Ki-Yeob Kang

A Comparative Study on Mechanical Behavior of Low Temperature Application Materials for Ships and Offshore Structures

Austenite stainless steel(ASS), aluminum alloy and nickel steel alloy are the most widely used in many cryogenic applications due to superior mechanical properties at low temperature. The Face-Centered Cubic(FCC) and Hexagonal Close-Packed(HCP) materials are used for the primary and secondary insulation barrier of Liquefied Natural Gas(LNG) carrier tank and various kinds of LNG applications currently. In this study, tensile tests of ASS, aluminum alloy and nickel steel alloy were carried out for the acquisition of quantitative mechanical properties under the cryogenic environment. The range of thermal condition was room temperature to -163℃ and strain rate range was 0.00016/s to 0.01/s considering the dependencies of temperatures and strain rates. The comprehensive test data were analyzed in terms of the characteristics of mechanical behavior for the development of constitutive equation and its application.

The Effect of Negative Pressure Phase in Blast Load Profile on Blast Wall of Offshore Plant Topside

As a gas explosion is the most fatal accident in shipbuilding and offshore plant industries, all safety critical elements on the topside of offshore platforms should retain their integrity against blast pressure. Even though many efforts have been devoted to develop blast-resistant design methods in the offshore engineering field, there still remain several issues needed to be carefully investigated. From a procedure for calculation of explosion design pressure, impulse of a design pressure model having completely positive side only is determined by the absolute area of each obtained transient pressure response through the CFD analysis. The negative pressure phase in a general gas explosion, however, is often quite considerable unlike gaseous detonation or TNT explosion. The main objective of this study is to thoroughly examine the effect of the negative pressure phase on structural behavior. A blast wall for specific FPSO topside is selected to analyze structural response under the blast pressure. Because the blast wall is considered an essential structure for blast-resistant design. Pressure time history data were obtained by explosion simulations using FLACS, and the nonlinear transient finite element analyses were performed using LS-DYNA.

Structural Response of Blast Wall to Gas Explosion on Semi-Confined Offshore Plant Topside

Since gas explosion is the most frequent accidental event occurring in the oil and gas industry, all safety-related critical elements on the topside of offshore platforms should retain their integrity against extreme pressure demands. Although considerable effort has been devoted to develop blast-resistant design methods for offshore structures, there remain several issues that require further investigation. The duration of the triangular-shaped blast design pressure curve with a completely positive side is usually determined by the absolute area of each measured transient pressure response, using the flame acceleration simulator (FLACS). The negative phase pressure in a general gas explosion, however, is often quite crucial, unlike gaseous detonation or TNT explosion. The objective of this study is to thoroughly examine the effect of the negative phase pressure on structural behavior. A blast wall for a specific floating production, storage, and offloading (FPSO) topside is considered as an exemplar structure for blast-resistant design to focus only on overpressure because there is no drag pressure in this type of obstacle. Gas dispersion and explosion simulations were carried out using FLACS, while LS-DYNA was used in the nonlinear transient finite element structural analysis.

An Influence of Gas Explosions on Dynamic Responses of a Single Degree of Freedom Model

Explosion risk analysis (ERA) is widely used to derive the dimensioning of accidental loads for design purposes. Computational fluid dynamics (CFD) simulations contribute a key part of an ERA and predict possible blast consequences in a hazardous area. Explosion pressures can vary based on the model geometry, the explosion intensity, and explosion scenarios. Dynamic responses of structures under these explosion loads are dependent on a blast wave profile with respect to the magnitude of pressure, duration, and impulse in both positive and negative phases. Understanding the relationship between explosion load profiles and dynamic responses of the target area is important to mitigate the risk of explosion and perform structural design optimization. In the present study, the results of more than 3,000 CFD simulations were considered, and 1.6 million output files were analyzed using a visual basic for applications (VBA) tool developed to characterize representative loading shapes. Dynamic response of a structure was investigated in both time and frequency domains using the Fast Fourier Transform (FFT) algorithm. In addition, the effects of the residual wave and loading velocity were studied in this paper.

Experimental Study on Evaluation of Bonding Strength of Adhesively Bonded Joints by Adhesive

Abstract In this study, the bonding strengths of adhesively bonded joints are experimentally investigated. A series of lap-shear tests are conducted using single lap type adhesive joints. In order to analyse the joint fabrication factors that affected the bonding strength, the parametric tests are conducted with various thickness of adhesive, surface roughness and fillet of adhesive. In addition, for the comparative study with the welded joint, lap-shear tests using specimens with 2 welded sides and 4 welded sides are also carried out. The quantitative results of the strength analysis are summarized, and some proposals are made on setting up testing standards for adhesively bonded joints.Key Words : Lap shear joint, Adhesive thickness, Surface roughness of adherends, Tensile-shear strength 연구논문1. 서 론 산업용 구조물의 설계·제작에는 부품 간의 결합이 필수적으로 요구된다. 이러한 결합에는 수많은 종류의 재료 및 구조단위 결합이 존재하며 이들이 합쳐져서 특정 목적을 달성하기 위한 구조물이 완성된다. 최근 산업의 발달로 인하여 구조물의 규모는 점점 커지고 있으며, 그로 인해 구조물의 중량 또한 점점 증가하고 있다. 하지만 접합으로 인해 발생하는 중량 증가 또는 비정상적 이음부는, 경제적 손실만이 아니라 피로파괴 등을 포함하는 각종 사고 사례들의 직 ·간접적인 원인이 될 수 있다. 이러한 측면에서 볼 때, 구조물의 중량을 줄이고 구조 안전성을 보장하기 위해서는 부품 및 하부구조물 간에 최적의 결합이 수행되어야 한다. 일반적으로 금속계 재료의 접합에 가장 손쉽게 사용되는 방법으로 용접이나 볼트이음 등을 들 수 있다. 용접의 경우는 수밀이나 기밀이 요구되는 부분의 접합에 매우 효율적인 기법이며, 최근에는 이종재료 간의 접합까지 가능한 수준에 이르고 있다. 하지만 최적의 용접량 산정 등은, 접합부위의 기하학적 형태 또는 피접합구조의 재질 특성에 따라 일괄적으로 정의하기가 어렵다. 이러한 이유로, 가끔 불필요한 중량 증가의 원인이 되기도 하며, 경우에 따라서는 최적의 용접구조가 형성되지 못하는 이유로 구조건전성에 악영향을 미치는 응력집중현상 발생 원인이 되기도 한다. 최근, 구조접합 기법으로서의 용접이 가지는 장점에도 불구하고, 구조 경량화에 대한 중요성이 부각됨에 따라 접착제를 이용한 구조접합 방법이 적극 검토되고 있다