海洋立管系统严重段塞流瞬态数值模拟

针对海底油气混输管线中常见的立管系统,采用OLGA 多相流瞬态模拟软件,对立管系统中出现的严重段塞流进行了数值模拟。根据实际情况,建立基于双流体模型的物理模型,结合海底管道实际工况,设置相应边界条件,分析了不同流量下的流态流型、压力、持液率等参数随时间的变化特性。研究结果表明,在不同流量产生的严重段塞流下,立管系统中流态流型、压力、持液率等特性参数具有明显的周期性变化规律,流量对严重段塞流的形成及其流动参数影响很大。研究结果对实际生产和管路结构优化具有指导意义,可为复杂流动现象的预测和控制提供一种新的手段。     

Automatic extraction of texture-periodicity using superposition of distance matching functions and their forward differences

In this paper, we propose a method of automatic detection of texture-periodicity using superposition of distance matching functions (DMFs) followed by computation of their forward differences. The method has been specifically devised for automatically identifying row and column periodicities and thereby the size of periodic units from textile fabrics belonging to any of the 17 wallpaper groups and is a part of automatic fabric defect detection scheme being developed by us that needs periodicities along row and column directions. Overall row-DMF (or overall column-DMF) is obtained based on superposition of DMF of all rows (or columns) from the input image and its second forward difference is computed to get the overall maximum which is a direct measure of periodicity along row (or column) direction. Results from experiments on various near-regular textures demonstrate the capability of the proposed method for automatic periodicity extraction without the need of human intervention.     

针对视频运动补偿帧率提升篡改的主动混噪取证算法

运动补偿帧率提升(MC-FRUC)是常见的视频时域篡改手段。现有方法依靠被动分析视频统计特征发现MC-FRUC篡改,然而,视频统计特性的非平稳性影响了取证性能的稳定性。该文提出一种主动混噪取证算法,通过预先混入统计特性已知的高斯白噪声,提高MC-FRUC取证的准确度。首先,利用伪随机序列生成高斯白噪声,加入原始视频序列。接着,由小波系数的绝对中位差预测各视频帧中混入高斯噪声的标准差。最后,检测高斯噪声标准差的时域变化周期性,通过硬阈值判决,自动甄别MC-FRUC篡改。实验结果表明,针对不同的MC-FRUC伪造方法,提出算法均表现出良好的取证性能,尤其是当采用去噪、压缩等操作后处理视频后,提出算法仍能确保较高的检测准确度。     

Cluster-based industrial KPIs forecasting considering the periodicity and holiday effect using LSTM network and MSVR

Key performance indicators (KPIs) are key indicators to measure the status and performance of various facilities, time, and resources in the process of production and life. Forecasting industrial KPIs helps in analyzing the future state to make better production and scheduling decisions. However, due to the complexity of industrial production activities, forecasting industrial KPIs becomes an important and challenging task. In this paper, considering the periodicity and holiday effect of data, a cluster-based industrial KPIs forecasting method using long short-term memory (LSTM) network and multi-output support vector regression (MSVR) is proposed. First, based on the knowledge of production and scheduling, the original daily data is divided into workdays, off-days, and holidays, and K-shape clustering divides holidays into multiple sub-series according to the characteristics of distinct holidays. Then, for the new prediction task, the most suitable historical sub-series is selected through a matching strategy combined with date information. Finally, a compatible model is adaptively selected for forecasting according to the type of sub-series. Specifically, LSTM network is employed to forecast the KPIs on workdays and off-days with a large amount of data, and MSVR is adopted to forecast the KPIs on holidays with few samples. To assess the effectiveness of the proposed method, experiments are conducted in two public datasets with several state-of-the-art methods. The results reveal the superiority of the proposed method in industrial KPIs forecasting.     

Two-Dimensional Prefix String Matching and Covering on Square Matrices

Two linear time algorithms are presented. One for determining, for every position in a given square matrix, the longest prefix of a given pattern (also a square matrix) that occurs at that position and one for computing all square covers of a given two-dimensional square matrix. Received December 21, 1995; revised September 12, 1996.     

The periodic Markov modulated batch Bernoulli process and its application to MPEG video traffic

The Markov modulated batch Bernoulli process (MMBBP) is widely used for modeling a superposition of multiple voices and data at multiplexers in asynchronous transfer mode (ATM) networks, because the MMBBP has the time correlation property and its autocorrelation function is exponentially decaying. However, experimental studies on the MPEG (Motion Pictures Expert Group) video traffic show that its autocorrelation function is periodic as well as exponentially decaying. So, the MMBBP is not adequate to describe the MPEG video traffic.

In this paper, we propose a new stochastic process which we call the periodic Markov modulated batch Bernoulli process (P-MMBBP) to describe the MPEG video traffic adequately. We derive the autocorrelation function of the P-MMBBP and show that the autocorrelation functions of the P-MMBBP and the MPEG video traffic are of the same pattern. We also propose a simple way to match parameters of the P-MMBBP from real MPEG video traffic. We consider the P-MMBBP/D/1 queue and derive the queue length distribution analytically. From numerical results, we show that periodicity gives a significant effect on the tail behavior of the queue length distribution. We also compare tail probabilities obtained by using the P-MMBBP with those obtained by using the 2-state MMBBP. Our comparison shows that the use of the 2-state MMBBP underestimates tail probabilities.     

煤矿水压安全阀异形阀腔瞬态空化特性研究

安全阀是煤矿液压支架水压化的关键元件,但由于水介质的汽化压力较高,导致液压元件在节流口处易产生空化。为了深入研究煤矿水压安全阀异形阀腔瞬态空化流场分布,通过Fluent软件,对简化后的安全阀异形阀腔流场分别进行网格和时间步长独立性验证,确定了网格数量与时间步长后对异形阀腔流场进行瞬态分析。通过瞬态模拟仿真结果可知：流场内部存在着一定的周期性空化流动,湍动能条带的前、后端处促进了空化云团的产生、发展和溃灭,空化周期的变化规律和湍动能值的变化趋势相反。速度漩涡和由高速射流区产生的湍动能条带是影响周期性变化的重要因素。     

Growth and Dielectric Properties of BaTiO 3 /SrTiO 3 Artificial Lattice with Asymmetric Stacking Sequence

BaTiO 3 /SrTiO 3 artificial lattices were deposited on (La,Sr)CoO 3 coated MgO(100) single crystal substrate by pulsed laser deposition (PLD). The stacking thickness ratio of consisting BTO and STO layers was varied while one of the both consisting layers was maintained at 2 unit cell layer thickness. The stacking periodicity of BTO/STO artificial lattice was, therefore in the range from asymmetric BTO 2 unit cell /STO 32 unit cell to BTO 32 unit cell /STO 2 unit cell structure with a total thickness of 100 nm. As the stacking thickness of the BTO layer increased with a fixed stacking thickness of the STO layer (i.e., 2 unit cell thickness), the lattice distortion of the STO layer increased due to mechanical constraint from the thick BTO layer while the lattice distortion of the BTO layer was relatively unchanged. The lattice distortion (c/a) of the STO layer reached at 1.10 for the stacking periodicity of BTO 32 unit cell /STO 2 unit cell . The multiplayer structure with variable stacking thickness of the STO layer and fixed stacking thickness of the BTO layer exhibited the large variation in the lattice distortion of the BTO layer. The dielectric constant of the BTO/STO artificial lattice decreased with the stacking thickness ratio of the BTO and STO layers. This was attributed to severe lattice distortion of the STO (or BTO) in the multiplayer structure of variable stacking thickness of the BTO (or STO) layer. The dielectric constant of the BTO/STO artificial lattice reached a maximum i.e., 1230 at a stacking periodicity of BTO 2 unit cell /STO 2 unit cell.     

基于环形缓冲区的实时系统负载平衡技术

对于具有多个确定性事件源的实时系统,分析表明当各事件源具有周期发生特征时,将会导致任务冲突。对此,提出利用“环形缓冲区”技术,通过调整事件源的发生周期达到负载平衡,在所设计的超声检测系统中利用较少的硬件资源满足了多事件并行处理的要求。     

正弦信号抽样序列的周期性与伪调制性

在满足抽样定理条件前提下,当抽样频率处于某个范围内时,正弦信号抽样序列的包络与抽样序列的周期性与原始信号相比产生了很大的变化,抽样序列的包络出现了不应有的调制——伪调制,这种调制干扰了对原始信号包络的分析和提取。文中首先研究了抽样序列的周期性规律,然后从理论上分析了伪调制性产生的原因,推导出了伪调制的普适公式,得到了伪调制的调制规律和调制规律的周期性,最后得出了消除伪调制两个基本的方法。