• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.5
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• pp.402-409
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• 2004

Numerical analysis of static and dynamic wind effects on civil engineering structures was performed. Long-span suspension bridges are flexible structures that are highly sensitive to the action of the wind. Aerodynamic effect often becomes a governing factor in the design process of bridges and aeroelastic stability boundary becomes a prime criterion which should be confirmed during the structural design stage of bridges because the long-span suspension bridges are prone to the aerodynamic instabilities caused by wind. If the wind velocity exceeds the critical velocity that the bridge can withstand, then the bridge fails due to the phenomenon of flutter. Buffeting caused by turbulence results in structural fatigue, which could lead to the failure of a bridge. Navier-Stokes equations are used for the aeroelastic analysis of bridge girder section. The aeroelastic simulation is carried out to study the aeroelastic stability of bridges using both Computational Fluid Dynamic (CFD) and Computational Structural Dynamic (CSD) schemes.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.133-138
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• 2010

This paper describes on aerodynamic characteristics of pantograph system for Next generation high speed train(HEMU-400). The pantograph which supports electric power is located on the roof. Because of this, it generate high drag, severe acoustic noise and vibration which induced unstable flow due to complex configuration. Therefore, the design of high efficient pantograph needs to increase operational speed. In this research, wind tunnel tests were performed to design a high efficient pantograph system using 1/4 scaled model which were KTX-II pantograph, single arm pantograph and periscope type pantograph with square cylinder shape panhead and optimized shape panhead. For real operational condition, flow directions were adapted by rotation of pantograph. From this results of wind tunnel, it is checked that the pantograph with optimized panhead and single arm type or periscope type has better aerodynamic performance. In addition, lift control device and spoiler in pantograph were tested to investigate the validity of application.

• Transactions of the Society of Information Storage Systems
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• v.3 no.4
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• pp.196-201
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• 2007

As the demand for the lap-top computer has been increased, most users ask quiet environment to work comfortably. Therefore, noise problems of an ODD are of great interest. For the high speed ODD, the flow induced noise is caused by the turbulent flow[1], which is known to be a major source of overall noise of a slim type ODD. In this study, we introduce a new attempt to reduce the noise level using the concept of Helmholtz resonator[2].The experimental analysis is carried out for several cases at different resonance frequencies and different hole patterns. The results show reductions in the noise level from the acoustic noise absorption point of view.

• Journal of computational fluids engineering
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• v.3 no.1
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• pp.82-88
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• 1998

As a par of a project related to the development of the design algorithm of a compact heat exchanger for the application of the electronic home appliances, the effect of the discreteness of the airflow boundary generated on the cooling fin surface on the heat transfer and pressure drop characteristics of the heat exchanger was studied numerically. In general, there are two critical design parameters seriously considered in the design of the heat exchanger; heat transfer rate(Q) and pressure drop coefficient(C/sub p/). Even though the higher heat transfer rate with lower pressure drop characteristics is required in a design of the heat exchanger, it is not an easy job to satisfy both conditions at the same time because these two parameters are phenomenally inversely proportional. To control the boundary layer thickness and its length along the streamline, the surface of the flat fin was modified to accelerate the heat transfer rate on the fin surface. To understand the effect of the discreted fin size(S/sub w/) and its location(S/sub h/) on the performance of the heat exchanger in the airflow field, the flat fin was modified as shown in Fig. 1. From this study, it was found that the smaller and more number of slits on the fin surface showed the higher energy diffusion rate. It means that the discreteness of the boundary layer is quite important on the heat transfer rate of the heat exchanger. On the other hand, if the fin surface configuration is very complex than needed, higher static pressure drop occurs than required in a system and it may be a reason of the induced aerodynamic noise in the heat exchanger.

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.95-102
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• 2024

Due to technological advances, the cruising speed of high-speed trains is increasing, and aerodynamic noise generated from the flow outside the train has been an important consideration in the design stage. To accurately predict the flow-induced noise, high-resolution generation of sound sources in the near field and low-dissipation of sound propagation in the far field are required. This should be accompanied by a numerical grid and time resolution that can properly consider both temporal and spatial scales for each component of the real high-speed train. To overcome these challenges, this research simultaneously calculates the external flow and acoustic fields of five high-speed train cars of real-scale and at operational running speeds using a threedimensional unsteady Large Eddy Simulation technique. To verify the numerical analysis, the measurements of the wall pressure fluctuation and numerical results are compared. The Ffowcs Williams and Hawking equation is used to predict the acoustic power radiated from the high-speed train. This research is expected to contribute to noise reduction based on the analysis of the aerodynamic noise generation mechanism of high-speed trains.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.340-346
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• 2013

This paper describes a helicopter vibration induced by main rotor in forward flight. The hub loads in the fixed frame, which are dominant source of helicopter vibration, are obtained by multi-blade summation of rotating blades loadings. The components of 3/rev, 4/rev, and 5/rev blades loadings are transmitted by blades to 4/rev hub loads in the fixed frame. The vertical vibrations of helicopter at pilot seat and copilot seat are calculated through rigid body transfer functions considering airframe to be rigid body. The blades are assumed to be elastic and undergo the flap, lag, and torsion motion and free wake aerodynamic model is used to calculate the precise blade loadings in the analysis. The 4/rev vertical vibration responses are analyzed from rotating blade loadings and fixed hub loadings.

• Journal of computational fluids engineering
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• v.19 no.2
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• pp.66-71
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• 2014

Aerodynamic design of a vehicle has very important meaning on the fuel economy, dynamic stability and the noise & vibration of a moving vehicle. In this study, the correlation of aerodynamic effect between two model vehicles moving inline on a road was studied with the basic SAE model vehicle. Drag and lift are two main physical forces acting on the vehicle and both of them directly effect on the fuel economy and driving stability of the vehicle. For the research, the distance between two vehicles is varied from 5m to 30m at the fixed vehicle speed, 100km/h and the side-wind was assumed to be zero. The main issue for this numerical research is on the understanding of the interaction forces; lift and drag between two vehicles formed inline. From the study, it was found that as the distance between two vehicles is closer, the drag force acting on both the front and rear vehicle decreases and the lift force has same trend for both vehicle. As the distance(D) is 5m, the drag of the front vehicle reduced 7.4% but 28.5% for the rear-side vehicle. As the distance is 30m, the drag of the rear vehicle is still reduced to 22% compared to the single driving.

• The Journal of the Acoustical Society of Korea
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• v.36 no.5
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• pp.314-320
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• 2017

A pressure relief valve is generally used to prevent piping systems from being broken due to high pressure gas flows. However, the sudden pressure drop caused by the pressure relief valve produces high acoustic energy which propagates in the form of compressible acoustic waves in the pipe and sometimes causes severe vibration of the pipe structure, thereby resulting in its failure. In this study, internal aerodynamic noise due to valve flow is estimated for a simple contraction-expansion pipe by combining the LES (Large-Eddy Simulation) technique with the wavenumber-frequency analysis, which allows the decomposition of fluctuating pressure into incompressible hydrodynamic pressure and compressible acoustic pressure. In order to increase the convergence, the steady Reynolds-Averaged Navier-Stokes equations are numerically solved. And then, for the unsteady flow analysis with high accuracy, the unsteady LES is performed with the steady result as the initial value. The wavenumber-frequency analysis is finally performed using the unsteady flow simulation results. The wavenumber-frequency analysis is shown to separate the compressible pressure fluctuation in the flow field from the incompressible one. This result can provide the accurate information for the source causing so-called acoustic-induced-vibration of a piping system.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.15 no.1
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• pp.16-20
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• 2004

Purpose : To assess perceptual, acoustic and aerodynamic measure of voice quality in patients with unilateral vocal cord paralysis before and after type I thyroplasty. Methods : The clinical records of patients operated type I thyroplasty in the Departement of otorhinoalryngolgy, Yongdong Severance hospital from November 2001 to November 2003 were reviewed. All patients uderwent a vocal function evaluation including perceptual, acoustic and aerodynamic measures of voice preoperative and on $60^{th}$ postoperative day. The perceptual and acoustic measures were obtained from recording of patients' reading a 'Sanchak' passage. The perceptual evaluation was performed by 2 speech pathologist using a 4-point rating scale. Acoustic parameters(voice range profile low(RAL), voice range profile high(RAH), average fundamental frequency(AFX), closed quotient, harmonic to noise ratio, jitter and shimmer) were investigated by Lx speech studio. Mean flow rate(MFR), subglottic pressure(Psub) and intensity were measured using the Phonatory function analyzer. The maximum phonation time was also measured. The data were statistically analyzed. A paired t-test (p<0.1) was used to compare preoperative and postoperative results. And multiple regression test was used to find which parameter was most correlated to improvement of postoperative voice quality. Results : Among aerodynamic parameters, Psub $(88.11mmH_2O{\rightarrow}58.7mmH_2O)$, MPT(7.87sec${\rightarrow}$12.53sec), MFR (359.8ml/sec${\rightarrow}$161.06ml/sec) were statistically improved. AFx(205.5Hz${\rightarrow}$163.27Hz), AQx(23.9%${\rightarrow}$48.3%), RAL, RAH. Jotter and shimmer were improved. In multiple regression test, AFx and AQx was noted as the two meost correlated parameters to improvement of postoperative breathiness. But general grade of voice quality was more correlated to Psub and shimmer. Conclusion : Vocal fold medialization procedures effectively reduce glottic gap. Increasing of contact area of both vocal folds induced improvement in aerodynamic parameters and leaded stabilizing of vocal fold vibration. That effect results in improvement in acoustic parameters (shimmer, jitter, signal-to-noise ratio, voice range profile) and voice quality.

• Advances in aircraft and spacecraft science
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• v.3 no.3
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• pp.243-257
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• 2016

The increase of air traffic volume has brought an increasing amount of issues related to carbon and NOx emissions and noise pollution. Aircraft manufacturers are concentrating their efforts to develop technologies to increase aircraft efficiency and consequently to reduce pollutant discharge and noise emission. Ultra High By-Pass Ratio engine concepts provide reduction of fuel consumption and noise emission thanks to a decrease of the jet velocity exhausting from the engine nozzles. In order to keep same thrust, mass flow and therefore section of fan/nacelle diameter should be increased to compensate velocity reduction. Such feature will lead to close-coupled architectures for engine installation under the wing. A strong jet-wing interaction resulting in a change of turbulent mixing in the aeroacoustic field as well as noise enhancement due to reflection phenomena are therefore expected. On the other hand, pressure fluctuations on the wing as well as on the fuselage represent the forcing loads, which stress panels causing vibrations. Some of these vibrations are re-emitted in the aeroacoustic field as vibration noise, some of them are transmitted in the cockpit as interior noise. In the present work, the interaction between a jet and wing or fuselage is reproduced by a flat surface tangential to an incompressible jet at different radial distances from the nozzle axis. The change in the aerodynamic field due to the presence of the rigid plate was studied by hot wire anemometric measurements, which provided a characterization of mean and fluctuating velocity fields in the jet plume. Pressure fluctuations acting on the flat plate were studied by cavity-mounted microphones which provided point-wise measurements in stream-wise and spanwise directions. Statistical description of velocity and wall pressure fields are determined in terms of Fourier-domain quantities. Scaling laws for pressure auto-spectra and coherence functions are also presented.