• Journal of Aerospace System Engineering
• /
• v.17 no.2
• /
• pp.26-37
• /
• 2023

Urban air mobility (UAM) is being developed as part of the next-generation aircraft, which could be a viable solution to entrenched problems of urban traffic congestion and environmental pollution. A new airport platform called vertiport as a space where UAM can take off and land vertically is also being introduced. Noise regulations for UAM will be strict due to its operation in a highly populated urban area. Ground effects caused by vertiport can directly affect aerodynamic forces and noise characteristics of UAM. In this study, ground effects of vertiport on aerodynamic loads, vorticity field, and far-field noise were analyzed using Lattice-Boltzmann Method (LBM) simulation and Ffowcs Williams and Hawkings (FW-H) acoustic analogy with a permeable surface method.

• The Journal of the Convergence on Culture Technology
• /
• v.6 no.2
• /
• pp.509-514
• /
• 2020

The conventional TTS system consists of several modules, including text preprocessing, parsing analysis, grapheme-to-phoneme conversion, boundary analysis, prosody control, acoustic feature generation by acoustic model, and synthesized speech generation. But TTS system with deep learning is composed of Text2Mel process that generates spectrogram from text, and vocoder that synthesizes speech signals from spectrogram. In this paper, for the optimal Korean TTS system construction we apply Tacotron2 to Tex2Mel process, and as a vocoder we introduce the methods such as WaveNet, WaveRNN, and WaveGlow, and implement them to verify and compare their performance. Experimental results show that WaveNet has the highest MOS and the trained model is hundreds of megabytes in size, but the synthesis time is about 50 times the real time. WaveRNN shows MOS performance similar to that of WaveNet and the model size is several tens of megabytes, but this method also cannot be processed in real time. WaveGlow can handle real-time processing, but the model is several GB in size and MOS is the worst of the three vocoders. From the results of this study, the reference criteria for selecting the appropriate method according to the hardware environment in the field of applying the TTS system are presented in this paper.

• Journal of the Korean Geotechnical Society
• /
• v.25 no.12
• /
• pp.5-12
• /
• 2009

As rock bolts become one of the main support systems in tunnels and underground structures, the integrity of the rock bolts affects the safety of these structures. The purpose of this study is the evaluation of rock bolt integrity using wavelet transforms of the guided ultrasonic waves by using transmission test in the field. After several rock bolts with various defect ratios are embedded into a large scale concrete block and rock mass, guided waves are generated by a piezo disk element and measured by an acoustic emission (AE) sensor. The captured signals are analyzed in the time-frequency domain using the wavelet transform based on a Gabor wavelet. Peak values in the time-frequency domain represent the interval of travel time of each echo. The energy velocities of the guided waves increase with an increase in the defect ratio. The suitable curing time for the evergy velocity analysis is proposed by the laboratory test, and in-situ tests are performed in two tunnelling sites to verify the applicability of rock bolt integrity tests performed after proposed curing time. This study proves that time-frequency domain analysis is an effective tool for the evaluation of the rock bolt integrity.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.32 no.5
• /
• pp.342-350
• /
• 2008

The effects of combustion instability on flow structure and flame dynamics with the inlet configurations in a model gas turbine combustor were investigated using large eddy simulation (LES). A G-equation flamelet model was employed to simulate the unsteady flame behaviors. As a result of mean flow field, the change of divergent half angle($\alpha$) at combustor inlet results in variations in the size and shape of the central toroidal recirculation (CTRZ) as well as the flame length by changing corner recirculation zone (CRZ). The case of ${\alpha}=45^{\circ}$ show smaller size and upstream location of CTRZ than those of $90^{\circ}$ and $30^{\circ}$ by the development of higher swirl velocity. The flame length in the case of ${\alpha}=45^{\circ}$ is shorter than other cases, while the case of ${\alpha}=30^{\circ}$ yields the longest flame length due to the decrease of effective reactive area with the absence of CRZ. Through the analysis of pressure fluctuation, it was identified that the case of ${\alpha}=45^{\circ}$ shows the largest damping effect of pressure oscillation in all configurations and brings in the noise reduction of 2.97dB, compared to that of ${\alpha}=30^{\circ}$ having the largest pressure oscillation. These reasons were discussed in detail through the analysis of unsteady phenomena related to recirculation zone and flame surface. Finally the effects of flame-acoustic interaction were evaluated using local Rayleigh parameter.

• Journal of Sensor Science and Technology
• /
• v.22 no.4
• /
• pp.249-255
• /
• 2013

Gas-sensor array technology, which has been much utilized in the field of food technology by the name of 'electronic nose' is drawing attention in diagnosing lung cancer based on the analysis of the exhaled human breath. Much understanding has been accomplished about the composition of the volatile organic compounds (VOCs) of the human exhaled breath, in spite of some variations depending on research groups due mainly to lack of the standardization of the sensing procedures. Since VOCs may be produced during the process of cellular metabolism, difference in the cellular metabolism between healthy cells and lung cancer cells are expected to be reflected on the composition variation of the exhaled VOCs. Several studies have attempted to apply the gas-sensor array technology to lung cancer analysis using many different types of sensors including metal oxide, carbon black-polymer composite, surface acoustic wave, and gold nanoparticles. In this mini-review VOC as biomarkers, sensor array technology and application of the array technology for the diagnosis of cancer disease have been described.

• Korean Journal of Food Science and Technology
• /
• v.38 no.1
• /
• pp.16-21
• /
• 2006

Effect of heat (160, 190, and $220^{\circ}C$ for 24 hr) on coconut oil was examined by principal component analysis using electronic nose consisting of six metal oxide sensors. Increase in heating temperature decreased ratio of resistance and first principal component score (from +0.952 to -0.325), indicating rancidity of coconut oil increased at high heating temperature. Result of electronic nose based on GC with surface acoustic wave sensor showed significant changes in volatile profiles of coconut oil. High resolution olfactory imaging $(VaporPrint^{TM})$ was particularly useful for evaluating oil quality. Peak numbers and areas increased with increasing heating time and temperature (160, $220^{\circ}C$). Electronic nose analysis can provide simple, fast, and straightforward results and is best suited for quality control and process monitoring in flavor field of food industry.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.12 no.11
• /
• pp.4732-4737
• /
• 2011

A standing grinder with a vacuum dust collection, which works grinding a surface and collecting dust occurred simultaneously, is needed to clean the surface before painting, or to remove a weld bead burr in the industrial field. In recent it trends to be compact and potable with high grinding and dust collection power, and low noise. As increasing these grinding and dust collection power, the noise and weight of standing grinder occurs an important problem. To solve these problem, an efficient cyclone separator was designed and developed by Ansys-CFX analysis and experiments. A weight of the developed grinder part was 5.9kg, which can be easily handled on standing by workers. and a noise level of the developed prototype was measured 69.9 dB(A).

• Journal of the Korean Society for Nondestructive Testing
• /
• v.26 no.2
• /
• pp.77-83
• /
• 2006

Ultrasonic nonlinearity has been considered as a solution for the detection of microcracks or interfacial delamination in a layered structure. The distinguished phenomenon in nonlinear ultrasonics is the generation of higher-order harmonic waves during the propagation. Therefore, in order to quantify the nonlinearity, the conventional method measures a parameter defined as the amplitude ratio of a second-order harmonic component and a fundamental frequency component included in the propagated ultrasonic wave signal. However, its application In field inspection is not easy at the present stage because no standard methodology has yet been made to accurately estimate this parameter. Thus, the aim of this paper is to propose an advanced signal processing technique for the precise estimation of a nonlinear ultrasonic parameter, which is based on power spectral and bispectral analysis. The method of estimating power spectrum and bispectrum of the pulse-like ultrasonic wave signal used in the commercial SAM (scanning acoustic microscopy) equipment is especially considered in this study The usefulness of the proposed method Is confirmed by experiments for a Newton ring with a continuous air gap between two glasses and a real semiconductor sample with local delaminations. The results show that the nonlinear parameter obtained tv the proposed method had a good correlation with the delamination.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1992.10a
• /
• pp.113-116
• /
• 1992

소음의 발생 원인은 공기역학적 측면과 구조적 측면으로 나누어지는데, 실제 로는 유동장에서 발생되는 음원과 구조물에서 발생되는 진동과의 상호 간섭 에 의해 보다 복잡한 형태로 발생된다. 음장 문제를 두가지 범주로 구분하면 첫째는 음원과 구조물과의 상호교란에 의한 산란문제(Scattering)와 둘째로 구조물의 자체 진동에 의한 음의 전파현상과 구조물내부에 회전체와 같은 음원이 존재하는 경우에 음의 전파를 관측하는 방사문제(Radiation)가 있다. 실제로 산업용 터빈이나 비행기 엔진 흡입구에서 발생되는 소음, 또는 자동 차의 배기구를 통해 발생되는 소음 그리고 엔진의 진동에 의한 구조적 소음, 기타 가전제품의 회전체(Fan & Motor)에 의한 소음은 방사(Radiation)의 문 제로서 중요 관심 과제이다 수치적 기법으로 근래에 많이 사용하는 방법으 로 BEM(경계요소법), FEM(유한요소법), FDM(유한차분법)이 있는데 본 연 구에서는 유한요소법을 이용하기로 한다. 지금까지는 주로 BEM을 통해서 Far-Field의 음향장을 해석하였지만 복잡한 형상을 갖는 구조물내부에서의 음향장 변화나 구조물 내부에 음원이 존재하는 경우 또는 구조물 자체가 갖 는 물리적 특성치 변화 즉 물체표면에서의 부분 진동문제의 음향장 해석에 있어서 가장 잘 대체해 나갈 수 있는 방법이 유한 요소법이라고 여겨진다. 본 연구에서는 2차원 또는 기하학적으로 축대칭인 3차원 Duct내부에 음원이 존재하는 경우 음원전파에 따른 Near-field와 far-field에서 음의 방향성을 예측하기 위해 먼저 기본적인 유한요소법에 의한 Robin 경계조건을 사용하 여 계산된 결과와 Infinite Element를 도입하여 계산할 결과를 비교하여, Infinite Element가 보다 효율적이며 타당한 결과를 얻음을 확인해 보기로 한다.다 복합적인 측면에서 치료에 임하여야 할 것으로 사료된다. with such configuration.trap with 2.88[eV] deep of injected space charge from the chathode in the crystaline regions. The origin of ${\alpha}$$_2$ peak was regarded as the detrapping process of ions trapped with 0.9[eV] deep originated from impurity-ion remained in the specimen during production process of the material, in the crystalline regions. The origin of ${\beta}$ peak was concluded to be due to the depolarization process of "C=0"dipole with the activation energy of 0.75[eV] in the amorphous regions. The origin of ${\gamma}$ peak was responsible to the process combined with the depolarization of "CH$_3$", chain segment, with the activation energy of carriers from the shallow trap with 0.4[eV], in he amorphous regions.의 증발산율은 우기의 기상자료를 이용하여 구한 결과 0.05 - 0.10 mm/hr 의 범위로서 이로 인한 강우손실량은 큰 의미가 없음을 알았다.재발이 나타난 3례의 환자

• The Journal of the Acoustical Society of Korea
• /
• v.32 no.4
• /
• pp.287-293
• /
• 2013

We present a parametric array signal generating system using $3{\times}16$ transducer array which is composed of multi-resonant frequency transducers of 20kHz and 32.5kHz. To drive transducer array, sixteen channel amplifier using LM1875 chips is designed and implemented, and the PXI system based on the LabView 8.6 for arbitrary signal generation and analysis is used. Using the proposed system, we measure sound pressure level and beam pattern of difference frequency and verify the nonlinear effect of difference frequency. The theoretical absorption range and the Rayleigh distance are 15.51m and 1.933m, respectively and we verify that sound pressure of difference frequency is accumulated and increased at the near-field shorter than the Rayleigh distance. We verify that the beam pattern of the measured difference frequency and the beam pattern obtained by the superposition of two primary frequencies are similar, and high directional parametric signal was generated.