Project 2C.2 Eric J. Barth 1
Georgia Institute of Technology | Milwaukee School of Engineering | North Carolina A&T State University | Purdue University University of Illinois, Urbana-Champaign | University of Minnesota | Vanderbilt University
Project 2C.2:
Advanced Strain Energy Accumulator
Assistant Prof. Eric J. Barth
Graduate Student: Alexander Pedchenko
Undergraduate Design Team: Abdullah Abidin, Karl Brandt, Danielle Patelis, Hafizah Sinin, Oliver Tan
Vanderbilt University, Department of Mechanical Engineering
Thursday March 31st, 2009
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Problem: Energy Consumption & the Environment
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Solution: Regenerative Braking
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Our Solution:Strain Accumulator
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PLEASE ANSWER THE FOLLOWING QUESTIONS DURING YOUR PRESENTATION.
• What is your research goal or question?
Goal: Design and experimentally implement a high energy density hydraulic accumulator utilizing strain energy as the storage mechanism.
• How does this project fit into the CCEFP’s overall research strategy? Contributes to the Center’s goal of breaking the barrier of a lack of compact energy storage.
• What is the competing research or methods? Why / what makes this technology better than the competition? What has been done in the past?Competing methods: 1) Gas Bladder Accumulators, 2) Piston Accumulators with gas pre-charge, 3) Spring Piston Accumulators, 4) Gas/Elastomeric Foam. What makes it better: 1) does not utilize thermal energy storage – thermal losses and thermal management does not dominate, 2) no gas diffusion through a bladder, 3) cheap!
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Initial Experiments
• Latex tubing served as the bladder– Bubble formation and propagation
• Occurs at yield point of the material• Agreement with FEA analysis conducted using
Patran/Nastran software package
– The “rolling” effect and its importance• Bubble propagation occurred by rolling• Helps avoid unpredictable behavior due to friction
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α-prototype Bladder Design
• Scaled prototype (size, pressure)
• Bladder design• Geometry similar to that of the latex bladder,
thereby assuming a similar radial and axial strain behavior (Poisson’s ratios similar)
• Dimensions determined by– Inner radius - connector– Outer radius - FEA analysis using PATRAN/NASTRAN
using set inner radius and pressure to reach yield stress– Length – based on loaded cross section and predicted
axial expansion to contain desired volume
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α-prototype Polyurethane (PU)Bladder
• Thinner walls serve to induce bubble creation at the base of the bladder
• Material: Andur RT 9002 AP– Prepolylmer which can
be cured at room temp.
– Yields an elastomer capable of 600% elongation
Dimensions in inches
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Mold for α-prototype bladder
• 4 openings in part A: Facilitate the removal of the casted polyurethane Allow prepolymer to seep out of or be added to the
mold
Part A – inside mold and top cap Part B – Outside mold
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α-prototype Setup
After filling the system with water and bleeding the air
Inflating Bladder:1. Set Screw down val.2. Open Sol. val. 13. Open Sol. val. 34. Close Sol. val. 3
Deflating bladder:1. Close Sol. val. 12. Open Sol. val. 23. Open Sol. val. 34. Close Sol. val. 2
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Testbed Setup
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α-prototype Testing
• Obtain experimental results for:– Energy storage– Round-trip energy storage efficiency
• Study how these metrics are effected by:– Bladder inflation/deflation rates– Hold times– Material creep caused by fatigue
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Experimental Procedure
• Obtain flow and pressure data for loading and unloading
• The Needle Valve:– Allows control of the flow rate in and out of the bladder– Set manually
• Multiple loading and unloading cycles (n>30 to obtain statistically reliable data) for a given:– Needle valve position– Holding time
• Tests will be repeated periodically– To check whether the bladder’s performance changes
significantly over time
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Experimental Data Analysis
• Energy delivered to and retrieved from the bladder:
Where t0=time at which sol. valve leading to bladder is opened, tf=time at which it is closed.
• Energy storage efficiency :
where η=efficiency, Eout=energy retrieved from bladder, and Ein = energy delivered to bladder
ft
t
PQdtE0
in
out
E
E
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Current Problems/Solutions• Problems:
– Molding Problems• Bubbles• Material
• Solutions:– Vacuum Chamber– Four new molding
materials and systems.
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Future Work
• Bladder redesign/scaling for full scale prototype (consult UMN sUV team)
• Incorporation of hyperelasticity and solid collision into redesigned bladder FEA model
• Selection of PU with appropriate mechanical characteristics– Guided by performance of α-Prototype
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END
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Energy Density
Energy Density [kJ /kg]0.001 0.01 0.1 1 10 100
Vol
umet
ric
Ener
gy D
ensi
ty [
MJ/
m̂3]
0.01
0.1
1
10
100
Polyisoprene Rubber (unreinforced)
Natural Rubber (unreinforced) Polyurethane Rubber (Unfilled)
SIS (Shore 60A)
Wrought aluminum pure, 1-0
Ingot Iron, annealed
Titanium metastable beta alloy, Ti-3Al-8V-6Cr-4Zr-4Mo, (Beta C)
Molybdenum high speed tool steel, AISI M44
BMI/HS Carbon Fiber, Woven Fabric Composite, Biaxial Lamina
Glass/Epoxy Unidirectional Composite
Wrought aluminum alloy, 2014, T652
Wrought aluminum alloy, 7150, T61511
Polyester (Glass Fiber, Preformed, Chopped Glass)
Cambridge Engineering Selector (CES), 2008
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Fatigue Strength and Service Temperature
Cambridge Engineering Selector (CES), 2008
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Elongation and Loss CoefficientCambridge Engineering Selector (CES), 2008
Note: The mechanical loss coefficient characterizes acoustic energy damping (high frequency, small amplitudes). This may not be the right metric for ascertaining loss in our system (low frequency, large amplitudes).
