• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.309-314
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• 2012

Flame flickering occurs mainly because of the buoyancy force for pool fires under ambient air. The cup-burner flame was used for experimental investigation of the effect of the oxidizer velocity on the gravitational instability. The results showed that the flickering frequency decreased with increasing oxidizer velocity. The frequency-buoyancy relation with nondimensional variables coincided with that of the buoyant flume and pool fires when the characteristic velocity was defined as the difference between the fuel and oxidizer velocities, which implies that the origin of the gravitational instability is the Kelvin-Helmholtz instability in the shear layer. The effect of the oxidizer composition on the instability was also examined through nitrogen dilution in the oxidizer stream. As the concentration of inert gas increased, the length of the blue flame increased and lift-off behavior was observed. The oscillation frequency was independent of the dilution ratio, but was related to the local flame structure.

• Journal of the Korean Institute of Gas
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• v.12 no.3
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• pp.24-30
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• 2008

In this paper, the stress and strain characteristics of a helmet shell structure have been analyzed by using the finite element method and Taguchi's design method as functions of the material properties, the thickness of a helmet, the thickness and the number of a bead frame. The optimized design of the helmets for a firefighter and a gas worker is very important for increasing the strength safety and an impact energy absorption capacity of a helmet shell due to an impulsive external force. Thus, the optimized design data of the helmet indicated that the uniform thickness of a helmet shell may be reduced for reducing the total weight of a helmet and increasing the strain energy absorption rate, but the thickness and the number of a bead frame would be increased for increasing the impact strength of the helmet.

• Journal of Environmental Health Sciences
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• v.49 no.3
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• pp.149-158
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• 2023

Background: Injury is one of the major health problems in South Korea. Few studies have evaluated both intentional and unintentional injury when investigating the association between exposure to air pollutants and injury. Objectives: We aimed to explore the association between short-term exposure to ambient air pollution and years of life lost (YLLs) due to injury. Methods: Data on daily YLLs for 2002~2019 were obtained from the the Death Statistics Database of the Korean National Statistical Office. This study estimated short-term exposure to particulate matter with an aerodynamic diameter of <10 ㎛ (PM₁₀), particulate matter with an aerodynamic diameter of <2.5 ㎛ (PM_2.5), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), carbon monoxide (CO), and ozone (O₃). This time series study was conducted using a generalized additive model (GAM) assuming a Gaussian distribution. We also evaluated a delayed effect of ambient air pollution by constructing a lag structure up to seven days. The best-fitting lag was selected based on smallest generalized cross validation (GCV) value. To explore effect modification by intentionality of injury (i.e., intentional injury [self-harm, assault] and unintentional injury), we conducted stratified subgroup analyses. Additionally, we stratified unintentional injury by mechanism (traffic accident, fall, etc.). Results: During the study period, the average daily YLLs due to injury was 307.5 years. In the intentional injury, YLLs due to self-harm and assault showed positive association with air pollutants. In the unintentional injury, YLLs due to fall, electric current, fire and poisoning showed positive association with air pollutants, whereas YLLs due to traffic accident, mechanical force and drowning/submersion showed negative associations with air pollutants. Conclusions: Injury is recognized as preventable, and effective strategies to create a safe society are important. Therefore, we need to establish strategies to prevent injury and consider air pollutants in this regard.

• Journal of Information Technology and Architecture
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• v.9 no.2
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• pp.143-154
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• 2012

With the realization of the importance of the NWI, iterated by the Cheonan Ship sink and the YP-Do shelling, this thesis separates the NWI from the peninsula, regarding it separate from the Korea Theater of Operations, and suggests the method to establish NCOE with consideration to the characteristics of separated theater as well as the current situation. Although the NWI holds strategic value, systematical NCOE of surveillance and reconnaissance system, command and control system, and precision strike system is not yet established. Pertaining to this issue, Architecting was utilized to identify improvement measures and of the identified improvement measures, improvement on the "strike on nK hardened artillery sites with K-9 Self-Propelled Artillery in correlations with theater ISR" shows greatly improved strike effects when conducting simulations based on the Operation-Plan Analysis Model. Such a method of NCOE establishment will serve as a standard model for military force building and operation execution system for separated theater operations such as the NWI.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.5
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• pp.491-496
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• 2015

The headed studs used extensively for steel-composite construction are specified as SS400 in the current Korean Standard specification considering the welding condition. And the corresponding equation for the shear force calculation is limited for the use of compression strength of concrete below $300kgf/cm^2$. However, it is expected that the high strengthening and precasting of both steel and concrete due to the necessity of shear connector or other connecting material for the combination of steel and concrete. Therefore, the experimental results obtained during the development process of high strength stud for the connection of high strength concrete and the steel member are reported in this paper. Also the effectiveness of newly developed shear connector using pipe(pipe stud) to increase the stiffness of a stud is verified by comparing both the stiffness and the strength with common stud bolt through the welding ability, mechanical characteristics and experimental investigation.

• Journal of the Korean Society of Safety
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• v.37 no.2
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• pp.1-9
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• 2022

Most factories deal with toxic or flammable chemicals in their industrial processes. These hazardous substances pose a risk of leakage due to accidents, such as fire and explosion. In the event of chemical release, massive casualties and property damage can result; hence, quantitative risk prediction and assessment are necessary. Several methods are available for evaluating chemical dispersion in the atmosphere, and most analyses are considered neutral in dispersion models and under far-field wind condition. The foregoing assumption renders a model valid only after a considerable time has elapsed from the moment chemicals are released or dispersed from a source. Hence, an initial dispersion model is required to assess risk quantitatively and predict the extent of damage because the most dangerous locations are those near a leak source. In this study, the dispersion model for initial consequence analysis was developed with three-dimensional unsteady advective diffusion equation. In this expression, instantaneous leakage is assumed as a puff, and wind velocity is considered as a coordinate transform in the solution. To minimize the buoyant force, ethane is used as leaked fuel, and two different diffusion coefficients are introduced. The calculated concentration field with a molecular diffusion coefficient shows a moving circular iso-line in the horizontal plane. The maximum concentration decreases as time progresses and distance increases. In the case of using a coefficient for turbulent diffusion, the dispersion along the wind velocity direction is enhanced, and an elliptic iso-contour line is found. The result yielded by a widely used commercial program, ALOHA, was compared with the end point of the lower explosion limit. In the future, we plan to build a more accurate and general initial risk assessment model by considering the turbulence diffusion and buoyancy effect on dispersion.

• The Journal of the Korea Contents Association
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• v.18 no.9
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• pp.614-622
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• 2018

As multiple weapons are fired simultaneously in multi-target and multi-weapon environments, a possibility always exists in the collision occurred by the intersection between weapon trajectories. The collision between weapons not only hinders the rapid reaction but also causes the loss of the asset of weapons of friendly force to weaken the responsive power against the threat by an enemy. In this paper, we propose an intersection validation and interference elimination algorithm between weapon trajectories in multi-target and multi-weapon environments. The core points of our algorithm are to confirm the possible interference through the analysis on the intersections between weapon trajectories and to eliminate the mutual interference. To show the superiority of our algorithm, we implement the evaluation and verification of performances through the simulation and visualization of our algorithm. Our experimental results show that the proposed algorithm performs effectively the interference elimination regardless of the number of targets and weapon groups by showing that no cross point exists.

• Journal of the Korean GEO-environmental Society
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• v.25 no.6
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• pp.13-17
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• 2024

The general soil nailing method, which is currently used domestically and internationally to stabilize the slopes of sandy slopes, is to form a kind of gravity-type retaining wall by drilling the ground and grouting it with a single steel bar. This method can reduce construction costs, ease of construction, relative strength and displacement, and is highly efficient. The difference between grouting and rebar adhesion to the yield pullout force and the difference between the amount of deformation in relation to the same pullout resistance was analyzed through field tests to identify engineering excellence, and in terms of construction cost, the reduction effect was evaluated by analyzing the difference in the number of drillings and the impact on the overall construction cost, such as material cost, when the same strength constant is applied to the ground with the same resistance.

• Journal of Energy Engineering
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• v.29 no.3
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• pp.97-102
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• 2020

In this study, one-way fluid structure interaction analysis was adapted to verify the durability of the outdoor evacuation stair structure operated in the event of a fire when wind pressure caused by a typhoon was applied. To this end, flow analysis was performed with the flow field around the structure of the evacuation stair in a steady state, and the durability was analyzed through structural analysis such as structural stress, deformation, and fatigue life using these analysis results by fluid data input data for structural analysis. As a result of flow numerical analysis, the air flow was different according to the shape of the evacuation stair structure, and this flow velocity distribution generated by the total pressure on the structure surface. Through the structural analysis results calculated by this total pressure, the safety factor calculated as the maximum stress value was found to be more than the safety factor, and durability was proven by fatigue life and deformation analysis.

• Journal of the Korea Society for Simulation
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• v.28 no.4
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• pp.33-43
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• 2019

Link-16 is a data link that provides joint interoperability to the US Navy, Air Force and NATO. Currently, the military relies entirely on foreign SW and tools for test environment, tactical simulation training and interoperability verification test for Link-16 operation. Therefore, it is necessary to develop Link-16 based operation environment test tool. In this paper, Link-16 network operational performance analysis simulator was developed by analyzing the function of Link-16 foreign tools. It also implements the SIMPLE standard interface for interworking with foreign SW and tools. The functional model for Link-16 network operation performance analysis consists of pre-analysis, real-time operational analysis, and post-analysis functional model. Each functional model test was performed through SIMPLE interworking with foreign SW and tools. Link-16 network operation performance analysis If we replace foreign SW through simulator, we can perform tactical training, network design verification and operation (scenario) verification for our military.