Particle Simulation in Magnetorheological Flows Norman M. Wereley - - PowerPoint PPT Presentation

University of Maryland GPU Summit

Particle Simulation in Magnetorheological Flows Norman M. Wereley

Minta Martin Professor and Department Chair wereley@umd.edu + contributions from graduate students, research staff, and collaborators Smart Structures Laboratory

• Dept. of Aerospace Engineering

University of Maryland

Adaptive Energy Absorption Systems Using MR Fluids

Objective: To dissipate energy in vehicle systems in order to protect occupants and payloads from injurious vibration, repetitive shock, crash and blast loads. Sponsors: General Motors, Boeing-Mesa US Army, US Navy

Protective Seating: Impact, Crash, Blast

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Events are rapid (< 50 ms)

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Flight qualification of SH-60 seat with MR vibration control and deploy

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Develop lightweight compact MREAs for adaptive crash safety

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Verify MREA control strategies via test

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Other vehicle applications

– Expeditionary Fighting Vehicle (EFV) semi- active seat technology

• Automatic adaptation b/w water-mode shock and

ground-mode vibrations

• Sea trials completed in 9/09

– Adaptive high speed watercraft seats

• Mark V SOC sea trials completed

– Adaptive Mine-blast attenuating seats

• Best “dynamic response index”

MR Fluids: Phase Transformation

Recipe Magnetorheological Fluid

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1 cup of oil (hydraulic)

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1/2 cup of carbonyl iron powder (heavy)

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Mix well

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Properties of MR Fluid:



High specific gravity

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Yield stress: 60-100 kPa at full field for high solids loading

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Full Field: 1 Tesla, 1 Amp in coil at 2- 3 Volts (under 3 Watts)

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Temperature insensitive

Microstructure of MR fluids

MR Fluid: Bingham Plastic Behavior

N S

No Field Condition Field Applied

Shear Stress, τ > 0 v Ferrous particle Carrier fluid Shear Stress, τ > τy N S

Optical Micrograph Image of Ferrous Particle Chains in MR Fluid

Dimorphic MR Fluids

(Collaboration: R. Bell, & D. Zimmerman, PSU)

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Morphology

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Microwires with fixed diameter and distribution of lengths (2-20 microns)

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Spheres with narrow distribution of diameters

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Magnetic dipole reorients with magnetic field

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Key physics

– Yield stress – Viscosity – Sedimentation

• Smart Materials Structures (3/09)

– Elastic percolation

• Appl. Physics Letters (7/01/09)

Magnetorheology

60 wt% Iron with 15% Nanometer Scale Particles

Shear Stress kPa

MR Fluids - Too Simple a Model?

(Bingham Plastic Model)

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Bingham plastic MR fluid behavior – Newtonian in absence of field – Bingham plastic in presence of field

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Viscosity (µ) independent of field

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Yield Stress (τy) dependent on field

Bingham Plastic Newtonian Fluid

Apparent Viscosity

MR Dampers

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MR fluids exhibit shear thinning at high shear rates

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Yield stress changes as a function of magnetic field

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MR fluid behaves approximately as a

– Bingham-plastic – Field dependent yield force – plus a viscous stress that is the product of viscosity and velocity

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Use nondimensional analysis

– Ndim plug thickness as independent variable – Ndim dynamic range as dependent variable – Damper performance

MR Fluid Damper

Pneumatic Reservoir Floating Piston Piston Head Piston Rod Coils Steel Core Spring Configuration: Coil-over damper Pneumatic Reservoir: N2 1.7 MPa Maximum Stroke: 9 cm Overall Length: 8 cm Bore Diameter: 4 cm Spring Retainer Flux Return

Damper Performance is Controllable

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Plug thickness varies as a function of field and yield stress

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Change in plug thickness is akin to

• pening and closing a

mechanical valve

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Leakage is added to the flow path to smoothen damper response hence the finite damping at plug thicknesses approaching the gap in the valve

Protective Seating: Impact, Crash, Blast

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Flight qualification of SH-60 seat with MR vibration control and deploy

q

Develop lightweight compact MREAs for adaptive crash safety

q

Verify MREA control strategies via test

q

Other vehicle applications

– Expeditionary Fighting Vehicle (EFV) semi- active seat technology

• Automatic adaptation b/w water-mode shock and

ground-mode vibrations

• Sea trials completed in 9/09

– Adaptive high speed watercraft seats

• Mark V SOC sea trials completed

– Adaptive Mine-blast attenuating seats

• Best “dynamic response index”

Control of Impact Loads

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Want to use all available stroke for every impact speed or payload mass

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Payload mass varies from 105 lbs (5th %tile female) to 225 lbs (95th %tile male)

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Impact speed varies from 0-15 mph (airbags take over at higher speeds)

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Must use an adaptive device like an MREA

payload mass

magnetorheological energy absorbers (MREAs)

Impact Plane

x S

neutral line V0

fd

reference line

δ

Magnetorheological Energy Absorber (MREA) Can Adapt

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Passive energy absorbers (EAs) cannot accommodate different occupant weights (Left)

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Use simple optimal control of a terminal trajectory to achieve soft landing for every occupant weight (right)

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Solution requires Lambert W functions

– Schottke diode equation – MREA utilizes entire stroke – Minimizes stroking load to the occupant

Extensive Sled Tests at GM

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Optimal control technique uses all available stroke (2 inches) regardless of impact speed

• r occupant weight

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Implemented in dSpace

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MREA sized to accommodate stroking loads needed for 5th female to 95th male

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Speeds up to 15 mph

Flight Qualification Ground Testing

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Seat was tested to ensure that vibration isolation system did not hinder seat integrity during high onset rate crash events

– Seat maintained structural integrity during tests

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Seat has been qualified for flight test in SH-60 Seahawk

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Flight test completed…

The dampers we are designing will require combinations of high force and high velocity that have not been attempted in known past research.

3000 6000 9000 12000 15000 18000 21000 5 10 15 20 25

Maximum Field-On Force (lb) Maximum Piston Velocity (ft/s)

UMD Other Researchers MD-500

Forward Damper at Low Sink Rate

Wereley et al, 2009 for Energy Absorbers

Forward and Aft Dampers at High Sink Rate Aft Damper at Low Sink Rate

Challenge Level of Current Design

Max Field-On Force vs. Max Velocity

Ahmadian et al, 2004 for Impact Dampers Carlson et al, 2006 for Seismic Dampers Wereley et al, 2005 for Impact Dampers

MR Fluid Characterization:

High Shear Rates

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Need data at high shear rates up to 100K /s

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Virtually all studies < 1K /s

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Lab-built Searle cell magnetorheometer can measure up to 25K / s

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Apparent viscosity

• vs. shear rate

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Is the data good?

MR Fluid Characterization for Shear Rates > 1000 / s

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Exploit the Mason number

– Ratio of viscous to magnetic stress – Klingenberg showed curves collapse for low shear rates

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Do apparent viscosity vs. Mason number curves should collapse onto a single curve?

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Data is good

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We are on the right track to provide design data for high shear rate devices

MR Fluid Characterization

Yield stress persists at 25K /s

Microstructures at High Shear Rate

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Bulk material perspective works for many applications

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Need simulation capabilities at high shear

– Need CFD for pressure driven flow – Need CFD for direct shear flow

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Current state of the art simulates a few hundred to a few thousand particles

CFD with MR Particle Interactions

q Most simulations

limited to particle counts in the low thousands

q To simulate practical

flow volumes, we need millions of particles

q Need a three order of

magnitude increase in particle count!!!

CFD with MR Fluids

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Dynamic simulation allows for insight into chain formation under shear

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Goal: Simulate at experimental volume scales

– Need N=1,000,000 particles but state of the art is N<10,000

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Use Nvidia’s CUDA environment to run code on desktop GPU

– Delivers 100x increase in computing performance

Chain Metrics

q Visual observation of

chain formation is difficult

q Developed simulation

scale independent chain metrics

– Chain length – Connectivity

q Demonstrated scale

independence

q Shown shear response

• f metrics is a function
• f Mason number

Lamellar Sheet Formation

q Static equilibrium

structure for MR fluids are chains

q Under shear, particles

form lamellar sheets

q Experimentally

demonstrated in MR fluids

q Requires large volume

size to simulate

Lamellar Sheet Formation

• f an ER fluid

Cao, J., Huang J., & Zhou, L. (2006).

Simulation Output

Sherman, S. & Wereley, N.M. (INTERMAG, 2012).

Million Particle Parallelized Simulations Using CUDA

Future Challenges in MR – Still a Rich Field of Research

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20 years of MR fluid Research

– Still many problems to solve!

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Demonstrate MR energy absorbers for crash protection systems

– General Motors – U.S. Navy Air Warfare Center (H60 crew seat in 40 ft/s crash) – US Army Research Lab (HDL) Blast mitigation (against IEDs) – US ARMY AATD Active Crash Protection Systems in Rotorcraft

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GPU simulations using CUDA enabled understanding of high shear rate MR fluid behavior

– Typically measured up to 1000 /s – Want up to 100,000 /s (we have measured to 25,000 /s) – Need GPU simulation because experiments are difficult at high shear rate – Need a full CFD capability in GPU

• Adaptive meshing for complex geometry
• Axisymmetric geometry
• Determine impacts of device on fluid flows

University of Maryland GPU Summit

Particle Simulation in Magnetorheological Flows

Questions?