• Journal of the Korean Geosynthetics Society
• /
• v.19 no.1
• /
• pp.55-63
• /
• 2020

In this study, a scaled model test of the shaking table and a seismic analysis considering effective stresses were performed to reveal the dynamic behavior characteristics of box structures deep located in multi-layered soils upon seismic loading. The input seismic wave was operated below the ground using five seismic waves, including long period wave (Hachinohe), short period wave (Ofunato), artificial wave and real earthquakes that occurred in Gyeong-ju and Po-hang. As a result of model test and numerical analysis, the vertical displacement of box structures upon seismic loading was greater than that of horizontal direction, and it was confirmed that an increase of excess pore water pressure below the foundation ground caused a displacement. In addition, behavior of the ground and structures during artificial seismic wave appeared to be larger than real earthquake wave.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37A no.9
• /
• pp.792-798
• /
• 2012

Network Quotient, an important figure in modern society, the intelligibility of speech as a conversation partner to maximize pulling up feeling of liking it as much as possible has become an important issue. The humidity of air in the intelligibility of speech have many influences. Therefore, in this paper, we carried out experiment to apply voice signal analysis techniques which to analyze influenced vocal cords in 30%, 50% and 80%, maintaining a constant humidity of the environment. With this in mind, we carried out experiments on intensity and pitch of voice signal on twenty male 20s in maintaining a constant humidity 30%, 50% and 80% of humidity. Finally, we carried out study to draw a significance through statistical analysis measuring characteristic parameter of vocal cord function to change of humidity.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.18 no.6
• /
• pp.19-26
• /
• 2014

A ground hot-firing test (HFT) was carried out to make a close examination into the pressure instability for the 70 N-class hydrazine thruster under development. Monopropellant grade hydrazine was adopted as a propellant for the HFT, and catalyst-bed was filled with $Ir/Al_2O_3$ catalyst. In order to investigate the effects of thrust-chamber diameter on combustion stability, evaluation tests for the development models were performed on three kinds of lower thrust chambers having the length-to-diameter ratio (L/D) of 1.03, 1.13, and 1.26. As results, it was found that low frequency instability (~ 50 Hz) was inherent in the models, and in addition, increase of the L/D and decrease of the operating pressure led to an amplification of pressure oscillation in the test condition specified.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 1997.11a
• /
• pp.10-11
• /
• 1997

고체 추진제를 사용하는 추진 시스템을 개발하는데 가장 커다란 문제로 인식되고 있는 것은 추진제의 연소 특성을 이해하는 일이다. 그 중에서도 연소실의 압력 진동과 추진제 벽면으로 흡수되는 복사 열전달에 의한 연소율(burning rate)의 변화로 인하여 발생하는 연소 불안정에 대한 이해는 아직도 완전히 규명되지 않고 있다. 고체 추진제의 연소 불안정에 대한 이론적 해석은 준-정상 1차원 해석(Quasi-Steady Homogeneous One-Dimension) 방법에 의하여 단순화된 지배방정식을 해석하는 것이 일반적으로 잘 알려져 있는 방법이다. 이 가정은 고체 추진제가 연수되는 영역을 두께가 매우 얇은 영역의 표면반응영역(surface reaction layer)과 화학반응이 없는 응축상태영역(condensed phase zone) 그리고 기체상태의 연료와 화염이 존재하는 기체상태영역(gas phase zone) 등의 3영역으로 구분하며, 기체상태영역에서 발생하는 교란에 대한 응축상태영역의 반응시간 크기(response time scale)가 매우 크기 때문에 응축상태영역의 반응은 준 정상적으로 일어난다고 가정하는 것이다.그러나, 연소실의 온도가 $3000^{\circ}K$ 정도의 높은 온도이어서 복사 열전달에 의한 고체 추진제의 가열이 중요한 열전달 방법으로 작용하게 되므로 이를 무시한 이론적 해석은 물리적인 중요성이 약하여질 수밖에 없다. 본 연구에서는 기체영역으로부터 전달되는 복사 열전달은 투명(transparent)한 표면반응영역을 통과하여 응축상태영역에서 모두 흡수되며 추진제 표면에서의 복사열방출(emission)을 고려하였다. 또한 연소불안정 현상을 해석하기 위하여 표면반응영역에서의 경계조건은 선형교란량으로 대치하는 Zn(Zeldovich-Novozhilov) 방법을 사용하였다. 이 방법은 기체상태영역에 대한 구체적인 해석없이도 연소불안정 현상을 해석할 수 있는 장점이 잇다. 즉 응축상태영역에서의 연소율과 표면온도는 각각 기체영역으로부터 전달되는 온도구배와 연소압력, 그리고 복사 열전달의 함수관계이므로 선형교란에 의한 추진제표면에서의 교란경계조건을 얻을 수 잇으며, 응축영역의 교란지배방정식과 함께 사용하여 압력교란과 복사 열전달의 교란에 대한 연소율의 교란 증감 여부를 판단하여 연소 불안정 현상을 해석할 수 있다.

• Journal of the Korea Society of Computer and Information
• /
• v.16 no.7
• /
• pp.77-84
• /
• 2011

The B$\'{e}$k$\'{e}$syaudiometry makes possible to determine not only hearing threshold but also assumption of recruit phenomenon. Additionally, it is helpful to investigate cause of hearing loss. In this paper, we describe a development of PC based B$\'{e}$k$\'{e}$syaudiometer which complies with ANSI standards and provides cost competitiveness. It dynamically produces sound having required frequency and sound pressure level and supports audiogram interface showing test result at realtime. To provide ANSI defined maximum sound level, an amplifier has been developed. We have been verified our system whether it conforms to ANSI standards.

• Journal of Biomedical Engineering Research
• /
• v.24 no.6 s.81
• /
• pp.501-507
• /
• 2003

Medical devices for helping the rehabilitation of the patients such as orthoses and prostheses should be designed to be strong enough. For the strength design, operational load should be identified first. Furthermore. medical devices are susceptible to dynamic load or shock frequently due to its characteristics. These type of the load may be identified by installing the sensors directly. However, it can modify the natural properties of the structures. Therefore, operational load should be identified indirectly from the system characteristics and responses such as vibrations. In this paper, the basic formulation of the indirect load identification is reviewed and the problems of conventional approach are checked. Then, the new approach based upon the principal component analysis is proposed and the validity of the proposed method is demonstrated using experiments.

• Journal of the Korean Magnetics Society
• /
• v.8 no.6
• /
• pp.357-361
• /
• 1998

For CoZr/Ag/CoCr trilayered films deposited by DC and FR magnetron sputtering method, ferromagentic resonance experiments have been used to investigate the dependence of the exchange coupling between CoZr and CoCr layers separated by Ag layer on the thickness of the Ag layer. The coupling strength K increases with increasing Ag thickness up to 10 $\AA$ with a maximum value of 748 Oe, but oscillates with increasing Ag thickness in the range from 20 to 100 $\AA$. The coupling strength is positive for all samples. Hence, it seems that the exchange coupling between CoZr and CoCr layers separated by Ag layer is ferromagnetic.

• Tribology and Lubricants
• /
• v.37 no.6
• /
• pp.261-272
• /
• 2021

This study investigates the structural characteristics of oil-free, gas beam foil journal bearings (GBFJBs) for use in high speed motors. Mathematical modeling was carried out, and reaction force modeling for static load was performed to predict the structural characteristics of the GBFJB. Mathematical modeling and reaction force modeling for static load are performed to predict the structural characteristics of GBFJBs. The reaction force of the test bearing against static loads was measured during experiments and compared with the predicted results. The measured experimental data reveal the nonlinear stiffness characteristics of the GBFJB against varying displacement and agree well with the predictions. Dynamic load tests using an exciter allow to identify the vibration characteristics of the GBFJB. Test results show that the vibration displacement, dynamic force, and acceleration measured on the test bearing are most dominant at the applied dynamic load (synchronization) frequency. Futhermore, the test results show that the hysteresis area recorded during the dynamic tests increases with the excitation amplitude and frequency, and that the beam stick phenomena occurr at high excitation frequencies. The single degree of freedom (DOF) vibration model aids to identify the stiffness and damping coefficient of the GBFJB, which decrease as the excitation frequency increases.

• The Journal of the Acoustical Society of Korea
• /
• v.40 no.6
• /
• pp.671-677
• /
• 2021

The present study aims to investigate the influence of the water to binder ratio of finishing mortar on the floor impact sound of apartments. For this, same resilient materials Expanded Polystyrene (EPS) with constant dynamic stiffness and different mortar layers with 52 %, 66 % and 72 % water to binder ratio respectively were used to build floating floor structures on which floor impact sounds were measured in standard testing facilities. As a result, it was found that light-weight floor impact sound was transmitted well when the water to binder ratio was 52% due to the high density. In case of heavy-weight floor impact sounds, since water to binder ratio of finishing mortar becomes higher as the weight of upper layer of resilient material lighter, it was shown that the natural frequency of floating floor structure moves to 63 Hz bandwidth which eventually cause a higher sound pressure level of floor impact sound. Thus, effect of water to binder ratio of mortar on the heavy-weight floor impact sounds was investigated.

• Journal of the Korean Geotechnical Society
• /
• v.22 no.1
• /
• pp.53-61
• /
• 2006

Soil liquefaction occurs by complex dynamic interaction between soil particles and pore fluid. Therefore, experimental researches have been widely performed to analyze liquefaction phenomena. In this research, centrifuge tests were performed to analyze the liquefaction behavior of horizontal sand ground. Centrifugal acceleration was 40g and the thickness of model ground was 25cm, which simulates 10m thickness in prototype scale. Viscous fluid was used as pore fluid to remove the time scaling difference between dissipation and dynamic shaking. Test results showed that the dissipation of excess pore pressure is the combined behavior of solidification and consolidation. In addition, the solidification rate, the ground acceleration amplitude, and the dynamic permeability during solidification were influenced by the confining pressure.