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All sources NASA NTRS DOE OSTI

DOE OSTI2012

Review of the Oak Ridge National Laboratory (ORNL) Neutronic Calculations Regarding the Conversion of the High Flux Isotope Reactor (HFIR) to the Use of Low Enriched Uranium (LEU) Fuel

In awareness of the risk caused by the proliferation of nuclear materials, the international community initiated in 1978 the Reduced Enrichment for Research and Test Reactors (RERTR) Program. The goal of the RERTR program is to seek solutions to convert the reactors using High Enriched Uranium (HEU) fuel ( 235 U/U ≥ 20 wt. %) to the use of Low Enriched Uranium (LEU) Fuel ( 235 U/U < 20 wt. %). Among the 200 reactors worldwide currently in the scope of the program, about 70 have been converted or shut down prior to conversion. In the U.S., six high reactors remain to be converted. One of the U.S. reactors is the High Flux Isotope Reactor (HFIR) located at Oak Ridge National Laboratory (ORNL). This multipurpose reactor is mainly used for neutron scattering experiments and isotope production. It has two fuel elements made of involute-shaped fuel plates. The ORNL Research Reactor Division (RRD) has prepared during FY2011 two series of calculations, one neutronic and one thermal-hydraulic (TH), in support of the conversion activities for HFIR. The neutronic calculations cover mainly the evaluation of the matrix of performance (cycle length and flux), the distribution of power in the fuel elements, kinetics parameters and reactivity coefficients. As defined by the RRD procedures, the calculations have to be reviewed. Per internal decision, the RRD proposed an external reviewer, Argonne National Laboratory (ANL). The results of the Argonne neutronic review are presented in this report. The results of the TH review are presented in a separate report. The main conclusion of the ORNL reactor physics analyses is that the proposed reference HFIR LEU core (using the so-called monolithic UMo fuel) could maintain the current level of performance (obtained with a HEU core at 85MW) if it is operated at 100MW. However, to operate within the same safety limits as the current HEU core, the thermal hydraulic analyses show that the peaking of the power distribution occurring at the bottom of the fuel plates has to be reduced. The RRD has found a potential solution by reducing the fuel thickness at the bottom of the fuel plate. This would require addition of an axial grading to the already radially-graded fuel. Thus, the review has been focused on independently recalculating all of the ORNL calculations and making an as fair as possible comparison between the current 85MW HEU core and the reference 100MW LEU core design. ORNL and ANL have used the same computational tools to perform the work. The codes MCNP and ORIGEN have been used to perform the steady state and depletion calculations, respectively. The communication between the two codes has been carried out by the code VESTA. Even though the code MCNP is able to handle complex geometries, it cannot model the involute shape. Nonetheless, ANL has developed an innovative methodology to model the involute shape with MCNP with an approximation that can be made as accurate as desired. Thus, ANL has been able to perform the calculations using an explicit (or discrete) description of the fuel elements. The current modeling used by ORNL consists in homogenizing the different fuel element components (cladding, fuel, coolant…). Although this method is easier to implement, it may also affect the reactor physics which may have an impact on the calculated results. Even though some differences in the physics parameters (flux for instance) have been detected between the HEU explicit (ANL) and homogenized (ORNL) models, they are small enough to not significantly impact the performance parameters. However, this is not the case for the LEU core where the differences in the physics parameters lead to significant differences in the performance parameters, especially the cycle length (found to be considerably longer in the explicit model). Nonetheless, the others parameters calculated by ANL (power distribution, kinetics parameters…) are in good agreement with those calculated by ORNL. Some inconsistencies have been detected in the original ORNL inputs that have been corrected in the reference ones used by ANL for the review and, therefore, the cycle length difference between the LEU homogenized and explicit models has been amplified. Consequently, the ANL comparison of the HFIR HEU and LEU cores has given different results than the ORNL results. The ORNL matrix of performance for the 100MW LEU reference design shows that the reactor cycle length would be as long and the flux as high as the current 85MW HEU core. In contrast, the ANL matrix of performance shows that the 100MW LEU design would have a significantly longer cycle length (~33days) than the current 85MW HEU core (~25days). In addition, it has been shown that, if the reactor is operated for 33days, the neutron fluence would be high enough to increase the overall reactor performance by a significant factor. If the reactor is forced to shut down after 25days, calculations show that the neutron flux would be high enough to maintain the performance of the neutron scattering experiments but losses are predicted to occur in several irradiation facilities. Increasing the cycle length may not be possible for other reasons. For instance, a longer cycle length can increase the cumulative oxide layer thickness growth on the plate. The increase in the neutron fluence may affect the lifetime of the reactor vessel and, by reducing the time for maintenance, pose operational challenges. An assessment of these as well as other potential questions associated with a 33 day cycle length is needed. Since such an assessment has not been carried out, ANL cannot conclude that the ORNL reference LEU core should or could operate at 100MW. The conclusions of the ANL review are different than those of the ORNL investigation mainly because the explicit and homogenized methodologies used to model the core are different. In this report, an attempt is made to justify and explain as clearly as possible why the ANL methodology is thought to be better suited for HFIR analyses. It is acknowledged that because the ANL and ORNL LEU models have not been benchmarked against experiments, it is possible that doubts could be raised concerning the ability of the models to correctly capture all of the physics behavior of the reactor.

Bergeron, A.↗

DOE OSTI2019

X-ray Scattering and Coarse-Grained Simulations for Clustering and Interactions of Monoclonal Antibodies at High Concentrations

Attractive protein-protein interactions (PPI) in concentrated monoclonal antibody (mAb) solutions may lead to reversible oligomers (clusters) that impact colloidal stability and viscosity. Herein, the PPI are tuned for two mAbs via the addition of arginine (Arg), NaCl, or ZnSO 4 as characterized by the structure factor ( S eff (q)) with small angle x-ray scattering (SAXS). The SAXS data are fit with molecular dynamics simulations by placing a physically relevant short-ranged attractive interaction on selected beads in coarse-grained 12 bead models of the mAb shape. The optimized 12-bead models are then used to differentiate key microstructural properties, including center of mass radial distribution functions ( g COM (r)), coordination numbers and cluster size distributions (CSD). The addition of co-solutes results in more attractive Seff(q) relative to the no co-solute control for all systems tested, with the most attractive systems showing an upturn at low q . Only the All1 model with an attractive site in each Fab and Fc region (possessing Fab-Fab, Fab-Fc and Fc-Fc interactions) can reproduce this upturn, and the corresponding CSDs show the presence of larger clusters compared to the control. In general, for models with similar net attractions, i.e., second osmotic virial coefficients, the size of the clusters increases as the attraction is concentrated on a smaller number of evenly distributed beads. Here, the cluster size distributions from simulations are used to improve the understanding and prediction of experimental viscosities. The ability to discriminate between models with bead interactions at particular Fab and Fc bead sites from SAXS simulations, and to provide real space properties (CSD and g COM (r)), will be of interest in engineering protein sequence and formulating protein solutions for weak PPI to minimize aggregation and viscosities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Effective field theory of non-attractor inflation

We present the model-independent studies of non attractor inflation in the context of effective field theory (EFT) of inflation. Within the EFT approach two independent branches of non-attractor inflation solutions are discovered in which a near scale-invariant curvature perturbation power spectrum is generated from the interplay between the variation of sound speed and the second slow roll parameter η. The first branch captures and extends the previously studied models of non-attractor inflation in which the curvature perturbation is not frozen on super-horizon scales and the single field non-Gaussianity consistency condition is violated. We present the general expression for the amplitude of local-type non-Gaussianity in this branch. The second branch is new in which the curvature perturbation is frozen on super-horizon scales and the single field non-Gaussianity consistency condition does hold in the squeezed limit. Depending on the model parameters, the shape of bispectrum in this branch changes from an equilateral configuration to a folded configuration while the amplitude of non-Gaussianity is less than unity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2015

The development of a population of 4D pediatric XCAT phantoms for imaging research and optimization

Purpose: We previously developed a set of highly detailed 4D reference pediatric extended cardiac-torso (XCAT) phantoms at ages of newborn, 1, 5, 10, and 15 yr with organ and tissue masses matched to ICRP Publication 89 values. In this work, we extended this reference set to a series of 64 pediatric phantoms of varying age and height and body mass percentiles representative of the public at large. The models will provide a library of pediatric phantoms for optimizing pediatric imaging protocols. Methods: High resolution positron emission tomography-computed tomography data obtained from the Duke University database were reviewed by a practicing experienced radiologist for anatomic regularity. The CT portion of the data was then segmented with manual and semiautomatic methods to form a target model defined using nonuniform rational B-spline surfaces. A multichannel large deformation diffeomorphic metric mapping algorithm was used to calculate the transform from the best age matching pediatric XCAT reference phantom to the patient target. The transform was used to complete the target, filling in the nonsegmented structures and defining models for the cardiac and respiratory motions. The complete phantoms, consisting of thousands of structures, were then manually inspected for anatomical accuracy. The mass for each major tissue was calculated and compared to linearly interpolated ICRP values for different ages. Results: Sixty four new pediatric phantoms were created in this manner. Each model contains the same level of detail as the original XCAT reference phantoms and also includes parameterized models for the cardiac and respiratory motions. For the phantoms that were 10 yr old and younger, we included both sets of reproductive organs. This gave them the capability to simulate both male and female anatomy. With this, the population can be expanded to 92. Wide anatomical variation was clearly seen amongst the phantom models, both in organ shape and size, even for models of the same age and sex. The phantoms can be combined with existing simulation packages to generate realistic pediatric imaging data from different modalities. Conclusions: This work provides a large cohort of highly detailed pediatric phantoms with 4D capabilities of varying age, height, and body mass. The population of phantoms will provide a vital tool with which to optimize 3D and 4D pediatric imaging devices and techniques in terms of image quality and radiation-absorbed dose.

60 APPLIED LIFE SCIENCES↗

NASA NTRS1988

Digital and optical shape representation and pattern recognition; Proceedings of the Meeting, Orlando, FL, Apr. 4-6, 1988

The present conference discusses topics in pattern-recognition correlator architectures, digital stereo systems, geometric image transformations and their applications, topics in pattern recognition, filter algorithms, object detection and classification, shape representation techniques, and model-based object recognition methods. Attention is given to edge-enhancement preprocessing using liquid crystal TVs, massively-parallel optical data base management, three-dimensional sensing with polar exponential sensor arrays, the optical processing of imaging spectrometer data, hybrid associative memories and metric data models, the representation of shape primitives in neural networks, and the Monte Carlo estimation of moment invariants for pattern recognition.

Juday, Richard D.↗

DOE OSTI2022

Mechanisms of shape transfer and preheating in indirect-drive double shell collisions

Implosions of Hohlraum-driven double shell targets as an alternative inertial confinement fusion concept are underway at the National Ignition Facility. The double shell system relies on a series of energy transfer processes starting from thermal x-ray absorption by the outer shell, followed by collisional transfer of kinetic energy to a heavy metal inner shell, and finally, conversion to the internal energy of the deuterium-tritium fuel. During each of these energy transfer stages, low-mode asymmetries can act to reduce the ideal transfer efficiency degrading double shell performance. Mechanisms, such as hard x-ray preheat from the Hohlraum, not only decrease the efficiency of kinetic energy transfer but may also be a source of low-mode asymmetry. In this article, we evaluate the shape transfer processes through the time of shell collision using two-dimensional integrated Hohlraum and capsule computations. We find that the dominant mode of the shape transfer is well described using a “radial impulse” model from the shape of the foam pressure reservoir. To evaluate the importance of preheat on inner shell shape, we also report on first measurements of Au L-shell preheat asymmetry in a double shell with a tungsten pusher. These measurements showed a 65% higher preheat velocity at the pole of the capsule relative to the equator. We also found that the experiments provided rigorous constraints by which to test the Hohlraum model settings that impact the amount and symmetry of Au L-shell preheat via the plasma conditions inside the outer cone Au bubble.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Computational modeling and neutron imaging to understand interface shape and solute segregation during the vertical gradient freeze growth of BaBrCl:Eu

In this work we apply continuum models to analyze phase change, heat transfer, fluid flow, solute transport, and segregation in order to understand prior neutron imaging observations of the vertical gradient freeze growth of Eu-doped BaBrCl. The models provide a rigorous framework in which to understand the mechanisms that are responsible for the complicated evolution of interface shape and dopant distribution in the growth experiment. We explain how a transition in the solid/liquid interface shape from concave to convex is driven by changes in radial heat transfer caused by furnace design. We also provide a mechanistic explanation of how dynamic growth conditions and changes of the flow structure in the melt result in complicated segregation patterns in this system. A growth pause caused by controller lock-up is shown to result in a band of solute depletion in accordance with classical theory. However, changing flow patterns during growth result in a non-monotonic axial distribution of solute that cannot be explained by simple application of classical segregation models. We assert that the approach presented here, namely the use of rigorous models in conjunction advanced diagnostics, such as neutron imaging, provides an exciting path forward for process optimization and control, accelerating the incremental advances that have, in the past, typically relied on empiricism, experience, and intuition.

36 MATERIALS SCIENCE↗

NASA NTRS1990

Simultaneous expansion and orthogonalization of measured modes for structure identification

Tests of large structures on-orbit will be performed with measurements at a relatively few structure points. Values for the unmeasured degrees of freedom (dofs) can be estimated based on measured dofs and analytical model dynamic information. These 'expanded' mode shapes are useful for optimal-update identification and damage location as well as test/analysis correlation. A new method of expansion for test mode shape vectors is developed from the orthogonal Procrustes problem from computational linear algebra. A subspace defined by the set of measured dofs is compared to a subspace defined by mode shapes from an analytical model of the structure. The method simultaneously expands and orthogonalizes the mode shape vectors. Two demonstration problems are used to compare the new method to current expansion techniques. One demonstration uses test data from a laboratory scale-model truss structure. Performance of the new method is comparable or superior to that of the previous expansion methods which require separate orthogonalization.

Smith, Suzanne Weaver↗

NASA NTRS1987

Improved shape-signature and matching methods for model-based robotic vision

Researchers describe new techniques for curve matching and model-based object recognition, which are based on the notion of shape-signature. The signature which researchers use is an approximation of pointwise curvature. Described here is curve matching algorithm which generalizes a previous algorithm which was developed using this signature, allowing improvement and generalization of a previous model-based object recognition scheme. The results and the experiments described relate to 2-D images. However, natural extensions to the 3-D case exist and are being developed.

Schwartz, J. T.↗

DOE OSTI2021

A vortex sheet based analytical model of the curled wake behind yawed wind turbines

Motivated by the need for compact descriptions of the evolution of non-classical wakes behind yawed wind turbines, we develop an analytical model to predict the shape of curled wakes. Interest in such modelling arises due to the potential of wake steering as a strategy for mitigating power reduction and unsteady loading of downstream turbines in wind farms. We first estimate the distribution of the shed vorticity at the wake edge due to both yaw offset and rotating blades. By considering the wake edge as an ideally thin vortex sheet, we describe its evolution in time moving with the flow. Vortex sheet equations are solved using a power series expansion method, and an approximate solution for the wake shape is obtained. The vortex sheet time evolution is then mapped into a spatial evolution by using a convection velocity. Apart from the wake shape, the lateral deflection of the wake including ground effects is modelled. Our results show that there exists a universal solution for the shape of curled wakes if suitable dimensionless variables are employed. For the case of turbulent boundary layer inflow, the decay of vortex sheet circulation due to turbulent diffusion is included. Finally, we modify the Gaussian wake model by incorporating the predicted shape and deflection of the curled wake, so that we can calculate the wake profiles behind yawed turbines. Model predictions are validated against large-eddy simulations and laboratory experiments for turbines with various operating conditions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS2012

An Analysis Technique/Automated Tool for Comparing and Tracking Analysis Modes of Different Finite Element Models

An analysis technique was developed to compare and track mode shapes for different Finite Element Models. The technique may be applied to a variety of structural dynamics analyses, including model reduction validation (comparing unreduced and reduced models), mode tracking for various parametric analyses (e.g., launch vehicle model dispersion analysis to identify sensitivities to modal gain for Guidance, Navigation, and Control), comparing models of different mesh fidelity (e.g., a coarse model for a preliminary analysis compared to a higher-fidelity model for a detailed analysis) and mode tracking for a structure with properties that change over time (e.g., a launch vehicle from liftoff through end-of-burn, with propellant being expended during the flight). Mode shapes for different models are compared and tracked using several numerical indicators, including traditional Cross-Orthogonality and Modal Assurance Criteria approaches, as well as numerical indicators obtained by comparing modal strain energy and kinetic energy distributions. This analysis technique has been used to reliably identify correlated mode shapes for complex Finite Element Models that would otherwise be difficult to compare using traditional techniques. This improved approach also utilizes an adaptive mode tracking algorithm that allows for automated tracking when working with complex models and/or comparing a large group of models.

Towner, Robert L.↗

NASA NTRS1994

Analytic Sensitivities for Shape Optimization in Equivalent Plate Structural Wing Models

Equivalent plate modeling techniques based on Ritz analysis with simple polynomials prove to be efficient tools for structural modeling of wings in the preliminary design stage. Accuracy problems are encountered, however, when these models are used to obtain finite difference behavior sensitivities with respect to planform shape. The accuracy problems are associated with the poor numerical conditioning of static and eigenvalue equations. As higher-order polynomials are being used to Improve the analysis itself, the more sensitive is the finite difference derivative to the step size used. This article describes a formulation of wing equivalent plate modeling in which it is simple to obtain analytic, explicit expressions for stiffness and mass matrix elements without the need to perform numerical integration. This formulation leads naturally to analytic expressions for the derivatives of displacements, stresses, and natural frequencies with respect to shape design variables. This article examines the accuracy of finite difference derivatives compared with the analytic derivatives, and shows that In some cases it is impossible to obtain any information of value by finite differences. Analytic sensitivities, in this case, are still sufficiently accurate for design optimization.

Livne, Eli↗

NASA NTRS1989

End-point control of a two-link manipulator with a very flexible forearm - Issues and experiments

For mechanical manipulators, a logical sensor location is at the manipulator end-point where tasks are performed. Unfortunately, when bending flexibility exists between an end-point sensor and a joint actuator, stability and performance are achieved only through sophisticated control design. Some of the issues involved in utilizing end-point sensing for two-link flexible manipulators are addressed. A modeling technique that properly represents the foreshortening of a flexible link undergoing deflections is presented. In order to realize fully the advantages of the assumed-modes modeling method, mode shapes are selected that allow a low-order model to be used effectively for simulation and control purposes. A nonlinear controller, incorporating state feedback and a constant-gain extended Kalman filter driven by end-point measurements, is designed and compared to a conventional proportional-plus-derivative controller that uses collocated sensors. Results from implementing these controllers on the experimental Stanford multilink flexible manipulator are given.

Oakley, Celia M.↗

NASA NTRS2014

Adaptive Shape Functions and Internal Mesh Adaptation for Modelling Progressive Failure in Adhesively Bonded Joints

Enhanced finite elements are elements with an embedded analytical solution that can capture detailed local fields, enabling more efficient, mesh independent finite element analysis. The shape functions are determined based on the analytical model rather than prescribed. This method was applied to adhesively bonded joints to model joint behavior with one element through the thickness. This study demonstrates two methods of maintaining the fidelity of such elements during adhesive non-linearity and cracking without increasing the mesh needed for an accurate solution. The first method uses adaptive shape functions, where the shape functions are recalculated at each load step based on the softening of the adhesive. The second method is internal mesh adaption, where cracking of the adhesive within an element is captured by further discretizing the element internally to represent the partially cracked geometry. By keeping mesh adaptations within an element, a finer mesh can be used during the analysis without affecting the global finite element model mesh. Examples are shown which highlight when each method is most effective in reducing the number of elements needed to capture adhesive nonlinearity and cracking. These methods are validated against analogous finite element models utilizing cohesive zone elements.

computational mechanics↗

NASA NTRSDate not supplied

4pPA1 - Turbulence Effects on Shaped Booms: Central Composite Design of Modeled Atmospheric Turbulence Parameters for Sonic Boom Propagation

Propagation of sonic booms through turbulence reduces mean sonic boom perception metric levels and also causes considerable variability. NASA’s PCBoom suite of sonic boom acoustic propagation modules includes an approximate method for accounting for the effects of turbulence on traditional N-wave sonic booms. The current implementation is ineffective for shaped sonic booms or low-booms, and it also has limited values for turbulence and ambient input parameters. NASA’s future X-59 low-boom community noise surveys require an accurate estimate of the effects of turbulence in regions across the USA, so the module must be improved. This work presents the methods of selecting which ambient and turbulence parameters should be included in an improved PCBoom turbulence module. Turbulence and ambient data were collected from two atmospheric model databases, the Climate Forecast System Version 2 and European Centre for Medium-Range Weather Forecast Reanalysis Version 5 (ERA5), hourly from 7 AM to 7 PM local time for 10 years at 19 locations across the USA. A fully-factorial propagation analysis using these parameters would be exceedingly computationally expensive. Instead, a central composite design was chosen resulting in 45 combinations of ambient and turbulence parameters. These 45 cases effectively sample the space balancing computational burden.

turbulence↗

DOE OSTI2018

Shape effect on drying behavior of cement-based materials: Mechanisms and numerical analysis

The shape of the specimen or structure has a direct impact on the behavior of drying concrete. This effect is not taken into account in most of shrinkage models and codes. Only the current B4 model and its previous version B3 model incorporate a shape factor. The determination of this coefficient is based on the nonlinear moisture diffusion analysis, which can explain the shape effect on the shrinkage rate. However, the model integrates this coefficient in the ultimate shrinkage values as well. An experimental study has been performed to confirm and understand this behavior. The mass loss and drying shrinkage of cylinders showed higher rate and ultimate values than the prisms, for the same effective cross section thickness. To explain this result, the drying, the differential shrinkage, the internal stress and the damaged depth were determined for both shapes through numerical modeling. The main input data of the model were the measured mass loss and shrinkage. The calculated desorption isotherm curve of the cylinder was below that of the prism, which is consistent with its higher ultimate mass-loss. The determination of stress profiles indicates slower stress mitigation for the cylinder. The cylinder develops a larger relative damaged area, defined as the part of the specimen where cracking is likely to occur due to tensile stresses. The results actually show that differential shrinkage between the edge and the core is more pronounced for the cylinder and decreases with time.

36 MATERIALS SCIENCE↗

NASA NTRS1976

An equipotential model for auroral arcs

Shaped charge barium release data and high-speed auroral image data show the likely existence of anomalously large (about 1 V/m referred to the 100-km level) electric fields at distances the order of one earth radius above the earth. A model of the electrostatic field above an auroral arc is proposed in which the magnetic field lines are not all equipotentials. Use is made of recent theoretical work on oblique current-driven electrostatic shocks to demonstrate the plausibility of nonequipotential field lines. The model is addressed to the structure of inverted-V electron spectra, current continuity between magnetosphere and ionosphere, and the results of recent shaped charge barium experiments. The model is used to identify specific gaps in our understanding of auroral phenomena.

Swift, D. W.↗

NASA NTRS1992

Experimental study of a generic high-speed civil transport

An experimental study of generic high-speed civil transport was conducted in the NASA Langley 8-ft Transonic Pressure Tunnel. The data base was obtained for the purpose of assessing the accuracy of various levels of computational analysis. Two models differing only in wingtip geometry were tested with and without flow-through nacelles. The baseline model has a curved or crescent wingtip shape, while the second model has a more conventional straight wingtip shape. The study was conducted at Mach numbers from 0.30 to 1.19. Force data were obtained on both the straight wingtip model and the curved wingtip model. Only the curved wingtip model was instrumented for measuring pressures. Selected longitudinal, lateral, and directional data are presented for both models. Selected pressure distributions for the curved wingtip model are also presented.

Belton, Pamela S.↗