• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.11 no.10
• /
• pp.5116-5131
• /
• 2017

This paper studies the radio frequency to direct current (RF-DC) conversion efficiency of rectennas applicable to wireless power transfer systems, where multiple receive antennas are arranged in serial, parallel or cascaded form. To begin with, a 2.45 GHz dual-diode rectifier is designed and its equivalent linear model is applied to analyze its output voltage and current. Then, using Advanced Design System (ADS), it is shown that the rectifying efficiency is as large as 66.2% in case the input power is 15.4 dBm. On the other hand, to boost the DC output, three composite rectennas are designed by inter-connecting two dual-diode rectifiers in serial, parallel and cascade forms; and their output voltage and current are investigated using their respective equivalent linear models. Simulation and experimental results demonstrate that all composite rectennas have almost the same RF-DC conversion efficiency as the dual-diode rectifier, yet the output of voltage or current can be significantly increased; in particular, the cascade rectenna obtains the highest rectifying efficiency.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.10
• /
• pp.1915-1927
• /
• 1992

A three-dimensional Navier-Stokes code has been developed for analysis of viscous flows through turbomachinery blade rows or other internal passages. The Navier-Stokes equations are written in a cartesian coordinate system, then mapped to a general body-fitted coordinate system. Streamwise viscous terms are neglected and turbulent effects are modeled using the baldwin-Lomax model. Equations are discretized using finite difference method on the stacked C-type grids and solved using LU-ADI decomposition scheme. calculations are made for a two-dimensional cascade in a transonic wind-tunnel to see the infuence of the endwalls. The flow pattern of the three-dimensional flow near the endwall is found to be different from that of the two-dimensional flow due to the existence of the endwalls.

• Proceedings of the KIEE Conference
• /
• 2009.07a
• /
• pp.1098_1099
• /
• 2009

In this paper, we present the estimation of wind turbine power generation using Cascade Architectures of Fuzzy Neural Networks(CAFNN). The proposed model uses the wind speed average, the standard deviation and the past output power as input data. The CAFNN identification process uses a 10-min average wind speed with its standard deviation. The method for rule-based fuzzy modeling uses Gaussian membership function. It has three fuzzy variables with three modifiable parameters. The CAFNN's configuration has three Logic Processors(LP) that are constructed cascade architecture and an effective optimization method uses two-level genetic algorithm. First, The CAFNN is trained with one-day average input variables. Once the CAFNN has been trained, test data are used without any update. The main advantage of using CAFNN is having simple structure of system with many input variables. Therefore, The proposed CAFNN technique is useful to predict the wind turbine(WT) power effectively and hence that information will be helpful to decide the control strategy for the WT system operation and application.

• 한국신재생에너지학회:학술대회논문집
• /
• 2009.06a
• /
• pp.422-425
• /
• 2009

A sea water source cascade heat pump was designed and tested in this study. The system was designed to perform a single stage operation in summer, as well as a cascade operation in winter to ensure the high temperature lift. A steady-state simulation model was developed to analyze and optimize its performance. The simulation results show that the R717 exhibits best performance among combinations considered in this study. A R410A also exhibits the highest performance among HFCs with the smallest compressor displacement. A 15-RT R410A-R134a pilot system was installed in the 5-story commercial building at Samcheok City by the East Sea. A scroll type R410A compressor, a reciprocating type R134a compressor, plate type condenser/evaporator/ cascade heat exchanger and two electronic expansion valves were used to build a pilot. A titanium plate type heat exchanger is also used for the heat exchanging with a sea water. The heat source/sink water is supplied from the well below the seashore in the depth of 5 m. In the initial test of the system, supply water temperature was rising up to $67^{\circ}C$ using a sea water heat source of $9^{\circ}C$, while an ambient temperature was $4.5^{\circ}C$.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.6 no.3
• /
• pp.29-36
• /
• 2002

A numerical analysis based on two-dimensional and three-dimensional incompressible Wavier-Stokes equations has been carried out for double-circular-arc compressor cascades and the results are compared with available experimental data at various incidence angles. The 2-D and 3-D computational codes based on SIMPLE algorithm adopt pressure weighted interpolation method for non-staggered grid and hybrid scheme for the convective terms. Turbulence modeling is very important for prediction of cascade flows, which are extremely complex with separation and reattachment by adverse pressure gradient. Considering computation times, $\kappa$-$\varepsilon$ turbulence model with wall function is used.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.48 no.12
• /
• pp.691-700
• /
• 1999

This paper proposes a novel switching strategy of 1Mvar STATCON using cascade multilevel H-bridge inverter(HBI) for FACTS application. To control the reactive power instantaneously, the d-q dynamic system model is described and analyzed. A single pulse pattern based on the SHEM(Selective Harmonic Elimination Method) technique is determined from the look-up table to reduce the line current harmonics and a rotating fundamental frequency switching scheme is presented to adjust the DC voltage of each inverter capacitor at the same value. So the voltage unbalance problem between separately DC bus voltage is improved by using the proposed switching scheme. As a result, the presented inverter configuration not only reduces the system complexity by eliminating the isolation at the AC input side transformer but also improves the dynamic response to the step change of reactive power.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2012.05a
• /
• pp.341-341
• /
• 2012

최근 기후변화로 인한 이상호우의 발생으로 도시유역에서의 홍수피해가 급증하고 있으며 이로 인해 도시유역에서의 설계홍수량 산정이 매우 중요시 되고 있다. 지금까지는 도시유역에서의 설계홍수량을 산정하기 위해 I-D-F 곡선을 이용하고 있으나 현실적으로 시간단위 이하의 관측강우량 자료의 부족으로 인해 신뢰성 있는 시간단위 이하의 설계강우량 산정에 많은 불확실성을 지니고 있다. 도시유역의 경우에는 자연유역에 비해 강우발생시 일반적으로 도달시간이 한 시간 이하이기 때문에 극한 강우사상 즉, 단시간에 집중적으로 많은 양의 강우가 발생 할 경우 시간단위 이하의 강우강도를 이용한 유출해석이 필요하다. 따라서 본 연구에서는 추계학적 강우발생기법을 통해 시간단위 강우시계열자료를 확충한 후 분해기법을 통해 시간단위이하강우를 생성하였다. 이를 위해 Bartlett-Lewis rectangular pulse 모형과 Cascade 분해 기법을 이용하여 5분단위 강우량자료를 모의발생 하였다. 또한 모의치와 관측치를 재현기간별로 비교, 분석하여 그 차이를 확인하였다.

• Water for future
• /
• v.20 no.3
• /
• pp.229-235
• /
• 1987

The purpose of this study is to estimate the parameters of linear reservoir models in order to derive the Instantaneous unit hydrograph from a given small experimental watershed. The linear reservoir model is a conceptual model, consisting of cascade or parallel equal linear reservoirs, preceded by a linear channel which involved Nash, SLR(single linear reservoir) and 2-PLR(two-parallel linear Reservoir) model. the Nash model have two parameters N and K, single linear reseroir has one parameter $K_I$ and two-parallel linear reservoirs have two parameters $K_1,\;K_2$; where N denote the number of reservoirs and K is the storage coefficient of each reservoirs.

• Proceedings of the Korea Water Resources Association Conference
• /
• 1987.07a
• /
• pp.151-158
• /
• 1987

The purpose of thes study is to estimate the parameters of linear reservoir models in order to derive the instantaneous unit hydrograph from a given small experimental watershed. The linear reservoir model is a conceptual model, consisting of cascade or parallel equal linear reservoirs, preceded by a linear channel which involved NASH, SLR(single linear reservoir)and 2-PLR(two-parallel linear reservoir)model. The NASH model have two parameters N and K, single linear reservoir has one parameter K1 and two-parallel linear reservoirs have two parameters K1, K2;where N denote the number of reservoirs and K is the storage coefficient of each reservoirs.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.57 no.6
• /
• pp.1048-1057
• /
• 2008

This paper represents a design method for PID or low-order controllers cascaded with a linear plant in the unit feedback system where it is required to meet the given time response specifications such as overshoot and settling time. This problem is difficult to solve because the zeros of the controller appear in the numerator of the overall system and thus those zeros may make the time response design difficult. In this paper, we propose a new approach based on the partial model matching and the so called K-polynomial. The partial matching problem is formulated to an optimization problem in which a quadratic function of coefficient errors between a target model and the resulting closed loop system is minimized. For the sake of satisfying the closed loop stability, a set of quadratic constraints associated with the cost function is introduced. As a result, the controller designed meets both time response requirements and the closed loop stability, if any. It is shown through several examples that the present method can be easily applied to these problems.