• Journal of the Korea Society of Computer and Information
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• v.23 no.10
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• pp.95-101
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• 2018

In this paper, we propose an image-based synthesis method that can effectively represent the spark effect in fire simulation. We use the real flame image or animated image as inputs and perform the following steps : 1) extract feature vectors from the image, 2) calculate artificial buoyancy, and 3) generate and advect spark textures. We detect the edge from images and then calculate the feature vectors to calculate the buoyancy. In the next step, we compute the high-quality buoyancy vector field by integrating the two-dimensional feature vector and the fluid equation. Finally, the spark texture is advect by buoyancy field. As a result, our method is performed much faster than the previous approach and high-quality results can be obtained easily and stably.

• Journal of Korean Elementary Science Education
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• v.19 no.1
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• pp.145-156
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• 2000

Elementary school teachers' understandings about buoyancy were investigated through the questionnaire method. The questionnaire was composed of 4 questions on hydraulic pressure and 8 questions on buoyancy. The questions on buoyancy asked about the correlation of buoyancy with following basic concepts, density of liquid, volume of submerged object and so forth. 295 teachers on the 22 elementary schools in Busan, Yangsan and Gimhae were selected through random sampling method. The results of this study were summarized as follows: On the correlation of the magnitude and direction of hydraulic pressure with the depth of water, a large portion of the respondents had a scientific conception. But on the correlation of hydraulic pressure with density, the relatively small portion of them appeared to have a scientific conception. The respondents, on the whole, had a scientific conception about the correlation of buoyancy with density of liquid. But they seemed to have naive conceptions about the correlation of buoyancy with the volume of a submerged object and with the depth of water, the amount of water in container and the reduced amount of water by the object from container. We found that the respondents were context dependent and tended to search for solutions for the questions of buoyancy using the concept of pressure in the water. From above results, we suggested that in the would-be revised elementary science text book, the contents of pressure in the water should be introduced after the concept of weight in the water was gained.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.3
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• pp.327-330
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• 2021

Though the stability review of buoyancy is generally done, the stability review of buoyancy moment, which is generated from the eccentricity between the center of fixed load and that of buoyancy, is not done in the water treatment concrete structure and the architectual structure. In this review, as the buoyancy force become larger, the action point of the fixed load (ΣW) and buoyancy (B), and the reaction distribution were considered to confirm the formation of the buoyancy moment rotational point and obtained the rotational uplift stability review formula for buoyancy moment in the water treatment concrete structure and the architechual structure, and put forward the stability review method for buoyancy moment.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2A
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• pp.75-83
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• 2012

In this study, an analytical studies were carried out for the buoyancy preflexion method to improve structural performance of concrete floating structures. The buoyancy preflexion means that the preflexion effects were induced to the floating structure due to the difference in buoyancy between the pontoon modules composing the floating structures. In order to verify the buoyancy preflexion effects, an analytical studies were carried out for the floating structures. The size and dimensions of FE model were determined through the structural design process. The parameter of this analytical study was length ratios of central module part, which induces buoyancy preflexion effects, to the total length. The analysis results were pre-compression on the bottom concrete slab and displacement of freeboard due to buoyancy preflexion effects. These results were processed according to the loading step, buoyancy preflexion loads on the bottom and live loads on the topside. Then, the buoyancy preflexion effects on structural performance was analyzed. As the results of this study, it was found that the buoyancy preflexion significantly influence on structural performance of floating structures. According to the length ratio, the buoyancy preflexion effects have a tendency of parabolic form and maximized at the length ratio of 40~60%. The buoyancy preflexion method is simple in principle and easy in application. Also, it can effectively induce pre-compression on the bottom concrete slab. Therefore, it can be concluded that the buoyancy preflexion method contribute to the improvement of structural performance and decreasing of the cross-sectional depth of floating structures.

• Journal of Ocean Engineering and Technology
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• v.30 no.1
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• pp.10-17
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• 2016

This paper reports a simulation-based design method for the optimized arrangement design of buoyancy modules in a marine riser system. A buoyancy module is used for the safe operation and structural stability of the riser. Engineers design buoyancy modules based on experience and experimental data. However, they are difficult to design because of the difficulty of conducting real sea experiments and quantifying the data. Therefore, a simulation-based design method is needed to tackle this problem. In this study, we developed a simulation-based design algorithm using a multi-body dynamic simulation and genetic algorithm to perform optimization arrangement design of a buoyancy module. The design results are discussed in this paper.

• Journal of the Korea Institute of Military Science and Technology
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• v.15 no.2
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• pp.121-129
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• 2012

In this study, in terms of the exercise vehicles of the weapon systems having negative buoyancy, the analysis on the operation concepts was performed and the new methods of floating to surface were proposed. In case of having negative buoyancy, the additional methods for recovering the exercise vehicle have to be considered. As parts of recovering the exercise vehicle, for floating to surface the new methods of weight discharge, weight separation and sea water discharge were proposed. The conceptual design about sea water discharge method was performed. It was confirmed that those methods could be applied to the design of the exercise vehicle having negative buoyancy.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.5
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• pp.375-393
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• 2022

This study was deal with blow-out and buoyancy stability evaluation method for slurry shield TBM. When applying a slurry shield TBM for the construction of a shallow tunnel under river or sea, the stability of slurry blow-out and segment lining buoyancy should be evaluated. However, there is a problem in that the currently applied theoretical formula is somewhat complicated, making it inconvenient to calculate in practice. In this study, some simple charts were proposed to easily evaluate the stability of slurry blow-out and segment lining buoyancy. In addition, the buoyancy safety factor of segment lining using the strength reduction method was evaluated and compared with the buoyancy safety factor based on the theoretical formula. The buoyancy safety factor by the theoretical formula was evaluated to be rather small, and it was confirmed that it was on the safe side. The simplified charts for the evaluation of slurry blow-out and buoyancy stability presented in this study are expected to be usefully utilized in the planning and design of undersea tunnels.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.4
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• pp.42-49
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• 2004

When a truck cab is conveyed at a constant speed by a hanger and immersed into the painting reservoir, it may fall off from the hanger by buoyancy. In order to reduce the buoyancy, on the bottom of a cab panel are holes placed, which allow paint to flow into the inside of a cab. In this study, a differential equation is derived which can be solved numerically by using 4th-Order Runge-Kutta method to calculate transient behavior of the buoyant force with sizes and locations of the holes given. The solution is utilized to optimally determine sizes and locations of the holes.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.1
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• pp.24-34
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• 1996

In ordaer to hold an underwater vehicle at a certain depth, buoyancy that acts on the underwater vehicle can be modulated. In this research, buoyancy that could control depth of underwater vehicle is generated by a buoyancy bag. Solenoid valves are operated by pulse with modulation(PWM) method. State equation, in consideration of the volume of buoyancy bag, pressure inside bag, and dynamic of the underwater vehicle, is derived. This system is very unstable, inculdes modelling error and nonlinearity. In depth control system, maintanance of performance is required., anainst vatiation of systerm parameter and operating depth, and designed. Through the computer simulation, performance is comparerd for each controllers.

• Journal of Korea Water Resources Association
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• v.57 no.8
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• pp.493-507
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• 2024

RANS-based CFD analysis is widely applied in various engineering fields, including practical hydraulic engineering, due to its high computational efficiency. However, problems of non-physical behavior in the analysis of two phase flow, such as free surfaces, have long been raised. The two-equation turbulence models used in general RANS-based analysis were developed for single phase flow and simulate unrealistically high turbulence energy at the interface where there are abrupt changes in fluid density. To solve this issue, one of the methods recently developed is the buoyancy-modified turbulence model, which has been partially validated in coastal engineering, but has not been applied to open channel flows. In this study, the applicability of the buoyancy-modified turbulence model is evaluated using the VOF method in the open-source program OpenFoam. The results of the uniform flow showed that both the buoyancy-modified k-𝜖 model and the buoyancy-modified k-ω SST model effectively simulated the reduction of turbulence energy near the free surface. Specifically, the buoyancy-modified k-ω SST model accurately simulated the vertical velocity distribution. Additionally, the model is applied to dam-break flows to examine cases with significant surface variation and cavity formation. The simulation results show that the buoyancy-modified turbulence models produce varying results depending on the VOF method and shows non-physical behavior different from experimental results. While the buoyancy-modified turbulence model is applicable in cases with stable surface shapes, it still has limitations in general application when there are rapid changes in the free surface. It is concluded that appropriate adjustments to the turbulence model are necessary for flows with rapid surface changes or cavity formation.