Sharif Digital Repository

This study proposes a computer modeling approach to find the optimal damping coefficients of the viscoelastic ankle-foot prostheses for each specific amputee. A two-dimensional locomotion model was developed for a transtibial amputee and personalized using his body measures and the reference gait pattern of an equivalent able-bodied subject. By employing the forward dynamic simulation, the amputee’s locomotion was synthesized for different prosthetic settings to find the optimal damping coefficients, based on a kinematics and a total work cost function. Results indicated a good agreement between the model predictions and the experimental observations. © 2018, © 2018 RESNA  

This study proposes a computer modeling approach to find the optimal damping coefficients of the viscoelastic ankle-foot prostheses for each specific amputee. A two-dimensional locomotion model was developed for a transtibial amputee and personalized using his body measures and the reference gait pattern of an equivalent able-bodied subject. By employing the forward dynamic simulation, the amputee’s locomotion was synthesized for different prosthetic settings to find the optimal damping coefficients, based on a kinematics and a total work cost function. Results indicated a good agreement between the model predictions and the experimental observations. © 2018, © 2018 RESNA  

The dynamic response of a Timoshenko beam with immovable ends resting on a nonlinear viscoelastic foundation and subjected to motion of a traveling mass moving with a constant velocity is studied. Primarily, the beam's nonlinear governing coupled PDEs of motion for the lateral and longitudinal displacements as well as the beam's cross-sectional rotation are derived using Hamilton's principle. On deriving these nonlinear coupled PDEs the stretching effect of the beam's neutral axis due to the beam's fixed end conditions in conjunction with the von-Karman strain-displacement relations is considered. To obtain the dynamic responses of the beam under the act of a moving mass, derived nonlinear... 

In this paper, a thorough investigation of response of a composite Timoshenko simply-supported beam with actuating layers, under the motion of a partially distributed mass is studied and a control system based on the feedback of beam's deflection velocity is applied to alleviate and suppress the vibration of the beam in either case when the mass is still traveling on the beam or departed the beam. The actuating layers are made up of Terfenol-D smart material which are sensitive to magnetic field (magnetostrictive materials) and this trait makes them very suitable to be used for vibration control. They introduce damping to the system through which the energy of system dissipates. The response... 

This article presents a comprehensive small signal model for a virtual synchronous generator (VSG) integrated into a microgrid. In the developed state-space, active and reactive power control loops of the VSG as well as resistances, and reactances of the lines are considered. Based on this model, the robust D-stable region in terms of different values of inertia constant $(M)$, and damping coefficient $(D)$ values of the VSG is obtained. To enhance both transient performance as well as guarantee the robust D-stable operation of VSG, an optimization problem is also proposed. Moreover, a new control method is suggested to damp frequency oscillations of the microgrid. The proposed controller is... 

The dynamic behavior of nonuniform-thickness laminated composite beams, such as helicopter blades, wind turbine blades, and robot arms, is of high importance in the design and fabrication of such elements. Changing the thickness of laminated structures is a significant challenge during fabrication because different tapering configurations may significantly alter the stiffness of the structures and thus the dynamic response of the structures. In this study, the effect of adding nanoparticles to resin on the stiffness and dynamic behavior of nonuniform-thickness laminated composite beam elements was investigated. A set of experiments were conducted to examine the natural frequencies and... 

This paper describes a three-dimensional (3D) finite-element (FE) model developed to assess the seismic behaviour of a novel prefabricated beam-to-beam connection termed a double-bolted flush end-plate beam (DBFEB) splice connection under cyclic loading. The seismic response was analysed and evaluated in terms of the hysteretic behaviour, rigidity, resistance degradation, ductility, energy dissipation capacity and equivalent damping coefficient. It is shown that the required performance can be achieved by controlling the end-plate thickness as well as the bolt grade and diameter; these parameters were therefore chosen as the key geometric variables investigated here for parametric study.... 

An experimental research study was carried out to investigate the life-time performance of unbounded Steel Reinforced Elastomeric Bearings (SREB), which are designed and used for service limit state in bridges, subjected to seismic demands. Such behaviour was investigated using 13 full-scale specimens in three phases; (1) effects of long-term service, namely the long term presence of vertical loading at service limit state, on the mechanical properties of the bearings, (2) effects of consecutive shear loading at different amplitude in presence of permanent loading, and (3) post-earthquake behaviour of the bearing against service load conditions. An innovative test setup was utilized in which... 

A novel semi-active control system for suspension systems of passenger car using Magnetorheological (MR) damper is introduced. The suspension system is considered as a mass-spring model with an eight-degrees-of-freedom, a passive damper and an active damper. The semi-active vibration control is designed to reduce the amplitude of automotive vibration caused by the alteration of road profile. The control mechanism is designed based on the optimal control algorithm, Linear Quadratic Regulator (LQR). In this system, the damping coefficient of the shock absorber changes actively trough inducing magnetic field. It is observed that utilizing the present control algorithm may significantly reduce... 

A dynamic model of an above-knee prosthesis during the complete gait cycle was developed. The model was based on a two-dimensional multi-body mechanical system and included a hydraulic and an elastic controller for the knee and a kinematical driver controller for the prosthetic ankle. The equations of motion were driven using Lagrange method. Simulation of the foot contact was conducted using a two-point penetration contact model. The knee elastic and hydraulic controller units, the knee extension stop, and the kinematical driver controller of the ankle were represented by a spring and a dashpot, a nonlinear spring, and a torsional spring-damper within a standard prosthetic configuration....