• Journal of Korea Society of Industrial Information Systems
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• v.25 no.5
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• pp.49-57
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• 2020

Conventional electric motors are not suitable for aircraft because of their large size and weight. High-temperature superconducting (HTS) motors have high current density, high magnetic field density, and low loss, so they can significantly reduce the size and weight compared to general electric motors. This paper presents the conceptual design and analysis results of HTS motors for electric propulsion in future aircraft. A 2.5 MW HTS motor with a rotational speed of 7,200 RPM was designed and the specific power (kW/kg) was analyzed. The operating temperature of the field coil of the HTS motor is 20K in consideration of LH2 cooling. The stator winding were connected in a multi-phase configuration and Litz wires were used to minimize eddy current losses. As a result, it was confirmed that the specific power of the motor is about 18.67 kW/kg, which is much higher than that of the conventional electric motor.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.354-358
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• 2007

An experimental study was performed to understand spray characteristics of the slinger injector. system for the micro turbojet engine. In this fuel injection system, fuel is sprayed and atomized in the combustor by centrifugal forces of engine shaft. This experimental apparatus consist of a high speed rotating Spindle, slinger injector, pressure tank and acrylic case. The droplet size and velocity were measured by PDPA(Phase Doppler Particle Analyzer) and spray was visualized by using Nd-Yag laser-based flash photography. From the test results, the droplet size(SMD) is largely affected to rotational speed, mass flow rate and the number of injection orifice. From the this experimental study, we could understand the spray characteristics of the slinger injection system and obtain the optimum shape of the slinger injector nozzle which is suitable for the micro turbojet engine.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2430-2435
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• 2015

In order to achieve high flexibility in manufacture, analysis of chip's shape is one of the most important problems. This paper describes the change of machining characteristics in workpiece materials depending on turning clearance angle. The experiments start from choosing three workpiece materials that are SM45C(machine structural carbon steel), STS303(stainless steel), SCM415 (chrome-molybdenum steel). Then, the experiments show specifically how features of selected materials changed when they were processed with diverse machining depths and with feed rate starting from fixed rotational speed. Especially, the experiments were also analyzed in chip's shape and wear of insert tip. In conclusion, these experiments show that chip's shape was changed by quality of the materials, depth of cut, and conveying speed. When machining feedrate and machining depth were 0.10mm/rev and 0.3mm respectively, workpiece materials showed the best shapes, not categorizing quality of the materials and machining characteristics.

• Transactions of the Society of Information Storage Systems
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• v.1 no.2
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• pp.169-174
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• 2005

Current information storage devices read/write data on the rotating disk. The axial vibration of a rotating disk should be suppressed for the successful operation of the device. Information storage devices widely used in these days adopt relatively thick disk which is stiff enough to suppress axial vibration under allowable limit. However, the thickness of the disk is going to be thinner and thinner as the small form factor of the devices is getting preferred by the consumer. In this study, a stabilizer system, which is composed with 8 air bearings, is proposed for suppressing the axial vibration of a $95{\mu}m$ thick PC disk in a non-contacting manner. The performance of the stabilizer system is simulated by numerical computation and then confirmed its results through a series of experiment. A thin and flexible disk has various vibration modes when it rotates in high speed. The stabilizer system generates positive as well as negative pressure due to the rotation of flexible disk so that the force due to the pressure distribution pushes and pulls rotating disk in a non-contacting manner. The balance between positive and negative pressure forces can be obtained by adjusting the area and the slope of the air bearing surface. The axial vibration of the flexible disk of 120mm diameter is suppressed successfully from over $1000{\mu}m$ to $30{\mu}m$ peak-to-peak value at the rotational speed of 5,000rpm.

• Tribology and Lubricants
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• v.30 no.6
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• pp.337-342
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• 2014

The reduction of drag torque is an important research issue in terms of improving transmission efficiency. Drag torque in a wet clutch occurs because of the viscous drag generated by the transmission fluid in a narrow gap (clearance) between the friction plate and a separate plate. The objective of this paper is to observe the effects of the friction plate area and the clearance on the drag torque using finite element simulation. The two-phase flow of air and oil fluid is considered and modeled for the simulation. The simulation analysis reveals that as the rotational speed increases, the drag torque generally increases to a critical point and then decreases sharply at a high speed regime. The clearance between the two plates plays an important role in controlling drag torque peak. An increase in the clearance causes a decrease in shear stress; thus, the drag torque also decreases according to Newton's law of viscosity. An observation of the effect of the area of contact between transmission fluid and friction plate shows that the drag torque increases with the contact area. The flow vectors inside the flow channel present clear evidence that the velocity of the fluid flows is faster with a larger friction plate, that is, in the case of a larger contact area. Therefore, the optimum size of the friction plate should be determined carefully, considering both the clutch performance and drag reduction. It is expected that the results from this study can be very useful as a database for clutch design and to predict the drag torque for the initial design with respect to various clutch parameters.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.12 no.5
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• pp.529-536
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• 2019

In this paper, the signals of the sensor for extracting characteristic parameters of the rotor are collected and the performance of the extraction technique is analyzed. To this end, a vibration test league was developed for conducting model tests to analyze the signal characteristics under normal operation. As a result, it is judged that no change in the measured the raw data amplitude will occur in the acceleration sensor with the unbalanced mass measured from the acceleration sensor. Performing FFT showed a significant increase in amplitude of the rotational frequency of 20 Hz as the unbalanced mass increased. The analysis results according to the change in the unequal mass of the speed sensor also showed a significant increase in the 1X Harmonics component, such as the acceleration sensor. There was no change in the amplitude of the acceleration sensor data when the misalignment occurred, and for the Envelope data, the amplitude of 2X (40 Hz) was increased depending on the degree of misalignment. The velocity sensor at change of misalignment also showed similar results to the acceleration sensor, and the peak was reduced at 600 Hz as the load increased in the frequency spectrum.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.843-846
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• 2004

For the fast growing Liquid Crystal Display (LCD) TV market, it is essential to make the LCD panels to show moving images without any visual difficulties such as blurring or tailing. Owing to reduction of the cell gap and the improved Liquid Crystal (LC) mixtures with low viscosity, it is possible that our S-IPS TFT-LCDs feature a response time (R/T) as fast as 1-frame time (16ms) for a white-black operation and less than a 16rns in all gray levels without Over Driving Circuit (ODC) technology. Currently, mass production of the large size IPS panels with high speed has been successfully achieved. In order to achieve faster response time, new LC mixtures have been developed, optimizing the physical properties of rotational viscosity (${\gamma}$1) and elastic constants (Kii). Also, the LC mixtures with high elastic constant allow us to increase the cell gap. In this paper, realization of fast switching time in IPS mode with optimized '${\gamma}$1/Kii' parameter in the LC mixtures forms the core of this paper.

• Journal of Advanced Navigation Technology
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• v.17 no.1
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• pp.107-114
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• 2013

In this paper, we propose controller to control the acceleration of unmanned aircraft turbojet engine. The high-gain observer to estimate the rotational speed of compressor is used, and the turbojet engine controller applying fuzzy heuristic techniques and PID control algorithm are designed. fuzzy PID controller produces the flow control input to prevent the surge and flame-out phenomena at the acceleration and deceleration of the turbojet engine. The standard acceleration is set and the fuel flow control is defined by the fuzzy heuristic. Computer simulations are performed using MATLAB in order to verify the performance of the proposed controller.

• Tribology and Lubricants
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• v.32 no.5
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• pp.154-159
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• 2016

This paper presents an experimental study of the leakage performance and endurance performance of a mechanical face seal in the 7-ton-class turbopump of the Korea Space Launch Vehicle 2 third-stage engine. We install a mechanical face seal between the fuel pump and turbine to prevent the mixing of the fuel and turbine gas. We design and manufacture a prototype mechanical face seal, which has two parts, namely, a bellows seal assembly and mating ring. We set up a test facility to measure the leakage and endurance of the mechanical face seal. For the similarity tests, we use water under real operating conditions such as high rotational speed, high temperature, and high pressure. Through investigation of the leakage and carbon wear rate, it is possible to evaluate the performance of the mechanical face seal. The results of the leakage and endurance performance test demonstrate the absence of any leakage from the prototype mechanical face seal after a trial run and clarify that the acceptable wear rate fully satisfies the turbopump requirements. Finally, we install a qualified mechanical face seal in a 7-ton-class turbopump and perform a validation test in the turbopump real-propellant test facility in the Korea Aerospace Research Institute. The test results confirm that the mechanical face seal works well under real operating conditions.

• The KSFM Journal of Fluid Machinery
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• v.18 no.6
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• pp.45-56
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• 2015

This paper aims to develop a submerged propeller turbine for micro hydropower plant which allows to sustain high values of efficiency in a broad range of hydrological conditions (H=2~6 m, $Q=0.15{\sim}0.39m^3/s$). The two aspects to be considered in this development are mechanical simplicity and high-efficiency operation. Unlike conventional turbines that have spiral casing and gear box, this is directing driving and no spiral casing. A 10 kW class turbine which has the most high potential of the power generation has been developed. The most important element in the design of turbine is the runner blade. The initial blade is designed using inverse design method and then the runner geometry is modified by classical hydraulic method. The design process is carried out in two steps. First, the blade shape is fix and then other components of submerged propeller turbine are designed. Computational fluid dynamics analyses based on the Navier-Stokes equations have been used to obtain overall performance data for the blade and the full turbine, respectively. The results generated by performance parameters(head, guide vane opening angle and rotational speed) variations are theoretically analysed. The evaluation criteria for the blade and the turbine performances are the pressure distribution and flow's behavior on the runner blades and turbine. The results of simulation reveals an efficiency of 91.5% and power generation of 10.5kW at the best efficiency point at the head of 4m and a discharge of $0.3m^3/s$.