• Tribology and Lubricants
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• v.34 no.5
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• pp.169-174
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• 2018

A multi-stage compressor (MSC) is comprised of several impellers installed in the pinion gear shaft driven by a main bull gear. In the pinion shaft, a thrust collar (TC) is installed to support the thrust load. The TC makes the lubrication system simpler in the MSC; therefore, it is widely used in similar kinds of machinery. Typically, TCs are installed on both sides of the bull gear and pressure is developed in the lubricated area by creating a taper angle on the TC and bull gear surface. In the current study, we developed a numerical analysis model to evaluate the performance of the TC considering its design parameters. We sloved the Reynolds equation using the finite element method and applied the half Sommerfeld condition to consider cavitation. Based on the pressure calculated in the lubricated area, we calculated the power loss and minimum film thickness. In addition, we calculated stiffness and damping using perturbation method. We performed parametric studies using the developed model. The results of the analysis show that the maximum pressure presents in the center area of the TC and it increases with the taper angle. The area over which pressure is developed decreases with the taper angle. The results also show that there is an optimum taper angle providing minimum power loss and maximum film thickness. Additionally, the stiffness and damping decrease with the taper angle. As the applied load increases, the power loss increases and the minimum film thickness decreases. However, the stiffness and damping increase with the applied load.

• Proceedings of the KIEE Conference
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• 1997.07b
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• pp.593-596
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• 1997

The main purpose of this paper is to develop sensing device of joint angle using loss of opfical fiber. The source of light to optical fiber is infrared rays diode, and receiver is a photo transistor. The bent angle of optical fiber is measured with rotary encoder, and The change of voltage due to the loss of light is measured with micro computer PIC16C74. The sensing device may be used to Functional Electrical stimulation(FES) System for Rehabilitation patient.

• Journal of the Optical Society of Korea
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• v.20 no.5
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• pp.614-622
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• 2016

In this paper, we propose a novel differential equation method for designing a total internal reflection (TIR) LED lens with double freeform surfaces. A complete set of simultaneous differential equations for the method is derived from the condition for minimizing the Fresnel loss, illumination models, Snell’s Law of ray propagation, and a new constraint on the incident angle of a ray on the light-exiting surface of the lens. The last constraint is essential to complete the set of simultaneous differential equations. By adopting the TIR structure and applying the condition for minimizing the Fresnel loss, it is expected that the proposed TIR LED lens can have a high luminous flux efficiency, even though its beam-spread angle is narrow. To validate the proposed method, three TIR LED lenses with beam-spread angles of less than 22.6° have been designed, and their performances evaluated by ray tracing. Their luminous flux efficiencies could be obviously increased by at least 35% and 5%, compared to conventional LED lenses with a single freeform surface and with double freeform surfaces, respectively.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3357-3368
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• 1994

Total pressure losses required to calculate the total-to-total efficiency are estimated by integrating empirical loss coefficients of four loss mechanisms along the mean-line of blades as follows; blade profile loss, secondary flow loss, end wall loss and tip clearance loss. The off-design points are obtained on the basis of Howell's off-design performance of a compressor cascade. Also, inlet-outlet air angles and camber angle are obtained from semi-empirical relations of transonic airfoils' minimum loss incidence and deviation angles. And nominal point is replaced by the design point. It is concluded that relatively simple loss models and Howell's off-design data permit us to calculate the off-design performance with satisfactory accuracy. And this method can be easily extended for off-design performance prediction of multi-stage compressors.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.11
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• pp.1028-1034
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• 2004

Recently, the ice storage system using ice slurry has been used increasingly since it has been introduced where the rapid cooling load change is required. Because it overcomes a decrease of the melting performance and an increase of the thermal resistance on the ice layer in static ice thermal storage system. This study is performed to understand the effects of transporting ice slurry through horizontal, vertical and inclined tubes ($30^{\circ},\;45^{\circ}$). It used propylene glycol-water solution and ice particles (diameter of about 2 mm) in this experiment. The experiments were carried out under various conditions, with concentration of water solution ranging from 0 to $20wt\%$, and velocity of water solution at the entry ranging from 1.5 to 2.5 m/s. The results were as follows: Regarding the angle of inclined tube, the highest pressure loss was measured for vertical tube and the pressure loss for $45^{\circ},\;30^{\circ}$, horizontal straight tubes were lower successively. The lowest pressure loss in these tubes was measured at velocity of $2.0{\sim}2.5m/s$ and concentration of $10wt\%$. The outlet IPF was likewise stable in these ranges.

• Journal of Advanced Navigation Technology
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• v.28 no.3
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• pp.278-287
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• 2024

In this paper, telemetry link budget model for small launch vehicle is proposed, and telemetry link budget simulator is implemented. The proposed link budget model consist of geometry model and propagation loss model. The geometry model is calculation of look angle between ground station and small launch vehicle. The propagation loss model consist of free space loss, polarization loss, and de-pointing loss which are appropriate to the small launch vehicle flight environment. The proposed propagation loss model can be calculate propagation loss without complex calculation of propagation environments. The link budget simulator is implemented in MATLAB. The simulator calculate look angle, free space loss, polarization loss parameter, de-pointing loss and received signal level in ground station by using position of ground station, routing of small launch vehicle, 3-D radiation patterns of antennas.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.10
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• pp.64-72
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• 1995

In this paper, atmospheric turbulence and absorption under clear weather condition, which affect the optical satellite up-link communication between geo-satellites and earth station, were studied. In case of the up-link communication, the received optical power is weakened by pointing loss caused by beam tilt which is the main effect of turbulent atmosphere. This pointing loss directly has relation to the diameter of optical transmitting antenna. From the inverse proportion of the pointing and spaced loss, it is the regions where the diameter of transmitting antenna increases abruptly and the efficient design of transmitting antenna is impossible. In case of using channel coding, it was shown that the peak value of diameter moved to the lower regions of elevation angle with increasing the coding gain and its width was also decreased. In case of considering both coding gain and transmission rate on the design of transmitting antenna, it was known that more coding gain was necessary as transmission rate was increased.

• Progress in Superconductivity and Cryogenics
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• v.7 no.3
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• pp.34-38
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• 2005

Multi-stacked HTS tapes are needed to conduct large current in the power application. In this paper, magnetization losses of the multi-stacked YBCO coated conductor and the BSCCO tape have been measured and compared. Magnetization losses of single tape, 2-stacked, 3-stacked and 4-stacked HTS tapes have been presented in this paper. Multi-stacked tapes have been fabricated using face-to-face type stacking method. Measurements of magnetization loss were performed under various angle of external magnetic field to consider the anisotropic characteristics of HTS tapes. Test results show that loss density per unit volume decreased for both YBCO coated conductors and BSCCO tapes when the stacking number of tapes is increased. The magnetization losses of YBCO CC are larger than those of BSCCO tapes when the external magnetic field is increased.

• The KSFM Journal of Fluid Machinery
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• v.10 no.4
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• pp.21-28
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• 2007

The ratio of disk friction loss in a centrifugal pump is very large for the total pump loss in the range of very low specific speed. Therefore, impeller radius should be shortened to increase the pump efficiency because the disk friction loss is proportional to the fifth power of impeller radius. In order to compensate the decreased head by the shortened impeller radius, vane angle at impeller outlet should be increased. However, as the vane angle at impeller outlet becomes larger, performance instability occurs at low flow rate regions. In this study, J-Groove is adopted to suppress the performance instability and detailed examination is performed for the influence of the J-Groove on the pump performance. The results show that J-Groove gives good effect on the suppression of performance instability. Moreover, as J-Groove increases pump head considerably, the pump size can be smaller for head requirements.

• Journal of Magnetics
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• v.16 no.4
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• pp.417-422
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• 2011

This paper presents the characteristics of PM eddy current loss and harmonic iron loss for PM step-skewed Interior Permanent Magnet Synchronous Motor (IPMSM) with concentrated windings and multi-layered PM under the running condition of maximum torque per ampere (MTPA) and flux-weakening control. In particular, PM eddy current loss and harmonic iron loss in IPMSM have been numerically computed with three-dimensional Finite Element Analysis (3D FEA), whereby IPMSM with concentrated windings and multi-layered PM has been designed to identify the optimized skew angle contributing to the reduced PM eddy current loss and torque ripples, while maintaining the required average torque. Furthermore, numerical investigation on PM eddy current loss and iron loss at MTPA and flux-weakening control has been carried-out in terms of PM step-skew.