Wave energy conversion under constrained wave-by-wave impedance matching with amplitude and phase-match limits     

《Applied Ocean Research》2019

This paper investigates an approach to limit the fullness of ‘tuning’ provided by wave-by-wave impedance matching control of wave energy devices in irregular waves. A single analytical formulation based on the Lagrange multiplier approach of Evans [1] is used to limit the velocity amplitude while also limiting the closeness of the phase match between velocity and exciting force. The paper studies the effect of the present technique in concurrently limiting the device velocity and the required control/actuation force. Time domain application requires wave-profile prediction, which here is based on a deterministic propagation model. Also examined in the time domain is the effect of possible violation of the displacement constraint, which for many designs implies impacts at hard stops within the power take-off mechanism. Time domain simulations are carried out for a 2-body axisymmetric converter (with physical end-stops) in sea states reported for a site off the US east coast. It is found that the approach leads to effective power conversion in the less energetic sea states, while as desired, considerable muting of the optimal response is found in the larger sea states. Under the assumptions of this work, the end-stop collisions are found to have a minor effect on the power conversion. The present approach could be used to guide the design of power take-off systems so that their displacement stroke, maximum force, and resistive and reactive power limits are well-matched to the achievable performance of a given controlled primary energy converter.  相似文献   

Two Quasi-periodic Oscillations in ESO 113-G010     

《Chinese Astronomy and Astrophysics》2020,44(1):32-40

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10~30 d延伸期可预报性与预报方法研究进展   总被引：1，自引：0，他引：1       下载免费PDF全文

章大全  郑志海  陈丽娟  张培群 《应用气象学报》2019,30(4):416-430

10~30 d延伸期的可预报性既依赖于初始条件,也与缓变的下垫面有关,寻找延伸期时段内可预报性较高的低频特征,识别延伸期的可预报性来源及影响的物理机制是提高延伸期预报水平的关键。近年延伸期可预报性来源、热带大气季节内振荡监测预测和影响等领域的研究取得较大进展,提出和应用了动力统计相结合以及大气低频信号释用等新的延伸期预报方法。对延伸期可预报性来源及其与初值和外强迫异常的关系分析表明,海气相互作用能提高亚洲和西太平洋区域延伸期时段大气环流和要素的可预报性。热带大气季节内振荡、平流层爆发性增温以及各种次季节尺度的海气、陆气耦合作用和大气响应均为延伸期预报提供了重要的可预报性来源。由于数值模式延伸期时段的预报性能与实际业务需求还存在一定距离,基于动力统计相结合和物理统计的延伸期预报方法被广泛应用于业务预报,表现出一定的预报技巧。  相似文献   

2016年1月低温事件的季节内振荡特征   总被引：1，自引：0，他引：1  

江雨霏  姚素香  王咏青  张秀年 《气象科学》2019,39(1):42-49

利用NECP/DOE逐日再分析资料,分析了2016年1月发生在我国南方的持续低温事件。结果表明,此次过程存在明显的季节内振荡特征,其中准双周振荡为气温变化的主要模态。此次低温事件之所以达到寒潮级别,是由于天气尺度变化与10~20 d气温准双周振荡处于相同的降温变化过程中。准双周尺度的冷中心与天气尺度冷中心均从中高纬度向低纬地区传播,并在我国南方汇合,从而引起持续性的低温。通过诊断温度局地变化方程发现,此次天气过程中,温度平流项和绝热变化项是近地层局地温度降低的主要原因。天气尺度气温变化与10~20 d低频振荡对持续降温都有较大贡献,天气尺度降温略大于低频降温。  相似文献   

高低频系统相互作用对Rossby波破碎过程的影响     

张潮  谭言科  李崇银  平已川 《大气科学》2019,43(2):221-232

利用美国国家环境预报中心和能源部（NCEP/DOE）的逐日再分析资料（NCEP-DOE AMIP-Ⅱ）,对2010年12月20日发生在北太平洋一次典型的反气旋式波破碎（AWB）事件进行研究,分析了波破碎过程中等熵位涡场的演变特征,揭示了波破碎过程中高频扰动以及低频信号的逐日演变特征,并对2010年冬季350 K等熵面上逐日高频位涡（PV）扰动和低频变化做经验正交函数（EOF）分析,得到了其主要模态,并从等熵位涡方程出发研究了波破碎过程中位涡高、低频变化的原因。研究表明,波破碎过程中高频低PV空气从北太平洋西部日本附近沿东北方向向对流层上层侵入,而来自阿拉斯加湾附近的高频高PV空气向对流层下层侵入。高频位涡场EOF分解得到的前两个模态共同描述了北太平洋中纬度地区自西向东移动的天气尺度波列;低频位涡场EOF分解的第一模态在北太平洋呈弧形波列结构。天气尺度波在传播过程中受到低频场的平流作用逐渐偏离其传播主要模态的位置,并发生破碎,同时高频流场对高频位涡的平流可以产生低频变化,使得低频变化的空间形态向其冬季主要模态转变。  相似文献   

南亚高压次季节尺度东西振荡对我国长江流域降水及水汽输送的影响   总被引：3，自引：2，他引：1  

葛家荣  任雪娟 《气象科学》2019,39(6):711-720

使用常规资料及HYSPLIT(Hybrid Single Particle Lagrangian Integrated Trajectory Model)模式,分析了早夏和晚夏期间南亚高压次季节尺度异常偏东事件和异常偏西事件发生时,我国长江流域降水及水汽输送异常特征。结果表明:早夏期间当南亚高压异常东伸时,西太平洋副热带高压可西伸至我国东南沿岸,此时,降水正异常场主要位于我国东部地区,表现为江淮区域降水异常偏多;而晚夏期间当南亚高压异常东伸时,西太平洋副热带高压的西脊点更偏东,降水正异常区位置比早夏偏西,表现为四川盆地的降水异常偏多。早夏期间,与南亚高压异常偏西事件相比,南亚高压异常偏东事件有利于更多的水汽从南方的水汽源地输送到我国江淮区域,加上此时江淮流域存在异常上升运动,动力和水汽条件共同使得江淮流域降水偏多。晚夏四川盆地地区有类似的结论。  相似文献   

两类El Niňo事件次年夏季长江-黄河流域降水低频特征及低频水汽输送途径差异          下载免费PDF全文

李丽平  倪语蔓  杨春艳  马晨誉 《大气科学学报》2019,42(3):420-433

利用1961年1月—2014年12月Hadley气候预测研究中心的全球海表温度(SST)资料,NECP/NCAR逐日风场、比湿等再分析资料,国家气象信息中心提供的中国753站逐日降水、160站逐月降水资料,对比分析了东部(EP)型和中部(CP)型两类El Niňo事件次年夏季长江-黄河流域降水(简记为EP型和CP型降水)低频特征,以及与之相关的低频水汽输送差异。结果表明,1)平均而言,EP型降水主要有10～20 d(最显著)以及20～30 d(次显著)低频周期;CP型降水主要有10～20 d的低频显著周期。与之相关的纬、经向水汽通量最显著低频周期也为10～20 d。2)影响EP、CP型低频降水共同的低频水汽环流系统主要有:菲律宾群岛附近的异常反气旋式水汽环流和渤海湾附近(日本东南侧)的异常气旋式(反气旋式)水汽环流。另外,影响EP(CP)型低频降水的还有来自巴尔喀什湖东北部异常气旋式水汽环流(孟加拉湾、苏门答腊岛以西的异常气旋式水汽环流对和贝加尔湖西、东两侧的异常气旋式、反气旋式环流)。3)EP型降水暖湿水汽主要源自南海,冷湿水汽主要源自西北太平洋,冷空气来自巴尔喀什湖东北部和贝加尔湖西北侧。CP型降水暖湿水汽少量来自阿拉伯海和印度洋,大量来自热带西太平洋,冷空气主要来自贝加尔湖西北侧。  相似文献   

IMPACT OF TROPICAL INTRASEASONAL OSCILLATIONS ON THE PRECIPITATION OF GUANGDONG IN JUNES     

林爱兰  李春晖  谷德军  郑彬 《热带气象学报(英文版)》2015,21(4):326-336

The impact of tropical intraseasonal oscillations on the precipitation of Guangdong in Junes and its physical mechanism are analyzed using 30-yr (1979 to 2008), 86-station observational daily precipitation of Guangdong and daily atmospheric data from NCEP-DOE Reanalysis. It is found that during the annually first rainy season (April to June), the modulating effect of the activity of intraseasonal oscillations propagating eastward along the equator (MJO) on the June precipitation in Guangdong is different from that in other months. The most indicative effect of MJO on positive (negative) anomalous precipitation over the whole or most of the province is phase 3 (phase 6) of strong MJO events in Junes. A Northwest Pacific subtropical high intensifies and extends westward during phase 3. Water vapor transporting along the edge of the subtropical high from Western Pacific enhances significantly the water vapor flux over Guangdong, resulting in the enhancement of the precipitation. The condition is reverse during phase 6. The mechanism for which the subtropical high intensifies and extends westward during phase 3 is related to the atmospheric response to the asymmetric heating over the eastern Indian Ocean. Analyses of two cases of sustained strong rainfall of Guangdong in June 2010 showed that both of them are closely linked with a MJO state which is both strong and in phase 3, besides the effect from a westerly trough. It is argued further that the MJO activity is indicative of strong rainfall of Guangdong in June. The results in the present work are helpful in developing strategies for forecasting severe rainfall in Guangdong and extending, combined with the outputs of dynamic forecast models, the period of forecasting validity.  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   

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