• 한국생산제조학회지
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• 제25권4호
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• pp.295-300
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• 2016

In the design of passive and active boring bars, the structural dimensions and shape of the vibration control boring bar are modified depending on the diameter and depth of the workpiece, which changes the dynamic behavior. Thus, the natural frequency, effective mass, and stiffness for the main structure of a tube-type boring bar need to be reset for each vibration control case. However, commercial finite element method (FEM) software and experimental modal analysis are mostly used at present despite being too time-consuming. To overcome the weaknesses of the two methods currently used for vibration control, we realized a graphical user interface (GUI) program for the modal analysis of a modified tube-type damping structure. The analysis results with the GUI program were compared to those with commercial FEM software in order to confirm the effectiveness of the former.

• Structural Engineering and Mechanics
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• 제44권1호
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• pp.51-60
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• 2012

Concrete sleepers are essential components of the conventional railway. As support elements, sleepers are always subjective to a variety of time-dependent loads attributable to the train operations, either wheel or rail abnormalities. It has been observed that the sleepers may deteriorate due to these loads, inducing the formation of hairline cracks. There are two areas along the sleepers that are more prone to crack: the central and the rail seat sections. Several non-destructive methods have been developed to identify failures in structures. Health monitoring techniques are based on vibration responses measurements, which help engineers to identify the vibration-based damage or remotely monitor the sleeper health. In the present paper, the dynamic effects of the cracks in the vibration signatures of the railway pre-stressed concrete sleepers are investigated. The experimental modal analysis has been used to evaluate the modal bending changes in the vibration characteristics of the sleepers, differentiating between the central and the rail seat locations of the cracks. Modal parameters changes of the 'healthy' and cracked sleepers have been highlighted in terms of natural frequencies and modal damping. The paper concludes with a discussion of the most suitable failure indicator and it defines the vibration signatures of intact, central cracked and rail seat cracked sleepers.

• 한국소음진동공학회논문집
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• 제13권10호
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• pp.813-820
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• 2003

Conventional modal analysis techniques are known to be inappropriate for asymmetrical rotor systems, when the equations of motion are written in the stationary coordinates, due to the presence of time varying parameters. This paper presents a generalized modal analysis method for asymmetrical rotor systems in the stationary coordinates, employing the modulated coordinates and the lambda matrix formulation. A numerical example with a flexible asymmetric rotor model is provided to demonstrate the effectiveness of the proposed modal analysis method. As an application of the proposed method, modal analysis is also performed with an open cracked rotor system.

• 한국소음진동공학회논문집
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• 제11권4호
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• pp.43-51
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• 2001

An experimental modal analysis is the process to identify structure's dynamic characteristics such as resonant frequencies, damping values and mode shapes. An experimental model was made of stainless steel in the shape of a circular cylindrical shell and installed on the test bed with jigs. For investigating vibrational characteristics of the continuous circular cylindrical shell with intermediate supports, modal testing is performed by using impact hammer, accelerometer and 8-channel FFT analyzer. The frequency response function(FRF) measurements are also made on the experimental model within the frequency range from 0 to 4kHz. Modal parameters are identified from resonant peaks in the FRF's and animated deformation patterns associated with each of the resonances are shown on a computer screen. The experimental results are compared with analytical and FEA results.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.526-531
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• 2003

Conventional modal analysis techniques are known to be inappropriate for asymmetrical rotor systems. when the equations of motion are written in the stationary coordinates, due to the presence of time varying parameters. This paper presents a generalized modal analysis method for asymmetrical rotor systems in the stationary coordinates, employing the modulated coordinates and the lambda matrix formulation. A numerical example with a flexible asymmetric rotor model is provided to demonstrate the effectiveness of the proposed modal analysis method. As an application of the proposed method, modal analysis is also performed with an open cracked rotor system.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 추계학술대회논문집; 한국과학기술회관; 6 Nov. 1997
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• pp.216-221
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• 1997

A strain modal testing method has been applied to a cantilever beam to investigate the characteristics of the method. By applying the method to an analytical and an experimental system, it was shown that accurate modal parameters can be estimated from the FRFs using a current modal parameter extraction algorithm. The modal parameters estimated by the method are more accurate than those by the conventional method which uses accelerometers when the tested system is of light weight. The strain response for a given excitation force and the force which causes the response can be predicted using the measured strain FRFS.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.275-278
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• 2005

The dynamic characteristics of rotor shafts for electric motors were investigated through the modal tests. The natural frequencies and modal dampings in each manufacturing stage of rotor core assembly were analyzed from the frequency response functions fer all 6 motors of a product model. The deviation of the each individual modal feature was found dependent on the mode shapes as well as the rotor assembly stage. The core stacking itself is known to widen the deviation of modal properties but fellowing processes of rotor bar insertion and swaging are confirmed to reduce the deviation. Finally the equivalent diameter of core part was estimated from the comparison of measured and calculated results to include the stiffness of core part.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.863-868
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• 2002

Operational Modal Analysis also known as Ambient Modal Analysis has an increasing interest in mechanical engineering. Especially on big structures where the excitation and not less important the determination of the forces is most often a problem. In a structure like a wind turbine wing where the modes occur both close in frequency and hi-directional the ambient excitation has big advantages. In this paper modal parameters are identified from the wing by operational modal analysis. For the parameter identification both parametric and non-parametric techniques are used. Advantages and disadvantages are discussed and results from the different techniques are compared

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.387-388
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• 2008

Finding reasonable flexural modes from the full vehicle modal testing has always been a difficult job to N&V engineers due to FRF inconsistency, nonlinearity, heavy damping and, in many cases, interactions between global body structural modes and massive isolate/non-isolated subsystem modes. This paper provides a brier overview of the mode map validation using single-run FRF measurement with highly sensitive accelerometers fur the full vehicle modal analysis and then it can be used to characterize the vehicle's global/local vibration performances, especially customer perceived "structural feel" typically below 40Hz.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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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.