Syn, Chol K.; Lesuer, Donald R.
1995-01-01
A laminated metal composite of low flow stress layers and high flow stress layers is described which is formed using flow constraining elements, preferably in the shape of rings, individually placed around each of the low flow stress layers while pressure is applied to the stack to bond the layers of the composite together, to thereby restrain the flow of the low flow stress layers from the stack during the bonding. The laminated metal composite of the invention is made by the steps of forming a stack of alternate layers of low flow stress layers and high flow stress layers with each layer of low flow stress material surrounded by an individual flow constraining element, such as a ring, and then applying pressure to the top and bottom surfaces of the resulting stack to bond the dissimilar layers together, for example, by compression rolling the stack. In a preferred embodiment, the individual flow constraining elements surrounding the layers of low flow stress material are formed of a material which may either be the same material as the material comprising the high flow stress layers, or have similar flow stress characteristics to the material comprising the high flow stress layers. Additional sacrificial layers may be added to the top and bottom of the stack to avoid damage to the stack during the bonding step; and these additional layers may then be removed after the bonding step.
Syn, C.K.; Lesuer, D.R.
1995-07-04
A laminated metal composite of low flow stress layers and high flow stress layers is described which is formed using flow constraining elements, preferably in the shape of rings, individually placed around each of the low flow stress layers while pressure is applied to the stack to bond the layers of the composite together, to thereby restrain the flow of the low flow stress layers from the stack during the bonding. The laminated metal composite of the invention is made by the steps of forming a stack of alternate layers of low flow stress layers and high flow stress layers with each layer of low flow stress material surrounded by an individual flow constraining element, such as a ring, and then applying pressure to the top and bottom surfaces of the resulting stack to bond the dissimilar layers together, for example, by compression rolling the stack. In a preferred embodiment, the individual flow constraining elements surrounding the layers of low flow stress material are formed of a material which may either be the same material as the material comprising the high flow stress layers, or have similar flow stress characteristics to the material comprising the high flow stress layers. Additional sacrificial layers may be added to the top and bottom of the stack to avoid damage to the stack during the bonding step; and these additional layers may then be removed after the bonding step. 5 figs.
Syn, C.K.; Lesuer, D.R.
1994-12-31
This invention relates to a laminated metal composite, comprising alternating layers of low flow stress material and high flow stress material, and formed using flow constraining elements around each low flow stress layer; and a method of making same. A composite is a combination of at least two chemically distinct materials with a distinct interface separating the two materials. A metal matrix composite (MMC) is a composite material composed of a metal and a nonmetallic reinforcing agent such as silicon carbide (SiC) or graphite in continuous or discontinuous fiber, whisker, or discrete particulate form. A laminate is a material composed of several bonded layers. It is possible to have a laminate composed of multi-layers of a single type of material bonded to each other. However, such a laminate would not be considered to be a composite. The term {open_quotes}laminated metal composite{close_quotes} (LMC), as used herein, is intended to include a structural material composed of: (1) layers of metal or metal alloys interleaved with (2) a different metal, a metal alloy, or a metal matrix composite (MMC) containing strengthening agents.
NASA Astrophysics Data System (ADS)
Grott, Matthias; Plesa, Ana-Catalina; Tosi, Nicola; Breuer, Doris
2014-05-01
The InSight mission (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) to be launched in 2016 will carry a seismometer (SEIS) and heat flow probe (HP3) to the martian surface, and address questions related to the size, physical state, and composition of the core and mantle, the thickness of the crust, and the thermal state of the interior. The heat flow measured at the surface depends on the amount of heat producing elements (HPE) present in the interior and offers a measurable quantity that can help to constrain the planetary heat budget. If the Urey ratio - the ratio between internal heat production and surface heat loss - is known, the heat production rate in the interior can be determined. We run thermal evolution models of increasing complexity and compared the obtained present-day Urey ratio for a set of different models/parameters. To this end, we used the 2D-3D mantle convection code Gaia [1], as well as 1D parameterized models [2]. We varied the initial amount of HPE [3, 4,5,6], used various viscosity formulations (temperature-, temperature- and depth-dependent viscosity, viscosity jump in the mid mantle), varied the size of the core, and considered models with and without phase transitions in the mantle. Additionally, we tested the effects of different partitioning of HPE between mantle and a fixed crust, different initial conditions (temperatures and boundary layer thicknesses) and reference viscosities. Our simulations show that, for a one-plate planet like Mars, the Urey ratio is mainly sensitive to the efficiency of mantle cooling, i.e. the mantle viscosity, and to the mean half-life of long-lived radiogenic isotopes. Given that models of the thermo-chemical evolution of Mars generally indicate reference viscosities below 1021 Pa s [3, 7], the martian Urey ratio is likely only a function of the Thorium concentration in the planetary interior. Surface radiogenic abundances determined from gamma-ray spectroscopy [8] are best
Spectral finite-element methods for parametric constrained optimization problems.
Anitescu, M.; Mathematics and Computer Science
2009-01-01
We present a method to approximate the solution mapping of parametric constrained optimization problems. The approximation, which is of the spectral finite element type, is represented as a linear combination of orthogonal polynomials. Its coefficients are determined by solving an appropriate finite-dimensional constrained optimization problem. We show that, under certain conditions, the latter problem is solvable because it is feasible for a sufficiently large degree of the polynomial approximation and has an objective function with bounded level sets. In addition, the solutions of the finite-dimensional problems converge for an increasing degree of the polynomials considered, provided that the solutions exhibit a sufficiently large and uniform degree of smoothness. Our approach solves, in the case of optimization problems with uncertain parameters, the most computationally intensive part of stochastic finite-element approaches. We demonstrate that our framework is applicable to parametric eigenvalue problems.
Extracting electron transfer coupling elements from constrained density functional theory
NASA Astrophysics Data System (ADS)
Wu, Qin; Van Voorhis, Troy
2006-10-01
Constrained density functional theory (DFT) is a useful tool for studying electron transfer (ET) reactions. It can straightforwardly construct the charge-localized diabatic states and give a direct measure of the inner-sphere reorganization energy. In this work, a method is presented for calculating the electronic coupling matrix element (Hab) based on constrained DFT. This method completely avoids the use of ground-state DFT energies because they are known to irrationally predict fractional electron transfer in many cases. Instead it makes use of the constrained DFT energies and the Kohn-Sham wave functions for the diabatic states in a careful way. Test calculations on the Zn2+ and the benzene-Cl atom systems show that the new prescription yields reasonable agreement with the standard generalized Mulliken-Hush method. We then proceed to produce the diabatic and adiabatic potential energy curves along the reaction pathway for intervalence ET in the tetrathiafulvalene-diquinone (Q-TTF-Q) anion. While the unconstrained DFT curve has no reaction barrier and gives Hab≈17kcal /mol, which qualitatively disagrees with experimental results, the Hab calculated from constrained DFT is about 3kcal /mol and the generated ground state has a barrier height of 1.70kcal/mol, successfully predicting (Q-TTF-Q)- to be a class II mixed-valence compound.
Constraining Jupiter's internal flows using Juno magnetic and gravity measurements
NASA Astrophysics Data System (ADS)
Galanti, E.; Cao, H.; Kaspi, Y.
2017-08-01
Deciphering the flow below the cloud-level of Jupiter remains a critical milestone in understanding Jupiter's internal structure and dynamics. The expected high-precision Juno measurements of both the gravity field and the magnetic field might help to reach this goal. Here we propose a method that combines both fields to constrain the depth-dependent flow field inside Jupiter. This method is based on a mean-field electrodynamic balance that relates the flow field to the anomalous magnetic field, and geostrophic balance that relates the flow field to the anomalous gravity field. We find that the flow field has two distinct regions of influence: an upper region in which the flow affects mostly the gravity field and a lower region in which the flow affects mostly the magnetic field. An optimization procedure allows to reach a unified flow structure that is consistent with both the gravity and the magnetic fields.
Groundwater availability as constrained by hydrogeology and environmental flows.
Watson, Katelyn A; Mayer, Alex S; Reeves, Howard W
2014-01-01
Groundwater pumping from aquifers in hydraulic connection with nearby streams has the potential to cause adverse impacts by decreasing flows to levels below those necessary to maintain aquatic ecosystems. The recent passage of the Great Lakes-St. Lawrence River Basin Water Resources Compact has brought attention to this issue in the Great Lakes region. In particular, the legislation requires the Great Lakes states to enact measures for limiting water withdrawals that can cause adverse ecosystem impacts. This study explores how both hydrogeologic and environmental flow limitations may constrain groundwater availability in the Great Lakes Basin. A methodology for calculating maximum allowable pumping rates is presented. Groundwater availability across the basin may be constrained by a combination of hydrogeologic yield and environmental flow limitations varying over both local and regional scales. The results are sensitive to factors such as pumping time, regional and local hydrogeology, streambed conductance, and streamflow depletion limits. Understanding how these restrictions constrain groundwater usage and which hydrogeologic characteristics and spatial variables have the most influence on potential streamflow depletions has important water resources policy and management implications. © 2013, National Ground Water Association.
Groundwater availability as constrained by hydrogeology and environmental flows
Watson, Katelyn A.; Mayer, Alex S.; Reeves, Howard W.
2014-01-01
Groundwater pumping from aquifers in hydraulic connection with nearby streams has the potential to cause adverse impacts by decreasing flows to levels below those necessary to maintain aquatic ecosystems. The recent passage of the Great Lakes-St. Lawrence River Basin Water Resources Compact has brought attention to this issue in the Great Lakes region. In particular, the legislation requires the Great Lakes states to enact measures for limiting water withdrawals that can cause adverse ecosystem impacts. This study explores how both hydrogeologic and environmental flow limitations may constrain groundwater availability in the Great Lakes Basin. A methodology for calculating maximum allowable pumping rates is presented. Groundwater availability across the basin may be constrained by a combination of hydrogeologic yield and environmental flow limitations varying over both local and regional scales. The results are sensitive to factors such as pumping time, regional and local hydrogeology, streambed conductance, and streamflow depletion limits. Understanding how these restrictions constrain groundwater usage and which hydrogeologic characteristics and spatial variables have the most influence on potential streamflow depletions has important water resources policy and management implications.
Constrained Large Eddy Simulation of Separated Turbulent Flows
NASA Astrophysics Data System (ADS)
Xia, Zhenhua; Shi, Yipeng; Wang, Jianchun; Xiao, Zuoli; Yang, Yantao; Chen, Shiyi
2011-11-01
Constrained Large-eddy Simulation (CLES) has been recently proposed to simulate turbulent flows with massive separation. Different from traditional large eddy simulation (LES) and hybrid RANS/LES approaches, the CLES simulates the whole flow domain by large eddy simulation while enforcing a RANS Reynolds stress constraint on the subgrid-scale (SGS) stress models in the near-wall region. Algebraic eddy-viscosity models and one-equation Spalart-Allmaras (S-A) model have been used to constrain the Reynolds stress. The CLES approach is validated a posteriori through simulation of flow past a circular cylinder and periodic hill flow at high Reynolds numbers. The simulation results are compared with those from RANS, DES, DDES and other available hybrid RANS/LES methods. It is shown that the capability of the CLES method in predicting separated flows is comparable to that of DES. Detailed discussions are also presented about the effects of the RANS models as constraint in the near-wall layers. Our results demonstrate that the CLES method is a promising alternative towards engineering applications.
SHARAD Constrains on Lava Flow Properties at Southeastern Utopia Planitia
NASA Astrophysics Data System (ADS)
Nunes, D. C.
2012-12-01
The volcanic flows originated at the southwestern flanks of Elysium Mons extend over 1,000 km into Utopia Planitia and overlie the knobby and polygonally cracked Vastitas Borealis Formation (VBF). These flows display rough and smooth lobate morphologies (RL and SL) morphologies and occur in conjunction with sinuous channels (SC). Russell and Head [2003] described these morphologies and hypothesized that RL correspond to debris flows that arose as lahars from the interaction between magma and ground water or ice. The mapping of Tanaka et al. [2003] identified these features similarly, attributing them to volcanoclastic flows formed from magma-volatile interactions. Crater counts by Werner et al. [2011] support surface ages between 1 and 2 Gyr for these flows. Analysis of the radargrams acquired throughout this area o show unambiguous subsurface reflectors that, individually, are relatively short and laterally intermittent. As a group, however, these reflectors are distributed sparsely over the flow field and correlate very well with the SL units. Delays to reflectors beneath the surface are generally in the order of < ~1 μs. In one locale with a high concentration of subsurface reflectors, centered at 117.61°E and 31.31°N, a sequence of smooth lobate flows overlie a smooth volcanic unit. The lobate flow in immediate contact with the smooth unit possesses subsurface reflections that correlate well with the flow edges, and where this flow is overlain by another lobate flow these reflections vanish. We interpret these reflections as a reflector that corresponds to the interface between the lobate flow and smooth unit. The average delay to this reflector is 0.68 - 0.71 μs along its length. The thickness of this lobate flow, estimated from MOLA elevation data, ranges between 35 and 40 m. The thickness estimate from MOLA and the delay to reflector from SHARAD together constrain the relative permittivity of the flow to between 6.5 and 9.5. These values are consistent
AMG by element agglomeration and constrained energy minimization interpolation
Kolev, T V; Vassilevski, P S
2006-02-17
This paper studies AMG (algebraic multigrid) methods that utilize energy minimization construction of the interpolation matrices locally, in the setting of element agglomeration AMG. The coarsening in element agglomeration AMG is done by agglomerating fine-grid elements, with coarse element matrices defined by a local Galerkin procedure applied to the matrix assembled from the individual fine-grid element matrices. This local Galerkin procedure involves only the coarse basis restricted to the agglomerated element. To construct the coarse basis, one exploits previously proposed constraint energy minimization procedures now applied to the local matrix. The constraints are that a given set of vectors should be interpolated exactly, not only globally, but also locally on every agglomerated element. The paper provides algorithmic details, as well as a convergence result based on a ''local-to-global'' energy bound of the resulting multiple-vector fitting AMG interpolation mappings. A particular implementation of the method is illustrated with a set of numerical experiments.
SUPG Finite Element Simulations of Compressible Flows
NASA Technical Reports Server (NTRS)
Kirk, Brnjamin, S.
2006-01-01
The Streamline-Upwind Petrov-Galerkin (SUPG) finite element simulations of compressible flows is presented. The topics include: 1) Introduction; 2) SUPG Galerkin Finite Element Methods; 3) Applications; and 4) Bibliography.
Drosophila Functional Elements Are Embedded in Structurally Constrained Sequences
Kenigsberg, Ephraim; Tanay, Amos
2013-01-01
Modern functional genomics uncovered numerous functional elements in metazoan genomes. Nevertheless, only a small fraction of the typical non-exonic genome contains elements that code for function directly. On the other hand, a much larger fraction of the genome is associated with significant evolutionary constraints, suggesting that much of the non-exonic genome is weakly functional. Here we show that in flies, local (30–70 bp) conserved sequence elements that are associated with multiple regulatory functions serve as focal points to a pattern of punctuated regional increase in G/C nucleotide frequencies. We show that this pattern, which covers a region tenfold larger than the conserved elements themselves, is an evolutionary consequence of a shift in the balance between gain and loss of G/C nucleotides and that it is correlated with nucleosome occupancy across multiple classes of epigenetic state. Evidence for compensatory evolution and analysis of SNP allele frequencies show that the evolutionary regime underlying this balance shift is likely to be non-neutral. These data suggest that current gaps in our understanding of genome function and evolutionary dynamics are explicable by a model of sparse sequence elements directly encoding for function, embedded into structural sequences that help to define the local and global epigenomic context of such functional elements. PMID:23750124
NASA Astrophysics Data System (ADS)
Dinwiddie, C. L.; Hooper, D. M.
2015-05-01
To explain how debris flows form at subfreezing air temperatures, we present meteorology-driven, numerical simulation-derived subsurface temperature and pore-water pressure profiles in the Great Kobuk Sand Dunes of Alaska, for incipient flow events.
Constraining neutrinoless double-beta decay matrix elements
NASA Astrophysics Data System (ADS)
Menendez, Javier
2015-10-01
Neutrinoless double-beta decay, if detected, would proof the Majorana nature of neutrinos. The decay lifetime is governed by the absolute neutrino masses and the nuclear matrix elements of the transition. Therefore accurate matrix elements are needed to asses the sensitivity of current and future experiments, and to determine the absolute neutrino masses and hierarchy with neutrinoless double-beta decay. However, present nuclear matrix element calculations show significant uncertainties. These affect the nuclear structure description of the mother and daughter nuclei, and also the treatment of the transition operator. In this talk I cover recent progress on neutrinoless double-beta decay nuclear matrix element calculations. On the one hand, I discuss the role of the size of the configuration space and of nuclear structure correlations. By comparing matrix elements obtained with different nuclear structure approaches and interactions, optimal strategies for improving the nuclear structure calculations capturing the most important correlations are identified. On the other hand, I describe first attempts to include two-body currents in the double-beta decay operator. They can be related to the ``quenching'' of the spin-isospin operator empirically found in nuclear structure studies.
How can we constrain the amount of heat producing elements in the interior of Mars?
NASA Astrophysics Data System (ADS)
Grott, M.; Plesa, A.; Breuer, D.
2013-12-01
The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission to be launched in 2016 will study Mars' deep interior and help improving our knowledge about the interior structure and the thermal evolution of the planet - the latter is also directly linked to its volcanic history and atmospheric evolution. Measurements planned with the two main instruments, SEIS (Seismic Experiment for Interior Structure) and HP3 (Heat Flow and Physical Properties Package) aim to constrain the main structure of the planet, i.e. core, mantle and crust as well as the rate at which the planet loses the interior heat over its surface. Since the surface heat flow depends on the amount of radiogenic heat elements (HPE) present in the interior, it offers a measurable quantity which could constrain the heat budget. Being the principal agent regulating the heat budget which in turn influences partial melting in the interior, crustal and atmospheric evolution, the heat producing elements have a major impact on the entire the present temperature thermal history of the planet. To constrain the radiogenic heat elements of the planet from the surface heat flow is possible assuming that the urey number of the planet, which describes the contribution of internal heat production to the surface heat loss, is known. We have tested this assumption by calculating the thermal evolution of the planet with fully dynamical numerical simulations and by comparing the obtained present-day urey number for a set of different models/parameters (Fig. 1). For one-plate planets like Mars, numerical models show - in contrast to models for the Earth, where plate tectonics play a major role adding more complexity to the system - that the urey ratio is mainly sensitive to two effects: the efficiency of cooling due to the temperature-dependence of the viscosity and the mean half-life time of the long lived radiogenic isotopes. The temperature-dependence of the viscosity results in the
Finite element modeling of nonisothermal polymer flows
NASA Technical Reports Server (NTRS)
Roylance, D.
1981-01-01
A finite element formulation designed to simulate polymer melt flows in which both conductive and convective heat transfer are important is described, and the numerical model is illustrated by means of computer experiments using extruder drag flow and entry flow as trial problems. Fluid incompressibility is enforced by a penalty treatment of the element pressures, and the thermal convective transport is modeled by conventional Galerkin and optimal upwind treatments.
Finite element analysis of constrained total Condylar Knee Prosthesis
1998-07-13
Exactech, Inc., is a prosthetic joint manufacturer based in Gainesville, FL. The company set the goal of developing a highly effective prosthetic articulation, based on scientific principles, not trial and error. They developed an evolutionary design for a total knee arthroplasty system that promised improved performance. They performed static load tests in the laboratory with similar previous designs, but dynamic laboratory testing was both difficult to perform and prohibitively expensive for a small business to undertake. Laboratory testing also cannot measure stress levels in the interior of the prosthesis where failures are known to initiate. To fully optimize their designs for knee arthroplasty revisions, they needed range-of-motion stress/strain data at interior as well as exterior locations within the prosthesis. LLNL developed computer software (especially NIKE3D) specifically designed to perform stress/strain computations (finite element analysis) for complex geometries in large displacement/large deformation conditions. Additionally, LLNL had developed a high fidelity knee model for other analytical purposes. The analysis desired by Exactech could readily be performed using NIKE3D and a modified version of the high fidelity knee that contained the geometry of the condylar knee components. The LLNL high fidelity knee model was a finite element computer model which would not be transferred to Exactech during the course of this CRADA effort. The previously performed laboratory studies by Exactech were beneficial to LLNL in verifying the analytical capabilities of NIKE3D for human anatomical modeling. This, in turn, gave LLNL further entree to perform work-for-others in the prosthetics field. There were two purposes to the CRADA (1) To modify the LLNL High Fidelity Knee Model to accept the geometry of the Exactech Total Knee; and (2) To perform parametric studies of the possible design options in appropriate ranges of motion so that an optimum design could be
Triangular spectral elements for incompressible fluid flow
NASA Technical Reports Server (NTRS)
Mavriplis, C.; Vanrosendale, John
1993-01-01
We discuss the use of triangular elements in the spectral element method for direct simulation of incompressible flow. Triangles provide much greater geometric flexibility than quadrilateral elements and are better conditioned and more accurate when small angles arise. We employ a family of tensor product algorithms for triangles, allowing triangular elements to be handled with comparable arithmetic complexity to quadrilateral elements. The triangular discretizations are applied and validated on the Poisson equation. These discretizations are then applied to the incompressible Navier-Stokes equations and a laminar channel flow solution is given. These new triangular spectral elements can be combined with standard quadrilateral elements, yielding a general and flexible high order method for complex geometries in two dimensions.
Critical flow constrains flow hydraulics in mobile-bed streams: A new hypothesis
NASA Astrophysics Data System (ADS)
Grant, Gordon E.
A new hypothesis predicts that in mobile-bed river channels, interactions between the channel hydraulics and bed configuration prevent the Froude number (Fr) from exceeding 1 for more than short distances or periods of time. Flow conditions in many steep, competent streams appear to be close to critical. Froude numbers of steep (slope ~0.01) sand-bed streams with considerable freedom to adjust boundaries oscillate between 0.7 and 1.3 over 20- to 30-s cycles, with an average of 1.0 at the channel thalweg. Critical flow in these streams is maintained by the interaction between the mobile bed and free water surface at high Fr, which results in a cyclical pattern of creation and destruction of bed forms. Field observations support that a similar mechanism of flow-bed form interaction constrains Fr<=1 in active-bed braided gravel rivers, step-pool streams, laboratory rills, lahar-runout channels, and even some bedrock channels. Empirical and analytical results show that as slope increases, competent flows tend to asymptotically approach critical flow. An assumption of critical flow would dramatically simplify paleohydraulic flow reconstructions and modeling of flow hydraulics in high gradient streams.
Finite element methods for high speed flows
NASA Technical Reports Server (NTRS)
Loehner, R.; Morgan, K.; Peraire, J.; Zienkiewicz, O. C.
1985-01-01
An explicit finite element based solution procedure for solving the equations of compressible viscous high speed flow is presented. The method uses domain splitting to advance the solution with different timesteps on different portions of the mesh. For steady inviscid flows, adaptive mesh refinement procedures are successfully employed to enhance the definition of discontinuities. Preliminary ideas on the application of adaptive mesh refinement to the solution of problems involving steady viscous flow are presented. Sample timings are given for the performance of the finite element code on modern supercomputers.
Quadratic finite elements and incompressible viscous flows.
Dohrmann, Clark R.; Gartling, David K.
2005-01-01
Pressure stabilization methods are applied to higher-order velocity finite elements for application to viscous incompressible flows. Both a standard pressure stabilizing Petrov-Galerkin (PSPG) method and a new polynomial pressure projection stabilization (PPPS) method have been implemented and tested for various quadratic elements in two dimensions. A preconditioner based on relaxing the incompressibility constraint is also tested for the iterative solution of saddle point problems arising from mixed Galerkin finite element approximations to the Navier-Stokes equations. The preconditioner is demonstrated for BB stable elements with discontinuous pressure approximations in two and three dimensions.
The Constrained Vapor Bubble Experiment - Interfacial Flow Region
NASA Technical Reports Server (NTRS)
Kundan, Akshay; Wayner, Peter C., Jr.; Plawsky, Joel L.
2015-01-01
Internal heat transfer coefficient of the CVB correlated to the presence of the interfacial flow region. Competition between capillary and Marangoni flow caused Flooding and not a Dry-out region. Interfacial flow region growth is arrested at higher power inputs. 1D heat model confirms the presence of interfacial flow region. 1D heat model confirms the arresting phenomena of interfacial flow region Visual observations are essential to understanding.
NASA Astrophysics Data System (ADS)
Shao, H.; Huang, Y.; Kolditz, O.
2015-12-01
Multiphase flow problems are numerically difficult to solve, as it often contains nonlinear Phase transition phenomena A conventional technique is to introduce the complementarity constraints where fluid properties such as liquid saturations are confined within a physically reasonable range. Based on such constraints, the mathematical model can be reformulated into a system of nonlinear partial differential equations coupled with variational inequalities. They can be then numerically handled by optimization algorithms. In this work, two different approaches utilizing the complementarity constraints based on persistent primary variables formulation[4] are implemented and investigated. The first approach proposed by Marchand et.al[1] is using "local complementary constraints", i.e. coupling the constraints with the local constitutive equations. The second approach[2],[3] , namely the "global complementary constrains", applies the constraints globally with the mass conservation equation. We will discuss how these two approaches are applied to solve non-isothermal componential multiphase flow problem with the phase change phenomenon. Several benchmarks will be presented for investigating the overall numerical performance of different approaches. The advantages and disadvantages of different models will also be concluded. References[1] E.Marchand, T.Mueller and P.Knabner. Fully coupled generalized hybrid-mixed finite element approximation of two-phase two-component flow in porous media. Part I: formulation and properties of the mathematical model, Computational Geosciences 17(2): 431-442, (2013). [2] A. Lauser, C. Hager, R. Helmig, B. Wohlmuth. A new approach for phase transitions in miscible multi-phase flow in porous media. Water Resour., 34,(2011), 957-966. [3] J. Jaffré, and A. Sboui. Henry's Law and Gas Phase Disappearance. Transp. Porous Media. 82, (2010), 521-526. [4] A. Bourgeat, M. Jurak and F. Smaï. Two-phase partially miscible flow and transport modeling in
Hypersonic Viscous Flow Over Large Roughness Elements
NASA Technical Reports Server (NTRS)
Chang, Chau-Lyan; Choudhari, Meelan M.
2009-01-01
Viscous flow over discrete or distributed surface roughness has great implications for hypersonic flight due to aerothermodynamic considerations related to laminar-turbulent transition. Current prediction capability is greatly hampered by the limited knowledge base for such flows. To help fill that gap, numerical computations are used to investigate the intricate flow physics involved. An unstructured mesh, compressible Navier-Stokes code based on the space-time conservation element, solution element (CESE) method is used to perform time-accurate Navier-Stokes calculations for two roughness shapes investigated in wind tunnel experiments at NASA Langley Research Center. It was found through 2D parametric study that at subcritical Reynolds numbers, spontaneous absolute instability accompanying by sustained vortex shedding downstream of the roughness is likely to take place at subsonic free-stream conditions. On the other hand, convective instability may be the dominant mechanism for supersonic boundary layers. Three-dimensional calculations for both a rectangular and a cylindrical roughness element at post-shock Mach numbers of 4.1 and 6.5 also confirm that no self-sustained vortex generation from the top face of the roughness is observed, despite the presence of flow unsteadiness for the smaller post-shock Mach number case.
NASA Astrophysics Data System (ADS)
Xie, Bin; Xiao, Feng
2016-12-01
We proposed a multi-moment constrained finite volume method which can simulate incompressible flows of high Reynolds number in complex geometries. Following the underlying idea of the volume-average/point-value multi-moment (VPM) method (Xie et al. (2014) [71]), this formulation is developed on arbitrary unstructured hybrid grids by employing the point values (PV) at both cell vertex and barycenter as the prognostic variables. The cell center value is updated via an evolution equation derived from a constraint condition of finite volume form, which ensures the rigorous numerical conservativeness. Novel numerical formulations based on the local PVs over compact stencil are proposed to enhance the accuracy, robustness and efficiency of computations on unstructured meshes of hybrid and arbitrary elements. Numerical experiments demonstrate that the present numerical model has nearly 3-order convergence rate with numerical errors much smaller than the VPM method. The numerical dissipation has been significantly suppressed, which facilitates numerical simulations of high Reynolds number flows in complex geometries.
Hypersonic Viscous Flow Over Large Roughness Elements
NASA Technical Reports Server (NTRS)
Chang, Chau-Lyan; Choudhari, Meelan M.
2009-01-01
Viscous flow over discrete or distributed surface roughness has great implications for hypersonic flight due to aerothermodynamic considerations related to laminar-turbulent transition. Current prediction capability is greatly hampered by the limited knowledge base for such flows. To help fill that gap, numerical computations are used to investigate the intricate flow physics involved. An unstructured mesh, compressible Navier-Stokes code based on the space-time conservation element, solution element (CESE) method is used to perform time-accurate Navier-Stokes calculations for two roughness shapes investigated in wind tunnel experiments at NASA Langley Research Center. It was found through 2D parametric study that at subcritical Reynolds numbers of the boundary layers, absolute instability resulting in vortex shedding downstream, is likely to weaken at supersonic free-stream conditions. On the other hand, convective instability may be the dominant mechanism for supersonic boundary layers. Three-dimensional calculations for a rectangular or cylindrical roughness element at post-shock Mach numbers of 4.1 and 6.5 also confirm that no self-sustained vortex generation is present.
Gauge finite element method for incompressible flows
NASA Astrophysics Data System (ADS)
E, Weinan; Liu, Jian-Guo
2000-12-01
A finite element method for computing viscous incompressible flows based on the gauge formulation introduced in [Weinan E, Liu J-G. Gauge method for viscous incompressible flows. Journal of Computational Physics (submitted)] is presented. This formulation replaces the pressure by a gauge variable. This new gauge variable is a numerical tool and differs from the standard gauge variable that arises from decomposing a compressible velocity field. It has the advantage that an additional boundary condition can be assigned to the gauge variable, thus eliminating the issue of a pressure boundary condition associated with the original primitive variable formulation. The computational task is then reduced to solving standard heat and Poisson equations, which are approximated by straightforward, piecewise linear (or higher-order) finite elements. This method can achieve high-order accuracy at a cost comparable with that of solving standard heat and Poisson equations. It is naturally adapted to complex geometry and it is much simpler than traditional finite element methods for incompressible flows. Several numerical examples on both structured and unstructured grids are presented. Copyright
Thinning and flow of Tibetan crust constrained by seismic anisotropy.
Shapiro, Nikolai M; Ritzwoller, Michael H; Molnar, Peter; Levin, Vadim
2004-07-09
Intermediate-period Rayleigh and Love waves propagating across Tibet indicate marked radial anisotropy within the middle-to-lower crust, consistent with a thinning of the middle crust by about 30%. The anisotropy is largest in the western part of the plateau, where moment tensors of earthquakes indicate active crustal thinning. The preferred orientation of mica crystals resulting from the crustal thinning can account for the observed anisotropy. The middle-to-lower crust of Tibet appears to have thinned more than the upper crust, consistent with deformation of a mechanically weak layer that flows as if confined to a channel.
State-constrained booster trajectory solutions via finite elements and shooting
NASA Technical Reports Server (NTRS)
Bless, Robert R.; Hodges, Dewey H.; Seywald, Hans
1993-01-01
This paper presents an extension of a FEM formulation based on variational principles. A general formulation for handling internal boundary conditions and discontinuities in the state equations is presented, and the general formulation is modified for optimal control problems subject to state-variable inequality constraints. Solutions which only touch the state constraint and solutions which have a boundary arc of finite length are considered. Suitable shape and test functions are chosen for a FEM discretization. All element quadrature (equivalent to one-point Gaussian quadrature over each element) may be done in closed form. The final form of the algebraic equations is then derived. A simple state-constrained problem is solved. Then, for a practical application of the use of the FEM formulation, a launch vehicle subject to a dynamic pressure constraint (a first-order state inequality constraint) is solved. The results presented for the launch-vehicle trajectory have some interesting features, including a touch-point solution.
State-constrained booster trajectory solutions via finite elements and shooting
NASA Technical Reports Server (NTRS)
Bless, Robert R.; Hodges, Dewey H.; Seywald, Hans
1993-01-01
This paper presents an extension of a FEM formulation based on variational principles. A general formulation for handling internal boundary conditions and discontinuities in the state equations is presented, and the general formulation is modified for optimal control problems subject to state-variable inequality constraints. Solutions which only touch the state constraint and solutions which have a boundary arc of finite length are considered. Suitable shape and test functions are chosen for a FEM discretization. All element quadrature (equivalent to one-point Gaussian quadrature over each element) may be done in closed form. The final form of the algebraic equations is then derived. A simple state-constrained problem is solved. Then, for a practical application of the use of the FEM formulation, a launch vehicle subject to a dynamic pressure constraint (a first-order state inequality constraint) is solved. The results presented for the launch-vehicle trajectory have some interesting features, including a touch-point solution.
NASA Astrophysics Data System (ADS)
Rae, J. W. B.; Adkins, J. F.; Foreman, A. D.; Charles, C.
2014-12-01
Deep ocean carbon storage and release is commonly invoked to explain glacial-interglacial CO2 cycles, but records of the carbonate chemistry of the glacial ocean have, until recently, been scarce. Here we present new boron isotope (δ11B) and trace metal data from benthic foraminifera from a suite of 15 cores from the South Atlantic from depths ranging from 1500 to 4000 m. These records show distinct changes in the water column depth structure of these tracers between the last glacial maximum (LGM) and late Holocene. Comparison of these paired trace element and isotope ratios reveals new insights to the shared and individual controls on tracers including Li/Ca, Sr/Ca, U/Ca, Mg/Li and δ11B. We further examine these data using a recently developed tracer fields modelling approach (Lund et al. 2011). This has previously been applied to δ18O data to investigate changes in circulation at the LGM. Here we extend this method to non-conservative isotopic and trace elemental tracers, allowing us to constrain the roles of circulation, the biological pump of organic carbon and CaCO3, and carbonate compensation, in setting deep ocean carbon storage at the LGM. Lund, D. C., J. F. Adkins, and R. Ferrari (2011), Abyssal Atlantic circulation during the Last Glacial Maximum: Constraining the ratio between transport and vertical mixing, Paleoceanography, 26, PA1213, doi:10.1029/2010PA001938.
NASA Technical Reports Server (NTRS)
Lundgren, Paul; Saucier, Fraancois; Palmer, Randy; Langon, Marc
1995-01-01
We compute crustal motions in Alaska by calculating the finite element solution for an elastic spherical shell problem. The method we use allows the finite element mesh to include faults and very long baseline interferometry (VLBI) baseline rates of change. Boundary conditions include Pacific-North American (PA-NA) plate motions. The solution is constrained by the oblique orientation of the Fairweather-Queen Charlotte strike-slip faults relative to the PA-NA relative motion direction and the oblique orientation from normal convergence of the eastern Aleutian trench fault systems, as well as strike-shp motion along the Denali and Totschunda fault systems. We explore the effects that a range of fault slip constraints and weighting of VLBI rates of change has on the solution. This allows us to test the motion on faults, such as the Denali fault, where there are conflicting reports on its present-day slip rate. We find a pattern of displacements which produce fault motions generally consistent with geologic observations. The motion of the continuum has the general pattern of radial movement of crust to the NE away from the Fairweather-Queen Charlotte fault systems in SE Alaska and Canada. This pattern of crustal motion is absorbed across the Mackenzie Mountains in NW Canada, with strike-slip motion constrained along the Denali and Tintina fault systems. In south central Alaska and the Alaska forearc oblique convergence at the eastern Aleutian trench and the strike-shp motion of the Denali fault system produce a counterclockwise pattern of motion which is partially absorbed along the Contact and related fault systems in southern Alaska and is partially extruded into the Bering Sea and into the forearc parallel the Aleutian trench from the Alaska Peninsula westward. Rates of motion and fault slip are small in western and northern Alaska, but the motions we compute are consistent with the senses of strike-slip motion inferred geologically along the Kaltag, Kobuk Trench
NASA Technical Reports Server (NTRS)
Lundgren, Paul; Saucier, Fraancois; Palmer, Randy; Langon, Marc
1995-01-01
We compute crustal motions in Alaska by calculating the finite element solution for an elastic spherical shell problem. The method we use allows the finite element mesh to include faults and very long baseline interferometry (VLBI) baseline rates of change. Boundary conditions include Pacific-North American (PA-NA) plate motions. The solution is constrained by the oblique orientation of the Fairweather-Queen Charlotte strike-slip faults relative to the PA-NA relative motion direction and the oblique orientation from normal convergence of the eastern Aleutian trench fault systems, as well as strike-shp motion along the Denali and Totschunda fault systems. We explore the effects that a range of fault slip constraints and weighting of VLBI rates of change has on the solution. This allows us to test the motion on faults, such as the Denali fault, where there are conflicting reports on its present-day slip rate. We find a pattern of displacements which produce fault motions generally consistent with geologic observations. The motion of the continuum has the general pattern of radial movement of crust to the NE away from the Fairweather-Queen Charlotte fault systems in SE Alaska and Canada. This pattern of crustal motion is absorbed across the Mackenzie Mountains in NW Canada, with strike-slip motion constrained along the Denali and Tintina fault systems. In south central Alaska and the Alaska forearc oblique convergence at the eastern Aleutian trench and the strike-shp motion of the Denali fault system produce a counterclockwise pattern of motion which is partially absorbed along the Contact and related fault systems in southern Alaska and is partially extruded into the Bering Sea and into the forearc parallel the Aleutian trench from the Alaska Peninsula westward. Rates of motion and fault slip are small in western and northern Alaska, but the motions we compute are consistent with the senses of strike-slip motion inferred geologically along the Kaltag, Kobuk Trench
NASA Astrophysics Data System (ADS)
Bakir, Pelin Gundes; Reynders, Edwin; De Roeck, Guido
2007-08-01
The use of changes in dynamic system characteristics to detect damage has received considerable attention during the last years. Within this context, FE model updating technique, which belongs to the class of inverse problems in classical mechanics, is used to detect, locate and quantify damage. In this study, a sensitivity-based finite element (FE) model updating scheme using a trust region algorithm is developed and implemented in a complex structure. A damage scenario is applied on the structure in which the stiffness values of the beam elements close to the beam-column joints are decreased by stiffness reduction factors. A worst case and complex damage pattern is assumed such that the stiffnesses of adjacent elements are decreased by substantially different stiffness reduction factors. The objective of the model updating is to minimize the differences between the eigenfrequency and eigenmodes residuals. The updating parameters of the structure are the stiffness reduction factors. The changes of these parameters are determined iteratively by solving a nonlinear constrained optimization problem. The FE model updating algorithm is also tested in the presence of two levels of noise in simulated measurements. In all three cases, the updated MAC values are above 99% and the relative eigenfrequency differences improve substantially after model updating. In cases without noise and with moderate levels of noise; detection, localization and quantification of damage are successfully accomplished. In the case with substantially noisy measurements, detection and localization of damage are successfully realized. Damage quantification is also promising in the presence of high noise as the algorithm can still predict 18 out of 24 damage parameters relatively accurately in that case.
Discrete Element Modeling of Complex Granular Flows
NASA Astrophysics Data System (ADS)
Movshovitz, N.; Asphaug, E. I.
2010-12-01
Granular materials occur almost everywhere in nature, and are actively studied in many fields of research, from food industry to planetary science. One approach to the study of granular media, the continuum approach, attempts to find a constitutive law that determines the material's flow, or strain, under applied stress. The main difficulty with this approach is that granular systems exhibit different behavior under different conditions, behaving at times as an elastic solid (e.g. pile of sand), at times as a viscous fluid (e.g. when poured), or even as a gas (e.g. when shaken). Even if all these physics are accounted for, numerical implementation is made difficult by the wide and often discontinuous ranges in continuum density and sound speed. A different approach is Discrete Element Modeling (DEM). Here the goal is to directly model every grain in the system as a rigid body subject to various body and surface forces. The advantage of this method is that it treats all of the above regimes in the same way, and can easily deal with a system moving back and forth between regimes. But as a granular system typically contains a multitude of individual grains, the direct integration of the system can be very computationally expensive. For this reason most DEM codes are limited to spherical grains of uniform size. However, spherical grains often cannot replicate the behavior of real world granular systems. A simple pile of spherical grains, for example, relies on static friction alone to keep its shape, while in reality a pile of irregular grains can maintain a much steeper angle by interlocking force chains. In the present study we employ a commercial DEM, nVidia's PhysX Engine, originally designed for the game and animation industry, to simulate complex granular flows with irregular, non-spherical grains. This engine runs as a multi threaded process and can be GPU accelerated. We demonstrate the code's ability to physically model granular materials in the three regimes
Using the modified matrix element method to constrain Lμ-Lτ interactions
NASA Astrophysics Data System (ADS)
Elahi, Fatemeh; Martin, Adam
2017-07-01
In this paper, we explore the discriminatory power of the matrix element method (MEM) in constraining the Lμ-Lτ model at the LHC. The Z' boson associated with the spontaneously broken U (1 )Lμ-Lτ symmetry only interacts with the second and third generation of leptons at tree level, and is thus difficult to produce at the LHC. We argue that the best channels for discovering this Z' are in Z →4 μ and 2 μ + ET. Both these channels have a large number of kinematic observables, which strongly motivates the usage of a multivariate technique. The MEM is a multivariate analysis that uses the squared matrix element |M |2 to quantify the likelihood of the testing hypotheses. As the computation of the |M |2 requires knowing the initial and final state momenta and the model parameters, it is not commonly used in new physics searches. Conventionally, new parameters are estimated by maximizing the likelihood of the signal with respect to the background, and we outline scenarios in which this procedure is (in)effective. We illustrate that the new parameters can also be estimated by studying the |M |2 distributions, and, even if our parameter estimation is off, we can gain better sensitivity than cut-and-count methods. Additionally, unlike the conventional MEM, where one integrates over all unknown momenta in processes with ET, we show an example scenario where these momenta can be estimated using the process topology. This procedure, which we refer to as the "modified squared matrix element," is computationally much faster than the canonical matrix element method and maintains signal-background discrimination. Bringing the MEM and the aforementioned modifications to bear on the Lμ-Lτ model, we find that with 300 fb-1 of integrated luminosity, we are sensitive to the couplings of gZ'≳0.002 g1 and MZ'<20 GeV , and gZ'≳0.005 g1 and 20 GeV
A methodology for constraining power in finite element modeling of radiofrequency ablation.
Jiang, Yansheng; Possebon, Ricardo; Mulier, Stefaan; Wang, Chong; Chen, Feng; Feng, Yuanbo; Xia, Qian; Liu, Yewei; Yin, Ting; Oyen, Raymond; Ni, Yicheng
2016-09-21
Radiofrequency ablation (RFA) is a minimally invasive thermal therapy for the treatment of cancer, hyperopia, and cardiac tachyarrhythmia. In RFA, the power delivered to the tissue is a key parameter. The objective of this study was to establish a methodology for the finite element modeling of RFA with constant power. Because of changes in the electric conductivity of tissue with temperature, a nonconventional boundary value problem arises in the mathematic modeling of RFA: neither the voltage (Dirichlet condition) nor the current (Neumann condition), but the power, that is, the product of voltage and current was prescribed on part of boundary. We solved the problem using Lagrange multiplier: the product of the voltage and current on the electrode surface is constrained to be equal to the Joule heating. We theoretically proved the equality between the product of the voltage and current on the surface of the electrode and the Joule heating in the domain. We also proved the well-posedness of the problem of solving the Laplace equation for the electric potential under a constant power constraint prescribed on the electrode surface. The Pennes bioheat transfer equation and the Laplace equation for electric potential augmented with the constraint of constant power were solved simultaneously using the Newton-Raphson algorithm. Three problems for validation were solved. Numerical results were compared either with an analytical solution deduced in this study or with results obtained by ANSYS or experiments. This work provides the finite element modeling of constant power RFA with a firm mathematical basis and opens pathway for achieving the optimal RFA power.
Chung, Chen-Yuan; Mansour, Joseph M.
2014-01-01
The feasibility of determining biphasic material properties using a finite element model of stress relaxation coupled with two types of constrained optimization to match measured data was investigated. Comparison of these two approaches, a zero-order method and a gradient-based algorithm, validated the predicted material properties. Optimizations were started from multiple different initial guesses of material properties (design variables) to establish the robustness of the optimization. Overall, the optimal values are close to those found by Cohen et al., (1998), but these small differences produced a marked improvement in the fit to the measured stress relaxation. Despite the greater deviation in the optimized values obtained from the zero-order method, both optimization procedures produced material properties that gave equally good overall fits to the measured data. Furthermore, optimized values were all within the expected range of material properties. Modeling stress relaxation using the optimized material properties showed an excellent fit to the entire time history of the measured data. PMID:25460921
Constraining the Rheologic Properties of Channelized Basaltic Flows on Earth and Mars
NASA Astrophysics Data System (ADS)
Ramsey, M. S.; Harris, A. J. L.; Crown, D. A.
2015-12-01
Basaltic volcanism is ubiquitous on the terrestrial planets and is the most common form of extrusive activity on Earth, with over half of the world's volcanoes consisting largely of basalt. Recently, new eruptions (or new phases of ongoing eruptions) have occurred at Tolbachik in Russia (2012-2013); Bardarbunga in Iceland (2014); Etna in Italy (2014); and Kilauea in Hawaii (2014-2015) emphasizing both the hazard potential and volumetric production of basaltic activity. Furthermore, new high-resolution data of flows on Arsia Mons volcano (Mars) show very similar features. Therefore, this style of effusive volcanism and especially its surface manifestation (lava flows) warrants continued study both from a fundamental science as well as a hazard mitigation point of view. Monitoring flow propagation direction and velocity are critical in these situations and a number of models have evolved over time focused on heat loss and down-flow topography to predict flow advance. In addition to topography, the dominant (internal) factors controlling flow propagation are the discharge rate combined with cooling and increasing viscosity. However, all these models rely on accurate temperature measurements derived from the cooling glassy surface using infrared (IR) non-contact instruments. New laboratory and field-based studies are attempting to characterize the cooling, formation, and dynamics of basaltic surfaces using IR data. Preliminary results are focused on resolving inconsistencies in the derived flow temperature, composition, texture and silicate structure, which can all impact the surface-leaving heat flux. Improved accuracy in these retrievals increases our ability to constrain and model flow surface and interior temperatures. The impact of this improved accuracy has now been assessed using flow model simulations of active terrestrial and well-preserved Martian flows, Results are improving our understanding of the initial eruption conditions of these channelized basaltic
NASA Astrophysics Data System (ADS)
Somasundaram, P.; Muthuselvan, N. B.
This paper presents new computationally efficient improved Particle Swarm algorithms for solving Security Constrained Optimal Power Flow (SCOPF) in power systems with the inclusion of FACTS devices. The proposed algorithms are developed based on the combined application of Gaussian and Cauchy Probability distribution functions incorporated in Particle Swarm Optimization (PSO). The power flow algorithm with the presence of Static Var Compensator (SVC) Thyristor Controlled Series Capacitor (TCSC) and Unified Power Flow Controller (UPFC), has been formulated and solved. The proposed algorithms are tested on standard IEEE 30-bus system. The analysis using PSO and modified PSO reveals that the proposed algorithms are relatively simple, efficient, reliable and suitable for real-time applications. And these algorithms can provide accurate solution with fast convergence and have the potential to be applied to other power engineering problems.
Grouped element-by-element iteration schemes for incompressible flow computations
NASA Astrophysics Data System (ADS)
Tezduyar, T. E.; Liou, J.
1989-05-01
Grouped element-by-element (GEBE) iteration schemes for incompressible flows are presented in the context of vorticity- stream function formulation. The GEBE procedure is a variation of the EBE procedure and is based on arrangement of the elements into groups with no inter-element coupling within each group. With the GEBE approach, vectorization and parallel implementation of the EBE method becomes more clear. The savings in storage and CPU time are demonstrated with two unsteady flow problems.
NASA Astrophysics Data System (ADS)
Chen, Miawjane; Yan, Shangyao; Wang, Sin-Siang; Liu, Chiu-Lan
2015-02-01
An effective project schedule is essential for enterprises to increase their efficiency of project execution, to maximize profit, and to minimize wastage of resources. Heuristic algorithms have been developed to efficiently solve the complicated multi-mode resource-constrained project scheduling problem with discounted cash flows (MRCPSPDCF) that characterize real problems. However, the solutions obtained in past studies have been approximate and are difficult to evaluate in terms of optimality. In this study, a generalized network flow model, embedded in a time-precedence network, is proposed to formulate the MRCPSPDCF with the payment at activity completion times. Mathematically, the model is formulated as an integer network flow problem with side constraints, which can be efficiently solved for optimality, using existing mathematical programming software. To evaluate the model performance, numerical tests are performed. The test results indicate that the model could be a useful planning tool for project scheduling in the real world.
Finite Element Modelling of the Apollo Heat Flow Experiments
NASA Astrophysics Data System (ADS)
Platt, J.; Siegler, M. A.; Williams, J.
2013-12-01
The heat flow experiments sent on Apollo missions 15 and 17 were designed to measure the temperature gradient of the lunar regolith in order to determine the heat flux of the moon. Major problems in these experiments arose from the fact that the astronauts were not able to insert the probes below the thermal skin depth. Compounding the problem, anomalies in the data have prevented scientists from conclusively determining the temperature dependent conductivity of the soil, which enters as a linear function into the heat flow calculation, thus stymieing them in their primary goal of constraining the global heat production of the Moon. Different methods of determining the thermal conductivity have yielded vastly different results resulting in downward corrections of up to 50% in some cases from the original calculations. Along with problems determining the conductivity, the data was inconsistent with theoretical predictions of the temperature variation over time, leading some to suspect that the Apollo experiment itself changed the thermal properties of the localised area surrounding the probe. The average temperature of the regolith, according to the data, increased over time, a phenomenon that makes calculating the thermal conductivity of the soil and heat flux impossible without knowing the source of error and accounting for it. The changes, possibly resulting from as varied sources as the imprint of the Astronauts boots on the lunar surface, compacted soil around the bore stem of the probe or even heat radiating down the inside of the tube, have convinced many people that the recorded data is unusable. In order to shed some light on the possible causes of this temperature rise, we implemented a finite element model of the probe using the program COMSOL Multi-physics as well as Matlab. Once the cause of the temperature rise is known then steps can be taken to account for the failings of the experiment and increase the data's utility.
Solution techniques for transient stability-constrained optimal power flow – Part II
Geng, Guangchao; Abhyankar, Shrirang; Wang, Xiaoyu; ...
2017-06-28
Transient stability-constrained optimal power flow is an important emerging problem with power systems pushed to the limits for economic benefits, dense and larger interconnected systems, and reduced inertia due to expected proliferation of renewable energy resources. In this study, two more approaches: single machine equivalent and computational intelligence are presented. Also discussed are various application areas, and future directions in this research area. In conclusion, a comprehensive resource for the available literature, publicly available test systems, and relevant numerical libraries is also provided.
Using measurements of the cosmic bulk flow to constrain f(R) Gravity
NASA Astrophysics Data System (ADS)
Seiler, Jacob; Parkinson, David
2016-10-01
As an alternate explanation for the cosmic acceleration, f(R) theories of gravity can predict an almost identical expansion history to standard Λ cold dark matter (ΛCDM), yet make very different predictions for the growth of cosmological structures. Measurements of the cosmic bulk flow provide a method for determining the strength of gravity over the history of structure formation. We use the modified gravity N-body code ECOSMOG to simulate dark matter particles and make predictions for the bulk flow magnitude in both ΛCDM and f(R) gravity. With the peculiar velocities output by ECOSMOG, we determine the bulk flow at depths ranging from 20 to 50 h-1Mpc, following the redshift and sky distribution of the 2MASS Tully-Fisher survey (2MTF). At each depth, we find that the ΛCDM and fR0 = 10-5 simulations produce bulk flow measurements that are consistent with ΛCDM predictions and the 2MTF survey at a 1σ level. We also find that adopting an f(R) strength of fR0 = 10-3 predict a much larger value for the bulk flow, which disagree with ΛCDM predictions at all depths considered. We conclude that fR0 must be constrained to a level no greater than 10-4 to agree with bulk flow measurements.
NASA Astrophysics Data System (ADS)
Sturtz, Timothy M.
Source apportionment models attempt to untangle the relationship between pollution sources and the impacts at downwind receptors. Two frameworks of source apportionment models exist: source-oriented and receptor-oriented. Source based apportionment models use presumed emissions and atmospheric processes to estimate the downwind source contributions. Conversely, receptor based models leverage speciated concentration data from downwind receptors and apply statistical methods to predict source contributions. Integration of both source-oriented and receptor-oriented models could lead to a better understanding of the implications sources have on the environment and society. The research presented here investigated three different types of constraints applied to the Positive Matrix Factorization (PMF) receptor model within the framework of the Multilinear Engine (ME-2): element ratio constraints, spatial separation constraints, and chemical transport model (CTM) source attribution constraints. PM10-2.5 mass and trace element concentrations were measured in Winston-Salem, Chicago, and St. Paul at up to 60 sites per city during two different seasons in 2010. PMF was used to explore the underlying sources of variability. Information on previously reported PM10-2.5 tire and brake wear profiles were used to constrain these features in PMF by prior specification of selected species ratios. We also modified PMF to allow for combining the measurements from all three cities into a single model while preserving city-specific soil features. Relatively minor differences were observed between model predictions with and without the prior ratio constraints, increasing confidence in our ability to identify separate brake wear and tire wear features. Using separate data, source contributions to total fine particle carbon predicted by a CTM were incorporated into the PMF receptor model to form a receptor-oriented hybrid model. The level of influence of the CTM versus traditional PMF was
Dissipation Element Analysis of Reacting- and Non-Reacting Flows
NASA Astrophysics Data System (ADS)
Denker, Dominik; Boschung, Jonas; Hennig, Fabian; Pitsch, Heinz
2016-11-01
Dissipation element analysis is a tried and tested method for analyzing scalar field in turbulent flows. Dissipation elements are defined as an ensemble of grid point whose gradient trajectories reach the same extremal points. Therefore, the scalar field can be compartmentalized in monotonous space filling regions. Dissipation elements can be described by two parameters, namely the Euclidean distance between their extremal points and their scalar difference in these points. The joint probability density function of these two parameters is expected to suffice for a statistical reconstruction of the scalar field. In addition, normalized dissipation element statistics show a remarkable invariance towards changes in Reynolds numbers. Dissipation element statistics of the passive scalar and the turbulent kinetic energy are compared for different flow configurations including reacting and non-reacting turbulent flows. Furthermore, the Reynolds number scaling of the dissipation element parameters is investigated.
Constraining Eruptive Conditions From Lava Flow Morphometry: A Case Study With Field Evidence
NASA Astrophysics Data System (ADS)
Bowles, Z. R.; Clarke, A.; Greeley, R.
2007-12-01
Volcanism is widely recognized as one of the primary factors affecting the surfaces of solid planets and satellites throughout the solar system. Basaltic lava is thought to be the most common composition based on observed features typical of basaltic eruptions found on Earth. Lava flows are one of the most easily recognizable landforms on planetary surfaces and their features may provide information about eruption dynamics, lava rheology, and potential hazards. More recently, researchers have taken a multi-faceted approach to combine remote sensing, field observations and quantitative modeling to constrain volcanic activity on Earth and other planets. Here we test a number of published models, including empirically derived relationships from Mt. Etna and Kilauea, models derived from laboratory experiments, and theoretical models previously applied to remote sensing of planetary surfaces, against well-documented eruptions from the literature and field observations. We find that the Graetz (Hulme and Felder, 1977, Phil.Trans., 285, 227 - 234) method for estimating effusion rates compares favorably with published eruption data, while, on the other hand, inverting lava flow length prediction models to estimate effusion rates leads to several orders of magnitude in error. The Graetz method also better constrains eruption duration. Simple radial spreading laws predict Hawaiian lava flow lengths quite well, as do using the thickness of the lava flow front and chilled crust. There was no observed difference between results from models thought to be exclusive to aa or pahoehoe flow fields. Interpreting historic conditions should therefore follow simple relationships to observable morphologies no matter the composition or surface texture. We have applied the most robust models to understand the eruptive conditions and lava rheology of the Batamote Mountains near Ajo, AZ, an eroded shield volcano in southern Arizona. We find effusion rates on the order of 100 - 200 cubic
NASA Astrophysics Data System (ADS)
Tsamados, Michel; Heorton, Harry; Feltham, Daniel; Muir, Alan; Baker, Steven
2016-04-01
The new elastic-plastic anisotropic (EAP) rheology that explicitly accounts for the sub-continuum anisotropy of the sea ice cover has been implemented into the latest version of the Los Alamos sea ice model CICE. The EAP rheology is widely used in the climate modeling scientific community (i.e. CPOM stand alone, RASM high resolution regional ice-ocean model, MetOffice fully coupled model). Early results from sensitivity studies (Tsamados et al, 2013) have shown the potential for an improved representation of the observed main sea ice characteristics with a substantial change of the spatial distribution of ice thickness and ice drift relative to model runs with the reference visco-plastic (VP) rheology. The model contains one new prognostic variable, the local structure tensor, which quantifies the degree of anisotropy of the sea ice, and two parameters that set the time scale of the evolution of this tensor. Observations from high resolution satellite SAR imagery as well as numerical simulation results from a discrete element model (DEM, see Wilchinsky, 2010) have shown that these individual floes can organize under external wind and thermal forcing to form an emergent isotropic sea ice state (via thermodynamic healing, thermal cracking) or an anisotropic sea ice state (via Coulombic failure lines due to shear rupture). In this work we use for the first time in the context of sea ice research a mathematical metric, the Tensorial Minkowski functionals (Schroeder-Turk, 2010), to measure quantitatively the degree of anisotropy and alignment of the sea ice at different scales. We apply the methodology on the GlobICE Envisat satellite deformation product (www.globice.info), on a prototype modified version of GlobICE applied on Sentinel-1 Synthetic Aperture Radar (SAR) imagery and on the DEM ice floe aggregates. By comparing these independent measurements of the sea ice anisotropy as well as its temporal evolution against the EAP model we are able to constrain the
Analytic Element Modeling of Multi-Aquifer Flow
NASA Astrophysics Data System (ADS)
Bakker, M.
2002-05-01
A new set of analytic elements has been developed for the modeling of steady-state flow in multi-aquifer systems. All analytic elements are exact solutions to the governing system of differential equations. As such, the leakage between aquifers is simulated exactly. Application of the new formulation has the advantage that the model domain is not discretized; all anlaytic elements represent hydrogeologic features in the aquifer system. The new elements may be used to simulate flow in systems with an arbitrary number of aquifers and leaky layers. They may also be applied to approximate three-dimensional flow to partially penetrating features if one is willing to discretize the aquifer vertically. Six multi-aquifer analytic elements have been developed and several more are under development. The following multi-aquifer hydrogeologic features may be modeled at the present time (March, 2002): an ambient flow gradient (uniform flow element); pumping wells, multi-aquifer wells, abandoned multi-aquifer wells, partially penetrating wells (well elements); river or stream segments, arms of radial collector wells (line-sink elements); areal recharge (circular area-sink elements); cylindrical domains with different aquifer and leaky layer properties, cylindrical holes in leaky layers (cylindrical inhomogeneity elements); single aquifers with polygonal domains consisting of multiple aquifers and leaky layers (aquifer-system inhomogeneity elements). Several new analytic elements are in different stages of development; they are intended for the modeling of the following features: impermeable walls, slurry walls (line-doublet elements), elliptical cylinder inclusions with different aquifer and leaky-layer properties (elliptical cylinder inhomogeneity elements), recharge areas bounded by polygons (polygonal area-sink elements). Analytic elements for multi-aquifer flow have been implemented in computational codes written in FORTRAN90 and Python. Practical applications include the
Mobile Monolith Polymer Elements For Flow Control In Microfluidic Systems
Hasselbrink, Jr., Ernest F.; Rehm, Jason E.; Shepodd, Timothy J.; Kirby, Brian J.
2006-01-24
A cast-in-place and lithographically shaped mobile, monolithic polymer element for fluid flow control in microfluidic devices and method of manufacture. Microfluid flow control devices, or microvalves that provide for control of fluid or ionic current flow can be made incorporating a cast-in-place, mobile monolithic polymer element, disposed within a microchannel, and driven by fluid pressure (either liquid or gas) against a retaining or sealing surface. The polymer elements are made by the application of lithographic methods to monomer mixtures formulated in such a way that the polymer will not bond to microchannel walls. The polymer elements can seal against pressures greater than 5000 psi, and have a response time on the order of milliseconds. By the use of energetic radiation it is possible to depolymerize selected regions of the polymer element to form shapes that cannot be produced by conventional lithographic patterning and would be impossible to machine.
Mobile monolithic polymer elements for flow control in microfluidic devices
Hasselbrink, Jr., Ernest F.; Rehm, Jason E.; Shepodd, Timothy J.; Kirby, Brian J.
2005-11-11
A cast-in-place and lithographically shaped mobile, monolithic polymer element for fluid flow control in microfluidic devices and method of manufacture. Microfluid flow control devices, or microvalves that provide for control of fluid or ionic current flow can be made incorporating a cast-in-place, mobile monolithic polymer element, disposed within a microchannel, and driven by fluid pressure (either liquid or gas) against a retaining or sealing surface. The polymer elements are made by the application of lithographic methods to monomer mixtures formulated in such a way that the polymer will not bond to microchannel walls. The polymer elements can seal against pressures greater than 5000 psi, and have a response time on the order of milliseconds. By the use of energetic radiation it is possible to depolymerize selected regions of the polymer element to form shapes that cannot be produced by conventional lithographic patterning and would be impossible to machine.
Mobile monolithic polymer elements for flow control in microfluidic devices
Hasselbrink, Jr., Ernest F.; Rehm, Jason E.; Shepodd, Timothy J.
2004-08-31
A cast-in-place and lithographically shaped mobile, monolithic polymer element for fluid flow control in microfluidic devices and method of manufacture. Microfluid flow control devices, or microvalves that provide for control of fluid or ionic current flow can be made incorporating a cast-in-place, mobile monolithic polymer element, disposed within a microchannel, and driven by either fluid or gas pressure against a retaining or sealing surface. The polymer elements are made by the application of lithographic methods to monomer mixtures formulated in such a way that the polymer will not bond to microchannel walls. The polymer elements can seal against pressures greater than 5000 psi, and have a response time on the order of milliseconds. By the use of energetic radiation it is possible to depolymerize selected regions of the polymer element to form shapes that cannot be produced by conventional lithographic patterning and would be impossible to machine.
High-order Finite Element Analysis of Boundary Layer Flows
NASA Astrophysics Data System (ADS)
Zhang, Alvin; Sahni, Onkar
2014-11-01
Numerical analysis of boundary layer flows requires careful approximations, specifically the use of a mesh with layered and graded elements near the (viscous) walls. This is referred to as a boundary layer mesh, which for complex geometries is composed of triangular elements on the walls that are inflated or extruded into the volume along the wall-normal direction up to a desired height while the rest of the domain is filled with unstructured tetrahedral elements. Linear elements with C0 inter-element continuity are employed and in some situations higher order C0 elements are also used. However, these elements only enforce continuity whereas high-order smoothness is not attained as will be the case with C1 inter-element continuity and higher. As a result, C0 elements result in a poor approximation of the high-order boundary layer behavior. To achieve greater inter-element continuity in boundary layer region, we employ B-spline basis functions along the wall-normal direction (i.e., only in the layered portion of the mesh). In the rest of the fully unstructured mesh, linear or higher order C0 elements are used as appropriate. In this study we demonstrate the benefits of finite-element analysis based on such higher order and continuity basis functions for boundary layer flows.
The Spectral Element Method for Geophysical Flows
NASA Astrophysics Data System (ADS)
Taylor, Mark
1998-11-01
We will describe SEAM, a Spectral Element Atmospheric Model. SEAM solves the 3D primitive equations used in climate modeling and medium range forecasting. SEAM uses a spectral element discretization for the surface of the globe and finite differences in the vertical direction. The model is spectrally accurate, as demonstrated by a variety of test cases. It is well suited for modern distributed-shared memory computers, sustaining over 24 GFLOPS on a 240 processor HP Exemplar. This performance has allowed us to run several interesting simulations in full spherical geometry at high resolution (over 22 million grid points).
A robust approach to chance constrained optimal power flow with renewable generation
Lubin, Miles; Dvorkin, Yury; Backhaus, Scott N.
2016-09-01
Optimal Power Flow (OPF) dispatches controllable generation at minimum cost subject to operational constraints on generation and transmission assets. The uncertainty and variability of intermittent renewable generation is challenging current deterministic OPF approaches. Recent formulations of OPF use chance constraints to limit the risk from renewable generation uncertainty, however, these new approaches typically assume the probability distributions which characterize the uncertainty and variability are known exactly. We formulate a robust chance constrained (RCC) OPF that accounts for uncertainty in the parameters of these probability distributions by allowing them to be within an uncertainty set. The RCC OPF is solved using a cutting-plane algorithm that scales to large power systems. We demonstrate the RRC OPF on a modified model of the Bonneville Power Administration network, which includes 2209 buses and 176 controllable generators. In conclusion, deterministic, chance constrained (CC), and RCC OPF formulations are compared using several metrics including cost of generation, area control error, ramping of controllable generators, and occurrence of transmission line overloads as well as the respective computational performance.
A robust approach to chance constrained optimal power flow with renewable generation
Lubin, Miles; Dvorkin, Yury; Backhaus, Scott N.
2016-09-01
Optimal Power Flow (OPF) dispatches controllable generation at minimum cost subject to operational constraints on generation and transmission assets. The uncertainty and variability of intermittent renewable generation is challenging current deterministic OPF approaches. Recent formulations of OPF use chance constraints to limit the risk from renewable generation uncertainty, however, these new approaches typically assume the probability distributions which characterize the uncertainty and variability are known exactly. We formulate a robust chance constrained (RCC) OPF that accounts for uncertainty in the parameters of these probability distributions by allowing them to be within an uncertainty set. The RCC OPF is solved usingmore » a cutting-plane algorithm that scales to large power systems. We demonstrate the RRC OPF on a modified model of the Bonneville Power Administration network, which includes 2209 buses and 176 controllable generators. In conclusion, deterministic, chance constrained (CC), and RCC OPF formulations are compared using several metrics including cost of generation, area control error, ramping of controllable generators, and occurrence of transmission line overloads as well as the respective computational performance.« less
A robust approach to chance constrained optimal power flow with renewable generation
Lubin, Miles; Dvorkin, Yury; Backhaus, Scott N.
2016-09-01
Optimal Power Flow (OPF) dispatches controllable generation at minimum cost subject to operational constraints on generation and transmission assets. The uncertainty and variability of intermittent renewable generation is challenging current deterministic OPF approaches. Recent formulations of OPF use chance constraints to limit the risk from renewable generation uncertainty, however, these new approaches typically assume the probability distributions which characterize the uncertainty and variability are known exactly. We formulate a robust chance constrained (RCC) OPF that accounts for uncertainty in the parameters of these probability distributions by allowing them to be within an uncertainty set. The RCC OPF is solved using a cutting-plane algorithm that scales to large power systems. We demonstrate the RRC OPF on a modified model of the Bonneville Power Administration network, which includes 2209 buses and 176 controllable generators. In conclusion, deterministic, chance constrained (CC), and RCC OPF formulations are compared using several metrics including cost of generation, area control error, ramping of controllable generators, and occurrence of transmission line overloads as well as the respective computational performance.
Some parametric flow analyses of a particle bed fuel element
Dobranich, D.
1993-05-01
Parametric calculations are performed, using the SAFSIM computer program, to investigate the fluid mechanics and heat transfer performance of a particle bed fuel element. Both steady-state and transient calculations are included, addressing such issues as flow stability, reduced thrust operation, transpiration drag, coolant conductivity enhancement, flow maldistributions, decay heat removal, flow perturbations, and pulse cooling. The calculations demonstrate the dependence of the predicted results on the modeling assumptions and thus provide guidance as to where further experimental and computational investigations are needed. The calculations also demonstrate that both flow instability and flow maldistribution in the fuel element are important phenomena. Furthermore, results are encouraging that geometric design changes to the element can significantly reduce problems related to these phenomena, allowing improved performance over a wide range of element power densities and flow rates. Such design changes will help to maximize the operational efficiency of space propulsion reactors employing particle bed fuel element technology. Finally, the results demonstrate that SAFSIM is a valuable engineering tool for performing quick and inexpensive parametric simulations addressing complex flow problems.
Structural power flow analysis using finite element
NASA Astrophysics Data System (ADS)
Buchmann, Patrick; Cuschieri, Joseph M.; Yong, Yan
In summary, this paper presents power flow results for a T-shaped beam structure using either FEA or MPF analysis. The FEA and the MPF results show good agreement. Using either of the two models (FE or MPF), structural intensity maps at given frequencies can be generated. The type of results that would be obtained in this case would be similar to those that were generated by Nefske for a simply supported beam or by Hambric for a cantilevered plate.
A 3-dimensional mass conserving element for compressible flows
NASA Technical Reports Server (NTRS)
Fix, G.; Suri, M.
1985-01-01
A variety of finite element schemes has been used in the numerical approximation of compressible flows particularly in underwater acoustics. In many instances instabilities have been generated due to the lack of mass conservation. Two- and three-dimensional elements are developed which avoid these problems.
NASA Astrophysics Data System (ADS)
Weigand, T. M.; Miller, C. T.; Dye, A. L.; Gray, W. G.; McClure, J. E.; Rybak, I.
2015-12-01
The thermodynamically constrained averaging theory (TCAT) has been usedto formulate general classes of porous medium models, including newmodels for two-fluid-phase flow. The TCAT approach provides advantagesthat include a firm connection between the microscale, or pore scale,and the macroscale; a thermodynamically consistent basis; explicitinclusion of factors such as interfacial areas, contact angles,interfacial tension, and curvatures; and dynamics of interface movementand relaxation to an equilibrium state. In order to render the TCATmodel solvable, certain closure relations are needed to relate fluidpressure, interfacial areas, curvatures, and relaxation rates. In thiswork, we formulate and solve a TCAT-based two-fluid-phase flow model. We detail the formulation of the model, which is a specific instancefrom a hierarchy of two-fluid-phase flow models that emerge from thetheory. We show the closure problem that must be solved. Using recentresults from high-resolution microscale simulations, we advance a set ofclosure relations that produce a closed model. Lastly, we solve the model using a locally conservative numerical scheme and compare the TCAT model to the traditional model.
Nonlinear stochastic controllers for power-flow-constrained vibratory energy harvesters
NASA Astrophysics Data System (ADS)
Cassidy, Ian L.; Scruggs, Jeffrey T.
2013-06-01
This study addresses the formulation of nonlinear feedback controllers for stochastically excited vibratory energy harvesters. Maximizing the average power generated from such systems requires the transducer current to be regulated using a bi-directional power electronic converter. There are many applications where the implementation of these types of converters is infeasible, due to the higher parasitic losses they must sustain. If instead the transducer current is regulated using a converter capable of single-directional power-flow, then these parasitic losses can be reduced significantly. However, the constraint on the power-flow directionality restricts the domain of feasible feedback laws. The only feasible linear feedback law imposes a static relationship between current and voltage, i.e., a static admittance. In stochastic response, the power generation performance can be enhanced significantly beyond that of the optimal static admittance, using nonlinear feedback. In this paper, a general approach to nonlinear control synthesis for power-flow-constrained energy harvesters is presented, which is analytically guaranteed to outperform the optimal static admittance in stationary stochastic response. Simulation results are presented for a single-degree-of-freedom resonant oscillator with an electromagnetic transducer, as well as for a piezoelectric bimorph cantilever beam.
ELEMENTAL MERCURY CAPTURE BY ACTIVATED CARBON IN A FLOW REACTOR
The paper gives results of bench-scale experiments in a flow reactor to simulate the entrained-flow capture of elemental mercury (Hgo) using solid sorbents. Adsorption of Hgo by a lignite-based activated carbon (Calgon FGD) was examined at different carbon/mercury (C/Hg) rat...
Modeling of supersonic flows near flying vehicle elements
NASA Astrophysics Data System (ADS)
Kovenya, V. M.; Slyunyaev, A. Yu.
2009-03-01
Supersonic flows near flying vehicle elements are calculated in the approximation of the full Navier-Stokes equations for a viscous compressible heat-conducting gas with different values of free-stream. Mach and Reynolds numbers and angles of attack. The main laws of the flow near the lifting surface. and in the inlet are obtained.
ELEMENTAL MERCURY CAPTURE BY ACTIVATED CARBON IN A FLOW REACTOR
The paper gives results of bench-scale experiments in a flow reactor to simulate the entrained-flow capture of elemental mercury (Hgo) using solid sorbents. Adsorption of Hgo by a lignite-based activated carbon (Calgon FGD) was examined at different carbon/mercury (C/Hg) rat...
Finite element analysis of inviscid subsonic boattail flow
NASA Technical Reports Server (NTRS)
Chima, R. V.; Gerhart, P. M.
1981-01-01
A finite element code for analysis of inviscid subsonic flows over arbitrary nonlifting planar or axisymmetric bodies is described. The code solves a novel primitive variable formulation of the coupled irrotationality and compressible continuity equations. Results for flow over a cylinder, a sphere, and a NACA 0012 airfoil verify the code. Computed subcritical flows over an axisymmetric boattailed afterbody compare well with finite difference results and experimental data. Interative coupling with an integral turbulent boundary layer code shows strong viscous effects on the inviscid flow. Improvements in code efficiency and extensions to transonic flows are discussed.
Valentín, A; Humphrey, J D; Holzapfel, G A
2013-08-01
We implemented a constrained mixture model of arterial growth and remodeling in a nonlinear finite element framework to facilitate numerical analyses of diverse cases of arterial adaptation and maladaptation, including disease progression, resulting in complex evolving geometries and compositions. This model enables hypothesis testing by predicting consequences of postulated characteristics of cell and matrix turnover, including evolving quantities and orientations of fibrillar constituents and nonhomogenous degradation of elastin or loss of smooth muscle function. The nonlinear finite element formulation is general within the context of arterial mechanics, but we restricted our present numerical verification to cylindrical geometries to allow comparisons with prior results for two special cases: uniform transmural changes in mass and differential growth and remodeling within a two-layered cylindrical model of the human aorta. The present finite element model recovers the results of these simplified semi-inverse analyses with good agreement.
Valentín, A.; Humphrey, J. D.; Holzapfel, G. A.
2013-01-01
We implemented a constrained mixture model of arterial growth and remodeling (G&R) in a nonlinear finite element framework to facilitate numerical analyses of diverse cases of arterial adaptation and maladaptation, including disease progression, resulting in complex evolving geometries and compositions. This model enables hypothesis testing by predicting consequences of postulated characteristics of cell and matrix turnover, including evolving quantities and orientations of fibrillar constituents and non-homogenous degradation of elastin or loss of smooth muscle function. The non-linear finite element formulation is general within the context of arterial mechanics, but we restricted our present numerical verification to cylindrical geometries to allow comparisons to prior results for two special cases: uniform transmural changes in mass and differential G&R within a two-layered cylindrical model of the human aorta. The present finite element model recovers the results of these simplified semi-inverse analyses with good agreement. PMID:23713058
Axisymmetric Flow Properties for Magnetic Elements of Differing Strength
NASA Technical Reports Server (NTRS)
Rightmire-Upton, Lisa; Hathaway, David H.
2012-01-01
Aspects of the structure and dynamics of the flows in the Sun's surface shear layer remain uncertain and yet are critically important for understanding the observed magnetic behavior. In our previous studies of the axisymmetric transport of magnetic elements we found systematic changes in both the differential rotation and the meridional flow over the course of Solar Cycle 23. Here we examine how those flows depend upon the strength (and presumably anchoring depth) of the magnetic elements. Line of sight magnetograms obtained by the HMI instrument aboard SDO over the course of Carrington Rotation 2097 were mapped to heliographic coordinates and averaged over 12 minutes to remove the 5-min oscillations. Data masks were constructed based on the field strength of each mapped pixel to isolate magnetic elements of differing field strength. We used Local Correlation Tracking of the unmasked data (separated in time by 1- to 8-hours) to determine the longitudinal and latitudinal motions of the magnetic elements. We then calculated average flow velocities as functions of latitude and longitude from the central meridian for approx 600 image pairs over the 27-day rotation. Variations with longitude indicate and characterize systematic errors in the flow measurements associated with changes in the signal from disk center to limb. Removing these systematic errors reveals changes in the axisymmetric flow properties that reflect changes in flow properties with depth in the surface shear layer.
Wing Rib Stress Analysis and Design Optimization Using Constrained Natural Element Method
NASA Astrophysics Data System (ADS)
Amine Bennaceur, Mohamed; Xu, Yuan-ming; Layachi, Hemza
2017-09-01
This paper demonstrates the applicability of a novel meshless method in solving problems related to aeronautical engineering, the constraint-natural element method is used to optimize a wing rib where it present several shape of cut-outs deals with the results findings we select the optimum design, we focus on the description and analysis of the constraint-natural element method and its application for simulating mechanical problems, the constraint natural element method is the alternative method for the finite element method where the shape functions is constructed on an extension of Voronoi diagram dual of Delaunay tessellation for non-convex domains.
NASA Technical Reports Server (NTRS)
Wayner, Peter C., Jr.; Kundan, Akshay; Plawsky, Joel
2014-01-01
The Constrained Vapor Bubble (CVB) is a wickless, grooved heat pipe and we report on a full- scale fluids experiment flown on the International Space Station (ISS). The CVB system consists of a relatively simple setup a quartz cuvette with sharp corners partially filled with either pentane or an ideal mixture of pentane and isohexane as the working fluids. Along with temperature and pressure measurements, the two-dimensional thickness profile of the menisci formed at the corners of the quartz cuvette was determined using the Light Microscopy Module (LMM). Even with the large, millimeter dimensions of the CVB, interfacial forces dominate in these exceedingly small Bond Number systems. The experiments were carried out at various power inputs. Although conceptually simple, the transport processes were found to be very complex with many different regions. At the heated end of the CVB, due to a high temperature gradient, we observed Marangoni flow at some power inputs. This region from the heated end to the central drop region is defined as a Marangoni dominated region. We present a simple analysis based on interfacial phenomena using only measurements from the ISS experiments that lead to a predictive equation for the thickness of the film near the heated end of the CVB. The average pressure gradient for flow in the film is assumed due to the measured capillary pressure at the two ends of the liquid film and that the pressure stress gradient due to cohesion self adjusts to a constant value over a distance L. The boundary conditions are the no slip condition at the wall interface and an interfacial shear stress at the liquid- vapor interface due to the Marangoni stress, which is due to the high temperature gradient. Although the heated end is extremely complex, since it includes three- dimensional variations in radiation, conduction, evaporation, condensation, fluid flow and interfacial forces, we find that using the above simplifying assumptions, a simple successful
Finite element solver for 3-D compressible viscous flows
NASA Technical Reports Server (NTRS)
Reddy, K. C.; Reddy, J. N.
1986-01-01
The space shuttle main engine (SSME) has extremely complex internal flow structure. The geometry of the flow domain is three-dimensional with complicated topology. The flow is compressible, viscous, and turbulent with large gradients in flow quantities and regions of recirculations. The analysis of the flow field in SSME involves several tedious steps. One is the geometrical modeling of the particular zone of the SSME being studied. Accessing the geometry definition, digitalizing it, and developing surface interpolations suitable for an interior grid generator require considerable amount of manual labor. There are several types of grid generators available with some general-purpose finite element programs. An efficient and robust computational scheme for solving 3D Navier-Stokes equations has to be implemented. Post processing software has to be adapted to visualize and analyze the computed 3D flow field. The progress made in a project to develop software for the analysis of the flow is discussed. The technical approach to the development of the finite element scheme and the relaxation procedure are discussed. The three dimensional finite element code for the compressible Navier-Stokes equations is listed.
Spectral element methods for transitional flows, in complex geometries.
Fischer, P. F.; Kruse, G. W.; Loth, F.; Mathematics and Computer Science; Juniata Coll.; Univ. of Illinois
2002-01-01
We describe the development and implementation of an efficient spectral element code for simulating transitional flows in complex three-dimensional domains. Critical to this effort is the use of geometrically nonconforming elements that allow localized refinement in regions of interest, coupled with a stabilized high-order time-split formulation of the semi-discrete Navier-Stokes equations. Simulations of transition in a model of an arteriovenous graft illustrate the potential of this approach in biomechanical applications.
Mathematical aspects of finite element methods for incompressible viscous flows
NASA Technical Reports Server (NTRS)
Gunzburger, M. D.
1986-01-01
Mathematical aspects of finite element methods are surveyed for incompressible viscous flows, concentrating on the steady primitive variable formulation. The discretization of a weak formulation of the Navier-Stokes equations are addressed, then the stability condition is considered, the satisfaction of which insures the stability of the approximation. Specific choices of finite element spaces for the velocity and pressure are then discussed. Finally, the connection between different weak formulations and a variety of boundary conditions is explored.
Predicting Rediated Noise With Power Flow Finite Element Analysis
2007-02-01
Defence R&D Canada – Atlantic DEFENCE DÉFENSE & Predicting Rediated Noise With Power Flow Finite Element Analysis D. Brennan T.S. Koko L. Jiang J...PREDICTING RADIATED NOISE WITH POWER FLOW FINITE ELEMENT ANALYSIS D.P. Brennan T.S. Koko L. Jiang J.C. Wallace Martec Limited Martec Limited...model- or full-scale data before it is available for general use. Brennan, D.P., Koko , T.S., Jiang, L., Wallace, J.C. 2007. Predicting Radiated
PC Windows finite element modeling of landfill gas flow
Mull, S.R.; Lang, R.J.; Vigil, S.A.; Cota, H.
1996-09-01
A two dimensional demonstration program, GAS, has been developed for the solution of landfill gas (LFG) flow problems on a personal computer (PC). The program combines a Windows{trademark} graphical user interface, object oriented programming (OOP) techniques, and finite element modeling (FEM) to demonstrate the practicality of performing LFG flow modeling on the PC. GAS is demonstrated on a sample LFG problem consisting of a landfill, one gas extraction well, the landfill liner, cap, and surrounding soil. Analyses of the program results are performed for successively finer grid resolutions. Element flux imbalance, execution time, and required memory are characterized as a function of grid resolution.
A finite element solver for 3-D compressible viscous flows
NASA Technical Reports Server (NTRS)
Reddy, K. C.; Reddy, J. N.; Nayani, S.
1990-01-01
Computation of the flow field inside a space shuttle main engine (SSME) requires the application of state of the art computational fluid dynamic (CFD) technology. Several computer codes are under development to solve 3-D flow through the hot gas manifold. Some algorithms were designed to solve the unsteady compressible Navier-Stokes equations, either by implicit or explicit factorization methods, using several hundred or thousands of time steps to reach a steady state solution. A new iterative algorithm is being developed for the solution of the implicit finite element equations without assembling global matrices. It is an efficient iteration scheme based on a modified nonlinear Gauss-Seidel iteration with symmetric sweeps. The algorithm is analyzed for a model equation and is shown to be unconditionally stable. Results from a series of test problems are presented. The finite element code was tested for couette flow, which is flow under a pressure gradient between two parallel plates in relative motion. Another problem that was solved is viscous laminar flow over a flat plate. The general 3-D finite element code was used to compute the flow in an axisymmetric turnaround duct at low Mach numbers.
Single element injector cold flow testing for STME swirl coaxial injector element design
NASA Technical Reports Server (NTRS)
Hulka, J.; Schneider, J. A.
1993-01-01
An oxidizer-swirled coaxial element injector is being investigated for application in the Space Transportation Main Engine (STME). Single element cold flow experiments were conducted to provide characterization of the STME injector element for future analysis, design, and optimization. All tests were conducted to quiescent, ambient backpressure conditions. Spray angle, circumferential spray uniformity, dropsize, and dropsize distribution were measured in water-only and water/nitrogen flows. Rupe mixing efficiency was measured using water/sucrose solution flows with a large grid patternator for simple comparative evaluation of mixing. Factorial designs of experiment were used for statistical evaluation of injector geometrical design features and propellant flow conditions on mixing and atomization. Increasing the free swirl angle of the liquid oxidizer had the greatest influence on increasing the mixing efficiency. The addition of gas assistance had the most significant effect on reducing oxidizer droplet size parameters and increasing droplet size distribution. Increasing the oxidizer injection velocity had the greatest influence for reducing oxidizer droplet size parameters and increasing size distribution for non-gas assisted flows. Single element and multi-element subscale hot fire testing are recommended to verify optimized designs before committing to the STME design.
Single element injector cold flow testing for STME swirl coaxial injector element design
NASA Technical Reports Server (NTRS)
Hulka, J.; Schneider, J. A.
1993-01-01
An oxidizer-swirled coaxial element injector is being investigated for application in the Space Transportation Main Engine (STME). Single element cold flow experiments were conducted to provide characterization of the STME injector element for future analysis, design, and optimization. All tests were conducted to quiescent, ambient backpressure conditions. Spray angle, circumferential spray uniformity, dropsize, and dropsize distribution were measured in water-only and water/nitrogen flows. Rupe mixing efficiency was measured using water/sucrose solution flows with a large grid patternator for simple comparative evaluation of mixing. Factorial designs of experiment were used for statistical evaluation of injector geometrical design features and propellant flow conditions on mixing and atomization. Increasing the free swirl angle of the liquid oxidizer had the greatest influence on increasing the mixing efficiency. The addition of gas assistance had the most significant effect on reducing oxidizer droplet size parameters and increasing droplet size distribution. Increasing the oxidizer injection velocity had the greatest influence for reducing oxidizer droplet size parameters and increasing size distribution for non-gas assisted flows. Single element and multi-element subscale hot fire testing are recommended to verify optimized designs before committing to the STME design.
Corrective Control to Handle Forecast Uncertainty: A Chance Constrained Optimal Power Flow
Roald, Line; Misra, Sidhant; Krause, Thilo; ...
2016-08-25
Higher shares of electricity generation from renewable energy sources and market liberalization is increasing uncertainty in power systems operation. At the same time, operation is becoming more flexible with improved control systems and new technology such as phase shifting transformers (PSTs) and high voltage direct current connections (HVDC). Previous studies have shown that the use of corrective control in response to outages contributes to a reduction in operating cost, while maintaining N-1 security. In this work, we propose a method to extend the use of corrective control of PSTs and HVDCs to react to uncertainty. We characterize the uncertainty asmore » continuous random variables, and define the corrective control actions through affine control policies. This allows us to efficiently model control reactions to a large number of uncertainty sources. The control policies are then included in a chance constrained optimal power flow formulation, which guarantees that the system constraints are enforced with a desired probability. Lastly, by applying an analytical reformulation of the chance constraints, we obtain a second-order cone problem for which we develop an efficient solution algorithm. In a case study for the IEEE 118 bus system, we show that corrective control for uncertainty leads to a decrease in operational cost, while maintaining system security. Further, we demonstrate the scalability of the method by solving the problem for the IEEE 300 bus and the Polish system test cases.« less
Corrective Control to Handle Forecast Uncertainty: A Chance Constrained Optimal Power Flow
Roald, Line; Misra, Sidhant; Krause, Thilo; Andersson, Goran
2016-08-25
Higher shares of electricity generation from renewable energy sources and market liberalization is increasing uncertainty in power systems operation. At the same time, operation is becoming more flexible with improved control systems and new technology such as phase shifting transformers (PSTs) and high voltage direct current connections (HVDC). Previous studies have shown that the use of corrective control in response to outages contributes to a reduction in operating cost, while maintaining N-1 security. In this work, we propose a method to extend the use of corrective control of PSTs and HVDCs to react to uncertainty. We characterize the uncertainty as continuous random variables, and define the corrective control actions through affine control policies. This allows us to efficiently model control reactions to a large number of uncertainty sources. The control policies are then included in a chance constrained optimal power flow formulation, which guarantees that the system constraints are enforced with a desired probability. Lastly, by applying an analytical reformulation of the chance constraints, we obtain a second-order cone problem for which we develop an efficient solution algorithm. In a case study for the IEEE 118 bus system, we show that corrective control for uncertainty leads to a decrease in operational cost, while maintaining system security. Further, we demonstrate the scalability of the method by solving the problem for the IEEE 300 bus and the Polish system test cases.
NASA Astrophysics Data System (ADS)
Wang, Yingjun; Benson, David J.
2016-12-01
In this paper, an approach based on the fast point-in-polygon (PIP) algorithm and trimmed elements is proposed for isogeometric topology optimization (TO) with arbitrary geometric constraints. The isogeometric parameterized level-set-based TO method, which directly uses the non-uniform rational basis splines (NURBS) for both level set function (LSF) parameterization and objective function calculation, provides higher accuracy and efficiency than previous methods. The integration of trimmed elements is completed by the efficient quadrature rule that can design the quadrature points and weights for arbitrary geometric shape. Numerical examples demonstrate the efficiency and flexibility of the method.
NASA Astrophysics Data System (ADS)
Vollstaedt, Hauke; Mezger, Klaus; Leya, Ingo
2016-09-01
Solar nebula processes led to a depletion of volatile elements in different chondrite groups when compared to the bulk chemical composition of the solar system deduced from the Sun's photosphere. For moderately-volatile elements, this depletion primarily correlates with the element condensation temperature and is possibly caused by incomplete condensation from a hot solar nebula, evaporative loss from the precursor dust, and/or inherited from the interstellar medium. Element concentrations and interelement ratios of volatile elements do not provide a clear picture about responsible mechanisms. Here, the abundance and stable isotope composition of the moderately- to highly-volatile element Se are investigated in carbonaceous, ordinary, and enstatite chondrites to constrain the mechanism responsible for the depletion of volatile elements in planetary bodies of the inner solar system and to define a δ 82 / 78 Se value for the bulk solar system. The δ 82 / 78 Se of the studied chondrite falls are identical within their measurement uncertainties with a mean of - 0.20 ± 0.26 ‰ (2 s.d., n = 14, relative to NIST SRM 3149) despite Se abundance depletions of up to a factor of 2.5 with respect to the CI group. The absence of resolvable Se isotope fractionation rules out a kinetic Rayleigh-type incomplete condensation of Se from the hot solar nebula or partial kinetic evaporative loss on the precursor material and/or the parent bodies. The Se depletion, if acquired during partial condensation or evaporative loss, therefore must have occurred under near equilibrium conditions to prevent measurable isotope fractionation. Alternatively, the depletion and cooling of the nebula could have occurred simultaneously due to the continuous removal of gas and fine particles by the solar wind accompanied by the quantitative condensation of elements from the pre-depleted gas. In this scenario the condensation of elements does not require equilibrium conditions to avoid isotope
Finite element analysis of periodic transonic flow problems
NASA Technical Reports Server (NTRS)
Fix, G. J.
1978-01-01
Flow about an oscillating thin airfoil in a transonic stream was considered. It was assumed that the flow field can be decomposed into a mean flow plus a periodic perturbation. On the surface of the airfoil the usual Neumman conditions are imposed. Two computer programs were written, both using linear basis functions over triangles for the finite element space. The first program uses a banded Gaussian elimination solver to solve the matrix problem, while the second uses an iterative technique, namely SOR. The only results obtained are for an oscillating flat plate.
Experimental Impedance of Single Liner Elements with Bias Flow
NASA Technical Reports Server (NTRS)
Follet, J. I.; Betts, J. F.; Kelly, Jeffrey J.; Thomas, Russell H.
2000-01-01
An experimental investigation was conducted to generate a high quality database, from which the effects of a mean bias flow on the acoustic impedance of lumped-element single-degree-of-freedom liners was determined. Acoustic impedance measurements were made using the standard two-microphone method in the NASA Langley Normal Incidence Tube. Each liner consisted of a perforated sheet with a constant-area cavity. Liner resistance was shown to increase and to become less frequency and sound pressure level dependent as the bias flow was increased. The resistance was also consistently lower for a negative bias flow (suction) than for a positive bias flow (blowing) of equal magnitude. The slope of the liner reactance decreased with increased flow.
Beam shaping in flow cytometry with diffractive optical elements
NASA Astrophysics Data System (ADS)
Qu, Weidong; Li, Derong; Jian, Peng
2016-10-01
Focusing elements are usually employed in the flow cytometry to focus the input laser beam into elliptically shaped Gaussian beam in order to increase power for excitation of fluorescence for high signal-to-noise ratio (SNR). While in order to ensure repeatable and reliable signal generation for accurate population discrimination - despite slight deviations of the cell from the flow centre, the shaped beam should be a cubic diffraction region with uniform power intensity across the cell flow stream. However, it is hard for beam shaping with refractive optical elements. In this paper, we present a beam shaping system in flow cytometry with diffractive optical elements (DOEs) to shape the input laser beam to a cubic diffraction region with uniform power intensity. The phase distribution of the DOE is obtained by using the inverse Fresnel diffraction based layered holographic stereogram, and the cubic diffraction region with uniform power intensity within the cell flow channel is well reconstructed. Simulation results demonstrate the good performance of the new beam shaping system.
Finite elements and finite differences for transonic flow calculations
NASA Technical Reports Server (NTRS)
Hafez, M. M.; Murman, E. M.; Wellford, L. C.
1978-01-01
The paper reviews the chief finite difference and finite element techniques used for numerical solution of nonlinear mixed elliptic-hyperbolic equations governing transonic flow. The forms of the governing equations for unsteady two-dimensional transonic flow considered are the Euler equation, the full potential equation in both conservative and nonconservative form, the transonic small-disturbance equation in both conservative and nonconservative form, and the hodograph equations for the small-disturbance case and the full-potential case. Finite difference methods considered include time-dependent methods, relaxation methods, semidirect methods, and hybrid methods. Finite element methods include finite element Lax-Wendroff schemes, implicit Galerkin method, mixed variational principles, dual iterative procedures, optimal control methods and least squares.
A finite element formulation for supersonic flows around complex configurations
NASA Technical Reports Server (NTRS)
Morino, L.
1974-01-01
The problem of small perturbation potential supersonic flow around complex configurations is considered. This problem requires the solution of an integral equation relating the values of the potential on the surface of the body to the values of the normal derivative, which is known from the small perturbation boundary conditions. The surface of the body is divided into small (hyperboloidal quadrilateral) surface elements which are described in terms of the Cartesian components of the four corner points. The values of the potential (and its normal derivative) within each element are assumed to be constant and equal to its value at the centroid of the element. This yields a set of linear algebraic equations whose coefficients are given by source and doublet integrals over the surface elements. Closed form evaluations of the integrals are presented.
NASA Astrophysics Data System (ADS)
Oberhofer, Harald; Blumberger, Jochen
2010-12-01
We present a plane wave basis set implementation for the calculation of electronic coupling matrix elements of electron transfer reactions within the framework of constrained density functional theory (CDFT). Following the work of Wu and Van Voorhis [J. Chem. Phys. 125, 164105 (2006)], the diabatic wavefunctions are approximated by the Kohn-Sham determinants obtained from CDFT calculations, and the coupling matrix element calculated by an efficient integration scheme. Our results for intermolecular electron transfer in small systems agree very well with high-level ab initio calculations based on generalized Mulliken-Hush theory, and with previous local basis set CDFT calculations. The effect of thermal fluctuations on the coupling matrix element is demonstrated for intramolecular electron transfer in the tetrathiafulvalene-diquinone (Q-TTF-Q-) anion. Sampling the electronic coupling along density functional based molecular dynamics trajectories, we find that thermal fluctuations, in particular the slow bending motion of the molecule, can lead to changes in the instantaneous electron transfer rate by more than an order of magnitude. The thermal average, ( {< {| {H_ab } |^2 } > } )^{1/2} = 6.7 {mH}, is significantly higher than the value obtained for the minimum energy structure, | {H_ab } | = 3.8 {mH}. While CDFT in combination with generalized gradient approximation (GGA) functionals describes the intermolecular electron transfer in the studied systems well, exact exchange is required for Q-TTF-Q- in order to obtain coupling matrix elements in agreement with experiment (3.9 mH). The implementation presented opens up the possibility to compute electronic coupling matrix elements for extended systems where donor, acceptor, and the environment are treated at the quantum mechanical (QM) level.
Oberhofer, Harald; Blumberger, Jochen
2010-12-28
We present a plane wave basis set implementation for the calculation of electronic coupling matrix elements of electron transfer reactions within the framework of constrained density functional theory (CDFT). Following the work of Wu and Van Voorhis [J. Chem. Phys. 125, 164105 (2006)], the diabatic wavefunctions are approximated by the Kohn-Sham determinants obtained from CDFT calculations, and the coupling matrix element calculated by an efficient integration scheme. Our results for intermolecular electron transfer in small systems agree very well with high-level ab initio calculations based on generalized Mulliken-Hush theory, and with previous local basis set CDFT calculations. The effect of thermal fluctuations on the coupling matrix element is demonstrated for intramolecular electron transfer in the tetrathiafulvalene-diquinone (Q-TTF-Q(-)) anion. Sampling the electronic coupling along density functional based molecular dynamics trajectories, we find that thermal fluctuations, in particular the slow bending motion of the molecule, can lead to changes in the instantaneous electron transfer rate by more than an order of magnitude. The thermal average, (<|H(ab)|(2)>)(1/2)=6.7 mH, is significantly higher than the value obtained for the minimum energy structure, |H(ab)|=3.8 mH. While CDFT in combination with generalized gradient approximation (GGA) functionals describes the intermolecular electron transfer in the studied systems well, exact exchange is required for Q-TTF-Q(-) in order to obtain coupling matrix elements in agreement with experiment (3.9 mH). The implementation presented opens up the possibility to compute electronic coupling matrix elements for extended systems where donor, acceptor, and the environment are treated at the quantum mechanical (QM) level.
NASA Astrophysics Data System (ADS)
Shulaker, D. Z.; Schmitt, A. K.; Zack, T.; Bindeman, I. N.
2013-12-01
Rutilated quartz, aka Venus' hair, is finely-acicular rutile intergrown with host quartz generated by fluid-mediated co-crystallization. It is commonly found in hydrothermal veins, including the renown cleft mineral locations of the Swiss Alps. Previous studies of Alpine cleft mineralizations used rare hydrothermal monazite [1] and titanite [2] to constrain vein formation to ~13.5-15.2 Ma, postdating peak metamorphism by ~2-4 Ma. Temperature (T) estimates of 150-450°C are based on fluid inclusions and bulk quartz-mineral oxygen isotope exchange equilibria, and formation pressures (P) are 0.5-2.5 kbar (for a geothermal gradient of 30°C/km) [2]. The potential of rutilated quartz as a thermochronometer, however, has not been harnessed previously. Here, we present the first results of age and P-T determinations for rutilated quartz from six locations in the Swiss Alps (San Gottardo; Feldbach, Binntal; Pi Aul, Vals; Faido, Leventina; Elm, Steinbach; Binntal). Samples were cut and mounted in epoxy discs to expose rutile (0.03 to 1 mm in diameter) and its host quartz which was also imaged in cathodoluminescence (CL). CL images for half of the samples' host quartz exhibited strong sector zoning, while others reveal only weak CL zonation. Isotopic and trace element analyses were carried out by SIMS using a CAMECA ims1270 for U-Pb, O-isotopes, and Ti-in-quartz, and a LA-ICP-MS system (213 nm New Wave laser coupled to an Agilent 7500a) for Zr-in-rutile. U-Pb rutile ages average 15.5×2.0 Ma (2σ). T estimates are 352-575°C (rutile-quartz oxygen isotopes in touching domains), 470-530°C (Zr-in-rutile assuming P = 0.5 and equilibrium with host-rock zircon), and 251-391°C (Ti-in-quartz at assumed P = 0.5 kbar and aTiO2 = 1). CL zones are isotopically unzoned. Rutile-quartz oxygen isotopes are pressure insensitive, whereas Zr-in-rutile and Ti-in-quartz are minimum temperatures. These results demonstrate that rutilated quartz can constrain timing and conditions of post
Highly Constrained Intergenic Drosophila Ultraconserved Elements Are Candidate ncRNAs
Kern, Andrew D.; Barbash, Daniel A.; Chang Mell, Joshua; Hupalo, Daniel; Jensen, Amanda
2015-01-01
Eukaryotes contain short (∼80–200 bp) regions that have few or no substitutions among species that represent hundreds of millions of years of evolutionary divergence. These ultraconserved elements (UCEs) are candidates for containing essential functions, but their biological roles remain largely unknown. Here, we report the discovery and characterization of UCEs from 12 sequenced Drosophila species. We identified 98 elements ≥80 bp long with very high conservation across the Drosophila phylogeny. Population genetic analyses reveal that these UCEs are not present in mutational cold spots. Instead we infer that they experience a level of selective constraint almost 10-fold higher compared with missense mutations in protein-coding sequences, which is substantially higher than that observed previously for human UCEs. About one-half of these Drosophila UCEs overlap the transcribed portion of genes, with many of those that are within coding sequences likely to correspond to sites of ADAR-dependent RNA editing. For the remaining UCEs that are in nongenic regions, we find that many are potentially capable of forming RNA secondary structures. Among ten chosen for further analysis, we discovered that the majority are transcribed in multiple tissues of Drosophila melanogaster. We conclude that Drosophila species are rich with UCEs and that many of them may correspond to novel noncoding RNAs. PMID:25618141
NASA Astrophysics Data System (ADS)
Roselyn, J. Preetha; Devaraj, D.; Dash, Subhransu Sekhar
2013-11-01
Voltage stability is an important issue in the planning and operation of deregulated power systems. The voltage stability problems is a most challenging one for the system operators in deregulated power systems because of the intense use of transmission line capabilities and poor regulation in market environment. This article addresses the congestion management problem avoiding offline transmission capacity limits related to voltage stability by considering Voltage Security Constrained Optimal Power Flow (VSCOPF) problem in deregulated environment. This article presents the application of Multi Objective Differential Evolution (MODE) algorithm to solve the VSCOPF problem in new competitive power systems. The maximum of L-index of the load buses is taken as the indicator of voltage stability and is incorporated in the Optimal Power Flow (OPF) problem. The proposed method in hybrid power market which also gives solutions to voltage stability problems by considering the generation rescheduling cost and load shedding cost which relieves the congestion problem in deregulated environment. The buses for load shedding are selected based on the minimum eigen value of Jacobian with respect to the load shed. In the proposed approach, real power settings of generators in base case and contingency cases, generator bus voltage magnitudes, real and reactive power demands of selected load buses using sensitivity analysis are taken as the control variables and are represented as the combination of floating point numbers and integers. DE/randSF/1/bin strategy scheme of differential evolution with self-tuned parameter which employs binomial crossover and difference vector based mutation is used for the VSCOPF problem. A fuzzy based mechanism is employed to get the best compromise solution from the pareto front to aid the decision maker. The proposed VSCOPF planning model is implemented on IEEE 30-bus system, IEEE 57 bus practical system and IEEE 118 bus system. The pareto optimal
Finite element methods of studying mechanical factors in blood flow.
Davids, N
1981-01-01
This paper reviews some biomechanical analyses of blood flow in large arteries based on a general computer modeling using the finite element method. We study the following question: What is the role played by the interrelated factors of mechanical stress, flow irregularities, and diffusion through the endothelium on the etiology of atherosclerosis or the aggravation of vascular injury. It presents the computational features of the method and stresses the physiological significance of the results, such as the effect of geometric complexities, material nonlinearities, and non-Newtonian rheology of the blood. The specific mechanical and fluid dynamic factors analyzed are wall shear stress, flow profiles, and pressure variations. After simulating tubes of circular cross section, we apply the analysis to a number of physiological situations of significance, including blood flow in the entrance region, at bifurcations, in the annular region between an inserted catheter of varying diameter and the vessel. A model study of pulsatile flow in a 60 degree bifurcated channel of velocity profiles provided corroborative measurements of these processes with special emphasis on reversed or distributed flow conditions. The corresponding analysis was extended to the situation in which flow separates and reverses in the neighborhood of stagnation points. This required developing the nonlinear expression for the convective velocity change in the medium. A computer algorithm was developed to handle simultaneous effects of pressure and viscous forces on velocity change across the element and applied to the canine prebranch arterial segment. For mean physiological flow conditions, low shear stresses (0-10 dynes/cm2) are predicted near the wall in the diverging plane, higher values (50 dynes/cm2) along the converging sides of the wall. Backflow is predicted along the outer wall, pressure recovery prior to and into the branches, and a peak shear at the divider lip.
A boundary element method for steady incompressible thermoviscous flow
NASA Technical Reports Server (NTRS)
Dargush, G. F.; Banerjee, P. K.
1991-01-01
A boundary element formulation is presented for moderate Reynolds number, steady, incompressible, thermoviscous flows. The governing integral equations are written exclusively in terms of velocities and temperatures, thus eliminating the need for the computation of any gradients. Furthermore, with the introduction of reference velocities and temperatures, volume modeling can often be confined to only a small portion of the problem domain, typically near obstacles or walls. The numerical implementation includes higher order elements, adaptive integration and multiregion capability. Both the integral formulation and implementation are discussed in detail. Several examples illustrate the high level of accuracy that is obtainable with the current method.
Cell-cooling in flow cytometry by Peltier elements.
Göttlinger, C; Meyer, K L; Weichel, W; Müller, W; Raftery, B; Radbruch, A
1986-05-01
We have built a cooling device for cell suspensions in flow cytometry that makes use of the Peltier effect (Barnard RD, Thermo electricity in Metals and Alloys, Taylor and Francis, London; Siemens-Z 34:383-88, 1963). The prototype described here is used for cooling collection tubes during long-duration cell sorting and is capable of maintaining a temperature of 2-5 degrees C in a cell suspension of up to 3 ml. In general, Peltier element-based cooling is useful for equilibrating the temperature of small volumes of fluids. Furthermore, Peltier element-based cooling devices are easy to build and handle.
Analysis of anelastic flow and numerical treatment via finite elements
Martinez, M.J.
1994-05-01
In this report, we reconsider the various approximations made to the full equations of motion and energy transport for treating low-speed flows with significant temperature induced property variations. This entails assessment of the development of so-called anelastic for low-Mach number flows outside the range of validity of the Boussinesq equations. An integral part of this assessment is the development of a finite element-based numerical scheme for obtaining approximate numerical solutions to this class of problems. Several formulations were attempted and are compared.
Smith, Emily M.; Lajoie, Bryan R.; Jain, Gaurav; Dekker, Job
2016-01-01
Three-dimensional genome structure plays an important role in gene regulation. Globally, chromosomes are organized into active and inactive compartments while, at the gene level, looping interactions connect promoters to regulatory elements. Topologically associating domains (TADs), typically several hundred kilobases in size, form an intermediate level of organization. Major questions include how TADs are formed and how they are related to looping interactions between genes and regulatory elements. Here we performed a focused 5C analysis of a 2.8 Mb chromosome 7 region surrounding CFTR in a panel of cell types. We find that the same TAD boundaries are present in all cell types, indicating that TADs represent a universal chromosome architecture. Furthermore, we find that these TAD boundaries are present irrespective of the expression and looping of genes located between them. In contrast, looping interactions between promoters and regulatory elements are cell-type specific and occur mostly within TADs. This is exemplified by the CFTR promoter that in different cell types interacts with distinct sets of distal cell-type-specific regulatory elements that are all located within the same TAD. Finally, we find that long-range associations between loci located in different TADs are also detected, but these display much lower interaction frequencies than looping interactions within TADs. Interestingly, interactions between TADs are also highly cell-type-specific and often involve loci clustered around TAD boundaries. These data point to key roles of invariant TAD boundaries in constraining as well as mediating cell-type-specific long-range interactions and gene regulation. PMID:26748519
Flow formed by spanwise gaps between roughness elements
NASA Technical Reports Server (NTRS)
Logan, E.; Lin, S. H.; Islam, O.
1985-01-01
Measurements of the three mean velocity components and the three Reynolds shear stresses were made in the region downstream of gaps between wall-mounted roughness elements of square cross section and high aspect ratio in a thick turbulent boundary layer. The effect of small and large gaps was studied in a wind tunnel at a Reynolds number of 3600, based on obstacle height and free-stream velocity. The small gap produces retardation of the gap flow as with a two-dimensional roughness element, but a definite interaction between gap and wake flows is observed. The interaction is more intense for the large gap than for the small. Both gaps generate a secondary crossflow which moves fluid away from the centerline in the wall region and toward the centerline in the outer (y greater than 1.5H) region.
Using rare earth elements to constrain particulate organic carbon flux in the East China Sea
Hung, Chin-Chang; Chen, Ya-Feng; Hsu, Shih-Chieh; Wang, Kui; Chen, Jian Feng; Burdige, David J.
2016-01-01
Fluxes of particulate organic carbon (POC) in the East China Sea (ECS) have been reported to decrease from the inner continental shelf towards the outer continental shelf. Recent research has shown that POC fluxes in the ECS may be overestimated due to active sediment resuspension. To better characterize the effect of sediment resuspension on particle fluxes in the ECS, rare earth elements (REEs) and organic carbon (OC) were used in separate two-member mixing models to evaluate trap-collected POC fluxes. The ratio of resuspended particles from sediments to total trap-collected particles in the ECS ranged from 82–94% using the OC mixing model, and 30–80% using the REEs mixing model, respectively. These results suggest that REEs may be better proxies for sediment resuspension than OC in high turbidity marginal seas because REEs do not appear to undergo degradation during particle sinking as compared to organic carbon. Our results suggest that REEs can be used as tracers to provide quantitative estimates of POC fluxes in marginal seas. PMID:27670426
Using rare earth elements to constrain particulate organic carbon flux in the East China Sea.
Hung, Chin-Chang; Chen, Ya-Feng; Hsu, Shih-Chieh; Wang, Kui; Chen, Jian Feng; Burdige, David J
2016-09-27
Fluxes of particulate organic carbon (POC) in the East China Sea (ECS) have been reported to decrease from the inner continental shelf towards the outer continental shelf. Recent research has shown that POC fluxes in the ECS may be overestimated due to active sediment resuspension. To better characterize the effect of sediment resuspension on particle fluxes in the ECS, rare earth elements (REEs) and organic carbon (OC) were used in separate two-member mixing models to evaluate trap-collected POC fluxes. The ratio of resuspended particles from sediments to total trap-collected particles in the ECS ranged from 82-94% using the OC mixing model, and 30-80% using the REEs mixing model, respectively. These results suggest that REEs may be better proxies for sediment resuspension than OC in high turbidity marginal seas because REEs do not appear to undergo degradation during particle sinking as compared to organic carbon. Our results suggest that REEs can be used as tracers to provide quantitative estimates of POC fluxes in marginal seas.
High speed inviscid compressible flow by the finite element method
NASA Technical Reports Server (NTRS)
Zienkiewicz, O. C.; Loehner, R.; Morgan, K.
1984-01-01
The finite element method and an explicit time stepping algorithm which is based on Taylor-Galerkin schemes with an appropriate artificial viscosity is combined with an automatic mesh refinement process which is designed to produce accurate steady state solutions to problems of inviscid compressible flow in two dimensions. The results of two test problems are included which demonstrate the excellent performance characteristics of the proposed procedures.
Mixed Element Type Unstructured Grid Generation for Viscous Flow Applications
NASA Technical Reports Server (NTRS)
Marcum, David L.; Gaither, J. Adam
2000-01-01
A procedure is presented for efficient generation of high-quality unstructured grids suitable for CFD simulation of high Reynolds number viscous flow fields. Layers of anisotropic elements are generated by advancing along prescribed normals from solid boundaries. The points are generated such that either pentahedral or tetrahedral elements with an implied connectivity can be be directly recovered. As points are generated they are temporarily attached to a volume triangulation of the boundary points. This triangulation allows efficient local search algorithms to be used when checking merging layers, The existing advancing-front/local-reconnection procedure is used to generate isotropic elements outside of the anisotropic region. Results are presented for a variety of applications. The results demonstrate that high-quality anisotropic unstructured grids can be efficiently and consistently generated for complex configurations.
Finite-Element Analysis of Multiphase Immiscible Flow Through Soils
NASA Astrophysics Data System (ADS)
Kuppusamy, T.; Sheng, J.; Parker, J. C.; Lenhard, R. J.
1987-04-01
A finite-element model is developed for multiphase flow through soil involving three immiscible fluids: namely, air, water, and a nonaqueous phase liquid (NAPL). A variational method is employed for the finite-element formulation corresponding to the coupled differential equations governing flow in a three-fluid phase porous medium system with constant air phase pressure. Constitutive relationships for fluid conductivities and saturations as functions of fluid pressures, which are derived in a companion paper by J. C. Parker et al. (this issue) and which may be calibrated from two-phase laboratory measurements, are employed in the finite-element program. The solution procedure uses backward time integration with iteration by a modified Picard method to handle the nonlinear properties. Laboratory experiments involving water displacement from soil columns by p cymene (a benzene-derivative hydrocarbon) under constant pressure were simulated by the finite-element program to validate the numerical model and formulation for constitutive properties. Transient water outflow predicted using independently measured saturation-capillary head data agreed with observed outflow data within the limits of precision of the predictions as estimated by a first-order Taylor series approximation considering parameter uncertainty due to experimental reproducability and constitutive model accuracy. Two-dimensional simulations are presented for a hypothetical field case involving introduction of NAPL near the soil surface due to leakage from an underground storage tank. Subsequent transport of NAPL in the variably saturated vadose and groundwater zones is analyzed.
Discrete-element modeling of particulate aerosol flows
Marshall, J.S.
2009-03-20
A multiple-time step computational approach is presented for efficient discrete-element modeling of aerosol flows containing adhesive solid particles. Adhesive aerosol particulates are found in numerous dust and smoke contamination problems, including smoke particle transport in the lungs, particle clogging of heat exchangers in construction vehicles, industrial nanoparticle transport and filtration systems, and dust fouling of electronic systems and MEMS components. Dust fouling of equipment is of particular concern for potential human occupation on dusty planets, such as Mars. The discrete-element method presented in this paper can be used for prediction of aggregate structure and breakup, for prediction of the effect of aggregate formation on the bulk fluid flow, and for prediction of the effects of small-scale flow features (e.g., due to surface roughness or MEMS patterning) on the aggregate formation. After presentation of the overall computational structure, the forces and torques acting on the particles resulting from fluid motion, particle-particle collision, and adhesion under van der Waals forces are reviewed. The effect of various parameters of normal collision and adhesion of two particles are examined in detail. The method is then used to examine aggregate formation and particle clogging in pipe and channel flow.
Anisotropic adaptive finite element method for modelling blood flow.
Müller, J; Sahni, O; Li, X; Jansen, K E; Shephard, M S; Taylor, C A
2005-10-01
In this study, we present an adaptive anisotropic finite element method (FEM) and demonstrate how computational efficiency can be increased when applying the method to the simulation of blood flow in the cardiovascular system. We use the SUPG formulation for the transient 3D incompressible Navier-Stokes equations which are discretised by linear finite elements for both the pressure and the velocity field. Given the pulsatile nature of the flow in blood vessels we have pursued adaptivity based on the average flow over a cardiac cycle. Error indicators are derived to define an anisotropic mesh metric field. Mesh modification algorithms are used to anisotropically adapt the mesh according to the desired size field. We demonstrate the efficiency of the method by first applying it to pulsatile flow in a straight cylindrical vessel and then to a porcine aorta with a stenosis bypassed by a graft. We demonstrate that the use of an anisotropic adaptive FEM can result in an order of magnitude reduction in computing time with no loss of accuracy compared to analyses obtained with uniform meshes.
A Finite element model of tactile flow for softness perception.
Battaglia, Edoardo; Bianchi, Matteo; D'Angelo, Maria Laura; D'Imperio, Mariapaola; Cannella, Ferdinando; Scilingo, Enzo P; Bicchi, Antonio
2015-01-01
Touch is an extremely dynamic sense. To take into account this aspect, it has been hypothesized that there are mechanisms in the brain that specialize in processing dynamic tactile stimuli, in a way not too dissimilar from what happens for optical flow in dynamic vision. The concept of tactile flow, related to the rate of expansion of isostrain volumes in the human fingerpad, was used to explain some perceptual illusions as well as mechanisms of human softness perception. In this paper we describe a computational model of tactile flow, and apply it to a finite element model of interaction between deformable bodies. The shape and material properties of the bodies are modeled from those of a human fingertip interacting with specimens with different softness properties. Results show that the rate of expansion of isostrain volumes can be used to discriminate different materials in terms of their softness characteristics.
A dual reciprocal boundary element formulation for viscous flows
NASA Technical Reports Server (NTRS)
Lafe, Olu
1993-01-01
The advantages inherent in the boundary element method (BEM) for potential flows are exploited to solve viscous flow problems. The trick is the introduction of a so-called dual reciprocal technique in which the convective terms are represented by a global function whose unknown coefficients are determined by collocation. The approach, which is necessarily iterative, converts the governing partial differential equations into integral equations via the distribution of fictitious sources or dipoles of unknown strength on the boundary. These integral equations consist of two parts. The first is a boundary integral term, whose kernel is the unknown strength of the fictitious sources and the fundamental solution of a convection-free flow problem. The second part is a domain integral term whose kernel is the convective portion of the governing PDEs. The domain integration can be transformed to the boundary by using the dual reciprocal (DR) concept. The resulting formulation is a pure boundary integral computational process.
NASA Astrophysics Data System (ADS)
BALAMURUGAN, V.; NARAYANAN, S.
2002-01-01
This work deals with the active vibration control of beams with smart constrained layer damping (SCLD) treatment. SCLD design consists of viscoelastic shear layer sandwiched between two layers of piezoelectric sensors and actuator. This composite SCLD when bonded to a vibrating structure acts as a smart treatment. The sensor piezoelectric layer measures the vibration response of the structure and a feedback controller is provided which regulates the axial deformation of the piezoelectric actuator (constraining layer), thereby providing adjustable and significant damping in the structure. The damping offered by SCLD treatment has two components, active action and passive action. The active action is transmitted from the piezoelectric actuator to the host structure through the viscoelastic layer. The passive action is through the shear deformation in the viscoelastic layer. The active action apart from providing direct active control also adjusts the passive action by regulating the shear deformation in the structure. The passive damping component of this design eliminates spillover, reduces power consumption, improves robustness and reliability of the system, and reduces vibration response at high-frequency ranges where active damping is difficult to implement. A beam finite element model has been developed based on Timoshenko's beam theory with partially covered SCLD. The Golla-Hughes-McTavish (GHM) method has been used to model the viscoelastic layer. The dissipation co-ordinates, defined using GHM approach, describe the frequency-dependent viscoelastic material properties. Models of PCLD and purely active systems could be obtained as a special case of SCLD. Using linear quadratic regulator (LQR) optimal control, the effects of the SCLD on vibration suppression performance and control effort requirements are investigated. The effects of the viscoelastic layer thickness and material properties on the vibration control performance are investigated.
Flowing Plasma Interaction with an Electric Sail Tether Element
NASA Technical Reports Server (NTRS)
Schneider, Todd; Vaughn, Jason; Wright, Kenneth; Andersen, Allen; Stone, Nobie
2017-01-01
Electric sails are a relatively new concept for providing high speed propellant-less propulsion. Employing multiple tethers biased to high positive voltage levels (kV), electric sails are designed to gain momentum from the solar wind by repelling solar wind protons. To maximize the area of the sail that interacts with the solar wind, electric sails rely on the formation of a large plasma sheath around each small diameter tether. Motivated by interest in advancing the development of electric sails, a set of laboratory tests has been conducted to study the interaction of a drifting plasma with a sheath formed around a small diameter tether element biased at positive voltages. The laboratory test setup was created with Debye length scaling in mind to offer a path to extrapolate (via modeling) to full scale electric sail missions. Using an instrument known as a Differential Ion Flux Probe (DIFP) the interaction between a positively biased tether element and a drifting plasma has been measured for several scenarios. Clear evidence of the tether element sheath deflecting ions has been obtained. Maps of the flow angle downstream from the tether element have been made and they show the influence of the plasma sheath. Finally, electron current collection measurements have been made for a wide range of plasma conditions and tether element bias voltages. The electron collection data will have an impact on electric sail power requirements, as high voltage power supplies and electron guns will have to be sized to accommodate the electron currents collected by each tether.
Finite element simulation of flow in twin screw extruder mixing elements
NASA Astrophysics Data System (ADS)
Bravo (Sananes), Victor
1998-12-01
In the plastics industry, twin screw extruders are widely used for melting, dispersing and homogenizing polymers. There are a diversity of designs employed throughout the polymer industry, each one having different operating principles and applications. Among the different arrangements of twin screw systems, the intermeshing co-rotating configuration has been found to be one of the most efficient mixers and it is one of the most commonly used pieces of equipment among the continuous mixers due to its self wiping properties. The problem of mixing of polymers involves aspects of fluid dynamics and rheology. Mixing is usually obtained through a combination of mechanical motion of the mixing device and the resulting deformation induced in the flowing material. The quantitative description of the flow patterns is now feasible even in the most complicated geometries through the development of computational fluid dynamics (CFD) tools and the continuous increase in computer resources at lower costs. Intermeshing co-rotating twin screw extruders (ICRTSE) are usually built in a modular fashion to meet the diversity of tasks performed by this type of machine. There are two main types of elements: full flight conveying elements and kneading block mixing elements. The kneading blocks have been the focus of attention for the theoretical analysis of flow due to their significant contribution to the mixing performance of the extruder and the fact that kneading blocks normally work under a fully filled channel condition, which is one of the fundamental assumptions in CFD simulations. The objective of this thesis is to understand the flow mechanisms in the kneading disc section of co-rotating twin screw extruders. This is done by means of the 3D numerical simulation of the flow process within the complex geometry involving intricate passages and continuously moving surfaces. A quasi-steady state finite element model was developed assuming isothermal, non-Newtonian flow. The
Finite element simulation of flow in twin screw extruder mixing elements
NASA Astrophysics Data System (ADS)
Bravo, Victor Sananes
In the plastics industry, twin screw extruders are widely used for melting, dispersing and homogenizing polymers. There are a diversity of designs employed throughout the polymer industry, each one having different operating principles and applications. Among the different arrangements of twin screw systems, the intermeshing co- rotating configuration has been found to be one of the most efficient mixers and it is one of the most commonly used pieces of equipment among the continuous mixers due to its self wiping properties. The problem of mixing of polymers involves aspects of fluid dynamics and rheology. Mixing is usually obtained through a combination of mechanical motion of the mixing device and the resulting deformation induced in the flowing material. The quantitative description of the flow patterns is now feasible even in the most complicated geometries through the development of computational fluid dynamics (CFD) tools and the continuous increase in computer resources at lower costs. Intermeshing co-rotating twin screw extruders (ICRTSE) are usually built in a modular fashion to meet the diversity of tasks performed by this type of machine. There are two main types of elements: full flight conveying elements and kneading block mixing elements. The kneading blocks have been the focus of attention for the theoretical analysis of flow due to their significant contribution to the mixing performance of the extruder and the fact that kneading blocks normally work under a fully filled channel condition, which is one of the fundamental assumptions in CFD simulations. The objective of this thesis is to understand the flow mechanisms in the kneading disc section of co-rotating twin screw extruders. This is done by means of the 3D numerical simulation of the flow process within the complex geometry involving intricate passages and continuously moving surfaces. A quasi-steady state finite element model was developed assuming isothermal, non- Newtonian flow. The
Finite element simulation of glottal flow and pressure.
Guo, C G; Scherer, R C
1993-08-01
Computational studies of laryngeal aerodynamics should help clarify the relationships among configuration, air flow, surface pressure, and vocal fold movement within the larynx, and the acoustic consequences of the output glottal air flow. The penalty finite element method [S. W. Kim, Comput. Fluids 16(4), 429-444 (1988a); NASA CR-179357 (1988b); S. W. Kim and R. A. Decker, Int. J. Num. Meth. Fluids 9, 43-57 (1989)] was adopted to simulate steady air flow and air pressure through the larynx. A total of 133 conditions of different glottal configurations and inflow rates were studied. The computational results were compared to empirical data from earlier experiments. Two cases are reported (1) constant glottal divergence (42 degrees) but variable diameter and (2) constant glottal diameter (0.04 cm) but variable glottal angle. For case (1), the average discrepancy for translaryngeal pressure drop between the computational results and empirical data was 6.8% for pressures between 3 and 15 cm H2O. Flow separation occurred just downstream of the minimal glottal diameter. For case (2), the computational results for translaryngeal pressure drop differed from the empirically derived Scherer-Guo (S-G) equation predictions by an average of 8.9% for pressure between 3 and 13 cm H2O. Pressure recovery in the glottis suggested that the optimal glottal diffuser angle was near 10 degrees. Results suggest that the computational method should be sufficient to study glottal aerodynamics (assuming quasisteady flow).
Doyle, Jessica M.; Gleeson, Tom; Manning, Andrew H.; Mayer, K. Ulrich
2015-01-01
Environmental tracers provide information on groundwater age, recharge conditions, and flow processes which can be helpful for evaluating groundwater sustainability and vulnerability. Dissolved noble gas data have proven particularly useful in mountainous terrain because they can be used to determine recharge elevation. However, tracer-derived recharge elevations have not been utilized as calibration targets for numerical groundwater flow models. Herein, we constrain and calibrate a regional groundwater flow model with noble-gas-derived recharge elevations for the first time. Tritium and noble gas tracer results improved the site conceptual model by identifying a previously uncertain contribution of mountain block recharge from the Coast Mountains to an alluvial coastal aquifer in humid southwestern British Columbia. The revised conceptual model was integrated into a three-dimensional numerical groundwater flow model and calibrated to hydraulic head data in addition to recharge elevations estimated from noble gas recharge temperatures. Recharge elevations proved to be imperative for constraining hydraulic conductivity, recharge location, and bedrock geometry, and thus minimizing model nonuniqueness. Results indicate that 45% of recharge to the aquifer is mountain block recharge. A similar match between measured and modeled heads was achieved in a second numerical model that excludes the mountain block (no mountain block recharge), demonstrating that hydraulic head data alone are incapable of quantifying mountain block recharge. This result has significant implications for understanding and managing source water protection in recharge areas, potential effects of climate change, the overall water budget, and ultimately ensuring groundwater sustainability.
NASA Astrophysics Data System (ADS)
Doyle, Jessica M.; Gleeson, Tom; Manning, Andrew H.; Mayer, K. Ulrich
2015-10-01
Environmental tracers provide information on groundwater age, recharge conditions, and flow processes which can be helpful for evaluating groundwater sustainability and vulnerability. Dissolved noble gas data have proven particularly useful in mountainous terrain because they can be used to determine recharge elevation. However, tracer-derived recharge elevations have not been utilized as calibration targets for numerical groundwater flow models. Herein, we constrain and calibrate a regional groundwater flow model with noble-gas-derived recharge elevations for the first time. Tritium and noble gas tracer results improved the site conceptual model by identifying a previously uncertain contribution of mountain block recharge from the Coast Mountains to an alluvial coastal aquifer in humid southwestern British Columbia. The revised conceptual model was integrated into a three-dimensional numerical groundwater flow model and calibrated to hydraulic head data in addition to recharge elevations estimated from noble gas recharge temperatures. Recharge elevations proved to be imperative for constraining hydraulic conductivity, recharge location, and bedrock geometry, and thus minimizing model nonuniqueness. Results indicate that 45% of recharge to the aquifer is mountain block recharge. A similar match between measured and modeled heads was achieved in a second numerical model that excludes the mountain block (no mountain block recharge), demonstrating that hydraulic head data alone are incapable of quantifying mountain block recharge. This result has significant implications for understanding and managing source water protection in recharge areas, potential effects of climate change, the overall water budget, and ultimately ensuring groundwater sustainability.
Massively parallel finite element computation of three dimensional flow problems
NASA Astrophysics Data System (ADS)
Tezduyar, T.; Aliabadi, S.; Behr, M.; Johnson, A.; Mittal, S.
1992-12-01
The parallel finite element computation of three-dimensional compressible, and incompressible flows, with emphasis on the space-time formulations, mesh moving schemes and implementations on the Connection Machines CM-200 and CM-5 are presented. For computation of unsteady compressible and incompressible flows involving moving boundaries and interfaces, the Deformable-Spatial-Domain/Stabilized-Space-Time (DSD/SST) formulation that previously developed are employed. In this approach, the stabilized finite element formulations of the governing equations are written over the space-time domain of the problem; therefore, the deformation of the spatial domain with respect to time is taken into account automatically. This approach gives the capability to solve a large class of problems involving free surfaces, moving interfaces, and fluid-structure and fluid-particle interactions. By using special mesh moving schemes, the frequency of remeshing is minimized to reduce the projection errors involved in remeshing and also to increase the parallelization ease of the computations. The implicit equation systems arising from the finite element discretizations are solved iteratively by using the GMRES update technique with the diagonal and nodal-block-diagonal preconditioners. These formulations have all been implemented on the CM-200 and CM-5, and have been applied to several large-scale problems. The three-dimensional problems in this report were all computed on the CM-200 and CM-5.
FEWA: a Finite Element model of Water flow through Aquifers
Yeh, G.T.; Huff, D.D.
1983-11-01
This report documents the implementation and demonstration of a Finite Element model of Water flow through Aquifers (FEWA). The particular features of FEWA are its versatility and flexibility to deal with as many real-world problems as possible. Point as well as distributed sources/sinks are included to represent recharges/pumpings and rainfall infiltrations. All sources/sinks can be transient or steady state. Prescribed hydraulic head on the Dirichlet boundaries and fluxes on Neumann or Cauchy boundaries can be time-dependent or constant. Source/sink strength over each element and node, hydraulic head at each Dirichlet boundary node, and flux at each boundary segment can vary independently of each other. Either completely confined or completely unconfined aquifers, or partially confined and partially unconfined aquifers can be dealt with effectively. Discretization of a compound region with very irregular curved boundaries is made easy by including both quadrilateral and triangular elements in the formulation. Large-field problems can be solved efficiently by including a pointwise iterative solution strategy as an optional alternative to the direct elimination solution method for the matrix equation approximating the partial differential equation of groundwater flow. FEWA also includes transient flow through confining leaky aquifers lying above and/or below the aquifer of interest. The model is verified against three simple cases to which analytical solutions are available. It is then demonstrated by two examples of how the model can be applied to heterogeneous and anisotropic aquifers with transient boundary conditions, time-dependent sources/sinks, and confining aquitards for a confined aquifer of variable thickness and for a free surface problem in an unconfined aquifer, respectively. 20 references, 25 figures, 8 tables.
Convective Enhancement of Icing Roughness Elements in Stagnation Region Flows
NASA Technical Reports Server (NTRS)
Hughes, Michael T.; McClain, Stephen T.; Vargas, Mario; Broeren, Andy
2015-01-01
To improve existing ice accretion simulation codes, more data regarding ice roughness and its effects on convective heat transfer are required. To build on existing research on this topic, this study used the Vertical Icing Studies Tunnel (VIST) at NASA Glenn Research to model realistic ice roughness in the stagnation region of a NACA 0012 airfoil. Using the VIST, a test plate representing the leading 2% chord of the airfoil was subjected to flows of 7.62 m/s (25 ft/s), 12.19 m/s (40 ft/s), and 16.76 m/s (55 ft/s). The test plate was fitted with 3 surfaces, each with a different representation of ice roughness: 1) a control surface with no ice roughness, 2) a surface with ice roughness with element height scaled by 10x and streamwise rough zone width from the stagnation point scaled by 10x, and 3) a surface with ice roughness with element height scaled by 10x and streamwise rough zone width from the stagnation point scaled by 25x. Temperature data from the tests were recorded using an infrared camera and thermocouples imbedded in the test plate. From the temperature data, a convective heat transfer coefficient map was created for each case. Additional testing was also performed to validate the VIST's flow quality. These tests included five-hole probe and hot-wire probe velocity traces to provide flow visualization and to study boundary layer formation on the various test surfaces. The knowledge gained during the experiments will help improve ice accretion codes by providing heat transfer coefficient validation data and by providing flow visualization data helping understand current and future experiments performed in the VIST.
NASA Astrophysics Data System (ADS)
Ohde, A.; Otsuka, H.; Kioka, A.; Ashi, J.
2015-12-01
The Nankai Trough is a plate convergent boundary where earthquakes with a magnitude of 8 take place repeatedly. Thermal structure in subduction zones affects pore pressure and diagenesis such as consolidation, dewatering and cementation, and constrains physical properties of a fault-slip plane. In the Nankai subduction zone, existence of methane hydrate is confirmed from acoustic reflectors called the Bottom Simulating Reflectors (BSRs) which parallel the seafloor on seismic reflection images with high-amplitude and reverse-polarity waveforms. As a depth of BSR is theoretically constrained by subseafloor profiles of temperature and pressure, the BSR depths effectively produce subseafloor geothermal information over a wide area without heat flow probe penetration or in-situ borehole temperature measurement that is fragmentary. In this study, we aim at calculating precise two-dimensional shallow thermal structure. First, we investigate detailed distribution of the BSRs in the Nankai area ranging from offshore Tokai to Hyuga using two-dimensional multi-channel seismic reflection data. The BSR depths are then forwarded to estimate heat flow values. Second, we use a simple two-dimensional thermal modeling of Blackwell et al. [1980] that takes into account topographical effects of the seafloor roughness. We also employ additional boundary conditions constrained by seafloor temperature and the heat flow estimated from BSR depths. In order to confirm reliability of the modeled thermal structure, we additionally estimate the base of gas hydrate stability zone which is proved to almost equal to observational BSR depths. We find in the modeled thermal structure that the convex portions that are subject to cooling by cold bottom water, while depressions are less subject to the cooling from observational BSRs and theoretical calculation. The thermal structure gained here provides essential data for seismic simulations in subduction zones and for laboratory experiments as
Adjoint-based constrained topology optimization for viscous flows, including heat transfer
NASA Astrophysics Data System (ADS)
Kontoleontos, E. A.; Papoutsis-Kiachagias, E. M.; Zymaris, A. S.; Papadimitriou, D. I.; Giannakoglou, K. C.
2013-08-01
In fluid mechanics, topology optimization is used for designing flow passages, connecting predefined inlets and outlets, with optimal performance based on selected criteria. In this article, the continuous adjoint approach to topology optimization in incompressible ducted flows with heat transfer is presented. A variable porosity field, to be determined during the optimization, is the means to define the optimal topology. The objective functions take into account viscous losses and the amount of heat transfer. Turbulent flows are handled using the Spalart-Allmaras model and the proposed adjoint is exact, i.e. the adjoint to the turbulence model equation is formulated and solved, too. This is an important novelty in this article which extends the porosity-based method to account for heat transfer flow problems in turbulent flows. In problems such as the design of manifolds, constraints on the outlet flow direction, rates and mean outlet temperatures are imposed.
FLASH: A finite element computer code for variably saturated flow
Baca, R.G.; Magnuson, S.O.
1992-05-01
A numerical model was developed for use in performance assessment studies at the INEL. The numerical model, referred to as the FLASH computer code, is designed to simulate two-dimensional fluid flow in fractured-porous media. The code is specifically designed to model variably saturated flow in an arid site vadose zone and saturated flow in an unconfined aquifer. In addition, the code also has the capability to simulate heat conduction in the vadose zone. This report presents the following: description of the conceptual frame-work and mathematical theory; derivations of the finite element techniques and algorithms; computational examples that illustrate the capability of the code; and input instructions for the general use of the code. The FLASH computer code is aimed at providing environmental scientists at the INEL with a predictive tool for the subsurface water pathway. This numerical model is expected to be widely used in performance assessments for: (1) the Remedial Investigation/Feasibility Study process and (2) compliance studies required by the US Department of Energy Order 5820.2A.
Boundary Element Microhydrodynamics: Stagnation of flow in protein cavities
NASA Astrophysics Data System (ADS)
Aragon, Sergio; Hahn, David
2007-03-01
A very precise boundary element solution of the exact Stokes flow surface integral equation has been implemented in our Fortan 90 program BEST. In our previous work (Aragon & Hahn, Biophys. J. 2006, 91: 1591-1603; J. Chem. Theory and Comput. 2006, 2: 1416-1428) we obtained very precise values of the tensorial transport properties (translation, rotation, and intrinsic viscosity) for a large set of proteins with a uniform water hydration thickness of 0.11 nm. In this work, we utilize the surface stress distribution thus obtained to evaluate the flow field as a function of distance away from the hydrodynamic surface for a variety of surface features in a dimpled sphere (test case) and for the proteins myoglobin, lysozyme, and human serum albumin. We demonstrate that solvent in small to large pockets on the hydrodynamic surface moves with the protein with distances up to 2 nm for deep pockets regardless of the direction of motion of the protein. On the other hand, the fluid flow pattern on protruding portions of the hydrodynamic surface decays much more rapidly with distance from the surface. The implications of these results with respect to the amount of water of associated with the surface and the rate of transport to active enzymatic sites in stirred solutions is discussed.
NASA Astrophysics Data System (ADS)
Shafii, Mahyar; Basu, Nandita; Craig, James R.; Schiff, Sherry L.; Van Cappellen, Philippe
2017-04-01
Hydrologic models are often tasked with replicating historical hydrographs but may do so without accurately reproducing the internal hydrological functioning of the watershed, including the flow partitioning, which is critical for predicting solute movement through the catchment. Here we propose a novel partitioning-focused calibration technique that utilizes flow-partitioning coefficients developed based on the pioneering work of L'vovich (1979). Our hypothesis is that inclusion of the L'vovich partitioning relations in calibration increases model consistency and parameter identifiability and leads to superior model performance with respect to flow partitioning than using traditional hydrological signatures (e.g., flow duration curve indices) alone. The L'vovich approach partitions the annual precipitation into four components (quick flow, soil wetting, slow flow, and evapotranspiration) and has been shown to work across a range of climatic and landscape settings. A new diagnostic multicriteria model calibration methodology is proposed that first quantifies four calibration measures for watershed functions based on the L'vovich theory, and then utilizes them as calibration criteria. The proposed approach is compared with a traditional hydrologic signature-based calibration for two conceptual bucket models. Results reveal that the proposed approach not only improves flow partitioning in the model compared to signature-based calibration but is also capable of diagnosing flow-partitioning inaccuracy and suggesting relevant model improvements. Furthermore, the proposed partitioning-based calibration approach is shown to increase parameter identifiability. This model calibration approach can be readily applied to other models.
Constrained optimisation in granular network flows: Games with a loaded dice
NASA Astrophysics Data System (ADS)
Lin, Qun; Tordesillas, Antoinette
2013-06-01
Flows in real world networks are rarely the outcome of unconditional random allocations as, say, the roll of a dice. Think, for example, of force transmission through a contact network in a quasistatically deforming granular material. Forces `flow' through this network in a highly conditional manner. How much force is transmitted between two contacting particles is always conditional not only on all the other forces acting between the particles in question but also on those acting on the other particles in the system. Broadly, we are interested in the nature and extent to which flows through a contact network favour certain pathways over others, and how the mechanisms that govern such biased flows for a given imposed loading history determine the future evolution of the contact network. Our first step is to solve a selection of fundamental combinatorial optimisation problems on the contact network from the perspective of force transmission. Here we report on solutions to the Maximum Flow Minimum Cost Problem for a weighted contact network where the weights assigned to the links of the contact network are varied according to their contact types. We found that those pathways through which the maximum flow of force is transmitted, in the direction of the maximum principal stress, at minimum cost - pass through the great majority of the force chains. Although the majority of the contacts in these pathways are elastic, the plastic contacts bear an undue influence on the minimum cost.
A Finite Element Method for Simulation of Compressible Cavitating Flows
NASA Astrophysics Data System (ADS)
Shams, Ehsan; Yang, Fan; Zhang, Yu; Sahni, Onkar; Shephard, Mark; Oberai, Assad
2016-11-01
This work focuses on a novel approach for finite element simulations of multi-phase flows which involve evolving interface with phase change. Modeling problems, such as cavitation, requires addressing multiple challenges, including compressibility of the vapor phase, interface physics caused by mass, momentum and energy fluxes. We have developed a mathematically consistent and robust computational approach to address these problems. We use stabilized finite element methods on unstructured meshes to solve for the compressible Navier-Stokes equations. Arbitrary Lagrangian-Eulerian formulation is used to handle the interface motions. Our method uses a mesh adaptation strategy to preserve the quality of the volumetric mesh, while the interface mesh moves along with the interface. The interface jump conditions are accurately represented using a discontinuous Galerkin method on the conservation laws. Condensation and evaporation rates at the interface are thermodynamically modeled to determine the interface velocity. We will present initial results on bubble cavitation the behavior of an attached cavitation zone in a separated boundary layer. We acknowledge the support from Army Research Office (ARO) under ARO Grant W911NF-14-1-0301.
Simulation of dry granular flows using discrete element methods
NASA Astrophysics Data System (ADS)
Martin, Hugo; Lefebvre, Aline; Maday, Yvon; Mangeney, Anne; Maury, Bertrand; Sainte-Marie, Jacques
2017-04-01
Granular flows are composed of interacting particles (for instance sand grains). While natural flow simulations at the field scale are generally based on continuum models, discrete element methods are very useful to get insight into the detailed contact interactions between the particles involved. We shall consider here both well known molecular dynamics (MD) and contact dynamics (CD) methods to simulate granular particle interaction. The difference between these methods is the linearisation of contact forces in MD. We are interested to compare these methods, and especially the effects of the linearisation in simulations. In the present work, we introduce a new rigid bodies model at the scale of the particles and its resolution by contact dynamics. The interesting aspect of our CD method is to treat the contacts in all the material system in one step without any iterative process required when the contacts are dealt with one after the other. All contacts are calculated here at the same time in just one iteration and the normal and tangential constraints are treated simultaneously. The present model follows from a convex optimization problem presented in [1] by B. Maury in which we add a frictional behaviour to the contact law between the particles. To analyse the behaviour of this model, we compare our results to analytical solutions when we can compute them and otherwise to simulations with molecular dynamics method. [1] A time-stepping scheme for inelastic collisions. Numerical handling of the nonoverlapping constraint, B. Maury, Numerische Mathematik, 17 january 2006.
An approach to the constrained design of natural laminar flow airfoils
NASA Technical Reports Server (NTRS)
Green, Bradford Earl
1995-01-01
A design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. After obtaining the initial airfoil's pressure distribution at the design lift coefficient using an Euler solver coupled with an integml turbulent boundary layer method, the calculations from a laminar boundary layer solver are used by a stability analysis code to obtain estimates of the transition location (using N-Factors) for the starting airfoil. A new design method then calculates a target pressure distribution that will increase the larninar flow toward the desired amounl An airfoil design method is then iteratively used to design an airfoil that possesses that target pressure distribution. The new airfoil's boundary layer stability characteristics are determined, and this iterative process continues until an airfoil is designed that meets the laminar flow requirement and as many of the other constraints as possible.
Adaptive entropy-constrained discontinuous Galerkin method for simulation of turbulent flows
NASA Astrophysics Data System (ADS)
Lv, Yu; Ihme, Matthias
2015-11-01
A robust and adaptive computational framework will be presented for high-fidelity simulations of turbulent flows based on the discontinuous Galerkin (DG) scheme. For this, an entropy-residual based adaptation indicator is proposed to enable adaptation in polynomial and physical space. The performance and generality of this entropy-residual indicator is evaluated through direct comparisons with classical indicators. In addition, a dynamic load balancing procedure is developed to improve computational efficiency. The adaptive framework is tested by considering a series of turbulent test cases, which include homogeneous isotropic turbulence, channel flow and flow-over-a-cylinder. The accuracy, performance and scalability are assessed, and the benefit of this adaptive high-order method is discussed. The funding from NSF CAREER award is greatly acknowledged.
A Method for the Constrained Design of Natural Laminar Flow Airfoils
NASA Technical Reports Server (NTRS)
Green, Bradford E.; Whitesides, John L.; Campbell, Richard L.; Mineck, Raymond E.
1996-01-01
A fully automated iterative design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. Drag reductions have been realized using the design method over a range of Mach numbers, Reynolds numbers and airfoil thicknesses. The thrusts of the method are its ability to calculate a target N-Factor distribution that forces the flow to undergo transition at the desired location; the target-pressure-N-Factor relationship that is used to reduce the N-Factors in order to prolong transition; and its ability to design airfoils to meet lift, pitching moment, thickness and leading-edge radius constraints while also being able to meet the natural laminar flow constraint. The method uses several existing CFD codes and can design a new airfoil in only a few days using a Silicon Graphics IRIS workstation.
An Approach to the Constrained Design of Natural Laminar Flow Airfoils
NASA Technical Reports Server (NTRS)
Green, Bradford E.
1997-01-01
A design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. After obtaining the initial airfoil's pressure distribution at the design lift coefficient using an Euler solver coupled with an integral turbulent boundary layer method, the calculations from a laminar boundary layer solver are used by a stability analysis code to obtain estimates of the transition location (using N-Factors) for the starting airfoil. A new design method then calculates a target pressure distribution that will increase the laminar flow toward the desired amount. An airfoil design method is then iteratively used to design an airfoil that possesses that target pressure distribution. The new airfoil's boundary layer stability characteristics are determined, and this iterative process continues until an airfoil is designed that meets the laminar flow requirement and as many of the other constraints as possible.
NASA Astrophysics Data System (ADS)
Loye, Alexandre; Jaboyedoff, Michel; Theule, Joshua Isaac; Liébault, Frédéric
2016-06-01
Debris flows have been recognized to be linked to the amounts of material temporarily stored in torrent channels. Hence, sediment supply and storage changes from low-order channels of the Manival catchment, a small tributary valley with an active torrent system located exclusively in sedimentary rocks of the Chartreuse Massif (French Alps), were surveyed periodically for 16 months using terrestrial laser scanning (TLS) to study the coupling between sediment dynamics and torrent responses in terms of debris flow events, which occurred twice during the monitoring period. Sediment transfer in the main torrent was monitored with cross-section surveys. Sediment budgets were generated seasonally using sequential TLS data differencing and morphological extrapolations. Debris production depends strongly on rockfall occurring during the winter-early spring season, following a power law distribution for volumes of rockfall events above 0.1 m3, while hillslope sediment reworking dominates debris recharge in spring and autumn, which shows effective hillslope-channel coupling. The occurrence of both debris flow events that occurred during the monitoring was linked to recharge from previous debris pulses coming from the hillside and from bedload transfer. Headwater debris sources display an ambiguous behaviour in sediment transfer: low geomorphic activity occurred in the production zone, despite rainstorms inducing debris flows in the torrent; still, a general reactivation of sediment transport in headwater channels was observed in autumn without new debris supply, suggesting that the stored debris was not exhausted. The seasonal cycle of sediment yield seems to depend not only on debris supply and runoff (flow capacity) but also on geomorphic conditions that destabilize remnant debris stocks. This study shows that monitoring the changes within a torrent's in-channel storage and its debris supply can improve knowledge on recharge thresholds leading to debris flow.
Mantle Flow Across the Baikal Rift Constrained With Integrated Seismic Measurements
NASA Astrophysics Data System (ADS)
Lebedev, S.; Meier, T.; van der Hilst, R. D.
2005-12-01
The Baikal Rift is located at the boundary of the stable Siberian Craton and deforming central Mongolia. The origin of the late Cenozoic rifting and volcanism are debated, as is the mantle flow beneath the rift zone. Here we combine new evidence from azimuthally-anisotropic upper-mantle tomography and from a radially-anisotropic inversion of interstation surface-wave dispersion curves with previously published shear-wave-splitting measurements of azimuthal anisotropy across the rift (Gao et al. 1994). While our tomographic model maps isotropic and anisotropic shear-velocity heterogeneity globally, the inversion of interstation phase-velocity measurements produces a single, radially-anisotropic, shear-velocity profile that averages from the rift to 500 km SE of it. The precision and the broad band (8-340 s) of the Rayleigh and Love wave curves ensures high accuracy of the profile. Tomography and shear-wave splitting both give a NW-SE fast direction (perpendicular to the rift) in the vicinity of the rift, changing towards W-E a few hundred kilometers from it. Previously, this has been interpreted as evidence for mantle flow similar to that beneath mid-ocean ridges, with deeper vertical flow directly beneath the rift also proposed. Our radially anisotropic profile, however, shows that while strong anisotropy with SH waves faster than SV waves is present in the thin lithosphere and upper asthenosphere beneath and SE of the rift, no anisotropy is required below 110 km. The tomographic model shows thick cratonic lithosphere north of the rift. These observations suggest that instead of a flow diverging from the rift axis in NW and SE directions, the most likely pattern is the asthenospheric flow in SE direction from beneath the Siberian lithosphere and across the rift. Possible driving forces of the flow are large-scale lithospheric deformation in East Asia and the draining of asthenosphere at W-Pacific subduction zones; a plume beneath the Siberian craton also cannot be
Constraining Paleo-Hydrologic Flow Fields from Iron Oxide Cementation Patterns
NASA Astrophysics Data System (ADS)
Wang, Y.; Chan, M. A.
2013-12-01
Fine-grained sandstone in Mesozoic sedimentary red beds of the Colorado Plateau (southwestern United States) contain iron oxides cements (e.g., hematite and goethite) that display spectacular pattern formation, including evenly spaced nodule formation and banding with nested scales spanning about two to three orders of magnitude (Fig. 1). These nodules are commonly referred to as concretions, which are cemented mineral masses. The size of concretions typically ranges from millimeters to centimeters, while the spacing of bands ranges from millimeters to sub-meters. Spatial transition of one pattern to another or one pattern superimposed on another is also observed. Such patterns may embed important information about paleo-environments of sediment diagenesis, especially regarding the fluid migration and geochemical conditions involved. Field evidence indicates that the formation of iron oxide bands in sandstone seems closely related to groundwater flows. Here we show that such patterns can autonomously emerge from a previously unrecognized Ostwald ripening mechanism and they capture rich information regarding ancient chemical and hydrologic environments. Using a linear stability analysis, we demonstrate that the pattern transition from nodules to bands results from symmetry breaking triggered by groundwater advection. Nodules tend to develop under nearly stagnant hydrologic conditions, while repetitive bands tend to form in the presence of persistent water flows. The banding is formed perpendicularly to the flow direction, and the flow rate is expected to be proportional to the square of banding spacing. Therefore, careful mapping of cementation patterns and banding spacing over rock outcrops will allow us to reconstruct a detail map of water flow field for a sandstone aquifer. Concretion nodules formed in Jurassic Navajo Sandstone have been proposed as a terrestrial analogue to hematite spherules detected by the rover Opportunity at the Meridiani Planum site on the
NASA Astrophysics Data System (ADS)
Cunningham, Andrew J.; Frank, Adam; Varnière, Peggy; Mitran, Sorin; Jones, Thomas W.
2009-06-01
A description is given of the algorithms implemented in the AstroBEAR adaptive mesh-refinement code for ideal magnetohydrodynamics. The code provides several high-resolution shock-capturing schemes which are constructed to maintain conserved quantities of the flow in a finite-volume sense. Divergence-free magnetic field topologies are maintained to machine precision by collating the components of the magnetic field on a cell-interface staggered grid and utilizing the constrained transport approach for integrating the induction equations. The maintenance of magnetic field topologies on adaptive grids is achieved using prolongation and restriction operators which preserve the divergence and curl of the magnetic field across collocated grids of different resolutions. The robustness and correctness of the code is demonstrated by comparing the numerical solution of various tests with analytical solutions or previously published numerical solutions obtained by other codes.
Bravo, H.R.; Jiang, F.; Hunt, R.J.
2002-01-01
Parameter estimation is a powerful way to calibrate models. While head data alone are often insufficient to estimate unique parameters due to model nonuniqueness, flow-and-heat-transport modeling can constrain estimation and allow simultaneous estimation of boundary fluxes and hydraulic conductivity. In this work, synthetic and field models that did not converge when head data were used did converge when head and temperature were used. Furthermore, frequency domain analyses of head and temperature data allowed selection of appropriate modeling timescales. Inflows in the Wilton, Wisconsin, wetlands could be estimated over periods such as a growing season and over periods of a few days when heads were nearly steady and groundwater temperature varied during the day. While this methodology is computationally more demanding than traditional head calibration, the results gained are unobtainable using the traditional approach. These results suggest that temperature can efficiently supplement head data in systems where accurate flux calibration targets are unavailable.
Rands, Chris M; Meader, Stephen; Ponting, Chris P; Lunter, Gerton
2014-07-01
Ten years on from the finishing of the human reference genome sequence, it remains unclear what fraction of the human genome confers function, where this sequence resides, and how much is shared with other mammalian species. When addressing these questions, functional sequence has often been equated with pan-mammalian conserved sequence. However, functional elements that are short-lived, including those contributing to species-specific biology, will not leave a footprint of long-lasting negative selection. Here, we address these issues by identifying and characterising sequence that has been constrained with respect to insertions and deletions for pairs of eutherian genomes over a range of divergences. Within noncoding sequence, we find increasing amounts of mutually constrained sequence as species pairs become more closely related, indicating that noncoding constrained sequence turns over rapidly. We estimate that half of present-day noncoding constrained sequence has been gained or lost in approximately the last 130 million years (half-life in units of divergence time, d1/2 = 0.25-0.31). While enriched with ENCODE biochemical annotations, much of the short-lived constrained sequences we identify are not detected by models optimized for wider pan-mammalian conservation. Constrained DNase 1 hypersensitivity sites, promoters and untranslated regions have been more evolutionarily stable than long noncoding RNA loci which have turned over especially rapidly. By contrast, protein coding sequence has been highly stable, with an estimated half-life of over a billion years (d1/2 = 2.1-5.0). From extrapolations we estimate that 8.2% (7.1-9.2%) of the human genome is presently subject to negative selection and thus is likely to be functional, while only 2.2% has maintained constraint in both human and mouse since these species diverged. These results reveal that the evolutionary history of the human genome has been highly dynamic, particularly for its noncoding yet
Element flows associated with marine shore mine tailings deposits.
Dold, Bernhard
2006-02-01
From 1938 until 1975, flotation tailings from the Potrerillos--El Salvador mining district (porphyry copper deposits) were discharged into the El Salado valley and transported in suspension to the sea at Chaliaral Bay, Atacama Desert, northern Chile. Over 220 Mt of tailings, averaging 0.8 +/- 0.25 wt % of pyrite, were deposited into the bay, resulting in over a 1 kilometer seaward displacement of the shoreline and an estimated 10-15 m thick tailings accumulation covering a approximately 4 km2 surface area. The Chaniaral case was classified by the United Nations Environmental Programme (UNEP) in 1983 as one of the most serious cases of marine contamination in the Pacific area. Since 1975, the tailings have been exposed to oxidation, resulting in a 70-188 cm thick low-pH (2.6-4) oxidation zone at the top with liberation of divalent metal cations, such as Cu2+, Ni2+, and Zn2+ (up to 2265 mg/L, 18.1 mg/L, and 20.3 mg/ L, respectively). Evaporation-induced transport capillarity led to metal enrichment atthe tailings surface (e.g. up to 2.4% Cu) in the form of secondary chlorides and/or sulfates (dominated by eriochalcite [CuCl.H2O] and halite). These, mainly water-soluble, secondary minerals were exposed to eolian transport in the direction of the Village of Chañaral by the predominant W-SW winds. Two element-flow directions (toward the tailings surface, via capillarity, and toward the sea) and two element groups with different geochemical behaviors (cations such as Cu, Zn, Ni, and oxyanions such as As and Mo) could be distinguished. It can be postulated, that the sea is mainly affected by the following: As, Mo, Cu, and Zn contamination, which were liberated from the oxidation zone from the tailings and mobilized through the tidal cycle, and by Cu and Zn from the subsurface waters flowing in the El Salado valley (up to 19 mg/L and 12 mg/L Zn, respectively), transported as chloro complexes at neutral pH.
Portegies, J. M.; Fick, R. H. J.; Sanguinetti, G. R.; Meesters, S. P. L.; Girard, G.; Duits, R.
2015-01-01
We propose two strategies to improve the quality of tractography results computed from diffusion weighted magnetic resonance imaging (DW-MRI) data. Both methods are based on the same PDE framework, defined in the coupled space of positions and orientations, associated with a stochastic process describing the enhancement of elongated structures while preserving crossing structures. In the first method we use the enhancement PDE for contextual regularization of a fiber orientation distribution (FOD) that is obtained on individual voxels from high angular resolution diffusion imaging (HARDI) data via constrained spherical deconvolution (CSD). Thereby we improve the FOD as input for subsequent tractography. Secondly, we introduce the fiber to bundle coherence (FBC), a measure for quantification of fiber alignment. The FBC is computed from a tractography result using the same PDE framework and provides a criterion for removing the spurious fibers. We validate the proposed combination of CSD and enhancement on phantom data and on human data, acquired with different scanning protocols. On the phantom data we find that PDE enhancements improve both local metrics and global metrics of tractography results, compared to CSD without enhancements. On the human data we show that the enhancements allow for a better reconstruction of crossing fiber bundles and they reduce the variability of the tractography output with respect to the acquisition parameters. Finally, we show that both the enhancement of the FODs and the use of the FBC measure on the tractography improve the stability with respect to different stochastic realizations of probabilistic tractography. This is shown in a clinical application: the reconstruction of the optic radiation for epilepsy surgery planning. PMID:26465600
NASA Astrophysics Data System (ADS)
Gharamti, M. E.; Kadoura, A.; Valstar, J.; Sun, S.; Hoteit, I.
2014-03-01
Isothermal compositional flow models require coupling transient compressible flows and advective transport systems of various chemical species in subsurface porous media. Building such numerical models is quite challenging and may be subject to many sources of uncertainties because of possible incomplete representation of some geological parameters that characterize the system's processes. Advanced data assimilation methods, such as the ensemble Kalman filter (EnKF), can be used to calibrate these models by incorporating available data. In this work, we consider the problem of estimating reservoir permeability using information about phase pressure as well as the chemical properties of fluid components. We carry out state-parameter estimation experiments using joint and dual updating schemes in the context of the EnKF with a two-dimensional single-phase compositional flow model (CFM). Quantitative and statistical analyses are performed to evaluate and compare the performance of the assimilation schemes. Our results indicate that including chemical composition data significantly enhances the accuracy of the permeability estimates. In addition, composition data provide more information to estimate system states and parameters than do standard pressure data. The dual state-parameter estimation scheme provides about 10% more accurate permeability estimates on average than the joint scheme when implemented with the same ensemble members, at the cost of twice more forward model integrations. At similar computational cost, the dual approach becomes only beneficial after using large enough ensembles.
Torres, Marta
2014-01-31
In November 2012, Oregon State University initiated the project entitled: Application of Crunch-Flow routines to constrain present and past carbon fluxes at gas-hydrate bearing sites. Within this project we developed Crunch-Flow based modeling modules that include important biogeochemical processes that need to be considered in gas hydrate environments. Our modules were applied to quantify carbon cycling in present and past systems, using data collected during several DOE-supported drilling expeditions, which include the Cascadia margin in US, Ulleung Basin in South Korea, and several sites drilled offshore India on the Bay of Bengal and Andaman Sea. Specifically, we completed modeling efforts that: 1) Reproduce the compositional and isotopic profiles observed at the eight drilled sites in the Ulleung Basin that constrain and contrast the carbon cycling pathways at chimney (high methane flux) and non-chimney sites (low methane, advective systems); 2) Simulate the Ba record in the sediments to quantify the past dynamics of methane flux in the southern Hydrate Ridge, Cascadia margin; and 3) Provide quantitative estimates of the thickness of individual mass transport deposits (MTDs), time elapsed after the MTD event, rate of sulfate reduction in the MTD, and time required to reach a new steady state at several sites drilled in the Krishna-Godavari (K-G) Basin off India. In addition we developed a hybrid model scheme by coupling a home-made MATLAB code with CrunchFlow to address the methane transport and chloride enrichment at the Ulleung Basins chimney sites, and contributed the modeling component to a study focusing on pore-scale controls on gas hydrate distribution in sediments from the Andaman Sea. These efforts resulted in two manuscripts currently under review, and contributed the modeling component of another pare, also under review. Lessons learned from these efforts are the basis of a mini-workshop to be held at Oregon State University (Feb 2014) to instruct
NASA Technical Reports Server (NTRS)
Morgan, K.; Thornton, E. A.
1982-01-01
The current capability of the finite element method for solving problems of viscous flow is reviewed. Much work has been directed to the simulation of incompressible flows and the relevant features are described. The methods available for, and the problems associated with, the finite element solution of high speed viscous compressible flows are analyzed. A plan for developing finite element research in this area with experimental support is presented.
Upgraded viscous flow analysis of multi-element airfoils
NASA Technical Reports Server (NTRS)
Brune, G. W.; Manke, J. W.
1979-01-01
A description of an improved version of the NASA/Lockheed multi-element airfoil analysis computer program is presented. The improvements include several major modifications of the aerodynamic model as well as substantial changes of the computer code. The modifications of the aerodynamic model comprise the representation of the boundary layer and wake displacement effects with an equivalent source distribution, the prediction of wake parameters with Green's lag-entrainment method, the calculation of turbulent boundary layer separation with the method of Nash and Hicks, the estimation of the onset of confluent boundary layer separation with a modified form of Goradia's method, and the prediction of profile drag with the formula of Squire and Young. The modifications of the computer program for which the structured approach to computer software development was employed are also described. Important aspects of the structured program development such as the functional decomposition of the aerodynamic theory and its numerical implementation, the analysis of the data flow within the code, and the application of a pseudo code are discussed.
NASA Astrophysics Data System (ADS)
Tarduno, J. A.; Bono, R.
2011-12-01
A wide range of investigations including plate circuit analyses, comparisons of the age progression of coeval hotspots on the Pacific plate and geodynamic modeling are consistent with paleomagnetic results that indicate motion of hotspots in Earth's mantle during Late Cretaceous to Paleogene times, with important changes in the rate of motion near 50 Ma. In the Pacific, the change has been hypothesized to reflect plume dynamics and hotspot-ridge capture; in the Cretaceous the two long-lived Pacific hotspots with well-defined age progressive tracks (Hawaii and Louisville) were near ridges that subsequently waned. In the case of the Hawaiian hotspot, the ridge in question appears to have become extinct close to the time of the bend in the hotspot track. Testing whether a deeper component of Pacific mantle flow also changed near 50 Ma requires a higher resolution investigation of reference frames for absolute plate motion. Here we use select paleomagnetic data prior to and after 50 Ma to test prior inferences about absolute plate motion changes and polar wander, and use these analyses to parse components of mantle flow.
A multi-agent technique for contingency constrained optimal power flows
Talukdar, S.; Ramesh, V.C. . Engineering Design Research Center)
1994-05-01
This paper does three things. First, it proposes that each critical contingency in a power system be represented by a correction time'' (the time required to eliminate the violations produced by the contingency), rather than by a set of hard constraints. Second, it adds these correction times to an optimal power flow and decomposes the resulting problem into a number of smaller optimization problems. Third, it proposes a multiagent technique for solving the smaller problems in parallel. The agents encapsulate traditional optimization algorithms as well as a new algorithm, called the voyager, that generates starting points for the traditional algorithms. All the agents communicate asynchronously, meaning that they can work in parallel without ever interrupting or delaying one another. The resulting scheme has potential for handling power system contingencies and other difficult global optimization problems.
The Anisotropic Structure of South China Sea: Using OBS Data to Constrain Mantle Flow
NASA Astrophysics Data System (ADS)
Li, L.; Xue, M.; Yang, T.; Liu, C.; Hua, Q.; Xia, S.; Huang, H.; Le, B. M.; Huo, D.; Pan, M.
2015-12-01
The dynamic mechanism of the formation of South China Sea (SCS) has been debated for decades. The anisotropic structure can provide useful insight into the complex evolution of SCS by indicating its mantle flow direction and strength. In this study, we employ shear wave splitting methods on two half-year seismic data collected from 10 and 6 passive source Ocean Bottom Seismometers (OBS) respectively. These OBSs were deployed along both sides of the extinct ridge in the central basin of SCS by Tongji University in 2012 and 2013 respectively, which were then successfully recovered in 2013 and 2015 respectively. Through processing and inspecting the global and regional earthquakes (with local events being processing) of the 2012 dataset, measurements are made for 2 global events and 24 regional events at 5 OBSs using the tangential energy minimization, the smallest eigenvalue minimization, as well as the correlation methods. We also implement cluster analysis on the splitting results obtained for different time windows as well as filtered at different frequency bands. For teleseismic core phases like SKS and PKS, we find the fast polarization direction beneath the central basin is approximately NE-SW, nearly parallel to the extinct ridge in the central basin of SCS. Whereas for regional events, the splitting analysis on S, PS and ScS phases shows much more complicated fast directions as the ray path varies for different phases. The fast directions observed can be divided into three groups: (1) for the events from the Eurasia plate, a gradual rotation of the fast polarization direction from NNE-SSW to NEE-SWW along the path from the inner Eurasia plate to the central SCS is observed, implying the mantle flow is controlled by the India-Eurasia collision; (2) for the events located at the junction of Pacific plate and Philippine plate, the dominant fast direction is NW-SE, almost perpendicular to Ryukyu Trench as well as sub-parallel to the absolute direction of
Microfilament Orientation Constrains Vesicle Flow and Spatial Distribution in Growing Pollen Tubes
Kroeger, Jens H.; Daher, Firas Bou; Grant, Martin; Geitmann, Anja
2009-01-01
Abstract The dynamics of cellular organelles reveals important information about their functioning. The spatio-temporal movement patterns of vesicles in growing pollen tubes are controlled by the actin cytoskeleton. Vesicle flow is crucial for morphogenesis in these cells as it ensures targeted delivery of cell wall polysaccharides. Remarkably, the target region does not contain much filamentous actin. We model the vesicular trafficking in this area using as boundary conditions the expanding cell wall and the actin array forming the apical actin fringe. The shape of the fringe was obtained by imposing a steady state and constant polymerization rate of the actin filaments. Letting vesicle flux into and out of the apical region be determined by the orientation of the actin microfilaments and by exocytosis was sufficient to generate a flux that corresponds in magnitude and orientation to that observed experimentally. This model explains how the cytoplasmic streaming pattern in the apical region of the pollen tube can be generated without the presence of actin microfilaments. PMID:19804712
Finite element analysis of high speed compressible flows using mesh refinement/movement procedures
NASA Technical Reports Server (NTRS)
Ramakrishnan, R.; Thornton, E. A.; Bey, K. S.
1989-01-01
An adaptive mesh refinement procedure for analyzing high-speed inviscid and viscous compressible flows is described. The adaptation procedure which uses both quadrilateral and triangular elements is implemented with an explicit finite element formulation. Elements in regions of strong and weak gradients are refined or coarsened based on inviscid and viscous indicators. Nodal locations are also adaptively moved to better resolve flow features. The effectiveness of the finite element procedure is demonstrated by modeling flows with complex shock structure and viscous-inviscid interactions. Numerical results are compared with experimental data.
Numerical simulation of the non-Newtonian fluid flow using the indirect boundary element method
NASA Astrophysics Data System (ADS)
Bessonova, M. P.; Yakutenok, V. A.
2017-02-01
The indirect boundary element method is formulated for a two-dimensional Stokes flow with the moving boundary when gravity force aids the flow. The governing equations of low Reynolds flow are formulated. The numerical technique is described. Two regimes of the fluid flow depending on the Stokes number value were detected: the regime of full filling and the jet flow regime. The comparison of obtained results with data of other authors is presented.
Numerical computation of transonic flows by finite-element and finite-difference methods
NASA Technical Reports Server (NTRS)
Hafez, M. M.; Wellford, L. C.; Merkle, C. L.; Murman, E. M.
1978-01-01
Studies on applications of the finite element approach to transonic flow calculations are reported. Different discretization techniques of the differential equations and boundary conditions are compared. Finite element analogs of Murman's mixed type finite difference operators for small disturbance formulations were constructed and the time dependent approach (using finite differences in time and finite elements in space) was examined.
A finite element method for the computation of transonic flow past airfoils
NASA Technical Reports Server (NTRS)
Eberle, A.
1980-01-01
A finite element method for the computation of the transonic flow with shocks past airfoils is presented using the artificial viscosity concept for the local supersonic regime. Generally, the classic element types do not meet the accuracy requirements of advanced numerical aerodynamics requiring special attention to the choice of an appropriate element. A series of computed pressure distributions exhibits the usefulness of the method.
Preece, D.S. Perkins, E.D.
1999-02-10
Techniques for modeling oil well sand production have been developed using the formulations for superquadric discrete elements and Darcy fluid flow. Discrete element models are generated using the new technique of particle cloning. Discrete element sources and sinks allow simulation of sand production from the initial state through the transition to an equilibrium state where particles are created and removed at the same rate.
Replacement of fluid-filter elements without interruption of flow
NASA Technical Reports Server (NTRS)
Kotler, R. A.; Ward, J. B.
1969-01-01
Gatling-type filter assembly, preloaded with several filter elements enables filter replacement without breaking into the operative fluid system. When the filter element becomes contaminated, a unit inner subassembly is rotated 60 degrees to position a clean filter in the line.
Schneider, Robert J; Perrin, Douglas P; Vasilyev, Nikolay V; Marx, Gerald R; del Nido, Pedro J; Howe, Robert D
2012-02-01
Measurement of the shape and motion of the mitral valve annulus has proven useful in a number of applications, including pathology diagnosis and mitral valve modeling. Current methods to delineate the annulus from four-dimensional (4D) ultrasound, however, either require extensive overhead or user-interaction, become inaccurate as they accumulate tracking error, or they do not account for annular shape or motion. This paper presents a new 4D annulus segmentation method to account for these deficiencies. The method builds on a previously published three-dimensional (3D) annulus segmentation algorithm that accurately and robustly segments the mitral annulus in a frame with a closed valve. In the 4D method, a valve state predictor determines when the valve is closed. Subsequently, the 3D annulus segmentation algorithm finds the annulus in those frames. For frames with an open valve, a constrained optical flow algorithm is used to the track the annulus. The only inputs to the algorithm are the selection of one frame with a closed valve and one user-specified point near the valve, neither of which needs to be precise. The accuracy of the tracking method is shown by comparing the tracking results to manual segmentations made by a group of experts, where an average RMS difference of 1.67±0.63mm was found across 30 tracked frames.
NASA Astrophysics Data System (ADS)
Hoyer, Lauren; Watkeys, Michael K.
2015-08-01
Shape ellipsoids that define the petrofabrics of plagioclase in Jurassic Karoo dolerite sills in KwaZulu-Natal, South Africa are rigorously constrained using the long axis lengths of plagioclase crystals and ellipse incompatibility. This has been undertaken in order to determine the most effective technique to determine petrofabrics when using the SPO-2003 programme (Launeau and Robin, 2005). The technique of segmenting an image for analysis is scrutinised and as a process is found redundant. A grain size threshold is defined to assist with the varying grain sizes observed within and between sills. Where grains exceed the 0.2 mm size threshold, images should be acquired at a high magnification (i.e., 10 × magnification). Petrofabrics are determined using the foliation and the lineation of the ellipsoid as defined by the maximum and minimum principal axes (respectively) of the resultant ellipsoid. Samples with strongly prolate fabrics are isolated allowing further constraint on the petrofabric to be made. Once the efficacy of the petrofabric determination process has been determined, the resultant foliations (and lineations) then elucidate the most accurate petrofabric attainable. The most accurate petrofabrics will be determined by using the correct magnification when the images are obtained and to run the analyses without segmenting the image. The fabrics of the upper and lower contacts of the Karoo dolerite sills are analysed in detail using these techniques and the fabrics are used as a proxy for magma flow.
Rands, Chris M.; Meader, Stephen; Ponting, Chris P.; Lunter, Gerton
2014-01-01
Ten years on from the finishing of the human reference genome sequence, it remains unclear what fraction of the human genome confers function, where this sequence resides, and how much is shared with other mammalian species. When addressing these questions, functional sequence has often been equated with pan-mammalian conserved sequence. However, functional elements that are short-lived, including those contributing to species-specific biology, will not leave a footprint of long-lasting negative selection. Here, we address these issues by identifying and characterising sequence that has been constrained with respect to insertions and deletions for pairs of eutherian genomes over a range of divergences. Within noncoding sequence, we find increasing amounts of mutually constrained sequence as species pairs become more closely related, indicating that noncoding constrained sequence turns over rapidly. We estimate that half of present-day noncoding constrained sequence has been gained or lost in approximately the last 130 million years (half-life in units of divergence time, d1/2 = 0.25–0.31). While enriched with ENCODE biochemical annotations, much of the short-lived constrained sequences we identify are not detected by models optimized for wider pan-mammalian conservation. Constrained DNase 1 hypersensitivity sites, promoters and untranslated regions have been more evolutionarily stable than long noncoding RNA loci which have turned over especially rapidly. By contrast, protein coding sequence has been highly stable, with an estimated half-life of over a billion years (d1/2 = 2.1–5.0). From extrapolations we estimate that 8.2% (7.1–9.2%) of the human genome is presently subject to negative selection and thus is likely to be functional, while only 2.2% has maintained constraint in both human and mouse since these species diverged. These results reveal that the evolutionary history of the human genome has been highly dynamic, particularly for its
Cellular Structures in the Flow Over the Flap of a Two-Element Wing
NASA Technical Reports Server (NTRS)
Yon, Steven A.; Katz, Joseph
1997-01-01
Flow visualization information and time dependent pressure coefficients were recorded for the flow over a two-element wing. The investigation focused on the stall onset; particularly at a condition where the flow is attached on the main element but separated on the flap. At this condition, spanwise separation cells were visible in the flow over the flap, and time dependent pressure data was measured along the centerline of the separation cell. The flow visualizations indicated that the spanwise occurrence of the separation cells depends on the flap (and not wing) aspect ratio.
Solving incompressible flow problems with parallel spectral element methods
Ma, Hong
1994-10-01
Parallel spectral element models are built for the Navier-Stokes equations and the shallow water equations with nonstaggered grid formulations. The optimized computational efficiency of these parallel spectral element models comes not only from the exponential convergence of their numerical solutions, but also from their efficient usage of the powerful vector-processing units of the latest parallel architectures. Furthermore, the communication cost of the spectral element model is lower than that of the h-type finite element model, partly because many fewer redundant nodal values have to be stored. The nonstaggered grid formulations perform well in iterative procedures which are highly in parallel. Implementations of these models are carried out on the Connection Machine systems. The present work shows that the high-order domain decomposition methods can be efficiently applied in a data parallel programming environment.
NASA Astrophysics Data System (ADS)
Klein-BenDavid, Ofra; Pearson, D. Graham; Nowell, Geoff M.; Ottley, Chris; McNeill, John C. R.; Cartigny, Pierre
2010-01-01
Sub-micrometer inclusions in diamonds carry high-density fluids (HDF) from which the host diamonds have precipitated. The chemistry of these fluids is our best opportunity of characterizing the diamond-forming environment. The trace element patterns of diamond fluids vary within a limited range and are similar to those of carbonatitic/kimberlitic melts that originate from beneath the lithospheric mantle. A convecting mantle origin for the fluid is also implied by C isotopic compositions and by a preliminary Sr isotopic study (Akagi, T., Masuda, A., 1988. Isotopic and elemental evidence for a relationship between kimberlite and Zaire cubic diamonds. Nature 336, 665-667.). Nevertheless, the major element chemistry of HDFs is very different from that of kimberlites and carbonatites, varying widely and being characterized by extreme K enrichment (up to ˜ 39 wt.% on a water and carbonate free basis) and high volatile contents. The broad spectrum of major element compositions in diamond-forming fluids has been related to fluid-rock interaction and to immiscibility processes. Elemental signatures can be easily modified by a variety of mantle processes whereas radiogenic isotopes give a clear fingerprint of the time-integrated evolution of the fluid source region. Here we present the results of the first multi radiogenic-isotope (Sr, Nd, Pb) and trace element study on fluid-rich diamonds, implemented using a newly developed off-line laser sampling technique. The data are combined with N and C isotope analysis of the diamond matrix to better understand the possible sources of fluid involved in the formation of these diamonds. Sr isotope ratios vary significantly within single diamonds. The highly varied but unsupported Sr isotope ratios cannot be explained by immiscibility processes or fluid-mineral elemental fractionations occurring at the time of diamond growth. Our results demonstrate the clear involvement of a mixed fluid, with one component originating from ancient
Khashan, S A; Alazzam, A; Furlani, E P
2014-06-16
A microfluidic design is proposed for realizing greatly enhanced separation of magnetically-labeled bioparticles using integrated soft-magnetic elements. The elements are fixed and intersect the carrier fluid (flow-invasive) with their length transverse to the flow. They are magnetized using a bias field to produce a particle capture force. Multiple stair-step elements are used to provide efficient capture throughout the entire flow channel. This is in contrast to conventional systems wherein the elements are integrated into the walls of the channel, which restricts efficient capture to limited regions of the channel due to the short range nature of the magnetic force. This severely limits the channel size and hence throughput. Flow-invasive elements overcome this limitation and enable microfluidic bioseparation systems with superior scalability. This enhanced functionality is quantified for the first time using a computational model that accounts for the dominant mechanisms of particle transport including fully-coupled particle-fluid momentum transfer.
Poteet, Charles A.; Whittet, Douglas C. B.; Draine, Bruce T.
2015-03-10
We investigate the composition of interstellar grains along the line of sight toward ζ Ophiuchi, a well-studied environment near the diffuse-dense cloud transition. A spectral decomposition analysis of the solid-state absorbers is performed using archival spectroscopic observations from the Spitzer Space Telescope and Infrared Space Observatory. We find strong evidence for the presence of sub-micron-sized amorphous silicate grains, principally comprised of olivine-like composition, with no convincing evidence of H{sub 2}O ice mantles. However, tentative evidence for thick H{sub 2}O ice mantles on large (a ≈ 2.8 μm) grains is presented. Solid-state abundances of elemental Mg, Si, Fe, and O are inferred from our analysis and compared to standard reference abundances. We find that nearly all of the Mg and Si atoms along the line of sight reside in amorphous silicate grains, while a substantial fraction of the elemental Fe resides in compounds other than silicates. Moreover, we find that the total abundance of elemental O is largely inconsistent with the adopted reference abundances, indicating that as much as ∼156 ppm of interstellar O is missing along the line of sight. After taking into account additional limits on the abundance of elemental O in other O-bearing solids, we conclude that any missing reservoir of elemental O must reside on large grains that are nearly opaque to infrared radiation.
Flow Applications of the Least Squares Finite Element Method
NASA Technical Reports Server (NTRS)
Jiang, Bo-Nan
1998-01-01
The main thrust of the effort has been towards the development, analysis and implementation of the least-squares finite element method (LSFEM) for fluid dynamics and electromagnetics applications. In the past year, there were four major accomplishments: 1) special treatments in computational fluid dynamics and computational electromagnetics, such as upwinding, numerical dissipation, staggered grid, non-equal order elements, operator splitting and preconditioning, edge elements, and vector potential are unnecessary; 2) the analysis of the LSFEM for most partial differential equations can be based on the bounded inverse theorem; 3) the finite difference and finite volume algorithms solve only two Maxwell equations and ignore the divergence equations; and 4) the first numerical simulation of three-dimensional Marangoni-Benard convection was performed using the LSFEM.
Flow Applications of the Least Squares Finite Element Method
NASA Technical Reports Server (NTRS)
Jiang, Bo-Nan
1998-01-01
The main thrust of the effort has been towards the development, analysis and implementation of the least-squares finite element method (LSFEM) for fluid dynamics and electromagnetics applications. In the past year, there were four major accomplishments: 1) special treatments in computational fluid dynamics and computational electromagnetics, such as upwinding, numerical dissipation, staggered grid, non-equal order elements, operator splitting and preconditioning, edge elements, and vector potential are unnecessary; 2) the analysis of the LSFEM for most partial differential equations can be based on the bounded inverse theorem; 3) the finite difference and finite volume algorithms solve only two Maxwell equations and ignore the divergence equations; and 4) the first numerical simulation of three-dimensional Marangoni-Benard convection was performed using the LSFEM.
A new method for constructing analytic elements for groundwater flow.
NASA Astrophysics Data System (ADS)
Strack, O. D.
2007-12-01
The analytic element method is based upon the superposition of analytic functions that are defined throughout the infinite domain, and can be used to meet a variety of boundary conditions. Analytic elements have been use successfully for a number of problems, mainly dealing with the Poisson equation (see, e.g., Theory and Applications of the Analytic Element Method, Reviews of Geophysics, 41,2/1005 2003 by O.D.L. Strack). The majority of these analytic elements consists of functions that exhibit jumps along lines or curves. Such linear analytic elements have been developed also for other partial differential equations, e.g., the modified Helmholz equation and the heat equation, and were constructed by integrating elementary solutions, the point sink and the point doublet, along a line. This approach is limiting for two reasons. First, the existence is required of the elementary solutions, and, second, the integration tends to limit the range of solutions that can be obtained. We present a procedure for generating analytic elements that requires merely the existence of a harmonic function with the desired properties; such functions exist in abundance. The procedure to be presented is used to generalize this harmonic function in such a way that the resulting expression satisfies the applicable differential equation. The approach will be applied, along with numerical examples, for the modified Helmholz equation and for the heat equation, while it is noted that the method is in no way restricted to these equations. The procedure is carried out entirely in terms of complex variables, using Wirtinger calculus.
Velocity-pressure integrated versus penalty finite element methods for high Reynolds number flows
NASA Technical Reports Server (NTRS)
Kim, Sang-Wook
1988-01-01
Velocity-pressure integrated and consistent penalty finite element computations of high Reynolds number, laminar flows are presented. In both of the methods, the pressure has been interpolated using linear shape functions for a triangular element. The triangular element is contained inside the bi-quadratic isoparametric element. It has been reported previously that the pressure interpolation method, when used in the velocity-pressure integrated method, yielded accurate computational results for high Reynolds number flows. It is shown that use of the same pressure interpolation method in the consistent penalty finite element method yielded accurate velocity and pressure fields which were comparable to those obtained using the velocity-pressure integrated method. Accuracy of the two finite element methods has been demonstrated by comparing the computational results with available experimental data and/or fine-grid finite difference computational results. Advantages and disadvantages of the two methods are discussed on the basis of accuracy and convergence nature. Example problems considered include a lid-driven cavity flow for Reynolds number of 10,000, a laminar backward-facing step flow, a laminar flow through a nest of cylinders, and a channel flow with an internal blockage. A finite element computer program (NSFLOW/P) for the 2-D, incompressible Navier-Stokes equations is also presented.
Elements of an improved model of debris‐flow motion
Iverson, Richard M.
2009-01-01
A new depth‐averaged model of debris‐flow motion describes simultaneous evolution of flow velocity and depth, solid and fluid volume fractions, and pore‐fluid pressure. Non‐hydrostatic pore‐fluid pressure is produced by dilatancy, a state‐dependent property that links the depth‐averaged shear rate and volumetric strain rate of the granular phase. Pore‐pressure changes caused by shearing allow the model to exhibit rate‐dependent flow resistance, despite the fact that the basal shear traction involves only rate‐independent Coulomb friction. An analytical solution of simplified model equations shows that the onset of downslope motion can be accelerated or retarded by pore‐pressure change, contingent on whether dilatancy is positive or negative. A different analytical solution shows that such effects will likely be muted if downslope motion continues long enough, because dilatancy then evolves toward zero, and volume fractions and pore pressure concurrently evolve toward steady states.
HAT-P-26b: A Neptune-mass exoplanet with a well-constrained heavy element abundance.
Wakeford, Hannah R; Sing, David K; Kataria, Tiffany; Deming, Drake; Nikolov, Nikolay; Lopez, Eric D; Tremblin, Pascal; Amundsen, David S; Lewis, Nikole K; Mandell, Avi M; Fortney, Jonathan J; Knutson, Heather; Benneke, Björn; Evans, Thomas M
2017-05-12
A correlation between giant-planet mass and atmospheric heavy elemental abundance was first noted in the past century from observations of planets in our own Solar System and has served as a cornerstone of planet-formation theory. Using data from the Hubble and Spitzer Space Telescopes from 0.5 to 5 micrometers, we conducted a detailed atmospheric study of the transiting Neptune-mass exoplanet HAT-P-26b. We detected prominent H2O absorption bands with a maximum base-to-peak amplitude of 525 parts per million in the transmission spectrum. Using the water abundance as a proxy for metallicity, we measured HAT-P-26b's atmospheric heavy element content ([Formula: see text] times solar). This likely indicates that HAT-P-26b's atmosphere is primordial and obtained its gaseous envelope late in its disk lifetime, with little contamination from metal-rich planetesimals. Copyright © 2017, American Association for the Advancement of Science.
HAT-P-26b: A Neptune-mass exoplanet with a well-constrained heavy element abundance
NASA Astrophysics Data System (ADS)
Wakeford, Hannah R.; Sing, David K.; Kataria, Tiffany; Deming, Drake; Nikolov, Nikolay; Lopez, Eric D.; Tremblin, Pascal; Amundsen, David S.; Lewis, Nikole K.; Mandell, Avi M.; Fortney, Jonathan J.; Knutson, Heather; Benneke, Björn; Evans, Thomas M.
2017-05-01
A correlation between giant-planet mass and atmospheric heavy elemental abundance was first noted in the past century from observations of planets in our own Solar System and has served as a cornerstone of planet-formation theory. Using data from the Hubble and Spitzer Space Telescopes from 0.5 to 5 micrometers, we conducted a detailed atmospheric study of the transiting Neptune-mass exoplanet HAT-P-26b. We detected prominent H2O absorption bands with a maximum base-to-peak amplitude of 525 parts per million in the transmission spectrum. Using the water abundance as a proxy for metallicity, we measured HAT-P-26b’s atmospheric heavy element content (4.8-4.0+21.5 times solar). This likely indicates that HAT-P-26b’s atmosphere is primordial and obtained its gaseous envelope late in its disk lifetime, with little contamination from metal-rich planetesimals.
SUPG Finite Element Simulations of Compressible Flows for Aerothermodynamic Applications
NASA Technical Reports Server (NTRS)
Kirk, Benjamin S.
2007-01-01
This viewgraph presentation reviews the Streamline-Upwind Petrov-Galerkin (SUPG) Finite Element Simulation. It covers the background, governing equations, weak formulation, shock capturing, inviscid flux discretization, time discretization, linearization, and implicit solution strategies. It also reviews some applications such as Type IV Shock Interaction, Forward-Facing Cavity and AEDC Sharp Double Cone.
NASA Technical Reports Server (NTRS)
Yu, Sheng-Tao
2001-01-01
This document reports the conclusion and findings of our research activities for this grant. The goal of the project is the development and application of the method of Space-Time Conservation Element and Solution Element, or the CE/SE method, to simulate chemically reacting flows. The product of this project will be a high-fidelity, time-accurate flow solver analyzing unsteady flow fields advanced propulsion concepts, including the low-emission turbojet engine combustion and flow fields of the Pulse Detonation Engines (PDE). Based on the documents and computer software of the CE/SE method that we have received from the CE/SE working group at NASA Lewis, we have focused our research effort on addressing outstanding technical issues related to the extension of the CE/SE method for unsteady, chemically reactive flows. In particular, we have made progresses in the following three aspects: (1) Derivation of the governing equations for reacting flows; (2) Numerical treatments of stiff source terms; and (3) Detailed simulations of ZND detonation waves.
The least-squares finite element method for low-mach-number compressible viscous flows
NASA Technical Reports Server (NTRS)
Yu, Sheng-Tao
1994-01-01
The present paper reports the development of the Least-Squares Finite Element Method (LSFEM) for simulating compressible viscous flows at low Mach numbers in which the incompressible flows pose as an extreme. Conventional approach requires special treatments for low-speed flows calculations: finite difference and finite volume methods are based on the use of the staggered grid or the preconditioning technique; and, finite element methods rely on the mixed method and the operator-splitting method. In this paper, however, we show that such difficulty does not exist for the LSFEM and no special treatment is needed. The LSFEM always leads to a symmetric, positive-definite matrix through which the compressible flow equations can be effectively solved. Two numerical examples are included to demonstrate the method: first, driven cavity flows at various Reynolds numbers; and, buoyancy-driven flows with significant density variation. Both examples are calculated by using full compressible flow equations.
NASA Astrophysics Data System (ADS)
Zeng, Gang; Huang, Xiao-Wen; Zhou, Mei-Fu; Chen, Li-Hui; Xu, Xi-Sheng
2016-08-01
Continental basalts have complicated petrogenetic processes, and their chemical compositions can be affected by multi-staged geological evolution. Compared to lithophile elements, chalcophile elements including Ni, platinum-group elements (PGEs) and Cu are sensitive to sulfide segregation and fractional crystallization during the evolution of mantle-derived magmas and can provide constraints on the genesis of continental basalts. Cenozoic intra-continental alkaline basalts in the Nanjing basaltic field, eastern China, include high-Ca and low-Ca varieties. All these basalts have poor PGE contents with Ir ranging from 0.016 ppb to 0.288 ppb and high Cu/Pd ratios from 0.7 × 105 to 4.7 × 105 (5.7 × 103 for DMM), indicating that they were derived from sulfide-saturated mantle sources with variable amounts of residual sulfide during melting or might undergo an early-sulfide segregation in the mantle. Relatively high Cu/Pd ratios along with high Pd concentrations for the high-Ca alkaline basalts indicate an additional removal of sulfide during magma ascent. Because these basalts have high, variable Pd/Ir ratios (2.8-16.8) with low Ce/Pb (9.9-19.7) ratios and εNd values (+ 3.6-+6.4), crustal contamination is proposed to be a potential process to induce the sulfide saturation and removal. Significantly increased Pd/Ir ratios for few high-Ca basalts can be explained by the fractionation of laurite or Ru-Os-Ir alloys with olivine or chromite. For low-Ca alkaline basalts, their PGE contents are well correlated with the MgO, Sc contents, incompatible element ratios (Lu/Hf, Na/Ti and Ca/Al) and Hf isotopes. Good correlations are also observed between Pd/Ir (or Rh/Ir) and Na/Ti (or Ca/Al) ratios. Variations of these elemental ratios and Hf isotopes is previously documented to be induced by the mixing of peridotite xenolith-released melts during ascent. Therefore, we suggest that such xenolith-magma interaction are also responsible for the variable PGE compositions of low
Prediction of overall and blade-element performance for axial-flow pump configurations
NASA Technical Reports Server (NTRS)
Serovy, G. K.; Kavanagh, P.; Okiishi, T. H.; Miller, M. J.
1973-01-01
A method and a digital computer program for prediction of the distributions of fluid velocity and properties in axial flow pump configurations are described and evaluated. The method uses the blade-element flow model and an iterative numerical solution of the radial equilbrium and continuity conditions. Correlated experimental results are used to generate alternative methods for estimating blade-element turning and loss characteristics. Detailed descriptions of the computer program are included, with example input and typical computed results.
Finite element analysis of low speed viscous and inviscid aerodynamic flows
NASA Technical Reports Server (NTRS)
Baker, A. J.; Manhardt, P. D.
1977-01-01
A weak interaction solution algorithm was established for aerodynamic flow about an isolated airfoil. Finite element numerical methodology was applied to solution of each of differential equations governing potential flow, and viscous and turbulent boundary layer and wake flow downstream of the sharp trailing edge. The algorithm accounts for computed viscous displacement effects on the potential flow. Closure for turbulence was accomplished using both first and second order models. The COMOC finite element fluid mechanics computer program was modified to solve the identified equation systems for two dimensional flows. A numerical program was completed to determine factors affecting solution accuracy, convergence and stability for the combined potential, boundary layer, and parabolic Navier-Stokes equation systems. Good accuracy and convergence are demonstrated. Each solution is obtained within the identical finite element framework of COMOC.
Spectral element simulations of laminar and turbulent flows in complex geometries
NASA Technical Reports Server (NTRS)
Karniadakis, George EM
1989-01-01
Spectral element methods are high-order weighted residual techniques based on spectral expansions of variables and geometry for the Navier-Stokes (NS) and transport equations. Here, practical aspects of these methods and their efficient implementation are examined, and several examples of flows in truly complex geometries are presented. The spectral element discretization for NS equations is introduced, and the convergence of the method is addressed. An efficient data management scheme is discussed in the context of parallel processing computations. The method is validated by comparing the spectral element solutions with the exact eigensolutions for the Orr-Sommerfeld equations in two and three dimensions. Computer-aided flow visualizations are presented for an impulsive flow past a sharp edge wedge. Three-dimensional states of channel flow disrupted by an array of cylindrical eddy promoters are studied, and the results of a direct simulation of the turbulent flow in a plane channel are presented.
Computational fluid flow in two dimensions using simple T4/C3 element
NASA Astrophysics Data System (ADS)
Jan, Y. J.; Huang, S. J.; Lee, T. Y.
2000-10-01
The application of the four nodes for velocity and three nodes for pressure (T4/C3) element discretization technique for simulating two-dimensional steady and transitional flows is presented. The newly developed code has been validated by the application to three benchmark test cases: driven cavity flow, flow over a backward-facing step, and confined surface rib flow. In addition, a transitional flow with vortex shedding has been studied. The numerical results have shown excellent agreement with experimental results, as well as with those of other simulations. It should be pointed out that the advantages of the T4/C3 finite element over other higher-order elements lie in its computational simplicity, efficiency, and less computer memory requirement. Copyright
Cochran, R.J.
1992-01-01
A study of the finite element method applied to two-dimensional incompressible fluid flow analysis with heat transfer is performed using a mixed Galerkin finite element method with the primitive variable form of the model equations. Four biquadratic, quadrilateral elements are compared in this study--the serendipity biquadratic element with bilinear continuous pressure interpolation (Q2(8)-Q1) and the Lagrangian biquadratic element with bilinear continuous pressure interpolation (Q2-Q1) of the Taylor-Hood form. A modified form of the Q2-Q1 element is also studied. The pressure interpolation is augmented by a discontinuous constant shape function for pressure (Q2-Q1+). The discontinuous pressure element formulation makes use of biquadratic shape functions and a discontinuous linear interpolation of the pressure (Q2-P1(3)). Laminar flow solutions, with heat transfer, are compared to analytical and computational benchmarks for flat channel, backward-facing step and buoyancy driven flow in a square cavity. It is shown that the discontinuous pressure elements provide superior solution characteristics over the continuous pressure elements. Highly accurate heat transfer solutions are obtained and the Q2-P1(3) element is chosen for extension to turbulent flow simulations. Turbulent flow solutions are presented for both low turbulence Reynolds number and high Reynolds number formulations of two-equation turbulence models. The following three forms of the length scale transport equation are studied; the turbulence energy dissipation rate ([var epsilon]), the turbulence frequency ([omega]) and the turbulence time scale (tau). It is shown that the low turbulence Reynolds number model consisting of the K - [tau] transport equations, coupled with the damping functions of Shih and Hsu, provides an optimal combination of numerical stability and solution accuracy for the flat channel flow.
Velocity-pressure integrated versus penalty finite element methods for high Reynolds number flows
NASA Technical Reports Server (NTRS)
Kim, S.-W.; Decker, Rand A.
1989-01-01
Velocity-pressure integrated and consistent penalty finite element computations of high Reynolds number laminar flows are presented. In both methods the pressure has been interpolated using linear shape functions for a triangular element which is contained inside the biquadratic flow element. It has been shown previously that the pressure interpolation method, when used in conjunction with the velocity-pressure integrated method, yields accurate computational results for high-Reynolds-number flows. It is shown in this paper that use of the same pressure interpolation method in the consistent penalty finite element method yields computational results which are comparable to those of the velocity-pressure integrated method for both the velocity and the pressure fields. Accuracy of the two finite element methods has been demonstrated by comparing the computational results with available experimental data and/or fine grid finite difference computational results. Advantages and disadvantages of the two finite element methods are discussed on the basis of accuracy and convergence nature. Example problems considered include a lid-driven cavity flow of Reynolds number 10000, a laminar backward-facing step flow and a laminar flow through a nest of cylinders.
Sturtz, Timothy M.; Adar, Sara D.; Gould, Timothy; Larson, Timothy V.
2016-01-01
PM10-2.5 mass and trace element concentrations were measured in Winston-Salem, Chicago, and St. Paul at up to 60 sites per city during two different seasons in 2010. Positive Matrix Factorization (PMF) was used to explore the underlying sources of variability. Information on previously reported PM10-2.5 tire and brake wear profiles was used to constrain these features in PMF by prior specification of selected species ratios. We also modified PMF to allow for combining the measurements from all three cities into a single model while preserving city-specific soil features. Relatively minor differences were observed between model predictions with and without the prior ratio constraints, increasing confidence in our ability to identify separate brake wear and tire wear features. Brake wear, tire wear, fertilized soil, and re-suspended soil were found to be important sources of copper, zinc, phosphorus, and silicon respectively across all three urban areas. PMID:27468256
Sturtz, Timothy M; Adar, Sara D; Gould, Timothy; Larson, Timothy V
2014-02-01
PM10-2.5 mass and trace element concentrations were measured in Winston-Salem, Chicago, and St. Paul at up to 60 sites per city during two different seasons in 2010. Positive Matrix Factorization (PMF) was used to explore the underlying sources of variability. Information on previously reported PM10-2.5 tire and brake wear profiles was used to constrain these features in PMF by prior specification of selected species ratios. We also modified PMF to allow for combining the measurements from all three cities into a single model while preserving city-specific soil features. Relatively minor differences were observed between model predictions with and without the prior ratio constraints, increasing confidence in our ability to identify separate brake wear and tire wear features. Brake wear, tire wear, fertilized soil, and re-suspended soil were found to be important sources of copper, zinc, phosphorus, and silicon respectively across all three urban areas.
NASA Astrophysics Data System (ADS)
Sturtz, Timothy M.; Adar, Sara D.; Gould, Timothy; Larson, Timothy V.
2014-02-01
PM10-2.5 mass and trace element concentrations were measured in Winston-Salem, Chicago, and St. Paul at up to 60 sites per city during two different seasons in 2010. Positive Matrix Factorization (PMF) was used to explore the underlying sources of variability. Information on previously reported PM10-2.5 tire and brake wear profiles was used to constrain these features in PMF by prior specification of selected species ratios. We also modified PMF to allow for combining the measurements from all three cities into a single model while preserving city-specific soil features. Relatively minor differences were observed between model predictions with and without the prior ratio constraints, increasing confidence in our ability to identify separate brake wear and tire wear features. Brake wear, tire wear, fertilized soil, and resuspended soil were found to be important sources of copper, zinc, phosphorus, and silicon, respectively, across all three urban areas.
NASA Astrophysics Data System (ADS)
Patterson, J. D.; Ramos, F. C.; Wolff, J. A.
2007-12-01
Characterizing the geochemical signatures of plumes is critical for evaluating the petrogenetic evolution of plume- related volcanic rocks. The main phase of Columbia River flood basalt activity (16.6 - 15.5 Ma), considered to represent the first clear manifestation of the Yellowstone hotspot on the North American continent, includes the Steens Mountain, Imnaha, Grande Ronde and Picture Gorge basalts. Isotopic and trace element covariations defined by Grande Ronde, Steens Mountains, and Picture Gorge basalts diverge radially from the field of Imnaha basalts, which retain signatures that most closely reflect the 'undiluted' geochemical characteristics of the Yellowstone mantle plume. Sr, Nd, Pb isotope ratios and incompatible trace element abundances and ratios of Imnaha basalts closely resemble those of some Pacific EM II OIB groups. Nonetheless, the compositions of some Imnaha lavas reflect mixing of the plume with different mantle types. Others have clearly been affected by interaction of plume-derived basalt with continental crust, although the latter process is much more significant in the genesis of the succeeding Grande Ronde basalts. We will review the geochemical characteristics of the Yellowstone plume as recorded in the Imnaha basalt in the context of later-erupted volcanic products of the Columbia - Snake - Yellowstone system, and Pacific mantle plumes more generally.
Elemental transport coefficients in viscous plasma flows near local thermodynamic equilibrium.
Orsini, Alessio; Kustova, Elena V
2009-05-01
We propose a convenient formulation of elemental transport coefficients in chemically reacting and plasma flows locally approaching thermodynamic equilibrium. A set of transport coefficients for elemental diffusion velocities, heat flux, and electric current is introduced. These coefficients relate the transport fluxes with the electric field and with the spatial gradients of elemental fractions, pressure, and temperature. The proposed formalism based on chemical elements and fully symmetric with the classical transport theory based on chemical species, is particularly suitable to model mixing and demixing phenomena due to diffusion of chemical elements. The aim of this work is threefold: to define a simple and rigorous framework suitable for numerical implementation, to allow order of magnitude estimations and qualitative predictions of elemental transport phenomena, and to gain a deeper insight into the physics of chemically reacting flows near local equilibrium.
Adaptive finite element methods for compressible flow problems
NASA Technical Reports Server (NTRS)
Oden, J. T.; Strouboulis, T.; Devloo, PH.
1986-01-01
Some recent work on adaptive FEMs for solving transient Euler equations in two-dimensional domains is summarized. The formulation of an FEM model of the Euler equations is shown, and the application of the adaptive strategies to data management schemes is addressed. Sample numerical results from the application of the model and strategies to the flow over a step and to transient cases are given.
Elements of an improved model of debris-flow motion
Iverson, R.M.
2009-01-01
A new depth-averaged model of debris-flow motion describes simultaneous evolution of flow velocity and depth, solid and fluid volume fractions, and pore-fluid pressure. Non-hydrostatic pore-fluid pressure is produced by dilatancy, a state-dependent property that links the depth-averaged shear rate and volumetric strain rate of the granular phase. Pore-pressure changes caused by shearing allow the model to exhibit rate-dependent flow resistance, despite the fact that the basal shear traction involves only rate-independent Coulomb friction. An analytical solution of simplified model equations shows that the onset of downslope motion can be accelerated or retarded by pore-pressure change, contingent on whether dilatancy is positive or negative. A different analytical solution shows that such effects will likely be muted if downslope motion continues long enough, because dilatancy then evolves toward zero, and volume fractions and pore pressure concurrently evolve toward steady states. ?? 2009 American Institute of Physics.
Mean and turbulent flow development through an array of rotating elements
NASA Astrophysics Data System (ADS)
Craig, Anna; Dabiri, John; Koseff, Jeffrey
2014-11-01
The adjustment of an incoming boundary layer profile as it impacts and interacts with an array of elements has received significant attention in the context of terrestrial and aquatic canopies and more recently in the context of horizontal axis wind farms. The distance required for the mean flow profile to stabilize, the energy transport through the array, and the structure of the turbulence within the array are directly dependent upon such factors as the element height, density, rigidity/flexibility, frontal area distribution, element homogeneity, and underlying topography. In the present study, the mean and turbulent development of the flow through an array of rotating elements was examined experimentally. Element rotation has been shown to drastically alter wake dynamics of single and paired elements, but the possible extension of such rotation-driven dynamics had not previously been examined on larger groups of elements. Practically, such an array of rotating elements may provide insight into the flow dynamics of an array of vertical axis wind turbines. 2D particle image velocimetry was used along the length of the array in order to examine the effects of an increasing ratio of cylinder rotation speed to streamwise freestream velocity on flow development and structure. Work supported by a NSF Graduate Research Fellowship & Stanford Graduate Fellowship to A.E.C, by funding to J.O.D. from ONR N000141211047 and the Gordon and Betty Moore Foundation through Grant GBMF2645, and by funding from the EFML.
Several advances in the analytic element method have been made to enhance its performance and facilitate three-dimensional ground-water flow modeling in a regional aquifer setting. First, a new public domain modular code (ModAEM) has been developed for modeling ground-water flow ...
Several advances in the analytic element method have been made to enhance its performance and facilitate three-dimensional ground-water flow modeling in a regional aquifer setting. First, a new public domain modular code (ModAEM) has been developed for modeling ground-water flow ...
Mathematical Aspects of Finite Element Methods for Incompressible Viscous Flows.
1986-09-01
irteir-rt In element pa ir 1: is je Tnit’ by f i F-t mii iidi rig * % % % % % % - 4* % VV 4 ~ % - ~ * .. . * *. PA - 33- Q into rectangular prisms , or...mtr.o gerier-il Iv, lrit h.-t ,- For the prpsstirp sputi-P w’e choose~ pi.p’ievi so. -- u t subregions. We subdi vIde each rectangular prism into 24 tetr...8217 Unfortunately, these boundary conditions have no PhV.- tico . meaninq. Thus the choice (4.5.1), or equivalently (4.10.1,, can only be used in conjunction
NASA Astrophysics Data System (ADS)
Veselsky, M.; Klimo, J.; Ma, Yu-Gang; Souliotis, G. A.
2016-12-01
The mechanism of fusion hindrance, an effect preventing the synthesis of superheavy elements in the reactions of cold and hot fusion, is investigated using the Boltzmann-Uehling-Uhlenbeck equation, where Coulomb interaction is introduced. A strong sensitivity is observed both to the modulus of incompressibility of symmetric nuclear matter, controlling the competition of surface tension and Coulomb repulsion, and to the stiffness of the density-dependence of symmetry energy, influencing the formation of the neck prior to scission. The experimental fusion probabilities were for the first time used to derive constraints on the nuclear equation of state. A strict constraint on the modulus of incompressibility of nuclear matter K0=240 -260 MeV is obtained while the stiff density-dependences of the symmetry energy (γ >1 ) are rejected.
A robust, finite element model for hydrostatic surface water flows
Walters, R.A.; Casulli, V.
1998-01-01
A finite element scheme is introduced for the 2-dimensional shallow water equations using semi-implicit methods in time. A semi-Lagrangian method is used to approximate the effects of advection. A wave equation is formed at the discrete level such that the equations decouple into an equation for surface elevation and a momentum equation for the horizontal velocity. The convergence rates and relative computational efficiency are examined with the use of three test cases representing various degrees of difficulty. A test with a polar-quadrant grid investigates the response to local grid-scale forcing and the presence of spurious modes, a channel test case establishes convergence rates, and a field-scale test case examines problems with highly irregular grids.A finite element scheme is introduced for the 2-dimensional shallow water equations using semi-implicit methods in time. A semi-Lagrangian method is used to approximate the effects of advection. A wave equation is formed at the discrete level such that the equations decouple into an equation for surface elevation and a momentum equation for the horizontal velocity. The convergence rates and relative computational efficiency are examined with the use of three test cases representing various degrees of difficulty. A test with a polar-quadrant grid investigates the response to local grid-scale forcing and the presence of spurious modes, a channel test case establishes convergence rates, and a field-scale test case examines problems with highly irregular grids.
Spectral Element Method for the Simulation of Unsteady Compressible Flows
NASA Technical Reports Server (NTRS)
Diosady, Laslo Tibor; Murman, Scott M.
2013-01-01
This work uses a discontinuous-Galerkin spectral-element method (DGSEM) to solve the compressible Navier-Stokes equations [1{3]. The inviscid ux is computed using the approximate Riemann solver of Roe [4]. The viscous fluxes are computed using the second form of Bassi and Rebay (BR2) [5] in a manner consistent with the spectral-element approximation. The method of lines with the classical 4th-order explicit Runge-Kutta scheme is used for time integration. Results for polynomial orders up to p = 15 (16th order) are presented. The code is parallelized using the Message Passing Interface (MPI). The computations presented in this work are performed using the Sandy Bridge nodes of the NASA Pleiades supercomputer at NASA Ames Research Center. Each Sandy Bridge node consists of 2 eight-core Intel Xeon E5-2670 processors with a clock speed of 2.6Ghz and 2GB per core memory. On a Sandy Bridge node the Tau Benchmark [6] runs in a time of 7.6s.
Compressible seal flow analysis using the finite element method with Galerkin solution technique
NASA Technical Reports Server (NTRS)
Zuk, J.
1974-01-01
High pressure gas sealing involves not only balancing the viscous force with the pressure gradient force but also accounting for fluid inertia--especially for choked flow. The conventional finite element method which uses a Rayleigh-Ritz solution technique is not convenient for nonlinear problems. For these problems, a finite element method with a Galerkin solution technique (FEMGST) was formulated. One example, a three-dimensional axisymmetric flow formulation has nonlinearities due to compressibility, area expansion, and convective inertia. Solutions agree with classical results in the limiting cases. The development of the choked flow velocity profile is shown.
Adaptive Meshing Techniques for Viscous Flow Calculations on Mixed Element Unstructured Meshes
NASA Technical Reports Server (NTRS)
Mavriplis, D. J.
1997-01-01
An adaptive refinement strategy based on hierarchical element subdivision is formulated and implemented for meshes containing arbitrary mixtures of tetrahendra, hexahendra, prisms and pyramids. Special attention is given to keeping memory overheads as low as possible. This procedure is coupled with an algebraic multigrid flow solver which operates on mixed-element meshes. Inviscid flows as well as viscous flows are computed an adaptively refined tetrahedral, hexahedral, and hybrid meshes. The efficiency of the method is demonstrated by generating an adapted hexahedral mesh containing 3 million vertices on a relatively inexpensive workstation.
A global spectral element model for poisson equations and advective flow over a sphere
NASA Astrophysics Data System (ADS)
Mei, Huan; Wang, Faming; Zeng, Zhong; Qiu, Zhouhua; Yin, Linmao; Li, Liang
2016-03-01
A global spherical Fourier-Legendre spectral element method is proposed to solve Poisson equations and advective flow over a sphere. In the meridional direction, Legendre polynomials are used and the region is divided into several elements. In order to avoid coordinate singularities at the north and south poles in the meridional direction, Legendre-Gauss-Radau points are chosen at the elements involving the two poles. Fourier polynomials are applied in the zonal direction for its periodicity, with only one element. Then, the partial differential equations are solved on the longitude-latitude meshes without coordinate transformation between spherical and Cartesian coordinates. For verification of the proposed method, a few Poisson equations and advective flows are tested. Firstly, the method is found to be valid for test cases with smooth solution. The results of the Poisson equations demonstrate that the present method exhibits high accuracy and exponential convergence. Highprecision solutions are also obtained with near negligible numerical diffusion during the time evolution for advective flow with smooth shape. Secondly, the results of advective flow with non-smooth shape and deformational flow are also shown to be reasonable and effective. As a result, the present method is proved to be capable of solving flow through different types of elements, and thereby a desirable method with reliability and high accuracy for solving partial differential equations over a sphere.
NASA Technical Reports Server (NTRS)
Bey, K. S.; Thornton, E. A.; Dechaumphai, P.; Ramakrishnan, R.
1985-01-01
Recent progress in the development of finite element methodology for the prediction of aerothermal loads is described. Two dimensional, inviscid computations are presented, but emphasis is placed on development of an approach extendable to three dimensional viscous flows. Research progress is described for: (1) utilization of a commercially available program to construct flow solution domains and display computational results, (2) development of an explicit Taylor-Galerkin solution algorithm, (3) closed form evaluation of finite element matrices, (4) vector computer programming strategies, and (5) validation of solutions. Two test problems of interest to NASA Langley aerothermal research are studied. Comparisons of finite element solutions for Mach 6 flow with other solution methods and experimental data validate fundamental capabilities of the approach for analyzing high speed inviscid compressible flows.
Response of hot element flush wall gauges in oscillating laminar flow
NASA Technical Reports Server (NTRS)
Giddings, T. A.; Cook, W. J.
1986-01-01
The time dependent response characteristics of flush-mounted hot element gauges used as instruments to measure wall shear stress in unsteady periodic air flows were investigated. The study was initiated because anomalous results were obtained from the gauges in oscillating turbulent flows for the phase relation of the wall shear stress variation, indicating possible gauge response problems. Flat plate laminar oscillating turbulent flows characterized by a mean free stream velocity with a superposed sinusoidal variation were performed. Laminar rather than turbulent flows were studied, because a numerical solution for the phase angle between the free stream velocity and the wall shear stress variation that is known to be correct can be obtained. The focus is on comparing the phase angle indicated by the hot element gauges with corresponding numerical prediction for the phase angle, since agreement would indicate that the hot element gauges faithfully follow the true wall shear stress variation.
NASA Technical Reports Server (NTRS)
Bey, K. S.; Thornton, E. A.; Dechaumphai, P.; Ramakrishnan, R.
1985-01-01
Recent progress in the development of finite element methodology for the prediction of aerothermal loads is described. Two dimensional, inviscid computations are presented, but emphasis is placed on development of an approach extendable to three dimensional viscous flows. Research progress is described for: (1) utilization of a commerically available program to construct flow solution domains and display computational results, (2) development of an explicit Taylor-Galerkin solution algorithm, (3) closed form evaluation of finite element matrices, (4) vector computer programming strategies, and (5) validation of solutions. Two test problems of interest to NASA Langley aerothermal research are studied. Comparisons of finite element solutions for Mach 6 flow with other solution methods and experimental data validate fundamental capabilities of the approach for analyzing high speed inviscid compressible flows.
NASA Technical Reports Server (NTRS)
Parikh, Paresh; Pirzadeh, Shahyar; Loehner, Rainald
1990-01-01
A set of computer programs for 3-D unstructured grid generation, fluid flow calculations, and flow field visualization was developed. The grid generation program, called VGRID3D, generates grids over complex configurations using the advancing front method. In this method, the point and element generation is accomplished simultaneously, VPLOT3D is an interactive, menudriven pre- and post-processor graphics program for interpolation and display of unstructured grid data. The flow solver, VFLOW3D, is an Euler equation solver based on an explicit, two-step, Taylor-Galerkin algorithm which uses the Flux Corrected Transport (FCT) concept for a wriggle-free solution. Using these programs, increasingly complex 3-D configurations of interest to aerospace community were gridded including a complete Space Transportation System comprised of the space-shuttle orbitor, the solid-rocket boosters, and the external tank. Flow solutions were obtained on various configurations in subsonic, transonic, and supersonic flow regimes.
Modified finite-element model for application to terrain-induced mesoscale flows
Lee, R.L.; Leone, J.M. Jr.; Gresho, P.M.
1982-11-01
Terrain-induced mesoscale flows are localized atmospheric motions generated primarily by surface inhomogeneities such as differential heating and irregular terrain. Well-known examples of such flows are sea-and-land breeze circulations, mountain-valley flows, urban heat island circulations and mountain lee waves. A numerical model capable of capturing the details of these frequently complicated flow patterns must often contain a realistic and rather accurate representation of the relevant terrain. Over the last decade, mesoscale models have been developed in which various approaches were used to incorporate variable terrain. In this study, a somewhat unique approach, based on a modified finite element procedure, was used to solve the nonhydrostatic planetary boundary layer equations. The nonhydrostatic and finite element features of the model are particularly advantageous for modeling flows over complex topography. The numerical aspects of the model, the parameterizations currently used, and a few preliminary results are presented.
Supercomputer implementation of finite element algorithms for high speed compressible flows
NASA Technical Reports Server (NTRS)
Thornton, E. A.; Ramakrishnan, R.
1986-01-01
Prediction of compressible flow phenomena using the finite element method is of recent origin and considerable interest. Two shock capturing finite element formulations for high speed compressible flows are described. A Taylor-Galerkin formulation uses a Taylor series expansion in time coupled with a Galerkin weighted residual statement. The Taylor-Galerkin algorithms use explicit artificial dissipation, and the performance of three dissipation models are compared. A Petrov-Galerkin algorithm has as its basis the concepts of streamline upwinding. Vectorization strategies are developed to implement the finite element formulations on the NASA Langley VPS-32. The vectorization scheme results in finite element programs that use vectors of length of the order of the number of nodes or elements. The use of the vectorization procedure speeds up processing rates by over two orders of magnitude. The Taylor-Galerkin and Petrov-Galerkin algorithms are evaluated for 2D inviscid flows on criteria such as solution accuracy, shock resolution, computational speed and storage requirements. The convergence rates for both algorithms are enhanced by local time-stepping schemes. Extension of the vectorization procedure for predicting 2D viscous and 3D inviscid flows are demonstrated. Conclusions are drawn regarding the applicability of the finite element procedures for realistic problems that require hundreds of thousands of nodes.
Garcia, C. Amanda; Halford, Keith J.; Laczniak, Randell J.
2010-01-01
Hydraulic conductivities of volcanic and carbonate lithologic units at the Nevada Test Site were estimated from flow logs and aquifer-test data. Borehole flow and drawdown were integrated and interpreted using a radial, axisymmetric flow model, AnalyzeHOLE. This integrated approach is used because complex well completions and heterogeneous aquifers and confining units produce vertical flow in the annular space and aquifers adjacent to the wellbore. AnalyzeHOLE simulates vertical flow, in addition to horizontal flow, which accounts for converging flow toward screen ends and diverging flow toward transmissive intervals. Simulated aquifers and confining units uniformly are subdivided by depth into intervals in which the hydraulic conductivity is estimated with the Parameter ESTimation (PEST) software. Between 50 and 150 hydraulic-conductivity parameters were estimated by minimizing weighted differences between simulated and measured flow and drawdown. Transmissivity estimates from single-well or multiple-well aquifer tests were used to constrain estimates of hydraulic conductivity. The distribution of hydraulic conductivity within each lithology had a minimum variance because estimates were constrained with Tikhonov regularization. AnalyzeHOLE simulated hydraulic-conductivity estimates for lithologic units across screened and cased intervals are as much as 100 times less than those estimated using proportional flow-log analyses applied across screened intervals only. Smaller estimates of hydraulic conductivity for individual lithologic units are simulated because sections of the unit behind cased intervals of the wellbore are not assumed to be impermeable, and therefore, can contribute flow to the wellbore. Simulated hydraulic-conductivity estimates vary by more than three orders of magnitude across a lithologic unit, indicating a high degree of heterogeneity in volcanic and carbonate-rock units. The higher water transmitting potential of carbonate-rock units relative
Garcia, C. Amanda; Halford, Keith J.; Laczniak, Randell J.
2010-02-12
Hydraulic conductivities of volcanic and carbonate lithologic units at the Nevada Test Site were estimated from flow logs and aquifer-test data. Borehole flow and drawdown were integrated and interpreted using a radial, axisymmetric flow model, AnalyzeHOLE. This integrated approach is used because complex well completions and heterogeneous aquifers and confining units produce vertical flow in the annular space and aquifers adjacent to the wellbore. AnalyzeHOLE simulates vertical flow, in addition to horizontal flow, which accounts for converging flow toward screen ends and diverging flow toward transmissive intervals. Simulated aquifers and confining units uniformly are subdivided by depth into intervals in which the hydraulic conductivity is estimated with the Parameter ESTimation (PEST) software. Between 50 and 150 hydraulic-conductivity parameters were estimated by minimizing weighted differences between simulated and measured flow and drawdown. Transmissivity estimates from single-well or multiple-well aquifer tests were used to constrain estimates of hydraulic conductivity. The distribution of hydraulic conductivity within each lithology had a minimum variance because estimates were constrained with Tikhonov regularization. AnalyzeHOLE simulated hydraulic-conductivity estimates for lithologic units across screened and cased intervals are as much as 100 times less than those estimated using proportional flow-log analyses applied across screened intervals only. Smaller estimates of hydraulic conductivity for individual lithologic units are simulated because sections of the unit behind cased intervals of the wellbore are not assumed to be impermeable, and therefore, can contribute flow to the wellbore. Simulated hydraulic-conductivity estimates vary by more than three orders of magnitude across a lithologic unit, indicating a high degree of heterogeneity in volcanic and carbonate-rock units. The higher water transmitting potential of carbonate-rock units relative
Bluff Body Flow Simulation Using a Vortex Element Method
Anthony Leonard; Phillippe Chatelain; Michael Rebel
2004-09-30
Heavy ground vehicles, especially those involved in long-haul freight transportation, consume a significant part of our nation's energy supply. it is therefore of utmost importance to improve their efficiency, both to reduce emissions and to decrease reliance on imported oil. At highway speeds, more than half of the power consumed by a typical semi truck goes into overcoming aerodynamic drag, a fraction which increases with speed and crosswind. Thanks to better tools and increased awareness, recent years have seen substantial aerodynamic improvements by the truck industry, such as tractor/trailer height matching, radiator area reduction, and swept fairings. However, there remains substantial room for improvement as understanding of turbulent fluid dynamics grows. The group's research effort focused on vortex particle methods, a novel approach for computational fluid dynamics (CFD). Where common CFD methods solve or model the Navier-Stokes equations on a grid which stretches from the truck surface outward, vortex particle methods solve the vorticity equation on a Lagrangian basis of smooth particles and do not require a grid. They worked to advance the state of the art in vortex particle methods, improving their ability to handle the complicated, high Reynolds number flow around heavy vehicles. Specific challenges that they have addressed include finding strategies to accurate capture vorticity generation and resultant forces at the truck wall, handling the aerodynamics of spinning bodies such as tires, application of the method to the GTS model, computation time reduction through improved integration methods, a closest point transform for particle method in complex geometrics, and work on large eddy simulation (LES) turbulence modeling.
NASA Astrophysics Data System (ADS)
Ren, Zhong-Yuan; Wu, Ya-Dong; Zhang, Le; Nichols, Alexander R. L.; Hong, Lu-Bing; Zhang, Yin-Hui; Zhang, Yan; Liu, Jian-Qiang; Xu, Yi-Gang
2017-07-01
Olivine-hosted melt inclusions within lava retain important information regarding the lava's primary magma compositions and mantle sources. Thus, they can be used to infer the nature of the mantle sources of large igneous provinces, which is still not well known and of the subject of debate. We have analysed the chemical compositions and Pb isotopic ratios of olivine-hosted melt inclusions in the Dali picrites, Emeishan Large Igneous Province (LIP), SW China. These are the first in-situ Pb isotope data measured for melt inclusions found in the Emeishan picrites and allow new constraints to be placed on the source lithology of the Emeishan LIP. The melt inclusions show chemical compositional variations, spanning low-, intermediate- and high-Ti compositions, while their host whole rocks are restricted to the intermediate-Ti compositions. Together with the relatively constant Pb isotope ratios of the melt inclusions, the compositional variations suggest that the low-, intermediate- and high-Ti melts were derived from compositionally similar sources. The geochemical characteristics of melt inclusions, their host olivines, and whole-rocks from the Emeishan LIP indicate that Ca, Al, Mn, Yb, and Lu behave compatibly, and Ti, Rb, Sr, Zr, and Nb behave incompatibly during partial melting, requiring a pyroxenite source for the Emeishin LIP. The wide range of Ti contents in the melt inclusions and whole-rocks of the Emeishan basalts reflects different degrees of partial melting in the pyroxenite source at different depths in the melting column. The Pb isotope compositions of the melt inclusions and the OIB-like trace element compositions of the Emeishan basalts imply that mixing of a recycled ancient oceanic crust (EM1-like) component with a peridotite component from the lower mantle (FOZO-like component) could have underwent solid-state reaction, producing a secondary pyroxenite source that was subsequently partially melted to form the basalts. This new model of pyroxenite
NASA Astrophysics Data System (ADS)
Fan, Yaqing; Durlofsky, Louis J.; Tchelepi, Hamdi A.
2012-06-01
A numerical simulation framework for coupled multiphase flow, multicomponent transport and geochemical reactions in porous media is presented. The approach is an element-based formulation that combines the compositional modeling capabilities used in oil reservoir simulation with the treatment of chemical reactions used in groundwater modeling. The procedure employs a conservative finite-volume method with a fully-implicit treatment in time in order to preserve the nonlinear coupling of flow, transport, reactions, and mass transfer across phases. Phase behavior is described using cubic equations of state. In this framework, all the governing equations and associated constraints are cast in discrete residual form, such that any variable, or coefficient, can depend on any other variable in the problem. Prior to linearization, which is applied to construct the Jacobian matrix, no algebraic or analytic manipulation need be performed to reduce the nonlinear sets of equations and unknowns. Once the complete Jacobian matrix is assembled, a series of algebraic reductions (Schur complements), of the type used in compositional reservoir simulation, are performed to reduce the number of discrete equations that must be solved simultaneously. A GMRES solution strategy with CPR (Constrained Pressure Residual) preconditioning is applied to solve the reduced linear system. We demonstrate the formulation using two CO2 sequestration problems, one of which involves chemical reactions. The simulations demonstrate the efficiency and applicability of the overall procedure for modeling the long-term fate of sequestered CO2.
Response of hot element wall shear stress gages in laminar oscillating flows
NASA Technical Reports Server (NTRS)
Cook, W. J.; Murphy, J. D.; Giddings, T. A.
1986-01-01
An experimental investigation of the time-dependent response of hot element wall shear stress gages in unsteady periodic air flows is reported. The study has focused on wall shear stress in laminar oscillating flows produced on a flat plate by a free stream velocity composed of a mean component and a superposed sinusoidal variation. Two types of hot element gages, platinum film and flush wire, were tested for values of reduced frequency ranging from 0.14 to 2.36. Values of the phase angle of the wall shear stress variation relative to the free stream velocity, as indicated by the hot element gages, are compared with numerical prediction. The comparisons show that the gages indicate a wall shear stress variation that lags the true variation, and that the gages will also not indicate the correct wall shear stress variation in periodic turbulent flows.
Response of hot element wall shear stress gages in laminar oscillating flows
NASA Technical Reports Server (NTRS)
Cook, W. J.; Murphy, J. D.; Giddings, T. A.
1986-01-01
An experimental investigation of the time-dependent response of hot element wall shear stress gages in unsteady periodic air flows is reported. The study has focused on wall shear stress in laminar oscillating flows produced on a flat plate by a free stream velocity composed of a mean component and a superposed sinusoidal variation. Two types of hot element gages, platinum film and flush wire, were tested for values of reduced frequency ranging from 0.14 to 2.36. Values of the phase angle of the wall shear stress variation relative to the free stream velocity, as indicated by the hot element gages, are compared with numerical prediction. The comparisons show that the gages indicate a wall shear stress variation that lags the true variation, and that the gages will also not indicate the correct wall shear stress variation in periodic turbulent flows.
NASA Technical Reports Server (NTRS)
Chung, T. J. (Editor); Karr, Gerald R. (Editor)
1989-01-01
Recent advances in computational fluid dynamics are examined in reviews and reports, with an emphasis on finite-element methods. Sections are devoted to adaptive meshes, atmospheric dynamics, combustion, compressible flows, control-volume finite elements, crystal growth, domain decomposition, EM-field problems, FDM/FEM, and fluid-structure interactions. Consideration is given to free-boundary problems with heat transfer, free surface flow, geophysical flow problems, heat and mass transfer, high-speed flow, incompressible flow, inverse design methods, MHD problems, the mathematics of finite elements, and mesh generation. Also discussed are mixed finite elements, multigrid methods, non-Newtonian fluids, numerical dissipation, parallel vector processing, reservoir simulation, seepage, shallow-water problems, spectral methods, supercomputer architectures, three-dimensional problems, and turbulent flows.
NASA Technical Reports Server (NTRS)
Chung, T. J. (Editor); Karr, Gerald R. (Editor)
1989-01-01
Recent advances in computational fluid dynamics are examined in reviews and reports, with an emphasis on finite-element methods. Sections are devoted to adaptive meshes, atmospheric dynamics, combustion, compressible flows, control-volume finite elements, crystal growth, domain decomposition, EM-field problems, FDM/FEM, and fluid-structure interactions. Consideration is given to free-boundary problems with heat transfer, free surface flow, geophysical flow problems, heat and mass transfer, high-speed flow, incompressible flow, inverse design methods, MHD problems, the mathematics of finite elements, and mesh generation. Also discussed are mixed finite elements, multigrid methods, non-Newtonian fluids, numerical dissipation, parallel vector processing, reservoir simulation, seepage, shallow-water problems, spectral methods, supercomputer architectures, three-dimensional problems, and turbulent flows.
NASA Technical Reports Server (NTRS)
Ecer, A.; Akay, H. U.
1981-01-01
The finite element method is applied for the solution of transonic potential flows through a cascade of airfoils. Convergence characteristics of the solution scheme are discussed. Accuracy of the numerical solutions is investigated for various flow regions in the transonic flow configuration. The design of an efficient finite element computational grid is discussed for improving accuracy and convergence.
NASA Technical Reports Server (NTRS)
Lindsay, John T.; Elam, Sandy; Koblish, Ted; Lee, Phil; Mcauliffe, Dave
1990-01-01
Due to observations of unsteady flow in the Space Shuttle Main Engine fuel preburner injector element, several flow studies have been performed. Real time neutron radiography tests were recently completed. This technique provided real time images of MiL-c-7024 and Freon-22 flow through an aluminum liquid oxygen post model at three back pressures (0, 150, and 545 psig) and pressure drops up to 1000 psid. Separated flow appeared only while operating at back pressures of 0 and 150 psig. The behavior of separated flow was similar to that observed for water in a 3x acrylic model of the LOX post. On the average, separated flow appeared to reattach near the exit of the post when the ratio of pressure drop to supply pressure was about 0.75.
NASA Technical Reports Server (NTRS)
Lindsay, John T.; Elam, Sandy; Koblish, Ted; Lee, Phil; Mcauliffe, Dave
1990-01-01
Due to observations of unsteady flow in the Space Shuttle Main Engine fuel preburner injector element, several flow studies have been performed. Real time neutron radiography tests were recently completed. This technique provided real time images of MiL-c-7024 and Freon-22 flow through an aluminum liquid oxygen post model at three back pressures (0, 150, and 545 psig) and pressure drops up to 1000 psid. Separated flow appeared only while operating at back pressures of 0 and 150 psig. The behavior of separated flow was similar to that observed for water in a 3x acrylic model of the LOX post. On the average, separated flow appeared to reattach near the exit of the post when the ratio of pressure drop to supply pressure was about 0.75.
NASA Astrophysics Data System (ADS)
Gartling, D. K.; Hickox, C. E.
1982-10-01
The theoretical background for the finite element computer program MARIAH is presented. The MARIAH code is designed for the analysis of incompressible fluid flow and heat transfer in saturated porous media. A description of the fluid/thermal boundary value problem treated by the program is presented and the finite element method and associated numerical methods used in MARIAH are discussed. Instructions for use of the program are documented in the Sandia National Laboratories report, SAND79-1623.
A new approach in cascade flow analysis using the finite element method
NASA Technical Reports Server (NTRS)
Baskharone, E.; Hamed, A.
1980-01-01
A new approach in analyzing the potential flow past cascades and single airfoils using the finite element method is developed. In this analysis the circulation around the airfoil is not externally imposed but is directly computed in the numerical solution. Different finite element discretization patterns, orders of piecewise approximation, and grid sizes are used in the solution. The results obtained are compared with existing experimental measurements and exact solutions in cascades and single airfoils.
Chemical Derivatives and Elemental Transport Coefficients in Plasma Flows Near Local Equilibrium
Orsini, Alessio; Kustova, Elena V.
2011-05-20
Elemental transport coefficients are extensively used for modeling chemically reacting and plasma flows when the proximity to local equilibrium is exploited to combine the ordinary transport coefficients into a few elemental coefficients. A deeper insight into the physics of chemically reacting flows near local equilibrium can be achieved by looking only at a reduced number of relevant parameters in the expression of the flow transport properties.A new technique to calculate chemical derivatives using an analytical method which strongly reduces computational effort and numerical errors is introduced. A general formalism for elemental diffusion velocities, heat flux and electric current for plasma flows near local equilibrium is then derived. An order of magnitude analysis shows how to identify the main contributions to the transport fluxes among: elemental fractions gradients, pressure or temperature gradients, electric field. The resulting theoretical framework is particularly suitable for numerical implementation.The present contribution aims to provide a summary of the theoretical framework described above. Numerical examples of chemical derivatives and elemental transport coefficients are given. Results are presented for a carbon dioxide mixture of practical interest for aerospace applications and atmospheric entry problems.
Khashan, S. A.; Alazzam, A.; Furlani, E. P.
2014-01-01
A microfluidic design is proposed for realizing greatly enhanced separation of magnetically-labeled bioparticles using integrated soft-magnetic elements. The elements are fixed and intersect the carrier fluid (flow-invasive) with their length transverse to the flow. They are magnetized using a bias field to produce a particle capture force. Multiple stair-step elements are used to provide efficient capture throughout the entire flow channel. This is in contrast to conventional systems wherein the elements are integrated into the walls of the channel, which restricts efficient capture to limited regions of the channel due to the short range nature of the magnetic force. This severely limits the channel size and hence throughput. Flow-invasive elements overcome this limitation and enable microfluidic bioseparation systems with superior scalability. This enhanced functionality is quantified for the first time using a computational model that accounts for the dominant mechanisms of particle transport including fully-coupled particle-fluid momentum transfer. PMID:24931437
Large-eddy simulation of turbulent flow using the finite element method
McCallen, Rose Clara
1995-02-15
The equations of motion describing turbulent flows (in both the low and high Reynolds-number regimes) are well established. However, present day computers cannot meet the enormous computational requirement for numerically solving the governing equations for common engineering flows in the high Reynolds number turbulent regime. The characteristics that make turbulent, high Reynolds number flows difficult to simulate is the extreme range of time and space scales of motion. Most current engineering calculations are performed using semi-empirical equations, developed in terms of the flow mean (average) properties. These turbulence "models" (semi-empirical/analytical approximations) do not explicitly account for the eddy structures and thus, the temporal and spatial flow fluctuations are not resolved. In these averaging approaches, it is necessary to approximate all the turbulent structures using semi-empirical relations, and as a result, the turbulence models must be tailored for specific flow conditions and geometries with parameters obtained (usually) from physical experiments. The motivation for this research is the development of a finite element turbulence modeling approach which will ultimately be used to predict the wind flow around buildings. Accurate turbulence models of building flow are needed to predict the dispersion of airborne pollutants. The building flow turbulence models used today are not capable of predicting the three-dimensional separating and reattaching flows without the manipulation of many empirical parameters. These empirical parameters must be set by experimental data and they may vary unpredictably with building geometry, building orientation, and upstream flow conditions.
NASA Astrophysics Data System (ADS)
Cochran, Robert James
A study of the finite element method applied to two-dimensional incompressible fluid flow analysis with heat transfer is performed using a mixed Galerkin finite element method with the primitive variable form of the model equations. Four biquadratic, quadrilateral elements are compared in this study--the serendipity biquadratic element with bilinear continuous pressure interpolation (Q2(8)-Q1) and the Lagrangian biquadratic element with bilinear continuous pressure interpolation (Q2-Q1) of the Taylor-Hood form. A modified form of the Q-2Q1 element is also studied. The pressure interpolation is augmented by a discontinuous constant shape function for pressure (Q2-Q1+). The discontinuous pressure element formulation makes use of biquadratic shape functions and a discontinuous linear interpolation of the pressure (Q2-P1(3)). Laminar flow solutions, with heat transfer, are compared to analytical and computational benchmarks for flat channel, backward-facing step and buoyancy driven flow in a square cavity. It is shown that the discontinuous pressure elements provide superior solution characteristics over the continuous pressure elements. Highly accurate heat transfer solutions are obtained and the Q2-P1(3) element is chosen for extension to turbulent flow simulations. Turbulent flow solutions are presented for both low turbulence Reynolds number and high Reynolds number formulations of two equation turbulence models. The following three forms of the length scale transport equation are studied: the turbulence energy dissipation rate (epsilon), the turbulence frequency (omega) and the turbulence time scale (tau). It is shown that the low turbulence Reynolds number model consisting of the k-tau transport equations, coupled with the damping functions of Shih and Hsu, provides an optimal combination of numerical stability and solution accuracy for the flat channel flow. Attempts to extend the formulation beyond the flat channel were not successful due to oscillatory
Finite element and experimental analyses of unsteady hydrodynamic flows in lakes
NASA Astrophysics Data System (ADS)
Watanabe, Masaji; Numaguchi, Satoshi
2005-01-01
We present a numerical result in finite element analysis of flows in the water environment. We also present a result that we obtained experimentally utilizing the global positioning system (GPS). We show how the numerical result can be incorporated in analysis to simulate the experimental result. We describe our technique with an example in which an unsteady flow generated in Kojima Lake was analyzed numerically and experimentally.
Efficient simulation of incompressible viscous flow over multi-element airfoils
NASA Technical Reports Server (NTRS)
Rogers, Stuart E.; Wiltberger, N. Lyn; Kwak, Dochan
1993-01-01
The incompressible, viscous, turbulent flow over single and multi-element airfoils is numerically simulated in an efficient manner by solving the incompressible Navier-Stokes equations. The solution algorithm employs the method of pseudo compressibility and utilizes an upwind differencing scheme for the convective fluxes, and an implicit line-relaxation scheme. The motivation for this work includes interest in studying high-lift take-off and landing configurations of various aircraft. In particular, accurate computation of lift and drag at various angles of attack up to stall is desired. Two different turbulence models are tested in computing the flow over an NACA 4412 airfoil; an accurate prediction of stall is obtained. The approach used for multi-element airfoils involves the use of multiple zones of structured grids fitted to each element. Two different approaches are compared; a patched system of grids, and an overlaid Chimera system of grids. Computational results are presented for two-element, three-element, and four-element airfoil configurations. Excellent agreement with experimental surface pressure coefficients is seen. The code converges in less than 200 iterations, requiring on the order of one minute of CPU time on a CRAY YMP per element in the airfoil configuration.
Efficient simulation of incompressible viscous flow over multi-element airfoils
NASA Technical Reports Server (NTRS)
Rogers, Stuart E.; Wiltberger, N. Lyn; Kwak, Dochan
1992-01-01
The incompressible, viscous, turbulent flow over single and multi-element airfoils is numerically simulated in an efficient manner by solving the incompressible Navier-Stokes equations. The computer code uses the method of pseudo-compressibility with an upwind-differencing scheme for the convective fluxes and an implicit line-relaxation solution algorithm. The motivation for this work includes interest in studying the high-lift take-off and landing configurations of various aircraft. In particular, accurate computation of lift and drag at various angles of attack, up to stall, is desired. Two different turbulence models are tested in computing the flow over an NACA 4412 airfoil; an accurate prediction of stall is obtained. The approach used for multi-element airfoils involves the use of multiple zones of structured grids fitted to each element. Two different approaches are compared: a patched system of grids, and an overlaid Chimera system of grids. Computational results are presented for two-element, three-element, and four-element airfoil configurations. Excellent agreement with experimental surface pressure coefficients is seen. The code converges in less than 200 iterations, requiring on the order of one minute of CPU time (on a CRAY YMP) per element in the airfoil configuration.
A spectral element method for fluid dynamics - Laminar flow in a channel expansion
NASA Technical Reports Server (NTRS)
Patera, A. T.
1984-01-01
A spectral element method that combines the generality of the finite element method with the accuracy of spectral techniques is proposed for the numerical solution of the incompressible Navier-Stokes equations. In the spectral element discretization, the computational domain is broken into a series of elements, and the velocity in each element is represented as a high-order Lagrangian interpolant through Chebyshev collocation points. The hyperbolic piece of the governing equations is then treated with an explicit collocation scheme, while the pressure and viscous contributions are treated implicitly with a projection operator derived from a variational principle. The implementation of the technique is demonstrated on a one-dimensional inflow-outflow advection-diffusion equation, and the method is then applied to laminar two-dimensional (separated) flow in a channel expansion. Comparisons are made with experiment and previous numerical work.
Kumar, B V; Naidu, K B
1995-01-01
A nonlinear pulsatile suspension flow in a dilated vessel is numerically analysed. Two sets of highly coupled nonlinear partial differential equations governing the suspension flow are numerically solved, to simulate the suspension flow dynamics. A transient velocity-pressure (UVP) finite element method (FEM) and a stable time integration scheme, based on a predictor-corrector strategy, with constant error monitoring are employed in the flow analysis. The pulsatile suspension flow is characterized by analysing the flow, pressure and stress fields. Effects of the nonlinear particulate phase on the nonlinear suspending fluid phase are brought out by comparing the suspension flow results with those of homogeneous flow. Particles are seen to dampen the flow velocity, wall and central axis pressure, pressure gradient and wall shear stress. time-dependent recirculation regions which are sensitive to the presence of particles are seen in the dilated portion of the vessel. These recirculation regions favour thrombogenesis. The nonlinear effects due to the vessel geometry and those due to the convective terms dominate the dampening effect of the particles. These nonlinear effects are depicted through the transverse velocity and pressure plots. Wall shear stresses of suspension flow are not only high but also alternate in direction.
Numerical Simulation of Flow Over a Savonius Wind Turbine Using a Spectral Element Method
NASA Astrophysics Data System (ADS)
Kandala, Sriharsha; Rempfer, Dietmar
2009-11-01
A parallel spectral element code, SpecSolve, is developed with the objective of modeling flows in complex geometries. This code supports both structured and unstructured meshes and allows exact representation of boundary surfaces which are particularly useful for modeling turbo machinery flows. In this talk we present the results from 2D Navier-Stokes simulations of flow over a Savonius turbine. The simulation uses a rotating mesh in regions surrounding the blade and a stationary mesh away from the rotor. Results of a 2D Optimization study involving overlap ratio and the number of blades are also presented. These results are compared with experimental data.
16 CFR Figure 7 to Part 1633 - Elements of Propane Flow Control for Each Burner
Code of Federal Regulations, 2013 CFR
2013-01-01
... 16 Commercial Practices 2 2013-01-01 2013-01-01 false Elements of Propane Flow Control for Each Burner 7 Figure 7 to Part 1633 Commercial Practices CONSUMER PRODUCT SAFETY COMMISSION FLAMMABLE FABRICS ACT REGULATIONS STANDARD FOR THE FLAMMABILITY (OPEN FLAME) OF MATTRESS SETS Pt. 1633, Fig. 7 Figure...
16 CFR Figure 7 to Part 1633 - Elements of Propane Flow Control for Each Burner
Code of Federal Regulations, 2011 CFR
2011-01-01
... 16 Commercial Practices 2 2011-01-01 2011-01-01 false Elements of Propane Flow Control for Each Burner 7 Figure 7 to Part 1633 Commercial Practices CONSUMER PRODUCT SAFETY COMMISSION FLAMMABLE FABRICS ACT REGULATIONS STANDARD FOR THE FLAMMABILITY (OPEN FLAME) OF MATTRESS SETS Pt.1633, Fig. 7 Figure...
16 CFR Figure 7 to Part 1633 - Elements of Propane Flow Control for Each Burner
Code of Federal Regulations, 2010 CFR
2010-01-01
... 16 Commercial Practices 2 2010-01-01 2010-01-01 false Elements of Propane Flow Control for Each Burner 7 Figure 7 to Part 1633 Commercial Practices CONSUMER PRODUCT SAFETY COMMISSION FLAMMABLE FABRICS ACT REGULATIONS STANDARD FOR THE FLAMMABILITY (OPEN FLAME) OF MATTRESS SETS Pt.1633, Fig. 7 Figure...
16 CFR Figure 7 to Part 1633 - Elements of Propane Flow Control for Each Burner
Code of Federal Regulations, 2014 CFR
2014-01-01
... 16 Commercial Practices 2 2014-01-01 2014-01-01 false Elements of Propane Flow Control for Each Burner 7 Figure 7 to Part 1633 Commercial Practices CONSUMER PRODUCT SAFETY COMMISSION FLAMMABLE FABRICS ACT REGULATIONS STANDARD FOR THE FLAMMABILITY (OPEN FLAME) OF MATTRESS SETS Pt. 1633, Fig. 7 Figure...
16 CFR Figure 7 to Part 1633 - Elements of Propane Flow Control for Each Burner
Code of Federal Regulations, 2012 CFR
2012-01-01
... 16 Commercial Practices 2 2012-01-01 2012-01-01 false Elements of Propane Flow Control for Each Burner 7 Figure 7 to Part 1633 Commercial Practices CONSUMER PRODUCT SAFETY COMMISSION FLAMMABLE FABRICS ACT REGULATIONS STANDARD FOR THE FLAMMABILITY (OPEN FLAME) OF MATTRESS SETS Pt.1633, Fig. 7 Figure...
Applications of Taylor-Galerkin finite element method to compressible internal flow problems
NASA Technical Reports Server (NTRS)
Sohn, Jeong L.; Kim, Yongmo; Chung, T. J.
1989-01-01
A two-step Taylor-Galerkin finite element method with Lapidus' artificial viscosity scheme is applied to several test cases for internal compressible inviscid flow problems. Investigations for the effect of supersonic/subsonic inlet and outlet boundary conditions on computational results are particularly emphasized.
Applications of Taylor-Galerkin finite element method to compressible internal flow problems
NASA Technical Reports Server (NTRS)
Sohn, Jeong L.; Kim, Yongmo; Chung, T. J.
1989-01-01
A two-step Taylor-Galerkin finite element method with Lapidus' artificial viscosity scheme is applied to several test cases for internal compressible inviscid flow problems. Investigations for the effect of supersonic/subsonic inlet and outlet boundary conditions on computational results are particularly emphasized.
Cross-flow vortex structure and transition measurements using multi-element hot films
NASA Technical Reports Server (NTRS)
Agarwal, Naval K.; Mangalam, Siva M.; Maddalon, Dal V.; Collier, Fayette S., Jr.
1991-01-01
An experiment on a 45-degree swept wing was conducted to study three-dimensional boundary-layer characteristics using surface-mounted, micro-thin, multi-element hot-film sensors. Cross-flow vortex structure and boundary-layer transition were measured from the simultaneously acquired signals of the hot films. Spanwise variation of the root-mean-square (RMS) hot-film signal show a local minima and maxima. The distance between two minima corresponds to the stationary cross-flow vortex wavelength and agrees with naphthalene flow-visualization results. The chordwise and spanwise variation of amplified traveling (nonstationary) cross-flow disturbance characteristics were measured as Reynolds number was varied. The frequency of the most amplified cross-flow disturbances agrees with linear stability theory.
Cross-flow vortex structure and transition measurements using multi-element hot films
NASA Technical Reports Server (NTRS)
Agarwal, Naval K.; Mangalam, Siva M.; Maddalon, Dal V.; Collier, Fayette S., Jr.
1991-01-01
An experiment on a 45-degree swept wing was conducted to study three-dimensional boundary-layer characteristics using surface-mounted, micro-thin, multi-element hot-film sensors. Cross-flow vortex structure and boundary-layer transition were measured from the simultaneously acquired signals of the hot films. Spanwise variation of the root-mean-square (RMS) hot-film signal show a local minima and maxima. The distance between two minima corresponds to the stationary cross-flow vortex wavelength and agrees with naphthalene flow-visualization results. The chordwise and spanwise variation of amplified traveling (nonstationary) cross-flow disturbance characteristics were measured as Reynolds number was varied. The frequency of the most amplified cross-flow disturbances agrees with linear stability theory.
NASA Technical Reports Server (NTRS)
Kirk, Benjamin S.; Bova, Stephen W.; Bond, Ryan B.
2011-01-01
Presentation topics include background and motivation; physical modeling including governing equations and thermochemistry; finite element formulation; results of inviscid thermal nonequilibrium chemically reacting flow and viscous thermal equilibrium chemical reacting flow; and near-term effort.
Discrete-Roughness-Element-Enhanced Swept-Wing Natural Laminar Flow at High Reynolds Numbers
NASA Technical Reports Server (NTRS)
Malik, Mujeeb; Liao, Wei; Li, Fei; Choudhari, Meelan
2015-01-01
Nonlinear parabolized stability equations and secondary-instability analyses are used to provide a computational assessment of the potential use of the discrete-roughness-element technology for extending swept-wing natural laminar flow at chord Reynolds numbers relevant to transport aircraft. Computations performed for the boundary layer on a natural-laminar-flow airfoil with a leading-edge sweep angle of 34.6 deg, freestream Mach number of 0.75, and chord Reynolds numbers of 17 × 10(exp 6), 24 × 10(exp 6), and 30 × 10(exp 6) suggest that discrete roughness elements could delay laminar-turbulent transition by about 20% when transition is caused by stationary crossflow disturbances. Computations show that the introduction of small-wavelength stationary crossflow disturbances (i.e., discrete roughness element) also suppresses the growth of most amplified traveling crossflow disturbances.
Adaptive quadrilateral and triangular finite-element scheme for compressible flows
NASA Technical Reports Server (NTRS)
Ramakrishnan, R.; Thornton, Earl A.; Bey, Kim S.
1990-01-01
The development of an adaptive mesh refinement procedure for analyzing high-speed compressible flows using the finite-element method is described. This new adaptation procedure, which uses both quadrilateral and triangular elements, was implemented with two explicit finite-element algorithms - the two-step Taylor-Galerkin and the multistep Galerkin-Runge-Kutta schemes. A von Neumann stability analysis and a rotating 'cosine hill'problem demonstrate the instability of the Taylor-Galerkin scheme when coupled with the adaptation procedure. For the same adaptive refinement scheme, the Galerkin-Runge-Kutta procedure yields stable solutions within its explicit stability limit. The utility of this new adaptation procedure for the prediction of compressible flow features is illustrated for inviscid problems involving strong shock interactions at hypersonic speeds.
NASA Technical Reports Server (NTRS)
Cook, C. H.
1977-01-01
The results of a comprehensive numerical investigation of the basic capabilities of the finite element method (FEM) for numerical solution of compressible flow problems governed by the two-dimensional and axis-symmetric Navier-Stokes equations in primitive variables are presented. The strong and weak points of the method as a tool for computational fluid dynamics are considered. The relation of the linear element finite element method to finite difference methods (FDM) is explored. The calculation of free shear layer and separated flows over aircraft boattail afterbodies with plume simulators indicate the strongest assets of the method are its capabilities for reliable and accurate calculation employing variable grids which readily approximate complex geometry and capably adapt to the presence of diverse regions of large solution gradients without the necessity of domain transformation.
NASA Technical Reports Server (NTRS)
Liou, J.; Tezduyar, T. E.
1990-01-01
Adaptive implicit-explicit (AIE), grouped element-by-element (GEBE), and generalized minimum residuals (GMRES) solution techniques for incompressible flows are combined. In this approach, the GEBE and GMRES iteration methods are employed to solve the equation systems resulting from the implicitly treated elements, and therefore no direct solution effort is involved. The benchmarking results demonstrate that this approach can substantially reduce the CPU time and memory requirements in large-scale flow problems. Although the description of the concepts and the numerical demonstration are based on the incompressible flows, the approach presented here is applicable to larger class of problems in computational mechanics.
NASA Technical Reports Server (NTRS)
Liou, J.; Tezduyar, T. E.
1990-01-01
Adaptive implicit-explicit (AIE), grouped element-by-element (GEBE), and generalized minimum residuals (GMRES) solution techniques for incompressible flows are combined. In this approach, the GEBE and GMRES iteration methods are employed to solve the equation systems resulting from the implicitly treated elements, and therefore no direct solution effort is involved. The benchmarking results demonstrate that this approach can substantially reduce the CPU time and memory requirements in large-scale flow problems. Although the description of the concepts and the numerical demonstration are based on the incompressible flows, the approach presented here is applicable to larger class of problems in computational mechanics.
NASA Astrophysics Data System (ADS)
Asimow, P. D.
2009-12-01
The consequences of source heterogeneity and reactive flow during melt transport in the mantle can be classified by scale. At the smallest spatial and longest temporal scales, we can assume complete equilibrium and use batch melting of homogenized sources or equilibrium porous flow treatments. At large enough spatial scale or short enough temporal scale to prevent any thermal or chemical interaction between heterogeneities or between melt and matrix, we can assume perfectly fractional melting and transport and apply simple melt-mixing calculations. At a somewhat smaller spatial or longer temporal scale, thermal but not chemical interactions are significant and various lithologies and channel/matrix systems must follow common pressure-temperature paths, with energy flows between them. All these cases are tractable to model with current tools, whether we are interested in the energy budget, major elements, trace elements, or isotopes. There remains, however, the very important range of scales where none of these simple theories applies because of partial chemical interaction among lithologies or along the flow path. Such disequilibrium or kinetic cases have only been modeled, in the case of mantle minerals and melts, for trace elements and isotopes, with fixed melting rates instead of complete energy budgets. In order to interpret volumes of magma production and major element basalt and residue compositions that might emerge from a heterogeneous mantle in this last range of scales, we must develop tools that can combine a kinetic formulation with a major element and energy-constrained thermodynamic calculation. The kinetics can be handled either with a chemical kinetic approach with rate constants for various net transfer and exchange reactions, or with a physical diffusion-limited approach. A physical diffusion-limited approach can be built with the following elements. At grain scale, spherical grains of an arbitrary number of solid phases can evolve zoning profiles
A Mixed Finite Volume Element Method for Flow Calculations in Porous Media
NASA Technical Reports Server (NTRS)
Jones, Jim E.
1996-01-01
A key ingredient in the simulation of flow in porous media is the accurate determination of the velocities that drive the flow. The large scale irregularities of the geology, such as faults, fractures, and layers suggest the use of irregular grids in the simulation. Work has been done in applying the finite volume element (FVE) methodology as developed by McCormick in conjunction with mixed methods which were developed by Raviart and Thomas. The resulting mixed finite volume element discretization scheme has the potential to generate more accurate solutions than standard approaches. The focus of this paper is on a multilevel algorithm for solving the discrete mixed FVE equations. The algorithm uses a standard cell centered finite difference scheme as the 'coarse' level and the more accurate mixed FVE scheme as the 'fine' level. The algorithm appears to have potential as a fast solver for large size simulations of flow in porous media.
A Mixed Finite Volume Element Method for Flow Calculations in Porous Media
NASA Technical Reports Server (NTRS)
Jones, Jim E.
1996-01-01
A key ingredient in the simulation of flow in porous media is the accurate determination of the velocities that drive the flow. The large scale irregularities of the geology, such as faults, fractures, and layers suggest the use of irregular grids in the simulation. Work has been done in applying the finite volume element (FVE) methodology as developed by McCormick in conjunction with mixed methods which were developed by Raviart and Thomas. The resulting mixed finite volume element discretization scheme has the potential to generate more accurate solutions than standard approaches. The focus of this paper is on a multilevel algorithm for solving the discrete mixed FVE equations. The algorithm uses a standard cell centered finite difference scheme as the 'coarse' level and the more accurate mixed FVE scheme as the 'fine' level. The algorithm appears to have potential as a fast solver for large size simulations of flow in porous media.
Aerodynamic Design of Axial-Flow Compressors. VII - Blade-Element Flow in Annular Cascades
NASA Technical Reports Server (NTRS)
Robbins, William H.; Jackson, Robert J.; Lieblein, Seymour
1955-01-01
Annular blade-element data obtained primarily from single-stage compressor installations are correlated over a range of inlet Mach numbers and cascade geometry. The correlation curves are presented in such a manner that they are related directly to the low-speed two-dimensional-cascade data of part VI of this series. Thus, the data serve as both an extension and a verification of the two-dimensional-cascade data. In addition, the correlation results are applied to compressor design.
NASA Astrophysics Data System (ADS)
Massiot, C.; Garcia-Sélles, D.; Nicol, A., , Prof; Mcnamara, D. D.; Townend, J.; Archibald, G.; Siratovich, P. A.; Villeneuve, M.
2015-12-01
Geothermal reservoirs hosted in volcanic rocks, like the Rotokawa Geothermal Field in the Taupo Volcanic Zone (TVZ), New Zealand, typically contain fracture networks that control fluid flow. Realistic discrete fracture network (DFN) models have the potential to improve geothermal resource management. However, the spatial distribution and geometries of fracture networks are often poorly understood due to limited data and complex deformation histories including lava emplacement, subsequent burial and faulting.To understand better the distribution of fractures formed during lava emplacement, we study andesitic flow exposures from Mt Ruapehu, at the southern end of the TVZ. Terrestrial Laser Scanner (TLS) acquisition on three 50-200 m2 outcrops provided large 3D point clouds of the shape of the outcrop. Delineation of thousands of individual fractures has been semi-automated using local geometrical constraints and a shape detection algorithm detecting planar and curved surfaces. Fracture orientation, length, area, linear (P10) and areal (P20) densities from the TLS data provide input parameters for the DFN models. Fracture detection is validated using high-resolution panoramic photographs (GigaPan) and manual scanline measurements. Cooling joints are highly connected via sub-horizontal joints that are aligned with vesicular layers. UCS tests show a mechanical anisotropy between vertical and horizontal samples. Most of the cooling joints terminate within or at the brecciated margins of individual flows which contrast mechanically with the massive flow interior. Thus, highly connected and curved fractures are mostly confined to lava flows.This study provides a framework for developing DFNs for geothermal reservoirs hosted in andesitic flows based on empirical observations of intrinsic fracturing and mechanical anisotropies of the host lithology. Fractures in individual lava flows may be interconnected in the reservoir by a combination of cooling joints, subsequent
A finite-element analysis for steady and oscillatory subsonic flow around complex configurations
NASA Technical Reports Server (NTRS)
Chen, L. T.; Suciu, E. O.; Morino, L.
1974-01-01
The problem of potential subsonic flow around complex configurations is considered. The solution is given of an integral equation relating the values of the potential on the surface of the body to the values of the normal derivative, which is known from the boundary conditions. The surface of the body is divided into small (hyperboloidal quadrilateral) surface elements, which are described in terms of the Cartesian components of the four corner points. The values of the potential (and its normal derivative) within each element is assumed to be constant and equal to its value at the centroid of the element. The coefficients of the equation are given by source and doublet integrals over the surface elements. Closed form evaluations of the integrals are presented. The results obtained with the above formulation are compared with existing analytical and experimental results.
A finite-element analysis for steady and oscillatory supersonic flows around complex configurations
NASA Technical Reports Server (NTRS)
Morino, L.; Chen, L. T.
1974-01-01
The problem of small perturbation potential supersonic flow around complex configurations is considered. This problem requires the solution of an integral equation relating the values of the potential on the surface of the body to the values of the normal derivative, which is known from the small perturbation boundary conditions. The surface of the body is divided into small (hyperboloidal quadrilateral) surface elements, sigma sub i, which are described in terms of the Cartesian components of the four corner points. The values of the potential (and its normal derivative) within each element is assumed to be constant and equal to its value at the centroid of the element, and this yields a set of linear algebraic equations. The coefficients of the equation are given by source and doublet integrals over the surface elements, sigma sub i. The results obtained using the above formulation are compared with existing analytical and experimental results.
FEMWATER: a finite-element model of water flow through saturated-unsaturated porous media
Yeh, G.T.; Ward, D.S.
1980-10-01
Upon examining the Water Movement Through Saturated-Unsaturated Porous Media: A Finite-Element Galerkin Model, it was felt that the model should be modified and expanded. The modification is made in calculating the flow field in a manner consistent with the finite element approach, in evaluating the moisture-content increasing rate within the region of interest, and in numerically computing the nonlinear terms. With these modifications, the flow field is continuous everywhere in the flow regime, including element boundaries and nodal points, and the mass loss through boundaries is much reduced. Expansion is made to include four additional numerical schemes which would be more appropriate for many situations. Also, to save computer storage, all arrays pertaining to the boundary condition information are compressed to smaller dimension, and to ease the treatment of different problems, all arrays are variably dimensioned in all subroutines. This report is intended to document these efforts. In addition, in the derivation of finite-element equations, matrix component representation is used, which is believed more readable than the matrix representation in its entirety. Two identical sample problems are simulated to show the difference between the original and revised models.
NASA Astrophysics Data System (ADS)
Payacán, Italo; Gutiérrez, Francisco; Gelman, Sarah E.; Bachmann, Olivier; Parada, Miguel Ángel
2014-12-01
This contribution illustrates a case study of a pluton (La Gloria pluton; LGP) where magnetic and magmatic fabrics are locally decoupled. We compare the magmatic fabric with the available magnetic fabric data to explore their abilities and elucidate the magma flow record of LGP. Results indicate that magnetic (controlled by multi-domain magnetite) and magmatic fabrics are generally consistent throughout LGP. Foliations define an axisymmetric pattern that gradually changes from vertical near lateral margins to less steep in the pluton interior, whereas lineations are subhorizontal following the elongation direction of the pluton. However, samples at the pluton center show marked differences between both fabrics: magnetic fabrics indicate subhorizontal magnetic lineations and foliations, and magmatic fabrics indicate subvertical lineations and foliations. Both magnetic and magmatic fabrics are interpreted to record strain caused by magma flow during thermal convection and lateral magma propagation at the transition between low and high crystallinity stages. We suggest that fabrics acquisition and consistency were determined by shear conditions (pure/simple shear rates ratio) and the orientation of the magma flow direction with respect to a rigid boundary (critical crystalline region) of the pluton. Magmatic fabric differs at the center of the pluton because pure shear is dominant and ascendant flows are orthogonal to the horizontal rigid boundary. LGP represents a whole-scale partly molten magma reservoir, where both thermal convection and lateral propagation of the magma are recorded simultaneously. This study highlights the importance of characterizing both fabrics to properly interpret magma flow recorded in plutons.
Yeh, G.T.; Wong, K.V.; Craig, P.M.; Davis, E.C.
1985-01-01
This paper presents the construction, verification, and application of two groundwater flow and contaminant transport models: A Finite Element Model of Water Flow through Aquifers (FEWA) and A Finite Element Model of Material Transport through Aquifers (FEMA). The construction is based on the finite element approximation of partial differential equations of groundwater flow (FEWA) and of solute movement (FEMA). The particular features of FEWA and FEMA are their versatility and flexibility for dealing with nearly all vertically integrated two-dimensional problems. The models were verified against both analytical solutions and widely used US Geological Survey finite difference approximations. They were then applied for calibration and validation, using data obtained in experiments at the Engineering Test Facility at Oak Ridge National Laboratory. Results indicated that the models are valid for this specific site. To demonstrate the versatility anf flexibility of the models, they were applied to two hypothetical, but realistic, complex problems and three field sites across the United States. In these applications the models yielded good agreement with the field data for all three sites. Finally, the predictive capabilities of the models were demonstrated using data obtained at the Hialeah Preston site in Florida. This case illustrates the capability of FEWA and FEMA as predictive tools and their usefulness in the management of groundwater flow and contaminant transport. 25 refs.
A spectral-element discontinuous Galerkin lattice Boltzmann method for nearly incompressible flows
NASA Astrophysics Data System (ADS)
Min, Misun; Lee, Taehun
2011-01-01
We present a spectral-element discontinuous Galerkin lattice Boltzmann method for solving nearly incompressible flows. Decoupling the collision step from the streaming step offers numerical stability at high Reynolds numbers. In the streaming step, we employ high-order spectral-element discontinuous Galerkin discretizations using a tensor product basis of one-dimensional Lagrange interpolation polynomials based on Gauss-Lobatto-Legendre grids. Our scheme is cost-effective with a fully diagonal mass matrix, advancing time integration with the fourth-order Runge-Kutta method. We present a consistent treatment for imposing boundary conditions with a numerical flux in the discontinuous Galerkin approach. We show convergence studies for Couette flows and demonstrate two benchmark cases with lid-driven cavity flows for Re = 400-5000 and flows around an impulsively started cylinder for Re = 550-9500. Computational results are compared with those of other theoretical and computational work that used a multigrid method, a vortex method, and a spectral element model.
A spectral-element discontinuous Galerkin lattice Boltzmann method for incompressible flows.
Min, M.; Lee, T.; Mathematics and Computer Science; City Univ. of New York
2011-01-01
We present a spectral-element discontinuous Galerkin lattice Boltzmann method for solving nearly incompressible flows. Decoupling the collision step from the streaming step offers numerical stability at high Reynolds numbers. In the streaming step, we employ high-order spectral-element discontinuous Galerkin discretizations using a tensor product basis of one-dimensional Lagrange interpolation polynomials based on Gauss-Lobatto-Legendre grids. Our scheme is cost-effective with a fully diagonal mass matrix, advancing time integration with the fourth-order Runge-Kutta method. We present a consistent treatment for imposing boundary conditions with a numerical flux in the discontinuous Galerkin approach. We show convergence studies for Couette flows and demonstrate two benchmark cases with lid-driven cavity flows for Re = 400-5000 and flows around an impulsively started cylinder for Re = 550-9500. Computational results are compared with those of other theoretical and computational work that used a multigrid method, a vortex method, and a spectral element model.
Nonlinear Spectral Element Model for the Blood Flow in Human Arteries
NASA Astrophysics Data System (ADS)
Lee, Usik; Jang, Injoon
2011-06-01
It has been well-known that the cardiovascular diseases are closely related to the blood flow characteristics such as blood pressure and blood flow rate in a blood vessel. Thus it is very important to predict such blood flow characteristics in an accurate and efficient way. To that end, this paper develops a nonlinear one-dimensional (1D) viscoelastic spectral element model for the blood flow in an artery with slowly varying cross-section by using the variational approach. In this study, the mechanical behavior of the artery wall is represented by the standard solid viscoelastic model and the nonlinear spectral element model is formulated by using the frequency-dependent dynamic shape functions which are derived from the free wave solutions to the governing differential equations in frequency-domain. A direct iterative method is used in conjunction with the alternating frequency-time method to obtain either frequency-domain or time-domain solutions from the nonlinear spectral element model.
Direct numerical simulation of instabilities in parallel flow with spherical roughness elements
NASA Technical Reports Server (NTRS)
Deanna, R. G.
1992-01-01
Results from a direct numerical simulation of laminar flow over a flat surface with spherical roughness elements using a spectral-element method are given. The numerical simulation approximates roughness as a cellular pattern of identical spheres protruding from a smooth wall. Periodic boundary conditions on the domain's horizontal faces simulate an infinite array of roughness elements extending in the streamwise and spanwise directions, which implies the parallel-flow assumption, and results in a closed domain. A body force, designed to yield the horizontal Blasius velocity in the absence of roughness, sustains the flow. Instabilities above a critical Reynolds number reveal negligible oscillations in the recirculation regions behind each sphere and in the free stream, high-amplitude oscillations in the layer directly above the spheres, and a mean profile with an inflection point near the sphere's crest. The inflection point yields an unstable layer above the roughness (where U''(y) is less than 0) and a stable region within the roughness (where U''(y) is greater than 0). Evidently, the instability begins when the low-momentum or wake region behind an element, being the region most affected by disturbances (purely numerical in this case), goes unstable and moves. In compressible flow with periodic boundaries, this motion sends disturbances to all regions of the domain. In the unstable layer just above the inflection point, the disturbances grow while being carried downstream with a propagation speed equal to the local mean velocity; they do not grow amid the low energy region near the roughness patch. The most amplified disturbance eventually arrives at the next roughness element downstream, perturbing its wake and inducing a global response at a frequency governed by the streamwise spacing between spheres and the mean velocity of the most amplified layer.
Tariq, S.M.
1987-05-01
This study presents results of finite-element modeling of steady-state flow in perforated natural completions. Use of a mesh chosen carefully by grid sensitivity analysis permits evaluation of flow with more precision than that achieved by previous investigators. Also, for the first time, flow characteristics of perforated completions are evaluated with the non-Darcy effect resulting form converging flow around the perforation taken into account. The results indicate confirmation of Locke's results qualitatively but 5 to 10% overprediction by the nomograph, the importance of angular phasing between adjacent perforations, the uncertainty in generally accepted severe permeability impairment in the compacted zone, and a significant reduction in productivity owing to a non-Darcy effect around the perforation for high-rate gas wells.
Tariq, S.M.
1984-04-01
This study presents results of finite element modelling of steady-state flow in perforated natural completions. Use of a carefully chosen mesh based on grid sensitivity analysis permits evaluation of flow with more precision than achieved by previous investigators. Also, for the first time, evaluation of flow characterstics of perforated completion is made taking into account the non-Darcy effect due to converging flow around the perforation. The results indicate: (1) confirmation of Locke's findings qualitatively but 5-10% overprediction by the nomograph (2) importance of angular phasing between adjacent perforations, (3) untenability of generally accepted severe permeability impairment in the compacted zone, and (4) significant reduction in productivity due to non-Darcy effect around the perforation for high-rate wells.
Finite volume and finite element methods applied to 3D laminar and turbulent channel flows
Louda, Petr; Příhoda, Jaromír; Sváček, Petr; Kozel, Karel
2014-12-10
The work deals with numerical simulations of incompressible flow in channels with rectangular cross section. The rectangular cross section itself leads to development of various secondary flow patterns, where accuracy of simulation is influenced by numerical viscosity of the scheme and by turbulence modeling. In this work some developments of stabilized finite element method are presented. Its results are compared with those of an implicit finite volume method also described, in laminar and turbulent flows. It is shown that numerical viscosity can cause errors of same magnitude as different turbulence models. The finite volume method is also applied to 3D turbulent flow around backward facing step and good agreement with 3D experimental results is obtained.
Solution of groundwater-flow equations using an orthogonal finite-element scheme
Yeh, G.T.
1983-01-01
A new finite-element scheme is presented for approximating the groundwater-flow equation, that will result in a matrix having the properties of the positive type and diagonal dominance. Because of these properties, the matrix equation is amenable to the pointwise iteration solution strategies. This scheme differs from the standard Galerkin scheme in that discretization is performed using a general weighted residual procedure and weighting functions orthogonal to basis functions. Numerical results have been obtained for two verification examples and are compared with results using the conventional Galerkin scheme and with analytical solutions. It is shown that both the direct elimination and pointwise iteration solutions of the new orthogonal finite-element equation yield as accurate results as those obtained by the direct elimination solution of the Galerkin finite-element scheme. However, while the pointwise iteration solution of the Galerkin finite-element method converges for one example, it generated divergent solutions for the other. A demonstration example of steady-state flow in a homogeneous medium is used to compare the utility and versatility of the new scheme with the conventional Galerkin finite-element method.
A Two Element Laminar Flow Airfoil Optimized for Cruise. M.S. Thesis
NASA Technical Reports Server (NTRS)
Steen, Gregory Glen
1994-01-01
Numerical and experimental results are presented for a new two-element, fixed-geometry natural laminar flow airfoil optimized for cruise Reynolds numbers on the order of three million. The airfoil design consists of a primary element and an independent secondary element with a primary to secondary chord ratio of three to one. The airfoil was designed to improve the cruise lift-to-drag ratio while maintaining an appropriate landing capability when compared to conventional airfoils. The airfoil was numerically developed utilizing the NASA Langley Multi-Component Airfoil Analysis computer code running on a personal computer. Numerical results show a nearly 11.75 percent decrease in overall wing drag with no increase in stall speed at sailplane cruise conditions when compared to a wing based on an efficient single element airfoil. Section surface pressure, wake survey, transition location, and flow visualization results were obtained in the Texas A&M University Low Speed Wind Tunnel. Comparisons between the numerical and experimental data, the effects of the relative position and angle of the two elements, and Reynolds number variations from 8 x 10(exp 5) to 3 x 10(exp 6) for the optimum geometry case are presented.
NASA Astrophysics Data System (ADS)
Valyrakis, Manousos; Yagci, Oral; Kitsikoudis, Vasileios; Koursari, Eftychia
2015-04-01
The presence of vegetation in rivers and estuaries has important implications for the modification of the flow field and sediment transport. In-stream vegetation has the potential to regulate the morphology and ecological health of a surface water body, and as such it finds a wide range of applications. Even though a number of controls influencing the local flow field past aquatic vegetation elements or patches of instream vegetation have been identified (such as shape, areal density, size and flexibility), conclusive evidence is lacking, particularly on how sediment transport processes are affected. Here, an experimental study is designed to identify how the flow field past different types of elements simulating in-stream emergent vegetation is modified. Two sets of experiments are conducted, each with a distinct value of high and low hydraulic roughness for the bed surface. In both experiments a rigid cylindrical element, a patch of rigid tubes and a plant shaped element (Cupressus Macrocarpa), simulating instream emergent vegetation are utilized. The flow field is measured at various locations downstream the element and average and turbulent flow statistics are obtained at near bed, mid-flow depth and near the water surface regions. It is found that different structural aspects of the elements, particularly the geometry, can significantly affect the flow field downstream the elements. Specifically, the average flow profiles are practically restored to near ambient flow conditions at about 5 diameters downstream the rigid element, while this happens at longer distances for the other elements. The flow structures shed past the elements are also very distinct, as confirmed via appropriately designed fluorescent dye flow visualizations. Potential ecosystem feedbacks and implications for formation of geospatial patterns are also discussed.
NASA Astrophysics Data System (ADS)
Fan, Y.; Collet, M.; Ichchou, M.; Li, L.; Bareille, O.; Dimitrijevic, Z.
2016-01-01
This paper presents a rapid and accurate numerical tool for the energy flow evaluation in a periodic substructure from the near-field to the far-field domain. Here we suppose that the near-field part contains a point source characterized by the injected power in the structure. The near-field part is then modeled by Finite Element Method (FEM) while the periodic structure and the far-field part are regarded as waveguides and modeled by an enhanced Wave and Finite Element Method (WFEM). Enhancements are made on the eigenvalue scheme, the condensation of the unit cell and the consideration of a reduced wave basis. Efforts are made to adapt substructures modeled by different strategies in a multi-scale manner such that the final matrices dimensions of the built-up structure are largely reduced. The method is then validated numerically and theoretically. An application is presented, where a structural dynamical system coupled with periodic resistive piezoelectric shunts is discussed.
GHARAKHANI,ADRIN; WOLFE,WALTER P.
1999-10-01
The prediction of potential flow about zero thickness membranes by the boundary element method constitutes an integral component of the Lagrangian vortex-boundary element simulation of flow about parachutes. To this end, the vortex loop (or the panel) method has been used, for some time now, in the aerospace industry with relative success [1, 2]. Vortex loops (with constant circulation) are equivalent to boundary elements with piecewise constant variation of the potential jump. In this case, extending the analysis in [3], the near field potential velocity evaluations can be shown to be {Omicron}(1). The accurate evaluation of the potential velocity field very near the parachute surface is particularly critical to the overall accuracy and stability of the vortex-boundary element simulations. As we will demonstrate in Section 3, the boundary integral singularities, which arise due to the application of low order boundary elements, may lead to severely spiked potential velocities at vortex element centers that are near the boundary. The spikes in turn cause the erratic motion of the vortex elements, and the eventual loss of smoothness of the vorticity field and possible numerical blow up. In light of the arguments above, the application of boundary elements with (at least) a linear variation of the potential jump--or, equivalently, piecewise constant vortex sheets--would appear to be more appropriate for vortex-boundary element simulations. For this case, two strategies are possible for obtaining the potential flow field. The first option is to solve the integral equations for the (unknown) strengths of the surface vortex sheets. As we will discuss in Section 2.1, the challenge in this case is to devise a consistent system of equations that imposes the solenoidality of the locally 2-D vortex sheets. The second approach is to solve for the unknown potential jump distribution. In this case, for commonly used C{sup o} shape functions, the boundary integral is singular at
On current aspects of finite element computational fluid mechanics for turbulent flows
NASA Technical Reports Server (NTRS)
Baker, A. J.
1982-01-01
A set of nonlinear partial differential equations suitable for the description of a class of turbulent three-dimensional flow fields in select geometries is identified. On the basis of the concept of enforcing a penalty constraint to ensure accurate accounting of ordering effects, a finite element numerical solution algorithm is established for the equation set and the theoretical aspects of accuracy, convergence and stability are identified and quantized. Hypermatrix constructions are used to formulate the reduction of the computational aspects of the theory to practice. The robustness of the algorithm, and the computer program embodiment, have been verified for pertinent flow configurations.
NASA Astrophysics Data System (ADS)
Örley, Felix; Pasquariello, Vito; Hickel, Stefan; Adams, Nikolaus A.
2015-02-01
The conservative immersed interface method for representing complex immersed solid boundaries or phase interfaces on Cartesian grids is improved and extended to allow for the simulation of weakly compressible fluid flows through moving geometries. We demonstrate that an approximation of moving interfaces by a level-set field results in unphysical oscillations in the vicinity of sharp corners when dealing with weakly compressible fluids such as water. By introducing an exact reconstruction of the cut-cell properties directly based on a surface triangulation of the immersed boundary, we are able to recover the correct flow evolution free of numerical artifacts. The new method is based on cut-elements. It provides sub-cell resolution of the geometry and handles flows through narrow closing or opening gaps in a straightforward manner. We validate our method with canonical flows around oscillating cylinders. We demonstrate that the method allows for an accurate prediction of flows around moving obstacles in weakly compressible liquid flows with cavitation effects. In particular, we show that the cavitating flow through a closing fuel injector control valve, which is an example for a complex application with interaction of stationary and moving parts, can be predicted by the method.
Green element simulations of multiaquifer flows with a time-dependent Green's function
NASA Astrophysics Data System (ADS)
Taigbenu, Akpofure E.
2003-12-01
A new formulation of the Green element method (GEM), based on the transient Green's function of the diffusion differential operator, is herein used to solve the problem of transient flow in multiply layered aquifers that are separated by aquitards (leaky strata) which provide hydraulic interactions between them. By adopting the commonly used hydraulic flow approximation, flow in the aquifers is considered to take place in two lateral dimensions and in one vertical direction in the aquitards. As with an earlier GE multiaquifer model, the current model solves the one-dimensional flow in the aquitards by the formulation of [Appl. Math. Model. 22 (1998) 687] but uses the transient Green's function of the diffusion operator to solve the two-dimensional aquifer flow instead of the logarithmic Green's function formulation of [Water Resour. Res. 36 (2000) 3631]. In essence, the current formulation uses the same form of Green's functions for both flows in the aquifers and aquitards. While this can be viewed as an advantage of the current formulation over the previous one, the former presents other computational challenges and intricacies that are discussed in this paper. Applying the current formulation, and incorporating a Picard-type iterative algorithm, solutions are provided for regional flows in heterogeneous multiaquifer systems of arbitrary geometries that are subjected to point and distributed recharge of arbitrary strengths.
NASA Technical Reports Server (NTRS)
Kim, Sang-Wook
1988-01-01
A velocity-pressure integrated, mixed interpolation, Galerkin finite element method for the Navier-Stokes equations is presented. In the method, the velocity variables were interpolated using complete quadratic shape functions and the pressure was interpolated using linear shape functions. For the two dimensional case, the pressure is defined on a triangular element which is contained inside the complete biquadratic element for velocity variables; and for the three dimensional case, the pressure is defined on a tetrahedral element which is again contained inside the complete tri-quadratic element. Thus the pressure is discontinuous across the element boundaries. Example problems considered include: a cavity flow for Reynolds number of 400 through 10,000; a laminar backward facing step flow; and a laminar flow in a square duct of strong curvature. The computational results compared favorable with those of the finite difference methods as well as experimental data available. A finite elememt computer program for incompressible, laminar flows is presented.
Weak Galerkin finite element methods for Darcy flow: Anisotropy and heterogeneity
Lin, Guang; Liu, Jiangguo; Mu, Lin; Ye, Xiu
2014-11-01
This paper presents a family of weak Galerkin finite element methods (WGFEMs) for Darcy flow computation. The WGFEMs are new numerical methods that rely on the novel concept of discrete weak gradients. The WGFEMs solve for pressure unknowns both in element interiors and on the mesh skeleton. The numerical velocity is then obtained from the discrete weak gradient of the numerical pressure. The new methods are quite different than many existing numerical methods in that they are locally conservative by design, the resulting discrete linear systems are symmetric and positive-definite, and there is no need for tuning problem-dependent penalty factors. We test the WGFEMs on benchmark problems to demonstrate the strong potential of these new methods in handling strong anisotropy and heterogeneity in Darcy flow.
Fischer, P.F.; Miller, N.I.; Tufo, H.M.
1998-10-29
As the sound speed is infinite for incompressible flows, computation of the pressure constitutes the stiffest component in the time advancement of unsteady simulations. For complex geometries, efficient solution is dependent upon the availability of fast solvers for sparse linear systems. In this paper we develop a Schwarz preconditioner for the spectral element method using overlapping subdomains for the pressure. These local subdomain problems are derived from tensor products of one-dimensional finite element discretizations and admit use of fast diagonalization methods based upon matrix-matrix products. In addition, we use a coarse grid projection operator whose solution is computed via a fast parallel direct solver. The combination of overlapping Schwarz preconditioning and fast coarse grid solver provides as much as a fourfold reduction in simulation time over previously employed methods based upon deflation for parallel solution of multi-million grid point flow problems.
Flow transition with 2-D roughness elements in a 3-D channel
NASA Technical Reports Server (NTRS)
Liu, Zhining; Liu, Chaoquin; Mccormick, Stephen F.
1993-01-01
We develop a new numerical approach to study the spatially evolving instability of the streamwise dominant flow in the presence of roughness elements. The difficulty in handling the flow over the boundary surface with general geometry is removed by using a new conservative form of the governing equations and an analytical mapping. The numerical scheme uses second-order backward Euler in time, fourth-order central differences in all three spatial directions, and boundary-fitted staggered grids. A three-dimensional channel with multiple two-dimensional-type roughness elements is employed as the test case. Fourier analysis is used to decompose different Fourier modes of the disturbance. The results show that surface roughness leads to transition at lower Reynolds number than for smooth channels.
Spectral element simulation of precession driven flows in the outer cores of spheroidal planets
NASA Astrophysics Data System (ADS)
Vormann, Jan; Hansen, Ulrich
2015-04-01
A common feature of the planets in the solar system is the precession of the rotation axes, driven by the gravitational influence of another body (e.g. the Earth's moon). In a precessing body, the rotation axis itself is rotating around another axis, describing a cone during one precession period. Similar to the coriolis and centrifugal force appearing from the transformation to a rotating system, the addition of precession adds another term to the Navier-Stokes equation, the so called Poincaré force. The main geophysical motivation in studying precession driven flows comes from their ability to act as magnetohydrodynamic dynamos in planets and moons. Precession may either act as the only driving force or operate together with other forces such as thermochemical convection. One of the challenges in direct numerical simulations of such flows lies in the spheroidal shape of the fluid volume, which should not be neglected since it contributes an additional forcing trough pressure torques. Codes developed for the simulation of flows in spheres mostly use efficient global spectral algorithms that converge fast, but lack geometric flexibility, while local methods are usable in more complex shapes, but often lack high accuracy. We therefore adapted the spectral element code Nek5000, developed at Argonne National Laboratory, to the problem. The spectral element method is capable of solving for the flow in arbitrary geometries while still offering spectral convergence. We present first results for the simulation of a purely hydrodynamic, precession-driven flow in a spheroid with no-slip boundaries and an inner core. The driving by the Poincaré force is in a range where theoretical work predicts multiple solutions for a laminar flow. Our simulations indicate a transition to turbulent flows for Ekman numbers of 10-6 and lower.
NASA Astrophysics Data System (ADS)
MacNamee, A.; Stockli, D. F.
2015-12-01
We present the first constraints on transient fluid flow using the novel application of apatite (U-Th)/He thermochronometry (AHe) in the geothermally active Dixie Valley area of central Nevada, western United States. The valley is bound to the west by a high angle normal fault, along which the adjacent Stillwater Range has been recently exhumed in the footwall. Zones of elevated shallow geothermal gradients (geothermal anomalies) occur in dilational corners along the range front and therefore make Dixie Valley an ideal site to test the sensitivity of the AHe thermochonometer to fluid flow in the shallow crust. Apatites yield (U-Th)/He ages ca. 0.2-16 Ma and three elevation transects record advective cooling of the footwall during exhumation commencing at 3-5 Ma. Many AHe ages are significantly younger (<4 Ma) and do not overlap exhumational cooling ages within error. Consequently, the younger AHe ages are distinguishable as hydrothermally reset and demonstrate the ability of this method to resolve conductive cooling ages from overprinted, fluid-reheated cooling ages. Interpolation of AHe ages shows that the youngest ages correspond with remarkable accuracy to the spatial extents of previously mapped geothermal anomalies. The capability of the AHe thermochronometer to constrain the timing and location of paleofluid flow recommends this technique as a powerful and cost-effective tool in geothermal exploration and petroleum systems evaluations.
Investigation of Mixed Element Hybrid Grid-Based CFD Methods for Rotorcraft Flow Analysis
2010-05-01
Nomenclature* CT thrust coefficient n iteration number n unit surface normal vector q flow state R rotor radius R coordinate vector S surface S ...NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR( S ) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME( S ) AND...ADDRESS(ES) Continuum Dynamics, Inc,Ewing,NJ,08618 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME( S ) AND ADDRESS(ES) 10
1982-10-01
7A1-Ai24 9877 FINITE ELEMENT PROGRRM FOR C ALCULATING FLOWS IN / 3 UN C((U) TURBOMACHINES WITH RESULTS FOR NASA TASK-i COMPRESSOR 98 IU) NAVAL...Aeronaut cs ean of Sdience and Engineering 3 C. ~% h~.c. c . .. . . . . ._ . . .. ABSTRACT A general mash generation code (MESHGEN) and finite ele...DESCRIPTION. ......... 36 B. SUBROUTINE DESCRIPTIONS . . . . . . . . . . 38 1. Subroutine INITI . . . . . . . . . . . 38 2. Subroutine INPUT ........... 39 3
A strongly conservative finite element method for the coupling of Stokes and Darcy flow
NASA Astrophysics Data System (ADS)
Kanschat, G.; Rivière, B.
2010-08-01
We consider a model of coupled free and porous media flow governed by Stokes and Darcy equations with the Beavers-Joseph-Saffman interface condition. This model is discretized using divergence-conforming finite elements for the velocities in the whole domain. Discontinuous Galerkin techniques and mixed methods are used in the Stokes and Darcy subdomains, respectively. This discretization is strongly conservative in Hdiv( Ω) and we show convergence. Numerical results validate our findings and indicate optimal convergence orders.
A p-version finite element method for steady incompressible fluid flow and convective heat transfer
NASA Technical Reports Server (NTRS)
Winterscheidt, Daniel L.
1993-01-01
A new p-version finite element formulation for steady, incompressible fluid flow and convective heat transfer problems is presented. The steady-state residual equations are obtained by considering a limiting case of the least-squares formulation for the transient problem. The method circumvents the Babuska-Brezzi condition, permitting the use of equal-order interpolation for velocity and pressure, without requiring the use of arbitrary parameters. Numerical results are presented to demonstrate the accuracy and generality of the method.
Han, Jing-Cheng; Huang, Guohe; Huang, Yuefei; Zhang, Hua; Li, Zhong; Chen, Qiuwen
2015-08-15
Lack of hydrologic process representation at the short time-scale would lead to inadequate simulations in distributed hydrological modeling. Especially for complex mountainous watersheds, surface runoff simulations are significantly affected by the overland flow generation, which is closely related to the rainfall characteristics at a sub-time step. In this paper, the sub-daily variability of rainfall intensity was considered using a probability distribution, and a chance-constrained overland flow modeling approach was proposed to capture the generation of overland flow within conceptual distributed hydrologic simulations. The integrated modeling procedures were further demonstrated through a watershed of China Three Gorges Reservoir area, leading to an improved SLURP-TGR hydrologic model based on SLURP. Combined with rainfall thresholds determined to distinguish various magnitudes of daily rainfall totals, three levels of significance were simultaneously employed to examine the hydrologic-response simulation. Results showed that SLURP-TGR could enhance the model performance, and the deviation of runoff simulations was effectively controlled. However, rainfall thresholds were so crucial for reflecting the scaling effect of rainfall intensity that optimal levels of significance and rainfall threshold were 0.05 and 10 mm, respectively. As for the Xiangxi River watershed, the main runoff contribution came from interflow of the fast store. Although slight differences of overland flow simulations between SLURP and SLURP-TGR were derived, SLURP-TGR was found to help improve the simulation of peak flows, and would improve the overall modeling efficiency through adjusting runoff component simulations. Consequently, the developed modeling approach favors efficient representation of hydrological processes and would be expected to have a potential for wide applications.
Bester-van der Merwe, Aletta E; Bitalo, Daphne; Cuevas, Juan M; Ovenden, Jennifer; Hernández, Sebastián; da Silva, Charlene; McCord, Meaghen; Roodt-Wilding, Rouvay
2017-01-01
The tope shark (Galeorhinus galeus Linnaeus, 1758) is a temperate, coastal hound shark found in the Atlantic and Indo-Pacific oceans. In this study, the population structure of Galeorhinus galeus was determined across the entire Southern Hemisphere, where the species is heavily targeted by commercial fisheries, as well as locally, along the South African coastline. Analysis was conducted on a total of 185 samples using 19 microsatellite markers and a 671 bp fragment of the NADH dehydrogenase subunit 2 (ND2) gene. Across the Southern Hemisphere, three geographically distinct clades were recovered, including one from South America (Argentina, Chile), one from Africa (all the South African collections) and an Australia-New Zealand clade. Nuclear data revealed significant population subdivisions (FST = 0.192 to 0.376, p<0.05) indicating limited gene flow for tope sharks across ocean basins. Marked population connectivity was however evident across the Indian Ocean based on Bayesian clustering analysis. More locally in South Africa, F-statistics and multivariate analysis supported moderate to high gene flow across the Atlantic/Indian Ocean boundary (FST = 0.035 to 0.044, p<0.05), with exception of samples from Struisbaai and Port Elizabeth which differed significantly from the rest. Discriminant and Bayesian clustering analysis indicated admixture in all sampling populations, decreasing from west to east, corroborating possible restriction to gene flow across regional oceanographic barriers. Mitochondrial sequence data recovered seven haplotypes (h = 0.216, π = 0.001) for South Africa, with one major haplotype shared by 87% of the individuals and at least one private haplotype for each sampling location except Port Elizabeth. As with many other coastal shark species with cosmopolitan distribution, this study confirms the lack of both historical dispersal and inter-oceanic gene flow while also implicating contemporary factors such as oceanic currents and thermal fronts
Cuevas, Juan M.; Ovenden, Jennifer; Hernández, Sebastián; da Silva, Charlene; McCord, Meaghen; Roodt-Wilding, Rouvay
2017-01-01
The tope shark (Galeorhinus galeus Linnaeus, 1758) is a temperate, coastal hound shark found in the Atlantic and Indo-Pacific oceans. In this study, the population structure of Galeorhinus galeus was determined across the entire Southern Hemisphere, where the species is heavily targeted by commercial fisheries, as well as locally, along the South African coastline. Analysis was conducted on a total of 185 samples using 19 microsatellite markers and a 671 bp fragment of the NADH dehydrogenase subunit 2 (ND2) gene. Across the Southern Hemisphere, three geographically distinct clades were recovered, including one from South America (Argentina, Chile), one from Africa (all the South African collections) and an Australia-New Zealand clade. Nuclear data revealed significant population subdivisions (FST = 0.192 to 0.376, p<0.05) indicating limited gene flow for tope sharks across ocean basins. Marked population connectivity was however evident across the Indian Ocean based on Bayesian clustering analysis. More locally in South Africa, F-statistics and multivariate analysis supported moderate to high gene flow across the Atlantic/Indian Ocean boundary (FST = 0.035 to 0.044, p<0.05), with exception of samples from Struisbaai and Port Elizabeth which differed significantly from the rest. Discriminant and Bayesian clustering analysis indicated admixture in all sampling populations, decreasing from west to east, corroborating possible restriction to gene flow across regional oceanographic barriers. Mitochondrial sequence data recovered seven haplotypes (h = 0.216, π = 0.001) for South Africa, with one major haplotype shared by 87% of the individuals and at least one private haplotype for each sampling location except Port Elizabeth. As with many other coastal shark species with cosmopolitan distribution, this study confirms the lack of both historical dispersal and inter-oceanic gene flow while also implicating contemporary factors such as oceanic currents and thermal fronts
Shadid, J.N.; Moffat, H.K.; Hutchinson, S.A.; Hennigan, G.L.; Devine, K.D.; Salinger, A.G.
1996-05-01
The theoretical background for the finite element computer program, MPSalsa, is presented in detail. MPSalsa is designed to solve laminar, low Mach number, two- or three-dimensional incompressible and variable density reacting fluid flows on massively parallel computers, using a Petrov-Galerkin finite element formulation. The code has the capability to solve coupled fluid flow, heat transport, multicomponent species transport, and finite-rate chemical reactions, and to solver coupled multiple Poisson or advection-diffusion- reaction equations. The program employs the CHEMKIN library to provide a rigorous treatment of multicomponent ideal gas kinetics and transport. Chemical reactions occurring in the gas phase and on surfaces are treated by calls to CHEMKIN and SURFACE CHEMKIN, respectively. The code employs unstructured meshes, using the EXODUS II finite element data base suite of programs for its input and output files. MPSalsa solves both transient and steady flows by using fully implicit time integration, an inexact Newton method and iterative solvers based on preconditioned Krylov methods as implemented in the Aztec solver library.
Gupta, Diksha; Kumar, Lokendra; Singh, Bani
2014-01-01
The objective of this investigation is to analyze the effect of unsteadiness on the mixed convection boundary layer flow of micropolar fluid over a permeable shrinking sheet in the presence of viscous dissipation. At the sheet a variable distribution of suction is assumed. The unsteadiness in the flow and temperature fields is caused by the time dependence of the shrinking velocity and surface temperature. With the aid of similarity transformations, the governing partial differential equations are transformed into a set of nonlinear ordinary differential equations, which are solved numerically, using variational finite element method. The influence of important physical parameters, namely, suction parameter, unsteadiness parameter, buoyancy parameter and Eckert number on the velocity, microrotation, and temperature functions is investigated and analyzed with the help of their graphical representations. Additionally skin friction and the rate of heat transfer have also been computed. Under special conditions, an exact solution for the flow velocity is compared with the numerical results obtained by finite element method. An excellent agreement is observed for the two sets of solutions. Furthermore, to verify the convergence of numerical results, calculations are conducted with increasing number of elements.
The semidiscrete Galerkin finite element modeling of compressible viscous flow past an airfoil
NASA Technical Reports Server (NTRS)
Meade, Andrew J.
1990-01-01
The primary project was the numerical simulation, by a finite element/finite difference method, of the viscous flow about an airfoil. The secondary project involved the numerical simulation of the three-dimensional separated and vortex-dominated flow about a hemispherically capped cylinder in the transonic regime. Preliminary calculations were started for the hemisphere-cylinder at 0 and 5 degree angle of attack. The solution of the flow field about airfoils and wings is required to determine the important parameters of lift, moment, and drag. Viscous effects must be accounted for if the drag is to be accurately calculated. At present there are basically two approaches to the numerical simulation of the flow field, the use of fully viscous models and the inviscid/viscous models. The fully viscous models require the solution of an approximation of the Navier-Stokes equations and therefore should simulate most of the physical mechanisms. A fast, accurate, and computationally efficient inviscid flow solver was recently developed by Hartwich. It is thought that Hartwich's program coupled to a fast, accurate, and computationally efficient boundary layer code, will make an excellent tool for airfoil design. The purpose of the primary project was to develop a compressible boundary layer code using the semidiscrete Galerkin finite element method. The numerical scheme employed used the combination of a Dorodnitsyn formulation of the boundary layer equations, with a finite difference/finite element procedure (semidiscrete Galerkin method), in the solution of the compressible two-dimensional boundary layer equations. A laminar compressible boundary layer code was developed and tested for a NACA 0012 airfoil at a Mach number of 0.5, a Reynolds number of 5000, and zero angle of attack. At present the boundary layer program solves up to, but not beyond, separation.
Large-scale computation of incompressible viscous flow by least-squares finite element method
NASA Technical Reports Server (NTRS)
Jiang, Bo-Nan; Lin, T. L.; Povinelli, Louis A.
1993-01-01
The least-squares finite element method (LSFEM) based on the velocity-pressure-vorticity formulation is applied to large-scale/three-dimensional steady incompressible Navier-Stokes problems. This method can accommodate equal-order interpolations and results in symmetric, positive definite algebraic system which can be solved effectively by simple iterative methods. The first-order velocity-Bernoulli function-vorticity formulation for incompressible viscous flows is also tested. For three-dimensional cases, an additional compatibility equation, i.e., the divergence of the vorticity vector should be zero, is included to make the first-order system elliptic. The simple substitution of the Newton's method is employed to linearize the partial differential equations, the LSFEM is used to obtain discretized equations, and the system of algebraic equations is solved using the Jacobi preconditioned conjugate gradient method which avoids formation of either element or global matrices (matrix-free) to achieve high efficiency. To show the validity of this scheme for large-scale computation, we give numerical results for 2D driven cavity problem at Re = 10000 with 408 x 400 bilinear elements. The flow in a 3D cavity is calculated at Re = 100, 400, and 1,000 with 50 x 50 x 50 trilinear elements. The Taylor-Goertler-like vortices are observed for Re = 1,000.
An investigation of noise produced by unsteady gas flow through silencer elements
NASA Astrophysics Data System (ADS)
Mawhinney, Graeme Hugh
This thesis presents an investigation of the noise produced by unsteady gas flow through silencer elements. The central aim of the research project was to produce a tool for assistance in the design of the exhaust systems of diesel powered electrical generator sets, with the modelling techniques developed having a much wider application in reciprocating internal combustion engine exhaust systems. An automotive cylinder head was incorporated in a purpose built test rig to supply exhaust pulses, typical of those found in the exhaust system of four stroke diesel engines, to various experimental exhaust systems. Exhaust silencer elements evaluated included expansion, re- entrant, concentric tube resonator and absorptive elements. Measurements taken on the test rig included, unsteady superposition pressure in the exhaust ducting, cyclically averaged mass flow rate through the system and exhaust noise levels radiated into a semi-anechoic measurement chamber. The entire test rig was modelled using the 1D finite volume method developed previously developed at Queen's University Belfast. Various boundary conditions, developed over the years, were used to model the various silencer elements being evaluated. The 1D gas dynamic simulation thus estimated the mass flux history at the open end of the exhaust system. The mass flux history was then broken into its harmonic components and an acoustic radiation model was developed to model the sound pressure level produced by an acoustic monopole over a reflecting plane. The accuracy of the simulation technique was evaluated by correlation of measured and simulated superposition pressure and noise data. In general correlation of superposition pressure was excellent for all of the silencer elements tested. Predicted sound pressure level radiated from the open end of the exhaust tailpipe was seen to be accurate in the 100 Hz to 1 kHz frequency range for all of the silencer elements tested.
a Finite Element Method for Flow Problems with Free Surfaces and Moving Fronts.
NASA Astrophysics Data System (ADS)
Westerberg, Kenneth William
A finite element technique to model a fluid flow with a liquid-gas free surface and/or a solid-liquid phase -change boundary has been developed. These types of problems are difficult because in addition to the flow and temperature fields, the domain boundaries are also unknown. Two specific applications where such a technique is needed are formulated and discussed. The first is the development of a model for the thermal printing of bar code labels. Thermal printer paper is heated by a moving print head and a heat-activated chemical reaction takes place to change the color of the paper. The extent of the region that has reacted is governed by the same equations that govern the melting of a pure material. The second application is building a model of an electron beam metal vaporizer. A beam of electrons strikes the surface of a pool of liquid metal causing the metal to vaporize. A pool of liquid metal forms in the vicinity of the beam impact area. The problem involves both a liquid-gas free surface and a solid-liquid phase -change front as well as a tri-junction point where solid, liquid and gas phases all meet. Both models two-dimensional and time-dependent. The technique is based on a deformable finite element mesh designed to keep the interfaces on element boundaries. There is a singularity in the force balance along the liquid-gas free interface due to surface tension and a singularity in the heat balance along the solid-liquid phase-change front due to the latent heat of the phase-change. These singularities are easily handled by the finite element method provided they are kept on element boundaries. The positions of the free and moving boundaries are tracked using spines. Special linear algebra techniques are developed to solve the equation system resulting from our finite element discretization of the free or moving boundary problem.
NASA Astrophysics Data System (ADS)
Gonzalez-Mancera, Andres; Gonzalez Cardenas, Diego
2014-11-01
Flow in the microcirculation is highly dependent on the mechanical properties of the cells suspended in the plasma. Red blood cells have to deform in order to pass through the smaller sections in the microcirculation. Certain deceases change the mechanical properties of red blood cells affecting its ability to deform and the rheological behaviour of blood. We developed a hybrid algorithm based on the Lattice-Boltzmann and Finite Element methods to simulate blood flow in small capillaries. Plasma was modeled as a Newtonian fluid and the red blood cells' membrane as a hyperelastic solid. The fluid-structure interaction was handled using the immersed boundary method. We simulated the flow of plasma with suspended red blood cells through cylindrical capillaries and measured the pressure drop as a function of the membrane's rigidity. We also simulated the flow through capillaries with a restriction and identify critical properties for which the suspended particles are unable to flow. The algorithm output was verified by reproducing certain common features of flow int he microcirculation such as the Fahraeus-Lindqvist effect.
NASA Astrophysics Data System (ADS)
Chaudhuri, A.; Jacobs, G. B.; Don, W. S.; Abbassi, H.; Mashayek, F.
2017-03-01
A spatio-temporal adaptive artificial viscosity (AV) based shock-capturing scheme is proposed for the solution of both inviscid and viscous compressible flows using a high-order parallel Discontinuous Spectral Element Method (DSEM). The artificial viscosity and artificial thermal conduction coefficients are proportional to the viscous and thermal entropy generating terms, respectively, in the viscous entropy conservation law. The magnitude of AV is limited based on the explicit stable CFL criterion, so that the stable artificial viscous time step size is greater than the convective stable time step size. To further ensure the stability of this explicit approach, an adaptive variable order exponential filter is applied, if necessary, in elements where the AV has been limited. In viscous flow computations a modified Jameson's sensor (Ducros et al., 1999 [61]) limits the AV to small values in viscous shear regions, so as to maintain a high-order resolution in smooth regions and an essentially non-oscillatory behavior near sharp gradients/shocks regions. We have performed a systematic and extensive validation of the algorithm with one-dimensional problems (inviscid moving shock and viscous shock-structure interaction), two-dimensional problems (inviscid steady and unsteady shocked flows and viscous shock-boundary layer interaction), and a three-dimensional supersonic turbulent flow over a ramped cavity. These examples demonstrate that the explicit DSEM scheme with adaptive artificial viscosity terms is stable, accurate and efficient.
A boundary element approach to estimate the free surface in stratified two-phase flow
NASA Astrophysics Data System (ADS)
Ren, Shangjie; Dong, Feng; Tan, Chao; Xu, Yaoyuan
2012-10-01
Two-phase flows widely exist in many industries. Measuring the phase distribution in two-phase flow is important for the optimization and control of some industrial processes. Electrical resistance tomography (ERT) is a promising non-intrusive visualization technique for monitoring the two-phase flow. However, due to its nonlinear and ill-posed character, high-quality image reconstruction is difficult and some iterative approach is time consuming. In this paper, a boundary element approach is presented for directly estimating the free-surface in two-phase flow using ERT. The unknown free surface is parameterized by a Bézier curve. Coefficients of its control points are estimated by minimizing a residual function using the iterative Levenberg-Marquardt method. To speed up the estimation process, the physical model of ERT is formulated using a boundary element method. Based on this formulation, the forward problem is fast solved through a small size system matrix and the Jacobian matrix is efficiently calculated using an analytic method. After several numerical experiments, this approach is proved fast and precise and several factors influencing the estimation quality are analyzed based on these simulations.
Modelling platelet–blood flow interaction using the subcellular element Langevin method
Sweet, Christopher R.; Chatterjee, Santanu; Xu, Zhiliang; Bisordi, Katharine; Rosen, Elliot D.; Alber, Mark
2011-01-01
In this paper, a new three-dimensional modelling approach is described for studying fluid–viscoelastic cell interaction, the subcellular element Langevin (SCEL) method, with cells modelled by subcellular elements (SCEs) and SCE cells coupled with fluid flow and substrate models by using the Langevin equation. It is demonstrated that: (i) the new method is computationally efficient, scaling as 𝒪(N) for N SCEs; (ii) cell geometry, stiffness and adhesivity can be modelled by directly relating parameters to experimentally measured values; (iii) modelling the fluid–platelet interface as a surface leads to a very good correlation with experimentally observed platelet flow interactions. Using this method, the three-dimensional motion of a viscoelastic platelet in a shear blood flow was simulated and compared with experiments on tracking platelets in a blood chamber. It is shown that the complex platelet-flipping dynamics under linear shear flows can be accurately recovered with the SCEL model when compared with the experiments. All experimental details and electronic supplementary material are archived at http://biomath.math.nd.edu/scelsupplementaryinformation/. PMID:21593027
Finite Element Analysis of Magnetic Damping Effects on G-Jitter Induced Fluid Flow
NASA Technical Reports Server (NTRS)
Pan, Bo; Li, Ben Q.; deGroh, Henry C., III
1997-01-01
This paper reports some interim results on numerical modeling and analyses of magnetic damping of g-jitter driven fluid flow in microgravity. A finite element model is developed to represent the fluid flow, thermal and solute transport phenomena in a 2-D cavity under g-jitter conditions with and without an applied magnetic field. The numerical model is checked by comparing with analytical solutions obtained for a simple parallel plate channel flow driven by g-jitter in a transverse magnetic field. The model is then applied to study the effect of steady state g-jitter induced oscillation and on the solute redistribution in the liquid that bears direct relevance to the Bridgman-Stockbarger single crystal growth processes. A selection of computed results is presented and the results indicate that an applied magnetic field can effectively damp the velocity caused by g-jitter and help to reduce the time variation of solute redistribution.
Preprocessor and postprocessor computer programs for a radial-flow finite-element model
Pucci, A.A.; Pope, D.A.
1987-01-01
Preprocessing and postprocessing computer programs that enhance the utility of the U.S. Geological Survey radial-flow model have been developed. The preprocessor program: (1) generates a triangular finite element mesh from minimal data input, (2) produces graphical displays and tabulations of data for the mesh , and (3) prepares an input data file to use with the radial-flow model. The postprocessor program is a version of the radial-flow model, which was modified to (1) produce graphical output for simulation and field results, (2) generate a statistic for comparing the simulation results with observed data, and (3) allow hydrologic properties to vary in the simulated region. Examples of the use of the processor programs for a hypothetical aquifer test are presented. Instructions for the data files, format instructions, and a listing of the preprocessor and postprocessor source codes are given in the appendixes. (Author 's abstract)
DNS of Flows over Periodic Hills using a Discontinuous-Galerkin Spectral-Element Method
NASA Technical Reports Server (NTRS)
Diosady, Laslo T.; Murman, Scott M.
2014-01-01
Direct numerical simulation (DNS) of turbulent compressible flows is performed using a higher-order space-time discontinuous-Galerkin finite-element method. The numerical scheme is validated by performing DNS of the evolution of the Taylor-Green vortex and turbulent flow in a channel. The higher-order method is shown to provide increased accuracy relative to low-order methods at a given number of degrees of freedom. The turbulent flow over a periodic array of hills in a channel is simulated at Reynolds number 10,595 using an 8th-order scheme in space and a 4th-order scheme in time. These results are validated against previous large eddy simulation (LES) results. A preliminary analysis provides insight into how these detailed simulations can be used to improve Reynoldsaveraged Navier-Stokes (RANS) modeling
Flow Dynamics of green sand in the DISAMATIC moulding process using Discrete element method (DEM)
NASA Astrophysics Data System (ADS)
Hovad, E.; Larsen, P.; Walther, J. H.; Thorborg, J.; Hattel, J. H.
2015-06-01
The DISAMATIC casting process production of sand moulds is simulated with DEM (discrete element method). The main purpose is to simulate the dynamics of the flow of green sand, during the production of the sand mould with DEM. The sand shot is simulated, which is the first stage of the DISAMATIC casting process. Depending on the actual casting geometry the mould can be geometrically quite complex involving e.g. shadowing effects and this is directly reflected in the sand flow during the moulding process. In the present work a mould chamber with “ribs” at the walls is chosen as a baseline geometry to emulate some of these important conditions found in the real moulding process. The sand flow is simulated with the DEM and compared with corresponding video footages from the interior of the chamber during the moulding process. The effect of the rolling resistance and the static friction coefficient is analysed and discussed in relation to the experimental findings.
A solution of two-dimensional magnetohydrodynamic flow using the finite element method
Verardi, S.L.L.; Cardoso, J.R.; Motta, C.C.
1998-09-01
The problem of magnetohydrodynamic flow through channels has become important because of several engineering applications such as design of nuclear reactor cooling systems, electromagnetic pumps, MHD flowmeters, MHD generators, blood flow measurements, etc. A numerical code based on the Finite Element Method (FEM) was developed to solve the two-dimensional, steady-state magnetohydrodynamic (MHD) flow in a rectangular channel. In order to apply the FEM, the Galerkin Weak Formulation was used. In this analysis, in contrast with the previous works, the thickness of the duct wall is taken into account and the results are compared to those obtained in the limit case when the thickness is much smaller than a characteristic dimension of the duct. In this case, convergence behavior of several iterative methods, for high Hartmann numbers, was also investigated.
Finite element methods of analysis for 3D inviscid compressible flows
NASA Technical Reports Server (NTRS)
Peraire, Jaime
1990-01-01
The applicants have developed a finite element based approach for the solution of three-dimensional compressible flows. The procedure enables flow solutions to be obtained on tetrahedral discretizations of computational domains of complex form. A further development was the incorporation of a solution adaptive mesh strategy in which the adaptivity is achieved by complete remeshing of the solution domain. During the previous year, the applicants were working with the Advanced Aerodynamics Concepts Branch at NASA Ames Research Center with an implementation of the basic meshing and solution procedure. The objective of the work to be performed over this twelve month period was the transfer of the adaptive mesh technology and also the undertaking of basic research into alternative flow algorithms for the Euler equations on unstructured meshes.
NASA Astrophysics Data System (ADS)
Jardani, A.; Revil, A.; BolèVe, A.; Dupont, J. P.
2008-09-01
We propose an algorithm to invert self-potential signals measured at the ground surface of the Earth to localize hydromechanical disturbances or to the pattern of groundwater flow in geothermal systems. The self-potential signals result from the divergence of the streaming current density. Groundwater flow can be either driven by topography of the water table, free convection, or deformation of the medium. The algorithm includes the electrical resistivity distribution of the medium obtained independently by DC resistance tomography or electromagnetic methods or by coding the assumed geology in terms of distribution of the electrical resistivity accounting for the effect of the temperature and salinity distributions and possibly constraints from borehole measurements. Inversion of the distribution of the source current density from ground surface and borehole self-potential measurements is achieved by solving the inverse problem using Tikhonov regularization solutions that are compatible with the physics of the primary flow problem. By introducing assumptions regarding the smoothness or the compactness of the source and the three-dimensional distribution of the electrical resistivity of the system, the inverse problem can be solved in obtaining the three-dimensional distribution of the current source density in the ground. However, an annihilator can be added to the inverted source geometry without affecting the measured self-potential field. Annihilators can be obtained from boundary conditions. Synthetic models and a sandbox experiment are discussed to demonstrate the validity of the algorithm. An application is presented to the geothermal field of Cerro Prieto, Baja California, Mexico, using literature data. Inversion of the self-potential and resistivity data allows observing a plume of hot groundwater rising to the ground surface in the central part of the investigated area and discharging to the ground surface in the southwest part. The temperature anomaly
NASA Astrophysics Data System (ADS)
Pilatova, Katarina; Ofterdinger, Ulrich
2015-04-01
Recharge estimates and in understanding flow process in hard rock aquifers pose significant challenges. These arise from structural complexities of the hardrock aquifers and are further complicated by variability of the superficial cover. A comparative study of three metamorphic catchments situated in the North of Ireland is presented in this study, each with contrasting geology, glaciation history and consequently superficial cover. The presented study focusses on two main strains. Firstly, due to lack of existing records, stable water isotopes in precipitation (δ18O and δ2H) were monitored at the research sites and their temporal and spatial variability was examined. Secondly, flow processes and dynamics of groundwater recharge based on continuous records of stable isotopes in groundwater, collected along catchment transects from various depths, and its variability in relation to the acquired precipitation signal were studied. Each precipitation station exhibited distinct isotopic signatures, where weather effect and proximity to coastline are the main controlling factors governing the isotope signatures. Moreover, in each of the stations the isotopic signature varied seasonally and thus stable isotopes proved a useful tool for assessing the dynamics of groundwater recharge. The analysis of isotope signatures in precipitation and groundwater from various depths within the hard rock aquifers allowed to evaluate the timescale of recharge, with rapid responses varying from few days up to several months. In general, the recharge appeared continuous over the hydrological year within wetter catchments with higher annual precipitation amounts purging the hardrock aquifers throughout the year. However, within comparatively dryer catchments recharge has a more seasonal character, predominantly taking place during the winter half of the year. Spatially, the recharge is highly localised within the elevated catchment areas, where superficial deposits are scarce and the
NASA Astrophysics Data System (ADS)
Alakus, Bayram
Mathematical modeling involving porous heterogeneous media is important in a number of composite manufacturing processes, such as resin transfer molding (RTM), injection molding and the like. Of interest here are process modeling issues as related to composites manufacturing by RTM, because of the ability of the method to manufacture consolidated net shapes of complex geometric parts. In this research, we propose a mathematical model by utilizing the local volume averaging technique to establish the governing equations and therein provide finite element computational developments to predict the flow behavior of a viscous and viscoelastic fluid through a porous fiber network. The developments predict the velocity, pressure, and polymeric stress by modeling the conservation laws (e.g. mass and momentum) of the flow field coupled with constitutive equations for polymeric stress field. The governing equations of the flow are averaged for the fluid phase. Furthermore, the simulations target a variety of viscoelastic models (e.g. Newtonian model, Upper-Convected-Maxwell Model, Oldroyd-B model and Giesekus model) to provide a fundamental understanding of the elastic effects on the flow field. To solve the complex coupled nonlinear equations of the mathematical model described above, a combination of Newton linearization and the Galerkin and Streamline-Upwinding-Petrov-Galerkin (SUPG) finite element procedures are employed to accurately capture the representative physics. The formulations are first validated with available test cases of viscoelastic flows without porous media. Therein, the simulations are described for viscoelastic flow through porous media and the comparative results of different constitutive models are presented and discussed at length.
A flow physics study of flap-mounted vortex generators on a multi-element airfoil
NASA Astrophysics Data System (ADS)
Klausmeyer, Steven Michael
Vortex generators are a commonly used aerodynamic "fix" for flow separation problems. They are typically used to remedy flow separation due to design shortcomings or changes in operating conditions that exceed the original design point. Flow separation is often encountered with high lift systems. Flaps and slats can be difficult to design due to complicated flow phenomena and large Reynolds number effects. Previous research has indicated the effectiveness of vortex generators in correcting flow separation over a flap. In fact, significant aerodynamic performance improvements were predicted for high-lift systems that incorporate vortex generators in the original design. Before this may be attempted, a better understanding of vortex generator flow physics must be obtained for the development of appropriate design tools and analysis methods. The research contained herein is focused on a detailed flow physics study of vortex generators mounted to the flap of a three-element high-lift airfoil. Detailed velocity measurements taken using a three-component laser Doppler velocimeter were used to vortex/boundary layer interactions and global flowfield effects. The full Reynolds stress tensor and mean velocity field was measured in addition to surface pressures. Three basic vortex generator arrangements were studied: upflow, downflow, and corotating. Although not optimized, all three types of vortex generators were effective at eliminating boundary layer separation. The vortices demonstrated a tendency to rise from the flap surface regardless of orientation and decayed rapidly, with cross-stream vorticity dropping below measurable levels by 75% flap chord. However, the embedded vortices produced significant perturbations in the turbulence field and mean flow of the flap boundary layer that persisted to the flap trailing edge.
NASA Astrophysics Data System (ADS)
Lundgren, P.; Lanari, R.; Manzo, M.; Sansosti, E.; Tizzani, P.; Hutnak, M.; Hurwitz, S.
2008-12-01
Campi Flegrei caldera, Italy, located along the Bay of Naples, has a long history of significant vertical deformation, with the most recent large uplift (>1.5m) occurring in 1983-1984. Each episode of uplift has been followed by a period of subsidence that decreases in rate with time and may be punctuated by brief episodes of lesser uplift. The large amplitude of the major uplifts that occur without volcanic activity, and the subsequent subsidence has been argued as evidence for hydrothermal amplification of any magmatic source. The later subsidence and its temporal decay have been argued as due to diffusion of the pressurized caldera fill material into the less porous surrounding country rock. We present satellite synthetic aperture radar (SAR) interferometry (InSAR) time series analysis of ERS and Envisat data from the European Space Agency, based on exploiting the Small Baseline Subset (SBAS) approach [Berardino et al., 2002]; this allows us to generate maps of relative surface deformation though time, beginning in 1992 through 2007, that are relevant to both ascending and descending satellite orbits. The general temporal behavior is one of subsidence punctuated by several lesser uplift episodes. The spatial pattern of deformation can be modeled through simple inflation/deflation sources in an elastic halfspace. Given the evidence to suggest that fluids may play a significant role in the temporal deformation of Campi Flegrei, rather than a purely magmatic or magma chamber-based interpretation, we model the temporal and spatial evolution of surface deformation as a hydrothermal fluid flow process. We use the TOUGH2-BIOT2 set of numerical codes [Preuss et al., 1999; Hsieh, 1996], which couple multi-phase (liquid-gas) and multi-component (H2O-CO2) fluid flow in a porous or fractured media with plane strain deformation and fluid flow in a linearly elastic porous medium. We explore parameters related to the depth and temporal history of fluid injection, fluid
NASA Astrophysics Data System (ADS)
Broderick, Avery E.; Fish, Vincent L.; Doeleman, Sheperd S.; Loeb, Abraham
2011-09-01
Millimeter wave very long baseline interferometry (mm-VLBI) provides access to the emission region surrounding Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, on sub-horizon scales. Recently, a closure phase of 0° ± 40° was reported on a triangle of Earth-sized baselines (SMT-CARMA-JCMT) representing a new constraint upon the structure and orientation of the emission region, independent from those provided by the previously measured 1.3 mm-VLBI visibility amplitudes alone. Here, we compare this to the closure phases associated with a class of physically motivated, radiatively inefficient accretion flow models and present predictions for future mm-VLBI experiments with the developing Event Horizon Telescope (EHT). We find that the accretion flow models are capable of producing a wide variety of closure phases on the SMT-CARMA-JCMT triangle and thus not all models are consistent with the recent observations. However, those models that reproduce the 1.3 mm-VLBI visibility amplitudes overwhelmingly have SMT-CARMA-JCMT closure phases between ±30°, and are therefore broadly consistent with all current mm-VLBI observations. Improving station sensitivity by factors of a few, achievable by increases in bandwidth and phasing together multiple antennas at individual sites, should result in physically relevant additional constraints upon the model parameters and eliminate the current 180° ambiguity on the source orientation. When additional stations are included, closure phases of order 45°-90° are typical. In all cases, the EHT will be able to measure these with sufficient precision to produce dramatic improvements in the constraints upon the spin of Sgr A*.
Broderick, Avery E.; Fish, Vincent L.; Doeleman, Sheperd S.; Loeb, Abraham
2011-09-01
Millimeter wave very long baseline interferometry (mm-VLBI) provides access to the emission region surrounding Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, on sub-horizon scales. Recently, a closure phase of 0{sup 0} {+-} 40{sup 0} was reported on a triangle of Earth-sized baselines (SMT-CARMA-JCMT) representing a new constraint upon the structure and orientation of the emission region, independent from those provided by the previously measured 1.3 mm-VLBI visibility amplitudes alone. Here, we compare this to the closure phases associated with a class of physically motivated, radiatively inefficient accretion flow models and present predictions for future mm-VLBI experiments with the developing Event Horizon Telescope (EHT). We find that the accretion flow models are capable of producing a wide variety of closure phases on the SMT-CARMA-JCMT triangle and thus not all models are consistent with the recent observations. However, those models that reproduce the 1.3 mm-VLBI visibility amplitudes overwhelmingly have SMT-CARMA-JCMT closure phases between {+-}30{sup 0}, and are therefore broadly consistent with all current mm-VLBI observations. Improving station sensitivity by factors of a few, achievable by increases in bandwidth and phasing together multiple antennas at individual sites, should result in physically relevant additional constraints upon the model parameters and eliminate the current 180{sup 0} ambiguity on the source orientation. When additional stations are included, closure phases of order 45{sup 0}-90{sup 0} are typical. In all cases, the EHT will be able to measure these with sufficient precision to produce dramatic improvements in the constraints upon the spin of Sgr A*.
Gray, William G.; Miller, Cass T.
2010-01-01
This work is the eighth in a series that develops the fundamental aspects of the thermodynamically constrained averaging theory (TCAT) that allows for a systematic increase in the scale at which multiphase transport phenomena is modeled in porous medium systems. In these systems, the explicit locations of interfaces between phases and common curves, where three or more interfaces meet, are not considered at scales above the microscale. Rather, the densities of these quantities arise as areas per volume or length per volume. Modeling of the dynamics of these measures is an important challenge for robust models of flow and transport phenomena in porous medium systems, as the extent of these regions can have important implications for mass, momentum, and energy transport between and among phases, and formulation of a capillary pressure relation with minimal hysteresis. These densities do not exist at the microscale, where the interfaces and common curves correspond to particular locations. Therefore, it is necessary for a well-developed macroscale theory to provide evolution equations that describe the dynamics of interface and common curve densities. Here we point out the challenges and pitfalls in producing such evolution equations, develop a set of such equations based on averaging theorems, and identify the terms that require particular attention in experimental and computational efforts to parameterize the equations. We use the evolution equations developed to specify a closed two-fluid-phase flow model. PMID:21197134
Gray, William G; Miller, Cass T
2010-12-01
This work is the eighth in a series that develops the fundamental aspects of the thermodynamically constrained averaging theory (TCAT) that allows for a systematic increase in the scale at which multiphase transport phenomena is modeled in porous medium systems. In these systems, the explicit locations of interfaces between phases and common curves, where three or more interfaces meet, are not considered at scales above the microscale. Rather, the densities of these quantities arise as areas per volume or length per volume. Modeling of the dynamics of these measures is an important challenge for robust models of flow and transport phenomena in porous medium systems, as the extent of these regions can have important implications for mass, momentum, and energy transport between and among phases, and formulation of a capillary pressure relation with minimal hysteresis. These densities do not exist at the microscale, where the interfaces and common curves correspond to particular locations. Therefore, it is necessary for a well-developed macroscale theory to provide evolution equations that describe the dynamics of interface and common curve densities. Here we point out the challenges and pitfalls in producing such evolution equations, develop a set of such equations based on averaging theorems, and identify the terms that require particular attention in experimental and computational efforts to parameterize the equations. We use the evolution equations developed to specify a closed two-fluid-phase flow model.
Large Eddy Simulation of Flow Over Surface-Mounted Cube Using a Spectral Element Method
NASA Astrophysics Data System (ADS)
Kandala, Sriharsha; Rempfer, Dietmar
2010-11-01
Unsteady three dimensional flow over a surface-mounted cube, with its rich set of features like flow turbulence, upstream boundary layer separation, curved mixing layer, unsteady three dimensional wake, etc., provides an excellent test case for evaluating the performance of CFD codes. We are developing a parallel spectral element code, SpecSolve, with the objective of modeling incompressible flows in complex geometries. The code is based on the fractional step method and uses the operator-integrating factor splitting scheme for temporal integration. In this talk, we provide a brief overview of the algorithm and implementation details. We present results from large-eddy simulations of flow over a surface-mounted cube using SpecSolve. The Reynolds number, based on bulk flow velocity and height of the cube, is 40,000. The dynamic Smagorinsky model is used for modeling turbulence. These results are compared with experimental data of Martinuzzi and Tropea, LES results of Shah and Ferziger and our FLUENT LES simulations.
Analysis of periodic 3D viscous flows using a quadratic discrete Galerkin boundary element method
NASA Astrophysics Data System (ADS)
Chan, Chiu Y.; Beris, Antony N.; Advani, Suresh G.
1994-05-01
A discrete Galerkin boundary element technique with a quadratic approximation of the variables was developed to simulate the three-dimensional (3D) viscous flow established in periodic assemblages of particles in suspensions and within a periodic porous medium. The Batchelor's unit-cell approach is used. The Galerkin formulation effectively handles the discontinuity in the traction arising in flow boundaries with edges or corners, such as the unit cell in this case. For an ellipsoidal dilute suspension over the range of aspect ratio studied (1 to 54), the numerical solutions of the rotational velocity of the particles and the viscosity correction were found to agree with the analytic values within 0.2% and 2% respectively, even with coarse meshes. In a suspension of cylindrical particles the calculated period of rotation agreed with the experimental data. However, Burgers' predictions for the correction to the suspension viscosity were found to be 30% too low and therefore the concept of the equivalent ellipsoidal ratio is judged to be inadequate. For pressure-driven flow through a fixed bed of fibers, the prediction on the permeability was shown to deviate by as much as 10% from the value calculated based on approximate permeability additivity rules using the corresponding values for planar flow past a periodic array of parallel cylinders. These applications show the versatility of the technique for studying viscous flows in complicated 3D geometries.
Froelich, Daniel R; Mullendore, Daniel L; Jensen, Kåre H; Ross-Elliott, Tim J; Anstead, James A; Thompson, Gary A; Pélissier, Hélène C; Knoblauch, Michael
2011-12-01
Since the first ultrastructural investigations of sieve tubes in the early 1960s, their structure has been a matter of debate. Because sieve tube structure defines frictional interactions in the tube system, the presence of P protein obstructions shown in many transmission electron micrographs led to a discussion about the mode of phloem transport. At present, it is generally agreed that P protein agglomerations are preparation artifacts due to injury, the lumen of sieve tubes is free of obstructions, and phloem flow is driven by an osmotically generated pressure differential according to Münch's classical hypothesis. Here, we show that the phloem contains a distinctive network of protein filaments. Stable transgenic lines expressing Arabidopsis thaliana Sieve-Element-Occlusion-Related1 (SEOR1)-yellow fluorescent protein fusions show that At SEOR1 meshworks at the margins and clots in the lumen are a general feature of living sieve tubes. Live imaging of phloem flow and flow velocity measurements in individual tubes indicate that At SEOR1 agglomerations do not markedly affect or alter flow. A transmission electron microscopy preparation protocol has been generated showing sieve tube ultrastructure of unprecedented quality. A reconstruction of sieve tube ultrastructure served as basis for tube resistance calculations. The impact of agglomerations on phloem flow is discussed.
Simulation of Fluid Flow and Collection Efficiency for an SEA Multi-element Probe
NASA Technical Reports Server (NTRS)
Rigby, David L.; Struk, Peter M.; Bidwell, Colin
2014-01-01
Numerical simulations of fluid flow and collection efficiency for a Science Engineering Associates (SEA) multi-element probe are presented. Simulation of the flow field was produced using the Glenn-HT Navier-Stokes solver. Three-dimensional unsteady results were produced and then time averaged for the heat transfer and collection efficiency results. Three grid densities were investigated to enable an assessment of grid dependence. Simulations were completed for free stream velocities ranging from 85-135 meters per second, and free stream total pressure of 44.8 and 93.1 kilopascals (6.5 and 13.5 pounds per square inch absolute). In addition, the effect of angle of attack and yaw were investigated by including 5 degree deviations from straight for one of the flow conditions. All but one of the cases simulated a probe in isolation (i.e. in a very large domain without any support strut). One case is included which represents a probe mounted on a support strut within a finite sized wind tunnel. Collection efficiencies were generated, using the LEWICE3D code, for four spherical particle sizes, 100, 50, 20, and 5 micron in diameter. It was observed that a reduction in velocity of about 20% occurred, for all cases, as the flow entered the shroud of the probe. The reduction in velocity within the shroud is not indicative of any error in the probe measurement accuracy. Heat transfer results are presented which agree quite well with a correlation for the circular cross section heated elements. Collection efficiency results indicate a reduction in collection efficiency as particle size is reduced. The reduction with particle size is expected, however, the results tended to be lower than the previous results generated for isolated two-dimensional elements. The deviation from the two-dimensional results is more pronounced for the smaller particles and is likely due to the reduced flow within the protective shroud. As particle size increases differences between the two
Effect of surface morphology on drag and roughness sublayer in flows over regular roughness elements
NASA Astrophysics Data System (ADS)
Placidi, Marco; Ganapathisubramani, Bharathram
2014-11-01
The effects of systematically varied roughness morphology on bulk drag and on the spatial structure of turbulent boundary layers are examined by performing a series of wind tunnel experiments. In this study, rough surfaces consisting of regularly and uniformly distributed LEGO™ bricks are employed. Twelve different patterns are adopted in order to methodically examine the individual effects of frontal solidity (λF, frontal area of the roughness elements per unit wall-parallel area) and plan solidity (λP, plan area of roughness elements per unit wall-parallel area), on both the bulk drag and the turbulence structure. A floating element friction balance based on Krogstad & Efros (2010) was designed and manufactured to measure the drag generated by the different surfaces. In parallel, high resolution planar and stereoscopic Particle Image Velocimetry (PIV) was applied to investigate the flow features. This talk will focus on the effects of each solidity parameter on the bulk drag and attempt to relate the observed trends to the flow structures in the roughness sublayer. Currently at City University London.
Detached Eddy Simulations of Incompressible Turbulent Flows Using the Finite Element Method
Laskowski, G M
2001-08-01
An explicit Galerkin finite-element formulation of the Spalart-Allmaras (SA) 1 - equation turbulent transport model was implemented into the incompressible flow module of a parallel, multi-domain, Galerkin finite-element, multi-physics code, using both a RANS formulation and a DES formulation. DES is a new technique for simulating/modeling turbulence using a hybrid RANSkES formulation. The turbulent viscosity is constructed from an intermediate viscosity obtained from the transport equation which is spatially discretized using Q1 elements and integrated in time via forward Euler time integration. Three simulations of plane channel flow on a RANS-type grid, using different turbulence models, were conducted in order to validate the implementation of the SA model: SA-RANS, SA-DES and Smagorinksy (without wall correction). Very good agreement was observed between the SA-RANS results and theory, namely the Log Law of the Wall (LLW), especially in the viscous sublayer region and, to a lesser extent, in the log-layer region. The results obtained using the SA-DES model did not agree as well with the LLW, and it is believed that this poor agreement can be attributed to using a DES model on a RANS grid, namely using an incorrect length-scale. It was observed that near the wall, the SA-DES model acted as an RANS model, and away from the wall it acted as an LES model.
A Hybrid Boundary Element-Finite Volume Method for Unsteady Transonic Airfoil Flows
NASA Technical Reports Server (NTRS)
Hu, Hong; Kandil, Osama A.
1996-01-01
A hybrid boundary element finite volume method for unsteady transonic flow computation has been developed. In this method, the unsteady Euler equations in a moving frame of reference are solved in a small embedded domain (inner domain) around the airfoil using an implicit finite volume scheme. The unsteady full-potential equation, written in the same frame of reference and in the form of the Poisson equation. is solved in the outer domain using the integral equation boundary element method to provide the boundary conditions for the inner Euler domain. The solution procedure is a time-accurate stepping procedure, where the outer boundary conditions for the inner domain are updated using the integral equation -- boundary element solution over the outer domain. The method is applied to unsteady transonic flows around the NACA0012 airfoil undergoing pitching oscillation and ramp motion. The results are compared with those of an implicit Euler equation solver, which is used throughout a large computational domain, and experimental data.
A 3D moving mesh Finite Element Method for two-phase flows
NASA Astrophysics Data System (ADS)
Anjos, G. R.; Borhani, N.; Mangiavacchi, N.; Thome, J. R.
2014-08-01
A 3D ALE Finite Element Method is developed to study two-phase flow phenomena using a new discretization method to compute the surface tension forces. The computational method is based on the Arbitrary Lagrangian-Eulerian formulation (ALE) and the Finite Element Method (FEM), creating a two-phase method with an improved model for the liquid-gas interface. An adaptive mesh update procedure is also proposed for effective management of the mesh to remove, add and repair elements, since the computational mesh nodes move according to the flow. The ALE description explicitly defines the two-phase interface position by a set of interconnected nodes which ensures a sharp representation of the boundary, including the role of the surface tension. The proposed methodology for computing the curvature leads to accurate results with moderate programming effort and computational cost. Static and dynamic tests have been carried out to validate the method and the results have compared well to analytical solutions and experimental results found in the literature, demonstrating that the new proposed methodology provides good accuracy to describe the interfacial forces and bubble dynamics. This paper focuses on the description of the proposed methodology, with particular emphasis on the discretization of the surface tension force, the new remeshing technique, and the validation results. Additionally, a microchannel simulation in complex geometry is presented for two elongated bubbles.
NASA Astrophysics Data System (ADS)
Wen, T.; Castro, M.; Hall, C. M.
2012-12-01
We present helium concentrations and isotopic ratios from groundwater of the shallow Saginaw aquifer in southern Michigan. Saginaw helium data are interpreted in conjunction with data from the underlying Marshall aquifer in order to further our overall understanding of groundwater flow in the Michigan Basin, including cross-formational flow. For most samples, 3He and 4He concentrations are higher than those expected for water in solubility equilibrium with the atmosphere (ASW), with values of up to two and over three orders of magnitude with respect to ASW for 3He and 4He, respectively. He concentrations are particularly high in the Saginaw Lowlands, the main discharge area of the Michigan Basin. R/Ra values (where Ra is the 3He/4He ratio in the atmosphere) vary from 0.932 to 0.043 and are far greater for modern groundwaters as compared to older ones. Higher R/Ra values indicate mostly the presence of ASW recharge water. The observed decrease in R/Ra values with groundwater age and distance from the recharge area is accompanied by an increase in crustally produced 3He and 4He concentrations. Except for samples close to the recharge area, the average R/Ra value in the Saginaw aquifer is close to typical R/Ra crustal production values of 0.02~0.05. Some samples located in the recharge area suggest the presence of a bomb tritium component between ~5-15TU while the presence of a small mantle component of ~2% is clearly identified in some samples. He excesses in the Saginaw aquifer, in particular those in the Saginaw Lowlands discharge area are unusually high for such shallow depths and require a source external to the aquifer, partly supplied by underlying formations within the sedimentary sequence, partly from the crystalline basement. The similarity of the Saginaw and Marshall noble gas concentrations and isotopic signatures suggests that there is some level of vertical connection and mass exchange between these two aquifers, possibly through both advection and
Adaptive finite element simulation of flow and transport applications on parallel computers
NASA Astrophysics Data System (ADS)
Kirk, Benjamin Shelton
The subject of this work is the adaptive finite element simulation of problems arising in flow and transport applications on parallel computers. Of particular interest are new contributions to adaptive mesh refinement (AMR) in this parallel high-performance context, including novel work on data structures, treatment of constraints in a parallel setting, generality and extensibility via object-oriented programming, and the design/implementation of a flexible software framework. This technology and software capability then enables more robust, reliable treatment of multiscale--multiphysics problems and specific studies of fine scale interaction such as those in biological chemotaxis (Chapter 4) and high-speed shock physics for compressible flows (Chapter 5). The work begins by presenting an overview of key concepts and data structures employed in AMR simulations. Of particular interest is how these concepts are applied in the physics-independent software framework which is developed here and is the basis for all the numerical simulations performed in this work. This open-source software framework has been adopted by a number of researchers in the U.S. and abroad for use in a wide range of applications. The dynamic nature of adaptive simulations pose particular issues for efficient implementation on distributed-memory parallel architectures. Communication cost, computational load balance, and memory requirements must all be considered when developing adaptive software for this class of machines. Specific extensions to the adaptive data structures to enable implementation on parallel computers is therefore considered in detail. The libMesh framework for performing adaptive finite element simulations on parallel computers is developed to provide a concrete implementation of the above ideas. This physics-independent framework is applied to two distinct flow and transport applications classes in the subsequent application studies to illustrate the flexibility of the
Power flow as a complement to statistical energy analysis and finite element analysis
NASA Technical Reports Server (NTRS)
Cuschieri, J. M.
1987-01-01
Present methods of analysis of the structural response and the structure-borne transmission of vibrational energy use either finite element (FE) techniques or statistical energy analysis (SEA) methods. The FE methods are a very useful tool at low frequencies where the number of resonances involved in the analysis is rather small. On the other hand SEA methods can predict with acceptable accuracy the response and energy transmission between coupled structures at relatively high frequencies where the structural modal density is high and a statistical approach is the appropriate solution. In the mid-frequency range, a relatively large number of resonances exist which make finite element method too costly. On the other hand SEA methods can only predict an average level form. In this mid-frequency range a possible alternative is to use power flow techniques, where the input and flow of vibrational energy to excited and coupled structural components can be expressed in terms of input and transfer mobilities. This power flow technique can be extended from low to high frequencies and this can be integrated with established FE models at low frequencies and SEA models at high frequencies to form a verification of the method. This method of structural analysis using power flo and mobility methods, and its integration with SEA and FE analysis is applied to the case of two thin beams joined together at right angles.
Pump-and-treat optimization using analytic element method flow models
NASA Astrophysics Data System (ADS)
Matott, L. Shawn; Rabideau, Alan J.; Craig, James R.
2006-05-01
Plume containment using pump-and-treat (PAT) technology continues to be a popular remediation technique for sites with extensive groundwater contamination. As such, optimization of PAT systems, where cost is minimized subject to various remediation constraints, is the focus of an important and growing body of research. While previous pump-and-treat optimization (PATO) studies have used discretized (finite element or finite difference) flow models, the present study examines the use of analytic element method (AEM) flow models. In a series of numerical experiments, two PATO problems adapted from the literature are optimized using a multi-algorithmic optimization software package coupled with an AEM flow model. The experiments apply several different optimization algorithms and explore the use of various pump-and-treat cost and constraint formulations. The results demonstrate that AEM models can be used to optimize the number, locations and pumping rates of wells in a pump-and-treat containment system. Furthermore, the results illustrate that a total outflux constraint placed along the plume boundary can be used to enforce plume containment. Such constraints are shown to be efficient and reliable alternatives to conventional particle tracking and gradient control techniques. Finally, the particle swarm optimization (PSO) technique is identified as an effective algorithm for solving pump-and-treat optimization problems. A parallel version of the PSO algorithm is shown to have linear speedup, suggesting that the algorithm is suitable for application to problems that are computationally demanding and involve large numbers of wells.
Simulation of Fluid Flow and Collection Efficiency for an SEA Multi-element Probe
NASA Technical Reports Server (NTRS)
Rigby, David L.; Struk, Peter M.; Bidwell, Colin
2014-01-01
Numerical simulations of fluid flow and collection efficiency for a Science Engineering Associates (SEA) multi-element probe are presented. Simulation of the flow field was produced using the Glenn-HT Navier-Stokes solver. Three dimensional unsteady results were produced and then time averaged for the collection efficiency results. Three grid densities were investigated to enable an assessment of grid dependence. Collection efficiencies were generated for three spherical particle sizes, 100, 20, and 5 micron in diameter, using the codes LEWICE3D and LEWICE2D. The free stream Mach number was 0.27, representing a velocity of approximately 86 ms. It was observed that a reduction in velocity of about 15-20 occurred as the flow entered the shroud of the probe.Collection efficiency results indicate a reduction in collection efficiency as particle size is reduced. The reduction with particle size is expected, however, the results tended to be lower than previous results generated for isolated two-dimensional elements. The deviation from the two-dimensional results is more pronounced for the smaller particles and is likely due to the effect of the protective shroud.
NASA Astrophysics Data System (ADS)
Kim, Ho J.; Beskok, Ali
2010-03-01
A spectral element algorithm for solution of the unsteady incompressible Navier-Stokes and scalar (species/heat) transport equations is developed using the algebraic factorisation scheme. The new algorithm utilises Nth order Gauss-Lobatto-Legendre points for velocity and the scalar, while (N-2)th order Gauss-Legendre points are used for pressure. As a result, the algorithm does not require inter-element continuity for pressure and pressure boundary conditions on solid surfaces. Implementations of the algorithm are performed for conforming and non-conforming grids. The latter is accomplished using both the point-wise matching and integral projection methods, and applied for grids with both polynomial and geometric non-conformities. Code validation cases include the unsteady scalar convection equation, and Kovasznay flow in two- and three-dimensional domains. Using cases with analytical solutions, the algorithm is shown to achieve spectral accuracy in space and second-order accuracy in time. The results for the Boussinesq approximation for buoyancy-driven flows, and the species mixing in a continuous flow micro-mixer are also included as examples of applications that require long-time integration of the scalar transport equations.
NASA Astrophysics Data System (ADS)
Shahraeeni, E.; Firoozabadi, A.
2012-12-01
We present a 3D model for fully compositional multi-phase multi-component flow in porous media with species transfer between the phases. Phase properties are modeled with the Peng-Robinson equation of state. Because phase properties may exhibit strong discontinuities, we approximate the mass transport update by the means of discontinuous Galerkin method. Pressure and velocity fields are continuous across the whole domain of solution, which is guaranteed by using the mixed hybrid finite element method. Complexity of the flow necessitates the use of either very fine mesh or higher-order schemes. The use of higher-order finite element methods significantly reduces numerical dispersion and grid orientation effects that plague traditional finite difference methods. We have shown that in 3D the convergence rate of our scheme is twice as first order method and the CPU time may improve up to three orders of magnitude for the same level of accuracy. Our numerical model facilitates accurate simulation of delicate feature of compositional flow like fingering and CO2 injection in complex reservoirs for a broad range of applications, including CO2 sequestration in finite aquifer and water flooded reservoirs with transfer of all species between the phases.
Flow tests of a single fuel element coolant channel for a compact fast reactor for space power
NASA Technical Reports Server (NTRS)
Springborn, R. H.
1971-01-01
Water flow tests were conducted on a single-fuel-element cooling channel for a nuclear concept to be used for space power. The tests established a method for measuring coolant flow rate which is applicable to water flow testing of a complete mockup of the reference reactor. The inlet plenum-to-outlet plenum pressure drop, which approximates the overall core pressure drop, was measured and correlated with flow rate. This information can be used for reactor coolant flow and heat transfer calculations. An analytical study of the flow characteristics was also conducted.
NASA Astrophysics Data System (ADS)
Bause, Markus
2008-02-01
In this work we study mixed finite element approximations of Richards' equation for simulating variably saturated subsurface flow and simultaneous reactive solute transport. Whereas higher order schemes have proved their ability to approximate reliably reactive solute transport (cf., e.g. [Bause M, Knabner P. Numerical simulation of contaminant biodegradation by higher order methods and adaptive time stepping. Comput Visual Sci 7;2004:61-78]), the Raviart- Thomas mixed finite element method ( RT0) with a first order accurate flux approximation is popular for computing the underlying water flow field (cf. [Bause M, Knabner P. Computation of variably saturated subsurface flow by adaptive mixed hybrid finite element methods. Adv Water Resour 27;2004:565-581, Farthing MW, Kees CE, Miller CT. Mixed finite element methods and higher order temporal approximations for variably saturated groundwater flow. Adv Water Resour 26;2003:373-394, Starke G. Least-squares mixed finite element solution of variably saturated subsurface flow problems. SIAM J Sci Comput 21;2000:1869-1885, Younes A, Mosé R, Ackerer P, Chavent G. A new formulation of the mixed finite element method for solving elliptic and parabolic PDE with triangular elements. J Comp Phys 149;1999:148-167, Woodward CS, Dawson CN. Analysis of expanded mixed finite element methods for a nonlinear parabolic equation modeling flow into variably saturated porous media. SIAM J Numer Anal 37;2000:701-724]). This combination might be non-optimal. Higher order techniques could increase the accuracy of the flow field calculation and thereby improve the prediction of the solute transport. Here, we analyse the application of the Brezzi- Douglas- Marini element ( BDM1) with a second order accurate flux approximation to elliptic, parabolic and degenerate problems whose solutions lack the regularity that is assumed in optimal order error analyses. For the flow field calculation a superiority of the BDM1 approach to the RT0 one is
NASA Astrophysics Data System (ADS)
Mandal, Sandip; Khakhar, D. V.
2016-10-01
Granular materials handled in industries are typically non-spherical in shape and understanding the flow of such materials is important. The steady flow of mono-disperse, frictional, inelastic dumbbells in two-dimensions is studied by soft sphere, discrete element method simulations for chute flow and shear cell flow. The chute flow data are in the dense flow regime, while the shear cell data span a wide range of solid fractions. Results of a detailed parametric study for both systems are presented. In chute flow, increase in the aspect ratio of the dumbbells results in significant slowing of the flow at a fixed inclination and in the shear cell it results in increase in the shear stress and pressure for a fixed shear rate. The flow is well-described by the μ-I scaling for inertial numbers as high as I = 1, corresponding to solid fractions as low as ϕ = 0.3, where μ is the effective friction (the ratio of shear stress to pressure) and I is the inertial number (a dimensionless shear rate scaled with the time scale obtained from the local pressure). For a fixed inertial number, the effective friction increases by 60%-70% when aspect ratio is increased from 1.0 (sphere) to 1.9. At low values of the inertial number, there is little change in the solid fraction with aspect ratio of the dumbbells, whereas at high values of the inertial number, there is a significant increase in solid fraction with increase in aspect ratio. The dense flow data are well-described by the Jop-Forterre-Pouliquen model [P. Jop et al., Nature 441, 727-730 (2006)] with the model parameters dependent on the dumbbell aspect ratio. The variation of μ with I over the extended range shows a maximum in the range I ∈ (0.4, 0.5), while the solid fraction shows a faster than linear decrease with inertial number. A modified version of the JFP model for μ(I) and a power law model for ϕ(I) is shown to describe the combined data over the extended range of I.
NASA Astrophysics Data System (ADS)
Trehan, Sumeet; Durlofsky, Louis J.
2016-12-01
A new reduced-order model based on trajectory piecewise quadratic (TPWQ) approximations and proper orthogonal decomposition (POD) is introduced and applied for subsurface oil-water flow simulation. The method extends existing techniques based on trajectory piecewise linear (TPWL) approximations by incorporating second-derivative terms into the reduced-order treatment. Both the linear and quadratic reduced-order methods, referred to as POD-TPWL and POD-TPWQ, entail the representation of new solutions as expansions around previously simulated high-fidelity (full-order) training solutions, along with POD-based projection into a low-dimensional space. POD-TPWQ entails significantly more offline preprocessing than POD-TPWL as it requires generating and projecting several third-order (Hessian-type) terms. The POD-TPWQ method is implemented for two-dimensional systems. Extensive numerical results demonstrate that it provides consistently better accuracy than POD-TPWL, with speedups of about two orders of magnitude relative to high-fidelity simulations for the problems considered. We demonstrate that POD-TPWQ can be used as an error estimator for POD-TPWL, which motivates the development of a trust-region-based optimization framework. This procedure uses POD-TPWL for fast function evaluations and a POD-TPWQ error estimator to determine when retraining, which entails a high-fidelity simulation, is required. Optimization results for an oil-water problem demonstrate the substantial speedups that can be achieved relative to optimizations based on high-fidelity simulation.
Que, Ruiyi; Zhu, Rong
2013-12-31
This paper demonstrates a novel flow sensor with two-dimensional 360° direction sensitivity achieved with a simple structure and a novel data fusion algorithm. Four sensing elements with roundabout wires distributed in four quadrants of a circle compose the sensor probe, and work in constant temperature difference (CTD) mode as both Joule heaters and temperature detectors. The magnitude and direction of a fluid flow are measured by detecting flow-induced temperature differences among the four elements. The probe is made of Ti/Au thin-film with a diameter of 2 mm, and is fabricated using micromachining techniques. When a flow goes through the sensor, the flow-induced temperature differences are detected by the sensing elements that also serve as the heaters of the sensor. By measuring the temperature differences among the four sensing elements symmetrically distributed in the sensing area, a full 360° direction sensitivity can be obtained. By using a BP neural network to model the relationship between the readouts of the four sensor elements and flow parameters and execute data fusion, the magnitude and direction of the flow can be deduced. Validity of the sensor design was proven through both simulations and experiments. Wind tunnel experimental results show that the measurement accuracy of the airflow speed reaches 0.72 m/s in the range of 3 m/s-30 m/s and the measurement accuracy of flow direction angle reaches 1.9° in the range of 360°.
Que, Ruiyi; Zhu, Rong
2014-01-01
This paper demonstrates a novel flow sensor with two-dimensional 360° direction sensitivity achieved with a simple structure and a novel data fusion algorithm. Four sensing elements with roundabout wires distributed in four quadrants of a circle compose the sensor probe, and work in constant temperature difference (CTD) mode as both Joule heaters and temperature detectors. The magnitude and direction of a fluid flow are measured by detecting flow-induced temperature differences among the four elements. The probe is made of Ti/Au thin-film with a diameter of 2 mm, and is fabricated using micromachining techniques. When a flow goes through the sensor, the flow-induced temperature differences are detected by the sensing elements that also serve as the heaters of the sensor. By measuring the temperature differences among the four sensing elements symmetrically distributed in the sensing area, a full 360° direction sensitivity can be obtained. By using a BP neural network to model the relationship between the readouts of the four sensor elements and flow parameters and execute data fusion, the magnitude and direction of the flow can be deduced. Validity of the sensor design was proven through both simulations and experiments. Wind tunnel experimental results show that the measurement accuracy of the airflow speed reaches 0.72 m/s in the range of 3 m/s–30 m/s and the measurement accuracy of flow direction angle reaches 1.9° in the range of 360°. PMID:24385032
NASA Astrophysics Data System (ADS)
Sneed, M.; Brandt, J.; Solt, M.
2011-12-01
Extensive groundwater withdrawal from the unconsolidated deposits in the San Joaquin Valley caused widespread aquifer-system compaction and resultant land subsidence between 1926 and 1970-locally exceeding 8 meters (m). To identify the extent of the subsidence, a monitoring network consisting of 31 extensometers was developed and maintained in the 1960s. The importation of surface water in the early 1970s resulted in decreased pumping and a steady recovery of water levels. This recovery reduced the rate of compaction, and consequently, the monitoring network deteriorated. However, lack of imported surface-water availability during 1976-77, 1986-92, and 2007-09 has caused groundwater pumping to increase, which has resulted in water levels to decline to near-historic lows and renewed compaction to occur. Land subsidence resulting from this compaction has reduced freeboard and flow capacity of the Delta-Mendota Canal, the California Aqueduct, and other canals that deliver irrigation water and transport floodwater, requiring expensive repairs. To identify existing and future subsidence, a monitoring network is being developed that includes resurrecting some of the extensometers and piezometers from the old network and augmenting these ground-based measurements with remotely-sensed measurements from Interferometric Synthetic Aperture Radar and continuous Global Positioning System stations. Preliminary results from the monitoring network indicate that subsidence is occurring in locations of known historical subsidence. These results are being used to develop groundwater-flow and subsidence models to help understand and effectively manage future subsidence. A 1-D model was developed to identify the depth of the compactable units near Oro Loma, where about 60 m of water-level decline is associated with about 3 m of subsidence. The subsurface geology is well-constrained by detailed descriptions of continuous core and by geophysical logs. Analysis indicates that the Corcoran
Computational Modeling For The Transitional Flow Over A Multi-Element Airfoil
NASA Technical Reports Server (NTRS)
Liou, William W.; Liu, Feng-Jun; Rumsey, Chris L. (Technical Monitor)
2000-01-01
The transitional flow over a multi-element airfoil in a landing configuration are computed using a two equation transition model. The transition model is predictive in the sense that the transition onset is a result of the calculation and no prior knowledge of the transition location is required. The computations were performed using the INS2D) Navier-Stokes code. Overset grids are used for the three-element airfoil. The airfoil operating conditions are varied for a range of angle of attack and for two different Reynolds numbers of 5 million and 9 million. The computed results are compared with experimental data for the surface pressure, skin friction, transition onset location, and velocity magnitude. In general, the comparison shows a good agreement with the experimental data.
Finite element modeling of cracked bodies using the Bodner-Partom flow law
NASA Technical Reports Server (NTRS)
Nicholas, T.; Bohun, M.
1985-01-01
The Bodner-Partom flow law which models viscoplastic material behavior has been used to represent two nickel-base superalloys, Gatorized IN100 and Inconel 718 at elevated temperature. Procedures for the determination of the material parameters are presented along with a discussion of the physical significance of each parameter. The material model is then used in finite element computations to evaluate the response of cracked bodies to monotonic, sustained, or cyclic loading. Geometries investigated include the center cracked panel, the compact tension specimen, and the single cracked ring under tension. A Hybrid Experimental Numerical (HEN) procedure has been used to deduce crack growth rates from experimental displacement measurements which are input into finite element computations. The results of several studies conducted over the last several years are summarized.
Computation of variably saturated subsurface flow by adaptive mixed hybrid finite element methods
NASA Astrophysics Data System (ADS)
Bause, M.; Knabner, P.
2004-06-01
We present adaptive mixed hybrid finite element discretizations of the Richards equation, a nonlinear parabolic partial differential equation modeling the flow of water into a variably saturated porous medium. The approach simultaneously constructs approximations of the flux and the pressure head in Raviart-Thomas spaces. The resulting nonlinear systems of equations are solved by a Newton method. For the linear problems of the Newton iteration a multigrid algorithm is used. We consider two different kinds of error indicators for space adaptive grid refinement: superconvergence and residual based indicators. They can be calculated easily by means of the available finite element approximations. This seems attractive for computations since no additional (sub-)problems have to be solved. Computational experiments conducted for realistic water table recharge problems illustrate the effectiveness and robustness of the approach.
Convection from Hemispherical and Conical Model Ice Roughness Elements in Stagnation Region Flows
NASA Technical Reports Server (NTRS)
Hughes, Michael T.; Shannon, Timothy A.; McClain, Stephen T.; Vargas, Mario; Broeren, Andy
2016-01-01
To improve ice accretion prediction codes, more data regarding ice roughness and its effects on convective heat transfer are required. The Vertical Icing Studies Tunnel (VIST) at NASA Glenn Research was used to model realistic ice roughness in the stagnation region of a NACA 0012 airfoil. In the VIST, a test plate representing the leading 2% chord of the airfoil was subjected to flows of 7.62 m/s (25 ft/s), 12.19 m/s (40 ft/s), and 16.76 m/s (55 ft/s). The test plate was fitted with multiple surfaces or sets of roughness panels, each with a different representation of ice roughness. The sets of roughness panels were constructed using two element distribution patterns that were created based on a laser scan of an iced airfoil acquired in the Icing Research Tunnel at NASA Glenn. For both roughness patterns, surfaces were constructed using plastic hemispherical elements, plastic conical elements, and aluminum conical elements. Infrared surface thermometry data from tests run in the VIST were used to calculate area averaged heat transfer coefficient values. The values from the roughness surfaces were compared to the smooth control surface, showing convective enhancement as high as 400% in some cases. The data gathered during this study will ultimately be used to improve the physical modeling in LEWICE or other ice accretion codes and produce predictions of in-flight ice accretion on aircraft surfaces with greater confidence.
Parallel finite element methods and iterative solution techniques for viscous incompressible flows
NASA Astrophysics Data System (ADS)
Barragy, Edward Joseph
The present work is motivated by a desire to map the solution structure of nonlinear systems of partial differential equations (PDE). Of particular interest are viscous flow problems in 2D, possibly with coupled heat transfer or species transport. Due to the nonlinearity of the governing PDE's, many complicated solution structures may arise. These may include sharp layers, multiple solutions, and the possibility of bifurcation. The existence of spurious solutions, arising from insufficiently refined meshes, underscores the need for highly accurate solution procedures. This, in turn, motivates the use of p type finite element discretizations. Continuation techniques have been developed by several authors for the solution of these types of nonlinear problems. These techniques involve the solution of linear algebraic systems arising from a Newton iteration, for many, possibly hundreds, of discrete parameter values. This large computational burden motivates the use of large scale, parallel supercomputing facilities. A study of the impact of high p finite element discretizations as applied to the continuation solution of viscous incompressible flows in two dimensions is presented. The impact of these methods is considered for a Newton type continuation method coupled with gradient type element-by-element (EBE) iterative solvers. Significant issues considered concern the effect of high p on performance for various supercomputing platforms, implementation issues for EBE schemes in a distributed memory setting, and issues of scalability in a distributed memory multiprocessor setting. These issues are examined in conjunction with the development of preconditioners appropriate for high p methods, and the development of bifurcation detection schemes appropriate for high p methods and gradient type solution schemes.
NASA Technical Reports Server (NTRS)
Guruswamy, Guru P.; Byun, Chansup
1993-01-01
A computational procedure is presented to study fluid-structural interaction problems for three-dimensional aerospace structures. The flow is modeled using the three-dimensional unsteady Euler/Navier-Stokes equations and solved using the finite-difference approach. The three dimensional structure is modeled using shell/plate finite-element formulation. The two disciplines are coupled using a domain decomposition approach. Accurate procedures both in time and space are developed to combine the solutions from the flow equations with those of the structural equations. Time accuracy is maintained using aeroelastic configuration-adaptive moving grids that are computed every time step. The work done by aerodynamic forces due to structural deformations is preserved using consistent loads. The present procedure is validated by computing the aeroelastic response of a wing and comparing with experiment. Results are illustrated for a typical wing-body configuration.
NASA Technical Reports Server (NTRS)
Cunningham, A. M., Jr.
1973-01-01
A study was conducted to investigate the feasibility of using combined subsonic and supersonic linear theory as a means for solving unsteady transonic flow problems in an economical and yet realistic manner. With some modification, existing linear theory methods are combined into a single program and a simple algorithm is derived for determining interference between lifting surface elements of different Mach number. The method is applied to a wide variety of problems for which measured unsteady pressure distributions and Mach number distributions are available. By comparing theory and experiment, the transonic method solutions show a significant improvement over uniform flow solutions. It is concluded that with these refinements the method will provide a means for performing realistic transonic flutter and dynamic response analyses at costs which are compatible with current linear theory based solutions.
NASA Technical Reports Server (NTRS)
Abrahamson, A. L.
1977-01-01
An accurate mathematical model for sound propagation in axisymmetric aircraft engine ducts with compressible mean flow is reported. The model is based on the usual perturbation of the basic fluid mechanics equations for small motions. Mean flow parameters are derived in the absence of fluctuating quantities and are then substituted into the equations for the acoustic quantities which were linearized by eliminating higher order terms. Mean swirl is assumed to be zero from the restriction of axisymmetry. A linear rectangular serendipity element is formulated from these equations using a Galerkin procedure and assembled in a special purpose computer program in which the matrix map for a rectangular mesh was specifically coded. Representations of the fluctuating quantities, mean quantities and coordinate transformations are isoparametric. The global matrix is solved by foreward and back substitution following an L-U decomposition with pivoting restricted internally to the blocks. Results from the model were compared with results from several alternative analyses and yielded satisfactory agreement.
A Finite-Element Approach for Modeling Inviscid and Viscous Compressible Flows using Prismatic Grids
NASA Technical Reports Server (NTRS)
Pandya, S. A.; Hefez, M.
2000-01-01
The Galerkin finite-element method is used to solve the Euler and Navier-Stokes equations on prismatic meshes. It is shown that the prismatic grid is advantageous for correctly and efficiently capturing the boundary layers in high Reynolds number flows. It can be captured accurately because of the ability to cluster grid points normal to the body. The efficiency derives from the implicit treatment of the normal direction. To treat the normal direction implicitly, a semi-implicit Runge-Kutta time stepping scheme is developed. The semi-implicit algorithm is validated on simple geometries for inviscid and viscous flows and its convergence history is compared to that of the explicit Runge-Kutta scheme. The semi-implicit scheme is shown to be a factor of 3 to 4 faster in terms of CPU time to convergence.
NASA Astrophysics Data System (ADS)
Begue, C.; Periaux, J.; Perrier, P.; Pouletty, C.
1985-11-01
A self-adaptive finite-element method, coupled to a homogenization model of turbulence, is presented for the numerical simulation of unsteady turbulent flow of viscous fluids in air intakes. The nonlinear subproblem due to the convection is solved by an iterative algorithm, and the linear Stokes subproblem due to the diffusion is solved by a Hood-Taylor type iterative algorithm. An efficient and precise minielement approximation is used, and the adaptive mesh procedure is automatic in the calculation, using the physical criteria of rotation and divergence to determine the submeshing zones. The numerical method is demonstrated for the example of three-dimensional laminar flow around and in air intake at a Reynolds number of 200.
Generalized multiscale finite element method for non-Newtonian fluid flow in perforated domain
NASA Astrophysics Data System (ADS)
Chung, E. T.; Iliev, O.; Vasilyeva, M. V.
2016-10-01
In this work, we consider a non-Newtonian fluid flow in perforated domains. Fluid flow in perforated domains have a multiscale nature and solution techniques for such problems require high resolution. In particular, the discretization needs to honor the irregular boundaries of perforations. This gives rise to a fine-scale problems with many degrees of freedom which can be very expensive to solve. In this work, we develop a multiscale approach that attempt to solve such problems on a coarse grid by constructing multiscale basis functions. We follow Generalized Multiscale Finite Element Method (GMsFEM) [1, 2] and develop a multiscale procedure where we identify multiscale basis functions in each coarse block using snapshot space and local spectral problems [3, 4]. We show that with a few basis functions in each coarse block, one can accurately approximate the solution, where each coarse block can contain many small inclusions.
Simulation of viscous flows using a multigrid-control volume finite element method
Hookey, N.A.
1994-12-31
This paper discusses a multigrid control volume finite element method (MG CVFEM) for the simulation of viscous fluid flows. The CVFEM is an equal-order primitive variables formulation that avoids spurious solution fields by incorporating an appropriate pressure gradient in the velocity interpolation functions. The resulting set of discretized equations is solved using a coupled equation line solver (CELS) that solves the discretized momentum and continuity equations simultaneously along lines in the calculation domain. The CVFEM has been implemented in the context of both FMV- and V-cycle multigrid algorithms, and preliminary results indicate a five to ten fold reduction in execution times.
[A five-element lumped-parameter model for cerebral blood flow autoregulation].
Wang, Shengzhang; Yao, Wei; Ding, Guanghong
2009-10-01
Utilizing the third-order polynomial curve fitted to the experimental data, which represents the relationship between cerebral blood flow (CBF) and mean artery blood pressure (MABP), we constructed a lumped-parameter dynamic model with 5 elements. In this model; the resistance is not constants it is determined by the fitted curve. We simulated the process of CBF autoregulation numerically by solving the govern equation of this model and got quite accurate results. Furthermore, we studied the influence of hemodynamic parameters on the CBF autoregulation by this model and proved that the characteristic resistance is the most important factor.
An hybrid finite volume finite element method for variable density incompressible flows
NASA Astrophysics Data System (ADS)
Calgaro, Caterina; Creusé, Emmanuel; Goudon, Thierry
2008-04-01
This paper is devoted to the numerical simulation of variable density incompressible flows, modeled by the Navier-Stokes system. We introduce an hybrid scheme which combines a finite volume approach for treating the mass conservation equation and a finite element method to deal with the momentum equation and the divergence free constraint. The breakthrough relies on the definition of a suitable footbridge between the two methods, through the design of compatibility condition. In turn, the method is very flexible and allows to deal with unstructured meshes. Several numerical tests are performed to show the scheme capabilities. In particular, the viscous Rayleigh-Taylor instability evolution is carefully investigated.
Characteristics of fluid flow in the combustion synthesis of TiC from the elements
NASA Technical Reports Server (NTRS)
Valone, S. M.; Behrens, R. G.
1987-01-01
The results of a numerical investigation of finite reservoir effects on capillary spreading at small reservoir dimensions are presently related to wave propagation phenomena in the combustion synthesis of TiC from its two elemental constituents. It is noted that gravitational forces can affect bubble coalescence by nonbuoyant means under the suitable conditions, although these conditions are expected to be rare in combustion synthesis. Finite-curved reservoirs can drive capillary flow due to surface tension and wall contact forces; these cause the wall and the metal to be completely reconfigured during combustion synthesis.
NASA Technical Reports Server (NTRS)
Sohn, J. L.; Heinrich, J. C.
1990-01-01
The calculation of pressures when the penalty-function approximation is used in finite-element solutions of laminar incompressible flows is addressed. A Poisson equation for the pressure is formulated that involves third derivatives of the velocity field. The second derivatives appearing in the weak formulation of the Poisson equation are calculated from the C0 velocity approximation using a least-squares method. The present scheme is shown to be efficient, free of spurious oscillations, and accurate. Examples of applications are given and compared with results obtained using mixed formulations.
A Global Interpolation Function (GIF) boundary element code for viscous flows
NASA Technical Reports Server (NTRS)
Reddy, D. R.; Lafe, O.; Cheng, A. H-D.
1995-01-01
Using global interpolation functions (GIF's), boundary element solutions are obtained for two- and three-dimensional viscous flows. The solution is obtained in the form of a boundary integral plus a series of global basis functions. The unknown coefficients of the GIF's are determined to ensure the satisfaction of the governing equations at selected collocation points. The values of the coefficients involved in the boundary integral equations are determined by enforcing the boundary conditions. Both primitive variable and vorticity-velocity formulations are examined.
Characteristics of fluid flow in the combustion synthesis of TiC from the elements
NASA Technical Reports Server (NTRS)
Valone, S. M.; Behrens, R. G.
1987-01-01
The results of a numerical investigation of finite reservoir effects on capillary spreading at small reservoir dimensions are presently related to wave propagation phenomena in the combustion synthesis of TiC from its two elemental constituents. It is noted that gravitational forces can affect bubble coalescence by nonbuoyant means under the suitable conditions, although these conditions are expected to be rare in combustion synthesis. Finite-curved reservoirs can drive capillary flow due to surface tension and wall contact forces; these cause the wall and the metal to be completely reconfigured during combustion synthesis.
A case of elasto-plastic flow using a new special element. [crack tip analysis
NASA Technical Reports Server (NTRS)
Swedlow, J. L.; Karabin, M. E., Jr.
1978-01-01
Using a new special element for elasto-plastic flow, a nearly square, center-cracked plate of simulated A533 steel is analyzed. Selected results are examined locally to the crack's tip. It is found that a sharp transition in the distribution of deformation and stress occurs after the initial elastic response, and that this state is followed by fairly stable behavior over a considerable portion of the load range. Distribution of strain energy density is noted, and implications for use of the parameter J and for additional work are discussed briefly.
Least-squares finite element solutions for three-dimensional backward-facing step flow
NASA Technical Reports Server (NTRS)
Jiang, Bo-Nan; Hou, Lin-Jun; Lin, Tsung-Liang
1993-01-01
Comprehensive numerical solutions of the steady state incompressible viscous flow over a three-dimensional backward-facing step up to Re equals 800 are presented. The results are obtained by the least-squares finite element method (LSFEM) which is based on the velocity-pressure-vorticity formulation. The computed model is of the same size as that of Armaly's experiment. Three-dimensional phenomena are observed even at low Reynolds number. The calculated values of the primary reattachment length are in good agreement with experimental results.
NASA Astrophysics Data System (ADS)
Seunarine, L.; Lowry, A. R.
2011-12-01
and temperature so that compositional and thermal mass contributions are nearly negligible. These results suggest that load accommodation produces less Moho deflection than would be expected for a crème brulee style of deformation and that stresses are accommodated, at least in part, by significant flow in the lower crust. Based on these results, we design a new series of models to better constrain the nature of this channel flow in the lower crust in terms of its average properties across the Western US, including channel dimensions and viscosity structure.
El-Awady, J.; Biner, S.; Ghoniem, N.
2007-11-07
We present a self-consistent formulation of 3-D parametric dislocation dynamics (PDD) with the boundary element method (BEM) to describe dislocation motion, and hence microscopic plastic flow in finite volumes. We develop quantitative measures of the accuracy and convergence of the method by considering a comparison with known analytical solutions. It is shown that the method displays absolute convergence with increasing the number of quadrature points on the dislocation loop and the surface mesh density. The error in the image force on a screw dislocation approaching a free surface is shown to increase as the dislocation approaches the surface, but is nevertheless controllable. For example, at a distance of one lattice parameter from the surface, the relative error is less than 5% for a surface mesh with an element size of 1000 x 2000 (in units of lattice parameter), and 64 quadrature points. The Eshelby twist angle in a finite-length cylinder containing a coaxial screw dislocation is also used to benchmark the method. Finally, large scale 3-D simulation results of single slip behavior in cylindrical microcrystals are presented. Plastic flow characteristics and the stress-strain behavior of cylindrical microcrystals under compression are shown to be in agreement with experimental observations. It is shown that the mean length of dislocations trapped at the surface is the dominant factor in determining the size effects on hardening of single crystals. The influence of surface image fields on the flow stress is finally explored. It is shown that the flow stress is reduced by as much as 20% for small single crystals of size less than 0.15 {micro}m.
Analytic Element Modeling of Steady Interface Flow in Multilayer Aquifers Using AnAqSim.
Fitts, Charles R; Godwin, Joshua; Feiner, Kathleen; McLane, Charles; Mullendore, Seth
2015-01-01
This paper presents the analytic element modeling approach implemented in the software AnAqSim for simulating steady groundwater flow with a sharp fresh-salt interface in multilayer (three-dimensional) aquifer systems. Compared with numerical methods for variable-density interface modeling, this approach allows quick model construction and can yield useful guidance about the three-dimensional configuration of an interface even at a large scale. The approach employs subdomains and multiple layers as outlined by Fitts (2010) with the addition of discharge potentials for shallow interface flow (Strack 1989). The following simplifying assumptions are made: steady flow, a sharp interface between fresh- and salt water, static salt water, and no resistance to vertical flow and hydrostatic heads within each fresh water layer. A key component of this approach is a transition to a thin fixed minimum fresh water thickness mode when the fresh water thickness approaches zero. This allows the solution to converge and determine the steady interface position without a long transient simulation. The approach is checked against the widely used numerical codes SEAWAT and SWI/MODFLOW and a hypothetical application of the method to a coastal wellfield is presented.
Numerical Modeling of Cavitating Venturi: A Flow Control Element of Propulsion System
NASA Technical Reports Server (NTRS)
Majumdar, Alok; Saxon, Jeff (Technical Monitor)
2002-01-01
In a propulsion system, the propellant flow and mixture ratio could be controlled either by variable area flow control valves or by passive flow control elements such as cavitating venturies. Cavitating venturies maintain constant propellant flowrate for fixed inlet conditions (pressure and temperature) and wide range of outlet pressures, thereby maintain constant, engine thrust and mixture ratio. The flowrate through the venturi reaches a constant value and becomes independent of outlet pressure when the pressure at throat becomes equal to vapor pressure. In order to develop a numerical model of propulsion system, it is necessary to model cavitating venturies in propellant feed systems. This paper presents a finite volume model of flow network of a cavitating venturi. The venturi was discretized into a number of control volumes and mass, momentum and energy conservation equations in each control volume are simultaneously solved to calculate one-dimensional pressure, density, and flowrate and temperature distribution. The numerical model predicts cavitations at the throat when outlet pressure was gradually reduced. Once cavitation starts, with further reduction of downstream pressure, no change in flowrate is found. The numerical predictions have been compared with test data and empirical equation based on Bernoulli's equation.
Transitional flow in the wake of a moderate to large height cylindrical roughness element
NASA Astrophysics Data System (ADS)
Plogmann, B.; Würz, W.; Krämer, E.
2015-12-01
The effect of an isolated, cylindrical roughness on the stability of an airfoil boundary layer has been studied based on particle image velocimetry and hot-wire anemometry. The investigated roughness elements range from a sub-critical to a super-critical behavior with regard to the critical roughness Reynolds number. For the sub-critical case, the nonlinear disturbance growth in the near wake is governed by oblique Tollmien-Schlichting (TS) type modes. Further downstream, these disturbance modes are, however, damped with the mean flow stabilization and no dominant modes persist in the far wake. By contrast, in the transitional configuration the disturbance growth is increased, but still associated with a TS-type instability in the near-wake centerline region of the low-aspect (height-to-diameter) ratio element. That is, the disturbances in the centerline region show a similar behavior as known for 2D elements, whereas in the outer spanwise domain a Kelvin-Helmholtz (KH) type, shear-layer instability is found, as previously reported for larger aspect ratio isolated elements. With increasing height and, thereby, aspect ratio of the roughness, the KH-type instability domain extends toward the centerline and, accordingly, the TS-type instability domain decreases. For high super-critical cases, transition is already triggered in the wall-normal and spanwise shear layers upstream and around the roughness. In the immediate wake, periodic shear-layer disturbances roll up into a—for isolated elements characteristic—shedding of vortices, which was not present at the lower roughness Reynolds number cases due to the decreased aspect ratio and, thereby, different instability mechanism.
Tyson, J.F.
1995-12-31
Flow injection (FI) techniques are a way of automating sampling pretreatment procedures with direct coupling to the instrument. For a variety of reasons, flame atomic absorption spectrometry (FAAS) would be the method of choice for the determination of trace elements in water samples were it not for some of the inherent limitations of this technique. These limitations are concerned with the various interferences that arise from matrix components and with the atom number density in the source. This together with the various noise sources sets detection limits which are not low enough for many applications. Thus many FI procedures are devised with the aim of overcoming these limitations and thus solid phase extraction (SPE) as a means of preconcentration features largely in recently published work. Results will be presented for the determination of trace elements in water samples (both fresh and saline) in which SPE procedures were used to (a) remove the potentially interfering sea-water matrix for determinations using ICP-MS and (b) preconcentrate cadmium from surface waters prior to determination by FAAS. Hydride generation methods have been applied for the determination of selenium and arsenic. In highly saline media the elevated recoveries of Se have been investigated and for the determination of As, an evaluation of the claim that the use of surfactants improves the performance of a flow based hydride generation system has critically evaluated.
A high order accurate finite element algorithm for high Reynolds number flow prediction
NASA Technical Reports Server (NTRS)
Baker, A. J.
1978-01-01
A Galerkin-weighted residuals formulation is employed to establish an implicit finite element solution algorithm for generally nonlinear initial-boundary value problems. Solution accuracy, and convergence rate with discretization refinement, are quantized in several error norms, by a systematic study of numerical solutions to several nonlinear parabolic and a hyperbolic partial differential equation characteristic of the equations governing fluid flows. Solutions are generated using selective linear, quadratic and cubic basis functions. Richardson extrapolation is employed to generate a higher-order accurate solution to facilitate isolation of truncation error in all norms. Extension of the mathematical theory underlying accuracy and convergence concepts for linear elliptic equations is predicted for equations characteristic of laminar and turbulent fluid flows at nonmodest Reynolds number. The nondiagonal initial-value matrix structure introduced by the finite element theory is determined intrinsic to improved solution accuracy and convergence. A factored Jacobian iteration algorithm is derived and evaluated to yield a consequential reduction in both computer storage and execution CPU requirements while retaining solution accuracy.
Finite element modeling of mass transport in high-Péclet cardiovascular flows
NASA Astrophysics Data System (ADS)
Hansen, Kirk; Arzani, Amirhossein; Shadden, Shawn
2016-11-01
Mass transport plays an important role in many important cardiovascular processes, including thrombus formation and atherosclerosis. These mass transport problems are characterized by Péclet numbers of up to 108, leading to several numerical difficulties. The presence of thin near-wall concentration boundary layers requires very fine mesh resolution in these regions, while large concentration gradients within the flow cause numerical stabilization issues. In this work, we will discuss some guidelines for solving mass transport problems in cardiovascular flows using a stabilized Galerkin finite element method. First, we perform mesh convergence studies in a series of idealized and patient-specific geometries to determine the required near-wall mesh resolution for these types of problems, using both first- and second-order tetrahedral finite elements. Second, we investigate the use of several boundary condition types at outflow boundaries where backflow during some parts of the cardiac cycle can lead to convergence issues. Finally, we evaluate the effect of reducing Péclet number by increasing mass diffusivity as has been proposed by some researchers. This work was supported by the NSF GRFP and NSF Career Award #1354541.
The semi-discrete Galerkin finite element modelling of compressible viscous flow past an airfoil
NASA Technical Reports Server (NTRS)
Meade, Andrew J., Jr.
1992-01-01
A method is developed to solve the two-dimensional, steady, compressible, turbulent boundary-layer equations and is coupled to an existing Euler solver for attached transonic airfoil analysis problems. The boundary-layer formulation utilizes the semi-discrete Galerkin (SDG) method to model the spatial variable normal to the surface with linear finite elements and the time-like variable with finite differences. A Dorodnitsyn transformed system of equations is used to bound the infinite spatial domain thereby permitting the use of a uniform finite element grid which provides high resolution near the wall and automatically follows boundary-layer growth. The second-order accurate Crank-Nicholson scheme is applied along with a linearization method to take advantage of the parabolic nature of the boundary-layer equations and generate a non-iterative marching routine. The SDG code can be applied to any smoothly-connected airfoil shape without modification and can be coupled to any inviscid flow solver. In this analysis, a direct viscous-inviscid interaction is accomplished between the Euler and boundary-layer codes, through the application of a transpiration velocity boundary condition. Results are presented for compressible turbulent flow past NACA 0012 and RAE 2822 airfoils at various freestream Mach numbers, Reynolds numbers, and angles of attack. All results show good agreement with experiment, and the coupled code proved to be a computationally-efficient and accurate airfoil analysis tool.
NASA Astrophysics Data System (ADS)
HO, Yat-Kiu; LIU, Chun-Ho
2015-04-01
The atmospheric boundary layer (ABL) immediately above the urban canopy is the roughness sublayer (RSL). In this layer, flows and turbulence are strongly affected by the roughness elements beneath, e.g. building obstacles. The wind flows over urban areas could be represented by conventional logarithmic law of the wall (log-law) in the neutrally stratified ABL. However, in the RSL region, the vertical wind profile deviates from that predicted from log-law and the effect could be extended from ground level up to several canopy heights. As a result, the Monin-Obukhov similarity theory (MOST) fails and an additional length scale is required to describe the flows. The key aim of this study is to introduce a simple wind profile model which accounts for the effect of the RSL in neutral stratification using wind tunnel experiments. Profile measurements of wind speeds and turbulence quantities over various two-dimensional (2D) idealised roughness elements are carried out in an open-circuit wind tunnel with test section of size 560 mm (width) × 560 mm (height) × 6 m (length). The separation between the roughness elements is varied systematically so that ten different types of surface forms are adopted. The velocity measurements are obtained by hot-wire anemometry using X-probe design (for UW- measurements) with a constant temperature anemometer. For each configuration, eight vertical profiles are collected over the canopy, including solid boundaries and cavities of the roughness elements. Firstly, we compute the measurement results using conventional MOST to determine different roughness parameters. Afterwards, we derive the RSL height from the Reynolds stress profiles. Since the profiles taken from different locations of the canopy are eventually converged with increasing height, we use this 'congregated height' to define the RSL height. Next, we introduce an alternative function, i.e. power-law function, instead of MOST, to describe the velocity profile in attempt to
Discrete Element Modeling of Oscillatory Sheet Flow Using Medium and Coarse Spherical Sand Grains.
NASA Astrophysics Data System (ADS)
Cobb, M. M.; Calantoni, J.; Holland, T.; Odonoghue, T.
2006-12-01
Oscillatory wave-driven sheet flow transports large quantities of surf and swash zone sediment and is fundamental to understanding the redistribution of sediments during the morphodynamic evolution of wave dominated sandy beaches. In order to better understand sheet flow processes and their sensitivity to grain size distributions sediment transport simulations that explicitly describe the small-scale grain-fluid interactions are performed. In this study asymmetric second order stokes wave oscillatory sheet flow is investigated using a discrete element model (DEM). We examine the time averaged total transport, time-dependent transport with depth, and time-dependent concentration with depth for second order stokes waves with periods of 5 and 7.5 seconds and amplitudes of 1 and 1.5 meters, respectively, over beds with medium (D50 = 0.28 mm) and coarse (D50 = 0.51 mm) grains. Direct comparisons are made between model results and data taken at the Aberdeen Oscillatory Flow Tunnel. For coarse grain cases the model predictions are 15-25% greater than the measured total transport in the experiments. Model-data comparisons of the time dependent concentration as a function of depth reveal good agreement within the bedload layer, suggesting that the DEM is successfully describing the same physical processes involved in the sheet flow transport. In addition, correlations between the time-dependent concentrations at different depths indicate that the model has the same spatio-temporal structure exhibited by the laboratory measurements. However, the DEM, which is coupled to a simple one-dimensional mixing length fluid model, underpredicts total transport for medium grains since it cannot account for the substantial amount of suspended sediment that most likely contributes to the measured total transport.
NASA Astrophysics Data System (ADS)
Kirilovskiy, S. V.; Poplavskaya, T. V.
2016-11-01
The work presents the results of numerical modeling of a supersonic flow around a blunted cone with an isolated cylindrical roughness on the forebody surface in the three-dimensional formulation. The roughness element is shown to distort the mean flow and to give rise to small-amplitude disturbances with distinguished spectral peaks in the boundary layer.
Modeling fluid flow in deformation bands with stabilized localization mixed finite elements
NASA Astrophysics Data System (ADS)
Sun, W.; Ostien, J. T.; Foulk, J. W.; Abdeljawad, F.
2012-12-01
Deformation bands in geological materials refer to narrow zones of inhomogeneous strain. Their onset and propagation may cause significant changes in microstructures and therefore profoundly enhance or suppress fluid flow and induce anisotropy. These changes in hydraulic properties have strong implications in geotechnical engineering, carbon dioxide sequestration and nuclear waste storage. The difficulty in modeling such multiphysics phenomena is threefold. 1. Monolithically coupled promechanics formulation may lead to non-physical oscillation in pore pressure near the undrained limit if identical mesh and basis functions are used for pore pressure and displacement. 2. Onsets of deformation bands may lead to non-converging mesh-dependent results if no length scale is introduced to the finite element formulation. 3. Modeling anisotropy induced by the deformation band may require a very fine mesh to capture the sharp pore pressure gradient and results in a computational intensive system. In this study, we introduce a projection-based technique to stabilize a large deformation finite element model that eliminates the non-physical oscillation in pore pressure. Using a 1D analytical solution as guideline, we introduce a simple scheme that can adaptively update the optimal value for the stabilization parameter that can restore stability without over-diffusing the system. This stabilized model is coupled with a localization element technique used to introduce proper length scale to regularize the governing equations and resolve the fluid flow jumps across the deformation bands. Numerical examples are presented to demonstrate the properties and performance of the proposed localized models. *Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000
Wilder, Shawn M; Jeyasingh, Punidan D
2016-11-01
Global warming and predation risk can have important impacts on animal physiology and life histories that can have consequences for ecosystem function. Zhang et al. () recently tested the separate and interactive effects of warming and predation risk on the body composition of Daphnia magna. By measuring both the elemental and biochemical composition of individuals, they showed that D. magna body elemental composition responded opposite to theoretical predictions and previous studies but that these changes were explained by adaptive life-history shifts in allocation to protein in eggs versus body lipid reserves. Photograph by Joachim Mergeay. Zhang, C., Jansen, M., De Meester, L. & Stoks, R. (2016) Energy storage and fecundity explain deviations from ecological stoichiometry predictions under global warming and size-selective predation. Journal of Animal Ecology 85, 1431-1441. Understanding the mechanisms through which energy and nutrients flow through ecosystems is critical to predicting and mitigating the consequences of climate change and other ecological disturbances. Ecological stoichiometry and nutritional geometry, using data on elements and macromolecules, respectively, have independently made major contributions towards this goal. Zhang et al. () provide data demonstrating that these two major frameworks can provide complementary insight into the consequences of global warming and predation risk for the physiology and life-history traits of a key aquatic herbivore, Daphnia magna. This study should catalyse further work to unite these two parallel and complementary frameworks.
A spectral-element dynamic model for the Large-Eddy simulation of turbulent flows
NASA Astrophysics Data System (ADS)
Chapelier, J.-B.; Lodato, G.
2016-09-01
A spectral dynamic modeling procedure for Large-Eddy simulation is introduced in the context of discontinuous finite element methods. The proposed sub-grid scale model depends on a turbulence sensor built from the computation of a polynomial energy spectrum in each of the discretization elements. The evaluation of the energy decay gives an estimation of the quality of the resolution in each element and allows for adapting the intensity of the sub-grid dissipation locally. This approach is simple, robust, efficient and it is shown that the sub-grid model adapts to the amount of numerical dissipation in order to provide an accurate representation of the true sub-grid stresses. The present approach is tested for the large-eddy simulation of transitional, fully-developed and wall-bounded turbulence. In particular, results are reported for the Taylor-Green vortex and periodic turbulent channel flows at moderate Reynolds number. For these configurations, the new model shows an accurate description of turbulent phenomena at relatively coarse resolutions.
Assessment of the ecological impacts of macroroughness elements in stream flows
NASA Astrophysics Data System (ADS)
Niayifar, Amin; Oldroyd, Holly J.; Perona, Paolo
2017-04-01
The environmental suitability of flow release rules is often assessed for different fish species by modeling (e.g., CASiMir and PHABSIM) Weighted Usable Area (WUA) curves. However, these models are not able to resolve the hydrodynamic at small scales, e.g. that induced by the presence of macroroughness (e.g., single stones), which yet determine relatively large wakes that may contribute significantly in terms of habitat suitability. The presence of stones generates sheltered zones (i.e., the wake), which are typically temporary stationary points for many fish species. By resting in these low velocity regions, fishes minimize energy expenditure, and can quickly move to nearby fast water to feed (Hayes and Jowett, 1994). Following the analytical model proposed by Negretti et al., (2006), we developed an analytical solution for the wake area behind the macroroughness elements. The total wake area in the river reach being monitored is a function of the streamflow, Q, and it is an actual Usable Area for fishes that can be used to correct the one computed by classic software such as PHABSIM or CASIMIR at each flow rate. By quantifying these wake areas we can therefore assess how the physical properties and number of such zones change in response to the changing hydrologic regime. In order to validate the concept, we selected a 400 meter reach from the Aare river in the center of Switzerland. The statistical distribution of macroroughness elements is obtained by taking orthorectified aerial photographs by drone surveys during low flow conditions. Then, the distribution of the wakes is obtained analytically as a derived distribution. This methodology allows to save computational costs and the time for detailed field surveys.
NASA Astrophysics Data System (ADS)
Roediger, T.; Siebert, C.; Krause, P.
2008-12-01
The arid to semiarid Middle East is a region of extreme growth of population. Hence, the rare and over- expoitated water resources in that region have to be more protected against antropogenic and geogenic pollution. One way to help solving that complex issue is to develop an intelligent and integrated strategy to manage all available water resources, which is the aim of the multilateral SMART-project in the Lower Jordan Valley. To generate such an IWRM, all water resources (groundwater, surface runoff, waste water) of the valley and its shoulders have to be quanti- and qualitatively evaluated. The strategy of SMART is to upscale knowledge, extracted from local catchment areas to the project scale, which covers the area between Sea of Galilee, Jerusalem, Dead Sea and Amman. The study areas of the here presented sub-project are the Wadis Qilt (Palestine) and Al Arab (Jordan). The aim of the sub-project is to evaluate natural resources on catchment scale by combining hydrochemical and hydraulical methods to develop a high precision model. Concerning the quantification of the system, two seperated models will be linked: a numerical finite element flow-model for the groundwater passage and a new devolped hydrological model JAMS, which is excellently prepared for humid conditions. The power of JAMS is the highly accurate assessment of soil moisture balance and consequently of surface runoff and groundwater recharge. However, the empirical equations and input parameters have to be adjusted onto the conditions of the semiarid Wadi Al Arab and the arid Wadi Qilt. After the adaption of JAMS, the spatially and temporarily differentiated calculation of runoff and groundwater recharge is possible. Beside climatic gradients, the key issue is, to correctly evaluate the evapotranspiration in respect to the different classes of landuse. In the study area Wadi Al Arab, the groundwater recharge was calculated as area-indicated output parameter of JAMS. This output was used to be the
Development of a Cl-impregnated activated carbon for entrained-flow capture of elemental mercury.
Ghorishi, S Behrooz; Keeney, Robert M; Serre, Shannon D; Gullett, Brian K; Jozewicz, Wojciech S
2002-10-15
Efforts to discern the role of an activated carbon's surface functional groups on the adsorption of elemental mercury (Hg0) and mercuric chloride demonstrated that chlorine (Cl) impregnation of a virgin activated carbon using dilute solutions of hydrogen chloride leads to increases (by a factor of 2-3) in fixed-bed capture of these mercury species. A commercially available activated carbon (DARCO FGD, NORITAmericas Inc. [FGD])was Cl-impregnated (Cl-FGD) [5 lb (2.3 kg) per batch] and tested for entrained-flow, short-time-scale capture of Hg0. In an entrained flow reactor, the Cl-FGD was introduced in Hg0-laden flue gases (86 ppb of Hg0) of varied compositions with gas/solid contact times of about 3-4 s, resulting in significant Hg0 removal (80-90%), compared to virgin FGD (10-15%). These levels of Hg0 removal were observed across a wide range of very low carbon-to-mercury weight ratios (1000-5000). Variation of the natural gas combustion flue gas composition, by doping with nitrogen oxides and sulfur dioxide, and the flow reactor temperature (100-200 degrees C) had minimal effects on Hg0 removal bythe Cl-FGD in these carbon-to-mercury weight ratios. These results demonstrate significant enhancement of activated carbon reactivity with minimal treatment and are applicable to combustion facilities equipped with downstream particulate matter removal such as an electrostatic precipitator.
Numerical Simulation of Dry Granular Flow Impacting a Rigid Wall Using the Discrete Element Method
Wu, Fengyuan; Fan, Yunyun; Liang, Li; Wang, Chao
2016-01-01
This paper presents a clump model based on Discrete Element Method. The clump model was more close to the real particle than a spherical particle. Numerical simulations of several tests of dry granular flow impacting a rigid wall flowing in an inclined chute have been achieved. Five clump models with different sphericity have been used in the simulations. By comparing the simulation results with the experimental results of normal force on the rigid wall, a clump model with better sphericity was selected to complete the following numerical simulation analysis and discussion. The calculation results of normal force showed good agreement with the experimental results, which verify the effectiveness of the clump model. Then, total normal force and bending moment of the rigid wall and motion process of the granular flow were further analyzed. Finally, comparison analysis of the numerical simulations using the clump model with different grain composition was obtained. By observing normal force on the rigid wall and distribution of particle size at the front of the rigid wall at the final state, the effect of grain composition on the force of the rigid wall has been revealed. It mainly showed that, with the increase of the particle size, the peak force at the retaining wall also increase. The result can provide a basis for the research of relevant disaster and the design of protective structures. PMID:27513661
MPSalsa a finite element computer program for reacting flow problems. Part 2 - user`s guide
Salinger, A.; Devine, K.; Hennigan, G.; Moffat, H.
1996-09-01
This manual describes the use of MPSalsa, an unstructured finite element (FE) code for solving chemically reacting flow problems on massively parallel computers. MPSalsa has been written to enable the rigorous modeling of the complex geometry and physics found in engineering systems that exhibit coupled fluid flow, heat transfer, mass transfer, and detailed reactions. In addition, considerable effort has been made to ensure that the code makes efficient use of the computational resources of massively parallel (MP), distributed memory architectures in a way that is nearly transparent to the user. The result is the ability to simultaneously model both three-dimensional geometries and flow as well as detailed reaction chemistry in a timely manner on MT computers, an ability we believe to be unique. MPSalsa has been designed to allow the experienced researcher considerable flexibility in modeling a system. Any combination of the momentum equations, energy balance, and an arbitrary number of species mass balances can be solved. The physical and transport properties can be specified as constants, as functions, or taken from the Chemkin library and associated database. Any of the standard set of boundary conditions and source terms can be adapted by writing user functions, for which templates and examples exist.
Finite Element Analysis of Material Flow in Mechanical Clinching with Extensible Dies
NASA Astrophysics Data System (ADS)
Lambiase, Francesco; Di Ilio, Antoniomaria
2013-06-01
An investigation of the material flow during the clinching process with extensible dies is carried out. Clinched joints were produced under different forming loads to evaluate the evolution of the joints' profile experimentally. Tensile-shear tests were conducted to evaluate the influence of the forming load on mechanical strength of the clinched joint. Since the joints' strength depends on the joints' profile, which in turn depends on the punch-die cavity volume, an analysis of the forces acting on the extensible dies was carried out. A finite element model was developed and validated by comparing the predicted and measured material flow and quality criteria (e.g., neck thickness and undercut). Therefore, the FE model was utilized to analyze the evolution of contact forces acting on the die sectors during the joining process. Furthermore, the main causes of the asymmetry in the cross section of such joints have been studied. It turned out that the axial asymmetry due to material flow within the gap between consecutive die sectors increases with the punch force and the sheet thickness.
Numerical Simulation of Dry Granular Flow Impacting a Rigid Wall Using the Discrete Element Method.
Wu, Fengyuan; Fan, Yunyun; Liang, Li; Wang, Chao
2016-01-01
This paper presents a clump model based on Discrete Element Method. The clump model was more close to the real particle than a spherical particle. Numerical simulations of several tests of dry granular flow impacting a rigid wall flowing in an inclined chute have been achieved. Five clump models with different sphericity have been used in the simulations. By comparing the simulation results with the experimental results of normal force on the rigid wall, a clump model with better sphericity was selected to complete the following numerical simulation analysis and discussion. The calculation results of normal force showed good agreement with the experimental results, which verify the effectiveness of the clump model. Then, total normal force and bending moment of the rigid wall and motion process of the granular flow were further analyzed. Finally, comparison analysis of the numerical simulations using the clump model with different grain composition was obtained. By observing normal force on the rigid wall and distribution of particle size at the front of the rigid wall at the final state, the effect of grain composition on the force of the rigid wall has been revealed. It mainly showed that, with the increase of the particle size, the peak force at the retaining wall also increase. The result can provide a basis for the research of relevant disaster and the design of protective structures.
An ALE Finite Element Approach for Two-Phase Flow with Phase Change
NASA Astrophysics Data System (ADS)
Gros, Erik; Anjos, Gustavo; Thome, John; Ltcm Team; Gesar Team
2016-11-01
In this work, two-phase flow with phase change is investigated through the Finite Element Method (FEM) in the Arbitrary Lagrangian-Eulerian (ALE) framework. The equations are discretized on an unstructured mesh where the interface between the phases is explicitly defined as a sub-set of the mesh. The two-phase interface position is described by a set of interconnected nodes which ensures a sharp representation of the boundary, including the role of the surface tension. The methodology proposed for computing the curvature leads to very accurate results with moderate programming effort and computational costs. Such a methodology can be employed to study accurately many two-phase flow and heat transfer problems in industry such as oil extraction and refinement, design of refrigeration systems, modelling of microfluidic and biological systems and efficient cooling of electronics for computational purposes. The latter is the principal aim of the present research. The numerical results are discussed and compared to analytical solutions and reference results, thereby revealing the capability of the proposed methodology as a platform for the study of two-phase flow with phase change.
Membrane-less hybrid flow battery based on low-cost elements
NASA Astrophysics Data System (ADS)
Leung, P. K.; Martin, T.; Shah, A. A.; Mohamed, M. R.; Anderson, M. A.; Palma, J.
2017-02-01
The capital cost of conventional redox flow batteries is relatively high (>USD 200/kWh) due to the use of expensive active materials and ion-exchange membranes. This paper presents a membrane-less hybrid organic-inorganic flow battery based on the low-cost elements zinc (
A single-element, thermal, flow-velocity sensor with wide dynamic range
NASA Astrophysics Data System (ADS)
Al-Salaymeh, A.; Durst, F.; Gad-El-Hak, M.
2001-11-01
Thermal flow sensors with a wide dynamic range approaching 1:1000 are presently not available in spite of the large demand for such sensors in practical fluid flow measurements. During the last meeting (paper JG4, Bul. Am. Phys. Soc. 45, no. 9, p. 141, 2000), we described such a probe consisting of a minute wire heated using sinusoidal alternating current and two sensing wires acting as resistance thermometers and set parallel to, and at a small distance on either side of, the pulsed wire. Herein we detail the development of a single wire heated using square waves of electrical current. The elimination of the sensing wires reduces the complexity as well as the cost of the sensor and improves its spatial resolution. Unlike time-of-flight sensors, however, the present single-element sensor is sensitive to the physical properties and temperature of the ambient fluid. The present device is suited for measuring slowly-varying unidirectional flows over a very wide dynamic range. For a given current amplitude and frequency, the nominal output of the single sensor is the increase in wire temperature (or resistance) between times just before the leading edge of the current pulse and just after the trailing edge of the pulse. In practice, an integral of the resistance over the pulse duration is computed and averaged over several pulses. This output is a function of the wire’s time constant or thermal inertia and thus of the flow speed as well as the heat convected from the heated wire to the flow. We exploit the fact that the time constant decreases as the flow speed increases while the rate of heat transfer increases. At very low flow speeds, the response is determined almost entirely by the time constant whereas at high speeds the device acts almost like a constant-current hot-wire anemometer. At low speeds, therefore, the wire thermal inertia augments the output signal of the basic hot wire increasing its speed range and sensitivity above that of a conventional hot
NASA Astrophysics Data System (ADS)
Mather, B.; Moresi, L. N.; Cruden, A. R.
2014-12-01
Uncertainty of the lithospheric thermal regime greatly increases with depth. Measurements of temperature gradient and crustal rheology are concentrated in the upper crust, whereas the majority of the lithospheric measurements are approximated using empirical depth-dependent functions. We have applied a Monte Carlo approach to test the variation of crustal heat flow with temperature-dependent conductivity and the redistribution of heat-producing elements. The dense population of precision heat flow data in Victoria, Southeast Australia offers the ideal environment to test the variation of heat flow. A stochastically consistent anomalous zone of impossibly high Moho temperatures in the 3D model (> 900°C) correlates well with a zone of low teleseismic velocity and high electrical conductivity. This indicates that transient heat transfer has perturbed the thermal gradient and therefore a steady-state approach to 3D modelling is inappropriate in this zone. A spatial correlation between recent intraplate volcanic eruption points (< 5 Ma) and elevated Moho temperatures is a potential origin for additional latent heat in the crust.
NASA Technical Reports Server (NTRS)
Cooke, C. H.; Blanchard, D. K.
1975-01-01
A finite element algorithm for solution of fluid flow problems characterized by the two-dimensional compressible Navier-Stokes equations was developed. The program is intended for viscous compressible high speed flow; hence, primitive variables are utilized. The physical solution was approximated by trial functions which at a fixed time are piecewise cubic on triangular elements. The Galerkin technique was employed to determine the finite-element model equations. A leapfrog time integration is used for marching asymptotically from initial to steady state, with iterated integrals evaluated by numerical quadratures. The nonsymmetric linear systems of equations governing time transition from step-to-step are solved using a rather economical block iterative triangular decomposition scheme. The concept was applied to the numerical computation of a free shear flow. Numerical results of the finite-element method are in excellent agreement with those obtained from a finite difference solution of the same problem.
Dynamic subgrid-scale modeling for finite element based simulation of complex turbulent flows
NASA Astrophysics Data System (ADS)
Tran, Steven
The focus of this thesis is the formulation and development of a turbulence-resolving simulation tool based on finite elements. There are many challenges to the development of a reliable numerical approach for predicting the behavior of complex turbulent flows. In such flows, the difficulties emanate from two aspects: (i) complicated geometry and solution features and (ii) a balance between the computational cost and the amount of resolution and modeling that is required to perform accurate predictions. The finite element (FE) method has proven to be a valuable numerical tool to handle complicated features. Specifically, the ease with which the FE method can be applied on unstructured meshes makes it a powerful option for investigating many complex problems of interest. Furthermore, the adaptive meshing, high-order, and parallelization capabilities of the FE method can significantly increase the computational efficiency. In terms of turbulence resolution, direct numerical simulation (DNS) is the most reliable option but it requires a proper resolution of all the relevant turbulent scales (with no modeling). This makes DNS prohibitively expensive from a computational viewpoint for many problems of interest. An attractive alternative is large eddy simulation (LES) which resolves the flow structures on the order of the grid size and models the effects of the scales that are too small to be resolved by the grid (i.e., subgrid scales). %Therefore, LES involves subgrid-scale (SGS) modeling. This thesis develops an LES methodology that entails the following features: (i) a combined subgrid-scale model in the context of stabilized finite element methods, (ii) a local dynamic procedure based on the variational Germano identity (VGI), (iii) an averaging scheme that makes the local dynamic procedure robust for complex inhomogeneous turbulent flows, and (iv) extension to problems with moving and deforming objects. In particular, the combined SGS model uses the residual
Better Strategies for Finite Element Solutions of Variable Viscosity Stokes Flow
NASA Astrophysics Data System (ADS)
Hasenclever, Jörg; Phipps Morgan, Jason; Shi, Chao
2010-05-01
Accurate numerical solution of variable viscosity Stokes Flow is one of the most important issues for better geodynamic understanding of mantle convection and mantle melting. While a good Stokes solver is usually an integral part of a good Navier-Stokes solver, typically Navier-Stokes equations are solved for flow of a fluid with uniform viscosity. The lumped-mass-matrix is an excellent and cheap preconditioner for uniform viscosity Stokes flow (cf. Maday and Patera, 1989), therefore for most applications to Navier-Stokes flow the ‘Stokes' part of the problem is viewed as well-resolved. Unfortunately, the inverse-viscosity-scaled lumped mass matrix does not work nearly as well to precondition Stokes flow in a fluid with strongly varying viscosity. This issue is already central to accurate numerical studies of convection in Earth's silicate-fluid mantle (May and Moresi, 2008; van Geenen et al., 2009; Burstedde et al., 2009) and may become central for researchers investigating Navier-Stokes problems with lateral variations in viscosity. Here we discuss several known computational hurdles to progress, and suggest strategies that offer promise in overcoming them. The choices for solving the discrete pressure equation arising from Stokes flow typically involve several tradeoffs between speed and storage requirements. In exact math, the discrete pressure matrix S is symmetric, so that it should be possible to use a symmetric preconditioned conjugate gradient (CG) Krylov algorithm instead of needing an asymmetric GMRES (cf. Saad, 2003) or GCR (Generalized Conjugate Residual, cf. Van der Vorst, 2003) that would require ~10-50 times more storage of past search directions. However, a CG-like method requires that the action of both S and any pressure preconditioner must be almost perfectly symmetric. This means that we must be very careful about the effects of roundoff in any iterative solver-based pressure preconditioner that may introduce numerically asymmetric operators
NASA Astrophysics Data System (ADS)
Hancock, W.; Weatherley, D.; Wruck, B.; Chitombo, G. P.
2012-04-01
The flow dynamics of granular materials is of broad interest in both the geosciences (e.g. landslides, fault zone evolution, and brecchia pipe formation) and many engineering disciplines (e.g chemical engineering, food sciences, pharmaceuticals and materials science). At the interface between natural and human-induced granular media flow, current underground mass-mining methods are trending towards the induced failure and subsequent gravitational flow of large volumes of broken rock, a method known as cave mining. Cave mining relies upon the undercutting of a large ore body, inducement of fragmentation of the rock and subsequent extraction of ore from below, via hopper-like outlets. Design of such mines currently relies upon a simplified kinematic theory of granular flow in hoppers, known as the ellipsoid theory of mass movement. This theory assumes that the zone of moving material grows as an ellipsoid above the outlet of the silo. The boundary of the movement zone is a shear band and internal to the movement zone, the granular material is assumed to have a uniformly high bulk porosity compared with surrounding stagnant regions. There is however, increasing anecdotal evidence and field measurements suggesting this theory fails to capture the full complexity of granular material flow within cave mines. Given the practical challenges obstructing direct measurement of movement both in laboratory experiments and in-situ, the Discrete Element Method (DEM [1]) is a popular alternative to investigate granular media flow. Small-scale DEM studies (c.f. [3] and references therein) have confirmed that movement within DEM silo flow models matches that predicted by ellipsoid theory, at least for mono-disperse granular material freely outflowing at a constant rate. A major draw-back of these small-scale DEM studies is that the initial bulk porosity of the simulated granular material is significantly higher than that of broken, prismatic rock. In this investigation, more
Simulation of 3-D viscous compressible flow in multistage turbomachinery by finite element methods
NASA Astrophysics Data System (ADS)
Sleiman, Mohamad
1999-11-01
The flow in a multistage turbomachinery blade row is compressible, viscous, and unsteady. Complex flow features such as boundary layers, wake migration from upstream blade rows, shocks, tip leakage jets, and vortices interact together as the flow convects through the stages. These interactions contribute significantly to the aerodynamic losses of the system and degrade the performance of the machine. The unsteadiness also leads to blade vibration and a shortening of its life. It is therefore difficult to optimize the design of a blade row, whether aerodynamically or structurally, in isolation, without accounting for the effects of the upstream and downstream rows. The effects of axial spacing, blade count, clocking (relative position of follow-up rotors with respect to wakes shed by upstream ones), and levels of unsteadiness may have a significance on performance and durability. In this Thesis, finite element formulations for the simulation of multistage turbomachinery are presented in terms of the Reynolds-averaged Navier-Stokes equations for three-dimensional steady or unsteady, viscous, compressible, turbulent flows. Three methodologies are presented and compared. First, a steady multistage analysis using a a-mixing- plane model has been implemented and has been validated against engine data. For axial machines, it has been found that the mixing plane simulation methods match very well the experimental data. However, the results for a centrifugal stage, consisting of an impeller followed by a vane diffuser of equal pitch, show flagrant inconsistency with engine performance data, indicating that the mixing plane method has been found to be inappropriate for centrifugal machines. Following these findings, a more complete unsteady multistage model has been devised for a configuration with equal number of rotor and stator blades (equal pitches). Non-matching grids are used at the rotor-stator interface and an implicit interpolation procedure devised to ensure
Impact of the Chemical Elements Upon the Convective Flows in the Molten Metal of the Weld Pool
NASA Astrophysics Data System (ADS)
Sarychev, V. D.; Chinakhov, D. A.; Solodsky, S. A.; Granovskii, A. Yu; Nevskii, S. A.
2017-05-01
World production of surfacing materials requires a large amount of alloying elements extracted from the Earth crust. Efficient use of scarce alloying elements and development of resource efficient surfacing techniques which reduce consumption of alloying elements together with improvement of the functional properties of the surfaced layer is a relevant problem of material science and preservation of the environment. In the paper the authors consider the problem of modeling the convective flows emerging under the plasma jets in the process of surfacing. The authors formulate the basic requirements to the thermal cycle of the surfacing ensuring obtaining identical functional properties of the surface while the amount of scarce alloying elements reduces.
NASA Astrophysics Data System (ADS)
Li, Xian-Hua; Putiš, Marián; Yang, Yue-Heng; Koppa, Matúš; Dyda, Marian
2014-09-01
Perovskite-bearing harzburgites occur in a “mélange” type blueschist-bearing accretionary wedge complex of the Inner Western Carpathians Meliata Unit in Slovakia. Although dark rounded, slightly hydrated relic “cores” of harzburgite boulders are perovskite-free, perovskite (Prv) occurrence in the surrounding serpentinites and rodingites enabled dating of hydration, resulting in two metamorphic-metasomatic Prv generations. Perovskite (1) grows parallel to relic clinopyroxene exsolution lamellae or forms randomly oriented grain clusters in serpentinized orthopyroxene (Opx1) porphyroclasts, often accompanied by tiny andradite lamellae clusters, or it is partly replaced by Ti-andradite. Perovskite crystallization indicates evolving rodingitization fluids pervading the boundary between the harzburgite “cores” and Prv-free serpentinite. This strictly limited occurrence of Prv (1) within a 1 to 20-cm across-zone implies slightly postponed Prv crystallization to serpentinization by LREE(Ce,La), Ca2+, Ti/Fe3+-enriched aqueous fluids. A grain scale metasomatic mechanism partitioned Ca and Ti from the host orthopyroxene porphyroclasts, spinel (Ti) and grain-boundary pervasive fluids to Prv. In contrast, Prv (2) occurs in a 1 to 3 cm across chlorite-rich blackwall zone between hosting serpentinite and rodingite veins, thus indicating channelled rodingitization fluid flow and accompanying hydraulic fracturing. Here, Prv (2) is ingrown by chlorite and apatite. Part of this Prv (2) formed in a rodingite vein mineral assemblage composed of diopside, andradite, vesuvianite, epidote/zoisite, apatite and chlorite. Both perovskite 1 and 2 are replaced by pyrophanite along the grain rims and interiors; most likely via fluid-aided coupled dissolution-reprecipitation at increased Si-Fe-Mn-Al element solubility in rodingitization fluids pervading serpentinized harzburgite. Both Prv generations, especially Prv (2), can be partly to almost totally replaced by (Ti-) Adr
NASA Technical Reports Server (NTRS)
Levine, H.
1980-01-01
Acoustic radiation from a source, here viewed as an immobile point singularity with periodic strength and a given multipolar nature, is affected by the presence of nearly structural elements (e.g., rigid or impedance surfaces) as well as that of a background flow in the medium. An alternative to the conventional manner of calculating the net source output by integrating the energy flux over a distant control surface is described; this involves a direct evaluation of the secondary wavefunction at the position of the primary source and obviates the need for a (prospectively difficult) flux integration. Various full and half-planar surface configurations with an adjacent source are analyzed in detail, and the explicit results obtained, in particular, for the power factor of a dipole brings out a substantial rise in its output as the source nears the sharp edge of a half-plane.
Computation of the steady viscous flow over a tri-element 'augmentor wing' airfoil
NASA Technical Reports Server (NTRS)
Lasinski, T. A.; Andrews, A. E.; Sorenson, R. L.; Chaussee, D. S.; Pulliam, T. H.; Kutler, P.
1982-01-01
The augmentor wing consists of a main airfoil with a slotted trailing edge for blowing, and two smaller aft airfoils which shroud the jet. This configuration has been modeled for numerical simulation by a novel discretization procedure which generates four separate grids: three surface-oriented airfoil grids and one outer free-stream grid. Grid lines and slopes are continuous across boundaries, so grid overlap at common boundaries provides boundary information without interpolation. A two-dimensional unsteady thin-layer Navier-Stokes code is used to calculate the flow for the no-blowing case at freestream Mach number = 0.7, Re = 12,600.000, and angles-of-incidence = 1.05 deg. Qualitative agreement with experimental data indicates the utility of this procedure in the analysis of multi-element configurations.
NASA Technical Reports Server (NTRS)
Levine, H.
1980-01-01
Acoustic radiation from a source, here viewed as an immobile point singularity with periodic strength and a given multipolar nature, is affected by the presence of nearly structural elements (e.g., rigid or impedance surfaces) as well as that of a background flow in the medium. An alternative to the conventional manner of calculating the net source output by integrating the energy flux over a distant control surface is described; this involves a direct evaluation of the secondary wavefunction at the position of the primary source and obviates the need for a (prospectively difficult) flux integration. Various full and half-planar surface configurations with an adjacent source are analyzed in detail, and the explicit results obtained, in particular, for the power factor of a dipole brings out a substantial rise in its output as the source nears the sharp edge of a half-plane.
Progress on a Taylor weak statement finite element algorithm for high-speed aerodynamic flows
NASA Technical Reports Server (NTRS)
Baker, A. J.; Freels, J. D.
1989-01-01
A new finite element numerical Computational Fluid Dynamics (CFD) algorithm has matured to the point of efficiently solving two-dimensional high speed real-gas compressible flow problems in generalized coordinates on modern vector computer systems. The algorithm employs a Taylor Weak Statement classical Galerkin formulation, a variably implicit Newton iteration, and a tensor matrix product factorization of the linear algebra Jacobian under a generalized coordinate transformation. Allowing for a general two-dimensional conservation law system, the algorithm has been exercised on the Euler and laminar forms of the Navier-Stokes equations. Real-gas fluid properties are admitted, and numerical results verify solution accuracy, efficiency, and stability over a range of test problem parameters.
Krabicka, J.; Yan, Y.
2009-08-15
Electrostatic sensors are used in certain industries for the flow measurement of pneumatically conveyed solids. However, despite various advances that have been made in recent years, relatively little information is known about the exact nature of the electrostatic charge induced onto the sensor electrode due to moving particles, which is dependent on electrode geometry, particle distribution, and particle velocity. This paper presents a novel approach to the study of the charge induced onto electrostatic sensors based on fitting a Lorentzian curve to the results of a finite-element model of the electrostatic sensor and pipeline. The modeling method is validated by comparing the modeling results of a nonintrusive circular electrode with an established analytical solution. The modeling results are used for in-depth analysis and informed design of a particular sensor configuration.
Progress on a Taylor weak statement finite element algorithm for high-speed aerodynamic flows
NASA Technical Reports Server (NTRS)
Baker, A. J.; Freels, J. D.
1989-01-01
A new finite element numerical Computational Fluid Dynamics (CFD) algorithm has matured to the point of efficiently solving two-dimensional high speed real-gas compressible flow problems in generalized coordinates on modern vector computer systems. The algorithm employs a Taylor Weak Statement classical Galerkin formulation, a variably implicit Newton iteration, and a tensor matrix product factorization of the linear algebra Jacobian under a generalized coordinate transformation. Allowing for a general two-dimensional conservation law system, the algorithm has been exercised on the Euler and laminar forms of the Navier-Stokes equations. Real-gas fluid properties are admitted, and numerical results verify solution accuracy, efficiency, and stability over a range of test problem parameters.
NASA Astrophysics Data System (ADS)
Percival, James; Xie, Zhihua; Pavlidis, Dimitrios; Gomes, Jefferson; Pain, Christopher; Matar, Omar
2013-11-01
We present results from a new formulation of a numerical model for direct simulation of bed fluidization and multiphase granular flow. The model is based on a consistent application of continuous-discontinuous mixed control volume finite element methods applied to fully unstructured meshes. The unstructured mesh framework allows for both a mesh adaptive capability, modifying the computational geometry in order to bound the error in the numerical solution while maximizing computational efficiency, and a simple scripting interface embedded in the model which allows fast prototyping of correlation models and parameterizations in intercomparison experiments. The model is applied to standard test problems for fluidized beds. EPSRC Programme Grant EP/K003976/1.
Laminar backward-facing step flow using the finite element method
Kornblum, B.; McCallen, R.; Christon, M.A.; Kollmann, W.
1995-11-01
Laminar, incompressible flow over a backward-facing step is calculated using a finite element spatial discretization with a piecewise continuous pressure approximation and an explicit time marching algorithm. The time-accurate evolution to steady state is demonstrated for both two-dimensional (2D) and three-dimensional (3D) simulations. This approach is shown to accurately predict the lengths of the recirculation zone on the top wall and at the step for various meshes and domain lengths, for a Reynolds number of 800 based on the average inlet velocity and twice the inlet channel height. The instantaneous and steady-state results are investigated. The steady-state solutions are evaluated by comparison to published numerical and experimental results.
NASA Astrophysics Data System (ADS)
Lavery, N.; Taylor, C.
1999-07-01
Multigrid and iterative methods are used to reduce the solution time of the matrix equations which arise from the finite element (FE) discretisation of the time-independent equations of motion of the incompressible fluid in turbulent motion. Incompressible flow is solved by using the method of reduce interpolation for the pressure to satisfy the Brezzi-Babuska condition. The k-l model is used to complete the turbulence closure problem. The non-symmetric iterative matrix methods examined are the methods of least squares conjugate gradient (LSCG), biconjugate gradient (BCG), conjugate gradient squared (CGS), and the biconjugate gradient squared stabilised (BCGSTAB). The multigrid algorithm applied is based on the FAS algorithm of Brandt, and uses two and three levels of grids with a V-cycling schedule. These methods are all compared to the non-symmetric frontal solver. Copyright
A discontinuous finite element approach to cracking in coupled poro-elastic fluid flow models
NASA Astrophysics Data System (ADS)
Wilson, C. R.; Spiegelman, M. W.; Evans, O.; Ulven, O. I.; Sun, W.
2016-12-01
Reaction-driven cracking is a coupled process whereby fluid-induced reactions drive large volume changes in the host rock which produce stresses leading to crack propagation and failure. This in turn generates new surface area and fluid-flow pathways for subsequent reaction in a potentially self-sustaining system. This mechanism has has been proposed for the pervasive serpentinization and carbonation of peridotite, as well as applications to mineral carbon sequestration and hydrocarbon extraction. The key computational issue in this problem is implementing algorithms that adequately model the formation of discrete fractures. Here we present models using a discontinuous finite element method for modeling fracture formation (Radovitsky et al., 2011). Cracks are introduced along facets of the mesh by the relaxation of penalty parameters once a failure criterion is met. It is fully described in the weak form of the equations, requiring no modification of the underlying mesh structure and allowing fluid properties to be easily adjusted along cracked facets. To develop and test the method, we start by implementing the algorithm for the simplified Biot equations for poro-elasticity using the finite element model assembler TerraFERMA. We consider hydro-fracking around a borehole (Grassl et al., 2015), where elevated fluid pressure in the poro-elastic solid causes it to fail radially in tension. We investigate the effects of varying the Biot coefficient and adjusting the fluid transport properties in the vicinity of the crack and compare our results to related dual-graph models (Ulven & Sun, submitted). We discuss issues arising from this method, including the formation of null spaces and appropriate preconditioning and solution strategies. Initial results suggest that this method provides a promising way to incorporate cracking into our reactive fluid flow models and future work aims to integrate the mechanical and chemical aspects of this process.
NASA Astrophysics Data System (ADS)
Bakker, Mark; Kuhlman, Kristopher L.
2011-09-01
Two new approaches are presented for the accurate computation of the potential due to line elements that satisfy the modified Helmholtz equation with complex parameters. The first approach is based on fundamental solutions in elliptical coordinates and results in products of Mathieu functions. The second approach is based on the integration of modified Bessel functions. Both approaches allow evaluation of the potential at any distance from the element. The computational approaches are applied to model transient flow with the Laplace transform analytic element method. The Laplace domain solution is computed using a combination of point elements and the presented line elements. The time domain solution is obtained through a numerical inversion. Two applications are presented to transient flow fields, which could not be modeled with the Laplace transform analytic element method prior to this work. The first application concerns transient single-aquifer flow to wells near impermeable walls modeled with line-doublets. The second application concerns transient two-aquifer flow to a well near a stream modeled with line-sinks.
Orozco, Gustavo A; Smith, Joshua H; García, José J
2014-10-01
A previously proposed finite element model that considers geometric and material nonlinearities and the free boundary problems that occur at the catheter tip and in the annular zone around the lateral surface of the catheter was revised and was used to fit a power-law formula to predict backflow length during infusions into brain tissue. Compared to a closed-form solution based on linear elasticity, the power-law formula for compliant materials predicted a substantial lower influence of the shear modulus and catheter radius on the backflow length, whereas the corresponding influence for stiffer materials was more consistent with the closed-form solution. The finite element model predicted decreases of the backflow length for reduction of the shear modulus for highly compliant materials (shear modulus less than 500 Pa) due to the increased area of infusion and the high fluid fraction near the infusion cavity that greatly increased the surface area available for fluid transfer and reduced the hydraulic resistance toward the tissue. These results show the importance of taking into account the material and geometrical nonlinearities that arise near the infusion surface as well as the change of hydraulic conductivity with strain for a proper characterization of backflow length during flow-controlled infusions into the brain.
Dual Reciprocity Boundary Element Method for studying thermal flow in cooling Magma Oceans
NASA Astrophysics Data System (ADS)
Drombosky, T.; Hier-Majumder, S.
2011-12-01
Earth's early history is marked by a giant impact with a Mars-sized object which lead to the formation of the moon. This impact event likely led to a substantial amount of melting of the Earth's interior. Subsequent cooling of the Earth involved extensive crystallization in this "magma ocean" over a relatively short period of time. While chemical evidence from ancient sources provides some clues on the rate of cooling, computational models of such phenomena are sparse. Modeling the crystal settling behavior requires solving a coupled system of partial differential equations, specifically the Stokes flow equation coupled with the heat equation through an advection term. Our work uses the dual reciprocity boundary element method (DRBEM) to model such a system. DRBEM extends on the boundary element method (BEM) to solve the heat equation for a multiparticle system in an infinite suspension fluid while avoiding the expensive rediscretization inherit in other methods. In DRBEM, terms arising from the material time derivative of temperature are expanded in a series of function, known as radial basis functions. By modeling this system we are able to simulate thermal interactions among an arbitrary number of crystals settling in a magma ocean. The types of interactions include the enhanced cooling of the magma due to an advecting matrix of cold crystal particles. We are also able to observe the interactions of the crystals' thermal profiles. As a crystal settles, it leaves behind a trail of lower temperature suspension fluid, which then interacts with surrounding particles.
Bermudo, Carolina; Sevilla, Lorenzo; Castillo López, Germán
2017-01-01
The present work shows the material flow analysis in indentation by the numerical two dimensional Finite Elements (FEM) method and the experimental two-dimensional Digital Image Correlation (DIC) method. To achieve deep indentation without cracking, a ductile material, 99% tin, is used. The results obtained from the DIC technique depend predominantly on the pattern conferred to the samples. Due to the absence of a natural pattern, black and white spray painting is used for greater contrast. The stress-strain curve of the material has been obtained and introduced in the Finite Element simulation code used, DEFORM™, allowing for accurate simulations. Two different 2D models have been used: a plain strain model to obtain the load curve and a plain stress model to evaluate the strain maps on the workpiece surface. The indentation displacement load curve has been compared between the FEM and the experimental results, showing a good correlation. Additionally, the strain maps obtained from the material surface with FEM and DIC are compared in order to validate the numerical model. The Von Mises strain results between both of them present a 10–20% difference. The results show that FEM is a good tool for simulating indentation processes, allowing for the evaluation of the maximum forces and deformations involved in the forming process. Additionally, the non-contact DIC technique shows its potential by measuring the superficial strain maps, validating the FEM results. PMID:28773038
Bermudo, Carolina; Sevilla, Lorenzo; Castillo López, Germán
2017-06-21
The present work shows the material flow analysis in indentation by the numerical two dimensional Finite Elements (FEM) method and the experimental two-dimensional Digital Image Correlation (DIC) method. To achieve deep indentation without cracking, a ductile material, 99% tin, is used. The results obtained from the DIC technique depend predominantly on the pattern conferred to the samples. Due to the absence of a natural pattern, black and white spray painting is used for greater contrast. The stress-strain curve of the material has been obtained and introduced in the Finite Element simulation code used, DEFORM™, allowing for accurate simulations. Two different 2D models have been used: a plain strain model to obtain the load curve and a plain stress model to evaluate the strain maps on the workpiece surface. The indentation displacement load curve has been compared between the FEM and the experimental results, showing a good correlation. Additionally, the strain maps obtained from the material surface with FEM and DIC are compared in order to validate the numerical model. The Von Mises strain results between both of them present a 10-20% difference. The results show that FEM is a good tool for simulating indentation processes, allowing for the evaluation of the maximum forces and deformations involved in the forming process. Additionally, the non-contact DIC technique shows its potential by measuring the superficial strain maps, validating the FEM results.
Mansilla Alvarez, Luis; Blanco, Pablo; Bulant, Carlos; Dari, Enzo; Veneziani, Alessandro; Feijóo, Raúl
2017-04-01
In this work, we present a novel approach tailored to approximate the Navier-Stokes equations to simulate fluid flow in three-dimensional tubular domains of arbitrary cross-sectional shape. The proposed methodology is aimed at filling the gap between (cheap) one-dimensional and (expensive) three-dimensional models, featuring descriptive capabilities comparable with the full and accurate 3D description of the problem at a low computational cost. In addition, this methodology can easily be tuned or even adapted to address local features demanding more accuracy. The numerical strategy employs finite (pipe-type) elements that take advantage of the pipe structure of the spatial domain under analysis. While low order approximation is used for the longitudinal description of the physical fields, transverse approximation is enriched using high order polynomials. Although our application of interest is computational hemodynamics and its relevance to pathological dynamics like atherosclerosis, the approach is quite general and can be applied in any internal fluid dynamics problem in pipe-like domains. Numerical examples covering academic cases as well as patient-specific coronary arterial geometries demonstrate the potentialities of the developed methodology and its performance when compared against traditional finite element methods. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.
NASA Astrophysics Data System (ADS)
Mostaghimi, P.; Percival, J. R.; Pavlidis, D.; Gorman, G.; Jackson, M.; Neethling, S.; Pain, C. C.
2013-12-01
Numerical simulation of multiphase flow in porous media is of importance in a wide range of applications in science and engineering. We present a novel control volume finite element method (CVFEM) to solve for multi-scale flow in heterogeneous geological formations. It employs a node centred control volume approach to discretize the saturation equation, while a control volume finite element method is applied for the pressure equation. We embed the discrete continuity equation into the pressure equation and assure that the continuity is exactly enforced. Anisotropic mesh adaptivity is used to accurately model the fine grained features of multiphase flow. The adaptive algorithm uses a metric tensor field based on solution error estimates to locally control the size and shape of elements in the metric. Moreover, it uses metric advection between adaptive meshes in order to predict the future required density of mesh thereby reducing numerical dispersion at the saturation front. The scheme is capable of capturing multi-scale heterogeneity such as those in fractured porous media through the use of several constraints on the element size in different regions of porous media. We show the application of our method for simulation of flow in some challenging benchmark problems. For flow in fractured reservoirs, the scheme adapts the mesh as the flow penetrates through the fracture and the matrix. The constraints for the element size within the fracture are smaller by several orders of magnitude than the generated mesh within the matrix. We show that the scheme captures the key multi-scale features of flow while preserving the geometry. We demonstrate that mesh adaptation can be used to accurately simulate flow in heterogeneous porous media at low computational cost.
Assessment of a hybrid finite element and finite volume code for turbulent incompressible flows
Xia, Yidong; Wang, Chuanjin; Luo, Hong; Christon, Mark; Bakosi, Jozsef
2015-12-15
Hydra-TH is a hybrid finite-element/finite-volume incompressible/low-Mach flow simulation code based on the Hydra multiphysics toolkit being developed and used for thermal-hydraulics applications. In the present work, a suite of verification and validation (V&V) test problems for Hydra-TH was defined to meet the design requirements of the Consortium for Advanced Simulation of Light Water Reactors (CASL). The intent for this test problem suite is to provide baseline comparison data that demonstrates the performance of the Hydra-TH solution methods. The simulation problems vary in complexity from laminar to turbulent flows. A set of RANS and LES turbulence models were used in the simulation of four classical test problems. Numerical results obtained by Hydra-TH agreed well with either the available analytical solution or experimental data, indicating the verified and validated implementation of these turbulence models in Hydra-TH. Where possible, we have attempted some form of solution verification to identify sensitivities in the solution methods, and to suggest best practices when using the Hydra-TH code.
A comparison of turbulence models in computing multi-element airfoil flows
NASA Technical Reports Server (NTRS)
Rogers, Stuart E.; Menter, Florian; Durbin, Paul A.; Mansour, Nagi N.
1994-01-01
Four different turbulence models are used to compute the flow over a three-element airfoil configuration. These models are the one-equation Baldwin-Barth model, the one-equation Spalart-Allmaras model, a two-equation k-omega model, and a new one-equation Durbin-Mansour model. The flow is computed using the INS2D two-dimensional incompressible Navier-Stokes solver. An overset Chimera grid approach is utilized. Grid resolution tests are presented, and manual solution-adaptation of the grid was performed. The performance of each of the models is evaluated for test cases involving different angles-of-attack, Reynolds numbers, and flap riggings. The resulting surface pressure coefficients, skin friction, velocity profiles, and lift, drag, and moment coefficients are compared with experimental data. The models produce very similar results in most cases. Excellent agreement between computational and experimental surface pressures was observed, but only moderately good agreement was seen in the velocity profile data. In general, the difference between the predictions of the different models was less than the difference between the computational and experimental data.
Zhao, Jingjing; You, Zheng
2016-01-01
This work introduces three rectangular quasi-flat-top spots, which are provided by binary optical elements (BOEs) and utilized for the illumination in a microflow cytometer. The three spots contain, respectively, one, two, and three rectangles (R1, R2, and R3). To test the performance of this mechanism, a microflow cytometer is established by integrating the BOEs and a three-dimensional hydrodynamic focusing chip. Through the experiments of detecting fluorescence microbeads, the three spots present good fluorescence coefficients of variation in comparison with those derived from commercial instruments. Benefiting from a high spatial resolution, when using R1 spot, the micro flow cytometer can perform a throughput as high as 20 000 events per second (eps). Illuminated by R2 or R3 spot, one bead emits fluorescence twice or thrice, thus the velocity can be measured in real time. Besides, the R3 spot provides a long-time exposure, which is conducive to improving fluorescence intensity and the measurement stability. In brief, using the spots shaped and homogenized by BOEs for illumination can increase the performance and the functionality of a micro flow cytometer. PMID:27733892
A comparison of turbulence models in computing multi-element airfoil flows
NASA Technical Reports Server (NTRS)
Rogers, Stuart E.; Menter, Florian; Durbin, Paul A.; Mansour, Nagi N.
1994-01-01
Four different turbulence models are used to compute the flow over a three-element airfoil configuration. These models are the one-equation Baldwin-Barth model, the one-equation Spalart-Allmaras model, a two-equation k-omega model, and a new one-equation Durbin-Mansour model. The flow is computed using the INS2D two-dimensional incompressible Navier-Stokes solver. An overset Chimera grid approach is utilized. Grid resolution tests are presented, and manual solution-adaptation of the grid was performed. The performance of each of the models is evaluated for test cases involving different angles-of-attack, Reynolds numbers, and flap riggings. The resulting surface pressure coefficients, skin friction, velocity profiles, and lift, drag, and moment coefficients are compared with experimental data. The models produce very similar results in most cases. Excellent agreement between computational and experimental surface pressures was observed, but only moderately good agreement was seen in the velocity profile data. In general, the difference between the predictions of the different models was less than the difference between the computational and experimental data.
Assessment of a hybrid finite element and finite volume code for turbulent incompressible flows
NASA Astrophysics Data System (ADS)
Xia, Yidong; Wang, Chuanjin; Luo, Hong; Christon, Mark; Bakosi, Jozsef
2016-02-01
Hydra-TH is a hybrid finite-element/finite-volume incompressible/low-Mach flow simulation code based on the Hydra multiphysics toolkit being developed and used for thermal-hydraulics applications. In the present work, a suite of verification and validation (V&V) test problems for Hydra-TH was defined to meet the design requirements of the Consortium for Advanced Simulation of Light Water Reactors (CASL). The intent for this test problem suite is to provide baseline comparison data that demonstrates the performance of the Hydra-TH solution methods. The simulation problems vary in complexity from laminar to turbulent flows. A set of RANS and LES turbulence models were used in the simulation of four classical test problems. Numerical results obtained by Hydra-TH agreed well with either the available analytical solution or experimental data, indicating the verified and validated implementation of these turbulence models in Hydra-TH. Where possible, some form of solution verification has been attempted to identify sensitivities in the solution methods, and suggest best practices when using the Hydra-TH code.
Assessment of a hybrid finite element and finite volume code for turbulent incompressible flows
Xia, Yidong; Wang, Chuanjin; Luo, Hong; ...
2015-12-15
Hydra-TH is a hybrid finite-element/finite-volume incompressible/low-Mach flow simulation code based on the Hydra multiphysics toolkit being developed and used for thermal-hydraulics applications. In the present work, a suite of verification and validation (V&V) test problems for Hydra-TH was defined to meet the design requirements of the Consortium for Advanced Simulation of Light Water Reactors (CASL). The intent for this test problem suite is to provide baseline comparison data that demonstrates the performance of the Hydra-TH solution methods. The simulation problems vary in complexity from laminar to turbulent flows. A set of RANS and LES turbulence models were used in themore » simulation of four classical test problems. Numerical results obtained by Hydra-TH agreed well with either the available analytical solution or experimental data, indicating the verified and validated implementation of these turbulence models in Hydra-TH. Where possible, we have attempted some form of solution verification to identify sensitivities in the solution methods, and to suggest best practices when using the Hydra-TH code.« less
Infrared thermography of transition due to isolated roughness elements in hypersonic flows
NASA Astrophysics Data System (ADS)
Avallone, F.; Schrijer, F. F. J.; Cardone, G.
2016-02-01
Boundary layer transition in high-speed flows is a phenomenon that despite extensive research over the years is still extremely hard to predict. The presence of protrusions or gaps can lead to an accelerated laminar-to-turbulent transition enhancing the thermal loads and the skin friction coefficient. In the current investigation, inverse heat transfer measurements using infrared thermography are performed on the flow past different roughness geometries in the form of cylinders and diamond at free stream Mach number equal to 7.5, h/δ ranging between 0.5 and 0.9 (where h is the roughness height and δ is the boundary layer thickness), and Reθ ranging between 1305 and 2450. The roughness elements are positioned on a 5° ramp placed at zero angle of attack. The measurements indicate that the roughness geometry influences the transitional pattern while the frontal area influences both the transition location and the maximum value of the Stanton number along the centreline. Moreover, there is a strong connection between the streamwise centreline Stanton number and the spreading of the wake width. In particular, the transition process is characterized by an approximately constant wake width. Differently, the wake width spreads at the location where the streamwise centreline Stanton number reaches the turbulent level. This point corresponds to a local maximum of the wake amplitude defined as one half of the maximum spanwise variation of the Stanton number.
LES of turbulent boundary layer flow over urban-like roughness elements
NASA Astrophysics Data System (ADS)
Tamura, Tetsuro; Tsubokura, Makoto; Nozu, Tsuyoshi; Onishi, Keiji
2014-11-01
LES of turbulent boundary layer flow over urban-like roughness elements has been performed. Final goal of this paper is to elucidate the availability of LES on the wind flow within the canopy among buildings in cities. Firstly rectangular blocks, definitely larger than those on conventional rough wall such as grain or sand, are homogeneously arrayed and above-region equilibrium profiles of mean velocity and turbulent statistics are investigated. Also, in order to predict the fluctuating velocity characteristics of urban boundary layer, actual complicated-shaped buildings are used for reproducing the surface shape in cities. For numerical modeling, this study employs the unstructured-grid system where grid lines correctly fit to the building shape and BCM (Building Cube Method) which is formulated on very fine Cartesian mesh system. Based on the GIS data, BCM employs the external forcing technique named IBM (Immersed Boundary Method). Also, in BCM, computational process is so simple that the parallel algorithm and the memory access obtain the perfect efficiency. Using both the LES results, turbulence structures in the urban canopy are discussed. Appropriate 3D vortical structures can be recognized at inflow, along the street and among a pack of tall buildings.
NASA Astrophysics Data System (ADS)
Delbridge, B. G.; Burgmann, R.; Fielding, E. J.; Hensley, S.; Schulz, W. H.
2013-12-01
This project focuses on improving our understanding of the physical mechanisms controlling landslide motion by studying the landslide-wide kinematics of the Slumgullion landslide in southwestern Colorado using interferometric synthetic aperture radar (InSAR) and GPS. The NASA/JPL UAVSAR airborne repeat-pass SAR interferometry system imaged the Slumgullion landslide from 4 look directions on eight flights in 2011 and 2012. Combining the four look directions allows us to extract the full 3-D velocity field of the surface. Observing the full 3-dimensional flow field allows us to extract the full strain tensor (assuming free surface boundary conditions and incompressible flow) since we have both the spatial resolution to take spatial derivates and full deformation information. COSMO-SkyMed(CSK) high-resolution Spotlight data was also acquired during time intervals overlapping with the UAVSAR one-week pairs, with intervals as short as one day. These observations allow for the quantitative testing of the deformation magnitude and estimated formal errors in the UAVSAR derived deformation field. We also test the agreement of the deformation at 20 GPS monitoring sites concurrently acquired by the USGS. We also utilize the temporal resolution of real-time GPS acquired by the UC Berkeley Active Tectonics Group during a temporary deployment from July 22nd - August 2nd. By combining this data with the kinematic data we hope to elucidate the response of the landslide to environmental changes such as rainfall, snowmelt, and atmospheric pressure, and consequently the mechanisms controlling the dynamics of the landslide system. To constrain the longer temporal dynamics, interferograms made from pairs of CSK images acquired in 2010, 2011, 2012 and 2013 reveal the slide deformation on a longer timescale by allowing us to measure meters of motion and see the average rates over year long intervals using pixel offset tracking of the high-resolution SAR amplitude images. The results of
Assessment of a hybrid finite element and finite volume code for turbulent incompressible flows
Xia, Yidong; Wang, Chuanjin; Luo, Hong; Christon, Mark; Bakosi, Jozsef
2016-02-15
Hydra-TH is a hybrid finite-element/finite-volume incompressible/low-Mach flow simulation code based on the Hydra multiphysics toolkit being developed and used for thermal-hydraulics applications. In the present work, a suite of verification and validation (V&V) test problems for Hydra-TH was defined to meet the design requirements of the Consortium for Advanced Simulation of Light Water Reactors (CASL). The intent for this test problem suite is to provide baseline comparison data that demonstrates the performance of the Hydra-TH solution methods. The simulation problems vary in complexity from laminar to turbulent flows. A set of RANS and LES turbulence models were used in the simulation of four classical test problems. Numerical results obtained by Hydra-TH agreed well with either the available analytical solution or experimental data, indicating the verified and validated implementation of these turbulence models in Hydra-TH. Where possible, some form of solution verification has been attempted to identify sensitivities in the solution methods, and suggest best practices when using the Hydra-TH code. -- Highlights: •We performed a comprehensive study to verify and validate the turbulence models in Hydra-TH. •Hydra-TH delivers 2nd-order grid convergence for the incompressible Navier–Stokes equations. •Hydra-TH can accurately simulate the laminar boundary layers. •Hydra-TH can accurately simulate the turbulent boundary layers with RANS turbulence models. •Hydra-TH delivers high-fidelity LES capability for simulating turbulent flows in confined space.
Bera, S C; Mandal, N; Sarkar, R
2011-07-01
In the present paper, design of a flow control loop using a thyristor driven pump as final control element has been described. In this technique, the load current of a thyristor driven pump motor has been utilized as a mass flow sensing parameter of a fluid passing through a pipeline. This thyristor driven pump has been utilized as a final control element of a flow control loop and the speed of the pump has been selected as the manipulated variable. The non-linearity between the thyristor input signal and pump output has been eliminated by using a modified PID control technique with inverse derivative control action. Thus without using any conventional flow meter and control valve only the thyristor driven pump has been utilized both as the final control element and flow indicating device by using the proposed technique. The whole system has been designed, fabricated and tested by using tap water as the flowing liquid through a pipe line. The experimental results along with the theoretical analysis are compared and reported in the paper.
Simon, Hélène A; Dasi, Lakshmi P; Leo, Hwa-Liang; Yoganathan, Ajit P
2007-08-01
Point-wise velocity measurements have been traditionally acquired to estimate blood damage potential induced by prosthetic heart valves with emphasis on peak values of velocity magnitude and Reynolds stresses. However, the inherently Lagrangian nature of platelet activation and hemolysis makes such measurements of limited predictive value. This study provides a refined fluid mechanical analysis, including blood element paths and stress exposure times, of the hinge flows of a CarboMedics bileaflet mechanical heart valve placed under both mitral and aortic conditions and a St Jude Medical bileaflet valve placed under aortic conditions. The hinge area was partitioned into characteristic regions based on dominant flow structures and spatio-temporal averaging was performed on the measured velocities and Reynolds shear stresses to estimate the average bulk stresses acting on blood elements transiting through the hinge. A first-order estimate of viscous stress levels and exposure times were computed. Both forward and leakage flow phases were characterized in each partition by dynamic flows dependent on subtle leaflet movements and transvalvular pressure fluctuations. Blood elements trapped in recirculation regions may experience exposure times as long as the entire forward flow phase duration. Most calculated stresses were below the accepted blood damage threshold. Estimates of the stress levels indicate that the flow conditions within the boundary layers near the hinge and leaflet walls may be more detrimental to blood cells than bulk flow conditions, while recirculation regions may promote thrombus buildup.
NASA Technical Reports Server (NTRS)
Ruf, Joseph H.
1992-01-01
Phase 2+ Space Shuttle Main Engine powerheads, E0209 and E0215 degraded their main combustion chamber (MCC) liners at a faster rate than is normal for phase 2 powerheads. One possible cause of the accelerated degradation was a reduction of coolant flow through the MCC. Hardware changes were made to the preburner fuel leg which may have reduced the resistance and, therefore, pulled some of the hydrogen from the MCC coolant leg. A computational fluid dynamics (CFD) analysis was performed to determine hydrogen flow path resistances of the phase 2+ fuel preburner injector elements relative to the phase 2 element. FDNS was implemented on axisymmetric grids with the hydrogen assumed to be incompressible. The analysis was performed in two steps: the first isolated the effect of the different inlet areas and the second modeled the entire injector element hydrogen flow path.
Boonjob, W.; Miro, M.; Cerda, V.
2008-10-01
There is a current trend in automation of leaching tests for trace elements in solid matrixes by use of flow injection based column approaches. However, as a result of the downscaled dimensions of the analytical manifold and execution of a single extraction at a time, miniaturized flow-through column approaches have merely found applications for periodic investigations of trace element mobility in highly homogeneous environmental solids. A novel flow-based configuration capitalized on stirred-flow cell extraction is proposed in this work for simultaneous fractionation of trace elements in three solid wastes with no limitation of sample amount up to 1.0 g. A two-step sequential extraction scheme involving water and acetic acid (or acetic acid/acetate buffer) is utilized for accurate assessment of readily mobilizable fractions of trace elements in fly ash samples. The W automated extraction system features high tolerance to flow rates ({<=} 6 mL min{sup -1}) and, as opposed to operationally defined batchwise methods, the solid to liquid ratio is not a critical parameter for, determination of overall readily leachable trace elements provided that exhaustive extraction is ensured. Analytical performance of the dynamic extractor is evaluated for fractionation analysis of a real coal fly ash and BCR-176R fly ash certified reference material. No significant differences were found at the 0.05 significance level between summation of leached concentrations in each fraction plus residue and concentration values of BCR-176R, thus revealing the accuracy of the automated method. Overall extractable pools of trace metals in three samples are separated in less than 115 min, even for highly contaminated ashes, versus 18-24 h per fraction in equilibrium leaching tests. The multiple stirred-flow cell assembly is thus suitable for routine risk assessment studies of industrial solid byproduct.
Axner, Lilit; Hoekstra, Alfons G; Jeays, Adam; Lawford, Pat; Hose, Rod; Sloot, Peter MA
2009-01-01
Background Systolic blood flow has been simulated in the abdominal aorta and the superior mesenteric artery. The simulations were carried out using two different computational hemodynamic methods: the finite element method to solve the Navier Stokes equations and the lattice Boltzmann method. Results We have validated the lattice Boltzmann method for systolic flows by comparing the velocity and pressure profiles of simulated blood flow between methods. We have also analyzed flow-specific characteristics such as the formation of a vortex at curvatures and traces of flow. Conclusion The lattice Boltzmann Method is as accurate as a Navier Stokes solver for computing complex blood flows. As such it is a good alternative for computational hemodynamics, certainly in situation where coupling to other models is required. PMID:19799782
Axner, Lilit; Hoekstra, Alfons G; Jeays, Adam; Lawford, Pat; Hose, Rod; Sloot, Peter M A
2009-10-02
Systolic blood flow has been simulated in the abdominal aorta and the superior mesenteric artery. The simulations were carried out using two different computational hemodynamic methods: the finite element method to solve the Navier Stokes equations and the lattice Boltzmann method. We have validated the lattice Boltzmann method for systolic flows by comparing the velocity and pressure profiles of simulated blood flow between methods. We have also analyzed flow-specific characteristics such as the formation of a vortex at curvatures and traces of flow. The lattice Boltzmann Method is as accurate as a Navier Stokes solver for computing complex blood flows. As such it is a good alternative for computational hemodynamics, certainly in situation where coupling to other models is required.
Gaston, L.; Glut, B.; Bellet, M.; Chenot, J.L.
1995-12-31
This paper presents a two-dimensional lagrangian-eulerian finite element approach of non-steady state Navier-Stokes fluid flows with free surfaces, like those occurring during the mould filling stage in casting processes. The proposed model is based on a mixed velocity-pressure finite element formulation, including an augmented Lagrangian technique and an iterative solver of Uzawa type. Mesh updating is carried out through an arbitrary lagrangian-eulerian method in order to describe properly the free surface evolution. Heat transfer through the fluid flow is solved by a convection-diffusion splitting technique. The efficiency of the method is illustrated on an example of gravity casting.
NASA Astrophysics Data System (ADS)
Xue, L. L.; Chen, S. H.; Shahrour, I.
2014-09-01
This paper presents a composite element algorithm of coupled normal stress and fluid flow process for fractured rock mass, developed from the composite element method (CEM). The coupled relation between the fracture flow and normal stress makes use of the "filled model", which examines the asperities in the fracture as a layer of granular medium having high porosity and being clipped by the two parallel plates. The existence of fractures is not considered in the mesh generation, but it will be considered explicitly in the mapped composite element. The coupled normal stress and fluid flow process has been simulated by applying a cross iterative algorithm between the two fields. The proposed algorithm considers not only the flow through the fractures, but also the flow exchange between fractures and the surrounding rock blocks. In addition, it can be used for both the filled and non-filled fractures. The verification of the proposed algorithm has been conducted through the illustration of three examples by comparison with the conventional finite element method (FEM), from which the advantages and reliability of the proposed algorithm have been shown clearly.
Effects of flow properties on the performance of a diffuser-nozzle element of a valveless micropump
NASA Astrophysics Data System (ADS)
Das, Partha Kumar; Hasan, A. B. M. Toufique
2016-07-01
The flow behaviour and performance parameters of a diffuser-nozzle element of a valveless micropump have been investigated for different driving pressure frequencies. When a fluctuating pressure is imposed on the inlet boundary of a diffuser-nozzle element, there is a net flow in diffuser direction due to the dynamic effect. The variation of this net flow along with rectification capacity, and diffuser efficiency has been investigated for different frequencies of driving pressure. Flow behaviour and recirculation region due to dynamic effect have been studied as qualitative study. Pressure and velocity have been analyzed for quantitative analysis and for validation with results found in literature. 2-D geometry has been used in the present study. 3-D geometry has been modeled to justify the results obtained from 2-D analysis. Five different pressure frequencies ranging from 5 kHz to 50 kHz have been used to investigate their effects on the performance of diffuser-nozzle element in high frequency ranges. The net flow and performance of the nozzle-diffuser element are found to be decreasing with the increasing frequency. The performance is found to be less sensitive to frequency at high pressure range (above 30 kHz).
NASA Astrophysics Data System (ADS)
Chen, Ling; Tang, Limei; Yu, Xing; Dong, Yanhui
2016-12-01
We present new major element, ICP-MS trace element, and Sr-Nd-Pb isotope data of basalts from four locations along the Carlsberg Ridge (CR), northern Indian Ocean. The basalts are low-K tholeiites with 7.52-9.51 wt% MgO, 49.40-50.60 wt% SiO2, 0.09-0.27 wt% K2O, 2.55-2.90 wt% Na2O, and 0.60-0.68 Mg#. Trace element contents of the basalts show characteristics similar to those of average normal MORB, such as LREE depleted patterns with (La/Sm)N ratio of 0.55-0.69; however, some samples are enriched in large-ion lithophile elements such as K and Rb, suggesting probable modification of the mantle source. Poor correlations between the compatible elements [e.g. Ni, Cr, and Sr (related to olivine, clinopyroxene and plagioclase, respectively)] and the incompatible elements (e.g. Zr and Y), and positive correlations in the Zr versus Zr/Y and Nb versus Nb/Y plots suggest a magmatic evolution controlled mainly by mantle melting rather than fractional crystallization. Our results extend the CR basalt range to higher radiogenic Pb isotopes and lower 143Nd/144Nd. These basalts and basalts from the northern Indian Ocean Ridge show lower 143Nd/144Nd and higher 87Sr/86Sr values than those of the depleted mantle (DM), defining a trend towards pelagic sediment composition. The Pb isotopic ratios of basalts from CR 3-4°N lie along the compositional mixing lines between the DM and the upper continental crust. However, the low radiogenic Pb of basalts from CR 9-10°N lie on the mixing line between the DM and lower continental crust. Since the Pb isotopic ratio of MORB would decrease if the source mantle was contaminated by continental lithospheric mantle, we suggest that CR contains continental lithospheric material, resulting in heterogeneous mantle beneath different ridge segments. The continental lithospheric material was introduced into the asthenosphere before or during the breakup of the Gondwana. These results support the long-term preservation of continental material in the
NASA Astrophysics Data System (ADS)
Chen, Ling; Tang, Limei; Yu, Xing; Dong, Yanhui
2017-06-01
We present new major element, ICP-MS trace element, and Sr-Nd-Pb isotope data of basalts from four locations along the Carlsberg Ridge (CR), northern Indian Ocean. The basalts are low-K tholeiites with 7.52-9.51 wt% MgO, 49.40-50.60 wt% SiO2, 0.09-0.27 wt% K2O, 2.55-2.90 wt% Na2O, and 0.60-0.68 Mg#. Trace element contents of the basalts show characteristics similar to those of average normal MORB, such as LREE depleted patterns with (La/Sm)N ratio of 0.55-0.69; however, some samples are enriched in large-ion lithophile elements such as K and Rb, suggesting probable modification of the mantle source. Poor correlations between the compatible elements [e.g. Ni, Cr, and Sr (related to olivine, clinopyroxene and plagioclase, respectively)] and the incompatible elements (e.g. Zr and Y), and positive correlations in the Zr versus Zr/Y and Nb versus Nb/Y plots suggest a magmatic evolution controlled mainly by mantle melting rather than fractional crystallization. Our results extend the CR basalt range to higher radiogenic Pb isotopes and lower 143Nd/144Nd. These basalts and basalts from the northern Indian Ocean Ridge show lower 143Nd/144Nd and higher 87Sr/86Sr values than those of the depleted mantle (DM), defining a trend towards pelagic sediment composition. The Pb isotopic ratios of basalts from CR 3-4°N lie along the compositional mixing lines between the DM and the upper continental crust. However, the low radiogenic Pb of basalts from CR 9-10°N lie on the mixing line between the DM and lower continental crust. Since the Pb isotopic ratio of MORB would decrease if the source mantle was contaminated by continental lithospheric mantle, we suggest that CR contains continental lithospheric material, resulting in heterogeneous mantle beneath different ridge segments. The continental lithospheric material was introduced into the asthenosphere before or during the breakup of the Gondwana. These results support the long-term preservation of continental material in the
1983-11-01
element u.-lei is readily applied to such flows. For lully developed flow V = 0, and U and H are functions of y only (i.e., J ■ U(y) and H ■ H(y...included, application of the basic momentum theorem yields T b |£| . / w+ Jb \\ T r ’dx’ I W < s,av where T is the average shear stress
Katyal, A.K.; Kaluarachchi, J.J.; Parker, J.C.
1991-05-01
The manual describes a two-dimensional finite element model for coupled multiphase flow and multicomponent transport in planar or radially symmetric vertical sections. Flow and transport of three fluid phases, including water, nonaqueous phase liquid (NAPL), and gas are considered by the program. The program can simulate flow only or coupled flow and transport. The flow module can be used to analyze two phases, water and NAPL, with the gas phase held at constant pressure, or explicit three-phase flow of water, NAPL, and gas at various pressures. The transport module can handle up to five components which partition among water, NAPL, gas and solid phases assuming either local equilibrium or first-order mass transfer. Three phase permeability-saturation-capillary pressure relations are defined by an extension of the van Genuchten model. The governing equations are solved using an efficient upstream-weighted finite element scheme. The report describes the required inputs for flow analysis and transport analysis. Time dependent boundary conditions for flow and transport analysis can be handled by the program and are described in the report. Detailed instructions for creating data files needed to run the program and example input and output files are given in appendices.
Isotopic and trace element sensors for fluid flow, heat- and mass transport in fractured rocks
NASA Astrophysics Data System (ADS)
DePaolo, D. J.
2012-12-01
The flow of fluids through fractured rocks is critically important in hydrothermal systems associated with geothermal energy production, base metal ore deposits, and global geochemical cycles through the enormous volumes of fluids in mid-ocean ridge systems. The nature of heat and mass transport in hydrothermal systems is determined by the spacing and volume of fractures, the nature of chemical transport in matrix blocks between fractures, the dissolution and precipitation rates of minerals in the matrix blocks, and the rates of fluid flow. Directly measuring these properties in active systems is extremely difficult, but the chemical and isotopic composition of fluids, where they can be adequately sampled, provides this information in coded form. Deciphering the signals requires appropriate models for the mineral-fluid chemical reactions and transport in the inter-fracture rock matrix. Ultimately, numerical reactive transport models are required to properly account for coupling between mineral reaction kinetics and fluid phase transport, but it is surprisingly difficult to adequately represent isotopic exchange in these models. The difficulty comes partly from the additional bookkeeping that is necessary, but more fundamentally from limitations in the detailed molecular dynamics of the mineral-fluid interfaces and how they control isotopic exchange and partitioning. Nevertheless, relatively simple analytical models illustrate how the isotopic and trace element composition of fluids relates to fracture aperture and spacing, mineral dissolution kinetics, competition between diffusive and advective transport, and competition between chemical exchange and heat exchange. The large number of geochemical parameters that can be measured potentially allows for detailed characterization of the effective mass transport and system characteristics like average fracture spacing and mineral dissolution rates. Examples of useful analytical models and applications to available data
NASA Astrophysics Data System (ADS)
Jones, A. G.; Afonso, J. C.
2015-12-01
The Earth comprises a single physio-chemical system that we interrogate from its surface and/or from space making observations related to various physical and chemical parameters. A change in one of those parameters affects many of the others; for example a change in velocity is almost always indicative of a concomitant change in density, which results in changes to elevation, gravity and geoid observations. Similarly, a change in oxide chemistry affects almost all physical parameters to a greater or lesser extent. We have now developed sophisticated tools to model/invert data in our individual disciplines to such an extent that we are obtaining high resolution, robust models from our datasets. However, in the vast majority of cases the different datasets are modelled/inverted independently of each other, and often even without considering other data in a qualitative sense. The LitMod framework of Afonso and colleagues presents integrated inversion of geoscientific data to yield thermo-chemical models that are petrologically consistent and constrained. Input data can comprise any combination of elevation, geoid, surface heat flow, seismic surface wave (Rayleigh and Love) data and receiver function data, and MT data. The basis of LitMod is characterization of the upper mantle in terms of five oxides in the CFMAS system and a thermal structure that is conductive to the LAB and convective along the adiabat below the LAB to the 410 km discontinuity. Candidate solutions are chosen from prior distributions of the oxides. For the crust, candidate solutions are chosen from distributions of crustal layering, velocity and density parameters. Those candidate solutions that fit the data within prescribed error limits are kept, and are used to establish broad posterior distributions from which new candidate solutions are chosen. Examples will be shown of application of this approach fitting data from the Kaapvaal Craton in South Africa and the Rae Craton in northern Canada. I
NASA Astrophysics Data System (ADS)
Glazkov, S. A.; Gorbushin, A. R.; Osipova, S. L.; Semenov, A. V.
2016-10-01
The report describes the results of flow field experimental research in TsAGI T-128 transonic wind tunnel. During the tests Mach number, stagnation pressure, test section wall perforation ratio, angles between the test section panels and mixing chamber flaps varied. Based on the test results one determined corrections to the free-stream Mach number related to the flow speed difference in the model location and in the zone of static pressure measurement on the test section walls, nonuniformity of the longitudinal velocity component in the model location, optimal position of the movable test section elements to provide flow field uniformity in the test section and minimize the test leg drag.
The response of a disturbed pipe flow to an upstanding roughness element
NASA Technical Reports Server (NTRS)
Chang, J.; Logan, E.; Alexander, M. B.; Camp, D. W.
1979-01-01
The paper describes measurements of mean velocity, turbulence intensity and Reynolds shear stress made downstream of a ring-type roughness element of rectangular cross section situated downstream of an identical element. The distance between the elements was varied, and velocity and turbulence profiles in the wake of the downstream element are compared with wake profiles behind a single element. The results show that the leading element can increase the power law exponent of the velocity profile as the spacing between elements is reduced. Turbulence generated in the wake of the first element raises turbulence intensity in the outer region of the wake of the second. The internal boundary layer originating with the second element grows at a rate which depends on the spacing. It is postulated that the internal boundary layers of subsequent roughness elements are determinants in the formation of a periodic wall layer.
Anisotropic poroelasticity and wave-induced fluid flow: harmonic finite-element simulations
NASA Astrophysics Data System (ADS)
Carcione, J. M.; Santos, J. E.; Picotti, S.
2011-09-01
A dominant P-wave attenuation mechanism in reservoir rocks at seismic frequencies is due to wave-induced fluid flow (mesoscopic loss). The P-wave induces a fluid-pressure difference at mesoscopic-scale inhomogeneities (larger than the pore size but smaller than the wavelength), generating fluid flow and slow (diffusion) Biot waves. The theory has been developed in the 1970s for the symmetry axis of the equivalent transversely isotropic (TI) medium corresponding to a finely layered medium, and has recently been generalized to all propagation angles. The new theory states that the fluid-flow direction is perpendicular to the layering plane and it is independent of the loading direction. As a consequence, the relaxation behaviour can be described by a single relaxation function, since the medium consists of plane homogeneous layers. Besides P-wave losses, the coupling between the qP and qSV waves generates shear-wave anisotropic velocity dispersion and attenuation. In this work, we introduce a set of quasi-static numerical experiments to determine the equivalent viscoelastic TI medium to a finely layered poroelastic medium, which is validated using a recently developed analytical solution. The modelling technique is the finite-element (FE) method, where the equations of motion are solved in the space-frequency domain. Numerical rock physics may, in many circumstances, offer an alternative to laboratory measurements. Numerical experiments are inexpensive and informative since the physical process of wave propagation can be inspected during the experiment. Moreover, they are repeatable, essentially free from experimental errors, and may easily be run using alternative models of the rock and fluid properties. We apply the methodology to the Utsira aquifer of the North Sea, where carbon dioxide (CO2) has been injected during the last 15 years. The tests consider alternating layers of the same rock saturated with gas and brine and a sequence of gas-saturated sandstone and
NASA Astrophysics Data System (ADS)
Katyal, A. K.; Kaluarachchi, J. J.; Parker, J. C.
1991-05-01
The manual describes a two-dimensional finite element model for coupled multiphase flow and multicomponent transport in planar or radially symmetric vertical sections. Flow and transport of three fluid phases, including water, nonaqueous phase liquid (NAPL), and gas are considered by the program. The program can simulate flow only or coupled flow and transport. The flow module can be used to analyze two phases, water and NAPL, with the gas phase held at constant pressure, or explicit three-phase flow of water, NAPL, and gas at various pressures. The transport module can handle up to five components which partition among water, NAPL, gas and solid phases assuming either local equilibrium or first-order mass transfer. Three phase permeability-saturation-capillary pressure relations are defined by an extension of the van Genuchten model. The governing equations are solved using an efficient upstream-weighted finite element scheme. The required inputs for flow and transport analysis are described. Detailed instructions for creating data files needed to run the program and examples of input and output files are given in appendices.
Billing, Justin M.; Daniel, Richard C.; Hallen, Richard T.; Schonewill, Philip P.; Shimskey, Rick W.; Peterson, Reid A.
2011-05-10
The Waste Treatment and Immobilization Plant (WTP) currently under construction for treatment of High-Level Waste (HLW) at the Hanford Site will rely on cross-flow ultrafiltration to provide solids-liquid separation as a core part of the treatment process. To optimize process throughput, periodic chemical cleaning of the porous stainless steel filter elements has been incorporated into the design of the plant. It is currently specified that chemical cleaning with nitric acid will occur after significant irreversible membrane fouling is observed. Irreversible fouling is defined as fouling that cannot be removed by backpulsing the filter. PNNL has investigated chemical cleaning processes as part of integrated tests with HLW simulants and with actual Hanford tank wastes. To quantify the effectiveness of chemical cleaning, the residual membrane resistance after cleaning was compared against the initial membrane resistance for each test in a series of long-term fouling tests. The impact of the small amount of residual resistance in these tests could not be separated from other parameters and the historical benchmark of >1 GPM/ft2 for clean water flux was determined to be an adequate metric for chemical cleaning. Using the results from these tests, a process optimization strategy is presented suggesting that for the simulant material under test, the value of chemical cleaning may be suspect. The period of enhanced filtration may not be enough to offset the down time required for chemical cleaning, without respect to the other associated costs.
NASA Astrophysics Data System (ADS)
Bozkaya, C.; Tezer-Sezgin, M.
2006-06-01
A numerical scheme which is a combination of the dual reciprocity boundary element method (DRBEM) and the differential quadrature method (DQM), is proposed for the solution of unsteady magnetohydrodynamic (MHD) flow problem in a rectangular duct with insulating walls. The coupled MHD equations in velocity and induced magnetic field are transformed first into the decoupled time-dependent convection-diffusion-type equations. These equations are solved by using DRBEM which treats the time and the space derivatives as nonhomogeneity and then by using DQM for the resulting system of initial value problems. The resulting linear system of equations is overdetermined due to the imposition of both boundary and initial conditions. Employing the least square method to this system the solution is obtained directly at any time level without the need of step-by-step computation with respect to time. Computations have been carried out for moderate values of Hartmann number (M50) at transient and the steady-state levels. As M increases boundary layers are formed for both the velocity and the induced magnetic field and the velocity becomes uniform at the centre of the duct. Also, the higher the value of M is the smaller the value of time for reaching steady-state solution.
NASA Astrophysics Data System (ADS)
Jankovic, I.
2002-05-01
Flow and transport in porous formations are analyzed using numerical simulations. Hydraulic conductivity is treated as a spatial random function characterized by a probability density function and a two-point covariance function. Simulations are performed for a multi-indicator conductivity structure developed by Gedeon Dagan (personal communication). This conductivity structure contains inhomogeneities (inclusions) of elliptical and ellipsoidal geometry that are embedded in a homogeneous background. By varying the distribution of sizes and conductivities of inclusions, any probability density function and two-point covariance may be reproduced. The multi-indicator structure is selected since it yields simple approximate transport solutions (Aldo Fiori, personal communication) and accurate numerical solutions (based on the Analytic Element Method). The dispersion is examined for two conceptual models. Both models are based on the multi-indicator conductivity structure. The first model is designed to examine dispersion in aquifers with continuously varying conductivity. The inclusions in this model cover as much area/volume of the porous formation as possible. The second model is designed for aquifers that contain clay/sand/gravel lenses embedded in otherwise homogeneous background. The dispersion in both aquifer types is simulated numerically. Simulation results are compared to those obtained using simple approximate solutions. In order to infer transport statistics that are representative of an infinite domain using the numerical experiments, the inclusions are placed in a domain that was shaped as a large ellipse (2D) and a large spheroid (3D) that were submerged in an unbounded homogeneous medium. On a large scale, the large body of inclusions behaves like a single large inhomogeneity. The analytic solution for a uniform flow past the single inhomogeneity of such geometry yields uniform velocity inside the domain. The velocity differs from that at infinity and
SIMULATIONS OF 2D AND 3D THERMOCAPILLARY FLOWS BY A LEAST-SQUARES FINITE ELEMENT METHOD. (R825200)
Numerical results for time-dependent 2D and 3D thermocapillary flows are presented in this work. The numerical algorithm is based on the Crank-Nicolson scheme for time integration, Newton's method for linearization, and a least-squares finite element method, together with a matri...
SIMULATIONS OF 2D AND 3D THERMOCAPILLARY FLOWS BY A LEAST-SQUARES FINITE ELEMENT METHOD. (R825200)
Numerical results for time-dependent 2D and 3D thermocapillary flows are presented in this work. The numerical algorithm is based on the Crank-Nicolson scheme for time integration, Newton's method for linearization, and a least-squares finite element method, together with a matri...
THE EFFECT OF WATER (VAPOR-PHASE) AND CARBON ON ELEMENTAL MERCURY REMOVAL IN A FLOW REACTOR
The paper gives results of studying the effect of vapor-phase moisture on elemental mercury (Hgo) removal by activated carbon (AC) in a flow reactor. tests involved injecting AC into both a dry and a 4% moisture nitrogen (N2) /Hgo gas stream. A bituminous-coal-based AC (Calgon WP...
THE EFFECT OF WATER (VAPOR-PHASE) AND CARBON ON ELEMENTAL MERCURY REMOVAL IN A FLOW REACTOR
The paper gives results of studying the effect of vapor-phase moisture on elemental mercury (Hgo) removal by activated carbon (AC) in a flow reactor. tests involved injecting AC into both a dry and a 4% moisture nitrogen (N2) /Hgo gas stream. A bituminous-coal-based AC (Calgon WP...
NASA Technical Reports Server (NTRS)
Olson, L. E.; Dvorak, F. A.
1975-01-01
The viscous subsonic flow past two-dimensional and infinite-span swept multi-component airfoils is studied theoretically and experimentally. The computerized analysis is based on iteratively coupled boundary layer and potential flow analysis. The method, which is restricted to flows with only slight separation, gives surface pressure distribution, chordwise and spanwise boundary layer characteristics, lift, drag, and pitching moment for airfoil configurations with up to four elements. Merging confluent boundary layers are treated. Theoretical predictions are compared with an exact theoretical potential flow solution and with experimental measures made in the Ames 40- by 80-Foot Wind Tunnel for both two-dimensional and infinite-span swept wing configurations. Section lift characteristics are accurately predicted for zero and moderate sweep angles where flow separation effects are negligible.
NASA Astrophysics Data System (ADS)
Dave, Pranav; Kashyap, Rahul; Fisher, Robert; Timmes, Frank; Townsley, Dean; Byrohl, Chris
2017-05-01
Recent Suzaku X-ray spectra of supernova remnant (SNR) 3C 397 indicate enhanced stable iron group element abundances of Ni, Mn, Cr, and Fe. Seeking to address key questions about the progenitor and explosion mechanism of 3C 397, we compute nucleosynthetic yields from a suite of multidimensional hydrodynamics models in the near-Chandrasekhar-mass, single-degenerate paradigm for Type Ia supernovae (SNe Ia). Varying the progenitor white dwarf (WD) internal structure, composition, ignition, and explosion mechanism, we find that the best match to the observed iron peak elements of 3C 397 are dense (central density ≥6 × 109 g cm-3), low-carbon WDs that undergo a weak, centrally ignited deflagration, followed by a subsequent detonation. The amount of 56Ni produced is consistent with a normal or bright normal SNe Ia. A pure deflagration of a centrally ignited, low central density (≃2 × 109 g cm-3) progenitor WD, frequently considered in the literature, is also found to produce good agreement with 3C 397 nucleosynthetic yields, but leads to a subluminous SN Ia event, in conflict with X-ray line width data. Additionally, in contrast to prior work that suggested a large supersolar metallicity for the WD progenitor for SNR 3C 397, we find satisfactory agreement for solar- and subsolar-metallicity progenitors. We discuss a range of implications our results have for the single-degenerate channel.
NASA Technical Reports Server (NTRS)
Baumeister, Kenneth J.; Baumeister, Joseph F.
1994-01-01
An analytical procedure is presented, called the modal element method, that combines numerical grid based algorithms with eigenfunction expansions developed by separation of variables. A modal element method is presented for solving potential flow in a channel with two-dimensional cylindrical like obstacles. The infinite computational region is divided into three subdomains; the bounded finite element domain, which is characterized by the cylindrical obstacle and the surrounding unbounded uniform channel entrance and exit domains. The velocity potential is represented approximately in the grid based domain by a finite element solution and is represented analytically by an eigenfunction expansion in the uniform semi-infinite entrance and exit domains. The calculated flow fields are in excellent agreement with exact analytical solutions. By eliminating the grid surrounding the obstacle, the modal element method reduces the numerical grid size, employs a more precise far field boundary condition, as well as giving theoretical insight to the interaction of the obstacle with the mean flow. Although the analysis focuses on a specific geometry, the formulation is general and can be applied to a variety of problems as seen by a comparison to companion theories in aeroacoustics and electromagnetics.
NASA Astrophysics Data System (ADS)
Bohrson, Wendy A.; Spera, Frank J.
2007-11-01
Volcanic and plutonic rocks provide abundant evidence for complex processes that occur in magma storage and transport systems. The fingerprint of these processes, which include fractional crystallization, assimilation, and magma recharge, is captured in petrologic and geochemical characteristics of suites of cogenetic rocks. Quantitatively evaluating the relative contributions of each process requires integration of mass, species, and energy constraints, applied in a self-consistent way. The energy-constrained model Energy-Constrained Recharge, Assimilation, and Fractional Crystallization (EC-RaχFC) tracks the trace element and isotopic evolution of a magmatic system (melt + solids) undergoing simultaneous fractional crystallization, recharge, and assimilation. Mass, thermal, and compositional (trace element and isotope) output is provided for melt in the magma body, cumulates, enclaves, and anatectic (i.e., country rock) melt. Theory of the EC computational method has been presented by Spera and Bohrson (2001, 2002, 2004), and applications to natural systems have been elucidated by Bohrson and Spera (2001, 2003) and Fowler et al. (2004). The purpose of this contribution is to make the final version of the EC-RAχFC computer code available and to provide instructions for code implementation, description of input and output parameters, and estimates of typical values for some input parameters. A brief discussion highlights measures by which the user may evaluate the quality of the output and also provides some guidelines for implementing nonlinear productivity functions. The EC-RAχFC computer code is written in Visual Basic, the programming language of Excel. The code therefore launches in Excel and is compatible with both PC and MAC platforms. The code is available on the authors' Web sites http://magma.geol.ucsb.edu/and http://www.geology.cwu.edu/ecrafc) as well as in the auxiliary material.
NASA Astrophysics Data System (ADS)
Deng, Q.; Ginting, V.; McCaskill, B.; Torsu, P.
2017-10-01
We study the application of a stabilized continuous Galerkin finite element method (CGFEM) in the simulation of multiphase flow in poroelastic subsurfaces. The system involves a nonlinear coupling between the fluid pressure, subsurface's deformation, and the fluid phase saturation, and as such, we represent this coupling through an iterative procedure. Spatial discretization of the poroelastic system employs the standard linear finite element in combination with a numerical diffusion term to maintain stability of the algebraic system. Furthermore, direct calculation of the normal velocities from pressure and deformation does not entail a locally conservative field. To alleviate this drawback, we propose an element based post-processing technique through which local conservation can be established. The performance of the method is validated through several examples illustrating the convergence of the method, the effectivity of the stabilization term, and the ability to achieve locally conservative normal velocities. Finally, the efficacy of the method is demonstrated through simulations of realistic multiphase flow in poroelastic subsurfaces.
Gaitan, Michael; Locascio, Laurie E
2004-01-01
This paper describes the first demonstration of temperature control and flow sensing of fluids using integrated circuit (IC)-based microheating elements embedded in microchannels molded in polydimethylsiloxane (PDMS). Fluid channels and connections to capillary tubing are molded in PDMS using a silicon wafer template. The PDMS film is then bonded to an IC that contains the micromachined microheating elements. Capillary tubes are inserted and fluids are externally pumped through the channels. Heating of the fluid is observed by the formation of bubbles on the microheating element. Sensing of fluid flow is demonstrated by measuring a change in the large signal resistance of the microheater analogous to a hot wire anemometer with a detection limit of ± 320 pL/s.
NASA Astrophysics Data System (ADS)
Baca, R. G.; Chung, J. N.; Mulla, D. J.
1997-03-01
A new computational method is developed for numerical solution of the Richards equation for flow in variably saturated porous media. The new method, referred to as the mixed transform finite element method, employs the mixed formulation of the Richards equation but expressed in terms of a partitioned transform. An iterative finite element algorithm is derived using a Newton-Galerkin weak statement. Specific advantages of the new method are demonstrated with applications to a set of one- dimensional test problems. Comparisons with the modified Picard method show that the new method produces more robust solutions for a broad range of soil- moisture regimes, including flow in desiccated soils, in heterogeneous media and in layered soils with formation of perched water zones. In addition, the mixed transform finite element method is shown to converge faster than the modified Picard method in a number of cases and to accurately represent pressure head and moisture content profiles with very steep fronts.
Bai, Junhong; Xiao, Rong; Zhao, Qingqing; Lu, Qiongqiong; Wang, Junjing; Reddy, K. Ramesh
2014-01-01
Soil profiles were collected in three salt marshes with different plant species (i.e. Phragmites australis, Tamarix chinensis and Suaeda salsa) in the Yellow River Delta (YRD) of China during three seasons (summer and fall of 2007 and the following spring of 2008) after the flow-sediment regulation regime. Total elemental contents of As, Cd, Cu, Pb and Zn were determined using inductively coupled plasma atomic absorption spectrometry to investigate temporal variations in trace elements in soil profiles of the three salt marshes, assess the enrichment levels and ecological risks of these trace elements in three sampling seasons and identify their influencing factors. Trace elements did not change significantly along soil profiles at each site in each sampling season. The highest value for each sampling site was observed in summer and the lowest one in fall. Soils in both P. australis and S. salsa wetlands tended to have higher trace element levels than those in T. chinensis wetland. Compared to other elements, both Cd and As had higher enrichment factors exceeding moderate enrichment levels. However, the toxic unit (TU) values of these trace elements did not exceed probable effect levels. Correlation analysis showed that these trace elements were closely linked to soil properties such as moisture, sulfur, salinity, soil organic matter, soil texture and pH values. Principal component analysis showed that the sampling season affected by the flow-sediment regulation regime was the dominant factor influencing the distribution patterns of these trace elements in soils, and plant community type was another important factor. The findings of this study could contribute to wetland conservation and management in coastal regions affected by the hydrological engineering. PMID:25216278
Bai, Junhong; Xiao, Rong; Zhao, Qingqing; Lu, Qiongqiong; Wang, Junjing; Reddy, K Ramesh
2014-01-01
Soil profiles were collected in three salt marshes with different plant species (i.e. Phragmites australis, Tamarix chinensis and Suaeda salsa) in the Yellow River Delta (YRD) of China during three seasons (summer and fall of 2007 and the following spring of 2008) after the flow-sediment regulation regime. Total elemental contents of As, Cd, Cu, Pb and Zn were determined using inductively coupled plasma atomic absorption spectrometry to investigate temporal variations in trace elements in soil profiles of the three salt marshes, assess the enrichment levels and ecological risks of these trace elements in three sampling seasons and identify their influencing factors. Trace elements did not change significantly along soil profiles at each site in each sampling season. The highest value for each sampling site was observed in summer and the lowest one in fall. Soils in both P. australis and S. salsa wetlands tended to have higher trace element levels than those in T. chinensis wetland. Compared to other elements, both Cd and As had higher enrichment factors exceeding moderate enrichment levels. However, the toxic unit (TU) values of these trace elements did not exceed probable effect levels. Correlation analysis showed that these trace elements were closely linked to soil properties such as moisture, sulfur, salinity, soil organic matter, soil texture and pH values. Principal component analysis showed that the sampling season affected by the flow-sediment regulation regime was the dominant factor influencing the distribution patterns of these trace elements in soils, and plant community type was another important factor. The findings of this study could contribute to wetland conservation and management in coastal regions affected by the hydrological engineering.
NASA Astrophysics Data System (ADS)
Liu, X.
2013-12-01
In many natural and human-impacted rivers, the porous sediment beds are either fully or partially covered by large roughness elements, such as gravels and boulders. The existence of these large roughness elements, which are in direct contact with the turbulent river flow, changes the dynamics of mass and momentum transfer across the river bed. It also impacts the overall hydraulics in the river channel and over time, indirectly influences the geomorphological evolution of the system. Ideally, one should resolve each of these large roughness elements in a computational fluid model. This approach is apparently not feasible due to the prohibitive computational cost. Considering a typical river bed with armoring, the distribution of sediment sizes usually shows significant vertical variations. Computationally, it poses great challenge to resolve all the size scales. Similar multiscale problem exists in the much broader porous media flow field. To cope with this, we propose a hybrid computational approach where the large surface roughness elements are resolved using immersed boundary method and sediment layers below (usually finer) are modeled by adding extra drag terms in momentum equations. Large roughness elements are digitized using a 3D laser scanner. They are put into the computational domain using the collision detection and rigid body dynamics algorithms which guarantees realistic and physically-correct spatial arrangement of the surface elements. Simulation examples have shown the effectiveness of the hybrid approach which captures the effect of the surface roughness on the turbulent flow as well as the hyporheic flow pattern in and out of the bed.
NASA Astrophysics Data System (ADS)
Moortgat, J.; Firoozabadi, A.
2013-12-01
Most problems of interest in hydrogeology and subsurface energy resources involve complex heterogeneous geological formations. Such domains are most naturally represented in numerical reservoir simulations by unstructured computational grids. Finite element methods are a natural choice to describe fluid flow on unstructured meshes, because the governing equations can be readily discretized for any grid-element geometry. In this work, we consider the challenging problem of fully compositional three-phase flow in 3D unstructured grids, discretized by tetrahedra, prisms, or hexahedra, and compare to simulations on 3D structured grids. We employ a combination of mixed hybrid finite element methods to solve for the pressure and flux fields in a fractional flow formulation, and higher-order discontinuous Galerkin methods for the mass transport equations. These methods are well suited to simulate flow in heterogeneous and fractured reservoirs, because they provide a globally continuous pressure and flux field, while allowing for sharp discontinuities in the phase properties, such as compositions and saturations. The increased accuracy from using higher-order methods improves the modeling of highly non-linear flow, such as gravitational and viscous fingering. We present several numerical examples to study convergence rates and the (lack of) sensitivity to gridding/mesh orientation, and mesh quality. These examples consider gravity depletion, water and gas injection in oil saturated subsurface reservoirs with species exchange between up to three fluid phases. The examples demonstrate the wide applicability of our chosen finite element methods in the study of challenging multiphase flow problems in porous, geometrically complex, subsurface media.
Vescovi, D.; Berzi, D.; Richard, P.
2014-05-15
We use existing 3D Discrete Element simulations of simple shear flows of spheres to evaluate the radial distribution function at contact that enables kinetic theory to correctly predict the pressure and the shear stress, for different values of the collisional coefficient of restitution. Then, we perform 3D Discrete Element simulations of plane flows of frictionless, inelastic spheres, sheared between walls made bumpy by gluing particles in a regular array, at fixed average volume fraction and distance between the walls. The results of the numerical simulations are used to derive boundary conditions appropriated in the cases of large and small bumpiness. Those boundary conditions are, then, employed to numerically integrate the differential equations of Extended Kinetic Theory, where the breaking of the molecular chaos assumption at volume fraction larger than 0.49 is taken into account in the expression of the dissipation rate. We show that the Extended Kinetic Theory is in very good agreement with the numerical simulations, even for coefficients of restitution as low as 0.50. When the bumpiness is increased, we observe that some of the flowing particles are stuck in the gaps between the wall spheres. As a consequence, the walls are more dissipative than expected, and the flows resemble simple shear flows, i.e., flows of rather constant volume fraction and granular temperature.
NASA Astrophysics Data System (ADS)
Alemayehu, Melesse; Zhang, Hong-Fu; Seitz, Hans-Michael
2017-02-01
Lithium (Li) elemental and isotopic compositions for mineral separates of coexisting olivine, orthopyroxene and clinopyroxene of mantle xenoliths from the Quaternary volcanic rocks of southern Ethiopian rift (Dillo and Megado) reveal the influence of late stage melt-peridotite interaction on the early depleted and variably metasomatized lithospheric mantle. Two types of lherzolites are reported (LREE-depleted La/Sm(N) = 0.11-0.37 × Cl and LREE-enriched, La/Sm(N) = 1.88-15.72 × Cl). The depleted lherzolites have variable range in Li concentration (olivine: 2.1-5.4 ppm; opx: 1.1-2.3 ppm; cpx: 1.0-1.8 ppm) and in Li isotopic composition (δ7Li in olivine: -9.4 to 1.5‰; in opx: -4.5 to 3.6‰; in cpx: -17.0 to 4.8‰), indicating strong disequilibrium in Li partitioning and Li isotope fractionation between samples. The enriched lherzolites have limited range in both Li abundances (olivine: 2.7-3.0 ppm; opx: 1.1-3.1 ppm; cpx: 1.1-2.3 ppm) and Li isotopic compositions (δ7Li in olivine: -1.3 to +1.3‰; in opx: -2.0 to +5.0‰; in cpx: -7.5 to +4.8‰), suggest that the earlier metasomatic event which lead to LREE enrichment could also homogenize the Li contents and its isotopes. The enriched harzburgite and clinopyroxenite minerals show limited variation in Li abundances and variable Li isotopic compositions. The Li enrichments of olivine and clinopyroxene correlate neither with the incompatible trace element enrichment nor with the Sr-Nd isotopic compositions of clinopyroxene. These observations indicate that the metasomatic events which are responsible for the LREE enrichment and for the Li addition are distinct, whereby the LREE-enrichment pre-dates the influx of Li. The presence of large Li isotopic disequilibria within and between minerals of depleted and enriched peridotites suggest that the lithospheric mantle beneath the southern Ethiopian rift has experienced recent melt-peridotite interaction. Thus, the Li data set reported in this study offer new
Kröpfelová, Lenka; Vymazal, Jan; Svehla, Jaroslav; Stíchová, Jana
2009-04-01
Between March 2006 and June 2008 removal of 34 trace elements was measured on a monthly basis at three horizontal-flow constructed wetlands in the Czech Republic designed to treat municipal wastewater. In general, the results indicated a very wide range of removal efficiencies among studied elements. The highest degree of removal (average of 90%) was found for aluminum. High average removal was also recorded for zinc (78%). Elements removed in the range of 50-75% were uranium, antimony, copper, lead, molybdenum, chromium, barium, iron and gallium. Removal of cadmium, tin, mercury, silver, selenium and nickel varied between 25 and 50%. Low retention (0-25%) was observed for vanadium, lithium, boron, cobalt and strontium. There were two elements (manganese and arsenic) for which average outflow concentrations were higher compared to inflow concentrations. Reduced manganese compounds are very soluble and therefore they are washed out under anaerobic conditions.
The Finite Element Analysis for a Mini-Conductance Probe in Horizontal Oil-Water Two-Phase Flow
Kong, Weihang; Kong, Lingfu; Li, Lei; Liu, Xingbin; Xie, Ronghua; Li, Jun; Tang, Haitao
2016-01-01
Oil-water two-phase flow is widespread in petroleum industry processes. The study of oil-water two-phase flow in horizontal pipes and the liquid holdup measurement of oil-water two-phase flow are of great importance for the optimization of the oil production process. This paper presents a novel sensor, i.e., a mini-conductance probe (MCP) for measuring pure-water phase conductivity of oil-water segregated flow in horizontal pipes. The MCP solves the difficult problem of obtaining the pure-water correction for water holdup measurements by using a ring-shaped conductivity water-cut meter (RSCWCM). Firstly, using the finite element method (FEM), the spatial sensitivity field of the MCP is investigated and the optimized MCP geometry structure is determined in terms of the characteristic parameters. Then, the responses of the MCP for the oil-water segregated flow are calculated, and it is found that the MCP has better stability and sensitivity to the variation of water-layer thickness in the condition of high water holdup and low flow velocity. Finally, the static experiments for the oil-water segregated flow were carried out and a novel calibration method for pure-water phase conductivity measurements was presented. The validity of the pure-water phase conductivity measurement with segregated flow in horizontal pipes was verified by experimental results. PMID:27563907
NASA Technical Reports Server (NTRS)
Dvorak, F. A.; Woodward, F. A.
1974-01-01
An analysis method and computer program have been developed for the calculation of the viscosity dependent aerodynamic characteristics of multi-element infinite swept wings in incompressible flow. The wing configuration consisting at the most of a slat, a main element and double slotted flap is represented in the method by a large number of panels. The inviscid pressure distribution about a given configuration in the normal chord direction is determined using a two dimensional potential flow program employing a vortex lattice technique. The boundary layer development over each individual element of the high lift configuration is determined using either integral or finite difference boundary layer techniques. A source distribution is then determined as a function of the calculated boundary layer displacement thickness and pressure distributions. This source distribution is included in the second calculation of the potential flow about the configuration. Once the solution has converged (usually after 2-5 iterations between the potential flow and boundary layer calculations) lift, drag, and pitching moments can be determined as functions of Reynolds number.
NASA Astrophysics Data System (ADS)
Moortgat, Joachim; Firoozabadi, Abbas
2016-06-01
Problems of interest in hydrogeology and hydrocarbon resources involve complex heterogeneous geological formations. Such domains are most accurately represented in reservoir simulations by unstructured computational grids. Finite element methods accurately describe flow on unstructured meshes with complex geometries, and their flexible formulation allows implementation on different grid types. In this work, we consider for the first time the challenging problem of fully compositional three-phase flow in 3D unstructured grids, discretized by any combination of tetrahedra, prisms, and hexahedra. We employ a mass conserving mixed hybrid finite element (MHFE) method to solve for the pressure and flux fields. The transport equations are approximated with a higher-order vertex-based discontinuous Galerkin (DG) discretization. We show that this approach outperforms a face-based implementation of the same polynomial order. These methods are well suited for heterogeneous and fractured reservoirs, because they provide globally continuous pressure and flux fields, while allowing for sharp discontinuities in compositions and saturations. The higher-order accuracy improves the modeling of strongly non-linear flow, such as gravitational and viscous fingering. We review the literature on unstructured reservoir simulation models, and present many examples that consider gravity depletion, water flooding, and gas injection in oil saturated reservoirs. We study convergence rates, mesh sensitivity, and demonstrate the wide applicability of our chosen finite element methods for challenging multiphase flow problems in geometrically complex subsurface media.
NASA Astrophysics Data System (ADS)
Xie, Zhihua; Pavlidis, Dimitrios; Percival, James; Gomes, Jefferson; Pain, Christopher; Matar, Omar
2013-11-01
Interfacial flows with surface tension are often found in industrial and practical engineering applications, including bubbles, droplets, liquid film and jets. Accurate modelling of such flows is challenging due to their highly complex dynamics, which often involve changes of interfacial topology. We present a balanced-force finite-element method with adaptive unstructured meshes for interfacial flows. The method uses a mixed control-volume and finite element formulation, which ensures the surface tension forces, and the resulting pressure gradients, are exactly balanced, minimising the spurious velocities often found in numerical simulations of such flows. A volume-of-fluid-type method is employed for interface capturing based on a compressive control-volume advection method, and second-order finite element methods. A distance function is reconstructed from the volume fraction on the unstructured meshes, which provides accurate estimation of the curvature. Numerical examples of an equilibrium drop and dynamics of bubbles (droplets) are presented to demonstrate the capability of this method.
Zheng, Jian-Ping; Lu, Ji-Dong; Zhang, Bo; Chen, Shi-He; Yao, Shun-Chun; Pan, Feng-Ping; Dong, Xuan; Zhang, Xi
2014-01-01
The logical range of laser power density and optimum laser power density were explored for multi-element analysis of pulverized coal flow with laser-induced breakdown spectroscopy in the present paper. The range of laser energy was chosen from 20 to 160 mJ in the experiment. Pulverized coal less than 200 microm in diameter of particles fell freely through feeder outlet and the rate of flow was controlled by screw feeder. Emissions were collected with pulse laser at 1 064 nm focusing on pulverized coal flow and plasma was generated. The intensity and cause of fluctuation of emission spectra at various laser energy levels were studied. A suitable range of laser power density is from 14.4 to 34.4 GW x cm(-2), and the optimum laser power density is 19.5 GW x cm(-2) for the determination of pulverized coal flow with LIBS.
NASA Astrophysics Data System (ADS)
Jankovic, I.; Barnes, R. J.; Soule, R.
2001-12-01
The analytic element method is used to model local three-dimensional flow in the vicinity of partially penetrating wells. The flow domain is bounded by an impermeable horizontal base, a phreatic surface with recharge and a cylindrical lateral boundary. The analytic element solution for this problem contains (1) a fictitious source technique to satisfy the head and the discharge conditions along the phreatic surface, (2) a fictitious source technique to satisfy specified head conditions along the cylindrical boundary, (3) a method of imaging to satisfy the no-flow condition across the impermeable base, (4) the classical analytic solution for a well and (5) spheroidal harmonics to account for the influence of the inhomogeneities in hydraulic conductivity. Temporal variations of the flow system due to time-dependent recharge and pumping are represented by combining the analytic element method with a finite difference method: analytic element method is used to represent spatial changes in head and discharge, while the finite difference method represents temporal variations. The solution provides a very detailed description of local groundwater flow with an arbitrary number of wells of any orientation and an arbitrary number of ellipsoidal inhomogeneities of any size and conductivity. These inhomogeneities may be used to model local hydrogeologic features (such as gravel packs and clay lenses) that significantly influence the flow in the vicinity of partially penetrating wells. Several options for specifying head values along the lateral domain boundary are available. These options allow for inclusion of the model into steady and transient regional groundwater models. The head values along the lateral domain boundary may be specified directly (as time series). The head values along the lateral boundary may also be assigned by specifying the water-table gradient and a head value at a single point (as time series). A case study is included to demonstrate the application
NASA Astrophysics Data System (ADS)
Alves, Adriana; Janasi, Valdecir de Assis; Campos Neto, Mario da Costa
2016-07-01
Whole rock elemental and Sr-Nd isotope geochemistry and in situ K-feldspar Pb isotope geochemistry were used to identify the sources involved in the genesis of Neoproterozoic granites from the Embu Terrane, Ribeira Belt, SE Brazil. Granite magmatism spanned over 200 Ma (810-580 Ma), and is dominated by crust-derived relatively low-T (850-750 °C, zircon saturation) biotite granites to biotite-muscovite granites. Two Cryogenian plutons show the least negative εNdt (-8 to -10) and highest mg# (30-40) of the whole set. Their compositions are strongly contrasted, implying distinct sources for the peraluminous (ASI ∼ 1.2) ∼660 Ma Serra do Quebra-Cangalha batholith (metasedimentary rocks from relatively young upper crust with high Rb/Sr and low Th/U) and the metaluminous (ASI = 0.96-1.00) ∼ 630 Ma Santa Catarina Granite. Although not typical, the geochemical signature of these granites may reflect a continental margin arc environment, and they could be products of a prolonged period of oceanic plate consumption started at ∼810 Ma. The predominant Ediacaran (595-580 Ma) plutons have a spread of compositions from biotite granites with SiO2 as low as ∼65% (e.g., Itapeti, Mauá, Sabaúna and Lagoinha granites) to fractionated muscovite granites (Mogi das Cruzes, Santa Branca and Guacuri granites; up to ∼75% SiO2). εNdT are characteristically negative (-12 to -18), with corresponding Nd TDM indicating sources with Paleoproterozoic mean crustal ages (2.0-2.5 Ga). The Guacuri and Santa Branca muscovite granites have the more negative εNdt, highest 87Sr/86Srt (0.714-0.717) and lowest 208Pb/206Pb and 207Pb/206Pb, consistent with an old metasedimentary source with low time-integrated Rb/Sr. However, a positive Nd-Sr isotope correlation is suggested by data from the other granites, and would be consistent with mixing between an older source predominant in the Mauá granite and a younger, high Rb/Sr source that is more abundant in the Lagoinha granite sample. The
NASA Astrophysics Data System (ADS)
Goodwin, L. B.; Williams, R. T.; Mozley, P.; Sharp, W. D.
2015-12-01
The link between fluid overpressure and the earthquake cycle has been documented through previous studies of vein arrays associated with faults and carefully designed experimental work. In the interseismic period, elevated pore fluid pressure (overpressure) will reduce the effective fault-normal stress, weakening the fault and promoting seismic rupture. Fractures produced during faulting will serve as fluid migration pathways until they are sealed by either collapse or precipitation of cement. Following sealing, pore fluid pressure is inferred to progressively increase until it reaches a level sufficient to start the cycle again. Though the rock record of this overpressure-driven seismic cycle is clear, the timescales of the different elements of the cycle have not been quantified. We have addressed this problem by dating calcite veins in the hanging wall damage zone of the Loma Blanca fault zone of the Socorro Basin, Rio Grande rift, New Mexico. These veins exhibit crack-seal microstructures that record repeated episodes of fracture opening, fluid migration, and fracture sealing, suggesting a prolonged history of recurrent seismicity and post-failure fluid migration. Stable isotope analyses of these veins reveal distinct fluid chemistries associated with individual fluid migration events. Carbon isotope values as high as +6.00‰ suggest depressurization and degassing of CO2 charged fluids, supporting the interpretation that fracturing was associated with fault slip. Preliminary U-series dating of calcite veins show a well-defined periodicity of fault slip and fracture formation, with a slip recurrence interval of approximately 73 ± 17 ka, consistent with previous studies of other faults in the Rio Grande rift. Analyses of cements deposited during single crack-seal events record sealing times of approximately 16 ± 4 ka. These results suggest that the time required to re-establish sufficient pore fluid pressure for failure following sealing of damage zone
Elasto-plastic flow in cracked bodies using a new finite element model. Ph.D. Thesis
NASA Technical Reports Server (NTRS)
Karabin, M. E., Jr.
1977-01-01
Cracked geometries were studied by finite element techniques with the aid of a new special element embedded at the crack tip. This model seeked to accurately represent the singular stresses and strains associated with the elasto-plastic flow process. The present model was not restricted to a material type and did not predetermine a singularity. Rather the singularity was treated as an unknown. For each step of the incremental process the nodal degrees of freedom and the unknown singularity were found through minimization of an energy-like functional. The singularity and nodal degrees of freedom were determined by means of an iterative process.
Summary of design and blade-element performance data for 12 axial-flow pump rotor configurations
NASA Technical Reports Server (NTRS)
Miller, M. J.; Okiishi, T. H.; Serovy, G. K.; Sandercock, D. M.; Britsch, W. R.
1973-01-01
A collection of noncavitating blade-element performance data for 12 axial-flow pump rotor configurations is presented in tabular form. Rotor design philosophy, test apparatus and procedure, and data reduction and evaluation are discussed. A data storage and recall computer program is described. All but one of the rotor configurations considered were composed of double-circular-arc blade sections and were designed for high inlet relative flow angles. Hub-tip radius ranged from 0.40 to 0.90.
The effect of a small isolated roughness element on the forces on a sphere in uniform flow
NASA Astrophysics Data System (ADS)
Norman, A. K.; McKeon, B. J.
2011-10-01
The effect of an isolated roughness element on the forces on a sphere was examined for a Reynolds number range of 5 × 104 < Re < 5 × 105 using a novel sting-mounted sphere apparatus. The roughness element was a circular cylinder, and its width and height was varied to be 1, 2, and 4% of the sphere diameter. At subcritical Re, a lateral force is produced in the direction of the roughness, while at supercritical Re, the force is in the opposite direction. This is caused by asymmetric boundary layer separation, as shown using particle image velocimetry. At supercritical Re, a roughness element that is only 1% the sphere diameter produces a lift to drag ratio of almost one. It was found that the isolated roughness element has the largest effect on the lateral forces when it is located between a streamwise angle of about 40° and 80°. In addition to the mean forces, the unsteady forces were also measured. It was found that at subcritical Re, vortex shedding is aligned to the plane of the roughness element. In addition, the probability distribution of the forces was nearly Gaussian for subcritical Re, but for supercritical Re, the skewness and kurtosis deviate from Gaussian, and the details are dependent on the roughness size. A simple model developed for the vortical structure formed behind the roughness element can be extended to explain aspects of nominally smooth sphere flow, in which external disturbances perturb the sphere boundary layer in an azimuthally local sense. These results also form the basis of comparison for an investigation into the effectiveness of a moving isolated roughness element for manipulating sphere flow.
Finite Element Simulation of Simple Three-Dimensional Fully Cavitating Flows.
1979-11-01
the separation condition which must be enforced while keeping the Jacobian of the isoparametric transformation nonsingular. The free surface is shown...2.2 FINITE ELEMENT MODEL 9 2.2.1 Finite Element Approximation 10 2.2.2 Isoparametric Transformation and Numerical Integration 13 2.2.3 Implementation...uniform surface load F force on the foil J Jacobian matrix for the isoparametric transformation e K j elemental stiffness matrix Kij global stiffness
NASA Astrophysics Data System (ADS)
Tariqul Islam, Md.; Sturkell, Erik; Sigmundsson, Freysteinn; Drouin, Vincent Jean Paul B.; Ófeigsson, Benedikt G.
2014-05-01
Iceland is located on the mid Atlantic ridge, where the spreading rate is nearly 2 cm/yr. The high rate of magmatism in Iceland is caused by the interaction between the Iceland hotspot and the divergent mid-Atlantic plate boundary. Iceland hosts about 35 volcanoes or volcanic systems that are active. Most of these are aliened along the plate boundary. The best studied magma chamber of central volcanoes (e.g., Askja, Krafla, Grimsvötn, Katla) have verified (suggested) a shallow magma chamber (< 5 km), which has been model successfully with a Mogi source, using elastic and/or elastic-viscoelastic half-space. Maxwell and Newtonian viscosity is mainly considered for viscoelastic half-space. Therefore, rheology may be oversimplified. Our attempt is to study deformation of the Askja volcano together with plate spreading in Iceland using temperature-dependent non-linear rheology. It offers continuous variation of rheology, laterally and vertically from rift axis and surface. To implement it, we consider thermo-mechanic coupling models where rheology follows dislocation flow in dry condition based on a temperature distribution. Continuous deflation of the Askja volcanic system is associated with solidification of magma in the magma chamber and post eruption relaxation. A long time series of levelling data show its subsidence trend to exponentially. In our preliminary models, a magma chamber at 2.8 km depth with 0.5 km radius is introduced at the ridge axis as a Mogi source. Simultaneously far field of rift axis stretching by 18.4 mm/yr (measured during 2007 to 20013) is applied to reproduce plate spreading. Predicted surface deformation caused of combined effect of tectonic-volcanic activities is evaluated with GPS during 2003-2009 and RADARSAT InSAR data during 2000 to 2010. During 2003-2009, data from the GPS site OLAF (close to the centre of subsidence) shows average rate of subsidence 19±1 mm/yr relative to the ITRF2005 reference frame. The MASK (Mid ASKJA) site is
The Conservation/Solution Element (STE) Method for Linear Potential Flow Problems
NASA Technical Reports Server (NTRS)
Adeyeye, John O.; Attia, Naguib F.; Jackson, Joy; Hunter, Timothy
1996-01-01
The potential equation is discretized on rectangular domains using the Conservation/Solution Element Method (STE) approach. Computational examples with a discussion of numerical experience gained are given.
Taylor, Howard E.; Garbarino, John R.; Murphy, Deirdre M.; Beckett, Ronald
1992-01-01
An inductively coupled plasma-mass spectrometer was used for the quantitative measurement of trace elements In specific,submicrometer size-fraction particulates, separated by sedimentation field-flow fractionation. Fractions were collected from the eluent of the field-flow fractionation centrifuge and nebulized, with a Babington-type pneumatic nebulizer, into an argon inductively coupled plasma-mass spectrometer. Measured Ion currents were used to quantify the major, minor, and trace element composition of the size-separated colloidal (< 1-microm diameter) particulates. The composition of surface-water suspended matter collected from the Yarra and Darling rivers in Australia is presented to illustrate the usefulness of this tool for characterizing environmental materials. An adsorption experiment was performed using cadmium lon to demonstrate the utility for studying the processes of trace metal-suspended sediment interactions and contaminant transport in natural aquatic systems.
NASA Astrophysics Data System (ADS)
Aul'chenko, S. M.; Zamuraev, V. P.; Kalinina, A. P.
2014-05-01
The present work is devoted to a criterial analysis and mathematical modeling of the influence of forced oscillations of surface elements of a wing airfoil on the shock-wave structure of transonic flow past it. Parameters that govern the regimes of interaction of the oscillatory motion of airfoil sections with the breakdown compression shock have been established. The qualitative and quantitative influence of these parameters on the wave resistance of the airfoil has been investigated.
NASA Astrophysics Data System (ADS)
Fielding, Christopher R.
2006-08-01
Fluvial strata dominated internally by sedimentary structures of interpreted upper flow regime origin are moderately common in the rock record, yet their abundance is not appreciated and many examples may go unnoticed. A spectrum of sedimentary structures is recognised, all of which occur over a wide range of scale: 1. cross-bedding with humpback, sigmoidal and ultimately low-angle cross-sectional foreset geometries (interpreted as recording the transition from dune to upper plane bed bedform stability field), 2. planar/flat lamination with parting lineation, characteristic of the upper plane bed phase, 3. flat and low-angle lamination with minor convex-upward elements, characteristic of the transition from upper plane bed to antidune stability fields, 4. convex-upward bedforms, down- and up-palaeocurrent-dipping, low-angle cross-bedding and symmetrical drapes, interpreted as the product of antidunes, and 5. backsets terminating updip against an upstream-dipping erosion surface, interpreted as recording chute and pool conditions. In some fluvial successions, the entirety or substantial portions of channel sandstone bodies may be made up of such structures. These Upper Flow Regime Sheets, Lenses and Scour Fills (UFR) are defined herein as an extension of Miall's [Miall, A.D., 1985. Architectural-element analysis: a new method of facies analysis applied to fluvial deposits. Earth Sci. Rev. 22: 261-308.] Laminated Sand Sheets architectural element. Given the conditions that favour preservation of upper flow regime structures (rapid changes in flow strength), it is suggested that the presence of UFR elements in ancient fluvial successions may indicate sediment accumulation under the influence of a strongly seasonal palaeoclimate that involves a pronounced seasonal peak in precipitation and runoff.
NASA Astrophysics Data System (ADS)
Chougule, Prasad; Nielsen, Søren R. K.
2014-06-01
Nowadays, small vertical axis wind turbines are receiving more attention due to their suitability in micro-electricity generation. There are few vertical axis wind turbine designs with good power curve. However, the efficiency of power extraction has not been improved. Therefore, an attempt has been made to utilize high lift technology for vertical axis wind turbines in order to improve power efficiency. High lift is obtained by double-element airfoil mainly used in aeroplane wing design. In this current work a low Reynolds number airfoil is selected to design a double-element airfoil blade for use in vertical axis wind turbine to improve the power efficiency. Double-element airfoil blade design consists of a main airfoil and a slat airfoil. Orientation of slat airfoil is a parameter of investigation in this paper and air flow simulation over double-element airfoil. With primary wind tunnel test an orientation parameter for the slat airfoil is initially obtained. Further a computational fluid dynamics (CFD) has been used to obtain the aerodynamic characteristics of double-element airfoil. The CFD simulations were carried out using ANSYS CFX software. It is observed that there is an increase in the lift coefficient by 26% for single-element airfoil at analysed conditions. The CFD simulation results were validated with wind tunnel tests. It is also observe that by selecting proper airfoil configuration and blade sizes an increase in lift coefficient can further be achieved.
Compositionally Constraining Elysium Lava Fields
NASA Astrophysics Data System (ADS)
Karunatillake, S.; Button, N. E.; Skok, J. R.
2013-12-01
Chemical provinces of Mars defined recently [1-3] became possible with the maps of elemental mass fractions generated with Mars Odyssey Gamma and Neutron Spectrometer (GS) data [4,5]. These provide a unique perspective by representing compositional signatures distinctive of the regolith vertically at decimeter depths and laterally at hundreds of kilometer scale. Some provinces overlap compellingly with regions highlighted by other remote sensing observations, such as the Mars Radar Stealth area [3]. The spatial convergence of mutually independent data with the consequent highlight of a region provides a unique opportunity of insight not possible with a single type of remote sensing observation. Among such provinces, previous work [3] highlighted Elysium lava flows as a promising candidate on the basis of convergence with mapped geologic units identifying Elysium's lava fields generally, and Amazonian-aged lava flows specifically. The South Eastern lava flows of Elysium Mons, dating to the recent Amazonian epoch, overlap compellingly with a chemical province of K and Th depletion relative to the Martian midlatitudes. We characterize the composition, geology, and geomorphology of the SE Elysium province to constrain the confluence of geologic and alteration processes that may have contributed to its evolution. We compare this with the North Western lava fields, extending the discussion on chemical products from the thermal evolution of Martian volcanism as discussed by Baratoux et al. [6]. The chemical province, by regional proximity to Cerberus Fossae, may also reflect the influence of recently identified buried flood channels [7] in the vicinity of Orcus Patera. Despite the compelling chemical signature from γ spectra, fine grained unconsolidated sediment hampers regional VNTIR (Visible, Near, and Thermal Infrared) spectral analysis. But some observations near scarps and fresh craters allow a view of small scale mineral content. The judicious synthesis of
NASA Astrophysics Data System (ADS)
Ortega, A. M.; Palm, B. B.; Hayes, P. L.; Day, D. A.; Cubison, M.; Brune, W. H.; Hu, W.; Graus, M.; Warneke, C.; Gilman, J.; De Gouw, J. A.; Jimenez, J. L.
2014-12-01
To investigate atmospheric processing of urban emissions, we deployed an oxidation flow reactor with measurements of size-resolved chemical composition of submicron aerosol during CalNex-LA, a field study investigating air quality and climate change at a receptor site in the Los Angeles Basin. The reactor produces OH concentrations up to 4 orders of magnitude higher than in ambient air, achieving equivalent atmospheric aging of hours to ~2 weeks in 5 minutes of processing. The OH exposure (OHexp) was stepped every 20 min to survey the effects of a range of oxidation exposures on gases and aerosols. This approach is a valuable tool for in-situ evaluation of changes in organic aerosol (OA) concentration and composition due to photochemical processing over a range of ambient atmospheric conditions and composition. Combined with collocated gas-phase measurements of volatile organic compounds, this novel approach enables the comparison of measured SOA to predicted SOA formation from a prescribed set of precursors. Results from CalNex-LA show enhancements of OA and inorganic aerosol from gas-phase precursors. The OA mass enhancement from aging was highest at night and correlated with trimethylbenzene, indicating the importance of relatively short-lived VOC (OH lifetime of ~12 hrs or less) as SOA precursors in the LA Basin. Maximum net SOA production is observed between 3-6 days of aging and decreases at higher exposures. Aging in the reactor shows similar behavior to atmospheric processing; the elemental composition of ambient and reactor measurements follow similar slopes when plotted in a Van Krevelen diagram. Additionally, for air processed in the reactor, oxygen-to-carbon ratios (O/C) of aerosol extended over a larger range compared to ambient aerosol observed in the LA Basin. While reactor aging always increases O/C, often beyond maximum observed ambient levels, a transition from net OA production to destruction occurs at intermediate OHexp, suggesting a transition
Devine, K.D.; Hennigan, G.L.; Hutchinson, S.A.; Moffat, H.K.; Salinger, A.G.; Schmidt, R.C.; Shadid, J.N.; Smith, T.M.
1999-01-01
The theoretical background for the finite element computer program, MPSalsa Version 1.5, is presented in detail. MPSalsa is designed to solve laminar or turbulent low Mach number, two- or three-dimensional incompressible and variable density reacting fluid flows on massively parallel computers, using a Petrov-Galerkin finite element formulation. The code has the capability to solve coupled fluid flow (with auxiliary turbulence equations), heat transport, multicomponent species transport, and finite-rate chemical reactions, and to solve coupled multiple Poisson or advection-diffusion-reaction equations. The program employs the CHEMKIN library to provide a rigorous treatment of multicomponent ideal gas kinetics and transport. Chemical reactions occurring in the gas phase and on surfaces are treated by calls to CHEMKIN and SURFACE CHEMK3N, respectively. The code employs unstructured meshes, using the EXODUS II finite element database suite of programs for its input and output files. MPSalsa solves both transient and steady flows by using fully implicit time integration, an inexact Newton method and iterative solvers based on preconditioned Krylov methods as implemented in the Aztec. solver library.
NASA Astrophysics Data System (ADS)
Yan, Chao; Huang, Wei-Xi; Miao, Shi-Guang; Cui, Gui-Xiang; Zhang, Zhao-Shun
2017-06-01
Turbulent flow over a vegetation canopy under neutral atmospheric conditions is investigated using large-eddy simulation. Each model tree, which consists of a sphere-shaped tree crown and a cylindrical trunk, is fully resolved. The resulting turbulence statistics and the drag force on the vegetation agree well with measurements from the corresponding wind-tunnel experiment described by Böhm et al. (Boundary-Layer Meteorol, 146:393-419, 2013). Statistically, this kind of model canopy exhibits both vegetation and bluff-body-flow characteristics. The time-averaged flow skims over the top of the underlying canopy, forming a low-momentum recirculation zone on the lee-side of the bluff elements, which causes significant dispersive stress within the canopy layer. Two other numerical representations of vegetation canopies, referred to as the drag-element and drag-crown approaches, have also been developed to assess the performance of simulations. Turbulence statistics suggest that the canopy shear layer interferes with wakes behind stems and crowns. The drag-crown approach yields better agreement between numerical results and experimental measurements than does the traditional drag-element approach, thus providing a promising numerical model for simulating canopy turbulence.
NASA Astrophysics Data System (ADS)
Taneja, Ankur; Higdon, Jonathan
2016-11-01
A spectral element method (SEM) is presented to simulate two-phase fluid flow (oil and water phase) in petroleum reservoirs. Petroleum reservoirs are porous media with heterogeneous geologic features, and the flow of two immiscible phases involves sharp, moving interfaces. The governing equations of motion are time-dependent, non-linear PDEs with strong hyperbolic nature. A fully-coupled numerical scheme using discontinuous Galerkin (DG) method with nodal spectral element basis functions for spatial discretization, and an implicit Runge-Kutta type time-stepping is developed to solve the PDEs in a robust, stable manner. Isoparameteric mapping is used to generate grids for reservoir and well geometry. We present the performance capabilities of the DG scheme with high-order basis functions to accurately resolve sharp fluid interfaces and a variety of heterogeneous geologic features. High-order convergence of SEM is demonstrated. Numerical results are presented for reservoir flows with various injection-production patterns. Typical reservoir heterogeneities like low-permeable regions, impermeable shale barriers, etc. are included in the numerical tests. Comparisons with commonly used finite volume methods and linear and quadratic finite element methods are presented. ExxonMobil Upstream Research Co.
NASA Astrophysics Data System (ADS)
Cagnoli, Bruno; Piersanti, Antonio
2017-02-01
We have carried out new three-dimensional numerical simulations by using a discrete element method (DEM) to study the mobility of dry granular flows of angular rock fragments. These simulations are relevant for geophysical flows such as rock avalanches and pyroclastic flows. The model is validated by previous laboratory experiments. We confirm that (1) the finer the grain size, the larger the mobility of the center of mass of granular flows; (2) the smaller the flow volume, the larger the mobility of the center of mass of granular flows and (3) the wider the channel, the larger the mobility of the center of mass of granular flows. The grain size effect is due to the fact that finer grain size flows dissipate intrinsically less energy. This volume effect is the opposite of that experienced by the flow fronts. The original contribution of this paper consists of providing a comparison of the mobility of granular flows in six channels with a different cross section each. This results in a new scaling parameter χ that has the product of grain size and the cubic root of flow volume as the numerator and the product of channel width and flow length as the denominator. The linear correlation between the reciprocal of mobility and parameter χ is statistically highly significant. Parameter χ confirms that the mobility of the center of mass of granular flows is an increasing function of the ratio of the number of fragments per unit of flow mass to the total number of fragments in the flow. These are two characteristic numbers of particles whose effect on mobility is scale invariant.
NASA Astrophysics Data System (ADS)
Estep, J.; Dufek, J.
2012-12-01
Surficial flows on volcanic edifices are often comprised of high concentrations of granular materials either derived from juvenile eruptive material or material sourced from an unstable edifice. Although much attention has been given to granular flow mobility, the physics that govern their internal behavior are still poorly understood. Our work builds on previous research showing that force chains transmit extreme localized forces to the substrates of free surface granular flows, and combines experimental and computational approaches to further investigate the forces at the bed of a simplified granular flow. A photoelastic experimental approach is used to resolve discrete forces in the granular flows, while discrete element model (DEM) simulations reproduce the experimental flows. Input parameters for the DEM are derived from measurable physical material properties, and DEM simulations using properties of natural materials corroborate experimental results. The DEM results show particular sensitivity to values prescribed for contact stiffness, which is in contrast with previous reports indicating that stiffness values have insignificant influence on flow behavior. The forces at the bed generated by force chain structures can transiently greatly exceed (by several 100%) the bed forces predicted from continuum approaches, and natural materials are more prone to excessive bed forces than photoelastic materials due to their larger contact stiffnesses. By varying the ratios of a bidisperse grain size population, continuing experiments investigate how further complexity in the granular flow regime influences force transmission via force chains. This work suggests that force chain activity may play an important role in the bed physics of dense volcanic flows by influencing substrate entrainment.
Heanes, D.L. )
1990-01-01
A rapid, accurate and reproducible procedure for determining total sulphur(S) and trace elements (copper, zinc, manganese and iron) in plant material is described. Plant material is digested in culture tubes with a mixture of nitric and perchloric acids containing ammonium metavanadate and calcium chloride. In the acid digest, concentrations of total-S as sulphate are determined by turbidimetry and trace-elements by flame atomic absorption spectrophotometry using flow injection analysis. The results for a range of plant materials compare well with those obtained by conventional procedures for the same elements. The microprocessor controlled digestion and multielement assay procedure described here offers improved laboratory efficiencies in materials, time and cost effectiveness. The techniques should be particularly useful when plant tissues are in limited supply.
Behavior of EBR-II Mk-V-type fuel elements in simulated loss-of-flow tests
Liu, Y.Y.; Tsai, H.; Billone, M.C.; Holland, J.W.; Kramer, J.M. )
1992-11-01
This report discusses three furnace heating tests which were conducted with irradiated, HT9-clad and U-19wt.%Pu-l0wt.%Zr-alloy fuel, Mk-V-type fuel elements in the Alpha-Gamma Hot Cell Facility at Argonne National Laboratory, Illinois. In general, very significant safety margins for fuel-element cladding breaching have been demonstrated in these tests, under conditions that would envelop a bounding unlikely loss-of-flow event in EBR-II. Highlights of the test results will be given, as well as discussions of the cladding breaching mechanisms, axial fuel motion, and fuel surface liquefaction found in high-temperature testing of irradiated metallic fuel elements.
NASA Technical Reports Server (NTRS)
Vijgen, P. M. H. W.; Hardin, J. D.; Yip, L. P.
1992-01-01
Accurate prediction of surface-pressure distributions, merging boundary-layers, and separated-flow regions over multi-element high-lift airfoils is required to design advanced high-lift systems for efficient subsonic transport aircraft. The availability of detailed measurements of pressure distributions and both averaged and time-dependent boundary-layer flow parameters at flight Reynolds numbers is critical to evaluate computational methods and to model the turbulence structure for closure of the flow equations. Several detailed wind-tunnel measurements at subscale Reynolds numbers were conducted to obtain detailed flow information including the Reynolds-stress component. As part of a subsonic-transport high-lift research program, flight experiments are conducted using the NASA-Langley B737-100 research aircraft to obtain detailed flow characteristics for support of computational and wind-tunnel efforts. Planned flight measurements include pressure distributions at several spanwise locations, boundary-layer transition and separation locations, surface skin friction, as well as boundary-layer profiles and Reynolds stresses in adverse pressure-gradient flow.
Shiomi, Masanori; Mori, Kenichiro; Osakada, Kozo
1995-12-31
Non-steady-state metal flow and temperature distribution in twin roll strip casting are simulated by the finite element method. In the present simulation, the viscoplastic finite element method is combined with that for heat conduction to calculate the metal flow and the temperature distribution during the casting process. The solid, mushy and liquid phases are assumed to be viscoplastic materials with individual flow stresses. In the temperature analysis, the latent heat due to solidification of the molten metal is taken into account by using the temperature recovery method. Since the metal flow and temperature distribution do not often attain to steady states, they are simulated by the stepwise calculation. To examine the accuracy of the calculated results, physical simulation of plane-strain twin roll strip casting is carried out by use of paraffin wax as a model material. The calculated profiles of the solid region agree qualitatively well with the experimental ones. Twin roll strip casting processes for stainless steel are also simulated. An optimum roll speed for obtaining a strip without a liquid zone under a minimum rolling load is obtained from the results of the simulation.
Mühlthaler, Hannes; Quatember, Bernhard; Fraedrich, Gustav; Mühlthaler, Markus; Pfeifer, Bernhard; Greiner, Andreas; Schocke, Michael F H
2008-10-01
Interventions for peripheral arterial disease should be designed to treat a physiological rather than an anatomic defect. Thus, for vascular surgeons, functional information about stenoses is as important as the anatomic one. In case of finding a stenosis by the use of magnetic resonance angiography, it would be a matter of particular interest to derive automatically and directly objective information about the hemodynamic influence on blood flow, caused by patient-specific stenoses. We developed a methodology to noninvasively perform numerical simulations of a patient's hemodynamic state on the basis of magnetic resonance images and by the means of the finite element method. We performed patient-specific three-dimensional simulation studies of the increase in systolic blood flow velocity due to stenoses using the commercial computational fluid dynamic software package FIDAP 8.52. The generation of a mesh defining the flow domain with a stenosis and some simulation results are shown.
Documentation of a finite-element two-layer model for simulation of ground-water flow
Mallory, Michael J.
1979-01-01
This report documents a finite-element model for simulation of ground-water flow in a two-aquifer system where the two aquifers are coupled by a leakage term that represents flow through a confining layer separating the two aquifers. The model was developed by Timothy J. Durbin (U.S. Geological Survey) for use in ground-water investigations in southern California. The documentation assumes that the reader is familiar with the physics of ground-water flow, numerical methods of solving partial-differential equations, and the FORTRAN IV computer language. It was prepared as part of the investigations made by the U.S. Geological Survey in cooperation with the San Bernardino Valley Municipal Water District. (Kosco-USGS)
A Least Square Finite Element Technique for Transonic Flow with Shock,
1977-08-22
character of the hodograph equations. one-dimensional, transonic flow in a laval nozzle in the vicinity of the throat was obtained in the For such...state of development, the hodograph method has 2 limitations. It can only be applied to the design a (3) problem in plane flow and cannot be used in
A Mechanical Power Flow Capability for the Finite Element Code NASTRAN
1989-07-01
perimental methods. statistical energy analysis , the finite element method, and a finite element analog-,y using heat conduction equations. Experimental...weights and inertias of the transducers attached to an experimental structure may produce accuracy problems. Statistical energy analysis (SEA) is a...405-422 (1987). 8. Lyon, R.L., Statistical Energy Analysis of Dynamical Sistems, The M.I.T. Press, (1975). 9. Mickol, J.D., and R.J. Bernhard, "An
Froelich, Daniel R.; Mullendore, Daniel L.; Jensen, Kåre H.; Ross-Elliott, Tim J.; Anstead, James A.; Thompson, Gary A.; Pélissier, Hélène C.; Knoblauch, Michael
2011-01-01
Since the first ultrastructural investigations of sieve tubes in the early 1960s, their structure has been a matter of debate. Because sieve tube structure defines frictional interactions in the tube system, the presence of P protein obstructions shown in many transmission electron micrographs led to a discussion about the mode of phloem transport. At present, it is generally agreed that P protein agglomerations are preparation artifacts due to injury, the lumen of sieve tubes is free of obstructions, and phloem flow is driven by an osmotically generated pressure differential according to Münch’s classical hypothesis. Here, we show that the phloem contains a distinctive network of protein filaments. Stable transgenic lines expressing Arabidopsis thaliana Sieve-Element-Occlusion-Related1 (SEOR1)–yellow fluorescent protein fusions show that At SEOR1 meshworks at the margins and clots in the lumen are a general feature of living sieve tubes. Live imaging of phloem flow and flow velocity measurements in individual tubes indicate that At SEOR1 agglomerations do not markedly affect or alter flow. A transmission electron microscopy preparation protocol has been generated showing sieve tube ultrastructure of unprecedented quality. A reconstruction of sieve tube ultrastructure served as basis for tube resistance calculations. The impact of agglomerations on phloem flow is discussed. PMID:22198148
NASA Astrophysics Data System (ADS)
Stetzenbach, Klaus J.; Farnham, Irene M.; Hodge, Vernon F.; Johannesson, Kevin H.
1999-12-01
Groundwater samples were collected from 11 springs in Ash Meadows National Wildlife Refuge in southern Nevada and seven springs from Death Valley National Park in eastern California. Concentrations of the major cations (Ca, Mg, Na and K) and 45 trace elements were determined in these groundwater samples. The resultant data were subjected to evaluation via the multivariate statistical technique principal components analysis (PCA), to investigate the chemical relationships between the Ash Meadows and Death Valley spring waters, to evaluate whether the results of the PCA support those of previous hydrogeological and isotopic studies and to determine if PCA can be used to help delineate potential groundwater flow patterns based on the chemical compositions of groundwaters. The results of the PCA indicated that groundwaters from the regional Paleozoic carbonate aquifers (all of the Ash Meadows springs and four springs from the Furnace Creek region of Death Valley) exhibited strong statistical associations, whereas other Death Valley groundwaters were chemically different. The results of the PCA support earlier studies, where potentiometric head levels, 18O and D, geological relationships and rare earth element data were used to evaluate groundwater flow, which suggest groundwater flows from Ash Meadows to the Furnace Creek springs in Death Valley. The PCA suggests that Furnace Creek groundwaters are moderately concentrated Ash Meadows groundwater, reflecting longer aquifer residence times for the Furnace Creek groundwaters. Moreover, PCA indicates that groundwater may flow from springs in the region surrounding Scotty's Castle in Death Valley National Park, to a spring discharging on the valley floor. The study indicates that PCA may provide rapid and relatively cost-effective methods to assess possible groundwater flow regimes in systems that have not been previously investigated.
Guérin, Frédéric; Arnaiz, Olivier; Boggetto, Nicole; Denby Wilkes, Cyril; Meyer, Eric; Sperling, Linda; Duharcourt, Sandra
2017-04-26
DNA elimination is developmentally programmed in a wide variety of eukaryotes, including unicellular ciliates, and leads to the generation of distinct germline and somatic genomes. The ciliate Paramecium tetraurelia harbors two types of nuclei with different functions and genome structures. The transcriptionally inactive micronucleus contains the complete germline genome, while the somatic macronucleus contains a reduced genome streamlined for gene expression. During development of the somatic macronucleus, the germline genome undergoes massive and reproducible DNA elimination events. Availability of both the somatic and germline genomes is essential to examine the genome changes that occur during programmed DNA elimination and ultimately decipher the mechanisms underlying the specific removal of germline-limited sequences. We developed a novel experimental approach that uses flow cell imaging and flow cytometry to sort subpopulations of nuclei to high purity. We sorted vegetative micronuclei and macronuclei during development of P. tetraurelia. We validated the method by flow cell imaging and by high throughput DNA sequencing. Our work establishes the proof of principle that developing somatic macronuclei can be sorted from a complex biological sample to high purity based on their size, shape and DNA content. This method enabled us to sequence, for the first time, the germline DNA from pure micronuclei and to identify novel transposable elements. Sequencing the germline DNA confirms that the Pgm domesticated transposase is required for the excision of all ~45,000 Internal Eliminated Sequences. Comparison of the germline DNA and unrearranged DNA obtained from PGM-silenced cells reveals that the latter does not provide a faithful representation of the germline genome. We developed a flow cytometry-based method to purify P. tetraurelia nuclei to high purity and provided quality control with flow cell imaging and high throughput DNA sequencing. We identified 61