• Proceedings of the KSME Conference
• /
• 2001.06d
• /
• pp.642-647
• /
• 2001

This study represents numerical analysis on the thermal and fluid flow of the air layer in a solar collector. The boundary conditions was assumed that the top and bottom wall of the air layer have a heating and cooling surface. respectively. and this calculation model have a solid body with a cooling temperature of $20^{\circ}C$. As the results of simulations. the magnitudes of the velocity vectors and isotherms are increased proportionally to the tilt angles. As the tilt angle is increased. the mean Nusselt numbers are increased and the maximum value of the mean Nusselt number was appeared at tilt angle ${\theta}=75^{\circ}$.

• Journal of the Korean Society of Visualization
• /
• v.15 no.3
• /
• pp.27-33
• /
• 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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.03a
• /
• pp.195-201
• /
• 2008

In the jet engines on the aircrafts cruising at high altitude over 20 km and subsonic speed, the Reynolds number in terms of the compressor blades becomes very low. In such an operating condition with low Reynolds number, it is widely reported that total pressure loss of the air flow through the compressor cascades increases dramatically due to separation of the boundary layer and the secondary-flow. But the detail of flow mechanisms causes the total pressure loss has not been fully understood yet. In the present study, two series of numerical investigations were conducted to study the effects of Reynolds number on the aerodynamic characteristics of compressor cascades. At first, the incompressible flow fields in the two-dimensional compressor cascade composed of C4 airfoils were numerically simulated with various values of Reynolds number. Compared with the corresponding experimental data, the numerically estimated trend of total pressure loss as a function of Reynolds number showed good agreement with that of experiment. From the visualized numerical results, the thickness of boundary layer and wake were found to increase with the decrease of Reynolds number. Especially at very low Reynolds number, the separation of boundary layer and vortex shedding were observed. The other series, as the preparatory investigation, the flow fields in the transonic compressor, NASA Rotor 37, were simulated under the several conditions, which corresponded to the operation at sea level static and at 10 km of altitude with low density and temperature. It was found that, in the case of operation at high altitude, the separation region on the blade surface became lager, and that the radial and reverse flow around the trailing edge become stronger than those under sea level static condition.

• Journal of computational fluids engineering
• /
• v.3 no.1
• /
• pp.73-81
• /
• 1998

The effect of vertical or horizontal throughflow on natural convection in horizontal porous layer was investigated. The computations were performed by employing Darcy-Brinkman-Forchheimer equation to consider the effect of inertia and viscous effect. The patterns of streamlines and isotherms are observed by changing the strength of throughflow. The vertical throughflow stabilizes the natural convection in porous layer. It also disturbs the developing vertical and horizontal velocity component of natural convection cell and increases the critical modified Rayleigh number. The horizontal throughflow influences the stabilization of natural convection in porous layer much more than the vertical throughflow. And it changes a stable convection into a oscillatory convection.

• Journal of the Korean Institute of Telematics and Electronics B
• /
• v.32B no.9
• /
• pp.1137-1153
• /
• 1995

It is not yet possible to solve the optimal number of neurons in hidden layer at neural networks. However, it has been proposed and proved by experiments that there is a limit in increasing the number of neuron in hidden layer, because too much incrememt will cause instability,local minima and large error. This paper proposes a module neural controller with pattern recognition ability to solve the above trade-off problems and to obtain fast learning convergence speed. The proposed neural controller is composed of several module having Multi-layer Perrceptron(MLP). Each module have the less neurons in hidden layer, because it learns only input patterns having a similar learning directions. Experiments with six joint robot manipulator have shown the effectiveness and the feasibility of the proposed the parallel module neural controller with pattern recognition perceptron.

• Journal of the Korean Society of Clothing and Textiles
• /
• v.46 no.4
• /
• pp.565-582
• /
• 2022

In recent years, Jumchi-Hanji made of mulberry paper is used as a material for fashion items. This study examined the effect of the type of Choji method (Oebal-teugi or Ssangbal-teugi), layer number (one or two layers) and Jumchichigi time (20, 40, or 60 minutes) on the tensile, wet tensile, tearing and bursting strengths of Jumchi-Hanji. Jumchi-Hanjis used as test samples in this study were made from mulbery paper which was manufactured with either bleached or unbleached paper mulberry from Thailand. The results showed that Jumchi-Hanji made with two layers of mulberry papers had higher strength properties than Jumchi-Hanji made with only one layer. The strength properties of Jumchi-Hanji also increased with longer Jumchichigi time. Furthermore, this study confirmed that the effects of Jumchichigi time on Jumchi-Hanji strengths differed based on the type of Choji method, the layer number of mulberry papers used, and the specific strength property measured. Therefore, to guarantee the strength properties required by the application of Jumchi-Hanji paper as a fashion material, it is necessary to carefully consider the adequate Choji method and layer number to apply in the manufacture of Thai mulberry paper and the adequate duration time needed to perform Jumchichigi to Thai mulbery paper.

• Archives of Plastic Surgery
• /
• v.32 no.3
• /
• pp.357-362
• /
• 2005

The aim of this study is to elucidate the effect of keratinase on epidermis of rat skin. Twenty-five male Sprague-Dolly rats were used. The hair on the back were removed and $2{\times}2cm$ area was marked. The rats were divided five groups; 1) Control group(Co), 2) Cleansing gel group(Cl), 3) Cleansing gel+keratinase group, 4) Exfoliant gel group(Ex), and 5) Exfoliant gel+ keratinase group(Ex+K). The solutions were applied to the back area twice a day for five days. On fifth day, the skins were harvested, fixed and prepared for histologic sections. The thickness of keratin layer, living epidermis, dermis, and cell layer number of living epidermis were measured. In the group containing keratinase(Cl+K, Ex+K), the thickness of keratin layer and living layer were thinner than other groups. However, there were no significant differences of the cell layer number of living epidermis and thickness of the dermis among the five groups. We think the keratinase may have the effect thinning the keratin layer as well as the thickness of living epidermis, without effecting the living cell and dermal component. The keratinase containing soap may be of benefit to remove the excess keratin layers in human.

• Nuclear Engineering and Technology
• /
• v.49 no.8
• /
• pp.1758-1771
• /
• 2017

In this study, to determine the most effective alloy for shielding against gamma-rays, the gamma-ray shielding parameters of six types of cerrobend alloys have been investigated. Gamma-ray interaction with the cerrobend alloys has been discussed mainly in terms of total mass attenuation coefficient (${\mu}_t$), half value layer (HVL), tenth value layer (TVL), effective atomic number ($Z_{eff}$), and effective electron density ($N_{eff}$). These parameters have been calculated by theoretical approach using the ParShield program in a photon energy range between 0.1 MeV and 100 GeV. The dependence of these parameters on the incident photon energy and chemical composition of the cerrobend alloys has been studied.

• Nuclear Engineering and Technology
• /
• v.49 no.1
• /
• pp.216-223
• /
• 2017

In this work, linear and mass attenuation coefficients, effective atomic number and electron density, mean free paths, and half value layer and $10^{th}$ value layer values of barium-bismuth-borosilicate glasses were obtained for 662 keV, 1,173 keV, and 1,332 keV gamma ray energies using MCNP-4C code and XCOM program. Then obtained data were compared with available experimental data. The MCNP-4C code and XCOM program results were in good agreement with the experimental data. Barium-bismuth-borosilicate glasses have good gamma ray shielding properties from the shielding point of view.

• International Journal of Aerospace System Engineering
• /
• v.2 no.2
• /
• pp.6-9
• /
• 2015

A new cross disciplinary conception of transitional aero-optics is built up during analyzing and measuring the linkage between the hypersonic boundary layer transition on a flat plate and the jittering characteristics of the small-aperture beam through that boundary layer. Based on that conception, the Small-Aperture Beam Technique (SABT) and high-speed Imaging Camera System (ICS) used in aero-optical studies are considered as new techniques for the assessment of the hypersonic transition in the boundary layer on a flat plate. In the FD-20 gun tunnel, for the free stream parameters with Mach number of 8 and unit Reynolds number of $1{\times}10^7$ (1/m), those two optical techniques are used to measure the jitter of the small-aperture beam. At the same free stream parameters, the distribution of the heat transfer along the centerline of the flat plate is also measured by the thin film resistance gauge technique. The results show the similarity of the increase trend between the heat transfer and the jitter of the small-aperture beam in the transitional region. It helps us to surmise that it may be feasible to diagnose the transition in a hypersonic boundary layer on a flat plate by means of those above optical techniques.