STUDY ON THE FORECAST METHOD FOR THE IMPACT OF CROSSWAY ON TIDAL CURRENT FIELD IN SEA AREA

This paper's method simulates the tidal current field near piles to derive and predict the scale oftheir impacts on the tidal current field, and presents the empirically obtained damp coefficient needed inpedicting the current field. The substituted plans used in the prediction are studied using Qingdao.Crossway as an example.     

LONGITUDINAL STREAM-PROFILES AS INDICATORS FOR GEOMETRIC SEGMENTATION OF THE LANGSHAN- HUANGBAISI FAULT ZONE, NORTHWEST BEIJING

The Langshan-Huangbaisi fault zone in northwest Beijing is the southwestern part of the normal fault zone on the northern margin of the Yanqing basin, 35.5km long and NNE-NEE-trending in general, on which two major 130°- 140° bends separate it into three segments with different strikes.Using the Hack's method, 71 longitudinal stream-profiles along the fault zone are analysed, shawing a well geomorphic response to the fault geometry. On these two major bends the gradient indices,K value     

Delay-dependent stability and added damping of SDOF real-time dynamic hybrid testing

It is well-recognized that a transfer system response delay that reduces the test stability inevitably exists in real-time dynamic hybrid testing (RTDHT).This paper focuses on the delay-dependent stability and added damping of SDOF systems in RTDHT.The exponential delay term is transferred into a rational fraction by the Padé approximation, and the delay-dependent stability conditions and instability mechanism of SDOF RTDHT systems are investigated by the root locus technique.First, the stability conditions are discussed separately for the cases of stiffness, mass, and damping experimental substructure.The use of root locus plots shows that the added damping effect and instability mechanism for mass are different from those for stiffness.For the stiffness experimental substructure case, the instability results from the inherent mode because of an obvious negative damping effect of the delay.For the mass case, the delay introduces an equivalent positive damping into the inherent mode, and instability occurs at an added high frequency mode.Then, the compound stability condition is investigated for a general case and the results show that the mass ratio may have both upper and lower limits to remain stable.Finally, a high-emulational virtual shaking table model is built to validate the stability conclusions.     

阻尼对行车荷载下大跨桥梁振动的影响

基于车桥相互作用,建立了车桥耦合单元,一个车辆模拟为4轴10个自由度模型,桥梁模拟为梁单元,推导出列车桥梁整体系统运动方程的有限元计算公式.采用随机数值模拟方法和功率谱密度函数生成随机轨道粗糙度.编制了计算程序,考虑各种不同的阻尼参数及车辆速度,对一座实际大跨斜拉桥的动力反应与冲击效应进行了分析研究.     

冻结黏土的动力学参数确定方法研究

基于黏弹性理论,对土的动弹性模量和阻尼比确定方法进行探讨,并结合青藏铁路沿线黏土在一系列温度下的动三轴试验结果,给出冻结黏土的动弹性模量和阻尼比的确定方法.结果表明：冻结黏土的骨干曲线不是双曲线,建议通过滞回曲线求冻土的动弹性模量和动应变幅,从而获得它们之间的关系;不同计算方法得到的阻尼比随动应变幅的变化趋势基本相同,用滞后角法计算得到的阻尼比整体小于用能量损失法计算得到的阻尼比,建议采用相关函数法计算应变滞后于应力的滞后角,然后用滞后角法计算土的阻尼比;冻结黏土的阻尼比随动应变幅的增加而增大.     

基于块体基础自由振动计算地基阻尼比的新方法

提出了一种基于能量守恒原理计算地基土阻尼比的新方法。不同于对数衰减法仅依据振幅计算阻尼比,该方法考虑了体系振动的整个反应时程,克服了对数衰减法对幅值测量精度要求很高的缺陷。数值仿真和实测结果表明：与对数衰减法相比,该方法计算精度较高,抗干扰能力强,稳定性好,即便对于信号干扰比较大的情况,采用该方法也能得到较好的结果。     

Who is the most stressed? Morphological disparity and mechanical behavior of the feeding apparatus of ceratopsian dinosaurs (Ornithischia,Marginocephalia)

Ceratopsians were herbivorous dinosaurs that dominated many of the terrestrial ecosystems in Asia and North America during the Cretaceous. The bizarre variety of skulls and lower jaw morphologies as well as the inferred ecological abundance of many species in this clade indicate that Ceratopsia was a successful group. Here we analyzed 126 lower jaws from 50 ceratopsian species, using two-dimensional geometric morphometrics and finite element analysis to investigate differences in shape and structural performance of this part of the feeding apparatus across Ceratopsia. Morphological differences in lower jaws across ceratopsian clades are said to originate from feeding adaptation.Our results show that the stress (physical loadings modeled in response to biting) in lower jaws was quite similar between “basal” and “derived” taxa, whereas major differences among clades occur for stress values associated with the coronoid process. The basal ceratopsians Hualianceratops and Yinlong had a highly stressed and primitive lower jaw, indicating that those animals may have fed on relatively soft foliage and fruits. A similar condition was found for basal neoceratopsians and protoceratopsids. Psittacosaurids possessed a well-integrated and compact lower jaw able to withstand high stress, at the cost of having a highly stressed coronoid process. Leptoceratopsids were characterized by the opposite condition. Taxa such as Leptoceratops, Prenoceratops, Zhuchengceratops and Cerasinops appear to have had a comparatively efficient feeding apparatus. Ceratopsidae represents the clade with the most efficient masticatory apparatus within Ceratopsia, even if the horizontal ramus of the lower jaw appears less able to withstand high levels of stress as compared with other ceratopsians. Additionally, we found the dentary and surangular–angular complex co-evolved to generate a masticatory apparatus able to withstand high stress, particularly in Protoceratopsidae and Triceratopsini. The major phenotypic evolutionary rate and morphological changes occurred during the mid- to Late Cretaceous, when intense climate change and angiosperm diversification could have affected the evolution of ecological diversity and feeding biomechanics in Ceratopsia.     

改进的薄层单元在桩-土动力相互作用中的应用

在地震荷载作用过程中,由于桩身材料性能与周围土体性质差异较大,土体在桩-土接触面上发生张开或滑移,该强非线性接触行为直接影响接触面附近土体与桩体应力状态,从而影响上部结构地震响应水平。真实桩-土接触面由于桩身表面混凝土约束关系,具有一定厚度且存在相关体变规律的接触带。通过有限元软件ABAQUS用户自定义单元UEL程序编写改进Desai薄层接触单元,在Desai薄层接触单元中加入Rayleigh阻尼项以模拟地震作用时桩-土强非线性接触行为能量耗散过程。接触面法向与两切向本构关系采用双曲线模型。规定了Desai薄层接触单元在桩-土接触面上的行为模式以模拟土体在接触面黏结、滑动、张开、再闭合等接触状态。建立精细三维桩-土-结构体系动力相互作用模型以研究改进Desai单元对上部结构峰值动力响应水平影响,为工程结构抗震设计时程分析提供参考依据。     

南海北部区域黏土循环动力特性试验研究

采用南海北部区域油田场址钻孔原状土样,开展黏土循环动力特性试验研究。结合共振柱与应变控制的循环单剪试验,获取动剪切模量和阻尼比随循环剪应变的变化规律,将最大动剪切模量与原位静力触探的计算结果进行对比。开展应力控制的循环单剪试验,采用对称加载方式获取土样动强度阈值,基于该阈值,通过单、双向加载方式获取土样动强度包络线,并将试验结果与Drammen黏土及世界范围内其余区域黏土进行对比。该研究初步获取了南海北部区域性黏土的循环特性及动力学参数,为南海北部区域油气田结构设计和地质风险评估提供基础资料,掌握了循环动力特性试验方法,为岩土工程动力学试验研究及数据分析提供技术参考。     

Universal model forms for predicting the shear modulus and material damping of soils

Numerous model forms have been used to predict the dynamic behaviours of soils, mainly the shear modulus and material damping. These models are used to represent normalised shear modulus reduction and material damping curves. The majority of the existing models are empirical and were proposed for specific soil types, strain ranges, etc. Some are limited to the data used in fitting, but fail to provide a good fit to other sets of data. The available model functions are not universal, which means that a model developed for one soil type may not be applicable for use with other soil types. In this paper, two universal mathematical models were proposed to predict the normalised shear modulus reduction and material damping curves. The mathematical model forms are sufficiently flexible to be widely used with different soil types. The models were evaluated using verification data of eight different soil types, i.e., data that were not used to fit the model parameters. The results indicate that the proposed model forms can accurately model the dynamic soil properties within the typical earthquake range. The advantage of developing the two universal models are two-fold, first the forms are applicable for sand, clay, and fibre-soil composite and second with further testing of soils, the model coefficients could ultimately be used to further understand the physical processes in soil behaviour, especially damping.