Parameter identification of a compliant nonlinear SDOF system in random ocean waves by reverse MISO method     

R. Panneer Selvam  S. K. Bhattacharyya   《Ocean Engineering》2001,28(9):33

The determination of the drag and inertia coefficients, which enter into the wave force model given by Morison's equation, is particularly uncertain and difficult when a linear spectral model is used for ocean waves, and the structure is compliant and has nonlinear dynamic response. In this paper, a nonlinear System Identification method, called Reverse Multiple Inputs–Single Output (R–MISO) is applied to identify the hydrodynamic coefficients as well as the nonlinear stiffness parameter for a compliant single-degree-of-freedom system. Four different types of problems have been identified for use in various situations and the R–MISO has been applied to all of them. One of the problems requires iterative solution strategy to identify the parameters. The method has been found to be efficient in predicting the parameters with reasonable accuracy and has the potential for use in the laboratory experiments on compliant nonlinear offshore systems.  相似文献   

纵横波独立成像的弹性波逆时偏移方法   总被引：1，自引：1，他引：1  

尧德中  周熙襄 《地球物理学报》1993,(5)

本文采用逆时递推,在空间域完成纵横波分离,同时实现了位移场成像和纵、横波的独立成像。模拟数据与实际资料试算表明,对纵波和横波分别成像不仅有理论意义,而且有明显的应用价值。文中还就偏移速度对成像结果的影响和实际资料的预处理问题进行了讨论。  相似文献   

关于菏泽－昆山北西向地震带的建立及其意义          下载免费PDF全文

方大卫  沈永盛 《地震地质》1994,16(4):365-372

根据地质构造、地震稠密区走向和地震迁移活动的规律，并结合重力和航磁资料探讨了菏冷昆山北西向地震带的存在及其规模和范围。这一地震带，无论在历史上或近期均甚活跃，对江淮流域及沪、杭、甬地区构成一定的震灾威胁，值得引起有关方面的重视，并予加强研究和监测  相似文献   

逆断裂在浅部松散层中的破裂传播方式     

向宏发  虢顺民 《地震地质》1995,17(3):225-230

根据实际资料分析研究，逆断裂破裂位错向上传播至松散层中有４种消减形式：端部分叉、从断裂向褶皱转换、破裂在松散层中的吸收与尖灭及逆断层前方碎砾物质的扰动变形等。端部分叉与扰动变形的消减可能与突发性位错相关；上覆层的褶皱及位错在松散层中的尖灭则多属弹－塑转换型的消减方式  相似文献   

Reverse time migration with Gaussian beams using optimized ray tracing systems in transversely isotropic media     

Qiang Liu  Zhen-Chun Li  Jian-En Xiao  Xue-Cheng Xu 《Geophysical Prospecting》2022,70(1):95-107

Prestack depth migration is a key technology for imaging complex reservoirs in media with strong lateral velocity variations. Prestack migrations are broadly separated into ray-based and wave-equation-based methods. Because of its efficiency and flexibility, ray-based Kirchhoff migration is popular in the industry. However, it has difficulties in dealing with the multi-arrivals, caustics and shadow zones. On the other hand, wave-equation-based methods produce images superior to that of the ray-based methods, but they are expensive numerically, especially methods based on two-way propagators in imaging large regions. Therefore, reverse time migration algorithms with Gaussian beams have recently been proposed to reduce the cost, as they combine the high computational efficiency of Gaussian beam migration and the high accuracy of reverse time migration. However, this method was based on the assumption that the subsurface is isotropic. As the acquired azimuth and maximum offsets increase, taking into account the influence of anisotropy on seismic migration is becoming more and more crucial. Using anisotropic ray tracing systems in terms of phase velocity, we proposed an anisotropic reverse time migration using the Gaussian beams method. We consider the influence of anisotropy on the propagation direction and calculate the amplitude of Gaussian beams with optimized correlation coefficients in dynamic ray tracing, which simplifies the calculations and improves the applicability of the proposed method. Numerical tests on anisotropic models demonstrate the efficiency and accuracy of the proposed method, which can be used to image complex structures in the presence of anisotropy in the overburden.  相似文献   

Identification and evolution of hydrogeochemical processes in the groundwater environment in an area of the Palar and Cheyyar River Basins,Southern India   总被引：5，自引：0，他引：5  

N.?Rajmohan  L.?ElangoEmail author 《Environmental Geology》2004,46(1):47-61

The Palar and Cheyyar River Basins in Tamil Nadu state of Southern India are characterised by different geological formations, and groundwater is the major source for domestic, agricultural and other water-related activities. Hydrogeochemical studies were carried out in this area with the objective of identifying the geochemical processes and their relation to groundwater quality. Groundwater samples were collected once a month from 43 groundwater wells in this area from January 1998 to July 1999. Sampling procedures and chemical analysis were carried out as per the standard methods. Chemical data are used for mathematical calculations and graphical plots to understand the chemical process and its relation to the groundwater quality. The chemical composition of groundwater in the central part of the study area mainly depends on the recharge from lakes and the river, which is explained by a mixing mechanism. In addition, weathering of silicate minerals controls the concentration of major ions such as sodium, calcium, magnesium and potassium in the groundwater of this area. Further, the activity ratios indicate that the groundwater is in equilibrium with kaolinite, smectite and montmorrillonite. The reverse ion exchange process controls the concentration of calcium, magnesium and sodium in hard rock formations, and dissolution of carbonate minerals and accessory minerals is the source of Ca and Mg, in addition to cation exchange in the sedimentary formations. In general, the chemical composition of the groundwater in this area is influenced by rock–water interaction, dissolution and deposition of carbonate and silicate minerals, ion exchange, and surface water interactions.  相似文献   

探地雷达衰减补偿逆时偏移成像方法   总被引：1，自引：1，他引：0       下载免费PDF全文

朱尉强  黄清华 《地球物理学报》2016,59(10):3909-3916

探地雷达信号在地下介质中传播时易受到电导率所产生的衰减影响,从而使得传统偏移成像结果在高衰减区域变得模糊.本文提出了衰减补偿的逆时偏移方法来消除电导率的影响.该方法基于麦克斯韦方程组实现电磁波的正演模拟和逆时传播.通过改变衰减项的正负号,保证了逆时传播的时间对称性,从而能够重构出原始波场,实现衰减补偿.数值实验比较了传统逆时偏移方法和衰减补偿逆时偏移方法在存在高导异常区域情况下的成像效果,结果证明了衰减补偿逆时偏移方法能够很好地恢复由电导率造成的信号衰减,从而提高探地雷达剖面的分辨率.  相似文献   

Generalized diffraction‐stack migration and filtering of coherent noise     

Ge Zhan  Wei Dai  Min Zhou  Yi Luo  Gerard T. Schuster 《Geophysical Prospecting》2014,62(3):427-442

We reformulate the equation of reverse‐time migration so that it can be interpreted as summing data along a series of hyperbola‐like curves, each one representing a different type of event such as a reflection or multiple. This is a generalization of the familiar diffraction‐stack migration algorithm where the migration image at a point is computed by the sum of trace amplitudes along an appropriate hyperbola‐like curve. Instead of summing along the curve associated with the primary reflection, the sum is over all scattering events and so this method is named generalized diffraction‐stack migration. This formulation leads to filters that can be applied to the generalized diffraction‐stack migration operator to mitigate coherent migration artefacts due to, e.g., crosstalk and aliasing. Results with both synthetic and field data show that generalized diffraction‐stack migration images have fewer artefacts than those computed by the standard reverse‐time migration algorithm. The main drawback is that generalized diffraction‐stack migration is much more memory intensive and I/O limited than the standard reverse‐time migration method.  相似文献   

中国大陆地区强震的逆向追踪方法研究     

刘文兵 《地震》2010,30(2):46-53

强震发生前, 震源附近的地震活动往往会呈现出一些空间和时间的异常特征, 分析和提取这些异常特征的方法较多。 本文采用了与常规强震预测方法迥异的地震预测方法地震活动反向追踪法(Reverse Tracing of Precursors, RTP), 对中国大陆近30年来的几个M_S≥7.5大震(含2008年5月12日汶川M_S8.0地震)进行了探索性的回溯研究。 结果表明, 该方法在中国大陆大震预测方面有一定的适用性, 并利用该方法对中国大陆地区的未来强震活动做了一定的预测。  相似文献   

Mitigation of reverse faulting deformation using a soil bentonite wall: Dimensional analysis,parametric study,design implications     

《Soil Dynamics and Earthquake Engineering》2016

Recent major seismic events, such as the Chi-Chi (1999) and the Wenchuan (2008) earthquakes occurred in Taiwan and China, have offered a variety of case histories on the performance of structures subjected to reverse faulting–induced deformation. A novel faulting mitigation method has recently been proposed, introducing a soft deformable wall barrier in order to divert the fault rupture away from the structure. This can be materialized by constructing a thick diaphragm-type soil bentonite wall (SBW) between the structure and the fault rupture path. The paper investigates the key parameters in designing such a SBW, aiming to mitigate the fault rupture hazard on shallow foundations. The paper employs a thoroughly validated finite element analysis methodology to explore the efficiency of a weak SBW barrier in protecting slab foundations from large tectonic deformation due to reverse faulting. A dimensional analysis is conducted in order to generalize the validity of the derived conclusions. The dimensionless formulation is then used to conduct a detailed parametric study, exploring the effect of SBW thickness w/H, depth H_SBWl/H, and shear strength τ_soil/τ_SBW, as well as the bedrock fault offset h/H, foundation surcharge load q/ρgB, and fault outcrop location s/B. It is shown that the wall thickness, depth, and shear strength should be designed on the basis of the magnitude of the bedrock fault offset, the location of the fault relative to the structure, and the shear strength of the soil. The efficiency of the weak barrier is improved using lower strength and stiffness material compared to the alluvium. A simplified preliminary design methodology is proposed, and presented in the form of a flowchart.  相似文献