Julian Lienhard

Flectofin: a hingeless flapping mechanism inspired by nature

This paper presents a novel biomimetic approach to the kinematics of deployable systems for architectural purposes. Elastic deformation of the entire structure replaces the need for local hinges. This change becomes possible by using fibre-reinforced polymers (FRP) such as glass fibre reinforced polymer (GFRP) that can combine high tensile strength with low bending stiffness, thus offering a large range of calibrated elastic deformations. The employment of elasticity within a structure facilitates not only the generation of complex geometries, but also takes the design space a step further by creating elastic kinetic structures, here referred to as pliable structures. In this paper, the authors give an insight into the abstraction strategies used to derive elastic kinetics from plants, which show a clear interrelation of form, actuation and kinematics. Thereby, the focus will be on form-finding and simulation methods which have been adopted to generate a biomimetic principle which is patented under the name Flectofin®. This bio inspired hingeless flapping device is inspired by the valvular pollination mechanism that was derived and abstracted from the kinematics found in the Bird-Of-Paradise flower (Strelitzia reginae, Strelitziaceae).

Active Bending, a Review on Structures where Bending is Used as a Self-Formation Process:

In this paper structures that actively use bending as a self-forming process are reviewed. By bringing together important material developments and various historical as well as recently built samples of such structures, the aim is to show coherences in their design approach, structural systems and behaviour. Different approaches to bending-active structures are defined and described. By making this work accessible and categorising it, this paper aims to contribute to an emerging development. A differentiation of such structures is suggested based on their design approaches. Three such approaches are differentiated: the behaviour based approach, the geometry based approach and current research that seeks to integrate the two. In this paper the nature of these approaches and some important project samples are discussed.

A methodology for transferring principles of plant movements to elastic systems in architecture

In architecture, kinetic structures enable buildings to react specifically to internal and external stimuli through spatial adjustments. These mechanical devices come in all shapes and sizes and are traditionally conceptualized as uniform and compatible modules. Typically, these systems gain their adjustability by connecting rigid elements with highly strained hinges. Though this construction principle may be generally beneficial, for architectural applications that increasingly demand custom-made solutions, it has some major drawbacks. Adaptation to irregular geometries, for example, can only be achieved with additional mechanical complexity, which makes these devices often very expensive, prone to failure, and maintenance-intensive.Searching for a promising alternative to the still persisting paradigm of rigid-body mechanics, the authors found inspiration in flexible and elastic plant movements. In this paper, they will showcase how todays computational modeling and simulation techniques can help to reveal motion principles in plants and to integrate the underlying mechanisms in flexible kinetic structures. By using three case studies, the authors will present key motion principles and discuss their scaling, distortion, and optimization. Finally, the acquired knowledge on bio-inspired kinetic structures will be applied to a representative application in architecture, in this case as flexible shading devices for double curved facades. Plant movements.Kinetic structures.Biomimetics.Facade shading.Compliant mechanisms.

Abstraction of bio-inspired curved-line folding patterns for elastic foils and membranes in architecture

Today’s architectural foils and membranes amaze with their superior strength-toweight ratio and are often implemented as lightweight building envelopes or shading devices. Most claddings, however, are optimized for high tensile strength, which reduces the design possibilities to pre-stressed inflexible shapes. Only a few projects are exploring the potential inherent in the membrane’s low bending stiffness. Nowadays, new materials and manufacturing methods allow for customized pliability of semi-rigid thin-shell structures, which fully tap the potential of reversible elastic deformation. While this concept has hardly been used in architecture, convertible surfaces are rampant in nature. Therefore, the aim of this paper is to review in general how nature’s soft, flexible, and forceadaptive structures may inspire the development of technical membrane structures and outline their architectural potential in particular. Focusing on bio-inspired pliable systems that show distinct curved-line folding principles will be the framework for a close collaboration among architects, engineers, and biologists. Examining the flower opening of Ipomoea alba will clarify the drawbacks and opportunities of elastic kinematics. Therefore, the first part of the study will introduce this nocturnal flower, whose environmentally responsive petals adapt their geometry in a circadian rhythm. Morphological and anatomical analyses will secondly lead to a better understanding of their primarily

Plant movements as concept generators for deployable systems in architecture

Plants, apparently not capable of complex movements, have always fascinated scientists when proving the contrary. A multitude of movements in plants have been revealed, showing a broad spectrum of motion sequences and underlying principles. Interestingly, many of these movements show high elasticity and flexibility of the respective structures and allow reversible deformations. With the investigation of suitable biological role models and the use of new construction materials, such as fibre-reinforced polymers (FRPs), the authors are developing deployable technical structures without local hinges. In this presentation the first steps of the applied biomimetic working process are described: the selection of role models, investigation and basic abstraction of plant movements. An overall screening through the plant kingdom has led to a wide-ranged matrix comprising many different types of plant movements, which constitutes the basis for our investigations. We distinguish between autonomous and non-autonomous movements. Active autonomous movements are characterized by motor organs, e.g. pulvini driven by a change of turgor pressure. Passive autonomous movements occur due to changing physical circumstances, e.g. bending through desiccation. Non-autonomous movements are mostly reversible deformations caused by a release of stored elastic energy after an external trigger or by direct application of mechanical forces. In a case study we applied morphological and anatomical investigations on the valvular pollination

Considerations on the Scaling of Bending-Active Structures

Bending-active structures are composed of curved beam or shell elements which base their geometry on the elastic deformation of an initially straight or planar configuration. In bending-active structures the moment of inertia has a direct influence on the residual stress and is therefore limited by a given minimal curvature in the system and the permissible bending stress capacities of the chosen material. These interdependencies may lead to a scaling issue that limit bending-active structures to a certain size range. This range may be widened if the systems reliance on elastic stiffness is compensated by other stiffening factors such as coupling of structural elements and stress stiffening effects. This paper will analyse the scaling effects in bending-active structures. Some basic systems are studied by means of dimensional analysis and FEM parameter studies to clarify at which power each influencing factor effects scaling. Based on these findings some more complex structures are studied for their scalability. This will offer the basis for some more general conclusions.

Elastic architecture: nature inspired pliable structures

At the interfaces of our mostly stationary architecture and surrounding nature we need to make constructions adaptable to ambient changes. Adaptability as a structural response to changing climate conditions, such as the intensity and direction of sun radiation, can be realised with deployable systems. These systems are often based on the combination of stiff compression members and soft tension members connected with hinges and rollers. Deployable systems in nature are often based on flexibility. This can be observed especially in plant movements. New construction materials such as fibre-reinforced polymers (FRP) can combine high tensile strength with low bending stiffness, allowing large elastic deformations. This may enable a completely new interpretation of convertible structures which work on reversible deformation, here referred to as elastic or pliable structures. In a current research project the kinematics for such systems are derived from certain applicable plant movements. This paper will focus on the biomimetic workflow used to develop elastic kinetic structures based on such movements. The abstraction and optimisation methods will be described from an engineering point of view, focusing on the technical approaches of converting the conceptual results of a first level abstraction into higher level abstractions and finally to physical design.

Biomimetic Deployable Systems in Architecture

The high elasticity of plant structures represents the basis of many plant movements and also allows for reversible deformations. By analyzing suitable biological role models and using new construction materials bio-inspired deployable technical structures without local hinges can be developed. The selection, investigation and basic abstraction of nastic plant movements are the first steps of the applied biomimetic working process. A broad screening of the plant kingdom has revealed a wide range of types of these movements, which can be distinguished in autonomous and non-autonomous movements. Active autonomous movements are driven by motor organs or cells, e.g. by a change of turgor pressure. Passive autonomous movements are typically caused by a change of the physical circumstances in cells or sub-cellular structures, e.g. movement caused by changes of humidity in cell walls. Non-autonomous movements are mostly reversible and occur due to a release of stored elastic energy after an external trigger or by application of mechanical forces. As these deformations show clearly defined actuating elements and mechanics, our investigation concentrates on the latter kinetic systems. Model plants are analyzed morphologically and biomechanically, e.g. by bending, tensile and pressure tests. In a close collaboration between biologists and engineers these kinetic systems are verified with the help of physical models, computer simulations and additional abstraction steps are performed which finally lead to technical applications in biomimetic deployable systems in architecture.

Bio-inspired, Flexible Structures and Materials

This chapter discusses the potential of biomimetics in formfinding and the development of structural systems based on constant or reversible elastic deformation. The existence of high strength elastic materials are the preconditions for the technical realisation of such elastic structures. Therefore, this chapter will start by introducing elastic building materials and biomimetic abstraction techniques individually before bringing the two together by presenting case studies which successfully combined both aspects.