Kwang-Ho Choi

Lab-scale impact test to investigate the pipe-soil interaction and comparative study to evaluate structural responses

Abstract This study examined the dynamic response of a subsea pipeline under an impact load to determine the effect of the seabed soil. A laboratory-scale soil-based pipeline impact test was carried out to investigate the pipeline deformation/strain as well as the interaction with the soil-pipeline. In addition, an impact test was simulated using the finite element technique, and the calculated strain was compared with the experimental results. During the simulation, the pipeline was described based on an elasto-plastic analysis, and the soil was modeled using the Mohr-Coulomb failure criterion. The results obtained were compared with ASME D31.8, and the differences between the analysis results and the rules were specifically investigated. Modified ASME formulae were proposed to calculate the precise structural behavior of a subsea pipeline under an impact load when considering sand- and clay-based seabed soils.

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.

Computational Analysis of Structural Behavior of Subsea Pipelines with Local Corrosion

To meet the increasing demand for energy around the world, offshore and subsea energy development is constantly being conducted. This trend is accompanied by an increasing demand for pipeline installation, which brings numerous problems, including those related to accessibility, high pressure, and corrosion. Among these, corrosion is a primary factor in pipeline fractures, and can cause severe environmental and industrial damage. Hence, accurate corrosion assessment for corroded pipelines is very important. For this reason, the present study investigated the mechanical behavior of an idealized corroded subsea pipeline with an internal/external pressure load using the commercial FEA code ABAQUS. Then, the analysis result was compared with corrosion assessment codes such as ASME B31G, DNV RP F101, ABS. Finally, a fitness-for-service assessment was conducted.

Numerical Prediction Method for Elasto-Viscoplastic Behavior of Glass Fiber Reinforced Polyurethane Foam Under Various Compressive Loads and Cryogenic Temperatures

In the present study, the material characteristics of a glass fiber-reinforced polyurethane foam (RPUF) which is widely adopted to a liquefied natural gas (LNG) insulation system was investigated by a series of compressive tests under room and cryogenic temperatures. In addition, a temperature- and strain rate-dependent constitutive model was proposed to describe the material nonlinear behavior such as increase of yield stress and plateau according to temperature and strain rate variations. The elasto-viscoplastic model was transformed to an implicit form, and was implemented into the ABAQUS user-defined subroutine, namely, UMAT. Through a number of simulation using the developed subroutine, the various stress-strain relationships of RPUF were numerically predicted, and the material parameters associated with the constitutive model were identified. In order to validate the proposed method, the computational results were compared to a series of test of RPUF.Copyright