Research On Vibration Energy Characteristics Of Machinery Medium-low Frequency Excitation In Coupling Interface

The ship structural vibration will lead to its noise radiation,and the noise caused by high-frequency vibration will decay faster during the transmission process,and it will be easier to be controlled.The vibration wave caused by low-frequency excitation have long wavelength characteristics,and it will spread long distance which affect the stealth of the ship.At present,the traditional vibration and noise reduction measures have basically reached the limit.The research on vibration energy is an exploration of the vibration transmission mechanism and it has become a key to solve the vibration problem.Therefore,the study of structural vibration energy characteristics under medium-low frequency excitation has important guiding significance for the vibration and noise reduction of ship.In this paper,the finite element method combined with two-dimensional power flow analysis method is used to simulate and perform the test of vibration energy characteristics of the typical plate structure of the ship,and the effects of different vibration reduction measures on the energy transfer of the typical ship base are analyzed.Based on the objective function of minimum input power flow,topology optimization of structure is performed.The main contents include:(1)The finite element model of the coupled plate structure is established,the modal simulation and test of coupled plate structure are carried out.Results show the error between simulation and test in the frequency range of 20~400 Hz is within the acceptable range;The in-plane and out-of-plane vibration characteristics of the coupled plate structure under medium-low frequency excitation show that the peak frequencies of the in-plane and out-of-plane vibration correspond to the natural frequencies,and medium-low frequency excitation in frequency range of 20~400 Hz is more likely to provoke the bending mode.(2)Based on the harmonic response calculation results,the vibration energy input,distribution,transformation and transfer characteristics of the coupled plate are analyzed,and the vibration energy characteristics of the coupled plate under different influencing factors are compared.The results show that the bending wave is the main waveform of the energy carried in the frequency range of 20~400 Hz.As the frequency increases,the difference between the energy carried by the longitudinal wave and the shear wave and the energy carried by the bending wave is gradually reduced,which cannot be ignored in the calculation of vibration energy.In the engineering,the input power of the structure can be reduced by reducing the excitation force,increasing the thickness of the plate where force acting or increasing the damping,and at the same time,selecting a suitable equipment installation position,structural improving in the vibration energy transfer intermediate plate is also effective measures to reduce energy transfer.(3)The energy characteristics of a typical base of a certain type of ship under medium-low frequency excitation are analyzed,and vibration energy transfer characteristics of the base after laying constrained damping layer and the additional damping mass are compared.The results show that the constrained damping layer laid in the cross-section plate has best effect on reducing the transmission power flow,and the additional damping mass can effectively reduce the power flow transfer rate,at the same time,the influence of waveform conversion in the frequency range of 325~400 Hz is obvious.(4)The vibration power flow of the coupled plate was measured by dual acceleration sensor.The test was evaluated in the case of free boundary and boundary coverage of nitrile rubber.It is found that the power flow measurement under the excitation at the natural frequency is more consistent with the simulation result than power flow under the excitation at non-natural frequency.The method of simulate the cutoff boundary with nitrile rubber adhering boundary has certain effects,power flow reflected in the boundary area is significantly reduced.(5)Based on the objective function of minimum input power flow,the topology optimization of the coupled plate is carried out based on OptiStruct,and the structural topological configuration under different excitation frequencies is analyzed.It is found that difference in cell density of topological configurations under natural frequency excitation is largest,and redesigned structure based on optimized topological configuration can reduce the power flow of the lower base plate of the coupled plate while reducing the input power flow.