• Journal of Korean Association for Spatial Structures
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• v.12 no.1
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• pp.59-68
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• 2012

The space frame structure is one of the large span structural system consisting of longitudinal and latitudinal members. The members are connected in three dimension. A space frame structure has high stiffness with a structure resisting external forces in steric conformation. According to many structural conditions, structural stability problems in the space frame are determined and considered very important. This study seeks to understand the space frame collapse mechanism using the 2-free nodes truss model in order to examine static structural instability characteristics of the latticed dome. According to geometrical shape, the star dome, parallel lamella dome and three way grid dome were selected as models. The models were examined for characteristics of instability under STEP Excitations behavior according to rise-span ratio(${\mu}$) and shape imperfection.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.5
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• pp.23-29
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• 2008

This study investigates the dynamic instability of strength-limited bilinear single degree of freedom (SDF) systems under seismic excitation. The strength-limited bilinear hysteretic model best replicates the hysteretic behavior of the steel moment resisting frames. To estimate the dynamic instability of SDF systems, the collapse strength ratio is used, which is the yield-strength reduction factor when collapse occurs. Statistical studies are carried out to estimate median collapse strength ratios and those dispersions of strength-limited bilinear SDF systems with given natural periods, hardening stiffness ratios, post-capping stiffness ratios, ductility and damping ratios ranging from 2 to 20% subjected to 240 earthquake ground motions recorded on stiff soil sites. Equations to calculate median and standard deviation of collapse strength ratios in strength-limited bilinear SDF systems are obtained through nonlinear regression analysis. By using the proposed equations, this study estimated the probabilistic distribution of collapse strength ratios, and compared this with the exact values from which the accuracy of the proposed equations was verified.

• Journal of Korean Society of Steel Construction
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• v.12 no.6
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• pp.737-748
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• 2000

This paper presents a numerical analysis procedure and a characteristics for dynamic of cylindrical panels. The panels with simply-simply or simply-clamped edge supports are subjectes to circumferential compressive or flexural stresses. The differential equations governing vibration and dynamic for these panels are derived by using the fundamental differential equation of the Love-Timoshenko and are solved numerically by the Galerkin method. The panel with simply-clamped edge supports is used a trigonometric function or an eigen function of a beam as a trial function and the effects of trial functions on numerical solutions are displayed. Numerical results are presented to demonstrate the effects of the flexural parameters in natural frequencies and coefficients of critical buckling, and some typical mode shapes of vibration and buckling are also presented.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.6
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• pp.98-106
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• 2011

This paper reviews the state-of-the-art thermoacoustic(TA) modeling techniques and research trend to predict major parameters determining combustion instabilities in lean premixed gas turbine combustors. Linear TA modeling results give us an information on eigenfrequencies and initial growth rate of the instabilities. For the prediction, linear relation equation between acoustic waves and heat release oscillations should be derived in the determined system. Key information for this analysis is to determine the heat release fluctuations in the combustor, which is typically obtained by using n-${\tau}$ function from flame transfer function measurements and/or predictions. Great advancement in the linear TA modeling has been made over a couple of decades, and some successful prediction results have been reported in actual gas turbine combustors. However nonlinear TA model developments which are required to analyze nonlinear system behaviors such as limit cycle saturation and transition phenomena are still limited in a very simple system. In order to fully understand combustion instabilities in a complicated real system, nonlinear flame dynamics and acoustic wave interaction with nonlinear system boundary conditions should be explained from the nonlinear TA model developments.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.10a
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• pp.51-56
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• 2001

공작기계로 금속을 절삭할 때 공작기계의 불안정, 즉 자려진동의 발생은 절삭과정과 공작기계구조 두 요소의 동적 거동에 기인한다. 공작기계의 채터와 구조의 동적인 거동은 모든 금속가공에서 가공물의 표면조도와 공구수명, 공작기계의 수명에 큰 영향을 미친다. 이와 같은 채터와 동적인 거동을 해석함으로써 최적의 절삭 조건을 결정할 수 있으나, 이러한 연구에서 가장 어려운 점은 기계구조와 절삭과정이 폐회를 구성하고 있기 때문이다.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.665-670
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• 2000

The paper presents the dynamic instability of a disc brake pad subjected to distributed friction forces. A brake pad can be modeled as a beam with two translational springs. The study of this prototypical model is intended to provide a fundamental understanding of disc brake pad instabilities. Governing equations of motion are derived form energy expressions and their corresponding solutions are obtained by employing the finite element method. The critical distributed friction force and the instability regions are demonstrated by changing two translational spring constants. Finally, the changes of eigen-frequencies of a beam determining instability types are investigated for various combinations of two spring constants.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.121-124
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• 2008

This paper presents experimental results of dynamic characteristics of fuel-rich gas generators. Pressure fluctuation measurements in the chamber and manifolds have been analyzed. Gas-generator-alone tests revealed stable combustion regardless of a chamber pressure but low-frequency combustion instabilities occurred for cases of turbine-manifold tests at chamber pressure conditions below 50 bar. The instabilities are considered as an axial resonant mode and acoustic intensity increases along with a chamber pressure.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.10
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• pp.140-147
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• 1998

The dynamic behavior of elastically restrained beams under the action of distributed tangential forces is investigated in this paper. The beam, which is fixed at one end, is assumed to rest on an intermediate spring support. The governing equations of motion are derived from the energy expressions, and the finite element formulation is employed to calculate the critical distributed tangential force. Jump phenomena for the critical distributed tangential force and instability types are presented for various spring stiffnesses and support positions. Stability maps are generated by performing parametric studies to show how the distributed tangential forces affect the frequencies and the stability of the system considered. Through the numerical simulations, the following conclusioils are obtained: (i) Only flutter type instability exists for the dimensionless spring stiffness K $\leq$ 97, regardless of the position of the spring support. (ii) For the dimensionless spring stiffness K $\leq$ 98, the transition from flutter to divergence occurs at a certain position of the spring support, and the transition position moves from the free end to the free end of the beam as the spring stiffness increases. (iii) For K $\leq$ 10$^{6}$ the support condition can be regarded as a rigid support condition.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.1957-1963
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• 2015

The purpose of this study is to examine the effect of dynamic stabilization exercise on unstable surface on thickness, muscle density and white area index (WAI) of transverse abdominis muscle and multifidus muscle. The subjects were 20s healthy adults and 27 people were measured for muscle thickness and muscle density, white area index after the experiment conducted during a six-week dynamic stabilization exercises divided into three groups, each in a different plane. The results showed a significant difference between the three groups (p <.05). Repeated measures analysis of variance (repeated ANOVA) results, transverse abdominis muscle and multifidus muscle thickness showed a significant difference between the groups in the time difference (p <.05), and between multifidus muscle density and white area index in the comparison between groups showed a significant difference (p <.05). In conclusion, showed significant difference in lumbar stabilization exercise part. These results seems to be utilized as a basis for future research on the lumbar stabilization exercise.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.259-261
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• 2005

기존 계통 안정도 평가와 제어의 방법은 전체 계통의 데이터를 취득한 후 평가하고 제어하는 방식으로 이루어져왔다. 하지만 이 방식은 계산 효율 측면과 통신상의 문제로 인해 신뢰성 측면에서 문제가 있다 더욱이 긴급한 상황에서 전압 불안정을 판단하기에는 많은 문제점이 발생한다. 이러한 문제를 해결하기 위하여 PMU(Phase Measurement Unit)와 같은 측정 장치에서 제공하는 지역정보를 이용한 VIP(테브난 임피던스와 부하 임피던스의 비교 분석하여 제어하는 방법)가 제시되었다. 본 논문에서는 VIP 알고리즘을 이용한 전압 불안정 현상 모의를 실시간 Digital Simulator (Hypersim)를 이용하여 계통을 분석하였다. Hypersim에서는 실제 계통과 유사한 모의를 통해 동적 모의가 가능케 하고 있다. 이것은 동안 실효치 데이터를 기반으로 하는 시간 모의에서 벗어나 실제 계통과 같이 순시치 데이터를 가지고 실제 상황처럼 모의 분석할 수 있는 것이다.