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The structural design of the rudder, traditionally based on quasisteady loads generated during worst manoeuvres, should account for load fluctuations associated with the interaction with the wake of the propeller in order to comply with the more stringent requirements on ship vibration and noise pollution. In this context, the present work analyses the dynamic response of a marine rudder located in the wake of the INSEAN E779A propeller by the one-way fluid–structure interaction approach. The time-dependent pressure distribution on the rudder, obtained through detached eddy simulation, is used to evaluate the pressure field that is the input for a structural solver to determine the resulting deformations and stresses. The computations consider the propeller at moderate loading, and rudder deflection angles at neutral and $4^{\circ }$. The analysis discusses the different contribution of the tip and hub vortex of the propeller on the static and vibratory response of the rudder in the two configurations. [ABSTRACT FROM AUTHOR]

The significance of the subject discussed in the paper is due to the fact that a damping of the resonance of torsional vibrations of the ship's shaft by means of a diesel engine automation system has been developed. The purpose of the paper is to determine the damping of the resonant moments of torsional vibrations of a propeller shaft line. The main research method in the present paper is dynamic visual modelling of torsional vibrations of the propeller shaft of a propulsive in-stallation of a vessel with a low speed diesel engine. It was determined that the use of an additional invariant feedback differential coupling by the difference in the frequencies of the diesel engine and the propeller makes it possible to significantly reduce the amplitude of torsional vibrations in the propeller shaft of the vessel under resonance conditions. A correction to the calculation formula taking into account this phenomenon is proposed. A damping device in the form of corrective feedback with a real differentiating section is proposed. It is recommended to pass through torsion frequency ranges forbidden for operation with the maximal possible fuel supply to the diesel engine. [ABSTRACT FROM AUTHOR]

Abstract The vibro-acoustic responses of a submerged propeller-shaft-hull coupled system under propeller forces in different directions are investigated by the coupled finite element/boundary element method. In the analysis, the acoustic transfer vector (ATV) approach is utilized to study the acoustic contribution from the elastic propeller and the hull. By applying the modal decomposition technology, the effects of the stern bearing on the acoustic response of the coupled system under transversal propeller force are observed. The numerical results are compared with those obtained from a hydroacoustic experiment of the propeller-shaft-hull coupled system. The effects of the decreasement of the stiffness of the thrust bearing on the acoustic response of the coupled system are discussed. [ABSTRACT FROM AUTHOR]

Abstract This paper presents an active control method for reducing the lateral vibration transmission in a shaft-hull coupled system of submerged vehicles under the excitation of propeller forces. In this method, a 6-DOF (degree of freedom) active stern support and the local velocity feedback control strategy are employed to suppress vibration transmission from the shaft to the hull. The dynamic model of the shaft-hull system embedded with the active stern support is established with the FRF (frequency response function)-based synthesis method and the FEM/BEM (finite element method/boundary element method). The six-channel local velocity feedback control strategy is employed to suppress vibrations of the strut-hull interface. Numerical results indicate that a noticeable attenuation of vibration and sound radiation can be achieved by the active stern support. In addition, the combination control at the stern support and the thrust bearing is able to obtain better attenuation at some critical frequencies. Suppression of the mean square velocity and radiated sound power of the hull surface are observed. Highlights • A novel active control method is proposed to suppress the lateral vibration transmission of the shaft-hull system. • A FRFSM/FEM/BEM method is adopted to analyze vibration characteristics under control. • A numerical implementation of the dynamic model validates the control performance. • A significant attenuation is obtained through the active stern support. • A combination control is able to achieve better attenuations of vibration and sound radiation. [ABSTRACT FROM AUTHOR]

Abstract A strategy is employed to address the coupling among propeller, shaft, hull and its contribution to acoustic radiation using the three-dimensional sono-elasticity method (Zou et al., 2010, 2014). Different from our previous work, the local resonance of the elastic propeller is taken into account which makes a significant difference in the response. Further, its impact on acoustic radiation is also analyzed. Through numerical discussion, it is indicated that the coupled acoustic radiation has peaks at the frequencies of the longitudinal modes of the hull, the longitudinal mode of the shaft system, and the umbrella mode of the propeller. The propeller damping could affect the coupled acoustic radiation significantly. This work would lend itself to further acoustic optimization of ships driven by propellers through relatively long shafts. Highlights • Propeller, shaft and hull are modelled as a whole coupled system. • The local resonance of elastic propeller is taken into account which makes a significant difference in the response. • All the peaks of coupled acoustic radiation for propeller-shaft-hull system are revealed. • Propeller hydrodynamic damping could affect the coupled acoustic radiation significantly. [ABSTRACT FROM AUTHOR]

The main objective of the present study is to establish a practical design strategy of air-balloons for a suppression of the propeller cavitation induced hull pressures at multi frequencies. Theoretical foundation is initiated with the existing modal series solution of a multiple scattering problem. An approximated form is then derived by a monopole regime which is valid in a low frequency range. Subsequent parametric analysis with a variation of the separation distance between the balloons provides an analytical evidence that the mutual interaction can be neglected unless they are too close to each other. Hence it is addressed that the individual balloon can be designed separately without a consideration of their coupling characteristics. Finally, the water tunnel test with two balloons demonstrates noticeable vibration reductions at the first- and second- order of blade passing frequencies by 72% and 59%, respectively. [ABSTRACT FROM AUTHOR]

Propeller-induced vibration on ships may originate from separation and wake non-uniformity and can be dealt with stern form redesign, wake adapted propeller design or wake modification devices such as fins, ducts or vortex generators. For an existing ship, the retrofit options are limited and vortex generators are the most cost efficient measure with quick and easy application. However, selection of the design parameters such as size, location and angle of attack relative to the flow are still not straightforward and can be very costly to be evaluated by model tests or full scale investigations. RANS based CFD methods can be used effectively to select these parameters. Current research presents a methodology through a full-scale test case consisting of initial numerical flow calculations and full scale testing, CFD calculations, final numerical flow calculations and full scale testing which shows significant improvements on the wake non-uniformity hence the suffered shipboard vibration. [ABSTRACT FROM AUTHOR]

The article discusses a key problem of ship propulsion system vibration diagnostics, which concerns assessing this part of mechanical energy transmitted from the main engine to the ship propeller which is dissipated due to propeller shaft vibration. A simplified calculation model is proposed which allows the total energy of the generated torsional vibration to be assessed from the shaft deflection amplitude measured at the mind-span point between the supports. To verify the developed model, pilot tests were performed on the laboratory rotational mechanical system test rig. In those tests, cyclic bending moment was applied to a unified (cylindrical) material sample, which modelled, at an appropriate scale, structural and functional properties of a real propeller shaft. [ABSTRACT FROM AUTHOR]

A simplified lumped-mass model was established using ordinary differential equations, focusing on the coupled torsional-longitudinal vibrations of a ship's propeller shaft. The numerical simulation based on the presented algorithm was then developed and the dynamic behavior was investigated. A theoretical solution setup with simple model was solved to demonstrate the accuracy of the proposed lumped-mass model. Based on this model, the coupled natural frequencies and the maximum acceleration of each direction were determined. Experimental tests were conducted to validate the applicability of the numerical model, over a range of rotational speeds and loading conditions. It is found that the natural frequencies are unaffected while the maximum acceleration are increased with the rotational speed as well as the loading. Natural frequencies representing other directions are induced by the coupling effect, and enhance the dynamical response. The ultimate response in the direction without excitation is enlarged because of the coupling effect. An appropriate coupling stiffness coefficient value has been proposed based on the discussion on modeling and experimental results. [ABSTRACT FROM AUTHOR]

• An innovative piezoelectric multicomponent balance embedded into a hollow shaft end is designed to measure the unsteady hydrodynamic excitation of a marine propeller. • n improved Kalman filter algorithm based on the subspace modal identification (SMI) method is established to reconstruct the equivalent excitation considering its direction and location with response-only networks. • The main factors of force reconstruction accuracy are numerically studied. Measuring the unsteady hydrodynamic excitation of a marine propeller at a shaft end accurately from multiple directions is crucial for minimizing the unwanted vibration and noise of ships. Due to the synchronous loading of high static thrust and torque, an innovative piezoelectric multicomponent balance embedded into a hollow shaft end is designed. However, complex coupling between the balance and shaft structure is formed. This leads to crosstalk disturbance and a modal dynamic amplification effect on all measuring channels. To overcome this, an improved Kalman filter algorithm based on the subspace modal identification (SMI) method is established, thus allowing us to reconstruct and locate equivalent unsteady excitations accurately in multiple directions with response-only networks. The effectiveness of proposed framework is test on a simulated nonrotating shaft end system with twelve force and three acceleration response channels. The selection of the smoothing delay parameter and whether crosstalk is considered are two main factors that influence the reconstruction accuracy. [ABSTRACT FROM AUTHOR]

• Detected VIV-induced structural resonance, a main cause of ship propeller damage. • Proposed a CNN-based detection algorithm using vibration signals inside the hull. • Generated large data with the same pattern as measurement data using mode superposition. • Verified with test data from a test rig and ship vibration measurement data. Vortex-induced vibration (VIV) resulting lock-in phenomenon which is the vibration frequency of the structure immersed in a fluid is locked in its resonance frequencies within a flow speed range is a potential cause of vibration fatigue and/or singing of the propellers of large merchant ships. A deep learning-based indirect VIV detection algorithm that works by vibration measurement data of a hull structure instead of a propeller during the sea trial phase is proposed in this study. RPM-frequency representations of the vibration signal by stacking the vibration frequency spectrum relative to various propeller RPM's, so-called waterfall chart of 2-dimensional data like an image, are measured and fed into the proposed convolutional neural network (CNN) architecture for VIV detection i.e. VIV frequency and RPM range. To generate the large data set, artificial data looks real, for learning, a method based on the modal superposition method instead of time-consuming fluid-structure interaction analysis is proposed. 10k set data for training, 1k set for hyper-parameter tuning, and 1k set for the test were generated. After the training, it showed a diagnosis success rate of 82% for the test set. To test the proposed VIV detection algorithm, investigations were carried out in a laboratory on a small-scale ship propulsion system designed in such a way that the vortex shedding frequency and the underwater natural frequency match each other. The proposed VIV detection algorithm was tested using the structural vibration signals measured at stationary structures in the air instead of the rotating propeller immersed in water. Lastly, the validity of the proposed algorithm was tested using the structural vibration signal measured at the hull structure of a crude oil carrier in which a propeller singing occurred during her sea trial. [ABSTRACT FROM AUTHOR]

To improve the stealth of a submarine, the sound power radiated from the hull can be reduced using active noise and vibration control. In this article, active control is applied to minimize hull excitation by propeller forces transmitted through the shaft. The dominant propeller axial force fluctuations are directly related to blade passage and the phase of the force is determined by the absolute angle of the propeller shaft. Because the propeller forces are deterministic, the application of feedforward control is appropriate. Numerical finite element/boundary element (FE/BE) models of a submarine have been developed to find the transfer functions. Different control strategies are investigated in which active control is applied to the propeller/shafting system and/or to the submarine hull. Active vibration control and discrete structural acoustic sensing based on the far-field radiated sound power were considered for development of the cost function. In addition, the performance of a system in which active control is combined with passive control using a resonance changer is investigated. It is shown that the combination of tuned control actuators and a resonance changer results in a significant reduction of radiated sound power. [ABSTRACT FROM AUTHOR]