Collision and grounding of ships and offshore structures

Collision and Grounding of Ships and Offshore Structures Collision and Grounding of Ships and Offshore Structures contains the latest research results and innovations presented at the 6th International Conference on Collision and Grounding of Ships and Offshore Structures (Trondheim, Norway, 1719 June 2013) The book comprises contributions made in the field of numerical and analytical analysis of collision and grounding consequences for ships and offshore structures in various scenarios, such as narrow passageways and arctic conditions including accidental ice impact A wide range of topics is covered: - Recent large-scale collision experiments - Innovative concepts and procedures to improve the crashworthiness of ships and offshore structures - Ship collisions with offshore renewable energy installations - Residual strength of damaged ship structures as well as mitigation measures for the consequences of such accidents - Statistical analysis of collision and grounding incidents to analyse and predict the probability of their occurrence - Developments concerning rational rules for structural design to avoid collisions - Grounding actions comprising the use of general risk assessment methodologies E Kim Collision and Grounding of Ships and Offshore Structures contributes significantly to increasing the safety and reliability of seaborne transport and operations, and will be useful to academics and engineers involved in marine technology-related research and the marine industry Tai ngay!!! Ban co the xoa dong chu nay!!! Amdahl Ehlers Leira Collision and Grounding of Ships and Offshore Structures Jørgen Amdahl Sören Ehlers Bernt J Leira an informa business COLLISION AND GROUNDING OF SHIPS AND OFFSHORE STRUCTURES This page intentionally left blank PROCEEDINGS OF THE 6TH INTERNATIONAL CONFERENCE ON COLLISION AND GROUNDING OF SHIPS AND OFFSHORE STRUCTURES, ICCGS, TRONDHEIM, NORWAY, 17–19 JUNE 2013 Collision and Grounding of Ships and Offshore Structures Editors Jørgen Amdahl, Sören Ehlers & Bernt J Leira Department of Marine Technology, Norwegian University of Science and Technology, Trondheim, Norway CRC Press/Balkema is an imprint of the Taylor & Francis Group, an informa business © 2013 Taylor & Francis Group, London, UK Typeset by MPS Limited, Chennai, India Printed and bound in Great Britain by CPI Group (UK) Ltd, Croydon, CR0 4YY All rights reserved No part of this publication or the information contained herein may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, by photocopying, recording or otherwise, without written prior permission from the publishers Although all care is taken to ensure integrity and the quality of this publication and the information herein, no responsibility is assumed by the publishers nor the author for any damage to the property or persons as a result of operation or use of this publication and/or the information contained herein Published by: CRC Press/Balkema P.O Box 11320, 2301 EH, Leiden, The Netherlands e-mail: Pub.NL@taylorandfrancis.com www.crcpress.com – www.taylorandfrancis.com ISBN: 978-1-138-00059-9 (Hbk + CD-ROM) ISBN: 978-1-315-88489-9 (eBook) Collision and Grounding of Ships and Offshore Structures – Amdahl, Ehlers & Leira (Eds) © 2013 Taylor & Francis Group, London, ISBN 978-1-138-00059-9 Table of contents Foreword VII Feasibility of collision and grounding data for probabilistic accident modeling M Hänninen, M Sladojevic, S Tirunagari & P Kujala Bridge crossings at Sognefjorden – Ship collision risk studies M.G Hansen, S Randrup-Thomsen, T Askeland, M Ask, L Skorpa, S.J Hillestad & J Veie VTS a risk reducer: A quantitative study of the effect of VTS Great Belt T Lehn-Schiøler, M.G Hansen, K Melchild, T.K Jensen, S Randrup-Thomsen, K.A.K Glibbery, F.M Rasmussen & F Ennemark 19 An improvement on a method for estimating number of collision candidates between ships F Kaneko 27 Modeling and simulation system for marine accident cause investigation S.G Lee, S.H Jun & G.Y Kong 39 Development of vessel collision model based on Naturalistic Decision Making model M Asami & F Kaneko 49 Material characterization and implementation of the RTCL, BWH and SHEAR failure criteria to finite element codes for the simulation of impacts on ship structures J.N Marinatos & M.S Samuelides 57 Prediction of failure strain according to stress triaxiality of a high strength marine structural steel A Woongshik Nam & J Choung 69 Fracture mechanics approach to assess the progressive structural failure of a damaged ship A Bardetsky 77 Evaluation of the fendering capabilities of the SPS for an offshore application G Notaro, K Brinchmann, E Steen & N Oma 85 Collision tests with rigid and deformable bulbous bows driven against double hull side structures I Tautz, M Schöttelndreyer, E Lehmann & W Fricke 93 Side structure filled with multicellular glass hollow spheres in a quasi-static collision test M Schöttelndreyer, I Tautz, W Fricke & E Lehmann 101 Response of a tanker side panel punched by a knife edge indenter R Villavicencio, B Liu & C Guedes Soares 109 A study on positive separating bulbous bow B Li, L.S Zhang & L.P Sun 117 Calculation of a stranding scenario B Zipfel & E Lehmann 127 Grounding resistance capacity of a bulk carrier considering damage confined to the bow Y Quéméner & C.H Huang 135 Loading on stranded ships C Souliotis & M.S Samuelides 143 Plastic mechanism analysis of structural performances for stiffeners on outer bottom plate during shoal grounding accident Z Yu, Z Hu, G Wang & Z Jiang V 151 A simplified approach to predict the bottom damage in tanker grounding M Heinvee, K Tabri & M Kõrgesaar Residual ultimate longitudinal strength – grounding damage index diagram of a corroded oil tanker hull structure D.K Kim, H.B Kim, X.M Zhang, J.K Paik & J.K Seo 161 171 Towards an integrated approach to collision and grounding damage assessment E La Scola & G Mermiris 179 Towards more rational design of ship structures against collisions S.R Cho, J.M Kim, Y.H Kim, J.S Lee & M.I Roh 187 Structural safety assessment of ship collision and grounding using FSI analysis technique S.G Lee, T Zhao & J.H Nam 197 Ship-ice collision analysis to define ice model according to the IACS Polar Rule M.J Kwak, J.H Choi, O.J Hwang & Y.T Oh 205 On the plastic and fracture damage of polar class vessel structures subjected to impact loadings D.K Min, Y.M Heo, D.W Shin, S.H Kim & S.R Cho 213 Review of existing methods for the analysis of the accidental limit state due to ice actions E Kim & J Amdahl 221 A particle swarm optimization-based procedure to obtain a crashworthy ice-classed LNG tanker S Ehlers 233 Drop tests of ice blocks on stiffened panels with different structural flexibility E Kim, M Storheim, J Amdahl, S Løset & R von Bock und Polach 241 Risk analysis for offloading operations in the Barents, Pechora and Caspian seas N.G Popov, L.G Shchemelinin & N.A Valdman 251 Safe jacket configurations to resist boat impact A.W Vredeveldt, J.H.A Schipperen, Q.H.A Nassár & C.A Spaans 261 Collision between a spar platform and a tanker T de Jonge & L Laukeland 267 Ship collisions against wind turbines, quays and bridge piers P.T Pedersen 273 Experimental and numerical investigations on the collision between offshore wind turbine support structures and service vessels S.R Cho, B.S Seo, B.C Cerik & H.K Shin 281 Ultimate strength of an intact and damaged LNG vessel subjected to sub-zero temperature S Ehlers, S Benson & K Misirlis 289 Ultimate strength of damaged hulls C Pollalis & M.S Samuelides 297 Longitudinal strength assessment of damaged box girders S Benson, M Syrigou & R.S Dow 305 The analysis and comparison of double side skin crashworthiness A.Y.F Gong, J.X Liu, B.S.M Xiao & N Wang 315 A methodology for comparison and assessment of three crashworthy side-shell structures: The X-core, Y-core and corrugation panel structures J.W Ringsberg & P Hogström 323 Crashworthiness study of LPG ship with type C tanks S Rudan, B Ašˇci´c & I Viši´c 331 Study on influence of striking bow strength to the side structure during ship collision K Liu, Y Zhang & Z Wang 339 Author index 345 VI Collision and Grounding of Ships and Offshore Structures – Amdahl, Ehlers & Leira (Eds) © 2013 Taylor & Francis Group, London, ISBN 978-1-138-00059-9 Foreword We are pleased to host the 6th International Conference on Collision and Grounding of Ships and Offshore Structures in Trondheim this year This conference has now served for almost two decades as an important and internationally recognized platform to disseminate the latest research results in the field of collision and grounding of ships and offshore structures The preparation of this conference and proceedings would not have been possible without the excellent support from Frank Klæbo, Martin Storheim and Ekaterina Kim and we would like to express our thankfulness to them In addition, we would like to thank Leila Dashtizadeh and Rouzbeh Siavashi for their efforts in formatting the manuscripts where needed Furthermore, we would like to thank the steering committee for promoting and supporting the conference as well as the reviewers for their valuable contributions to this event The financial support of DNV, MARINTEK and DYNAmore Nordic is also greatly acknowledged Finally, we are wishing all participants a fruitful, stimulating and professionally rewarding stay at NTNU’s Marine Technology Centre the editors VII This page intentionally left blank Collision and Grounding of Ships and Offshore Structures – Amdahl, Ehlers & Leira (Eds) © 2013 Taylor & Francis Group, London, ISBN 978-1-138-00059-9 Feasibility of collision and grounding data for probabilistic accident modeling M Hänninen, M Sladojevic, S Tirunagari & P Kujala Aalto University, Department of Applied Mechanics, Espoo, Finland ABSTRACT: There exist various sources of data related to marine traffic safety, and the amount of data seems to be further growing in the future However, the data sets have different formats, scopes, and initial purposes The paper discusses the feasibility of maritime traffic accident and incident data to probabilistic modeling of collision and grounding accidents, especially their causal factors In addition, a case study is conducted for examining the data feasibility First, categorical Finnish accident causal data is utilized in learning a Bayesian network model from the data The data feasibility is then evaluated based on the how well the model matches to unseen accident cases and how it performs in classification of the accidents The results indicate that the dataset does not contain enough information for the applied of modeling approach Finally, recommendations to improving the data or ways to cope with the uncertainty are given INTRODUCTION (VTS) violation and incident reports Other potential data sources such as Port State Control inspection data, occupational safety data, data from insurance companies or classification societies are not addressed The systems and practices of accident or incident reporting or the corresponding data formats might differ from country to country Here the emphasis is on data describing the marine traffic in Finland The rest of the paper is organized as follows Chapters 2–4 describe the features of the aforementioned accident and incident data sources and discusses their feasibility to probabilistic collision and grounding modeling Chapter presents the data, methods, results and discussion of the case study, learning a Bayesian network of reported accident causes in Finnish collisions and groundings Finally, conclusions from the data, the literature review and the case study results are drawn in Chapter The purpose of accident modeling is to learn more about accidents in order to prevent them in the future Probabilistic accident models, depending on the underlying theoretical accident model type used (see e.g Hollnagel 2004), quantitatively describe accident causes, mechanisms, event chains, or system variability Such a model could be utilized within a cost-benefit analysis, risk management or safetyrelated decision making However, a ship, and further the marine traffic system as a whole, can be considered as a complex socio-technical system In such a system an accident is hardly ever a result of a single cause or a chain of events (Hollnagel, 2004) On the other hand, accidents are low probability events and thus relatively little data about accidents exists Therefore, the lack of data combined to the complexity of the problem might result in unreliable or invalid probabilistic models This paper discusses the feasibility of ship accident data for probabilistic collision and/or grounding modeling purposes In addition, as incidents or nearmisses occur more frequently than accidents but might be partly governed by the same underlying mechanisms and thus could provide additional information about marine traffic accidents (Harrald et al 1998), also incident data is considered The study is based on examining the data itself when available, reviewing relevant literature, and a case study of evaluating accident data feasibility to learning a Bayesian network model of the dependencies between the reported accident causes The examination is limited to accident databases providing categorical information on the accidents, accident investigation reports, a nearmiss reporting database, and Vessel Traffic Service ACCIDENT DATABASES 2.1 EMCIP All Member States of the European Union are obligated to report any marine casualty or accident occurrence involving merchant ships, recreational crafts and inland waterway vessels to the European Marine Casualty Information Platform (EMCIP) operated by European Maritime Safety Agency EMSA (Correia 2010) In EMCIP, the casualty events are classified into 25 event types Collisions and groundings can be categorized as a collision with another ship, a collision with multiple ships, a collision when the ship is not underway, contact with floating cargo, contact structures are proposed as space-saving solution for hull side structure, having in addition a very good crashworthy property (Klanac et al 2005) Due to the accentuated cargo space requirement, a novel, low profile, laser-welded sandwich structure arise as an interesting alternative to type C tanks LPG ship classic hull design In this article, a comparison between classic and novel sandwich hull side will be made through typical scenario collision analysis Table Two ship in collision particulars Parameters LPG ship Ferry Length over all Ship weight Mass of the cargo Displacement (at 1.025 t/m3 ) Draft aft Draft fore Middle draft Ship center of gravity height Ship center of gravity by length 114.89 3607 t 2148.6 t 5755.6 t 4.85 m 4.59 m 4.71 m 4.31 m 63.74 m 128.13 m 5757 t 6889 t 6889 t 5.25 m 5.30 m 5.28 m 8.388 m 61.082 m SHIP COLLISION SCENARIO Ship collision is a rather frequent marine accident, ranging from a minor collision with another ship or other structure to a severe incident with significant damage on ship, environment pollution and, in the worst case, human casualties Collisions occur due to various reasons such as negligence and a system malfunction The collision risk is increased in heavy traffic areas, such as narrow passages, bays, in the vicinity of harbors etc Worldwide, and in closed seas in particular, the imperative of fast and economical delivery of goods and people leads to natural grouping of ships on optimal routes, which are often intersecting and so increasing the risk of collision even more Ship collisions, as well as other marine accidents statistics, are usually reported by the official bodies in the particular country In addition, statistics may cover vessels ranging from fishing and leisure boats to the commercial fleet vessels Therefore, obtaining relevant data may be a complex task European Maritime Safety Agency presented marine accidents statistics “in and around EU waters” in (EMSA, 2010) Through years 2007 to 2010 a total of 1192 collisions were recorded, making approximately 43% of all marine accidents in that period This fact alone points out the need for crashworthy analysis of present and future ship structures – if collisions cannot be prevented, at least their consequences should be as low as possible Traditionally collision analysis is decoupled into external mechanics and internal mechanics The former considers global ship motions, while the latter considers localized structural response at the location of impact By recent advances in software both effects may be coupled in a single, fully non-linear analysis in time domain The finite element method and explicit analysis is commonly used for that purpose Following collision scenario is considered in this article: motionless Type C tank LPG ship (struck ship) is being hit amidships at the right angle by the similar size ferry (striking ship) Striking ship sailing speed is 16 knots Both struck and striking ship main particulars are listed in Table LPG deadweight is approximately two times less than a ferry, while displacement is much closer, being 5755 t for the fully laden LPG and 6889 t for the light loaded ferry Two different structures of LPG amidships are considered: classic single hull and laser-welded type sandwich hull structure Figure LPG ship with type C bi-lobe tank cross section at the saddle support section LPG SHIP AMIDSHIPS STRUCTURE LGP ships, containing nonstructural tanks of type C, are designed to maximize cargo space while taking into account specific cargo requirements Hull cross section of the struck ship, at the location of the saddle support, is presented in Figure The main deck, single hull and double bottom may be observed around the bi-lobe tank A bi-lobe tank is comprised of two incomplete cylindrical tanks that are joined along the longitudinal bulkhead The bulkhead compensates the membrane forces from the cylindrical part of the structure Below the bi-lobe tank a saddle support structure is present, connecting tank with ship double bottom and side structure The application of steel sandwich structures in shipbuilding is already considered in the scientific community with great interest (Klanac et al 2009, Romanoff 2011, Hogström and Ringsberg 2013) However, due to 332 Figure FE model of a struck LPG ship Figure Sandwich structure Figure Sandwich plate thickness space-saving demand, only very thin sandwich structure is applicable to LPG ships A novel, laser-welded sandwich solution may be acceptable alternative to classic single hull structure due to its advantages (Romanoff et al 2007, Jelovica et al 2012) Due to precision welding, thin sandwich plates may replace standard, thicker single hull plating without adding significant amount of additional weight and possibly improving the crashworthiness of ship structure Production technology, though, is out of the scope of this article and will not be considered Figure indicates the main particulars of the sandwich plate introduced in the struck ship starboard hull amidships, where: a × b × c = 22 × × 0.1 m and s = 0.145 m Figure presents the thicknesses of the sandwich plate components which were chosen to match as close as possible the amount of steel on classic structure, where: t1 = t2 = t3 = mm Figure Fine mesh FE model of struck ship – classic structure In this way amidships masses are calculated automatically from the finite element properties Ballast state is considered, with empty cargo tanks A fine mesh detail of the classic structure in the collision zone at the amidships starboard is presented Figure It extends between two saddle supports including two additional frames on each side The fine mesh area is approximately 22 × meters (length × height) A fine mesh detail of the novel structure in the collision zone is presented in Figure The sandwich structure is replacing hull shell between saddle supports, from upper tank to double bottom The frames STRUCK SHIP MODEL Commercial finite element software LS-Dyna, version ls971_d_7600, is used for setting up the collision model The collision model contains both ships and takes into account hydrodynamic forces to certain extent Struck ship consists of three parts, Figure Two parts, fore and aft par, are modeled as rigid structures represented with ships outer shell only Their masses are modeled by concentrated mass elements constrained to corresponding rigid parts Third is the middle part of the ship and it is modeled using elastoplastic material representing Grade A steel behavior Figure Fine mesh FE model of struck ship – sandwich structure 333 Figure Classic (left) and sandwich (right) cross-section of the struck ship Figure Struck ship hydrostatic and hydrodynamic forces Figure Classic and sandwich structure connection at the location of saddle support (all upper elements are removed) are now missing, but longitudinal girder and web frame knuckles remain Struck ship cross-section for both classic (left) and sandwich structure (right) is presented in Figure It should be noted that sandwich structure is partially curved near the double bottom which may be technologically demanding in production Figure presents connection of the sandwich structure with a strong saddle support in detail Upper ship structure is removed for the sake of the clarity of display No additional brackets or other stiffening elements are added along sandwich-to-classic structure connection zone The model is supported by hydrostatic and hydrodynamic load as presented in Figure Vertical, i.e hydrostatic nodal forces, acting along the model bottom, have a constant value and are in equilibrium with the mass of the ship middle part The side nodal forces, acting in negative-y direction and are defined twice Two control nodes, one at the fore and one at the aft model peak, are used by the software to evaluate average ship velocity and acceleration The first set of nodal forces is proportional to the evaluated ship velocity while the second set of nodal forces is proportional to evaluated ship acceleration Both sets of nodal forces are acting along the Figure 10 Boundary conditions – z-constrained edges ship side, Figure (down) and represent the resistance of water due to ship motion during collision In the above expressions: ρ is water density, VY is the velocity of the reference node, A is the area accepting node velocity related force,  is displacement and ACCY is the acceleration of the reference node In addition, Fv value is increased deliberately by 1.5 in the attempt to model water resistance in more realistic way In this way the resistance of the hull not subjected to nodal forces is taken into account This however is not further elaborated here The model boundary conditions are illustrated in Figure 10 Sides of the ship middle part i.e fore bulkhead and aft open section are constrained from moving 334 Figure 11 Striking ship model in z-direction In this way, minor difference between mass and hydrostatic force is compensated through reactions in boundary nodes At the same time, all six degree of freedom of nodes in collision zone and middle ship part in general are unconstrained Fore and aft peak concentrated masses are constrained from moving in z-direction STRIKING SHIP MODEL Striking ship model is presented in Figure 11 Model consists of 3D bow model generated using plate elements and 1D hull model generated using beam models Spring elements are used to model nonlinear hydrostatic forces They support the model through balance of model mass and vertical hydrostatic (spring) forces when gravity load is applied In this way heave and pitch motion of the model is allowed Although this is not of main concern here, the model is prepared in this way to study heave and pitch motions in a different collision scenarios Detailed description of the model can be found in (Srdeli´c and Rudan 2011) The striking ship model is subjected to nodal forces that accelerate the model to a collision speed just before the impact Since lower spring nodes are constrained to follow the y-direction movement of the upper nodes, it was not possible to constrain the striking ship nodes with initial velocity condition Then the model is released to perform collision due to inertial movement Within this scenario the hydrodynamic resistance due to a model movement is not modeled and bow nodes are restricted from moving in z-direction The hydrodynamic resistance of the striking ship has no effect on the collision but may have effect on global motions of the ships afterwards COLLISION PARAMETERS Both model share some collision parameters All the plate elements are modeled using *MAT_ PIECEWISE_LINEAR_PLASTICITY material model while all the beam elements are modeled using *MAT_SIMPLIFIED_JOHNSON_COOK material model The later is used as it is one of the few elastic-plastic materials applicable to resultant beam formulation used in model Termination time set for the analysis was seconds Figure 12 Grade A steel – true stress-strain curve Since various element size is implemented in both models, an average element size is detected for both coarse and fine mesh and the Peschmann failure criteria is adopted for each corresponding part The Peschmann and other failure criteria is critically analyzed in (Ehlers et al 2008) Average deformation before failure was found to be 0.13, while ranging from 0.09 for the largest to 0.285 for the smallest elements Grade A steel true stress-strain curve is applied, Figure 12 Both models consists of beam elements (BelytschkoSchwer resultant beam formulation), shell elements (Belytschko-Tsay formulation), concentrated mass elements and discrete elements (springs) Striking model is generated in Femap preprocessor and then converted to LS-Dyna analysis model Struck ship model was generated within SESAM software for the purpose of the long-term fatigue analysis and was converted to LS-Dyna analysis model Both fine mesh models embedded into global struck model, classic and sandwich structure, were generated using Femap preprocessor and assembled in LS-Prepost prior to analysis DISCUSSION OF RESULTS Two non-linear FE analyses are performed in LS-Dyna for the same collision scenario: one with classic single hull and one for sandwich hull structure on struck ship Top view on ships position at time instances t = s, t = 2.16 s and t = s are presented in Figure 13 (left to right) Only a part of the struck ship is presented Situation on Figure 13 is typical for both analyses Approximately at time instance t = 2.16 s maximum penetration of the striking ship bow is achieved During the rest of the simulation, up to t = s, kinetic energy of the striking ship is transferred to the global motion of the struck ship At the end of simulation both ships are still moving, although slowing down due to forces described by equations (1) and (2) Analysis of the hydrodynamic effects is outside of the scope of this article but will be studied in detail as a part of the future work Figure 14 (up) presents damage on the classic hull at t = 2.15 seconds and sandwich hull (down) at t = 2.16 seconds The von Mises stress field is presented It 335 Figure 13 Ships position at t = s, t = 2.16 s and t = s (from left to right) Figure 16 Comparison of resultant force Figure 14 Comparison of damage – classic structure (up) and sandwich structure (down) Figure 17 Collision situation at t = s in cross section view Figure 15 Comparison of kinetic energy change can be noticed that hull stiffness is insufficient to prevent significant damage of the ship side in both case However, sandwich structure is able to withstand collision with less damage, although not by large margin The major difference is that sandwich structure has very big number of interconnected structural elements which consume additional energy during tearing and can remain connected even at small undamaged area This does not change the fact that penetration is significant in both cases, significantly reducing bending capacity of the struck ship Figure 15 presents comparison of kinetic energy for two collision scenarios It may be noticed that total kinetic energy is being absorbed faster by deformation of sandwich than classic hull structure At the time instance t = s the ratio between kinetic energies is approximately 1.2 indicating 20% higher strain energy absorption by a sandwich than a classic structure Figure 16 presents resultant force during the contact Although the peak force is of similar value, a better resistance to tearing of the structure is present in the case of sandwich structure, as expected, and can be noticed as steeper force increase at the beginning of collision Figure 17 presents cross section in collision situation at t = s when sandwich structure is present At this moment maximum penetration is achieved and then both ships continue to move in the direction of striking ship movement, with a slow but steady loss of common velocity, due to action of nodal forces applied on the struck ship The hydrodynamic resistance applied in this way roughly models inertial forces proportional to ship displacement mass and water resistance forces proportional to ship side projected area It remains to study this in detail in further research It may be noticed that cargo tanks didn’t fail during collision, see also Figure 18 Striking ship damage is not significant and possible reason for that 336 • Single parts should not contain element with significant difference in size as only one failure criterion per part is possible • The contact between large and small finite elements is sensitive with respect to the failure criteria applied Figure 18 Plastic strain and maximum damage of bi-lobe tank at t = 2.16 s is that the Peschmann criterion is applied with difficulties if elements vary in size significantly with a single LS-Dyna part Figure 18 presents maximum damage on bi-lobe tank at t = 2.16 s Although plastic deformation of the tank is significant there is no rupture in the structure CONCLUSION Non-linear FEM analysis of collision is now a widely applied method for evaluation of structural crashworthiness and comparative analysis of different structural solutions A particular collision scenario is defined to evaluate the application of a novel sandwich structure in an LPG ship hull in comparison with common single hull design The results indicate that crashworthiness may indeed be increased by the application of thin, laser welded sandwich structure but not to an extraordinary level Some 20% decrease in kinetic energy during collision indicates higher energy absorption by the sandwich structure In addition, the total damage of the novel hull is less pronounced due to the many structural interconnections within the sandwich structure grid The Peschmann failure criterion was applied to all parts in both ship structures The plastic deformation of the bow was found to be lower than expected The application of the failure criterion was already recognized as a problem in literature, and here the conclusions from the study experience are listed: • The finite element mesh should be carefully planned when modeling for collision analysis Due to variation in dimensions of elements only their average size may be considered in the application of the failure criterion The transition from small to large elements should occur far from the collision zone The present collision model combines elements of external dynamics and internal mechanics and may be considered as a state-of-the-art model, excluding fluid-structure interaction (FSI) models Further improvements of the collision model, in particular water resistance modeling, may provide better insight into collision event Even so, parametric analysis of the present model might answer the following questions: to what extent sandwich structure may be improved to increase crashworthiness in economical way, will the internal tanks be damaged in collision up to rupture, can the ship roll during collision be captured realistically The answers to these questions remain for the future study REFERENCES Germanischer Lloyd, ‘Rules for Classification and Construction, I Ship Technology, Seagoing Ships, Liquefied Gas Tankers’, 2008 Ehlers, S.; Broekhuijsen, J.; Alsos, HS.; Biehl, F & Tabri, K 2008 Simulating the collision response of ship side structures A failure criteria benchmark study, International Shipbuilding Progress 55: 127–144 European Maritime Safety Agency (EMSA), Maritime Accident Review 2010 Hogström, P & Ringsberg, JW 2013 Assesment of the crashworthiness of selection of innovative ship structures Ocean Engineering 59: 58–72 Jelovica, J.; Romanoff, J.; Ehlers, S & Varsta, P 2012 Influence of weld stiffness on buckling strength of laserwelded web-core sandwich plates Journal of Constructional Steel Research 77: 12–18 Klanac, A.; Ehlers, S.; Tabri, K.; Rudan, S & Broekhuijsen, J Qualitative design assessment of crashworthy structures, Proceedings of the 12th International Congress of the International Maritime Association of the Mediterranean, IMAM 2005 Maritime Transportation and Exploitation of Ocean and Coastal Resources 1: 461–469 Klanac, A.; Ehlers, S & Jelovica, J 2009 Optimization of crashworthy marine structures Marine Structures 22 (4): 670–690 Romanoff, J.; Remes, H.; Socha, G.; Jutila, M & Varsta, P 2007 The stiffness of laser stake welded T-joints in webcore sandwich structures Thin-Walled Structures 45 (4): 453–462 Romanoff, J 2011 Interaction between laser-welded webcore sandwich deck plate and girder under bending loads Thin-Walled Structures 49 (6): 772–781 Srdeli´c, M & Rudan, S 2011 Non-linear FEM study of a ship grounding Proceedings of Fourth conference on marine technology, in memoriam of the academician Zlatko Winkler, Rijeka: 107–120 337 This page intentionally left blank Collision and Grounding of Ships and Offshore Structures – Amdahl, Ehlers & Leira (Eds) © 2013 Taylor & Francis Group, London, ISBN 978-1-138-00059-9 Study on influence of striking bow strength to the side structure during ship collision K Liu State Key Lab of Ocean Engineering, Shanghai Jiaotong University, Shanghai, China Y Zhang & Z Wang School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang Jiangsu, China ABSTRACT: The problem about ship collision is the hot point of the ship mechanics However, due to the complexity of the problem during ship collision, the striking ship was often appropriately simplified during analyzing the collision performance in order to save computational resources and improve the computational efficiency In fact, the simplifications of striking bow will have certain effect on the calculation results This paper focuses on the influence of striking bow strength to the collision capabilities of struck structures The quantitative comparison analysis was performed for striking with different bow strength The results show that the different strength of actual bows take effects to the collision performance of the struck structures, the bigger of the strength , the lower of the limited penetration, the higher of the collision force, the more of the energy absorption at the same penetration INTRODUCTION With the continued development of the world’s shipping industry, water transportation becomes increasingly busy, collision and grounding accidents have always occurred, which often results in disastrous consequences such as damaged hull structures, cargo leakage, environmental pollution, casualties and so on (Wang, 2000; Yamada, 2006) Therefore, the protection during ship collision has attracted more and more attention of governments in the world In recent years, the study on ship collision has become a hot focus all over the world Now, researches on this problem mainly focused on the two aspects, they are collision performance and crashworthy design In fact, the two are closely related The former is the foundation which is focus on the damage characteristics and energy absorption mechanism, while the latter is the target which mainly helps the struck ship improves the crashworthiness Many scholars have carried out numerous studies on collision performance (Wang, 2002; Kim J Y, 2000), proposed a variety of crashworthiness structures (Wang and Zhang, 2008, 2007, 2002, 2001; Urban, 2003), which greatly improved the crashworthiness of the ship structure However, due to the complexity of the problem during ship collision, the striking ship was often appropriately simplified during analyzing the collision performance in order to save computational resources and improve the computational efficiency These simplifications of striking bow are certainly useful, but they will have certain effect on the calculation results Therefore, this paper focuses on the influence of striking bow strength to the collision capabilities of struck structures through changing the strength of striking bulbous bows DESCRIPTION OF THE COLLISION SCENARIO 2.1 Collision scenario The collision scenario is chosen a 159,000 DWT VLCC impacted by a 176,000 DWT bulk carrier with a bulbous bow The impact velocity is 10 m/s and impact angle is 90◦ 2.2 Collision scheme In order to analyze the influence of the striking bow strength to the crashworthiness of struck ship, the striking bow is defined as five structures with different materials and plate thickness, calculating their crushing strength and then takes them as bulbous bows to impact the stroke ship Figure Finite element models 339 Structural collision simulations were performed using the commercial code MSC/DYTRAN, version 2010 We used PATRAN 2010 to build the finiteelement models The structural material is marine low carbon steel, and the mechanical properties of the material (Table 1) used in the finite element models are obtained from the references (Wang, 2000) which obtained from in-house quasi-static tensile tests carried out on material of marine low carbon steel The cowper-symonds model is selected as material model, and considering the material strain harden effect 3.1 bulbous bow with a certain velocity The bulbous bow and rigid wall are using 4-node quadrilateral shell element, the heavy hammer is using 8-node hexahedral element The end of the bulbous bow connected to the rigid wall Figure shows the inner structures of the bulbous bow There are transverse frames, a longitudinal bulkhead and a platform In order to make the striking CALCULATION ON THE CRUSHING STRENGTH OF STRIKING BULBOUS BOWS Crushing strength calculation The theoretical study often neglects the influence of the load-deformation curve and uses the average crushing force Pm because of the load–deformation curve showing a repeating morphology, the total axial displacement greatly exceeds the displacement corresponding to the first load peak In order to avoid the human error, the Pm is solved by the deformation energy Ek divided by the crushing depth s, that is: Figure Bulbous bow collision experiment (Yamada, 2006) The equivalent strength of the bulbous bows σm can be calculated by the average crushing force Pm and the average area A which calculated from the total section area divided by the length of the bow, that is Figure Finite element model of bulbous bow 3.2 Calculation on the crushing strength of different bulbous bows According to the experimental methods provided by the reference (Yamada, 2006), finite element numerical simulation method is applied to study on the crushing performance of different bulbous bows and get the equivalent strength Figure shows the bulbous bows crushing experiment (Yamada, 2006), and FE model corresponding to the experimental model (Yamada, 2006) was re-created by the present authors as shown in Figure The model uses a rigid heavy hammer crushing the Table The main factors of materials in simulation Poisson ratio Critical strain Yield stress MPa 0.3 0.16 235 Elastic modulus GPa 206 Parameters of strain rate D q 40.4 Figure Inner structures 340 bulbous bows have different strength, bulbous bows are built and they are same in the structural size but different in the plate thickness and yield stress Table shows the material parameters Table Material parameters of different bulbous Striking bows Outplate mm Bulkhead platform mm Frames mm Yield stress MPa Bow A Bow B Bow C Bow D 12 16 20 24 10 14 18 22 12 16 20 235 275 315 355 3.3 The crushing strength of the bulbous bows Figure and figure are the crushing forces and crushing deformation of different strength bows It can be found that when crushed by the heavy hammer, the response of the bows is unstable; the loaddeformation curves show a kind of morphology which have repeated and irregular cycle changed The buckling mode of the bows is a axisymmetric mode, and the buckle is formed from the upper end, and then propagated down On the basis of the formula (1), (2) and loaddeformation curves, the equivalent strength of different striking bows are got, they are given in Table Figure Collision force of bulbous with different strength 341 Figure Deformation of bulbous collision (Photos from Yamada, 2006) Figure The limited penetration-strength curve Table The equivalent strength of different striking bows Bows Bow A Bow B Bow C Bow D σm (MPA) 1.42 2.45 3.58 5.03 using an added mass 0.04 times of total ship mass by increasing density of elements of ship rearward part in this paper 4.1 Limited penetration Figure FE model of inner structures of striking ship bow THE COLLISION PERFORMANCE OF SIDE STRUCTURES UNDER DIFFERENT STRENGTH OF BOWS The limited penetration is defined as the penetration when the inner side plate of the struck structure began to rupture Figure shows the relationship between the limited penetrations and the equivalent strength of the striking ship bows It can be seen from the figure: with the increase of bow strength the limited penetrations decrease This is because that the more of the strength, the less of the relative strength of the struck structures, and they are easier to be damaged; The bow strength has a great impact on the limited penetration, when σm = 1.42 MPa, the striking bow is crushed and the struck structure hasn’t be damage d, while σm = 5.03 MPa, limited penetration is 2.89 m; The limited penetrations of the struck structures impacted by striking bows B,C,D are very close It indicates that when the strength of striking bows increasing to a certain extent, it will not obvious effect on the struck structures So, when it exceeds a certain range, it can be used as a rigid 4.2 Collision force This part, the bulbous bows with different strength will be applied to the striking ship, to study on the collision performance of side structures under the different strength of striking bows Figure shows the finite element model The boundary condition of the struck side structure is fixed of the four edges and considering the influence on the striking ship motion from the water When the striking ship normally collides, it only moves in longitudinal direction The influence on the ship motion from the water is relative little and depicted Figure and Figure 10 show the relationship between the collision force and the strength of the different striking bows Figure shows the collision force at the limited penetrations; we can see that with the increase of the strength of the striking bow, the collision force decreased continuously This is related to the limited penetrations; the stronger of the striking bow, the less of the limited penetrations, and the collision area reduce d Figure 10 shows the collision force when the penetration is 2.8 m It can be seen that with the increase of the strength of striking bows, the collision force increasing constantly It is not contradictory to 342 Figure Curve of collision force-strength at the limited penetration Figure 11 Structure energy absorbing-penetration curves structural damage deformation thereby affecting the overall energy absorption of the structure To carry out structural crashworthiness design should take the actual striking bow angles into account CONCLUSIONS Through comparing and analyzing the limited penetration, collision force, and energy absorption of the struck side structures under the striking of bulbous bows with different strength, the main conclusions are as followings: Figure 10 Curve of collision force-strength at the penetration of 2.8 m the figure 9.At the same penetration, the stronger striking bow can make more s rious damage to de struck structures, so the collision force increased 4.3 Energy absorption Figure 11 shows the relationship between energy absorption of struck side structures and collision penetrations under the striking bows with different strength We can see from the figure that the stronger of the striking bow the more of the energy absorption at the same collision penetration With the increase of the collision penetration, the difference becomes more obvious.The difference mainly caused by the different strength of the striking bows When the strength of the bow is less, it will deform in the collision process, and then the area and the degree of the components involved in damage deformation became more, so the struck structures can absorb more energy It illustrated that the contact area is one of the important factors that affects 1) With the increase of bow strength the limited penetrations decrease, but when the strength of striking bows exceeds a certain range, the striking bow can be used as a rigid 2) The contact area is one of the important factors that affect the collision force and the structural damage deformation thereby affecting the overall energy absorption of the structure To carry out structural crashworthiness design should take the actual striking bow angles into account REFERENCES Cho, S & Lee, H 2009 Experimental and analytical investigations on the response of stiffened plates subjected to lateral collisions Marine Structures 22: 84–95 Endo, H & Yamada, Y 2002 Model test on the collapse strength of the buffer bow structures Marine Structures 15: 365–381 Huatao, J & Yongning, Gu 2003 Discussion on Buffer Bulbous BOW-Influence of Bow Curvature on Ship Collision Shipbuilding of China 44(2): 25–32 Jones, N 1989 Structural Impact Cambridge: Cambridge University Press 343 Kazeminezhad, M 2009 A comparison of low carbon steel and Al–Mg alloy 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Structure Crashworthy Design Based on Sandwich Panel Shipbuilding of China 49(1): 60–65 Wang, Z & Zhang, Y 2007 Study on Crashworthiness of Honeycomb Sandwich Panel under Lateral Dynamic Load Journal of Jiangsu University of Science and Technology 21(3): 1–5: Natural Science Edition Wang, Z & Yongning, Gu 2002 A crashworthy type of double hull structure of VLCC Journal of Ship Mechanics 6(1): 27–36 Wang, Z &Yongning, Gu 2001 A crashworthy side structure for single-hull LPG carrier Ship Engineering (2): 12–14 Yagi, S.; Kumamoto, H.; Muragishi, O.; Takaoka, Y & Shimoda, T 2009 A study on collision buffer characteristic of sharp entrance angle bow structure Marine Structures 22: 12–23 Yamada, Y 2006 Bulbous Buffer Bow: A Measure to Reduce Oil Spill in Tanker Collisions PhD thesis, DTU Yamada, Y & Pedersen, P 2008 A benchmark study of procedures for analysis of axial crushing of bulbous bows Marine Structures 21: 257–293 344 This page intentionally left blank Collision and Grounding of Ships and Offshore Structures Collision and Grounding of Ships and Offshore Structures contains the latest research results and innovations presented at the 6th International Conference on Collision and Grounding of Ships and Offshore Structures (Trondheim, Norway, 1719 June 2013) The book comprises contributions made in the field of numerical and analytical analysis of collision and grounding consequences for ships and offshore structures in various scenarios, such as narrow passageways and arctic conditions including accidental ice impact A wide range of topics is covered: - Recent large-scale collision experiments - Innovative concepts and procedures to improve the crashworthiness of ships and offshore structures - Ship collisions with offshore renewable energy installations - Residual strength of damaged ship structures as well as mitigation measures for the consequences of such accidents - Statistical analysis of collision and grounding incidents to analyse and predict the probability of their occurrence - Developments concerning rational rules for structural design to avoid collisions - Grounding actions comprising the use of general risk assessment methodologies E Kim Collision and Grounding of Ships and Offshore Structures contributes significantly to increasing the safety and reliability of seaborne transport and operations, and will be useful to academics and engineers involved in marine technology-related research and the marine industry Amdahl Ehlers Leira Collision and Grounding of Ships and Offshore Structures Jørgen Amdahl Sören Ehlers Bernt J Leira an informa business