A common assumption about fluid power systems is that the outlet pressure ripple is a primary source for air-borne noise. Fluid pressure fluctuations are caused by flow ripples generated by positive displacement units that are the prime power movers in these systems. The present research aims to leverage previous efforts in the topic of noise generation in hydrostatic units, formulating a method to predict air-borne noise for a particular reference machine. A numerical model has been developed to gain knowledge on the mechanisms of noise generation in external gear machines. The simulated noise sources are then applied to the structure in order to predict the propagation of noise to the surroundings. Also, experimental activity based on an innovative method of interpretation of noise measurements is also accomplished in order to better characterize the dependency between fluid-borne noise and air-borne noise. Measurements are made of total sound power level as well as sound pressure level at representative points to better understand the acoustic performance of external gear machines at a wide variety of operating conditions.

As a key component in power transfer, positive displacement machines often represent the major source of noise in hydraulic systems. Thus, investigation into the sources of noise and discovering strategies to reduce noise is a key part of improving the performance of current hydraulic systems, as well as applying fluid power systems to a wider range of applications. The present work aims at developing modeling techniques on the topic of noise generation caused by external gear pumps for high pressure applications, which can be useful and effective in investigating the interaction between noise sources and radiated noise and establishing the design guide for a quiet pump. In particular, this study classifies the internal noise sources into four types of effective load functions and, in the proposed model, these load functions are applied to the corresponding areas of the pump case in a realistic way. Vibration and sound radiation can then be predicted using a combined finite element and boundary element vibro-acoustic model. The radiated sound power and sound pressure for the different operating conditions are presented as the main outcomes of the acoustic model. The noise prediction was validated through comparison with the experimentally measured sound power levels.

The study of displacement machines, and in particular external gear pumps has improved the understanding of the important features of operation. Applying these underlying phenomena to new design methodologies has brought new advances in quieter machines by designing for the reduction of fluid-borne noise, cavitation, and pressure peaks. The present work seeks to expand on the previous modeling and experimental efforts by directly considering the effect that design changes to the pump and to the system apply on the total sound power and the sound quality emitted from displacement machines and the attached lines. In particular, the current document focuses on efforts related to the noise propagation into hydraulic lines and out of the lines to the environment where a pump is the primary excitation of this noise.

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Noise generation in fluid power systems remains an important problem in current applications, and in the expansion of fluid power to new lighter applications such as passenger vehicles. The current research looks to understand noise generation from two main angles, experimental measurements and numerical modeling. This activity shows the experimental procedures and results towards better understanding the noise performance in the particular case of external gear pumps. Sound intensity measurements and analysis of the frequency characteristics of these machines are used to characterize the airborne noise generated. Better understanding of the key sources and transmission paths of the noise can lead to a better understanding of how to improve the noise performance from a design standpoint. The method of measuring and interpreting the noise performance of several different displacement machines is explained along with the significance of the results pertaining to the design of new quieter hydraulic solutions. This research serves the more general goal as a validation reference for modeling noise generation and propagation from the sources inside the machine and out to the environment.