• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2157-2161
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• 2003

In this paper, the response surface method using three-dimensional Navier-Stokes analysis to optimize the shape of a forward-curved blades centrifugal fan, is described. For numerical analysis, Reynolds-averaged Navier-Stokes equations with standard k-e turbulence model are transformed into non-orthogonal curvilinear coordinate system, and are discretized with finite volume approximations. Due to the large number of blades in forward-curved blades centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models for economic calculations. Linear Upwind Differencing Scheme(LUDS) is used to approximate the convection terms in the governing equations. SIMPLEC algorithm is used as a velocity-pressure correction procedure. Design variables, location of cur off, radius of cut off, expansion angle of scroll and width of impeller were selected to optimize the shapes of scroll and blades. Data points for response evaluations were selected by D-optimal design, and linear programming method was used for the optimization on the response surface. As a main result of the optimization, the efficiency was successfully improved. It was found that the optimization process provides reliable design of this kind of fans with reasonable computing time

• 한국전산유체공학회지
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• 제15권4호
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• pp.25-31
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• 2010

Interface tracking of two phase is significant to analyze multi-phase phenomena. The VOF(Volume of Fluid) and level set are well known interface tracking method. However, they have limitations to solve compressible flow and incompressible flow at the same time. CIP(Cubic Interpolate Propagation) method is appropriate for considering compressible and incompressible flow at once by solving the governing equation which is divided up into advection and non-advection term. In this article, we analyze the droplet impingement according to various We number using improved CIP method which treats nonlinear term once more comparison with original CIP method. Furthermore, we compare spread radius after droplet impingement on the wall with the experimental data and original CIP method. The result using improved CIP method shows the better result of the experiments, comparison with result of original CIP method, and it reduces the mass conservation error which is generated in the numerical analysis comparison with original CIP method.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.233-236
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• 2007

멀티포트 하이브리드 로켓 고체연료 그레인의 열민감도에 관한 연구를 수행하였다. 고온의 비반응 유동의 포트를 통과하며 연료 그레인으로 열전달 시, 연료 그레인 내부의 온도 분포 변화를 비정상 열해석을 통해 계산하였다. 계산은 총 9개의 포트 반경에서 수행되었으며, 연료 내부 온도가 민감하게 거동하는 임계 포트 반경을 결정하였다. 열에 민감하게 반응하는 임계 포트반경 이후는 고체 폴리머 연료의 구조상의 취약점이 발생할 것으로 판단되므로, 임계 포트반경은 설계 시 중요한 고려대상으로 사용될 것으로 예상된다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권5호
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• pp.1654-1675
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• 2014

In practical wireless systems, the erroneous channel state information (CSI) sometimes deteriorates the performance drastically. This paper focuses on robust design of coordinated set planning of coordinated multi-point (CoMP) transmission, with respect to the feedback delay and link error. The non-ideal channel models involving various uncertainty conditions are given. After defining a penalty factor, the robust net ergodic capacity optimization problem is derived, whose variables to be optimized are the number of coordinated base stations (BSs) and the divided area's radius. By the maximum minimum criterion, upper and lower bounds of the robust capacity are investigated. A practical scheme is proposed to determine the optimal number of cooperative BSs. The simulation results indicate that the robust design based on maxmin principle is better than other precoding schemes. The gap between two bounds gets smaller as transmission power increases. Besides, as the large scale fading is higher or the channel is less reliable, the number of the cooperated BSs shall be greater.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1726-1731
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• 2004

This paper presents the response surface optimization method using three-dimensional Navier-Stokes analysis to optimize the shape of a forward-curved blades centrifugal fan. For numerical analysis, Reynolds-averaged Navier-Stokes equations with $k-{\varepsilon}$ turbulence model are discretized with finite volume approximations. In order to reduce huge computing time due to a large number of blades in forward-curved blades centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models. Three geometric variables, i.e., location of cut off, radius of cut off, and width of impeller, and one operating variable, i.e., flow rate, were selected as design variables. As a main result of the optimization, the efficiency was successfully improved. And, optimum design flow rate was found by using flow rate as one of design variables. It was found that the optimization process provides reliable design of this kind of fans with reasonable computing time.

• 대한기계학회논문집B
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• 제28권11호
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• pp.1332-1338
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• 2004

This paper presents the response surface optimization method using three-dimensional Navier-Stokes analysis to optimize the shape of a forward-curved blades centrifugal fan. For numerical analysis, Reynolds-averaged Navier-Stokes equations with k-$\varepsilon$ turbulence model are discretized with finite volume approximations. In order to reduce huge computing time due to a large number of blades in forward-curved blades centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models. Three geometric variables, i.e., location of cut off, radius of cut off, and width of impeller, and one operating variable, i.e., flow rate, were selected as design variables. As a main result of the optimization, the efficiency was successfully improved. And, optimum design flow rate was found by using flow rate as one of design variables. It was found that the optimization process provides reliable design of this kind of fans with reasonable computing time.

• 소성∙가공
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• 제7권5호
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• pp.439-444
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• 1998

Recently many automotive parts have been made with stainless steels by deep drawing processes, But there are various problems occurred in deep drawing works of stainless steels compared with low carbon steels. For the severe deep drawing of complex cylindrical housing optimum process planning is required to eliminate intermediate annealing improve shape accuracy and maintain surface integrity without drawing defects such as tears wrinkles and scratches or galling. Therefore in this study a sample process planning of the severe of the severe deep drawing process is applied to a complex cylindrical housing needed for a 6 multi-stepped deep drawing of type STS 305 . A series of experiments are performed to investigate optimum process variables such as drawing rate radius and clearance. Through experiments the variations of the thickness strain distribution and hardness distribution in each drawing step are observed. Also the effects of other factors on formability such as drawing oil, blank holding force and die geometry are examined and discussed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.326-331
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• 2007

This paper conducts a vibratory loads reduction analysis of an Advanced Active Trailing-edge Flap (AATF) blade utilizing single crystal piezoelectric actuators. For an AATF blade, a new L-L piezostack actuator using single crystal PMN-PT materials is designed. The AATF blade is designed to have similar characteristics to the Advanced Active Twist Rotor (AATR) blade. The active trailingedge flap is assumed to be 20% of the blade span and 15% of the chord, located at 75% of the blade radius. In order to conduct the vibratory loads reduction analysis of the AATF blade in forward flight, DYMORE, a multi-body dynamics analysis code, is used. The simulation result shows that the hub vibratory loads may be reduced by approximately 89% even with a much lower input-voltage when comparing with the other active rotor systems.

• Tribology and Lubricants
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• 제19권2호
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• pp.85-93
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• 2003

In this study, a multigrid multi-integration method has been used to solve the steady-state, elastohydrodynamic lubrication (EHL) point contact problem of a ball joint mechanism used in small reciprocating compressors. Pressure and film thickness profiles have been calculated at minimum and maximum Moes M parameter conditions during one revolution of crankshaft. The effects of various lubricant viscosities, loads, ball velocities, elastic modulli, and radii of curvature on the calculated pressure distribution and film thicknesses have been investigated. The results indicate that the viscosity of lubricant, the sliding velocity of ball, and the reduced radius of curvature have considerable effects on the minimum and central film thicknesses. Solutions obtained with the multigrid analysis are compared with results calculated according to the Hamrock ＆ Dowson relations for the minimum and central film thicknesses.

• International Journal of Aeronautical and Space Sciences
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• 제8권2호
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• pp.82-88
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• 2007

Thermal Buckling and free vibration analyses of multi-layered composite conical shells based on a layerwise displacement theory are performed. The Donnell's displacement-strain relationships of conical shell structure are applied. The natural frequencies are compared with the ones existing in the previous literature for laminated conical shells with several cone semi-vertex angles. Moreover, the thermal buckling behaviors of the laminated conical shell are investigated to consider the effect of the semi-vertex angle, subtended angle, and radius to thickness ratio on the structural stability.