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CivilComp Proceedings
ISSN 17593433 CCP: 81
PROCEEDINGS OF THE TENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING Edited by: B.H.V. Topping
Paper 114
Coupled FluidStructure Simulation of the Coriolis Flowmeter under Forced Vibration N. Mole+, G. Bobovnik*, J. Kutin*, B. Štok+ and I. Bajsic*
+Laboratory for Numerical Modelling and Simulation,
, "Coupled FluidStructure Simulation of the Coriolis Flowmeter under Forced Vibration", in B.H.V. Topping, (Editor), "Proceedings of the Tenth International Conference on Civil, Structural and Environmental Engineering Computing", CivilComp Press, Stirlingshire, UK, Paper 114, 2005. doi:10.4203/ccp.81.114
Keywords: Coriolis flowmeter, fluidstructure interaction, numerical modelling, coupled simulation.
Summary
A fluid conveying measuring tube that is maintained vibrating at its first natural
frequency under imposed forced vibration conditions is a primary sensing element in
a Coriolis flowmeter. As a result of the fluid forces acting on a straight clamped tube, the
tube's first mode shape, which is otherwise symmetric with respect to the tube
length, is distorted in an antisymmetric way. This effect, which is actually caused
by the appearance of the Coriolis forces, is exploited as the basic measuring
principle. To enable a periodic operation of the flowmeter a point in the central
crosssection of the measuring tube is harmonically excited by the first natural
frequency of the measuring tube.
For reliable prediction of the measuring characteristics of the considered Coriolis mass flowmeter, a proper numerical model for the interaction between the fluid flow and the measuring tube is required. In our case this is realized by a threedimensional coupled numerical model, which uses the finite volume method (FVM) for solving the dynamics of a viscous fluid flow, while the structural dynamics problem is considered within the finite element method (FEM) framework. For the solution of the specified tasks commercially available codes Comet 2.1 (FVM) and Abaqus 6.4 (FEM) are used respectively, and an appropriate coupling technique exploiting the computed results of each individual problem is used to perform computer simulations of the vibrating fluidstructure system considered. Coupling is numerically based on a staggered partitioned algorithm with additional pressure predictor and interfield iterations to minimize the time lag in the fluidstructure coupling procedure. In the numerical model of the Coriolis flowmeter the fluid and the structural domain are discretized in a way that the two meshes, based respectively on the FEM and the FVM discretization, coincide at the fluidstructure interface. As a consequence, the finite volume mesh follows in time with the motion of the tube, which is actually modelled as a shell. In order to keep in time with the same FVM mesh topology the displacements of internal nodes are correspondingly adjusted in each time step. To achieve a fast numerical steadystate response of the considered coupled system a special twostep solution procedure has been developed. The main idea behind the proposed solution procedure is to ensure monotonic and smooth convergence by finding the steadystate response of the free oscillating coupled system first, and only then to consider the imposed excitation force to keep the system in oscillation. The simulation results are presented for four different fluid average axial velocities: 0.2m/s, 0.4m/s, 1.5m/s and 5.0m/s. Observation of the motion exhibited by a point in the central crosssection of the tube shows, that after the excitation force is entered in the computation only a few oscillation cycles are required for the amplitudes of the kinematic values to become constant, while the phase difference established between the motion of that point and the excitation force converges close to a quarter of oscillation period. Finally, being of major significance for experimental application, the relationship is established between the phase difference of the respective responses at the two measuring points, located symmetrically to the central crosssection of the tube. Hence the fluid mass flow through the tube was analysed and discussed. References
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