• Journal of the Korean Wood Science and Technology
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• 제47권5호
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• pp.644-654
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• 2019

참오동나무의 섬유방향기체투과성(gas permeability), 횡단방향 흡음율(sound absorption coefficient)과 음향투과손실(sound transmission loss)을 평가하고 열처리의 영향을 파악하고자 참오동나무 원반을 100, 160, $200^{\circ}C$로 열처리하고 기체투과성, 흡음율, 음향투과손실을 각각 측정하여 무처리 원반의 결과와 비교하였다. 그 결과, 두께 20 mm 참오동나무 원반의 섬유방향 기체투과성(specific permeability)은 무처리, 100, 160, $200^{\circ}C$ 열처리의 경우 각각 0.254, 0.279, 0.314, 0.452로 열처리에 의해 기체투과성이 약간 증가하였다. 두께 20 mm 무처리 참오동나무 원반의 50-6400 Hz 평균흡음율은 0.101이었으며 온도 100, 160, $200^{\circ}C$로 열처리한 목재의 50-6400 Hz 평균흡음율은 0.109, 0.096 그리고 0.106이었다. NRC (noise reduction coefficient) 는 각각 0.060, 0.067, 0.062 그리고 0.071 이었다. 두께 20 mm 무처리 참오동나무 원반의 50-6400 Hz 주파수범위에서 음향투과손실은 평균 36.93 dB이었다. 열처리에 의해 참오동나무 원반의 기체투과성과 흡음율은 열처리에 의해 그리고 열처리 온도 증가에 의해 약간 증가하였으나 증가정도는 미미하였다.

• Ocean and Polar Research
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• 제37권3호
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• pp.235-247
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• 2015

The main purpose of procuring the oceanographic research vessel with state-of-the-art technology is to provide a floating laboratory to conduct field work on the global oceans. The vessel should be properly utilized to locate and evaluate unexplored natural resources as well as to contribute international efforts to better understand and manage global environmental issues. Top priorities in the vessel design are high safety standards, noise and vibration control efficiency, and effective application of research equipment. For the accomplishment of all activities, the vessel length over all should be extended ~100 m with a gross tonnage of ~5,900 ton. In particular, the dynamic positioning system II will essentially operate at sea state 6. The high efficiency emissions reduction system will also be adopted in preparation for entry into force of 3rd exhaust emission control (Tier III). About 130 navigational and scientific instruments will be installed. The final design and model test of the new research vessel were reviewed and completed, respectively, in 2014. Currently, the ship is being built on schedule and expected to be delivered in December 2015. Within the near future, the new vessel will assume the role of carrying out multidisciplinary oceanographic researches of the highest standards in a technologically advanced and environment friendly manner.

• 산업기술연구
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• 제37권1호
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• pp.1-4
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• 2017

Speeding up of railway vehicles requires weight reduction of the vehicle body. However, when the vehicle body is lighter, the sound insulation performance for blocking the noise from the outside is reduced. Aluminum is an important material used in the bodywork of transportation vehicles such as railway vehicles, aircraft, and automobiles. In this study, the bending stiffness and sound insulation performance of foamed aluminum with sandwich structure are investigated experimentally. The transmission loss is measured in accordance with the international standard ASTM E 2249-02. The mass-law deviation is used to evaluate the sound insulation performance per weight. In order to examine the applicability of the foamed aluminum sandwich panel to railway vehicles, the analysis of bending stiffness and an experimental review are carried out at the same time.

• 전력전자학회논문지
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• 제21권2호
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• pp.182-189
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• 2016

A modeling method of electric power network inside a fishing boat less than 5 tons is proposed for its high-energy efficiency with renewable energy sources. The power network inside the fishing boat consists of a diesel engine, a starter motor, an alternator, battery packs, and electric loads, which are connected in parallel. To obtain proper power network model, the voltage -current characteristics of the electric components are considered to develop elaborate electrical models under several load conditions. Measured data of the battery and alternator current include noise. By using an average method, the AC components from the power network of the fishing boat can be reduced, which is verified by KCL rule. Using the proposed power network model, the power generation of the alternator and the reduction of diesel consumption in the boat's engine are predictable under various operating conditions. The validity of the proposed methodology is verified by comparing simulation results with experimental measurements using statistical inferences.

• ETRI Journal
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• 제37권4호
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• pp.824-832
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• 2015

Heart sounds are the main obstacle in lung sound analysis. To tackle this obstacle, we propose a diagnosis algorithm that uses singular spectrum analysis (SSA) and frequency features of heart and lung sounds. In particular, we introduce a frequency coefficient that shows the frequency difference between heart and lung sounds. The proposed algorithm is applied to a synthetic mixture of heart and lung sounds. The results show that heart sounds can be extracted successfully and localizations for the first and second heart sounds are remarkably performed. An error analysis of the localization results shows that the proposed algorithm has fewer errors compared to the SSA method, which is one of the most powerful methods in the localization of heart sounds. The presented algorithm is also applied in the cases of recorded respiratory sounds from the chest walls of five healthy subjects. The efficiency of the algorithm in extracting heart sounds from the recorded breathing sounds is verified with power spectral density evaluations and listening. Most studies have used only normal respiratory sounds, whereas we additionally use abnormal breathing sounds to validate the strength of our achievements.

• Smart Structures and Systems
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• 제25권3호
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• pp.345-368
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• 2020

The present work proposes a self-controlled multi-stage optimization method for damage identification of structures utilizing standard particle swarm optimization (PSO) algorithm. Damage identification problem is formulated as an inverse optimization problem where damage severity in each element of the structure is considered as optimization variables. An efficient objective function is formed using the first few frequencies and mode shapes of the structure. This objective function is minimized by a self-controlled multi-stage strategy to identify and quantify the damage extent of the structural members. In the first stage, standard PSO is utilized to get an initial solution to the problem. Subsequently, the algorithm identifies the most damage-prone elements of the structure using an adaptable threshold value of damage severity. These identified elements are included in the search space of the standard PSO at the next stage. Thus, the algorithm reduces the dimension of the search space and subsequently increases the accuracy of damage prediction with a considerable reduction in computational cost. The efficiency of the proposed method is investigated and compared with available results through three numerical examples considering both with and without noise. The obtained results demonstrate the accuracy of the present method can accurately estimate the location and severity of multi-damage cases in the structural systems with less computational cost.

• Journal of the Korean Wood Science and Technology
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• 제47권1호
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• pp.33-39
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• 2019

The square timbers of larch having cross section of $90mm{\times}90mm$ were glued laterally to be formed $1,200mm{\times}2,400mm$ panels which were used as cores for CLT wall panels. Then, structural plywood panels having size of $1,200mm{\times}2,400mm$ were used as cross band covering the small square timber cores to manufacture CLT wall panels. The sound absorption rate of CLT wall panels and polyester board attached CLT wall panels were investigated. The mean sound absorption coefficients of the former and the latter in the frequency range of 100-6400 Hz were 0.21 and 0.74, respectively. The noise reduction coefficients (NRC) of those were 0.21 and 0.40, respectively. Also, the mean sound transmission loss of CLT wood panel in the frequency range of 50-1600 Hz was 45.12 dB and that value at the frequency of 500 Hz was 42.49 dB. It was suggested that the polyester board attached CLT wall panels could be used as housing wall because of its high sound absorption rate and high sound transmission loss.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권9호
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• pp.4518-4540
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• 2019

With the development of IT convergence technology, autonomous driving has gradually developed; however, the vehicle is still operated by the driver, who should always be in good health - but sometimes, this is not the case. It is especially dangerous to drive when drowsy, and unable to fully concentrate on driving, such as when taking certain medicines, or through fatigue. Drowsy driving is at least eight times more dangerous than normal driving, and as dangerous as drunk driving. Previous research has looked at technology to detect drowsiness, in order to wake up drivers when necessary, or to safely stop the vehicle. Furthermore, many studies have been conducted to find out when drowsiness occurs. However, it is more desirable for the driver to take sufficient rest during a break, in order to be able to continue to focus and drive. In other words, it is important to maintain a normal state before drowsiness. In this study, we introduce a sound source to increase driver concentration and prevent drowsiness, another that can improve the quality of sleep, and a system that produces these sound sources. The proposed system has a noise reduction effect of about 15 dB. We have confirmed that the proposed sound induces an EEG of the desired form.

• 한국건축시공학회지
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• 제17권4호
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• pp.349-360
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• 2017

콘크리트 건축물 공사에 있어, 거푸집공사는 전체공사비의 10%를 차지하는 중요한 공정이다. 최근의 건축물은 대형화, 고층화가 이루어지고 있다. 이러한 거푸집공사의 고효율과 안전성을 위하여 거푸집공정의 시스템화가 이루어지고 있으나, 여전히 인명사고와 해체공정에서 발생하는 소음 민원이 빈번히 발생하고 있으며, 이러한 문제의 해결을 위하여 대부분 해외기술에 의존하여 국내 건설현장 여건을 고려하지 않는 관계로 외면되어 기존 거푸집 공법을 답습하고 있는 실정이다. 본 연구는 공정개선, 안전성 향상 및 해체소음 저감이 가능한 슬래브, 보 전용 테이블형 다단 드롭 시스템 거푸집을 개발하고 시스템 내에 사용되는 주요 부재인 장선 멍에와 동바리의 물성을 평가하고, 이 시스템의 현장 적용을 위한 해체공정에서의 소음을 기존 공법과 비교 평가하는 연구로서 실험결과, 멍에 빔과 동바리 모두 슬래브 및 보 타설용 가설재로 사용하기에 충분한 내력이 있는 것으로 나타났으며, 평균소음도가 기존 공법에 비해 10dB(A) 이상 저감되는 것으로 확인되었으며 타설 시의 처짐량을 측정한 결과, 기존 공법 대비 처짐이 저감되는 것을 확인하였다.

• 핵의학기술
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• 제18권1호
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• pp.134-139
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• 2014

ASIR기법은 statistical noise modeling을 사용하여 CT image를 reconstruction하는 방법으로, mA를 낮춰도 이미지 질을 보전하며 noise reduction 효과가 있다고 알려져 왔다. 본 논문은 본원에서 주로 하는 bone SPECT/CT에 ASIR 기법을 적용하여 이미지를 평가하였다. GE의 Discorvery 670을 이용하여 120 kVp, 100 mA를 기준으로 mA를 변화시켜서 ASIR의 적용 전과 적용 후 영상을 비교하였다(ASIR level: 20-80%). Anthropomorphic phantom으로 ASIR (%)의 변화에 따른 SPECT image의 감쇠 보정 정도를 측정하였다. 두번째로 ACR phantom으로 CT image의 CNR, image noise, spatial resolution을 평가하였다. 세 번째로 lower torso phantom을 이용하여 spine에 최적화할 수 있는 ASIR level을 선택한 후 2명의 bone SPECT/CT follow up 환자에게 ASIR를 적용하여 영상을 획득한 후 5년 이상의 경험이 있는 10명의 방사선사에게 blind test를 시행하였다. SPECT의 영상의 감쇠 보정 정도는 ASIR의 변화와는 무관하게 모두 유의한 차이가 없었다(P>0.05). ASIR을 적용했을 때 CT image의 noise는 mA의 변화에 따라 최소 17%에서 최대 52%까지 감소하였다. ASIR를 적용하지 않았을 때 CNR은 40 mA에서 0.42를 보여준 반면 ASIR를 적용한 40 mA (ASIR 60%)에서도 0.8 이상을 유지하였다. High contrast 영역의 비교에서는 ASIR 적용과 상관없이 40 mA까지 12 lp/cm 영역을 구별할 수 있었다. Lower torso phantom의 spine image에서 100 mA image와 육안적으로 비슷한 ASIR level은 60% (40 mA) 정도였고, bone SPECT/CT에 적용한 후 blind test에서 육안적으로 ASIR를 적용하지 않았을 때와 차이를 구별하지 못하였다. 본 논문의 결과는 SPECT/CT에서 ASIR 기법을 사용했을 때 SPECT와 CT image의 특별한 영상의 질 저하 없이 radiation dose를 줄일 수 있다는 것을 보여준다. 또한 관심부위가 bone에 한정되어 있는 bone SPECT/CT 특성상 더 높은 ASIR level도 가능할 것으로 사료된다.