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At least 343 records · Page 19

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NASA NTRS1998

Superelement Analysis of Tile-Reinforced Composite Armor

Super-elements can greatly improve the computational efficiency of analyses of tile-reinforced structures such as the hull of the Composite Armored Vehicle. By taking advantage of the periodicity in this type of construction, super-elements can be used to simplify the task of modeling, to virtually eliminate the time required to assemble the stiffness matrices, and to reduce significantly the analysis solution time. Furthermore, super-elements are fully transferable between analyses and analysts, so that they provide a consistent method to share information and reduce duplication. This paper describes a methodology that was developed to model and analyze large upper hull components of the Composite Armored Vehicle. The analyses are based on two types of superelement models. The first type is based on element-layering, which consists of modeling a laminate by using several layers of shell elements constrained together with compatibility equations. Element layering is used to ensure the proper transverse shear deformation in the laminate rubber layer. The second type of model uses three-dimensional elements. Since no graphical pre-processor currently supports super-elements, a special technique based on master-elements was developed. Master-elements are representations of super-elements that are used in conjunction with a custom translator to write the superelement connectivities as input decks for ABAQUS.

Davila, Carlos G.↗

DOE OSTI2020

Self-Assembly of Metallo-Supramolecules under Kinetic or Thermodynamic Control: Characterization of Positional Isomers Using Scanning Tunneling Spectroscopy

Coordination-driven self-assembly has been extensively employed to construct a variety of discrete structures as a bottom-up strategy. However, mechanistic understanding regarding whether self-assembly is under kinetic or thermodynamic control is less explored. To date, such mechanistic investigation has been limited to distinct, assembled structures. It still remains a formidable challenge to study the kinetic and thermodynamic behavior of self-assembly systems with multiple assembled isomers due to the lack of characterization methods. Herein, we use a stepwise strategy which combined self-recognition and self-assembly processes to construct giant metallo-supramolecules with 8 positional isomers in solution. With the help of ultrahigh-vacuum, low-temperature scanning tunneling microscopy and scanning tunneling spectroscopy, we were able to unambiguously differentiate 14 isomers on the substrate which correspond to 8 isomers in solution. Through measurement of 162 structures, the experimental probability of each isomer was obtained and compared with the theoretical probability. Finally, such a comparison along with density functional theory (DFT) calculation suggested that although both kinetic and thermodynamic control existed in this self-assembly, the increased experimental probabilities of isomers compared to theoretical probabilities should be attributed to thermodynamic control.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Bottlebrush Polymers at Liquid Interfaces: Assembly Dynamics, Mechanical Properties, and All-Liquid Printed Constructs

Bottlebrush polymer surfactants (BPSs), formed by the interfacial interactions between bottlebrush polymers (BPs) with poly(acrylic acid) side chains dissolved in an aqueous phase and amine-functionalized ligands dissolved in the oil phase, assemble and bind strongly to the fluid-fluid interface. The ratio between N BB (backbone degree of polymerization) and N SC (side chain degree of polymerization) defines the initial assembly kinetics, interface packing efficiency, and stress relaxation. The equilibrium interfacial tension (γ) increases when N BB < N SC , but decreases when N BB $\gg$ N SC , correlating to a pronounced change in the effective shape of the BPs from being spherical to worm-like structures. The apparent surface coverage (ASC), i.e., the interfacial packing efficiency, decreases as N BB increases. The dripping-to-jetting transition of an injected polymer solution, as well as fluorescence recovery after photobleaching experiments, revealed faster initial assembly kinetics for BPs with higher N BB . Furhter, Euler buckling of BPS assemblies with different N BB values was used to characterize the stress relaxation behavior and bending modulus. The stress relaxation behavior was directly related to the ASC, reflecting the strong influence of macromolecular shape on packing efficiency. The bending modulus of BPSs decreases for N BB < N SC , but increased when N BB $\gg$ N SC , showing the effect of molecular architecture and multisite anchoring. All-liquid printed constructs with lower N BB BPs yielded more stable structured liquids, underscoring the importance of macromolecular packing efficiency at fluid interfaces. Overall, this work elucidates fundamental relationships between nanoscopic structures and macroscopic properties associated with various bottlebrush polymer architectures, which translate to the stabilization of all-fluidic printed constructs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS2005

Pre-biotic stage of life origin under non-photosynthetic conditions

Spontaneous assembling of a simplest bacterial cell even if all necessary molecules are present in a solution seems to be extremely rare event and from the scientific standpoint has to be considered as impossible. Therefore, a predecessor of a living cell has to be very simple for providing its self-assembling and at the same time it should be able of progressive increase in complexity. Now phase-separated particles, first of all micelles, are put forward as possible predecessors of living cell. According to the offered working concept only phase-separated particles possessing autocatalytic properties can be considered as predecessors of living cells. The first stage of evolution of these phase-separated autocatalytic systems is the appearance of pre-biotic metabolism providing synthesis of amphiphiles for formation of capsules of these systems. This synthesis is maintained by the energy of a base reaction being a component of a planet-chemical cycle. Catalytic system providing functioning of pre-biotic metabolism is based on multivariate oligomeric autocatalyst, which reproduces itself from monomers, penetrating the particles from the outside. Since the autocatalyst realizes random polymerization then a collection of other oligomers possessing different catalytic functions is produced. In the paper the functioning of multivariate oligomeric autocatalyst in flow reactor is analyzed. c2005 Published by Elsevier Ltd on behalf of COSPAR.

Biogenesis↗

DOE OSTI2025

Reference Fuel Development for Non-Aluminum Spent Nuclear Fuel Management

The Savannah River Site (SRS) L Area Facility provides for the safe receipt, storage, handling, and shipping of spent nuclear fuel (SNF) and has received more than 47,000 SNF assemblies since 1964. In order to consolidate receipt and storage analysis, L Area criticality safety has historically used several aluminum-clad “reference fuels” to establish bounding storage, handling, and cask loading limits and then applied a reactivity comparison approach to demonstrate that candidate fuels may be processed under the reference fuel limits. Currently, only aluminum-clad SNF from off-site research reactors are transferred on-site. The Accelerated Basin De-Inventory (ABD) program will begin the removal of bundled Non-Aluminum Spent Nuclear Fuel (NASNF) from the L Area disassembly basin for dissolution and disposition, which has driven the need for a non-aluminum reference fuel. This paper discusses the process and results of creating a new fictional homogenous NASNF highly enriched uranium reference fuel, “MITZ,” to be used in nuclear criticality safety evaluations for upcoming SNF disposition operations. Data demonstrating the relationship between neutron multiplication behavior and fuel spacing is generated for the new reference fuel MITZ as well as existing reference fuels representing several types of SNF assemblies.

Reference Fuel↗

DOE OSTI2025

Reference Fuel Development for Non-Aluminum Spent Nuclear Fuel Management

Reference Fuel↗

DOE OSTI2022

Hierarchical Materials from High Information Content Macromolecular Building Blocks: Construction, Dynamic Interventions, and Prediction

Hierarchical materials that exhibit order over multiple length scales are ubiquitous in nature. Because hierarchy gives rise to unique properties and functions, many have sought inspiration from nature when designing and fabricating hierarchical matter. More and more, however, nature’s own high-information content building blocks, proteins, peptides, and peptidomimetics, are being coopted to build hierarchy because the information that determines structure, function, and interfacial interactions can be readily encoded in these versatile macromolecules. Here, we take stock of recent progress in the rational design and characterization of hierarchical materials produced from high-information content blocks with a focus on stimuli-responsive and “smart” architectures. We also review advances in the use of computational simulations and data-driven predictions to shed light on how the side chain chemistry and conformational flexibility of macromolecular blocks drive the emergence of order and the acquisition of hierarchy and also on how ionic, solvent, and surface effects influence the outcomes of assembly. Furthermore, continued progress in the above areas will ultimately usher in an era where an understanding of designed interactions, surface effects, and solution conditions can be harnessed to achieve predictive materials synthesis across scale and drive emergent phenomena in the self-assembly and reconfiguration of high-information content building blocks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Supramolecular Assembly of Halide Perovskite Building Blocks

The structural diversity and tunable optoelectronic properties of halide perovskites originate from the rich chemistry of the metal halide ionic octahedron [MX 6 ] n- (M = Pb 2+ , Sb 3+ , Te 4+ , Sn 4+ , Pt 4+ , etc.; X = Cl - , Br - , and I - ). The properties of the extended perovskite solids are dictated by the assembly, connectivity, and interaction of these octahedra within the lattice environment. Hence, the ability to manipulate and control the assembly of the octahedral building blocks is paramount for constructing new perovskite materials. Here, we propose a systematic supramolecular strategy for the assembly of [MX 6 ] n- octahedra into a solid extended network. Interaction of alkali metal-bound crown ethers with the [M(IV)X 6 ] 2- octahedron resulted in a structurally and optoelectronically tunable "dumbbell" structural unit in solution. Further, single crystals with diverse packing geometries and symmetries will form as the solid assembly of this new supramolecular building block. This supramolecular assembly route introduces a new general strategy for designing halide perovskite structures with potentially new optoelectronic properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Multi-material ALE remap with interface sharpening using high-order matrix-free finite element methods

The arbitrary Lagrangian-Eulerian (ALE) technique involves remapping field quantities from a Lagrangian mesh to an optimized mesh in a conservative, accurate and bounds-preserving manner. For methods based on arbitrary order finite elements, as described in a reference, material volume fractions are advected in pseudo-time using flux-corrected transport (FCT) without any form of interface reconstruction. In practice, this can lead to excessive propagation of small volume fractions throughout the domain. In addition, this method requires assembly of a global advection matrix to compute the bounds-preserving low-order FCT solution. In this work, we introduce a new approach for ALE remap using a high-order matrix-free technique which incorporates a flux modification to sharpen material interfaces in a conservative manner. Our approach begins with computing a bounds-preserving low-order solution to the ALE remap equations at the element level. We then compute a sharp interface solution (not guaranteed to be bounds-preserving) which comes from solving an augmented version of the ALE remap equations with a conservative flux modification which acts to sharpen material volume fractions based on their gradients and transport directions. Using the sharp interface solution, we make global corrections to the bounds-preserving solution while maintaining preservation of bounds. By blending with the sharpened solution at the global level we are able to globally conserve mass without hindering the remap pseudo-time step. This new interface-aware ALE remap method is based entirely on partial assembly techniques where globally assembled matrix operators are no longer needed, resulting in a globally matrix-free FCT method for multi-material, multi-field ALE remap with high performance on GPU architectures. We present results of our new remap method on 1D, 2D and 3D benchmarks and describe the algorithmic tailoring for GPU architectures that was developed.

Vargas, Arturo [Lawrence Livermore National Labora↗

NASA NTRSDate not supplied

Understanding Dynamic Challenges of In-Space Modular Assembly and Reconfiguration of Flexible Structures from Early Efforts

A review of 1980s to early 2010s research supporting and documenting successful missions for on-orbit assembly of large space structures was conducted to bring together flexible space structure dynamics challenges and progress toward solutions. Research in this period focused on issues ranging from ground validation via unique test beds to in-space modal characterization and model adjustment. The phased assembly of the International Space Station (ISS), along with its evolving structural loads and dynamics, provides the central example, with ground and on-orbit tests of other systems providing contributing and contrasting examples of potential value for researchers facing today’s challenges.

Modal Space Testing↗

NASA NTRS2001

The Use of Non-Standard Devices in Finite Element Analysis

A general mathematical description of the response behavior of thin-skin pneumatic envelopes and many other membrane and cable structures produces under-constrained systems that pose severe difficulties to analysis. These systems are mobile, and the general mathematical description exposes the mobility. Yet the response behavior of special under-constrained structures under special loadings can be accurately predicted using a constrained mathematical description. The static response behavior of systems that are infinitesimally mobile, such as a non-slack membrane subtended from a rigid or elastic boundary frame, can be easily analyzed using such general mathematical description as afforded by the non-linear, finite element method using an implicit solution scheme if the incremental uploading is guided through a suitable path. Similarly, if such structures are assembled with structural lack of fit that provides suitable self-stress, then dynamic response behavior can be predicted by the non-linear, finite element method and an implicit solution scheme. An explicit solution scheme is available for evolution problems. Such scheme can be used via the method of dynamic relaxation to obtain the solution to a static problem. In some sense, pneumatic envelopes and many other compliant structures can be said to have destiny under a specified loading system. What that means to the analyst is that what happens on the evolution path of the solution is irrelevant as long as equilibrium is achieved at destiny under full load and that the equilibrium is stable in the vicinity of that load. The purpose of this paper is to alert practitioners to the fact that non-standard procedures in finite element analysis are useful and can be legitimate although they burden their users with the requirement to use special caution. Some interesting findings that are useful to the US Scientific Balloon Program and that could not be obtained without non-standard techniques are presented.

Schur, Willi W.↗

DOE OSTI2021

A nodal transport method for coupled fast-thermal reactor analysis

We report that for efficient core analyses of coupled fast-thermal reactors, a new deterministic method has been developed based on the variational nodal transport method of VARIANT. A new multigroup cross section generation procedure was devised by combining Monte Carlo lattice calculations for thermal assemblies and the two-step procedure of the MC 2 -3 code for fast assemblies. To reduce assembly homogenization errors in nodal transport calculations, a new nodal equivalence method was developed based on the partial current discontinuity factor (PCDF) and incorporated in VARIANT. A practical procedure to calculate PCDFs with fixed source supercell calculations was also devised. The performance of the proposed method was investigated using a test problem derived from the versatile coupled test reactor (VCTR) design. The new procedure produced multigroup cross sections accurately for all assemblies. VARIANT transport calculations with PCDFs produced accurate multiplication factor and power distribution compared to reference Serpent-2 Monte Carlo solutions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

NASA NTRS2018

Establishing In-Space Assembly Technical Collaboration Environments Through Functional Capability Analyses

NASA OCT strategically collaborates with other government space agencies to find enterprise synergistic technology solutions to benefit the Nation through leadership of the interagency Science and Technology Partnership Forum. Successful collaborations depend on integrating knowledge across the intersection of industry, academe, and government within pioneering technical areas such as in-space assembly. High-quality data products that are timely, accurate, and trusted are used to communicate with internal and external stakeholders to influence portfolios by focusing investments to maximize impact on NASA missions and the U.S. economy. These data products succinctly describe and convey the breadth and dependencies of multiple capabilities, while incorporating diverse technical perspectives, to articulate and inform interagency collaborative developments of autonomous on-orbit assembly technologies.

Rodgers, Erica↗

DOE OSTI2021

Progress on the reevaluation and validation of the n+233U neutron cross sections

The set of 233 U resonance parameters of the ENDF/B-VIII.0 nuclear data library was adopted from the previous ENDF/B-VII.1 evaluation using the external levels to update the thermal values. Adoption of IAEA 2017 thermal standards ( σ f = 533.0 ± 2.2 b, σ c = 44.9 ± 0.9 b, and ν ‾ tot = 2.487 ± 0.011 ) and of the IAEA-recommended thermal-neutron induced prompt fission neutron spectrum (PFNS) with average PFNS energy of 2.030 ± 0.013 MeV requires a re-evaluation of 233 U neutron cross sections in the resolved resonance region. A newly produced evaluation is being tested on benchmarks carefully selected from the Handbook of International Criticality Safety Benchmark Experiments (ICSBEP) which are highly sensitive to 233 U data. An important goal of this work was to eliminate the strong negative gradient of the calculated effective multiplication factors with respect to the epithermal fission fraction observed in the validation of the ENDF/B-VIII.0 library for those assemblies. A significant improvement in integral performance of critical 233 U solutions is observed for the newly proposed evaluation. Further work addressing the fast neutron region is needed.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2023

Transformations in crystals of DNA-functionalized nanoparticles by electrolytes

Colloidal crystals have applications in water treatments, including water purification and desalination technologies. It is, therefore, important to understand the interactions between colloids as a function of electrolyte concentration. We study the assembly of DNA-grafted gold nanoparticles immersed in concentrated electrolyte solutions. Increasing the concentration of divalent Ca 2+ ions leads to the condensation of nanoparticles into face-centered-cubic (FCC) crystals at low electrolyte concentrations. As the electrolyte concentration increases, the system undergoes a phase change to body-centered-cubic (BCC) crystals. This phase change occurs as the interparticle distance decreases. Molecular dynamics analysis suggests that the interparticle interactions change from strongly repulsive to short-range attractive as the divalent-electrolyte concentration increases. A thermodynamic analysis suggests that increasing the salt concentration leads to significant dehydration of the nanoparticle environment. We conjecture that the intercolloid attractive interactions and dehydrated states favour the BCC structure. Our results gain insight into salting out of colloids such as proteins as the concentration of salt increases in the solution.

Chemistry↗

NASA NTRS1975

Improved fabrication of electrolytic capacitors

After processing parts for assembly, insulative cup is fitted to bottom of can, then electrolytic solution consisting of white sulfuric acid gel is inserted into can. Pellet is put in can and is fitted tightly into cup. Finally, bead weld is formed between can and header plug.

Gamari, F. J.↗

NASA NTRS1972

Precision time distribution within a deep space communications complex

The Precision Time Distribution System (PTDS) at the Golstone Deep Space Communications Complex is a practical application of existing technology to the solution of a local problem. The problem was to synchronize four station timing systems to a master source with a relative accuracy consistently and significantly better than 10 microseconds. The solution involved combining a precision timing source, an automatic error detection assembly and a microwave distribution network into an operational system. Upon activation of the completed PTDS two years ago, synchronization accuracy at Goldstone (two station relative) was improved by an order of magnitude. It is felt that the validation of the PTDS mechanization is now completed. Other facilities which have site dispersion and synchronization accuracy requirements similar to Goldstone may find the PTDS mechanization useful in solving their problem. At present, the two station relative synchronization accuracy at Goldstone is better than one microsecond.

Curtright, J. B.↗

NASA NTRS1992

Design and testing of the Space Station Freedom Propellant Tank Assembly

Propellant storage and management functions for the Propulsion Module of the U.S. Space Station Freedom are provided by the Propellant Tank Assembly (PTA). The PTA consists of a surface-tension type propellant acquisition device contained within a welded titanium pressure vessel. The PTA design concept was selected with high reliability and low program risk as primary goals in order to meet stringent NASA structural, expulsion, fracture control and reliability requirements. The PTA design makes use of Shuttle Orbital Maneuvering System and Peacekeeper Propellant Storage Assembly design and analysis techniques. This paper summarizes the PTA design solution and discusses the underlying detailed analyses. In addition, design verification and qualification test activities are discussed.

Dudley, D. D.↗