The extended finite element method (XFEM) and the level set method (LSM) are applied to simulate the solidification phenomenon and the behavior of the liquid-solid phase transition. The temperature-based energy equati...
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The extended finite element method (XFEM) and the level set method (LSM) are applied to simulate the solidification phenomenon and the behavior of the liquid-solid phase transition. The temperature-based energy equation is loosely-coupled with the incompressible Navier-Stokes (INS) equations and solved by XFEM using the Stefan condition to express the energy conservation law for phase change. The INS equations are additionally supplemented with the Boussinesq approximation for the buoyancy force that drives the ensuing melt flow. The temperature, pressure, and fluid velocity are discontinuous at the interface, and the LSM implicitly captures its location. A modified abs-enrichment scheme (where abs stands for the absolute value function) is used for the weakly-discontinuous temperature field, and a sign-enrichment scheme is employed for the strongly-discontinuous pressure field. The penalty method imposes the interface temperature and velocity and allows for fluid-structure interactions. The numerical model is verified with several benchmark tests: 1D solidification, infinite corner solidification, Frank sphere, flow over a cylinder, as well as fin melting with non-constant density. Once the simulation results have been shown to be in good agreement with analytical solutions and results obtained with other methods, the present methodology is applied to a melting ice cylinder at a high Reynolds number.
This paper investigates the effect of fluid-structure interaction (FSI) on the efficiency of transient-based reflections analysis (TBRA) applied to the detection of extended deteriorations in a reservoir-pipe-valve sy...
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This paper investigates the effect of fluid-structure interaction (FSI) on the efficiency of transient-based reflections analysis (TBRA) applied to the detection of extended deteriorations in a reservoir-pipe-valve system. A waterhammer-with-FSI solver, based on the method of characteristics (MOC) and the finite-element method (FEM), is used and validated against available numerical and experimental results. Analytical expressions for the magnitudes of pressure reflections caused by FSI are derived. They tell how the system parameters affect FSI. The results obtained for the considered situation reveal that both pipe wall vibration (FSI) and pipe wall deteriorations may affect transient pressure in a similar, and possibly indistinguishable, way. Neglecting FSI in TBRA would skew the estimated locations, lengths, and numbers of the deteriorations in systems with considerable pipe wall axial vibration, thus making TBRA a more complicated method in flexible pipe systems.
fluid flows around a pointed object, e.g. the flow around a triangular prism, are often encountered. In this study, numerical simulation of the flow around a triangular prism was carried out using COMSOL Multiphysics ...
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fluid flows around a pointed object, e.g. the flow around a triangular prism, are often encountered. In this study, numerical simulation of the flow around a triangular prism was carried out using COMSOL Multiphysics (R) software. Two cases were considered: the entire area of the triangular prism is fixed;and only the center is fixed. The first case is divided into three different flow models according to the flow state: the separation bubble model, the edge separation model and the attached flow model. The effects of different flow models on the lift coefficient, drag coefficient and Strouhal number were discussed from the perspective of fluid flow. For the second case, the triangular prism periodically rotates while the vortices are separated from the surface. It was found that a stable rotation stage exists after a certain period of time for prisms with different initial positions. The lift and drag coefficients of the triangular prism satisfy the jagged and sinusoidal variation.
The purpose of the study was to evaluate the optimal cut-off value of CT-Fractional Flow Reserve (CT-FFR) using fluid-structure interaction and how to adjust the CT-FFR's underestimation from a standpoint of minim...
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The purpose of the study was to evaluate the optimal cut-off value of CT-Fractional Flow Reserve (CT-FFR) using fluid-structure interaction and how to adjust the CT-FFR's underestimation from a standpoint of minimize 1-year cardiac events. Subjects were 38 cases with 44 vessels in which stenosis of 30-90% was detected using one-rotation scanning by 320-row coronary CT angiography (CCTA) and invasive FFR (i-FFR) was performed within subsequent 90 days. CT-FFR was calculated using on-site from the multiple cardiac phases. A hypothetical 1-year cardiac event incidence was estimated using previous evidences when revascularization was decided based on CT-FFR. We assessed the optimal cut-off value of CT-FFR and how to correct the CT-FFR to minimize hypothetical cardiac events under four different disease prevalence (20%, 25%, 30%, 35%, and 40%). A total of 16 vessels had i-FFR <= 0.8. On per-patient basis, the sensitivity, specificity, positive predict value, negative predict value, and diagnostic accuracy of CT-FFR <= 0.8 vs CCTA > 50% to detect functional stenosis defined as invasive FFR <= 0.80 were 93.3% vs 73.3%, 73.9% vs 26.1%, 70.0% vs 39.3%, 94.4% vs 60.0%, and 81.6% vs 44.7%, respectively. For minimize 1-year cardiac events, the optimal cut-off value for more than 30% of disease prevalence was 0.80. However, the optimal cut-off value for 20, 25, and 30% was 0.54 in any cases. After the adjustment of CT-FFR using a formula of 0.3X + 0.634 for CT-FFR < 0.7 to counteract its underestimation, the % reduction of the events for 20, 25, 30, 35, and 40% at a 0.80 cut-off were 19.0%, 15.6%, 12.6%, 10.0%, and 7.7% respectively. It was reasonable to support that the optimal cut-off value was 0.80 in disease prevalence of more than 30% for minimize 1-year cardiac events. However, underestimation should be adjusted to reduce cardiac events, especially when disease prevalence is low.
AP1000 nuclear power plant has an advanced passive cooling system with a vast water tank located above the shield building, which may affect the seismic performance of the structure. This paper conducts a fragility as...
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AP1000 nuclear power plant has an advanced passive cooling system with a vast water tank located above the shield building, which may affect the seismic performance of the structure. This paper conducts a fragility assessment of shield building and considers the fluid-structure interaction (FSI) effect on the damage of the shield building. Arbitrary Lagrangian Eulerian algorithm is applied to calculate the FSI and eight cases of water levels are considered. Three different fragility analysis methods, namely linear regression, quadratic regression and truncated maximum likelihood estimation, are adopted for assessing the seismic vulnerability of shield building. It is indicated from the results that the regression and the truncated maximum likelihood estimation are close to each other. The maximum likelihood estimation not only can effectively save the computational cost, but also can assure the reasonable calculated results. It is observed that different water levels have the individual probabilities of failure, and case 6 has the smallest probability of failure with a more considerable seismic reduction, whereas the case 1 and case 2 have the higher failure probabilities. The fragility analysis framework can thus be applied for evaluating the vulnerability of shield building under earthquakes considering the FSI effect.
The effect of a wind gust impacting on the blades of a large horizontal-axis wind turbine is analyzed by means of high-fidelity fluid-structure interaction (FSI) simulations. The employed FSI model consisted of a comp...
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The effect of a wind gust impacting on the blades of a large horizontal-axis wind turbine is analyzed by means of high-fidelity fluid-structure interaction (FSI) simulations. The employed FSI model consisted of a computational fluid dynamics (CFD) model reproducing the velocity stratification of the atmospheric boundary layer (ABL) and a computational structural mechanics (CSM) model loyally reproducing the composite materials of each blade. Two different gust shapes were simulated, and for each of them, two different amplitudes were analyzed. The gusts were chosen to impact the blade when it pointed upwards and was attacked by the highest wind velocity due to the presence of the ABL. The loads and the performance of the impacted blade were studied in detail, analyzing the effect of the different gust shapes and intensities. Also, the deflections of the blade were evaluated and followed during the blade's rotation. The flow patterns over the blade were monitored in order to assess the occurrence and impact of flow separation over the monitored quantities.
Bayesian calibration is widely used for inverse analysis and uncertainty analysis for complex systems in the presence of both computer models and observation data. In the present work, we focus on large-scale fluid-st...
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Bayesian calibration is widely used for inverse analysis and uncertainty analysis for complex systems in the presence of both computer models and observation data. In the present work, we focus on large-scale fluid-structure interaction systems characterized by large structural deformations. Numerical methods to solve these problems, including embedded/immersed boundary methods, are typically not differentiable and lack smoothness. We propose a framework that is built on unscented Kalman filter/inversion to efficiently calibrate and provide uncertainty estimations of such complicated models with noisy observation data. The approach is derivative-free and non-intrusive, and is of particular value for the forward model that is computationally expensive and provided as a black box which is impractical to differentiate. The framework is demonstrated and validated by successfully calibrating the model parameters of a piston problem and identifying the damage field of an aircraft wing under transonic buffeting.
Emphysema, a chronic lung disease characterized by respiratory distress and reduced lung function, poses significant challenges. Computational fluid Dynamics (CFD) coupled with fluidstructureinteraction (FSI) is a h...
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ISBN:
(纸本)9780791887622
Emphysema, a chronic lung disease characterized by respiratory distress and reduced lung function, poses significant challenges. Computational fluid Dynamics (CFD) coupled with fluidstructureinteraction (FSI) is a highly effective simulation technique that offers valuable insights into the mechanics of lung function and the influence of diseases like emphysema. The intricate lung alveolar sacs play a vital role in gas exchange, and CFD with FSI enables the simulation of mechanical forces that shape and impact their functionality. By employing CFD with FSI, we can simulate the fluid dynamics of emphysema and acquire a comprehensive understanding of disease progression. These simulations allow us to explore the contributions of tidal breathing and surface tension forces. This study has demonstrated through FSI that a lung alveolus affected by pulmonary emphysema, and therefore collapsed, causes reduced air intake with each breath. This is due to the significantly compromised deformability of the alveolar wall. Ultimately, this technique plays a critical role in developing therapeutic interventions to improve patient outcomes.
A high-order accurate finite-difference scheme modeling the fluid-structure interaction inside a pneumatic seismic source is presented. The model consists of two deforming fluid compartments separated by a moving shut...
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A high-order accurate finite-difference scheme modeling the fluid-structure interaction inside a pneumatic seismic source is presented. The model consists of two deforming fluid compartments separated by a moving shuttle. The fluid is governed by the 1D Euler equations. Well-posedness of the continuous problem is analyzed and proven in the frozen coefficient case. A stable discretization is derived using summation-by-parts operators with the boundary conditions imposed weakly using the simultaneous-approximation-term method. The theoretical convergence rate of the numerical scheme is verified by numerical experiments. Simulation results are compared to pressure measurements from inside a pneumatic seismic source and capture many of the features observed in the data. (C) 2020 Elsevier Inc. All rights reserved.
In this work the partitioned solution approach for the fluid-structure interaction (FSI) of thin-walled structures and high-Reynolds number (Re) flows modeled using Reynolds-Averaged Navier-Stokes (RANS) and hybrid Re...
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In this work the partitioned solution approach for the fluid-structure interaction (FSI) of thin-walled structures and high-Reynolds number (Re) flows modeled using Reynolds-Averaged Navier-Stokes (RANS) and hybrid Reynolds-Averaged Navier-Stokes - Large Eddy Simulation (RANS-LES) turbulence models are described. The advanced turbulence modeling is needed to capture very complex fluid phenomena which triggers instabilities of thin-walled structures present in supersonic flow regimes. The finite element (FE) updated Lagrangian formulation (ULF) for the nonlinear elastic solids is used to predict its dynamical behavior. The main contribution addresses to the linear stress-strain relation Laplacian members, which are solved implicitly, on that way decreasing required memory resources and improving solution stability in the same time. The structures of the interest include the vast variety of membranes, curved shells and plates. The instabilities encountering these structures include limit cycle oscillations (LCO), flutter and buckling of the panels. The phenomena appear in everyday engineering practice and a need for the powerful tools to handle such problems is a common goal. Utilization of the unstructured non-regular meshes allows the precise distribution of computational nodes at the physical boundaries of the fluid and solid domains. It is naturally allowing application of the common approach for the fluid-solid interface coupling, as well as classical data interpolation schemes between fluid and solid on the FSI interface. High-Re flows, both 2D (benchmark) and 3D turbulent FSI case are chosen for the validation. Two numerical methods are coupled via a moving boundary treatment, in a staggered way. The proposed coupling method showed a good agreement with the reference test cases. The current FSI framework is developed to serve as a tool for the liquid rocket engine development. (C) 2021 Elsevier Masson SAS. All rights reserved.
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