• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.7
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• pp.492-499
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• 2008

The cooling load in winter is significant in many commercial buildings and hotels because of the usage of office equipments and the high efficiency of wall insulation. The development of a multi-heat pump that can cover heating and cooling simultaneously for each indoor unit is required. In this study, the performance of a multi-heat pump with 3-piping system was investigated as a function of refrigerant charge and its performance was analyzed in cooling mode, heating mode, and heat recovery mode. COP in the heating or cooling mode showed little dependence on refrigerant charge at overcharge conditions, while those were strongly dependent on refrigerant charge at undercharge conditions and outdoor inlet temperature. In the heat recovery mode, the performance of the system was very sensitive to charge amount at all conditions. Optimum charge amount in the heat recovery mode was 14% lower than that in the cooling mode at the standard condition because the refrigerant only passed the indoor units. It is required to store the excessive refrigerant charge in a storage tank to optimize the system performance at operating modes.

• Journal of Information Technology Services
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• v.15 no.4
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• pp.97-109
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• 2016

The rapid deployment of millions of mobile sensors and smart devices has resulted in high demand for opportunistic encounter-based networking. For the cooperative video surveillance of dashboard cameras in nearby vehicles, a fast and energy-efficient asynchronous neighbor discovery protocol is indispensable because a dashboard camera is an energy-hungry device after the vehicle's engine has turned off. In the existing asynchronous neighbor discovery protocols, all nodes always try to discover all neighbors. However, a dashboard camera needs to discover nearby dashboard cameras when an event is detected. In this paper, we propose a fast and energy-efficient asynchronous neighbor discovery protocol, which enables nodes : 1) to have different roles in neighbor discovery, 2) to discover neighbors within a search range, and 3) to report promptly the exact discovery result. The proposed protocol has two modes: periodic wake-up mode and active discovery mode. A node begins with the periodic wake-up mode to be discovered by other nodes, switches to the active discovery mode on receiving a neighbor discovery request, and returns to the periodic wake-up mode when the active discovery mode finishes. In the periodic wake-up mode, a node wakes up at multiples of number ${\alpha}$, where ${\alpha}$ is determined by the node's remaining battery power. In the active discovery mode, a node wakes up for consecutive ${\gamma}$ slots. Then, the node operating in the active discovery mode can discover all neighbors waking up at multiples of ${\beta}$ for ${\beta}{\leq}{\gamma}$ within ${\gamma}$ time slots. Since the proposed protocol assigns one half of the duty cycle to each mode, it consumes equal to or less energy than the existing protocols. A performance comparison shows that the proposed protocol outperforms the existing protocols in terms of discovery latency and energy consumption, where the frequency of neighbor discovery requests by car accidents is not constantly high.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.292-297
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• 2003

A diode-pumped single-mode Nd:YV $O_4$ green laser was developed. Frequency doubling of the laser was achieved by using an intracavity KTP generated green beam (532 nm). By comparing the diode laser spectrum with absorption spectrum of the Nd:YV $O_4$ crystal, we found optimal operating temperature of the diode laser. From output power measured for various mirror curvatures and cavity lengths, we found the optimal matching of TE $M_{00}$ mode with the pump beam gives the best efficiency. When the pump power was 1.9 W, 80 ㎽ of TE $M_{00}$ mode green beam was obtained. We tried to get a single longitudinal mode lasing as the fluctuation of the laser power was caused by the shift of longitudinal modes and the beating between the modes. We tested the intracavity etalon method and birefringent filter method for single mode operation. The etalon method resulted in the best single mode output power of 60 ㎽. The power fluctuation of the single-mode laser was reduced to 1/10 of that of the multi-mode laser.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.12 no.1
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• pp.17-22
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• 2016

It is very important to obtain a out-of season production in horticultural greenhouses corresponding with higher crop prices. A ground source heat pump system has been highly spotlighed as an energy efficient heating system for the greenhouse. This paper investigated the operating cost of the ground source heat pump system with the variation of generating temperature and designing methods for heating system of the greenhouse. Even though the COP of the ground source heat pump system decreased with an increment of generating temperature in heating mode, the operating cost could be reduced. By adopting the high temperature heat pump system and heat storage tank, it could be achieved to save energy and reduce the operating time of auxiliary oil heating system for producing good plant-growth in the greenhouse.

• International Journal of Precision Engineering and Manufacturing
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• v.6 no.3
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• pp.45-50
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• 2005

This paper proposed an efficient manufacturing system using the OMM (on-machine measurement) system. The OMM system is software-based 3D modeler for inspection on machine, and it is interfaced with machine tools via RS232C. The software is composed of two inspection modules; one is touch probe operating module, and the other is laser displacement sensor operating module. The module for touch probe needs the inspection feature extracted from CAD data. The touch probe moves to workpiece by three operating modes as follows: manual, general and automatic mode. The operating module of the laser displacement sensor is used to inspect profiles and very small holes. An advantage of this inspection method is the ability to execute on-line inspection during machining or afterward. The efficiency of proposed system which can predict and define the machining errors of each process was verified, so the developed system was applied to inspect a mold-base (cavity, core).

• Journal of Ocean Engineering and Technology
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• v.27 no.3
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• pp.53-60
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• 2013

A drillship is a representative floating offshore installation. The boom in oil and gas field development has dramatically increased the demands for drillships. Drillships have a moonpool in the center area of the ship for the purpose of drilling. This moonpool has an effect on the seakeeping performance of a drillship in the vicinity of the resonance frequency. Because of the moonpool, drillships act in different resonance modes, called the sloshing mode and piston mode. The objective of this study was to find the moonpool effect on the motion of a drillship through the motion analysis of a currently operating modern compact drillship. The predicted resonance frequencies based on Molin's theoretical formula, Fukuda's empirical formula, and BEM-based numerical analysis are compared. The accuracy of the predictions using the theoretical and empirical formulas is compared with the numerical analysis and evaluated. In the case of the piston mode, the difference between the resonance frequency from theoretical formula and the resonance frequency from the numerical analysis is analyzed. The resonance frequency formula for more a complex moonpool geometry such as a moonpool with a cofferdam is necessarily emphasized.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.5
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• pp.614-622
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• 2018

Based on army operating road profile, the endurance test of military vehicle aims to reproduce the similar loading conditions with mixture of proving ground tracks. It is so called as endurance test mode and its optimal generation is important to meet high reliability of endurance test. In this paper, proving ground optimization is proposed to achieve a close match to the target profile. Several performance measures such as torque-revolution counts or transmission ratio for the powertrain system can be considered as one of the objective functions. However, the one-side optimal endurance test mode may give the poor solution in the whole system point of view. To incorporate several goals simultaneously, this paper employs multi-objective optimization technique to generate endurance test mode. One of the most widely used method, weighted-sum method is applied here and the case study is discussed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.2
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• pp.116-122
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• 2016

The performance characteristics of a TBCC engine considering the transition mode from a turbojet to a ramjet engine has been investigated. The performance of each engine was proposed and a transition mode of the TBCC engine has been evaluated by adjusting the operating rate of the ramjet engine and turbojet engine performance changes continuously. Based on the transition model, it was confirmed that the performance is continuously changed at various flight Mach numbers and altitudes. The performance characteristics including thrust and specific impulse considering various flight conditions and transition mode were analyzed, which testifies characteristics of the engine itself, as well as transition of the combined cycle.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.8
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• pp.1495-1505
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• 2002

As combining the functions of a 2K-H B type differential gear unit and a V-belt type continuously variable unit(CVU), 16 different mechanisms are presented. Some useful theoretical formula related to speed ratio, power flow and efficiency are derived and analyzed. Continuously variable transmission(CVT) mechanisms are proposed, which can of ffr a backward mode, a geared neutral, an underdrive mode and an overdrive mode. They are not required of a starting device as a torque converter. CVT mechanisms developed here present two distinct operating modes which are a power circulation mode and a power split mode. The transition of two modes takes place at the particular CVU speed ratio. For these CVT mechanisms, performance analysis related to speed ratio, power ratio and theoretical efficiency are executed.

• Journal of Satellite, Information and Communications
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• v.8 no.3
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• pp.10-14
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• 2013

In this paper, when applying current-mode circuit design technique showing constant power dissipation none the less operation frequency, to the low power design of dynamic voltage frequency scaling, we introduce the low power current-mode circuit design technique applying MOSFET in sub-threshold region, in order to solve the problem that has large power dissipation especially on the condition of low operating frequency. BSIM 3, was used as a MOSFET model in circuit simulation. From the simulation result, the power dissipation of the current memory circuit with sub-threshold MOSFET showed $18.98{\mu}W$, which means the consumption reduction effect of 98%, compared with $900{\mu}W$ in that with strong inversion. It is confirmed that the proposed circuit design technique will be available in DVFS using a current-mode circuit design.