Action Of External Disturbances Research Articles

Study on the damage mechanism of hydraulic concrete under the alternating action of freeze-thaw and abrasion

This study investigates the damage mechanism of hydraulic concrete under the alternating action of freeze–thaw (F) and abrasion (W) in cold regions. To this end, three groups of working conditions were established with a constant water-binder ratio. The mass loss and relative dynamic elastic modulus (RDEM) of each cycle were evaluated using the fast-freezing method and underwater method. The phase composition and relative content change of hydration products, pore characteristic parameters and pore size distribution, morphology and microstructure of interfacial transition zone (ITZ) were analyzed by X-ray diffraction (XRD), mercury intrusion porosimeter(MIP), scanning electron microscopyn (SEM) and image recognition technology, respectively. The results indicate that the alternating effect will accelerate the mass loss of concrete and the reduction of the RDEM compared with the single factor. Following four consecutive alternating cycles, the mass loss rates of working conditions W and F group were found to be 4.61 % and 97.66 % lower, respectively, than those of working condition F-W group. The RDEM damage coefficient (γ < 1) was also observed. At the micro level, the freeze-thaw effect will result in the formation of a considerable number of micropores and the expansion of microcracks, with the abrasion effect continuing to promote this process. In the process of alternating action, the dissolution of Ca(OH)2 by external water through microcracks and interconnected pores is accelerated. Concurrently, the pores and microcracks in the ITZ expand, the morphology is roughened, and the microstructure is complicated. The interfacial bonding ability and compactness of different material components decrease. Under the action of external disturbance, cement paste and aggregate fall off, resulting in mass loss and a decreased RDEM.

Моделювання системи стабілізації обладнання мобільного робота в умовах руху по місцевості з нахилом та нерівностями

The article is devoted to the development of a system of stabilization and guidance of equipment, which is installed on land-based small-scale mobile robots of the wheel type. During the operation of such objects, problems arise due to modes of movement, over-coming obstacles, movement on terrain with different types and profiles of the terrain. During such a movement, there are disturbances in the place of installation of the equip-ment, which leads to its deviation from the horizon plane. A stabilization system is used to ensure accuracy requirements in a wide range of movement speeds and operating condi-tions of mobile robots. In the article, the simulation of the stabilization system under the action of external disturbances caused by the influence of the movement of the mobile robot through terrain with a complex profile in combination with the inclination of the different steepness of the movement surface was carried out. A stabilization system simulation scheme with a basic structure and with an additionally introduced proportional-integrating controller was developed, realizations of various types of disturbances were generated by a combination of different inclination angles and different road profile classes. As a result of the simula-tion, the time realizations of the system’s response to the generated disturbances, which are the dependences of the stabilization error, were obtained, the root mean square devia-tions and the maximum value of the angle of deviation of the place of installation of the equipment from the horizon plane were determined. The results of the study showed that the system with an additionally introduced pro-portional-integrating regulator provides acceptable stabilization error values under the con-ditions of action of all considered types of disturbances. The obtained results will be used for the development of an adaptive digital system of stabilization of equipment installed on small-sized mobile robots of the wheel type.

L2$$ {L}_2 $$‐gain analysis and fault‐tolerant control for nonlinear discrete‐time switched systems with time‐varying delay and actuator saturation

AbstractThe ‐gain analysis and fault‐tolerant control of a class of uncertain nonlinear discrete‐time switched systems with time‐varying delay and actuator saturation are studied by using the multiple Lyapunov functions method. The fault‐tolerant state feedback controllers and the switching law are designed such that the closed‐loop system with actuator failures satisfies the disturbance attenuation performance indicator. The problem of estimating the capacity of admissible disturbance is transformed into a constrained optimization problem to ensure that the state trajectory of the closed‐loop system is bounded under the action of external disturbances. The upper bound of restricted ‐gain is estimated by solving constrained optimization problems. Then, when the fault‐tolerant controller can be regard as the design variable, the optimization problems above are adjusted for solving control synthesis problems. Finally, the numerical example is given to verify the effectiveness of the design method.

Study on the Sensitivity of a Gyroscope System Homing a Quadcopter onto a Moving Ground Target under the Action of External Disturbance

This paper investigates the sensitivity (resistance) of a quadcopter on-board gyroscope system for the observation and tracking of a moving ground target to changing parameters of its regulator under interference conditions. It was shown that the gain in matrix elements is most sensitive, and even their slightest deviation from optimal values can lead to reduced target tracking efficiency and even loss of control system stability. Furthermore, the authors studied the energy expenditure at various gyroscope system control parameter values, while homing a quadcopter onto a ground target. A Matlab/Simulink environment was used to conduct simulations of the controlled gyroscope system dynamics. Selected test results are shown in graphic form.

A composite robust reactive control strategy for quadruped robot under external push disturbance

In order to solve the walking stability problem of quadruped robot under lateral disturbance, a robust stabilization reactive control strategy based on capture point stability theory is proposed. This novel control strategy consists of an active adaptive stepping control strategy at the upper planning layer and a joint disturbance rejection controller based on virtual model control at the bottom layer. The adaptive stepping control strategy is based on the capture point stability theory, which determines the stable stepping point of the robot under the action of external disturbance according to the speed and attitude of the body, and the joint disturbance rejection controller at bottom layer realizes the stable torque control of the robot and adjusts the attitude of the body through the virtual model controller. Finally, the effectiveness of the designed composite control strategy is verified by co-simulation of Simulink and ADAMS. Simulation results show that the robot with the proposed composite reactive control strategy is able to cope with large external disturbance and recover to be stable from external force disturbance.

Optimum Design of CDM-Backstepping Control with Nonlinear Observer for Electrohydraulic Servo System Using Ant Swarm

Abstract This paper introduces an application of an Ant Colony Optimization algorithm to optimize the parameters in the design of a type of nonlinear robust control algorithm based on coefficient diagram method and backstepping strategy with nonlinear observer for the electrohydraulic servo system with supply pressure under the conditions of uncertainty and the action of external disturbance. Based on this model, a systematic analysis and design algorithm is developed to deal with stabilization and angular displacement tracking, one feature of this work is employing the nonlinear observer to achieve the asymptotic stability with state estimations. Finally, numerical simulations are given to demonstrate the usefulness and advantages of the proposed optimization method.

A CDM-backstepping control with nonlinear observer for electrically driven robot manipulator

This paper presents a CDM-backstepping strategy for motion control of Electrically-driven manipulator under the conditions of uncertainty and the action of external disturbance, while incorporating a nonlinear observer. Based on this model, a systematic analysis and design algorithm is developed to deal with stabilization and trajectory tracking of elbow robot, one feature of this work is employing the backstepping observer to achieve the exponential stability with position and velocity estimations. The results of computer simulations demonstrate that accurate and robust motion control can be achieved by using the proposed approach.

Health, homeostasis, and longevity

Concepts of health and homeostasis are discussed and their connection to longevity is analyzed. Homeostasis is one of cardinal properties of the organism, which arises in evolution basing on mechanisms maintaining stationarity. Health represents the organisms' ability to sustain homeostasis and return to it after action of external disturbances. Maintaining the health of a human determines longevity. The factors affecting the health, aging and longevity are discussed. Potential reserves of longevity are estimated and possible ways to achieve them are provided.

Design of Actuator Networks for Dynamic Displacement Tracking of Beams

Adaptive and smart structures have become a major subject of contemporary research. Smart structures are structures that—like human beings—are capable of automatically reacting to disturbances exerted upon them by the environment they are operating in. Typically, smart structures are put into practice by embedding or attaching smart materials to a substrate structure. These materials have both actuating and sensing capabilities; a popular example would be piezoelectric materials that exhibit the direct and the converse piezoelectric effect. As many of the structures, which are considered as candidates for implementing smart materials, are continuous structures, there is an inherent need for properly distributing the actuation as well as the sensing. A method that has been successfully utilized for the design of distributed actuators is shape control. In general, shape control is concerned with finding a distributed actuation such that a structure assumes a desired shape. The latter shape may be the undistorted shape of the structure, despite the action of external disturbances, or it may be a prescribed new shape for the structure. In the present paper we consider the case of the structure taking on a prescribed shape; i.e., we present a method for finding distributed actuators or dense actuator networks such that a desired displacement field is tracked. We use eigenstrain type actuators for that sake. In the first part we discuss dynamic deflection tracking of beams by distributed actuation, and in the second part we focus on the use of dense networks of actuator patches with a section-wise constant intensity to approximate the effectiveness of the distributed actuators. In the example problem we assume the actuator patches made of piezoelectric materials, taking into account the mass and stiffness of the patches as well as the electromechanical coupling due to the direct piezoelectric effect. The efficiency of the presented method is clearly demonstrated by the latter study.

Theoretical fundamentals for constructing an integrated safety system of airborne ergatic complex operation

The initial statements are formulated and a technique is considered to solve a problem of providing trouble-free airborne ergatic complex (AEC) operation under the action of external disturbances, equipment failure, pilot’s errors and other unfavorable factors.

Cascade Design of a Manipulator Control System with Consideration for Dynamics of Electric Drives

A methodological approach is suggested to cascade design (synthesis) of a control system of a robotic manipulator operating under the conditions of uncertainty and the action of external disturbances with due regard for the dynamics of direct-current drives. To solve the problem of tracking of prescribed trajectories, suggestion is made of the algorithmic two-level decomposition with the separation of the initial problem of control synthesis into independently solvable subproblems of a smaller dimension: synthesis of control actions in a mechanical subsystem and synthesis of control actions in actuators with the further subdivision of the problems of synthesis in each of subsystems into elementary subproblems. A problem is solved for the security of invariance to disturbances with the aid of the methods involving the systems with high gains and discontinuous controls and the composite control. Decomposition procedures are evolved of the synthesis of observers on the basis of measurements of positions of a manipulator and armature currents of electric drives.

Accomodation of external disturbances in linear regulator and servomechanism problems

Modern linear regulator and servomechanism theories (of the deterministic type) either ignore system disturbances altogether or assume they can be represented by initial conditions on the plant state vector. Controllers designed by such theories may fail to meet performance specifications when the system is subjected to persistently acting disturbances. In this paper, we show how one can modify existing regulator and servomechanism theories to take into account the presence of persistent fluctuating disturbances. By this means one can design a deterministic controller which consistently maintains set-point regulation, or servotracking, in the face of a bread class of realistic external disturbances. In addition, we show how one can systematically exploit any useful effects that may be present in the action of external disturbances.