251 research outputs found
Cavitation tunnel tests for "The Princess Royal" model propeller behind a 2-dimensional wake screen
No full textPropeller noise, especially in the presence of cavitation, is usually the main contributor to the acoustic signature of ships. Due to this fact, considerable efforts have been devoted to the study of underwater radiated noise induced by propeller cavitation during years: firstly, for military reasons; more recently, for other reasons relevant for merchant vessels, such as comfort on board and mitigation of the undesired impacts on marine fauna. Different approaches are available for the study and prediction of the cavitation noise, including statistical and CFD based methods as well as approaches based on model tests in cavitation tunnels or depressurised tanks. Amongst these approaches, the model test based approach is still the most reliable and commonly adopted method. However, when the aim of the model experiments is the prediction of noise radiated by a full-size ship, scale effects need to be analysed and taken into account to interpret model scale data and to achieve consistent prediction. Within this framework, each testing facility follows a procedure, which is developed through its own experience, theoretical considerations and possibly semi-empirical approaches to manage the different possible issues. The definition and harmonisations of the standards for the noise test and post-processing procedures of the propeller noise are still within the current tasks of the ITTC Specialist Committee on Hydrodynamic Noise and other standardization institutes. This results in more uncertainty compared to other more established tests such as resistance and self-propulsion. This paper presents the model scale tests carried out at the University of Genova (UNIGE) cavitation tunnel on the model propeller of the Newcastle University research catamaran, “The Princess Royal”. Tests have been carried out using a 2D wake screen to approximate the real ship condition. The details of the experimental setup and results are presented and compared with the full-scale measurements in terms of cavitation and underwater radiated noise. This allows to explore the issues of the scale effects associated with these phenomena, focusing the attention on possible problems related to small-medium size cavitation tunnel
Data-driven Underwater Radiated Noise Modelling of Cavitating Marine Propellers
No full textThe potential impact of ships underwater radiated noise (URN) on marine fauna has become an important issue. The most dominant noise source on a propeller-driven vessel is propeller cavitation, and the accurate prediction of its noise signature is fundamental for the design process. In this work, we investigate the potential of using Machine Learning methods for the prediction of URN from cavitating marine propellers that can be conveniently implemented within the design process. We compare computational and experimental results on a subset of the Meridian standard propeller series, behind different severities of axial wake, for a total of 432 experiments
Investigation of the manoeuvrability characteristics of a Gate Rudder system using numerical, experimental, and full-scale techniques
No full textThe Gate Rudder is a recently introduced twin rudder system whose major advantages stem from its energy saving properties. The two foil-shaped blades of the rudder, placed aside of the propeller, act as a partial duct in the wake of the hull producing additional thrust. However, since the rudder is a primary safety device on any vessel, investigating the manoeuvrability performance of the Gate Rudder is a critical aspect that needs careful and detailed consideration. Owing to its peculiar working principle and location, the standard manoeuvrability prediction methods cannot produce reliable results since they are applied to r udders acting behind the propellers. This paper presents the first comprehensive investigation into the manoeuvrability performance of a Gate Rudder system, which includes the development of a modified MMG model, towing tank experiments and fullscale measurements. The modified MMG model was conceived to predict the manoeuvring motions of a ship with the Gate Rudder system. A generalised prediction method is defined based on this modified MMG model and detailed CFD analysis of the flow pattern around the Gate Rudder for two commercial hull-forms. The simulation model of the Gate Rudder is validated by means of towing tank tests and full-scale manoeuvring trials. The sea trials were conducted onboard two sister container vessels, the first fitted with the first-ever Gate Rudder system and the second with a high-performance flap rudder. This also allowed to compare the two different steering systems
Computational prediction of underwater radiated noise of cavitating marine propellers: On the accuracy of semi-empirical models
No full textThe potential impact of underwater radiated noise from maritime operations on marine fauna has become an important issue. The most dominant noise source on a propeller-driven vessel is propeller cavitation, producing both structure-borne and radiated noise, with a broad spectrum that covers a wide range of frequencies. To ensure acceptable noise levels for sustainable shipping, accurate prediction of the noise signature is essential, and procedures able to provide a reliable estimate of propeller cavitation noise are becoming a fundamental tool of the design process. In this work, we investigate the potential of using computationally cheap methods for the prediction of underwater radiated noise from cavitating marine propellers. We compare computational and experimental results on a subset of the Meridian standard propeller series, behind different severities of axial wake, for a total of 432 experiments. The results indicate that the approaches employed can be a convenient solution for noise analysis during the design process
Data-driven ship digital twin for estimating the speed loss caused by the marine fouling
No full textShipping is responsible for approximately the 90% of world trade leading to significant impacts on the environment. As a consequence, a crucial issue for the maritime industry is to develop technologies able to increase the ship efficiency, by reducing fuel consumption and unnecessary maintenance operations. For example, the marine fouling phenomenon has a deep impact, since to prevent or reduce its growth which affects the ship consumption, costly drydockings for cleaning the hull and the propeller are needed and must be scheduled based on a speed loss estimation. In this work a data driven Digital Twin of the ship is built, leveraging on the large amount of information collected from the on-board sensors, and is used for estimating the speed loss due to marine fouling. A thorough comparison between the proposed method and ISO 19030, which is the de-facto standard for dealing with this task, is carried out on real-world data coming from two Handymax chemical/product tankers. Results clearly show the effectiveness of the proposal and its better speedloss prediction accuracy with respect to the ISO 19030, thus allowing reducing the fuel consumption due to fouling
Physically plausible propeller noise prediction via recursive corrections leveraging prior knowledge and experimental data
No full textFor propeller-driven vessels, cavitation is the most dominant noise source producing both structure-borne and radiated noise impacting wildlife, passenger comfort, and underwater warfare. Physically plausible and accurate predictions of the underwater radiated noise at design stage, i.e., for previously untested geometries and operating conditions, are fundamental for designing silent and efficient propellers. State-of-the-art predictive models are based on physical, data-driven, and hybrid approaches. Physical models (PMs) meet the need for physically plausible predictions but are either too computationally demanding or not accurate enough at design stage. Data-driven models (DDMs) are computationally inexpensive ad accurate on average but sometimes produce physically implausible results. Hybrid models (HMs) combine PMs and DDMs trying to take advantage of their strengths while limiting their weaknesses but state-of-the-art hybridisation strategies do not actually blend them, failing to achieve the HMs full potential. In this work, for the first time, we propose a novel HM that recursively correct a state-of-the-art PM by means of a DDM which simultaneously exploits the prior physical knowledge in the definition of its feature set and the data coming from a vast experimental campaign at the Emerson Cavitation Tunnel on the Meridian standard propeller series behind different severities of the axial wake. Results in different extrapolating conditions, i.e., extrapolation with respect to propeller rotational speed, wakefield, and geometry, will support our proposal both in terms of accuracy and physical plausibility.Ship Design, Production and Operation
An experimental investigation of the frictional drag characteristics of nanostructured and fluorinated fouling-release coatings using an axisymmetric body
No full textThe hydrodynamic performance of two, recently developed, nanostructured and fluorinated polymer coatings was explored in a systematic experimental study using the Newcastle University Cavitation Tunnel. The experiments consisted of testing the two coatings on an axisymmetric body apparatus to measure their boundary layer flow and frictional drag simultaneously. The tests also included a smooth reference surface as well as a state-of-the-art commercial fouling-release coating (Intersleek(®) 900). The boundary layer measurements were performed using a two-dimensional Laser Doppler Velocimetry (LDV) system whilst the direct frictional force measurements were taken using a special load cell installed in the testing body. Careful surface roughness measurements of the test surfaces were also performed including the use of a non-contact high precision laser profilometer. The tests and subsequent analysis of the data highlighted the exceptionally good frictional properties of all the coatings tested as well as some of the drag benefits of the new polymer coatings in the investigated Reynolds number range
Noise Measurements of a Cavitating Propeller in Different Facilities: Results of the Round-Robin Test Programme
No full textMitigation of shipping noise is a topical issue in marine engineering because of the dramatic increase in the levels of anthropogenic underwater noise and its impact on marine life. In recent years, hydroacoustic research has focussed on the development of reliable methods for predicting underwater radiated noise (URN) due to cavitation, which is known to be the dominant contribution to the overall radiated noise spectrum of ships above the cavitation inception threshold. Model-scale measurements are currently considered the most reliable approach to study URN problems in marine engineering and are crucial for the verification and validation of numerical methods. However, their reliability is affected by several uncertainty sources for which suitable test procedures and post-processing techniques are needed. As a means to better understand the accuracy and reliability of underwater radiated noise measurements, a round-robin (RR) test programme for an open water propeller setup was organized within the Community-of-Practice “Noise” of the HydroTesting Forum, with the aim of comparing results among several institutes (i.e. University of Genova UNIGE, University of Newcastle UNEW, NMRI, SSPA, KRISO, CNR-INM and MARIN). This paper reports an overview of the RR programme and compares the different approaches and results
Experimental investigation of the turbulent boundary layer of surfaces coated with marine antifoulings
No full textTurbulent boundary-layer measurements have been carried out on flat surfaces coated with two different new generation marine antifoulings. The coatings were applied on 1-m-long test sections that were fitted in a 2.1-m-long flat plate setup. The measurements were carried out in two different recirculating water tunnels by means of two-component laser Doppler velocimetry and were compared with measurements of a smooth steel reference surface and a surface covered with sand grit. Both coatings exhibited an increase in frictional resistance compared to the reference surface, but the increase was significantly smaller for the Foul(ing) Release coatings than for the Tin-free SPC coating. The coatings did not significantly affect the boundary-layer thickness. When expressed in inner variables, the coatings did not have an effect on the turbulence intensity profiles, but when expressed in outer variables, the coatings affected the near-wall turbulence intensities. Copyright \ua9 2005 by ASME
Noise measurements of a cavitating propeller in different facilities: Results of the round robin test programme
No full text\ua9 2020 Elsevier LtdMitigation of shipping noise is a topical issue in marine engineering because of the dramatic increase in the levels of anthropogenic underwater noise and its impact on marine life. In recent years, hydro-acoustic research has focussed on the development of reliable methods for predicting underwater radiated noise (URN) due to cavitation, which is known to be the dominant contribution to the overall radiated noise spectrum of ships above the cavitation inception threshold. Model-scale measurements are currently considered the most reliable approach to study URN problems in marine engineering and are crucial for the verification and validation of numerical methods. However, their reliability is affected by several uncertainty sources for which suitable test procedures and post-processing techniques are needed. As a means to better understand the accuracy and reliability of underwater radiated noise measurements, a round-robin (RR) test programme for an open water propeller setup was organized within the Community-of-Practice “Noise” of the HydroTesting Forum, with the aim of comparing results among several institutes (i.e. University of Genova UNIGE, University of Newcastle UNEW, NMRI, SSPA, KRISO, CNR-INM and MARIN). This paper reports an overview of the RR programme and compares the different approaches and results
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