Vibration Reduction Technology Research Of Marine Power Machine Based On Mass-spring System Dynamic Modification

Power plant is the main vibration noise source of ships.The implementation of new IMO regulations required that the ship cabin noise needed to be reduced by 5dB(A)from July 2014.Reducing the vibration of the ship’s power plant is an indispensable part to reduce the ship’s vibration and noise.The main engine(diesel engine)and auxiliary power generation are both the most important power source of ships,and also the largest source of the vibration.Vibration characteristics of diesel engine are strong line spectrum,and high energy which consentrate in low-frequency.Additional dynamic vibration absorber and adjust the stiffness are the vibration reduction common methodes for the diesel host and its shaft torsional vibration and diesel auxiliary equipments.The traditional design method of dynamic vibration absorber and traditional mass or stiffness matching method of shaft coupling ordinarily adopts direct problem method,which always needs to be computed repeatedly because of the difference between the results and the targets,resulting in the heavy workload and long design period.In this paper,the inverse problem idea of structural dynamic modification is proposed,exploring a design method by adding multiple dynamic absorbers based on several design targets(natural frequencies and its vibration modes)and a method of matching mass and stiffness parameters of the shaft coupling.Besides,in order to meet the dual needs of vibration isolation and shock suppression,a vibration control system with its control strategy based on semi-active vibration absorber is developed in this paper.The main contents are as follows:Firstly,a dynamic vibration absorber optimal design method based on dynamic receptances data was developed,which combined the inverse problem optimization theory based on structure receptances data and the needs for optimizing vibration characteristics of marine power machinery.The natural frequencies required and the corresponding vibration modes are the design goal in this method,and the method proposed is based on the system test data of receptances and not changes the original functional design by adding mass-spring systems(dynamic vibration absorbers)to the original structure.A set of structural optimization methods by adding multiple additional dynamic vibration absorbers was developed through solving the optimization problem to acquire the system configurations.The method is particularly suitable for situations in which the mass and stiffness parameters are difficult to obtain.The optimal problem of multiple dynamic design objectives is established through setting up a numerical experiment,and the effectiveness of the proposed method was verified by comparing with results of an internationally recognized method which modifies the original structure.Secondly,a structural optimization method based on shaft receptances data is developed.The natural frequencies and vibration modes of the shaft system are designed as the optimization targets in the method proposed.Combined with the test method of shafting torsional receptances,the method proposed overcomes the problem of accurate data source.The optimum coupling configuration of the mass and stiffness parameters are solved by the optimization method.After further theoretically deducing,a modified calculation method of shafting system is developed which the data demand greatly reduced.A numerical experiment was carried out to optimize of the propulsion shaft model in this paper.The results showed that the method could accurately configure the system parameters,and accurately achieve the requirements of modifying natural frequencies and modes,which proved the effectiveness of the method.The vibration isolation system of diesel auxiliary equipments is aimed to effectively isolate high-frequency vibration and attenuate spectral-characteristic vibration in peacetime,and there is also a demand of quickly absorb the energy to protect devices after the impact of external shocks.In another word,it is to control the vibration in peacetime and resist the shock during impacting.This paper develops a new method to modify the structure by adding a semi-active dynamic vibration absorber,in the usual vibration damping period,which is mainly for control the low-frequency line spectrum vibration of diesel engine;and once the system suffering an external sudden shock,the absorber changes strategy to absorb external impacting energy.In this paper,an online adjustable mass-spring system is designed and developed,which is a new type of electromagnetic beam-shape semi-active vibration absorber.The structure and electromagnetic characteristics of the semi-active vibration absorber were analyzed by finite element method,and a real model device is designed and machined.Moreover,a experiment was setup.The frequency response of the semi-active vibration absorber is tested by "sweep" excitation in the experiment,and the vibration absorption characteristics of the system under steady-state excitation are also tested.The experimental results showed that the design of the new semi-active vibration absorber has the advantages of stiffness online adjustment,fast response and stable operation.In order to effectively absorb the transient energy of external shock,especially for marine diesel auxiliary equipments vibration isolation devices which often have a large residual impact response or even occur the of the secondary impact,a semi-active shock control strategy based on on-line adjusting stiffness is proposed.For the shock occur duration,the strategy adjusts the absorber’s stiffness to the best impact-resist stiffness value and reduces the peak response value.For the residual vibration,the stiffness switching strategy is adopted to make the residual response fast decay.The numberical system model and compiled the simulation program were established,the simulation results showed that the control strategy proposed can effectively suppress the primary shock peak response and its residual response.An experimental was established to test and verify the impact residual response decay control strategy,which the experimental results showed the feasibility and effectiveness.