复合材料船舶底部结构搁浅的性能研究

应用有限元软件ABAQUS/explicit对复合材料船中底部结构与礁石碰撞的动力学过程进行仿真模拟。通过对比分析复合材料船舶在不同航速以及不同材料铺层下的船底结构的搁浅性能,包括接触力、结构吸能及速度变化历时过程,研究表明,在船舶搁浅过程中,船舶初始速度对搁浅性能有很大影响;船舶骨材的吸能要显著于板材;复合材料的铺层形式对搁浅性能的提高具有一定作用。     

船舶搁浅于台型礁石场景极限强度解析预报方法

针对双层底油轮搁浅于台型礁石的事故场景,通过对船底构件结构损伤机理的分析,提出一套结合船底结构损伤程度推算方法和Smith方法,评估损伤后船体剩余极限强度的解析计算预报方法。研究中应用数值仿真技术,模拟了船舶搁浅过程中的结构损伤及搁浅后船体极限承载过程,并与解析预报方法的结果进行了对比。结果表明,文中提出的对搁浅损伤后船舶剩余强度的解析预报方法准确性较好,对船舶双层底耐撞性结构设计和安全性评估都有一定的指导意义。     

高能搁浅下双层底结构的损伤特性研究

船舶搁浅事故会引起船体破损、环境污染和人员伤亡等严重后果.研究船舶搁浅,不仅有利于海上生命安全、防止海洋污染,还可为船体结构的抗冲击设计及规范航运繁忙区域中船舶的航速、操作规程提供一定的依据.本文用数值仿真法研究了船舶高能搁浅中的内部力学问题,分析了典型双层底结构的损伤变形、受力和能量耗散等结果,提出了一种新式的抗搁浅YF双层底结构,并与原结构进行了比较.研究表明,损伤变形集中于结构与礁石相接触的区域,高能搁浅内部力学问题的研究可以主要考虑局部的船体结构;肋板的存在显著增加了船底结构的抗搁浅能力;高能搁浅过程中,由于垂直方向的接触力,礁石对双层底的垂向贯入量会略有减小;当纵桁远离搁浅区域时,它的吸能能力无法发挥,抗搁浅作用很弱;YF双层底结构比原结构具有更大的吸能能力和抗搁浅力.     

船舶结构的搁浅数值仿真研究

文章用数值仿真法研究了船舶结构搁浅中的内部力学问题,分析了典型双层底结构的损伤变形、受力和能量耗散结果。研究表明,损伤变形集中于搁浅的区域,搁浅力学问题主要考虑局部的船体结构;肋板的存在显著地增加船底结构的抗搁浅能力,使礁石的垂向贯入量会略有减小;当纵桁远离搁浅区域时,它的吸能能力无法发挥,抗搁浅作用明显削弱。     

船舶双层底结构与台形礁石碰撞能量及搁浅阻力分析

提出一套基于双层底油轮搁浅于台型礁石场景下的结构损伤变形非线性机理模型和解析计算方法,并通过数值仿真计算验证该机理模型和解析方法的准确性。在整合双层底板材变形解析计算模型和加强筋变形解析计算模型的基础上,提出的结构变形机理模型能够同时考虑船底板材和加强筋的变形模态。以双层底油轮的一个舱段作为研究对象,使用数值仿真软件LS_DYNA在较大的撞深和礁石倾角变化范围内进行仿真计算,并进行比较。研究结果表明该解析计算模型的总变形能和平均水平搁浅阻力与数值结果吻合得较好,从而验证了机理模型和解析计算方法的可靠性。研究成果可以方便地应用到双层底船舶搁浅场景的结构性能快速预报,以及船舶耐撞性能结构设计中。     

单点搁浅船舶的横倾预报方法

本文用船舶静水力性能计算的方法解决了单点或小面积触底搁浅的船舶船底所受支承力及其受力中心位置的计算方法问题，并以此为基础，提出了搁浅船舶在潮高下降时横倾角及倾覆危险的预报方法。     

双壳船体结构在楔形物撞击下的损伤特性试验及数值仿真分析

[目的]船舶碰撞的后果往往是灾难性的,尤其是由双壳油轮碰撞或搁浅事故所造成的海洋生态灾难,多年都难以恢复。为评估双壳结构的耐撞性能,开展双壳船体结构在楔形物撞击下的损伤特性试验与仿真研究。[方法]首先,针对双壳体结构模型开展准静态碰撞实验;然后,利用有限元软件LS-DYNA对双壳体结构试验模型进行数值仿真。[结果]结果显示:试验和数值仿真结果在撞击载荷响应与变形破坏模式上吻合较好;双壳体结构内、外壳板的变形及破坏模式区别较大;内、外壳板之间的横隔板产生的塑性变形会延迟外壳板的断裂。[结论]所做研究可用于船体舷侧结构或船底结构在遭受碰撞或搁浅时的损伤性能评估。     

考虑弹塑性土体作用的船舶搁浅损伤特性研究

船舶软搁浅是指船舶搁置在由较软粘土构成的海床或者在柔软的浅滩上的事故。航运业的发展与船舶的大型化趋势使船舶发生软搁浅的风险大大增加,研究船舶的软搁浅性能对船舶设计与制造具有重要意义。本文基于有限元分析软件ABAQUS,选取典型的软搁浅场景,以12,000DWT油船舱段结构为分析对象,研究舱段结构在搁浅过程中的变形、吸能、加速度响应等性能参数。通过系统分析不同速度对船体结构的搁浅性能的影响,全面分析其搁浅性能。本文的相关结论可以为分析船舶软搁浅事故及设计抗冲击舱段结构有一定指导作用。     

预报搁浅船舶船体强度的一种简化方法（一）

虽然对搁浅事故造成的破坏后果已有所了解，但可被设计者用来来评估船舶发生搁浅时船体强度的工具却非常少。本文提出了一种发生搁浅事故时预报船底强度的简化方法。船体的结构单元在船舶长度方向呈现周期性布置的特征，因此，船舶搁浅过程产生的船体变形阻力在某种程度上也是呈现纵向周期性的特征。对于船底的主结构单元，本文主要考虑以下四种破坏模式：横向结构的拉伸破坏、船底板的凹陷破坏、撕裂破坏以及蛇腹形撕裂破坏。将用于这些特定破坏模式的计算公式组合起来，建立了预报船底强度的简化方法。对照一系列大尺度搁浅试验结果以及某实际发生的搁浅事故对所提出的简化预报方法加以校核，证明所提出的预测方法是正确的。该方法最具吸引力的地方在于万一发生船舶搁浅事故时能采用这种方法通过手工计算来预报船体的强度。     

船底座礁实验数值模拟中选择参数影响研究

非线性有限元方法是分析船舶碰撞和搁浅问题的一个强有力工具,但是数值模拟结果的可靠性很大程度上依赖于对工程问题的恰当处理和有限元软件中主要参数的准确控制.本文以某单壳船底结构准静态座礁实验结果为例,用非线性有限元软件LS-DYNA进行数值模拟,研究了下列选择参数对单壳船底结构抗撞性的影响:边界条件;船底结构的材料模型;壳单元类型;船底结构与礁石模型之间的摩擦系数;船底结构的残余应力.通过比较计算结果的碰撞力曲线,能量吸收曲线来评价这些参数对数值模拟的影响并给出了一些建议.     

试样极限塑性和船舶触礁模型试验校准计算

船舶碰撞与搁浅时的结构损伤是一个复杂的动态非线性过程。国际船舶与离岸结构会议碰撞与搁浅委员会（ISSC－V.3)组织其成员进行了两项专题研究：（1）材料极限塑性极限应变试验数据用于有限元模型计算时的尺度修正系数；（2）各种计算方法用于船舶搁浅（触礁）计算的准确性。介绍了作者承担上述两项研究的成果，给出了极限塑性极限应变的尺度修正系数的计算方法和结果，论证了非线性有限元显式积分方法及MSC／Dytran软件用于搁浅计算的准确性。     

Research on shafting alignment considering ship hull deformations

Ship hull deformation is one of the most significant influences on propulsion shafting alignment. Based on the calculation fundamentals of ship hull deformations, a new method of shafting alignment considering ship hull deformations is proposed in this paper. Ship loadings, wave loads and environment temperature differences in some extreme conditions, as well as elastic constraints, are simulated and applied to the finite element model of 76,000 DWT product oil tanker, so that ship hull deformations can be solved. Then, the deformations of the double bottom are converted to bearing offsets, which behave as boundary constraints for shafting alignment calculations. Taking the condition of light ship in calm water as a reference, the impact of hull deformations on shafting alignment is analyzed and optimized shafting alignment considering ship hull deformations is realized.     

Analysis of structural crashworthiness of double-hull ships in collision and grounding

A conceptual design framework for collision and grounding analysis is proposed to evaluate the crashworthiness of double-hull structures. This work attempts to simplify the input parameters needed for the analysis, which can be considered as a step towards a design-oriented procedure against collision and grounding. Four typical collision and grounding scenarios are considered: (1) side structure struck by a bulbous bow, (2) side structure struck by a straight bow, (3) bottom raking, (4) bottom stranding. The analyses of these scenarios are based on statistical data of striking ship dimensions, velocities, collision angles and locations, as well as seabed shapes and sizes, grounding depth and location. The evaluation of the damage extent considers the 50- and 90-percentile values from the statistics of collision and grounding accidents. The external dynamics and internal mechanics are combined to analyse systematically the ship structural damage and energy absorption under accidental loadings.     

Full six degrees of freedom coupled dynamic simulation of ship collision and grounding accidents

By taking advantage of the user-defined load subroutine (loadud) and the user common subroutine (usercomm) in LS-DYNA, the authors proposed a new coupled approach for simultaneously calculating structural damage and the planar 3DOF ship motions in ship collisions. The coupled procedure aimed at predicting the detailed structural damage together with reasonable global ship motions. This paper extends the method to consider the full 6DOF ship motions; thus, ship collision as well as grounding accidents can be properly handled. This method is particularly useful for design purposes because the detailed ship hull profile is not needed.A traditional ship maneuvering model is used for the in-plane surge, sway and yaw degrees of freedom with a series of nondimensional coefficients determined from experiments. It is assumed that the out-of-plane degrees of freedom are not coupled with the in-plane ship motions, and there is no coupling among roll, pitch and heave motions. The implementation is verified through free decay tests, and the obtained natural periods show good agreement with theoretical results.Several collision and grounding cases are simulated in which a supply vessel crashes into rigid plates with different orientations. The effects of the roll motion, the heave and pitch motions and the full 6DOF motions are studied. The results are compared with those from a 6DOF decoupled method. Ship motions through the proposed method compare reasonably well with SIMO results. It is found that several consecutive impacts may occur in the simulation of one collision case due to the periodic motions. This is not taken into account in the decoupled method, which makes this method unconservative.     

A simplified method to predict grounding damage of double bottom tankers

This paper presents a set of analytical expressions for the calculation of damage opening sizes in tanker groundings. The simplified formulas were given for the grounding force, longitudinal structural damage and the opening width in the inner and outer plating of a tanker's double bottom. The simplified formulas derived are based on a set of numerical simulations conducted with tankers of different dimensions- 120, 190 and 260 m in length. The simulations were performed for five penetration depths and for several rock/ground topologies.The formula for the horizontal grounding force was derived provided the grounding force is proportional to the contact area and the contact pressure. By use of regression analysis it was shown that the contact pressure for any combination of ship and rock size can be expressed with a single normalized polynomial. The actual contact pressure was found by scaling the normalized pressure with the structural resistance coefficient. Given the formulation for the normalized contact pressure, the actual contact force for a ship can be found as a product of average contact pressure and the contact area.The longitudinal length of the damage was evaluated based on the average contact force and the kinetic energy of the ship. The damage opening widths in the outer and inner bottom of the ship were derived separately for two ranges of relative rock sizes as they have strong influence on the deformation mode. The damage widths were given as a function of rock size, penetration depth and double bottom height. To improve the prediction of the onset of the inner bottom failure, a critical relative penetration depth as a function of the ratio of the rock size and the ship breadth was established.Comparison to the numerical simulations showed that the derived simplified approach describes the horizontal grounding force and the damage length well for the penetration depths above 0.5 m. For the range of specified relative rock sizes, the damage width in the inner and outer bottom deviates from numerical simulations approximately up to 25%, which was considered sufficient for the analyses where rapid damage assessment is needed. Comparison was also made to real accidental damage data and to the results of several simplified formulas.     

Analytical modelling of ship bottom grounding considering combined surge and heave motions

This paper provides a new contribution to the analytical treatment of ship grounding accidents. New formulations are proposed to assess the resisting force of outer/inner bottom plating and transverse floors when the vessel undergoes combined surge and heave motions during the grounding event. Considering shallow and sharp rocks described by parabolic functions, analytical solutions are derived from plastic limit analysis and validated by comparison to non-linear finite element simulations. A failure criterion is also proposed to trigger the rupture of the bottom plating and all the derived closed-form expressions are implemented into an in-house solver. The solver is then coupled to a 6-DOFs external dynamics program, which allows to account for the action of the surrounding water. Resulting tool is first validated on a full scale cruise ship by comparison to finite element results. It appears than although some discrepancies arise, especially in the response of transverse floors after rupture, the bottom damage distribution seems to be well predicted. Finally, the developed tool is used to quickly predict the grounding response of different types of ships and the influence of their mass and hydrodynamic properties on the damage extent is investigated.     

Plate tearing and bottom damage in ship grounding

A theoretical method for plate tearing by a rigid wedge is developed in this paper. The studied model is an idealization of ship-grounding and collision damage. The analysis model postulates that the plate curls up into two curved surfaces behind the wedge tip and that the plate material ahead of the wedge is tensioned and ruptured due to the direct pushing. Based on a parametric study, a semi-empirical formula is proposed for determining grounding force in the event of a ship running onto rocks in a high-energy grounding. The bottom strengths of single hull structures and double hull structures in ship-grounding incidents are compared. Finally, simple formulae for determining damage resistance and the extent of damage in ship grounding, expressed in terms of the ship principal particulars, are developed.     

Investigation on structural performance predictions of double-bottom tankers during shoal grounding accidents

An investigation is carried out in this paper for the predictions of structural performance of double-bottom tankers during ship grounding over the “shoal” type seabed obstacles. Hong and Amdahl developed a simplified analytical model for the unstiffened double bottom. This method is carefully studied, verified and then used as the first stage of our prediction. The second stage is concerned with stiffeners since stiffeners are indispensable components for double-bottom tankers. A prevailing way to handle is to smear stiffeners onto their attached plating known as the smeared thickness method. However, the effective ratio in this method is dubious in such shoal grounding accidents. Proper values of this parameter are determined in stage two, and then together with the method in stage one, constitute a reliable and efficient tool for structural performance predictions of double-bottom structures in shoal grounding accidents.A double-bottom tanker is chosen as object for the case study. Finite element models of the hold both stiffened and unstiffened are created for numerical simulations using the LS_DYNA software. Simulation cases cover a wide range of slope angles of the indenter and indentations. Numerical results show that Hong and Amdahl's model in stage one is capable of predicting energy dissipation with high precision but poor accuracy for grounding resistances, and a possible reason may be the neglect of vertical resistance. The updated smeared method proposed in stage two is also proved to be capable of grasping major characteristics of stiffeners. Results and conclusions drawn from this paper can be conveniently applied for assessments of the performance of ship double-bottom structures during shoal sliding grounding scenarios, and will benefit the application of accidental limit state design concept in the ship design stage.