• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.5
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• pp.437-444
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• 2020

This study was focused on the stabilization of surge motions of a moored vessel under irregular head seas. A two-point moored vessel shows strong non-linearity even in regular sea, owing to its inherent non-linear restoring force. A long-crested irregular wave is subjected to the vessel system, resulting in more complex nonlinear behavior of the displacement and velocities than in the case of regular waves. Sliding mode control (SMC) is implemented in the moored vessel to control both surge displacement and surge velocity. The SMC can provide a closed-loop system with performance and robustness against parameter uncertainties and disturbances; however, chattering is the main drawback for implementing SMC. The goal of minimizing the chattering and state convergence with accuracy is achieved using a quasi-sliding mode that approximates the discontinuous function via a continuous sigmoid function. Numerical simulations were conducted to validate the effectiveness of the proposed control algorithm.

• 한국노년학
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• v.30 no.3
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• pp.993-1003
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• 2010

his study was to investigate effects of improvement of balance abilities through 8-weeks Transcutaneous Electrical Nerve Stimulation (TENS) and balance training in the women elderly. 42 women elders who were participated in silver college. Randomized study design of two groups was used: TENS group (21 women, 84.53 years old) and balance training group(21 women, 79.93 years old). Each group had a application of TENS, balance training by a researcher three times per week for 8 weeks. Measurements of static postural sway velocity on the floor and foam, timed get up and go test (TUG), functional reach test (FRT), and lateral functional reach test (LFRT) were evaluated at initial presentation (pretest) and after completion of the each intervention program (posttest). The results showed that the TUG was significantly decreased in all groups (p<.05) and the postural sway velocity using force plate in all conditions was significantly decreased in all groups (p<.05). FRT and LFRT were significantly increased in all groups (p<.05). There were significantly differences in TUG and postural sway velocity on the eye closed condition between two groups (p<.05). In conclusion, the application of TENS to older adults whose somatosensory were deteriorated was effective for improvement balance ability.

• Bulletin of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.36-39
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• 1995

본고에서는 고속선의 항행 안전성과 관련된 공통의 문제로서 파랑중 조종성능에 관해서 언급하 고자 한다. 파랑중 조종성능이 문제시되는 것은 선박이 추파(following seas) 또는 추사 파(quartering seas)를 받으면서 고속으로 항해할 때이다. 보통의 속도 범위에서 운항되는 일반 선박중에서도 컨테이너선, 어선 등과 같이 비교적 속력이 빠른 선박은 추사파중에서 선수 동 요가 크게 일어나며, 보침을 위한 조타량이 커짐과 동시에 힁동요가 심하게 일어나는 것으로 알려져 있다. 이러한 불안정 현상은 정도의 차이는 있을지언정 고속선에서도 마찬가지 경향을 보이고 있다. 파랑중 조종성능을 요약하면 추파 또는 추사파중에서의 복원성과 보침성 문제에 귀착된다, 추사파중에서의 복원성 문제는 선체 중심이 파정에 위치할 때 복원력 저하로써 설명될 수 있으며, 이러한 현상은 파장과 선체 길이가 거의 같고 선속이 파속과 거의 같은 조건하에서 일어난다고 알려져 있다. 이러한 조건을 만족하는 선속은 Froude수 0.4 정도로서 고속선의 운항 범위에 미달되는 속도이다. 추사파중에서의 보침성 문제는 브로칭(broaching-to) 현상으로써 설명될 수 있으며, 브로칭 현상은 파장이 선체 길이의 2배 정도이고, 선속과 파속이 거의 같은 조건하에서 일어난다고 알려져 있다. 이러한 조건을 만족하는 선속은 Froude수 0.56 정도로서 고속선의 운항 범위와 일치하는 속도이다. 따라서 본고에서는 고속선을 대상으로 하기 때문에 복원성 문제는 다루지 아니하고 브로칭 현상에 관해서만 간략히 기술하기로 한다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.4
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• pp.501-509
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• 2010

A floating crane is a crane-mounted ship and is used to assemble or to transport heavy blocks in shipyards. In this paper, the static and dynamic response of a floating crane and a heavy block that are connected using elastic booms and wire ropes are described. The static and dynamic equations of surge, pitch, and heave for the system are derived on the basis of flexible multibody system dynamics. The equations of motion are fully coupled and highly nonlinear since they involve nonlinear mass matrices, elastic stiffness matrices, quadratic velocity vectors, and generalized external forces. A floating frame of reference and nodal coordinates are employed to model the boom as a flexible body. The nonlinear hydrostatic force, linear hydrodynamic force, wire-rope force, and mooring force are considered as the external forces. For numerical analysis, the Hilber-Hughes-Taylor method for implicit integration is used. The dynamic responses of the cargo are analyzed with respect to the results obtained by static and numerical analyses.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.6
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• pp.2767-2772
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• 2013

Balance is the foundation for all active daily livings. Evaluation of balance has been conducted to measure postural sway of center of pressure(COP). The purpose of this study is to introduce the Balancia and to examine the validity and inter-, intra-reliability for measure of balance with stroke patients. COP was measured by Wii balance board. The subjects Participated in this study were 39 stroke patients. Intra- and inter-reliability was examined using intraclass correlation coefficient(ICC) with 95% confidence interval. In the result of intra- and inter-reliability, all COP parameters of postural sway showed high to very high reliability with ICC=.793-.939 and ICC=.791-.955. Validity was determined by correlation with Accusway force plate. There were high validity with ICC=.851-.955 between tools. According to these results, the Balancia showed high validity and reliability. It is a useful clinical tool for evaluating balance in stroke patients.

• Journal of The Korean Society of Integrative Medicine
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• v.1 no.4
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• pp.75-83
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• 2013

Purpose : This research was conducted to see the correlation between sway speed and muscle activity for lower extremity of stroke patients through unstable surface training. Methods : A total of 60 patients were randomly divided unstable surface group (30 peoples) and stable surface group (30 people). Then they were asked to carry out the same exercise program for 6 weeks. The unstable surface group and stable surface group performed the exercise program on the balance mat and on the hard wood block. We checked the changes of sway speed and the changes in muscle activity for lower extremity. Results : The unstable surface group displayed significantly reduced sway speed, and improved muscle activity of lower extremity. There were significant correlation between change amount of muscle activity and sway velocity in Gastrocnemius, Biceps femoris during unstable surface training(r=.373, p<.05)(r=.369, p<.05). And there were not show significant differences during stable surface training. Conclusion : Judging from this, we can have knowledge that the correlation between increase of muscle activity and decrease of sway velocity for Gastrocnemius, Biceps femoris in the unstable surface training.

• 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.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.11
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• pp.4418-4426
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• 2010

Muscle fatigue often induces deterioration of postural balance and muscle contraction, such as strength or maximal voluntary contraction(MVC). This study was to investigate the effects of transcutaneous electrical stimulation(TENS) applied to the fatigued muscles on postural imbalance and decline in muscle strength following fatigue of triceps surae. For the 4 months from March, 2010, twenty healthy subjects without vestibular disease and visual disturbance were recruited and induced muscle fatigue of triceps surea performed by repeated voluntary contraction. TENS was applied to gastocnemius immediately after development of muscle fatigue. Postural sway length, velocity and MVC were recorded under these conditions: pre-fatigue, post-fatigue, and TENS application to fatigued muscle during post-fatigue. Muscle fatigue increased postural imbalance as expressed by sway length and velocity and decreased muscle contraction(p<.05), while TENS improved the postural imbalance and MVC following muscle fatigue during stance(p<.05). The results suggested that fatigue on plantar flexor is associated with postural balance and muscle contraction, and TENS application to fatigued muscle was effective in improving postural imbalance and decline in muscle strength following muscle fatigue. TENS will be an effective method in exercise, working environment and daily life.

• Journal of Navigation and Port Research
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• v.37 no.3
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• pp.239-244
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• 2013

To increase the safety of onboard evacuation of guests who is unfamiliar with onboard living conditions, this study measured and compared the onboard walking speeds of 81 participants on a passenger ship, I t were found that the walking speeds at corridor on navigation were slower than those at berth by 27.2%, and the speeds of walking on the corner on navigation were slower than those at berth by 23.2%. This means that the ship motion on navigation directly influenced walking speeds. The walking speeds of upward-stairs and downward-stairs were measured to be 0.71m/s and 0.75m/s, respectively. From the crowd counter-flow experiments, because of the narrow space between participants, the walking speeds were decreased as person after person. And it was clear that the group's walking speeds were determined by the walking speeds of leading person(s) of the group. The walking speeds obtained this study were different from those of IMO guideline(MSC/Circ 1033).

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 2002.05a
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• pp.90-94
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• 2002

이전연구에서 가상현실에 몰입하는 동안 넓은 시야 (Field of view: 150$^{\circ}$)와 빠른 운행속도 (70 km/sec)가 사이버멀미를 심화시킨다는 결과를 얻었다: 피험자의 90%가 좁은 시야 (50$^{\circ}$)와 느린 운행속도 (30 km/sec)에서 사이버멀미 증상이 적었다. 본 실험에서는 피험자가 생리적인 동요를 경험할 때마다 바이오피드백 방법을 사용해서 사이버멀미 감소 가상환경 (cybersickness alleviating virtual environment, CAVE)을 제시한 후, 그 효과를 관찰하였다. 피부전도도, 말초체온, 말초혈류량, 심박률, 눈 깜박임, 뇌전위의 변수들을 입력으로 하는 인공신경망으로 구성된 실시간 멀미 탐지 시스템과 CAVE-제시 피드백 시스템을 구축하였다. 이 시스템은 생리적 측정치들이 사이버멀미의 출현을 신호할 때마다 피드백 출력으로 좁은 화면과 감소된 운행속도를 일시적으로 제공했다. 36명의 피험자를 대상으로 SSQ (simulator sickness questionnaires)와 자기보고를 이용하여 사이버멀미의 빈도와 심각도를 조사하였다. 모든 피험자는 한달 간격으로 CAVE 조건과 non-CAVE 조건에서 두 번 가상현실을 경험하였다. 사이버멀미의 빈도와 심각도는 non-CAVE 조건보다 CAVE 조건에서 유의미하게 감소하였다. 즉, 전기생리학적 특징들에 기반한 인공신경망에 의해 제공된 좁은 시야와 느린 운행의 가상환경은 사이버멀미 증상들을 의미있게 감소시켰다. 이러한 결과들은 생체신호 피드백 시스템을 이용하여 인간 친화적 가상환경을 구축할 수 있는 가능성을 보인 것이다.