速度传感反馈地震计的参数稳定性分析     

杨晓源  邵玉平  杜瑶 《地震地磁观测与研究》2011,32(6):109-115

从理论上定量分析机械摆和环路滤波等开环诸参数变化对速度传感反馈地震计闭环参数的影响.研究指出,在环路设计中可半自由选取的开环阻尼取值对参数稳定性有重要影响.过大或过小的开环阻尼取值均可能造成参数稳定性急剧变差,影响地震计在只标不调的状况下长期连续稳定工作.  相似文献   

基于细化分层法探讨面波频散曲线反演参数的简化     

邵广周  李庆春 《地球科学与环境学报》2011,(3):317-320

常规频散曲线反演过程中需要不停地改变分层数、层厚度和层速度等参数,实现过程相对繁琐,而采用细化分层法对反演参数进行简化则避免了上述缺点。具体思路为:根据目的层探测深度(如20m)将地下介质分为若干个(20个)厚度为1m的薄层和1个均匀半空间层(共21层),这样在反演中分层数和层厚度均为已知参量,反演过程只需修改速度参数即可,避免了改变分层数和层厚度等参数,显著简化了反演计算过程。正演计算和反演结果均表明:细化分层与实际分层计算出的频散曲线是等效的,细化分层反演结果的总体效果与真实模型非常接近,这说明细化分层方法用于频散曲线反演是切实可行且有效的;将地下介质划分为1m厚的薄层,反演后每层均可得到1个横波速度,能满足反演分辨率的要求;由于实际地下介质的速度是随深度渐变的,细化分层后比按频散曲线拐点分层(每分层的厚度可能是几米或几十米,同一分层内介质的横波速度相等)更接近实际情况。  相似文献   

砂质海滩地形动力分类研究进展     

于吉涛  陈子燊 《热带地理》2011,31(1):107-112

海滩状态是一个地形与水动力相互作用的三维地形动力问题.国外对海滩状态的地形动力分类已开展了大量卓有成效的研究工作,既包括波控、小潮、开阔海岸海滩状态的研究,也包括波控、不同潮差海岸海滩类型的研究和岬间海岸海滩类型的研究.文中回顾并概括了自20世纪70年代至今国外在砂质海滩地形动力分类方面代表性的研究工作,这些对于我国的...  相似文献   

沙源供给条件对风沙流结构的影响   总被引：2，自引：1，他引：1  

任春勇  武生智 《中国沙漠》2011,30(3):597-601

 针对风沙运动的气固两相流特点,利用FLUNET 软件,对不同沙源供给条件下各种床面的风沙积蚀平衡进行了数值模拟,给出了风速分布和沙粒体积分数随沙源供给条件和下垫面变化的线图,比较了流动边界条件对流场的影响。计算结果揭示了风沙运动中沙粒的体积浓度分布在风速变化和床面形态变化下的变化规律,为沙漠化的防治和理论研究提供了基础。  相似文献   

地表覆盖对坡面流流速影响的模拟试验   总被引：3，自引：0，他引：3  

曹颖  张光辉  唐科明  罗榕婷 《山地学报》2011,29(6)

植被覆盖对坡面流流速的影响,会引起坡面输沙特征的改变,但在陡坡条件下盖度与流速的响应关系尚不明确.针对目前国内外研究的不足,本研究采用变坡实验水槽在较大坡度(5°～ 25°)、流量(0.25 ～2 L/s)和盖度(0％～25％)范围内,系统研究了坡面流平均流速与盖度、坡度、流量之间的关系.结果表明:坡面流流速在0.15～ 1.35 m/s内变化,流速与盖度、坡度和流量关系密切.随着地表模拟盖度的增加,水流克服覆盖物的阻碍作用而消耗的能量越多,水流流速随之减小.随着坡度和流量的增加,坡面流重力势能与水流动能增加,因此流速随坡度和流量呈幂函数增加.通过统计回归发现,盖度对流速的影响最大,占45％左右,坡度和流量次之.三个因子可以较好模拟陡坡、定床条件下水流流速(R2 =0.93).研究结果有助于认识陡坡地表覆盖下坡面流的水动力学特性,为建立土壤侵蚀过程模型提供理论基础.  相似文献   

Assessment of the Evolution in Velocity of Two Debris‐Covered Valley Glaciers in Nepal and New Zealand          下载免费PDF全文

Umesh K. Haritashya  Mark S. Pleasants  Luke Copland 《Geografiska Annaler: Series A, Physical Geography》2015,97(4):737-751

Feature tracking of orthorectified pairs of Advanced Spaceborne Thermal Emission and Reflection Radiometer satellite images is used to calculate velocities for the Tasman Glacier, New Zealand (2002–2014) and the Khumbu Glacier, Nepal (2001–2008). Velocities in the middle and upper ablation zones of both glaciers show a long‐term decrease of ～10–20%, while the terminus of Khumbu Glacier has remained near stagnation throughout the study period. In contrast, there has been a recent acceleration of the lower terminus of Tasman Glacier, from ～5 m a^–1 in 2002 to 40 m a^–1 in 2014. Both of these glaciers have an extensive supraglacial debris cover across their lower ablation regions, with the Khumbu Glacier terminating on land and the Tasman Glacier terminating in a proglacial lake. The rapid recent increase in velocity of the terminus of Tasman Glacier is closely correlated with the increase in size of its proglacial lake. These results indicate the complex dynamic changes that mountain valley glaciers may undergo in response to long‐term negative mass balance.  相似文献   

Influence of filling velocity on stability of subgrade with marine soft soil     

WANG Chang-ming  ZHANG Shu-hua  FAN Jian-hua 《世界地质(英文版)》2004,7(2)

Filling velocity and thickness of soft layer are major factors affecting subgrade stability according to an example study by means of finite element stress method (FESM). A case is studied and shows that the subgrade was slided because of excessive filling velocity. To determine a reasonable filling velocity is a key problem to a subgrade with marine soft soil.  相似文献   

地形地表的不规则起伏对雷电电磁场传输的影响   总被引：2，自引：0，他引：2  

张其林  张源源  李东帅  樊艳峰  高金阁 《气象学报》2013,71(2):357-365

为了研究地形地表的不规则起伏(简称粗糙地表)对雷电电磁场传播的影响,首先利用二维分形方法模拟了粗糙地表,然后利用Barrick表面阻抗理论和Wait近似算法研究了粗糙地表对雷电电磁场传播的影响。结果表明,粗糙地表对地闪首次回击垂直电场的影响较小,但对继后回击存在明显的影响。随着粗糙度的增加,继后回击垂直电场峰值的衰减程度明显增加,且时域脉冲波形上升沿时间增大。如继后回击电磁场传播100 km,均方高为30 m的粗糙地表(电导率σ=0.1 S/m)引起时域电磁场波形上升沿时间额外增约1.5μs,电场峰值额外减小约12%,且其影响随着地面电导率的减小而增大。因此,在实际工作中应考虑复杂地形地表对闪电定位系统探测精度和效率的可能影响。  相似文献   

Observations and analyses of floc size and floc settling velocity in coastal salt marsh of Luoyuan Bay, Fujian Province, China   总被引：1，自引：0，他引：1  

WANG Aijun  YE Xiang  CHEN Jian 《海洋学报(英文版)》2010,29(3):116-126

In coastal environments, fine-grain sediments often aggregate into large and porous flocs. ElectroMagnetic Current Meters (EMCM) and Laser In Situ Scattering and Transmissometry (LISST-ST) have been deployed within a Spartina alterniflora marsh of the Luoyuan Bay in Fujian Province, China, to measure the current velocity, the floc size and the settling velocity between 15 and 22 January 2008. During the observations, the near-bed water was collected in order to obtain the suspended sediment concentration (SSC) and constituent grain size. Data show that: (1) the nearbed current velocities vary from 0.1 to 5.6 cm/s in the central Spartina alterniflora marsh and 0.1–12.5 cm/s at the edge; (2) the SSCs vary from 47 to 188 mg/dm 3 . The mean grain size of constituent grains varies from 7.0 to 9.6 μm, and the mean floc sizes (MFS) vary from 30.4 to 69.4 μm. The relationship between the mean floc size and settling velocity can be described as: w s =ad b , in which w s is the floc settling velocity (mm/s), a and b are coefficients. The floc settling velocity varies from 0.17 to 0.32 mm/s, with a mean value of 0.26 mm/s, and the floc settling velocity during the flood tide is higher than that during the ebb tide. The current velocity and the SSC are the main factors controlling the flocculation processes and the floc settling velocity.  相似文献   

GPS在机载雷达测速精度鉴定中的应用     

王云河  王存良 《全球定位系统》2010,35(2):5-8

论述了利用GPS来鉴定机载雷达的测速精度，推导了雷达对目标径向的速度基准值计算公式及其精度计算公式，并计算了该速度基准值及其精度，结果表明：能够满足速度基准值精度要求。强调了在做测速精度鉴定方案时，需要计算在被鉴定速度方向上的速度基准值精度是否满足要求。  相似文献