• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2014년도 춘계학술대회 논문집
• /
• pp.466-471
• /
• 2014

The interior vehicle noise due to the exterior aerodynamic field is an important topic in the acoustic design of a car. The air flow detached from the A-pillar and impacting the side windows are of particular interest as they are located close to the driver / passenger and provides a lower insulation index than the trimmed car body parts. This paper presents a numerical analysis method for a simplified vehicle model. The internal air cavity including trim component are included in the simulation. The car body includes the windshield and two side windows. The body is made of aluminum and trimmed with porous layers. The methodology proposed in this paper relies on two steps: the first step involves the computation of the exterior flow and turbulence induced non-linear acoustic field using PowerFlow. The second step consists in the computation of the vibro-acoustic transmission through the window using the finite element vibro-acoustic solver Actran. Additionally in order to validate the numerical process, an experimental set-up has been created based on the simplified vehicle. The vibration of the windshield and windows, the total wind noise level results and the relative contributions of the different windows are then presented and compared to measurements. The influence of the flow yaw angle (different wind orientation) is also assessed.

• 한국강구조학회 논문집
• /
• 제25권3호
• /
• pp.223-231
• /
• 2013

최근 구조물의 고층화, 대형화 및 장스팬 활용 등의 요구로 고강도 고성능 재료의 건축물과 교량에의 적용이 증가하는 추세이다. 본 논문은 고성능강(HSA800)의 건축구조용 재료 특성과 고성능강재를 사용한 부재의 설계 기준을 위한 기본적인 연구의 일부이다. 조립각형강관 기둥의 국부좌굴 거동과 현행 폭두께비 설계 제한치를 검토하기 위하여 다양한 폭두께비 변수를 계획하고, 단축압축실험을 실시하였다. 또한, 유한요소결과로 얻어낸 단주의 국부좌굴거동을 실험결과와 비교하였으며 검증된 해석모델을 이용하여 변수연구를 수행하였고 현행 설계기준의 적용성에 대해 검토하였다.

• 한국항공우주학회지
• /
• 제36권4호
• /
• pp.346-351
• /
• 2008

본 논문에서는 MR 댐퍼를 헬기 착륙장치 완충기에 적용하여 반능동형 헬기 착륙장치 시스템을 설계하고, 헬기 착륙장치의 반능동제어를 수행하였다. MR 유체는 자기장 내에서는 유체의 물성치가 바뀌게 되는 빙햄거동을 시뮬레이션 하여 MR 댐퍼의 성능을 평가하였다. MR 댐퍼 내에서 자기장을 설계하고, 자기장의 변화에 대해 내부감쇠력의 변화를 고찰하고 자기장에 따른 착륙장치의 거동을 평가하였다. 또한 반능동형 헬기 착륙장치에 제어 알고리즘을 적용하여 착륙특성 성능을 해석하였고, 수동계의 착륙특성과 반능동형의 착륙특성을 비교하였다.

• 한국항공우주학회지
• /
• 제30권8호
• /
• pp.46-55
• /
• 2002

본 연구에서는 저가형 PC-클러스터 환경에서 운영 가능한 고속 병렬처리 기법을 활용하여 전기체 항공기 및 발사체 형상을 고려할 수 있는 천음속/초음속 비선형 플러터 해석시스템을 개발하였다. 이는 이론적으로 진보된 수치해석 기법인 전산구조동역학(CSD), 유한요소법(FEM) 및 전산유체역학(CFD) 기법을 동시에 연계하고 있으며, 각종 비행체의 공탄성안정성 설계 과정에서 공학적으로 매우 정밀한 데이터 제공이 가능하다. 개발된 공탄성 해석시스템의 뛰어난 응용성을 보이기 위해 국내에서 개발 중인 초음속 항공기의 전기체 형상에 대해 천음속/초음속 비선형 공탄성 해석을 수행하였다.

• 한국산업정보학회논문지
• /
• 제23권1호
• /
• pp.31-41
• /
• 2018

이 논문에서는 대 전류, 고온 초전도 직류 리액터를 위한 전도 냉각 시스템의 구조 설계에 대해 논의하고자 한다. 초전도 자석, 보 빈, 전류 리드, 고정용 구조물 그리고 열 교환기가 포함된 전도 냉각 시스템 부품의 크기를 3D CAD 프로그램을 사용하여 계산하였다. 또한, 최적의 설계 변수를 결정하고 열적-기계적 특성을 분석하기 위해서 유한 요소법 모델을 제작하였다. 리액터 자석의 운전 전류와 인덕턴스는 각각 1,500 A 400 mH이며, 이에 따른 극저온 냉동기의 냉각 용량을 결정하기 위해 초전도 직류 리액터에서 발생하는 열 부하를 계산하였다. 또한, 대 전류가 흐르는 1 단부전도 냉각 시스템의 작동 테스트를 수행하였다. 구리 바는 40 K까지 냉각되었고 초전도 리드는 안정적으로 작동했다. 실험 결과로써, 1 단부 영역의 총 열 부하는 190 W였다. 본 연구 결과는 상용 초전도 직류 리액터의 설계 및 제조에 있어 효과적으로 활용 될 것이다.

• Structural Engineering and Mechanics
• /
• 제56권4호
• /
• pp.549-567
• /
• 2015

A first-order moment method (FORM) reliability analysis is commonly used for structural stability analysis. It requires the values and partial derivatives of the performance to function with respect to the random variables for the design. These calculations can be cumbersome when the performance functions are implicit. A Gaussian process (GP)-based response surface is adopted in this study to approximate the limit state function. By using a trained GP model, a large number of values and partial derivatives of the performance functions can be obtained for conventional reliability analysis with a FORM, thereby reducing the number of stability analysis calculations. This dynamic renewed knowledge source can provide great assistance in improving the predictive capacity of GP during the iterative process, particularly from the view of machine learning. An iterative algorithm is therefore proposed to improve the precision of GP approximation around the design point by constantly adding new design points to the initial training set. Examples are provided to illustrate the GP-based response surface for both structural and non-structural reliability analyses. The results show that the proposed approach is applicable to structural reliability analyses that involve implicit performance functions and structural response evaluations that entail time-consuming finite element analyses.

• Advances in environmental research
• /
• 제3권1호
• /
• pp.45-69
• /
• 2014

The groundwater has been a major source of water supply throughout the ages. Around 50% of the rural as well as urban population in the developing countries like India depends on groundwater for drinking. The groundwater is also an important source in the agriculture and industrial sector. In many parts of the world, groundwater resources are under increasing threat from growing demands, wasteful use and contamination. A good planning and management practices are needed to face this challenge. A key to the management of groundwater is the ability to model the movement of fluids and contaminants in the subsurface environment. It is obvious that the contaminant source activities cannot be completely eliminated and perhaps our water bodies will continue to serve as receptors of vast quantities of waste. In such a scenario, the goal of water quality protection efforts must necessarily be the control and management of these sources to ensure that released pollutants will be sufficiently attenuated within the region of interest and the quality of water at points of withdrawal is not impaired. In order to understand the behaviour of contaminant transport through different types of media, several researchers are carrying out experimental investigations through laboratory and field studies. Many of them are working on the analytical and numerical studies to simulate the movement of contaminants in soil and groundwater of the contaminant transport. With the advent of high power computers especially, a numerical modelling has gained popularity and is indeed of particular relevance in this regard. This paper provides the state of the art of contaminant transport and reviews the allied research works carried out through experimental investigation or using the analytical solution and numerical method. The review involves the investigation in respect of both, saturated and unsaturated, porous media.

• Structural Engineering and Mechanics
• /
• 제75권4호
• /
• pp.435-444
• /
• 2020

Ultrasonic guided wave testing is a very promising non-destructive testing method for rails, which is of great significance for ensuring the safe operation of railways. On the basis of the semi-analytical finite element (SAFE) method, a analytical model of 59R2 grooved rail was proposed, which is commonly used in the ballastless track of modern tram. The dispersion curves of ultrasonic guided waves in free rail and supported rail were obtained. Sensitivity analysis was then undertaken to evaluate the effect of rail elastic modulus on the phase velocity and group velocity dispersion curves of ultrasonic guided waves. The optimal guided wave mode, optimal excitation point and excitation direction suitable for detecting rail integrity were identified by analyzing the frequency, number of modes, and mode shapes. A sinusoidal signal modulated by a Hanning window with a center frequency of 25 kHz was used as the excitation source, and the propagation characteristics of high-frequency ultrasonic guided waves in the rail were obtained. The results show that the rail pad has a relatively little influence on the dispersion curves of ultrasonic guided waves in the high frequency band, and has a relatively large influence on the dispersion curves of ultrasonic guided waves in the low frequency band below 4 kHz. The rail elastic modulus has significant influence on the phase velocity in the high frequency band, while the group velocity is greatly affected by the rail elastic modulus in the low frequency band.

• Wind and Structures
• /
• 제30권6호
• /
• pp.663-678
• /
• 2020

Robust semi-active vibration control of wind turbines using tuned mass dampers (TMDs) is a promising technique. This study investigates a 1.5 megawatt wind turbine controlled by eight different types of tuned mass damper systems of equal mass: a passive TMD, a semi-active varying-spring TMD, a semi-active varying-damper TMD, a semi-active varying-damper-and-spring TMD, as well as these four damper systems paired with an additional smaller passive TMD near the mid-point of the tower. The mechanism and controllers for each of these TMD systems are explained, such as employing magnetorheological dampers for the varying-damper TMD cases. The turbine is modelled as a lumped-mass 3D finite element model. The uncontrolled and controlled turbines are subjected to loading and operational cases including service wind loads on operational turbines, seismic loading with service wind on operational turbines, and high-intensity storm wind loads on parked turbines. The displacement and acceleration responses of the tower at the first and second mode shape maxima were used as the performance indicators. Ultimately, it was found that while all the semi-active TMD systems outperformed the passive systems, it was the semi-active varying-damper-and-spring system that was found to be the most effective overall - capable of controlling vibrations about as effectively with only half the mass as a passive TMD. It was also shown that by reducing the mass of the TMD and adding a second smaller TMD below, the vibrations near the mid-point could be greatly reduced at the cost of slightly increased vibrations at the tower top.

• 한국산학기술학회논문지
• /
• 제18권7호
• /
• pp.726-733
• /
• 2017

마그네틱 셔터 기어는 원주상에 마주하는 영구자석 레이어간의 자기장을 고조파 모듈레이터를 통해 동기화시켜 동력을 전달하는 장치이다. 이러한 장치는 기계식 감속기에 필적할만한 토크를 발생시키기 위해 과다한 희토류 영구자석이 이용되기 때문에 본 논문에서는 영구자석간의 자기 경로를 변화시켜 영구자석의 양을 기존 마그네틱 기어 대비 50% 수준으로 감소시킨 새로운 방식의 축형 마그네틱 기어를 제안한다. 제안한 시스템의 토크 크기는 공극 자기장의 고조파 분석과 유한 요소 해석을 통해 기존 시스템과 비교된다. 모듈레이터 두께와 개방비가 전달 토크의 크기에 영향을 미치는 주요 설계변수로 고려되어 민감도 해석이 수행되며 고속측과 저속측의 영구자석 극수에 의해 결정되는 기어비에 따른 코깅의 크기가 분석된다. 기계적인 접촉없이 커플링되어 동력을 전달하는 고속측과 저속측 사이의 동적 지배 모델이 유도된다. 2관성 공진계의 동특성을 갖는 유도된 모델을 기초로 하여 선형 제어기를 설계하여 고속측의 계단 입력 위치 제어를 수행하였다.