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Title of the thesis: Tribology of Marine Thruster Lip Seals: Behavior Under Typical Operating Conditions and a Condition Monitoring Approach

Thesis defender: Omar Morad
Opponent: Prof. Janne Juoksukangas, Tampere University, Finland
Custos: Prof. Raine Viitala, Aalto University School of Engineering

This doctoral thesis investigates large diameter marine lip seals in propulsion thrusters, focusing on a standard nitrile butadiene rubber (NBR) seal and two alternatives: a polyurethane (PU) seal and a hybrid design PU seal with a polytetrafluoroethylene (PTFE) insert. A full-scale rig was built to measure frictional torque and subsurface contact temperature (0.5 mm beneath the contact surface) across 27 typical operating conditions, using air bearings for precise torque measurement and embedded wireless temperature probes. Three samples (n = 3) of each seal design were tested. The study was the first of its kind to study seals as large as 300 mm in diameter.

The results showed that the frictional torque increased with increasing oil pressure and decreased with increasing oil temperature, while the subsurface contact temperature increased with increasing oil pressure, oil temperature, and rotational speed. Material differences were significant (p < 0.05): PU generated the highest frictional torque and subsurface temperatures, NBR was intermediate, while PTFE seals were lowest. Building on these findings, the thesis proposes a practical condition-based monitoring method using a simplified conjugate heat transfer model that estimates contact temperature from a low-cost, near lip oil temperature measurement. The proposed method is cost effective and feasible, and shall allow the vessel operator to monitor the condition of the seal and take corrective measures. 

Thesis available for public display 7 days prior to the defence at . 

Contact information: omar.morad@aalto.fi