• 소음진동
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• 제7권2호
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• pp.215-222
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• 1997

The flow and acoustic fields due to a vortex ring interaction with a rigid sphere are simulated numerically. The flow field is regarded as three-dimensional inviscid and incompressible. The vorticity is assumed to be concentrated inside the finite core of vortex filament. The vortex filament curve, described by parabolic blending curve function, is used to effectively solve the modified Biot-Savart equation. The interaction between a vortex ring and a rigid sphere using the parabolic blending curve is calculated. The trajectory of the vortex ring is obtained with several different initial positions between the ring and the sphere. The force variations acting on the sphere are calculated by using the boundary integral method. Finally, we can also obtain the acoustic signals at the far field observation positions from the force variations acting on the rigid surface. We can find that the dipole axis of the directivity patterns are rotated during the interacting phenomena.

• ETRI Journal
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• 제27권2호
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• pp.153-165
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• 2005

The main purpose of a spatial audio system is to give a listener the same impression as if he/she were present in a recorded environment. A dummy head microphone is generally used for such purposes. Because of its human-like shape, we can obtain good spatial sound images. However, its shape is a restriction on its public use and it is difficult to convert a 2-channel recording into multi-channel signals for an efficient rendering over a multi-speaker arrangement. In order to solve the problems mentioned above, a spatial audio system is proposed that uses multiple microphones on a rigid sphere. The system has five microphones placed on special points of the rigid sphere, and it generates audio signals for headphone, stereo, stereo dipole, 4-channel, and 5-channel reproduction environments. Subjective localization experiments show that front/back confusion, which is a common limitation of spatial audio systems using the dummy head microphone, can be reduced dramatically in 4-channel and 5-channel reproduction environments and can be reduced slightly in a headphone reproduction.

• 대한기계학회논문집
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• 제3권4호
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• pp.181-184
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• 1979

Three-dimensional potential flow due to the translation of a sphere touching a rigid plane wall or a free wall is investigated by use of tangent sphere coordinates. Exact expressions for the velocity potential are derived in integral formes. Added mass and lift force on the sphere are also calculated.

• 한국가시화정보학회지
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• 제19권2호
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• pp.15-25
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• 2021

Numerical studies on the hydrodynamics of a freely falling rigid sphere in bounded and unbounded water domains are presented having investigation on the drag coefficient, normalized velocity, surface pressure and skin friction coefficient as a function of time. Two different conditions of the bounded and unbounded domains have been simulated by setting the blockage ratio. Four cases of bounded domains (B.R. = 1%, 25%, 45%, 55%, 65% and 75%) have been taken, whereas the unbounded domain has been considered with 0.01%. In the case of the bounded domain (higher values of B.R.), a substantial reduction in normalized velocity and increase in the drag coefficient have been found in presence of the bounded domain. Moreover, bounded domains also yield a significant increase in the pressure coefficient when the sphere is partially submerged, but the insignificant effect is found on the skin friction coefficient. In the case of the unbounded domain, a significant reduction in normalized velocity occurs with a decrease in Reynolds number (Re) and also increase in the drag coefficient.

• 한국수소및신에너지학회논문집
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• 제9권3호
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• pp.119-125
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• 1998

The modified statistical-mechanical theory for dense fluid mixtures of rigid spheres has been applied to rigid sphere fluids in the nonoverlapping pore model. The resulting expressions for the partition coefficient and diffusivity illustrate the influence of steric hindrance on the thermodynamic and transport properties in such systems. The open membrane model without the size-exclusion and shielding effects shows considerable overestimation of the diffusion flux when the effective mean pore radii of the order of $20{\AA}$ or less are involved. Theoretical predictions investigated here were also compared with experimental data for hydrogen gases in inorganic porous membranes and it was observed a qualitative agreement in the low pressure limit.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.455-461
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• 2000

A multichannel signal processing algorithm for generating real time virtual sound field was proposed. Evaluation of the system performance was done by an objective function that minimizes the difference between the real and generated signals at each control point. Since impulse responses at the surface of a rigid sphere show characteristics similar to those of real HRTF, a rigid sphere model was adequate to simulate the multichannel sound system. A two-channel system and two four-channel systems were studied with various combinations of source locations and speaker positions. The results show that a two-channel system has its best configuration when the angle spanned by the loudspeakers is less than $60^{\circ}$. In the case of four-channel systems, the overall performance was highly improved with one pair of speakers fixed at an optimal position. Left/right symmetry was a reasonable choice, but the additional front/back symmetry degraded the performance of system.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 봄 학술발표회 논문집
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• pp.295-302
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• 1999

This paper is the experimental and analytic of reinforced concrete hemisphere dome under vertical load. It is described that when the reinforced concrete hemispherical dome supported on cylindrical wall is loaded vertically, how the opening part of dome will behave mechanically The experimental and analytic model is a Hemispherical dome with opening and the meridian angle of opening is 76$^{\circ}$at the center of sphere under concentrated load around the opening, but this is reinforced by a ring is sufficient stiffness. The diagrams of crack development are represented to understand the behavior of the reinforced concrete hemispherical dome. The method of crack analysis will be applied the rigid element spring model. The rigid element spring model is a new discrete element analysis, each divided element is assumed by rigid elements without deformation which is interconnected with elasto-plastic spring system.

• Advances in biomechanics and applications
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• 제1권2호
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• pp.85-93
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• 2014

In this paper, two procedures of enumerating the axial rotation are proposed using the unit sphere of the spherical rotation coordinate system specifying 3D rotation. If the trajectory of the movement is known, the integration of the axial component of the angular velocity plus the geometric effect equal to the enclosed area subtended by the geodesic path on the surface of the unit sphere. If the postures of the initial and final positions are known, the axial rotation is determined by the angular difference from the parallel transport along the geodesic path. The path dependency of the axial rotation of the three dimensional rigid body motion is due to the geometric effect corresponding to the closed loop discontinuity. Firstly, the closed loop discontinuity is examined for the infinitesimal region. The general closed loop discontinuity can be evaluated by the summation of those discontinuities of the infinitesimal regions forming the whole loop. This general loop discontinuity is equal to the surface area enclosed by the closed loop on the surface of the unit sphere. Using this quantification of the closed loop discontinuity of the axial rotation, the geometric effect is determined in enumerating the axial rotation. As an example, the axial rotation of the arm by the Codman's movement is evaluated, which other methods of enumerating the axial rotations failed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
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• pp.622-628
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• 1998

The SONAR(SOund NAvigation and Ranging) is the system that detects objects and finds their locations in water by using the echo ranging technique. In this paper, the scattering phenomena for a rigid spherical scatterer will be analyzed using closed form solution, Boundary Element Method and Finite Element Method. Scattering analysis for an elastic spherical scatterer will be analyzed, later. In oder to analyzing the sound wave scattering phenomena for an elastic scatterer in water coupled problem between acoustic and vibration must be considered.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1994년도 춘계학술대회논문집; 영남대학교, 20 May 1994
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• pp.185-190
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• 1994

본 연구에서는 와선 지배방정식의 계산을 위해 쌍곡선 blending 함수를 이용하여 와선운동의 정확한 계산을 할 수 있었고 이 방법을 통하여 임의로 거동하는 와선이 강체구와 간섭하는 경우의 3차원 유동장에 대한 해석과 이에 의한 쌍극 음향장 해석을 수행하였다. 경계치 적분방법을 통해 강체구에 작용하는 힘을 계산할 수 있었고 이 방법은 물체의 형태에 구애 받지 않으므로 임의 형상에 대해서도 유동장과 음향장 계산이 가능하다고 본다.