• Nuclear Engineering and Technology
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• v.55 no.9
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• pp.3252-3259
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• 2023

The influence of hold-down spring (HDS) on the vibration characteristics of core barrel is studied in this paper. First, the vibration characteristics experiment of core barrel was carried out with four type of different hold-down spring. These hold-down springs represent the same hold-down force under different spring stiffness and different hold-down force under the same spring stiffness. And then a new finite element method for researching the influence of hold-down spring on the vibration characteristics of core barrel was presented. This new method could consider the influence of the hold-down force and the spring stiffness at the same time. The results suggest that, the hold-down force and friction have greater influence on the vibration characteristics of core barrel than the spring stiffness, and the influence is nonlinear. The influence of the boundary condition on beam mode is greater than that on shell mode for core barrel.

• Journal of computational fluids engineering
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• v.13 no.2
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• pp.62-67
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• 2008

This study aims to investigate numerically the static stiffness characteristics of porous air bearing and to estimate appropriate permeability values of porous medium. In particular, a new roughness model is proposed and implemented into the commercial CFD code (FLUENT Ver. 6.2) by using C language based user subroutine. The predicted results are extensively compared with experimental data. The roughness model is also validated through comparison with the results from open literature. It is found that the predictions for static stiffness are in good agreement with experimental data. Therefore, the suggested model based on the roughness Reynolds number can be used in studying the stiffness characteristics of porous air bearing effectively. In addition, numerical simulations of various diameter size and conditions are conducted. According the results, it is expected that the static stiffness of porous air bearing has the non-linear characteristics.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.7
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• pp.1055-1063
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• 2004

In this study, we developed an automatic veneer sorting system controlled by nonlinear friction and nonlinear stiffness. With these nonlinear characteristics, it was difficult to analysis and to control the system in the fast. However it is necessary to consider nonlinear characteristics to satisfy accurate and rapid control demand in these days. We used not only nonlinear friction but also nonlinear stiffness and combined both to control the system. An experimental device was designed with 4 AC servo-motors and 2 Sensors. Through a series of experiment, we found nonlinear friction characteristics among roller versus veneer and veneer versus veneer and nonlinear stiffness characteristics with stacked veneers. Finally, we showed that the proposed control algorithm was very effective for veneer sorting system with nonlinear friction and stiffness.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.4 s.19
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• pp.107-113
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• 2004

In order to model a connection part between a control fin and actuator, the related characteristics of a dynamic stiffness were extracted from experiments. These characteristics include the static stiffness of a control fin and the dynamic stiffness of an actuator, so they are called the mixed dynamic stiffness here. This mixed dynamic stiffness is used as the boundary condition of a control fin connected to an actuator when the flutter characteristics are analyzed. The simulated stiffness of an actuator is corrected from the experiment results and the mixed dynamic is finally formulated in the domain of frequencies.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.206-210
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• 2003

Machining of deep holes with conventional boring bars frequently induce chatter vibration because of their low dynamic stiffness which is defined as the product of static stiffness and damping of conventional boring bar materials. In addition, the specific stiffness ($E/{\rho}g$) of boring bars is more important than the static stiffness to increase the fundamental natural frequency of boring bars in high speed machining. Therefore, boring bar materials should have high static stiffness and high damping as well as high specific stiffness. The best way to meet requirements is to employ fiber reinforced composite materials for high speed boring bars because composite materials have high static stiffness, high damping and high specific stiffness compared to conventional boring bar materials. In this study, the dynamic characteristics of carbon fiber epoxy composite boring bars were investigated. From the metal cutting test, it was found that the chatter was not initiated up to the ratio of length to diameter of 10.7 at the rotating speed of 2,500 rpm.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1274-1277
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• 2004

The objective of this research work is to investigate into characteristics of bending stiffness and failure for the ISB ultra-lightweight panel with internally structured material. The expanded metal with a pyramid shape and woven metal are employed as an internally structured material. In order to investigate the characteristics, the specific stiffness and failure map are estimated using the results of three-points bending test. From the results of the experiment, the influence of design parameters of ISB panel on the specific stiffness and failure mode has been found. In addition, it has been shown that ISB panel with expanded metal is prefer to that with woven metal from the view point of optimal design for ISB panel.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.4
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• pp.176-184
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• 2007

The missile for this study has shown different natural frequency characteristics depending on the test conditions; natural frequencies obtained from its flight test are higher than those in its ground test. It was found that the hinged joints connecting front airframe to rear one had the nonlinear stiffness and caused the missile to show very complex dynamic characteristics. The angular stiffness at hinged joints was calculated using 3D finite element analysis, and it was verified that there was a highly nonlinear relationship between angular stiffness and external load. Natural frequencies calculated considering the nonlinearity of angular stiffness were nearly the same as test results. Through this study, the dynamic characteristics of a missile having split airframes with hinged joints could be clearly identified and a way of maintaining its natural frequencies consistent was generated.

• Tribology and Lubricants
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• v.12 no.2
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• pp.55-64
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• 1996

Frictional characteristics with the change of loading method and normal stiffness at dry sliding surfaces were experimentally and theoretically evaluated in this study. For the study, a ball-on-disk typed test rig was built and implemented, which allowed a proper selection of loading mechanism and normal stiffness of the test rig. Loading method were varied from dead weight to pneumatic cylinder and spring loading, and the normal stiffness was varied by a spring of different stiffness. Test results showed that frictional characteristics at various loading methods were different even though the operating variables were the same. Discrepancy in the frictional characteristics, such as coefficient of friction and fluctuation in the normal load, were explained by the change in dynamic parameters of the test rigs. Results also showed that coefficient of friction, which defines as a ratio of frictional force divided a normal load, could be differently evaluated in the calculation when fluctuation in the normal load was significant.

• Journal of the Korean Society for Railway
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• v.3 no.3
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• pp.131-138
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• 2000

The design of current collection system of high speed train requires the fundamental understandings for the dynamic characteristics of catenary system and pantograph. The stiffness of catenary system of high speed train has the varying characteristics for the change of contact point with pantograph, since the supporting pole and hanger make the different boundary conditions for the up-down stiffness of a trolley wire. The variation of stiffness results in Mathiue equation, which characterizes the stability of the system. However, the two-term variation of the stiffness due to span length and hanger distance cannot be solved analytically. In this paper, the stiffness variations are calculated and the physical reasoning of linear model and one term Mathieu equation are reviewed. And the numerical analysis for the two-term variation of the stiffness is done for the several design parameters of pantograph.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.253-260
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• 2004

Many scholars and researchers has been studied for many kinds of soil characteristics, but a lot of part are still unsolved. Cyclic load-induced decreasing characteristics of strength and stiffness of soils are also well not known among them. To know that, the characteristics of five kinds of soils; clay, plastic and non-plastic silt, sand, and a weathered soil are compared with dividing two types as plastic or non-plastic soils through direct simple shear(DSS) test. From the results of DSS test, it is known that decreasing characteristics of strength and stiffness are different according to soil types. The strength of plastic and non-plastic soils increases with increment of plasticity index and decrement of volume decrease potential, respectively. And the decreasing stiffness of plastic and non-plastic soils increases with decrement of plasticity index and increment of volume decrease potential, respectively.