In recent years, vulnerability against high-velocity impact loads has become an increasingly critical issue in the design of composite aerospace structures. The effects of Hydrodynamic Ram (HRAM), a phenomenon that oc...
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In recent years, vulnerability against high-velocity impact loads has become an increasingly critical issue in the design of composite aerospace structures. The effects of Hydrodynamic Ram (HRAM), a phenomenon that occurs when a high-energy object penetrates a fluid-filled container, are of particular concern in the design of wing fuel tanks for aircraft because it has been identified as one of the important factors in aircraft vulnerability. The projectile transfers its momentum and kinetic energy through the fluid to the surrounding structure, increasing the risk of catastrophic failure. In the present paper, the commercial finite-element code ABAQUS/Explicit has been used to simulate an HRAM event due to the impact of a steel spherical projectile into a water-filled woven CFRP square tube. In order to simulate the fluid-structure interaction, the Coupled Eulerian Lagrangian (CEL) approach is used. Experimental tests which indicate the pressure at different points of the fluid, strains of the walls and cavity evolution for different impact velocities are compared with the numerical results in order to assess the validity and accuracy of CEL technique in reproducing such a complex phenomenon. Also, several numerical impacts at different initial projectile velocities are performed to study its influence in the HRAM phenomenon. (C) 2012 Elsevier Ltd. All rights reserved.
The hybrid Cartesian/immersed boundary method is applied to fluid-structure interaction of a moving flexible foil. A new algorithm is suggested to classify immersed boundary nodes based oil edges crossing a boundary. ...
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The hybrid Cartesian/immersed boundary method is applied to fluid-structure interaction of a moving flexible foil. A new algorithm is suggested to classify immersed boundary nodes based oil edges crossing a boundary. Velocity vectors are reconstructed at the immersed boundary nodes by using the interpolation along a local normal line to the boundary. For eliminating pressure reconstruction, the hybrid staggered/non-staggered grid method is adapted. The deformation of an elastic body is modeled based on dynamic thin-plate theory, TO validate the developed code first, free rotation of a foil in a channel flow is simulated and the computed angular motion is compared with other computational results. The code is then applied to the fluid-structure interaction of a moving flexible foil which undergoes large deformation due to the fluid loading Caused by horizontal sinusoidal motion. It has been shown that the moving flexible foil call generate much larger vertical force than the corresponding rigid foil and the vertical force call be attributed to the downward fluid jet due to the alternating tail deflection.
A weak form and an implementation are given for fluid-structure interaction by the immersed/fictitious element method for compressible fluids. The weak form is applicable to models where the fluid is described by Eule...
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A weak form and an implementation are given for fluid-structure interaction by the immersed/fictitious element method for compressible fluids. The weak form is applicable to models where the fluid is described by Eulerian coordinates while the solid is described by Lagrangian coordinates, which suits their intrinsic characteristics. A unique feature of the method is the treatment of the fictitious fluid by a Lagrangian description, which simplifies the interface conditions. Methods for enforcing volumetric consistency between the fluid and solid and treating thin members are given. Although a compressible viscous fluid is considered here, the new developments can be applied to incompressible fluids. Copyright (C) 2007 John Wiley & Sons, Ltd.
The entry and exit of flexible bodies through an air-water interface is studied using a tightly coupled fluid-structure interaction solver. The fluid domain is modeled using finite-volume CFD and the flexible structur...
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The entry and exit of flexible bodies through an air-water interface is studied using a tightly coupled fluid-structure interaction solver. The fluid domain is modeled using finite-volume CFD and the flexible structure is represented by a modal basis. The current work uses finite elements to generate the structural mode shapes and frequencies. The modal description allows for a reduction in structural degrees of freedom to reduce computation time. A linearized boundary condition is used on the mutual interface to eliminate mesh deformation. The accuracy of the method is quantified using the constant-velocity-wedge-impact problem. The quality of the fluid solution for the entry and exit problem is evaluated using a rigid wedge case and comparison to Von Karman and Wagner theories. Finally, the response of an elastic wedge during entry and exit is studied with the fluid-structure interaction solver. The results are used to assess two common approximations, namely the rigid-quasi-static and rigid-dynamic approximations. It is shown that for entry and exit, hydroelastic effects may be important for a wide range of loading conditions. (c) 2012 Elsevier Ltd. All rights reserved.
This paper describes a coupling scheme for fluid-structure interaction (FSI) applications extended to high-density fluids. The scheme is based on the classical iterative partitioned approach (one solver per physics), ...
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This paper describes a coupling scheme for fluid-structure interaction (FSI) applications extended to high-density fluids. The scheme is based on the classical iterative partitioned approach (one solver per physics), an approach easy to implement, but which traditionally has only been used in aeroelasticity applications. As fluid density increases convergence is no longer ensured, being clearly dependent on the ratio between the total fluid mass and the mass of the structure. An approach based on the estimation of the added mass matrix is here presented in detail, and validated using the classical 1D problem of a piston in a cylinder. Results are shown for a cylinder moving in a moderate fluid flow, and the case of an elastic membrane allows conclusions to be drawn regarding the applicability of this approach to general FSI cases. (C) 2013 Elsevier Ltd. All rights reserved.
A finite point method for solving compressible flow problems involving moving boundaries and adaptivity is presented. The numerical methodology is based on an upwind-biased discretization of the Euler equations, writt...
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A finite point method for solving compressible flow problems involving moving boundaries and adaptivity is presented. The numerical methodology is based on an upwind-biased discretization of the Euler equations, written in arbitrary Lagrangian-Eulerian form and integrated in time by means of a dual-time steeping technique. In order to exploit the meshless potential of the method, a domain deformation approach based on the spring network analogy is implemented, and h-adaptivity is also employed in the computations. Typical movable boundary problems in transonic flow regime are solved to assess the performance of the proposed technique. In addition, an application to a fluid-structure interaction problem involving static aeroelasticity illustrates the capability of the method to deal with practical engineering analyses. The computational cost and multi-core performance of the proposed technique is also discussed through the examples provided. Copyright (c) 2013 John Wiley & Sons, Ltd.
A submerged evacuated circular cylindrical shell subjected to a sequence of two external shock waves generated at the same source is considered. A semi-analytical model combining the classical methods of mathematical ...
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A submerged evacuated circular cylindrical shell subjected to a sequence of two external shock waves generated at the same source is considered. A semi-analytical model combining the classical methods of mathematical physics with the finite-difference methodology is developed and employed to simulate the interaction. Both the hydrodynamic and structural aspects of the problem are considered, and it is demonstrated that varying the delay between the first and second wavefronts has a very significant effect on the stress-strain state of the structure. In particular, it is shown that for certain values of the delay, the constructive superposition of the elastic waves travelling around the shell results in a 'resonance-like' increase of the structural stress in certain regions. The respective stress can be so high that it sometimes exceeds the overall maximum stress observed in the same structure but subjected to a single-front shock wave with the same parameters, in some cases by as much as 50%. A detailed parametric analysis of the observed phenomenon is carried out, and an easy-to-use diagram summarizing the finding is proposed to aim the pre-design analysis of engineering structures. (C) 2013 Elsevier Ltd. All rights reserved.
Incompressible smoothed particle hydrodynamics generally requires particle distribution smoothing to give stable and accurate simulations with noise-free pressures. The diffusion-based smoothing algorithm of Lind et a...
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Incompressible smoothed particle hydrodynamics generally requires particle distribution smoothing to give stable and accurate simulations with noise-free pressures. The diffusion-based smoothing algorithm of Lind et al. (J. Comp. Phys. 231 (2012) 1499-1523) has proved effective for a range of impulsive flows and propagating waves. Here we apply this to body-water slam and wave-body impact problems and discover that temporal pressure noise can occur for these applications (while spatial noise is effectively eliminated). This is due to the free-surface treatment as a discontinuous boundary. Treating this as a continuous very thin boundary within the pressure solver is shown to effectively cure this problem. The particle smoothing algorithm is further generalised so that a non-dimensional diffusion coefficient is applied which suits a given time step and particle spacing. We model the particular problems of cylinder and wedge slam into still water. We also model wave-body impact by setting up undisturbed wave propagation within a periodic domain several wavelengths long and inserting the body. In this case, the loads become cyclic after one wave period and are in good agreement with experiment. This approach is more efficient than the conventional wave flume approach with a wavemaker which requires many wavelengths and a beach absorber. Results are accurate and virtually noise-free, spatially and temporally. Convergence is demonstrated. Although these test cases are two-dimensional with simple geometries, the approach is quite general and may be readily extended to three dimensions. (C) 2013 Elsevier B.V. All rights reserved.
The main purpose of this study is to reproduce in silico the dynamics of a bileaflet mechanical heart valve (MHV,- St Jude Hemodynamic Plus, 27 min characteristic size) by means of a fully implicit fluid-structure int...
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The main purpose of this study is to reproduce in silico the dynamics of a bileaflet mechanical heart valve (MHV,- St Jude Hemodynamic Plus, 27 min characteristic size) by means of a fully implicit fluid-structure interaction (FSI) method, and experimentally validate the results using an ultrafast cinematographic technique. The computational model was constructed to realistically reproduce the boundary condition (72 beats per minute (bprn), cardiac output 4.51/min) and the geometry of the experimental setup, including the valve housing and the hinge configuration. The simulation was carried out coupling a commercial computational fluid dynamics (CFD) package based on finite-volume method with user-defined code for solving the structural domain, and exploiting the parallel performance of the whole numerical setup. Outputs are leaflets excursion from opening to Closure and the fluid dynamics through the valve. Results put in evidence a favorable comparison between the computed and the experimental data: the model captures the main features of the leaflet motion during the systole. The use of parallel computing drastically limited the computational costs, showing a linear scaling on 16 processors (despite the massive use of user-defined subroutines to manage the FSI process). The favorable agreement obtained between in vitro and in silico results of the leaflet displacements confirms the consistency of the numerical method used, and candidates the application of FSI models to become a major tool to optimize the MHV design and eventually provides useful information to surgeons. (C) 2008 Elsevier Ltd. All rights reserved.
In this work an iterative strategy to implicitly couple dimensionally-heterogeneous blood flow models accounting for the continuity of mean total normal stress at interface boundaries is developed. Conservation of mea...
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In this work an iterative strategy to implicitly couple dimensionally-heterogeneous blood flow models accounting for the continuity of mean total normal stress at interface boundaries is developed. Conservation of mean total normal stress in the coupling of heterogeneous models is mandatory to satisfy energetic consistency between them. Nevertheless, existing methodologies are based on modifications of the Navier-Stokes variational formulation, which are undesired when dealing with fluid-structure interaction or black box codes. The proposed methodology makes possible to couple one-dimensional and three-dimensional fluid-structure interaction models, enforcing the continuity of mean total normal stress while just imposing flow rate data or even the classical Neumann boundary data to the models. This is accomplished by modifying an existing iterative algorithm, which is also able to account for the continuity of the vessel area, when required. Comparisons are performed to assess differences in the convergence properties of the algorithms when considering the continuity of mean normal stress and the continuity of mean total normal stress for a wide range of flow regimes. Finally, examples in the physiological regime are shown to evaluate the importance, or not, of considering the continuity of mean total normal stress in hemodynamics simulations. (C) 2013 Elsevier Inc. All rights reserved.
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