• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2008년도 추계학술대회논문집
• /
• pp.527-532
• /
• 2008

In this study, numerical analysis is performed to investigate the sound radiation characteristics of an apartment house according to the type of the slab system. In order to satisfy the boundary condition of the apartment house, the whole floor is modelled with FEM model for three different structural system: wall, RC, flat slab system. From the analytical results, it Is shown that heavy weight floor impact noise of wail type slab is larger than that of the other slab systems and the noise radiated from the wall have great effect on the sound pressure level. The results also show that the vibration energy of RC or flat slab system is widely distributed over the whole slab, which is main reason that the noise induced by the slab systems is reduced in comparison with wail slab system.

• Tribology and Lubricants
• /
• 제27권2호
• /
• pp.101-108
• /
• 2011

In this paper, a study on the frictional losses and dynamic behaviors of a reciprocating compression mechanism used in small refrigeration compressor is performed. In the problem formulation of the compressor dynamics, the viscous frictional force between piston and cylinder wall is considered in order to determine the coupled dynamic behaviors of piston and crankshaft supported on a thrust ball bearing. The solutions of the equations of motion of the reciprocating mechanism along with the time dependent Reynolds equations for the lubricating film between piston and cylinder wall and lubricant films of the journal bearings are obtained simultaneously. The hydrodynamic forces of journal bearings are calculated using finite bearing model and G$\hat{u}$m-bel boundary condition. And, a Newton-Raphson procedure was employed in solving the nonlinear equations of piston and crankshaft with a thrust ball bearing. The results explored the effects of design parameters on the frictional losses and dynamic stability of the compression mechanism.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
• /
• pp.676-679
• /
• 2008

Numerical simulations of fluid injection into particulate materials were conducted to observe cavity initiation and propagation using distinct element method. After generation of initial particles and wall elements, confining stress was applied by servo-control method. The fluid scheme solves the continuity and Navior-Stokes equations numerically, then derives pressure and velocity vectors for fixed grid by considering the existence of particles within the fluid cell. Fluid was injected as 7-step into the assembly in the x-direction from the inlet located at the center of the left boundary under confining stress condition, 0.1MPa and 0.5MPa, respectively. For each simulation, movement of particles, flow rate, fluid velocity, pressure history, wall stress including cavity initiation and propagation by interaction of flulid-paricles were analyzed.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.717-720
• /
• 2002

The present study is to evaluate the performances of flow velocity and wall shear stress in the stenosed coronary artery using human in vivo hemodynamic Parameters and computer simulation. Initial and follow-up coronary angiographics in the patients with angulated coronary stenosis are performed. Follow-up coronary angiogram demonstrated significant difference in the percent of diameter in the stenosed coronary between two groups ($Group\;1:\;40.3{\%},\;Group\;2:\;25.5{\%}$). Flow-velocity wave obtained from in vivo intracoronary Doppler ultrasound data is used for the boundary condition for the computer simulation. Spatial and temporal variations of flow velocity vector and recirculation area are drawn throughout the selected segment of coronary models. The WSS of pre- and post-intracoronary stenting are calculated from three-dimensional computer simulation. Then negative shear stresses area on 3D simulation we noted on the inner wall of the post-stenotic area before stenting. The negative WSS is disappeared after stenting. High spatial and temporal WSS before stenting fell into within physiologic WSS after stenting. This finding was prominent in Model 2. The present study suggest that hemodynamic forces exerted by pulsatile coronary circulation termed WSS might affect on the evolution of atherosclerosis within the angulated vascular curvature. The local recirculation area which has low or negative WSS, might lead to progression of atherosclerosis.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• 제20권4호
• /
• pp.333-354
• /
• 2016

The present investigation deals, heat and mass transfer characteristics with the effect of slip on the hydromagnetic pulsatile flow through a parallel plate channel filled with saturated porous medium. Based on the pulsatile flow nature, exact solution of the governing equations for the fluid velocity, temperature and concentration are obtained by using two term perturbation technique subject to physically appropriate boundary conditions. The expressions of skin friction, Nusselt number and Sherwood number are also derived. The numerical values of the fluid velocity, temperature and concentration are displayed graphically whereas those of shear stress, rate of heat transfer and rate of mass transfer at the plate are presented in tabular form for various values of pertinent flow parameters. By increasing the slip parameter at the cold wall the velocity increases whereas the effect is totally reversed in the case of shear stress at the cold wall.

• 한국추진공학회지
• /
• 제11권5호
• /
• pp.14-22
• /
• 2007

측면 표면 기울기가 변화하는 역 사다리꼴 핀이 2차원 해석적 방법을 사용하여 최적화된다. 핀 바닥 경계조건을 위해서, 내부유체로부터 내벽까지의 대류와 내벽부터 핀 바닥까지의 전도가 고려된다. 핀 끝 면으로부터의 열손실은 무시되지 않는다. 실제적인 핀 길이에서의 최대 열손실, 그 최대 열손실이 발생할 때의 최적의 효율, 핀 길이 그리고 핀 바닥 높이가 핀 내 외부의 대류특성계수의 함수로 나타내어진다. 결과 중 하나는 핀 바닥 높이에 대한 핀 끝 높이의 비가 커질수록 최적의 핀 형상은 두껍고 짧아지는 형상이 됨을 보여준다.

• Nuclear Engineering and Technology
• /
• 제17권4호
• /
• pp.279-289
• /
• 1985

U-tube 증기 발생기 내부의 재순환 loop에서의 밀도파 진동 형태의 불안정성 분석을 하고자 한다. 단상과 2상 영역에서의 압력 강하의 섭동치를 계산하기 위하여, 상간의 slip과 비균일 열유랑 그리고 heated wall dynamics를 고려하여 drift-flux model에 근거를 둔 노드 내의 섭동 보즌 방정식이 유도되었다. Loop를 통한 일정 압력강하 경계조건하에 Nyquist 조건을 사용하여 안정성이 분석되었다. SASG computer program을 개발하여 고리 1호기의 증기 발생기에 대한 안정성을 분석하였으며, 아울러, 중요한 계통인자들의 안정성 여유도에 미치는 영향도 분석하였다.

• 대한기계학회논문집
• /
• 제11권3호
• /
• pp.425-436
• /
• 1987

본 연구에서는 강제대류가 있는 층류막비등유동을 벽면온도와 주수속도를 변 화시키며 수치해석하여 열전달계수와 유동특성을 구하였고, 열력학적 상태량들을 일정 하다고 가정하는 경우가 열전달계수에 어떠한 영향을 미치는가를 검토한 결과, 열전달 계수는 주수속도에는 큰 영향을 받지 않으나, 벽면온도와 열력학적 상태량의 변화에는 상당히 큰 영향을 받는 것으로 나타나고 있다.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
• /
• pp.197-200
• /
• 2015

Understanding the slag flow behavior is important in an entrained coal gasifier for its influence of ash discharge and wall heat transfer rate. This study presents a new model to predict the transient behavior of the liquid and solid slag layers. Unlike the previous steady-state model, the solid slag layer was included in solving the governing equations in order to identify the temporal and spatial transformation between the solid-liquid slag, rather than treating the solid region as a boundary condition of the liquid layer. The performance of the new model was evaluated for changes in the slag deposition rate (${\pm}10%$) and gas temperature (${\pm}50K$) in a simple cylindrical gasifier. The results show that the characteristic times to reach a new steady-state ranged between 80 s to 180s for the changes in the two parameters. Because the characteristic times of the gasifier temperature and slag deposition rate by changes in the coal type and/or operating conditions would be almost instantaneous, the time-scale for the slag thickness at the bottom of the gasifier to stabilize was much larger.

• 한국항공우주학회지
• /
• 제37권5호
• /
• pp.476-482
• /
• 2009

본 논문에서는 Fluent의 Spalart-Allmaras 난류모델을 적용하여 연소실 내부에 설치된 핀틀 형상이 핀틀 추진기관 추력 크기에 미치는 영향을 수치해석으로 분석하였다. 핀틀이 존재하면 노즐목을 지나는 질량 유량율은 이론적으로 예측된 값 보다 항상 작았으며, 핀틀 직경이 커질수록 노즐목에서 경계층 두께가 차지하는 비율이 증가되어 노즐목의 질량 유량율이 더욱 감소하였다. 핀틀 직경이 커질수록 핀틀 팁에 나타나는 재순환 영역의 압력에 의한 추력은 증가하지만 노즐 및 연소실 압력에 의한 추력은 감소하여 총 추력은 핀틀 직경이 작은 것 보다 감소하였다. 핀틀 추진기관의 비추력은 큰 차이가 없었다.