Sharif Digital Repository

Patellofemoral joint has an important role in knee extension. Because of this joint importance and complicated mechanical behavior, a lot of mathematical models have been used, to obtain a better understand of this joint, considering this joint as a part of knee joint or as a separate joint. Although these works have comprehensively studied the patellofemoral joint but they don’t emphasis on dynamic aspects. Also there is no work to compare the experimental and theoretical results calculated from one specified subject knee.In this study, the kinematic and dynamic of patellofemoral joint has been studied, constructing a three dimensional dynamic model of patellofemoral joint and experimental... 

The purpose of this study is to analytically study the aeroelastic characteristics of the cylindrical shells fully treated with passive constrained layer damping (PCLD) to indicate the effects of various parameters on the behavior of such structures. Constraining the viscoelastic layers increases the amount of dissipated energy and the bending stiffness of the structure without considerable change of the weight.
A thin shell theory in conjunction with the Donell assumptions is employed for the shell and the constraining layer (CL) and the first order shear deformation theory (FSDT) is used for the viscoelastic layer to construct the model. The effects of rotary inertia and shear... 

Bitumen ageing is one of the principal factors causing the deterioration of asphalt pavements. Ageing is a complex process that is affected by different parameters.With the rapid growth of modified binders in road paving applications over the past twodecades, it is important to study the ageing properties of these binders. A number of laboratory methods are used tosimulatethe bitumenageing at various stages of the production and service of hot mix asphalt.Recent studies have shown that Superpave testing protocol does not fully address the ageing of modified binders. To study the ageing properties of modified binders, three different types of binder modifiers, plastomer, elastomer, and ground... 

Determining nonlinear dynamic behavior of structures is always one of the main goals of structure and earthquake engineers. The Modal Incremental Dynamic Analysis (MIDA) is one of the newest methods for analyzing the seismic behavior of structures. Indeed, this method has superseded the exact IDA method which is too complicated and prolix. Although, this method represents approximate results, high accuracy, fastness and low cost procedure made it an efficient and useful technique. Many researchers have used this method and investigated the accuracy of that and achieved proper results. Up to now no one has applied this method on structures which are equipped with dampers. In the procedure of... 

Different aspects of oscillatory behaviors of sandwich structures with viscoelastic cores are investigated in the present study in four parts. In the first part, an analytical study is conducted to determine the variation of linear frequencies and damping ratio of different families of modes with system parameters. The participation of different families of modes such as the so-called pumping or thickness-shear modes along with the overall bending modes in the transverse response of the structure to transverse wide-band excitation is also investigated in this part. The formulation of the problem is established by assuming quadratic variation of displacement components of the core through the... 

In this thesis, equations related to large deformation of a polymer were derived by considering viscoelastic effects. To express type of material behavior which includes elastoplastic and viscoelastic property at the same time, two-layer viscoplastic model was used. An axisymmetric model was used for modeling problem in finite element software. By derivation of parameters related to two layer model and entering them in finite element software and also entering other properties required to model the forming process, modeling was performed by special profile connecting input and output sections. Due to favorable properties of spline functions, profiles used in die geometry, were selected from... 

Vibrations with high amplitudes in continuous systems and models with multiple degrees of freedom, in specific conditions, is concomitant with a phenomenon called internal resonance. In the presence of this phenomenon, energy is transferred from one directly excited mode to the other vibrating modes of the structure results in response of the structure to be combination of the excited modes. In that situation occurrence of the internal resonance may decrease the level of undesired vibrations of the structure. This behavior is of interest especially in sandwich structures with viscoelastic cores that are designated to improve the damping characteristics of the structure and the property may... 

Dissemination of an analyte under the laminar flows plays a major role in measuring and assessment of biological fluids such as sample preparation in the context of microfluidic systems. Due to the development of manufacturing technology in the Lab-on-a-chip devices, the production of rectangular microchannels with finite aspect ratios and micron and submicron sizes has been provided by which the effect of electrokinetic phenomena on concentration distribution will be magnified in these systems. On the other hand, these biofluids are viscoelastic and show extraordinary flow behaviors, not existing in Newtonian fluids and adopting appropriate constitutive equations these exotic flow behaviors... 

Torsional vibrations of internal combustion engines and reciprocating compressors, is one of the challenges in the design process. It can reduce power of productivity, equipment operating lifetime and increase noise of the system. Torsional viscous damper is a method to reduce torsional vibrations in rotating equipment. In this study, three-dimensional simulations of torsional viscous damper is performed as a matter of FSI, with consider harmonic excitation on the external walls and calculation of damping response inertia ring in CFX software. The viscoelastic non-Newtonian model properties of damping fluid is calculated in MATLAB software with respect to viscoelastic parameters. For... 

Polycarbonate (PC) and polyethylene-terephthalate (PET) are important engineering thermoplastics. During last decades these polymers and their blends have been studied extensively due to their wide range of applications. Blends of PET and PC combine mechanical properties and chemical resistance together, which make applicable in various components such as automotive, electrical and of medical parts. It has been accepted that PET/PC immiscible blends are subjected to transesterification reactions during thermal processing, which produces PET-PC copolymer chains. In fact, scissioning and substitution of ester/carbonate functional groups of PC and PET at the interface, transforms the initial... 

Acidizing efficiency depends on various factors such as formation properties, reservoir and stimulation fluid types and injection scenario. Among these factors, heterogeneity of reservoir’s formation (layered reservoirs and permeability variation versus depth) strongly affect acidizing performance. Accordingly, applying a reliable technique that distribute stimulation fluid uniformly is essential. The aim of carbonate matrix acidizing is to improve fluid flow specially in low permeability zones. Stimulation fluid cannot enter into the low permeability layer due to existence of high permeability layers which are in contact with low permeability ones. So, the stimulation fluid should be... 

Wound is a defect or failure in the skin texture which occurs as a result of physical or heat injuries or physiological conditions. The wound dress as a temporary cover can improve wound healing process and due to the unique properties, hydrogels have become appropriate choice for this application. Hydrogel’s structure allows drug to be loaded in the wound dress. Hydrogel wound dress should have adequate fluidity to cover wound’s bed and make full contact with the skin. Sufficient cohesion and strength is also necessary to allow the wound dress to remove from wound completely. Therefore, the study on the viscoelastic properties of hydrogel is important. In this study, polyvinyl alcohol... 

Although many aspects of helical strand have been carried out, there are still some situations which need more studies. Based on previous studies of wire rope the constitutive equations regarding the rope tension and torque to the rope deformations are carried out. In which constitutive constants depend on both the rope material and geometry of the rope. Equations of motion for straghit rope loaded simultaneously in tension and torque are derived, and with using extensional-torsional deformations in both side of the rope, dynamic stiffness matrix is derived. Some experimental results and currently models are compared with my research model numerically. Finally, mechanic response of helically... 

In this work, the viscoelastic fluids flow and their short fiber suspensions has been modeled in contraction geometry using conformation models, these models predict behavior of polymeric chains in contraction geometry. Prediction of viscoelastic fluids flow through a contraction is very important, especially in polymer processing where a polymer melt in barrel of an extruder is going to pass through a narrow die. We expect to see an eddy in each corner of barrel. The result has shown that increasing of De number enhances the eddy magnitude; also with making acute angle, we see decreasing of eddy magnitude. Normal stresses and velocity were investigated in contraction and their results had... 

In the present dissertation model based grasping of soft tissue with the laparoscopic gripper, tissue deformation under the applied load and control of the tissue-instrument interaction have been studied. As the first step a cantilevered beam under bending and tension has been modeled statically and dynamically using the meshless EFG based method. Results show that an increase in the number of nodes at the displacement boundary and the area of force insertion improves the accuracy of the predicted displacement in the model compared to the analytical solution. In the second step the model is developed for a hemisphere under vertical and lateral compression. Comparison of the deformation of... 

Tire is one component of the suspension system and has beneficial effects on reducing vibrations caused to the vehicle. This study aims to determine the factors affecting the damping and stiffness of the tire is carried out. The modeling of factors were identified. For testing the modeling effort is to be made to the instruments used to measure the damping and stiffness of the tires. To make the structural static analysis, dynamic and modal was to have sufficient structural strength and the displacements and stresses are sensibly placed. Factors that have influence on the hardness of the ring diameter, the outer diameter of the tire, tire pressure, tire tread depth, tire wall thickness,... 

Asphalt concrete exhibits viscoelastic and viscoplastic behavior which is dependent on rate and temperature. To model this behavior, various mechanical modelshave been presented in which total strain, as the response of the applied stress, is decomposed by various researchers to recoverable and permanent strains.Accumulation and expansion of permanent response result in rutting which is a dominant and prevalent distress in hot mixed asphalt (HMA) in hot climates. The available models are not capable of accurately calculate the viscoplastic strain under cyclic loading.
To close this gap, recovered viscoelastic strain at rest (unloading) period was introduced. This parameter accounted for... 

In the present study, the performance of Viscoelastic Dampers in reducing the seismic response of the structures was investigated. For this purpose, first the effect of added damping to the system was studied. Number of 3-D steel structural models, with and without eccentricity which are designed with the 2800 code (first edition) and 519 code provisions that is not satisfied the provisions of the code-2800(third edition) is considered. It is assume that this system is located on a relatively stiff soil (soil type II based on Iranian Seismic Standard Code - 2800), a number of compatible earthquake records also considered to be used in the parametric studies. The results indicate that in... 

Including control systems structures against lateral forces such as dynamic loads, earthquakes etc. are viscoelastic damper, that their use in recent years on the structure had positive results. Although the use of dampers improve certain behavioral characteristics, such as relative displacement, but can increase the structural acceleration and energy absorption structures. Passive damper performance depends on several factors such as temperature, time, frequency, stiffness of bracing and structures, type of loading that should any of these uncertain in the optimal design of controlled structures taken into account. Common method of achieve proper placement pattern of passive dampers, which... 

Red blood cells (RBC, erythrocytes) are cells with an average diameter of 8 microns, the thickness of 2-3 microns and the volume of 90 fl. The biconcave shape of red blood cells,together with cell membrane flexibility, enables them to pass the capillaries whose diameter is considerably less than 8 micrometers. Mechanical properties of RBC are related to their membrane and cytoskeleton, which consists of spectrin network. Optical tweezers is able to exert very precise forces to erythrocytes using beed as a handle. In this report, we studied mechanical properties of RBC such as elasticity and viscoelasticity using single trap optical tweezers with beads with antibody coated in order to attach...