基于弱牛顿方程的一种无记忆方法

给出了一种求解无约束优化问题的方法,为了求下一次迭代点时它不需要进行矩阵计算,在不精确线搜索下,该方法对一般目标为全局收敛,且对一类特殊的凸函数,其定步长型算法蛮有收敛的,并给出了计算的步骤和计算的数值例子。     

基于金枪鱼算法的最大似然信号方位与频率联合估计

针对多维非线性搜索在传统最大似然估计(ML)上的波达方向(DOA)估计存在计算量大、传统网格搜索速度慢等不足,提出了一种基于金枪鱼算法的窄带信号频率方位联合估计的最大似然DOA估计,该算法体现了良好的估计性能。仿真结果表明,该算法对单声源有精确的角度和频率估计值;在声源个数不同的情况下,与基于松鼠搜索算法、正余弦算法、原子搜索优化算法、人工蜂群算法等的估计相比,该算法有着更快的收敛速度和更低的均方根相对误差。     

折算质量对活塞式压力计专用砝码的影响

<正>0引言在常用的压力计量范围内,活塞式压力计是目前最理想的压力计量仪器。由于具有准确度高、性能稳定、测量范围广、使用方便等优点,使其在压力计量技术中占有重要的地位。活塞式压力计是利用流体静力平衡(即作用在活塞有效面积上的流体压力与其所负荷的重力相平衡)原理进行压力测量的计量标准器。对于一台活塞式压力计,一般先检定其活塞的有效面积,再根据有效面积的数据计算     

多目标快速群搜索优化算法及在模型修正中的应用

为解决群搜索算法在求解多目标优化问题时易陷于局部最优或过早收敛,限制其在复杂结构模型修正中的应用问题,提出改进的群搜索优化算法-多目标快速群搜索优化算法(MQGSO)。采用LPS搜索方法对发现者进行迭代更新,能使发现者更快到达最优位置,提升寻优效率;对追随者增加速度更新机制,考虑其自身历史最优信息以保证收敛精度,并在算法后期采用交叉变异策略增加追随者个体多样性,避免陷入局部最优;在游荡者迭代更新中引入分量变异控制策略,增加其搜索的随机性,提高算法的全局寻优性能。通过7个典型多目标优化测试函数及某发射台有限元模型修正实例,对算法性能进行验证分析。结果表明,与已有MPSO(Multi-objective Particle Swarm Optimization)及MBFO(Multi-objective Bacterial Foraging Optimization)两种算法相比,所提MQGSO算法搜索性能更强、收敛速度更快、计算精度更高,不失为求解复杂多目标优化问题的有效方法。     

快速被动群搜索优化算法及其在空间结构中的应用

在快速群搜索优化算法QGSO(quick group search optimizer)基本原理的基础上,提出了改进的快速群搜索优化算法--快速被动群搜索优化算法QGSOPC(quick group search optimizer with passive congregation),并应用于结构优化设计.采用QGSOPC优化算法分别对空间结构进行离散变量的截面优化设计,并与QGSO优化算法、群搜索优化算法GSO(group search optimize)和启发式粒子群优化算法(HPSO)的计算结果进行比较,结果表明改进的快速被动群搜索优化算法QGSOPC与QGSO算法、GSO算法和HPSO算法相比不但具有较好的收敛精度和更快的收敛速度,而且具有很好的稳定性.该算法可有效率地应用于实际结构的优化设计.     

基于改进萤火虫算法的有限元模型修正

针对标准萤火虫算法后期收敛速度慢、收敛精度低、易陷入局部最优解的问题,提出了参数自适应策略的改进萤火虫算法,建立了基于改进萤火虫算法的有限元模型修正方法。通过隔代随机吸引度因子扩大了算法搜索路径,提升了算法遍历性,避免计算陷入局部最优;通过自适应步长因子使得算法寻优过程中能随迭代次数逐渐减少随机搜索范围,从而提高收敛速度。单、多峰测试函数计算结果表明,改进算法显著提高了收敛速率与收敛精度;简支梁数值算例与某刚构桥实桥有限元模型修正结果表明,简支梁参数最大误差由初始的66.7%降低至修正后的1.08%,刚构桥频率最大误差由14.47%降低至3.25%。所提方法具有良好的更新精度,适用于大型复杂结构的有限元模型修正。     

基于直接搜索方法的层合板多目标优化设计

直接多目标搜索方法(DMS)是一种不需要计算梯度信息并且能实现全局收敛的多目标优化方法。基于直接多目标搜索方法,以简支层合板铺设角度为设计变量,基频和声功率为目标函数进行层合板结构振动与声多目标优化。分别以4层、8层复合材料层合板为例,用DMS方法对其优化设计,并与传统的遗传算法(GA)对比。结果表明,对于4层复合材料层合板,DMS方法比GA方法优化速度快,且能得到全局最优解;对于8层复合材料层合板,用DMS方法比4层板优化所需时间多,但相比GA方法,DMS方法优化更快。     

基于改进粒子群算法的最小二乘影响系数法的理论及实验研究

针对最小二乘影响系数法平衡过程中出现的某些测点残余振动较大及平衡质量较大等问题,将一种基于遗传交叉因子改进的粒子群算法引入到转子动平衡最小二乘影响系数法中。实例计算说明改进后的算法具有很好收敛特性和全局搜索能力,与基本最小二乘影响系数法计算结果相比,有效降低最大配重质量和最大残余振动大小。通过实验验证了结果的正确性和方法的可行性。     

电子光学系统最优化设计中的非线性规划:应用与比较

以电子光学系统中发射系统为实例，从收敛速度、搜索效果、整体收敛性等几个方面，系统地对非线性规划的五种搜索方法在电子光学系统设计中的应用进行分析和比较，得出了一些有价值的结果。计算表明Rosenbrock法是电子光学系统最优化设计中最值得推荐的方法。     

采用贪婪遗传算法实现图像阈值的自动选取

将贪婪思想引入到遗传算法中设计了贪婪遗传算法,以最大类间方差函数作为遗传算法中适应度的评价函数,利用贪婪算法局部搜索能力强和遗传算法全局搜索能力强的特点,实现图像阈值的自动选取。与基本遗传算法相比,本文算法具有更强的寻优性能,从而加快了收敛速度。实验表明基于贪婪遗传算法的阈值自动选取方法具有计算耗时少的特点,更适用于实时图像处理系统。     

Ab initio calculations of lattice stability of sigma-phase and phase diagram in the Cr–Fe system

Total energy of pure metals in the sigma-phase structure and in the standard element reference (SER) structure were calculated by full-potential linear augmented plane waves method in the general gradient approximation at the equilibrium volume of all phases. Relaxation of lattice parameters of sigma-phase and SER structure were performed. The difference of total energy of sigma-phase and of standard element phase for pure constituents (Δ⁰E_i^σ–SER) was used in a new two-sublattice model of sigma-phase, which was subsequently employed for calculation of phase diagram.

Entropy term of Gibbs energy of elements in sigma-phase structure and excess Gibbs energy of mixing of sigma-phase have still to be adjusted to the experimental phase equilibrium data. This procedure was tested on the Fe–Cr system.     

Ca-La2O3-Ni体系的热力学研究

计算了用Ca还原La2O3生成纯金属La(3Ca La2O3=2La 3CaO),La与Ni反应生成LaNi5合金（La 5Ni=LaNi5)的标准吉布斯自由能和吉布斯自由能变化,以及反应平衡时的钙分压,在1223,1273,1323,1373K温度下制得了LaNi5合金,XRD鉴定了反应产物的物相,热力学计算说明在La-NI系化合物中生成物只能是L aNi5。     

Multiangular elements in plate bending

The problem of bending a thin plate is solved by the finite element method. Using a differential equation of the plate element equilibrium determines the potential energy by contour values of displacements and their first derivatives. In the equilibrium state they have to be such that the potential energy reaches its minimum. The suggested calculation algorithm enables the use of multiangular elements of arbitrary shape instead of integration in the area of this element in which curvilinear integrals appear along the element contour. Elaborated also is the program for calculation by computer and verified usability of the method for various elements based on the example of the square plate.     

Parameter estimation and thermodynamic model fitting for components in mixtures for bio-diesel production

In the search of clean, sustainable and renewable energy sources, at present the use of bio-diesel from vegetable oils is one of the possibilities being considered. The knowledge of phase equilibrium in mixtures found in the bio-diesel production is essential for the correct design and operation of the process. However, there is still a lack of information about the parameter values for the models used to describe the phase equilibrium, which could lead to incorrect design of the reactors and the separation processes, and to low efficiency caused by low mass transfer due to the presence of heterogeneous mixtures. In this study, two algorithms are described for the model fitting and parameter estimation, which were used to estimate the values of the parameters in the UNIQUAC and NRTL model for a mixture of vegetable oils and bio-diesel. One of the algorithms uses the Simulated Annealing (SA) method, to find good initial estimates, without any previous knowledge of the parameters. Another algorithm uses Successive Quadratic Programming, using the estimates calculated in the SA algorithm to refine these estimates. In both algorithms, the criterion for fitting is the minimization of the square of the difference between calculated and experimental values. In both algorithms, the equilibrium is calculated using the direct global minimization of the Gibbs free energy with respect to the number of moles of each component, at constant T and P, for a given set of model parameters. The results obtained were able to correctly reproduce the experimental values of phase equilibrium composition.     

Calculation of the P–T phase diagram of hafnium

The FP-LMTO method is used to calculate the total energy and equilibrium lattice properties for the observed phases of hafnium (Hf). The temperature dependences of the Gibbs energy are found for these structures within the Debye model. A quantitative agreement with the experimental points of the P–T phase diagram is obtained.     

Analysis of partly wrinkled membranes by the method of dynamic relaxation

A version of the method of dynamic relaxation is developed to analyze equilibrium configurations of partly wrinkled membranes. In this method equilibria are regarded as long time limits of a damped dynamical problem. The membrane theory considered is based on the concept of a relaxed strain energy function that automatically incorporates the effects of wrinkling. For neo-Hookean materials, existence theorems of nonlinear elasticity are used to show that the relaxed potential energy possesses minimizers in a certain function space. Moreover, solutions of the equilibrium equations furnish global minima of the energy, for certain classes of boundary data. Such deformations are automatically stable according to the minimum-energy criterion. This result motivates the search for solutions of the equilibrium equations, although the existence theory does not guarantee that energy minimizers possess the degree of regularity required by these equations. Several examples of two-and three-dimensional deformations are presented.     

The Gibbs equation versus the Kelvin and the Gibbs-Thomson equations to describe nucleation and equilibrium of nano-materials

The Kelvin equation, the Gibbs equation and the Gibbs-Thomson equation are compared. It is shown that the Kelvin equation (on equilibrium vapor pressure above nano-droplets) can be derived if the inner pressure due to the curvature (from the Laplace equation) is substituted incorrectly into the external pressure term of the Gibbs equation. Thus, the Kelvin equation is excluded in its present form. The Gibbs-Thomson equation (on so-called equilibrium melting point of a nano-crystal) is an analog of the Kelvin equation, and thus it is also excluded in its present form. The contradiction between the critical nucleus size (from the Gibbs equation) and the so-called equilibrium melting point of nano-crystals (from the Gibbs-Thomson equation) is explained. The contradiction is resolved if the Gibbs equation is applied to study both nucleation and equilibrium of nano-crystals. Thus, the difference in the behavior of nano-systems compared to macro-systems is due to their high specific surface area (Gibbs) and not to the high curvature of their interface (Kelvin). Modified versions of the Kelvin equation and the Gibbs-Thomson equation are derived from the Gibbs equation for phases with a general shape and for a spherical phase.     

Calculation of Thermodynamic Properties from Two-liquid Coexisting Phase Diagram of Al-In System by Means of NRTL Equation

1.IntroductionV!agnerhadpointedoutthatthesolidusandliquidscurvesofphasediagramsareusuallyeasiertobedeterminedexperimentallythanotherthermody-namicpropertiesl'J.Sofarmanyauthorshavepre-sentedsomemethodstoextractthermodynamicprop-ertiesfrombinaryalloyphasediagrams['l3].Thesepreviousattemptshavebeenrestrictedtoapply-ingsomesolutionmodels,includingregularsolutionmodelandquasi-chemicalequilibriumapproaches,etc..However,whensomealloysystemscannotbesuccessfullydescribedbythesesolutionmodelsitisneces…     

Thermodynamic study on codeposition of ZrC-SiC from MTS-ZrCl<Subscript>4</Subscript>-CH<Subscript>4</Subscript>-H<Subscript>2</Subscript>

Thermodynamic equilibrium condensed phases for chemical vapor deposition of ZrC-SiC from the MTS-ZrCl₄-CH₄-H₂ system were calculated by FactSage programs based on Gibbs free energy minimization of the reaction system. The deposition phase diagrams, which indicated the condense phases, were constructed according to the calculation results. The effects of temperature and partial pressure of precursors on the final condensed phases were studied. The results indicate that the codeposition is more effective in the presence of an independent carbon source, CH₄, with a reasonable partial pressure than in the absence of CH₄. The experimental results are in good agreement with the thermodynamic calculation results.