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At least 1,765 records · Page 98
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Dose Escalation for Metastatic Spinal Cord Compression in Patients With Relatively Radioresistant Tumors

Purpose: Radiotherapy alone is the most common treatment for metastatic spinal cord compression (MSCC) from relatively radioresistant tumors such as renal cell carcinoma, colorectal cancer, and malignant melanoma. However, the results of the 'standard' regimen 30 Gy/10 fractions need to be improved with respect to functional outcome. This study investigated whether a dose escalation beyond 30 Gy can improve treatment outcomes. Methods and Materials: A total of 91 patients receiving 30 Gy/10 fractions were retrospectively compared to 115 patients receiving higher doses (37.5 Gy/15 fractions, 40 Gy/20 fractions) for motor function and local control of MSCC. Ten further potential prognostic factors were evaluated: age, gender, tumor type, performance status, number of involved vertebrae, visceral or other bone metastases, interval from tumor diagnosis to radiotherapy, pretreatment ambulatory status, and time developing motor deficits before radiotherapy. Results: Motor function improved in 18% of patients after 30 Gy and in 22% after higher doses (p = 0.81). On multivariate analysis, functional outcome was associated with visceral metastases (p = 0.030), interval from tumor diagnosis to radiotherapy (p = 0.010), and time developing motor deficits (p < 0.001). The 1-year local control rates were 76% after 30 Gy and 80% after higher doses, respectively (p = 0.64). On multivariate analysis, local control was significantly associated with visceral metastases (p = 0.029) and number of involved vertebrae (p = 0.043). Conclusions: Given the limitations of a retrospective study, escalation of the radiation dose beyond 30 Gy/10 fractions did not significantly improve motor function and local control of MSCC in patients with relatively radioresistant tumors.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Phase 1 Study of Spinal Cord Constraint Relaxation With Single Session Spine Stereotactic Radiosurgery in the Primary Management of Patients With Inoperable, Previously Unirradiated Metastatic Epidural Spinal Cord Compression

We seek to establish the feasibility of using spine stereotactic radiosurgery (SSRS), allowing for spinal cord dose constraint relaxation, as the primary management of metastatic epidural spinal cord compression (MESCC) in inoperable patients.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2011

An algorithm for LES of premixed compressible flows using the Conditional Moment Closure model

A novel numerical method has been developed to couple a recent high order accurate fully compressible upwind method with the Conditional Moment Closure combustion model. The governing equations, turbulence modelling and numerical methods are presented in full. The new numerical method is validated against direct numerical simulation (DNS) data for a lean premixed methane slot burner. Although the modelling approaches are based on non-premixed flames and hence not expected to be valid for a wide range of premixed flames, the predicted flame is just 10% longer than that in the DNS and excellent agreement of mean mass fractions, conditional mass fractions and temperature is demonstrated. This new numerical method provides a very useful framework for future application of CMC to premixed as well as non-premixed combustion.

Computer Science↗
DOE OSTI2014

Compressible, multiphase semi-implicit method with moment of fluid interface representation

A unified method for simulating multiphase flows using an exactly mass, momentum, and energy conserving Cell-Integrated Semi-Lagrangian advection algorithm is presented. The deforming material boundaries are represented using the moment-of-fluid method. Our new algorithm uses a semi-implicit pressure update scheme that asymptotically preserves the standard incompressible pressure projection method in the limit of infinite sound speed. The asymptotically preserving attribute makes the new method applicable to compressible and incompressible flows including stiff materials; enabling large time steps characteristic of incompressible flow algorithms rather than the small time steps required by explicit methods. Moreover, shocks are captured and material discontinuities are tracked, without the aid of any approximate or exact Riemann solvers. As a result, wimulations of underwater explosions and fluid jetting in one, two, and three dimensions are presented which illustrate the effectiveness of the new algorithm at efficiently computing multiphase flows containing shock waves and material discontinuities with large “impedance mismatch.”

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

A study of solid wall models for weakly compressible SPH

This paper is concerned with a comparison of two methods of treating solid wall boundaries in the weakly compressible (SPH) method. They have been chosen because of their wide use in simulations. These methods are the boundary force particles of Monaghan and Kajtar [24] and the use of layers of fixed boundary particles. The latter was first introduced by Morris et al. [26] but has since been improved by Adami et al. [1] whose algorithm involves interpolating the pressure and velocity from the actual fluid to the boundary particles. For each method, we study the effect of the density diffusive terms proposed by Molteni and Colagrossi [19] and modified by Antuono et al. [3]. We test the methods by a series of simulations commencing with the time-dependent spin-down of fluid within a cylinder and the behaviour of fluid in a box subjected to constant acceleration at an angle to the walls of the box, and concluding with a dam break over a triangular obstacle. In the first two cases the results from the two methods can be compared to analytical solutions while, in the latter case, they can be compared with experiments and other methods. These results show that the method of Adami et al. together with density diffusion is in very satisfactory agreement with the experimental results and is, overall, the best of the methods discussed here.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Arbitrary Lagrangian–Eulerian methods for modeling high-speed compressible multimaterial flows

This paper reviews recent developments in Arbitrary Lagrangian Eulerian (ALE) methods for modeling high speed compressible multimaterial flows in complex geometry on general polygonal meshes. We only consider the indirect ALE approach which consists of three key stages: a Lagrangian stage, in which the solution and the computational mesh are updated; a rezoning stage, in which the nodes of the computational mesh are moved to improve grid quality; and a remapping stage, in which the Lagrangian solution is transferred to the rezoned mesh.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

An unstructured-mesh finite-volume MPDATA for compressible atmospheric dynamics

An advancement of the unstructured-mesh finite-volume MPDATA (Multidimensional Positive Definite Advection Transport Algorithm) is presented that formulates the error-compensative pseudo-velocity of the scheme to rely only on face-normal advective fluxes to the dual cells, in contrast to the full vector employed in previous implementations. This is essentially achieved by expressing the temporal truncation error underlying the pseudo-velocity in a form consistent with the flux-divergence of the governing conservation law. The development is especially important for integrating fluid dynamics equations on non-rectilinear meshes whenever face-normal advective mass fluxes are employed for transport compatible with mass continuity—the latter being essential for flux-form schemes. In particular, the proposed formulation enables large-time-step semi-implicit finite-volume integration of the compressible Euler equations using MPDATA on arbitrary hybrid computational meshes. Furthermore, it facilitates multiple error-compensative iterations of the finite-volume MPDATA and improved overall accuracy. The advancement combines straightforwardly with earlier developments, such as the nonoscillatory option, the infinite-gauge variant, and moving curvilinear meshes. A comprehensive description of the scheme is provided for a hybrid horizontally-unstructured vertically-structured computational mesh for efficient global atmospheric flow modelling. The proposed finite-volume MPDATA is verified using selected 3D global atmospheric benchmark simulations, representative of hydrostatic and non-hydrostatic flow regimes. Besides the added capabilities, the scheme retains fully the efficacy of established finite-volume MPDATA formulations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

A sharp interface method for compressible liquid–vapor flow with phase transition and surface tension

The numerical approximation of non-isothermal liquid–vapor flow within the compressible regime is a difficult task because complex physical effects at the phase interfaces can govern the global flow behavior. We present a sharp interface approach which treats the interface as a shock-wave like discontinuity. Any mixing of fluid phases is avoided by using the flow solver in the bulk regions only, and a ghost-fluid approach close to the interface. The coupling states for the numerical solution in the bulk regions are determined by the solution of local two-phase Riemann problems across the interface. The Riemann solution accounts for the relevant physics by enforcing appropriate jump conditions at the phase boundary. A wide variety of interface effects can be handled in a thermodynamically consistent way. This includes surface tension or mass/energy transfer by phase transition. Moreover, the local normal speed of the interface, which is needed to calculate the time evolution of the interface, is given by the Riemann solution. The interface tracking itself is based on a level-set method. The focus in this paper is the description of the two-phase Riemann solver and its usage within the sharp interface approach. One-dimensional problems are selected to validate the approach. Finally, the three-dimensional simulation of a wobbling droplet and a shock droplet interaction in two dimensions are shown. In both problems phase transition and surface tension determine the global bulk behavior.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Lagrangian particle method for compressible fluid dynamics

A new Lagrangian particle method for solving Euler equations for compressible inviscid fluid or gas flows is proposed. Similar to smoothed particle hydrodynamics (SPH), the method represents fluid cells with Lagrangian particles and is suitable for the simulation of complex free surface / multi-phase flows. The main contributions of our method, which is different from SPH in all other aspects, are (a) significant improvement of approximation of differential operators based on a polynomial fit via weighted least squares approximation and the convergence of prescribed order, (b) a second-order particle-based algorithm that reduces to the first-order upwind method at local extremal points, providing accuracy and long term stability, and (c) more accurate resolution of entropy discontinuities and states at free inter-faces. While the method is consistent and convergent to a prescribed order, the conservation of momentum and energy is not exact and depends on the convergence order . The method is generalizable to coupled hyperbolic-elliptic systems. As a result, numerical verification tests demonstrating the convergence order are presented as well as examples of complex multiphase flows.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

A general peridynamics model for multiphase transport of non-Newtonian compressible fluids in porous media

Herein a general state-based peridynamics model is developed to simulate transport of fluids in an arbitrary heterogeneous porous medium. The generality encompasses modeling of multiphase, multi-component flow of non-Newtonian and compressible fluids, which is often encountered in but not limited to subsurface reservoirs. Peridynamic model is especially useful for solving non-local problems, such as crack propagation, since it does not assume spatial continuity of field variables. Thus, the formulation presented here, combined with peridynamics-based damage model, can be used to simulate hydraulic fracturing with complex fluids. To demonstrate its capability to simulate multi-phase flow in porous media, the derived model is verified against the analytical Buckley-Leverett solution for immiscible Newtonian two-phase flow. Further, the non-Newtonian two-phase fluid flow in porous media is verified by simulating the polymer flood process involving immiscible displacement of a Newtonian fluid by a non-Newtonian fluid against a generalized solution obtained by Wu et al. The non-local solutions are shown to be consistent with the corresponding local solutions in limiting cases. Moreover, mass conservation of all the phases is satisfied, irrespective of discretization and extent of non-locality.

42 ENGINEERING↗
DOE OSTI2023

Robust second-order approximation of the compressible Euler equations with an arbitrary equation of state

Here, this paper is concerned with the approximation of the compressible Euler equations supplemented with an arbitrary or tabulated equation of state. The proposed approximation technique is robust, formally second-order accurate in space, invariant-domain preserving, and works for every equation of state, tabulated or analytic, provided the pressure is nonnegative. An entropy surrogate functional that grows across shocks is proposed. The numerical method is verified with novel analytical solutions and then validated with several computational benchmarks seen in the literature including problems with composite waves.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2026

Siloxane-modified polycarbosilane flexible Prepregs for fabrication of ceramic matrix composites via compression molding and PIP densification

For this work, the development of ceramic matrix composites (CMCs) using 5 harness satin carbon fiber fabric impregnated with commercial polycarbosilane precursor plasticized by siloxane copolymer was investigated aiming to improve wetting behavior and shape conformability. The polycarbosilane precursor and polysiloxane plasticizer were mixed at varying weight ratios to obtain flexible preceramic resin prepreg cloths. 13 plies of preceramic polymer prepreg cloths were stacked in 0/90° layup and cured by compression molding, followed by densified via PIP process. The CMCs were densified with eight PIP cycles followed by final crystallization at 1600 °C. The CMCs made with 10 wt% polysiloxane loading showed lower viscosity of the prepreg resin as well as higher strength and displacement to failure compared to those fabricated from unplasticized polycarbosilane prepolymer. In contrast, at higher concentration of plasticizer, viscosity of the prepreg resin increased, and the CMC became more brittle; however, it exhibited considerably higher thermal conductivity.

Carbosilane↗
DOE OSTI2025

Fast-rate joining of thermoplastic composites using integrated additive manufacturing and compression molding process

The integration of additive manufacturing (AM) technology with compression molding (CM), has emerged as a high-performance composite manufacturing technology in recent years. In the AM-CM process, quickly deposited AM preform on a mold undergoes a rapid compaction cycle to fabricate structurally robust composite parts due to highly controlled fiber alignment (from AM) and reduced porosity (from CM). Currently, AMCM-based part size is limited by the size of the mold volume, thus posing a challenge to manufacture scalable parts. Here, this work focuses on joining techniques developed to enable fast rate joining of short fiber-reinforced thermoplastic composite parts using the AM-CM process. Acrylonitrile butadiene styrene resin reinforced with 20 wt% short carbon fiber composites was printed onto a flat mold and pressed under a hydraulic press. Fabricated panels were joined by the (a) mechanical impression at the joining interface and (b) over-molded continuous carbon fiber (CCF) sheet. Tensile tests were performed to characterize the joining strength of both mechanical impression-based joints and CCF over molded joints. Among the mechanical impression-based joints, a U-shape channel allowed the fibers to flow between two joint parts, and 280 % increased mechanical properties were observed. The continuous carbon fiber-based over molded joint CCF showed 350 % increase in tensile strength compared to the butt joints.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Compression behavior of lithium fluoride up to 80 GPa and 2300 K

Here, the high-temperature compression behavior of lithium fluoride (LiF) has been determined to ∼80 GPa and 2300 K by means of high-resolution synchrotron-based x-ray diffraction in a laser-heated diamond-anvil cell. The room-temperature Vinet equation of state (EOS) for LiF yields an isothermal room-temperature, ambient-pressure lattice parameter a 0 = 4.028 (±0.003) Å, volume V 0 = 65.35 (±0.03) Å 3 , bulk modulus K 0 = 67.57 (±0.34) GPa, and its pressure derivative K 0 ’ = 4.64 (±0.03). This expanded experimental dataset is in good agreement with the LiF thermal equation of state by Myint et al. (2019) up to ∼2300 K and 25 GPa. At higher pressures and temperatures our data shows reduced thermal expansion compared to the prediction and may be particularly important for experiments at more extreme conditions.

High-pressure behavior↗
DOE OSTI2022

Compressible battery foams to prevent cascading thermal runaway in Li-ion pouch batteries

Lithium-ion battery packs require thermal management to achieve optimum life and safety. This is becoming crucial for battery packs composed of high-energy-density cells. Pouch cells themselves achieve highest packaging efficiency but require additional structural support and thermal management when grouped into modules, especially under abusive conditions such as thermal runaway. Novel foam battery pads have demonstrated to cushion volume changes of pouch cells and are reengineered in this study to mitigate cell-to-cell thermal runaway propagation. The compressible pads are made of polyurethane foams incorporating flame-retardant additives or coatings, including intumescent and fire wall materials. Here their performances were evaluated by conducting nail penetration tests on modules composed of pouch cells at 100% state of charge (SOC), with the foams placed in between the cells. Experimental results show cascading thermal runaway was considerably delayed by polyurethane foams incorporating flame-retardant additives or coatings. Complete prevention of cascading failure was achieved with dense polyurethane foams with multilayered coatings of both fire wall and intumescent materials.

25 ENERGY STORAGE↗
DOE OSTI2016

Structural and electronic evolution of Cr[subscript 2]O[subscript 3] on compression to 55 GPa

Synchrotron single-crystal x-ray diffraction experiments have been performed on corundum-type Cr{sub 2}O{sub 3} up to a pressure of 55 GPa in Ne and He pressure transmitting media. Diffraction experiments were complemented by measurements of optical absorption spectra with single crystal samples up to 60 GPa. Results of the diffraction data analysis rule out the earlier reported monoclinic distortion at 15-30 GPa, but indicate evidence of two discontinuous transitions of electronic or magnetic nature, most likely associated with a change in magnetic ordering and charge transfer. The compression mechanism established from single crystal refinements indicates much smaller distortion of the Cr{sup 3+} coordination environment than was previously assumed.

Dera, Przemyslaw↗
DOE OSTI2014

Dynamic recrystallization behavior of an as-cast TiAl alloy during hot compression

High temperature compressive deformation behaviors of as-cast Ti–43Al–4Nb–1.4W–0.6B alloy were investigated at temperatures ranging from 1050 °C to 1200 °C, and strain rates from 0.001 s{sup −1} to 1 s{sup −1}. Electron back scattered diffraction technique, scanning electron microscopy and transmission electron microscopy were employed to investigate the microstructural evolutions and nucleation mechanisms of the dynamic recrystallization. The results indicated that the true stress–true strain curves show a dynamic flow softening behavior. The dependence of the peak stress on the deformation temperature and the strain rate can well be expressed by a hyperbolic-sine type equation. The activation energy decreases with increasing the strain. The size of the dynamically recrystallized β grains decreases with increasing the value of the Zener–Hollomon parameter (Z). When the flow stress reaches a steady state, the size of β grains almost remains constant with increasing the deformation strain. The continuous dynamic recrystallization plays a dominant role in the deformation. In order to characterize the evolution of dynamic recrystallization volume fraction, the dynamic recrystallization kinetics was studied by Avrami-type equation. Besides, the role of β phase and the softening mechanism during the hot deformation was also discussed in details. - Highlights: • The size of DRXed β grains decreases with increasing the value of the Z. • The CDRX plays a dominant role in the deformation. • The broken TiB{sub 2} particles can promote the nucleation of DRX.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Grain size dependence of dynamic mechanical behavior of AZ31B magnesium alloy sheet under compressive shock loading

The effects of grain size on the dynamic deformation behavior of rolled AZ31B alloy at high strain rates were investigated. Rolled AZ31B alloy samples with grain sizes of 6, 18 and 37 μm, were subjected to shock loading tests using Split Hopkinson Pressure Bar at room temperature and at a strain rate of 1100 s{sup −} {sup 1}. It was found that a double-peak basal texture formed in the shock loaded samples. The strength and ductility of the alloy under the high strain-rate compressive loading increased with decreasing grain size. However, twinning fraction and strain hardening rate were found to decrease with decreasing grain size. In addition, orientation imaging microscopy showed a higher contribution of double and contraction twins in the deformation process of the coarse-grained samples. Using transmission electron microscopy, pyramidal dislocations were detected in the shock loaded sample, proving the activation of pyramidal slip system under dynamic impact loading. - Highlights: • A double-peak basal texture developed in all shock loaded samples. • Both strength and ductility increased with decreasing grain size. • Twinning fraction and strain hardening rate decreased with decreasing grain size. • ‘g.b’ analysis confirmed the presence of dislocations in shock loaded alloy.

36 MATERIALS SCIENCE↗