The document summarizes a master's thesis on modeling the structural behavior of an atmospheric reentry vehicle during ditching. The thesis studied the Intermediate eXperimental Vehicle (IXV) project, which aims to develop and test technologies for controlled atmospheric reentry in Europe. Numerical models of the IXV vehicle and surrounding fluid were created and simulations were run to analyze acceleration and pressure data during impact. The results showed good correlation with experimental data, validating the modeling approach. Further refinements to account for flexibility and fluid behavior were recommended.

1. POLITECNICO OF TURIN
MASTER DEGREE THESIS IN AEROSPACE
ENGINEERING
Study on structural behavior of an atmospheric
reentry vehicle during ditching
Supervisors:
• Prof. Giulio Romeo – Politecnico of Turin
• Ing. Roberto Ullio – Thales Alenia Space
Candidate
• Maurizio Coltro

2. Thesis activity
Part of ESA’s Future Launchers Preparatory Programme has
been devoted to optimizing a long-term European roadmap for
in-flight experimentation with atmospheric re-entry enabling
systems and technologies.
The Intermediate
eXperimental Vehicle (IXV)
project is the next core step
of this effort.
This work has been developed within the IXV project and with
closed collaboration of TAS-I and ESA.
Many thanks to ESA and TAS for their support. Thanks also to Altair
Engineering for providing the software suite for the analysis.

3. The IXV Project
Technology platform
• Intermediate element of technology-effective and cost efficient European
roadmap
• Prepare future ambitious operational system developments with limited risks
for Europe
Project objectives
• Design, development, manufacturing, on-ground and in-flight verification of
autonomous European lifting and controlled re-entry system
Critical technologies of interest
• Advanced instrumentation for aerodynamics and aerothermodynamics
• Thermal protection and hot-structures solutions
• Guidance, navigation and flight control
Success of IXV mission
• Correct performance of re-entry
• Safe landing and recovery with its experimental data
1/17

4. Experimental measurements
Mockup
• representative of external shape
• inertial properties
• scale factors
Physical quantities
• accelerations
• pressures
Test facility
• electromagnets to release vehicle
• high frequency cameras
• high pool dimension to perform impact
2/17

5. Modeling methodology
Solver
• Hyperview
• Hypermesh • Radioss
• Hypercrash BLOCK V10
Preprocessor Postprocessor
Explicit
Suited for
solution Drawbacks
problems
tecnique
• short duration
• high velocity
• highly nonlinear
nature
3/17

6. IXV numerical model
STRUCTURE MODELING
CONFIGURATION ASSUMPTIONS
External dimensions taken
Fuselage into account
components
Bidimensional rapresentation
of surfaces
Flaps assembly Rigid body description
RIGID BODY INERTIAL PROPERTIES
Mass Jxx Jyy Jzz
[kg]
27,82 1,17 4,52 4,31
4/17

7. Fluid numerical model
MODELING
FLUID DESCRIPTION
ASSUMPTIONS
Gas volume extension
LAW37 Biphas
ALE approach
Liquid volume extension
5/17

8. Fluid numerical model
HORIZONTAL EXTENSION
• LimitedZ Acceleration -to
front dimensions Accelerometer T1064-63 (COG)
avoid wave reflection
VERTICAL EXTENSION
• Limited in-deep dimensions
to lighten fluid model
WATER BASIN COMPARISON
Deep water model Shallow water model
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
Horizontal 1,22 x 2,14 [m] 1,22 x 2,14 [m]
Vertical Time [s]
0,8 [m] 0,4 [m]
N Elements 335265 Deep Water Model 189317
Shallow Water Model
CPU Time 8413 [s] 5077 [s]
6/17

9. Characteristic elements dimension
Finest mesh Sensitivity
normal to analysis
phenomenon
2D ELEMENTS 3D ELEMENTS 3D ELEMENTS
(VEHICLE) (AIR) (WATER)
HEIGHT 20 [mm] 20 [mm] 20 [mm]
WIDTH 20 [mm] 20 [mm] 20 [mm]
DEPTH / 10 [mm] 10 [mm]
N ELEMENTS 3564 78324 287188
7/17

10. Fluid-structure interface
FLUID
STRUCTURE
INTERFACE
TYPE18
SENSITIVITY STFAC GAP
ANALYSIS Interface Activation
PERFORMED
stiffness distance
PRESSURE PROBES • Single TYPE18 interface to
INTERFACE represent sensors separately
8/17

11. Boundary-initial conditions
• Atmospheric pressure to water free
surface
WATER • DYREL dynamic relaxation for convergence
BOUNDARY • Gravity load to water volume
CONDITIONS • Lateral/bottom surfaces locked
• FLRD = 1 upper surface
• Initially locked in all DOFs
VEHICLE • Gravity load to master node
BOUNDARY
CONDITIONS • Initial velocity to master node
• Initial distance from free surface
9/17

12. Numerical - Experimental Correlation
All loadcases computed from 0 to 200 ms
FOURTH
SECOND
THIRD
FIRST • Impact angle 51 deg
19
35 deg
• Flaps position 21deg
0 deg
LOADCASE • Vertical velocity 3,4 m/s
10/17

13. First Loadcase
0.2
AX - COG
0.1
0
-0.1 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
-0.2
-0.3
-0.4
-0.5
t [s]
0.6
AZ - COG
0.4
0.2
0
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
-0.2
t [s]
Numerical
Experimental
11/17 All curves normalized to 1

14. Second Loadcase
0.1
AX - COG
0
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
-0.1
-0.2
-0.3
-0.4
t [s]
0.8
AZ - COG
0.6
0.4
0.2
0
-0.2 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
-0.4
t [s]
Numerical
Experimental
12/17 All curves normalized to 1

15. Third Loadcase
0.3
AX - COG
0.2
0.1
0
-0.1 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
-0.2
-0.3
-0.4
t [s]
0.4
AZ - COG
0.3
0.2
0.1
0
-0.1 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18
-0.2
t [s]
Numerical
Experimental
13/17 All curves normalized to 1

16. Third Loadcase
19 deg Sensor
0.40
0.30
0.20
0.10
0.00
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
-0.10
t [s]
Numerical Experimental
35 deg Sensor
0.80
0.60
0.40
0.20
0.00
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
-0.20
t [s]
Numerical Experimental
1.00
51 deg Sensor
0.80
0.60
0.40
0.20
0.00
-0.20 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
t [s]
14/17

17. Correlation results summary
model updating activity
• improvement of modelling
Correlation approaches
process • correction of individual
parameters
Main outcomes from acceleration results
• very good correlation at COG in X and Z directions
• satisfactory correlation at NOSE and REAR parts
Main outcomes from pressure results
• good correlation
• impact event chronology
• pressure time history signature
• satisfactory correlation
• pressure peak values
15/17

18. Remarks and further developments
Experimental
numerical results
deviation
Flexible body Statistic data Exposed impact areas and
behaviour dispersion mathematical model
Alternative modeling methodology
Structure
Deformable body
Fluid
LAW51 Multimaterial with
SPH method
outlet treatment
16/17

19. Thanks for your attention
17/17