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At least 451 records · Page 25

All sources NASA NTRS DOE OSTI

DOE OSTI2022

Thermal-Hydraulics Modeling and Simulations of Hot Pool Using the SAS-CFD Coupled Code

The main goal of this activity is to test the dynamic coupling of the SAS4A/SASSYS-1 (SAS) and CFD models, using a recently patched version of the SAS code intended to address an undocumented limitation that hindered the Versatile Test Reactor (VTR) simulation efforts in FY21. As described in previous VTR calculation reports, the undocumented limitation in SAS v5.4 does not allow the user to activate the CFD coupling option during restart calculations. Since the analysts were unaware of this limitation, prior SAS-CFD simulation results for the protected station blackout (PSBO) transient were erroneous. Root-cause analysis was performed to determine the cause of this undocumented limitation in SAS v5.4, the SAS software was updated in a new patch, and the SAS-CFD simulations were repeated with this patched software. The results of the SAS-CFD simulations documented in this report show that the software patch does address the cited issue, and that the patched software indeed supports the activation of the CFD coupling model in restart calculations. The SAS development team will determine the schedule for implementing the patch in an official software release. This report documents updated SAS-CFD simulations of the PSBO transient response in the VTR. The hot pool is modeled with the CFD code STAR-CCM+, which is coupled at the flow boundaries to the SAS model of the primary heat transport system. SAS computes the mass flow rate and temperature at each core subassembly outlet, the thermal insulation cavity bypass, and the IHX inlet windows. CFD in turn computes the absolute pressure and temperature at each of these boundaries. The SAS code will ignore the temperature data at flow boundaries where flow is directed into the hot pool, i.e., at the core subassembly outlets unless flow reversal occurs. Similarly, CFD will ignore temperature data at boundaries where the flow is directed out of the hot pool, i.e., at the IHX inlets except under flow reversal. The focus of this work is to ensure that the SAS software patch addresses the undocumented limitation described in prior VTR calculation reports, rather than the accurate assessment of thermal stratification in the VTR during protected transients. This motivates the development of a new, simplified CFD model with a coarser mesh to accelerate the testing process. The updated model, and simplifying assumptions, are documented in this report. In future work, the thermal stratification assessment should be performed in more detail. The simplified CFD model can be improved by performing grid convergence studies sensitivity studies of turbulence parameters (e.g., Prandtl number, turbulence production and dissipation parameters) on temperature distributions and thermal stratification.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2022

Composing preconditioners for multiphysics PDE systems with applications to Generalized MHD

New patch smoothers or relaxation techniques are developed for solving linear matrix equations coming from systems of discretized partial differential equations (PDEs). One key linear solver challenge for many PDE systems arises when the resulting discretization matrix has a near null space that has a large dimension, which can occur in generalized magnetohydrodynamic (GMHD) systems. Patch-based relaxation is highly effective for problems when the null space can be spanned by a basis of locally supported vectors. The patch-based relaxation methods that we develop can be used either within an algebraic multigrid (AMG) hierarchy or as stand-alone preconditioners. These patch-based relaxation techniques are a form of well-known overlapping Schwarz methods where the computational domain is covered with a series of overlapping sub-domains (or patches). Patch relaxation then corresponds to solving a set of independent linear systems associated with each patch. In the context of GMHD, we also reformulate the underlying discrete representation used to generate a suitable set of matrix equations. In general, deriving a discretization that accurately approximates the curl operator and the Hall term while also producing linear systems with physically meaningful near null space properties can be challenging. Unfortunately, many natural discretization choices lead to a near null space that includes non-physical oscillatory modes and where it is not possible to span the near null space with a minimal set of locally supported basis vectors. Further discretization research is needed to understand the resulting trade-offs between accuracy, stability, and ease in solving the associated linear systems.

97 MATHEMATICS AND COMPUTING↗

NASA NTRS1984

The computation of all plane/surface intersections for CAD/CAM applications

The problem of the computation and display of all intersections of a given plane with a rational bicubic surface patch for use on an interactive CAD/CAM system is examined. The general problem of calculating all intersections of a plane and a surface consisting of rational bicubic patches is reduced to the case of a single generic patch by applying a rejection algorithm which excludes all patches that do not intersect the plane. For each pertinent patch the algorithm presented computed the intersection curves by locating an initial point on each curve, and computes successive points on the curve using a tolerance step equation. A single cubic equation solver is used to compute the initial curve points lying on the boundary of a surface patch, and the method of resultants as applied to curve theory is used to determine critical points which, in turn, are used to locate initial points that lie on intersection curves which are in the interior of the patch. Examples are given to illustrate the ability of this algorithm to produce all intersection curves.

Hoitsma, D. H., Jr.↗

NASA NTRS1988

Space Station pressure wall repair techniques

Space Station components are susceptible to hypervelocity impact damage from orbital debris and meteoroids. An especially vulnerable and critical space station component is the module pressure wall. Even with shielding, sufficiently large impacting particles can create penetrations ranging from pinholes to large jagged holes. This paper describes pressure wall damage repair patches along with procedures and tools for performing the repair. One patch incorporates an aluminum foil protected from the jagged hole edge with a Kevlar or foam pad. An adhesive holds the patch in place. Another patch uses a stiff plate held away from the damaged area by a low durrometer rubber ring which also seals the plate edge. An adhesive will also secure this patch in place. Procedures were developed to prepare the punctured wall surface and apply the patch under weightless and unpressurized conditions. The procedures were tested in a laboratory and in the MSFC Neutral Buoyancy Simulator with models of the patches and tools.

Gibbins, Martin N.↗

NASA NTRS1993

Resonant frequencies of irregularly shaped microstrip antennas using method of moments

This paper describes an application of the method of moments to determine resonant frequencies of irregularly shaped microstrip patches embedded in a grounded dielectric slab. For analysis, the microstrip patch is assumed to be excited by a linearly polarized plane wave that is normal to the patch. The surface-current density that is induced on the patch because of the incident field is expressed in terms of subdomain functions by dividing the patch into identical rectangular subdomains. The amplitudes of the subdomain functions, as a function of frequency, are determined using the electric-field integral equation (EFIE) approach in conjunction with the method of moments. The resonant frequencies of the patch are then obtained by selecting the frequency at which the amplitude of the surface-current density is real. The resonant frequencies of the equilateral triangular and other nonrectangular patches are computed using the present technique, and these frequencies are compared with measurements and other independent calculations.

Deshpande, Manohar D.↗

NASA NTRS2003

Electromagnetic Scattering From a Polygonal Thin Metallic Plate Using Quadrilateral Meshing

The problem of electromagnetic (EM) scattering from irregularly shaped, thin, metallic flat plates in free space is solved using the electric field integral equation (EFIE) approach in conjunction with the method of moments (MoM) with quadrilateral meshing. An irregularly shaped thin plate is discretized into quadrilateral patches and the unknown electric surface current over the plate is expressed in terms of proper basis functions over these patches. The basis functions for the electric surface current density that satisfy the proper boundary conditions on these quadrilateral patches are derived. The unknown surface current density on these quadrilateral patches is determined by setting up and solving the electric field integral equation by the application of the MoM. From the knowledge of the surface current density, the EM scattering from various irregularly shaped plates is determined and compared with the earlier published results. The novelty in the present approach is the use of quadrilateral patches instead of well known and often used triangular patches. The numerical results obtained using the quadrilateral patches compare favorably with measured results.

Deshpande, Manohar D.↗

NASA NTRS2005

Ability of Impedance-Based Health Monitoring To Detect Structural Damage of Propulsion System Components Assessed

Impedance-based structural-health-monitoring uses piezoelectric (PZT) patches that are bonded onto or embedded in a structure. Each individual patch behaves as both an actuator of the surrounding structural area as well as a sensor of the structural response. The size of the excited area varies with the geometry and material composition of the structure, and an active patch is driven by a sinusoidal voltage sweep. When a PZT patch is subjected to an electric field, it produces a mechanical strain; and when it is stressed, it produces an electric charge. Since the patch is bonded to the structure, driving a patch deforms and vibrates the structure. The structure then produces a localized dynamic response. This structural system response is transferred back to the PZT patch, which in turn produces an electrical response. The electromechanical impedance method is based on the principle of electromechanical coupling between the active sensor and the structure, which allows researchers to assess local structural dynamics directly by interrogating a distributed sensor array. Because of mechanical coupling between the sensor and the host structure, this mechanical effect is picked up by the sensor and, through electromechanical coupling inside the active element, is reflected in electrical impedance measured at the sensor s terminals.

Martin, Richard E.↗

NASA NTRS2008

Microstrip Yagi Antenna with Dual Aperture-Coupled Feed

A proposed microstrip Yagi antenna would operate at a frequency of 8.4 GHz (which is in the X band) and would feature a mechanically simpler, more elegant design, relative to a prior L-band microstrip Yagi antenna. In general, the purpose of designing a microstrip Yagi antenna is to combine features of a Yagi antenna with those of a microstrip patch to obtain an antenna that can be manufactured at low cost, has a low profile, and radiates a directive beam that, as plotted on an elevation plane perpendicular to the antenna plane, appears tilted away from the broadside. Such antennas are suitable for flush mounting on surfaces of diverse objects, including spacecraft, aircraft, land vehicles, and computers. Stated somewhat more precisely, what has been proposed is a microstrip antenna comprising an array of three Yagi elements. Each element would include four microstrip-patch Yagi subelements: one reflector patch, one driven patch, and two director patches. To obtain circular polarization, each driven patch would be fed by use of a dual offset aperture-coupled feed featuring bow-tie-shaped apertures. The selection of the dual offset bow-tie aperture geometry is supported by results found in published literature that show that this geometry would enable matching of the impedances of the driven patches to the 50-Omega impedance of the microstrip feedline while maintaining a desirably large front-to-back lobe ratio.

Pogorzelski, Ronald↗

NASA NTRS2014

Ultra-Wideband, Dual-Polarized, Beam-Steering P-Band Array Antenna

A dual-polarized, wide-bandwidth (200 MHz for one polarization, 100 MHz for the orthogonal polarization) antenna array at P-band was designed to be driven by NASA's EcoSAR digital beam former. EcoSAR requires two wide P-band antenna arrays mounted on the wings of an aircraft, each capable of steering its main beam up to 35deg off-boresight, allowing the twin radar beams to be steered at angles to the flight path. The science requirements are mainly for dual-polarization capability and a wide bandwidth of operation of up to 200 MHz if possible, but at least 100 MHz with high polarization port isolation and low cross-polarization. The novel design geometry can be scaled with minor modifications up to about four times higher or down to about half the current design frequencies for any application requiring a dual-polarized, wide-bandwidth steerable antenna array. EcoSAR is an airborne interferometric P-band synthetic aperture radar (SAR) research application for studying two- and three-dimensional fine-scale measurements of terrestrial ecosystem structure and biomass, which will ultimately aid in the broader study of the carbon cycle and climate change. The two 2×8 element Pband antenna arrays required by the system will be separated by a baseline of about 25 m, allowing for interferometry measurements. The wide 100-to- 200-MHz bandwidth dual-polarized beams employed will allow the determination of the amount of biomass and even tree height on the ground. To reduce the size of the patches along the boresight dimension in order to fit them into the available space, two techniques were employed. One technique is to add slots along the edges of each patch where the main electric currents are expected to flow, and the other technique is to bend the central part of the patch away from the ground plane. The latter also facilitates higher mechanical rigidity. The high port isolation of more than 40 dB was achieved by employing a highly symmetrical feed mechanism for each pair of elements: three apertures coupling to the patch elements were placed along the two symmetry lines of the antenna element pair. Two apertures were used in tandem to excite two of the stacked patch elements for one polarization; the other was used to excite one element from one side and the other element from the other side, opposite in phase, taking care of the remaining polarization. The apertures narrow down to a small gap where they are excited by a crossing microstrip line to prevent any asymmetrical excitation of the two sides of the aperture gap, minimizing port-to-port coupling. Using patches that are non-planar leads to higher mechanical rigidity and smaller patch sizes to fit into the available space. Aperture coupling minimizes direct metal-to-metal connections. Using an aperture coupling feed mechanism results in a feed network for two antenna elements with a total of three feed points, plus one simple in-phase combiner to reduce it to two ports. It greatly reduces the complexity of the alternative, but more conventional, way of feeding a pair of two dual-polarized elements with high port isolation.

duToit, Cornelis↗

DOE OSTI2017

Shape-Specific Patterning of Polymer-Functionalized Nanoparticles

Chemically and topographically patterned nanoparticles (NPs) with dimensions on the order of tens of nanometers have a diverse range of applications and are a valuable system for fundamental research. Recently, thermodynamically controlled segregation of a smooth layer of polymer ligands into pinned micelles (patches) offered an approach to nanopatterning of polymer-functionalized NPs. Control of the patch number, size, and spatial distribution on the surface of spherical NPs has been achieved, however, the role of NP shape remained elusive. Here, we report the role of NP shape, namely, the effect of the local surface curvature, on polymer segregation into surface patches. For polymer-functionalized metal nanocubes, we show experimentally and theoretically that the patches form preferentially on the high-curvature regions such as vertices and edges. An in situ transformation of the nanocubes into nanospheres leads to the change in the number and distribution of patches; a process that is dominated by the balance between the surface energy and the stretching energy of the polymer ligands. The experimental and theoretical results presented in this work are applicable to surface patterning of polymer-capped NPs with different shapes, which then enables the exploration of patch-directed self-assembly, as colloidal surfactants, and as templates for the synthesis of hybrid nanomaterials.

36 MATERIALS SCIENCE↗

NASA NTRS1999

A laser microsurgical method of cell wall removal allows detection of large-conductance ion channels in the guard cell plasma membrane

Application of patch clamp techniques to higher-plant cells has been subject to the limitation that the requisite contact of the patch electrode with the cell membrane necessitates prior enzymatic removal of the plant cell wall. Because the wall is an integral component of plant cells, and because cell-wall-degrading enzymes can disrupt membrane properties, such enzymatic treatments may alter ion channel behavior. We compared ion channel activity in enzymatically isolated protoplasts of Vicia faba guard cells with that found in membranes exposed by a laser microsurgical technique in which only a tiny portion of the cell wall is removed while the rest of the cell remains intact within its tissue environment. "Laser-assisted" patch clamping reveals a new category of high-conductance (130 to 361 pS) ion channels not previously reported in patch clamp studies on plant plasma membranes. These data indicate that ion channels are present in plant membranes that are not detected by conventional patch clamp techniques involving the production of individual plant protoplasts isolated from their tissue environment by enzymatic digestion of the cell wall. Given the large conductances of the channels revealed by laser-assisted patch clamping, we hypothesize that these channels play a significant role in the regulation of ion content and electrical signalling in guard cells.

Non-NASA Center↗

DOE OSTI2019

Climate change and invasion may synergistically affect native plant reproduction

Global change drivers can interact in synergistic ways, yet the interactive effect of global change drivers, such as climatic warming and species invasions, on plant pollination are poorly represented in experimental studies. We paired manipulative experiments to probe two mechanistic pathways through which plant invasion and warming may alter phenology and reproduction of native plant species. In the first, we tested how experimental warming (+1.7°C) modulated flowering phenology and how this affected flowering overlap between a native plant (Dracophyllum subulatum) and an invasive plant (Calluna vulgaris L.). In the second experiment, we explored how variation in the ratio of native to invasive flowers, and the overall quantity of resources in a floral patch, affected the reproduction of the native species. We hypothesized that the flowering overlap of native and invasive plants would be altered by warming, given that invading plants typically exhibit greater phenological plasticity than native plants. Further, we hypothesized that pollination of native plant flowers would decrease in floral patches dominated by invasive plant flowers, but that this effect would depend on total floral density in the patch. As predicted, the invasive plant had a stronger phenological response to experimental warming than the native plant, resulting in increased flowering overlap between the native the invasive plants. There was a four-fold increase in the number of native flowers co-flowering with high densities of invasive flowers suggesting native plant competition for pollinators with invasive plants under a warmed climate. In the second experiment, we found depressed seed masses of the native species in high density floral patches that were dominated by invasive flowers relative to high density floral patches dominated by native flowers. At low floral densities, seed mass of native plants was unaffected by invasion. Together, these results demonstrate that by increasing their phenological overlap, warming may enhance the magnitude of existing competition for pollination exerted by an invasive plant on a native plant, particularly in plant patches with high floral density. Finally, our results illustrate a novel pathway through which global change drivers can operate synergistically to alter an important ecosystem service: pollination.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2018

Delta size and plant patchiness as controls on channel network organization in experimental deltas

Understanding the feedbacks between water, sediment, and vegetation in deltas is an important part of understanding deltas as ecomorphodynamic systems. Here, we conducted a set of laboratory experiments using alfalfa (Medicago sativa) as a proxy for delta vegetation to investigate (1) the effects of plants on delta growth and channel network formation and (2) the timescales controlling delta evolution in the presence of plants. Experiments were conducted with fluctuating discharge (i.e. flood and base flow periods) and variable seeding densities. We found that when deltas were small, channels had no memory across flood cycles, as floods could completely fill the incised channel network. When deltas were large, the larger channel volume could remain underfilled to keep channel memory. Plant patches also helped to increase the number of channels and make a more distributive network. Patchiness increased over time to continually aid in bifurcation, but as vegetation cover and patch sizes increased, patches began to merge. Larger patches blocked the flow to enhance topset deposition and channel filling, even for the case of large deltas with a high channel volume. We conclude that both plant patchiness and delta size affect the development of the channel network, and we hypothesize that their influences are manifested through two competing timescales. The first timescale, T v , defines the time when the delta is large enough for channels to have memory (i.e., remain underfilled), and the second, T p , defines the time when vegetation patches merge, amplifying deposition and blocking channels. Finally, when run time is between these two timescales, the delta can develop a persistent distributary network of channels aided by bifurcation around plant patches, but once T p is reached, the channel network can again be destroyed by vegetation.

58 GEOSCIENCES↗

DOE OSTI2018

Liquid metasurface‐based periodically stacked radome design

Abstract We present liquid metasurface‐based periodically stacked radome design. Radome is a layer placed above the antenna to protect it from weather disturbances. The layer protects the antenna but reduces its gain. Periodic stacking of liquid metasurface based radome improve the antenna parameters like gain and bandwidth. Microstrip patch antenna is used as basic antenna to check the improvement in gain. The comparison of microstrip patch antenna, patch antenna with simple multilayer radome, patch antenna with liquid metasurface multilayer radome and patch antenna with liquid metasurface periodically stacked multilayer radome is presented in the manuscript. The improvement in terms of gain is clearly visible from the comparison of results for all the designs. Efficiency is also increasing by adding liquid metasurface periodically stacked multilayer radome to patch antenna.

Patel, Shobhit K.↗

DOE OSTI2018

Transdermal Delivery of Nicotine Using Pectin Isolated from Durian Fruit-Hulls-Based Polymer Blends as a Matrix Layer

Many natural polymers with various chemical structures are used to prepare transdermal patches. Pectin is a one interesting type of polymer because it can control drug release when used in transdermal patches. In Thailand, the waste from durian fruit-hulls is a major problem for the environment. However, the pectin from it can be isolated under acid conditions and used to prepare transdermal patches for nicotine delivery which has not yet been reported. As the isolated pectin is a natural polymer, the film made from isolated pectin is a brittle; therefore, adding a low protein natural rubber latex (LPNRL) polymer was needed to increase its flexibility. The transdermal patches were amorphous and had T{sub g} values ranging from 81.0 to 93.3 °C. Moisture uptake, swelling ratio, and erosion values of the patches were significantly decreased after addition of LPNRL, which resulted in low hydrophilicity. The in vitro release and permeation of nicotine depends on the hydrophilicity of the patches. The kinetic models for in vitro release and permeation of nicotine were Higuchi model and zero order, respectively. In conclusion, pectin isolated from fruit-hulls of Mon Thong durians is an effective polymer to control the release of nicotine. It also is an option that could solve the environmental problems caused by durian fruit-hulls waste.

36 MATERIALS SCIENCE↗

DOE OSTI2019

On behaviour and scaling of small repeating earthquakes in rate and state fault models

With abundant seismic data for small repeating earthquakes, it is important to construct a dynamic model that can explain various aspects of related observations. We report on small repeating earthquakes on a fault governed by rate- and state-dependent friction laws. The earthquakes occur on a velocity-weakening patch surrounded by a much larger velocity-strengthening region. The whole fault is subject to long-term tectonic loading. The model with a circular patch and the aging form of rate- and state-dependent friction laws has been shown to reproduce the scaling of recurrence time versus seismic moment for small repeating earthquakes in a previous study. In this work we investigate the behaviour of small repeating earthquakes in related models under different scenarios, including several forms of the state evolution equations in rate- and state-dependent friction laws, rectangular velocity-weakening patch geometries, quasi-dynamic versus fully dynamic representation of inertial effects and 2-D versus 3-D simulations. We discover that the simulated scalings between the recurrence time and seismic moment for these different scenarios is similar while differences do exist. We propose a theoretical consideration for the scaling between the recurrence time and seismic moment of small repeating earthquakes. For patch radii smaller than or comparable to the full nucleation size, the scaling is explained by the increase of seismic to aseismic slip ratio with magnitude. For patch radii larger than the full nucleation size, the scaling is explained by the model in which the recurrence time is determined by the earthquake nucleation time, which is in turn determined by the time for aseismic slip to penetrate the distance of the full nucleation size into the patch. The obtained theoretical insight is used to find the combinations of fault properties that allow the model to fit the observed scaling and range of the seismic moment and recurrence time.

58 GEOSCIENCES↗

DOE OSTI2025

Deer Vigilance and Movement Behavior Are Affected by Edge Density and Connectivity

ABSTRACT Animal behavior is an important component of individual, population, and community responses to anthropogenic habitat alteration. For example, antipredator behavior (e.g., vigilance) and animal movement behavior may both be important behavioral responses to the increased density of habitat edges and changes in patch connectivity that characterize highly modified habitats. Importantly, edge density and connectivity might interact, and this interaction is likely to mediate animal behavior: linear, edge‐rich landscape features often provide structural connectivity between patches, but the functional connectedness of patches for animal use could depend upon how edge density modifies animal vigilance and movement. Using remote cameras in large‐scale experimental landscapes that manipulate edge density (high‐ vs. low‐density edges) and patch connectivity (isolated or connected patches), we examined the effects of edge density and connectivity on the antipredator behavior and movement behavior of white‐tailed deer ( Odocoileus virginianus ). Deer vigilance was 1.38 times greater near high‐density edges compared to low‐density edges, regardless of whether patches were connected or isolated. Deer were also more likely to move parallel to connected high‐density edges than all other edge types, suggesting that connectivity promotes movement along high‐density edges. These results suggest that increases in edge density that accompany human fragmentation of existing habitats may give rise to large‐scale changes in the antipredator behavior of deer. These results also suggest that conservation strategies that simultaneously manipulate edge density and connectivity (i.e., habitat corridors) may have multiple effects on different aspects of deer behavior: linear habitat corridors were areas of high vigilance, but also areas where deer movement behavior implied increased movement along the habitat edge.

Bartel, Savannah L. [University of Wisconsin‐Madis↗

DOE OSTI2026

3D reconstruction and neural rendering for adversarial machine learning

While evasion attacks on computer vision systems have been widely studied, creating attacks that remain effective under significant changes in viewpoint continues to be challenging. Traditional approaches often rely on affine transformations of images, but these approaches degrade at larger perspective shifts and often produce unrealistic or ineffective perturbations. Recent methods use differentiable renderers to improve viewpoint robustness, but they typically depend on manually constructed 3D models. We introduce a semi-automated pipeline that generates physically printable and perspective-invariant adversarial patches using only a small set of 2D images. Our method integrates 3D reconstruction, neural rendering, adversarial patch optimization, and an object detection victim model into a unified workflow. We use 2D Gaussian Splatting for high fidelity mesh reconstruction and FlexPara for surface parameterization that produces texture maps suitable for patch editing. Together, these components form a fully differentiable pipeline in PyTorch3D that links texture modification to model outputs, enabling efficient optimization of patches that remain effective across many viewpoints. The complete process, from image capture to patch printing and physical evaluation, can be completed within a few hours. We demonstrate the effectiveness of the resulting patches through attacks on the YOLOv8 object detection model and discuss remaining challenges and opportunities for improving robustness and scalability.

Singhvi, Vivaan [ORNL] (ORCID:0009000586288221)↗