【作者】 李杰；

【导师】 李乔； 杨万理；

【作者基本信息】 西南交通大学 ， 桥梁与隧道工程， 2019， 硕士

【摘要】 改革开放以来,我国交通建设事业得益于经济发展而取得迅速进步。作为基础设施的跨海大桥相关建设也随之而起。跨海大桥的基础不仅要承受上部结构自重和车辆荷载,还受到海域水体的水动力作用。群桩承台基础是跨海大桥常用的基础形式,但目前相关规范中尚无关于群桩承台基础的波流作用力的计算方法。因此,本论文结合物理模型试验与数值模拟方法重点研究了桩心距l/D=2的五桩群桩在纯波、波流共同作用条件下的受力特征。首先设计了物理模型试验,测取了单桩和群桩结构物在3个不同相对水深各3个不同波陡共9个非线性波浪参数条件下的各向波浪力,以及在3个不同流速分别与波浪联合作用共27个波流参数条件下的各向波流力。利用CFD软件Fluent结合速度入口造波、动量源消波方法建立了三维数值水槽,模拟了纯波动流场对群桩和孤立单桩的作用。然后探讨了纯波作用条件下,波向角对群桩整体波向力的影响,分析了0°群桩各组成桩的波向力特征,并从流场作用过程角度与孤立单桩工况对比,分析了群桩效应的具体影响。最后通过力系数分析方法分析了单桩及群桩的波向力系数、横向力系数及合力系数分别与KC数的关系,并对单桩、群桩在纯波及波流共同作用条件下横向力的时域和频域特征做了详细分析。得到以下主要结论:(1)计算纯波作用条件下群桩整体的波向力时,当KC>7.5时,以0°群桩正向峰值作为最不利计算依据。当KC数为2.5~7.5时,以45°度群桩负向峰值作为最不利计算依据。(2)由于流的影响,单桩在波流共同作用条件下的波向力系数与合力系数之比的离散性、横向力系数与合力系数之比的离散性,都比纯波作用时大;单桩在波流共同作用条件下的波向力占合力的比重较纯波作用时小,波流横向力占合力的比重较纯波作用时大。(3)相较于单桩工况,群桩各组成桩间的相位差,使得群桩横向力正负相互抵消,减小了横向力占合力的比重。而在波流共同作用条件下,群桩各组成桩相互干扰对横向力比重的减小效果更为明显。(4)计算单桩和群桩整体的纯波合力、波流合力时,横向力的作用均不可忽视。(5)对于单桩,在波流横向力的频谱中,0.5倍波频(0.5f_W)的整数倍(0.5f_W、1f_W、1.5f_W、2f_W……)的频率,对应幅值在频谱中的比重明显比纯波作用时大。流对单桩波流横向力频谱的贡献主要在低频段,即流增大纯波横向力、纯流横向力中已有低频成分对应幅值在波流横向力频谱中的比重。(6)流对群桩整体波流横向力频谱的影响作用和单桩相同。但对于群桩,无论纯波或纯流作用时,水质点速度较大时,由于各组成桩的相互影响,在群桩整体横向力的频谱中均会出现较多高频成分。因此,对于群桩,群桩波流横向力的频率成分在频谱中的比重分配,由群桩各桩干扰引起的高频成分和流贡献的低频成分共同决定。更多还原

【Abstract】 Since the reform and opening up,China’s transportation construction has made rapid progress due to economic development.As an infrastructure,the construction of cross-sea bridge has also started.The foundation of sea-crossing bridge not only bears the self-weight of superstructure and vehicle loads,but also is affected by the hydrodynamic force of sea water.Pile group and cap foundation is a common form of foundation for sea-crossing bridges,but there is no calculation method for wave-current force of pile group and cap foundation in relevant codes at present.Therefore,based on physical model tests and numerical simulation,the force characteristics of five-pile group with distance l/D=2 under wave and wave-current conditions are studied in this paper.Firstly,the physical model tests of single pile and pile group were designed.The waveinduced forces of structures were measured,which was caused by 9 non-linear wave cases with three different relative water depths and three different wave steepness.Also,the wave-current forces of structures were measured,which was caused by 27 wave-current cases with three different velocities combined with 9 wave parameters.Then a three-dimensional numerical flume was built by CFD software ANSYS Fluent,combined with velocity inlet wave-making method and momentum source wave-eliminating method.The effect of wave field around pile group and single pile were simulated.Then,the effect of wave propagation direction on the overall force of pile group under wave condition is discussed,and the force characteristics of each pile in 0° pile group are analyzed.And the detailed influence of pile group effect is analyzed by comparing with that of single pile.Finally,the relationship between force coefficients including wave direction force coefficient,transverse force coefficient and resultant force coefficient and KC is analyzed.Then the time-frequency domain characteristics of transverse force of single pile and pile group under wave and wave-current conditions are analyzed in detail.The main conclusions are as follows:(1)The wave direction force of pile group is calculated as a whole under wave condition.When KC > 7.5,the most disadvantageous calculation basis is the positive peak value of 0°-pile group.When the KC is 2.5-7.5,the negative peak value of 45°-pile group is the most disadvantageous basis for calculation.(2)Because of the influence of current,the discreteness of the ratio of wave direction force coefficient to resultant force coefficient and the discreteness of the ratio of transverse force coefficient to resultant force coefficient of single pile under the condition of wave-current are larger than those under wave condition;the proportion of wave direction force to resultant force of single pile under the condition of wave-current is smaller than that under wave condition,and the proportion of transverse force to resultant force is larger than that under wave condition.(3)The phase difference between the piles makes the positive and negative transverse forces of piles cancel each other out in pile group,which reduces the proportion of the transverse force to resultant force.Under wave with current condition,the effect of interaction between piles of pile group on the reduction of transverse force ratio to resultant force is more obvious.(4)The transverse force can not be neglected when calculating the resultant forces of single pile and pile group,whether under wave or wave-current conditions.(5)For a single pile,in the spectrum of wave-current transverse force,at the frequency which is 0.5 times of wave frequency and its integral multiple frequency,the proportion of corresponding amplitude in the spectrum is obviously larger than that of wave condition.The contribution of current to the wave-current transverse force spectrum of a single pile is mainly in the low frequency band,that is,in the spectrum of wave-current transverse force,current enlarges the proportion of corresponding amplitude of the low frequency components that also exist under the condition of wave or current.(6)The effect of current on wave-current transverse force spectrum of pile group is the same as that of single pile.But for pile group,regardless of wave or current conditions,when the velocity of water particle is high,the interaction of piles in pile group makes more high frequency components appear in the transverse force frequency spectrum of pile group.Therefore,for pile group,the distribution of frequency components in wave-current transverse forces spectrum of pile group are determined by the high frequency component caused by the interference of piles in pile group and the low frequency component of the flow contribution.更多还原