• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.62 no.7
• /
• pp.913-917
• /
• 2013

During the restoration process of primary restorative transmission system, some over voltages may happen due to nonlinear interaction between unloaded transformers and transmission systems. These over voltages caused by harmonic resonance can be suppressed by inserting damping loads before energizing transformers. But it is very difficult to predict the occurrence possibility of harmonic resonance and complex simulation must be repeated to estimate the sufficient damping loads. This paper presents a damping loads prediction system to prevent harmonic resonance. Detailed analysis of the relationship between harmonic resonance and the amount of damping loads is discussed. The prediction system is developed using a curve fitting and a neural network based on this relationship. A curve fitting used a Gaussian function based on non-linear least square method and multi-layer back-propagation neural network is applied. The system is applied to primary restorative transmission lines in korean power system and the result showed satisfactory performance.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2006.05a
• /
• pp.355-358
• /
• 2006

A linear acoustic analysis is conducted to examine bituning of acoustic resonators for acoustic damping in a combustion chamber of liquid rocket engine. Bituned resonators are tuned to the two principal modes, the first tangential(1T) and the first radial(1R) modes. First, the acoustic-damping effect of monotuned resonators is investigated. The damping capacity is quantified by damping factor as a function of the number of the resonators monotuned to 1T or 1R mode. Next, the damping characteristics of the bituned resonators are investigated. From the numerical data, the number of resonators, to be tuned to 1T and 1R modes, respectively, can be selected properly.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.21 no.7
• /
• pp.71-76
• /
• 2022

This study describes an evaluation of the vibration-level reduction effect of natural rubber inserted between two aluminum blocks, in which the modal parameters are predicted using two different damping systems. A numerical model with two degrees of freedom was established for both the cases. One was an eigenvalue problem analysis using a state space method and general viscous damping, whereas the other was a method using hysteretic damping. The modal parameters obtained from these two approaches were compared with those obtained from the finite element method using a commercial package. As a result, the natural frequencies observed in the complex frequency response curve were consistently less than the average of four percents. The damping ratios also showed good agreement within a reasonable range. However, the hysteretic damping system showed a relatively larger difference for all modal parameters. This suggests that the analysis procedure makes it easier to predict the vibration transmission characteristics of the shape and configuration of any cushioning layer.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 1995.04a
• /
• pp.130-135
• /
• 1995

Wind-induced vibration of buildings with viscoelastic dampers are studied analytically. The added viscoelastic dampers change the damping distribution and reduce the response of buildings. The distribution of damping resistance that results from these viscoelastic dampers is known as non-classical or non-proportional. Non-classically damped structures are analyzed by state-space approach. However, this approach is complex and time-consumming compared to classical approach. This paper is aimed at the analysis of wind-induced Vibration Of buildings With Viscoelastic dampers. The Process Of State-Space approach is studied and the approximate analysis is suggested to overcome the complex and time-consuming access. For numerical certification, PSDF(Power Spectral Density Function) is obtained. Autocorrelation function is obtained in time domain and PSDF is obtained by fourier transformation of this function in frequency domain. It is found that Approximate method can give close approximation to exact solution.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2007.11a
• /
• pp.708-713
• /
• 2007

Finite element model updating has been performed using an optimization technique in the paper. The objective function consists of natural frequencies, modal assurance criterion values, and bandwidths of modes, which are obtained from finite element analysis and experiment. Young's modulus and damping coefficient of the material are selected as design variables whose values are modified to make the objective function as small as possible. To consider the loading effect of an accelerometer, its mass and moment of inertia are added to design variables. This model updating method has been applied to a cantilever beam, and experimental data are measured by modal test.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.11a
• /
• pp.950-953
• /
• 2006

The floor impact noise of concrete structures in apartments buildings is affected from the flexural wave propagation characteristics. Accordingly, the measurement of wave propagation characteristics is required for suggestion of efficient method to reduce the impact noise. The purpose of this article is to propose an experimental technique to measure dynamic properties of concrete structures. The method was proposed using the flexural wave propagation characteristics. Wave speeds, bending stiffness and their loss factors are estimated from which the vibration dissipation capabilities are investigated. Several different concrete beam structures were custom-built for measurement. The damping treatments using viscoelastic materials for reducing noise generation are also tested. The beam transfer function of the damped beam is predicted using the compressional damping model from which the mechanism of the vibration energy dissipation is investigated.

• Coupled systems mechanics
• /
• v.5 no.2
• /
• pp.157-190
• /
• 2016

This paper deals with frequency analysis of Euler-Bernoulli beams carrying an arbitrary number of Kelvin-Voigt viscoelastic dampers, subjected to harmonic loads. Multiple external/internal dampers occurring at the same position along the beam axis, modeling external damping devices and internal damping due to damage or imperfect connections, are considered. The challenge is to handle simultaneous discontinuities of the response, in particular bending-moment/rotation discontinuities at the location of external/internal rotational dampers, shear-force/deflection discontinuities at the location of external/internal translational dampers. Following a generalized function approach, the paper will show that exact closed-form expressions of the frequency response under point/polynomial loads can readily be derived, for any number of dampers. Also, the exact dynamic stiffness matrix and load vector of the beam will be built in a closed analytical form, to be used in a standard assemblage procedure for exact frequency response analysis of frames.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2009.10a
• /
• pp.850-854
• /
• 2009

Approximate analysis for a building installed with a friction damper is revisited to get insight of its dynamic behavior. Energy balance equation is used to have a closed analytical form solution of dynamic magnification factor (DMF) for the building with combined viscous and friction damping. It is found out that DMF is dependent on friction force ratio and resonance frequency. Linear transfer function from input external force to output building displacement is obtained by simplifying DMF equation. Root mean square of building displacement is derived under earthquake-like random excitation. Finally, design of friction damper is proposed by processing target control ratio, damping ratio factor, and friction force in sequence.

• Proceedings of the KSME Conference
• /
• 2004.11a
• /
• pp.1110-1115
• /
• 2004

Acoustic behavior in gas turbine combustor with acoustic resonator is investigated numerically by adopting linear acoustic analysis. Helmholtz-type resonator is employed as acoustic resonator to suppress acoustic instability passively. The tuning frequency of acoustic resonator is adjusted by varying its length. Through harmonic analysis, acoustic-pressure responses of chamber to acoustic excitation are obtained and the resonant acoustic modes are identified. Acoustic damping effect of acoustic resonator is quantified by damping factor. As the tuning frequency of acoustic resonator approaches the target frequency of the resonant mode to be suppressed, mode split from the original resonant mode to lower and upper modes appears and thereby complex patterns of acoustic responses show up. Considering mode split and damping effect as a function of tuning frequency, it is desirable to make acoustic resonator tuned to broad-band frequencies near the maximum frequency of those of the possible upper modes.

• Smart Structures and Systems
• /
• v.4 no.3
• /
• pp.279-290
• /
• 2008

The modeling and parameter estimation of a damped one-degree-of-freedom mass-spring system is examined. This paper presents a method for estimating the system parameters (damping coefficients and natural frequency) from measured free-vibration motion of a system that is modeled to include both subcritical viscous damping and kinetic Coulomb friction. The method applies a commercially available least-squares curve-fitting software function to fit the known solution of the equations of motion to the measured response. The method was tested through numerical simulation, and it was applied to experimental data collected from a laboratory mass-spring apparatus. The mass of this apparatus translates on linear bearings, which are the primary source of light inherent damping. Results indicate that the curve-fitting method is effective and accurate for both perfect and noisy measurements from a lightly damped mass-spring system.