• Journal of Mechanical Science and Technology
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• v.20 no.1
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• pp.125-132
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• 2006

To understand fluid dynamic forces acting on a structure subjected to two-phase flow, it is essential to get detailed information about the characteristics of two-phase flow. Stratified steady and unsteady two-phase flows between two parallel plates have been studied to investigate the general characteristics of the flow related to flow-induced vibration. Based on the spectral collocation method, a numerical approach has been developed for the unsteady two-phase flow. The method is validated by comparing numerical result to analytical one given for a simple harmonic two-phase flow. The flow parameters for the steady two-phase flow, such as void fraction and two-phase frictional multiplier, are evaluated. The dynamic characteristics of the unsteady two-phase flow, including the void fraction effect on the complex unsteady pressure, are illustrated.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1212-1219
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• 2009

In this paper, a state feedback gain controller using linear matrix inequality(LMI) for the multi-objective synthesis is designed, in the multi-layer structure with integral type servo system. The design objectives include $H_{\infty}$ performance, asymptotic disturbance rejection, time-domain constraints, on the closed-loop pole location. The results of computer simulation show the validity of the designed controller.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.264-268
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• 2003

Recently reduction of industrial products in size and weight has been increased by application of micro-drills in gadgets of high precision and a great interest of a micro-drilling has been raised. Due to the lack of tool stiffness and the chip packing, the micro-drilling requires not only the robust tool structure which has not affected by vibration but also effective drilling methods designed to prevent tool fracture from cutting troubles. This paper presents an optimum design shape of a 0.15 mm micro-drill associated with a new manufacturing process to improve the production rate and to lengthen the tool life and suggestions on the micro-drilling characteristic properties associated with the tool life and workpiece quality.

• Journal of Korean Neurosurgical Society
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• v.54 no.3
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• pp.265-267
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• 2013

We report a case of bilateral chronic subdural hematoma (CSDH) in a 75-year-old man after exercise using a vibrating belt machine on the head. He suffered from headache and intermittent left side numbness for ten days. He denied any head injuries except eccentric exercise using a vibrating belt on his own head for 20 days. An MRI revealed bilateral CSDH. The hematoma was isodense on the CT scan. We made burr-holes on the both sides under local anesthesia. We identified the neomembrane and dark red subdural fluid on both sides. In the postoperative CT scan, we found an arachnoid cyst on the left temporal pole. Although the arachnoid cyst itself is asymptomatic, trivial injury such as vibrating the head may cause a CSDH.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.4
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• pp.816-826
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• 2017

In this paper, a generalized discretization scheme is proposed that can derive general-order finite difference equations representing the joint probability density function of dynamic response of stochastic systems. The various order of finite difference equations are applied to solutions of the Fokker-Planck-Kolmogorov (FPK) equation. The finite difference equations derived by the proposed method can greatly increase accuracy even at the tail parts of the probability density function, giving accurate reliability estimations. Compared with exact solutions and finite element solutions, the generalized finite difference method showed increasing accuracy as the order increases. With the proposed method, it is allowed to use different orders and types (i.e. forward, central or backward) of discretization in the finite difference method to solve FPK and other partial differential equations in various engineering fields having requirements of accuracy or specific boundary conditions.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.185-192
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• 2005

Using existing static methods, it is possible to estimate accurately the reponses of structures governed by the fundamental mode. However, these methods do not provide reliable estimates for the structure where higher mode effects are significant. Parametric study was performed to analyze the dynamic characteristics of the structure with long vibration period. Based on the investigations, a new modal combination method using modal combination coefficients, Factored Modal Combination, was developed, and static earthquake load patterns addressing higher mode effects reasonably were proposed. Existing modal combination methods, such as SRSS and CQC, lack a theoretical basis to be applied to inelastic structures. In contrast, the proposed method can be applied conveniently in inelastic range as well as in elastic range.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2019.05a
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• pp.120-121
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• 2019

In this study, FT-IR analysis was performed by exposing cement paste to high temperature in order to characterize the change of hydration behavior of concrete structure damaged by fire accident. As the holding time increased, the Al-O vibration region increased due to the increase of Si-O symmetric Ca₂(SiO₄) and Brownilerite, and the OH stretching region tended to increase due to thermal decomposition of Ca(OH)₂.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.2
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• pp.124-132
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• 2009

Experiments have been performed to investigate fluid-elastic instability of tube bundles, subjected to twophase cross flow. Fluid-elastic is the most important vibration excitation mechanism for heat exchanger tube bundles subjected to the cross flow. The test section consists of cantilevered flexible cylinder(s) and rigid cylinders of normal square array. From a practical design point of view, fluid-elastic instability may be expressed simply in terms of dimensionless flow velocity and dimensionless mass-damping parameter. For dynamic instability of cylinder rows, added mass, damping and the threshold flow velocity are evaluated. The Fluid-elastic instability coefficient is calculated and then compared to existing results given for tube bundles in normal square array.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.805-810
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• 2005

The main functions of suspension system of railway vehicle are isolating vibration from track irregularity to car-body for the Ride quality and keeping its stability with limitation of vehicle's movement. These two functions conflict with each other, then it is impossible to achieve both of performance with traditional passive suspension which has constant characteristics. So, to improve this situation the active suspension was suggested and in specially the semi-active suspension is noticed for its effectiveness on cost despite of its lower performance than full-active suspension. In this study the control logic made through LQG theory was designed with simplified vehicle model and variable damper model defined by $1^{st}$ order system, then the analysis of simulation results was done to understand influence on the performance of semi-active suspension with running conditions and response characteristics of variable damper.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.2
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• pp.29-37
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• 1994

In this paper the modelling procedure and analysis technique for the prediction of accurate critical speeds of marine propeller shafts are suggested. As a solution method the transfer matrix method is employed to calculate the critical speeds, which are correspond to natural frequencies of the shaft in lateral vibration, and whirling responses. Furthermore, in order to check the validity of the simple prediction formulae, such as Jasper's formula and Panagopulos's formula, numerical calculations were performed. From the numerical results it was found that the critical speed of the propeller shaft is sensitive to the position and the supporting conditions of journal bearings.