• Proceedings of the KSME Conference
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• 2004.04a
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• pp.31-35
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• 2004

The speed competition of optical disk drive has been accelerated with the fast advancement of its storage density and data transmission technology. The continuous increase of the spinning speed of CD meets the unexpected and catastrophic failure of disk during the operation. The effect of its thickness and outer radius of disk were investigated to reduce stresses and J-integral around the crack tip. The effect of its thickness was considered ahead of the crack tip. In the effect of outer radius of disk, linear elastic fracture mechanics was used to obtain the critical crack length, which indicates the onset length for unstable crack growth. This approach is so significant as to detect the growing crack by disk drive before the catastrophic failure, which will provide the standard size of its safety for high-speed disk drive.

• Journal of Magnetics
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• v.9 no.4
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• pp.101-104
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• 2004

The crystallization behaviours of nanocomposite made by a function of quenching rate (roller speed) were studied. The results showed that there was one step c$\mathbb{r}$ystallization process for the alloy quenched at roller speed of 32 m/s, which could be shown as, Am (amorphouse) + ${\alpha}-Fe/Nd_2Fe_{14}B$ ${\rightarrow}$ ${\alpha}-Fe/Nd_2Fe_{14}B$ . For the alloy quenched at roller speed of 40 m/s, there was steps crystallization process taking place at different temperatures, which could be shown as, Am ${\rightarrow}$ ${\alpha}-Fe/Nd_2Fe_{23}B_3+Nd_2Fe_{14}B+Am`$ ${\rightarrow}$ ${\alpha}-Fe/Nd_2Fe_{14}B$. The presence of transition phase ($Nd_2Fe_{23}B_3$) was harmful to get fine and uniform grain size during crystallization process. Uniform microstructures and high magnetic properties could be attained for the as-quenched alloy containing less amorphous phase and no presence of transition phase during annealing treatment. For the alloy prepared at roller speed of 32 m/s, the following properties were obtained, $B_r= 0.904 T,_iH_c = 801 kA/m, (BH)_{max} = 122 kJ/m^3 and M_r/M_s = 0.6$.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.11
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• pp.1584-1590
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• 2017

This paper presents a implementation method of reliable speed limitation controller considering motor parameter variation in high speed operation. In spinning process of drum washing machine, speed increase has to be limited when unallowable imbalance mass is detected. Otherwise, severe noise and vibration can happen because noise and vibration are proportional to imbalance mass. To detect imbalance mass, d-axis current magnitude is used. However, we have to compensate for back-emf and power supply variation by means of detecting them because d-axis current is affected by both of them. On the other hand, we have to carefully estimate back-emf because back-emf is affected by stator resistance variation and inverter voltage error. Stator resistance variation can happen by manufacturing process for mass production or temperature variation in running. And there are inverter voltage errors between command voltage from micro-computer to inverter and real voltage from inverter to motor because of rising and falling time delay and turn-on resistance of power semiconductor switch. To solve this problem, we propose 2-step align current injection method which is to inject step-wise current right before starting. By this method, we can simply obtain stator resistance by ratio of voltage without inverter voltage error and current, and we can measure inverter voltage error. So we can obtain more exact model current, and then by simple calculation with compensation gain, we can estimate more accurate motor back-emf. We show that this method works well. It is verified through experiments.

• New & Renewable Energy
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• v.10 no.3
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• pp.14-21
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• 2014

As the world supply of fossil fuel sources decreases, the need for efficient energy consevation and develping green energy technologies becomes critical. Because of the high cost of the foundation for large turbines and optional high wind speed (over 12 m/s), it is very difficult to be located at inland city. For the solution above mentioned problem, we have been experimented about that not only using the adaption of wind power system on buildings for improving turbine efficiency, but also applying a wound rotor type induction generator for a small wind turbine.In this research, we try to find out the wind direction and wind speed those were measured every 1 min., during operation period, using the anemometers which consist of horizontally spinning cups on a vertical post. Performance testing for small wind turbine generating system was carried out by using the induction motor and invertor. Finally, we measured the power of 1 kW wind turbine system with the clamp meter and a voltmeter.

• Journal of Mechanical Science and Technology
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• v.17 no.2
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• pp.181-186
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• 2003

In order to assure the quality of the bent axis design axial piston pumps driven by tapered pistons, it is necessary to know the characteristics of force applied to tapered pistons and the mechanism for driving the tapered pistons. Since they are able to perform both reciprocating and spinning motions in cylinder block, it is difficult to understand the driving mechanismand-tomeasure the forces applied to tapered pistons experimentally In the present study, the theoretical mechanism for driving the tapered pistons is studied by use of the geometric method. The driving area of the tapered pistons is measured by measuring the strain of a cylinder forced against a tapered piston using an electric strain gauge and a slip ring. The forces applied to tapered pistons is also investigated with the change of discharge pressure and the rotational speed. As a results of this investigation, it is concluded that the cylinder block is driven by one tapered piston in a limited area and the driving area is changed due to space angle of the tapered pistons and the swivel angle of the cylinder block. It is also observed that the force applied to tapered pistons increases as the discharge pressure and the rotational speed increase.

• Journal of the Semiconductor & Display Technology
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• v.23 no.1
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• pp.88-91
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• 2024

The europium doped yttrium oxide (Y₂O₃:Eu³⁺) thin film was formed on a Si substrate by the conventional spin-coating process followed by rapid thermal annealing (RTA) treatment. The spinning profiles such as rotation speed, acceleration and holding times were controlled during the spin-coating process for the best condition of the Y₂O₃:Eu³⁺ thin film. The RTA treatment was conducted for several temperature in order to crystallize the spin coated film. The Y₂O₃:Eu³⁺ thin film presented best performance in the conditions of 4000 rpm, 30 s and 10 s of rotation speed, acceleration time and holding time, respectively, at a fixed RTA temperature of 900 ℃.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.15 no.3
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• pp.166-175
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• 2005

Health effects associated with metal working fluid (MWF) exposures include dermatitis, respiratory disease, hypersensitive pneumonitis, and asthma. Frequently, occupational exposures to MWFs are controlled by ventilating an enclosure with an air cleaning unit that includes a fan preceded by various kinds of filtration. There are several kinds of air cleaning units used in machining centers. But the associated troubles have hindered from efficiently using these devices. The main problem is the relatively short period of filter replacement. The reason is that the air cleaning units usually do not have the de-oiling systems, thus leading the earlier clogging of filters and reducing the flow rate of hood. Thus, the first stage of study was conducted to overcome this problem by developing the new oil mist collector equipped with the easy de-oiling system. The principle of de-oiling is that the centrifugal force generated by spinning the drum covered by filter fabric separates oils from the filter fabric. It would be very similar to the spin-dry laundry. By adopting this de-oiling technique, the problems associated with the conventional oil mist collectors could be solved. Several tests/analyses were performed to make the lab-scale oil mist collector. The collection efficiencies and the de-oiling efficiencies of commercially available filter fabrics were tested. Subsequently, the endurance test were conducted by observing SEM photos of filter fabrics and measuring tensile strength/expansion coefficient after spinning the filter drum for 20 minutes at the different rotation speeds. By doing these experiments, the most appropriate filter fabric and rotation speed/duration were selected. Finally, the new oil mist collector was designed. In the near future, this device must be tested in the real machining center.

• 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.

• Tribology and Lubricants
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• v.39 no.6
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• pp.268-272
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• 2023

This study explores the characteristics of tilting pad journal bearings used in the high-speed rotating shaft systems of centrifugal compressors. A centrifugal compressor is a high-speed rotating machine that is widely used to compress gases or vapors employed in various industrial applications. It transfers the centrifugal force of a fast-spinning impeller to the fluid and compresses it under high pressure. Many high-speed rotating shaft systems, which require high stability, use tilting pad journal bearings. The characteristics of these bearings can vary depending on several properties, and identifying the appropriate characteristics is essential to optimize the design on a case-to-case basis. In this study, the authors perform a time-dependent analysis of the properties of tilting pad journal bearings and the rotordynamics of the rotating shaft system using COMSOL Multiphysics software. Specifically, the authors analyze the characteristics of the tilting pad journal bearings by performing a parametric sweep using parameters such as pad clearance, maximum tilting angle, preload, number of pads, and pad pivot offset. The authors then use the results of the bearing-characteristics analysis to evaluate the vibration of the rotating shaft and verify its operation within a desirable range. The understanding gained from this study will allow us to determine the optimal properties of these bearings and the limiting operational speed using COMSOL Multiphysics software.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.2
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• pp.39-45
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• 1999

In case of field weakening region, torque is directly affected by flux. In this region, the flux reference is cIecreased inversely proportional to the rotor speed. As the flux is decreased, the magnetizing inductance is nonnally increased The increased magnetizing inductance limited voltage for controlling current In this paper, rreasuring q axis voltage in field weakening region, magnetizing inductance in flux calculating can be readjusted. Computer simulation and experiment results demostrate the efficacy of the prqx>sed rrethod. Proposed algorithm is expected to the application of the adjustable drive system in the spinning and weaving field. field.