• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.1
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• pp.26-33
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• 2001

Thrust vector control system is control device which is mounted exit of the nozzle to generate pitch, yaw and roll directional force by deflecting flow direction of the supersonic jet from the nozzle. By obtaining control force, jetvane which is exposed in jet flow is working thermal and aerodynamic load. Axial thrust loss and side thrust is affected by shock patterns and interactions between jetvanes according to jetvane geometry and turning angle. In this study, we designed 6 types of jetvane to evaluate pitch, yaw and roll characteristics of ietvane in supersonic flow, and perform the cold flow test in range of turning angles of jetvanes between $0^{\cire}$ and $25^{\cire}$ by $5^{\cire}$ respectively. Also, calculation is going side by side to analyse flow interaction. Results show that there is no interactions between jetvanes upto turning angle 20$^{\circ}$, chord and lead length ratio is very important parameter to aerodynamic performance and maximum thrust loss is appeard to 17% of axial thrust in roll directional control.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.109-112
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• 2004

Of late, the thrust vectoring control, using fluidic co-flow and counter-flow concepts, has been received much attention since it not only improves the maneuverability of propulsive engine but also reduces an additional material load due to the trailing control wings, which in turn reduce the aerodynamic drag. However, the control effects are not understood well since the flow field involves very complicated non: physics such as shock wave/boundary layer interaction, separation and significant unsteadiness. Existing data are not enough to achieve the effectiveness and usefulness of the thrust vectoring control, and systematic work is required for the purpose of practical applications In the present study, computational study has been performed to investigate the effects of the thrust vector control using the fluidic co-and counter-flow concepts. The results obtained show that, for a given pressure ratio, the thrust deflection angle has a maximum value at a certain suction flow rate, which is at less than $5\%$ of the mass flow rate of the primary jet. With a longer collar, the same vector angle is achievable with smaller mass flow rate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.2
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• pp.143-148
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• 2007

An impulse turbine, which is a main component of a liquid rocket engine, needs to be a small size with light weight and generate large power. Since the impulse turbine is being operated under complicated supersonic conditions, flow analysis and performance prediction largely depend on CFD technique. In order to increase the reliability of the prediction code, however, it often requires an experimental data to compare. In this research a rotating turbine rotor with multiple blades is simulated with a two-dimensional stationary cascade to check the effect of major flow parameters. Mach number is measured at nozzle exit by using a pitot tube and the blade thrust was also measured with a load cell. The measured thrust coefficient and the power are compared well with the designed conditions, which proves the design procedures are properly taken.

• Journal of Aerospace System Engineering
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• v.12 no.4
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• pp.26-34
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• 2018

Structural static test and the performance test were conducted to determine whether the propeller developed for a multi-copter with the take-off weight of 25 kg satisfies the design requirement. The result of the structural test revealed that the propeller had a safety margin of 3 or more as the ultimate load and requirement load did not cause the specimen breakage. In the performance test, the propeller generated the hover thrust and maximum thrust of design requirement, and hover efficiency in the operating thrust range was greater than 0.73. Maximum hover efficiency increased by more than 3% compared to the reference propeller and electric power consumption decreased by more than 4% in the operating range. The propeller was found to be successfully developed based on the satisfaction rate of the structural strength requirement and the performance requirement.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.1
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• pp.87-95
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• 2000

The two eigenvalues (elastic critical load and natural frequency of lateral vibration) of sinusoidally tapered bats with simply supported ends were determined by the finite element method. For the convenience of structural engineers who are engaged in the structural design or vibration analysis of tapered beam-columns, eigenvalue coefficients were expressed by simple algebraic equations. The validity of each algebraic equation was confirmed by the value of unity for each correlation coefficient. The influence of axial thrust on the lateral vibration frequency was also investigated. For this purpose, the axial thrust was increased successively and the corresponding frequency was calculated. The approximate linear relationship between the axial thrust and the square of the frequency was confirmed lot each of the tapered members.

• Structural Engineering and Mechanics
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• v.76 no.2
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• pp.175-191
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• 2020

In this study, the effect of Nano silica (SiO2) on the buckling strength of the glass fiber reinforced laminates containing the machining process causes holes were investigated. The tests have been applied on two status milled and non-milled. To promote the mechanical behavior of the fiber-reinforced glass epoxy-based composites, Nano sio2 was added to the matrix to improve and gradation. Nano sio2 is chosen because of flexibility and high mechanical features; the effect of Nanoparticles on surface serenity has been studied. Thus the effect of Nanoparticles on crack growth and machining process and delamination caused by machining has been studied. We can also imply that many machining factors are essential: feed rate, thrust force, and spindle speed. Also, feed rate and spindle speed were studied in constant values, that the thrust forces were studied as the main factor caused residual stress. Moreover, entrance forces were measured by local calibrated load cells on machining devices. The results showed that the buckling load of milled laminates had been increased by about 50% with adding 2 wt% of silica in comparison with the neat damaged laminates while adding more contents caused adverse effects. Also, with a comparison of two milling tools, the cylindrical radius-end tool had less destructive effects on specimens.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.4 s.181
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• pp.29-36
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• 2006

Micro drilling by high-speed air bearing spindle is very useful manufacturing technology in electronic industry For the design of high speed air bearing spindle, there are considered stability of air bearing spindle, allowable load of air bearing, run out and tooling system design for micro drill's attach and remove. According to suggested details, we designed and manufactured high-speed air bearing spindle and carried out performance estimation such as run out, temperature change in running air bearing spindle, stiffness, chucking torque. Results are follows; Run out was measured under $5{\mu}m$ at air bearing spindle revolution $20,000\sim125,000rpm$. High speed air bearing spindle's temperature rose about $20^{\circ}C$ after 5 minutes from running and then was fixed. Allowable thrust load of spindle was 17kgf. Chucking torque of collet was 15kgfcm.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.278-291
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• 2021

This paper applies load variation method to predict speed-power-rpm relationship along with propulsive performances in regular head waves, and to derive overload factors (ITTC, 2018). 'Calm-water tests' and 'resistance test in waves' are used. The modified overload factors are proposed taking non-linearity into consideration, and applied to the direct powering, and resistance and thrust identity method. These indirect methods are evaluated through comparing the speed-power-rpm relationships with those obtained from the resistance and self-propulsion tests in calm water and in waves. The objective ship is KVLCC2. The load variation method predicts well the speed-power-rpm relationship and propulsion performances in waves. The direct powering method with modified overload factors also predicts well. The resistance and thrust identity method with modified overload factor predicts with a little difference. The direct powering method with overload factors predicts with a relatively larger difference.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.2
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• pp.82-90
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• 2011

The small precision spindle motors in the high value-added products including the visible home appliances such as DLP projector require not only the energy conversion devices but also high efficiency, low vibration and sound operation. However, the spindle motors using the conventional ball bearing and sintered porous metal bearing have following problems, respectively: the vibration by the irregularity of balls and the short motor life cycle by the ball's abrasion and higher sound noises by dry contact between shaft and sleeve. In this paper, it is proposed that the spindle motor with a fluid dynamic bearing is suitable for the motor to drive the color wheel of the DLP(digital lightening processor) in the visible home appliances. The proposed spindle motor is composed of the fluid dynamic bearing with both the radial force and the thrust force. The fluid dynamic bearing is solved by the finite element analysis of the mechanical field with the Reynolds equations. The magnetic part of spindle motor, which is a type of Brushless DC Motor, is designed by the electro-magnetic field analysis coupled with the Maxwell equation. And the load capacity and the friction loss of fluid dynamic bearing are analyzed to bearing clearance variation by the fabrication error in designed motor. The design of the proposed motor is implemented by the load torque caused by the eccentricity and the unbalance of the fluid dynamic bearing when the motors are fabricated in error. The prototype of the motor with the fluid dynamic bearing is manufactured, and experiment results show the vibration, sound, and phase current at no load and color wheel load of the motors in comparison. The high performance characteristics with the low vibration, the low acoustic noise and the optimal mechanical structure are verified by the experimental results.

• Journal of Ocean Engineering and Technology
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• v.35 no.5
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• pp.347-359
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• 2021

This study aims to evaluate the dynamic responses of the jacket-type offshore wind turbine using FAST software (Fatigue, Aerodynamics, Structures, and Turbulence). A systematic series of simulation cases of a 5 MW jacket-type offshore wind turbine, including wind-only, wave-only, wind & wave load cases are conducted. The dynamic responses of the wind turbine structure are obtained, including the structure displacement, rotor speed, thrust force, nacelle acceleration, bending moment at the tower bottom, and shear force on the jacket leg. The calculated time-domain results are transformed to frequency domain results using FFT and the environmental load with more impact on each dynamic response is identified. It is confirmed that the dynamic displacements of the wind turbine are dominant in the wave frequency under the incident wave alone condition, and the rotor thrust, nacelle acceleration, and bending moment at the bottom of the tower exhibit high responses in the natural frequency band of the wind turbine. In the wind only condition, all responses except the vertical displacement of the wind turbine are dominant at three times the rotor rotation frequency (considering the number of blades) generated by the wind. In a combined external force with wind and waves, it was observed that the horizontal displacement is dominant by the wind load. Additionally, the bending moment on the tower base is highly affected by the wind. The shear force of the jacket leg is basically influenced by the wave loads, but it can be affected by both the wind and wave loads especially under the turbulent wind and irregular wave conditions.