Physical Sciences and Mathematics Commons^™

Suspended Sediment Size Distribution In A Numerical Sediment Transport Model For A Partially-Mixed Estaury, Danielle Tarpley, Courtney Harris, Carl Friedrichs

Presentations

Particle settling velocity impacts the transport of suspended sediment to the first order but fine-grained material like muds tend to form loosely bound aggregates (flocs) whose settling velocity can vary widely. Properties of flocculated sediment such as settling velocity and particle density are difficult to predict because they change in response to several factors including salinity, suspended sediment concentration, turbulent mixing, and organic content. Knowledge of the mechanisms governing flocculation of cohesive sediment is rapidly expanding; especially in response to recent technical advances. As the understanding of particle dynamics progresses, numerical models describing flocculation and break-up are being developed with …

Fractal Floc Size, Density, Settling Velocity, And Implications For Water Clarity In Partially Mixed-Estuaries: The Role Of Small, Organic-Rich Particles, Kelsey Fall, Carl Friedrichs, Grace M. Massey, Jessie Turner

Presentations

Typical near-surface estuarine particles are not single solid particles, but clusters of inorganic and organic particles and water, called flocs. Floc properties that influence water clarity (such as size, composition, density and settling velocity) are challenging to observe in-situ, so their influence on the optical properties of the system is not well understood. The preliminary results presented here are part of a larger effort utilizing a combination of particle imaging equipment, water sampling, and optical instrumentation to measure important floc properties, to investigate the influence of organic particles and local hydrodynamics on those properties, and to evaluate the influence of …

Street-Level Inundation Modeling Of Hurricanes Matthew And Hermine And Emerging Flood Monitoring Methods In Hampton Roads, Jon Derek Loftis, H. V. Wang, D R. Forrest

Presentations

No abstract provided.

Plasma Deflection Test Setup For E-Sail Propulsion Concept, Allen Andersen, Jason Vaughn, Todd Schneider, Ken Wright

Presentations

The Electronic Sail or E-Sail is a novel propulsion concept based on momentum exchange between fast solar wind protons and the plasma sheath of long positively charged conductors comprising the E-Sail. The effective sail area increases with decreasing plasma density allowing an E-Sail craft to continue to accelerate at predicted ranges well beyond the capabilities of existing electronic or chemical propulsion spacecraft. While negatively charged conductors in plasmas have been extensively studied and flown, the interaction between plasma and a positively charged conductor is not well studied. We present a plasma deflection test method using a differential ion flux probe …

Space Environment Effects Of Ionizing Radiation On Seed Germination And Growth, Alex Souvall, Takuyuki Sakai, Takahiro Shimizu, Yuta Takahashi, Midori Morikawa, Shusuke Okita, Akihiro Nagata, Toshihiro Kameda, Shaunda Wenger, Jr Dennison

Presentations

An initial limited set of tests of germination rate and seed growth in a controlled environment have identified statistically significant differences between control samples and seed flown in a Russian LEO research flight. Most significantly, average seed germination of space borne seeds was 2 days less than the 6 days for the control seeds. Modification of the seed coat leading to enhanced rate of water uptake, as a result of radiation from the space environment or abrasion due to launch vibrations, is hypothesized to cause early germination. High school students will conduct growth tests on seeds exposed to simulated space …

Fractal Floc Size, Settling Velocity And Implications For Water Clarity In Partially Mixed-Estuaries: The Role Of Small, Organic-Rich Particles, Kelsey Fall, Carl Friedrichs, Grace M. Cartwright, D.G. Bowers

Presentations

Observations and analysis presented here suggest that properties of suspended particulate matter (SPM) in the water column of partially mixed estuaries, including floc size and settling velocity, are strongly related to the relative concentrations of inorganic versus organic matter in suspension. In regions with high inorganic SPM concentrations, addition of organic matter tends to increase the median size and settling velocity of flocs, removing both organic and inorganic SPM from the water column and enhancing water clarity relative to that in the absence of organics. In contrast, in regions with lower inorganic SPM concentration, suspended organic matter appears to decrease …

In Situ Differentiation Among Suspended Primary Particles, Resilient Pellets And Flocs Of Similar Size Using A Particle Image Camera System (Pics) In A Muddy Estuary, Grace M. Massey, Kelsey Fall, Carl Friedrichs, S.J. Smith

Presentations

No abstract provided.

Relationships Among Estuarine Floc Size, Optical Properties, Organic Content, And Settling Velocity: Insights Gained From Combining Lisst And A Particle Imaging Camera System, Kelsey Fall, Carl Friedrichs, Grace M. Cartwright, D.G. Bowers

Presentations

No abstract provided.

Self-Burial Of Objects On Sandy Beds By Wave- And Current-Induced Scour, Carl Friedrichs, S.E. Rennie, A. Brandt

Presentations

When an object sitting on the bed extends above the surrounding bed roughness, the object will alter the local flow pattern relative to the far field boundary layer. Such perturbations increase the velocities and stresses impinging on sediment immediately adjacent to the object. Nearby grains tend to be dispersed, resulting in a scour pit that deepens until the tendency for sediment to be dispersed is balanced by a tendency for sediment to fall back into the pit. The difference in pressure at the bed upstream and downstream of the object may also drive seepage flow which can cause piping and …

Comt Chesapeake Bay Hypoxia Modeling, M.A.M. Friedrichs, Carl T. Friedrichs, M. Scully, I. Irby, Comt Estaurine Hypoxia Team

Presentations

No abstract provided.

Comparison Of Modeled And Observed Bed Erodibility In The York River Estuary, Virginia, Over Varying Time Scale, Danielle Tarpley, Courtney Harris, Carl Friedrichs

Presentations

In general, the availability of sediment for transport increases with the magnitude of bed shear stress, which varies over various temporal and spatial scales. However, in a muddy setting, consolidation or swelling of the bed also contributes to fluctuations in sediment mobility. One such environment is the York River estuary, a partiallymixed tidal tributary of the Chesapeake Bay, USA. The York River often has a Secondary Turbidity Maximum (STM) mid-estuary at the transition from a shallower, less stratified section upstream to a deeper, more stratified section downstream. Since 2006 various instrument arrays have been deployed as part of the Multidisciplinary …

Us-Ioos/Comt Estuarine Hypoxia Nowcast/Forecast Product: Identification And Feedback, Carl T. Friedrichs, Marjorie A.M. Friedrichs, David R. Forrest, R.R. Hood

Presentations

The Estuarine Hypoxia component of the U.S. Integrated Ocean Observing System (US-IOOS) Coastal and Ocean Modeling Testbed (COMT) is evaluating existing hydrodynamic and water quality models used or likely to be used for operations and/or for regulation in the Chesapeake Bay and other, similar estuarine environments. The outcomes of this work are expected to help with the development of operational hypoxia forecast capabilities for the Bay. As a proof-of-concept, the ChesROMS hydrodynamic model, linked to a 1-term constant respiration equation for dissolved oxygen (DO), is presently being used to produce realtime now-casts and shortterm (3-day) forecasts of DO for the …

Consolidation And Stratification Within A Muddy, Partially Mixed Estuary: A Comparison Between Idealized And Realistic Models For Sediment Transport In The York River Estuary, Virginia, Danielle Tarpley, Courtney Harris, Carl Friedrichs

Presentations

The York River estuary is a partially mixed semi-diurnal tidal tributary of the Chesapeake Bay with salinities ranging from 0 to 26 psu and an ~0.8 m tidal range. Sediment within many estuaries, including the York River, Virginia, is dominated by mixtures of mud. Due to its cohesive nature, estimating sediment fluxes for mud is a complex problem that can be addressed using numerical models such as the Community Sediment Transport Modeling System (CSTMS), which incorporates suspended sediment transport, erosion, and deposition within the hydrodynamic Regional Ocean Modeling System (ROMS). One version of the CSTMS accounts for cohesive processes via …

Instrumentation Enhancements For Electron Yield Measurements Of Extremely Low-Conductivity High-Yield Dielectrics, Justin Christensen, Gregory Wilson, Jr Dennison

Presentations

Electron yield, a material dependent property which describes how it will charge under incident electron irradiation of a given energy, is defined as the number of electrons emitted from a material per incident electron. While very important for spacecraft charging modelling, the measurement of electron yield for insulating materials is very challenging because insulators quickly charge up under electron irradiation, thereby modifying the yield measurements.

Improved techniques have been implemented to reduce charging with each yield measurement, as well as to neutralize acquired charge between measurements. The goal is to determine the “intrinsic yield” (yield of uncharged insulator). New analysis …

Identification Of Suspended Resilient Pellets In Particles Tracked By A Particle Image Camera System (Pics) In A Muddy Estuary, Grace M. Massey, Kelsey Fall, Carl Friedrichs, S.J. Smith

Presentations

No abstract provided.

Hypoxia Forecasts As A Tool For Chesapeake Bay Fisheries, Marjorie A.M. Friedrichs, Carl T. Friedrichs, David R. Forrest, R.R. Hood

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No abstract provided.

Determining Intrinsic Electron Emission Yields Of High Resistivity Ceramic Materials, Jr Dennison, Justin Christensen, Justin Dekany

Presentations

We describe and contrast methods for measuring the intrinsic—or zero-accumulated charge limit—electron emission yields of highly insulating materials with relatively large yields. The intrinsic electron yield is an essential measure of how charge will accumulate in such materials exposed to space environment fluxes and for predicting and mitigating spacecraft charging effects. There are three commonly used methods to determine the intrinsic electron yield: (i) the DC-yield method, which ratios constant incident and emission currents; (ii) the pulsed-yield method, which ratios integrated charge of short-duration, low-current pulses, thereby minimizing the amount of charge being deposited into the material during a measurement, …

Extremely Low Secondary Electron Emission From Metal/Dielectric Particulate Coatings, Isabel Montero, L Aguilera, Leandro Olano, María E. Dávila, Luis Galán, Jr Dennison, Gregory Wilson

Presentations

Research on low secondary electron emission coatings is essential for the design and manufacture of space high-power RF devices without multipactor discharge. This paper discusses some of the factors that reduce secondary electron emission for metal-dielectric surfaces. We have studied the total electron yield (TEY) behavior of a particulate coating composed of a mixture of a metal (aluminum) nanoparticulates in solid state contact with a particulate dielectric material (polyimide thermosetting resin). Surface charging, roughness, and volume fraction are utilized as the main parameters to characterize the electron emission behavior, which can effectively be determined by continuous (total dose 42.5 nC/mm …

Validation Of Enhanced Electron Yield Measurements Of Low-Conductivity, High-Yield Materials, Justin Christensen, Gregory Wilson, Jr Dennison

Presentations

Materials exposed to electron bombardment can charge positively or negatively, depending on the number of electrons ejected from the material. This electron emission is the main mechanism which drives spacecraft charging, which can induce electrostatic breakdown of insulators and damage pertinent electrical, optical, and mechanical components. The electron yield (ratio of emitted to incident electrons) is an intrinsic property which characterizes how a material will charge under these types of conditions. However electron yield of insulators is very difficult to measure because measurement causes charge buildup.

To measure the intrinsic yield (yield of uncharged material) of insulators new methods have …

Perspectives On The Distributions Of Esd Breakdowns For Spacecraft Charging Applications, Allen Andersen, Krysta Moser, Jr Dennison

Presentations

Electrostatic discharge (ESD) continues to pose significant risks to space missions despite decades of intense study. We emphasize here the advantages to spacecraft designers and modelers from considering the stochastic distributions of breakdown and how it can be affected by factors including spacecraft environment conditions, design geometries, material temperature, material purity, charging history, and appropriate timescales. Spacecraft charging models and spacecraft designs typically rely on tabulated values or ranges of breakdown strength, often based on cursory measurements with little or no experimental detail. Depending on the timescales and history of environmental and orbital changes or durations of specific missions, it …

Dependence Of Electrostatic Field Strength On Voltage Ramp Rate For Spacecraft Materials, Krysta Moser, Allen Andersen, Jr Dennison

Presentations

This work investigated the dependence of electrostatic field strength for spacecraft materials on voltage ramp rate, by applying an increasing electrostatic field until electrostatic breakdown (a permanent, catastrophic failure of a dielectric material) occurs. Enhanced understanding of prolonged exposure to high static electric fields (DC aging) of insulating materials based on expanded experimental studies is of critical to understand the physics of highly disordered insulating materials, as well as for applications in spacecraft charging, high voltage DC power transmission cables and switching, thin film dielectrics, and semiconductor devices and sensors. Electrostatic discharge (ESD) and the associated material breakdown at the …

Pea System Modeling And Signal Processing For Measurement Of Volume Charge Distributions In Thin Dielectric Films, Lee H. Pearson, Jr Dennison, Erick W. Griffiths, A. C. Pearson

Presentations

This paper discusses an effort to develop advanced pulsed electroacoustic (PEA) measurement system capabilities that incorporate state-of-the-art hardware and improved signal processing and modeling to characterize embedded charge distributions in thin dielectric films. Objectives in developing this system include: (1) improved spatial resolution, while maintaining reasonable temporal resolution; (2) improved signal processing tools for increased signal/noise ratios; (3) integrated PEA modeling tools; and (4) integrated environmental controls. We emphasize system improvements required to achieve high spatial resolution for in vacuo measurements of thin dielectrics charged using electron beam injection, which are most applicable for spacecraft charging tests. PEA measurement systems …

Absolute Electron Emission Calibration: Round Robin Tests Of Au And Polyimide, Jr Dennison, Justin Christensen, Justin Dekany, Clint Thomson, Neal Nickles, Robert E. Davies, Mohamed Belhai, Kazuhiro Toyoda, Arifur R. Khan, Kazutaka Kawasaki, Shunsuke Inoue, Isabel Montero, Maria E. Davila, Leandro Olano

Presentations

Accurate determination of the absolute electron yields of conducting and insulating materials are essential for models of spacecraft charging and related processes involving charge accumulation and emission due to electron beams and plasmas. Apparatus using low-fluence pulsed electron beam sources and various methods to minimize charge accumulation have been developed at facilities around the world. This study presents a round robin comparison of such tests performed in CSIC at Instituto de Ciencia de Materiales de Madrid, LaSeine at Kyushu Institute of Technology, DESSE at ONEREA, and the Space Environment Effects Materials (SEEM) test facility at Utah State University. The primary …

Temporal And Spatial Correlations In Electron-Induced Arcs Of Adjacent Dielectric Islands, Justin Christensen, Jr Dennison, Justin Dekany

Presentations

This study investigates very short duration (

The data for this project were collected at Marshall Space Flight Center. The epoxy “glue dot” samples were mounted inside a high vacuum (<10^-4 Pa) chamber on a Black Kapton substrate attached to a large grounded metal plate, cooled with liquid nitrogen to ~120 K. An electron gun was used to bombard the sample with electrons of a known energy (12 to 40 keV) and flux density (0.3 to 5 nA/cm²), similar to what would be seen in a typical space environment. Light emitted from the samples was monitored with …

Examining Spring-Neap Cycle Variation In Bed Erodibility In The York River Estuary, Va: A Numerical Study, Danielle Tarpley, Courtney Harris, Carl Friedrichs

Presentations

The York River estuary is categorized as micro-tidal with a tidal range ~0.8 m; however, periodically produce enough shear stress to erode sediment from the bed and redistribute it along the estuary. However, the supply of mobile sediment differs over various temporal and spatial scales. The primary focus here is to examine the tidal variation in bed mobility by comparing variations in bed erodibility over the spring-neap cycle. To accomplish this goal, the Community Sediment Transport Modeling System (CSTMS) is implemented in a three-dimensional domain using the Regional Ocean Modeling System (ROMS). This version of the CSTMS accounts for suspended …

Influence Of Suspended Particle Properties On Optical Properties And Resultant Water Clarity Along A Partially-Mixed Estuary, York River, Virginia, Usa, Kelsey Fall, Carl Friedrichs, Grace M. Cartwright, David Bowers

Presentations

The Chesapeake Bay and its associated tidal tributaries are among the many coastal systems where degraded water clarity is a major concern. Despite long-term decreases in sediment input, water clarity has continued to deteriorate, especially in the southern Bay. Here it is proposed that the disconnect between water clarity and sediment input is related to the dynamic nature of locally suspended estuarine particles, as well as the interaction between suspended organic particles and inorganic solids. Typical estuarine particles are not single solid particles, but clusters of inorganic and organic particles and water (i.e., flocs). Floc properties (such as size, composition, …

What Controls Bed Erodibility In Muddy, Partially-Mixed Estuaries? Insights From The York River, Virginia, Carl Friedrichs, Grace M. Cartwright, P.J. Dickhudt, Kelsey Fall

Presentations

Appropriate parameterization of time-dependent erodibility of muddy seabeds is a significant barrier to improved understanding and accurate modeling of sediment dynamics in estuaries and other coastal regions. In an effort to better understand controls on muddy seabed erodibility, bed erodibility and associated bed sediment properties have been measured by our group on cores collected on dozens of cruises over the last decade in the York Estuary. We have also inferred time-varying erodibility indirectly in the York Estuary over several years by vertically integrating observations of tidally-varying suspended sediment concentration. This presentation synthesizes the results of these long-term observations in this …

Controls On Suspended Particle Properties And Water Clarity Along A Partially-Mixed Estuary, York River, Virginia, Kelsey Fall, Carl Friedrichs, Grace M. Cartwright, David Bowers

Presentations

The Chesapeake Bay and its associated tidal tributaries, which together form one of the United States’ largest and most important estuaries, are among the many coastal systems where degraded water clarity is a major concern. Despite long-term decreases in sediment input, water clarity has continued to deteriorate in the southern Bay. Paradoxically, clarity has declined less in the northern Bay where riverine sediment load has recently increased. Here it is proposed that the disconnect between water clarity and sediment input is related to the dynamic nature of locally suspended estuarine particles, as well as the interaction between suspended organic particles …

What Controls Bed Erodibility In Muddy, Partially-Mixed Estuaries? Insights From The York River, Virginia, Carl Friedrichs, Grace M. Cartwright, P.J. Dickhudt, Kelsey Fall

Presentations

Appropriate parameterization of time-dependent erodibility of muddy seabeds is a significant barrier to improved understanding and accurate modeling of sediment dynamics in estuaries and other coastal regions. In an effort to better understand controls on muddy seabed erodibility, bed erodibility and associated bed sediment properties have been measured by our group on cores collected on dozens of cruises over the last decade in the York Estuary. We have also inferred time-varying erodibility indirectly in the York Estuary over several years by vertically integrating observations of tidally-varying suspended sediment concentration. This presentation synthesizes the results of these long-term observations in this …

Evaluating The Effects Of Cohesive Processes On Sediment Distribution In An Idealized, Partially-Mixed Estuary Using A Numerical Model, Danielle Tarpley, Courtney Harris, Carl Friedrichs

Presentations

An idealized two-dimensional model is designed to represent a longitudinal section of a partially-mixed estuary, accounting for a freshwater source, tides, and estuarine circulation, but neglecting across-channel variations. The Community Sediment Transport Modeling System (CSTMS) is used to simulate suspended transport, erosion, and deposition within the Regional Ocean Modeling System (ROMS). This version of the model also includes cohesive processes such as consolidation and swelling of the sediment bed; sediment-induced stratification; and variable settling velocities. To better understand the processes controlling fine-grained sediment transport in the York River, VA, the primary features of the idealized estuary mimic that system, and …