• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.283-284
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• 2002

Ball bearings (BB) are generally used in spindle of‘ disk drives at present, but they have been known that BB generate high frequency vibration. Fluid dynamic bearings (FDB) having high-rotational accuracy and small vibration characteristics have been developed as next generation spindles. Especially. a ferro fluid bearing (FFB) spindle has the advantage to prevent leakage and dispersion of lubricating oil using a ferro seal. In this study, we measured damping characteristics and frequency characteristics of these bearing spindles using a high-frequency vibration base. High frequency excitation was added to these bearing spindles mounted on the vibration base, and we proved that FFB and FDB spindles have effective damping.

• Smart Structures and Systems
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• v.17 no.6
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• pp.1107-1127
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• 2016

Studies on dynamic characteristics of the hanger vibration using field monitoring data are important for the design and evaluation of high-speed railway truss arch bridges. This paper presents an analysis of the hanger's dynamic displacement responses based on field monitoring of Dashengguan Yangtze River Bridge, which is a high-speed railway truss arch bridge with the longest span throughout the world. The three vibration parameters, i.e., dynamic displacement amplitude, dynamic load factor and vibration amplitude, are selected to investigate the hanger's vibration characteristics in each railway load case including the probability statistical characteristics and coupled vibration characteristics. The influences of carriageway and carriage number on the hanger's vibration characteristics are further investigated. The results indicate that: (1) All the eight railway load cases can be successfully identified according to the relationship of responses from strain sensors and accelerometers in the structural health monitoring system. (2) The hanger's three vibration parameters in each load case in the longitudinal and transverse directions have obvious probabilistic characteristics. However, they fall into different distribution functions. (3) There is good correlation between the hanger's longitudinal/transverse dynamic displacement and the main girder's transverse dynamic displacement in each load case, and their relationships are shown in the hysteresis curves. (4) Influences of the carriageway and carriage number on the hanger's three parameters are different in both longitudinal and transverse directions; while the influence on any of the three parameters presents an obvious statistical trend. The present paper lays a good foundation for the further analysis of train-induced hanger vibration and control.

• Structural Engineering and Mechanics
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• v.75 no.4
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• pp.519-527
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• 2020

Dynamic analysis of a vehicle-track coupling system is important to structural design, damage detection and condition assessment of the structural system. Deterministic analysis of the vehicle-track coupling system has been extensively studied in the past, however, the structural parameters of the coupling system have uncertainties in engineering practices. It is essential to treat the parameters of the vehicle-track coupling system with consideration of uncertainties. In this paper, a method for predicting the bounds of the vehicle-track coupling system responses with uncertain parameters is presented. The uncertain system parameters are modeled as fuzzy variables instead of conventional random variables with known probability distributions. Then, the dynamic response functions of the coupling system are transformed into a component function based on the high dimensional representation approximation. The Lagrange interpolation method is used to approximate the component function. Finally, the bounds of the system's dynamic responses can be predicted by using Monte Carlo method for the interpolation polynomials of the Lagrange interpolation function. A numerical example is introduced to illustrate the ability of the proposed method to predict the bounds of the system's dynamic responses, and the results are compared with the direct Monte Carlo method. The results show that the proposed method is effective and efficient to predict the bounds of the system's dynamic responses with fuzzy variables.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.04a
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• pp.291-300
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• 1998

This paper demonstrates how ambient vibration measurements at a limited number of locations can be effectively utilized to estimate parameters of a finite element model of a large-scale structural system involving a large number of elements. System identification using ambient vibration measurements presents a challenge requiring the use of special identification techniques, which ran deal with very small magnitudes of ambient vibration contaminated by noise without the knowledge of input farces. In the present study, the modal parameters such as natural frequencies, damping ratios, and mode shapes of the structural system were estimated by means of appropriate system identification techniques including the random decrement method. Moreover, estimation of parameters such as the stiffness matrix of the finite element model from the system response measured by a limited number of sensors is another challenge. In this study, the system stiffness matrix was estimated by using the quadratic optimization involving the computed and measured modal strain energy of the system, with the aid of a sensitivity relationship between each element stiffness and the modal parameters established by the second order inverse modal perturbation theory. The finite element models thus identified represent the actual structural system very well, as their calculated dynamic characteristics satisfactorily matched the observed ones from the ambient vibration test performed on a large-scale structural system subjected primarily to ambient wind excitations. The dynamic models identified by this study will be used for design of an active mass damper system to be installed on this structure fer suppressing its wind vibration.

• International Journal of Automotive Technology
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• v.6 no.4
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• pp.383-390
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• 2005

This study proposes an innovative design guideline to assist the evaluation and improvement of the dynamic comfort of vehicle seating. The existing evaluation method for the comfort of vehicle seating was investigated to broach problems in evaluation. It was found that the currently existing evaluation method employs the resonance frequency of the vibration system composed of the seat and the human body and the maximum vibration transmissibility. This study proposes a design guideline aimed at the enhancement of vibration transmission characteristics above the resonance range, particularly within the range of 10-18 Hz. In order to meet this guideline, a seat was constructed out of foam having a low damping coefficient. It was then installed in a vehicle for a driving test. The driving test confirmed the improvement of the dynamic comfort of the seat. The result of evaluation of the improved seat using the SEAT index, an industry standard widely used to evaluate the dynamic comfort of a seat considering the perceptivity characteristics of the human body, showed that the perceptive vibration transmission had reduced by more than $11\%$. The effect of the modification of seat foam was also verified through a subjective assessment of dynamic comfort of the seats.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.485-491
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• 2000

We obtain the mathematical model of the hard disk drive actuator system from the system response data of the finite element analysis or experimental results. System response data including the dynamics of the considered system are expressed as the mathematical model. It allows the dynamic analysis of the actuator system without resort to the repetitive finite element modeling work. Even though the dynamic characteristics of the system are affected somewhat by the structural modification and the change of the dynamic properties, we can use the modified size and material properties of the actuator system in the mathematical model to some extent. In this study, we express the mathematical model of the simplified rectangular plate first and then proceed to the actual hard disk drive actuator system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.305-310
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• 2007

This paper presents a damper system design in torque converter to minimize the vibration in powertrain of automatic transmission vehicle. The lock-up clutch in torque converter makes engine and transmission connected directly. When the lock-up clutch is engaged the torque fluctuation of engine is attenuated by the damper system. This function decides the vehicle power-train dynamic characteristics. At first, the dynamic hysteresis effect with any self and surface to surface contact problems of the damper springs in the damper system for torque converter is analyzed by using FEM. It is shown that these simulation results have a good design reference to energy dissipation operating by damper system in torque converter. And, to calculate dynamic characteristics, the vehicle model is structured by using $AMESim^{(R)}$?? that is a common use program. The vehicle model shows the frequency response of vehicle by changing the stiffness of damper spring, and these results lead the most suitable stiffness of spring. Also, new damper system is analyzed resonance frequency variation and is compared with prior damper.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.258-263
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• 2005

The nearest variety of the industrial world requires using the high precision and resolution positioning technology to do a semi-conductor, information field , and measurement field. It is especially important for the positioning technology that makes up a proper controller, is affected by the minimal heat and vibration, and can control a structurally generated non-linear friction factor to determine the efficiency of the system. The paper is to analyze the vibration characteristic according to the speed of linear motor and grasp the dynamic characteristic through the modal test and show the verification of the experimental result and design parameters by using FEM(Finite Element Method). Also, it shows the optimum standard analyzed the acceleration patterns of the moving part that lead to the vibration source in linear motor. It presents the analyzed dynamic of linear motor in compliance with a change of the non-linear factor.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.10a
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• pp.31-35
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• 2001

Three dimensional dynamic cutting can be postulated as an equivalent orthogonal dynamic cutting through the plane containing both the cutting vector and the chip flow velocity vector in cutting process. An analytical expression of dynamic cutting force is obtained from the cutting parameters determined by the static three dimensional cutting experiments. Particular attention is paid to the energy supplied to the vibration of the tool behind the vertical vibration and the direction. The phase lag of the horizontal vibration of the tool behind the vertical vibration and the direction angel of the fluctuating cutting force must be regarded in point of stability limits. Chatter vibration can effectively be suppressed by enlarging the dynamic rigidity of the cutting system in the vertical cutting force direction. A good agreement is found between the stability limits predicted by theory and the critical width of cut determined by experiments.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.6
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• pp.717-725
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• 2004

A power generation systems are proposed to convert ambient mechanical vibration into electrical energy using cantilever-type piezoelectric materials. The vibration-based power device can be used for self-powered systems without batteries. This paper presents the theoretical analysis for the coupled equations of piezoelectric and structural motions and investigates the dynamic characteristics of the self-power system using transfer function method. The theoretical model is verified by the finite element analysis of the resonance frequency, the dynamic response of the structure and the sensor sensibility. Experimental results measured using a prototype system agree with the theoretical predictions. The system is shown to produce 34.5 ㎼ in average. Finally, we perform the optimal design for system variables to maximize output power.