Bradley International Airport Improvements: An Economic Impact Analysis

Bradley Airport, improvements

The Economic Impact of Connecticut's Information Technology Industry

information technology, economic impact, Tornqvist index

Topology Optimization Algorithms for Improved Manufacturability and Cellular Material Design

Topology optimization is a free-form approach to structural design in which a formal optimization problem is posed and solved using mathematical programming. It has been widely implemented for design at a range of length scales, including periodic cellular materials. Cellular materials in this context refer to porous materials with a representative unit cell that is repeated in all directions. For cellular material design an upscaling law is required to connect the unit cell topology to the bulk material properties. This has limited most work on topology optimization of cellular materials to linear properties, such as elastic moduli or thermal conduction, where numerical homogenization can be used. Although topology-optimized materials are often shown to outperform conventional cellular material designs, the optimized designs are often complex and can therefore be di cult to fabricate. This is true despite the rapid development of manufacturing technologies that have provided radically new capabilities. Although such technologies have reduced the manufacturing constraints, there are still limitations. This thesis looks to advance topology optimization of cellular materials on two fronts: (i) by more formally integrating manufacturing constraints and capabilities into topology optimization methodology, and (ii) by moving beyond linear properties to consider the nonlinear response of cellular materials. In this work we propose to implicitly integrate manufacturing considerations into the topology optimization formulation by using projection based approaches. We seek to improve the manufacturability of topology-optimized structures by providing the designer minimum length scale control of both the design’s solid and void phases. The new two-phase projection algorithm is demonstrated on benchmark examples and uses nonlinear weighting functions to let the design variable magnitude determine if solid or void should be actively projected. In addition, we utilize a multi-phase cellular design approach that can leverage the new capability of deposition of multiple solids that is o ered by current 3D printing technologies. These multi-phase designs generally outperform two-phase topologies and potentially o er new functionalities. Our algorithm is based on an existing multimaterial formulation and used to design cellular topologies for various elastic properties, including negative Poisson’s ratio, and for multiobjectives including mechanical and thermal properties. Expanding topology optimization to cellular design governed by nonlinear mechanics enables designing e ective materials with a range of new improved properties such as energy absorption. However, considering material– and/or geometric nonlinearities in cellular design faces the challenge of the lack of a recognized upscaling technique. Previous works have turned to nite periodicity. This thesis will explore the necessary steps in developing a topology optimization algorithm for cellular design governed by nonlinear mechanics. Further, the forward homogenization problem of how the unit cell topology e ects the e ective material’s energy absorption will be numerically investigated for a range of conventional and topology-optimized unit cells

Mekaniseringsspørgsmaalet i Landbruget.

Mekaniseringsspørgsmaalet i Landbruget

Nanosecond laser texturing for high friction applications

AbstractA nanosecond pulsed Nd:YAG fibre laser with wavelength of 1064nm was used to texture several different steels, including grade 304 stainless steel, grade 316 stainless steel, Cr–Mo–Al ‘nitriding’ steel and low alloy carbon steel, in order to generate surfaces with a high static friction coefficient. Such surfaces have applications, for example, in large engines to reduce the tightening forces required for a joint or to secure precision fittings easily. For the generation of high friction textures, a hexagonal arrangement of laser pulses was used with various pulse overlaps and pulse energies. Friction testing of the samples suggests that the pulse energy should be high (around 0.8mJ) and the laser pulse overlap should be higher than 50% in order to achieve a static friction coefficient of more than 0.5. It was also noted that laser processing increases the surface hardness of samples which appears to correlate with the increase in friction. Energy-Dispersive X-ray spectroscopy (EDX) measurements indicate that this hardness is caused by the formation of hard metal-oxides at the material surface

Improved Two-Phase Projection Topology Optimization

Abstract Projection-based algorithms for continuum topology optimization have received considerable attention in recent years due to their ability to control minimum length scale in a computationally efficient manner. This not only provides a means for imposing manufacturing length scale constraints, but also circumvents numerical instabilities of solution mesh dependence and checkerboard patterns. Standard radial projection, however, imposes length scale on only a single material phase, potentially allowing small-scale features in the second phase to develop. This may lead to sharp corners and/or very small holes when the solid (load-carrying) phase is projected, or one-node hinge chains when only the void phase is projected. Two-phase length scale control is therefore needed to prevent these potential design issues. Ideally, the designer would be able to impose different minimum length scales on both the structural (load-carrying) and void phases as required by the manufacturing process and/or application specifications. A previously proposed algorithm towards this goal required a design variable associated with each phase to be located at every design variable location, thereby doubling the number of design variables over standard topology optimization [2]. This work proposes a two-phase projection algorithm that remedies this shortcoming. Every design variable has the capability to project either the solid or the void phase, but nonlinear, design dependent weighting functions are created to prevent both phases from being projected. The functions are constructed intentionally to resemble level set methods, where the sign of the design variable dictates the feature to be projected. Despite this resemblance to level sets, the algorithm follows the material distribution approach with sensitivities computed via the adjoint method and MMA used as the gradient-based optimizer. The algorithm is demonstrated on benchmark minimum compliance and compliant inverter problems, and is shown to satisfy length scale constraints imposed on both phases. 2. Keywords: Topology Optimization, Projection Methods, Manufacturing Constraints, Length Scale, Heaviside Projection. Introduction Topology optimization is a design tool used for determining optimal distributions of material within a domain. System connectivity and feature shapes are optimized and thus, as the initial guess need not be informed, topology optimization is capable of generating new and unanticipated designs. It is well-known, however, that this may result in impractical solutions that are difficult to fabricate or construct, such as ultra slender structural features or small scale pore spaces. A key focus of this work is to improve manufacturability of topology-optimized designs by controlling the length scale of the topological features. The length scale is generally defined as the minimum radius or diameter of the material phase of concern. It is thus a physically meaningful quantity that can be selected by the designer based on fabrication process. The fabrication process also dictates the phase (or phases) on which the restriction is applied. For example, for topologies constructed by deposition processes, it is relevant to consider constraining the minimum length scale of the solid phase. Similarly, for designs that are manufactured by removing material, for example by milling, the manufacturability constraints should include minimum length scale and maximum curvature of the voids as dictated by the machine. Moreover, it is well established that controlling the length scale has the additional advantage that it circumvents numerical instabilities, such as checkerboard patterns and mesh dependency. Several methods for controlling the length scale of a topology optimization design exist ([1], [3]). Herein, the Heaviside Projection Method (HPM) [1] is used. HPM is capable of yielding 0-1 designs in which the minimum length scale is achieved naturally, without additional constraints. In HPM, the design variables are associated with a material phase and projected onto the finite element space by a Heaviside function. This mathematical operation is independent of the problem formulation and the governing physics. The projection is typically done radially and the projection radius is chosen as the prescribed minimum length scale. In its original form [1], the method projects a single phase onto the elements and

Sexuality and Affection among Elderly German Men and Women in Long-Term Relationships: Results of a Prospective Population-Based Study

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.The study was funded by the German Federal Ministry for Families, Senior Citizens, Women and Youth (AZ 314-1722-102/16; AZ 301-1720-295/2), the Ministry for Science, Research and Art Baden-Württemberg, and the University of Rostock (FORUN 989020; 889048)