LPT Main Options Tab

The LPT Main Options tab is shown in Figure 1. Within the LPT Computational Method & Timing frame, switch on drifters with the Compute Drifters checkbox before LPT can be implemented. Here the user will set the global computational period starting and ending days for the particle tracking in Julian days for all groups. The frequency (in minutes) of writing the particle positions to the EE_Drifters file is specified here.  This output frequency is for all groups and is independent of the normal EE output frequency.

Figure 1  LPT Options: Main Options.

The Vertical Movement Option frame provides the user the option of fixing the temporal position of the particles at their initial seeding depths. If this is unchecked, the particles will drift vertically as Fully 3D Lagrangian Neutrally Buoyant Particles.  A sub-option is Adjust Particle Depth.  This is the default option and adjusts particle depth with a change in water depth. In some cases, the user may wish to disallow this so that particles are not adjusted by the change in water depth, and so can turn off this adjustment by unchecking this box. If the Adjust Particle Depth is selected, the amount of adjustment in the vertical direction depends on the ratio of particle depth and water depth. The formula of the vertical adjustment is:

dzp=  pdep/wdep*dH

In which dzp is the adjustment of vertical particle depth, pdep is particle depth, wdep is water depth and dH the discrepancy of water depth of the current and previous timestep.

Wind Drift Effects frame provides three options for wind impact on the particle movement:

No Wind Drift Effect:  wind has no impact on the particles.

Same Drag Coeff. for Both Wind Components: the user should define coefficients A and B and then enter the values in the text boxes.

Separated Drag Coeff. for Each Wind Component:  the user should define coefficients A and B and then enter the values in the text boxes.

Within the Initial Particle Vertical Position Input Option the user may specify whether the vertical positions provided are elevations or depths.

If the Random Walk checkbox is checked, the user has a number of options for the Random Walk Dimensional Options. The user may select the random walk-in only the vertical direction, in only the horizontal direction, or both vertical and horizontal directions at the same time. In addition, the user may specify the Random Walk Size Options by selecting to allow EFDC Diffusion calculations to be used for the AH and AV. Alternatively, there is the option for Specified Constant Diffusivities that should be inputted by the user.

Wall Slippage frame allows the user to set the wall slip factor. For most real-world cases, the wall slip should be 0.0. However, for flume and other test cases, it may be better to use 1.0 or full slip.