• Title/Summary/Keyword: Non-linear Coupling

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DYNAMICAL AND STATISTICAL ASPECTS OF GRAVITATIONAL CLUSTERING IN THE UNIVERSE

  • SAHNI V.
    • Journal of The Korean Astronomical Society
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    • v.29 no.spc1
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    • pp.19-21
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    • 1996
  • We apply topological measures of clustering such as percolation and genus curves (PC & GC) and shape statistics to a set of scale free N-body simulations of large scale structure. Both genus and percolation curves evolve with time reflecting growth of non-Gaussianity in the N-body density field. The amplitude of the genus curve decreases with epoch due to non-linear mode coupling, the decrease being more noticeable for spectra with small scale power. Plotted against the filling factor GC shows very little evolution - a surprising result, since the percolation curve shows significant evolution for the same data. Our results indicate that both PC and GC could be used to discriminate between rival models of structure formation and the analysis of CMB maps. Using shape sensitive statistics we find that there is a strong tendency for objects in our simulations to be filament-like, the degree of filamentarity increasing with epoch.

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Numerical analysis of the vortex induced vibration of the 2-D cylinder using dynamic deforming mesh (동적격자변형기법을 이용한 2차원 실린더의 와류유발진동에 대한 수치해석)

  • Lee, Namhun;Baek, Jiyoung;Lee, Seungsoo
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.41 no.1
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    • pp.1-9
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    • 2013
  • In this paper, numerical simulations are performed on the lock-in phenomena of vortex induced vibration(VIV) of a two dimensional cylinder. A deforming grid as well as a rigidly moving grid are used to simulate the movement of the cylinder. The grid deformation is accomplished by the linear spring analogy. Converged solutions, which are obtained by controling the grid size and the non-dimensional time step, are used for comparison and validation of the analysis results. Moreover, the efficiency and the accuracy of the coupling methods for fluid-structure interaction are examined.

Study on Steady Flow Effects in Numerical Computation of Added Resistance of Ship in Waves

  • Lee, Jae-Hoon;Kim, Beom-Soo;Kim, Yonghwan
    • Journal of Advanced Research in Ocean Engineering
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    • v.3 no.4
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    • pp.193-203
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    • 2017
  • This study investigated the steady-flow effects present in the numerical computation of the resistance added to a ship in waves. For a ship advancing in the forward direction, a time-domain 3D Rankine panel method is applied to solve the ship motion problem, and the added resistance due to waves is calculated using a near-field method, with the direct integration of the second-order pressure on the hull surface. In the linear potential theory, the steady flow is approximated by the basis potential of a uniform flow or double-body flow in order to linearize the boundary conditions. By applying these two different linearization schemes, the coupling effects between steady and unsteady solutions were examined. Furthermore, in order to analyze the steady-flow effects on the hull geometry, the computation results for two realistic hull forms, a KVLCC2 tanker and DTC containership, were compared. In particular, the mj term, which represents the coupling effects under the body boundary condition, was evaluated considering the geometry of a non-wall-sided ship. Lastly, the characteristics of the linearization schemes were examined in relation to the disturbed waves around a ship and the components of added resistance.

Forced Vibration and Loads Analysis of Large-scale Wind Turbine Blades Considering Blade Bending and Torsion Coupling (굽힘 및 비틀림 연성 효과를 고려한 대형 풍력 터빈 블레이드의 강제 진동 및 하중 해석)

  • Kim, Kyung-Taek;Park, Jong-Po;Lee, Chong-Won
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2008.11a
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    • pp.256-263
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    • 2008
  • The assumed modes method is developed to derive a set of linear differential equations describing the motion of a flexible wind turbine blade and to propose an approach to investigate the forced responses result from various wind excitations. In this work, we have adopted Euler beam theory and considered that the root of the blade is clamped at the rigid hub. And the aerodynamic parameters and forces are determined based on Blade Element Momentum (BEM) theory and quasi-steady airfoil aerodynamics. Numerical calculations show that this method gives good results and it can be used fur modeling and the forced vibration analysis including the coupling effect of wind-turbine blades, as well as turbo-machinery blades, aircraft propellers or helicopter rotor blades which may be considered as straight non-uniform beams with built-in pre-twist.

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Compensation of the secondary voltage of a coupling capacitor voltage transformer in the time-domain (히스테리시스 특성을 고려한 CCVT 2차 전압 보상 방법)

  • Kang, Yong-Cheol;Zheng, Tai-Ying;Kim, Yeon-Hee;Jang, Sung-Il;Kim, Yong-Gyun
    • Proceedings of the KIEE Conference
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    • 2006.07a
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    • pp.266-267
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    • 2006
  • A coupling capacitor voltage transformer (CCVT) is used in extra high voltage and ultra high voltage transmission systems to obtain the standard low voltage signal for protection and measurement. To obtain the high accuracy at the power system frequency, a tuning reactor is connected between a capacitor and a voltage transformer (VT). Thus, no distortion of the secondary voltage is generated when no fault occurs. However, when a fault occurs, the secondary voltage of the CCVT has some errors due to the transient components resulting from the fault. This paper proposes an algorithm for compensating the secondary voltage of the CCVT in the time domain. With the values of the secondary voltage of the CCVT, the secondary and the primary currents are obtained; then the voltage across the capacitor and the tuning reactoris calculated and then added to the measured secondary voltage. The proposed algorithm includes the effect of the non-linear characteristic of the VT and the influence of the ferro-resonance suppression circuit. Test results indicate that the algorithm can successfully compensate the distorted secondary voltage of the CCVT irrespective of the fault distance, the fault inception angle and the fault impedance.

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Nonlinear thermal buckling behavior of functionally graded plates using an efficient sinusoidal shear deformation theory

  • Bouiadjra, Rabbab Bachir;Bedia, E.A. Adda;Tounsi, Abdelouahed
    • Structural Engineering and Mechanics
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    • v.48 no.4
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    • pp.547-567
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    • 2013
  • Nonlinear behavior of functionally graded material (FGM) plates under thermal loads is investigated here using an efficient sinusoidal shear deformation theory. The displacement field is chosen based on assumptions that the in-plane and transverse displacements consist of bending and shear components, and the shear components of in-plane displacements give rise to the sinusoidal distribution of transverse shear stress through the thickness in such a way that shear stresses vanish on the plate surfaces. Therefore, there is no need to use shear correction factor. Unlike the conventional sinusoidal shear deformation theory, the proposed efficient sinusoidal shear deformation theory contains only four unknowns. The material is graded in the thickness direction and a simple power law based on the rule of mixture is used to estimate the effective material properties. The neutral surface position for such FGM plates is determined and the sinusoidal shear deformation theory based on exact neutral surface position is employed here. There is no stretching-bending coupling effect in the neutral surface-based formulation, and consequently, the governing equations and boundary conditions of functionally graded plates based on neutral surface have the simple forms as those of isotropic plates. The non-linear strain-displacement relations are also taken into consideration. The thermal loads are assumed as uniform, linear and non-linear temperature rises across the thickness direction. Closed-form solutions are presented to calculate the critical buckling temperature, which are useful for engineers in design. Numerical results are presented for the present efficient sinusoidal shear deformation theory, demonstrating its importance and accuracy in comparison to other theories.

The Effect of Fluid-Structure Interaction on the Dynamic Response of Reactor Internals (유체-구조물 상호작용이 원자로내부구조물의 동적응답에 미치는 영향)

  • 정명조;박찬국;황원걸
    • Computational Structural Engineering
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    • v.6 no.4
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    • pp.73-82
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    • 1993
  • Investigated in this paper is the effect of fluid-structure interaction between reactor internal components due to their immersion in a confining fluid on the dynamic responses. A non-linear mathematical model is developed for the dynamic analysis of the reactor internals, which includes lumped masses, stiffnesses and hydrodynamic couplings. The hydrodynamic mass matrix which characterizes the fluid-structure interaction is calculated. Also, the equations of motion containing hydrodynamic mass matrix are presented. The responses of the reactor internals due to seismic and pipe break excitations are obtained for the case of with- and without-hydrodynamic couplings and the different response characteristics are investigated.

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Definition of Power Quality Factors at The Point of Common Coupling in Single-Phase Systems and Three-Phase Systems

  • Kim Hyosung;Blaabjerg Frede;Bak-Jensen Birgitte
    • Proceedings of the KIPE Conference
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    • 2001.10a
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    • pp.489-496
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    • 2001
  • This paper proposes an unified definition of powers for various circuit conditions such as balanced/unbalanced, sinusoidal/non-sinusoidal, and linear/nonlinear, for single-phase systems and three-phase systems. Conventional reactive power is more classified into an interactive power and a scattering power. These powers are defined both in the time domain and the frequency domain consistently, and agree well with the conservation law. Several important power quality factors are defined to measure and evaluate the power quality for the various circuits in the single-phase and three-phase systems. Simulation results show the power quality factors can evaluate and classify the various circuit conditions clearly.

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A bicoherence analysis of EEG during Yes/No decision task (긍/부정 문답 과제 수행시 뇌파의 바이코히어런스 분석)

  • 남승훈;류창수;임태규;송윤선;유창용
    • Proceedings of the Korean Society for Emotion and Sensibility Conference
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    • 2003.05a
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    • pp.115-119
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    • 2003
  • 본 연구는 인간에 있어서 가장 간단한 의사라고 여겨지는 긍정과 부정 응답에 대해 나타나는 뇌파의 변화를 잘 반영하는 특징을 찾아내고자 하기 위한 것이다. 고차 통계적 방법(high order statical analysis)인 바이스펙트럼(bispectrum)은 뇌파의 다른 부위와 다른 주파수 사이의 비선형위상커플링(non-linear phase coupling)을 잘 반영하므로, 이를 이용하여 긍정이나 부정을 선택할 때 나타나는 뇌파를 분석하였다. 분석결과, 반응 전 1.25초∼0.5초 에 유의미한 차이를 보였다. 긍정과 부정 응답에 대한 뇌파의 주파수와 부위를 찾아 신경회로망의 입력으로 사용하여 긍정과 부정 응답에 대해 분별하였다. 2번의 뇌파실험에서 각각 실험 데이터에 대해서는 긍/부정 차이가 존재하지만 공통적인 특징이 나타나지는 않았다.

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Response Characteristics Of Steel Frame Structuresw With Added Elastic Dampers (탄성 댐퍼가 추가된 대형철골 구조물의 응답특성)

  • Bae, Chun-Hee;Cho, Cheul-Whan;Yang, Kyeong-Hyeon;Park, Young-Pil
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2002.11b
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    • pp.593-598
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    • 2002
  • Coupling adjacent steel frame using elastic dampers for control of response to low and moderate dynamic event is investigated in this paper. The complex modal superposition method is first used to determine dynamic characteristic, mainly modal damping ratio and modal frequency, of damper linked linear adjacent steel frame for fractical use. Dynamic response of steel frame linked by hydraulic-excitation method. This combined method can efectively and accurately determine dynamic response of non-clasically damped systems in the frequency domain. Parametric studties are finally performed to identify optimal parameters of elastic dampers for achieving the maximum modal damping ratio or the maximum response reduction of steel frame. It is demonstrated that using discrete elasatic dampers of proper parameters to link steel frame can reduce dynamic response significantly.

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