• Journal of Korean Society of Steel Construction
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• v.29 no.2
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• pp.99-110
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• 2017

This paper presents the study of the bending behavior of mooring chain links for keeping the position of the offshore floating structures. In general, chain links have been thought as the axial members due to the fundamental boundary condition. But, the flexural stiffness can be induced to the contact surface between chain links when friction occurs at the surface of the chain links due to high tensile force. Especially, the mooring chains for offshore floating platforms are highly tensioned. If the floater suffers rotational motion and the mooring chain links are highly tensioned, the rotation between contact links, induced by the floater rotation, generates the bending moment and relevant stresses due to the unexpected bending stiffness. In 2005, the mooring chain links for the Girassol Buoy Platform were failed after just 5 months after facility installation, and the accident investigation research concluded the chain failure was mainly caused by the fatigue due to the unexpected bending stress fluctuation. This study investigates the pattern of the induced bending stiffness and stresses of the highly tensioned chain links by nonlinear finite element analysis.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.2 no.4
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• pp.23-32
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• 1982

In order to obtain the necessary data for the safety maintenance, repair, and reinforcement of steel structures, experiment was carried out to examine the mechanical capacity and toughness variation for steel with service history and without. In this paper, hardening and embrittlement by fatigue accumulation, and the decrease of toughness was examined and weld that was commonly used as the connection method of steel structure was also examined. It was found that hardening and embrittlement have more effect on the decrease of toughness than the increase of strength. Such a tendency was also similary state in case of weld. And it was found that, in the weld of steel with service history and without, embrittlement was observed at normal temperature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.5
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• pp.665-671
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• 2013

In a Korean Generation IV prototype sodium-cooled fast reactor (SFR), various types of high-temperature heat exchangers such as IHX (intermediate heat exchanger), DHX (decay heat exchanger), AHX (air heat exchanger), FHX (finned-tube sodium-to-air heat exchanger), and SG (steam generator) are to be designed and installed. In this study, the high-temperature design and integrity evaluation of the sodium-to-air heat exchanger AHX in the STELLA-1 (sodium integral effect test loop for safety simulation and assessment) test loop already installed at KAERI (Korea Atomic Energy Research Institute) and FHX in the SEFLA (sodium thermal-hydraulic experiment loop for finned-tube sodium-to-air heat exchanger) test loop to be installed at KAERI have been performed. Evaluations of creep-fatigue damage based on full 3D finite element analyses were conducted for the two heat exchangers according to the high-temperature design codes, and the integrity of the high-temperature design of the two heat exchangers was confirmed.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.6
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• pp.435-443
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• 2015

Offshore structure may be considerably vulnerable to fatigue failure while initial flaw propagates under cyclic loading, so crack propagation analysis/fracture/yield assessments about initial flaw detected by NDT are necessarily required. In this paper, case studies have been conducted by flaw assessment program using engineering criticality analysis (ECA) approach. Variables such as flaw geometry, flaw size, structure geometry, dynamic stress, static stress, toughness, crack growth rate, stress concentration factor (SCF) affected by weld are considered as analysis conditions. As a result, the safety of structure was examined during fatigue loading life. Also, critical initial flaw size was calculated by sensitivity module in the developed program. The flaw assessments analysis using ECA approach can be very useful in offshore industries owing to the increasing demand on the engineering criticality analysis of potential initial flaws.

• International Journal of Highway Engineering
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• v.5 no.1 s.15
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• pp.1-10
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• 2003

The objective of pavement design, just as with the design of other structures, is to obtain the most economical designs at specified levels of reliability. Methods that yield designs with different levels of reliability are undesirable, and over the course of time design approaches in the U.S. and Europe have converged toward the Load and Resistance Factor Design (LRFD) format in order to assure uniform reliability. At present the LRFD format has been implemented in concrete, steel, wood and bridge design specifications. In this paper, reliability theories are used to illustrate the development of an LRFD format for Mechanistic-Empirical (M-E) design of flexible pavements as an alternative of its reliability module. It is shown in this paper that ten candidate pavement sections designed with a reliability level using the AASHTO design guide (1986) do not have uniform structural reliability in terms of pavement mechanistic distress such as fatigue cracking and the uniform reliability can be achieved by using the LRFD format.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2379-2384
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• 2015

Bellows product is an important part in the area of plant engineering, shipbuilding and petrochemistry. For safety and durability it is necessary to consider lots of factors when designing it. This research developed a U-shaped metal bellows design software based on EJMA 9th Edition manual. This GUI software was developed by using Matlab software and can be able to design four types of bellows, Unreinforced Single Bellows, Unreinforced Double Bellows, Reinforced Single Bellows and Reinforced Double Bellows. The already proven bellows model was designed to verify this software. We investigated the behavior while changing the thickness of the bellows. As the thickness of bellows increases, spring rate, thrust force, stress increase and fatigue life decreases. This software will be helpful design engineers save time and effort.

• Special Issue of the Society of Naval Architects of Korea
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• 2011.09a
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• pp.12-16
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• 2011

During the shipbuilding construction, the repair works will be occurred by various reasons such as the natural disaster, mistakes of engineers or workers, defect of material, and so on. The one of the engineer's responsibilities is to design considering every possibility and to prevent the repair works due to the mistakes during construction stages, but actually it is very difficult and impossible to avoid every mistake. However, it is also the responsibility of engineers to find the best solution for the unavoidable mistakes which is to maintain the capacity of vessel and guarantee the safety for the repair works considering the construction schedules and economic cost. In this paper, it will be introduced the brief of repair works to the structural damage of the moon-pool structure in drillship which is built in our shipyard. For the verification of the structural strength, the fatigue analysis has been carried out based on the guide of Classification society. Furthermore, the modifications of structure design and welding procedure have been applied to avoid the stress concentration in the moon-pool structure.

• Journal of the Society of Disaster Information
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• v.8 no.4
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• pp.391-400
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• 2012

Recently, the construction industry commonly uses FRP as a reinforcement material because of its material advantages. FRP attached reinforcement has various advantages such as high strength, stiffness, excellent durability and construction practicability comparing to its weight. However, external attachment of FRP is water-tighted with low water permeable material, not draining water, probably causing damages on a permanent structure. The study manufactured it through pultrusion and examined GP(glass fiber panel) of which material-mechanical properties are almost same as the existing FRP but durability and attachment performance are better by stationary experiments, testing load-deflection curve, destruction types and load-deflection relation under repetitive loading test. As a result of 2,000,000 fatigue tests, it did not result in the destruction and showed excellent permanent attachment and durability as it displays significantly low compressive strain of concrete.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.2
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• pp.126-131
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• 2010

The purpose of this study is to assess the condition of composites used in aircraft under varying temperature environment with ultrasound guided wave technique. Investigation of crucial influential factor on the composite health monitoring related to aircraft operational environments such as the number of thermal cycles and temperature deviation between ground level and flight altitude has been of a great concern for aircraft safety issue. In this study, ultrasonic guided wave health monitoring scheme is proposed to evaluate composite specimens damaged with the thermal fatigue simulating aircraft operational condition. Guided wave dispersion curves are used to select right modes which show a promising sensitivity to each different thermal fatigue damage level. The present approach can be also implemented as one of on-lines health monitoring tools for aircraft.

• The Journal of Korean Obstetrics and Gynecology
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• v.29 no.1
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• pp.78-91
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• 2016

Objectives: Breast cancer patients in Korea need to care about symptoms with complementary medicine including acupuncture. We reviewed the randomized controlled studies using acupuncture in breast cancer patients to establish a basic knowledge of clinical practice guidelines. Methods: We searched the following databases through July 2015: the Cochrane Central Register of Controlled Trials, Ovid-Medline, Ovid-EMBASE, the Allied and Complementary Medicine Databases and OASIS. The articles of RCTs using acupuncture in breast cancer for all symptoms were selected and analyzed. The acupoints, treatment period, inclusion criteria of participants, follow-up period and effectiveness were extracted. Results: Three hundred fifty five records after duplicate were screened, and 14 RCTs were selected. RCTs of Hot flush, pain, fatigue were reviewed. The adverse symptoms using medical treatment in breast cancer patients were targets of acupuncture in RCTs. The acupuncture treatment was decreased the hot flush, pain and fatigue. However, the effect was not confirmed due to various study design. Conclusions: The analysis of the research would be conjugated to establish a basic knowledge of clinical practice guidelines. Well designed studies in Korea are needed to confirm the efficacy and safety of acupuncture in patients with breast cancer.