337 research outputs found
Application of the Real-Time Kinematic Global Positioning System in Bridge Safety Monitoring
No full textA real-time kinematic (RTK) global positioning system (GPS) has been developed and installed on the Human Bridge (China) for on-line monitoring of bridge deck movement, which may occur as a result of seismic activity, traffic load, and such environmental elements as temperature and wind. This paper presents the main features of the on-line GPS RTK system and its value for on-line safety monitoring
Improving the Evolutionary Optimization of Interplanetary Low-Thrust Trajectories Using a Neural Network Surrogate Model
No full textBuilding on recent advances in the fields of low-thrust trajectory optimization based on shaping methods, Artificial Neural Networks, and surrogate models in Evolutionary Algorithms, an investigation into a novel optimization routine is conducted. A flexible Python tool to evaluate linked trajectories in a two-body model based on hodographic shaping is implemented and used to develop a novel evolutionary optimization approach where a Genetic Algorithm is assisted in finding new candidate solutions by an online surrogate. The algorithm and different surrogate designs are experimentally investigated on two example problems based on the Dawn trajectory and the GTOC2 problem. Employing the surrogate yields new candidate solutions that improve the population’s fitness especially when the surrogate is used to approximate the shaping computation. Additionally, the use of a surrogate pretrained on a general data set of low-thrust transfers is tested and found to considerably improve the initial quality of the model, meaning that more good candidate solutions are found early on, accelerating the algorithm’s convergence.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Astrodynamics & Space Mission
Global Optimization of Low-Thrust Interplanetary Trajectories Using a Machine Learning Surrogate
No full textIn this work, we propose a new method to approximate the cost function of Low-Thrust, Multiple-Gravity-Assist interplanetary trajectories using a Machine Learning surrogate. We identified the computation time required to obtain training data as the main limitation when using Machine Learning methods for this purpose so we present a strategy to build the surrogate with limited training data. We built an Online-Sequential Extreme Learning Machine Multi-Agent System (OS-ELM-MAS) surrogate due to its theoretical good performance when the training data is limited. In addition, we define a method to include the surrogate during the optimization process that can be used with any gradient-free algorithm, and study the effect of several surrogate parameters on the optimization results. Finally, several interplanetary trajectories are optimized with and without the surrogate. Employing the surrogate results in up to 12% lower fuel cost values after a fixed optimization time. The parameters that control the interaction have to be carefully selected to achieve this improvement, and we show that the optimal value of these parameters can be narrowed down based on the characteristics of the transfers.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Astrodynamics & Space Mission
Integration of process scheduling and control
No full textThe objective of this dissertation is to develop integrated models and optimization methods to solve for chemical process scheduling and control problems. A traditional approach to handle process operations at scheduling and control levels is to consider them as separate optimization problems. However, scheduling and dynamic optimization at control level are naturally connected. An integrated decision making helps to achieve an overall optimality and thus improves the profitability of process operations. Integration of scheduling and control results in Mixed Integer Dynamic Optimization (MIDO) which is computationally expensive. To reduce the complexity brought by integration, research efforts of this dissertation target two goals focusing on first reducing the model complexity, and second reducing the solution computational time especially in the case of online implementations (i.e. closed loop implementations). In this dissertation, we first proposed an approach of implementing closed loop scheduling and control when the processes are subject to disturbance. Then we proposed a decomposition approach for the large size Mixed Integer Nonlinear Programming (MINLP) resulted from the integration of scheduling and control through sensitivity analysis. To facilitate online applications, we adopt multi-parametric Model Predictive Control (mp-MPC) at the control level and built a new integrated model using the explicit control solution generated by mp-MPC. We also developed an integrated model using a Piecewise Affine (PWA) model and used fast MPC at the control level to overcome the exponential dimension increasing in mp-MPC. Finally we discuss the uncertainty in process operations and present solution procedures of robust MPC for nonlinear problem at the control level. Throughout this dissertation, detailed integrated models and the solution algorithms are developed and case studies are used to demonstrate the effectiveness of the proposed approaches.Ph.D.Includes bibliographical referencesby Jinjun Zhug
Development of a spherical motor with a 3-DOF sensing system
No full textThe thesis proposes a new design of a spherical wheel motor (SWM) with three layers of permanent magnets (PMs) located both inside and outside of double layers of electrical magnets (EMs), so as to fully utilize the magnetic field generated by the EMs and enhance the inclination torque density. The inclination torque is generally weak due to the limited number and space for the PMs and EMs involved in inclination compared to spinning. Finite element modeling (FEM) has been utilized for simulation, and important design parameters are optimized to maximize the inclination torque. The FEM modeling has been verified by experiments with discrepancy of less than 10% achieved. The optimized design can generate strong inclination torque which can support heavy loadings. Iron stator cores are applied in the new design to improve magnetic torque, and the magnetic field distribution (MFD) and magnetic torque become nonlinear due to magnetic saturation characteristics of the iron cores. Based on the analysis of the MFD of the whole SWM applying different current inputs, the thesis has constructed a dynamic model for SWMs with current inputs within the working range. A multi-DOF non-contact sensing system based on magnetic sensors and neural networks (NNs) is proposed. NNs are applied to approximate the function between orientations and MFD. The proposed sensing system is simulated and verified by experimental investigations. The sensing error to working range ratio is about 1.4%, which verifies its feasibility. With the proposed SWM design with enhanced torque capability, dynamic model and sensing system, the present findings provide strong basis to realize an integrated system of an SWM and take it a step closer to industrial applications.DOCTOR OF PHILOSOPHY (MAE
Short- and long-term impact of remarkable economic events on the growth causes of China-Germany trade in agri-food products
No full textThis paper focuses on a systematic quantitative discussion of the short- and long-term impact of remarkable economic events on international trade in a two-stage framework. Firstly, procedures based on dummy variables are proposed to detect structural breaks, types and sizes of jumps caused by such events. Then we propose to apply a hierarchical CMS (Constant Market Share) model to all sub-periods defined by the detected change points to study the short- and long-term impact of those events on growth causes. Application to China-Germany trade in agri-food products shows that China’s accession to WTO had a negative short-term impact on corresponding series. But its long-term impact on China’s export competitiveness was definitely positive. The short-term impact of the EU’s CAP (Common Agricultural Policy) reform on Germany’s exports to China was also negative. Its long-term impact on export competitiveness was sometimes positive and sometimes negative. The financial crisis of 2008 caused a significant reduction of China’s agri-food exports to Germany. But Germany’s exports to China in 2009 were not affected by the financial crisis as much.Growth causes of agri-food trade; the CMS model; the EU’s CAP reform; China’s accession to WTO; financial crisis
SOFC anode modelling using TPB based kinetics
No full textSolid oxide fuel cell exhibits its advantages such as fuel variability. Capable of running on renewable fuels, SOFCs are regarded as potential solution to carbon-neutral energy conversion path. SOFCs operate on fuel supplied to the anode and oxidant supplied to the cathode. The anode should facilitate the oxidation of fuel and transport of electrons from the reaction site to the current collector. It should also enable the diffusion of gaseous fuel to the reaction sites and reaction products away from the reaction sites. Meeting abovementioned requirements, Ni/YSZ cermets are competent SOFC anodes, where Ni is an electronic conductor, YSZ is an ionic conductor, and pores in between Ni and YSZ facilitate the fuel supply. Fuel oxidation occurs in the vicinity of triple phase boundaries (TPBs), where Ni particles, YSZ particles and pore interact. Thus, TPB length quantifies the electrochemically active sites within the anode. The fuel oxidation involves physical processes and multi-elementary reaction steps in reality, among which exists a rate-limiting step. The overall reaction rate can be represented by the rate-limiting step whose kinetics are proposed as a function of the TPB length. In many past computational studies of the cermet anode, a global electrochemical reaction expressed by Butler-Volmer equation is put forward, simplifying electrode reaction to a single step process and probably inadequately to present insights into intrinsic processes occurring within the anode. In this work, TPB-based kinetics, derived from the pattern anode experiment, are implemented in a CFD model to evaluate the performance of Ni/YSZ cermet-based cells. For model validation, simulated polarization curves are compared with the experimental ones. TPB length as a fitting parameter is determined to ensure the agreement between simulated polarization curves and experimental ones. The fitted TPB length is found to be several orders of magnitudes lower than physical TPB length of typical Ni-YSZ cermet anode, which might imply that only a small fraction of the physical TPB length actually participates in the electrochemical reactions. CFD behavior like species distribution and electrochemical behavior like overpotential breakdown are investigated. The gradient of species molar fraction in anode turns to be larger than that in fuel channel, agreeing with the fact that fluid flow is much slower in anode where species transport in porous electrode is dominated by diffusion rather than convection. The cathode activation overpotential makes the most significant contribution to the overall overpotential. The anode activation overpotential at high current density region in the case of low molar fraction of inlet hydrogen yields rapid increase, which could be explained as a consequence of rapid decrease of exchange current density in the vicinity of anode/electrolyte interface. Parametric study of operating temperature is conducted later to see its effect on the cell performance. The higher the operating temperature is, the slower drop of cell voltage with respect to cell current is observed. At a fixed cell voltage, an elevated temperature will cause intensified fuel consumption/vapor generation within anode, leading to a larger gradient of species molar fraction and accordingly a larger concentration overpotential
Magnetic Resonance Features of Lower-grade Gliomas in Prediction of the Reverse Phase Protein A
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Effect of Municipal Solid Waste Incineration Fly Ash on the Mechanical Properties and Microstructure of Geopolymer Concrete
No full textGeopolymers are environmentally friendly materials made from industrial solid waste with high silicon and aluminum contents, and municipal solid waste incineration fly ash (MFA) contains active ingredients such as Si, Al and Ca. According to this fact, a green and low-carbon geopolymer concrete was prepared using MFA as a partial replacement for metakaolin in this study. The mechanical properties of the MFA geopolymer concrete (MFA-GPC) were investigated through a series of experiments, including a compressive strength test, splitting tensile strength test, elastic modulus test and three-point bending fracture test. The effect of the MFA replacement ratio on the microstructure of MFA-GPC was investigated by SEM test, XRD analysis and FTIR analysis. MFA replacement ratios incorporated in GPC were 5%, 10%, 15%, 20%, 25%, 30%, 35% and 40% by replacing metakaolin with equal quality in this study. In addition, toxic leaching tests of MFA and MFA-GPC were performed by ICP-AES to evaluate the safety of MFA-GPC. The results indicated that the mechanical properties of MFA-GPC decreased with the increase of the MFA replacement ratio. Compared with the reference group of GPC without MFA, the maximum reduction rates of the cubic compressive strength, splitting tensile strength, axial compressive strength, elastic modulus, initiation fracture toughness, unstable fracture toughness and fracture energy of MFA-GPC were 83%, 81%, 78%, 93%, 77%, 73% and 61%, respectively. The microstructure of MFA-GPC was porous and carbonized; however, the type of hydrated gel products was still a calcium silicoaluminate-based silicoaluminate gel. Moreover, the leaching content of heavy metals from MFA-GPC was lower than that of the standard limit. In general, the appropriate amount of MFA can be used to prepare GPC, and its mechanical properties can meet the engineering requirements, but the amount of MFA should not be too high
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