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Spherical harmonics method for neutron transport equation based on unstructured-meshes

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Nuclear Science and Techniques 2004年第6期15卷 335-339页

作者： CAOLiang-Zhi WU-Hong-Chun SchoolofEnergyandPowerEngineering Xi＇anJiaotongUniversityXi＇an710049 SchoolofEnergyandPowerEngineering Xi＇anJiaotongUniversityXi＇an710049

Based on a new second-order neutron transport equation, self-adjoint angular flux (SAAF) equation, the spherical harmonics (PN) method for neutron transport equation on unstructured-meshes is derived. The spherical harmonics function is used to expand the angular flux. A set of differential equations about the spatial variable, which are coupled with each other, can be obtained. They are solved iteratively by using the finite element method on un- structured-meshes. A two-dimension transport calculation program is coded according to the model. The numerical results of some benchmark problems demonstrate that this method can give high precision results and avoid the ray effect very well.

关键词：有限元中子传输方程球形谐函数无结构网偏微分方程

Mockup tests for developing the CARR-CNS with a two-phase thermo-siphon loop

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Nuclear Science and Techniques 2004年第6期15卷 375-380页

作者： DUShe-Jiao BIQin-Cheng CHENTing-Kuan FENGQuan-Ke LIXiao-Ming StateKeyLaboratoryofMultiphaseFlowinPowerEagiaeeriag Xi＇anJiaotoagUniversityXi＇an710049 StateKeyLaboratoryofMultiphaseFlowinPowerEagiaeeriag Xi＇anJiaotoagUniversityXi＇an710049

The cold neutron source (CNS) is a facility to increase cold neutrons by scattering thermal neutrons in liquid hydrogen or deuterium around 20 K. For extracting a stable cold neutron flux from the CNS, the liquid quantity in the moderator cell should be maintained stably against disturbance of nuclear heating. The China Institute of Atomic Energy (CIAE) is now constructing the China Advanced Research Reactor (CARR: 60 MW), and designing the CARR-CNS with a two-phase thermo-siphon loop consisting of a condenser, two moderator transfer tubes and an annular cylindrical moderator cell. The mock-up tests were carried out using a full-scale loop with Freon-113, for validating the self-regulating characteristics of the loop, the void fraction less than 20% in the liquid hydrogen of the moderator cell, and the requirements for establishing the condition under which the inner shell has only vapor. The density ratio of liquid to vapor and the volumetric evaporation rate due to heat load are kept the same as those in normal operation of the CARR-CNS. The results show that the loop has the self-regulating characteristics and the in- ner shell contains only vapor, while the outer shell liquid. The local void fraction in the liquid increases with increas- ing of the loop pressure.

关键词： CARR 空隙组分自动调节热虹吸管环柱面慢化剂单元核物理

A BRANCH AND BOUND ALGORITHM FOR SEPARABLE CONCAVE PROGRAMMING

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Journal of Computational Mathematics 2004年第6期22卷 895-904页

作者： Hong-gangXue Cheng-xianXu Feng-minXu DepartmentofMathematics FacultyofScienceXi'anJiaotongUniversityxi'an710049China DepartmentofMathematics FacultyofScienceXi'anJiaotongUniversityXi'an710049China

In this paper, we propose a new branch and bound algorithm for the solution of large scale separable concave programming problems. The largest distance bisection (LDB) technique is proposed to divide rectangle into sub-rectangles when one problem is branched into two subproblems. It is proved that the LDB method is a normal rectangle subdivision(NRS). Numerical tests on problems with dimensions from 100 to 10000 show that the proposed branch and bound algorithm is efficient for solving large scale separable concave programming problems, and convergence rate is faster than ω-subdivision method.

关键词： Branch and bound algorithm Separable programming Largest distance bisection Normal rectangle subdivision subdivision

Study on dryout point in vertical narrow annuli

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Nuclear Science and Techniques 2005年第1期16卷 53-58页

作者： TIANWen-Xi AYEMyint QIUSui-Zheng JIADou-Nan StateKeyLaboratoryofMultilphaseFlowinPowerEngineering Xi＇anJiaotongUniversityXi＇an710049 StateKeyLaboratoryofMultilphaseFlowinPowerEngineering Xi＇anJiaotongUniversityXi＇an710049

Prediction of dryout point is experimentally investigated with deionized water upflowing through narrow annular channel with 1.0 mm and 1.5 mm gap respectively. The annulus with narrow gap is bilaterally heated by AC current power supply. The experimental conditions covered a range of pressure from 0.8 to 3.5 MPa, mass flux of 26.6 to 68.8 kg?m-2?s-1 and wall heat flux of 5 to 50 kW?m-2. The location of dryout is obtained by observing a sudden rise in surface temperature. Kutateladze correlation is cited and modified to predict the location of dryout and proved to be not a proper one. Considering in detail the effects of geometry of annuli, pressure, mass flux and heat flux on dryout, an empirical correction is finally developed to predict dryout point in narrow annular gap under low flow condition, which has a good agreement with experimental data.

关键词：窄环轨道双侧加热烘干点临界质量环流

Preparation of nanosized W/Cu composite powder by sol-gel technique

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Rare Metals 2005年第2期24卷 170-173页

作者： LIBinghu KANGZhanying CHENWenge DINGBingjun StatekeyLaboratoryforMechanicalBehaviorofMaterials Xi＇anJiaotongUniversityXi＇an710049China SchoolofScience Xi＇anJiaotongUniversityXi＇an710049China

Cu(NO3)(2) and (NH4)(6)H(2)W(12)O(40)center dot 4H(2)O were used to prepare W/Cu nanosized composite powder by sol-gel technique. The influences of heat treatment process, pH value of the solution and the amount of an addition agent on particle size were investigated by DSC, XRD and TEM. The results show that, at a certain heat treatment temperature, the W/Cu nanoparticle size increases with the pH value or the amount of the addition agent increasing.

关键词： composite nanosized composite powder sol-gel particle size W/Cu

A TWO-LEVEL FINITE ELEMENT GALERKIN METHOD FOR THE NONSTATIONARY NAVIER-STOKES EQUATIONS II： TIME DISCRETIZATION

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Journal of Computational Mathematics 2004年第1期22卷 33-54页

作者： Yin-nianHe Huan-lingMiao Chun-fengRen FacultyofScience(StateKeyLaboratoryofMultiphaseFlowinPowerEngineering) Xi'anJiaotongUniversityXi'an710049China

In this article we consider the fully discrete two-level finite element Galerkin method for the two-dimensional nonstationary incompressible Navier-Stokes equations. This method consists in dealing with the fully discrete nonlinear Navier-Stokes problem on a coarse mesh with width H and the fully discrete linear generalized Stokes problem on a fine mesh with width h << H. Our results show that if we choose H = O(h^1/2) this method is as the same stability and convergence as the fully discrete standard finite element Galerkin method which needs dealing with the fully discrete nonlinear Navier-Stokes problem on a fine mesh with width h. However, our method is cheaper than the standard fully discrete finite element Galerkin method.

关键词： Navier-Stokes equations Mixed finite element Error estimate Finite element method

WAVEFORM RELAXATION METHODS OF NONLINEAR INTEGRAL-DIFFERENTIAL-ALGEBRAIC EQUATIONS

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Journal of Computational Mathematics 2005年第1期23卷 49-66页

作者： Yao-linJiang DepartmentofMathematicalSciences Xi'anJiaotongUniversityXi'an710049China

In this paper we consider continuous-time and discrete-time waveform relaxation meth-ods for general nonlinear integral-differential-algebraic equations. For the continuous-time case we derive the convergence condition of the iterative methods by invoking the spec-tral theory on the resulting iterative operators. By use of the implicit difference forms,namely the backward-differentiation formulae, we also yield the convergence condition of the discrete waveforms. Numerical experiments are provided to illustrate the theoretical work reported here.

关键词： nonlinear integral-differential-algebraic equations waveform relaxation parallel solutions convergence of iterative methods engineering applications

NONLINEAR DYNAMIC CHARACTERISTICS OF HYDRODYNAMIC JOURNAL BEARING-FLEXIBLE ROTOR SYSTEM

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Chinese Journal of Mechanical Engineering 2005年第1期18卷 58-63页

作者： LuYanjun YuLie LiuHeng TheoryofLubricationandBeadngInstitue Xi＇anJiaotongUniversityXi＇an710049China TheoryofLubricationandBeadngInstitue Xi＇anJiaotongUniversityXi＇an710049China

The nonlinear dynamic behaviors of flexible rotor system with hydrodynamicbearing supports are analyzed. The shaft is modeled by using the finite element method that takesthe effect of inertia and shear into consideration. According to the nonlinearity of thehydrodynamic journal bearing-flexible rotor system, a modified modal synthesis technique withfree-interface is represented to reduce degrees-of-freedom of model of the flexible rotor *** to physical character of oil film, variational constrain approach is introduced tocontinuously revise the variational form of Reynolds equation at every step of dynamic integrationand iteration. Fluid lubrication problem with Reynolds boundary is solved by the isoparametricfinite element method without the increasing of computing efforts. Nonlinear oil film forces andtheir Jacobians are simultaneously calculated and their compatible accuracy is obtained. Theperiodic motions are obtained by using the Poincare -Newton-Floquet (PNF) method. A method,combining the predictor-corrector mechanism to the PNF method, is presented to calculate thebifurcation point of periodic motions to be subject to change of system parameters. The localstability and bifurcation behaviors of periodic motions are obtained by Floquet theory. The chaoticmotions of the bearing-rotor system are investigated by power spectrum. The numerical examples showthat the scheme of this study saves computing efforts but also is of good precision.

关键词： Nonlinear dynamics Bearing-rotor system Stability Bifurcation ChaosFinite element method

Studies on fluid model for numerical simulation of gas discharges in color plasma displays

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Nuclear Science and Techniques 2005年第2期16卷 120-125页

作者： HEFeng LIUChun-Liang KeyLaboratoryforPhysicalElectronicsandDevicesoftheMinistryofEducation Xi＇anJiaotongUniversityXi＇an710049

The fluid models of gas discharge in alternating current plasma display panel (AC PDP) cell are discussed. From the Boltzmann equation, the hydrodynamic equations are derived, but this model consumes much computa- tional time for simulation. The drift-diffusion approximation model and the local field approximation model are ob- tained to simplify the numerical computation, and the approximation conditions of these two models are discussed in detail. The drift-diffusion approximation model gives more satisfactory result for PDP simulation, and the expression of energy balance equation is given completely in this model.

关键词：等离子体显示器流体模式数字模拟漂移扩散逼近