• Journal of the Korean Institute of Gas
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• v.5 no.3 s.15
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• pp.1-8
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• 2001

This study was carried out for the purpose of determination of maintenance period and investigation of weak point due to freeze when the gas heater of KOGAS valve station Is not operated in winter season. 3-dimensional non-linear numerical simulation was conducted in order to predict the time and location which bath water in heater reaches to ice point. FLUENT V 5.0, commercial code, is used for thermal fluid flow analysis. We thought this was problem of heat conduction solving the energy equation and modeled gas heater by using the real geometry and scale for performing the 3-dimensional simulation. It was analyzed complex heat transfer phenomena considering convection due to air on surface, conduction in insulation material, natural convection of liquid in heater and heat loss through the pipe.

• Smart Structures and Systems
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• v.13 no.4
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• pp.587-614
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• 2014

In recent years the interest in online monitoring of lightweight structures with ultrasonic guided waves is steadily growing. Especially the aircraft industry is a driving force in the development of structural health monitoring (SHM) systems. In order to optimally design SHM systems powerful and efficient numerical simulation tools to predict the behaviour of ultrasonic elastic waves in thin-walled structures are required. It has been shown that in real industrial applications, such as airplane wings or fuselages, conventional linear and quadratic pure displacement finite elements commonly used to model ultrasonic elastic waves quickly reach their limits. The required mesh density, to obtain good quality solutions, results in enormous computational costs when solving the wave propagation problem in the time domain. To resolve this problem different possibilities are available. Analytical methods and higher order finite element method approaches (HO-FEM), like p-FEM, spectral elements, spectral analysis and isogeometric analysis, are among them. Although analytical approaches offer fast and accurate results, they are limited to rather simple geometries. On the other hand, the application of higher order finite element schemes is a computationally demanding task. The drawbacks of both methods can be circumvented if regions of complex geometry are modelled using a HO-FEM approach while the response of the remaining structure is computed utilizing an analytical approach. The objective of the paper is to present an efficient method to couple different HO-FEM schemes with an analytical description of an undisturbed region. Using this hybrid formulation the numerical effort can be drastically reduced. The functionality of the proposed scheme is demonstrated by studying the propagation of ultrasonic guided waves in plates, excited by a piezoelectric patch actuator. The actuator is modelled utilizing higher order coupled field finite elements, whereas the homogenous, isotropic plate is described analytically. The results of this "semi-analytical" approach highlight the opportunities to reduce the numerical effort if closed-form solutions are partially available.

• Advances in aircraft and spacecraft science
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• v.5 no.5
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• pp.581-594
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• 2018

This paper is the follow-on of a previous paper by the author where it was pointed out that the forthcoming, manned exploration missions to Mars, by means of complex geometry spacecraft, involve the study of phenomena like shock wave-boundary layer interaction and shock wave-shock wave interaction also along the entry path in Mars atmosphere. The present paper focuses the chemical effects both in the shock layer and on the surface of a test body along the Mars orbital entry and compares these effects with those along the Earth orbital re-entry. As well known, the Mars atmosphere is almost made up of Carbon dioxide whose dissociation energy is even lower than that of Oxygen. Therefore, although the Mars entry is less energized than the Earth re-entry, one can expect that the effects of chemistry on aerodynamic quantities, both in the shock layer and on a test body surface, are different from those along the Earth re-entry. The study has been carried out computationally by means of a direct simulation Monte Carlo code, simulating the nose of an aero-space-plane and using, as free stream parameters, those along the Mars entry and Earth re-entry trajectories in the altitude interval 60-90 km. At each altitude, three chemical conditions have been considered: 1) gas non reactive and non-catalytic surface, 2) gas reactive and non-catalytic surface, 3) gas reactive and fully-catalytic surface. The results showed that the number of reactions, both in the flow and on the nose surface, is higher for Earth and, correspondingly, also the effects on the aerodynamic quantities.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1367-1372
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• 2008

A plate type supporting structure of a tube bundle in axial flow generates a certain band of a high frequency periodic excitation of a vortex shedding and/or a flow separation due to sharp edge of the plate thickness and a severe pressure drop due to a cross-sectional area of the supports. With a design consideration of the low vibration and a small flow resistance, the analysis method is uniquely confined to an experimental approach because a complex geometry of a cylindrical tube bundle and/or physical phenomena related to the fluid-structure interaction of tube bundle in a flow impede a theoretical or a numerical approach. A 5x5 cylindrical tube bundle with 5 supports which were discretely located along the bundle's axis was tested in the FIVPET hydraulic test loop for a design evaluation and an analysis perspectives. A high frequency flow-induced vibration of the supporting structures of the cylindrical tube bundle was measured at a outer surface of a supporting structure through a transparent flow housing by the laser dopper vibrometer. Pressure drop in-between three measurement distances was measured by the differential pressure transmitter. High frequency vibration and pressure drop fairly depends on the geometric design of supporting structure. So, these two parameters would be used as a qualitative design variables for design evaluation and analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.11
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• pp.983-989
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• 2007

The bird strike simulation is a problem characterized by a high degree of uncertainty. It deals with nonlinear dynamics, complicated models of bird materials and geometry, as well as a plenty of possible boundary and initial conditions. In this complex field, uncertainty management plays an important role. This paper aims to assess the effect of input uncertainty of bird strike analysis on the impact behavior of the leading edge of the WIG(Wing in Ground Effect) craft obtained with finite element analysis using LS-DYNA 3D. The uncertainties of the bird strike simulation arise due to imprecision or lack of information, due to variability or scatter, or as a consequence of model simplification. These uncertain parameters are represented by fuzzy numbers with their membership functions quantifying an initial guess for the actual value of the model parameter. Using the transformation method as a special implementation of fuzzy arithmetic, the model can be analyzed with the intention of determining the influence of each uncertain parameter on the overall bird strike behavior.

• Journal of Korea Water Resources Association
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• v.35 no.5
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• pp.485-500
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• 2002

Hydraulic model was developed to analyze the complex flow due to channel structures, tide, and tributaries in the lower Han river and Imjin river. DWOPER-2K model which can automatically process the data transformation in the model was developed as the 1-D hydraulic routing model. Observed data in tidal zone and the recent channel geometry data were collected for hydraulic model. And the flow over the Jamsil and Singok submerged weir was analyzed properly and roughness coefficient was optimized to each regions and each discharges. By the results of verification of the model, the model developed in this study may contribute to improvement of the accuracy of flood forecasting and channel management because this model can efficiently and properly analyze the various kind of flow occurred in the region of the lower Han river and Imjin river.

• Journal of the Korean Chemical Society
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• v.45 no.5
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• pp.401-412
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• 2001

The geometrical parameters, vibrational frequencies, and dissociation energies for $H_{2n+1}^+$ (n=1~6) clusters have been investigated using high level ab initio quantum mechanical techniques with large basis sets. The equilibrium geometries have been optimized at the self-consistent field (SCF), the single and double excitation configuration interaction (CISD), the coupled cluster with single and double excitation (CCSD), and the CCSD with connected triple excitations [CCSD(T)] levels of theory. The highest levels of theory employed in this study are TZ2P+d CCSD(T) up to $H^+_g$ and TZ2P CCSD(T) for $H_{11}^+$ and $H_{13}^+$. Harmonic vibrational frequencies are also determined at the SCF level of theory with various basis sets and confirm that all the optimized geometries are true minima. The dissociation energies, $D_e$, for $H_{2n+1}^+$ (n=26) have been predicted using energy differences at each optimized geometry and zero-point vibrational energies(ZPVEs) have been considered to compare with experimental dissociation energies, $D_0$.

• Journal of the korean society of oceanography
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• v.37 no.3
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• pp.169-177
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• 2002

An eddy-resolving free-surface primitive-equation model with nonlinear terrain-following coordinates is established to study the exchange of water masses among the Asian marginal seas and their adjacent waters. A curvilinear coordinate system is used to generate the horizontal grid with a variable resolution for the regional oceans from $5^{\circ}$S to $45^{\circ}$N and $100^{\circ}$E to $155^{\circ}$E. The higher resolution region has about a 10 km by 10 km grid covering the complex geometry of the coastal marginal seas, while the lower resolution region has about a 30 km by 30 km grid covering the eastern Pacific. The model is initialized by the Levitus annual climitology and forced by the monthly mean air-sea fluxes of momentum, heat, and freshwater derived from the Comprehensive Ocean-Atmosphere Data Set. High-resolution and low-viscosity are identified as the key factors for a better representation of the exchange of waters through narrow straits and passages between the marginal seas and their adjacent waters. The dynamics of the loop currents and eddies in the South China Sea and Celebes Sea are examined in detail. It has found that the anticyclonic loop and detached eddies from the Kuroshio through the Luzon Strait play an important role in transporting warm and salty water into the South China Sea, while the cyclonic circulation of the Mindanao Current in the Celebes Sea plays a role in contributing cold water to the Indonesian throughflow. The deep undercurrent of the western Pacific is shown to provide fresher water to the South China Sea and Celebes Sea. These modeling results suggest that the exchange processes via the narrow straits and passages are of fundamental importance to the maintenance of water masses for the marginal sea region.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1456-1464
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• 1993

The achievable machining accuracy depends upon the level of the micro-engineering, and the dimensional tolerances in the order of 10 nm and surface roughness in the order of 1 nm are the accuracy targets to achieved today. Such requirements cannot be satisfied by the conventional machining processes. Single point diamond turning is one of the new techniques which can produce the parts with such accuracy limits. The aims of this thesis are to get a better understanding of the complex cutting forces. A cutting model for describing the influence of cutting conditions (cutting speed, feedrate and depth of cut), material properties of the workpiece and tool geometry has been proposed after estimating the two cutting force models-the Recht model and the Dautzenberg model. The experiments with Al-alloy workpieces, which have been carried out in order to estimate the models, show that the proposed model in this thesis is better than the two models. As the depth of cut and feedrate are increased in the operations settings (depth of cut 8-100$\mu{m}$, feedrate 8-140$\mu{m}$/rev, and cutting speed 8 m/sec), the relation of dimensionless cutting forces from experiments are similar to the proposed model. With the undeformed chip area of $30-80{\times}10^{2}$\mu{m}^2$, the experimental cutting forces accord with the force prediction.

• Journal of Biosystems Engineering
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• v.19 no.2
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• pp.124-137
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• 1994

Visual features of a mushroom(Lentinus Edodes, L.) are critical in grading and sorting as most agricultural products are. Because of its complex and various visual features, grading and sorting of mushrooms have been done manually by the human expert. To realize the automatic handling and grading of mushrooms in real time, the computer vision system should be utilized and the efficient and robust processing of the camera captured visual information be provided. Since visual features of a mushroom are distributed over the front and back sides, recognizing sides and states of the stalk including the stalk orientation from the captured image is a prime process in the automatic task processing. In this paper, the efficient and robust recognition process identifying the front and back side and the state of the stalk was developed and its performance was compared with other recognition trials. First, recognition was tried based on the rule set up with some experimental heuristics using the quantitative features such as geometry and texture extracted from the segmented mushroom image. And the neural net based learning recognition was done without extracting quantitative features. For network inputs the segmented binary image obtained from the combined type automatic thresholding was tested first. And then the gray valued raw camera image was directly utilized. The state of the stalk seriously affects the measured size of the mushroom cap. When its effect is serious, the stalk should be excluded in mushroom cap sizing. In this paper, the stalk removal process followed by the boundary regeneration of the cap image was also presented. The neural net based gray valued raw image processing showed the successful results for our recognition task. The developed technology through this research may open the new way of the quality inspection and sorting especially for the agricultural products whose visual features are fuzzy and not uniquely defined.