Hutchinson Research Center is located in Montargis, France. As part of a multinational group of 25,000 employees, it is a center of excellence in high-tech research. Hutchinson group is a leading provider of sealing, insulation and fluid transfer systems for the aerospace industry, among other sectors.
Whether boarding a large jet or a small turbo-propeller aircraft, passengers always hope for a peaceful, quiet and comfortable flight. For a few hours, they might sleep, work, watch videos or listen to music in the secluded space of the aircraft’s passenger cabin. A quiet cabin is essential for enabling customers to avoid stress and be comfortable. Designing a silent interior for a powerful jumbo airliner or a tiny business jet is always a challenge for acousticians.
Take the example of a mid-sized, twinpropeller aircraft: the rotating propeller blades generate a high level of noise that is transmitted through the fuselage into the cabin. This noise is a source of discomfort, especially for passengers sitting in the areas that are located near the blades. That is why aircraft manufacturers seek expert advice to help them silence the annoying low-frequency noise of rotating blades. Those experts are the engineers of the Hutchinson Research Center (Hutchinson). Hutchinson is a world-leading provider of sealing, insulation and fluid transfer systems. As part of a multinational group of 25,000 employees, the Hutchinson Research Center, located in Montargis, France, is a center of excellence in high-tech research.
It employs nearly 200 engineers and technicians and nurtures the expertise of the many disciplines operating within the group.
This multidisciplinary team has expertise in the fields of vibration and acoustic analysis, physical characterization, chemical analysis, materials formulation and digital simulation. The role of the Research Center is twofold: first, the engineers use their expertise to deliver solutions to the various Hutchinson business units; second, they perform advanced research and development on innovative materials, expanding on Hutchinson’s primary expertise as a rubber specialist.
Hutchinson has more than 15 years of experience in acoustics, and works in partnership with its clients to design and manufacture cladding, damping patches and acoustic panels for fixed-wing aircraft and helicopters. Hutchinson engineers assess various sound insulation methods using testing and 3D acoustic simulation techniques. Engineers rely on simulation in a comparative process.
“We model the aircraft and experiment with different virtual solutions for sound insulation,” says Christophe Barras, numerical simulation engineer at Hutchinson Research Center. “Only the best-performing solutions will be implemented on the prototype aircraft. The simulation step is crucial to guiding prototyping. With strict test schedules, there is no room for trial-anderror. Last-minute acoustic troubleshooting is not an option since engineers have a very limited time slot to test an aircraft.”
Hutchinson continuously innovates by inventing new materials that offer better sound absorption, vibration damping, improved shock resistance and elasticity. Hutchinson engineers use LMS Virtual.Lab™ Acoustics software from product lifecycle management (PLM) specialist Siemens PLM Software to virtually test new acoustic insulation and absorption concepts in order to assess and rank the benefits of proposed solutions. The resulting time and cost savings are often significant since only the most valuable solution is implemented in the prototype aircraft.
Hutchinson engineers use well-mastered techniques on the twin-propeller aircraft to build structural and acoustic models based on the customer’s virtual design. Whether performed on a full aircraft or only a section of it, the modeling step always requires close cooperation with the aircraft manufacturer or other partners. The engineers either rely on a shared simulated model of the aircraft or synchronize their tools and methodologies to reach the common goal. The coupled structural/ acoustic approach is one of the techniques that Hutchinson engineers employ to improve cabin acoustic insulation. As a first step, they perform a modal analysis on the structural model delivered by the aircraft manufacturer.
The modal approach speeds up the analysis process since it only takes a limited set of modes into account. It also gives insight into the full aircraft’s structural behavior. Sound insulation solutions, such as additional blankets, panels or tuned mass absorbers, are integrated into the model. In a second step, Hutchinson engineers create the acoustic model of the aircraft with LMS Virtual.Lab Acoustics and define the distributed load pressure on parts of the fuselage. This load pressure is generated by the propellers and can be of an acoustic or aerodynamic nature. Although the pressure is particularly complex to model, the engineers can rely on their long-term experience using past measurements and computational fluid dynamics (CFD) calculations to create the most accurate model.
The structural model and the structure’s eigenmodes are imported into LMS Virtual.Lab Acoustics. The structure’s eigenmodes are projected on the acoustic mesh for a coupled structural/acoustic calculation. The coupled approach delivers better engineering insight into the full aircraft acoustic behavior.
“In the beginning, we only tested new material properties by virtually testing them on the aircraft’s components model,” says Barras. “But this approach was misleading. We needed to take into account the full environment: in this case, the full airplane. Only then can we demonstrate the added value of our sound insulation solutions.”
To do just that, the Hutchinson team recently worked closely with an aircraft manufacturer to validate the simulation results using standard aerospace testing procedures. To support its advanced simulation work, Hutchinson also completed several test-based, vibro-acoustic measurement campaigns to validate the design choices. Working on the physical aircraft, the Hutchinson team performed a ground vibration test (GVT) as well as in-flight test campaigns using a dedicated 96-channel LMS SCADAS™ hardware system and LMS Test.Lab™ software. The physical test results calculated in LMS Test.Lab verified that the LMS Virtual.Lab Acoustics simulation was correct and validated the choices made for the vibro-acoustic treatments.
In acoustic simulations, model size matters. Large acoustic models are complex to solve but deliver the most accurate results.
“Modeling only a small aircraft section can yield erroneous results if the boundary conditions are not well defined,” says Barras. “In order to gain precision, we constantly try to create acoustic meshes of ever larger sections of the aircraft. Another problem that we encounter is the presence of high-frequency acoustic sources around the airplane. For example, aerodynamic turbulence can excite the fuselage at high frequencies.
“The derived simulated acoustics models are huge. We definitely need super-fast solvers to tackle these issues; solvers like LMS Virtual.Lab Acoustics.”
In addition to outstanding solver speed, Hutchinson engineers rely on advanced calculation features that simplify and speed up their daily tasks.
“LMS Virtual.Lab Acoustics lets us parallelize calculations to shorten overall calculation time,” says Barras. “For example, we compute several blade passing frequencies and harmonics simultaneously. Thus, we retrieve complete results faster. We also submit vibro-acoustic calculations to our computer cluster. The possibility of relying on the cluster’s job scheduler definitely quickens and simplifies our processes. We are now able to fully exploit the computer capacities at our disposal.”
Hutchinson engineers are continually challenged to improve the precision of their calculations for better acoustics prediction. The modal approach lacks accuracy on structures that have local or complex damping, such as structures damped with tuned mass absorbers or with viscoelastic materials, such as rubber. Also, to constantly increase their cutting-edge expertise, Hutchinson engineers investigate innovative methodologies.
“For example, we try to integrate new elastic materials, foams, ceramics or silicates into our sound insulation solutions,” says Barras. “Those materials give frequency-dependent responses to excitations and are, thus, difficult to characterize in a modal approach.”
In order to model damping more accurately, the Hutchinson engineers consider performing the vibro-acoustic calculations in the physical space.
“We’re always trying to improve our vibroacoustics modeling approach,” says Barras. “In that sense, we welcome the LMS Virtual.Lab vibro-acoustic solver, a valuable addition to the LMS Virtual.Lab portfolio. This solver could indeed help us reach our acoustics goals faster.”