Research On Structure Acoustic Radiation Optimization And Application Based On Wave Superposition Method

The noise pollution is rising sharply with the development of science,technology,industrial modernization,and it is harmful to people’s physical and mental health.The acoustic radiation optimization design for the radiator source is the most effective mehod to control noise level.The radiation impedance resistance which is decided by the structure surface shape represents the ability of radiation sound power,so it is an effective method to reduce sound power emission by shape optimization.Based on wave superposition method,a new method named additional source wave superposition method is presented to overcome the non-uniquniess problem of pressure in the critical wave number.The radiation impedance resistance matrix which represents the radiation ability is derived and computed based on wave superposition method,and the radiation resistance testing equipment is also designed to verify the theoretical calculation results.A new acoustic shape optimization method which chooses the radiation resistance as objective function is presented and used to optimize the 200 kW motor sound power radiation.Main research works include these as below.(1)The problem of non-uniqueness for critical wave numbers will be encountered when the filed pressure is computed by using the monopole wave superposition method.The additional sources wave superposition method is a method by adding additional sources inside the radiator based on monopole wave superposition method,which could overcome the problem of non-uniqueness.The relative error of volume velocity is considered as objective function and the location of sources is optimized when the pressure field is computed by using additional sources wave superposition method.(2)The sound experiment platform of rectangle plate is designed.The sound pressure of testing is compared with the result of wave superposition method.The radiation sound pressure of the experiment platform is compared with the result of the finite element method and wave superposition method under the condition of the same exciting force amplitude.The acceleration of the platform with the same exciting force is tested and achieved to be used to the input of wave superposition method,then the computed result of sound pressure is compared and verified with the testing result.(3)This thesis calculates structure acoustic radiation resistance with the relationship of field pressure,source amplitude and normal velocity of boundary surface based on wave superposition method.The radiation resistance computing program is derived.The radiation resistance testing equipment is designed according to the concept of radiation resistance.The point sound source is simulated by using a loudspeaker sealed the back side.Then the volume velocity of the point source is calculated by the designed calibrator.The point sound pressure wich is exciting by the point source is tested,then the radiation resistance is computed.Then the theoretical radiation resistance of typical structure is computed and verified by experiment testing.(4)By choosing the resistance impedance as design objective,a shape optimization method of structure which could solve the problem of parameterized modeling and sound power calculation is presented.The structure surface shape is restructured with mode shapes superiposition,the problem of computing the sound power for acoustic optimization is avoided by choosing the resistance impedance as design objective.By using genetic algorithm,the weight coefficient of each mode shape is optimized to get the surface shape with minimum sound power radiation.(5)The 200 kW induction motor’s nonlinear component such as bolt joint surface,antifriction bearing,stator and rotor core winding are complicated to build the model.By using VDI2230,the bolt joint surface is built and the antifriction bearing is also modeled by using spring and damp based on Hertz contact theory.The stator and rotor is equivalent with the solid element.Then the 200 kW induction motor’s model is verified by comparing the modal analysis result and modal testing result.(6)The vibration response and sound pressure radiation under rated operating condition is simulated with the accurate finite element of the motor and the strongest radiated panel of the motor is located.By choosing the resistance impedance as design objective,the panel is shape optimized to minimize the motor’s radiation sound power.In brief,the problem of non-uniqueness for critical wave numbers of wave superposition method is overcomed by adding additional sources,and then structure acoustic radiation resistance is formed and veried by using resistance testing experiments.By choosing the resistance impedance as design objective which could avoid the problem of computing the sound power again and again,a shape optimization method is used to optimize a 200 kW motor radiation sound power.The shape optimization method could be used to the other applications.