Pass by noise simulation

Eisma, T. (2016) Pass by noise simulation.

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Abstract:Pass-by noise (PBN) is measured for every new designed vehicle on a test track before it is approved for the European market. For all vehicle categories are different limits set on the dB values it may produce during this acceleration or constant speed test. With the introduction of the new EU-law 540/2014 [1] these limits will be reduced from July 2016 for every vehicle category. Because it becomes with this limitations more important to know these PBN values in early design stages, there is a need for virtual PBN simulations at Daimler AG. These simulations must give insight in individual noise sources, such as the engine and exhaust, which help reducing the total PBN. For this reason a method and PBN software program is developed and described in this report. The method starts with multibody simulations of the engine, which can be done with a simplified calculation in Matlab or where results of specialized departments can be used. This results, which contain the dynamic main forces on multiple nodes in a prescribed format, can be used as input for the simulations in Nastran. This so called modal frequency response simulations contain detailed engine and exhaust models. A way is described to export the surface velocities of the structures and the particle velocities at the tailpipe. For the exterior acoustic PBN simulation the software program Actran is used. This program makes it possible to integrate the velocities (shell and tailpipe noise) in a fluid domain which contains the total vehicle surface. With the use of semi-infinite elements the far field is described in which the PBN microphones are located. The Actran simulation visualize the acoustic behavior around the vehicle and has as result the PBN values. To couple all these simulations and to make it possible to simulate for different engine speeds for accelerating tests a PBN program is developed. This program creates a standard for every PBN simulation at Daimler AG and makes model sharing possible. The program exists out of four subprograms and can be used in a ordered way to walk through the complete simulation process. A new project folder with all necessary subfolders and an overview of all necessary models can be made with the first program. Thereafter the visualization of the engine and vehicle speed can be made with the second program, which exports a text file with engine speeds and corresponding microphone positions. This file can be used as input of the third and main program, which has a GUI for all three simulations, MBS, Nastran and Actran. Models, files and parameters can be easily selected as input for these simulations. The program writes after a check automatically simulation input files for all load cases and engine speeds and couples the simulations after each other. As last the PBN results can be shown with the post processor for individual components and together. The total program save time, prevents making input faults, walks the user through all necessary steps and creates a standard for all PBN simulations. In the future the program can be extended with more noise sources and physical effects to improve the accuracy.
Item Type:Internship Report (Master)
Daimler AG, Germany
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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