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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 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

A Python Library for Radiance Matrix-based Simulation Control and EnergyPlus Integration

Radiance matrix-based methods enable efficient parametric simulations, allowing users to vary sky conditions, fenestration systems, and other model parameters at a minimal cost to computation. However, the steep learning curve and complex workflow hinder the widespread adoption of matrix-based methods. The frads Python library with a series of command-line tools was developed to automate the entire matrix-based simulation process, lowering entry barriers and reducing human error. Co-simulation between EnergyPlus and Radiance was also enabled using the Python library from EnergyPlus. Key Innovations • Command-line based automation of Radiance matrix-based simulation methods • Python library facilitates broader adoption of Radiance matrix-based simulation methods • Radiance EnergyPlus run-time integration enabling the modeling of advanced control systems Practical Implications The frads library, with associated command-line tools, provides practitioners with the capability to easily adopt and use Radiance matrix-based simulation methods for various daylighting, solar control, and energy-related evaluations. Frads' current form is designed for 1) users familiar with a command-line interface and 2) software developers to integrate the matrix-based methods into existing software packages.

Wang, Taoning↗
DOE OSTI2013

Optimization strategies for sustainable fuel cycle of the BR2 Reactor

The objective of the present study is to achieve a sustainable fuel cycle in a long term of reactor operation applying advanced in-core loading strategies. The optimization criteria concern mainly enhancement of nuclear safety by means of reactivity margins and minimization of the operational fuel cycle cost at a given (constant) power level and same or longer cycle length. An important goal is also to maintain the same or to improve the experimental performances. Current developments are focused on optimization of control rods localization; optimization of fresh and burnt fuel assemblies in-core distribution; optimization of azimuth and axial fuel burn up strategies, including fuel assembly rotating and flipping upside down. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

How systems engineering and human factors can assist SMR vendors with the licensing process - 345

There is growing interest in the development of small modular reactors (SMRs) as a cost-effective renewable source of energy. Most of the current conceptual designs propose advanced and automated control and monitoring technologies which would require complex human system interfaces. The proposals also include a reduction in the number of staff, and partial or full remote control of the facilities. The human factors challenges of such a design philosophy range from identification of information requirements of users to assessing workload to deciding on best information visualization techniques to ensure situation awareness is maintained in a remote control facility. Addressing these challenges will require a systems engineering approach where user requirements are identified through a systematic approach for various contexts, including normal, abnormal, and accident conditions. A systems engineering process will integrate human factors as well as other specialty disciplines such as reliability and design optimization in a coherent fashion that would lead to realization of a successful system that addresses user requirements. The licensing model in Canada is based upon a graded approach and is largely technology neutral. A key factor in ensuring effective licensing effort is identification of regulatory requirements. This paper discusses how adopting a systems engineering approach and early consideration of human factors principles and requirements will not only ensure an efficient design process, but will also help with developing a design that meets the regulatory requirements. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2019

A High-Speed Z-Axis MEMS STM Nanopositioner

Scanning tunneling microscope (STM) is a powerful and versatile tool, not only capable of obtaining topographic information at atomic levels from a conductive surface, but also suited for patterning, manipulation and other applications, all with unprecedented precision. A typical STM’s operation relies on the quantum tunneling phenomenon. Providing a few angstroms of tip-sample separation, and a bias voltage between the two, a tunneling current (TC) is established. The tunneling current is logarithmically proportional to the tip sample separation . During imaging, a three degree of freedom (DOF) piezotube is employed to scan the tip over the surface, while a PI controller drives the Z axis in order to maintain the tunneling current at the set value. Therefore, an image of the sample surface can be constructed using the Z axis controller output, along with the corresponding X, and Y coordinates from the piezotube. Despite its well-established use in high precision applications, the achievable scan speed of the conventional STM has remained limited since its advent. One of the main reasons limiting the achievable scan speed is the relatively low operation bandwidth of the bulky piezotube Z-axis positioner, which is typically less than 1 kHz in conventional systems . This limitation correspondingly hinders the ability of the Z-axis controller to rapidly respond to the changes in the topography during the scan. To address this limitation, we design, build and characterize a high-bandwidth, 1-DOF nanopositioner with an electrostatic parallel plate actuation mechanism and a conductive tip, to replace the Z axis of the currently available STM piezotubes (Figure 1). The device is microfabricated using an SOI wafer with two device layers, where the top-most layer is designated for the tunneling current sensing, and contains the conductive tip realized by FIB induced deposition. The bottom device layer, on the other hand, comprises the actuation mechanism along with the shuttle and mechanical flexures, that provides 2-µm displacement range in one direction, comparable to a typical STM piezoelectric tube scanner. Importantly, the nanopositioner is structurally designed to have a -3dB bandwidth of 15.6 kHz, increasing the STM positioners’ Z axis bandwidth more than an order of magnitude as experimentally shown in Figure 2. Using this system we were able to demonstrate that tunneling current can be successfully established on an HOPG sample in air and successfully maintained for over two minutes (Figures 3-4).

FIB↗
DOE OSTI2020

Metal-ion-controlled growth and nanoindentation response of 3D, bicontinuous Cu–Fe thin films

Bicontinuous, nanocomposite thin film morphologies depend largely on the deposition conditions applied during physical vapor deposition. With the introduction of high power impulse magnetron sputtering (HiPIMS), the range of potential morphologies achieved during deposition has been increased. In this work, we compare the deposition outcomes between traditional direct-current magnetron sputtering (DCMS) and HiPIMS for a thin film co deposit of Cu and Fe. Modular control of the columnarity, porosity and roughness was achieved by varying the Cu and Fe metal ion currents during deposition. The directionality of the nanostructured phase-separated morphology was also controlled as the ion current increased. At zero ion current for both Cu and Fe sputtered species during DCMS, the film exhibited lateral concentration modulations of Cu and Fe. The directionality of the Cu- and Fe-rich phases shifted to vertical concentration modulations at low ion currents of I Fe = 1A and I Cu = 0:1A and to lateral concentration modulations at relatively moderate ion currents of I Fe = 5A and I Cu = 2A: At high ion currents of I Fe = 18A and I Cu = 2A; a more randomized phase domain structure was observed on the nanoscale. This structural shift is rationalized using an interdiffusion model. Here, the role of different kinds of phase separated morphologies, achieved during DCMS deposition, on the mechanical properties has also been studied. Results indicated increase in hardness, indentation modulus and flow strength values with the increase in indentation strain rates. Bicontinuous Cu-Fe nanocomposites are found to be stronger than multilayer Cu-Fe samples.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Leveraging neural control variates for enhanced precision in lattice field theory

Results obtained with stochastic methods have an inherent uncertainty due to the finite number of samples that can be achieved in practice. In lattice QCD this problem is particularly salient in some observables like, for instance, observables involving one or more baryons and it is the main problem preventing the calculation of nuclear forces from first principles. The method of control variables has been used extensively in statistics and it amounts to computing the expectation value of the difference between the observable of interest and another observable whose average is known to be zero but is correlated with the observable of interest. Recently, control variates methods emerged as a promising solution in the context of lattice field theories. In our current study, instead of relying on an educated guess to determine the control variate, we utilize a neural network to parametrize this function. Using 1 + 1 dimensional scalar field theory as a testbed, we demonstrate that this neural network approach yields substantial improvements. Notably, our findings indicate that the neural network ansatz is particularly effective in the strong coupling regime. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2019

TRANSP-based Optimization Towards Tokamak Scenario Development

An optimization approach that incorporates the predictive transport code TRANSP is proposed for tokamak scenario development. Optimization methods are often employed to develop open-loop control strategies to aid access to high performance tokamak scenarios. In general, the optimization approaches use control-oriented models, i.e. models that are reduced in complexity and prediction accuracy as compared to physics-oriented transport codes such as TRANSP. In the presented approach, an optimization procedure using the TRANSP code to simulate the tokamak plasma is considered for improved predictive capabilities. As a test case, the neutral beam injection (NBI) power is optimized to develop a control strategy that maximizes the non-inductive current fraction during the ramp-up phase for NSTX-U. Simulation studies towards the achievement of non-inductive ramp up in NSTX-U have already been carried out with the TRANSP code. The optimization-based approach proposed in this work is used to maximize the non-inductive current fraction during ramp-up in NSTX-U, demonstrating that the scenario development task can be automated. An additional test case considers optimization of the current ramp rate in DIII-D for obtaining a stationary plasma characterized bya flat loop voltage profile in the flattop phase.

DIII-D↗
DOE OSTI2025

Analog Signal Multiplexing System for the IOTA Proton Injector

he Fermilab Accelerator Science and Technology (FAST) Facility at FNAL is a dedicated research and development center focused on advancing particle accelerator technologies for future applications worldwide. Currently, a key objective of FAST Opera-tions is to commission the 2.5 MeV IOTA Proton Injec-tor (IPI) and enable proton injection into the Integrable Optics Test Accelerator (IOTA) storage ring. The low and medium-energy sections of the IPI include four frame-style dipole trims and two multi-function cor-rectors with independently controlled coils, requiring readout of 32 analog channels for current and voltage monitoring in total. To reduce cost and optimize rack space within the PLC-based control system, a 32-to-4 analog signal multiplexing system was designed and implemented. This system enables real-time readback of excitation parameters from all magnetic correctors. This paper presents the design, construction, implementation, and performance of the multiplexing system.

MacLean, Daniel R. [Fermilab] (ORCID:0000000210103↗
DOE OSTI2019

Model Predictive Control of GTAW Weld Pool Penetration

Weld pool penetration is a major implication of weld integrity but it is not directly measurable. The key to solving this issue is to find or create observable phenomena that can be used to derive the penetration. An innovative method has recently been proposed/developed to derive the penetration from the reflection of projected laser from an oscillating weld pool surface. Yet, in addition to the penetration, the oscillation, thus the reflection determined by it, also depends on the pulse amplitude of the current, which needs to be adjusted as the control variable to feedback control the penetration as the output. This dependence imposes a constraint on the control algorithm such that the adjustment of the control variable must be relatively slow to minimize additional sources that affect the oscillation/sensor. This restriction on the control variable adjustment also brings challenges to the identification of the dynamic model of the weld process to be controlled, which has to apply a varying control signal to stimulate the dynamics. To solve these issues, this letter proposes using a low order model to catch the dominant dynamics such that a high speed variation in the control signal can be avoided when choosing the model predictive control algorithm. This allows use of relatively poor models to determine the adjustment on the pulsing amplitude, and still achieves relatively accurate control. Experimental results verified the effectiveness of the resultant penetration control system despite the restrictions imposed by the penetration sensor, which affect the identification of high order dynamics and free adjustments of control variables.

42 ENGINEERING↗
DOE OSTI2015

A new apparatus design for high temperature (up to 950 °C) quasi-elastic neutron scattering in a controlled gaseous environment

A design for a sample cell system suitable for high temperature Quasi-Elastic Neutron Scattering (QENS) experiments is presented. The apparatus was developed at the Spallation Neutron Source in Oak Ridge National Lab where it is currently in use. The design provides a special sample cell environment under controlled humid or dry gas flow over a wide range of temperature up to 950 °C. Using such a cell, chemical, dynamical, and physical changes can be studied in situ under various operating conditions. While the cell combined with portable automated gas environment system is especially useful for in situ studies of microscopic dynamics under operational conditions that are similar to those of solid oxide fuel cells, it can additionally be used to study a wide variety of materials, such as high temperature proton conductors. The cell can also be used in many different neutron experiments when a suitable sample holder material is selected. The sample cell system has recently been used to reveal fast dynamic processes in quasi-elastic neutron scattering experiments, which standard probes (such as electrochemical impedance spectroscopy) could not detect. In this work, we outline the design of the sample cell system and present results demonstrating its abilities in high temperature QENS experiments.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Experiment and simulation on one-dimensional plasma photonic crystals

The transmission characteristics of microwaves passing through one-dimensional plasma photonic crystals (PPCs) have been investigated by experiment and simulation. The PPCs were formed by a series of discharge tubes filled with argon at 5 Torr that the plasma density in tubes can be varied by adjusting the discharge current. The transmittance of X-band microwaves through the crystal structure was measured under different discharge currents and geometrical parameters. The finite-different time-domain method was employed to analyze the detailed properties of the microwaves propagation. The results show that there exist bandgaps when the plasma is turned on. The properties of bandgaps depend on the plasma density and the geometrical parameters of the PPCs structure. The PPCs can perform as dynamical band-stop filter to control the transmission of microwaves within a wide frequency range.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Update of the Electron Cloud Simulations for DAFNE

A strong horizontal instability, limiting the positron current at I {approx} 500mA, has been observed at DAFNE since the installation of the FINUDA detector in 2003. Experiments and simulations seem to provide evidence that the electron cloud build-up in the wigglers and bending magnets of the DAFNE positron ring induces coupled bunch instability with features compatible with observations. Recently the installation of a new horizontal feedback system allowed to control the instability for value of the positron current as high as possible (I {approx} 1000mA). To better understand the electron cloud effects and possibly to find a remedy, a detailed simulation study is undergoing. In this communication we present recent simulation results relative to the single bunch instability induced by an electron cloud interacting with the beam.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Improving DFIG performance under fault scenarios through evolutionary reinforcement learning based control

The double-fed induction generator (DFIG) usually experiences high rotor current and DC capacitor link voltage during system fault events. In this paper, a novel data-driven approach is proposed to enhance the DFIG performance under fault scenarios. An advanced reinforcement learning (RL) algorithm called guided surrogate-gradient-based evolution strategy (GSES) is used to control the DFIG power and capacitor DClink voltage by adjusting the optional reference signals. This controller is able to prevent the rotor of DFIG from overcurrent risk and maintain the grid-connected operation. The proposed GSES-based control algorithm was evaluated through simulations on a 3.6-MW DFIG in PSCAD/EMTDC software. Results have validated the effectiveness of the proposed GSESbased control algorithm in improving the DFIG performance under fault scenarios.

42 ENGINEERING↗
DOE OSTI2014

Control of linear modes in cylindrical resistive magnetohydrodynamics with a resistive wall, plasma rotation, and complex gain

Feedback stabilization of magnetohydrodynamic (MHD) modes in a tokamak is studied in a cylindrical model with a resistive wall, plasma resistivity, viscosity, and toroidal rotation. The control is based on a linear combination of the normal and tangential components of the magnetic field just inside the resistive wall. The feedback includes complex gain, for both the normal and for the tangential components, and it is known that the imaginary part of the feedback for the former is equivalent to plasma rotation [J. M. Finn and L. Chacon, Phys. Plasmas 11, 1866 (2004)]. The work includes (1) analysis with a reduced resistive MHD model for a tokamak with finite β and with stepfunction current density and pressure profiles, and (2) computations with a full compressible visco-resistive MHD model with smooth decreasing profiles of current density and pressure. The equilibria are stable for β = 0 and the marginal stability values β{sub rp,rw} < β{sub rp,iw} < β{sub ip,rw} < β{sub ip,iw} (resistive plasma, resistive wall; resistive plasma, ideal wall; ideal plasma, resistive wall; and ideal plasma, ideal wall) are computed for both models. The main results are: (a) imaginary gain with normal sensors or plasma rotation stabilizes below β{sub rp,iw} because rotation suppresses the diffusion of flux from the plasma out through the wall and, more surprisingly, (b) rotation or imaginary gain with normal sensors destabilizes above β{sub rp,iw} because it prevents the feedback flux from entering the plasma through the resistive wall to form a virtual wall. A method of using complex gain G{sub i} to optimize in the presence of rotation in this regime with β > β{sub rp,iw} is presented. The effect of imaginary gain with tangential sensors is more complicated but essentially destabilizes above and below β{sub rp,iw}.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

Boost of plasma current with active magnetic field shaping coils in rotamak discharges

A set of magnetic shaping coils is installed on the Prairie View (PV) rotamak for the study of active plasma shape control in the regimes with and without toroidal field (TF). In the spherical tokamak regime (with TF), plasma current I{sub p} can be boosted by 200% when all five shaping coils (connected in series) are energized. The enhancement of current drive efficiency is mainly attributed to the radial compression and the substantially axial extension of the plasma column; this in turn improves the impedance matching and thus increases antenna input power. In the field-reversed configuration (without TF), plasma current can be boosted by 100% when one middle coil is used; the appearance of radial shift mode limits the achievable value of I{sub p}. The experiments clearly demonstrate that the plasma shape control plays a role in effectively driving plasma current in rotamaks.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Memory functions of nanocrystalline cadmium selenide embedded ZrHfO high-k dielectric stack

Metal-oxide-semiconductor capacitors made of the nanocrystalline cadmium selenide nc-CdSe embedded Zr-doped HfO{sub 2} high-k stack on the p-type silicon wafer have been fabricated and studied for their charge trapping, detrapping, and retention characteristics. Both holes and electrons can be trapped to the nanocrystal-embedded dielectric stack depending on the polarity of the applied gate voltage. With the same magnitude of applied gate voltage, the sample can trap more holes than electrons. A small amount of holes are loosely trapped at the nc-CdSe/high-k interface and the remaining holes are strongly trapped to the bulk nanocrystalline CdSe site. Charges trapped to the nanocrystals caused the Coulomb blockade effect in the leakage current vs. voltage curve, which is not observed in the control sample. The addition of the nanocrystals to the dielectric film changed the defect density and the physical thickness, which are reflected on the leakage current and the breakdown voltage. More than half of the originally trapped holes can be retained in the embedded nanocrystals for more than 10 yr. The nanocrystalline CdSe embedded high-k stack is a useful gate dielectric for this nonvolatile memory device.

36 MATERIALS SCIENCE↗
DOE OSTI2015

SU-E-J-12: An Image-Guided Soft Robotic Patient Positioning System for Maskless Head-And-Neck Cancer Radiotherapy: A Proof-Of-Concept Study

Purpose: We propose a surface-image-guided soft robotic patient positioning system for maskless head-and-neck radiotherapy. The ultimate goal of this project is to utilize a soft robot to realize non-rigid patient positioning and real-time motion compensation. In this proof-of-concept study, we design a position-based visual servoing control system for an air-bladder-based soft robot and investigate its performance in controlling the flexion/extension cranial motion on a mannequin head phantom. Methods: The current system consists of Microsoft Kinect depth camera, an inflatable air bladder (IAB), pressured air source, pneumatic valve actuators, custom-built current regulators, and a National Instruments myRIO microcontroller. The performance of the designed system was evaluated on a mannequin head, with a ball joint fixed below its neck to simulate torso-induced head motion along flexion/extension direction. The IAB is placed beneath the mannequin head. The Kinect camera captures images of the mannequin head, extracts the face, and measures the position of the head relative to the camera. This distance is sent to the myRIO, which runs control algorithms and sends actuation commands to the valves, inflating and deflating the IAB to induce head motion. Results: For a step input, i.e. regulation of the head to a constant displacement, the maximum error was a 6% overshoot, which the system then reduces to 0% steady-state error. In this initial investigation, the settling time to reach the regulated position was approximately 8 seconds, with 2 seconds of delay between the command start of motion due to capacitance of the pneumatics, for a total of 10 seconds to regulate the error. Conclusion: The surface image-guided soft robotic patient positioning system can achieve accurate mannequin head flexion/extension motion. Given this promising initial Result, the extension of the current one-dimensional soft robot control to multiple IABs for non-rigid positioning control will be pursued.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Design of a Single Controller for Multiple Paralleled Inverters

Paralleling power electronics inverters is an effective way to increase dc-ac system power level. Accurately synchronized switching action and independent closed-loop regulator are necessary to prevent circulating current in paralleled inverters. There are many challenges for the controller design, when the number of paralleled inverters is large, and control period gets short for high switching frequency applications. This paper presents a single controller design based on DSP + FPGA that is suitable for paralleling multiple inverters. A simple synchronization scheme between DSP and FPGA based on universal parallel port (UPP) is proposed to eliminate the synchronization delay among inverters, and independent control of each converter can also be implemented. The controller is built for a system consisting of 4 paralleled three-level, three-phase high frequency ANPC inverters using space vector modulation, and it can be easily adopted to other topologies and modulations. Experimental results have demonstrated the effectiveness of this controller.

Niu, Jiahao↗