• Computational Structural Engineering
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• v.10 no.4
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• pp.291-302
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• 1997

This paper presents an analytical method for evaluating the free vibration of a circular cylindrical tank filled with bounded compressible fluid. The analytical method was developed by means of the finite Fourier series expansion method. The compressible fluid motion was determined by means of the linear velocity potential theory. To clarify the validity of the analytical method, the natural frequencies of a circular cylindrical tank with the clamped-clamped boundary condition, and filled with water, were obtained by the analytical method and the finite element method using a comercial ANSYS 5.2 software. Excellent agreement on the natural frequencies of the liquid-filled tank structure was found. The compressiblity and the fluid density effects on the normalized coupled natural frequencies were investigated. The density of fluid affects on all coupled natural frequencies of the tank, whereas the compressibility of fluid affects mainly on the natural frequencies of lower circumferential modes.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.11
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• pp.1157-1169
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• 2008

This paper presents spectral element formulation which approximates Lamb wave propagation by PZT transducers bonded on a thin plate. A two layer beam model under 2-D plane strain condition is introduced to simulate high-frequency dynamic responses induced by a piezoelectric (PZT) layer rigidly bonded on a base plate. Mindlin-Herrmann and Timoshenko beam theories are employed to represent the first symmetric and anti-symmetric Lamb wave modes on a base plate, respectively. The Euler-Bernoulli beam theory and 1-D linear piezoelectricity are used to model the electro-mechanical behavior of a PZT layer. The equations of motions of a two layer beam model are derived through Hamilton's principle. The necessary boundary conditions associated with the electro-mechanical properties of a PZT layer are formulated in the context of dual functions of a PZT layer as an actuator and a sensor. General spectral shape functions of response field and the associated boundary conditions are obtained through equations of motions converted into frequency domain. Detailed spectrum element formulation for composing the dynamic stiffness matrix of a two layer beam model is presented as well. The validity of the proposed spectral element is demonstrated through numerical examples.

• Journal of Navigation and Port Research
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• v.26 no.3
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• pp.281-288
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• 2002

It might be true that both experimental and analytic techniques have been developed in the vibration analysis end engineering. It could not be said, however, that the experimental method has been also developed as much as analytic method, such as Finite Element Method One of the reason is that computation time becomes longer and that the solution often diverges depending on the choice of initial value in solving nonlinear equation. The equation in experimental modal analysis is usually composed of the nonlinear term of natural frequency and modal damping ratio, and the linear one of equivalent stiffness. In this study, the nonlinear terms were solved first, and then the linear term was obtained. The experimental modal parameters were estimated, applying the developed experimental modal analysis curve-fitting method to the super-structure model. In addition, the number of modes and modal damping ratio could be easily determined by the developed program with the application of graphical techniques and with easy handling button.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.5 s.51
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• pp.49-61
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• 2006

The floor impact sound insulations are installed frequently for reducing the floor impact sound into the floor slab of the residential buildings in recent years. Therefore the analytical FE model considering the insulation is needed for the sound and vibration analysis of the floor and it is necessary to use a refined finite element model fer considering the large number of modes involved dynamic responses. So it is very difficult to use FE model because of the tiresome task for constructing the FE model, taking a lot of times for analysis and the impossibility of using the proportional damping. The efficient analysis and modeling method are proposed to the dynamic analysis for the floor with damping layer in this study. The floor slabs and finished layers are modeled individually and the spring elements that mean damping layers used to connect two parts. The dynamic analysis by the $Newmark-{\beta}$ method is performed to solve the non-proportional damping problem due to the damping coefficient of insulations.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.10 s.103
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• pp.1177-1185
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• 2005

This paper investigates the noise radiated by a cascade of flat-plate airfoils interacting with homogeneous, isotropic turbulence. At frequencies above the critical frequency, all wavenumber components of turbulence excite propagating cascade modes, and cascade effects are shown to be relatively weak. In this frequency range, acoustic power was shown to be approximately proportional to the number of blades. Based on this finding at high frequencies, an approximate expression is derived for the power spectrum that is valid above the critical frequency and which is in excellent agreement with the exact expression for the broadband power spectrum. The approximate expression shows explicitly that the acoustic Power above the critical frequency is proportional to the blade number, independent of the solidity, and varies with frequency as ${\phi}_{ww}(\omega/W$), where ${\phi}_{ww}$ is the wavenumber spectrum of the turbulence velocity and W is mean-flow speed. The formulation is used to perform a parametric study on the effects on the power spectrum of the blade number stagger angle, gap-chord ratio and Mach number. The theory is also shown to provide a close fit to the measured spectrum of rotor-stator interaction when the mean square turbulence velocity and length-scale are chosen appropriately.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.4
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• pp.619-628
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• 2002

This paper deals with the FE analysis for the free vibration of sloshing in horizontal cylindrical tank with baffles. We use Laplace equation based on potential theory as governing equation. This problem is solved by FEM using lineal isoparametric elements. We assume that the tank as well as baffles is rigid body and by separating nodes into two at the baffle location, baffle effect is obtained by separating nodes into two at the baffle location. For the calculation of natural frequencies and mode shapes, we introduce Lanczos transformation and Jacobi iteration methods. Numerical results of the first longitudinal and transverse modes, while comparing with literature cited, are very good. In order for the baffle effects on the free vibration of sloshing, various combinations of baffle parameters, which are location, inner diameter and number, are examined.

• Smart Structures and Systems
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• v.29 no.3
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• pp.499-512
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• 2022

This work proposes a novel contactless vibration damping and thermal isolation tripod platform based on Superconducting Magnetic Levitation (SML). This prototype is suitable for cryogenic environments, where classical passive, semi active and active vibration isolation techniques may present tribological problems due to the low temperatures and/or cannot guarantee an enough thermal isolation. The levitating platform consists of a Superconducting Magnetic Levitation (SML) with inherent passive static stabilization. In addition, the use of Operational Modal Analysis (OMA) technique is proposed to characterize the transmissibility function from the baseplate to the platform. The OMA is based on the Stochastic Subspace Identification (SSI) by using the Expectation Maximization (EM) algorithm. This paper contributes to the use of SSI-EM for SML applications by proposing a step-by-step experimental methodology to process the measured data, which are obtained with different unknown excitations: ambient excitation and impulse excitation. Thus, the performance of SSI-EM for SML applications can be improved, providing a good estimation of the natural frequency and damping ratio without any controlled excitation, which is the main obstacle to use an experimental modal analysis in cryogenic environments. The dynamic response of the 510 g levitating platform has been characterized by means of OMA in a cryogenic, 77 K, and high vacuum, 1E-5 mbar, environment. The measured vertical and radial stiffness are 9872.4 N/m and 21329 N/m, respectively, whilst the measured vertical and radial damping values are 0.5278 Nm/s and 0.8938 Nm/s. The first natural frequency in vertical direction has been identified to be 27.39 Hz, whilst a value of 40.26 Hz was identified for the radial direction. The determined damping values for both modes are 0.46% and 0.53%, respectively.

• Journal of KSNVE
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• v.6 no.1
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• pp.35-44
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• 1996

This paper presents a new type of fuzzy-sliding mode controller for robust tip position control of a single-link flexible manipulator subjected to parameter variations. A sliding mode controller is formulated with an assumption that imposed parameter variations are bounded so that certain deterministic performance can be guaranted. In the design of the sliding mode controller, so called moving sliding surface is adopted to minimize the reaching phase and thus mitigate system sensitivity to the variations. The sliding mode controller is then incorporated with a fuzzy technique to reduce inherently ever-existing chattering which is impediment in position control of flexible manipulators. A set of fuzzy parameters and control rules are obtained from a relation between predetermined sliding surface and representative points in the state space. Computer simulations are undertaken in order to demonstrate superior control performance of the proposed methodology.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.393-398
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• 2015

A very important part in vibration analysis is to calculate the frequency response function (FRF). In general, a large sized or/and complicated structure has many thousands to millions of degrees. Therefore, the FRF cannot be calculated by the traditional analysis method using an inverse matrix. This paper presents a new FRF calculation method of a superstructure by synthesizing sub-structure modes, of which the DOF can be deduced by partitioning into some sub-structures. To confirm its analysis results, the method was applied to an assembled plate ($B300{\times}L900{\times}t5mm$) with three diagonal sub-plates($B300{\times}L300{\times}t5mm$) in series and compared with the measured data. The test results have were comparable those of the calculated ones with an error less than 5%.

• Computational Structural Engineering
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• v.5 no.4
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• pp.93-102
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• 1992

The design of reactor internals requires the accurate vibration characteristics of each component for subsequent dynamic structural response analyses. For Korean standard nuclear power plant some modifications on the Control Element Assembly shroud from the reference design have been made, Since the shroud is complex in geometry having an array of vertical round tubes and webs in a square grid pattern, and being tied down by preloaded tie rods into position, it is planned to perform a vibration measurement program consisting of both experimental and analytical modal studies upon that component. The shroud modal testing was performed on the low frequency global survey to measure the first several modes. The analysis using the finite element model was also performed for the as-tested conditions. The natural frequencies and mode shapes from both test and analysis have been acquired and compared to be in good agreement. It is concluded that finite element model generated is good enough to be used in the design for the dynamic response analysis under various loading conditions.