# Performance Research and Optimization of Sound Insulation Hood of Air Compressor Unit
## 1 Introduction  
The noise control of a compressor has always been a hot spot in the field of industrial application. Researchers have carried out comprehensive studies on the noise problem of compressor from various aspects, such as the cause of air compressor noise, noise transmission path [1], noise control method, and so on. In order to solve the noise problem of compressors, many scholars have conducted extensive theoretical and experimental research on the mechanism of noise induction. [PERSON] et al. [2] comprehensively measured the vibration and noise of a screw compressor. [PERSON] [3], [PERSON] [4], and [PERSON] [5] conducted theoretical and experimental analysis of the noise and vibration caused by pressure oscillations in the suction and discharge chambers caused by intermittent gas flowing through the suction and discharge ports of a compressor. Subsequently, [PERSON] et al. [6] measured the sound intensity of the main noise sources of a compressor and determined that the motor and inlet air pulsation were the main noise sources. In addition, [PERSON] et al. found that the amplitude of discharge airflow pulsation of a screw compressor was related to the shape of the discharge cavity [7, 8]. After determining the causes of air compressor noise, many scholars have also studied and analyzed the noise caused by pressure pulsation in a compressor. [PERSON] et al. [9] investigated the airflow pulsation produced by the discharge process of screw compression and conducted an in-depth study on the mechanism of airflow pulsation noise, which provided a theoretical analysis for reducing the airflow pulsation noise of screw air compressorand important guidance for the improvement of noise reduction measures in engineering application. [PERSON] et al. [10; 11; 12] analyzed vibration and noise induced by unsteady flow inside a centrifugal compressor. A weakly coupled fluid-structure-sound method and extrapolation techniques were combined to simulate the multi-physics fields of internal flow, structural vibration, and external noise. In addition, [PERSON] et al. [13] conducted experimental research on the pressure pulsation of a twin-screw refrigeration compressor and tested the pressure pulsation energy at different radial positions of the screw shell, the pressure pulsation energy in exhaust chamber, and the energy transmitted to downstream components during operation. At the same time, in order to reveal its influence on the pressure pulse kinetic energy of a twin-screw refrigeration compressor, the effects of different oil parameters on the pressure pulse kinetic energy of the twin-screw refrigeration compressor were studied. The results showed that the flow and injection position had a great influence on the pressure pulsation. The noise emitted by the noise source in an air compressor propagates through the medium, resulting in noise pollution. Many scholars have studied the effect of noise reduction through vibration reduction. The principle is to reduce the vibration amplitude of the compressor through some vibration control methods, thereby reducing the vibration and noise [14]. [PERSON] et al. investigated the noise of a fuel injection screw compressor [15], and the method of synthetic wave was used to study the meshing between screws. [PERSON] found that the natural frequency of the muffler itself affected the noise suppression effect by studying the muffler of a dry air compressor [16]. The effects of inlet geometry on performance, surge margin, and noise emission of an automotive turbocharger compressor were also investigated [17]. [PERSON] et al. [18] proposed a typical passive noise reduction method for screw compressor noise with prominent low-frequency components.