In this paper the problem of designing a robust controller with given structure for a plant describing a drag-free satellite is addressed. From recent experiences in drag-free control design we first derive an uncerta...
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In this paper the problem of designing a robust controller with given structure for a plant describing a drag-free satellite is addressed. From recent experiences in drag-free control design we first derive an uncertain plant set representative of many drag-free missions with nonspherical test masses. The design plant is uncertain and a performance requirement is imposed on the absolute acceleration of the test mass along a measurement axis. The v-gap metric is first used to derive a simplified uncertain design plant. Then the main performance requirement is broken down into requirements on the uncertain closed loop behavior of the simplified system. The fulfillment of this new set of requirements guarantees robust achievement of the overall system goal. Then optimal single-input-single-output controllers are designed that robustly achieve the desired level of performance. The method proposed allows one to properly account for the uncertainties in the system retaining the decentralized structure (of the controller suggested by the peculiar features of the design plant.
Cross validation for estimating the correlation between the prediction variance and the errors was proposed. The correlation between the square root of the prediction variance, s, and the absolute value of the error i...
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Satellites that use low-thrust propulsion systems for maneuvering, although efficient, can take a long time to complete significant orbit changes. Determining the nonlinear optimal controls for such multirevolution ma...
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Satellites that use low-thrust propulsion systems for maneuvering, although efficient, can take a long time to complete significant orbit changes. Determining the nonlinear optimal controls for such multirevolution maneuvers using the instantaneous orbital state dynamics can he riddled with numerical errors and are often subject to long computation times, due to the large number of discretization nodes required by the optimization algorithm. An approach to optimal control of an electrodynamic tether is examined using averaged orbital state dynamics as constraints instead of instantaneous dynamic constraints. A mean-square libration state is introduced in the dynamic model that captures the average of the out-of-plane libration of the tether. A sample long-term optimal orbit change maneuver of a librating electrodynamic tether subject to atmospheric drag is investigated. The method of averaging is employed to transform the optimal control problem from the time domain into Fourier space, in which the complex problem is significantly reduced to a Zermelo-type problem that is solved using a pseudospectral method. To validate the dynamic model of averaged states, the instantaneous states are propagated from the initial conditions using the resulting optimal controls.
. This study describes two types of algorithms for skid-to-turn unmanned aerial vehicles to plan paths between two waypoints under constant wind conditions. The first type of algorithm is a rigorous optimization algor...
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. This study describes two types of algorithms for skid-to-turn unmanned aerial vehicles to plan paths between two waypoints under constant wind conditions. The first type of algorithm is a rigorous optimization algorithm based on the Euler-Lagrange formulation with analytical integration of the path. The second type of algorithm is a fast algorithm describing the path by two circular arcs connected by a line segment or another circular are in the air mass frame, which is similar to the Dubins path. The latter algorithm is developed for actual airborne application, whereas the former algorithm is developed to check the quasi-optimality of the path calculated by the latter algorithm. We present a convergence proof of the latter algorithm under certain assumptions and its quasi-optimality in comparison with the former algorithm. Furthermore, the computational efficiency and the convergence reliability of the latter algorithm are demonstrated through numerical examples.
This research investigates strategies to enable a deputy satellite to hover within a defined volume fixed in the vicinity of a chief satellite in a circular orbit for an extended period of time. Previous research deve...
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This research investigates strategies to enable a deputy satellite to hover within a defined volume fixed in the vicinity of a chief satellite in a circular orbit for an extended period of time. Previous research developed initial methodologies for maintaining restricted teardrop hover orbits that exist in a plane fixed within the chief's local reference frame. These methods use the natural drift of the deputy satellite in the relative frame and impulsive thrust to keep the deputy in a bounded volume relative to the chief, but do not address fuel optimality. This research extends and enhances that work by finding the optimal trajectories produced with discrete thrusts that minimize fuel spent per unit time and stay within the user-defined volume, thus providing a practical hover capability in the vicinity of the chief. The work assumes that the Clohessy-Wiltshire closeness assumption between the deputy and chief is valid. Using the new methodology developed in this work, feasible closed- and nonclosed-relative orbits are found and evaluated based on a fuel criterion and are compared with an easily calculated continuous-thrust baseline. It is shown that in certain scenarios (generally corresponding to a smaller total time of flight) a discrete-thrust solution provides a lower overall fuel cost than a continuous-thrust solution. A simple check is proposed that enables the mission planner to make the correct strategy choice.
In a three-dimensional (3-D) model-based objects tracking and recognition system, the key problem of objects location is to establish the relationship between 2-D objects image and 3-D model. Based on 3-D model projec...
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ISBN:
(纸本)9781424427239
In a three-dimensional (3-D) model-based objects tracking and recognition system, the key problem of objects location is to establish the relationship between 2-D objects image and 3-D model. Based on 3-D model projection and 2-D image feature extraction, a modified Hausdorff distance is used to establish the matching function. The relationship between matching parameters are described with a probability model, and the distribution of parameter evolves towards the direction of dominant character through probability model learning and the corresponding operation, which is proposed to solve the problem of overmany iteration and slow constringency velocity The experiments show that the optimal matching parameters between 3-D model and 2-D image feature can be found accurately and efficiently, and then the accurate object location is completed.
Genetic algorithm(GA) has a good robust and global optimization *** this paper,a supercavitation regime problem is transformed into an equivalent shape optimization problem by defining the objective function as a squa...
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Genetic algorithm(GA) has a good robust and global optimization *** this paper,a supercavitation regime problem is transformed into an equivalent shape optimization problem by defining the objective function as a square error integral of pressure *** combining the commercial CFD soft ANSYS with GA,this problem has been solved *** show that genetic algorithm is feasible and effective used in supercavitation flow analysis,the method is good for the reduction of computational complexity and more *** the frame can be expanded to study the cavitator optimization in which the regime optimization can be as a sub-optimization.
In this paper, a new method is presented for double nonlinear analysis of the simply-supported beam with elastic-perfectly plastic model. The major character of the new method is that the equilibrium state with elasti...
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In this paper, a new method is presented for double nonlinear analysis of the simply-supported beam with elastic-perfectly plastic model. The major character of the new method is that the equilibrium state with elastic-plastic large deformation is chosen as the study object. The constitutive law adopts elastic-perfectly plastic model and the shearing deformation is taken into account. The endpoint coordinates are given by means of coordinate recursion formulae, and the objective function is defined by unknown endpoint coordinates of slight segments. The optimization problem is established for double nonlinear analysis of the simply-supported beam, and the optimization program is programmed. Typical numerical examples are calculated by optimization algorithm, and the results are in very good agreement with those by FEM. So this paper provides a new and effective idea for double nonlinear problem of the simply-supported beam.
A Mobile Ad hoc NETwork (MANET) is an autonomous system of mobile nodes connected by wireless links. There is no static infrastructure such as base station as that was in cell mobile communication. Due to the dynamic ...
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ISBN:
(纸本)078039335X
A Mobile Ad hoc NETwork (MANET) is an autonomous system of mobile nodes connected by wireless links. There is no static infrastructure such as base station as that was in cell mobile communication. Due to the dynamic nature of the network topology and restricted resources, quality of service (QoS) and multicast routing in MANET is a challenging task. In this paper, we present an entropy-based model to support QoS multicast routing optimization algorithm in mobile ad hoc networks (EQMOA). The basic motivations of the proposed modeling approach stem from the commonality observed in the location uncertainty in mobile ad hoc wireless networks and the concept of entropy. The simulation results demonstrate that the proposed approach and parameters provide an accurate and efficient method of estimating and evaluating the route stability in dynamic mobile networks.
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