Greg Chini

A multiscale algorithm for simulating spatially-extended Langmuir circulation dynamics

A multiscale algorithm is proposed for simulations of the spatially-extended dynamics of Langmuir circulation, a wind- and surface-wave-driven convective flow that dominates vertical transport and mixing on the scale of the O ( 100 ) -m deep ocean surface boundary layer. The algorithm is motivated by multiple scale asymptotic analysis of the master partial differential (Navier-Stokes-like) equations and comprises coupled equation sets for the fine- and coarse-scale dynamics. A primary virtue of the resulting multiscale formulation is that dynamical teleconnections between the fine and coarse scales are explicitly identified and computed, enabling fewer fine-scale domains than coarse-scale grid points to be used. Quantitative comparisons between the multiscale simulations and direct numerical simulations of the master partial differential equations are made. Good agreement is demonstrated in the appropriate parameter regime at a cost that is orders of magnitude less than that required for brute-force simulations using the single-scale algorithm. Several novel multiscale physical interactions are identified, highlighting the utility of the algorithm and the potential importance of spatiotemporal modulation of the convective flow on the mean dynamics.

Langmuir Circulation: An Agent for Vertical Restratification?

AbstractComparably little is known about the impact of down-front-propagating surface waves on the stability of submesoscale lateral fronts in the ocean surface mixed layer. In this investigation, the stability of lateral fronts in gradient–wind balance to two-dimensional (down-front invariant) disturbances is analyzed using the stratified, rotating Craik–Leibovich (CL) equations. Through the action of the CL vortex force, the surface waves fundamentally alter the superinertial, two-dimensional linear stability of these fronts, with the classical symmetric instability mode being replaced by a hybrid Langmuir circulation/symmetric mode. The hybrid mode is shown to exhibit much larger growth rates than the pure symmetric mode, to exist in a regime in which the vertical Richardson number is greater than 1, and to accomplish significant cross-isopycnal transport. Nonhydrostatic numerical simulations reveal that the nonlinear evolution of this hybrid instability mode can lead to rapid, that is, superinertial, ...

Arbitrary Lagrangian Eulerian FEA Method to Predict Wavy Pattern and Weldability Window During Magnetic Pulsed Welding

Finite element simulations of high strain rate forming processes have received significant attention over the last decade. For instance, in Magnetic Pulsed Welding (MPW), extremely high plastic strain regions develop. Thus, a traditional pure Lagrangian analysis is not able to accurately model the process due to excessive element distortion near the contact zone. In this study, the Arbitrary Lagrangian Eulerian (ALE) method is used to simulate a MPW process while retaining a high-quality mesh. Also the ALE method was able to numerically predict the necessary process parameters to achieve a wavy pattern region for two Al6061-T6 plates impacted during the MPW process. The captured wavy pattern region in this study can be used as a first estimation of parameters necessary to achieve a successful MPW component and thus reduce trial and error experimental investigations.© 2015 ASME