Sharif Digital Repository

A molecular dynamics simulation of the shock-wave propagation in the face-centered cubic (FCC) structured C60 fullerene along the <100>, <110> and <111> crystallographic directions is performed. For this purpose, the response of the material under different shock-wave loadings is studied through Hugoniot curves. Three regimes of the material behavior have been observed from fully elastic to elastic-plastic to plastic. The Hugoniot elastic limit and the phase transition are also investigated along different crystallographic directions. It is shown that the shock wave travels faster along the <110> and <111> directions than in the <100> direction in the material. Comparing the results with the... 

A molecular dynamics (MD) simulation is employed to study the phase transition process in argon induced by shock wave transmission. Deriving the relation between the shock and piston velocities, the theoretical equation of state for argon is presented. Also, argon equation of state is obtained by measuring the quantities directly from simulations to be able to detect the phase transitions. The phase transition is also detected by using argon phase diagram and free energy calculations. A comparison shows good agreement between the theoretical and MD results for the phase transitions. Based on these simulations, it is concluded that under a shock wave transmission with suitable energy, the... 

One of the main subjects in automotive industries is to enhance the efficiency of internal combustion engines. Wear between cylinder and ring is one of the major parameters reducing the engine performance. So many parameters are affecting the wear losses. Temperature plays a key role on the severity of wear condition in internal combustion engines. In conventional cast iron cylinders, it is not possible to increase the temperature from a defined level, as it causes excessive wear in contact area between cylinder liner and piston ring. One of the major benefits of using ceramic coating is their ability to withstand in higher temperatures, while having adequate hardness to improve wear rate... 

In this study, a novel prototype high-efficiency miniature pump that uses magnetic properties of a ferrofluid in both pumping and valving mechanisms is presented. The minichannel consisting of a cylindrical pumping chamber, a check valve, an inlet and an outlet, comprises six bonded layers of PMMA. A cylindrical permanent magnet that is placed inside the chamber and is externally actuated by a motorized off-center permanent magnet, functions as a revolving piston which sweeps the perimeter of the cylinder. Ferrofluid is used to cover the gaps between the magnetic piston and the channel walls, also serves as a separating plug between the inlet and the outlet of the chamber preventing... 

This paper presents the prototype design and fabrication of a magnetically actuated miniature pump that utilizes self-sealing capability of ferrofluid-covered permanent magnets in both pumping and valving mechanisms. The valving action is performed by employing one active valve along with two nozzle/diffuser elements. Two cylindrical permanent magnets are placed inside the flat-wall channels: One magnet acts as the active valve and the other one serves as a reciprocating piston actuating the working fluid. In order to seal the gaps between the channel walls and the permanent magnet of the valve/piston, ferrofluid is used to cover the surfaces of both magnets. The valve and the piston are... 

The problem of nonlinear aeroelasticity of a general laminated composite plate in supersonic air flow is examined. The classical plate theory along with the von-Karman nonlinear strains is used for structural modeling, and linear piston theory is used for aerodynamic modeling. The coupled partial differential equations of motion are derived by use of Hamilton's principle and Galerkin's method is used to reduce the governing equations to a system of nonlinear ordinary differential equations in time, which are then solved by a direct numerical integration method. Effects of in-plane force, static pressure differential, fiber orientation and aerodynamic damping on the nonlinear aeroelastic... 

Aero-thermoelastic analysis of a simply supported functionally graded truncated conical shell subjected to supersonic air flow is performed to predict the flutter boundaries. The temperature-dependent properties of the FG shell are assumed to be graded through the thickness according to a simple rule of mixture and power-law function of volume fractions of material constituents. Through the thickness steady-state heat conduction is considered for thermal analysis. To perform the stability analysis, the general nonlinear equations of motion are first derived using the classical Love's shell theory and the von Karman-Donnell-type of kinematic nonlinearity together with the linearized... 

This paper is devoted to study the effects of pressure drop in heat exchangers on the dynamics of a free piston Stirling engine. First, the dynamic equations governing the pistons as well as the gas pressure equations for hot and cold spaces of the engine are extracted. Then, by substituting the obtained pressure equations into the dynamic relationships the final nonlinear dynamic equations governing the free piston Stirling engine are acquired. Next, effects of the gas pressure drop in heat exchangers on maximum strokes of the pistons and their velocities and accelerations are investigated. Furthermore, influences of pressure drop increase in the heat exchangers on maximum and minimum gas... 

This paper presents the prototype design, fabrication, and characterization of a magnetically actuated micropump. The pump body consists of three nozzle/diffuser elements and two pumping chambers connected to the ends of a flat-wall pumping cylinder. A cylindrical permanent magnet placed inside the pumping cylinder acts as a piston which reciprocates by using an external magnetic actuator driven by a motor. The magnetic piston is covered by a ferrofluid to provide self-sealing capability. A prototype composed of three bonded layers of polymethyl-methacrylate (PMMA) has been fabricated. Water has been successfully pumped at pressures of up to 750 Pa and flow rates of up to 700 μl min-1 while... 

Engines that extract energy from low-grade heat sources, e.g., from other processes, have received considerable attention recently. The use of Fluidyne, which is a liquid piston Stirling engine, is quite popular. Herein, we explore the use of liquid-to-vapor phase change in a Fluidyne. This provides two considerable differentiators; (1) exploitation of very low temperature difference ΔT≈30 K, and (2) relatively low temperature ΔT≈330 K heat sources, for producing mechanical work, and thus electrical energy. The influence of three operating parameters, i.e., input heat flux, working fluid, and filling ratio, on the performance of the engine was characterized. Their optimum values, which yield... 

The purpose of this study is to analyze the nonlinear dynamic responses of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) beams exposed to axial supersonic airflow in thermal environments. The dynamic model of the FG-CNTRC beam is developed with regard to the first-order shear deformation theory incorporating the von Kármán geometrical nonlinearity. The thermomechanical properties of the constituents are assumed to be temperature dependent. The third-order piston theory is adopted to estimate the nonlinear aerodynamic pressure induced by the supersonic airflow. Harmonic differential quadrature method is implemented to discretize the equations of motion in the spatial... 

The significant importance of micro-scaled devices in medicine, lab-on-a-chip, and etc resulted in a vast variety of researches. The idea behind the novel hydro magnetic micro-pump and flow controller is that ferromagnetic particles, mixed and dispersed in a carrier fluid, can be accumulated and retained at specific sites to form pistons in a micro-tube using some external magnetic field sources along the micro-tube. This external magnetic field is related to some solenoids, which are turned on and off alternatively. Depending upon dragging speed of these pistons, which itself is a function of switching time, this device can be used to either increase (pumping) or decrease (valving) the flow... 

LM13 alloy is widely used in piston industry, due to its low coefficient of thermal expansion, excellent castability and hot tear resistance. In this research effect of casting process on wear behavior of LM13 alloy was investigated. First, samples were produced using two casting processes and heat treated. Then wear behavior of these samples under dry sliding condition was examined. Results of hardness and strength tests indicated that squeeze cast specimens exhibited higher mechanical properties. Wear experiment results showed that in both squeeze and gravity cast specimens, amount of weight loss increases with increase in sliding distance which is accompanied by reduction in wear rate and... 

In this paper, a metallic yielding damper, called piston metallic damper (PMD) is introduced for the first time. The PMD is comprised of a set of parallel hollow circular plates that interconnect inner shaft of the PMD to its outer pipe. Experiments and numerical models are used to examine its applicability as a seismic energy dissipating device. In this novel damper seismic input energy will be dissipated through flexural yielding of circular steel plates when system experiences small to medium displacements. At large displacements, tensile behavior will dominate and causes significant increase in stiffness of the system. In experimental program, different specimens were tested and the...