1. Verification & Validation
QIP Course on CFD
June 2-6, 2003
K Sudhakar SKSane Amitay Isaacs
Department of Aerospace Engineering
Indian Institute of technology, Mumbai

2. Verification & Validation
What?
Why?
When?
How?
Who?

3. Verification & Validation
What?
Verification & Validation
No computer code can be proved to have no errors. But Can be proved wrong if evidence to this effect is collected.
Process of increasing our confidence in results of a computation
Practiced with rigour in critical applications.
IV&V, ADA, Bangalore
ISRO, DRDL, . .
CFVDS - Centre for Formal Verification & Design of Software, IIT Bombay

4. Verification & Validation
What?
Verification & Validation
Validation
simple systems m c k
Reality
Validation
Model
Qualification
Code
Verification

5. What? Validation Validation - Is the correct model being solved? k c
If resistance due to air is significant
the model will be incorrect.
How to confirm if model is good?
Analytically integrate?
Conduct experiments.
Compare
Possible only for simple Models.
Verification - Is the model being solved correctly

6. Verification & Validation
What?
Verification & Validation
Reality
Model
Code
Verification
Validation
Qualification

7. Verification & Validation
Why?
Verification & Validation
Affects critical performance
Loss of life?
Loss of prestige?
Financial/Social loss
Affects important performance
Loss of revenue
How frequently
etc.
Incorrect results
Integrity Level
scale of 0 to 4
0  No IV&V required
……………
4  rigorous IV&V required

8. Verification & Validation
When?
Verification & Validation
Most effective if conducted in parallel with s/w development
Concept V&V
Requirements V&V
Design V&V
Implementation V&V
Test V&V
Installation & Checkout V&V
Operation V&V
Maintenance V&V

9. Verification & Validation
When?
Verification & Validation
V&V are defined as the process of determining; ie.
They are on-going activities
No end point 0%
100%
Confidence
Cost
Value
Time

10. Verification & Validation
How?
Verification & Validation
Are the results given by a computer program correct?
How to investigate this?
Any standard processes to perform V&V?
IEEE Std , etc.
Common sense, logic, discipline, . .

11. How? Verification Verification - Is the model being solved correctly?
Solution Verification. Numerical techniques
Sources of error - spatial & temporal discretisation, iterative convergence, round off
ODE’s
Time step adequate for all situations? Adaptive?
PDEs
round off, iterative convergence are better understood and can be addressed.
Discretisation errors in PDE are less understood

12. How? Verification Verification - Is the model being solved correctly?
Code Verification
Coding language,
Coding practices, (S/W Engineering)
Model to code translation
Static & dynamic analysis.
Statically unreachable code
Dynamically unreachable code
FTNCHK, FORCHEK etc.

13. How? Verification = Model Solution Code Answers from highly accurate
solutions
Analytical
Benchmark
Solution =

14. How? Verification Checks must cover all paths through the code?
if (0<m=<0.9) then
gama = 1.4
call abc (….)
elseif (0.9<m<1.2) then
gama =14.
call def ( )
elseif (1.2=<m<2.0)
call ghi ( ….)
endif
Verification checks
m = 0.6, 0.8, 0.9, 1.3, 1.5, 2.
Does not check one path.
m = 0.6, 0.8, 0.9, 1.0, 1.3, 1.5, 2.
Checks all paths

15. How? Validation Is the model correct? Conceptual Model Code Reality
Results
Experience
Validation
domain
Simple systems
Verification

16. Validation for Complex Systems
How?
Validation for Complex Systems
Code
Validation
Experiments
Outcome of
Experiment
Computational
Predictions
Model
Experimental
Prediction

17. Validation for Complex Systems
How?
Validation for Complex Systems
Computational
Predictions
Code
Computational
Results of Exp
outcome
Model
Difference
Validation
Experiments
Outcome of
Experiment

18. How?
Validation
Prediction
Confidence?
Predictive domain
Validation
domain
Can validation domain cover the predictive requirements?

19. How? Validation x - Validation experiments x
Predictive domain x
Where to conduct experiments?
How to assess predictive confidence?

20. How? Validation Computation Region 3 Region 1 Region 2
Validation Experiment
Computation
Region 1
Region 2
Region 3

21. How? Validation Design & Analysis of Computer Experiments
Where to conduct computational & physical experiments for validation?
How to build predictive models?
How to assess predictive confidence?
Computational results
corrected using fixed no
of physical experiments x
Estimates of
Predictive error

22. How? Validation = Real World Model Solution Answers from validation
experiments
Benchmark
solutions
Specially
conducted
Code
Solution =
Model

23. Verification & Validation
Who?
Verification & Validation
Independent Verification & Validation (IV&V)
Technical Independence. V&V done by people who are not involved in design & development
Managerial Independence. An organization separate from that did design & development.
Financial Independence. Budget for V&V is not in anyway controlled by those responsible to design & development.

24. Verification & Validation in CFD
Less valued in CFD than in FEM (for historical reasons)
AIAA Aerosp. Sciences Meeting & Exhibit 2002
DLR-F4 Wing Body
35 different CFD Calculations (Advanced research codes & commercial codes)
After weeding out outliers this gave a standard deviation in CD = (for wind tunnel testing this figure is put at )

25. Thank you

26. Coding Practice - Not Done!
How?
Coding Practice - Not Done!
if (x) 100, 200, 300
200 if (y) 400, 500, 600
z= z +1
goto 750
xsq = x**2.
goto 850
300 xcu = x**3
…..
t1 = a1*2. + b1
t2 = sqrt(t1)+c1
t3 = t2**1.3+b1
. . .
real a(100)
integer b(50)
complex c(10)
equivalence (a(1),b(1)),