Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “control simulation”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Flexible structure control experiments using a real-time workstation for computer-aided control engineering

A Real-Time Workstation for Computer-Aided Control Engineering has been developed jointly by the Communications Research Centre (CRC) and Ruhr-Universitaet Bochum (RUB), West Germany. The system is presently used for the development and experimental verification of control techniques for large space systems with significant structural flexibility. The Real-Time Workstation essentially is an implementation of RUB's extensive Computer-Aided Control Engineering package KEDDC on an INTEL micro-computer running under the RMS real-time operating system. The portable system supports system identification, analysis, control design and simulation, as well as the immediate implementation and test of control systems. The Real-Time Workstation is currently being used by CRC to study control/structure interaction on a ground-based structure called DAISY, whose design was inspired by a reflector antenna. DAISY emulates the dynamics of a large flexible spacecraft with the following characteristics: rigid body modes, many clustered vibration modes with low frequencies and extremely low damping. The Real-Time Workstation was found to be a very powerful tool for experimental studies, supporting control design and simulation, and conducting and evaluating tests withn one integrated environment.

Stieber, Michael E.↗
NASA NTRS2024

Investigating Zonal Asymmetries in Stratospheric Ozone Trends From Satellite Limb Observations and a Chemical Transport Model

This study investigates the origin of a zonal asymmetry in stratospheric ozone trends at northern high latitudes, identified in satellite limb observations over the past two decades. We use a merged data set consisting of ozone profiles retrieved at the University of Bremen from SCIAMACHY and OMPS-LP measurements to derive ozone trends. We also use TOMCAT chemical transport model (CTM) simulations, forced by ERA5 reanalyses, to investigate the factors that drive the asymmetry observed in the long-term changes. By studying seasonally and longitudinally resolved observation-based ozone trends, we find, especially during spring, a well-pronounced asymmetry at polar latitudes with values up to +6 % per decade over Greenland and −5 % per decade over western Russia. The control CTM simulation agrees well with these observed trends, whereas sensitivity simulations indicate that chemical mechanisms involved in the production and removal of ozone, or their changes, are unlikely to explain the observed behavior. The decomposition of TOMCAT ozone time series and ERA5 geopotential height into the first two wavenumber components shows a clear correlation between the two variables in the middle stratosphere and demonstrates a weakening and a shift in the wavenumber-1 planetary wave activity over the past two decades. Finally, the analysis of the polar vortex position and strength points to a decadal oscillation with a reversal pattern at the beginning of the century. The same is found in the ozone trend asymmetry. This further stresses the link between changes in the polar vortex position and the identified ozone trend pattern.

Instrumentation↗
NASA NTRS2003

Evaluation of Two Unique Side Stick Controllers in a Fixed-Base Flight Simulator

A handling qualities analysis has been performed on two unique side stick controllers in a fixed-base F-18 flight simulator. Each stick, which uses a larger range of motion than is common for similar controllers, has a moving elbow cup that accommodates movement of the entire arm for control. The sticks are compared to the standard center stick in several typical fighter aircraft tasks. Several trends are visible in the time histories, pilot ratings, and pilot comments. The aggressive pilots preferred the center stick, because the side sticks are underdamped, causing overshoots and oscillations when large motions are executed. The less aggressive pilots preferred the side sticks, because of the smooth motion and low breakout forces. The aggressive pilots collectively gave the worst ratings, probably because of increased sensitivity of the simulator (compared to the actual F-18 aircraft), which can cause pilot-induced oscillations when aggressive inputs are made. Overall, the elbow cup is not a positive feature, because using the entire arm for control inhibits precision. Pilots had difficulty measuring their performance, particularly during the offset landing task, and tended to overestimate.

Mayer, Jann↗
NASA NTRS2012

A Turbine Based Combined Cycle Engine Inlet Model and Mode Transition Simulation Based on HiTECC Tool

An inlet system is being tested to evaluate methodologies for a turbine based combined cycle propulsion system to perform a controlled inlet mode transition. Prior to wind tunnel based hardware testing of controlled mode transitions, simulation models are used to test, debug, and validate potential control algorithms. One candidate simulation package for this purpose is the High Mach Transient Engine Cycle Code (HiTECC). The HiTECC simulation package models the inlet system, propulsion systems, thermal energy, geometry, nozzle, and fuel systems. This paper discusses the modification and redesign of the simulation package and control system to represent the NASA large-scale inlet model for Combined Cycle Engine mode transition studies, mounted in NASA Glenn s 10- by 10-Foot Supersonic Wind Tunnel. This model will be used for designing and testing candidate control algorithms before implementation.

Csank, Jeffrey T.↗
NASA NTRS2012

A Turbine Based Combined Cycle Engine Inlet Model and Mode Transition Simulation Based on HiTECC Tool

An inlet system is being tested to evaluate methodologies for a turbine based combined cycle propulsion system to perform a controlled inlet mode transition. Prior to wind tunnel based hardware testing of controlled mode transitions, simulation models are used to test, debug, and validate potential control algorithms. One candidate simulation package for this purpose is the High Mach Transient Engine Cycle Code (HiTECC). The HiTECC simulation package models the inlet system, propulsion systems, thermal energy, geometry, nozzle, and fuel systems. This paper discusses the modification and redesign of the simulation package and control system to represent the NASA large-scale inlet model for Combined Cycle Engine mode transition studies, mounted in NASA Glenn s 10-foot by 10-foot Supersonic Wind Tunnel. This model will be used for designing and testing candidate control algorithms before implementation.

Csank, Jeffrey↗
NASA NTRS1989

End-point control of a two-link manipulator with a very flexible forearm - Issues and experiments

For mechanical manipulators, a logical sensor location is at the manipulator end-point where tasks are performed. Unfortunately, when bending flexibility exists between an end-point sensor and a joint actuator, stability and performance are achieved only through sophisticated control design. Some of the issues involved in utilizing end-point sensing for two-link flexible manipulators are addressed. A modeling technique that properly represents the foreshortening of a flexible link undergoing deflections is presented. In order to realize fully the advantages of the assumed-modes modeling method, mode shapes are selected that allow a low-order model to be used effectively for simulation and control purposes. A nonlinear controller, incorporating state feedback and a constant-gain extended Kalman filter driven by end-point measurements, is designed and compared to a conventional proportional-plus-derivative controller that uses collocated sensors. Results from implementing these controllers on the experimental Stanford multilink flexible manipulator are given.

Oakley, Celia M.↗
NASA NTRSDate not supplied

A Methodology for Actuating RCS Jets in a Continuous, Time-Accurate CFD Simulation

Computational fluid dynamics simulations of Mars entry vehicle reaction control systems have been used to gain a better understanding of the wide range of flow phenomena encountered during various phases of flight. One aspect of this is simulating the system during controlled flight. Current practices model the system in a continuously actuated state, but this methodology is unable to accurately model the dynamic behavior of the system during EDL. One method to improve this is to create a coupled CFD-RBD-Control simulation. The first step to this is establishing a method of accurately actuating an RCS jet during a time accurate CFD simulation. This paper presents a method to achieve this actuation. There are three phases to the methodology: establishing the off state, creating a ramping function that will initialize the jet flow, and establishing the on state. A test case of a jet in a supersonic crossflow is implemented to establish the success of the methodology in being able to actuate a jet in the midst of an ongoing CFD simulation. It shows significant improvement in boundary condition responsiveness for linear and exponential ramping functions in comparison to the step function. A preliminary demonstration of the methodology is presented for the MSL vehicle which shows significant advantages for the implementation of a linear ramping function over a step function.

Alexandra Hickey↗
NASA NTRSDate not supplied

A Methodology for Actuating RCS Jets in a Continuous, Time-Accurate CFD Simulation

Computational fluid dynamics simulations of Mars entry vehicle reaction control systems have been used to gain a better understanding of the wide range of flow phenomena encountered during various phases of flight. One aspect of this is simulating the system during controlled flight. Current practices model the system in a continuously actuated state, but this methodology is unable to accurately model the dynamic behavior of the system during EDL. One method to improve this is to create a coupled CFD-RBD-Control simulation. The first step to this is establishing a method of accurately actuating an RCS jet during a time accurate CFD simulation. This paper presents a method to achieve this actuation. There are three phases to the methodology: establishing the off state, creating a ramping function that will initialize the jet flow, and establishing the on state. A test case of a jet in a supersonic crossflow is implemented to establish the success of the methodology in being able to actuate a jet in the midst of an ongoing CFD simulation. It shows significant improvement in boundary condition responsiveness for linear and exponential ramping functions in comparison to the step function. A preliminary demonstration of the methodology is presented for the MSL vehicle which shows significant advantages for the implementation of a linear ramping function over a step function.

Alexandra Hickey↗
DOE OSTI2020

A Model Tree Generator (MTG) Framework for Simulating Hydrologic Systems: Application to Reservoir Routing

Data-driven algorithms have been widely used as effective tools to mimic hydrologic systems. Unlike black-box models, decision tree algorithms offer transparent representations of systems and reveal useful information about the underlying process. A popular class of decision tree models is model tree (MT), which is designed for predicting continuous variables. Most MT algorithms employ an exhaustive search mechanism and a pre-defined splitting criterion to generate a piecewise linear model. However, this approach is computationally intensive, and the selection of the splitting criterion can significantly affect the performance of the generated model. These drawbacks can limit the application of MTs to large datasets. To overcome these shortcomings, a new flexible Model Tree Generator (MTG) framework is introduced here. MTG is equipped with several modules to provide a flexible, efficient, and effective tool for generating MTs. The application of the algorithm is demonstrated through simulation of controlled discharge from several reservoirs across the Contiguous United States (CONUS).

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1994

Automated Test Environment for a Real-Time Control System

An automated environment with hardware-in-the-loop has been developed by Rocketdyne Huntsville for test of a real-time control system. The target system of application is the man-rated real-time system which controls the Space Shuttle Main Engines (SSME). The primary use of the environment is software verification and validation, but it is also useful for evaluation and analysis of SSME avionics hardware and mathematical engine models. It provides a test bed for the integration of software and hardware. The principles and skills upon which it operates may be applied to other target systems, such as those requiring hardware-in-the-loop simulation and control system development. Potential applications are in problem domains demanding highly reliable software systems requiring testing to formal requirements and verifying successful transition to/from off-nominal system states.

Hall, Ronald O.↗
NASA NTRS2014

Cross Support Transfer Service (CSTS) Framework Library

Within the Consultative Committee for Space Data Systems (CCSDS), there is an effort to standardize data transfer between ground stations and control centers. CCSDS plans to publish a collection of transfer services that will each address the transfer of a particular type of data (e.g., tracking data). These services will be called Cross Support Transfer Services (CSTSs). All of these services will make use of a common foundation that is called the CSTS Framework. This library implements the User side of the CSTS Framework. "User side" means that the library performs the role that is typically expected of the control center. This library was developed in support of the Goddard Data Standards program. This technology could be applicable for control centers, and possibly for use in control center simulators needed to test ground station capabilities. The main advantages of this implementation are its flexibility and simplicity. It provides the framework capabilities, while allowing the library user to provide a wrapper that adapts the library to any particular environment. The main purpose of this implementation was to support the inter-operability testing required by CCSDS. In addition, it is likely that the implementation will be useful within the Goddard mission community (for use in control centers).

Ray, Timothy↗
NASA NTRS1991

RMS active damping augmentation

The topics are presented in viewgraph form and include: RMS active damping augmentation; potential space station assembly benefits to CSI; LaRC/JSC bridge program; control law design process; draper RMS simulator; MIMO acceleration control laws improve damping; potential load reduction benefit; DRS modified to model distributed accelerations; accelerometer location; Space Shuttle aft cockpit simulator; simulated shuttle video displays; SES test goals and objectives; and SES modifications to support RMS active damping augmentation.

Michael G Gilbert↗
NASA NTRS1994

Aortic baroreflex control of heart rate after 15 days of simulated microgravity exposure

To determine the effects of simulated microgravity on aortic baroreflex control of heart rate, we exposed seven male subjects to 15 days of bed rest in the 6 deg head-down position. The sensitivity of the aortic-cardiac baroreflex was determined during a steady-state phenylephrine-induced increase in mean arterial pressure combined with lower body negative pressure to counteract central venous pressure increases and neck pressure to offset the increased carotid sinus transmural pressure. The aortic-cardiac baroreflex gain was assessed by determining the ratio of the change in heart rate to the change in mean arterial pressure between baseline conditions and aortic baroreceptor-isolated conditions (i.e., phenylephrine + lower body negative pressure + neck pressure stage). Fifteen days of head-down tilt increased the gain of the aortic-cardiac baroreflex. Reductions in blood volume and/or maximal aerobic capacity may represent the underlying mechanism(s) responsible for increased aortic baroreflex responsiveness after exposure to a ground-based analogue of microgravity.

Crandall, Craig G.↗
DOE OSTI2020

Optimization-Based Fast-Frequency Estimation and Control of Low-Inertia Microgrids

The lack of inertial response from non-synchronous, inverter-based generation in microgrids makes the power system vulnerable to a large rate of change of frequency (ROCOF) and frequency excursions. Energy storage systems (ESSs) can be utilized to provide fast-frequency support to prevent such large excursions in the system. However, fast-frequency support is a power-intensive application that has a significant impact on the ESS lifetime. In this paper, a framework that allows the ESS operator to provide fast-frequency support as a service is proposed. The framework maintains the desired quality-of-service (limiting the ROCOF and frequency) while taking into account the ESS lifetime and physical limits. The framework utilizes moving horizon estimation (MHE) to estimate the frequency deviation and ROCOF from noisy phase-locked loop (PLL) measurements. These estimates are employed by a model predictive control (MPC) algorithm that computes control actions by solving a finite-horizon, online optimization problem. Additionally, this approach avoids oscillatory behavior induced by delays that are common when using low-pass filters as with traditional derivative-based (virtual inertia) controllers. MATLAB/Simulink simulations on a test system from Cordova, Alaska, show the effectiveness of the MHE-MPC approach to reduce frequency deviations and ROCOF of a low-inertia microgrid.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS2007

Assessment of the Atmospheric Channel for Short (Ka-Band and Optical) Wavelengths

Atmospheric turbulence under clear sky conditions is an impairment of the atmospheric channel that greatly affects propagation of optical signal in the troposphere. The turbulence manifests itself in a number of forms within the optical domain, from the twinkling of a star in a clear night, to resolution degradation in a large aperture telescope. Therefore, a body of analytical, numerical, and experimental tools has been developed in optics to study, simulate, and control effects of atmospheric turbulence on an optical signal. Incidentally, there has been an increasing demand for high data rate returns from NASA missions which has led to envision utilizing a carrier signal in the Ka-Band range. The impact of atmospheric turbulence effects must be evaluated and considered for this frequency domain. The purpose of this work is to show that when the turbulence strength from the optical case to the KaBand ease is properly scaled, one can apply the same mathematical simulation developed for optical to predict turbulence effects within the Ka-Band domain. As a demonstration of this principle, we present how the scintillations of a Ka-Band downlink return of a deep space signal was successfully reproduced through wave-optics simulation.

optical communications↗
DOE OSTI2022

TRIPOLI-4 neutronics calculations for IAEA-CRP benchmark of CEFR start-up tests using new libraries JEFF-3.3 and ENDF/B-VIII

Sodium-cooled Fast Reactors (SFR) are one of the promising Generation IV fast reactors. The China Experimental Fast Reactor (CEFR) is a 65 MWth pool-type SFR with a high neutron leakage core using high enriched uranium oxide fuel. The CEFR start-up tests in 2010 consist of series of neutronics experiments. Essential experimental data are available from the 2018 IAEA-CEFR-CRP benchmark document and useful for the validation of neutron transport codes and nuclear data libraries. The TRIPOLI-4 Monte Carlo transport code is a general-purpose neutronics code using continuous-energy nuclear data libraries. It has a rich validation database covering different computational and experimental benchmark data sets to assure the accuracy and credibility of numerical studies. Previous TRIPOLI-4 SFR core physics calculations used mainly MOX fuels. SFR control rod worth studies with TRIPOLI-4 were mainly on big-size cores. To test the modeling capability of TRIPOLI-4 on fuel loading patterns and on variable control rods positions for SFRs and to check recent nuclear data libraries, it is interesting to investigate the CEFR start-up tests in this work, including core states from subcritical to supercritical, control rods and rod group worth, point kinetics parameters, and radial foil activation measurements. TRIPOLI-4 calculation results using new data libraries JEFF-3.3, ENDF/B-VIII, and those of ENDF/B-VII.1 for different CEFR core states are reported here. By means of different options of TRIPOLI-4, control-rod SAs reactivity worth, point kinetics parameters, and radial {sup 237}Np(n,f) fission rate distribution were successfully evaluated. Both ENDF/B-VIII and JEFF-3.3 nuclear data libraries provided reliable results with a difference of 170 +/- 11 pcm in k{sub eff}.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
NASA NTRS2007

Orion Orbit Control Design and Analysis

The analysis of candidate thruster configurations for the Crew Exploration Vehicle (CEV) is presented. Six candidate configurations were considered for the prime contractor baseline design. The analysis included analytical assessments of control authority, control precision, efficiency and robustness, as well as simulation assessments of control performance. The principles used in the analytic assessments of controllability, robustness and fuel performance are covered and results provided for the configurations assessed. Simulation analysis was conducted using a pulse width modulated, 6 DOF reaction system control law with a simplex-based thruster selection algorithm. Control laws were automatically derived from hardware configuration parameters including thruster locations, directions, magnitude and specific impulse, as well as vehicle mass properties. This parameterized controller allowed rapid assessment of multiple candidate layouts. Simulation results are presented for final phase rendezvous and docking, as well as low lunar orbit attitude hold. Finally, on-going analysis to consider alternate Service Module designs and to assess the pilot-ability of the baseline design are discussed to provide a status of orbit control design work to date.

Jackson, Mark↗