33 research outputs found
Μελέτη του συστήματος ελέγχου κίνησης και της προστασίας έναντι της οξείδωσης της κατεργαζόμενης περιοχής σε πρωτότυπη μηχανή SLS/SM
No full textGPyro-TD.zip
No full textThermal Imaging data used for developing the model GPyro in the article: "GPyro: uncertainty-aware temperature predictions for additive manufacturing".
The dataset is comprised of the thermal recordings produced during the deposition of a structure consisting of 9 pockets using Wire-arc additive manufacturing (WAAM). The structure was deposited with 27 unique torch paths resulting in different thermal fields. While our thermal camera has a resolution of 1024x720 pixels, we downsampled the images and only used 81 points for efficiency and size considerations (total files need ~4TB of space). The locations of each point can be found in the Recorded_points.csv file (pixels and millimeters); the torch path used in each experiment is located in the Coordinate_Time folder, with the corresponding thermal fields being in the temperatures folder. Every experiment has a unique id, starting with T and then followed by the experiment number, e.g., "T1".</p
Multi-objective evolutionary optimization in time-changing environments
Get PDFThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 127-135).This research is focused on the creation of evolutionary optimization techniques for the solution of time-changing multi-objective problems. Many optimization problems, ranging from the design of controllers for time-variant systems to the optimal asset allocation in financial portfolios, need to satisfy multiple conflicting objectives that change in time. Since most practical problems involve costly numerical simulations, the goal was to create algorithmic architectures that increase computational efficiency while being robust and widely applicable. A combination of two elements lies at the core of the proposed algorithm. First, there is an anticipatory population that helps the algorithm discover the new optimum when the objective landscape moves in time. Second, a preservation of the balance between convergence and diversity in the population which provides an exploration ability to the algorithm. If there is an amount of predictability in the landscape's temporal change pattern the anticipatory population increases performance by discovering each timestep's optimal solution using fewer function evaluations. It does so by estimating the optimal solution's motion with a forecasting model and then placing anticipatory individuals at the estimated future location.(cont.) In parallel, the preservation of diversity ensures that the optimum will be discovered even if the objectives motion is unpredictable. Together these two elements aim to create a well-performing and robust algorithmic architecture. Experiments show that the overall concept functions well and that the anticipatory population increases algorithm performance by up to 30%. Constraint handling methods for evolutionary algorithms are also implemented, since most of the problems treated in this work are constrained. In its final form the constraint handling method applied is a hybrid variant of the Superiority of Feasible Points, which works in a staged manner. Three different real-world applications are explored. Initially a radar telescope array is optimized for cost and performance as a practical example of a static multi-objective constrained problem. Subsequently, two time-changing problems are studied: the design of an industrial controller and the optimal asset allocation for a financial portfolio. These problems serve as examples of applications for time-changing multi-objective evolutionary algorithms and inspire the improvement of the methods proposed in this work.by Iason Hatzakis.Ph.D
On the Failure of Bombieri’s Conjecture for Univalent Functions
No full textA conjecture of Bombieri (Invent Math 4:26–67, 1967) states that the coefficients of a normalized univalent function f should satisfy lim inff→Kn-Reanm-Ream=mint∈Rnsint-sin(nt)msint-sin(mt),when f approaches the Koebe function K(z)=z(1-z)2. Recently, Leung [10] disproved this conjecture for n= 2 and for all m≥ 3 and, also, for n= 3 and for all odd m≥ 5. Complementing his work, we disprove it for all m> n≥ 2 which are simultaneously odd or even and, also, for the case when m is odd, n is even and n≤m+12. We mostly not only make use of trigonometry but also employ Dieudonné’s criterion for the univalence of polynomialsAcknowledgements The author has been supported by a fellowship of the International Excellence Graduate Program in Mathematics at Universidad Autónoma de Madrid (422Q101) and also partially supported by Grant MTM2015-65792-P by MINECO/FEDER-EU. This work forms part of his Ph.D. thesis at UAM under the supervision of professor Dragan Vukotić. The author would like to thank him for his encouragement and help. The author would also like to thank professor Yuk J. Leung for providing him with a copy of [10] and suggesting that formula (6) should be true under the hypothesis (a) and (b) of Theorem 1
Energy Reduction Façade Renovation System for different building typologies and climates
No full textCurrent renovation practices cannot reach the energy reduction goal that the European Union has set by 2050. The traditional renovation methods are very time-consuming and cannot ensure the final energy improvement. The aim of this thesis focuses on the design of a prefabricated modular façade system that can be adaptable to different building typologies and climates. The main focus is to create a system that will reduce the current energy demands of existing buildings while at the same time giving the opportunity for a faster renovation approach.Architecture, Urbanism and Building Science
Probabilistic coastal vulnerability assessment to storms at regional scale: Application to the coast at North-East Aegean Sea (Thrakiko Pelagos), Greece
No full textIn this study, a probabilistic vulnerability assessment to the impact of storms in the coast of Thrace, Greece was carried out. To this end, the methodology presented by Bosom and Jiménez (2011) has been applied with some modifications. The introduced modifications, for this work, were the use of a different run-up model to deal with the uncertainty in the predicted magnitude (due to some reported under-prediction of run-up, using Stockdon et al. equation, 2006) observed in recent studies (Laudier et al. 2011). In addition, the vulnerability framework has been extended by including overtopping in order to characterize better the flooding hazard. For this project, the study area was the coast of Thrace, Greece and the used data were 3-h hindcasts of the WAM model for a time period of 10 years (January of 1995 – December of 2004) at fifteen stations of the N. Aegean Sea. Its variables were the significant wave height, Hs, the wave peak period Tp, the wave direction, Hdir. With this dataset, the return values of the hazards’ (i.e. inundation and erosion) for the return periods of 5, 10, 30 and 50 years were estimated, using the Reis and Stockdon equation to calculate the wave-induced run-up and the numerical model SBEACH to calculate the storm-induced erosion. Aim of these estimations was to compare the difference between each hazard magnitude with the corresponding geomorphologic parameter (i.e. beach height and width, respectively) in order to characterize the vulnerability of the coast against each hazard and for each return period. The obtained results along the coast reflect the relative variation of the hazard magnitude in function of the beach morphology, which is mild-sloped and low beaches presenting the largest values for inundation, while the steeper and narrower ones are the most sensitive to erosion. Finally, an integrated vulnerability assessment was presented and some possible recommendations to mitigate the problems were given. It must be stressed that coastal managers play an important role in the final assessment, since they must decide the probability of occurrence to be accepted as well as the period of concern of the analysis. These two variables will determine the return period to be considered for the decision-making.Coastal EngineeringHydraulic EngineeringCivil Engineering and Geoscience
Energy Yield Comparison of Spar & Monopile Offshore Wind Turbines using BEM & OLAF Models
No full textEnergy transition is imperative to effectively address the pressing issue of climate change resulting from global warming. In this transition, offshore wind power assumes a pivotal role as a crucial and indispensable source of clean and renewable energy. Offshore benefits become more pronounced as the offshore locations progress far offshore. In deep-water areas, where 80% of the worldwide offshore wind energy can be potentially harnessed, the utilization of floating foundations becomes essential instead of traditional bottom fixed ones. The present study seeks to investigate the disparities in power generation and energy production that arise from the replacement of bottom fixed wind turbines with floating counterparts. The former is represented by the monopile foundation, while the latter by the spar buoy. The power performance difference lies in the ability of floating structures to move, which can lead to suboptimal positioning of the rotor relative to the incoming wind inflow, mainly due to spar’s pitch and surge motions. The investigation is conducted using two distinct aerodynamic model of lower and higher fidelities, BEM and OLAF, respectively, to assess their effects on the outcomes.In the field of offshore wind turbine design, engineers rely on aero-hydro-servo-elastic software codes to simulate the dynamic behavior of floating offshore wind turbine systems in offshore environments. OpenFAST, an open-source software, has been extensively developed and validated for conducting such investigations. In this study, OpenFAST is employed to develop both floating and bottom fixed wind turbine models. Specifically, a coupled aero-hydro-servo-elastic model of a floating spar wind turbine is created, and the simulated motion of the spar is compared with measurements obtained from an actual floating turbine deployed in the Hywind Scotland floating offshore wind farm. Metocean data, spar measurement data, and spar system descriptions are provided by Equinor to facilitate this benchmarking process. Additionally, an equivalent monopile wind turbine model is developed for energy yield comparison purposes. The simulated spar motion results of the developed OpenFAST model exhibit reasonable realism when benchmarked with the measured data for all load cases and modal analysis, despite assumptions and uncertainties influencing the model's accuracy. Model discrepancies primarily stem from undisclosed wind turbine parameters and controller strategy as well as some modeling simplifications inherent in OpenFAST. Nevertheless, through statistical, time series and power spectral density comparisons against full-scale Hywind measurements encompassing various wind speeds (below-rated, rated, and above cut-out), the developed floating model is validated, thereby ensuring the reliability of its energy production outcomes.It is observed that the spar’s pitch and surge mean offset is mostly affected by the current speeds while varying wave conditions (height and period) influence their oscillation amplitudes. Power is slightly affected by the ocean conditions, primarily the wave effects, while it is more strongly influenced by the spar nacelle’s velocity and direction relative to the incoming wind, especially when subjected to lower wind speed fields. Finally, for both BEM and OLAF simulations, monopile bottom fixed structures produce higher amounts of energy annually compared to the floating spar counterparts. The implementation of alternative controllers specifically designed for FOWT, with optimization objectives focused on either maximizing power performance or ensuring structural integrity and longevity, results in estimated AEP reductions when utilizing a spar floater instead of a monopile foundation. For the BEM model, the estimated AEP decrease ranges from 3.46% to 8.62%, depending on the specific controller optimization objective. On the other hand, when employing the VPM-OLAF model, the estimated AEP reduction for a spar floater compared to a monopile substructure ranges from 4.50% to 9.58%, under similar conditions as previously mentioned. By employing OLAF instead of BEM, the computed annual energy yield for both Bottom Fixed and Floating offshore wind turbines increases by approximately 25%. In conclusion, it is recommended that future research prioritizes resolving identified discrepancies in the model setup, addressing phenomena not adequately captured by the current OpenFAST model, and conducting additional validation of the spar model using a wider range of measured parameters. Electrical Engineering | Sustainable Energy Technolog
A generalization of Livingston's coefficient inequalities for functions with positive real part
Get PDFFor functions p(z)=1+∑n=1∞pnzn holomorphic in the unit disk, satisfying Rep(z)>0, we generalize two inequalities proved by Livingston [10,11] and simplify their proofs. One of our results states that |pn-wpkpn-k|≤2max[1,|1-2w|], w∈. Another result involves certain determinants whose entries are the coefficients pn. Both results are sharp. As applications we provide a simple proof of a theorem of Brown [2] and various inequalities for the coefficients of holomorphic self-maps of the unit diskThe author is supported by a fellowship of the International Program of Excellence in Mathematics at Universidad Autónoma de Madrid ( 422Q101 ) and also partially supported by MINECO grant MTM2012-37436-C02-02 , Spain. This work forms part of his Ph.D. thesis at UAM under the supervision of professor Dragan Vukotić. The author would like to thank him for his encouragement and help
„Hálátlan Iason: hitvesed felismered?”: Seneca Medeájáról
No full textEach of the three great Roman tragedians of the Republic, Ennius, Accius and Pacuvius, wrote plays concerned with Medea, but only fragments of these texts have survived. Seneca’s Medea is the only extant dramatic representation of the myth composed between Euripides and Seneca. The paper will try to demonstrate the ways in which the Medea–material is remodelled by this author. The analysis includes the dramatic structure, the narrative strategies and their comparison with relevant passages of other ancient and modern authors on the same material. I will focus on the ambiguous character and the polarities of Seneca’s heroine in connection with his philosophical prose work, De ira.Each of the three great Roman tragedians of the Republic, Ennius, Accius and Pacuvius, wrote plays concerned with Medea, but only fragments of these texts have survived. Seneca’s Medea is the only extant dramatic representation of the myth composed between Euripides and Seneca. The paper will try to demonstrate the ways in which the Medea–material is remodelled by this author. The analysis includes the dramatic structure, the narrative strategies and their comparison with relevant passages of other ancient and modern authors on the same material. I will focus on the ambiguous character and the polarities of Seneca’s heroine in connection with his philosophical prose work, De ira
Hyperbolic convexity of holomorphic level sets
No full textWe prove that the sublevel set {z∈D:kD(z,z0)−kD(f(z),w0)0. This extends a result of Solynin (2007) and solves a problem posed by Arango, Mejía and Pommerenke (2019). We also propose several open questions aiming at possible extensions to more general settingsThe first author is partially supported by PID2019-106870GB-I00 from MICINN, Spain. The second author is partially supported by GNSAGA INdAM (Istituto Nazionale di Alta Matematica “Francesco Severi”) Italy
