SAE International A Practical CAE Approach to Determine Acoustic Cavity Modes for Vehicle NVH Development 2012-01-1184

The role of acoustic cavity modes in vehicle NVH (noise, vibration and harshness) development is well established in the automotive industry today. Prior knowledge of these modes can help prevent potential issues later in the development cycle, as well as aid in root cause analysis of vibro-acoustic issues. OEMs utilize them as part of their overall modal alignment strategy and cascade them to major system and sub-system suppliers for robust NVH designs. Today, acoustic cavity modes can be obtained rather easily using CAE (computer aided engineering) methods early in the development cycle. However, unlike acoustic modal testing, the CAE normal mode solution cannot scale the relative amplitudes of the modes. The sheer number of acoustic modal frequencies to be avoided can be a serious deterrent during the early design phase. This paper proposes an alternate approach for acoustic modal analyses using CAE to scale the relative amplitudes of cavity modes. An omni-directional acoustic source is placed at critical interior cavity locations and acoustic frequency responses are generated akin to an acoustic modal test. This approach is successful in scaling the relative importance of the acoustic cavity modes, and has a reasonable correlation with modes found from actual testing. This information holds much more value from a vehicle NVH development perspective because the relative strengths of the modes are known and the number of acoustic modal frequencies to avoid is greatly reduced. From a practical vehicle NVH development perspective, this approach has clear benefits over traditional CAE acoustic normal mode analysis methodology in use today.