The evaluation method of total damage to ship in underwater explosion

Whipping response will happen when a ship is subjected to underwater explosion bubble load. In that condition, the hull would be broken, and even the survivability will be completely lost. A calculation method on the dynamic bending moment of bubble has been put forward in this paper to evaluate the impact of underwater explosion bubble load on the longitudinal strength of surface ships. Meanwhile the prediction equation of bubble dynamic bending moment has been concluded with the results of numerical simulation. With wave effect taken into consideration, the evaluation method of the total damage of a ship has been established. The precision of this evaluation method has been proved through the comparison with calculation results. In order to verify the validity of the calculation results, experimental data of real ship explosion is applied. Prediction equation and evaluation method proposed in this paper are to be used in ship structure design, especially in the preliminary prediction of the ultimate withstanding capability of underwater explosion damage for the integrated ship in preliminary design phase.     

港池爆炸兴波响应的计算方法

本文以爆炸兴波的ＭＡＣ法轴对称计算结果为初值，提出了对于实际港池后期兴波响应的两种计算方法。其一是基于溶器内液体驻留运动的振型叠加法，其二是爆炸早期兴波与浅水波理论的时域衔接法。进行了一千吨ＴＮＴ当量在港池内触水爆兴波的实例计算。计算表明，该方法能够合理地描述波浪演化特征，与爆炸现场的景观相吻合，可为工程设计提供简易、实用的结果。     

Numerical Calculation Methods for Wavemaking Response Induced by Explosion in Harbour

Using the axial symmetry results of marker and cell (MAC) method as initial value in this paper, two numerical calculating methods are presented for the late wavemaking response induced by explosion in harbour. One of the methods is the superposition method of the vibration mode based on fluid slosh in container. Another one is the joining method of the MAC results with the shallow wave theory calculation in time domain. As a practical example, it is conducted to the numerical calculation about 1000 ton TNT equivalent explosion within touch of water surface. The results show that it can be rationally described with the methods to the wavemaking progress and character. The numerical results are identical with the observed scene on the spot experiment. The methods are simple and applicable in the engineering design.     

Dynamic Plastic Analysis of Ship-Platform Collision

This paper studies intensively the problems of ship-platform collision.The ship and platformare treated as one structural system connected with spring elements and then motion equation of the colli-sion system is established.A nonlinear force-displacement relationship is derived for the simulation of lo-cal dent in a hit member and the yield surface of a dented tubular section is developed to consider the re-duction of load carrying capacity of hit members.Large deformations,plasticity and strain-hardening ofthe beam-column element are taken into account by combining the elastic large displacement analysis theo-ry with the plastic node method.The effect of the hydrodynamic forces acting on the platform,the rubberfender the property of the local dent and the buckling behavior of beam-column on collision are analyzed.The numerical simulation of the nonlinear dynamic response is carried out by Wilson θ method with updat-ed Newton-Raphson iteration.And the numerical example of the dynamic response of a offs     

动力定位船舶二阶低频慢漂力模型试验研究

对一艘动力定位船舶二阶低频慢漂力进行了模型试验,并将试验得到的纵向慢漂力谱、横向慢漂力谱与势流理论方法得到的理论值进行比较,结果表明,该模型试验方法与理论计算较为吻合。可为动力定位系统的设计和应用提供参考。     

Investigation of ship hydroelasticity

The importance of hydroelastic analysis of large and flexible container ships of today is pointed out. A methodology for investigation of this challenging phenomenon is drawn up and a mathematical model is worked out. It includes definition of ship geometry, mass distribution, structure stiffness, and combines ship hydrostatics, hydrodynamics, wave load, ship motion and vibrations. Based on the presented theory, a computer program is developed and applied for hydroelastic analysis of a flexible segmented barge for which model test results of motion and distortion in waves have been available. A correlation analysis of numerical simulation and measured response shows quite good agreement of the transfer functions for heave, pitch, roll, vertical and horizontal bending and torsion. The tool checked in such a way can be further used for reliable hydroelastic analysis of ship-like structures.     

水下武器抗爆试验爆源等效问题分析

针对水下武器装备抗爆试验中等效药包试验缺乏明确实施规范和标准的问题,从常用的经验公式出发,通过分析计算和实例,对冲击波超压等效和冲击因子等效方法进行了比对。 其中冲击因子等效方法考虑到了药包质量、爆距、爆炸与目标相对位置和姿态等因素,以等效试验结论的合理性和贴近实际程度为依据,以实际试验为例对等效试验实施进行了分析,建议等效试验爆源药量选择15 ~ 20 kgTNT 当量为宜。     

MOSES软件在系泊浮体运动计算中的应用研究

采用MOSES软件计算某起重船迎浪下的水动力性能和运动响应,并对该船进行缩尺比为1:50的模型试验。通过软件计算结果和试验结果的对比,分析计算模型的网格划分、二阶波浪力计算方法和粘性阻尼等关键参数的选取对MOSES计算系泊浮体运动的影响,为MOSES软件在系泊下运动计算方面提出建议。     

Parametric study for underwater blast-induced pipeline response embedded in marine sediments

Abstract

Blast response of submerged pipelines has been a research focus in recent years. In this article, a three-dimensional numerical model is established to investigate dynamic response of pipelines due to underwater explosion. The u–p approximation is integrated into finite element method (FEM) to simulate pore water effect in the seabed. Numerical continuity between hydraulic pressure in the flow field and pore pressure in the marine sediment is guaranteed to realize the blast response of submerged pipelines in ocean environment. Both fluid–structure interaction (FSI) and pipeline–seabed interaction (PSI) have been considered in the proposed model simultaneously. A comprehensive parametric study is carried out after validation of the present model with test data from underground explosion and underwater explosion, respectively. The effect of embedment depth, TNT equivalent, stand-off distance, pipeline diameter, and pipeline thickness to blast response of the submerged pipelines is investigated based on numerical results. Variation of deformation patterns and stress distribution of the pipeline with various installation and structure parameters has been illustrated and discussed to facilitate engineering practice.     

风和流作用下单链式系泊养殖工船“鱼尾运动”研究

单点系泊船舶在受到风、流等外力作用下通常会产生大幅周期性艏摇运动，称为“鱼尾运动”。剧烈的鱼尾运动可能会导致系泊系统的锚链承受过大的张力从而遭到破坏。为了充分认识单点系泊状态下养殖工船的鱼尾运动，针对一艘十万吨级单链式系泊养殖工船进行了数值分析及模型试验研究。首先，通过风洞模型试验测得养殖工船的风、流载荷系数，以此作为输入对风、流联合作用下养殖工船的动力响应进行了数值模拟分析；同时，开展水池模型试验验证了数值计算结果的准确性和可靠性；最后，通过数值计算研究了不同风速和流速下单链式系泊养殖工船鱼尾运动的特性和规律，为实际工程设计提供一定的参考。     

Stability and capsizing analysis of nonlinear ship rolling in wind and stochastic beam seas

Considering the actual seaway condition, stability and capsizing of nonlinear ship rolling system in stochastic beam seas is of significant importance for voyage safety. Safe zone are defined in the phase space plan of the unperturbed Hamilton system to qualitatively distinguish ship motions as capsize and noncapsize. Capsize events are defined by solutions passing out of the safe zone. The probability of such an occurrence is studied by virtue of the random Melnikov function and the concept of phase space flux. In this paper, besides conventional wave excitation, the effect of wind load is also taken into account. The introduction of wind load will lead to asymmetry, in other words, it transforms the symmetric heteroclinic orbits into asymmetric homoclinic orbits. For asymmetric dynamical system, the orbital analytic solutions and its power spectrum are not readily available, and the technique of discrete time Fourier transformation (DTFT) is used. In the end, as verification of theoretical critical significant wave height, capsizing probability contour diagram is generated by means of numerical simulation. The contour diagram shows that these analytical methods provide reliable and predictive results about the likelihood of a vessel capsizing in a given seaway condition.     

Prediction of design wave loads of the ocean structure by equivalent irregular wave approach

The present study is employing the equivalent irregular wave approach to predict the wave loads for a ship encountering the worst sea state with respect to the critical dynamic loading parameter. Two different hydrodynamic numerical models, i.e. 3D pulsating source technique and 3D translating pulsating source technique, are applied to calculate the corresponding RAO of the ship moving in waves. Incorporating the RAO of the related physical properties, we can calculate the extreme value for the corresponding ship loading factor, which can be regarded as the worst sea state in the service lifetime of the ship. With the time and period of the occurrence of the corresponding extreme value, we can simulate the time history of the wave load in this period, which is so-called equivalent irregular wave approach. Comparing with the results calculated by the traditional equivalent regular wave approach, we find that the equivalent irregular wave approach can simulate the corresponding wave load more realistic, especially for dynamic pressure. Using the equivalent irregular wave approach can offer the effective and practical base for the ship structural analysis.     

Experimental investigation on a two-part underwater towed system

An experimental set-up is developed and proved to be effective for laboratory study of an underwater towed system. The experimental technique gives a practical method for monitoring the kinematic and dynamic performance of an underwater towed system in a ship towing tank. Both the theoretical and experimental results in the investigation indicate that the hydrodynamic response of a towed vehicle to the wave induced motion of a towing ship can be significantly reduced by applying a two-part tow method. A comparison of the numerical and experimental results in the investigation demonstrates that the numerical simulation results are close to the experimental data, overall agreement between experimental and theoretical results is satisfactory. The results qualitatively verify the mathematical model of a two-part underwater towed system proposed by Wu and Chwang [Wu, J., Chwang, A.T., 2000. A hydrodynamic model of a two-part underwater towed system. Ocean Engineering 27 (5), 455–472].     

Time-domain numerical and segmented ship model experimental analyses of hydroelastic responses of a large container ship in oblique regular waves

Real sea conditions are characterized by multidirectional sea waves. However, the prediction of hull load responses in oblique waves is a difficult problem due to numeral divergence. This paper focuses on the investigation of numerical and experimental methods of load responses of ultra-large vessels in oblique regular waves. A three dimensional nonlinear hydroelastic method is proposed. In order to numerically solve the divergence problem of time-domain motion equations in oblique waves, a proportional, integral and derivative (PID) autopilot model is applied. A tank model measurement methodology is used to conduct experiments for hydroelastic responses of a large container ship in oblique regular waves. To implement the tests, a segmented ship model and oblique wave testing system are designed and assembled. Then a series of tests corresponding to various wave headings are carried out to investigate the vibrational characteristics of the model. Finally, time-domain numerical simulations of the ship are carried out. The numerical analysis results by the presented method show good agreement with experimental results.     

Numerical analysis and validation of weakly nonlinear ship motions and structural loads on a modern containership

This paper aims to validate a numerical seakeeping code based on a 3D Rankine panel method by comparing its results with experimental data. Particularly, the motion response and hull-girder loads on a real modern ship, a 6500 TEU containership, are considered in this validation study. The method of solution is a 3D Rankine panel method which adopts B-spline basis function in the time domain. The numerical code is based on the weakly nonlinear scheme which considers nonlinear Froude-Krylov and restoring forces. The main focus of this study is given to investigate the nonlinear characteristics of wave-induced loads, and to validate this present scheme for industrial use in the range of low Froude number. The comparisons show that the nonlinear motions and hull-girder loads, computed by the present numerical code, have good overall agreements with experimental results. It is found that, for the better accuracy of computational results, particularly at extreme waves in oblique seas, the careful treatment of soft-spring (or compatible) system is recommended to the control of non-restoring motions such as surge, sway, and yaw.     

A comparative study of numerical simulations for fluid–structure interaction of liquid-filled tank during ship collision

Although International Maritime Organization (IMO) has taken many measures to minimize ship collisions, ships carrying liquid cargo sometimes do get struck by other vessels. The outflow of crude oil causes very serious consequences to the environment. In such cases it is necessary to analyze the response of structure of struck liquid cargo-filled tank to account for fluid–structure interaction accurately. In this paper, numerical simulation of collision between a container ship with double hull very large crude carrier (VLCC) is presented. Three different numerical simulation mothods were adopted to model fluid–structure interaction in liquid-filled cargo tank, namely arbitrary Lagrangian–Eulerian finite element method, Lagrangian finite element method and linear sloshing model. The numerical simulation results reveal that the fluid–structure interaction of liquid cargo-filled tank has a significant effect on the motion and structural response of the struck cargo tank. Compared with the calculation results of ALE FE method, the linear sloshing model underestimates the influence of fluid–structure interaction of liquid cargo tank while the Lagrangian–Eulerian finite element method may be considered as the practical method for engineering applications as it provided more reasonable results with a relatively low central processing unit (CPU) time.     

Calculation Methods of Added Resistance and Ship Motion Response Based on Potential Flow and Viscous Flow Theory

To improve the energy efficiency of ships and to predict ship motion response under actual sea conditions, the far-field theory, strip theory, and Fujii and Takahashi’s modified semi-empirical method are based and studied to calculate the wave-induced added resistance. Firstly, a new modified formula based on the Maruo method is presented to calculate the radiation added resistance for the ship with a complex surface. Meanwhile, some calculation details such as the Green function, the shape of the sections (shape below the still water level or shape below the wave level) in the strip theory, and so on are discussed. Finally, the CFD method is used to simulate the motions of the hull and the added resistance, and the results of the CFD method and those of other numerical methods are analyzed and compared with the experiment results. The modified method in the paper can predict the added resistance in waves for the complex-hull-surface ships well and quickly.

     

Research on propeller dynamic load simulation system of electric propulsion ship

A dynamic marine propeller simulation system was developed, which is utilized for meeting the experimental requirement of theory research and engineering design of marine electric propulsion system. By applying an actual ship parameter and its accurate propeller J’~ KT’ and J’~KP’ curve data, functional experiments based on the simulation system were carried out. The experiment results showed that the system can correctly emulate the propeller characteristics, produce the dynamic and steady performances of the propeller under different navigation modes, and present actual load torque for electric propulsion motor.     

Numerical analysis of a propeller during heave motion in cavitating flow

In practical maritime conditions, ship hulls experience heave motion due to the action of waves, which can further drive the ship’s propellers to oscillate relative to the surrounding water. In order to investigate the motion of a propeller working behind a surface vessel sailing in waves, a numerical simulation is conducted on a propeller impacted by heave motion in cavitating flow using the Reynolds-averaged Navier-Stokes (RANS) method. The coupling of the propeller’s rotation and translation is fulfilled using equations of motion defined for this purpose. The heave motion is simplified as a periodic motion based on a sinusoidal function. The numerical transmission of information from the unsteady flow field is achieved using the overset grid approach. In this manner, the unsteady thrust coefficient and torque coefficient of propellers in different periods of heave motion are analyzed. A comparative study is implemented on the unsteady cavitation performance and wake characteristics of propeller. With the propeller’s heave motion, the flow field non-uniformity constantly changes the load on the propeller during each revolution period and each heaving period, the propeller load and the wake field are closely related to the variation of heave motion period. The results obtained from the numerical simulation are expected to serve as a useful theoretical reference for the numerical analysis of a propeller in a heave motion.     

多稳态夹芯金属压杆的滞后阻尼增强机制与被动减振性能

破碎波浪砰击于导管架等海洋工程结构,产生瞬态强载荷及长时振动。高刚度金属结构可抵抗瞬时强载,但金属固有阻尼极低而难以有效抑制振动,从而加剧结构损伤乃至失效。为使单一结构同时具有高刚度和高阻尼,设计一种多稳态夹芯金属压杆,有限元模拟表明该类压杆稳态随循环载荷依序转换,对应刚度变化使力—位移间产生滞后关系,使高刚度金属压杆具有高效耗散能力;采用夹芯结构弹性理论和发展变边界结构稳定理论,给出了该类压杆的稳态转换阈值和刚度变化过程,与有限元模拟一致;以有限元模拟方法获得了承载和阻尼特性的几何参数相关性;以该类压杆替换导管架斜撑,用有限元方法模拟瞬态强载下结构振动,计算结果表明多稳态夹芯金属压杆保证导管架高刚度同时显著增强了阻尼。