1,720,967 research outputs found
Energy Efficiency, Environmental Protection and Commercial Competitiveness : Conflicting Requirements facing the Maritime Transportation
No full textIn July 2011 the International Maritime Organization (IMO) defined important changes to the Annex VI of MARPOL Convention, to reduce the CO2 emissions of ships, especially during the port callas. In particular a new Energy Efficiency Index and a Ship Energy Efficiency Management Plan have been defined and will enter into force on the 1st January 2013.
The new measures decided by IMO impose new and more restrict rules to the ship design and the respect of new and more pressing restrictions during the operative stage of ships. This second aspect is more stringent and conflicts with the market rules, constrained to the fuel cost. To reduce the running cost, it is important to operate by managing new ships the design of which has been defined previously with the aim of reducing the fuel consumption and the running expenses. In general this choice requires a larger starting investment capital to define better hull lines and equipment on board with small consumption. Energy systems using renewable resources can be planned to be used on board for the ship propulsion or to supply local electrical plants or to be used for local equipment. The design of new engines for ship propulsion is a subject of long and important engine manufacturers and new proposals are launched on the market, as the new bi-fuel engines, operating with fuel oil during the navigation and gases in harbor calls and in coastal navigation. This problem can be important to reduce the pollution in closed waters, like the upper Adriatic Sea
Multi-objective optimisation of a semi-planing hull using CFD RANSE simulations with low number of cells
No full textAn integrated use of a CFD software with an algorithm for multi-objective optimization is proposed in this paper. Currently, optimisations regarding hydrodynamic performance for a given ship or marine vehicle design (eg. choice of best shape for the minimization of wave resistance) can be carried out interfacing multiobjective algorithms with parametric 3D modelers and suitable hydrodynamic solvers. Having to manipulate a great number of alternatives, the requirement for the computing chain is to rely on fast and tested methodologies especially for the flow solvers. The use of RANS viscous CFD simulations offers more complete and detailed information to evaluate the resistance and the flow around ships hulls and is now well established. These methods, however generally require to represent the flow domain by a high number of cells with consequent substantial increase of hardware and computing time requirements. A research has been carried out to define and standardize operating modes to carry out viscous simulations with a number of cells as low as possible. It has allowed to obtain adequate results within a reasonable short time and without the necessity of requiring high computing resources. In this way it is possible to achieve adequate RANS simulations in a short time so as to make them competitive as far as computational costs with panel methods also in optimization problems, especially in the evaluation phase of many different design alternatives. The optimization of a hard-chine semi-planing hull, based on the reduction of the total resistance at two different speeds through the integration of software optimisation with the RANS simulations with low number of cells has been performed and is presented and discussed. The results obtained are validated by experimental tests in towing tank
Evoluzioni e tendenze nello sviluppo idrodinamico delle moderne carene veloci
No full textLa tendenza che accompagna l'evoluzione delle linee delle carene veloci ha evidenziato degli aspetti che riguardano sia le linee di carena, intese nell'aspetto globale, sia l'applicazione di appendici atte a modificare gli assetti ed a ridurre la resistenza all'avanzamento, nonché i moti nave delle stesse. Tra le forme di carena maggiormente studiate ci sono certamente quelle dei trimarani, ottenuti modificando la tradizionale geometria degli scafi. Le monocarene sono sempre più oggetto di varianti che coinvol-gono modifiche locali che comportano l'applicazione di appendici (flap poppieri, interceptors o forme BLB) per ridurre gli assetti in corsa e la resistenza all'avanzamento. L'applicazione di foils portanti, su monocarene e catamarani, introduce poi ulteriori elementi di sviluppo, che portano a miglior tenuta al mare ed a evidenti riduzioni della resistenza al moto. Nel lavoro saranno presentate alcune recenti soluzioni provate alla vasca navale dell'Università di Trieste
Computational simulations with low cells number for displacement hulls and planing boats: a rational approach
No full textThe aim of work is to study and standardize the operating modes to do viscous simulations with a rational approach with low cells-number, for carrying out quickly the calculations, without any necessity of super-computers. This methodology involves the study of different hulls, displacement and planing, evaluating a system of localized mesh-sizing of the computational grid that could be standardized for each type of examined hull.In addition a protocol to get a good simulation in the shortest time possible is attempted. In the first part of the study 3-DOF simulations for evaluating trim, resistance, pressure field and waves of a series of vesselswere carried out. Then the numerical results were compared with experimental towing tank tests. Finally , the method was applied for searching the best dynamic trim for some displacement and semidisplacement hulls
CFD Simulations to Evaluate the Ships Resistance: Development of A Systematic Method with Use of Low Number of Cells
No full textThe use of viscous CFD simulations to evaluate the resistance of ships is well established. These methods, however, often require a high number of calculation cells with consequent substantial hardware requirements. The objective of this paper is to standardize the operating modes to perform viscous simulations with a rational approach basing on a lower number of cells, for carrying out more rapidly the calculations, without super-computers. This operating mode will be supported by the study of different hulls, displacement and planing, to evaluate a system of localized mesh-sizing of the computational grid that could be standardized for each type of examined hull and to define a protocol to get a good simulation in the shortest time possible
Multi-objective optimisation of a semi-planing hull using CFD RANSE simulations with low number of cells
No full textABSTRACT: An integrated use of a CFD software with an algorithm for multi-objective optimization is proposed in this paper.
Currently, optimisations regarding hydrodynamic performance for a given ship or marine vehicle design (eg. choice of best shape for the minimization of wave resistance) can be carried out interfacing multiobjective algorithms with parametric 3D modelers and suitable hydrodynamic solvers. Having to manipulate a great number of alternatives, the requirement for the computing chain is to rely on fast and tested methodologies especially for the flow solvers.
The use of RANS viscous CFD simulations offers more complete and detailed information to evaluate the resistance and the flow around ships hulls and is now well established. These methods, however generally require to represent the flow domain by a high number of cells with consequent substantial increase of hardware and computing time requirements.
A research has been carried out to define and standardize operating modes to carry out viscous simulations with a number of cells as low as possible. It has allowed to obtain adequate results within a reasonable short time and without the necessity of requiring high computing resources.
In this way it is possible to achieve adequate RANS simulations in a short time so as to make them competitive as far as computational costs with panel methods also in optimization problems, especially in the evaluation phase of many different design alternatives.
The optimization of a hard-chine semi-planing hull, based on the reduction of the total resistance at two different speeds through the integration of software optimisation with the RANS simulations with low number of cells has been performed and is presented and discussed.
The results obtained are validated by experimental tests in towing tank
STUDY AND EXPERIMENTS ON THE HULL RESISTANCE REDUCTION BY AIR VENTILATION IN CALM WATER FOR SEMI-DISPLACEMENT HULLS
No full textOne of the most interesting viscous drag reduction techniques for a boat hull is the so called air lubrication. Although this method has been known for many years, it is scarcely applied in the shipbuilding industry, because it requires to re-design the hull bottom, to define and generate the artificial cavities where the air bubbles can be generated and supplied by using an airflow. It has been demonstrated that the drug reduction is more consistent on full form and slow hulls, where the viscous resistance component is the prevailing one. Recently, as found in (Sverchkov, 2010), it has been demonstrated that the drag reduction can be obtained also for planing hulls. But information regarding applications for semi-displacement hulls characterized by FN ≥0.45 and FN≤ 0.65, which are navigation conditions in which many boat hulls used for recreational activities operate, is more scarce. A series of tests have been carried out on some models, navigating in semi-displacement condition at the towing tank of the University of Trieste and the results will be presented and discussed (Pugnetti and Zotti, 2005
Comparison between Rans Simulations with Low Number of Cells and BEM Analysis for a High Speed Trimaran Hull
No full textThe use of RANS viscous CFD simulations to evaluate the resistance of ships is well established. These methods, however, often require a high number of calculation cells with consequent substantial hardware requirements. BEM analysis can be performed in a short time and with modest hardware resources, but returned more qualitative results without the viscous part, even if proven and reliable. The objective is to achieve good RANS simulations in a short time so as to make them competitive with panel methods especially in the evaluation phase of different design alternatives. The aim of this work is to study and standardize the operating modes to do viscous simulations with low number of cells, for carrying out more rapidly the calculations, without any necessity of super-computers.
The foregoing methods are applied to study high speed trimaran hulls. For the RANS method a system of localized mesh-sizing of the computational grid is evaluated to get a good simulation in the shortest time possible. Results for resistance and trim from RANS 3-DOF simulations are compared with experimental towing tank tests and with BEM analysis also using transverse and longitudinal wave-cuts
Imbarcazioni con Sistema Propulsivo ad Alta Efficienza Energetica e Basso Impatto Ambientale
No full textLa riduzione delle emissioni inquinanti è un problema sempre più sentito anche in campo navale e nautico. Da uno studio condotto dalle Università di Trieste (Dip. Di Ingegneria e Architettura – Sezione Navale) e di Roma (Terza università, Dipartimento di Ingegneria Elettronica) si evince che per minimizzare l’impatto ambientale dato dalla movimentazione dei natanti è necessario intervenire su tutti gli elementi della catena propulsiva, partendo da carena ed elica per arrivare a motori e generatori.
Il sistema oggetto dello studio propone di accoppiare carene multiscafo dalle forme innovative atte a minimizzare la resistenza al moto a sistemi propulsivi ibridi o diesel-elettrici compatti studiati ad hoc per minimizzare ingombri e pesi e massimizzare l’efficienza utilizzando macchine elettrice a magneti permanenti, funzionanti a frequenza e tensione variabile.
Le carene oggetto dello studio sono multiscafo, con particolare attenzione ai catamarani semidislocanti, progettati con forme tali da minimizzare la superficie bagnata onde ridurre l’attrito e soprattutto con geometrie ed interferenza relativa tra gli scafi atti minimizzare la formazione ondosa e la conseguente resistenza.
Il progetto del sistema di propulsione prevede la realizzazione, a seconda dei casi, o di un sistema diesel-elettrico puro oppure di un sistema ibrido, entrambi progettati per ridurre al minimo la dimensione ed il peso dei componenti, in modo da non aumentare il dislocamento rispetto ad una nave tradizionale diesel-meccanica. La miniaturizzazione dei componenti permette inoltre di gestire gli spazi a bordo in maniera diversa rispetto al tradizionale schema che prevede una grande sala macchine quasi a centro nave.
La soluzione diesel-elettrica pura studiata ha come punti di forza la ridondanza, l’estrema compattezza dei macchinari utilizzati e la possibilità di “spostare” la sala macchine rivoluzionando la gestione degli spazi abitabili.
La soluzione ibrida studiata, detta cross-feed, consiste nel collegare ai motori diesel di propulsione dei motori elettrici compatti del 10% della potenza nominale, che fungono sia da generatori di corrente (risparmiando di conseguenza l’imbarco del gen-set a bordo), sia da motori di propulsione alimentati indifferentemente dal pacco batterie, dai motori diesel o da uno solo di essi.
Entrambe le soluzioni proposte permettono di spegnere completamente i diesel-generatori e navigare in modalità ZERO EMISSION
Computational Simulations with low cell number for displacement hulls and planing boats: a rational approach
No full textThe aim of work is to study and standardize the operating modes to do viscous simulations with a rational approach with
low cells-number, for carrying out quickly the calculations, without any necessity of super-computers. This methodology
involves the study of different hulls, displacement and planing, evaluating a system of localized mesh-sizing of the
computational grid that could be standardized for each type of examined hull.In addition a protocol to get a good simulation
in the shortest time possible is attempted. In the first part of the study 3-DOF simulations for evaluating trim, resistance,
pressure field and waves of a series of vesselswere carried out. Then the numerical results were compared with experimental
towing tank tests. Finally, the method was applied for searching the best dynamic trim for some displacement and semidisplacement
hulls
- …
