In it, they wrote, "Determining the minimum, or critical, force necessary to dislodge a particle out of its pocket, arguably constitutes one of the most fundamental and elementary problems in mechanics, regardless of the type of movement. When it comes to flow-induced forces, identifying this critical condition has confounded scientists and engineers for several hundred years.
"The main culprit for this problem is the fluctuating nature of the applied fluid forces, due to the turbulent nature of the flow, while the resistance to particle movement remains the same."
Diplas pointed to "coherent flow structure characteristics typically encountered in turbulent flows which dominate natural phenomena" and how they impact particle entrainment in water. He believes that particle dislodging in waterways is due to more than just force magnitude. The duration of the applied hydrodynamic forces is "relevant in predicting grain removal from the channel bed surface," he wrote in his book chapter.
Also, in the article that won him the Hilgard Prize, Diplas argued that "flow and turbulence are more influenced by the vegetation density" than by other factors.
Vegetation in aquatic environments "considerably alters the turbulent flow in streams, rivers, and floodplains. The additional drag exerted by plants largely influencesthe transport of sediments" and dissolved substances, Diplas said. This research was already substantiated.
Diplas' new contribution in this area of study is the result of his large-eddy simulation studies of turbulent flow. He was able to show through analysis that flow and turbulence are more influenced by vegetation density than by the cylinder-based diameter Reynolds number. In fluid mechanics the Reynolds number is used to characterize different flow regimes. When forces resistant to change dominate turbulent flow, it is likely to create eddies, vortices, and other flow instabilities.
|Contact: Lynn Nystrom|