Adaptive Control for State Synchronization of Nonlinear Haptic Telerobotic Systems with Asymmetric Varying Time Delays

In this paper, we introduce a new adaptive controller design scheme for nonlinear telerobotic systems with varying time delays where the delays and their variation rates are unknown. The designed controller has the ability to synchronize the state behaviors of the local and the remote robots. In this paper, asymptotic stability in the presence of varying time delays is of interest. Using the proposed controller, asymptotic stability of the bilateral telerobotic system subject to any bounded yet unknown varying delay with a bounded yet unknown rate of change can be guaranteed. Besides the varying time delay, the proposed adaptive controller has the ability to adapt to the parameter variations in the local and the remote robots’ dynamics. It is shown that position and velocity errors between the local and the remote manipulators converge to the zero asymptotically, thus ensuring teleoperation transparency. Experimental and simulation results with a pair of PHANToM haptic devices and a pair of planar manipulators under varying time delays in the communication channel demonstrate the effectiveness of the proposed scheme.     

An analytical solution for static stability of multi-scale hybrid nanocomposite plates

An analytical answer to the buckling problem of a composite plate consisted of multi-scale hybrid nanocomposites is presented here for the first time. In other words, the constituent material of the structure is made of an epoxy matrix which is reinforced by both macro- and nanosize reinforcements, namely, carbon fiber (CF) and carbon nanotube (CNT). The effective material properties such as Young’s modulus or density are derived utilizing a micromechanical scheme incorporated with the Halpin–Tsai model. To present a more realistic problem, the plate is placed on a two-parameter elastic substrate. Then, on the basis of an energy-based Hamiltonian approach, the equations of motion are derived using the classical theory of plates. Finally, the governing equations are solved analytically to obtain the critical buckling load of the system. Afterward, the normalized form of the results is presented to emphasize the impact of each parameter on the dimensionless buckling load of composite plates. It is worth mentioning that the effects of various boundary conditions are covered, too. To show the efficiency of presented modeling, the results of this article are compared to those of former attempts.

     

An efficient compressed domain video indexing method

Video indexing is employed to represent the features of video sequences. Motion vectors derived from compressed video are preferred for video indexing because they can be accessed by partial decoding; thus, they are used extensively in various video analysis and indexing applications. In this study, we introduce an efficient compressed domain video indexing method and implement it on the H.264/AVC coded videos. The video retrieval experimental evaluations indicate that the video retrieval based on the proposed indexing method outperforms motion vector based video retrieval in 74 % of queries with little increase in computation time. Furthermore, we compared our method with a pixel level video indexing method which employs both temporal and spatial features. Experimental evaluation results indicate that our method outperforms the pixel level method both in performance and speed. Hence considering the speed and precision characteristics of indexing methods, the proposed method is an efficient indexing method which can be used in various video indexing and retrieval applications.     

Cost minimization for bag-of-tasks workflows in a federation of clouds

We address the problem of resource allocation for bag-of-tasks (BoT) workflows in a federation of clouds and formulate it as an integer linear programming problem. The proposed model minimizes financial cost including fees for running VMs and fees for data transfer, and fulfills deadline and resource constraints in the clouds. We also formulate the problem of BoT scheduling in the hybrid clouds, and compare the financial cost in the federation of clouds with that in the hybrid clouds. Moreover, this paper discusses sensitivity analysis to investigate stability in the related allocation problem. Numerical results show that the resource allocation in the federation is considerably preferred to that in the hybrid clouds in terms of stability and cost-saving. In this paper, we also propose an approach named GRASP-FC for obtaining an approximate optimal solution of BoT scheduling in the federation. GRASP-FC is an extension of greedy randomized adaptive search procedure (GRASP), and it can be of great interest from the computational points of view.

     

Postbuckling analysis of piezoelectric multiscale sandwich composite doubly curved porous shallow shells via Homotopy Perturbation Method

In this study postbuckling behaviors of multiscale composite sandwich doubly curved piezoelectric shell with a flexible core and MR layers by employing Homotopy Perturbation Method in hygrothermal environment has been investigated. By using Reddy third shear deformable theory the face sheets and third-order polynomial theory of the flexible core the strains and stresses are obtained. A mathematical model for the multiscale composite layered shell with a flexible core and magnetorheological layer (MR) that incorporates the nonlinearity of the in-plane and the vertical displacements of the core is assumed. Three-phase composite shells with polymer/Carbon nanotube/fiber and polymer/Graphene platelet/fiber either uniformly or non-uniformly based on different patterns according to Halpin–Tsai model have been considered. The governing equations of multiscale shell have been derived by implementing Hamilton’s principle. Meanwhile, simply supported boundary conditions are employed to the shell. For investigating correctness and accuracy, this paper is validated by other previous researches. Finally, different parameters such as temperature rise, various distribution patterns, magnetic fields and curvature ratio are considered in this article. It is found these parameters have significant effect on the frequency–amplitude curves.

     

Magneto-electro-elastic analysis of piezoelectric–flexoelectric nanobeams rested on silica aerogel foundation

This article explores that the study on bending of magneto-electric-elastic nanobeams relies on nonlocal elasticity theory. The Vlasov’s model foundation utilizes the silica aerogel foundation. The guiding expressions of nonlocal nanobeams in the considered framework are used extensively and where parabolic third-order beam theory is achieved after using Hamilton’s principle. Parametric work is introduced to scrutinize the influence of the magneto-electro-mechanical loadings, nonlocal parameter, and aspect ratio on the deflection characteristics of nanobeams. It is noticed that the boundary conditions, nonlocal parameter, and beam geometrical parameters have significant effects on dimensionless deflection of nanoscale beams.

     

Agglomeration Effects on Static Stability Analysis of Multi-Scale Hybrid Nanocomposite Plates

We propose a multiscale approach to study the influence of carbon nanotubes’ agglomeration on the stability of hybrid nanocomposite plates. The hybrid nanocomposite consists of both macro- and nano-scale reinforcing fibers dispersed in a polymer matrix. The equivalent material properties are calculated by coupling the Eshelby-Mori-Tanaka model with the rule of mixture accounting for effects of CNTs inside the generated clusters. Furthermore, an energy based approach is implemented to obtain the governing equations of the problem utilizing a refined higher-order plate theorem. Subsequently, the derived equations are solved by Galerkin’s analytical method to predict the critical buckling load. The influence of various boundary conditions is studied as well. After validation, a set of numerical examples are presented to explain how each variant can affect the plate’s natural frequency.     

A mathemathical model for the calculation of the concentration at the outlet of an ozone generator

A mathematical model was generated to predict the composition of the outlet gas of ozone generators. In order to make the modelling possible it was important to predict the occurrence time and the exact location of each individual discharge zone. This was done by connecting a specially constructed ozone generator, which would locate the discharge zones, to a nanosecond pulse generator which would impose regular occurrence times for discharge columns. The experimental and theoretical outlet concentrations of this ozone generator were compared. The result was an excellent match which justified the assumptions made in the model. The mathematical model was also used to study the effect of different factors affecting the production of ozone.