Twin-screw Ship Research Articles

A study on interaction among hull, diesel engine and propellers of a twin-screw ship during turning circle maneuver

A marine propulsion plant will experience power fluctuations during ship maneuvers. In the turning circle maneuver, the propulsive load increases significantly, and the power required by the two shafts of a twin-screw ship may be completely inconsistent. To protect the propulsion plant, the interaction between the engine and the propellers should be studied in depth. In this paper, the twin-screw ONRT ship and the 16PA6-STC diesel engine are selected as the study objects. A series of captive model tests are simulated by using CFD method to obtain the hydrodynamic derivatives and hull-propeller-rudder interaction coefficients in the MMG model. The effective wake fraction is computed under the maneuvering conditions. Turning circle maneuver of the ship is predicted by using the established MMG model, and the predicted ship maneuvering characteristics show good agreement with the available experimental results, which verifies the CFD-based modeling method. Finally, a dynamic model of hull-engine-propeller system is established on the simulation platform for evaluating the operating characteristics of propulsion plant. The propeller loads are predicted and the interaction among hull, engine and propellers is investigated. This study helps to provide a deeper insight into the engine operation behaviors during turning circle maneuver of a ship.

Experimental investigation of the effect of inward and outward propeller rotation on single blade and propeller loads

This paper is a sequel of the experimental investigation presented in Ortolani and Dubbioso (2019a) that addressed the single blade and propeller loads during the steady phase of the turning circle. In particular, the effect of inward and outward propeller sense of revolution on the propulsive performance has been investigated for a twin screw ship model equipped with a novel set-up pursued for the measurements of the single blade loads. On the basis of previous numerical investigations (Muscari et al., 2017; Dubbioso et al., 2022), the propeller sense of revolution should be evaluated as a passive mean to mitigate the amplification of the mean or fluctuating component of the blade loads and associated side effects (i.e., noise) caused by blade–wake interactions that occur during maneuvering conditions. The understanding and the accurate quantification of propeller loads, in these realistic operative scenario, is pivotal to design low emission and comfortable ships, fulfilling the requirements of safety and continuity of operations at sea. The analysis is carried out revisiting the investigation in Ortolani and Dubbioso (2019a) for the approach speed at FN=0.26 and a large set of rudder angles that span from moderate to tight maneuvers.

Numerical analysis of marine propellers low frequency noise during maneuvering. Part II: Passive and active noise control strategies

Maneuvering motion inevitably modifies the acoustic signature of marine propellers due to alteration of the wake field past the hull. This aspect is crucial to fulfill the stringent requirements for the noise abatement in the environment. Therefore, design procedures, mainly targeted to rectilinear motion in calm water, should encompass these conditions for achieving a low emission profile. In the present work, the analysis presented in Dubbioso et al., (2020) on the noise generated by a marine propeller in behind-hull is contextualized for the development of holistic tools for design and mission planning, with attention to both passive and active noise control strategies. Passive solutions consist of modification of stern appendages and inversion of propeller rotational direction, while active control is implemented by limiting of the absorbed power, load fluctuation and their combination. The noise sources are first computed by a non-interacting RANS–BEMT procedure and given as input to the acoustic analogy based on the Formulation 1A by Farassat. The test case is a modern twin screw ship undergoing rectilinear advance and turning maneuvers at two different rudder angles for a moderate speed at FN=0.265.

Development and assessment of CFD methods to calculate propeller and hull impact on the rudder inflow for a twin-screw ship

The purpose of this study is to investigate the feasibility of a simple but robust approach for the identification of the main interaction effect of hull and propeller on the rudder inflow in a conventional manoeuvring simulator. The manoeuvring simulator adopts a modular/MMG based approach in which the hull, the rudders and the propellers are described by separate mathematical models which take into account the interaction phenomena. The propeller–rudder interaction factor is examined by means of a numerical model developed in OpenFOAM for the prediction of the performance of a rudder in behind propeller condition. Differently the hull–rudder interaction factor is numerically obtained by means of two different approaches. The proposed kinematic method shows the minimum additional computational cost without loss of accuracy. It is based on the analysis of rudder inflow fields (in a PIV fashioned), therefore It can be carried out in a post-processing phase of CFD simulations adopted to extract the hydrodynamic coefficients. This study validates the method by comparing it with the classical approach also used in the experimental campaign, based on the analysis of rudder forces from virtual captive tests. The approaches demonstrate to improve the overall accuracy of the main manoeuvring parameters with respect to the ones obtained by means of a calibrated semi-empirical model.

CFD and system-based investigation on the turning maneuver of a twin-screw ship considering hull-engine-propeller interaction

Ship maneuver is a dynamic process accompanied by strong interaction among hull, engine, and propeller, and the interaction phenomenon is more complicated for twin-screw ships. In this paper, numerical investigation on the turning maneuver of a twin-screw ship considering hull-engine-propeller interaction is carried out by using CFD and system-based methods. Taking the twin-screw ship ONRT model as the study object, a series of captive model tests are simulated by using RANS method. Based on the computed global loads on the propellers and the corresponding flow field details, the hydrodynamic characteristics of the propellers operating under the maneuvering conditions are analyzed. The effective wake fraction is computed and the mathematical model of propeller performance under the maneuvering conditions is obtained through data fitting. Based on the established mathematical model, the turning circle maneuver considering hull-engine-propeller interaction is simulated. Three control strategies of main engine, i.e., constant RPM, constant torque, and constant power, are considered. The effects of the control strategies on the turning motion and the propulsive loads during turning motion are explored. This study is useful to provide a deeper insight into the ship maneuvering behaviors and the propeller characteristics during maneuvering motion under the influence of hull-engine-propeller interaction.

쌍축선의 정적 횡경사각에 따른 조종성능 변화에 관한 실험적 연구

The manoeuvrability of a ship with an unwanted heel angle due to a maritime accident is changed from the original characteristics. The purpose of this study is to quantitatively investigate the change in the manoeuvring performance of a twin-screw ship under various hee angles and speed conditions. A series of free running model test campaigns were performed in the Ocean Engineering Basin of Korea Research Institute of Ships & Ocean Engineering (KRISO) for a twin-screw car ferry vessel. Turning circle test and zig-zag 10/10 and 20/20 tests were carried out on the heel angles of 0, -10, and -19.5 degrees. In addition, two-speed conditions were considered to understand the effect of ship speed. In order to examine the effect of the bilge keel, a heel angle of -22 degree where the bilge keel is exposed outside the water surface, was considered. Finally, the change of manoeuvring characteristics according to the heel angle for a twin-screw and a single-screw vessel is discussed.

A SOURCE OF PROPELLER EXCITED BROADBAND VIBRATION ON A HIGH-SPEED TWIN SCREW SHIP

The cause of the severe propeller excited broadband vibration on a twin screw ship’s stern was investigated in a cavitation tunnel using conventional modelling methods. At first sight the results did not indicate anything untoward about the stern and propeller designs tested, apart from some unusual cavitation patterns in the propellers’ slipstreams. The fluctuating pressure levels on the model hull varied considerably depending on the propeller designs and loading conditions used in the tests, but these did not provide an explanation for the vibration on the ship. Some unusual patterns in the relative levels of the harmonic pressures on the stern were noticed in addition to the presence of a large cavitation disturbance in a propeller trailing vortex that was captured in a single frame of a video recording. This latter observation led to a plausible explanation for the broadband vibration on the ship’s stern.

A RANS-based study of the impact of rudder on the propeller characteristics for a twin-screw ship during maneuvers

The propeller behavior of a ship is highly related to ship maneuverability and main engine safety. Especially for a twin-screw ship, the propellers exhibit complicated characteristics during ship maneuvers. In this study, the impact of rudder deflection on the propeller characteristics is investigated for a twin-screw ship during maneuvers by using CFD method. Taking the typical twin-screw ship model DTMB5415 as the study object, a series of captive model tests, including rudder force test, static drift test and rotating arm test, are simulated by using RANS method. The flow field around the stern under the maneuvering condition is visualized and analyzed by the vortex structures and constrained streamlines around the stern. The computed hydrodynamic forces acting on the propellers and rudders are compared with the available experimental data, and the effectiveness of the adopted numerical method is verified. The impact of the rudder deflection on the propeller characteristics is further discussed based on the obtained nominal wake at the propeller disk and the pressure distribution on the blades. The present paper is an extension of the previous study (Guo et al., 2020), in order to provide a deeper insight into the propeller characteristics of a twin-screw ship during maneuvers.

Pre- and post-swirl fins design for improved propulsive performances

ABSTRACT Pre- and post-swirl fins-based energy-saving devices (ESD) are designed to improve the propulsive performances of a twin-screw ship. To this aim, BEM and RANSE calculations are employed. Depending on the application, a simple actuator disc model (post-swirl) with radially varying load or a combined BEM/RANSE method for self-propulsion prediction (pre-swirl) are required. Both the approaches are included in a framework for a design by optimization, where systematic variations of the ESD geometry are used to explore the design space and maximize the energy-saving effect of the devices. Considering the particularity of the case selected for the study, results show encouraging improvements that reach a promising 5% in the case of the combined action of both devices.

Modification and Analysis of Twin Screw Ship Stern for Optimizing Propulsive Coefficient Values in Propulsive System

Twin-screw ship has the advantage of being able to reduce the diameter of propeller by using the same rotation and engine power as a single-screw ship. With the result that twin-screw ship can be operated in areas with lower water depth. However, the type of twin-screw ship has a deficiency in the value of hull efficiency ( ) and the relative rotative efficiency ( ). This occurs because of the propeller position which is far from the field of the flow of the ship’s hull speed (V). So that the value of the water flow to the propeller (advance velocity/) becomes low. Various studies have been conducted to increase wake fraction (w) and reduce the thrust deduction factor (t) values some of which are by modifying the shape of the ship’s stern parts bossing to increase the water speed to the propeller (advance velocity/) which will have a large effect on the wake fraction (w) and thrust deduction factor (t). Among them is by modifying the shape of the ship’s stern bossing so that it can increase the speed of water to the propeller (advance velocity/) which will greatly affect the value of the wake fraction (w) and thrust deduction factor (t) to increase the propulsive coefficient (PC). In this study, it is known that the QPC value for the ship model tested in the Hydrodynamics Laboratory Indonesia (LHI) is 0.54 while for the four models tested using the CFD method is model one 0.63, model two 0.55, model three 0.63, and model four amount 0.51. Based on the above test it can be concluded that the third hull model has the highest QPC. be in ALARP compared to acceptance criteria.

Numerical analysis of marine propellers low frequency noise during maneuvering

In this paper the effects of maneuvering motion on the hydro–acoustic performance of a marine propeller in behind–hull configuration is investigated. Velocities induced by ship motions markedly modify the inflow to the propeller and hence noise sources and emission can be different with respect to the rectilinear motion, that traditionally is exclusively considered during the design process. This problem is crucial from a practical perspective, because the success of many types of operations at sea relies on the stealthy qualities of the vehicle and, moreover, for it can provide an additional aid to preserve marine life. In this paper this topic is tackled by a multidisciplinary approach that involves the use of hydrodynamic solvers and an acoustic analogy based on the Formulation 1A by Farassat. In particular, the noise sources, input to the acoustic analogy, are computed by an hybrid approach consisting of CFD simulation to obtain the inflow to the propellers and a blade element momentum theory solver (BEMT), enhanced with linear, partially cavitating hydrofoil theory to account for cavitating conditions too. The test case is a modern twin screw ship undergoing rectilinear advance and turning maneuvers at two different rudder angles for a moderate speed at FN=0.265.

Numerical investigation on the asymmetric propeller behavior of a twin-screw ship during maneuvers by using RANS method

Aiming to improve the safety of ship navigation and main engine operation, the propulsive loads are investigated for a twin-screw ship under the maneuvering condition by using CFD method. The proposed models that describe the propeller performance during ship maneuvers are summarized. Taking the twin-screw ship model DTMB 5415M as the study object, RANS simulation is performed for a series of static drift tests and rotating arm tests. The computed propulsive loads are validated by the available experimental data. The contours of axial velocity and vortex around the hull are presented to demonstrate the influence of upstream hull on the inflow to propeller under the maneuvering conditions. The details of the velocity field around the stern provide a deeper insight into the hydrodynamic mechanism of ship wake affecting the propeller performance. It is shown that the propeller behavior is highly related to the vortices shedding from the hull and appendages, which would change remarkably with the propeller position (windward and leeward) and the maneuvering motion (drift and turning). Finally, a regression analysis is performed with the proposed propeller models, and a reasonable composite model describing the asymmetric propeller behavior of a twin-screw ship during maneuvers is obtained.

Analysis of fretting inception for marine propeller by single blade loads measurement in realistic operating conditions. Straight ahead and turning circle maneuver

Controllable pitch propeller (CPP) is a versatile solution to fulfill high hydrodynamic efficiency and low environmental emissions for different operative scenario of a seagoing vessel because it allows the most suitable matching between the prime mover and the propulsor. In contrast, this configuration is a complex mechanical system and, therefore, it may be subjected to a wide range of failures related to the automation system of blade pitch variation, strength and fatigue life of the various mechanical components. This paper focuses on blade fretting, that is a small amplitude vibratory motion of the blade with respect to its lodging in the hub; this motion causes the wear between the contact surfaces, reducing the fatigue life of the material as well. The prediction of this phenomenon in realistic sailing conditions during the design stage is of utmost importance to prevent damages and failures during ship operations, by developing suitable control laws. The analysis is based on single blade loads measurements, obtained with a novel set–up installed on a free running maneuvering, self–propelled model of a twin screw ship. The experimental campaign was aimed to characterize single blade loads during different ship operations, with particular effort on maneuvering (standard and safety maneuvers) and motion in waves. This paper is focused on the straight ahead motions as well as steady and transient phases of the turning circle maneuver, performed at different rudder angles and speeds. The results show that the onset of fretting is sensitive to the wake evolution, and, hence, to the rudder angles; moreover, consistently to the asymmetric behavior of the propellers, fretting is differently triggered on the port and starboard propeller.

Propeller performance on a model ship in straight and steady drift motions from single blade loads and flow field measurements

In the field of marine hydrodynamics, propeller operations in off-design conditions represent a challenging topic that has been increasingly attracting interest among industry and research institutions. Over the ship operating life, off-design conditions and the associated modifications of the propeller inflow are connected to a wide range of events such as degradation of the overall efficiency, amplification of unwanted side effects of propeller operations (pressure pulses, vibration and noise) and, ultimately, failure of the ship propulsion system. In this work, the performance of a propeller operating in off-design conditions is investigated by a comprehensive experimental activity aimed at synthesizing the cause-and-effect relation between the propeller loads and its inflow. To this purpose, two novel set-ups are employed: the first one is dedicated to the measurement of single blade loads, whereas the second, a boroscopic-based Stereo-PIV (SPIV) system, is focused on the inflow analysis. The overall measurement apparatus is installed on a twin-screw ship model. Experiments, carried out in the CNR-INM towing tank, consist of straight ahead and steady drift motions at drift angles ±13∘ and ±27∘. This test matrix is representative of weak and tight maneuvering conditions.

Analysis of the hull wake of a twin-screw ship in steady drift by Borescope Stereo Particle Image Velocimetry

The hull wake of a twin-screw ship in steady drift is analysed by means of a novel Stereo Particle Image Velocimetry (SPIV) system based on rigid endoscopic devices (borescope). The measurement apparatus is described in detail; advantages, drawbacks, processing methodology are presented and discussed. In particular the main advantages are: on-board measurement capability, low intrusiveness and no need to develop water-proof camera casings. Steady drift testing are carried out at CNR-INM towing tank, drift angles β=8.4∘,±13∘,±27∘. Modifications of the windward and leeward sides of the hull wake are investigated and their asymmetric features highlighted. In particular, the former is found to be perturbed to a larger extent at moderate drift angles, whereas the latter is characterized by the presence of coherent vortex structures which feature a high degree of spatial and time coherency.

Propeller modeling approaches for off–design operative conditions

In adverse situations, such as maneuvering and motion in waves, severe variations of the propeller inflow may be experienced, resulting in an increase of propeller thrust and torque and in the generation of in-plane loads. This may cause undesired hull-vibratory loads, stress of the propulsive system and even affect somehow the ship dynamic response. Thus, a reliable prediction of these phenomena during design phases is necessary to comply with the increasingly stringent constraints on safety at sea, propulsive efficiency, vibration and noise pollution. In the present work, the capabilities of a propeller solver based on a potential, boundary element method, routinely used in the optimization process of the propulsive device, to analyze the propeller performance under different maneuvering conditions are considered. After a first validation against uRANS simulations considering a simple oblique flow, the analysis is broadened to a propeller operating in the wake field of a twin screw ship in different maneuvering conditions, for which experimental results from free running tests in model scale are available. The BEM solver is compared also to a steady blade element approach in order to achieve an overview of the respective pros and cons in view of their inclusion in CFD simulations.

Investigation on hull-propeller-rudder interaction by RANS simulation of captive model tests for a twin-screw ship

The hull-propeller-rudder interaction of a twin-screw ship is investigated by using CFD method. The hydrodynamic performances of propeller and rudder during maneuvers are analyzed based on the relevant modules in MMG model, with the propeller side force and asymmetric flow-straightening effect being taken into account. Taking the ONR tumblehome ship model as the study object, self-propulsion test, rudder force test, circular motion test, and static drift test are simulated by using RANS method. The interaction coefficients among the hull, propeller, and rudder, as well as the models of propeller side force and rudder normal force are obtained from the computed hydrodynamic forces and moments. The obtained parameters in the modules show reasonable agreement with the available experimental data. The velocity field around the stern and the pressure distribution on the rudder surface are presented to provide deeper insight into the effects of ship motion and propeller load on the rudder performance. The turning circle test is simulated using the obtained hydrodynamic modules. The simulated trajectory and time histories of kinematic and dynamic quantities show good agreement with the available experimental data and other CFD results, indicating the validity of the CFD-based modelling method for hull-propeller-rudder interaction of twin-screw ships.

Numerical and experimental investigation of propulsion in waves

The effects of head waves on propulsion characteristics of a single and a twin screw ship were investigated based on a Reynolds-averaged Navier-Stokes (RANS) solver and physical tests. Initially, propeller open water characteristics were determined in a homogeneous inflow. Next, computations of the towed models without propeller(s) in calm water and in waves were performed to obtain calm water resistances and waves added resistances. Finally, forces acting on the self-propelled models in calm water and in regular head waves were computed. Using obtained results propulsion characteristics in calm water and in waves were determined. Computations were performed using a RANS based flow-solver coupled with the nonlinear six-degrees-of-freedom equations of motion. When needed, the sliding interface method was used, enabling rotation of the geometrically modeled propeller. All computations were performed on the same numerical grid to keep errors originating from different spatial and temporal discretizations as small as possible. Grid studies were conducted to evaluate discretization errors. Computational results were compared to experimental results obtained from physical model tests. It was shown that the RANS solver is capable of investigating the propulsion behavior of a ship in regular head waves. Fair agreement between numerical and experimental results was obtained.

Investigation on maneuverability of a twin-screw ship driven by one screw

It is possible for a twin-screw ship that one screw failure occurs during navigation, and the maneuverability in this case should be noticed by ship designers and operators. It is of great significance to evaluate the related risk. Firstly, a mathematical model for the twin-screw ship maneuvering motion with one failed screw is developed based on the maneuvering model group (MMG) equations, and verified by the model test results. Secondly, the maneuvering motions of a twin-screw liquefied natural gas (LNG) ship with one free rotating failure screw or with one locked failure screw are simulated and compared by using the mathematical model. It is shown that the numerical modeling results are in agreement with the model test results. Compared with those of normal navigation, the port turning ability of the ship with one failed port screw is better, but the starboard turning ability and yaw checking ability become worse. The maneuverability of the ship with locked failure screw is better than that with free failure screw, although the ship speed drops obviously.

쌍축 추진 선박의 단독 타 고장 상태에서의 조종성능에 대한 수치적 연구

쌍축 추진 선박의 단독 타 고장 상태에서의 조종성능에 대한 수치적 연구