• Tribology and Lubricants
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• v.12 no.3
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• pp.107-114
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• 1996

MoS$_{2}$ bonded film was applied to reduction gears, and its lubricating properties were experimentally evaluated in terms of the power transmission efficiency and the frictional noise with a dynamo-typed gear test rig. Tests were performed in both oil lubrication and dry condition where the rotating velocity and loading torque were varied. In dry condition, MoS$_{2}$ bonded films effected the power transmission efficiency to increase about 5%, and the frictional noise level to decrease about 6 dB under the test operating conditions. It well proved that MoS$_{2}$ bonded films were a very effective solid lubricant for reduction gears. In oil lubricating conditions, the frictional properties of the coated gears were mainly governed by the lubricating oil, and lubricating effects of MoS2 bonded films were not evident. The result suggested that lubricating effect of MoS$_{2}$ bonded films would be limited to prevent a damage of reduction gears in the initial run when they were used in oil lubrication conditions.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1029-1037
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• 2008

The finite element analysis of transient water flow through unsaturated soils was used to investigate effects of hydraulic characteristics, initial relative degree of saturation, methods to consider boundary condition, and rainfall intensity and duration on water pressure in slopes. The finite element method with shear strength reduction technique was used to evaluate the stability of slopes under rainfall. The slope-related disasters in Korea usually occur between July and September during the typhoon and localized heavy rain. This means that the rainfall is the most important factor that leads to the slope-related disasters. The slope-related disasters can happen at very short time and lead to big damage. To forecast the change of the heave of the groundwater in slope the Seep/w program was used.

• International Journal of High-Rise Buildings
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• v.4 no.3
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• pp.191-198
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• 2015

It is important to accurately predict structural responses to external excitations such as typhoons and earthquakes when designing structures for serviceability. One of the key procedures to predict reliable vibration responses is to evaluate accurate structural dynamic properties using finite element (FE) models, which properly represent the realistic behavior of buildings. In the case of historic masonry buildings, structural damage could also be caused by ambient vibrations or impacts. Therefore, the preservation plans of historic buildings for low-level vibrations or impacts should be provided by analyzing structural damages within serviceability levels. For this purpose, it is required to provide FE model construction and response analysis methods verified with field measurement data. In this research, long-term field measurement was performed for a cathedral and its dynamic properties were evaluated using measured data. Then, the model was calibrated based on the measured dynamic properties and an overall construction method for the masonry cathedral was proposed. Using the measured accelerations, the vibrations of the belfry were analyzed using the calibrated FE model and finally, the FE model for the cathedral was verified by comparing the measured accelerations with the modeled results.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.6
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• pp.541-545
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• 2007

The critical current degradation behaviors of multifilamentary Bi-2223 superconducting tapes under pressurized liquid nitrogen were investigated using a r-shaped sample holder which gives a series of bending strains to tape. Three kinds of externally-reinforced Bi-2223 tapes with different hermeticity were used as samples. The tape with the thicker reinforcement layer had a better bending strain tolerance of $I_c$, but when the bending strain was calculated at the outermost filament, the $I_c$ degradation behavior became identical. For all samples, $I_{c0}$ decreased with the increase of applied pressure, but the $I_c$ degradation behavior with bending strain at each pressure level was similar. Furthermore, after depressurization from 1 MPa to atmospheric pressure, $I_c$ was completely recovered to its initial values. When the samples were warmed up to room temperature after pressurization tests, the ballooning damage occurred at lower bending strain regions. The region where ballooning was observed was identical to the one where the significant $I_c$ degradation occurred.

• Earthquakes and Structures
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• v.7 no.3
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• pp.271-294
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• 2014

In recent years, along with the advances made in performance-based design optimization, the need for fast calculation of response parameters in dynamic analysis procedures has become an important issue. The main problem in this field is the extremely high computational demand of time-history analyses which may convert the solution algorithm to illogical ones. Two simplifying strategies have shown to be very effective in tackling this problem; first, simplified nonlinear modeling investigating minimum level of structural modeling sophistication, second, wavelet analysis of earthquake records decreasing the number of acceleration points involved in time-history loading. In this paper, we try to develop an efficient framework, using both strategies, to solve the performance-based multi-objective optimal design problem considering the initial cost and the seismic damage cost of steel moment-frame structures. The non-dominated sorting genetic algorithm (NSGA-II) is employed as the optimization algorithm to search the Pareto optimal solutions. The constraints of the optimization problem are considered in accordance with Federal Emergency Management Agency (FEMA) recommended design specifications. The results from numerical application of the proposed framework demonstrate the capabilities of the framework in solving the present multi-objective optimization problem.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.3
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• pp.205-213
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• 2021

Due to the advantage of reducing the voltage applied to the switch semiconductor, the input series and output parallel combination is widely used in systems with high input voltage and large output current. On the other hand, the LLC converter is widely used as a high-efficiency power converter, and when connected by ISOP combination, there is a possibility that input voltage imbalance may occur due to a mismatch of passive devices. To avoid damaging the switching device, this study analyzed the DC-link voltage imbalance of a high-capacity supply using an ISOP LLC converter. In addition, the case where DC-link unbalance control was applied and the case not applied was analyzed respectively. Based on this analysis, an initial start-up algorithm was proposed to prevent input power semiconductor device damage due to DC-link over-voltage. The effectiveness of the proposed algorithm has been verified through simulations and experiments.

• Childhood Kidney Diseases
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• v.26 no.1
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• pp.63-67
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• 2022

Nephrocalcinosis often occurs in infants and is caused by excessive calcium or vitamin D supplementation, neonatal primary hyperparathyroidism, and genetic disorders. Idiopathic infantile hypercalcemia (IIH), a rare cause of nephrocalcinosis, results from genetic defects in CYP24A1 or SLC34A1. Mutations in CYP24A1, which encodes 25-hydroxyvitamin D 24-hydroxylase, disrupt active vitamin D degradation. IIH clinically manifests as failure to thrive and hypercalcemia within the first year of life and usually remits spontaneously. Herein, we present a case of IIH wih CYP24A1 mutations. An 11-month-old girl visited our hospital with incidental hypercalcemia. She showed failure to thrive, and her oral intake had decreased over time since the age of 6 months. Her initial serum parathyroid hormone level was low, 25-OH vitamin D and 1,25(OH)₂ vitamin D levels were normal, and renal ultrasonography showed bilateral nephrocalcinosis. Whole-exome sequencing revealed compound heterozygous variants in CYP24A1 (NM_000782.4:c.376C>T [p.Pro126Ser] and c.1310C>A [p.Pro437His]). Although her hypercalcemia and poor oral intake spontaneously resolved in approximately 8 months, we suggested that her nephrocalcinosis and renal function be regularly checked in consideration of potential asymptomatic renal damage. Hypercalcemia caused by IIH should be suspected in infants with severe nephrocalcinosis, especially when presenting with failure to thrive.

• Tribology and Lubricants
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• v.39 no.4
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• pp.123-132
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• 2023

In this study, the expansion, stress, and operating clearance of bearing elements during operation are observed using the inner/outer ring temperature test data of a 3.0×10⁶ DN-class roller bearing. The operating clearance characteristics of inner-/outer-ring cooling (IORC) bearings are compared to those of inner-ring cooling (IRC) bearings. For IRC bearings, the thermal expansion of the outer ring is the most important factor in clearance variation. As a result, the operating clearance is less than the initial clearance of 61 ㎛, and the operating clearance decreases to 0.5 ㎛ at 25,500 rpm. Conversely, the temperature of the outer ring of IORC bearings is lower than that of IRC bearings, so the operating clearance is kept smaller. When the coolant flow rate to the outer ring is approximately 1.5 to 2.0 L/min, the temperature difference between the inner and outer rings is minimized and the operating clearance is maintained at a significantly lower level than IRC bearings. Small operating clearances are expected to be effective in reducing cage slip and skid damage in roller bearings. The results and analysis procedures of this study can be utilized to design of bearing clearance, lubricant flow rate, and assembled interference in the early design stage of aerospace roller bearings.

• Journal of Korean Association for Spatial Structures
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• v.22 no.4
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• pp.89-98
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• 2022

The recent earthquake in Korea caused a lot of damage to reinforced concrete (RC) columns with non-seismic details. The nonlinear analysis enables predicting the hysteresis behavior of RC columns under earthquakes, but the analytical model used for the columns must be accurate and practical. This paper studied the nonlinear analysis models built into a commercial structural analysis program for the existing RC columns. The load-displacement relationships, maximum strength, initial stiffness, and energy dissipation predicted by the three analysis models were compared and analyzed. The results were similar to those tested in the order of the fiber, Pivot, and Takeda models, whereas the fiber model took the most time to build. For columns subjected to axial load, the Pivot model could predict the behavior at a similar level to that of the fiber model. Based on the above, it is expected that the Pivot model can be applied most practically for existing RC columns.

• Journal of Korean Association for Spatial Structures
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• v.24 no.3
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• pp.95-107
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• 2024

In South Korea, over 400,000 Non-building Structures are inadequately managed and exposed to potential risks due to insufficient inspection systems, leading to an increase in accidents and significant losses of life and property. Therefore, it is crucial for users to conduct proactive self-inspections to identify and mitigate potential hazards. This study reclassified Non-building Structures into four main categories by analyzing their structural characteristics and associated risks through statistical analysis. Among these, retaining walls, which account for the largest proportion, were systematically analyzed to identify common damage patterns. Based on this analysis, self-inspection checklists were developed for both non-experts and experts. The proposed process involves an initial visual inspection using a simple non-expert checklist, followed by a more detailed expert-level inspection if any anomalies are detected. The reliability of this process was validated through approximately 120 validation processes.