“Taking the straddle monorail as the research object, the SEA noise prediction model of the monorail was established by using the statistical energy method software VA One, and the equivalent sound insulation treatment was adopted for the hollow aluminum profiles, and the ideal noise source was used as the load for the noise source. The main noise source was found out by predicting and analyzing the noise inside the vehicle. At the same time, the acoustic package was loaded on the whole vehicle, and the noise reduction effect was predicted and analyzed, which provided guidance for the subsequent noise reduction design and the development of low-noise monorail vehicles. and suggestions.
With the continuous development and progress of the economy, rail trains have become the main means of transportation in many cities due to their advantages of convenience, punctuality, speed, low pollution and low energy consumption, and constitute an important part of urban transportation development. Straddle-type monorail is favored by people because of its strong climbing ability, small turning radius, small footprint, low cost, fast and convenient, and environmental protection. With the large-scale application of urban rail trains, its noise problem has attracted more and more attention, and it is also a key indicator that affects its market competitiveness.
1. Establishment of calculation model and simulation calculation analysis
1.1 Establishment of SEA model
The vehicle model is reasonably pre-processed by relevant pre-processing software, and then imported into the statistical energy method software VA One. According to the basic assumptions and modeling principles of the statistical energy analysis model, the symmetry of the vehicle and the simulation of Statistical energy analysis (SEA) model was established.
In the process of establishing the vehicle SEA model, it is necessary to carry out reasonable subsystem division first.When building the vehicle model in VA One software, the modal similarity group method is used to simplify the vehicle model. The vehicle body structure is simulated by the flat panel and single-curved panel subsystems, and the body aluminum profiles are treated with equivalent sound insulation, including the roof, side walls and floor. The sound field environment inside and outside the car is simulated by the three-dimensional acoustic cavity subsystem, and the external acoustic cavity subsystem is connected with semi-infinite fluid to simulate the external sound field environment without reflection.
1.2 Sound insulation performance parameters of vehicle SEA model and loading of noise excitation
During the operation of monorail trains, the main noise sources are powertrain parts (including motors and brake discs, etc.), air-conditioning units, etc. According to the actual load of the monorail train, in the process of establishing the vehicle interior noise prediction model, the main loads are: the noise excitation of the powertrain area and the noise excitation of the air-conditioning unit above the roof. The loading method is to use the ideal noise source to load the sound cavity at the corresponding position of the bottom of the car body and the top of the car body.
1.3 Calculation Results and Analysis of Main Contributing Noise Sources
The above model is for the case where no acoustic package is added to the whole vehicle. After adding the excitation load, the sound pressure level of the driver’s cab and passenger compartment is calculated. Since the load is an ideal noise source, the calculation results are only related to the test results in the lateral direction. Compare and guide. The sound pressure level in the driver’s cab is higher than that in the passenger compartment.
In order to find out the contribution of the subsystems that directly provide energy input to the noise inside the vehicle and the contribution of related subsystems to the noise at the target observation, before adding the acoustic material, the sound power contribution of the acoustic cavity subsystem at the target observation is calculated and analyzed to find out The main noise transmission path, so as to carry out noise reduction processing on the target observation.
Figure 1 shows the main energy input histogram of the acoustic cavity subsystem in the passenger compartment of the head car. It can be seen from the figure that the main energy of the acoustic cavity subsystem comes from the adjacent bottom acoustic cavity subsystem and the front acoustic cavity subsystem, and then respectively. Perform energy input analysis on these two acoustic cavity subsystems.
Figure 2 shows the main energy input histogram of its adjacent bottom acoustic cavity subsystem. It can be seen from the figure that the main energy of the acoustic cavity subsystem comes from the acoustic cavity subsystem at the powertrain.
From the above analysis, it can be seen that the main noise sources and main noise transmission paths at the target observation positions of the driver’s cab and passenger cab are: the noise of the powertrain part causes vibration of adjacent structural parts through the air, and is transmitted to the ears of the driver and passengers.
2 Vehicle interior noise control
Through the above analysis, we know that the main noise in the car comes from the powertrain part, and understand the main transmission path of the noise. Therefore, for the powertrain part, we load the corresponding sealed sound insulation cover: for the noise propagation path, the car body structure is loaded with acoustic packages such as sound absorption and insulation materials and damping materials for noise reduction. The model after loading the acoustic package is analyzed and calculated again, and the results are shown in Figure 3 and Figure 4.
It can be seen from the calculation results in the figure that after loading the corresponding acoustic package on the sound source and the noise transmission path, the noise level in the vehicle is well controlled.
In this paper, using the statistical energy method, based on the VA0ne software, a SEA model for predicting the interior noise of the monorail train is established, and the interior noise is simulated and analyzed, and the sound pressure level at the target observation position and the power input contribution of the interior noise are obtained. The noise transmission path in the vehicle is obtained, and then a reasonable acoustic package is loaded on the noise source and transmission path to control the noise. The research method in this paper can provide certain guidance for the selection of materials for the initial acoustic package design of monorail trains, the determination of the location of the acoustic package and the noise reduction treatment of specific locations in the vehicle.
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