• Design & Manufacturing
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• v.15 no.2
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• pp.23-29
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• 2021

The specific strength of magnesium alloy is four times that of iron and 1.5 times that of aluminum. For this reason, its use is increasing in the transportation industry which is promoting weight reduction. At room temperature, magnesium alloy has low formability due to Hexagonal closed packed (HCP) structure with relatively little slip plane. However, as the molding temperature increases, the formability of the magnesium alloy is greatly improved due to the activation of other additional slip systems, and the flow stress and elongation vary greatly depending on the temperature. In addition, magnesium alloys exhibit asymmetrical behavior, which is different from tensile and compression behavior. In this study, a jig was developed that can measure the plane deformation behavior on the surface of a material in tensile and compression tests of magnesium alloys in warm temperature. A jig was designed to prevent buckling occurring in the compression test by applying a certain pressure to apply it to the tensile and compression tests. And the tensile and compressive behavior of magnesium at each temperature was investigated with the developed jig and DIC equipment. In each experiment, the strain rate condition was set to a quasi-static strain rate of 0.01/s. The transformation temperature is room temperature, 100℃. 150℃, 200℃, 250℃. As a result of the experiment, the flow stress tended to decrease as the temperature increased. The maximum stress decreased by 60% at 250 degrees compared to room temperature. Particularly, work softening occurred above 150 degrees, which is the recrystallization temperature of the magnesium alloy. The elongation also tended to increase as the deformation temperature increased and increased by 60% at 250 degrees compared to room temperature. In the compression experiment, it was confirmed that the maximum stress decreased as the temperature increased.

• Korean Journal of Food Science and Technology
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• v.30 no.2
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• pp.348-355
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• 1998

The developments of various processed foods and the high quality dried fruits, in particular, are urgently needed for the enhancement of fruit consumption and their competitive values. Therefore, in this study, three variables by three level factorial design and response surface methodology were used to determine optimum conditions for osmotic dehydration of kiwifruit. The relationships of moisture losses, solid gains, weight reductions, sugar contents, titratable acidities and vitamin C contents depending on changes with temperature, sugar concentration and immersion time were investigated. The moisture loss, solid gain, weight reduction and reduction of moisture content after osmotic dehydration were increased as temperature, sugar concentration and immersion time increased. The effect of concentration was more significant than those of temperature and time on mass transfer. Sugar content was increased by increasing sugar concentration, temperature, immersion time during osmotic dehydration. Titratable acidity and vitamin C content were increased by decreasing temperature, immersion time and increasing concentration during osmotic dehydration. The regression models showed a significant lack of fit (P>0.05) and were highly significant with satisfying values of $R^2$. At the given conditions such as $66{\sim}69%$ moisture content, above $24^{\circ}Brix$ sugar content and more than 23 mg% vitamin C, the optimum condition for osmotic dehydration was $37^{\circ}C,\;55^{\circ}Brix$ and 1.5 hour.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.3
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• pp.181-192
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• 2022

Active vibration control system(AVCS) for helicopter enables to control the vibration generated from the main rotor and has the superb vibration reduction performance with low weight compared passive vibration reduction device. In this paper, FxLMS algorithm-based vibration control software of the light civil helicopter tansmits the control command calculated using the signals of the tachometer and accelerometers to the circular force generator(CFG) is developed and verified. According to the RTCA DO-178C/DO-331, the vibration control software is developed through the model based design technique, and real-time operation performance is evaluated in PILS(processor in-the loop simulation) and HILS(hardware in-the loop simulation) environments. In particular, the reliability of the software is improved through the LDRA-based verification coverage in the PIL environments. In order to AVCS to light civil helicopter(LCH), the dynamic response characteristic model is obtained through the ground/flight tests. AVCS configuration which exhibits the optimal performance is determined using system optimization analysis and flight test and obtain STC certification.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.151-165
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• 2019

In this study, the four types of improvement methods (increase self weight and reducing sliding force etc.) were proposed depending on install location with compaction grouting to improve seismic performance of existing port structure and optimal methods by analyzing the effects of improvement (stability, constructability and economy) by theoretical and numerical methods. From the dynamic time history analysis for artificial seismic waves, the results indicated that the horizontal displacement after improvement decreased compared to before improvement, however the displacement reduction effect among improvement methods was not significantly different. Slope stability based on the strength reduction method and the limit equilibrium analysis method, it is confirmed that the passive pile method is more safe than other methods. It is due to the shear strength at the failure surface is increased. In addition, the analysis of constructability and economy showed that the reduction of earth pressure method (type 02) and the passive pile method (type 03) are excellent. However, in the case of the passive pile method is concerned that there is a shortage of design cases and the efficiency can be reduced depend on various constraints such as ground conditions.

• Journal of Korean Neurosurgical Society
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• v.29 no.10
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• pp.1296-1302
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• 2000

Objective : Traumatic brain injury including diffuse axonal injury has been shown to result in a decrease in brainfree magnesium concentration, an endogenous inhibitor of calcium entry into neuron, that is associated with the development of neurological motor deficits. The goal of this study is to establish the therapeutic window during which the therapy with $MgSO_4$ and/or hypothermia improve damaged neurons by TUNEL stain. Method : Moderate brain injury was induced in 64 adult Sprague-Dawley rats, weighing 350 to 450gm each, by using a simple weight-drop device(Marmarou model). The animals were randomly assigned to four groups(sixteen rats each, a control group, a group treated with $MgSO_4$, a group treated with hypothermia, and a group treated with $MgSO_4$ and hypothermia) and the rats in each group were sacrificed and studied after 12 hrs, 24 hrs, 1 wk, and 2 wks after insult. In hypothermic group, these rats were subjected to hypothermia after injury, with their rectal temperatures maintained at $32^{\circ}C$ for 1 hour. After 1-hour period of hypothermia, rewarming to normothermic level was accomplished over 30-minute period. In the groups treated $MgSO_4$, hypothermia and $MgSO_4$ were subsequently treated with $MgSO_4$($750{\mu}moles/kg$) infused intra-muscularly at 30 minutes after trauma. Result : In all treated groups, a significant reduction in TUNEL positive cells was found in comparison with the control group each time(p<0.001). Between treatment groups, No differnce was seen 12hrs, 24hrs, and 1wk. However, hypothermic group treated with or without $MgSO_4$ showed more significant reduction in apoptotic cells than group treated with $MgSO_4$ 2 weeks after trauma(p<0.05). However, hypothermic group treated with $MgSO_4$ showed no significant reduction in apoptotic cells compared with hypothermic group(p>0.05). Conclusion : These findings suggest that both hypothermia and $MgSO_4$ significantly improve pathological changes. Otherwise simultaneously $MgSO_4$ and hypothermia treatment groups is failed to provide additional neuroprotection. These results may be relevant to the design of future clinical trials of therapeutic hypothermia and $MgSO_4$ for traumatic brain injury.

• Research in Plant Disease
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• v.11 no.1
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• pp.43-47
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• 2005

To investigate control efficacy of flusulfamide GR (granule) on Chinese cabbage clubroot caused by Plasmodiophora brassicae, experiment was accomplished in field located in Gangneungshi alpine area contaminated by P. brassicae. Flusulfamide GR provided control value of 84.6% and that was statistically significant difference from standard fungicides containing untreated control. To investigate ratio of reduction of resting spore according to fungicide treatment, soil of Chinese cabbage field before and after fungicide treatment were sampled and investigated density of resting spore. Resting spore density was not uniform in soil before fungicide treatment. Therefore, to investigate control efficacy of fungicide against clubroot, investigation on resting spore density was conducted before experiment and reflected in experimental design. Flusulfamide GR and DP (dust powder) provided 64.2% and 63.7% of reduction of resting spore on field soil after fungicide treatments. This result indicated that control efficacy of the fungicides was correlated with reduction of resting spore of P. brassicae. The increasing rate in fresh weight of above-ground part of Chinese cabbage by flusulfamide DP and GR, fluazinam DP and trifloxystrobin SC (suspension concentrate) was 14.3%, 13.0%, 13.8% and 3.8%, respectively. From above result, flusulmide GR have outstanding control efficacy against clubroot of Chinese cabbage and is effectively decreasing of resting spore density in soil.

• Land and Housing Review
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• v.2 no.2
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• pp.195-204
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• 2011

During mechanical demolition of RC structures, weights of dismantling equipment and demolition waste of building are applied to unexpected load which did not be considered during the design of structural member. Nevertheless, the loading of dismantling equipment and dismantling process are mainly dependent on field managers' field workers' or experiences without considering safety of structural member by a structural engineer. It is urgently required that reflecting actual circumstance of mechanical demolition, safety evaluation method to evaluate the safety and the guideline for appropriate capacity of structural member to support dismantling equipment weight, be provided. Through site investigation and questionnaire on field workers, this paper proposed demolition waste load, load factor, strength reduction factor, and so on. These are essential to safe evaluation of a building, ready to demolition. Considering actual circumstance of mechanical demolition, safety evaluation method of building and design method of slab and beam was suggested to a dilapidated building. An capability to loading of dismantling equipment was proposed, applied to RC slab and RC beam. Therefore, the suggested safety evaluation method and the guideline for an capability to loading of dismantling equipment weight can reasonably evaluate the capacity of structural member in demolition and use effectively as increasing efficiency and improving safety of demolition through proper management of dismantling equipments.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.54-63
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• 2022

This paper is a study on the friction damper, which is one of the seismic reinforcement devices for structures. This study developed a damper by replacing the internal friction material with ultra high molecular weight polyethylene (UHMWPE), a type of composite material. In addition, this study applied a multi-friction method in which the internal structure where frictional force is generated is laminated in several layers. To verify the performance of the developed multi-friction damper, this study performed a characteristic analysis test for the basic physical properties, wear characteristics, and disc springs of the material. As a result of the wear test, the mass reduction rate of UHMWPE was 0.003%, which showed the best performance among the friction materials based on composite materials. Regarding the disc spring, this study secured the design basic data from the finite element analysis and experimental test results. Moreover, to confirm the quality stability of the developed multi-friction damper, this study performed an seismic load test on the damping device and the friction force change according to the torque value. The quality performance test result showed a linear frictional force change according to the torque value adjustment. As a result of the seismic load test, the allowable error of the friction damper was less than 15%, which is the standard required by the design standards, so it satisfies the requirements for seismic reinforcement devices.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.1
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• pp.7-15
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• 2021

In this study, we developed Void Plywood Slab (VPS) that improved the shape of existing hollow materials. Its performance was evaluated through one-way flexural and one-way shear tests using the developed VPS. As a result of the one-way flexural performance tests of VPS, the yield load value for FPS series(longitudinal direction specimens with hollow materials) was approximately 97.5% compared to FPS-00(without hollow materials) specimen. The tests showed that the yield load was not much different. In addition, FNS series(transverse direction specimens with hollow materials) also represented about 97% of FPS-00 specimen. The one-way flexural performance was shown to have little impact from void materials. Therefore, it is confirmed that the presented system is applicable to the VPS to the slab design. The results of the one-way shear performance tests of VPS showed that it was about 92% compared to the SS-00(without hollow materials) specimen. These results were somewhat insufficient for the SS-00 specimen. Shear strength equation is expressed as the sum of shear force by concrete and shear force by reinforcement. However, in the case of void slab, it is believed that the concrete section has been deleted by the void material. However, the strength of the structure applied to the shear design, as with the flexural design, is also applied to the design based on the yield load value.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.7
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• pp.992-1001
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• 2023

OWEC (Overtopping Wave Energy Converter) is a wave power generation system using the wave overtopping. The performance and safety of the OWEC are affected by wave characteristics, such as wave height, period. To mitigate this issue, optimal OWEC designs based on wave characteristics must be investigated. In this study, the environmental conditions along the Ulleungdo coast were used. The hydraulic efficiency of the OWEC was calculated using SPH (Smoothed Particle Hydrodynamics) by comparing 4 models that changed the substructure. As a result, it was possible to change the substructure. Through design optimization, a new truss-type structure, which is a substructure capable of carrying the design load, was proposed. Through a case study using member diameter and thickness as design variables, structural safety was secured under allowable stress conditions. Considering wave load, the natural frequency of the proposed structure was compared with the wave period of the relevant sea area. Harmonic response analysis was performed using wave with a 1-year return period as the load. The proposed substructure had a reduced response magnitude at the same exciting force, and achieved weight reduction of more than 32%.