多自由度减震结构体系分析

本文对多自由度减震结构体系建立了数学模型，进行了力学分析，给出了完整的计算方法。另外还对正弦激励和一般地震波作用下的响应进行了减震效果分析。     

Passive control of offshore jacket platforms

The wave-induced dynamic force is one of the most important excitations to be dealt with in the design of offshore structures. In order to perform a reliable design of an offshore structure, it is important to obtain an exact evaluation of its dynamic response but also to examine the ways of reducing the response. This paper presents the response of offshore jacket platforms installed with energy dissipation devices such as viscoelastic, viscous and friction dampers under wave loading. The offshore jacket platforms are modeled as multi-degrees-of-freedom system provided with dampers at each floor location. The wave forces are modeled as per Morison's equation. The governing equations of motion of the jacket platform with dampers are derived and their solution in the frequency domain is presented. The uni-directional random wave loading is expressed by the Pierson-Muskowitz spectrum. The response of the jacket platform with viscoelastic, viscous and friction dampers is compared with the corresponding response without dampers in order to investigate the effectiveness of the passive control systems. It is observed that the additional dampers add substantial damping to structure and thus favorably control the response of platform structure. Among the various energy dissipation devices used for study, the viscoelastic dampers perform better in comparison to the other dampers. This is due to the fact that the added viscoelastic dampers contribute to increased viscous damping as well as lateral stiffness which reduces the response of the offshore jacket platforms significantly.     

An integral swash zone model with friction: an experimental and numerical investigation

Experimental and numerical analyses have been used to assess the validity and potentialities of the integral swash zone model by Brocchini and Peregrine (Proc. Coastal Dynamics '95, ASCE 1 (1996) 221) which is extended to include seabed friction effects previously neglected. Applications of the model to experimental data show it represents a simple and useful tool for modelling swash zone flows. The model allows for computation of integral swash zone properties and shoreline motion from local variables defined at the seaward limit of the swash. For most properties, correlation between local and integral properties is very good (correlation coefficient about 0.80).A suitable parametric form of frictional forces in the swash zone is defined on the basis of both experimental data and analytical investigation. Numerical tests showed that the proposed parameterization models well integral frictional forces within the swash zone. The parametric friction force improves capabilities of the integral swash zone model of representing real swash motions. This is particularly evident when considering the momentum equation: the correlation coefficient between the rate of change of the onshore momentum in the swash zone and its forcings increases from about 0.85 to about 0.95 due to the inclusion of the seabed friction.     

Nonlinear hydrodynamic pressures generated by a moving high-rise offshore cylinder

Both analytical (small time expansion) and numerical (finite-difference) approaches have been used to solve the earthquake-induced nonlinear hydrodynamic pressure acting on a rigid high rise offshore cylinder. For the high rise offshore cylinder, the most part of the flow field is independent of z and a three dimensional hydrodynamic analysis can be reduced to a two dimensional analysis. At onset, the dimensionless ground displacement ?² = 0 for the two dimensional analysis, the normalized hydrodynamic pressures across cylinder face is a constant and is independent of the radius of the cylinder. The normalized horizontal force coefficient C_fx is independent of intensity of ground acceleration and is approximately linear and proportional to ?² and its onset value is equal to π. For a linear analysis i.e. neglecting nonlinear convective acceleration, the normalized hydrodynamic pressure coefficient is also independent of the radius of cylinder. The analytical method was good for ground motion in a single direction, the results of simultaneous action of two components of ground acceleration can be obtained by the superposition of the results due to separate excitation. But the superposition method is only valid in the linear analysis. For highly nonlinear problem, the present finite difference approach is recommended.     

转角阻尼器对海洋平台-摇摆墙体系抗振分析

在海洋平台摇摆墙体系基础上,提出在海洋平台和摇摆墙之间刚性连接杆的铰接点处安装粘弹性转角阻尼器的减振措施,对海洋平台进行进一步减振控制。对粘弹性转角位移阻尼器的刚度和阻尼参数进行了优化分析,可知阻尼器的阻尼与刚度在结构减振中起到了十分重要的作用,且存在特定范围内的优化值。以JZ20-2北高点井口平台为例,利用ANSYS进行地震荷载作用和实测挤压冰荷载下的仿真分析,研究了粘弹性转角阻尼器在海洋平台和摇摆墙之间刚性连接杆铰接点处的不同安装方式,对比分析减振效果。结果表明,在该体系刚性连接杆的铰接点处安装粘弹性转角阻尼器能显著降低结构的振动反应,连接杆右侧安装粘弹性转角阻尼器的方式为减振效果最佳方式。     

Dynamic estimation of hydrodynamic damping

Data on the acceleration of an oscillating cylinder in water are analysed by a Kalman extended filter. A hydrodynamical forcing model based upon Morison's equation appears to be reasonable and drag estimation appears simple using simulated data. Estimation based upon real data gives an average drag coefficient decreasing with the oscillation amplitude. An assymetric drag coefficient variation over the oscillation period is estimated.     

随机波作用下埋管海床动态响应及液化研究

基于广义Biot动力理论和Longuet-Higgins线性叠加模型,构建波浪-海床-管线动态响应的有限元计算模型,求解随机波作用下,多层砂质海床中管线周围土体孔隙水压力和竖向有效应力的分布。采用基于超静孔隙水压力的液化判断准则,得出液化区的最大深度及横向范围,从而判断海床土体液化情况。考虑海洋波浪的随机性,将海床视为多孔介质,海床动态响应计算模型采用u-p模式,孔隙水压力和位移视为场变量。并考虑孔隙水的可压缩性、海床弹性变形、土体速度、土体加速度以及流体速度的影响,忽略孔隙流体惯性作用。参数研究表明:土体渗透系数、饱和度以及有效波高等参数对海床土体孔隙水压力、竖向有效应力和液化区域分布有显著影响。     

Wave-induced vibration control of offshore jacket platforms through SMA dampers

Since permanent wave-induced vibrations of offshore jacket platforms reduce the service life of the jacket structure and deck equipment and increase the fatigue failure of the welded connections, this research has used SMA (shape memory alloy) dampers to control the jacket platform oscillations. Superelasticity, high durability, and energy dissipation capability make SMA elements good nominees for the design of vibration control devices. In this research, to model the force-displacement hysteretic behavior of SMA elements their idealized multi-linear constitutive model has been implemented and the time history responses of vibration equations have been evaluated by direct integration method. To analyze the SMA damper effects on the vibration suppression of the jacket platforms, a 90 (m) high jacket located 80 (m) deep in water has been selected as a case study. Numerical results have shown that optimized SMA dampers with constant-geometry SMA bars will improve the dynamic behavior of the jacket platform under the action of an extreme regular wave. However, under the action of two irregular waves, SMA dampers with varying-geometry SMA bars will cause significant reduction in the dynamic responses of the jacket platform. The power spectral density function of the deck displacements have shown that the previously mentioned SMA dampers avoid resonance by shifting the natural frequencies of the jacket structure away from the excitation frequencies.     

Seismic Passive Earth Pressure with Seepage for Cohesionless Soil

The authors deal with the computing seismic passive earth pressure acting on a vertical rigid wall. The wall is provided with a drainage system along soil-structure interface and retains the cohesionless backfill subjected to water seepage. A general solution for the seismic passive earth pressure is presented. The solution is based on Coulomb's theory wherein seismic forces are assumed to be pseudostatic. The solution considers the pore water pressures induced by water seepage and earthquake shaking. Some important parameters are included in the solution. The parameters are the soil effective internal friction angle, wall friction, soil unit weight, and horizontal and vertical seismic acceleration coefficients. The comparison of the total seismic passive earth pressure in horizontal direction from the present method with published works indicates that the present method may be reasonable. The variations of the passive earth pressure coefficient with the soil effective internal friction angle are investigated for different wall friction angles and seismic forces. The effect of the water seepage on the seismic passive earth pressure is also investigated.     

近十年来的海洋灾害与减灾

10年来，我国沿海地区经济尤其海岸带（沿海带）经济和海洋经济持续、高速发展，社会财富积累量迅速攀升，使承灾体在量上讯速增大，同时也使海洋及海岸灾害经济损失和人员伤亡急速增长，海洋灾害成为中国自然灾害中损失增长最快的。但由于在沿海实施了正确的减灾战略，加大了防灾减灾能力的建设，不但较好地保证了沿海和海洋经济的可持续发展，而且使我国的海洋灾害经济损失系数（灾害经济损失/GDP）保持在1.23%的较好水平，这仅为同期全国自然灾害经济损失系数的1/3，接近于世界减轻自然灾害较先进的发达国家。     

Field Studies of Dynamic Compaction on Marine Deposits

Marine deposit ground usually need significant improvement before the construction of civil structures in coastal areas due to the poor mechanical properties of soils. Dynamic compaction (DC) is a widely used technique in such projects. In this study, a case history of DC tests in sandy soils with a weak embedded layer is introduced. Two series of DC tests—single point tests and impact zone tests—were applied to test zones with similar geological conditions to investigate the effect of energy level on the depth of improvement (DI). The highest energy used is up to 15000 kN · m. Field measurements were conduct before and after DC in each series to validate the effectiveness of improvement, including crater settlement, excessive pore pressure, and acceleration measurement for single point tests, and the pressure meter and CPT tests for impact zone tests. For single point tests, the effectiveness of improvement increases as the energy level increases to 12000 kN · m. Further increase of compaction energy does not have an effect on settlement, pore pressure, or ground acceleration. For impact zone tests, the energy level does not show a positive correlation with the DI, mainly due to the presence of an embedded weak layer.     

HY-1C卫星海岸带成像仪叶绿素a浓度反演研究

叶绿素a作为最重要的水质参数之一,是评价水体富营养化和初级生产力状况的主要因素。我国海洋一号C（HY-1C）卫星海岸带成像仪（CZI）具有高时空分辨率的观测优势。本文基于东海和南海现场实测数据建立了HY-1C卫星CZI叶绿素a浓度反演模型并在实测水域进行反演,与MODIS叶绿素a浓度反演产品进行了对比验证,应用CZI叶绿素a浓度模型在珠江口、长江口、渤海湾水域进行了叶绿素a浓度反演示例试验。结果表明,叶绿素a浓度模型估算浓度与实测浓度相关系数为0.774 3,平均相对误差为24.58%,利用实测叶绿素a浓度对模型进行精度验证,相关系数达到0.993 9,平均相对误差为18.49%。模型在实测水域反演得到的叶绿素a浓度分布与MODIS叶绿素a浓度产品分布大体一致。在珠江口水域反演得到叶绿素a浓度空间分布为由西北向东南逐级递减,峰值出现在珠江口西沿岸。在长江口、渤海湾反演叶绿素a浓度空间分布均符合地理实情。研究表明HY-1C卫星CZI数据可应用于中国近海水色定量化研究。     

西伯利亚极地海域表层沉积硅藻分布特征及其与海洋环境变量的相关性研究

北冰洋西伯利亚陆架海是北极气候快速变化最为显著的海域之一,而沉积硅藻作为极地海洋生态系统的重要组成部分,对环境变化具有敏感的响应。对楚科奇海、东西伯利亚海和拉普捷夫海表层沉积物开展了硅藻组成鉴定,利用典型对应分析方法分析了硅藻属种与1986～2015年环境变量之间的关系。结果表明,夏季和秋季海冰密集度、表层海水盐度是影响研究区表层硅藻分布特征最主要的因素。此外,根据表层站位与环境变量的典型对应分析,可将西伯利亚极地海域划分为4个区域,分别为海冰硅藻组合带、暖水硅藻组合带、沿岸硅藻组合带和混合硅藻组合带。这些表层站位的分区与相应区域的海流模式有明显的相关性,海冰硅藻组合带仅分布于研究区北部的高纬度地区;暖水硅藻组合带位于受白令水和太平洋海水的分支——阿拉斯加沿岸水影响为主的区域;拉普捷夫海南部的沿岸硅藻组合带则受到河流径流和西伯利亚沿岸流的强烈影响;混合硅藻组合带受极地冷水、海冰覆盖、太平洋暖水和陆地径流的共同影响。     

规则波和不规则波作用下消波建筑物前的波高分析

消波建筑物在国内外已得到广泛应用。本文采用近似方法分析了明基床上直立式消波建筑物前的波高及消波室内的波高，从而确定建筑物的消波效果。并在规则波的基础上将成果推广至不规则波作用下的情况。     

基于UDF的水平轴潮流能水轮机被动旋转水动力性能研究

针对水平轴潮流能水轮机被动旋转问题,基于Fluent 17.0,运用UDF(User Defined Function)控制滑移网格对网格进行动态调整,仿真研究水轮机在不同安放角下被动旋转的水动力特性。通过仿真分析,结果表明:潮流能水轮机随着叶片安放角度的增加,尖速比、输出功率、捕能系数都是先增大后减小,叶片安放角为6°时,叶轮前后速度差最大,对潮流能利用充分,且各项性能均达到最佳;通过分析叶片受力,叶尖叶素在安放角为2°时阻力最大,3°时升力最大,升阻比在6°时最大,此时叶尖叶素升阻比C_L/C_D=6.27、攻角α=3.06°。由仿真结果可知水平轴潮流能叶轮的自启动过程由5个阶段组成,即加速度增大的加速运动段—加速度减小的加速运动段—加速度反向增大的减速运动段—加速度反向减小的减速运动段—稳定运行段,这对潮流能水轮机的设计具有重要的指导意义。     

安达曼海东南部海域表层沉积物粒度特征及净输运趋势

海底沉积物粒度是反映水动力格局最直接的指标,可以有效指示不同时间尺度陆源碎屑物质输运过程。利用激光粒度仪对取自安达曼海东南部海域的98个表层沉积物样品进行粒度分析,结果表明,研究区表层沉积物以粉砂、砂质粉砂及粉砂质砂为主,且粒度组成空间分区明显：北部陆架为粗粒级且分选差的残留砂质沉积区;南部内陆架为混合沉积区,以砂质粉砂、粉砂质砂和粉砂沉积为主;丹老阶地和陆坡为细粒级且分选较好的粉砂和泥质沉积区。在此基础上选用Gao-Collins“粒径趋势”方法分析了该区域表层沉积物的净输运趋势,结果显示,当特征距离<0.8°时,普吉岛东南部海域存在沉积中心,研究区沉积物有向该区域汇聚的明显趋势,沉积物分布特征和输运趋势主要受陆源物质供给、季节性变化的西南季风流以及潮流的综合影响。     

黏土中防沉板—桩复合基础地震反应特性研究

为了研究海底防沉板—桩复合基础在地震荷载作用下的动力反应特性,以我国南海深水工程实例为研究对象,利用Flac3D有限差分仿真软件建立了计算模型,土体采用Mohr-Coulomb本构模型,模型底部输入EL Centro地震波,对不同桩长的复合基础进行分析计算.在该特定工程背景下,研究结果表明:随着桩长的增加,防沉板顶部加速度放大系数呈减小趋势;地震荷载下,复合基础发生震陷,沉降量在地震波加速度峰值过后趋于稳定;当桩长为6m时,复合基础的水平振动程度和震陷量最小;由于桩基础把震动能量传输到深部土层中,复合基础周围土体的加速度响应值小于远场土体.在动力时域内,防沉板与桩连接处弯矩最大,需要在此处增设加固装置.     

Analysis of loads,motions and cavity dynamics during freefall wedges vertically entering the water surface

In this paper, theoretical models are developed and numerical methods are used to analyze the loads, motions and cavity dynamics for freefall wedges with different deadrise angles vertically entering the water surface at Froude numbers: 1 ≤ Fn < 9. The time evolutions of the penetration depth, the velocity and the acceleration are analyzed and expressed explicitly. The maximum and average accelerations are predicted. The theoretical results are compared with numerical data obtained through a single-fluid BEM model with globally satisfactory agreement. The evolution of the pressures on the impact side is investigated. Before flow separation, gravity and the acceleration of the wedge have negligible influence on the pressure on the impact side for large Froude numbers or small deadrise angles; with increasing the deadrise angle or decreasing Froude number, the effects of gravity and the acceleration of the wedge tend to become more important. Global loads, with the main emphasis on the drag coefficient, are also studied. It is found that for the light wedge, the transient drag coefficient has slow variation in the first half of the collapse stage and rapid variation in the last half of the collapse stage. For the heavy wedge, the transient drag coefficients vary slowly during the whole collapse stage and can be treated as constant. The characteristics of the transient cavity during its formation are investigated. The non-dimensional pinch-off time, pinch-off depth and submergence depth at pinch-off scale roughly linearly as the Froude number.