• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.64-64
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• 2021

댐의 중요 구성요소 중 하나인 여수로 구조물은 관행적으로 단위길이당 100m³/s 정도의 유량이 흐를 수 있도록 설계를 하고, 이를 초과할 때는 여수로 구조물에 피해가 가지 않도록 공기혼입 장치를 설치하거나 콘크리트의 설계강도를 증가시키는 대책을 사용하는 것이 일반적이다(댐설계 기준·해설, 2011) 그러나 건설된 지 오래된 댐의 경우 여수로 콘크리트 구조물의 설계강도가 낮고(최저 16.7MPa) 수문방류 횟수가 많아 최근에 건설된 댐 여수로 보다 상대적으로 많은 손상이 발생되어 있어 잦은 보수보강이 요구되고, 점차 유지관리 비용이 증대되고 있어 노후된 여수로 구조물일수록 기능을 유지하면서도 유지관리 비용을 절감할 수 있는 방안의 수립이 요구되고 있다. 이에 본 연구에서는 𐩒𐩒𐩒댐 여수로를 대상으로 2020년 홍수기 전·후의 여수로 바닥슬래브의 손상상태를 3D드론 매핑, 육안조사 및 내구성 조사결과 등을 이용한 정밀분석을 통해 수문방류시 여수로 바닥슬래브에 가장 큰 손상을 일으키는 손상메커니즘으로 유수에 의한 부상(uplift)에 의한 파손 메커니즘(Flow-driven uplift failure mechanism)을 제시하였으며, 여수로 바닥슬래브의 가장 일반적 손상원인으로 간주되고 있는 공동현상(cavitation)이 공동지수(cavitation index)가 0.3이상인 경우에도 발생할 수 있음을 확인하였다. 이와 같은 관찰 및 분석결과는 보다 많은 사례를 통하여 보완될 경우 향후 여수로 구조물의 설계 뿐만 아니라 보수보강 방법이나 유지관리, 더나아가서는 종합적 댐시설물 자산관리 계획을 수립하는데 매우 유용한 자산이 될 수 있다.

• Journal of Dental Rehabilitation and Applied Science
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• v.38 no.3
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• pp.138-149
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• 2022

The clinical applicability of ceramics can be increased by analyzing the causes of fractures after fracture testing of dental ceramics. Fractography to analyze the cause of fracture of dental ceramics is being widely applied with the development of imaging technologies such as scanning electron microscopy. Setting the experimental conditions is important for accurate interpretation. The fractured specimens should be stored and cleaned to avoid contamination, and metal pretreatment is required for better observation. Depending on the type of fracture, there are dimple rupture, cleavage, and decohesive rupture mainly observed in metals, and fatigue fractures and conchoidal fractures observed in ceramics. In order to reproduce fatigue fracture in the laboratory, which is the main cause of fracture of ceramics, a dynamic loading for observing slow crack growth is essential, and the load conditions and number of loads must be appropriately set. A typical characteristic of a fracture surface of ceramic is a hackle, and the causes of fracture vary depending on the shape of hackle. Fractography is a useful method for in-depth understanding of fractures of dental ceramics, so it is necessary to follow the exact experimental procedure and interpret the results with caution.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.448-454
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• 2020

This study aims to determine the cause of structural defects occurring during aircraft operations and to verify the structural integrity of the improved features. The fracture plane was analyzed to verify the characteristics of the cracks and the fatigue failure leading to the final fracture was determined by the progress of the cracks by the repeated load. During aircraft operations, the comparative analysis of the load measurement data at the cracks with the aircraft design load determined that the measured load was not at the level of 30% of the design to be capable of being damaged. A gap analysis resulted in a significant stress of approximately 32 ksi at the crack site. Pre-Load testing also confirmed that the M.S. was reduced by more than 50% from +0.71 to +0.43, resulting in a sharp increase in aircraft load and the possibility of cracking when combined. Thus, structural reinforcement and the removal of the gap for aircraft cracking sites improved the defect. Based on the structural strength analysis of the improvement features, the bulkhead has a margin of about +0.88 and the fitting feature is about +0.48 versus allowable stress. In addition, the life analysis results revealed an improvement of approximately 84000 hours.

• Journal of Wetlands Research
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• v.20 no.3
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• pp.219-226
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• 2018

Interceptor sewer is installed underground near to the river side mostly ofstate-owned land and the management efficiency of public sewage disposal facilities is decreasing as too much infiltration/inflow(I/I) and river flow to interceptor sewer are caused by broken or deteriorated sewer. This also affects the sewer pipeline project and decreases its efficiency. Therefore, the aim of this study is to investigate interceptor sewer which has influence on the reduction of the project effect. The investigation were performed for three study areas. The study includes the investigation of current condition of interceptor sewer(sewer extension, pipe diameter, pipe type, installed year, installed locations, etc), investigation of inside of sewer by CCTV accompanied by pumping and dredging works where required, investigation of inside of manholes by eyes, calculation of pollutant load using the results of investigation of flow quantity and quality. Multipoint investigations were simultaneously performed for flow quantity at confluence area and other investigations were also performed for flow quantity and BOD for interceptor sewer and comparison of pollutant load, investigation of infiltration/inflow(I/I) caused by deterioration of interceptor sewer. As the result of the study, a main reason for reduced effect of sewer pipe improvement project was analyzed as the low-density sewage and I/I in public seweage treatment Facility due to deteriorated and unmanaged interceptor sewers.

• Journal of Conservation Science
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• v.7 no.1
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• pp.9-18
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• 1998

There are about 1470 stone-cultural properties in Korea which have been registered and protected by the government. Representative of them are pagoda, stupa, stone-buddha, stele support of banner pole and stone-lanterns. Most of them have been exposed to and weathered by natural environments. Stone-cultural properties are destroyed and/or destructed mostly by weathering and its related features of rocks. Therefore, it is necessary to conduct geological studies on the weathering phenomena and related features as well as characteristics of the rock itself must be done for the conservation. Thus geological investigation should include detail measurements, rock varieties and phases, structural lineaments of the rock, cause and degree of weathering, degree and patterns of crack development structural stability, identification of reusable parts for restoration, geomorphological characteristics of the site, and etc. The interaction among these factors must be investigated and analyzed, which must be used as basic data to establish the guideline of conservation and to plan for repair and/or restoration. The conservation plan should involve parts to be repaired, method of repair, type of cementing material, the characteristics of rock phases to be supplemented, method for maintaining structural stability, and method to delay or to prevent the rock weathering.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.3
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• pp.230-236
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• 2020

A trash screen is installed in front of the inflow channel of a drainage pumping station, sewage treatment plant, and a power plant to block floating contaminants. The bottleneck phenomenon, which decreases the water inflow, causes damage to the damper as a result of clogging in between the screen if string type obstacles are not removed. In this paper, the apron was removed, and the screen was expanded, to prevent breakage of the bottleneck phenomenon and string type obstacles. This was designed using an extended rake by adding an inner rake in between the screen interspace to remove the bottleneck phenomenon and string type obstacles. To design the inner rake that satisfies the allowable stresses of the existing damper rake, the experiment points were determined according to the experimental design method using the inner rake vertical length and the thickness of the reinforced section as parameters. The use of the ANSYS static structural module and statistical analysis tool R software gives the optimized shape according to the response surface method. The relative error between the response surface analysis results and the simulation results was 1.63% of the determined optimal design-point rake length of 210.2 mm and the reinforcement section thickness of 2 mm. Through empirical experiments, a test rake was constructed to the actual size, and approximately 97% of the bottleneck phenomenon and string type obstacles could be removed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.10
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• pp.459-467
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• 2019

The landing gear is a component that requires a high degree of safety to protect the lives of rotary-wing aircraft and boarding personnel, absorbing the impact on transfer/landing and supporting the fuselage during taxiing and mooring on the ground. In particular, the wheel landing gear supporting the aircraft fuselage absorbs most of the shock from the ground through the shock absorber and tires. This ensures the safety of the pilot on board the aircraft and satisfies the operational capability of the soldiers between missions. During the operation of a rotary-wing aircraft, a number of piston pins, which are a component of the right main wheel landing gear, were found to be broken. Therefore, this study examined the root cause of the piston pin crack phenomenon found in the main wheel landing gear. For this purpose, various causes were identified from fracture surface analysis of a flight test. In particular, the possibility of cracking was analyzed based on the influence on the fastening torque with the drag beam component applied to the piston pin at the time of development. This ensures the fatigue life and structural integrity.

• Fire Science and Engineering
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• v.21 no.4
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• pp.59-64
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• 2007

We studied on the fires about the electrical motors in this paper. We compared and analyzed about the transformation and damage state of single-phase induction motors used in the home appliances when we applied electrical overload and exterior flame. This experiment was progressed by the electrical overload application test and the exterior flame application test through the locked rotor of motor. In case of the exterior flame application test, it is divided into the apply voltage case and not apply voltage case. The result of an experiment through the locked rotor of motor, it was able to observe the short-circuit marks between layers at the winding coil parts, and it was appeared a transformed dendritic tissue structure of winding coil by the electrical overload test. The application voltage and the application exterior flame, it was confirmed that the stator winding coil parts were remain original shapes and observed that the color of the winding coil's circumference was changed to red. The non-application voltage and the application exterior flame, it was observed that the stator winding coil parts were transformed quite from original shapes. It was observed that the color of the winding coil and circumference parts was changed to red at the same case of non-application voltage.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.490-497
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• 2020

Asphalt pavement accounts for more than 90% of the total pavement in Korea. Pavement is most widely constructed among construction structures. The heat transfer characteristics (Thermophysical Properties) of the asphalt pavement cause the heat island effect in downtown areas. An increasing asphalt surface temperature is one of the major causes of damage to asphalt pavement. This study examined the heat transfer characteristic factors according to solar energy accumulation in an asphalt mixture. The specimens (WC-2 & PA-13, Recycled aggregate used WC-2) used in the experiment were compacted with a Gyratory Compactor. The thermo-physical properties (thermal conductivity, specific heat capacity, thermal diffusivity, and thermal emissivity) and solar energy accumulation were evaluated. The thermal accumulation and HFM tests revealed a 1.2- to 2.0-fold difference. This indicates that the thermal conductivity of the asphalt mixture pavement changes with the accumulation of solar energy. An analysis of the correlation of thermal conductivity according to the surface temperature of the asphalt mixture showed that WC-2 was logarithmic, and PA-13 was linear. Experiments on the heat transfer characteristics of asphalt pavement that can be used for thermal failure modeling of asphalt were conducted.

• Journal of the Korean GEO-environmental Society
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• v.22 no.3
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• pp.31-35
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• 2021

The expansion joints installed on the bridge for the accommodation of expansion and contraction of the supper structure are essential members of the bridge. However, the expansion joints are deteriorated over time and the waterproof function weakens, causing rainwater to penetrate and deteriorate the structure. In order to solve the traffic congestion caused by frequent replacement of the old expansion joints along with the deterioration of the structure, a post-integrated abutment bridge in which the existing expansion joints are removed and replaced with reinforced concrete link connection has been applied to highway bridges since 2016. After the post-integrated abutment method was applied, it was partially applied to bridges in which the superstructure and abutment were jammed. In this study, the causes of problems that may occur when the post-integrated abutment method is applied to the jammed bridge were analyzed numerically. It was analyzed that damage occurred in the link connection part. Based on the results of this study, the application condition for the post-integrated abutment method is reinforced as it is not possible to apply the post-integrated abutment method to bridges are already jammed.