Understanding the conditions of extreme water flows will lead to more resilient infrastructure
Extreme events such as storm surges in coastal regions or dam failures further inland, can result in hazardous, particle-laden flows, as the water’s motion picks up debris directly from the ground or from destroyed infrastructure. The debris is then distributed by the flow over substantial distances. However, the exact conditions under which this happens, along with a clear understanding of how debris-burden impacts on manmade structures, remains under-explored. The EU-funded IMPLOADIS project set out to use experimental and numerical modelling methods to add to this stock of knowledge. The team reproduced natural flows in a laboratory based on dam-breaks and very long waves. Additionally, innovative techniques were used to measure debris accumulation and distribution, resulting in the development of ‘debris tracking methods’. This work has implications for structural design which can incorporate resistance to floating or submerged debris, as well as multi-object impact. Getting to grips with the right experimental techniques As the project coordinator Dr. Nils Goseberg of the Leibniz Universität Hannover, Germany, points out, ‘Studies on floating objects unlike rigid fixed structures had been scarce prior to this project. Partially, this has been due to major difficulties in monitoring the object's motion but also due to lack of testing facilities. Additionally, combining novel instrumentation in this field had not been attempted before as the research had elements of risk where contingency planning was crucial.’ Research focussed on experimental work using tsunami-like flows which were generated by opening reservoirs quickly and releasing violent flows. The water would then envelop, and carry, any objects in its path, creating the debris for tracking. Additionally, with the help of a Swedish SME, IMPLOADIS was able to customise off-the-shelf radio-wave-technology normally used to track sports equipment and shopping behaviour, for use with the water flows. Using this approach, the project was able for the first time to conduct three-dimensional water flow models for shipping containers. Due to its complexity, this modelling required a multi-method approach with novel instrumentation and optical methods to track the debris distribution. This actually presented the biggest challenge to the project. As Dr. Goseberg recalls, ‘Surprisingly, the varying lighting conditions of an outside experimental facility we used in Japan, posed a major challenge as it made analysing video images very difficult. Conditions could easily vary from thunderstorm to bright daylight for which the algorithms had to be adapted quite substantially.’ Better preparation for the unexpected One of the key findings of the project was that the elasticity of the structure-debris interaction was crucial to estimating impact forces. As Dr. Goseberg puts it, ‘This implies that the elasticity of structures needs to be taken into account in future design guidelines for impact-prone areas.’ This more comprehensive understanding of the consequences of extreme flow conditions, such as those experienced during natural disasters, will contribute to the development of more resilient buildings and critical infrastructure. The IMPLOADIS research group are continuing to work on ways to more accurately estimate impact loads. As Dr. Goseberg sums up, ‘This research has probably doubled the amount of questions we had before, so high on our agenda will be looking especially at elastic structural impact with new experimental techniques.’
