病态线性方程组的简单迭代解法   总被引：9，自引：0，他引：9  

毛先进  杨玲英 《物探化探计算技术》1999,21(1):14-18

针对地球物理反问题中经常碰到的病态线性方程组的求解问题。本文提出了一种简单迭代（ＳＩ）算法,从理论上证明了解序列收敛且收敛到方程组的真解,然后给出了几个算例,将计算结果与对付病态问题能力很强的ＣＧ类算法的结果进行了对比,结果表明：ＳＩ算法具有极强的抗病态能力,计算精度明显高于ＣＧ类算法,但计算速度稍低于后者  相似文献   

Study and application of an improved four-dimensional variational assimilation system based on the physical-space statistical analysis for the South China Sea     

Yumin Chen  Jie Xiang  Huadong Du  Sixun Huang  Qingtao Song 《海洋学报(英文版)》2021,40(1):135-146

The four-dimensional variational assimilation (4D-Var) has been widely used in meteorological and oceanographic data assimilation. This method is usually implemented in the model space, known as primal approach (P4D-Var). Alternatively, physical space analysis system (4D-PSAS) is proposed to reduce the computation cost, in which the 4D-Var problem is solved in physical space (i.e., observation space). In this study, the conjugate gradient (CG) algorithm, implemented in the 4D-PSAS system is evaluated and it is found that the non-monotonic change of the gradient norm of 4D-PSAS cost function causes artificial oscillations of cost function in the iteration process. The reason of non-monotonic variation of gradient norm in 4D-PSAS is then analyzed. In order to overcome the non-monotonic variation of gradient norm, a new algorithm, Minimum Residual (MINRES) algorithm, is implemented in the process of assimilation iteration in this study. Our experimental results show that the improved 4D-PSAS with the MINRES algorithm guarantees the monotonic reduction of gradient norm of cost function, greatly improves the convergence properties of 4D-PSAS as well, and significantly restrains the numerical noises associated with the traditional 4D-PSAS system.  相似文献   

Effects of non-submerged boulder on flow characteristics – A field investigation     

Hossein Afzalimehr  Mohammad Reza Maddahi  Danial Naziri  Jueyi Sui 《国际泥沙研究》2019,34(2):136-143

The effect of fully submerged boulders on the flow structure in channels has been studied by some researchers. However, many natural streams have bed material with boulders that are not fully submerged under water. In many natural streams, boulders cover between 1% and 10% of the area of the stream reach. The effect of non-submerged boulders on the velocity profile and flow characteristics is very important for assessing riverbed deformation. The objectives of this paper are to find the pattern of velocity distribution around a non-submerged boulder and to compare it with the classical studies on flow resistance and Reynolds stress distribution in open channels. Also, by considering the variation in the Reynolds stress distribution at different locations around a non-submerged boulder, the effect of a non-submerged boulder on the estimation of shear velocity and resistance to flow has been investigated. Results indicates that inside the scour hole caused by a non-submerged boulder in a river velocity distributions are irregular. However, velocity distributions are regular outside the scour hole. The presence of the boulder causes a considerable deviation of the Reynolds shear stress from the classic distribution, showing a non-specific distribution with negative values. The classical methods for calculating shear velocity are not suitable because these methods do not give detailed velocity and Reynolds stress distributions in natural rivers with a lot of boulders. Thus, the effect of a non-submerged boulder on the estimation of the resistance to flow by considering the variations in velocity and Reynolds stress distributions at different locations around a non-submerged boulder is important and needs to be studied in a natural river instead of just in laboratory flumes. The negative values in Reynolds stress distribution around a boulder indicate that the classical methods are unable to predict resistance to flow, and also show strong turbulence inside the scour hole where the complex flow conditions present ambiguous Reynolds stress distributions. In the current study, to obtain a reasonable estimation of parameters in natural rivers, the classical method has been modified by considering velocity and Reynolds stress distributions through the boundary layer method.  相似文献   

一次中尺度对流系统的闪电演变特征   总被引：30，自引：11，他引：19  

冯桂力  郄秀书  周筠珺 《高原气象》2006,25(2):220-228

利用地面雷电探测网资料、多普勒雷达和卫星资料对一次典型的MCS过程的地闪变化特征进行了分析,结果表明,在系统发展的最初阶段全为负地闪;在MCS的成熟阶段地闪频数一直较高,在10次/min以上,负地闪占绝对优势;在消散阶段,地闪频数急剧下降,同时正地闪所占比例越来越大,甚至超过负地闪。地闪基本出现在<-50℃的云区和前部大的温度梯度区内,集中发生于<-60℃的云区。负地闪主要发生在强对流区(>40 dBz),其持续时间和强对流的维持时间几乎相当,说明负地闪可以很好地指示或有助于识别强对流区;密集的正地闪也与强回波区相对应,而稀疏的正地闪则多发生在系统后部的稳定性降水或云砧部位。同时,在MCS成熟阶段出现高正地闪频数的瞬间突增有可能对应着地面强天气的发生,在强对流天气的临近预报中应予以关注。  相似文献   

上海及周边地区地闪活动特征及海陆差异     

宋晓爽  郑栋  张义军  姚雯  戴建华  王强 《气象科技》2014,42(1):164-172

利用LS8000闪电定位系统2009—2011年的地闪观测资料对上海及周边地区(120~122.5°E,30~32°N)的地闪活动特征进行了研究。结果表明:分析区域内正地闪的比例约占8.5%,大电流地闪(电流绝对值大于50kA)的比例约为5.6%。地闪活动主要集中在6—9月,峰值出现在8月;日变化上,12:00—19:00闪电活动最为活跃,峰值出现在14:00,凌晨闪电活动最弱。从日变化上来说,正地闪和大电流地闪比例在地闪活动较强时段低于地闪活动较弱时段;在月分布上,在地闪活动最强的夏季,正地闪比例普遍在10%以下,在地闪活动较弱的春、秋、冬季,正地闪比例普遍在10%以上。以北纬31°为界,分析区域北部地闪密度基本在6~12次·km-2·a-1以上,南部基本在2.4~4.8次·km-2·a-1。同时陆地上的地闪密度要显著高于湖泊和海洋上的地闪密度,而海洋上的正地闪比例和大电流地闪比例要显著高于陆地。闪电空间分布的时间变化说明,下午地闪活动主要出现在陆地,而凌晨地闪主要出现在水体附近,其它时段则表现出过渡特征,这与下垫面的加热作用紧密相关。  相似文献   

人工触发闪电放电过程分析：I.先导放电过程   总被引：4，自引：3，他引：1  

言穆弘 《高原气象》1998,17(3):271-279

利用人工触发闪电电场,电流和闪电通道亮度高速摄像观测资料,分析了第一次回击前衔导过程的放电特性,结果指出,对于空中触发,先导传输具有“双向”特征,由于下行先导发展,先导通道电流分布具有不均匀性,连接导线汽化都发生在上行先导阶段。人工闪电第一次回击虽然与自然闪电继后回击特性十分相似,但两者放电特征仍有差别,前者具有曾长的连续电流过程。  相似文献   

人工触发闪电放电过程分析：Ⅱ.闪击间放电过程   总被引：4，自引：3，他引：1  

言穆私 《高原气象》1998,17(4):403-411

详细分析了一次人工闪电继后回击之间的放电过程。结果指出：“无边奄流阶段”是激发直窜先导和继后回击的重要条件。  相似文献   

以分析有机磷农药为例研究多反应气-负化学电离源质谱的行为     

桂建业  张莉  张永涛  左海英  李晓亚  田来生  赵国兴  邢晨曦 《岩矿测试》2012,31(5):863-867

在气相色谱-质谱分析中,负化学电离源质谱特别适合于高电负性目标物的分析,但不同反应气的对比研究工作至今未见报道。本研究采用甲烷、异丁烷、氨气、甲烷+氨气混合气、异丁烷+氨气混合气作为反应气,在负化学离子源内对电负性较高的有机磷农药进行电离实验,对反应气压力、离子源温度、灯丝发射电流等多项参数进行了考察。结果表明:采用纯氨气作为反应气,检测背景低,质谱真空负荷小,并可在负化学源质谱上获得最高的灵敏度。配合加速溶剂萃取方法,对土壤中的有机磷农药残留进行分析,方法全流程回收率为73.3%～108.1%,精密度为2.5%～8.8%,检出限为0.01～0.32μg/kg,各项指标均可满足实际样品测试需求。  相似文献   

An environmental snapshot of the Bølling interstadial in Southern Iberia     

Antonio García-Alix  Gonzalo Jiménez-Moreno  Francisco J. Jiménez-Espejo  Fernando García-García  Antonio Delgado Huertas 《Quaternary Research》2014

The Bølling–Allerød interstadial is the closest warm time period to the Holocene. The study of the climate variability during this most recent warm scenario provides a natural record of potential environmental changes related with global temperature variations. Little is known about this interstadial in the Southern Iberian Peninsula. Therefore, the exceptional climatic record of the Otiñar paleo-lake (ca. 14.5–14.0 cal ka BP), provides environmental information about the first part of this interstadial (Bølling) in this key region. Although the studied high-resolution isotopic record point to almost invariant hydrological conditions in the paleo-lake, with little change in the carbon budget and important limestone dissolution, the pollen record shows an increase in forest species that can be interpreted as a warming trend and an increase in humidity during the Bølling in the area. This record is one of the few continental archives that show this climatic trend in Southern Iberia, agreeing with many other regional records from the western Mediterranean. This does not agree with higher latitude records that show an opposite trend. This opposite pattern in precipitation between the western Mediterranean and more northern latitudes could be explained by a persistent and increasing negative NAO mode during the Bølling in this area.  相似文献   

CG型重力仪性能对比分析     

邓友茂  王振亮  孙诚业 《大地测量与地球动力学》2021,41(4):432-435

对6台CG型重力仪分别进行静态和动态稳定性试验,结果表明,CG-6型重力仪继承了CG-5型重力仪的静态稳定性优点,静态曲线拟合成直线的拟合中误差小于3 μGal,最大拟合差小于5 μGal;CG-6型重力仪动态精度和动态零漂率明显优于CG-5型重力仪。  相似文献