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This article presents research results on building a model to reproduce ship vibrations based on a parallel robot with 6 degrees of freedom on the Gough-Stewart platform. Vibration data at the ship's center of gravity, calculated by simulation software, will be inputted into the model. The regenerative control system uses a simple PID controller to control input trajectory tracking. Simulation results on Matlab/Simulink software have demonstrated the reproduction of ship vibrations within the allowable error. [ABSTRACT FROM AUTHOR]

The vibration in ships causes structural fatigue, damage to electrical and mechanical devices, excessive level of noise and discomfort to the passengers and crews. Sometimes the increase in ship vibration leads to unsafe operating conditions and thereby discarding it. Thus, the research on vibration reduction is essential in the maritime field and this paper deals with the reduction of vibrations in marine machinery using elastomeric bearings. The numerical analysis of the performance of passive vibration isolators with different damping materials was conducted using ANSYS and the results are validated experimentally. With the help of a vibration exciter, vibration transmissibility at different frequencies is plotted and the hysteresis curve was generated numerically by applying a cyclic load to the bearing. Then, the best damping material was deducted by comparing the calculated loss factor of different elastomeric materials such as natural rubber, styrene-butadiene rubber and polybutadiene Rubber (PBR) and their combinations. The natural rubber blended with styrene-butadiene rubber (SBR) and polybutadiene rubber (PBR) shows an increase in the damping property of the elastomer and can be used for high-frequency damping applications. [ABSTRACT FROM AUTHOR]

Purpose: This paper aim to take the ship shaft stern bearing as the research object, and studies the influence of journal axial vibration on bearing dynamic characteristics under different misaligned angles and rotation speeds. Design/methodology/approach: Computational fluid dynamics (CFD) and harmonic excitation method were used to build bearing unstable lubrication model, and the dynamic mesh technology was used in calculation. Findings: The results indicate that journal axial vibration has a significant effect on bearing dynamic characteristics, like maximum oil film pressure, bearing stiffness and damping coefficients, and the effect is positively correlated with journal misaligned angle. The effect of shaft rotation speed and journal axial vibration on bearing dynamics characteristics are independent; they have no coupling. Bearing axial stiffness is mainly affected by the journal axial displacement, bearing axial damping is mainly affected by journal axial velocity and they are positively correlated with the misaligned angle. The influence of rotational speed on bearing axial stiffness and axial damping is not obvious. Originality/value: This paper establishes the bearing dynamic model by CFD and harmonic excitation method with consideration of cavitation effect and analyzing the influence of journal axial vibration on the dynamic characteristics. The results are benefit to the design of ship propulsion shaft and the selection of stern bearing. Also, they are of great significance to improve the operation stability of the shaft bearing system and the vitality of the ship. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2022-0337/ [ABSTRACT FROM AUTHOR]

Locally resonant phononic crystals are a kind of artificial periodic composite material/structure with an elastic wave band gap that show attractive application potential in low-frequency vibration control. For low-frequency vibration control problems of ship power systems, this paper proposes a phononic crystal board structure, and based on the Bloch theorem of periodic structure, it uses a finite element method to calculate the band structure and the displacement fields corresponding to the characteristic mode and vibration transmission curve of the corresponding finite periodic sandwich plate structure, and the band gap characteristics are studied. The mechanism of band gap formation is mainly attributed to the mode coupling of the phononic crystal plate structure. Numerical results show that the sandwich plate structure has a double periodicity, so it has a multi-stage elastic wave band gap, which can fully inhibit the transmission of flexural waves and isolate the low-frequency flexural vibration. The experimental measurements of flexural vibration transmission spectra were conducted to validate the accuracy and reliability of the numerical calculation method. On this basis, the potential application of the proposed vibration isolation method in a marine power system is discussed. A vibration isolation platform mounted on a steel plate is studied by numerical simulation, which can isolate low-frequency vibration to protect electronic equipment and precision instruments. [ABSTRACT FROM AUTHOR]

Shipping traffic is recognised as the main man-noise source of the anthropogenic noise generated in the marine environment. The underwater acoustic pollution is increased due to the increment of the human activity at seas supposing a threat for marine habitats. The ship as acoustic source must be understood and controlled to manage the maritime areas both in time and space to reduce the impact of noise in marine fauna. Shipping noise is mainly composed of flow noise, propeller noise and machinery noise. This research is focused on the analysis and estimation of the underwater radiated noise generated by the vibrations of the onboard machinery or structure-borne noise based on the calculation of the transfer function. This function relates the acceleration levels of the vibrations of the hull's panels and the radiated noise by them using the radiation efficiency. Different analytical methods to estimate the radiation efficiency are presented and compared with data collected at sea. The measurements are performed acquiring simultaneously acceleration and acoustic levels by means on accelerometers installed on the hull's panels at different positions and hydrophones deployed close to the bow, middle and stern of the ship. The analysis of the transmission of the vibrations along the ships is performed using the data from different locations of the hydrophones. The quality of the measurements is analysed using the coherence function through the spectral correlation between the measurement of vibrations and acoustic levels. On the other hand, signal-to-noise ratio is computed to verify the strength of the noise sources. The computed transfer function is used to predict the underwater radiated noise from vibrations showing differences less than 2 dB re to 1 μPa2. [ABSTRACT FROM AUTHOR]

Ship hull vibration is a major contributor to fatigue crack growth and main engine excitation is identified as an important vibration source. A general method to solve any vibration problem arising onboard a ship does not exist, which encourages the use of a reliability-based framework for assessing ship vibration and its consequences. A stochastic model of vibration response is developed for the probabilistic formulation of the failure probability of the occurrence of crack propagation of a secondary structural hull component. The secondary structural component considered is a pipe stack support. The pipe stack support connects a cargo pump pipe stack to the wall inside the cargo tank, and the support is welded directly onto this wall. First, a generic cargo hold model is analysed with engine speed and the relative distance between the engine and the structural component under consideration as stochastic variables. Then, submodels are used to investigate the local vibration of the support and the stress response is evaluated for a combination of different engine speeds and relative distances. A surface is fitted to the vibration response and used for probabilistic analysis by Monte Carlo (MC/DSPS) and FORM/SORM reliability methods. The limit state is formulated as the possibility of fatigue crack growth based on a threshold stress intensity factor. This threshold factor depends on the initial crack size and different initial sizes are investigated. The adequacy of the functional representation for the stochastic model, which is fitted to discrete data points, is also assessed. It is seen that a functional representation using a sum of sine terms give an adequate fit for describing the stress response induced by engine speed, while a polynomial representation was adequate for the relative distance variable. The failure probability estimated by Monte Carlo simulations and SORM indicates that the pipe stack support is not critical for the occurrence of fatigue crack growth. A main observation from the analysis is that the reliability-based design of secondary structural components, also looking at the interaction with the global structure, may help to improve the vibration-induced stresses in local hull details by application of proper design measures. [ABSTRACT FROM AUTHOR]

The load that borne by ship mining system is very complex. The vibration of lifting pipe can be significantly affected by ocean current and wind load, which has a key impact on material lifting, ore bin storage and ship towing. Considering the composite load condition, the vibration control equation of mining ship is established based on the transverse swing mechanism of ship hull, and the variation law of transverse disturbance is obtained. The dynamic equation is constructed according to the bearing characteristics of the lifting system and the D'Alembert principle. The Wilson method is used to analyze and obtain the transverse vibration spectrum response of the lifting pipe under different wind loads, hull disturbance velocity and water depth. Based on the analogy method and hammering method, the vibration feedback test-bed of the lifting system is built, and the time-domain and frequency-domain vibration characteristics of the lifting pipe model under different water depths are obtained. The results show that in shallow water, the disturbance of mining ship and the composite load of ocean current are the key factors affecting the vibration amplitude of lifting pipe respectively. With the increase of water depth, the characteristic frequency and amplitude of the system decrease, and the amplitude gradually presents a discontinuous phenomenon. [ABSTRACT FROM AUTHOR]

The pulse force generated by the propeller excites the hull through the propulsion shafting system, which is the primary source of vibration and noise of ships. In order to control the transmission of longitudinal vibration of ship shafting, a multimodal dynamic vibration absorber (MDVA) with broadband vibration control performance is proposed. A magnetorheological elastomer (MRE) was prepared and used as an elastic element to construct a semi-active dynamic vibration absorber (SDVA), designed spiral flexible springs and embedded SDVA into the proposed MDVA. An equivalent propeller propulsion shaft system model was established, and its first three longitudinal vibrations were controlled based on the MDVA. Furthermore, the stiffness and damping of the MDVA were optimized by fixed point theory. A design scheme for the MDVA considering the changes in oil film stiffness of thrust bearings under different propeller speed conditions was proposed. The results indicate that the MDVA has excellent vibration transmission control performance at the first three natural frequencies. The proposed MDVA also has a broader frequency band for controlling vibration near first-order resonance than the traditional single degree of freedom DVA, which has excellent vibration control performance under variable speed conditions. [ABSTRACT FROM AUTHOR]

Aiming at the problems existing in the method of using sensors to detect the rotor position of marine main propulsion motor at low speed, a sensorless rotor position identification method based on high-frequency pulse vibration signal is proposed. In this method, the low-pass filter is used to separate the high-frequency signal component, and the current component of d-axis to q-axis is demodulated. The control mode of PI action law is used to phase-locked processing of the demodulated signal, in which purpose is to obtain the rotor position signal. The design method is simulated and verified by MATLAB/Simulink software. The error between the estimated position and the actual position of the rotor in the simulation waveform is small, and the accuracy is high. The simulation results show that this method can achieve good results when applied to the ship electric propulsion system without position sensor, which provides a theoretical reference for the design of marine main propulsion motor control system. [ABSTRACT FROM AUTHOR]

The greatest vibration occurs in the engine room, but all other parts of the ship also experience vibrations because it is propagating. Even though there are methods to reduce these vibrations such as engine beds, they can only reduce the damaging effects and cannot completely eliminate the vibrations themselves. The method used in this research is to compare the measurement of good vibrations in the conditions before the addition of construction and after the addition of construction for later comparison with numerical calculation data. The purpose of this study is to obtain the maximum vibration value in the conditions after the addition of the gorger construction before the addition of the side deck girder construction as a means of evaluating the side deck girder construction planning in the ship engine room ship 2000 DWT. The result consideration of adding construction becomes one or the alternative in providing reinforcement so that it can reduce the vibration that occurs. From analyze results after addition of a sized T profile FB 180 x 8 mm FP 75 x 10 mm, which ranges from 28 - 29 m/s2 for the x-axis vibration value, while for vibrations on the y-axis the maximum is 10-11 m/s2, and on the maximum z-axis. at 20-21 m/s2, this analyze vibration is based on the time between 0 - 15 seconds or per 15 second interval, able to reduce percentage of vibration in the ship engine room area is 34.91%. [ABSTRACT FROM AUTHOR]

The fault diagnosis is always a key issue in the security field of marine propulsion system. There are obvious problems like the unsteady working of sensors, distortion of original data, and ambivalent feature information from marine shafting's vibration or motion. It is therefore critical to develop a more effective method to identify the fault information so that the safety of marine propulsion system can be pre-estimated. Hence, a composite method which is based on the ensemble empirical mode decomposition (EEMD) and coupled with the autocorrelation method (AM), the fast Fourier transform (FFT), is mixed and applied to identify the fault information of marine shafting during its operating by hull vibration. The contrastive analysis of the three methods and fault feature study are then conducted to assess the effectiveness of the proposed method thoroughly and validated by the author previously. The research indicates that the composite method is available to fault diagnosis of marine shafting by hull vibration which coupled the shafting vibration with fault feature. [ABSTRACT FROM AUTHOR]

The propulsion shafting is one of the main excitation sources of ship vibration and noise. Thus, shafting vibration and alignment are very important issues in the design of a propulsion system. In the present paper, the effects of shafting alignment on shafting whirling and bearing vibrations will be discussed. This study has been carried out experimentally on a test rig designed by the Wuhan University of Technology (WHUT). The results indicated that in design conditions, the effects of shafting alignment on both vibrations are mainly in the horizontal direction. It was found that both shafting whirling and bearing vibrations can be effectively reduced by adjusting the shafting alignment. However, compared to the vertical direction, the vibration in the horizontal direction can be more effectively reduced. Also, the minimum values of whirling vibration and bearing vibration are not in the same shafting alignment state. In addition, the effect of shafting whirling vibration on bearing vibration was little. Also, the bearing vibration changes little when the shafting rotation speed is between 90 and 300 r/min. Finally, it was found that at high rotation speeds, the bearing supporting performance is significantly affected by the shaft whirling effect. [ABSTRACT FROM AUTHOR]

To reduce the transmission of shafting longitudinal vibration in surface ships, a design of thrust bearing integrated with internal disc springs is proposed and the longitudinal vibration characteristics of the shafting are studied. According to the structural characteristics of thrust bearing and the deformation characteristics of disc springs, the specific size and combination forms of disc springs in the thrust bearing are designed, and the effective disc springs schemes are achieved according to the static and dynamic design requirements. With the integration of the disc springs into the thrust bearing, the peak of longitudinal displacement response at the base of thrust bearing can be reduced by 10 dB by two schemes of disc springs. The proposed design can effectively suppress the transmission of shaft longitudinal vibration to the hull, which has engineering significance for the longitudinal vibration control of the shafting of the surface ship. [ABSTRACT FROM AUTHOR]

Focusing solely on a single objective during the ship structure optimization process may negatively impact the performance of other aspects, this study proposes a collaborative method for cruise ship optimization, which can achieve both vibration control and lightweight while maintaining the structure's original strength. In this method, transfer path analysis is performed before vibration control, and a concept of structural intensity weighted sum (SIWS) is proposed to overcome the limitation of traditional SI analysis, which can only identify the main transfer paths at a single frequency. This concept calculates the weighted sum of SI in coordinate directions at different frequencies, aiming to identify the transfer paths of the weighted root mean square (WRMS) of vibration acceleration (ACC) at different frequencies, with its effect validated through performing vibration sensitivity analysis on structures along these paths. Furthermore, in the optimization to control vibration with mass and maximum stress as constraints, the response surface method (RSM) is used to construct surrogate models for the maximum stress of the cabin section, and constraints are applied to the surrogate model's values to guarantee structural strength. The optimization results reveal that the proposed collaborative method for vibration control and lightweight successfully achieves both objectives without compromising structural strength. Additionally, optimizing the primary transfer paths identified through SIWS analysis is shown to enhance the vibration control effect. • A collaborative control method for cruise ships' vibration and mass is proposed to achieve both vibration control and lightweight while maintaining the structure's original strength. • The values of stress surrogate models are constrained in vibration control optimization with fluid-structure coupling as the boundary condition, which can achieve vibration control while constraining the maximum stress. • A concept of structural intensity weighted sum is proposed for identifying the main transfer paths of frequency domain weighted root mean square values of vibration. • Optimizing based on the main paths identified through analysis of structural intensity weighted sum further enhances the effectiveness of vibration control. [ABSTRACT FROM AUTHOR]

A floating-raft vibration-isolation system can effectively inhibit the transmission of mechanical vibration energy to the hull. In this study, a new sandwich plate-type metastructure (SPM) raft is designed based on the construction of acoustic metamaterials for vibration isolation. Unlike conventional rafts, the SPM features periodic rubber-mass subsystems arranged in the core layer of the sandwich plate, as well as faceplates slotted to reduce the mass and offset the weight increase caused by additional resonators. An equivalent model of an SPM with graded resonators is established, and the dispersion equation is derived by combining Kirchhoff's law and Bloch's theorem. Based on dispersion analysis, multiple bandgaps lower than 200 Hz, through which elastic waves cannot propagate, are identified. The vibration transmission performance of the SPM is analysed via finite-element simulation. The numerical results show that the proposed SPM exhibits low-frequency vibration attenuation and that the frequency band in which vibration attenuates is robust. Finally, vibration-transmission experiments are conducted, and the effectiveness of the proposed SPM is validated. This design strategy provides new possibilities for the development of sandwich structures for ship vibration and noise control. • A new type of sandwich plate-type metastructures (SPMs) for low frequency vibration reduction was designed and fabricated. • The bandgaps of the SPMs where vibration attenuates is robust and adjustable. • The SPMs can be used as raft in the double-layer vibration isolation system of the floating raft. [ABSTRACT FROM AUTHOR]

Considering the longitudinal vibration of the ship shaft system, there are disadvantages such as small damping bandwidth of passive control and complicated design of active control. An NES-GMM is proposed by the combination of nonlinear energy sink (NES) and giant magnetostrictive material (GMM) for the vibration reduction and energy harvesting of the ship thrust bearing unit. The vibration reduction effect and energy harvesting of the proposed NES-GMM device are analyzed based on actual measured longitudinal excitation as input signals. The vibration behavior including the transient and harmonic response of the thrust bearing and NES device are calculated. Meanwhile, the kinetic, potential, and damping energies of the primary system and the electrical and magnetic energy harvested by the NES-GMM are obtained. Moreover, the effects of mass, damping, and stiffness of the NES structure are also discussed over a range of rotational speeds. The research demonstrates that energy is irreversibly transferred from the primary system to the NES system. Additionally, more energy absorption and better vibration reduction of the NES-GMM device will be achieved with larger mass and damping of the NES. • Nonlinear energy sink (NES) combined with giant magnetostrictive material (GMM) to reduce vibration and harvest energy. • The vibration reduction and energy harvesting of the NES-GMM device are analyzed based on measured excitation. • The proposed NES-GMM can continuously output power while reducing vibration by magnetostrictive energy harvesting device. • The effects of NES parameters are discussed concerning vibration reduction and energy harvesting at different speeds. [ABSTRACT FROM AUTHOR]

Ship vibration not only causes safety issues, but also easily generates noise pollution. Therefore, this paper introduces the quasi-zero stiffness (QZS) vibration isolator to solve the problem of low-frequency vibration. In terms of static analysis, this paper proposes a discretized beam constraint model (DBCM) to study the static properties of flexible beams with large deformation, and the finite element analysis (FEA) verifies the accuracy of DBCM. Regarding dynamic analysis, this paper combines the harmonic balance method (HBM) and the pseudo-arc length method (PALM) to analyze the dynamic response and explore the influence of excitation and damping ratio on the response stability. In addition, the performance of equivalent linear isolators is compared, revealing significant advantages of QZS isolator in terms of isolation bandwidth and peak transmissibility. The experimental data demonstrates that QZS isolator's initial isolation frequency (2.14 Hz) is 68.5% lower than that of linear isolators (6.79 Hz), and the isolation efficiency at 5.35 Hz can reach 90%, making it suitable for low-frequency isolation. Furthermore, experimental data validate the accuracy of the theoretical model and FEA. The static and dynamic theoretical models can optimize the structural parameters of flexible beams and serve as valuable inspiration and reference for designing and improving isolator. • The QZS isolator is composed of eight flexible beams and a linear spring. • DBCM can accurately calculate the nonlinear statics of flexible beams. • The QZS isolator has a wider isolation frequency band and lower transmissibility. [ABSTRACT FROM AUTHOR]

Ship's propulsion shafting is one of the main sources of ship vibration and noise. The shafting, whirling vibrations, and alignment are important factors that affect the comfort, stability, and reliability during a ship's navigation. However, the mechanism of the interacting of the both factors is not fully revealed. In this paper, the effect of shafting alignment on whirling vibration and the bearing temperature response is studied by experiment. The test scheme is designed reasonably according to the theoretical analysis. The results show that the horizontal component of the shafting whirling vibration can be effectively reduced by adjusting the shafting alignment state while the vertical component is not. The shafting axis balancing position (SABP) slightly moves upward in high speed, which should be considered in the dynamic alignment design of the shafting, especially for the high-speed shafting. Little ABSB (the angle between the shafting centre line and the No. 1 bearing centre line) is beneficial to the stable operation of shafting, while appropriately increasing the ABSB and bearing load is beneficial to reducing the shafting whirling vibration. By balancing the relationship between bearing load and ABSB, the performance of whirling vibration and bearing temperature response can be optimized. [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]

In this paper, flexural vibration and power flow transmission of a ship propulsion shafting structure are analyzed via energy principle description in conjunction with Rayleigh–Ritz procedure, in which the shafting vibration displacement is constructed as a superposition of Fourier series and boundary-smoothing supplementary functions. Effect of the distributed bearing support and thrust loading of propulsion shafting system is considered in terms of potential energy of system Lagrangian. Numerical examples are presented to demonstrate the reliability and effectiveness of the established model by comparing results with those from finite element method. Results show that the current model can deal with the vibration analysis of ship propulsion shafting with thrust loading and distributed bearing very well. Influence of boundary restraints, stiffness of distributed bearings, and thrust loading on vibration characteristics of ship shafting system is studied and addressed. Numerical study on power flow analysis is also conducted to investigate the characteristics of vibrational energy transmission in such practical structure. Results show that the stiffness of spatial bearing support has significant influence on vibrational energy transmission and thrust force will greatly affect the total input power into such structure. [ABSTRACT FROM AUTHOR]

With the development of ship enlargement, the problems of coupling vibration between hull and propulsion system and vibration transmission via bearings are more and more prominent. Based on the theory of shaft vibration and the experimental system for dynamic characteristics of the shaft, an experiment plan about propulsion shaft vibration under dynamic excitations is designed in this paper. The performance of propulsion shaft vibration under hull deformation excitations applied on intermediate and stern bearings is studied. Hydraulic excitations in horizontal and vertical directions on the intermediate bearing and stern bearing of the experimental model of propulsion shaft are considered in this paper to simulate hull deformation on bearings of the ship. Vibration characteristics of the shaft under different excitations are gained and coupling effects are discussed. Moreover, the influences of amplitude and direction of excitations on bearings and the shaft rotation speed on the vibration of propulsion are studied. The results show that aiming at improving the safety and reliability of navigation, the hull deformation, especially the horizontal hull deformation excitation on the intermediate bearing, is not neglectable and should be considered during primary design. Also, rotation speed and resonant frequency are needed to be well designed with the frequencies of hull deformation excitations. [ABSTRACT FROM AUTHOR]

Human-induced vibration and noise significantly influence passenger ship comfort. Predicting and controlling human-induced vibration and noise are imperative. The excitation sources of the vibration and noise are human-induced loading (HIL). HIL models are introduced to describe the impact loading with time-variant stochastic fields by single-person or multi-person walking. A numerical analysis of human-induced noise is implemented in a cabin corridor of a passenger ship under single-person or multi-person walking. Finally, a real ship experiment test is implemented, validating the proposed method's feasibility and effectiveness. The results provide a better understanding of passenger ships' vibration and noise reduction design. • ►The human-induced loading model is obtained by introducing the equivalent model. • ►The human-induced noise analysis of passenger ships is implemented. • ►The feasibility and effectiveness of the proposed method are verified by experimental test. [ABSTRACT FROM AUTHOR]

This paper presents research results on the causes and effects of human errors in relation to typical ship design factors, such as noise, vibrations and ship motions. Following a review of the relevant literature, aimed to the identification and quantification of pertinent parameters and effects, a detailed questionnaire has been developed and answered by seafarers. The questionnaire results are presented in the form of quantitative risk models, using Bayesian networks with applications on two safety-critical ships, namely containerships and tankers. Finally, we present the generic collision and grounding causation probabilities for both ship types. The results are found to be in good agreement with current literature. Knowledge of the ship design factor effects on the human performance in quantitative form would be useful in the ship design and the development of new safety rules and regulations. • The causes and effects of human errors in relation to typical ship design factors are studied • A detailed questionnaire has been developed and answered by seafarers. • Generic collision and grounding causation probabilities for container and tanker ship are presented. • A high-level model risk for collisions and grounding are presented. [ABSTRACT FROM AUTHOR]

The propulsion system is one of the main sources of ship vibrations. A typical propulsion system consists of an engine, a shaft line and a propeller. In order to estimate the vibration levels of a ship propulsion system, analytical methods are still relevant in the preliminary ship design stage. In this paper, three analytical procedures for the vibration analysis of a ship shafting system are presented. The shafting system dynamic behaviour is simulated by reducing the problem to two-, three-, and multi-mass models. Propeller and engine damping is taken into account. Differential equations of motion for the two- and the three-mass models are solved analytically. In the case of the multi-mass model, Rayleigh's quotient and the Galerkin method are used for free and forced vibration analysis, respectively. Since the first natural mode of the shaft line is dominant, the problem can be reduced to a single d.o.f. in the modal space and solved analytically. For all three models, relatively simple formulae for the engine torque transfer factor to the intermediate shaft are derived. The presented procedures are validated by a comparison with measurements. The comparison indicates the high accuracy of the proposed procedures. [ABSTRACT FROM AUTHOR]

In this paper, the effect of weather routing and ship operations on the extreme vertical bending moment (VBM) in a 6000TEU class large container ship which is operated in North Atlantic Ocean is addressed. A direct time-domain nonlinear response simulation method taking account of the wave-induced vibrations is combined with a voyage simulation based on 10 years of meteorological data in the area. The probability distribution of the ship's operational parameters conditional upon the meteorological conditions is considered. It is clarified that the most severe wave condition with the significant wave height over 16 m in the area may not be encountered by the ship due to the weather routing and the extreme value is determined mostly by the wave condition much milder than the most severe in the area. It is also found out that the ship speed assumed in the most contributing sea state strongly affects the extreme value of the total VBM. It is explained by the fact that the wave-induced vibrations in the ship tend to be excited at faster speed. [ABSTRACT FROM AUTHOR]

Abstract Vibrations in ship and offshore structures owing to various ocean environmental loads and excitations of power systems become increasingly serious. In this paper, the flexural wave propagation and vibration attenuation characteristics in periodic bi-directionally orthogonal stiffened plates are investigated. The dispersion relations and the displacement fields of the eigenmodes of infinite periodic bi-directionally orthogonal stiffened plates are calculated by using the finite element method in combination with Bloch periodic boundary conditions. Numerical results show that periodic bi-directionally orthogonal stiffened plates can yield complete and directional flexural wave band gaps, in which the propagation of flexural vibrational waves is prohibited and flexural vibration suppression is dramatically achieved. With the introduction of bi-directionally orthogonal stiffeners, the flexural wave and vibration energy is confined in the four corners of the plate owing to the scattering effect of the bi-directionally orthogonal stiffeners. The transmission spectra for a finite periodic stiffened plate are numerically and experimentally achieved to verify the existence of the flexural wave band gaps and vibration suppression characteristics. Furthermore, the effects of geometrical parameters on the flexural wave vibration band gaps are carried out. The flexural wave band gaps and vibration attenuation properties can be artificially modulated by changing the geometrical parameters of periodic bi-directionally orthogonal stiffened plates. [ABSTRACT FROM AUTHOR]

Abstract After a long period of crisis and uncertainty the yacht market seems to exit from the tunnel. Many shipyards are developing new interesting projects, especially for vessels over 50 m in length. The high intrinsic value of these vessels fosters technical offices to deepen the research on some critical subjects to increase competitiveness. The onboard comfort, with particular reference to vibrations, is probably one of the key aspects of this trend which nowadays drives most of the design choices relatively to structure lay out and materials for interior outfit. A great help comes from Classification Society new rules and regulations for the evaluation of noise and vibration. The so called "Comfort Class Rules" contain the general criteria for noise and vibration measurements in various yacht areas and suggest maximum limit values as a function of the required quality level of the yacht. In this paper a study carried out in cooperation between the University of Genova and a leading Italian shipyard on the dynamic behaviour of superyacht structures is presented. A detailed FEM analysis of the global and local natural frequencies of a 60 m superyacht was carried out in order to evaluate the reliability of simplified procedures based on reduced numerical models. The investigation has been carried out by two different FEM codes and the numerical results have been compared with experimental data measured during the construction of the vessel. Highlights • The global and local vibration of a superyacht structure has been evaluated by using 2 different FE commercial codes. • The reliability of reduced numerical models in terms of local vibration has been evaluated as well. • The eigenfrequency analyses have been compared with experimental results obtained during the superyacht construction. [ABSTRACT FROM AUTHOR]

Abstract In this study, an efficient time-domain prediction model is developed to predict unsteady flow vortex-induced vibrations (VIV) of flexible risers. The hydrodynamic forces on flexible risers are calculated on the basis of forced oscillation experiments on rigid cylinders. A period identification criterion, based on the spatial and temporal variations of reduced velocity, is proposed to divide the entire vibration process into exciting and damping periods of each exited mode. In exciting periods, assuming that VIV enters an ideal lock-in stage, a non-iterative solving model is established under modal space for response calculations, which efficiently predicts time domain VIV responses. In damping periods, free-decay vibration theory based recurrence formulas are established under modal space, and they get solved stepwise for modal responses. After some slight response adjustments to smooth period transitions, the VIV response time history can be obtained efficiently. This model is validated by steady flow VIV prediction cases, and further applied to predict oscillatory flow VIV experimental results. The prediction cases reveal that this model is able to realize high-speed VIV predictions with satisfactory results and no convergence problems. This model, with high efficiency and stability, is highly suitable for unsteady flow VIV prediction in engineering applications. Highlights • An efficient time-domain prediction model is proposed for high-speed VIV predictions under unsteady flows. • A period identification criterion is developed to distinguish exciting- and damping-dominant periods for each exited mode. • In exciting periods, a non-iterative response solver is further developed to calculate time-domain VIV responses. • In damping periods, free-decay vibration theory based recurrence formulas are established for response calculations. • The model is validated by experimental results in steady flow and oscillatory flow VIV prediction cases. [ABSTRACT FROM AUTHOR]

Abstract It has recently been pointed out that the vertical shear stresses at pile-soil interface play an important role in static responses of offshore monopiles with large diameters, and traditional p - y curves cannot fully capture this influence. However, the influences of the vertical shear stresses on the dynamic response of monopiles are still not clear. This is the main focus of this study. The coupled horizontal and rocking vibration of a monopile embedded in a fully saturated poroelastic seabed is studied in this paper. The focus of the study is the difference between the responses with and without the vertical shear stresses on the pile. The monopile dynamic response is studied by the integral equation method, with both 3D elastodynamic theory and Euler-Bernoulli beam theory. Selected numerical results for highlighting the influence of the vertical shear stresses on the dynamic contact load distributions, pile displacements, and lateral dynamic impedance functions are examined for different length to diameter (l/d) ratios as well as poroelastic materials and frequencies of excitation. These results confirm that exclusion of the vertical shear stresses will lead to potentially very conservative design for monopiles with l / d < 6 in soft soil, and monopiles with l / d < 10 in medium to stiff soils. The computed dynamic responses of the monopile when the vertical shear stress is ignored can be up to 30% larger than the case when the vertical shear stress is considered. Highlights • The influence of vertical shear stresses on the dynamic responses of monopiles is studied. • A rigorous integral equation method is used. • Exclusion of vertical shear stresses will lead to a potentially very conservative design. • When the vertical shear stress is ignored, dynamic responses can be up to 30% larger. [ABSTRACT FROM AUTHOR]

Abstract The paper presents a comparison of two vibration-based methods for the damage detection of a laboratory scale model of a tripod. Tripods are a part of the supporting structures for offshore wind turbines. The tripod model structure allows the investigation of the propagation of a circumferential representative crack in one of the cylindrical upper braces of the tripod itself. The first damage detection method addresses the use of acceleration signals in a genuine experimental modal analysis (i.e. input-output modal analysis) while the second one is based on operational modal analysis (i.e. output only modal analysis). The progressive damage is monitored by the calculation of the modal parameters and following their deviations. Both methods were performed on the undamaged and damaged structure for different support conditions and excitations (shaker, hammer, in water basin under wave excitation). The results suggest that both the methods can be considered useful tools for damage detection in dry and in-water conditions for offshore support structures. The presented technique proves to be effective for detecting and assessing the presence of representative cracks. Highlights • Vibration-based methods for damage detection of wind turbine tripod. • Experimental modal analysis of a damage tripod in dry condition. • Operational modal analysis of a damage tripod with wave motion in a tank. • Useful tools for damage detection in dry and in-water conditions for tripod. [ABSTRACT FROM AUTHOR]

Abstract One trend in ship development is low noise characteristics. As one of the major noise sources of ship underwater radiated noise is the power equipment, it is critical to predict the ship underwater radiated noise caused by power equipment during the design phase. In this study, the incentive spectrums of power plants were obtained by testing on an oil tanker ship, and the hull vibration was calculated and measured in the middle and low frequency. The results show that the calculation model satisfies the accuracy requirement. To calculate the ship underwater radiated noise in the middle and low frequency, the finite element and boundary element method (FE-BEM), finite element and infinite element method (FE-IFEM), and finite element and automatic matching layer (FE-AML) were used, respectively. It is found that the FE-BEM is the preferred method for calculating ship underwater radiated noise in modeling scale and computational efficiency. The calculation of hull vibration and underwater radiated noise in the high frequency were performed by using the statistical energy analysis (SEA). Full frequency underwater radiated noise prediction of the oil tanker was completed. In the end, the far field of ship underwater sound radiation was studied. The far field can be determined when the sound radiation directivity of the ship no longer changes with distance. [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 Offshore wind turbines are influenced not only by environmental loads such as the wind and waves, but also by various harmonic excitations and have always been considered as complex coupled vibration systems under operational conditions. Generally, the proposed excitations and corresponding vibration sources have a direct relationship with the structural operational safety of the offshore wind turbine and can be reflected by the vibration responses. Nevertheless, existing studies in this area mainly focus on understanding the effect of environmental excitations on the structural vibrations of offshore wind turbines and identifying the dynamic parameters. The research on the identification of the vibration sources and the corresponding energy distribution of offshore wind turbine structures based on the observation data have not yet been carried out. Therefore, using the measured vibration responses of an offshore wind turbine prototype, an identification technology based on optimized spectral kurtosis (OSK) and the ensemble empirical mode decomposition (EEMD) methods, which is capable of determining both the structural vibration sources and the corresponding energy distribution was presented for the first time. It can be demonstrated that the structural vibration sources changed from environmental excitations to forced harmonic loads when the rotating speed and power of the turbine increased. At the same time, the main vibration energy underwent a transformation from random vibration energy to harmonic vibration energy with a change in the operational factors. Furthermore, it is suggested that the relationship between the rotating frequency and structural modal frequencies in the structural operational safety assessment of offshore wind turbines should be further investigated. Highlights • An identification method of the structural vibration source and energy distribution is presented. • Environmental excitations and harmonic excitations are considered as main vibration sources. • Variation law of the main vibration source and corresponding energy proportion of offshore wind turbine are distinct. • Appropriately enlarging the safety standard between 1P harmonic frequency and first modal frequency is reasonable. [ABSTRACT FROM AUTHOR]

Abstract Highly dynamic nature of the applied loads on flexible and lightly damped offshore wind turbine (OWT) foundations affects the lifetime and serviceability of the system. In this study, the excessive vibration responses of OWTs are minimized using tuned mass dampers (TMD) and tuned liquid column dampers (TLCD). Due to high efficiency of TLCDs and TMDs for certain loading conditions, a combined TLCD-TMD is also utilized to improve the overall performance in a wide range of loading conditions. First, a parametric study was performed that highlights the sensitivity of these structural control devices. The effect of two devices on fixed offshore wind turbine foundations for the benchmark 5 MW NREL turbine in various loading patterns was investigated. Then, the model was subjected to stochastically generated wind loading in operational, parked, startup, and shutdown conditions. The results suggest that the standard deviation of the dynamic responses can be greatly reduced with all structural control devices. However, TMDs are more efficient in operational conditions, whereas TLCDs show better performances in parked conditions. This highlights the possibility and efficiency of a combined TLCD-TMD system in which the dynamic responses are minimized efficiently in a wider selection of loading conditions. [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 This paper presents a grid-independent numerical methodology that couples the strip theory based discrete vortex method (SDVM) with the finite element method (FEM) to simulate the vortex-induced vibration (VIV) of a long flexible vertical riser. Based on the strip theory, a three-dimensional flow filed is approximately simulated by a series of computational 'flow strips'. A Lagrangian discrete vortex method is employed to numerically solve the unsteady vorticity transport equations of each 'flow strip'. The flexible riser is modelled as a tensioned Bernoulli-Euler beam with the dynamical equation solved by the finite element method in time domain. The two-dimensional DVM code is firstly validated for the VIV simulation of a rigid cylinder that was experimentally studied by Khalak and Williamson (1996). Referring to two typical experimental configurations of Lehn (2003) and Chaplin et al. (2005), the VIV of a long flexible riser immersed in a uniform and stepped incoming flow are numerically simulated, respectively. A good agreement was achieved through detailed comparisons between the present numerical prediction and the experimental data, including the structural in-line and cross-flow VIV response modes, root mean square amplitudes and the dominant frequency. The occurrence of standing and travelling wave responses, dual resonance between in-line and cross-flow motions and figure-eight trajectory are reported. The wake patterns corresponding to two response waves are also presented and investigated. Related to structural local vibration amplitude, two principle vortex patterns resembling the '2S' and '2P' modes are identified in the wake. The standing wave component of structural response determines the vortex shedding pattern. The travelling wave component affects the spanwise vortices shedding at different phases. Highlights • A SDVM-FEM coupled numerical methodology is developed to simulate the VIV of long flexible risers. • Simulation has been carried on two typical experimental configurations to validate the numerical model. • The occurrence of standing and travelling wave responses are reported. • The wake patterns corresponding to two response waves are presented and investigated. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the hydroelastic vibration analysis of clamped rectangular plates, vertically or horizontally submerged in fluid by using isogeometric finite element and boundary element methods. The method of analysis is divided into two parts. In the first part, the dynamic characteristics of the structure, in vacuo conditions and in the absence of external forces, are obtained by NURBS-based isogeometric finite element method (IGAFEM). In the second part of the analysis, the fluid-structure interaction effects are calculated by using a NURBS-based isogeometric boundary element method (IGABEM) in conjunction with the method of images, in order to impose appropriate boundary condition on the fluid's free surface. By adopting the linear hydroelasticity theory, the fluid is assumed ideal, i.e., inviscid, incompressible and its motion is irrotational. The fluid-structure interaction effects are calculated in terms of the generalized added mass coefficients. In order to demonstrate the applicability of the proposed method, two different clamped rectangular plates were adopted for the calculations. The effects of the plate thickness and aspect ratio are also investigated. The predictions compare well with available numerical and experimental results found in the literature. [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]

Abstract Over the past seven years, the capsizing of considerable bulk carriers with nickel ores in the South China Sea has made shipping industry shocked. Although a number of countermeasures have been taken by ship owners, it doesn't seem to prevent the ship accidents from happening, possibly implying that we may not yet fully understand some fundamental aspects of the accidents. Clay lateritic nickel ore is characterized by liquefaction under the influence of waves or long-time engine vibrations during transportation. However, the existing methods based on the calculation of GM (metacentric height) values fail in explaining the capsizing of the bulk carriers during shipment. Experimental investigation into the accidents shows that the blending liquid (not pure water) after liquefied is highly viscous and can generate free surface. In contrast to the prevailing theories of ship stability, this free surface may create negative influence on ship's stability, and sometimes may result in a severe consequence of capsizing. Therefore, we speculate that the viscosity coefficient may play a critical role in ship's capsizing. Here we take advantage of numerical simulations to make a thorough analysis on the physical mechanisms of capsizing. The conclusion has been drawn that the collapse of the shear force which is mainly determined by the viscosity coefficient has led to a shift of the liquefied cargo when the inertial force of the liquefied cargo is greater than the shear stress, thus causing an abrupt loss of the stability. Finally, the increasing external moments result in capsizing and sinking. This finding may be profound because it reveals a substantial relationship between the capsizing of a ship and the viscosity of the liquefied cargo which has never been described in previous literature. Highlights • Liquefaction of the nickel ores during shipment has led to numerous capsizing and sinking. • The collapse of the shear stress force may play a critical role. • Numerical simulations have demonstrated that the sloshing of the cargo after liquefied increases the heeling moments. • The collapse of the shear stress force is significantly associated with the frequency and amplitude of the ship rolling. [ABSTRACT FROM AUTHOR]

Abstract The shock absorption support of a ship is a type of welding structure for reducing vibrations. In this paper, the vibration modal and frequency responses are first analysed using the finite element method, which is helpful to obtain exciting loads and the high stress areas of the support. Then, the vibration fatigue life of the support is analysed according to the power spectral density method and Miner linear cumulative damage theory. Based on the experimentally measured welding residual stresses of the support, the S – N curves are modified. The vibration fatigue life of the support is then calculated considering the welding residual stresses, and the key areas prone to cause vibration-fatigue damage are obtained. Finally, by improving the local structure of these key areas, the vibration fatigue strength of the support is increased. The results show that the vibration fatigue failure of the ship's shock absorption support usually occurs at the places where the structure suffers from larger stresses, defects, or stress concentrations. The welding residual stresses greatly influence the vibration fatigue of the support. Consequently, the welding residual stresses must be minimized or eliminated at the key areas of the support. [ABSTRACT FROM AUTHOR]

Abstract Power flow method (PFM) is firstly applied to the structural analysis of autonomous underwater vehicle (AUV). By finite element analysis, the numerical model of AUV is established. The propulsive force of the propeller is calculated and the dynamic responses of AUV are discussed. The characteristics of power flow distribution in AUV are studied, and the optimization of AUV shape by PFM is developed. The results show that the performances of AUV's anti-vibration are improved. The present work may lay the foundation for the propagation characteristics of structural vibration power flow under the multi-source load excitations, and also provide a novel optimization approach for AUV shape. Highlights • Power flow method (PFM) is firstly applied to the structural analysis of autonomous underwater vehicle (AUV). • The distribution characteristics of vibration power flow of AUV are investigated. • The scheme of optimizing the AUV shell by PFM is proposed. • The performances of AUV's anti-vibration are improved. [ABSTRACT FROM AUTHOR]

Offshore platforms are anchored to the ocean floor using moorings to prevent excessive drifting, and these moorings need to be monitored for damage, an expensive process. Is it possible to detect a change in moorings stiffness by measuring the motion of the platform under random wave forcing? The platform's response is strongly dependent on the wave spectrum and direction of forcing, this forcing is random, and the measurements are indirect, so it seems unlikely. To examine the feasibility we examine a much simpler but analogous spring-plate-table system with table rotation mimicking wave action. We find that by using a modal analysis of the underlying system one can unscramble the plate's response and thus determine spring stiffness changes under random forcing, however, as one would expect, the forcing has to have components in an ‘active’ frequency and direction range. In principle the same type of analysis can be used for real moorings. Whilst the spring-plate-table system model was developed with moorings in mind, such fault detection issues often arise under circumstances in which direct fault detection is impossible but the basic underlying system is ‘known’. The simple spring-plate system examined here is perhaps the simplest non-trivial example of this situation. [ABSTRACT FROM AUTHOR]

Ji, Q. and Kun, L., 2018. Numerical simulation solutions for wind-induced vibration of ship rearview mirrors caused by airflow noise in shallow seas. In: Ashraf, M.A. and Chowdhury, A.J.K. (eds.), Coastal Ecosystem Responses to Human and Climatic Changes throughout Asia. The fluid–solid coupling method was used for numerical simulation of the problem of wind-induced vibration of an exterior rearview mirror caused by airflow. The finite element model was established. The fluid–solid coupling method was used to consider the process of interaction between fluid and solid. The dynamic characteristics of the rearview mirror under the coupling condition at different speeds were calculated. Experimental results show that when the vortex shedding frequency is close to the natural frequency of the rearview mirror structure, a strong vibration in the rearview mirror can result. This numerical simulation can simulate the actual situation. [ABSTRACT FROM AUTHOR]