• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.5
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• pp.627-637
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• 1985

The combustion process and the performance of a diesel engine are seriously affected by the ignition delay period of the fuel used. Some methods for improving the combustion process in the engine cylinder are to well match the strength of air swirl with the space of sprays in the cylinder, to blend an ignition improver in the fuel, to inject a small amount of auxiliary fuel prior to main injection and so on. Recently, the improvement of fuel economy and the reduction of exhaust smoke and NO have been successfully achieved by supplying diesel engines with emulsified fuel. However, it is very difficult to know real combustion mechanism under such special conditions, because of many factors affecting on the combustion process in practical reciprocating engine. In the present paper, the combustion processes of diesel fuel and emulsion fuel were tried to improve and to observe by making contact with various lean pre-mixtures in the hot air stream duct. This hot air stream method has an advantage that the spontaneous combustion process can be observed under a simplified condition.

• Tribology and Lubricants
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• v.28 no.6
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• pp.315-320
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• 2012

For proper functioning, general machines usually need lubricant oil as a cooling, cleaning, and sealing agent at points of mechanical contact. The quality of lubricant oil can deteriorate during operation owing to various causes such as high temperature, combustion products and extraneous impurities. In this study, a heavy load stopped during operation, and the oil was analyzed to check whether any impurities were added. Extraction using acetonitrile followed by reaction with BSTFA(bistrimethylsilyl trifluoroacetamide) showed that, trimethylsilylated ethylene glycol was present in the lubricant oil. To quantify the ethylene glycol in the oil, deuterium-substituted ethylene glycol, which acted as an internal standard, was added to the sample and then extracted with the solvent. Next, the extract was reacted with the derivatizing agent(BSTFA) and then analyzed with GC/MS. The detection limit of this method was found to be $0.5{\mu}g/g$ and the recovery of oil containing $20,000{\mu}g/g$ of ethylene glycol was measured to be 94.8%. A damaged O-ring and eroded cylinder liner were found during the overhaul, which implied the leakage of coolant containing ethylene glycol into the lubricating system. The erosion of the cylinder liner was assumed to be due to cavitation of the coolant in the cooling system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.2
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• pp.181-186
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• 2009

The objective of this study is ensuring safety of cabin when the blade impacts into a obstacle by verifying safety of the rotor mast and the transmission using impact loads calculated from the simulation. The rotor mast shall not fail and the transmission shall not be displaced into occupiable space when the main rotor composite blade impact into a 8 inch rigid cylinder in diameter on the outer 10% of the blade at operational rotor speed. To calculate the reaction loads at the spherical bearing and lead-lag damper, blade impact analysis was performed with FE model consist of composite blade, tree(or rigid cylinder) using elastic-plastic with damage material and several contact surfaces which were created to describe a progress of actual failure. Also, the reaction loads were investigated in change of blade rotation speed and pitch angle.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.2
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• pp.75-82
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• 2022

Nondestructive method to predict buckling load for the propellant tank of launch vehicle should be evaluated. Vibration correlation technique can predict the global buckling load of unstiffened cylindrical structure with geometric initial imperfection using correlation of natural frequency and compressive load from compressive test below the buckling load. In this study, vibration and buckling tests of a thin metal unstiffened propellant tank model subjected to internal pressure and compressive loads were performed and the test results were used for VCT to predict global buckling load. For the vibration test of thin structure, non-contact excitation method using a speaker was used. The response was measured with piezoelectric polymer(PVDF) sensor. Prediction results of VCT were compared with the measured buckling load in the test and the nondestructive global buckling load prediction method was verified.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.5
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• pp.375-380
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• 2017

This paper reports the results of an acceleration test to predict the contact-induced failure that could occur at the cylinder-to-hole joint for the fuel rod of a sodium-cooled fast reactor (SFR). To incorporate the fuel life of the SFR currently under development at KAERI (around 35,000 h), the acceleration test method of reliability engineering was adopted in this work. A finite element method was used to evaluate the flow-induced vibration frequency and amplitude for the test parameter values. Five specimens were tested. The failure criterion during the life of the SFR fuel was applied. The S-N curve of the HT-9, the material of concern, was used to obtain the acceleration factor. As a result, a test time of 16.5 h was obtained for each specimen. It was concluded that the $B_{0.004}$ life would be guaranteed for the SFR fuel rods with 99％ confidence if no failure was observed at any of the contact surfaces of the five specimens.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.4
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• pp.345-350
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• 2002

In recent years, as changing the habit of eating, the pathology in the colon grows up annually. The colonoscopy is generalized, but if requires much time to acquire a dexterous skill to perform an operation and the procedure is painful to the patient. biomedical and robotic researchers are developing a locomotive colonoscope that can travel safe1y in colon. In this paper, we propose a new actuator and concept of semi-autonomous colonoscope. The micro robot comprises camera and LED for diagnosis, steer- ing system to pass through the loop, pneumatic actuator and bow-shaped flexible supporters to control a contact force and to pass over haustral folds in colon. For locomotion of semi-autonomous colonoscope, we suggest an actuator that is based on impact force between a cylinder and a piston. In order to validate the concept and the performance of the actuator, we carried out the simulation of moving characteristics and the preliminary experiments in rigid pipes and on the colon of pig.

• Tribology and Lubricants
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• v.31 no.3
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• pp.125-140
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• 2015

In this paper, we present the results of the wear analysis of journal bearings on a stripped-down single-cylinder engine during start-up and coast-down by motoring. We calculate journal bearing wear by using a modified specific wear rate considering the fractional film defect coefficient and load-sharing ratio for the asperity portion of a mixed elastohydrodynamic lubrication (EHL) regime coupled with previously presented graphical data of experimental lifetime linear wear in radial journal bearings. Based on the calculated wear depth, we obtain a new oil film thickness for every crank angle. By examination of the oil film thickness, we determine whether the oil film thickness at the wear scar region is in a mixed lubrication regime by comparing dimensionless oil film thickness, h/σ, to 3.0 at every crank angle. We present the lift-off speed and the crank angles involved with the wear calculation for bearings #1 and #2. The dimensionless oil film thickness, h/σ, illustrates whether the lubrication region between the two surfaces is still within the bounds of the mixed lubrication regime after scarring of the surface by wear. In addition, we present in tables the asperity contact pressure, the real minimum film thickness at the wear scar region, the modified specific wear rate, and the wear angle, α, for bearings #1 & #2. To show the real shape of the oil film at wear scar region, we depict the actual oil film thickness in graphs. We also tabulated the ranges of bearing angles related with wear scar. We present the wear volume for bearings #1 and #2 after one turn-on and turn-off of the engine ignition switch for five kinds of equivalent surface roughness. We show that the accumulated wear volume after a single turn-on and turn-off of an ignition switch normally increases with increasing surface roughness, with a few exceptions.

• Journal of Mechanical Science and Technology
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• v.15 no.3
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• pp.291-299
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• 2001

Recently, severe wear on the shutdown rod cladding of Ulchin Nuclear Power Plant #1, #2 were observed by the Eddy Current Test(E.C.T.). In particular, the wear at the sixth card location was up to 75%. The test results indicated that the Flow Induced Vibration(F.I.V.) might be the cause of the fretting wear resulting from the contact between Rod Cluster Control Assemblies(RCCAs) and their spacing cards(guide plates) arranged in the guide tube. From reviewing RCCAs fretting wear repots and analyzing the general characteristics of F.I.V. mechanism in the reactor, geometric layout and flow conditions around the control rod, it is concluded that the turbulence excitation is the most probable vibration mechanism of RCCA. To identify the governing mechanism of RCCA vibration, an experiment was performed for a representative rod position in which the most serious fretting wear experienced among the six rod positions. The experimental rig was designed and set up to satisfy the governing nondimensional numbers which are Reynolds number and mass damping parameter. The vibration amplitude measurement by the non-contact laser displacement sensor showed good agreements in the frequency and the maximum wearing(vibration) location with Ulchin E.C.T. results and Framatome report, respectively. The sudden increase in the vibration amplitude was sensed around the 6th guide plate with mass flow rate variation. Comparing the similitude rod behaviour with the idealized response of a cylinder in flow induced vibration, it was found that he dominant mechanism of vibration was transferred from turbulence excitation to periodic shedding at the mass flow ate 90ι/min. Also the critical velocity of the vibration in RCCAs was determined and the vibration can be prevented by reducing the bypass flow rate below the critical velocity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.6
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• pp.1753-1761
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• 1996

The wear behaviors of ${Si_3}{N_4}$ under the different sliding conditions were investigated. The cylinder-on-disc wear tester was used. Using the servo-metor, the sliding speed did ot alternate due to the frictional forces. Threekinds of loads and speeds were selected to watch the variation of the wear rates and the frictional forces. Also three kinds of sliding condition under a constant speed were used to see the effects of the oxidationand the abrasion. The contact pressure was more effective than the repeated cycle on the wear behavior of ${Si_3}{N_4}$. With the low loads, the effect of the asperity-failure was more dominant than that of oxidation and abrasion. As increasing the load, the effects of oxidation and abrasion were increased, but the asperity-failure effects were decreased. The wear particles destroyed the ozide layers formed on sliding surfaces. The wear rate could be decreased due to delaying the oxidation. The frictional power and the wear weight per time were usefuel to see the transition of wear.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.3
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• pp.277-283
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• 2008

Balance shaft module contributes to reduce the engine-born vibration by compensating it from a unbalance mass with opposite phase but practically, this device has some problems during the operation in a high speed owing to the considerable amount of unbalance mass that leads to the large quantity of bending deformation as well as torque fluctuation at the balance shaft. To tackle two main problems, the design strategy on balance shaft is suggested by addressing the optimal location of unbalance mass and supporting hearing based on the formulation of objective function that minimizes critical issues, both bending deformation as well as torque fluctuation. The boundary condition of balance shaft assumes to be free such that any external force or contact component is not taken into consideration in this study.