• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.383-388
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• 2003

As an effective way of response evaluation in structural vibration analysis, the phase vector sum(PVS) method used in shaft torsional vibration analysis is introduced. Basic relation of PVS applicable to structural problem is derived and applied to Diesel engine structures. Concepts of forced phase vector sum (FPVS) and significance level (SL) are proposed to visualize the correlation between excitation orders and vibration modes in the SL map. The maximum responses and SL are compared and reviewed to confirm the validity of the method. It is regarded FPVS is adequate to newly evaluate the structural vibration based on excitation information.

• Journal of Power System Engineering
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• v.12 no.1
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• pp.58-65
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• 2008

A method to test thin-walled tubes by guided ultrasonic wave is reported. The principle is that applicate two types of axially symmetric ultrasonic tube modes and "longitudinal" modes with particle displacement, which is coupled in axial and radial directions for transverse failures and torsional modes, oscillating in the circumferential direction only, for longitudinal failures. Both types of modes propagate along the tube in the axial direction. Therefore, a pulse-echo technique is possible. The pulses are excited and received at one end of the tube without contact electro-dynamic transducers. As soon as the tubes is put into a transducer coil at one end, the test of the whole tube can be accomplished in a few milliseconds. It is not necessary to rotate and transport the tubes during the test.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1994.03a
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• pp.37-46
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• 1994

In metal forming, there ar problems with recurrent geometric characteristics and without explicitly prescribed boundary conditions. In such problems, so-called recurrent boundary conditions must be introduced. The present study deals with nonsteady-state three-dimensional finite element analysis for extrusion of a trocoidal helical gear through a curved die. The boundary-directed remeshing scheme based on the modular remeshing technique is developed to reduce the errors arising in fitting old and new mesh systems. The computed extrusion pressure in reaching the near steady-state loading stage is compared with the results of the experiment and the steady-state analysis. The three-dimensional deformed pattern involving warping at the extruded end due to torsional deformation mode is demonstrated.

• Journal of the Korean Society for Railway
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• v.9 no.1 s.32
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• pp.12-17
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• 2006

The bridge to be analyzed is a self-anchored suspension bridge which is constructed within the country. Forced vibration test was performed with oscillator for verification of safety, maintenance and management. In this study, the feasibility of deduction was verified with the modified analysis model by comparing natural frequency, natural mode and damping ratio of the real bridge, which are obtained from the vibration test of the whole bridge after construction of 3-dimensional self-anchored cable suspension bridge, with the eigenvalue of analytic computation model and evaluating them. As a result of study, the friction of bridge bearing must be considered to get the natural frequencies of flexural vibration, and evaluating the polar moment of inertia is critical factor in analysis modeling in case of torsional vibration. The logarithmic damping ratio of the test appeared to exceed the ordinary one assumed at the design phase.

• Steel and Composite Structures
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• v.13 no.3
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• pp.225-238
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• 2012

Steel structural elements with web-tapered I cross section, are usually made of welded thin plates. Due to the nonrectangular shape of the element, thin web section may be obtained at the maximum cross section height. The buckling strength is directly influenced by lateral restraining, end support and initial imperfections. If no lateral restraints, or when they are not effective enough, the global behaviour of the members is characterized by the lateral torsional mode and interaction with sectional buckling modes may occur. Actual design codes do not provide a practical design approach for this kind of elements. The paper summarizes an experimental study performed by the authors on a relevant number of elements of this type. The purpose of the work was to evaluate the actual behaviour of the web tapered beam-columns when applying different types of lateral restraints and different web thickness.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.992-998
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• 1992

This paper presents a method for dynamic analysis of golf club. In the analysis, the sweet spot of golf club is defined based on the magnitude of torsional vibration, and transfer matrix method is employed for numerical calculations. It is shown that the calculated natural frequencies, mode shapes and transfer function agree well with the experimental results.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.10
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• pp.967-975
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• 2007

A rotordynamic analysis was performed with a dry vacuum pump, which is a major equipment in modern semiconductor and LCD manufacturing processes. The system is composed of screw rotors, lobes picking air, helical gears, driving motor, and support rolling element bearings of rotors and motor. The driving motor-screw rotor system has a rated speed of 6,300 rpm, and was modeled utilizing a rotordynamic FE method for analysis, which was verified through 3-D FE analysis and experimental modal analysis. As loadings on the bearings due to the gear action were significant in the system considered, each resultant bearing load was calculated by considering the generalized forces of the gear action as well as the rotor itself. Each resultant bearing loading was used in calculating each stiffness of rolling element bearings. Design goals are to achieve wide separation margins of lateral and torsional critical speeds, and favorable unbalance responses of the rotor in the operating range. Then, a complex rotordynamic analysis of the system was carried out to evaluate its forward synchronous critical speeds, whirl natural frequencies and mode shapes, unbalance responses under various unbalance locations, and torsional interference diagram. Results show that the entire system is well designed in the operating range. In addition, the procedure of rotordynamic analysis for dry vacuum pump rotor-bearing system was proposed and established.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.1
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• pp.114-119
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• 2009

The authors have investigated the NVH problems of drive system in full vehicle test. However it is difficult to define the NVH problems of driveline system. Since it is hard to measure the rotating part and it is vague that only the drive system induces the NVH problem. Vibration in a driveline is presented in this paper. In the experiment, the rear sub-frame and propeller shafts and axle were composed and mounted with rubber each other. For applying the vibration input instead of the torsional vibration effect of an engine, the shaker was taken. In particular, torsional vibration due to fluctuating forced vibration excitation across the joint between driveline and rear sub-frame was carefully examined. Accordingly, the joint response was checked from experiments and the FE-simulation using FRF (frequency response function) analysis was performed. All test results were signal processed and validated against numerical simulations. In present study, the new test bench for measuring the vibration signal and simulating the vehicle chassis system was proposed. The modal value and the mode shape of components were analyzed using the CAE model to identify the important components affecting driveline noise and vibration. It could be reached that the simplified test bench could be well established and be used for design guide and development of the vehicle chassis components.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.2
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• pp.9-18
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• 1999

The seismic over-strength factor Ω is evaluated for 4-story reinforced concrete buildings in Korea, which has low seismic intensity. For this study, the seismic load suggested in' Aseismic guideline research- phase ll' (in Korea) is used. When 3D study-models are designed, span length and bay number are varied and accidental torsional moment is considered. And the models are analyzed by push-over analysis, in which external and internal frame are connected by rigid-link. As a result of numerical experiments, Ω is increased as the bay number or span length is increased. Because, by the including of accidental torsional moment in designing process, the increased ratio of strength of external columns is larger than the increased ratio of span length or bay number. And this makes the failure mode of model closer or strong-column and weak-beam mechanism.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.4
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• pp.243-248
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• 2022

Weight optimization was performed for a rotorcraft shaft system using one-dimensional Euler-Bernoulli beam elements. Torsion, shaft support stiffness such as bearings, flange mass are all considered. To guarantee structural dynamic stability, eigenvalue analysis was performed to avoid critical speed and tooth mesh excitation form the gearbox. The weight optimization was performed by adjusting the thickness and radius while the length of the shaft was fixed, and the optimization process was divided into two stages. In the first, the weight is optimized with the torsional strength constraint. In the second, the difference between the primary mode of shaft and the critical speed is maximized so that the primary mode of the shaft can avoid the critical speed while the constraint on the torsional strength of the shaft is satisfied according to the standard for shaft system stability (AMC P 706-201, 1974). The proposed method was verified by comparing the results of the optimal design using the given one-dimensional beam elements with the stress results of the 3D finite element and the actual manufactured shaft.