• Tribology and Lubricants
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• v.31 no.4
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• pp.177-182
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• 2015

Tapered roller bearings are widely used in equipment where high combined thrust and radial loads are experienced. A certain amount of tilting between the tapered rollers and the races always occurs because of bending moment load conditions and shaft deflection. It is now well understood that a coherent elastohydrodynamic lubrication (EHL) film separates the rollers and races. In spite of extensive study on EHL problems for over half a century, relatively few studies have focused on the finite line contacts problem. This study presents a complete numerical analysis of the effects of roller tilting on the EHL characteristics in a tapered roller bearing. We systematically analyze this highly nonlinear problem using finite differences with fully non-uniform grids and the Newton-Raphson method. Detailed EHL pressure distributions and film shapes are presented under moderate loads and material parameters. A very small roller tilting significantly affects the pressure distributions and film shapes near both ends of the roller. Moreover, the effect of tilting on the EHL characteristics at the small end is much greater than that at the large end. Therefore, in designing optimum profiles for tapered roller bearings, the profile radius should be larger at the small end.

• International Journal of Aeronautical and Space Sciences
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• v.9 no.2
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• pp.48-57
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• 2008

The noise is one of the serious problems concerning helicopters operations. The issue of helicopter external noise generated mainly from a helicopter rotor has always affected the use of rotorcrafts, especially in the urban environment. The noise sources depend on the flight configurations. In particular, a noise generated by the interaction between blades and tip vortices mainly occurs during descent flight. This noise is called blade-vortex interaction (BVI) noise, and this BVI noise is particularly penalizing for helicopters. In this paper, a numerical study to capture the BVI noise is carried out. The numerical study is performed in two phases. In the first phase, a 2D simulation based on parallel BYI event of Kitapliglu et al experiment is performed. In the second phase, 3D simulation based on HART Ⅱ experiment is performed. Several experimental data such as thrust, torque, blade sectional load, its derivative and vortex location are compared with calculation results and the comparison showed reasonably good agreement.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.2
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• pp.210-224
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• 2010

The aim of the present study is to investigate the buckling strength of plates and stiffened panels with opening under transverse thrust and shear actions. It is observed that the existing design formulation for critical-buckling strength of plates are not valid for perforated plates, because the current design formulation trends can significantly overestimate or underestimate the load-carrying capacity of plates when plates have large opening and/or are thick. A series of eigen value and elastic.plastic large deflection finite element analyses are carried out with varying the aspect ratio of plate, the opening size and location on plate until and after the ultimate strength is reached. Based on the results obtained from the present study, closed-form design formulations for the elastic buckling strength of plates and stiffened panels with opening are derived. The derived design formulations are considered plasticity correction of the material and verified by experimental tests and results of nonlinear finite element computations.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.285-290
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• 2009

The main thrust of this paper is to investigate acceptable supply air conditions of a dedicated outdoor air system (DOAS) for highrise apartment buildings. As for a typical $132-m^2$ apartment unit, it was assumed that centralized DOAS-Ceiling Radiant Cooling Panel was installed. Transient behavior and control characteristics of each system were modeled numerically using a commercial equation solver program. The optimized dew point temperature of the DOAS was discussed on the basis of the ASHRAE standard 62.1-2007 and the current Korean ventilation standard for apartments. It was found that the optimized dew point temperature of the DOAS supply air accommodating total latent load of a space is $11-12^{\circ}C$ and the appropriate supply air temperature of the DOAS is $11-12^{\circ}C$ in cooling period and neutral temperature of $18-20^{\circ}C$ in intermediate period.

• The KSFM Journal of Fluid Machinery
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• v.7 no.5 s.26
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• pp.20-28
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• 2004

Static and dynamic structural analyses of a turbine bladed-disk for a liquid rocket turbopump are performed to investigate the safety level of strength and vibration at design point. During operation, turbopump is exposed to various external loads. Therefore, the effects of them should be carefully considered and properly modeled. First, due to the high rotational speed of the turbopump, effects of centrifugal forces are considered in the structural analysis. Thermal load caused by severe temperature differences is also considered. A three dimensional finite element method (FEM) is used for linear and nonlinear structural analyses with modified Newton-Raphson iteration method. After the nonlinear solution is obtained from the structural analysis, dynamic characteristics are obtained as a function of rotational speed from the linearized eigenvalue analysis at an equilibrium position. From the analysis results, characteristics of stress distribution and vibration were thoroughly examined and investigated.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.1063-1066
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• 2003

This paper presents the design and characteristics analysis of axial-flux permanent-magnet (PM) synchronous generator of two air-gap. Dual axial-flux type PM synchronous generator commonly appears in applications where the generator axial dimension is more limited than the radial dimension. The strengths of dual axial-flux generator include ; (1) by employing two air-gaps, the rotor-stator attractive forces are balanced and no net axial or thrust load appeals on the generator hearings ; (2) heat produced by the stator windings appears on the outside of the generator, making it relatively easy to remove, and so on. In this paper, the simple magnetic equivalent circuit approach is used for initial design iteration, and the finite-element method is applied to analyze the detailed characteristics. The test results of driving characteristics are presented as well. The results are very similar to predicted performance of design.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.285-287
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• 1995

In the case of driving the SLIM(Single-sided Linear Induction Motor) as the VVVF inverter, the performance of SLIM, which is a thrust, normal force and so on, varies according to a slip frequency as a function of the external load. It is impossible that the open-loop control method control the speed of a SLIM accurately. So that, this paper is proposed the speed control method of a SLIM for a automatic conveyor system with the slip frequency vector control method. To analyze the dynamic characteristics of a SLIM, the state equation is derived from the equivalent circuit of the SLIM, ignored the end effect. The slip frequency and the normal force of SLIM are constantly controlled at the steady state. The simulated results is compared with the experimental values.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1063-1070
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• 1988

The influence of the inlet pressure on bearing performance of tilting pad bearings in laminar regime is examined. A simple flow model is presented to calculate the inlet pressure in inlet flow that occurs at a short distance ahead of the bearing inlet. The bearing performances are obtained, load capacity, friction torque and lubricated flow-rate, etc, numerically for the inlet pressure boundary conditions with and without pressure jump. The computed results of both cases show that bearing performance and the optimum pivot position changes remarkably according to the bearing operating conditions. The influence of the inlet pressure on bearing performance must be considered to analyze the bearing performance precisely.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.810-812
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• 2008

Previously study on structural design of the main wing of the twenty-seat class WIG(Wing in Ground Effect) craft. In the final design, three spars construction was selected for safety in the critical flight load, and the Carbon-Epoxy material was selected for lightness and structural stability. In this study, the forced vibration analysis was performed on the composite main wing structure of the twenty-seat class WIG craft with two-stroke pusher type reciprocating engine. The vibration analysis based on the finite element method was performed using a commercial FEM code, MSC/NASTRAN. Excitations for the frequency response analysis were assumed as the H-mode(horizontal mode), the V-mode(vertical mode) and the X-mode(twisted mode) which are typical main vibration modes of engine. And excitations for the transient response analysis were assumed as the L-mode(longitudinal mode) with the oscillating propeller thrust which occurs in operation. According to the result of forced vibration analysis, structural design was modified to reduce the vibrations.

• International Journal of Air-Conditioning and Refrigeration
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• v.17 no.4
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• pp.115-122
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• 2009

Numerical simulations for scroll, two-stage twin rotary, and two-cylinder reciprocating compressors have been carried out to understand the effectiveness of each type compressor for heat pump water heater application using $CO_2$ as refrigerant. For suction pressure of 3.5 MPa and discharge pressure of 9 MPa, clearance volume ratio of the reciprocating compressor needs to be about 5% or less to have the volumetric efficiency comparable to that of the scroll compressor with tip clearance of $5\;{\mu}m$. Volumetric efficiency of the scroll compressor is quite sensitive to tip clearance. Adiabatic efficiency of the twin rotary compressor was calculated to be the lowest among the three types, and the most severe drawback of the $CO_2$ scroll compressor was a significant increase in the mechanical loss at the thrust surface supporting the orbiting scroll member. While the scroll compressor showed very smooth torque load variation, peak-to-peak torque variations of the twin rotary and two-cylinder reciprocating compressors were about 50% and 250%, respectively.