Study on inelastic displacement ratio spectra for near-fault pulse-type ground motions

In displacement-based seismic design, inelastic displacement ratio spectra （IDRS） are particularly useful for estimating the maximum lateral inelastic displacement demand of a nonlinear SDOF system from the maximum elastic displacement demand of its counterpart linear elastic SDOF system. In this study, the characteristics of IDRS for near-fault pulse-type ground motions are investigated based on a great number of earthquake ground motions. The influence of site conditions, ratio of peak ground velocity （PGV） to peak ground acceleration （PGA）, the PGV, and the maximum incremental velocity （MIV） on IDRS are also evaluated. The results indicate that the effect of near-fault ground motions on IDRS are significant only at periods between 0.2 s - 1.5 s, where the amplification can approach 20%. The PGV/PGA ratio has the most significant influence on IDRS among the parameters considered. It is also found that site conditions only slightly affect the IDRS.

Improvement of Computation Method of Fault Motion Coordination Ratio and Analysis of Earthquake Cases

According to the concept of the fault motion coordination ratio( FCR),this paper discusses the effect of the starting point on the result of FCR calculation and puts forward the calculation method for FCR using the sliding window and the index for evaluating the dispersion. Earthquake cases analysis shows that at the Lijiang site across the fault: the FCR value varied greatly and its distribution was dispersive before the MS7. 0 Lijiang earthquake,while the value was stable and less dispersive after the earthquake,which reflects the strain accumulation of the fault during the seismogenic process and the poor movement coordination between the motion of the three components. After the earthquake,the fault was in a free activity state,the accumulated strain energy released, and the movement of the three components was coordinated mutually. At present,FCR dispersion of Lijiang is at a low value,and fault strain accumulation is at a low level.

Dynamic shear modulus of undisturbed soil under different consolidation ratios and its effects on surface ground motion

The dynamic shear modulus for three types of undisturbed soil under different consolidation ratios is presented by using the resonant column test method. Its effects on surface ground motion is illustrated by calculation. The test results indicate that the power function is a suitable form for describing the relationship between the ratio of the maximum dynamic shear modulus due to anisotropic and isotropic consolidations and the increment of the consolidation ratio. When compared to sand, the increment of the maximum dynamic shear modulus for undisturbed soil due to anisotropic consolidation is much larger. Using a one-dimensional equivalent linearization method, the earthquake influence factor and the characteristic period of the surface acceleration are calculated for two soil layers subjected to several typical earthquake waves. The calculated results show that the difference in nonlinear properties due to different consolidation ratios is generally not very notable, but the degree of its influence on the surface acceleration spectrum is remarkable for the occurrence of strong earthquakes. When compared to isotropic consolidation, the consideration of actual anisotropic consolidation causes the characteristic period to decrease and the earthquake influence factor to increase.

Relative energy zero ratio-based approach for identifying pulse-like ground motions

Pulse-like ground motions are capable of inflicting significant damage to structures. Efficient classification of pulse-like ground motion is of great importance when performing the seismic assessment in near-fault regions. In this study, a new method for identifying the velocity pulses is proposed, based on different trends of two parameters: the short-time energy and the short-time zero crossing rate of a ground motion record. A new pulse indicator, the relative energy zero ratio(REZR), is defined to qualitatively identify pulse-like features. The threshold for pulse-like ground motions is derived and compared with two other identification methods through statistical analysis. The proposed procedure not only shows good accuracy and efficiency when identifying pulse-like ground motions but also exhibits good performance for classifying records with high-frequency noise and discontinuous pulses. The REZR method does not require a waveform formula to express and fit the potential velocity pulses;it is a purely signal-based classification method. Finally, the proposed procedure is used to evaluate the contribution of pulse-like motions to the total input energy of a seismic record, which dramatically increases the seismic damage potential.

不同浓度离子溶液中气泡运动特性的实验研究

气泡运动特性可以分析流型形成和演化,是探究两相流模型构建的基础。为了进一步研究气泡在多种溶液内的运动特性,搭建了气泡运动特性实验平台。在3种浓度的FeCl_(3)、CaCl_(2)、NH_(4)Cl离子溶液及去离子水内,对单个气泡运动特性进行了实验研究,利用高速相机拍摄图片并导入MATLAB软件进行了计算。据此,分析了离子溶液内单个气泡的上升时间,脱离时间,初始当量直径,以及纵横比。结果表明:离子溶液,尤其是CaCl_(2)溶液在一定程度上可以促进气泡在喷嘴处的脱离,使得脱离时间减少,当喷嘴为1.5 mm时,促进作用最为明显;三种离子溶液和去离子水比较,气泡上升时间都有所缩短,但是相差不大;三种离子溶液中,FeCl_(3)溶液中气泡纵横比变化最大;NH_(4)Cl溶液对气泡的当量直径促进作用最强,CaCl_(2)溶液会抑制气泡当量直径的发展,因此在特殊流体机械内部,应适当增加钙离子以降低冲击带来的腐蚀与振动;在去离子水和三种离子溶液中气泡的纵横比δ都会有一个“L”型分布,且最大值均出现在气泡脱离喷嘴的瞬间。

基于注视特征的多因素飞行冲突探测策略研究

为研究不同空域复杂性条件下的飞行冲突探测策略,设计最小间距(MD)×汇聚角度(CA)×速度特性(SC)的被试内三因素重复测量实验方案,基于马尔科夫链的注视平稳分布概率和兴趣区注视时长分布特征,判断被试所采用的冲突探测策略并分析不同策略下的任务绩效指标。研究结果表明:在汇聚角度较大、最小间距更接近告警间隔的实验场景中,被试多采用距离-速度比(DV)策略;在汇聚角度较小、最小间距较小、航空器速度相同的实验场景中,被试多采用认知运动外推(CME)策略。多数情况下,采用CME策略判断飞行冲突的反应时更短、正确率更高。研究结果可为提高冲突探测的感知和预判能力提供参考。

旋转对置活塞发动机运动学特性研究

高功率密度发动机是未来内燃机的发展趋势.旋转对置活塞发动机结构简单,做功频率是传统往复式活塞发动机的两倍,可以显著提高发动机的理论功率密度,是小型无人机、混合动力系统的理想动力源.文中通过建立数学模型,探究了旋转对置活塞发动机的结构参数对活塞运动规律、气缸容积变化规律和压缩比的影响,分析了相邻活塞运动碰撞的边界条件.研究结果表明,活塞线速度对椭圆齿轮节曲线偏心率的变化最为敏感,当线速度大于平均值时,线速度与偏心率成正比,线速度小于平均值时则成反比;偏心率的增大可以减小气缸的余隙容积,且使下止点对应的气缸容积增大,进而调节发动机的压缩比;活塞端面夹角增大可以减小气缸的余隙容积;偏心率和活塞端面夹角在±10%的范围内变化时,压缩比相应的变化范围分别为5.62~12.04和5.01~23.45,当偏心率过大时将导致相邻活塞发生碰撞.

滚刀滑移状态下的受力与磨损仿真分析

为探究滚刀滑移状态下破岩的受力与磨损的变化规律,基于离散单元法,建立了同时考虑滚刀自转和绕刀盘公转的滚动圆周切割模型。定义了一个滑移率参数η用于描述滚刀的滑移状态,对不同滑移率工况下滚刀破岩受力和磨损进行了对比分析,并结合工程实例对数值仿真结论进行了验证,结果表明:数值仿真中垂直力F_(V)和滚动力F_(R)在CSM模型计算值附近波动,两者较为吻合,表明了本文模型的合理性。数值仿真结果表明,随着滑移率η的增大,垂直力F_(V)呈轻微减小趋势,滚动力F_(R)明显变大,从滚动破岩到滑动破岩,垂直力F_(V)降幅为23.6%,滚动力F_(R)增幅达83.7%,滑动破岩将导致滚刀偏磨。工程实测数据表明,刀盘上大量滚刀处于正常磨损状态时,主要表现为推力增大。大量滚刀处于偏磨状态时,主要表现为扭矩增大,其中偏磨滚刀占比19.05%和28.57%时,扭矩增幅分别为55.85%和261.51%。滚刀正常磨损和偏磨均大量存在时,表现为扭矩推力同步增大,其中偏磨滚刀占比21.43%时,扭矩增幅为80.89%。数值仿真和实测数据表现出较高的一致性。综合4次开仓换刀结果,可将刀盘扭矩增幅超过50%作为判定大量滚刀发生偏磨的重要依据。

基于地震动反应谱与傅里叶谱确定场地卓越频率的差异性

强震动记录的HVSR法常用于评估场地卓越频率,计算强震动记录HVSR时常采用加速度反应谱或加速度傅里叶谱,但两者会给出不同的评估值。为揭示反应谱比和傅里叶谱比评估场地卓越频率的差异,本文选取日本KiK-net台网中场地条件可近似为一维场地模型的16个台站,以其获取的强震动记录开展场地卓越频率研究。首先提出了评估场地卓越频率的数据处理方法,主要包括S波截取、Taper预处理、基于高斯拟合的自动寻峰。探讨并给出了阻尼比、平滑的带宽系数取值对场地卓越频率评估的影响规律;对反应谱阻尼比取10%,对傅里叶谱平滑的带宽系数取20~40之间获取的场地卓越频率较为准确。然后对比分析了利用地震动加速度反应谱比和傅里叶谱比得到的场地卓越频率与场地土层模型计算得到的基于传递函数的自振频率。研究结果表明,对大多数台站而言,采用傅里叶谱比计算场地卓越频率具有明显的优势,对于Ⅱ、Ⅲ、Ⅳ类场地上的台站均有如此结论,只有对少数特定台站,采用反应谱比方法效果更好。

近场地震动竖向与水平分量统计特性对比

为研究近场地震动竖向与水平分量特性,本文对PEER数据库中1202组近场强震的地震动进行统计分析,研究了竖向水平加速度峰值比PGAv/PGAh、反应谱之比Sav(T)/Sah(T)、竖向水平峰值到达时间的特性。讨论了PGAv/PGAh与断层距、场地条件、震源机制的关系,并采用对数正态分布拟合不同场地条件、不同震源机制的PGAv/PGAh分布;对比了不同断层距、不同场地条件Sav(T)/Sah(T)的变化规律;研究了近场强震水平竖向分量峰值加速度的大小和到达时间上的相关性,并对结构分析过程中竖向地震动的选择提出建议。结果表明:断层距、场地条件、震源机制都会影响近场地震动的竖向分量,断层距小、走滑断层、场地条件差都易产生较大的竖向地震动;断层距小、场地条件差时,地震动竖向分量高频成分越强,断层距大、场地条件好,竖向地震动低频成分越强;竖向分量峰值加速度的大小与到达时间和两正交水平分量峰值加速度的大小与到达时间的几何平均数有明显的线性关系。

一种基于改进SIFT的视频稳像方法

为提高计算效率并保持良好的稳像效果,本文提出一种基于改进SIFT的视频稳像方法。首先对SIFT进行改进,并命名为BO-SIFT(Binarized Octagonal SIFT)。该算法引入了同心八边形环特征描述子,通过降维和二值化对特征向量进行处理,然后使用汉明距离进行特征点匹配,有效缩短了描述和匹配时间。其次将BO-SIFT算法应用于视频稳像,提取视频帧的特征点进行匹配,并计算出帧与帧之间的运动偏移量,以此实现运动估计。最后采用卡尔曼滤波器对估计出的运动偏移量进行平滑处理,并利用仿射变换对视频帧进行逆向补偿,从而得到稳定的图像序列。实验结果表明:相较于原始的SIFT算法,BO-SIFT算法使稳像时间减少了56.404%;相较于现有的较好算法,BO-SIFT算法稳像后的视频具有更高的平均峰值信噪比。此外,本文算法在不同视频上进行稳像效果测试,也具有一定的可靠性和优越性。

SolidWorks运动分析在周转轮系传动比计算教学中的应用研究

周转轮系传动比计算是机械基础教学中的重点与难点内容,其计算原理较为抽象,过程也比较复杂,学生不易掌握.为更简捷高效地求解周转轮传动比,应用SolidWorks建立了周转轮系各零件模型,并完成了仿真模型装配.在SolidWorks运动分析组件下模拟了周转轮系的运动过程,并依据模拟结果计算出了具有复杂结构的周转轮系传动比.模拟结果与理论计算结果比较接近,证明使用此方法计算周转轮系传动比是可行的.

结构特性对基础隔震结构隔震层响应的影响

明确结构特性的改变对基础隔震结构响应的影响可为近场地区基础隔震结构的设计提供指导。通过分析基础隔震结构隔震层的阻尼比、原始结构与隔震结构的频率比、上部结构与隔震层的质量比,探讨结构参数变化对基础隔震结构响应的影响问题。分析结果表明结构参数改变,不影响基础隔震结构隔震层反应谱的谱型,但会对谱值产生一定的影响,同时给出了周期比的范围及质量比的要求,为基础隔震结构的设计提供了建议。

地震作用下山体地形地震动偏振效应研究

基于汶川M_(S)8.0地震后在窦圌山坡顶和坡脚测点获得的9次余震记录,通过基线校正、滤波处理,得到各余震记录的傅里叶谱谱比及质点运动轨迹图,结果表明山体的自振频率具有多阶段性,其最大位移方位会出现在山体的横向或走向上,且山体存在偏振效应。将9次余震东西向和南北的水平向加速度时程以10°为单位进行分解得到324条新的时程曲线,基于分解合成后的时程记录,将坡顶与坡脚相同分解角度下的时程作比值,对其峰值加速度比和傅里叶谱谱比进行分析,结果表明二者最大值所在的方位均与山体最大位移所在的方位相同。结合9次余震坡脚测点的傅里叶谱分析可知,各输入地震动频率成分丰富的频段有所不同,低频段容易激发山体的低阶振型,导致山体在横向上发生偏振;高频段容易激发山体的高阶振型,导致山体在走向上发生偏振;当二者同时存在时,山体会同时产生低阶和高阶偏振效应。

冲击螺杆钻具结构设计与参数优化

为了高效钻进硬岩地层,将螺杆钻具的大扭矩与轴向冲击工具的高频低幅冲击特性相结合,研制了一种冲击螺杆钻具。在工具结构原理讨论的基础上,建立了轴向冲击短节的冲锤运动控制方程,分析了冲锤的运动特性,并以工具冲击功和最大能量利用率为评价指标,采用正交试验方法对主要工具结构参数进行了优化研究。研究结果表明:冲锤往复运动过程为加速度逐渐减小的非线性加速运动,节流喷嘴直径和冲锤运动行程是影响冲击功的主要因素,而冲锤质量、承压面积和腔体通孔面积是次要因素。节流喷嘴直径和冲锤承压面积是影响最大能量利用率的主要因素;而冲锤运动行程、冲锤质量和腔体通孔面积是次要因素。所得结论可为对冲击螺杆钻具的进一步优化设计和现场应用提供参考。

基于相机运动轨迹的鲁棒无人机航拍稳像算法

针对高空颠簸环境影响无人机采集延时稳定图像问题,提出了一种适用于悬停拍摄及移动拍摄的航拍视频防抖算法。通过无人机摄像头获取延时摄影视频,提取全局范围内的部分视频帧进行直方图分布比较,进而确定视频是否是在无人机移动状态下拍摄的,并将视频划分为包含与不包含摄像机主动运动两类。对于包含摄像机主动运动的一类,首先,采用FAST角点检测加光流法进行特征点提取配对;其次,利用RANSAC算法剔除误匹配特征点并进行摄像机运动轨迹估计;最后,利用高斯滤波对运动估计参数进行平滑以得到稳定的摄像机运动轨迹。对于不包含摄像机主动运动的一类,首先,对首帧进行网格划分并基于Harris矩阵提取各网格的特征点;其次,在后续帧对这些特征点进行光流追踪;再次,通过反向光流及Harris矩阵计算,增加特征点约束,完成特征点提取及匹配;最后,利用保留的特征点估计后续帧至首帧的稳定变换。利用该算法对视频进行场景分类及画面稳定,实验结果表明:视频分类模块能正确区分两类视频;对比其他两种方法,稳定后的视频图像平均峰值信噪比提升更大;对于不含摄像机主动运动的视频,可实现画面绝对稳定,图像平均峰值信噪比提升超过39%,而其他两种方法仅提升10%~12%。

基于强震记录的大阪盆地竖向地震动的放大效应研究

文章基于日本KIK-net强震观测台网,分离大阪盆地水平向与竖向分量S波和盆地次生波,并为研究竖向地震动与水平向的关系,采用井上井下谱比法分析。研究表明,盆地中竖向分量S波和盆地次生波放大倍数虽整体小于水平分量,但在不同周期内不同盆地深度竖向S波、次生波放大均有超抗震设计时,竖向地震动峰值取水平峰值的最大值2/3;盆地S波与次生波对浅层土层竖向地震动的影响明显大于深层土层,并且在长周期中影响逐渐增大。

Effect of seawater on incident plane P and SV waves at ocean bottom and engineering characteristics of offshore ground motion records off the coast of southern California, USA

The effect of seawater on vertical ground motions is studied via a theoretical method and then actual offshore ground motion records are analyzed using a statistical method. A theoretical analysis of the effect of seawater on incident plane P and SV waves at ocean bottom indicate that on one hand, the affected frequency range of vertical ground motions is prominent due to P wave resonance in the water layer if the impedance ratio between the seawater and the underlying medium is large, but it is greatly suppressed if the impedance ratio is small; on the other hand, for the ocean bottom interface model selected herein, vertical ground motions consisting of mostly P waves are more easily affected by seawater than those dominated by SV waves. The statistical analysis of engineering parameters of offshore ground motion records indicate that:(1) Under the infl uence of softer surface soil at the seafl oor, both horizontal and vertical spectral accelerations of offshore motions are exaggerated at long period components, which leads to the peak spectral values moving to a longer period.(2) The spectral ratios(V/H) of offshore ground motions are much smaller than onshore ground motions near the P wave resonant frequencies in the water layer; and as the period becomes larger, the effect of seawater becomes smaller, which leads to a similar V/H at intermediate periods(near 2 s). These results are consistent with the conclusions of Boore and Smith(1999), but the V/H of offshore motion may be smaller than the onshore ground motions at longer periods(more than 5 s).

Seismic ground motion variations resulting from site conditions

Amplification of seismic ground motions in the territory of Almaty city is evaluated by using different methods. The pattern and probable causes of ground motion variations in different engineering-geological conditions are characterized. An expeditious application of these techniques within a complex methodical approach for Almaty city microzonation is considered.

Engineering characteristics of near-fault vertical ground motions and their effect on the seismic response of bridges

A wide variety of near-fault strong ground motion records were collected from various tectonic environments worldwide and were used to study the peak value ratio and response spectrum ratio of the vertical to horizontal component of ground motion, focusing on the effect of earthquake magnitude, site conditions, pulse duration, and statistical component. The results show that both the peak value ratio and response spectrum ratio are larger than the 2/3 value prescribed in existing seismic codes, and the relationship between the vertical and horizontal ground motions is comparatively intricate. In addition, the effect of the near-fault ground motions on bridge performance is analyzed, considering both the material nonlinear characteristics and the P-A effect.