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고체입자를 이용한 열교환기에서의 유동 및 열전달의 유한요소해석
이완술,윤성기,박상일,Lee, Wan-Sul,Youn, sung-kie,Park, Sang-Il 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.4
Numerical analysis for the flow and heat transfer in solid particle moving beds of heat exchangers is presented. The solid particle flow through the bundle of heat source tubes by the gravitational force. The heat energy is transferred through the direct contact of particles with the heat source tubes. The viscous-plastic fluid model and the convective heat transfer model are employed in the analysis. The flow field dominantly influences the total heat transfer in a heat exchanger. As the velocities of solid particles around the heat source tubes increase, the amount of heat transfer from the tubes increases. Some examples are presented to show the performance of the numerical model. The flow effect on the heat transfer is also studied through the examples.
다중 해상도 중심점 탐색법을 이용한 샥-하트만 센서용 상관관계법의 속도 개선
유재은,윤성기,Yoo, Jae-Eun,Youn, Sung-Kie 한국광학회 2008 한국광학회지 Vol.19 No.1
샥-하트만(Shack-Hartmann) 파면 측정 센서는 여러 분야에서 다양하게 사용되고 있다. 특히 적응광학은 주요 응용분야 중 하나이다. 적응광학 시스템은 실시간으로 빠르게 동작되어야 하므로 고속 파면 측정이 필수적이다. 고속 파면 측정에서는 카메라의 노출시간이 매우 작기 때문에 파면 측정시에 광자 잡음(photon noise)와 판독 잡음(readout noise)등의 잡음의 영향을 크게 받는다. 따라서 잡음에 둔감한 고속 중심점 탐색 알고리즘이 요구된다. 본 논문에서는 잡음에 둔감한 고속 중심점 탐색 알고리즘으로 다중 해상도 상관관계법이 제안되었다. 이 방법은 고속 푸리에 변환(fast Fourier transform)을 이용한 상관관계법과 비교하여 다중 해상도 이미지를 이용함으로써 계산시간을 향상시켰다. 본 논문에서는 무게중심법(center of mass method)과 상관관계법(correlation method)과 다중해상도 상관관계법(multi-resolution correlation method)의 계산시간과 측정 정확도를 비교하기 위해 전산모사 방법이 사용되었다. 제안된 방법의 정확도는 기존의 상관관계법과 유사한 것을 확인하였다. Shack-Hartmann sensors are widely employed as a wavefront measuring device in various applications. Adaptive optics is one of the major applications. Since an adaptive optics system should be operated in real-time, high-speed wavefront sensing is essential. In high-speed operation, integration time of an image detector is very short. In this case, noises such as readout noise and photon noise greatly influence the accuracy of wavefront sensing. Therefore a fast and noise-insensitive centroid finding algorithm is required for the real-time wavefront sensing. In this paper, the multi-resolution correlation method is proposed. By employing multi-resolution images, this method greatly reduces the computation time when compared to the fast Fourier transform (FFT) correlation method. The verification is performed through the computational simulation. In this paper, the center of mass method, correlation method and multi-resolution correlation method are employed to compare the measurement accuracy of the centroid finding algorithms. The accuracy of a Shack-Hartmann wavefront sensor using the proposed algorithm is proved to be comparable to that of the conventional correlation method.
장수영,윤성기,김철순,오동호,Chang, Su-Young,Youn, Sung-Kie,Kim, Cheol-Soon,Oh, Dong-Ho 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.7
A study on the topology optimization of Hard-Disk-Driver(HDD) actuator arm in free vibration is presented. The purpose of this research is to increasse the natural frequency of the first lateral mode of the HDD actuator arm under the constraint of total moment of inertia, so as to facilitate the position control of high speed actuator am. The first lateral mode is an important factor in the position control process. Thus the topology optimization for 2-D model of the HDD actuator arm is considered. A new objective function corresponding to multieigenvalue optimization is suggested to improve the solution of the eigenvalue optimization problem. The material density of the structure is treated as the design variable and the intermediate density is penalized. The effects of different element types and material property functions on the final topology are studied. When the problem is discretized using 8-node element of a uniform density, the smoothly-varying density field is obtained without checker-board patterns incurred. As a result of the study an improved design of the HDD actuator arm is suggested. Dynamic characteristics of the suggested design are compared computationally with those of the old design. With the same amount of the moment of inertia, the natural frequency of the first lateral mode or the suggested design is subsequently increased over the existing one.
권기찬,윤성기,Gwon, Kie-Chan,Youn, Sung-Kie 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.12
A parallel approach using a network of engineering workstations is presented for the efficient computation in the elastoplastic analysis of strip rolling process. The domain decomposition method coupled with the frontal solver for elimination of internal degrees of freedom in each subdomain is used. PVM is used for message passing and synchronization between processors. A 2-D plane strain problem and the strip rolling process are analyzed to demonstrate the performance of the algorithm and factors that have a great effect on efficiency are discussed. In spite of much communication time on the network the result illustrates the advantages of this parallel algorithm over its corresponding sequential algorithm.
회전하는 타이어의 변형에너지 손실에 의한 온도분포 해석
박현철,윤성기,송태석,김남전,Park, Hyun-Cheol,Youn, Sung-Kie,Song, Tae-Sok,Kim, Nam-Jeon 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.5
This paper addresses the systematic procedure using sequential approach for the analysis of the coupled thermo-mechanical behavior of a steady rolling tire. Not only the knowledge of mechanical stresses but also of the temperature loading in a rolling tire are very important because material damage and material properties are significantly affected by the temperature. In general, the thermo-mechanical behavior of a pneumatic tire is highly complex transient phenomenon that requires the solution of a dynamic nonlinear coupled themoviscoelasticity problem with heat source resulting from internal dissipation and friction. In this paper, a sequential approach, with effective calculation schemes, to modeling this system is presented in order to predict the temperature distribution with reasonable sccuracies in a steady state rolling tire. This approach has the three major analysis modules-deformation, dissipation, and thermal modules. In the dissipation module, an analytic method for the calculation of the heat source in a rolling tire is established using viscoelastic theory. For the verification of the calculated temperature profiles and rolling resistance at different velocities, they were compared with the measured ones.
분자 첨점조건을 고려한 격자 기반 토마스-페르미-아말디 방정식
김민성(Min sung Kim),윤성기(Sung-Kie Youn),강정구(Jeung Ku Kang) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
First, the Thomas-Fermi-Amaldi (TFA) equation was formulated with a newly-derived condition to remove the singularities at the nuclei, coincided with the molecular cusp condition. Next, the collocation method was applied to the TFA equation using the grid-based density functional theory. In this paper, the electron densities for specific atoms (He, Be, Ne, Mg, Ar, Ca) and total energies for specific atoms (He, Ne, Ar, Kr, Xe, Rn) and molecules (H2, CH4) were found to agree with those from the Hartree-Fock method using the Pople basis set 6-31G. In addition, the computational expense to determine the electron density and its corresponding energy for a large scale structure, such as a carbon nanotube, is shown to be much more efficient compared to the conventional Hartree-Fock method using the 6-31G Pople basis set.
권기찬,박상훈,윤성기,Kwon, Kie-Chan,Park, Sang-Hoon,Youn, Sung-Kie 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.11
The first-order least-squares meshfree method for linear elasticity is presented. The conventional and the compatibility-imposed least-squares formulations are studied on the convergence behavior of the solution and the robustness to integration error. Since the least-squares formulation is a type of mixed formulation and induces positive-definite system matrix, by using shape functions of same order for both primal and dual variables, higher rate of convergence is obtained for dual variables than Galerkin formulation. Numerical examples also show that the presented formulations do not exhibit any volumetric locking for the incompressible materials.