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 = 2.86

69.6 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

Accelerations

Yield

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) MS

Propulsion Frame 2.14 79.7 2.14

E-MOD 40.60 72.1 2.75

E-MOD Floor Support 3.62 92.1 1.93

C-Channels 3.46 92.1 1.93

Lander 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) MS

Propulsion Frame 2.74 106 1.55

E-MOD 40.9 82.7 2.26

E-MOD Floor Support 4.62 118 1.29

C-Channels 4.55 118 1.29

Lander 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