Scholarly article on topic 'Investigation on the Structural Damage of a Double-Hull Ship, Part II – Grounding Impact'

Investigation on the Structural Damage of a Double-Hull Ship, Part II – Grounding Impact Academic research paper on "Materials engineering"

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{"Impact phenomenon" / "grounding impact" / "numerical simulation" / "structural damage" / "collision force"}

Abstract of research paper on Materials engineering, author of scientific article — Aditya Rio Prabowo, Hyun Jin Cho, Seung Geon Lee, Dong Myung Bae, Jung Min Sohn, et al.

Abstract Possibility of marine and offshore structures to experience accidental loads has been seriously considered up to this day. Remarkable casualties on related aspects are rising demand to ensure ship safety which in this subject is observed on marine structure. Ship is an example of marine structure that may be subjected to accidental loads during its operation. The aim of this paper is to investigate damage extent of the target ship under different accidental loads, namely collision and grounding with considerations to failure process and deformation contours. This work is divided into two parts which in the Part I, ship collision is discussed, and the Part II deals with interaction of ship structure with sea bottom in grounding. In Part II - Grounding impact, evaluating tearing damage on the bottom structure is essential in estimating environmental casualties caused by oil leakage. A chemical tanker is modelled to be the target ship in a series of grounding scenarios. Condition of the structural damage and tendency of the internal energy, crushing force and structural acceleration are observed. Prediction of the tearing opening and location of the initial failure in further grounding process are also presented in this paper. Virtual experiment is conducted by nonlinear finite element method in order to calculate the defined grounding scenarios which are built based on the target location on the bottom structure. Based on calculation results, condition of the double-hull structure after grounding is found to be highly influenced by arrangement of the longitudinal members which is evidenced by the fact that these members provide higher resistance than the transverse part. Finally, influence of the indenter's position on structural responses in grounding is summarized.

Academic research paper on topic "Investigation on the Structural Damage of a Double-Hull Ship, Part II – Grounding Impact"

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Procedia Structural Integrity 5 (22017) 9403-950

www.elsevier.com/locate/procedia

2nd International Conference on Structural Integrity, ICSI 2017, 4-7 September 2017, Funchal,

Madeira, Portugal

Investigation on the Structural Damage of a Double-Hull Ship,

Part II - Grounding Impact

Aditya Rio Prabowoa, HMn Jin Chob, Seufg Geon Leeb, Dong Myung Baeb, Jung Min Sohnb*, Joung Hyung Choa

"Interdisciplinary Program of Marine Convergence Design, Nam-gu, Yongso-ro 45, Daeyeon-dong, Busan 48513, South Korea bDepartment of Naval Architecture and Marine Systems Engineering, Nam-gu, Yongso-ro 45, Daeyeon-dong, Busan 48513, South Korea

Potsibility oC mcrinn cnd offshore structures to nxpnticncn accidental l¡cds lies been seriously gnnsidnrnd u¡ to this dcy. Remarkable gesuclties on relcted aspects ere riting detcend to brasure ship safety which in this subj ect ie observed on merine structure. SIiíjv is en extm¡le of marine structure that mey be subjected to cccidenUal loeds (euréng its operation. The aimof this paper ii3 to investiccte d¡mcge extend of the target ship under different eccidental loads, neimely collision cnd grounding with considerations to feilure pro cess and defortnation contours. This work is divideit into ttgo parts avhinh in Hie Pert I, ship collisicn is discussede and the Part II dej^].s avith interaction o f eemip structure with sea bettom nn grounding. In Part II - Grounding impact, evnlurting tearing domege on the bottom structure is essentiel in estimating enviaonmentel casualties caused by oü leakage. A themiccl tanker is modeSled to be eht targee thip in a series of grounding scenarios. Condition of the structural damage cnd tendency of the internal energy, crushing force and structurel cc;ce^er^t^on are observed. Prediction oathe tearing opening and locction of the mitiel tcHure in furthir grounding ¡roctss cre also ¡retenVed ín this s'^Si|er■ Virtual ex¡erimfnt is conducted by rtonlinear finira element methog ln ordcr to calculate the; defined grounding srencrios which are built bceed on the target location on the bottom struature. Based on calculation resums, condition oetiie daublelhull structure after grounding is feund to be highly influenced by errangemhnt of the tongitudincl membert which is evidenced by tde acct that these membfrt ¡rovide higher resistance than the transverse pprt. ]rinarly, ittfluence eSthe iadetiter's position on rtlpctural responses in grounding is summarized.

© S0-7 The Authors. Published by Elsevter B|V.

Peer-review under responsibility of the SrientificCommittee ofII(reI 2017

Keywords: Impact ¡Uenomenoa; grounding impact; aumericcl simulation; structural fchcge; collisioa force

* Corresponding author. Tel.: +82(0)-51-629-6613; fax: +82(0)-51-629-6608. Cmail addrnss: jminz@¡kn+.ec.er

Abstract

2452-3216 © 2017 The Authors. Published by Elsevier B.V.

Peer-review under responsibility of the Scientific Committee of ICSI 2017

10.1016/j.prostr.2017.07.129

Nomenclature

Éb the rate of bending energy dissipation

Èc the rate of dissipated energy in the crack tip zone

Éf the rate of dissipated energy by frictional forces on the surface of the structure

Èm the rate of membrane energy dissipation

Èp the rate of dissipated plastic energy

Fh the resisting force of the structure in the direction of V. This direction is assumed to be horizontal

Fp the so-called plastic resistance which here includes both plasticity and fracture

Fvm the von Mises' plane stress

Nafi the membrane force tensor

Mafi the bending moment tensor

p the normal pressure on the rock from the plate element dS

S the contact area between rock and plate

V the relative velocity between ship and rock

Vrel the relative velocity between rock and plate element, dS

Safi the corresponding generalised strain rate in the deformed configuration

Kafi the corresponding generalised curvature rate in the deformed configuration

M the Coulomb coefficient of friction

Oo the uniaxial yield stress - average flow stress

Oxx the direct stress in x-direction

Oxy the shear stress in xy-plane

Oyy the direct stress in y-direction

Ozz the direct stress in z-direction

1. Introduction

Ship is the main transportation for export-import activity. It has various capacities and reasonable delivery time, which makes this transportation mode flexible to be used depending on situation (cargo type and size) and condition (sailing route) that are demanded by client. In this case, safety is the top priority to ensure cargo, crew and ship can arrive to a destination in good condition. There is a challenge to obtain the satisfaction in delivery time considering accidental loads that may be experienced by the ship. Statistical data of the International Oil Pollution Funds (IOPCF, 2005) showed that from ten forms of accident on the sea, approximately 23% of oil spill occurred after grounding impact. Moreover, a famous catastrophe of the Exxon Valdez in Alaska and ship a grounding case of the MV Drake in Australia indicate that serious attention should be given to ship grounding cases. Tanker is an important subject in grounding since the oil (tanker's cargo) can be spilled after impact and can massively influence or even destroy ecosystems surrounding the grounding location. In case of the Exxon Valdez, extinctions of animals and vegetation were unavoidable and its effect to Alaska's water territory existed for decades. As its nature as an accidental phenomenon, ship grounding is observed by wide range of researchers as its occurrence and scenario may be different to each other. Results of these studies are always needed due to structural development and safety demand.

In this study, a series of ship grounding models are determined. Impact location is focused to observe detail behavior of structural component on the target ship including its failure process. Structural damage in process of impact between ship structure and seabed is presented and correlations of the damage with other structural responses are summarized.

2. Review on impact phenomena

Ship grounding needs to be carefully estimated so that the casualties after this event takes place can be controlled and anticipated as soon as possible. Relation of grounding and other accidental impact is close especially with ship collision and ice-structure interaction. In this section, a brief review to observe pioneer works of impact phenomena and development and a fundamental theory to assess ship grounding are presented.

2.1. Observation of impact load on ships

Ship grounding is observed using various methods to estimate its effect to the target ship. These methods develop as rapid growth of technology. In late of 1990's, a mechanic model of ship grounding was introduced by Simonsen (1997a-b). Global deformation kinematics and extent of deformation were presented in analytical expressions. An attempt to observe impact mechanism was conducted by Alsos and Amdahl (2009) using an experimental study. The stiffened plates were subjected to penetration of indenter similarly to collision and grounding cases. Advance development of computational instrument has introduced numerical simulation to conduct almost all phenomena in branches of science and engineering. Grounding models were proposed by Nguyen et al. (2011) who described ship-grounding events and AbuBakar and Dow (2013) who performed finite element analysis.

Ship grounding is a complex process which involves large contact forces and crushing hull structure. The consequences are severe either locally or globally that can be influenced by interaction with seabed. A survey of actual seabed topologies is carried in water territories which grounding most likely takes place. HARDER project was launched in 2000 and finished by May 2003. Probabilistic damage stability of ship was the main objective of this project (Alsos and Amdahl, 2007). The damage data is presented by Lützen and Simonsen (2003) a trend being found that if the deformation occurs deeply into the hull, the structural damage is likely local. In other case, if large part of ship breadth is damaged, the penetration may be small. Interaction of ship and seabed in ship grounding is concluded similar in term of fundamental basis of interaction between two entities with other phenomena, e.g. ship collision. In ship collision, interaction of two solids is expected. The condition in contact may be different depends on definition of scenario. It can be advance penetration (Prabowo et al., 2016a-b; Prabowo et al., 2017a-d and Bae et al., 2016a) or even present a rebounding behavior (Prabowo et al., 2017e). Interaction of a ship structure with ice in polar region (Bae et al., 2016b and Zhou et al., 2016) is also similar, but with difference on the indenter's property and penetration direction during impact.

2.2. Theoretical reference for ship grounding

There are several methods to predict structural response in impact as presented in previous sub-section. In previous work in ship grounding by Simonsen (1997c) the balance of power method is introduced to define internal mechanics model. If a rigid-plastic structure is assumed and no elastic energy is stored, the power of external loads equals with the rate of dissipated energy by plastic deformation, fracture and frictional effects. This relation is presented in Eq. 1. With rigid-plastic material according to von Mises' yield criterion, the plane stress yield condition is defined in Eq. 2. For a deforming plate, the rate of internal energy can be expressed in Eq. 3. It is assumed that the deformation zone (see Simonsen, 1997c, pp. 81) consists of a series of discrete lines and deformed plate components.

3. Preparation and methodology

Grounding analyses are performed using numerical simulation with the explicit FE code ANSYS LS-DYNA (ANSYS, 2013) which is deployed in this study to calculate damage estimation for various penetrations. Descriptions of the ship geometry and seabed topology are presented with the steel and rock properties for the ship and seabed.

3.1. Engineering model

In grounding model, a chemical tanker is used with dimensions 144 m in length, 22.6 m for breadth and 12.5 for overall height. The bottom structure is modelled (Fig. 1) using the fully integrated version of Belytschko-Tsay shell

Fh . V = Ep + Ec + Ef = Fp . V + Is p / Vrei dS

Fvm = &xx2 + Oxx Oyy + ffyy2 + 3 Oxy - Oo2 = 0

Ep Em + Eb Is Naß Saß dS + Is Maß Käß dS

element to avoid shear locking and hourglass phenomena that influence the accuracy of calculation result. Inner structure component of the bottom structure consists of several main parts, namely longitudinal stiffener, bottom plate, inner bottom plate, girder and bilge plate. A deformable model and the plastic-kinematic materials are augmented on the bottom. The applied material considers the applied steel of Prabowo et al. (2016b) which has yield strength ay = 440 MPa, Poisson's ratio v^eei = 0.3, density psteei = 7,850 kg/m3 and Young's modulus Ex = 210,000 MPa. The failure criterion is applied to define structural failure during crushing process of the bottom structure by the seabed. The proposed expression of a European classification society, Germanischer Lloyd (2003) is applied in this work. A topology of seabed takes a conical obstacle as the indenter in grounding. Illustration of this indenter is presented in Fig. 2. The seabed is assumed to be a hard rock which is modelled by rigid properties. The material of this seabed itself is taken from a mineral material that can be found in seabed, namely pyroxene. This entity has several main properties, including Poisson's ratio vmck = 0.281 and density prock = 4,002 kg/m3.

Fig. 1. Inner ship structure of the bottom structure. Deformable structure is applied Fig. 2. The conical indenter for grounding analysis.

3.2. Grounding configuration

Grounding is assumed as a contact between the bottom structure and a conical indenter. Initial distance of two entities is determined to be 0.1 m in longitudinal direction (x-axis). Position of the indenter is varied in vertical direction (z-axis) which a gap 0.25 m in height and fully parallel on the lower part of the bottom structure and indenter. Both positions are denoted as Position 1 and Position 2 consecutively and set on the grounding scenarios. The conical indenter is given a velocity 10 m/s to move to three target components, namely center girder, side girder and inner shell. In the end of model, the shell is restrained and bottom structure is set to be fix in the centerline during grounding.

4. Results and discussion

This section presents simulation results of several scenarios calculated by the finite element method. Discussions are addressed into two subjects regarding the sequence of structural failure and responses of the bottom structure during penetration of the indenter during grounding.

4.1. Structural failure during grounding

In grounding, the indenter was set to three different targets on the bottom structure. An evaluation to each target strength is performed which indicates that the center girder produced the highest energy. The internal energy (Fig. 3) was taken as consideration to represent energy which was used to crush the target component and surrounding in impact. Similar trend was shared for three targets approximately until 0.05 s. After passing through this time, the center girder produced higher energy than side girder and inner shell which continued until the end of simulation time. Considering impact time, longer similarity was shown by the side girder and inner shell until 0.125 s. These components had similar thickness, but geometry near each component was quite distinct. Surrounding the side girder was strengthened by the longitudinal stiffener on the bottom plate which was similar with the center girder. In other hand, the inner shell connected to the transverse frame which connected the outer and inner shells. In the end of penetration, the results can be concluded that the inner shell has better capability to resist the indenter.

----Center girder

- Side girder -------Inner shell

The indenter reached half of distance between the 2nd and 3,d floors

The indenter breached the 2nd floor

The indenter reached half of distance between the Ist and 2nd floors

Initial failure of the 1 ' flooi

0.2 0.3

Time (s)

Fig. 3. Magnitude of the internal energy during penetration of the indenter. Solid black line highlights crushing progress

on the bottom structure.

Structural failure progress is presented in Fig. 3 which indicates penetration of the conical indenter taking place until space between the second and third transverse floors in impact time 0.5 s. Approximation of the damage length reaches 5 m in longitudinal direction. Damage extent and stress contour on the bottom structure are presented in next discussion. Confirmation of the failure sequence in the internal energy is successfully verified with the damage extent in Fig. 4. In the end of grounding impact, the conical indenter almost reached the third floors with a gap between them of 0.6 - 0.7 m. Stress contours were observed similar for each target with the highest stress occurred on the bottom part. However, in the center girder grounding, the highest stress magnitude was also experienced by the longitudinal stiffener. Further penetration will make the initial structural failure occurring in these components.

(a) (b) (c)

Fig. 4. Damage extent and von Mises' stress contours on the penetrated zone for each target: (a) center girder, (b) side girder and (c) inner shell.

Attention should be given after grounding to the center and side girders of the bottom structure. Tearing opening on these precise locations will present a possibility for lubrication oil or waste of two tanks (left and right sides of the side girder) to come out and contaminate water territory. Mitigation process of the grounded ship is also influenced volume of a spilled oil or waste. Larger volume of a spilled cargo (in this case is oil) from side girder case than a direct contact to space between two girders possibly occurs as content of two tanks can come out during the girder is crushed.

4.2. Force and acceleration responses of the bottom structure

An observation of structural crashworthiness is also conducted to other structural responses, namely force and acceleration of the target structure. Two defined positions of the indenter in grounding simulation are concluded to provide different tendency of the responses. In terms of resultant force, the Position 1 which is lower than the Position 2 produced later penetration on the bottom structure. Topology of the indenter was directly influencing the force that conical indenter becomes smaller to the top part of its body. In the Position 1, the indenter was set to be lower than the bottom structure which the top part (has smaller section) impacted the structure. Range of this part was short so that the initial contact with structure of the Position 1 was later than the other one.

Time (s)

Fig. 5. Structural response in grounding with two different positions of the indenter: resultant force.

Fig. 6. The resultant acceleration of the bottom structure. Sequences of the crushing process throughout impact time are denoted by the dotted lines.

Similar tendency is found on the acceleration of the bottom structure during penetration of the conical indenter. For time range between 0 - 0.4 s, the magnitude of the acceleration was found significantly higher for the Position 2 than the Position 1. Based on these structural responses, besides impact target, position of the indenter during grounding can deliver significantly differences. In terms of Position 2 resultant force, the initial contact between indenter and structure was found remarkable with three peak points being produced in time range 0 - 0.1 s. Distinction was spotted in penetration of the Position 1 that peak point of the force magnitude continued to decrease. Nevertheless, similarity was observed for both Positions 1 and 2 that in the moment of crushing process was begun on the T-intersection and X-interaction (intersection of center girder and transverse floor), the bottom structure experienced significant increment of the force than penetration in other locations which without intersection.

5. Conclusions

This study presented a material preparation and analysis simulation for an impact phenomenon, namely ship grounding. The study was successfully conducted by numerical method and results were discussed. The internal energy was presented to estimate energy magnitude in crushing of the involved components of the bottom structure in grounding. Tendency of this response provided good correlation with damage extent after indenter's penetration. The force and acceleration were discussed to measure influence of the indenter range to the occurred magnitude tendency, which was varied based its relative position to the target. Grounding process during the indenter was completely parallel with the target (Position 2) produced earlier contact and larger magnitude (resultant force) in the initial contact. The acceleration during the indenter was set lower than the bottom structure in the Position 1 being overwhelmed by response of other position. The structure in this grounding model experienced lower fluctuation than grounding with the indenter in parallel position to the target.

Acknowledgements

This work was successfully published with the grant from BK21 plus MADEC Human Research Development Group, South Korea.

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