The Quest for Predicting Cavitation Nuisance by Ship Propellers: Seeking to Understand and Predict Cavitation Induced Vibrations, Noise and Erosion
Friday, February 26, 2021 @ 2:30 p.m.
Professor Tom van Terwisga – Delft University of Technology
E201 Ocean Engineering Seminar Series
Abstract: The presentation gives a review of the state of art of predicting Cavitation Nuisance in ship propulsion. Cavitation Nuisance covers cavitation induced vibrations in the aftbody of the ship, underwater radiated noise and cavitation erosion on propeller and rudder. Cavitation nuisance is important in ship design as comfort levels and erosion risk levels need to be met, as well as sometimes required radiated noise levels. Meeting these requirements can generally be fulfilled by ensuring sufficient margins in the design against exceeding the limits. This is however typically at the cost of efficiency. With the current focus on fuel saving, we see that contemporary propeller designs aim at reducing these margins, sometimes at the cost of unacceptable nuisance. In designing toward the limits of acceptability, the reliability of the predictions becomes more and more important.
Before we review experimental and computational achievements over the past decades, the question is addressed whether we truly understand the physical mechanisms of cavitation nuisance. Only after a sufficient understanding we can draw conclusions on an effective physical and numerical modelling. Examples of experimental and numerical achievements will be given, along with some of the more challenging sensitivities which are not yet under control, such as scale effects in vortex cavitation and sensitivities for water quality (free and dissolved air content).
The presentation ends with an example of the implementation of cavitation nuisance in propeller optimization and gives an outlook on the yet unexploited potential of integrated ship-propeller optimization. The question is addressed as to how far we can reduce the propeller tip clearance to enhance propulsive efficiency?
Biography: Professor Tom van Terwisga started working after obtaining his MSc at Delft University at MARIN in Wageningen (Netherlands) in 1985, where he is currently for 70% of his time team leader in the R&D dept on Ship Propulsion and Operational Performance. For the remaining time he is visiting Prof. at Delft University of Technology at the Chair of Resistance and Propulsion of Ships since 2001.
Hosted by: Asst. Prof. S.A. Mäkiharju, 6119 Etcheverry Hall (firstname.lastname@example.org)
Tracing Unnatural Disasters: Sensing Wildfires, Atmospheres and Radiation in the Chernobyl Exclusion Zone
Tuesday, March 2, 2021 @ 10:00 a.m.
via Zoom (Register for webinar)
Dr. Christine Eriksen – Senior Researcher, Center for Security Studies (CSS), ETH Zürich
Abstract: On 26 April 1986, the explosion and subsequent open-air graphite fire at Reactor No. 4 of the Chernobyl Nuclear Power Plant contaminated the soil, water and atmosphere alike with radioactive material. The 30-km2 Chernobyl Exclusion Zone remains one of the most contaminated areas in the world today. Over a thousand wildfires have burnt inside the zone since it was established, raising international concern that combustion from a high-intensity wildfire will reanimate radioisotopes currently held in the vegetation and soil. This presentation focuses on the wildfires that blazed in the Chernobyl Exclusion Zone in the spring of 2020, to examine the lingering health effects, political manoeuvring, and insurance implications of the Chernobyl nuclear disaster. The affective atmospheres of these wildfires require attention in order to understand the impacts of unnatural disasters. To think through the consequences of events that are not bound by two-dimensional cartographies, and that transcend geopolitical borders in space and time, we bring ideas regarding affective atmospheres and volumetric/voluminous sovereignty from cultural geography and cognate disciplines into conversation with insurance studies.
Biography: Dr. Christine Eriksen is a Senior Researcher in the Center for Security Studies at the Swiss Federal Institute for Technology (ETH Zurich). Prior to that, she worked for 13 years as an academic at the University of Wollongong, Australia. She gained international recognition in the field of disaster research by bringing human geography, social justice and environmental hazards into dialogue. With a particular interest in social dimensions of disasters, her widely published work examines social vulnerability and risk adaptation in the context of environmental history, cultural norms, and political agendas. She is the author of two books: ‘Alliances in the Anthropocene: Fire, Plants and People’ (2020) and ‘Gender and Wildfire: Landscapes of Uncertainty’ (2014). Her work has twice been highly commended by the Resilient Australia Awards (2018 and 2013). She was selected as a ‘World Social Science Risk Interpretation and Action Fellow’ by the International Social Science Council in 2013, named as a ‘2016 Woman of Impact’ for outstanding contributions to research as part of the Science in Australia Gender Equity (SAGE) program, and recognised as a ‘Woman Leader in Fire Science’ by the journal Fire in 2018.