• Wind and Structures
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• v.12 no.4
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• pp.383-400
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• 2009

Low rise building roofs can be subjected to large fluctuating pressures during a tropical cyclone resulting in fatigue failure of cladding. Following the damage to housing in Tropical Cyclone Tracy in Darwin, Australia, the Darwin Area Building Manual (DABM) cyclic loading test criteria, that loaded the cladding for 10000 cycles oscillating from zero to a permissible stress design pressure, and the Experimental Building Station TR440 test of 10200 load cycles which increased in steps to the permissible stress design pressure, were developed for assessing building elements susceptible to low cycle fatigue failure. Recently the 'Low-High-Low' (L-H-L) cyclic test for metal roofing was introduced into the Building Code of Australia (2007). Following advances in wind tunnel data acquisition and full-scale wind loading simulators, this paper presents a comparison of wind-induced cladding damage, from a "design" cyclone proposed by Jancauskas, et al. (1994), with current test criteria developed by Mahendran (1995). Wind tunnel data were used to generate the external and net pressure time histories on the roof of a low-rise building during the passage of the "design" cyclone. The peak pressures generated at the windward roof corner for a tributary area representative of a cladding fastener are underestimated by the Australian/New Zealand Wind Actions Standard. The "design" cyclone, with increasing and decreasing wind speeds combined with changes in wind direction, generated increasing then decreasing pressures in a manner similar to that specified in the L-H-L test. However, the L-H-L test underestimated the magnitude and number of large load cycles, but overestimated the number of cycles in the mid ranges. Cladding elements subjected to the L-H-L test showed greater fatigue damage than when experiencing a five hour "design" cyclone containing higher peak pressures. It is evident that the increased fatigue damage was due to the L-H-L test having a large number of load cycles cycling from zero load (R=0) in contrast to that produced during the cyclone.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.3
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• pp.347-353
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• 2012

Recently, multi-functionalization (as in smart phones) has been in demand, and the connectors connecting the electrical signals of each board in a cellular phone have become key components. The miniaturization of these connectors is required to achieve a finer pitch design and enhance the electrical signal transfer capacity. However, the miniaturization of connectors reduces the structural safety, and a finer pitch design may cause contact problems under external impact. In this paper, a preliminary design for miniaturized, finer-pitch connectors is suggested for a product with 50 pins and a thickness of 0.2 mm. The assembly process of the FPCB (Flexible Printed Circuit Board) and connector was simulated to ensure the holding force between the two components and avoid overstressing. The design optimization process was performed with the Taguchi method. Fatigue analysis was also conducted to predict the fatigue life of the terminal, and the theoretical and experimental results were compared.

• Journal of Digital Convergence
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• v.10 no.9
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• pp.89-100
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• 2012

This study is designed to explore whether the integration of product development and quality management have influence on the success of localization of weapon system. To that end, empirical analysis has been conducted on a total of 110 systematic major defense contractors, their subcontractors and small-and-medium sized defense contractors. The result shows that success of the localization of weapons system, as well as the price of localization, manufacturing time, and quality turn out to have significantly influenced by factors of quality management capabilities including human resources development capability, organizational capability and process capability and R&D development factors including human resources capabilities, capability to accumulate technology and internal/external collaborative capabilities. To sum up, this study suggests that integration of quality management and product development continuously provides a competitive strength in developing new product by a non-defense company as well as localization of core parts of weapon system.

• Tribology and Lubricants
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• v.31 no.1
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• pp.6-12
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• 2015

This paper investigates the stick-slip characteristic of magnetorheological elastomer (MRE) between an aluminum plate and the surface of the MRE. MRE is a smart material and it can change its mechanical behavior with the interior iron particles under the influence of an applied magnetic field. Stick-slip is a movement of two surfaces relative to each other that proceeds as a series of jerks caused by alternate sticking from friction and sliding when the friction is overcome by an applied force. This special tribology phenomenon can lead to unnecessary wear, vibration, noise, and reduced service life of work piece. The stick-slip phenomenon is avoided as far as possible in the field of mechanical engineering. As this phenomenon is a function of material property, applied load, and velocity, it can be controlled using the characteristics of MRE. MRE as a soft smart material, whose mechanical properties such as modulus and stiffness can be changed via the strength of an external magnetic field, has been widely studied as a prospective replacement for general rubber in the mechanical domain. In this study, friction force is measured under different loads, speed, and magnetic field strength. From the test results, it is confirmed that the stick-slip phenomenon can be minimized under optimum conditions and can be applied in various mechanical components.

• Korean Journal of Materials Research
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• v.22 no.3
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• pp.136-139
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• 2012

Magnetic nanoparticles for ferromagnetic fluids and magnetorheological fluids were prepared by chemical coprecipitation and mechanical milling, respectively. The surface-treated particles were dispersed at various weight ratios into a medium of polyethylene glycol. In order to evaluate the elastic modulus of the fluids, ultrasonic pulse velocities were measured with an ultrasonic test using transducers of 5MHz and 2.25MHz. The ultrasonic signals were only available with a transducer of 2.25 MHz at fluid concentrations of 5 mg/ml and lower. In the case of applying transducers over 2.25 MHz and concentrations over 5 mg/ml to the fluids, it was impossible to observe effective ultrasonic signals due to an excessive scattering of the pulses by the dispersed particles. Elastic moduli of the magnetorheological fluids were 5.44 GPa and 6.13 GPa with concentrations of 25 mg/ml and 50 mg/ml, respectively; these values were higher by 40% than the values of 4.04 GPa and 4.28 GPa of ferromagnetic fluids at the same concentrations. As for the effect of an external magnetic field on these dilute fluids, the ultrasonic signals were positioned in a very similar way, which was probably due to insufficient arrangement of the particles even though the reflection energy of the ultrasonic waves apparently increased.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.10 no.4
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• pp.304-310
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• 2017

In this paper, we propose the architecture of an IPM based lane detector for autonomous vehicles to detect and control the driving route along the curved lane. In the IPM image, we divide the area into two fields, Far/Near Field, and the lane candidate region is detected using the Hough transform to perform the matching for the curved lane. In autonomous vehicles, various algorithms must be embedded in the system. To reduce the system resources, we proposed a method to minimize the number of memory accesses to the image and various parameters on the external memory. The proposed circuit has 96% lane recognition rate and occupies 16% LUT, 5.9% FF and 29% BRAM in Xilinx XC7Z020. It processes Full-HD image at a rate of 42 fps at a 100 MHz operating clock.

• Journal of the Korean Society of Safety
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• v.35 no.4
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• pp.74-83
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• 2020

In Korea, about 110,000 LPG small storage tanks of less than three tons have been installed in restaurants, houses and factories, and are used as LPG supply facilities for cooking, heating and industrial use. In the case of combustible liquefied gas storage tanks, the tank may rupture due to the temperature increase of the tank steel plate (approximately 600℃) even when the safety valve is operating normally, causing large-scale damage in an instant. Therefore, in the event of a fire near the LPG small storage tank, it is necessary to accurately predict the timing of the BLEVE(Boiling Liquid Expanding Vapour Explosion) outbreak in order to secure golden time for lifesaving and safely carry out fire extinguishing activities. In this study, we have first investigated the results of a prior study on the prediction of the occurrence of BLEVE in the horizontal tanks. And we have developed thermodynamic models and simulation program on the prediction of BLEVE that can be applied to vertical tanks used in Korea, have studied the effects of the safety valve's ability to vent, heat flux strength of external fires, size of tanks, and gas remaining in tanks on the time of BLEVE occurrence and have suggested future utilization measures.

• Journal of Science and Technology Studies
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• v.2 no.1 s.3
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• pp.63-83
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• 2002

This article examines the historical and general characteristics of science and technology policy in Korea. Historical characteristics are analyzed through formation period, growth period, and transition period. Korea institutional sis for the promotion of science and technology was made from the initial stage of industrialization. As national R&D programs were launched, technological activities in the private sector were rapidly increased from the 1980s. Korea pursued new directions of science and technology policy with the formation of related laws and Plans from the late 1990s. General characteristics are analyzed by the concept of 'policy regime'. The prime policy goal of science and technology policy in Korea has been related to industrial development so far. In the policy means, input element has been increased focusing on the external aspects. Bureaucratic policy culture has dominated other cultures including economic culture, academic culture, and civic culture.

• Journal of IKEEE
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• v.24 no.2
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• pp.385-391
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• 2020

Overcurrent and abnormal voltages in the distribution system can cause not only burden of power plant but also damage to customers. As a result, researches related to the distribution automation have been widely conducted by utilizing a real time digital simulation to improve the reliability of power supply through rapid failure handing, reduction of power failure intervals and failure recovery. However, the distribution automation systems using the real time digital simulator are expensive and limited to verify actual hardwares. Therefore, in this paper, an external hardware devices was developed based on the distribution system analysis results of the digital simulator. And real-time simulation and functional verification are implemented by the real feeder remote terminal units used in distribution automation. The effectiveness of the proposed system is verified through several experiments.

• Journal of the Korean Ceramic Society
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• v.45 no.12
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• pp.772-776
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• 2008

The Korea Electric Power Research Institute (KEPRI) has been developing planar solid oxide fuel cells (SOFCs) and power systems for combined heat and power (CHP) units. The R&D work includes solid oxide fuel cell (SOFC) materials investigation, design and fabrication of single cells and stacks, and kW class SOFC CHP system development. Anode supported cells composed of Ni-YSZ/FL/YSZ/LSCF were enlarged up to $15{\times}15\;cm^2$ and stacks were manufactured using $10{\times}10\;cm^2$ cells and metallic interconnects such as ferritic stainless steel. The first-generation system had a 37-cell stack and an autothermal reformer for use with city gas. The system showed maximum stack power of about $1.3\;kW_{e,DC}$ and was able to recover heat of $0.57{\sim}1.2\;kW_{th}$ depending on loaded current by making hot water. The second-generation system was composed of an improved 48-cell stack and a prereformer (or steam reformer). The thermal management subsystem design including heat exchangers and insulators was also improved. The second-generation system was successfully operated without any external heat source. Under self-sustainable operation conditions, the stack power was about $1.3\;kW_{e,DC}$ with hydrogen and $1.2\;kW_{e,DC}$ with city. The system also recuperated heat of about $1.1\;kW_{th}$ by making hot water. Recently KEPRI manufactured a 2kW class SOFC stack and a system by scaling up the second-generation 1kW system and will develop a 5kW class CHP system by 2010.