Sound radiation at the nozzle of a pipeline system and noise reduction based on a non-anechoic pool

Abstract

Ship noise comprises mechanical noise, propeller noise, and hydrodynamic noise. The development of technology for reducing vibration and noise means that the noise of a ship’s propeller and that of its main and auxiliary engines are now controlled effectively, leaving the sea pipelines as the main source of noise. Therefore, it is very important to investigate how to measure the acoustic radiation at the nozzle of a pipeline. In this paper, a bench pipeline test system is established in a non-anechoic pool, and a method for measuring in the non-anechoic pool is proposed to solve the problem that when measuring directly in the pipeline, the results are distorted by the flow. By inserting the nozzle of the bench pipeline test system into the non-anechoic pool, the radiated sound power of the nozzle of the pipeline system is measured in different frequency bands by using a combination of near-field direct measurements and far-field spatial averages. The above measurement method is used to evaluate the effects of different noise sources in the pipeline system, given that they work independently of each other. The research results show that (i) this method can measure accurately the noise radiated at the nozzle of a pipeline system, (ii) in the pipeline system, the main sources of noise are the pump and the structural vibration that it generates, and (iii) the noise radiated at the nozzle of a pipeline system can be controlled effectively by replacing straight pipelines with hoses and reducing the number of pipeline components such as elbows.