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Resonant response of spar-type floating platform in coupled heave and pitch motion
J.R. Cho,조진래,W. B. JEONG 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.5
In this paper, the resonance response of spar-type floating platform in coupled heave and pitch motion is investigated using a CPU time-effective numerical method. A coupled nonlinear 2-DOF equation of motion is derived based on the potential wave theory and the rigid-body hydrodynamics. The transient responses are solved by the fourth-order Runge-Kutta (RK4) method and transformed to the frequency responses by the digital Fourier transform (DFT), and the first-order approximation of heave response is analytically derived. Through the numerical experiments, the theoretical derivation and the numerical formulation are verified from the comparison with the commercial software AQWA. And, the frequencies of resonance arising from the nonlinear coupling between heave and pitch motions are investigated and justified from the comparison with the analytically derived first-order approximation of heave response.
국부 상세 단열 구조 모델을 이용한 LNG 운반선 화물창의 해석
박성우(S. W. Park),조진래(J. R. Cho) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
There are many numerical methods to solve the fluid-structure interaction(FSI) systems. However, these methods require very fine mesh to attain the numerical accuracy and stability owing to the concentrated and fluctuating sloshing hydrodynamic pressure. As a result, the numerical analysis targeting for the long-period time response with the desired accuracy is highly time-consuming. The aim of this paper is to present a new method to analyze the sloshing behavior of the LNG containment by using the locally detailed model. According to the global-local analysis method, the local responses of the LNG containment are efficiently obtained only with small increase of computation time.
이홍우(H.W.Lee),조진래(J.R.Cho),이진규(J.K.Lee),장문석(M.S.Chang),안동수(D.S.Ahn) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
In this paper we discuss the dynamic characteristics of the in-am1 type hydropneumatic suspension unit(ISU). For this, two accurate models are introduced. The first one is the Benedict-Webb-Rubin equation which is adopted for the spring behavior of a real gas. This equation is applicable for the high pressure of the nitrogen gas which acts as a spring in ISU system. The second one describes the behavior of a damper. which is divided into four parts - jounce-loading. jounce-unloading. rebound-loading and rebound-unloading. This approach gives a good approximation of the real damper system. For the comparison purpose. the numerical results of the dynamic behavior of ISU system using a real gas and an ideal gas are given in the paper.
국부 임계치를 반영한 슬로싱 수반 대형 유탄성 해석 기법에 관한 연구
박성우(S. W. Park),조진래(J. R. Cho) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
There exist many researches to solve the fluid-structure interaction(FSI) problems. However, these methods require very fine mesh to achieve the reasonable numerical accuracy and stability due to the concentrated and volatile hydrodynamic pressure caused by the liquid sloshing. Consequently, the numerical analysis targeting for the long-period time response with the desired numerical accuracy is very highly time-consuming. The aim of this paper is to suggest a new method to analyze the sloshing behavior of the FSI system by using the local critical results of the rigid sloshing. This method can reduce the analysis time in considering the fluctuation in the responses at the initial analysis step. At first, the propriety of the presented method is verified, moreover, according to the analysis method, the local responses of the large FSI system are efficiently acquired only with small increase of computation time.
홍상일(S. I. Hong),김민정(M. J. Kim),조진래(J. R. Cho),박태학(T. H. Park),이우용(W. Y. Lee) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.4
The dynamic response of a baffled fuel-storage tank in turnaround motion is simulated using the ALE finite element method. Fuel-storage tank is a representative example of fluid-structure interaction problems, in which structure deformation and fluid motion interact strongly. For the accurate dynamic-response analysis of this complicated fluid-structure system, we employed ALE(arbitrary Lagrangian-Eulerian) numerical approach. Five types of fuel-storage tank models with respect to the baffle number are considered to examine the effect of baffles on the dynamic-response, such as effective stress, displacement and the free surface motion of internal fluid.
신성우(S. W. Shin),박형종(H. J. Park),조진래(J. R. Cho) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.8
For the high temperature engineering applications, materials used are required to possess superior thermo-mechanical performances, such as high temperature strength and creep resistance, especially fracture toughness and thermal shock resistance. So, laminated composites have been used for several decades as a heat-resisting material. But, there exists one inevitable disadvantage in classical laminate composites. To resolve this problem, a notion of functionally graded materials(FGM) was introduced. In FGMs, a material composition varies continuously from one end to the other of graded layer. In oder to find suitable volume fraction distribution in the graded layer for relaxing thermal stress, we apply optimization technique and neural network algorithm. The purpose of the use of neural network is to minimize the total CPU time by reducing the number of finite element analysis. As well, we confirmed that the neural network leads to reliable approximation of the objective function.
Wi-Fi Backscatter Systems for IoT Sensors with Enhanced Communication Reliability
김찬규(Chankyu Kim),백성민(Seongmin Baek),이성주(Seongjoo Lee) 대한전자공학회 2020 대한전자공학회 학술대회 Vol.2020 No.8
IoT 기술이 발전함에 따라 배터리 문제가 대두되었다. 미국의 워싱턴 대학에서 저전력으로 Tag를 동작시키는 Wi-Fi 백스케터 기술을 처음 제시하였다. 그러나 이 방식은 전송 성능 및 전송률이 낮다는 단점이 있었다. 이를 개선하기 위해 Tag에서 에너지를 조절하는 M-레벨 변조 방식을 통해 전송률을 높이는 방법이 제시되었다. 그러나 M-레벨 변조 방식은 낮은 SNR환경에서 신뢰성이 떨어지는 문제점이 있었다. 본 논문에서는 딥러닝 기반의 수신기를 구성함으로써 낮은 SNR 환경에서도 Wi-Fi backscatter 시스템의 성능을 높일 수 있도록 하였다. 또한, Tag의 구성을 그대로 적용하기 때문에 전송률뿐 아니라 Tag에서 배터리가 필요하지 않으며, 사용되는 에너지가 적다는 장점도 있다. 제안하는 딥러닝 방식은 2-level일 때 22dB SNR 환경에서 10-3 BER 성능을 확인하였다.