AN IMPROVED PROCEDURE FOR THE DETERMINATION OF HOT SPOT STRESSES IN TUBULAR JOINTS

Abstract— A conventional finite element method may show a weakness when determining the hot spot stress distributions in the brace/chord intersection region of offshore tubular joints. This is because the chosen element displacement functions do not implicitly satisfy the conditions which prevail on the free surfaces. A procedure has been proposed to modify the conventional finite element method so as to allow the hot spot stresses, which occur at the free boundary of the weld toe of tubular joints, to be determined with improved accuracy. The results obtained by this modified method are compared with both an experimental and a traditional finite element solution. The comparison shows that the modified solution is in better agreement with the experimental data as compared with the traditional solution.     

经济预测模型中参数估计的一种方法

简单介绍了经济预测中最小一乘法和最小二乘法的含义,并指出了它们的不足。为了改善预测效果,采用加权最小一乘法来进行参数估计。在该方法中采用了一种新的赋权方法,并把加权最小一乘法问题转化为线性规划问题去求解,最后通过一个应用实例来说明此种方法的有效性和实用性。     

Optimal choice of modes for aggregation

In this note a method of system simplification by aggregation is proposed. This method is based on the hypothesis of non-observability of conserved modes on the output error. It leads to a simple combinatorial algorithm of optimization.     

ASYMPTOTIC EXPANSIONS FOR THE DISTRIBUTION OF AN ESTIMATOR IN THE FIRST-ORDER AUTOREGRESSIVE PROCESS

Abstract. In this paper, two asymptotic expansions for the distribution for an estimator of the parameter in a first-order autoregressive process are derived, according to two situations. Some well known estimators are special cases of the estimator discussed here. The series expansions are carried to terms of order T ^-1.     

On overtaking optimal tracking for linear systems

Optimal tracking problems involving a time-varying linear plant and infinite-horizon quadratic performance index are considered. In general, such problems yield an unbounded performance index for every control and thus must be interpreted as so-called overtaking optimal control problems. A completing-the-square argument is used to derive the overtaking optimal control for a general problem formulation, and various properties are discussed.     

超声提取香草兰豆荚中香兰素的工艺研究

香草兰(Vanilla spp.)豆荚中含有香兰素等香料成分,是当今世界上最为风行的香味物质。文章研究超声提取香草兰豆荚中香兰素等香料成分的萃取工艺,以香兰素质量为检测指标,使用均匀设计-偏最小二乘法回归分析优化萃取工艺的温度、时间、料液比和浓度四个因子,确定最佳提取工艺条件为:时间为20 min,温度为60℃,料液比1∶10,溶剂乙醇的浓度为45%。此时萃取物中香兰素的理论产量为212.92 mg。并对该技术应用于香草兰中香兰素提取产业化的前景和可行性进行分析探讨。     

PHBV/PLA纤维和其他纤维混合试样的定量分析方法研究

采用化学分析和红外光谱分析相结合的方法研究了生物基聚3-羟基丁酸-戊酸酯/聚乳酸(PHBV/PLA)纤维和其他纤维(涤纶、棉纤维、羊毛、锦纶6)混合的试样(简称多组分混合纤维试样)的定量分析方法。结果表明:首先在常温条件下,采用二氯甲烷溶解多组分混合纤维试样中的PHBV/PLA纤维,得到PHBV/PLA纤维的含量和其他纤维的含量,该方法的绝对误差为-0.5%~0.5%,95%置信界限为(-0.2%,0.2%);然后选定合适溶剂对多组分纤维混合试样中的其他纤维进行溶解得到PHBV/PLA纤维,对PHBV/PLA纤维中的PHBV和PLA的含量采用红外光谱法进行定量分析,将1707.2~1731.8 cm^-1的峰面积和1731.8~2038.8 cm^-1峰面积之比作为PHBV和PLA组分的对应质量比,以此来计算试样中PHBV和PLA的含量,该方法采用经典最小二乘法建立模型,7个校准点拟合的回归方程其线性相关系数为0.9978,校正标准偏差为0.442;10个验证点拟合的回归方程的线性相关系数为0.9943,预测标准偏差为0.617%。     

Frequency domain parameter estimation of two common frequency single-tone signals

This paper describes a new algorithm for parameter estimation of two channel single-tone signals. The algorithm works in the frequency domain and uses least squares optimization to estimate the amplitudes, phases and common frequency of the signals. The estimation process is based on the weighted least squares best-fitting of the theoretical spectrums of single-tone signals on the measured spectrums. The performance of the algorithm is shown on simulated and measured signals in different operating situations.     

基于直线拟合的高温板材边缘检测方法

提出了一种基于最小二乘原理的垂直拟合边缘检测方法。该方法针对高温板材热膨胀率测量过程中异常边缘点随机出现的特点,利用最小二乘法同时拟合两个相互垂直方向上的边缘直线,并进行多次重复拟合使边缘直线逐渐接近真实值。实验表明,该方法能在异常点存在的情况下准确、快速地拟合出高温钢板图像的边缘直线。     

基于图像处理的微小孔光学特征识别技术研究

对微小孔的成型结构特点和边缘光学特征进行了研究,提出了一种有效检测微小孔质量的方法。通过中值滤波、灰度阈值变化等图像处理技术,准确地提取了微小孔的边缘,并将最小二乘圆拟合算法、新圆度判定算法和锥度检测算法综合应用于微小孔的几何结构识别过程中。实验结果证明,本方法具有检测结果准确、检测精度高等特点,能够满足微小孔质量检测的要求。