• The Journal of the Acoustical Society of Korea
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• 제21권4E호
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• pp.164-169
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• 2002

This paper proposes a hybrid method for vibration analysis in the medium to high frequency ranges using Power Flow Analysis (PFA) algorithm and Statistical Energy Analysis (SEA) coupling concepts. The main part of the developed method is the application of coupling loss factor (CLF) suggested in SEA to the power transmission, reflection coefficients in PI' A boundary conditions. The developed hybrid method shows very promising results with regard to the applications for the various damping loss factors in wide frequency ranges. And also this paper presents the applied results of Power Flow Finite Element Method (PFFEM) by forming the new joint element matrix with CLF to analyze the various plate structures in shape. The analytical results of automobile, complex plate structures show good agreement with those of PFFEM using the PFA coefficients.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.19-22
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• 2001

This paper proposes a double cantilever sandwich-beam method for evaluating the frequency dependence of material dynamic characteristics. The flexural vibration of a double cantilever sandwich-beam specimen with a partially inserted rubber layer was studied using a finite element simulation in combination with the sine-sweep test. Quadratic relationships of dynamic elastic modulus and material loss factor of rubbers with frequency were quantitatively suggested employing the least square error method.

• 한국음향학회지
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• 제21권4호
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• pp.164-164
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• 2002

This paper proposes a hybrid method for vibration analysis in the medium to high frequency ranges using Power Flow Analysis (PFA) algorithm and Statistical Energy Analysis (SEA) coupling concepts. The main part of the developed method is the application of coupling loss factor (CLF) suggested in SEA to the power transmission, reflection coefficients in PI' A boundary conditions. The developed hybrid method shows very promising results with regard to the applications for the various damping loss factors in wide frequency ranges. And also this paper presents the applied results of Power Flow Finite Element Method (PFFEM) by forming the new joint element matrix with CLF to analyze the various plate structures in shape. The analytical results of automobile, complex plate structures show good agreement with those of PFFEM using the PFA coefficients.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 춘계 학술발표회 논문집
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• pp.373-382
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• 2002

In this paper, the characteristic dependencies of LRB(lead rubber bearing) were studied by various prototype tests on LRB for buildings. The characteristics of LRB were dependent on displacements, repeated cycles, frequencies, vertical pressures and temperatures. The prototype test showed that the displacement was the most governing factor influencing on characteristics of LRB. The effective stiffness and equivalent damping of LRB were decreased with large displacement, and increased with high frequency. After the repeated cyclic test with 50 cycles, the effective stiffness and equivalent damping of LRB were reduced by approximately 20% compared with those of the 1$^{st}$ cycle. The effective stiffness was decreased with high vertical pressure, while the equivalent damping was increased. In which, the equivalent damping was more dependent on the vertical pressure than the effective stiffness.s.

• 대한기계학회논문집B
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• 제28권8호
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• pp.945-952
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• 2004

Acoustic characteristics of combustion chamber having various baffle configurations are numerically investigated by linear acoustic analysis to suggest reliable baffle specifications in first stage of KSLV-I. To determine the configuration of baffles, an acoustic modal analysis as well as the macroscopic analysis has been done. Hub has another effect of suppressing transverse acoustic mode by confining flow in baffled compartment over general effect of increase in acoustic damping of radial acoustic modes. So, a sufficient number of hub needs to be installed to obtain acoustic damping capacity. 3-blade configuration designed to suppress the first tangential mode has relatively low damping capacity, compared to 5 or 6-blade one. Optimum value of axial baffle length has been determined by comparing acoustic characteristics of combustion chamber having various baffle lengths.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.259-262
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• 2002

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 various specifications of these devices. Next, the unbaffled chambers with/without acoustic cavities are tested experimentally for several operating conditions. The unbaffled chamber shows the specific stability characteristics depending on the operating condition and has small dynamic stability margin. The most hazardous frequency is clearly identified through Fast Fourier Transform. 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. Thrust loss caused by baffle installation is about $2{\%}$.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.1404-1408
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• 2006

In this paper, a hybrid-type vibration isolator which has air chamber(spring) and viscous damper in series is developed. The developed vibration isolator is designed to perform 3 following functions : spring function for normal operating conditions, damping function to reduce an impact for sudden move of upper beam, and finally leveling function. Based on the given natural frequency and damping factor, the design procedure is proposed. The performance of the developed isolator is tested by measuring stiffness and damping.

• 동력기계공학회지
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• 제22권1호
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• pp.87-93
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• 2018

Specimens were machined out from hot-rolled AZ31 magnesium alloy, and deformed at 623K with rolling reduction of 30%. After hot rolling, specimens were annealed at various range of temperature and time. In this study, static recrystallization was occurred during heat treatment, however, variation of main component and intensity of texture was not revealed. The results of microstructure observation, damping capacity test and dislocation mechanism indicated that increasing of damping capacity was caused by grain growth. It means that grain size is effective factor to damping capacity.

• 임산에너지
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• 제17권1호
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• pp.36-46
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• 1998

이 연구는 점탄성 고분자재료를 사용하여 진동·충격음 흡수성능을 지니는 목질계 복합재료의 제조를 목적으로, 가소화 PVC의 동적점탄성 및 고분자 적층 복합체의 진동흡수성능에 미치는 고분자의 점탄성의 영향을 검토하였다. 가소제는 디옥틸프탈레이트(DOP)를 사용하여, 20∼140 phr까지 첨가하였다. 고분자의 동적점탄성의 측정은 Rheovibron을 사용하여 110Hzdml 인장진동을 가하여, -100∼150℃까지 매분 1℃를 상승시키면서 측정하였다. PVC와 DOP는 전조성에서 완전상용성이었으며, T(E"max)와 T(tan δmax)는 가소제의 첨가량이 증가함에 따라 저온 측으로 이동하였다. 고분자 적층 복합체의 진동흡수성능은 Rheovibron을 개조한 양단지지 중심하중에 의한 강제 휨진동법 및 공진법에 하나인 양단자유 휨진동법을 사용하였다. 샌드위치구조 복합체의 진동흡수계수(tanδc)는 고분자의 손실계수(tanδ)와 정의 상관성을 나타내었으며, 피복체의 진동흡수계수는 고분자의 손실탄성률(E")에 의존하는 경향을 나타내었다. 또한 샌드위치구조 복합체의 대수감쇠율(Δc)은 tanδc곡선과 유사한 곡선을 나타내었다.

• 대한기계학회논문집B
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• 제41권3호
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• pp.171-181
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• 2017

2상 횡 유동은 응축기, 증발기와 원자력의 증기 발생기와 같은 열교환기의 튜브와 셀 사이에 존재한다. 공기/물의 2상 유동에 놓인 관군에 작용하는 항력을 실험적으로 평가하였다. 2상 유동에 놓인 관군은 정사각형 배열이다. 피치 직경 비는 1.35이었고, 실린더의 직경은 18 mm이다. 관군에 유동방향으로 작용하는 항력을 측정하여 항력계수와 2상 유동 감쇠비를 계산하였다. 2상 유동 감쇠비는 균질 2상 유동의 이론식을 사용하여 구하여 실험의 결과와 비교하였다. 압력과 항력의 상관계수를 실험결과를 고려하여 평가하였다. 상관계수는 이론적으로 항력을 계산할 때에 사용된다. 질량유량을 증가할수록 측정된 항력으로부터 구한 항력계수와 감쇠비가 균질 유동의 이론적 결과와 잘 일치함을 보이고 있다. 결과적으로 충분히 큰 질량 유량의 기포 유동인 경우에는 감쇠비를 균질 유동에 근거한 이론식으로 계산할 수 있다.