• Smart Structures and Systems
• /
• 제30권1호
• /
• pp.107-119
• /
• 2022

Modal parameters are widely used in bridge damage detection, finite element model (FEM) updating and design optimization. However, the conventional modal identification approaches require large number of sensors, enormous data processing workload, but normally result in mode shapes with low accuracy. This paper proposes a modal identification method of time-varying vehicle-bridge system using a single sensor. Firstly, the essential physical relationship between the instantaneous frequency of the vehicle-bridge system and the bridge mode shapes are derived. Subsequently, based on the synchroextracting transform, the instantaneous frequency of the system is tracked through the dynamic response collected by a single sensor, and further the modal parameters are estimated by using the derived physical relationship. Then numerical and experimental examples are conducted to examine the feasibility and effectiveness of the proposed method. Finally, the modal parameters identified by the proposed method are applied in bridge FEM updating. The results manifest that the proposed method identifies the modal parameters with high accuracy via a single sensor, and can provide reliable data for the FEM updating.

• Earthquakes and Structures
• /
• 제14권6호
• /
• pp.599-614
• /
• 2018

This study focuses on the earthquake performance of two URM buildings having typical architectural configurations common for residential use constructed per pre-modern code in Albania. Both buildings are unreinforced clay brick masonry structures constructed in 1960 and 1984, respectively. The first building is a three-storey unreinforced one with masonry walls. The second one is confined masonry rising on five floors. Mechanical characteristics of masonry walls were determined based on experimental tests conducted according to ASTM C67-09 regulations. A global numerical model of the buildings was built, and masonry material was simulated as nonlinear. Pushover analyses are carried out to obtain capacity curves. Displacement demands were calculated according to Eurocode 8 and FEMA440 guidelines. Causes of building failures in recent earthquakes were examined using the results of this study. The results of the study showed that the URM building displays higher displacement and shear force demands that can be directly related to damage or collapse. On the other hand, the confined one exhibits relatively higher seismic resistance by indicating moderate damage. Moreover, effects of demand estimation approaches on performance assessment of URM buildings were compared. Deficiencies and possible solutions to improve the capacity of such buildings were discussed.

• Nuclear Engineering and Technology
• /
• 제55권4호
• /
• pp.1287-1299
• /
• 2023

A new Monte-Carlo-based computer program (RDS-BASIC) is developed to simulate the transport of energetic ions in pure matter. This computer program is utilizing an algorithm that uses detailed numerical solutions for the classical scattering integral for evaluating the outcomes of the binary collision processes. This approach is adopted by several prominent similar simulation programs and is known to provide results with higher accuracy compared to other approaches that use approximations to shorten the simulation time. Furthermore, RDS-BASIC simulation program contains special methods to reduce the displacement energy threshold of surface atoms. This implementation is found essential for accurate simulation results for sputtering yield in the case of very low energy ions irradiation (near sputtering energy threshold) and also successfully solve the problem of simultaneously obtaining an acceptable number of atomic displacements per incident ions. Results of our simulation for several irradiation systems are presented and compared with their respective TRIM (SRIM-2013) and the state-of-the-art SDTrimSP simulation results. Our sputtering simulation results were also compared with available experimental data. The simulation execution time for these different simulation programs has also been compared.

• Smart Structures and Systems
• /
• 제14권4호
• /
• pp.659-678
• /
• 2014

The study is aimed at investigating the feasibility of a high TRL solution for a wing flap segment characterized by morphable camber airfoil and properly tailored to be implemented on a real-scale regional transportation aircraft. On the base of specific aerodynamic requirements in terms of target airfoil shapes and related external loads, the structural layout of the device was preliminarily defined. Advanced FE analyses were then carried out in order to properly size the load-carrying structure and the embedded actuation system. A full scale limited span prototype was finally manufactured and tested to: ${\bullet}$ demonstrate the morphing capability of the conceived structural layout; ${\bullet}$ demonstrate the capability of the morphing structure to withstand static loads representative of the limit aerodynamic pressures expected in service; ${\bullet}$ characterize the dynamic behavior of the morphing structure through the identification of the most significant normal modes. Obtained results showed high correlation levels with respect to numerical expectations thus proving the compliance of the device with the design requirements as well as the goodness of modeling approaches implemented during the design phase.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2008년 영문 학술대회
• /
• pp.723-728
• /
• 2008

We performed numerical analysis of base drag phenomenon, when a projectile with backward step flies into atmosphere at supersonic speed. We compared with other researchers. From our previous studies that were 2-dimensional simulation, we found out from sophisticated simulations that need dense mesh points to compare base pressure and velocity profile after from base with experimental data. Therefore, we focus on high order spatial disceretization over 3rd order with TVD such as MUSCL TVD 3rd, 5th, and WENO 5th order, and Limiters such as minmod, Triad. Moreover, we enforce to flux averaging schemes such as Roe, RoeM, HLLE, AUSMDV. In present, one dimensional result of Euler tests, there are Sod, Lax, Shu-Osher and interacting blast wave problems. AUSMDV as a flux averaging scheme with MUSCL TVD 5th order as spatial resolution is good agreement with exact solutions than other combinations. We are carrying out the same approaches into 3-dimensional base flow only candidate flux schemes that are Roe, AUSMDV. Additionally, turbulence models are used in 3-dimensional flow, one is Menter s SST DES model and another is Sparlat-Allmaras DES/DDES model in Navier-Stokes equations.

• Wind and Structures
• /
• 제34권1호
• /
• pp.127-136
• /
• 2022

In this work a multi-fidelity non-intrusive polynomial chaos (MF-NIPC) has been applied to a structural wind engineering problem in architectural design for the first time. In architectural design it is important to design structures that are safe in a range of wind directions and speeds. For this reason, the computational models used to design buildings and bridges must account for the uncertainties associated with the interaction between the structure and wind. In order to use the numerical simulations for the design, the numerical models must be validated by experi-mental data, and uncertainties contained in the experiments should also be taken into account. Uncertainty Quantifi-cation has been increasingly used for CFD simulations to consider such uncertainties. Typically, CFD simulations are computationally expensive, motivating the increased interest in multi-fidelity methods due to their ability to lev-erage limited data sets of high-fidelity data with evaluations of more computationally inexpensive models. Previous-ly, the multi-fidelity framework has been applied to CFD simulations for the purposes of optimization, rather than for the statistical assessment of candidate design. In this paper MF-NIPC method is applied to flow around a rectan-gular 5:1 cylinder, which has been thoroughly investigated for architectural design. The purpose of UQ is validation of numerical simulation results with experimental data, therefore the radius of curvature of the rectangular cylinder corners and the angle of attack are considered to be random variables, which are known to contain uncertainties when wind tunnel tests are carried out. Computational Fluid Dynamics (CFD) simulations are solved by a solver that employs the Finite Element Method (FEM) for two turbulence modeling approaches of the incompressible Navier-Stokes equations: Unsteady Reynolds Averaged Navier Stokes (URANS) and the Large Eddy simulation (LES). The results of the uncertainty analysis with CFD are compared to experimental data in terms of time-averaged pressure coefficients and bulk parameters. In addition, the accuracy and efficiency of the multi-fidelity framework is demonstrated through a comparison with the results of the high-fidelity model.

• Composites Research
• /
• 제15권5호
• /
• pp.27-34
• /
• 2002

본 연구의 목적은 (주)한국와이바의 CF3327 평직 복합재료의 열전도도를 실험적으로 계측하고 이를 이론적인 예측과 비교하는데 있다. 열전도도 계측을 위하여 비교계측법의 원리를 이용한 실험 장치를 제작하였으며 열전도도가 잘 알려진 그라파이트를 실험함으로써 장비의 정확성을 확인하였다. 미시역학적인 방법은 섬유 및 기지의 물성, 섬유체적비, 직조 형태 등의 변수들이 복합재료의 유효물성치에 미치는 영향을 평가하는데 유용하다. 본 연구에서는 3차원 직-병렬 열저항 개념을 주기적으로 반복되는 평직의 단위구조에 적용하여 열전도도를 예측하였다. 해석 결과를 실험 결과와 비교한 결과 잘 일치함을 확인하였고 섬유체적비가 에폭시 수지 복합재료의 열전도도에 미치는 영향을 고찰하였다.

• Journal of the Korean Physical Society
• /
• 제73권10호
• /
• pp.1486-1494
• /
• 2018

Based on the semiclassical theory of chaotic scattering, Tanner et al. [J. Phys. B 40, F157 (2007)] proposed the fluctuation in the partial photoionization cross section of helium below the double-ionization threshold would show the same characteristics as in the total cross section, predicting that the Fourier spectrum of the fluctuation reveals peaks at the classical actions of closed triple collision orbits and the amplitude of the fluctuation decreases algebraically as the energy approaches the double-ionization threshold. In that paper, however, the predictions were not clearly confirmed due to the lack of experimental data with sufficient accuracy. So instead, we calculate the partial photoionization cross sections of collinear eZe helium for the energy range from the single-ionization threshold $I_{20}$ to $I_{32}$ in order to numerically confirm the predictions. Analysis of the fluctuation in the partial cross section shows that the predictions are indeed valid. Our findings mean that the fluctuation in the partial photoionization cross section can be described by classical triple collision orbits in the semiclassical limit. Thus it explains in a natural way the mirroring and mimicking structures observed in cross section signals for different ionization channels.

• 한국해양환경ㆍ에너지학회지
• /
• 제10권3호
• /
• pp.173-180
• /
• 2007

파력에너지 변환을 위해 설계된 착저식 진동수주형 공기실 내의 파진폭 변화를 우리나라 연안의 특징적인 파랑 조건을 적용하여 조사하였다. 진동수주형 공기실의 형상인자가 파력에너지 변환에 미치는 영향을 파력에너지의 흡수 효율 관점에서 분석하였다. 실험적 및 수치적 접근법을 함께 사용하여 그 결과들을 상호 비교하였으며, 주어진 파랑 분포 하에서 파력에너지 흡수가 최대가 되는 형상인자들의 최적화를 목적으로 연구가 수행되었다. 실험은 공기실의 이차적원 형상을 가정하여 이차원 조파수조에서 실시되었으며, 수치적 해석은 공기실 내에서는 변동하는 공기압을 고려할 수 있도록 Rankine Green 함수를 적용하고 공기실 밖에서는 Kelvin Green 함수를 적용하는 합성 적분방정식에 기초하여 수행되었다. 공기실 상부의 덕트 직경, 공기실 폭, 공기실 전면벽 및 후면벽의 깊이는 흡수되는 파력에너지의 크기와 정점 주기를 민감하게 변화시키는 주요한 형상인자들임을 확인하였다.

• 한국지반공학회논문집
• /
• 제35권12호
• /
• pp.35-44
• /
• 2019

본 연구에서는 수직증축 공동주택 하부 신설 보강말뚝의 축강성(K_vr)을 기존말뚝의 열화를 고려한 이론적인 접근과 수치해석을 통하여 산정하였다. 3차원 유한요소 수치해석을 수행하는 과정에서, 이론적인 접근과 38본의 시험 말뚝계측 결과를 통하여 제안된 열화를 고려한 기존말뚝 축강성(K_ve)의 상한 값을 적용하였다. 이를 통해, 수직증축 리모델링으로 인하여 증가된 하중을 안정적으로 지지하기 위한 신설 보강말뚝의 최소 축강성을 산정하였다. 신설 보강말뚝의 축강성 제안은 선단지지 말뚝과 마찰말뚝에 대해 수행하였고, 다양한 세장비(L/D)에 따라 제안하였다. 해석기법은 기존말뚝의 설계 당시의 양호한 상태를 고려한 말뚝지지 전면기초 거동 해석과 열화가 고려된 기존말뚝의 축강성을 적용한 말뚝지지 전면기초 거동 해석을 수행하였다. 두 해석기법에 대한 검증을 수행한 결과 말뚝지지 전면기초 거동해석이 가능한 것으로 확인되었고, 이를 통하여 기존말뚝의 열화가 발생하였을 때 선단지지 신설 보강말뚝 축강성이 44 - 67% 증가되어야 수직증축 구조물의 안정성이 확보됨을 알 수 있었다.