• The KSFM Journal of Fluid Machinery
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• v.14 no.6
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• pp.96-101
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• 2011

Korea Aerospace Research Institute is performing 3 stage transonic axial compressor development program. This paper introduces design step of the compressor, the performance test results and its analysis. In the fore part of the paper, aerodynamic process of the 3 stage axial compressor is presented. To satisfy both of the mass flow and pressure rise, the compressor should rotate at a high rotational speed. Therefore the transonic flow field forms in the rotor stages and it is designed with a relatively high pressure rise per stage to satisfy its design target. The compressor stage consists of 3 stages, and the bulk pressure ratio is 2.5. The first stage is burdened with the highest pressure ratio and less pressure rises occur in the following stages. Also it is designed that tip Mach number of the first rotor row does not exceed 1.3, while the maximum relative Mach number in the rotor stage is between 1.3~1.4 to increase the compressor flow coefficient. The final design has been confirmed by iterating three dimensional CFD calculations to verify design target and some design intentions. In the latter part of the paper, its performance test processes and results are presented. The performance test result shows that the overall compressor performance targets; pressure ratio and efficiency are well achieved. The stator static pressure distributions show that the blade loading is gradually increasing from the downstream of the compressor.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.3
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• pp.275-280
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• 2011

In the present study, a unified viscoplastic-damage model has been applied in order to describe the mechanical characteristics of fresh water ice such as nonlinear material behavior and volume fraction. The strain softening phenomenon of fresh water ice under quasi-static compressive loading has been evaluated based on unified viscoplastic model. The material degradation such as growth of slip/fraction has quite close relation with material inside damage. The volume fraction phenomenon of fresh water ice has been identified based on volume fraction (nucleation and growth of damage) model. The viscoplastic-damage model has been transformed to the fully implicit formulation and the discretized formulation has been implemented to ABAQUS user defined subroutine (User MATerial: UMAT) for the benefit of application of commercial finite element program. The proposed computational analysis method has been compared to uni-axial compression test of fresh water ice in order to validate the compatibilities, clarities and usefulness.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.7
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• pp.723-728
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• 2011

Since the performance of a vacuum circuit breaker (VCB) mainly depends on the spring operating mechanism, an analysis of the spring operating mechanism is required in order to improve the design of a VCB. In this study, the static stiffness of the spring was determined by using a material testing machine, and the test results were used to model the spring through computer simulation. The multi-body dynamic model of the spring was established by using the RecurDyn program. The dynamic model was verified by comparing the results of stem displacements and rotating angles of the brake shaft obtained from the simulation and from the experiments. After verification of the dynamic model of VCB, the cam profile of the VCB was optimized through multi-body dynamics simulation in order to improve the performance of the closing mechanism.

• Smart Structures and Systems
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• v.8 no.2
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• pp.173-190
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• 2011

As a practical and effective seismic resisting technology, the base isolation system has seen extensive applications in buildings and bridges. However, a few problems associated with conventional lead-rubber bearings have been identified after historical strong earthquakes, e.g., excessive permanent deformations of bearings and potential unseating of bridge decks. Recently the applications of shape memory alloys (SMA) have received growing interest in the area of seismic response mitigation. As a result, a variety of SMA-based base isolators have been developed. These novel isolators often lead to minimal permanent deformations due to the self-centering feature of SMA materials. However, a rational design approach is still missing because of the fact that conventional design method cannot be directly applied to these novel devices. In light of this limitation, a displacement-based design approach for highway bridges with SMA isolators is proposed in this paper. Nonlinear response spectra, derived from typical hysteretic models for SMA, are employed in the design procedure. SMA isolators and bridge piers are designed according to the prescribed performance objectives. A prototype reinforced concrete (RC) highway bridge is designed using the proposed design approach. Nonlinear dynamic analyses for different seismic intensity levels are carried out using a computer program called "OpenSees". The efficacy of the displacement-based design approach is validated by numerical simulations. Results indicate that a properly designed RC highway bridge with novel SMA isolators may achieve minor damage and minimal residual deformations under frequent and rare earthquakes. Nonlinear static analysis is also carried out to investigate the failure mechanism and the self-centering ability of the designed highway bridge.

• Journal of Convergence for Information Technology
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• v.10 no.8
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• pp.213-222
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• 2020

This research aimed to verify whether family competency reinforcement had a mediating role on the effect of family cohesion of the Down syndrome family upon the independent life of children with Down syndrome. For the research, 146 families belonged to Down Syndrome Parent Assembly were surveyed and the statistical program SPSS WIN 25.0 was utilized for the data analysis. To verify the mediating effect, Baron and Kenny's causal step strategy was performed. As a result of the study, the higher the family cohesion of the Down syndrome family was, the greater the level of independence of the child was, indicating that the family cohesion had a significant static effect on the independence life. In addition, it was confirmed that the family competency reinforcement played a mediating role between the family cohesion and the children's independent living. Therefore, the results of this research suggested that it might be used as a policy approach and supporting plan for the realization of support for independence of Down syndrome children.

• Journal of Digital Convergence
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• v.16 no.7
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• pp.381-391
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• 2018

The purpose of this research is to propose a new method of PSD(Platform Screen Door) ads using animated image for efficiency, based on the theoretical background that moving objects have a stronger visual attractiveness effect than static objects. For this, we analyze the relationship between the screen door and the train, then derive the positional and visual elements which help to create efficient animated images. Based on this analysis, we made an example and applied into 3D program to confirm the implementation process of the animated PSD ads. As the result, the research shows that it is possible to produce a new type of PSD ads that can show dynamic visual effects and can give diversity to the PSD advertising media through the combination of the images using time difference.

• Ocean Systems Engineering
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• v.5 no.3
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• pp.139-160
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• 2015

The global performance of the 5MW OC4 semisubmersible floating wind turbine in random waves was numerically simulated by using the turbine-floater-mooring fully coupled and time-domain dynamic analysis program FAST-CHARM3D. There have been many papers regarding floating offshore wind turbines but the effects of second-order wave-body interactions on their global performance have rarely been studied. The second-order wave forces are actually small compared to the first-order wave forces, but its effect cannot be ignored when the natural frequencies of a floating system are outside the wave-frequency range. In the case of semi-submersible platform, second-order difference-frequency wave-diffraction forces and moments become important since surge/sway and pitch/roll natural frequencies are lower than those of typical incident waves. The computational effort related to the full second-order diffraction calculation is typically very heavy, so in many cases, the simplified approach called Newman's approximation or first-order-wave-force-only are used. However, it needs to be justified against more complete solutions with full QTF (quadratic transfer function), which is a main subject of the present study. The numerically simulated results for the 5MW OC4 semisubmersible floating wind turbine by FAST-CHARM3D are also extensively compared with the DeepCWind model test results by Technip/NREL/UMaine. The predicted motions and mooring tensions for two white-noise input-wave spectra agree well against the measure values. In this paper, the numerical static-offset and free-decay tests are also conducted to verify the system stiffness, damping, and natural frequencies against the experimental results. They also agree well to verify that the dynamic system modeling is correct to the details. The performance of the simplified approaches instead of using the full QTF are also tested.

• Advances in aircraft and spacecraft science
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• v.6 no.2
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• pp.117-144
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• 2019

High Altitude and Long Endurance (HALE) aircraft are capable of providing intelligence, surveillance and reconnaissance (ISR) capabilities over vast geographic areas when equipped with advanced sensor packages. As their use becomes more widespread, the demand for additional range, endurance and payload capability will increase and designers are exploring non-conventional configurations to meet the increasing demands. One such configuration is the joined-wing concept. A joined-wing aircraft is one that typically connects a front and aft wings in a diamond shaped planform. One such example is the Boeing SensorCraft configuration. While the joined-wing configuration offers potential benefits regarding aerodynamic efficiency, structural weight, and sensing capabilities, structural design requires careful consideration of elastic buckling resulting from the aft wing supporting, in compression, part of the forward wing structural loading. It has been shown already that this is a nonlinear phenomenon, involving geometric nonlinearities and follower forces that tend to flatten the entire configuration, leading to structural overload due to the loss of the aft wing's ability to support the forward wing load. Severe gusts are likely to be the critical design condition, with flight control system interaction in the form of Gust Load Alleviation (GLA) playing a key role in minimizing the structural loads. The University of Victoria Center for Aerospace Research (UVic-CfAR) has built a 3-meter span scaled and flexible wing UAV based on the Boeing SensorCraft design. The goal is to validate the nonlinear structural behavior in flight. The main objective of this research work is to perform Ground Vibration Tests (GVT) to characterize the dynamic properties of the scaled flight vehicle. Results from the experimental tests are used to characterize the modal dynamics of the aircraft, and to validate the numerical models. The GVT results are an important step towards a safe flight test program.

• Journal of The Korean Society of Integrative Medicine
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• v.9 no.2
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• pp.1-12
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• 2021

Purpose : We aimed to determine whether improvements in balance, gait, and motor function were different when the same exercise was performed, with and without mirror therapy, by patients with subacute stroke using the affected and unaffected lower limbs. Methods : Eight patients with subacute stroke were randomly divided into experimental groups 1, 2 and the control group. A mirror therapy program was performed with group 1 using the unaffected lower limb and group 2 the affected lower limb. The exercise lasted 30 min per session, five times weekly, for 4 weeks. The control group did not perform the exercises. BT-4, BBS, POMA, 10MWT, and BRS were used to evaluate balance, gait, and motor function before and after the intervention. Results : Post-intervention analysis showed that all three groups had higher BBS scores. After training, the postural sway in groups 1 and 2 decreased in the post eye opened and closed positions; that of the control group increased. The scores of two subjects in group 1 increased by 4 and 5 points in POMA, resulting in significant changes compared to those in the other groups. No group showed significant results in 10MWT. BRS improved in all subjects in group 1 from BRS 2 to 1 and in only one subject in group 2 there was no change in the control group. Conclusion : Static and dynamic balance and significant results are noted in POMA, BBS, but not gait velocity. Therefore, mirror therapy seems to show a positive change in subacute patients, but the research results are not clear and the difference between groups is unknown due to the small number of subjects. The effects of mirror therapy and exercise therapy should be compared using more subjects in future.

• PNF and Movement
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• v.19 no.2
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• pp.183-193
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• 2021

Purpose: The purpose of this research was to investigate the effects of performing Pilates exercises for eight weeks on the isokinetic trunk strength and balance of female middle school students with lumbago. Methods: Twenty-four female students who met the test requirements were recruited and randomly divided into a control group (CG, n = 16) and a Pilates exercise group (Pilates group; PG, n = 8). The PG performed a Pilates program, which consisted of lumbar muscle strengthening exercises, for 60 minutes three times a week for eight weeks. Data analysis was conducted by two-way repeated ANOVA, and a Bonferroni test was carried out when significant differences appeared. The alpha level was set at 0.05. Results: Following the experimental treatment, the PG showed an increased trunk flexion peak torque of 17% and 13% at angular velocities of 180°/sec and 300°/sec, respectively. The intergroup comparison showed no significant difference at pre-measurement, while the PG increased about 31% (180°/sec) and 15% (300°/sec) higher than the control group at post-measurement. Following the experimental treatment, the PG showed an increased trunk extensor peak torque of approximately 29% and 21% at angular velocities of 180°/sec and 300°/sec, respectively. The intergroup comparison showed no significant difference at pre-measurement, while the PG increased approximately 27% (180°/sec) and 15% (300°/sec) higher than the control group at post-measurement. Both the CG and the PG showed a 20% and 50% decrease in pain index after the experimental treatment, respectively. After the experimental treatment, the PG had about 50% lower pain than the CG. The average error rate of static balance in the PG reduced by 19% from 3.28±0.45 to 2.65±0.36, confirming a significant improvement. Conclusion: Regular Pilates exercise for eight weeks improved the isokinetic trunk muscle strength of female middle school students with lumbago and relieved their pain. Pilates was also shown to be effective in improving balance.