双拱初始缺陷海底管线水平向整体屈曲数值模拟分析   总被引：1，自引：0，他引：1  

刘润  刘文彬  洪兆徽  闫澍旺 《海洋科学》2015,39(8):86-94

为了研究具有双拱反对称初始缺陷海底管线的整体屈曲特性,采用模态分析法将最可能出现的缺陷形态引入数值分析模型中。针对管线在高温高压作用下发生整体屈曲的动态变形特征,运用显式动力数值模拟方法研究了管线整体屈曲过程中水平向变形与轴向变形随温度和内压的变化规律,建立了在整体屈曲过程中屈曲管段与滑动管段轴力的变化过程与初始缺陷形态的关系。将数值模拟结果同经典解析解和室内模型实验结果进行对比,验证了本方法的可靠性。工程算例的分析结果表明,管线整体屈曲的发生是一个由低阶向高阶发展的过程,具有双拱缺陷的管线首先发生二阶模态的整体屈曲,而后过渡到四阶模态;管线整体屈曲的变形包括屈曲段的水平向变形和滑动管段的轴向缩进,其中水平变形释放了管壁内的轴力,轴力的释放量随初始缺陷尖锐程度的降低而增大;轴向缩进变形由于受到地基土的摩阻力使滑动管段内的轴力发生累积,轴力的累积量随初始缺陷的尖锐程度的降低而增加。以上研究成果对指导实际工程具有现实意义。  相似文献   

一种CORS站高程序列噪声识别算法     

吉长东  吕广涵  张恒璟  崔东东 《测绘科学》2021,46(3):8-16

针对能量密度谱判断噪声与信号主导模态分界点性能不稳定的问题,该文提出基于夹角余弦的分界点判断方法。该方法首先利用EEMD对CORS站高程数据进行分解,其次计算原始信号与各阶模态分量的夹角余弦值,最后根据夹角余弦值的首次逆向转折位置判定噪声主导模态和信号主导模态的分界点。以4个CORS基准站近20年原始高程时间序列信号为研究对象,对噪声与信号模态分量分界点进行判定,实验结果表明采用基于夹角余弦的判定方法可以一次判断出噪声和信号模态分量的分界点。该方法应用到CORS站高程信号与噪声序列的识别中性能更加稳定。  相似文献   

中高纬度大气低频模态研究进展   总被引：1，自引：0，他引：1  

张曼  许小峰  闵锦忠  高庆九 《气象科学》2015,35(6):799-806

大气低频模态是导致中高纬地区季节及气候变化的主要因素,加强低频模态动力机制的认识对于提高短期气候预测水平具有十分重要的科研意义和应用价值。由于中高纬大气低频环流本身的复杂性,关于其动力机制的研究仍然是大气动力学中重点难点问题。本文简单回顾了激发维持低频模态的前两种机制,即:外源强迫、气流的纬向非均匀性对大气低频模态的影响。从观测事实和模式结果出发,着重介绍了瞬变波与基本气流相互作用激发维持低频模态的第三种机制,且详细阐述了线性假设条件下,瞬变波与基本气流相互作用的动力机制。本文最后针对瞬变波与基本气流相互作用研究中一些尚未解决的问题进行了讨论。  相似文献   

南半球中纬度偶极模态与亚洲—非洲夏季降水   总被引：1，自引：1，他引：0  

明静  孙建奇  李国平  裴军林 《大气科学》2015,39(2):413-421

南半球大气环流第一模态为南极涛动, 它表现出较好的纬向对称结构。本工作利用经验正交分解方法研究发现, 在南半球的东半球, 夏季(6~9月)大气环流还存在一个重要的模态。不同于南极涛动, 该模态表现为显著的纬向偶极分布, 本文定义其为偶极模态。在海平面气压场上, 该模态的解释方差可以达到20%以上, 表现出显著的年际变化特征。进一步的研究发现, 该偶极模态与亚非夏季降水存在密切联系, 尤其与我国华南、南亚以及热带非洲东部地区的夏季降水存在显著的正相关关系。机制分析表明, 南半球这一偶极模态的异常会影响东半球越赤道气流的变化, 从而造成向上述三个地区的水汽输送的多寡, 并最终导致这三个地区夏季降水发生变化。本工作揭示的偶极模态变化独立于南极涛动, 研究结果不但可以深化对南半球环流系统变化特征及影响的认识, 而且对亚非夏季降水的变化特征和机制研究也具有重要意义。  相似文献   

The Asymmetry of Subsurface Temperature Anomalies Associated with ENSO in the Equatorial Western Pacific          下载免费PDF全文

HUA Li-Juan  YU Yong-Qiang 《大气和海洋科学快报》2015,8(1):23-28

The phenomenon of ENSO asymmetry has been recognized for many years, but most studies have focused on the asymmetry of surface temperature anomalies in the equatorial eastern Pacific. Here, the authors investigate the temperature asymmetry associated with ENSO in the subsurface of the western Pacific through analysis of observations and numerical experiments with an ocean GCM. Both the observation and simulation exhibit significant ENSO asymmetry, characterized by negative temperature skewness in the equatorial western Pacific and positive skewness in the eastern Pacific. Heat budget analysis reveals that nonlinear dynamical heating results in the positive temperature asymmetry in the equatorial eastern Pacific, but tends to weaken the negative temperature asymmetry in the equatorial western Pacific. The climatological meridional current transports the temperature anomalies and corresponding negative asymmetry from the off-equator region to the equator in the subsurface of the western Pacific. Through a sensitivity experiment with reversed wind stress forcing, the authors suggest that the skewness of the wind stress anomalies does not contribute to the negative temperature asymmetry in the western Pacific in the first-order approximation, while the internal nonlinear dynamics does play a key role. The study suggests that, as a result of nonlinear processes, the oceanic responses to anomalous wind stress are nonlinear and asymmetric in the tropical Pacific.  相似文献   

Influence of positive and negative Indian Ocean Dipoles on ENSO via the Indonesian Throughflow: Results from sensitivity experiments     

ZHOU Qian  DUAN Wansuo  MU Mu  FENG Rong 《大气科学进展》2015,32(6):783-793

The role of the Indonesian Throughflow(ITF) in the influence of the Indian Ocean Dipole(IOD) on ENSO is investigated using version 2 of the Parallel Ocean Program(POP2) ocean general circulation model. We demonstrate the results through sensitivity experiments on both positive and negative IOD events from observations and coupled general circulation model simulations. By shutting down the atmospheric bridge while maintaining the tropical oceanic channel, the IOD forcing is shown to influence the ENSO event in the following year, and the role of the ITF is emphasized. During positive IOD events,negative sea surface height anomalies(SSHAs) occur in the eastern Indian Ocean, indicating the existence of upwelling.These upwelling anomalies pass through the Indonesian seas and enter the western tropical Pacific, resulting in cold anomalies there. These cold temperature anomalies further propagate to the eastern equatorial Pacific, and ultimately induce a La Nia-like mode in the following year. In contrast, during negative IOD events, positive SSHAs are established in the eastern Indian Ocean, leading to downwelling anomalies that can also propagate into the subsurface of the western Pacific Ocean and travel further eastward. These downwelling anomalies induce negative ITF transport anomalies, and an El Nio-like mode in the tropical eastern Pacific Ocean that persists into the following year. The effects of negative and positive IOD events on ENSO via the ITF are symmetric. Finally, we also estimate the contribution of IOD forcing in explaining the Pacific variability associated with ENSO via ITF.  相似文献   

经验模态分解方法在树木年轮宽度序列标准化中的应用     

张永 《沙漠与绿洲气象(新疆气象)》2015,9(5):9-15

高分辨率的树木年轮是记录历史时期气候变化的良好生物载体,在古气候研究中被广泛应用。但年轮宽度与气候因子之间有着复杂的联系,这种关系受气候因子之间的相互制衡和因物种而异的树木生长节律的共同影响。在利用树木年轮开展历史时期气候变化的研究中,剔除树木年轮与年龄相关的生长趋势是准确获取气候信号的先决条件。然而,传统的和相对改进的一些树轮标准化方法在拟合并剔除树龄相关的趋势及非气候干扰信息方面仍存在一些问题。本文利用经验模态分解(EMD)方法进行树轮资料的标准化方法研究, 对已获得的树轮生长序列所记录的信息进行分解,得到一系列不同物理意义的本征模态分量,结合多样本信息的对比及生物学特性,深入解读各分量表征的气候变化、环境干扰及缓慢生长趋势项等不同物理意义,进而剔除非气候信息,得到可以准确反映气候变化的代用序列,并将该方法与目前广泛采用的标准化方法进行对比,分析不同方法的利弊所在,为进一步改进树轮标准化方法提供新思路。  相似文献   

IMPACT OF ENSO ON THE PRECIPITATION OVER CHINA IN WINTER HALF-YEARS     

李天然  张人禾  温敏 《热带气象学报(英文版)》2015,21(2):161-170

In this paper, the impact of ENSO on the precipitation over China in the winter half-year is investigated diagnostically. The results show that positive precipitation anomalies with statistical significance appear over southern China in El Nio episodes, which are caused by the enhanced warm and humid southwesterlies along the East Asian coast in the lower troposphere. The enhanced southwesterlies transport more water vapor to southern China, and the convergence of water vapor over southern China increases the precipitable water and specific humidity. In La Nia episodes,although atmospheric elements change reversely, they are not statistically significant as those in El Nio periods. The possible physical mechanism of the different impact of ENSO cycle on the precipitation over southern China is investigated by analyzing the intraseasonal oscillations(ISOs) in El Nio and La Nia winter half-years, respectively. By comparing the characteristics of ISOs in El Nio and La Nia, a physical mechanism is proposed to explain the different responses of the precipitation over China to ENSO in the winter half-year. In El Nio episodes, over western North Pacific(WNP) and South China Sea(SCS) the ISOs are inactive and exert little effect on water vapor transport and convergence, inducing positive precipitation anomalies with statistical significance over southern China in El Nio episodes. In La Nia episodes, however, the ISOs are active, which weaken the interannual variation signals of ENSO over WNP and southern China and lead to the insignificance of the interannual signals related to ENSO. Therefore, the different responses of precipitation over China to ENSO in the winter half-year are possibly caused by the difference of intraseasonal oscillations over WNP and SCS between El Nio and La Nia.  相似文献   

基于VMD和WinLSP相结合的GNSS-R海平面高度估测模型     

胡媛  袁鑫泰  刘卫  胡庆松  江志豪  钟李程 《海洋学报》2022,44(11):170-178

全球导航卫星系统反射（Global Navigation Satellite System-Reflectometry,GNSS-R）技术是一种新兴的监测海平面高度变化的技术。本文依据GNSS-R技术中的信噪比分析法的原理,通过分析其分离趋势项和提取振荡频率的过程,建立了新的估测模型以提高反演精度。针对传统模型存在的信号分离不佳的问题,本文提出使用变分模态分解（Variational Mode Decomposition,VMD）算法替换传统的最小二乘拟合法（Least Squares Fitting, LSF）进行趋势项分量的分离。在此基础上,本文引入基于凯塞窗函数改进的LSP（Lomb-Scargle Periodogram）频谱分析法（记为WinLSP）来减弱因频谱泄露带来的反演误差。在瑞典翁萨拉的GTGU站和美国阿拉斯加州的SC02站开展的海平面高度反演实验结果表明,本文建立的估测模型相比于传统模型具有更高的反演精度。基于VMD+WinLSP估测模型得到的GTGU站反演结果的均方根误差（RMSE）、相关系数和反演点数分别为4.70 cm、0.98和5 647。与传统的LSF+LSP估测模型相比,反演精度和GNSS数据利用率分别提高了约29.7%和15.0%。SC02站的RMSE、相关系数和反演点数分别为14.34 cm、0.99和1 785,反演精度和GNSS数据利用率分别提高了约12.3%和9.4%。  相似文献   

大风影响下的莱州湾西岸单站底层泥沙输运特征分析     

李海  万凯  宋新  宋德海  王楠  鲍献文 《海洋学报》2022,44(6):68-79

基于2018年10月21日至11月6日莱州湾西岸连续站观测数据,本文利用集合经验模态分解、希尔伯特?黄变换和小波分析法对底层单宽输沙率的小尺度特征做分析,并针对观测期间出现的大风天气对泥沙输运的影响进行了探究。结果表明,单宽输沙率在观测时间段内具有高频、潮周期、低频以及长周期尺度变化特征,周期尺度从小到大。其中高频和潮周期分量方差贡献率及所含能量最高,对输沙率的影响最强。边际谱显示东西方向输沙率的显著周期为13.3 h,南北方向大于11 h的周期较为显著。观测期间底层净泥沙通量分别为东向305.77 kg/m、南向597.25 kg/m,余流分量贡献最大,低频和高频分量贡献最小。上强迫风场主要在风速衰减期通过湍流和波浪影响输沙速率的时频分布,使其低频变化显著增强的同时,产生1 h周期左右的高频波动。交叉小波分析显示,风速和单宽输沙率在低频波段上相干性较强,且单宽输沙率会滞后风速1/4至1/2个周期。另外,风浪会增强泥沙输运的涨落潮不对称性,进而增加潮周期分量上的泥沙净输运。  相似文献