• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.17-22
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• 2002

Non-uniform and unsteady inflow into a Horizontal Axis Wind Turbine (HAWT) brings about an asymmetric flow field on the rotor plane and an unsteady aerodynamic load on the blades. In the present paper effects of yawed inflow and wind shear are analyzed by an inviscid aerodynamic model based on the asymptotic acceleration potential method. In the analysis the rotor blades are represented by spanwise and chordwise pressure distribution composed of analytical first-order asymptotic solutions for the Laplace equation. As the actual wind field experienced by a HAWT is turbulent, the effects of the turbulence are also examined using the Veers' model.

• 한국전자파학회논문지
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• 제26권11호
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• pp.1012-1019
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• 2015

본 논문은 공동구조의 RCS(Radar Cross Section)을 계산하는 반복적 물리 광학법(Iterative Physical Optics: IPO)의 연산속도를 가속하는 기법들을 효과적으로 적용하는 방법을 제시한다. IPO는 기존에 공동 구조 내부에서 발생하는 다중 반사 효과 계산 시 기하 광학법(Geometric Optics: GO)를 사용하는 SBR(Shooting and Bouncing Rays)과는 달리 근거리 필드 식을 활용하기 때문에 정확도가 향상된 산란 계산이 가능하다. 하지만 PO(Physical Optics)에 비해 크게 느리며, 실질적인 사용을 위해서는 계산속도의 향상을 위한 기법이 필요하다. 이를 해결하기 위해 IPO에서 특징적으로 사용되는 반복적 부분을 GPU(Graphic Processing Unit)으로 계산하고, AIPO-CR(Adaptive Iterative Physical Optics-Change Rate)으로 반복횟수를 최적화하여 효과적으로 연산속도를 향상시킨다.

• 한국자동차공학회논문집
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• 제16권5호
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• pp.77-83
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• 2008

Semi-active cabin air suspension system improves driver's comfort by controlling the damping characteristics in accordance with driving situation. For the driver's comfort evaluation, test procedure has the two methodologies which are filed test and lab test. A field test method has a drawback. It requires a lot of time and money on repetitive test, due to the sensitivity of field test. On the other hand, the test with six axes simulation table at laboratory can obtain the repeatability of test, better than the field test method. In this paper, the procedures of ride performance test and control logic tuning with the table are presented. Drive files of the table can be represented with the almost same input condition as field test data. According to the result from the comparative test using six axes simulation table between passive and semi-active system by making ECU logic tuning, the RMS acceleration of semi-active cabin air suspension system was reduced by 29.6% compared with passive system.

• 한국유체기계학회 논문집
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• 제6권3호
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• pp.51-57
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• 2003

Characteristics of the high frequency pulsatile flow have been investigated experimentally to understand the flow phenomena in the hydraulic system. One axis fatigue test bed, which is widely used for automobile field test, is used. Four pressure transducers, an amplifier and a A/D convertor are used to obtain the high frequency pulsatile pressure waveform in hydraulic system. The characteristics of frequency are analyzed by power spectrum method. According to the variations of pump input pressure and actuator acceleration frequency, the pressure is measured with or without an accumulator. The amplitude of pressure with accumulator is very lower than those without accumulator due to absorbing function of accumulator. As the frequency of actuator acceleration is increased, the effect of accumulator become very important to decrease the amplitude of pulsatile pressure waveform with high frequencies.

• Nuclear Engineering and Technology
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• 제55권7호
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• pp.2642-2649
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• 2023

A real-time unmeasured dynamic response prediction process for the nuclear power plant pressure pipeline is proposed and its performance is tested in the test-loop system (KAERI). The aim of the process is to predict unmeasurable or unreachable dynamic responses such as acceleration, velocity, and displacement by using a limited amount of directly measured physical responses. It is achieved by combining a well-constructed finite element model and robust inverse force identification algorithm. The pressure pipeline system is described by using the displacement-pressure vibro-acoustic formulation to consider fully filled liquid effect inside the pipeline structure. A robust multiphysics modal projection technique is employed for the real-time sensor synchronized prediction. The inverse force identification method is also derived and employed by using Bathe's time integration method to identify the full-field responses of the target system from the modal domain computation. To validate the performance of the proposed process, an experimental test is extensively performed on the nuclear power plant pressure pipeline test-loop under operation conditions. The results show that the proposed identification process could well estimate the unmeasured acceleration in both frequency and time domain faster than 32,768 samples per sec.

• 문화기술의 융합
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• 제9권6호
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• pp.1057-1063
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• 2023

본 연구대상인 도시철도 침목플로팅궤도(STEDEF)는 구조물로 전달되는 진동을 저감시키기 위한 방진궤도이다. 현재 침목플로팅궤도의 침목방진패드 교체주기(정적 스프링강성 변화율, 25±2%)는 하중기반(궤도충격계수와 궤도지지강성)으로 설정되어 운영중인 실정이다. 그러나 대부분의 선행연구는 침목방진패드의 피로수명평가와 스프링강성 증가에 따른 궤도충격계수 및 궤도지지강성의 증가 등 하중기반의 구조적 안전성 측면의 연구가 진행되었다. 따라서 본 연구에서는 분석 구간별 도상 진동가속도를 측정하고 700만회 피로시험결과를 이용하여 구간별 침목방진패드 스프링강성을 산출하고자 한다. 구간별 산출한 침목방진패드 스프링강성을 해석제원으로 설정하여 도상 진동가속도를 해석적으로 도출하였다. 구간별 해석 도상 진동가속도가 현장측정 도상 진동가속도 범위 이내로 나타나 해석모델링의 적정성이 검증되었다. 도출된 스프링강성 변화에 따른 진동가속도 선도(g-k curve)를 이용하여 측정 도상 진동가속도로 침목방진패드 스프링강성을 추정하고자 한다. 따라서 측정 도상 진동가속도를 이용한 운행선로의 침목방진패드 스프링강성을 추정할 수 있는 기법을 제시하고자 한다.

• 대한조선학회논문집
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• 제43권5호
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• pp.538-549
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• 2006

A code is developed to simulate a viscous flow field around a deformable body using the hybrid Cartesian/immersed boundary method. In this method, the immersed boundary(IB) nodes are defined near the body boundary then velocities at the IB nodes are reconstructed based on the interpolation along the normal direction to the body surface. A new method is suggested to define the IB nodes so that a closed fluid domain is guaranteed by a set of IB nodes and the method is applicable to a zero-thickness body such as a sail. To validate the developed code, the vorticity fields are compared with other recent calculations where a cylinder orbits and moves into its own wake. It is shown the code can handle a sharp trailing edge at Reynolds number of $10^5$ under moderate requirements on girds. Finally the developed code is applied to simulate the vortex shedding behind a deforming foil with flapping tail like a fish. It is shown that the acceleration of fluids near the flapping tail contributes to the generation of the thrust for propulsion.

• Interdisciplinary Bio Central
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• 제2권2호
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• pp.6.1-6.5
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• 2010

Fragment molecular orbital (FMO) method provides a novel tool for ab initio calculations of large biomolecules. This method overcomes the size limitation difficulties in conventional molecular orbital methods and has several advantages compared to classical force field approaches. While there are many features in this method, we here focus on explaining the issues related to protein-ligand binding: FMO method provides useful interaction-analysis tools such as IFIE, CAFI and FILM. FMO calculations can provide not only binding energies, which are well correlated with experimental binding affinity, but also QSAR descriptors. In addition, FMO-derived charges improve the descriptions of electrostatic properties and the correlations between docking scores and experimental binding affinities. These calculations can be performed by the ABINIT-MPX program and the calculation results can be visualized by its proper BioStation Viewer. The acceleration of FMO calculations on various computer facilities is ongoing, and we are also developing methods to deal with cytochrome P450, which belongs to the family of drug metabolic enzymes.

• 대한토목학회논문집
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• 제29권3D호
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• pp.363-371
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• 2009

자동차 창유리 틴팅암도 규제를 위한 도로교통법 개정이 상당기간 논란이 되고 있다. 이는 과도한 선팅이 안전에 위협을 준다는 가설에 기초한다. 그러나 일부 운전자들은 여전히 이를 불필요한 규제로 보는 시각도 상존한다. 한편, 틴팅차량(Window tinting)이 교통류에 미치는 영향을 직접적으로 자료를 취득하여 분석한 구체적인 실험연구는 전무하다. 본 연구는 시각을 달리하여 과도한 선팅차량이 후미차량에 영향을 끼쳐 용량저해 요인으로 작용할 수도 있다는 가설을 세우고 이를 분석하기 위한 자료수집 방법을 구상하고 실현하여 취득한 현장자료로 가설이 참임을 입증하기 위한 개연성을 확인하는 기초연구를 수행하였다. 틴팅차량 후미를 주행하는 차량의 미시적 운행자료를 정밀하게 측정하는 방안으로 본 연구는 RTK GPS 수신장치를 활용한 방법을 구상하였다. 미시적(Microscopic) 분석을 위해서 차량추종(Car-following) 상태인 세 차량의 상대적 측위 및 속도를 매 0.1초 마다 측정해내는 것을 목표로 설정하였다. 측정된 자료를 이용하여 통행속도, 차두시간(Time headway), 차두거리(Distance headway) 및 가속소음(Acceleration noise)을 분석하였다. 제한적인 현장실험이었으나 분석을 통해 선행차량의 틴팅 수준이 높아질수록 교통류의 불안정성이 높아지는 경향을 실측자료로 확인할 수 있었다. 제시된 RTK GPS 수신장치를 통한 현장자료 수집방법을 활용하여 다양한 도로교통 및 운전자를 고려한 확대연구는 향후 연구로 남긴다.

• Wind and Structures
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• 제37권6호
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• pp.445-460
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• 2023

Accurate estimation of modal parameters (i.e., natural frequency, damping ratio) of tall buildings is of great importance to their structural design, structural health monitoring, vibration control, and state assessment. Based on the combination of variational mode decomposition, smoothed discrete energy separation algorithm-1, and Half-cycle energy operator (VMD-SH), this paper presents a method for structural modal parameter estimation. The variational mode decomposition is proved to be effective and reliable for decomposing the mixed-signal with low frequencies and damping ratios, and the validity of both smoothed discrete energy separation algorithm-1 and Half-cycle energy operator in the modal identification of a single modal system is verified. By incorporating these techniques, the VMD-SH method is able to accurately identify and extract the various modes present in a signal, providing improved insights into its underlying structure and behavior. Subsequently, a numerical study of a four-story frame structure is conducted using the Newmark-β method, and it is found that the relative errors of natural frequency and damping ratio estimated by the presented method are much smaller than those by traditional methods, validating the effectiveness and accuracy of the combined method for the modal identification of the multi-modal system. Furthermore, the presented method is employed to estimate modal parameters of a full-scale tall building utilizing acceleration responses. The identified results verify the applicability and accuracy of the presented VMD-SH method in field measurements. The study demonstrates the effectiveness and robustness of the proposed VMD-SH method in accurately estimating modal parameters of tall buildings from acceleration response data.