Material effects on strawbale wall seismic capacity

Strawbale construction is a sustainable, viable alternative to conventional building practices. As a newly introduced appendix to the International Residential Code (IRC), the strawbale construction requirements may benefit from further evaluation and possible refinement. Such evaluation and refinement may lead towards code change proposals that will improve the provisions and make strawbale construction safer and more accessible to the general public. This seismic test series addressed the effect of mesh wire type on ductility and the validity of the existing wall slenderness limits. The tests focused on slender walls dominated by flexural deformations. Welded wire mesh wall performed better than the woven wire mesh wall of the same detailing, yet fell short of expected values. Slenderness must continue to be analyzed as the results of a wall using 14” bales were impacted by bale irregularity. The additional tests done as part of this thesis, including vertical load tests and materials testing, added to the understanding of strawbale construction performance and expanded the corpus of strawbale wall test data. All tested walls performed satisfactorily under vertical loading in post-seismic conditions. The purpose of this test series was to validate and potentially suggest improvements to the building code provisions to enhance the prevalence and safety of strawbale construction

Differentiable graph-structured models for inverse design of lattice materials

Architected materials possessing physico-chemical properties adaptable to disparate environmental conditions embody a disruptive new domain of materials science. Fueled by advances in digital design and fabrication, materials shaped into lattice topologies enable a degree of property customization not afforded to bulk materials. A promising venue for inspiration toward their design is in the irregular micro-architectures of nature. However, the immense design variability unlocked by such irregularity is challenging to probe analytically. Here, we propose a new computational approach using graph-based representation for regular and irregular lattice materials. Our method uses differentiable message passing algorithms to calculate mechanical properties, therefore allowing automatic differentiation with surrogate derivatives to adjust both geometric structure and local attributes of individual lattice elements to achieve inversely designed materials with desired properties. We further introduce a graph neural network surrogate model for structural analysis at scale. The methodology is generalizable to any system representable as heterogeneous graphs.Comment: Code: https://gitlab.com/EuropeanSpaceAgency/pylattice2

Surface Modeling and Analysis Using Range Images: Smoothing, Registration, Integration, and Segmentation

This dissertation presents a framework for 3D reconstruction and scene analysis, using a set of range images. The motivation for developing this framework came from the needs to reconstruct the surfaces of small mechanical parts in reverse engineering tasks, build a virtual environment of indoor and outdoor scenes, and understand 3D images. The input of the framework is a set of range images of an object or a scene captured by range scanners. The output is a triangulated surface that can be segmented into meaningful parts. A textured surface can be reconstructed if color images are provided. The framework consists of surface smoothing, registration, integration, and segmentation. Surface smoothing eliminates the noise present in raw measurements from range scanners. This research proposes area-decreasing flow that is theoretically identical to the mean curvature flow. Using area-decreasing flow, there is no need to estimate the curvature value and an optimal step size of the flow can be obtained. Crease edges and sharp corners are preserved by an adaptive scheme. Surface registration aligns measurements from different viewpoints in a common coordinate system. This research proposes a new surface representation scheme named point fingerprint. Surfaces are registered by finding corresponding point pairs in an overlapping region based on fingerprint comparison. Surface integration merges registered surface patches into a whole surface. This research employs an implicit surface-based integration technique. The proposed algorithm can generate watertight models by space carving or filling the holes based on volumetric interpolation. Textures from different views are integrated inside a volumetric grid. Surface segmentation is useful to decompose CAD models in reverse engineering tasks and help object recognition in a 3D scene. This research proposes a watershed-based surface mesh segmentation approach. The new algorithm accurately segments the plateaus by geodesic erosion using fast marching method. The performance of the framework is presented using both synthetic and real world data from different range scanners. The dissertation concludes by summarizing the development of the framework and then suggests future research topics

Regular mosaic pattern development: A study of the interplay between lateral inhibition, apoptosis and differential adhesion

<p>Abstract</p> <p>Background</p> <p>A significant body of literature is devoted to modeling developmental mechanisms that create patterns within groups of initially equivalent embryonic cells. Although it is clear that these mechanisms do not function in isolation, the timing of and interactions between these mechanisms during embryogenesis is not well known. In this work, a computational approach was taken to understand how lateral inhibition, differential adhesion and programmed cell death can interact to create a mosaic pattern of biologically realistic primary and secondary cells, such as that formed by sensory (primary) and supporting (secondary) cells of the developing chick inner ear epithelium.</p> <p>Results</p> <p>Four different models that interlaced cellular patterning mechanisms in a variety of ways were examined and their output compared to the mosaic of sensory and supporting cells that develops in the chick inner ear sensory epithelium. The results show that: 1) no single patterning mechanism can create a 2-dimensional mosaic pattern of the regularity seen in the chick inner ear; 2) cell death was essential to generate the most regular mosaics, even through extensive cell death has not been reported for the developing basilar papilla; 3) a model that includes an iterative loop of lateral inhibition, programmed cell death and cell rearrangements driven by differential adhesion created mosaics of primary and secondary cells that are more regular than the basilar papilla; 4) this same model was much more robust to changes in homo- and heterotypic cell-cell adhesive differences than models that considered either fewer patterning mechanisms or single rather than iterative use of each mechanism.</p> <p>Conclusion</p> <p>Patterning the embryo requires collaboration between multiple mechanisms that operate iteratively. Interlacing these mechanisms into feedback loops not only refines the output patterns, but also increases the robustness of patterning to varying initial cell states.</p

Vision Science and Technology at NASA: Results of a Workshop

A broad review is given of vision science and technology within NASA. The subject is defined and its applications in both NASA and the nation at large are noted. A survey of current NASA efforts is given, noting strengths and weaknesses of the NASA program

Mechanics of Micro-Architected Lattice Structures

Honeybees construct nests that consist of tessellated hexagonal prismatic structures. The bees develop a linear succession of tetrapod structures that serve as the nest’s foundation in the initial stage of construction. This natural hexagonal lattice structure has been the epitome of extensive aerospace applications. And, has particularly been widely used on aircraft control surfaces as they provide an ideal set of mechanical properties; minimal density and ability to withstand high magnitudes of compressive and shear force. This paper analyses this hexagonal lattice configuration using theoretical analysis and simulations. It first analyses the lattice structure by breaking it down into three individual components somewhat resembling the constructional stages in which the nests are developed: cantilever beam, unit cell which is initially the tetrapod structure, and the complete system of the lattice itself. In further chapters, refined geometries, namely stepped and quadratic lattice of the honeycomb, are then analysed with the objective of enhancing its strength to weight ratio, this is again analysed through the same bottom-up approach and procedure. Two approaches are implemented in the enhancement procedure. The obtained numerical results are then reviewed through simulations using multiple computer-aided software, Solidworks and ANSYS where the mechanical properties are established and compared

Conceptual design and analysis of a large antenna utilizing electrostatic membrane management

Conceptual designs and associated technologies for deployment 100 m class radiometer antennas were developed. An electrostatically suspended and controlled membrane mirror and the supporting structure are discussed. The integrated spacecraft including STS cargo bay stowage and development were analyzed. An antenna performance evaluation was performed as a measure of the quality of the membrane/spacecraft when used as a radiometer in the 1 GHz to 5 GHz region. Several related LSS structural dynamic models differing by their stiffness property (and therefore, lowest modal frequencies) are reported. Control system whose complexity varies inversely with increasing modal frequency regimes are also reported. Interactive computer-aided-design software is discussed

Connectivity, Coverage and Placement in Wireless Sensor Networks

Wireless communication between sensors allows the formation of flexible sensor networks, which can be deployed rapidly over wide or inaccessible areas. However, the need to gather data from all sensors in the network imposes constraints on the distances between sensors. This survey describes the state of the art in techniques for determining the minimum density and optimal locations of relay nodes and ordinary sensors to ensure connectivity, subject to various degrees of uncertainty in the locations of the nodes