Networked Control Systems: The Communication Basics and Control Methodologies

As an emerging research field, networked control systems have shown the increasing importance and attracted more and more attention in the recent years. The integration of control and communication in networked control systems has made the design and analysis of such systems a great theoretical challenge for conventional control theory. Such an integration also makes the implementation of networked control systems a necessary intermediate step towards the final convergence of control, communication, and computation. We here introduce the basics of networked control systems and then describe the state-of-the-art research in this field. We hope such a brief tutorial can be useful to inspire further development of networked control systems in both theory and potential applications

Modern control approaches for next-generation interferometric gravitational wave detectors

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Heterogeneous and hybrid control with application in automotive systems

Control systems for automotive systems have acquired a new level of complexity. To fulfill the requirements of the controller specifications new technologies are needed. In many cases high performance and robust control cannot be provided by a simple conventional controller anymore. In this case hybrid combinations of local controllers, gain scheduled controllers and global stabilisation concepts are necessary. A considerable number of state-of-the-art automotive controllers (anti-lock brake system (ABS), electronic stabilising program (ESP)) already incorporate heterogeneous and hybrid control concepts as ad-hoc solutions. In this work a heterogeneous/hybrid control system is developed for a test vehicle in order to solve a clearly specified and relevant automotive control problem. The control system will be evaluated against a state-of-the-art conventional controller to clearly show the benefits and advantages arising from the novel approach. A multiple model-based observer/estimator for the estimation of parameters is developed to reset the parameter estimate in a conventional Lyapunov based nonlinear adaptive controller. The advantage of combining both approaches is that the performance of the controller with respect to disturbances can be improved considerably because a reduced controller gain will increase the robustness of the approach with respect to noise and unmodelled dynamics. Several alternative resetting criteria are developed based on a control Lyapunov function, such that resetting guarantees a decrease in the Lyapunov function. Since ABS systems have to operate on different possibly fast changing road surfaces the application of hybrid methodologies is apparent. Four different model based wheel slip controllers will be presented: two nonlinear approaches combined with parameter resetting, a simple linear controller that has been designed using the technique of simultaneously stabilising a set of linear plants as well as a sub-optimal linear quadratic (LQ)-controller. All wheel slip controllers operate as low level controllers in a modular structure that has been developed for the ABS problem. The controllers will be applied to a real Mercedes E-class passenger car. The vehicle is equipped with a brake-by-wire system and electromechanical brake actuators. Extensive real life tests show the benefits of the hybrid approaches in a fast changing environment

강상 페르미 기체의 상전이 동역학에서 키블-주렉 기작의 보편성

학위논문(박사)--서울대학교 대학원 :자연과학대학 물리·천문학부(물리학전공),2020. 2. 신용일.Understanding strongly correlated quantum many-body systems remains as one of the most challenging problems of modern physics. Ultracold atomic Fermi gases with strong interactions have arisen as a versatile platform where a variety of many-body phenomena can be studied owing to their favorable characteristics such as the clean environment, dynamics control, and high tunability, including the interactions, potential, and defects. This thesis concerns with three aspects: the achievement of large (10^6 atoms per spin state) strongly interacting fermionic superfluids of 6Li and two experiments with it. Standard laser cooling techniques and the sympathetic cooling by bosonic Na-23 cooled Li-6 atoms down to degeneracy, and they were subsequently brought to the strongly interacting regime by exploiting the magnetic Feshbach resonance that enables a free and precise control over the interactions via the s-wave scattering length. By an evaporative cooling in the regime, we obtained ultracold atomic Fermi superfluids of Li-6 with strong interactions at T/TF=0.1. Especially, the microscopic nature of superfluidity is dramatically but smoothly transformed from Bose-Einstein condensate (BEC) of tightly bound diatomic molecules to Bardeen-Cooper-Schrieffer (BCS) superfluid of long-range Cooper pairs across the BEC-BCS crossover. The dissipation through the nucleation of quantum vortices in a strongly interacting fermionic superfluid is investigated by measuring the critical velocity for vortex shedding as a function of the sweeping length in the BEC-BCS crossover. The large critical velocity near unitarity demonstrated the robustness of fermionic superfluidity in the regime, and our simple dissipation model explains the relation between the critical velocity and the sweeping length. The comparison between the vortex shedding critical velocity for an in nite sweeping distance and the Landau critical velocity in the crossover suggests the involvement of the pair-breaking mechanism in the vortex-shedding dynamics. The Kibble-Zurek universality in a strongly interacting Fermi superfluid is observed. The thermal quench across the normal to superfluid phase transition of a strongly interacting Fermi gas in the BEC-BCS crossover spontaneously created an unprecedentedly large number of quantized vortices by the Kibble-Zurek mechanism, where their statistics revealed di erent aspects of the mechanism. The characteristic power-law relation between the density of the created vortices and the quench rate for slow quenches showed that the Kibble-Zurek mechanism holds true in the strongly correlated regime including unitarity, and the constant exponents across the BEC-BCS crossover verified that BEC and BCS superfluids belong to the same universality class. The density deviates from the scaling and saturates for rapid quenches because of the destructive interactions among the vortices, where the saturated values in the BEC-BEC crossover reveal the coherence length of a strongly interacting fermionic superfluid in the crossover.강하게 상관된 양자 다체계 시스템을 이해하는 것은 현대물리학의 난제 중 하나로 남아있다. 강하게 상호작용하는 극저온 페르미 원자 기체는 자유로운 상호작용, 퍼텐셜 및 결점의 조절 등 높은 자유도와 깨끗한 환경, 동적 통제 등의 유리한 특성들 때문에 다양한 다체계 현상을 연구할 수 있는 다목적 플랫폼으로 부상해왔다. 이 학위논문은 3가지 측면을 다룬다: 한 스핀 상태당 10^6 개의 원자로 구성된 커다란 강하게 상호작용하는 Li-6 페르미 초유체의 구현, 그리고 이 시료를 사용한 두 가지 실험. 표준적인 레이저 냉각과 보존 Na-23를 사용한 동조냉각이 Li-6 원자들을 축퇴(degeneracy)상태까지 냉각시켰고, s-파 충돌 거리를 통해 상호작용을 자유롭게 조절하게 해주는 자성 Feshbach 공진을 이용해 냉각된 Li-6 원자들을 강하게 상호작용하는 영역으로 데려왔다. 이 영역에서 추가적인 증발냉각을 통해 우리는 T/TF=0.1 를 가지는 강하게 상호작용하는 극저온 Li-6 원자 페르미 초유체를 얻었다. 특히, 초유체성의 미시적인 근원이 BEC-BCS 교차영역을 지나면서 강하게 결합된 이원자 분자들의 보즈-아인슈타인 응집체(BEC)에서 긴 거리의 Cooper 쌍들의 BCS 초유체로 극적이지만 부드럽게 변해간다. BEC-BCS 교차영역에서 양자 소용돌이가 생성되는 임계 속도를 장애물이 움직이는 거리의 함수로 측정함으로써 강상 페르미 초유체에서 양자 소용돌이의 생성을 통한 에너지 소실을 연구했다. Unitarity 근처에서의 큰 임계 속도는 이 영역에서 페르미 초유체성이 탄탄함을 입증했고, 우리의 간단한 에너지 소실 모델은 임계 속도와 장애물이 움직인 거리 간의 관계를 설명해냈다. 무한한 거리에 대한 양자 소용돌이 생성 임계 속도와 Landau 임계 속도 간의 비교는 양자 소용돌이 생성 동역학에 쌍-부서짐(pair-breaking) 기작이 연관되어 있음을 시사한다. 강상 페르미 초유체에서 키블-주렉(Kibble-Zurek)기작의 보편성이 관측되었다. BEC-BCS 교차영역에서 강상 페르미 기체의 보통-초유체 상태 상전이를 가로지르는 열적 퀜치(quench)는 키블-주렉 기작을 통해 전례 없는 많은 수의 양자 소용돌이들을 만들어냈고, 이들의 통계는 기작의 여러 면들을 드러냈다. 느린 퀜치에서 나타난 생성된 소용돌이들의 밀도와 퀜치 속도 간의 멱법칙(power-law) 관계는 키블-주렉 기작이 unitarity를 포함한 강하게 상관하는 영역에서도 적용됨을 보였고, BEC-BCS 교차영역에서 일정한 멱법칙의 지수들은 BEC와 BCS 초유체가 같은 보편성 부류에 속한다는 것을 확인해 주었다. 빠른 퀜치에서는 양자 소용돌이 간의 충돌 소멸로 인해 소용돌이의 밀도가 법칙에서 벗어나 포화되고, BEC-BCS 교차영역에서 이 포화된 값들은 교차영역에서 강상 페르미 초유체의 일관성 길이(coherence length)를 드러낸다.Chapter 1 Introduction 1 1.1 Superfluidity of two types - BEC vs. BCS 2 1.1.1 Bose-Einstein condensate 2 1.1.2 Bardeen-Cooper-Schrieffer superfluid 3 1.1.3 BEC-BCS crossover 6 1.2 Ultracold atomic gases - a model system for bosonic and fermionic superfluids 9 1.3 My five and half years at Quantum Gas Laboratory 16 1.4 Outline 17 Chapter 2 The apparatus upgrades 18 2.1 Oven upgrade - from 23Na to 23Na-6Li 19 2.2 Laser system 24 2.2.1 6Li laser system 24 2.2.2 23Na laser system 40 2.3 Feshbach coil 42 2.4 Deeper optical dipole trap 49 2.5 Manipulating the hyperne states of 6Li 52 Chapter 3 Producing a large 106 strongly interacting Fermi superfluid of 6Li 57 3.1 Sympathetic cooling of 6Li by 23Na 58 3.2 Interacting Fermi mixture and its condensation 63 3.3 Time-of-flight imaging of 6Li condensate 67 Chapter 4 Critical vortex shedding in a strongly interacting fermionic superfluid 70 4.1 Quantum vortices and the dissipation of a superfluid 71 4.2 Speed of sound in the BEC-BCS crossover 75 4.2.1 Experimental measurement 76 4.2.2 Theoretical estimate 77 4.3 Critical vortex shedding across the BEC-BCS crossover 82 4.3.1 Measuring the critical velocity for vortex shedding 82 4.3.2 Characterization of the optical obstacle 86 4.3.3 Adiabaticity of the obstacle beam switch-off 87 4.4 Results: critical velocity for vortex shedding 89 4.5 Modeling the vortex shedding mechanism: involvement of pairbreaking? 93 4.6 Conclusion 97 Chapter 5 Kibble-Zurek universality in a strongly interacting Fermi superfluid 99 5.1 Kibble-Zurek mechanism and universality 99 5.1.1 The Kibble-Zurek mechanism .99 5.1.2 Universality of phase transition . 102 5.1.3 Kibble-Zurek universality and a strongly interacting Fermi gases 104 5.2 Thermal quench of a strongly interacting Fermi gas across the normal to superfluid phase transition and the creation of quantum vortices 105 5.3 Kibble-Zurek universality in the BEC-BCS crossover 116 5.4 Defect density saturation and the coherence length of a strongly interacting Fermi superfluid in the BEC-BCS crossover 119 5.5 Conclusion 122 Chapter 6 Conclusion and outlook 123 초록 125 감사의 글 127Docto

Active vibration control of civil engineering structures

This thesis is in the area of active vibration control of Civil Engineering structures subject to earthquake loading. Existing structural control methods and technologies including passive, active, semi-active and hybrid control are first introduced. An extensive analysis of a frame-pendulum model is developed and analysed to investigate under what conditions effective energy dissipation is achieved in Tuned Mass Damper systems and the limitation of these devices under stiffness degradation when the structure enters the inelastic region. Linear Quadratic Gaussian and H-infinity active control schemes are designed, simulated and assessed for buildings, modelled as lumped parameter systems, including base and actuator dynamics. Various aspects of the designs are extensively evaluated using multiple criteria and loading conditions and validated in large-scale benchmark problems under practical limitations and implementation constraints. A novel design method is proposed for minimising peak responses of regulated signals via a deadbeat parametrisation of all stabilising controllers in discrete-time. The method incorporates constraints on the magnitude and rate of the control signal and is solved via efficient Linear Programming methods. It is argued that this type of optimisation is more relevant for structural control, as failure occurs when maximum member displacements are exceeded. The problem of stiffness matrix estimation from experimental data is formulated as an optimisation problem and solved under various conditions (positive definiteness, tridiagonal structure) via an alternating convex projection scheme. Both static and dynamic loading is considered. The method is finally incorporated in an adaptive control scheme involving the redesign in real-time of an LQR (Linear Quadratic Regulator) active vibration controller. It is shown that the method is successful in recovering the stability and performance properties of the nominal design under conditions of significant uncertainty in the stiffness parameters

A COLLISION AVOIDANCE SYSTEM FOR AUTONOMOUS UNDERWATER VEHICLES

The work in this thesis is concerned with the development of a novel and practical collision avoidance system for autonomous underwater vehicles (AUVs). Synergistically, advanced stochastic motion planning methods, dynamics quantisation approaches, multivariable tracking controller designs, sonar data processing and workspace representation, are combined to enhance significantly the survivability of modern AUVs. The recent proliferation of autonomous AUV deployments for various missions such as seafloor surveying, scientific data gathering and mine hunting has demanded a substantial increase in vehicle autonomy. One matching requirement of such missions is to allow all the AUV to navigate safely in a dynamic and unstructured environment. Therefore, it is vital that a robust and effective collision avoidance system should be forthcoming in order to preserve the structural integrity of the vehicle whilst simultaneously increasing its autonomy. This thesis not only provides a holistic framework but also an arsenal of computational techniques in the design of a collision avoidance system for AUVs. The design of an obstacle avoidance system is first addressed. The core paradigm is the application of the Rapidly-exploring Random Tree (RRT) algorithm and the newly developed version for use as a motion planning tool. Later, this technique is merged with the Manoeuvre Automaton (MA) representation to address the inherent disadvantages of the RRT. A novel multi-node version which can also address time varying final state is suggested. Clearly, the reference trajectory generated by the aforementioned embedded planner must be tracked. Hence, the feasibility of employing the linear quadratic regulator (LQG) and the nonlinear kinematic based state-dependent Ricatti equation (SDRE) controller as trajectory trackers are explored. The obstacle detection module, which comprises of sonar processing and workspace representation submodules, is developed and tested on actual sonar data acquired in a sea-trial via a prototype forward looking sonar (AT500). The sonar processing techniques applied are fundamentally derived from the image processing perspective. Likewise, a novel occupancy grid using nonlinear function is proposed for the workspace representation of the AUV. Results are presented that demonstrate the ability of an AUV to navigate a complex environment. To the author's knowledge, it is the first time the above newly developed methodologies have been applied to an A UV collision avoidance system, and, therefore, it is considered that the work constitutes a contribution of knowledge in this area of work.J&S MARINE LT