• Journal of the Society of Naval Architects of Korea
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• v.38 no.4
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• pp.11-22
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• 2001

The interaction between forward mounted propeller and wing in ground effect, and its aerodynamic performance are analyzed by potential flow approximation. A Vortex Lattice Method(VLM) for the propeller analysis and a potential based panel method for the WIG are used together with an image method by assuming the free surface as a rigid wall. The interaction of propeller and wing in the proximity of the ground is taken into account by an iterative procedure where the boundary conditions are satisfied with the given convergence criteria. The program developed is first checked by comparing its numerical results with the experimental data and other numerical results for the propeller MP101-rudder MR21 system. Then, the propeller-WIG interaction and its performance versus ground clearance are investigated by changing parameters such as propeller position, diameter and speed of revolution. It is shown that the forward mounted propeller increases the lift forces of the wing and also enhances the height stability, depending on the design parameter. Therefore, the appropriate selection of the design parameter such as propeller diameter, revolution, the longitudinal and vertical position of propeller is necessary.

• Journal of Korean Foot and Ankle Society
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• v.24 no.3
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• pp.113-119
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• 2020

Purpose: A flatfoot that fails to form a longitudinal foot arch is a common lower limb deformity in children. This study evaluated the structural and functional effects of the insole for pediatric flexible flat foot (PFFF). Materials and Methods: Twenty-nine PFFF patients (20 boys and 9 girls, 58 feet) with bilateral symptomatic flatfoot deformities between February 2017 and May 2019 were included in this study. Sixteen patients (32 cases, study group) were treated with a pressured based 3-dimensional printing insole, and 13 patients (26 cases, control group) were followed up regularly without any treatment. Flatfoot was diagnosed by a lateral talo-first metatarsal angle of more than 4° in convex downward and talocalcaneal angles of more than 30° and a calcaneal pitch of less than 20°. The foot pressures, including the midfoot pressure, total foot pressure, and the ratio of the midfoot pressure to the total foot pressure, were evaluated by pedobarography. The clinical scores were assessed using the visual analogue scale (VAS), American Orthopaedic Foot and Ankle Society (AOFAS), and Pediatrics Outcomes Data Collection Instrument (PODCI) scores. Results: The mean age of the study group was 9.16 years, and the mean age of the control group was 7.73 years. The mean follow-up period was 16 months. The change in the lateral talocalcaneal angle was -4.664°±1.239° in the study group and -0.484°±1.513° in the control group. A significant difference in the amount of change of the lateral talocalcaneal angle was observed between the two groups (p=0.034). The midfoot pressures were similar in the two groups. Conclusion: Pressure based customized 3-dimensional printing insole in PFFF may have some effect on the hindfoot bony alignment, but it does not affect the changes in midfoot pressure.

• Composites Research
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• v.18 no.6
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• pp.9-18
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• 2005

With the wide applications of fiber-reinforced composite material in aero-structures and mechanical parts, the design of composite joints have become a very important research area because the joints are often the weakest areas in composite structures. This paper presents an analytical study of the stress distributions in mechanically single-fastened and multi-fastened composite laminates. The finite element models which treat the pin and hole contact problem using a contact stress analysis are described. A dimensionless stress concentration factor is used to compare the stress distributions in composite laminates quantitatively In the case of single-pin loaded composite laminate, the effects of stacking sequence, the ratio of a hole diameter and the width of a laminate (W/D ratio), the ratio of hole diameter and distance from edge to hole (E/D ratio), friction coefficient and clamping force are considered. In the case of multi-pin loaded composite laminate, the influence of the number of pins, pitch distance, number of rows, row spacing and hole pattern are considered. The results show that P/D ratio and E/D ratio affect more on stress distributions near the hole boundary than the other factors. In the case of multi-pin loaded composite laminate, the stress concentration in the double column case is better than the other cases of multi-pin loaded composite laminate.

• Journal of Korean Foot and Ankle Society
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• v.13 no.2
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• pp.113-117
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• 2009

Purpose: To evaluate the short-term results of medial displacement calcaneal osteotomy without flexor digitorum longus transfer for flexible flatfoot deformity. Materials and Methods: Twenty four patients (25 feet) who had undergone medial displacement calcaneal osteotomy without flexor digitorum longus transfer for flexible flatfoot between July 2004 and May 2007 were included. The mean age was 43.6 years (16~78 years). The mean follow-up was 26 months (14~50 months). Clinical outcomes were assessed using American Orthopaedic Foot and Ankle Society (AOFAS) score and visual analogue scale (VAS). Six radiographic parameters were measured from weightbearing radiographs to assess the difference between preoperative and postoperative radiographs. Results: The mean AOFAS score improved from 57.9 points preoperatively to 89.2 points at latest follow-up (p=0.000). The mean VAS improved from 62 points preoperatively to 23 points at latest follow-up (p=0.000). The mean talonavicular coverage angle on anteroposterior (AP) view changed from 20.2 degrees to 16.0 degrees (p=0.002). The mean calcaneal pitch angle on lateral view changed from 12.6 degrees preoperatively to 14.5 degrees at latest follow-up (p=0.001). Regarding these radiographic parameters, the difference between interobserver measurements was larger than that between pre- and post-operative measurements. The calcaneus was transferred medially by average 11.8 mm (p=0.003), which was 27.9% of the width of calcaneal tuberosity (p=0.000). The mean talo-first metatarsal angle on AP and lateral views, and navicular height on lateral view were not significantly changed. Conclusion: Medial displacement calcaneal osteotomy without flexor digitorum longus transfer for flexible flatfoot could lead to improve the clinical outcomes, although the restoration of medial longitudinal arch was not clinically significant.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.1-9
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• 2017

Spiral reinforcement in a circular column plays an effective role in the ductile behavior of a column through position fixing and buckling restraining of the longitudinal reinforcement, and confining core-concrete. Each country has suggested the minimum volumetric ratio of spiral reinforcement in order to secure the ductility of concrete columns. The minimum volumetric ratio of spiral reinforcement suggested by ACI 318-14 and the national concrete structure design standard was developed based on the theory of Richard et al. (1928); furthermore it has been used until now. However, their theory cannot consider the effects of high strength concrete and high strength reinforcement, and arrangement condition of the spiral reinforcement. In this study, a modified minimum volumetric ratio equation is suggested, which is required to improve the ductility of reinforced concrete circular columns and to recover their stress. The modified minimum volumetric ratio equation suggested here considers the effect of the compressive strength of concrete, the yield strength of spiral reinforcement, the cross sectional area of columns, the pitch of spiral reinforcements and the diameter of spiral reinforcement. In this paper, the validity of the minimum volumetric ratios from ACI 318-14 and this study was investigated and compared based on the results of uniaxial compression experiment for specimens in which the material strength and the spiral reinforcements ratio were used as variables. In the end of the study, the modification method for the suggested equation was examined.

• The KSFM Journal of Fluid Machinery
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• v.18 no.6
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• pp.63-70
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• 2015

This paper proposes a novel airfoil named "KA2" for the blade of the wind turbine systems. Dynamic loads characteristics are analyzed and compared using aerodynamic data of ten airfoils including the proposed airfoil. The blade is divided into the sixteen elements in the longitudinal direction of the blade for applying the Blade Element Method Theory (BEMT) method, and in each element, torque, thrust, and pitching moment are calculated using turbulent time varying wind speed and aerodynamic data of each wing. Additionally, each force and torque is accumulated in the whole region of the blade for the estimation of representative values. The magnitude of such forces is comparatively analyzed for different airfoils. The angle of attack is constant below the rated wind speed due to the fact that the tip speed ratio is kept at the constant value, and it increases in the region of over rated wind speed as the tip speed ratio decreasing with constant rated rpm and increasing wind speed. Such increase in the angle of attack causes the changes of the force acting on the airfoil with different characteristics of lift and drag in the stall region of each different airfoil. Even though the mean wind speed is in the rated speed in a given time, because of the turbulence, it has either the over rated or under rated speed most of the time. Furthermore, the dynamic properties of each force are analyzed in this rated wind speed in order to objectively understand the dynamic properties of the blades which are designed based on the different airfoils. These dynamic properties are also compared by the standard deviation of time varying characteristics. Moreover, the output characteristics of the wind turbine are investigated with different airfoils and wind speeds. Based on these investigations, it was revealed that the proposed airfoil (KA2) is well applicable to the blade with passive pitch control system.

• Journal of Navigation and Port Research
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• v.38 no.5
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• pp.485-491
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• 2014

In this paper, it is proposed that the effects of simulator sickness due to scene movement in ship handling simulator can be measured by using center of pressure (COP) and a simulator sickness questionnaire (SSQ). For experiments of simulator sickness, twelve participants are exposed to scenes movement from ship handling simulator according to three steps of sea states. During experiments, COPs for subjects are measured by force plate. After exposure to scenes movement, subjects describe their sickness symptoms by answering the SSQ. Throughput analysing the results of scene movement, SSQ, and COP, the relation between the simulator sickness and COP is investigated. It is suggested that formulations for SSQ score and COP with respect to sea state are obtained by the curve fitting technique, and the longitudinal COP can be used for measuring the simulator sickness.