Predictive Model for Lunar Percussive...

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Predictive Model for Lunar Percussive Excavation By: Alex Green (University of California, Berkeley) Advisor: Dr. Dennis Lieu (University of California, Berkeley) Mentor: Rob Mueller (Kennedy Space Center) In collaboration with: Dr. Kris Zacny (Honeybee Robotics) & Dr. W. David Carrier III (Lunar Geotechnical Institute) 1

Transcript of Predictive Model for Lunar Percussive...

Predictive Model for Lunar Percussive Excavation

By: Alex Green (University of California, Berkeley) Advisor: Dr. Dennis Lieu (University of California, Berkeley)

Mentor: Rob Mueller (Kennedy Space Center) In collaboration with: Dr. Kris Zacny (Honeybee Robotics) &

Dr. W. David Carrier III (Lunar Geotechnical Institute)

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Lunar Excavation

Earth approach •  Increase body forces to

balance large reaction forces

Lunar approach •  Decrease the reaction

forces to meet the small body forces

The Problem: Excavation induces large reaction forces which must be overcome for soil failure

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Addressing Reaction Forces

Extensive work has been done up to this point to empirically test and validate the effects of percussion on draft force reduction

Figures and data taken from [1] and [2] 3

The Focus Of This Work

Reaction Force

Percussion Parameters

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Current Models Being Used

1.  Balovnev, Gill 2.  Vanden Berg 3.  Luth and Wismer 4.  McKeys 5.  Osman 6.  Quisen and Shuren 7.  Swick and

Perumpral 8.  and Zeng*.

*Zeng seems to be the currently most popular model. Figures taken from [3]

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Current Model Limitations

All models use a static passive pressure term. Some models incorporate an inertia effect by using the Mononobe Okabe term and pseudo static approximations.

Approximation is only valid for accelerations up to .3g

*Diagrams are taken from Zeng Model 6

New Dynamic Pp Term

Work in translating respective volumes OAB, OBC, and OCD

Seismic inertial energy for volumes OAB, OBC, and OCD

Damping dissipation energy from seismic effects on volumes OAB, OBC, and OCD

Sliding and frictional dissipation energy for volumes OAB, OBC, and OCD

+ + =

Pp value in the energy terms is isolated and solved for by use of energy conservation

Model is based off of the Chen and Liu upper limit analysis approach

Rate at which external forces do work Rate of internal dissipation

Figure and approach taken from [4] 7

New Pp Derivation

Rate of External Forces Doing Work

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New Pp Derivation

Rate of Internal Dissipation

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Dynamic Soil Properties

= dynamic internal friction angle = infinite internal friction angle (minimum value during dynamic tests) = static internal friction angle

β = grain size coefficient depending on acceleration η = relative acceleration amplitude (a/g)

Experimental work done by Sactchenko and Barkan in which they tried to determine the effects of vibrations on foundational stiffness for dry cohesionless sand.

The internal friction angle asymptotically changes as a function of the relative acceleration amplitude ( ).

Figures and worked referenced in [5] 10

Dynamic Soil Properties

ρmin=1.15 g/cm3 (emax=1.7) and ρmax=1.82 g/cm3(emin=0.7). *Data taken from [6]. Material tested is a basaltic simulant

Adjusting regolith properties to be functions of internal friction angle.

***Minimum and maximum density & void ratio values are from [6]. Material values are assumed to represent lunar core samples

**All functions assume a friction angle in radians

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Dynamic Soil Properties Shear Modulus

Gmax=1000*K2*(σm’)1/2

*strain is defined as taumax/ Gmax

Damping Ratio

Graphical data presented by Seed and Idriss, but based on expressions given by Hardin and Drnevich

Graphical representations of functions used in new dynamic model

Figures and data taken from [7] & [8] 12

Code Structure

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Analytic Results

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Analytic Results

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Empirical Testing 11ft x 3ft x 3ft chamber

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Empirical Testing Capability

Excavation Axis Transmission Excavation Travel

• Stroke: 73 cm • Trenching Load Capacity: 900 N (based on Linear slide) • Trenching Load Capacity: 1000 N (Based on Motor torque limit) • Penetration Load Capacity: 1556 N

Excavation Axis Rail

6X Trenching Double Roller Bearings

Travel for Trenching Depth Uniaxial Load

cell Piezo Load Cell

Camera

Percussive Mechanism

6 Axis Load Cell

Percussive Mechanism

Piezo Load Cell

Surveyor-Like Scoop

Bearing Plate

Linear Slide

Ground to Bearing Axis Slide

Vibration Damper

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Percussive Head

Description •  Rotating helical cam is used to preload the ram against a

compression spring. “Ski Jump” in cam rapidly releases the ram, allowing it to impact a ram rod

•  Impact energy is dependent on spring constant and cam height

References 1.  B. Szabo, F. Barnes, S. Sture, H. y. Ko. “ Effectiveness of Vibrating Bulldozer and Plow

Blades on Draft Force Reduction” Transactions of the ASABE. VOL. 41(2):283-290 .1998 2.  M. T. Sulatisky, P.R. Ukrainetz. “ Draft Reduction by Vibratory Soil Cutting” Transactions

of the Canadian Society for Mechanical Engineering. Vol. 1 Issue 4. 1972 3.  R.H. King, P.J. van Susante, R.P. Mueller. “Comparison of Lance Blade Data and

Analytical Force Models” . Space Resources Roundtable XI / Planetary & Terrestrial Mining Sciences Symposium. June 2010

4.  Wai-Fah Chen, X. L. Liu. Limit Analysis in Soil Mechanics Chapters. Elsevier. 1990. Chapter 5

5.  D.D. Barkan Dynamics of Bases and Foundations. McGraw-Hill, 1962. Chapter 2 6.  W. David Carrier, Gary R. Olhoeft, and Wendell Mendell. “Physical Properties of the

Lunar Surface”. Lunar Sourcebook. Cambridge University Press. 1991. Chapter 9 7.  Bobby O. Hardin and Vincent P. Drnevich “Shear Modulus and Damping in Soils: Design

Equations and Curves” . Journal of Soil Mechanics & Foundations Div. Vol. 98. Issue sm7. 1972-7 pp 667-92

8.  H. Bolton Seed, Robert T. Wong, I.M. Idriss, K. Tokimatsu. “Moduli and Damping Factors for Dynamic Analysis of Cohesionless Soils” Earthquake Engineering Research Center. Report NO UCB/EERC-84/14. September 1984

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Questions?

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