• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.1
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• pp.32-38
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• 2024

In the case of apartment building, it is difficult to conduct non-destructive testing due to the actual presence of people and the dust and noise generated during the core test, so inspections are performed each time in the common area and underground parking lot, and the tests are conducted on the finishing material rather than on the concrete surface due to low-cost orders. As the process progresses, poor inspection is inevitable. In addition, the proposed formulas for strength estimation have large fluctuations depending on the differences in test conditions and environments, and even if they show the same measured value, the deviation between each proposed formula is large, making it difficult to accurately estimate strength, making it difficult to use. Accordingly, we would like to select finishing materials mainly used in apartment complexes and compare and evaluate the compressive strength of concrete according to the type of finishing material by using non-destructive testing methods directly on the finishing materials without removing the finishing materials. The reliability evaluation results of the estimated compressive strength of concrete using the ultrasonic velocity method according to the type of finishing material are as follows. The error rate between the estimated compressive strength and compressive strength derived through the ultrasonic velocity method shows a wide range of variation, ranging from 21.83% to 58.89%. The effect of the presence or absence of finishing materials on the estimated compressive strength was found to be insignificant. Accordingly, it is necessary to select more types of finishing materials and study ultrasonic velocity methods according to the presence or absence of finishing materials, and to study estimation techniques that can increase reliability.

• The Journal of the Acoustical Society of Korea
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• v.34 no.6
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• pp.411-422
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• 2015

This paper presents an overview of the geological environment investigation and underwater acoustic measurements for the purpose of "Study on the Relationship between the Geological Environment and Acoustic Propagation in Shallow Water", which are jointly carried out by KIOST (Korea Institute of Ocean Science & Technology) and Hanyang University in the western shallow water off the Taean peninsula in the Yellow Sea in April-May 2013. The experimental site was made up of various sediment types and bedforms due to the strong tidal currents and coastal geomorphological characteristics. The geological characteristics of the study area were intensively investigated using multi-beam echo sounder, sub-bottom profiler, sparker system and grab sampler. Acoustic measurements with a wide range of research topics in a frequency range of 20~16,000 Hz: 1) low frequency sound propagation, 2) mid-frequency bottom loss, 3) spatial coherence analysis of ambient noise, and 4) mid- frequency bottom backscattering were performed using low- and mid-frequency sound sources and vertical line array. This paper summarizes the topics that motivated the experiment, methodologies of the acoustic measurements, and acoustic data analysis based on the measured geological characteristics, and describes summary results of the geological, meteorological, and oceanographic conditions found during the experiments.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.4
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• pp.69-79
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• 2017

The purpose of this study is to reconsider the rating method for the floor impact sound insulation performance in current criterion. Although there are some arguments about proper standard heavy impact source with reproducibility of actual impact source in residence building, bang machine is adopted as the only standard heavy impact source in domestic criterion. To inspect the rating methods of evaluation criteria, this study conducted vibration test for both of standard heavy impact sources and actual impact sources. Using the test results, the floor impact sound insulation performance levels were assessed by each of several criteria. In addition, low frequency noise beyond current criteria was evaluated. Consequently, the floor impact sound levels have different performance levels according to adopted criteria, and measured floor impact sounds are bound to annoy the neighbors in the low frequency range. Current criteria does not consider the spectrum characteristics of floor impact sound according to impact sources and low frequency noise. This may cause the difference between the floor impact sound insulation performance level and human perception. Thus current criterion needs to be complemented to reflect the spectrum characteristics of floor impact sound levels according to impact sources and sound pressure levels in low frequency range.

• Journal of computational fluids engineering
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• v.15 no.2
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• pp.7-13
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• 2010

Flight vehicles such as wheel wells and bomb bays have many cavities. The flow around a cavity is characterized as an unsteady flow because of the formation and dissipation of vortices brought by the interaction between the free stream shear layer and the internal flow of the cavity. The resonance phenomena can damage the structures around the cavity and negatively affect the aerodynamic performance and stability of the vehicle. In this study, a numerical analysis was performed for the cavity flows using the unsteady compressible three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation with Wilcox's turbulence model. The Message Passing Interface (MPI) parallelized code was used for the calculations by PC-cluster. The cavity has aspect ratios (L/D) of 5.5 ~ 7.5 with width ratios (W/D) of 2 ~ 4. The Mach and Reynolds numbers are 0.4 ~ 0.6 and $1.6{\times}10^6$, respectively. The occurrence of oscillation is observed in the "shear layer and transient mode" with a feedback mechanism. Based on the Sound Pressure Level (SPL) analysis of the pressure variation at the cavity trailing edge, the dominant frequencies are analyzed and compared with the results of Rossiter's formula. The dominant frequencies are very similar to the result of Rossiter's formula and other experimental datum in the low aspect ratio cavity (L/D = ~4.5). In the high aspect ratio cavity, however, there are other low dominant frequencies of the leading edge shear layer with the dominant frequencies of the feedback mechanism.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.13-18
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• 2009

Flight vehicles such as wheel wells and bomb bays have many cavities. The flow around a cavity is characterized as an unsteady flow because of the formation and dissipation of vortices brought about by the interaction between the free stream shear layer and the internal flow of the cavity. The resonance phenomena can damage the structures around the cavity and negatively affect the aerodynamic performance and stability of the vehicle. In this study, a numerical analysis was performed for the cavity flows using the unsteady compressible three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equation with Wilcox's turbulence model. The Message Passing Interface (MPI) parallelized code was used for the calculations by PC-cluster. The cavity has aspect ratios (L/D) of 2.5 ~ 7.5 with width ratios (W/D) of 2 ~ 4. The Mach and Reynolds numbers are 0.4 ~ 0.6 and $1.6{\times}106$, respectively. The occurrence of oscillation is observed in the "shear layer and transient mode" with a feedback mechanism. Based on the Sound Pressure Level (SPL) analysis of the pressure variation at the cavity trailing edge, the dominant frequencies are analyzed and compared with the results of Rossiter's formula. The dominant frequencies are very similar to the result of Rossiter's formula and other experimental data in the low aspect ratio cavity (L/D = ~ 4.5). In the large aspect ratio cavity, however, there are other low dominant frequencies due to the leading edge shear layer with the dominant frequencies of the feedback mechanism. The characteristics of the acoustic wave propagation are analyzed using the Correlation of Pressure Distribution (CPD).

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.1
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• pp.182-189
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• 2009

The noise from the sunroof can be divided into the low frequency buffeting noise and the high frequency turbulence noise generated when a car runs at the high driving speed. The wind deflector suppresses the buffeting noise generation by accelerating the vortex shedding from the front edge of sunroof opening, and guides the flow direction so that air can pass smoothly over the sunroof opening. To reduce the buffeting noise and the high frequency noise, it is very important to locate a deflector in a proper position depending on the driving speed and the sunroof opening width. The deflector's sectional shape also plays an important role in efficiently reducing the buffeting and high frequency noise. In this paper, we determined the optimum deflector's sectional shape and examined the flow characteristics behind a sunroof deflector through CFD analysis with changing the deflector height, the driving speed and the sunroof opening width. It is found that the deflector needs to be located in the higher location to control the buffeting noise by shedding the higher frequency vortices to accelerating vortices from the sunroof front edge. The deflector may act as a new noise source at the high driving speed, then it is desirable to put the deflector at the proper height to reduce the flow fluctuations and the noise generation. We also made a road test to verify CFD analysis results in this study.

• Water for future
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• v.22 no.4
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• pp.415-415
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• 1989

자연재해연구는 인간.자연환경 관계를 연구하는 학문이다. 금세기초 환경결정론, 환경가능주의, 그리고 인지에 의한 행동과학주의로 연구 Paradigm이 변화.발전되어 오며서 지리학에서도 이러한 이론적 방법론의 바탕위에 인간-자연환경 관계를 설명하려고 노력했다. 1920년대 초 Barrow가 인간생태학 개념을 발표, 1950, 1960년대 이에 영향받은 White, Kate와 Burton 같은 미국의 자연재해지리학자들은 미국에서 홍수재해문제를 인간적응, 특히 "인식"의 역할에 중점을 두어 재해지역에서 자원이용과 이의 관리문제를 연구하였다. 1970년대 들어오면서 재해의 양상, 적응방법등이 연구되고, 또한 적응의 여러 비교연구가 있었으며, 사회성과 관련 사회학적 연구 접근과 다양한 레벨의 케이스 Study 또한 이루어졌다. 오늘날의 자연재해연구는 일반재해연구로 발전하여 핵반응, 각종산업.교통재해, 화학물질 및 환경오염문제, 각종 소음공해, 폭발물 사고 등 참으로 여러 종류의 사회문제가 재해연구의 대상이 되었고, 근래에는 약물중독, 성폭행, 그리고 복잡한 현대사회에서 제기되는 정신질환까지 일종의 재해문제로 다루어 지리학내에서 연구되고 있다. 이와같이 연구의 많은 변환.발전과 함께 처음 Academic한 연구로 시작된 재해문제 연구가 이에 관심을 같는 여러분야 즉, 경제.사회, 심리학자, 토지이용개발자, 보험, 은행, 부동산업자 재해와 관련있는 민간단체, 정부기관, 정책실행기관등이 참여하는 공동연구가 활발히 행하여지고 있다. 최근에는 "세계 자연재해 감소 10개년 계획"이라는 Program을 미국이 주동이 되어 국제적인 기구로 만들어 관심있는 여러국가의 과학자, 재해연구가, Engineer, 정부관계자들이 참여 서로 정보와 지식의 교환, 세계의 개발.재개발에 대한 계획, 재해감소의 교육훈련등 다채로운 Project을 가지고 세계 자연재해 감소를 위하여 공동연구의 노력을 하려는 움직임이다. 세계의 권위있는 재해통계에 의하면 한국이 매년 자연재해로 인하여 100만명당 1,000명이 희생되는 나라로 방글라대시, 이란, 중남미와 페루, 과태말라, 동남아시아의 뉴기니와 나란히 중진개발도상국으로 몇안되는 나라의 하나로 들어있는 것을 볼 때 유감이 아닐수 없다. 우리나라는 하루빨리 이러한 자연재해로부터 아까운 생명과 재산을 잃어버리고 있는 고통과 문제를 해결하려는 민간.정부차원에서 관심을 기울이고 우선 기본적인 연구의 기틀을 마련하는 제도적 장치와 분위기가 아쉽다고 않을 수 없다.와 분위기가 아쉽다고 않을 수 없다.

• The Journal of the Acoustical Society of Korea
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• v.22 no.2
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• pp.88-95
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• 2003

The auditory experiments based on subjective responses were undertaken for the standard heavy and light weight impact noise and rubber ball impact noise, jumping noise to investigate relations between floor Impact noise levels and subjective responses and to establish the upper/lower limits of floor impact noises. As a result, it was shown that relations between floor Impact noise levels and subjective responses was linear and the lower limit of heavy-weight impact noise was L/sub i, Fmax, AW/=46㏈ and the lower limit of light-weight impact noise was L'/sub n,AW/=56㏈. Finally the 3 subjective classes of floor impact noises were established.

• Journal of the Korea Institute of Building Construction
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• v.24 no.2
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• pp.261-271
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• 2024

The widespread adoption of aluminum slab formwork in modern construction, evident in both domestic and international projects, offers numerous advantages. However, a critical challenge persists regarding the dismantling process for these slabs. The current industry standard involves dropping the slabs to the ground floor upon removal. This practice raises several concerns, notably the generation of significant noise pollution that disrupts nearby communities. More importantly, the risk of worker injuries due to falls from height during the dismantling process is a serious safety hazard. Additionally, the impact from dropping the slabs can damage the aluminum itself, leading to increased replacement costs. These drawbacks necessitate the exploration of alternative dismantling techniques that prioritize worker safety, material sustainability, and overall process efficiency. Accordingly, in this study, when the entire first-generation slab formwork of an apartment house is simultaneously lowered to a reachable position for workers, it is then disassembled and lifted for transport to the next floor. This approach has the potential to demonstrate improvements in safety, quality, economy, and process efficiency.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.3
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• pp.93-101
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• 2017

The shortage of parking lots in aged apartment complexes built from the 1980s to the mid 1990s is serious. When we look at the case of parking lot expansion in the aged apartment complexes, the method of extending the underground parking lot vertically occupies the majority. It is very important to secure the structural safety of the foundations when the existing buildings are enlarged. In the case of underground vertical work, the work space should be narrow, so that a method with excellent safety, environmental and construction properties should be applied. Urban construction is also required to use construction methods and equipment with low noise and vibration. This study analyzed the factors influencing the selection of the foundation reinforcement method for the expansion of the underground parking lot and Weights of influence factors were calculated. The purpose of this study was to analyze the applicability of the foundation reinforcement method. Factors influencing the applicability of the foundation reinforcement method were derived through expert interviews and The AHP technique was used to calculate the weight of the influencing factors. It was evaluated by experts on the applicability of the foundation reinforcement method. It conducted a case study on two types of underground parking lot expansion type and compared the applicability of the foundation reinforcement method.