• Korean Journal of Applied Biomechanics
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• v.12 no.1
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• pp.115-124
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• 2002

The purpose of this study is to analyze the ground reaction force of arm landing on arm and leg during sports aerobics. Subjects of this study were total 10 players of 5 males and 5 females who have are domain sports aerobics medalists more than the third place in national tournaments. The subjects jumped between the two ground reaction force analyzers, while landing their right hand on the front platform(#1) and their right leg on the rear platform(#2), and the data frequency was set to 200Hz. Findings of this study are as follows; More than 3 times of impact peak force of vertical reaction force acted on arm joint than on leg joint. And, when ground reaction force on foot increased, ground reaction force on hand decreased. 3 impact peaks of curve of ground reaction force were found - Impact Peak 1 incurred on the time the palm lands on the ground, Impact Peak 2 absorbing shock secondarily on wrist joint, and Active Peak incurred on the time of holding the weight while pushing out the severly bent elbow joint.

• Journal of the Ergonomics Society of Korea
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• v.14 no.2
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• pp.75-85
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• 1995

The purpose of this study is to develop a force-platform system suitable for real situations in industry. The developed system is a 3-axis measurement type. It consists of force-transmission, force measuring circuit, and the software that analyzes the measured force. The force-transmission transmits forces to 3 axes, which has a physical structure to minimize the interference among those axes. Force measuring circuit consists of DSP (digital signal processor) for flexible disposal of change of measurement algorithm, elimination of noise and maintenance of precision. The functions of the software are the calibration which revises the measurement error occuring during data acquisition, and various analyses of forces. The result of the experiment shows that the developed system has about 1% measurement error, is stable for repeated experiments, and is not effected by temperature change.

• Coupled systems mechanics
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• v.2 no.1
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• pp.111-126
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• 2013

The structural design requirements of an offshore platform subjected to wave induced forces and moments in the jacket can play a major role in the design of the offshore structures. For an economic and reliable design; good estimation of wave loadings are essential. A nonlinear response analysis of a fixed offshore platform under structural and wave loading is presented, the structure is discretized using the finite element method, wave plus current kinematics (velocity and acceleration fields) are generated using 5th order Stokes wave theory, the wave force acting on the member is calculated using Morison's equation. Hydrodynamic loading on horizontal and vertical tubular members and the dynamic response of fixed offshore structure together with the distribution of displacement, axial force and bending moment along the leg are investigated for regular and extreme conditions, where the structure should keep production capability in conditions of the 1-yr return period wave and must be able to survive the 100-yr return period storm conditions. The result of the study shows that the nonlinear response investigation is quite crucial for safe design and operation of offshore platform.

• Journal of Ocean Engineering and Technology
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• v.20 no.2 s.69
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• pp.1-7
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• 2006

This paper, presents a comparison between numerical analysis and field test on a real offshore platform in Bohai Bay, China. This platform is a steel jacket offshore platform with vertical piles. The field testing under wave-induced force and wind force etc. was conducted, in order to obtain the dynamic parameters of the structure, including the frequencies of the jacket platform, as well as the corresponding damping ratios and mode shapes. The natural excitation technology (NexT) combined with eigensystem realization algorithm (ERA) and the peak picking (PP) method in frequency domain are carried out for modal parameter indentification under operational conditions. The three-dimeansional finite element model (FEM) is constructed by ANSYS and analytical modal analysis is performed to generate modal parameters. The analytical results were compared with experimental results. A good agreement was achieved between the finite element and analysis and field test results. It is further demonstrated that the numerical and experimental modal analysis provide a comprehensive study on the dynamic properties of the jacket platform. According to the analysis results, the modal parameters identification under ambient excitation can calibrate finite element model of the jacket platform structures, or can be used for the structural health monitoring system.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.5 s.98
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• pp.200-208
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• 1999

The statics relation of the Stewart platform has been investigated from the viewpoint of the forward and inverse force transmission analyses. Two eigenvalue problems corresponding to the forward and inverse force transmission analyses have been formulated. The forward force transmission analysis is to determine the ranges of the magnitudes of the force and moment generated at the end-effector for the given magnitude of linear actuator forces. In reverse order, the inverse force transmission analysis is to find the range of the magnitude of actuator forces for the given ranges of the magnitudes of the force and moment at the end-effector. The inverse force transmission analysis is important since it can provide a designer with a valuable information about how to choose the linear actuators. It has been proved that two eigenvalue problems have a reciprocal relation, which implies that solving either of the eigenvalue problems may complete the forward/inverse force transmission analysis. A numerical example has been also presented.

• Science of Emotion and Sensibility
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• v.5 no.4
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• pp.45-49
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• 2002

Recently, virtual environment systems are used in various application fields such as industry, medicine, and training and education. However, the negative effect, cybersickness including nausea, visual fatigue, and disorientation, could be happened while using VR systems. It prevents VR system from spreading much more. To control the cybersickness, first of all, the objective measurement method should be established. As one of alternative methods, the postural instability could be a measure of cybersickness. In this study, 45 participants' postural sway before and after experiencing a H driving simulator was measured by using a force platform. Especially, we examined if two factors, motion and feedback, could affect on the postural instability The results showed the postural instability slightly increased after experiencing the VR driving simulator. For the factors, the providing of motion synchronized to visual display showed statistical significant decrease in postural sway along lateral side. To check the effectiveness of postural instability as a cybersickness measure, further studies are needed.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.6
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• pp.121-130
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• 2007

In this paper, we present the development of a new training system for equilibrium sense and postural control. This system consists of an unstable platform, a force plate, a computer, and training programs. The unstable platform provides 360 degrees of movement allowing for training in all directions. To evaluate the effects of the training system, we performed various experiments to train the ability of equilibrium sense and postural control of fifteen young healthy subjects. We measured the time a subject maintains his or her center of pressure on a target, the time a subject moves his or her center of pressure to a target, and the mean absolute deviation of the trace before and after the training. We analyzed these parameters obtained before and after the training using paried-sample T-test. The result shows that the subjects experienced distinctive enhancement in their ability of postural control through the training using our system.

• Korean Journal of Applied Biomechanics
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• v.26 no.2
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• pp.191-195
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• 2016

Purpose: The purpose of this study was to analyze the immediate effects of ankle restriction with an elastic band on ground reaction force during a golf swing. Method: There were five subjects who were teaching pros with an average golf score of 75. A force platform (9281B, Switzerland) was used. The independent variable was the presence of an elastic band. The dependent variables were three-dimensional ground reaction forces to analyze the transfer of momentum with the timing, control and coordination of the three forces. A paired t-test within subject repeated measure design was used via an SPSS 20.0. Results: Wearing an elastic band around one's ankles significantly makes shorter time differences between the moment of cross anterior / posterior forces and vertical force and median value of anterior / posterior forces during the backswing, between medial and lateral maximum and anterior / posterior force from the top of the back swing to the mid down swing, and creates an anterior / posterior maximum force. Conclusion: Wearing an elastic band around one's ankles affects control and coordination between three dimensional forces, and anterior force power according to each phase of the golf swing.

• Journal of Ocean Engineering and Technology
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• v.28 no.6
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• pp.508-516
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• 2014

A numerical method to investigate the non-linear motion characteristics of a TLP is established. A time domain simulation that includes the memory effect using the convolution integral is used to consider the transient effect of TLP motion. The hydrodynamic coefficients and wave force are calculated using a potential flow model based on the HOBEM(higher order boundary element method). The viscous drag force acting on the platform and tendons is also considered by using Morison’s drag. The results of the present numerical method are compared with experimental data. The focus is the nonlinear effect due to the viscous drag force on the TLP motion. The ringing, springing, and drift motion are due to the drag force based on Morison's formula.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.367-375
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• 2020

This paper presents an integrated analysis about dynamic performance of a Floating Offshore Wind Turbine (FOWT) OC4 DeepCwind with semi-submersible platform under real sea environment. The emphasis of this paper is to investigate how the wave mean drift force and slow-drift wave excitation load (Quadratic transfer function, namely QTF) influence the platform motions, mooring line tension and tower base bending moments. Second order potential theory is being used for computing linear and nonlinear wave effects, including first order wave force, mean drift force and slow-drift excitation loads. Morison model is utilized to account the viscous effect from fluid. This approach considers floating wind turbine as an integrated coupled system. Two time-domain solvers, SIMA (SIMO/RIFLEX/AERODYN) and FAST are being chosen to analyze the global response of the integrated coupled system under small, moderate and severe sea condition. Results show that second order mean drift force and slow-drift force will drift the floater away along wave propagation direction. At the same time, slow-drift force has larger effect than mean drift force. Also tension of the mooring line at fairlead and tower base loads are increased accordingly in all sea conditions under investigation.