Effect of thickness of planar nozzles on erosion depth of levee soils subjected to plunging water

In this study, the effect of the thickness of a planar jet on the erosion depth when the jet impinges on a surface composed of cohesive soil was analytically and numerically evaluated. The results showed that the erosion depth was practically independent of the nozzle thickness for erosion depths shallower than the potential core length (i.e. the region of the jet in which the central flow velocity is the same as the nozzle velocity). The relation between nozzle thickness and erosion depth was non-linear with continuously variable slope for erosion depths deeper than the potential core length. Finally, the relation was approximately linear when the erosion depth converged to the equilibrium erosion depth. The findings of this study indicate that direct and fast prediction of the erosion depth in the field is possible using the data from a small scale soil erosion test with similar flow velocities.     

Development and evaluation of a storm surge warning system in Taiwan

An operational storm surge forecasting system aimed at providing warning information for storm surges has been developed and evaluated using four typhoon events. The warning system triggered by typhoon forecasts from Taiwan Cooperative Precipitation Ensemble Forecast Experiment (TAPEX) has been executed with two storm surge forecasting scenarios with and without tides. Three numerical experiments applying different meteorological inputs have been designed to assess the impact of typhoon forcing on storm surges. One uses synthetic wind fields, and the others use realistic wind fields with and without adjustments to the initial wind fields for the background circulation. Local observations from Central Weather Bureau (CWB) weather stations and tide gauge stations are used to evaluate the wind fields and storm surges from our numerical experiments. The comparison results show that the accuracy of the storm surge forecast is dominated by the track, the intensity, and the driving flow of a typhoon. When the structure of a typhoon is disturbed by Taiwan’s topography, using meteorological inputs from real wind fields can result in a better typhoon simulation than using inputs from synthetic wind fields. The driving flow also determines the impact of topography on typhoon movement. For quickly moving typhoons, storm forcing from TAPEX is reliable when a typhoon is strong enough to be relatively unaffected by environmental flows; otherwise, storm forcing from a sophisticated typhoon initialization scheme that better simulates the typhoon and environmental flows results in a more accurate prediction of storm surges. Therefore, when a typhoon moves slowly and interacts more with the topography and environmental flows, incorporating realistic wind fields with adjustments to the initial wind fields for the background circulation in the warning system will obtain better predictions for a typhoon and its resultant storm surges.     

Study and application of PS-wave pre-stack migration in HTI media and an anisotropic correction method

Anisotropy correction is necessary during the processing of converted PSwave seismic data to achieve accurate structural imaging, reservoir prediction, and fracture detection. To effectively eliminate the adverse effects of S-wave splitting and to improve PSwave imaging quality, we tested methods for pre-stack migration imaging and anisotropic correction of PS-wave data. We based this on the propagation rules of seismic waves in a horizontal transverse isotropy medium, which is a fractured medium model that reflects likely subsurface conditions in the field. We used the radial (R) and transverse (T) components of PS-wave data to separate the fast and slow S-wave components, after which their propagation moveout was effectively extracted. Meanwhile, corrections for the energies and propagation moveouts of the R and T components were implemented using mathematical rotation. The PS-wave imaging quality was distinctly improved, and we demonstrated the reliability of our methods through numerical simulations. Applying our methods to three-dimensional and three-component seismic field data from the Xinchang-Hexingchang region of the Western Sichuan Depression in China, we obtained high-quality seismic imaging with continuous reflection wave groups, distinct structural features, and specific stratigraphic contact relationships. This study provides an effective and reliable approach for data processing that will improve the exploration of complex, hidden lithologic gas reservoirs.     

Oceanic plate subduction history in the western Pacific Ocean: Constraint from late Mesozoic evolution of the Tan-Lu Fault Zone

The NE- to NNE-striking Tan-Lu Fault Zone (TLFZ) is the largest fault zone in East China, and a typical representative for the circum-Pacific tectonics. Its late Mesozoic evolution resulted from subduction of the Paleo-Pacific Plate, and can be used for indication to the subduction history. The TLFZ reactivated at the end of Middle Jurassic since its origination in Middle Triassic. This phase of sinistral motion can only be recognized along the eastern edge of the Dabie-Sulu orogenis, and indicates initiation of the Paleo-Pacific (Izanagi) Plate subduction beneath the East China continent. After the Late Jurassic standstill, the fault zone experienced intense sinistral faulting again at the beginning of Early Cretaceous under N-S compression that resulted from the NNW-ward, low-angle, high-speed subduction of the Izanagi Plate. It turned into normal faulting in the rest of Early Cretaceous, which was simultaneous with the peak destruction of the North China Craton caused by backarc extension that resulted from rollback of the subducting Izanagi Plate. The TLFZ was subjected to sinistral, transpressive displacement again at the end of Early Cretaceous. This shortening event led to termination of the North China Craton destruction. The fault zone suffered local normal faulting in Late Cretaceous due to the far-field, weak backarc extension. The late Mesozoic evolution of the TLFZ show repeated alternation between the transpressive strike-slip motion and normal faulting. Each of the sinistral faulting event took place in a relatively short period whereas every normal faulting event lasted in a longer period, which are related to the subduction way and history of the Paleo-Pacific Plates.     

基于贝叶斯方法的深层充电效应风险模型评估

高能电子穿透航天器并在其内部沉积电荷从而引发深层充电效应,是导致卫星故障的重要因素之一.为了评估深层充电效应诱发卫星异常的风险,本文基于贝叶斯方法,使用一颗地球同步轨道卫星的异常数据和GOES-8卫星的电子通量探测数据,计算了不同能量阈值及累积时间的电子注量、不同卫星配置下模拟仿真的沉积电荷,并分别与卫星异常建立一系列概率风险模型.本文从模型中随机抽样得到模拟异常,并与实测异常构造混淆矩阵以评估模型拟合优度,结果表明1.0MeV电子3日累积注量-卫星异常概率风险模型为该卫星最优模型.本文利用最优模型对该卫星深层充电效应风险进行了计算,在1.0MeV电子3日累积注量达到2.0×10~(10)cm~(-2)·sr~(-1)时,该卫星发生深层充电异常的平均后验概率为27%,且95%最小可信值为22%.根据最优模型,我们对该卫星最可能导致异常的部件的材料和结构等特征做出了推断.     

面向目标的起伏地表组合震源延时参数计算方法

组合震源技术通过调节延迟激发时间和震源埋藏深度能够实现地震波场的定向传播,提高地震波的照明能量和地震数据信噪比.然而,目前国内外对基于特定目标的组合震源最佳聚焦方向的选取以及起伏地表组合震源定向理论的研究相对较少.在聚焦方向选取方面,目前基本是利用多种不同延时参数的组合震源分别进行试验,从而确定较好的组合震源延时参数.本文则利用爆炸反射面原理,在目的层界面上均匀布置震源同时激发地震波,能够产生垂直于地层界面传播的平面波,当初至波传播至地表时进行地表方向统计.根据互易性原理,以初至波传播方向的反方向为聚焦方向,激发产生的地震波主波束方向将垂直入射到目的层界面上,从而精确的计算出组合震源的最佳聚焦方向.在组合震源定向方面,目前主要是利用组合震源方向因子公式进行计算,但该方法要求震源布置在同一条直线上,并不能满足起伏地表的应用要求.本文以惠更斯-菲涅尔原理为理论基础,提出通过炮点向量在聚焦方向上的投影来确定组合震源传播至虚拟波前的走时,从而确定任意起伏地表组合震源的延迟激发时间.该方法不仅能够计算出沿给定地质模型的目的层界面垂直入射的组合震源聚焦方向,也能够确定任意起伏地表情况下形成沿该聚焦方向定向传播地震波场的组合震源延迟激发时间.因此,本文提出的面向目标的起伏地表组合震源延时参数计算方法对组合震源数据采集具有理论与实践意义.     

Seafloor topography and landform characteristics of Zengmu Shoal waters and their evolvement

The topography data of the Zengmu Shoal and its adjacent area are acquired by the SeaBat-8111 multibeam system.The full survey covering over the Zengmu Shoal area gives us new knowledge about the area. It is a flat underwater platform consisting ofcoral reefs, its fathom line is like a trap in near SN direction and its shape is like an isosceles triangle with the acute angle pointing to the north. The east and west sides ofthe shoal are steep while its south side is more gentle. As viewed from geological evolution, the Zengmu Shoal is a typical biologic coral landform caused by tectonic uplift.     

Modeling of an actively braced full‐scale building considering control–structure interaction

Recently, the application of active control to seismic‐excited buildings has attracted international attention. To demonstrate the practical applicability of active control, we have conducted experimental tests using a full‐scale three‐storey building equipped with active bracing systems on the shake table at the National Center for Research on Earthquake Engineering (NCREE), Taiwan. Experimental results indicate that the control–structure interaction (CSI) effect is significant. A state‐space analytical model of this actively controlled building taking into account the CSI effect is established in this paper using a system identification technique based on curve‐fitting of transfer functions. To verify the accuracy of the analytical model for simulating the controlled response, four sets of linear quadratic Gaussian (LQG) controllers using acceleration feedback are designed and further experimental tests are conducted for comparison. It is demonstrated that the correlations between the simulation and experimental results are remarkable. The construction of an accurate analytical model is important for active control, and such an analytical model can be used for future benchmark studies of different control algorithms based on numerical simulations. Copyright © 2000 John Wiley & Sons, Ltd.