Project 2C.2Eric J. Barth 1 Georgia Institute of Technology | Milwaukee School of Engineering | North Carolina A&T State University | Purdue University

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


Problem: Energy Consumption & the Environment


Solution: Regenerative Braking


Our Solution:Strain Accumulator


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!


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


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


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


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


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


Testbed Setup


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


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


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


Current Problems/Solutions• Problems:

– Molding Problems• Bubbles• Material

• Solutions:– Vacuum Chamber– Four new molding

materials and systems.


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


END


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


Fatigue Strength and Service Temperature

Cambridge Engineering Selector (CES), 2008


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).

Documents

Project 2C.2Eric J. Barth 1 Georgia Institute of Technology | Milwaukee School of Engineering | North Carolina A&T State University | Purdue University