• Journal of Advanced Marine Engineering and Technology
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• 제31권7호
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• pp.833-841
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• 2007

The aim of this paper is to analyze the conjugate problems of heat conduction in solid walls coupled with laminar free convection flow adjacent to a vertical flat plate under boundary layer approximation. Using the similarity transformations the governing boundary layer equations for momentum and energy are reduced to a system of partial differential equations and then solved numerically using Finite Difference Method(FDM) known as the Keller-box scheme. Computed solutions to the governing equations are obtained for a wide range of non-dimensional parameters that are present in this problem, namely the coupling parameter P. the Prandtl number Pr and the heat generation parameter Q. The variations of the local heat transfer rate as well as the interface temperature and the friction along the plate and typical velocity and temperature profiles in the boundary layer are shown graphically. Numerical solutions have been consider for the Prandtl number Pr=0.70

• 대한기계학회논문집B
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• 제21권4호
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• pp.509-517
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• 1997

Results of flat plate compressible boundary layer calculation, based on discrete formulation of DSMC method, are presented in low Mach number and low Knudsen number range. The free stream is a uniform flow of pure nitrogen at various Mach numbers in low pressures (i.e. rarefied gas). Complete thermal accommodation and diffuse molecular reflections are used as the wall boundary condition, replacing unreal no-slip condition used in continuum calculations. In the discrete formulation of DSMC method, there is no need to use ad hoc assumptions on transport properties like viscosity and thermal conductivity, instead viscosity is calculated from values of other field variables (velocity and shear stress). Also the results are compared with existing self-similar continuum solutions. In all Mach number cases computed, velocity slip is most pronounced in regions near the leading edge where continuum formulation renders the solution singular. As the boundary layer develops further downstream, velocity slips asymptote to values that are between 10 to 20% of the magnitude of free stream velocity. When the free stream number density is reduced, so the gas more rarefied, the velocity slip increases as expected.

• Journal of Mechanical Science and Technology
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• 제15권10호
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• pp.1451-1460
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• 2001

The critical condition of the onset of buoyancy-driven convective motion of uniformly heated horizontal fluid layer was analysed by the propagation theory which transforms the disturbance quantities similarly. The dimensionless critical time, $\tau$$\sub$c/, is obtained as a function of the Rayleigh number and the Prandtl number. Based on the stability criteria and the boundary-layer instability model, a new heat transfer correlation which can cover whole range of Rayleigh number was derived. Our theoretical results predict the experimental results quite reasonably.

• International journal of advanced smart convergence
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• 제7권4호
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• pp.57-65
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• 2018

Artificial neural network is inspired by the biological neural network. For simplicity, in computer science, it is represented as a set of layers. Many research has been made in evaluating the number of neurons in the hidden layer but still, none was accurate. Several methods are used until now which do not provide the exact formula for calculating the number of thehidden layer as well as the number of neurons in each hidden layer. In this paper model selection approach was presented. Proposed model is based on geographical analysis of decision boundary. Proposed model selection method is useful when we know the distribution of the training data set. To evaluate the performance of the proposed method we compare it to the traditional architecture on IRIS classification problem. According to the experimental result on Iris data proposed method is turned out to be a powerful one.

• 대한전자공학회논문지SD
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• 제39권4호
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• pp.41-54
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• 2002

본 논문에서는 등가회로를 이용하여 브래그 반사층형 FBAR (Film Bulk Acoustic Wave Resonator) 와 membrane 형 FBAR 그리고 상 하부 전극이 공기와 접하는 이상적인 FBAR 의 특성을 서로 비교함으로서 브래그 반사층과 membrane 이 공진 특성에 미치는 영향을 분석하였다. 압전층으로는 ZnO, membrane 층과 낮은 음향적인 임피던스 반사층은 SiO₂, 높은 음향적인 임피던스 반사층으로는 W, 전극층으로는 Al를 가정하였고 각 층은 탄성파 전달 손실을 가정하였다. 1-port 의 등가회로를 ABCD 파라미터를 추출할 수 있는 단순화된 등가회로로 변환하여 ABCD 파라미터를 추출하여 입력임피던스를 계산하였다. 필터 설계에서는 구하여진 파라미터를 산란행렬로 변환하여 필터의 대역폭 및 삽입손실을 구하였다. 전극층, 반사층, membrane 층의 두께 변화에 의한 공진주파수의 변화는 membrane 층과 전극 바로 아래의 반사층의 두께 변화가 가장 큰 영향을 미친다는 결과를 확인하였다. 반사층 구조에서 반사층수에 따른 공진특성과 K/sub eff/와 electrical Q 의 변화에서는 반사층수가 K/sub eff/ 에는 거의 영향을 미치지 않지만 electrical Q 는 층수가 증가할수록 증가하다가 7층 이상에서 포화되었다. 또한 FBAR의 electrical Q 는 membrane 층과 반사층의 mechanical Q 에 의존함을 알 수 있었다. Ladder 필터와 SCF(Stacked Crystal Filters) 모두 공진기의 수가 증가할수록 삽입손실과 out-of-band rejection 이 증가하였고 층수가 증가할수록 삽입손실은 감소하지만 대역폭에는 거의 변화가 없었다. membrane형의 ladder 필터와 SCF 는 불효 공진 특성으로 인한 불효응답특성이 나타났다. 또한 ladder 필터는 보다 우수한 대역폭의 skirt-selectivity 특성을 나타내었으며 SCF 는 대역폭의 삽입손실 측면에서 더 우수하였다.

• 한국CDE학회논문집
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• 제10권6호
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• pp.421-431
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• 2005

This paper introduces a new approach for saving build time of hybrid rapid prototyping by decomposing a part into minimum number of layers. In the hybrid rapid prototyping, a part of a complicated shape is realized by adding layers of a simpler shape, each of which is obtained by machining a sheet of constant thickness from its top and bottom surfaces. Thus it is desired to decompose a given part into the minimum number of layers while guaranteeing each layer to be fabricated from the given sheets using a 3-axis milling machine. To satisfy these requirements, a concave edge-based algorithm is proposed to decompose a part into layers by considering the tool accessibility, the total number of layers, and the allowable sheet thickness.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.683-686
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• 2002

The hydrodynamic instability of the three-dimensional boundary-layer over a rotating disk has been numerically investigated for three cases flows using linear stability theory (i.e. Rossby number, Ro = -1, 0, and 1). Detailed numerical values of the disturbance wave number, wave frequency, azimuth angle, radius (Reynolds number, Re) and other characteristics have been calculated for $K{\acute{a}}rm{\acute{a}}n$, Ekman and $B{\"{o}}ewadt$ boundary-layer flows. Neutral curves for these flows are presented. Presented are the neutral stability results concerning the two instability modes (Type I and Type II) by using a two-point boundary value problem code COLUEW that was based upon the adaptive orthogonal collocation method using B-spline. The prediction from the present results on both instability modes among the three cases agrees with the previously known numerical and experimental data well.

• 대한기계학회논문집
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• 제19권7호
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• pp.1720-1730
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• 1995

Finite-difference analysis was conducted to study the natural convection of a stably stratified salt-water solution in an annulus due to lateral heating. The main purpose of this study is to examine in detail the multi-layered flow structure. Calculation was thus made for R $a_{\eta}$=2*10$^{5}$ and 6.5*10$^{5}$ . Formation of layered flow structure, merging process of layers, the corresponding temperature and concentration distributions, Nusselt number variations with time are examined. Numerical results show that in each layer, the temperature profile looks 'S`-shaped and the concentration profile is uniform due to the convective mixing. The formation of the roll and the layer is governed by natural convection due to the temperature gradient and the merging process of the layer by diffusion of the concentration.ation.

• 한국가시화정보학회지
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• 제15권3호
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• pp.27-33
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• 2017

Direct numerical simulations of turbulent channel flows with moving wall conditions on the top wall are performed to examine the effects of the moving wall on the turbulent characteristics. The moving wall velocity only applied to the top wall with the opposite direction to the main flow is systematically varied to reveal the sustained-mechanism for turbulence. The turbulence statistics for the Couette-Poiseuille flow, such as mean velocity, root mean square of the velocity fluctuations, Reynolds shear stress and pre-multiplied energy spectra of the velocity fluctuations, are compared with those of canonical turbulent channel flows. The comparison suggests that although the turbulent activity on the top wall increases with increasing the Reynolds number, that on the bottom wall decreases, contrary to the previous finding for the canonical turbulent channel flows. The increase of the turbulent energy on the top wall is attributed to not only the increase of the Reynolds number but also elongation of the logarithmic layer due to increase of the wall layer on the top wall. However, because the logarithmic layer is shortened on the bottom wall due to the decrease of the wall layer, the turbulence energy on the bottom wall decreases despite of the increase of the Reynolds number.

• 한국환경복원기술학회지
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• 제16권2호
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• pp.53-61
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• 2013

The present study elucidated the growth properties of Sasa borealis communities distributed in the lower layer of deciduous broadleaf forests in temperate zones and analyzed the correlation between the growth properties of S. borealis and positional environmental factors. The higher the culm height of S. borealis was, the higher the values of the leaf number, leaf area, and foliage layer thickness became. This might be because as the culm height of S. borealis increased, the acquisition of light sources became easier so that the biomass of leaves increased simultaneously for smooth anabolism. S. borealis seem to change their growth mode for smooth acquisition of light resources. The culm density of S. borealis and the leaf number, leaf area and foliage layer thickness of S. borealis did not show any clear correlation. The values of the culm height, leaf number, leaf area, and foliage layer thickness of S. borealis as the above altitude of the location of S. borealis increased. It seems like that growth conditions such as temperatures and winds are deteriorated as the above altitude of the location of S. borealis increased so that S. borealis becomes smaller. No clear correlations were shown between the physiochemical properties of soil and S. borealis' growth properties. It seems like that the growth of S. borealis complexly intertwined with diverse environmental factors and that due to the physiological integration of S. borealis, certain physiochemical properties do not unilaterally affect S. borealis' growth properties.