How simulation and modelling can address NVH in innovative drivetrains

The event was held in partnership with Geislinger as part of Riviera’s Marine Propulsion Webinar Week.

Geislinger managing director Torsten Philipp, AVL manager Multi-Body and NVH Simulation Christoph Priestner and Wärtsilä Shaft Line Solutions area sales manager Europe & Africa - Shaft Line Repair Services, Marco Gordon analysed how the drivetrain supply chain – from propeller to propulsor – is innovating to meet ship designer and operator requirements for optimised vessel performance at the right cost.

Mr Priestner opened the proceedings by explaining how AVL’s powerful simulation deals with the requirements of modelling NVH generated by traditional marine engines and non-traditional drivetrains such as electric and hybrid propulsion. With traditional powertrains, the NVH of the whole powertrain is taken into consideration, he said.

“The same applies to electric drivetrains. Lightweight structures have issues with NVH. NVH is always there,” Mr Priestner said. AVL’s approach to the issue is to build a complete engine assembly NVH simulation.

“The model is large, but you can answer high frequency and low frequency issues,” said Mr Priestner. “The same applies for electric drives. Like with ICE (internal combustion engine) propulsion, the whole system is simulated, including the inverter, batteries and anything coupled to the system.”

The AVL simulation focuses on the source of the NVH as well as its transfer path.

“Powerful optimisation procedures are used,” said Mr Priestner, “with parametrisation of the baseline model," and the NVH model being well-developed by the simulation.

Picking up on Mr Priestner’s opening remarks, Mr Philipp described how couplings and damper are setting new benchmarks in a subset of NVH – noise. He described how the Geislinger-integrated coupling “adds elasticity and damping to the gear train and this results in a reduced gear excitation and again reduces the various forces and the noise excitation to the structure,” he said.

The primary source of acoustics excitation in the ship’s structure is through the drivetrain mounts, Mr Phillip said, where multiple sets of frequencies have to be addressed. And the overall impact can be very significant. In a case study involving a luxury yacht, there was “clear reduction of sound level in the range of up to 20 dB,” according to Mr Philipp.

Mr Gordon spoke on the importance of regular shaft alignment of the drivetrain. “Stresses and vibrations caused by a misaligned shaft can lead to a breakdown in the engine shaft assembly,” he said.

Mr Gordon also took the time to explain one of the common myths regarding shaft alignment and bearing wear. "It is all fine as long as the temperature does not rise,” he said. “A vibrating shaft causes a suppression in the lubrication film. When the lubrication film gets suppressed, there is a loss of the damping effect between the static and the rotating part. At that point, extensive bearing wear starts almost immediately and this can ruin your bearing within minutes. Then the bearing temperature rises."

According to Mr Gordon, the solution to avoid this situation is to fit sensors to the drivetrain during the next drydocking. The data from the sensors is analysed in real-time and used by Wärtsilä Shaft Line Solutions to build a 3D model of the drivetrain.

Polls

Surveyed on issues including NVH, webinar attendees were asked to rank the importance on a scale from one to five, measuring how important it is to avoid passive NVH measures. All of those surveyed felt the subject was important, with 59% ranking it as medium in importance, 30% of high importance and 11% ranking it as extremely important.

On the question of whether marine electric drives will be direct or via transmission, the survey found a close split of 51% in agreement and 49% opposed. There was overwhelming agreement (92%) that longer service intervals and longer service life of drivetrain components will become more important in future.

In the light of digitalisation and hybridisation of the marine industry, attendees were also asked how important powertrain monitoring will be in the future. A majority, 55%, replied this was of the highest importance and 40% ranked this a very important with the remaining 5% ranking it of lesser importance.

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