考虑多场耦合的碰撞载荷下水中悬浮隧道动力响应

水中悬浮隧道通过系泊系统使其悬浮在水下一定深度处,与潜器的碰撞可能会使隧道结构产生较大运动响应,呈现大幅度的非线性位移,会使隧道失去原有的稳定性甚至对隧道安全性产生较大的影响。因此,本文开展考虑多场耦合场景下碰撞载荷作用下,水中悬浮隧道的运动响应研究。通过与文献中试验结果的对比分析,验证数值模型的有效性。建立水中悬浮隧道及其系泊系统的三维运动模型,同时通过Abaqus建立水中悬浮隧道的碰撞场景与STAR-CCM+进行双向耦合联合仿真,开展水中悬浮隧道被潜器撞击后的运动响应研究,并分析不同碰撞场景下水中悬浮隧道的运动响应变化规律。     

波流作用下悬浮隧道局部锚索的破断动力响应

为研究波流作用下悬浮隧道局部锚索的破断动力响应,运用ANSYS/AQWA软件建立悬浮隧道及其锚泊系统的有限元模型.通过单元生死功能和时控法模拟锚索破断行为,对比分析不同波流条件对悬浮隧道局部锚索破断动力响应的影响.研究结果表明:锚索破断之后,会对剩余锚索产生冲击效应,缆力瞬态增量随着与破断位置距离的增加而逐步递减;规则波、均匀流和锚索破断作用引起的悬浮隧道动力响应具有不同的特征,规则波主要引起结构产生周期运动,均匀流主要引起结构产生大幅偏移和低频运动,锚索破断主要引起结构产生冲击效应和高频振动;锚索破断之后,剩余结构的阻尼增大、刚度降低,导致锚索破断前后的结构运动行为出现明显的不同.     

洋流作用下悬浮隧道动力学行为试验研究

本研究根据相似准则和试验条件设计试验模型。在试验模拟的1节悬浮隧道管段上分别布置2组和3组锚索支撑，测试在不同流速条件下，悬浮隧道管体结构的环向应变、轴向应变及张力腿锚索的轴力。根据试验结果，初步分析悬浮隧道应力的空间分布特征和张力腿的轴力情况；给出在相同环境条件下，张力腿锚索数量对结构应力的影响、洋流速度对悬浮隧道管段结构变形和张力腿轴力的影响关系等。     

悬浮隧道水动力问题研究概述

悬浮隧道作为一种新型的跨水域交通方式近年来引起各国学者广泛的关注,文章在介绍悬浮隧道研究背景与各国发展状况的基础上,首先梳理了悬浮隧道断面形式与管体连接方式的相关研究,分析了不同断面形式的优缺点,概述了管段之间连接、支撑悬浮系统连接以及隧道两端连接的相关成果。文章重点围绕悬浮隧道水动力问题,系统梳理了针对悬浮隧道水动力荷载、不同荷载作用下的运动响应及锚索系统的涡激振动及其抑制问题的研究,最后通过总结前人的研究成果,提出了悬浮隧道水动力研究方面需要进一步关注的问题。     

水流作用下悬浮隧道耦合动力数值模拟分析

安装在深水区的悬浮隧道在水流作用下会产生交替脱落的漩涡,从而使得悬浮隧道受到周期性的力,进一步导致悬浮隧道产生涡激振动。当涡脱落频率与悬浮隧道固有频率相接近时会发生"锁定"现象,进而导致悬浮隧道发生振幅较大的运动,类似于结构的共振状态。文章利用有限元数值方法求解不可压缩粘性流体雷诺平均Navier-Stokes方程,并结合任意拉格朗日-欧拉(ALE)动网格方法,对不同雷诺数下(Re=1 000～100 000)悬浮隧道的涡激振动问题进行了数值模拟研究。计算中悬浮隧道受到弹簧和阻尼的约束,并允许其仅发生横流向的运动,研究了不同结构自振频率下悬浮隧道的受力和运动情况以及不同浮重比情况下悬浮隧道的受力和运动的结果。结果表明,在计算的各雷诺数下,悬浮隧道发生"锁定"的频率基本一致,但是悬浮隧道不同浮重比对"锁定"区间存在影响作用。     

低速碰撞载荷下钢制波纹夹层板动态响应研究

基于有限元软件Ansys/LS-DYNA,对钢制梯形波纹夹层板在低速碰撞载荷作用下的动态响应进行数值仿真研究,分析碰撞能量、冲头直径大小、碰撞位置和冲头撞击方向对夹层板动响应特性的影响。结果表明,随着碰撞能量从100 J增加到400 J,面板变形呈现出线性增加的趋势,碰撞能量达到一定水平后,结构出现损伤破坏,并且发现这种损伤的发生存在相对恒定的临界值,上面板吸能占比减小了30.5%,芯层和下面板吸能占比依次增加了12.4%,18.1%。冲头直径过小会带来明显的载荷局部效应,碰撞位置位于芯层胞元跨中时芯层无法对冲头进行直接支撑,这都会引起上面板的撕裂破坏,甚至被冲头贯穿。随着冲头撞击角度增加,上面板的撕裂破口逐渐由横向变为纵向,夹层板整体的能量吸收速率逐渐变大。在给定的载荷状况下,冲头30°撞击时,夹层板的耐撞性能较优;冲头90°撞击时,夹层板的耐撞性能较差。     

多浮筒悬链线系泊系统计算软件的开发及试验

构建多浮筒悬链线静力学模型,在此基础上进行系泊线姿态计算软件开发。应用均匀弦横向运动模型推导出悬链线方程,对多浮筒悬链线非线性方程组进行迭代计算,获得多浮筒悬链线系泊缆索姿态参数,并试验验证算法的正确性。研究表明:开发的多浮筒悬链线系泊系统计算软件在水平系泊力、系泊缆索参数、海底系锚泊位置、悬跨长度和浮筒规格一定时,能够准确输出系泊系统的真实形状,并准确判断浮筒在水中的位置,满足安装工程施工需求。研究结果可为多浮筒悬链线系泊系统动力分析提供参考。     

考虑静水压力的加筋圆柱壳体径向碰撞机理研究

水下碰撞是水下结构物的主要事故形式之一,而深水静压载荷环境下的碰撞、触礁等问题是深水静压和碰撞联合载荷作用下的结构响应问题,是最为危险的碰撞环境.采用MSC/Dytran大型非线性动力有限元程序,建立数值有限元模型,考虑深水静压和外物撞击的联合作用,进行深水静压环境、无水压力环境下以及不同撞击载荷多工况碰撞环境和撞击历程的数值分析,对加筋圆柱壳体碰撞载荷作用下的变形、失效机理和变形历程进行比较,分析了不同速度、质量撞击物撞击载荷作用下撞击强度、深水压力载荷等对碰撞历程的影响和加筋圆柱壳体深水碰撞环境下的动态响应特性和碰撞机理.结果显示:由于准静压载荷的附连联合作用,撞击形变将不可避免地带来准静压载荷的做功,其能量将直接由结构吸收,从而将导致加筋圆柱壳体结构的防撞能力急剧下降.同时,随着静水压力的增大,撞击初始阶段所产生的小变形将导致圆柱壳体的整体环向失稳,从而导致壳体整体迅速压溃,因此,深水环境下结构碰撞问题的研究主要是结构的初始稳定性问题的研究.圆柱壳体通过横向平台的加强后将有效提高壳体结构的横向失稳临界应力,从而能够明显地改善加筋圆柱壳体结构的径向耐撞能力.     

撞击参数对双层舷侧结构碰撞响应的影响

深入了解船体结构碰撞损伤特性和能量吸收机制是开展船舶耐撞性优化设计的前提。文章利用显式非线性有限元数值仿真技术对不同撞击条件下的双层舷侧结构碰撞响应进行了系列研究。研究结果表明：撞击位置、撞击角度和撞击速度的改变可能导致不同的碰撞损伤过程或结构损伤变形。     

内河航道桥梁船撞时船体最大变形量研究

目前在桥梁船撞防护的专项设计或船撞力专题研究中,对船舶撞击力的研究和桥梁在船舶撞击作用下的响应关注较多,而对船体最大变形量的研究较少。基于ANSYSLS-DYNA软件,对4种不同载质量的内河代表船舶在3种航速、2种碰撞角度下撞击4种墩型的船撞工况进行数值模拟,提取船体最大变形量,并分析船体最大变形量与船舶载质量、撞击速度、桥墩类型及撞击角度的关联性,同时与经验公式做对比。研究结果表明,撞击速度及撞击角度是船体最大变形量的主要控制因素,桥墩类型与之关系不明显。     

On the slack phenomena and snap force in tethers of submerged floating tunnels under wave conditions

Under severe sea wave conditions, the mooring tethers of submerged floating tunnel (SFT) might go slack. It may cause the structure failure during the service lifetime of SFT. The paper investigated SFT dynamics when going through tether slacking and the related snap force under wave conditions. Besides the nonlinearity of fluid drag and of structural geometry for a relative large structure displacement, the problem is characterized by the nonlinearity due to the discontinuity in axial stiffness of the tethers. To include these nonlinearities, the method of Lagrange energy is used to build the governing equations of SFT motion, and a bilinear oscillator is introduced to simulate the mooring tether operating in an alternating slack-taut state. The sensitivities of the occurrence of tether slacking to wave height and wave period are investigated. Results show that at a large wave height SFT tether will go slack and snap force occurs. SFT responses are categorized into three types of state according to the dynamic response characteristics of tether tension. Effects of two fundamental structure parameters, buoyancy-weight ratio (BWR) and inclined mooring angle (IMA), on the dynamic responses of SFT are analyzed. A slack-taut map of SFT tethers is built. It intuitively describes the occurrences of slack and snap force with different combinations of the two parameters. An analytical approach for slack prediction by deriving the slack criterion is provided to reveal the mechanism of the presented slack-taut map. By present research, the authors tried to make their effort to provide an alternative philosophy for SFT structural design on concerning preventing the occurrence of tether slacking and snap force.     

Optimization of submerged floating tunnel cross section based on parametric Bézier curves and hybrid backpropagation - genetic algorithm

The cross-section geometry of a submerged floating tunnel (SFT) has a large effect on hydrodynamic characteristics, structural behavior and service level, making the tunnel cross section the primary factor in optimizing efficiency. Minimizing the mean drag and the dynamic variability in the lift of the SFT cross section under bi-directional (i.e., tidal) flow has a dramatic impact on the reduction of structural displacements and mooring loads. Based on a parametric Bézier curve dynamically comprising the leading-edge radius, tunnel height and width to define the SFT geometry, a sensitivity analysis of the Bézier curve parameters for a fixed aspect ratio with prototype dimensions under uniform flow conditions was conducted by applying Computational Fluid Dynamics (CFD), and the pressure distribution around the SFT cross-section surface was analyzed. A theoretical method comprising the Kármán vortex street parameters was employed to verify the CFD simulation results. In order to determine the SFT cross section with optimal hydrodynamic properties, the mean drag and Root Mean Square (RMS) lift coefficients were selected as optimization objectives, and four Bézier curve parameters were the input variables, in a neural network and genetic algorithm optimization process (a hybrid BP-GA structure), which is less likely to become trapped in local minima. The results show the optimal tunnel cross section has a mean drag and a RMS lift coefficient reduced by 0.9% and 6.3%, respectively, compared to the original CFD dataset.     

Hydrodynamic experiment of submerged floating tunnel under regular wave and current actions during construction period

Submerged floating tunnel (SFT) is an innovative cable-supported structural system for crossing deep and long-distance ocean environments. In the complex ocean environment, the construction of SFT needs to consider wave and current forces. Specific construction measures and control also require in-depth study and understanding of the dynamic response of SFT under such environmental loads. In this study, the dynamic response of SFT and cable forces under the action of waves alone and wave-current interactions are investigated by using a large wave-current basin. A total of 138 regular wave and wave-current cases were conducted during the experiments, and the influence of waves and wave-current interactions on the dynamic response of SFT and cable forces are discussed in detail by combining experimental data with corresponding analysis. Results show that the wave height, current velocity, and ratio of wavelength to structure size are important factors affecting the dynamic response of SFT and cable forces. The multi-anchor cable arrangement used in the present experimental tests distribute cable force more effectively and reduce the potential safety hazard caused by cable breakage. This study can provide a useful reference for the construction and control of the single SFT segment under construction in a complex ocean environment, especially under the interaction of waves and currents.     

Cyclic bending performance of joint on precast composite hollow RC for submerged floating tunnels

In case of a submerged floating tunnel (SFT), which is difficult to cast in-site underwater construction, it is modularized on land and then assembled them in the field. Therefore, it is influential to investigate the structural performance of the joints between the modules. A concept of the steel-concrete composite hollow in the SFT, which stably maintains the joints, has been proposed by applying prestressing method to resist various external loads. In this study, the bending behavior of module joints was experimentally analyzed to evaluate the safety for the bending deformation that is dominant in SFT. Test results show that there is a difference at the module joint portion in the performance depending on whether or not the inner steel tube is connected. The bending stiffness of the module joints in the SFT was very similar but there was a difference in strength. The maximum strength was increased from 700 kN to 1200 kN when the inner tube was connected, and the residual displacement was increased from 15 mm to 40 mm. As a result, in the design of the module joint, depending on the purpose of SFT, it is possible to consider both methods which is allowing the ductility behavior of internal tube and controlling the tight connection. Moreover, the failure criterion of the bending behavior of the module joint can be selected as the maximum load or deformation limit.     

Three-dimensional equivalent static analysis for design of submerged floating tunnel

Stress evaluation of a submerged floating tunnel (SFT) is an issue important for determining the section dimensions required to resist environmental loads. However, the complex interaction between an SFT and surrounding fluid has confined most research on SFTs to longitudinal global time-history analyses based on Morison's equation [1]. Even though these analyses give sufficient information in the longitudinal direction, too little information about the circumferential direction compels an SFT section to be designed conservatively. This means that SFT design requires additional information on the structural behavior of the tunnel in the circumferential direction for efficient design. Accordingly, a supplementary approach by which to obtain structural responses in the circumferential direction is introduced in this paper. Upon consideration of the static responses equivalent to the dynamic behavior, three-dimensional (3-D) finite-element analyses of an SFT were performed by application of static loads corresponding to dynamic loads equivalent to those of wave, current and earthquake. The validation of each equivalent static load was supported by the results from comparison of the tension forces in mooring lines obtained using OrcaFlex [2] and ABAQUS [3]. These were used mainly for longitudinal dynamic analysis and 3-D stress evaluation, respectively, of an SFT. Based on the stresses obtained in the longitudinal and circumferential directions, the selection of suitable section dimensions for an SFT is considered.     

Time-domain coupled dynamic simulation for SFT-mooring-train interaction in waves and earthquakes

In this study, Submerged Floating Tunnel (SFT)-mooring-train coupled dynamics is solved in the time domain to investigate their dynamic and hydro-elastic interactions under wave and earthquake excitations. The SFT is modeled by the rod-FE (finite element) theory, and it is connected to mooring lines through dummy-connection-mass and linear and rotational springs. A 3D rigid-multi-body dynamic model is developed for train dynamics that consists of seven rigid bodies. The tunnel-train interaction is taken into consideration based on the wheel-rail correspondence assumption and the simplified Kalker linear creep theory. The developed computer simulation program is validated through comparisons with commercial programs and published results when possible. In the case of earthquake-induced dynamics of the coupled system, the effects of soil conditions, tunnel length, mooring interval, seismic-wave propagation, and seaquake are investigated. The magnitudes of the SFT downward motions induced by the moving train are small compared with the motions induced by earthquakes. The earthquake causes transient SFT responses especially at their lowest wet natural frequencies while high-frequency motions are induced by seaquake effect. Structural damping and seismic propagation play an important role in dynamic responses. The interaction of the tunnel and moving train is also evaluated for various train speeds in terms of the derailment and offload factors and riding-comfort criterion. For the given SFT and train designs, the offload factor and riding-comfort criterion can slightly exceed their limits at certain earthquake conditions with the speed as high as 70 m/s, which can be adjusted by reducing train speed.     

Effects of roughness on hydrodynamic characteristics of a submerged floating tunnel subject to steady currents

The effects of surface roughness as induced by marine fouling on the hydrodynamic forces on a submerged floating tunnel (SFT) are experimentally and numerically investigated in detail at Reynolds numbers Re = 8.125 × 10³–5.25 × 10⁴. A sensitivity analysis to different roughness parameters including roughness height, skewness, coverage ratio, and spatial arrangement is performed. In addition, an optimized parametric cross-section for an SFT is proposed, and the hydrodynamic performance of the parametric shape and circular SFT cross-section shape with roughness elements is compared. The pressure distribution along the SFT, flow separation and wake characteristics are analyzed to provide a systematic insight into the fundamental mechanism relating the roughness parameters and flow around an SFT. In order to better understand the nonlinear relationships among structural geometry, roughness parameters, flow states, and structural response, an artificial intelligence method using Random Forest (RF) for feature importance ranking is applied. The results show that with the parametric shape, the hydrodynamic forces on the fouled SFT can be effectively mitigated. The roughness height and coverage ratio affect the equivalent blockage and hence, change flow separation and recirculation length in the wake. Lower skewness of the roughness elements can increase the critical Re by changing the relative roughness parameter. Horizontal arrangement of the roughness elements on an SFT generally results in the largest hydrodynamic forces, compared to staggered and vertical distributions. Throughout the feature importance ranking, the flow regime is found to be the most important feature of the hydrodynamics of the SFT. In addition, the SFT cross-section shape and roughness coverage ratio play a dominant role.     

越江盾构隧道纵向受力及变形分析研究

以某越江盾构隧道工程为背景，采用三维梁-弹簧模型对水位变化、河床冲刷等不同情况下盾构隧道的纵向受力及纵向变形进行数值模拟，并对数值计算结果进行了分析。分析可知，纵向上的沉降主要发生在地质条件变化处、地形条件突然变化处以及盾构隧道与竖井的连接处。探讨了盾构隧道与竖井的不同连接方式对于隧道纵向内力及变形的影响，并进行了对比分析．根据分析结果提出采用柔性连接的建议。     

基于有限元的浅埋隧道受力分析及变形破坏处理

采用有限元软件对浅埋隧道受力进行分析,分别从垂直向位移、主应力及剪应变来分析隧道围岩受力情况,分析结果与实际变形破坏一致。垂直向位移最大发生在拱顶,主应力最大集中在拱顶及拱脚,剪应变最大在拱脚。根据分析结果制定合理的隧道变形破坏处理方案,处理后,隧道变形较小,结构稳定。     

Experimental study on the wave-induced dynamic response and hydrodynamic characteristics of a submerged floating tunnel with elastically truncated boundary condition

Hydrodynamic load and motion response are the first considerations in the structural design of a submerged floating tunnel (SFT). Currently, most of the relevant studies have been based on a two-dimensional model test with a fixed or fully free boundary condition, which inhibits a deep investigation of the hydrodynamic characteristics with an elastic constraint. As a result, a series of difficulties exist in the structural design and analysis of an SFT. In this study, an SFT model with a one-degree-of-freedom vertical elastically truncated boundary condition was established to investigate the motion response and hydrodynamic characteristics of the tube under the wave action. The effect of several typical hydrodynamic parameters, such as the buoyancy-weight ratio, γ, the relative frequency, f/f_N, the Keulegan–Carpenter (KC) number, the reduced velocity, U_r, the Reynolds number, Re, and the generalized Ursell_s number, on the motion characteristics of the tube, were selectively analyzed, and the reverse feedback mechanism from the tube's motion response to the hydrodynamic loads was confirmed. Finally, the critical hydrodynamic parameters corresponding to the maximum motion response at different values of γ were obtained, and a formula for calculating the hydrodynamic load parameters of the SFT in the motion state was established. The main conclusions of this study are as follows: (i) Under the wave action, the motion of the SFT shows an apparent nonlinearity, which is mainly caused by the intensive interaction between the tube and its surrounding water particles, as well as the nonlinearity of the wave. (ii) The relative displacement of the tube first increases and then decreases with increasing values of f/f_N, U_r, KC number, Re, and the generalized Ursell_s number. (iii) γ is inversely proportional to the maximum relative displacement of the tube and the wave force on the tube in its motion direction. (iv) Under the motion boundary condition (as opposed to the fixed boundary condition), the peak frequency of the wave force on the SFT in its motion direction decreases and approaches the natural vibration frequency of the tube, whereas the wave force perpendicular to the motion direction increases. When the incident wave frequency is close to the natural vibration frequency of the tube, the tube resonates easily, leading to an increased wave force in the motion direction. (v) If the velocity in the Morison equation is substituted by the water particle velocity measured when the tube is at its equilibrium position, the inertia coefficient in the motion direction of the tube is linearly related to its displacement, whereas that in the direction perpendicular to the motion direction is logarithmically related to its displacement.