晃荡要求对散货船压载舱结构的影响探讨

协调版共同结构规范（CSR-H）对散货船液舱的晃荡强度提出新的要求。针对散货船专用压载舱,通过对晃荡载荷的规范计算,并结合实船统计数据对比,探讨了基于CSR-H的晃荡要求对散货船专用压载舱结构设计的影响,包括有效晃荡长度、有效晃荡宽度和构件尺寸等。     

Ship motion-sloshing interaction using a field method

Even in relatively calm waters, low amplitude wave-induced motions of an LNG carrier may induce large amplitude liquid sloshing inside the ship's partially filled tanks, and the interaction between ship motions and sloshing may affect the ship's seekeeping properties. A computational procedure, here referred to as the RANS-RANS method, was developed to account for this interaction, and this method was then employed to predict the free surface flow inside the tanks and the corresponding motions of the ship in regular head and beam waves. This method coupled a compressible VoF technique with a generic wave generation and absorption scheme to obtain wave-induced ship motions with and without considering the effects of sloshing in the ship's tanks. Systematic grid studies were performed to obtain a sufficiently fine grid needed to yield converging predictions. The resulting wave patterns, ship motions, and internal sloshing elevations were compared with results obtained from a computational method, here referred to as the RANS-BEM method, that relied on a boundary element method to obtain ship motions. This RANS-RANS method was validated against model test measurements.     

Optimal ballast water exchange sequence design using symmetrical multitank strategy

The quality of the ballast water exchange scheme affects many aspects of a ship, including intact stability, structural strength, building and operational expenses, etc. This paper focuses on developing an optimization methodology for large-scale sequential ballast water exchange. The method of transversely symmetrical ballast water tanks being exchanged simultaneously is adopted, and the potentials of multiple tanks being exchanged at a time are explored. The mathematical model for the symmetrical ballast water exchange problem is built by minimizing the occurred maximum trims, maximum hull girder bending moments, and shearing forces as objectives, and the related safety assessment criteria as constraints. A multiobjective genetic algorithm with some operators specially designed for the problem is presented to obtain a set of approximate Pareto-optimal solutions for engineers to choose from. Finally, a real case study on the symmetrical ballast water exchange of a 176,000 DWT bulk carrier is conducted to illustrate the effectiveness of the proposed approach.     

Model-scale experiments of symmetric ship collisions

This study was initiated due to the lack of experimental data on ship collisions. The feasibility of model-scale ship collision experiments was examined and a series of model-scale ship collision experiments is presented. The theoretical background for the analysis of experiments is given together with the principles of scaling. Proper scaling should assure physical similarity to the large-scale experiments conducted in the Netherlands. The Froude scaling law was followed, resulting in the improper scaling of some forces: the effects of this are discussed. The study concentrates on the dynamics of collisions. The structural response, properly scaled from the large-scale experiments, was modelled using polyurethane foam as the ship’s side structure. The collision process was analysed and the results of model-scale tests, large-scale experiments, and a simple analytical model were compared, showing that there was both quantitative and qualitative agreement in the results of the experiments conducted at different scales. The analytical model yielded good quantitative assessment of the deformation energy.     

波浪引起破损船的垂向运动和弯矩（英文）

The wave-induced vertical ship motions and bending moments of a double hull-oil tanker in realistic flooding conditions are studied. The scenarios investigated are represented by water ingress into the starboard ballast tanks for collision damage cases and both starboard and portside ballast tanks for grounding situations. Seakeeping computations are performed for eight damage scenarios and for the intact condition, each corresponding to different changes in displacement, trim, and heel. For each of the damage conditions, transfer functions of vertical motions and loads are calculated using a potential linear 3 D panel hydrodynamic code in the frequency domain that includes effect of the motion of the water in flooded tanks. A MATLAB code is developed to facilitate automated hydrodynamic simulation of many damage scenarios. Verification of seakeeping results is performed by comparing transfer functions with results of the previous study. Wave-induced vertical responses of damaged ship are then compared to those of intact ship using two spectral-based methods originating from uncertainty analysis of wave loads, which are convenient tools to assess consequences of damage on short-term ship responses. Generally, observed trend is that vertical wave-induced responses of damaged ship converge toward those of intact ship with increasing wave period. Fairly small differences between responses of asymmetrically damaged ship with respect to the symmetrical incoming wave directions are found. The results of the study are an efficient method for seakeeping assessment of damaged oil tankers and the framework for evaluating consequences of damage scenarios, heading angles, and sea conditions on seakeeping responses of damaged ships.The results can be used to decide if the intact ship model can be used instead of the damaged one for the emergency response procedure or for the risk assessment studies when modeling and computational time represent important limitations.     

Study on alternative approaches to corrosion protection of ballast tanks using an economic model

One of the most relevant problems in ship construction and maintenance nowadays is corrosion in ballast tanks of modern merchant vessels. On the one hand, there is a general consensus that the economic lifespan of such a vessel depends, to a large degree, upon the corrosion state of its ballast tanks, while on the other hand these ballast tanks, located between the outer hull and the cargo tanks, makes routine inspection and maintenance a difficult task.Today, ship's ballast tanks are usually constructed in steel and protected with an epoxy coating backed up by sacrificial zinc anodes. Such a construction has been applied without significant alterations for many years. The objective of this economic study is to compare this construction method with some potential alternatives. The considered alternatives are: (1) an increase in structural scantlings, eliminating the necessity to replace corroded at a cost of real cargo carrying capacity of the ship, (2) application of the novel and more durable TSCF₂₅ coating (3), the use of corrosion resistant steel in ship construction and (4) a standard PSPC₁₅ coating combined with lifetime lasting aluminum sacrificial anodes. A cost model was used to evaluate these alternative options together with sensitivity analysis. It is concluded that the durable coating and the use of lifetime lasting aluminum anodes are bound to improve the actual basic tank concept. Corrosion resistant steel becomes attractive when the steel price becomes competitive.     

浅液深和挡板影响下遭受横摇激励的晃荡问题数值研究（英文）

Sloshing is relevant in several applications like ship tanks,space and automotive industry and seiching in harbours.Due to the relationship between ship and sloshing motions and possibility of structural damage,it is important to represent this phenomenon accurately.This paper investigates sloshing at shallow liquid depths in a rectangular container using experiments and RANS simulations.Free and forced sloshing,with and without baffles,are studied at frequencies chosen specifically in proximity to the first mode natural frequency.The numerically calculated free surface elevation is in close agreement with observations from experiments.The upper limit of the resonance zone,sloshing under different filling depths and roll amplitudes and sloshing with one,two and four baffles are also investigated.The results show that the extent of the resonance zone is reduced for higher filling depth and roll amplitude.It is also found that the inclusion of baffles moves the frequency at which the maximum free surface elevation occurs,away from the fundamental frequency.Finally,a submerged baffle is found to dissipate more energy compared to a surface piercing baffle and that the effect of several submerged baffles is similar to that of a single submerged baffle.     

LNG船薄膜型液舱晃荡条件下的数值模拟以及受力情况研究

建立描述晃荡条件下液货舱的运动数学模型,对薄膜型液舱在晃荡条件下的受力情况进行研究分析.通过与实验结果的对照,验证了模型的正确性.针对晃荡周期这个主要影响因素,研究薄膜型液舱的受力和内部波形变化等,从而确定所研究液舱的充满度限制条件;研究新的薄膜型液舱型式下对晃荡的敏感性程度,得到双列结构的液舱有效地降低了晃荡的冲击影响,有利于LNG船的安全运行.     

晃荡对CSR油船设计的影响

为明确船舶营运过程中晃荡载荷对不同船型液货舱构件的影响,基于《散货船和油船结构共同规范》,分析晃荡载荷的形成及决定晃荡载荷的因素,结合纵向和横向晃荡在油船中的具体载荷水平,分析晃荡运动对CSR油船液货舱结构的影响,以VLCC制荡舱壁为优化目标,提出新的设计方案,采用MSC.Patran&Nastran有限元分析软件,论...     

频域范围内液舱晃荡对FLNG运动影响的研究

FLNG是一种新型的浮式海洋结构物,其外形与FPSO相似并配备天然气的液化装置以及LNC储罐.FLNG概念的出现使得海上边际油气的开发不再依赖于长距离的管道运输,从而节约了此类油气田的开发成本.文中基于WADAM并针对液舱晃荡与船体运动之间的相互影响进行了频域范围内的研究,在研究过程中将液舱内湿表面包含于船体外湿表面中从而形成一个统一的边界表面.通过计算得出考虑液舱晃荡与忽略液舱晃荡两种情况下的六自由度运动的RAO.对于两种情况下的计算结果进行分析研究,从而得到液舱晃荡对船体运动影响的重要规律.     

考虑晃荡耦合船舶运动的晃荡压力算法（英文）

The effect of coupling between sloshing and ship motions in the evaluation of slosh-induced interior pressures is studied. The coupling between sloshing loads and ship motions is modelled through a hybrid algorithm which combines a potential flow solution based on transient Green function for the external ship hydrodynamics with a viscous flow solution based on a multiphase interface capturing volume of fluid(VOF) technique for the interior sloshing motion. The coupled algorithm accounts for full nonlinear slosh forces while the external forces on the hull are determined through a blended scheme of linear radiationdiffraction with nonlinear Froude-Krylov and restoring forces. Consideration of this level of nonlinearities in ship motions is found to have non-negligible effects on the slosh-coupled responses and slosh-induced loads. A scheme is devised to evaluate the statistical measure of the pressures through long-duration simulation studies in extreme irregular waves. It is found that coupling significantly influences the tank interior pressures, and the differences in the pressures between coupled and uncoupled cases can be as much as 100% or more. To determine the RAO over the frequency range needed for the simulation studies in irregular waves, two alternative schemes are proposed, both of which require far less computational time compared to the conventional method of finding RAO at each frequency, and the merits of these are discussed.     

Reducing the cost of ballast tank corrosion: an economic modeling approach

One of the most relevant problems in ship construction and maintenance nowadays concerns the corrosion in the double hull space ballast tanks of modern merchant vessels. On the one hand, there is a general consensus that the economic life span of such a vessel depends primarily upon the corrosion state of its ballast tanks, while on the other hand, the position of these tanks, squeezed between the outer hull and the loading tanks, makes routine inspection and maintenance almost impossible.Today, ship's ballast tanks are usually constructed in grade A steel and protected with a standard epoxy coating, backed up with sacrificial zinc anodes. Such a construction has been applied without significant alterations for many years. However, the objective of this economic study is to compare this construction method with some feasible alternatives. The considered alternatives are: (1) an increase of the scantlings, eliminating the necessity to replace corroded steel but diminishing the cargo carrying capacity of the ship, (2) application of the novel and more durable TSCF₂₅ coating (3), the use of corrosion resistant steel in ship construction or (4) a standard PSPC₁₅ coating combined with lifetime lasting aluminum sacrificial anodes. After running each alternative through a cost model including an extensive sensitivity analysis, it is concluded that the durable coating and the use of lifetime lasting aluminum anodes are bound to improve the actual basic tank concept. Corrosion resistant steel becomes attractive depending upon the evolution of the international steel market.     

VLCC液舱晃荡仿真及结构响应

当船体在波浪中运动的频率与液舱内液体振动的固有频率相近时,舱内液体将会发生剧烈的运动,即晃荡产生了.在船舶结构设计中,必须要考虑这种晃荡载荷及结构的响应.该文针对一超大型油轮(VLCC)液舱晃荡问题进行了三维仿真模拟.在DNV基于压力的晃荡评估方法的基础上,提出了应用有限元方法和任意拉格朗日-欧拉耦合技术进行该船全生命期内液舱晃荡仿真及强度评估的工程实用的步骤方法.     

The applicability of hydrofoils as a ship control device

Centrifugal forces are commonly created when ships turn, which may cause a ship to capsize in a critical situation. A mathematical model has been developed to optimize the stability coefficients for ship, with the aim to prevent capsizing and to increase ship maneuverability in high-speed water craft. This model can be used to develop algorithms for control system improvement. The mathematical model presented in this paper optimized the use of multipurpose hydrofoils to reduce heeling and the trimming moment, maintaining an upright ship’s position and lessening the resistance via transverse force. Conventionally, the trimming and heeling of a ship are controlled using ballast water; however, under variable sea conditions it is sometimes difficult to control a ship’s motion using ballast water. In this case, a hydrofoil would be more stable and maneuverable than a ballast tank controlled vessel. A movable hydrofoil could theoretically be adapted from moveable aerofoil technology. This study proves the merit of further investigation into this possibility.     

Numerical and experimental motion simulations of nonsymmetric ship collisions

A calculation model to simulate nonsymmetric ship collisions, implying an arbitrary impact location and collision angle, is described in the paper. The model that is introduced is based on the time integration of twelve equations of motion, six for each ship. The motions of the ships are linked together by a mutual contact force. The contact force is evaluated as an integral over the surface tractions at the contact interface. The calculation model provides full time histories of the ship motions and the acting forces. Physical understanding of the underlying phenomena was obtained by a series of model-scale experiments in which a striking ship collided with an initially motionless struck ship. In this paper, numerical simulations of four nonsymmetric collisions are presented and the calculations are validated with the results of the experiments.     

基于OpenFOAM的船舶与液舱流体晃荡在波浪中时域耦合运动的数值模拟

波浪中载液船舶运动激励舱内液体的晃荡,舱内液体晃荡产生的冲击力同时作用在舱壁上,进而影响船舶的运动姿态。波浪中船体水动力和时延函数是在势流理论范畴下采用切片法和脉冲响应函数方法计算获得的,液舱内液体非线性晃荡是基于粘性流理论实时计算模拟,两者耦合建立了波浪中载液船舶与液舱流体晃荡耦合的运动方程。论文基于开源CFD开发平台OpenFOAM,自主开发实现了船体运动与液舱晃荡的耦合计算程序,并进行了相应的数值模拟计算和验证工作。该方法完整地考虑了波浪、船体和液舱晃荡之间的耦合作用,并结合船体内外流场特点分别采用了势流和粘性流理论,具有较高的计算效率。通过数值模拟计算和模型实验研究表明,数值模拟计算能够清晰显现出液舱晃荡对船体全局运动影响,船体运动计算结果与模型实验结果吻合良好。     

作为船舶控制装置的水翼艇的适用性研究（英文）

Centrifugal forces are commonly created when ships turn, which may cause a ship to capsize in a critical situation. A mathematical model has been developed to optimize the stability coefficients for ship, with the aim to prevent capsizing and to increase ship maneuverability in high-speed water craft. This model can be used to develop algorithms for control system improvement. The mathematical model presented in this paper optimized the use of multipurpose hydrofoils to reduce heeling and the trimming moment, maintaining an upright ship's position and lessening the resistance via transverse force. Conventionally, the trimming and heeling of a ship are controlled using ballast water; however, under variable sea conditions it is sometimes difficult to control a ship's motion using ballast water. In this case, a hydrofoil would be more stable and maneuverable than a ballast tank controlled vessel. A movable hydrofoil could theoretically be adapted from moveable aerofoil technology. This study proves the merit of further investigation into this possibility.     

独立B型LNG船液舱晃荡强度分析方法

为了保证液舱舱容大且无装载限制的新型独立B型LNG船在晃荡载荷下的强度满足使用要求,提出液舱结构晃荡强度直接分析方法.采用规范公式确定液舱晃荡载荷,根据该方法对液舱模型进行粗网格分析,进行典型区域横摇工况下超出应力许用值的精细网格分析.结果表明,该方法可以对独立液舱晃荡强度进行有效评估,其中的精细网格计算结果可真实反映高应力梯度区域的应力情况.分析结果可为液舱晃荡强度评估、液舱结构优化以及同类LNG船的设计开发提供参考.     

A field study of the effectiveness of sacrificial anodes in ballast tanks of merchant ships

Sacrificial anodes have become a standard practice for the protection of ballast tanks of merchant vessels against corrosive damage. A well protected tank should extend the life span of a ship and consequently enhances its economic value. An in situ survey comprising more than 100 merchant vessels provided the opportunity to measure the impact of these anodes on the life expectancy of these vessels. Contrary to the general belief of these anodes’ beneficial effect, no significant difference was found in our observations in terms of corrosion occurrence between ship populations with and without sacrificial anodes, across all ship ages. This may be explained by the highly variable conditions and the complex geometry in a ballast tank severely impede optimal and straightforward installation of these anodes in these tanks. Also, poorly placed anodes in it may harm the integrity of the coating of the tank. We therefore plead for uniform and clear rules on anode installation and inspection.     

多液舱晃荡与船体运动耦合数值研究

针对多液舱养殖工船耐波性数值研究计算量过大的问题，建立了一套耦合数值求解系统。使用脉冲响应函数法求解船体运动方程，基于计算流体力学方法数值模拟液舱晃荡，在时域上离散求解两者的耦合方程。讨论了CFD软件FLUENT的用户自定义函数的编制，验证了横摇回转中心位于重心所在轴线的假设的合理性。为验证计算方法的有效性，在循环水槽中进行了不同载液率下的横摇自由衰减试验。对比数值模拟结果与试验结果，计算的横摇角时历与试验值吻合良好，验证了该方法的有效性，为高效数值研究养殖工船耐波性打下了基础。