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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Automatic computation of wing-fuselage intersection lines and fillet inserts with fixed-area constraint

Procedures for automatic computation of wing-fuselage juncture geometry are described. These procedures begin with a geometry in wave-drag format. First, an intersection line is computed by extrapolating the wing to the fuselage. Then two types of filleting procedures are described, both of which utilize a combination of analytical and numerical techniques appropriate for automatic calculation. An analytical technique for estimating the added volume due to the fillet is derived, and an iterative procedure for revising the fuselage to compensate for this additional volume is given. Sample results are included in graphical form.

Barger, Raymond L.↗
DOE OSTI2015

Normal mode analysis of macromolecular systems with the mobile block Hessian method

Until recently, normal mode analysis (NMA) was limited to small proteins, not only because the required energy minimization is a computationally exhausting task, but also because NMA requires the expensive diagonalization of a 3N{sub a}×3N{sub a} matrix with N{sub a} the number of atoms. A series of simplified models has been proposed, in particular the Rotation-Translation Blocks (RTB) method by Tama et al. for the simulation of proteins. It makes use of the concept that a peptide chain or protein can be seen as a subsequent set of rigid components, i.e. the peptide units. A peptide chain is thus divided into rigid blocks with six degrees of freedom each. Recently we developed the Mobile Block Hessian (MBH) method, which in a sense has similar features as the RTB method. The main difference is that MBH was developed to deal with partially optimized systems. The position/orientation of each block is optimized while the internal geometry is kept fixed at a plausible - but not necessarily optimized - geometry. This reduces the computational cost of the energy minimization. Applying the standard NMA on a partially optimized structure however results in spurious imaginary frequencies and unwanted coordinate dependence. The MBH avoids these unphysical effects by taking into account energy gradient corrections. Moreover the number of variables is reduced, which facilitates the diagonalization of the Hessian. In the original implementation of MBH, atoms could only be part of one rigid block. The MBH is now extended to the case where atoms can be part of two or more blocks. Two basic linkages can be realized: (1) blocks connected by one link atom, or (2) by two link atoms, where the latter is referred to as the hinge type connection. In this work we present the MBH concept and illustrate its performance with the crambin protein as an example.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

SU-E-J-134: An Augmented-Reality Optical Imaging System for Accurate Breast Positioning During Radiotherapy

Purpose: Breast radiotherapy, particularly electronic compensation, may involve large dose gradients and difficult patient positioning problems. We have developed a simple self-calibrating augmented-reality system, which assists in accurately and reproducibly positioning the patient, by displaying her live image from a single camera superimposed on the correct perspective projection of her 3D CT data. Our method requires only a standard digital camera capable of live-view mode, installed in the treatment suite at an approximately-known orientation and position (rotation R; translation T). Methods: A 10-sphere calibration jig was constructed and CT imaged to provide a 3D model. The (R,T) relating the camera to the CT coordinate system were determined by acquiring a photograph of the jig and optimizing an objective function, which compares the true image points to points calculated with a given candidate R and T geometry. Using this geometric information, 3D CT patient data, viewed from the camera's perspective, is plotted using a Matlab routine. This image data is superimposed onto the real-time patient image, acquired by the camera, and displayed using standard live-view software. This enables the therapists to view both the patient's current and desired positions, and guide the patient into assuming the correct position. The method was evaluated using an in-house developed bolus-like breast phantom, mounted on a supporting platform, which could be tilted at various angles to simulate treatment-like geometries. Results: Our system allowed breast phantom alignment, with an accuracy of about 0.5 cm and 1 ± 0.5 degree. Better resolution could be possible using a camera with higher-zoom capabilities. Conclusion: We have developed an augmented-reality system, which combines a perspective projection of a CT image with a patient's real-time optical image. This system has the potential to improve patient setup accuracy during breast radiotherapy, and could possibly be used for other disease sites as well.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Multiplexed infrared photodetection using resonant radio-frequency circuits

We demonstrate a room-temperature semiconductor-based photodetector where readout is achieved using a resonant radio-frequency (RF) circuit consisting of a microstrip split-ring resonator coupled to a microstrip busline, fabricated on a semiconductor substrate. The RF resonant circuits are characterized at RF frequencies as function of resonator geometry, as well as for their response to incident IR radiation. The detectors are modeled analytically and using commercial simulation software, with good agreement to our experimental results. Though the detector sensitivity is weak, the detector architecture offers the potential for multiplexing arrays of detectors on a single read-out line, in addition to high speed response for either direct coupling of optical signals to RF circuitry, or alternatively, carrier dynamics characterization of semiconductor, or other, material systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Working with Bézier Curves as bases for Functional Expansion Tallies

Functional expansion tallies (FETs) are powerful tools for getting more information per history from Monte Carlo simulations, but in the past they have been constrained to orthogonal bases. Bézier curves are used widely in computer aided design (CAD) geometry kernels and could be well-suited for FETs due to their ability to assume many arbitrary shapes, but they use nonorthogonal bases. Recent developments in 2021 have made nonorthogonal FETs possible. The convergence of Bézier curve FETs in both polynomial order and number of samples is explored in this work. It is shown that these bases are well-suited for representing normal distributions and this opens the door to the possibility of other CAD-derived FET bases.

97 - MATHEMATICS AND COMPUTING↗
DOE OSTI2022

On the closedness and geometry of tensor network state sets

Tensor network states (TNS) are a powerful approach for the study of strongly correlated quantum matter. The curse of dimensionality is addressed by parametrizing the many-body state in terms of a network of partially contracted tensors. These tensors form a substantially reduced set of effective degrees of freedom. In practical algorithms, functionals like energy expectation values or overlaps are optimized over certain sets of TNS. Concerning algorithmic stability, it is important whether the considered sets are closed because, otherwise, the algorithms may approach a boundary point that is outside the TNS set and tensor elements diverge. Here we discuss the closedness and geometries of TNS sets, and we propose regularizations for optimization problems on non-closed TNS sets. We show that sets of matrix product states (MPS) with open boundary conditions, tree tensor network states, and the multiscale entanglement renormalization ansatz are always closed, whereas sets of translation-invariant MPS with periodic boundary conditions (PBC), heterogeneous MPS with PBC, and projected entangled pair states are generally not closed. The latter is done using explicit examples like the W state, states that we call two-domain states, and fine-grained versions thereof.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS2007

Automatic Conversion of Conceptual Geometry to CFD Geometry for Aircraft Design

Conceptual aircraft design is usually based on simple analysis codes. Its objective is to provide an overall system performance of the developed concept, while preliminary aircraft design uses high-fidelity analysis tools such as computational fluid dynamics (CFD) analysis codes or finite element structural analysis codes. In some applications, such as low-boom supersonic concept development, it is important to be able to explore a variety of drastically different configurations while using CFD analysis to check whether a given configuration can be tailored to have a low-boom ground signature. It poses an extremely challenging problem of integrating CFD analysis in conceptual design. This presentation will discuss a computer code, called iPatch, for automatic conversion of conceptual geometry to CFD geometry. In general, conceptual aircraft geometry is not as well-defined as a CAD geometry model. In particular, a conceptual aircraft geometry model usually does not define the intersection curves for the connecting surfaces. The computer code iPatch eliminates the gap between conceptual geometry and CFD geometry by accomplishing the following three tasks automatically: (1) use bicubic B-splines to extrapolate (if necessary) each surface in a conceptual geometry so that all the independently defined geometry components (such as wing and fuselage) can be intersected to form a watertight CFD geometry, (2) compute the intersection curves of surface patches at any resolution (up to 10-7 accuracy) specified by users, and (3) write the B-spline surface patches and the corresponding boundary points for the watertight CFD geometry in the format that can be directly exported to the meshing tool VGRID in the CFD software TetrUSS. As a result, conceptual designers can get quick feedback on the aerodynamic characteristics of their concepts, which will allow them to understand some subtlety in their concepts and to be able to assess their concepts with a higher degree of confidence. This integration of CFD analysis in conceptual aircraft design will greatly eliminate some uncertainty due to simple analysis codes used to develop the concepts and improve the feasibility/credibility of the final concept. The presentation will highlight the mathematical challenges of accomplishing the aforementioned three tasks and the computational algorithms used by iPatch.

Li, Wu↗
NASA NTRS1983

Deformable subreflector computed by geometric optics

Using a Cassegrainian geometry, the 64-meter antenna with its distorted paraboloidal reflecting surface is forced to produce a uniform phase wavefront by a pathlength-compensating subreflector. First, the computed distortion vectors at the joints or nodes of the main reflector structure supporting the surface panels are best fitted to a paraboloid. Second, the resulting residual distortion errors are used to determine a compensating subreflector surface by ray tracing using geometric optics principles. Third, the totally corrected subreflector surface is defined by the normal directions and distances to the surface of the original symmetric hyperboloid for the purpose of evaluation. Finally, contour maps of distortions of the paraboloid reflector and the compensating subreflector are presented. A field-measured check of the subreflector in focused position as computed by the described methodology is also presented for the antenna position at horizon look with the geometry at 45 degrees elevation.

Katow, M. S.↗
DOE OSTI2013

Infinitesimal and global rigidity and inflexibility of surfaces of revolution with flattening at the poles

The subject of this article is one of the most important questions of classical geometry: the theory of bendings and infinitesimal bendings of surfaces. These questions are studied for surfaces of revolution and, unlike previous well-known works, we make only minimal smoothness assumptions (the class C{sup 1}) in the initial part of our study. In this class we prove local existence and uniqueness theorems for infinitesimal bendings. We then consider the analytic class and establish simple criteria for rigidity and inflexibility of compact surfaces. These criteria depend on the values of certain integer characteristics related to the order of flattening of the surface at its poles. We also show that in the nonanalytic situation there exist nonrigid surfaces with any given order of flattening at the poles. Bibliography: 22 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

CFD Evaluation of Pressure Change Along Coolant Passages in Sodium-Cooled Fast Reactor with Nek5000

To support the design efforts of advanced sodium-cooled fast reactors (SFRs), a series of computational fluid dynamics (CFD) simulations are performed to investigate the pressure change along various flow passages in the proposed SFR system. The simulations are carried out with the state-of-the-art spectral element flow solver, Nek5000. Two specific case studies are presented in this paper: the flow exiting the axial neutron reflector channels and the flow entering the fuel pin bundle. Due to the high Reynolds numbers expected, a Reynolds-averaged Navier-Stokes (RANS) approach is necessary to model the turbulence. A newly developed regularized k-omega RANS model is adopted in the related CFD calculations. The first case study explores the effect of Reynolds number on the pressure change when flow exits the reflector channels. The pressure change in this case has two major contributors: the change due to wall friction and the Bernoulli effect. It is noted that the nondimensional pressure loss follows a log-linear trend up to Re = 10 5 , and then the trend is flattened. In the second case study, the advanced NekNek coupling capability is tested where an integral domain can be divided into multiple subdomains with coupling interfaces, which would greatly ease the meshing process of complex engineering geometries and potentially save computational resources. The preliminary results obtained so far confirm the consistency between the NekNek results and those produced by regular Nek5000 simulation. The presented work demonstrates the readiness and flexibility of the related CFD techniques, which is part of the broader effort to leverage cutting-edge CFD to inform the advanced nuclear reactor designs.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2024

Direct, simple and efficient computation of all components of the virtual-casing magnetic field in axisymmetric geometries with Kapur–Rokhlin quadrature

In a recent publication (Toler et al., J. Plasma Phys., vol. 89, issue 2, 2023, p. 905890210), we demonstrated that for axisymmetric geometries, the Kapur–Rokhlin quadrature rule provided an efficient and high-order accurate method for computing the normal component, on the plasma surface, of the magnetic field due to the toroidal current flowing in the plasma, via the virtual-casing principle. The calculation was indirect, as it required the prior computation of the magnetic vector potential from the virtual-casing principle, followed by the computation of its tangential derivative by Fourier differentiation, to obtain the normal component of the magnetic field. Our approach did not provide the other components of the virtual-casing magnetic field. In this letter, we show that a more direct and more general approach is available for the computation of the virtual-casing magnetic field. The Kapur–Rokhlin quadrature rule accurately calculates the principal value integrals in the expression for all the components of the magnetic field on the plasma boundary, and the numerical error converges at a rate nearly as high as the indirect method we presented previously.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Comparative structural and computational analysis supports eighteen cellulose synthases in the plant cellulose synthesis complex

A six-lobed membrane spanning cellulose synthesis complex (CSC) containing multiple cellulose synthase (CESA) glycosyltransferases mediates cellulose microfibril formation. The number of CESAs in the CSC has been debated for decades in light of changing estimates of the diameter of the smallest microfibril formed from the β-1,4 glucan chains synthesized by one CSC. We obtained more direct evidence through generating improved transmission electron microscopy (TEM) images and image averages of the rosette-type CSC, revealing the frequent triangularity and average cross-sectional area in the plasma membrane of its individual lobes. Trimeric oligomers of two alternative CESA computational models corresponded well with individual lobe geometry. A six-fold assembly of the trimeric computational oligomer had the lowest potential energy per monomer and was consistent with rosette CSC morphology. Negative stain TEM and image averaging showed the triangularity of a recombinant CESA cytosolic domain, consistent with previous modeling of its trimeric nature from small angle scattering (SAXS) data. Six trimeric SAXS models nearly filled the space below an average FF-TEM image of the rosette CSC. In conclusion, the multifaceted data support a rosette CSC with 18 CESAs that mediates the synthesis of a fundamental microfibril composed of 18 glucan chains.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1996

Computer Simulation of Spatial Arrangement and Connectivity of Particles in Three-Dimensional Microstructure: Application to Model Electrical Conductivity of Polymer Matrix Composite

Computer simulation is a powerful tool for analyzing the geometry of three-dimensional microstructure. A computer simulation model is developed to represent the three-dimensional microstructure of a two-phase particulate composite where particles may be in contact with one another but do not overlap significantly. The model is used to quantify the "connectedness" of the particulate phase of a polymer matrix composite containing hollow carbon particles in a dielectric polymer resin matrix. The simulations are utilized to estimate the morphological percolation volume fraction for electrical conduction, and the effective volume fraction of the particles that actually take part in the electrical conduction. The calculated values of the effective volume fraction are used as an input for a self-consistent physical model for electrical conductivity. The predicted values of electrical conductivity are in very good agreement with the corresponding experimental data on a series of specimens having different particulate volume fraction.

Louis, P.↗
DOE OSTI2014

SU-E-J-26: Analysis of Image Quality in CBCT QA Using a Treatment Planning System

Purpose: The objective of this study is to propose an alternative QA technique that analyzes imaging quality(IQ) in CBCT-QA processing. Methods: A catphan phantom was used to take CT imaging data set that were imported into a treatment planning system - Eclipse. The image quality was analyzed in terms of in-slice geometry resolution, Hounsfield numbers(HU) accuracy, mean-slice thickness, edge-to-center uniformity, low contrast resolution, and high contrast spatial resolution in Eclipse workstation. The CBCT-QA was also analyzed by OBI-workstation and a commercial software. Comparison was made to evaluation feasibility in a TPS environment. Results: The analysis of IQ was conducted in Eclipse v10.0 TPS. In-slice geometric resolution was measured between 2-rods in section CTP404 and repeated for all 4 rods with the difference between expected and measured values less than +/−0.1 cm. For HU, the difference between expected and measured values in HU was found much less than +/−40. Mean slice thickness measured by a distance on the wire proportional to scanner increment multiplying by a factor of 0.42. After repeating measurements to 4 wires, the average difference between expected and measured values was less +/−0.124 mm in slice thickness. HU uniformity was measured in section CTP486 with the tolerance less than +/−40 HU. Low contrast resolution in section CTP515 and high contrast resolution in section CTP528 were found to be 7 disks in diameter of 4 mm and 6 lp/cm, respectively. Eclipse TPS results indicated a good agreement to those obtained in OBI workstation and ImagePro software for major parameters. Conclusion: An analysis of IQ was proposed as an alternative CBCT QA processing. Based upon measured data assessment, proposed method was accurate and consistent to IQ evaluation and TG142 guideline. The approach was to utilize TPS resource, which can be valuable to re-planning, verification, and delivery in adaptive therapy.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Characterization of a novel 2D array dosimeter for patient-specific quality assurance with volumetric arc therapy

Purpose: In this study, the authors are evaluating a new, commercially available 2D array that offers 3D dose reconstruction for patient specific intensity modulated radiation therapy quality assurance (IMRT QA).Methods: The OCTAVIUS 4D system and its accompanying software (VERISOFT) by PTW were evaluated for the accuracy of the dose reconstruction for patient specific pretreatment IMRT QA. OCTAVIUS 4D measures the dose plane at the linac isocenter as the phantom rotates synchronously with the gantry, maintaining perpendicularity with the beam, by means of an inclinometer and a motor. The measurements collected during a volumetric modulated arc therapy delivery (VMAT) are reconstructed into a 3D dose volume. The VERISOFT application is used to perform the analysis, by comparing the reconstructed dose against the 3D dose matrix from the treatment planning system (TPS) that is computed for the same geometry and beam arrangement as that of the measurement. In this study, the authors evaluated the 3D dose reconstruction algorithm of this new system using a series of tests. Using the Octavius 4D phantom as the patient, dose distributions for various field sizes, beam orientations, shapes, and combination of fields were calculated using the Pinnacle3, TPS, and the respective DICOMRT dose was exported to the VERISOFT analysis software. Measurements were obtained by delivering the test treatment plans and comparisons were made based on gamma index, dose profiles, and isodose distribution analysis. In addition, output factors were measured and the dose linearity of the array was assessed. Those measurements were compared against measurements in water using a single, calibrated ionization chamber as well as calculations from Pinnacle for the same delivery geometries.Results: The number of voxels that met the 3%/3 mm criteria for the volumetric 3D gamma index analysis ranged from 92.3% to 98.9% for all the patient plans that the authors evaluated. 2D gamma analysis in the axial, sagittal, and coronal planes produced similar results to those in the 3D gamma analysis. The new detector system does not require an angular dependence correction because it rotates in synchrony with the gantry and the detector array maintains a constant SAD while always perpendicular to the beam axis. Output factors were within 2% when compared to ionization chamber measurements and Pinnacle calculations. Similar agreement was observed when testing the MU linearity (for MU values above 2) as well as dose rate effect.Conclusions: The OCTAVIUS 4D system has some unique characteristics that can potentially improve the patient specific pretreatment IMRT QA data collection and analysis. The ability of the software to reconstruct from the measurements the true 3D dose distribution in the phantom, provides a unique perspective for the medical physicist that evaluates a patient's QA plan.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2019

Valence : A Massively Parallel Implementation of the Variational Subspace Valence Bond Method

This work describes the software package, Valence, for the calculation of molecular energies using the variational subspace valence bond (VSVB) method. VSVB is an ab initio electronic structure method based on nonorthogonal orbitals. Important features of practical value include high parallel scalability, wave functions that can be constructed automatically by combining orbitals from previous calculations, and ground and excited states that can be modeled with a single configuration or determinant. Here, the open-source software package includes tools to generate wave functions, a database of generic orbitals, example input files, and a library build intended for integration with other packages. We also present the interface to an external software package, enabling the computation of optimized molecular geometries and vibrational frequencies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Nonperturbative negative geometries: amplitudes at strong coupling and the amplituhedron

The amplituhedron determines scattering amplitudes in planar N = 4 super Yang-Mills by a single “positive geometry” in the space of kinematic and loop variables. We study a closely related definition of the amplituhedron for the simplest case of four-particle scattering, given as a sum over complementary “negative geometries”, which provides a natural geometric understanding of the exponentiation of infrared (IR) divergences, as well as a new geometric definition of an IR finite observable F(g, z) — dually interpreted as the expectation value of the null polygonal Wilson loop with a single Lagrangian insertion — which is directly determined by these negative geometries. This provides a long-sought direct link between canonical forms for positive (negative) geometries, and a completely IR finite post-loop-integration observable depending on a single kinematical variable z, from which the cusp anomalous dimension Γ cusp (g) can also be straightforwardly obtained. We study an especially simple class of negative geometries at all loop orders, associated with a “tree” structure in the negativity conditions, for which the contributions to F(g, z) and Γ cusp can easily be determined by an interesting non-linear differential equation immediately following from the combinatorics of negative geometries. This lets us compute these “tree” contributions to F(g, z) and Γ cusp for all values of the ‘t Hooft coupling. The result for Γ cusp remarkably shares all main qualitative characteristics of the known exact results obtained using integrability.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

One-loop integrals from volumes of orthoschemes

Recently in arXiv:2012.05599 Rudenko presented a formula for the volume of hyperbolic orthoschemes in terms of alternating polylogarithms. We use this result to provide an explicit analytic result for the one-loop scalar n -gon Feynman integral in n dimensions, for even n , with massless or massive internal and external edges. Furthermore, we evaluate the general six-dimensional hexagon integral in terms of classical polylogarithms.

97 MATHEMATICS AND COMPUTING↗