易挥发弱电解质体系化学及相平衡计算的遗传算法

基于Gibbs自由能最小化原理,提出用遗传算法计算易挥发弱电解质体系化学及相平衡问题。首先建立了易挥发弱电解质体系Gibbs自由能的计算模型,将含化学反应平衡和相平衡计算问题转化为有约束的最优化问题．并应用遗传算法求解;其次在算法实施时提出两点改进,即通过对优化变量采取动态边界的可行域编码方法来处理问题约束和引入反应平衡常数来提高低含量组分的计算精度;最后对两个算例进行了计算。计算表明,本文计算结果与文献值相吻合,并且简单易实施,是这类问题计算的有效方法。     

关于受限制的部分平衡复杂反应体系组成的计算

对于因动力学原因使某些反应不发生的受限制的复杂反应体系，本文介绍了计算组成的方法，它是在原有元素原子守恒方程组中加入了附加的“元素”，守恒条件，在新的物质守恒方程组和组成非负条件限制下，用自由能最小化方法计算受限制的部分平衡复杂反应体系的组成，根据上述原理编制了通用程序，对氨催化氧化和合成甲醇等受限制的复杂反应体系进行了计算，结果与文献值相符。     

无机盐-恒沸有机水溶液体系相平衡计算

针对无机盐-恒沸有机水溶液体系相平衡问题,提出用Gibbs自由能最小法计算。通过Pitzer理论与NRTL方程相结合来描述体系中各组分的活度系数,建立体系Gibbs自由能的计算模型,从而将相平衡计算转化为有约束的最小化问题,并应用遗传算法求解,进而得到体系平衡时的各相组成。以2个体系的相平衡计算为例,结果表明此方法可行有效,可为无机盐作盐析剂分离恒沸有机水溶液体系这一化工过程建立一定的理论基础和计算依据。     

Recent developments for molten salt systems in Thermochimica

The modified quasi-chemical model in the quadruplet approximation has been implemented in the open-source equilibrium thermodynamics library Thermochimica, enabling single point equilibrium calculations and sophisticated multi-physics simulations of molten salt nuclear reactor systems. Here, the derivations necessary to obtain the chemical potentials of the quadruplet species required for Gibbs energy minimization are provided. The implementation is verified via code-to-code benchmarking against FactSage. A scheme to increase computational efficiency of multi-physics simulations including Thermochimica is described and its effectiveness for molten salt systems demonstrated. Finally, a multi-physics simulation of a molten salt nuclear fuel system is presented as a demonstration problem: ORIGEN-S is used to calculate the isotopic evolution of a fuel-loaded FLiBe mixture with fission and activation products as Thermochimica predicts the phase evolution and number of moles of Cs in various phases.     

An algorithm and computer program for calculating composition phase diagrams

An algorithm has been developed to determine the minimum Gibbs energy surfaces and composition phase diagrams of chemical systems. In order to apply the algorithm, phases are represented by points in the parametric space of a system. This requires that the compositional variation of solutions be described by a series of “pseudo-compounds” of differing compositions. All phase regions of an approximated c component system are thus linear as they are defined by the coordinates of c point phases (i.e., phases of fixed composition), which may correspond in part or entirely to a single solution phase. These regions form c-1 dimensional simplicial facets on the Gibbs energy-composition surface of the system and are identified by an abbreviated combinatorial method. This method is feasible because the chemical potentials of the components are constant in any region and can be rapidly determined from linear algebraic techniques. The true phase rule variance of phase regions is found by counting the number homogeneous phases, which may be represented by one or more point phases, in each region as identified by the algorithm. The algorithm can be generalized to other thermodynamic state functions for systems with additional extensive independent variables, such as volume and entropy. The procedure has been coded as a FORTRAN computer program, Bounds, which is capable of treating five component systems with up to eight hundred point phases. Because the calculation of stable phase equilibria is assured by the algorithm, Bounds can be used to calculate composition phase diagrams for systems with complex phase relations, e.g., multinodal solvi. Bounds also provides the basis for a simple method of calculating phase diagrams as a function of both composition and variables like pressure, temperature, and chemical potentials.     

The calculation of ternary miscibility gaps using the linear contributions method: Problems,benchmark systems and an application to (K,Li, Na)Br

Hypothetical systems are useful to enhance the rigor of computerized algorithms and to enhance the applicability of the developed software to physically realistic systems. This paper deals with the calculation of miscibility gaps using the method of the addition of linear contributions. We derived a formalism, which underlies the method, for a multicomponent system. We applied the method to hypothetical miscibility gaps in a single ternary solution form for which the Gibbs energy is characterized by more than two minima. We show that specific Gibbs energy expressions at constant pressure and temperature result in the formation of multiple three-phase fields and multiple critical points. We present an algorithm for the calculation of miscibility gaps in ternary systems, which are characterized by these properties. We applied our method to the system KBr–LiBr–NaBr, having the characteristic that the solid form may separate into three phases with the same crystal structure at low temperatures.     

Minimax method in optimizing energy consumption in real-time embedded systems

The main principles of the minimax method designed for solving energy consumption optimization problems in real-time embedded systems are presented. Results of comparing ways to minimize energy consumption in systems with on-line minimax and off-line DVS/DFS scheduling are given. In terms of energy consumption minimization, the minimax method is shown to ensure optimal division of the task into two subtasks. This method can be applied both to systems with tasks arbitrarily distributed in time and to periodic multitasking systems with rigid timing constraints.     

A general computer program for the calculation of chemical equilibria and heat balances

A general purpose computer program for chemical process design has been developed on the basis of the Eriksson method for Gibbs energy minimization. A simple directive language and an on-line databank of thermodynamic data have been provided, as well as facilities for rapid exploration and optimization of chemical systems.     

Phase diagram reassessment of Ag–Au system including size effect

CALPHAD approach is a very useful technique to reproduce the phase diagram of bulk materials with thermodynamic database such as chemical potentials of pure substances and excess Gibbs energy of mixtures as a function of composition, temperature and pressure. In order to extend the use of CALPHAD approach to small metallic particles on sub-micron and nano scale, due to the surface effect, the chemical potentials and the excess Gibbs energy should be expressed with an additional parameter, viz, the particle size. In this article, a new approach to describe the thermodynamic properties including the size effect is suggested. As a simple example, the chemical potentials and the excess Gibbs energy of Ag–Au system were reassessed as functions of composition, temperature and particle size.     

A novel constrained texture mapping method based on harmonic map

In this paper, we present a novel constrained texture mapping method based on the harmonic map. We first project the surface of a 3D model on a planar domain by an angle-based-flattening technique and perform a parametrization. The user then specifies interactively the constraints between the selected feature points on the parametric domain of the 3D model and the corresponding pixels on the texture image; the texture coordinates of other sample points on the 3D model are determined based on harmonic mapping between the parametric domain of the model and the texture image; finally we apply an adaptive local mapping refinement to improve the rendering result in real-time. Compared with other interactive methods, our method provides an analytically accurate solution to the problem, and the energy minimization characteristic of the harmonic map reduces the potential distortion that may result in the constrained texture mapping. Experimental data demonstrate good rendering effects generated by the presented algorithm.     

采用迭代求解的电动汽车优化充电算法

电动汽车优化充电对配电网的安全经济运行具有十分重要的意义.利用配电网辐射状运行结构采用迭代修正节点电压的方法能够大幅降低优化变量的维数,提高计算速度.该方法已被应用于以网损最小为目标函数、常规负荷模型为恒功率负荷、不计及节点电压、支路功率约束的三相平衡配电网中.该文提出了将其推广至一般情形的方法,目标函数为配电网供电能量最小、运行费用最小或利润最大,不再局限于网损最小,负荷模型不再局限于恒功率负荷.而且计及了配电网的三相不平衡、节点电压、支路功率约束.文中分析了负荷模型对优化计算结果的影响.研究发现,当负荷模型只包含恒功率、恒阻抗负荷时,每次迭代中优化模型仍为线性约束凸二次规划模型;当负荷模型包含恒电流负荷时,每次迭代中优化模型不再为线性约束凸二次规划模型,但仍为线性约束凸规划模型.3个算例的仿真结果表明,所提方法收敛性好、计算精度高、速度快,能够改善电压,提高配电网的经济效益.     

Task-level approaches for the control of constrained multibody systems

This paper presents a task-level control methodology for the general class of holonomically constrained multibody systems. As a point of departure, the general formulation of constrained dynamical systems is reviewed with respect to multiplier and minimization approaches. Subsequently, the operational space framework is considered and the underlying symmetry between constrained dynamics and operational space control is discussed. Motivated by this symmetry, approaches for constrained task-level control are presented which cast the general formulation of constrained multibody systems into a task space setting using the operational space framework. This provides a means of exploiting task-level control structures, native to operational space control, within the context of constrained systems. This allows us to naturally synthesize dynamic compensation for a multibody system, that properly accounts for the system constraints while performing a control task. A set of examples illustrate this control implementation. Additionally, the inclusion of flexible bodies in this approach is addressed.     

Quantitative simultaneous fit to the liquidus surface and thermodynamic data for the GaInSb system using an associated solution model for the liquid

The liquidus surface and extensive thermodynamic properties in the Ga-In-Sb system are fit simultaneously in a quantitatively satisfactory manner. The Ga_uIn_l-uSb solid solution phase is described as quasiregular in the components GaSb and InSb. The liquid phase is assumed to consist of the species, Ga, In, Sb, GaSb, and InSb which contribute to the excess Gibbs energy of mixing by quadratic and cubic terms in the species mole fractions. The simplest version of this model that leads to an asymmetric behavior of the component chemical potentials in the Ga-Sb and In-Sb systems is identified and found to be adequate. Contrary to common usage in the literature it is not assumed a priori that the relative (to its pure liquid elements) heat capacity of CaSb(s) (or InSb(?)) is equal to that of GaSb(?) (inSb(s)). This assumption is generally incorrect for associated solution models. Moreover, the parameters of the liquid phase are constrained so that the enthalpy and entropy of mixing of GaSb(?) at the melting point of GaSb(s) are properly related to the enthalpy and entropy of formation of GaSb(s). Two similar constraints are used for InSb(l).     

Calculation of phase equilibria for an alloy nanoparticle in contact with a solid nanowire

Phase equilibria in a system constituted of an alloy nanoparticle in contact with a solid nanowire have been modelled based on the minimization of a Gibbs free energy function. The Gibbs free energy consists of a bulk, surface and interface contribution. The bulk contribution is taken from CALPHAD thermodynamic databases and the surface properties from the literature. The effect of particle size and surface and interfacial properties on the liquidus line of the Au-Ge and In-Si systems has been studied. The results are compared to the bulk phase diagram and phase equilibria calculated for nano-systems with different geometries.     

Representing and computing regular languages on massively parallelnetworks

A general method is proposed for incorporating rule-based constraints corresponding to regular languages into stochastic inference problems, thereby allowing for a unified representation of stochastic and syntactic pattern constraints. The authors' approach establishes the formal connection of rules to Chomsky grammars and generalizes the original work of Shannon on the encoding of rule-based channel sequences to Markov chains of maximum entropy. This maximum entropy probabilistic view leads to Gibbs representations with potentials which have their number of minima growing at precisely the exponential rate that the language of deterministically constrained sequences grow. These representations are coupled to stochastic diffusion algorithms, which sample the language-constrained sequences by visiting the energy minima according to the underlying Gibbs probability law. This coupling yields the result that fully parallel stochastic cellular automata can be derived to generate samples from the rule-based constraint sets. The production rules and neighborhood state structure of the language of sequences directly determine the necessary connection structures of the required parallel computing surface. Representations of this type have been mapped to the DAP-510 massively parallel processor consisting of 1024 mesh-connected bit-serial processing elements for performing automated segmentation of electron-micrograph images.     

大规模过程系统优化方法

基于非线性约束的序列界无约束极小化方法,对大规模过程系统稳态优化的序列界约束极小化方法(SBCMM)进行了研究.对工程模型引进松弛变量处理后,SBCMM的罚函数仅包含等式约束的惩罚项,不包含界约束及不等式约束的惩罚项.原问题的解由求解一系列界约束极小化子问题而非无约束极小化子问题来获得.最后,用一类规模可变的非线性规划...     

Robust receding horizon control of constrained nonlinear systems

We present a method for the construction of a robust dual-mode, receding horizon controller which can be employed for a wide class of nonlinear systems with state and control constraints and model error. The controller is dual-mode. In a neighborhood of the origin, the control action is generated by a linear feedback controller designed for the linearized system. Outside this neighborhood, receding horizon control is employed. Existing receding horizon controllers for nonlinear, continuous time systems, which are guaranteed to stabilize the nonlinear system to which they are applied, require the exact solution, at every instant, of an optimal control problem with terminal equality constraints. These requirements are considerably relaxed in the dual-mode receding horizon controller presented in this paper. Stability is achieved by imposing a terminal inequality, rather than an equality, constraint. Only approximate minimization is required. A variable time horizon is permitted. Robustness is achieved by employing conservative state and stability constraint sets, thereby permitting a margin of error. The resultant dual-mode controller requires considerably less online computation than existing receding horizon controllers for nonlinear, constrained systems     

A procedure to estimate equilibrium concentrations in molticompokent systems amd related applications

A technique has been developed to provide a close estimate of the equilibrium composition in multiphase multicomponent systems. Both the standard Gibbs energies of species and mass constraints are considered in this computation. The estimates accelerate the rate of convergence of more general Gibbs energy minimization methods and are useful in predicting stoichiometric reactions. Special situations where the output may be taken as the final solution are discussed. These include the computation of multielement stability diagrams involving stoichiometric phases.     

Adaptive neural optimal control via command filter for nonlinear multi-agent systems including time-varying output constraints

In this article, an optimal command-filtered backstepping control approach is proposed for uncertain strict-feedback nonlinear multi-agent systems (MASs) including output constraints and unmodeled dynamics. One-to-one nonlinear mapping (NM) is utilized to recast constrained systems as corresponding unrestricted systems. A dynamical signal is applied to cope with unmodeled dynamics. Based on dynamic surface control (DSC), the feedforward controller is designed by introducing error compensating signals. The optimal feedback controller is produced applying adaptive dynamic programming (ADP) and integral reinforcement learning (IRL) techniques in which neural networks are utilized to approximate the relevant cost functions online with established weight updating laws. Therefore, the entire controller, including feedforward and feedback controllers, not only ensures that all signals in the closed-loop systems are cooperative semi-globally uniformly ultimately bounded (SGUUB) and the outputs maintain in the provided time-varying constraints, but also makes sure that the cost functions achieve minimization. A simulation example is presented to illustrate the feasibility of the proposed control algorithm.