| Ship piping system has various functions,various types and wide distribution,which plays an important role in the normal operation of the ship and the normal life of the crew.However,the piping system also produces noise while working.Pipeline noise not only affects the physical and mental health of crew members and damages the machinery and equipment on board,but also seriously affects the lives of port residents and underwater creatures in the river and sea.For military ships,pipeline noise reduces the safety and stealth performance.In this paper,the computational fluid dynamics software Fluent and acoustic software Virtual.Lab are used to calculate ship pipeline system elbow noise,based on acoustic boundary element method.The control methods of elbow noise are studied.In this paper the following work has been done:(1)This paper states the theory and equation of pipeline noise,including the turbulence model and the theory of sound analogy.The characteristics of theoretical calculation,model test and numerical calculation method are analyzed.Then the numerical simulation method of elbow noise calculation is determined.Firstly,flow field calculation is carried out in Fluent software to output pipe wall pressure results,which are used as sound source in Virtual.Lab software.The acoustic calculation of the monitoring point of the elbow outlet is finished based on the acoustic boundary element method.The result shows that the noise of the elbow outlet has broadband characteristics and the noise is relatively high in low frequency band.By comparing the results of model test and numerical calculation,the reliability of numerical calculation method is verified.(2)The influence of the cross-section radius,section form,inlet flow and bend angle of the pipe on the noise of the elbow outlet is studied.The flow field and pressure of the elbow noise are analyzed and the frequency spectrum characteristics of one-third octave band sound pressure level at the monitoring point of the elbow outlet under different factors are compared.The results show that the flow velocity near the inner wall increases while the flow velocity near the outer wall decreases.In the back straight section of the elbow,the flow velocity near the inner wall begins to decrease while the flow velocity near the outer wall increases.The pressure near the inner wall of the pipe decreases while the pressure near the outer wall of the pipe increases.The pressure at the front straight section of the elbow is larger than that at the back straight section of the elbow.When the flow rate remains constant,the noise of elbow pipes outlet decreases with the increase of section radius,especially in middle and high frequency band.When the cross-section is round,the noise is smaller than that when the crosssection is square,especially at low frequency.The spectrum characteristics of the sound pressure level at the monitoring points under different inlet velocities are similar.When the inlet velocity increases,the noise of the elbow outlet increases,especially in the middle frequency band.The increase of bend angle leads to the increase of elbow outlet noise.(3)The noise reduction effect of damping materials and elastic supports on the noise of elbow pipe is calculated.The influence rule of damping materials with different Young’s modulus,loss factor and thickness and elastic supports with different stiffness and installation position is analyzed.The results show that laying damping materials and installing elastic supports can reduce the elbow outlet noise.The noise reduction effect gets better with the increase of Young’s modulus,especially in low frequency band.The noise reduction increases as the loss factor and thickness of damping material increases.At low frequency band,increasing the stiffness of elastic supports can improve the noise reduction effect of installing elastic support on elbows.The noise reduction effect of installing elastic supports near the bend section is better. |
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