• Journal of the Korean Society for Precision Engineering
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• v.19 no.5
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• pp.168-175
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• 2002

The hydraulic acoustic attenuator fur an automotive active suspension system is so highly nonlinear and of high order that the analysis in time-domain has been performed quite little. In this paper, a state-space representation of the dynamics for a hydraulic attenuator was presented utilizing the electrical analogy. And the results of experiment were compared with those of simulation to validate the state-space model proposed. The comparison revealed that the state-space model proposed is practically applicable to estimate the dynamic responses of the hydraulic attenuator in time-domain.

• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.115-120
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• 1998

Aerodynamic noise generated by automobile cooling fan is investigated. Automobile cooling fans radiate both discrete frequency noise as well as broadband noise. In the present work, the former is considered through free-wake panel method coupled with acoustic analogy fully considering the retarded time variation on the blade surface, while the latter is taken into account by three well-established broadband noise components. Experiments were performed to supplement necessary inputs as well as to provide the final comparison with the predicted noise spectrum. The predicted noise levels at blade passing frequencies agree well with the experimental data for the first few harmonics. Although the predicted broadband noise levels at higher frequencies fall below the experimental data due to the fundamental shortcomings of the utilized formulations, the analysis offers a detailed physical understanding of the fan noise generation processes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.768-773
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• 2001

The self-noise from blade cascade at off-design points mainly comes from separated boundary layer and vortex sheddings, and is also dependent on blade shape. If the incidence angle to the cascade increases, the stalling in blades may occur and the noise level increases significantly. The hybrid method using acoustic analogy was employed to compute the far-field noise spectra and directivity patterns from the separated vortex shedding at off-design points of the cascade of impeller. This paper is compared with the experimental data of a stationary cascade in the same conditions. The simulated result is in excellent .agreement with the measured data except th slight under-prediction near the maximum radiation angle for a dipole sound.

• The Journal of the Acoustical Society of Korea
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• v.16 no.1E
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• pp.29-34
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• 1997

Numerical prediction of aerodynamic noise radiated by subsonic rotors are carried out. A computer program has been developed which incorporates both the discrete frequency noise as well as the broadband noise arising from the ingestion of turbulence. Acoustic analogy is used in conjunction with Homicz's formulation of turbulence ingestion noise. Formulation 1A of Farassat is used to enhance the numerical analysis performance of Ffowcs-Williams Hawkings equation by eliminating the numericla time differentiation. Homicz's trubulence ingestion noise prediction technique is used to understand the characteristics of broadband noise radiated by isotropic trubulence in gestion. Numerical predictions are carried out for a number of rotor configurations and compared with experimental data. Monopole consideration of transonic rotor agrees well with both the experimental data and the linear theory. Noise radiation characteristics of rotor at lifting hover are investigated utilizing simple blade loading obtained by thin wing section theory. By incorporating discrete noise prediction of steady loading with broadband spectrum, much better agreement with experimental data is obtained in the low frequency region. The contributions from different noise mechanisms can also be analyzed through this method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.847-847
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• 2004

Automobile cooling fans are operated with a radiator module. To design low noise, high performance cooling fan, radiator resistance should be considered in the design process. The system (radiator) resistance reduces axial velocity and increases effective angle of attack. This increasing effective angle of attack mechanism causes blade stall, performance decrease and noise increase. In this paper, To analyze fan performance, freewake and 3D CFD calculations are used To design high performance fan with consideration of system resistance, optimal twist concept is applied through momentum and blade element theory. To predict fan noise, empirical formula and acoustic analogy methods are used.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.84-90
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• 2000

Integrated tools are developed for the analysis of the aerodynamic performance and aeroacoustics of helicopter rotors. Heli-NK(Helicopter Navier-Stokes & Kirchhoff) code is for hovering and heli-PA(Helicopter Panel & Acoustic analogy) for forward flight. The former showed its ability to predict the hovering efficiency and high-speed impulsive noise level. Thrust calculation, noise levels, and noise directivity patterns are investigated to confirm the availability of the latter. With some proper validation and improvements. these codes will be more useful and practical.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1386-1392
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• 2000

This paper presents a new prediction method of radiated noise from grille of the airconditioning appliance. Laminar vortex sheddings behind a circular cylinder are simulated by solving two dimensional unsteady incompressible Navier-Stokes equation. The Finite Elements Method(FEM) and unstructured grid generation technique are applied to solve, the unsteady lift/drag coefficients are obtained to compute far-field noise using Lighthill's acoustic analogy. Grille is divided into some cylinder segments, and radiated noise from grille is obtained by summing noise generated from each segment. The effects of changing cross section of cylinder and grille geometry are studied. And sound pressure levels radiated from typical H-type grille are measured in KAIST anechoic wind tunnel at various inflow conditions and compared with numerical predictions.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.5
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• pp.468-474
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• 2011

Underwater radiated noises from marine vehicles are mostly due to the propulsion systems. Recently, the propeller noise problems are becoming crucial issues in terms of habitability of passenger ships. Especially in military area, propeller noise is directly related to the survivability of submarines and warships, and thus propeller noise analysis and reductions are very important. Generally, propeller noise can be classified into non-cavitating noise and cavitating noise which is dominant. In this paper the methodology of propeller noise analysis is announced and new approach to consider scattering effect is proposed. Unsteady blade surface pressure and sheet cavity volume analyzed with potential based panel method are used as noise source.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.475-481
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• 2011

Underwater radiated noises from marine vehicles are mostly due to the propulsion systems. Recently, the propeller noise problems are becoming crucial issues in terms of habitability of passenger ships. Especially in military area, propeller noise is directly related to the survivability of submarines and warships, and thus propeller noise analysis and reductions are very important. Generally, propeller noise can be classified into non-cavitating noise and cavitating noise which is dominant. In this paper the methodology of propeller noise analysis is announced and new approach to consider scattering effect is proposed. Unsteady blade surface pressure and sheet cavity volume analyzed with potential based panel method are used as noise source.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.166-171
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• 2013

In this study, low noise designs of a Savonius wind turbines are numerically investigated. From a previous study, it was found that the high harmonic components whose fundamental frequency is higher than the BPF were found to be dominant in noise spectrum of a Savonius wind turbine. On a basis of this observation, S-shaped blade tip is proposed as a low design factors that decrease wind turbine noise by inducing phase differences in vortex shedding. The conventional Savonius and S-shaped turbines are investigated using Hybrid CAA method where flow field around the turbine are computed using CFD techniques and the radiated noise are predicted by applying acoustic analogy to the computed flow data. Noise reductions by these design factors are confirmed by comparing the predicted noise levels from these turbines.