• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.39-39
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• 2000

축류 압축기 블레이드(blade)와 베인(vane)이 정하중(static load)에서 충분한 강도를 지니고 있더라도 반복하중이나 교번하중을 받게되면, 그 하중이 작더라도 파괴가 일어날 수 있다. 축류 압축기 블레이드와 베인의 피로파괴(fatigue failure) 현상은 개발 중인 가스터빈엔진 뿐만 아니라 현재 운용중인 엔진에서도 발생할 수 있는 엔진손상의 주요 원인이다. 블레이드나 베인의 동적 안정성 평가는 에어포일(airfoil)의 피로특성과 엔진운용조건에 따라서 발생하는 복잡한 공력가진과의 연관성을 고려하여 수행되어야 하기 때문에, 해석과 구성품 시험을 통하여 우선적으로 강도 평가를 실시하여야 한다.(중략)

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.163-167
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• 2008

This paper presents pressure fluctuation characteristics of a 30 ton-f class liquid rocket engine combustor. Combustion stability of the combustor was evaluated using the results 46 firing tests performed with a varying O/F ratio and chamber pressure. The RMS value of pressure fluctuation during the steady state combustion was less than 2.6% of the static chamber pressure, demonstrating static stability of the combustion phenomenon. The decay time of pressure fluctuation caused by forced disturbance of a pulse gun was found to be less than 3.5 msec verifying dynamic stability of the combustor.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.689-697
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• 2002

The dynamic loads and load-point displacements of concrete three-point bend (TPB) specimens had been measured. The average crack velocities measured with strain gages were 0.16 ㎜/sec ∼ 66 m/sec. The fracture energy for crack extension was determined from the difference of the kinetic energy for the load-point velocity and the strain energy without permanent deformation from the measure external work. For all crack velocities, there were micro-cracking for 23 ㎜ crack extension, stable cracking for 61 ㎜ crack extension at the maximum strain energy, and then unstable cracking. The unstable crack extension was arrested at 80 ㎜ crack extension except the tests of 66 m/sec crack velocity. The tests less than 13 ㎜/sec crack velocity and faster than 1.9 m/sec showed static and dynamic fracture behaviors, respectively. In spite of much difference of the load and load-point displacement relations for the crack velocities, the crack velocities of dynamic tests did not affect on fracture energy rate during the stable crack extension due to the reciprocal action of kinetic force, crack extension and strain energy. During stable crack extension, the maximum fracture resistances of the dynamic tests was 147％ larger than that of the static tests.

• Journal of the Korean Society for Railway
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• v.15 no.2
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• pp.147-153
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• 2012

Precise estimation f a structure's dynamic characteristics is indispensable for ensuring stable dynamic response during life time especially for the structures which can experience resonance such as railway bridges. Especially, concrete track can change the modal properties of the railway bridge, through the contribution of stiffness as well as mass effects, generally only the mass effect is considered in dynamic analysis of the railway bridge. In this paper, static and dynamic behaviors of railway bridge with concrete track were investigated through experimental study. Also, numerical analysis was performed about considering only mass of concrete track and together with stiffness and mass of concrete track. These were compared with experiment value. Numerical analysis value considering together with stiffness and mass of concrete track was similar experiment value. Therefore, when dynamic analysis of railway bridge with concrete track is performed, the contribution of stiffness as well as mass effects for concrete track is considered.

• Journal of the Korean GEO-environmental Society
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• v.24 no.12
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• pp.5-11
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• 2023

Economic damage is occurring due to landslides and debris flows that occur when the ground artificially created for roads or photovoltaic power generation facilities is weakened by rainfall such as torrential rain. In order to understand the stability of the artificially created ground, it is very important to check the ground information such as the compositional state and mechanical characteristics of the stratum. However, since most of the investigation sites are steep slopes or there are no access roads, it is not easy to enter the drilling equipment commonly used to check ground information and perform standard penetration tests. In this study, a dynamic cone penetration test (DCP) device using a miniaturized auger drilling equipment and an automatic drop device was developed to check the cone resistance value and the dynamic cone penetration test value and analyze the correlation with the standard penetration test value to confirm its applicability at the mountain solar power generation site. As a result, the cone resistance value is q_d = 0.46 N and the dynamic cone penetration test value is N_d = 1.58 N, confirming a value similar to the results of existing researchers to secure its reliability.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.79-87
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• 2003

Application of combustion stabilization devices such as baffle and acoustic cavity to liquid propellant rocket engine is investigated to suppress high-frequency combustion instability, i.e., acoustic instability. First, these damping devices are designed based on linear damping theory. As a principal design parameter， damping factor is considered and calculated numerically in the chambers with/without these devices. Next, the unbaffled chambers with/without acoustic cavities are tested experimentally for several operating conditions. The unbaffled chamber shows the peculiar stability characteristics depending on the operating condition and it is found to have small dynamic stability margin. As a result, the acoustic cavity with the present design has little stabilization effect in this specific chamber. Finally， stability rating tests are conducted with the baffled chamber, where evident combustion stabilization is observed, which indicates sufficient damping effect.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.10 no.2
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• pp.133-139
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• 2016

An electric wheelchair is a assistive device to maneuver on the ground. Tip-over of an electric wheelchair is increasing every year. Dynamic stability metric test item in KS P 7176 has not ensured safety of electric wheelchair on the slope. This study presents design the foldable electric wheelchair that can load in the car and analysis of tip-over measurement which is easily computed for electric wheelchair. Wheelchair frame is designed with a four-bar link mechanism for a foldable structure, and seat module, battery and power driving module can be separated. This analysis is performed during a maneuver on the ground by force-moment stability metric. Several elements, center of gravity position, rotational radius and acceleration, were evaluated how to affect stability metric. This stability metric can reduce tip-over of wheelchair and provide a clue to make of dynamic stability test item.

• International Journal of Highway Engineering
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• v.11 no.1
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• pp.233-245
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• 2009

Availability of pressuremeter test for evaluation of geotechnical properties of foundation soil into which guardrail post is to be installed is investigated in this study. First, an analysis method of the post based on the pressuremeter test is proposed that can obtain bending moment and load-deformation profiles of the post. Then static horizontal load test onto a small scale guardrail post is performed in order to get bearing capacity and load-deformation pattern of the model post. The obtained results are compared with the load-deformation curves and bearing capacity of the post obtained from the pressuremeter method. In addition horizontal impact test to the post is performed using a model bogie car in order to check failure pattern around the model foundation and to investigate dynamic bearing capacity due to deceleration and inertia force of the soil. It is verified that the pressuremeter test is so useful and reasonal technique to analyze road foundation-post interaction.

• Journal of the Korean Society for Railway
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• v.20 no.5
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• pp.577-587
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• 2017

In the design process of dynamic characteristics of a railway vehicle, demand for analysis, testing and estimation methods of running stability are increasing as railway vehicle speed is increasing. Critical speed tests and estimation have been carried out using computer simulation or special test facilities, like roller rigs, because real track testing at critical speed is very dangerous. This paper introduces a test and assessment method for critical speed and estimates the validity using several roller rig tests. The test results show that it is difficult to estimate the critical speed using safety and instability assessment method in UIC 518, but that there is good agreement between the reduction of the equivalent damping ratio and the critical speed.

• Geophysics and Geophysical Exploration
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• v.16 no.1
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• pp.45-52
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• 2013

We developed a Impulse Response Measurement System, including hardware system and data analysis software, for non-destructive test of slab structure. And, we carried out impulse response measurements on the pavement to test performance of the system. In the field test, the developed system measured impulse response stably and showed parameters immediately. Test results showed that dynamic stiffness and average mobility varies significantly depending on the characteristics of the pavement materials. Some data showed anomalous values those reflect variations in pavement itself or subsurface ground. Developed system gives informations of conditions of slab structure easily and quickly. So, 2-D monitoring with the system will be helpful in maintaining various slab structures.