• 대한기계학회논문집B
• /
• 제29권12호
• /
• pp.1344-1351
• /
• 2005

Three-dimensional, time-dependent solutions of fluid flow past a circular cylinder with a periodic array of circular fins are obtained using an accurate and efficient spectral multidomain methodology. A Fourier expansion with a corresponding uniform grid is used along the circumferential direction. A spectral multidomain method with Chebyshev collocation is used along the r-z plane to handle the periodic array of circular fins attached to the surface of the cylinder. Unlike the flow past a circular cylinder, Second instabilities like mode A and mode B are not found in the Reynolds number range $100\~500$. It is found that three-dimensional instability of vortical structures is suppressed due to the presence of fin. The present numerical solutions report the detailed information of flow quantities near wake of finned cylinder.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 춘계학술대회논문집B
• /
• pp.282-289
• /
• 2000

Direct numerical solution for flow and heat transfer for Benard convection with a body is obtained using an accurate and efficient Fourier-Chebyshev collocation and multi-domain method. The flow and temperature fields are obtained fur different Rayleigh numbers and thermal boundary conditions of body. The body has adiabatic and constant temperature conditions. The existence of a body gives different flow and heat transfer fields in the system, compared to pure Benard convection. The flow and temperature fields are also affected by the thermal boundary condition of a body.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume II
• /
• pp.651-654
• /
• 2006

Infrared channels of newly launched Japanese geostationary satellite, MTSAT-1R are compared with well calibrated MODIS/Terra infrared measurements at 3.7, 6.7, 11, 12 ${\mu}m$ bands. There are four steps in this intercalibration method: 1) data collection, 2) spectral response function correction, 3) data collocation, and 4) calculation of mean bias and conversion coefficients. In order to minimize the navigation error of MTSAT-1R, comparisons are made over the area in which the viewing angle of MTSAT-1R is less than 50$^{\circ}$. The calibration method was tested for August 2005 and within the 40$^{\circ}N$-40$^{\circ}S$, 100$^{\circ}$E-180$^{\circ}$E domain. The differences of spectral response functions were corrected through radiative transfer model simulation. Constructing collocated data differences in viewing geometry, observation time and space were taken into account. In order to avoid the radiance variation induced by cloud presence, clear-sky targets are selected as intercalibration target. The mean biases of 11, 12, 6.7, and 3.7 ${\mu}m$ bands are about -0.16, 0.36, 1.31, and -6.69 K, suggesting that accuracies of 3.7 ${\mu}m$ is questionable while other channels are comparable to MODIS

• 대한조선학회논문집
• /
• 제43권3호
• /
• pp.285-293
• /
• 2006

Three-dimensional and time-dependent solution for the fluid flow and heat transfer past a circular cylinder with fins is obtained using accurate and efficient spectral methods. A Fourier expansion with a corresponding uniform grid is used along the circumferential direction. A spectral multi-domain method with a corresponding Chebyshev collocation is used along r-z plane to handle fins attached to the surface of a circular cylinder. At the Reynolds number of 300 based on a cylinder diameter, results with fins are compared with those without fins in order to see the effects of the presence of fins on three-dimensional and unsteady fluid flow and heat transfer past a bluff body. The detail structures of fluid flow and temperature field are obtained as a function of time to investigate how the presence of fins changes heat transfer mechanism related to the vortical structure in the wake region.

• Nuclear Engineering and Technology
• /
• 제26권2호
• /
• pp.212-224
• /
• 1994

원형도관내의 비점성유동장에 놓인 동심인 유연성 실린더의 안정성을 분석하기 위하여 수치해석적방법이 개발되었다. 진동하는 실린더에 작용하는 비정상·비점성 유체유발력을 스펙트럼 배치방법을 사용하여 지배방정식을 단순화시키지 않음으로서 더 정밀하게 예측하였다. 본 수치해석이론은 기존의 퍼텐샬이론과 비해 비교적 넓은 환의 경우와 짧은 실린더의 경우에도 적용할 수 있다. 비점성유동의 지배방정식은 라플라스방정식으로부터 구하였다. 유체유동과 결부된 실린더의 유동방정식은 갤러킨의 방법에 의하여 불연속방정식으로 표시되며 이로부터 계의 운동특성을 검토하였다. 계가 좌굴현상에 의하여 안정성을 잃는 임계유속에 대한 환의 간격과 실린더의 길이의 영향이 검토되었다. 수치해석방법을 입증하기 위하여 얇은 막 근사이론에 근거를 두고 호프슨이 제안한 퍼텐샬이론을 개선하였다. 계의 안정성과 동적특성을 수치해석방법에 의하여 예시하였고 기존의 이론과 본 연구에서 제안된 근사법으로 구한 결과와 비교하여 잘 일치함을 보였다. 무차원화된 임계유속은 환의 간격이 넓을수록 실린더의 길이 가 짧을수록 증가함을 보였다.

• Journal of Magnetics
• /
• 제21권3호
• /
• pp.468-475
• /
• 2016

In this article, entropy generation on MHD Williamson nanofluid over a porous shrinking sheet has been analyzed. Nonlinear thermal radiation and chemical reaction effects are also taken into account with the help of energy and concentration equation. The fluid is electrically conducting by an external applied magnetic field while the induced magnetic field is assumed to be negligible due to small magnetic Reynolds number. The governing equations are first converted into the dimensionless expression with the help of similarity transformation variables. The solution of the highly nonlinear coupled ordinary differential equation has been obtained with the combination of Successive linearization method (SLM) and Chebyshev spectral collocation method. Influence of all the emerging parameters on entropy profile, temperature profile and concentration profile are plotted and discussed. Nusselt number and Sherwood number are also computed and analyzed. It is observed that entropy profile increases for all the physical parameters. Moreover, it is found that when the fluid depicts non-Newtonian (Williamson fluid) behavior then it causes reduction in the velocity of fluid, however, non-Newtonian behavior enhances the temperature and nanoparticle concentration profile.