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A full-pose, position and orientation, trajectory-tracking control of kinematically redundant flexible-macro-rigid-micro manipulators is proposed. Redundancy is resolved such that the forces exciting the lowest-frequency 'modal coordinates' of the system are minimized, while imposing a proportional damping on the flexural dynamics, rendering it stable under certain conditions. The simulation results show that the initial posture of the manipulator plays an important role in satisfying the foregoing stability conditions. [DOI: 10.1115/1.1870039]

The work reported here was motivated by the development of manipulator systems comprising one long-reach, flexible-link subsystem, termed the macromanipulator, and a short-reach, rigid-link subsystem, called the micromanipulator. The flexural states of the macromanipulator, needed for controlling such systems effectively, are not usually measurable directly. For this reason, a state-estimation algorithm is proposed which uses the velocity and angular-velocity data of the micromanipulator base to estimate the flexural states of the macromanipulator. The velocity data are inferred from the acceleration signals delivered by a kinematically redundant set of triaxial accelerometers. The accelerometer signals are also utilized to calculate the translational and angular accelerations of the micromanipulator base, which are, in turn, used along with the dynamics equations of the micromanipulator to obtain the reaction force and moment acting between the two subsystems. Treating the force and the moment as inputs, the dynamics equations of the macromanipulator alone are used in the observer, thus reducing the order of the dynamics model. The state-output relations, on the other hand, are linearized in closed form to lower the computational cost. The relations thus obtained are then used in an extended Kalman filter to estimate the flexural states of the system. Index Terms--Flexible manipulator, flexural coordinates, linearized kinematics, macro-micro manipulator, state estimation, twist vector.

Using an order N Lagrangian formulation, the paper studies attitude control of a rigid platform supporting a flexible tether connected to a rigid satellite. The system, in an arbitrary orbit, is free to undergo three-dimensional motion in both rigid and flexible degrees of freedom. As can be expected, the governing equations of motion, in general, are highly nonlinear, nonautonomous, and coupled, and are amenable only to numerical integration. The control is achieved through time dependent offset of the tether attachment point, as determined through the Liapunov method, thus providing regulated amount of tether tension induced damping moment. Results suggest that the controller is quite successful in stabilizing the platform about its nominal equilibrium position in a few orbits, even in the presence of relatively large disturbances. Furthermore, extensive parametric study suggests that the controller is quite versatile in imparting any desired orientation to the platform. This would enable the system to undertake diverse missions aimed at communications, launch and retrieval of spacecraft, monitoring the Earth's environment, planetary, and galactic observations, etc.

DOS or Denial-of-service attacks are found in many forms and they're an explicit attempt to block the genuine access of user to the system via reducing availability of the system just similar to physical Dos attacks where for example intentionally the electrical power is removed. Sometimes the attacker may also play with a computing devices and make it inaccessible by altering the existem specification of the management information system. These physical intrusions are tackled by tough security measures and strategies. Although few software guards against some attacks, yet it flops to defend against DoS flooding attacks and it may further exploit unrestricted forwarding of internet packets. DDoS distributed denial of service attacks are another contiguous type of attack over the availability of Internet resources. The attackers are smart enough to penetrate into comparatively large number of computers exploiting weaknesses of different softwares so as to setup distributed attacks. These computers are unsuspecting in nature so they can be easily invoked for planning and attempting attack over more victim systems. Over the time the counter measures are developed attackers also improve the existing attack tools developing as well as imitating techniques for distributed denial-of-service attacks. So it is imperative develop complete expositions for defending against known attack variants of such kinds. However this procedure needs a complete understanding of techniques, prerequisites and scope used in diverse kinds of attacks. This paper tries to describe the scope of DDoS problem in possible comprehensive capacity. We have tried to propose new methods to categories different techniques used in DDoS attack, also categories attack networks and defining characteristics of different software tools that help to build up such attack networks. With this new approach we attempt to propose different classes' methods the target this problem during, before, and after actual DDoS attacks. This work envisioned to stimulate research into efficient creative an effective ramparts, detection mechanism and methods for such attacks. This intern may help to create broad and ample solutions providing generalized approach towards countering known as well as derived DDoS attacks. [ABSTRACT FROM AUTHOR]

The tethered formation and the coulomb formation are two important concepts in constructing satellite formation architecture, and they have the advantage that the relative motion between satellites can be maintained quite accurately with minimal active control. In this study, a formation termed the "coulomb tether double-pyramid" is proposed to combine the best features of the tethered formation and the coulomb formation. Chief and deputy satellites are charged bodies and located in the Earth-facing plane normal to the geostationary orbit, with the chief at the center. Each deputy is connected with two anchor satellites via a massless, straight tether, such that the Earthfacing plane can be maintained by using gravity-gradient torques. First, the equations of motion are obtained via Lagrange equations. Then, the charges and tether extensions necessary to support a Hill-frame stationary formation are analytically determined. Finally, open-loop charge control strategies are designed to maintain the spinning formation or carry out reconfiguration. The proposed coulomb tether double-pyramid formation has great potential to enhance the surveillance and imaging of Earth objects in future missions. [ABSTRACT FROM AUTHOR]

Recently, active control of aeroelastic oscillations and the use of piezoelectric materials in vibration analysis and control of structures have been the subjects of many researches in air vehicle design. The present paper deals with the use of bonded piezoelectric sensors and actuators in control of aeroelastic oscillations of a cantilever plate under the effects of unsteady subsonic aerodynamic loading. The aerodynamic loading is calculated using a numerical panel method. The structural model of the plate undergoing small transverse oscillations is modeled using finite element formulation. The aerodynamic and structural models are coupled through an interactive computer model to transfer the data simultaneously and an active feedback control is applied to suppress the oscillations. A systematic method is also presented to obtain the gains of the feedback controller. The numerical results show that the controller can effectively reduce the amplitude of the oscillations in small amount of time and with small gains, hence lower cost. [ABSTRACT FROM PUBLISHER]