Energy efficiency and sustainability play an increasingly important role in modern architecture. As a result, the demand for adaptive structures is increasing. These structures are constantly adapting to their requirements, for example by changing their geometry, thus saving structural weight and energy. Accordingly, the design of deployable structures is of great relevance.
Examples are adaptive building shells that have to undergo large deformations or retractable structures for the opening and closing of stadium roofs. But not only the geometry in the different, e.g. open and closed states must meet certain requirements, but also the shape transition. This shall also be designed in such a way that it meets the condition of efficiency.
The basic idea of this research project is therefore to find the most efficient motion between two geometrical configurations of a structure such as an open and a closed configuration of a roof.
Plants as concept generators for adaptive structures
Movements of many plant surfaces fulfill these criteria. Petals and leaves show countless robust motion principles important for many biologically vital functions. They are based on the locally adapted stiffness of their components and avoid highly concentrated strain. An important point is the elucidation of the patterns of movement and principles of actuation and its interplay with the structural set-up of the mechanism: plant movements can be actuated hydraulically in an active way by turgor changes that lead to reversible (nastic) movement or irreversibly (tropistic) growth by cell-shape changes, in a passive manner by hygroscopic swelling and shrinking or because, of cohesion forces. Other mechanisms use the release of stored elastic energy in pre-stressed structures or are initiated by external mechanical forces.
This property of plant movements is transferred to flexible structures in architecture using a biomimetic approach. Simulation methods are used to gain new insights into the biological model. With finite element simulations, hypotheses of biology were investigated and possible movement mechanisms and actuations identified. The simulation allows to isolate different principles of motion and to perform parameter studies, which is not possible with experiments on real plants. For application in architecture, the movements of orchid flowers and the snapping mechanism of carnivorous plants are of particular interest. The Venus flytrap and its sister, the water wheel plant, were investigated.
Method of motion design
A logical assumption is that movements in nature, in this case of plants, follow the principle of maximum efficiency. This is why a biomimetic approach was chosen for the design of motions of adaptive structures. However, it is often not clear which properties are important for the efficient movement of plants. The demands of plants for their motions can differ significantly from the requirements of moving structures in civil engineering. While a plant is a growing structure and other biological processes such as digestion are important, these aspects do not play a role in building structures. For these reasons, a new research idea was generated based on the findings in reverse biomimetics of plant movements, namely to consider the design of motions in a generally valid and more abstract way, i.e. independent of plants. Thereby, a method based on a variational formulation was developed, which allows to design a motion between two geometrical configurations with a defined objective.
If certain properties are required for the non-linear deformation behaviour of a structure, the motion can be designed and the required load collective for a realization can be determined. Thus, structures can perform different transitions between two geometrical configurations by varying the load and thereby fulfill the given properties, such as an energy-minimized motion. The motion design method is based on an additional discretization of the deformation path. This can be approximated with different shape functions. For example, linear Lagrange polynomials, but also B-splines, which enable a better approximation of smooth curves, are possible. Besides, the method allows the easy integration of different element types that are commonly used in FEM for structural-mechanical problems, such as rod elements, quadrilateral elements and isogeometric shell elements.
Among other promising results, this procedure enables to calculate inextensional deformations of shells that are extremely relevant in real applications. Since the bending stiffness of shell structures is much lower compared to their membrane stiffness, this type of deformation can be actuated with very small loads and is therefore highly efficient. Especially for adaptive structures in architecture and building construction, such inextensional deformations are of great interest.
This allows not only to design motions of adaptive structures in civil engineering with a user selectable property, but also to analyze plant movements or deployable structures in other fields such as satellite technology or biomedical technology.
Bio-inspirierte elastische Materialsysteme und Verbundkomponenten für nachhaltiges Bauen im 21ten Jahrhundert.
Ministerium für Wissenschaft, Forschung und Kunst Baden-Württemberg: Zukunftsoffensive IV Innovation und Exzellenz
Plant Biomechanics Group Freiburg (PBG), University of Freiburg
Institute for Computational Design and Construction (ICD), University of Stuttgart
Department of Microsystems Engineering (IMTEK): Chemistry and Physics of Interfaces (CPI), University of Freiburg
Renate Sachse, Rebecca Thierer
- Sachse, R., & Bischoff, M. (2021). A variational formulation for motion design of adaptive compliant structures. International Journal for Numerical Methods in Engineering, 122, 972–1000. https://doi.org/10.1002/nme.6570
- Sachse, R., Geiger, F., & Bischoff, M. (2021). Constrained motion design with distinct actuators and motion stabilization. International Journal for Numerical Methods in Engineering. https://doi.org/10.1002/nme.6638
- Sachse, R., Westermeier, A., Mylo, M., Nadasdi, J., Bischoff, M., Speck, T., & Poppinga, S. (2020). Snapping mechanics of the Venus flytrap (Dionaea muscipula). Proceedings of the National Academy of Sciences (PNAS), 117, 16035–16042. https://doi.org/10.1073/pnas.2002707117
- Tahouni, Y., Cheng, T., Wood, D., Sachse, R., Thierer, R., Bischoff, M., & Menges, A. (2020). Self-shaping Curved Folding:: A 4D-printing method for fabrication of self-folding curved crease structures. Proceedings of SCF ’20: Symposium on Computational Fabrication, November 2020. https://doi.org/10.1145/3424630.3425416
- Westermeier, A. S., Sachse, R., Poppinga, S., Vögele, P., Adamec, L., Speck, T., & Bischoff, M. (2018). How the carnivorous waterwheel plant (Aldrovanda vesiculosa) snaps. Proceedings of the Royal Society B, 285. https://doi.org/10.1098/rspb.2018.0012
- Bischoff, M., Sachse, R., Körner, A., Westermeier, A., Born, L., Poppinga, S., Gresser, G., Speck, T., & Knippers, J. (2017). Modeling and analysis of the trapping mechanism of Aldrovanda vesiculosa as biomimetic inspiration for façade elements. Proceedings of the IASS Annual Symposium 2017. Annette Bögle, Manfred Grohmann (eds.) “Interfaces: architecture.engineering.science”. 25-28th September, 2017, Hamburg, Germany, 2017.