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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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183 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS2024

Finite Element Simulation of the Direct Energy Deposition using Comsol Multiphysics

Direct Energy Deposition (DED) is an emerging technology extensively employed in metal Additive Manufacturing (AM). Despite its widespread industrial application, mathematical modeling in this domain remains challenging. This complexity arises from the intricate nature of the modeling approach and the nonlinear behavior of material parameters across a broad temperature range. Consequently, experimentalists often resort to a trial-and-error method to achieve structures with desired properties. However, this approach can be time-consuming and may not always yield parts with the requisite characteristics, highlighting the necessity for mathematical modeling to enhance manufacturing success. This study focuses on thin-walled manufacturing with a single bead thickness, adjusting laser parameters to produce such structures. The laser cladding speed, typical for DED manufacturing, is considered to be on the order of centimeters per second. The various wall thicknesses and heights are explored to discern the general characteristics of walls manufactured via this DED approach. Our modeling approach diverges from the conventional DED modeling based on activation-deactivation of predefined mesh domains, commonly implemented in many finite element codes. Instead, a method is proposed that effectively models layer cladding and melt pool dynamics, enabling predictions of the microstructure in the resulting structures. The formation mechanisms of cellular, dendritic columnar, and stray (equiaxed) grains, which arise from the interplay between nucleation and growth from the surface is analyzed. The study also examines the feasibility of microstructure formation to demonstrate the various thermal characteristics inherent in wall manufacturing. Our results illustrate how different process parameters influence the temperature gradient and cooling rate of the molten pool, subsequently affecting the primary dendrite arm spacing (PDAS). This modeling technique allows for the investigation of diverse thermal conditions, facilitating the prediction of microstructure and residual stresses in the manufactured parts.

modeling↗
NASA NTRSDate not supplied

A Golden Era of PSC Observations From the A-Train By CALIOP and MLS

The fundamental role of polar stratospheric clouds (PSCs) in the depletion of stratospheric ozone is well established. Heterogeneous reactions on PSCs convert the stable chlorine reservoirs HCl and ClONO2 to chlorine radicals that destroy ozone catalytically. PSCs also prolong ozone depletion by delaying chlorine deactivation through the removal of gas-phase HNO3 and H2O by sedimentation of large PSC particles. There has been substantial recent progress in our understanding of PSC processes due to the long-term, vortex-wide observations from the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) lidar on the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite and the MLS (Microwave Limb Sounder) on the Aura satellite. The CALIOP observations provide unprecedented high spatial resolution information on particulate aerosol/PSC morphology and composition, while MLS provides complementary collocated measurements of gas-phase HNO3 and H2O, the major constituents of all PSC particles. The combined analyses of these datasets have enabled better PSC composition discrimination and provided valuable new insight into PSC formation processes and particle growth kinetics. The more than 17 years of CALIOP and MLS data have uniquely captured the primary aspects of the seasonal and multi-year variability of PSCs in the Arctic and Antarctic, enabling the development of a state-of-the-art reference PSC data record and climatology. In this presentation, we highlight the significant advances in our understanding achieved during this golden era of spaceborne PSC observations and identify remaining gaps in our knowledge that future spaceborne lidar missions may help resolve.

polar stratospheric clouds↗
NASA NTRS2024

Two mechanisms for the spontaneous emergence, execution, and reprogramming of chemical logic circuits

A key question in origin-of-life research is how primitive life or life-like systems obtained reusable and reprogrammable machinery of processing information to respond to various environmental and internal stimuli. One strategy to approach this question is to view living systems as universal chemical computers. This approach focuses upon uncovering how reusable and reprogrammable chemical NOT, AND, and OR logic gates could appear under prebiotically possible scenarios where simple chemicals and second- or lower-order reactions are more frequent than macromolecules and higher-order reactions. In this article, we theoretically model two generic mechanisms of forming Boolean gates based on geochemically plausible reaction systems that could have preceded complex biopolymers. The mechanisms exploit simple bistable autocatalytic systems to encode binary variables and use heterogeneous dilution rates to differentially activate or deactivate autocatalysis in different reactors. We found that NOT, AND, and OR gates, as well as more complex logic circuits, can spontaneously arise from connected, well-mixed flow reactors based on (i) catalysis by a heterodimer between mutually inhibitory autocatalysts or (ii) selectively permeable tunnels connecting reactors. Our results suggest that simple machinery can support the prebiotic emergence of complex chemical logic circuits and provide new guides for experimentally actualizing chemical computation.

Zhen Peng↗