Cabin Noise Prediction And Control Of Multi-purpose Offshore Carrier

With the “Ship noise level rules” to be carried out as the compulsory requirement,the cabin noise level has become an important admittance of ship classification.However,cabin noise prediction is the premise of the noise control,it's very important to acquire the accurate result.In order to make multi-purpose offshore carrier fulfill the newly revised cabin noise standard,it need to predict the cabin noise in the whole frequency,this thesis devides the predicted frequency into three parts,as low,middle and high,distinguishes these different solve methods into finite element analysis,FE-SEA hybrid analysis and statistical energy analysis.In addition to evaluate the noise level by ship noise level rules,this paper focus on the sound source researches,provide proper noise reduction measures with some sound absorbing material,the main wooks are described as below:Firstly,vibration-acoustic couping finite element method and hybrid-method are respectively described with the dynamic response equations.Moreover,based on numerical analyses,the reason of time consumption is explained when using hybrid-solver to caculate large complex system's response,so it comes to be necessary to simpfy the model.The keypoint is applying N-subsystem couping model to illustrate the energy balance equation.The measurements to quantify the modal density,damping loss factor,couping loss factor and input power are stated in detail.In order acquire the accurate geometry model,refer to CAD drawing of multi-purpose offshore carrier,a more universal ship-modeling method is proposed.By the way,two kinds of models with different simplifications are also offered.Following,the whole ship SEA model is established from above-mentioned detail SEA parameters,and the solving frequency is devided by the same time.Then,according to comparative analysis between the two SEA models,the simplified model is lagical and could be used to predicted cabin noise by hybrid method.In the low frequency,engine compartment located in the bow and cabins of stern are selected as research objects,and separated predictions are given based on finite element theory.Apparently,these low-frequency results has less effect on the sound pressure level compared the other frequencies,so low-frequency prediction can be neglected in other cabins' caculationes.Subsequently,noise contribution is investigated in both engine compartment and central control room.Noise transmission path analysis is also considered from noise-vibration temperature and entropy,a practical operation method is provided by VAone software.Finally,combining with prediction results,cabin noise evaluation is made by IMO noise level.Next,three different types of steady-state sound fields are respectively given physical descriptions,it aims to instruct that the concrete condition of room soubd field is determined by wall surface average sound absorption coefficient.Afterwards,a series of different measuring method presented,among which transfer function method is highlighted,both theory and devices are introduced by the way.The laws on sound absorption property are concluded by the measuring results of four different kinds of material.The research focuses on the determination accuracy of sound absorption coefficient when adding needles in melamine foam,and analysises the resonant frequency of perforated plate with back cavity,compares the difference between determination and empirical equation.Lastly,the bow-cabins with noise control requirements are regard as objects,studies on the noise source in both contribution and decay fields indicate the direction of noise reduction.Based on the insulation requirements and deck accessories,the detail noise reduction projects are put forward.