Rolf H. Luchsinger

Morphological computation and morphological control: Steps toward a formal theory and applications

Morphological computation can be loosely defined as the exploitation of the shape, material properties, and physical dynamics of a physical system to improve the efficiency of a computation. Morphological control is the application of morphological computing to a control task. In its theoretical part, this article sharpens and extends these definitions by suggesting new formalized definitions and identifying areas in which the definitions we propose are still inadequate. We go on to describe three ongoing studies, in which we are applying morphological control to problems in medicine and in chemistry. The first involves an inflatable support system for patients with impaired movement, and is based on macroscopic physics and concepts already tested in robotics. The two other case studies (self-assembly of chemical microreactors; models of induced cell repair in radio-oncology) describe processes and devices on the micrometer scale, in which the emergent dynamics of the underlying physical system (e.g., phase transitions) are dominated by stochastic processes such as diffusion.

Self-Repairing Membranes for Inflatable Structures Inspired by a Rapid Wound Sealing Process of Climbing Plants

A new self-repairing membrane for inflatable light weight structures such as rubber boats or Tensairity® constructions is presented. Inspired by rapid self-sealing processes in plants, a thin soft cellular polyurethane foam coating is applied on the inside of a fabric substrate, which closes the fissure if the membrane is punctured with a spike. Experimental tests are carried out with a purpose built setup by measuring the air mass flow through a leak in a damaged membrane sample. It is shown that the weight per unit area of the self-repairing foam as well as the curing of the two component PU-foam under an overpressure influence the repair efficiency. Curing the foam under overpressure affects the relative density as well as the microstructure of the foam coatings. Maximal median repair efficiencies of 0.999 have been obtained with 0.16 g·cm−2 foam cured at 1 bar overpressure. These results suggest that the bio-inspired technique has the potential to extend the functional integrity of injured inflatable structures dramatically.

Experimental and Numerical Study of Spindle Shaped Tensairity Girders

The new structural concept Tensairity® is a synergetic combination of cables, struts, membranes and low pressure compressed air. The role of the air and membrane is to pretension the cables and to stabilize the compression element against buckling. The new light weight structure has a variety of applications ranging from wide span roof structures to temporary bridges. Recent realizations of Tensairity as the roof of the parking garage in Montreux Switzerland rely on the spindle shape of the girders. First experimental investigations of a spindle shaped Tensairity girder under bending load are presented and compared to numerical results and some analytical results. Geometrical properties and simple approximation formulas for the surface area, the volume and the stresses in an inflated spindle are given.

Pressure induced stability: from pneumatic structures to Tensairity~

Structural stabilization by a pressurized fluid is very common in nature, however hardly found in technology. Car tires, hot air balloons, airships and airhouses are among the few technical exceptions, which are stabilized by a compressed medium, typically air. Restricted by simple geometries and a very limited load bearing capacity these pneumatic structures could succeed only in very specialized applications. Nevertheless, prospective concepts ag has systematically investigated pneumatic structures during the last few years. As a major result, it was demonstrated that almost any shape can be made with pneumatic structures and that astonishing structures such as the pneumatic airplane Stingray can be realized even with low air pressure. On top of that, Airlight Ltd. in close collaboration with prospective concepts ag has recently developed the fundamental new structural concept Tensairity. The synergetic combination of an inflated structure with conventional structural elements such as cables and struts yields pneumatic light-weight structures with the load bearing capacity of steel girders. Thus, complex forms and high strength open up many new opportunities for pressure induced stability in technology. An overview of these recent developments is presented and the close relationship of pneumatic structures with biology is outlined.

Pumping Cycle Kite Power

Simple analytical models for a pumping cycle kite power system are presented. The theory of crosswind kite power is extended to include both the traction and retraction phase of a pumping cycle kite power system. Dimensionless force factors for the reel out and reel in phase are introduced which describe the efficiency of the system. The optimal reel out and reel in speed of the winch is derived where the cycle power becomes maximal. These optimal speeds are solely determined by the ratio of the force factors. Scenarios for wind speeds higher than the nominal wind speed are considered and power curves for the pumping cycle kite power system derived. The average annual power for a given wind distribution function allows to estimate the annual energy production of the pumping cycle kite power system. The role of the elevation angle of the tether is highlighted and a simple model to demonstrate the influence of the kite mass on the power output is discussed.

Structural and mechanical properties of flexible polyurethane foams cured under pressure

Flexible two-component polyurethane foam was synthesized under various extents of overpressure up to 2 bar. The influence of the pressure conditions on shrinkage and basic foam properties such as the relative density, microstructure, and ratio of open to closed pores as well as the elastic mechanical properties were investigated. The relationship between the relative foam density and the applied overpressure is shown to be rather linear. An abrupt change of the mainly open pore structure to essentially closed-cell foam was found in the narrow range between 50% and 60% relative density. A way to control the shrinkage properties of closed-cell foam via the extent and duration of overpressure applied during the foam synthesis was found and a hypothetic qualitative model describing the basic underlying mechanisms is given. Closed-cell flexible foam showing no effective shrinkage was produced this way. The achieved foam properties display an interesting potential for the application as e.g. gasket material.

Simulation Based Wing Design for Kite Power

A framework for simulating tethered wings for kite power is presented. The simulation tool contains a detailed aerodynamic model and a realistic tether model. With the aerodynamic tool, two different wings are analyzed regarding their efficiency. The aerodynamic efficiency of kites is determined with a parameter study showing the trends of the most important geometrical parameters. Those wings are manually flown in the simulator and the flight behavior is discussed. Finally, power cycles of a pumping system are simulated and controlled automatically and results are compared.

Structural Behavior of Symmetric Spindle-Shaped Tensairity Girders

AbstractThe load-bearing behavior of a symmetric spindle-shaped Tensairity girder with 5-m span and thin chords is studied experimentally, numerically, and analytically. The influence of the air pressure on the load-deflection behavior is investigated for homogeneous distributed load, asymmetric distributed load, and central local load. An m-shaped deflection with two maxima at about one- and three-quarter of the span was obtained for homogeneous distributed loads whose distribution is not linearly dependent on the applied load. The slope of the load-deflection curve as well as the maximal load increases with increasing air pressure, demonstrating the stabilizing role of the inflated hull. An analytical model based on two beams coupled by an elastic foundation with air pressure-dependent properties is presented for the homogeneous distributed load case, and simple predictions for the average displacement and the maximal load are given. The model reveals the subtle interplay between the chords and the infl...

An inflatable wing using the principle of Tensairity

The paper describes the new concept Tensairity which can be used to significantly improve the load bearing capacity of inflatable wings. The basic principle of Tensairity is to use an inflatable structure to stabilize conventional compression and tension elements. So far, Tensairity has been mainly used in civil engineering application like roof structures and bridges. In this work, considerations to apply Tensairity to wing structures are given and the construction of two wing-like Tensairity kite prototypes is described. Test results on the Tensairity structure used in these kites are presented and compared to purely air inflated structures. Finally, the advantages of Tensairity wings are discussed and some application areas of these wings are suggested.

Effect of Fabric Webs on the Static Response of Spindle-Shaped Tensairity Columns

Tensairity is a lightweight structural concept comprising struts and cables stabilized by a textile membrane which is inflated by low pressurized air. This paper addresses the effect of fabric webs inside the membrane hull on the static response of spindle-shaped Tensairity columns to axial compression. Two full-scale spindle-shaped columns, one without and one with webs, were fabricated and tested. The columns were subjected to axial compressive loading for various levels of internal air pressure to quantify its effect on the global structural response. It was found that the stiffness and the load bearing capacity for both columns increased with increasing air pressure. The experimental results also revealed the benefits of including fabric webs in the spindle configuration in terms of axial stiffness and buckling load. Comparisons with an analytical solution and finite-element predictions showed good correlation for the axial stiffness in the case without webs. For the case with web deviations between predicted and experimental results indicated that structural detailing and imperfections in the manufacturing process strongly influence the performance of Tensairity columns with internal webs.