Iranian Journal of Mechanical Engineering Transactions of ISME
Volume:10 Issue: 2, Sep 2010

In the present paper the behavior of an elastically mounted cylinder in low and high mass-damping ratio is investigated. For high mass-damping ratio, a classical wake oscillator model is used. At the first, by neglecting all damping and nonlinear terms of this model, the possibility of using a linear model for determination of the lock-in range and the dominant mode is investigated. Then, without neglecting any terms, the nonlinear model is analyzed and the results are compared with experimental results. Due to change of the behavior of the system in low mass-damping ratio and disability of classic model in modeling of this change, a modified wake oscillator model is presented and the results of this model, in both low and high mass-damping ratio, are compared with experimental results.

Modeling and Wrench feasible workspace analysis of a spatial cable suspended robots is presented. A six-cable spatial cable robot is used the same as Stewart robots. Due to slow motion of the robot we suppose the motion as pseudostatic and kinetostatic modeling is performed. Various workspaces are defined and the results of simulation are presented on the basis of various workspaces and applied wrenches (forces/moments) on the robot. The results show that enlarging the size of fixed platform, increasing vertical payload, reducing applied lateral forces and elimination of applied moments on moving platform, cause expansion of workspaces volumes for the purpose of heavy loads handling.

In previous papers authors have considered agents as inertialess self driven particles and designed a flocking algorithm. Application of this algorithm to agents with considerable inertial characteristics needs a behavioural controller. The controller uses the local information and helps every agent to imitate the desired behaviour as a member of the flocking frame which covers the main issue in this paper. All agents are assumed to possess limited identical influencing/sensing radius. The sliding-mode control technique is used, hence; effect of bounded disturbances and uncertainties can be omitted too. Once inertial agents are equipped with the behavioural controller, the multi-agent system behaves similar to a group of self-driven inertia-less particles which; coordination control algorithms and cohesion analyses are previously designed for.

In this article, thermal stability of beams made of functionally graded material (FGM) is considered. The derivations of equations are based on the one-dimensional theory of elasticity. The material properties vary continuously through the thickness direction. Tanigawa's model for the variation of Poisson's ratio, the modulus of shear stress, and the coefcient of thermal expansion is considered. The equilibrium and stability equations for the functionally graded beam under thermal loading are derived using the variational and force summation methods. A beam containing six different types of boundary conditions is considered and closed form solutions for the critical normalized thermal buckling loads related to the uniform temperature rise and axial temperature difference are obtained. The results are reduced to the buckling formula of beams made of pure isotropic materials.