with Pauli blocking
for fermions and induced emission for bosons, characteristic of particle scattering in
a quantumdegenerate manybody medium, are fully accounted for. I show that the
molecular conversion efficiency is represented by a power series in terms of a dimensionless
parameter which, in the zerotemperature limit, depends solely on the initial
gas density and the LandauZener parameter. This result reveals a hindrance of the
canonical LandauZener transition probability due to manybody effects, and presents
an explanation for the experimentally observed deviations.
A second topic treated in this thesis concerns the study of nonadiabatic transitions
in Nstate LandauZener systems. In connection to this, I provide a proof of
the conjecture put forth by Brundobler and Elser, regarding the survival probability
on the diabatic levels with maximum/minimum slope.

9 
Synthesis of controllers for nonminimum phase and unstable systems using nonsequential MIMO quantitative feedback theoryLan, Chenyang 29 August 2005 (has links)
Considered in this thesis is multiinput multioutput (MIMO) systems with nonminimum phase (NMP) zeros and unstable poles where some of the unstable poles are located to the right of the NMP zeros. In the singleinput singleoutput (SISO) case such systems pose serious difficulties in controller synthesis for performance and stability. In spite of the added degrees of freedom the MIMO case also poses difficulties as has been shown in the stabilization of the X29 aircraft. When using the MIMO QFT technique the synthesis starts by considering a set of equivalent SISO plants derived from the plant transfer function matrix that are used to develop a controller. In effect the design problem is reduced to several MISO designs with the diagonal entries of as the equivalent SISO plants. Developed is a transformation scheme that can be used to condition the resulting equivalent SISO plants so that the difficult problem of NMP zeros lying to the left of unstable poles is avoided. Examples illustrate the use of the proposed transformation.

10 
Composite Anomaly in Supergravity and String Amplitude Comparison / Autour de supergravité par l'anomalie composée et l'amplitude en théorie de cordesSasmal, Soumya 06 September 2017 (has links)
Dans ce projet de thèse, nous étudions le rôle joué par l'anomalie dû à la connexion composée dans les théories de supergravités dans l'espacetemps à huit dimensions. Ce genre d'anomalie est en effet engendrée par la structure quotient d'espace des champs moduli de la supergravité là où le nombre des supercharges posent des contraintes rigoureux. Notre accomplissement principal est de proposer des termes supplémentaires pour annuler cette anomalie dans la théorie de supergravité en huit dimensions avec seize supercharges. Ces termes, en outre, peuvent être considérés comme une manifestation des corrections provenant de la théorie de supercordes et nous montrons par des calculs explicites qu'une amplitude sur une boucle dans la théorie de cordes correspondante reproduit ces termes. Motivés par cette démonstration de la cohérence entre la supergravité et la théorie de cordes, nous proposons un seuil mathématique pour la compactification de ces théories dans huit dimensions vers six dimensions sur une sphère en présence des branes de codimension 2. Ceci est une simulation de compactification sur une surface K3 à l'aide des branes. Nous montrons que la présence d'anomalie composé ne peut être justifiée que par des branes de codimensions deux. Nous discutons la dualité entre la théorie Heterotic et la théorieF sous la lumière de 7branes et puis la compactification des supergravités de dix dimensions sur K3 en présence des 5branes. Tous cela nous ouvrent nouvelles voies pour étudier des aspects nonperturbatives de la théorie de cordes. Nous concluons avec un calcul sur deux boucles dans la théorie de cordes Heterotic de dix dimensions qui n'ont pas été beaucoup exploré dans la littérature. / We examine the structure of composite anomaly in maximal and halfmaximal supergravity theories especially in eight spacetime dimensions. The number of supercharges dictates the structure of the coset space of the moduli fields of the theory which in turn engenders the composite anomaly in such theories. Our main achievement lies in proposing counterterms for such anomalies. These terms are of stringy nature and we show by explicit 1loop amplitude calculations in corresponding string theories that those counterterms are consistently provided by string amplitude. In the light of nonperturbative higher dimensional theories like Ftheory, the anomaly cancelling counterterms are seen to be related to codimension two branes e.g. 7branes. We then use these results of 8dimensional theories to provide for supergravity theories in sixdimensions by compactifying on a sphere in the presence of 5branes. This is in fact a simulation of K3 compactification and our knowledge of composite connection provide us with threshold conditions to achieve such compactifications. All these analysis provide for greater insight into the nonperturbative regime of string theory. We then conclude with a calculation of 2loop Heterotic string amplitude which has been very less explored in the literature.

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