• 대한조선학회논문집
• /
• 제28권2호
• /
• pp.77-94
• /
• 1991

일정속도로 항주하는 배에 치하여 생성되는 파를 유한차분법을 이용하여 수치적으로 시뮬레이션 하였다. 지배방정식으로는 3차원 운동량방정식(Euler Eq.)과 연속방정식을 사용하였으며, 직교 좌표 계상에서의 수치계산은 FTCS(forward time/central space)로 차분화하고 시간전진 방법(time marching scheme)으로 수행하였다. 좌표계로 staggered variable mesh system을 채용하여 기존의 계산조직을 개선하므로써, 유체 유동의 변화가 심한 선체주위에 계산 정도를 높이기 위하여 cell을 집중시켰다. 개선된 전산프로그램을 이용하여 Wigley, Series 60($C_{b}$=0.6), 그리고 MS416B 산적화물선 선형등을 대상으로 수치계산을 수행하였으며, 그 결과들을 실험값과 비교하였다.

• 감성과학
• /
• 제6권3호
• /
• pp.29-43
• /
• 2003

본 연구에서는 남성과 여성에 있어서 정서적 자극에 대한 기억이 다른지를 알아보고자 하였다. 또한 제시되는 자극의 기억을 측정할 것이라는 기억지시문을 주고, 또한 자극제시 후 곧바로 자유회상의 방법으로 기억을 측정함으로써 정서적 자극으로 유발된 정서의 표현을 조절할 필요성을 가능한 최소화시켰다. 그리고 남성과 여성의 정서적 자극과 중성적 자극에 대한 기억을 측정함으로써 선행사건초점 정서조절 과정에 의해 남성들의 정서적 자극에 대한 기억이 손상됨을 밝히고자 하였다. 전체적으로 여성들이 남성들보다 제시된 자극에 대하여 더 많이 기억하고 있었으며, 특히 중성적 자극보다 정서적 자극에 대해 남성들보다 더 많은 내용을 회상하였다. 회상내용을 중심적 요소에 대한 기억과 지엽적 요소에 대한 기억으로 나누어 남녀 차이를 분석해본 결과, 여성들은 정서적 자극의 중심적 요소에 대하여 중성적 자극보다 더 많이 기억하였으나 남성들은 정서적 자극과 중성적 자극에 대한 중심적 요소에 대한 기억차이가 나타나지 않았다.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2012년도 추계 학술논문 발표대회
• /
• pp.55-57
• /
• 2012

In this study, the field applicability on reducing the heat of hydration of mass concrete by using the hydration heat difference method is analyzed with the following summary. As a result of applying the hydration heat difference method by using low heating combination, the temperature difference between the central part and the surface part of mass material was reduced, and as a result of visual observation, there was no showing of cracks by the hydration heat on the upper surface part. Therefore, the cracking index of the field to apply this method was shown to be approximately 1.57 with very little crack occurrence probability of less than 3%.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 춘계학술대회
• /
• pp.1827-1832
• /
• 2003

In this research, the simulation method for acoustic sounds by a uniform flow around a two-dimensional circular cylinder by using the finite difference lattice Boltzmann model is explained. To begin with, we examine the boundary condition which determined with the distribution function $f_i^{(0)}$ concerning with density, velocity and internal energy at boundary node. Very small acoustic pressure fluctuation, with same frequency as that of Karman vortex street, is compared with the pressure fluctuation around a circular cylinder. The acoustic sound' propagation velocity shows that acoustic approa ching the upstream, due to the Doppler effect in the uniform flow, slowly propagated. For the do wnstream, on the other hand, it quickly propagates. It is also apparently the size of sound pressure was proportional to the central distance $r^{-1/2}$ of the circular cylinder. The lattice BGK model for compressible fluids is shown to be one of powerful tool for simulation of gas flows.

• 한국멀티미디어학회논문지
• /
• 제18권12호
• /
• pp.1453-1461
• /
• 2015

Since digital images and videos are rapidly increasing in the internet with the spread of mobile computers and smartphones, research on image retrieval has gained tremendous momentum. Color, shape, and texture are major features used in image retrieval. Especially, color information has been widely used in image retrieval, because it is robust in translation, rotation, and a small change of camera view. This paper proposes a new method for histogram refinement based on local color difference. Firstly, the proposed method converts a RGB color image into a HSV color image. Secondly, it reduces the size of color space from 256³ to 32. It classifies pixels in the 32-color image into three groups according to the color difference between a central pixel and its neighbors in a 3x3 local region. Finally, it makes a color difference vector(CDV) representing three refined color histograms, then image retrieval is performed by the CDV matching. The experimental results using public image database show that the proposed method has higher retrieval accuracy than other conventional ones. They also show that the proposed method can be effectively applied to search low resolution images such as thumbnail images.

• Geomechanics and Engineering
• /
• 제23권1호
• /
• pp.1-13
• /
• 2020

To give a solution for seismic stability of tunnel faces subjected to earthquake ground shakings, the pseudo-dynamic approach is originally introduced to analyze tunnel face stability in this study. In the light of the upper-bound theorem of limit analysis, an advanced three-dimensional mechanism combined with pseudo-dynamic approach is proposed. Based on this mechanism, the required support pressure on tunnel face can be obtained by equaling external work rates to the internal energy dissipation and implementing an optimization searching procedure related to time. Both time and space feature of seismic waves are properly accounted for in the proposed mechanism. For this reason, the proposed mechanism can better represent the actual influence of seismic motion and has a remarkable advantage in evaluating the effects of vertical seismic acceleration, soil amplification factor, seismic wave period and initial phase difference on tunnel face stability. Furthermore, the pseudo-dynamic approach is compared with the pseudo-static approach. The difference between them is illustrated from a new but understandable perspective. The comparison demonstrates that the pseudo-static approach is a conservative method but still could provide precise enough results as the pseudo-dynamic approach if the value of seismic wavelengths is large or the height of soil structures is small.

• 한국윤활학회:학술대회논문집
• /
• 한국윤활학회 1999년도 제29회 춘계학술대회
• /
• pp.182-188
• /
• 1999

A theoretical study of elastohydrodynamic lubrication of elliptical contacts with both rolling and spin has been carried out. A finite difference method and the Newton-Raphson method are applied to solve the problem. The velocity vectors resulting from combined spin and rolling/sliding motion lead to asymmetric pressure distributions and film shapes. Film contours and variations of the minimum and central film thicknesses are compared with various spin-roll ratios. At high spin-roll ratios the minimum film thickness is considerably reduced, whereas the central film thickness decreases less dramatically, The present numerical scheme can be used in the analysis of general elliptical contact problems.

• Tribology and Lubricants
• /
• 제23권2호
• /
• pp.49-55
• /
• 2007

A numerical analysis of elastohydrodynamic lubrication of elliptical contacts with both rolling and spinning has been carried out. A finite difference method with non-uniform grid systems and the Newton-Raphson method are applied to solve the problems. The velocity vectors resulting from combined spinning and rolling/sliding motion lead to asymmetric pressure distributions and film shapes. Pressure distributions, film contours and variations of the minimum and central film thicknesses are compared with various spin-roll ratios. Reduction of the minimum film thickness under spinning is remarkable whereas the central film thickness is relatively less. The spin motion have large effect on variations of the minimum film thickness with load parameter which are small in pure rolling/sliding cases. Therefore present numerical scheme can be used in the analysis of general elliptical contact EHL problems and further studies are required.

• Tribology and Lubricants
• /
• 제24권6호
• /
• pp.355-361
• /
• 2008

In highly stressed machine elements such as angular contact ball bearings and toroidal type traction drives, the elastohydrodynamic lubrication of elliptical contacts with both rolling and spinning motion are occur. In this paper, a finite difference method with non-uniform grid systems and the Newton-Raphson method are applied to solve the problems. Pressure distributions, film contours and variations of the minimum and central film thicknesses are compared with various ellipticity parameter, dimensionless speed and load parameter. The results showed that the spinning motion has significant influence especially on the film shapes. Reduction of the minimum film thickness under spinning is remarkable whereas the central film thickness is relatively less. Especially variations of the minimum film thicknesses with rolling velocity, load and ellipticity ratio are a great different from those of pure rolling. Therefore present numerical scheme can be used in the analysis of general elliptical contact EHL problems and further studies are required.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1996년도 가을 학술발표회 논문집
• /
• pp.210-217
• /
• 1996

Under strong shock loads including earthquake or blast, structures may start to crack in stress concentrated members. The continuous behavior of the structure changes to the discontinuous. In this study, numerical method analyzing continuous and discontinuous behavior of a structure is developed using a modified distinct element method. Equations of motion of each distinct element are integrated using the central difference method, one of the finite difference methods. Interactions between he elements are considered by an element and pore spring. The forces acting in the center of an element include contact stress transferred by element spring; tensile stress by pore spring; and external traction such as earthquake or blast load. To verify the proposed method, the behavior of the cantilever beam subject to the quasi-static concentrated force at the end is investigated. The failure behavior of the simply supported beam subject to the strong shock at the center is studied. The proposed method can predict the failure behavior of the structure due to the shock loading and the post-failure discontinuous behavior of the structure.