• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.394-400
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• 2008

This paper presents an analytical method to investigate the stability of FDBs (fluid dynamic bearings) considering the tilting motion. The perturbed equations of motion are derived with respect to translational and tilting motion for the general rotor-bearing system with five degrees of freedom. The Reynolds equations and their perturbed equations are solved by using the FEM in order to calculate the pressure, load capacity, and the stiffness and damping coefficients. This research introduces the radius of gyration to the equations of notion in order to express the mass moment of interia with respect to the critical mass. Then the critical mass of FDBs is determined by solving the eigenvalue problem of the linear equations of motion. This research is numerically validated by comparing the stability chart of FDBs with the time response of the whirl radius obtained from the direct integration of the equations of motion. This research shows that the tilting motion is one of the major design considerations to determine the stability of rotating system. It also shows that the stability of FDBs considering only translation is overestimated in comparison with the stability of FDBs considering both translational and tilting motion.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.12-23
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• 2021

In the conventional experiment to assess the towing operations, the towing stability of the towed vessel has been evaluated under the condition without lateral motion of the tug-boat. However, the tug-boats may have a lateral force to change the direction of the towed vessel. In this study, experiments have been conducted considering unsteady conditions in the towing system. First, a towing test system in a Circular Water Channel (CWC) using the conventional experimental method is built. Second, the towing characteristics of the towed vessel are investigated using the conventional method, and they are compared with other research results and stability discriminant criteria. Third, the lateral motion of the tug-boat was modeled as a sinusoidal motion using a forced oscillation device changing frequency and amplitude. Finally, the discussion is given in terms of both towing- and course-stability of the towed vessel according to the lateral motion of the tug-boat.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.366-371
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• 2001

Dynamic stability of an oscillating cantilever plate is investigated in this paper. The equations of motion include harmonically oscillating parameters which originate from the motion-induced stiffness variation. Using the multiple scale perturbation method is employed to obtain a stability diagram. The tability diagram shows that relatively large unstable regions exist when the frequency of oscillation is near twice the frequencies of the 1st torsion natural mode and the 1st chordwide bending mode.

• Journal of the Korean Society of Physical Medicine
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• v.10 no.2
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• pp.35-45
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• 2015

PURPOSE: The aim of this study is to investigate how upper thoracic manipulation and cervical stability training affects cervical range of motion and neck disability index of patients with chronic mechanical neck pain. METHODS: 30 patients with chronic mechanical neck pain, and randomly divided into the upper thoracic manipulation and the cervical stability training group. Upper thoracic manipulation group was conducted to the upper thoracic manipulation, and cervical stability training was conducted to the cervical stability training. Intervention period was 6 weeks, and 3 sessions, each of which was run for 5~10 minutes. The subjects were measured neck range of motion before and after intervention by electro-goniometer. Neck disability index was used to measure neck disability index Korean version. RESULTS: Comparison within groups, there were significant difference in neck range of motion before and after intervention, and Neck disability index significantly reduced in the cervical stability training group. The comparison between groups, there were no significant difference in neck range of motion and neck disability index. CONCLUSION: Upper thoracic manipulation and cervical stability training to the patients with chronic neck pain was helpful to improve neck range of motion and cervical stability training was helpful to improve neck disability index.

• Journal of the Korean Society of Physical Medicine
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• v.12 no.4
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• pp.19-28
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• 2017

PURPOSE: The purpose of this study was to describe the Proprioceptive Neuromuscular Facilitation (PNF) Intervention strategy applied International Classification of Functioning, Disability and Health (ICF) Tool about strength, range of motion, scapular stability, pain and function of shoulder for patients with adhesive capsulitis. METHODS: The data was collected by patient with adhesive capsulitis. The patient was a 50-year-old male diagnosed with right shoulder with adhesive capsulitis. We applied the PNF Intervention strategy applied ICF Tool to patient with adhesive capsulitis. PNF interventions were consisting of such as combination of isotonic and stabilizing reversal technique and various positions. PNF interventions were applied, such as those aiming at decreasing pain and disability and increasing range of motion and function for the four weeks. Parameters of result were collected for strength, range of motion, scapular stability, pain and function of shoulder using the hand held dynamometer, goniometer, lateral scapula slide test, and shoulder pain and disability index, respectively. RESULTS: Clinical benefits were observed the patient with adhesive capsulitis for strength, range of motion, scapular stability, pain, and function of shoulder. The patient with adhesive capsulitis improved strength, range of motion, scapular stability, pain, and function of shoulder. CONCLUSION: Patient reported improved strength, range of motion, scapular stability, pain, and function of shoulder after intervention.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.2 s.140
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• pp.124-128
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• 2005

This paper describes motion stability of a spar platform with and without a damping plate in regular waves. The heave and pitch motion equation is derived in terms of Mathieu equation and the stability diagram is obtained. It is shown that the spar platform with damping plate has smaller unstable region than that without damping plate in the stability diagram. Model tests are carried out to verify the mathematical analysis. Under the condition that the pitch natural period is approximately double the heave natural period and the heave motion is amplified at heave resonance, unstable pitch motions are evoked. However the unstable motion is stabilized in cases of spar platform with damping plate. Therefore the damping plate is an effective device to stabilize the motion of spar platform.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.2 s.107
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• pp.176-182
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• 2006

Modeling and verification for stability analysis of axially oscillating cantilever beams are investigated in this paper Equations of motion for the axially oscillating beams are derived and transformed into dimensionless forms. The equations include harmonically oscillating parameters which are related to the motion-induced stiffness variation. stability diagram is obtained by using the multiple scale perturbation method. To verify the accuracy of the modeling method, several points in the plane of the stability diagram are presented and solved. The present modeling method proves to be as accurate as a nonlinear finite element modeling method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.708-713
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• 2005

Modeling and verification for stability analysis of axially oscillating cantilever beams are investigated in this paper. Equations of motion for the axially oscillating beams are derived and transformed into dimensionless forms. The equations include harmonically oscillating parameters which are related to the motion-induced stiffness variation. Stability diagram is obtained by using the multiple scale perturbation method. To verify the accuracy of the modeling method, several points in the plane of the stability diagram are presented and solved. The present modeling method proves to be as accurate as a nonlinear finite element modeling method.

• Ocean Systems Engineering
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• v.9 no.2
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• pp.157-177
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• 2019

Studies on motion response of a vessel is of great interest to researchers, since a long time. But intensive researches on stability of vessel during motion under dynamic conditions are few. A numerical model of vessel is developed and responses are analyzed in head, beam and quartering sea conditions. Variation of response amplitude operator (RAO) of vessel based on Strip Theory for different wave heights is plotted. Validation of results was done experimentally and numerical results was considered to obtain effect of damping on vessel stability. A scale model ratio of 1:125 was used which is suitable for dimensions of wave flume at National Institute of Technology Calicut. Stability chart are developed based on Mathieu's equation of stability. Ince-Strutt chart developed can help to capture variations of stability with damping.

• Journal of the Korea Institute of Military Science and Technology
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• v.5 no.2
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• pp.62-71
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• 2002

A free oscillation technique for obtaining the dynamic stability derivatives in yaw is applied to the pure yawing motion. The procedure of wind tunnel testing is to compute the derivatives after measuring deflecting angles of the model during the free oscillating motion. The charging compressed air is supplied for the initial excitation. The results of this experiment predicted feasible characteristics of the yawing motion, comparing with the data previously reported in the literature.