地震和波流作用下海底悬跨管线模型实验研究

利用水下地震-波流联合模拟实验系统研究了海底管线在波浪、水流和地震作用下的动态响应特征。实验中考虑了有无地震作用、悬跨长度、波浪高度、水深、水流速度以及是否满管状态等因素。通过DDP动态数据后处理软件对实验结果进行处理分析,得到海底悬跨管道的动态响应特性。实验结果表明:在浅海海域,悬跨管线的动态反应受波浪及水深变化的影响不明显,悬跨长度是影响管道动态响应的主要影响因素;悬跨管线在地震与波流共同作用下的反应与仅地震作用下的应变存在差别;在波浪力作用下,空管时管线的应变要小于满管时的情况。     

随机波浪作用下近岸波流场的数值模拟

结合近岸波浪抛物型缓坡模型和近岸波流场模型，对近岸不规则波浪及其破碎后所产生的流 场进行了数值模拟. 在不规则波浪场的模拟中，采用JONSWAP波浪谱对入射单向不规则波浪 要素按等分频率法进行离散，应用考虑波浪不规则性和破碎效应的抛物型缓坡方程对波浪场进行 数值模拟，并基于抛物型缓坡方程中的波浪势函数等参数计算波浪辐射应力，以波浪辐射应 力为主要动力因素基于近岸流数学模型对近岸波浪破碎所产生的近岸流场进行数值模拟，并 对数值模拟结果进行了验证. 模拟结果表明该模型可有效地用于研究波浪破碎产生的近岸波 流场.     

波浪场中物质输移离散系数的理论分析

海岸水域波浪引起的物质输移扩散存在着不同于水流引起的物质 输移扩散的特征. 通过解析的方法对垂向扩散方程进行求解, 推导出波浪和潮流共同作 用下的海岸水域物质输移离散系数的理论公式. 分析中将总的离散系数分为潮流、质量输移 流、纯波浪波动作用以及潮流与质量输移流、潮流与波浪波动、质量输移流与波浪波动的相 互作用6部分, 通过分析各组成部分特征, 得出海岸水域物质输移中波浪所产生的离散效应 主要是质量输移流贡献, 波浪水质点运动及波流相互作用对时间平均离散系数的贡 献较小的结论. 仅波浪的作用(不包括潮流)的有关结果与他人数值模拟和实验结果的吻合良好, 证 明了该理论推导的正确性. 给出了时间平均离散系数及离散系数波动幅值随波浪周期和波高 的变化特征,同时将结果应用于垂向环流, 给出了垂向环流对应于质量输移流所产生的离散 系数的特征.     

海冰与波流耦合动力学的研究进展

随着全球气候变暖,北极活动频次的逐渐增加,海冰与波流的耦合作用成为了国内外的热点研究问题. 海冰的存在会改变波浪的传播特性和色散关系,也会改变海流运动的边界条件,使得海流在冰面下边界处可能产生漩涡脱落等现象;而海冰在波浪、海流等动力作用下,也会不断发生生消、断裂、重叠和堆积等动力学行为.海冰与波流耦合动力学中存在几大难点问题:一是海冰模型的构建,需要针对海冰类型和性质的不同,考虑不同区域的海冰分布情况建立合适的海冰模型.二是冰水之间的耦合问题,海冰边界影响着冰水之间的动量和能量交换,对于冰盖、浮冰等不同类型海冰,需分别处理边界问题;冰水耦合引起的海冰破坏,其破坏模式也是多样的.三是波流联合场的构建,目前尚无较好的方法构建波流联合场,导致海冰与波流联合场作用的相关研究仍极其匮乏.因此,本文针对海冰与波流相互作用问题,回顾和讨论国内外对海冰与波浪、海冰与海流及海冰与波流相互作用的研究现状和技术难点,展望了未来可以进一步深入研究的问题,提出了初步的思路以供参考.      

河口混合与泥沙输运

根据振荡边界层理论和波流分解方法,导出了河口往复水流的流速垂向分布廓线,据此建立了河口垂向准二维水流、盐度、泥沙运动模型。对泥沙输运,完整地考虑了其对流、扩散、起动和沉降的动力学过程。模拟结果与实测资料进行了对比。应用该模型研究河口泥沙输运,分析了河口混合对泥沙输运的影响及最大浑浊带的时空变化规律。     

非均匀水流水域波浪的传播变形

将两个不同的、考虑波流相互作用和能量耗散项的、依赖时间变化的双曲型缓坡方程分别化 为一组等价的控制方程组，具体分析了底摩阻项对相对频率和波数矢的影响，从而选择了合 适的数学模型. 将所选择的缓坡方程化为依赖时间变化的抛物型方程，并用ADI法进 行数值求解，建立了缓变水深水域非均匀水流中波浪传播的数值模拟模型. 通过和波流共线 的解析解的比较，说明数值解和解析解相一致. 结合Arthur(1950)水流这一经典算例，定 量地讨论了考虑联合折射-绕射作用后的波数和仅考虑折射作用的波数的差别及其对波高分 布的影响. 在基本同样的条件下, 本文的数值解与他人的计算结果一致.     

非均匀水流中非线性波传播的数值模拟

以一种考虑波流相互作用的新型{Boussinesq}型方程为控制方程组， 采用五阶{Runge}-{Kutta}-{England}格式离散时间积分，采用七点 差分格式离散空间导数，并通过采用恰当的出流边界条件，从而建立了非均匀水流中非线性 波传播的数值模拟模型. 通过对均匀水流与水深水域内和潜堤地形上存在弱流或强流时波浪 传播的数值模拟，说明模型能有效地反映水流对波浪传播的影响.     

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本文以ANSYS软件为平台建立了近底床钢管-混凝土单层悬跨海管有限元模型，综合应用PIPE59单元、MATRIX27单元和COMBIN40单元模拟了管内流体流动引起的科氏力、离心力以及海管与底床的弹性接触，计算了不同悬跨长度下的海管位移、应力及固有频率，通过与工程常用规范对照，验证了模型的正确性。研究表明，应用ANSYS软件可模拟近底床悬跨海管在内流、外流共同作用下的位移、应力及固有频率，本文建模方法便于工程应用。     

海底悬跨管线涡激振动实验方法探讨

随着我国海洋石油开采业的发展,海底悬跨管线涡激振动的研究越来越受到重视。本文总结了海底悬跨管线涡激振动的实验研究与进展,对海底悬跨管线的涡激振动实验方法、测试技术、分析方法以及实验中可能存在的难点问题进行了详细讨论和分析;给出了波流水槽内稳定流、波浪以及波流联合作用等条件下海底悬跨管线的涡激振动实验设计原则和方法,进行了海底悬跨管线的涡激振动实验设计,实验主要关注于涡激共振由一阶共振向二阶共振过渡的模态过渡特征以及过渡范围内管线的振动特征,目前实验已在大连理工大学海岸和近海工程国家重点实验室的波流水槽中完成;最后,提出了相关的研究建议。     

波流场中的桩柱结构地震反应研究

采用理论分析及有限元模拟的方法, 对波流场中桩柱结构的地震动力反应进行了研究. 除考虑波流场作用在桩柱上的波流力和动水压力外, 根据模型试验结果认为还需考虑作用在 桩柱上的涡振横向力. 通过地震作用下波流场中四桩平台的有限元模拟计算, 发现 水中地 震放大了桩柱结构的动力反应; 波流力和涡振横向力共同作用导致桩的相对位移、剪力及弯 矩值大幅提高, 但是对桩身加速度影响较小; 桩底部位易于发生地震破坏.     

明渠中悬移质的弥散-对流方程及悬浮机理

悬移质泥沙通常构成冲积河流总输沙量的主体, 研究悬移质的悬浮机理具有重要的意义. 以双流体模型为基础, 通过引入弥散速度的概念, 建立了悬移质泥沙的输沙方程以及泥沙扩散系数的本构关系. 应用该方程分析了二维明渠均匀流中悬移质泥沙浓度垂向分布规律, 并与Einstein 和Chien 的泥沙浓度实验资料及经典扩散理论进行了对比. 以此为基础, 分析了紊动扩散、颗粒自身的紊动、颗粒碰撞应力对泥沙悬浮的影响在垂向上的变化, 以及浓度、粒径等对这些因素的影响. 结果表明, 泥沙颗粒在明渠紊流中的扩散是浑水的紊动扩散、颗粒自身的紊动、颗粒碰撞应力3 部分不同机制共同作用的结果, 把泥沙颗粒的悬浮简单归因于水流的紊动是不全面的.     

细颗粒泥沙净冲刷和输移的大涡模拟研究

在传统水沙输移数值模拟研究中一般采用雷诺时均模拟技术(Reynolds-averaged simulation,RANS).与RANS相比,大涡模拟技术(large eddy simulation,LES)能够更加精确反映细部流动结构,计算机的发展使得采用LES探讨水流和泥沙运动规律成为可能.本文尝试给出净冲刷条件下悬沙计算的边界条件,采用动态亚格子模式对循环槽道和长槽道中的水流运动和泥沙输移进行了三维大涡模拟研究.利用直接数值模拟(direct numerical simulation,DNS)结果对LES模型进行了率定,计算结果符合良好,在此基础上初步探讨了泥沙浓度、湍动强度和湍动通量等的分布特征.结果表明,净冲刷条件下输沙平衡时泥沙浓度符合Rouse公式分布,单向流动中泥沙浓度沿着流向逐渐增大.泥沙浓度湍动强度和湍动通量都在近底部达到最大值,沿着垂向迅速减小.湍动黏性系数和扩散系数基本上在水深中间处达到最大.湍动Schmidt数沿着水深方向不是常数,在近底部和自由水面附近较大,在水深中间处较小.     

Wave propagation analysis of porous functionally graded piezoelectric nanoplates with a visco-Pasternak foundation

This study investigates the size-dependent wave propagation behaviors under the thermoelectric loads of porous functionally graded piezoelectric(FGP) nanoplates deposited in a viscoelastic foundation. It is assumed that(i) the material parameters of the nanoplates obey a power-law variation in thickness and(ii) the uniform porosity exists in the nanoplates. The combined effects of viscoelasticity and shear deformation are considered by using the Kelvin-Voigt viscoelastic model and the refined hi...     

Stress diffusion and high order viscoelastic effects in the 3D flow past a sedimenting sphere subject to orthogonal shear

The effect of polymer stress diffusion in the unbounded flow past a sedimenting, freely rotating, rigid sphere subject to shear in a plane perpendicular to the direction of sedimentation is investigated analytically. Steady state, creeping, incompressible, and isothermal flow is assumed. For viscoelastic fluids following the Oldroyd-B constitutive model, three-dimensional results for the velocity vector, pressure, and viscoelastic extra-stress tensor are derived by including an artificial diffusion term in the constitutive equation and using regular perturbation theory with the small parameter being the Deborah number. The analytical solution reveals that the influence of the stress diffusion term on the results may be significant (and sometimes unexpected) and strongly depends on the magnitude of the dimensionless diffusion coefficient. For instance, it is shown that the critical Deborah number, below which a physical solution arises, decreases with the increase in the diffusion coefficient. Also, comparison against simulation results from the literature shows excellent agreement up to shear Weissenberg number (defined as the product of the imposed shear rate with the single relaxation time of the fluid) approximately equal to unity.     

Structuring of suspended sediments in periodic vortex flow over a vortex ripple

The formation of spatially ordered structures in a suspended sediment under the action of two-dimensional standing surface gravity waves is studied experimentally for the first time in a rectangular vessel oscillating in the vertical direction. The parameters of the structured regions in vessels with individual vortex ripples and groups of ripples are found for the first and second wave modes. Isolated structured regions of the suspended sediment appear over the bottom topography and gradually reach the free surface. The corresponding spatial horizontal scales are determined by the sand ripple dimensions, while the vertical scale of the clouds increases with time. In all experiments, the structures formed remained unchanged during the whole interval of the fluid wave motion and disappeared when the parametric excitation of the waves stopped.     

Dispersion of fine settling particles from an elevated source in an oscillatory turbulent flow

The present paper examines the stream-wise dispersion of suspended fine particles with settling velocities in an oscillatory turbulent shear flow with or without a non-zero mean over a rough-bed surface when the particles are being released from an elevated continuous source. A finite-difference implicit method is employed to solve the unsteady turbulent convective-diffusion equation. A combined scheme of central and four-point upwind differences is used to solve the steady state equation and the Alternating Direction Implicit (ADI) method is adopted for unsteady equation. It is shown how the mixing of settling particles is influenced by the tidal oscillatory current and the corresponding eddy diffusivity when the initial distribution of concentration regarded as a line-source. The vertical concentration profiles of suspended fine particles with settling velocities are presented for different downstream stations for various values of settling velocity and the frequency of the oscillation in tidal flow. For two-dimensional unsteady dispersion equation, the behaviour of iso-concentration lines for different values of settling velocity, frequency of the oscillation, dispersion time and releasing height is studied in terms of the relative importance of convection and eddy diffusion.     

结构中微裂纹与超声波的混频非线性作用数值仿真研究

针对结构中微裂纹检测难题,本文对结构中微裂纹与超声波的混频非线性作用进行了数值仿真研究。基于经典非线性理论,得到了两列超声纵波相互作用产生混频效应的理论条件。通过有限元仿真,研究了两列纵波与微裂纹相互作用产生混频的条件,并分析了界面处静应力、摩擦系数和裂纹方向对混频效应的影响。研究发现,超声波与微裂纹相互作用产生混频非线性效应的发生条件仍符合经典非线性理论下的混频产生条件。裂纹界面处施加的静应力对差频横波幅值有明显影响;当施加静应力与无裂纹模型得到的最大应力值接近时,混频非线性效应最强;裂纹界面的摩擦系数对超声波的混频非线性效应影响较小;透射差频横波传播方向与经典非线性理论预测的理论差频分量方向基本一致,且几乎不受裂纹方向变化的影响,而反射差频横波的传播方向随裂纹方向的改变而有所不同。本文研究工作为微裂纹检出及方向识别做了有益探索。     

General Spatial Dynamic Problem for an Elliptic Crack under the Action of a Normal Shear Wave,with Consideration for the Contact Interaction of the Crack Faces

Consideration is given to the contact interaction of the faces of a stationary plane elliptical crack under the action of a harmonic shear wave normally incident on the crack surface. The dependence of the mode II and III stress intensity factors on the wave number is studied for different values of the friction coefficient     

Experimental study on near wall transport characteristics of slug flow in a vertical pipe

In this work, the wall shear stress and the mass transfer coefficient of the gas–liquid two-phase upward slug flow in a vertical pipe are investigated experimentally, using limiting diffusion current probes and digital high-speed video system. In experiments, the instantaneous and averaged characteristics of wall shear stress and mass transfer coefficient are concerned. The experimental results are compared with the numerical results in previous paper of the authors. Both experiment and numerical simulation show that the superficial gas and liquid velocities have an obvious influence on the instantaneous characteristics of the two profiles. The mass transfer coefficient has characteristics similar to the wall shear stress. The instantaneous wall shear stress and mass transfer coefficient profiles have the periodicity of slug flow. The averaged wall shear stress and mass transfer coefficient increase with increased superficial gas velocity. However, there is inconsistency in the variation trends of the averaged wall shear stress and mass transfer coefficient with superficial liquid velocity between experimental result and numerical simulation result, which can be attributed to the difference in flow condition. Moreover, the Taylor bubble length is also another impacting factor. The experimental and numerical results all shows that the product scale can not be damaged directly by the flow movement of slug flow. In fact, the alternative forces and fluctuations with high frequency acting on the pipe wall due to slug flow is the main cause for the slug flow enhanced CO₂ corrosion process.