保护性耕作条件下影响蒸发量因素的试验研究

为分析保护性耕作条件下影响日棵间蒸发量的因素,在一年两熟地区保护性耕作条件下对影响蒸发的各因素进行田间试验研究,对10种保护性耕作模式的各参数与日棵间蒸发量的拟合关系进行分析。结果表明:8种耕作模式条件下日棵间蒸发量与叶面积指数、地表覆盖率有较好的三次函数关系,7种耕作模式下日棵间蒸发量与地表含水率具有较好的三次函数关系,3种耕作模式下日棵间蒸发量与地表温度具有三次函数关系。保护性耕作条件下日棵间蒸发量可近似用叶面积指数、地表覆盖率或者地表含水量计算。     

土壤持水曲线van Genuchten模型求参的Matlab实现

土壤持水曲线是研究土壤水力学性质必不可少的 ,在已经建立的众多数学模型中 ,vanGenuchten模型是目前运用最广泛的模型 ,而运用该模型的关键是其 4个参数的求解。为此 ,本文对同一组东北褐土的土壤水吸力和对应的土壤含水量数据较详细地介绍了Matlab软件的非线性拟合和非线性回归函数的运用 ,得出了该土壤vanGenuchten模型的 4个参数值 ,分别建立了该土壤的vanGenuchten模型 ,并利用Mat lab强大的绘图功能对它们进行了直观比较。最后运用方差分析和残差分析对该模型的计算值与实测数据进行了分析 ,结果表明 :非线性拟合和非线性回归函数求参结果的显著水平均达到p<0 0 0 0 1,残差平方和均小于 0 0 0 0 5 ,其中非线性回归函数的求参结果较非线性拟合好。因此 ,运用Matlab软件的非线性拟合和非线性回归函数对土壤持水曲线的vanGenuchten模型进行求参是切实可行的 ,从而为土壤学工作者寻求出了一条运用数值计算方法的新途径。     

基于MATLAB渠道渐变体土方量计算的改进算法研究

基于MATLAB强大的数学计算功能与友好的界面,针对现有渠道渐变体工程土方量计算方法的不足,提供了用三次样条函数拟合断面面积函数,再运用复化梯形求积公式计算土方量的新方法;并用实例说明了该方法的应用及其误差分析。结果表明,该方法计算过程简单、计算误差小,可供设计、施工人员参考。     

基于最小二乘曲面拟合的泵装置特性预测方法

根据水泵相似理论,运用最小二乘曲面拟合法建立了原型泵和模型泵无因次扬程、效率与叶片角度、叶轮直径和转速的同一数学表达。结合无因次管道性能曲线,建立了原、模型泵装置无因次的特性参数预测模型,并运用该数学模型预测了广东省惠州市文头岭大型排涝泵站模型泵任意角度的装置特性。结果表明,该数学模型可为大型水泵的装置特性预测提供一个新颖、实用的方法。     

Optimization of Curve Fitting Used in Development of Magic Formula Tire Model

Characteristics of a tire are the foundation of vehicle dynamics studying, especially play a vital role in vehicle handling study. It is necessary to establish a tire model in the simulation for vehicle handling because the tire characteristics got by test can not be satisfied.The optimization of fitting to the tire test data curves by Magic Formula is discussed, included the digitalization of tire test data curves, designing objective functions and optimization processes,etc. Finally the parameters in Magic Formula tire model are obtained and they lay a foundation for the development of vehicle handling aftertime.     

Probability Statistics and Sensitivity Analysis of Parameters of Soil-Water Characteristic Curves

To study the characteristic of soil-water characteristic curves (SWCC) of several different types of soils, a number of data sets of matric suction-volume water content were studied for UNSODA clay, UNSODA sand, Guangxi expansive soil and Hefei expansive soil. Three types of Fredlund-Xing models and three types of van Genuchten models were used to study the influence of SWCC models, and three types of functions in the scientific programming language MATLAB were applied to analyze the effect of different fitting methods. Through the data fitting and statistic analysis, the probabilistic characteristics of the fitting parameters of SWCCs for the four types of soils were obtained. For analyzing the relative sensitivity of the normalized volume water content to the three fitting parameters of SWCC, a formula which considers the correlation of parameters was proposed. Through the data fitting of many data sets, it is found that the fitting methods influence the value of parameters of SWCC, while the influence is less than that of fitting models from the statistical point of view. The SWCCs of all the models are nearly the same when the suction is low. With the increase of the suction, the SWCCs of FX2 and VG2 are very close, and the SWCCs of FX3 and VG3 are the same. The sensitivity analysis shows that the normalized volume water content is more sensitive to parameters n and m than to parameter a.     

浅谈桥梁博士计算变截面连续箱梁时通用截面拟合的应用

通过利用桥梁博士对变截面连续箱梁的结构计算,阐述了单箱双室截面、斜腹板的变截面连续箱梁（箱梁截面变化复杂,顶板、底板、腹板厚度,梁高均为变化值,且梁底呈二次抛物曲线变化）的建模过程。阐明若采用普通方法输入截面,需计算各个节点截面特性,然后逐个输入;采用通用截面拟合工具输入函数,可一次完成。     

A variance-covariance structure to take into account repeated measurements and heteroscedasticity in growth modeling

This study proposes a within-subject variance-covariance (VC) structure to take into account repeated measurements and heteroscedasticity in a context of growth modeling. The VC structure integrates a variance function and a continuous autoregressive covariance structure. It was tested on a nonlinear growth model parameterized with data from permanent sample plots. Using a stand-level approach, basal area growth was independently modeled for red spruce (Picea rubens Sarg.) and balsam fir [Abies balsamea (L.) Mill.] in mixed stands. For both species, the implementation of the VC structure significantly improved the maximum likelihood of the model. In both cases, it efficiently accounted for heteroscedasticity and autocorrelation, since the normalized residuals no longer exhibited departures from the assumptions of independent error terms with homogeneous variances. Moreover, compared with traditional nonlinear least squares (NLS) models, models parameterized with this VC structure may generate more accurate predictions when prior information is available. This case study demonstrates that the implementation of a VC structure may provide parameter estimates that are consistent with asymptotically unbiased variances in a context of nonlinear growth modeling using a stand-level approach. Since the variances are no longer biased, the hypothesis tests performed on the estimates are valid when the number of observations is large.     

粮仓温度场数学模型研究

粮仓温度的传统测试方法存在硬件结构复杂、电气元件过多,可靠性低等缺点。本文根据测量得到的有限个典型的离散温度数据,利用最小二乘法拟合出粮仓温度在其空间坐标上的分布函数,从而可以较精确地估计粮仓内任一点的温度值,大大节约了硬件资源,方便了测量工作。