1,721,043 research outputs found
Harmonic oscillations of laminae in non-Newtonian fluids: a lattice Boltzmann-immersed boundary approach
No full textIn this paper, the fluid dynamics induced by a rigid lamina undergoing harmonic oscillations in a non-Newtonian calm fluid is investigated. The fluid is modelled through the lattice Boltzmann method and the flow is assumed to be nearly incompressible. An iterative viscosity-correction based procedure is proposed to properly account for the non-Newtonian fluid feature and its accuracy is evaluated. In order to handle the mutual interaction between the lamina and the encompassing fluid, the Immersed Boundary method is adopted. A numerical campaign is performed. In particular, the effect of the non-Newtonian feature is highlighted by investigating the fluid forces acting on a harmonically oscillating lamina for different values of the Reynolds number. The findings prove that the non-Newtonian feature can drastically influence the behaviour of the fluid and, as a consequence, the forces acting upon the lamina. Several considerations are carried out on the time history of the drag coefficient and the results are used to compute the added mass through the hydrodynamic function. Moreover, the computational cost involved in the numerical simulations is discussed. Finally, two applications concerning water resources are investigated: the flow through an obstructed channel and the particle sedimentation. Present findings highlight a strong coupling between the body shape, the Reynolds number, and the flow behaviour inde
A lattice Boltzmann model for multiphase flows interacting with deformable bodies
No full textIn this paper, a numerical model to simulate a multiphase flow interacting with deformable solid bodies is proposed. The fluid domain is modeled through the lattice Boltzmann method and the Shan-Chen model is adopted to handle the multiphase feature. The interaction of the flow with immersed solid bodies is accounted for by using the Immersed Boundary method. Corotational beam finite elements are used to model the deformable bodies and non-linear structure dynamics is predicted through the Time Discontinuous Galerkin method. A numerical campaign is carried out in order to assess the effectiveness and accuracy of the proposed modeling by involving different scenarios. In particular, the model is validated by performing the bubble test and by comparing present results with the ones from a numerical commercial software. Moreover, the properties in terms of convergence are discussed. In addition, the effectiveness of the proposed methodology is evaluated by computing the error in terms of the energy that is artificially introduced in the system at the fluid-solid interface. Present findings show that the proposed approach is robust, accurate and suitable of being applied to a lot of practical applications involving the interaction between multiphase flows and deformable solid bodies
Lattice Boltzmann modelling of bacterial colony patterns
Full text linkThe formation of branches in bacterial colonies is influenced by both chemical interactions (reactions) and the movement of substances through space (diffusion). These colonies can exhibit a variety of fascinating branching patterns due to the interplay of nutrient transport, bacterial growth, and chemotaxis. To understand this complex process, researchers have developed several mathematical models based on solving reaction-diffusion equations. In this letter, we introduce an innovative application of the lattice Boltzmann method to investigate the diverse morphological patterns observed in bacterial colonies. This method is concise, compact, and easy to implement. Our study demonstrates its effectiveness in accurately predicting various types of bacterial colony patterns, offering a new tool to obtain insights into the dynamics of bacterial growth andpattern formation
Ground-induced lift enhancement in a tandem of symmetric flapping wings:Lattice Boltzmann-immersed boundary simulations
No full textThe behavior of a tandem of symmetric flapping wings immersed in a quiescent viscous fluid is numerically dissected. The attention focuses on the effect on the flight performance of a solid surface which idealizes the presence of the ground. A wide numerical campaign is carried out. The author demonstrates that the presence of a solid surface can drastically modify the lift force, thus giving a remarkable advantage for the vertical take-off. Therefore, a proper governing parameter is proposed, which accounts for the ratio between the initial gap from the solid surface and the length of the wing.</p
Non-linear flow-induced vibrations in deformable curved bodies: A lattice Boltzmann-immersed boundary-finite element study
No full textThe dynamic response of a deformable curved
solid body is investigated as it interacts with a flow field.
The fluid is assumed to be viscous and the flow is nearly
incompressible. Fluid dynamics is predicted through a
lattice Boltzmann solver. Corotational beam finite elements
undergoing large displacements are adopted to idealize
the submerged body, whose presence in the lattice
fluid background is handled by the immersed boundary
method. The attention focuses on the solid’s deformation
and a numerical campaign is carried out. Findings are reported
in terms of deformation energy and deformed configuration.
On the one hand, it is shown that the solution
of the problem is strictly dependent on the elastic properties
of the body. On the other hand, the encompassing
flow physics plays a crucial role on the resultant solid dynamics.
With respect to the existing literature, the present
problem is attacked by a new point of view. Specifically,
the author proposes that the problem is governed by four
dimensionless parameters: the Reynolds number, the normalized
elastic modulus, the density and aspect ratii. The
formulation and the solution strategy for curved solid bodies
herein adopted are introduced for the first time in this
paper
On the dynamics of a tandem of asynchronous flapping wings: Lattice Boltzmann-immersed boundary simulations
No full textIn this paper, the flight performance of a tandem of symmetric flapping wings immersed in a viscous fluid is investigated. A harmonic motion is imposed to the wings which can travel only in the vertical direction. Specifically, the attention focuses on the role of the initial phase difference. The fluid domain is modeled through the lattice Boltzmann method. In order to account for the presence of the wings immersed in the lattice fluid background, the immersed boundary method is adopted. Once fluid forces acting upon the wings are computed, their position is updated by solving the equation of solid motion by the time discontinuous Galerkin method according to a strategy already validated by the author. A wide numerical campaign is carried out by varying the initial phase difference. Moreover, scenarios accounting for the presence of a lateral wind gust are shown. The flight conditions and performance are discussed for a wide set of configurations and compared with an in-sync configuration, showing that the wind gust reduces the performance in certain scenario
Aeroelastic study of flexible flapping wings by a coupled lattice Boltzmann-finite element approach with immersed boundary method
No full textIn this paper, the behavior of two-dimensional symmetric flapping wings moving in a viscous fluid is investigated. Harmonic motion is applied to idealize flying organisms with flexible wings and extensive testing is carried out to investigate the resultant flight behavior related to the ability to take-off or accelerate the flapping wing system away from a starting location. Special attention is paid to analyze the effect of the main mechanical parameters, as well as the effect of lateral wind on flight performances. Moreover, aiming to investigate the possible benefits of flying in flocks, a couple of synchronously flapping wings is considered in addition to the single arrangement. The numerical simulations are performed by solving the fluid-structure interaction problem through a strongly coupled partitioned approach. Fluid dynamics are modeled at the mesoscopic scale by the lattice Boltzmann method. The resulting macroscopic quantities are derived, as usual, based on the statistical molecular-level interpretation
Lattice Boltzmann simulations of flapping wings: the flock effect and the lateral wind effect
No full textIn this paper, numerical analysis aiming at simulating biological organisms immersed in a fluid are carried out. The fluid domain is modeled through the lattice Boltzmann (LB) method, while the immersed boundary method is used to account for the position of the organisms idealized as rigid bodies. The time discontinuous Galerkin method is employed to compute body motion. An explicit coupling strategy to combine the adopted numerical methods is proposed. The vertical take-off of a couple of butterflies is numerically simulated in different scenarios, showing the mutual interaction that a butterfly exerts on the other one. Moreover, the effect of lateral wind is investigated. A critical threshold value of the lateral wind is defined, thus corresponding to an increasing arduous take-off
Performance estimation of linear algebra numerical libraries
No full textInternational audienceIn this work, numerical algebraic operations are performed by using several libraries whose algorithm are optimized to drain resources from hardware architecture. In particular, dot product of two vectors and the matrix-matrix product of two dense matrices are computed. In addition, the Cholesky decomposition on a real, symmetric, and positive definite matrix is performed through routines for band and sparse matrix storage. The involved CPU time is used as an indicator of the performance of the employed numerical tool. Results are compared to naive implementations of the same numerical algorithm, highlighting the speed-up due to the usage of optimized routines
ANALYSIS OF BLOOD FLOW IN DEFORMABLE VESSELS VIA A LATTICE BOLTZMANN APPROACH
No full textIn this paper, the lattice Boltzmann (LB) method is used in order to simulate non-Newtonian blood flows in deformable vessels. Casson's rheological model is adopted and a local correction to the relaxation time is implemented in order to modify the viscosity. The hyperelastic, hardening and anisotropic behavior of a flexible arterial wall is discussed and a closed-form solution is used to predict the deformed configuration of the vessel. A partitioned staggered-explicit strategy to couple the LB method and such analytical prediction is proposed
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