• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.840-840
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• 2003

Operational Modal Analysis (OMA) is a technique for identification of modal parameters by measurement of only the system's response. On many lightweight structures, such as load-speaker cones and disk drive read/write heads, is impossible or impractical to measure the input forces. Another characteristic of lightweight structure is their sensitivity to mass loading from sensors. The Scanning Laser Doppler Vibrometry(SLDV) allows response measurements to be taken without mass loading. One disadvantage of OMA testing compared to tradition input output modal testing is the OMA mode shapes are un-scaled. This means that the mode shape obtained from an OMA test can not used for analytical structural modification studies. However, the un-scaled mode shapes from an OMA test can be used to update a Finite Element Model (FEM). The updated FEM can then be used to analytically predict the effect of structural modifications. This paper will present the results of an OMA test performed on a simple plate and motor in operating conditions. The un-scaled mode shapes from this test will be used to update a FEM model of the system. The updated FEM model will be then be used to predict the effect of attaching a mass to the plate. The shapes predicted by the FEM for the modified system will be compared to a second OMA test on the modified system

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1086-1088
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• 2005

It is necessary to modify the state-of-the-art of vector control theory, because of the phase asymmetry(static end effect) in the Linear Induction Motor(LIM). The dynamic characteristic analysis method of the vector controlled LIM using coupled FEM and control algorithm taking into account the movement is proposed. The focus of this paper is the analysis relative to phenomena of static end effect due to the motor structure. To prove the propriety of the proposed method, the Digital Signal Processor(DSP) installed experimental devices are equipped and the experiment is performed.

• International Journal of High-Rise Buildings
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• v.4 no.1
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• pp.9-25
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• 2015

Field measurements of various structures have been conducted for many purposes. Measurement data obtained by field measurement is very useful to determine vibration characteristics including dynamic characteristics such as the damping ratio, natural frequency, and mode shape of a structure. In addition, results of field measurements and modal identification can be used for modal updating of FEM analysis, for checking the efficiency of damping devices and so on. This paper shows some examples of field measurements and modal identification for structural health monitoring. As the first example, changes of dynamic characteristics of a 15-story office building in four construction stages from the foundation stage to completion are described. The dynamic characteristics of each construction stage were modeled as accurately as possible by FEM, and the stiffness of the main structural frame was evaluated and the FEM results were compared with measurements performed on non-load-bearing elements. Simple FEM modal updating was also applied. As the next example, full-scale measurements were also carried out on a high-rise chimney, and the efficiency of the tuned mass damper was investigated by using two kinds of modal identification techniques. Good correspondence was shown with vibration characteristics obtained by the 2DOF-RD technique and the Frequency Domain Decomposition method. As the last example, the wind-induced response using RTK-GPS and the feasibility of hybrid use of FEM analysis and RTK-GPS for confirming the integrity of structures during strong typhoons were shown. The member stresses obtained by hybrid use of FEM analysis and RTK-GPS were close to the member stresses measured by strain gauges.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.645-650
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• 2004

There have been lots of efforts to analyze the dynamic characteristics of mechanical systems. However, it is difficult to know the dynamic characteristics of mechanical systems composed of many parts with joints. Specially, in case of a bolted joint structure, no effective modeling method has been defined to acquire dynamic characteristics of the structure, using the finite element (FE) analysis. In this research, a linear dynamic model is developed for bolted joints and large interfaces using con frusta method and linear spring elements, respectively. The developed modeling method for bolted joints is verified based on the experimental result.

• Journal of Mechanical Science and Technology
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• v.16 no.4
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• pp.436-447
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• 2002

In this study, the dynamic response of a catenary system that supplies electrical power to high-speed trains is investigated. One of the important problems which is accompanied by increasing the speed of a high-speed rail, is the performance of stable current collection. Another problem which has been encountered, is maintaining continuous contact force between the catenary and the pantograph without loss of panhead. The dynamic analyses of the catenary based on the Finite Element Method (FEM) are performed to develop a pantograph suitable for high speed operation. The static deflection of the catenary, the stiffness variation in contact lines, the dynamic response of the catenary undergoing the force of a constantly moving load and the contact force were calculated. It was confirmed that a catenary model is necessary to study the dynamic characteristics of the pantograph system.

• KSTLE International Journal
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• v.1 no.1
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• pp.43-47
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• 2000

Oil seals will experience a small amplitude dynamic excitation due to the shaft eccentricity as well as out-of-roundness of the shaft. The direct integration method is selected to analyze the time domain response of the seal lip-shaft contact. The physical properties of rubber seal materials are experimentally analyzed. Effects of both frequency and temperature on the material stiffness behavior are investigated for the linear viscoelastic materials of the seal. Using the nonlinear transient model, a finite element analysis of the lip-shaft contact behaviors under dynamic conditions is presented as a function of the shaft eccentricity, the shaft interference and the garter spring stiffness. The FEM results based on the experimental data indicate that the increased rotating speed may produce the separation conditions. These results will be very useful in predicting the leakage of oil seals under dynamic conditions.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.6
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• pp.44-52
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• 1997

As part of the effort to reduce the weight of powertrain, a hollow crankshaft has been designed. The mass reduction of the crankshaft changes the dynamic properties of the crankshaft such as moment of inertia, and torsional, bending stiffness. The purpose of this paper is to compare the dynamic behavior of the hollow crankshaft with that of the original, solid crankshaft. Global dynamic behavior of the crankshaft is analyzed bgy the transfer matrix method(TMM). The crankshaft has been modeled by 38 lumped mass and stiffness elements. The dynamic patameters of each lumped element are provided by Finite Element Method(FEM). The responses of the crankshaft from TMM are fed back as loading conditions to the Finite Element model to obtain dynamic stresses for critical areas of the crankshaft.

• Journal of Power System Engineering
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• v.1 no.1
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• pp.91-97
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• 1997

Recently, it is increased by degrees to construct complex and large structures. In general, in order to solve the dynamic problem of these structures they have used finite element method(FEM). In this method, however, it is necessary to prove whether its results are correct or not. Therefore it requires much effort, time and many expenses for dynamic analysis of complex and large structures. Authors have developed the transfer dynamic stiffness coefficient method(TDSCM) which is the new vibration analysis method for complex and large structures on personal computer, and confirmed that the results of this method are good for these structures on personal computer. In this paper, TDSCM is applied to the torsional vibration analysis for the shaft system which consist of concentrated disks and shafts of continuous body. First, we formulate algorithms for torsional free and forced vibration analysis, and compare the results of TDSCM and FEM.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.190-195
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• 1997

Recently it is increased by degrees to construct complex or large lattice type structures such as bridges, towers, cranes, and structures that can be used for space technology. In general, in order to analyze, these structures we have used the finite element method(FEM). In this method, however, it is necessary to use a large amount of computer memory and computation time because the FEM requires many degrees of freedom for solving dynamic problems for these structures. For overcoming this problem, the authors have developed the transfer dynamic stiffness coefficient method(TDSCM). This method is based on the concepts of the transfer and the synthesis of the dynamic stiffness coefficient which is related to force and displacement vector at each node. In this paper, the authors formulate vibration analysis algorithm for a complex and large lattice type structure using the transfer of the dynamic stiffness coefficient. And the validity of TDSCM demonstrated through numerical computational and experimental results.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.1
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• pp.10-18
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• 2003

This paper presented a design and control of a biped walking RGO(robotic gait orthosis) and its simulation. The biped walking RGO was distinguished from the other one by which had a very light-weight and a new RGO system will be made of 12-servo motors and 12-controllers. The vibration evaluation of the dynamic PLS(posterior leaf splint) on the biped walking RGO was used to access by the 3-axis accelerometer with a low frequency vibration of less than 30 Hz. The galt of the biped walking RGO depends on the constrains of mechanical kinematics and the initial posture. The stability of dynamic walking was investigated by analyzing the ZMP (zero moment point) of the biped walking RGO. It was designed according to the human wear type and was able to accomodate itself to the environments of S.C.I. Patients. The Joints of each leg were adopted with a good kinematic characteristics. To analyse joint kinematic properties. we made the strain stress analysis of the dynamic PLS and the analysis study of FEM with a dynamic PLS.