Sharif Digital Repository

Through the combination of two types of seismic resisting systems including braced frames and steel shear walls, braced steel shear panel systems can be formed. This new lateral load-resisting system solves some of the defects of current special steel shear walls, such as imposing significant loads on boundary elements along with gravity load effects. Analysis and design of this new structural system underline the importance of having simple and precise finite-element models. To this aim, this paper presents two types of equivalent braced frames termed ‘overall equivalent brace’ and ‘equivalent mid-brace’. The equations of brace area, material strength and strain-hardening ratio are obtained... 

This study presents an online motion planning algorithm for generating reference trajectories during flight phases of a planar monopedal robot to transfer the configuration of the mechanical system from a specified initial pose to a specified final one. The algorithm developed in this research is based on the reachability and optimal control formulations of a time-varying linear system with input and state constraints. A two-level control scheme is developed for asymptotic stabilisation of a desired period-one orbit during running of the robot. Within-stride controllers, including stance and flight phase controllers, are employed at the first level. The flight phase controller is a feedback... 

Al6063 powder was subjected to severe plastic deformation via high-energy mechanical milling to prepare ultrafine-grained (UFG) aluminium alloy. Uniaxial compression test at various temperatures between 300 and 450 °C and strain rates between 0.01 and 1 s-1 was carried out to evaluate hot workability of the material. Microstructural studies were performed by EBSD and TEM. The average activation energy and strain rate sensitivity of the hot deformation process were determined to be 280 kJ mol-1 and 0.05, respectively. The deformation temperature and applied strain rate significantly affected the grain structure of UFG Al alloy. A finer grain structure was obtained at lower temperatures and... 

The general goal of the facility layout problem is to arrange a given number of facilities to minimize the total cost associated with the known or projected interactions between them. One of the special classes of the facility layout problem is the Single Row Facility Layout Problem (SRFLP), which consists of finding an optimal linear placement of rectangular facilities with varying dimensions on a straight line. This paper first presents and proves a theorem to find the optimal solution of a special case of SRFLP. The results obtained by this theorem prove to be very useful in reducing the computational efforts when a new algorithm based on tabu search for the SRFLP is proposed in this... 

In this paper, we have discussed the results of sensitivity analysis in a payoff matrix of the Matching Pennies game. After representing the game as a LP model, the sensitivity analysis of the elements of the payoff matrix is presented. The game value and the optimal strategies for different values of parameters are determined and compared  

Delaminated composite beam under general edge loading conditions is studied. Based on a technical engineering theory an analytical procedure for calculation of strain energy release rate and its separation into modes I and II of delamination is presented. By choosing a suitable displacement field based on second-order shear-thickness deformation theory and using the principle of minimum total potential energy, the equations of equilibrium are obtained along with the appropriate boundary conditions. The J integral and its definition for different modes of fracture is used for calculation of strain energy release rate and its separation into different modes. Double cantilever beam (DCB)... 

This study presents a motion planning algorithm to generate a feasible periodic solution for a hybrid system describing running by a three-dimensional (3-D), three-link, three-actuator, monopedal robot. In order to obtain a symmetric running gait along a straight line, the hybrid system consists of two stance phases and two flight phases. The motion planning algorithm is developed on the basis of a finite-dimensional optimisation problem with equality and inequality constraints. By extending the concept of hybrid zero dynamics to running, the authors propose a time-invariant control scheme that is employed at two levels to locally exponentially stabilise the generated periodic solution for... 

Presented is a novel approach for online trajectory modification of joint motions to transfer a free open kinematic chain, undergoing flight phase, from a specified initial configuration to a specified final configuration. Formally, it is assumed that a nominal trajectory, computed offline, can reorient the kinematic chain (reconfiguration problem) for a given angular momentum on a time interval. A modification algorithm of body joints, based on optimal control, is developed such that for different angular momentums and time intervals, the same reconfiguration problem can be solved online. This approach can be utilised for space robotics applications and online computation of planar running... 

This paper presents an analytical approach to design a continuous time-invariant two-level control scheme for asymptotic stabilization of a desired period-one trajectory for a hybrid model describing walking by a planar biped robot with noninstantaneous double-support phase and point feet. It is assumed that the hybrid model consists of both single- and double-support phases. The design method is based on the concept of hybrid zero dynamics. At the first level, parameterized continuous within-stride controllers, including single- and double-support-phase controllers, are employed. These controllers create a family of 2-D finite-time attractive and invariant submanifolds on which the dynamics... 

In the present work, graphene oxide (GO) and reduced graphene oxide (RGO) were incorporated at low-density polyethylene (LDPE)/ethylene vinyl acetate (EVA) copolymer blend using solution casting method. Monolayer GO with 1-nm thickness and good transparency was synthesized using the well-known Hummers's method. Fourier transform infrared and X-ray photoelectron spectroscopy data exhibited efficient reduction of GO with almost high C/O ratio of RGO. Scanning electron microscopy showed the well distribution of GO and RGO within LDPE/EVA polymer matrix. The integrating effects of GO and RGO on mechanical and gas permeability of prepared films were examined. Young's modulus of nanocomposites are... 

Presented is a novel approach for designing continuous-time update laws to update the parameters of stabilising controllers during continuous phases of bipedal walking such that (i) a general cost function, such as the energy of the control input over single support, can be minimised in an online manner, and (ii) the exponential stability of the corresponding limit cycle for the closed-loop impulsive system is not affected. Formally, a class of update laws with a radial basis step length is developed to minimise a cost function in terms of the stabilising controller parameters and initial states of the mechanical system  

The necessity of dynamic equivalents for power system analysis has been well known since the expansion of large interconnected power networks, and has been discussed during the last decades. The present paper proposes a new method for constructing dynamic equivalents of power systems. In this method, at the first step the "study system" is modeled completely via a single machineinfinite bus modeling procedure. Then the "external system" is identified as a MIMO feedback block of this model in such a manner that can include dynamic effects of the latter on the behavior of the former. The method is successfully experimented on a part of the Iranian southern network. Copyright © 2007 The... 

By locating a steel shear panel on the intersection point of the X-braces, concentrically or eccentrically braced shear panel (CBFSP or EBFSP) is formed. In this paper, to perform parametric study, 1-story CBFSP and EBFSP models with span length greater or less than height are considered. Using linear static analyses, the effects of size and location of the shear panel on the lateral stiffness of the frame with respect to the moment resisting frame with the same member sections are investigated. Next, for 1- And 3-story models, maximum displacement, along with base shear, and the ratio between the dissipated energy and input energy are examined under 4 ground motion records. Behavior of the...