Thrust 2: Compactness
Title
2D: Multi-Functional Fluid-Power Components Using Engineered Structures and Materials
Project Leader
Douglas Cook (MSOE)
Statement of Project Goals
The goal of Project 2D is to characterize the structural-thermal-acoustic coupling of three of the five unit-lattice structure types identified earlier to allow for the design of passive, noise-reducing, heat-dissipating fluid-power components. Structural-acoustic and thermal-structural couplings will be defined through virtual testing; and, physical, non-destructive testing for validation of the couplings will be conducted in Year 6. In collaboration with Test Bed 6 and Projects 2B.2 & 3B.1, heat-dissipating/-shielding and quiet PAAFO components will be designed and fabricated in Year 6. Based on research, the target level of noise attenuation by the structure is 9dB, at the "stop band;" however, Project 3B.1's work will complement this for greater total noise suppression. Passive, multi-functional structures will also be applied to components of the Parker PV046 axial-piston pump to integrate the desired noise reduction. Fluid-borne-noise attenuation afforded by the new components will be measured through Project 1G.1. Radiated noise will later be measured by Parker in their anechoic/fully-reverberant chamber, likely in Year 7, followed by potential implementation in both TB1 and TB3.
Project's Role in Support of the Strategic Plan
Project 2D addresses the transformational barrier of efficient components by integrating mass reduction, thermal management and noise reduction into the design of fluid-power components, minimizing the need for peripheral components or systems to achieve these multiple functions. The technical barriers of efficient systems, safety, quietness and containment (leak-free) will be addressed by extension.
In collaboration with Test Bed 6, Project 2D will work to define a minimal-mass, heat-dissipating and/or noise-reducing structure, to achieve the goals set. While the Rev. 2 PAAFO is near the one kilogram target, the maximum output torque is much lower than desired. Increasing torque output will require a combination of higher pressure, improved efficiency and a larger actuator; therefore, thermal management and structural optimization are critical, regardless of the final choice for portable power generation. Additionally, this active orthosis must be safe and quiet to garner acceptance from the end-user. Component integration, heat dissipation and noise reduction through multi-functional component design will address this as well. Likewise, mass reduction and thermal management afforded by custom, multi-functional components will benefit Test Bed 4.
Hydraulic pumps and motors have been demonstrated to carry significant amounts of "dead weight. With additional considerations for multi-functional components, i.e. heat dissipating and noise reducing, efficiencies would be improved; and, noise would be reduced. Cooler operating temperatures of these devices also result in longer life for their components, and even the hydraulic fluid. Efficient pumps and motors, if light and quiet, are certainly beneficial to the goals of Testbeds 1 & 3, as well.
Description and explanation of research approach
Fluid-power technology's competitiveness/market penetration, despite high theoretical volumetric and gravimetric energy/power densities, is significantly hindered by; the lack of efficient commercial components and the levels of noise generated.
The challenges are then thermal and noise management, while also considering total mass and size. Heat must be effectively removed from the components and working fluid to maintain maximum efficiency throughout the operation period (an efficiency issue), and shielded from end users to prevent injury (an effectiveness issue). Excessive noise levels prevent the use of fluid-power components and devices in personal assistive devices or passenger vehicles due to the resulting discomfort of the user (an effectiveness issue). Add-on components or systems to mitigate these issues increase mass and volume of the system, hindering performance of mobile systems (a compactness issue).
Commercial heat sinks are limited by conventional fabrication limitations; and, primarily, do not bear significant structural loads, resulting in dead weight. Seepersad, et al. applied topology optimization to profiles of extruded geometries to determine the optimal load-bearing and heat-dissipating structure, under active cooling, for gas turbine engines [1]. This optimization was simplified by axial symmetry and minimal degrees of freedom. Research has also been conducted for "open-cell," load-bearing lattices as heat sinks, for both forced convection [2] and conductance [3]. The research proposed here will complement this prior work through multi-directional, geometry-dependent characterization of the selected unit-lattice structures for the definition of a load-bearing heat sink of minimal required mass.
In addition to thermal management, cellular materials are also used for noise suppression. Polymeric foam is a ubiquitous example; however, this material, primarily, absorbs the energy through cyclical mechanical loading of the polymer. The low stiffness and conductivity also significantly limit their application for load bearing and heat dissipation. Carbon and metal foams are much stiffer and more thermally conductive than their polymer counterparts [4]; but, tailoring of their properties to meet a specific application is exceptionally difficult. An engineered lattice can be optimized to meet the structural, thermal and noise-suppression requirements, and fabricated via additive manufacturing methods. This also allows for the integration of other component geometries into the lattice structure, such as the outer case of a pump, motor, actuator, valve, etc.
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The innovation being proposed is the coupling of the structure's stiffness requirements for bearing loads, leveraging the structure-characterization work completed in Years 1-4, with the lattice-spacing requirements for filtering noise and effectively dissipating heat through natural convection, within a fully-integrated lattice structure. Figure 1 shows a conceptual sketch of such a lattice that integrates the HCCI engine into the Test Bed 6 orthosis structure, while also dissipating the waste heat of combustion and providing noise suppression for the engine. This is a significant design advancement because three functions are integrated into the design of a single structure. However, in this coupled system, not all functions can be fully optimized and trade-offs are necessary.
References
1. Seepersad, Carolyn Conner, Janet K. Allen, David L. McDowell, & Farrokh Mistree. "Multifunctional Topology Design of Cellular Material Structures." Proceedings of International Design Engineering Technical Conferences & Computers and Information in Engineering (IDETC/CIE) Conference, Philadelphia, Pennsylvania (2006).
2. Kim, T., C.Y. Zhao, T.J. Lu, & H.P. Hodson. "Convective heat dissipation with lattice-frame materials." Mechanics of Materials 36: 767-780 (2004).
3. Schneider, Adam J. "Fabrication of a Thermally Gradient Fin via a Volumetric Transitioning Tetralattice Structure." Milwaukee School of Engineering, Rapid Prototyping Center. Milwaukee, Wisconsin (2002).
4. Yu, Qijun, Brian E. Thompson, & Anthony G. Straatman. "A Unit Cube-Based Model for Heat Transfer and Fluid Flow in Porous Carbon Foam." Journal of Heat Transfer 128: 352-360 (2006).
5. Remmers, Richard & Vito Gervasi. "Use of Additive Manufacturing to Create Functional Fluid Power Components." Proceedings of the 6th Fluid Power Net International (FPNI) PhD Symposium. West Lafayette, Indiana (2010).
6. Remmers, Richard, Doug Cook, & Vito Gervasi. "Custom, Integrated, Pneumatic, Rotary Actuator for an Active Ankle-Foot Orthosis." Proceedings of the 21st Annual International Solid Freeform Fabrication (SFF) Symposium. Austin, Texas (2010).
7. Cook, D., B. Knier., V. Gervasi & D. Stahl. "Automatic Generation of Strong, Light, Multi-Functional Structures from FEA Output." Proceedings of the 21st Annual International Solid Freeform Fabrication (SFF) Symposium. Austin, Texas (2010).
8. Knier, B. "Fabricating Efficient Variable-Density Lattice Structures." Proceedings for the National Conference on Undergraduate Research Asheville, North Carolina (2009).
9. Vikberg, Gunnar & Douglas Cook. " Voronoi Diagrams and Stress-Directed Lattice Structures Applied to Weight Reduction," Proceedings of the 6th Fluid Power Net International (FPNI) PhD Symposium. West Lafayette, Indiana (2010).
10. Bendsoe, M. P. and O. Sigmund, Topology Optimization. 2nd Edition. Springer Verlag. Berlin (2004).
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14. Hirsekorn, Martin, et al. "Modal Analysis and Wave Propogation Simulations in Locally Resonant Sonic Materials." Proceeding of the Twelfth International Congress on Sound and Vibration. Lisbon (2005).
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16. Sigalas, Mihail, et al. "Classical Vibrational Modes in Phononic Lattices: Theory and Experiment." Zeitschrift für Kristallographie 220: 765-809 (2005).
17. Wang, Yi-Ze, et al. s.l. "Wave Localization in Randomly Disordered Layered Three-Component Phononic Crystals with Thermal Effects." Archive of Applied Mechanics 0939-1533 (Print) 1432-0681 (Online) (2009).
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