• 대한조선학회논문집
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• 제47권3호
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• pp.398-409
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• 2010

This paper considers the numerical computation of added resistance on ships in the presence of incident waves. As a method of solution, a higher-order Rankine panel method is applied in time domain. The added resistance is evaluated by integrating the second-order pressure on the body surface. Computational results are validated by comparing with experimental data and other computational results on a hemi-sphere, a barge, Wigley hull models, and Series 60 hull, showing very fair agreements. The study is extended to the comparison between Neumann-Kelvin and double-body linearization approaches, and their differences are discussed.

• 대한의용생체공학회:의공학회지
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• 제39권2호
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• pp.69-79
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• 2018

The present study proposes an algorithm that can discriminate between normal subjects and paroxysmal atrial fibrillation (PAF) patients, which is conducted using electrocardiogram (ECG) without PAF events. For this, time-domain features and random forest classifier are used. Time-domain features are obtained from Poincare plot, Lorenz plot of ${\delta}RR$ interval, and morphology analysis. Afterward, three features are selected in total through feature selection. PAF patients and normal subjects are classified using random forest. The classification result showed that sensitivity and specificity were 81.82% and 95.24% respectively, the positive predictive value and negative predictive value were 96.43% and 76.92% respectively, and accuracy was 87.04%. The proposed algorithm had an advantage in terms of the computation requirement compared to existing algorithm, so it has suggested applicability in the more efficient prediction of PAF.

• 한국해양공학회지
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• 제19권4호
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• pp.1-8
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• 2005

A nonlinear time-domain strip theory for vertical wave loads and ship responses is to be investigated. The hydrodynamic memory effect is approximated by a higher order differential equation without convolution. The ship is modeled as a non-uniform Timoshenko beam. Numerical calculations are presented for the S175 Containership translating with the forward speed in regular waves. The approach described in this paper can be used in evaluating ship motions and wave loads in extreme wave conditions and validating nonlinear phenomena in ship design.

• Wind and Structures
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• 제3권1호
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• pp.41-58
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• 2000

According to research currently developed by several authors (including the present ones) a multimode approach to the aeroelastic instability can be appropriate for suspension bridges with very long span and so with close natural frequencies. Extending that research, this paper deals in particular with: i) the role of along-wind modes, underlined also by means of the flutter mode representation; ii) the effects of a variation of the mean wind speed along the span. A characterisation of the response in the time domain by means of an energetic approach is also discussed.

• 한국군사과학기술학회지
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• 제11권4호
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• pp.159-165
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• 2008

The purpose of this paper is to study the impact of concentrated nonlinearities, freeplays, on the aeroelastic behaviors of single- and double-folded control fins. The nonlinearities may cause limit cycle oscillation(LCO) below the linear flutter boundary. The effects of nonlinear hinges on LCO characteristics of the fins are examined as flight condition changes. Nonlinear time-domain flutter analyses are performed, using ZAERO. The results show that the aeroelastic stability boundaries of double-folded fin(DF) are higher than those of the single-folded fin(SF) and the lower hinge freeplay impact more critically on the stability than the upper hinge freeplay of the DF.

• 한국소음진동공학회논문집
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• 제12권11호
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• pp.864-872
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• 2002

In this study, the effect of planform curvature on the stability of coupled flow/structure vibration is examined in transonic and supersonic flow regions. The aeroelastic analysis for the frequency and time domain is performed to obtain the flutter solution. The doublet lattice method(DLM) in subsonic flow is used to calculate unsteady aerodynamics in the frequency domain. For all speed range, the time domain nonlinear unsteady transonic small disturbance code has been incorporated into the coupled-time integration aeroelastic analysis (CTIA). Two curved wings with experimental data have been considered in this paper MSC/NASTRAN is used for natural free vibration analyses of wing models. Predicted flutter dynamic pressures and frequencies are compared with experimental data in subsonic and transonic flow regions.

• Advances in aircraft and spacecraft science
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• 제9권3호
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• pp.217-242
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• 2022

This paper proposes a novel time-domain homogenization model combining the viscoelastic constitutive law with Eshelby's inclusion theory-based micromechanics model to predict the mechanical behavior of the particle reinforced composite material. The proposed model is intuitive and straightforward capable of predicting composites' viscoelastic behavior in the time domain. The isotropization technique for non-uniform stress-strain fields and incremental Mori-Tanaka schemes for high volume fraction are adopted in this study. Effects of the imperfectly bonded interphase layer on the viscoelastic behavior on the dynamic mechanical behavior are also investigated. The proposed model is verified by the direct numerical simulation and DMA (dynamic mechanical analysis) experimental results. The proposed model is useful for multiscale analysis of viscoelastic composite materials, and it can also be extended to predict the nonlinear viscoelastic response of composite materials.

• Steel and Composite Structures
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• 제48권3호
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• pp.293-303
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• 2023

In this paper, geometrically nonlinear free vibration analysis of Mindlin viscoelastic plates with various geometrical and material properties is studied based on the Von-Karman assumptions. A novel solution is proposed in which the nonlinear frequencies of time-dependent plates are predicted according to the nonlinear frequencies of plates not dependent on time. This method greatly reduces the cost of calculations. The viscoelastic properties obey the Boltzmann integral law with constant bulk modulus. The SHPC meshfree method is employed for spatial discretization. The Laplace transformation is used to convert equations from the time domain to the Laplace domain and vice versa. Solving the nonlinear complex eigenvalue problem in the Laplace-Carson domain numerically, the nonlinear frequencies, the nonlinear viscous damping frequencies, and the nonlinear damping ratios are verified and calculated for rectangular, skew, trapezoidal and circular plates with different boundary conditions and different material properties.

• 한국음향학회지
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• 제39권3호
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• pp.216-225
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• 2020

본 논문은 음선 경로법에 기반한 광대역 수중음향 전달 채널을 모델링하는 방법을 다루었다. 수중음향 전달 채널은 종종 주파수 영역에서 시간 조화 함수로 취급되어, 광대역 시계열 신호 모의 시 활용이 어렵다. 따라서 수중 음파 전달 환경을 반영한 광대역 시간영역 모델링 기법이 요구되며, 본 논문에서는 이를 위해 시간영역에서 다중 경로의 도달 시간지연이 계산 가능한 고유 음선 분석 기법을 활용하였다. 또한 연속 시간의 파동방정식으로부터 산출된 고유 음선의 분석 결과를 컴퓨터 모의가 가능한 이산시간 시스템에 적용하기 위해, 음선의 위상, 주파수별 손실 및 도달 시간지연을 유한 임펄스 응답으로 근사하여, 광대역 수중음향 전달 채널을 모의하는 방법을 제안하였다.

• 한국전자파학회논문지
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• 제10권6호
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• pp.935-950
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• 1999

A multiresolution time-domain analysis scheme is derived for the analysis of microwave structures by using Haar wavelets to discretize the Maxwell's curl equation. This technique requires less computational effort than the conventional FDTD method because larger space grid can be used in the simulations. To validate this scheme, several 2-D·3-D microwave structures are simulated and the results are compared with those of the conventional FDTD scheme.