• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.17 no.1
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• pp.14-22
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• 2021

Drilling equipment is an essential part used in various fields such as construction, mining, etc., and it has drawn increasing attention in recent years. The drilling method is generally divided into three types. There are a top hammer method that strikes on the ground, a DTH (Down-The-Hole) method that directly strikes a bit in an underground area, and a rotary method that drills by using rotational force. Among them, the DTH method is most commonly used because it enables efficient drilling compared to other drilling methods. In the conventional DTH hammer, the valve between the piston and the bit is opened and closed using a face to face method. In order to improve the power of the DTH hammer, a DTH hammer with foot valve which is capable of instantaneous opening and closing is used in the drilling field. In this study, we designed a lab-scale DTH hammer with the foot valve, and manufactured an evaluation device for the experiment of the DTH hammer. In addition, we analyzed the performance of the DTH hammer adopted with foot valve according to the pressure range of 3-10 bar. As a result, the internal pressure distribution in the DTH hammer was experimentally analyzed, and then, the movement of the piston according to the pressure was predicted. We believe that this study provides the useful results to explain the performance characteristics of the DTH hammer with the foot valve.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.4
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• pp.479-490
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• 2018

The granite melting concept, which was suggested by Gibb's group for the closing of a deep borehole, was experimentally checked for KURT granite. The granite melting experiments were performed in two pressure conditions of atmospheric melting with certain inorganic additives and high pressure melting formed by water vaporization. The results of atmospheric tests showed that KURT granite started to melt at a lower temperature of $1,000^{\circ}C$ with NaOH addition and that needle shaped crystals were formed around partially melted crystals. In high pressure tests, vapor pressure was increased by adding water with maximum pressure of about 400 bars. KURT granite was partially melted at $1,000^{\circ}C$ when vapor pressure was low. However, it was not melted at vapor pressures higher than 200 bars. Therefore, it was determined that high pressure with a small amount of water vapor more effectively decreased the melting point of granite. Meanwhile, high temperature and high pressure vapor caused severe corrosion of the reactor wall.

• Steel and Composite Structures
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• v.43 no.2
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• pp.165-183
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• 2022

Most transportation departments have recognized and developed procedures to address the ever-increasing weights of trucks traveling on bridges in a service today. Transportation agencies also recognize the issues with overheight vehicles' collisions with bridges, but few stakeholders have definitive countermeasures. Bridges are becoming more vulnerable to collisions from overheight vehicles. The exact response under lateral impact force is difficult to predict. In this paper, nonlinear impact analysis shows that the degree of deformation recorded through the modeling of the unprotected vehicle-girder model provides realistic results compared to the observation from the US-61 bridge overheight vehicle impact. The predicted displacements are 0.229 m, 0.161 m, and 0.271 m in the girder bottom flange (lateral), bottom flange (vertical), and web (lateral) deformations, respectively, due to a truck traveling at 112.65 km/h. With such large deformations, the integrity of an impacted bridge becomes jeopardized, which in most cases requires closing the bridge for safety reasons and a need for rehabilitation. We proposed different sacrificial cushion systems to dissipate the energy of an overheight vehicle impact. The goal was to design and tune a suitable energy absorbing system that can protect the bridge and possibly reduce stresses in the overheight vehicle, minimizing the consequences of an impact. A material representing a Sorbothane high impact rubber was chosen and modeled in ANSYS. Out of three sacrificial schemes, a sandwich system is the best in protecting both the bridge and the overheight vehicle. The mitigation system reduced the lateral deflection in the bottom flange by 89%. The system decreased the stresses in the bridge girder and the top portion of the vehicle by 82% and 25%, respectively. The results reveal the capability of the proposed sacrificial system as an effective mitigation system.

• Journal of the Korean Society of Safety
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• v.23 no.3
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• pp.17-24
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• 2008

Elbows with various shapes of local wall thinning were numerically analyzed by finite element method to get load-displacement curves and the maximum loads. Results were compared with the experimental data obtained by another study. Elastic-plastic analysis were carried out under the combined loading conditions of internal pressure and in-plane bending loads. Two types of bending loads were considered such as elbow opening mode and elbow closing mode. Also, two different wall thinning geometries were modeled. Wall thinning area located extrados or intrados of elbow inner surface was considered. Longitudinal and circumferential lengths of the thinning area and the thinned thickness were varied for analysis. The results showed that the maximum load of the wall-thinned elbow decreased with increasing of the circumferential thinning length and the thinned thickness in both of extrados and intrados thinning locations in both loading types. The maximum load obtained by the analysis were in good agreement with the experimentally measured maximum load with the same wall thinning type and dimensions. This supports accuracy of the analysis results obtained in this study.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.6
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• pp.584-589
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• 2009

As the automobile energy efficiency stands out an important matter of interest, the magnetic engine valve system receives attention. It has an advantage of no engine power leakage in opening and closing the valve. Moreover, it generates much bigger force than the piezo actuator system, so it can be a good alternative system of the cam and camshaft system. However, since the valve system is not light enough, it is necessary to make its weight reduce. In this study, topology optimization is applied to find the optimal shape of the armature in a magnetic valve system combined with the finite element analysis for the magnetic field analysis. The result is used to obtain a concept design. The adjoint variable method is employed in order to calculate the design sensitivity of the magnetic driving force in the armature component mostly to reduce the computational time during the repeated sensitivity calculation. The sequential linear programming is employed for the optimization algorithm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.7 s.262
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• pp.777-783
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• 2007

Since the performance of the circuit breaker mainly depends on the spring operating mechanism, the analysis of the spring operating mechanism is required. The spring, especially closing spring, stores the deformation energy due to the compression and then accelerates the big loads rapidly in the circuit breaker. To accurately carry out the kinematic and dynamic analysis of the circuit breaker, the precise modeling of the spring behavior is necessary. In this paper, the static stiffness of the spring is captured by using the tester. A simple mechanism similar to the spring operating mechanism was designed to generate the release motion of the spring. A high speed camera was used to capture the behavior of the spring. Three types of spring models such as a linear spring model, modal spring model, and nodal spring model are suggested and compared with the experimental results.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.868-869
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• 2011

Domestic Foreign automaker's are focused on the high-efficiency, low emission cars development. On the way, the hybrid car is the first priority. Hybrid electric vehicle battery pack configurations, EV Relay one of the key components of the engine driving, to assist in the drive motor to supply electrical energy to the battery is a device for opening and closing of the output device. EV Relay determine the longevity and the replacement cycle, The EV Relay environmental conditions and duty cycle considering the reliability tests are essential requirements of many automotive companies to respond to RFQ, this test is essential. This paper using Maxwell Software for Prediction of the Ev Relay impulse, the theoretical data to obtain the impulse to develop methods for mechanical testing after to take advantage of it.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1603-1605
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• 2001

Eight 300kJ modularized capacitor-banks have been constructed. These modules have been installed and assembled to make a 2.4MJ pulse power system (PPS). This 2.4MJ PPS was developed to be used as a driver of an electrothermal-chemical (ETC) gun. Each capacitor bank has six 22kV, 50kJ capacitors connected in parallel. A triggered vacuum switch (TVS-43) was adopted as a main pulse power-closing switch in each module. The module also contains a crowbar circuit made of three high-voltage diode-stacks, a multi-tap inductor and an energy-dumping resistor. Various current shapes have been formed by a sequential firing of multiple capacitor banks. Resistive dummy load has been used and various combinations of experimental parameters, such as charging voltage, trigger time and inductance, were tested to make flexible current shapes.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.284-292
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• 2009

The stack-effect in high-rise buildings in winter causes many problems such as difficulties in opening or closing doors, infiltration, energy loss, noise and fire protection. Stack effect is influenced by temperature difference between the interior and exterior of building and the height of building. As an attenuation method for stack effect, the architectural methods are generally used. However, as though architectural methods were fully adopted, the problems are reported as ever in tall building. In this study, a new method to reduce stack effect will be suggested. As an active control method against the stack effect, E/V shaft natural cooling method is suggested. In this paper, the concept of E/V shaft natural cooling system and its reduction performance of stack effect by simulation and field measurement will be reported.

• Journal of Distribution Science
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• v.12 no.3
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• pp.75-83
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• 2014

Purpose - The oil price affects company value, which is the present value of the expected cash flow, by affecting the discount rate and cash flow. This study examines the nonlinear relationships between oil price and stock price using the AlphaShares Chinese Volatility Index as the threshold. Research design, data, and methodology - Data comprise daily closing values of the Shanghai Stock Exchange Composite Index, Shenzhen Stock Exchange Composite Index, and Hang Seng Index of ChinaWest Texas Intermediate crude oil spot price and AlphaShares Chinese Volatility Index from May 25, 2007 to May 24, 2012. The Threshold Error Correction Model is used. Results - The results demonstrate different relationships between the stock price index and oil price under different investor sentiments; however, the stock price index and oil price could adjust to a long-term equilibrium the long-term causality tests between them were all significant. Conclusions - The relationship between the WTI and HANG SENG Index is more significant than the Shanghai Composites Index and Shenzhen Composite Index, when using the AlphaShares Chinese Volatility Index (ASC-VIX) as the investor sentiment variable and threshold.