• Journal of the Computational Structural Engineering Institute of Korea
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• 제20권6호
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• pp.789-799
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• 2007

In this paper, we propose a stochastic finite element formulation which takes into account the randonmess in the material and geometrical parameters. The formulation is proposed for plate structures, and is based on the weighted integral approach. Contrary to the case of elastic modulus, plate thickness contributes to the stiffness as a third-order function. Furthermore, Poisson's ratio is even more complex since this parameter appears in the constitutive relations in the fraction form. Accordingly, we employ Taylor's expansion to derive decomposed stochastic field functions in ascending order. In order to verify the proposed formulation, the results obtained using the proposed scheme are compared with those in the literature and those of Monte Carlo analysis as well.

• Journal of Ocean Engineering and Technology
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• 제37권3호
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• pp.81-88
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• 2023

Maneuverability is a crucial factor for the safety and success of submarine missions. This paper introduces a mathematical model that considers the large drift and angle of attack motions of submarines. Various computational fluid dynamics (CFD) simulations were performed to adapt Karasuno's fishery vessel maneuvering mathematical model to submarines. The study also presents the procedure for obtaining the physics-based hydrodynamic coefficients proposed by Karasuno through CFD calculations. Based on these coefficients, the reconstructed forces and moments were compared with those obtained from CFD and to the hydrodynamic derivatives expressed by a Taylor expansion. The study also discusses the mathematical maneuvering model that accounts for the large drift angles and angles of attack of submarines. The comparison results showed that the proposed maneuvering mathematical model based on modified Karasno's model could cover a large range of motions, including horizontal motion and vertical motions. In particular, the results show that the physics-based mathematical maneuvering model can represent the forces and moments acting on the submarine hull during large drift and angle of attack motions. The proposed mathematical model based on the Karasuno model could obtain more accurate results than the Taylor third-order approximation-based mathematical model in estimating the hydrodynamic forces acting on submarines during large drift and angle of attack motions.

• The Bulletin of The Korean Astronomical Society
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• 제39권2호
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• pp.78.1-78.1
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• 2014

An ionization front (IF) surrounding an H II region is a sharp interface through which a cold neutral gas makes transition to a warm ionized phase by absorbing UV photons from central massive stars. We investigate the structure and instability of a plane-parallel D-type IF threaded by magnetic fields parallel to the front. We find that magnetic fields increase the maximum propagation speed of the IFs, while reducing the expansion factor, defined as the density ratio of neutral to ionized phases. IFs become unstable to distortional perturbations due to gas expansion across the fronts, exactly analogous to the Darrieus-Landau instability of ablation fronts in terrestrial flames. The growth rate of the IF instability is proportional linearly to the perturbation wavenumber as well as the upstream flow speed. The IF instability is stabilized by gas compressibility and becomes completely quenched when the front is D-critical. The instability is also stabilized by magnetic pressure when the perturbations propagate in the direction perpendicular to the fields. When the perturbations propagate in the direction parallel to the fields, on the other hand, it is magnetic tension that reduces the growth rate, completely suppressing the instability when ${\beta}$ < 1.5, with ${\beta}$ denoting the square of the ratio of the sound speed to the Alfven speed in the pre-IF region. When the front experiences an acceleration, the IF instability cooperates with the Rayleigh-Taylor instability to make the front more unstable. We discuss potential effects of IF instability on the evolution and dynamics of IFs in the interstellar medium.

• Journal of the Optical Society of Korea
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• 제2권2호
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• pp.74-79
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• 1998

The use of a fiber Fabry-Perot interferometer (FFPI) as an optical current transducer is demonstrated. A conventional inductive pickup coil converts the time-varying current I(t) being measured to a voltage waveform V(t) applied across a piezeolectric strip to which the FFPI is bonded. The strip experiences a longitudinal expansion and contraction, resulting in an optical phase shift ${\phi}(t)$ in the fiber proportional to V(t). This phase shift is measured using a frequency-modulated semiconductor light source, photodiodes to monitor the reflected light from the FFPI and the laser power, and a digital signal processor. Calibration routines compute V(t) and I(t) from the measured phase shift at a l KHz rate. Response to 60 Hz ac over the design range 0-1300A rms is characterized Transient response of the FFPI transducer is also measured.

• Transactions of the Korean Society of Automotive Engineers
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• 제12권2호
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• pp.131-138
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• 2004

In the proto design stage of a new car, the performances of an occupant protection system can be evaluated by CAE even though the real test should be carried out. The number of the real test is reduced by the exact predictions followed by the appropriate design recommendation. However, the existing researches using CAE in predicting the performances do not consider the uncertainties of parameters. That often leads to inconsistency between test and CAE. In this research, the robust design of a protection system such as airbag and load limiter is suggested considering the frontal crash. The parameter design scheme of the Taguchi method is introduced to obtain the robust design of arbitrary airbag and load limiter. It is performed based on the frontal crash test condition of US-NCAP with an arbitrary passenger car. The variances of the performances such as HIC, chest acceleration and probability of combined injury are calculated by the outer array and the Taylor series expansion. Through the analysis of the Taguchi method, the robust optimum is determined.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2009년도 추계학술대회 논문집
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• pp.113-118
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• 2009

A designer regards the vibration system as a linear system. However, in real world, nonlinearity of a vibration system should exist caused by various factors like manufacturing conditions or uncertain material properties. So, properties of a spring and a damper which are consisting the vibration system have statistical distribution. Therefore, a designer needs to analyze the statistical nonlinearity in a vibration system. In this paper, $1^{st}$ Taylor series expansion method and univariate dimension reduction method apply to a performance measure of nonlinear vibration system, and compare each result. And then, merits and demerits of each method are discussed. For apply more actual problem, a performance measure population is estimated based on design variable samples like properties of spring or damper.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.2-7
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• 2008

A highly efficient moving least squares finite difference method (MLS FDM) for heat transfer analysis of composite material with interface. In the MLS FDM, governing differential equations are directly discretized at each node. No grid structure is required in the solution procedure. The discretization of governing equations are done by Taylor expansion based on moving least squares method. A wedge function is designed for the modeling of the derivative jump across the interface. Numerical examples showed that the numerical scheme shows very good computational efficiency together with high aocuracy so that the scheme for heat transfer problem with different heat conductivities was successfully verified.

• Proceedings of the KIEE Conference
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• 대한전기학회 1991년도 추계학술대회 논문집 학회본부
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• pp.35-38
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• 1991

Recent, problems on the voltage-instability have been paid attention in power system and methods to find the limit of voltage-stability, concerned with these problems, were developed. However, these methods are short of precision on the limit of voltage-instability. Here, using the second-order load flow, constraint equation(d Pi/d Vi=0) and its patial differentiations are precisely formulated. Also, since the taylor series expansion of power flow equations terminates at the second-order terms, partial differentiations of constraint equation, that is Hessian, are constant. Then, Hessian matrix are calculated once during iteration process.

• International Journal of Aeronautical and Space Sciences
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• 제13권2호
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• pp.199-209
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• 2012

An advanced aeroelastic formulation for flutter analyses is presented in this paper. Refined 1D structural models were coupled with the doublet lattice method, and the g-method was used for flutter analyses. Structural models were developed in the framework of the Carrera Unified Formulation (CUF). Higher-order 1D structural models were obtained by using Taylor-like expansions of the cross-section displacement field of the structure. The order (N) of the expansion was considered as a free parameter since it can be arbitrarily chosen as an input of the analysis. Convergence studies on the order of the structural model can be straightforwardly conducted in order to establish the proper 1D structural model for a given problem. Flutter analyses were conducted on several wing configurations and the results were compared to those from literature. Results show the enhanced capabilities of CUF 1D in dealing with the flutter analysis of typical wing structures with high accuracy and low computational costs.

• Journal of the Korean Society for Precision Engineering
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• 제21권1호
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• pp.173-180
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• 2004

This paper presents the effect of varying boundary conditions such as ground subsidence, internal pressure and temperature variation for buried pipelines on failure prediction by using a failure probability model. The first order Taylor series expansion of the limit state function incorporating with von-Mises failure criteria is used in order to estimate the probability of failure mainly associated with three cases of ground subsidence. Using stresses on the buried pipelines, we estimate the probability of pipelines with von-Mises failure criterion. The effects of varying random variables such as pipe diameter, internal pressure, temperature, settlement width, load for unit length of pipelines, material yield stress and pipe thickness on the failure probability of the buried pipelines are systematically studied by using a failure probability model for the pipeline crossing ground subsidence regions which have different soil properties.