• Structural Engineering and Mechanics
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• v.46 no.4
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• pp.549-569
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• 2013

A passive control using flaps will be an alternative solution for flutter stability and buffeting response of a long suspension bridge. This method not only enables a lightweight economic stiffening girder without an additional stiffness for aerodynamic stability but also avoid the problems from the malfunctions of control systems and energy supply system of an active control by winglets and flaps. A time domain approach for predicting the coupled flutter and buffeting response of bridge deck with flaps is investigated. First, the flutter derivatives of bridge deck and flaps are found by experiment. Next, the derivation of time domain model of self-excited forces and control forces of sectional model is reported by using the rational function approximation. Finally, the effectiveness of passive flap control is investigated by the numerical simulation. The results show that the passive control by using flaps can increase the flutter speed and decrease the buffeting response. The experiment results are matched with numerical ones.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.17 no.1
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• pp.43-48
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• 2006

Background and Objectives: Countertenors who can produce higher vocal pitch like female classical singer's voice and use both modal and falsetto register. This study was conducted to study phonatory characteristics between modal and falsetto register of the countertenor. Materials and Methods: A male countertenor who had 8 years of experience was examined using a videostroboscopy and his voice was analyzed using aerodynamic measures; fundamental frequency(F0), Mean air flow rate(MFR), intensity(SLP), subglottal air pressure(Psub) with phonatory function analyzer(Nagashima) and acoustic measures; jitter, shimmer, HNR, closed quotient(CQ) using a Electro-glottography(EGG) of Lx. Speech Studio(Laryngoscope, Ltd, UK) and voice range profile of CSL(Kay elemetrics). Results: In the stroboscopy finding, the longitudinal length of vocal folds was increased at the falsetto register and the upper margin of vocal folds vibrated with incomplete closure of true vocal folds. In aerodynamic analysis, intensity was same at the modal and falsetto register. However, MFR, Psub, MPT were higher at the falsetto register. In the electroglottographic analysis, closed quotient(CQ) at the modal register was high and also much higher at the high-pitch falsetto than at the loud falsetto. In the VRP, intensity was similar though F0 was different between modal and falsetto register. Conclusion: It implied that countertenor could produce powerful voice quality by increasing of respiratory pressure and respiratory volume though glottal closure was incomplete. In addition, no change of EGG waveform, similar voice range with alto was observed.

• Journal of computational fluids engineering
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• v.19 no.2
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• pp.86-92
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• 2014

In this paper, prediction of separation trajectory for Two-stage-To-Orbit space launch vehicle has been numerically simulated by using an aerodynamic database based on steady state analysis. Aerodynamic database were obtained for matrix of longitudinal and vertical positions. The steady flow simulations around the launch vehicle have been made by using a 3-D RANS flow solver based on unstructured meshes. For this purpose, a vertex-centered finite-volume method was adopted to discretize inviscid and viscous fluxes. Roe's finite difference splitting was utilized to discretize the inviscid fluxes, and the viscous fluxes were computed based on central differencing. To validate this flow solver, calculations were made for the wind-tunnel experiment model of the LGBB TSTO vehicle configuration on steady state conditions. Aerodynamic database was constructed by using flow simulations based on test matrix from the wind-tunnel experiment. ANN(Artificial Neural Network) was applied to construct interpolation function among aerodynamic variables. Separation trajectory for TSTO launch vehicle was predicted from 6-DOF equation of motion based on the interpolated function. The result of present separation trajectory calculation was compared with the trajectory using experimental database. The predicted results for the separation trajectory shows fair agreement with reference[4] solution.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.11 no.1
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• pp.98-103
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• 2000

Background and Objectives : The etiology and pathophysiology of spasmodic dysphonia is yet unknown. This study was performed to determine if any laryngeal aerodynamic parameter distinguish the voice of patient diagnosed as having adductor spasmodic dysphonia from individuals with normal voice production and to investigate the pathophysiology of spasmodic dysphonia. Materials and Methods : fifteen women diagnosed as having adductor spasmodic dysphonia and fifteen normal control women participitated in this study Maximum phonation time, mean air flow rate, subglottic pressure, vocal efficiency, Vfo, NHR, VTI, FTRI, ATRI, Jitter percent, Shimmer percent were obtained from the participants using 'MDVP(multi-dimensional voice program)' of CSL(Computerized Speech lab, Kay Elemetrics, Co., Model No. 4300), and 'maximum sustained phonation' and 'IPIPI test' of AP II(Aerophone II, Kay Elemetrics, Co., Model 6800). Results : T-test statistical analysis revealed statistically different values for vocal efficiency, Vfo, NHR, MPT, litter percent, Shimmer percent between the spasmodic dysphonia group and the control group. Conclusions : Spasmodic dysphonia affects the ability of the laryngeal mechanism to function effectively. Results from our study demonstrate that certain aerodynamic and acoustic parameters distinguish adductor spasmodic dysphonia from normal voice.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.2
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• pp.139-145
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• 2012

The low speed aerodynamic characteristics of modified sonic arc airfoil which is developed to fit the transonic regime are investigated. This airfoil is designed by using the shape function of sonic arc proposed by Schwendenman, the data of NACA0012, and commercial program Maple. In order to investigate the low speed aerodynamic characteristic of sonic arc airfoil, the numerical analysis is conducted below Mach number 0.3 and the results are compared and analyzed with it of NACA0012 airfoil. At each Mach number, the drag of modified sonic arc airfoil is less 1.5% than NACA0012's drag and the lift of modified sonic arc airfoil is less 2% than NACA0012's lift. The moment coefficient of modified sonic arc airfoil is also less 1.4% than it of NACA0012 at each Mach number.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.16 no.2
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• pp.152-157
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• 2005

Background and Objectives : 10 normal Korean native speakers participated subjects to investigate the acoustic and aerodynamic study of Korean fricatives, affricates, and plosives and to make good use of the results for the patients with articulation problems. Materials and Method Their productions of [asa], [as'a], [aca], $[ac^ha]$, (ac'a), (ata) , $[at^ha]$, and [at'a] were analyzed with Lx Speech Studio Program (Laryngogrtaph Ltd, UK) for acoustic analysis and Phonatory Function Analyze. (Nagashima Ltd. Model PS 77H, Tokyo, Japan) for aerodynamic analysis. Results : The results are as follows : 1) Plosives showed higher Qx1 in vocal folds closure ratio than fricatives and affricates. 2) Tense fricatives, affricates, and plosives showed higher Qx2 in vocal folds closure ratio than asperated and 1ax. 3) Asperated showed higher Qx1 in vocal folds closure ratio than tense and 1ax. 4) Asperated showed higer peak flow rate than tense and 1ax. Conclusion This results may be helpful for treatment in articulation disorders.

• Wind and Structures
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• v.1 no.3
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• pp.225-241
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• 1998

The high-rise supporting towers of long-span suspension and cable-stayed bridges commonly comprise a pair of slender prisms of roughly square cross-section with a center-to-centre spacing of from perhaps 2 to 6 widths and connected by one or more cross-ties. The tower columns may have a constant spacing as common for suspension bridges or the spacing may reduce towards the top of the tower. The present paper is concerned with the aerodynamics of such towers and describes an experimental investigation of the overall aerodynamic forces acting on a pair of square cylinders in two-dimensional flow. Wind tunnel pressure measurements were carried out in smooth flow and with a longitudinal intensity of turbulence 0.10. Different angles of attack were considered between $0^{\circ}$ and $90^{\circ}$, and separations between the two columns from twice to 13 times the side width of the column. The mean values of the overall forces proved to be related to the bias introduced in the flow by the interaction between the two cylinders; the overall rms forces are related to the level of coherence between the shedding-induced forces on the two cylinders and to their phase. Plots showing the variation of the force coefficients and Strouhal number as a function of the separation, together with the force coefficients spectra and lift cross-correlation functions are presented in the paper.

• Wind and Structures
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• v.7 no.6
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• pp.421-447
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• 2004

This paper presents a time domain approach for predicting buffeting response of long suspension bridges under skew winds. The buffeting forces on an oblique strip of the bridge deck in the mean wind direction are derived in terms of aerodynamic coefficients measured under skew winds and equivalent fluctuating wind velocities with aerodynamic impulse functions included. The time histories of equivalent fluctuating wind velocities and then buffeting forces along the bridge deck are simulated using the spectral representation method based on the Gaussian distribution assumption. The self-excited forces on an oblique strip of the bridge deck are represented by the convolution integrals involving aerodynamic impulse functions and structural motions. The aerodynamic impulse functions of self-excited forces are derived from experimentally measured flutter derivatives under skew winds using rational function approximations. The governing equation of motion of a long suspension bridge under skew winds is established using the finite element method and solved using the Newmark numerical method. The proposed time domain approach is finally applied to the Tsing Ma suspension bridge in Hong Kong. The computed buffeting responses of the bridge under skew winds during Typhoon Sam are compared with those obtained from the frequency domain approach and the field measurement. The comparisons are found satisfactory for the bridge response in the main span.

• Wind and Structures
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• v.31 no.6
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• pp.561-573
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• 2020

Unsteady self-excited forces are commonly represented by parametric models such as rational functions. However, this requires complex multiparametric nonlinear fitting, which can be a challenging task that requires know-how. This paper explores the alternative nonparametric modeling of unsteady self-excited forces based on relations between flutter derivatives. By exploiting the properties of the transfer function of linear causal systems, we show that damping and stiffness aerodynamic derivatives are related by the Hilbert transform. This property is utilized to develop exact simplified expressions, where it is only necessary to consider the frequency dependency of either the aeroelastic damping or stiffness terms but not both simultaneously. This approach is useful if the experimental data on aerodynamic derivatives that are related to the damping are deemed more accurate than the data that are related to the stiffness or vice versa. The proposed numerical models are evaluated with numerical examples and with data from wind tunnel experiments. The presented method can evaluate any continuous fitted table of interpolation functions of various types, which are independently fitted to aeroelastic damping and stiffness terms. The results demonstrate that the proposed methodology performs well. The relations between the flutter derivatives can be used to enhance the understanding of experimental modeling of aerodynamic self-excited forces for bridge decks.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.6
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• pp.145-154
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• 2013

Recently, damage occurrence by wind erosion has been increasing in society. In times past, such problems only took place in desert area ; however, in recent years, the wind erosion problem is spreading out to agricultural land. Wind erosion in agricultural land can cause loss of loam soils, the disturbance of the photosynthesis of the crop fields and serious economic losses. To overcome the mentioned problems, installation of windbreak fence can be recommended which function as disturbing strong wind and wind erosion. However, there is still no proper guideline to install the windbreak fence and the installation used to rely on the intuition of the workers due to the lack of related studies. Therefore, this study measured the aerodynamic resistance of screens of the windbreak fence using the apparatus for testing screens. The apparatus for testing screens was designed to measure pressure loss around the screen. Measured pressure loss by wall friction compensated for pressure loss to calculate the aerodynamic resistance of screens. The result of pressure loss by regression analysis derived the aerodynamic coefficient of Darcy-Forchheimer equation and power law equation. The aerodynamic resistance was constant regardless of the overlapped shape when the screen was overlapped into several layers. Increasing the number of layers of the screen, internal resistance increased significantly more, and pressure loss caused by the screen also increased linearly when the wind speed was certain conditions, but permeability had no tendency. In the future, the results of this study will be applied to the computational fluid dynamics simulation. The simulation models will be also validated in advance by wind tunnel experiments. It will provide standard of a design for constructing windbreak fence.