• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.4
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• pp.430-437
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• 2018

For a ship navigating in waves, added resistance, sway force and yaw moment due to waves differ from still water conditions, which affects the maneuverability of the ship. Therefore, it is important to estimate the sway force and yaw moment generated by waves. In this study, numerical simulations were carried out to calculate the hydrodynamic forces acting on a barge in still water and waves using CFD. Based on the results, the characteristics of course stability of a barge were investigated and analyzed. The hydrodynamic forces acting on the barge in waves were stronger than in still water, and it was confirmed that hydrodynamic forces become greater as wavelength becomes longer. In long wavelength regions, the (-) value of the yaw damping lever was larger than in still water. However, in short wavelength regions and when wavelength coincided with the length of the ship, values were smaller than in still water. In this region, it can be assumed that course stability improved. In other words, in long wavelength regions, the course stability of the barge was worse than in still water and short wavelength regions. Therefore, attention is required for safe navigation in long wavelength regions.

• International Journal of Ocean System Engineering
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• v.4 no.1
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• pp.19-28
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• 2014

The tension leg platform (TLP) is a vertically moored structure with excess buoyancy. The TLP is regarded as moored structure in horizontal plan, while inherit stiffness of fixed platform in vertical plane. In this paper, a numerical study using modified Morison equation was carried out in the time domain to investigate the influence of nonlinearities due to hydrodynamic forces and the coupling effect between surge, sway, heave, roll, pitch and yaw degrees of freedom on the dynamic behavior of TLP's. The stiffness of the TLP was derived from a combination of hydrostatic restoring forces and restoring forces due to cables and the nonlinear equations of motion were solved utilizing Newmark's beta integration scheme. The effect of tethers length and wave characteristics such as wave period and wave height on the response of TLP's was evaluated. Only uni-directional waves in the surge direction was considered in the analysis. It was found that for short wave periods (i.e. 10 sec.), the surge response consisted of small amplitude oscillations about a displaced position that is significantly dependent on tether length, wave height; whereas for longer wave periods, the surge response showed high amplitude oscillations about that is significantly dependent on tether length.

• Journal of the Korean Society of Physical Medicine
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• v.9 no.4
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• pp.475-483
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• 2014

PURPOSE: The purpose of the study was to determine the effects of close kinetic chain resistant exercise of lower extremity on the gait with stroke patients. METHODS: The subjects were 50 patients who were diagnosed with cerebrovascular accident. They were randomly assigned either to a close kinetic chain resistant exercise of lower extremity group (study group)(n=25) or open kinetic chain resistant exercise of lower extremity exercise group (control group)(n=25). Gait abilities were measured by using Timed Up & Go (TUG) test, Functional Gait Assessment (FGA) and spatio-temporal gait variable that were velocity, cadence, stride length, double limb support by 3 axises wireless accelerometer and sway angle of center of mass by same instrument. RESULTS: Study group and control group before and after the intervention there were significantly difference in TUG, FGA, spatio-temporal gait variables and sway angle of center of mass (p<.05). There were significantly different between study group and control group for all variables at post-exercise. CONCLUSION: When all is said and done it is expected to be used as a method for the treatment and prevention in the process of rehabilitation of patients with stroke. In its final analysis when applying resistant exercise of lower extremity to stroke patients' gait, close kinetic chain is more effective than open kinetic chain.

• Journal of the Korean Society of Physical Medicine
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• v.15 no.2
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• pp.11-21
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• 2020

PURPOSE: This study examined the effects of posture improvement exercise using virtual reality programs on the posture and balance of patients with forward head postures. METHODS: Thirty men and women in their 20 s, who had a forward head posture, were divided randomly into a group with posture correction exercise and a group with posture correction exercise combined with virtual reality programs. The posture correction exercise was composed of squats, XCO training, and chin-tuck exercise. In contrast, exercise with virtual reality games involved the Hot Squat, Climbey, and Baskhead programs while wearing a headset. Both groups performed the exercises 15 min a day, three times per week, for four weeks. The balance ability, distance between the acromion and earlobe, and neck joint range of motion were assessed before and after the exercises. RESULTS: Both groups showed significant reductions in the distance between the acromion and the earlobe, along with significant improvements in the range of joint motion. The group that performed the virtual reality exercises showed a significant increase in the limit of stability. Both groups showed a significant decrease in the sway length. In contrast, the group given the virtual reality exercises showed a significant reduction in the sway speed while standing with their eyes closed. CONCLUSION: Exercise applying virtual reality programs can be used in clinical and home programs to correct the postures of individuals with a forward head posture because they can trigger interest in inducing active participation.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2002.11a
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• pp.113-119
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• 2002

Recently, an automatic crane control system is required with high speed and rapid transportation. During the operation of crane system in container yard it is necessary to control the crane trolley position and loop length so that the swing of the hanging container is minimized We can do development of unmanned automation control system using automation travel control technique and anti-sway technique in crane system. Therefore, we designed a controller for Automation travel control to control the transfer crane system. Analyzed crane system through simulation, and proved excellency of control performance than other conventional controllers.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.10 no.1
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• pp.25-30
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• 2010

This paper is proposed about three axis motion control camera design method based on wires. Original motion control camera consists of track, boom, L-Head, Camera and so on and is enormous and expensive. But proposed motion control camera adjusts wire length using encoders and motors. And position control use position based straight line of straight-line move method for moving precise position. Proposed simple design is able to use various place and inexpensive than original motion control camera. But, camera was vibrated and rotated due to basic property of wire. So we proposed solutions that connected method of wire and using a tensional object for reducing rotation. For proposed algorithm verification, we realized three axis motion control camera based on wire and measured oscillation while moving same trace. We confirmed the results that standard deviation of oscillation was reduced 4.93 degree than before design method.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.1
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• pp.98-118
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• 2014

An auto weather-vaning system for a Dynamic Positioning (DP) vessel is proposed. When a DP vessel is operating, its position keeping is hindered by ocean environmental disturbances which include the ocean current, wave and wind. Generally, most ocean vessels have a longitudinal length that is larger than the transverse width. The largest load acts on the DP vessel by ocean disturbances, when the disturbances are incoming in the transverse direction. Weather-vaning is the concept of making the heading angle of the DP vessel head toward (or sway from) the disturbance direction. This enables the DP vessel to not only perform marine operations stably and safely, but also to maintain its position with minimum control forces (surge & sway components). To implement auto weather-vaning, a nonlinear controller and a disturbance observer are used. The disturbance observer transforms a real plant to the nominal model without disturbance to enhance the control performance. And the nonlinear controller deals with the kinematic nonlinearity. The auto weather-vaning system is completed by adding a weather-vaning algorithm to disturbance based controller. Numerical simulations of a semi-submersible type vessel were performed for the validation. The results show that the proposed method enables a DP vessel to maintain its position with minimum control force.

• Journal of The Korean Society of Integrative Medicine
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• v.7 no.2
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• pp.95-109
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• 2019

Purpose : This study was conducted to evaluate the effects of FES with abdominal muscle contraction before virtual reality training on balance and gait ability in patients of stroke patients. Methods : The subjects were 30 stroke patients who satisfied the selection criteria. They were randomly assigned to a group receiving functional electrical stimulation with a virtual reality training program (the experiment group, n=15) and placebo functional electrical stimulation with a virtual reality training program (the control group, n=15). The program consisted of three 30-min sessions per week for six weeks. The timed up and go test (TUG), the BT4, the G-WALK were used to estimate subjects' balance, gait before and after the program. For the experiment group, the functional electrical stimulation was applied to the external oblique and the rectus abdominis, For the control group, the same program and the placebo functional electrical stimulation were applied. Results : There were significant improvements in the subscales of the balance and gait ability test of those who participated in the functional electrical stimulation, while the control group showed no significant changes. Conclusion : Therefore, functional electrical stimulation with virtual reality effectively improved the balance and gait ability in patients with chronic stroke.

• Physical Therapy Rehabilitation Science
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• v.12 no.3
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• pp.320-326
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• 2023

Objective: The purpose of this study is to investigate the impact of visual biofeedback methods utilizing pressure sensors on the static balance of stroke patients. Design: Randomized crossover study. Methods: A total of 27 patients with hemiparesis participated in this study. The following three feedback conditions were considered: condition 1 (Knowledge of performance feedback), condition 2 (Knowledge of result feedback), and condition 3 (None feedback). A force plate was used to measure static balance. The total sway length, average sway velocity, x-axis excursion, and y-axis excursion of the center of pressure were measured. One-way repeated-measures analysis of variance was employed for comparisons of variables between each condition. The statistical significance level was set at α = 0.05 for all analyses. Results: There was a significant difference in the static balance results between each feedback condition (p<0.05). In the post-hoc results, it was confirmed that the static balance was significant in the order of knowledge of performance feedback, knowledge of result feedback, and none feedback. Conclusions: When comparing the three conditions, it was observed that knowledge of performance feedback showed the most improved effect on static balance ability. As further research progresses, that this approach could be used as an effective intervention method in clinical settings.

• Journal of the Korea Convergence Society
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• v.8 no.7
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• pp.295-304
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• 2017

The purpose of this study was to identify the immediate effect of the joint mobilization with an elastic taping on standing balance in patients with knee osteoarthritis. Thirty patients with knee osteoarthritis were randomly divided into three groups: a taping group, a joint mobilization group, and a joint mobilization with taping group. A foot pressure platform (Zebris) was used to evaluate standing balance ability, and the sway area, path length and average velocity were measured during eyes open condition and eyes closed condition. All the groups showed a significant improvement in the sway area during eyes closed condition after intervention, and the joint mobilization with taping group revealed significant improvements in the path length and average velocity. There was no significant difference in the standing balance ability among all the groups. Both the joint mobilization and taping method were effective methods for standing balance during eyes closed condition, and it has been found that the convergence of the two interventions had an effect on diverse balance variables. Thus, it is recommended to apply the convergence of the two interventions for patients with knee osteoarthritis.