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At least 199 records · Page 11

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NASA NTRS1984

Output feedback and generic stabilizability

Attention is given to questions of pole placement and stabilization for generic linear systems with prescribed state, input and output dimension for the case where the controller must be implemented by linear memoryless output feedback. A criterion is presented in terms of a special pole placement property for generic stabilizability, and this criterion is used to describe constraints on the dimension which are consistent with generic stabilizability. Also treated are the rationality and solvability by radicals of stabilizing or pole positioning gains, and the way in which decision algebra can theoretically handle existence questions for generic systems is described.

Byrnes, C. I.↗

NASA NTRS1984

Input-output description of linear systems with multiple time-scales

It is pointed out that the study of systems evolving at multiple time-scales is simplified by studying reduced-order models of these systems valid at specific time-scales. The present investigation is concerned with an extension of results on the time-scale decomposition of autonomous systems to that of input-output systems. The results are employed to study conditions under which positive realness of a transfer function is preserved under singular perturbation. Attention is given to the perturbation theory for linear operators, the multiple time-scale structure of autonomous linear systems, the input-output description of two time-scale linear systems, the positive realness of two time-scale systems, and multiple time-scale linear systems.

Madriz, R. S.↗

NASA NTRS1983

An eigenvalue/eigenvector assignment algorithm using output feedback

An eigenvalue/eigenvector assignment algorithm using stationary output feedback is presented. The algorithm permits assignment of min (n, m + r - 1) eigenvalues and max (m-1, r-1) eigenvectors, where n, m, r refer to the system state, input and output dimensions, respectively. An example is given to illustrate the design procedures.

Mielke, R. R.↗

NASA NTRS1984

Two time scale design of output feedback systems

Singular perturbation techniques are used in this paper to develop a two time scale procedure for designing static gain output feedback controllers. It is shown that, if certain control spillover conditions are satisfied, control designs based on reduced-order models will stabilize the corrgsponding full system. Optimal output feedback control theory is used to derive the necessary conditions for the stabilizing gain matrix. The problem of stabilizing a model for a large space structure is used to illustrate the practicality of the approach.

Calise, A. J.↗

NASA NTRS1985

Use of observational and model-derived fields and regime model output statistics in mesoscale forecasting

Various empirical and statistical weather-forecasting studies which utilize stratification by weather regime are described. Objective classification was used to determine weather regime in some studies. In other cases the weather pattern was determined on the basis of a parameter representing the physical and dynamical processes relevant to the anticipated mesoscale phenomena, such as low level moisture convergence and convective precipitation, or the Froude number and the occurrence of cold-air damming. For mesoscale phenomena already in existence, new forecasting techniques were developed. The use of cloud models in operational forecasting is discussed. Models to calculate the spatial scales of forcings and resultant response for mesoscale systems are presented. The use of these models to represent the climatologically most prevalent systems, and to perform case-by-case simulations is reviewed. Operational implementation of mesoscale data into weather forecasts, using both actual simulation output and method-output statistics is discussed.

Forbes, G. S.↗

NASA NTRS1986

Collector-Output Analysis Program

Collector-Output Analysis Program (COAP) programmer's aid for analyzing output produced by UNIVAC collector (MAP processor). COAP developed to aid in design of segmentation structures for programs with large memory requirements and numerous elements but of value in understanding relationships among components of any program. Crossreference indexes and supplemental information produced. COAP written in FORTRAN 77.

Glandorf, D. R.↗

NASA NTRS1985

Research on output feedback control

In designing fixed order compensators, an output feedback formulation has been adopted by suitably augmenting the system description to include the compensator states. However, the minimization of the performance index over the range of possible compensator descriptions was impeded due to the nonuniqueness of the compensator transfer function. A controller canonical form of the compensator was chosen to reduce the number of free parameters to its minimal number in the optimization. In the MIMO case, the controller form requires a prespecified set of ascending controllability indices. This constraint on the compensator structure is rather innocuous in relation to the increase in convergence rate of the optimization. Moreover, the controller form is easily relatable to a unique controller transfer function description. This structure of the compensator does not require penalizing the compensator states for a nonzero or coupled solution, a problem that occurs when following a standard output feedback synthesis formulation.

Calise, A. J.↗

NASA NTRS1986

Calculating far-field radiated sound pressure levels from NASTRAN output

FAFRAP is a computer program which calculates far field radiated sound pressure levels from quantities computed by a NASTRAN direct frequency response analysis of an arbitrarily shaped structure. Fluid loading on the structure can be computed directly by NASTRAN or an added-mass approximation to fluid loading on the structure can be used. Output from FAFRAP includes tables of radiated sound pressure levels and several types of graphic output. FAFRAP results for monopole and dipole sources compare closely with an explicit calculation of the radiated sound pressure level for those sources.

Lipman, R. R.↗

NASA NTRS1986

Two time scale output feedback regulation for ill-conditioned systems

Issues pertaining to the well-posedness of a two time scale approach to the output feedback regulator design problem are examined. An approximate quadratic performance index which reflects a two time scale decomposition of the system dynamics is developed. It is shown that, under mild assumptions, minimization of this cost leads to feedback gains providing a second-order approximation of optimal full system performance. A simplified approach to two time scale feedback design is also developed, in which gains are separately calculated to stabilize the slow and fast subsystem models. By exploiting the notion of combined control and observation spillover suppression, conditions are derived assuring that these gains will stabilize the full-order system. A sequential numerical algorithm is described which obtains output feedback gains minimizing a broad class of performance indices, including the standard LQ case. It is shown that the algorithm converges to a local minimum under nonrestrictive assumptions. This procedure is adapted to and demonstrated for the two time scale design formulations.

Calise, A. J.↗

NASA NTRS1985

Approximations of nonlinear systems having outputs

For a nonlinear system with output derivative x = f(x) and y = h(x), two types of linearizations about a point x(0) in state space are considered. One is the usual Taylor series approximation, and the other is defined by linearizing the appropriate Lie derivatives of the output with respect to f about x(0). The latter is called the obvservation model and appears to be quite natural for observation. It is noted that there is a coordinate system in which these two kinds of linearizations agree. In this coordinate system, a technique to construct an observer is introduced.

Hunt, L. R.↗

NASA NTRS1985

Anomalous light output from lightning dart leaders

About 5 percent of the multiple-stroke cloud-to-ground lightning discharges recorded at the NASA Kennedy Space Center during the summer of 1981 contained dart leaders that produced an unusually large light output. An analysis of these cases indicates that the average peak light output per unit length in the leader may be comparable to or even exceed that of the return stroke that follows.

Guo, C.↗

NASA NTRS1987

An optimal output feedback gain variation scheme for the control of plants exhibiting gross parameter changes

A concept for optimally designing output feedback controllers for plants whose dynamics exhibit gross changes over their operating regimes was developed. This was to formulate the design problem in such a way that the implemented feedback gains vary as the output of a dynamical system whose independent variable is a scalar parameterization of the plant operating point. The results of this effort include derivation of necessary conditions for optimality for the general problem formulation, and for several simplified cases. The question of existence of a solution to the design problem was also examined, and it was shown that the class of gain variation schemes developed are capable of achieving gain variation histories which are arbitrarily close to the unconstrained gain solution for each point in the plant operating range. The theory was implemented in a feedback design algorithm, which was exercised in a numerical example. The results are applicable to the design of practical high-performance feedback controllers for plants whose dynamics vary significanly during operation. Many aerospace systems fall into this category.

Moerder, Daniel D.↗

NASA NTRS1987

Means for phase locking the outputs of a surface emitting laser diode array

An array of diode lasers, either a two-dimensional array of surface emitting lasers, or a linear array of stripe lasers, is phase locked by a diode laser through a hologram which focuses the output of the diode laser into a set of distinct, spatially separated beams, each one focused onto the back facet of a separate diode laser of the array. The outputs of the diode lasers thus form an emitted coherent beam out of the front of the array.

Lesh, James R.↗

NASA NTRS1986

Output time response approximation

The approximation of the output response of a nonlinear system by the output response of a linear system to a desired order irrespective of the admissible input applied should prove useful for purposes of control generation and simulation. Given a nonlinear system, an integer k, and an open subset of state space, sufficient conditions are stated that such a linear approximation exists to order k for every point in the set. In addition, a method for finding the approximating linear systems is presented.

Hunt, L. R.↗

NASA NTRS1987

Model-following output feedback controller for oblique-wing aircraft

A variable-skew oblique-wing offers a substantial aerodynamic performance advantage for aircraft missions that require both high efficiency in subsonic flight and supersonic dash or cruise. The most obvious characteristics of the oblique-wing concept is the asymmetry of the wing-skew angle that causes a significant aerodynamic and inertial cross coupling between the aircraft longitudinal and lateral-directional axes. This paper presents a technique for synthesizing a decoupling controller while providing the desired stability augmentation. The use of output feedback in control law synthesis without the requirement of state estimation is presented. An explicit model-following control system with output feedback is developed. The effectiveness of the control laws developed in achieving the desired decoupling is illustrated for a given flight condition for an oblique-wing aircraft.

Alag, Gurbux Singh↗

NASA NTRS1988

Algorithm For The Discrete-O timal-Output-Feedback Problem

Change in cost function due to change in feedback gain calculated. Algorithm for feedback control systems considers stochastic, infinite-time, discrete-output-feedback problem for time-invariant linear systems. Optimal-output-feedback problem formulates modern control-law-design problem in which only selected number of plant-state variables used.

Halyo, Nesim↗

NASA NTRS1987

Input error versus output error model reference adaptive control

Algorithms for model reference adaptive control were developed in recent years, and their stability and convergence properties have been investigated. Typical algorithms in continuous time involve strictly positive real conditions on the reference model, while similar discrete time algorithms do not require such conditions. It is shown how algorithms differ by the use of an input error versus an output error, and present a continuous time input error adaptive control algorithm which does not involve SPR conditions. The connections with other schemes are discussed. The input error scheme has general stability and ocnvergence properties that are similar to the output error scheme. However, analysis using averaging methods reveals some preferable convergence properties of the input error scheme. Several other advantages are also discussed.

Bodson, Marc↗

NASA NTRS1989

Increasing And Combining Outputs Of Semiconductor Lasers

Paper reviews methods of increasing and combining outputs of semiconductor lasers, with references to literature of recent years (mostly 1986 and 1987). This is a field of great practical importance: Necessary to increase or combine outputs of individual lasers to obtain sufficient power for such uses as communication, ranging, remote sensing, printing, and pumping solid-state lasers.

Katz, Joseph↗