The function and morphology of Endothelial Cells (ECs) play a key role in atherosclerosis. The mechanical stimuli of ECs, such as Wall Shear Stress (WSS) and arterial wall strain, greatly influence the function and mo...
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The function and morphology of Endothelial Cells (ECs) play a key role in atherosclerosis. The mechanical stimuli of ECs, such as Wall Shear Stress (WSS) and arterial wall strain, greatly influence the function and morphology of these cells. The present article deals with computations of these stimuli for a 3D model of a healthy coronary artery bifurcation. The focus of the study is to propose an accurate method for computations of WSS and strains. Two approaches are considered: Coupled simultaneous simulation of arterial wall and blood flow, called fluid-structure interaction (FSI) simulation, and decoupled, which simulates each domain (fluid and solid domain) separately. The study demonstrates that the computed circumferential strains resulting from both methods are identical. However, longitudinal strain and WSS are very different from these two approaches. The resulting Time Averaged Wall Shear Stress (TAWSS) from the decoupled fluid model is always higher than the corresponding value from FSI simulation, while the Oscillatory Shear Index (OSI) from the rigid wall model is lower than the values resulting from FSI. Therefore, the decoupled simulation may underestimate the atheroprone sites of the artery, which suggests that using FSI simulation for mechanical stimuli of ECs is inevitable. (C) 2016 Sharif University of Technology. All rights reserved.
A vorticity based approach for the numerical solution of the fluid-structure interaction problems is introduced in which the fluid and structure(s) can be viewed as a continuum. Retrieving the vorticity field and reca...
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A vorticity based approach for the numerical solution of the fluid-structure interaction problems is introduced in which the fluid and structure(s) can be viewed as a continuum. Retrieving the vorticity field and recalculating a solenoidal velocity field, specially at the fluid-structure interface, are the kernel of the proposed algorithm. In the suggested method, a variety of constitutive equations as a function of left Cauchy-Green deformation tensor can be applied for modeling the structure domain. A nonlinear Mooney-Rivlin and Saint Venant-Kirchhoff model are expressed in terms of the left Cauchy-Green deformation tensor and the presented method is able to model the behavior of a visco-hyperelastic structure in the incompressible flow. Some numerical experiments, with considering the neo-Hookean model for structure domain, are executed and the results are validated via the available results from literature.
Low-speed aerodynamics has gained increasing interest due to its relevance for the design process of small flying air vehicles. These small aircraft operate at similar aerodynamic conditions as, e.g. birds which there...
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Low-speed aerodynamics has gained increasing interest due to its relevance for the design process of small flying air vehicles. These small aircraft operate at similar aerodynamic conditions as, e.g. birds which therefore can serve as rolemodels of how to overcome the well-known problems of low Reynolds number flight. The flight of the barn owl is characterized by a very low flight velocity in conjunction with a low noise emission and a high level of mancuverability at stable flight conditions. To investigate the complex three-dimensional flow field and the corresponding local structural deformation in combination with their influence on the resulting aerodynamic forces, time-resolved stereoscopic particle-image velocimetry and force and moment measurements are performed on a prepared natural barn owl wing. Several spanwise positions are measured via PIV in a range of angles of attack 0 degrees <= alpha <= 6 degrees and Reynolds numbers 40 000 <= Re-c <= 120 000 based on the chord length. Additionally, the resulting forces and moments are recorded for -10 degrees <= alpha <= 15 degrees at the same Reynolds numbers. Depending on the spanwise position, the angle of attack, and the Reynolds number, the flow field on the wing's pressure side is characterized by either a region of flow separation, causing large-scale vortical structures which lead to a time-dependent deflection of the flexible wing structure or wing regions showing no instantaneous deflection but a reduction of the time-averagedmean wing curvature. Based on the force measurements the three-dimensional fluid-structure interaction is assumed to considerably impact the aerodynamic forces acting on the wing leading to a strong mechanical loading of the interface between the wing and body. These time-depending loads which result from the flexibility of the wing should be taken into consideration for the design of future small flying air vehicles using flexible wing structures.
Irregular temperature profiles inside nuclear reactors cause the deformation of fuel rods. Due to difficulties in implementing this phenomenon, it is usually neglected in computational fluid dynamics (CFD) analyses. T...
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Irregular temperature profiles inside nuclear reactors cause the deformation of fuel rods. Due to difficulties in implementing this phenomenon, it is usually neglected in computational fluid dynamics (CFD) analyses. Thermoelasticity effect was analyzed in this study for a 7-rod test fuel assembly. The overall problem was simplified on both the fluid-dynamical and the structural side. Existing technology is capable of executing such analysis;although for reliable results, improvement in the mesh deformation algorithm is needed. The deflection proves to have a distinct impact on surface temperature in a limited area. To obtain reliable results, more thorough analysis regarding both domains is necessary.
The behavior of a submerged floating tunnel (SFT) exposed to a water current of variable velocity is investigated through complex numerical analyses based on the Computational fluid Dynamics (CFD) and the Finite Eleme...
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The behavior of a submerged floating tunnel (SFT) exposed to a water current of variable velocity is investigated through complex numerical analyses based on the Computational fluid Dynamics (CFD) and the Finite Element Method (FEM) implemented in the ABAQUS code. An accurate modelling of turbulent phenomena is made, based on both Implicit Large Eddy Simulation and the RANS-based Spalart-Allmaras model, followed by a co-simulation procedure in which the fluid dynamics and the structural analysis are carried out separately and interfaced with each other. Circular and elliptical cross sections are considered, each of them fitted for combined railway and motorway services. The analysis is carried out in both static and dynamic way, by varying the current velocity with a given value of the residual buoyancy of the tunnel. The results emphasize the effect of the main parameters investigated, evidencing the great potentials of the adopted calculation tool for carrying out further investigations aimed at achieving useful elements for the design and optimization of the SFT.
Vibration and dynamic stress caused by the interaction between the fluid and the structure can affect the reliability of pumps. This study presents an investigation of internal flow field and the structure response of...
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Vibration and dynamic stress caused by the interaction between the fluid and the structure can affect the reliability of pumps. This study presents an investigation of internal flow field and the structure response of residual heat removal pump using a combined calculation for turbulent flow, and the structure response of rotor was first defined using a two-way coupling method. For the calculation, the flow field is based on the shear stress transport k-v turbulence model and the structure response is determined using an elastic structural dynamic equation. The results show that the domain frequencies of pressure fluctuations of monitors on the outlet of impeller are the integer multiples of rotating shaft frequency (f(n)) and the amplitude of the relatively large pressure fluctuation peak is the lowest under the design flow rate operating condition. Meanwhile, the time-average radial force value at the design flow rate condition is the smallest and the hydraulic force magnitude at the maximum operating flow rate condition is the largest, and phase difference can be clearly seen among the results obtained under different flow rates. Furthermore, the relatively large stress of rotor for all operating conditions is the biggest at shaft shoulder where the bearing is installed, and it increases with flow rate.
The combined interface boundary condition (CIBC) method devises the increments to correct traditional interface conditions for partitioned computation of fluid-structure interaction. However, the restricted use of the...
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The combined interface boundary condition (CIBC) method devises the increments to correct traditional interface conditions for partitioned computation of fluid-structure interaction. However, the restricted use of the CIBC method has been realized recently. In this paper we present some improvements and extensions of the CIBC method as follows: (1) the method is reformulated in the general situation by using the complete fluid stress tensor;(2) the structural traction rate, which results in the inconsistency in the interfacial traction and may cause the loss of numerical accuracy, is totally removed from the CIBC formulation via a simple revision;(3) we analyze the instability source due to the CIBC compensation and propose an approach to recover the two-sided corrections for Dirichlet and Neumann interface conditions;(4) the CIBC method is extended to the generalized planar rigid-body motion. A novel CBS-based partitioned semi-implicit coupling approach is adopted to couple different fields within the nondimensional ALE finite element framework. The interaction between incompressible flows and a rigid/flexible body is numerically simulated to demonstrate the validity of the developed method. The reasonable agreement is disclosed between the present and available data. (C) 2015 Elsevier Ltd. All rights reserved.
This paper introduces a topology optimization approach that combines an explicit level set method (LSM) and the extended finite element method (XFEM) for designing the internal structural layout of fluid-structure int...
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This paper introduces a topology optimization approach that combines an explicit level set method (LSM) and the extended finite element method (XFEM) for designing the internal structural layout of fluid-structure interaction (FSI) problems. The FSI response is predicted by a monolithic solver that couples an incompressible Navier-Stokes flow model with a small-deformation solid model. The fluid mesh is modeled as an elastic continuum that deforms with the structure. The fluid model is discretized with stabilized finite elements and the structural model by a generalized formulation of the XFEM. The nodal parameters of the discretized level set field are defined as explicit functions of the optimization variables. The optimization problem is solved by a nonlinear programming method. The LSM-XFEM approach is studied for two- and three-dimensional FSI problems at steady-state and compared against a density topology optimization approach. The numerical examples illustrate that the LSM-XFEM approach convergences to well-defined geometries even on coarse meshes, regardless of the choice of objective and constraints. In contrast, the density method requires refined grids and a mass penalization to yield smooth and crisp designs. The numerical studies show that the LSM-XFEM approach can suffer from a discontinuous evolution of the design in the optimization process as thin structural members disconnect. This issue is caused by the interpolation of the level set field and the inability to represent particular geometric configurations in the XFEM model. While this deficiency is generic to the LSM-XFEM approach used here, it is pronounced by the nonlinear response of FSI problems.
A novel parallel monolithic algorithm has been developed for the numerical simulation of large-scale fluidstructureinteraction problems. The governing incompressible Navier-Stokes equations for the fluid domain are ...
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A novel parallel monolithic algorithm has been developed for the numerical simulation of large-scale fluidstructureinteraction problems. The governing incompressible Navier-Stokes equations for the fluid domain are discretized using the arbitrary Lagrangian-Eulerian formulation-based side-centered unstructured finite volume method. The deformation of the solid domain is governed by the constitutive laws for the nonlinear Saint Venant-Kirchhoff material, and the classical Galerkin finite element method is used to discretize the governing equations in a Lagrangian frame. A special attention is given to construct an algorithm with exact total fluid volume conservation while obeying both the global and the local discrete geometric conservation law. The resulting large-scale algebraic nonlinear equations are multiplied with an upper triangular right preconditioner that results in a scaled discrete Laplacian instead of a zero block in the original system. Then, a one-level restricted additive Schwarz preconditioner with a block-incomplete factorization within each partitioned sub-domains is utilized for the modified system. The accuracy and performance of the proposed algorithm are verified for the several benchmark problems including a pressure pulse in a flexible circular tube, a flag interacting with an incompressible viscous flow, and so on. John Wiley & Sons, Ltd.
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