Broken crankshaft mystery solved
When a DNV client experienced a broken generator crankshaft that was only two years old, they asked DNV to help figure out the cause
The research laid down by Geir Dahler and his team at DNV's Rotating Machinery Technical Advisory section, was based on a hypothesis validated with the Nauticus Machinery Torsional Vibration software tool by DNV.
Calculation tool
“We used Nauticus Machinery Torsional Vibration Calculation tool to find the reason it broke,” says Geir Dahler. “It was essential to use it as troubleshooting support. It let us perform a thorough analysis of the shafting systems, calibrated with measurements.”
Rotating machinery
The case started with a broken crankshaft in a generator motor on a vessel, despite being only two years old. The fracture point was in the middle of the motor. Using the Nauticus tool, the experts in Rotating Machinery were able to calculate the loads that exceeded the acceptable limit.
Mr Dahler is a principal engineer at DNV and head of section Rotating Machinery. He has more than 20 years of experience with technical engineering and research in propulsion machinery and shafting dynamics, and diesel engines and power generation.
The analysis took several weeks, and included analysing the design and also doing on-site measurements. With Software’s Nauticus Machinery Torsional Vibration Calculation tool, the team created one main model of the generator set and also a handful of alternative models based on various hypotheses. The results were enlightening.“We could from the analysis understand the way it was malfunctioning. We pinpointed a faulty vibration damper.”
Foresaw the results
They needed to be certain, because in order to prove it was the damper, they had to open it and do destructive testing, thereby making it unusable. Although the vessel operators might have been a bit anxious, Geir Dahler and his team were confident. The producers of the motor were also involved in the project as observers.
“And surely enough, we found the results that we had foreseen,” says Mr Dahler.
With this knowledge in hand, the vessel’s operators could not only fix the matter, they could make sure the problem would not reoccur. They could not recover their costs from the producer, as the guarantee period had already passed. But since then routine maintenance procedures have been altered according to the advice of DNV.
Teamwork with DNV
“This is a good example of the way that DNV - Digital Solutions and DNV work together as a team,” says Jo Øvstaas, DNV - Digital Solutions. “Geir’s team in Technical Advisory has the domain expertise, and in many cases they need special features in the software to be able to solve specific problems. Our development team usually deliver on this. We’re a software house that is lucky to have access to world-class expertise. Any other independent software house would normally have to pay for this knowledge, or only read about it in a magazine several years later. All we have to do is walk the 200 metres to our Technical Advisory unit.”
“We work on such cases every day,” says Mr Dahler. “When we found that it was a faulty damper, it was important to determine whether it was a one-off fault, or whether it was a generic problem. If it was generic, it could happen on other vessels – then the problem would be much bigger. But this time it was a one-off. The problem was solved and the case was closed,” he says. “Our customer was very satisfied."
Nauticus Machinery
Nauticus Machinery is a set of marine propulsion calculation tools intended for strength assessment of rotating machinery components and systems. The Nauticus Machinery software package includes:
The first two are class-free for design and troubleshooting, the others are DNV Rule based.1/10/2014 3:44:19 PM
