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CFD Techniques Quiz. What is the weight of an adult hippo skin?. 0.5 tons 1 ton 2 tons. 10. What type of equation is this if the flow is supersonic?. elliptic parabolic hyperbolic. 10. I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
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Presentation Transcript ### CFD Techniques Quiz   What is X in the definition below?The X is the difference between the PDE and the finite difference representation
• Rounding error
• Goodness of fit
• Truncation error
• Convergence measure
• Marching error

10 Consider the finite difference approximation to the first derivative below. Which statement is false?
• If the grid spacing is halved the error goes down by 1/4
• This is a central difference approximation
• This form might be useful close to a wall
• This form might be useful near the edge of the simulation

10 What is X in the description below?A X is one for which errors from any source (round-off, truncation, mistakes) are not permitted to grow in the sequence of numerical procedures as the calculation proceeds from one marching step to the next.

• consistent numerical scheme
• stable numerical scheme
• convergent numerical scheme
• second-order numerical scheme

10 What is X in the description below?A solution to a finite difference representation is said to be X if it approaches the true solution to the PDE having the same initial and boundary conditions as the mesh is refined.

• consistent
• stable
• convergent
• Ill-posed

10 What is X in the description below?By X, we mean those errors that arise as a result of the rounding to a finite number of digits in the arithmetic operations.

• truncation
• round-off errors
• systematic errors
• happy accidents

10 What is X in the definition below?A finite difference representation is said to be X if we can show that the difference between the PDE and its finite difference representation vanishes as the mesh is refined.

• consistent
• convergent
• stable
• first order
• most excellent

10 Which statement is false?
• Parabolic equations have degenerate characteristics
• The initial value problem is ill-posed for elliptic problems
• Discontinuities can appear in elliptic problems
• The unsteady heat conduction equation is an example of a parabolic problem

10 What is X in the definition below? X error is the error in the solution to the PDE subject to the given initial values and boundary conditions caused by replacing the continuous problem by a discrete one and is defined as the difference between the exact solution of the PDE (round-off free) and the exact solution to the finite difference equations (round-off free).

• Discretisation
• Truncation
• Round-off
• Integration

10 Which statement is false?
• The Courant number has no units
• If you double the sound speed, the Courant number doubles
• If you halve the space grid the Courant number doubles
• If you halve the time grid, the Courant number doubles

10 Which term would NOT be required in a von Neumann stability analysis of the equation below? Hint:

1.

2.

3.

4.

5.

10 The amplitude in a von Neumann stability test is found to have the following modulus. What can we say about the finite difference representation?

• It’s unconditionally stable
• It’s conditionally stable
• It’s conditionally unstable
• It’s unconditionally unstable

10  What is the equilibrium value of A in the square grid used to solve Laplace’s equation in 2-d?
• 2.3
• 2.4
• 2.5
• 2.6
• 2.7

10   • Dirichlet
• Neumann
• Mixed

10 Which of these is the correct expression for the iteration at point 3 in an explicit (Jacobi) method?
• 1.
• 2.
• 3.
• 4.

10 Which of these is the correct expression for the iteration at point 2 in an implicit (Gauss-Seidel) method?
• 1.
• 2.
• 3.
• 4.

10 1.

2.

3.

4.

5.

10 A solution of this equation is Which way is the wave travelling and what is its speed?
• Left to right (toward positive x) speed 2
• Right to left (toward negative x) speed 2
• Left to right (toward positive x) speed 0.5
• Right to left (toward positive x) speed 0.5

10  Which of the following statements is false?
• Dispersion is caused by odd derivative terms in a PDE truncation
• Diffusion is caused by odd derivative terms in a PDE truncation

10 A CFD simulation of a shock develops ‘waviness’ as pictured below? This is evidence for what in the solution?
• Dispersion
• Diffusion

10  Which of these is NOT a point at the entry to the duct (x=0) joined to the point P by 45 degree characteristics (i.e. lines of slope -1 and +1) ?

• (0,0.6)
• (0,-0.6)
• (0,0.4)
• (0,-0.4)

10