A Guide to Direct Field Acoustic Testing (DFAT®) and Simulation for Aerospace Engineers

Massimiliano: Can you provide an overview of vibroacoustic analysis and how it helps prove that hardware is launch-ready?

Alexis: A vibroacoustic analysis qualifies the interaction between the acoustic output of various systems and the resulting mechanical vibrations. In the space industry, it simulates the aggressive conditions that occur during launch to ensure that spacecraft and payloads remain unaffected.

This involves subjecting hardware and aerospace structures to intense vibration and acoustic loads to understand structural integrity and performance. Engineers can identify potential faults, verify design reliability, meet regulatory standards, and confirm that spacecraft can withstand the harsh dynamic environment. With the high stakes and costs involved, it is mission-critical to ensure that acoustic loading does not negatively impact hardware.

That means, by using VA One, engineers can prepare for their on-site DFAT by simulating a diffuse acoustic field, testing different speaker configurations, evaluating the sound field uniformity, and delivering pre-test structural qualification—without needing specialized acoustic reverberation rooms and avoiding the risks and costs of transporting sensitive components to remote test facilities. This is particularly important when working with a new or unusual test where no previous experience can help foresee unexpected behaviors.

Massimiliano: Can you elaborate on the mathematics involved in DFAT testing and simulation?

Alexis: Of course. A dedicated DFAT control model is key to predicting how the various elements will behave during testing.

A typical DFAT test setup comprises numerous speakers, amplifiers, control microphones and a closed-loop MIMO acoustic control and data acquisition system. We use the Boundary Element Method (BEM) to model these components and employ the Finite Element Method (FEM) to model the test article. This enables engineering teams to evaluate all of the criteria inherent to a successful test and also get ahead of any potential issues that may crop up. We break our DFAT simulation theory down into a three-step process:

1. The first involves a mathematical formula that uses the BEM solver to generate two matrices—one represents the transfer function between each acoustic source and the microphone in the model, and the other is the transfer function between each source and a mode on the structure under test. We use cross-spectral matrices to analyze the sound sources and their response. VA One then utilizes this information to calculate excitation metrics, determine the amplitude and cross-correlation between various speaker surfaces, and reproduce the desired acoustic field. However, the initial mathematical model can’t differentiate between amplitude and cross-correlation, which can lead to numerous test inaccuracies.
2. The optimization stage is designed to correct this through an algorithm that prioritizes amplitude over cross-correlation as much as the customer desires.
3. Finally, we solve the model and perform post-processing. This allows us to measure numerous important metrics—how loud the sound is at different points, how the test article moves or vibrates in response to the sound, and how much stress the sound puts on different parts of the structure, for example.

Massimiliano: Let’s delve into VA One a bit further. What’s unique about the software specifically for aerospace structures?

Alexis: VA One enables engineers to meet their requirements by providing numerous capabilities designed specifically for space applications. The platform allows engineers to model complex dynamic environment loads efficiently and predict vibrations, acoustics, and shock responses with singular accuracy. In tandem with physical testing, this ensures that spacecraft will survive all of the critical stages of operation—from launch and liftoff through to separation and re-entry. Engineers can also use VA One to assess astronaut comfort and safety criteria in human-rated spacecraft.

NASA, the European Space Agency, Boeing, Raytheon, and Northrop Grumman all utilize VA One for Space Structural Qualification. The simulation enables these and other space companies to prove that the analysis is correct, the software is accurate, and that similar analyses have been correct. VA One customers can capitalize on ESI’s repository of technical research that goes back 40 years. To put it simply, this gives them confidence that their simulation results align with testing results.

As space missions become more frequent and complex, the challenge of testing payloads and launch vehicles intensifies. Accelerated launch schedules compress design cycles, limiting time for thorough vibro-acoustic analyses. The variety of launch vehicles, each with unique acoustic and vibrational profiles, further complicates testing. Accurate and proven simulation software enables space companies to enhance collaboration between payload and vehicle teams, optimize resource allocation, and empower engineers to validate new space technologies' robustness within constrained timelines and budgets.

With VA One, engineers can tackle these challenges, achieve faster development cycles, and ensure their designs comply with stringent launch certification requirements. VA One is changing traditional ways of working towards more digitalized qualification and certification of virtual spacecraft or payload prototypes without sacrificing safety and robustness. The software gives engineers confidence their tests will be successful.

Massimiliano: This has been such an interesting discussion—Wes and Alexis, thanks so much for your time.