An Improved Direct-Forcing Immersed Boundary Method for Fluid-Structure Interaction Simulations
07 Jul 2013-
TL;DR: In this article, the authors developed a FSI solver by coupling a direct forcing immersed boundary method for the fluid with a finite difference method of the structure, and several flow problems are simulated to validate their method.
Abstract: Simulation of fluid-structure interaction (FSI) of flexible bodies are challenging due to complex geometries and freely moving boundaries. Immersed boundary method has found to be an efficient technique for dealing with FSI problems because of the use of non-body-fitted mesh and simple implementation. In the present work, we developed a FSI solver by coupling a direct forcing immersed boundary method for the fluid with a finite difference method of the structure. Several flow problems are simulated to validate our method. The testing cases include flow over a stationary cylinder and flat plate, two-dimensional flow past an inextensible flexible filament and three-dimensional flow past a flag. The results obtained agree well with those from previously published literatures.Copyright © 2013 by ASME
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TL;DR: In this paper, the effect of the foil flexibility on the wake symmetry properties of a self-propelled plunging foil is studied numerically, and the results indicate that flexibility can either inhibit or trigger the symmetry breaking of the wake.
Abstract: The wake symmetry properties of a flapping-foil system are closely associated with its propulsive performance. In the present work, the effect of the foil flexibility on the wake symmetry properties of a self-propelled plunging foil is studied numerically. We compare the wakes of a flexible foil and a rigid foil at a low flapping Reynolds number of 200. The two foils are of the same dimensions, flapping frequency, leading-edge amplitude and cruising velocity but different bending rigidities. The results indicate that flexibility can either inhibit or trigger the symmetry breaking of the wake. We find that there exists a threshold value of vortex circulation above which symmetry breaking occurs. The modification of vortex circulation is found to be the pivotal factor in the influence of the foil flexibility on the wake symmetry properties. An increase in flexibility can result in a reduction in the vorticity production at the leading edge because of the decrease in the effective angle of attack, but it also enhances vorticity production at the trailing edge because of the increase in the trailing-edge flapping velocity. The competition between these two opposing effects eventually determines the strength of vortex circulation, which, in turn, governs the wake symmetry properties. Further investigation indicates that the former effect is related to the streamlined shape of the deformed foil while the latter effect is associated with structural resonance. The results of this work provide new insights into the functional role of passive flexibility in flapping-based biolocomotion.
76 citations
TL;DR: In this article, a group of flexible flags was modelled as a collection of individuals arranged in a combination of tandem and side-by-side formations and three different flag formations were modelled to cover the basic structures involved in fish schooling: triangular, diamond and conical formations.
Abstract: Fish schooling is not merely a social behaviour; it also improves the efficiency of movement within a fluid environment. Inspired by the hydrodynamics of schooling, a group of flexible bodies was modelled as a collection of individuals arranged in a combination of tandem and side-by-side formations. The downstream bodies were found to be strongly influenced by the vortices shed from an upstream body, as revealed in the vortex–vortex and vortex–body interactions. To investigate the interactions between flexible bodies and vortices, the present study examined flexible flags in a viscous flow by using an improved version of the immersed boundary method. Three different flag formations were modelled to cover the basic structures involved in fish schooling: triangular, diamond and conical formations. The drag coefficients of the downstream flags could be decreased below the value for a single flag by adjusting the streamwise and spanwise gap distances and the flag bending coefficient. The drag variations were influenced by the interactions between vortices shed from the upstream flexible flags and those surrounding the downstream flags. The interactions between the flexible flags were investigated as a function of both the gap distance between the flags and the bending coefficients. The maximum drag reduction and the trailing flag position were calculated for different sets of conditions. Single-frequency and multifrequency modes were identified and were found to correspond to constructive and destructive vortex interaction modes, which explained the variations in the drag on the downstream flags.
54 citations
Cites result from "An Improved Direct-Forcing Immersed..."
...From figure 2 we can see that the present results agreed well with those of Zhang et al. (2013) on both the flapping amplitude and frequency....
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TL;DR: In this paper, a three-dimensional numerical model was developed to simulate wave-structure interaction over an uneven bottom, which is an extension of the earlier multiple-layer σ -coordinate model by including the direct-forcing immersed boundary method to deal with curved body surfaces.
21 citations
TL;DR: In this paper, the fluid-structure interaction problems of two side-by-side flexible plates with a finite aspect ratio in a 3D uniform flow are numerically studied.
Abstract: The fluid-structure interaction problems of two side-by-side flexible plates with a finite aspect ratio in a three-dimensional (3D) uniform flow are numerically studied. The plates’ motions are entirely passive under the force of surrounding fluid. By changing the aspect ratio and transverse distance, the coupling motions, drag force and energy capture performance are analyzed. The mechanisms underlying the plates’ motion and flow characteristics are discussed systematically. The adopted algorithm is verified and validated by the simulation of flow past a square flexible plate. The results show that the plate’s passive flapping behavior contains transverse and spanwise deformation, and the flapping amplitude is proportional to the aspect ratio. In the side-by-side configuration, three distinct coupling modes of the plates’ motion are identified, including single-plate mode, symmetrical flapping mode and decoupled mode. The plate with a lower aspect ratio may suffer less drag force and capture less bending energy than in the isolated situation. The optimized selection for obtaining higher energy conversion efficiency is the plate flapping in single-plate mode, especially the plate with a higher aspect ratio. The findings of this work provide several new physical insights into the understanding of fish schooling and are expected to inspire the developments of underwater robots or energy harvesters.
13 citations
DOI•
01 Jan 2017
TL;DR: A partitioned approach to compute FSI that integrates the direct forcing technique with the Immersed Boundary Method which is able to handle complex rigid, moving, solid and elastic structures is proposed.
Abstract: A PARTITIONED APPROACH FOR COMPUTING FLUID-STRUCTURE INTERACTION, WITH APPLICATION TO TUMOR MODELING AND SIMULATION Asim Timalsina Old Dominion University, 2017 Director: Dr. Fang Hu Modeling and Simulation plays a critical role in understanding complex physical and biological phenomena as it provides an efficient and controlled test environment, without the risk of costly experiments and clinical trials. In this dissertation, we present an extensive study of two such systems with integrated application: Fluid structure interaction (FSI) and virotherapy on tumor. Moreover, we substantiate a few preliminary results of FSI application on tumor. The FSI problem comprises of fluid forces exerted on the solid body and the motion of the structure affecting the fluid flow. FSI problems are of great interest to applied industries, however they are also computationally challenging due to the complex structures involved and freely moving boundaries. We propose a partitioned approach to compute FSI that integrates the direct forcing technique with the Immersed Boundary Method which is able to handle complex rigid, moving, solid and elastic structures. We then propose and analyze a virotherapy model for tumor treatment that includes both the innate and adaptive immune cells which are then studied in a variety of settings. We demonstrate that immune responses, burst sizes, and repeated administration of viral doses on regular intervals play a huge role in the success of the virotherapy. A detailed stability analysis of the ODE tumor virotherapy model is also performed. We analyzed some of the biologically meaningful equilibrium analytically and computationally, whenever analytic solution was impossible. We confirm that tumor can be controlled by showing the existence of endemic equilibria that are locally (or globally if certain criteria are met) stable for a set of parameters. Finally, the FSI method is applied to multiple non-stationary discs to gain some insights in the behavior of the cellular aggregation. This will serve as a stepping stone to our future work of understanding the intra-cellular interaction among tumor cells.
3 citations
Cites methods from "An Improved Direct-Forcing Immersed..."
...Some recent work related to the direct-forcing method includes, among others, [9, 29, 34]....
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...For distinction, we refer to the algorithm originated from [34] as described above as Method...
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