• Title/Summary/Keyword: Central difference method

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A Numerical Simulation of Ship Waves by Finite Difference Method (유한차분법에 의한 임의 선체주위의 조파 Simulation)

  • Kyu-Jong Cho;Kang-Hoon Lee;Young-Gill Lee
    • Journal of the Society of Naval Architects of Korea
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    • v.28 no.2
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    • pp.77-94
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    • 1991
  • A finite difference method based on MAC method is used to simulate free-surface waves around a ship. Euler equations and continuity equation are differentiated using the forward time and central space, and solved by time marching scheme. By the employment of variable mesh system in horizontal and vertical direction, the numerical accuracy of wave simulation results is grossly improved. To verify the improvement of numerical accuracy, some numerical simulations are accomplished for Wigley, Series 60($C_{b}$=0.6) and a bulk carrier model. The computational results are compared to the various experimental data and show good agreements.

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Sex Differences in the memories for emotional stimuli (정서적 자극에 대한 기억에 있어서의 남녀 차이에 관한 연구)

  • 박수애;안진경
    • Science of Emotion and Sensibility
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    • v.6 no.3
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    • pp.29-43
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    • 2003
  • This study examined the difference in memories for emotional stimuli. After giving participants the memory task instruction that they should remember the given stimuli, the emotion-induced photographs and the neutral photographs were presented. To minimize the possibility to regulate the expressions of their mood which induced by emotional stimuli and to find out whether the antecedent-focused emotion regulation process would damaged the memory of emotional stimuli in men, participant's memory was measured directly after the presentation of each photograph by free reflection method. Also Sex differences in memories about emotional and neutral stimuli were measured and compared. Women memorized stimuli more than men, and as expected, women remembered more about the emotional stimuli than neutral ones. The analysis of sex difference about central and peripheral features indicated that women remembered central features of emotional stimulus more than those of neutral ones, but that men had no difference between central features of emotional stimuli and those of neutral ones. These results showed that men's damaged memories of emotional stimuli were caused by the antecedent-focused emotion regulation process.

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Field Application of a Technique for Reducing Hydration Heat-induced Cracks in Mass Concrete (수화발열량차 공법을 이용한 매트기초 매스콘크리트 균열저감 및 현장적용)

  • Jo, Man-Ki;Kim, Jun-Ho;Heo, Young-Sun;Han, Min-Cheol;Han, Cheon-Goo
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2012.11a
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    • pp.55-57
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    • 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%.

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Direct Simulation of Acoustic Sound by the Finite Difference Lattice Boltzmann Method (차분격자볼츠만법에 의한 유체음의 직접계산)

  • Kang, Ho-Keun;Ro, Ki-Deok;Lee, Young-Ho
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.1827-1832
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    • 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.

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Image Retrieval Using Histogram Refinement Based on Local Color Difference (지역 색차 기반의 히스토그램 정교화에 의한 영상 검색)

  • Kim, Min-KI
    • Journal of Korea Multimedia Society
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    • v.18 no.12
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    • pp.1453-1461
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    • 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.

Seismic stability analysis of tunnel face in purely cohesive soil by a pseudo-dynamic approach

  • Huang, Qi;Zou, Jin-feng;Qian, Ze-hang
    • Geomechanics and Engineering
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    • v.23 no.1
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    • pp.1-13
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    • 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.

An Analysis of Elastohydrodynamic Lubrication of Elliptical Contacts : Part II (타원접촉의 탄성유체윤활해석 : 제2보)

  • 박태조;현준수
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1999.06a
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    • pp.182-188
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    • 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.

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An Elastohydrodynamic Lubrication of Elliptical Contacts : Part II - The Effect of Spin Motion (타원접촉의 탄성유체윤활 : 제2보 - 스핀운동의 영향)

  • Park, Tae-Jo
    • Tribology and Lubricants
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    • v.23 no.2
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    • pp.49-55
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    • 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.

Elastohydrodynamic Film Thickness in Elliptical Contacts with Rolling and Spinning (구름/스핀 운동을 하는 경우의 타원접촉 EHL 유막두께)

  • Park, Tae-Jo
    • Tribology and Lubricants
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    • v.24 no.6
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    • pp.355-361
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    • 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.

A Study on Failure Behavior of Structures by Modified Distinct Element Method (수정개별요소법을 이용한 구조물의 파괴거동에 관한 연구)

  • 김문겸;오금호;김상훈;김우진
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 1996.10a
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    • pp.210-217
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    • 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.

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