• International Journal of Ocean System Engineering
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• v.3 no.2
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• pp.68-76
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• 2013

In this study, a 3D numerical model was used to predict nonlinear wave forces on a cylindrical pile installed in a shallow water region. The model was based on solving the viscous and incompressible Navier-Stokes equations for a two-phase flow (water and air) model and the volume of fluid method for treating the free surface of water. A new application was developed based on the cut-cell method to allow easy installation of complicated obstacles (e.g., bottom geometry and cylindrical pile) in a computational domain. Free-surface elevation, water particle velocities, and inline wave forces were calculated, and the results show good agreement with experimental data obtained by the Danish Hydraulic Institute. The simulation results revealed that the proposed model can, without the use of empirical formulas (i.e., Morison equation) and additional wave analysis models, reliably predict non-linear wave forces on an offshore wind turbine foundation installed in a shallow water region.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.5
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• pp.1-8
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• 2007

The present research is based upon the numerical analysis of a car windshield in order to represent the optimum design guide to improve the overall defrosting performance of the system. First, the control factors that highly affect the defrosting performance of a car windshield are chosen and afterwards, the optimum variables of each control factor are extracted out to analyze its performance. The main control factors for this research are respectively, the air injection angle of a defroster nozzle, the height of a nozzle outlet, and the ratio of the width to the height of a nozzle outlet. For such case when the air inlet angle is relatively small, the flow near the vicinity of the inner face of a windshield tends to expand. As a consequence, the heat transfer rate through the windshield decreases. Also, the height of a nozzle outlet is recommended to maintain its size to minimum. However, when the ratio mentioned before is designed less than unity, the defrosting performance decreases.

• Journal of Chest Surgery
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• v.14 no.3
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• pp.302-306
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• 1981

Aorticopulmonary window is a rare anomaly among congenital heart disease. Various terms have been suggested including A-P window, A-P fenestration, fistula, aorticseptal defect etc. The defect lies usually between the left side of the ascending aorta and right wall of the pulmonary artery just anterior to the origin of the right main pulmonary artery. We have experienced one case of aorticopulmonary septal defect which was diagnosed as V5D with pulmonary hypertension in 1 4/12 year old, 7.2 Kg, male patient. Operation was done under the hypothermic cardiopulmonary bypass using 5t. Thomas cardioplegic solution. Vertical right ventriculotomy over the anterior wall of RVOT revealed no defect in the ventricular septum, and incision was extended up to the main pulmonary artery to find the source of massive regurgitation of blood through MPA. Finger tip compression of the aorticopulmanary window was replaced with Foley bag catheter balloon, and the $7{\times}10$ mm aorticoseptal defect located 15mm above the pulmonic valve was sutured continuously wih 3-0 nylon suture during azygos flow of cardiopulmonary cannula which was located distal to the window resulted massive air pumping systemically, and temporary reversal of pumping was tried to minimize cerebral air embolism. Remained procedure was done as usual, and pump off was smooth and uneventful. Postoperatively, patient was attacked frequent opistotonic seizure with no recovery sign mentally and p.hysically. Vital signs were gradually worsen with peripheral cyanosis and oliguria, and cardiac activity was arrested 1485 minutes after operation. Autopsy was performed to find the sutured window and massive edema of the brain.

• Advances in aircraft and spacecraft science
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• v.10 no.4
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• pp.317-334
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• 2023

This paper presents a basic methodology and a set of numerical tools for the preliminary design of solid-fueled ramjet missiles. An elementary code determines the baseline system configuration comprised of warhead, guidance-control, and propulsion masses and geometries from specific correlations found in the literature. Then, the system is refined with the help of external and internal ballistics codes. Equations of motion are solved for the flight's ascending, cruising, and descending stages and the internal ballistic set of equations designs the ramjet engine based on liquefying fuels. The combined tools sized the booster and the ramjet sustainer engines for a long-range missile, intended to transport 200 kg of payload for more than 300 km range flying near 14,000 m altitude at Mach 3.0. The refined system configuration had 600 mm in diameter and 8,500 mm in length with overall mass of 2,128 kg and 890 kg/m3 density. Ramjet engine propellant mass fraction was estimated as 74%. Increased missile range can be attained with paraffin-polyethylene blend burning at near constant regression rate through primary air mass flow rate control and lateral 2-D air intakes.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.525-530
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• 2001

As a part of efforts to examine feasibility of warm forging near-net-shape process for non-heat-treated steel to replace quenched and tempered S45C steel, the optimized process condition has been determined to be $820^{\circ}C$ for heating, 10/sec for strain rate of forging and approximately 250MPa for flow stress from observed results such as the $A_{3}$ transformation temperature of about $790^{\circ}C$, the fully dynamic recrystallized behavior between $800^{\circ}C\;and\;850^{\circ}C$ when compressed up to 63% engineering strain at 10/sec strain rate, and the high temperature microsturctural stability. Also, controlled cooling rate of $6.3^{\circ}C/sec$ by water-spraying at a rate of $0.10cc/sec-cm^{2}$ for 60seconds followed by air-cooling right after forging process has been considered in this study as a feasible approach based on examination of the microsturcture of mixed ${\alpha}-ferrite$ and pearlite, the hardness and tensile properties meeting specification, and the reduced total cooling time to room temperature. Successive works would be carried out for the impact strength, machinalility, and forgeability at this process in the near future.

• Journal of Environmental Impact Assessment
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• v.20 no.3
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• pp.299-311
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• 2011

The objective of this paper is to present a methodology for the classification of spatial patterns considering the parameters of urban form which play a significant role in the formation of the urban climate. The urban morphological parameters, i.e. building coverage, impervious pavement, vegetation, water, farmland and landuse types were used to classify the spatial patterns by a K-means cluster analysis. And the presented methodology was applied on Changwon city, South Korea. According to the results of cluster analysis, the total spatial patterns were classified as 24 patterns. First of all, The spatial patterns(A-1, A-2, A-3, B-1, B-2, B-3, C-1, C-2, C-3, D-1, D-2, D-3, E-1, E-2, E-3, F-1, F-2, F-3, G-1, G-2, G-3), which distributed in the rural area and the suburban area, can have the positive impacts of cold air generation and wind corridor on an urban climate environment, were distributed in the rural area. On the other hand, the spatial patterns of the downtown area including A-4, B-4, C-4 and D-4 are expected to have the negative impacts on urban climate owing to the of artificial heat emission or the wind flow obstruction. Finally, it will require the future research to analysis the climatic properties according to the same spatial patterns by the field survey.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.54-61
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• 2018

Incomplete combustion in automotive engines is a major cause of harmful exhaust gases. In this study, to prevent incomplete combustion and reduce exhaust gas emissions, a gasket blade for increasing the air velocity was applied to the intake manifold, and the change in exhaust gas was investigated theoretically and experimentally. First, simulation analysis for flow according to the number and angle of the gasket blade was performed using a 3D flow analysis program. As an analysis result, the internal average velocity of the gasket blade was optimum at 6-blade with an angle of $30^{\circ}$. Based on the simulation results, experiments were conducted to verify the effects of the gasket blades on the exhaust gas in a non-load engine simulation system. As the engine speed was increased from 2000 to 4000 rpm, exhaust gases of HC, CO, and NOx decreased by 23.4%, 16.5%, and 3.8%, respectively, and the emission decreasing effect was reduced.

• Ocean Systems Engineering
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• v.6 no.3
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• pp.245-264
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• 2016

The iterative boundary element method (IBEM) developed originally before for cavitating two-dimensional (2-D) and three-dimensional (3-D) hydrofoils moving under free surface is modified and applied to the case of 2-D (two-dimensional) airfoils and 3-D (three-dimensional) wings over water. The calculation of the steady-state flow characteristics of an inviscid, incompressible fluid past 2-D airfoils and 3-D wings above free water surface is of practical importance for air-assisted marine vehicles such as some racing boats including catamarans with hydrofoils and WIG (Wing-In-Ground) effect crafts. In the present paper, the effects of free surface both on 2-D airfoils and 3-D wings moving steadily over free water surface are investigated in detail. The iterative numerical method (IBEM) based on the Green's theorem allows separating the airfoil or wing problems and the free surface problem. Both the 2-D airfoil surface (or 3-D wing surface) and the free surface are modeled with constant strength dipole and constant strength source panels. While the kinematic boundary condition is applied on the airfoil surface or on the wing surface, the linearized kinematic-dynamic combined condition is applied on the free surface. The source strengths on the free surface are expressed in terms of perturbation potential by applying the linearized free surface conditions. No radiation condition is enforced for downstream boundary in 2-D airfoil and 3-D wing cases and transverse boundaries in only 3-D wing case. The method is first applied to 2-D NACA0004 airfoil with angle of attack of four degrees to validate the method. The effects of height of 2-D airfoil from free surface and Froude number on lift and drag coefficients are investigated. The method is also applied to NACA0015 airfoil for another validation with experiments in case of ground effect. The lift coefficient with different clearance values are compared with those of experiments. The numerical method is then applied to NACA0012 airfoil with the angle of attack of five degrees and the effects of Froude number and clearance on the lift and drag coefficients are discussed. The method is lastly applied to a rectangular 3-D wing and the effects of Froude number on wing performance have been investigated. The numerical results for wing moving under free surface have also been compared with those of the same wing moving above free surface. It has been found that the free surface can affect the wing performance significantly.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.8-16
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• 2017

Most of small air vehicles with moving wing fly at low Reynolds number condition and the reduced frequency of the moving wing ranges from 0.0 to 1.0. The physical phenomena over the wing dramatically vary with the reduced frequency. This study examines experimentally the effect of the reduced frequency at low Reynolds number. The NACA0012 airfoil performs sinusoidal pitching motion with respect to the quarter chord with the four reduced frequencies of 0.1, 0.2, 0.4 and 0.76 at the Reynolds number $2.3{\times}10^4$. Smoke-wire flow visualization, unsteady surface pressure measurement, and unsteady force calculation are conducted. At the reduced frequency of 0.1 and 0.2, various boundary layer events such as reverse flow, discrete vortices, separation and reattachment change the amplitude and the rotation direction of the unsteady force hysteresis. However, the boundary layer events abruptly disappear at the reduced frequency of 0.4 and 0.76. Especially at the reduced frequency of 0.76, the local variation of the unsteady force with respect to the angle of attack completely vanishes. These results lead us to the conclusion that the unsteady aerodynamic characteristics of the reduced frequency of 0.2 and 0.4 are clearly distinguishable and the unsteady aerodynamic characteristics below the reduced frequency of 0.2 are governed by the boundary layer events.

• Journal of computational fluids engineering
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• v.18 no.3
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• pp.1-7
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• 2013

A pure oxygen combustion technology is crucial in Carbon Capture and Storage (CCS) technology especially in capturing of $CO_2$, where CCS will reduce 9 $GtCO_2$ by 2050, which is 19% of the total $CO_2$ reduction amount. To make pure oxygen combustion feasible, a regenerative system is required to enhance the efficiency of pure oxygen combustion system. However, an existing air combustion technology is not directly applicable due to the absence of nitrogen that occupies the 78% of air. This study, therefore, investigates the heat and fluid flow in a regenerative system for pure oxygen combustion by using commercial CFD software, FLUENT. Our regenerative system is composed of aluminium packed spheres. The effect of the amount of packed spheres in regenerator and the effect of presence or absence of a bypass of exhaust gas are investigated. The more thermal mass in regenerator makes the steady-state time longer and temperature variation between heating and regenerating cycle smaller. In the case of absence of bypass, the regenerator saturates because of enthalpy imbalance between exhaust gas and oxygen. We find that 40% of exhaust gas is to be bypassed to prevent the saturation of regenerator.