The long-time existence of a weak solution is proved for a nonlinear, fluid-structure interaction (FSI) problem between an incompressible, viscous fluid and a semilinear cylindrical Koiter membrane shell with inertia....
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The long-time existence of a weak solution is proved for a nonlinear, fluid-structure interaction (FSI) problem between an incompressible, viscous fluid and a semilinear cylindrical Koiter membrane shell with inertia. No axial symmetry is assumed in the problem. The fluid flow is driven by the time dependent dynamic pressure data prescribed at the inlet and outlet boundaries of the 3D cylindrical fluid domain. The fluid and the elastic structure are fully coupled via continuity of velocity and continuity of normal stresses. Global existence of a weak solution is proved as long as the lateral walls of the cylinder do not touch each other. The main novelty of the work is the nonlinearity in the structure model: the model accounts for the fully nonlinear Koiter membrane energy, supplemented with a small linear fourth-order derivative term modeling the bending rigidity of shells. The existence proof is constructive, and it is based on an operator splitting scheme. A version of this scheme can be implemented for the numerical simulation of the underlying FSI problem by extending the FSI solver, developed by the authors in [5], to include the nonlinearity in the structure model discussed in this manuscript.
This paper deals with numerical simulation of fluid-structure interaction as it occurs during aircraft ditching - an emergency condition where an aircraft is forced to land on water. The work is motivated by the requi...
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This paper deals with numerical simulation of fluid-structure interaction as it occurs during aircraft ditching - an emergency condition where an aircraft is forced to land on water. The work is motivated by the requirement for aircraft manufactures to analyze ditching as part of the aircraft certification process requested by airworthiness authorities. The strong interaction of highly non-linear fluid flow phenomena and structural responses requires a coupled solution of this transient problem. Therefore, an approach coupling Smoothed Particle Hydrodynamics and the Finite Element method within the commercial, explicit software Virtual Performance Solutions has been pursued. In this paper, several innovative features are presented, which allow for accurate and efficient solution. Finally, exemplary numerical results are successfully compared to experimental data from a unique test campaign of guided ditching tests at quasi-full scale impact conditions. It may be concluded that through the application of state-of-the-art numerical techniques it has become possible to simulate the coupled fluid-structure interaction as occurring during ditching. Therefore, aircraft manufacturers may significantly benefit from numerical analysis for design and certification purposes.
For solving the prediction problem of sound radiation from structures, both the structural and acoustical regions have to be researched. fluid-structure interaction incorporates the mutual influence of acoustical medi...
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ISBN:
(纸本)9781467399784
For solving the prediction problem of sound radiation from structures, both the structural and acoustical regions have to be researched. fluid-structure interaction incorporates the mutual influence of acoustical medium and structure. This interaction occurs at the coupling interface between the two adjacent domains. In case of thin structures and dense fluids, a strong coupling scheme between the two problems is essential, since the feedback of the acoustic pressure onto the structure is not negligible. In this paper, the structural part is modeled with the finite element (FE) method. An interface to the commercial finite element package ANSYS is set up to import the structural matrices of stiffness and mess. The exterior acoustic problem is efficiently modeled with the boundary element method, and the CHIEF method with internal nodes generated randomly is adopted to avoid non-uniqueness of solution. Classical BEM formulations suffer from fully populated matrices, leading to a restriction in both memory consumption and computing time. The fast multipole method are widely used for the acceleration of BEM, however, its dependency of kernels and order of elements caused difficulties on the implementation for engineering applications. Since the H-matrices techniques are robust and easy to implement, the adaptive cross approximation is adapted to overcome the well-known drawback of fully populated acoustical system matrices in boundary element method. Since decreases of convergence rate when frequency raises are observed in former researches on the iterative solvers for underwater vibro-acoustical problems, engineering application of FE-BE method is restricted by the absence of robustness in fast iterative solvers. Using the traditional directly coupled scheme, a new preconditioner is developed in this paper. With a group of iterative solvers implemented, the efficiency with respect to their memory consumption and computation time is compared for a simple model and a mo
In this work, we experimentally study the water entry of flexible cylinders. Experiments are performed in free fall and we explore variations of the entry velocity by varying the drop height. High speed imaging is uti...
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ISBN:
(纸本)9780735412873
In this work, we experimentally study the water entry of flexible cylinders. Experiments are performed in free fall and we explore variations of the entry velocity by varying the drop height. High speed imaging is utilized to study the fluid kinematics, the pile-up evolution, the cavity formation, and the overall structural deflection. The impact dynamics is analyzed through accelerometers, whereby fibre bragg gratings (FBG) measure the punctual deformation at characteristic locations on the cylinder surface. A modal decomposition approach is utilized to reconstruct the overall structural deflection from the punctual strain measurements. The proposed reconstruction methodology is compared against high-speed images. Results show that during the water entry the cylinder mainly deforms in the direction of the hydrodynamic loading, whereby marked vibrations whose amplitude increase with the entry velocity dominate the dynamic response.
Sensitivity analysis of fluid-structure interaction (FSI) provides an important tool for assessing the reliability and performance of coastal infrastructure subjected to storm and tsunami hazards. As a preliminary ste...
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Sensitivity analysis of fluid-structure interaction (FSI) provides an important tool for assessing the reliability and performance of coastal infrastructure subjected to storm and tsunami hazards. As a preliminary step for gradient-based applications in reliability, optimization, system identification, and performance-based engineering of coastal infrastructure, the direct differentiation method (DDM) is applied to FSI simulations using the particle finite-element method (PFEM). The DDM computes derivatives of FSI response with respect to uncertain design and modeling parameters of the structural and fluid domains that are solved in a monolithic system via the PFEM. Geometric nonlinearity of the free surface fluid flow is considered in the governing equations of the DDM along with sensitivity of material and geometric nonlinear response in the structural domain. The analytical derivatives of elemental matrices and vectors with respect to element properties are evaluated and implemented in an open source finite element software framework. Examples involving both hydrostatic and hydrodynamic loading show that the sensitivity of nodal displacements, pressures, and forces computed by the finite-difference method (FDM) converge to the DDM for simple beam models as well as for a reinforced-concrete frame structure. (C) 2015 American Society of Civil Engineers.
In this study, the flow field and impeller structure response in the mixed-flow pump are cooperative solved based on the bidirectional synchronization solving method, to study the vibration characteristics of the mixe...
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In this study, the flow field and impeller structure response in the mixed-flow pump are cooperative solved based on the bidirectional synchronization solving method, to study the vibration characteristics of the mixed-flow pump impeller rotor under the fluid-structure interaction. The pressure distributions of blade surface in the mixed-flow pump under different flow rate conditions were compared, and the deformation, equivalent stress distribution and natural vibration frequency of impeller blade under static force load were studied. Meanwhile, the deformation of impeller blade and coupling stress distribution was analyzed based on bidirectional fluid-structure interaction. The results show that the deformation of impeller blade increases from hub to rim, and the maximum deformation occurs at the rim of the blade. The stress distribution of impeller blade in the circumferential direction is symmetrical, and the maximum equivalent stress occurs at the blade outlet edge near the hub. The maximum deformation position and the stress concentration location are basically consistent before and after coupling calculation, but the maximum deformation value increases and the maximum equivalent stress value decreases under the fluid-structure interaction. The influence of water pressure on the strength and frequency of vibration is very limited. With the increase of flow rate, the maximum equivalent stress of impeller decreases and the total deformation increases gradually. The results of this research provide reference basis for the structure design and reliability analysis of the mixed-flow pump.
In this paper, we study the fluid-structure interaction in a weakened basilar artery. The aim is to study how the wall shear stress changes in space and time because of the weakening, because spatial and temporal chan...
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In this paper, we study the fluid-structure interaction in a weakened basilar artery. The aim is to study how the wall shear stress changes in space and time because of the weakening, because spatial and temporal changes are thought to be possible causes of aneurysm and vascular deseases. The arterial wall, in its natural configuration, is modeled as a hyperelastic cylinder, inhomogeneous along its axis, in order to simulate the axis-symmetric weakening. The fluid is studied exploiting a recent approach for quasi-one-dimensional flows in slowly varying ducts, which allows to write the averaged equations of mass and energy balance on the basis of the velocity profile in a straight duct. The unknowns are the wall pressure, the average velocity, and the wall radial displacement. The problem is solved in two parts: first, the stationary non-linear coupled problem is solved, and an intermediate configuration is obtained. Then, we study the variation of the basic unknowns about the intermediate configuration, considering time dependence over the cardiac cycles. The results suggest that, with a 10% reduction of the main elastic modulus, the shear stress in the weakened zone changes its sign and doubles the maximum stress value detected in the healthy zone. Copyright (c) 2015 John Wiley & Sons, Ltd.
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.
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