Optimization of structural components for Ariane 5ME upper stage Andreas Reim, Astrium ST Bremen, TEB11 mechanical engineering Gerrit Quappen,

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1 Optimization of structural components for Ariane 5ME upper stage Andreas Reim, Astrium ST Bremen, TEB11 mechanical engineering Gerrit Quappen, Astrium ST Bremen, TEB11 mechanical engineering

2 Overview Introduction Astrium company overview Objective of the presented work Established optimization process Analysis problem description Optimization problem definition Derivation of optimization procedure Application of the method in the frame of A5ME Conclusion Page 2

3 Astrium: part of EADS, a global leader in aerospace and defense EADS Airbus Airbus Military Eurocopter Astrium Cassidian Page 3

4 Astrium s activities are based in three key areas Page 4 Astrium Space Transportation Astrium Satellites Astrium Services The European prime contractor for civil and military space transportation and manned space activities A world leader in the design and manufacture of satellite systems At the forefront of satellite services in the secure communications, Earth observation and navigation fields

5 Objective of the presented work Optimization method for structural optimization of bare tank structures in order to reduce mass Consideration of special requirements in the analysis of structures in cryogenic environment demonstrate feasibility of optimization process by application on preliminary design of A5ME upper stage bare tank components (Y-rings) Y-rings Concept for new A5ME upper stage Credits: ESA / CNES / Arianespace / Photo Optique vidéo du CSG Photo available under Page 5

6 Loads to be considered for preliminary design General loads inertia and aerodynamic loads engine loads Pressure loads internal gas pressure hydrostatic pressure quasi static hydrodynamic pressure Thermal mapping (see also /1/) <100K <100K >250K Page 6

7 Developing methods Methods for calculation of the mechanic characteristics (see also /2/) Handbook calculation Simplified analytical methods Finite Element analyses Optimization strategies (see also /3/) Page 7

8 Definition of the optimization problem Optimization problem contains (see also /4/) system parameters Geometrical parameters optimization objective Minimization of mass Simultaneously keeping the design in the constraints limits optimization constraints Maximum von Mises stress Maximum Shear stress (for weld dimensioning) Manufacturing constraints system function Finite element analysis The system function is also influenced additional parameters Finite element mesh definition linear vs. nonlinear calculation of the finite element results Page 8

9 Derived optimization procedure 1. Free shape optimization (see also /5/) Shape modification performed by the optimization algorithm Generation of engineering information Main steps: NASTRAN *.bdf File preprocessing Integration of optimization constraints and objective Perform Optimization using linear FEM used commercial software: Altair OptiStruct 2. Shape optimization Predefined shapes are scaled and superposed leading to a mass minimum Main Steps: NASTRAN *.bdf File preprocessing Integration of optimization constraints and objective Perform Optimization using nonlinear FEM used commercial software: Altair HyperStudy in combination with MSC NASTRAN Page 9

10 Free Shape Optimization Preprocessing of FE Modell Generate temperature based element sets Derive material properties for different temperatures within the material Connect the element sets to the corresponding material properties Set the maximum von Mises and shear stress considering the temperature in the element sets and set it as a constraint Advantage of the free shape optimization Shape generated without input from human Common understanding about how the structure can be modified Page 10

11 Free Shape Optimization Output considers Information about desired shape of the component Indicator for mass reduction potential Output does not consider Geometrical restrictions in weld area Nonlinear effects on stress distribution Possible optimized shape after Free Shape optimization Distribution of linear stress to deal with Page 11

12 Shape Optimization Preprocessing of FE Model Derivation of shape variables from the free shape analysis results Integrate the shapes derived from the FSO into the FE model Add mass calculation into NASTRAN deck Define elements for which constraints will be calculated Model the optimization problem using HyperStudy Advantage of the shape optimization Minimization of structural weight Optimized shape considers manufacturing aspects Page 12

13 Application of the method in the frame of A5ME Analysis of a simplified FE model for the A5ME bare tank (rotational symmetric model) Loads considered: general loads pressure loads thermal mapping Margin of safety policy respected Critical yield/ultimate load cases modeled (4 in total) Page 13

14 Resulting shape: Free Shape Optimization Lower Y-Ring Upper Y-Ring -6% Computational time ~15h -6% Page 14

15 Shape derivation for shape optimization No thickness change in clamping area Translation of radius in order to reduce stress peaks Shoulder definition (see also /6/) (straight lines) Radius modification in order to reduce stress peaks Page 15

16 Resulting shape: Shape Optimization Initial design Free Shape Optimization Shape Optimization Lower Y-Ring Upper Y-Ring -7% Computational time ~12d -5% Page 16

17 Summary 1. Generation of a reference design Defines the topology under investigation Design may violated single constraints 2. Free Shape optimization derivation of mass reduction potential Information about advantageous shapes 3. Shape optimization Derivation of components mass All requirements are met 4. Optimal structural design Page 17

18 Conclusion Positive influence of nonlinear FEM: The peak stresses within the linear FEM results overestimate the more realistic nonlinear stresses. nonlinear FEM can consider these effects Negative influence of predefined shapes The shape optimization is limited to a number of predefined geometric shapes. This restricts the possible mass reduction. The implemented optimization method efficiently improves the mass budget of the given structures. For the components under consideration, a 9% mass reduction seems to be achievable, if the influence of the design change is also considered in the adjacent structures Page 18

19 Literature /1/ Frey, B. (2010): Thermalkonzept der Kryogenen Oberstufe von ARIANE 5 Midlife Evolution, 60. Deutscher Luft- und Raumfahrtkongress 2011, Bremen /2/ ESA Requirements and Standards Division ESTEC (2010): Space engineering - Buckling of structures, Noordwijk /3/ Schumacher, A. (2005): Optimierung mechanischer Strukturen: Grundlagen und industrielle Anwendungen, Berlin, Heidelberg: Springer /4/ Lawden, D, F. (2006): Analytical Methods of Optimization, Mineola: Dover Publications /5/ Thue, R. B. et al (2010): Application of Structural Optimization Technologies and Methods to Reduce Design Time and Improve Structural Robustness, in proceedings of AIAA SPACE 2010 Conference & Exposition, AIAA /6/ Öry, H. (1991): Structural Design of Aerospace Vehicles I, SPACE COURSE, Institut für Leichtbau, RWTH Aachen, Proceedings, Page 19