• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.851-856
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• 2012

Automotive turbochargers have become common in gasoline engines as well as diesel engines. They are excellent devices to effectively increase fuel efficiency and power of the engines, but they unfortunately cause several noise problems. The noises are classified into mechanical noises induced from movement of a rotating shaft and aerodynamic noises by air flow in turbochargers. The mechanical noises are whine and howling noises, and the aerodynamic noises are BPF (blade-passing frequency), pulsation, surge, some special frequency noises. These noises are bothering passengers because their levels are higher or their frequencies are clearly separated from engine or vehicle noises. The noise investigated in this paper is a BPF noise induced by compressor wheels, whose frequency is the multiplication of the number of compressor wheel blades and its rotational speed. The noise is strongly dependent upon the geometry of wheels and the number of blades. This study tried to apply a groove close to the inlet side of compressor wheels in order to reduce the BPF noise. The groove has successfully reduced the noise of narrow band frequency of a turbocharger. It shows that the groove could reduce the wide band frequency noise, the compressor BPF noise with a best shape of the groove.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10a
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• pp.456-459
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• 1993

CADET is used to analyze the performance of the missile. Miss distance is calculated for a given lateral fin force saturation level due to the aerodynamic characteristics, target acceleration, and glint and fading noises which is assumed as Gaussian noises. As .alpha.-.betha. filter is studied to attenuate the noises, the results are compared with those of without filter. For the easy simulation, the transfer function of a discrete .alpha.-.betha. filter is converted into the continuous model. Simulation results show that the results of CADET simulation is similar to those of Monte-Carlo simulation. Moreover CADET is the better in computing time demand.

• Journal of the Korean Society for Railway
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• v.15 no.3
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• pp.231-236
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• 2012

In this paper, aerodynamic noise characteristics of high-speed trains were deduced from the beamforming method. First, pass-by noise of high-speed trains was measured by a microphone array system. This measurement suggested that the majority of the aerodynamic noise produced came from the bogie area, the pantograph and its cover, and inter-coach gaps. Then, beampower outputs of a position in high-speed trains were obtained from the beamforming method. By Fourier transform, sound characteristics of the position in the frequency domain were deduced from the beamforming power spectrum. From this study, aerodynamic noise characteristics from the major sources of high-speed trains were drawn.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.8-15
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• 2005

Aerodynamic sounds generated by a uniform flow around a two-dimensional circular cylinder at Re=150 are simulated by applying the finite difference lattice Boltzmann method. Thethird-order-accurate up-wind scheme (UTOPIA) is used for the spatial derivatives, and the second-order-accurate Runge-Kutta scheme is applied for the time marching. We have succeed in capturing very small pressure fluctuations with the same frequency of the Karman vortex street compared with the pressure fluctuation around a circular cylinder. The propagation velocity of the acoustic waves shows that the points of peak pressure are biased upstream due to the Doppler effect in the uniform flow. For the downstream, on the other hand, it is faster. It is also apparent that the amplitude of sound pressure is proportional to r /sup -1/2/,r being the distance from the center of the circular cylinder. To investigate the effect of the lattice dependence, furthermore, 2D computations of the tone noises radiated by a square cylinder and NACA0012 with a blunt trailing edge at high incidence and low Reynolds number are also investigate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.212-217
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• 2008

Acoustic noises generated during motor operation in mechanical system are from electromagnetic, mechanical, aerodynamic, and electrical sources. For identification of mechanical noise origins, misalignment, unbalance, fan shape, resonance, and vibration modes have been extensively considered to describe noise behavior. An experiment-based approach as well as a mathematical approach needs to be adopted for a realistic study into noise and vibration of the motor, because motor noise characteristics differ from type to type due to various noise sources. In this paper, a brushless DC motor for air-conditioner fan is analyzed by finite element method to identify noise source, and the analysis results are verified by experiments, and sensitivity analysis is performed by design of experiments.

• Journal of computational fluids engineering
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• v.18 no.2
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• pp.26-34
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• 2013

In modern days, automobiles are the most important means of transportation. With the development of automobiles, noises generated during operation has been recognized as a significant factor of performance to provide drivers with better driving environment along with other passengers. In this study, drone noise(pulsating noise), generated at the rear window when its opened, is predicted to understand the physics of its phenomenon at various velocities. The compressible Navier-stokes equation will be used with $6^{th}$ order compact finite difference scheme to analyze the characteristics.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.115-122
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• 2007

The noises which occurs from the rolling stock can be divided largely into three classes and they are Rolling noise, Traction noise and Aerodynamic noise. In the event of braking the rolling stock which enter into the station, Brake shoes cause Fraction noise (braking noise) and excessive braking noise makes passengers and operators uncomfortable. This study is to reduce squeal noise and minimize displeasure by measuring the braking noise and defining the major noise sources and noise mechanism

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.9
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• pp.863-869
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• 2009

Acoustic noises generated during motor operation in mechanical system are from electromagnetic, mechanical, aerodynamic and electrical sources. For identification of mechanical noise origins, misalignment, unbalance, fan shape, resonance, and vibration modes have been extensively considered to describe noise behavior. An experiment-based approach as well as a mathematical approach needs to be adopted for a realistic study into noise and vibration of the motor, because motor noise characteristics differ from type to type due to various noise sources. This paper analyzes noise characteristics of a brushless DC motor for air-conditioner fan, and proves that the test motor noise originates from acoustic modes of airspace in the motor. The motor noise sensitivity analysis by design of experiments reveals that the noise characteristics are closely related to switching frequency and frame thickness.

• Journal of the Korean Society for Railway
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• v.10 no.1 s.38
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• pp.22-28
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• 2007

During the passage of the train, the railway bridge undergoes vibration and noise. The noise of railway bridge can be occurred from various sources. The wheel-rail contact, noise from machinery parts, structural-borne noise, pantagraph noise and aerodynamic noise of the train work in combination. Running train is one of the most important factors for railway bridge vibration. The repeated forces with equidistant axles cause the magnification of dynamic responses which relates with maintenance of the track structure and structure-borne noises. The noise problem is one of the most important issues in services of light rail transit system which usually passes through towns. In the present study, The vibration and noise of the LRT bridge will be investigated with utilizing dynamics responses from moving train as input data for noise analysis.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.6
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• pp.790-798
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• 2018

Discrete noise signals from a small scale tactical unmanned aerial vehicle(UAV) propeller were predicted numerically using time domain approach. Two-bladed 29 inch propeller in diameter and 150 kgf in gross weight were used for main parameters of the UAV based on the actual size of the similar scale vehicle. Panel method and Farassat formula A1 were adopted for aerodynamic and aeroacoustic analysis respectively. Time domain signals of both thickness and loading noises were transformed into frequency domain to analyze the discrete noise characteristics. Directivity pattern in a plane perpendicular to the rotating disc plane and attenuation of noise intensity according to double distance were also presented.