川滇地区陆态网络基准站运动噪声模型分析

基于陆态网络GNSS基准站资料,文章利用极大似然估计方法对川滇地区的基准站运动噪声进行了研究.通过对“白噪声”、“白噪声+闪烁噪声”、“白噪声+随机游走噪声”以及“白噪声+幂指噪声”等四种噪声模型的比较,发现川滇地区的基准站运动噪声可以较好地由“白噪声+闪烁噪声”或“白噪声+幂指噪声”模型来描述.在进行基准站速率估计时,相对于“白噪声+闪烁噪声”模型,仅用白噪声模型会使误差估计过于乐观,且会产生一定的速率偏差.因此,在川滇地区利用基准站资料进行地壳运动与变形分析时,除了扣除基准站的周期性运动之外,还需要考虑其对应的噪声组合模型.     

基于GIS的遥感影像管理技术研究

结合黑龙江省国土资源遥感信息管理系统的建设,阐述海量影像无缝数据库管理系统实现的关键技术,包括海量遥感影像的快速显示和查询,以及影像管理中一些辅助功能的开发实现,从而实现了一个多时态、多尺度、多分辨率、多数据源、多种类的遥感影像数据库系统,并且满足遥感影像、矢量和属性数据的高效存储要求。     

甘肃省区域发展的资源环境基础评价

应用资源环境要素综合评价指标,选取决定区域社会经济发展最为关键的5大资源,对甘肃省经济社会发展的资源环境基础及其相互协调状态进行了测算评价。结果表明:①甘肃省资源环境要素的自然禀赋状况薄弱,且要素空间组合结构不合理;资源结构的稳定性差,生态系统脆弱,尤其是水资源,成为制约经济社会发展的关键因子。②目前,甘肃省人地关系演进状态系数较低,多年平均值为0.0337,然而,随着人口增长与经济发展,加之本来脆弱的生态系统的硬性约束,未来人地关系协调状况将进入全面紧张阶段,到2020年人地关系演进状态系数将达到0.2577。③区域发展政策的相应调整和自身发展能力的提升是实现经济社会与资源环境协调发展的必然要求。     

交通路况基态修正模型及其效率分析

 交通路况在时间上和空间上具有连续变化的特征,在时空维度上对交通路况进行高分辨率采样得到的数据,对研究交通路况的时空动态十分有利。但长时间大范围的高分辨率交通路况信息数据量巨大,给数据的组织和管理带来了困难。目前,尚没有一种成熟的时空数据模型对高时空分辨率交通路况数据进行高效(顾及数据存储与访问效率)的组织管理。本文提出一种基于线性参照系统的交通路况基态修正模型。此模型应用基态修正模型的基本思想,在时间维度上对交通路况数据进行无损压缩,又引入动态分段技术和线性参照系统,以路划作为交通路况载体,在空间维度上对交通路况数据进行压缩存储。利用成都市区真实交通路况数据,本文验证了此模型的有效性,比较了6种不同参数下交通路况基态修正模型的存储和访问效率,给出了最佳模型建议。     

Horizontal floor response spectra of base‐isolated buildings due to vertical excitation

A mechanism of horizontal floor response spectra amplification in the vicinity of higher modes' frequencies is investigated. It is demonstrated, by means of a simple two‐degrees‐of‐freedom model, that in the case of unsymmetrical superstructure, such amplification may occur because of the coupling between vertical excitation and horizontal response of the non‐isolated modes. This phenomenon is further illustrated by the results of analyses of a model of a nuclear plant. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of near‐fault ground motions on the nonlinear dynamic response of base‐isolated r.c. framed buildings

Near‐fault ground motions are characterized by long‐period horizontal pulses and high values of the ratio between the peak value of the vertical acceleration, PGA_V, and the analogous value of the horizontal acceleration, PGA_H, which can become critical for base‐isolated (BI) structures. The objective of the present work is to check the effectiveness of the base isolation of framed buildings when using High‐Damping‐Rubber Bearings (HDRBs), taking into consideration the combined effects of the horizontal and vertical components of near‐fault ground motions. To this end, a numerical investigation is carried out with reference to BI reinforced concrete buildings designed according to the European seismic code (Eurocode 8). The design of the test structures is carried out in a high‐risk region considering (besides the gravity loads) the horizontal seismic loads acting alone or in combination with the vertical ones and assuming different values of the ratio between the vertical and horizontal stiffnesses of the HDRBs. The nonlinear seismic analysis is performed using a step‐by‐step procedure based on a two‐parameter implicit integration scheme and an initial‐stress‐like iterative procedure. At each step of the analysis, plastic conditions are checked at the potential critical sections of the girders (i.e. end sections of the sub‐elements in which a girder is discretized) and columns (i.e. end sections), where a bilinear moment–curvature law is adopted; the effect of the axial load on the ultimate bending moment (M‐N interaction) of the columns is also taken into account. The response of an HDRB is simulated by a model with variable stiffness properties in the horizontal and vertical directions, depending on the axial force and lateral deformation, and linear viscous damping. Copyright © 2011 John Wiley & Sons, Ltd.     

Experimental simulation of base‐isolated buildings pounding against moat wall and effects on superstructure response

Base‐isolated buildings are typically important facilities expected to remain functional after a major earthquake. However, their behavior under extreme ground shaking is not well understood. A series of earthquake simulator experiments were performed to assess performance limit states of seismically isolated buildings under strong ground motions, including pounding against a moat wall. The test setup consists of a quarter scale three‐story frame isolated at the base with friction pendulum bearings and a moat wall model. An effort was made to properly scale the strength and the stiffness of the frame relative to the bearings properties from a professionally designed isolated three‐story steel intermediate moment‐resisting frame so that realistic yielding mechanisms can be observed. The moat wall was modeled as either a rigid triangle steel stopper or a concrete wall of various thicknesses with soil backfill. The moat wall gap was set to various displacement increments to examine the sensitivity of this parameter and also to assess the effects of impact on the superstructure at different velocities. The test results indicate that the contact forces are largely dependent on the gap distance, impact velocity and wall flexibility and, in extreme cases, pounding can induce yielding in the superstructure. Copyright © 2012 John Wiley & Sons, Ltd.     

The cause of unproportionately large higher mode contributions in the inelastic seismic responses of high‐rise core‐wall buildings

In the conventional seismic design of high‐rise reinforced concrete core‐wall buildings, the design demands such as design shear and bending moment in the core wall are typically determined by the response spectrum analysis procedure, and a plastic hinge is allowed to form at the wall base to limit the seismic demands. In this study, it is demonstrated by using a 40‐story core‐wall building that this conventional approach could lead to an unsafe design where the true demands—the maximum inelastic seismic demands induced by the maximum considered earthquake—could be several times greater than the design demands and be unproportionately dominated by higher vibration modes. To identify the cause of this problem, the true demands are decomposed into individual modal contributions by using the uncoupled modal response history analysis procedure. The results show that the true demands contributed by the first mode are reasonably close to the first‐mode design demands, while those contributed by other higher modes are much higher than the corresponding modal design demands. The flexural yielding in the plastic hinge at the wall base can effectively suppress the seismic demands of the first mode. For other higher modes, however, a similar yielding mechanism is either not fully mobilized or not mobilized at all, resulting in unexpectedly large contributions from higher modes. This finding suggests several possible approaches to improve the seismic design and to suppress the seismic demands of high‐rise core‐wall buildings. Copyright © 2012 John Wiley & Sons, Ltd.     

Digital system for recording fish echoes

A system to record digitised echo information from echo sounders has been developed as part of a project to improve methods of estimating the abundance of fish stocks around New Zealand. The depth of echoes appearing at the echo‐sounder receiver is determined, followed by a sequence of samples of the echo envelope defining its shape. All data are digitised and recorded on a seven‐track digital magnetic tape recorder. The system is designed to preserve as much information about the echoes as possible. In contrast to other published systems designed to either “count” or “integrate” fish echoes, this system allows free choice of methods of analysis.     

Installation of ocean bottom bases for observation of seafloor crustal movement

Abstract

Ocean bottom bases (OBBs) have been installed on both sides of the axis of the Sagami Trough east of the Izu Peninsula, central Japan, as the first step toward long‐term geodetic and geophysical observations at the plate boundary (subduction zone). The OBB is a platform for seafloor measurements; otherwise it is difficult to find an appropriate place for precise seafloor measurements in the subduction zones. It is made of a nonmagnetic concrete block of size 1100 × 1100 × 500 mm. It was lowered from a ship using a winch wire and installed on a predetermined place with its position being monitored by an acoustic transponder system and a 30‐kHz bottom pinger with an accuracy of about 2 m.

It was confirmed later during the divings on board the submersible Shinkai 2000 that the OBB was installed on a flat mud bottom in normal condition. No change has been recognized in the installation condition in 3 years; the OBB is stable enough to be used for acoustic range measurements on the seafloor as well as for several geophysical measurements.

The resolution of seafloor range measurement can be improved by two orders by using phase measurement techniques with the aid of pulse compression. Precise acoustic range measurement of the order of 10^?5 is feasible under the following conditions: two‐way measurements between the two OBBs installed on the slope facing each other with angles larger than 1.5°. Correction is necessary for the effect of long‐term temperature variation.