Marc Secanell

Design of a Morphing Airfoil Using Aerodynamic Shape Optimization

An in-house high-fidelity aerodynamic shape optimization computer program based on a computational fluid dynamics solver with the Spalart-Allmaras turbulence model and a sequential-quadratic-programming algorithm is used to obtain a set of optimal airfoils at the different flight conditions of a light unmanned air vehicle. For this study, the airfoil requirements at stall, takeoff run, climb gradient, rate of climb, cruise, and loiter conditions are obtained. Then, the aerodynamic shape optimization program is used to obtain the airfoil that has the optimal aerodynamic characteristics at each one of these flight conditions. Once the optimal airfoils at each flight condition are obtained, the results are analyzed to gain a better understanding of the most efficient initial airfoil configuration and the possible mechanisms that could be used to morph the single element airfoil. The results show that a very thin airfoil could be used as the initial configuration. Furthermore, a morphing mechanism that controls the camber and leading-edge thickness of the airfoil will almost suffice to obtain the optimal airfoil at most operating conditions. Lastly, the use of the optimal airfoils at the different flight conditions significantly reduces the installed power requirements, thus enabling a greater flexibility in the mission profile of the unmanned air vehicle.

Optimal Design of Ultralow-Platinum PEMFC Anode Electrodes

A computational, two-dimensional agglomerate anode electrode model is presented. The model provides insight on the mass and charge transport in the anode and implements the recent proposed dual-pathway kinetics for the hydrogen oxidation reaction. Results from this model highlight the potential for platinum reduction on the anode. In order to systematically assess the possible reductions on platinum loading, an optimization problem is formulated to minimize platinum loading while maintaining performance of typical state-of-the-art electrodes. The results reveal that platinum loading can be reduced by more than one order of magnitude, from 0.4 to less than 0.018 mg/cm 2 , by changing the gas diffusion layer (GDL) and catalyst layer (CL) composition. Furthermore, if the CL thickness and the GDL and CL compositions are optimized simultaneously, the amount of platinum can be further reduced by an extra order of magnitude by depositing a catalyst layer of 1.25 μm with a platinum loading of 0.0026 mg/cm 2 .

Multi-objective optimization of a polymer electrolyte fuel cell membrane electrode assembly

A multi-objective multi-variable gradient-based fuel cell optimization framework is presented in order to optimize fuel cell membrane electrode assembly fabrication. The optimization target is to simultaneously maximize the cell current density at a given voltage and minimize its production costs. The design variables are electrode composition parameters such as platinum loading and porosity. To develop this framework, a two-dimensional through-the-channel single-phase membrane electrode assembly model is implemented and coupled to an optimization algorithm. In order to solve the optimization problem in a reasonable time, a gradient-based optimization method in conjunction with analytical sensitivities of the electrode model with respect to design parameters such as amount of electrolyte are used. Results show the trade-offs between performance and cost and illustrate that large gains in performance and reductions in production costs are possible. They also highlight the problems associated with formulating the optimization problem without taking into account production costs.

Design of a Morphing Airfoil for a Light Unmanned Aerial Vehicle Using High-Fidelity Aerodynamics Shape Optimization

An in -house high -fidelity aerodynamic shape optimization computer program based on a computational fluid dynamics solver with the Spalart -Allmaras turbulence model and a sequential quadratic programming algorithm is used in order t o obtain a set of optimal airfoils at the different stages of flight of a light unmanned air vehicle. For this study, the airfoil requirements at stall, takeoff run, climb gradient, rate of climb, cruise and loiter conditions are obtained . Then, t he aerody namic shape optimization program is used to obtain the airfoil that has the optimal aerodynamic characteristics at each one of the se stages of flight. Once the optimal airfoils at each stage of flight are obtained, the results are analyzed in order to gain a better understanding of the most efficient initial airfoil configuration and the possible mechanisms that could be used to morph the single element airfoil. The results show that a very thin airfoil could be used as the initial configuration. Furthermor e, a morphing mechanism that controls the camber and leading edge thickness of the airfoil will almost suffice to obtain the optimal airfoil at most operating conditions. Lastly, the use of the optimal airfoils at the different stages of flight significant ly reduce s the installed power requirements, thus enabling a greater flexibility in the mission profile of the unmanned air vehicle.

Optimization analysis for plane orientation in 3-dimensional cephalometric analysis of serial cone-beam computerized tomography images

OBJECTIVES The purpose of this study was to evaluate and reduce potential errors associated with superimposition of serial cone-beam computerized tomography (CBCT) images using planes based on cranial base landmarks. METHODS CBCTs from 10 patients were analyzed. The potential impact of errors in cranial base landmark identification on assessment of the relative position of distant landmarks is mitigated by means of a mathematical algorithm that ensures that the distances and angles between landmark identification points are maintained for different images by readjusting the landmark coordinates. RESULTS Significant improvement was observed after optimization. The errors found in a previous study were significantly reduced, some by more than 90%. Errors found in the standardization were viewed in both infraorbitals and mentons ranging from 1 to 3 mm. CONCLUSIONS The mathematical transformation to readjust the coordinates of ELSA, left and right auditory external meatus (AEM), and dorsum foramen magnum (DFM) points significantly improves their use for image superimposition.

Multigrid hierarchical simulated annealing method for reconstructing heterogeneous media.

A reconstruction methodology based on different-phase-neighbor (DPN) pixel swapping and multigrid hierarchical annealing is presented. The method performs reconstructions by starting at a coarse image and successively refining it. The DPN information is used at each refinement stage to freeze interior pixels of preformed structures. This preserves the large-scale structures in refined images and also reduces the number of pixels to be swapped, thereby resulting in a decrease in the necessary computational time to reach a solution. Compared to conventional single-grid simulated annealing, this method was found to reduce the required computation time to achieve a reconstruction by around a factor of 70-90, with the potential of even higher speedups for larger reconstructions. The method is able to perform medium sized (up to 300(3) voxels) three-dimensional reconstructions with multiple correlation functions in 36-47 h.

Multiobjective optimization framework for landmark measurement error correction in three-dimensional cephalometric tomography.

The purpose of this study is to minimize errors that occur when using a four vs six landmark superimpositioning method in the cranial base to define the co-ordinate system. Cone beam CT volumetric data from ten patients were used for this study. Co-ordinate system transformations were performed. A co-ordinate system was constructed using two planes defined by four anatomical landmarks located by an orthodontist. A second co-ordinate system was constructed using four anatomical landmarks that are corrected using a numerical optimization algorithm for any landmark location operator error using information from six landmarks. The optimization algorithm minimizes the relative distance and angle between the known fixed points in the two images to find the correction. Measurement errors and co-ordinates in all axes were obtained for each co-ordinate system. Significant improvement is observed after using the landmark correction algorithm to position the final co-ordinate system. The errors found in a previous study are significantly reduced. Errors found were between 1 mm and 2 mm. When analysing real patient data, it was found that the 6-point correction algorithm reduced errors between images and increased intrapoint reliability. A novel method of optimizing the overlay of three-dimensional images using a 6-point correction algorithm was introduced and examined. This method demonstrated greater reliability and reproducibility than the previous 4-point correction algorithm.

Precision and accuracy of suggested maxillary and mandibular landmarks with cone-beam computed tomography for regional superimpositions: An in vitro study

INTRODUCTION Our objective was to identify and evaluate the accuracy and precision (intrarater and interrater reliabilities) of various anatomic landmarks for use in 3-dimensional maxillary and mandibular regional superimpositions. METHODS We used cone-beam computed tomography reconstructions of 10 human dried skulls to locate 10 landmarks in the maxilla and the mandible. Precision and accuracy were assessed with intrarater and interrater readings. Three examiners located these landmarks in the cone-beam computed tomography images 3 times with readings scheduled at 1-week intervals. Three-dimensional coordinates were determined (x, y, and z coordinates), and the intraclass correlation coefficient was computed to determine intrarater and interrater reliabilities, as well as the mean error difference and confidence intervals for each measurement. RESULTS Bilateral mental foramina, bilateral infraorbital foramina, anterior nasal spine, incisive canal, and nasion showed the highest precision and accuracy in both intrarater and interrater reliabilities. Subspinale and bilateral lingulae had the lowest precision and accuracy in both intrarater and interrater reliabilities. CONCLUSIONS When choosing the most accurate and precise landmarks for 3-dimensional cephalometric analysis or plane-derived maxillary and mandibular superimpositions, bilateral mental and infraorbital foramina, landmarks in the anterior region of the maxilla, and nasion appeared to be the best options of the analyzed landmarks. Caution is needed when using subspinale and bilateral lingulae because of their higher mean errors in location.

Optimization of a PEM Fuel Cell System for Low-Speed Hybrid Electric Vehicles

Design optimization is performed by presenting a systematic method to obtain the optimal operating conditions of a Proton Exchange Membrane (PEM) fuel cell system targeted towards a vehicular application. The fuel cell stack model is a modified version of the semi-empirical model introduced by researchers at the Royal Military College of Canada and one that is widely used by industry. Empirical data obtained from tests of PEM fuel cell stacks are used to determine the empirical parameters of the fuel cell performance model. Based on this stack model, a fuel cell system model is built in MATLAB. Included in the system model are heat transfer and gas flow considerations and the associated Balance of Plant (BOP) components. The modified ADVISOR vehicle simulation tool is used to integrate the New York City Cycle (NYCC) drive cycle and vehicle model to determine the power requirements and hence the load cycle of the fuel cell system for a low-speed fuel cell hybrid electric vehicle (LSFCHEV). The optimization of the powerplant of this vehicle type is unique. The vehicle model has been developed in the work to describe the characteristics and performance of an electric scooter, a simple low-speed vehicle (LSV). The net output power and system exergetic efficiency of the system are maximized for various system operating conditions using the weighted objective function based on the load cycle requirement. The method is based on the coupling of the fuel cell system model with three optimization algorithms (a) sequential quadratic programming (SQP); (b) simulated annealing (SA); and (c) genetic algorithm (GA). The results of the optimization provide useful information that will be used in future study on control algorithms for LSFCHEVs. This study facilitates research on more complex fuel cell system modeling and optimization, and provides a basis for experimentation to verify the fuel cell system model.Copyright

Mass Transport Measurements in Porous Transport Layers of a PEM Fuel Cell

Porous transport layers are an integral part of polymer electrolyte fuel cells (PEMFC). In order to optimize the catalyst layer performance and reduce catalyst consumption, a thorough understanding of mass transport through porous media is necessary. Currently, there is a lack of experimental measurements of effective mass transport properties of porous transport layers. Further, mass transport theories in the literature, such as the binary friction model by Kerkhof [1], have not been extensively validated for porous media. In the present study, mass transport measurements have been performed on the porous media of a PEMFC, namely a GDL and an MPL. The experimental setup described by Pant et al. [2] has been used. The setup uses the diffusion bridge/counter-diffusion technique for the mass transport measurements. The experimental setup has the advantage that it can be used to perform studies for pure diffusion and convection-diffusion mass transport. The setup also facilitates measurement of permeability of porous media, which can then be used in convection-diffusion studies. Preliminary permeability measurements of GDL and MPL from the setup show good agreement with values available in literature. In preliminary experimentation, the conventional diffusivity correlations like Bruggeman equation have been found to overpredict the diffusivities.Copyright