Sharif Digital Repository

Exoskeleton is a wearable active device used to augment human power in upper or lower extremities. The integration of robotic devices and conventional physiotherapy is becoming more and more acceptable worldwide. The main scope of this thesis is to design and develop a prototype of a light, low-cost and wearable robotic exoskeleton to rehabilitate the upper extremity in stroke patients at home. For this purpose mechanism of a wearable exoskeleton will be proposed compatible with upper extremity degrees of freedoms with minimum number of actuators which is constructed inexpensively to eliminate the demand of expensive and professional therapists. The conceptual design of such a system should... 

The aim of this thesis is the concept extraction of sequential patterns for imitative learning for humanoid robots. In such a way that an existent that has the physical and cognitive similarities, begins to extract concepts and learns by observing the behavior of the other existent. In this project, it is assumed a humanoid robot that can understand the concepts such as hello, goodbye and different concepts and does the corresponding actions from the visual and auditory information. In this thesis, a new model has been presented to eliminate the improper and meaningless elasticity in patterns sequence, such as changes in accent or elasticity in movements. This model is called the fuzzy... 

This work examines the problem of the fully coupled magneto-electro-elastic (MEE) scattering of SH-waves incident upon a heterogeneous MEE scatterer which is embedded in an unbounded medium. The scatterer consists of a circular core and a circular encapsulator with eccentricity. All three regions: the core, encapsulator, and the surrounding matrix have distinct MEE properties and fully coupled constitutive relations. The generated coupled MEE fields coexist simultaneously in all these regions without resort to any simplifying assumptions. The precise description of the multifunctionality involves the solution of three fully coupled partial differential equations in three different regions.... 

Normal aggregates are replaced by polystyrene beads (EPS) due to their low unit weight. EPS concrete is known for its low density and environmentally friendly properties apart from having various pros such as better heat and sound isolation, affordability, and ease of construction. EPS grain size can also affect the compressive strength, and the tensile strength of EPS concrete compression is also inversely related to EPS grain diameter. The EPS concrete has four different percentages of EPS; 0%, 25%, 50%, and 75%. Each EPS percentage has six different unit weights; 15,20,25,30,35 and 40 kg/m3. In the present study 19 different types of mixing designs were used, the one with no EPS beads has... 

In this study, elastic analysis of a functionally graded full-space with quadratic variations under various types of loading is addressed. The elastic responses of the medium are obtained in closed-form under various types of loading including point load, concentrated moment, distributed patch load of rectangular and circular shape, normal ring load, and concentrated torsion. The displacement fields are derived by virtue of the appropriate Green’s functions corresponding to the FGMs with a quadratic variation of elastic moduli and constant poisons ratio of = 0.25 .For the special case of homogeneous medium, the results are verified with available solutions. Furthermore, effects of degree of... 

Nowadays, by adding a small amount of a desired nanomaterial to a matrix having certain properties one may design a multifunctional nanocomposites with a remarkably improved macroscopic properties of interest. The capability of conventional continuum theories in treating the problems of embedded ultra-small inhomogeneity with any of its dimensions comparable to the characteristic lengths of the involved constituent phases is questioned, mainly, on the grounds of the accuracy and the size effect. In this work, effort is firstly directed at the prediction of the macroscopic shear modulus of composites consisting of nano-/micro-size fibers of elliptic cross-sections via couple stress theory, a... 

In this paper, the elastic response of a surface-stiffened transversely isotropic half-space subjected to a surface normal load is addressed. The half-space is reinforced by a Kirchhoff thin plate bonded to its surface. Two different boundary conditions are considered across the plate-half-space interface: (i) the classic approach in which the plate in-plane deformation is neglected by writing the interfacial boundary conditions across the plate mid-plane, and (ii) the refined approach that considers the in-plane deformation of plate due to bending by writing the boundary conditions across the bottom face of plate. By virtue of appropriate displacement potentials, the complete set of elastic... 

A theory of gradient elasticity is used and numerically implemented by a meshless method that is called reproducing kernel particle method (RKPM) to model size effects. Some of the problems are modeled under the consideration of gradient elasticity for the first time and all of them are also modeled with classical elasticity to compare with gradient elasticity. First of all, the RKPM formulation and computing the amount of shape functions and requisite derivatives will be explained with details and a mathematical innovation that will decrease the computational cost seriously proposed for the first time. Several 1D and 2D shape functions with first and second derivatives that are resulted... 

Recently, there has been a strong interest in the development of a new class of meshfree methods. As an alternative to the finite element method (FEM), mainly due to elimination of high cost mesh generation processes. In addition, the size effect is currently a subject of increasing interest since it is an important parameter in predicting, correctly, the mechanical behavior of materials with microstructure. It was well established that classical linear elastic continua which neglects the higher order terms is not able to describe size effects. In contrast, enhanced continuum theories such as nonlocal or gradient-dependent models do involve an internal length scale. Thorough this length... 

In many structures, crack creation is one of the most significant fracture mechanisms. To predict these fracture mechanisms accurate numerical modeling is necssary. Finite Element Method (FEM) is one of the substantial methods in analysis of numerical fracture problems in recent past decades. But, this method has difficulties in remeshing of elements in each step of calculation in fracture mechanics or large deformation analysis. Therefore, the theory was defined that, without using elements, just with setting of characteristics nodes in geometry of problem, the differential equations can be solved. These methods are called Meshfree or Meshless methods. RKPM is a new meshfree method for... 

Queuing algorithms are used in packet forwarding elements such as routers or switches and the goal is to minimize transmission delays as well as to help manage network congestions. On the other hand, over 90 to 95% of the packets in the Internet use TCP and correspond to the transfer of digital documents of one form or another (Web pages, data files, MP3 tracks etc.) ; this kind of traffic is called elastic. In this thesis, we present a new Start-time Fair Queuing (SFQ) algorithm called Weighted Start-time Fair Queuing (WSFQ) which is more efficient and achieves better fairness than SFQ in the presence of small and huge elastic traffic flows. WSFQ scheduler, like SFQ uses a start time... 

Outer membrane proteins play the role of molecular machines in the outer membrane of bacteria to regulate their basic functions. These macromolecules have nano-scale dimensions and they are involved in the classifications of nano-machines and nano-pores. Protein structure is constructed of chain of amino acids. Coarse grained elastic network model of the protein introduces a network of selected point masses, which is located on α-carbon of each amino acid, linked together with harmonic springs that represent the interactions between residues, both the chemical (protein backbone) and physical bonds. Using the harmonic network potential and theory of mechanical vibration, normal modes of... 

The broad range of applicability of nano devices particularly in electronics, optoelectronics, and micro/ nano-electro- mechanical systems has drawn the attentions of the industrial and scientific communities of various disciplines. This work is devoted to study the effect of surface and interface elasticity in the analysis of the mechanical behavior of ultra-thin objects in the presence of some statical or dynamical loadings. Based on the fact that the surface-volume ratio increases in nano-scale, description of the behavior of such a small structure via usual classical theories, which generally neglect the surface/interface effect, ceases to hold. In the present study, first, a... 

In this study, the effect of the initial bow on vibrations and stability of the rotor with nonlinear supports has been investigated. Using the energy method, the rotor’s equations of motion for the four-degree of freedom Jeffcott rotor and the elastic rotor assuming Tymoshenko beam relations are calculated. It is very important to study the initial bow as one of the common faults in rotating machines that has a great effect on system vibrations. A method was proposed to reduce rotor vibrations and balancing systems. Choosing a way to eliminate machine defects is one of the points considered by rotor dynamic engineers. Many factors can cause a bow in the rotor, some of the most important of... 

In this study, the nonlinear vibrations of an elastic rotor that is under the elastic support and under the follower force caused by the airflow passing through the rotating plane are investigated. The elastic shaft is modeled by the Timoshenko beam theory, which is connected to a motor through a flexible coupling and the motor increases the rotational speed of the rotor by applying torque. Gibbons’ equations have been used to model the misalignment forces. First, the kinetic energy of the rotating system is calculated nonlinearly to take into account the effect of nonlinear terms due to the rotational inertia of the system, and then the potential energy and The work of external forces on... 

A simple control system contains at least an actuator, a controlled link, and a foundation. These structures are not ideally rigid, this flexibility can appear willingly or unwillingly in any parts of the system or the connections between them. As a consequence of this flexibility, the movement of the controlled part will fluctuate unintentionally. In this thesis, a control system with rigid controller and flexible torsional base is investigated and controllers are designed and compared to reduce these unwanted vibrations. Finally, by implementing the controllers on the constructed system, the experimental results are obtained and compared with the analytical results.To fabricate the... 

This thesis aims to introduce a numerical method for investigating the appropriate arrangement of visco-pseudo-elastic dampers applicable to shell and plate structures under large deformation. These passive dampers are considered as viscoelastic layers and discrete shape memory alloy (SMA) wires in which this combination improves their overall efficiency and reduces their drawbacks. Also, the main advantages of these dampers are discussed during some illustrative problems. The current finite element formulation is based on an incremental updated Lagrangian (UL) approach along with the Newmark's integration technique. In the layerwise shell element, the Mindlin-Reissner theory is adopted in... 

The use of metal matrix composite materials (MMC) in aerospace structures and engine parts has become more frequent recently. These materials are composed of metal matrices reinforced by hard discontinuous ceramic fibers, usually oriented longitudinally within the matrix, and due to the stability of the mechanical properties, including the hardness and the strength at high working temperatures, have found various applications.Stress transfer from the matrix to the fiber is known as the most important mechanism governing the deformation and the fracture response of such MMCs. The stress transfer characteristic of fiber reinforced composite materials under various mechanical and thermal... 

In recent years, lattice Boltzmann method (LBM) has been developed to be used as an alternative and promising computational technique to simulate various flows. It originates from classical statistical physics. The ability to simply solve complex flows, simulating of multiphase and multi-component without need to follow the boundaries of different phases, and the inherent ability of parallel processing are notable features of this approach. On the other hand, finite element method (FEM) is widely used in many practical engineering fields, especially in solid mechanics. In this study, in addition to simulating flow over a rigid body, flow over an elastic body is also simulated with a... 

In this study, static and dynamic buckling of laminated composite beams resting on an elastic foundation under thermal and mechanical load is studied. Beam is resting on an elastic foundation with hardening/softening term. Nonlinear governing equations are obtained based on the energy method and are solved via the multi-term Galerkin method and the Newton-Raphson numerical method. Critical dynamic load is estimated by the Hoff Simitses criterion. The results are validated with the results of available articles in this field. In the following, the effects of different parameters of the problem on the results are examined. Results reveal that for a sufficiently stiff softening elastic...