• Journal of Electrical Engineering and Technology
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• v.11 no.4
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• pp.869-877
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• 2016

Necessity has compelled man to improve upon the art of tapping wind energy for power generation; an apt reliever of strain exerted on the non-renewable fossil fuel. The power generation in a Wind Farm (WF) depends on site and wind velocity which varies with time and season which in turn determine wind power modeling. It implies, the development of an accurate wind speed model to predict wind power fluctuations at a particular site is significant. In this paper, Box-Jenkins ARIMA (Auto Regressive Integrated Moving Average) time series model for wind speed is developed for a 99MW wind farm in the southern region of India. Because of the uncertainty in wind power developed, the economic viability and reliability of power generation is significant. Life Cycle Costing (LCC) method is used to determine the economic viability of WF generated power. Reliability models of WF are developed with the help of load curve of the utility grid and Capacity Outage Probability Table (COPT). ARIMA wind speed model is used for developing COPT. The values of annual reliability indices and variations of risk index of the WF with system peak load are calculated. Such reliability models of large WF can be used in generation system planning.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.1
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• pp.84-98
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• 2021

The hydrodynamic characteristics of amphibious assault vehicles are investigated using commercial CFD code, STAR-CCM+. Resistance performances of a displacement-type vehicle and a semi-planing type vehicle are analyzed in calm water. The self-propelled model is also computed for the semi-planing type vehicle. All computations are performed using an overset mesh system and a RANS based flow-solver coupled with a two-degree of freedom equations of motion. A moving reference frame is applied to simulate revolutions of impeller blades for a waterjet propulsion system. Grid dependency tests are performed to evaluate discretization errors for the mesh systems. The numerical analysis results are compared with the experimental results obtained from model tests. It is shown that RANS is capable of investigating the resistance and self-propulsion characteristics of high-speed amphibious assault vehicles. It is also found that a fully covered side skirt, which is covering tracks, reduces resistance and stern trim, besides increasing propulsive efficiency.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.15 no.2
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• pp.53-64
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• 2005

Previous secure routing protocols for wireless sensor networks assume that a sink is static. In many cases, however, a sink operated by man or vehicle is moving. A mobile sink creates a lot of technical problems such as reconfiguration of routing path exposure of sink location. and selection of secure access point node, which are not considered by many previous researches. In this paper, we propose a new secure routing scheme for solving such problems using hi-directional hash chain and delegation nodes of grid structure. This scheme provides a secure routing path and prevents attacker from recognizing the location of a mobile sink in sensor networks. This new method reduces the resource requirements compared to the cashed routing schemes. Simulation results also show that the system is secure and efficient enough.

• Journal of computational fluids engineering
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• v.16 no.2
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• pp.1-10
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• 2011

A new computational program, which is based on the CIP/CCUP(Constraint Interpolation Profile/CIP Combined Unified Procedure) method, has been developed to numerically analyse sloshing phenomena dealt as multiphase-flow problems. For the convection terms of Navier-Stokes equations, the RCIP(Rational function CIP) method was adopted and the THINC-WLIC(Tangent of Hyperbola for Interface Capturing-Weighted Line Interface Calculation) method was used to capture the air/water interface. To validate the present numerical method, two-dimensional dam-breaking and sloshing problems in a rectangular tank were solved by the developed method in a stationary Cartesian grid system. In the case of sloshing problems, simulations by using a improved MPS(Moving Particle Simulation) method, which is named as PNU-MPS(Pusan National University-MPS), were also carried out. The computational results are compared with those of experiments and most of the comparisons are reasonably good.

• Journal of computational fluids engineering
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• v.19 no.4
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• pp.61-67
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• 2014

Since the most of the existing non-Newtonian models are not adequate to apply to the lattmce Boltzmann method, it is a challenging task from both the theoretical and the numerical points of view. In this research the hydro-kinetic model was modified and applied to the 3-D moving sphere in the circular channel flow and the characteristics of the shear thinning effect by the HK-model was evaluated and the condition of ${\Gamma}$ in the model was suggested for the stable simulation to generate non-trivial prediction in three dimension strong shear flows. On the wall boundaries of circular channel the curved wall surface treatment with constant velocity condition was applied and the bounceback condition was applied on the sphere wall to simulate the relative motion of the sphere. The condition is adequate at the less blockage than 0.7 but It may need to apply a multi-scale concept of grid refinement at the narrow flow region. to obtain the stable numerical results.

• Journal of Mechanical Science and Technology
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• v.14 no.8
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• pp.867-878
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• 2000

In order to study unsteady aerodynamic loads on high speed trains passing by each other 350km/h, three-dimensional flow fields around trains during the crossing event are numerically simulated using three-dimensional Euler equations. Roe's FDS with MUSCL interpolation is employed to simulate wave phenomena. An efficient moving grid system based on domain decomposition techniques is developed to analyze the unsteady flow field induced by the restricted motion of a train on a rail. Numerical simulations of the trains passing by on the double-track are carried out to study the effect of the train nose-shape, length and the existence of a tunnel on the crossing event. Unsteady aerodynamic loads-a side force and a drag force-acting on the train during the crossing are numerically predicted and analyzed. The side force mainly depends on the nose-shape, and the drag force depends on tunnel existence. Also. a push-pull (i.e.impluse force) force successively acts on each car and acts in different directions between the neighborhood cars. The maximum change of the impulsive force reaches about 3 tons. These aerodynamic force data are absolutely necessary to evaluate the stability of high speed multi-car trains. The results also indicate the effectiveness of the present numerical method for simulating the unsteady flow fields induced by bodies in relative motion.

• Journal of computational fluids engineering
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• v.17 no.1
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• pp.44-53
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• 2012

Immersed boundary method(IBM) is a numerical scheme proposed to simulate flow field around complex objectives using simple Cartesian grid system. In the previous studies, the IBM has mostly been implemented to fractional step method based Navier-Stokes solvers. In this study, we implement the IBM to an incompressible Navier-Stokes solver which uses SIMPLE algorithm. The weight coefficients of the bi-linear and quadratic interpolation equations were formulated by using only geometric information of boundary to reconstruct velocities near IB. Flow around 2D circular cylinder at Re=40 and 100 was solved by using these formulations. It was found that the pressure buildup was not observed even when the bi-linear interpolation was adopted. The use of quadratic interpolation made the predicted aerodynamic forces in good agreement with those of previous studies. For an analysis of moving boundary, we smulated an oscillating circular cylinder with Re=100 and KC(Keulegan-Carpenter) number of 5. The predicted flow fields were compared with experimental data and they also showed good agreements.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1487-1494
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• 1990

In this paper the dynamic characteristics of self acting air lubricated slider bearing of hard disk/head system are investigated. The dynamic equations of magnetic head mechanism considering both parallel and pitch motion and the time dependent modified Reynolds equation are analyzed and the dynamic pressure distribution of air film is numerically calculated in frequency domain by small perturbation method and finite difference scheme with variable grid. The dynamic response of the slider spacing is obtained accordingly as the moving recording surface vibrates in parallel mode.

• 한국공간정보시스템학회:학술대회논문집
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• 2004.12a
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• pp.60-65
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• 2004

최근 무선/이동 통신 기술과 GPS 기술의 발달은 휴대폰을 소지하고 이동하는 사람이나 GPS 수신기를 탑재한 차량과 같은 이동객체의 위치 정보와 관련된 서비스의 제공을 가능하게 하였다. 이러한 환경에서 연속적으로 변경되는 이동객체의 위치 정보는 데이터베이스에 빈번한 갱신 연산을 요구하게 되고, 이는 전체 시스템의 성능을 저하시키는 원인이 된다. 이러한 문제를 해결하기 위하여 R-Tree와 같은 공간색인 구조를 확장하여 갱신 효율을 높이기 위한 연구가 진행되어 왔지만, 시스템의 전체 성능은 오히려 저하되는 문제를 가져왔다. 이 논문에서는 이동객체의 질의 처리 성능뿐만 아니라 객체의 빈번한 위치 갱신을 효율적으로 처리할 수 있는 방법으로 고정 그리드와 R-Tree를 혼합한 형태의 색인 기법을 제안한다. 제안된 색인 기법은 R-Tree에서 색인의 재조직화로 인해 갱신 성능이 저하되는 문제를 해결하기 위하여 셀 기반 색인 기법인 고정 그리드를 이용하여 이동객체의 위치 정보를 저장하고, 고정 그리드에서 객체의 편중 분포로 인한 오버플로 문제를 처리하기 위하여 오버플로가 발생한 각각의 셀들을 R-Tree로 관리한다. 또한, 객체의 밀도가 낮은 셀들을 하나의 버켓으로 공유하여 관리함으로써 저장 공간을 효율적으로 활용한다. 제안된 방법을 다양한 평가 요소를 통해 실험한 결과, 기존의 R-Tree보다 뛰어난 갱신 성능을 보였으며, 질의 처리에 대해서도 성능이 향상되었음을 보였다.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.188-192
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• 2004

A Numerical analysis method is developed in order to compute the flaw and wave field for 2-dimensional floating body in the free roll motion with 3 degrees of freedom. Navier-Stokes and continuity equations are gaverning equations in tire present study. Finite Difference method is introduced to discretize the governing equation. The free surface is traced by the interface tracking method and the grid system is fitted to boundaries including free surface and body surface, which is moving in the flow field. The numerical scheme is based on Maker and Cell method. For the sake of validation of the numerical method, the computed roll decay factors according to tire midship section shapes are compared with measured results. The numerical results are discussed in order to understand the effect of midship section shape on roll motion.