• Journal of Power System Engineering
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• v.16 no.1
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• pp.24-29
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• 2012

Recently, in the movie theater, the special chair is installed to maximize the viewing effect of movies. It is structured to convey a vibrational stimulus to a specially-designated parts of human body by attaching a vibration transducer to a existing theater chair. This paper describes the analysis of the vibration transfer characteristic of a foaming sponge seat for the design of the special chair. We could not apply the structural analysis S/W because it is difficult to obtain the mechanical properties and damping coefficients of the various type sponges. And then we computed the transfer functions by the global curve fitting program based on experimental modal analysis. The experimental response results comparatively coincide with those by the global curve fitting program. We also could obtain the natural frequencies, the modal damping coefficient ratio, the modal vectors and the whole transfer functions. Therefore we could analyze the dynamic characteristic for design of foaming sponge seat.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.8
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• pp.749-756
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• 2004

While designing shafting in reciprocating machines with internal combustion engines which derive generators, pumps, and vehicles, it is very important to calculate the additional stress of shafting by torsional vibration. In this paper, the transfer stiffness coefficient method which is based on the successive transfer of stiffness coefficient was applied to the calculation of the additional stress of shafting in reciprocating machine by torsional vibration. In order to confirm the effectiveness of the present method, a propulsion shafting with a diesel engine in a vessel was considered as the computational example of shafting in reciprocating machine. The results calculated by the present method were compared with those of the modal analysis method, the mechanical impedance method, and free vibration analysis.

• Journal of KSNVE
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• v.9 no.4
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• pp.703-713
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• 1999

A side mirror is an important safety tool with which the driver can observe objects out of sight. This paper presents an organized design technology for the side mirror of improved vibration characteristics. Resonance response to forced vibration is critical to observability through the mirror to be designed. This study aims at the reduction of vibration level by the modification of mirror structures and consequent effects are predicted by computer simulations. We used a three-dimensional solid modeling and the modal and frequency analysis ; Pro/Engineer is used as a solid modeler; Pro/Mechanica for vibration analysis. The simulation results are compared with those obtained in experiemnts to check the validity by the three-dimensional modeling. The design technique of side mirror has been established and found to be effective in vibration analysis of redesigned parts.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.12 s.105
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• pp.1332-1339
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• 2005

The vibration of Powertrain are one of the import design characteristics of a vehicle. Powertrain is mostly mounted to the front subframe and powertrain mounting has an important role in determining the vehicle vibration characteristics. In this paper, the accuracy of the vibration analysis for the front subframe is discussed. The dynamic characteristic of subframe are measured from vehicle test and the finite element model updating are performed that natural frequency, mass and MAC of the experimental and theoretical modal analysis are compared. The subframe mounting stiffness are obtained the iteration method based on the vibration of subframe from vehicle test. Finally, the result of dynamic analysis which is operated dynamic load is compared with experimental one of vehicle test.

• International Journal of Aerospace System Engineering
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• v.8 no.1
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• pp.1-13
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• 2021

Contra-rotating fan is comprised of two rotors which are rotating in the opposite direction. The fan stages are named rotor-1 and rotor-2. Benefits from the use of contra rotation are in terms of better efficiency and improved thrust to weight ratio. Failure of contra-rotating fan stage blade in-service results in safety risks, repair costs, and revenue losses. This paper focuses on the vibration analysis and one way fluid-structure interaction of high aspect ratio, low speed contrarotating fan rotors. Modal analysis and modal pre-stress analysis of contra-rotating fan rotors were carried out to calculate the natural frequencies, One way fluid-structure interaction (FSI) was carried out where the computational analysis of the blades was performed using ANSYS CFX. The boundary conditions for CFD analysis were considered from the actual experimental velocity flow field at the inlet and pressure outlet. Based on the results obtained from the CFD analysis, the structural analysis such as deformation and Von-Misses stresses was carried out by using the finite element method (FEM) with ANSYS. The results provide necessary guidelines for the safe running of the contra-rotating fan. The analysis also will be helpful to understand the change of flow behavior due to a rotor deformation.

• Smart Structures and Systems
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• v.17 no.2
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• pp.209-230
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• 2016

The Canton Tower is a high-rise slender structure with a height of 610 m. A structural health monitoring system has been instrumented on the structure, by which data is continuously monitored. This paper presents an investigation on the identified modal properties of the Canton Tower using ambient vibration data collected during a whole day (24 hours). A recently developed Fast Bayesian FFT method is utilized for operational modal analysis on the basis of the measured acceleration data. The approach views modal identification as an inference problem where probability is used as a measure for the relative plausibility of outcomes given a model of the structure and measured data. Focusing on the first several modes, the modal properties of this supertall slender structure are identified on non-overlapping time windows during the whole day under normal wind speed. With the identified modal parameters and the associated posterior uncertainty, the distribution of the modal parameters in the future is predicted and assessed. By defining the modal root-mean-square value in terms of the power spectral density of modal force identified, the identified natural frequencies and damping ratios versus the vibration amplitude are investigated with the associated posterior uncertainty considered. Meanwhile, the correlations between modal parameters and temperature, modal parameters and wind speed are studied. For comparison purpose, the frequency domain decomposition (FDD) method is also utilized to identify the modal parameters. The identified results obtained by the Bayesian method, the FDD method and a finite element model are compared and discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.72-77
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• 2011

In this study, the natural frequencies and mode shape of an external mounting pod were verified using the modal analysis and modal testing technique for a pod mounted on an aircraft. The procedure associated with the FEM building of an external mounted pod to predict the dynamic behavior of aircraft structures is described. The simplified FEM reflecting the results of the modal testing of a pod is built through the optimization, applied to the structural dynamic model of an Aircraft, used to verified the stability of vibration and flutter of an aircraft.

• Structural Engineering and Mechanics
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• v.64 no.3
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• pp.279-285
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• 2017

Modal expansion technique (MET) is a method to estimate the vibration fields of flexible structures by using eigenmodes of the structure and the signals of sensors. It is the useful method to estimate the vibration fields but has the truncation error since it only uses the limit number of the eigenmodes in the frequency of interest. Even though block-wise MET performed frequency block by block with different valid eigenmodes was developed, it still has the truncation error due to the absence of other eigenmodes. Thus, this paper suggested an improved block-wise modal expansion technique. The technique recovers the truncation errors in one frequency block by utilizing other eigenmodes existed in the other frequency blocks. It was applied for estimating the vibration fields of a cylindrical shell. The estimated results were compared to the vibration fields of the forced vibration analysis by using two indices: the root mean square error and parallelism between two vectors. These indices showed that the estimated vibration fields of the improved block-wise MET more accurately than those of the established METs. Especially, this method was outstanding for frequencies near the natural frequency of the highest eigenmode of each block. In other words, the suggested technique can estimate vibration fields more accurately by recovering the truncation errors of the established METs.

• Structural Engineering and Mechanics
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• v.61 no.2
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• pp.267-274
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• 2017

In this study was investigated of possibility using the recorded micro tremor data on ground level as ambient vibration input excitation data for investigation and application Operational Modal Analysis (OMA) on the bench-scale earthquake simulator (The Quanser Shake Table) for model steel structures. As known OMA methods (such as EFDD, SSI and so on) are supposed to deal with the ambient responses. For this purpose, analytical and experimental modal analysis of a model steel structure for dynamic characteristics was evaluated. 3D Finite element model of the building was evaluated for the model steel structure based on the design drawing. Ambient excitation was provided by shake table from the recorded micro tremor ambient vibration data on ground level. Enhanced Frequency Domain Decomposition is used for the output only modal identification. From this study, best correlation is found between mode shapes. Natural frequencies and analytical frequencies in average (only) 2.8% are differences.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.59-62
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• 2008

This paper presents the procedure and the results of modal identification testing of a seismic monitoring system central processing unit cabinet for a nuclear power plant. This paper also provides a model updating for making effective analytical modeling of cabinet-type electrical equipment by comparing the test results with the analysis results. From the test results and their interpretation, modal properties (modal frequency, mode shape, and modal damping) of the specimen were satisfactorily identified. However, the analysis results may need to study further to find the effective and presentative model for the cabinet-type electrical equipment. This paper just presents the first stage of the research project "Development of dynamic behavior analysis technique of dynamic structure system" which is trying to build the lumped mass beam stick model even their results do not agree well with the test results.