The Research On The Exciting Load Calculation Method Of Ship Equipment Based On Bench Test

Mechanical noise is the main noise source of surface ships at slow speed,ship equipment exciting load is an important input parameter for the prediction of ship mechanical noise.For the same prediction model,forecast results will be significant differences if equipment exciting loads are different.At the same time,exciting load by the ship equipment is an important reference object for the control and optimization process of a ship mechanical noise,accurately grasping the exciting load by the ship equipment is significant for mechanical noise prediction and control of a ship.In the process of ship mechanical noise prediction and control,exciting loads of ship equipmentsare directly adopted from bench test and measurement results given by equipment manufacturers.However,dynamicboundarycondition of a equipment in the process of bench test and measurement has great difference from the one after the equipment installation to the ship,as a result,the exciting load of the equipment from bench test and measurement is different from the one to the hull structure after the equipment installed on the ship.In order to ensure the accuracy of the ship machinery noise prediction,The study on the load conversion method of equipment from bench test to ship structure is needed.This paper mainly studied the following contents:In the low frequency band the equipment and base have been simplified as rigid body in this paper,the formula of the machinery exciting force to ship structure has been deduced under the hypothesis of rigid body,and the conversion coefficient of exciting force from bench test to ship structure has been defined,the conversion method has been given;In the high frequency band,for vertical load,the method of impedance has been used,the Thevenin's equivalence theory of vibration source has been introduced,and the free speed has been used as a bridge to proposed the load conversion method.The exciting load conversion methods for vertical load in both low and high frequency band have been proved by experiment.The impedance of the base is needed in the exciting load conversion method of high frequency.The impedance of the base also plays an important role in analysis of ship load and prediction of mechanical noise,in the paper,the numerical calculation method has been combined with theoretical formula calculation method,and the full frequency band estimation method of base impedance has been presented,and the method has been proved by experiment.The influences on the calculation results of the method to applythe loads have been analyzed in the process of mechanical noise prediction in this paper.The situation that only the 1/3Oct acceleration load is given without detailed spectrum result may be met,the feasibility and accuracy of 1/3Oct load have been studied,and the error ranges have been analyzed when different methods to deal with 1/3Oct acceleration load have been adopted;The influence on the forecast result when the load amplitudes of equipment feet are different and the effect of the load's angle have been studied.