Wave-height distributions and nonlinear effects   总被引：2，自引：0，他引：2  

M. Aziz Tayfun  Francesco Fedele 《Ocean Engineering》2007,34(11-12):1631-1649

Theoretical distributions proposed for describing the crest-to-trough heights of linear waves are reviewed briefly. To explore the effects of nonlinearities, these are generalized to second-order waves, utilizing quasi-deterministic results on the expected shape of large waves. The efficacy of Gram–Charlier models in describing the effects of third-order nonlinearities on the distributions of wave heights, crests and troughs are examined in detail. All models and a fifth-order Stokes–Rayleigh type model recently proposed are compared with linear and nonlinear waves simulated from the JONSWAP spectrum representative of long-crested extreme seas, and also with oceanic data gathered in the North Sea. Uncertainties arising from the variability of probability estimates derived from sample populations of limited size are considered. Ultimately, the comparisons show that nonlinearities do not have any discernable effect on the crest-to-trough heights of oceanic waves. Most of the linear models considered yield similar and reasonable predictions of the observed data trends. Gram–Charlier type distributions seem neither effective nor particularly useful in describing the statistics of large wave heights or crests under oceanic conditions. However, they do surprisingly well in predicting unusually large wave heights and crests observed in some 2D wave-flume experiments and 3D numerical simulations of long-crested narrow-band random waves.  相似文献   

利用希尔伯特变换解释重力异常     

于涛  王硕儒 《中国海洋大学学报(自然科学版)》1987,(2)

本文给出了几种规则形状二度体和三度体重力异常的希尔伯特变换式,提出了一种利用希尔伯特变换反演异常体的方法。这种方法充分利用了重力异常信息:利用重力异常Δg(x)曲线和它的希尔伯特变换H(x)曲线及Δg(x)-H(x)参量图上的某些特征点直接反演异常体形状参数及埋深。方法简单、实用。  相似文献   

A Multiple Criteria Decision Modelling approach to selection of estimation techniques for fitting extreme floods     

L. Duckstein  B. Bobée  F. Ashkar 《Stochastic Hydrology and Hydraulics》1991,5(3):227-238

The problem of fitting a probability distribution, here log-Pearson Type III distribution, to extreme floods is considered from the point of view of two numerical and three non-numerical criteria. The six techniques of fitting considered include classical techniques (maximum likelihood, moments of logarithms of flows) and new methods such as mixed moments and the generalized method of moments developed by two of the co-authors. The latter method consists of fitting the distribution using moments of different order, in particular the SAM method (Sundry Averages Method) uses the moments of order 0 (geometric mean), 1 (arithmetic mean), –1 (harmonic mean) and leads to a smaller variance of the parameters. The criteria used to select the method of parameter estimation are:

–	- the two statistical criteria of mean square error and bias;
–	- the two computational criteria of program availability and ease of use;
–	- the user-related criterion of acceptability.

These criteria are transformed into value functions or fuzzy set membership functions and then three Multiple Criteria Decision Modelling (MCDM) techniques, namely, composite programming, ELECTRE, and MCQA, are applied to rank the estimation techniques.  相似文献   

Simulation of long‐term consolidation behavior of soft sensitive clay using an elasto‐viscoplastic constitutive model     

M.R. Karim  F. Oka  K. Krabbenhoft  S. Leroueil  S. Kimoto 《国际地质力学数值与分析法杂志》2013,37(16):2801-2824

The phenomenon of excess pore water pressure increase or stagnation and continuing large ground deformation in soft sensitive clay following the completion of construction of embankment is simulated for a case study at Saint Alban, Quebec, Canada. The present model employs an updated Lagrangian finite element framework and is combined with an automatic time increment selection scheme. The simulation based on an elasto‐viscoplastic constitutive model considers soil‐structure degradation effect. It is shown that without consideration for the microstructural degradation effect, it is not possible to reproduce the field responses of soft sensitive clay even during the construction of the embankment. When the soil‐structure degradation effect is considered, the present model can offer reasonably accurate prediction for the consolidation behavior of soft sensitive clay, including the so‐called anomalous pore water pressure generation and continuing large deformation even after the end of construction, which has been posing numerous uncertainties on the long‐term performance of earth structures. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Role of unusual moisture transport across Equatorial Indian Ocean on the extreme rainfall event during Kerala flood 2018     

《Dynamics of Atmospheres and Oceans》2021

Southwestern Indian state, Kerala experienced extreme devastating statewide flood event of the century during 2018 monsoon season. In this study, an attempt has been made to bring out the salient dynamical factors contributed to the Kerala flood. There were 3 active spells over Kerala during 2018 Monsoon season. All the three spells were accustomed with the intrinsic factors of low frequency components of the active spells such as strength of monsoon Low Level Jet (LLJ), Monsoon depressions in the Bay of Bengal, favorable Madden-Julian oscillation (MJO) phases and Western Pacific systems. Though all the common ingredients remain same, the third spell is distinct with the less evaporation flux over Western and Central Arabian Sea and unusual moisture transport from maritime continent through South Equatorial Indian ocean (SEIO) towards the Kerala coast across Equator. Strong meridional pressure gradient force created by the combined effect of high pressure anomaly oriented Northwest-Southeast direction across tropical Indian ocean and anomalous low pressure along monsoon trough might have contributed to this unusual moisture transport across SEIO originating from west of Australia. The anomalous high pressure in South Indian ocean was greatly influenced by the position of the Mascarene high. Subtropical Indian ocean dipole (SIOD) also exhibits an influential role by altering tropical Southern Indian ocean dynamics in favor of the unusual moisture transport. The position of the monsoon depression and presence of typhoons in Western Pacific might have aided to this moisture transport. However, the normal moisture transport from Central Arabian sea towards Kerala coast by virtue of the strong LLJ along with additional moisture transport directly from South of maritime continent through SEIO across the Equator towards Kerala coast might have played a dominant role in the historical flood event over entire Kerala state.  相似文献   

洞穴滴水、石笋中元素及元素比值对气候环境变化响应的研究进展     

马源  殷建军  袁道先 《地质论评》2022,68(3):2022062017-2022062017

滴水/石笋元素是除δ18O和δ13C,研究气候环境变化的又一重要代用指标。外界气候环境变化通过改变表层岩溶带和岩溶含水层中的水文环境,甚至洞穴环境,进而影响元素的溶解、运移和沉淀过程,从而使得滴水/石笋中元素表现一定的变化规律。本文通过分析影响洞穴滴水元素及元素比值变化的因素：元素来源、水—岩相互作用和滞留时间、差异性淋滤、先期碳酸盐沉淀及分配系数的基础上,从元素对岩溶区“二元结构”和极端天气/气候事件响应的角度,探讨了滴水/石笋中元素的气候环境指示意义。取得了以下认识：① 强降水带来的冲刷作用和溶解作用,促进土壤和基岩中元素、胶体和天然有机质（NOM：Natural Organic Matter）等物质在短时间内快速溶解和运移,使滴水中元素含量增加;但随着降水增多带来的稀释作用,使得滴水/石笋中Mg,Sr和Ba等元素含量降低,因此,单一元素的解译较为复杂;② 但基岩/溶液中元素溶解和沉积的差异,导致元素相对含量的变化,使得元素X/Ca比值对外界环境的响应具有同一性,尤其是Mg/Ca和Sr/Ca比值：在干旱条件下,降水减少导致方解石先期沉积（PCP：Prior Calcite precipitation）作用增强,使Mg/Ca和Sr/Ca比值增大。但目前存在着一些问题：① Mg/Ca和Sr/Ca比值变化对强降水事件的响应并不明显,可能与新、老水混合及元素溶解过程中的溶解比例差别不大有关;② 多源、多期混合水源会导致洞穴滴水元素对极端事件响应减弱;③ Mg/Ca和Sr/Ca的变化为解释δ18O的“雨量效应”及“源效应”提供了见解,但元素变化能否反映季风强度的变化,仍有待进一步的研究。基于以上认识,笔者提出开展更加系统的大气—土壤—包气带—洞穴的监测;开展更高分辨率、更长时间尺度的洞穴监测;开展多区域、多洞穴系统对比研究来更加深入地开展洞穴石笋元素研究。  相似文献   

1960—2014年淮河流域极端降水发生时间的时空特征     

潘欣  尹义星  王小军 《高原气象》2019,(2):377-385

利用淮河流域25个分布相对均匀站点的逐日降水资料,借助线性趋势、圆形统计、EOF分析等方法对1960—2014年流域的极端降水发生时间的时空特征进行分析。研究表明:(1)淮河流域极端降水发生时间主要集中在7月中下旬,并表现出明显的年际振荡。流域平均的极端降水发生时间表现出提前趋势,但未达到0. 05显著性水平。发生时间集中程度随年份上升,上升趋势达到了0. 05显著性水平。综合分析表明,流域7月份发生极端降水的可能性增大。(2)流域极端降水发生时间在空间上由西南向东北逐渐推迟,大部分站点发生时间呈微弱提前的趋势,该分布规律与梅雨和台风的影响有关,而提前趋势与20世纪90年代以来我国主雨带的年代际北移有关。(3)流域极端降水发生时间的EOF分析结果显示,第一模态空间典型场呈"西北-东南"反位相分布;第二模态空间典型场呈一致性分布,分别揭示了流域极端降水发生时间在空间上的分异特征和近似一致性分布特征。  相似文献   

1960-2011年辽宁省大暴雨时空分布特征   总被引：2，自引：0，他引：2  

杨青  韩秀君  高松影  阎琦  卢秉红  田莉 《气象与环境学报》2015,31(1):34-42

利用1960-2011年辽宁省61个国家气象站地面20-20时降水及逐小时降水观测资料,统计分析辽宁大暴雨时空分布特征。结果表明：辽宁省年平均大暴雨日数为6.5 d,年平均影响范围为17.5站次,两个大暴雨多发区分别位于辽宁东南部和南至西南沿海地区。辽宁东南部大暴雨多发区由于受台风、江淮气旋、华北气旋和蒙古气旋等多种系统及地形影响,易出现区域性和局地性大暴雨,大暴雨发生次数较多,降水量变化较大;降水量和降雨强度极值均较大,大暴雨中心出现在凤城,降雨强度最大达212 mm/h^-1。南至西南沿海大暴雨多发区易受台风和华北气旋及地形影响,以区域性大暴雨为主,降水量和降雨强度极值也较大,但最大降水量和降雨强度极值均与大暴雨日数的中心不一致。区域性大暴雨的降水量极值对大暴雨降水量极值的贡献最大。大暴雨平均降雨强度的逐时变化呈单峰型分布,08时降雨强度达最强,20时降雨强度最弱。辽宁省大暴雨日集中出现在7月下旬至8月上旬,8月大暴雨日略多于7 月。最早和最晚区域性大暴雨均是受江淮气旋影响,并出现在辽宁省南部地区。大暴雨日数具有明显的周期变化,主要年代际变化周期为10 a。区域性和局地性大暴雨主要周期分别为36 a和10 a。预计未来6 a辽宁省仍处于大暴雨较多的阶段,并可能多以局地性大暴雨的形式出现。  相似文献   

西南地区极端降水变化趋势   总被引：7，自引：3，他引：4  

罗玉  范广洲  周定文  华维  李金建 《气象科学》2015,35(5):581-586

利用西南地区90个气象台站1970-2010年逐日降水量资料,依据世界气象组织(WMO)定义的连续5d最大降水量、总降水量、强降水比等6种极端降水指数,采用F检验、11a滑动平均等统计方法,研究了西南地区极端强降水变化趋势的时空变化特征。在时间上,西南地区近41年来冬、春、夏季连续5d最大降水量缓慢波动上升,秋季连续5d最大降水量呈下降趋势;强降水、降水强度及强降水比呈上升趋势,但总降水量和最长持续无降水日数呈减少趋势;另外,各极端降水指数还存在明显的年际、年代际变化。在空间上,西南地区极端降水变化趋势具有显著的地域差异,呈东西或西北东南向梯度变化特征。其中冬季连续5d最大降水量、降水强度、强降水比及最长持续无降水日数,在西南大部分地区呈增加趋势。秋季连续5d最大降水量与总降水量在西南大部分地区呈减少趋势。而春、夏季连续5d最大降水量和强降水的增减区域大致相当。  相似文献   

中国东部地区夏季极端高温的特征分析   总被引：6，自引：2，他引：4  

梁梅  吴立广 《气象科学》2015,35(6):701-709

利用中国东部地区449个气象站的日最高气温资料,应用趋势分析法等,分析了1960-2012年夏季极端高温日数、持续高温日数的时空变化特征。分析发现:北方地区、华南地区和杭州湾周围地区两个高温指数都呈现增加趋势,长江与黄河之间的中部地区都减小。而在长江下游南部地区极端高温日数显著增加,但持续高温日数却明显减少。从季节特征上看,淮河以北的地区两个高温指数主要集中在6、7月;而以南的区域主要集中在7、8月。各个地区的这两个高温指数与降水日数均呈现显著的负相关,但南北有明显的差异,北方地区负相关的在年际变率以及5 a尺度都很显著,而中部地区则只在年际尺度上显著。杭州湾与华南地区持续高温日数与降水日数的相关体现在5 a尺度上。北方极端高温的显著增加与该地区降水日数与降水量明显减少密切相关。西北太平洋副热带高压显著的西伸,与东南地区的两个高温指数的变化有关。  相似文献