Highlights

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  • Frandsen, J.B. (2008). “Free-surface Lattice Boltzmann modeling in single phase flows”. Advanced numerical models for simulating tsunami waves and runup. Eds.: P.L.-F. Liu, H. Yeh, C. Synolakis. Advances in Coastal and Ocean Engineering. Vol. 10. World Scientific. doi

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Summary: Initial developments towards wave breaking predictions have been carried out by investigating the usage of Lattice Boltzmann Methods (LBM) for free-surface flows. The method offers potentially an alternative approach to improve the understanding of underlying mechanisms of nonlinear processes at the free surface than traditional macroscopic Navier-Stokes and Non-Linear Shallow Water (NLSW) solvers. A series of computational and model scale experiments of period bore propagation and run-up on beaches have been done including tsunami generated waves. It was found that the bore and tsunami LBGK free- surface predictions compare well with classical depth-integrated models, Riemann solvers, volume of fluid solvers and the recent advances of the smooth particles hydrodynamics method.

 

  • Frandsen, J.B. (2005). “Numerical predictions of tuned liquid tank structural systems”.

In Journal of Fluids and Structures, Vol. 20, No. 3, pp. 309-329. doi

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Summary: Structural frequencies were tested in large structures where liquid tanks were mounted. Energy from free-surface motions in these tanks were utilized to suppress structural vibrations. The system equations consist of 2-D inviscid nonlinear potential flow eqns. which are coupled to a single degree-of-freedom linear elastic support structure. Computational experiments are undertaken testing the performance of the tuned liquid damper. A practical system of multiple tanks would involve non-water-based solutions to minimize additional mass. This coupled model is novel and useful for guidance of practical developments of liquid dampers. Further works were done on breaking waves in a coupled magnetohydrodynamic system to extract maximum damping.

 

  • Frandsen, J.B. (2004). “Sloshing motions in excited tanks”.

In Journal of Computational Physics, Vol. 196, 1, pp. 53-87, 2004. doi

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Summary: Nonlinear effects of standing wave motions in fixed, horizontally and vertically excited tanks are investigated. The 2-D inviscid finite difference solver performs well for non overturning waves, and is a robust method for the treatment of nonlinear waves in deep water. It is shown that vertical excitation causes the instability associated with parametric resonance of the combined motion for a certain set of frequencies and amplitudes while the horizontal motion is related to classical resonance. It was further found that infinite number of additional resonance frequencies exist due to the combined motion of the tank. The solver captures mode interaction events well including detuning effects. The work was later reproduced experimentally. It was shown that solver performs well in deep water and tends to overpredict the free-surface amplitudes due the potential flow approach (as expected). Experimentally it was shown that it takes very little energy to generate 3-D flow. Further works were also carried out with other methods.

 

  • Frandsen, J.B. (2001). “Simultaneous pressures and accelerations measured full-scale on the Great Belt East suspension bridge.”

In Journal of Wind Engineering and Industrial Aerodynamics, Vol.89, No.1, pp.95-129. doi

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Summary: The study involves measurement of flow around a long span suspension bridge involving Vortex-Induced Vibrations (VIV). Several long-span bridges have problems with VIV. For example, lock-in was recorded and reported (at 8 m/s and 0.2 Hz) full-scale. The bluff-bodies are wide and time dependent flow attachment points in turbulent boundary layers exist. The wind induced motions result in hysteresis solutions. The series of computational experiments did, however, not reproduce the full-scale measured lock-in convincingly. The measurement is the first one with simultaneous records of structural motions and fluid flow variables. It is also unique because the structure went into nonlinear resonance motions during the 3 month of experiments (repeatedly).

 

  • Frandsen, J.B. (2004). “Numerical bridge deck studies using finite elements. Part I: Flutter”.

In Journal of Fluids and Structures, Vol.19, No. 2, pp.171-191. doi

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Summary: Modeling of aeroelastic phenomena using fluid and structural finite elements embedded in an arbitrary Lagrangian Eulerian method. Investigations were conducted to identify the importance of weakly versus fully coupling between high Reynolds no. flow and large motions of bluff bodies to include full-scale measurements. At this time, it was novel to use finite elements for fluid flow and the coupling to a structure in large amplitude oscillations in the context of aeroelastic phenomena. While flutter might be predicted with decoupled approaches due to the thin boundary layer near compressible limits, the predictions vortex-induced vibrations is still an open question.

 

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Fluid-Structure Systems is a civil engineering company who offer services in consultancy, research and eduction in the fields of ocean-, coastal-, wind- and structural engineering.