Weak wide-band signal detection method based on small-scale periodic state of Duffing oscillator

The conventional Duffing oscillator weak signal detection method, which is based on a strong reference signal, has inherent deficiencies. To address these issues, the characteristics of the Duffing oscillator＇s phase trajectory in a small- scale periodic state are analyzed by introducing the theory of stopping oscillation system. Based on this approach, a novel Duffing oscillator weak wide-band signal detection method is proposed. In this novel method, the reference signal is discarded, and the to-be-detected signal is directly used as a driving force. By calculating the cosine function of a phase space angle, a single Duffing oscillator can be used for weak wide-band signal detection instead of an array of uncoupled Duffing oscillators. Simulation results indicate that, compared with the conventional Duffing oscillator detection method, this approach performs better in frequency detection intervals, and reduces the signal-to-noise ratio detection threshold, while improving the real-time performance of the system.

肌肉超声回声联合血浆炎性因子对ICUAW诊断及预后评估的价值研究

目的:探讨重症监护病房(intensive care unit,ICU)获得性肌无力(ICU acquired weakness,ICUAW)患者肌肉超声回声与血浆炎性因子的相关性,以及其对ICUAW的诊断价值和预后的预测价值。方法:选择重庆市急救医疗中心ICU住院患者,分别在第1、3、7天使用床旁超声检测患者肌肉回声,获得的总体肌肉回声评分(global muscle echogenicity score,GEM),测定血清白细胞介素-6(interleukin-6,IL-6)和降钙素原(procalcitonin,PCT)浓度,采用医学研究理事会肌力评分法(medical research council scales,MRC-ss)评估肌肉力量。根据患者入ICU第7天MRC-ss评分将患者分为ICUAW组和非ICUAW组,分析比较2组患者GEM、IL-6、PCT的差异及各指标的相关性。利用受试者工作特征(receiver operator characteristic,ROC)曲线分析以上参数对ICUAW诊断效能,分析GEM、IL-6、PCT对ICUAW患者的预测预后价值。结果:ICUAW组第3天GEM、第7天IL-6浓度、GEM高于非ICUAW组(P<0.05)。GEM与第7天IL-6水平呈正相关(r=0.221),第7天GEM与MRC-ss评分呈负相关(r=-0.581)。ROC曲线分析显示,第7天GEM对ICUAW有诊断预测价值,ROC曲线下面积(area under the curve,AUC)为0.838,使用GEM、IL-6、PCT联合诊断,AUC=0.885(P<0.05)。ICUAW组Barthel指数评分(Barthel index,BI)低于非ICUAW组,ICUAW组中总体肌肉超声回声评分(global muscle echogenicity score,GEM)高的患者BI低于GEM低的患者(P<0.05)。结论:ICU住院患者GEM与IL-6、PCT浓度相关,其对ICUAW具有一定的诊断价值,并能够预测ICUAW患者的预后。

计及锁相环非线性特性的跟网型逆变器暂态稳定性分析

锁相环作为跟网型逆变器实现相位同步的关键环节,由于其本身所固有的非线性特性,在弱电网情况下,传统小信号模型可能存在不能准确预测锁相环暂态稳定性的问题。为保证受扰后锁相环的稳定运行,提出了一种基于非线性数学模型的稳定性分析方法。首先,根据锁相环工作原理,建立其二阶非线性微分方程,通过相平面法对锁相环输出特性进行定性分析,评估不同参数对锁相环暂态特性的影响;然后,基于等面积法则分析锁相环暂态失稳机理,鉴于传统等面积法则可能导致稳定性的误判,采用非线性动力学多尺度法对锁相环受扰后的暂态时域表达式进行求解,明确锁相环暂态稳定边界;最后,通过Matlab仿真和RT⁃LAB半实物平台验证了所得解析解和锁相环暂态稳定域的准确性,为弱电网条件下锁相环控制参数及电路参数选取提供一定参考。

弱天气背景下天津三次局地突发暴雨中尺度特征及触发机制

利用ERA5再分析(0.25°×0.25°)、加密自动气象站、多普勒天气雷达和变分多普勒天气雷达分析系统等高时空分辨率资料,对比分析了2018年7月22日、2019年7月18日、2021年8月23日天津中心城区三次局地突发性暴雨过程的中尺度特征及其触发机制。结果表明:三次局地突发性强降雨均无明显天气尺度系统主导,但环境大气具备较高的对流不稳定能量和较小的对流抑制能量,抬升凝结高度仅0.2~0.4 km,且低层均存在一定的湿层。局地突发性暴雨的发生与城市热岛及海陆下垫面特征差异造成的中小尺度系统有关,暴雨发生前天津中心城区与沿海地区之间的温差和气压差增大,中心城区附近温压场具有明显的非均匀分布特性,中尺度暖低压及其东侧的高温度梯度为局地对流发生提供了有利的中尺度环境条件。此外,暴雨发生前沿海地区均出现了明显的海风加强,城市热岛暖低压辐合与海风风速辐合共同作用使得中尺度辐合强度明显加强,是局地突发性暴雨发生的主要原因,初生的γ中尺度对流单体均位于地面强辐合中心边缘上空。

纤维增强复合材料拉伸强度的weak-link比例预测

为了讨论weak-link比例对强度预测的适用范围,基于纤维增强复合材料的渐进破坏机理,考虑纤维强度的统计特性,采用Monte-Carlo方法对材料在热/机械载荷作用下的拉伸强度分布进行了数值模拟分析。研究结果表明,在形状参数β=10的条件下,如果希望通过weak-link缩放比例对大尺寸材料的强度分布进行预测,则复合材料的临界尺寸应达到25根纤维的规模。小尺寸材料拉伸强度的分散性趋于稳定,即达到临界尺寸,是采用weak-link比例预测大尺寸材料强度分布规律的先决条件。研究方法为进一步发展基于损伤机理分析的复合材料在循环载荷作用下的疲劳寿命预测理论奠定了基础。

结构空间约束对钢筋混凝土梁受弯性能的影响

为探究结构空间约束对框架结构屈服机制的影响,借助多尺度数值方法,建立了具有不同边界条件的钢筋混凝土(reinforced concrete,RC)梁模型.定量分析了端部约束及添加现浇楼板对RC框架梁刚度和受弯承载力,即试件所能承受的最大弯矩的影响,揭示了端部约束及现浇楼板对RC梁弯曲机制的影响机理.此外,对各国规范计算的受弯承载力进行对比分析.结果表明,结构空间约束会影响RC框架梁的破坏形态.固支梁的刚度和受弯承载力显著高于简支梁,固支梁的受弯承载力和刚度最高可达简支梁的3.06倍和4.10倍.添加现浇楼板可显著提高梁的受弯承载力与刚度.各国规范可准确地计算简支梁的受弯承载力.然而,计算的固支梁及楼盖梁的受弯承载力极其保守,剪跨比为5.0的固支加板梁的受弯承载力模拟值分别是中国、美国和加拿大规范值的6.25倍、6.76倍和6.06倍.

暂态电压稳定薄弱区域辨识的Louvain分区算法

针对大电网暂态电压稳定整体研究过于复杂的问题,提出一种暂态电压稳定薄弱区域辨识方法。首先,引入节点间电气距离计算模块度,运用Louvain算法对电网进行分区;然后,考虑线路负载率与线路开断对节点电压的影响,利用熵值法构建关键线路辨识指标筛选出关键线路,将关键线路三相短路故障作为预想故障集;最后,利用基于暂态电压稳定判据构建的节点暂态电压稳定评价指标,评价出暂态电压薄弱的区域。通过广东电网仿真结果验证所提方法的有效性。

Insights into Convective-scale Predictability in East China: Error Growth Dynamics and Associated Impact on Precipitation of Warm-Season Convective Events

This study investigated the regime-dependent predictability using convective-scale ensemble forecasts initialized with different initial condition perturbations in the Yangtze and Huai River basin(YHRB)of East China.The scale-dependent error growth(ensemble variability)and associated impact on precipitation forecasts(precipitation uncertainties)were quantitatively explored for 13 warm-season convective events that were categorized in terms of strong forcing and weak forcing.The forecast error growth in the strong-forcing regime shows a stepwise increase with increasing spatial scale,while the error growth shows a larger temporal variability with an afternoon peak appearing at smaller scales under weak forcing.This leads to the dissimilarity of precipitation uncertainty and shows a strong correlation between error growth and precipitation across spatial scales.The lateral boundary condition errors exert a quasi-linear increase on error growth with time at the larger scale,suggesting that the large-scale flow could govern the magnitude of error growth and associated precipitation uncertainties,especially for the strong-forcing regime.Further comparisons between scale-based initial error sensitivity experiments show evident scale interaction including upscale transfer of small-scale errors and downscale cascade of larger-scale errors.Specifically,small-scale errors are found to be more sensitive in the weak-forcing regime than those under strong forcing.Meanwhile,larger-scale initial errors are responsible for the error growth after 4 h and produce the precipitation uncertainties at the meso-β-scale.Consequently,these results can be used to explain underdispersion issues in convective-scale ensemble forecasts and provide feedback for ensemble design over the YHRB.

Comparing the reinforcement capacity of welded steel mesh and a thin spray-on liner using large scale laboratory tests

Steel mesh is used as a passive skin confinement medium to supplement the active support provided by rock bolts for roof and rib control in underground coal mines. Thin spray-on liners(TSL) are believed to have the potential to take the place of steel mesh as the skin confinement medium in underground mines.To confirm this belief, large scale laboratory experiments were conducted to compare the behaviour of welded steel mesh and a TSL, when used in conjunction with rock bolts, in reinforcing strata with weak bedding planes and strata prone to guttering, two common rock conditions which exist in coal mines. It was found that while the peak load taken by the simulated rock mass with weak bedding planes acting as the control sample(no skin confinement) was 2494 kN, the corresponding value of the sample with 5 mm thick TSL reinforcement reached 2856 kN. The peak load of the steel mesh reinforced sample was only2321 kN, but this was attributed to the fact that one of the rock bolts broke during the test. The TSL reinforced sample had a similar post-yield behaviour as the steel mesh reinforced one. The results of the large scale guttering test indicated that a TSL is better than steel mesh in restricting rock movement and thus inhibiting the formation of gutters in the roof.

Renormalization Group Analysis of Weakly Rotating Turbulent Flows

Dynamic renormalization group(RNG)analysis is applied to the investigation of the behavior of the infrared limits of weakly rotating turbulence.For turbulent flow subject to weak rotation,the anisotropic part in the renormalized propagation is considered to be a perturbation of the isotropic part.Then,with a low-order approximation,the coarsening procedure of RNG transformation is performed.After implementing the coarsening and rescaling procedures,the RNG analysis suggests that the spherically averaged energy spectrum has the scaling behavior E(k)∝k−11/5 for weakly rotating turbulence.It is also shown that the Coriolis force will disturb the stability of the Kolmogorov−5/3 energy spectrum and will change the scaling behavior even in the case of weak rotation.

ON THE EVOLUTION OF LARGE SCALE STRUCTURES IN THREE-DIMENSIONAL MIXING LAYERS

In this paper, several mathematical models for the large scale structures in some special kinds of mixing layers, which might be practically useful for enhancing the mixing, are proposed. First, the linear growth rate of the large scale structures in the mixing layers was calculated. Then, using the much improved weakly non-linear theory, combined with the energy method, the non-linear evolution of large scale structures in two special mixing layer configurations is calculated. One of the mixing lavers has equal magnitudes of the upstream velocity vectors, while the angles between the velocity vectors and the trailing edge were pi /2 - phi and pi /2 + phi, respectively. The other mixing layer was generated by a splitter-plate with a 45-degree-sweep trailing edge.

Asymptotic analysis on weakly forced vibration of axially moving viscoelastic beam constituted by standard linear solid model

The weakly forced vibration of an axially moving viscoelastic beam is inves- tigated. The viscoelastic material of the beam is constituted by the standard linear solid model with the material time derivative involved. The nonlinear equations governing the transverse vibration are derived from the dynamical, constitutive, and geometrical relations. The method of multiple scales is used to determine the steady-state response. The modulation equation is derived from the solvability condition of eliminating secular terms. Closed-form expressions of the amplitude and existence condition of nontrivial steady-state response are derived from the modulation equation. The stability of non- trivial steady-state response is examined via the Routh-Hurwitz criterion.

弱连接VSC在“外环-锁相环”时间尺度下的一类小扰动稳定性提升方法及等效性分析

大量理论研究发现电压源换流器(voltagesource converter,VSC)接入薄弱电网后,易发生由“外环–锁相环”交互所主导的小扰动失稳现象,且在多个实际工程中也发现此类稳定问题。为此,国内外学者提出了大量改进控制方法,其基本原理为在有功外环、无功外环与锁相环三者之间施加附加补偿控制,以提升弱连接VSC(weak-grid connected VSC,WG-VSC)并网稳定性。该文将这些方法归纳为WG-VSC在“外环–锁相环”时间尺度下的一类小扰动稳定性提升方法。试想,这些策略都能提升稳定性,那么它们是否存在某种等效性?此外,基于等效性原理,还能否推导出其他的改进控制措施?该文研究动机是期望从方法论的视角回答上述问题,进而为解决此类稳定性问题提供基本依据。该文创新工作是基于一种能够清晰展现“外环–锁相环”交互关系的等效锁相环模型,首次揭示了这一类改进控制方法在提升WG-VSC“外环–锁相环”时间尺度小扰动稳定性方面具有等效性。此外,通过观察分析现有补偿控制策略在拓扑结构和作用机理上的特点,该文还预测了其余多种新型小扰动稳定性提升控制策略,并基于等效锁相环(phaselockedloop,PLL)模型分析得出,通过特定的控制器设计方法,可使得此类补偿控制策略在WG-VSC系统小扰动稳定性提升方面具有等效性。最后,基于PSCAD/EMTDC的详细电磁暂态仿真模型验证了该文理论分析的准确性。

弱天气系统强迫下一次突发性大暴雨成因分析

2021年7月18日西安东北部、渭南南部等地出现突发性暴雨、大暴雨及局地特大暴雨天气,全球模式和多个中尺度模式漏报,为了深入认识此类暴雨天气发生发展机制,提高其预报准确率,本文利用高空、地面观测、ERA5再分析、FY-2G云顶亮温TBB、临潼激光雷达风矢量、泾河雷达及微波辐射计等数据对此次大暴雨发生的环流形势、环境场条件、中尺度对流系统发展演变及触发机制进行分析。结果表明:(1)此次大暴雨天气是在弱天气系统强迫下发生的,大暴雨区位于500 hPa大陆高压边缘,850 hPa和700 hPa无切变线和暖平流、无较大风速输送水汽,地面无冷锋或暖锋。(2)大暴雨发生前环境场有着有利的抬升、充沛的水汽和不稳定能量等条件。地面弱降水造成低的大气抬升凝结高度和云底高度,有利于中尺度对流系统的生成及提高降水效率;低层偏东风风速增大并维持较大风速为大暴雨区输送充沛水汽及能量,大气有一定的对流有效位能,中低层弱上升运动使得暴雨区有着较厚的湿层和较大的整层可降水量。(3)突发性大暴雨由准静止孤立的中-β尺度对流系统造成,中-β尺度对流系统由多个中-γ或中-β尺度对流单体组成。对流单体最先在骊山附近生成,结构松散,组织性差,单体反射率因子有较低的质心及高效率暖云降水特征。(4)地面弱冷空气造成的地面辐合线与骊山地形抬升、灞河谷地狭管效应共同作用触发对流单体,产生强降水,形成地面冷池。冷池出流形成地面辐合线主要在泾河东侧高温、高湿、高能区触发多个新的对流单体。大暴雨区中-β尺度对流系统后向传播,其中多个中-γ或中-β尺度尺度对流单体自东北向西南方向缓慢移动,形成“列车效应”,经过泾河造成大暴雨天气。(5)对于弱天气系统强迫下的暴雨预报,需要增强对其形成机制的认识及新型观测资料的使用,密切关注前期弱降水对近地面增湿和抬升凝结高度的影响,增大的低层风对暴雨区水汽和不稳定能量的输送,地面弱冷空气及地形的触发作用,结合多家中尺度数值模式预报的极值,综合考虑突发性大暴雨的可能性。

CS自适应随机共振与ITD相结合的轴承弱故障诊断

为了解决轴承早期弱故障诊断的问题,提出将固有时间尺度分解(intrinsic time-scale decomposition,ITD)与布谷鸟自适应随机共振(cuckoo adaptive stochastic resonance,CASR)相结合的方法进行滚动轴承早期弱故障特征频率提取。针对采集到的滚动轴承振动信号复杂且信噪比(SNR)低、故障特征难以提取的问题,结合ITD能抑制端点效应、运算复杂度低等优势,该方法将信噪比作为随机共振的目标函数,通过仿真信号分析及实例验证,将ITD作为CASR处理信号的前处理,使滚动轴承故障信号显著加强,信噪比提高2.17倍,故障特征得到有效提取。

浙江夏季弱天气尺度强迫背景下午后局地热对流特征分析

利用常规高空观测资料、浙江多普勒雷达产品、ERA5逐小时再分析资料(0.25°×0.25°),统计分析了2015—2021年浙江夏季(6—8月)弱天气尺度强迫背景下午后局地热对流(根据移动速度分为移动型和少动型两类)的时空分布特征、生命周期特征、环境参数特征等。(1)两类热对流触发频次相当,年际变化均较大,但年、月、日变化趋势基本一致,午后出现少动型局地热对流的可能性更大,而傍晚出现移动型局地热对流的可能性更大。(2)局地热对流的触发与地形密切相关,对流高频区位于浙东沿海、浙西北、浙西南山区,浙中北平原和盆地均为低频区,热对流触发频次均随高度增加而减少,多触发于山脉及其附近的中低海拔处,中高海拔地区更容易触发少动型局地热对流。(3)两类对流均在弱垂直风切变环境下即可触发,移动型单体更容易得到发展。

基于小波的弱光照图像增强算法仿真

针对通过人工参数调整图像,容易出现细节纹理缺失或失真等问题,提出一种基于双尺度图像分解的弱光照图像增强算法。将小波变换函数与软阈值结合,通过小波包频带变换明确图像频带值,分解复数小波包,提取去噪处理后原始弱光照图像中的像素点,计算目标点邻域范围,并实施双尺度矩阵分割。利用同态滤波算法分析图像中像素点对弱光照的透射特性,在待处理图像上覆盖“雾”形成伪雾,分析去雾后图像透射点的分布情况,自动调整对应增强阈值。分析透射率与亮度分量之间的正向关联,得出图像透射率与亮度分量的变化规律,完成图像增强分析。仿真结果证明,所提算法鲁棒性强,在满足弱光照增强效果的同时还能保证图像的细节,增强后的图像细节更丰富,视觉观感更好。

随钻远探测电磁波测井技术问题分析与探讨

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