Yeon Chul Ha

Assessing the risk of ship hull collapse due to collision

This study proposes a method for assessing the risk of ship hull collapse following a collision. A probabilistic approach is applied to establish the relationship between the exceedance probability of collision and the residual ultimate longitudinal strength index. A set of credible collision scenarios which represent the entire range of possible collision accidents is selected using a sampling technique based on probability density distributions of influencing parameters. The amount and location of collision damage for selected individual collision scenarios are characterised using the LS-DYNA nonlinear finite element method. The ultimate hull girder strength of a ship with predefined collision damage is then calculated using the ALPS/HULL intelligent supersize finite element method. To demonstrate the applicability of the proposed method, applied examples are given, involving collisions with a hypothetical Suezmax-class double-hull oil tanker. Based on the results, design formulations for predicting the residual strength index of damaged ship hulls are derived in an empirical manner. The examples show that the proposed method will be very useful for evaluating the risk of collapse of a ships hull after sustaining collision damage, which may contribute to a collision risk-based design framework. Moreover, the method will be useful in rescue and salvage operations immediately after a collision by permitting a rapid assessment of the structural safety of a damaged ship.

Environmental consequences associated with collisions involving double hull oil tanker

As the total world trade of oil by tankers grow, the potential risk to the marine environment increases. When oil tankers are involved in accidents (e.g., collision or grounding), a consequence of the resulting damage could be the release of crude oil or petroleum products into the sea. The aim of the present study is to investigate the environmental consequences of the involnement of oil tankers in collision. Using probabilistic approaches, credible scenarios of ship–ship collision are selected to create a representative sample of the most possible ones. The LS-DYNA non-linear finite element method is used to predict the resulting damage or opening associated with the individual scenarios. The environmental consequences are then estimated by calculation of the amount of oil spilled in each scenario. In addition, the potential damage to the environment is presented in terms of monetary units that can be understandable to all stakeholders.

Rapid hull collapse strength calculations of double hull oil tankers after collisions

ABSTRACT The primary objective of this study is to develop a rapid method for calculating hull collapse strength of double hull oil tankers after collisions. For this purpose, the statistical characteristics of hull girder collapse after collision are studied. Four double hull oil tankers with different size are considered: Panamax, Aframax, Suezmax and Very Large Crude Carrier. A set of 50 credible collision scenarios are selected by a sampling technique associated with the collision hazard identification based on the historical ship collision database. Four parameters, namely vertical collision location, damage penetration, striking ships bulbous bow height, and striking ships bulbous bow length are determined as a consequence of the corresponding collision scenario. The intelligent supersize finite element method is used to compute the progressive collapse behaviour of hull girder structures with the collision damages so determined. The residual hull girder strength indices can then be determined and formulated in a closed expression associated with collision damages and ship length. The developed formulations will be useful to quickly calculate the hull collapse strength of double hull oil tankers immediately after collisions.

A methodology for determining efficient gas detector locations on offshore installations

More than 70% of accidents that occur on offshore installations are result of hydrocarbon explosions and fires, which, because they involve blast effects and heat, are extremely hazardous and have serious consequences in terms of human health, structural safety and the surrounding environment. Most such accidents are caused by gas leaks, which, if undetected, can lead to the formation of a concentrated gas cloud that can ignite or explode. An effective gas detection system is important for preventing gas-related catastrophic accidents and can mitigate risk on offshore installations. The aim of this study is to develop a risk-based methodology to aid the initial placement of gas detectors for an efficient gas detection system that will function optimally in all possible scenarios on offshore installations.

Nonlinear impact response analysis of LNG FPSO cargo tank structures under sloshing loads

This is a sequel to a previous paper by the same authors, which proposed a probabilistic approach to determine the nominal values of tank sloshing loads in the structural hull design of liquefied natural gas, floating production, storage and offloading units (LNG FPSO or FLNG). This study presents a procedure for the numerical computation of nonlinear impact responses in FLNG cargo tank structures under sloshing loads. The computations are performed using ANSYS/LS-DYNA nonlinear finite element software. Applied examples using a hypothetical FLNG are presented. The insights and conclusions obtained from the study are documented.

A New Method for Determining the Design Sloshing Loads for LNG FPSOs

The aim of this study was to develop a new method for determining nominal values for sloshing loads in the design of storage tanks in LNG FPSO (liquid natural gas, floating production, storage and offloading units). Details of the procedure are presented in a flow chart showing the key sub-tasks. The applicability of the method is demonstrated using an example of a hypothetical LNG FPSO operating in a natural gas site off a hypothetical oceanic region. It is concluded that the developed method is useful for determining the design sloshing loads of storage tanks in ship-shaped offshore LNG installations in combination with virtual metocean data and operational conditions.Copyright

Cost–benefit analysis of corrugated blast walls

Blast walls are generally used to reduce explosion consequences as a form of passive mitigation for offshore installations. Currently, three main types of blast wall are used; flat, stiffened panel and corrugated. Given its particular geometric characteristics, corrugated blast walls are better energy-absorbing systems than other types of blast wall. Thus, corrugated blast walls are often installed in offshore installations to protect against hydrocarbon explosions. However, limited information is available on the influence of parameters of corrugated blast walls such as breadth, height, angle and thickness on lateral deflection, as well as cost. Hence, optimised parameters that consider the comparison between damage (deformation) and cost must be determined for corrugated blast walls. The aim of this study is to investigate the effects of design parameters on the nonlinear structural characteristics and cost of corrugated blast walls in association with cost-benefit analysis. A dynamic finite element analysis was performed by analysis system/Livermore software-dynamics (ANSYS/LS-DYNA) by varying wall thickness, breadth, height and angle of corrugation. Design guidance is offered with an example of how to determine the parameters of a blast wall.

Toward a Probabilistic Approach to Determine Nominal Values of Tank Sloshing Loads in Structural Design of Liquefied Natural Gas FPSOs

The aim of this study is to develop a new probabilistic approach to determine nominal values for tank sloshing loads in structural design of LNG FPSO (liquefied natural gas, floating production, storage, and offloading units). Details of the proposed procedure are presented in a flow chart showing the key subtasks. The applicability of the method is demonstrated using an example of a hypothetical LNG FPSO operating in a natural gas site off a hypothetical oceanic region. It is noted that the proposed method is still under development for determining reliable estimates of extreme sloshing induced impact loads. It is concluded that the developed method is useful for determining the sloshing design loads in ship-shaped offshore LNG installations in combination with virtual metocean data and operational conditions.

Collision Tests on Steel-Plated Structures in Low Temperature

The aim of the study reported herein was to investigate the effects of low temperatures on the crashworthiness of steel-plated structures. A series of material tensile tests were performed to examine the material behaviors at low temperatures. Then, unstiffened steel-plated structure and stiffened steel-plated structure were collided with a cone-shaped drop object to estimate the crashworthiness of steel-plated structures. The material tensile test specimens and test structures were made of Polar class steel for ships and offshore structures which is a sufficient condition of the IACS requirements concerning Polar Class and Strength of Ships. The tests considered room and low temperatures relevant to an Arctic environment and a cryogenic condition. LS-DYNA nonlinear finite element simulations applying a practical approach of modeling techniques were performed to investigate the structural crashworthiness of the steel-plated structures numerically with results of material tensile tests.Copyright

Test Facilities for Safety Studies of Ships and Offshore Structures Associated With Extreme and Accidental Conditions

Ships and offshore structures can face extreme and accidental events that can result in catastrophic consequences in association with casualties, property damages and pollution. Because the mechanism and its responses of structures in extreme and accidental events are highly nonlinear, it is essential to take advantage of experimental approaches as well as computational approaches in terms of identifying such nonlinear responses. Relevant test facilities are then required to meet the needs where full scale or at least large scale models should be dealt with. The objective of this article is to introduce test facilities recently built in the Korea Ship and Offshore Research Institute (KOSORI) at Pusan National University in Korea in terms of specifications and capabilities of various test facilities. Those facilities include test infrastructures in association with ultra-high subsea pressure, fires, explosions, structural failure and dropped object as well as high speed material test.Copyright