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Toward a system of real-time prediction and monitoring ofbottom damage conditions during ship grounding

By Tan-Hoi Nguyen

Abstract

<p>This work o ers an analysis of the ship grounding process, examining a range of topics from the ability to predict the location of obstructions to a ship bottom's resistance to penetration and outer and inner hull plates' resistance to fracture. This thesis is composed of a collection of articles and consists of two parts. The rst part gives an overview of the thesis topic, and the second part consists of the articles.</p><p>Stranding refers to a ship that runs aground and comes to a complete stop. Several important factors are related to stranding, including the number of contact points and their corresponding locations along the bottom of the ship and the associated penetration and contact force. This thesis proposes a new procedure that may help address these issues. The bending moment distribution along the hull girder is calculated and compared with an \assumed" bending moment distribution obtained from a Hull Monitoring System (HMS). The HMS is becoming increasingly common for a wide range of lique ed natural gas (LNG) commercial vessels, crude oil tankers and bulk carriers. Hence, the procedure presented here can be useful as a decision-making tool in relation to stranding events.</p><p>The grounding problem depends heavily on the condition of the seabed. Unfortunately, there is very little information in the literature related to seabed topology, except for some special cases such as the geometry of the pipeline corridors in connection with oil and gas transportation. Accordingly, this study generalizes the representation of the seabed as a paraboloid, which, in general, can characterize a local region of the seabed topology. A set of resistances { penetration curves corresponding to variation in the shape of the seabed { is obtained by means of nonlinear nite element analysis (NLFEA). The seabed is of a generally arbitrary shape that is also asymmetric. Its composition can be a combination of rock and/or reef and/or shoal. However, the model presented here is able to capture the main characteristics of these categories.</p><p>Finite element (FE) analysis is a versatile tool that can be used to simulate the crashworthiness of ships and can provide information relevant to collision and grounding. However, this tool is costly with large and complex structures like ships; FE analysis is time consuming and requires substantial computational resources. Therefore, a model with only two tanks of 64 m length is applied here. This - nite element model consists of about 630,000 elements, which is within the reach of the current computational resources at the Department of Marine Technology at Norwegian University of Science and Technology (NTNU). Thus, this study introduces simpli ed formulas to estimate average grounding forces. A good agreement between the simpli ed formulas and the numerical results is obtained. This result indicates a promising application of these simpli ed formulas for quick estimation of the grounding forces for each seabed topology. The application of the simpli ed sliding force method is illustrated using simpli ed simulations of dynamic powered grounding. It is shown that the process is indeed dynamic, and large hull girder bending moments and shear forces may be induced, especially at the initial collision with the obstruction. These shear forces and bending moments may become larger than the rule requirements set by classi- cation societies. The static and dynamic grounding conditions are investigated for a variety of seabed shapes and ship speeds. The results show that a static approach can be used for a dynamic grounding event. It is also found that bottom damage and seabed topology can be estimated during powered grounding by using a simple static-based procedure.</p><p>The application of such a procedure to the successful identi cation of damage evolution and seabed topology is examined by means of a comparison with a database of F{ curves corresponding to di erent seabed shapes. This information represents an important element in the assessment of countermeasures and emergency intervention plans that can be particularly useful to e orts to avoid oil leakage or hull girder collapse during stranding.</p>PhD i marin teknikkPhD in Marine Technolog

Publisher: Norges teknisk-naturvitenskapelige universitet, Fakultet for ingeniørvitenskap og teknologi, Institutt for marin teknikk
Year: 2011
OAI identifier: oai:brage.bibsys.no:11250/238098
Provided by: NILU Brage
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