Sang-Rai Cho

• PHD University of Glasgow
• Professor (Full) at University of Ulsan

Offshore structures and ships can be progressively damaged due to repeated mass impacts induced by contacts with ships, ice floes, and dropped and/or floating other objects while in service. This paper aims to predict the residual deflection evolution of the marine structures under such impact repetitions. The side hull structures of the general ic...

As the number of offshore wind-power installations increases, collision accidents with vessels occur more frequently. This study investigates the risk of collision damage with operating vessels that may occur during the operation of an offshore wind turbine. The floater used in the collision study is a 15 MW UMaine VolturnUS-S (semi-submersible typ...

The residual strength of denting- and fracture-damaged box girders were experimentally and numerically investigated. The experiments were conducted under a pure bending moment using the four-point bending test method. The load, deflection, and strain were measured. The strains of the extension structures were also measured, and the frictional force...

Marine structures are exposed to repeated impact loads such as slamming, sloshing, green water, and ice impacts. Such loadings can cause local and global damage to structures. This paper presents an investigation on the response of clamped steel plates subjected to repeated impacts. Numerical simulations were performed by adopting strain hardening...

The present paper describes a general procedure of the structural safety assessment for the independent type C tank of LNG bunkering ship. This strength assessment procedure consists of two main scheme, global Finite Element Analysis (FEA) model primarily for hull structure assessment and detailed LNG Tank structures FEA model including the cylind...

Tubular member structures are the major component structures of jacket of fixed floating offshore platforms, tension leg platforms (TLPs), or drilling jack-up rigs. During its operations, these structures are constantly serviced by support vessels. Collisions between them are unavoidable. One key considers during the design and safety of these stru...

In this paper, the dynamic implosion responses of ring-stiffened cylindrical tubes under external hydrostatic pressure are reported. The ring-stiffened cylinder models were fabricated from commercial seamless aluminium-alloy 6061-T6 tubes. Six external stiffened models were constructed: three models with three stiffeners, and the other three with f...

In this paper the ultimate longitudinal strength of a container ship in grounding and collision cases is generated by Monte Carlo simulation with 10000 samples, the effect of randomness in an extent damaged dimension of collision and grounding scenarios, yield strength and plate thickness of midship section will be considered. For each sample, the...

This paper aims to derive new simple and consistently reliable residual strength equations for predicting the residual ultimate strength of steel dented stiffened cylinders under combined axial compression and radial pressure including hydrostatic pressure. For this, two types of the stiffened cylinders, namely, stringer- and/or ring-stiffened cyli...

This paper focusses on steel-welded hemispherical shells subjected to external hydrostatic pressure. The experimental and numerical investigations were performed to study their failure behaviour. The model was fabricated from mild steel and made through press forming and welding. We therefore considered the effect of initial shape imperfection, var...

In this study, the genetic algorithm (GA) was implemented for the multi-objective optimization of the structural design of a pressure hull. The objective functions sought the maximum ultimate strength of the ring-stiffened cylindrical shell structure with minimum structural weight and maximum volume of the configured structural member. First, the e...

In this study, the tensile and compressive behaviours of corroded steel-stiffened plates were experimentally investigated, and the effects of pitting- and grooving-corrosion damage on the residual strengths of corroded stiffened plates were evaluated. Two series of tests were conducted for this study: one involved tensile test on specimens having n...

In the present paper, implosion responses of two adjacent cylindrical tubes under external hydrostatic pressure were experimentally investigated. The cylinder models were fabricated of aluminium alloy 6061-T6 commercial tubes. In the experiment, a pair of two-cylinders were placed inside of a support frame in a medium-size pressure chamber, whose d...

In recent years, Liquefied Natural Gas (LNG) becomes one of the most suitable solutions to fulfil world primary eco-friendly energy demand. Consequently, bunkering ship is designed to charge liquefied gas with the increasing need for natural gas. Due to the extremely dangerous and cryogenic cargo, the design of LNG bunkering ship requires very high...

The objective of this study is to develop a new formulation for predicting the permanent local denting damage of steel ring and/or stringer-stiffened cylinders under dynamic lateral mass impact. The considered scenarios could represent the collisions of offshore cylindrical structures with bow or stern of service vessels or floating objects. Before...

Experimental studies are conducted to investigate the implosion characteristics of thin cylindrical aluminium-alloy tubes. The effects of various parameters that generate different responses on the implosion behaviours are investigated. Aluminium-alloy tubes are fabricated from a 6061-T6 material and designed in the range of 2.5–6.7 length to diame...

This paper presents a series of experimental and numerical investigation results on the structural responses of the T-joints of H-shaped tubular structures under dynamic lateral mass impact. The considered scenarios represent collisions between unstiffened tubular members of offshore structures-including offshore jacket platform and wind turbine su...

This paper reports experimental and numerical investigations on the ultimate strength responses of steel-welded, ring-stiffened conical shells when subjected to external hydrostatic pressure. Four small-scale shell models were fabricated from general structural steel by cold bending and arc welding. First, hydrostatic pressure tests were performed...

The present paper illustrates a numerical investigation on the failure behaviour of ring-stiffened cylinder subjected to external hydrostatic pressure. The published test data of steel welded ring-stiffened cylinder are surveyed and collected. Eight test models are chosen for the verification of the modelling and FE analyses procedures. The imperfe...

This study focuses on the prediction of the residual strength of dented steel stiffened cylinders under combined axial compression and radial pressure. Two types of stiffened cylinders, namely, ring-and stringer-stiffened cylinders are investigated, which are common marine structural elements used in submarines and various types of floating offshor...

This paper focusses on deriving formulations to predict the ultimate strength of both intact and damaged steel ring-stiffened cylinders subjected to hydrostatic pressure. The damage scenario considered in this study can represent the collision accidents of offshore ring-stiffened cylinder structures such as submarines, semi-submersibles, spars and...

This study focusses on deriving a formulation to predict the permanent damage of steel ring-stiffened cylinders subjected to dynamic lateral mass impact and their ultimate strength in both intact and damaged conditions under hydrostatic pressure. The damage scenario considered in this study can represent the collision accidents of offshore ring-sti...

The aim of the study is to examine the effect of damages on the load carrying capacity of stringer-stiffened cylinders under external hydrostatic pressure. Experiments were conducted on three small-scale steel stringer-stiffened cylinder models that were fabricated by cold bending and arc welding. Drop tests with a knife-edge indenter were conducte...

A series of collapse tests were performed on box girder models to evaluate the effect of collision damage on the residual longitudinal strength of the hull girder. The experiments were carried out under pure bending moment using, so-called 4-point bending test method, the load, deflection and strain were measured. Ten experimental models were fabri...

This paper reports the implosion tests of aluminium alloy 6061-T6 tube models under external hydrostatic pressure. The investigations took an emphasis on how to replicate the deep-ocean pressure environment of the implosion phenomenon on a laboratory scale. The parameters which affected the implosion pressure pulse were also observed. Two kinds of...

This paper presents a benchmark study on collision simulations that was initiated by the MARSTRUCT Virtual Institute. The objective was to compare assumptions, finite element models, modelling techniques and experiences between established researchers within the field. Fifteen research groups world-wide participated in the study. An experiment invo...

This paper outlines empirical formulas to provide adequate predictions of the ultimate strength of ring-stiffened cylinders under hydrostatic pressure. The ultimate strength formulation was derived from published test data found in the open literature. The formulas consider the failure mode interactions, which include the parameter of shell yieldin...

This paper reports on the experimental investigations on the failure modes of ring-stiffened cylinder models subjected to external hydrostatic pressure. Nine models were welded from general structural steel. The shells were initially formed by cold-rolling, and flat-bar ring frames were welded to the shell. The hydrostatic pressure tests were condu...

This paper presents the experimental and numerical investigation results of the response of low-temperature steel (LT-FH32 grade steel) beams under repeated impacts at room temperature and a single impact at a sub-zero temperature. After conducting tensile tests at room and sub-zero, repeated impact tests were conducted on two clamped single-beam m...

This study investigates the response of marine aluminium-alloy plates to repeated impulsive pressure loadings due to slamming. The numerical simulations performed using the ABAQUS commercial software package were validated against relevant experimental data from the open literature. In the calculations, linear strain hardening was applied and no st...

심해를 운항하는 구조물은 주 구조물 외에 다양한 종류의 부 구조물이 주 구조물 외부에 설치될 수 있다 . 주 구조물의 구조 치수는 주로 붕괴강도 ( 붕괴 압력 ; 최종강도 ) 를 기준으로 결정되고 있다 . 하지만 주 구조물의 붕괴강도와 아울러 고려해야 할 현상이 부 구조물의 내파 (implosion) 발생 여부이다 . 내파는 구조물에 작용하는 외압이 내압보다 커서 발생하게 된다 . 실제 해중에서는 구조물이 좌굴에 의해 급격히 내부로 찌그러지는 붕괴가 일어나더라도 외부 유체가 차지하는 부피는 거의 변화가 없고 , 따라서 외부의 압력 또한 변화가 없 게 된다 . 하지만 내압용기 (pressure chamber) 를 사용하...

Experimental and numerical studies on the collapse of thin cylindrical aluminium-alloy tubes under external hydrostatic pressure have been performed and reported in this paper. The effects of the geometric and shape imperfection parameters of the models on the structural behaviours were investigated. The 6061-T6 aluminium-alloy tube models were des...

Protection structures for FPSO (Floating Production Storage and Offloading) caissons should be sufficiently strong so as not to contact caisson pipes even when the protection structure is damaged by an impact by attendant vessels. In the present structural design process, non-linear commercial packages are employed for collision analyses. However,...

Most offshore structures including offshore wind turbines, ships, etc. suffer from the impulsive pressure loads due to slamming phenomena in rough waves. The effects of elasticity & plasticity on such slamming loads are investigated through wet free drop test results of several steel unstiffened flat bottom bodies in the rectangular water tank. Als...

This paper presents the experimental and numerical investigation results of the residual strengths of damaged ring-stiffened cylinders subjected to external hydrostatic pressure. The damage generation procedure adopted in this paper could represent the collision accidents of marine ring-stiffened cylinders with floating subjects or support vessels....

This paper reports the experimental and numerical investigations regarding the effect of initial geometry imperfection of certain types of local and overall collapse mode on the buckling analysis of ring-stiffened cylinder under hydrostatic pressure. Comparison among imperfection modeling techniques are made. The initial imperfections which were mo...

This paper presents the experimental and numerical investigation results on plastic response of steel grillages representing stiffeners with associated plates of marine structures under repeated mass impacts. Repeated impact tests were conducted on three grillage models at room and sub-zero temperatures. The ends of the grillage models were firmly...

Lateral collision tests were conducted on two steel double-hull side structure models, models DH-3 and DH-4. The models were approximately one-seventh scale of a VLCC (Very Large Crude Carrier), and the small longitudinal stiffeners of a VLCC were smeared into the shell plates. The collision tests were performed using a car crash testing facility....

This paper presents the experimental and numerical investigation results of the residual strength of damaged ring-stiffened cylinders which are typical components of submarine pressure hulls or the main legs of tension leg platforms, semi-submersibles, spars and more recently as buoyancy columns of floating offshore wind turbine foundations, subjec...

This paper focuses on the behaviour of tubular members when subjected to low-velocity mass impact. Particular emphasis is given to the numerical assessment of impact damage and the classification of impact response of tubular members. Damage extents of 12 tubular frame test models were predicted and used for quantifying the modelling uncertainties...

This paper compares the formulae results of classification society design rules, against experimental results for predicting the failure modes of submarine ring-stiffened cylinder; inter-frame yield, inter-frame buckling, and general instability which aims to provide a specific analytic tool that can distinguish the failure mode which occurred in r...

Tubular members are widely used in various divisions as the main load-bearing textures of marine structures including the support structures of drilling rigs and offshore wind turbines. During its service life, those tubular structures may be collided to service vessels which resulted in significant damages in terms of local denting and overall ben...

Tubular members are widely used in various divisions as the main load-bearing textures of marine structures including the support structures of drilling rigs and offshore wind turbines. During its service life, those tubular structures may be collided to service vessels which resulted in significant damages in terms of local denting and overall ben...

This paper addresses the impact response of large-diameter thin-walled steel ring-stiffened cylinders subjected to low velocity mass impact and resulting local damage. Drop-weight impact tests with a striking mass, which had a knife-edge indenter, were conducted on two fabricated steel small-scale models. Details of the experiment setup, the proced...

Tubular members are widely used in various divisions as the main load-bearing textures of marine structures including the support structures of drilling rigs and offshore wind turbines. During its service life, those tubular structures may be collided to service vessels which resulted in significant damages in terms of local denting and overall ben...

This paper presents the ultimate strength characteristics of damaged ring stiffened cylinders under external hydrostatic pressure are investigated using the finite element software package Abaqus FEA. Three ring-stiffened cylinders which are typical components of submarines and floating offshore platforms, subjected to damage arising from collision...

This paper presents the experimental and numerical investigations on the dynamic response of single T-sectional beams subjected to repeated mass impacts at room temperature. Also, the single impact tests were conducted on two single beams to investigate the response of the T-sectional beam under impact load at sub-zero temperature. At room temperat...

In this paper, an experimental and numerical evaluation of the impact response of ring-stiffened cylinders struck at mid-bay with a mass having a rigid knife-edge indenter is presented. The experiments aimed at reproducing a collision scenario involving offshore installations with supply vessels. Dynamic force-displacement curves and strain measure...

This paper experimentally and numerically investigates the effect of repeated impacts on the response of steel beams at room and sub-zero temperatures. Repeated dynamic impact tests were conducted on four beam models. Both ends of the beam models were fixed onto a strong bed. Repeated impacts were applied by releasing a knife-edge striker using a d...

In this paper, the effects of residual stresses on the ultimate strength of stiffened cylinders are numerically investigated with an emphasis on shakedown which might occur during the service of these structures. Residual stresses caused by two types of actions, namely, cold bending and welding, are simulated with simplified approaches in numerical...

A robust ultimate strength formulation is proposed for stiffened plates subjected to combined axial compression, transverse compression, shear force and lateral pressure loadings. Before deriving the formulation, a simplified numerical method was developed to trace the structural behaviour of stiffened plates under combined loadings. A rigorous par...

In t his study, experimental investigations on repeated impacts of polar class ship structures were performed at room and low temperature. As a part of the study lateral repeated impact tests were conducted on four single frame models and a series of tensile coupon tests were also performed to obtain their material properties at room and low temper...

This paper examines the application of structural reliability analysis to submarine pressure hulls to clarify the merits of probabilistic approach in respect thereof. Ultimate strength prediction methods which take the inelastic behavior of ring-stiffened cylindrical shells and hemi-spherical shells into account are reviewed. The modeling uncertain...

The objective of this paper is to numerically investigate the effects of residual stresses on ultimate strength of stiffened cylinders. Simplified approaches were used in nonlinear finite element analysis for the inclusion of residual stresses caused by cold forming and welding. Cold forming stresses are accounted by simulating the cold rolling and...

Single frame structures with notches were fractured by applying drop impact loadings at room temperature and low temperature. Johnson-Cook shear failure model has been employed to simulate the fractured single frame structures. Through several numerical analyses, material constants for Johnson-Cook shear failure model have been found producing the...

Numerical simulations are presented, on the dynamic response of a one-tenth scaled tanker double hull structure struck laterally by a knife edge indenter. The small stiffeners of the full-scale prototype are smeared in the small-scale model by increasing the thicknesses of the corresponding plates. The dynamic response is evaluated at an impact vel...

In this study, a plastic hardening constitutive equation for steels of polar class vessels at low temperature is proposed. The equation was derived using the experimental data obtained from tensile tests at room and low temperatures. Tensile tests at low temperature are both costly and time consuming because an expensive cold chamber is necessary a...

The effects of temperature on the structural behavior of polar class vessels have been experimentally and numerically investigated. Experiments were carried out on single frame structures made of steel material, DH36, which is used for outer shell of the vessels making transit through the polar region. A knife edge type striker was dropped down ont...

A reliability-based structural analysis for submarine pressure hull main component ring-stiffened cylinders is presented. The ultimate limit state of submarine pressure hull is associated with elasto-plastic collapse in various modes. The collapse prediction methods describing the inelastic behavior of ring-stiffened cylindrical shells are reviewed...

This paper estimates the residual longitudinal strength of a damaged double hull VLCC (Very Large Crude Carrier) under combined vertical and horizontal bending moments using Smith's method. The damage estimated in this study occurred due to collision or grounding accidents. The effects of the randomness of the yield stress, plate thickness, extent...

Tensile tests were conducted at low temperatures for the steel materials which are used for outer shell of the vessels making transit through the polar regions. The selected steel materials were GL-DH32, GL-DH36 and GL-EH36. In comparison with the results at room temperature, the yield stress increases approximately by 10 to 13 percent at -30^{\cir...

A robust ultimate strength formulation is proposed for stiffened plates subjected to combined axial compression, transverse compression, shear force and lateral pressure loadings. Before the formulation was derived, a simplified numerical method was developed to trace the structural behavior of stiffened plates under combined loadings. A rigorous p...

When ships are sailing with large motions in rough waves, the slamming phenomenon occurs and the ships suffer from impulsive pressure loadings. Recently, ships are becoming lager and faster than before and it becomes more possible that the ships experience larger impacts on their bows and sterns. Many researchers have been performing the investigat...

CSRs (Common Structural Rules for bulker and tanker), which came into effect in 2006, invoke the concept of the ultimate strength of hull girders. While numerous studies associated with the ultimate capacities regarding global hull girders and stiffened panels have been carried out, there are few application cases of the ultimate strengths for deck...