Model for Mixture Theory Simulation of Vortex Sand Ripple Dynamics

• Published in: Journal of waterway, port, coastal, and ocean engineering Vol. 137; no. 5; pp. 225 - 233
• Main Authors: Penko, Allison M, Slinn, Donald N, Calantoni, Joseph
• Format: Journal Article
• Language: English
• Published: Reston, VA American Society of Civil Engineers 01.09.2011
• Subjects: Applied sciences; Buildings. Public works; Computation methods. Tables. Charts; Exact sciences and technology; Hydraulic constructions; Port facilities and coastal structures. Lighthouses and beacons; Structural analysis. Stresses; TECHNICAL PAPERS; Bedform; Sand; Hydraulics; Mixture theory; Modeling; Mixture; Coastal zone; Sediment transport; hydraulic; Simulation model; Vortex; Boundary layer; Vortex sand ripples; Bed forms; Theoretical study; Bottom boundary layer flow; Seabed geometry; Ocean bottom; Sediments; Geometry; Simulation; Sea floor; Bedforms; Ripple; Particle transport; Comparative study; Boundary layer flow
• ISSN: 0733-950X; 1943-5460
• DOI: 10.1061/(ASCE)WW.1943-5460.0000084

The complex coupled interactions between fluid and sandy sediment on the seafloor are simulated with a three-dimensional bottom boundary layer model (SedMix3D) developed from mixture theory. SedMix3D solves the unfiltered Navier-Stokes equations for a fluid-sediment mixture treated as a single continuum with effective properties that parameterize the fluid-sediment and sediment-sediment interactions including a variable mixture viscosity, a bulk hindered settling velocity, and a shear-induced, empirically calibrated, mixture diffusion term. A sediment flux equation models the concentration of sediment by describing the balance of sediment flux by advection, gravity, and shear-induced diffusion. The grid spacing is on the order of a sediment grain diameter, and simulated flows had maximum free-stream velocities between 20 and 120  cm/s and periods between 2 and 4 s. Modeled ripple geometries ranged from a single ripple to multiple ripples with varying heights, lengths, and steepness. Only noncohesive sediments (d=0.04  cm) with the material properties of quartz in water were considered. The model predicted ripple heights and lengths that compare reasonably to existing ripple predictor formulae. SedMix3D also predicts the merging and separation of ripples as they transition from an initial state to an equilibrium state.