NICOP Developing a Probabilistic Model for Sediment Transport in Oscillatory Flow Using Direct Numerical Simulations
Abstract
The reliable prediction of the initiation of sediment transport and an accurate evalu-ation of the time development of both sedimen"t transport rate and bottom morphologyin the coastal region is of fundamental importance in a large number of applications,includi""ng underwater warfare operations, the design of o -shore and coastal structures,the prediction of transport of toxic chemicals by se""a waves and the preservation of ben-thic communities. Almost all actual methods, which are used to determine the conditionsleading"" to sediment motion and to quantify the sediment transport rate, are based on em-pirical approaches which are tuned using steady o""w data and neglect important aspectsof the phenomenon when the sediment motion is driven by sea waves. For instance, theassumption" that the unsteadiness of the driving ow has a negligible e -ect on the dynam-ics of the sediment is perhaps the reason of the de?c"iencies of the actual approaches inpredicting the sediment transport rate, which are characterized by relative errors that caneasi""ly overcome 100%. At the present, a detailed investigation of the nearbed turbulencein an oscillatory ow and the associated hydrod"ynamic forces that mobilize sedimentparticles is only possible by the means of Direct Numerical Simulations (DNS) of the in-compre"ssible Navier-Stokes equations, i.e. resolving the ow around the sediment grainsand without the introduction of any turbulence mod""el, and using the Newton equationsand a collision model to determine sediment dynamics.DNSs will be performed using the DNS code o"f Mazzuoli and Vittori (2016)1 andMazzuoli et al. (2016)2 which e?ciently handles complex geometries by the means ofan oct-tree adaptive mesh re?nement. Lubrication and mechanical contact forces willbe added to the resolved hydrodynamic forces to model particle collisions. The role ofdi -erent contributions to the hydrodynamic force acting on individual sediment particleswill be investigat"ed and the drag force as well as the added mass and horizontal buoyancyforces will be singled out. Then, as a second goal of the pr""oject, a correlation between thehydrodynamic force, which in turn depends on the (spatial and temporal) probabilisticdistribution"" of supercritical conditions for the transport of sediments associated withthe occurrence of turbulent events, and the transport ra""te will be possibly identi?ed fordi -erent values of the Reynolds and Keulegan-Carpenter numbers. Hence, a probabilisticmodel for t"he sediment transport in an oscillatory boundary layer will be developed onthe basis of the numerical results. The research project will lay the groundwork for thedevelopment of a more reliable and accurate model to describe sediment transport undersea waves an"d it will contribute to address a lot of issues that are fundamental for coastalengineering applications. Moreover, the expected re""sults will be useful in the predictionof mine burial and of water optical characteristics of turbidity. Finally, the numericalappr""oach will augment the existing NRL base program e -orts concerned with the erosionand deposition of sediments.1Mazzuoli, M. and Vit""tori, G. (2016). Transition to turbulence in an oscillatory ow over a roughwall. Journal of Fluid Mechanics 792, 67{97.2Mazzuoli,"" M., Blondeaux, P., Simeonov, J. and Calantoni, J. (under revision). Direct numericalsimulation of the oscillatory ow around a sph"ere resting on a rough bottom. Journal of Fluid Mechanics.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 03, 2017
- Source ID
- N629091712144
Entities
People
- Paolo Blondeaux
Organizations
- Office of Naval Research
- United States Navy
- University of Genoa