SEARCH · Engineering Papers
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.
Water purification system keeps urea and ammonium ion concentration below toxic limits in recirculated water of closed loop aquatic habitat. Urea is first converted to ammonium ions and carbon dioxide by enzygmatic action. Ammonium ions are removed by ion exchange. Bioburden is controlled by filtration through 0.45 micron millipore filters.
The parameters of a human pilot-model transfer function are estimated by applying the extended Kalman filter to the corresponding retarded differential-difference equations in the time domain. Use of computer-generated data indicates that most of the parameters, including the implicit time delay, may be reasonably estimated in this way. When applied to two sets of experimental data obtained from a closed-loop tracking task performed by a human, the Kalman filter generated diverging residuals for one of the measurement types, apparently because of model assumption errors. Application of a modified adaptive technique was found to overcome the divergence and to produce reasonable estimates of most of the parameters.
A procedure for predicting lateral-directional pilot ratings on the basis of the characteristics of the pilot model and the closed-loop system characteristics is demonstrated. A correlation is shown to exist between experimentally obtained pilot ratings and the computed pilot ratings.
A mathematical model of an active control landing gear (ACOLAG) was developed and programmed for operation on a digital computer. The mathematical model includes theoretical subsonic aerodynamics; first-mode wing bending and torsional characteristics; oleo-pneumatic shock strut with fit and binding friction; closed-loop, series-hydraulic control; empirical tire force-deflection characteristics; antiskid braking; and sinusoidal or random runway roughness. The mathematical model was used to compute the loads and motions for a simulated vertical drop test and a simulated landing impact of a conventional (passive) main landing gear designed for a 2268-kg (5000-lbm) class airplane. Computations were also made for a simply modified version of the passive gear including a series-hydraulic active control system. Comparison of computed results for the passive gear with experimental data shows that the active control landing gear analysis is valid for predicting the loads and motions of an airplane during a symmetrical landing. Computed results for the series-hydraulic active control in conjunction with the simply modified passive gear show that 20- to 30-percent reductions in wing force, relative to those occurring with the modified passive gear, can be obtained during the impact phase of the landing. These reductions in wing force could result in substantial increases in fatigue life of the structure.
A FORTRAN digital computer program which performs the general analysis of linearized control systems is described. State variable techniques are used to analyze continuous, discrete, and sampled data systems. Analysis options include the calculation of system eigenvalues, transfer functions, root loci, root contours, frequency responses, power spectra, and transient responses for open- and closed-loop systems. A flexible data input format allows the user to define systems in a variety of representations. Data may be entered by inputing explicit data matrices or matrices constructed in user written subroutines, by specifying transfer function block diagrams, or by using a combination of these methods.
Studies of human orientation and manual control in high order systems are summarized. Data cover techniques for measuring and altering orientation perception, role of non-visual motion sensors, particularly the vestibular and tactile sensors, use of motion cues in closed loop control of simple stable and unstable systems, and advanced computer controlled display systems.
The purpose of this paper is to summarize results obtained for the adaptive control of the F-8C aircraft using the so-called Multiple Model Adaptive Control method. The discussion includes the selection of the performance criteria for both the lateral and the longitudinal dynamics, the design of the Kalman filters for different flight conditions, the 'identification' aspects of the design using hypothesis testing ideas, and the performance of the closed loop adaptive system.
A technique is presented for calculating feedback and feedforward gain matrices that enable a VTOL aircraft to track input commands of forward and vertical velocity while maintaining acceptable responses to pilot inputs. Leverrier's algorithm is used for determining a set of state-variable, feedback gains that force the closed-loop poles and zeros of one pilot-input transfer function to pre-selected positions in the s-plane. This set of feedback gains is then used to calculate the feedback and feedforward gains for the velocity-command controller. The method is computationally attractive since the gains are determined by solving systems of linear, simultaneous equations. The method is used in a digital simulation of the CH-47 helicopter to control longitudinal dynamics.
Tensile tests of six nickel-base and one cobalt-base alloy were conducted in 34.5 MN/sq m helium and hydrogen environments at temperatures from 297 K to 1,088 K. Mechanical properties tests of the nickel-base alloy MAR M-246 (Hf modified), in two cast conditions, were conducted in gaseous environments at temperatures from 297 K to 1,144 K and pressures from one atmosphere to 34.5 MN/sq m. The objective of this program was to obtain the mechanical properties of the various alloys proposed for use in space propulsion systems in a pure hydrogen environment at different temperatures and to compare with the mechanical properties in helium at the same conditions. All testing was conducted on solid specimens exposed to external gaseous pressure. Smooth and notched tensile properties were determined using ASTM tensile testing techniques, and creep-rupture life was determined using ASTM creep-rupture techniques. Low-cycle fatigue life was established by constant total strain and constant stress testing using smooth specimens and a closed-loop test machine.
Variations in design methods for aircraft digital flight control are evaluated and compared. The methods fall into two categories; those where the design is done in the continuous domain (or s plane) and those where the design is done in the discrete domain (or z plane). Design method fidelity is evaluated by examining closed loop root movement and the frequency response of the discretely controlled continuous aircraft. It was found that all methods provided acceptable performance for sample rates greater than 10 cps except the uncompensated s plane design method which was acceptable above 20 cps. A design procedure based on optimal control methods was proposed that provided the best fidelity at very slow sample rates and required no design iterations for changing sample rates.
A technique has been developed for calculating feedback and feedforward gain matrices that stabilize a VTOL aircraft while enabling it to track input commands of forward and vertical velocity. Leverrier's algorithm is used in a procedure for determining a set of state variable, feedback gains that force the closed loop poles and zeroes of one pilot input transfer function to be at preselected positions in the s plane. This set of feedback gains is then used to calculate the feedback and feedforward gains for the velocity command controller. The method is computationally attractive since the gains are determined by solving systems of linear, simultaneous equations. Responses obtained using a digital simulation of the longitudinal dynamics of the CH-47 helicopter are presented.
A dispersion analysis considering 3 beta uncertainties in platform, vehicle, and environmental parameters is described. Powered explicit guidance used to develop closed loop steering commands, the nominal profile, and entry interface conditions are discussed. The groundrules and assumptions for the analysis are reviewed. The results presented include dispersion data at specific time slices from liftoff to entry interface, covariance matrices, summary data, and exchange ratios.
A dispersion analysis considering 3 sigma uncertainties (or perturbations) in platform, vehicle, and environmental parameters was performed for baseline reference mission 3A. Powered explicit guidance (PEG) was used to develop closed loop steering commands for this dispersion analysis. The nominal profile for the dispersion analysis is identical to the nominal profile of Reference 1 ascent trajectory with the exception that generalized linear tangent (GLT) guidance is used in Reference 1. Nominal trajectory differences which result from using PEG instead of GLT were determined and dispersion data were developed using PEG for comparison with similar data developed using GLT guidance.
Human eye tracking of a foveal afterimage during angular head oscillation in the dark produced smooth eye movements exceeding those for normal vestibular nystagmus, and a reduction in the frequency of the fast phase component of nystagmus eye movements. These results may support a closed loop extension of the corollary discharge theory, with oculomotor commands based on perceived object velocity.
The primary objective of the Spacecraft Attitude Precision Pointing and Slewing Adaptive Control (SAPPSAC) experiment is to establish feasibility and evaluate capabilities of a ground-based spacecraft attitude control system, wherein RF command and telemetry links, together with a ground station on-line minicomputer, perform closed loop attitude control of the Applications Technology Satellite-6 (ATS-6). The ground processor is described, including operational characteristics and the controller software. Attitude maneuvers include precision pointing to fixed targets, slewing between targets, and generation of prescribed ground tracks. Test results show high performance and reliability for over 30 hours of on-line control with no serious anomalies. Attitude stabilization relative to a prescribed target has been achieved to better than 0.007 deg in pitch and roll and 0.02 deg in yaw for a period of 43 min. Ground tracks were generated which had maximum latitude/longitude deviations less than 0.15 deg from reference.
Unsteady flow in a cavitating axial inducer pump is analyzed with the help of a simple two-dimensional cascade model. This problem was motivated by a desire to study the effect of unsteady cavitation on the so-called POGO instability in the operation of liquid rocket engines. Here, an important feature is a closed loop coupling between several different modes of oscillation, one of which is due to the basic unsteady characteristics of the cavitation itself. The approaching and leaving flow velocities up- and downstream of the inducer oscillate, and the cavity-blade system participates dynamically with the basic pulsating flow. In the present work, attention is focused on finding a transfer matrix that relates the set of upstream variables to those downstream. This quantity, which is essentially equivalent to cavitation compliance in the quasi-static analyses, is found to be complex and frequency dependent.
A digital computer algorithm for desensitized specific optimal system design for general time-invariant nonlinear systems is presented. The algorithm utilizes a technique of partitioning and uncoupling of the original specific closed-loop system state and sensitivity equations into linear, nonlinear, and control subsystems. Results of the application of the algorithm in the design of a Saturn V Launch Vehicle analog attitude control system and an LST image motion compensation digital controller are given.
The author proposes a new sinusoidal input describing function which accounts for the serial combination of hysteresis followed by elementary backlash in a single nonlinear element. The output of the hysteresis element drives the elementary backlash element. Various analytical forms of the describing function are given, depending on the a/A ratio, where a is the half width of the hysteresis band or backlash gap, and A is the amplitude of the assumed input sinusoid, and on the value of the parameter representing the fraction of a attributed to the backlash characteristic. The negative inverse describing function is plotted on a gain-phase plot, and it is seen that a relatively small amount of backlash leads to domination of the backlash character in the describing function. The extent of the region of the gain-phase plane covered by the describing function is such as to guarantee some form of limit cycle behavior in most closed-loop systems.