Sharif Digital Repository

Vehicular ad hoc networks have attracted the attention of many researchers during the last years due to the emergence of autonomous vehicles and safety concerns. Most of the frameworks which are proposed for the modeling and analysis VANET applications make use of simulation techniques. Due to the high level of concurrency in these applications, simulation results do not guarantee the correct behavior of the system and more accurate analysis techniques are required. In this paper, we have developed a framework to provide model checking facilities for the analysis of VANET applications. To this end, an actor-based modeling language, Rebeca, is used which is equipped with a variety of model... 

Physicians use charts that are prepared by experiments on animals or humans to prescribe drug dosage for patients. This method requires some precious amount of time by the Ministry of Health to approve new drugs to be used in healthcare centers. Three-dimensional modeling of the inner medulla by considering the known physiological features help us to predict the distribution of a drug or any minerals in the kidney. In this study we present modeling of the important species distribution including Na+ and urea in the rat inner medulla that influence the urine concentrating mechanism. We use a C++ code to develop the inner medulla geometry based on physiological data to better capture the... 

Muscle fatigue affects the underlying EMG-force relationship on which EMG-assisted biomechanical models rely. The aim of this study was to evaluate the impact of short duration muscle fatigue on the muscle gain value. Participants performed controlled, isometric trunk extension exertions at 10, 20, and 30 degrees of trunk flexion and controlled isokinetic trunk extension exertions at 5 and 15°/sec on five separate days. Fatigue of the lumbar extensors was generated by moderate-intensity, trunk extension exertions. Participants performed controlled test contractions at defined intervals throughout the fatiguing bout and the EMG activities of trunk muscles were collected. These EMG data were... 

In this paper, the extended finite element method is presented for thermo-hydro-mechanical (THM) modeling of impermeable discontinuities in saturated porous media. The X-FEM technique is applied to the THM governing equations for the spatial discretization, followed by a generalized Newmark scheme for the time domain discretization. The displacement field is enriched by the Heaviside and crack tip asymptotic functions, and the pressure and temperature fields are enriched by the Heaviside and appropriate asymptotic functions. The process is accomplished by partitioning the domain with triangular sub-elements. Numerical examples are presented to demonstrate the capability of proposed technique... 

In this paper, a fully coupled thermo-hydro-mechanical model is presented for two-phase fluid flow and heat transfer in fractured/fracturing porous media using the extended finite element method. In the fractured porous medium, the traction, heat, and mass transfer between the fracture space and the surrounding media are coupled. The wetting and nonwetting fluid phases are water and gas, which are assumed to be immiscible, and no phase-change is considered. The system of coupled equations consists of the linear momentum balance of solid phase, wetting and nonwetting fluid continuities, and thermal energy conservation. The main variables used to solve the system of equations are solid phase... 

The effect of welding current and polarity, i.e. AC and DCEN, on imposed thermal cycles, mechanical properties, microstructural events and residual stresses was investigated in GTA welding of AA5052. A three-dimensional thermo-mechanical model was utilized to evaluate thermal responses and residual stresses distribution in the weldments. Tensile testing and hardness measurements were also conducted to study the effect of welding polarity on the mechanical properties of components. Microstructural observations utilizing optical microscopy were carried out to assess the microstructural evolutions. The results show that wide varieties of microstructures are produced in DCEN sample from cells at... 

In this work, the effect of tool geometric parameters on thermo-mechanical behaviour in friction stir welding of AA5086 has been investigated. For doing so, the thermo-mechanical responses of material during welding with different tools have been predicted by a three-dimensional finite-element model using the finite-element code ABAQUS. In addition, welding experiments have been carried out to study the developed microstructures and the mechanical properties of welded alloy. The results show that tool geometry significantly affects the energy input, deformation pattern, plunge force, microstructures, and mechanical properties of the joint. The conical tool with the shoulder angle of 2° has... 

The finite element method has been used to predict the stress intensity factors for cracked annular discs under constant central torque. Linear elastic fracture mechanics finite element analyses have been performed and the results are demonstrated in the form of crack configuration factors. To this end, the extensive ranges of crack configuration factors have been employed while considering the effect of disc stiffness. Then, the finite element results are applied to develop equivalent prediction equations using a statistical multiple nonlinear regression model. The accuracy of this model is measured using a multiple coefficient of determination, R2, where 0 ≤R2 ≤1. This coefficient is found... 

A hallmark of more advanced models is their higher details of trunk muscles represented by a larger number of muscles. The question is if in reality we control these muscles individually as independent agents or we control groups of them called "synergy". To address this, we employed a 3-D biomechanical model of the spine with 18 trunk muscles that satisfied equilibrium conditions at L4/5, with different cost functions. The solutions of several 2-D and 3-D tasks were arranged in a data matrix and the synergies were computed by using non-negative matrix factorization (NMF) algorithms. Variance accounted for (VAF) was used to evaluate the number of synergies that emerged by the analysis, which... 

The lasing mechanism and temporal output profile of distributed feedback dye lasers is investigated, using a model based on induced polarization in the dye solution, where a more accurate behavior of the laser output is predicted. It is found that the temporal output profile of the laser is mostly determined by the concentration of dye solution and the lifetime of the upper laser level of dye molecules. To a large extent, the results of this work agree with experimental studies, even at high-level pump intensities where the self Q-switched model fails to be applied. Especially, the experimentally observed irregular intensity profile of laser output is explained. It is also shown that, when... 

The mechanical stability of conductive, single-walled carbon nanotubes (SWCNTs) under applied electric field and compressive loading is investigated. The distribution of electric charges on the nanotube surface is determined by employing a method based on the classical electrostatic theory. For mechanical stability analysis, a hybrid atomistic-structural element is proposed, which takes into account the nonlinear features of the stability. Nonlinear stability analysis based on an iterative solution procedure is used to determine the buckling force. The coupling between electrical and mechanical models is accomplished by adding Coulomb interactions to the mechanical model. The results show... 

Range of motion (ROM) of the thoracic spine has implications in patient discrimination for diagnostic purposes and in biomechanical models for predictions of spinal loads. Few previous studies have reported quite different thoracic ROMs. Total (T1-T12), lower (T5-T12) and upper (T1-T5) thoracic, lumbar (T12-S1), pelvis, and entire trunk (T1) ROMs were measured using an inertial tracking device as asymptomatic subjects flexed forward from their neutral upright position to full forward flexion. Correlations between body height and the ROMs were conducted. An effect of measurement errors of the trunk flexion (T1) on the model-predicted spinal loads was investigated. Mean of peak voluntary total...