Structural Design and Response in Collision and Grounding

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modifications on oil outflow the DAMAGE calculationsshould be coupled with outflow analysis.The next step in the study is to carry out aprobabilistic analysis of damage in grounding scenariosdefined by probability density functions of the inputparameters. This analysis will be coupled with outflowcalculations. The objective of the study will be to providea tool for comparative studies between vessel designs.5 COLLISION MODELS5.1 Background and PlanIn 1979, the Ship Structure Committee (SSC) conducted areview of collision research and design methodologies[18]. They concluded that the most promising simplifiedcollision analysis alternative was to extend Minorsky’soriginal analysis of high-energy collisions by includingconsideration of shell membrane energy absorption. Asimple and fast model is important in probabilisticanalysis because thousands of different scenarios must berun to develop statistically significant results.A more recent review of the literature and of theapplicability of available methods for predicting structuralperformance in collision and grounding was made in the1997 International Ship and Offshore Structures Congress(ISSC 97) by Specialist Panel V.4 [9]. Their report states:“Knowledge of behavior on a global level only (i.e., totalenergy characteristics like the pioneering Minorskyformula) is not sufficient. The designer needs detailedknowledge on the component behavior (bulkheads,girders, plating, etc.) in order to optimize the design foraccident loads.”The approach taken in this study is to progressivelyincrease the complexity of SIMCOL (Simplified CollisionModel), the Ad Hoc Panel’s baseline collision model,until results with sufficient accuracy and sensitivity todesign characteristics are obtained. In order to assess themodel’s consistency and sensitivity, the model is appliedin a series of collision scenarios with a range of tankersizes and designs. SIMCOL results are compared toresults obtained using three other collision models:DAMAGE [10,19], ALPS/SCOL [20,21], and a TechnicalUniversity of Denmark (DTU) model. The DTU modeland ALPS/SCOL were also further developed during thisstudy. Determining the ideal trade-off between simplicityand sufficiency is a primary concern of this process.5.2 Models Included in the Current StudyThree types of collision were identified for investigationby the panel:• Low energy puncture at a point• Low energy raking puncture• Penetrating Collision – right angle and obliquesufficient to penetrate outer hull with significantdamage extending in at least 2 directions(penetration, horizontal, vertical)Work thus far is focused on models for penetratingcollision.Each collision model must consider two verydifferent aspects of the collision event:• External problem – includes the globalcharacteristics of the striking and struck ships andtheir motion before, during and after collision;• Internal problem - includes the internal deformationmechanics and structural response of the struck shipand the striking ship bow during collision.The four models studied by the panel take differentapproaches to solving and coupling these two problems.Although not a formal validation, comparison andagreement between these models provides useful insightinto their performance and increases confidence in thevalidity of their results.5.2.1 Simplified Collision Model (SIMCOL) [22]SIMCOL uses a time -domain simultaneous solutionof external dynamics and internal deformation mechanicssimilar to that originally proposed by Hutchison [23].Figure 12 shows the SIMCOL simulation process. Theexternal sub-model uses a three degree-of-freedomsystem for ship dynamics shown in Figure 13. Theinternal sub-model determines reacting forces from sideand bulkhead structures using detailed mechanismsadapted from a 1981 Rosenblatt study [24,25]. Itdetermines the energy absorbed by the crushing andtearing of decks, bottoms and stringers using theMinorsky correlation [26] as modified by Reardon andSprung [27].Go to the next time step:i = i+1At time step iBased on current velocities, calculate thenext positions and orientation angles of theships, and the relative motion at impactCalculate the change of impact locationalong the struck ship and the increment ofpenetration during the time stepCalculate the average reaction forces duringthe time step by internal mechanismsCalculate the average accelerations of bothships, the velocities for the next time step,and the lost kinetic energy based on externalship dynamicsNoMeet stoppingcriteria ?YesCalculate maximumpenetration and damagelengthFigure 12 - SIMCOL Simulation Process8
ybeginning of time step nStriking ShipP 4,n+1, P5,n+1 P1,n P1,n+1G 2Striking ShipG 1θ2φξP4,n, P5,nend of time step nφ ′ nP3,nαP2,nP2,n+1side shellStruck Shiplθ1Struck ShipP3,n+1damaged area duringtime step nNote: The positive direction of angle is alwayscounterclockwise.xFigure 14. Sweeping Segment MethodηFigure 13. SIMCOL External Ship DynamicsV.U. Minorsky conducted the first and best known ofthe empirical collision studies based on actual data [26].His method relates the energy dissipated in a collisionevent to the volume of damaged structure. Actualcollisions in which ship speeds, collision angle, andextents of damage are known were used to empiricallydetermine a linear constant. This constant relates damagevolume to energy dissipation. In the original analysis thecollision is assumed to be totally inelastic, and motion islimited to a single degree of freedom. Under theseassumptions, a closed form solution for damaged volumecan be obtained. With additional degrees of freedom, atime-stepped solution must be used.Crake and Brown developed SIMCOL Version 0.0 aspart of the work of SNAME Ad Hoc Panel #3 [6,28].Based on further research, test runs and the need to makethe model sensitive to a broader range of design andscenario variables, improvements were progressivelymade by Chen and Brown at Virginia Tech [22]. Asweeping segment method, shown in Figure 14, is addedto the model in SIMCOL Version 1.0 to improve thecalculation of damage volume and the direction ofdamage forces. Models from the Rosenblatt study [24,25]are applied in Version 1.1 assuming rigid web frames. InVersion 2.0, the lateral deformation of web frames isincluded as shown in Figure 15. In Version 2.1, thevertical extent of the striking ship bow is considered.Table 1 describes the evolution of SIMCOL over thecourse of the study thus far.Design data required for the striking ship includesbow half-entrance angle, bow height, length, beam, draftand displacement.Scenario data required includes striking and struckship velocity, collision angle, and longitudinal location ofimpact in the struck ship.Web frames acting as a vertical beamdistort in bending, shear or compressionStrike at webframeAnalyze each shellseparatelyconsistent withweb deformation.Strike betweenweb frameAnalyze each shellseparately withnodes consistentwith webdeformation.Figure 15. Web Deformation in SIMCOL 2.0 [24,25]5.2.2 DAMAGE 4.0 [19]The DAMAGE 4.0 collision module solves the externalproblem uncoupled from the internal problem, and appliesthe calculated absorbed energy to plastic deformation ofthe struck ship. Structural components, motions, massesetc. are described in ship coordinate systems local to eachship and in one global coordinate system. Degrees offreedom in DAMAGE include striking ship surge andstruck ship sway and yaw.The following assumptions are applied in DAMAGE4.0:• Both ships are perpendicular before and duringimpact, i.e. only right angle collisions are considered.• The forward motion of the struck ship is assumed tobe zero.9
Page 1 and 2: Brown, A.J., Tikka, K., Daidola, J.
Page 3 and 4: 3 PROBABILISTIC FRAMEWORKFigure 2 i
Page 5 and 6: 4.2.2 Method by Wang [15]Dr. Wang d
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Page 11 and 12: location, COG, and detailed structu
Page 13: Ship Type150,000 dwtbulk carrierLen
Page 16 and 17: 6.2 DATA FOR MODEL VALIDATIONThe se
Page 18 and 19: Force (N)8.00E+087.00E+086.00E+085.
Page 20 and 21: Figure 37 - Macro flow diagram for
Page 22 and 23: enhance resistance to collision. Th
Page 24 and 25: Figure 42 - Load versus lateral ind
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Structural Design and Response in Collision and Grounding

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