# Prediction and Experimental Study of Low-Frequency Acoustic and Vibration Responses for an Aircraft Instrument Compartment Based on the Virtual Material Method

## TL;DR

This study shows that the virtual material method accurately predicts acoustic and vibration responses in an aircraft instrument compartment.

## Contribution

The virtual material method is validated for precise simulation of bolted joints in aircraft structures.

## Key findings

- The first four modal shapes from calculations and experiments were completely consistent with less than 3% frequency error.
- The virtual material model's RMS acceleration response (11.23 g) closely matched the experimental value (10.35 g).
- The predicted sound pressure level (136.98 dB) aligned closely with the experimental result (135.76 dB).

## Abstract

Bolted connections are extensively utilized in aircraft structures, and accurately simulating these connections is a critical factor affecting the precision of vibration and noise response predictions for aircraft. This study focuses on an instrument compartment of a specific aircraft model, employing the virtual material method to simulate the bolted joints within the structure. Parameters for the virtual material layer were obtained through theoretical calculations combined with parameter identification methods, achieving precise modeling of the instrument compartment. By comparing the calculated modes with the experimental modes of the instrument compartment, it was found that the first four modal shapes from both calculation and experiment were completely consistent, with the error in natural frequencies within three percent. Subsequently, acoustic and vibration computations were performed using both the virtual material model and the tied constraint model, with comparisons made against experimental results. The findings indicate that the root mean square (RMS) acceleration response of the virtual material model was 11.23 g, closely matching the experimental value of 10.35 g. Additionally, the total sound pressure level inside the acoustic cavity was 136.98 dB, closely aligning with the experimental value of 135.76 dB. These results demonstrate that the virtual material method offers higher accuracy in structural acoustic and vibration calculations.