PSI - Issue 5

Jung Min Sohn et al. / Procedia Structural Integrity 5 (2017) 943–950 Aditya Rio Prabowo et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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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 19 90’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. 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. F H . V = Ė p + Ė c + Ė f = F p . V + ∫ s p μ V rel dS (1) 2.2. Theoretical reference for ship grounding

F vm = σ xx Ė p = Ė m + Ė b = ∫ s N αβ ε̇ αβ dS + ∫ s M αβ κ̇ αβ dS 2 + σ xx σ yy + σ yy 2 + 3 σ xy 2 – σ 0 2 = 0

(2)

(3)

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