• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.7
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• pp.702-708
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• 2010

Reaction wheel assemblies(RWA) are expected to be one of the largest high frequency disturbance sources to the optical payload of satellites. To ensure the tight pointing-stability budget and high image quality of satellites, a vibration isolation device should be applied to the main disturbances. For developing the isolating system, the disturbances need to be identified and modeled accurately. In the present study, a modeling technique of RWA and its disturbance was described. The micro-vibration disturbances were generated numerically by using an analytical wheel and disturbance model. The parameter estimation scheme of the model was suggested, and the RWA and disturbance modeling technique was verified through the numerical example analysis. The analytical results show that the wheel and disturbance model can be accurately established by using the modeling technique proposed in the present study. The wheel and disturbance model is expected to be useful for development of the RWA isolator system.

• Journal of Satellite, Information and Communications
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• v.6 no.2
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• pp.46-50
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• 2011

In order to perform the satellite structural analysis, FE-Model(Finite Element Model) considering all mechanical properties is necessary. Generally, different companies develop several satellite components, and sometimes it is very difficult to obtain FE-Model. In this case, FE-Model reduction using superelement method can be good solution. For developing satellite, antenna manufacturer required satellite FE-Model to calculate microvibration induced by antenna operation, and condensed model using superelement method was provided. Superelement method is based on Craig-Bampton method, and it is applied to spacecraft FE-Model reduction in this paper. From modal analysis and the frequency response analysis results between full FE-Model and condensed model, the usefulness of reduced model is confirmed.

• Journal of Aerospace System Engineering
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• v.12 no.6
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• pp.9-16
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• 2018

This paper describes how to find out the optimum position of the reaction wheel assembly (RWA) to minimize image quality degradation through the integrated system jitter prediction combining the micro-vibration test with finite element analysis considering optical coefficients. Micro-vibration generated from RWA that is widely used for satellite maneuver, is one of key factors that degrades the quality of satellite image. Due to varying vibration characteristics of each RWA, its accommodation position may affect image quality even though the same company manufactured them. To resolve this issue, an integrated system jitter prediction is conducted with all possible RWA accommodation location, and finally we determine optimal RWA position from the analysis results.

• Journal of People, Plants, and Environment
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• v.22 no.6
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• pp.611-619
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• 2019

This study was conducted to investigate changes in the mental functions of the elderly in nursing facilities affected by a horticultural therapy program based on validation therapy. To meet the purpose, we conducted a horticultural therapy program based on validation therapy with 58 elderly participants (average age 79.12±6.84, men and women) once a week, 50 minutes per session, in a total of 10 sessions. Participants were divided into the control and experimental group with convenience sampling. The program was carried out from March 15 to November 22, 2018. Vibraimage 8 pro(ELSYS, 2014) is a recent, psychologically based, emotional-recognition visual imaging technology that measures pixels microvibration in terms of digital frequency and amplitude parameters. To examine the effects of the horticultural therapy program based on validation therapy, Vibraimage was used to assess aggression, stress, tension, suspect, balance, charm, energy, self-regulation, inhibition, neuroticism and positive, negative, physiological domains of mental functions before and after program. As a result, the mean score of the positive domain in the control group significantly decreased from 63.89±5.09 to 60.74±5.48, but it decreased without statistical significance in the experimental group from 63.98±5.45 to 61.39±6.02. The mean score of neuroticism in the experimental group significantly decreased from 31.64±10.94 to 22.87±13.79. Moreover, the mean score of the physiological domain in the experimental group also significantly decreased from 25.08±6.27 to 19.42±8.80. Accordingly, horticultural therapy program based on validation therapy can be utilized as a program to promote mental health, especially maintaining positive mental health function of the eldery, helping those who live in long-term care facilities enjoy a happier life more happier.