• Structural Engineering and Mechanics
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• 제78권5호
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• pp.599-610
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• 2021

Early detection of small concrete crack or reinforcement corrosion is necessary for Structural Health Monitoring (SHM). Global vibration based methods are advantageous over local methods because of simple equipment installation and cost efficiency. Among vibration based techniques, FRF based methods are preferred over modal based methods. In this study, a new coupled method using frequency response function (FRF) and proper orthogonal modes (POM) is proposed by using the dynamic characteristic of a damaged beam. For the numerical simulation, wave finite element (WFE), coupled with traditional finite element (FE) method is used for effectively incorporating the damage related information and faster computation. As reported in literature, hybrid combination of wave function based wave finite element method and shape function based finite element method can addresses the mid frequency modelling difficulty as it utilises the advantages of both the methods. It also reduces the dynamic matrix dimension. The algorithms are implemented on a three-dimensional reinforced concrete beam. Damage is modelled and studied for two scenarios, i.e., crack in concrete and rebar corrosion. Single and multiple damage locations with different damage length are also considered. The proposed methodology is found to be very sensitive to both single- and multiple- damage while being computationally efficient at the same time. It is observed that the detection of damage due to corrosion is more challenging than that of concrete crack. The similarity index obtained from the damage parameters shows that it can be a very effective indicator for appropriately indicating initiation of damage in concrete structure in the form of spread corrosion or invisible crack.

• 한국정보통신학회논문지
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• 제24권4호
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• pp.459-466
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• 2020

멀티로터 UAV(Unmanned Aerial Vehicle)를 이용해서 수집한 음향 데이터는 모터나 프로펠러에서 발생하는 자체 소음이나 비행 중 발생하는 바람 소리 등으로 인해 음향 품질이 크게 손상되는 문제가 발생한다. 멀티로터 UAV 환경에서는 목표 음향의 크기뿐만 아니라 위상도 크게 손상되기 때문에 크기와 위상을 모두 고려해서 음향을 향상시킬 필요가 있다. 하지만 위상은 크기와 달리 구조적인 특징이 잘 나타나지 않으므로 향상시키는 것이 쉽지 않다. 따라서 본 연구에서는 크기와 위상을 모두 표현할 수 있는 복소 스펙트로그램을 기초로 잡음을 제거해서 목표 음향의 품질을 향상시키는 CNN 기반 복소 스펙트로그램 향상 방법을 제안한다.

• 한국수자원학회논문집
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• 제53권12호
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• pp.1097-1107
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• 2020

본 연구에서는 하도단면의 기하학적 특성과 그에 관한 특성값들의 종방향 변화를 통해 하천지형의 시·공간적 변화양상을 파악하기 위한 방법론을 제안하고자 한다. 이를 위해 낙동강 구미보 ~ 칠곡보 구간에 대한 음향측심기를 이용한 상세 수심측량을 통해 하상에 대한 3차원 공간정보를 취득하였다. 취득된 자료를 이용하여 기준단면에 대한 기하학적 정보를 추출하였다. 추출된 하천단면의 기하특성치들을 비교함으로써 특정 하도구간에서의 지형 특징을 파악할 수 있었다. 과거 측량성과와의 비교를 통해 단면변화량과 체적하상변동량을 정량적으로 파악할 수 있었다. 향후 본 연구에서 제안한 방법의 다양한 하천구간에서 대한 적용을 통해 하천지형변화에 대한 정량적 평가방법을 제시할 것으로 기대하는 바이다.

• 한국추진공학회지
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• 제25권2호
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• pp.66-78
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• 2021

본 연구에서는 환형연소기에서 연소불안정성이 발생하는 당량비 조건과 노즐 개수에 따라서 대칭성파괴(Symmetry Breaking) 효과를 비교하였다. 일반적으로 환형연소기에서는 연소실의 길이가 짧으므로 종-방향 연소불안정성이 잘 발생하지 않으나, 발전용 가스터빈시스템의 트랜지션피스(Transition piece) 같은 덕트가 존재하였을 때는 연소불안정성이 발생하였다. 이 경우 덕트로 인하여 종-방향의 불안정성 모드만 관찰되었다. 5개의 희박노즐 개수와 당량비 조건에 따라서 대칭성파괴 특성을 조사하였는데, 당량비가 감소할수록 대칭성파괴 효과가 빠르게 발생하여 불안정성이 극적으로 사라지면서 진폭이 크게 감소하였다. 또한, 희박노즐 개수가 증가할수록 당량비 감소와 같은 현상이 나타나는 것을 확인하였다.

• 대한후두음성언어의학회지
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• 제32권3호
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• pp.124-129
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• 2021

Background and Objectives This study compares Vocal Fatigue Index (VFI) scores according to the presence or absence of external laryngeal tension in hyperfunctional voice disorder. And through this, it is to confirm the usefulness of VFI to hypertension of extrinsic laryngeal muscles. Materials and Method The subjects were 61 female diagnosed with hyperfunctional voice disorder (hypertension group 41, non-hypertension group 20). The author palpated extrinsic laryngeal muscles for evaluation of hypertension and classified them as the presence or absence. The voice measurements were jitter, shimmer, Korean-Voice Handicap Index-10 (K-VHI-10), and Korean-Vocal Fatigue Index (K-VFI). The voice compared were according to the diagnosis and presence of hypertension only for patients with hyperfunctional voice disorder. Results As a result of comparing the voice measurement according to the presence or absence of hypertension, there was no significant difference in the acoustic variables, K-VHI-10 and K-VFI-Total, K-VFI-Fatigue. Whereas, K-VFI-Physical (p=0.006) and K-VFI-Rest (p=0.022) were significantly higher in the hypertension group. Conclusion These results indicate that the hypertension group has more physical discomfort and less voice recovery than the group without hypertension. It means that K-VFI can measure the physical discomfort and limitations of voice recovery due to hypertension of the external laryngeal muscle. The VFI can be used as one of the methods to evaluate the hypertension of the external laryngeal muscle in Hyperfunctional voice disorder.

• Nuclear Engineering and Technology
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• 제54권6호
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• pp.2107-2119
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• 2022

Accurate remaining useful life (RUL) prediction for critical components of nuclear power equipment is an important way to realize aging management of nuclear power equipment. The electric gate valve is one of the most safety-critical and widely distributed mechanical equipment in nuclear power installations. However, the electric gate valve's extended service in nuclear installations causes aging and degradation induced by crack propagation and leakages. Hence, it is necessary to develop a robust RUL prediction method to evaluate its operating state. Although the particle filter(PF) algorithm and its variants can deal with this nonlinear problem effectively, they suffer from severe particle degeneracy and depletion, which leads to its sub-optimal performance. In this study, we combined the whale algorithm with regularized particle filtering(RPF) to rationalize the particle distribution before resampling, so as to solve the problem of particle degradation, and for valve RUL prediction. The valve's crack propagation is studied using the RPF approach, which takes the Paris Law as a condition function. The crack growth is observed and updated using the root-mean-square (RMS) signal collected from the acoustic emission sensor. At the same time, the proposed method is compared with other optimization algorithms, such as particle swarm optimization algorithm, and verified by the realistic valve aging experimental data. The conclusion shows that the proposed method can effectively predict and analyze the typical valve degradation patterns.

• 한국음향학회지
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• 제40권2호
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• pp.161-168
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• 2021

본 논문에서는 발성하고 있는 입 주변에 40 kHz의 주파수를 갖는 초음파 신호를 방사하고 되돌아오는 신호의 도플러 변이를 검출하여 발성음을 합성하는 무 음성 대화기술을 제안하였다. 무음성 대화 기술에서는 비 음성 신호로 부터 추출된 특징변수와 해당 음성 신호의 파라메터 간 대응 규칙을 생성하고 이를 이용하여 음성신호를 합성하게 된다. 기존의 무 음성 대화기술에서는 추정된 음성 파라메터와 실제 음성 파라메터간의 오차가 최소화되도록 대응규칙을 생성한다. 본 연구에서는 추정 음성 파라메터가 실제 음성 파라메터의 분포와 유사하도록 생성적 적대 신경망을 도입하여 대응 규칙을 생성하도록 하였다. 60개 한국어 음성을 대상으로 한 실험에서 제안된 기법은 객관적, 주관적 지표상 으로 기존의 신경망 기반 기법보다 우수한 성능을 나타내었다.

• 한국전자통신학회논문지
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• 제18권1호
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• pp.71-76
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• 2023

본 논문은 음향잡음감쇠기에서 신경망 구조의 Wiener 필터를 이용하여 비선형 잡음을 감쇠시키는 방법에 대하여 연구하였다. 이 시스템은 기존의 적응필터를 이용하는 대신 신경망 위너필터를 이용한 심층학습 알고리즘으로 비선형 잡음감쇠 성능을 개선한다. 128-neuron, 8-neuron 은닉층과 오차 역전파(back propagation) 알고리즘을 이용하여 비선형 잡음이 포함된 단일입력 음성신호로부터 음성을 추정한다. 본 연구에서 비선형 잡음에 대한 감쇠 성능을 검증하기 위하여 Keras 라이브러리를 사용한 시뮬레이션 프로그램을 작성하고 모의실험을 수행하였다. 모의실험 결과, 본 시스템은 비선형 잡음이 포함되어 있는 경우에도 위너필터 대신 FNN 필터를 사용하면 잡음감쇠 성능이 상당히 개선되는 것을 볼 수 있다. 이는 FNN 필터의 복잡한 구조가 어떤 형태의 비선형 특성도 잘 표현하기 때문이다.

• 한방안이비인후피부과학회지
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• 제36권2호
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• pp.45-59
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• 2023

Objectives : The purpose of this study is to analyze the various methods of sound therapy(ST) applied to tinnitus patients and their effectiveness, and to suggest an effective method that can be applied in clinical settings. Methods : Studies published from January 2018 to March 2023 were searched on 5 databases(Pubmed, RISS, OASIS, KISS, KCI). All RCTs that applied sound therapy as a main treatment method were included. Results : 14 studies were included. In 13 studies, sound therapy was statistically significant in improving tinnitus. Basic sound therapy was used in 6 studies(42%), followed by tinnitus rehabilitation therapy(TRT)(n=5, 35%). White noise(n=11, 75%) and nature sound(n=4, 28%) were the most frequently used sound sources. In the case of intensity, mixing point were the most common with 6 studies(42%). The mobile application(n=4) was the most frequently used implement. The application time of sound therapy per day was more than 3 hours(n=7), and the total treatment period was more than 3 months(n=9). Conclusions : Our findings indicate that sound therapy could be considered as an intervention for tinnitus patients. For better use, we suggest a basic type of sound therapy or TRT using white noise or nature sound at the mixing point level provided as a mobile phone application. In addition, the treatment period is recommended to be more than 3 hours/day for 3 months.

• 대한음성학회:학술대회논문집
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• 대한음성학회 1996년도 10월 학술대회지
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• pp.514-514
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• 1996

Igbo, a new Benue Congo language has a vowel harmony system which, like that of Akan, is based on the pharynx size or tongue root position. In this study we examine Igbo vowel harmony with particular reference to assimilatory patterns of vowels in different harmony sets. This is to gain some insight into the factors involved in Igbo vowel assimilation, and to establish to what extent reports on Akan vowel assimilation are validated in Igbo. Tokens of the eight phonemic vowels of Standard Igbo are recorded from three native speakers of Igbo. The vowels are acoustically investigated (using the LPC analysis of CSL) in individual lexical items and within carefully designed carrier phrases. The F1 and F2 values of the vowels are obtained as these formant values are generally useful in establishing the salient characteristics of vowels. Vowels from the harmony sets are juxtaposed in the carrier phrases to ascertain the extent of assimilation. Results of the investigation show that the F1 values, to a large extend, are enough to characterize these vowels. The (-Expanded) vowels have higher F1 values than their (+Expanded) counterpart. Where there is an overlap in F1 values for some vowels the F1 bandwidth values serve to distinguish between the vowels. The overlap often reported in Akan for /I/ and /e/ on the one hand and /${\mho}$/ and /o/ on the other is not validated in Igbo. While the F1 values for these pairs of vowels are quite similar for one of our speakers, there is an appreciable difference between the F1 values of these vowels for the other two speakers. There is however an overlap for /e/ and /o/ for one of the speakers. Assimilations are generally regressive across word boundaries. It is, however, necessary to point out that the general perceptual impression that one of the vowels completely assimilates to the other, is not borne out by our investigation. Most of our F1 and F2 values for the vowels in individual lexical items are altered in assimilations. This then suggests that assimilation involving these vowels is partial rather than complete. The emerging 'allophones' are acoustically similar to the (+Expanded) vowel involved in the assimilation, that is when vowels from different harmony sets are involved. We conclude that while assimilation of Igbo vowels involves some phonological considerations, phonetic factors appear to be permanent in deciding the final form of the vowels.