1,721,134 research outputs found
The smart detection of ship severe roll motions and decision-making for evasive actions
No full textThis paper presents a numerical model for the smart detection of synchronous and parametric roll resonance of a ship. The model implements manoeuvring equations superimposed onto ship dynamics in waves. It also features suited autopilot and rudder actuator models, aiming at a fair depiction of the control delay. The developed method is able to identify and distinguish between synchronous and parametric roll resonance, based on the estimation of encounter wave period from ship motions. Therefore, it could be useful as a smart tool for manned vessels and, also, in the perspective of unmanned and autonomous vessels (in the paper it is assumed a hypothetical remote crew). Once the resonance threat is identified, different evasive actions are simulated and compared, based on course and speed change. Calculations are carried out on a ro-ro pax vessel vulnerable to parametric roll. We conclude that, in roll resonance situations, and in the absence of roll stabilisation systems on-board, course change could be the most effective countermeasure
On the development of fast numerical methods for the estimation of hull girder loads for a flooded ship in waves
No full textThis paper reports on fast numerical methods capable of modelling the behaviour of a flooded hull in waves. The focus of the current research concerns the development and the application of such methods for hull girder loads. Prior dealing with damage scenarios, a lightened numerical model for hull girder loads in intact case is proposed, i.e. operating on a reduced number of input data. Four approaches for modelling damaged ship dynamics, based on “lumped mass” technique, are developed and compared, finalized to hull girder outcomes. They exploit different assumptions, in particular on the free-surface inclination and on the amount of flooded water in an open-to-sea compartment. Comparisons with available experimental data are carried out, for the frigate hull named DTMB5415, in head and beam seas. The outcomes of the current research point out the levels of accuracy of the proposed methodologies on ship dynamics and on sea loads according to the investigated wave scenario
A new logic for controllable pitch propeller management
No full textIn this study we want to propose an active logic that, continuously, optimizes the configuration of the propeller and motor speed taking into account changes in resistance and wake. The working principle of the control system is based on the measurement of the torque absorbed by the propeller and the engine speed, to obtain the actual thrust and advance speed coefficients. Based on these data, the controller identifies the configuration of the propeller for the best performance of the entire propulsion chain, from engine to propeller. Moreover, in addition to torque and speed limits of the engine, the control system chooses pitch angle taking into consideration the propeller's cavitation. © 2012 Taylor & Francis Group, London, UK
Displacement-dependent microstructural and petrophysical properties of deformation bands and gouges in poorly lithified sandstone deformed at shallow burial depth (Crotone Basin, Italy)
Full text linkWe present the results of meso-and micro-structural analyses performed on fault-related soft-sediment deformation structures affecting poorly lithified, high-porosity siliciclastic sediments in the Crotone Basin, Southern Italy. The investigated extensional fault zone has a total displacement of ~90 m and juxtaposes marine clayish sediments in the hanging wall against arkosic to lithic arkosic sandstone in the footwall. In the footwall damage zone, deformation is achieved by a network of conjugate deformation bands, whereas the foliated fault core hosts cm-thick gouges. Deformation bands and black gouges accommodated displacement between 0.2 and 20 cm. Microstructural observations and quantitative image analysis pointed out that particulate flow operated during the early stages of faulting, followed by cataclasis after significant porosity loss. Mineralogy of clasts controlled grain-scale deformation mechanism: following this, feldspar experienced extensive intragranular crushing, while quartz grains were deformed mainly by splitting and abrasion. Permeability of pristine sandstone spans from 5.4 × 104 to 1.4 × 105 mD, while inside deformation bands is reduced by 1-2 orders of magnitude, reaching 3-4 orders of magnitude within fault gouges. Permeability drop inside the fault zone is related to the accommodated displacement along each deformation structure, potentially leading to hydraulic compartmentalization of high-porosity sandstone reservoir
Fingerprints and energy budget of the earthquake cycle in shallow sediments
No full textEarthquake cycle consists of alternating transient coseismic slip and long-lasting interseismic periods, covering a wide range of slip rates. Unveiling the deformational signature of earthquake cycles in major seismogenic fault systems is an essential component of seismic hazard evaluation. Here, we present a study combining field and microstructural data acquired from an extensional fault zone with ∼100 m displacement, developed in poorly lithified siliciclastic sediments of the Crotone Basin, South Italy. The maximum burial depth of faulted sediments did not exceed 500 m. Within the fault core a dense network of mutually cross-cutting dark gouges and deformation bands is hosted. Dark gouges and deformation bands display striking distinctive features (i.e., geometric arrangement, grain size distribution, displacement, fractal dimension and clast preferential orientation), suggesting their genesis occurred under different slip rates. Based on grain size distribution data, total surface energies required for dark gouge and deformation band development are in the order of 106 and 104 J/m2, respectively. These values are in accordance with literature fault scaling laws regarding moment magnitude-surface energy relationship. Our results support the genesis of deformation bands during inter-seismic, creeping fault activity periods, while dark gouges were produced during coseismic slip events
Reply to: Discussion on «Geological map of the partially dolomitized Jurassic succession exposed in the central sector of the Montagna dei Fiori Anticline, Central Apennines, Italy» by M. Santantonio, S. Fabbi & S. Bigi
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Design and control of coupled inductor DC–DC converters for MVDC ship power systems
No full textThis paper deals with the design and control aspects of modern ship power systems within the paradigm of an all-electric ship. The widespread use of power electronic converters is central in this context due to the technological advances in automation systems and the integration of the electrical propulsion systems and other components, such as electrical energy storage systems and renewable energy sources. The issue to address in this scenario is related to the request of increased performances in dynamic operation while pursuing advantages in terms of energy savings and overall system security. In addition, the presence of large load changes requires providing robustness of the control in terms of system stability. This paper is focused on medium voltage direct current (MVDC) ship power systems and the design and control of coupled inductor DC-DC converters. The load is handled in terms of a constant power model, which generally is considered the most critical case for testing the stability of the system. The robustness of the design procedure, which is verified numerically against large and rapid load variations, allowed us to confirm the feasibility and the attractiveness of the design and the control proposal
Optimal Control of CP Propeller based on real-time measurements
No full textThe aim of this paper is to present the working principle of an automatic speed and pitch controller for CPP. The advantage of this kind of propellers becomes relevant when the ship operates in speed and loading conditions quite different from the designed ones; generally the master acts on fixed pairs of propeller pitch and revolution speed, defined in the design stage. In previous works, the authors considered a rpm and pitch control based on direct torque measurements and an offline optimization process, that generated a surface of optimum working points with respect of Kt/J2 and other parameters. A critique to this method may be that, in this way, the uncertainties on model data affects the optimum working point estimate. In this paper the optimization problem is solved by applying an extremum seeking technique, based on realtime torque shaft (as in the previous work), speed and consumption measurements. Moreover, in order to improve the wake data for the simulated test cases, a series of self-propulsion towing tank tests in different model load condition are carried out
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