• Journal of the Korea Computer Graphics Society
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• v.23 no.4
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• pp.11-19
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• 2017

We propose a new pipeline of fluid surface reconstruction that incorporates hybrid SDF(signed distance fields) and adaptive fluid surface techniques to finely reconstruct liquid-solid mixed surfaces. Previous particle-based fluid simulation suffer from a noisy surface problem when the particles are distributed irregularly. If a smoothing scheme is applied to reduce the problem, sharp and detailed features can be lost by over-smoothing artifacts. Our method constructs a hybrid SDF by combining signed distance values from the solid and liquid parts of the object. We also proposed a method of adaptively reconstructing the surface of the fluid to further improve the overall efficiency. This not only shows the detailed surface of the solid and liquid parts, but also the detail of the solid surface and the smooth fluid surface when both materials are mixed. We introduce the concept of guiding shape and propose a method to get signed distance value quickly. In addition, the hybrid SDF and mesh reconstruction techniques are integrated in the adaptive framework. As a result, our method improves the overall efficiency of the pipeline to restore fluid surfaces.

• Korean Journal of Heritage: History & Science
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• v.49 no.1
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• pp.120-145
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• 2016

An understanding of 'original form' plays an important role as it is the starting point of heritage conservation. This paper delineated several types of understanding on 'original form' over times, and aims at analyzing the way how such concepts has provided a platform of repair works of timber buildings in Korea over times. Conservation in Korea was initiated by the attitude of the Japanese authority during the Colonial period and 'restoring into the earliest form', which had been set in the early stage of the Japanese conservation, has strongly influenced on Korean practice during the period. Such attitude has lasted even after the independence of Korea. In Japan, however, the attitude has shifted to taking a careful decision on the alteration of the existing form during the 1930s. In addition, examination and research in the repair work became essential steps to conduct along with the publication of the report of works. In Korea there has been lack of understanding on the importance of examination and research in repair works and the publication of report of the works has not been mandatory so that it has emphasized on the 'form' in conservation aiming at 'restoring the earliest form'. Such attitude has created the problem of replacing original material during the work which should aim at preserving and maintaining heritage in Korea. Because of these circumstances in preserving the architectural cultural properties in Korea, cultural buildings had succeeded in preserving the outer appearance but there are remaining questions on preserving the original states of them. This paper has pointed out that it is necessary to set out the principles of conserving 'original condition' through further study and discussion based on the careful consideration on both the international principles and Korean context.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.477-484
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• 2019

As the residence time in the vehicle increases, the passenger desires a pleasant and stable riding environment in addition to the high driving performance of the vehicle. The windshield defrosting performance is one of the performance requirements that is essential for driver's safe driving. In order to improve the defrosting performance of the windshield of a vehicle, relevant elements such as the shape of the defrost nozzle should be appropriately designed. In this paper, CFD based numerical analysis is conducted to improve defrost performance of small electric vehicles. The defrost performance analysis was performed by changing the angle of the defrost nozzle and the guide vane that spray hot air to the windshield of the vehicle. Numerical simulation results show that the defrosting performance is best when the defrost nozzle angle is $70^{\circ}$ and the guide vane installation angle is $60^{\circ}$. Based on the analytical results, the defrosting experiment was performed by fabricating the defrost nozzle and the guide vane. As a result of the experiment, it is confirmed that the frost of windshield is removed by 80% within 20 minutes, and it is judged that the defrost performance satisfying the FVMSS 103 specification is secured.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.5
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• pp.187-194
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• 2021

The damage caused by typhoons is gradually increasing due to the climate change recently. Hence, many studies have been conducted over a long period of time on various factors that determine the characteristics of storm surge, and most of relationships have been discovered. Because storm surge is complexly determined by various factors, it often show different results and draw different conclusions. For this reason, this study was conducted to understand the various characteristics of storm surge caused by changes in the forward speed of typhoons. This study was carried out with a numerical model, and the effect of forward speed could be analyzed by simplifying other factors as much as possible. When forward speed is increased, storm surges caused by typhoons tended to increase gradually. The storm surge showed a wide and gentle increase at a slow speed, but a narrow and steep one at a fast speed. In the case of the same forward speed, it was found that the storm surge was significantly influenced by the water depth of actual sea area. It was confirmed that the change in forward speed after passing Jeju Island did not significant affect on the storm surge in the south coast of Korea.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.511-519
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• 2021

Slewing bearing is applied to the transmission of rotational power of the body and turret in a special vehicle for anti-aircraft weapons that overcomes the enemy flight system approaching at low altitudes with rapid response fire. When the turret load and impact load generated when shooting are combined in performing the combat mission of a special vehicle, structural stability must be secured to achieve a successful function. Among the components of the slewing bearing, the stability of the components against the complex loads acting by the turret drive and shooting was evaluated by considering the shape and material characteristics of the ring-gear, roller, and wire-race. As a research method for stability evaluation, based on engineering theory, the strength characteristics of the components were examined by numerical calculations. Finite element analysis was performed on components using the ANSYS analysis program. The results of theoretical analysis and the results of finite element analysis were very similar. A structural stability evaluation for the slewing bearing, which was performed mainly on the analysis, confirmed that the design strength of the slewing bearing determined in the preliminary design in the early stage of localization development was sufficient.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.1
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• pp.461-467
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• 2021

Among the defect factors that can occur when a wafer-level lens is molded using a thermosetting material, the mold sticking problem of a molded lens during the release process can damage the molded substrate and deform the substrate at the wafer level. An experiment was conducted to examine the factors affecting the demolding force in the lens forming process. The demolding force was examined according to the coating material of the molds. The mold was surface-treated with ITO and Ti, followed by plasma treatment in an O2 atmosphere. A DLC coating was then performed, and the curing and releasability were examined. A coating method for the pull-off experiment was selected based on the results. To measure the demolding force according to the curing process conditions, a method of curing at a constant pressure and a method of curing at a constant position were applied. As a result, the TiO2 surface treatment reduced the release force. When cured by controlling the location, curing shrinkage can reduce the adhesion energy of the interface during curing, resulting in better demolding.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.3
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• pp.231-245
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• 2022

When vertical shafts are constructed in soft clay with low strength, there is a risk of basal heave, which causes the excavation surface to heave due to the low bearing capacity of the ground against the imbalance of earth pressure at the excavation surface. Methods of deriving a safety factor have been proposed to evaluate the stability against the basal heave. However, there are limitations in that it is difficult to accurately evaluate the heave stability because many assumptions are included in the theoretical derivation. In this study, assuming that a circular vertical shaft is constructed in soft clay, the existing safety factor equation proposed through a theoretical approach was supplemented. Bearing capacity according to the shaft geometry, inhomogeneity of the soil, and the effect of soil plug were considered theoretically and applied in a previous safety factor equation. A three-dimensional numerical analysis was conducted to simulate the occurrence of basal heave and review the supplemented equation through various case studies. Several series of case studies were conducted targeting various factors affecting heave stability. It was verified that the additionally considered characteristics were properly reflected in the supplemented equation. Furthermore, the effects of each factor constituting the safety factor equation were examined using the results of the numerical analysis performed by simulating various cases. It was confirmed that considering the undrained shear strength increment according to depth had the most significant effect on the calculation of the safety factor.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.1
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• pp.1-10
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• 2022

In this study, the two horizontal shroud tidal current energy converter, which can generate power even under low flow speed conditions, was developed. In order to determine the shape of the shroud system, a three-dimensional numerical simulation test was conducted, and a 1/6 scale down model was made to perform a hydraulic model experiment. The hydraulic model experiment was performed under four flow conditions, and the flow speed, torque, and RPM were measured for each experimental case. As a result of the numerical simulation test, it was found that the flow speeds passing through the nozzle were increased by about 2~3 times in the cylinder, and when the extension ratio was 2:1, the highest flow speed was shown. In addition, it was found that the flow speeds increased 2.8 times when the diameter ratio between the nozzle and the cylinder was 1.5:1. Meanwhile, as a result of the hydraulic model experiment, it was found that when the tip speed ratio was between 1.75 and 2, the power coefficient was 0.32 to 0.34.

• The Journal of the Convergence on Culture Technology
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• v.8 no.6
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• pp.667-674
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• 2022

In this study, the correlation between the damage type and operating conditions of the sleepers was analyzed based on the design data and visual inspection results for the concrete sleepers of the sleeper floating track (STEDEF) that have been in operation for more than 20 years. It appeared in the form of cracks, breakages, and breaks in the concrete at the center and tie bar contact and buried areas. As a result of the numerical analysis, it was analyzed that the change in the left and right spring stiffness of the sleeper resilience pad increases the maximum stress, tensile stress, compressive stress, and displacement of the concrete sleeper, and stress concentration in the concrete at the tie bar contact area. It was proved analytically that the sleeper resilience pad can affect the damage of the concrete sleeper. Therefore, damage of concrete sleepers in the sleeper floating track in urban transit could be caused by changes in spring stiffness of sleeper resilience pads. It was reviewed that preventive maintenance such as improvement and timely replacement of sleeper resilience pads was necessary.

• Geophysics and Geophysical Exploration
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• v.1 no.2
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• pp.127-135
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• 1998

The Born approximation is widely used for solving the complex scattering problems in electromagnetics. Approximating total internal electric field by the background field is reasonable for small material contrasts as long as scatterer is not too large and the frequency is not too high. However in many geophysical applications, moderate and high conductivity contrasts cause both real and imaginary part of internal electric field to differ greatly from background. In the extended Born approximation, which can improve the accuracy of Born approximation dramatically, the total electric field in the integral over the scattering volume is approximated by the background electric field projected to a depolarization tensor. The finite difference and elements methods are usually used in EM scattering problems with a 2D model and a 3D source, due to their capability for simulating complex subsurface conductivity distributions. The price paid for a 3D source is that many wavenumber domain solutions and their inverse Fourier transform must be computed. In these differential equation methods, all the area including homogeneous region should be discretized, which increases the number of nodes and matrix size. Therefore, the differential equation methods need a lot of computing time and large memory. In this study, EM modeling program for a 2D model and a 3D source is developed, which is based on the extended Born approximation. The solution is very fast and stable. Using the program, crosshole EM responses with a vertical magnetic dipole source are obtained and the results are compared with those of 3D integral equation solutions. The agreement between the integral equation solution and extended Born approximation is remarkable within the entire frequency range, but degrades with the increase of conductivity contrast between anomalous body and background medium. The extended Born approximation is accurate in the case conductivity contrast is lower than 1:10. Therefore, the location and conductivity of the anomalous body can be estimated effectively by the extended Born approximation although the quantitative estimate of conductivity is difficult for the case conductivity contrast is too high.