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Results for “continuous control”

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 361 records · Page 20

All sources NASA NTRS DOE OSTI

NASA NTRS2017

An Autonomous System for Experimental Evolution of Microbial Cultures: Test Results Using Ultraviolet-C Radiation and Escherichia Coli.

At its core, the field of microbial experimental evolution seeks to elucidate the natural laws governing the history of microbial life by understanding its underlying driving mechanisms. However, observing evolution in nature is complex, as environmental conditions are difficult to control. Laboratory-based experiments for observing population evolution provide more control, but manually culturing and studying multiple generations of microorganisms can be time consuming, labor intensive, and prone to inconsistency. We have constructed a prototype, closed system device that automates the process of directed evolution experiments in microorganisms. It is compatible with any liquid microbial culture, including polycultures and field samples, provides flow control and adjustable agitation, continuously monitors optical density (OD), and can dynamically control environmental pressures such as ultraviolet-C (UV-C) radiation and temperature. Here, the results of the prototype are compared to iterative exposure and survival assays conducted using a traditional hood, UV-C lamp, and shutter system.

Microbial Cultures↗

DOE OSTI2023

Deep Reinforcement Learning for Distribution System Cyber Attack Defense with DERs

The use of smart inverter capabilities of distributed energy resources (DERs) enhances the grid reliability but in the meanwhile exhibits more vulnerabilities to cyber-attacks. This paper proposes a deep reinforcement learning (DRL)-based defense approach. The defense problem is reformulated as a Markov decision making process to control DERs and minimizing load shedding to address the voltage violations caused by cyber-attacks. The original soft actor-critic (SAC) method for continuous actions has been extended to handle discrete and continuous actions for controlling DERs' setpoints and loadshedding scenarios. Numerical comparison results with other control approaches, such as Volt-VAR and Volt-Watt on the modified IEEE 33-node, show that the proposed method can achieve better voltage regulation and have less power losses in the presence of cyber-attacks.

active distribution systems↗

NASA NTRS1986

Necessary conditions for maximax problems with application to aeroglide of hypervelocity vehicles

This paper presents the necessary conditions for solving Chebyshev minimax (or maximax) problems with bounded control. The jump conditions obtained are applicable to problems with single or multiple maxima. By using Contensou domain of maneuverability, it is shown that when the maxima are isolated single points the control is generally continuous at the jump point in the minimax problems and discontinuous in the maximax problems in which the first time derivative of the maximax function contains the control variable. The theory is applied to the problem of maximizing the flight radius in a closed circuit glide of a hypervelocity vehicle and to a maximax optimal control problem in which the control appears explicitly with the first time derivative of the maximax function.

Vinh, N. X.↗

NASA NTRS1973

Analytical and experimental performance of optimal controller designs for a supersonic inlet

The techniques of modern optimal control theory were applied to the design of a control system for a supersonic inlet. The inlet control problem was approached as a linear stochastic optimal control problem using as the performance index the expected frequency of unstarts. The details of the formulation of the stochastic inlet control problem are presented. The computational procedures required to obtain optimal controller designs are discussed, and the analytically predicted performance of controllers designed for several different inlet conditions is tabulated. The experimental implementation of the optimal control laws is described, and the experimental results obtained in a supersonic wind tunnel are presented. The control laws were implemented with analog and digital computers. Comparisons are made between the experimental and analytically predicted performance results. Comparisons are also made between the results obtained with continuous analog computer controllers and discrete digital computer versions.

Zeller, J. R.↗

NASA NTRS1985

A GCM Study of the Atmospheric Response to Tropical SST Anomalies

The purpose is to understand the evolution of the atmospheric anomalies associated with the most recent warm episode by the use of simulation studies with the UCLA general circulation model (GCM). The approach is to integrate the model using the observed sequence of Sea Surface Temperature (SST) anomalies during 1982 to 1983, and compare it with a control run in which all boundary conditions vary from month to month as in the climatology. The control for the experiment was a three year simulation using seasonally varying climatological SSTs. The anomaly calculation was initialized from 15 June of the first year of the control. From 15 June to 1 July, the SST was gradually modified by the anomalies observed during June and July of 1982. From 1 July on, the run was continued using the control's SST plus the 1982 to 1983 anomalies. SSTs were varied daily, interpolating between monthly means. This second integration as carried to the end of February of the second year (1983 in the anomaly). Only anomalies over the tropical Pacific were used.

Suarez, M. J.↗

NASA NTRS1988

Momentum management strategy during Space Station buildup

The use of momentum storage devices to control effectors for Space Station attitude control throughout the buildup sequence is discussed. Particular attention is given to the problem of providing satisfactory management of momentum storage effectors throughout buildup while experiencing variable torque loading. Continuous and discrete control strategies are compared and the effects of alternative control moment gyro strategies on peak momentum storage requirements and on commanded maneuver characteristics are described.

Bishop, Lynda↗

DOE OSTI2021

Cyber Protection of Grid-Connected Devices Through Embedded Online Security

Cybersecurity research regarding the electric power grid has primarily been focused on protecting the communication layer of grid-connected devices against cyber-attack threats. Although many developed methods have greatly reduced the effects of a cyber-attack on the vulnerabilities of grid-connected devices, discovering new vulnerabilities is inevitable and a constant threat. As a result, the overall reliability and security of network communications with regard to grid-connected devices is a concern. Here, this paper proposes a method that further secures a system by focusing on the control and hardware layer of grid-connected devices. The device’s controller firmware will be validated and authenticated using integrated device emulation resources prior to being activated to control the grid-connected device. This verification process is performed while the controller is online and actively controlling power flows related to the device. Therefore, an attack to the system through a malicious firmware patch would be detected by the online security and rejected while safely maintaining continuous and stable control of the device. This method integrates the concepts of firmware hot-patching, digital twins, and active monitoring into an overall cybersecurity protection system.

cybersecurity↗

NASA NTRS1989

Neural computing for numeric-to-symbolic conversion in control systems

A type of neural network, the multilayer perceptron, is used to classify numeric data and assign appropriate symbols to various classes. This numeric-to-symbolic conversion results in a type of information extraction, which is similar to what is called data reduction in pattern recognition. The use of the neural network as a numeric-to-symbolic converter is introduced, its application in autonomous control is discussed, and several applications are studied. The perceptron is used as a numeric-to-symbolic converter for a discrete-event system controller supervising a continuous variable dynamic system. It is also shown how the perceptron can implement fault trees, which provide useful information (alarms) in a biological system and information for failure diagnosis and control purposes in an aircraft example.

Passino, Kevin M.↗

NASA NTRS2012

Lossless Convexification of Control Constraints for a Class of Nonlinear Optimal Control Problems

In this paper we consider a class of optimal control problems that have continuous-time nonlinear dynamics and nonconvex control constraints. We propose a convex relaxation of the nonconvex control constraints, and prove that the optimal solution to the relaxed problem is the globally optimal solution to the original problem with nonconvex control constraints. This lossless convexification enables a computationally simpler problem to be solved instead of the original problem. We demonstrate the approach in simulation with a planetary soft landing problem involving a nonlinear gravity field.

planetary soft landing↗

NASA NTRS1993

Hybrid state-space self-tuning control of uncertain linear systems

The paper presents a hybrid state-space self-tuner using a new dual-rate sampling scheme for digital adaptive control of continuous-time uncertain linear systems. A state-space-based recursive least-squares algorithm, together with a variable forgetting factor, is used for direct estimations of both the equivalent discrete-time uncertain linear system parameters and the associated discrete-time state of a continuous-time uncertain linear system from the sampled input and output data. An analogue optimal regional pole-placement design method is used for designing an optimal observer-based analogue controller. A suboptimal observer-based digital controller is then designed from the designed analogue controller using digital redesign technique. To enhance the robustness of parameter identification and state estimation algorithms, a dynamic bound for a class of uncertain bilinear parameters and a fast-rate digital controller are developed at each fast-sampling period. Also, to accommodate computation loads and computation delay for developing the advanced hybrid self-tuner, the designed analogue controller and observer gains are both updated at each slow-sampling period. This control technique has been successfully applied to benchmark control problems.

Shieh, L. S.↗

DOE OSTI2017

Demonstrating Hybrid Heat Transport and Energy Conversion System Performance Characterization Using Intelligent Control Systems

The debate continues on the magnitude and validity of climate change caused by human activities. However, there is no debate about the need to make buildings, modes of transportation, factories, and homes as energy efficient as possible. Given that climate change could occur with the wasteful use of fossil fuel and the fact that fossil energy costs could and will swing wildly, it is imperative that every effort be made to utilize energy sources to their fullest. Hybrid energy systems (HES) are two or more separate energy producers used together to produce energy commodities. The HES this report focuses on is the use of nuclear reactor waste heat as a source of further energy utilization. Nuclear reactors use a fluid to cool the core and produce the steam needed for the production of electricity. Traditionally this steam, or coolant, is used to convert the energy then cooled elsewhere. The heat is released into the environment without being used further. By adding technologies to nuclear reactors to use the wasted heat, a system can be developed to make more than just electricity and allow for loading following capabilities.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2021

Synthesis of Highly Active Pd@Cu–Pt/C Methanol Oxidation Electrocatalysts via Continuous, Co-Electroless Deposition

Controlled deposition of metals is essential for the creation of bimetallic catalysts having predictable composition and character. Continuous co-electroless deposition (co-ED) permits the creation of bimetallic catalysts with predictive control over composition. This method was applied to create a suite of Cu–Pt mixed-metal shell catalysts for use in methanol electrooxidation in direct methanol fuel cell applications (DMFCs). Enhanced performance of Cu–Pt compositions over Pt alone was predicted by existing computational studies in the literature. Experimental evidence from this study supports the bifunctional catalyst explanation for enhanced activity and confirms the optimum Cu:Pt ratio as Cu 3 Pt for this methanol electrooxidation. This ability to control the composition of a bimetallic shell can be extended to other systems where the ratio of two metals is critical for catalytic performance.

preparation↗

DOE OSTI2023

Controllable branching of robust response patterns in nonlinear mechanical resonators

In lieu of continuous time active feedback control in complex systems, nonlinear dynamics offers a means to generate desired long-term responses using short-time control signals. This type of control has been proposed for use in resonators that exhibit a plethora of complex dynamic behaviors resulting from energy exchange between modes. However, the dynamic response and, ultimately, the ability to control the response of these systems remains poorly understood. Here, we show that a micromechanical resonator can generate diverse, robust dynamical responses that occur on a timescale five orders of magnitude larger than the external harmonic driving and these responses can be selected by inserting small pulses at specific branching points. We develop a theoretical model and experimentally show the ability to control these response patterns. Hence, these mechanical resonators may represent a simple physical platform for the development of springboard concepts for nonlinear, flexible, yet robust dynamics found in other areas of physics, chemistry, and biology.

42 ENGINEERING↗

DOE OSTI2024

Adaptive Laboratory Evolution for Enhanced Performance of Cupriavidus necator on Formic Acid

The need to decarbonize our economy is becoming ever more pressing. CO2, can be electrochemically reduced to formic acid, a soluble C1 molecule that can be used to store carbon and energy. Cupriavidus necator H16, a soil bacterium, capable of consuming and growing on formic acid as its sole carbon source, is well positioned to upgrade CO2-derived formic acid into value added chemicals such as sustainable aviation fuel. To improve the performance of C. necator on formic acid adaptive laboratory evolution (ALE), a proven tool for improving microbial fitness, has been conducted using continuous pH-stat bioreactors. The system works on the basis that consumption of formic acid raises the pH and triggers the addition of more formic acid to maintain the pH at 6.7, such that formic acid is provided at the same rate as it is consumed. This system has been coupled with level control to achieve continuous fermentation where cells acquiring mutations that improve growth on formic acid become more abundant in the population, from which they can be isolate and characterized. This configuration where the dilution rate is controlled by pH-stat has been found to seek out a dilution rate that matches the exponential growth rate of the organism. During developmental experiments it was discovered that formic acid accumulated to inhibitory levels. It was determined that the nitrogen source, ammonium hydroxide, must be tailored to the carbon consumption to avoid formic acid accumulation. ALE has run in three lineages for 2000+ hours and 300+ generations. Growth of evolved isolates derived from all lineages will be evaluated on formic acid and those with improved growth rates or biomass yield will be subjected to whole genome sequencing to identify potentially causative mutations. These mutations will be evaluated individually and in combination to identify those that improve growth on formic acid.

adaptive laboratory evolution↗

NASA NTRS1973

Optimization of control gain by operator adjustment

An optimal gain was established by measuring errors at 5 discrete control gain settings in an experimental set-up consisting of a 2-dimensional, first-order pursuit tracking task performed by subjects (S's). No significant experience effect on optimum gain setting was found in the first experiment. During the second experiment, in which control gain was continuously adjustable, high experienced S's tended to reach the previously determined optimum gain quite accurately and quickly. Less experienced S's tended to select a marginally optimum gain either below or above the experimentally determined optimum depending on initial control gain setting, although mean settings of both groups were equal. This quick and simple method is recommended for selecting control gains for different control systems and forcing functions.

Kruse, W.↗

NASA NTRS1984

Directional solidification of flake and nodular cast iron during KC-135 low-g maneuvers

Alloys solidified in a low-gravity environment can, due to the elimination of sedimentation and convection, form unique and often desirable microstructures. One method of studying the effects of low-gravity (low-g) on alloy solidification was the use of the NASA KC-135 aircraft flying repetitive low-g maneuvers. Each maneuver gives from 20 to 30 seconds of low-g which is between about 0.1 and 0.001 gravity. A directional solidification furnace was used to study the behavior of off eutectic composition case irons in a low-g environment. The solidification interface of hypereutectic flake and spheroidal graphite case irons was slowly advanced through a rod sample, 5 mm in diameter. Controlled solidification was continued through a number of aircraft parabolas. The known solidification rate of the sample was then correlated with accelerometer data to determine the gravity level during solidification for any location of the sample. The thermal gradient and solidification rate were controlled independently. Samples run on the KC-135 aircraft exhibited bands of coarser graphite or of larger nodules usually corresponding to the regions solidified under low-g. Samples containing high phosphorous (used in order to determine the eutectic cell) exhibited larger eutectic cells in the low-g zone, followed by a band of coarser graphite.

Curreri, P. A.↗

NASA NTRS2000

Coordinated continual planning methods for cooperating rovers

This paper compares and contrasts several coordination schemes for a system that continuously plans to control collections of rovers (or spacecraft) using collective mission goals, instead of goals or command sequences for each spacecraft.

continual planning rovers multiple agents↗

DOE OSTI2020

Optimal Energy Storage Schedules for Load Leveling and Ramp Rate Control in Distribution Systems

Continued integration of distributed energy resources (DERs) into the grid, such as solar PVs, at a large-scale, contributes into the famous Duck Curve. New DER management algorithms are therefore deemed necessary to alleviate rapid variations within net load profiles of distribution systems. Herein this paper proposes a process to determine the optimal energy storage schedules for leveling the distribution circuit feederhead net load. A series of sensitivity analyses shows how the proposed method can be used to determine the optimal energy storage schedules with different capacities, state of charge requirements, and net load ramp rate limitations.

25 ENERGY STORAGE↗