Predictive Model for Lunar Percussive...
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
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
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
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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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