An experimental database has been obtained in order to quantify the hydrodynamical drag and added-mass coefficients of a circular cylinder encrusted with rigid and large-size biofouling, such as coral. The tests have been carried out in the wave and current flume tank of IFREMER in Boulogne-sur-mer. The experimental working section is 4m wide by 2m deep and 18m long. The range of the upstream flow velocity used for these trials is between 0.15 and 1.55m/s, with a turbulence rate of 3%.
The experimental set-up consists of a 2 meters long cylinder supported by a frame, fixed under a motion generator system, by the use of a six-components load-cell, in order to measure the global forces on the assembly. The motion generator system is used to impose sinusoidal motions to the cylinder, fixed to the frame by the use of six-components load-cells at each extremity, in order to measure the forces only on the cylinder. Two different kinds of biofouling are studied and compared to a reference cylinder of 200mm diameter.
Trials have been carried out with current only, with imposed motions and with a combination of imposed motions and current. Results presented in the paper Effet des concrétions marines sur le comportement hydrodynamique de structures circulaires (Journées de l'Hydrodynamique, 2014) show that the hydrodynamic coefficients are from 1.5 to 4 times higher than those obtained for the reference cylinder. Differences between the two tested kinds of roughness are low and limited to the highest speeds and accelerations of motions.