Experimental and numerical investigations on the blast reducing effects of plants

In the area of structural protection, the broad range of terrorist threats is opposed by a diverse range of structures and concepts for the protection of people and infrastructures. The emphasis is traditionally on special structural solutions designed specifically for these types of loads. Especially in the case of blast loads, it can be questioned whether structures that were not originally designed for this purpose can substantially contribute to the overall protection concept. The research group headed by Professor Norbert Gebbeken focuses especially on elements for the design of urban spaces. In this context, it is also interesting to what extent plants can be used as blast reducing elements.

Initial experimental studies on the protective potential of thuja and cherry laurel hedges provided promising results and valuable information on the suitability of plants for this purpose. Especially for the reduction of the peak overpressures of the blast waves, the expectations were in some cases clearly exceeded. Experimental investigations are complex, time-consuming and expensive. Therefore, numerical simulations are used to limit the experimental effort. Numerical simulations of blast wave propagation are generally very computation-intensive and become more complex with increasing complexity of the structures to be investigated. Since each plant is a unique specimen of a very complex structure, an abstract and largely simplified numerical model is intended. Such a model should on the one hand, capture the blast reducing effect of the plants with sufficient precision and, on the other hand, keep the modelling and calculation effort within reasonable limits.

For this purpose, it needs to be investigated phenomenologically which flow effects occur within the plants under blast loads and how they influence the propagation of the blast wave. For this purpose, smaller parts of different real plants are scanned three-dimensionally by laser in order to generate numerical models with a high degree of detail (see figure). These models are subjected to different blast loads in numerical simulations in order to analyse the flow conditions around the flexible branches and leaves. The results are used to investigate how far the level of detail in the numerical modelling of plants under blast loads can be reduced. Finally, an efficient approach for the consideration of the blast reducing effects of plants in numerical simulations of blast wave propagations should be developed.