Efficient Coupled Approaches for PracticalParachute Simulation

XV Jornada de Recerca del Departament de Física

Enrique Ortega and Roberto Flores

Barcelona, 31 January 2020

Institut d’Estudis Catalans

L’AIRE LaboratoriAeronàutic i

IndustrialdeRecercaiEstudi

Challenges in parachute simulation

Parachutes have complex shape and structure

No-compression response of fabric and cables

Subject to very large changes in geometryduring extraction, deployment and inflation

Complex flow physics: unsteady flow, usuallywith extensive detachment

Strong coupling between fluid and structure

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Experiments and semi-empirical calculation methods (e.g. Ewing and Knackedesign guides).

Solution Approaches

Physical modeling and scope is limitedOnly model surfaces must be discretizedTraining in computational mechanics is neededFeasible for practical analysis

Improved physical modeling and scopeFull-domain discretizationExpertise in computational mechanics is requiredNot affordable for most manufacturers and designersExamples: DDS/SST techniques, LS-DYNA

Low-fidelity (80s): potentialflow panel methods + FEMfor structure with staggeredcoupling

High-fidelity (90s): CFD +FEM with staggered ormonolithic coupling

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• Research started at CIMNE in 2005 as a join workwith CIMSA Ingeniería en Sistemas.

• Important advances: EU’s Paraplane 2012-2015(validation and development of the userinterface)

• In 2015, interest in the software encouraged us tostep to market. First license sold to AIRBUS.PARACHUTES is in use in the Kite Project(www.airseas.com). Others: NIVIUK, DLR…

• Further validation and improvements are beingcarried out with CIMSA under ESA’s Space RIDERproject

www.airseas.com

Development overview

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Initially intended for ram-air parachutes (limited flowseparation)

Low computational cost (no need for high-performance hardware). Parallelization throughOpenMP directives.

Robustness and ease of use (intended for non-specialized users)

Suitable for transient and steady-state simulations

Modeling of interaction between the parachute and thepayload

Our approach: design constraintswww.cimne.com/parachutes

6Flores, R.; Ortega, E.; Oñate, E. Simple and efficient numerical tools for the analysis of parachutes. Eng. Comp., 2014

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Solution Methodology (I)

Aerodynamic model

Assumptions: incompressible irrotational flow

( 0 V

2 0 0 V

V

Boundary conditions:

ˆ 0 n

Away of the body

Slip condition on the body

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• The potential is obtained by means of Green’s theorem. Constant-strength doubletand source distributions are used with internal Dirichlet (i=) and Neumannconditions (thick/thin bodies)

• Time-marching wake model

• Pressures are obtained from the velocity field by means of Bernoulli’s equation

• Empirical drag functions are defined for the canopy, lines and payload

1 1 1ˆ ˆ04 4 4

B B W

WS S S

dS dS dSr r r

n n

N1 1ˆ ˆ ˆ ˆ ˆ V

4 4 P

B W

p W p pS S

dS dSr r

vn n n n n

N 0 ˆV rel V v r nThick bodies:

Thin bodies: U L

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Solution Methodology (II)

Structural model

• Explicit dynamic analysis. Noconvergence issues in highly non-linearproblems (e.g. large displacements anddeformations, complex material behavior)

• Three-node linear membrane elements,two-node linear cable elements and four-node solid elements

• Includes wrinkling model

• Rayleigh damping and bulk viscosity fornoise control

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Explicit Central difference Operator

Finite Element Space-Discrete Equation Set

0

0

:

bulk viscosity

N N N

V S

N N

V

P dV dS

I dV

C

N F N t

β σ

M K +

2

2i id d

dt dt M P Ix xC

External Loads

Internal Forces

1 2 1 21 ( )2

n nnn n

ii i i

i

tt tm

RHSv v v

1 21 1 nn n ni i it

x x v1 1/2 1

2n ni i i v v v

1/2 1/2n ni i iv v v

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Fluid-Structure coupling

• 2-way staggered coupling (rapid solutions on modest computerplatforms)

• The aerodynamic and structural models share the same mesh

• Since the structural stability limit is small (explicit method), severalstructural steps are performed per aerodynamic step

• Effects on high-frequency response are generally local. Low-frequency modes are well resolved

• Added-mass effects are included through the Lissaman and Brownmodel

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Examples of Application

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Validation under EU’s FP7 PARAPLANE

Ortega, E.; Flores, R.; Pons-Prats, J. Ram-air parachute simulation withpanel methods and staggered coupling. AIAA J. Aircraft, 2016

2012-2015 Development of a New Steerable Parachute System for Rescueof Small and Medium Size Airplanes (PARAPLANE)Coordinator CIMSA Ingeniería en Sistemas, participants: NLR, DLR, SSBV, Flight Design, among others.

Objective: design, construction and testing of an autonomous parachutesystem for the rescue of small airplanes

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Symmetric brake deflection

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Satisfactory agreement with flight-test data Computational time:

~1 hour CPU time for ~5s physical time~1/2 hour for steady solutions

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Focus on system trajectory, loads andstresses

Empirical-based aerodynamics (filling timeand Ludtke’s are law)

Mass-spring-damper model (initial stages)

FE dynamic solver to complete inflationand terminal descent

Other applications (1/2): Deployment and inflation

Ortega, E.; Flores, R. Aeroelastic analysis of parachute deceleration system with empiricalaerodynamics. Journal of Aerospace Engineering, 2019 18

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Other applications (2/2): Inflatable structures Work developed with Buildair (www.buildair.com)

The inviscid pressure field is corrected for separation effects.

Flow separation is automatically detected (Stratford, 1958)

Cuartero Zaragozá, E. Estudio y aplicación de un método acoplado fluido-estructura alanálisis de estructuras de membrana hinchables, 2017. ETSECCPB-UPC

Preliminary validation: EU’s Ulites project

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90 km/h lateral wind, with atmospheric boundary layer profile(EN 1991-1-4 standard)

Re = 47M, fully turbulent flow 30 mbar pressure, E=0,38 GPa, t=0.5 mm, r=590 kg/m3 Model includes reinforcement tapes and seams

Separation zone (red) 

Ortega, E.; Flores, Cuartero, E., Oñate, E. Efficient aeroelastic analysis of inflatable structures using enhancedpotential flow aerodynamics. Journal of Fluids and Structures, 2019

Buildair’s H20 hangar (1/2)

Corrected pressure

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Approximate solution similar to high-fidelity CFDat much lower cost (CPU-time for convergenceabout 30 min)

Approximate solution much more realistic thanEurocode design loads

Pressure distribution along central tube

Buildair’s H20 hangar (2/2)

X‐displacement with lateral wind 21

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Current lines of research

PhD. Thesis: Pimentel, C. Development of advanced aerodynamic toolsfor the simulation of parachute systems

Particle vortex method for simulation of extensive detached flow.Applications to conventional parachutes and inflatable structuresPanel method + vortex particles for boundary layers and wakes

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List of TFG/TFM• Guerra, A. Development and validation of a numerical code for analysing parachutes. Master Thesis at ESEIAAT-UPC, 2009.• Rita Espada, D. Aerodynamic assessment of humpback whale ventral fin shapes. Master Thesis at ESEIAAT-UPC, 2011.• Perez, J. Flow separation modelling through discrete vortex methods. Master Thesis presented at the EETAC-UPC, 2011• Valles, J. Estudi de noves eines pel programa de càlcul de paracaigudes PARACHUTES. Master Thesis at ESEIAAT-UPC, 2014.• Somoza, P. Study, development and application of vorticity techniques for airfoil flow separation. Undergraduate Dissertation at ESEIAAT-UPC, 2016.• Pérez, D. Study of a methodology for the flight simulation of ram-air parachutes using a vortex-lattice aerodynamic model. Undergraduate Dissertation at

ESEIAAT-UPC, 2017.• Cuartero Zaragozá, E. Estudio y aplicación de un método acoplado fluido-estructura al análisis de estructuras de membrana hinchables. Master Thesis

presented at the ETSECCPB-UPC, 2017• Moreno, J. Aerodynamic performance of a paraglider wing. Undergraduate Dissertation at EETAC-UPC, 2017.• Frigola, O. Study on the influence of wing deformation on the aerodynamic performance of paragliders. Undergraduate Dissertation at ESEIAAT-UPC,

2018• Gutierrez, D. Study and implementation of a control system for autonomous guided parachutes. Undergraduate Dissertation at ESEIAAT-UPC, 2018• Toledo, O. Study of entry, descent and landing of a low mass system at Mars. Undergraduate Dissertation at ESEIAAT-UPC, 2019• Sol, J. Numerical simulation of wind conditions over an inflatable structure. Master Thesis presented at the ETSECCPB-UPC, 2019

AcknowledgementsOriol Frigola Manzano (research fellow 2017‐2018)David de la Torre Sangrà, Carlos Pimentel García (PhD. Students) 

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Efficient Coupled Approaches for PracticalParachute Simulation

XV Jornada de Recerca del Departament de Física

Enrique Ortega and Roberto Flores

Barcelona, 31 January 2020

Institut d’Estudis Catalans

L’AIRE LaboratoriAeronàutic i

IndustrialdeRecercaiEstudi