From wind tunnels to computer simulations: Dr Jennifer Keenahan on climate resilient design
Friday, 28 July, 2023
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Dr Jennifer Keenahan (pictured) is Assistant Professor in Civil Engineering at University College Dublin. Her research looks at protecting the built environment from the effects of wind, a more pressing issue in light of climate change.
Last January 15th, high winds toppled a ‘big rig’ truck on San Francisco’s Golden Gate Bridge at rush hour. Luckily no casualties were reported, other than the thousands of commuters inconvenienced by hours-long delays.
“We can see from worsening climate change that winds are definitely getting stronger and these extreme wind events are becoming more frequent,” says Dr Jennifer Keenahan, whose work looks at mitigating the effects of these dangerous gusts, which are not confined to America.
“Ireland is a small island off the west coast of Europe so it's really important that we consider the effects of these extreme winds on our built environment - our buildings, bridges and public realms - and how our cyclists and pedestrians might be affected by these extreme winds.”
Keenahan develops computer simulations of the built environment and models how the wind will interact with it. She does this using computational fluid dynamics (CFD), a science that uses applied mathematics, physics and computer software to visualise how a gas or liquid flows.
“One of the most important things I do is validate my models with data from the real world. For example, some of the big bridges that are being constructed now have sensors built into them as part of the construction. There's a bridge in Edinburgh that has nearly 2,000 sensors. We can use the data from those sensors to cross check that our model is behaving the way we expect it to.”
Traditional wind tunnel testing - which involves blasting a large fan on scaled down versions of bridges and buildings - has “a lot of challenges”. For one, the “scaling isn’t appropriate”.
Especially for complicated real-life situations, such as a lorry crossing a bridge over a river in a storm.
“Particularly if that lorry is empty and it's not a rigid one; it's one of those ones that has that curtain fabric side to it. Effectively that's going to behave like the sail of a boat. If you get a gust of wind impacting that lorry on a bridge, it's quite likely that it could topple over. And that's a very big concern.”
Part of Keenahan’s research looks at what speed limits to impose on bridges during extreme weather events. Too slow and you risk congestion and driver frustration.
“Equally if we suggest a speed limit that's still quite high, we may not have done enough to protect the drivers and the lorries. It’s a question that’s yet to be answered.”
It’s not the only middle ground her work assesses.
“What's really interesting is here in Ireland we seem to go from, ‘Well, it's a bit windy out there, but it's okay, go about your business’, to, ‘Red Alert, stay at home, nobody leaves their house’. We don't have that guidance in the middle. That's a big piece that's missing and I hope to be able to address that.”
She is also interested in applying CFD modelling to the optimal design of offshore wind farms.
“I'm quite interested in the modelling of the sea and how the erosion of the seabed can undermine the infrastructure that we might install there. Wind turbines, cables, anchors, any type of infrastructure that we put onto the seabed is vulnerable to erosion by the sea.”
Before joining UCD, Keenahan worked with design company Arup.
“I was involved in designing some bridges on the M17/M18 motorway, which goes from Gort to Tuam in Galway. I was also involved in some of the other projects in Dublin and Ireland and abroad, particularly with CFD modelling.”
This industry experience has made an “enormous difference” to her teaching.
“I have a really strong understanding and appreciation for how things are designed in the built environment, why they're designed that way, how they are operated, how they're procured and where everybody's role comes into the process”.
Keenahan has gone against the long tradition of universities teaching engineering and architecture students separately.
“My teaching has the unique opportunity of having engineering students and architecture students in the same classroom together at the same time taking the same module,” she says of her ‘engineering and architecture of structures’ course.
“It's a really fantastic opportunity for creating a learning environment to help these students develop the skills they're going to need in teamwork, in group work, in collaboration and in understanding each other's disciplines.”
Now she hopes to see the field adapting faster to emerging technologies.
“An enormous amount of our design practices and our analysis methods in civil engineering are quite primitive. We've not modernised a huge amount in terms of what's possible. I would love to see us close the gap compared with other disciplines like computer science and electronic and electrical engineering. I would love to see more of that computational analysis, particularly as we see so much happening now with AI. I'd like to see more of that in the discipline; I think that's the future.”
She hopes to see the development of trustworthy, validated computer models and simulations that can accurately forecast the impact of wind on structures.
“Then running predictive analysis, running parametric analysis, so that we can anticipate, ‘What if this? What if that?’” she explains. “I think there's a huge opportunity there, particularly when we see what's happening to our environment because of climate change. It’s going to be really important to look at some of those questions into the future.”
Listen to the (opens in a new window)podcast.