• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.4
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• pp.275-283
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• 2013

In this paper, the structural optimum design method of composite rotor blade cross-section was investigated with the genetic algorithm. An auto-mesh generation program was developed for iterative calculations of optimum design, and stresses in the blade cross-section were analyzed by VABS (variational asymptotic beam sectional analysis) program. Minimum mass of rotor blade was defined as an object function, and stress failure index, center mass and blade minimum mass per unit length were chosen as constraints. Finally, design parameters such as the thickness and layup angles of a skin, and the thickness, position and width of a torsion box were determined through the structural optimum design method of composite rotor blade cross-section presented in this paper.

• Tribology and Lubricants
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• v.37 no.6
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• pp.224-231
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• 2021

Recently, the waterproofing performance of high-voltage connectors in automotive vehicles has attracted increased interest. In this study, an optimal cross-sectional shape was derived to obtain uniform contact pressure and strain by considering stress relaxation problems caused by initial tension when mounting a seal. A high strain of 52.1 was distributed in the round region, owing to excessive initial tension. The finite element method (FEM) analysis indicated that the strain corresponding to the optimal initial tensile was 11. We adopted six design factors to optimize the seal cross-section and three factors as the main design factors. An orthogonal arrangement table was prepared using Minitab. FEM analyses of 16 study models were conducted to determine the optimized model. The contact pressure of the optimization model is the most evenly distributed while satisfying the waterproof performance of 0.47 MPa. Compared to the initial model, the difference in strain decreases from 35.5% to 19.6%. Finally, the derived cross-sectional shape can reduce the strain of the round region by 33.8% and the differences in the contact pressure at the upper and lower surfaces by 42% and 76%, respectively.

• Journal of the Korean Society of Safety
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• v.33 no.5
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• pp.15-20
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• 2018

This paper describes the fusing time characteristics of Light PVC Sheathed Circular Cord(VCTF) and Tray Frame Retardant(TFR) cables according to increased temperature under over current condition. The experimental equation will be used to determine the validity and reliability of the test results. The over current flowed 3, 5 and 10 times higher than the amount of allowable current using DC power supply with DAQ(Data Acquisition) measurement system. An infrared radiation heater, which was controlled by a variable AC auto transformer, was used to increase the temperature from room temperature to 50, 100 and 150 degrees Celsius. First, two type of cables were analyzed those with different cross-sectional areas with in the same structure and those with different structures with in the same cross-sectional areas. Then, it was determined how fusing time had been influenced according to the cross-sectional areas and different structures, respectively. The cable resistance was increased by joule heating according to increasing temperature. Therefore, the allowable current of cable is decreased. Finally, the fusing time of the cable was decreased due to increased temperatures at current flow, which were 3 times the amount of allowable current. The instantaneous breakdown was observed when current flow was 5 and 10 times over the amount of allowable current. The fusing time is directly affected by the structure of cable insulation.

• Journal of the Korean Society of Physical Medicine
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• v.15 no.2
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• pp.121-128
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• 2020

PURPOSE: This study examined the changes in the cross-sectional area (CSA) of the abductor hallucis muscle during various ankle positions while performing toespread-out (TSO) exercise. METHODS: Thirty subjects with an average age of 22.1 years were recruited for this study. All subjects were firstly measured for the angle of their first metatarsophalangeal joint using a goniometer. Those with angles greater than 15° were allocated to the HV group. The remaining subjects were placed in the normal group. The CSA of the abductor hallucis was measured by ultrasound in the resting position with no movement and three ankle positions: neutral (0°), plantarflexion (30°), and dorsiflexion (30°). All data were analyzed using a two-way mixed analysis of variance between the groups (normal and HV group) and within the groups (resting, neutral, plantarflexion, and dorsiflexion) to determine the group x position interaction effects. RESULTS: During TSO exercise in the normal group, the CSA of the abductor hallucis was significantly greater in both the plantarflexion and neutral positions compared to the resting position (p_adj < .01), and plantarflexion was significantly greater than the dorsiflexion position (p_adj < .01). During the TSO exercise in the HV group, the CSA of the abductor hallucis for plantarflexion was significantly greater than it was for the resting, neutral, and dorsiflexion positions (p_adj < .01). CONCLUSION: Based on the above results, the TSO exercise in plantarflexion is an effective rehabilitation exercise for subjects with HV.

• Imaging Science in Dentistry
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• v.37 no.3
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• pp.133-138
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• 2007

Purpose: The purpose of this study was to evaluate the morphologic features of posterior edentulous mandible for Korean patients using cross-sectional CT images. Materials and Methods: Computed tomographic cross-sectional views taken in 2004 and 2005 at Seoul National University Dental Hospital were analyzed by an oral and maxillofacial radiologist. Four indices were measured to meet the purpose of this study: 1) the horizontal distance between the alveolar crest and mandibular canal (Type), 2) the angle of the mandibular long axis (Angle), 3) the bucco-lingual location of mandibular canal, and 4) the depth of the submandibular fossa. The averages and standard deviations of the measurements were compared according to the location (the first and second molar area) and sex of the patients. Results: Statistically significant difference was found in Type, Angle, and submandibular fossa depth between the first and second molar area (p<0.05). However, there was no significant difference between men and women in any of the measured indices. Most of the mandibular canals were located in lingual side of posterior mandible. Conclusion: More care should be taken when an implant is installed on the mandibular second molar area.

• Journal of the Earthquake Engineering Society of Korea
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• v.18 no.4
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• pp.201-212
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• 2014

The plastic hinge region of RC pier ensures its nonlinear behavior during strong earthquake events. It is assumed that the piers secure sufficient strength and ductility in order to prevent the collapse of the bridge during strong earthquake. However, the presence of a lap-splice of longitudinal bars in the plastic hinge region may lead to the occurrence of early bond failure in the lap-splice zone and result in significant loss of the seismic performance. The current regulations for seismic performance evaluation limit the ultimate strain and displacement ductility considering the eventual presence of lap-splice, but do not consider the lap-splice length. In this study, seismic performance test and analysis are performed according to the cross-sectional size and the lap-splice length in the case of longitudinal bars with lap-splice located in the plastic hinge region of existing RC bridge columns with circular cross-section. The seismic behavioral characteristics of the piers are also analyzed. Based upon the results, this paper presents a more reasonable seismic performance evaluation method considering the lap-splice length and the cross-sectional size of the column.

• The korean journal of orthodontics
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• v.53 no.5
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• pp.317-327
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• 2023

Objective: This study aimed to evaluate the association between low tongue position (LTP) and the volume and dimensions of the nasopharyngeal, retropalatal, retroglossal, and hypopharyngeal segments of the upper airway. Methods: A total of 194 subjects, including 91 males and 103 females were divided into a resting tongue position (RTP) group and a LTP group according to their tongue position. Subjects in the LTP group were divided into four subgroups (Q1, Q2, Q3, and Q4) according to the intraoral space volume. The 3D slicer software was used to measure the volume and minimum and average cross-sectional areas of each group. Airway differences between the RTP and LTP groups were analyzed to explore the association between tongue position and the upper airway. Results: No significant differences were found in the airway dimensions between the RTP and LTP groups. For both retropalatal and retroglossal segments, the volume and average cross-sectional area were significantly greater in the patients with extremely low tongue position. Regression analysis showed that the retroglossal airway dimensions were positively correlated with the intraoral space volume and negatively correlated with A point-nasion-B point and palatal plane to mandibular plane. Males generally had larger retroglossal and hypopharyngeal airways than females. Conclusions: Tongue position did not significantly influence upper airway volume or dimensions, except in the extremely LTP subgroup.

• Journal of Space Technology and Applications
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• v.4 no.1
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• pp.62-73
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• 2024

This study analyzed the effectiveness of orbital change through attitude change in nano-satellites operating in low Earth orbit (LEO) without thrusters, focusing on collision avoidance maneuvers. The results revealed that changes in the satellite's cross-sectional area significantly impact its in-track direction, influenced by the aspect ratio of cross-sectional area change and mission altitude. Notably, satellites at lower altitudes demonstrated significant reduction in collision risks with a small amount of attitude change. Through this study, it is judged that the changing the cross-sectional area through attitude maneuver is a sufficiently suitable method in the operation of nano-satellites without thrusters, and is expected to contribute to improving the safety of satellite operations in the New Space era.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.3
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• pp.127-133
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• 2018

To reduce fuel consumption, research on the weight reduction of vehicles is being actively carried out. Researchers have typically tried to replace metal materials with composites materials, but these materials did not satisfy the required strength and rigidity of a vehicle. Composites are usually not used because of their high cost. There are incomplete studies on lightweight trucks that transport cargo. Therefore, in this paper, we enhance the lightness and mechanical strength through design optimization of the deck frame for a lightweight truck. For that purpose, the side member and cross member, which are mounted on the lower part of the truck to assure the safety of the vehicle and support the luggage load, were targeted. The result of numerical analysis on the safety of the frame was obtained by changing the shape of each cross-section. To verify the numerical analysis, we compared it with the theoretical value of a cantilever beam. As a result, the suitability of the cross-sectional shapes of each frame was confirmed through numerical analysis.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.6
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• pp.460-472
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• 2023

This study was conducted based on the case of an accident (excessive deformation) that occurred during the hydraulic test of a shipboard tank manufactured in accordance with the design regulations. Over-pressure phenomenon was noted as the main cause of accidents in the process of testing tanks without physical damage, which can be found in external factors such as cross-sectional difference between inlet pipe and air pipe and higher water filling rate than the recommended one. The main goal of this paper is to establish a safe water filling rate according to the range of sectional area ratio(SAR) reduced below the regulations for each test situation. The simulation was conducted in accordance with the hydraulic test procedure specified in the Ship Safety Act, and the main situation was divided into two types: filling the tank with water and increasing the water head to the test pressure. The structural safety evaluation of the pressure generated inside the tank and the effect on the structure during the test was reviewed according to the SAR range. Based on the results, guidelines for the optimal filling rate applicable according to SAR during the hydraulic test were presented for the shipboard tanks used in this study.