Parallel Algorithms for Using Lagrangian Markers in Immersed Boundary Method with Adaptive Mesh Refinement in FLASH

The Svenning, E. Mark, A. Edelvik, F. Fluid structure interaction Immersed boundary methods Sloshing tank FSI benchmark aim of this paper is to present and validate a modeling framework that can be used for simulation of industrial applications involving fluid structure interaction with large deformations. Fluid structure interaction phenomena involving elastic structures frequently occur in industrial applications such as rubber bushings filled with oil, the filling of liquid in a paperboard package or a fiber suspension flowing through a paper machine. Simulations of such phenomena are challenging due to the strong coupling between the fluid and the elastic structure. In the literature, this coupling is often achieved with an Arbitrary Lagrangian Eulerian framework or with smooth particle hydrodynamics methods. In the present work, an immersed boundary method is used to couple a finite volume based Navier-Stokes solver with a finite element based structural mechanics solver for large deformations. The benchmark of an elastic rubber beam in a rolling tank partially filled with oil is simulated. The simulations are compared to experimental data as well as numerical simulations published in the literature. 2D simulations performed in the present work agree well with previously published data. Our 3D simulations capture effects neglected in the 2D case, showing excellent agreement with previously published experiments. The good agreement with experimental data shows that the developed framework is suitable for simulation of industrial applications involving fluid structure interaction. If the structure is made of a highly elastic material, e.g. rubber, the simulation framework must be able to handle the large deformations that may occur. Immersed boundary methods are well suited for such applications, since they can efficiently handle moving objects without the need of a body-fitted mesh. Combining them with a structural mechanics solver for large deformations allows complex fluid structure interaction problems to be studied.

A hybrid immersed boundary method for dense particle-laden flows

The numerical simulation of the parachute deployment/inflation process involves fluid structure interaction problems, the inherent complexities in the fluid structure interaction have been posing several computational challenges. In this paper a high fidelity Eulerian computational approach is proposed for the simulation of parachute deployment/inflation. Unlike the arbitrary Eulerian Lagrangian (ALE) method widely employed in this area, the Eulerian computational approach is established on three computational techniques: computational fluid dynamics, computational structure dynamics and computational moving boundary. A set of stationary, non-deforming Cartesian grids is adopted in our computational fluid dynamics, our computational structure dynamics is enhanced by non-linear finite element method and membrane wrinkling algorithm, instead of conventional computational mesh dynamics, an immersed boundary method is employed to avoid insurmountable poor grid quality brought in by moving mesh approaches. To validate the proposed numerical approach the deployment/inflation of C-9 parachute is simulated using our approach and the results show similar characteristics compared with experimental results and previous literature. The computed results have demonstrated the proposed method to be a useful tool for analyzing dynamic parachute deployment and subsequent inflation.

The computational fluid dynamics (CFD) and computational structural mechanics (CSM) focus areas at Argonne's Transportation Research and Analysis Computing Center (TRACC) initiated a project to support and compliment the experimental programs at the Turner-Fairbank Highway Research Center (TFHRC) with high performance computing based analysis capabilities in August 2010. The project was established with a new interagency agreement between the Department of Energy and the Department of Transportation to provide collaborative research, development, and benchmarking of advanced three-dimensional computational mechanics analysis methods to the aerodynamics and hydraulics laboratories at TFHRC for a period of five years, beginning in October 2010. The analysis methods employ well-benchmarked and supported commercial computational mechanics software. Computational mechanics encompasses the areas of Computational Fluid Dynamics (CFD), Computational Wind Engineering (CWE), Computational Structural Mechanics (CSM), and Computational Multiphysics Mechanics (CMM) applied in Fluid-Structure Interaction (FSI) problems. The major areas of focus of the project are wind and water effects on bridges - superstructure, deck, cables, and substructure (including soil), primarily during storms and flood events - and the risks that these loads pose to structural failure. For flood events at bridges, another major focus of the work is assessment of the risk to bridges caused by scour of stream and riverbed material away from the foundations of a bridge. Other areas of current research include modeling of flow through culverts to assess them for fish passage, modeling of the salt spray transport into bridge girders to address suitability of using weathering steel in bridges, CFD analysis of the operation of the wind tunnel in the TFCHR wind engineering laboratory, vehicle stability under high wind loading, and the use of electromagnetic shock absorbers to improve vehicle stability under high wind conditions. This quarterly report documents technical progress on the project tasks for the period of July through September 2011.

Composite B-spline regularized delta functions for the immersed boundary method: Divergence-free interpolation and gradient-preserving force spreading.

Parallel workstation clusters and MPI for sparse systems in computational science

An analysis of the spatio-temporal resolution of the immersed boundary method with direct forcing

Body-fitted and Cartesian grid methods are two typical types of numerical approaches used for modelling fluid–structure interaction problems. Despite their extensive applications, there is a lack of comparing the performance of these two types of approaches. In order to do this, the present paper presents benchmark numerical solutions for two two-dimensional fluid–structure interaction problems: flow-induced vibration of a highly flexible plate in an axial flow and a pitching flexible plate. The solutions are obtained by using two partitioned fluid–structure interaction methods including the deforming-spatial-domain/stabilized space–time fluid–structure interaction solver and the immersed boundary–lattice Boltzmann method. The deforming-spatial-domain/stabilized space–time fluid–structure interaction solver employs the body-fitted-grid deforming-spatial-domain/stabilized space–time method for the fluid motions and the finite-difference method for the structure vibrations. A new mesh update strategy is developed to prevent severe mesh distortion in cases where the boundary does not oscillate periodically or needs a long time to establish a periodic motion. The immersed boundary–lattice Boltzmann method uses lattice Boltzmann method as fluid solver and the same finite-difference method as structure solver. In addition, immersed boundary method is used in the immersed boundary–lattice Boltzmann solver to handle the fluid–structure interaction coupling. Results for the characteristic force coefficients, tail position, plate deformation pattern and the vorticity fields are presented and discussed. The present results will be useful for evaluating the performance and accuracy of existing and new numerical methodologies for fluid–structure interaction.

In recent years, computational simulations have emerged as valuable tools for the evaluation of atherosclerosis progression in coronary anatomies, although only a few studies have utilized more realistic Fluid-Structure Interaction (FSI) simulations. This work aims to compare the results of Computational Fluid Dynamics (CFD), Structural Finite Element Analysis (structural FEA) and FSI simulations in order to assess differences in plaque progression indices estimation. We performed structural FEA, CFD and FSI on five patient-specific epicardial coronary anatomies using the commercial software LS-Dyna. To account for the vessel pre-stress, the zero-pressure configuration was calculated for each anatomy with an inverse elastostatic algorithm. CFD, structural FEA and FSI simulations were performed applying boundary conditions based on physiological values. The comparison between structural FEA and FSI showed similar stress distribution and vessel expansions, with differences found only in the distal parts of the coronaries, where pressure reduction due to pressure loss affects the vessel walls. The elastic walls of the coronaries impact blood flow, resulting in a more disturbed flow. However, time averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) distributions are similar across each coronary between CFD and FSI; TAWSS is slightly higher in CFD while OSI peaks are higher in FSI. In conclusion, given the significantly higher computational costs of FSI, we believe that CFD and structural FEA offer a more practical and cost-effective approach, providing results comparable to those of FSI, making them preferable options.

We present a framework for coupled multiphysics in computational fluid dynamics, targeting massively parallel systems. Our strategy is based on general problem formulations in the form of partial differential equations and the finite element method, which open for automation, and optimization of a set of fundamental algorithms. We describe these algorithms, including finite element matrix assembly, adaptive mesh refinement and mesh smoothing; and multiphysics coupling methodologies such as unified continuum fluid-structure interaction (FSI), and aeroacoustics by coupled acoustic analogies. The framework is implemented as FEniCS open source software components, optimized for massively parallel computing. Examples of applications are presented, including simulation of aeroacoustic noise generated by an airplane landing gear, simulation of the blood flow in the human heart, and simulation of the human voice organ.

<p>Recent increase in construction of long span bridges requires wind-resistance design for dynamic stability. Conventional wind tunnel tests of scaled model are still widely, but applications of computational fluid dynamics(CFD) have recently been increasing. One of the major drawbacks of CFD application based on body-fitted grid to wind flow around bridge is complexity in grid system and inaccuracy due to unfavorable mesh. In order to overcome these, immersed boundary method (IBM) is applied in this paper, which utilized Cartesian, non-body conforming grid. Instead of traditional extrapolation scheme for momentum forcing in IBM often yielding numerical instability when the body has sharp corners such as in bridge decks, interpolation scheme is adopted and shown to result in stable results. In this paper, the numerical stability and accuracy of developed scheme were verified from numerical analysis for unsteady, viscous flow around 2-dimensional equilateral triangular at =250 by comparing results with previous studies. In addition, aerodynamic forces on isosceles triangular shape cylinders of aspect ratio from 0.5 to 4 of at =250 are simulated. The results show the reduction of mean drag and the increase of lift fluctuation as increase of aspect ratio. As the aspect ratio approaches to 2:1, the relatively large amplitude of lift with low frequency is observed due to the reattachment of separated flow and leading vortex shedding of long period when the windward side of the triangular section is vertical to the inflow. The present results show that the interpolation scheme adapted to IBM can be applied to CFD of wind flow around bridges.</p>

In recent years, increased evidences suggest that offshore structures such as wind farms, tidal turbine farms, piles of bridge and breakwater have great impact on the hydrodynamics and hence may have a strong influence on the sediment transport at a site. The open-source hydrodynamic suite of software TELEMAC has been used for the study of such environmental influence around Unite Kingdom. However, the use of the 3-D version of the software, TELEMAC-3D is restricted by how structures are accounted for in the meshes, as water columns have the same number of layers all over the domain. Moreover, a large scale farm has a large impact on turbulence mixing in the coastal regional scale, and this is not properly understood. The PhD project focuses on 3-D hydrodynamics and development of an 3-D unstructured capability using an immersed boundary method to account for obstacles in the flow. Two large eddy simulation models (the 2eddy LES model and the Wall-adapted Large Eddy model) have been incorporated into TELEMAC-3D to get a more realistic and effective representation of the turbulence mixing and to account for the unsteadiness of the flow past the structures. The simulations have been performed using High Performance Computing to enable large scale applications using TELEMAC-3D and fine spatial and temporal resolutions in 3-D. The implementations carried out in the code are fully parallel. The numerical models have been validated for two laboratory scale cases, including the flow around a circular cylinder and the flow over a submerged structure. Then a far-field simulation at the southern North Sea has been carried out, where the hydrodynamics and morphological impacts of the London Array offshore wind turbine farm have been investigated. The numerical results of turbulence model implementation indicate that both turbulence models have good performance in the representation of the flow past a cylinder in laboratory scale. However in the large scale application, only the 2eddy LES model is successfully applied because the WALE model relies on a very fine mesh in the vertical direction. The implementation of IBM suggested that when dealing with an obstacle going from the bottom though the surface of the water, the immersed boundary method offers good accuracy in the prediction of surrounding flow structures. For the submerged obstacles, they can be simulated by TELEMAC-3D by implementing the Immersed Boundary method. Although the accuracy is limited currently, qualitative analysis can still be performed.

Recurrent Neural Networks (RNNs) with dimensionality reduction and break down in computational mechanics; application to multi-scale localization step

A fast moving least squares approximation with adaptive Lagrangian mesh refinement for large scale immersed boundary simulations

A phase field-immersed boundary-lattice Boltzmann coupling method for fluid-structure interaction analysis