带导流墙的门槽结构在闸门全开工况下的应用

从空穴特性、流态特征方面出发,分析了带导流墙的门槽结构在闸门全开泄洪情况下改善流态、降低门槽受冲刷和空蚀危险性方面的作用,认为其在深孔泄水道闸门及其他高水头平面闸门中有很好的推广应用价值。     

闸下海漫柔性加糙体消能防冲机理试验

通过室内水工模型试验,量测了采用废旧轮胎加糙后三维流速的分布。结果表明:加糙后近底流速明显降低,但整个断面的平均流速近似相等;随着轮胎排数的增加,水流紊流强度平均值增大,附加切应力增大,流体质点间相互混掺的情况加剧,从而使消能效率得以提高。     

大气湍流图像像素偏差机理分析

对大气湍流导致图像畸变和像素偏差的因素进行了深入分析,对大气湍流状态下激光发射远距离光束的光束漂移均方值进行仿真,分析光束漂移均方值曲线,为后续对图像畸变、像素偏差校正及克服湍流影响提供有效的理论依据。     

Coherent structure formation,phase correlations,and finite-size effects in 2D turbulence

General conditions for the formation of long-lived coherent vortices in decaying and force-driven 2-D turbulence are investigated. It is shown by a series of numerical simulations that the emergence of closed streamlines leading to the trapped trajectories of vorticity is a necessary, but not sufficient condition for this phenomenon, so that these trapped trajectories may be considered only as seed vortices. Numerical experiments which demonstrate the relations between phase correlations, finite-size effects, and the formation of coherent vortices in 2-D decaying turbulence are presented. It is shown that there is a universal dimensionless time for the onset of intermittency in the flow which corresponds to the time of establishment of phase correlations. The stricter conditions for appearance of coherent vortices in forced turbulence in comparison with decaying turbulence are associated with phase mixing introduced by random forcing. The universal features of decaying turbulence are discussed in terms of phase portraits based on inviscid constants of motion and their decay rates.     

部分相干径向偏振拉盖尔-高斯脉冲光束在大气湍流中传输的光谱移动和光谱开关

研究了部分相干径向偏振拉盖尔-高斯(partially coherent radially polarized Laguerre-Gaussian, PCRPLG)脉冲光束在大气湍流中传输时的光谱移动和光谱开关。研究发现,在湍流大气传输时,光束轴上点光谱因受湍流影响产生的双谱峰现象会发生跃变,湍流越强,光谱在跃变后相对谱移变化越稳定,而轴外点光谱在越强的湍流中相对谱移变化范围越小。研究还发现,适当增加脉冲宽度会明显减小大气湍流对光束轴上点和轴外点光谱移动的影响。在不同脉宽下,轴上和轴外点光谱均会出现光谱开关,且轴外点光谱会产生两次光谱跃变的独特现象。在固定的传输距离上,拓扑荷越大,轴上点光谱移动越小,近轴范围内光谱相对谱移的变化范围越小,此外,不同拓扑荷下光谱均会出现谱开关。相干度越大时,光谱的变化越稳定,轴外点光谱的光谱开关发生位置越远。本文的研究结果为多普勒激光雷达的应用提供理 论依据,PCRPLG脉冲光束本身具有较强抗湍流能力,且通过调控光束参数可以减小光束光谱移动。     

Performance of orthogonal frequency division multiplexing based M-ary quadrature amplitude modulation in asymmetrical dual-hop mixed RF-FSO transmission system

This paper investigates the performance of a dual-hop mixed relay system with radio frequency (RF) and free-space optics (FSO) communication under the effect of pointing error (PE) and atmospheric turbulence (AT). This paper considers a system where RF and FSO links are cascaded. The RF link is modeled by Nakagami-m fading, and the FSO link is modeled as gamma–gamma (G-G) fading channel. Both the channel models use orthogonal frequency division multiplexing (OFDM) with M-ary quadrature amplitude modulation (QAM). The expressions for probability density function, cumulative distribution function, signal-to-noise ratio, and ergodic capacity are derived. The moment generating function (MGF) of fading and the bit error rate (BER) of the OFDM-based M-ary QAM scheme is derived in terms of Meijer's G-function. It has been observed that, in fixed gain relay systems, the modulation scheme's BER is dominated by the SNR of the RF link. While in a variable gain relay system, the turbulence conditions of the FSO system affect the SNR and the BER of the modulation method. The feasibility of heterodyne detection and intensity modulation direct detection (IM/DD) is analyzed in terms of outage probability and ergodic capacity. The results can be used to choose the optimal modulation order and relay system for QAM-OFDM-based optical wireless systems.     

Effective identification of dominant fully absorbing sets for Raptor-like LDPC codes

The error-rate floor of low-density parity-check (LDPC) codes is attributed to the trapping sets of their Tanner graphs. Among them, fully absorbing sets dominantly affect the error-rate performance, especially for short blocklengths. Efficient methods to identify the dominant trapping sets of LDPC codes were thoroughly researched as exhaustively searching them is NP-hard. However, the existing methods are ineffective for Raptor-like LDPC codes, which have many types of trapping sets. An effective method to identify dominant fully absorbing sets of Raptor-like LDPC codes is proposed. The search space of the proposed algorithm is optimized into the Tanner subgraphs of the codes to afford time-efficiency and search-effectiveness. For 5G New Radio (NR) base graph (BG) 2 LDPC codes for short blocklengths, the proposed algorithm finds more dominant fully absorbing sets within one seventh of the computation time of the existing search algorithm, and its search-effectiveness is verified using importance sampling. The proposed method is also applied to 5G NR BG1 LDPC code and Advanced Television Systems Committee 3.0 type A LDPC code for large blocklengths.     

Fully distributed consensus for fuzzy multiagent systems with jointly connected topology

This paper investigates the problem of fully distributed consensus for polynomial fuzzy multiagent systems (MASs) under jointly connected topologies. First, a polynomial fuzzy modeling method is presented to characterize the error dynamics that is constructed by one leader and multiple followers. Then, using the relative state information and the agents' dynamics, a distributed adaptive protocol is designed to guarantee that MASs under jointly connected topologies can achieve consensus in a fully distributed fashion. Utilizing the Lyapunov technique, a relaxed sufficient criterion is proposed to ensure consensus for fuzzy MASs under jointly connected topologies. Moreover, the adaptive coupling weights between neighboring agents can converge to certain values. The derived condition is transformed into a sum-of-squares form, which can be solved numerically. We provide an example to illustrate the proposed distributed adaptive consensus technique's validity.     

A parallelized eno procedure for direct numerical simulation of compressible turbulence

In this paper, a finite-difference based ENO (essentially nonoscillatory) procedure has been chosen for the direct numerical simulation (DNS) of compressible turbulence. The implementation of the ENO scheme follows the relatively efficient procedure in Shuet al. (1992), but the latter has been modified in the present paper to admit scalar conservation equations and to run on the iPSC/860 Paragon parallel supercomputer. DNS results with our procedure are in excellent agreement with pseudo-spectral and Padé approximation calculations in two and three dimensions. This is the case for a variety of initial conditions for compressible turbulence. The parallel algorithms presented are simple but quite efficient for DNS, with a speedup that approaches the theoretical value. Some of the attractive features include 1) minimum communication whereby a processor only communicates with two neighbors, 2) almost one hundred percent load balancing, 3) a checker-board approach to solve the Poisson equation reduces communication by a factor of approximately 2, and, 4) obtaining turbulence statistics is based on a global collect approach, which is implemented to ensure that a single number, rather than a large matrix of numbers, is communicated between processors. The ENO code presented in this paper should be quite useful in its own right, while the parallel implementation should allow the simulation of fairly realistic problems.     

极薄煤层综采技术的研究与应用

介绍了我国极薄煤层采煤技术的现状,指出现有的综采设备不适用于极薄煤层开采;介绍了适合极薄煤层综采的新型采煤机、液压支架、刮板运输机的结构、性能特点,提出了极薄煤层综采工艺。实践表明,该新型极薄煤层综采装备与综采工艺有效提高了采煤效率,创造了很好的经济效益,但还需进一步研究爬底式采煤机滚筒可调高技术、如何减少端头开缺口的工作量以及极薄煤层工作面的自动化技术。