A laboratory study of directional spectra with maximum likelihood method-Ⅰ Developing wind wave     

Zhao Dongliang  Masuda Akir  Wen Shengchang  Guan Changlong 《海洋学报(英文版)》1999,18(1):59-74

measurements by a circular array consisting of 18 wave gauges in a large wave tank, directional spectra of wind-generated waves in deep water are systematically determined by using maximum likelihood method The investigations reveal that the angular spreading of the wave energy is consistent with cos^2s(θ/2) proposed by Longuet-Higgins et al.(1963, Ocean Wave Spectra, 111-136), if the bimodal distributions of wave energy are not taken into account. Bimodality occurring on higher frequency than peak frequency is too rare to affect our whole resalts. Surprisingly, a much broader directional spreading than that of the field, which is interpreted by the strongly nonlinear energy transfer because of the very young waves in laboratory, is found. The parameter s depends on frequency in the same way as observed by Mitsuyasu et al.(1975, Journal of Physical Oceanography, 5, 750-760) and Hasselmann et al.(1980, Journal of Physical Oceanography, 10, 1264-1280) in the field, and the relationship between the four nondimensional parameters s_m, f_o, b₁ and b₂, determining the directional width, and ū₁₀ (corresponding to the inverse of wave age) are given respectively. The observed distributions are found to agree well with the suggestion of Donelan et al.(1985, Philosophical Transaction of Royal Society of London, A315, 509-562) when applied to field waves.  相似文献   

A Possible Mechanism of Ocean Finestructure Part Ⅰ: Energy and Coherence     

范植松  方欣华 《中国海洋大学学报(自然科学版)》1999,(2)

依据在作者的前文（１９９８）中对于考虑旋转向量水平分量（ｆ～）的大洋内波方程求出的渐近解,文中对Ｓ场（考虑ｆ～条件下的总的内波场）,ＳＩ场（不计ｆ～影响的内波场）和ＳＦ场（Ｓ场中与ｆ～相关联的部分）导出了能量谱和相干谱。此理论谱与Ｍｕｌｅｒ等（１９７８）的ＩＷＥＸ实验的观测结果相比较表明,ＳＦ场的水平动能谱和铅直位移谱基本上与水平流细结构和铅直位移细结构的观测谱一致。作者推测ＳＦ场对应于中纬度大洋可逆细结构。但是对于相干谱的观测结果,在不考虑内波非线性相互作用和破碎过程的条件下,仅考虑ＳＦ场的影响还不能给予满意的解释。  相似文献   

近断层竖向地震动P-Δ效应研究   总被引：1，自引：1，他引：0  

范优铭  夏群 《震灾防御技术》2017,12(1):177-184

竖向效应是近断层地震动的主要特点,竖向地震动对工程结构形成的P-Δ效应是造成结构破坏的主要原因。本文以单自由度体系为研究对象,选取汶川地震的近断层强震数据进行研究,分析竖向地震动所产生P-Δ效应的放大作用特征。分析结果表明汶川地震中,相比于中远场区域,近断层区域内竖向地震动作用所产生的P-Δ效应具有明显的放大作用,且近断层内这种放大作用具有普遍性;当自振周期一定时,不同台站获得地震动的放大系数离散性较小,主要分布于均值附近;其分析结果符合地震动的一般规律,分析结果合理。在此基础上建立了以均值为代表值的放大系数谱,可以与抗震设计反应谱结合使用,从而为活断层附近区域内的结构抗震设计问题提供定量化参考依据。  相似文献   

汶川地震科学钻探3号井孔附近微震震源参数确定及其意义   总被引：4，自引：1，他引：3       下载免费PDF全文

叶庆东  丁志峰  王生文  余大新  郑晨 《地球物理学报》2017,60(7):2716-2732

基于微震监测仪器频带及波形记录的时频特征,我们筛选出汶川地震科学钻探3号井孔周围微震台阵2012年记录的218个t_s-t_p1 s的微震.通过盖戈法与和达法相结合确定微震震源的几何参数,发现这些微震分布大体呈NE-SW展布,与龙门山断裂带的走向基本一致.无论是采用《地震台站观测规范》中的量规函数(量规函数GF)还是李学政等(2003)的量规函数(量规函数LXZ),近震震级均与矩震级呈现出较好的线性关系,向震级小的一端延伸时都表现为M_LM_W,但采用李学政等的量规函数时该趋势更加明显.同时采用Brune和Boatwright震源谱衰减模型对观测震源谱的拟合表明拐角频率具有模型依赖性:基于Brune模型拟合得到的拐角频率大于基于Boatwright模型得到的拐角频率.无论基于哪一种模型,矩震级与拐角频率、破裂半径的对数线性关系均较弱,与应力降、视应力的对数则存在较好的线性关系.这些关系不支持应力降、折合能量、视应力为常数的观点,表明微震与大地震的震源物理过程存在差异.视应力与应力降成比例,比例系数小于0.5,表明破裂动力学模式符合SavageWood模式.近震震级与矩震级拟合关系Mw=a+bM_L中b的大小与应力降和地震矩的关系有关,△σ∝M_0~γ,则b=1/(1+γ),因此从b的大小可以粗略地判断应力降与地震矩的关系.本文对应于γ≈1的情况,与基于量规函数LXZ得到的近震震级与矩震级关系中系数b=0.53吻合,这说明仅从辐射能量的角度考虑量规函数LXZ较量规函数GF准确.  相似文献   

Evaluation of ASCE 7 equations for designing acceleration‐sensitive nonstructural components using data from instrumented buildings     

Hamidreza Anajafi  Ricardo A. Medina 《地震工程与结构动力学》2018,47(4):1075-1094

This study uses instrumented buildings and models of code‐based designed buildings to validate the results of previous studies that highlighted the need to revise the ASCE 7 F_p equation for designing nonstructural components (NSCs) through utilizing oversimplified linear and nonlinear models. The evaluation of floor response spectra of a large number of instrumented buildings illustrates that, unlike the ASCE 7 approach, the in‐structure and the component amplification factors are a function of the ratio of NSC period to the supporting building modal periods, the ground motion intensity, and the NSC location. It is also shown that the recorded ground motions at the base of instrumented buildings in most cases are significantly lower than design earthquake (DE) ground motions. Because ASCE 7 is meant to provide demands at a DE level, for a more reliable evaluation of the F_p equation, 2 representative archetype buildings are designed based on the ASCE 7‐16 seismic provisions and exposed to various ground motion intensity levels (including those consistent with the ones experienced by instrumented buildings and the DE). Simulation results of the archetype buildings, consistent with previous numerical studies, illustrate the tendency of the ASCE 7 in‐structure amplification factor, [1 + 2(z/h)] , to significantly overestimate demands at all floor levels and the ASCE 7 limit of to in many cases underestimate the calculated NSC amplification factors. Furthermore, the product of these 2 amplification factors (that represents the normalized peak NSC acceleration) in some cases exceeds the ASCE 7 equation by a factor up to 1.50.  相似文献   

Model for multiblock columns subjected to base excitation          下载免费PDF全文

Tamás Ther  László P. Kollár 《地震工程与结构动力学》2018,47(2):418-437

A new model is presented for multiblock columns subjected to earthquakes, which contains an impact and an opening model. Both in the impact and in the opening model, all the possible opening configurations are investigated because it was found that in many practical cases, unexpected patterns may occur. The model is purely mechanical: assuming rigid blocks and classical (inelastic) impact. The effect of energy dissipation during impact was investigated. Using our model in accordance with the literature, it was found that monolithic blocks are more vulnerable to overturning than multiblock systems.  相似文献   

A review of diagnostic emission line ratios in the Narrow Line Region of Active Galactic Nuclei     

M. Radovich  G. Hasinger  P. Rafanelli 《Astronomische Nachrichten》1998,319(6):325-346

The availability of new observing facilities both from ground and space such as the Keck 10m telescope and the Hubble Space Telescope is casting new light on the spectroscopic investigation of emission line galaxies. In particular, it is now possible to detect spectra with a significantly improved signal to noise ratio in a very wide wavelength range, from the ultraviolet to the near infrared (HST, Keck) and beyond (ISO is unveiling the far infrared domain). As we move to high redshifts, however, it is more likely that the observed spectra are given by the contribution of different components in the galaxy: in particular, this may be the case if an Active Galactic Nucleus (AGN hereafter) emitting a power-law continuum is surrounded by regions with strong star formation activity. The identification of the source which ionizes the line emitting regions is then complicated by the fact that we are observing the integrated spectrum from regions which are ionized by different sources. In this paper we wish to review which line ratios may be used in order to discriminate between photoionization by young stars and power-law continuum in the wavelength range from 1200 Å to 100 μm. To this aim we used the photoionization code Cloudy (Ferland 1996) to present a series of diagnostic diagrams showing the dependence of emission line ratios on the main input parameters of photoionization models in the case of one component models with gaseous clouds ionized by (1) a stellar continuum typical of an HII region and (2) a power-law continuum typical of an AGN: these line ratios are plotted as isoratio maps for different values of the hydrogen density, ionization parameter and slope of the power-law continuum. We then show how the results may be affected by more realistic assumptions about the environment of the ionized gas: to this aim, we show the effects on selected line ratios of (a) the presence of two populations of clouds with different densities and (b) an AGN surrounded by regions with strong star formation activity.  相似文献   

地震动输入界面的选取对深软场地地震效应的影响   总被引：4，自引：0，他引：4  

陈国兴  陈继华 《世界地震工程》2005,21(2):36-43

以天津和上海两个典型的深厚软弱场地为研究背景,探讨了地震动输入界面对场地地表地震动参数的影响。对于场地1(天津)和场地2(上海),分别选择7个和8个剪切波速(υs)大小不同的土层位置作为地震动输入界面,并选用Taft、Northridge地震加速度记录和南京人工波作为输入地震动,将Taft波、Northridge波和南京人工波的加速度峰值水平调整为0．35m／s^2、0．70m／s^2和0．98m／s^2,用SHAKE91程序对这两个场地进行了不同的地震动输入界面、输入地震波和峰值加速度水平的128种组合的场地地震反应分析。与从假想基岩面(υs≥500m／s)输入地震动的结果(假想的实际值)相比,可得到如下结论：(1)随着地震动输入界面深度(剪切波速)的增加,场地地表加速度反应谱逐渐地向实际值接近;(2)地震动输入界面的深度相同时,地震动加速度峰值水平越高,两者的加速度反应谱谱值的相对差异也越大;(3)对于一般建筑物,可以把剪切波速为400m／s左右的土层作为地震动输入界面;对于中长周期的建筑物,则应慎重选择地震动输入界面,最好选取υs≥500m／s^2的土层或基岩面作为地震动输入界面。  相似文献   

On the correction of spectra by a displacement reduction factor in direct displacement-based seismic design and assessment     

Gian Michele Calvi 《地震工程与结构动力学》2019,48(6):678-685

The application of some design and assessment approaches, such as the direct displacement-based design (DDBD) and the capacity spectrum methods, requires the modification of elastic design spectra by some displacement reduction factor, to account for the appropriate energy dissipation capacity of different structures. While several equations to correlate dissipation and hysteresis cycles are available, once the displacement reduction factor has been obtained, the correction of the spectra is operated reducing the displacement demand accordingly and conserving the period of vibration at each point. This procedure is here discussed and proved to be conceptually inappropriate, because the spectral acceleration rather than the period should be kept at each point. The application of this alternative procedure may result in increased shear strength demand in design and in larger required displacement capacity for the same level of strength in assessment, if all other factors are not modified. However, the calibration of the reduction factors applied in DDBD has been extensive, and the method has proved to be effective in predicting displacement demands consistent with those resulting from refined nonlinear time history analysis; therefore, a possible introduction of the proposed correction will require equally extensive studies and possibly compensating corrections in the calculation of the equivalent damping. On the contrary, an appropriate calibration of the factors to be used in the application of the “capacity spectrum” method is still being developed, and the consideration of a constant acceleration may facilitate the derivation of effective equations.  相似文献   

残余位移反应谱的参数影响研究     

李宇  梁亚东  李琛 《震灾防御技术》2019,14(4):790-796

从PEER强震数据库中选取4类场地的320条地震动记录作为输入,采用BISPEC程序对非线性单自由度（SDOF）体系（周期T=0.05—5s）进行非线性时程分析,得到相应的残余位移反应谱（Dres）,进而研究地震动特性和恢复力模型动力参数对Dres的影响,得到如下结论:①Dres谱值随震级和PGA的增加而增大;其他设防烈度的Dres可由PGA_其他与PGA_基准之比调整基准烈度的Dres得到。②场地土较硬时,场地类型对Dres的影响较小;场地土较软时,Dres谱值随土质的变软而增大。③当位移延性比μ较小时,屈服后刚度比η对Dres的影响可忽略;但当μ较大时,Dres谱值随η的增加而减小。另外,Dres谱值还随阻尼比ξ的增加而减小。④随着T或μ的增大,Dres谱值均呈递增趋势;但当μ>3后,μ对Dres谱值的影响有所下降。  相似文献