• 수산해양기술연구
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• 제56권4호
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• pp.395-406
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• 2020

The objectives of this study were to develop the optimal structures of recirculating aquaculture tank for improving the removal efficiency of solid materials and maintaining water quality conditions. Flow analysis was performed using the CFD (computational fluid dynamics) method to understand the hydrodynamic characteristics of the circular tank according to the angle of inclination in the tank bottom (0°, 1.5° and 3°), circulating water inflow method (underwater, horizontal nozzle, vertical nozzle and combination nozzle) and the number of inlets. As the angle in tank bottom increased, the vortex inside the tank decreased, resulting in a constant flow. In the case of the vertical nozzle type, the eddy flow in the tank was greatly improved. The vertical nozzle type showed excellent flow such as constant flow velocity distribution and uniform streamline. The combination nozzle type also showed an internal spiral flow, but the vortex reduction effect was less than the vertical nozzle type. As the number of inlets in the tank increased, problems such as speed reduction were compensated, resulting in uniform fluid flow.

• 대한기계학회논문집B
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• 제27권3호
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• pp.347-356
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• 2003

The characteristics of near wakes of circular cylinders with serrated fins are investigated experimentally using a hot-wire anemometer for various freestream velocities. Near wake structures of the fin tubes are observed using a phase average technique. With increasing fin height and decreasing fin pitch. oscillation of streamwise velocity increases. It file oscillation of lateral velocity decreases. The time averaged V-component velocity distribution of the finned tube is contrary to that of the circular cylinder due to the different strength of entrainment flow. This strength is affected by the distance of (equation omitted) = 1.0 contour lines. (equation omitted) = 1.0 contour line approaches to the wake center line when the fin density is increased. When the distance between (equation omitted) = 1.0 contour lines comes close the shear force should be increased and the flow toward the wake center line can be more strengthened because of the shear force. Factors related to the velocity recovery in the near wake of the finned tube are attributed to tile turbulent intensity, the boundary layer thickness. the position and strength of entrainment process.

• 한국소음진동공학회논문집
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• 제17권1호
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• pp.41-47
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• 2007

Scattering fields of two dimensional acoustic waves by a circular cylinder are investigated. The present numerical approach for the acoustic scattering problem has difficulties of numerical robustness, long-time stability and suitability of far-field boundary treatments. The time-dependent periodic acoustic source is used to analyze Interference patterns between incident waves and waves reflected by the cylinder. Characteristic boundary algorithms coupled with 4th order Modified-Flux-Approach ENO(essentially non-oscillatory) schemes are employed in generalized coordinates to examine the effect of the wane frequency on the interference patterns. Non-reflecting boundary conditions, which is crustal for accurate computations of aeroacoustic problems, are used not to contaminate scattering fields by reflected waves at the outer boundary. Computed scattering fields show the circumferential acoustic modes generated by interacting between acoustic sources and scattered waves. At a lower frequency, the wave passes almost straight through the cylinder without Interacting with circular cylinder. Simulation results are presented and compared with the analytic solution. Computed RMS-pressure distribution on the cylinder wall is good agreement with exact solution.

• Applied Microscopy
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• 제27권1호
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• pp.1-12
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• 1997

Dorsal and ventral epithelium of leech, Whitemenia edentula, were observed, using both light and electron-microscope. Results are as follows. Epithelia are composed of simple columnar or irregularly-shaped epithelium, the transveral folds were seen in the cross-sectioned dorsal and ventral epithelia, but only longitudinal folds(depth $500{\mu}m$, width $350{\mu}m$) were discovered in the ventral epithelium. As to muscular tissue under the dorsal epithelium of Whitemenia edentula, that of longitudinal muscle layer is thicker and more developed than that of circular muscle layer. Seven gland cells (type-A, B, C, D, E, F and H cells) and one pigment cell (type-G cell) were discovered in the whitemenia edentula. Those were identified as three kinds of the neutral mucopolysaccharide granoles (type-A, B and F cells), two kinds of acidic mucopolysaccharide granules (type-C and D cells), and two kinds of non-reactive granules respectively (type-E and F cells). The glanules of the type-A and type-B gland cells ae electronly high-dense, and surrounded by the muscular tissue. As to the distribution of gland cells, the type-A, type-B, type-C, type-D, type-I and type-H gland cells were discovered only between the connective tissue and the circular muscle layer, while type-F gland cells were discovered only between tile circular muscle layer and the longitudinal muscle layer.

• Wind and Structures
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• 제5권1호
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• pp.49-60
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• 2002

This paper describes a simple method for evaluating the design wind loads for the structural frames of circular flat roofs with long spans. The dynamic response of several roof models were numerically analyzed in the time domain as well as in the frequency domain by using wind pressure data obtained from a wind tunnel experiment. The instantaneous displacement and bending moment of the roof were computed, and the maximum load effects were evaluated. The results indicate that the wind-induced oscillation of the roof is generally dominated by the first mode and the gust effect factor approach can be applied to the evaluation of the maximum load effects. That is, the design wind load can be represented by the time-averaged wind pressure multiplied by the gust effect factor for the first mode. Based on the experimental results for the first modal force, an empirical formula for the gust effect factor is provided as a function of the geometric and structural parameters of the roof and the turbulence intensity of the approach flow. The equivalent design pressure coefficients, which reproduce the maximum load effects, are also discussed. A simplified model of the pressure coefficient distribution is presented.

• Fibers and Polymers
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• 제4권3호
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• pp.135-144
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• 2003

Permeability of the preform is one of key factors in design of RTM (Resin Transfer Molding) mold, determination of processing conditions, and modeling of flow in the mold. According to previous studies, permeability measured in the unsaturated fiber mats are higher than that in the saturated fiber mats by about 20% because of the capillary pressure. In this study, permeabilities of several fiber preforms are measured for both saturated and unsaturated flows. A saturated experiment of radial flow has been adopted to measure the permeability of anisotropic fiber preforms with high fiber content, i.e., circular braided preforms. In this method, four pressure transducers are used to measure the pressure distribution. Permeabilities in different directions are determined and the experimental results show a good agreement with the theory. Since permeability is affected by the capillary effect, permeability should be measured in the unsaturated condition for the textile composites to be manufactured under lower pressure as in the Vacuum Assisted Resin Transfer Molding (VARTM).

• 대한기계학회논문집B
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• 제35권10호
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• pp.1005-1012
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• 2011

본 연구의 목적은 원형과 타원형 노즐에 발생되는 캐비테이션 유동에 대해 수치 계산을 통해 각각의 특성을 파악하는 것이다. 수치해석을 위해 상용코드인 FLUENT 6.2 을 사용하였고, 실험결과의 캐비테이션 형태와 수치계산에서 얻은 결과를 비교함으로써 계산결과의 타당성을 확인하였다. 주목할만한 결과로는 원형 노즐 내부의 캐이테이션 형상은 노즐 축방향으로 대칭적인 원통형을 가지는 반면, 타원형 노즐의 경우 장축의 캐이테이션 길이가 단축의 캐이테이션 길이보다 긴 말발굽 (horseshoe) 형태가 관찰되었다. 또한, 타원형 노즐의 경우 오리피스의 반경방향 속도는 오리피스의 장, 단축에서 확연히 다른 분포가 관찰되었다.

• 한국광학회지
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• 제4권1호
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• pp.90-100
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• 1993

단면의 모양이 반달꼴인 이산화규소 광도파로의 모우드특성을 분석할 수 있는 수치계산 프로그램을 구성하고, 이것을 써서 광도파로의 도파특성을 살펴보았다. 수치계산의 기본 원리는 파동함수를 비교적 모양이 간단한 조화함수로 전개함으로써 파동방정식을 행렬방정식으로 바꾸고, 이 행렬을 대각화하여 고유값과 고유벡터를 구하는 것이다. 이 논문에서는 이 원리를 실제 프로그램에 실현시키는 과정과 그때 생기는 문제점들의 해결방법을 설명하였다. 이 프로그램을 써서 단면의 모양이 반달꼴인 이산화규소 광도파로와 그외에 다른 몇몇 전형적인 단면을 갖는 광도파로의 도파모우드의 특성을 분석하였다.

• Smart Structures and Systems
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• 제18권3호
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• pp.525-540
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• 2016

The CFRP-confined circular concrete-filled steel tubular column is composed of concrete, steel, and CFRP. Its failure mechanics are complex. The most important difficulties are lack of an available method to establish a relationship between a specific damage mechanism and its acoustic emission (AE) characteristic parameter. In this study, AE technique was used to monitor the evolution of damage in CFRP-confined circular concrete-filled steel tubular columns. A fuzzy c-means method was developed to determine the relationship between the AE signal and failure mechanisms. Cluster analysis results indicate that the main AE sources include five types: matrix cracking, debonding, fiber fracture, steel buckling, and concrete crushing. This technology can not only totally separate five types of damage sources, but also make it easier to judge the damage evolution process. Furthermore, typical damage waveforms were analyzed through wavelet analysis based on the cluster results, and the damage modes were determined according to the frequency distribution of AE signals.

• Structural Engineering and Mechanics
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• 제85권3호
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• pp.419-432
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• 2023

This paper studies the effects of porosity distributions on buckling and post-buckling behaviors of a functionally graded saturated porous (FGSP) circular plate. The plate is under the uniformly distributed radial loading and simply supported and clamped boundary conditions. Pores are saturated with compressible fluid (e.g., gases) that cannot escape from the porous solid. Elastic modulus is assumed to vary continuously through the thickness according to three different functions corresponding to three different cases of porosity distributions, including monotonous, symmetric, and asymmetric cases. Governing equations are derived utilizing the classical plate theory and Sanders nonlinear strain-displacement relations, and they are solved numerically via shooting method. Results are verified with the known results in the literature. The obtained results for the monotonous and symmetric cases with the asymmetric case presented in the literature are shown in comparative figures. Effects of the poroelastic material parameters, boundary conditions, and thickness change on the post-buckling behavior of the plate are discussed in details. The results reveal that buckling and post-buckling behaviors of the plate in the monotonous and symmetric cases differ from the asymmetric case, especially in small deflections, that asymmetric distribution of elastic moduli can be the cause.