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SOLAS damage stability regulations do not embed a probabilistic description for the damage extent below water. A “worst case approach” is therefore used for the s factor when there are horizontal subdivision boundaries below water. This can lead to the underestimation of the ship survivability, and it prevents an effective assessment of the effect of horizontal subdivision boundaries below water. To make a step forward, this paper presents a “u-factor”, derived from statistical analysis of accidents data, which can be embedded in the SOLAS framework to account for horizontal subdivision boundaries below water, avoiding the need for the “worst case approach”.

While floating offshore wind turbines (FOTWs) are gathering an increasing interest for renewable energy production, there is still a limited associated design experience. Furthermore, the design of these objects is complicated by their novelty and their inherent complex multi-disciplinary nature. From the point of view of offshore seakeeping assessment, with focus on motions and mooring system design, such complexity can become problematic particularly at early design stages. It is therefore useful to assess the possibility of introducing some simplifications to reduce the amount of required data for early design assessment and to enlarge the set of simulation tools which can be potentially used for such purpose. This study deals, in particular, with the effects of simplification of the aerodynamic modelling. Motions and quasi-static mooring loads of a FOWT in irregular waves and gusty wind are compared using three different approaches for the modelling of the wind turbine aerodynamics. Results from the analysis indicate that an intermediate simplification of the rotor aerodynamics, which takes into account only the rotor thrust and allows modelling the system as a single rigid body, could be still sufficient for the early design stage.

Stability related failures are known to represent an important cause of accidents involving fishing vessels, and are usually related to the crew lack of capability for assessing the stability level of their ships in an objective way. The use of simplified guidance systems could be adopted as a possible risk control option for trying to address this problematic situation. However, the need for manual interaction with the crew, is one of the major drawbacks of such systems. In this paper, a sample application of a methodology based on spectral analysis of roll motion for obtaining the natural roll frequency of the vessel is presented. The final intention is to have a tool which, from roll frequency estimation, could be used for the estimation of initial ship stability characteristics. The proposed methodology is tested by using roll motion results from a nonlinear one degree of freedom roll model, under the excitation of beam irregular waves and lateral gusty winds. The obtained results are promising, but some open aspects, relevant to the real application of such approach, require further discussion and investigation.

X-band radar system is able to provide information about direction and intensity of the sea surface currents and dominant waves in a range of few kilometers from the observation point (up to 3 nautical miles). This capability, together with their flexibility and low cost, makes these devices useful tools for the sea monitoring either coastal or off-shore area. The data collected from wave radar system can be analyzed by using the inversion strategy presented in [1,2] to obtain the estimation of the following sea parameters: peak wave direction; peak period; peak wavelength; significant wave height; sea surface current and bathymetry. The estimation of the significant wave height represents a limitation of the wave radar system because of the radar backscatter is not directly related to the sea surface elevation. In fact, in the last period, substantial research has been carried out to estimate significant wave height from radar images either with or without calibration using in-situ measurements. In this work, we will present two alternative approaches for the reconstruction of the sea surface elevation from wave radar images. In particular, the first approach is based on the basis of an approximated version of the modulation transfer function (MTF) tuned from a series of numerical simulation, following the line of [3]. The second approach is based on the inversion of radar images using a direct regularised least square technique. Assuming a linearised model for the tilt modulation, the sea elevation has been reconstructed as a least square fitting of the radar imaging data [4]. References [1] F. Serafino, C. Lugni, and F. Soldovieri, “A novel strategy for the surface current determination from marine X-band radar data,” IEEE Geosci.Remote Sens. Lett., vol. 7, no. 2, pp. 231–235, Apr. 2010. [2] Ludeno, G., Brandini, C., Lugni, C., Arturi, D., Natale, A., Soldovieri, F., Serafino, F. (2014). Remocean System for the Detection of the Reflected Waves from the Costa Concordia Ship Wreck. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 7(7). [3] Nieto Borge, J., Rodriguez, G.R., Hessner, K., González, P.I., (2004). Inversion of Marine Radar Images for Surface Wave Analysis. J. Atmos. Oceanic Technol. 21, 1291–1300. [4] Fucile, F., Ludeno, G., Serafino, F.,Bulian, G., Soldovieri, F., Lugni, C. “Some challenges in recovering wave features from a wave radar system”. Paper submitted to the International Ocean and Polar Engineering Conference, ISOPE, Rhodes 2016

Deterministic models for wave and ship motion forecasting, based on measurements collected from wave radar, are becoming more and more appealing with the improvement of marine wave radar technologies. Although these devices are largely validated for the assessment of the characteristics of the sea spectrum, several improvements are still necessary to achieve an accurate deterministic reconstruction of the wave field in time and space. The common filtering techniques adopted for the analysis of the marine wave radar imaging are nowadays targeting the identification of the more prominent wave field features of the sea spectrum. This work instead investigates the feasibility of reconstructing the instantaneous wave field from radar imaging. To this end two different methodologies are compared. The first approach, referred to as LSQR, is a novel approach based on a regularised inversion of the radar tilt modulation model. The use of a linearised model for the wave radar imaging and a linear wave model for the sea elevation allows the derivation of a linear discrete inverse problem which is solved through a least-squares technique. The second approach, which is also the more common in the wave radar community, is based on the concept of Modulation Transfer Function (MTF). The adopted MTF approach is based on the idea of deriving a tuned MTF form a series of numerical simulation. The performances of two different approaches in inverting series of synthetic radar images derived from a known set of wave elevation time histories are then compared.

This paper presents the results of ongoing research efforts aimed at the theoretical development and practical implementation of a probabilistic framework for regulatory assessment of ship survivability following grounding accidents, with particular attention to passenger vessels. In the envisioned framework, the probabilities of flooding of a compartment, or a group of compartments, i.e. the so-called “p-factors”, are determined using a flexible and easily updatable direct non-zonal approach. The assessment of the conditional ship survivability, on the other hand, is based on the SOLAS “s-factor”. The general framework is described, together with implementation details in the specific case of bottom grounding. Testing results, carried out using a specifically developed software tool, are also reported.

Seakeeping is one of the frontiers of marine hydrodynamics knowledge where progress is currently being faster, supported by the increasing computers performance. More specifically, modeling the full coupling between the vessel and the flow motion inside cargo tanks is significantly attracting the attention of researchers. An efficient coupled system between a time domain nonlinear ship motions solver, SHIXDOF, and an OpenCL accelerated SPH code, AQUAgpusph, is presented, focusing on the communication, via TCP/IP, between the codes and on the SPH aspects of the implementation. This is an industrial problem in which the SPH method is competitive with other fluid simulation techniques. Results are presented for the case of a benchmarking geometry, a Series 60, which is equipped with an anti-rolling tank.

Guaranteeing a sufficient level of safety from the point of view of stability is typically considered to be a matter of design. However, it is impossible to ensure safety only by design measures, and operational measures can then represent a complementary tool for efficiently and cost-effectively increasing the overall safety of the vessel. Time could therefore be coming for systematically considering operational measures as a recognised and normed integral part of a holistic approach to ship safety from the point of view of stability. In this respect, the scope of this paper is to identify open challenges and to provide, in general, food for thoughts for stimulating a discussion on the topic of operational measures, with specific attention to the intact ship condition. The aim of the discussion should be to provide ground for further proceeding towards the goal of implementing a virtuous integrated approach to ship stability safety which gives due credit to effective and robust operational risk control options.

This paper investigates the coupled nonlinear dynamics of a vessel with a free surface tank onboard. To this end, a 6-DOF ship motions simulation code is coupled with a CFD solver addressing the behaviour of the fluid in the tank. The nonlinear ship motions code is of the blended (hybrid) type, intended for the simulation of free running vessels in waves. The nonlinear CFD solver is a GPU-based 3D Weakly-Compressible Smoothed-Particle Hydrodynamic (WCSPH) solver. Numerical results are presented for the nonlinear roll motion of a vessel with and without a free surface tank in regular beam waves with different steepnesses.

Scheduled and emergency towing operations are carried out daily, both at sea and in restricted waters, as a means of transporting goods, aiding ships during berthing and casting-off or rescuing units in distress. Even in mild weather conditions, such activities can pose serious threats to the safety of the personnel and units involved and to the environment. This study investigates the dynamics of a tug-tow system, where towing is carried out by means of a single elastic towing line. A simplified model is used, in which the tug is modelled as a point-particle with a prescribed motion, while the dynamics of the towed object is modelled as a 3-DOF (surge/sway/yaw) nonlinear dynamical system. Equilibria of the system are analysed through a bifurcation analysis technique, supplemented by time-domain simulations, if/when necessary. An example application is reported for the case of towing of a barge-like hull, showing the effects of several parameters: ship speed, towline length, water depth and wind. The performed calculations confirm that, depending on the configuration parameters, multiple stable/unstable steady-state towing positions may exist. It is also clarified in this study that, in the absence of stable equilibria, the potentially dangerous oscillating phenomenon called “fishtailing” takes place. Maniobras de remolque, programadas y de emergencia, se llevan a cabo diariamente, tanto en mar abierto como en aguas restringidas, con el fin de transportar mercancías, asistir a buques durante el atraque y zarpe o rescatar unidades en situación de emergencia. Incluso en condiciones climáticas leves, estas actividades pueden suponer serias amenazas a la seguridad del personal y las unidades involucradas y al medio ambiente. Este estudio investiga las dinámicas de un sistema de remolque-empuje, donde el remolque se lleva a cabo por medio de una sola línea elástica de remolque. Se ha utilizado un modelo simplificado, en el cual el empujador se modela como una partícula puntual con un movimiento preestablecido, mientras que las dinámicas del objeto remolcado se modelan como un sistema dinámico no lineal a 3 grados de libertad (avance/deriva/guiñada). Los equilibrios del sistema son analizados por medio de una técnica de análisis de bifurcación, añadiendo simulaciones en dominio del tiempo cuando, en caso, sean necesarias. Se presenta un ejemplo de aplicación para el caso del remolque de una carena similar a una barcaza, mostrando los efectos de varios parámetros: velocidad del buque, longitud de la línea de remolque, profundidad del canal y viento. Los cálculos realizados confirman que, dependiendo de la configuración de los parámetros, pueden existir múltiples posiciones, estables e inestables, de estado estacionario del remolque. En el estudio también se aclara que, en ausencia de equilibrios estables, aparece el potencialmente peligroso fenómeno oscilatorio denominado “fishtailing”.