• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.1
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• pp.40-48
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• 2019

Hybrid electric propulsion systems (H-EPSs) are an intermediate step for integrated full electric propulsion warships. H-EPSs are a dynamic combination of mechanical and electrical propulsion systems to achieve the required mission performances. The system modes could adapt to meet the requirement of the various operation conditions of a warship. This paper presents a configuration and operating modes of H-EPSs considering the operation conditions of a destroyer class warship. The system has three propulsion modes, namely, motoring mode, generating mode [power take off (PTO) mode], and mechanical mode. The PTO mode requires a careful fuel efficiency analysis because the fuel consumption rate of propulsion engines may be low compared with the generator's engines depending on the loading power. Therefore, the calculation of fuel consumption according to the operating modes is performed in this study. Although the economics of the PTO mode depends on system cases, it has an advantage in that it ensures the reliability of electric power in case of blackout or minimum generator operation.

• Progress in Superconductivity and Cryogenics
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• v.24 no.2
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• pp.27-38
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• 2022

Urban air mobility (UAM) has recently attracted lots of attention as a solution to urban centralization and global warming. Electric vertical take-off and landing (eVTOL) is a concept that emerges as one of the promising and clean technologies for UAM. There are two difficult challenges for eVTOL aircraft to solve. One is how to improve the weight efficiency of aircraft, and the other is how to complete long-range missions for UAM's flight scenarios. To approach these challenges, we propose a consolidated concept design of battery-fuel cell hybrid tiltrotor aircraft with a liquid hydrogen (LH₂) fuel tank. The efficiency of a battery-fuel cell hybrid powertrain system on the designed eVTOL aircraft is compared to that of a battery-only powertrain system. This paper shows how much payload can increase and the flight scenario can be improved by hybridizing the battery and fuel cell and presenting a detailed concept of a cryogenic storage tank for LH₂.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.30 no.4
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• pp.184-190
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• 2022

In an attempt to apply hybrid rocket to the RATO (Rocket-Assisted Take Off) system, combustion characteristics of the non-circular grain were figured out in this study. Having larger combustion area, it was reconfirmed that the non-circular grain has advantages over regression rate, characteristic velocity and chamber pressure in which all gave higher values. Experiments were performed to understand the effect of the non-circular grain geometry over time where local regression rates depending on grain location were analyzed. It was found that the regression rate of five distinct locations were different. Partial conclusion driven was that these differences are due to the heat transfer caused by dissimilar distances from the flame layer. Besides, as combustion duration increased, the fuel port became circular, and the regression rate converged to a single value over the whole grain.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2000.11a
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• pp.335-339
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• 2000

In the weaving process, tension control of the warp is important. The variation of the warp tension cause irregularities of the weft density and low quality of the woven fabrics. Due to the fact that the warp tension varies in depending on the difference between take-up velocity and let-off velocity, it is necessary to regulate the velocity of let-off in relation to that of take-up for keeping the warp tension. Futhermore, the diameter of warp beam changes in the weaving process. The changing diameter of warp beam cause changing inertia of warp beam and the velocity of the let-off. It makes the control of such a system more complex. In this paper, we propose a fuzzy controller for the warp tension control. From the computer simulation, it was observed that a developed fuzzy controller has a better performance than that of conventional PI controller.

• Journal of Ocean Engineering and Technology
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• v.15 no.1
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• pp.26-30
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• 2001

Up to now, Most studies of hydroelasticity are about frequency domain analysis. Those aren't suited for analysis of the landing take-off, and dropping of aircraft on a structure. So, the concern of this paper is the transient behavior of a VLFS subjected to dynamic load, induced by airplane landing and take-off. To predict the added mass, damping coefficient, and wave exciting force, the source-dipole distribution method was used in the frequency domain. The responses are accomplished by using the FEM scheme. A time domain analysis method is based on the Newmark β method to pursue the time step procedure, taking advantage of memory effect function for hydrodynamic effects.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• 2008.11a
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• pp.744-747
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• 2008

Quantity information focused on a design drawing plays a critical role in a decision making related to cost for project participants during project life cycles. Related participants absolutely depend on quantity take-off working which produces the quantity information by hand, and then a worker's mistake often causes many errors. The difference of quantity by the know-how of the person in charge of the estimation also occurs. In addition, the worker passes through the whole quantity take-off processes again in case of re-working for quantity take-off produced by a change order. The requirements about the automated estimation increase because of the needs for the accurate quantity take-off and dealing with the change order and recently, the studies about the automated estimation working process based on 34 cad model from 3d cad modeler are attempted in various viewpoints. However, the existing studies reach the limits such as common quantity data type framework for getting Quantity information. Focused on a certain 34 cad modeler and BIM based automation of estimation using it Therefore, the objective of this study is to develop the a series of system which can extract, analyze, and verify Quantity Data Type in modeler to automate quantity take-off originated from various 3d cad modelers as a foundation study for BIM based automation of estimation framework.

• Korean Journal of Applied Biomechanics
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• v.21 no.5
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• pp.595-602
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• 2011

The long jump motion of 8 finalist of men's long jump of IAAF World Championships Daegu 2011 were analysed and the kinematic characteristics of the technique were investigated. The kinematic characteristics of long jump motion of 8 finalist were as follows. In the run-up phase, the average length of 3, 2, and 1 stride were $2.21{\pm}0.08$ m, $2.46{\pm}0.18$ m, and $2.19{\pm}0.16$ m, respectively. The change in the height of the center of gravity was $0.09{\pm}0.02$ m. The average velocity of 3, 2, and 1 stride was $10.37{\pm}0.32$ m/s, $9.63{\pm}0.32$ m/s, and $10.69{\pm}10.69$ m/s, respectively. In the take-off phase, the horizontal velocity, the vertical velocity, the reduction of horizontal velocity was $9.00{\pm}0.37$ m/s, $3.04{\pm}0.27$ m/s, and $1.69{\pm}0.34$ m/s, respectively. The minimum knee angle and the take off angle was $157{\pm}6.57^{\circ}$ and $18.5{\pm}2.24^{\circ}$, respectively. In the flight phase, the flight time and the maximum height of the center of gravity was $0.82{\pm}0.05$ s, and $1.70{\pm}0.10$ m, respectively. In the landing phase, the landing length was $0.51{\pm}0.06$ m. The body angle, the knee angle, and the hip angle was $71{\pm}20.93^{\circ}$, $136{\pm}19.19^{\circ}$, and $85{\pm}9.58^{\circ}$, respectively. The kinematic characteristics of long jump motion with good record were shown as follows. The reduction of the horizontal velocity in the take-off phase was minimized while the velocity of the run-up were maximally maintained. The vertical velocity in the take-off phase was increased with rapidly extended knee and the high center of gravity.

• Journal of the Korea Institute of Building Construction
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• v.8 no.2
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• pp.63-70
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• 2008

Reinforcing steel work plays an important role in terms of its structural performance or weight of construction cost for reinforced concrete structures. Precise estimation of re-bar quantity gives a basis for managing the reinforcing steel work effectively. However, the estimation process is still performed ineffectively based upon the expert's experience or manpower in spite of the advanced technology or improvement efforts. Therefore, the purpose of this research is to develop a prototype system for taking-off the quantity of reinforcing steel bars quickly and accurately in an order consistent with the specific members identified on the drawings. An estimate algorithm considering the connection, settlement and coating thickness of re-bars was suggested regarding to their replacement conditions which places more emphasis on constructibility. Also, this system produces the shop drawings automatically with the calculation results with work zone information.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.4
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• pp.477-482
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• 2012

This paper describes a new rotor position sensorless control method for SRM drives based on an improved simplified flux linkage method. In the traditional simplified flux linkage method, every phases take turns conduction and current chopping control method is used. Every phases take turns conduction means turning on the incoming working phase while turning off the working phase. This conduction mode causes coupling between turn-on and turn-off angles, which goes against optimal efficiency or torque ripple minimization with sensorless speed control. In the improved simplified flux linkage method, turn-off angle is calculated by flux loop, the turn-on angle can be given arbitrarily and has no relations with the turn-off angle, and the current chopping control method is used. The speed and rotor position can be estimated then. Finally, a sensorless SRM speed control system and an experiment platform with DSP are built and validity of this method is confirmed.

• Aerospace Engineering and Technology
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• v.12 no.1
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• pp.10-21
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• 2013

As helicopter technology has been upgraded, today its oceanic operation is considered to be usual. In oceanic operation of helicopter, the effect of severe wind, wave, and corrosion must be investigated and the operation procedures for safety as well as the motion of shipboard arising from maneuvers of ship must also be considered. In this paper, it describes the result of trade-off study for shipboard landing and its operation procedure including dynamic interface between ship and aircraft in ship operation and gives a simulation results to implement the oceanic operation of tilt rotor aircraft.