Striking Ship Research Articles

Impact force-damage depth model for ship-bridge collision

The impact force-damage depth model, i.e., P-a model, provides a feasible approach to design and evaluate bridge resistance under ship collisions, which is inadequately addressed in the existing specifications and literature. In the present study, based on an 18500 DWT (deadweight tonnage) bulbous bow bulk carrier and the main tower of cable-stayed bridges, the P-a model for ship-bridge collision is established with consideration of pile cap, bridge pylon and striking ship. Firstly, the refined finite element (FE) model of prototype ship was established with detailed modeling of both the main and stiffening components. The material model parameters and FE analysis approach were validated through the existing tensile tests on marine steel coupons and crush tests on ship bow specimens. It is found that the modeling of stiffening components has rationality in predicting the impact force and asymmetrical folding collapse of ship bow. Then, concerning two collision scenarios with the main tower of cable-stayed bridges, i.e., only bulbous bow-pile cap collision and sequential bulbous bow-pile cap and bow overhang-bridge pylon collisions, the influences of nine critical parameters from pile cap (height, curvature and water level), bridge pylon (width, curvature, angle and bow overhang-bridge pylon distance) and striking ship (mass and velocity) on the impact forces and failure patterns of ship bow were comprehensively discussed. It indicates that: (i) the larger impact forces of bulbous bow and bow overhang appear with increased pile cap height, decreased bridge pylon curvature and inward inclined pylon angle; (ii) the loading paths of P-a relationships are approximately identical with different striking ship masses and velocities. Finally, the P-a model for ship-bridge collision was established by response surface methodology, and the corresponding calculation procedure was further given and validated.

Mechanical analysis and interior stiffeners arrangement discussion of a specific ship side collision situation

Collision between ships of different sizes may result in a situation where a vessel with a higher deck height impacts another vessel with a lower deck height. In such case, the absence of bearing structure above the lower-draft struck ship's deck means that the bow of the high-draft striking ship transfers pressure to both the deck and side plates of the struck ship during collision. According to this situation, the numerical simulation of small scale compartment impacted by a higher-draft ship bow was carried out. Based on the analysis of the numerical results, the main impact area of the small scale compartment was simplified into a typical L-shaped plate-frame structure to facilitate the experiment. A small scale quasi-static experiment was implemented and the force-displacement curve and energy absorption data of the L-shaped structure penetrated by a rigid approximate bow indenter were obtained. Moreover, material tensile tests provided parameters for numerical simulation and the deformation process of the structure was analyzed. Based on that, several L-shaped structure cases with different stiffeners of height and position were calculated in LS-DYNA. Failure process, structural energy absorption and efficiency were summarized and the excellent structural characteristics for this ship side collision situation were obtained.

Floating bridge response under combined ship collision, wind and wave loads

ABSTRACT Floating bridges over navigable fjords with exposed substructures are at risk of accidental ship collisions. Other hazards such as extreme wind and wave loads are also critical for floating bridges. This study investigates the global dynamic responses of a floating bridge subjected to different combinations of ship collision, wind and wave loads. A numerical model of a floating bridge is developed using OrcaFlex. The ship-bridge interaction is modelled by defining a constraint element attached to the striking ship. The stiffness of the constraint is described by a nonlinear force-displacement curve. The full turbulent wind field is generated using TurbSim, and the bridge buffeting response is calculated in time domain based on the linear quasi-steady theory. The wind-bridge interaction is accounted for by considering the relative angle of attack and the relative wind velocity at each time step. The bridge responses under individual hazards are compared with those considering multi-hazards.

A probabilistic analytics method to identify striking ship of ship-buoy contact at coastal waters

The identification of the ship that contact with the buoy can provide evidence for accident accountability. To this aim, the paper develops a probabilistic analytics method to evaluate the ship-buoy contact risk for the striking ship identification at the coastal areas by combining buoy domain and bounding box models. The method makes use of Automatic Identification System (AIS) data and navigational buoy data. Firstly, an AIS-based probabilistic buoy domain model is adopted for the determination of the safety boundary of the buoy to detect potential striking ships with a higher contact probability. Then, the bounding boxes of the navigational buoy and the detected potential striking ships are developed to detect the real striking ship by analyzing the interaction between the ship bounding box and the buoy bounding box. Finally, the probabilistic analytics method is demonstrated in the South China Sea and validated using historical ship-buoy contact records. Results indicated that, from a probabilistic perspective, the safety buoy domain (critical boundary) existed with diverse distances dynamically. The proposed method could assist the identification of striking ships while aiding the definition of the safety buoy domain for preventing ship-buoy contacts. As a result, it has the potential to support the development of ship-buoy contact risk management and assist surveillance operators and master on board by improving their cognitive abilities in dangerous traffic scenarios.

Dynamic responses of a flexible floating modular system subjected to ship impact

An innovative flexible floating anti-collision system (FFAS) has been proposed and developed as restraining structure against ship direct collisions. Consisting of multiple horizontal buoy modules, the collision behaviors of the FFAS were greatly influenced by the intricate interaction between striking ship and the modular system, as well as the complicated coupling of fluid and structure. Hence, the colliding process was always oversimplified by restricting the degree of freedom and dereferencing constant added mass in the past research. To address this problem, experimental tests are conducted in a 3D water basin to build a more realistic simulation of the collision process between the FFAS and head-on navigating ship. The six-DOF motion of the stuck buoy and the tension of the block and mooring lines are synchronously monitored for hundreds of impact cases. The results indicate that the impulse load and ship sliding will occur and the impact duration and the peak tension of the lines are affected significantly. Considering various impact positions, the worst-case scenarios for the block and mooring lines are determined and the safe distance for the FFAS setup is suggested for practical design.

Mechanical model for the analysis of ship collisions against reinforced concrete floaters of offshore wind turbines

This paper presents a simplified mechanical model to study ship collisions against Reinforced Concrete (RC) floaters of Floating Offshore Wind Turbines (FOWTs). The model accounts for the deformability of both striking ships and struck RC structures, including a method to evaluate the elastic–plastic response of RC slabs with normal horizontal restraints, while considering contact area effects and punching shear failure. In the proposed model, the internal mechanics are coupled to the external body dynamics, whilst the hydro-mechanical effects acting on the collided bodies such as hydrostatic restoring, viscous, and wave damping forces are accounted for by the large rotations rigid-body dynamics solver MCOL. A parametric analysis is conducted on the model to study its sensitivity to changes in impact energy, impact location, reinforcement ratios, wall thicknesses, and striker rigidities, whose outcomes are compared with Non-Linear Finite Element (NLFE) simulations. The results show that the proposed model can accurately capture the penetrations in both structures, their body dynamics, and the contact force through the collision at a significantly lower computational cost than their NLFE counterpart.

Collision-accidental limit states-based safety studies for a LNG-fuelled containership

Liquefied natural gas (LNG) is an increasingly popular fuel alternative of ships for reducing greenhouse gas emissions. The interest in LNG fuel propulsion systems is rapidly growing, yet certain important safety design and engineering issues remain poorly constrained. The safety of LNG-fuelled ships must be assessed in terms of the potential structural damage owing to collision accidents and resulting LNG spills, especially for ship types that store the LNG storage tank within the cargo hold. In this paper, accidental limit state (ALS) based safety assessment for LNG-fuelled containership structures using nonlinear finite element methods is studied at the most unfavourable scenario of collisions between a striking ship's bow and a struck ship's LNG fuel tank, where the struck ship is in full load condition at a standstill, while the striking ship of the same size as the struck ship has different loading conditions in the ballast load condition, 50% partial load condition and full load condition, with varying collision speed at 0.5, 3, 6 and 9 knots. A hypothetical 9,000 TEU (Twenty-foot Equivalent Unit) LNG-fuelled containership was designed in accordance with the requirements for the international gas fuel transport standards, accommodating a membrane-type LNG fuel tank located amidship. It is found from the present study that inner side hull structures of the struck ship can be damaged in ship-ship collisions, and the current industrial guidelines for LNG fuel tank designs are required to amend to apply for LNG-fuelled ships.

Numerical modelling and dynamic response analysis of a 10 MW semi-submersible floating offshore wind turbine subjected to ship collision loads

The number of installed offshore wind turbines is continuously growing worldwide in recent years. Offshore wind farms are generally located near the coast close to traffic lanes and are exposed to the risk of collisions from visiting and passing ships. Potential consequences of collisions may vary from local structural damage to the detachment of turbine nacelles and rotors, and even tower collapse and capsizing of the turbine platform, causing significant economic loss and fatalities.This paper investigates ship collision responses of a semi-submersible floating offshore wind turbine (FOWT), i.e. the OO-STAR floater with the DTU 10 MW blades, using the nonlinear finite element code USFOS. The OO-STAR floater is made of post-tensioned concrete designed by Dr. techn. Olav Olsen. The striking ships are selected to be a modern supply vessel of 7500 tons and a shuttle tanker of 150,000 tons, representing respectively service/coastal merchant vessels and large passing vessels. Modelling of the FOWT in USFOS is described in detail including the OO-STAR floater, the DTU 10 MW turbine blade, the turbine tower, and the mooring system. The modelled hydrodynamic loads include buoyancy loads and motion induced radiation loads using the Morrison equation. The effects of external waves and currents are assumed to be small and ignored in all directions. Eigenmode analysis of the turbine model is performed to verify the established model.Global collision response analyses of the FOWT were performed in both parked and operating conditions. The ship resistance is modelled as nonlinear springs in USFOS containing force displacement curves simulated in LS-DYNA. In operating conditions, wind loads are introduced including wind thrust loads and wind induced torque to rotate the turbine blades. The changes of upstream wind speeds and rotor/wake interactions during collisions are neglected. The results are discussed with respect to energy absorption of the ship and the FOWT, and structural responses of the FOWT including global motions, nacelle accelerations, tower clearance, tower vibrations, and responses of the mooring system.

Structural assessment of a 500-cbm liquefied natural gas bunker ship during bunkering and marine operation under collision accidents

ABSTRACT This paper presents the structural assessment of a 500-cbm liquefied natural gas bunker ship, which is operated as a ship-to-ship transporter in the coastal area of South Korea, under collision accidents by a numerical approach. Based on marine traffic data, it was assumed that an oil tank is the colliding ship and the bunker ship is the struck ship. A non-linear finite element analysis was conducted under credible scenarios to consider the hydrodynamic response on the struck ship. It was compared to the structural response of the struck ship in bunkering which does not consider the hydrodynamic effect. In addition, major collision parameters that lead to severe damage on the struck ship was observed, and the specific values for ship speed and displacement of a third-party colliding ship during bunkering were suggested to minimise the risk of structural failure.

Improvement of the Ship Emergency Response Procedure in Case of Collision Accident Considering Crack Propagation during Salvage Period

Specialized procedures to help in the emergency response situations following ship accidents have been under development by the Classification Societies. Such procedures consider the hull-girder collapse as the most important failure mode, without the possibility of crack propagation caused by fluctuating wave loads. In the present study, the fatigue crack propagation in the main deck of the oil tanker damaged in collision during salvage is investigated. The shape and size of the damage are modelled using the realistic bow shape of the striking ship and historical data of ship accidents. The stress intensity factor (SIF) across the main deck of the struck ship is calculated numerically and by the method based on the available experimental results of the crack propagation in the stiffened panel. Fluctuating wave–induced stresses in short-term sea conditions during salvage are obtained by Monte Carlo simulation (MC) based on Rayleigh distribution. Cycle-by-cycle crack propagation is calculated using Paris law. Many salvage simulations are performed to cover different possible time-histories of the fatigue loading. Results of the analysis are presented as histogram of the crack increase during salvage. Parametric analysis is performed to investigate the influence of the sea state severity, initial crack size, and towing duration on the final crack size. The proposed procedure can be considered as a part of a software tool for emergency response action during salvage of damaged ship.

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.

Design of bridges against ship collisions

The paper outlines a rational design procedure for bridge piers and pylons against ship collision impacts. Firstly, a set of risk acceptance criteria are proposed. This is followed by a mathematically based procedure for calculation of the probability of critical ship meeting situations near the bridge, and the probability of ship collision accidents caused by human errors as well as technical errors. This first part of the paper leads to identification of the largest striking ship, “design vessels”, a given bridge pier must withstand without structural failure in order for the bridge connection to fulfil the risk acceptance criteria. The final part of the paper is devoted to an analysis of the needed impact capacity for the bridge pylons and piers exposed to ship bow impact loads from these “design vessels”. For a number of different ship types and different tonnage merchant vessels, load – displacement relations for ship bow collisions against rigid walls are derived. Based on these comprehensive numerical results, a new empirical relation is derived which is suited for design against bow collisions. This expression for maximum bow collision forces is compared with a previously published expression for ice-strengthened ships and with existing standards for assessment of bow crushing forces. It is shown that there is need for an update of these existing standards. For design of piers and pylons against local impact pressure loads, a pressure - area relation for bulbous bow impacts is derived.

Post-accidental structural reliability of double-hull oil tanker with near realistic collision damage shapes

ABSTRACT The consequence of the near realistic modelling of collision damage shape on the post-accidental ultimate hull girder strength of double-hull oil tanker is investigated. For known striking ship’s geometry of the bulbous bow, damaged elements are removed from the finite element model of the midship section of the struck ship. Progressive finite element collapse analysis is then performed to determine residual strength index (RSI) of damaged ship. The analysis is performed for set of 50 collision scenarios, obtained from the historical ship collision database. In addition, probabilistic analysis of RSI is performed by approximating damage shape as ‘rectangular box’, based on IMO and GOLADS project. Structural reliability analysis is then employed to assess the consequences of various modelling assumptions used in RSI computations. Results of the analysis show that near realistic modelling of damage shape results in much lower failure probability of damaged ship compared to the ‘rectangular box’ models.

FPSO collision local damage and ultimate longitudinal bending strength analyses

Abstract In offshore oil &gas production there is a large concentration of platforms in a limited area of the sea, with the consequent increase of vessel traffic in the region. Platform supply vessels (PSVs), shuttle tankers and maintenance and safety units operate very close to these production platforms, creating a propitious scenario for collisions. Thus, the risk of collision between vessels and platforms has significantly increased, causing concern from the point of view of life loss, material damage and marine environment degradation. It is important to adequately design the structures and to predict the effects of accidents on the involved vessels. In the structural analysis of collision, geometric and material nonlinearities must be considered, as well as the striking ship velocity, the vessels draft difference, among other variables. In this work, the collision of a platform supply vessel with a single-hull Floating Production Storage and Offloading (FPSO) platform is studied through numerical simulation using the ANSYS LS-DYNA computational system. Damage is locally characterized by the collision force on the FPSO hull and the depth of penetration (displacement). In addition, it is also shown the energy absorption capacity of each type of structural element for the collision scenarios studied and a criterion is proposed to determine which structural element group should receive more attention in the design phase in order to reduce the effects of a collision. Both the longitudinal strengths of the intact FPSO as well as the remainder after collision are evaluated by assessing the bending moment versus curvature curves. It is observed that a single-hull FPSO platform with the thicknesses of the structural elements maintained unchanged in the conversion of the original oil tanker (VLCC) shows a significant ultimate longitudinal strength even after collision of a larger support vessel at higher velocity than recommended by the IACS rule.

On the Structural Behaviour to Penetration of Striking Bow under Collision Incidents between Two Ships

This work addressed the evaluation of collision angle and indenter on the behaviour of target object. A series of collision scenarios based on the mentioned parameters were calculated using finite element method. In the analysis process, several striking ships of different sizes relative to the struck ship are deployed as the collision angles ranging from 0° to 180° are taken into consideration. The results relative to the angles show that the perpendicular collision or a collision angle of 90° produces the lowest level of the internal energy in the side collision category by comparison with oblique collisions in the range of collision angles from 30° to 150°. The internal energy is found to be satisfactory when it is compared with the extent of the damage on the outer shell, which is also matched with the predicted energy behaviour from energy formulae.

Environmental protection using structural analysis of ships

Naval accidents are one of the most common causes of water and coast around pollution and also for the deterioration of the associated ecosystems. In order to reduce the risk of spills of hazardous substances in water one of the methods is to study the behavior of naval structures in the event of collisions.This paper aims to propose a methodology for collision analyze, the case study being a river barge structure with side impact generated by another barge. The structural analysis used the finite element method with an explicit solver and the dynamic load of the side impact collision was applied in form of initial kinetic energy of the striking ship. Standard ship design Rules are compared with an original approach to reveal the advantages and disadvantages of each method.The influence of variation of the different parameters on the obtained results is analyzed, in order to outline an efficient and as accurate as possible methodology, considering the necessary computational effort.

Study on the influence of ship collision upon propulsion shafting

In this study, a mathematical model of a struck ship based on the dynamic stiffness of the hull was developed; a comparison of the impact of collision in the models of dynamic stiffness and static stiffness, showed that the vibration amplitude in the dynamic stiffness was larger than that in the static stiffness in the stress accumulation stage. A simulation of shafting in colliding ships was performed based on a finite-element model using the ANSYS software, and the numerical simulation values and theoretical values were observed to be similar. To analyze the influence of ship collision on propulsion shafting, a test rig on ship collision based on dynamic stiffness was designed, and the experimental values agreed well with the numerical simulation values. From a practical perspective, this study could generate a map similar to an operating guide.

Numerical investigations of a prestressed pontoon wall subjected to ship collision loads

The paper presents a numerical investigation of the ship collision response for a floating pontoon. High fidelity finite element models of a container ship bow and a prestressed concrete pontoon wall are established. The effect of prestressing on the collision resistance of the pontoon is discussed. Integrated numerical simulations are conducted to study the structural deformation and energy absorption of the striking ship and the struck pontoon. The results are compared with the structural responses when a rigid ship collides with a deformable pontoon and a deformable ship collides against a rigid pontoon. Parametric studies are also carried out to investigate the effect of the pontoon wall thickness and the strength and dimension of the ship bulb. A dynamic punching shear check procedure that can be used in the preliminary design phase is proposed.

Study on Striking Ship with Loading Impact on the Performance of the Double Hull Oil Tanker Collision

Abstract Due to the great danger of the collision of oil tankers, lots of research on the collision of oil tankers has been carried out. But, at present, the research on the collision of oil tankers mainly focuses on the loading condition of the struck ship, ignores the impact on the loading condition of the striking ship. However, during the actual oil tanker collision, the striking ship is generally in the state of loading. Therefore, it is necessary to carry out the analysis of the impact of the loading condition of the striking ship on the collision damage of the oil tanker. In this paper, the effect of striking ship with loading on the impact performance of the side structure during the collision of the cargo double hull oil tanker has been investigated. The ship collision model was established by using the finite element software ANSYS/LS-DYNA which is based on 7000 tons of double hull oil tankers. Based on the analysis of the collision force, impact of striking speed changes, impact of striking deep changes and structural energy absorption during the collision process, the influence of the striking ship with loading on the damage mechanism and the impact performance of the double shell oil ship side structure was expounded. The results show that the influence of the striking ship with loading can be great to the damage to side hull during the research of the collision performance of the oil tanker.

Effects of a deformable striking ship's bow on the structural crashworthiness in ship–ship collisions

ABSTRACTShip–ship collision accidents continue to occur regardless of the continuous efforts to prevent them, and they essentially involve highly nonlinear problems associated with structural crashworthiness due to crushing and fracture. The nonlinear finite-element method is one of the most powerful techniques to solve the problems. In industry practice, the bow structure of a striking ship is often modelled as a rigid body as it is usually much stiffer than the side structure of a struck ship. However, reality is that the initial kinetic energy in a ship–ship collision accident can be absorbed by the damages of not only the struck ship's side structures but also the striking ship's bow structures because the striking ship bow structure is actually deformable. The aim of the present study is to examine the effects of a deformable striking ship's bow on the structural crashworthiness in ship–ship collisions. In the present study, two scenarios are considered where the side structure of a VLCC class double hull oil tanker is collided by the bow structure of a VLCC class double hull oil tanker or a SUEZMAX class double hull oil tanker. All of the ships considered are real ships in operation. The structural crashworthiness in terms of the collision force–penetration relation and the collision energy–penetration relation is then studied with two cases in which the striking ship's bow structures are either rigid or deformable. It is concluded that the striking ship's bow may be modelled as a rigid body in minor collisions at a collision angle of about 90° where the initial kinetic energy is entirely consumed before the inner hull structure is ruptured, but it should be modelled as a deformable body in a major collision accident or at an inclined collision angle where the maximum penetration can be greater than the double side breadth.