Jeroen Hillewaere

NUMERICAL INVESTIGATION OF WIND INDUCED OVALLING VIBRATIONS IN SILO GROUPS

Wind induced ovalling vibrations were observed during a sto rm in October 2002 on several empty silos of a closely spaced group consisting of 8by 5 thin-walled silos in the port of Antwerp (Belgium). In the present study, it is investigatedif the observed ovalling oscillations can be numerically predicted. To this end, the silo structur es are modeled using a finite element (FE) model and the wind flow around a single silo is investigat ed using 3D computational fluid dynamics (CFD) simulations. A wind tunnel experiment w as set up to validate the CFD simulations. To explain the onset of the wind induced ovalli ng vibrations, the interaction of the wind field with the structural vibrations has to be taken intoaccount. Therefore, the complex interplay of both fields is investigated with both one-way an d two-way coupling simulations. It is interesting to compare the results of both coupling app roaches to assess the necessity of performing the computationally much more time-consuming t wo-way coupling simulations. It is found in both coupling approaches that the mode shapes with t he lowest natural frequencies are excited dynamically. The results in the one-way coupling si mulations differ however from those in the two-way coupling, demonstrating the importance of pe rforming fully coupled simulations for suchlike aeroelastic problems.

Computational aspects of simulating wind induced ovalling vibrations in silo groups

During a storm in October 2002, wind induced ovalling vibrations were observed on several empty silos of a closely spaced group of eight by five thin-walled silos in the port of Antwerp (Belgium). To determine realistic dynamic wind loads and hence clarify the cause of the wind induced ovalling vibrations in the silo group, 2D URANS simulations are performed for seven angles of incidence between 0^o and 90^o. The emphasis in this paper is on the extensive verification and validation of the simulations to ascertain the accuracy of the numerical results. Subsequent analysis of the fluctuating wind pressures on the silo surfaces shows that ovalling oscillations of the eigenmodes with three and four circumferential wavelengths will be induced at the lee side of the silo group, corresponding to the lowest structural eigenfrequencies of the silos and the pattern of the visually detected vibrations during the 2002 storm.