Considering that differential evolution algorithm (DE) is sensitive to the selection of control parameters and population diversity's decrease leads to the loss of power as DE is applied in heat exchanger network (HEN), a weighted differential evolution algorithm (WDE) is applied in this study. Effectiveness of the algorithm has been proved in continuous variable optimization. This study applies it in mixed integer nonlinear programming problems of HEN without controlling parameters. Three cases ranging from small to medium testify the effectiveness of WDE. By setting up equal mutation factor and analyzing its distribution, we explore WDE's optimization mechanism which provides reference for algorithm improvements.

Individual gathering could cause decline of search ability as heuristic methods are applied to heat exchanger network (HEN) optimization. An evaluation methodology for HEN structure diversity was designed to measure degree of individual structure gathering, and guided algorithm improvement. Firstly, group division of population was performed, individuals of a certain scale with a common structure were classified as a group to get individual structure distribution. Then dispersal search strategy was proposed to give perturbation to heat exchangers randomly selected from common structure of individuals in each group except the best one, which aimed at dispersing individual structures in groups. Concentration search strategy was then proposed to enhance exploitation for excellent structure by making other individuals accept a common structure of the optimal group. Finally, two cases involving nine and fifteen streams proved that dispersal search strategy strengthened global search ability and concentration search strategy strengthened local search ability. It obtained results decreased by 7 008 $·a^-1 and 17 973 $·a^-1, respectively, compared to those obtained by original algorithm. They are superior to results in literature.

To avoid the problem of being disturbed by stochastic acceptance of imperfect solution for evolution process of individual optimal solution existing in optimization of heat exchanger network by random walk algorithm with compulsive evolution, an improved RWCE based on trilevel protection strategy is proposed. Individuals in population are divided into three levels. The lower-level is optimized by basic RWCE to protect global search ability of individuals. The middle-level reads historical optimal solution of the lower-level's individuals, and optimized by RWCE with fine tuning to protect evolution process of each individual's optimal solution from disruption. All individuals in the upper-level are initialized by solution of the best individuals in the middle-level, and optimized by RWCE with automatic fine search to ensure that the best individuals are fully searched. Finally, result of the upper-level is passed to corresponding individual at the lower-level. Two cases are optimized by using the algorithm,and results are better than those in literature. Evolution process of individual optimal solution is protected while accepting imperfect solution, therefore, both global search ability and local search ability are realized.

Applicability of numerical prediction method of dynamic derivatives is studied with forced oscillation method and free oscillation method on the airframe/propulsion integrative vehicle with and without fairing. Effect of parameters on dynamic derivative prediction in forced oscillation method such as time step and oscillation frequency is analyzed in detail. It shows that forced oscillation method is well applied in dynamic derivative prediction of integrative vehicle with internal and external flow, while parameters select of time step, computational time and oscillation frequency are quite different from external-flow-only vehicle. Dynamic derivatives by free oscillation method are in agreement with results with forced oscillation method on external-flow-only vehicle. There is a difference about 50% on integrative vehicle with internal and external flow. Origin and mechanism of differences in two methods need to be deeply studied.

We adopt lattice Boltzmann method to investigate double diffusive natural convection around a heated cylinder in an enclosure with Soret and Dufour effects. The inner heated cylinder is located at center of a square enclosure and four surrounding walls are assumed with low temperature and concentration. In the model, distributions of velocity, temperature and concentration are solved with three independent LBGK equations which are combined into a coupled equation through Boussinesq approximation. Influences of Soret number and Dufour number on double diffusive natural convection are analyzed. Streamlines, isotherms, isoconcentrations, average Nusselt and Sherwood numbers around heated cylinder in enclosure are presented. It shows that Soret and Dufour effects have significant influence on double diffusive natural convection.

Optimization in random walking algorithm with compulsive evolution (RWCE) for heat exchanger network synthesis (HENS) turns to slow down in late evolution as heat load of all heat exchangers are optimized simultaneously. A random walk algorithm with compulsive evolution combined with restrictive-evolution strategy for heat unit (RS-RWCE) is proposed, in which number of evolved heat units in HEN is restricted in each random walk evolution to keep fast convergence of total annual cost in early evolution process and fine search in late evolution process. Specific examples are applied to verify high computational efficiency and accuracy of the strategy. It gives consideration to integer variable and continuous variable. The results are encouraging.

Particle swarm optimization (PSO) algorithm has strong ability to explore global optimal region for heat exchanger networks synthesis. However, particles may trap into local optima and converge prematurely in late evolution. Therefore, an improved particle swarm optimization algorithm based on diversity feedback and real-time updating strategy is proposed. Firstly, index of population health degree is established to evaluate population diversity during evolution. Secondly, a random perturbation strategy and a centrifugal strategy are combined respectively with PSO algorithm to enrich population diversity and enhance global search ability. Furthermore, gradient search strategy is applied to search efficiently local optima and improve computational efficiency of PSO algorithm. Finally, a feedback mechanism of population health degree is proposed to real-time monitor health status of population and further to adopt different update strategies for keeping particles healthy during evolution. The method was applied to several cases taken from literature and results are encouraging. They are better than those of other improvements for PSO.

It is shown that various closed circuits formed by line-shaped metallic particles in composite induce great permeability. Effect of temperature on magnetic response is weak. Based upon effective medium theory,electric and magnetic response of composites containing line-shaped tungsten particles are addressed. Microwave absorbing composites are designed and optimized, which may be applied in high temperature circumstances.

Lattice Boltzmann method is adopted to investigate mixed convection in an enclosure filled with porous medium.A heated cylinder (D/L=0.4) is located at center of the enclosure with high temperature.Inlet flow with low temperature is located at lower-left wall of the enclosure and exit is at upper-left wall.Other walls are assumed adiabatic.Influences of Richardson number Ri and Darcy number Da on average Nusselt number Nu around heated cylinder are investigated while Prandtl and Grashof numbers are kept at 0.71 and 1.4×10⁴, respectively.It indicates that Nu decreases with increasing Ri.Influence of Richardson number on Nu is significant as Darcy number is great.At 10^-5≤Da≤10^-2, Nu increases with increasing Darcy number as forced convection dominates flow (Ri≤0.1).As natural convection dominates flow (Ri=10), Nu is not sensitive to Darcy number.

Generally, differential evolution (DE) algorithm is easily stuck into local optima as well as suffers from low convergence accuracy when employed for optimization of heat exchanger network. To solve these issues, an opposition-based multi-population parallel differential evolution algorithm is proposed. Firstly, opposite population is built by using initial population. Then, new generation of individuals are generated through information exchange, which is produced by mutated operation between opposite population and its original correspondence. The final step is to retain evolution of multi-population in parallel by applying multi-round opposites, so that the population is enable to keep current solution information and search new solutions in a larger space as well. Computing results of improved DE algorithm on 9sp and 15sp suggests that the method improves population diversity, jumps out local optima and at the same time achieves higher speed and accuracy.

Lattice Boltzmann method is adopted to numerically analyze nonlinear characteristics of double diffusive mixed convection in an enclosure. A heated cylinder is located at center of the enclosure. Fluid flows from an inlet at lower-left wall of enclosure and an outlet is at upper-right,upper-middle and upper-left wall respectively. Simulation results indicate that there are steady stationary solution,periodic and aperiodic oscillatory solutions in double diffusive mixed convection at different parameters. Phase path of velocity of monitoring point finally reaches a point,a closed loop and irregular curves,respectively.

First-principles calculations on mechanical behavior of V-Ta( Ta=0 to~20 wt. %) alloys are performed. Calculated Young's modulus,shear modulus,Cauchy pressure and bulk modulus/shear modulus indicate that as content of Ta is around 10 wt. %,V-Ta alloy shows good mechanical properties with large strength and good ductility. To examine calculation predictions,binary V-Ta alloys including V-10 wt. % Ta,V-15 wt. % Ta,V-20 wt. % Ta were processed and tested at room temperature. Computational results agree with experiment well. It indicates that the approach is a promising way for alloy design.

A semi-discrete central-upwind scheme for multi-class Lighthill-Whitham-Richards (LWR) traffic flow model is presented. It combines improved fifth-order weighted essentially non-oscillatory (WENO) reconstruction called WENO-Z with semi-discrete central-upwind numerical flux. WENO-Z reconstruction improves accuracy of solution with non-oscillatory property. Time integration is carried out with strong stability preserving Runge-Kutta method. Numerical results demonstrate the scheme is efficient.

With a self-developed numerical model, we simulate seepage flows in reservoir of an imaginary doublet EGS and perform a systemic investigation on flow pattern correlating with the reservoir hydraulic permeability. It reveals that the flow pattern in reservoir is mainly decided by relative magnitude of "basic pressure difference" caused by gravity and hydrodynamic-hydrostatic pressure transformation to fluid flow resistance through fractured rock mass. Circulation flow rate exhibits a limited effect on the flow pattern. Based on this we bring forward two strategies, horizontal well and multiple well layouts, to restrain the down-hole flow circuit in EGS reservoir, which acts as theoretical guidelines for practical construction of EGSs.

With a self-developed numerical model, we simulate long-time operation processes of an imaginary doublet enhanced geothermal system (EGS) with different geological conditions and analyze effects of thermal compensation on evolution of production temperature and fluid and rock temperature in the heat reservoir. The model treats heat reservoir as an equivalent porous media while considers thermal non-equilibrium between rock matrix and fluid. It uses two energy equations to describe temperature field of rock and circulating fluid, respectively, enabling thorough investigations on local heat exchange processes of rock and fluid. It reveals that influence of thermal compensation from rocks encircling heat reservoir is strongly correlated with flow pattern in the reservoir, and it does not always have positive effect on EGS production temperature. If there appears an obvious preferential flow in depth direction of the reservoir, thermal compensation can even lower production temperature during early period of EGS operation. With advance of EGS operation, rock temperature in reservoir decreases and thermal compensation gradually brings a pronounced positive effect on production temperature.

A radial symmetrical model of radon transport in vicinity of an underground tunnel is developed with continuum mechanics theory.Distribution of radon concentration in the vicinity of tunnel is analyzed under the assumption that only diffusion and permeation are considered.Analytic solutions are obtained.A rock mass range affecting the radon concentration in the tunnel is defined as effective transport distance.Effective transport distance as functions of effective porosity and velocity are given.Expressions of radon exhalation rate on tunnel wall are shown.

A Langevin equation of fluctuating velocity of fluid ‘seen’ by particle is simplified in Minier's model.Autocorrelation of turbulence fluctuating velocity is obtained,which has non-isotropic property.Corresponding PDF model of particle is obtained and a simplified form is used to predict turbulent particle dispersion in grid-generating turbulence flow.PDF model is solved analytically and solutions are compared with experimental results of Wells and Stock.

In a model for interaction between one atmosphere uniform glow discharge plasma (OAUGDP)and air proposed by Shyy,electric field and electric forces acting on air as body force are obtained.The electric field is calculated with electric potential equation. The influence of OAUGDP on flows around a NACA0015 airfoil at low speed is investigated by solving N-S equation with a body force term.Plasma located upstream of the separation point damps the flow separation around the airfoil efficiently,while plasma located downstream of the separation point has little effect on the flow.It agrees with experimental observations. Effect of plasma on aerodynamics of airfoil and pressure distribution on airfoil surface are investigated.

Electronic structures of possible F-type color centers in PbMoO₄ crystals are studied within the framework of a fully relativistic selfconsistent Dirac-Slater theory with a numerically discrete variational (DV-Xα) method. The results show that:F and F⁺ centers result in donor energy levels in forbidden band; optical transition energies are 2.141 eV and 2.186 eV, corresponding to 518 nm and 567 nm absorption, respectivly. The 580 nm absorption band after photo-chromic effect results from F-type color centers in PbMoO₄.

A fifth-order semi-discrete central-upwind scheme for hyperbolic conservation laws is proposed. In one dimension, the scheme is based on a fifth-order central weighted essentially non-oscillatory(WENO) reconstruction:In two dimensions, the reconstruction is generalized by a dimension-by-dimension approach. A Runge-Kutta method is employed in time integration. The method requires neither Riemann solvers nor characteristic decomposition and therefore enjoys main advantage of the central schemes. The present scheme is verified by one and two dimensional Euler equations of gas dynamics and shows high resolution and high accuracy.

With a high-order weighted compact nonlinear scheme(WCNS) for space discretization,several different implicit methods,including LU-SGS,Gauss-Seidel point-relaxation,line-relaxation and GMRES(generalized minimal residual),are compared in the simulation of hypersonic viscous flows.Both point and line relaxations with analytical Jacobian matrix converge faster than those of LU-SGS.GMRES obtains a faster convergence rate combined with line relaxation.

For hyperbolic conservation laws, a third-order semi-discrete central-upwind scheme with less numerical dissipation is presented. The scheme is based on a third-order non-oscillatory reconstruction proposed by Liu and Tadmor. The local speed of wave propagation is also considered. An optimal third-order strong stability preserving(SSP) Runge-Kutta method is used for time integration. The resulting scheme is free of Riemann solvers and hence no characteristic decomposition is involved, so that it enjoys the advantages of central schemes. The present scheme is tested on a variety of numerical experiments in one dimension. To illustrate the improvement of the method, the results are compared with that of the original third-order semi-discrete central-upwind scheme. The numercial results demonstrate that the presented method reduce the numerical dissipation of the semi-discrete central-upwind scheme further and improve resolution of contact waves.

Multi-block patched grids in conjunction with a finite volume time domain (FVTD) algorithm are used to solve classic multi-body electromagnetic scattering problems. The governing equations of the Maxwell equations are cast into three-dimensional general curvilinear coordinates. The approach uses four-stage Runge-Kutta scheme for time integration and flux vector splitting based on eigen structure of flux Jacobian matrices for spatial discretization. Monotonic upstream shemes for conservation laws (MUSCL) scheme for interpolation is used for the dependent variable. The resolution for temporal discretization is second order and that for spatial discretization is third order. Numerical results for the radar cross section(RCS) of a classical configuration agree well with the analytical results. And the results for multi-body calculation agree well with that in references. It shows that the algorithm developed is able to simulate complex topology configuration (including multi-body) problems.

The ground-state geometries of Rh_n(n=2~20) clusters are calculated with a TB many-body potential in the Genetic Algorithm(GA). Based on the optimized geometries, we calculate the average bond length(R), average coordination number(CN), average binding energy E_b per atom. The average magnetic moment per atom μ_n and the average total density of states(DOS) of Rh_n(n=15,17,18,19) clusters are calculated in a self-consistent tight-binding model considering 4 d, 5 s, 5 p valence electrons with both global and local neutrality. Our result reveals relations between structure and electronic and magnetic properties of small Rh clusters.

Based on the third-order ENN scheme, a fourth-or fifth-order WENN scheme is developed by using the weighted function, and then this scheme is applied to a shock-induced mixing flow. Numerical results show that the degree of mixing enhancement can be increased by the shock-induced technique, and that this WENN scheme exhibits a good resolution for the flow field.

Mold-filling of polymer melt in three dimensional thin parts is a viscous incompressible flow with moving boundaries.Based on generalized Hele-Shaw flow theory,the finite element systems for pressure fields are constructed by the Control Volume Methods.The advancing of melt front is traced by a hybrid FEM/Control-Volume method and the dynamic simulation of the mold-filling process is achieved.

The relationship between ray tracing、symplectic algorithm and wave field simulation is presented. The long time conservation property of symplectic algorithm and the necessity of ray tracing using symplectic algorithm are demonstrated. In addition, wave field simulation using Maslov asymptotic theory and symplectic algorithm for linear layer model is performed. The comparison of the numerical solution with the analytic solution is carried out.

By using the quasi-3D coupled current method presented, the influences of structure of cold crucible, power frequency, electricity property of charge(melt), coil(inductor)position and current on the electromagnetic field(EMF) and the levitation characteristics in the melting processes are analyzed. It is shown that in the melting process, power frequency and crucible structure are the decisive factors for the ability of penetrating magnetic flux into cold crucible. The magnetic flux density in cold crucible is reduced with the rising of power frequency, and this tendency becomes stronger when that is higher than 100 kHz. The segmented structure of cold crucible can reduce the induction eddy in itself effectively, and the higher the power frequency is, the better the result is. So, a cold crucible can be segmented into(16~20) sectors for higher frequency electromagnetic field(f>100 kHz),(8~12) sectors for high frequency one(10 kHz≤f≤100kHz), and(4~8) sectors for mid-high frequency one(f<10 kHz). It is also shown that the levitation force in melting charge is related to coil current as a parabolic function.

The LSQ coupled states of l-shell are constructed by (U,D)L-LSQ scheme, where U(D) is the total orbital angular momentum of spin up(down) electrons, the LS and Q are the total orbital angular momentum, spin and quasispin respectively, the (U,D) L-LSQ is unitary transformation. The scalar operators which commute with the total orbital angular momentum, spin and quasispin operators, are constructed from 4 creation-annihilation operators, and the LSQ coupled states are further or complete classified by its eigenvalues. The complete classifications of coupled states for f- and g-shell are obtained, the primary results of complete classifications of coupled states for g-shell are listed.

Based on Delaunay triangulation an algorithm is presented for generation triangle mesh over any planar domain which have complicated characteristic constraints.Charateritic constraints in a planar domain can be constructed by point,line,circle,arc,spline curves,open loops and closed loops which are made up of them.