• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.681-687
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• 2001

Two-phase cross-flow exists in many shell-tube heat exchangers such as steam generators, condensers and reboilers. An understanding of flow-induced vibration excitation mechanism is necessary to avoid problems due to excessive tube vibration. This paper presents the results of a series of experiments done on tube bundles of different geometries subjected to two-phase cross-flow simulated by air-water mixtures. Normal(30$^{\circ}$) and rotated (60$^{\circ}$)triangular, and normal(90$^{\circ}$) and rotated (45$^{\circ}$) square tube bundle configurations of pitch-to-diameter ratio of 1.2 to 1.5 were tested over a range of mass fluxes from 0 to 1,000kg/$m^2$ㆍ s and void fraction from 0 to 100%. The effects of tube bundle geometry on vibration excitation mechanism such as fluidelastic instability and random turbulence, and on dynamic parameters such as damping and hydrodynamic mass are discussed. A lower pitch-to-diameter results in a higher hydrodynamic mass. The effect of tube bundle configurations on damping and random turbulence excitation is minor. The effect of pitch-to-diameter on the fluidelastic instability, however, is significant.

• 한국소음진동공학회논문집
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• 제16권10호
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• pp.1057-1066
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• 2006

Acoustic streaming Induced by longitudinal vibration at 30 kHz is visualized for a test fluid flow between the stationary glass plate and ultrasonic vibrating surface with particle imaging velocimetry (PIV) To measure an increase in the velocity of air flow due to acoustic streaming, the velocity of air flow in a gap between the heat source and ultrasonic vibrator is obtained quantitatively using PIV. The ultrasonic wave propagating into air in the gap generates steady-state secondary vortex called acoustic streaming which enhances convective cooling of the stationary heat source. Heat transfer through air in the gap is represented by experimental convective heat transfer coefficient with respect to the gap. Theoretical analysis shows that gaps for maximum heat transfer enhancement are the multiple of half wavelength. Optimal gaps for the actual design are experimentally found to be half wavelength and one wavelength. A drastic temperature variation exists for the local axial direction of the vibrator according to the measurement of the temperature distribution in the gap. The acoustic streaming velocity of the test fluid in the gap is at maximum when the gap agrees with the multiples of half wavelength of the ultrasonic wave, which are specifically 6 mm and 12 mm.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 춘계학술대회 논문집
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• pp.911-916
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• 2012

It is important to identify dynamic characteristics of nuclear fuel components. Since the fuel always exposed to turbulent flow, the dynamic contact between grids and rods is one of the fuel failure modes. The dynamic behavior of grids in nuclear fuels is quite complex, since two pairs of spring support are placed in the limited space. The strap in a cell has single spring and double dimples and this paper focuses on investigation of the grid strap(Test Fuel Strap, TFS) vibration in one cell. To identify the grid strap vibration, modal analysis of the strap is performed using Finite Element Method (FEM). Modal testing on a $5{\times}5$ grid structure without rods is performed. The modal testing results are compared to analytic results. In addition, random test considering rod effect is performed about a $5{\times}5$ grid with rods under real contact condition in the air. Finally, the strap vibration of a $5{\times}5$ fuel bundle in INvestigation of Flow INduced vIbraTion(INFINIT) facility is measured in real fluid velocity condition without heating. It is shown that modal frequencies from the test are almost equal to those peak frequencies in the INFINIT test.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.798-803
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• 2003

The objective of the present study is to investigate the changes in the acoustic source characteristics and far-field noise propagation in an incompressible round jet at Re=10000 for single-frequency excitations using large eddy simulation and Lighthill acoustic analogy. We apply excitations at a frequency corresponding to the jet-column mode ($St_{D}=0.85$) or maximum growth rate in the shear layer ( $St_{\theta}=0.017$ ). The acoustic source derived from the Lighthill acoustic analogy is the second spatial derivative of the Reynolds stresses. In the case of $St_{D}=0.85$, vortex ring and large scale structures are dominant sources, whereas in the case of $St_{\theta}=0.017$, the main sources are located at an upstream position along the shear layer than in the uncontrolled case. Also, the far-field noise propagates along the axial direction due to excitation.

• 한국자동차공학회논문집
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• 제9권2호
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• pp.210-215
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• 2001

The pole antenna of vehicles for AM/FM radio broadcasting receptions has many probems, such as damageable mechanical system and noise etc. It is considered that noise is composed of the structural vibration noise and the air flow induced aerodynamic noise. Also we find out that the setting process of a printed on-glass automobile antenna has many difficulties. Recently, the above mentioned problems can be reduced by employing enhanced wiper antenna which utilizes the windshied wiper arm. The new system is a passive antenna. In this study, experiments for the characteristics of a wiper antenna by measuring the SWR, radiation pattern and received powe have been carried out. The experimental results show that the efficiency of the wiper antenna has better performance than any other antenna.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.753-756
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• 2013

The demand for sailing yacht is increasing in consonance the improvement of people's live. These yachts can be dually propelled by wind and by diesel engine power. A singing (humming, whistling) phenomenon induced on the propeller was discovered on a 55-foot catamaran sailing yacht. As a result, an increase in the structural vibration of the stern tube room and propulsion system with abnormal noise was detected due to this flow. In this study, the cause of the phenomenon is investigated and its possible countermeasures proposed.

• 한국소음진동공학회논문집
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• 제24권12호
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• pp.962-968
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• 2014

The lattice Boltzmann method(LBM) has attracted attention as an alternative numerical algorithm for solving fluid mechanics since the end of the 90's. In these days, its intrinsic unsteadiness and rapid increase in computing power make the LBM be more applicable for computing flow-induced noise as well as fluid dynamics. The lattice Boltzmann method is a weakly compressible scheme, so we can get information about both aerodynamics and aeroacoustics from single simulation. In this paper, numerical analysis on Aeolian tone noise generated by tandem-twin square cylinders in duct is performed using the LBM. For simplicity, laminar two-dimensional fluid models are used. To verify the validity and accuracy of the current numerical techniques, numerical results for the laminar duct and the cylinder flows are compared with the analytical solution and the measurement, respectively. Then, aerodynamic noise of the twin tandem square cylinders is investigated. It is shown that the aerodynamic noise from the twin tandem square cylinders can be reduced by controlling the distance between the cylinders.

• 해양환경안전학회지
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• 제21권6호
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• pp.751-758
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• 2015

공조시스템의 소음 예측은 주로 NEBB에서 제안한 경험적인 방법에 의해 수행된다. 그러나, NEBB에서 제안한 방법은 선박에만 있는 대형 덕트의 요소를 반영하지 못하므로 선박에 적용하는데 한계가 있다. 본 논문에서는 선박용 대형 덕트의 소음 예측을 위한 전산해석방법을 연구하였다. 경계요소법을 사용하여 대형 덕트의 단위 길이당 소음 감소량에 대한 추정식을 개발하였고, 경계요소법과 전산유체역학을 사용하여 보강재가 설치된 대형 덕트에서의 유동기인소음을 예측하였다. 유입 유속이 10m/s, 보강재의 종류가 200플랫 바인 경우 100 dB 이상의 큰 소음이 발생하는 것을 알 수 있었다. 또한, 경계요소법과 유한요소법을 사용하여 덕트 투과 소음을 예측하였다. 덕트 내부와 외부의 음압 값 차이는 대략 10~15 dB정도 인 것을 알 수 있었다. 이를 통해 조선소에서는 대형 덕트를 포함한 선박 HVAC 소음 예측을 할 수 있을 것으로 기대한다.

• Journal of Mechanical Science and Technology
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• 제18권9호
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• pp.1648-1660
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• 2004

The suction nozzle of a vacuum cleaner was modified to enhance the power performance and to reduce the airflow-induced acoustic noise. The suction power efficiencies of the vacuum cleaner were measured for various nozzles; (1) original nozzle, (2) original nozzle with modified trench height, (3) original nozzle with modified connecting chamber, and (4) a combination of (2) and (3). In addition, the suction pressure and sound pressure level around the suction nozzle were measured to validate the reduction of acoustic noise. The power efficiency and mean suction pressure increased when the trench height of the suction nozzle was increased. This was attributed to the suppression of the flow separation in the suction channel. Modification of the connecting chamber in the original nozzle, which had an abrupt contraction from a rectangular chamber into a circular pipe, into a smooth converging contraction substantially improved the suction flow into the connecting pipe. When both modifications were applied simultaneously, the resulting suction nozzle was more effective from the viewpoints of aerodynamic power increase and sound pressure level reduction.

• 한국소음진동공학회논문집
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• 제13권2호
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• pp.83-91
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• 2003

Pantograph design Process must be considered in terms of stability of aerodynamics and reduction of aeroacoustics. Furthermore pantograph needs to be insensible to severe circumstance condition like typhoon, tunnel, a change of season. In this paper, robust design of panhead sections is conducted based on the Taguchi's design of experiment method. In the aeroacoustic noise analysis, an acoustic analogy using the Ffowcs Williams and Hawkings(FW-H) equation is used to calculate the flow induced sound pressure level in aeroacoustics. From the near-field CFD analysis data, the far-field noise is predicted at the positions of 25 m away from Pantograph. Based on aerodynamic(CFD) and aeroacoustic(FW-H) analysis data, the optimal sizing and Positioning of panhead elements are determined using robust design optimization method. Design parameters such as thickness, length and radius are controllable factors, while outdoor air temperature and atmospheric pressure are considered as uncontrollable factors in the context of Taguchi's approach. A number of CFD simulation and aeroacoustic analysis are performed based on orthogonal arrays. In this paper, two-step optimization method is used as a parameter design procedure. It is executed using signal to noise(S/N) ratio and analysis of means(ANOM) method. So Thus, an optimal level of design parameters Is extracted to minimize the disconnection ration between contact strips and catenary system, and reduce the far-field aeroacoustic noise.