This article presents a two-dimensional axisymmetric combined conduction and radiation model for the prototype of the programmable multizone furnace, which is under design at NASA Lewis Research Center. The actual fur...
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This article presents a two-dimensional axisymmetric combined conduction and radiation model for the prototype of the programmable multizone furnace, which is under design at NASA Lewis Research Center. The actual furnace is intended for growing high-quality semiconductor crystals and performing other materials processing experiments in space. A novel feature of the model is a control algorithm that automatically adjusts the power in any number of independently controlled heaters to establish the desired sample temperatures during the numerical simulations. The control algorithm eliminates the need for numerous trial and error runs previously required to obtain the same results. The finite element code, FIDAP, was modified to directly incorporate the control algorithm. This algorithm, which presently uses proportional-integral-derivative (PID) control, and the associated heat transfer model are briefly discussed. Together, they have been used to predict the heater power distributions for a variety of furnace configurations and desired temperature profiles. Examples are included to demonstrate the effectiveness of the PID-controlled model in establishing isothermal, Bridgman, and other complicated temperature profiles in the sample. An example is also given to show how the algorithm can be used to change the desired profile with time according to a prescribed temperature-time evolution.
An unstable double-mass system consisting of a reversible pendulum on a controlled trolley is considered in the situation in which the pendulum is affected by an unmeasurable parametrically undetermined moment. The pa...
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An unstable double-mass system consisting of a reversible pendulum on a controlled trolley is considered in the situation in which the pendulum is affected by an unmeasurable parametrically undetermined moment. The parameters of the object are assumed to be unknown, and the initial conditions are any conditions under which the deflection of the reversible pendulum does not exceed pi/2.
The performance-seeking-control algorithm (PSC) is designed to continuously optimize the performance of propulsion systems. The PSC uses a nominal model of the propulsion system and estimates, in night, the engine dev...
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The performance-seeking-control algorithm (PSC) is designed to continuously optimize the performance of propulsion systems. The PSC uses a nominal model of the propulsion system and estimates, in night, the engine deviation parameters (EDPs) characterizing engine deviations with respect to nominal conditions. In practice, the measurement biases (or model uncertainties) may prevent the estimated EDPs from reflecting the engine's actual off-nominal condition. This factor has a direct impact on the PSC scheme exacerbated by the open-loop character of the algorithm. An observability analysis shows that the biases cannot be estimated together with the EDPs. Moreover, biases and EDPs turn out to have equivalent effects on the measurements, leaving it undecided whether the estimated EDPs represent the actual engine deviation or whether they simply reflect the measurement biases. In this article, the effects produced by unknown measurement biases over the estimation algorithm are evaluated. This evaluation allows for identification of the most critical measurements for application of the PSC algorithm to an F100 engine.
The Kalman filter approach for the estimation process of performance-seeking control (PSC) is found to present some practical inconveniences from the standpoint of the analysis, implementation, tuning, and design. Mos...
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The Kalman filter approach for the estimation process of performance-seeking control (PSC) is found to present some practical inconveniences from the standpoint of the analysis, implementation, tuning, and design. Most of these difficulties can be overcome if a simpler Luenberger-type observer is applied directly to the same steady-state model used for the optimization. With the Kalman filter approach, two independent sets of local linear models need to be stored in memory, whereas with the proposed technique, the estimation and optimization processes share the same piecewise linear model. Thus, no extra on-line model switching is required, less computer memory is needed, and the identity between the local optimization model and the local estimation model is guaranteed at any moment. Tests with flight data from an F-15 propulsion system show that the neglected engine's dynamics do not have any noticeable effects on the estimates, and that similar or better noise rejection and convergence speed can be obtained. (AIAA)
A new self-tuning regulator for control of mean arterial blood pressure using sodium nitroprusside is presented. In addition to adapting to various patient response gains and time constants, the controller can accommo...
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A new self-tuning regulator for control of mean arterial blood pressure using sodium nitroprusside is presented. In addition to adapting to various patient response gains and time constants, the controller can accommodate variations in pure time delays, a problem that has not been addressed fully in previously proposed controllers. The control algorithm derivation is based on incorporating a self-tuning controller with an adaptive discrete time delay compensator. The derivation, however, is general and can potentially be applied to other pharmacological agents in addition to sodium nitroprusside. The a priori information required for implementation of the controller is the estimate of the order of the patient response transfer function and the range of the pure time delay. An attractive feature of the controller is its capability to optimize the level of the infused drug during the transient phase of the control without creating an output offset. This feature tends to reduce the overall level of the infused drug. Hence, it may be useful when the cost of a drug or its long-term administration side effects is of concern, such as in the case of sodium nitroprusside.
Experiments were performed to demonstrate positive poststall roll control of a free-to-roll wind-tunnel delta wing model using tangential leading-edge blowing. Previous static experiments had shown that significant ro...
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Experiments were performed to demonstrate positive poststall roll control of a free-to-roll wind-tunnel delta wing model using tangential leading-edge blowing. Previous static experiments had shown that significant rolling moments could be produced up to an angle of attack of 55 deg using asymmetric tangential leading-edge blowing. The implication was that poststall dynamic roll control ought to be possible using only blowing. To demonstrate experimentally that this was indeed the case, a free-to-roll wind-tunnel model sting mounting system and a pair of fast acting blowing control servo-valves were developed and manufactured. An automatic feedback roll control algorithm using tangential leading-edge blowing was then synthesized and implemented on a digital controller. Results from the present dynamic experiments indicated that with just symmetric blowing alone, wing rock at an angle of attack of 55 deg was damped. Furthermore, with the use of an automatic roll feedback control algorithm employing asymmetric blowing, the same wing rock was stopped in less than one cycle of the limit-cycle oscillation.
The paper deals with rate and attitude control of a rigid body. The discussed control system contains an inner velocity loop that tracks the desired rate command and an outer attitude loop that tracks the desired atti...
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The paper deals with rate and attitude control of a rigid body. The discussed control system contains an inner velocity loop that tracks the desired rate command and an outer attitude loop that tracks the desired attitude command. The control algorithm uses quaternions as a measure of attitude errors to achieve tracking via instantaneous eigenaxis rotation. The paper discusses the stability of the new algorithm and presents its application to multiaxis gimbal attitude control.
We consider the problem of Earth-pointing control of a space platform B connected by means of tethers to an orbiting space station A that is independently controlled so as to remain Earth pointing. The intuitive idea ...
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We consider the problem of Earth-pointing control of a space platform B connected by means of tethers to an orbiting space station A that is independently controlled so as to remain Earth pointing. The intuitive idea that is explored is that of achieving pointing control by pulling on the tethers. The concept presented in this Note for pointing control in a plant with two tethers has the potential of extension to three-dimensional attitude control with three tethers. We present nonlinear and linearized equations of motion of the system, and a control law design based on feedforward control plus full state feedback with an actuator prefilter, followed by simulation results.
Tethered spacecraft are particularly well suited to serve as isolation platforms for space-borne observatories. It has previously been shown that, due to the relatively large tether force, conventional means of perfor...
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Tethered spacecraft are particularly well suited to serve as isolation platforms for space-borne observatories. It has previously been shown that, due to the relatively large tether force, conventional means of performing attitude control for tethered satellites are inefficient for any mission with pointing requirements more stringent than about 1 deg. A particularly effective method of implementing attitude control for tethered satellites is to use the tether tension force to generate control moments by moving the tether attach point relative to the subsatellite center of mass. This paper presents the development of a precision pointing control algorithm for tethered satellites and the simulation of the control system with laboratory hardware. The control algorithm consists of a linear quadratic regulator feedback law and a Kalman filter. The control algorithm has been shown to regulate the vehicle orientation to within 0.60 arcsec rms. This level of precision was achieved only after including a mass center estimator and accurately modeling the effects of the nonlinear attach point motion actuator.
This Note explores the effectiveness and limitations of linear feedback control on a structure with closely spaced natural frequencies. Closed-form expressions are presented for the fundamental case of a structure wit...
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This Note explores the effectiveness and limitations of linear feedback control on a structure with closely spaced natural frequencies. Closed-form expressions are presented for the fundamental case of a structure with two modes controlled by a single force. Three algorithms are investigated: velocity feedback, pole allocation, and optimal control. The paper has shown the following: 1) The normalized difference of the open-loop frequencies β governs the effectiveness and robustness of the control algorithms. 2) Velocity feedback, pole allocation, and optimal control yield responses that are nearly equal for small gains but are significantly different for velocity gains on the order of β or greater. 3) The lower bound for the response of optimally controlled structures is on the order of 1/β. 4) It is possible, through pole allocation, to increase the modal damping of the closed-loop system by increasing the feedback gains. 5) The stable region is bounded by two cones, with geometry determined by the control parameters.
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