Closed-loop Shaping Research Articles

Asymmetric Two-Step Thermosiphon for Containment Cooling of Small Modular Reactors

A thermosiphon is a heat transfer device that utilizes the phase change of a liquid and has a single closed-loop shape in a gravity-dominant field. This can be expressed as a single-step thermosiphon because boiling and condensation occur once per cycle. In contrast, the multistep thermosiphon, introduced for the first time in the field of thermal engineering in this study, is a new heat transfer mechanism in which boiling and condensation occur several times per cycle in a single loop with multiple channels. The new mechanism has a superior heat transfer rate compared to the existing single-step thermosiphon, and the operating pressure of the loop can be lowered. However, as the heat transfer rate increases, the circulation flow in the channel tends to pulsate. This thermohydraulic characteristic was confirmed through theoretical and computational analyses of a two-step thermosiphon. In this study, an improved concept of an asymmetric two-step thermosiphon was developed that can be applied to heat exchanger design by eliminating pulsating flow while maintaining the advantages of a two-step thermosiphon. The newly proposed heat transfer mechanism, termed the multistep thermosiphon, can be effectively used in the design of heat exchangers in industrial fields. In particular, if the asymmetric two-step thermosiphon is applied to the design of small nuclear reactor containments currently being developed in several countries, there are several advantages associated with the reduction of the containment volume and design pressure.

Closed-loop Shape Control of Deformable Linear Objects Based on Cosserat Model

Closed-loop Shape Control of Deformable Linear Objects Based on Cosserat Model

Gust Reconstruction for Rotorcraft Based on Closed-Loop Shaping

Expensive and time-consuming flight tests are required to evaluate different helicopters and flight control systems in terms of handling and ride qualities. If gusts occur during these flights, they can distort the flight crew’s perception of the handling and ride qualities. Therefore, it is desired to quantify the influence of gusts on these criteria. This requires the determination of gusts that occur during the flights. Indirect methods are favored for quantification of the gusts to avoid the complex mounting of expensive measuring devices. Existing gust reconstruction approaches rely on gust models in addition to dynamic models of the vehicle, so the quality of these approaches depends on the validity and quality of the gust models. Hence, an approach that is only bound to the model validity of the vehicle dynamics is preferred. Unfortunately, such an approach is currently not available. This paper addresses this gap by deriving an observer using the closed-loop shaping method. The proposed observer reconstructs gusts from measured accelerations considering the gust rejection properties of the helicopter. Consequently, it works independently of any gust model and provides an easy-to-use alternative to existing methods. The quality of the approach is evaluated with simulation data under various flight conditions.

Exosomal circular RNAs: New player in breast cancer progression and therapeutic targets.

Breast cancer is the most prevalent type of malignancy among women. Exosomes are extracellular vesicles of cell membrane origin that are released via exocytosis. Their cargo contains lipids, proteins, DNA, and different forms of RNA, including circular RNAs. Circular RNAs are new class of non-coding RNAs with a closed-loop shape involved in several types of cancer, including breast cancer. Exosomes contained a lot of circRNAs which are called exosomal circRNAs. By interfering with several biological pathways, exosomal circRNAs can have either a proliferative or suppressive role in cancer. The involvement of exosomal circRNAs in breast cancer has been studied with consideration to tumor development and progression as well as its effects on therapeutic resistance. However, its exact mechanism is still unclear, and there have not been available clinical implications of exo-circRNAs in breast cancer. Here, we highlight the role of exosomal circRNAs in breast cancer progression and to highlight the most recent development and potential of circRNAas therapeutic targets and diagnostics for breast cancer.

Graph-based Automated Macro-Molecule Assembly.

We present a general molecular framework assembly algorithm that takes a largely arbitrary molecular fragment database and a user-supplied target template graph as input. Automatic assembly of molecular fragments from the database, following a prescribed, user-supplied set of connection rules, then turns the template graph into an actual, chemically reasonable molecular framework. Assembly capabilities of our algorithm are tested by producing several abstract, closed-loop shapes. To indicate a few of many possible application areas we demonstrate a host-guest complex and a road toward catalysis. Postassembly substituent exchange can be used to produce electric fields of desired values at desired points inside the framework or at its surface as a stepping stone toward rationally designed, artificial heterogeneous catalysts.

An Integrated Visual Odometry System With Stereo Camera for Unmanned Underwater Vehicles

Navigation is a challenging problem in the area of underwater unmanned vehicles, due to the significant electronmagnetic wave attenuation and the uncertainties in underwater environments. The conventional methods, mainly implemented by acoustic devices, suffer limitations such as high cost, terrain effects and low refresh rate. In this paper, a novel low-cost underwater visual navigation method, named Integrated Visual Odometry with a Stereo Camera (IVO-S), has been investigated. Unlike pure visual odometry, the proposed method fuses the information from inertial sensors and a sonar so that it is able to work in context-sparse environments. In practical experiments, the vehicle was operated to follow specific closed-loop shapes. The Integrated Visual Odoemtry with Monocular Camera (IVO-M) method and other popular open source Visual SLAMs (Simultaneous Localisation and Mappings), such as ORB-SLAM2 and VINS-Mono, have been used to provide comparative results. The cumulative error ratio is used as the quantitative evaluation method to analyse the practical test results. It is shown that the IVO-S method is able to work in underwater sparse-feature environments with high accuracy, whilst also being a low cost solution.

DETERMINING ROBUST PARAMETERS IN STABILIZING SET OF BACKSTEPPING BASED NONLINEAR CONTROLLER FOR SHIP COURSE KEEPING

The authors have addressed an important topic that is needed for backstepping algorithm to guarantee the robust performance of the closed-loop system. A novel method of determining parameters was presented based on ship maneuvering empirical knowledge and closed-loop shaping theory, and theoretical proof had shown the uniformly asymptotic stability of an established nonlinear Nomoto model. However, the following important points are suggested for the improvement of this paper.

DETERMINING ROBUST PARAMETERS IN STABILIZING SET OF BACKSTEPPING BASED NONLINEAR CONTROLLER FOR SHIP COURSE KEEPING

In order to solve the problem that backstepping method cannot effectively guarantee the robust performance of the closed-loop system, a novel method of determining parameter is developed in this note. Based on the ship manoeuvring empirical knowledge and the closed-loop shaping theory, the derived parameters belong to a reduced robust group in the original stabilizing set. The uniformly asymptotic stability is achieved theoretically. The training vessel “Yulong” and the tanker “Daqing232” are selected as the plants in the simulation experiment. And the simulation results are presented to demonstrate the effectiveness of the proposed algorithm.

A novel method for optimal robust PID design based on mixed sensitivity closed loop shaping and convex programming

In industry, the PID controller remains ubiquitous. Its design is typically tackled from classical design methods which do not properly take into account model uncertainty. Robustness is therefore typically a major issue with classically tuned PID controllers. This in turn results in PID controllers that are ‘detuned’ experimentally by an operator in order to avoid these robustness issues. A more generic method is hence required for tuning robust PID controllers.This paper proposes a novel method to enforce a PID (classic and higher order PID) architecture in the mixed sensitivity controller synthesis problem (which is the basis for the mixed sensitivity H∞ design), based on sequential convex second order programming with guaranteed convergence to a stationary point of the optimization problem.Numerical validation of the proposed method is presented by means of some toy problems illustrating the flexibility and practicality of the proposed method. The resulting PID controllers are compared with classical H∞ controllers illustrating the viability of the method to synthesise robust PID controllers based on H∞ controller design specification.

Unified CACSD Toolbox for Hybrid Simulation and Robust Controller Synthesis with Applications in DC-to-DC Power Converter Control

The current article presents the design, implementation, validation, and use of a Computer-Aided Control System Design (CACSD) toolbox for nonlinear and hybrid system uncertainty modeling, simulation, and control using μ synthesis. Remarkable features include generalization of classical system interconnection operations to nonlinear and hybrid systems, automatic computation of equilibrium points for nonlinear systems, and optimization of least conservative uncertainty bounds, with direct applicability for μ synthesis. A unified approach is presented for the step-down (buck), step-up (boost), and single-ended primary-inductor (SEPIC) converters to showcase the use and flexibility of the toolbox. Robust controllers were computed by minimization of the H∞ norm of the augmented performance systems, encompassing a wide range of uncertainty types, and have been designed using the well-known mixed-sensitivity closed loop shaping μ synthesis method.

Generalised system level approach

Recently, system level approach has been proposed as a novel design tool for large-scale cyber physical systems in the discrete time LTI framework. The main idea of the new paradigm is a shift from constructing and parametrizing the desired optimal controller to the parametrization of the achievable closed loop behaviours (closed loop shape). Then, the controller is synthesised from the system level data in a way that keep the imposed structural constraints intact. In this paper we lift the main idea of the system level parametrization to a general level, that also includes the class of LPV systems. We also provide a general scheme for the realization related to different Möbius transforms which are formulated in terms of the original data and also keep intact the structural information.

An Interactive Software Tool to Learn/Teach Robust Closed-Loop Shaping Control Systems Design

Models are always subject to uncertainty. This can come mainly from parameter uncertainty, reduced order dynamics, or unmodelled dynamics. The model uncertainty is a concept that is difficult to introduce in automatic control introductory courses. The mathematical formalization of many of the ideas necessary to introduce students to robust control is complex for most students, causing many students to get lost in the mathematics and do not understand the important control concepts. The closed-loop shaping control design methodology allows introducing the model uncertainty in a simple way. It has some very interesting characteristics from a teaching point of view, since it allows concentrating on shaping the closed-loop frequency response in order to obtain the desired performance and robustness. This paper presents the main features and functionality of RCLSD an interactive software tool developed by the authors for learning and teaching the robust closed-loop shaping control design methodology.

Circular RNAs in Cardiac Regeneration: Cardiac Cell Proliferation, Differentiation, Survival, and Reprogramming.

Circular RNAs (circRNAs) are classified as long non-coding RNAs (lncRNAs) that are characterized by a covalent closed-loop structure. This closed-loop shape is the result of a backsplicing event in which the 3' and 5' splice sites are ligated. Through the lack of 3' poly(A) tails and 5' cap structures, circRNAs are more stable than linear RNAs because these adjustments make the circular loop less susceptible to exonucleases. The majority of identified circRNAs possess cell‐ and tissue-specific expression patterns. In addition, high-throughput RNA-sequencing combined with novel bioinformatics algorithms revealed that circRNA sequences are often conserved across different species suggesting a positive evolutionary pressure. Implicated as regulators of protein turnover, micro RNA (miRNA) sponges, or broad effectors in cell differentiation, proliferation, and senescence, research of circRNA has increased in recent years. Particularly in cardiovascular research, circRNA-related discoveries have opened the door for the development of potential diagnostic and therapeutic tools. Increasing evidence links deviating circRNA expression patterns to various cardiovascular diseases including ischemic heart failure. In this mini-review, we summarize the current state of knowledge on circRNAs in cardiac regeneration with a focus on cardiac cell proliferation, differentiation, cardiomyocyte survival, and cardiac reprogramming.

An interactive teaching/learning approach to the design of robust linear control systems using the closed-loop shaping methodology

Usually the controller is designed working on the open-loop transfer function. However, it is also possible to design the controller working on the closed-loop transfer functions. The closed-loop shaping methodology offers a straightforward framework which allows designers and students to focus on the required specification fulfillment and dealing with inherent linear systems limitations without complex computations or using difficult algorithms. This article summarizes the basic ideas of the manual closed-loop shaping methodology, and its application to the design of robust controllers for uncertainty linear systems. An interactive software tool for learning/teaching this methodology is also presented.

Closed-Loop Shaping Linear Control System Design: An Interactive Teaching/Learning Approach [Focus on Education

The frequency domain is one of the most popular and powerful frameworks for designing control systems. Usually, the controller is designed by working on the openloop transfer function. However, it is also possible to design the controller by working on the closed-loop transfer functions. This closed-loop shaping methodology offers a straightforward framework that enables designers and students to focus on fulfilling the required specifications and dealing with inherent linear systems limitations without the need for complex computations or the use of difficult algorithms. In comparison to open-loop shaping, closed-loop shaping offers an exact approach in a very simple framework. Interactive software tools have proven to be particularly useful techniques with high impact on control education. This kind of interactive tool has been demonstrated to help students learn in a much more active way. This article summarizes the basic ideas of manual closed-loop shaping and presents the basic functionality of the Interactive Tool for Closed-Loop Shaping Control Design (ITCLSD). Different illustrative examples are included to show the uses of the ITCLSD.

Unmanned Surface Vessel Steering L2 Gain Robust Control Based on Closed-Loop Shaping Filter

With the introduction of the closed-loop shaping filtering method into the L2 gain robust controller design strategy, a nonlinear robust steering controller for unmanned surface vessel is designed under the planning and control strategy in this paper. The rigorous mathematical analysis and synthesis characteristics of the L2 gain robust control theory and the Lyapunov design method are fully utilized in the controller design process. Furthermore, the concept of the closed-loop shaping filtering based on the classical closed-loop control theory is taken into the controller design strategy. Therefore, the time domain controller design methods integration with the frequency domain controller design strategy are merged togehter to complete the unmanned surface vessel steering controller design in the view of practical engineering and planning and control strategy. Finally, compared with several practical controller design methods in the multi-direction irregular waves, the simulation results show that the proposed steering controller design strategy has concise structure, distinctive physic meanings of the controller parameters and superior comprehensive control performance.

Active shape control of an antenna reflector using piezoelectric actuators

The surface precision of an antenna reflector can be improved using the actuation of piezoelectric materials to obtain a high-performance space antenna. In this study, the active shape control of a reflector with piezoceramic (lead zirconate titanate) actuators assembled on ribs is proposed by theoretical and experimental approaches. A finite element model of the integrated reflector–actuator system is established using piezoelectric constitutive equations and the virtual work’s principle. For a desired shape, a closed-loop iterative shape control method based on the influence coefficient matrix model is developed, which resolves the issue of high-precision shape control of the antenna reflector in the presence of model errors. The shape controller based on the proposed closed-loop shape control method is implemented on a planar hexagonal reflector with 30 lead zirconate titanate actuators. Experimental results demonstrate that the closed-loop control is an effective way to improve the surface precision of the reflector considering uncertainties.

Steering Controller Design for Smart Autonomous Surface Vessel Based on CSF L2 Gain Robust Strategy

During the mission at sea, the yaw motion of the smart autonomous surface vessel (SASV) is always subject to the external disturbances. These issues make the design of a robust controller for steering autopilot system a quite challenging task. This paper focuses on the utilization of closed-loop shaping filter (CSF) to improve the SASV steering L2 gain robust control scheme. First, the mathematical model of the SASV is proposed and the parameters of the SASV model are obtained by the recursive least squares method (RLSM) based on the SASV turning test. Then the CSF L2 gain nonlinear robust controller design for SASV steering autopilot is described, and the stability and robustness of the proposed controller are proved based on the Lyapunov synthesis. Finally, the strong robustness and superior control performance are demonstrated through the practical SASV experiments. At the same time, the concise controller structure and definite physical meaning of SASV controller parameters are also concluded.

Trajectory linearization control on SO(3) with application to aerial manipulation

The dynamics of multi-DOF aerial manipulators is complex system evolving in non-Euclidean Lie group, making design and tuning of the control of such systems challenge. In this paper we consider the nonlinear geometric control for aerial manipulation system. The linearized tracking error kinematic equation of motion on SO(3) is obtained from the variation on SO(3). Based on the linearized tracking error kinematic equation of motion on SO(3), the trajectory linearization control for the kinematics on SO(3) is investigated. The decoupled dynamics of multi-DOF aerial manipulator enables us to apply the results of trajectory linearization control for the kinematics on SO(3). We then design the entire controller for aerial manipulation system by composing different trajectory linearization control loops. Such controller structure eases the controller implementation and tuning procedure. The stability of the proposed controlled system is analyzed using Lyapunov’s method. The proof is finished from inner loop to outer loop. It is proven that the closed loop shape system is exponentially stable. The attraction basin of the configuration error for the shape system can almost cover the whole SO(3)×Rn. The stability of the system considering the actuator dynamics and perturbations is also discussed in this paper. From the stability of the shape system, the stability of the entire system is proven. The stability analysis results are further verified through several numerical simulations.

The use of interactivity in the controller design: Loop shaping versus closed-loop shaping

Frequency domain is one of the most popular and powerful framework to design control system. Usually this procedure is done using the open-loop transfer function. In this work, it is explored the possibility to perform the controller design by closed-loop shaping. It is analyzed how graphical representation and interactivity can be used in this framework to help automatic control students during the learning process.