This document summarizes Nicolò Di Domenico's master's thesis analyzing fluid structure interaction and vortex shedding induced vibrations. It investigates these phenomena for a NACA 0009 hydrofoil using computational fluid dynamics and finite element analysis with a radial basis function mesh morphing technique. The analysis captures lock-in and lock-off behavior for the hydrofoil by evaluating frequencies, lift coefficients, and turbulent kinetic energy at different inlet velocities, matching experimental data. The radial basis function method allows simulations to be run around 12 times faster than a traditional two-way fluid structure interaction approach.

1. University of Rome Tor Vergata
Engineering macro-area
Master thesis in mechanical engineering
Advisor:
Prof. Marco Evangelos Biancolini
Co-Advisor:
Andy Wade (ANSYS-UK)
Tobias Berg (ANSYS-Sweden)
Candidate:
Nicolò Di Domenico
Fluid structure interaction analysis:
vortex shedding induced vibrations.

2. ‹N›Nicolò Di Domenico 2
AEROELASTICITY
«The study of the mutual interaction that takes place within the triangle of the inertial,
elastic, and aerodynamic forces acting on structural members exposed to an airstream,
and the influence of this study on design». (Collar, 1947)

3. ‹N›Nicolò Di Domenico 3
AEROELASTICITY
«The study of the mutual interaction that takes place within the triangle of the inertial,
elastic, and aerodynamic forces acting on structural members exposed to an airstream,
and the influence of this study on design». (Collar, 1947)
Static phenomena

4. ‹N›Nicolò Di Domenico 4
AEROELASTICITY
«The study of the mutual interaction that takes place within the triangle of the inertial,
elastic, and aerodynamic forces acting on structural members exposed to an airstream,
and the influence of this study on design». (Collar, 1947)
Static phenomena Dynamic phenomena

5. ‹N› 5
VORTEX SHEDDING
«Big whorls have little whorls,
Which feed on their velocity;
And little whorls have lesser
whorls, and so on to viscosity».
(L.F.Richardson)
Nicolò Di Domenico

6. ‹N› 6
VORTICES INDUCED VIBRATIONS
Fluctuant vortices affect the pressure field:
 side forces, moments;
 noise.
Periodic stress
System dynamic response
+
Takoma narrow bridge, US, 1940
Nicolò Di Domenico

7. ‹N›7
VORTICES INDUCED VIBRATIONS
Fluctuant vortices affect the pressure field:
 side forces, moments;
 noise.
Periodic stress
System dynamic response
+
Fatigue and instability
problems
Lock in
Takoma narrow bridge, US, 1940
Nicolò Di Domenico

8. ‹N› 8
WORK GOALS
• NACA 0009 hydrofoil analysis;
• Obtain a good fluid structure coupling;
• Simplify the fsi approaches;
• Validate the case study with
experimental results.
Nicolò Di Domenico

9. ‹N› 9
NACA 0009 HYDROFOIL
• Thickness law:
Nicolò Di Domenico

10. ‹N› 10
TOOLS AND METHODS
RBF Morph
ANSYS Mechanical
System Coupling
ANSYS FluentANSYS Fluent
Nicolò Di Domenico

11. ‹N›11
TOOLS AND METHODS
FSI: two way
RBF MorphANSYS Mechanical
System Coupling
ANSYS Fluent ANSYS Fluent
• Bidirectional process;
• Mesh regeneration.
• Radial Basis Functions;
• Modal theory;
• Only one analysis software;
• Mesh morphing.
FSI: modal superposition
Nicolò Di Domenico

12. ‹N› 12
MULTI MORPH MODAL SUPERPOSITION
• Modal analysis:
1133.8 Hz 1587.1 Hz 3660.9 Hz
Nicolò Di Domenico

13. ‹N› 13
• Modal analysis
• RBF Morph:
1. Source points definition and their displacement
Points:
11052
MULTI MORPH MODAL SUPERPOSITION
Interpolating function:
FEM CFD
Nicolò Di Domenico

14. ‹N›14
• Modal analysis
• RBF Morph:
1. Source points definition and their displacement
Points:
11052
MULTI MORPH MODAL SUPERPOSITION
Interpolating function:
FEM CFD
Nicolò Di Domenico

15. Polinomial
correction for the
rigid motions
compatibility
‹N›15
• Modal analysis
• RBF Morph:
1. Source points definition and their displacement
Points:
11052
MULTI MORPH MODAL SUPERPOSITION
Interpolating function:
FEM CFD
Nicolò Di Domenico

16. ‹N› 16
• Modal analysis
• RBF Morph:
2. Deformation’s volume and morphing effect
Radius 0,15 m
# Points 557
Lencap > Lala
MULTI MORPH MODAL SUPERPOSITION
Range of action and
interest area around the
source points:
Mesh morphing
Nicolò Di Domenico

17. ‹N› 17
• Modal analysis
• RBF Morph
• Fluid dynamics analysis:
Inlet
Wall
Outlet
RANS SST k-ω model
Time step 2e-5
Iterations per time step 5
Number of time step 10000
Boundary conditions
Velocity 12÷22 m/s
Pressure 101325 Pa
Density 998 kg/m3
Temperature 288,15 K
Kinematic viscosity 10-6 mm2/s
MULTI MORPH MODAL SUPERPOSITION
Nicolò Di Domenico

18. ‹N› 18
MULTI MORPH MODAL SUPERPOSITION
RBF Morph is fully integrated in Fluent and at any time step it resolves the equation in modal form
Dynamic model
it follows
Journal file
Nicolò Di Domenico

20. ‹N›
• Water added mass effect and damping of the medium;
• Free oscillations induced by an initial deformation;
• RANS SST k-ω: stationary fluid.
20
MODES ANALYSIS UNDER WATER
Air case Water case
Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 Mode 6
1133.8 Hz 1587.1 Hz 3660.9 Hz 3917.7 Hz 5936.6 Hz 6789.6 Hz
Mode 1 Mode 2 Mode 3 Mode 4
891.9 Hz 1118.8 Hz 1619.6 Hz 2902.7 Hz
Nicolò Di Domenico

21. ‹N› 21
LOCK IN
• Probe coordinates (0.08000 m, 0.03788 m, 0.1125 m);
• Dominant frequency 909.91 Hz;
• Inlet velocity16 m/s.
Nicolò Di Domenico

22. ‹N› 22
LOCK IN
• Reynolds number
• Lift coefficient
Nicolò Di Domenico
Turbulent kinetic energy
(t=0,2s)

23. ‹N› 23
LOCK OFF
• Probe coordinates (0.08000 m, 0.03788 m, 0.1125 m);
• Dominant frequency 1209.9 Hz;
• Inlet velocity 22 m/s.
Nicolò Di Domenico

24. ‹N› 24
LOCK OFF
• Reynolds number
• Lift coefficient
Nicolò Di Domenico
Turbulent kinetic energy
(t=0,2s)

25. ‹N› 25
RESULTS ANALYSIS
Nicolò Di Domenico

26. ‹N› 26
RESULTS ANALYSIS
Experimental data
Lock In
• Cref ≅ 16 m/s
• fs ≅ 900 Hz
Lock Off
• Cref ≅ 22 m/s
• fs ≅ 1200 Hz
Nicolò Di Domenico

27. ‹N› 27
DATA COMPARISON: LOCK IN
RBF MorphTwo way
35 h to simulate 0.1s
of the phenomenon
on a calculator with
144 cores
37 h to simulate 0.2s
of the phenomenon
on a calculator with
da 32 cores
Nicolò Di Domenico

28. ‹N› 28
DATA COMPARISON: LOCK OFF
RBF MorphTwo way
35 h to simulate 0.1s
of the phenomenon
on a calculator with
144 cores
37 h to simulate 0.2s
of the phenomenon
on a calculator with
da 32 cores
Nicolò Di Domenico

29. ‹N› 29
CONCLUSIONS
• Good fluid structure coupling in terms of induced vibrations;
• With the same calculator RBF Morph allows a speed up factor ≈ 12
compared to the two way method;
• General approach to calculate natural frequencies under water;
• The modal superposition method with mesh morphing detects the
renonance physics;
• Boundary conditions strongly affect the vortex shedding phenomen;
Nicolò Di Domenico

30. ‹N› 30
FUTURE DEVELOPMENTS
• Overcome the limits of the RANS model (strong influence of the
turbulent model);
• Wake control (CFD): numerical solutions to reduce the phenomenon,
trying to limit the drag penalty;
• Wake control (FEM): numerical solutions focused on the shape
optimization of the bodies affected by these phenomena;
• Industrial numerical applications: mesh morphing requires less
computational costs than remeshing;
• Perform the experiment in laboratory, using different material and
holding the initial geometry (i.e. Orthotropic materials).
Nicolò Di Domenico

31. THANK YOU FOR THE
ATTENTION