Optimization of a piezoelectric fan using fluid-structure interaction simulation

In this paper, the heat transfer from a single heat fin to the air flow in the wake of a piezoelectric fan (piezofan) is optimised. Both the heat fin and the piezofan are positioned in a channel, which has a significant influence on the flow field. The design variable is the frequency of the voltage applied to the piezofan. The heat transfer for different excitation frequencies is calculated using unsteady fluid-structure interaction simulations. To obtain a modular simulation environment, the flow equations and the structural equations are solved separately. However, the equilibrium on the fluid-structure interface is not satisfied automatically in this partitioned approach. Therefore, the interface quasi-Newton technique with an approximation for the inverse of the Jacobian from a least-squares model (IQN-ILS) is used to perform coupling iterations between the flow solver and the structural solver in each time step. With the unsteady fluid-structure interaction model, a surrogate model is constructed. The optimization of the surrogate model yields a frequency close to the first eigenfrequency of the structure

Fluid-structure interaction simulation of parachute dynamic behaviour

The work presented concerns the numerical simulation on the dynamic behaviour of full size parachute models using a non linear explicit Fluid-Structure Interaction method. As a previous result of the partnership between ENSICA and CEV/TL, some partial solutions to model the parachute, the suspension lines, the surrounding air, and the coupling phenomenon were first determined. Validation criteria used for the presented results are the drag force, the kinematics and pressures in the fluid domain known from previous simulation work, and the inflated shape of a known cross parachute. These results, though inaccurate, were a major marker pole on the way to parachute opening simulation which requires many intermediary checks and developments. Some specific phenomena, like those related to the apparent mass increase during the parachute opening, will be correctly simulated when the basics of FSI are mastered well. The comparison between the obtained results and experimental measures allowed us in 2004 to propose the development of new features in the numerical methods of the hydrodynamic explicit code LS-DYNA, especially a new coupling method for air vs. porous fabric. The current achievement is also considered as a good basis for the coming simulations of opening and full descent

A Numerical Simulation of Fluid-Structure Interaction for Refrigerator Compressors Suction and Exhaust System Performance Analysis

To analyze the performance of refrigerator compressor suction and exhaust system , fluid-structure interaction based compressor suction and exhaust system analysis theory and method were researched, fluid structure interaction simulation model of suction and exhaust system was established. The structure stress and motion of valve leaf, mass flow rate, p-v diagram etc were obtained. The simulation result data was validated by experiment. The fluid-structure interaction simulation method has been used in new high performance compressor development

Fluid-Structure Interaction Simulation of a Coriolis Mass Flowmeter using a Lattice Boltzmann Method

In this paper we use a fluid-structure interaction (FSI) approach to simulate a Coriolis mass flowmeter (CMF). The fluid dynamics are calculated by the open source framework OpenLB, based on the lattice Boltzmann method (LBM). For the structural dynamics we employ the open source software Elmer, an implementation of the finite element method (FEM). A staggered coupling approach between the two software packages is presented. The finite element mesh is created by the mesh generator Gmsh to ensure a complete open source workflow. The Eigenmodes of the CMF, which are calculated by modal analysis are compared with measurement data. Using the estimated excitation frequency, a fully coupled, partitioned, FSI simulation is applied to simulate the phase shift of the investigated CMF design. The calculated phaseshift values are in good agreement to the measurement data and verify the suitability of the model to numerically describe the working principle of a CMF

A fast strong coupling algorithm for the partitioned fluid–structure interaction simulation of BMHVs

The numerical simulation of Bileaflet Mechanical Heart Valves (BMHVs) has gained strong interest in the last years, as a design and optimisation tool. In this paper, a strong coupling algorithm for the partitioned fluidstructure interaction simulation of a BMHV is presented. The convergence of the coupling iterations between the flow solver and the leaflet motion solver is accelerated by using the Jacobian with the derivatives of the pressure and viscous moments acting on the leaflets with respect to the leaflet accelerations. This Jacobian is numerically calculated from the coupling iterations. An error analysis is done to derive a criterion for the selection of useable coupling iterations. The algorithm is successfully tested for two 3D cases of a BMHV and a comparison is made with existing coupling schemes. It is observed that the developed coupling scheme outperforms these existing schemes in needed coupling iterations per time step and CPU time

Multi-Level quasi-Newton methods for the partitioned simulation of fluid-structure interaction

In previous work of the authors, Fourier stability analyses have been performed of Gauss-Seidel iterations between the flow solver and the structural solver in a partitioned fluid-structure interaction simulation. These analyses of the flow in an elastic tube demonstrated that only a number of Fourier modes in the error on the interface displacement are unstable. Moreover, the modes with a low wave number are most unstable and these modes can be resolved on a coarser grid. Therefore, a new class of quasi-Newton methods with more than one grid level is introduced. Numerical experiments show a significant reduction in run time

Fluid-structure interaction simulation of pulse propagation in arteries : numerical pitfalls and hemodynamic impact of a local stiffening

When simulating the propagation of a pressure pulse in arteries, the discretization parameters (i.e. the time step size and the grid size) need to be chosen carefully in order to avoid a decrease in amplitude of the traveling wave due to numerical dissipation. In this paper the effect of numerical dissipation is examined using a numerical fluid-structure interaction (FSI) model of the pulse propagation in an artery. More insight in the influence of the temporal and spatial resolution of the wave on the results of these simulations is gained using an analytical study in which the scalar linear one-dimensional transport equation is considered. Although this model does not take into account the full complexity of the problem under consideration, the results can be used as a guidance for the selection of the numerical parameters. Furthermore, this analysis illustrates the difference in accuracy that can be obtained using a second-order implicit time integration scheme instead of a first-order scheme. The results from the analytical and numerical studies are subsequently used to determine the settings necessary to obtain a grid and time step converged simulation of the wave propagation and reflection in a simplified model of an aorta with repaired aortic coarctation. This FSI model allows to study the hemodynamic impact of a stiff segment and demonstrates that the presence of a stiff segment has an important impact on a short pressure pulse, but has almost no influence on a physiological pressure pulse. This phenomenon is explained by analyzing the reflections induced by the stiff segment

Fluid-structure interaction simulation of the brachial artery undergoing flow-mediated dilation

Flow-mediated dilation (FMD) permits a non-invasive clinical assessment of endothelial dysfunction, a key indication of early atherosclerosis and cardiovascular diseases. This has significant implications with paediatric patients. FMD necessitates the measurement of brachial artery dilation from transient hyperaemia following a period of temporary ischemic occlusion. In addition to arterial diameter changes, the wall shear stress, blood pressure, and wall stiffness vary transiently in FMD, making it a complex fluid-structure interaction (FSI) problem. This work seeks to model the haemodynamic mechanisms associated with FMD utilising the open- source OpenFOAM-extend library1. Prior studies have demonstrated the suitability of this library for cardiovascular simulations2. Two FSI solvers, based on strong and weak coupling, were implemented for comparison. Both solvers utilise a partitioned approach, where the fluid and structure are solved separately and the information in each domain is exchanged at the FSI interface for each timestep. This is achieved using a dynamic mesh solver based on a discretisation of Laplace’s equation. The fluid flow solution is based on the finite volume method (FVM) and the displacement of the solid domain is solved by a Lagrangian FVM solver. The artery wall was modelled as a straight tube with physiological values for the internal diameter, density, wall thickness, Young’s modulus, and Poisson’s ratio3. A Newtonian incompressible fluid was assumed with physiological density and viscosity4. The inlet velocity for the fluid domain is specified from an in-vivo hyperaemic condition5. The simulation results demonstrate an important variation in the diameter of the arterial vessel during FMD, while haemodynamic wall shear stress and pressure values are also ascertained. These preliminary results are useful for comparing the implementation of strong and weak FSI solvers and for correlating arterial wall displacement with the prescribed in-vivo inlet velocity. Future work will focus on FMD in idealised and patient-specific bifurcation models where ischemic occlusion will be prescribed for the distal branching arteries