• Geomechanics and Engineering
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• v.29 no.2
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• pp.155-170
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• 2022

An accurate analysis of structures supported on soft soils and subjected to seismic loading requires the consideration of the soil-foundation-structure interaction. An important aspect of this interaction lies with the energy dissipation due to soil material damping. Unlike advanced constitutive models that can induce energy loss, the use of simple elastoplastic constitutive models requires additional damping. The frequency dependent Rayleigh damping is a formulation that is frequently used in dynamic analysis. The main concern of this formulation is the correct selection of the target damping ratio and the frequency range where the response is frequency independent. The objective of this study is to investigate the effects of the Rayleigh damping parameters in soil-pile-structure and soil-inclusion-platform-structure systems in the presence of soft soil under seismic loading. Three-dimensional analyses of both systems are carried out using the finite difference software Flac3D. Different values of target damping ratios and minimum frequencies are utilized. Several earthquakes are used to study the influence of different excitation frequencies in the systems. The soil response in terms of accelerations, displacements and strains is obtained. For the rigid elements, the results are presented in terms of bending moments and normal forces. The results show that when the frequency of the input motion is close to the minimum (central) frequency in the Rayleigh damping formulation, the overdamping amount is reduced, and the surface spectral acceleration of the analyzed pile and inclusion systems increases. Thus, the bending moments and normal forces throughout the piles and inclusions also increase.

• Journal of the Korean Geotechnical Society
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• v.24 no.12
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• pp.113-120
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• 2008

One-dimensional site response analysis is widely used to simulate the seismic site effects. The equivalent linear analysis, which is the most widely used type of site response analysis, is essentially a linear method. The method applies constant shear modulus and damping throughout the frequency range of the input motion, ignoring the dependence of the soil response on the loading frequency. A new type of equivalent linear analysis method that can simulate the frequency dependence of the soil behavior via frequency-strain curve was developed. Various forms of frequency-strain curves were proposed, and all curves were asserted to increase the accuracy of the solution. However, its validity has not been extensively proven and the effect of the shape of the frequency-strain curve is not known. This paper used two previously proposed frequency-strain curves and three additional curves developed in this study to evaluate the accuracy of the frequency-dependent equivalent linear method and the influence of the shape of the frequency-strain curves. In the evaluation, six recordings from three case histories were used. The results of the case study indicated that the shape of the frequency-strain curve has a dominant influence on the calculated response, and that the frequency dependent analysis can enhance the accuracy of the solution. However, a curve that results in the best match for all case histories did not exist and the optimum curve varied for each case. Since the optimum frequency-strain curve can not be defined, it is recommended that a suite of curves be used in the analysis.

• Korean Journal of Applied Biomechanics
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• v.21 no.4
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• pp.391-395
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• 2011

To investigate the anticipatory effect on landing patterns during side-cutting maneuver, thirteen healthy female elite college soccer players participated in this study. Three-dimensional knee kinematics, effective mass and correlation between both these were measured and analyzed using a motion analysis and force plates. Each testing session included anticipated tasks, $45^{\circ}$ side-cutting tasks (AC), followed by a set of unexpected side-cutting (UC) in a random order. Knee flexion/extension, valgus/varus and internal/external rotation angles and effect mass were compared by using paired t-test. Also, correlation analysis was performed to identify the relationship between knee angles and effective mass. Effective mass during UC was greater than that during AC. Effective mass and maximum knee flexion angle were positively correlated during AC and not during UC. Based on the relationship between effective mass and knee flexion angle in AC, shock absorption can be controlled by knee joint flexion in pre-predicted movement condition. However, effective mass can not be controlled by knee flexion in UC condition. The unexpected load affects were more irregular on the knee joint, which may be one of the injury mechanisms of anterior cruciate ligament (ACL) in female soccer players.

• Korean Journal of Applied Biomechanics
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• v.21 no.4
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• pp.421-427
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• 2011

The purpose of this study was to analyze the difference between male and female tennis players' two-handed backhand stroke and to provide basic data which helps precise and efficient instruction for the sake of precise postures, enhanced performances and skills. 5 male and 5 female university players were recruited as subjects, and the mean difference between the kinematic variables such as the time from backswing to impact and total swing time, racket head velocity, change of the center of body gravity in two-handed backhand stroke through three-dimensional motion analysis. The test data was analyzed by t-test, and the alpha level of ${\alpha}$=.05 was set for all tests of significance. The findings of the study were as follows; First, there was no difference in the time from backswing to impact and total time of

• Physical Therapy Rehabilitation Science
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• v.5 no.2
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• pp.84-88
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• 2016

Objective: Generally, it is known that there is a correlation between excessive calcaneus eversion and a patient with low back pain and it also affects pelvic alignment. However, there are not enough studies that show calcaneal eversion having an effect on the alignment of the trunk. Design: Cross-sectional study. Methods: A 3-dimensional motion analysis system was used to assess the lower limbs, pelvic alignment, and trunk alignment with increased unilateral and bilateral calcaneal eversion in twenty-one subjects. All subjects were asked to maintain a static posture for seven seconds on a wedge three times per posture for measurement and analysis purposes. The wedge used in the process was a lateral wedge with a 10-degree tilt to the lateral direction. To unify all of the subjects' foot position, the front and inner side of the wedge were marked. The height of the tilted wedge's inner side and flat wedge were balanced equally in order to be able to maintain the lateral part of the foot to the same height when producing an increased calcaneal eversion. Results: Comparing the changes in trunk and pelvic alignment in accordance to calcaneal eversion for each posture, there was a significant different in the X and Y-axis for each posture, but not in the Z-axis (p<0.05). Thus, it can be confirmed that calcaneal eversion in the sagittal plane and frontal plane may have and effect on the pelvis and the trunk. Conclusions: Postures with increased bilateral and unilateral calcaneal eversion has an effect on pelvic alignment, but does not cause any changes in trunk alignment.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.366-375
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• 1991

In this study, vibrational behavior of uniform pipe carrying a moving medium is studied by using a transfer matrix and the displacement function derived from the conventional beam theory. In various boundary conditions, flow velocity and mechanical property change of the variation of natural frequency are investigated. The Coriolis term in the original differential equation of motion has been ignored in the investigation. This method is used to study the variation of natural frequency with flow velocity for clamped-clamped, cantilevered, clamped-pinned, pinned-pinned, free-free straight pipe element. It is shown that clamped-clamped, free-free pipe have the highest natural frequency and critical velocity values while cantilevered pipe have the smallest natural frequency for the same mechanical properties. From the vibration effects of mechanical property variation, it is shown that bending stiffness and pipe length variation has large influence on natural frequency and critical velocity. Since the order of transfer matrix is not changed with boundary conditions of pipe element, this method proposed can be easily applied to personal-computer for vibration analysis of pipe element. Furthermore, this method can be extended to three-dimensional system by using a coordinate transformation for the analysis of piping systems.

• Journal of Biomedical Engineering Research
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• v.28 no.2
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• pp.187-194
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• 2007

The purpose of this study is to determine the characteristics of ground reaction force(GRF) in golf swing for various slopes of flat lie and uphill lies of 5 and 10 degrees. Five right-handed professional golfers were selected for the experiment and the 7 iron club was used. We used four forceplates to measure GRF and synchronized with the three-dimensional motion analysis system. Results showed that slope did not affect the total time for golf swing, but the time until the impact had a tendency to slightly increase for the uphill lie(p<0.05). The medial-lateral GRF of the right foot increased toward the medial direction during back swing, but less increases were found with the angle of uphill lie(p<0.05). The GRF of the left foot increased rapidly toward the medial direction at the uncocking and the impact during down swing, but decreased with the increase in the angle of uphill lie(p<0.05). The anterior-posterior GRF of both feet showed almost the same for different slopes. With the slopes, the vertical GRF of the right foot increased, but the vertical GRF of left foot decreased(p<0.05). Uphill lies would have negative effect to provide the angular momentum during back swing, restricting pelvic and trunk rotations, and to provide the precise timing and strong power during down swing, limiting movements of body's center of mass. The present study could provide valuable information to quantitatively analyze the dynamics of golf swing. Further study would be required to understand detailed mechanism in golf swing under different conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.11
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• pp.1105-1110
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• 2012

The spine is one of the most important skeletal joints, and it strongly affects the health of the musculoskeletal system. A normal spine has an S-shape, and it is very important to maintain this shape. Recently, spinal diseases such as low back pain have increased rapidly, especially among the elderly. Some of these diseases are caused by congenital spinal disorders and sporting and accident injuries as well as by bad postures. Improper spinal postures could generate excessive disc pressure, which is related to degeneration and pain. Therefore, in this study, we investigated the three-dimensional kinematic parameters of the thoraco-lumbar joint in several bad postures using a motion capture analysis technique. Different bad postures created a significant amount of flexion/extension, side bending, and axial rotation angle compared with neutral postures. Further study is necessary to investigate the disc pressure and ligament force due to the increase in joint rotation from the bad postures.

• Korean Journal of Applied Biomechanics
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• v.21 no.2
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• pp.141-152
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• 2011

The purpose of this study was to investigate the projectile factors and biomechanical characteristics of men's hammer throwing during turning phases. Four national leveled athletes including Korea national record holder participated in this study. After full warm-up, each participant performed 6 trials of hammer throwing with their best. The best recorded trial was selected from each participant and they were analyzed for this study. Three-Dimensional motion analysis using a system of 5 video cameras at a sampling frequency 60Hz was performed for this study. As the number of turns increased, athletes revealed following characteristics. 1) The single and double support time decreased. 2) The rotation foot was closed to axis foot and it revealed greater medio-lateral displacement than that of horizontal one. 3) At the transition point from double support to single support, ball was in front of rotation foot so that not much angular velocity obtained. For the projectile factors, projectile angle did not show differences while projectile height and velocity revealed differences among the participants. It may indicated that each athlete has different fitness and skill level to resist centrifugal force which become larger as the number of turn increased.

• Journal of the Korea Convergence Society
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• v.11 no.6
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• pp.393-400
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• 2020

This study used a three-dimensional motion analysis system for 15 elite tennis players (male 8, female7) to identify the relevance of scapula movement to shoulder pain. During the flat serve, the angular velocity and joint moment of scapula anterior/posterior tilt, downward/upward rotation, internal/external rotation were calculated and this was compared between groups. As a result, the maximum angular velocity for the anterior and posterior tilt tended to be higher in control group(CG) than in the shoulder pain group(SPG), and the maximum angular velocity for internal and external rotation in all phases except the follow-through phase was higher than that of CG. The maximum moment for the anterior and posterior tilt in the late coking phase was statistically significantly higher than that of SPG, the joint moment for the downward and upward rotation of the coking phase was statistically significantly lower than that of CG, and the moment for the internal and external rotation, the SPG was found to be lower than that of CG in the whole phases.