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ESTEC, October 9, 2003 Ariane 5 Coupled Loads Analysis 1
IntroductionIntroduction• Dynamic coupled loads analysis (CLA) is carried out as part of the mission
analysis study and is used as verification tool for payload dimensioning.• CLA predicts responses of launcher (LV) & payload (PL) caused by dynamic
and quasi-static loads such as
– Liftoff from launch table – Gravity loads– Engine startup and shutdown – Engine thrust (constant)– Blastwaves from solid rocket ignition – Stage separation loads– Aerodynamic loads, gust at Transonic and Qmax– Internal acoustic modes in solid rockets
• Results are used to design or to verify the design of the payload, its qualification test plan including a notching procedure if applicable, to verify the final in-flight loads, and to make sure that the PL does not affect the behaviour of the LV or its stability.
ESTEC, October 9, 2003 Ariane 5 Coupled Loads Analysis 4
– Dynamic effects up to about 100 Hz– 3D FE models of EPC, EAP, UC– Structure/fluid interaction– Incompressible or compressible fluid models for liquid propellants – Nearly incompressible SRB solid propellant modeling– Pressure and stress effects on launcher stiffness– Flexible interfaces between modules and LV-PL
interface (1, 16 or 36 node I/F)– SRB propellant and DIAS structural damping
evaluated for major modes (equivalent viscousdamping ratios used in direct transient or frequency response analysis)
ESTEC, October 9, 2003 Ariane 5 Coupled Loads Analysis 8
MethodsMethods• For accurately and efficiently performing CLA a number of methods are used
– Modal synthesis (Craig-Bampton method)– Prestress effects in tanks– Substructuring techniques – BEM for slosh and coupled structure/fluid modes of LV with liquid propellant– Efficient direct transient analysis for systems with changing boundary conditions– OTMs for accurate and efficient recovery of physical responses in the PL (mode
• A number of different tools are used to perform specific computations, execute repetitive tasks, avoid error through editing, visualisation of results and pre- and postprocessing
– MSC.NastranTM (DMAP)– Fabe (Fluid Analysis with Boundary Elements)– MSC.PatranTM
– DynaWorks® (software package for managingand analysing dynamic environmental data, suchas vibrations, shocks, acoustics and thermalmeasurements)
– Fortran routines– UNIX scripts
Module
Mf,Kf
δ K
CB M,D,K
CB F
Flight event
f90
ESTEC, October 9, 2003 Ariane 5 Coupled Loads Analysis 13
• Results are obtained directly from response analysis in time or frequency domain or after postprocessing
– Time histories of accelerations, forces and displacements– Min/max values accelerations, forces and displacements– Quasi-static load factors (equivalent to low frequency dynamic loads,
• For CLA a number of phenomena are taken into account
– Elastic behaviour of a structure– Sloshing in large tanks including fluid-structure interaction– Aerodynamic and acoustic loading
– Gimballing of nozzles (SRB, cryogenic stage, considered by QSL factor)
– Aeroelasticity: interactions between structural dynamics and airloads– Effects of buffeting: excitation of nozzle pendulum modes– Loading generated by control system: loads ⇒ f (control law)
• CLA needs a ready-for-use LV model to respond quickly to project request