Abstract: The distance protection mainly the impedance relay which is considered as the main protection for transmission lines can be subjected to impedance measurement error which is, mainly, due to the fault resistance and to the power fluctuation. Thus, the impedance relay may not operate for a short circuit at the far end of the protected line (case of the under reach) or operates for a fault beyond its protected zone (case of overreach). In this paper, an approach to fault detection by a distance protection, which distinguishes between the faulty conditions and the effect of overload operation mode, has been developed. This approach is based on the symmetrical components; mainly the negative sequence, and it is taking into account both the effect of fault resistance and the overload situation which both have an effect upon the reliability of the protection in terms of dependability for the former and security for the latter.
Abstract: A dual-reciprocity boundary element method is presented
for the numerical solution of a class of axisymmetric elastodynamic
problems. The domain integrals that arise in the integrodifferential
formulation are converted to line integrals by using the
dual-reciprocity method together suitably constructed interpolating
functions. The second order time derivatives of the displacement
in the governing partial differential equations are suppressed by
using Laplace transformation. In the Laplace transform domain, the
problem under consideration is eventually reduced to solving a system
of linear algebraic equations. Once the linear algebraic equations are
solved, the displacement and stress fields in the physical domain can
be recovered by using a numerical technique for inverting Laplace
transforms.
Abstract: This paper presents a procedure of forming the
mathematical model of radial electric power systems for simulation
of both transient and steady-state conditions. The research idea has
been based on nodal voltages technique and on differentiation of
Kirchhoff's current law (KCL) applied to each non-reference node of
the radial system, the result of which the nodal voltages has been
calculated by solving a system of algebraic equations. Currents of the
electric power system components have been determined by solving
their respective differential equations. Transforming the three-phase
coordinate system into Cartesian coordinate system in the model
decreased the overall number of equations by one third. The use of
Cartesian coordinate system does not ignore the DC component
during transient conditions, but restricts the model's implementation
for symmetrical modes of operation only. An example of the input
data for a four-bus radial electric power system has been calculated.
Abstract: Adopting the measured constitutive relationship of
stress-strain of river ice, the finite element analysis model of
percussive force of river ice and pier is established, by the explicit
dynamical analysis software package LS-DYNA. Effects of element
types, contact method and arithmetic of ice and pier, coupled modes
between different elements, mesh density of pier, and ice sheet in
contact area on the collision force are studied. Some of measures for
the collision force analysis of river ice and pier are proposed as
follows: bridge girder can adopt beam161 element with 3-node; pier
below the line of 1.30m above ice surface and ice sheet use solid164
element with 8-node; in order to accomplish the connection of
different elements, the rigid body with 0.01-0.05m thickness is defined
between solid164 and beam161; the contact type of ice and pier adopts
AUTOMATIC_SURFACE_TO_SURFACE, using symmetrical
penalty function algorithms; meshing size of pier below the line of
1.30m above ice surface should not less than 0.25×0.25×0.5m3. The
simulation results have the advantage of high precision by making a
comparison between measured and computed data. The research
results can be referred for collision force study between river ice and
pier.
Abstract: In this paper we develop an efficient numerical method for the finite-element model updating of damped gyroscopic systems based on incomplete complex modal measured data. It is assumed that the analytical mass and stiffness matrices are correct and only the damping and gyroscopic matrices need to be updated. By solving a constrained optimization problem, the optimal corrected symmetric damping matrix and skew-symmetric gyroscopic matrix complied with the required eigenvalue equation are found under a weighted Frobenius norm sense.
Abstract: The effect of porous medium on the capillary instability of a cylindrical interface in the presence of axial electric field has been investigated using viscous potential flow theory. In viscous potential flow, the viscous term in Navier-Stokes equation vanishes as
vorticity is zero but viscosity is not zero. Viscosity enters through normal stress balance in the viscous potential flow theory and tangential stresses are not considered. A dispersion relation that accounts for the growth of axisymmetric waves is derived and stability is discussed theoretically as well as numerically. Stability criterion is given by critical value of applied electric field as well as critical wave number. Various graphs have been drawn to show the effect of various physical parameters such as electric field, viscosity ratio, permittivity ratio on the stability of the system. It has been observed that the axial electric field and porous medium both have stabilizing effect on the stability of the system.
Abstract: Hypersonic flows around spatial vehicles during their
reentry phase in planetary atmospheres are characterized by intense
aerothermal phenomena. The aim of this work is to analyze high
temperature flows around an axisymmetric blunt body taking into
account chemical and vibrational non-equilibrium for air mixture
species. For this purpose, a finite volume methodology is employed
to determine the supersonic flow parameters around the axisymmetric
blunt body, especially at the stagnation point and along the wall of
spacecraft for several altitudes. This allows the capture shock wave
before a blunt body placed in supersonic free stream. The numerical
technique uses the Flux Vector Splitting method of Van Leer. Here,
adequate time stepping parameter, along with CFL coefficient and
mesh size level are selected to ensure numerical convergence, sought
with an order of 10-8
Abstract: Cardiovascular disease mostly in the form of atherosclerosis is responsible for 30% of all world deaths amounting to 17 million people per year. Atherosclerosis is due to the formation of plaque. The fatty plaque may be at risk of rupture, leading typically to stroke and heart attack. The plaque is usually associated with a high degree of lumen reduction, called a stenosis. The initiation and progression of the disease is strongly linked to the hemodynamic environment near the vessel wall. The aim of this study is to validate the flow of blood mimic through an arterial stenosis model with computational fluid dynamics (CFD) package. In experiment, an axisymmetric model constructed consists of contraction and expansion region that follow a mathematical form of cosine function. A 30% diameter reduction was used in this study. Particle image velocimetry (PIV) was used to characterize the flow. The fluid consists of rigid spherical particles suspended in waterglycerol- NaCl mixture. The particles with 20 μm diameter were selected to follow the flow of fluid. The flow at Re=155, 270 and 390 were investigated. The experimental result is compared with FLUENT simulated flow that account for viscous laminar flow model. The results suggest that laminar flow model was sufficient to predict flow velocity at the inlet but the velocity at stenosis throat at Re =390 was overestimated. Hence, a transition to turbulent regime might have been developed at throat region as the flow rate increases.
Abstract: The accelerated growth in aircraft industries desire
effectual schemes, programs, innovative designs of advanced systems
and facilities to accomplish the augmenting need for home-free air
transportation. In this paper, a contemporary conceptual design of a
cambered airfoil has been proposed in order to providing augmented
effective lift force relative to the airplane, and to eliminating
drawbacks and limitations of an airfoil in a commercial airplane by
using a kind of smart materials. This invention of an unsymmetrical
airfoil structure utilizes the amplified air momentum around the
airfoil and increased camber length to providing improved aircraft
performance and assist to enhancing the reliability of the aircraft
components. Moreover, this conjectured design helps to reducing
airplane weight and total drag.
Abstract: The Navier–Stokes equations for unsteady, incompressible, viscous fluids in the axisymmetric coordinate system are solved using a control volume method. The volume-of-fluid (VOF) technique is used to track the free-surface of the liquid. Model predictions are in good agreement with experimental measurements. It is found that the dynamic processes after impact are sensitive to the initial droplet velocity and the liquid pool depth. The time evolution of the crown height and diameter are obtained by numerical simulation. The critical We number for splashing (Wecr) is studied for Oh (Ohnesorge) numbers in the range of 0.01~0.1; the results compares well with those of the experiments.
Abstract: Saturated two-phase fluid flows are often subject to
pressure induced oscillations. Due to compressibility the vapor
bubbles act as a spring with an asymmetric non-linear characteristic.
The volume of the vapor bubbles increases or decreases differently if
the pressure fluctuations are compressing or expanding;
consequently, compressing pressure fluctuations in a two-phase pipe
flow cause less displacement in the direction of the pipe flow than
expanding pressure fluctuations. The displacement depends on the
ratio of liquid to vapor, the ratio of pressure fluctuations over average
pressure and on the exciting frequency of the pressure fluctuations.
In addition, pressure fluctuations in saturated vapor bubbles cause
condensation and evaporation within the bubbles and change
periodically the ratio between liquid to vapor, and influence the
dynamical parameters for the oscillation. The oscillations are
conforming to an isenthalpic process at constant enthalpy with no
heat transfer and no exchange of work.
The paper describes the governing non-linear equation for twophase
fluid oscillations with condensation and evaporation, and
presents steady state approximate solutions for free and for pressure
induced oscillations. Resonance criteria and stability are discussed.
Abstract: S-boxes (Substitution boxes) are keystones of modern
symmetric cryptosystems (block ciphers, as well as stream ciphers).
S-boxes bring nonlinearity to cryptosystems and strengthen their
cryptographic security. They are used for confusion in data security
An S-box satisfies the strict avalanche criterion (SAC), if and only if
for any single input bit of the S-box, the inversion of it changes each
output bit with probability one half. If a function (cryptographic
transformation) is complete, then each output bit depends on all of
the input bits. Thus, if it were possible to find the simplest Boolean
expression for each output bit in terms of the input bits, each of these
expressions would have to contain all of the input bits if the function
is complete. From some important properties of S-box, the most
interesting property SAC (Strict Avalanche Criterion) is presented
and to analyze this property three analysis methods are proposed.
Abstract: In this paper the authors propose a protocol, which uses Elliptic Curve Cryptography (ECC) based on the ElGamal-s algorithm, for sending small amounts of data via an authentication server. The innovation of this approach is that there is no need for a symmetric algorithm or a safe communication channel such as SSL. The reason that ECC has been chosen instead of RSA is that it provides a methodology for obtaining high-speed implementations of authentication protocols and encrypted mail techniques while using fewer bits for the keys. This means that ECC systems require smaller chip size and less power consumption. The proposed protocol has been implemented in Java to analyse its features and vulnerabilities in the real world.
Abstract: The study of the stress distribution on a hollow
cylindrical fiber placed in a composite material is considered in this
work and an analytical solution for this stress distribution has been
constructed. Finally some parameters such as fiber-s thickness and
fiber-s length are considered and their effects on the distribution of
stress have been investigated. For finding the governing relations,
continuity equations for the axisymmetric problem in cylindrical
coordinate (r,o,z) are considered. Then by assuming some conditions
and solving the governing equations and applying the boundary
conditions, an equation relates the stress applied to the representative
volume element with the stress distribution on the fiber has been
found.
Abstract: We consider a Principal-Agent model with the
Principal being a seller who does not know perfectly how much the
buyer (the Agent) is willing to pay for the good. The buyer-s
preferences are hence his private information. The model corresponds
to the nonlinear pricing problem of Maskin and Riley. We assume
there are three types of Agents. The model is solved using
“informational rents" as variables. In the last section we present the
main characteristics of the optimal contracts in asymmetric
information and some possible extensions of the model.
Abstract: In this paper, we present parallel alternating two-stage
methods for solving linear system Ax=b, where A is a symmetric
positive definite matrix. And we give some convergence results of
these methods for nonsingular linear system.
Abstract: We investigate an asymmetric connections model with a
dynamic network formation process, using an agent based simulation.
We permit heterogeneity of agents- value. Valuable persons seem
to have many links on real social networks. We focus on this
point of view, and examine whether valuable agents change the
structures of the terminal networks. Simulation reveals that valuable
agents diversify the terminal networks. We can not find evidence that
valuable agents increase the possibility that star networks survive the
dynamic process. We find that valuable agents disperse the degrees
of agents in each terminal network on an average.
Abstract: The electrokinetic flow resistance (electroviscous
effect) is predicted for steady state, pressure-driven liquid flow at
low Reynolds number in a microfluidic contraction of rectangular
cross-section. Calculations of the three dimensional flow are
performed in parallel using a finite volume numerical method. The
channel walls are assumed to carry a uniform charge density and the
liquid is taken to be a symmetric 1:1 electrolyte. Predictions are
presented for a single set of flow and electrokinetic parameters. It is
shown that the magnitude of the streaming potential gradient and the
charge density of counter-ions in the liquid is greater than that in
corresponding two-dimensional slit-like contraction geometry. The
apparent viscosity is found to be very close to the value for a
rectangular channel of uniform cross-section at the chosen Reynolds
number (Re = 0.1). It is speculated that the apparent viscosity for the
contraction geometry will increase as the Reynolds number is
reduced.
Abstract: A property-s selling price is described as the result of
sequential bargaining between a buyer and a seller in an environment
of asymmetric information. Hedonic housing prices are estimated
based upon 17,333 records of New Zealand residential properties
sold during the years 2006 and 2007.
Abstract: Let G be a graph of order n. The second stage adjacency matrix of G is the symmetric n × n matrix for which the ijth entry is 1 if the vertices vi and vj are of distance two; otherwise 0. The sum of the absolute values of this second stage adjacency matrix is called the second stage energy of G. In this paper we investigate a few properties and determine some upper bounds for the largest eigenvalue.