Sharif Digital Repository

In this paper we present a method for transient analysis of availability and survivability of a system with the identical components and identical repairmen. The considered system is supposed to consist of series of k-out-of-n or parallel components. We employed the Markov models, eigen vectors and eigenvalues for analyzing the transient availability and survivability of the system. The method is implemented through an algorithm which is tested in MATLAB programming environment. The new method enjoys a stronger mathematical foundation and more flexibility for analyzing the transient availability and survivability of the system. © 2006 Elsevier Inc. All rights reserved  

This paper proposes a low-cost fault-tolerant Carry Look-Ahead (CLA) adder which consumes much less power and area overheads in comparison with other fault-tolerant CLA adders. Analytical and experimental results show that this adder corrects all single-bit and multiple-bit transient faults. The Power-Delay Product (PDP) and area overheads of this technique are decreased at least 82% and 71%, respectively, as compared to adders which use traditional TMR, parity prediction, and duplication techniques. © 2009 IEEE  

The fast and very fast transient overvoltages can endanger the insulation of transformer windings. Therefore, it is necessary to develop models, to study these transients. This paper compares the two well-known multiconductor transmission line (MTL) and lumped parameter detailed (RLC ladder network) models. The high-voltage (HV) winding of a 220/35-kV, 50-MVA transformer has been modeled using these models. The simulation results of the MTL and the RLC ladder network models have been compared with the measurements results in the frequency domain, by application of the Pearson's correlation coefficients. It is shown that the RLC Ladder Network model should be used for fast transient... 

This paper presents an experimental evaluation of transient effects on SRAM-based FPGAs. A total of 9000 transient faults were injected into the target FPGA using Power Supply Disturbances (PSD). The results show that nearly 60 percent of faults cause system failures and about 58 percent of the faults lead to corruption of the configuration data of the FPGA chip. © 2005 IEEE  

The paper aims at addressing the effect of the bonding time on the metallurgical and mechanical properties of a transient-liquid-phase (TLP) bonded IN718 nickel-based superalloy using an Ni-15.2Cr-4B (%) amorphous filler alloy. The results showed that after a partial isothermal solidification, the residual liquid in the joint centerline transformed, during the cooling, to non-equilibrium eutectic-type microconstituents composed of Ni-rich boride, Cr-rich boride and eutectic γ-solid solution phase. The complete isothermal solidification which resulted in a formation of an intermetallic-free joint centerline occurred after a holding period 40 min at the bonding temperature of 1100 °C. An... 

Mixing of solid nanoparticles in viscous fluids is a key stage in synthesis of nanocomposites and can affect their final properties. A multi-step preparatory mixing is developed to synthesize the nanocomposites of layered silicate in thermosetting polymers. This study aims to investigate the influences of mixing conditions and steps taken to process the thermosetting nanocomposites on the viscoelastic properties of suspensions. We also examine subsequent influences of mixing on the microstructure and dispersion state of cured hybrids of organically modified clays in a polyester resin. The nanocomposites were prepared in a sequential mixing process developed for the model nanocomposites of... 

In this research, production of ferrite - martensite dual phase Steels with different martensite morphology was considered during transient liquid phase bonding of a low carbon steel. The steel was bonded using an iron base interlayer with melting point of 1443 K and 40 μm thickness. Bonding process carried out at 1473 K, under pressure of 0.5 MPa, at different holding time of 10, 20, 30 and 40 minutes. Microstructural studies of joint region showed that isothermal solidification completed at the bonding time of 40 minutes. Microstructure of joints made at the bonding time of 10, 20, and 30 minutes consists of two distinct region, athermal and isothermal solidified zones. Microstructure of... 

In this study, transient 2D/axisymmetric simulations of cavitating flows are performed using a modified 'Volume-of-Fluid' (VOF) technique. Simulation of the cavitation is based on a homogenous equilibrium flow model. To predict the shape of the cavity, the Navier-Stokes equations in addition to an advection equation for the liquid volume fraction are solved. Mass transfer between the phases is treated as a sink term in the VOF equation. The numerical method is used for different geometries in a wide range of cavitation numbers. Computed shapes of cavities were found to be in good agreement with those of the reported experiments. The simulation results also compared well with those obtained... 

Electrical power system is subjefcted to disturbances. A large disturbance may bring the system to the complete blackout or partial outage. Restoration of power system to normal state constitutes several stages including transmission line connection. In closing network loops, power system operators sometimes encounter an excessive Standing Phase Angle (SPA) across a line. SPA should be within allowable limits before any attempt is made to close breaker. In this paper, the effect of reduction of SPA in improving transient stability and impact on adjacent generators is discussed. Also, the effect of closing of breakers at two ends of the line is studied. At the end, the effect of loading... 

This paper deals with design and analysis of intermittent supersonic wind tunnels. System can be constructed by allowing air at atmospheric pressure to pass through a converging-diverging nozzle, a test section and a diffuser into a vacuum tank. The governing equations of compressible fluid flow have been solved numerically using flux vector splitting method to obtain running time under which it works at the design Mach number. The formulation has been tested on the theory of quasi one-dimensional compressible flow. The numerical results are in good agreement with the results of the theory  

Information integrity in cache memories is a fundamental requirement for dependable computing. As caches comprise much of a CPU chip area and transistor counts, they are reasonable targets for single and multiple transient faults. This paper presents: 1) a fault detection scheme for tag arrays of cache memories and 2) an architectural cache to improve dependability as well as performance. In this architecture, cache space is divided into sets of different sizes and different tag lengths. The error detection scheme and the cache architecture have been evaluated using a trace driven simulation with soft error injection and SPEC 2000 applications. The results show that error detection... 

Exhaust gas emissions from mobile sources and its importance in urban pollution have currently attracted lots of interests towards studying on alternative fuel systems for road vehicles usage. One of the best replacements is the natural gas/diesel dual fuel, which offers an alternative to standard compression-ignition diesel engines. In the dual fuel system the primary fuel is natural gas, which may replace as much as 90% of the diesel fuel with a small amount of diesel fuel required ensuring effective ignition. Methane, the main constituent of natural gas, has high combustion efficiency. Dual fuel engines produce lower NOx emissions and fewer particulates. However, at moderate engine loads,... 

Various attempts has been made to derive linearized, reduced order models of induction generators. Due to the fact that there is usually numerous number of these machines in wind power plants, these models provide great facilities in calculations, and therefore are used widely in power system transient stability studies.Among various order reduction methods the most applicable ones are those based on neglecting the stator transients of the machine.In this paper, some of these methods are discussed and a criterion has been introduced to evaluate the accuracy of resultant reduced order models. Copyright © 2003 IFAC  

Advanced Static Var Compensators (ASVCs) are used to improve transient stability of power systems. Transient stability enhancement is one of such applications which employs Flexible AC Transmission System (FACTS). This paper proposes a new method for calculating the current references for an ASVC. These current references are calculated based on Transient Energy Function (TEF). The simulations have been carried out using C++ and Matlab Sirnulink, and the corresponding results are provided. © 2003 IEEE  

This paper proposes an alternative method to determine the characteristic polynomial based on closed loop desired transient response. To develop the method, we have found optimal characteristic rations in simple arrangement of these parameters via performance map method. Despite its simplicity, the resulted system exhibits better transient response in comparison with the systems obtained from existing methods of determining the characteristics polynomials. Numerical simulations are used to illustrate the specifications of the proposed method  

Thrust termination dynamics of a solid propellant rocket motor that is crucial to the performance of the rocket has been analyzed. Active thrust termination or reversing of a separating motor facilitate the staging process and enhance the performance of a multistage rocket. This can be achieved by opening a secondary nozzle located on the motor head and causing rapid depressurization of the motor chamber. The strong dependence of the solid propellant burning rate on the chamber pressure causes a transient nonlinear behavior that can result in premature dynamic extinguishments of the motor. It was confirmed that there is a maximum achievable level of equilibrium reverse thrust due to... 

Network equivalents can be used to represent parts of a power system to reduce the complexity and the computation time during the simulation of electromagnetic transients. The goal is to simplify the representation while preserving the accuracy of transients in the remainder. In this work a method is developed for construction of single and multi-port Frequency Dependent Network Equivalent (FNDE). In this equivalent model the input admittance matrix is approximated by a rational function in the frequency domain. This method is developed for both single and multi phase systems. Several examples showing the accuracy and efficiency of the developed FDNE is presented  

In this paper, a new method for the calculation of electromagnetic fields around a transmission line subjected to a lightning strike is described and discussed. The electric fields and magnetic fields are presented graphically as a function of spatial coordinate, as a function of time and as a function of both. It is believed that this exact solution have not been published before. First, a double exponential lightning surge current is injected into a transmission line. Once The temporal variations of current is known, then electric and magnetic fields can be calculated by using the field expressions for electric dipoles over infinitely conducting ground. As the calculation was done for each... 

Fast and accurate estimation of soft error rate in VLSI circuits is an essential step in a soft error tolerant ASIC design. In order to have a cost effective protection against radiation effects in combinational logics, an accurate and fast method for identification of most susceptive gates and paths is needed. In this paper, an efficient, fast and accurate method for soft error propagation probability (SEPP) estimation is presented and its performance is evaluated. This method takes into account all three masking factors in multi cycles. It also considers multiple event transients as a new challenge in soft error tolerant VLSI circuit design. Compared with Monte Carlo (MC) simulation-based... 

With the emerging nanoscale CMOS technology, Multiple Event Transients (METs) originated from radiation strikes are expected to become more frequent than Single Event Transients (SETs). In this paper, a fast and accurate layout- based Soft Error Rate (SER) estimation technique with consideration of both SET and MET fault models is pro- posed. Unlike previous techniques in which the adjacent MET sites are obtained from logic-level netlist, we perform a comprehensive layout analysis to extract MET adjacent cells. It is shown that layout-based technique is the only effective solution for identification of adjacent cells as netlist-based techniques significantly underestimate the overall SER....