A Fully Eulerian Formulation for Fluid-Structure Interaction Problems

In this work, we present a Fully Eulerian framework for fluid-structure interaction (fsi) problems coupling the incompressible Navier-Stokes equations with a hyperelastic solid. The Fully Eulerian framework is a monolithic implicit variational formulation for the coupled problem. In contrast to the well-established Arbitrary Lagrangian Eulerian (ALE) coordinates, the Fully Eulerian framework formulates both subproblems, fluid and solid, in Eulerian coordinates. This concept circumvents various difficulties connected to ALE coordinates since no artificial domain mapping is used. The formulation is an interface-capturing method and uses an extension of the solid’s deformation, the Initial Point Set, to detect the interface location. By construction, very large deformation as well as topology changes like contact of the solid to the domain boundary or other solid parts are possible

Numerical modelling of granular cargo on bulk carriers in seaway

This paper outlines the development of a numerical model for granular cargo on bulk carriers. In order to study the vessel behaviour including the motion of the load, a monolithic approach is chosen to model the fully coupled problem. The formulation of the granular material therefore has to be fully Eulerian. A nonlinear elastic solid phase is implemented in the Finite Volume solver FreSCo+ following the approach of Richter et. al [19] and Sugyiama et. al [22]. The method is then verified with the help of different Fluid-Structure interaction test cases

Modelling of thrombus formation using smoothed particle hydrodynamics method

In this paper a novel model, based on the smoothed particle hydrodynamics (SPH) method, is proposed to simulate thrombus formation. This describes the main phases of the coagulative cascade through the balance of four biochemical species and three type of platelets. SPH particles can switch from fluid to solid phase when specific biochemical and physical conditions are satisfied. The interaction between blood and the forming blood clot is easily handled by an innovative monolithic FSI approach. Fluid-solid coupling is modelled by introducing elastic binds between solid particles, without requiring detention and management of the interface between the two media. The proposed model is able to realistically reproduce the thromboembolic process, as confirmed by the comparison of numerical results with experimental data available in the literature

Semi-implicit Eulerian method for the fluid structure interaction of elastic membranes

In this paper we propose a novel and general approach to design semi-implicit methods for the simulation of fluid-structure interaction problems in a fully Eulerian framework. In order to properly present the new method, we focus on the two-dimensional version of the general model developed to describe full membrane elasticity. The approach consists in treating the elastic source term by writing an evolution equation on the structure stress tensor, even if it is nonlinear. Then, it is possible to show that its semi-implicit discretization allows us to add to the linear system of the Navier-Stokes equations some consistent dissipation terms that depend on the local deformation and stiffness of the membrane. Due to the linearly implicit discretization, the approach does not need iterative solvers and can be easily applied to any Eulerian framework for fluid-structure interaction. Its stability properties are studied by performing a Von Neumann analysis on a simplified one-dimensional model and proving that, thanks to the additional dissipation, the discretized coupled system is unconditionally stable. Several numerical experiments are shown for two-dimensional problems by comparing the new method to the original explicit scheme and studying the effect of structure stiffness and mesh refinement on the membrane dynamics. The newly designed scheme is able to relax the time step restrictions that affect the explicit method and reduce crucially the computational costs, especially when very stiff membranes are under consideration

Geometric re-meshing strategies to simulate contactless rebounds of elastic solids in fluids

The paper deals with the rebound of an elastic solid off a rigid wall of a container filled with an incompressible Newtonian fluid. Our study focuses on a collision-free bounce, meaning a rebound without topological contact between the elastic solid and the wall. This has the advantage of omitting any artificial bouncing law. In order to capture the contact-free rebound for very small viscosities an adaptive numerical scheme is introduced. The here-introduced scheme is based on a Glowinski time scheme and a localized arbitrary Lagrangian-Eulerian map on finite elements in space. The absence of topological contact requires that very thin liquid channels are solved with sufficient accuracy. It is achieved via newly developed geometrically driven adaptive strategies. Using the numerical scheme, we present here a collection of numerical experiments. A rebound is simulated in the absence of topological contacts. Its physical relevance is demonstrated as, with decreasing viscosities, a free rebound in a vacuum is approached. Further, we compare the dynamics with a second numerical scheme; a here-introduced adaptive purely Eulerian level-set method. The scheme produced the same dynamics for large viscosities. However, as it requires a much higher computational cost, small viscosities can not be reached by this method. The experiments allow for a better understanding of the effect of fluids on the dynamics of elastic objects. Several observations are discussed, such as the amount of elastic and/or kinetic energy loss or the precise connection between the fluid pressure and the rebound of the solid

Dynamic Responses of Sliding Isolation Concrete Liquid Storage Tank under Far-Field Long-Period Earthquake

Under far-field long-period earthquake, liquid storage tanks are easy to be failure because of large amplitude liquid sloshing. In this paper, nonlinear contact is used to simulate behavior of sliding isolation bearing, nonlinear dynamic equation is used to solve fluid-structure interaction, bilinear material model is used to simulate limiting-device, and 3-D calculation model of sliding isolation concrete rectangular liquid storage tank (CRLST) with limiting-devices is established. Firstly, artificial far-field long-period earthquake waves are synthesized based on the existing seismic records. Secondly, dynamic responses of sliding isolation CRLST under the action of short-period and far-field long-period earthquakes are studied. Thirdly, effects of bi-directional earthquake and structure size on dynamic responses are investigated. Lastly, displacement control measures are discussed. Results show that far-field long-period earthquakes mainly affect horizontal displacement of structure and liquid sloshing wave height, and sliding isolation has obvious control effect on liquid sloshing wave height. Besides, horizontal displacement of structure and liquid sloshing wave height are increased with increase of seismic dimension and structure size. The reasonable designs of sliding isolation bearing and limiting-device can solve the problem that the maximum horizontal displacement of sliding isolation CRLST may exceed the limit under far-field long-period earthquake

Numerical simulation of solid deformation driven by creeping flow using an immersed finite element method

An immersed finite element method for solid–fluid interaction is presented with application focus on highly deformable elastic bodies in a Stokes flow environment. The method is based on a global balance equation which combines the solid and fluid momentum balances, the fluid mass balance and, in weak form, the interface conditions. By means of an Updated Lagrangian description for finite elasticity, only one analysis mesh is used, where the solid particles are backtracked in order to preserve the deformation history. The method results in a full coupling of the solid-fluid system which is solved by an exact Newton method. The location of the material interface is captured by a signed distance function and updated according to the computed displacement increments and the help of an explicit surface parameterisation; no body-fitted volume meshes are needed. Special emphasis is placed on the accurate integration of finite elements traversed by the interface and the related numerical stability of the shape function basis. A number of applications for compressible Neo-Hookean solids subject to creeping flow are presented, motivated by microfluidic experimentation in mechanobiology