• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.04a
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• pp.71-76
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• 2004

To deal with ship collision or grounding, double hull structure has been applied to ships carrying dangerous cargoes. Studies about ability of double hull structure to absorb collision energy and determining fracture state are still under researching. In this study, commercial analysis code, LS-DYNA3D, is used to analyze collision strength of ships in various scenarios. 46K Chemical／Product Carrier is used as analysis subject ship. Study about Energy-Indentation and Force-Indentation is conducted under conditions that weight and collision velocity are changed. Results of this study are very helpful to make mechanism of collision accident clear and to supply useful information about collision strength criteria.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.1
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• pp.41-49
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• 2015

Analysis and test of hydrodynamic ram in welded metallic tanks containing water were performed to investigate the phenomena and to understand the effects on the resulting structural behavior. Arbitrary Lagrange-Euler coupling method was used for the analysis of the fluid-structure interaction occurring in the hydrodynamic ram, where the projectile, tank, and water are exchanging load, momentum, and energy during the traveling of the projectile through the water of the tank. For a better representation of the physical phenomena, modeling of the welded edges is added to the analysis to simulate the earlier weld line fracture and its influence on the resulting hydrodynamic ram behavior. Corresponding hydrodynamic tests were performed in a modified gas gun facility, and the following panel-based examinations of various parameters, such as displacement, velocity, stress, and energy, as well as hydrodynamic ram pressure show that the analysis and test are well correlated, and thus the results of the study reasonably explain the characteristics of the hydrodynamic ram. The methodology and procedures of the present study are applicable to the hydrodynamic ram assessment of airframe survivability design concepts.

• Nuclear Engineering and Technology
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• v.46 no.4
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• pp.529-540
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• 2014

In this research, a drop impact analysis of a fuel assembly in a research reactor is carried out to determine whether the fuel plate integrity is maintained in a drop accident. A fuel assembly drop accident is classified based on where the accident occurs, i.e., inside or outside the reactor, since each occasion results in a different impact load on the fuel assembly. An analysis procedure suitable for each drop situation is systematically established. For an accident occurring outside the reactor, the direct impact of a fuel assembly on the pool bottom is analyzed using implicit and explicit approaches. The effects of the key parameters, such as the impact velocity and structural damping ratios, are also studied. For an accident occurring inside the reactor, the falling fuel assembly may first hit the fixing bar at the upper part of the standing fuel assembly. To confirm the fuel plate integrity, a fracture of the fixing bar should be investigated, since the fixing bar plays a role in protecting the fuel plate from the external impact force. Through such an analysis, the suitability of an impact analysis procedure associated with the drop situation in the research reactor is shown.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1085-1090
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• 2003

An iterative modal analysis approach is developed to determine the effect of transverse open cracks on the dynamic behavior of simply supported Euler-Bernoulli beams with the moving masses. The influences of the velocities of moving masses, the distance between the moving masses and a crack have been studied on the dynamic behavior or a simply supported beam system by numerical method. no presence or crack results in large deflection of beam. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments i.e. the crack is modelled as a rotational spring. This flexibility matrix defines the relationship between the displacements and forces across the crack section and is derived by applying fundamental fracture mechanics theory. Totally, as the velocity of the moving masses and the distance between the moving masses are increased, the mid-span deflection of simply supported beam with the crack is decreased.

• Composites Research
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• v.13 no.4
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• pp.1-10
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• 2000

SiC particulate reinforced metal matrix composites(MMCs) are emerging as candidate materials for the automobile and aerospace industries due to their significant increase in elastic modulus and strength compared to conventional metallic materials. However, in order to make successful application of MMCs, it is very important to understand micro-failure mechanism under cyclic loading because failure mechanism of MMC is dominated by accumulation of micro-failure due to applied loading. In this study, ultrasonic Lamb wave and acoustic emission(AE) have been used to monitor microscopic damage accumulation under cyclic loading for SiC particulate reinforced metal matrix composite(SiCp/A356). It was found that the change in velocity and attenuation of ultrasonic Lamb wave due to the increase of loading cycles could be characterized by three different stages corresponding to the microscopic fracture processes. The characteristic of AE signal at each stage was analyzed and discussed by comparing with the change of ultrasonic characteristic in MMCs.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2008.11a
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• pp.153-154
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• 2008

High velocity oxy-fuel (HVOF) thermal spraying coating has been used widely throughout the last 60 years mainly in defense, aerospace, and power plants. Recently this coating technique is considered as a promising candidate for the replacement of the traditional electrolytic hard chrome plating (EHC) which pollutes the environment and causes lung cancer by toxic hexa-valent $Cr^{6+}$. In this study, two kinds of cermet coatings, WC-CoCr and WC-CrC-Ni, are formed by HVOF spraying. The wear properties of coatings are evaluated comparatively by reciprocating sliding wear tests at $25^{\circ}C$, $250^{\circ}C$ and $450^{\circ}C$ respectively. Wear rates show that WC-CoCr coatings have better sliding wear resistance than WC-CrC-Ni coatings regardless of temperature due to more, compact and homogeneously distributed WC particles, less metal content, Co, Cr rich metallic bindermatrix with higher fracture strength and better adhesive strength with WC particles.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.4
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• pp.113-120
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• 2005

In order to investigate the characteristics of penatration and the effect of surface treatment in A15052-H34, Al5082-Hl31 and titanium alloy laminates which were treated by anodizing and PVD(Physical Vapor Desposition) method, ballistic tests were conducted. Thickness of surface membrane in A15052-H34, Al5082-Hl31, were $25{\mu}m$ and that of titanium $0.9{\mu}m$ respectively. Surface hardness test was conducted using micro Vicker's hardness tester. Resistance to penetration is determined by the protection ballistic limit(V50), a statistical velocity with $50\%$ probability for complete penetration. Fracture behaviors and ballistic tolerance, described by penetration modes, are observed from the results of V50 test and Projectile Through Plate(PTP) test at velocities greater than protection ballistic limit, respectively. Present experimental results derived from this research help to optimize laminate impact behavior by varing the laminate thickness and surface treated materials.

• Korean Journal of Materials Research
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• v.4 no.5
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• pp.590-599
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• 1994

A work on the brittle to ductile transition (BDT) in single crystal alumina has been performed to understand and assess the dynamics of dislocation mobility around crack tip of brittle material. The critical stress intensity factor and yield strengths were obtained from bending test using precracked specimens at elevated temperatures. It was found that the BDT temperature was dependent on strain rate and orientation of specimen : for (1120) fracture surface, $1034^{\circ}C$, $1150^{\circ}C$ for $4.2 \times 10^{-6}$, $4.2 \times 10^{-7}s^{-1}$ respectively. Under a 4 point bending test, the moving distance of dislocation generated near crack front in ductile range is determined by an etch pits method. The velocity of dislocation in sapphire obtained from the double etching method was applied to modelling study.

• KEPCO Journal on Electric Power and Energy
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• v.7 no.2
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• pp.241-248
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• 2021

High cycle fatigue life for the cables with two different types of clamps is estimated comparatively through acceleration testing. The high cycle fatigue fracture of overhead lines is caused mainly by the aeolian vibration which is induced by vortex shedding. It is necessary to manage the integrity of cables continuedly considering that the aeolian vibration is unavoidable since it occurs in steady and relatively low wind velocity. Two types of clamps which are largely used for overhead lines of the distribution grids are selected and failure data are obtained by step stress testing with a electrodynamic shaker with them. The inverse power law is assumed to describe the stress-life relationship and the fatigue limit at any specified life is supposed to follow Weibull distribution. The life of the cable is defined as the number of cycles to the time that one of strands is completely broken. Finally, the fatigue limits of the cables with two clamp types are estimated at the reference life of 500 Mcycles and compared each other based on a bending vibration amplitude.

• Journal of Ocean Engineering and Technology
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• v.38 no.3
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• pp.124-136
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• 2024

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 type), and the colliding ships are selected as multi-purpose vessels, service operation vessels, or anchor-handling tug ships based on their operational purpose. Collision analysis is performed using ABAQUS and substantiation is performed via a drop impact test. The collision analyses are conducted by varying the ship velocity, displacement, collision angle, and ship shape. By applying this numerical model, the extent of damage and deformation of the collision area is confirmed. The analysis results show that a vessel with a bulbous bow can cause flooding, depending on the collision conditions. For damage caused by collision, various collision angles must be considered based on the internal stiffener arrangement. Additionally, the floater can be flooded with relatively small collision energy when the colliding vessel has a bulbous bow.