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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
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Outboard Wing Coupling
Structural-Aero Coupling
Aeroelastic Model Creation
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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