分段修正系数建模数控机床热误差

首先分析了建立在最小二乘法基础上的线性回归分析建模原理的不足及其局限性,在此基础上提出了分段修正系数建模机床热误差方法,并对其原理及建模补偿策略进行了详细推导.通过对数控车削加工中心主轴径向热误差进行建模补偿试验,可以看到,在建模时使用的原始采样点处,拟合误差几乎为零,代入非原始采样点数据时,由模型算得的热误差补偿值和原始采样数据具有很好的拟合性,表明这种建模方法可有效提高热误差补偿精度.

XML中对复杂关系数据建模初探

首先阐述了由于数据表示方式上的差异,为了使XML和传统数据库之间能够互通信息,必须在XML文档和传统数据库之间建立数据转换机制。然后提出在XML中使用ID/IDREF/IDREFS属性类型针对多元复杂联系的关系数据进行建模的方法。

关系数据的建模分析

本文采用E-R图直观地描述现实世界的实体、属性及联系等信息,建立数据处理的概念模型,在概念模型的基础上分析关系数据的建模,以适应关系数据库管理系统的应用,概念模型转换为关系模型的方法很多,同一概念模型不同的转换方法得出关系模型不同,但分析比较会得出好的结论。

基于Contourlet系数的广义高斯分布参数的混合估计方法

提出采用广义高斯概率密度建模的Contourlet变换系数的形状参数混合估计方法。当形状参数值较小时,对于小样本采用熵匹配方法估计,而对于大样本利用最大似然方法估计。当形状参数值较大时,采用矩方法估计。实验结果表明,所提出的方案可以有效准确地对Contourlet变换子带进行建模。

基于径向基函数广义回归网络混合模型的园区短时热负荷预测

冷、热、电三联供机组作为一种发展迅速的分布式能源在提高区域多元能源综合利用效率方面表现优越,其通过对热能的阶梯式利用实现高效供能。在用能高峰时段,开启冷、热、电三联供机组,减轻了用能单位对市电的依赖,降低了用能成本。目前,用能单位缺乏历史用能数据积累,小样本学习无法准确预测用能需求,无法形成基于预测结果的冷、热、电三联供机组的优化运行策略。为此提出了一种基于径向基函数广义回归网络混合模型的短时热负荷预测方法,该方法可在小样本历史数据的情况下,准确预测下一时刻的热负荷需求。试验结果验证了该方法的有效性。

小波域图像降噪概述

小波域图像降噪是图像处理中一个引人注目的研究方向,为了使人们对小波域图像降噪有一概括了解,在对小波域图像降噪相关文献进行分析和理解的前提下,首先给出了小波变换的特性,同时阐述了小波去噪的最优准则和对图像进行小波变换时小波基的选取原则,然后评述了用于图像降噪的方法,并分析了利用小波系数建模的常用方法,最后探讨了小波域图像降噪的发展方向。

正交多项式在非定常气动建模上的运用

介绍了一种基于多变量正交多项式的全局非线性气动系数建模方法。首先由离散数据点生成多变量正交函数;然后根据建立的最小平方误差预测准则,对正交函数进行筛选,保留下来的正交函数均可以分解成普通的独立变量多项式,最后的模型可以看作是多变量幂级数展开系列中的选择性保留项。将该方法应用于某高超声速飞行器的阻力系数建模;将所建模型和仿真数据进行分析比较,其误差小于3%,能够满足工程应用要求。

基于电压型控制DC-DC变换器双脉宽调制对电流谐波抑制的研究

物理滤波是传统变换器开关产生动作的基础,本研究基于谐波对滤波的严重依赖,探寻减少此依赖的方法,并抑制电流谐波而展开研究,通过调制双脉宽减少源头谐波的产生来实现。BUCK电路这种直流斩波器,开关是基于双脉冲来进行控制的,当电流是连续时,就会对输出波执行傅里叶展开操作,双脉冲相位差直接影响到各次谐波的幅值。对比例系数H(n, D),G(n, D)与谐波周期占空比Don以及谐波次数n建立数学模型,构建它们之间的函数关系,基于Matlab仿真对谐波抑制的效果进行分析比较。除此之外,设计并选择最简控制电压型的手段以及其实现方法。

Dynamic model of saturator based on a global heat and mass transfer coefficient

Saturator is one of the core components of humid air turbine （HAT） and is the main feature of HAT making it different from other gas turbine cycles. Due to the lack of sufficient experience in commercial plant operation, HAT cycle has a great demand for modeling and simulation of the system and its components, especially the saturator, to provide reference for system design and optimization. The conventional saturator models are usually based on the theory of heat and mass transfer, which need two accurate coefficients to ensure convincing results. This work proposes a global heat and mass transfer coefficient based on cooling tower technology to model the saturator in small-scale HAT cycle. Compared with the experimental data, the simulation results show that the proposed model well predicts the dynamic humidity and temperature distribution characteristics of saturator at low air pressure and temperature.

Modeling and simulation of quadrotor UAV based on Simscape

In order to speed up and simplify the design of the quadrotor unmanned aerial vehicle(UAV)and carry out experimental simulation and verification of relevant control algorithms,this paper analyzed the system dynamics model of the mechanical structure and flight principle of the quadrotor aircraft,and used the Newton-Euler method to derive the non-linear dynamic equations.Aiming at improving the modeling accuracy and system integrity of the quadrotor,the physical system modeling was combined with the CAD software and the Matlab/Simscape toolbox.The three-dimensional quadrotor solid model built by CAD software was imported into the Simscape simulation platform to construct the body and power system model of the quadrotor.Based on this,the control algorithm designed by Simulink was added to the simulation platform to facilitate the experiment verification and parameter tuning.The simulation results show that the designed aircraft can achieve hover and tracking well and meet the control performance requirements of the system.

Modelling spatial vagueness based on type-2 fuzzy set

The modelling and formal characterization of spatial vagueness plays an increasingly important role in the imple- mentation of Geographic Information System (GIS). The concepts involved in spatial objects of GIS have been investigated and acknowledged as being vague and ambiguous. Models and methods which describe and handle fuzzy or vague (rather than crisp or determinate) spatial objects, will be more necessary in GIS. This paper proposes a new method for modelling spatial vagueness based on type-2 fuzzy set, which is distinguished from the traditional type-1 fuzzy methods and more suitable for describing and implementing the vague concepts and objects in GIS.

Experimental study of a simple pressure loss coefficient model for multi-hole orifice

A throttling experiment for the multi-hole orifice （MO） using water was conducted based on the conclusion of key parameters affecting the MO throttling performance. Testing MOs and standard orifice plates （ SO ） were designed for the throttling experiment to compare the throttling effect using the equivalent diameter ratio （RED） and diameter ratio （RD ） as key parameters, respectively. Meanwhile, effective metrical conditions were provided for experimental accuracy. The throttling model form was determined according to the theoretical throttling model of SO. Then the unknown parameters involved were identified by experimental data. A good concordance between the modeling computation and experimental results shows a validation of the MO throtting model.

Chemical Modeling of Nesquehonite Solubility in Li+Na+K+NH_4+Mg+Cl+H_2O System with a Speciation-based Approach

A chemical model,based on Pitzer activity coefficient model,is developed with a speciation approach to describe the solubility and chemistry of nesquehonite in concentrated chloride solutions.The chemical equilibrium constants for nesquehonite and aqueous species,i.e.0 3 MgCO,3 MgHCO,and MgOH +,are precisely calculated as a function of temperature according to the Van't Hoff equation by use of standard Gibbs free energy,standard formation enthalpy and heat capacity.The most recent solubility data are regressed to obtain new Pitzer parameters with good agreement.The predictive ability of the new model is improved significantly in comparison with previous models.The behavior of speciation chemistry for nesquehonite in various chloride media is explained through this modeling work on the basis of the 2 3 Mg /CO bearing species distribution,activity coefficient and pH changes.

Geometry model construction in infrared image theory simulation of buildings

Geometric model construction is the basis of infrared image theory simulation. Taking the construction of the geometric model of one building in Harbin as an example, this paper analyzes the theoretical groundings of simplification and principles of geometric model construction of buildings. It then discusses some particular treatment methods in calculating the radiation transfer coefficient in geometric model construction using the Monte Carlo Method.

Modeling effects of constituents and dispersoids on tensile ductility of aluminum alloy

The modeling effects of constituents and dispersoids on the tensile ductility of aluminum alloy were studied.The results show that the tensile ductility decreases with the increase of the volume fraction and size of constituents.Thus,purification can improve the tensile ductility by decreasing the volume fraction of constituents(normally compositions of Fe and Si)and the first-class microcracks.The model also indicates that the tensile ductility decreases with the increase in the volume fraction of dispersoids.Decreasing the volume fraction of dispersoids along the grain boundaries by proper heat-treatment and improving the cohesion strength between dispersoids and matrix can also improve the tensile ductility by decreasing the volume fraction of the second-class microcracks.

Levitation mechanism modelling for maglev transportation system

A novel maglev transportation system was proposed for large travel range ultra precision motion.The system consists of a levitation subsystem and a propulsion subsystem.During the propulsion subsystem driving the moving platform along the guideway,the levitation subsystem uses six pairs of electromagnets to steadily suspend the moving platform over the guideway.The model of the levitation system,which is a typical nonlinear multi-input multi-output coupling system and has many inner nonlinear coupling characteristics,was deduced.For testifying the model,the levitation mechanism was firstly controlled by proportional-integral-differential(PID) control,and then a lot of input-output data were collected for model parameter identification.The least-square parameter identification method was used.The identification results prove that the model is feasible and suitable for the real system.

Observations and Modeling of Ice Water Content in a Mixed-Phase Cloud System

The ice water content(IWC) distribution in a mixed-phase cloud system was investigated using Cloud-Sat data,aircraft measurements,and the Weather Research and Forecasting(WRF) model.Simulated precipitation and IWC were in general agreement with rain gauge,sat-ellite,and aircraft observations.The cloud case was char-acterized by a predominant cold layer and high IWC throughout the cloud-development and precipitation stages.The CloudSat-retrieved products suggested that the IWC was distributed from 4.0 to 8.0 km,with the maximum values(up to 0.5 g m-3) at 5.0-6.0 km at the earlymature stage of cloud development.High IWC(up to 0.8 g m-3) was also detected by airborne probes at 4.2 and 3.6 km at the late-mature stage.The WRF model simulation re-vealed that the predominant riming facilitated rapid ac-cumulation of high IWC at 3.0-6.0 km.

Modelling of heat transfer for progressive freeze concentration process by spiral finned crystallizer

This study presents a novel design for a spiral finned crystallizer which is the primary element of progressive freeze concentration(PFC) system, which simplifies the setup of the conventional system. After the crystallizer has been designed, the research experiments have been conducted and evaluated through a thorough analysis of its performance by developing a mathematical model that can be used to predict the productivity of ice crystal at a range of coolant temperature. The model is developed based on the basic heat transfer equation, and by considering the solution's and the coolant's convective heat transfer coefficient(h) under the forced flow condition.The model's accuracy is verified by making comparison between the ice crystal mass' experimental value and the values predicted by the model. Consequently, the study found that the model helps in enhancing the PFC system.

Synthesis of Multi-component Mass-exchange Networks

This paper presents a superstructure-based formulation for the synthesis of mass-exchange networks (MENs) considering multiple components. The superstructure is simplified by directly using the mass separation agents (MSA) from their sources, and therefore the automatic synthesis of the multi-component system involved in the MENs can be achieved without choosing a 'key-component' either for the whole process or the mass exchangers. A mathematical model is proposed to carry out the optimization process. The concentrations, flow rates, matches and unit operation displayed in the obtained network constitute the exact representation of the mass exchange process in terms of all species in the system. An example is used to illustrate and demonstrate the application of the proposed method.

Proposal and evaluation of a new norm index-based QSAR model to predict pEC50 and pCC50 activities of HEPT derivatives

The search and development of anti-HIV drugs is currently one of the most urgent tasks of pharmacological studies. In this work, a quantitative structure-activity relationship （QSAR） model based on some new norm indexes, was obtained to a series of more than 150 HEPT derivatives （1-[（2-hydroxyethoxy）methyl]-6-（phenylthio）thymine） to find their pEC50 （the required effective concentration to achieve 50% protection of MT-4 cells against the cytopathic effect of virus） and pCC50 （the required cytotoxic concentration to reduce visibility of 50% mock infected cell） activities. The model efficiencies were then validated using the leave-one-out cross validation （LOO-CV） and y- randomization test. Results indicated that this new model was efficient and could provide satisfactory results for prediction of pECso and pCC50 with the higher R2 train and the higher Rt2est. By using the leverage approach, the applicability domain of this model was further investigated and no response outlier was detected for HEFT derivatives involved in this work. Comparison results with reference methods demonstrated that this new method could result in significant improvements for predicting pEC50 and pCC50 of anti-HIV HEPT derivatives. Moreover, results shown in this present study suggested that these two absolutely different activities pECso and pCC50 of anti-HIV HEPT derivatives could be predicted well with a totally similar QSAR model, which indicated that this model mizht have the potential to be further utilized for other biological activities of HEFT derivatives.