• Communications of the Korean Mathematical Society
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• v.39 no.2
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• pp.513-534
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• 2024

The main goal of this work is to study an initial boundary value problem relating to the unsteady flow of a rigid, viscoplastic, and incompressible Bingham fluid in an elastic bounded domain of ℝ². By using the approximation sequences of the Faedo-Galerkin method together with the regularization techniques, we obtain the results of the existence and uniqueness of local solutions.

• Journal of Mechanical Science and Technology
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• v.18 no.9
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• pp.1500-1511
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• 2004

In this paper, the anti-plane transient response of a central crack normal to the interface between a piezoelectric ceramics and two same elastic materials is considered. The assumed crack surfaces are permeable. By virtue of integral transform methods, the electro elastic mixed boundary problems are formulated as two set of dual integral equations, which, in turn, are reduced to a Fredholm integral equation of the second kind in the Laplace transform domain. Time domain solutions are obtained by inverting Laplace domain solutions using a numerical scheme. Numerical values on the quasi-static stress intensity factor and the dynamic energy release rate are presented to show the dependences upon the geometry, material combination, electromechanical coupling coefficient and electric field.

• Journal of Ocean Engineering and Technology
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• v.15 no.4
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• pp.115-119
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• 2001

The simulation of motion responses of a dolphin-moored ocean structure in shallow water when it cllides with a ship, has been carried out. The equation of motion in the time domain according to Cummin's theory is employed, and solved by making use of the Newmark-${\beta}$ method. The added mass and damping coefficients involved in the equations are abtained from a three-dimensional panel method in the frequency domain. The impact forces due to ship collision are calculated using both the elastic and non-elastic modelings. The mooring forces for dolphin systems of ocean structure are regarded as linear spring forces.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.103-107
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• 2001

When ship claps against the ocean structure sited at shallow water, the time simulation of motion responses of dolphin-moored ocean structure is presented. The equatien of motion based on Cummin's theory of impulse responses are employed, and solved in time domain by using the Newmark $\beta$ method. The added mass and damping coefficients involved in the equations are obtained from a three-dimensional panel method in the frequency domain. The impact forces due to ship collision are modeled as two method, and those are elastic and non-elastic collisions. The mooring forces for dolphin systems of scean structure are considered as linear spring system.

• Journal of the Korean Society of Safety
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• v.17 no.2
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• pp.58-62
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• 2002

Longitudinal wave tests with finite elastic medium were performed to investigate the difference between measured values and theoretical values of propagation velocity and elasticity modulus. Each accelerometer was attached on finite elastic medium with same phase and different positions to check the particle motion. The results show that measured values of elasticity moduli from both time domain and frequency domain were similiar to theoretical value. Polarity of signal depends entirely on the phase of accelerometer. It proved that the propagation velocity and the particle motion are in the same direction when a compressive stress is applied. And also the propagation velocity and the particle motion depend on the intensity of the stress and material properties respectively.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.3
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• pp.266-281
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• 2017

Hydroelastic interactions of a deformable floating body with random waves are investigated in time domain. Both hydroelastic motion and structural dynamics are solved by expansion of elastic modes and Fourier transform for the random waves. A direct and efficient structural analysis in time domain is developed. In particular, an efficient way of obtaining distributive loads for the hydrodynamic integral terms including convolution integral by using Fubini theory is explained. After confirming correctness of respective loading components, calculations of full distributions of loads in random waves are expedited by reformulating all the body loading terms into distributed forms. The method is validated by extensive convergence tests and comparisons against the counterparts of the frequency-domain analysis. Characteristics of motion/deformation responses and stress resultants are investigated through a parametric study with varying bending rigidity and types of random waves. Relative contributions of componential loads are identified. The consequence of elastic-mode resonance is underscored.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.329-336
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• 2007

For scaling of the gradient of misfit function, we develop a new pseudo-Hessian matrix constructed by combining amplitude field and pseudo-Hessian matrix. Since pseudo- Hessian matrix neglects the calculation of the zero-lag auto-correlation of impulse responses in the approximate Hessian matrix, the pseudo-Hessian matrix has a limitation to scale the gradient of misfit function compared to the approximate Hessian matrix. To validate the new pseudo- Hessian matrix, we perform frequency-domain elastic full waveform inversion using this Hessian matrix. By synthetic experiments, we show that the new pseudo-Hessian matrix can give better convergence to the true model than the old one does. Furthermore, since the amplitude fields are intrinsically obtained in forward modeling procedure, we do not have to pay any extra cost to compute the new pseudo-Hessian. We think that the new pseudo-Hessian matrix can be used as an alternative of the approximate Hessian matrix of the Gauss-Newton method.

• Structural Engineering and Mechanics
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• v.51 no.4
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• pp.685-705
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• 2014

This paper presents a new formulation for forward scalar wave simulations in semi-infinite media. Perfectly-Matched-Layers (PMLs) are used as a wave absorbing boundary layer to surround a finite computational domain truncated from the semi-infinite domain. In this work, a hybrid formulation was developed for the simulation of scalar wave motion in two-dimensional PML-truncated domains. In this formulation, displacements and stresses are considered as unknowns in the PML domain, while only displacements are considered to be unknowns in the interior domain. This formulation reduces computational cost compared to fully-mixed formulations. To obtain governing wave equations in the PML region, complex coordinate stretching transformation was introduced to equilibrium, constitutive, and compatibility equations in the frequency domain. Then, equations were converted back to the time-domain using the inverse Fourier transform. The resulting equations are mixed (contain both displacements and stresses), and are coupled with the displacement-only equation in the regular domain. The Newmark method was used for the time integration of the semi-discrete equations.

• 한국기계연구소 소보
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• s.17
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• pp.99-109
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• 1987

Mechanisms with fully elastic members must consider both inertial forces due to the rigid motion of mechanisms and due to the elastic vibration of links. The main objectives of the kineto-elasto static and dynamic analyses are to calculate the quasi-static and the time-domain responses, respectively. An iterative transfer matrix method is used for a four-bar, fully elastic linked mechanism. Houbolt direct integration scheme is incorporated for the inertial effects due to the elastic link vibration. The analytical results are compared with the experimental responses and both responses show in good agreement.

• Structural Engineering and Mechanics
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• v.69 no.3
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• pp.293-306
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• 2019

In current seismic design codes, various elastic design acceleration spectra are defined considering different seismological and soil characteristics and are widely used tool for calculation of seismic loads acting on structures. Response spectrum analyses directly use the elastic design acceleration spectra whereas time history analyses use acceleration records of earthquakes whose acceleration spectra fit the design spectra of seismic codes. Due to the fact that obtaining coherent structural response quantities with the seismic design code considerations is a desired circumstance in dynamic analyses, the response spectra of earthquake records used in time history analyses had better fit to the design acceleration spectra of seismic codes. This paper evaluates structural response distributions of multi-story reinforced concrete frames obtained from nonlinear time history analyses which are performed by using the scaled earthquake records compatible with various elastic design spectra. Time domain scaling procedure is used while processing the response spectrum of real accelerograms to fit the design acceleration spectra. The elastic acceleration design spectra of Turkish Seismic Design Code 2007, Uniform Building Code 1997 and Eurocode 8 are considered as target spectra in the scaling procedure. Soil classes in different seismic codes are appropriately matched up with each other according to $V_{S30}$ values. The maximum roof displacements and the total base shears of considered frame structures are determined from nonlinear time history analyses using the scaled earthquake records and the results are presented by graphs and tables. Coherent structural response quantities reflecting the influence of elastic design spectra of various seismic codes are obtained.