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Jet boundary corrections for partly open and partly closed elliptical wind tunnels for the cases of one and two solid wall segments are presented. Also presented are the combinations of model span and extent of the solid portion of the tunnel wall for which the average correction factor is zero.
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Introduction: Meteorite thin and thick sections are routinely shipped from NASA Johnson Space Center to fulfill sample allocation requests from principle investigators around the world. Sections are also re-turned to JSC when researchers are finished studying them since, in most cases, they can be reused for other studies. The sections are very fragile unfortunately, and sometimes return to us needing repairs. The fol-lowing should give you an idea of how we repair sections here in the very lab where they were created. NOTE: Please do not attempt to repair ANSMET meteorite sections that are in your possession. We will perform the repairs for you at NASA JSC if you send the section back to us. Section Delamination: The majority of the meteorite sections that we produce here are secured to the glass slide using a high quality, two-part epoxy. Occasionally, we are asked to use superglue if the researcher wishes to dismount the section from the slide. Both epoxy and superglue are excellent adhesives, but they both tend to embrittle with time which results in delamination from the slide. Exposure to vacuum can also degrade the adhesion between the sample section and the glass slide. Repeated handling of the slide edges can accelerate delamination and, as a preventive measure, the outer 1-2 mm of epoxy is trimmed from newly created sections at JSC. If conductive tapes (copper, carbon, etc.) are used on the section during analysis, great care must be taken in removing the tape so that the epoxy is not pulled up with it. If in doubt, the tape can be left on the section when it is returned to JSC. Before we perform any repairs to sample sections, carbon, gold, or other coatings are removed. We accomplish this using a slurry of 0.05 micron alumina and 190 proof ethyl alcohol applied to a felt polishing pad fitted to a rotating lap wheel. Coatings are re-moved in this manner from all sections that are re-turned to JSC. The extent of the delamination determines how we proceed with the section repair. If the meteorite sample area of the section is not disturbed, then we carefully remove the delaminated epoxy. This is done using a binocular microscope with a 6X zoom, cut-proof gloves, and a very sharp, single edged razor blade. We cut the delaminated epoxy with the blade angled away from the sample area and using very light pressure. The trimmed section is then cleaned in an ultrasonic bath of 200 proof ethyl alcohol for no more than 10 seconds and carefully dried using a lint-free clean room wipe. The section is then placed into a lab oven at 110o F in preparation for epoxy. We mix the resin and hardener components of the low viscosity epoxy and very small amounts are applied to the cut edges of the section using a needle probe and the binocular microscope. Warming the epoxy helps secure the existing section by filling any voids between the glass slide and the section. After the new epoxy cures, we give the section a light polish on a lap wheel fitted with cotton polishing paper that is charged with 1 micron diamond paste. If the section has delaminated to the point of sample area being lifted from the glass, then it may be irreparable. We employ the above technique along with clamping the section in a Teflon pad arrangement in order to flatten the sample while the epoxy cures. Otherwise, the sample will tend to curl. This works to some degree, but once the sample area curls, it seldom re-turns to the original flatness without cracking or bending. Canada Balsam and Crystalbond: We repair damaged sections that had originally been prepared using Canada Balsam or Crystalbond adhesives through the gradual application of heat. We take great care with these samples since these bonding materials tend to get brittle with age. The section is heated in gradual steps (40-50o F per hour) to the melting point of the adhesive. We repair the sample while the adhesive is fluid and then the section is cooled in the same gradual manner in which it was heated. Slide Cracks and Breaks: Accidents happen. Especially with something as small and fragile as a thin/thick section. We all know someone who has driven a microscope objective into a section. As bad as the damage may look, the section can be repaired in most instances. NOTE: Please do not try to tape or glue section pieces back together prior to returning the dam-aged section. This practice usually renders the section irreparable. If the glass slide is cracked but the section is still in one piece, we repair it by infilling the crack with the low viscosity epoxy mentioned earlier. If the slide is in pieces, we can reassemble it with epoxy on a new backer slide. This is a tricky task as the pieces need to be in the correct plane with respect to each other, especially if the sample area is split among several pieces.
Nuclear cross sections are basic inputs to any nuclear computation. Campaigns of experiments are fitted with the parametric R-matrix model of quantum nuclear interactions, and the resulting cross sections are documented—both pointwise and as resonance parameters (with uncertainties)—in standard evaluated nuclear data libraries (ENDF, JEFF, BROND, JENDL, CENDL, TENDL): these constitute our common knowledge of fundamental low-energy nuclear cross sections. In the past decade, a collaborative effort has been deployed to establish a new nuclear cross-section library format—the Windowed Multipole Library—with the goal of considerably reducing the computational cost of cross-section calculations in nuclear transport simulations. This work lays the theoretical foundations underpinning these efforts. From general R-matrix scattering theory, we derive the windowed multipole representation of nuclear cross sections. Though physically and mathematically equivalent to R-matrix cross sections, the windowed multipole representation is particularly well suited for subsequent temperature treatment of angle-integrated cross sections, in particular Doppler broadening, which is the averaging of cross sections over the thermal motion of the target atoms. Doppler broadening is of critical importance in neutron transport applications, as it ensures the stability of many nuclear reactors (negative thermal reactivity). Yet, Doppler broadening of nuclear cross sections has been a considerable bottleneck for nuclear transport computations, often requiring memory-costly pretabulations. We show that the windowed multipole representation can perform accurate Doppler broadening analytically (up to the first reaction threshold), from which we derive cross-section temperature derivatives to any order—all computable on the fly (without precalculations stored in memory). Furthermore, we here establish a way of converting the R-matrix resonance parameters uncertainty (covariance matrices) into windowed multipole parameters uncertainty. We show that generating stochastic nuclear cross sections by sampling from the resulting windowed multipole covariance matrix can reproduce the cross-section uncertainty in the original nuclear data file. The windowed multipole representation is therefore a novel nuclear physics formalism able to generate Doppler broadened stochastic nuclear cross sections on the fly, unlocking breakthrough computational gains for nuclear computations. Through this foundational paper, we hope to make the windowed multipole representation accessible, reproducible, and usable for the nuclear physics community, as well as provide the theoretical basis for future research on expanding its capabilities.
The generation of high-order neutron scattering cross sections consistent with high-fidelity simulations remains an area of active research. Popular options include generating cross sections from continuous energy Monte Carlo calculations or generating cross sections from a deterministic neutron transport calculation with high-fidelity tabulated cross sections. Both options present challenges. Monte Carlo simulations can naturally process continuous energy cross section data and allow for the general description of anisotropic neutron scattering given a scattering law. However, Monte Carlo simulations are inherently related to particle weighting and it has been suggested that this may be unacceptable for generating high-order neutron scattering cross sections. Deterministic neutron transport calculations can easily calculate high-order moments of the flux to appropriately calculate higher-order neutron scattering cross sections but are generally limited by discretization of space, energy, and angle. In this work, the trade-offs between generation of high-order neutron scattering cross sections via Monte Carlo and deterministic neutron transport methods are investigated. The methods implemented in the Monte Carlo computer program Serpent and the deterministic fast reactor neutron cross section generator MC2-3 are compared. Cross sections resulting from these methods are used in Rattlesnake, a deterministic neutron transport code developed by Idaho National Laboratory (INL), and results are compared to a reference continuous energy Monte Carlo calculation. Whereas previous work investigating the effects of anisotropic neutron scattering has focused on light water reactor (LWR) simulations, this work focuses on high-order neutron scattering cross sections as they relate to fast reactor simulations. To investigate the consequences of the Serpent and MC2-3 methodologies, a test problem is developed. The test problem is a one-dimensional geometry with fast reactor materials designed to demonstrate deep penetration and exacerbate the effects of high-order neutron scattering. Based on the results of the deep penetration test problem, it is concluded that P3 neutron scattering cross sections are sufficient to describe anisotropic scattering in fast reactor materials. Any neutron scattering of order higher than P3 offers negligible change in the eigenvalue of the test problem. Additionally, it is determined that the methodology as implemented in Serpent is applicable for generating high-order neutron scattering cross sections through at least P3 in fast reactor materials.
During 2017, two vertical drop tests were conducted on two partial sections removed from a Fokker F28 MK4000 aircraft as a part of a joint NASA / Federal Aviation Administration (FAA) effort to investigate the crashworthiness characteristics of Transport Category Aircraft, as defined by 14 Code of Federal Regulations, Part 25. The first test was a pure vertical drop test of a relatively uniform forward section, which included an underfloor area for luggage. The second test was a canted drop test onto a sloped surface of a portion of the fuselage representing the wingbox stiffened structure. In both tests, accelerometers were installed on the floor, seat track, luggage, and overhead bin to measure responses in the two airframe sections. In addition, ten Anthropomorphic Test Devices (ATDs, a.k.a. crash test dummies) were included in each test to measure the potential of onboard occupant injury. Self-contained data recorders, logging accelerations and rotational rates, were also used on the seat tracks and lower structure for evaluation as potential crash recording devices in future tests. Finally, the starboard side of each section was painted with a stochastic black and white speckle pattern for use in full field photogrammetric imaging techniques. The results collected show notable differences in the Forward and Wingbox Section responses. The Forward Section floor accelerations showed a relatively uniform response of approximately 7 g throughout the impact event. This section exhibited large amounts of subfloor crushing, floor stiffener failures and seat deformation upon impact. These results are contrasted by the Wingbox Section accelerations, which showed large differences when comparing accelerations recorded from either the rear or the front portion of the section reaching peaks of 39 g in some locations. Additionally, the Wingbox Section test induced a forward motion caused from the rotation at impact. With the exception of the lower cavity, there was minimal deformation in the Wingbox Section, and ATD responses were consistently higher than those for the Forward Section. A complete set of results are presented for the airframe, seat, ATD, overhead bin, and subfloor regions for each section. The ATD results are compared to current injury criteria, and determinations will be made on the likelihood of injury. Additional results for cargo-hold stored luggage are presented in an attempt to provide a component-level characterization for better understanding of under-floor loading. Finally, a discussion of the relevance of the results for a proposed airframe level crashworthiness guideline are presented.
In this paper, two methods for computing temperature-dependent unresolved resonance region cross sections on-the-fly within continuous-energy Monte Carlo neutron transport simulations are presented. The first method calculates Doppler broadened cross sections directly from zero-temperature average resonance parameters. In a simulation, at each event that requires cross section values, a realization of unresolved resonance parameters is generated about the desired energy and temperature-dependent single-level Breit-Wigner resonance cross sections are computed directly via the analytical Ψ-x Doppler integrals. The second method relies on the generation of equiprobable cross section magnitude bands on an energy-temperature mesh. Within a simulation, the bands are sampled and interpolated in energy and temperature to obtain cross section values on-the-fly. Both of the methods, as well as their underlying calculation procedures, are verified numerically in extensive code-to-code comparisons. Energy-dependent pointwise cross sections calculated with the newly-implemented procedures are shown to be in excellent agreement with those calculated by a widely-used nuclear data processing code. Relative differences at or below 0.1% are observed. Integral criticality benchmark results computed with the proposed methods are shown to reproduce those computed with a state-of-the-art processed nuclear data library very well. In simulations of fast spectrum systems which are highly-sensitive to the representation of cross section data in the unresolved region, k-eigenvalue and neutron flux spectra differences of <10 pcm and <1.0% are observed, respectively. The direct method is demonstrated to be well-suited to the calculation of reference solutions — against which results obtained with a discretized representation may be assessed — as a result of its treatment of the energy, temperature, and cross section magnitude variables as continuous. Also, because there is no pre-processed data to store (only temperature-independent average resonance parameters) the direct method is very memory-efficient. Typically, only a few kB of memory are needed to store all required unresolved region data for a single nuclide. However, depending on the details of a particular simulation, performing URR cross section calculations on-the-fly can significantly increase simulation times. Alternatively, the method of interpolating equiprobable probability bands is demonstrated to produce results that are as accurate as the direct reference solutions, to within arbitrary precision, with high computational efficiency in terms of memory requirements and simulation time. Analyses of a fast spectrum system show that interpolation on a coarse energy-temperature mesh can be used to reproduce reference k-eigenvalue results obtained with cross sections calculated continuously in energy and directly at an exact temperature to within <10 pcm. Probability band data on a mesh encompassing the range of temperatures relevant to reactor analysis usually require around 100 kB of memory per nuclide. Finally, relative to the case in which probability table data generated at a single, desired temperature are used, minor increases in simulation times are observed when probability band interpolation is employed.
In MCNP6.1, materials are constructed by identifying the constituent isotopes (or elements in a few cases) individually. This list selects the corresponding microscopic cross sections calculated from the free-gas model to create the material macroscopic cross sections. The free-gas model and the corresponding material macroscopic cross sections assume that the interactions of atoms do not affect the nuclear cross sections. With certain compounds, the free-gas model cross sections are not sufficient because molecular effects or crystalline structure effects do affect the neutron scattering cross sections at low energies. These effects are included in the MCNP6.1 thermal scattering kernels, or S(α,β) thermal neutron scattering data. To treat a particular isotope (or isotopes) as a molecular compound in the thermal regime, one or more of the available S(α,β) data sets is selected (with the MT card). As MCNP6.1 transports particles, the free-gas model cross sections are used down to the energy where S(α,β) data are available. At that point, the S(α,β) cross sections automatically overrides the free-gas cross sections. Most of the S(α,β) files have a maximum energy of 10 eV. In MCNP6.1, a binary compound may have one or two S(α,β) libraries. Beryllium oxide (BeO) is one of the materials that has two S(α,β) libraries one for the beryllium S(α,β) cross sections (be-o) and one for the oxygen S(α,β) cross sections (o-be). From its moderating properties, it is apparent that the S(α,β) library for the beryllium must be included to accurately model beryllium oxide. The necessity of the S(α,β) library for oxygen is less clear because oxygen is a relatively poor moderator. This paper investigates the effect of using only the be-o S(α,β) library or using both be-o and o-be S(α,β) libraries. The objective is to provide guidance on the use of the beryllium oxide S(α,β) libraries in criticality safety analyses. (authors)
The NACA 6A-series airfoil sections were designed to eliminate the trailing-edge cusp which is characteristic of the NACA 6-series sections. Theoretical data are presented for NACA 6A-series basic thickness forms having the position of minimum pressure at 30-, 40-, and 50-percent chord and with thickness ratios varying from 6 percent to 15 percent. Also presented are data for a mean line designed to maintain straight sides on the cambered sections. The experimental results of a two dimensional wind tunnel investigation of the aerodynamic characteristics of five NACA 64A-series airfoil sections and two NACA 63A-series airfoil sections are presented. An analysis of these results, which were obtained at Reynolds numbers of 3 x 10(exp 6), 6 x 10(exp 6), and 9 x 10(exp 6), indicates that the section minimum drag and maximum lift characteristics of comparable NACA 6-series and 6A-series airfoil sections are essentially the same. The quarter-chord pitching-moment coefficients and angles of zero lift of NACA 6A-series airfoil sections are slightly more negative than those of corresponding NACA 6-series airfoil sections. The position of the aerodynamic center and the lift-curve slope of smooth NACA 6-series sections. The addition of standard leading-edge roughness causes the lift-curve slope of the newer sections to decrease with increasing airfoil thickness ratio.
The Japanese space agency's (JAXA) Hayabusa mission returned the first particulate samples (typically <100micron) from the surface of an asteroid (25143 Itokawa). These precious samples provide important insights into early Solar System processes, but their sizes pose tremendous challenges to coordinated analysis using a variety of nano- and micro-beam techniques. The ability to glean maximal information from individual particles has become increasingly important and depends critically on sample preparation. We developed a hybrid technique combining traditional ultramicrotomy with focused ion beam (FIB) techniques, allowing for more thorough in situ investigations of grain surfaces and interiors. Using this method, we increase the number of FIB-prepared sections that can be recovered from a particle with dimensions on the order of tens of microns. These sections can be subsequently analyzed using a variety of analytical techniques. Particle RA-QD02-0211 is a approx. 40×40×20 micron particle from Itokawa containing olivine and Fe sulfides. It was embedded in low viscosity epoxy and partly sectioned to a depth of approx 10 micron; sections are placed on Cu grids with thin amorphous films for transmission electron microscope (TEM) analyses. With the sample surface partly exposed, the epoxy bullet is trimmed to a height of approx. 5mm to accommodate the allowable dimensions for FIB work (FEI Quanta 600 3D dual beam FIB-SEM). Using a diamond trim knife, the epoxy surrounding the grain is removed on 3 sides (to within a few microns of the grain); the depth of material removed extends well below the bottom of the particle. The sample is attached to an SEM pin mount, the epoxy coated with conductive paint, and the entire assembly coated with approx. 40nm of carbon to eliminate sample charging during FIB work. A protective carbon cap is placed according to the plan for the 15 FIB sections. The central 'spine' of the cap runs perpendicular to the front of the sample, and the 'ribs' protruding from either side run parallel. Each rib indicates the location of a planned FIB section, and the spine contains the final two planned sections. We use a cap with a 4 micron-wide spine and 2micron-wide ribs that have ≳3.5 micron of space between them (narrower cuts result in too much re-deposition of material inside the trenches). Using a 30kV, 3nA ion-beam we expose the front surface of the grain and commence milling trenches between sections. Rather than using the typical C-cut to prepare the sample for lift-out, an L-cut is used instead, leaving the sample connected by an interior tab. tab. Sections are lifted out, attached to TEM grids and thinned to electron transparency. TEM analyses show that our hybrid technique preserves both interior and edge features, including surface modifications from exposure to the space environment, such as damaged rims that form in response to solar wind implantation effects and adhering grains. In addition, the FIB sections provide larger areas that are free of fractures and chatter effects in comparison to the microtome thin sections, thus enabling more accurate measurements of solar flare particle track densities that are used to determine the surface exposure age of the particles.
In March 2017, a vertical drop test of a forward fuselage section of a Fokker F-28 MK4000 aircraft was conducted as part of a joint NASA/FAA project to investigate the performance of transport aircraft under realistic crash conditions. In June 2017, a vertical drop test was conducted of a wing-box fuselage section of the same aircraft. Both sections were configured with two rows of aircraft seats, in a triple-double configuration. A total of ten Anthropomorphic Test Devices (ATDs) were secured in seats using standard lap belt restraints. The forward fuselage section was also configured with luggage in the cargo hold. Both sections were outfitted with two hat racks, each with added ballast mass. The drop tests were performed at the Landing and Impact Research facility located at NASA Langley Research Center in Hampton, Virginia. The measured impact velocity for the forward fuselage section was 346.8-in/s onto soil. The wing-box section was dropped with a downward facing pitch angle onto a sloping soil surface in order to create an induced forward acceleration in the airframe. The vertical impact velocity of the wing-box section was 349.2-in/s. A second objective of this project was to assess the capabilities of finite element simulations to predict the test responses. Finite element models of both fuselage sections were developed for execution in LS-DYNA(Registered Trademark), a commercial explicit nonlinear transient dynamic code. The models contained accurate representations of the airframe structure, the hat racks and hat rack masses, the floor and seat tracks, the luggage in the cargo hold for the forward section, and the detailed under-floor structure in the wing-box section. Initially, concentrated masses were used to represent the inertial properties of the seats, restraints, and ATD occupants. However, later simulations were performed that included finite element representations of the seats, restraints, and ATD occupants. These models were developed to more accurately replicate the seat loading of the floor and to enable prediction of occupant impact responses. Models were executed to generate analytical predictions of airframe responses, which were compared with test data to validate the model. Comparisons of predicted and experimental structural deformation and failures were made. Finally, predicted and experimental soil deformation and crater depths were also compared for both drop test configurations.