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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Management of Irradiated Control Rods: Cost of an Industrial Approach - 18009

This paper concerns the sorting of irradiated control rods that can be done to limit the volume of Intermediate Level Long-lived Waste. More specifically it assesses the cost of an industrial approach. For this we used numerical simulations, penalizing hypotheses and measurements. The cost is given in term of the increased volume of the control rods placed into deep geological storage. To calculate the radioactive inventories, we have developed a calculation scheme which includes a mapping of the neutron flux, a calculation of the isotopic compositions evolution, and a validation of the results. For the state of the art simulations, all operational fuel loading patterns were considered and coupled with all effective power distributions. The analysis of the calculated results shows that the simulations produce a slight overestimation of the measurements. For envelope simulations, penalizing fuel loading patterns and nominal power distribution conditions were used. Most of the radionuclides needed to declare the radiological inventories are difficult to measure. Therefore, for each radionuclide a scaling factor referred to a key radionuclide, can be calculated. Then during the dismantling operations these calculated scaling factors are multiplied by the measured key radionuclide to determine the radiological inventory. The industrial approach consists of combining envelope simulations with scaling factors. Applied to PWR control rods, the industrial approach overestimates the radiological inventories by a factor of 2. As such, the calculated position of the Intermediate Level Long Lived part limit moves +6 cm. Compared to the 1 meter of the control rod pins classified as Intermediate Level Long Lived, the industrial approach would increase by 6 % the volume of the control rods placed into the deep geological storage. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

$\mathrm{IH}$-$\mathrm{GAN}$: A conditional generative model for implicit surface-based inverse design of cellular structures

Variable-density cellular structures can overcome connectivity and manufacturability issues of topologically optimized structures, particularly those represented as discrete density maps. However, the optimization of such cellular structures is challenging due to the multiscale design problem. Past work addressing this problem generally either only optimizes the volume fraction of single-type unit cells but ignoring the effects of unit cell geometry on properties, or considers the geometry–property relation but builds this relation via heuristics. In contrast, we propose a simple yet more principled way to accurately model the property to geometry mapping using a conditional deep generative model, named Inverse Homogenization Generative Adversarial Network (IH-GAN). It learns the conditional distribution of unit cell geometries given properties and can realize the one-to-many mapping from properties to geometries. Here we further reduce the complexity of IH-GAN by using the implicit function parameterization to represent unit cell geometries. Results show that our method can 1) generate various unit cells that satisfy given material properties with high accuracy (R 2 -scores between target properties and properties of generated unit cells >98%) and 2) improve the optimized structural performance over the conventional variable-density single-type structure. In the minimum compliance example, our IH-GAN generated structure achieves a 79.7% reduction in concentrated stress and an extra 3.03% reduction in displacement. In the target deformation examples, our IH-GAN generated structure reduces the target matching error by 86.4% and 79.6% for two test cases, respectively. We also demonstrated that the connectivity issue for multi-type unit cells can be solved by transition layer blending.

42 ENGINEERING↗
DOE OSTI2017

Intramolecular Interactions Overcome Hydration to Drive the Collapse Transition of Gly 15

Simulations and experiments show oligo-glycines, polypeptides lacking any side chains, can collapse in water. We assess the hydration thermodynamics of this collapse by calculating the hydration free energy at each of the end points of the reaction coordinate, here taken as the end-to-end distance (r) in the chain. To examine the role of the various conformations for a given r, we study the conditional distribution, P(R g |r), of the radius of gyration for a given value of r. The free energy change versus Rg, -k B T ln P(R g |r), is found to vary more gently compared to the corresponding variation in the excess hydration free energy. Using this observation within a multistate generalization of the potential distribution theorem, we calculate a tight upper bound for the hydration free energy of the peptide for a given r. On this basis, we find that peptide hydration greatly favors the expanded state of the chain, despite primitive hydrophobic effects favoring chain collapse. The net free energy of collapse is seen to be a delicate balance between opposing intrapeptide and hydration effects, with intrapeptide contributions favoring collapse.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Meteorological Drivers of North American Monsoon Extreme Precipitation Events

Abstract In this paper the meteorological drivers of North American Monsoon (NAM) extreme precipitation events (EPEs) are identified and analyzed. First, the NAM area and its subregions are distinguished using self‐organizing maps applied to the Climate Prediction Center global precipitation data set. This reveals distinct subregions, shaped by the inhomogeneous geographic features of the NAM area, with distinct extreme precipitation character and drivers. Next, defining EPEs as days when subregion‐mean precipitation exceeds the 95th percentile of rainy days, five synoptic features and one mesoscale feature are investigated as potential drivers of EPEs. Essentially all EPEs can be associated with at least one selected driver, with only one event remaining unclassified. This analysis shows the dominant role of Gulf of California moisture surges, mesoscale convective systems and frontal systems in generating NAM extreme precipitation. Finally, a frequency and probability analysis is conducted to contrast precipitation distributions conditioned on the associated meteorological drivers. The findings demonstrate that the co‐occurrence of multiple features does not necessarily enhance the EPE probability.

Meteorology & Atmospheric Sciences↗
DOE OSTI2023

Bayesian-Motivated Probabilistic Model of Hurricane-Induced Multimechanism Flood Hazards

Multimechanism floods (MMFs) are caused by the simultaneous occurrence of more than one flood mechanism such as storm surge, precipitation, tides, and waves. MMFs can lead to more severe or differing impacts than single-mechanism floods. As a result, comprehensive risk assessments require the ability to assess the multivariate probabilistic behaviors of hazards from MMFs. Here this study introduces a novel Bayesian-motivated approach for the probabilistic assessment of hurricane-induced hazards from the combination of the surge, precipitation, tides, and river antecedent flow. A Bayesian network (BN) is developed to capture the physical (conditional) relationship between variables and facilitate the generation of a hazard curve for river discharge that captures the contributions from multiple flood drivers. A case study located along the Delaware River is used to illustrate the proposed approach. Five computationally efficient representative predictive models are developed to estimate the conditional distributions required for the BN as a means of demonstrating the overall framework. The predictive models used in this study act as placeholders and can be replaced with more sophisticated and high-fidelity models depending on the desired accuracy level. While the predictive models are intended to be representative and illustrative, the model performance is evaluated using three historical storms that affected the area. Overall, the proposed framework is shown to be transparent, effective, and adaptable.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Differentially Private Synthesis and Sharing of Network Data Via Bayesian Exponential Random Graph Models

Abstract Network data often contain sensitive relational information. One approach to protecting sensitive information while offering flexibility for network analysis is to share synthesized networks based on the information in originally observed networks. We employ differential privacy (DP) and exponential random graph models (ERGMs) and propose the DP-ERGM method to synthesize network data. We apply DP-ERGM to two real-world networks. We then compare the utility of synthesized networks generated by DP-ERGM, the DyadWise Randomized Response (DWRR) approach, and the Synthesis through Conditional distribution of Edge given nodal Attribute (SCEA) approach. In general, the results suggest that DP-ERGM preserves the original information significantly better than two other approaches in network structural statistics and inference for ERGMs and latent space models. Furthermore, DP-ERGM satisfies node DP through modeling the global network structure with ERGM, a stronger notion of privacy than the edge DP under which DWRR and SCEA operate.

graph synthesis↗
DOE OSTI2024

Fate of supernova progenitors in massive binary systems

ABSTRACT How massive stars end their lives depends on the core mass, core angular momentum, and hydrogen envelopes at death. However, these key physical facets of stellar evolution can be severely affected by binary interactions. In turn, the effectiveness of binary interactions itself varies greatly depending on the initial conditions of the binaries, making the situation much more complex. We investigate systematically how binary interactions influence core–collapse progenitors and their fates. Binary evolution simulations are performed to survey the parameter space of supernova progenitors in solar metallicity binary systems and to delineate major evolutionary paths. We first study fixed binary mass ratios ($q=M_2/M_1$ = 0.5, 0.7, and 0.9) to elucidate the impacts of initial mass and initial separation on the outcomes, treating separately Type Ibc supernova, Type II supernova, accretion-induced collapse (AIC), rapidly rotating supernova (Ibc-R), black hole formation, and long gamma ray burst (long GRB). We then conduct 12 binary population synthesis model calculations, varying the initial condition distributions and binary evolution parameters, to estimate various supernova fractions. We obtain a Milky Way supernova rate $R_{\rm SN} = (1.78$–$2.47) \times 10^{-2} \, {\rm yr}^{-1}$ which is consistent with observations. We find the rates of AIC, Ibc-R, and long GRB to be $\sim 1/100$ the rate of regular supernovae. Our estimated long GRB rates are higher than the observed long GRB rate and close to the low luminosity GRB rate, although care must be taken considering our models are computed with solar metallicity. Furthering binary modelling and improving the inputs one by one will enable more detailed studies of these and other transients associated with massive stars.

Astronomy & Astrophysics↗
DOE OSTI2021

Leveraging Topological Events in Tracking Graphs for Understanding Particle Diffusion

Abstract Single particle tracking (SPT) of fluorescent molecules provides significant insights into the diffusion and relative motion of tagged proteins and other structures of interest in biology. However, despite the latest advances in high‐resolution microscopy, individual particles are typically not distinguished from clusters of particles. This lack of resolution obscures potential evidence for how merging and splitting of particles affect their diffusion and any implications on the biological environment. The particle tracks are typically decomposed into individual segments at observed merge and split events, and analysis is performed without knowing the true count of particles in the resulting segments. Here, we address the challenges in analyzing particle tracks in the context of cancer biology. In particular, we study the tracks of KRAS protein, which is implicated in nearly 20% of all human cancers, and whose clustering and aggregation have been linked to the signaling pathway leading to uncontrolled cell growth. We present a new analysis approach for particle tracks by representing them as tracking graphs and using topological events – merging and splitting, to disambiguate the tracks. Using this analysis, we infer a lower bound on the count of particles as they cluster and create conditional distributions of diffusion speeds before and after merge and split events. Using thousands of time‐steps of simulated and in‐vitro SPT data, we demonstrate the efficacy of our method, as it offers the biologists a new, detailed look into the relationship between KRAS clustering and diffusion speeds.

McDonald, T.↗
DOE OSTI2016

2015 Advanced Site Investigation and Monitoring Report Riverton, Wyoming, Processing Site September 2016

The U.S. Department of Energy conducted initial groundwater characterization of the Riverton, Wyoming, Processing Site in the 1990s. The characterization culminated in a Site Observational Work Plan in 1998 that recommended a natural flushing compliance strategy. Results of verification monitoring indicated that natural flushing was generally progressing as expected until June 2010, when significant increases in contaminant concentrations were measured in several monitoring wells downgradient of the site after the area flooded. In response to the unexpected results following the flood, an enhanced characterization of the surficial aquifer was conducted in 2012, which included installation of 103 boreholes along nine transects with a Geoprobe, collection of 103 water samples and 65 soil samples, laboratory tests on the soil samples, and additional groundwater modeling. This advanced site investigation report summarizes additional investigation in 2015 through the use of backhoe trenching, sonic drilling, multilevel monitoring wells, direct-push drilling, and temporary well points to collect soil and groundwater samples. Additional surface water measurements were made included the installation of a stilling well and the measurement of stream elevation along the Wind River to approximate upgradient groundwater heads. Groundwater sampling included the addition of geochemical constituents and isotopes that have not been sampled in the past to better understand post-flood conditions and the possibility of additional or ongoing contaminant sources. This sampling was performed to (1) better define the contaminant plumes, (2) verify the occurrence of persistent secondary contaminant sources, (3) better understand the reason for the contaminant spikes after a 2010 flood, and (4) assess contaminant plume stagnation near the Little Wind River. This report provides data analyses and interpretations for the 2015 site investigation that addresses these issues and provides recommendations for future efforts. Observations from trenches and sonic drilling indicate the general lithology of the shallow, unconsolidated sediments consists of a silt zone at the surface that ranges from 2.5 to 4.8 feet below ground surface, underlain by sand and gravel, underlain by the top of the weathered bedrock (Wind River Formation). Soil data from trenches and sonic drilling indicate (1) elevated concentrations of several constituents in the silt zone, likely due to the formation of evaporites, (2) uranium is the only measured element that appears to be concentrated in the silt over the groundwater contaminant plume, (3) in the former tailings impoundment area, there may be a thin unsaturated zone with elevated uranium in the native material just below the fill, (4) in the former tailings impoundment area, slightly higher uranium concentrations occur in the underlying saturated sand and gravel, and (5) several bedrock samples have a unique geochemical signature, generally related to a higher silt content. Assessment of groundwater flow included measuring river elevations along the Wind River and installing the temporary well points adjacent to the Little Wind River that provided additional data points to refine contours for water table elevations. These data confirm past interpretations of groundwater flow to the southeast across the site toward the Little Wind River. Hydraulic head elevations between paired surficial and semiconfined aquifer wells indicate variable vertical gradients across the site with the potential for upward and downward flow. Additional direct-push drilling and groundwater sampling confirmed the contaminant plume configuration, but it also revealed a low-sulfate-concentration zone at the edge of the former tailings impoundment. Temporary well points provided better definition of plume concentrations at the bank of the Little Wind River, and data from these wells indicate plume discharge to the river. Additional sampling in an area southwest of the plume that had elevated uranium groundwater concentrations in the past did not have any uranium concentrations above the U.S. Environmental Protection Agency maximum concentration limit for uranium. Results from multilevel monitoring wells indicate some geochemical differences with depth, but overall concentrations are similar to those in nearby conventional monitoring wells in the long-term monitoring program. Geochemistry data from these multilevel monitoring wells confirm the general increase in contaminant concentrations toward the river and toward the plume centerline for chloride, sulfate, and uranium but highlight geochemical controls on calcium. Iron data indicate slightly reducing conditions, especially near water table and bedrock surfaces, with more oxidizing conditions in the middle of the sand and gravel. Uranium activity ratios (234U/238U) confirm the uranium plume in the surficial aquifer as being mill related, and the area to the southwest outside the plume as natural, non-mill related. In the semiconfined aquifer, evidence of aquifer connection and impacts from the mill is inconclusive. Values of δD and δ 18 O suggest water is derived from different sources and tritium data confirm that the semiconfined aquifer water is generally older than the surficial aquifer water. However, these data do indicate some groundwater communication from the surficial aquifer into the semiconfined aquifer, which resulted in δD and δ 18 O and tritium values in the semiconfined aquifer that are more similar to those in the surficial aquifer. Values of δ 34 S sulfate in the semiconfined aquifer combined with sulfate concentrations indicate the potential for some mill- related sulfate in the semiconfined aquifer, albeit limited to an area near and beneath the former tailings impoundment. Uranium and molybdenum concentrations in the semiconfined aquifer are below groundwater standards in all wells. However, the elevated molybdenum concentrations at one semiconfined aquifer well underneath the former tailings impoundment suggests a mill- derived source for the uranium and molybdenum in that well. It is possible that aquifer cross- communication occurred when the tailings impoundment was active and created a higher head. Current cross-communication appears unlikely given the large differences in tritium values and an upward hydraulic head at this location. Nine domestic wells are located within the institutional control boundary (eight in the confined aquifer and one in the semiconfined aquifer). Uranium and molybdenum concentrations in all samples collected from these wells were one or two orders of magnitude below the groundwater standards. Surface water flow in the Little Wind River in September 2015 was low compared to historical averages for that time of year. As a result, the uranium concentration measured in the Little Wind River was at a historical maximum at the sampling location upstream of the site. However, the impact of uranium discharge from the groundwater plume into the Little Wind River was not measureable. Elevated sulfate concentrations were observed in an outfall ditch related to an active sulfuric acid plant. Uranium concentrations in the oxbow lake remain at concentrations above the groundwater standard. Plume contaminant concentrations had returned to levels found prior to the 2010 flood by the end of 2015. However, these concentrations still exceed model predictions for natural flushing, and the current data indicate that natural flushing to achieve remediation goals within the 100-year time period is not likely, especially with the high potential for additional floods in the update to the conceptual site model (CSM), soil data indicate additional contaminant sources, specifically uranium, in evaporites within the silt layer over the uranium plume and in naturally reduced zones (NRZs). Additional zones of slightly elevated uranium concentration are in the native sediments just above the water table but below the fill layer in the former tailings impoundment area. This area also has slightly elevated uranium in the sand and gravel below the water table. Mass balance calculations indicate that small amounts of dissolution in any of these zones with increased uranium in the solid phase can produce groundwater uranium concentrations above the groundwater standard and could account for the post-flood uranium spike. The additional uranium near the former tailings impoundment provides a mechanism for a continuing source for the uranium plume that was not considered in earlier natural flushing models. In addition, uranium released from the silt layer or the NRZs seasonally and during flooding may add uranium to the groundwater plume near the Little Wind River. These mechanisms provide a possible explanation for plume persistence, along with spikes in concentrations during floods, that creates the current plume configuration. Additional updates to the CSM include (1) chloride flushes more rapidly than uranium beneath the former mill site, (2) chloride in the silt layer provides a scenario in which chloride cannot be used as a conservative tracer (especially in areas prone to flooding), (3) uranium concentrations with depth can be variable (especially below NRZs), and (4) calcite and gypsum solubility limits appear to provide important geochemical controls on groundwater geochemistry. The conclusion of this study provides several recommendations for additional work to refine the CSM and continue assessment of the natural flushing compliance strategy. Recommendations for additional work include targeted soil and groundwater sampling to assess geochemical conditions, distribution of contaminants, and groundwater/surface water interaction; additional column tests to provide data for geochemical modeling; and development of an updated groundwater flow model, which will be used in conjunction with a geochemical model to assess the viability of the natural flushing compliance strategy.

2015 Monitoring Riverton, WY↗
DOE OSTI2017

A local structure model for network analysis

The statistical analysis of networks is a popular research topic with ever widening applications. Exponential random graph models (ERGMs), which specify a model through interpretable, global network features, are common for this purpose. In this study we introduce a new class of models for network analysis, called local structure graph models (LSGMs). In contrast to an ERGM, a LSGM specifies a network model through local features and allows for an interpretable and controllable local dependence structure. In particular, LSGMs are formulated by a set of full conditional distributions for each network edge, e.g., the probability of edge presence/absence, depending on neighborhoods of other edges. Additional model features are introduced to aid in specification and to help alleviate a common issue (occurring also with ERGMs) of model degeneracy. Finally, the proposed models are demonstrated on a network of tornadoes in Arkansas where a LSGM is shown to perform significantly better than a model without local dependence.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2015

Technology Solutions Case Study: Long-Term Monitoring of Mini-Split Ductless Heat Pumps in the Northeast, Devens and Easthampton, Massachusetts

Transformations, Inc., has extensive experience building high-performance homes - production and custom - in a variety of Massachusetts locations and uses mini-split heat pumps (MSHPs) for space conditioning in most of its homes. The use of MSHPs for simplified space-conditioning distribution provides significant first-cost savings, which offsets the increased investment in the building enclosure. In this project, the U.S. Department of Energy Building America team Building Science Corporation evaluated the long-term performance of MSHPs in 8 homes during a period of 3 years. The work examined electrical use of MSHPs, distributions of interior temperatures and humidity when using simplified (two-point) heating systems in high-performance housing, and the impact of open-door/closed-door status on temperature distributions.

BSC↗
DOE OSTI2019

Impacts of microbial assemblage and environmental conditions on the distribution of anatoxin-a producing cyanobacteria within a river network

Blooms of planktonic cyanobacteria have long been of concern in lakes, but more recently, harmful impacts of riverine benthic cyanobacterial mats been recognized. As yet, we know little about how various benthic cyanobacteria are distributed in river networks, or how environmental conditions or other associated microbes in their consortia affect their biosynthetic capacities. We performed metagenomic sequencing for 22 Oscillatoriales-dominated (Cyanobacteria) microbial mats collected across the Eel River network in Northern California and investigated factors associated with anatoxin-a producing cyanobacteria. All microbial communities were dominated by one or two cyanobacterial species, so the key mat metabolisms involve oxygenic photosynthesis and carbon oxidation. Only a few metabolisms fueled the growth of the mat communities, with little evidence for anaerobic metabolic pathways. We genomically defined four cyanobacterial species, all which shared <96% average nucleotide identity with reference Oscillatoriales genomes and are potentially novel species in the genus Microcoleus . One of the Microcoleus species contained the anatoxin-a biosynthesis genes, and we describe the first anatoxin-a gene cluster from the Microcoleus clade within Oscillatoriales. Occurrence of these four Microcoleus species in the watershed was correlated with total dissolved nitrogen and phosphorus concentrations, and the species that contains the anatoxin-a gene cluster was found in sites with higher nitrogen concentrations. Microbial assemblages in mat samples with the anatoxin-a gene cluster consistently had a lower abundance of Burkholderiales (Betaproteobacteria) species than did mats without the anatoxin-producing genes. The associations of water nutrient concentrations and certain co-occurring microbes with anatoxin-a producing Microcoleus motivate further exploration for their roles as potential controls on the distributions of toxigenic benthic cyanobacteria in river networks.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Influence of Ink Formulation and Drying Conditions on Ionomer Distribution in High-Performance Roll-to-Roll-Coated Gas-Diffusion Electrodes

To enable mass production of fuel cell membrane electrode assemblies (MEAs) catalyst layers production will require continuous roll-to-roll (R2R) coating processes. Gas diffusion electrodes (GDEs) are advantageous for mass production because the catalyst layer can be directely coated on the microporous layer of the gas diffusion media without the need for a decal-transfer process. It is known that the water-to-alcohol ratio in the catalyst ink influences the interactions of the ionomer with the catalyst leading to different distributions of ionomer in spray-coated catalyst layers. It is also known that during drying of colloidal mixtures, like fuel cell inks, factors such as drying rate, particle size, and agglomeration influence how the materials distribute themselves throughout the thickness of the dired film. Thus far there have only been limited studies to understand how process conditions such as ink formulation and drying temperature influence the distribution of ionomer and catalyst coated using scalable methods. This understanding is especially important for GDEs since it is known that having a sufficient amount of ionomer at the catalyst layer-membrane interface is critical for high performance. In this study we have focused on determining how the ratio of water to 1-propanol in the catalyst ink ink and drying temperature influence the distribution of ionomer throughout the thickness of the catalyst layer. Using a combination of Kelvin probe and x-ray photoelectron spectroscopy we show that an ionomer-rich surface is promoted by a higher drying rate and a water-rich catalyst ink. In contrast, a 1-propanol catalyst ink leads to a lower concentration of ionomer on the top surface. Using x-ray computed tomography, we are able to characterize the ionomer distribution throughout the thickness of the layer. We find that, in addition to promoting an ionomer-rich top surface, water-rich inks lead to a more homogenous distribution of ionomer, whereas a 1-propanol-rich ink leads to a more irregular distribution. It is found that MEA performance is improved by selecting conditions and ink formulations that promote ionomer enrichment at the top surface to facilitate a good interface with the membrane. MEAs prepared with a 75 wt% water catalyst ink with a 0.9 I/C have equivalent performance to spray-coated GDEs. Critically, these R2R-coated GDEs do not need an additional ionomer overlayer like the spray-coated GDEs do, reducing the number of processing steps in a manufacturing setting. This work shows that with the appropriate selection of materials, ink formulation, and processing conditions gas-diffusion electrodes are a viable pathway for fuel cell manufacturing.

ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION↗
DOE OSTI2016

RAPID OPTIMAL SPH PARTICLE DISTRIBUTIONS IN SPHERICAL GEOMETRIES FOR CREATING ASTROPHYSICAL INITIAL CONDITIONS

Creating spherical initial conditions in smoothed particle hydrodynamics simulations that are spherically conformal is a difficult task. Here, we describe two algorithmic methods for evenly distributing points on surfaces that when paired can be used to build three-dimensional spherical objects with optimal equipartition of volume between particles, commensurate with an arbitrary radial density function. We demonstrate the efficacy of our method against stretched lattice arrangements on the metrics of hydrodynamic stability, spherical conformity, and the harmonic power distribution of gravitational settling oscillations. We further demonstrate how our method is highly optimized for simulating multi-material spheres, such as planets with core–mantle boundaries.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Evaluation of nonlinear control performance of air handling units under variable operation conditions using root distribution approach

The control systems at Air handling units (AHUs) have nonlinear nature, resulting potentially in sluggish, aggressive, or oscillatory responses under variable operation conditions. This paper is to develop an approach for evaluating the nonlinear control performance of AHUs under variable operation conditions and for identifying the impact of varying multiple operation parameters which guides controller design. To do so, an operation parameter-based root distribution technique, intended to sketch the paths traced by closed-loop poles as multiple operation parameters are varied, is first introduced. The technique—which may be viewed as an extension of conventional, single-variable root locus—is then applied to a fan speed control system that includes a motor with a variable frequency drive and a supply fan with an air duct under variable fan speed and duct static pressure. Using the technique, the system’s stability region is graphically identified. The system is also found to be aggressive and gradually lose its stability as the fan speed decreases and the duct static pressure increases, which is validated by the field tests. Here, the root distribution approach is an effective tool to evaluate the performance of any nonlinear control systems at AHUs with multiple variable operation parameters without requiring time-domain simulations.

42 ENGINEERING↗
DOE OSTI2024

Dependence of Cloud Macrophysical Properties and Phase Distributions on Environmental Conditions Over the North Atlantic and Southern Ocean: Results From COMBLE and MARCUS

The accurate representation of Cold Air Outbreaks (CAOs) and affiliated mixed-phase boundary layer (BL) clouds in models is challenging. How BL cloud properties evolve during CAOs and their dependence on meteorological conditions is not well understood but is important for the simulation of Earth's energy budgets. Here the properties of polar BL clouds over the North Atlantic (NA) and Southern Ocean (SO) are compared using observations from the Measurements of Aerosol Radiation and CloUds over the SO (MARCUS) and CAOs in the Marine BL Experiment (COMBLE) conducted over the NA. MARCUS observations show a stronger BL inversion than COMBLE, with a higher mean EIS (estimated inversion strength)/LTS (lower tropospheric stability) of -0.03 K/13 K compared to COMBLE’s -3.2 K/9.3 K. 39% of CAOs observed during COMBLE were intense with M > 5 K, while MARCUS only had 1.3%. 78%/72% of clouds sampled in CAOs during COMBLE/MARCUS had cloud top heights <4 km. The mean BL cloud top height was over 400 m higher, and the BL was over 500 m deeper for M of 10 K compared to 0 K for both regions. MARCUS observed a 27% moister BL structure than COMBLE when M > 5 K due to stronger BL inversion trapping more moisture within the BL. Under the same LTS, EIS, and M conditions, MARCUS observed a 12% drier BL structure, and clouds were 46% more turbulent than COMBLE. During CAOs, 54% of single-layer BL clouds sampled during MARCUS had liquid-dominated bases compared to 39% during COMBLE.

54 ENVIRONMENTAL SCIENCES↗