An immersed-body method is developed here to model fluid-structure interaction for multiphase viscous flows. It does this by coupling a finite element multiphase fluid model and a combined finite-discrete element soli...
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An immersed-body method is developed here to model fluid-structure interaction for multiphase viscous flows. It does this by coupling a finite element multiphase fluid model and a combined finite-discrete element solid model. A coupling term containing the fluid stresses is introduced within a thin shell mesh surrounding the solid surface. The thin shell mesh acts as a numerical delta function in order to help apply the solid-fluid boundary conditions. When used with an advanced interface capturing method, the immersed-body method has the capability to solve problems with fluid-solid interfaces in the presence of multiphase fluid-fluid interfaces. Importantly, the solid-fluid coupling terms are treated implicitly to enable larger time steps to be used. This two-way coupling method has been validated by three numerical test cases: a free falling cylinder in a fluid at rest, elastic membrane and a collapsing column of water moving an initially stationary solid square. A fourth simulation example is of a water-air interface with a floating solid square being moved around by complex hydrodynamic flows including wave breaking. The results show that the immersed-body method is an effective approach for two-way solid-fluid coupling in multiphase viscous flows. (C) 2016 Elsevier Inc. All rights reserved.
作者：
Wick, ThomasAustrian Acad Sci
Johann Radon Inst Computat & Appl Math RICAM Altenberger Str 69 A-4040 Linz Austria
In this work, a concept for coupling fluid-structure interaction with brittle fracture in elasticity is proposed. The fluid-structure interaction problem is modeled in terms of the arbitrary Lagrangian-Eulerian techni...
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In this work, a concept for coupling fluid-structure interaction with brittle fracture in elasticity is proposed. The fluid-structure interaction problem is modeled in terms of the arbitrary Lagrangian-Eulerian technique and couples the isothermal, incompressible Navier-Stokes equations with nonlinear elastodynamics using the Saint-Venant Kirchhoff solid model. The brittle fracture model is based on a phase-field approach for cracks in elasticity and pressurized elastic solids. In order to derive a common framework, the phase-field approach is re-formulated in Lagrangian coordinates to combine it with fluidstructureinteraction. A crack irreversibility condition, that is mathematically characterized as an inequality constraint in time, is enforced with the help of an augmented Lagrangian iteration. The resulting problem is highly nonlinear and solved with a modified Newton method (e.g., error-oriented) that specifically allows for a temporary increase of the residuals. The proposed framework is substantiated with several numerical tests. In these examples, computational stability in space and time is shown for several goal functionals, which demonstrates reliability of numerical modeling and algorithmic techniques. But also current limitations such as the necessity of using solid damping are addressed. (C) 2016 Elsevier Inc. All rights reserved.
In this paper we present a novel semi-implicit time-discretization of the level set method introduced in [8] for fluid-structure interaction problems. The idea stems from a linear stability analysis derived on a simpl...
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In this paper we present a novel semi-implicit time-discretization of the level set method introduced in [8] for fluid-structure interaction problems. The idea stems from a linear stability analysis derived on a simplified one-dimensional problem. The semi-implicit scheme relies on a simple filter operating as a pre-processing on the level set function. It applies to multiphase flows driven by surface tension as well as to fluid-structure interaction problems. The semi-implicit scheme avoids the stability constraints that explicit scheme need to satisfy and reduces significantly the computational cost. It is validated through comparisons with the original explicit scheme and refinement studies on two-dimensional benchmarks. (C) 2016 Elsevier Inc. All rights reserved.
In this work we analyze the stability and convergence properties of a loosely-coupled scheme, called the kinematically coupled scheme, and its extensions for the interaction between an incompressible, viscous fluid an...
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In this work we analyze the stability and convergence properties of a loosely-coupled scheme, called the kinematically coupled scheme, and its extensions for the interaction between an incompressible, viscous fluid and a thin, elastic structure. We consider a benchmark problem where the structure is modeled using a general thin structure model, and the coupling between the fluid and structure is linear. We derive the energy estimates associated with the unconditional stability of an extension of the kinematically coupled scheme, called the beta-scheme. Furthermore, for the first time we present a priori estimates showing optimal, first-order in time convergence in the case where beta-1. We further discuss the extensions of our results to other fluid-structure interaction problems, in particular the fluid-thick structureinteraction problem. The theoretical stability and convergence results are supported with numerical examples.
The Quasi-Newton Inverse Least Squares method has become a popular method to solve partitioned interaction problems. Its performance can be enhanced by using information from previous time-steps if care is taken of th...
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The Quasi-Newton Inverse Least Squares method has become a popular method to solve partitioned interaction problems. Its performance can be enhanced by using information from previous time-steps if care is taken of the possible ill-conditioning that results. To enhance the stability, filtering has been used. In this paper we show that a relatively minor modification to the filtering technique can substantially reduce the required number of iterations. (C) 2016 Elsevier Ltd. All rights reserved.
Vibrational analysis of the complex structure of reactor internals using the finite element method leads to considerable computational expense. Additionally, fluid-structure interaction (FSI) effects due to liquid coo...
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Vibrational analysis of the complex structure of reactor internals using the finite element method leads to considerable computational expense. Additionally, fluid-structure interaction (FSI) effects due to liquid coolant result in a large number of fluid elements. Here, we describe a model reduction method based on Guyan theory to solve these complex numerical problems efficiently. The master degrees of freedom selection process, which is based on the shapes of vibrational modes, is discussed. We consider the structural characteristics of the cylindrical parts of the reactor, and include FSI effects. To verify the model reduction method, several numerical examples of simple cylindrical shells are described with and without the coolant. Practical application to the internals of an advanced pressurized reactor 1400 (APR1400) is discussed with various different conditions.
We present a loosely coupled approach for the solution of fluid-structure interaction problems between a compressible flow and a deformable structure. The method is based on staggered Dirichlet-Neumann partitioning. T...
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We present a loosely coupled approach for the solution of fluid-structure interaction problems between a compressible flow and a deformable structure. The method is based on staggered Dirichlet-Neumann partitioning. The interface motion in the Eulerian frame is accounted for by a conservative cut-cell Immersed Boundary method. The present approach enables sub-cell resolution by considering individual cut-elements within a single fluid cell, which guarantees an accurate representation of the time-varying solid interface. The cut-cell procedure inevitably leads to non-matching interfaces, demanding for a special treatment. A Mortar method is chosen in order to obtain a conservative and consistent load transfer. We validate our method by investigating two-dimensional test cases comprising a shock-loaded rigid cylinder and a deformable panel. Moreover, the aeroelastic instability of a thin plate structure is studied with a focus on the prediction of flutter onset. Finally, we propose a three-dimensional fluid-structure interaction test case of a flexible inflated thin shell interacting with a shock wave involving large and complex structural deformations. (C) 2015 Elsevier Inc. All rights reserved.
Cyclic loading tests were conducted for quasi-isotopically laminated glass fiber composite beams in air and water, respectively, to analyze their structural behavior and failure under fluid-structure interaction (FSI)...
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Cyclic loading tests were conducted for quasi-isotopically laminated glass fiber composite beams in air and water, respectively, to analyze their structural behavior and failure under fluid-structure interaction (FSI). Experimental results showed a significant FSI effect on fatigue failure of the composites under frequency loading of 10 and 5 Hz. The FSI reduced the fatigue life cycles by approximately 50% at those cyclic loads. While the experiments were undertaken using the displacement-controlled mode, a computational study was also performed using the force-controlled mode to complement the experimental study as well as to provide enhanced understanding of the FSI effect on composites under cyclic loading. The knowledge gained from this study would contribute to the development of future life cycle prediction tools that would help to prevent premature failures of a composite structure in contact with water and subjected to cyclic loading.
Recent advance in flapping-wing MAVs has led to greater attention being paid to the interaction between the structural dynamics of the wing and its aerodynamics, both of which are closely related to the performance of...
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Recent advance in flapping-wing MAVs has led to greater attention being paid to the interaction between the structural dynamics of the wing and its aerodynamics, both of which are closely related to the performance of a flapping wing. In this paper, an improved computational framework to simulate a flapping wing is developed. This framework is established by coupling a preconditioned Navier-Stokes solution and a co-rotational beam analysis with a restrained warping degree of freedom. Validation of the present framework is performed by a comparison with examples from either earlier analyses or experiments. Further, a numerical analysis of a wing under simultaneous pitching and plunging motion is examined. The results are compared with those obtained with a wing under pure plunging motion, in order to assess the additional motion effect within a spanwise flexible wing. The comparison shows different aerodynamic characteristics induced by the flexibility of the wing, which can be beneficial.
This paper is devoted to the convergence analysis of the generalized Robin-Neumann schemes introduced in Fernandez et al. (2015, Generalized Robin-Neumann explicit coupling schemes for incompressible fluid-structure i...
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This paper is devoted to the convergence analysis of the generalized Robin-Neumann schemes introduced in Fernandez et al. (2015, Generalized Robin-Neumann explicit coupling schemes for incompressible fluid-structure interaction: stability analysis and numerics. Internat. J. Numer. Methods Engrg., 101, 199-229) for the coupling of a viscous incompressible fluid with a thick-walled elastic or viscoelastic structure. To this purpose, a representative linearized setting is considered. The methods are formulated within a class of operator splitting schemes which treat implicitly the coupling between the fluid and the solid inertia contributions. This guarantees energy stability. A priori error estimates are derived for all the explicit and semi-implicit variants. The analysis predicts a nonuniformity in space of the splitting error, hence confirming the numerical evidence of Fernandez et al. (2015, Generalized Robin-Neumann explicit coupling schemes for incompressible fluid-structure interaction: stability analysis and numerics. Internat. J. Numer. Methods Engrg., 101, 199-229) for the explicit variants. Besides, the analysis demonstrates that the genesis of this accuracy loss is the spatial nonuniformity of the discrete elastic or viscoelastic solid operator. The theoretical findings are illustrated via a numerical study which shows, in particular, that alternative splitting schemes recently reported in the literature also suffer from these accuracy issues.
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