Modular Design Methods for Photovoltaic Reverse Osmosis
To accommodate the large number of design choices, a hierarchical design method has been developed, shown in Figure 1. The method uses a series of filters to limit the design space based on engineering principles and calculations. The system is then configured from the reduced design space using optimization methods and detailed system models. The design method also accounts for uncertainty in factors which affect the system performance, such as the solar radiation and water demand. A set of detailed physics-based system models were developed to enable this process. A novel method of representing a PVRO system using a graph was developed to enable rapid evaluation of different system configurations. This modeling technique was validated using the MIT Experimental PVRO system, shown in the video below, which was designed and constructed as part of this research.
Figure 1: Modular design architecture.
MIT experimental PVRO system.
Control of Binary Actuated Solar Mirrors
Modelling and controlling these binary actuated structures is difficult and is the focus of this research. Analytical models have been developed for one-dimensional and two-dimensional compliant structures with embedded binary actuators. In addition, a model-predictive control approach has been developed to determine which binary actuator configuration corrects a given mirror deformation. These analytical models and control approaches are validated using finite element analysis and experimental studies. The experimental system built to validate the modelling approaches and the control techniques is shown in the video below.
MIT experimental binary mirror system.
Vibration Estimation of Large Space Structures using Vision and Inertial Sensors
Future space structures such as solar power stations and telescopes are expected to be very large. These structures will require on-orbit construction. Due to the risks and costs of human extravehicular work, teams of robots will be essential for the on-orbit assembly of the large space structures. There are a number of technical challenges presented by such robotic construction. The structures will need to be made of lightweight materials and will be very flexible. Autonomous robots will require information about the vibrations of the flexible structures and their dynamic parameters in order to perform the construction efficiently. Often models of the structures are imperfect, therefore the magnitude of the vibrations of the structure must be estimated on-orbit. This thesis presents a method for estimating the shape and dynamic parameters of a vibrating large space structure. This technique is a cooperative sensing approach using remote free-flying robot observers equipped with vision sensors and structure-mounted accelerometers. This approach exploits the complementary nature of the two types of sensors.
Vision sensors are able to measure structure deflections at a high spatial frequency but are bandwidth limited. Accelerometers are able to make measurements at high temporal frequency, but are sparsely located on the structure. The fused estimation occurs in three steps. First, the vision data is condensed in a modal decomposition that results in coarse estimates of modal coefficients. In the second step, the coarse estimates of the modal coefficients obtained from vision data are fused with the accelerometer measurements in a multi-rate nonlinear Kalman filter, resulting in a refined estimate of the modal coefficients and dynamic properties of the structure. In the final step, the estimated modal coefficients are combined with the mode shapes to provide a shape estimate of the entire structure. Simulation and experimental results demonstrated that the performance of this fused estimation approach was superior to the performance achieved when using only a single type of sensor.
Optimal Shape Design of a Solar Powered Vehicle
The shape design of a solar vehicle is a constrained multi-disciplinary optimization problem. The shape of the vehicle not only determines a vehicles aerodynamic performance but also affects the energy which is collected by the solar array. In this research, an optimization strategy was developed to design the shape of a solar powered vehicle. A set of candidate designs were generated using CAD software. The aerodynamics and light capturing capabilities were analyzed using Ansys CFX and custom written code. A gradient-based search was then utilized to determine the optimum vehicle shape parameters.
Publications & Patents
Bilton, A.M., Lee, S.J., and Dubowsky, S., “The Kinematic
Control of Hyper-Redundant Binary Actuated Compliant Systems
with Application to Solar Mirrors with Experimental
Validation,” submitted to the ASME Journal of Mechanisms and
Bilton, A. M., and Dubowsky, S., “The Modular Design of
Photovoltaic Reverse Osmosis Systems – Making Technology
Accessible to Non-Experts,” Desalination and Water Treatment, Vol. 51,
pp. 702-712, 2012.
Bilton, A. M., Wiesman, R., Arif, A. F. M., Zubair, S. M.,
and Dubowsky, S., "On the Feasibility of Community-Scale
Photovoltaic Powered Reverse Osmosis Systems for Remote
Energy, Vol. 36, No. 12, pp. 3246-3256, December
Bilton, A. M., Kelley, L. C., and Dubowsky, S., “Photovoltaic Reverse Osmosis – Feasibility and a Pathway to Develop Technology,” Desalination and Water Treatment, Vol. 31, pp 24-36, July 2011.
Bilton, A. M., Ishijima, Y., Lichter, L., and Dubowsky, S. "A Sensor Architecture for the Robotic Control of Large Flexible Space Structures." The Journal of Field Robotics, Vol. 24, No. 4, pp. 287-310, April 2007.
Lienhard, J. H., Antar, M. A., Bilton, A. M., Blanco, J.,
Zaragoza, G., "Solar Desalination," in Annual Review of Heat Transfer,
Vol. 15, New York: Begell House Inc., 2012.
Reed, E. A., Bilton, A. M., and Dubowsky, S., “Controllable
Energy Recovery for a Smart PVRO System,” Submitted to the IEEE/ASME
International Conference on Advanced Intelligent
Mechatronics 2013, July 9-12, 2013, Wollongong,
Meng, L., Bilton, A. M., You, Z., and Dubowsky, S.,
“Adaptive Heliostat Solar Arrays using Shape-Optimized
Compliant Mirrors,” Proceedings
of the ASME 2012 International Design Engineering
Technical Conferences & Computers and Information in
Engineering Conference IDETC/CIE 2012, Aug. 12-15,
2012, Chicago, Illinois, USA.
Bilton, A.M., and Dubowsky, S., “Inverse Kinematics for the
Control of Hyper-Redundant Binary Mechanisms with
Application to Solar Concentrator Mirrors,” Proceedings of the
International Symposium on Advances in Robot Kinematics
2012, June 24-28, 2012, Innsbruck, Austria.
Kelley, L. C., Bilton, A. M., and Dubowsky, S., “Enhancing
the Performance of Photovoltaic Powered Reverse Osmosis
Desalination Systems by Active Thermal Management,” Proceedings of the ASME 2011
International Mechanical Engineering Congress &
Exposition, November 11-17, 2011, Denver, Colorado,
Bilton, A. M., Kelley, L. C., and Mazzini, F., “Design
Optimization of Sustainable Off-Grid Power Systems for the
Developing World,” Proceedings
the ASME 2011 Energy Sustainability Conference,
August 7-10, 2011, Washington, DC, USA.
Bilton, A. M., Kelley, L. C., and Dubowsky, S.,
“Photovoltaic Reverse Osmosis – Feasibility and a Pathway to
Develop Technology,” Proceedings
of EuroMed 2010, Desalination for Clean Water and Energy,
October 3-7, 2010, Tel Aviv, Israel.
Lee, S. J., Bilton, A. M., and Dubowsky, S., “On the
Kinematics of Solar Mirrors Using Massively Parallel Binary
of the ASME 2010 International Design Engineering
Technical Conferences & Computers and Information in
Engineering Conference IDETC/CIE, August 15-18,
2010, Montreal, Quebec, Canada.
Dubowsky, S., Bilton, A. M., and Lee, S. J., “System for
Discretely Actuated Solar Mirrors,” US Patent Application
Number 12/839479, July 20, 2010.
Dubowsky, S., Bilton, A. M., and Kelley, L. C., “Photovoltaic Reverse Osmosis System with Thermal Management,” US Patent Application Number 13/032896, February 23, 2011.