• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.5
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• pp.1-9
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• 2004

The performance analysis code has been developed for vertical take-off and landing(VTOL) UAV which can be utilized as a trade analysis tool in the pre-conceptual design phase. The UAV requires VTOL capability and high speed cruise performance. The main logic of this performance analysis code is to estimate performance parameters of each mission segment by mission fuel weight iteration. The reliability of this performance analysis code is discussed by comparing the data of existing dual flight mode VTOL UAVs such as Boeing CRW and Bell Tilt Rotor.

• Nuclear Engineering and Technology
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• v.48 no.2
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• pp.505-517
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• 2016

The structural integrity of a dual-purpose metal cask currently under development by the Korea Radioactive Waste Agency (KORAD) was evaluated, through numerical simulations and a model test, under high-speed missile impact reflecting targeted aircraft crash conditions. The impact conditions were carefully chosen through a survey on accident cases and recommendations from literature. In the impact scenario, a missile flying horizontally hits the top side of the cask, which is freestanding on a concrete pad, with a velocity of 150 m/s. A simplified missile simulating a commercial aircraft engine was designed from an impact loade-time function available in literature. In the analyses, the dynamic behavior of the metal cask and the integrity of the containment boundary were assessed. The simulation results were compared with the test results for a 1:3 scale model. Although the dynamic behavior of the cask in the model test did not match exactly with the prediction from the numerical simulation, other structural responses, such as the acceleration and strain history during the impact, showed very good agreement. Moreover, the containment function of the cask survived the missile impact as expected from the numerical simulation. Thus, the procedure and methodology adopted in the structural numerical analyses were successfully validated.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.98-106
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• 2000

A conceptual design of propulsion system for a geosynchronous communication satellite with 12 years design life is presented in this paper. Propellant mass budget for the design life is calculated using total velocity increment ($\Delta$V) flowed-down from mission requirement analysis. Sizes of the fuel and oxidizer tank are derived based on the calculated propellant mass budget, and mass of the pressurant as well as the size and Pressure of pressurant tank are calculated too. Thruster positioning, number of rocket engines, and position of tank are determined through trade-off study with Structure & Mechanical Subsystem. Propulsion system configuration and its schematics are presented finally.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.407-412
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• 2008

"KAGUYA"(SELENE) is a Japanese Lunar Explorer launched by H-IIA rocket from Tanegashima Space Center on 14 September 2007. The dual-mode bipropellant propulsion subsystem of KAGUYA includes two fuel tanks, an oxidizer tank, propellant and pressurant control components, twelve monopropellant 20N thrusters, eight monopropellant 1N thrusters, and a bipropellant 500N Orbit Maneuver Engine(OME). Once the KAGUYA separated from the rocket, it circled the Earth twice and traveled to the Moon, where it entered lunar orbit. All maneuvers were performed through multiple 500N OME/20N thruster firings. This paper describes the in-space performance of KAGUYA Lunar Explorer bipropellant propulsion subsystem.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.1
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• pp.9-15
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• 2019

Sensorless electric superchargers have recently been actively developed to provide a large amount of oxygen to engines in order assist the combustion process for miniaturizing the engines and improving fuel efficiency. The model-based sensorless method for surface-mounted permanent magnet synchronous motors has a disadvantage in that the system may become unstable due to parameter variations in low-speed operation and the rapid-acceleration section. An electric supercharger requires fast response to improve the engine response delay, such as the turbocharger turbo-rack. Therefore, the responsiveness must be improved to use the model-based sensorless system. The position compensation algorithm designed in this study is controlled by converting the position error into the beta, which is the angle formed by the d-axis and the stator current during sudden speed change. In this study, we improved the response of the model-based sensorless system through the algorithm and verified the algorithm validity by applying the algorithm to an actual dual-motor supercharger.

• Advances in aircraft and spacecraft science
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• v.10 no.1
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• pp.1-18
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• 2023

This paper investigates the integrated control of an air-breathing hypersonic vehicle considering the safety of propulsion system under acceleration. First, the vehicle/engine coupling model that contains a control-oriented vehicle model and a quasi-one-dimensional dual-mode scramjet model is established. Next, the coupling process of the integrated control system is introduced in detail. Based on the coupling model, the integrated control framework is studied and an integrated control system including acceleration command generator, vehicle attitude control loop and engine multivariable control loop is discussed. Then, the effectiveness and superiority of the integrated control system are verified through the comparison of normal case and limiting case of an air-breathing hypersonic scramjet coupling model. Finally, the main results show that under normal acceleration case and limiting acceleration case, the integrated control system can track the altitude and speed of the vehicle extremely well and adjust the angle deflection of elevator to offset the thrust moment to maintain the attitude stability of the vehicle, while assigning the two-stage fuel equivalent ratio to meet the thrust performance and safety margin of the engine. Meanwhile, the high-acceleration requirement of the air-breathing hypersonic vehicle makes the propulsion system operating closer to the extreme dangerous conditions. The above contents demonstrate that considering the propulsion system safety will make integrated control system more real and meaningful.

• Transactions of Materials Processing
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• v.32 no.3
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• pp.107-113
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• 2023

The importance of dual-fuel engines has increased for reducing CO₂ emissions. However, the low operating temperature of this engine may induce low-temperature corrosion at combustion parts, which reduces the engine service life. To overcome this problem, NiCr38Al4 alloy was developed for valve spindle, but the cost of this alloy is expensive due to its high Cr content. For reducing the manufacturing cost of valve spindle, in the present work, NiCr38Al4 alloy was welded with Nimonic80A alloy by conducting friction welding. The tensile test results show that the strength of friction-welded specimens follows the properties of the lower-strength parent materials, without severe cracks at the interface. The large shear strain and frictional heat from friction welding not only reduce grain size but also induce solute element diffusion at the interfacial region. Because of the low Cr diffusivity compared with Ti, Cr carbides were not observed in the Nimonic80A matrix, while Ti carbides were distributed in both the Nimonic80A and SNCrW matrices.

• Nuclear Engineering and Technology
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• v.56 no.9
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• pp.3812-3825
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• 2024

The axial-flow-induced vibration of fuel rods in the nuclear power plant is closely related to nuclear safety. In this article, a numerical study is performed on vibration of two elastic cylinders arranged side-by-side in axial flow. Large eddy simulation is employed to predict the turbulent flow. The numerical method has been verified using the experimental root-mean-square vibration amplitude of a single cylinder. A wide range of inflow velocities u^*, incident turbulence intensity T_u and space ratio P/D have been examined, where D and P are the diameter and centre-to-centre distance of the cylinders, respectively. The results show that the vibration amplitudes increase with an increasing u^*, comparable to the case of a single cylinder in axial flow. However, the two cylinders could bend outwards during a relatively high u^* and low T_u. Although T_u significantly affects the amplitudes of the cylinders, it does not change the vibration frequency and the critical velocity at which buckling instability occurs. As the gap between the two cylinders is sufficiently small, the vibration amplitude enhances significantly due to the pronounced hydrodynamic interaction between the two elastic cylinders and surrounding fluid. The direction of buckling is no longer random but fixed.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.7
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• pp.799-805
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• 2014

Recently, the regulations of the Local and Global for a variety of air pollution prevention has been enhanced by the steep rise in fuel oil prices. So, the appearance of Gas Fuelled Ships became necessary. In this study, we configured a regasification system which uses Eglycol water as a heating medium to evaporate before being supply fuel to the DF engine, then we analysed the system properties according to the Eglycol water mixing ratio. The results were as follows. When pressure, temperature, and flux of natural gas(NG) which are supplied to DF engines are uniformly kept, the higher mixing ratio of Eglycol is, the lower mixing specific heat of Eglycol water. And the cycle flux and electric power were 1.65 and 1.54 times more required. respectively, than water was used as the heating medium. Basic variables including mass flux according to the mixing ratio of Eglycol water, required electric power of operating fluid pumps, the temperature of natural gas which is supplied to the engine, and the heat exchanger's capacity were drawn from the gotten results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.52-60
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• 2018

In the automobile industry, in order to increase the fuel efficiency and conform to the safety regulations, it is necessary to make the vehicles as light as possible. Therefore, it is crucial to manufacture dual phase steels, complex phases steels, MS steels, TRIP steels, and TWIP from high strength steels with a tensile strength of 700Mpa or more. In order to apply ultra-high tensile strength steel to the body, the welding process is essential. Resistance spot welding, which is advantageous in terms of its cost, is used in more than 80% of cases in body welding. It is generally accepted that ultra-high tensile strength steel has poor weldability, because its alloy element content is increased to improve its strength. In the case of the resistance spot welding of ultra-high tensile steel, it has been reported that the proper welding condition area is reduced and interfacial fracture and partial interfacial fracture occur in the weld zone. Therefore, research into the welding quality judgment that can predict the defect and quality in real time is being actively conducted. In this study, the dynamic resistance of the weld was monitored using the secondary circuit process variables detected during resistance spot welding, and the factors necessary for the determination of the welding quality were extracted from the dynamic resistance pattern. The correlations between the extracted factors and the weld quality were analyzed and a regression analysis was carried out using highly correlated pendulums. Based on this research, a regression model that can be applied to the field was proposed.