• Journal of Ocean Engineering and Technology
• /
• v.30 no.4
• /
• pp.277-286
• /
• 2016

The first part of this study found the tendencies of the mechanical properties of two arctic structural steels (EH32 and FH32). In the second part, the crashworthiness of stiffened panels scaled down from the side frame structure of a Korean research icebreaker was determined. A procedure for designing the shapes and sizes of the stiffened panels, mass and shape of a drop striker, and a large temperature chamber, and then manufacturing these, is introduced in detail. From impact bending tests for the stiffened panels, the residual permanent deformations and deformation histories over time were captured using manual measurement and video image analyses. Numerical simulations of the impact bending tests were carried out for three different finite element models, which were mainly composed of shell elements, solid elements, and solid elements, with welding beads. It was proven from a comparison of the test results and numerical simulation results that the solid element model with the welding bead consideration approached the test results in terms of the residual deformations as long as the strain rate effect was taken into account.

• Journal of Welding and Joining
• /
• v.30 no.3
• /
• pp.66-70
• /
• 2012

Welding is an essential process in the automotive industry. Most welding processes that are used for auto body is spot welding. And $CO_2$ arc welding is used in a small part. In production field, $CO_2$ arc welding process is decreased and spot welding process is increased due to welding quality is poor and defects are occurred in $CO_2$ arc welding process frequently. But $CO_2$ arc welding process should be used at robot interference parts and closed parts where spot welding couldn't. $CO_2$ welding is divided into lap welding and plug arc spot welding. In case of plug arc spot welding, burn through and under fill were caused in various welding environment such as different thickness combinations of base metal, teaching point, over the two steps welding and inconsistent voltage/current. It makes some problem like poor quality of welding area and decrease the productivity. In this study, we will evaluate the effect of teaching point through the weld pool behavior and bead geometry in the arc spot welding at the plut hole. Welding position is horizontal position. And galvanized steel sheet of 2.0mm thickness that has plug hole of 6mm diameter was used. Teaching point was changed by center, top, bottom, left and right of the plug hole. At each condition, the phenomenon of weld pool behavior was confirmed using a high-speed camera. As the result, we find the center of plug hole is the most optimal teaching point. In the other teaching point, under fill was occurred at the plug hole. This phenomenon is caused by gravity and surface tension. For performance of arc spot welding at the plug hole, the teaching condition should be controlled at a center of plug hole.

• Journal of Industrial and Engineering Chemistry
• /
• v.68
• /
• pp.274-281
• /
• 2018

Experimental studies of the hydrodynamic performance of the draft tube conical spout-fluid bed (DCSF) were conducted using pharmaceutical pellets. The experiments were carried out in a DCSF consisted of two sections: (a) a conical section with the cross section of $120mm{\times}250mm$ and the height of 270 mm, (b) a cylindrical section with the diameter of 250 mm and the height of 600 mm. The flow characteristics of solids were investigated with a high speed camera and a pezoresistive absolute pressure transducer simultaneously. These characteristics revealed different flow regimes in the DCSF: packed bed at low gas velocities, fluidized bed in draft tube at higher gas velocities until minimum spouting, and spouted bed. The stable spouting was identified by the presence of two dominant frequencies of the power spectrum density of pressure fluctuation signature: (i) the frequency band 6-9 Hz and (ii) the frequency band 12-15 Hz. The pressure drops across the draft tube as well as the annulus measured in order to better recognize the flow structure in the DCSF. It was observed that the pressure drop across the draft tube, the pressure drop across the annulus, and the minimum spouting velocity increase with the increase in the height of draft tube and distance of the entrainment zone, but with the decrease in the distributor hole pitch. Finally, this study provided novel insight into the hydrodynamic of DCSF, particularly minimum spouting and stable spouting in the DCSF which contains valuable information for process design and scale-up of spouted bed equipment.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.20 no.4
• /
• pp.68-76
• /
• 2016

This research is carried out for the performance evaluation of the injector that is one of the critical components of bipropellant-rocket-engine. Spray characteristics are investigated in detail according to the recess length and injection pressure on the swirl-coaxial-injector using gaseous methane and liquid oxygen as propellants. A visualization is conducted by the Schlieren photography that is composed of a light source, concave mirrors, knife, and high-speed-camera. A hollow-cone-shape is identified in the liquid spray that is spread only by inner injector and the spray angle is decreased due to the diminution of swirl strength in accordance with the increase of the length of injector orifice. When the injector sprays the liquid through the inner injector with the aid of gas through the outer injector, the spray angle in external mixing region tends to increase with rise of the recess length, while in internal mixing region, it is decreased. It is also confirmed that the same tendency of the spray angle with recess length appears irrespective of the injection pressure of liquid spray.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.25 no.7
• /
• pp.962-970
• /
• 2021

The cause of the majority of vehicle accidents is a safety issue due to the driver's inattention, such as drowsy driving. A forward collision warning system (FCWS) can significantly reduce the number and severity of accidents by detecting the risk of collision with vehicles in front and providing an advanced warning signal to the driver. This paper describes a low power embedded system based FCWS for safety. The algorithm computes time to collision (TTC) through detection, tracking, distance calculation for the vehicle ahead and current vehicle speed information with a single camera. Additionally, in order to operate in real time even in a low-performance embedded system, an optimization technique in the program with high and low levels will be introduced. The system has been tested through the driving video of the vehicle in the embedded system. As a result of using the optimization technique, the execution time was about 170 times faster than that when using the previous non-optimized process.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.22 no.5
• /
• pp.88-96
• /
• 2018

Effects of injector position and momentum flux ratio on a vertical jet in a cross-flow field are qualitatively studied and displayed using air and water. The position of the injector hole and the momentum flux ratio is changed and image visualization is performed using a shadowgraph technique and a high-speed camera. The visualized images are compared to find differences in spraying using density gradient magnitude image. It is observed that, as the x/d of the apparatus increases, the jet break-up height decreases. When x/d is 0, the spray reaches the bottom and ceiling at any momentum flux ratio.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.13 no.6
• /
• pp.1229-1234
• /
• 2018

In this paper, a fire prevention system based on a broadband powerline communication (PLC) system is implemented and a demonstration experiment is carried out to prevent from or promptly dealing with possible fires within the nacelle of a wind turbine generator system (WTGS). For this purpose, an inductive coupler having satisfactory attenuation characteristic in the frequency region for high-speed PLC is also manufactured. It is confirmed that the implemented system can monitor the environmental change inside the nacelle in real time by transmitting various information obtained by the sensors such as temperature, flame, and smoke sensor installed in the nacelle and thermal image recorded by a thermal camera to the ground control center through the PLC system. Therefore, it is, considered that the implemented system will significantly improve the reliability of the fire monitoring and prevention system of the WTGS in conjunction with the existing safety system.

• Journal of the Korean Society of Safety
• /
• v.34 no.1
• /
• pp.40-44
• /
• 2019

Experimental studies have been carried out to investigate characteristics of gas explosion using a multi layered water gel barrier in a vented explosion chamber. The chamber is consisted of 1600 mm in length, with a square cross-section of $100{\times}100mm^2$. The gel concentration of inner layer of MLWGB ranged from 10% to 90% with intervals of 10% by weight of gel. Displacement of the MLWGB was photographed with a measured using a high-speed video camera, and pressure development was measured using a data acquisition system. It was found that MLWGBs with 10 ~ 20% inner layer concentrations were ruptured during the explosions. As the concentrations of inner layer increased from 30% to 90%, the barriers were not ruptured. As the gel concentrations of the inner layer increased, the displacement increased toward the chamber exit and the pressure decreased for the ruptured barriers. It was found that the pressure attenuation obtained from the MLWGB was higher than that of the single water gel barrier. For the cases of non-ruptured barriers, the pressure inside the chamber less increased with increasing gel concentrations of the inner layer. It was also found that the displacement moved back into the chamber for non-ruptured MLWGBs, and it was sensitive to the gel concentrations.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.25 no.1
• /
• pp.19-28
• /
• 2021

In rotating detonation engine(RDE), only the detonation wave is moving around the outer wall of the combustor. Neither a mechanical part nor flow is rotating in RDE. Thus, the RDE cross section is not necessary to be circular, but arbitrary closed section is possible. A RDE of tri-arc cross section is designed and As an example of an arbitrary cross sectioned RDE, a RDE of tri-arc cross section is designed in this study, and operational and performance characteristics were examined experimentally. The rotation of the detonation wave is confirmed by dynamic pressure sensor and high-speed camera, while the characteristics of the detonation wave were investigated at the concave and convex surfaces. In the present study, the thrust level of 17.0 N to 96.0 N was obtained depending on the mass flow rate.

• Journal of the Korean Society of Visualization
• /
• v.19 no.3
• /
• pp.84-91
• /
• 2021

Effervescent tablets generate gas bubbles when chemical reaction occurs between water and tablets. Most of previous studies have been focused on pharmaceutical characteristics of tablets. However, for their applications in disinfectants, cleaners, and pesticides, physical characteristics of bubbles released from the effervescent tablets when they are in water are important. In this study, we experimentally investigated the characteristics of microbubbles generated by an effervescent tablet made of sodium bicarbonate and tartaric acid using PDPA and high-speed camera. Microbubbles were generated using different weights of effervescent tablet as well as in different water temperature. The experimental study shows increase in reaction time, bubble concentration and rise velocity as the weight of effervescent tablet increases from 1 to 20 g. The decrease in average bubble diameter was observed when the temperature of water increased from 25 to 45 ℃. Further, reaction time varies inversely with increase in water temperature, while bubble rise velocity is directly proportional to increase in water temperature. Effervescent table continuously generates the bubble with approximately constant diameter (235 ㎛) in the water. However, bubble concentration and bubble rise velocity decreased over time.