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Optimal Multi-Impulse Orbit Transfer Using Nonlinear Relative Motion Dynamics

The Journal of the Astronautical Sciences 2014年第1期59卷 237-258页

作者： Huang, Weijun PhD student Department of Mechanical and Aerospace Engineering University of Missouri-Columbia Columbia 65201

Trajectory planning for satellite formation flying missions requires the ability to find the optimal control law to transfer a satellite from one periodic relative orbit to another. This article modifies Jezewski’s linear impulsive trajectory optimization method for solving nonlinear problems described in the relative coordinate frame, and proposes the concept of standard problems for the initialization of the optimizer. With this modified optimizer and the standard problem concept, the article studies the impulse number, the cost, and the nonlinearity of fixed-time coplanar transfer problems.

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Comparison of CO 2 and Steam in Transcritical Rankine Cycles for Concentrated Solar Power

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Energy Procedia 2014年 49卷 1138-1146页

作者： P. Garg K. Srinivasan P. Dutta P. Kumar Ph.D. Candidate Department of Mechanical Engineering Indian Institute of Science Bangalore INDIA Professor (Retd.) Department of Mechanical Engineering Indian Institute of Science Bangalore INDIA Professor Department of Mechanical Engineering Indian Institute of Science Bangalore INDIA Assistant Professor Department of Mechanical Engineering Indian Institute of Science Bangalore INDIA

High temperature, high pressure transcritical condensing CO2 cycle (TC-CO2) is compared with transcritical steam (TC-steam) cycle. Performance indicators such as thermal efficiency, volumetric flow rates and entropy generation are used to analyze the power cycle wherein, irreversibilities in turbo-machinery and heat exchangers are taken into account. Although, both cycles yield comparable thermal efficiencies under identical operating conditions, TC-CO2 plant is significantly compact compared to a TC- steam plant. Large specific volume of steam is responsible for a bulky system. It is also found that the performance of a TC-CO2 cycle is less sensitive to source temperature variations, which is an important requirement of a solar thermal system. In addition, issues like wet expansion in turbine and vacuum in condenser are absent in case of a TC-CO2 cycle. External heat addition to working fluid is assumed to take place through a heat transfer fluid (HTF) which receives heat from a solar receiver. A TC-CO2 system receives heat though a single HTF loop, whereas, for TC-steam cycle two HTF loops in series are proposed to avoid high temperature differential between the steam and HTF.

关键词： Transcritical Brayton cycle solar power cycle irreversibility steam Rankine cycle

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Use of MEMs and optical sensors for closed loop heliostat control

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AIP Conference Proceedings 2016年第1期1734卷

作者： Paul Julian Harper Janto Dreijer Karel Malan James Larmuth Paul Gauche 1DSc MA(Cantab) Research Scientist Helio100 project CRSES Stellenbosch University. 10 Devon Valley Road Stellenbosch 7600 South Africa 2PhD MSc.Eng (Mechatronic) Research Engineer Helio100 project CRSES Stellenbosch University South Africa 3MEng (Mechatronic) Research Engineer Helio100 project CRSES Stellenbosch University South Africa 4MEng (Mechatronic) Research Engineer Helio100 project CRSES Stellenbosch University South Africa 5PhD Candidate Project Lead Helio100 project STERG Department of Mechanical and Mechatronic Engineering Stellenbosch University Stellenbosch 7600 South Africa

The Helio 100 project at STERG (Stellenbosch Solar Thermal Research Group) aims to help reduce the cost of Concentrated Solar Thermal plants by deploying large numbers of small (1x2 m) low cost heliostats. One of the methods employed to reduce the cost of the heliostat field is to have a field that requires no site preparation (grading, leveling, vegetation clearance) and no expensive foundations or concrete pouring for each individual heliostat base. This implies that the heliostat pod frames and vertical mounts might be slightly out of vertical, and the normal method of dead reckoning using accurately surveyed and aligned heliostat bases cannot be used. This paper describes a combination of MEMs and optical sensors on the back of the heliostat, that together with a simple machine learning approach, give accurate and reproducible azimuth and elevation information for the heliostat plane. Initial experiments were done with an android phone mounted on the back of a heliostat as it was a readily available platform combining accelerometers’ and camera into one programmable package. It was found quite easy to determine the pointing angle of the heliostat to within 1 milliradian using the rear facing camera and correlating known heliostat angles with target image features on the ground. We also tested the accuracy at various image resolutions by halving the image size successively till the feature detection failed. This showed that even a VGA (640x480) resolution image could give mean errors of 1.5 milliradian. The optical technique is exceedingly simple and does not use any camera calibration, angular reconstruction or knowledge of heliostat drive geometry. We also tested the ability of the 3d accelerometers to determine angle, but this was coarser than the camera and only accurate to around 10 milliradians.

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A numerical study on high-pressure water-spray cleaning for CSP reflectors

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AIP Conference Proceedings 2016年第1期1734卷

作者： Francesco Anglani John Barry Willem Dekkers 1Affiliations: PhD Candidate MSc Mechanical Engineering. Address: Queensland University of Technology (QUT) O Block Level 7 Room 724 Garden Point Campus 2 George St Brisbane 4000 Queensland Australia +61 07 81382451 2Professor John Barry Queensland University of Technology (QUT) P Block Level 7 Garden Point Campus Australia 3Dr Wim Dekkers Associate Lecturer Queensland University of Technology (QUT) O Block Level 7 Garden Point Campus Australia

Mirror cleaning for concentrated solar thermal (CST) systems is an important aspect of operation and maintenance (O&M), which affects solar field efficiency. The cleaning process involves soil removal by erosion, resulting from droplet impingement on the surface. Several studies have been conducted on dust accumulation and CSP plant reflectivity restoration, demonstrating that parameters such as nozzle diameter, jet impingement angle, interaxial distance between nozzles, standoff distance, water velocity, nozzle pressure and others factors influence the extent of reflectance restoration. In this paper we aim at identifying optimized cleaning strategies suitable for CST plants, able to restore mirror reflectance by high-pressure water-spray systems through the enhancement of shear stress over reflectors’ surface. In order to evaluate the forces generated by water-spray jet impingement during the cleaning process, fluid dynamics simulations have been undertaken with ANSYS CFX software. In this analysis, shear forces represent the “critical phenomena” within the soil removal process. Enhancing shear forces on a particular area of the target surface, varying the angle of impingement in combination with the variation of standoff distances, and managing the interaxial distance of nozzles can increase cleaning efficiency. This procedure intends to improve the cleaning operation for CST mirrors reducing spotted surface and increasing particles removal efficiency. However, turbulence developed by adjacent flows decrease the shear stress generated on the reflectors surface. The presence of turbulence is identified by the formation of “fountain regions” which are mostly responsible of cleaning inefficiency. By numerical analysis using ANSYS CFX, we have modelled a stationary water-spray system with an array of three nozzles in line, with two angles of impingement: θ = 90° and θ = 75°. Several numerical tests have been carried out, varying the interaxial distance of nozzles, st

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Optimal linear control driven for piezoelectric non-linear energy harvesting on non-ideal excitation sourced

Optimal linear control driven for piezoelectric non-linear e...

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2014 International Conference on Mechatronics and Intelligent Materials, MIM 2014

作者： Da Costa Ferreira, Douglas Chavarette, Fábio Roberto Peruzzi, Nelson José UNESP - Univ. Estadual Paulista Mechanical Engineering PhD Program Ilha Solteira SP Brazil UNESP - Univ. Estadual Paulista Mathematics Department Ilha Solteira SP Brazil

ISBN: (纸本)9783038351412

Non-linear energy harvesting system was project to enhance interaction to ambient vibration that is wide band and low power which difficult the design for resonant solution. To improve efficiency of a non-linear design it was project a control system based in optimal linear control (OLC). Applying numerical evaluations it was possible to analyze the kinetic energy from the system as also the resulting output voltage. As main result there was a considerable increase of output voltage due controlled system in comparison to open loop for the same excitation. © (2013) Trans Tech Publications, Switzerland.

关键词： Energy harvesting

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Multiphysics Modeling and Simulation of Selective Laser Sintering Manufacturing Processes

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Procedia CIRP 2014年 14卷 299-304页

作者： Rishi Ganeriwala Tarek I. Zohdi Doctoral Candidate Department of Mechanical Engineering 6102 Etcheverry Hall University of California Berkeley CA 94720-1740 USA Professor Department of Mechanical Engineering 6117 Etcheverry Hall University of California Berkeley CA 94720-1740 USA

A significant percentage of materials used in industry start in particulate form. In many modern applications, these systems undergo processing which necessitate a multiphysical analysis. Several manufacturing applications have arisen that involve the multiphysical response of particulate systems in the presence of strongly coupled electromagnetic, optical, and thermal fields. The significant multifield coupling requires methods that can capture the unique and essential physics of these systems. Specifically, in this work, the modeling and simulation of selective laser sintering of particulate materials is discussed. Such processes involve harnessing optical energy to heat and fuse powdered materials together in an additive process. Selective laser sintering allows for the rapid manufacturing or prototyping of parts with complex geometries. In order to simulate such a process in a rapid manner, the approach pursued by the authors is to develop a computational tool by assembling relatively simple, physically meaningful, models at the small scale, for many interacting particles. This allows for much more refined estimates of the resulting overall system temperature and, ultimately, its change of phase from a solid, to a liquid, and possibly even to a gas. Large-scale three-dimensional examples are provided.

关键词： selective laser sintering additive manufacturing rapid manufacturing rapid protoyping

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Corrigendum to “Elevated temperature nanoindentation characterization of poly( para -phenylene vinylene) conjugated polymer films” [Polym. Test. 41 (2015) 17–25]

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Polymer Testing 2015年 42卷 234-234页

作者： Nimitt G. Patel Arvind Sreeram Ramaswamy I. Venkatanarayanan Sitaraman Krishnan Philip A. Yuya Department of Mechanical and Aeronautical Engineering Clarkson University Potsdam NY 13699 USA Materials Science and Engineering PhD Program Clarkson University Potsdam NY 13699 USA Department of Chemical and Biomolecular Engineering Clarkson University Potsdam NY 13699 USA

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Model-Free Observer for MIMO systems

Model-Free Observer for MIMO systems

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Conference on Control Applications

作者： Younes A1 Younes Hassan Noura Abdelhamid Rabhi Ahmed El Hajjaji Mechanical Engineering Faculty at Higher Colleges of Technology Al Ain UAE and PhD student at the University of Picardie Jules Verne Amiens France PhD is Professor and Chairman of Electrical Engineering Department at United Arab Emirates University Al Ain UAE PhD is Assistant Professor in Modeling Information & System Lab - Control & Vehicle Group- at University of Picardie Amiens France PhD is Professor in Modeling Information & System Lab - Control & Vehicle Group- at University of Picardie Amiens France

ISBN: (纸本)9781479977970

In this paper, a novel observer design is introduced to estimate the outputs of a Multi-Input-Multi-Output (MIMO) system. From the synthesis of state observer and Model-Free technique, the Model-Free Observer (MFO) is proposed to compensate for the un-modeled dynamics, modeling errors, and the system uncertainties. The developed output estimation technique using MFO is validated using real flights of a quadrotor UAV. Two flight-test missions are conducted to validate the proposed observer performance, in the fault free case as well as in the presence of actuator faults.

关键词： MFO proposed actuator faults

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Motion Removal from Moving Platforms: An RGB-D Data-based Motion Detection, Tracking and Segmentation Approach

Motion Removal from Moving Platforms: An RGB-D Data-based Mo...

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IEEE International Conference on Robotics and Biomimetics

作者： Yuxiang Sun Ming Liu Max Q.-H. Meng PhD student and Professor. They are both at the Department of Electronic Engineering The Chinese University of Hong Kong Shatin N.T. Hong Kong SAR China Assistant Professor at the Department of Mechanical and Biomedical Engineering City University of Hong Kong Tat Chee Avenue Kowloon Hong Kong SAR China

ISBN: (纸本)9781467396769

Moving objects are the primary concern for most robot vision applications in dynamic environments. The existence of moving objects can lead to ambiguous decisions such as searching loop closure in visual mapping applications. Eliminating moving objects from the image sequences captured by moving camera is the key challenge. In this paper, a novel approach for moving objects removal using a hand-held RGBD camera is proposed. Only the visual and depth data are used. No other sensor or prior information is needed in this paper. Our approach can be exploited as a pre-processing stage to filter out data that are associated with moving objects. We test our approach with various ego-motion patterns in different environments. The experimental results demonstrate that our approach can provide a practical solution for motion removal from moving platforms using an RGB-D camera.

关键词： existence moving motion removal

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Computational Simulation to Predict the Syngas Composition Produced during Charcoal Gasification

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Journal of Chemistry and Chemical engineering 2014年第9期8卷 889-897页

作者： Ignacio Contreras-Andrade Santiago Ramirez-Rubio Jonathan Parra-Santiago Fabio Sierra-Vargas Carlos Alberto Guerrero-Fajardo Doctor Chemical Engineering Autonomous University of Sinaloa Culiacan Rosales 80040 Mexico Department of Aeronautical Engineering San Buenaventura University Bogota 11001 Colombia Chemical Engineering (C) National University of Colombia Bogota 11001 Colombia Oepartment of Mechanical Engineering National University of Colombia Bogota 11001 Colombia Chemical Engineering and Mechanical Master in Environmental Engineering PhD in Chemical Engineering National Universityof Colombia Bogota 11001 Colombia

Charcoal gasification could mitigate the energetic problems in the rural zones since these regions have considerable amounts of wood, which is the base of such a fuel available. This paper presents some CFD （computational fluid dynamic） predictions of the experimental results obtained from the fixed bed gasification of charcoal made in a pilot-scale downdraft reactor using air, which was designed and built by the Research Group in Clean Development Mechanisms and Energy Management, from the National University of Colombia. The quality of the syngas obtained from the process was evaluated through the CO and CO2 percentages measured in its composition. The performance at various air flow rates （measured at the system entrance, through an analog flow meter） is evaluated with the help of 11 thermocouples, which give the information to create a temperature profile, and three load cells to measure the solid fuel conversion rate. To simulate the process, the information from temperature profile, charcoal proximate analysis, air flow meter and load cells were taken as inputs and the syngas composition was obtained as the result from the calculation. The domain was defined as 2D with an axis-symmetric description, using quads as mesh elements. The calculation and results were performed in a CFD commercial code widely used for this type of simulations： ANSYS FLUENT. The predictions made by the software were validated with the experimental results obtained in the laboratory.

关键词： Biomass charcoal fixed bed gasification syngas CFD.

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