Using 3-D computer models, University of Arkansas researchers have demonstrated the influence of hills on tornadoes. Their models revealed that the height of a hill and the size of a tornado’s vortex have a significant effect on the tornado’s destructive power. The findings could be used to identify safer areas for construction.
This illustration – stills taken from a computer animation of computational fluid dynamics – shows the disruptive effect of a hill on a tornado’s vortex.
The researchers found that lower levels of a tornado’s vortex are significantly disrupted if the height of a hill is equal to or greater than the radius of the vortex. The models also confirmed an important finding from a previous field study – that wind velocities are significantly reduced on the leeward side of hills.
“A preliminary observation from this study indicates that there is a region behind a hill where velocities are reduced due to disruption of the tornado vortex,” said Panneer Selvam, professor of civil engineering. “Of course this disruption depends on the height of the hill, as well as tornado size and velocity. We measured this effect in scenarios in which the width of the hill was perpendicular to the direction of the tornado.”
Selvam and civil engineering graduate student Piotr Gorecki used computational fluid dynamics, a widely used method to study the effect of wind on structures, to create 3-D computer models showing the interaction of hills and tornadoes. The study was conducted to reveal the influence of the hill height on the tornado-hill interaction. Three different rectangular hill heights – 12, 24 and 36 meters – were investigated, although each hill had the same width and length. For each study, the size of the tornado’s vortex – diameter of 8 meters – was the same, as was its maximum velocity – 86.5 meters per second.
Selvam and Gorecki’s simulations revealed that tornado-hill interaction depends on the ratio of a tornado’s radius to the height of a hill. If a tornado’s radius was equal to hill height, the lower levels of the tornado’s vortex were significantly disrupted during the interaction. This contributed a low-velocity region on the leeward side of a rectangular hill. In this region, the researchers found, wind speeds were reduced by at least 41 percent compared to the maximum tornado velocity, the speed at which it was traveling when it hit the hill.
The results showed that the tornado flowed smoothly over the 12-meter hill, the cylindrical shape of its vortex preserved through the entire interaction. At this height, the tornado adjusted to the minimal change in altitude and maintained its strength as it traveled over the hill.
But the 36-meter hill disrupted the tornado’s vortex. The interaction caused the tornado to split into two vortex tips, one in front of the hill and one behind the hill. The vortex tip in front of the hill weakened while the tornado moved over the hill. Eventually, the tip in front of the hill disappeared, and the tip behind the hill strengthened, but the overall strength of the tornado was weakened.
Selvam said the best sheltering abilities would be on the leeward side of bigger hills. This would require a further, historical investigation of the direction from which most tornadoes travel at a given location. For example, most tornadoes that hit southwest Missouri, including the massive EF5 tornado that struck Joplin, Mo., on May 22, 2011, travel from the west to the east.
Selvam previously found that large structures can reduce the force of a tornado vortex. That research showed that tornado forces are reduced if the side of a building is larger than the vortex diameter.
Earlier this year Selvam and a different graduate student released findings of the first field investigations of the effect of terrain elevation changes on tornado path, vortex, strength and damage. They analyzed Google Earth images of the 2011 Tuscaloosa, Ala., and Joplin tornadoes and found tornadoes cause greater damage when they travel uphill and less damage as they move downhill.
That study also revealed that whenever possible, tornadoes tend to climb toward higher elevations rather than going downhill. They also reported that when a region is surrounded by hills, tornadoes skip or hop over valleys beneath and between these hills, and damage is noticed only on the top of the hills.
The results of the field study and the 3-D computer models study were presented at the 12tth Americas Conference on Wind Engineering.
Selvam is holder of the James T. Womble Professorship in Computational Mechanics and Nanotechnology Modeling. He directs the university’s Computational Mechanics Laboratory.CONTACTS:
Matt McGowan | Newswise
Water - as the underlying driver of the Earth’s carbon cycle
17.01.2017 | Max-Planck-Institut für Biogeochemie
Modeling magma to find copper
13.01.2017 | Université de Genève
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
17.01.2017 | Earth Sciences
17.01.2017 | Materials Sciences
17.01.2017 | Architecture and Construction