278 research outputs found
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
Message from RBchain 2019 chairs
No full textPresents the introductory welcome message from the conference proceedings. May include the conference officers' congratulations to all involved with the conference event and publication of the proceedings record
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
Robust human face tracking in eigenspace for perceptual human-robot interaction
No full textThis chapter introduces a robust human face tracking scheme for vision-based human-robot interaction, where the detected face-like regions in the video sequence are tracked using unscented Kalman filter (UKF), and face occlusion are tackled by using an online appearance-based scheme using principle component analysis (PCA). The experiment is carried out with the standard test video, which validates that the proposed PCA-based face tracking can attain robust performance in tackling face occlusions
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
Several conjectures about the existence of the ether
No full textThe "zero result" of Michelson Morley's experiment was not enough to deny the existence of a fifth element---ether, as conceived by Aristotle. Hubble's explanation of the Doppler effect of the systematic cosmic the red shift was incomplete and needed to be introduced into the ether.The physical significance of universal gravitation constant reveals the possibility of the existence of ether. After much thought and logical reasoning, there is good reason to think that the ether is negative energy, stream of consciousness, and space itself, it combines with photons to build elementary particles, elementary elements, everything in the universe, including ourselves. In addition, it is feasible to explain the causes of gravitation, electromagnetic force, strong force and weak force from the perspective of the ether, which seems to be easier for us to understand. The most tragic conclusion is that the universe was created out of nothing and will eventually return to nothing
Hypothes About The Motion Of Photon In The Space
No full textThis paper attempts to photons and known according to the axiom of the definition, using simple logic, reasoning about propositions of photons and its movement in space.The light is by the space motion photon component. The space motion photon has the energy and the quality. Photon in space along straight line direction movement speed identically equal in c. A photon moves in space with uniform helical motion, which is a combination of uniform circular motion and uniform linear motion in which the speed of the linear motion and the linear speed of the circular motion are always equal to c. Photon's Planck energy formula E=hv=2π v, is the approximate Planck constant, which is the angular momentum of photons moving along the circumference plane direction mcr, r is the photon along the circumference plane motion radius; v is photon each second completes the circular motion by link speed c the number of times c/2πr, also is the photon frequency. By replacing the mcr and c/2πr with the Planck energy formula, may obtain Einstein mass energy formula E=mc2.The greater its mass and energy, the smaller the radius of its circular motion, the higher its frequency, and the shorter its wavelength. The lower its mass and energy, the greater the radius of its circular motion, the lower its frequency, and the longer its wavelength. The uncertainty principle is essentially caused by our misunderstanding of the motion of light. The existence and motion of light can be determined
Supplemental materials for preprint: The principle of commodity utility and its equations
No full text- …
