旋转层状液的自由震动(英文)

考虑两种互不混合的理想不可压缩液体部分或全部充满刚体中在惯性力场中转动时的自由震动 ,在系统不受扰动时 ,其运动就象一个刚体 ,将其考虑成部分或完全充盈的刚体在惯性力场中的转动。确定层状液震动频谱就可归结为求解边界的特征值问题 ,这可以用解析的方法或数值的方法来求解。导出了在柱状空腔中快速旋转的两种互不混合的层状液边值问题的解析解。给出的不同半径处分层在不同充盈深度震动频率计算结果表明 :液体质量一定时分层液自震频率高于均质液 ;分层对某一平均半径内表面固有频率有决定性影响 。

六自由度地震动测量方法及其误差分析

根据无陀螺捷联惯导原理,提出一种用八支力平衡加速度计测量六自由度地震动的方法,并对该测量方法的误差进行了分析。

斜入射出平面自由波场勒让德谱元时域模拟方法

远场地震作用下的复杂场地(复杂场地-城市建筑群耦合)地震响应时域分析需在计算截断边界给定自由平面波场输入。为规避边界节点时程存储带来的内存浪费和频繁读写导致并行计算效率低下等问题,有必要构建与地震响应时域分析相匹配的自由平面波场时域模拟方案。面向基于勒让德谱元的复杂场地时域分析方法,以出平面波动为例,构建斜入射自由平面波场时域模拟方案。首先,给出平面波输入下自由波场计算问题的构建,基于勒让德谱元和显式积分格式建立了时空解耦离散方案,并利用解析算例验证了离散方案的精度与稳定性。其次,将该方案应用于四川、加州层状地下介质构造,对比了两个区域内地震波地壳放大效应的差异。结果表明:二者放大效应在中低频段存在系统性差异,在高频段趋于一致,定性解释了基于全球第二代地震动衰减关系预测汶川地震主震记录中长周期反应谱存在显著偏差的原因。最后,以地震动地形效应分析为例,阐述该方案与勒让德谱元、透射边界条件结合在近场外源波动问题模拟中的应用。

基于自由振动响应的基础隔震建筑减震能力评估方法研究

随着技术的进步,国内外也已建造了大量的隔震建筑物,但只有少数能够经受住地震工作的考核,而大多数隔震构件的减灾力量是否能够达到设计的要求,仍然是一个未知数。因此,我们给出了一套采用自由度振动响应的减震能力方法,以期解决这一问题。首先,通过多级幅值初定位自由震动原位试验,得出隔震建筑物的抗震能力曲线;然后,依据地震反应谱,构建地震需求曲面,以明确隔震结构的性能点;结尾,按照抗震设计规范,计算出水平减震系数,以评价隔震结构的减震能力。

小麦单株抗倒伏的数力分析

应用材料力学、结构力学、结构动力学等力学知识,建立多种类型的数学模型,解释倒伏现象及发生原因。由伯努利公式算出风压,结合麦穗迎风面积算出风荷载;利用单自由度振动模型,确定最大动力位移,求得最大倒伏弯矩;利用多自由度振动模型,将质量分别集中到各个级节,确定多自由度模型的固有频率和固有振型;最后计算了各个质点的侧向位移。根据建立的多自由度模型,应用第一强度理论,算出各截面的最大正应力,发现基部第2节间形成的应力值高于其他级节间的应力值,确定最易发生折断截面位置。计算结果与实际的麦田观察结果吻合。

Dynamic Properties of Long Large Cross-section Underground Structures in Dynamic Seismic Analysis

Seismic safety of underground structures is one of the main concerns in underground space exploitation. As the first step for dynamic seismic response analysis, the free vibration of long large cross-section underground structures is studied in the present paper. The general free transverse vibration motion equation of long large cross-section underground structure is derived with the comprehensive consideration of internal and external damping, effects of shear, cross-sectional rotational inertia and axial force, and a twoparameter soil model. In this way, Timoshenko＇s beam theory is extended. Two limit cases of free transverse vibration of underground structures are discussed. Parameter study shows that in general wave propagation velocities in structures increase with soil elastic parameters. However the influence of Winkler＇s parameter k is significant while the effect of the second soil elastic parameter gp is insignificant. The free vibration frequency of underground structures increases with relative wave number and soil elastic parameters. Unlike the influence of soil elastic parameters on wave propagation velocities, the influence of soil elastic parameters k and gp on the vibration frequency of underground structures have the same order; therefore the influence of the second soil parameter gp on the free vibration of underground structures should not be neglected in dynamic seismic analysis of underground structures

Maximum Relative Displacement of Adjacent Buildings During Ground Motions

In order to give the reasonable width of seismic gaps to prevent the structural pounding during ground motions,the maximum relative displacement of adjacent structures is studied in this paper.The factors that may have effects on the maximum relative displacement are discussed.As for multi-degree-of-freedom(MDOF) systems,they can be equivalent to single-degree-of-freedom(SDOF) systems with the influences of high modes neglected.The results show that the period ratio,height ratio and peak ground acceleration are the main factors that have great effects on the maximum relative displacement of adjacent structures.The maximum relative displacement of MDOF systems can be obtained from calculating the maximum relative displacement of the equivalent SDOF systems.