Hull Vibration Research Articles

Developing a predictive method based on the vibration behavior of a naval ship hull model using hybrid fuzzy meta-heuristic algorithms

Ships are complex structures composed of various components with exclusive dynamic behaviors and natural frequencies, so assessing their vibration behavior is essential. Some situations in practical applications could alter the ship's dynamic characteristics and cause significant changes in its vibration behavior. Since the ship's mass is one of the most important dynamic parameters in determining vibration behavior, local mass change can lead to changes in its dynamic characteristics and must be considered. This study aims to develop a method to predict the effect of the location and magnitude of mass change on the ship hull's vibration behavior. It would be feasible to enhance the dynamic behavior and reduce undesirable noises by locating the mass change on the ship hull. In this regard, experimental and numerical modal analysis is performed on a scaled model of a naval ship hull. The baseline FE model is used to calculate the variation in frequencies of the model caused by different local mass change scenarios. Using these measurements a fuzzy system is generated and optimized by Genetic and Particle Swarm Optimization algorithms. Finally, the efficiency of the fuzzy-PSO is validated by different mass change scenarios foreseen on the physical model of the ship hull.

Concurrent event‐triggered adaptive neural control for MASS under cross‐water scenarios

AbstractThis article discusses the control problem of marine autonomous surface ships (MASS) under cross‐water scenarios, that is, from open water to restricted water, where several practical facts, such as uncertain dynamic, unknown disturbance and actuator wear suppression, are taken into account. To resolve such a control design challenge, the predefined performance control (PPC)‐based and barrier Lyapunov function (BLF)‐based ideas are employed, and a prespecified performance function (PPF) is designed to implement the transformation of cross‐water design. Under the adaptive backstepping design framework, with aid of PPC‐based and BLF‐based design ideas, an adaptive neural control solution is developed for MASS under cross‐water scenarios. Furthermore, to reduce the actuator wear and tear caused by high‐frequency corresponding control commands and hull vibration, a new multichannel concurrent event‐triggered protocol (ETP) is constructed in the controller‐actuator (C‐A) channel. Finally, a concurrent event‐triggered adaptive neural control scheme is proposed for MASS under cross‐water scenarios. The theoretical analysis indicates that all signals in the control system are ultimately bounded, and the Zeno behavior is avoided. The simulation and comparison results verify the effectiveness and superiority of the developed control scheme.

Finite element simulation analysis of vibration transmission characteristics of double shell based on ANSYS

Ship noise contains a large number of low-frequency line spectrum features. It is difficult to distinguish where they come from and even more difficult to identify the ship’s target types using the line spectrum. Therefore, research on ship targets’ vibration transmission characteristics and radiation noise is of great importance for underwater target recognition. From the perspective of underwater acoustic target recognition, this article establishes a simplified finite element model of the double shell using ANSYS, calculates the displacement response of the double shell under harmonic loads, and conducts modal analysis, harmonic response analysis, and transient dynamic analysis, which verifies the consistency of vibration between the inner shell and outer shell. Marine experimental data show that the low-frequency line spectrum of ship noise is related to the vibration frequency of ship main engines. It may be caused by diesel engine vibration transmitted through ship hull vibration and can be used as an auxiliary feature for underwater acoustic target recognition.

Safety Improvements for High-Speed Planing Craft Occupants: A Systematic Review

Moving fast by high-speed planing craft (HSPC) is advantageous for some special missions, though it causes severe hull vibrations and shocks that can transfer to the human body and increase health and comfort risks. This study reviews the current safety standards to avoid human safety risks affected by whole-body vibrations (WBVs), as well as the safety status of HSPC occupants. In addition, the efficiency of motion-reduction devices (trim tab and interceptor) and shock/vibration-mitigation devices (shock-mitigation seat) in improving the safety of HSPC occupants is examined according to existing documents. The research methodology was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRIS-MA) method, and published papers in the Scholar, Scopus, and Web of Science databases were analyzed. Because most of these publications are academic research, issues of bias in the eligible publications were not of particular interest. During this systematic review, many gaps and challenges in current information on safety improvement devices were found that need to be addressed in future studies, such as a lack of information on motion-reduction devices and shock-mitigation seat performance in reducing lateral and fore-and-aft motions. Referring to these gaps and challenges can be valuable as a suggestion to improve current knowledge in research and reduce safety risks.

Study on the application of vortex generator to suppress ship propeller cavitation excitation

ABSTRACT A triangular vortex generator (VG) is used to suppress the hull vibration induced by propeller cavitation in this paper. Firstly, the numerical simulation method is used to simulate the original flow field around the ship, and the high wake area caused by the separation of the flow at the stern is analysed, which leads to serious cavitation on the propeller and induced hull vibration. Then, the effects of the installation angle and position of the VG on the wake of the ship are analysed, and the appropriate design parameters of the VG are obtained. Through the numerical simulation of cavitation on the propeller, the effects of VG on cavity shape and hull fluctuating pressure induced by cavitation are analysed. The VG can improve the non-uniformity of wake field, delay cavitation generation, and weaken the cavitation on the propeller tip area. The maximum reductions of the first, second, and third harmonics of fluctuating pressure are about −41.2%, −36.6%, and −78.5%, respectively. Finally, the vibration of each cabin of the full scale vessel is significantly reduced after the installation of the VG, especially in the cabin near the propeller. The reduction range is up to −54.5%, and a good vibration reduction effect is obtained.

Reliability Analysis of Crack Growth Occurrence for a Secondary Hull Component due to Vibration Excitation

Abstract Ship hull vibration is a significant contributor to fatigue crack growth and the major sources of vibrations are found to be the main engine vibration excitation, the wave-induced springing and whipping loads, and the action of the propeller. In the midship region, wave-induced loads and the main engine are the major contributors, whereas propeller excitation dominates in the aft region of the ship hull. No general method exists to solve all kinds of vibration problems and they need to be evaluated through a cost-by-case approach. The complex and uncertain aspects of hull vibration and fatigue crack growth motivate the need for a reliability-based scheme for assessing the resulting fatigue crack propagation. In the present paper, a probabilistic formulation for the failure probability of the occurrence of crack propagation of a secondary hull component is outlined. A generic cargo hold model is analyzed with engine excitation and wave-induced loading as vibration sources, and a stochastic model for vibration response is outlined. The limit state is formulated as the possible occurrence of fatigue crack growth. The secondary hull component considered is a pipe stack support, which is a supporting component that attaches the cargo pipes to the wall inside a cargo tank. Different initial crack sizes are implemented to evaluate the adequacy of the applied stochastic model for vibration response and the accuracy of the estimated failure probability is assessed.

Investigation on Lateral Vibration Transmission Control of a Shaft-hull System with a Piezoelectric Actuator Support

A piezoelectric actuator support (PAS) is proposed to suppress lateral vibration transmission from the shaft to the hull of underwater vehicles subjected to the excitation of propeller forces. The PAS consists of eight rhombic structures with embedded piezoelectric actuators and is arranged between the stern bearing housing and the hull. The dynamic model of the shaft-PAS-hull system is developed to analyze the characteristics of power flow through the PAS. The suppression performance of acoustic radiation of the hull is analyzed to verify the effectiveness of the PAS. Numerical results have shown that the PAS is able to suppress the transmission of lateral vibration induced by the propeller forces and accordingly reduce the hull vibration as well as sound radiation.

Numerical analysis of wake field and unsteady forces on submarine propeller with twisted rudders

A twisted submarine rudder was designed to reduce the unsteady force on and improve the propulsion efficiency of the propeller. The twisted rudder not only switches the wake in the pre-rotation state in the direction opposite to the propeller rotation but also increases the mismatch between the circumferential phase-angle distribution characteristics of the wake peak and propeller profile at each radius. To investigate the influence of this rudder on the submarine's flow field and the propeller's hydrodynamic performance, the shear stress transport (SST) k−ω turbulence model was used to calculate and compare the resistance characteristics and flow field at the aft of the submarine without a propeller when the ordinary and twisted rudders were installed, as well as the wake field of and unsteady force on the propeller with the propeller. The circumferential velocity in the propeller wake was significantly reduced, and the propulsion efficiency was improved by approximately 7.31%. In addition, the pulsation amplitude of the unsteady force was significantly reduced. The main blade-passing frequency (1BPF) amplitudes of the force and torque decreased by more than 40% and 35%, respectively, which significantly reduced the hull vibration caused by the unsteady force on the propeller.

Теоретическое исследование стабилизатора вибрации с обратной связью по интегралу смещения для энергетического оборудования

Reducing the vessel hull vibration caused by the power equipment is usually obtained by the effective vibration-isolating fastening. Vibration impact on the mechanisms and automation tools greatly reduces their reliability, affects the health of passengers and crew members. Despite the modern vibration-insulating materials and compensators, the problems of eliminating the variable forces transmitted from the vibration source have not been fully solved. Increasing the operational requirements for the vibration safety of water transport requires the scientifically based and technical solutions, improving the designs of vibration isolation supports for mounting the marine power plants. Vibration reduction problems must be solved both at the design stage and at the stage of construction, repair and modernization. The conducted studies of vibrations under the influence of the harmonic force, step load and gradually increasing load have shown high efficiency of the support in all cases of load application under different simulation modes. At stabilization of the position the support was controlled by the integral of the displacement. The results of the studies conducted on the test model for the vibration protection of marine power equipment showed the effectiveness of the stabilizer. There is presented a theoretical study of a stabilizer with feedback on the displacement integral in the MathCAD software package. The numerical experiment is based on the Newton equation. The parameters of the stabilizer are determined, on the basis of which it is possible to design the actuator. It can be an electric motor, the direction of rotation of which depends on the direction of displacement of the protected object. The motor rotates a screw pair that compresses the spring. The spring acts on the clutch, the torque changes and maintains the vibration source. The simulation results helped to infer that it is necessary to stabilize the position of the unit for all load application modes.

Nonlinear seakeeping and hydroelasticity of ships using potential flow simulations

ABSTRACT Accurate predictions of the behavior of ships in steep regular waves or in a natural seaway must take into account nonlinear wave responses, especially for roll motions, section moments, and hull vibration excitation. In contrast to CFD methods, here fully nonlinear seakeeping simulations are presented based on potential flow with empirical corrections. This reduces the computing effort by several orders of magnitude. Comparisons with other calculations and model experiments for benchmark cases show that the accuracy of the present method is not worse than that of the best other computations and model experiments. After about ten years of development, the method appears mature for routine applications. The source code of the program is available from the author if an adequate gift is donated to the Mèdecins Sans Frontières.

Analysis of the Underwater Radiated Noise Generated by Hull Vibrations of the Ships.

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.

Development of a reliability model for crack growth occurrence for a secondary hull component

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.

Influence of the Numerical Modelling Methods on Dispersions and Errors of Analysis Results of Ship Hull and Deckhouse Vibrations

Abstract Ships’ (especially containers) vibrations significantly impact navigation safety. The presented analyses aims to identify the main forces exciting the ship’s superstructure and hull vibrations, test their influence on vibration levels, and verify the assumptions of the computational methodology. Two container ships were analysed. The influence of different modeling methods on the obtained calculation results was investigated. The impact of various operating parameters on the vibration level was also analysed. The numerical analyses results are compared with some empirical formulas. As a result, the calculation confidence level was estimated. The calculation results have been verified by comparison with measurement tests carried out on the real ship.

Research on acoustic reconstruction methods of the hull vibration based on the limited vibration monitor data

The prediction of hull vibration response is the basis for the quantitative control of cabin noise and underwater radiated noise, which has an important engineering value to obtain vibration characteristics accurately. In this paper, a new method is proposed to reconstruct hull vibration by some monitoring data in low frequencies. The hull vibration response is reconstructed by the monitoring data and the transfer function, and the ill-posed problem of inversion for the transfer function matrix is solved by the total least-squares regularization. A P-GRU (Peak-based Gated Recurrent Unit) neural network correction model is proposed to improve the prediction accuracy of vibration response. Taking a certain cabin structure as an example, some research such as the hull vibration data monitoring, the vibration transfer function calculation, vibration response reconstruction, and correction based on experimental data were carried out, and the simulation calculations and verification of experiment models were obtained. The multi-parameter comprehensive method is adopted to quantitatively evaluate the results between the simulation and the experiment. The results show that the acoustic reconstruction results are in good agreement with the experimental data. The overall level error is within 3 dB, the main peak value correlation coefficient is above 0.9, and the main peak difference is within 4 dB. The mechanism of the rapid and accurate prediction of the low-frequency vibration for the hull based on limited monitoring data is discussed by using a semi-physical simulation method combining the simulation calculation, vibration monitoring, and machine learning. The problem of phase asynchrony was solved, and strong support was provided for the construction of the ship's acoustic digital twin.

Fast average prediction method based on the upper -lower limit theory for ship’s mechanical noise

The equipment loads include acoustic excitation and mechanical excitation which is characterized by acceleration, and a reliable prediction method of mechanical noise is important to control the hull vibration noise and improve the accuracy of hydroacoustic detection. To address the issue, an accurately and efficiently predicting method is proposed and verified by the hydroacoustic experiments which included the three different diesel engine working conditions. In the method, for the acceleration loads with complete information, an equivalent load model and a gradient meshing model are used to identify the generalized forces, and the mechanical noise is predicted by the identified load and acoustic BEM. For the acceleration loads with missing partly information, the interval theory and the energy superposition method are introduced to calculate the mechanical noise, and the upper-lower limit theory and the average method are proposed to determine the range of mechanical noise and average value. The effect of acoustic excitation generated by diesel engines on mechanical noise is also discussed in detail. The results of hydroacoustic experiments show that the identified forces and mechanical noise can be obtained by the present method, with an error nearby 1 dB, under the accelerations with complete information. For the average acceleration, the range of mechanical noise is obtained and the average sound power is used to represent the ship's mechanical noise, with an error of less than 3 dB. The experimental results also reveal that the effect of acoustic cavity resonance should be included in low frequencies.

A Composite Method of Marine Shafting’s Fault Diagnosis by Ship Hull Vibrations Based on EEMD

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.

Numerical method to determine the cavitation inception speed of a submarine propeller based on the noise obtained from bubble dynamics

Cavitation is accompanied by increased hull vibrations, reduced propulsion performance, and increased radiated noise. This can be particularly fatal for warships and submarines. Hence, navies worldwide introduced and managed a propeller performance index called cavitation inception speed (CIS). Among the many types of propeller cavitation, the first to occur is tip vortex cavitation (TVC). In this paper, the CIS decision procedure of TVC is presented via numerical analysis in terms of noise, which is the most prominent characteristic of cavitation inception. For the CIS decision, the cavitation noise from the propeller is obtained from bubble dynamics. Cavitation is simulated with cavitation nuclei, and the input data for nuclei is obtained from computational fluid dynamics (CFD) simulations. The noise from each nucleus was modeled with a monopole assumption. Additional impulse noise due to the bubble's implosion is used as the basis for the CIS decision. The usefulness of the proposed procedure is demonstrated by applying it to three propeller geometries with different skew and rake angles. Additionally, various aspects, such as propeller stern vortex and added mass, are analyzed; the results are consistent with the CIS simulation results for each propeller.

PROPELLER CAVITATION AND INDUCED VIBRATION

The demand to increase the efficiency of propellers has led to optimized propeller blade designs finding their way into the construction of high-powered commercial vessels, such as containers or LNG carriers and certain categories of passenger vessels, to mention but a few. It has become increasingly common to see the propeller tip rotate closer to the hull surface, sweeping the thick turbulent boundary layer attached to the hull, causing fluid structure interaction. At the same time, increasing the loading on marine propellers can lead to problems, such as noise, hull vibration, and cavitation. The degree above which, such phenomena as propeller cavitation can be the main perpetrators for intensive vibration during operation, their diagnosis and the solutions to mitigate this risk, such as the use of vortex generators, are discussed here, taking into account cost and longevity of the vessel as well as the involvement of classification rules.

Research of Vibrations of an Armoured Personnel Carrier Hull with FE Implementation

Modern wheeled armoured vehicles can perform a variety of tasks, making the development of weapon systems that can be safely and effectively integrated with the vehicle structure an area of interest. Due to the cost of implementing new models, it is more economical to test potential configurations using numerical methods, such as the finite element method. The numerical model has been validated to confirm the reliability of the obtained results. Modal tests were also performed using four configurations to identify the frequency and mode shape of natural vibrations occurring within the support structure. In an experimental setting, hull vibrations were forced using the modal hammer testing method. The modal assurance criterion (MAC) and the authors’ procedure were used to confirm the experimental and numerical test results. Additional testing in the form of impact loads was carried out for turret-containing structures. Structural strain at indicated points and forces transmitted by brackets to the bottom of the hull were compared.

Cavitation and Induced Excitation Force of Ice-Class Propeller Blocked by Ice

The presence of broken ice in the flow field around a propeller causes severe blade erosion, shafting, and hull vibration. This study investigates the performance of the propeller of a ship sailing in the polar regions under the propeller–ice non-contact condition. To this end, we construct a test platform for the propeller-induced excitation force due to ice blockage in a large circulating water channel. The hydrodynamic load of the propeller, and the cavitation and propeller-induced fluctuating pressure, were measured and observed by varying the cavitation number and ice–propeller axial distance under atmospheric pressure and decompression conditions. The results show that the fluctuation range of the blade load increases with a decrease in cavitation number and ice–propeller axial distance. The decrease in the cavitation number leads to broadband characteristics in the frequency-domain curves of the propeller thrust coefficient and blade-bearing force. Under the combined effects of ice blockage and proximity, propeller suction, the circumfluence zone around the ice, and the Pirouette effect, propeller–hull vortex cavitation is generated between the ice and propeller. The decrease in cavitation number leads to a sharp increase in the amplitude of the high-order frequency of the propeller-induced fluctuating pressure.