10:30
Fluid structural inter-actions I
Chair: Odd Magnus Faltinsen
10:30
30 mins
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IMPLEMENTATION AND VERIFICATION OF FLUID-STRUCTURE INTERACTION SIMULATION CAPABILITIES IN A FINITE-VOLUME FLOW SOLUTION METHOD
Sietse Jongsma, Edwin van der Weide, Jaap Windt
Abstract: The present research has been focussed on developing fluid-structure interaction simulation capabilities for a finite-volume flow solution method.
The viscous-flow solution method considered, simulates flows modelled by the Navier-Stokes equations for incompressible flow. The structure is modelled by means of a finite-element model, for which linear elastic material properties have been assumed. For the coupling, a partitioned approach is adopted, in which the equations for the flow and structural degrees of freedom are solved in a sequential manner. Time-integration for both the flow and the structure is done by means of a second-order accurate implicit time-integration method. The partitioned approach has certain implications for the coupling of the structure and the fluid. To ensure stable time-integration, strong coupling is used. This means that the flow and the structure are updated iteratively until an equilibrium situation is reached. To realize an efficient coupling method, a quasi-Newton method is employed to update the interface position. The interface between the fluid and structural domain can be matching or non-matching. For the non-matching case nearest neighbour or radial basis function interpolation is used. For deforming the fluid domain — to accommodate the deformation of the structure — either a radial basis function interpolation method or an inverse distance weighting method can be used.
The consequences of the various implementation details, like time-integration and coupling method, have been demonstrated by means of solving a 2D benchmark problem. A verification study — using a series of grids — has been performed, showing the efficiency of the coupling method and the accuracy of the interface interpolation. Results of the present implementation are compared with results from the literature and results from calculations performed with the open-source CFD method SU2. Finally, the method is demonstrated for practical maritime applications.
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11:00
30 mins
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ON THE ELASTIC MEMBRANE-FLUID INTERACTION BASED ON STRUCTURAL MODES SHAPES
Seyed Matin Hosseini Zahraei, Ido Akkerman, Arthur Veldman, Rene Huijsmans
Abstract: The concept of FSI has a vast range of practical engineering applications. Different approaches like weak coupling which utilizes the flexibility or strong coupling which exploit mathematical advantages has been introduced and implemented. On the other hand, several have come up with the idea of catching the presence of the structure through an interaction law which if it is well defined could lead to a hybrid method preserving advantages of both weak and strong couplings. Weak coupling in contrary to its simplicity faces limitations such as the added mass ratio which as it increases, numerical instabilities will occur which could be prohibited by under relaxation at the cost of extra structure-fluid iterations or it could also broke down the coupling if it exceeds one. This will lead to an inefficient way to solve such a coupled systems, therefore a well-known challenge in computing fluid structure interaction in complex systems is to provide an effective interaction law.
In this paper a structure shape mode based interaction law has been introduced and formulated. Shape modes of the structure represent a proper general behavior of the object. The approach strongly enforces the information exchange on the fluid-structure interface which leads not to be dependent on the added mass ratio. This paper also presents the first test model case which is selected to be a 1D Euler-Bernoulli beam at the bottom of a basin with an oscillating square shaped object within the fluid which will excite the beam modes dependent on its own motion frequency. The results are shown and then discussed.
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11:30
30 mins
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NUMERICAL STUDY OF THE INTERACTION BETWEEN TWO IMMERSED CYLINDERS
Zhonglu Lin, Dongfang Liang, Ming Zhao
Abstract: The interaction between two adjacent cylinders immersed in fluid is studied numerically by solving the two-dimensional Navier-Stokes (NS) equations using a finite element method (FEM). The two rigid cylinders are immersed in otherwise stationary fluid. One cylinder (C1) undergoes forced vibration that disturbs the fluid, whereas another cylinder (C2), which has one-degree-of-freedom (1DOF), vibrates correspondingly under the action of the imbalanced hydrodynamic force. All the simulations carried out in this study have a constant Reynolds number of 100 and a constant mass ratio of 2.5. Simulations are conducted with 9 initial gap ratios, G, ranging from 0.05 to 3 times of the cylinder diameter, with various forced vibration amplitude A1 and frequency f1 of C1. We find that C2’s amplitude (A2) reaches maximum when C1’s vibration frequency (f1) is approximately 80% of C2’s structural natural frequency (fn). The increase of C1’s amplitude (A1) leads to the rise of C2’s amplitude (A2) but the decrease of its relative amplitude (A2/A1). The increase in A1 also slightly reduces the value of f1 at the maximum A2. In addition, the vibration centre of C1 is observed to shift away from original location in cases with the large gap ratio. The shift becomes increasingly obvious with an increase of A1 and f1. Finally, C2 is found to respond to the vibration of C1 with bigger amplitude in some situations with small gap ratios, which can be interpreted as the occurrence of resonance.
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