• PNF and Movement
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• v.13 no.3
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• pp.135-143
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• 2015

Purpose: The purpose of this study was to assess the effect of the proprioceptive neuromuscular facilitation (PNF) relaxation technique (hold relax; HR, contract relax; CR) and static stretch (SS) on hamstring flexibility and vertical jump performance in healthy adults over a four-week period. Methods: Twenty-four healthy adults volunteered to participate in PNF and static stretch sessions. The subjects were divided into three groups as follows: 8 subjects in the SS group, 8 subjects in the HR group, and 8 subjects in the CR group. In the HR and CR groups, contractions lasted 15 seconds per trial and consisted of 5 sets of 15 seconds of hamstring contraction immediately followed by 15 seconds of passive static hamstring stretching. For the static group, the participants were asked to stretch by hanging a leg over a table for 30 seconds. Subjects in all groups performed the exercises three days per week for 4 weeks. The active straight leg raising (ASLR) test, active knee extension (AKE) test, and vertical jump test were performed before the intervention and after 1, 2, and 4 weeks. Results: The SS, HR, and CR techniques effected positive improvement in hamstring flexibility and vertical jump performances but neither of the stretching methods had any statistically significant different effects according to group, although there were interactions (between group and time) in the ALSR group from 1 week to 2 week and in the AKE test from pretest to 1 week. Conclusion: Based on the results of the current study, SS, HR, and CR were shown to affect hamstring flexibility and vertical jump performance in healthy adults. In particular, it was determined that within a short period, hamstring flexibility could be attributed more to CR than to SS.

• The KSFM Journal of Fluid Machinery
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• v.20 no.2
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• pp.63-68
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• 2017

This paper predicts the rotordynamic force coefficients of tilting pad journal bearings (TPJBs) with ball-socket pivot and compares the predictions to the published test data obtained under load-between-pad (LBP) configuration. The present TPJB model considers the pivot stiffness calculated based on the Hertzian contact stress theory. Due to the compliance of the pivot, the predicted journal eccentricity agree well with the measured journal center trajectory for increasing static loads, while the early prediction without pivot model consideration underestimates it largely. The predicted pressure profile shows the significant pressure development even on the unloaded pads along the direction opposite to the loading direction. The predicted stiffness coefficients increase as the static load and the rotor speed increase. They agree excellently with test data from open literature. The predicted damping coefficients increase as the static load increases and the rotor speed decreases. The prediction underestimates the test data slightly. In general, the current predictive model including the pivot stiffness improves the accuracy of the rotordynamic performance predictions when compared to the previously published predictions.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.5
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• pp.566-573
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• 2015

The most important factor for the penetration performance of shaped charge is the liner design. By designing the liner to have properties of both high jet tip velocity and long jet break-up time, the better penetration performance could be acquired. Usually it is very difficult to satisfy above two conditions simultaneously. In this study, the liner with the shape of ogive was developed to have relatively larger jet mass compared to the conventional trumpet liner. The designed shaped charge showed jet properties with high jet tip velocity and long jet break-up time by using ogive liner and wave shaper. A commercially available hydro-dynamic code AUTODYN-2D was used for numerical analysis of jet formation. The flash X-ray test and the static penetration test were conducted to verify the results of numerical analysis.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1679-1688
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• 2008

Recently, the bogie frame weight of Light Rail Transit system has been reduced in order to save energy and materials. However, this light weighted vehicle structure is very important to verify the fatigue strength at the development stage. Bogie system consists of bogie frame, suspensions, wheel-sets, braking system and transmission system. Among these components, the bogie frame is most significant component subjected to the whole vehicle and passenger loads. In this study, the bogie frame for the New LRT power car is evaluated to the static and fatigue strength. And the evaluation method is used the LRT Performance Test Standards Specification throughout the FEM analysis and static load test. The static and fatigue test results for the LRT bogie frame of power car has been appeared very safety and stable for the design load conditions.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.788-793
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• 2001

Test experience with a micro-turbine jet engine is introduced. The engine provides us with valuable opportunities to experience know-hows essential for engine development. It consists of a single radial compressor and a single stage turbine. Engine starting procedure has been established after many trials and errors. Static and dynamic engine performance tests were conducted. Static performance was found to be inferior to that advertised by the manufacturer. Further improvement is needed. Dynamic performance revealed that engine thrust overshoots unfavorably for the purpose of UAV control.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.187-193
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• 2001

The object of this research is to evaluate the seismic performance of existing circular reinforced concrete bridge piers by the Quasi-static test. Existing reinforced concrete bridge piers, which were non-seismical]y designed in accordance with the conventional provisions of Korea Highway Design Specification, are needed to rating evaluate seismic performance fur probable earthquake motions in future by developing a seismic analysis computer program with estimation algorithm. This study has been performed to verify the effect of lap spliced longitudinal steel, confinement steel type and confinement steel ratio for the seismic behavior of reinforced concrete bridge piers. Quasi-static test has been done to investigate the physical seismic performance of RC bridge piers, such as displacement ductility, energy absorption, strength degradation etc.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.2
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• pp.55-66
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• 1999

Eight RC bridge plers have been made on a 1/3.4 scale model and have been tested in a quasi-static cyclic load so as to investigate their seismic performance. The ultimate objective of this experimental study is to investigate the hysteretic behavior of reinforced concrete plers, which have been widely used for urban transportation facilities in Korea. Improtant test parameters are hoop ratio, axial load, load pattern, and etc. And noninear behaviors of test columns have been evaluated through their yield and ultimate strength, energy dissipation, ductility and load-deflection characteristics under quasi-static cyclic loads. From the quasi-static tests on 8 bridge piers, it is concluded that energy dissipation, ultimate strength and curvature for a given displacement factor ${\mu}={\Delta}/{\Delta}_y$ are higher for the seismically designed columns than for the nonseismically designed columns.

• Journal of the Society of Disaster Information
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• v.19 no.4
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• pp.851-858
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• 2023

Purpose: A study was conducted to ensure the structural safety of a raised girder bridge with improved cross-sectional efficiency compared to the conventional PSC girder. For this purpose, the cross-sectional specifications such as girder length, height, and width were determined, the arrangement of the tendons was designed, and the practical performance of the raised girder under static and dynamic loads was verified. Method: The static performance experiment examined the serviceability limit state by measuring behavioral responses such as deflection and cracking to primary and secondary static loads. In addition, the dynamic load loading experiment measured the acceleration and displacement behavior response over time to calculate the natural frequency and damping ratio to examine the usability limit state. Result: As a result of the static performance test, the deflection value based on the maximum applied load showed stable behavior, and the crack width measured at the maximum applied load level was very small, satisfying the serviceability limit state. In addition, a natural frequency exceeding the natural frequency calculated during the design of the dynamic loading experiment was found, and a damping ratio that satisfies the current regulations was found to be secured.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.33 no.2
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• pp.145-155
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• 2023

Objectives: A fit test panel is needed to identify the fit performance of a respirator and its face seal. This is a criterion for selecting subjects that can represent the facial characteristics of users. Although anthropometry data has been developed for people in United States and China it is not yet present in Korea. This study aimed to develop a Korean fit test panel and test headform. Methods: For the 7th and 8th waves of the Size Korea anthropometry data, facial measurements of 11,429 people aged 15 to 69 years were used for analysis. PCA and bivariate panel were classified using the ISO16976-2:2022(E) anthropometrics analysis method. Based on this result, a static headform was developemed and a fit test chamber was constructed. Results: Of the 11,429 Korean people used for principal component analysis, 11,300 were included in the ellipse, marking an acceptance rate of 98.87% on PCA panel. The face types were classified into five types. Among them, a large, medium, and small static headform were printed using a 3D printer. In addition, 10,985 people (96.12%) were included in the bivariate panel based on face length and face width. The y-axis (face length) boundary was 97.87 to 134.59 mm, and the x-axis (face width) boundary was 120.75 to 158.23 mm. Conclusions: Compared to the ISO analysis, the Korean principal component was narrower in the width item (PC1) and longer in the length item (PC2). For the future, it is necessary to conduct a fit test using the developed headform and chamber device to confirm the usefulness of this Korean test panel. Therefore, this study is considered valuable as basic research for Korean test panels.

• Physical Therapy Rehabilitation Science
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• v.2 no.2
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• pp.115-118
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• 2013

Objective: Whole body vibration training is a relatively new approach for enhancement of muscle strength, physical performance, and balance. The aim of this study was to assess the effect of unilateral whole body vibration training. Design: One group pretest-posttest design. Methods: Sixteen healthy, physically active volunteers participated in this study. Whole body vibration was applied with a frequency of 20 Hz and an amplitude of 3 mm for 3 minutes. Muscle performance and static balance were assessed before and after unilateral whole body vibration training. One leg standing broad jump test was measured to determine muscle performance which is closely linked to lower extremity muscle function. The good balance system was used in evaluation static balance. All test were measured 3 times and the average value was analyzed. Results: Jumping length was significantly improved by 0.11m in all participants after intervention (p<0.05). Among static parameters, significant results were observed where in the eyes opened condition, X-speed (medial-lateral sway) changed from 4.20 mm/s to 4.95 mm/s, Y-speed (anterior-posterior sway) changed from 5.77 mm/s to 6.54 mm/s and velocity moment changed from $12.77mm^2/s$ to $13.57mm^2/s$ (p<0.05). In the eyes closed condition, X-speed changed from 4.34 mm/s to 4.85 mm/s, Y-speed changed from 7.84 mm/s to 8.16 mm/s and velocity moment changed from $16.03mm^2/s$ to $16.11mm^2/s$ (p<0.05). Conclusions: Immediate unilateral whole body vibration improved muscle performance but impaired static balance in young adults.