• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.306-311
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• 2002

Non-singular boundary element method (BEM) codes are developed in acoustics application. The BEM code is then used to calculate unknown boundary surface normal displacements and surface pressures from known exterior near Held pressures. And then the calculated surface normal displacements and surface pressures are again applied to the BEM in forward in order to calculate reconstructed field pressures. The initial exterior near field pressures are very well agreed with the later reconstructed field pressures. Only the same number of boundary surface nodes (1178) are used far the initial exterior pressures which are initially calculated by Finite Element Method (FEM) and BEM. Pseudo-inverse technique is used for the calculation of the unknown boundary surface normal displacements. The structural object is a tuning fork with 128.4 Hz resonant. The boundary element is a quadratic hexahedral element (eight nodes per element).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.326-331
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• 2009

An algorithm is proposed for computing dynamic displacements of a bridge using FBG sensors. An existing algorithm for estimating dynamic displacements of a simply supported beam through mode superposition is extended and applied to various types of bridges with bending and torsional modes. The proposed algorithm is examined through field tests on a suspension span steel deck plate box girder bridge. Guidelines are provided for determining the number of modes and the number of strain gages to be used.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1379-1388
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• 2008

In this paper, we present the equations of motion by which the natural vibration of a rotating annular disk can be accurately analyzed. These equations are derived from the theory of finite deformation and the principle of virtual work. The radial displacements of annular disk which is rotating at constant angular velocity are determined by non-linear equations formulated using 1-dimensional finite elements in radial direction. The equations of the in-plane vibrations at disturbed state are also formulated using 1-dimensional finite elements in radial direction along the number of nodal diameters. They are expressed as in functions of the radial displacements at the steady state and the disturbed displacements about the steady state. In-plane static deformation modes of the annular disk are used as the interpolation functions of 1-dimensional finite elements in radial direction. The natural vibrations of an annular disk with different boundary conditions are analyzed by using the presented model and the 3-dimensional finite element model to verify accuracy of the presented equations of motion. Its results are compared and discussed.

• Nuclear Engineering and Technology
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• v.33 no.6
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• pp.619-625
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• 2001

An axial-flow-induced vibration model was proposed for a rod supported by two translational springs at both ends. For developing the model, a one-mode approximation was made based on the assumption that the first mode was dominant in vibration behavior of the single span rod. The first natural frequency and mode shape functions for the flow-induced vibration, called the FIV model were derived by using Lagrange＇s method. The vibration displacements at reactor conditions were calculated by the proposed model for the spring-supported rod and by the previous model for the simple-supported(55) rod. As a result, the vibration displacement for the spring-supported rod was larger than that of the 55 rod, and the discrepancy between both displacements became much larger as flow velocity increased. The vibration displacement for the spring-supported rod appeared to decrease with the increase of the spring constant. AS flow velocity increased, the increase rate of vibration displacement was calculated to go linearly up, and that of the rod having the short span length was larger than that of the rod having the long span length although the displacement value itself of the long span rod was larger than that of the short one.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.10
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• pp.749-757
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• 2002

Excessive vibration in flexible structures is a problem encountered in many different fields, causing fatigue of structural components. Passive techniques, though sometimes limited in their capabilities, have been used in the past to attenuate vibrations. Recently active techniques have been developed to enhance vibration control performance beyond that provided by their passive counterparts. Most often, the focus of active control methods has been to suppress structure displacements. In cases where vibration results in structure failures, displacement suppression may not be the best choice of control approaches (it can, in fact, increase dynamic loads which would be even more harmful to supports) . This paper presents two optimal control methods for attenuating steady state vibrations in flexible structures. One method minimizes shaft displacements while another minimizes dynamic reaction forces. The two methods are applied to a model of a typical flexible structure system and their results are compared. It is found that displacement minimization can increase loads, while load minimization decreases loads.

• Journal of Advanced Marine Engineering and Technology
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• v.11 no.2
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• pp.51-60
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• 1987

Recently, the problem of the axial vibration for the marine diesel engine shafting has become important due to the increased exciting forces resulting from high supercharging and large output, and the reduced natural frequencies resulting from long stroke and show speed. The effects of the axial vibration on the propulsion shafting induce cracks of the connecting point of crankpin and crankarm, the severe wear of thrust bearing, the fatigue failure of each fixing bolt and jointed parts, the hull and local hull vibrations, and also the wear and the noise due to intense hammering phenomena of thrust collar. Therefore, each classification society requires the calculation of natural frequencies and their amplitudes and also measurements of the forced damped axial vibration. At present, the technical and theoretical level is at the stage of estimating the resonant points and their maximum displacements, but the estimated displacements of the resonant points are not so reliable as the torsional one. In this study, induced stresses and amplitudes of the forced damped axial vibration are calculated. For this purpose, the equation of forced axial vibration with damping for the propulsion shafting is derived and its steady-state response is calculated by the mechanical impedance method. A computer program for above calculations is developed. The measured values are analyzed and the calculated results are compared with the measured ones. They show fairly good agreements and the reliability of developed program is confirmed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1126-1131
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• 2001

Excessive vibration in rotating machinery is a problem encountered in many different fields, causing such difficulties as fatigue of machinery components and failure of supporting bearings. Passive techniques, though sometimes limited in their capabilities, have been used in the past to attenuated vibrations. Recently active techniques have been developed to provide vibration control perform beyond that provided by their passive counters. Most often, the focus of active control methods has been to suppress rotating machinery displacements. In cases where vibration results in bearing failures, displacement suppression may not be the best choice of control approaches (it can, in fact, increase dynamic bearing loads which would be even more harmful to bearings). This paper presents two optimal control methods for attenuating steady state vibrations in rotating machinery. One method minimizes shaft displacements while the other minimizes dynamic bearing reaction forces. The two methods are applied to a model of a typical rotating machinery system and their results are compared. It is found that displacement minimization can increase bearing loads, while bearing load minimization, on the other hand, decreases bearing loads.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.957-962
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• 2010

Foundation systems in urban sites are often necessary to be constructed with little vibrations and displacements to surroundings. In order to assess applicability of a new foundation system for urban sites based on soil-cement mixing technique, vibrations and displacements induced by soil-cement construction process is evaluated. Soil-cement columns were constructed to reinforce soft ground near an old masonry wall in an urban redevelopment site, and the vibrations and displacements of the old masonry wall during construction were measured. Results indicate that the vibrations and displacements induced by soil-cement construction were little and not critical to the stability of the masonry wall.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.664-669
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• 1998

This research is concerned with the active vibration controller design for smart structures by a modified LQG controller. The smart structure is defined as the structure equipped with smart actuators and sensors. Various analog and digital control, techniques aimed for the piezoceramic sensors and actuators have been proposed for the active vibration control of smart structures. In this paper, the modified LQG controller is developed for the active vibration suppression of smart structures to implement the predefined decay rate on modal displacements. The proposed modified LQG controller proved its effectiveness by experiments.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.29 no.6
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• pp.561-568
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• 2011

The purpose of this study is to measure displacements that occurs on a surface and interior of slope model and the shape when the slope is destroyed at vibration experiment of the slope model using close range photogrammetry. The circle targets and sphere targets are installed on a chamber and a slope model, while the earthquake wave are applied in regular time interval. The close range photogrammetric images are acquired in each displacements step until the slope model is destroyed. Those photos are processed by image processing method and the center points of targets are automatically extracted. Furthermore, the three-dimensional coordinates of targets are calculated by image orientation and bundle adjustment processing. As a result, amount of displacement at each level is precisely measured and provided the basic information for assessing the slope stability using three-dimensional measurement of the target movement and slope destruction.