Δείκτες Ενεργειακής Απόδοσης Πλοίου στο Πλαίσιο του ΙΜΟ

140 σ.Στο πλαίσιο της παρούσας διπλωματικής εργασίας, μελετώνται οι Δείκτες Ενεργειακής Απόδοσης, που έχουν προταθεί από τον IMO (International Maritime Organization) και αφορούν στην Σχεδίαση και Λειτουργία των Πλοίων, εστιάζοντας στην απεικόνιση της ενεργειακής απόδοσης των ηλεκτρικών συστημάτων ενέργειας και στα ζητήματα που προκύπτουν γενικότερα κατά την εφαρμογή των δεικτών αυτών. Συγκεκριμένα για τον Δείκτη Ενεργειακής Απόδοσης που αφορά στην Σχεδίαση Νέων Πλοίων (EEDI), τα ζητήματα αφορούν: α) την περιορισμένη δυνατότητα του να εκφράσει την ενεργειακή απόδοση του πλοίου για περισσότερες από μία καταστάσεις λειτουργίας, β) την έλλειψη εξαγωγής συγκρίσιμων αποτελεσμάτων κατά την εφαρμογή του σε ορισμένες κατηγορίες πλοίων (Επιβατηγά), γ) την ακαταλληλότητα του για πλοία με μη συμβατικά συστήματα πρόωσης (Δηζελοηλεκτρική Πρόωση) και δ) την εξαγωγή πλασματικών αποτελεσμάτων που στην πράξη οδηγούν στην σχεδίαση λιγότερο ενεργειακά αποδοτικών νέων πλοίων. Επιπροσθέτως, ε) η έλλειψη σαφούς ορισμού του Δείκτη Ενεργειακής Απόδοσης για την Λειτουργία των Πλοίων (EEOI) και στ) η απουσία ενός Δείκτη που να απεικονίζει με μεγαλύτερη ακρίβεια τα ενεργειακά οφέλη από την εγκατάσταση νέων τεχνολογιών, ειδικότερα για την παραγωγή ηλεκτρικής ενέργειας, καθώς και από την εφαρμογή βέλτιστων σεναρίων λειτουργίας, είναι μερικά μόνο από τα ζητήματα που επιζητούν λύση. Για τον λόγο αυτό, προτείνεται η εφαρμογή ενός εναλλακτικού δείκτη VENEFI (Vessel Energy Efficiency Index) για την συνολική λειτουργία του πλοίου που προκύπτει από την σύνθεση επιμέρους δεικτών που περιγράφουν την ενεργειακή απόδοση σε κάθε κατάσταση λειτουργίας. Οι επιμέρους δείκτες δύναται να περιγράψουν με μεγαλύτερη ακρίβεια την ενεργειακή απόδοση του πλοίου σε κάθε κατάσταση ξεχωριστά, τόσο κατά την λειτουργία του όσο και κατά την σχεδίαση ενός νέου πλοίου. Επιπλέον, προτείνονται επιμέρους δείκτες που αξιολογούν την ενεργειακή απόδοση του συστήματος πρόωσης και του ηλεκτρικού συστήματος παραγωγής. Όλοι οι δείκτες συνδέονται μεταξύ τους μέσω κατάλληλων σχέσεων ενώ είναι συγκρίσιμοι υπό προϋποθέσεις και με τους υφιστάμενους δείκτες EEDI & EEOI. Για την περεταίρω διερεύνηση, αναπτύχθηκε ένα φύλλο υπολογισμού των δεικτών και χρησιμοποιήθηκαν στοιχεία από υφιστάμενα πλοία για την πραγματοποίηση υπολογισμών και την εξαγωγή αποτελεσμάτων. Στο Κεφάλαιο 4 παρουσιάζεται αναλυτικά ο υπολογισμός του δείκτη VENEFI για το πλοίο “BS1” ενώ στο Παράρτημα 3 παρουσιάζονται επιπλέον υπολογισμοί καθώς και η διερεύνηση βέλτιστου σεναρίου συνολικής λειτουργίας με χρήση ή μη αξονικής γεννήτριας. Τα αποτελέσματα που προέκυψαν έδειξαν ότι μέσω του δείκτη VENEFI είναι εφικτή η διερεύνηση βέλτιστων σεναρίων λειτουργίας αλλά και η διερεύνηση του μέτρου της ενεργειακής απόδοσης με την εφαρμογή μιας νέας τεχνολογίας, ειδικότερα όσον αφορά την ηλεκτρική ενέργεια, ενώ παράλληλα επιλύθηκαν και τα υπόλοιπα προαναφερθέντα ζητήματα εφαρμογής των Δεικτών.This dissertation analyzes the proposed by the IMO (International Maritime Organization) Energy Efficiency Indices for the Design and Operation of Ships (EEDI & EEOI respectively), focusing on energy efficiency of electric power systems and the arising implementation issues of these indices. More specifically, the issues considering the Energy Efficiency Design Index (EEDI) are: a) its limited ability to express the energy efficiency of the ship for more than one operating condition, b) the failure to produce comparable results when applied to certain ship categories (Passenger Vessels), c) it is not applicable to ships with non-conventional propulsion systems (Diesel-Electric Propulsion) and d) it produces misleading results driving practically to the design of less energy efficient ships. Additionally: e) the definition of Energy Efficiency Operation Index (EEOI) which is not precise and f) the absence of an index that reflects more accurately the benefits of: i) installing new energy efficient technologies onboard vessels, particularly for electrical power generation and ii) the implementation of optimal operating scenarios; are some of the issues seeking a solution. Therefore, it is proposed an alternative index VENEFI (Vessel Energy Efficiency Index) for the complete operation of the vessel, as a resultant of individual indices that describe the energy efficiency in each operation mode of the vessel. Individual indices may describe more accurately the energy efficiency of the ship in every activity mode during operation and at design stage for new vessels. In addition, there are proposed specific indices of energy efficiency for the propulsion and the auxiliary power system, individually. All indices are linked through appropriate formulas, while under conditions are comparable with existing indices EEDI & EEOI. For further investigation on VENEFI, there was developed a spreadsheet for calculating the proposed indices using data from existing ships, performing the calculations and exporting the results. Chapter 4 presents in detail the sample calculation of VENEFI on the ship "BS1", while in Annex 3 are presented additional calculations and an investigation on the effect of the use of shaft generator on VENEFI. The results showed that through the index VENEFI is possible to investigate optimal operating scenarios and account the benefits of energy efficiency by implementing new technologies, particularly for electric power systems, while the rest of the issues considering indices implementation were resolved.Νικόλαος Κ. Τσεκούρα

Parallel Coupling of Symmetric and Asymmetric Exclusion Processes

A system consisting of two parallel coupled channels where particles in one of them follow the rules of totally asymmetric exclusion processes (TASEP) and in another one move as in symmetric simple exclusion processes (SSEP) is investigated theoretically. Particles interact with each other via hard-core exclusion potential, and in the asymmetric channel they can only hop in one direction, while on the symmetric lattice particles jump in both directions with equal probabilities. Inter-channel transitions are also allowed at every site of both lattices. Stationary state properties of the system are solved exactly in the limit of strong couplings between the channels. It is shown that strong symmetric couplings between totally asymmetric and symmetric channels lead to an effective partially asymmetric simple exclusion process (PASEP) and properties of both channels become almost identical. However, strong asymmetric couplings between symmetric and asymmetric channels yield an effective TASEP with nonzero particle flux in the asymmetric channel and zero flux on the symmetric lattice. For intermediate strength of couplings between the lattices a vertical cluster mean-field method is developed. This approximate approach treats exactly particle dynamics during the vertical transitions between the channels and it neglects the correlations along the channels. Our calculations show that in all cases there are three stationary phases defined by particle dynamics at entrances, at exits or in the bulk of the system, while phase boundaries depend on the strength and symmetry of couplings between the channels. Extensive Monte Carlo computer simulations strongly support our theoretical predictions.Comment: 16 page

Inhomogeneous Coupling in Two-Channel Asymmetric Simple Exclusion Processes

Asymmetric exclusion processes for particles moving on parallel channels with inhomogeneous coupling are investigated theoretically. Particles interact with hard-core exclusion and move in the same direction on both lattices, while transitions between the channels is allowed at one specific location in the bulk of the system. An approximate theoretical approach that describes the dynamics in the vertical link and horizontal lattice segments exactly but neglects the correlation between the horizontal and vertical transport is developed. It allows us to calculate stationary phase diagrams, particle currents and densities for symmetric and asymmetric transitions between the channels. It is shown that in the case of the symmetric coupling there are three stationary phases, similarly to the case of single-channel totally asymmetric exclusion processes with local inhomogeneity. However, the asymmetric coupling between the lattices lead to a very complex phase diagram with ten stationary-state regimes. Extensive Monte Carlo computer simulations generally support theoretical predictions, although simulated stationary-state properties slightly deviate from calculated in the mean-field approximation, suggesting the importance of correlations in the system. Dynamic properties and phase diagrams are discussed by analyzing constraints on the particle currents across the channels

Phase diagram of two-lane driven diffusive systems

We consider a large class of two-lane driven diffusive systems in contact with reservoirs at their boundaries and develop a stability analysis as a method to derive the phase diagrams of such systems. We illustrate the method by deriving phase diagrams for the asymmetric exclusion process coupled to various second lanes: a diffusive lane; an asymmetric exclusion process with advection in the same direction as the first lane, and an asymmetric exclusion process with advection in the opposite direction. The competing currents on the two lanes naturally lead to a very rich phenomenology and we find a variety of phase diagrams. It is shown that the stability analysis is equivalent to an `extremal current principle' for the total current in the two lanes. We also point to classes of models where both the stability analysis and the extremal current principle fail

Nonextensivity of the cyclic Lattice Lotka Volterra model

We numerically show that the Lattice Lotka-Volterra model, when realized on a square lattice support, gives rise to a {\it finite} production, per unit time, of the nonextensive entropy $S_q= \frac{1- \sum_ip_i^q}{q-1}$ $(S_1=-\sum_i p_i \ln p_i)$. This finiteness only occurs for $q=0.5$ for the $d=2$ growth mode (growing droplet), and for $q=0$ for the $d=1$ one (growing stripe). This strong evidence of nonextensivity is consistent with the spontaneous emergence of local domains of identical particles with fractal boundaries and competing interactions. Such direct evidence is for the first time exhibited for a many-body system which, at the mean field level, is conservative.Comment: Latex, 6 pages, 5 figure

Dynamics at barriers in bidirectional two-lane exclusion processes

A two-lane exclusion process is studied where particles move in the two lanes in opposite directions and are able to change lanes. The focus is on the steady state behavior in situations where a positive current is constrained to an extended subsystem (either by appropriate boundary conditions or by the embedding environment) where, in the absence of the constraint, the current would be negative. We have found two qualitatively different types of steady states and formulated the conditions of them in terms of the transition rates. In the first type of steady state, a localized cluster of particles forms with an anti-shock located in the subsystem and the current vanishes exponentially with the extension of the subsystem. This behavior is analogous to that of the one-lane partially asymmetric simple exclusion process, and can be realized e.g. when the local drive is induced by making the jump rates in two lanes unequal. In the second type of steady state, which is realized e.g. if the local drive is induced purely by the bias in the lane change rates, and which has thus no counterpart in the one-lane model, a delocalized cluster of particles forms which performs a diffusive motion as a whole and, as a consequence, the current vanishes inversely proportionally to the extension of the subsystem. The model is also studied in the presence of quenched disordered, where, in case of delocalization, phenomenological considerations predict anomalously slow, logarithmic decay of the current with the system size in contrast with the usual power-law.Comment: 24 pages, 13 figure

Cation-swapped homogeneous nanoparticles in perovskite oxides for high power density

Exsolution has been intensively studied in the fields of energy conversion and storage as a method for the preparation of catalytically active and durable metal nanoparticles. Under typical conditions, however, only a limited number of nanoparticles can be exsolved from the host oxides. Herein, we report the preparation of catalytic nanoparticles by selective exsolution through topotactic ion exchange, where deposited Fe guest cations can be exchanged with Co host cations in PrBaMn1.7Co0.3O5+delta. Interestingly, this phenomenon spontaneously yields the host PrBaMn1.7Fe0.3O5+delta, liberating all the Co cations from the host owing to the favorable incorporation energy of Fe into the lattice of the parent host (Delta E-incorporation = -0.41 eV) and the cation exchange energy (Delta E-exchange = -0.34 eV). Remarkably, the increase in the number of exsolved nanoparticles leads to their improved catalytic activity as a solid oxide fuel cell electrode and in the dry reforming of methane