Effect of temporal aggregation on multiple time series in the frequency domain

The effect of temporal aggregation on bivariate spectral measures is investigated. First, the low‐frequency regression coefficient turns out to be invariant under aggregation irrespective of differencing, with the exception of when the aggregation of flow and stock variables is combined. Second, the long‐run squared coherency is invariant with respect to aggregation irrespective of differencing. Third, for frequencies different from zero, limiting results for a growing aggregation level m are obtained equal to those at frequency 0 of the underlying basic series. Hence, all frequency domain information is distorted by aggregation apart from the long‐run one. This also holds true for the phase angle that always approaches zero with growing aggregation level m. The sole exception to these findings is the case of the skip sampling stationary series. Moreover, for finite aggregation level, one may exactly quantify the aggregational effect on each cycle of interest. Numerical examples illustrate our results.     

电力系统暂态信号频谱特征的仿真研究

功率谱估计结果可作为暂态保护判据计算和校核依据。采用功率谱估计方法对电力系统故障暂态信号的频域特征进行了分析。仿真结果表明，功率谱估计结果与故障条件密切相关；故障条件对低频端谱估计的幅值影响很小，对高频端谱估计的幅值影响很大。     

液体管道高频水力瞬变过程的数值模拟

目前在液体管道高频水力瞬变分析中,人们通常采用经典的拟稳态摩阻模型进行分析.但这种方法针对管壁切应力具有拟稳态特性的缓慢瞬变的分析是可行的,而对高频瞬变流动过程而言却不能准确预测水击压力波具体的衰减过程以及出现的波形畸变现象.介绍了一种新的考虑瞬时加速度对高频水力瞬变过程影响的非恒定摩阻模型,并结合特征线法给出了其数值解法,最后通过实例验证了该模型能比经典的拟恒定摩阻模型更为准确地模拟液体管道中高频瞬变流压力波的衰减和波形畸变.该模型对计算机的要求和计算耗时与经典的拟稳态摩阻模型相差不大,是一种具有良好工程应用潜力的液体管道高频瞬变分析数学模型.     

转换波地震资料中面波的压制

转换波资料的信噪比较低，有效信号往往被面波干扰淹没，因此需要对面波进行压制，但是将面波作为线性干扰的压制方法很难得到好的效果。面波的频散和衰减以及近地表速度存在差异等特性，使得面波干扰在能量分布、道间时差和子波形态等方面都不同于数学意义上对线性同相轴的定义，更多地表现为“视”线性的特征。通过对面波能量和道间时差调整。使面波干扰更接近真正意义上的线性同相轴，可以增强利用，f-k滤波压制面波的能力，在一定程度上消除面波干扰对转换波处理的影响。利用该方法对某煤田和某油田的实际转换波资料进行了处理，面波得到了有效压制。转换波从面波的干扰背景下被很好地恢复出来。     

弱约束管道系统水锤研究与进展

充液管道中瞬变流的研究有着悠久的历史，积累了极为丰富的文献和资料。人们对系统不稳定流的认识也随着科学技术的进步不断发展开拓，内容及航空航天，石油化工，机械传动，水利电力等２０多个研究方向。     

道间距对偏移结果影响的讨论

对偏移算法进行了简要回顾，提出对偏移结果产生影响的因素除偏移算法、速度场的准确程度和地震资料的品质之外，还应包括道间距及采样率等。指出道间距过大对偏移结果的影响主要是导致空间假频现象的出现，偏移速度场难以准确建立，偏移横向误差大及偏移信息量少，这些影响与具体偏移算法无关。应用理论模型及实际资料对上述结论进行了验证。根据验证结果，建议在野外施工设计过程中，应根据勘探目的不同、地下构造的复杂程度及勘探精度，并考虑道间距对偏移结果的影响，合理地设计道间距。     

LATTICE BOLTZMANN SCHEME TO SIMULATE TWO-DIMENSIONAL FLUID TRANSIENTS

ＮＯＭＥＮＣＬＡＴＵＲＥｐα ———ｐｒｅｓｓｕｒｅｄｉｓｔｒｉｂｕｔｉｏｎｆｕｎｃｔｉｏｎｐ(0 )α ———ｅｑｕｉｌｉｂｒｉｕｍｄｉｓｔｒｉｂｕｔｉｏｎｆｕｎｃｔｉｏｎｅα———ｌｏｃａｌｐａｒｔｉｃｌｅｓｔｒｅａｍｖｅｌｏｃｉｔｙｒ———ｌｏｃａｔｉｏｎｏｆｃｏｍｐｕｔａｔｉｏｎａｌｇｒｉｄｎｏｄｅδｔ ———ｔｉｍｅｉｎｃｒｅｍｅｎｔτ———ｔｈｅＢＧＫｒｅｌａｘａｔｉｏｎｐａｒａｍｅｔｅｒα———ｉｎｄｅｘｏｆｐａｒｔｉｃｌｅｓｔｒｅａｍｄｉｒｅｃｔｉｏｎｂ———ｔｈｅｎｕｍｂｅｒｏｆｐａ…     

Alloyed Branch History: Combining Global and Local Branch History for Robust Performance

This paper introduces alloyed prediction, a new hardware-based two-level branch predictor organization that combines global and local history in the same structure, combining the advantages of current two-level predictors with those of hybrid predictors. The alloyed organization is motivated by measurements showing that wrong-history mispredictions are even more important than conflict-induced mispredictions. Wrong-history mispredictions arise because current two-level, history-based predictors provide only global or only local history. The contribution of wrong history to the overall misprediction rate is substantial because most programs have some branches that require global history and others that require local history. This paper explores several ways to implement alloyed prediction, including the previously proposed bi-mode organization. Simulations show that mshare is the best alloyed organization among those we examine, and that mshare gives reliably good prediction compared to bimodal (two-bit), two-level, and hybrid predictors. The robust performance of alloying across a range of predictor sizes stems from its ability to attack wrong-history mispredictions at even very small sizes without subdividing the branch prediction hardware into smaller and less effective components.     

Solution for the Closed-Loop Problem in Pressurized Multipipe Systems

The fundamental background of the solution for the steady-state flow in pressurized water closed-loop pipe systems, without any reservoirs in-between, is presented in this paper. The use of the steady-state mass balance and energy equations to calculate discharges and heads in this type of hydraulic system leads to an undetermined problem. The way to solve this indeterminacy is to consider an additional continuity equation associated with the difference between initial and final conditions, taking into account fluid compressibility and pipe-wall deformability. A complete formulation is derived considering pressure and temperature changes in the hydraulic system. Simplified formulae are presented for isothermal flows in simple systems and multiple closed-loops with pipes in series and in parallel. This problem can also be solved by a pseudotransient analysis technique applied to steady-state conditions. Proposed solutions for this problem are applied to steady-state flows and tested for different system configurations.