【作者】 张帆；

【导师】 柳春光；

【作者基本信息】 大连理工大学 ， 结构工程， 2024， 硕士

【摘要】 随着全球对交通基础设施的持续投资,深水桥梁的建设受到了广泛关注。由于深水桥梁因部分或全部结构位于深水中,在地震与流体联合作用下受力复杂,并且,由于桥梁跨度不断增长,桥梁的墩高也逐渐增大,桥墩柔性进一步增强。但现有墩水耦合模型通常认为结构是刚性的,不考虑由于外部荷载引起的结构弹性变形。为了更精确的求解,符合实际情况,本文提出了一种考虑柔性变形的双向流固耦合模型,并分析了静水中结构在地震作用下的动力特性及响应机制。本研究基于现有流固耦合分析理论,采用Navier-Stokes方程模拟流体流动受力,通过有限元法计算结构振动响应,利用Fluent自定义函数进行双向流固耦合仿真。主要研究内容包括:(1)开发出考虑柔性的双向流固耦合振动响应时域分析模型以及求解器,并对该模型进行验证。与现有方法相比,新模型在计算中引入结构的柔性变形,更接近实际情况。同时,该求解器可用于模拟静止及振动圆柱的流场,分析不同频率和振幅下的结构振动影响,能够有效的捕捉到由于结构弹性变形引起的振动响应;其次,求解器添加了倾斜模块,可以模拟更真实的环境,用于分析不同倾斜角度下结构的振动响应,通过有限元建模的方法,能够精确采集到结构的高阶模态。(2)通过与现有墩水耦合模型进行对比,本文提出的新型模型在处理高频激励时显示出更高的精确性和有效性。新模型能够捕捉到在高频和大振幅激励下,结构可能遭受的剧烈影响和潜在破坏。(3)对不同工况下的竖直圆柱型桥墩进行受力分析,研究了不同的频率和振幅的外部激励对于结构的影响。研究结果表明,静水中结构对外部激励的频率更加敏感,当频率相同,振幅不同时,结构阻力和升力、顶点的位移和速度随激励加速度的振幅增大而增大;当振幅相同,频率不同时,结构阻力和升力随激励加速度的振幅增大而急剧增大,结构顶点的位移和速度随激励加速度的变化相对不明显。(4)研究了在中等强度工况下,桥墩结构周围的流场分布情况:在一个受力周期内,结构表面自由水面和动水压强沿180°处对称分布;在同一时刻,结构表面不同高度处动水压强幅值变化激烈,在z=15m处动压最大,z=5m处和15m处动压变化相近。对不同工况下结构不同分段处的阻力和升力进行研究,发现在高频时,最大阻力出现在结构中部,最大升力出现在自由水面附近和底部,结构受力频率集中结构的高阶频率和外界输入频率附近;在低频时大阻力和最大升力出现在结构中部,结构受力频率集中在基频和外界输入频率附近。对于不同的激励频率,需要综合考虑结构的受力情况。(5)通过对结构周围的流场分析,发现:结构受到的动水压力分布与外界的频率输入有关。当外界频率属于较低时,如0.5Hz,1.75Hz,结构表面及附近流场的动水压强表现出沿结构竖直方向均匀分布,较远处保持原状;当外界频率较高时,如3Hz,结构的一侧在中部会形成一个大面积压强区,并在自由水面附近迅速降低,在另一侧则并未出现,由此导致了高频下结构在c1段合力为负,在静水面处受力达到合力的90%。这种现象表明对于易受到高频振动影响的静水结构,不仅要考虑结构下端的承载能力,在静水面附近也需要进行优化设计。更多还原

【Abstract】 With continuous global investment in transportation infrastructure,construction of deepwater bridges has received extensive attention.Because the deep water bridge is located in the deep water partially or wholly,the stress is complex under the combined action of earthquake and fluid,and the pier height of the bridge is gradually increased due to the continuous increase of bridge span,so the pier flexibility is further enhanced.However,the existing pier water coupling model usually considers the structure to be rigid,and the elastic deformation caused by external load is not considered.In order to solve the problem more accurately and conform to the actual situation,a two-way fluid-solid coupling model considering flexible deformation is proposed in this paper,and the dynamic characteristics and response mechanism of structures under earthquake in still water are analyzed.Based on the existing theory of fluid-solid coupling analysis,the Navier-Stokes equation is used to simulate the fluid flow stress,the finite element method is used to calculate the vibration response of the structure,and the Fluent self-defined function is used to simulate the two-way fluid-solid coupling.The main research contents include:(1)The time domain analysis model and solver for two-way fluid-solid coupling vibration response considering flexibility are developed and verified.Compared with the existing method,the new model introduces the flexible deformation of the structure in the calculation,which is closer to the actual situation.At the same time,the solver can be used to simulate the flow field of static and vibrating cylinder,analyze the influence of structural vibration under different frequencies and amplitudes,and effectively capture the vibration response caused by the elastic deformation of the structure;Secondly,a tilt module is added to the solver to simulate a more realistic environment,which is used to analyze the vibration response of the structure under different tilt angles.The high order modes of the structure can be accurately acquired by the finite element modeling method.(2)Compared with the existing pier water coupling model,the new model proposed in this paper shows higher accuracy and effectiveness in dealing with high frequency excitation.The new model captures the potentially severe effects and potential damage to structures under high frequency and large amplitude excitations.(3)The influence of external excitations of different frequencies and amplitudes on the structure is studied.The results show that the structure in still water is more sensitive to the frequency of external excitation.When the frequency is the same and the amplitude is different,the structure resistance and lift,displacement and velocity of the vertex increase with the increase of the amplitude of the excitation acceleration;When the amplitude is the same and the frequency is different,the structure resistance and lift increase sharply with the increase of the amplitude of the excitation acceleration,and the displacement and velocity of the structure vertex change with the excitation acceleration is relatively insignificant.(4)The distribution of the flow field around the pier structure under the moderate intensity condition is studied: the free water surface and the hydrodynamic pressure on the structure surface are symmetrically distributed at 180 ° in a lifting period;At the same time,the dynamic pressure varies strongly at different heights of the structure surface,and the maximum dynamic pressure is at z=15m,and the dynamic pressure changes similarly at z=5m and 15 m.The resistance and lift at different sections of the structure under different working conditions are studied.It is found that at high frequency,the maximum resistance occurs in the middle of the structure,the maximum lift occurs near the free water surface and the bottom,and the higher frequency of the structure with concentrated stress frequency and the external input frequency;At low frequency,the large resistance and the maximum lift occur in the middle of the structure,and the stress frequency of the structure concentrates around the fundamental frequency and the external input frequency.For different excitation frequencies,the stress of the structure shall be comprehensively considered.(5)Through the analysis of the flow field around the structure,it is found that the hydrodynamic pressure distribution of the structure is related to the external frequency input.When the external frequency is low,such as 0.5Hz and 1.75 Hz,the hydrodynamic pressure on the surface of the structure and near the flow field is uniformly distributed along the vertical direction of the structure,and remains unchanged at a distance;When the external frequency is high,such as 3Hz,one side of the structure will form a large area of pressure zone in the middle,which will rapidly decrease near the free water surface,and the other side does not appear.Therefore,the resultant force of the structure at section c1 is negative under high frequency,and the force at the static water surface reaches 90% of the resultant force.This phenomenon indicates that the bearing capacity at the lower end of the structure and the optimal design near the static water surface should be taken into consideration for the still water structure vulnerable to high frequency vibration.更多还原