• 한국해양공학회지
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• 제20권1호
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• pp.48-54
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• 2006

In this paper, flowfield and acoustic-field around moving bodies are simulated by the Arbitrary Lagrangian Eulerian (ALE) formulation in the finite difference lattice Boltzmann method. Some effects are checked by comparing flaw about a square cylinder in ALE formulation and that in the fixed coordinates, and both agree very well. Matching procedure between the moving grid and fixed grid is also considered. The applied method in which the both grids are connected through buffer region is shown to be superior to moving overlapped grid. Dipole-like emissions of sound wave from harmonically vibrating bodies in two- and three-dimensional cases are simulated.

• 한국수산과학회지
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• 제50권5호
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• pp.605-615
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• 2017

A multi-resonant broadband acoustic transducer with six Tonpilz elements operating at different resonant frequencies in a transducer assembly was fabricated, tested, and analyzed. A compensated transducer, modified by adding series inductance to the developed multi-resonant broadband transducer, was shown to provide improved bandwidth performance with a relatively more uniform frequency response compared with the uncompensated transducer. By controlling the series inductance, flat frequency response characteristics at two frequency bands were obtained over the range 38-52 kHz with 1.1 mH inductance and 50-60 kHz with 0.4 mH inductance. These results suggest that the operating frequency of the developed multi-resonant broadband transducer in a chirp echo sounder can be shifted to a different frequency band that is optimized according to the environment for more effective echo surveys of fishing grounds.

• 한국소음진동공학회논문집
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• 제17권4호
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• pp.289-297
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• 2007

SAFRS is the system designed to reproduce the harmonic sound into the space according to the environmental factors. Here the harmonic sound means the sound which judged by the subjective tests, and the methods were suggested in the former studies. In this research, SAFRS was applied into the Square of D University to evaluate and verify the effectiveness of the system and a few evaluations were carried out as follows; 1) sound perception, frequency, volume and harmony with the space, 2) images of the square and acoustic environment and 3) acoustic environment with existing sounds, fountain sound, produced sound by SAFRS, and both of them respectively. The results can be summarized as follows; 1) According to the evaluation on acoustic environment, no relationships were shown between the cognition of sounds produced by SAFRS and the frequency or volume, but inverse proportion was shown between the volume and special harmony. 2) As the result of image evaluation. the relationship between space and sound image was shown proportional only except the evaluation on main road at night time, it means that the sound proposal with the visual contents matching with the sounds would be more effective than the proposal of sound only. 3) Results of evaluation on acoustic environment showed that the cognition effect at night time was shown higher than that of day time when only the acoustic element was given and the effect was increased when the visual elements matches with the acoustic elements if both of them were given. It confirmed the harmony between visual and acoustic elements was very important.

• Journal of Electrical Engineering and Technology
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• 제13권6호
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• pp.2434-2440
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• 2018

A new type of piezoelectric micromachined ultrasonic transducer (pMUT) with high resonant frequency was developed by using a thin lead zirconate titanate (PZT) as an insulation layer on a floating $10{\mu}m$ silicon membrane. The PZT insulation layer facilitated acoustic impedance matching at active pMUT, leading to a high performance in the acoustic conversion property compared with the transducer using $SiO_2$ insulation layer. The fabricated ultrasonic devices were wirelessly measured by connecting two identical acoustic transducers to two separate ports in a single network analyzer simultaneously. The acoustic wave emitted from a transducer induced a $3.16{\mu}W$ on the other side of the transducer at a distance of 2 cm. The transducer performances in terms of device diameters, PZT thickness, annealings, and different DC polings, etc. were investigated. COMSOL simulation was also performed to predict the device performances prior to fabrication. Based on the COMSOL simulation, the device was fabricated and the results were compared.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.1205-1205
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• 2003

Rotary compressors are one of the most important parts of air-conditioners in the industry This device usually has noise problems during the circulation process of the refrigerant and muffler is used for the noise reduction. The acoustic performance of the muffler depends on its shape and its hole locations on the upper surface. Therefore finding the optimum location of the muffler holes is a topic of increasing importance in the compressor industry. In this research the optimization of the muffler hole locations and the importance of the resonator cavity on the lower surface of the muffler in acoustic point of view is studied. At first, the topology optimization for the 2 hole muffler is performed based on a model without resonator cavity by using genetic algorithm. The 2 hole muffler's acoustic analysis and experiment results are matching, however, the optimized model's results are not. By adding the resonator cavity and also by changing the cavity shape, the acoustic analysis and experiment result comparison is Performed for different cavity shapes. The topology optimization of the revised model with cavity is carried out for noise reduction. Finally, the optimized design is produced and tested for validation.

• 비파괴검사학회지
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• 제36권1호
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• pp.9-17
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• 2016

The elastic modulus of a 3D-printed Kelvin foam plate is investigated by measuring the acoustic wave velocity of 1 MHz ultrasound. An isotropic tetrakaidecahedron foam with 3 mm unit cell is designed and printed layer upon layer to fabricate a Kelvin foam plate of 14 mm thickness with a 3D CAD/printer using ABS plastic. The Kelvin foam plate is completely filled with paraffin wax for impedance matching, so that the acoustic wave may propagate through the porous foam plate. The acoustic wave velocity of the foam plate is measured using the time-of-flight (TOF) method and is used to calculate the elastic modulus of the Kelvin foam plate based on acousto-elasticity. Finite element method (FEM) and micromechanics is applied to the Kelvin foam plate to calculate the theoretical elastic modulus using a non-isotropic tetrakaidecahedron model. The predicted elastic modulus of the Kelvin foam plate from FEM and micromechanics model is similar, which is only 3-4% of the bulk material. The experimental value of the elastic modulus from the ultrasonic method is approximately twice as that of the numerical and theoretical methods because of the flexural deformation of the cell edges neglected in the ultrasonic method.

• 한국산학기술학회논문지
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• 제14권7호
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• pp.3191-3196
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• 2013

초음파 센서는 거리를 측정하는 센서이다. 초음파 센서의 피에조 세라믹과 매칭레이어 접착기술이 가장 핵심이 되는 기술이다. 본 논문에서는 초음파를 공기 중으로 발진해 주는 매칭레이어에 대한 관계의 연구와 함께 피에조 세라믹과 매칭레이어를 접착한 경우 변화될 수 있는 결과를 추출하여 제 2의 사용가능 주파수를 발견하는 것이 목적이다. 또한 실제 압전소자인 피에조 세라믹과 케미컬우드인 매칭레이어를 사용하여 실험하였다. 피에조 세라믹의 OD는 ${\Phi}50{\times}3T$로 설계 되었으며 매칭레이어 OD는 ${\lambda}=1/4$인 ${\Phi}62{\times}12t$로 설계하였다. 가장 최적의 공진 주파수는 53 Khz에서 음향 임피던스 값을 나타냈다. 실험결과, 유연성을 가진 접착제 보다 고체에 가까운 접착제를 사용할 경우에 많은 사용가능 주파수를 생성할 수 있는 결과를 얻을 수 있다.

• 한국음향학회지
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• 제19권1호
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• pp.54-60
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• 2000

고차모드를 고려하여 단순확장관을 해석한 많은 선행연구가 이루어 졌고, 이러한 연구는 모드적합법, 속도포텐셜법, 유한요소법으로 분류할 수 있다. 이들 중 모드적합법은 동심관형확장관을 해석하는 데 유용하다. 일반적으로 입·출구의 단면적이 중간확장관의 단면적보다 작으므로 입·출구에 고려하는 고차모드의 개수는 중간확장관에 고려하는 고차모드의 개수보다 작을 수 있다. 그러나 모드적합법은 입·출구와 중간확장관에 같은 개수의 고차모드를 사용하여야 한다. 그래서 입·출구에 불필요한 고차모드를 포함하게 되어 계산시간을 늘이는 결과를 초래한다. 본 논문에서는 입구, 중간확장관 그리고 출구에 각각 임의의 고차모드의 개수를 선택할 수 있는 새로운 방법을 제시하였다. 그리고 이 방법의 정확성을 검증하기 위하여 전통적인 모드적합법, 유한요소법과 비교하였고, 이 새로운 방법이 계산시간을 줄일 수 있다는 것을 보였다.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 후기학술대회논문집
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• pp.248-249
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• 2005

In this paper, flowfield and acoustic-field around moving bodies are simulated by the Arbitrary Lagrangian Eulerian (ALE) formulation in FDLBM. The effect of the ALE is checked by comparing flow about a square cylinder in ALE formulation and that in the fixed coordinates, and the results show good agreement. Matching procedure between the moving grid and fixed grid is also considered. The applied method in which the both grids are connected through buffer zone is shown to be superior to moving overlapped grid. Dipole-like emissions of sound wave from harmonically vibrating bodies in 2- and 3-dimensional cases are simulated.

• 한국수산과학회지
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• 제54권6호
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• pp.1036-1044
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• 2021

A linear array acoustic transducer with 12 tonpilz elements mounted independently on a gradual wedge-shaped tail mass was fabricated, tested and analyzed. The compensated transducer, which is modified by including a series inductance of 137 µH in the developed linear array transducer, attained improved figure of merit (FOM) performance characteristics compared with the uncompensated transducer. The four resonant frequency bands were identified from the measured FOM curve. The FOM response patterns over the frequency ranges of 31 to 40 kHz and 50 to 60 kHz were relatively uniform, whereas sharp resonance peaks were observed at around 73 kHz and 84 kHz. These results indicate that the developed linear array transducer can be used as an enhanced broadband transducer of echo sounder, and the operating frequency can be selected for more effective echo surveys in the fishing ground.