Extending the ArmingDistance of MOFA

(MOFA & MOFN S&A Modeled in DADS & ABAQUS)

Keith LewisNaval Surface Warfare Center Dahlgren

47th Annual Fuze Conference“Enhancing Weapon Performance”

April 8-10, 2003

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Background• MOFN proposes to use the MOFA S&A• MOFA S&A will nominally arm at 250 ft• MOFN needs a 400 ft minimum arming distance

• Previous work by Honeywell indicated that a MOFAS&A with a heavier pallet and lighter rotor wouldarm at 430 ft and would not arm at 375 ft

MOFA = 250’

MOFN >400’

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Easy Arming Distance?• Options:

– Different S&Aor– More gears– More teeth– Modify Pallet/Star-wheel interaction– Mass properties

• Rotor Body and Pallet

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Analysis Tools• Rule-of Thumb Calculations:

• DADS (Dynamic Analysis and Design System) fromLMS International

– Rigid Body Dynamics

• ABAQUS from ABAQUS, Inc.– Finite Element Analysis

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1

111

2

2

222

2

1

2

1

×+

×+

=

θ

θ

NInertiaInertia

NInertiaInertia

StarwheelPallet

StarwheelPallet

Rotor

Rotor

Rotor

Rotor

MassMass

SpeedSpeed

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Analysis with DADS

View Rotates with S&A

• Analyze MOFA S&A with Dynamic Analysis andDesign System

• Feature of DADS Model– Rigid Bodies– Implicit Solver– Limited contact

capability– Ideal constraints such

as journals and gears– Coefficient of

restitution

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Analysis with DADS

Ideal Pallet Pivot

• Analyze MOFA S&A with Dynamic Analysis andDesign System

• Feature of DADS Model– Rigid Bodies– Implicit Solver– Limited contact

capability– Ideal constraints such

as journals and gears– Coefficient of

restitution

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Analysis with DADS

Ideal Gear

• Analyze MOFA S&A with Dynamic Analysis andDesign System

• Feature of DADS Model– Rigid Bodies– Implicit Solver– Limited contact

capability– Ideal constraints such

as journals and gears– Coefficient of

restitution

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Results with DADS• MOFA Nominal Arming – 280ft

– Fast MOFA – 234ft– Slow MOFA – 400ft Huh?

• MOFN w/ Aluminum Rotor Body and Double-ThickPallet – 427 ft

• Concern about friction model and gears in DADS

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Modeling with ABAQUS• Based on FEA, but

– No Deformable bodies - Rigid Bodies only– Mesh for contact

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Analysis with ABAQUS

View Does Not Rotate with S&A

• Analyze MOFA S&A with ABAQUS

• Features of ABAQUS Model– Rigid bodies – no

Deformable bodies– Explicit solver– General contact

capability for journalsand gears

– Contact dampingcoefficient

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Analysis with ABAQUS

Realistic Pallet Pivot

• Analyze MOFA S&A with ABAQUS

• Features of ABAQUS Model– Rigid bodies – no

Deformable bodies– Explicit solver– General contact

capability for journalsand gears

– Contact dampingcoefficient

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Analysis with ABAQUS

Realistic Pallet Pivot

• Analyze MOFA S&A with ABAQUS

• Features of ABAQUS Model– Rigid bodies – no

Deformable bodies– Explicit solver– General contact

capability for journalsand gears

– Contact dampingcoefficient

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Analysis with ABAQUS

Contacting Gear Teeth

• Analyze MOFA S&A with ABAQUS

• Features of ABAQUS Model– Rigid bodies – no

Deformable bodies– Explicit solver– General contact

capability for journalsand gears

– Contact dampingcoefficient

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Results

* aluminum rotor body & double-thick pallet

0 100 200 300 400 500 600 700 800

Nominal MOFA

Fast MOFA

Slow MOFA

Nominal MOFN*

Fast MOFN

Tungsten Pallet

Slow Tungsten

Arming Distance - feet

Hearsay Testing Calculated DADS ABAQUS

400Did Not Arm

Erratic

MOFA

NavalizedMOFA

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Conclusions• Increasing the Nominal Arming Distance to 400’

Possible• Increasing the Minimum Arming Distance to 400’

May be Risky Due to Friction• Longer Arming Distances Through Pallet and Rotor

Modifications Very Risky

• Analysis Tools Need More Validation– Especially Friction

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Comparison

No frictioneffectsLimited tosmall changes

0 sec each

10 seconds

10 minutes

HandCalculation

4 weeks2 weeks4 weeksInitial modeldevelopment

10 minutes10 minutes2 weeksRevised casesetup

ExcellentTrack recordfor FEA.TBD for rigidbodies, but allrelevantphysicsmodeled

Excellenttrack record inindustry, butgear frictionnot modeled

Very accurateAccuracy

3 hours5 minutes15 minutesRun times

ABAQUSDADSTesting