We have developed a fluid-structure interaction (FSI) procedure to investigate large-scale ocean current turbine blades by combining blade element momentum theory and finite element method. FSI procedure included chan...
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We have developed a fluid-structure interaction (FSI) procedure to investigate large-scale ocean current turbine blades by combining blade element momentum theory and finite element method. FSI procedure included changes in inflow velocity, lift coefficient and drag coefficient of blade elements. Geometric non-linearity was also considered. Three case studies were investigated to visualise effects of FSI to predict blade deflection and turbine's performance. It was observed that at an inflow velocity of 5 m/s, the flap-wise tip deflection decreased by 10% due to inclusion of FSI. This decrease was mostly due to change in lift and drag coefficients. Power coefficients were also calculated for both rigid and deformed blades. It was observed that power coefficient decreased by 2% due to blade deflection. For validation, a comparison of pressure coefficients along the chord length was made with published literature and a good correlation was observed.
The newly developed node-based partly smoothed point interpolation method (NPS-PIM) and immersed technique are coupled to simulate fluid -structureinteraction (FSI) problems associated with largely deformable solid/s...
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The newly developed node-based partly smoothed point interpolation method (NPS-PIM) and immersed technique are coupled to simulate fluid -structureinteraction (FSI) problems associated with largely deformable solid/structure. Under the framework of immersed method, the governing equations can be decomposed into three components based on fictitious fluid assumption, i.e. equations for incompressible viscous fluid, FSI conditions and nonlinear solid. The semi-implicit characteristic-based split algorithm is used to solve the Navier-Stokes equation of incompressible viscous fluid, and the fictitious fluid domain can be used to calculate the FSI force. Owing to the properly softened stiffness by the node-based partly strain smoothing operation, NPS-PIM can effectively solve the large deformation problem of solids discretized with the simplest linear triangular mesh. The immersed framework makes the present method avoid the troublesome re-meshing process and the triangular mesh further simplifies the preprocessing operation. In comparison with the models using FEM and node-based smoothed point interpolation method (NS-PIM) as solid solver, numerical results have shown that the present method using NPS-PIM can provide more accurate solutions for both steady and transient problems with regard to large-displacement FSI problems.
A parallel fully coupled (monolithic) fluid-structure interaction (FSI) algorithm has been applied to the deformation of red blood cells (RBCs) in capillaries, where cell deformability has significant effects on blood...
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A parallel fully coupled (monolithic) fluid-structure interaction (FSI) algorithm has been applied to the deformation of red blood cells (RBCs) in capillaries, where cell deformability has significant effects on blood rheology. In the present FSI algorithm, fluid domain is discretized using the side-centered unstructured finite volume method based on the Arbitrary Lagrangian-Eulerian (ALE) formulation;meanwhile, solid domain is discretized with the classical Galerkin finite element formulation for the Saint Venant-Kirchhoff material in a Lagrangian frame. In addition, the compatible kinematic boundary condition is enforced at the fluid-solid interface in order to conserve the mass of cytoplasmic fluid within the red cell at machine precision. In order to solve the resulting large-scale algebraic linear systems in a fully coupled manner, a new matrix factorization is introduced similar to that of the projection method, and the parallel algebraic multigrid solver BoomerAMG is used for the scaled discrete Laplacian provided by the HYPRE library, which we access through the PETSc library. Three important physical parameters for the blood flow are simulated and analyzed: (1) the effect of capillary diameter, (2) the effect of red cell membrane thickness, and (3) the effect of red cell spacing (hematocrit). The numerical calculations initially indicate a shape deformation in which biconcave discoid shape changes to a parachute-like shape. Furthermore, the parachute-like cell shape in small capillaries undergoes a cupcake-shaped buckling instability, which has not been observed in the literature. The instability forms thin riblike features, and the red cell deformation is not axisymmetric but three-dimensional.
A vibration excitation system has been developed to excite the rotor blades of an axial compressor, in the specified nodal diameter mode and at the specified frequency, by injecting additional compressed air into the ...
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A vibration excitation system has been developed to excite the rotor blades of an axial compressor, in the specified nodal diameter mode and at the specified frequency, by injecting additional compressed air into the compressor flow path. The system was fitted to the Rofanco compressor test bench at the University of Stellenbosch in South Africa. A two-way staggered fluid-structure interaction (FSI) model was constructed that was capable of simulating the vibrations of the rotor blades excited by the vibration excitation system. The results of the FSI simulations were verified using available experimental data. It was concluded that the FSI model is able to recreate the vibrations of the rotor blades with sufficient accuracy. The results of the FSI simulations also indicated that the vibration excitation system should be capable of exciting the blades in the selected mode shape and at the selected frequency, provided the excitation frequency is close to the natural frequency of the first bending mode of each rotor blade.
Heart failure is a progressive and often fatal pathology among the main causes of death in the world. An implantable total artificial heart (TAH) is an alternative to heart transplantation. Blood damage quantification...
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Heart failure is a progressive and often fatal pathology among the main causes of death in the world. An implantable total artificial heart (TAH) is an alternative to heart transplantation. Blood damage quantification is imperative to assess the behavior of an artificial ventricle and is strictly related to the hemodynamics, which can be investigated through numerical simulations. The aim of this study is to develop a computational model that can accurately reproduce the hemodynamics inside the left pumping chamber of an existing TAH (Carmat-TAH) together with the displacement of the leaflets of the biological aortic and mitral valves and the displacement of the pericardium-made membrane. The proposed modeling workflow combines fluid-structure interaction (FSI) simulations based on a fixed grid method with computational fluid dynamics (CFD). In particular, the kinematics of the valves is accounted for by means of a dynamic mesh technique in the CFD. The comparison between FSI- and CFD-calculated velocity fields confirmed that the presence of the valves in the CFD model is essential for realistically mimicking blood dynamics, with a percentage difference of 2% during systole phase and 13% during the diastole. The percentage of blood volume in the CFD simulation with a shear stress above the threshold of 50 Pa is less than 0.001%. In conclusion, the application of this workflow to the Carmat-TAH provided consistent results with previous clinical studies demonstrating its utility in calculating local hemodynamic quantities in the presence of complex moving boundaries.
We consider a fluid-structure interaction problem consisting of the time-dependent Stokes equations in the fluid domain coupled with the equations of linear elastodynamics in the solid domain. For simplicity, all chan...
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We consider a fluid-structure interaction problem consisting of the time-dependent Stokes equations in the fluid domain coupled with the equations of linear elastodynamics in the solid domain. For simplicity, all changes of geometry are neglected. We propose a new method in terms of the fluid velocity, the fluid pressure, the structural velocity and the Cauchy stress tensor. We show that the new weak formulation is well-posed. Then, we propose a new semidiscrete problem where the velocities and the fluid pressure are approximated using a stable pair for the Stokes problem in the fluid domain and compatible finite elements in the solid domain. We obtain a priori estimates for the solution of the semidiscrete problem, prove the convergence of these solutions to the solution of the weak formulation and obtain error estimates. A time discretization based on the backward Euler method leads to a fully discrete scheme in which the computation of the approximated Cauchy stress tensor can be decoupled from that of the remaining unknowns at each time step. The displacements in the structure (if needed) can be recovered by quadrature. Finally, some numerical experiments showing the performance of the method are provided. (C) 2017 IMACS. Published by Elsevier B.V. All rights reserved.
Generally, when a model is made of the same material as the prototype in shaking table tests, the equivalent material density of the scaled model is greater than that of the prototype because mass is added to the mode...
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Generally, when a model is made of the same material as the prototype in shaking table tests, the equivalent material density of the scaled model is greater than that of the prototype because mass is added to the model to satisfy similitude criteria. When the water environment is modeled in underwater shaking table tests, however, it is difficult to change the density of water. The differences in the density similitude ratios of specimen materials and water can affect the similitude ratios of the hydrodynamic and wave forces with those of other forces. To solve this problem, a coordinative similitude law is proposed for underwater shaking table tests by adjusting the width of the upstream face of the model or the wave height in the model test to match the similitude ratios of hydrodynamic and wave forces with those of other forces. The designs of the similitude relations were investigated for earthquake excitation, wave excitation, and combined earthquake and wave excitation conditions. Series of numerical simulations and underwater shaking table tests were performed to validate the proposed coordinative similitude law through a comparison of coordinative model and conventional model designed based on the coordinative similitude law and traditional artificial mass simulation, respectively. The results show that the relative error was less than 10% for the coordinative model, whereas it reached 80% for the conventional model. The coordinative similitude law can better reproduce the dynamic responses of the prototype, and thus, this similitude law can be used in underwater shaking table tests.
In this paper, we develop a new mass conservative numerical scheme for the simulations of a class of fluid-structure interaction problems. We will use the immersed boundary method to model the fluid-structure interact...
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In this paper, we develop a new mass conservative numerical scheme for the simulations of a class of fluid-structure interaction problems. We will use the immersed boundary method to model the fluid-structure interaction, while the fluid flow is governed by the incompressible Navier-Stokes equations. The immersed boundary method is proven to be a successful scheme to model fluid-structure interactions. To ensure mass conservation, we will use the staggered discontinuous Galerkin method to discretize the incompressible Navier-Stokes equations. The staggered discontinuous Galerkin method is able to preserve the skew-symmetry of the convection term. In addition, by using a local postprocessing technique, the weakly divergence free velocity can be used to compute a new postprocessed velocity, which is exactly divergence free and has a superconvergence property. This strongly divergence free velocity field is the key to the mass conservation. Furthermore, energy stability is improved by the skew-symmetric discretization of the convection term. We will present several numerical results to show the performance of the method.
In this paper, we consider a monolithic approach to handle coupled fluid-structure interaction problems with different hyperelastic models in an all-at-once manner. We apply Newton's method in the outer iteration ...
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In this paper, we consider a monolithic approach to handle coupled fluid-structure interaction problems with different hyperelastic models in an all-at-once manner. We apply Newton's method in the outer iteration dealing with nonlinearities of the coupled system. We discuss preconditioned Krylov sub-space, algebraic multigrid and algebraic multilevel methods for solving the linearized algebraic equations. Finally, we compare the results of the monolithic approach with those of the corresponding partitioned approach that was studied in our previous work. (C) 2016 International Association for Mathematics and Computers in Simulation (IMACS). Published by Elsevier B.V. All rights reserved.
fluid-structure interaction (FSI) problems are computationally very challenging. In this paper we consider the monolithic approach for solving the fully coupled FSI problem. Most existing techniques, such as multigrid...
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fluid-structure interaction (FSI) problems are computationally very challenging. In this paper we consider the monolithic approach for solving the fully coupled FSI problem. Most existing techniques, such as multigrid methods, do not work well for the coupled system since the system consists of elliptic, parabolic and hyperbolic components all together. Other approaches based on direct solvers do not scale to large numbers of processors. In this paper, we introduce a multilevel unstructured mesh Schwarz preconditioned Newton-Krylov method for the implicitly discretized, fully coupled system of partial differential equations consisting of incompressible Navier-Stokes equations for the fluid flows and the linear elasticity equation for the structure. Several meshes are required to make the solution algorithm scalable. This includes a fine mesh to guarantee the solution accuracy, and a few isogeometric coarse meshes to speed up the convergence. Special attention is paid when constructing and partitioning the preconditioning meshes so that the communication cost is minimized when the number of processor cores is large. We show numerically that the proposed algorithm is highly scalable in terms of the number of iterations and the total compute time on a supercomputer with more than 10,000 processor cores for monolithically coupled three-dimensional FSI problems with hundreds of millions of unknowns.
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