Development of a New Span-Morphing Wing Core Design

This paper presents a new design for the core of a span-morphing unmanned aerial vehicle (UAV) wing that increases the spanwise length of the wing by fifty percent. The purpose of morphing the wingspan is to increase lift and fuel efficiency during extension, to increase maneuverability during contraction, and to add roll control capability through asymmetrical span morphing. The span morphing is continuous throughout the wing, which is comprised of multiple partitions. Three main components make up the structure of each partition: a zero Poisson’s ratio honeycomb substructure, telescoping carbon fiber spars and a linear actuator. The zero Poisson’s ratio honeycomb substructure is an assembly of rigid internal ribs and flexible chevrons. This innovative multi-part honeycomb design allows the ribs and chevrons to be 3D printed separately from different materials in order to offer different directional stiffness, and to accommodate design iterations and future maintenance. Because of its transverse rigidity and spanwise compliance, the design maintains the airfoil shape and the cross-sectional area during morphing. The telescoping carbon fiber spars interconnect to provide structural support throughout the wing while undergoing morphing. The wing model has been computationally analyzed, manufactured, assembled and experimentally tested.

Influence of Rotary-Steerable-System Design on Borehole Spiraling

Summary The paper investigates the influence of the design of push-the-bit rotary-steerable systems (RSSs) on the tendency to drill spiraled boreholes by analyzing the directional stability of the bit trajectory. In this model, differences in RSS designs are accounted for conceptually by assigning a lateral stiffness to the RSS pads. This simple device, which introduces a dependence of the force on the pads upon the deflection of the bottomhole assembly (BHA) relative to the borehole axis, enables exploration of the influence of the actuation mechanism, with the RSS behaving at the ends of the spectrum either as a soft or as a stiff node of the drilling structure. According to this analysis, low pad stiffness has little consequence on the general behavior of the system. However, as the pad stiffness increases, any perturbation in the borehole geometry sensed by the pads alters the drilling direction of the bit and triggers, under certain conditions, self-excited oscillations in the borehole geometry. By increasing the transverse rigidity of the BHA in the vicinity of the bit, stiff RSS pads thus enhance the propensity of a drilling structure to drill spiraled holes and generate, if the system is directionally unstable, borehole oscillations with pitch that corresponds to the distance between the bit and the pads. In contrast, a directionally unstable BHA equipped with RSS characterized by a low stiffness produces spiraled holes with a wavelength corresponding to the distance between the bit and the first stabilizer.

Cell wall structure and formation of maturing fibres of moso bamboo ( Phyllostachys pubescens ) increase buckling resistance

The mechanical stability of the culms of monocotyledonous bamboos is highly attributed to the proper embedding of the stiff fibre caps of the vascular bundles into the soft parenchymatous matrix. Owing to lack of a vascular cambium, bamboos show no secondary thickening growth that impedes geometrical adaptations to mechanical loads and increases the necessity of structural optimization at the material level. Here, we investigate the fine structure and mechanical properties of fibres within a maturing vascular bundle of moso bamboo, Phyllostachys pubescens , with a high spatial resolution. The fibre cell walls were found to show almost axially oriented cellulose fibrils, and the stiffness and hardness of the central part of the cell wall remained basically consistent for the fibres at different regions across the fibre cap. A stiffness gradient across the fibre cap is developed by differential cell wall thickening which affects tissue density and thereby axial tissue stiffness in the different regions of the cap. The almost axially oriented cellulose fibrils in the fibre walls maximize the longitudinal elastic modulus of the fibres and their lignification increases the transverse rigidity. This is interpreted as a structural and mechanical optimization that contributes to the high buckling resistance of the slender bamboo culms.

Structural and Dynamical Properties of Intercalated Layered Silicates

Structural and dynamical properties of intercalated solids in general [1], and layered silicates of the type AxB1−x -Vermiculite in particular, are of both fundamental and practical interest. In these systems, two types of ions A and B with different ionic radii occupy the space between two silicate layers. On the fundamental side, one is interested in studying the average interlayer spacing as a function of (1) the concentration x of the large ion, (2) sizes and compressibilities of the intercalated ions and (3) the transverse rigidity of the silicate layers. In addition, one is interested in the dynamic properties of these solids. On the practical side, when the size difference between the two intercalants is large, one obtains pillared clays which are characterized by widely spaced silicate layers that are propped apart by sparsely distributed larger interlayer cations (sometimes referred to as pillars) [2]. The enormous free volume of accessible interior space that is derived from such an open structure has significent practical application in the field of catalysis and sieving.