• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.2
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• pp.186-193
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• 2011

The NDIF method(non-dimensional dynamic influence function method) for free vibration analysis of arbitrarily shaped plates with the simply supported edge is newly developed in the paper. In order to extract the system matrix that gives the natural frequencies and natural modes of the plate of interest, the difficulty of measuring higher differential terms involved in the simply supported boundary condition is successfully overcome. Finally, the excellence of the characteristics of convergence and accuracy of the proposed method is shown through two verification examples, which indicate that natural frequencies and natural modes obtained by the proposed method are very accurate and swiftly converged even though a small number of nodes are used compared with FEM.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.998-1003
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• 2003

The aerodynamically excited vibration and natural frequency of rotating CD and DVD disks are analytically and experimentally studied in this paper The theoretical analysis uses a fluid-structure model where the aerodynamic effects are represented in terms of elastic, lift and damping components. The explicit expression on natural frequency of the air coupled disk is obtained as functions of the three aerodynamic coefficients. The experiments performed using a vacuum chamber and CD/DVD disks rotating in vacuum, open air and enclosure give three main results. One is that the aerodynamic effect by the surrounding air reduces the natural frequencies and critical speeds of the vibration modes. The second is that natural frequency of disks rotating in open air is larger than that in enclosure. Finally, it is shown that the disk vibration is reduced as the gap between the disk and the rigid wall decreases.

• Journal of Magnetics
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• v.21 no.3
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• pp.431-436
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• 2016

In the design of transformer winding, natural vibration frequency is an important parameter. This paper presents a 2D model to calculate axial vibration natural frequency of power transformer winding based on the elastic dynamics theory, and according to the elastic support equivalent principle of radial pressboards. The 3D model to calculate natural vibration frequency can be simplified as a 2D one as the support of pressboards on the winding is same. It is verified that results of the 2D model are consistent with those of 3D one, but the former can achieve much higher calculation efficiency. It shows that increasing the width and number of pressboards can improve axial natural frequency through formula analysis and simulation, and also the relations between the changes of axial pre-compression and axial natural vibration frequency on the windings are investigated. Finally, the proposed 2D model's effectiveness is proved when compared with tested ones.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.10a
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• pp.43-51
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• 2004

As the slenderness ratio of a high-rise building increases, the lateral load resisting system for the building is more often determined by serviceability design criteria. In serviceability design, the maximum drift and the level of vibration are controlled not to exceed the design criteria. Even though many drift method have been developed in various forms, no practical design method for wind induced vibration has been developed so far. Structural engineers rely upon heuristic or experience in designing wind induced vibration. Development of practical design method for wind induced vibration is required. Generally, wind induced acceleration responses are depending on several variables such as the weight density of a building, damping ratio, the natural period, and etc.. All parameters except the natural period or frequency are usually out of reach for structural engineers, then the wind acceleration response may be proportioned to the natural period. Therefore, in this paper, a wind induced vibration design method based on frequency control technique for high-rise is proposed. The method is applied to vibration design of a 25-story office building for performance evaluation.

• Journal of Power System Engineering
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• v.18 no.4
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• pp.43-51
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• 2014

In this paper, transient temperature and vibration characteristics of a brushless DC (BLD(c) motor are studied for external load (165W~495W) and rotational speed (2000 rpm~4000 rpm). For experiment, a simple measurement system is developed to allow a change in load and speed for measuring transient temperature and vibration simultaneously. Temperature and vibration were also measured under the conditions of natural convection and forced convection. Vibrations in the directions of x-axis (#Ch1), y -axis (#Ch2) and z -axis (#Ch3) were obtained by three accelerometers and temperature was obtained by a thermo-couple with respect to time until the motor is steady. Experimental results show that the amplitude of vibration is higher in the order of z-axis (#Ch3), x -axis (#Ch1) and y-axis (#Ch2) and the amplitude of vibration at the forced convection conditions is 10.6% to 17.8% lower than that of vibration at the natural convection. However, the ratio of the vibration value is similar on average regardless of external convection condition.

• Structural Engineering and Mechanics
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• v.55 no.3
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• pp.655-674
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• 2015

In this paper, a new and simplified method is presented in which the natural frequencies of the uniform and non-uniform beams are calculated through simple mathematical relationships. The various vibration problems such as: Rayleigh beam under variable axial force, axial vibration of a bar with and without end discrete spring, torsional vibration of a bar with an attached mass moment of inertia, flexural vibration of the beam with laterally distributed elastic springs and also flexural vibration of the beam with effects of viscose damping are investigated. The governing differential equations are first obtained and then; according to a harmonic vibration, are converted into single variable equations in terms of location. Through repetitive integrations, the governing equations are converted into weak form integral equations. The mode shape functions of the vibration are approximated using a power series. Substitution of the power series into the integral equations results in a system of linear algebraic equations. The natural frequencies are determined by calculation of a non-trivial solution for system of equations. The efficiency and convergence rate of the current approach are investigated through comparison of the numerical results obtained with those obtained from other published references and results of available finite element software.

• International Journal of Highway Engineering
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• v.15 no.3
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• pp.23-29
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• 2013

PURPOSES: This paper aims to give a guideline and the way to apply the advanced composite materials theory to the road structures with different cross sections to the practicing engineers. METHODS: To simple but exact method of calculating natural frequencies corresponding to the modes of vibration of road structures with different cross sections and arbitrary boundary conditions. The effect of the $D_{22}$ stiffness on the natural frequency is rigorously investigated. RESULTS: Simple method of vibration analysis for calculating the natural frequency of the different cross sections is presented. CONCLUSIONS: Simple method of vibration analysis for calculating the natural frequency of the different cross sections is presented. This method is a simple but exact method of calculating natural frequencies of the road structures with different cross sections. This method is extended to be applied to two dimensional problems including composite laminated road structures.

• Journal of Korean Association for Spatial Structures
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• v.6 no.3 s.21
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• pp.43-50
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• 2006

This paper is concerned with the natural periods of ambient vibration and eigenvalue analysis. Ambient vibration tests were conducted to four bearing-wall reinforced concrete buildings ranging from twelve to nineteen stories. The performance of modeling in eigenvalue analysis was investigated using consideration of rigidity out of the plane in the slab and the non-structural bearing wall. Measured natural period was also compared with the value by the KBC2005. Natural period of the short direction in eigenvalue analysis is well fitted with the measured one. In the other hand, Natural period of the long direction in eigenvalue analysis is slightly more overestimated than the measured one. Natural period of the long direction in eigenvalue analysis was found to be enhanced by considering the effect of the stiffness out of the plane of the slab and non-structural wall in the structural modeling.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.1
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• pp.29-37
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• 2012

This paper is concerned with the natural vibration characteristics of a rectangular plate with a rectangular hole in contact with the water. The addressed problem was solved by using the Rayleigh-Ritz method combined with the Green function method. This study presents the numerical approach, numerical results and experimental results. In addition, the validity of the approximate formula which mainly depends on the so-called non-dimensionalized added virtual mass incremental factor and the natural mode shape change due to the presence of the water were investigated. Experiments were also carried out to validate theoretical results. The theoretical results are in good agreement with the experimental results. It was found that the effect of a square hole on the natural frequencies of the square plate in contact with water is different from the effect of a square hole on the natural frequencies of the square plate in air and the approximate formula can predict lower natural frequencies in water with a good accuracy.

• Journal of Korean Association for Spatial Structures
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• v.15 no.4
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• pp.99-105
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• 2015

The serviceability design of the high-rise building is affected by the wind response vibration such as the acceleration, at this time it is important to calculate the natural frequency correctly. Since the suggestion equation of the natural frequency being used in the design phase is not the regression equation obtained from the vibration measurement of the high-rise building, the verification to use for the serviceability design of the high-rise building is necessary. This thesis conducted an ambient vibration measuring on the high-rise building through the mobile-phone application to calculate the natural frequency and suggested a natural frequency approximate expression following the building's height, and compared with the domestic/foreign standard and the result of the eigen-value analysis.