Lecture 7: Results and Tests

Grid-refinement tests helps us find:
Coding errors
The accuracy of the solution
Both coding errors and how accurate the solution is
If the results agree with experiments
None of the above

For numerical scheme with second order spatial accuracy, the error should
Always decrease by two if the grid size is doubled
Generally decrease by two if the grid size is doubled
Always increase by two if the grid size is doubled
Sometimes decrease by two if the grid size is doubled
Not change at all

The motion of a drop is governed by the density and viscosity ratio plus
One nondimensional number
Two nondimensional numbers
Three nondimensional numbers
Depends on the whether the drop is water or oil
None of the above

If we change the sign of the gravity acceleration
Nothing should happen
The drop should slow down
The drop should speed up
The drop should move toward the top boundary
None of the above

The area of the drop can be found
Only by integrating over the area of the drop
Only by integrating over the surface of the drop
By integrating over either the area or the surface of the drop
Taking the time derivative of the location of the points
None of the above

The centroid of the drop can be found
Only by integrating over the area of the drop
Only by integrating over the surface of the drop
By integrating over either the area or the surface of the drop
Taking the time derivative of the location of the points
All of the above

As we refine the grid and reduce the time step, we expect
The drop to go faster
The drop to go slower
The drop to become more circular
The solution to become independent of the grid
None of the above

To simulate a bubble we need to
Make horizontal boundaries full slip
Make vertical boundaries full slip
Make the density of the bubble smaller than the ambient fluid
Set surface tension to zero
All of the above

To simulate the Rayleigh-Taylor instability we need to
Change the interface to run across the domain
Make the vertical boundaries rigid no-slip walls
Change the way we compute surface tension
Change the way we find the marker function
None of the above

The small-scale structures appearing at late time in the Rayleigh-Taylor instability
Show that there is an error in the code
Always appear in simulations of multiphase flow
Can only be captured by tracking the front with marker particles
Are a common feature in multiphase flows
None of the above