Aeroelastic Gust Response

Civil Transport Aircraft - xxx

Presented By: Fausto Gill Di Vincenzo04-06-2012

What is Aeroelasticity?Aeroelasticity studies the effect of aerodynamic loads on flexible structures, taking into account the

dependence of the aerodynamic loads on the deformation of the structure and vice-versa

Input Output

Steady Aerodynamics Static Stability Derivatives

Stiffness Properties Trim Analysis

Standard Analysis available in MSC Nastran (Structure & Aero linear)

• Static Aeroelasticity (Sol144) longitudinal Trim Analysis

6/5/2012 2

Inertia Properties Static Loads

Static Deformations

Input Output

Oscillatory Aerodynamics Flutter Analysis

Structural Stiffness Dynamic Stability Derivatives

Inertia Properties

Control System (Optional)

• Flutter (Sol145) Stability Margin - Root Locus

Aeroelasticity studies the effect of aerodynamic loads on flexible structures, taking into account the

dependence of the aerodynamic loads on the deformation of the structure and vice-versa

Input Output

Oscillatory Aerodynamics Frequency Response

Structural Stiffness Transient Response

Standard analysis available in MSC Nastran (Structure & Aero linear)

• Dynamic Aeroelasticity (Sol146) Civil Transport Aircraft – Gust Response

What is Aeroelasticity?

6/5/2012 3

Inertia Properties Random Response

Control System (optional) Dynamic Loads

Excitation

Input Output

Static Aeroelastic and / or

Flutter Input

Resized Structure

Design Model

1.Objective

2.Constraints

3.Design Variables

Analysis Results

• Design Sensitivity and Optimization(Sol200)

Mode Exp [Hz] Num [Hz] Error [%]

First 9.60 9.5683 0.33

Second 38.10 38.109 0.02

Third 50.70 50.836 0.27

Fourth 98.50 98.672 0.17

Structural Modal tuning

Aeroelasticity studies the effect of aerodynamic loads on flexible structures, taking into account the

dependence of the aerodynamic loads on the deformation of the structure and vice-versa

Input Output

Unsteady Aerodynamics Transient Response

Structural Stiffness Dynamic Loads

Inertia Properties

Non Standard FSI analysis available in MSC Nastran OpenFSI (Structure & Aero linear or nonlinear)

• Transient Dynamic Aeroelasticity (Sol400) Transient Longitudinal Maneuver

What is Aeroelasticity?

6/5/2012 4

Inertia Properties

Control System (optional)

Excitation

• Non linear Dynamic Aeroelasticity (Sol400)

Input Output

Unsteady Aerodynamics Transient Response

Structural Stiffness Dynamic Loads

Inertia Properties

Control System (optional)

Excitation

HALEHA145 – Acusolve.OpenFSI

Topics

Standard Aeroelastic Gust Response - Sol146

• Civil Transport Aircraft - Gust Load Certification

• Deterministic approach - Discrete Gust

• Stochastic approach - Continuous Turbulence

• Static Aeroelastic Analysis with CFD data for Steady 1-g Load condition (UAV) - Sol144

6/5/2012 5

• Static Aeroelastic Analysis with CFD data for Steady 1-g Load condition (UAV) - Sol144

Advanced Aeroelastic Gust Response - Sol400 UVLM.OpenFSI

• Unmanned Aerial Vehicle

• Structural Dynamic Optimization - Sol200

• Discrete Gust Response at Trim Flight condition

• Aeroelastic Gust Response with Control System

Aeroelastic Model CreationCivil Transport Aircraft - xxx

6/5/2012 6

Structural Stick Model Aerodynamic Model

Aeroelastic Model Creation

Inboard Wing Coupling

Structural-Aero Coupling

6/5/2012 7

Outboard Wing Coupling

Structural-Aero Coupling

Aeroelastic Model Creation

6/5/2012 8

From Structural and Aerodynamic models

Civil Transport Aircraft CertificationAeroelastic Model

6/5/2012 9

Aerodynamics given by DLM(Potential theory - Lifting surface)

Mode # 27 - 32.38 Hz Mode # 39 - 49.56 Hz

Mode # 4 - 1.62 Hz

Civil Transport Aircraft Certification

Structural-Aero Coupling

6/5/2012 10

Mode # 6 - 5.4 Hz

Civil Transport Aircraft Certification

Structural-Aero Coupling

6/5/2012 11

Solution - SPLINE Verification

Mode # 7 - 6.3 Hz

Structural-Aero Coupling

6/5/2012 12

Certification Specification for Large Aeroplanes

CS 25.341 - Gust and turbulence loads

There are two methods widely accepted by the aeronautical authorities. Dynamic gust load conditions

applied to aircraft consist of discrete gust and continuous turbulence (or continuous gust)

• Deterministic approach (Discrete gust)

The deterministic method describes the “worst case“ atmospheric gust approach. For

European Aviation Safety Agency (EASA)

The deterministic method describes the “worst case“ atmospheric gust approach. For

discrete gust loads the atmospheric turbulence is assumed to have one-minus-cosine

velocity profile that can be described as a function of time. Response and load time

history correspond to solutions of the airplane equation of motion in time domain.

• Stocastical approach (Continuous turbulence)

For contuinuous gust loads, the atmospheric turbulence is assumed to have a Gaussian

distribution of gust velocity intensities that can be specified in the frequency domain

as a power spectral density (PSD) function.

For both methods a set of gust velocities for specific flight conditions has been defined. From several

types of gust PSD functions the Von Kármán and Dryden function are widely used.

6/5/2012 13

• Compute the Gust Response

• Aeroelastic Model Creation

• Aerodynamic Model DLM

• Aero-Structure Coupling - Splining Check

Tasks of the Simulation

6/5/2012 14

• Compute the Gust Response

• Tuned Discrete Gust (TDS) - One-minus-cosine Gust model

• Results of interest

• Acceleration over the Wing

• Wing Root Bending Moment

• Deterministic approach - Discrete Gust (Time domain)

Civil Transport Aircraft Certification

The Aircraft has to be able to withstand the Dynamic Gust Load

6/5/2012 15

( )[ ]HsU

U ds πcos12

−=

Deterministic approach - Discrete Gust Definition

6/5/2012 16

( )[ ]LsU

U ds π2cos12

−=

• Uds - Maximum Gust Velocity

• H - Gust Gradient Length

• L/2 - Half length of Gust

• s - Distance into the Gust

( )[ ]LsU

U ds π2cos12

−=

inLH 30.11712 ==

Deterministic approach - Discrete Gust Definition

]4200360[]35030[ ininftftH ÷=÷∈(Aircraft Length)

6/5/2012 17

inLH 30.11712 ==

sinsftUds /75,356/75,29 ==

lbMTOW 104700=

lbMLW 84800=lbOWE 62500=lbMFW 51800=

ftZmo 32275=

• Altitude - Sea level

• True Air Speed - 6886.36 in/s

(Aircraft Length)

• Flight Velocity 6886.36 in/s

• Speed of sound 13512 in/s (1126 ft/s)

• Mach Number 0.51

• Air Density 1.1468E-7 pound*s/in/in^3

• Reference Chord 170 in

Problem Data

6/5/2012 18

• Reference Chord 170 in

• Gust length 1171.30 in

• Gust Amplitude Uds 356.97 in/s

• Simulation time 3 s

• ∆x=0.08*V/Fmax 11 in

• ∆f 0.01 Hz

• Determine the frequency range to be considered.

• Determine the number of modes to be used.

• Use enhanced modal reduction with a residual vector

generated for the response degree of freedom.

Guideline

6/5/2012 19

generated for the response degree of freedom.

• Determine the reduced frequencies at which aerodynamic

matrices are to be computed.

• Take care of the rigid body motion

Compute the Gust responseTranslational Displacement – Side View

6/5/2012 20

Translational Displacement – Front View

Results - Tip Displacement

Max Wing Tip Deflection

6/5/2012 21

Max ≈ 25.3 in (0.64 m)

Node 2064

Results - Acceleration

Max ≈ 0.497 g

Nz @ Node 2001

6/5/2012 22

Min ≈ -0.510 g

Results - Acceleration

Max ≈ 0.587 g

Confidential

Nz @ Node 2007

6/5/2012 23

Min ≈ -0.648 g

Results - Acceleration

Max ≈ 1.271 g

Confidential

Nz @ Node 2025

6/5/2012 24

Min ≈ -0.724 g

Results - Acceleration

Max ≈ 13.04 g

Confidential

Nz @ Node 2064

6/5/2012 25

Min ≈ -18.61 g

Results - Acceleration over the Wing

Positive Normal Load Factor - Nz (Max)

Getting the Maximum of the Aeroelastic response over the wing

6/5/2012 26

13.04 g

0.587 g1.271 g

0.497 g

Results - Forces

Max ≈ 453391 N-m

Bending Moment @ Station#1 - Nz (Max)

6/5/2012

Min ≈ -393991 N-m

• Stochastic approach - Continuous Turbulence (Frequency domain)

Civil Transport Aircraft Certification

The Aircraft has to be able to withstand the Dynamic Gust Load

6/5/2012 28

• Compute the Gust Response

• Power Spectral Density (PSD) - Von Kármán function

Tasks of the Simulation

6/5/2012 29

• Results of interest

• PSD Acceleration of Wing Root

• PSD Bending Moment of Wing Root

Continuous Turbulence Design Criteria

• Normalized gust intensity, Ā

6/5/2012 30

• RMS of any response variable, σX

• Characteristic frequency, N0

Continuous Turbulence Design Criteria

•

6/5/2012 31

•

•

•

StaticIncremental Dynamic Load

Sol146Sol144

Limit Load

Effect of L on Von Kármán PSD

6/5/2012 32

Continuous Turbulence Design Criteria

PSD of Turbulence

6/5/2012 33

• Flight Velocity 6886.36 in/s

• Speed of sound 13512 in/s (1126 ft/s)

• Mach Number 0.51

• Air Density 1.1468E-7 pound*s/in/in^3

• Reference Chord 170 in

Problem Data

6/5/2012 34

• Reference Chord 170 in

• Scale of Turbulence 30000 in (2500) ft

• Frequency Range 0-60 Hz s

• ∆x=0.08*V/Fmax 11 in

• ∆f 0.01 Hz

Results - PSD AccelerationNz @ Node 2001

6/5/2012

F06 Output Extract RMS N0

35

Incremental Load

Results - PSD AccelerationNz @ Node 2007

6/5/2012 36

Incremental Load

Normal Load Factor

Results - PSD AccelerationNz @ Node 2025

6/5/2012 37

Incremental Load

Normal Load Factor

Results - PSD AccelerationNz @ Node 2001

6/5/2012 38

Incremental Load

Normal Load Factor

Results - Acceleration over the Wing

Normal Load Factor - Nz (Max)

Getting the Dynamic Load Increment over the wing

6/5/2012 39

14.82 g

1.31 g1.69 g

1.52 g

Results - PSD Vertical Bending Moment

Bending Moment @ Station#1

6/5/2012 40

Static Load

Incremental Dynamic Load

Continuous Turbulence Design Criteria

1-g Steady State by Sol144Incremental Dynamic Load got by Sol146

6/5/2012 41

Solution needs a high fidelity approach to get the 1-g steady state

MSC Software has developed an advanced capability to use CFD aerodynamic pressure in Sol144

Hybrid Static Aeroelastic Solution with CFD data - Sol144

1-g Steady State by Sol144

Advanced Aeroelastic Solution - Sol400 OpenFSI

Transient Longitudinal Maneuver Analysis without Control System - UAV

• MSC Nastran UVLM.OpenFSI RESTART functionality

• Pilot input command - Control surface

• Starting point for AeroServoElasticity (ASE)..

Transient Longitudinal Trim Analysis with Control System - UAV

• MD Nastran UVLM.OpenFSI RESTART functionality

• Elevator Control system

6/5/2012 42

Non Linear Aeroelastic Analysis - Non conventional Aircraft HALE

• MSC Nastran Large Displacement Capability

• Comparison with standard solution

Transient Gust Response Analysis with Control System - UAV

• MD Nastran UVLM.OpenFSI RESTART functionality

• Elevator Control system

• Comparison with standard solution

IFASD-2011-205 “Time Domain Linear and Nonlinear FSI Simulation of the AGARD 445.6 Wing using MD Nastran’s OpenFSITM Unsteady Vortex lattice Method”

Aerodynamic Code - UVLM• Geometric nonlinearity at subsonic flows

• Time domain aeroelastic simulation

• Free wake formation

• Lift due to vortex roll up at high angle of attack

• Aeroelastic response due to 1-D/2-D discrete gustand pilot input command

• Cp distribution from Tunnel test or CDF

• Stall modeling by strip method

6/5/2012 43

• Stall modeling by strip method

• Airfoil definition – NACA series or user defined

• Aerodynamic body modeling

• Aerodynamic blade component

α = 2.73°°°°

Vertical displacement of the UAV center of mass Overall vertical aerodynamic load vs UAV weight

δE = -2.5°°°° δE

Transient Longitudinal Maneuver Analysis without C.S.

6/5/2012 44

• No Control System ���� The UAV is not balanced ���� Altitude lost about 1.34 m

• Structural and Aerodynamic solution stored RESTART Analysis

Maneuver path - Front view Maneuver path - Side view

Vertical displacement of the UAV center of mass

I II III

Time history of the pilot input command - Elevator

• Structural and Aerodynamic data recovered from the previous FSI simulation (δE = -2.5°°°°)

δE = -2.8°°°°

δE = 2.3°°°°

t = 6:7 s

t = 5:6 s

δ = 1.72 °°°°t = 7:7.4 s

II

I

III

I

II

III

• Aeroelastic response to a Pilot Input Command on the Elevator

Transient Longitudinal Maneuver Analysis

Pitch down

Pitch up

Pitch down

Elev

6/5/2012 45

Maneuver path - Side view Maneuver path - Front view

δE = 1.72 °°°°t = 7:7.4 sIII

• It is possible to evaluate the aeroelastic response delay to a control surface input

• TRIM algorithmComparison with standard gust response Sol146• Control system

Pitch down

α = 2.73°°°° δE = -2.5°°°° δE

• Wake formation

• The free wake is part of the solution

• The aerodynamic mesh deforms with the structure

Vortex Tip Rollup Free vortex wake propagation

Transient Longitudinal Maneuver Analysis without C.S.

6/5/2012 46

Transient Longitudinal Trim Analysis with Control System

Wind

x

zL

α

FzWing

FxWing

Aerodynamic load components - Reference cord system

Fz

Fx

Load Balance

Fz

W

∆δE

∆ax

6/5/2012 47

• Control System on the Elevator

TRIM algorithm developed in python

• Translational Balance within X direction

• Translational Balance within Z direction

• Rotational Balance along Y axis

Dynamic of Flight equations to be satisfied∑ My = 0

∑ Fz = 0

∑ Fx = 0

Aerodynamic overall Load - Fz

WeightFz

Ae

rod

yn

am

ic L

oa

d [

N]

Transient Longitudinal Trim Analysis with Control System

6/5/2012 48

Time [s]

Ae

rod

yn

am

ic L

oa

d [

N]

∑ Fz, ∑ Fx = 0 Translational balance is satisfied!

CG - Rotation along y

Ry

Ro

tati

on

[D

eg

ree

]

Transient Longitudinal Trim Analysis with Control System

6/5/2012 49

Time [s]

Structural deformation @ Trimmed condition

AOA Elev

All Dynamic of Flight equations are satisfied Trim solution is got!

∑ My = 0 Rotational balance along y is satisfied

∑ My, ∑ Fz, ∑ Fx = 0

It is now possible to perform Gust Analysis!

Transient Gust Response Analysis with Control System

EASA Certification Specification for light Aircraft:

• Ude - Maximum Gust Velocity

• H - Gust Gradient Length

• 25C/2 - Half length of Gust

• s - Distance into the Gust

• C - mean geometric chord

6/5/2012 50

Discrete Gust Profile – 1 - cos

Ude=15,74 m/s

T=0.393 s

Transient Gust Response Analysis with Control System

6/5/2012 51

Structure Aerodynamics

The Control system makes the UAV get back the trimmed flight condition!

Transient Gust Response Analysis with C.S.Normal Load Factor Normal Load Factor

Acc

ele

rati

on

[g]

6/5/2012 52

(Structure is linear)

Normal Load Factor

Time [s]

Sol146 and Sol400 are in good accordance

It is possible to take into account for nonlinearities

to study Aeroelastic response of structure with

large displacement

Transient Gust Response Analysis

The UAV is able to restore the Trim flight condition thanks to the Control System

Without Control

With Control

CG - Z Displacement

Dis

pla

cem

en

t[m

]

6/5/2012 53

It could be possible to act on Airelons to reduces load on Wings

Time [s]

Dis

pla

cem

en

t

Gust Alleviation

Application - Nonlinear Aeroelastic AnalysisMD Nastran Structural Model UVLM Aerodynamic Model

• Geometry

6/5/2012 54

• Span of 72.78 m

• Constant chord of 2.44 m

• 10 degrees dihedral angle at ends

• Two pods at 2/3 of from the mid-span 22.69 Kg

• Central pod weighs 254 Kg.

• Overall weight of about 952.53 Kg

• 12 panels chordwise

• 30 panels spanwise

• Vortices shed from trailing edge and wing tip

All six DOFs of the mid-span central

section constrained to be zero.

Gravity is not considered

• Geometry

• Shells for the wing

• Solid for pods

• FEM

• Aerodynamic

Application - Nonlinear Aeroelastic Analysis• Flight condition

• M = 0.1 Sea Level

• Flight cruise velocity 12.5 m/s

• α = 16α = 16α = 16α = 16°°°°

Wake propagation - Ortho view

• Max vertical deflection of about 18 m

• No dynamic instability found

6/5/2012 55

Structural deformation - Front view