Creation of nonlinear density gradients for use in internal wave research

Abstract

A method was developed to create a nonlinear density gradient in a tank of water. Such gradients are useful for studying internal waves, an ocean phenomenon that plays an important role in climate and ocean circulation. The method was developed by expanding on the two-tank system currently used to create linear density gradients. A mathematical model of the two-tank system was used and a Matlab script was written to solve the model for the required flow rates in the system given a desired density gradient. The method was tested by creating three different density gradients: a linear gradient, a hyperbolic gradient, and a two-layer gradient. It was discovered that for a two-layer gradient the flow rates for each layer must be calculated independently of each other, because of problems integrating over a density gradient with a non-continuous slope. It was also discovered that the system failed at very low flow rates; insufficient mixing in the two-tank system led to gradients weaker than expected. Overall, the measured gradients matched up well with the expected gradients, and it was concluded that the system can successfully produce nonlinear density gradients.