• Earthquakes and Structures
• /
• v.8 no.6
• /
• pp.1481-1497
• /
• 2015

Vertical earthquake ground motion may magnify vertical dynamic responses of structures, and thus cause serious damage to bridges. As main support structures, piers and bearings play an important role in vertical seismic response analysis of girder bridges. In this study, the pier and bearing are simplified as a vertical series spring system without mass. Then, based on the assumption of small displacement, the equation of motion governing the simply-supported straight girder bridge under vertical ground motion is established including effects of vertical deformation of support structures. Considering boundary conditions, the differential quadrature method (DQM) is applied to discretize the above equation of motion into a MDOF (multi-degree-of-freedom) system. Then seismic responses of this MDOF system are calculated by a step-by-step integration method. Effects of support structures on vertical dynamic responses of girder bridges are studied under different vertical strong earthquake motions. Results indicate that support structures may remarkably increase or decrease vertical seismic responses of girder bridges. So it is of great importance to consider effects of support structures in structural seismic design of girder bridges in near-fault region. Finally, optimization of support structures to resist vertical strong earthquake motions is discussed.

• Journal of the Optical Society of Korea
• /
• v.13 no.3
• /
• pp.379-385
• /
• 2009

The vergence control of binocular stereoscopic camera is the most essential factor for acquiring high quality stereoscopic images. In this paper, we proposed a binocular stereoscopic camera vergence control method using disparity information by the simple image processing and estimate the quantity of vergence control using the Lagrange interpolation equation. The method of extracting disparity information through image processing is as follows: first the key-object in left & right images was extracted through labeling of the central area of the image, and then a simple method was used for calculating the disparity value of the same key-object in the labeled left and right images. The vergence control method uses disparity information and keeps the convergence distance of left & right cameras and the distance of the key-object the same. According to the proposed method, variance in the distance of the key-object and application of calculated disparity information of obtained left & right images to the quadratic Lagrange interpolation equation could estimate the quantity of vergence control, which confirmed that the method of stereoscopic camera vergence control can be simplified through experiments on various key-objects and other convergence distance.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.23 no.1
• /
• pp.23-32
• /
• 1986

By virtue of an application of the receptance method, simplified formulae to calculate natural frequencies of stiffened plates having a resiliently mounted or concentrated mass are obtained. Some numerical results are compared with those based on Lagrange's equation of motion and with experimental results. For the problem formulation the stiffened plate is reduced to an equivalent orthotropic plate, a resiliently mounted mass to a spring-mass system, and mode shapes of the plate are assumed with comparison functions consisting of Euler beam functions. The proposed formulae give results in good conformity to both numerical results based on Lagrange's equation of motion and experimental results for in-phase modes of the coupled system. For out-of-phase modes the conformity is assured only in case that the natural frequency of the attached system is less than a half of that the stiffened plate. It is also found that a resiliently mounted mass having its own natural frequency of about two or more times that of the stiffened plate can be reduced to a concentrated mass with assurance of a few percent error in the frequency.

• Coupled systems mechanics
• /
• v.1 no.3
• /
• pp.247-268
• /
• 2012

A finite element model is developed for dynamic response prediction of floating offshore wind turbine systems considering coupling of wind turbine, floater and mooring system. The model employs Morison's equation with Srinivasan's model for hydrodynamic force and a non-hydrostatic model for restoring force. It is observed that for estimation of restoring force of a small floater, simple hydrostatic model underestimates the heave response after the resonance peak, while non-hydrostatic model shows good agreement with experiment. The developed model is used to discuss influence of heave plates and modeling of mooring system on floater response. Heave plates are found to influence heave response by shifting the resonance peak to longer period, while response after resonance is unaffected. The applicability of simplified linear modeling of mooring system is investigated using nonlinear model for Catenary and Tension Legged mooring. The linear model is found to provide good agreement with nonlinear model for Tension Leg mooring while it overestimates the surge response for Catenary mooring system. Floater response characteristics under different wave directions for the two types of mooring system are similar in all six modes but heave, pitch and roll amplitudes is negligible in tension leg due to high restraint. The reduced amplitude shall lead to reduction in wind turbine loads.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.18 no.6
• /
• pp.145-151
• /
• 2004

The purpose of isolated grounding system is to protect own electrical facilities from the other grounding systems in order to avoid the potential interference between ground grid areas. But the physically close distances involved could lead to potential interference problems. The simplified equation for determining potential interferences based on the measured data under the case study grounding system is proposed in this paper. The results obtained with the equation to verify the accuracy have been compared with the results obtained from the CDEGS program.

• Nuclear Engineering and Technology
• /
• v.49 no.6
• /
• pp.1259-1268
• /
• 2017

The alpha eigenvalue problem in multigroup neutron diffusion is studied with particular attention to the theoretical analysis of the model. Contrary to previous literature results, the existence of eigenvalue and eigenflux clustering is investigated here without the simplification of a unique fissile isotope or a single emission spectrum. A discussion about the negative decay constants of the neutron precursors concentrations as potential eigenvalues is provided. An in-hour equation is derived by a perturbation approach recurring to the steady state adjoint and direct eigenvalue problems of the effective multiplication factor and is used to suggest proper detection criteria of flux clustering. In spite of the prior work, the in-hour equation results give a necessary and sufficient condition for the existence of the eigenvalue-eigenvector pair. A simplified asymptotic analysis is used to predict bands of accumulation of eigenvalues close to the negative decay constants of the precursors concentrations. The resolution of the problem in one-dimensional heterogeneous problems shows numerical evidence of the predicted clustering occurrences and also confirms previous theoretical analysis and numerical results.

• Journal of Ocean Engineering and Technology
• /
• v.22 no.2
• /
• pp.91-98
• /
• 2008

In order to establish a design guide for the bottom plate structure of a 4.3 ton aluminum planning boat, the feasibilities of bottom plate scantling of the ship are investigated based on the results of structural strength analysis and a simple equation and evaluation system are developed for initial structural design purposes. This study consists of 5 steps: First, the background, necessity, and purpose of this study are explained briefly, Second, the principal dimensions of this ship, the position of the considered bottom plate members and material characteristics are introduced. Third, the equivalent design pressure concept is introduced and evaluated based on experience and experimental data. Fourth, the strength of bottom plate members are examined using elasto-plastic nonlinear structural analysis, and response levels and several boundary conditions are reviewed based on the analysis results. Finally, in order to suggest design guides in respect to the ship's structural design, a simple design equation and evaluation system for bottom plate members are suggested for boats in the 4.3 ton aluminumboat range through the introduction of safety factorsbased on the ultimate design pressure concept.

• Steel and Composite Structures
• /
• v.17 no.5
• /
• pp.753-776
• /
• 2014

In this paper, nonlinear vibration and post-buckling analysis of beams made of functionally graded materials (FGMs) resting on nonlinear elastic foundation subjected to thermo-mechanical loading are studied. The thermo-mechanical material properties of the beams are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and to be temperature-dependent. The assumption of a small strain, moderate deformation is used. Based on Euler-Bernoulli beam theory and von-Karman geometric nonlinearity, the integral partial differential equation of motion is derived. Then this PDE problem which has quadratic and cubic nonlinearities is simplified into an ODE problem by using the Galerkin method. Finally, the governing equation is solved analytically using the variational iteration method (VIM). Some new results for the nonlinear natural frequencies and buckling load of the FG beams such as the influences of thermal effect, the effect of vibration amplitude, elastic coefficients of foundation, axial force, end supports and material inhomogenity are presented for future references. Results show that the thermal loading has a significant effect on the vibration and post-buckling response of FG beams.

• Earthquakes and Structures
• /
• v.27 no.3
• /
• pp.209-226
• /
• 2024

The susceptibility of Reinforced Concrete (RC) buildings to earthquake-induced damage is a critical concern, primarily attributed to their inadequate seismic performance. The existing earthquake-resistant design code of India prescribes guidelines to minimize seismic damage but does not provide any means for evaluating the actual seismic performance and damage. To ascertain the seismic performance of the structures quantitatively, it is crucial to classify damage into measurable damage states. Damage Index (DI) acts as an important tool for this purpose. Among various procedures for computation of DI, the modified Park and Ang Damage Index appears to be highly accurate. However, the major drawback of this method is that it is lengthy and time-consuming. On the other hand, structural performances can be evaluated using various performance parameters such as interstory drift ratio (IDR), inelastic deformation, etc., as described in FEMA-356 and ASCE-41 17. The present study explores the correlation between seismic DI and structural performance in RC frame buildings designed according to IS code. Sixteen building models, incorporating diverse configurations, are examined using nonlinear static and time history analyses. A simplified equation is developed by regression analysis to predict DI based on IDR, offering a computationally efficient alternative. Validation tests are done to confirm the equation's accuracy. Furthermore, a unified damage scale integrating DI and seismic performance is also proposed for seismic damage evaluation of buildings designed by IS code.

• Structural Monitoring and Maintenance
• /
• v.11 no.3
• /
• pp.219-234
• /
• 2024

The strength reduction factor spectrum is traditionally obtained from a single-degree-of-freedom (SDOF) system with a constant damping coefficient. However, according to the principle of Rayleigh damping, the damping coefficient matrix of a system changes with the stiffness matrix, and the damping coefficient of an equivalent SDOF system changes with the tangent stiffness coefficient. In view of that, this study proposes an equivalent SDOF system with an adaptive damping coefficient and derives a standardized reaction balance equation. By iteratively adjusting the strength reduction factor, the corresponding spectrum with an equivalent ductility factor is obtained. In addition, the ratio between the strength reduction factor that considers adaptive damping and the traditional strength reduction factor, denoted by η, is determined, and the η-μ-T relationship is obtained. Seismic records of Classes C, D, and E sites are selected as excitations. Moreover, a nonlinear response time-history analysis is performed to establish the relationship between the η and T values for the equivalent ductility factor μ. Further, by exploring the effects of the site class, ductility factor, second-order stiffness coefficient, and period T on the mean value of η, a simplified calculation equation of mean η is derived, and η is used as a modified value for the traditional strength reduction factor R spectrum.