• Journal of the Korean Society for Precision Engineering
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• v.28 no.1
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• pp.80-88
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• 2011

The dental high-speed air turbine handpiece is one of the most popular devices that have been widely used as the main means of cutting tooth structure and restorative material in dentistry. In consideration of usage and marketability of the dental handpiece, it is obviously worthy of investigating it. The goal of this paper is to establish the relationship between the air turbine speed and the supply route inside the handpiece. To do this, the Computational Fluid Dynamics(CFD) tool, Fine$^{TM}$/Turbo is used and the optimal supply route position is suggested from the simulation results. In addition, as an attempt for domestic product, the reverse engineering process of a high speed dental handpiece by 3D X-Ray CT equipment and wire cutting is presented for the Mark II model in NSK. In doing so, the 3D modeling of the handpiece parts is carried out with CATIA V5, and the interference between parts is examined. Finally, the result of performance test for the prototype produced in this research is presented.

• Journal of Korean Society of Transportation
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• v.33 no.5
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• pp.461-469
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• 2015

The next generation high-speed train, HEMU-430X, was developed and is now being tested. However, the existing mode choice models based on the guidelines for feasibility studies do not consider a high-speed train with a higher speed than KTX. This limitation might result in inaccurate demand forecasting. In this research, a stated preference survey was conducted in order to supplement the problem by considering the characteristics of HEMU-430X. Based on the survey results, this research developed two mode choice models, including a multinomial logit model and a nested logit model. For this purpose, the utility functions of travel time and travel costs were estimated using a Limdep 8.0 NLOGIT 3.0 package. After comparing the two models, it was concluded that the nested logit model is appropriate. The paper suggested a plan to implement the nested logit model and presented a policy implication.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.7 s.172
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• pp.146-154
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• 2005

Recently, the high-speed and intelligence technology of machine tools are developed for the high efficiency of productivity Under the operating condition from the high-speed of machine tools, the various failure modes can occur in core units of manufacturing system. Therefore it is for the reliability concept of machine tool to be required in a design level. And the above-stated technology must be accommodated in the feeding and spindle subsystem, etc those are the core units of machine tools. In this study, we are developed the test-bed of sliding cover (C-plate) in order to evaluating reliability and estimating failure modes of feeding subsystem under operating conditions. The reliability experiment using the developed test-bed and the additional structural analysis executed on single and double structure. We found out the weak parts of sliding cover and were able to predict a life cycle from the experiment results. In this study, we propose the new C-plate model with double link structure to apply the high-speed machine tool in the fundamental guideline.

• Journal of Mechanical Science and Technology
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• v.16 no.10
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• pp.1314-1319
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• 2002

A mathematical model and control laws for an Electronic-Vacuum Booster (EVB) for application to vehicle cruise control will be presented. Also this paper includes performance test result of EVB and vehicle cruise control experiments. The pressure difference between the vacuum chamber and the apply chamber is controlled by a PWM-solenoid-valve. Since the pressure at the vacuum chamber is identical to that of the engine intake manifold, the output of the electronic-vacuum booster Is sensitive to engine speed. The performance characteristics of the electronic-vacuum booster have been investigated via computer simulations and vehicle tests. The mathematical model of the electronic-vacuum booster developed in this study and a two-state dynamic engine model have been used in the simulations. It has been shown by simulations and vehicle tests that the EVB-cruise control system can provide a vehicle with good distance control performance in both high speed and low speed stop and go driving situations.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.6
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• pp.663-668
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• 2014

Mechanical and electrical devices in various forms are used in many different fields. These can be exposed to external environmental factors such as shock. Therefore, a shock test machine is commonly used to test these devices and evaluate their shock resistance. In this test, the break-down or permanent deformation and malfunction of inner parts due to a high stress or acceleration can be evaluated. As part of a shock test machine, a velocity generator is needed to create shocks between objects. In this study, a hydraulic velocity generator was conceptually designed and an AMESim model was developed to simulate the velocity under different conditions. Simulation results using this model were compared with the test results from a reduced-size velocity generator, and we designed a velocity generator that fits the target payload and velocity using the simulation results.

• Structural Engineering and Mechanics
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• v.77 no.2
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• pp.231-243
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• 2021

In this paper, a dynamic response mapping model of the wheel-rail system is established by using the support vector regression (SVR) method, and the hierarchical safety thresholds of the subgrade void are proposed based on the reliability theory. Firstly, the vehicle-track coupling dynamic model considering the subgrade void is constructed. Secondly, the subgrade void area, the subgrade compaction index K30 and the fastener stiffness are selected as random variables, and the mapping model between these three random parameters and the dynamic response of the wheel-rail system is built by using the orthogonal test and the SVR. The sensitivity analysis is carried out by the range analysis method. Finally, the hierarchical safety thresholds for the subgrade void are proposed. The results show that the subgrade void has the most significant influence on the carbody vertical acceleration, the rail vertical displacement, the vertical displacement and the slab tensile stress. From the range analysis, the subgrade void area has the largest effect on the dynamic response of the wheel-rail system, followed by the fastener stiffness and the subgrade compaction index K30. The recommended safety thresholds for the subgrade void of level I, II and III are 4.01㎡, 6.81㎡ and 9.79㎡, respectively.

• Wind and Structures
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• v.6 no.3
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• pp.221-248
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• 2003

The design of high-rise building is often influenced by wind-induced motions such as accelerations and lateral deflections. Consequently, the building's structural stiffness and dynamic (vibration periods and damping) properties become important parameters in the determination of such motions. The approximate methods and empirical expressions used to quantify these parameters at the design phase tend to yield values significantly different from each other. In view of this, there is a need to examine how actual buildings in the field respond to dynamic wind loading in order to ascertain a more realistic model for the dynamic behavior of buildings. This paper describes the findings from full-scale measurements of the wind-induced response of typical high-rise buildings in Singapore, and recommends an empirical forecast model for periods of vibration of typical buildings in Singapore, an appropriate computer model for determining the periods of vibration, and appropriate expressions which relate the wind speed to accelerations in buildings based on wind tunnel force balance model test and field results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.4
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• pp.290-296
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• 2018

In this study, the cold test and the numerical analysis were carried out according to the shape parameters of the test model in order to confirm the operation range of high altitude environment simulation test facility for the supersonic vehicle. The blockage ratio, angle and length ratio were considered as the design parameters. The blockage rate is expected to be limited in the region of more than 40% due to the normal shock and expansion fan. It was confirmed that the angle of model should be selected at the size of 45 degrees or less due to the influence of the strong shock wave. There was no difference in performance between the lengths of 8 times the model diameter. Finally, we obtained the performance database according to the shape parameters of the conical test model and confirmed the operable range of the semi-freejet type high altitude environment simulation test facility.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.664-670
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• 2010

The study on mechanical behavior of the structure at the site includes experimental method and numerical analysis method. Experimental method is categorized into true-scale test and laboratory model test. A laboratory model test is to monitor the failure mechanism with a model simulated similar with a real ground so as to identify the quantitative result, while a true-scale model test is the approach which enables to identify the potential problems that may occur with a simulated construction situation similar with a real site circumstance. Thus this study was intended to carry out the experimental test of non open-cut excavation by pipe roof method which is mostly common in domestic sites. as well as was aimed at identifying the ground behavior occurred during pipe penetration using laboratory model test. Appropriate reduced-scale model was selected, taking into account of domestic geological characteristics and operation characteristics of traditional and high-speed rail trains and the qualitative evaluation of displacement was carried out based on a certain ground loss volume depending on excavation after categorizing trackbed settlement pattern by depth of top soil.

• Wind and Structures
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• v.36 no.1
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• pp.1-14
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• 2023

To evaluate the wind shielding effect of bridge towers with multiple limbs on high-speed trains, a wind tunnel test was conducted to investigate the aerodynamic characteristics of vehicles traversing multi-limb towers, which represented a combination of the steady aerodynamic coefficient of the vehicle-bridge system and wind environment around the tower. Subsequently, the analysis model of wind-vehicle-bridge (WVB) system considering the additional moments caused by lift and drag forces under nonuniform wind was proposed, and the reliability and accuracy of the proposed model of WVB system were verified using another model. Finally, the factors influencing the wind shielding effect of multi-limb towers were analyzed. The results indicate that the wind speed distributions along the span exhibit two sudden changes, and the wind speed generally decreases with increasing wind direction angle. The pitching and yawing accelerations of vehicles under nonuniform wind loads significantly increase due to the additional pitching and yawing moments. The sudden change values of the lateral and yawing accelerations caused by the wind shielding effect of multi-limb tower are 0.43 m/s² and 0.11 rad/s² within 0.4 s, respectively. The results indicate that the wind shielding effect of a multi-limb tower is the controlling factor in WVB systems.