• Korean Journal of Applied Biomechanics
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• v.16 no.2
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• pp.121-134
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• 2006

The purpose of this study was to analyze the effect of different types of rehabilitation training program on the kinetic and kinematic parameters during sit-to-stand movement(STS) in chronic stroke patients. Two groups of hemiparetic patients, experimental and control, participated in the study. The experimental group participated in a 10-week training program (three sessions/wk, $1{\sim}1.5\;hr/session$) consisting of a warm-up, aerobic exercises, lower extremity strengthening. and a cool-down. The control group participated in an aerobic exercise. Three dimensional kinematic analysis and force platform; were used to analyze the duration of STS, lower extremity angle, and weight bearing ability. The experimental group which had more strength of lower extremity displayed decrease in duration of STS. However, the control group showed increases in duration during sit-to-stand movement. The control group flexed their trunk more than the group did Therefore, it took more time to extend their trunk during STS. The duration in sit-to-stand was affected by the strength of lower extremity and the angle of trunk movement. The angles of ankle and knee joint had an influenced on duration of STS. The post experimental group performed with their feet near the front leg of the chair during sit-to-stand, therefore the duration was decreased. The repetitive sit-to-stand movements as a resistance exercise was effective to hemiparetic patients in learning mechanism of sit-to-stand. The control group showed decreased differences in the vertical ground reaction forces between paretic and non-paretic limbs. Their training program included strengthening exercise that may help improving weight bearing ability. The control group showed increases in the center of pressure in the anteroposterior and mediolateral displacement. This means that the stability of movement was low in the control group. Their training program which combined aerobic and strengthening exercises that are more effective to improve the stability of movement.

• Journal of Biomedical Engineering Research
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• v.18 no.2
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• pp.157-166
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• 1997

Postural balancing in human is known to be maintained by the complex mechanism coupled with cerebellum, equilibrium organ of ear, proprioception and other various organs. We developed a Computerized Balance Evaluation and Training system(COBET system) to evaluate postural control and to rehabilitate geriatrics and disabled patient. In addition, 55 normal adult were tested to investigate the influencing factors on balancing posture. For the analysis of static postural sway, areas of the moving center of pressure were calculated under 8 different positions of subjects. And subjects were also asked to follow the visual targets on monitor for the evaluation of the dynamic postural sway. In comparison of the first and the second sets of tests, there was test-retest reliability($\textit{p}$< 0.05). The controllability of the static pmtwn sway was decreased as the ages of subjects increase. When the ages of subject are over 60, the controllability was significantly decrease4 The dynamic postural sway was significantly greater in the age groups of 7th and 8th decade than the younger groups. It is concluded that COBET system is a reliable system in the evaluation of postural sway. The COBET system is considered to be a valuable training modality for the disabled patients as well as the elderly.

• Journal of the Ergonomics Society of Korea
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• v.24 no.1
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• pp.1-7
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• 2005

This paper investigates the effects of scene movements on cybersickness to develop the guidelines of scene movements in virtual environments. The types of scene movements were made for both scene navigations(through the axes of X: lateral, Y: fore & after, and Z: vertical) and scene rotations(by pitch, roll and yaw). And there were each three levels of speed; 2.7, 4.5 and 6.3 /s(for navigation), and 10, 20 and 30 /s(for rotation) were conducted. Twelve participants were exposed to each scene for 15 minutes, and three tests were performed to measure the degree of sickness. Before and after subjects were exposed to virtual environments, they were requested to describe their sickness symptoms by means of answering the Simulator Sickness Questionnaire(SSQ). And the postural stability tests, in which the Center of Pressure(COP) of subjects were traced and recorded by a 'force platform', were conducted. During the exposure on virtual environments, the subjects were requested to rate the degree of nausea. For both navigation and rotation, the effects of speeds and axes were significant in the SSQ scores and the nausea ratings, while it was not in the COP. The correlation between the SSQ scores and the COP data was not found. Therefore, it was inappropriate to use COP as a measure of cybersickness. The degree of sickness increased, except for the case of the yaw, as the speed increased. The sickness was most severe in the scene navigation through the axis X and in the scene rotation by the yaw.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.41 no.2
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• pp.16-23
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• 2018

Postural instability can increase the likelihood of hazardous slip and fall accidents in workplaces. The present study intended to extend understanding of the effect of abnormal neck posture on postural control during quiet standing. The effect of body fatigue on the postural control was also of primary concern. Twelve healthy undergraduate students volunteered to participate in the experiment. Standing on a force platform with the neck neutral, flexed, extended, or rotated, subjects' center of pressures (COP) were measured under the two levels of body fatigue. For the fatigue condition, Subjects exercised in a treadmill to meet the predetermined level of body fatigue. Analyzing the position coordinates of COPs, the length of postural sway path was assessed in both medio-lateral (ML) axis and anterior-posterior (AP) axis. Results showed that, in AP direction, neck extension or rotation significantly increased the sway length as compared with neck neutral. Neck extension led to greater sway length compared to neck rotation. Neck flexion did not differ from neck neutral. The sway length in the AP direction also became significantly larger as the body fatigue accumulated after treadmill exercise. In ML direction, as compared to neutral posture, the neck extension, flexion, or rotation did not significantly affect the length of postural sway path. However, the sway length seemed to increase marginally with the neck extended during the fatigued condition. This study demonstrates that abnormal neck posture may interfere with postural control during standing. The ability to maintain postural stability decreases significantly with the neck extended or rotated. Body fatigue leads to postural instability further.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.5
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• pp.438-447
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• 2018

For a fixed jacket type offshore structure directly supported by the seabed, the structural behavior of offshore structure depends on the soil properties. Soil properties affect on the stiffness of the piles and the boundary condition in the structural analysis. The structural analysis is performed using PSI (Pile-Soil Interaction) suggested in the code and design rule. PSI analysis of the jacket structure is carried out after various soil types are selected according to the soil properties like internal friction angle, undrained shear strength, unit weight and so on. Three types of soil are selected by varying strength for a clay and sand, respectively. The structural analysis of the jacket structure is performed using these soils. The results about axial and lateral reaction force and the stress and displacement on the structure are compared. As a results, the structural response is smaller as the soil becomes more stiff. In conclusion, it is confirmed that the structural response of fixed jacket type offshore platform supported by seabed is sensitive to the change of soil properties.

• Journal of Biomedical Engineering Research
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• v.20 no.5
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• pp.559-566
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• 1999

환자의 기능평가를 위하여 중요한 자세균형의 유지는 압력중심(COP) 의 동요 신호를 직접 연속적으로 계측함으로써 가능하다. COP 신호로부터 다양한 종류의 자세안정도지표를 산출할 수 있으나 임상적으로 유용한 최소한의 지표종류로는 규명된 바 없다. 이에 본 연구에서는 인체가 서있는 상태의 정적자세를 유지할 때 압력중심 신호로부터 자세안정도지표를 산출하여 분석함으로써 임상적 유용성이 가장 큰 지표의 종류를 결정하고자 하였다. 양발을 편안히 벌리거나 (FS), 모두 모으거나(FT), 한쪽발 만으로(RL, LL)서있는 자세에 대해서 양쪽 눈을 뜨거나(EO) 감은(EC)8가지 정적자세를 취하며 30초간 자세균형을 유지시켰다. 자세형태에 따른 안정도의 척도로서 신체가 지면을 차지하는 면적(S)을 사용하였다. 자세안정도지표로서 1)position deviation, 2) position turn 3) velocity의 3가지로 분류할 수 있는 18가지 지표를 설정하였다. 피검자는 20, 30, 40 ,50 대 정상인을 연령대 별로 각각 남·녀 5명씩 고르게 총 40명을 선정하여 실험하였다. 자세안정도지표 모두가 S와 비교적 높은 유의한 상관관계를 보인 바 인을 연령대 별로 각각 남·녀 5명씩 고르게 총 40명을 선정하여 실험하였다. 자세안정도지표 모두가 S와 비교적 높은 유의한 상관관계를 보인바 (상관계수=0.6∼0.8, P<0.0001), S가 자세형태를 정량화 할 수 있음을 입증하였다. 모든 지표들에 있어서 시각의 영향이 뚜렷하였으며 특히 자세가 불안해질수록 상대적으로 시각의 영향이 두드러졌다. 그러나 시각의 영향의 지표들간의 차이는 없었다. 반면 노화(연령증가)에 따른 안정도지표의 변화는 미미하였으며 위의 3가지 안정도지표분류 중 position deviation 지표만이 통계적으로 유의한(P<0.05) 상관관계를 보였다. 따라서 정적자세유지시 안정도지표로는 position deviation 지표들이 가장 예민함을 알 수 있었다. 그러나 position deviation 지표들과 연령과의 상관계수는 0.5이하로서 매우 느슨한 상관관계를 보였으며, 연령증가에 따른 자제불안정도의 증가도 매우 작아서 그 임상적 응용가능성은 의문시되었다. 또한 위에서 제시한 3가지의 분류의 지표중 position turn 과 velocity 지표의 의미에 관해서는 향후 심층적인 연구가 필요한 것으로 판단되었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.341-348
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• 2017

This study examined the effects of the location and direction of the scolioti curve on postural balance in patients with idiopathic scoliosis. Fifteen subjects were divided into three groups: right thoracic curve group, left lumbar curve group, and double curve group. The dynamic trunk motion (angle variation in the lumbar, thoracolumbar, lower thoracic and upper thoracic region) and plantar pressure distribution (maximum force and peak pressure) were assessed using an ultrasound-based motion analysis system and Emed-at platform system. From the results, it was confirmed that patients with idiopathic scoliosis showed postural imbalance with an increased angle and pressure asymmetry according to the location and direction of the scoliotic curve for dynamic trunk motion and plantar pressure distribution. In addition, there were differences in the postural balance pattern between the single curve and double curve groups. Further studies for developing a rehabilitation training device will be conducted to improve the postural control ability and trunk balance as well as treat scoliosis based on the results of this study.

• 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.

• Nuclear Engineering and Technology
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• v.53 no.9
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• pp.3085-3099
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• 2021

Investigations of large commercial aircraft impact effect on nuclear power plant (NPP) buildings have been drawing extensive attentions, particularly after the 9/11 event, and this paper aims to numerically assess the damage and vibrations of NPP buildings subjected to aircrafts crash. In Part I of present paper, two shots of reduce-scaled model test of aircraft impact on NPP were conducted based on the large rocket sled loading test platform. In the present part, the numerical simulations of both scaled and prototype aircraft impact on NPP buildings are further performed by adopting the commercial program LS-DYNA. Firstly, the refined finite element (FE) models of both scaled aircraft and NPP models in Part I are established, and the model impact test is numerically simulated. The validities of the adopted numerical algorithm, constitutive model and the corresponding parameters are verified based on the experimental NPP model damages and accelerations. Then, the refined simulations of prototype A380 aircraft impact on a hypothetical NPP building are further carried out. It indicates that the NPP building can totally withstand the impact of A380 at a velocity of 150 m/s, while the accompanied intensive vibrations may still lead to different levels of damage on the nuclear related equipment. Referring to the guideline NEI07-13, a maximum acceleration contour is plotted and the shock damage propagation distances under aircraft impact are assessed, which indicates that the nuclear equipment located within 11.5 m from the impact point may endure malfunction. Finally, by respectively considering the rigid and deformable impacts mainly induced by aircraft engine and fuselage, an improved Riera function is proposed to predict the impact force of aircraft A380.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.9
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• pp.1144-1151
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• 2021

The pressing process is a compression process in which a product is made by applying force to a heated or unheated material to transform it into the desired shape. Due to the characteristics of press equipment that produces products through continuous compression for a short time, product defects occur continuously, and systems for solving these problems are being developed using various technologies. This paper proposes a real-time defect detection system based on an artificial intelligence algorithm that detects defects. By attaching various sensors to the press device, the relationship between equipment status and defects is defined and collected based on a big data platform. By developing an artificial intelligence algorithm based on the collected data and implementing the developed algorithm using an embedded board, we will show the practicality of the system by applying it to the actual field.