• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.63-73
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• 1987

This study is a part of the research on the coupled vibration of train wheel with the stepped thickness and rail. The research was conducted for the purpose of examining the dynamic characteristics of train wheel at the running state and preventing the vibrations of the high speed railway. The stress at the boundary surface of web and rim, .sigma.$_{c}$, was analyzed in consideration of the uniform In-plane compressive stress depending on the conditions of rolling and the In-plane compressive stress depending on the rotation of train wheel. Then the equation of transverse vibration of the annular plate with the stepped thickness was analyzed by Rayleigh-Ritz's method. As a result of study, it was known that the rotational speed increase the natural frequency slightly and the acceleration level highly while the reaction force between train wheel and rail decrease the natural frequency linearly and the critical buckling is generated at n=1.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.531-536
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• 2006

In four cylinder engine, the second order inertia force occurs due to the reciprocating parts of the cylinder. Because the magnitude of the inertia force is proportional to a square of the angular velocity of crank shaft, engine gets suffered from vibration excited by unbalanced inertia force in high speed. This vibration excited by the unbalanced inertia force can be canceled by applying a balance shaft. Balance shaft has one or more unbalance mass and rotates twice quickly than the crank shaft. In this paper, an unbalanced force caused by the rotating of unbalance mass of balance shafts was calculated. The directional equivalent stiffness and damping coefficients of the journal bearing of balance shafts was calculated. Equations of rotational vibration modes were derived using directional stiffness and damping coefficients. The dynamic stability of balance shafts was analyzed and evaluated for two type models using the equivalent stiffness and damping coefficients. An efficient procedure to he able to evaluate dynamic stability and design optimal balance shaft was proposed.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2095-2100
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• 2003

This Experimental study concerns the characteristics of vortex flow in a concentric annulus with a diameter ration of 0.52, whose outer cylinder is stationary and inner one is rotating. Pressure losses and skin-friction coefficients have been measured for fully developed flow of bentonite-water solution(5%) when the inner cylinder rotates at the speed $0{\sim}400rpm$. The results of present study reveal the relation of the bulk flow Reynolds number Re and Rossby number $R_o$ With respect to the skin friction coefficients. The effect of rotation on the skin friction coefficient is significantly dependent on the flow regime. In all flow regime, the skin friction coefficient is increased by the inner cylinder rotation. The critical (bulk flow) Reynolds number $Re_c$ decreases as the rotational speed increases. Thus, the rotation of the inner cylinder promotes the onset of transition due to the excitation of Taylor vortices.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.275-281
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• 2001

While basic input parameters for the performance and noise of axial fan are flow rate, pressure rise, rotating speed, and fan diameter, the geometric parameters of blade are sweep angle, solidity, and camber angle. The sweep angle does not affect fan performance much, but on fan noise significantly. Solidity and camber angle are very critical design parameters acting on the fan performance directly. The solidity and camber angle are closely related, therefore they have to be carefully determined for the low-noise and high-performance fan. In This paper, different design points are selceted and also geometric parameters are deliberately changed for the comparison of fan noise. As a result, at the same performance, the input rotational speed affects radiated noise more significantly than others. When solidity and camber angle are increased more than those by iDesignFan／sup TM／ program, more noise is experienced. The blade sweep method and blade numbers at same solidity are observed to results in different levels of performance and noise.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.373-384
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• 1989

The motions of a spinning rotor and a fluid enclosed in its cavity are known to have mutual interactions, which change the frequencies of forced vibrations and cause instabilities. These phenomena are of technical importance for fluid-cooled turbines as well as spin-stabilized satellites or rockets containing liquid fuels. In this paper the characteristics of unstable whirling of a rotor containing a partitioned cavity filled with two kinds of liquids are investigated experimentally. It studies the influence of rotational speed and filling ratio of two kinds of liquids on unstable whiring. As a result, it is found that the whirl velocity is approximately equal to, or slightly lower for large masses of trapped fluid than rotor critical speed. In case of a spinning rotor partially filled with two kinds of liquids the boundary surface plays a similar role to the free surface, and cases unstable forward whirl.

• Structural Engineering and Mechanics
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• v.81 no.4
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• pp.411-428
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• 2022

This paper presents the Campbell diagram analysis of the rotordynamic system using the full order model (FOM) and the reduced order model (ROM) techniques to determine the critical speeds, identify the stability and reduce the computational time. Due to the spin-speed-dependent matrices (e.g., centrifugal stiffening matrix), several model order reduction (MOR) techniques may be considered, such as the modal superposition (MS) method and the Krylov subspace-based MOR techniques (e.g., Ritz vector (RV), quasi-static Ritz vector (QSRV), multifrequency quasi-static Ritz vector (MQSRV), multifrequency/ multi-spin-speed quasi-static Ritz vector (MMQSRV) and the combined Ritz vector & modal superposition (RV+MS) methods). The proposed MMQSRV method in this study is extended from the MQSRV method by incorporating the rotational-speed-dependent stiffness matrices into the Krylov subspace during the MOR process. Thus, the objective of this note is to respond to the question of whether to use the MS method or the Krylov subspace-based MOR technique in establishing the Campbell diagram of the shaft-disc-blade assembly systems in three-dimensional (3D) finite element analysis (FEA). The Campbell diagrams produced by the FOM and various MOR methods are presented and discussed thoroughly by computing the norm of relative errors (ER). It is found that the RV and the MS methods are dominant at low and high rotating speeds, respectively. More precisely, as the spinning velocity becomes large, the calculated ER produced by the RV method is significantly increased; in contrast, the ER produced by the MS method is smaller and more consistent. From a computational point of view, the MORs have substantially reduced the time computing considerably compared to the FOM. Additionally, the verification of the 3D FE rotordynamic model is also provided and found to be in close agreement with the existing solutions.

• Journal of Biosystems Engineering
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• v.36 no.3
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• pp.163-170
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• 2011

Analysis of load on major parts of the tractor power drive line is critical for efficient and optimum design of a tractor. The purpose of this study was to evaluate severeness of the tractor PTO driving axle during rotary tillage operation. First, S-N (stress vs. number of cycle) curve of a PTO driving gear was obtained through the fatigue life test using a PTO dynamometer. Second, PTO severeness was evaluated during rotary tillage operation. Torque measurement system was constructed with strain-gauge sensors to measure torque of a PTO axle, an I/O interface to acquire the sensor signals, and an embedded system to calculate severeness. The severeness of PTO was analyzed using measured torque data during rotary tillage. In the PTO gear life fatigue test, breakage time and bending stress of the gear were measured by tooth widths and torque change during the fatigue life test. The S-N curve showed a good linear relationship between bending stress and number of cycle (life) with a coefficient of determination of 0.97. For PTO severenss evaluation, rotary tillage operations were conducted at two PTO rotational speeds (level-1, level-2) under different paddy and upland field sites with different soil conditions. Results of averaged relative severeness for PTO level-1 and PTO level-2 were 1.96 and 3.34, respectively, at paddy field sites, and they were 1.36 and 2.51, respectively, at upland field sites. The results showed that the PTO driving axle experienced more severe load during rotary tillage at paddy fields than at upland sites, and relative severeness was greater at the higher PTO rotational speed under all of the soil conditions.

• ALGAE
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• v.39 no.2
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• pp.109-127
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• 2024

High production and efficient harvesting of microalgae containing high omega-3 levels are critical concerns for industrial use. Aeration can elevate production of some microalgae by providing CO₂ and O₂. However, it may lower the production of others by generating shear stress, causing severe cell damage. The mixotrophic dinoflagellate Gymnodinium smaydae is a new, promising microalga for omega-3 fatty acid production owing to its high docosahexaenoic acid content, and determining optimal conditions and methods for high omega-3 fatty acid production and efficient harvest using G. smaydae is crucial for its commercial utilization. Therefore, to determine whether continuous aeration is required, we measured densities of G. smaydae and the dinoflagellate prey Heterocapsa rotundata in a 100-L semi-continuous cultivation system under no aeration and continuous aeration conditions daily for 9 days. Furthermore, to determine the optimal conditions for harvesting through centrifugation, different rotational speeds of the continuous centrifuge and different flow rates of the pump injecting G. smaydae + H. rotundata cells into the centrifuge were tested. Under continuous aeration, G. smaydae production gradually decreased; however, without aeration, the production remained stable. Harvesting efficiency and the dry weights of omega-3 fatty acids of G. smaydae + H. rotundata cells at a rotational speed of 16,000 rpm were significantly higher than those at 2,000-8,000 rpm. However, these parameters did not significantly differ at injection pump flow rates of 1.0-4.0 L min^-1. The results of the present study provide a basis for optimized production and harvest conditions for G. smaydae and other microalgae.

• Tribology and Lubricants
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• v.13 no.1
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• pp.62-69
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• 1997

Rapid increase of refrigeration and air-conditioning systems 9r & a systems) in modern industries brings attention to the urgency of research & development as a core technology in the area. And it is required to the compatibility problem of r & a systems to alternative refrigerant for the protection of environment. The, it is requested to study the lubrication characteristics of refrigerant compressor which is the core technology in the r & a systems. The study of lubrication characteristics in the critical sliding component is essential for the design of refrigerant compressor. Therefore, theoretical investigation of the lubrication characteristics of rotary compressor for r & a systems is studied. The newton-Raphson method is used for the EHL analysis between vane and rolling piston in the rotary compressor. The results show that the rotational speed of a shaft and the discharge pressure influence significantly the friction force between vane and rolling piston. This results give important basic data for the further lubrication analysis and design of a rotary compressor.

• KSTLE International Journal
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• v.8 no.1
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• pp.11-15
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• 2007

The mechanical face seal has been tested in Korea Aerospace Research Institute (KARl) for turbopump applications. In the turbopump under current development, the mechanical face seal is installed between fuel pump and turbine to prevent a mixture of fuel and combustion gas. Generally the mechanical face seal in turbopump is exposed to severe environment because of great rotational speed, high temperature of combustion gas and high level of pressure difference. Thus a series of tests were performed to guarantee the reliability of mechanical face seal by means of simulating the practical operating conditions. The tests were conducted up to 20,000 rpm with pressure difference of 800 kPa and temperature of 620 K In addition several carbon materials for mechanical face seal were conducted to the tests to compare the life time. During the tests, the performance against leakage was monitored and the carbon wear was also measured to estimate the life of a mechanical face seal The results show that the leakage flow rates of mechanical face seal is ignorable compared to an overall flow rate of fuel pump. The carbon material which has the finest wear resistance was found during the tests. Lastly no critical failure of mechanical face seal was found during the tests and the reliability of mechanical face seal for turbopump was successfully proved.