• Journal of Advanced Marine Engineering and Technology
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• 제32권4호
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• pp.522-527
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• 2008

On designing of hydrostatic bearing, load, quantity of oil, stiffness and friction load are considered as basic characteristics. For the analysis of these basic characteristics, pressure distribution by oil film is obtained. Speed of piston, clearance, leakage of oil, eccentricity, shape and roughness of bearing affect the results which are the analysis of basic characteristics of load, quantity of oil, stiffness and friction load. The relationship among those factors are required for optimum designing of hydrostatic bearing for machining tool. Reynold's Equation is calculated through finite element method. Load, leakage of quantity and pressure distribution as variation of length, land length ratio, eccentricity and axial velocity of bearing are investigated. Then optimum design variables are obtained.

• Tribology and Lubricants
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• 제28권1호
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• pp.12-18
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• 2012

This application study of a swash-plate type axial piston pump was concerned about the lubrication characteristics between cylinder barrel and valve plate which are the main rotating body and its opposite sliding part respectively. A computer simulation was implemented to assess bearing and sealing functions of the fluid film between cylinder barrel and valve plate. A numerical algorithm was developed to facilitate simultaneous calculations of dynamic cylinder pressure, 3 degree-of-freedom barrel motions considering inertia effect, and fluid film pressure assuming full fluid film lubrication regime. Central clearance, tilt angle, and azimuth angle of the rotating body were calculated for each time step. Surface waviness was found to be an influential factor due to the small fluid film thickness which can appear in flat land bearings. Five surface lays which can form on the lubrication surface in accordance with machining process were defined and analyzed using the simulation tool. Oil leakage flow and frictional torque in the fluid film between cylinder barrel and valve plate were also calculated to discuss in the viewpoint of energy loss. The simulation results showed that in actual sliding conditions proper surface non-flatness can make a positive effect on the energy efficiency and reliability of the thrust bearing.

• Tribology and Lubricants
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• 제21권5호
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• pp.201-208
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• 2005

This paper presents the FEM analysis on the contact behavior characteristics of mechanical face seals in a small hydro-power turbine. Especially, the axial displacement and contact normal stress between a seal ring and a seal seat of a primary sealing unit have been analyzed as functions of rotating speed of a hydro-turbine, sealing gap, water and cooling fluid temperature. Those are strongly related to a leakage of water and wear between a seal ring and a seal seat. The FEM computed results present that the rotating speed of a hydro-turbine may be kept less than 800 rpm, and the sealing gap in a primary sealing unit is restricted $0.5\~5$. The coolant temperature in which is most influential parameter to the contact behaviors of a sealing unit may be kept less than $15^{\circ}C$ for a safe operation of a sealing unit without a leakage and wear.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.638-641
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• 2008

Computational investigation was conducted to study the effects of the shape parameter of shroud on the performance of the outdoor unit of an air-conditioners. For this study the Design of Experiment(4-factor 3-level) was created and the an automatic program was composed using VBA to reduce the load of pre-process for CFD. The estimated mathematical equation was produced from this analysis and it was found that the gap between fan and shroud affects more heavily than the other parameters. As a result, the composition of the best parameters was verified that its flow rate was increased by 10 percents and sound pressure level was reduced by 1.2 dBA compare with the worst. And finally, a kind of Propeller fan with blades which were attached to the shroud, so-called 'ProBeller Fan' was introduced in this study.

• 대한기계학회논문집B
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• 제31권4호
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• pp.357-366
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• 2007

The present study investigated local heat/mass transfer characteristics on the surface of the rotating turbine blade with various incidence angles. The experiments are conducted in a low speed annular cascade with a single stage turbine. The blade has a flat tip with the mean tip clearance of 2.5% of the blade chord. A naphthalene sublimation method is used to measure detailed mass transfer coefficient on the blade. At design condition, the inlet Reynolds number is $Re_c=1.5{\times}10^5$ which results in the blade rotation speed of 255.8 rpm. Also, the effect of off-design condition is examined with various incidence angles between $-15^{\circ}$ and $+7{\circ}$. The results indicated that the incidence angle has significant effects on the blade surface heat transfer. In mid-span region, the laminar separation region on the pressure side is reduced and the laminar flow region on the suction side shrinks with increasing incidence angle. Near the tip, the effect of tip leakage flow increases in span wise and axial directions as the incidence angle decreases because the tip leakage flow is formed near the suction side surface. However, the effect of tip leakage flow is reduced with positive incidence angle.

• Tribology and Lubricants
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• 제34권1호
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• pp.9-15
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• 2018

Modern high-performance automotive turbochargers (TCs) implement ceramic hybrid angular contact ball bearings in series with squeeze film dampers (SFDs) to enhance transient responses, thereby reducing the overall emission levels. The current study predicts the rotordynamic responses of the commercial automotive TCs (compressor wheel diameter = ~53 mm, turbine wheel diameter = ~43 mm, and shaft diameter at the bearing locations = ~7 mm) supported on ball bearings and SFDs for various design parameters of SFDs, including radial clearance, axial length, lubricant viscosity, and rotor imbalance conditions (i.e., amplitudes and phase angles) while increasing rotor speed up to 150 krpm. This study validates the predictive rotor finite element model against measurements of mass, polar and transverse moments of inertia, and free-free mode natural frequencies and mode shapes. A nonlinear rotordynamic model integrates nonlinear force coefficients of SFDs to calculate the transient responses of the TC rotor-bearing system. The predicted results show that SFD radial clearances, as well as phase angles of rotor imbalances, have the paramount effect on the dynamic responses of TC shaft motions.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 추계학술대회논문집
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• pp.582-585
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• 2004

Most of hard disk drives currently employ fluid dynamic bearing (FDB) for their rotor support. Stiffness of the FDB is affected by many design factors such as bearing clearance, fluid viscosity, and rotational speed. For the high rotating speed HDDs stiffness of the rotor is normally high enough to accomodate load disturbances. However small form factor HDDs that are to be operated in low power consumption are often designed with low stiffness rotors. Although the low stiffness rotor clearly benefits low power operation, it could damage the entire motor structure or head disk interface even by a light mechanical load disturbance such as shock or vibration. In addition, since a single channel HDD does not provide gram load equilibrium in axial direction the rotor could be tilted and make a hard contact to stator. A non-symmetric groove pattern could successfully compensate the tilted rotor angle during operation.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.578-583
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• 2006

This paper introduces conceptual design of scroll expander-compressor unit for fuel cell. Since air discharged out of the fuel cell stack after reaction has still high pressure energy, some power can be extracted out of it by directing it to pass through an expanding device so that the extracted power can be used to drive an auxiliary compressor. For this purpose, a scroll type expander coupled to a scroll type compressor was designed: orbiting scroll of the expander and that of the compressor were made to share three of common drive pins installed in the mid frame plate, and central cavity in the mid-plate was used as a back pressure chamber to provide axial compliance for both orbiting scrolls. Performance analysis for the expander showed that the shaft power of the expander could reduce the auxiliary power consumption in the fuel cell by about one third at the scroll clearance of $10{\mu}m$.

• Tribology and Lubricants
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• 제25권2호
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• pp.108-113
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• 2009

This paper presents a experimental results for the performance evaluation of a double-bumped air foil bearing. The test results of a double-bumped AFB is compared with a single-bumped AFB at a heavily-loaded condition. The diameter of the test bearing is 50 mm, and the axial length is 50 mm. Nominal clearance of the single-bumped AFB is evaluated as $105{\mu}m$, and that of the double-bumped AFB is as $95{\mu}m$. The test of the AFBs are demonstrated at 3 test mode; the load variation mode, the speed variation mode, and start-stop mode. The single-bumped AFB demonstrated a upward load-carrying capacity of 95 N and a downward load-carrying capacity of 130 N at 20,000 rpm. The double-bumped AFB demonstrated a upward load-carrying capacity of 170 N and a downward load-carrying capacity of 170 N at 20,000 rpm. The single-bumped AFB demonstrated a downward lift-off speed of 16,300 rpm at 105 N. The double-bumped AFB demonstrated a downward lift-off speed of 15,400 rpm at 105 N. The start-stop test of the AFBs assure 5,000 cycle endurance life. The test results are compared with the theoretical calculation results. The test and theorectical results show thata double-bump air foil bearing provides a higher load-carrying capacity, stiffness and damping than a single-bump air foil bearing in a heavily-loaded condition.

• Tribology and Lubricants
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• 제34권1호
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• pp.33-41
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• 2018

This paper describes a new test rig for identification of rotordynamic force coefficients of squeeze film dampers (SFDs) in automotive turbochargers (TCs). Prior studies have mainly concentrated on relatively large-sized SFDs used in aircraft engines, turbocompressors, and turbopumps. The main objective of the current study is to propose a test rig for identification of dynamic force coefficients of small-sized SFDs (a journal diameter of ~11 mm). The current test rig consists of a journal, a SFD cartridge, four support rods, an upper structure, a data acquisition (DAQ) system, and an oil circulation unit. The annular gaps between the journal outer surface and SFD cartridge inner surface create SFD film lands. The damper has two parallel film lands separated by a central groove, having an axial length and depth of 3 mm. Each film land has a length of 4 mm with a $40{\mu}m$ radial clearance. The static load and dynamic impact tests identify the structural characteristics (i.e., stiffness and natural frequency) of the journal and assembled test rig. The measurements show good agreement with predictions. The SFD performance data from this test rig will be used to develop innovative TC rotor systems with improved NVH and reliability characteristics incorporating advanced SFD technology.