Numerical investigation on the hydrodynamic performance of fast SWATHs with optimum canted struts arrangements     

《Applied Ocean Research》2017

Small Waterplane Area Twin Hulls (SWATHs) are known to have superior seakeeping performance but higher resistance compared to equivalent catamarans or mono-hulls. A way to improve their resistance characteristics is to use unconventional hull forms parametrically defined and optimized by CFD methods. This study builds on previous SWATH optimization studies proposing a comprehensive, systematic investigation on the effect of different shapes and canting angles of the struts. For the first time we demonstrate the importance of considering the shape of the strut that is fully parametrized in our study. The effect of the design speed on the best shape is addressed through a multi-objective optimization targeting the minimum total resistance at two very different speeds, namely the cruise and slow transfer speeds. Optimum hull shapes are discussed in terms of maximum resistance reduction, together with the predicted free waves patterns.  相似文献   

高水固化材料在南京铅锌银矿中的应用   总被引：3，自引：0，他引：3  

李兆平  张弥 《地质灾害与环境保护》1999,10(2):30-36

南京铅锌银矿是地下开采矿山,历史上遗留的大量采空区已严重威胁地面风景区的稳定,区内不断发生地面沉降、塌陷等地质灾害;１９８８年以后,采矿方法更改为分级尾砂充填法后,随之又带来对井下作业环境的污染;选矿后产生的尾泥直接排入长江,造成环境污染。在本项研究中,提出“用全尾砂加高水固化材料充填采空区和生产采场”方案,并进行工业性试验,效果良好,可解决上述三大问题。  相似文献   

Separation of multi-mode surface waves by supervised machine learning methods     

Jing Li  Yuqing Chen  Gerard T. Schuster 《Geophysical Prospecting》2020,68(4):1270-1280

Logistic regression, neural networks and support vector machines are tested for their effectiveness in isolating surface waves in seismic shot records. To distinguish surface waves from other arrivals, we train the algorithms on three distinguishing features of surface-wave dispersion curves in the domain: spectrum coherency of the trace's magnitude spectrum, local dip and the frequency range for a fixed wavenumber k in the spectrum. Numerical tests on synthetic data show that the kernel-based support vector machines algorithm gives the highest accuracy in predicting the surface-wave window in the domain compared to neural networks and logistic regression. This window is also used to automatically pick the fundamental dispersion curve. The other two methods correctly pick the low-frequency part of the dispersion curve but fail at higher frequencies where there is interference with higher-order modes.  相似文献   

小笠原1982年7月4日深震震源参数的确定     

赵明  臧绍先 《中国地震》1994,(4)

对利用全波理论地震图确定震源参数的方法进行研究，在原有的计算程序的基础上，增加了有限移动源效应，以确定破裂面；研究了理论合成地震图“时间窗”的选取及理论合成地震图起始的选取，使其更适用于震源研究。利用世界台网数字化记录，采用ＰＲＥＭ地球模型，确定小笠原１９８２年７月４日深震震源参数。结果表明，震源破裂面的倾向为Ｎ７５°Ｅ，倾角为１７°，走向为３４５°，接近Ｗａｄｉｔｉ－Ｂｅｎｉｏｆｆ带的走向，形成小倾角的正断层。震源破裂的结果有使介质沿水平方向伸展的趋势。  相似文献   

On the effects of petrographic composition on coalbed methane sorption     

Gareth R.L. Chalmers  R. Marc Bustin 《International Journal of Coal Geology》2007,69(4):288-304

The effect of petrographic composition on the methane sorption capacity has been determined for a suite of coals and organic-rich shales. Subbituminous and bituminous coals were separated into bright and dull lithotypes by hand-picking. The methane sorption capacities range between 0.5 and 23.9 cm³/g at a pressure of 6 MPa. The low volatile bituminous Canmore coal and the anthracite sample have the highest capacities with the “natural coke” having the lowest. For low-rank coals there is no significant difference between bright and dull samples except for one coal with the dull sample having a greater sorption capacity than its bright equivalent. For higher-rank coals, the bright samples have a greater methane capacity than the dull samples and the difference between sample pairs increases with rank. The boghead coal samples have the highest sorption capacities in the liptinite-rich coals suite and are higher than subbituminous to medium volatile bituminous samples. Pore size distribution indicates that methane is held as solution gas in liptinite-rich coals and by physical sorption in micropores in liptinite-poor coals. These contrasting processes illustrate that liptinite-rich samples need to be independently assessed. The positive relationship between reactive inertinite content and methane sorption capacity occurs within the subbituminous to medium volatile bituminous coals because the reactive inertinite is structurally similar to vitrinite and have a higher microporosity than non-reactive inertinite. Reactivity of inertinite should be assessed in CBM studies of dull coals to provide a better understanding of petrographic composition effects on methane capacity.  相似文献   

Nonlinear heave radiation forces on two-dimensional single and twin hulls     

Sangita Maiti  Debabrata Sen   《Ocean Engineering》2001,28(8):662

A study of nonlinear heave radiation of two-dimensional single and double hulls has been carried out in the time domain. The problem is analyzed by means of a fully nonlinear mathematical model, referred to as the mixed Eulerian–Lagrangian (MEL) model, which is based on an integral relation formulation coupled with time-integration of the nonlinear free-surface boundary conditions. The integral equation solver is based on a cubic-spline boundary-element scheme in which both potential and velocity continuity conditions can be enforced through the intersection points. The body undergoes periodic forced heave oscillation. By implementing effective wave-absorbing beaches at the two ends of the rectangular numerical tank, long-term steady-state force-histories could be achieved consistently in all computations.Results in terms of radiation forces for rectangular and triangular single- and twin-hull geometries are presented and discussed. Linear hydrodynamic forces in terms of added-mass and damping are validated for the rectangular hull. The Fourier-analyzed results reveal the extent of nonlinear (higher-order) components in the force-signals over different parameters which include the amplitudes of oscillation, hull-spacing for the twin-hulls and water depth.  相似文献   

Full‐wavefield migration: using surface and internal multiples in imaging          下载免费PDF全文

M. Davydenko  D.J. Verschuur 《Geophysical Prospecting》2017,65(1):7-21

Multiple scattering is usually ignored in migration algorithms, although it is a genuine part of the physical reflection response. When properly included, multiples can add to the illumination of the subsurface, although their crosstalk effects are removed. Therefore, we introduce full‐wavefield migration. It includes all multiples and transmission effects in deriving an image via an inversion approach. Since it tries to minimize the misfit between modeled and observed data, it may be considered a full waveform inversion process. However, full‐wavefield migration involves a forward modelling process that uses the estimated seismic image (i.e., the reflectivities) to generate the modelled full wavefield response, whereas a smooth migration velocity model can be used to describe the propagation effects. This separation of modelling in terms of scattering and propagation is not easily achievable when finite‐difference or finite‐element modelling is used. By this separation, a more linear inversion problem is obtained. Moreover, during the forward modelling, the wavefields are computed separately in the incident and scattered directions, which allows the implementation of various imaging conditions, such as imaging reflectors from below, and avoids low‐frequency image artefacts, such as typically observed during reverse‐time migration. The full wavefield modelling process also has the flexibility to image directly the total data (i.e., primaries and multiples together) or the primaries and the multiples separately. Based on various numerical data examples for the 2D and 3D cases, the advantages of this methodology are demonstrated.  相似文献   

基于精确震源函数的解调包络多尺度全波形反演   总被引：3，自引：3，他引：0       下载免费PDF全文

胡勇  韩立国  许卓  张天泽 《地球物理学报》2017,60(3):1088-1105

本文提出解调包络方法来重构地震记录中缺失的低频信号,同时该方法能够降低全波形反演的非线性程度;提出伴随状态震源函数反演方法来得到精确的震源函数,并推导了梯度计算公式;解调包络方法结合低通滤波技术,实现了从低频到高频的多尺度反演策略,有效缓解了全波形反演的周波跳跃问题.数值算例证明了解调包络、伴随状态震源函数反演方法和低通滤波多尺度反演策略的可行性及优越性.震源函数反演精度测试结果表明:即使观测记录在缺失低频信息的情况下,也能反演得到精确的震源函数.缺失低频测试和抗噪能力测试结果表明:即使地震数据中缺失9Hz以下的低频信号或者信噪比极低的情况下,利用反演得到的精确震源函数进行解调包络多尺度全波形反演,同样可以得到高精度的全波形反演结果.与Hilbert包络全波形反演对比结果表明:解调包络在重构低频和降低伴随震源主频方面具有一定优势.  相似文献   

2013年前郭M_S5.8震群矩张量研究          下载免费PDF全文

刘俊清  刘财  雷建设  甘卫军  杨清福  张晨侠 《地球物理学报》2017,60(9):3418-3431

2013年吉林前郭M_S5.8震群为爆发性震群,目前余震活动仍然在持续.基于吉林、辽宁、黑龙江、内蒙古四省地震台网记录的前郭震群波形资料,利用波形信噪比、震源类型、台站及速度模型组合的指标选择最佳的反演方案,应用矩张量的三种反演模式,对序列中5个M_S≥5.0地震进行矩张量反演研究,获得了全矩张量、偏矩张量和纯双力偶的矩张量.使用F-test对地震的三种模式的矩张量反演结果进行显著性检验来确定最佳反演模式.结果显示,5个地震的最优矩张量解均为全矩张量模式反演获得的结果,其双力偶分量仅有20%~65%,矩心深度位于地下3~4 km处,地震在Hudson震源类型图上的投影远离双力偶震源类型区域.这些结果表明,震源类型并非典型的构造地震,推断前郭地震可能是与人类活动有关的诱发地震.  相似文献   

基于各向异性全变分约束的多震源弹性波全波形反演          下载免费PDF全文

张盼  韩立国  巩向博  孙宏宇  毛博 《地球物理学报》2018,61(2):716-732

多震源编码技术可以提高全波形反演的计算效率,但同时会引入串扰噪声使反演结果质量降低. 全变分约束可以有效地压制层内噪声并突出模型界面,其与多震源技术的结合,能在大大提高弹性波全波形反演效率的同时提高反演质量. 本文提出了一种高效的动态多震源全波形反演策略,可以在离散串扰噪声的同时保证照明的均匀性. 根据残留串扰噪声的分布特征,构建了与之匹配的基于各向异性全变分约束的弹性波全波形反演方法. 为了减少周期跳跃效应,将基于稀疏约束的低频重构算法应用于弹性波地震记录,给出了利用快速梯度投影算法求解各向异性全变分约束的全波形反演流程. 模型数据测试结果表明本文的方法不仅能有效地抑制多震源方法导致的串扰噪声,同时也能降低观测数据中的噪声对反演结果的影响.  相似文献