Sharif Digital Repository

The prediction of interfacial turbulence characteristics is one of the still challenging of two-phase stratified flow. The evaluation of some important parameters such as interfacial heat transfer coefficient based on turbulence kinetic energy and turbulence dissipation rate in some models, intensifies the importance of turbulence flow correct simulation. High gradient of velocity and turbulence kinetic energy at the interface of two-phase stratified flow leads to a major overestimation or underestimation of flow characteristics without any special treatment. Consideration of a source function of turbulence eddy frequency at the interface is one of the common solution employed in past... 

Effect of random signals with various powers, as current loads, on positioning and disturbance rejection problems on micro-step PID closed loop control system is addressed in this paper. Experimental results due to implementing different white noise power, speed, and a 0.3 N.m disturbance load torque show that, Random noise source changes current profile and affects the accuracy of positioning in tracking and disturbance rejection problems. Performance of the PID proposed controller under the implementation of random noise on phases of the HSM has been proved to be accurate enough even under disturbance torque acting on the system. Copyright © 2005 by ASME  

This paper gives the results of simulation and experimental investigation on the effects of random signals on the accuracy of micro-stepping control positioning. For studying and simulation of the effect of random noise signals on performance of the accurate position control systems, such as Hybrid Stepper Motors (HSMs), a micro-step driver and controlling unit using PID controller has been designed and constructed. Several parametric studies have been carried out including different white noise power and micro-step per revolution. Tracking problem for a HSM model has been simulated, and the experimental study for similar cases has been carried out by implementing the designed controller in... 

Exceptions are an indispensable part of the software development process. However, developers usually rely on imprecise results from a web search to resolve exceptions. More specifically, they should personally take into account the context of an exception, then, choose and adapt a relevant solution to solve the problem. In this paper, we present Exception Tracer, an Eclipse plug in that helps developers to resolve exceptions with respect to the stack trace in Java programs. In particular, Exception Tracer automatically provides candidate solutions to an exception by mining software systems in the Source Forge, as well as listing relevant discussions about the problem from the Stack Overflow... 

We use field emission scanning electron microscope (FE-SEM) to investigate the growth of palladium colloids over the surface of thin films of WO3/glass. The film is prepared by Pulsed Laser Deposition (PLD) at different temperatures. A PdCl2 (aq) droplet is injected on the surface and in the presence of steam hydrogen the droplet is dried through a reduction reaction process. Two distinct aggregation regimes of palladium colloids are observed over the substrates. We argue that the change in aggregation dynamics emerges when the measured water drop Contact Angel (CA) for the WO3/glass thin films passes a certain threshold value, namely CA ≈ 46°, where a... 

During the past decade, Electro-Hydraulic system has performed a significant role in industrial engineering as an actuator for high performance and precision positioning applications. In this case, many control methods have been developed for an electro-hydraulic actuated clutch. In this paper a Linear Quadratic Regulators (LQR) is proposed to trajectory control of a wet clutch actuated by a hydraulic servo valve mechanism. Simulation study was performed using linearized mathematical model of the system implemented in MATLAB software. Based on the simulation results performance of the proposed controller was evaluated and discussed  

Temperature gradient on the thick Reactor Pressure Vessel (RPV), caused by sudden overcooling events, especially in the downcomer, would intensify the propagation of structural defects. This situation known as Pressurized Thermal Shock (PTS) could be created in case of Emergency Core Cooling System (ECCS) actuation which leads to injection of cold water into the cold leg of the primary loop in some accidents, e.g. Loss Of Coolant Accident (LOCA). Prediction of Plant response to LOCA and water temperature gradient in the downcomer are performed in thermal-hydraulic section of PTS analysis. Employment of system codes is one of the proposed procedures in literature to obtain plant response and... 

Injection of Emergency Core Cooling System (ECCS) water into the primary loops of the Pressurized Water Reactors (PWRs) leads to rapid cooling of Reactor Pressure Vessel (RPV) inside wall after Loss Of Coolant Accident (LOCA). This condition, known as Pressurized Thermal Shock (PTS) intensifies the propagation of the RPV structural defects and would be considered as an ageing mechanism. For structural and fracture analysis of RPV wall, thermal-hydraulic analysis of PTS should be accomplished to obtain the steam/water flow characteristics in the downcomer. For this purpose, simulation of steam/water stratified flow (due to density difference) after the injection point should be done by... 

Non-uniform temperature distribution at horizontal pipes cross section leads to an asymmetric thermal stress. This condition would be considered as an ageing mechanism due to fatigue effect, known as thermal stratification. To evaluate this ageing mechanism, the stress analysis should be done in horizontal pipelines like surge-line connected the pressurizer to the hot leg of primary loop of NPPs by consideration of operational or transient conditions. During these conditions, the status of surge-line would be single phase or two-phase stratified flow. To estimate the equivalent stress in horizontal section of surge-line, the developed CFD model for both single and two-phase flow is coupled... 

In this paper, the general analysis of two-dimensional steady-state thermal and mechanical stresses for a hollow thick infinite cylinder made of Functionally Graded Piezoelectric Materials (2D-FGPMs) is performed and developed. The general form of thermal, mechanical, and electrical boundary conditions is considered on the inside and outside surfaces. A direct method is used to solve the heat conduction equation and the non-homogenous system of partial differential Navier equations, using the complex Fourier series and the power law functions method. The material properties are assumed dependent on the radial and circumferential variables and are expressed as power law functions along the... 

In this paper, the general analysis of two-dimensional steady-state thermal and mechanical stresses for a hollow thick infinite cylinder made of Functionally Graded Piezoelectric Materials (2D-FGPMs) is performed and developed. The general form of thermal, mechanical, and electrical boundary conditions is considered on the inside and outside surfaces. A direct method is used to solve the heat conduction equation and the non-homogenous system of partial differential Navier equations, using the complex Fourier series and the power law functions method. The material properties are assumed dependent on the radial and circumferential variables and are expressed as power law functions along the... 

Axial-Offset (AO), as an important operational parameter, should be monitored in the load-following procedure due to the safety limits related to xenon oscillation and axial peaking factor in a nuclear power plant. In this study, to calculate AO for a Small Modular Reactor, a neutronic/thermal–hydraulic simulator has been developed based on coarse mesh methods. In this simulator, the average current nodal expansion method and the single heated channel approach have been used for neutronic and thermal–hydraulic analysis, respectively. The developed simulator is verified by the IAEA-3D model and thermal–hydraulic benchmark model. As the iPWR small modular reactor case study, SMART reactor has... 

The precise manipulation of the magnetic catheters is of great importance for different applications, ensuring efficacy while minimizing potential complications. This research delves into the position control of a magnetically actuated catheter guided with an external permanent magnet. Due to the complexity of governing equations describing the system's behavior, a neural network approach was deemed suitable for modeling. Using a five degrees of freedom manipulator carrying an external permanent magnet as a payload, data was gathered from real-world positionings, tracking the coordination of the magnetic catheter's end point. These data points served to train the neural network, subsequently... 

Exoskeletons are robotic devices which are used in power augmentation and rehabilitation robotics. The exoskeleton control system is one of the most challenging issues in humanrobot interaction systems. Although the rehabilitation robotic control methods are well studied, little research has been conducted on power augmenting control methods. This paper presents a novel idea in control system of exoskeletons for load carrying and power augmentation. Here, the desired linear velocity of the exoskeleton in interaction points are taken to be proportional to interaction force at the corresponding location. The introduced control method is merely based on kinematic model and thus easy to... 

In order to be adapted to changes in user requirements and/or the environment, many software systems need to run continuously while they evolve. Most current approaches for such dynamic reconfiguration assume that the evolved system will behave as expected and thus will be reliable if the reconfiguration is consistent. This assumption may not correspond to reality because the delivered quality estimated previously could vary due to parameter changes at runtime. To ensure that the system acts correctly in the field after the reconfiguration, reliability of changes has to be checked at runtime. Existing approaches, however, are not applicable in highly available systems due to the possibility... 

For a successful repair and reconstruction of bladder tissue, fabrication of scaffolds with proper biochemical and biomechanical characteristics is necessary. Decellularized bladder tissue has been proposed in previous studies as a gold standard material for scaffold fabrication. However, weak mechanical properties of such a load-bearing tissue has remained a challenge. Incorporation of both biological and synthetic materials has been known as an effective strategy for improving mechanical and biological properties of the scaffolds. In the present work, a simple process was developed to fabricate hybrid hydrogel scaffolds with a biomimetic architecture from the natural urinary bladder... 

In this paper, we study graphs whose matching polynomials have only integer zeros. A graph is matching integral if the zeros of its matching polynomial are all integers. We characterize all matching integral traceable graphs. We show that apart from K7(set minus)(E(C3)∪E(C4)) there is no connected k-regular matching integral graph if k≥2. It is also shown that if G is a graph with a perfect matching, then its matching polynomial has a zero in the interval (0,1]. Finally, we describe all claw-free matching integral graphs  

In this paper, we study graphs whose matching polynomials have only integer zeros. A graph is matching integral if the zeros of its matching polynomial are all integers. We characterize all matching integral traceable graphs. We show that apart from K7∖(E(C3)∪E(C4)) there is no connected k-regular matching integral graph if k≥2. It is also shown that if G is a graph with a perfect matching, then its matching polynomial has a zero in the interval (0,1]. Finally, we describe all claw-free matching integral graphs. © 2017 Elsevier B.V