Field Investigations of Scour Around Scaled Piles in a Region of Wave Breaking

Ocean renewable energy has strong potential for substituting power plants that rely on the combustion of fossil fuels. Due to maturity, offshore wind farms  are one of the most promising forms of ocean renewable energy. There are several windfarms around the world located in nearshore/beach regions (e.g. Bangui Wind Farm, Philippines). Scour around the foundation of nearshore windfarm structures is one of the important technical aspects to be addressed. In this study, field  investigations on the development of scour around scaled model piles  are carried out in two regions of wave breaking, viz.,  i) Uthandi beach, South Chennai, India, open coast having no structures and (ii) Muttukadu beach, South Chennai, India, which is 8 km south of Uthandi beach, having two breakwaters at Muttkadu lake mouth with eight groins in varying lengths with spacing of 50-200m.  Field investigations show rapid increases of the scour depth during swash due to wave uprush around piles and the scour depth reduces significantly during back wash. The field measurements on scour depth (S) around piles of various diameters (D) are well matching with previous published results of scour analysis (Sumer et al..2001).  The relative scour depth (S/D) increases with increase of upstream water run up heights, flow velocities, Froude number and pile positions relating to the location of wave breaking. The comparison of observed scour depths around piles in plunging and spilling wave breaker region indicates that the relative scour depth in plunging wave breaker is higher by around a factor of 1.3 times than that of the scour depth observed in the spilling breaker region.  The present study indicates that, to determine the foundation design depth of the piles for construction of pile supported structure in the region of wave breaking or in the surf zone, the scour depth must be estimated by considering additional depth variation on the beach profile for different monsoon season.  It is observed that the maximum relative scour depth (S_max / D) and width of scour hole are reduced significantly about 50% to 75% with presence of cotton cloths around piles.  However, for a full-scale wind turbine, a suitable geotextile material should be used. This presentation details the various aspects of hydrodynamic field measurements on scaled pile models, which serve as design parameters for designing the pile supported coastal structures including wind energy farms in nearshore regions.

 

Key Words:  Ocean Renewable Energy, near offshore wind farms, hydrodynamics, scour measurements, swash region, offshore piles

 

 

 

Reference:

• Mohamed Rajab. P.(2019), Hydrodynamic Analysis of Scour Around Offshore Piles.

             Ph.D. Thesis., AMET University, India.

 

• Sumer, B.M., Whitehouse, R.J.S. and Tørum, A.,(2001). Scour around coastal structures: a summary of recent research. Coastal Engineering, Vol.44:153-190.