• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.4
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• pp.379-384
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• 2014

The most critical rotating parts of a gas turbine engine are turbine blades and disc, given that they must operate under severe conditions such as high turbine inlet temperature, high speeds, and high compression ratios. Owing to theses operating conditions and high rotational speed energy, some failures caused by turbine disks and blades are categorized into catastrophic and critical, respectively. To maximize the margin of structural integrity, we aim to optimize the vulnerable area of disc-blade interface region. Then, to check the robustness of the obtained optimized solution, we evaluated structural reliability under uncertainties such as dimensional tolerance and fatigue life variant. The results highlighted the necessity for and limitations of optimization which is one of deterministic methods, and pointed out the requirement for introducing reliability-based design optimization which is one of stochastic methods. Thermal-structural coupled-filed analysis and contact analysis are performed for them.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.1
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• pp.64-71
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• 2006

For SUAV is required to have the capacity of VTOL and fast forward flight, the SUAV development program has decided to adopt the tiltrotor mechanism which includes helicopter and turboprop mechanisms. From the engine point of view, the key engine parameters such as engine operating mechanism, engine control scheme, the dynamics characteristic of power train, engine intake/exhaust concept, and engine installation requirements should fulfill the requirements of the two different mechanisms, helicopter and turboprop. And for the maximum efficiency of the rotor, rotational speed for the two modes are 20% different, the power train shall find a way to make it so. Meeting these specific requirements for the tiltrotor mechanism, this research begins with a conventional OTS(off-the-shelf) turboshaft engine survey and minimizes engine modification to develop an economical propulsion system. The engine technical review has been performed on the basis of those requirements and capabilities.

• Journal of Aerospace System Engineering
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• v.11 no.6
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• pp.84-91
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• 2017

The dynamic characteristics of a ducted fan in hovering condition were investigated. The section properties of the fan blade were calculated, and a simulation model was developed according to the rotor system components. Dynamic analyses were conducted relative to the rotational speed and the collective pitch. The proposed ducted fan system showed less aero-elastic instability within the designated operating ranges. To verify the analytical approach, a rotating test stand of the ducted fan was set up. A functional test of the assembly was carried out to determine the kinematics and interference between components. The non-rotating and rotating normal frequencies were measured by excitation of the collective pitch using hydraulic actuators. The results indicated a correlation between the test equipment and the simulation model.

• 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.

• Tunnel and Underground Space
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• v.30 no.5
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• pp.496-507
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• 2020

A prediction of the performance of EPB TBM is significant for improving the constructability of tunnels. Thus, various attempts to simulate TBM excavation by the numerical method have been made until these days. In this paper, to evaluate the performance of TBM with different operating conditions, a parametric study was carried out using coupled discrete element method (DEM) and finite difference method (FDM) EPB TBM driving model. The analysis was conducted by changing the penetration rate (0.5 and 1.0 mm/sec) and the rotational speed of screw conveyor (5, 15, and 25 rpm) while the rotation velocity of the cutter head kept constant at 2 rpm. The torque, thrust force, chamber pressure, and discharging with different TBM operating conditions were compared. The result of parametric study shows that the optimum driving condition can be determined by the coupled DEM-FDM numerical model.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.10
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• pp.174-180
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• 2020

This paper presents the development of a tacho generator that is applicable to a DC motor for anti-aircraft weapon systems. In general, devices such as tacho generators and resolvers are used as feedback devices for controlling DC motors. A tacho generator with a wide operating temperature range was developed, which has robust characteristics against shock loads and vibrations according to the operational characteristics of anti-aircraft weapon systems. The target specifications were set based on the requirements of the tacho generator currently in operation. A rotor coupled to the shaft of the motor and a stator coupled to the housing of the motor were then designed and manufactured. The inductance was 31.0 mH, the terminal resistance was 147.7 ohms, and the rotational measurement factor was satisfactory under both normal operation and operating conditions after the maximum speed for the standard of 9.500 ± 0.475 V/krpm. In addition, the environmental suitability of the applied equipment was confirmed through the rate of change in unit temperature, and it was found that the temperature characteristics were all within 0.03 %/℃.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.3
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• pp.221-231
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• 2021

In the present study, numerical simulation was performed to investigate aerodynamic characteristics of a ducted fan-upper/lower vanes system in hover. Sensitivity analysis of aerodynamic forces for a system component was conducted with the deflection angle of upper vanes varying but at the constant rotational speed and the collective pitch angle of fan blades. Then, vane control performance and duct airload distributions were analyzed in detail to physically understand operating mechanisms of individual vane and interference effect between duct and vanes. Finally, new control concept of operating upper vanes has been proposed to improve the control performance of the full configuration. It is found that the side force and rolling moment of upper vanes increase linearly with the variation of those deflection angle; however, the total side force is significantly small due to the reaction force acted on the duct. It is also found that upper vanes close to the duct contraction side have a key role in changing vane control forces. It is revealed that the duct suction pressure is induced by the interaction with the suction side of upper vanes, while duct pressure recovery by the interaction with the pressure side, leading to increase in duct asymmetric force. When four upper vanes are kept in situ at 0° deflection angle or removed, the total control performance was improved with duct asymmetric force reduced and the total magnitude of roll remarkably increasing up to 80%.

• Journal of Biosystems Engineering
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• v.36 no.2
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• pp.79-88
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• 2011

The purpose of this study was to analyze power requirement of an agricultural tractor by major field operations. First a survey was conducted to obtain annual usage ratio of agricultural tractor by field operation. Plowing, rotary tillage, and loader operations were selected as major field operations of agricultural tractor. Second, a power measurement system was constructed with strain-gauge sensors to measure torque of four driving axles and a PTO axle, speed sensors to measure rotational speed of the driving axles and an engine shaft, pressure sensors to measure pressure of hydraulic pumps, an I/O interface to acquire the sensor signals, and an embedded system to calculate power requirement. Third, the major field operations were experimented under fields with different soil conditions following planned operation paths. Power requirement was analyzed during the total operation period consisted of actual operation period (plowing, rotary tillage, and loader operations) and period before and after the actual operation (3-point hitch operating, forward and reverse driving, braking, and steering). Power requirement of tractor major components such as driving axle part, PTO part, main hydraulic part, and auxiliary hydraulic part were measured and calculated to determine usage ratio of agricultural tractor power. Results of averaged power requirement for actual field operation and total operation were 23.1 and 17.5 kW, 24.6 and 19.1 kW, and 14.9 and 8.9 kW, respectively, for plowing, rotary tillage, and loader operations. The results showed that rotary tillage required the greatest power among the operations. Averaged power requirement of driving axles, PTO axle, main hydraulic part, and auxiliary part during the actual field operation were 8.1, 7.8, 3.4, and 1.5 kW, respectively, and the total requirement power was about 70 % (20.8 kW) of the rated power. Averaged power requirement of driving axles, PTO axle, main hydraulic, and auxiliary hydraulic for the total operation period were 6.5, 6.0, 2.1, 0.9 kW, respectively, and total requirement power was about 52 % (15.5 kW) of the rated power. Driving axles required the greatest amount of power among the components.

• Journal of Broadcast Engineering
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• v.6 no.3
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• pp.246-259
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• 2001

Due to recent rapid deployment of Internet streaming service and digital broadcasting service, the issue of how to efficiently support streaming workload in so called "Internet Home Appliance" receives prime interests from industry as well as academia. The underlying dilemma is that it may not be feasible to put cutting edge CPU, boards, disks and other peripherals into that type of device. The primary reason is its cost. Usually, Internet Home Appliances has its dedicated usage, e.g. Internet Radio, and thus it does not require high-end CPU nor high-end Va subsystem. The same reasoning applies to I/O subsystem. In Internet Home Appliances dedicated to handle compressed moving picture, it is not equipped with high end SCSI disk with fast rotational speed. Thus, it is mandatory to devise elaborate software algorithm to exploit the available hardware resources and maximize the efficiency of the system. This paper presents our experiences in the design and implementation of a new multimedia file system which can efficiently deliver the required disk bandwidth for a periodic I/O workload. We have implemented the file system on the Linux operating system, and examined itsperformance under streaming I/O workload. The results of the study show that the proposed file system exhibits superior performance than the Linux Ext2 file system under streaming I/O workload. The result of this work not only contribute to advance the state f art file system technology for multimedia streaming but also put forth the software which is readily available and can be deployed. deployed.