• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.20 no.5
• /
• pp.629-640
• /
• 2007

In this paper an analytical study is carried out to improve the capacity of absorbing boundary using dashpot, one of the most widely used absorbing boundaries in FEM. Using 2-D harmonic plane wave equation, absorbing boundary condition is modified to maximize its capacity according to the incident angle. Validity of the absorbing boundary conditions which is modified is investigated by adopting the solution of Miller and Pursey. The Miller and Pursey's problem is then numerically simulated using the finite element method. The absorption ratios are calculated by comparing the displacements at the absorbing boundary to those at the free field without the absorbing boundary. The numerical study is carried out through comparison of displacement at the interior region and the boundary of the numerical model.

• Journal of Korean Philosophical Society
• /
• v.117
• /
• pp.399-418
• /
• 2011

Die vorliegende Untersuchung zielt darauf ab, erstens die Entstehung der $Fr{\ddot{u}}hromantik$ in Bezug auf damalige Kantkritik zu betrachten, zweites Jacobis Gedanke, der die Bewegung der $Fr{\ddot{u}}hromantik$ $ansto{\ss}t$, mittels seines Zentralbegriffs "Unbedingtes" und "$Gef{\ddot{u}}hls$" zu rekonstruieren und drittens den Kerngedanke der $Fr{\ddot{u}}hromantik$, der die unendliche $Ann{\ddot{a}}herung$ betont, durch Novalis zu $erl{\ddot{a}}utern$. $F{\ddot{u}}r$ Jacobi wird das Unbedingte als "Glaube" angesehen, weil es nicht nur der $M{\ddot{o}}glichkeitsgrund$ des Wissens ist, sondern die Vermittlung des Wissens ${\ddot{u}}berschreitet$. $W{\ddot{a}}hrend$ es die Bedingung des Wissens ist, ist es das "Sein", das den Bereich des $Bewu{\ss}tseins$ transzendiert. Somit Jacobis "Unbedingte" bzw. "Ur-Sein" ist nicht nur die Grundlage des metaphysischen Monismus, sondern die realistische Substrat, die auf den Bereich des Wissens nie reduziert wird. $F{\ddot{u}}r$ Novalis wird das Unbeclingte dem $Bewu{\ss}tsein$ nicht gegeben, vielmehr ist es der Gegenstand der Sehnsucht und des Strebens. Hier wird die Philosophie als unendliche $Ann{\ddot{a}}herung$ zum Unbedingten bestimmt. Philosophie ist sowohl die $urspr{\ddot{u}}ngliche$ $T{\ddot{a}}tigkeit$ des mit dem Transzendeten $ber{\ddot{u}}hrenden$ $Gef{\ddot{u}}hls$ als der unendliche Trieb, der den Grund zu erkennen versucht.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.13 no.3
• /
• pp.237-245
• /
• 2008

We developed a computational method on coupled dynamics of tracked vehicle on seafloor and long flexible pipe. The tracked vehicle is modeled as rigid-body vehicle, and the linked flexible pipe is discretized according to a lumped-parameter model. The equations of motion of the rigid-body vehicle on the soft seafloor are combined with the governing equations of flexible pipe dynamics. Four Euler parameters method is used to express the orientations of the vehicle and the flexible pipe. In order to solve the nonlinear coupled dynamics of vehicle and flexible pipe an incremental-iterative formulation is implemented. For the time-domain integration $Newmark-\beta$ method is adopted. The total Jacobean matrix has been derived based on the incremental-iterative formulation. The interactions between the dynamics of flexible pipe and the mobility of the tracked vehicle on soft seafloor are investigated through numerical simulations in time domain.

• Journal of IKEEE
• /
• v.3 no.1 s.4
• /
• pp.29-38
• /
• 1999

In this paper, the effects of superstrate on the radiation patterns of dipole on cylindrical bianisotropic subtrates were studied. Special constitutive relations are used to describe the bianisotropic properties of a material, such that the Green's function can be formulated. Electromagnetic fields and hounds conditions in spectral region were used to find Creen's function of the spectral representation and electromagnetic fields in space region were derived through inverse Fourier transformations of fields in spectral region using asymptotic formula for far zone. Radiation characteristics of axial Hertzian dipole on superstrate leaded cylindrical bianisotropic substrates were analyzed.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.2
• /
• pp.91-97
• /
• 2002

Dynamic extinction of solid propellants subjected to rapid pressure drop was studied with the aid of energy equation of condensed phase and flame model in gas phase. It is found that the total residence time($\tau_\gamma$) which measures the residing time of fuel in the reaction zone may play a crucial role in determining the dynamic response of the combustuion to extinction. Residence time was modeled by various combinations of diffusion and chemocal kinetic time scale. Effect of pressure history coupled with chamber volume on the extinction response was also performed and was found that dynamic extinction is more susceptible in a confined chamber than in open geometry. And, dynamic extinction was revealed to be affected profoundly by diffysion time scale rather than chemical kinetic time scale.

• Journal of the Korean Chemical Society
• /
• v.40 no.5
• /
• pp.317-326
• /
• 1996

The frequency dependent longitudinal polarizabilities ${\alpha}zz(\omega)$ and the second hyper-polarizabilities ${\gamma}zzzz(\omega)$ of the linear polyenes, $C_4H_6\;to\;C_{30}H_{32}$, have been evaluated using the ab initio time-dependent coupled perturbed Hartree-Fock (TDCPHF) theory with the 6-31G basis set. The ratios of the dynamic properties to the static values have been examined to illustrate the relative dispersion effect and extrapolated to the infinite polymer limit. Also the effect of interchain interaction for linear and nonlinear optical properties has been investigated for $C_4H_6$ and the theoretical discussion has been described to overcome the limitation of ab initio TDHF method in the resonance region.

• Geophysics and Geophysical Exploration
• /
• v.20 no.3
• /
• pp.121-128
• /
• 2017

Interpretation of time-domain electromagnetic (TEM) data has been made mostly based on one-dimensional (1-D) inversion scheme in Korea. A proper interpretation of TEM data should employ 3-D TEM forward and inverse modeling algorithms. This study developed a 3-D TEM modeling algorithm using a finite difference time-domain (FDTD) method with staggered grid. In numerically solving Maxwell equations, fictitious displacement current is included based on an explicit FDTD method using a central difference approximation scheme. The developed modeling algorithm simulated a small-coil source configuration to be verified against analytic solutions for homogeneous half-space models. Further, TEM responses for a 3-D anomaly are modeled and analyzed. We expect that it will contribute greatly to the precise interpretation of TEM data.

• Geophysics and Geophysical Exploration
• /
• v.24 no.4
• /
• pp.164-170
• /
• 2021

Frequency-domain and time-domain induced polarization methods can provide spectral information about subsurface media. Analysis of spectral characteristics has been studied mainly in the frequency-domain, however, time-domain induced polarization research has recently become popular. In this study, assuming a homogeneous half-space model, an inversion method was developed to extract Cole-Cole parameters from the measured secondary potential or electrical resistivity. Since the Cole-Cole parameters of chargeability, time constant, and frequency index are not independent of each other, various problems, such as slow convergence rate, initial model problem, local minimum problem, and divergence, frequently occur when conventional nonlinear inversion is applied. In this study, we developed an effective inversion method using the initial model close to the true model by introducing a grid search method. Finally, the validity of the developed inversion method was verified using inversion experiments.

• Geophysics and Geophysical Exploration
• /
• v.17 no.3
• /
• pp.129-136
• /
• 2014

Electromagnetic (EM) methods are generally divided into frequency-domain EM (FDEM) and time-domain EM (TDEM) methods, depending on the source waveform. The FDEM and TDEM fields are mathematically related by the Fourier transformation, and the TDEM field can thus be obtained as the Fourier transformation of FDEM data. For modeling in time-domain, we can use fast frequency-domain modeling codes and then convert the results to the time domain with a suitable numerical method. Thus, frequency-to-time transformations are of interest to EM methods, which is generally attained through fast Fourier transform. However, faster frequency-to-time transformation is required for the 3D inversion of TDEM data or for the processing of vast air-borne TDEM data. The diffusion expansion method (DEM) is one of smart frequency-to-time transformation methods. In DEM, the EM field is expanded into a sequence of diffusion functions with a known frequency dependence, but with unknown diffusion-times that must be chosen based on the data to be transformed. Especially, accuracy of DEM is sensitive to the diffusion-time. In this study, we developed a method to determine the optimum range of diffusion-time values, minimizing the RMS error of the frequency-domain data approximated by the diffusion expansion. We confirmed that this method produces accurate results over a wider time range for a homogeneous half-space and two-layered model.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.22 no.4
• /
• pp.343-348
• /
• 2009

In this study, an efficient sequential bridging method to characterize both the particle size effect and concentration effect on the mechanical properties of nanocomposites at high volume fraction is suggested through a molecular dynamics(MD) simulations and micromechanics of composites materials. The Young's modulus and the shear modulus of the nanocomposites at various particle radius and at 12% volume fraction were obtained from MD simulations and multi-inclusion model was adopted to describe both modulus in continuum model. In order to describe the particle size effect, an additional phase, effective interface, was adopted as characteristic phase and the non-dilute concentration effect which appears at 12% volume fraction was describe via the variation of the elastic modulus of the infinite medium. Both the elastic modulus of the interface and infinite medium were fitted into functions of particle radius for the applicability of the present bridging method at various particle radii. Using the present bridging method the elastic modulus of the nanocomposites was efficiently obtained with accuracy. In addition, the effect of the interface thickness and modulus on the elastic modulus of the nanocomposite was investigated.