1. Project 2C.2Eric 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 31 st, 2009

2. Project 2C.2Eric J. Barth 2 Problem: Energy Consumption & the Environment

3. Project 2C.2Eric J. Barth 3 Solution: Regenerative Braking

4. Project 2C.2Eric J. Barth 4 Our Solution: Strain Accumulator

5. Project 2C.2Eric J. Barth 5 PLEASE ANSWER THE FOLLOWING Q U E S T I O N S D U R I N G Y O U R P R E S E N T A T I O N. 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!

6. Project 2C.2Eric J. Barth 6 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

7. Project 2C.2Eric J. Barth 7 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

8. Project 2C.2Eric J. Barth 8 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

9. Project 2C.2Eric J. Barth 9 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 capPart B – Outside mold

10. Project 2C.2Eric J. Barth 10 α-prototype Setup After filling the system with water and bleeding the air Inflating Bladder: 1. Set Screw down val. 2. Open Sol. val. 1 3. Open Sol. val. 3 4. Close Sol. val. 3 Deflating bladder: 1. Close Sol. val. 1 2. Open Sol. val. 2 3. Open Sol. val. 3 4. Close Sol. val. 2

11. Project 2C.2Eric J. Barth 11 Testbed Setup

12. Project 2C.2Eric J. Barth 12 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

13. Project 2C.2Eric J. Barth 13 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

14. Project 2C.2Eric J. Barth 14 Experimental Data Analysis Energy delivered to and retrieved from the bladder: Where t 0 =time at which sol. valve leading to bladder is opened, t f =time at which it is closed. Energy storage efficiency : where η=efficiency, E out =energy retrieved from bladder, and E in = energy delivered to bladder

15. Project 2C.2Eric J. Barth 15 Current Problems/Solutions Problems: –Molding Problems Bubbles Material Solutions: –Vacuum Chamber –Four new molding materials and systems.

16. Project 2C.2Eric J. Barth 16 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

17. Project 2C.2Eric J. Barth 17 END

18. Project 2C.2Eric J. Barth 18 Energy Density Cambridge Engineering Selector (CES), 2008

19. Project 2C.2Eric J. Barth 19 Fatigue Strength and Service Temperature Cambridge Engineering Selector (CES), 2008

20. Project 2C.2Eric J. Barth 20 Elongation and Loss Coefficient Cambridge 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).