低频检波器频谱补偿算法建模及仿真

采用数值仿真的方法建立了动圈式检波器的仿真模型,推导检波器传递函数,通过对实际动圈式检波器频率特性的测试,验证了动圈式检波器数值仿真模型的正确性,分析动圈检波器频率响应特性,分别对动圈式检波器的自然频率、灵敏度、阻尼比进行仿真,对不同自然频率、灵敏度、阻尼比对检波器输出频率特性的影响进行了分析,使用二阶二次型反馈补偿方法,设计检波器低频补偿结构,结果表明:数值仿真模型与实际检波器的频率响应一致,补偿结构使检波器自然频率由2 Hz降低至0.2 Hz.     

IM‐based and EDP‐based decision models for the verification of the seismic collapse safety of buildings

Decision models for the verification of seismic collapse safety of buildings are introduced. The derivations are based on the concept of the acceptable (target) annual probability of collapse, whereas the decision making involves comparisons between seismic demand and capacity, which is familiar to engineering practitioners. Seismic demand, which corresponds to the design seismic action associated with a selected return period, can be expressed either in terms of an intensity measure (IM) or an engineering demand parameter (EDP). Seismic capacity, on the other hand, is defined by dividing the near‐collapse limit‐state IM or EDP by an appropriate risk‐targeted safety factor (γ _im or γ _edp ), which is the only safety factor used in the proposed decision model. Consequently, the seismic performance assessment of a building should be based on the best possible estimate. For a case study, it is shown that if the target collapse risk is set to 10^?4 (0.5% over a period of 50 years), and if the seismic demand corresponds to a return period of 475 years (10% over a period of 50 years), then it can be demonstrated that γ _im is approximately equal to 2.5 for very stiff buildings, whereas for buildings with long periods the value of γ _im can increase up to a value of approximately 5. The model using γ _edp is equal to that using γ _im only if it can be assumed that displacements, with consideration of nonlinear behavior, are equal to displacements from linear elastic analysis.     

新型预制装配式楼盖抗倒塌试验研究

地震及爆炸荷载下的结构连续倒塌问题对人民的生命财产造成重大威胁,是土木工程领域研究的一个热门方向。为了提高新型预应力空心楼板结构的整体性,防止由于竖向支承构件的失效形成楼板的局部或者连续倒塌,对2块新型预应力空心板足尺模型进行四分点静力加载试验,研究新型预制装配式两跨连续楼板的抗连续倒塌能力。试件均由预应力空心短板通过板端伸出U形筋和胡子筋进行对接连接,板侧纵向拼缝通过胡子筋和植筋与边梁的纵筋进行连接,2个试件的计算跨度相同。本文采用在加载过程中突然拆除中间支座,得到楼板破坏形态、裂缝发展、承载能力、应变、最大变形等试验结果。对试件的受力过程、悬索作用机理进行分析,最后得到楼盖拼缝及板侧边梁连接构造的布置合理,新型预制装配式楼盖采用合适的周边连系和横向拼缝连接可以达到理想的抗倒塌能力。     

不同柱梁抗弯承载力比对框架结构抗倒塌性能的影响

设计不同柱梁抗弯承载力比(ηc-bua)的5个纤维增强混凝土(FRC)框架结构及3个钢筋混凝土(RC)框架结构,利用性能评估软件Perform-3D进行Pushover及IDA计算分析,得出其破坏机制及易损性曲线。结果表明,柱、梁端部局部采用FRC后,承载力有一定提高,峰值位移有较大提高;ηc-bua对FRC框架结构的破坏机制影响很大;ηc-bua对FRC框架结构地震反应也有一定的影响,其比值越大,超越概率越小,且随期望破坏程度的加重,这种影响也趋于明显,当ηc-bua在1.2以上时,结构的倒塌概率均小于10%,满足大震不倒的概率要求。     

Location and probability of shoal margin collapses in a sandy estuary

Channel bank failure, and collapses of shoal margins and beaches due to flow slides, have been recorded in Dutch estuaries for the past 200 years but have hardly been recognized elsewhere. Current predictions lack forecasting capabilities, because they were validated and calibrated for historic data of cross‐sections in specific systems, allowing local hindcast rather than location and probability forecasting. The objectives of this study were to investigate where on shoal margins collapses typically occur and what shoal margin collapse geometries and volumes are, such that we can predict their occurrence. We identified shoal margin collapses, generally completely submerged, from bathymetry data by analyzing digital elevation models of difference of the Western Scheldt for the period 1959–2015. We used the bathymetry data to determine the conditions for occurrence, specifically to obtain slope height and angle, and applied these variables in a shoal margin collapse predictor. We found 299 collapses along 300 km of shoal margin boundaries over 56 years, meaning that more than five collapses occur on average per year. The average shoal margin collapse body is well approximated by a 1/3 ellipsoid shape, covers on average an area of 34 000 m² and has an average volume of 100 000 m³. Shoal margin collapses occur mainly at locations where shoals take up a proportionally larger area than average in the cross‐section of the entire estuary, and occur most frequently where lateral shoal margin displacement is low. A receiver operating characteristic curve shows that the forecasting method predicts the shoal margin collapse location well. We conclude that the locations of the shoal margin collapses are well predicted by the variation in conditions of the relative slope height and angle within the Western Scheldt, and likely locations are at laterally relatively stable shoal margins. This provides hypotheses aiding the recognition of these features in sandy estuaries worldwide. Copyright © 2018 John Wiley & Sons, Ltd.     

2017年四川九寨沟7.0级地震前地震应变场分析

以地震应变场作为地震活动的变量,通过自然正交函数展开方法,计算2017年8月8日四川九寨沟7.0级地震前的地震应变场,提取出震前时间因子的异常变化。计算结果发现应变场前4个时间因子在震前1~3年的中短期异常并不显著,只有第2个和第4个时间因子震前有小幅度的异常变化,分析其原因,时间因子可能受到2008年汶川8.0级地震和2013年岷县漳县6.6级地震前大幅度异常的影响。与时间因子对应的空间等值线形成局部应变高值异常危险区,可能是2013年岷县漳县6.6级地震和2017年九寨沟7.0级地震空间异常的中短期特征。再对比九寨沟7.0级地震前后与松潘-平武7.2级双震的空间异常随时间演变,分析异常发展变化模式的差异,最后应用地震资料的累积频次从物理角度解释异常形成的机制。     

江西地区地方性震级的量规函数与台基校正值研究

本文采用《江西测震台网地震观测报告》,选取2007年10月~2015年12月所记录的499次M_L≥1.5地震事件,对各子台测定震级与台网平均震级偏差进行定量的统计分析,从震级偏差频次分布、量规函数、台基、方位角等方面分析产生震级偏差的原因。在对量规函数和台基进行校正后,震级偏差绝对值在0.2以内的样本数达到了68.6%,并给出了适合江西地区的量规函数和台基校正值。     

应急演练中基于G-R关系的主余型地震余震震级模拟

在现有的日常地震演练过程中,与应急救援密切相关的地震余震信息产品较为缺乏,直接影响发震构造的判断以及影响场修正等关键环节。本文从计算机系统提供的均匀分布随机数出发,运用反函数法模拟生成余震序列,并进行系统检验,证实该方法产生的余震序列满足G-R频次关系。模拟生成的余震震级数据既有助于增强地震应急救援演练的现实性,也有助于丰富地震应急宣传产品,提升地震部门的履职能力。     

应用经验正交函数估算顶部电离层电子密度剖面

本文基于IRI模型、地面数字测高仪和GNSS TEC数据,提出了一种利用经验正交函数(Empirical Orthogonal Function,简称EOF)估算顶部电离层电子密度剖面的方法,并将其应用于美国Millstone Hill测高仪和GNSS数据以估算顶部电离层电子密度剖面.通过将估算的临界频率、峰值高度、400km以上电子密度分别与测高仪实测临界频率、测高仪实测峰值高度以及非相干散射雷达实测400km以上电子密度作对比以对方法的有效性进行验证.统计结果显示估算临界频率、峰值高度与测高仪实测数据基本一致,400km以上估算电子密度相较于非相干散射雷达实测的绝对误差平均值仅是测高仪推算400km以上电子密度绝对误差平均值的一半左右.所以本文提出的方法可以更加精确地估算顶部电离层电子密度.     

利用接收函数方法研究中国东北东南部地区不同构造体的地壳特征

基于我们布设的探测深俯冲的中国东北地震台阵NECsaids台阵和固定地震台长时段的观测记录及NECESSArray流动台阵共计152个台站数据提取得到的33752条P波接收函数,采用H-κ叠加分析和共转换点（CCP）叠加成像等方法进行统一分析处理,并汇集他人接收函数研究结果得到中国东北东南部地区迄今为止最高分辨率的地壳厚度和平均波速比分布图像.对中国东北东南部地区不同构造体的地壳特征综合分析研究表明：研究区不同陆块的地壳属性存在明显差别,张广才岭地块中南部的地壳厚度和波速比与华北克拉通东北缘相当,地壳厚度同地表地形之间显示有明显的正相关关系;松辽地块东南缘地壳最薄、波速比最高,地壳厚度同壳内波速比之间显示出明显的负相关关系;兴凯地块西部地区的地壳结构表现为稍厚的地壳厚度和研究区内最低的壳内波速比,其地壳厚度同壳内波速比之间亦显示出明显的负相关关系;佳木斯地块西南缘在具有"正常"的壳内波速比同时地壳最厚.研究区内的郯庐断裂带北延段在切穿其下Moho面的同时表现出南北分段的特征：北段（44.4°N—47°N）两分支之下的Moho面整体下凹,而南段（41.5°N—43.3°N）两分支之下的Moho面则整体上隆.长白山天池火山下方表现为Moho面下凹沉落及高壳内波速比特征,推测其壳内岩浆囊很可能存在于火山口东北隅至少10 km的范围内.