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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Turbine blade with friction and impact vibration damping elements

A turbine blade includes an airfoil body having an outer tip and a platform; and a part-span shroud positioned between the outer tip and the platform of the airfoil body. The part-span shroud has a first opening extending through the airfoil body and having a first inner surface. The airfoil body includes a second opening extending radially from the first opening and having a second inner surface. A first elongated vibration-damping element is disposed in the first opening, and a second elongated vibration-damping element disposed radially in the second opening. The second elongated vibration-damping element includes a free radially outer end and a radially inner end coupled to the first elongated vibration-damping element. The first elongated vibration-damping element frictionally damps vibration, and the second elongated vibration-damping element damps vibration using impact within the second opening.

Zhang, James↗
DOE OSTI2023

Separable self-aligning waveguide connector using a ball detent assembly having ball elements engaged with mating divots

Provided herein are various examples of separable waveguide couplers. In one example, a collar element is provided to surround a member comprising a faying surface, a waveguide conduit, and alignment protrusions arranged radially about a perimeter of the faying surface, where the collar element is configured to accept insertion of a mating member comprising a mating faying surface and a mating waveguide conduit. A ball detent assembly is provided having a spring element that retains ball elements in holes formed through the collar element. The waveguide conduit and the mating waveguide conduit are configured to be aligned radially by at least engagement of the alignment protrusions with alignment channels in the mating member and restrained axially by at least engagement of the ball elements with mating divots in the mating member.

Weems, Weyman Albert↗
DOE OSTI2017

Integration of uncooled scraper elements and its diagnostics into Wendelstein 7-X

The modular stellarator Wendelstein 7-X in Greifswald (Germany) successfully started operation in 2015 with short pulse limiter plasmas. In 2017, the next operation phase (OP) OP1.2 will start once 10 uncooled test divertor units (TDU) with graphite armor will be installed. The TDUs allow for plasma pulses of 10 s with 8 MW heating. OP2, allowing for steady state operation, is planned for 2020 after the TDUs will be replaced by 10 water cooled CFC armored divertors. Due to the development of plasma currents like bootstrap currents in long pulse plasmas in OP2, the plasma could hit the edge of the divertor targets which has a reduced cooling capacity compared to the central part of the target tiles. To prevent overloading of these edges, a so-called scraper element can be positioned in front of the divertor, intersecting those strike lines that would otherwise hit the divertor edges. As a result, these edges are protected but as a drawback the pumping efficiency of neutrals is also reduced. As a test an uncooled scraper element with graphite tiles will be placed in two out of ten half modules in OP1.2. A decision to install ten water cooled scraper elements for OP2 is pending on the results of this test in OP1.2. To monitor the impact of the scraper element on the plasma, Langmuir probes are integrated in the plasma facing surface, and a neutral gas manometer measures the neutral density directly behind the plasma facing surface. Moreover, IR and VIS cameras observe the plasma facing surface and thermocouples monitor the temperatures of the graphite tiles and underlying support structure. This paper describes the integration of the scraper element and its diagnostics in Wendelstein 7-X.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Improving the accuracy of discretisations of the vector transport equation on the lowest-order quadrilateral Raviart-Thomas finite elements

Within finite element models of fluids, vector-valued fields such as velocity or momentum variables are commonly discretised using the Raviart-Thomas elements. However, when using the lowest-order quadrilateral Raviart-Thomas elements, standard finite element discretisations of the vector transport equation typically have a low order of spatial accuracy. This paper describes two schemes that improve the accuracy of transporting such vector-valued fields on two-dimensional curved manifolds. The first scheme that is presented reconstructs the transported field in a higher-order function space, where the transport equation is then solved. The second scheme applies a mixed finite element formulation to the vector transport equation, simultaneously solving for the transported field and its vorticity. In this work, an approach to stabilising this mixed vector-vorticity formulation is presented that uses a Streamline Upwind Petrov-Galerkin (SUPG) method. These schemes are then demonstrated, along with their accuracy properties, through some numerical tests. Two new test cases are used to assess the transport of vector-valued fields on curved manifolds, solving the vector transport equation in isolation. The improvement of the schemes is also shown through two standard test cases for rotating shallow-water models.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

The NonConforming Virtual Element Method for the Stokes Equations

In this paper, we present the nonconforming virtual element method (VEM) for the numerical approximation of velocity and pressure in the steady Stokes problem. The pressure is approximated using discontinuous piecewise polynomials, while each component of the velocity is approximated using the nonconforming virtual element space. On each mesh element the local virtual space contains the space of polynomials of up to a given degree, plus suitable nonpolynomial functions. The virtual element functions are implicitly defined as the solution of local Poisson problems with polynomial Neumann boundary conditions. As typical in VEM approaches, the explicit evaluation of the non-polynomial functions is not required. This approach makes it possible to construct nonconforming (virtual) spaces for any polynomial degree regardless of the parity, for two- and three-dimensional problems, and for meshes with very general polygonal and polyhedral elements. We show that the nonconforming VEM is inf-sup stable and establish optimal a priori error estimates for the velocity and pressure approximations. Finally, numerical examples confirm the convergence analysis and the effectiveness of the method in providing high-order accurate approximations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

A Least-Squares-Based Weak Galerkin Finite Element Method for Second Order Elliptic Equations

Here, in this article, we introduce a least-squares-based weak Galerkin finite element method for the second order elliptic equation. This new method is shown to provide very accurate numerical approximations for both the primal and the flux variables. In contrast to other existing least-squares finite element methods, this new method allows us to use discontinuous approximating functions on finite element partitions consisting of arbitrary polygon/polyhedron shapes. We also develop a Schur complement algorithm for the resulting discretization problem by eliminating all the unknowns that represent the solution information in the interior of each element. Optimal order error estimates for both the primal and the flux variables are established. An extensive set of numerical experiments are conducted to demonstrate the robustness, reliability, flexibility, and accuracy of the least-squares-based weak Galerkin finite element method. Finally, the numerical examples cover a wide range of applied problems, including singularly perturbed reaction-diffusion equations and the flow of fluid in porous media with strong anisotropy and heterogeneity.

nite element methods↗
DOE OSTI2016

Depletion Analysis of Additively Manufactured Control Elements in HFIR

The High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory is a flux-trap type research reactor which provides one of the highest steady-state neutron sources in the world. HFIR neutrons are used for a range of research applications, including scattering experiments, materials irradiation, and isotope production. The HFIR core operates at 85 MW and is light water cooled and moderated. The core consists of several concentric cylindrical regions, as depicted in Fig. 1. At the center of the core is the flux trap, where the thermal flux reaches a maximum on the order of 10{sup 15} neutrons/cm{sup 2}-s. Immediately surrounding the flux trap are two annular fuel elements, an inner fuel element and an outer fuel element, each loaded with hundreds of thin fuel plates curved into an involute shape. Surrounding the outer fuel element are two thin control elements (CEs), an inner CE (ICE) and an outer CE (OCE). The CEs are axially zoned into three regions according to absorption strength: the white regions contain only structural aluminum and do not significantly contribute to absorption; the gray regions contain tantalum (Ta) as the primary absorber with a concentration of 30% by volume; and the black regions contain europium in the form of Eu{sub 2}O{sub 3} with a concentration of 33% by volume. A thick beryllium reflector is the final core component surrounding the CEs. A particular challenge to efficient maintenance and continued operation of HFIR is fabrication of the CEs, the current methods for which are tedious, outdated, and expensive. In an effort to improve the operational economics of HFIR and to demonstrate the application of advanced manufacturing techniques to the production of nuclear reactor components, the ultrasonic additive manufacturing (UAM) process is being investigated for fabrication of the HFIR CEs. This application of UAM involves directly embedding small cylindrical compacts (∼5.6 mm diameter, ∼1.7 mm thick) containing 60% neutron poison by volume into an aluminum matrix, using energy from ultrasonic vibrations to bond the compacts to the aluminum. The CEs contain discrete regions of absorbing material, in contrast to the standard design with homogeneously distributed absorbers. This novel design necessitates an investigation into how the HFIR core neutronic behavior differs from the case with homogeneous CEs so as to ascertain the feasibility of using additively manufactured CEs in HFIR. From an operations perspective, it is desirable for the discrete CEs to match the performance of the homogeneous CEs as closely as possible so as to avoid reconsideration of established safety margins. Earlier analyses of HFIR under beginning of cycle (BOC) conditions have indicated that although absorption properties on a local scale differ significantly between CE designs, the macroscopic behavior (neutron multiplication and flux and power distributions) of the HFIR core is not significantly altered. This study now addresses CE performance throughout depletion of the HFIR core during a reactor cycle. These analyses help to construct a more complete picture of the feasibility of employing additively manufactured CEs in HFIR and will reveal any adjustments which must be made to the design in order to maintain acceptable performance. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Mechanism of formation of wiggly compaction bands in porous sandstone: 2. Numerical simulation using discrete element method

Wiggly compaction bands in porous aeolian s andstone vary from chevron shape to wavy shape to nearly straight. In some outcrops these variations occur along a single band. Here, a bonded close-packed discrete element model is used to investigate what mechanical properties control the formation of wiggly compaction bands (CBs). To simulate the volumetric yielding failure of porous sandstone, a discrete element shrinks when the force state of one of its bonds reaches the yielding cap defined by the failure force and the aspect ratio (k) of the yielding ellipse. A Matlab code “MatDEM 3D ” has been developed on the basis of this enhanced discrete element method. Mechanical parameters of elements are chosen according to the elastic properties and the strengths of porous sandstone. In numerical simulations, the failure angle between the band segment and maximum principle stress decreases from 90° to approximately 45° as k increases from 0.5 to 2, and compaction bands vary from straight to chevron shape. With increasing strain, subsequent compaction occurs inside or beside compacted elements, which leads to further compaction and thickening of bands. The simulations indicate that a greater yielding stress promotes chevron CBs, and a greater cement strength promotes straight CBs. Combined with the microscopic analysis introduced in the companion paper, we conclude that the shape of wiggly CBs is controlled by the mechanical properties of sandstone, including the aspect ratio of the yielding ellipse, the cri tical yielding stress, and the cement strength, w hich are d etermined primarily by petrophysical attributes, e.g., grain sorting, porosity, and cementation.

58 GEOSCIENCES↗
DOE OSTI2025

Enriched immersed finite element and isogeometric analysis: algorithms and data structures

Immersed finite element methods provide a convenient analysis framework for problems involving geometrically complex domains, such as those found in topology optimization and microstructures for engineered materials. However, their implementation remains a major challenge due to, among other things, the need to apply nontrivial stabilization schemes and generate custom quadrature rules. This article introduces the robust and computationally efficient algorithms and data structures comprising an immersed finite element preprocessing framework. The input to the preprocessor consists of a background mesh and one or more geometries defined on its domain. The output is structured into groups of elements with custom quadrature rules formatted such that common finite element assembly routines may be used without or with only minimal modifications. The key to the preprocessing framework is the construction of material topology information, concurrently with the generation of a quadrature rule, which is then used to perform enrichment and generate stabilization rules. While the algorithmic framework applies to a wide range of immersed finite element methods using different types of meshes, integration, and stabilization schemes, the preprocessor is presented within the context of the extended isogeometric analysis. This method utilizes a structured B-spline mesh, a generalized Heaviside enrichment strategy considering the material layout within individual basis functions’ supports, and face-oriented ghost stabilization. Using a set of examples, the effectiveness of the enrichment and stabilization strategies is demonstrated alongside the preprocessor’s robustness in geometric edge cases. Additionally, the performance and parallel scalability of the implementation are evaluated.

Computer implementation↗
DOE OSTI2018

Crank–Nicolson WSGI difference scheme with finite element method for multi-dimensional time-fractional wave problem

In this article, a second-order Crank–Nicolson weighted and shifted Grünwald integral (WSGI) time-discrete scheme combined with finite element method is studied for finding the numerical solution of the multi-dimensional time-fractional wave equation. The time-fractional wave equation with Caputo-fractional derivative is transformed into the time-fractional integral equation by integral technique, then the second-order Crank–Nicolson finite element scheme with a time second-order WSGI discrete approximation for fractional integral is formulated. The analysis of stability is made, then a priori error estimate is given by making use of the conversion technique between the WSGI formula and fractional integral. At the end of the article, some numerical examples covering two two-dimensional cases with rectangular element and triangular element and a three-dimensional case with tetrahedral element are shown to test and verify our theoretical results.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Matrix-free subcell residual distribution for Bernstein finite element discretizations of linear advection equations

In this work, we introduce a new residual distribution (RD) framework for the design of bound-preserving high-resolution finite element schemes. The continuous and discontinuous Galerkin discretizations of the linear advection equation are modified to construct local extremum diminishing (LED) approximations. To that end, we perform mass lumping and redistribute the element residuals in a manner which guarantees the LED property. The hierarchical correction procedure for high-order Bernstein finite element discretizations involves localization to subcells and definition of bound-preserving weights for subcell contributions. Using strong stability preserving (SSP) Runge–Kutta methods for time integration, we prove the validity of discrete maximum principles under CFL-like time step restrictions. The low-order version of our method has roughly the same accuracy as the one derived from a piecewise (multi)-linear approximation on a submesh with the same nodal points. In high-order extensions, we use an element-based flux-corrected transport (FCT) algorithm which can be interpreted as a nonlinear RD scheme. The proposed LED corrections are tailor-made for matrix-free implementations which avoid the rapidly growing cost of matrix assembly for high-order Bernstein elements. The results for 1D, 2D, and 3D test problems compare favorably to those obtained with the best matrix-based approaches.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Stress-hybrid virtual element method on six-noded triangular meshes for compressible and nearly-incompressible linear elasticity

In this paper, we present a first-order Stress-Hybrid Virtual Element Method (SH-VEM) on six-noded triangular meshes for linear plane elasticity. Here, we adopt the Hellinger–Reissner variational principle to construct a weak equilibrium condition and a stress based projection operator. In each element, the stress projection operator is expressed in terms of the nodal displacements, which leads to a displacement based formulation. This stress-hybrid approach assumes a globally continuous displacement field while the stress field is discontinuous across each element. The stress field is initially represented by divergence-free tensor polynomials based on Airy stress functions, but we also present a formulation that uses a penalty term to enforce the element equilibrium conditions, referred to as the Penalty Stress-Hybrid Virtual Element Method (PSH-VEM). Numerical results are presented for PSH-VEM and SH-VEM, and we compare their convergence to the composite triangle FEM and B-bar VEM on benchmark problems in linear elasticity. The SH-VEM converges optimally in the L 2 norm of the displacement, energy seminorm, and the L 2 norm of hydrostatic stress. Furthermore, the results reveal that PSH-VEM converges in most cases at a faster rate than the expected optimal rate, but it requires the selection of a suitably chosen penalty parameter.

42 ENGINEERING↗
DOE OSTI2019

Multilayered triangular and quadrilateral flat shell elements based on the Refined Zigzag Theory

The paper presents a class of C 0 -continuous, flat shell elements based on the Refined Zigzag Theory (RZT) for the analysis of multilayered and curved composite and sandwich structures. In this study, the use of the interdependent interpolation strategy allows eliminating the shear-locking phenomenon and introducing the drilling rotation necessary to complete the set of classical nodal degrees of freedom (three displacements and three rotations). Additional kinematic variables are present in RZT, the zigzag rotations around the in-plane axes that measure the normal distortion typical of multilayered structures. An additional “drilling” zigzag rotation is therefore included among the nodal degrees of freedom in order to properly model curved and built-up structures. A stabilization procedure is adopted to suppress spurious zero-energy modes. A three-node triangular and a four-node quadrilateral flat shell element are formulated with 9 degrees of freedom per node. Example problems involving flat and curved multilayered structures are presented and discussed in order to assess the accuracy and convergence properties of the presented elements. Both static response predictions and free vibrations analyses are considered and the comparison is made with analytic RZT solutions, high-fidelity 3D finite element models and FSDT-based flat shell elements.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

An automated micro-separation system for the chromatographic removal of uranium matrix for trace element analysis by ICP-OES

An automated, miniaturized, off-line separation technique is presented here using an Elemental Scientific Inc. microFAST MC system with UTEVA resin to extract the uranium matrix from its trace element impurities in aqueous media. The collected fractions were analyzed for ~30 trace elements using inductively coupled plasma – optical emission spectroscopy. Ten replicate samples were processed with a single column resulting in precision ranging from 3.3% to 6.2% relative standard deviation with regards to the trace element recoveries. Accuracy, with respect to trace element concentrations in the U 3 O 8 Certified Reference Material 124-1, resulted in an average of 13.9% relative deviation while accuracy to the Canadian U3O8 reference material, CUP-2, resulted in an average relative deviation of 8.6%. In conclusion, the total separation time of this automated process was reduced to ~30 min per sample while employing a 0.5 mL UTEVA chromatographic resin bed and 2.5 mg of uranium.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Geochemical Evidence for Rare-Earth Element Mobilization during Kaolin Diagenesis

This study investigates how saprolization influences inherent rare-earth element (REE) source rock signatures and how depositional environment(s) and diagenetic reactions ultimately impact the REE signature within sedimentary kaolin bodies. Rare-earth element geochemistry signatures are particularly useful for tracking element sources and mobility and are, therefore, powerful tools in the investigation of clay mineral formation and diagenesis. Rare-earth element and bulk chemical compositions were determined using discrete chemical analyses and chemical imaging. Saprolitic materials show an enrichment in the light and heavy REEs, compared with the parent material, with enhanced Ce/Eu anomalies. Light REEs within sedimentary kaolins are associated with phosphate mineralogy and have experienced variable degrees of diagenetic fractionation and mobilization. Cretaceous kaolins display more light REE mobility compared with Tertiary kaolins, which show very little REE fractionation. Degrees of REE fractionation are driven primarily by differences in sedimentary kaolin physical properties and the presence of organic acids in groundwater. Unfortunately, the provenance of the Georgia kaolins could not be determined based solely on the trace-element and REE compositions because fractionations during saprolization and diagenesis mask much of the inherent provenance signatures. Lastly, implications for the REEs as an economic deposit and their beneficiation are discussed.

58 GEOSCIENCES↗
DOE OSTI2014

Diversity of abundance patterns of neutron-capture elements in very metal-poor stars

Observations of Very Metal-Poor stars indicate that there are at least two sites to r-process; “weak r-process” and “main r-process”. A question is whether these two are well separated or there exists a variation in the r-process. We present the results of abundance analysis of neutron-capture elements in the two Very Metal-Poor stars HD107752 and HD110184 in the Milky Way halo observed with the Subaru Telescope HDS. The abundance patterns show overabundace at light n-capture elements (e.g. Sr, Y), inferring the element yielding of weak r-process, while heavy neutron-capture elements (e.g. Ba, Eu) are deficient; however, the overabundance of light ones is not as significant as that previously found in stars representing the weak r-process (e.g. HD122563; Honda et al. 2006). Our study show diversity in the abundance patterns from light to heavy neutron-capture elements in VMP stars, suggesting a variation in r-process, which may depend on electron fraction of environment.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Matrix elements and duality for type 2 unitary representations of the Lie superalgebra gl(m|n)

The characteristic identity formalism discussed in our recent articles is further utilized to derive matrix elements of type 2 unitary irreducible gl(m|n) modules. In particular, we give matrix element formulae for all gl(m|n) generators, including the non-elementary generators, together with their phases on finite dimensional type 2 unitary irreducible representations which include the contravariant tensor representations and an additional class of essentially typical representations. Remarkably, we find that the type 2 unitary matrix element equations coincide with the type 1 unitary matrix element equations for non-vanishing matrix elements up to a phase.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Elemental analysis of different varieties of rice samples using XRF technique

Rice is most consumed staple food in the world providing over 21% of the calorie intake of world’s population having high yielding capacity. Elements detected in rice are Al, As, Br, Cd, Cl, Co, Cs, Cu, Fe, Hg, K, Mg, Mn, Mo, Rb, Se and Zn by using Instrumental Neutron Activation with k0 standardization (R. Jayasekera etal,2004). Some of these trace elements are C, H, O, N, S, Ca, P, K, Na, Cl, Mn, Ti, Mg, Cu, Fe, Ni, Si and Zn are essential for growth of human physique The deficiency or excess of these elements in food is known to cause a variety of malnutrition or health disorders in the world. Every year, various varieties of rice are launched by Punjab Agriculture University, Ludhiana. The main purpose of which is to increases the yield to attain the maximum profit. But this leads to changing the elemental concentration in them, which may affect the human health according to variation in the nutrition values. The main objective is to study the presence of elemental concentration in various varieties of rice using EDXRF technique.

60 APPLIED LIFE SCIENCES↗