• 항공우주시스템공학회지
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• 제15권2호
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• pp.1-9
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• 2021

In this paper, a thickness compensation function is introduced to consider the shear deformation and warping effect resulting from increased thickness in the composite multi-cell wing box. The thickness compensation function is used to perform the structure optimization of the multi-cell. It is determined by minimizing the error of an analytical formula using solid mechanics and the Ritz method. It is used to define a structural performance prediction expression due to the increase in thickness. The parameter is defined by the number of spars and analyzed by the critical buckling load and the limited failure index as a response. Constraints in structural optimization are composed of displacements, torsional angles, the critical buckling load, and the failure index. The objective function is the mass, and its optimization is performed using a genetic algorithm.

• 항공우주시스템공학회지
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• 제13권2호
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• pp.51-59
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• 2019

이번 연구에서는 앞서 Part I [1]에서 수행한 단일-셀(single-cell) 모델에 이어, 시위 방향으로 비대칭성 단면을 가지는 다중-셀(multi-cell) 복합재료 박벽보(thin-walled beam) 모델을 선정하여, 단면의 형상에 대한 이론적인 동특성을 해석하였다. 이를 위해 와핑 구속 효과와 전단 변형 효과, 보의 테이퍼비와 단면비 등을 고려하였다. Part I에서와 마찬가지로 다중-셀 단면의 질량 및 강성 계수와 고유 진동수 등의 특성을 조사하였다. 특히, 다중-셀과 단일-셀 단면을 비교하고, 다중-셀 단면의 고유 진동수에 미치는 테이퍼비와 단면비의 영향을 비교 분석하였다. 또한, 단면의 비대칭성과 와핑 함수를 보정하지 않은 경우에 대해 그 결과를 비교하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권9호
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• pp.2086-2097
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• 2012

A terminal-based dynamic clustering algorithm is proposed in a multi-cell scenario, where the user could select the cooperative BSs from the predetermined static base stations (BSs) set based on dynamic channel condition. First, the user transmission rate is derived based on linear precoding and per-cell feedback scheme. Then, the dynamic clustering algorithm can be implemented based on two criteria: (a) the transmission rate should meet the user requirement for quality of service (QoS); (b) the rate increment exceeds the predetermined constant threshold. By adopting random vector quantization (RVQ), the optimized number of cooperative BSs and the corresponding channel conditions are presented respectively. Numerical results are given and show that the performance of the proposed method can improve the system resources utilization effectively.

• 제어로봇시스템학회논문지
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• 제10권12호
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• pp.1164-1171
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• 2004

A new multi-scale simulation model is proposed to analyze heart mechanics. Electrophysiology of a cardiac cell is numerically approximated using the previous model of human ventricular myocyte. The ion transports across cell membrane initiated by action potential induce an excitation-contraction mechanism in the cell via cross bridge dynamics. Negroni and Lascano model (NL model) is employed to calculate the tension of cross bridge which is closely related to the ion dynamics in cytoplasm. To convert the tension on cell level into contraction force of cardiac muscle, we introduce a simple geometric model of ventricle with a thin-walled hemispheric shape. It is assumed that cardiac tissue is composed of a set of cardiac myocytes and its orientation on the hemispheric surface of ventricle remains constant everywhere in the domain. Application of Laplace law to the ventricle model enables us to determine the ventricular pressure that induces blood circulation in a body. A lumped parameter model with 7 compartments is utilized to describe the systemic circulation interacting with the cardiac cell mechanism via NL model and Laplace law. Numerical simulation shows that the ion transports in cell level eventually generate blood hemodynamics on system level via cross bridge dynamics and Laplace law. Computational results using the present multi-scale model are well compared with the existing ones. Especially it is shown that the typical characteristics of heart mechanics, such as pressure volume relation, stroke volume and ejection fraction, can be generated by the present multi-scale cardiovascular model, covering from cardiac cells to circulation system.

• 조명전기설비학회논문지
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• 제25권8호
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• pp.70-81
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• 2011

In this paper, a multi-agent control system for DC-coupled photovoltaic (PV), fuel cell (FC), ultracapacitor(UC) and battery hybrid power system is studied for commercial buildings & apartment buildings microgrid. In this proposed system, the PV system provides electric energy to the electrolyzer to produce hydrogen for future use and transfer to the load side, if possible. Whenever the PV system cannot completely meet load demands, the FC system provides power to meet the remaining load. A multi-agent system based-power management and control algorithm is proposed for the hybrid power system by taking into account the characteristics of each power source. The main works of this paper are hybridization of alternate energy sources with FC systems using long and short storage strategies to build the multi-agent control system with pragmatic design, and a dynamic model proposed for a PV/FC/UC/battery bank hybrid power generation system. A dynamic simulation model for the hybrid power system has been developed using Matlab/Simulink, SimPowerSystems and Stateflow. Simulation results are also presented to demonstrate the effectiveness of the proposed multi-agent control and management system for building microgrid.

• 한국통신학회논문지
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• 제34권11A호
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• pp.844-851
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• 2009

핸드오버는 multi-hop relay 시스템에서 이동성을 제공하기 위해 필요하다. 핸드오버의 주요 목적은 MS가 한 BS의 air-interface에서 다른 BS의 air-interface로 이동할 때 연속 연결을 제공하는 것이다. 특히 이종기계간의 핸드오버는 차세대 네트워크에 필수적이다. Mobile WiMAX MMR system에서의 수직 핸드오버 기술은 기술자들이 Mobile WiMAX system을 overlaid cell환경으로 가져오는데 매우 유용하다. 이 기술은 Micro cell(Frequency 1,FA1) and Macro cell(Frequency 2,FA2)사이에 놓인 Ubiquitous 환경에서 시스템 성능향상을 위해 MRS를 다른 시스템으로 핸드오버 하는 기술에 적용될 것이다. 이 논문에서 FA1과 FA2 주파수를 사용하여 제안된 조건들에 따라 MRS들이 수직 핸드오버를 수행했다. 그리고 중심에 있는 Macro cell과 그것을 싸고 있는 6개의 Macro cell들의 BS나 섹터로부터 받은 간섭 및 성능을 분석한다.

• Transactions on Electrical and Electronic Materials
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• 제4권5호
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• pp.10-14
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• 2003

A low-cost, large area, random, maskless texturing scheme independent of crystal orientation is expected to have significant impact on terrestrial photovoltaic technology. We investigated silicon surface microstructures formed by reactive ion etching (R IE) in Multi-Hollow cathode system. Desirable texturing effect has been achieved when radio-frequency (rf) power of about 20 Watt per one hollow cathode glow is applied for our RF Multi -Hollow cathode system. The black silicon etched surface shows almost zero reflectance in the visible region as well as in near IR region. The etched silicon surface is covered by columnar microstructures with diameters from 50 to 100 nm and depth of about 500 nm. We have successfully achieved 11.7 % efficiency of mono-crystalline silicon solar cell and 10.2 % for multi-crystalline silicon solar cell.

• Journal of Electrical Engineering and Technology
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• 제11권2호
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• pp.367-376
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• 2016

This paper presents a cell balancing method for a single switch flyback converter with a multi-winding transformer. The conventional method using a flyback converter with a multi-winding transformer is simple and easy to control, but the voltage of each secondary winding coil might be non-uniform because of the unequal effective turn-ratio. In particular, it is difficult to control the non-uniform effect using turn-ratios because secondary coil has a limited number of turns. The non-uniform secondary voltages disturb the cell balancing procedure and induce an unbalance in cell voltages. Individual cell control by adding a switch for each cell can reduce the undesirable effect. However, the circuit becomes bulky, resulting in additional loss. The proposed method here uses the conventional flyback converter with an adjustment made to the output filters of the cells, instead of the additional switch. The magnitude of voltage applied to a particular cell can be reduced or increased according to the adjusted filter and the selected switching frequency. An analysis of the conventional converter configuration and the filter design method reveals the possibility of adequate cell balancing control without any additional switch on the secondary side.

• 전기학회논문지
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• 제58권4호
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• pp.700-707
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• 2009

The application of renewable energy in electric power systems is growing rapidly in order to make provision for the inequality of the climate, the dwindling supplies of coal, oil and natural gas and a further rise in oil prices. Solar cell generators(SCG) is one of the fastest growing renewable energy. This paper presents a methodology on probabilistic production cost simulation of a power system including SCGs. The generated power by SCGs is variable due to the random variation of solar radiation. In order to solve this problem, the SCGs is modeled as multi-state operational model in this paper. Probabilistic production cost of a power system can be calculated by proposed method considering SCGs with multi-state. The results show that the impacts of SCGs added to a power system can be analyzed in view point of production cost using the proposed method.

• Journal of Information Processing Systems
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• 제6권3호
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• pp.403-412
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• 2010

Multi-Relay Networks should accommodate mobile users of various speeds. The cellular system should meet the minimum residency time requirements for handover calls while considering an efficient use of available channels. In this paper, we design speed-sensitive handover under dynamic hierarchical cellular systems, in which mobile users are classified according to the mean speed of mobile users and each class has its cellular layer. In order to meet the minimum residency time, the cell size of each cellular layer is dynamically determined depending on the distributions of mean speeds of mobile users. Since the speed-dependent non-preferred cell can provide a secondary resource, overflow and take-back schemes are adopted in the system. We develop analytical models to study the performance of the proposed system, and show that the optimal cell size improves the blocking probability.