AAE450 Spring 2009
Finite Element Analysis (FEA) for Orbital Transfer
Vehicle (OTV)Tim Rebold STRC
[Tim Rebold] [STRC]
[1]
AAE450 Spring 2009
Boundary Conditions (BC’s) 8 holes on Payload Attach Fitting
(PAF) equally spaced around Spacecraft attached by bolting into
launch vehicle interface Bolt acts as a clamped boundary
condition
[Tim Rebold] [STRC][2]
All 6 degrees offreedom constrained
Clamped BC
z
yx
AAE450 Spring 2009
Applied Loads - Dnepr Payload Requirements
[Tim Rebold] [STRC]
Payload Acceleration Loads (g's)
Acceleration
Axial Lateral
1st stage burn:Maximum lateral acceleration
3.0±0.5 0.5±0.5
2nd stage burn:Maximum longitudinal acceleration
7.8±0.5 0.2
Notes:1. Lateral accelerations may act in any direction, simultaneously
with longitudinal ones2. Dynamic accelerations are preceded by “±” symbol
Spacecraft System Stiffness Requirements
Thrust (Hz) Lateral (Hz)
20 10 Tables based from Dnepr User’s Guide
[3]
AAE450 Spring 2009
System Representations Lander Propulsion System E-MOD System
Systems represented by placing lumped mass elements at the center of mass of that system
These elements have the same mass & inertia properties
[Tim Rebold] [STRC][4]
AAE450 Spring 2009
FEA Analysis Von Mises Stress observed
Material allowables based on Aluminum 6061-T6 yield strength
Margin of Safety (MS) reported and documented for all major systems and components
[Tim Rebold] [STRC][5]
AAE450 Spring 2009
Lander
Clamped boundaryconditions representingbolted hole interface
[Tim Rebold] [STRC][6]
Skirt Analysis – Set Up (100 grams)
The skirt joins the larger 1.8 m diameter OTV to the smaller 1.3 m diameter Lander
AAE450 Spring 2009 [Tim Rebold] [STRC][7]
Skirt Analysis – Peak Stress
Peak Stressσ = 70 N/mm2
σY = 270 N/mm2
MS = 2.8669.6 N/mm2
64.3 N/mm2
AAE450 Spring 2009 [Tim Rebold] [STRC][8]
Skirt Analysis - Peak Displacement = 0.5 mm, Buckling Load Factor = 2.21
AAE450 Spring 2009
Skirt Analysis (100 grams) - Observations
Stress is not a concern
Buckling of thin sheet webs will determine sizing of skirt
As a result of reducing mass, the modal frequencies will decrease which is an adverse effect
[Tim Rebold] [STRC][9]
AAE450 Spring 2009
OTV Analysis100 grams
[Tim Rebold] [STRC][10]
AAE450 Spring 2009
AccelerationsYield
Propulsion Frame - Stress
[Tim Rebold] [STRC][11]
Peak Stressσ = 324 N/mm2
σY = 270 N/mm2
MS = -0.17
AAE450 Spring 2009
Buckling
[Tim Rebold] [STRC][12]
Buckling loadFactor = 0.19
Buckling
AAE450 Spring 2009
FEA – SummaryObservations Yielding in propulsion frame member 4 due to lateral
acceleration applied in that member’s direction Displacement in E-MOD floor skin relatively high, but stresses
are low and displacement does not interfere with anything in the surroundings
E-MOD floor supports are stronger than necessary Buckling in C-Channels Lateral mode too low
[Tim Rebold] [STRC][13]
1
4
32
Design Changes Increase cross section of member 4 of propulsion frame, and
connect propulsion components to more structural members Decrease cross-sectional dimensions of E-MOD floor beams Increase cross section dimensions of C-Channels until
buckling occurs at a higher load
AAE450 Spring 2009
OTV Final Analysis100 grams
[Tim Rebold] [STRC][14]
AAE450 Spring 2009
Accelerations
Propulsion Frame - Stress
[Tim Rebold] [STRC][15]
Peak Stressσ = 80 N/mm2
σY = 270 N/mm2
MS = 2.38
Peak displacement is 2.19 mm
AAE450 Spring 2009
E-MOD - Stress
[Tim Rebold] [STRC][16]
Peak Stressσ = 72 N/mm2
σY = 270 N/mm2
MS =2.75
Peak displacement remains at 40 cm
AAE450 Spring 2009
E-MOD floor support - Stress
[Tim Rebold] [STRC][17]
Peak Stressσ = 92 N/mm2
σY = 270 N/mm2
MS = 1.93
Peak displacement is 3.62 mm and occurs at ring interface
AAE450 Spring 2009
OTV Frame – Peak Stress in OTV
[Tim Rebold] [STRC][18]
Peak Stressσ = 92 N/mm2
σY = 270 N/mm2
MS = 1.93
Peak stress occurs at a joint where a C-Channel and E-MOD floor support beam meet
AAE450 Spring 2009
Buckling Load Factor is 1.42
[Tim Rebold] [STRC][19]
AAE450 Spring 2009
Modes – Lateral mode at 10.6 Hz
[Tim Rebold] [STRC][20]
Axial mode is not a concern
AAE450 Spring 2009
FEA Analysis - Conclusions Stiffness and buckling were driving factors in
determining size
Members act together effectively to limit peak stresses and displacements
Low stresses ensure welds and other connection methods will meet strength criteria
[Tim Rebold] [STRC][21]
AAE450 Spring 2009
FEA Analysis Breakdown – 100 g
[Tim Rebold] [STRC][22]
Peak Stress & Displacement BreakdownSystem Displacement (mm) Stress (N/mm2) MSPropulsion Frame 2.14 79.7 2.14E-MOD 40.60 72.1 2.75E-MOD Floor Support 3.62 92.1 1.93
C-Channels 3.46 92.1 1.93Lander Integration Ring
0.53 69.6 2.86
PAF 0.27 28.7 8.41
AAE450 Spring 2009
Structural Budget – 100 g
[Tim Rebold] [STRC][23]
MASS (kg)
Components
PAF (not included in OTV mass) 47.04
E-MOD floor beams & overlay 5.25
Shear / Skin panels 15.00
Propulsion support frame 3.01
Stringers / Stiffeners 12.48
Integration (Lander Skirt) 12.19
Fasteners (welds, rivets, bolts, adhesives) 2.01*
TOTAL 49.94*Estimates
AAE450 Spring 2009
FEA Analysis Breakdown – 10 kg
[Tim Rebold] [STRC][24]
Peak Stress & Displacement BreakdownSystem Displacement (mm) Stress (N/mm2) MSPropulsion Frame 2.74 106 1.55E-MOD 40.9 82.7 2.26E-MOD Floor Support 4.62 118 1.29
C-Channels 4.55 118 1.29Lander Integration Ring
0.41 63.2 3.27
PAF 0.307 34.2 6.89
AAE450 Spring 2009
Structural Budget – 10 kg
[Tim Rebold] [STRC][25]
*Estimates
MASS (kg)
Components
PAF (not included in OTV mass) 41.36
E-MOD floor beams & overlay 5.25
Shear / Skin panels 15
Propulsion support frame 3.01
Stringers / Stiffeners 12.12
Integration (Lander and propulsion module) 14.24
Fasteners (welds, rivets, bolts, adhesives) 2.12*
TOTAL 51.74
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