When temperatures drop to below zero in Denmark, ice formation may occur on the suspension bridge of the Great Belt Fixed Link. When temperatures return above zero and the ice begins to melt, chunks of ice (measured up to seven kilos) may constitute a hazard if they fall down onto the carriageway. Even if they just hit the road, they can startle road users so much that it may cause problems and accidents. However, this situation requires a very special combination of temperature changes within a short period of time, and, fortunately, it does not happen very often.
However, when there is a risk of ice falling down onto the roadway, the Great Belt Fixed Link closes for traffic. Next to wind, falling chunks of ice is the most frequent cause of closure of the bridge.
“We close the bridge for safety’s sake. This may be highly frustrating to all road users, but we take no chances with safety,” says Jesper Brink—Maintenance Manager at A/S Storebælt—and continues:
“We want to know much more precisely when the chunks of ice start to melt, so that we can predict with greater accuracy when it is necessary to close the bridge.”
A/S Storebælt, which operates the Great Belt Fixed Link, today uses various types of sensors—including inspection cameras—for visual assessment of the risk of falling ice. However—with these methods—it may be very difficult to provide an accurate risk assessment of falling ice.
"It was the opportunity to work on a tangible and specific problem that no one else has studied before that really got me hooked"
Rasmus Hvidberg, Master Student, DTU Fotonik
Rasmus Hvidberg—MSc student at DTU Fotonik—has been working to solve precisely this problem:
“I’ve performed a project in which I analysed so-called speckle patterns that form on the surface of ice when it is illuminated with a laser. I studied how these speckle patterns change when the ice melts. By analysing a large volume of data, I was able to pinpoint fairly accurately when the ice starts to melt,” he says.
The method gives an immediate indication of when the very first ice crystals begin to melt, also even if the melting process starts right at the steel wire.
Rasmus Hvidberg’s project was a BSc project which A/S Storebælt had designed together with DTU Fotonik supervisor Michael Linde Jakobsen—Senior Researcher at DTU Fotonik— and Thim Nørgaard Andersen, who is a lighting engineer with the firm of consulting engineers Light Bureau.
Thim says the following about the project:
“Rasmus has done an excellent piece of work, and it’s a pleasure that there’s such a high level among the students. Rasmus’ results have helped us clarify that the principle we had imagined can actually be applied in practice. In collaboration with A/S Storebælt, we’re therefore now applying for funding for the continued development needed before the sensors are ready to be installed on the Great Belt Bridge.”
To the left is a piece of the same type of cable that holds up the roadway on the Great Belt Bridge. The inner part shows cut-off steel wires which have been assembled to form the strong cables that hold up the carriageway of the Great Belt Bridge. The outer black ring is insulation material that protects against wind and weather. To the right is a chunk of ice of about one kilo.
BSc project gave Rasmus an interest in photonics engineering
However, it was not immediately in the cards that Rasmus Hvidberg would pave the way for this new laser solution. In fact, he was enrolled in a completely different study programme at DTU:
“At Earth and Space Physics and Engineering—where I studied before—I had acquired an insight into problems regarding communication in space. It has inspired me to think about how you can use optical sensors to solve all kinds of problems,” he says and continues:
"But it was the opportunity to work on a tangible and specific problem that no one else has studied before that really got me hooked. Being the first to ‘play around’ with new ideas and explore them is something that I find tremendously exciting.”
The BSc project made Rasmus Hvidberg change study programme track:
“I got a little insight into the enormous potential that light has. It aroused my curiosity.”
Rasmus Hvidberg is currently studying at DTU’s MSc programme in photonics, where the students work with most of the current light-based technologies. It spans all the types of light we know, including ultraviolet light (UV), visible light, infrared light, and even terahertz:
“I find photonics very interesting, as it turns out that light can be used in virtually all areas: Health technology, communication technology, quantum technology, and many of the technologies that make the world more sustainable. Its great potential—and the opportunity to study and work in the way that I like—is a good combination for me,” says Rasmus Hvidberg.
Rasmus Hvidberg has just started on a special project in which—together with his former BSc project supervisor, Michael Linde Jakobsen, Senior Researcher at DTU Fotonik—he will continue to work with speckle patterns, and the plan is that it will result in a scientific article.