• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.388-393
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• 2012

Vibration condition monitoring at low rotational speeds is still a challenge. Acoustic emission (AE) is the most used technique when dealing with low speed bearings. At low rotational speeds, the energy induced from surface contact between raceway and rolling elements is very weak and sometimes buried by interference frequencies. This kind of issue is difficult to solve using vibration monitoring. Therefore some researchers utilize artificial damage on inner race or outer race to simplify the case. This paper presents vibration signal analysis of low speed slewing bearings running at a low rotational speed of 15 rpm. The natural damage data from industrial practice is used. The fault frequencies of bearings are difficult to identify using a power spectrum. Therefore the relatively improved method of empirical mode decomposition (EMD), ensemble EMD (EEMD) is employed. The result is can detect the fault frequencies when the FFT fail to do it.

• Journal of Welding and Joining
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• v.15 no.1
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• pp.109-115
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• 1997

The arc stability and the metal transfer mode of high deposition GMA welding were investigated using various compositions of shielding gas with two types of filler, ie solid wire and metal cored wire. As for a solid wire, the transfer mode changed from axial spray to rotational spray with increasing wire feed rate (welding current) and the transition current was different with the gas composition. The gas composition also affected the apparent stability of rotating arc. As for a metal cored wire, on the other hand, no transition occurred and thus spray transfer mode could be applied with the welding current over 500A (deposition rate over 300g/min). Looking for the development of high deposition GMA welding process, above results were discussed in two different ways, one is to elevate the transition current, the other is to stabilize the rotational transfer mode.

• International Journal of Fluid Machinery and Systems
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• v.3 no.3
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• pp.211-220
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• 2010

The objective of this study is to clarify the occurrence of the high-speed mode of unsteady swirling flows in straight tubes. The unsteady flows generated in the tube were measured by means of a semiconductor-type pressure transducer and an FFT analyzer. The high-speed mode measured has rotational speed which is approximately equal to or higher than the peripheral velocity of the swirling flow. The unsteady flow is due to cell rotation in the circumferential direction of the tube. The occurrence of the high-speed mode was confirmed, and the characteristics (rotational speed, pressure amplitude, and phase) of this mode were clarified. In order to understand the measured unsteady flows, the three dimensional vortex core profiles were discussed based on the distributions of the pressure amplitude and phase.

• Proceedings of the KIEE Conference
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• 2001.07d
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• pp.2467-2469
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• 2001

A strategy for the swing-up and stabilization control method for a two-links rotational pendulum according to states of each link of the rotational pendulum is proposed. The proposed controller consists of two modes of control such as divergence mode and stabilization mode. When the controller is in divergence mode, control input is generated using sinusoidal function, which is developed based on resonance period of the pendulum in linear region, to make the second link (pendulum) reach top position. After the controller finishes operation in divergence mode, stabilization control is initiated to keep the pendulum around the top position using pole placement control method. Experimental results are given to show the effectiveness of the proposed method.

• Journal of KSNVE
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• v.11 no.1
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• pp.111-117
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• 2001

Present work deals with a study on the deployment or retraction of cantilever beam that includes the rigid-body motion of large displacement of beam through the translational and rotational motions in 2-dimensional plane. The equations of motion are derived with respect to non-Cartesian coordinate system. In the formulation of equations of motion, shear deformations and geometrically non-linear effect are included. An assumed mode method is applied and numerical convergence characteristics are studied also. Types of motion of the moving beam are assumed to be classified as‘slow’or‘fast’motion, and the dynamic characteristics are investigated.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.10
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• pp.99-106
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• 2008

5kWh FESS(Flywheel Energy Storage System) using AMB(Active Magnetic Bearing) has been under development and 1st trial system has been finished and run the operating test. Unfortunately, the test result was not satisfactory because FESS could increase the rotational speed up to 9,000 rpm only although the target rotational speed is 18,000rpm. It's because 1st bending mode frequency of flywheel shaft was too low and imbalance response was too big. To achieve the target speed, 1st bending mode and imbalance response must be improved and the whole FESS needed to be designed again. This paper presents the newly designed FESS and what has been changed from the 1st trial FESS to improve 1st bending mode and imbalance response. The experimental results to see how much 1st bending mode frequency was improved are presented, too.

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.542-548
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• 2012

The viscosity of a ceramic slurry depends on the slurry concentration, particle shape and size, hydrodynamic interactions, temperature, shear rate, pre-treatment condition and the method of measurement with the selected equipment. Representative ceramic slurries with low to high viscosity levels are selected from colloidal silica, barium titanate slurry and glass frit paste. Rotational rheometers and vibrational viscometers are used to compare the measured viscosity for various ceramic slurries. The rotational rheometer measured the viscosity according to the change of the shear rate or the rotational speed. On the other hand, the vibrational viscometer measured one point of the viscosity in a fixed vibrational mode. The rotational rheometer allows the measurement of the viscosity of a ceramic paste with a viscosity higher than 100,000 cP, while the vibrational viscometer provides an easy and quick method to measure the viscosity without deformation of the ceramic slurry due to the measurement method. It is necessary to select suitable equipment with which to measure the viscosity depending on the purpose of the measurement.

• International Journal of Fluid Machinery and Systems
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• v.7 no.2
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• pp.42-53
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• 2014

Phase resonance in Francis type hydraulic turbine is studied. The phase resonance is a phenomenon that the pressure fluctuation in the penstock of hydraulic turbine installation can become very large when the pressure waves from each guide vane caused by the interaction with the runner vane reach the penstock with the same phase. Experimental and numerical studies have been carried out using a centrifugal fan. In the present study, comparisons between the pump mode and the turbine mode operations are made. The experimental and numerical results show that the rotational direction of the rotor does not affect characteristics of the pressure fluctuation but the propagation direction of the rotorstator interaction mode plays an important role. Flow rate fluctuations through the stator are examined numerically. It has been found that the blade passing flow rate fluctuation component can be evaluated by the difference of the fluctuating pressure at the inlet and the outlet of the stator. The amplitude of the blade passage component of the pressure fluctuation is greater at the stator inlet than the one at the stator outlet. The rotor-stator interaction mode component is almost identical at the inlet and the outlet of the stator. It was demonstrated that the pressure fluctuation in the volute and connecting pipe normalized by the flow rate fluctuation becomes the same for pump and turbine mode operations, and depends on the rotational direction on the interaction mode.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.3
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• pp.284-290
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• 2012

In this research, a new type of haptic master device using electrorheological(ER) fluid for minimally invasive surgery(MIS) is devised and control performance of the proposed haptic master is evaluated. The proposed haptic master consists of ER bi-directional clutch/brake for 2 DOF rotational motion(X, Y) using gimbal structure and ER brake on the gripper for 1 DOF rotational motion (Z). Using Bingham characteristic of ER fluid and geometrical constraints, principal design variables of the haptic master are determined. Then, the generation of torque of the proposed master is experimentally evaluated as a function of applied field of voltage. A sliding mode controller which is robust to uncertainties is then designed and empirically realized. It has been demonstrated via experiment that the proposed haptic master associated with the controller can be effectively applied to MIS in real field conditions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.601-606
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• 1993

The natural frequency measurement of passenger car tire under the load and rotation are studied. In order to obtain theoretical natural frequency and mode shape, the plane vibration of a tire is modeled to that of circular beam. By using the Tickling method based on Hamilton's principle, theoretical results are determined by considering tension force due to tire inflation pressure, rotational velocity and tangential, radial stiffness. Modal parameters varying the inflation pressure, load, rotational velocity are determined experimentally by using frequency response function method. The results show that experimental conditions are parameter for shifting of natural frequency.