• Title, Summary, Keyword: 확산계수

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Diffusion of a Steady Horizontal Line Source in a Turbulent Shear Flow (난류전단(亂流剪斷) 흐름에서의 정상(定常) 수평(水平) 선오염원(線汚染源)의 확산(擴散))

  • Jun, Kyung Soo;Lee, Kil Seong
    • Journal of The Korean Society of Civil Engineers
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    • v.13 no.2
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    • pp.191-199
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    • 1993
  • Diffusion of a steady horizontal line source in a turbulent shear flow is simulated by numerically solving a steady two-dimensional advective diffusion equation. The computational result is compared with the analytic solution for uniform velocity and diffusivity distributions over the depth. The analytic solution for constant velocity and diffusivity overestimates the degree of vertical mixing. The normalized equation indicates that friction factor is the only physical parameter that governs the vertical diffusion process. Sensitivities of the diffusion process to the friction factor and initial source position are analyzed. The rate of vertical mixing varies approximately as the square root of the friction factor. The optimal source position, which gives the most rapid mixing, lies above the mid-depth and moves toward the water surface as the friction factor increases.

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Diffusion Coefficients of Polyimide/N-Methyl-2-Pyrrolidone Systems below Glass Transition Temperature (유리전이온도이하에서의 Polyimide/N-Methyl-2-Pyrrolidone계의 확산계수)

  • 박광승;김덕준
    • Polymer Korea
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    • v.24 no.2
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    • pp.194-200
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    • 2000
  • The diffusion coefficients in polyimide/N-methyl-2-pyrrolidone (NMP) systems were proposed using tile Vrentas-Duda's hole free volume theory. Several free volume parameters included in the diffusion coefficients were obtained from the fundamental physical properties of polyimide and NMP and group contribution theory, and the pre-exponential diffusion coefficient, D$_{0}$ was also determined from the dynamic swelling behavior of polyimide in NMP solution. The experimental swelling behavior of polyimide films in NMP was well described by the theoretical one using the proposed diffusion coefficient.t.

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Evaluation of Apparent Chloride Diffusion Coefficient and Surface Chloride Contents of FA concrete Exposed Splash zone Considering Crack Width (비말 지역에 노출된 FA 콘크리트의 균열을 고려한 겉보기 염화물 확산계수 및 표면 염화물량 평가)

  • Yoon, Yong-Sik;Kwon, Seung-Jun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.23 no.6
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    • pp.18-25
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    • 2019
  • The cracks occurred during service life of concrete structure should be considered in durability design, because of the concrete's material property which is weak in tensile strength. In this study, the fly ash concrete mixtures considering 2 levels of strength is designed and outdoor exposure tests are conducted for those concrete specimens. The exposure environment is set to a splash zone, and in order to evaluate the effect of crack width on the behavior of chloride diffusion, the crack width of up to 1.0 mm is generated at intervals of 0.1 mm at each concrete mixture. After that, apparent chloride diffusion coefficient and surface chloride contents are deducted considering 3 levels of exposure periods(180 days, 365 days, 730 days). The diffusion coefficients of two types of mixture increase with the increase of crack width, and the diffusion coefficients decrease with the increase of exposure periods. In addition, the effect of the crack width on the diffusion coefficient is reduced as the exposure periods increase, which is attributed to the extra hydrate by chloride ion reducing the diffusivity of concrete. The behavior of the surface chloride contents does not significantly change by the increase in crack width, compared to the behavior of apparent chloride diffusion coefficient. Also, In the high strength FA concrete mixture, the surface chloride contents are 78.9 % ~ 90.7 % than the normal FA strength concrete mixture. Thus, Surface chloride contents have correlation with the strength of concrete.

Relationship between Crack Width and Gas Diffusion Coefficient of Cracked Acrylic Specimens (균열 아크릴 시편의 기체 확산계수와 균열폭의 관계)

  • Lee, Do-Keun;Lim, Min-Hyuk;Shin, Kyung-Jun
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.6 no.4
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    • pp.245-251
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    • 2018
  • Recently, as the importance of structural maintenance has been increased, studies on self - healing concrete technology are being actively carried out. On the other hand, test for evaluating the self-healing performance is not standardized yet. Although visual test is used as a basic method for measuring crack widths, it is difficult to observe the crack width inside the specimen, and there is a disadvantage that only the local measurement of the surface can be measured due to the inhomogeneous cracking characteristics. Although permeability test has been widely used as an indirect method for measuring crack width, there is a problem due to the viscosity of water, and also a possibility that the internal material of the specimen may be eluted during the test. In this study, we propose a crack width evaluation method using gas diffusion characteristics. Idealized straight cracks were fabricated by acrylic and the diffusion coefficients of specimens were analyzed with respect to crack width and thickness. The experimental results show that the crack width and the diffusion coefficient are in a linear relationship and that the thickness and diffusion coefficient are inversely related.

Evaluation of Chloride Diffusion Coefficients in Cold Joint Concrete Considering Tensile and Compressive Regions (인장 및 압축영역에서 콜드조인트 콘크리트의 염화물 확산계수 평가)

  • Mun, Jin-Man;Kwon, Seung-Jun
    • Journal of the Korea Concrete Institute
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    • v.28 no.4
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    • pp.481-488
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    • 2016
  • Concrete member has been subjected to dead and live loads in use, and the induced stress can affect not only structural but also durability behavior. In mass concrete construction, construction joint are required, however cold joint usually occur due to poor surface treatment and delayed concrete placing. The concrete with joint is vulnerable to both shear stress and chloride ingress. This paper presents a quantitative evaluation of cold joint and loading conditions on chloride diffusion behavior. With increasing tensile stress from 30% to 60%, chloride diffusion coefficient gradually increases, which shows no significant difference from result in the sound concrete. However chloride diffusion coefficient under 30% level of compressive stress significantly increases by 1.70 times compared with normal condition. Special attention should be paid for the enlarged diffusion behavior cold joint concrete under compressive stress.

Sensitivity Analysis of Parameters in a Depth Averaged Two-Dimensional Sediment Transport Model (수심적분 2차원 유사이동모형에 관계된 인자들의 민감도분석에 관한 연구)

  • Seo, Sang-Won;Yun, Byeong-Man
    • Journal of Korea Water Resources Association
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    • v.31 no.1
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    • pp.115-120
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    • 1998
  • In this paper, a depth-averaged two-dimensional transport model is introduced, and its error bound is presented as the results of sensitivity analysis. The results show that the calculated SS concentration is highly dependant on Manning roughness coefficient, mixing coefficient. fall velocity. and critical shear stress. On the other hand, water level and dispersion coefficient are proved to be less significant in the variation of SS concentration.

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Influence of Temperature on Chloride Ion Diffusion of Concrete (콘크리트의 염화물이온 확산성상에 미치는 온도의 영향)

  • So, Hyoung-Seok;Choi, Seung-Hoon;Seo, Chung-Seok;Seo, Ki-Seog;So, Seung-Young
    • Journal of the Korea Concrete Institute
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    • v.26 no.1
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    • pp.71-78
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    • 2014
  • The long term integrity of concrete cask is very important for spent nuclear fuel dry storage system. However, there are serious concerns about early deterioration of concrete cask from creaking and corrosion of reinforcing steel by chloride ion because the cask is usually located in seaside, expecially by combined deterioration such as chloride ion and heat, carbonation. This study is to investigate the relation between temperature and chloride ion diffusion of concrete. Immersion tests using 3.5% NaCl solution that were controlled in four level of temperature, i.e. 20, 40, 65, and $90^{\circ}C$, were conducted for four months. The chloride ion diffusion coefficient of concrete was predicted based on the results of profiles of Cl- ion concentration with the depth direction of concrete specimens using the method of potentiometric titration by $AgNO_3$. Test results indicate that the diffusion coefficient of chloride ion increases remarkably with increasing temperature, and there was a linear relation between the natural logarithm values of the diffusion coefficients and the reciprocal of the temperature from the Arrhenius plots. Activation energy of concrete in this study was about 46.6 (W/C = 40%), 41.7 (W/C = 50%), 30.7 (W/C = 60%) kJ/mol under a temperature of up to $90^{\circ}C$, and concrete with lower water-cement ratio has a tendency towards having higher temperature dependency.

Analysis of Correlation between Compressive Strength, Void Ratio and Chloride Diffusion Coefficient of Concrete Using Various Kinds of Cement (시멘트의 종류별 콘크리트외 강도 및 공극률과 염화물 확산계수의 상관관계 분석)

  • Yoon Eui-Sik;Lee Taek-Woo;Park Seung-Bum
    • Journal of the Korea Concrete Institute
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    • v.17 no.5
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    • pp.735-742
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    • 2005
  • The purpose of this study was to evaluate the salt water resistance of concrete depending on various types of cement. In this regard, 5 types of concrete were selected and their strength, void ratio and chloride ion diffusion characteristics were tested, and mutual correlation were analyzed. From the test results, the compressive strength and void ratio of concrete which using Type V cement was as good as Type I cement at long-term ages but the chloride diffusion coefficient of Type V cement was larger than Type I cement. And the concrete replacing some portion of the Type I cement with fly ash was superior in the cases of compressive strength, void ratio and the resistance of chloride ion permeation compared to the Type I cement with the lapse of ages. On the other hand, the compressive strength, the void ratio and the chloride diffusion coefficient of the concrete all indicated high levels of the correlation coefficient and the coefficient of determination regardless of the type of cement.

Assessment of Osteoporosis Based on Changes in SNR and ADC Values on MR Diffusion Weighted Images (확산강조영상에서 신호대 잡음비, 현성 확산 계수 변화에 따른 골다공증 평가)

  • Cho, Jae-Hwan;Kim, Yeong-Soo
    • Progress in Medical Physics
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    • v.21 no.1
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    • pp.70-77
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    • 2010
  • This study tested how S/N (Signal to Noise Ratio) ratios and ADC (apparent diffusion coefficient) values vary with different T-scores in a group of patients with osteoporosis. Based on DEXA (Dual Energy X-ray Absorptiometry) T-scores for L1.L4 for two groups of subjects consisting of 30 healthy people without osteoporosis and 30 patients who came for treatment of waist (lumbar or low back) pain and were suspected to have osteoporosis as judged from the simple X-ray findings, this study classified every spine into two groups of osteoporosis and osteopenia. Signal intensity measurements were made in the four regions of L1 to L4 on diffusion-weighted MR images obtained using 1.5T MR scanner, while ADC measurements were obtained from ADC map images. As an approach for quantitative analysis, the comparison of the variances in S/N ratios and ADC values for varying T-scores in the selected regions of interest was carried out based on averaged T-scores, S/N ratios, and ADC values. Also, the variances in S/N ratios and ADC values for each of the groups of osteoporosis and osteopenia, which were classified into by T-scores, were compared. For qualitative analysis, a careful naked eye examination of signal intensity differences in the area of L4 was made on T1-weighted sagittal images for each of the healthy (normal), osteopenia, and osteoporosis groups. In the qualitative analysis, it was found that for both the osteopenia group and the osteoporosis group, as T-scores deceased, the S/N ratios on diffusion-weighted MR images also decreased, with the greatest decrease in the S/N ratio found in the osteoporosis group. Additionally, among the three groups, the lowest S/N ratio was found in the osteoporosis group. With respect to ADC map, it was found that for both the osteopenia group and the osteoporosis group, as T-scores deceased, the ADC values on diffusion-weighted MR images also decreased, with the greatest decrease in the ADC values found in the osteoporosis group. Additionally, among the three groups, the lowest ADC value was found in the osteoporosis group. On the other hand, in the qualitative analysis, the osteoporosis group showed the highest signal intensity. Additionally, among the three groups, the lowest signal intensity was found in the healthy (normal) group. It was found that as osteoporosis progressed, S/N ratio and ADC decreased, whereas signal intensity increased on T1-weighted images. Also, in diagnosing osteoporosis, MRI tests turned out to be (more) effective.

쇄파대내의 확산

  • 유동훈
    • Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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    • pp.146-151
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    • 1993
  • 쇄파대에서 발생되는 연안류의 분포는 완만한 곡선분포를 보이는데 단순파인 경우이의 해석은 확산계수의 도입으로만 가능하다는 점은 널리 알려진 사실이다. Harris(1967)는 현장관측과 수조실험으로 이 분야 초기연구로서 쇄파대 확산의 변이를 무시하고 평균확산계수치만을 고려하였다. 연안류해석의 확고한 이론적 기초를 마련한 Longuet-Higgins(1970)는 그의 이론식 도출고정에서 확산계수 도입의 필요성을 인식하였으며, 특성길이로서 연안선으로부터의 거리를 택하고 특성속도로서 파속을 택하였으며 쇄파대내에서 파속은 군속도와 같다고 가정하였다. (중략)

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