## Lecture 5-2: Front Tracking (2/2)

We need to construct a marker function from the location of the interface in order to
Set the material properties of the fluids
Advect the momentum
Compute surface tension
All of the above
Knowing where the interface is, is enough, and we do not need a marker function

To determine how the marker function value depends on the exact location of the interface and the distance to each grid point it is necessary to:
Determine the distance from the interface to each point on the fixed grid,
Decide how the marker value depends on the distance to the interface
Determine which part of the interface is closest to a given point on the fixed grid
All of the above
None of the above

To construct a marker function, we need to
Update every grid point on the fixed grid at every step
Only update the grid points on the downstream side
Only update the grid points on the upstream side
Only update the grid points close to the interface
None of the above

In the present code the marker at a grid point located exactly where the interface is, is
0.0
0.5
1.0
Depends to on the distance to the interface
None of the above

When setting the value of the marker at grid points close to the grid, we loop over the interface points because
We are setting the marker value at the interface points
Grid points close to an interface point are easily found
Front points close to an interface point are easily found
We could just as well loop over the grid points, we just picked one
None of the above

In the present code the density at a grid point close to the front is set based on
The distance from the closest front point
The distance to the point in the lower left corner
Normal distance from the closest front point
Closest distance from the normal front point
None of the above

When advecting the density using front tracking
The drop does not deform
The drop moves slower
The drop can reach the bottom wall
The interface separating the different densities remains sharp
All of the above

When we replace the simple advection equation used to update the density by the front tracking, we need to add
The setup of the front
The interpolation of the grid velocity to the front and the advection of the front
The adding and deletion of points to keep the resolution reasonably uniform
The construction of a marker function from the location of the front
All of the above

The thickness of the interface in the current code is
About one grid spacing
One to two grid spacing
Two to three grid spacing
More than three grid spacing
None of the above

The current code
Lacks surface tension
Assumes the viscosities of both fluids are equal
Is only first order in time
Assumes one closed interface
All of the above