基于3次B样条函数的黄河调水调沙排沙量预测

根据2004年6-7月黄河第三次调水调沙试验期间的实测资料,分析了排沙量与时间、排沙量与水流量的预测模型,采用3次B样条函数对数据进行插值预测排沙量。计算结果表明,总排沙量为1.844×108t,调水调沙试验效果显著。     

THE CHARACTERISTICS AND ESTIMATION OF FLOW THROUGH A SINGLE ROUGH-WALLED FRACTURE

The flow through a single fracture is numerically studied by means of the Fluent Software. The results show that the roughness of the fracture significantly affects the hydraulic conductivity in the fracture as compared with the cubic law model widely used to describe the flow between two smooth parallel plates. A new model is proposed in this paper, the non-symmetric sinusoidal fracture model, to simulate the flow in a real fracture. This model involves two sinusoidal-varying walls with different phases to replace the flat planes in the cubic law model. The relationships between the effective hydraulic apertures and the phase retardation for different relative amplitudes and wavelengths are numerically investigated. A simple expression of the effective hydraulic aperture of the fracture is obtained, together with the law of the effective hydraulic aperture against the amplitude, the phase retardation and the wavelength of two sinusoidal-varying walls.     

基于指数平滑法的航材消耗定额预测研究

由于一次、二次和三次指数平滑法对不同消耗规律的航材预测拟合度不同,本文同时采用这三种指数平滑法进行航材消耗定额预测,其平滑系数采用使误差平方和最小的值,最后选择三种方法中误差平方和最小的结果作为航材消耗定额。预测结果表明综合利用三种指数平滑法进行预测要比单一方法预测更加准确,该研究方法具有较高的实用性和推广性。     

改进的二维典型相关分析及其人脸识别应用

针对二维典型相关分析(2DCCA)中类标矩阵维数较大及算法耗时过多的问题,提出一种改进的2DCCA特征提取方法。利用图像的频谱性质定义低维的类标矩阵,从有利于模式分类的角度构造出新的准则函数,采用二维主成分分析对所得特征进一步降维,得到更具分类判别能力的低维特征。在ORL和组合人脸数据库上的实验结果表明,该特征具有较好的分类能力。     

基于遗传退火三次指数平滑的期货预测研究

为更准确地对期货价格进行预测分析,提出了一种对三次指数平滑法的平滑初值和平滑参数值进行自适应选取的预测方法.该方法根据样本预测误差平方和最小来自适应地调整平滑参数与平滑初值,以避免对其进行主观选取,并将此方法应用于期货价格的预测中.实验结果表明,该方法与单独的三次指数平滑法相比,对于期货价格预测的准确率有所提高,可以得到比较有效的预测值.     

Degradation prediction and rolling predictive maintenance policy for multi-sensor systems based on two-dimensional self-attention

Traditional preventive maintenance policy gradually failed to guarantee the security and economy of current mechanical systems. This paper proposed a highly efficient rolling predictive maintenance (RPdM) policy for multi-sensor system, to make maintenance decisions. In this policy, to cope with the uncertainty of remaining useful life (RUL) prediction, the degradation process of the system is first divided into four intervals according to the inspection interval and spare parts lead time. Then, the two-dimensional self-attention (TDSA) method, which extract time dimensional and feature dimensional features by parallel computation, is developed to predict the probabilities of system RUL in the four intervals instead of the point of RUL. In addition, the output probabilities of the TDSA method are utilized to calculate the maintenance cost rate of the current inspection point and future point. The maintenance decision including spare parts ordering time and maintenance time is determined by comparing the maintenance cost rate of each inspection point, and the decision is updated at the next inspection point. To verify the effectiveness of the proposed RPdM policy, the C-MAPSS dataset provided by NASA is employed to implement degradation prediction and maintenance decision. Experiment results show that the cost rate of RPdM policy is lower than preventive maintenance policy, and only 27.7% higher than ideal maintenance policy which is impossible in real engineering. Moreover, the impact of different out-of-stock costs and corrective costs are explored and shows the good robustness of the RPdM policy.     

基于原子范数最小化的二维稀疏阵列波达角估计算法

基于二维稀疏平面阵列的波达角(Direction-of-arrival,DOA)估计问题在第五代移动通信大规模多输入多输出阵列的应用中日益重要。无网格稀疏重构技术促进了DOA估计问题的发展,原子范数理论则使得DOA估计的超分辨率得到进一步的提高。文中研究了多个方向的频谱稀疏信号入射到二维稀疏阵列时的DOA估计问题。为了准确、成对地识别出所有入射信号的仰角和方向角,提出了一种基于多个测量矢量(Multiple Measurement Vectors,MMV)的二维原子范数算法,并用半正定规划进行求解。所提算法将二维DOA估计问题中的压缩感知理论从单个测量矢量拓展到多个测量矢量,从而有效利用MMV的联合稀疏性。数值仿真结果表明,随着MMV矢量的增长,可识别的信源个数增加,稀疏阵列中物理传感器所占比例降低到30%,DOA估计误差也显著降低,并且在信噪比增大时,所提算法能够取得很好的收敛效果。     

基于三次剩余的新Paillier签名方案

针对基于二次剩余Paillier数字签名方案标签设置过程和签名过程比较复杂等问题,提出了一个基于三次剩余的新Paillier数字签名方案。分析结果表明所提出的方案在计算效率上优于已有的签名方案。在大整数难以分解的假设下,提出的签名方案可抵抗存在性伪造以及适应性选择消息攻击。     

There is no EPTAS for two-dimensional knapsack

In the d-dimensional (vector) knapsack problem given is a set of items, each having a d-dimensional size vector and a profit, and a d-dimensional bin. The goal is to select a subset of the items of maximum total profit such that the sum of all vectors is bounded by the bin capacity in each dimension. It is well known that, unless P=NP, there is no fully polynomial-time approximation scheme for d-dimensional knapsack, already for d=2. The best known result is a polynomial-time approximation scheme (PTAS) due to Frieze and Clarke [A.M. Frieze, M. Clarke, Approximation algorithms for the m-dimensional 0-1 knapsack problem: worst-case and probabilistic analyses, European J. Operat. Res. 15 (1) (1984) 100-109] for the case where d?2 is some fixed constant. A fundamental open question is whether the problem admits an efficient PTAS (EPTAS).In this paper we resolve this question by showing that there is no EPTAS for d-dimensional knapsack, already for d=2, unless W[1]=FPT. Furthermore, we show that unless all problems in SNP are solvable in sub-exponential time, there is no approximation scheme for two-dimensional knapsack whose running time is , for any function f. Together, the two results suggest that a significant improvement over the running time of the scheme of Frieze and Clarke is unlikely to exist.     

New explicit two-dimensional higher order filters

In the present work, a new class of explicit two-dimensional filter is proposed that is significantly different from the conventional one-dimensional Padè type filters. Comparison of performance between one- and two-dimensional filters are made in studying propagation problems and actual viscous flow problems. In this preliminary work, the focus is kept solely on developing central filters with its real transfer function. Many applications related to Navier–Stokes equation have been shown to demonstrate that these two-dimensional filters help in numerical stabilization; control aliasing and control over spurious upstream propagating disturbances. Furthermore, its potential for large eddy simulation (LES) is suggested by band-limiting the solution via filters in post-processing mode.