• Proceedings of the KWS Conference
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• 2004.05a
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• pp.246-248
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• 2004

It has been well known that ductile fracture of steels is accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using two-parameters criterion based on equivalent plastic strain and stress triaxiality. This study provides the fundamental clarification of the effect of strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, loading mode and loading rate on critical condition to initiate ductile crack from notch root using equivalent plastic strain and stress triaxiality based on the two-parameter criterion obtained on homogeneous specimens under static tension. The critical condition to initiate ductile crack from notch root for strength mismatched bend specimens under both static and dynamic loading would be almost the same as that for homogeneous tensile specimens with circumferential sharp notch under static loading.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.453-455
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• 1997

일반적으로 제철공정에서 각 공정사이의 철판의 속도와 장력은 브라이드롤을 이용하여 제어하는데 여기서 입력 측의 브라이드롤은 장력을 제어하고 출력 측의 브라이드롤은 공정의 속도를 제어한다. 이와 같은 방법은 시스템 기동의 순간을 포함하여 공정속도의 변경이 있을 경우 제철 공정 상에서는 특히 철판의 높은 탄성에 기인하여 시스템이 상당히 불안정하게 된다. 본 논문에서는 각 전동기가 정해진 역할에 따라 독립적으로 장력 혹은 공정속도를 제어하고 장력의 모델링에서 비선형의 요소를 되먹임하여 원래의 시스템을 선형화시켰고 이때 미분관측기를 이용하였다. 이 제어기의 장점은 무엇보다도 독립적인 역할의 분담으로 인해 다수의 전동기로 확장이 용이하도록 하는 것이다.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.144-148
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• 2005

Cylinder frame manufactured by casting is assembled with the components such as cylinder head, cylinder liner and main bearing cap, etc. The mechanical contact between all of the neighboring components due to bolt tightening was taken into consideration. The loads used in structural analysis were the bolt tightening forces induced by hydraulic jack and the dynamic forces calculated from kinematic analysis. The difference of forces between the neighboring cylinders was taken into account. The maximum stress, stress amplitude and mean stress calculated from the results of structural analyses were used to evaluate the static and fatigue strength. Gray cast iron which is material of cylinder frame has the material characteristics of very small elongation and different strength in tension and compression. Based on such an material characteristics, the strength evaluation of cylinder frame was carried out with in-house program developed internally.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.830-834
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• 2013

This study presents a method to monitor cable force of a long-span cable-stayed bridge using a smart piezoelectric sensor system. The following approaches are implemented in order to achieve the objective. Firstly, the method to utilize piezoelectric materials for the health monitoring of stay cables is presented. For strain measurement of a stay cable, a PZT-embedded smart skin is designed to overcome the difficulties of bonding PZT sensors directly on stay cables. Secondly, a piezoelectric strain monitoring system for stay cables is designed. For the operation of the sensor board, the Imote2 sensor platform is used to provide the computation, wireless communication and power supply units. The feasibility of the proposed monitoring system is then evaluated on a full-scale cable of a cable-stayed bridge.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.371-376
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• 1996

The damping force of shock absorber in an automobile is determined by the components which construct the S/A. In this study we investigate the individual effect of these components on damping force. In addition, opening of important valve doling compression and tension cycle due to up-down reciprocation movement is also researched. Thus we are to strictly control the properties and tolerance of components having important effects on tile damping force and to produce S/A of better quality.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.945-952
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• 1994

In this paper, a mathematical model for a belt driven system is proposed to analyse the vibtation characteristics of the driving units with belts and the free and forced vibration analyses are carried out. The mathematical model for model for the belt-driven system includes belts,pulleys, spindle and bearings. Using the Hamilton principle, the 4 nonlinear governing equations and the 12 nonlinear boundary conditions are derived. To linearize and discretize the nonlinear govering equations and boundary conditions, the perturbation method and Galerkin method are used. Also, the free vibration analyses for the various parameters of the belt driven system, which are belt tension, belt length, material property of belt, belt speed and pulley mass are made. The forced vibration analyses of the system are made and the dynamic responses for the main parmeters are analysed with the belt driven system.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.220-228
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• 2001

Journal locus with aerated lubricant is analyzed under the dynamic loading condition. In this analysis, we have found that aerated lubricant influences two major factors on the film formation. One is the density variation of the lubricant due to the volume change by the bubbles and the other is the viscosity changes of the lubricant due to the surface tension of the bubble. Those two major factors surprisingly increase the load capacity in certain ranges of bubble sizes and densities. Modified Reynolds'equation is developed with the consideration of aerated ratio in the lubricant and journal locus is computed with Mobility method with the computation of two dimensional pressure distribution over the bearing area.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.676-679
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• 2006

The media transport in automatic office machines such as printers, ATMs, copying machines is achieved by a complicated belt system. The system generally uses a crowning roller and belt which has been well-known for its intrinsic belt centering advantage during its operation. Since the modern office machines require precise high operating speed, stabilization of media transporting system has been one of the important issues of the machine design. Even a minor defect of the belt or the roller in the transport system directly affects its operating stability. This paper delivers a simulation technique that combines a multi-body dynamics analysis routine and a FEM based flexible continuum modeling for the efficient simulation of the flexible media transport problems.

• Proceedings of the Korean Society of Laser Processing Conference
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• 2001.11a
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• pp.43-47
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• 2001

This paper presents a study of the uniform metal droplet generation using laser. The theoretical model, based on the variational principle instead of solving the Wavier-Stokes equation with moving boundaries, is developed. Our model is considered the Young-Laplace equation and force equilibrium conditions. Surface tension coefficient is determined under the statical condition with induced differential equation by using experimental result. In case of dynamic vibration, metal droplet shape and critical detaching volume are predicted by recalculating of proposed model. The simulation result revealed that the developed model could reasonably describe the molten metal droplet behavior on vibration with metal wire.

• 기술발표회
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• s.2006
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• pp.75-85
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• 2006

The project comprised the construction of the new oil pier and associated topside facilities and demolition of exiting south pier. The site is located approximately 33km south of Kuwait city at MAA refinery. The approach trestle and berth structures of the new oil pier were designed to be supported by steel tubular piles Total 2,480 numbers of piles(795 piles at Approach Trestle, 1187 piles at Berth 1 -4 and 498 piles at Berth 5-6) had to be driven through the calcareous silty sand In this study, the design procedures for offshore steel pipe piles, evaluation for the compression and tension capacities by static and dynamic load test and effective driving criteria by the final set values are discussed