• Korean Journal of Applied Biomechanics
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• v.30 no.3
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• pp.197-204
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• 2020

Objective: The purpose of this study was to investigate the effect of increased running speed on the magnitude of impact shock attenuation in high frequency (9~20 Hz) at support phase on the treadmill running. Method: Twenty-four healthy male heel-toe runners participated in this study. Average age, height, mass, and preference running speed were 23.43±3.78 years, 176.44±3.38 cm, 71.05±9.04 kg, and 3.0±0.5 m/s, respectively. Three triaxial accelerometer (Noraxon, USA) were mounted to the tuberosity of tibia, PSIS (postero-superior iliac spine), and forehead to collect acceleration signals, respectively. Accelerations were collected for 20 strides at 1,000 Hz during treadmill (Bertec, USA) running at speed of 2.5, 3.0, 3.5, and 4.0 m/s. Power Spectrum Density (PSD) of three acceleration signals was calculated to use in transfer function describing the gain and attenuation of impact shock between the tibia and PSIS, and forehead. One-way ANOVA were performed to compare magnitude of shock attenuation between and within running speeds. The alpha level for all statistical tests was .05. Results: No significant differences resulted for magnitude of the vertical and resultant impact shock attenuation between the tibia and PSIS, and forehead between running speeds. However, significant differences within running speed were found in magnitude of the vertical shock attenuation between tibia and PSIS, tibia and forehead at speed of 2.5, 3.0 m/s, respectively. Conclusion: In conclusion, it might be conjectured that muscles covering the knee and ankle joints and shoe's heel pad need to strengthen to keep the lower extremities from injuries by impact shock at relatively fast running speed that faster than preferred running speed.

• Journal of Korean Society of Steel Construction
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• v.29 no.5
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• pp.369-376
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• 2017

This paper is the sequel of a companion paper (I. Seismic Design) for design and assessment of the torsional irregular structure using ASCE 7-10 criteria. This study evaluates the influence of torsional provisions on the performance of the designed steel moment frame with different eccentricity, taking the collapse probability as performance metric using the methodology in FEMA P695. The result show that torsional irregular structure designed according to ASCE 7-10 has an excessive seismic performance and the collapse strength is low as the eccentricity increases. To make the design reasonable, a new design approach is proposed in this study.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.5
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• pp.439-446
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• 2016

The characteristics of bearingless main rotor of helicopter are investigated through non-rotating tests and rotating tests. The stiffness and natural frequencies of rotor blades, flexbeam, and torque tube which are core components of baearingless rotor are measured to obtain input material properties for rotor analysis. The functional test on ground for assembly of one hub with damper, snubber, and no blade is carried out to check interfaces between components, kinematics of components, and pitch motion ranges under applied loads including centrifugal load. The 4-bladed bearingless rotor with 5.82m of rotor radius is tested on the whirl tower with rotation plane of 9.65m height. The thrust and power are measured to obtain hover performance and the frequencies and dampings of the rotor are obtained by excitation of cyclic pitch by hydraulic actuators.

• The Journal of Korean Physical Therapy
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• v.24 no.2
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• pp.90-97
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• 2012

Purpose: The purpose of this study was to assess the effects of virtual reality-based continuous slow exercise on muscle strength and dynamic balance capacity, in older adults over 65 years of age. Methods: Twenty-six volunteers were randomly divided into two groups; a Virtual Reality (VR) exercise-group ($67.8{\pm}4.1$ yrs) and a Control group ($65.5{\pm}5.2$ yrs). The VR group participated in eight weeks of virtual reality exercise, utilizing modified Tai-Chi provided by a motion capture system, and the Control group had no intervention. The hip muscle strength and dynamic balance of the members of both the VR group and the Control group were measured at pre- and post-intervention, using a multimodal dynamometer, and backward stepping test, respectively. Results: 1. After the 8-week VR-based exercise, the VR group showed significant improvement of hip strength, compared to the control group: hip extension (p=0.00), flexion (p=0.00), abduction (p=0.00), and adduction (p=0.00). 2. After the 8-week VR-based exercise, the VR group showed significant improvement of dynamic balance capacity as ground reaction force, compared to the control group. Eyes opened backward stepping test: Fx (+) (p=0.00), Fy (-) (p=0.02), Ver (+) (p=0.02) direction. Eyes closed backward stepping test: Fx (+) (p=0.04), Fy (-) (p=0.04), Ver (+) (p=0.03) direction. Conclusion: The VR group showed improvement of their hip muscle strength, and dynamic balance capacity. Therefore VR-based continuous slow exercise would contribute to reducing the risk of falls in the elderly.

• Korean Journal of Applied Biomechanics
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• v.22 no.1
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• pp.105-111
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• 2012

The purpose of this study was to investigate the effect that difference in forefoot of shoe flexibility during the quick lunge from a jump smashing on the lower limbs and the plantar pressure distribution. For this 10 elite badminton players with over 10 years experience and right handed participated. Two kinds of badminton shoes were selected and tested mechanical testing for the forefoot flexibility. Motion analysis, ground reaction forces and plantar pressure distribution were recorded. It was required to conduct lunge movement after jumping smashing as possible as high. Photo sensor was located in 3 meter away from standing position and its height was 40 cm. Subjects were conducted to return original position after touching the sensor as under clear movement as possible as fast. Forefoot stiffness had an effect on shoe peak bending degree and peak bending angular velocity in propulsion phase. Forefoot flexibility had an effect on ankle plantar flexion and knee flexion moment. It appears that joint power on lower limb and peak plantar pressure were not influenced by the flexibility of shoes.

• Journal of Korean Association for Spatial Structures
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• v.10 no.1
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• pp.103-110
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• 2010

In this study, the possibility of seismic response control of semi-active tuned mass damper (TMD) for spatial structures has been investigated. To this end, an arch structure was used as an example structure because it has primary characteristics of spatial structures and it is a comparatively simple structure. A TMD and semi-active TMD were applied to the example arch structure and the seismic control performance of them were evaluated based on the numerical simulation. In order to regulate the damping force of the semi-active TMD, groundhook control algorithm, which is widely used for semi-active control, was used. El Centro (1940) and Northridge (1994) earthquakes and harmonic ground motion were used for performance evaluation of passive TMD and semi-active TMD. Based on the analytical results, the passive TMD could effectively reduce the seismic responses of the arch structure and it has been shown that the semi-active TMD more effectively decreased the dynamic responses of the arch structure compared to the passive TMD with respect to all the excitations used in this study.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.91-91
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• 2011

The passage of the interplanetary discontinuity (i.e., sudden increases in the solar wind speed, density, and IMF strength) was detected by ACE near GSE (x, y, z) ~ (222, -36, 3) Re upstream of Earth around 22:48 UT on November 24, 2008. About 55 min later, this solar wind discontinuity was observed by Geotail near GSE (x, y, z) ~ (23, 18, -7) Re in front of Earth's bow shock. From the propagation time of the solar wind discontinuity between ACE and Geotail, it is expected that the discontinuity front is aligned with the Parker spiral and strikes the postnoon dayside magnetopause first. Using coordinated multi-point measurements (THEMIS and GOES) at or in geosynchronous orbit, we observed a tailward propagating sudden impulse (SI), excited by the interplanetary discontinuity, around 23:50 UT with its front retaining alignment similar to that of solar wind discontinuity. The SI event appears a negative-then-positive variation in the H component at high latitude Chokurdakh (CHD: MLAT ~ 64.7 deg) in the prenoon sector, which is opposite sense of normal SI event. During the positive deflection at CHD, the SuperDARN Hokkaido radar detected the downward motion of the ionosphere, implying westward electric field enhancement, at subauroral latitudes near CHD meridian. In our study we will discuss magnetospheric and ionospheric responses to the passage of the solar wind discontinuity using multi-point observations in space and on the ground.

• Korean Journal of Applied Biomechanics
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• v.16 no.2
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• pp.25-35
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• 2006

The purpose of this study was to investigate the shock attenuation mechanisms while varying the loads in a backpack during drop landing. Ten subjects (age: $22.8{\pm}3.6$, height: $173.5{\pm}4.3$, weight: $70.4{\pm}5.2$) performed drop landing under five varying loads (0, 5kg. 10kg. 20kg. 30kg). By employing two cameras (Sony VX2100) the following kinematic variables (phase time, joint rotational angle and velocity of ankle, knee and hip) were calculated by applying 2D motion analysis. Additional data, i.e. max vertical ground force (VGRF) and acceleration, was acquired by using two AMTI Force plates and a Noraxon Inline Accelerometer Sensor. Through analysing the power spectrum density (PSD), drop landing patterns were classified into four groups and each group was discovered to have a different shock attenuation mechanism. The first pattern that appeared at landing was that the right leg absorbed most of the shock attenuation. The second pattern to appear was that subject quickly transferred the load from the right leg to the left leg as quickly as possible. Thus, this illustrated that two shock attenuation mechanisms occurred during drop landing under varying load conditions.

• Korean Journal of Applied Biomechanics
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• v.16 no.2
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• pp.193-205
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• 2006

This study was to analysis the kinematic and kinetic differences between new walking shoe(NWS : RYN) and general walking shoe(GWS). The subjects for this study were 10 male adults who had the walking pattern of rearfoot shrike with normal foot. The movement of one lower leg was measured using plantar pressure and Vicon Motion Analysis Program(6 MX13 and 2 MX40 cameras : 100 f / s) while the subjects walked at the velocity(1.5m/s. on 2m).. The results of this study was as follows : 1. The NWS was better than the GWS that caused injuries such as adduction, abduction and pronation are reduced While walking on a perpendicular surface, the landing angle and the knees angles were extensive which makes walking more safe which reduces anxiety and uneasiness. 2. The bottom of the NWS were now made into a more circular arch which supports the weight of the body and reduces the irregular angles when wearing GWS. This arch made the supporting area more wide which made the upholding the trunk of the body more effective. The whole bottom of the foot that supports the weight is more flexible in addition, increases the safeness of walking patterns and the momentum of the body. 3. The moment the heel of the foot of the NWS touch the ground, the range of the pressure were partially notable and the range of the pressure on the upper part of the thigh were dispersed The injuries that occurred while walking. primary factors when a shock related injuries are reduced Judgements of the impacts of the knees and the spinal column dispersing could be made.

• Journal of Korean Physical Therapy Science
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• v.3 no.1
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• pp.919-927
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• 1996

Recently sports injuries are increasing due to the development of sports leisure industries as well as the increase of exercising population, and the study for sports injuries is needed more than before. Then the author studied the reasons for injuries, incidence rate, sites and sorts of sports injuries for the middle and high school football players during one year period from Jan. to Dec. 1994. The study subjects were 319 middle and high school players in Pusan and the method was questionnaire method. The results were as follows; 1. The average injury rate due to football play was 3.3 times per person for the 319 subjects during the last one year, and it was highest in goalkeeper as 4.6 times by position. 2. 68 % of the subjects did not receive periodic health examination, 74.9 % wore body protectors. The sports injuries due to football play occurred most commonly in soil play-ground(79.6 %), during training(52.3 %), and in winter time(33.7 %). 3. The commonly occurred injuries by motion were coalition(39.2 %), tackle(12.9 %), dribble (11.4 %) in order; those by sorts were contusion(34.4 %), sprain (32.9 %), spasm(9.0 %) ; and those by body portions lower extremities(82 %), trunk(17.6 %), upper extremities(12.5 %). 4. The frequently used treatment area was home care as in 42.7 % ; treatment methods were physical therapy, acupuncture/moxacautery, rest, operation in order; choices of treatment method were recommendation by coach/manager, and that by medical professional was the lowest as in 2.2 %. 5. If sports injury occurred during play, coach or manager let the players take rest in 56.2 %, but emergent management by medical professional was done only in 1.9 %. The return to play was decided mostly by the player himself(52.8 %), but that decided by a doctor was only in 1.0 %. In conclusion, to lessen the sports injuries due to football play, annual physical check-up, strengthening of play rules, improvement of playground, conditioning exercise, regulation of body protectors, and preventive training for expected injuries behaviors should be done and the decision to return to play and emergent management should be done by a medical professional as well. Football player, sports injury, injured body portions, sorts of injury, treatment method.