Pore-scale reactive transport and flow behavior involving dissolution and precipitation in heterogeneous porous media
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Yoon, Hongkyu↗
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Insights into the hydro-mechanical behavior of a decimeter-scale fracture using the mini-SIMFIP probe
ABSTRACT: Understanding hydro-mechanical couplings in fractured rocks is essential for predicting the rock mass response during high-pressure fluid injection, including the stimulation of enhanced geothermal systems. However, fluid-driven fracture dislocations are challenging to measure due to the need for local displacement data at high fluid pressures. In this study, fluid-driven displacement across a decimeter-scale laboratory fracture was investigated using the mini-SIMFIP (step rate injection method for fracture in-situ properties) probe, which is a smaller version of the SIMFIP tool (Guglielmi et al., 2014). The mini-SIMFIP probe is able to resolve the full 3D displacement vector of a fracture. The probe was installed in one of two boreholes across a decimeter-scale saw-cut granite fracture. Two pressure step injection tests were conducted under the same isotropic stress conditions. By varying injection between the boreholes, we estimated the aperture profile across the fracture. The results show a consistent pressure-dependent opening as long as steady-state flow was maintained. At a certain pressure step, steady-state conditions were no longer achievable and the fracture opened rapidly. The pressure-opening relationship diverged between the two tests and indicated a homogenization of the aperture profile and an increase in the non-linearity of the flow regime.
Osten, J↗
Transport of cosmic rays in the solar corona
A method by which energetic cosmic ray particles in the interplanetary medium can diffuse in solar longitude. The method consists of particle motion occurring along current sheets separating discontinuous field structures in the corona. These sheets can serve as pathways along which energetic particles drift at nearly their propagation speed. A model of the coronal magnetic field and the large scale field behavior are analyzed. A mechanism by which particles can travel across the coronal magnetic field and arrive at the earth is suggested.
Schatten, K. H.↗
A perturbative treatment of motion near the 3/1 commensurability
A semianalytic perturbation theory for motion near the 3/1 commensurability in the planar elliptic restricted three-body problem is presented. The predictions of the theory are in good agreement with the features found on numerically generated surfaces of section; a global understanding of the phase space is achieved. The principal cause of the large chaotic zone near the 3/1 commensurability is identified, and a new criterion for the existence of large-scale chaotic behavior is presented.
Wisdom, J.↗
Functional reasoning in diagnostic problem solving
This work is one facet of an integrated approach to diagnostic problem solving for aircraft and space systems currently under development. The authors are applying a method of modeling and reasoning about deep knowledge based on a functional viewpoint. The approach recognizes a level of device understanding which is intermediate between a compiled level of typical Expert Systems, and a deep level at which large-scale device behavior is derived from known properties of device structure and component behavior. At this intermediate functional level, a device is modeled in three steps. First, a component decomposition of the device is defined. Second, the functionality of each device/subdevice is abstractly identified. Third, the state sequences which implement each function are specified. Given a functional representation and a set of initial conditions, the functional reasoner acts as a consequence finder. The output of the consequence finder can be utilized in diagnostic problem solving. The paper also discussed ways in which this functional approach may find application in the aerospace field.
Sticklen, Jon↗
Relationships between persistent large-scale flow anomalies and variation in synoptic-scale eddy activity and cyclogenesis
Observational analyses to study the relationships between large-scale flow anomalies and variations in synoptic-scale eddy activity and cyclogenesis are presented. The way in which changes in the large-scale flow influence the behavior of synoptic-scale eddies and the way in which changes in eddies may feedback to influence the large-scale flow anomalies are examined. Situations characterized by differing large-scale flows are compared, showing well-defined diferences in synoptic-scale eddy activity. The net forcings of anomalous mean flows by eddies as deduced from tendency methods and E-vector analyses suggest that synoptic-scale eddies may play an important role in maintaining certain anomalous flow patterns such as blocking.
Dole, Randall M.↗
Spatial gradients in the heliospheric magnetic field - Pioneer 11 observations between 1 AU and 24 AU, and over solar cycle 21
The large-scale temporal behavior and spatial gradients in the heliospheric magnetic field were investigated using magnetic field observations by Pioneer 11 and ISEE 3/ICE satellites, including observations out to a radial distance of 24 AU and over a time interval that includes the recent solar minimum. It was found that, to first order, the gradients in the magnetic field magnitude and in the azimutal component agree well with the Parker (1958) model. The analysis of the Pioneer data confirms previous reports of a magnetic field flux deficit of about 1 percent/AU, so that at 20 AU the relative deficit is of the order of 20 percent. It is argued that most of the magnetic field deficit is in the radial gradient.
Winterhalter, Daniel↗
An equation for the evolution of solar and stellar flare loops
An ordinary differential equation describing the evolution of a coronal loop subjected to a spatially uniform but time-varying heating rate is discussed. It is assumed that the duration of heating is long compared to the sound transit time through the loop, which is assumed to have uniform cross section area. The form of the equation changes as the loop evolves through three states: 'strong evaporation', 'scaling law behavior', and 'strong condensation'. Solutions to the equation may be used to compute the time dependence of the average coronal temperature and emission measure for an assumed temporal variation of the flare heating rate. The results computed from the model agree reasonably well with recent published numerical simulations and may be obtained with far less computational effort. The model is then used to study the May 21, 1980, solar flare observed by SMM and the giant April 12, 1985, flare observed on the star AD Leo.
Fisher, George H.↗
Accretion disks in active galactic nuclei - Vertically explicit models
A region of the parameter space accessible to accretion disks in AGN is explored using vertically integrated models to describe the thin-disk structure. Particular attention is paid to the role of convection. From a comparison of strongly convective solutions with varying mixing lengths to solutions obtained using a recent theory of convection developed for accretion disks, it is argued that it may be appropriate to take the mixing length to be roughly one-third of a pressure scale height when applying standard mixing-length theory to disks. Scalings are presented for various critical points in the locus of steady-state solutions, and rough estimates of time scales for behavior associated with disk instability are provided.
Cannizzo, John K.↗
An Overview of Research Activity at the Launch Systems Testbed
This paper summarizes the acoustic testing and analysis activities at the Launch System Testbed (LST) of Kennedy Space Center (KSC). A major goal is to develop passive methods of mitigation of sound from rocket exhaust jets with ducted systems devoid of traditional water injection. Current testing efforts are concerned with the launch-induced vibroacoustic behavior of scaled exhaust jets. Numerical simulations are also developed to study the sound propagation from supersonic jets in free air and through enclosed ducts. Scaling laws accounting for the effects of important parameters such as jet Mach number, jet velocity, and jet temperature on the far-field noise are investigated in order to deduce full-scale environment from small-scale tests.
Vu, Bruce↗
Engineering Feasibility and Trade Studies for the NASA/VSGC MicroMaps Space Mission
Knowledge of airborne CO concentrations is critical for accurate scientific prediction of global scale atmospheric behavior. MicroMaps is an existing NASA owned gas filter radiometer instrument designed for space-based measurement of atmospheric CO vertical profiles. Due to programmatic changes, the instrument does not have access to the space environment and is in storage. MicroMaps hardware has significant potential for filling a critical scientific need, thus motivating concept studies for new and innovative scientific spaceflight missions that would leverage the MicroMaps heritage and investment, and contribute to new CO distribution data. This report describes engineering feasibility and trade studies for the NASA/VSGC MicroMaps Space Mission. Conceptual studies encompass: 1) overall mission analysis and synthesis methodology, 2) major subsystem studies and detailed requirements development for an orbital platform option consisting of a small, single purpose spacecraft, 3) assessment of orbital platform option consisting of the International Space Station, and 4) survey of potential launch opportunities for gaining assess to orbit. Investigations are of a preliminary first-order nature. Results and recommendations from these activities are envisioned to support future MicroMaps Mission design decisions regarding program down select options leading to more advanced and mature phases.
Abdelkhalik, Ossama O.↗
Formation and Growth of Micro and Macro Bubbles on Copper-Graphite Composite Surfaces
Micro scale boiling behavior in the vicinity of graphite micro-fiber tips on the coppergraphite composite boiling surfaces is investigated. It is discovered that a large number of micro bubbles are formed first at the micro scratches and cavities on the copper matrix in pool boiling. In virtue of the non-wetting property of graphite, once the growing micro bubbles touch the graphite tips, the micro bubbles are sucked by the tips and merged into larger micro bubbles sitting on the tips. The micro bubbles grow rapidly and coalesce to form macro bubbles, each of which sitting on several tips. The growth processes of the micro and macro bubbles are analyzed and formulated followed by an analysis of bubble departure on the composite surfaces. Based on these analyses, the enhancement mechanism of the pool boiling heat transfer on the composite surfaces is clearly revealed. Experimental results of pool boiling heat transfer both for water and Freon-113 on the composite surfaces convincingly demonstrate the enhancement effects of the unique structure of Cu-Gr composite surfaces on boiling heat transfer.
Chao, David F.↗
Model Development of Large-Scale Spacecraft Fires During the Saffire-IV Experiments
An accidental fire can pose dire consequences to crew safety and mission success. The Saffire Project aims to investigate large-scale fire behavior in microgravity in order to aid in the prediction of spacecraft fires. These series of experiments ignite solid materials within the Northrup Grumman Cygnus vehicle after it departs from a resupply mission to the International Space Station. A model of the Cygnus vehicle during the Saffire-IV experiment was developed using the commercial software PyroSim. The cargo arranged during the descent phase was used for the geometry of the model. In the model, cabin air flows into the Saffire payload while heat and combustion species flow out of the Saffire downstream through a standoff to a bed of sensors called the Far Field Diagnostic (FFD). The temperature sensors near the Saffire payload were used to determine the heat release rate at the outlet of Saffire, while the details of the combustion and stoichiometry are used to determine the species flow at the outlet. Gas measurements previously reported for the Saffire-IV experiments are compared against the simulation results and sources of error are discussed.
Modeling↗
LECTURE 8: Understanding Global Cloud Radiative Impacts
The influence of clouds on the radiation budget is one of the most important facets of the Earth’s climate. Satellite observations in the last 35 years have helped us understand the bulk radiative effects of different classes of clouds. Bill Rossow has spearheaded efforts in that direction, demonstrating the value of the International Satellite Cloud Climatology Project (ISCCP) cloud retrievals as a foundation for the full reconstruction of Earth’s Radiation Budget components. This main aim of this document is to provide an overview of the global radiative impacts of clouds at annual time scales. While geographical and seasonal aspects receive some attention, it is cloud radiative effect decomposition by cloud category (or“class” ) that is the main focal point. Furthermore, this document addresses the large-scale radiative behavior of clouds only for the current climate, with no further discussion of how this behavior may change in the future and what its climatic impact may be [please refer to Del Genio (2018) for an excellent overview of this topic]. Cloud classes can be defined in many ways, and are often referred to with terms such as “cloud type”and “cloud regime”. Some of the definitions are more meaningful at the level of individual instrument footprints (“pixels” for passive or “rays” for active satellite observations) while others for larger areas (e.g., “mesoscale”).This distinction will become apparent below.
Lazaros Oreopoulos↗
Softening the Gap between Wöhler and Paris – New Approaches for Fatigue Analysis –
Fatigue analysis tools can vary across industries. For example, automotive engineers often use the Wöhler (S-N) approach to design for safe-life, while aerospace engineers prioritize damage tolerance and inspection intervals, relying instead on crack growth models such as Paris’ law. Although both approaches may deal with the control of cracks in similar materials, their analysis tools and material characterizations are fundamentally distinct. This divide mirrors the classic split between stress-based strength analysis and linear elastic fracture mechanics. However, modern nonlinear models that incorporate material softening, such as cohesive laws, blur this boundary and capture fracture behaviors across scales. This presentation describes the CF23 fatigue model, which uses cohesive softening to link S-N crack initiation with crack propagation rates. CF23 spans the full fatigue spectrum, from initial propagation transients to steady-state growth and threshold conditions, offering a unified framework that bridges Wöhler and Paris-based methodologies. Example applications include fatigue crack propagation transients in adhesive interfaces and skin/stiffener separation.
cohesive elements↗
Femto-second Laser’s Enabling New Length Scale Fabrications for Rapid Post Irradiation Examination of Materials: Concluding LDRD Project Poster
Mechanical testing campaigns are required to qualify materials for advanced reactor conditions, yet economical and safety limitations restrict the number of standardized mechanical tests that can be performed. Reducing the size of the sample is one approach to addressing these challenges and to accelerating testing. Previous research has shown that smaller mechanical test samples produce higher yield and ultimate stress values compared to values measured from standard sample sizes: the “smaller is stronger” effect. Specimens used in accelerated material testing campaigns must reflect bulk material performance to enable engineering scale material property measurement. The objective of this research project was to determine if engineering scale mechanical behavior—the yield stress—could be measured with micro-tensile test samples smaller than traditional standard testing geometries. The relationship between yield stress and sample size was explored with two different nuclear-relevant structural materials: Zircaloy-4 and tungsten. Mechanical testing of both metals demonstrated decreasing yield stress values with increasing sample gauge size across three different sizes. Yield stress values from the largest gauge size, fabricated with a femto-second laser ablation system, approach bulk material yield stress values reported in published literature. Preliminary analysis of the tungsten samples indicates the yield stress value depends on the grain characteristics within the gauge section, in addition to the gauge size. Accompanying modeling efforts, including response surface generation and crystal plasticity approaches, further demonstrated that the size of the sample gauge section alone cannot explain the change in yield stress values.
36 MATERIALS SCIENCE↗
Machine Learning based Correlation of the Mechanical Properties of Sub-sized and Standard-sized Specimens
Mechanical testing with sub-sized specimens is essential in the nuclear industry, offering the ability to conduct tests in confined spaces with lower irradiation and expediting material qualification. However, smaller specimens exhibit different material behavior across scales, a phenomenon known as the "specimen size effect". In this study, we compiled over 1,000 tensile testing records, covering 54 parameters such as material type, composition, manufacturing details, irradiation conditions, specimen dimensions, and tensile properties through a comprehensive literature review. We focus on correlating sub-sized and standard specimens’ tensile mechanical properties on SS316 alloy, which has the most extensive dataset available. We explore ML-based models and uncertainty quantification for tensile properties, analyze key factors influencing these properties, and compare the effectiveness of ML models with existing analytical methods in addressing the specimen size effect.
tensile properties↗