基于外场实验的风力机叶片三维效应研究

针对一台33 kW水平轴风电机组开展了外场实验,得到其叶片7个断面翼型的压力分布曲线;基于求解时均N-S方程对风轮进行三维数值模拟,以及将叶片各断面作为二维翼型进行数值计算,分别得到各断面翼型的压力分布曲线及升阻力系数．通过将外场实验、三维和二维数值计算所得压力分布曲线及升阻力系数进行对比分析,研究了三维效应对风力机气动性能的影响．研究表明,从叶尖到叶根各断面翼型的压差先增大后逐渐减小,叶片表面压力分布曲线比较明显地反映了从叶尖到叶根流动分离的变化;叶片表面压力分布的三维数值计算结果较二维计算结果更加接近于外场实验值;风力机叶片表面的三维流动对叶片的气动性能影响较大,在叶尖和叶根部分尤为突出.     

基于时间有限元方法的旋转柔性叶片动力学响应分析

将时间有限元方法引入到柔性多体系统的数值计算中,研究了旋转柔性叶片系统的刚-柔耦合响应问题.首先,基于非线性梁理论,建立了旋转柔性叶片系统的中心刚体-柔性梁模型,构造柔性叶片系统考虑一次近似耦合的Lagrange函数;其次,采用假设模态方法对空间坐标进行离散,建立系统的时间有限元格式;最后,通过数值实验,分析了柔性叶片的动力学响应.该方法直接构造了系统的离散积分格式,并自动保证了该格式是保辛的,因而具有较高的数值精度和稳定性.数值结果表明:时间有限元可以有效地求解旋转柔性叶片系统内低频大范围运动与高频弹性振动之间的刚-柔耦合问题.     

关于建立玉米叶片的数学模型的几种方法的讨论

分别运用拉格朗日插值法、最小二乘的三次多项式拟合法和经典三次样条插值法建立了玉米叶片的数学模型,并从收敛性、稳定性、光滑性等方面对三种方法进行了对比分析,通过对所给实例的绘图效果进行比较,指出了拉格朗日插值法、最小二乘的三次多项式拟合法和经典三次样条插值法在描述玉米叶片形态特征的效能上的利弊.     

计算流体力学在大型风力机空气动力学的应用进展北大核心CSCD

针对大型风力机设计中的关键空气动力学问题,比较系统地介绍了计算流体力学(computational fluid dynamics,CFD)方法的主要应用,特别是在大型风力机翼型气动分析、风力机流动的数值模拟、风轮空气动力特性的数值计算以及大型风力机叶片的多目标气动优化设计方面的进展.基于CFD方法分别实现了风力机翼型与叶片二维/三维气动特性的准确预测,风力机尾流场涡系结构的准确捕捉;并结合多目标遗传算法对1.5 MW风力机叶片进行了优化,获得了具有高风能利用效率的叶片方案.     

植物叶片厚度日变化的微分方程模型

对植物叶片厚度精密测量的日变化时间序列给出了微分方程模型,经数值例子的拟合发现,该模型对叶片厚度日变化的时间序列有很好的拟合精度,从而对研究植物叶片厚度的精密测量、预测与控制等都具有一定的参考价值和实用性.     

基于麻雀搜索算法和广义回归神经网络的玉米产量预测

针对新疆北部地区在玉米生产过程中存在的水肥利用率低下问题,提出一种基于麻雀搜索算法和广义回归神经网络模型的玉米产量预测方法,以探索水肥因素与玉米产量间的非线性关系,可为优化新疆北部地区春播玉米灌溉制度及水肥配饰方略提供理论指导.该方法采用36组既有玉米生产数据,通过广义回归神经网络技术建立模型,使用麻雀搜索算法对关键参数进行优化,降低了人为因素对模型超参数选择的影响.该模型用于新疆灌溉中心试验站的玉米产量预测仿真实验,证明该模型预测性能良好,相较于传统模型,在学习速度、预测精度及鲁棒性上具有优势,可有效预测新疆北部地区春播玉米产量.     

回归设计在作物间作技术研究中的应用

本研究采用回归正交组合设计的方法,选择春玉米间作春大豆的畦幅、春玉米密度、春大豆密度三个农艺因子,布置田间参数试验,通过对试验结果的分析,建立了春玉米间作春大豆的总产、春玉米产量、春大豆产量及净产值的三元二次回归模型。根据建立的模型,进行了因子效应分析,并结合计算机模拟寻优,对春玉米间作春大豆的畦幅及其复合群体结构进行了优化。     

汽轮机调节级的气流激振力分析

从流体动力学出发,应用动量定理研究汽轮机调节级叶片由于间隙引起的气流激振力问题,综合考虑了叶片及喷嘴的各项设计参数并应用理论分析的方法首次导出了汽轮机调节级叶片由于间隙引起的气流激振力的计算公式,并分析了调节级在各工况的激振力.     

高寒草甸地区陆面过程观测及耦合模式研究

对海北高寒草甸地区水热传输过程进行了系统观测,特别考虑了叶片气孔为非饱和水汽条件下的交换情况,结合修正的根系吸水公式,发展了一个多层陆气耦合模式．利用该模式对中国科学院海北高寒草甸生态试验站地区矮嵩草草甸陆气水热交换进行了数值模拟,分析了湍流交换的物理过程,给出了沿高度分布的各物理量．模拟结果与实测值吻合较好．     

三维数值流形方法的理论研究

在二维数值流形方法的基础上,对三维数值流形进行了理论研究．研究了三维覆盖位移函数,进行了三维数值流形的力学分析,给出了三维流形单元的刚度矩阵,详细推导了三维数值流形的Hammer积分及剖分规则,系统地研究三维数值流形的理论体系与数值实现方法．作为数值算例,给出了相应的悬臂梁的计算结果,计算结果表明算法的精度和计算效益较高．     

A model for determining weights of traits in simultaneous multitrait selection

Simultaneous multitrait selection in plant breeding requires knowledge of the relative values, or tradeoffs, of the various traits being considered. An optimization model is developed which will allow quantification of the relative weights present in a breeder's subjective ranking of genotypes, the ranking being based on the apparent relative value of the genotypes. The model is completely general in nature. It allows specification of nonlinear solution functions as well as a linear solution function. It is not specific to any single plant species, nor is it specific to any number or type of traits. While the model is completely general, for purposes of illustration the development of the model is restricted to the linear case. The use of the model in an applied breeding experiment is illustrated using data provided by an experienced maize breeder. The data represent selected and ranked families of genotypes, where the selection and ranking criteria are the relative family performances of three traits considered of economic importance. Relative weights for the three traits are obtained from the initial ranking, and the technique is then used iteratively to demonstrate its usefulness as an interactive procedure.     

Asymptotic theory of dependent Bayesian multiple testing procedures under possible model misspecification

We study asymptotic properties of Bayesian multiple testing procedures and provide sufficient conditions for strong consistency under general dependence structure. We also consider a novel Bayesian multiple testing procedure and associated error measures that coherently accounts for the dependence structure present in the model. We advocate posterior versions of FDR and FNR as appropriate error rates and show that their asymptotic convergence rates are directly associated with the Kullback–Leibler divergence from the true model. The theories hold regardless of the class of postulated models being misspecified. We illustrate our results in a variable selection problem with autoregressive response variables and compare our procedure with some existing methods through simulation studies. Superior performance of the new procedure compared to the others indicates that proper exploitation of the dependence structure by multiple testing methods is indeed important. Moreover, we obtain encouraging results in a maize dataset, where we select influential marker variables.

     

A Day-to-Day Buying Policy for Commodities — A Study of Purchasing Maize

The majority of the imported raw materials used by European industry have to be purchased in commodity markets where prices fluctuate over time. The overall purchasing decision contains several component stages. The work described in this paper concentrates on the final stage of this process, the tactical buying policy. A major difficulty lies in the definition of a proper measure of performance, so as to assess the merits of any proposed buying policy. The measures previously suggested by Kingsman and Taylor are discussed, and a new measure, thought to be more appropriate, is put forward. The paper describes a new heuristic buying policy, which is applied to the purchasing of maize. The policy uses Taylor's price-trend forecasting model and leads to purchasing costs which are shown to be significantly lower than the average market prices and better than those obtained from Kingsman's pricebreak policy.     

Selecting an agricultural technology package based on the flexible and interactive tradeoff method

Annals of Operations Research - The aim of this paper is to solve an agricultural technology packages selection problem by considering multiple dimensions which influence a maize producer’s...     

A spatial rainfall simulator for crop production modeling in Southern Africa

This paper describes a methodology for simulating rainfall in dekads across a set of spatial units in areas where long-term meteorological records are available for a small number of sites only. The work forms part of a larger simulation model of the food system in a district of Zimbabwe, which includes a crop production component for yields of maize, small grains and groundnuts. Only a limited number of meteorological stations are available within or surrounding the district that have long time series of rainfall records. Preliminary analysis of rainfall data for these stations suggested that intra-seasonal temporal correlation was negligible, but that rainfall at any given station was correlated with rainfall at neighbouring stations. This spatial correlation structure can be modeled using a multivariate normal distribution consisting of 30 related variables, representing dekadly rainfall in each of the 30 wards. For each ward, log-transformed rainfall for each of the 36 dekads in the year was characterized by a mean and standard deviation, which were interpolated from surrounding meteorological stations. A covariance matrix derived from a distance measure was then used to represent the spatial correlation between wards. Sets of random numbers were then drawn from this distribution to simulate rainfall across the wards in any given dekad. Cross-validation of estimated rainfall parameters against observed parameters for the one meteorological station within the district suggests that the interpolation process works well. The methodology developed is useful in situations where long-term climatic records are scarce and where rainfall shows pronounced spatial correlation, but negligible temporal correlation.     

Two-Stage Optimization in a Transportation Problem

A study of the economic distribution of maize throughout South Africa is reported. Although the problem of minimizing total transportation costs in such a situation is a classical one, and its solution is well known, there was in this case a high degree of degeneracy in the system and thus the solution was not unique. Also, since a user is required to pay his own transportation costs, the various optimal solutions were not equivalent. A secondary problem thus arose, viz. that of selecting from these optimal solutions the one which would be fairest to all users. A heuristic and a goal programming method for solving this secondary problem are discussed.     

On the natural Fiber (Maize) Composite material

This work is focused on the compressive behavior in the elastic region of a composite material made out of stalk-based maize fiber and unsaturated polyester resin polymer as matrix with methyl ethyl ketone peroxide as a catalyst and Cobalt Octoate as a promoter [1]. Deformation and fracture behavior are investigated by using Extended Finite Element Method (XFEM). XFEM enables the accurate approximation of solutions with jumps, discontinuities or general high gradients across interfaces between the fibers and the matrix [2], [3]. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Markov相依风险模型的等价定理及概率结构

严格定义了Markov相依风险模型.证明了该模型的一个等价定理,使得Markov相依风险模型中的诸过程之间的关系更清晰.获得了Markov相依风险模型的概率结构,构造性地证明了该模型的存在定理.