INTERVIEW: From the Large Wave Flume to Your Screen, Dr. Pedro Lomonaco
Oregon State University holds one of the few wave research flumes in the world. Looking like an Olympic-sized swimming pool and able to pound out waves at hurricane speeds, this research environment is used to determine how different forces will obliterate a house under the right conditions.
At the head of this research tool is Dr. Pedro Lomonaco. He came to Corvallis just to run this unique and exciting project. We sat down and asked him about what he has learned and where the lessons have improved our building methods.
TCA: Hi, I’m Sally Lehman, and I’m with The Advocate. There’s been a lot of interest in how things are built, partly because of the 2011 tsunami in Japan, partly because of the increasingly violent hurricane seasons being experienced in the south and northeast of the U.S. Today, we’re speaking with Dr. Pedro Lomonaco, who works with the Oregon State University Wave Research Laboratory Large Wave Flume to develop a means of testing structures against large amounts of water. Thank you for being here today, Dr. Lomonaco.
Lomonaco: Thank you for inviting me.
TCA: Your education has taken you all over the world, from Mexico to the Netherlands to Spain. How did you end up in Corvallis, Oregon?
Lomonaco: Well, our activities that we do here at the lab is relatively small in terms of the number of laboratories that you can find in the world that do similar things. So we know each other. The coastal engineering community is relatively small and the coastal engineering experimentation part of that community is even smaller. So we know each other. And there was this opportunity in one of these communication streams regarding the possibility of being the Director of the Hinsdale Wave Research Laboratory, which has a world class reputation. I was just finishing the construction and starting to run another laboratory in Spain, and it was an opportunity to grow a step further and also was related with the family on seeing other countries are learning different languages and increase their experience in a worldwide type of education.
TCA: In your latest paper, you discuss creating scale homes that are meant to fail in hurricanes. What intensity of hurricane on the Saffir-Simpson Hurricane Wind Scale have you tested for?
Lomonaco: We didn’t test it on wind. We tested on their waves only. And those are ways produced by that wind. And it’s not only the waves, but also the storm surge, the increase in water elevation, plus the waves arriving to the coast. Those conditions were tested to the maximum for the storm surge.
The waves are limited by the water. That is a condition that is obvious when you go to the coast, you see the waves breaking because of the limited water depth. So when you have a storm surge, the increased water level allows those waves to propagate inland and hit those houses, which are not designed to withstand those waves. But some of those waves are going to be breaking if they are bigger than a certain size. So that’s what we tested.
We increased the water level to a certain storm surge, which was rising all the way to the first story or the first grade level of the house on stilts. And then we run the waves until those waves were breaking. So we have the maximum waves possible in that situation.
This is not a specific condition for a hurricane. It was the maximum wave that could be reached. And that is something that you see in the coast normally and in hurricanes like the one you see in the coast and recently happened in Louisiana. So we run those waves and those are the waves that are hitting the structure and deforming and producing damage to those structures until we make them fail.
TCA: How do you fully instrument a model to see its reactions waves?
Lomonaco: Ok, that’s a very complex question because it depends on each and every case. How we instrument structure changes depends on the specific objectives of our research project. And in the case, for example, of those houses, the first thing which was very important is to replicate the house with the strength that was scaled down and replicating the behavior of a house that is full scale. Normally, this is not done that way.
Normally, you have a house that is stronger than what would be the prototype, the real, full sized house. And we study the forces, but we don’t study the deformation and destruction of the house.
That means introducing instruments to measure how the water level changing or how the velocities are nearby the structure or the forces on the structure. In the particular case of the houses that we were testing that were deformed and destroyed, we also incorporated other instruments like accelerometers that are telling you how the structure is shaking. And we did a specific test on applying a certain force to see how it was deformed by that force. We know how that house is responding. Then when we send the waves and we see how it’s deforming, we can indirectly estimate those forces that were producing that damage.
TCA: There is some terminology in your work that I would like to clear up or explain. What are High Reynolds regimes. Can you tell me what that means?
Lomonaco: Well, there is in the fluid flow a series of forces that are producing the motion of that fluid flow – or the fluid flow produces some forces in the different structures. The way we correlate or make these forces dimension is we correlate some acting forces and reaction forces.
For example, the gravity forces and the inertial forces. So what is the mass of the fluid or what is the mass of the object? And for example, viscosity is another force that increases the drag of the flow around that structure. So one of those parameters that are describing the flow is Reynolds.
Reynolds is a researcher from the 19th century who described how the flow was behaving. And he basically characterized the conditions of turbulent flow, which is what you see every now and then in nature. Most of the flows are turbulent because nature is complex enough to produce turbulence, so you see those eddies happening. When the flow is not strong enough, that means that you don’t have turbulence created. And then what you have is what we call laminar flows, which is very slow motion. Similar to what you have, for example, in ice or something that is relatively nonviscous – it has no viscosity.
When we talk about fluid Reynolds developed numbers, we are talking about fully turbulent flow. So the turbulence evolves and it starts growing and the eddies are going bigger and bigger until a certain point when you have enough complexity in that flow that is considered fully turbulent. And that is a high Reynolds number when we talk about high Reynolds numbers, that’s what happens.
The important thing there is that what we are trying to do is to replicate what nature is doing in the laboratory. In the laboratory, we are not necessarily always producing a fully turbulent flow, which is not representing the forces the way it should be.
TCA: Another term that comes up is LiDAR. What does that stand for?
Lomonaco: Oh, LiDAR, I have to say, I don’t remember exactly the different elements of LiDAR
LiDAR is a series of different technologies that were developed using lasers, or rather infrared light, to measure distances on a really fast pace. So, for example, it’s been said that recently some of the devices that we can find in the market for general public include LiDAR, which is a way of measuring distance and creating a picture of what’s going on surrounding us.
Imagine you have, instead of having a single ruler that you measure in only one direction from one point, you have several rulers measuring in different directions. And that is what LiDAR or laser scanners are doing now, and they are very, very popular nowadays and the technology’s out there for the general public.
So that gives us more access that allows us to measure things before and after something happens, especially when, for example, we produce damage to some structures. LiDAR or laser scanners are being used, for example, in, for example, what happened in Louisiana to measure how that damage was produced and what was the characteristic of that damage. In minutes, we can have a very nice picture, a very detailed picture, on how those houses were damaged and what was the element of failure. And there is a record, a continuous record, of what would happen in those houses.
We used LiDAR in our experiments, because it was a way of capturing three dimensionally what happened to the houses, how they were destroyed during and after the fact of the waves.
TCA: Some of the scale houses were elevated, some were at ground level. It would be expected that an elevated house would withstand flooding better than a house built on the ground. But were the elevated homes more susceptible to wind damage?
Lomonaco: That’s correct. Certainly, the elevated houses are more susceptible to wind than the grade level houses. But when the storm surge of the waves reaches the house, the forces produced by the waves are an order of magnitude – actually two orders of magnitude – larger than the wind.
That doesn’t mean that the forces of the wind are not destructive enough to produce the damage that, for example, we recently observed in Louisiana. But when you have the water, the amount of damage that you produce, and that’s something that you observe, for example, in areas where storm surge happened or tsunamis when the waves are hitting, is as fluid as the wind, but the water is a thousand times heavier than the wind and that produces, you can imagine, significant more damage.
TCA: What is uplift pressure and how does its distribution affect an elevated home in a storm?
Lomonaco: Because we are engineers, we like to separate forces in different directions to understand that better, when we build a house and again, the house is a very square rectangular shape because it’s easier for us to understand, we divide the forces. The horizontal forces are the ones that are pushing the house inland. And then the uplift forces are the forces that are trying to lift it vertically.
So, let’s say we separate the forces, the horizontal forces and vertical forces. The only forces are the ones that are trying to lift the house. And we, because the size of the houses is big enough to have differences between one point and the other. When a wave hits, those forces trying to leave the house may also overturn the house. And that creates forces or strains in the different elements of the house that are not designed to withstand those forces.
And that’s how sometimes we have seen those houses that are basically floating on the river, because they are being lifted by the water and then just carried away. But the house basically remains intact. When we have variations in those uplift forces, the house is ripped off and separated in smaller pieces, and it’s destroyed. There is no further possibility to make that house survive those forces.
So understanding the differences between how storm surge waves and wind are producing those opposite forces gives us a way of understanding how we have to design, and how those houses could be damaged during hurricanes.
TCA: Your lab also exerts horizontal and vertical forces on the model, and you have shown through your work that the two maximums of those forces don’t necessarily occur at the same time. Why is that an important finding?
Lomonaco: Going back to the previous question, when we have a horizontal force that is trying to push and raise the house at the same time, the resisting forces that we have to take into account to make that house survive those forces are different than if we have one force that is pulling in one direction and the other one is pushing the different direction. These variations in the direction of the force may introduce rotations of the house, which are the ones that produces significant damages.
It’s also important for another reason. The reason is, and I think that’s even more important, when we have a simplified design, as we have done up to relatively recent times, we assume that the maximum forces happen at the same time because it’s easier – we don’t have to take into account the changes in time, which makes the computation more difficult. So that simplification allows us to use empirical formulas of simplified formulas to [say to] us, ‘OK, if you have this maximum force, this is going to happen, and you have this other maximum uplift force, this is going to happen.’
But if you realize that those maximum forces are not happening at the same time, maybe the house is under worse conditions if the maximum force is happening in one direction to another. And then the problem is more complex, because then we have to take into account time in the picture of the computations. That’s one of the major components there.
TCA: The fourth dimension being time.
Lomonaco: The fourth dimension. It’s very important,
TCA: And would a more complicated house design that was not simply a square box be more likely to withstand those forces.
Lomonaco: I don’t know if we are in that stage that we can talk about that. I mean, that we can really consider the shape of a house that would be able to withstand those forces.
At this moment, I would say the first component would be to reinforce those elements that are weakest in the design so they don’t break. Is there is a shape of the house that is more efficient to withstand those forces? I don’t know.
My first approach would be – knowing how nature is – the best shape is the one that doesn’t exist. If we don’t have houses on the beach, then we don’t have this problem, and we are just basically using space that doesn’t belong to us. It belongs to the ocean and nature will take over that space eventually. So that’s what would be the best shape.
TCA: Another study that you’ve done concerns tsunamis and the destruction of bridges. Were you able to find a way to make bridges more resilient to tsunami waves?
Lomonaco: Yes. During those experiments, we tested different options on how the bridge is resting on the what is called bent cap – so the structure that supports the deck of the bridge. By how these connection elements are dissipating energy, we are able to reduce the forces on the bridge itself.
Other findings include, for example, allowing the air that is trapped underneath the bridge to escape easily. When the air that is trapped underneath is compressed to a certain extent, it will basically try to explode… Bridges [are not designed] to withstand those forces. So allowing venting on some of these [bridges] was a significant improvement. And [something] even as simple as the guardrail. How to deviate the first force that impacts the bridge… significantly [changed] the forces that were measured by those bridges.
It is interesting to say that, actually, we are doing additional experiments on bridging impact forces as we speak in the Flume, including waves for other hurricanes and tsunamis. So it is, as you see, an ongoing research that is not limited to a series of experiments that we did a number of years ago.
TCA: Your research as a whole seems to look at every component of a structure. How important is that observational data to builders?
Lomonaco: And there is a step in between from our observation data all the way to the builders – probably two steps. One step is the in-between step, which is the designer who needs to understand what that data represents in the changes in the design so the builders can take that into account. And the other step is to also transform that data into a general expression that can help the designers to use the best approach for dimensioning those structures. So those sequence of elements is important, and I think another element important for the builders is feedback. If they have observed a way of constructing that is not the most efficient and it could be affected by these conditions, these data that we are observing, it would be interesting for us to replicate that in the laboratory, for example.
TCA: With so many eyes on the West Coast and the Cascadia Subduction Zone, can we really estimate the impact of both a large earthquake and the resultant tsunami that may happen if or when that earthquake happens in our area?
Lomonaco: We can estimate the impact of those. The question is not whether we can assess how big those forces [might be], because that’s what we’ve been doing over the last 10 or 15 years. It’s how to be prepared for those and identify those locations where those forces are exceeding the capacity of the communities in the coast.
And also you mentioned the earthquake. That is a little bit outside of our research, but also it happens in the same way. We know what an earthquake with a certain magnitude is going to produce. What we don’t know is which of these areas in the whole of the state and at the coast are susceptible to be damaged? What are vulnerable for because of tsunami or an earthquake.
TCA: Does the coast range help in our tsunami protection on the coast of Oregon? We have a mountain range that we’re building houses on as opposed to building them directly on the beaches. Will that be of help?
Lomonaco: Well, certainly. The fact that we have in this particular area of the country, a relatively steep coastline so we can reach relatively high elevations in short spaces. That helps a lot because those buildings are not going to be hit by the tsunami. But we have to remember that structures are still going to be under the effects of the earthquake. That those structure need to be designed and considered under those conditions.
And there is an additional component there in that all the communications and lifelines that might not be subject to the effect of the tsunami, are going to be the way of the coastal communities to exit or be being accessed for help and for resilience, for recovering the from the tsunami. So we also have to pay attention to those things. That is, even if my house on my road is in the right location and is going to be withstanding those forces, then I’m going to use these as a way of helping others and help rebuild the community.
TCA: Thank you for your time, Dr. Lomonaco.
Lomonaco: Thank you for inviting me and nice to meet you.