• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 C
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• pp.1879-1881
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• 2003

In this paper, acoustic signals in $SF_6$ gas were analyzed using wavelet transform. For this, the PD sources in the $SF_6$ gas were divided into corona discharge surface discharge void discharge and crossing particle and acoustic signals were used to detect the PD sources. The measured signals were time-frequency distribution by wavelet transform and the features were extracted from the PD sources. As a result the characteristics of the PD sources were different. And this results is going to be used for basis diagnosis of $SF_6$ gas insulated apparatus.

• 대한음성학회지:말소리
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• 제35_36호
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• pp.25-36
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• 1998

The prosodic properties of Korean and English stress were examined with focus on syllable duration and pitch by loan words. 14 loan words were selected by the criteria of the numbers of syllables and stress positions. 3 Korean males using Seoul dialect and 3 American males using general American English served as subjects. Each tokens were uttered 3 times and second one was chosen to be analysed by CSL. We measured the duration and F0 of each syllable. In English, duration is the most salient acoustic correlates of stress, and pitch is the second. In Korean, by contrast, it seems that neither duration nor pitch is the acoustic features of stress, from our data

• Structural Monitoring and Maintenance
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• 제6권3호
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• pp.173-190
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• 2019

Steel-confined reinforced concrete (SCRC) columns feature highly complex and invisible mechanisms that make damage evaluation and pattern recognition difficult. In the present article, the prevailing acoustic emission (AE) technique was applied to monitor and evaluate the damage process of steel-confined RC columns in a quasi-static test. AE energy-based indicators, such as index of damage and relax ratio, were proposed to trace the damage progress and quantitatively evaluate the damage state. The fuzzy C-means algorithm successfully discriminated the AE data of different patterns, validity analysis guaranteed cluster accuracy, and principal component analysis simplified the datasets. A detailed statistical investigation on typical AE features was conducted to relate the clustered AE signals to micro mechanisms and the observed damage patterns, and differences between steel-confined and unconfined RC columns were compared and illustrated.

• 한국수산과학회지
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• 제55권2호
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• pp.195-206
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• 2022

The separation of spectrally overlapped broadband echo signals from free-swimming Japanese needlefish Hypohamphus sajori using the fractional Fourier transform (FrFT) was investigated. The broadband echo signals were measured over frequency ranges of 40-80 and 110-220 kHz. The overlapped echo signals were separated after eliminating noise signals in the smoothed pseudo-Wigner-Ville distribution domain. The echo signal from a 40 mm WC sphere suspended just below a chirp transducer was used to calibrate the broadband of the chirp echo sounder and estimate the frequency dependence of target strength for the separated echo signals. The experimental results show that the proposed FrFT method can analyze the time-frequency image of broadband echo signals from free-swimming individual fish effectively and can be used as a quantitative tool for extracting the acoustic features used for fish species identification.

• Fisheries and Aquatic Sciences
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• 제27권4호
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• pp.225-230
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• 2024

We examined the dB difference in target strength at multiple frequencies (ΔTS) for the identification of Antarctic krill (Euphausia superba) and ice krill (Euphausia crystallorophias) using a stochastic distorted-wave Born approximation model. Our investigation focused on ΔTS patterns at multiple frequencies in relation to size, along with key acoustic properties influencing TS, including density and sound speed contrast, fatness, and orientation. The findings revealed that the orientation and fatness significantly affect the ΔTS patterns. The results provide insight into the importance of the multi-frequency technique for estimating krill biomass and their ecological interactions with environmental features in the Southern Ocean.

• International Journal of Computer Science & Network Security
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• 제22권9호
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• pp.195-207
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• 2022

COVID-19 has remained one of the most serious health crises in recent history, resulting in the tragic loss of lives and significant economic impacts on the entire world. The difficulty of controlling COVID-19 poses a threat to the global health sector. Considering that Artificial Intelligence (AI) has contributed to improving research methods and solving problems facing diverse fields of study, AI algorithms have also proven effective in disease detection and early diagnosis. Specifically, acoustic features offer a promising prospect for the early detection of respiratory diseases. Motivated by these observations, this study conceptualized a speech-based diagnostic model to aid in COVID-19 diagnosis. The proposed methodology uses speech signals from confirmed positive and negative cases of COVID-19 to extract features through the pre-trained Visual Geometry Group (VGG-16) model based on Mel spectrogram images. This is used in addition to the K-means algorithm that determines effective features, followed by a Genetic Algorithm-Support Vector Machine (GA-SVM) classifier to classify cases. The experimental findings indicate the proposed methodology's capability to classify COVID-19 and NOT COVID-19 of varying ages and speaking different languages, as demonstrated in the simulations. The proposed methodology depends on deep features, followed by the dimension reduction technique for features to detect COVID-19. As a result, it produces better and more consistent performance than handcrafted features used in previous studies.

• 한국추진공학회지
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• 제19권4호
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• pp.15-23
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• 2015

본 연구는 유한요소해석 기반의 Helmholtz solver인 ASCI3D를 사용하여 예혼합 가스터빈 연소기에서 연소불안정 현상과 관련된 주요 결과들을 예측하였다. 해석결과는 실험결과와 비교할 때 일반적인 불안정 특성 예측에는 성공하였으나, 불안정 구간이 나타나는 영역을 다소 과대 예측하는 경향이 발견되었다. 이를 개선하기 위한 노력으로 반사계수가 불안정 특성에 미치는 영향이 분석되었다. 결과로부터 반사계수는 불안정 특성에 큰 영향을 미치고, 정확한 예측 결과를 얻기 위해서는 정확한 음향 경계 조건의 정의가 필수적인 것으로 나타났다.

• 응용통계연구
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• 제34권6호
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• pp.979-993
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• 2021

음향 장면 분류는 오디오 파일이 녹음된 환경이 어디인지 분류하는 문제이다. 이는 음향 장면 분류와 관련한 대회인 DCASE 대회에서 꾸준하게 연구되었던 분야이다. 실제 응용 분야에 음향 장면 분류 문제를 적용할 때, 모델의 복잡도를 고려하여야 한다. 특히 경량 기기에 적용하기 위해서는 경량 딥러닝 모델이 필요하다. 우리는 경량 기술이 적용된 여러 모델을 비교하였다. 먼저 log mel-spectrogram, deltas, delta-deltas 피쳐를 사용한 합성곱 신경망(CNN) 기반의 기본 모델을 제안하였다. 그리고 원래의 합성곱 층을 depthwise separable convolution block, linear bottleneck inverted residual block과 같은 효율적인 합성곱 블록으로 대체하고, 각 모델에 대하여 Quantization를 적용하여 경량 모델을 제안하였다. 경량화 기술을 고려한 모델은 기본 모델에 대비하여 성능이 비슷하거나 조금 낮은 성능을 보였지만, 모델 사이즈는 503KB에서 42.76KB로 작아진 것을 확인하였다.

• 한국항공우주학회지
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• 제46권11호
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• pp.883-891
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• 2018

본 연구에서는 항공기 랜딩 기어와 유사한 형태의 탠덤 실린더에 대해 DES (Detached Eddy Simulation)와 FW-H (Ffowcs Williams and Hawkings) 음향상사법을 이용한 전산공력 소음해석을 수행하였다. 실린더 중심 간 거리 3.7D 조건에 대한 전산공력소음해석 결과를 탠덤 실린더를 지나는 외부 유동 특성 및 원거리 소음을 계측한 선행 연구 결과와 비교하였다. 전방 실린더의 상/하부에서 발생한 와류(Vortex)가 특징적인 주파수를 갖고 후방 실린더에 충돌하면서 소음 발생원이 되는 것을 확인하였다. DES 와 FW-H 음향상사법을 이용한 전산공력소음해석 방법의 타당성을 확인한 후, 전방 실린더의 후방에 분할판을 적용한 경우의 전산공력소음해석을 수행하였다. 전방 실린더의 후방에 분할판이 적용되면 전방 실린더의 상/하부에서 발생하는 와류의 특징을 변화시키고 이극자 소음원 크기를 감소시켜 특정 주파수 대역에서 발생하는 소음 크기가 감소하는 것을 확인하였다.

• 드라이브 ㆍ 컨트롤
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• 제18권1호
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• pp.1-8
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• 2021

This paper presents research on methods for the reduction of forklifts' noise level for the increased comfort and safety of its operator. A cooling fan with a high air volume flow rate installed in the forklift acts as an important design parameter which efficiently cools the heat exchanger system, helping to transfer internal heat from the engine room to the outdoors with both transmitted and diffracted opening noises. The cooling fan contributes significantly to both the forklift's emitted sound power and the operator room's noise level, thereby necessitating research on the forklift's reduction of acoustic power level and transmission. A noise analysis for various fan models with a biomimetic design based on eagle-wing geometry was conducted. In addition to the acoustic power generation, the aerodynamic performance of the cooling blade is also strongly influenced by the design of airfoil distribution, thereby requiring optimization. The cooling fans were fabricated and installed in the forklift in order to check the efficacy of the forklift engine's cooling, and the final version of the fan was measured for its ability to lower acoustic power level and cool the engine room. This study explains the aerodynamic and acoustic features of the designed fans with the use of BEM analysis and forklift test results.