海域地震动竖向加速度反应谱阻尼修正系数

该文提出了一个用于调整5%阻尼比海域地震动竖向加速度反应谱的阻尼修正系数(Damping modification factor, DMF)模型。基于S-net台网的5680条海底竖向地震动记录，利用DMF比值和Z检验分析了地震类型对DMF的影响，提出了考虑阻尼比和谱周期的DMF模型，与陆域DMF模型进行了对比，并获取了不同阻尼比下的竖向加速度反应谱，最后对残差及标准差进行分析。研究表明：地震类型对DMF的影响可以忽略；可用三次多项式模拟阻尼比对DMF的影响；由于海域地震动特性导致海陆DMF模型之间差异显著；阻尼比能够影响5%阻尼比反应谱1倍标准差的谱值；残差分析表明可引入矩震级、断层深度和震源距改善DMF模型的拟合度。该文提出的海域地震动加速度谱竖向DMF模型，为海域工程多阻尼抗震设计谱的确定提供了参考。     

随机地震作用下TMD等效附加阻尼比研究

针对随机地震作用下TMD给结构提供的附加阻尼比展开研究。随机地震动采用过滤白噪声Kanai-Tajimi功率谱模型,并将Kanai-Tajimi功率谱模型描述的场地过滤效应表示成传递函数形式,进而推导出结构相对于基岩的位移动力放大系数。然后,结合SRSS方法,以结构位移响应均方值作为评价准则,提出了随机地震作用下TMD提供给结构任意阶模态的等效附加阻尼比理论公式。最后,以某景观塔作为工程算例展示了TMD等效附加阻尼比的求解流程,并验证了该等效附加阻尼比公式的有效性。算例分析结果表明,使用等效附加阻尼比指标来评估TMD减震性能是合理有效的,且使用推导的TMD等效附加阻尼比理论公式能更准确地评估TMD对结构位移响应的控制效果。     

多自由度一般积分型粘弹性阻尼减震结构的 随机响应与等效阻尼

该文对任意多自由度带支撑一般积分型粘滞和粘弹性阻尼器减震结构的随机响应与等效阻尼比的解析分析法进行了系统研究。首先建立了结构一般运动方程;然后将运动方程化为振型广义坐标的微分和积分混合地震响应方程组;继而基于多自由度随机平均法理论,获得了结构随机平均Itô方程组的解析式,推导出耗能结构各振型振子的振幅与相位瞬态联合概率密度函数、位移与速度瞬态联合概率密度函数、位移与速度瞬态响应方差的一般解析解;最后,基于与多自由度随机平均法分析完全相同的等效准则,建立了耗能结构各振型等效阻尼比的一般解析式,并根据CQC和SRSS组合方法,建立了耗能结构随机地震响应方差的解析式,给出了带支撑广义Maxwell阻尼器和广义微分模型阻尼器减震结构随机响应和各振型等效阻尼比的一般解析式,通过与一些典型问题的模态应变能法的计算精度对比分析,表明了所提方法的有效性,使耗能结构可直接应用反应谱法进行设计,从而建立了带支撑任意线性粘滞和粘弹性阻尼器一般耗能结构随机响应与特性等效阻尼分析的完备解析解法。     

Uncertainty modeling in the fatigue reliability calculation of offshore structures

This paper presents a procedure of modeling uncertainties in the spectral fatigue analysis of offshore structures with reference to the reliability assessment. Uncertainties of the fatigue damage are generally embedded in response characteristics of the stress process and the damage-model used. Besides commonly accepted uncertainties in offshore structural analysis, which are associated with the modeling of structures and the random wave environment, there are also uncertainties arising from joint flexibilities that occur during the response, the wave–current and water–structure interactions. Uncertainties in joint flexibilities are associated with degradation of member connectivities during a response process. Uncertainties introduced by the wave–current interaction are related to the modeling of a random sea state, applied wave loads and water–structure interaction effects in general. The water–structure interaction, which is an important phenomenon to be considered in the analysis of dynamic-sensitive structures, introduces some added hydrodynamic damping. The associated uncertainties are reflected in the response analysis via the damping term. Therefore, in a quasi-static response analysis, these uncertainties disappear. In the spectral fatigue damage, in addition to the uncertainties of stress statistical characteristics there are some other uncertainties associating with the damage-model used. These uncertainties are related to experimentally determined fatigue data and configurations of selected joints at which damages are likely to occur due to high stress concentrations. This paper presents these uncertainty issues with emphasis on the application of a reliability assessment. However, some other uncertainties arise from approximations inherent in the model. They are assumed to be either comparatively negligible or can be considered within the current uncertainty models so that they are not treated further in this paper. In the calculation of the fatigue damage, a non-narrow banded stress process is used.     

行波效应对深水连续刚构桥地震响应的影响

跨海或库区的大跨度桥梁在地震作用下不仅需要考虑水体与桥墩的动力相互作用,同时由于各桥墩间跨度较大应考虑地震输入的行波效应。该文采用辐射波浪理论求解桥墩地震动水压力,建立了考虑地震动输入空间效应的深水桥梁地震响应分析方法,并考虑行波效应对深水连续刚构桥进行地震响应分析。研究表明：动水压力增大了桥梁结构的地震响应,其影响程度随着输入地震波和墩梁约束条件的不同而有所差异;考虑行波效应时地震动水压力对桥梁结构动力响应的影响较一致激励而言有所差别,同时地震动水压力对桥梁地震响应的影响随着视波速的不同而变化。由此得出结论,为合理评价地震动水压力对深水长大桥梁动力响应的影响应考虑地震动输入的行波效应。     

地震作用下海冰与桥墩的间距对桥墩动力响应的影响研究

位于冰水海域的桥墩,在波浪力作用下,桥墩结构与周围海冰往往出现间隙,地震作用下海冰与结构的动力相互作用呈现复杂多样化。本文在弹性力学中的弹性波传播理论及结构动力学的基础上,考虑不同的海冰与桥墩间距,建立了地震作用下桥墩、冰与水体的流固耦合动力方程。并以一矩形桥墩为研究对象,研究了地震作用下,海冰与桥墩的间距对矩形桥墩结构的动力响应及动水压力的影响。研究表明：地震作用下,海冰与桥墩间距对桥墩顶部的最大位移和最大加速度响应的影响不显著,但是对桥墩侧面动水压力和墩底内力影响较大;当海冰与桥墩存在间距且小于1倍结构尺寸时,墩底的弯矩和剪力达到最大值。     

Motion trapping structures in the three-dimensional water-wave problem

Trapped modes in the linearized water-wave problem are free oscillations of finite energy in an unbounded fluid with a free surface. It has been known for some time that such modes are supported by certain structures when held fixed, but recently it has been demonstrated that in two dimensions trapped modes are also possible for freely floating structures that are able to respond to the hydrodynamic forces acting upon them. For a freely floating structure such a mode is a coupled oscillation of the fluid and the structure that, in the absence of viscosity, persists for all time. Here previous work on the two-dimensional problem is extended to give motion trapping structures in the three-dimensional water-wave problem that have a vertical axis of symmetry. Nick Newman has made many important contributions to the theory of the interaction between water waves and structures, and his panel code WAMIT has been adopted as one of the industry standards for the calculation of wave loading on offshore structures. It gives us great pleasure to celebrate Nick’s achievements through the presentation of this work on a new type of structure that both draws on his theoretical work and uses WAMIT to perform relevant computations.     

Pore pressure response of earth dams in random seismic environment

The progressive development of pore water pressure due to earthquake loading and associated loss of strength may be a major cause of instability in earth dams consisting of low to medium dense saturated sands and hydraulic fill materials.In this study a procedure is developed for the analysis of pore pressure response of an earth dam subjected to a random seismic environment. The ground motion is modelled as a portion of the stationary random process which may be defined alternatively by (a) Kani—Tajimi spectral density function, or (b) a design response spectrum. The earth dam is modelled as a series of shear slices and is considered to be homogeneous. The nonlinearity in shear modulus and damping are incorporated by using an equivalent linear model for the stress-strain behavior of soils. The dynamic response to vertically propagating shear waves is formulated in the frequency domain providing the transfer functions for various parameters, viz, stress, strain and acceleration, etc. The power spectra of these parameters are then readily obtained.Using a simple linear model for the generation of pore water pressure the expected value of associated damage is obtained. Numerical results of an example analysis and a parametric study are presented.     

序列型地震动物理随机模型研究

通过引入主震与余震间的震级、震源参数以及峰值速度的物理关系,将已有的单震物理随机模型推广到序列型地震动,并利用实测主余震记录拟合获得了模型中各参数的概率分布,进一步结合窄带谐波叠加法实现了序列型地震动的工程模拟。从典型样本时程和反应谱两个层面上与实测地震动记录进行了对比,结果表明模拟地震动具有与实测记录相同的频谱特性,能够反映实际地震动的时域、频域非平稳性,建议模型所给出的反应谱均值和标准差与实测记录的统计结果基本一致,可用于序列型地震作用下工程结构的抗震性能分析。     

水下生产系统跨接管结构在地震作用下动力响应分析

研究水下生产系统跨接管结构在地震波载荷下的动力响应特性。分析中计及了地震波沿水平和竖向两个方向的载荷输入,采用非线性弹簧模型模拟跨接管与海床的耦合作用,同时考虑了地震作用下跨接管的动水作用效应。通过对不同影响因素下结构的动力响应结果分析表明：竖向地震波对跨接管结构水平响应幅值影响较小,但显著改变其响应频率;管土接触引起跨接管响应幅值变化明显,并激发跨接管高阶振型;地震下动水作用力对跨接管的响应幅值影响较大。所建立的分析方法对跨接管结构设计和安全性评估有一定借鉴意义。     

Taylor dispersion of contaminants by random waves

The longitudinal dispersion of contaminants due to mass transport induced by random surface waves is examined. The wave kinematics under random waves are first derived, including the second-order drift profile. The relationship between the dispersive coefficient and wave drift is then established following the approach in J. Hydraul. Res. (2000) 38:41–48. Subsequently, the magnitude of the longitudinal dispersive coefficient is examined under both developed and developing sea states, represented by the P–M spectrum and the Wen spectrum, respectively. The results show that the longitudinal dispersion by random waves is significantly stronger than an equivalent regular sea state with a similar wave energy density. Furthermore, the dispersive effect in the developing sea state is found to be stronger than the developed sea state with comparable wave-energy density, which can be attributed to the differences in the spectral shape between the two states.     

地震动方向对海上风力发电机动力响应的影响

叶轮-塔架耦合及气动阻尼作用使得海上风力发电机前后向、侧向动力特性存在差别。针对NREL 5 MW单桩式海上风力发电机,通过理论分析,探讨海上风力发电机前后向与侧向振型、阻尼特性的差异;然后,针对停机和运行两种工作状态,采用气动-伺服-水动-弹性完全耦合方法,分析输入地震动方向影响海上风力发电机结构动力响应的规律,探讨最不利方向;最后,还分析了平均风速对最不利输入地震动方向的影响。结果表明:输入地震动方向可能显著影响海上风力发电机支撑结构泥面弯矩和塔顶位移幅值;对于运行状态,强震作用下,侧向为最不利输入地震动方向,弱震作用下,前后向为最不利输入地震动方向。     

Extreme response statistics for drag dominated offshore structures

The paper presents a study of extreme response statistics of drag dominated offshore structures, subjected to severe sea states. The nature of the hydrodynamic forces acting on the structure is highly nonlinear under such conditions. Additionally to drag forces, the so-called inundation effect must also be taken into account. In the present paper a stochastic force model is introduced that captures both these phenomena in a fairly simple manner allowing for efficient calculation of the extreme response statistics. In fact, the proposed model opens up the possibility to calculate efficiently even long-term extreme response statistics, which is an important issue for the design of offshore structures. Comparison with the results of Monte Carlo simulations for a jacket structure indicates that good accuracy can be obtained for the extreme response predictions.     

一种粘滞阻尼体系阻尼矩阵识别新方法

由不同材料组成的混合结构,其阻尼矩阵不再满足与质量矩阵、刚度矩阵的比例关系,具有非比例特性。我国设计规范中常用的振型分解反应谱法是基于比例阻尼建立的,并不严格适用于计算非比例阻尼体系的地震作用效应。该文在基于等效黏性阻尼模型的复模态叠加法基础上,结合虚拟激励法和平稳随机理论,推导了基于等效黏性阻尼模型的反应谱CCQC(Complex Complete Quadratic Combination)法实数表达式,建立了一种解决非比例阻尼混合结构的地震作用效应计算问题的理论方法。算例分析表明：与基于分块Rayleigh阻尼模型的反应谱CCQC法相比,该文建立的基于等效黏性阻尼模型的反应谱CCQC法直接依赖于结构的质量、刚度和阻尼参数,不受振型组合的影响,具有计算结果唯一的优点,且仅涉及位移相关系数的计算;与基于能量法的反应谱CQC法相比,基于等效黏性阻尼模型的反应谱CCQC法可有效考虑结构的非比例特性,适用于非比例特性较强的混合结构。     

基于等效黏性阻尼模型的非比例阻尼体系反应谱CCQC法

由不同材料组成的混合结构,其阻尼矩阵不再满足与质量矩阵、刚度矩阵的比例关系,具有非比例特性。我国设计规范中常用的振型分解反应谱法是基于比例阻尼建立的,并不严格适用于计算非比例阻尼体系的地震作用效应。该文在基于等效黏性阻尼模型的复模态叠加法基础上,结合虚拟激励法和平稳随机理论,推导了基于等效黏性阻尼模型的反应谱CCQC(Complex Complete Quadratic Combination)法实数表达式,建立了一种解决非比例阻尼混合结构的地震作用效应计算问题的理论方法。算例分析表明:与基于分块Rayleigh阻尼模型的反应谱CCQC法相比,该文建立的基于等效黏性阻尼模型的反应谱CCQC法直接依赖于结构的质量、刚度和阻尼参数,不受振型组合的影响,具有计算结果唯一的优点,且仅涉及位移相关系数的计算;与基于能量法的反应谱CQC法相比,基于等效黏性阻尼模型的反应谱CCQC法可有效考虑结构的非比例特性,适用于非比例特性较强的混合结构。     

The asymptotic behaviour of second-order stochastic Volterra series models of slow drift response

The paper presents a detailed study of the structure and asymptotic behaviour of a second-order stochastic Volterra series model of the slow drift response of large volume compliant offshore structures subjected to random seas. A long standing challenge has been to develop efficient and accurate methods for calculating the response statistics of compliant offshore structures to random seas. Recent work has revealed that the statistical properties of the response process, which consist of a linear, first-order component and a nonlinear, second-order component, is surprisingly complex. The goal of the research work presented here is to complement efforts to develop numerical procedures to calculate the statistics of the response process.     

Evaluation of earthquake ground motions by empirical analysis

Abstract

The design ground motion is based on the seismicity and geologic conditions at the site and expressed in such a manner that it can be applied to the dynamic analysis of structures. For the seismic analysis of safety‐related structures, design ground motions are made based on the evaluation of earthquake ground motion by empirical analysis, of which some important features are discussed in the present study: (1) Develop reasonable peak ground acceleration attenuation form for the Taiwan area. The proposed attenuation forms take into account the PGA level at the near‐field which compensates for the insufficiency of the available data base. (2) Generation of spectra compatible time history with multiple damping. By simultaneously matching several spectral curves for different dampings, the conservatism in design based on a single damping spectrum‐enveloping accelerogram, especially for low damping values, may be substantially reduced. (3) Development of a minimum requirement for the power spectral density function, which is a secondary requirement to prevent the design ground motion from encountering severe power deficiency.     

近断层地震作用下弹性位移反应谱的研究

为研究近断层地震作用下基于位移的抗震设计方法,选择了30次地震,132组近断层地震记录作为统计样本,根据得到的平均弹性位移反应谱,给出了近断层地震设计弹性位移反应谱表达式,该表达式可以反映震源机制和场地土等因素的影响作用。研究结果表明：提出的近断层地震弹性位移设计反应谱与实际地震波平均弹性位移反应谱较为接近,可以应用于近断层地震作用下结构的抗震设计中。     

Dynamic response of adjacent structures under spatially variable seismic waves

In this paper the dynamic response of a system of two structures placed adjacent to each other is studied. The force on the system consists of earthquake loading applying for its spatial variability over short distances. The spatially variable ground motion is defined and explored by two different approaches. First, the deterministic approach accounting only for effects of wave passage of surface waves and inclined body waves, and second, the stochastic (random) approach considering also degree of coherency between motions at every two points of the ground surface as a factor. Effects of the ground motions identified as above on the response of the system are examined assuming a harmonic excitation and considering type of the wave and angle of incidence of the body waves. It is shown that resonance frequency increases with closeness of structures. Moreover, for some cases depending on the distance between the adjacent structures, the structural response increases. The random approach gives more satisfactory results in this comparison study.     

多点激励下绝对位移直接求解算法的误差频域分析

多点激励地震响应分析时,相对运动法将结构内部节点绝对位移分解成拟静位移和动态位移两部分分别进行求解,而绝对位移直接求解法直接对内部节点绝对位移进行求解,在两种求解算法中,阻尼分别假定与内部结点相对速度、绝对速度成比例。两种算法的阻尼假定不同可能会引起计算结果误差,在瑞利阻尼、单元阻尼模型下,采用随机振动方法对两种算法计算结果误差在频域内进行了理论分析,指出了瑞利阻尼模型下两种算法求得的结构动态内力功率谱密度误差主要受结构阻尼比、激励频率与结构基频率比值影响,但单元阻尼模型下两种算法得出的动态内力功率谱密度不存在误差。最后从概率意义上指出：瑞利阻尼模型下,两种算法得出的结构内力响应方差的误差随结构阻尼比的增大而增大,当结构阻尼比不大于5%时,两种算法计算结果误差很小。