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991.
Differential evolution (DE) is a well known and simple population based probabilistic approach for global optimization over continuous spaces. It has reportedly outperformed a few evolutionary algorithms and other search heuristics like the particle swarm optimization when tested over both benchmark and real world problems. DE, like other probabilistic optimization algorithms, has inherent drawback of premature convergence and stagnation. Therefore, in order to find a trade-off between exploration and exploitation capability of DE algorithm, a new parameter namely, cognitive learning factor (CLF) is introduced in the mutation process. Cognitive learning is a powerful mechanism that adjust the current position of individuals by the means of some specified knowledge (previous experience of individuals). The proposed strategy is named as cognitive learning in differential evolution (CLDE). To prove the efficiency of various approaches of CLF in DE,?CLDE is tested over 25 benchmark problems. Further, to establish the wide applicability of CLF,?CLDE is applied to two advanced DE variants. CLDE is also applied to solve a well known electrical engineering problem called model order reduction problem for single input single output systems. 相似文献
992.
Differential Evolution (DE) is a well known and simple population based probabilistic approach for global optimization. It has reportedly outperformed a few Evolutionary Algorithms and other search heuristics like Particle Swarm Optimization when tested over both benchmark and real world problems. But, DE, like other probabilistic optimization algorithms, sometimes exhibits premature convergence and stagnates at suboptimal point. In order to avoid stagnation behavior while maintaining a good convergence speed, a new position update process is introduced, named fitness based position update process in DE. In the proposed strategy, position of the solutions are updated in two phases. In the first phase all the solutions update their positions using the basic DE and in the second phase, all the solutions update their positions based on their fitness. In this way, a better solution participates more times in the position update process. The position update equation is inspired from the Artificial Bee Colony algorithm. The proposed strategy is named as Fitness Based Differential Evolution ( $FBDE$ ). To prove efficiency and efficacy of $FBDE$ , it is tested over 22 benchmark optimization problems. A comparative analysis has also been carried out among proposed FBDE, basic DE, Simulated Annealing Differential Evolution and Scale Factor Local Search Differential Evolution. Further, $FBDE$ is also applied to solve a well known electrical engineering problem called Model Order Reduction problem for Single Input Single Output Systems. 相似文献
993.
Farook Rahaman Raju Maulick Anil Kumar Yadav Saibal Ray Ranjan Sharma 《General Relativity and Gravitation》2012,44(1):107-124
We propose a model for an anisotropic dark energy star where we assume that the radial pressure exerted on the system due
to the presence of dark energy is proportional to the isotropic perfect fluid matter density. We discuss various physical
features of our model and show that the model satisfies all the regularity conditions and is stable as well as singularity-free. 相似文献
994.
An experimental setup comprising up of an indoor soil bin, a single wheel tester (SWT), a soil processing trolley, a drawbar pull loading device and an instrumentation unit was developed to perform traction tests in the soil bin to study the effect of soil, tyre and system parameters on the performance of tyres. The design of the single wheel tester was such that the dynamic weight reaction force is equal to that measured statically. It is a simple wheeled device, capable of testing tyres of up to 1.5 m in diameter, vertical force up to 19 kN, net pull up to 7.2 kN, torque up to 5.5 kN m, and speed up to 3.5 km/h. 相似文献
995.
This study discusses wave propagation in perhaps the most general model of a poroelastic medium. The medium is considered as a viscoelastic, anisotropic and porous solid frame such that its pores of anisotropic permeability are filled with a viscous fluid. The anisotropy considered is of general type, and the attenuating waves in the medium are treated as the inhomogeneous waves. The complex slowness vector is resolved to define the phase velocity, homogeneous attenuation, inhomogeneous attenuation, and angle of attenuation for each of the four attenuating waves in the medium. A non-dimensional parameter measures the deviation of an inhomogeneous wave from its homogeneous version. An numerical model of a North-Sea sandstone is used to analyze the effects of the propagation direction, inhomogeneity parameter, frequency regime, anisotropy symmetry, anelasticity of the frame, and viscosity of the pore-fluid on the propagation characteristics of waves in such a medium. 相似文献
996.
997.
In the theory of classical mechanics, the two-body central forcing problem is formulated as a system of the coupled nonlinear
second-order deterministic differential equations. The uncertainty introduced by the small, unmodeled stochastic acceleration
is not assumed in the particle dynamics. The small, unmodeled stochastic acceleration produces an additional random force
on a particle. Estimation algorithms for a two-body dynamics, without introducing the stochastic perturbation, may cause inaccurate
estimation of a particle trajectory. Specifically, this paper examines the effect of the stochastic acceleration on the motion
of the orbiting particle, and subsequently, the stochastic estimation algorithm is developed by deriving the evolutions of
conditional means and conditional variances for estimating the states of the particle-earth system. The theory of the nonlinear
filter of this paper is developed using the Kolmogorov forward equation “between the observations" and a functional difference
equation for the conditional probability density “at the observation." The effectiveness of the nonlinear filter is examined
on the basis of its ability to preserve perturbation effect felt by the orbiting particle and the signal-to-noise ratio. The Kolmogorov forward equation, however, is not appropriate for the numerical simulations, since it is the equation for
the evolution of “the conditional probability density." Instead of the Kolmogorov equation, one derives the evolutions for
the moments of the state vector, which in our case consists of positions and velocities of the orbiting body. Even these equations
are not appropriate for the numerical implementations, since they are not closed in the sense that computing the evolution
of a given moment involves the knowledge of higher order moments. Hence, we consider the approximations to these moment evolution
equations. This paper makes a connection between classical mechanics, statistical mechanics and the theory of the nonlinear
stochastic filtering. The results of this paper will be of use to astrophysicists, engineers and applied mathematicians, who
are interested in applications of the nonlinear filtering theory to the problems of celestial and satellite mechanics. Simulation
results are introduced to demonstrate the usefulness of an analytic theory developed, in this paper. 相似文献
998.
Two-dimensional numerical studies of flow and temperature fields for turbulent natural convection and surface radiation in
inclined differentially heated enclosures are performed. Investigations are carried out over a wide range of Rayleigh numbers
from 108 to 1012, with the angle of inclination varying between 0° and 90°. Turbulence is modeled with a novel variant of the k–ε closure model. The predicted results are validated against experimental and numerical results reported in literature. The
effect of the inclination of the enclosure on pure turbulent natural convection and the latter’s interaction with surface
radiation are brought out. Profiles of turbulent kinetic energy and effective viscosity are studied to observe the net effect
on the intensity of turbulence caused by the interaction of natural convection and surface radiation. The variations of local
Nusselt number and average Nusselt number are presented for various inclination angles. Marked change in the convective Nusselt
number is found with the orientation of enclosure. Also analyzed is the influence of change in emissivity on the flow and
heat transfer. A correlation relevant to practical applications in the form of average Nusselt number, as a function of Rayleigh
number, Ra, radiation convection parameter, N
RC and inclination angle of the enclosure, φ is proposed. 相似文献
999.
Abstract Aim of the paper is to investigate the effects of linearly varying thermal conductivity, viscous dissipation and
Ohmic heating on steady free convection flow of a viscous incompressible electrically conducting liquid having low Prandtl
number along an inclined isothermal non-conducting porous plate in the presence of transverse magnetic field. The governing
equations of continuity, momentum and energy are transformed into ordinary differential equations using similarity transformation.
The resulting coupled and non-linear ordinary differential equations are solved using Runge-Kutta fourth order method and
shooting technique. The velocity and temperature distributions are discussed numerically and presented through graphs. Skin-friction
coefficient and Nusselt number at the plate are derived, discussed and their numerical values for various values of physical
parameters are presented through tables. 相似文献
1000.
The vibronic vapour phase photoacoustic spectrum of Br2 in the wavelength region 505–541 nm (19796–18480 cm−1) has been recorded using microphone as well as pump-probe method. Discrete vibronic bands superimposed on a monotonically
increasing continuum background towards the dissociation limit results from the overlapping B
3Π
0u
/+
← X
1Σ
g
/+
and 1Π1u
← X
1Σ
g
/+
electronic transitions. Vibronic bands originating from υ″=0 have been used to estimate the relative rate of non-radiative relaxation as a function of the excited state B
3Π0u
vibrational quantum number υ′. A comparison with the optical absorption spectroscopy of Br2 leads to the identification of three broad spectral regions between 505 and 541 nm (19796 and 18480 cm−1) on the basis of different non-radiative relaxation processes. 相似文献