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Integrated approach encompasses modeling, identification of parameters, estimation of states, and control. Applies to models specified in part by possibly interconnected elliptic partial differential equations for deflections of structures under static loads. Appropriate for systems in which time-dependent effects negligibleand where control forces applied without exciting significiant dynamic behavior.
The combined problem of slew maneuver control and vibration suppression of NASA Spacecraft Control Laboratory Experiment (SCOLE) is considered. The coupling between the rigid body modes and the flexible modes together with the effect of the control forces on the flexible antenna is discussed. The nonlinearities in the equations are studied in terms of slew maneuver angular velocities.
Joint NASA/Army efforts at the Ames Research Center to develop rotorcraft handling-qualities design criteria began in earnest in 1975. Notable results were the UH-1H VSTOLAND variable stability helicopter, the VFA-2 camera-and-terrain-board simulator visual system, and the generic helicopter real-time mathematical model, ARMCOP. An initial series of handling-qualities studies was conducted to assess the effects of rotor design parameters, interaxis coupling, and various levels of stability and control augmentation. The ability to conduct in-flight handling-qualities research was enhanced by the development of the NASA/Army CH-47 variable-stability helicopter. Research programs conducted using this vehicle include vertical-response investigations, hover augmentation systems, and the effects of control-force characteristics. The handling-qualities data base was judged to be sufficient to allow an update of the military helicopter handling-qualities specification, MIL-H-8501. These efforts, including not only the in-house experimental work but also contracted research and collaborative programs performed under the auspices of various international agreements. The report concludes by reviewing the topics that are currently most in need of work, and the plans for addressing these topics.
The combined problem of slew maneuver control and vibration suppression of NASA Spacecraft Control Laboratory Experiment (SCOLE) is considered. The coupling between the rigid body modes and flexible modes together with the effect of the control forces on the flexible antenna is discussed. The nonlinearities in the equations are studied in terms of slew maneuver angular velocities.
The concept of adaptive structures is brought up in connection with the need in ultra lightweight structural systems to maintain desired properties and configurations without human intervention when subjected to dynamic, thermal, and other environmental forces. Examples are large antenna structures and flexible robotic structures. In the both cases such adaptivity would allow less massive structural members to be employed under normal loading conditions. During special circumstances when unusually large loads are encountered, temporary stiffening would allow the use of less sturdy structures, resulting in large savings in their cost, and in increasing their mobility and efficiency. Within the framework of a finite-dimensional representation of structural dynamics, the adaptivity can be implemented by the dependence of the stiffness matrix (k) upon the expected load (Q), or expected (programmed) changes in configurations, i.e., (k) = (k(t)) where the dependence upon time is programmed in advance. In order to sustain unexpected loads the adaptive structure can be provided by feedback force control, or by a parametrical stiffness control.
Independent Modal Space Control (IMSC) is a technique that is often used for the control of large order structural systems. The pertinent optimization problem in the simultaneous design and control of structures is a min - min problem that minimizes with respect to the structural design variables, the minimum value of the performance index with respect to the control forces obtained using the IMSC technique. The minimization process requires derivatives of eigenvalues and eigenvectors with respect to the design variables. These derivatives can be computed by a rather involved analytical procedure or a relatively simple finite difference procedure. The computer cost effectiveness of these two procedures for the derivative calculations is examined.
A methodology is described for developing a task complexity index based on combining the six basic motion primitives (three translation, three orientation) with force control and accuracy requirements. The result of this development is a set of complexity values that can be assigned to the high-level task primitives derived from a relatively shallow top-down mission analysis. These values are then averaged to arrive at total average mission complexities, such as for the mission of exchanging the Hubble Space Telescope (HST) battery modules. Application of this metric to a candidate set of NASA Flight Telerobotic Servicer evaluation tasks is discussed using the HST battery module mission for an in-depth example.
The history of the analyses for the hydraulic force control systems of the T-97 test facility is presented. Two approaches that were investigated for softening the hydraulic systems for improved performance are presented. A valve modification and inclusion of a proportional-integral controller that finally stabilized the system are described. A simulated test case is shown and compared to actual test data from the QM-7 test. The simulated results are very close to the real results but indicate a slightly higher open-loop gain than for the real system.
The injection of thin, high-momentum jets of air into the fuselage forebody boundary layers of the F-18 aircraft is explored numerically as a means of controlling the onset of fuselage vortices and of generating yaw control forces. The study was carried out for an angle of attack of 30 deg with symmetrical and asymmetrical blowing configurations. One-sided blowing results in a strongly asymmetrical flow pattern in the fore portion of the fuselage, leading to a net lateral force.
Active control of dynamical behavior of rotor systems involves the following modeling of the rotor system including active elements as a control process, positioning of actuators and sensors, implementation of problem-adapted control concepts. The key to attaining the desired influence on the dynamic behavior of rotor systems lies in the presence of suitable actuators. Some types of actuators (magnetic, electrohydraulic and piezoelectric) will be discussed and their respective drawbacks indicated. Their design will be outlined and functional correlations will be presented. Theoretical and experimental results demonstrate that an improvement of the system dynamics by the use of control forces is always possible.
Decelerator problems of the knee are emphasized since the lower leg musculature is known to atrophy in response to weightlessness. However, other important decelerator functions are served by the shoulder muscles, in particular the rotator cuff muscles. Problems in these muscles often result in tears and dislocations as seen in baseball pitchers. It is noteworthy that at least one device currently exists that can measure concentric and eccentric muscle loading including a submaximal simulated free weight exercise (i.e., force-controlled) and simultaneously record integrated EMG analysis appropriate for assessment of all muscle functional activities. Studies should be undertaken to provide information as to the performance of maximal and submaximal exercise in space travelers to define potential problems and provide rationale for prevention.
Interest lies in a mathematical formulation capable of accommodating the problem of maneuvering a space structure consisting of a chain of articulated flexible substructures. Simultaneously, any perturbations from the 'rigid body' maneuvering and any elastic vibration must be suppressed. The equations of motion for flexible bodies undergoing rigid body motions and elastic vibrations can be obtained conveniently by means of Lagrange's equations in terms of quasi-coordinates. The advantage of this approach is that it yields equations in terms of body axes, which are the same axes that are used to express the control forces and torques. The equations of motion are nonlinear hybrid differential quations. The partial differential equations can be discretized (in space) by means of the finite element method or the classical Rayleigh-Ritz method. The result is a set of nonlinear ordinary differential equations of high order. The nonlinearity can be traced to the rigid body motions and the high order to the elastic vibration. Elastic motions tend to be small when compared with rigid body motions.
A new method has been developed to design an active vibration isolation system for microgravity space experiments. This method yields the required controller transfer functions for a specified transmissibility. Hence, it is a straightforward task to guarantee that the desired vibration isolation performance is achieved at each frequency. The theory for such a controller design has been presented by considering a single degree of freedom system. The magnitude of the control force required by the new method has been found to be less than that used by a standard phase lead/lag compensator.
In this study a method is presented to integrate the design space of structural/control system optimization problems in the case of state feedback control. Conventional structural sizing variables and elements of the feedback gain matrix are both treated as strictly independent design variables in the optimization by extending design variable linking concepts to the control gains. Examples which involve a variety of behavior constraints, including dynamic transient response and control force limits, are effectively solved by using the method presented.
Very large space structures require structural reactions to control forces associated with nanometer-level displacements; JPL has accordingly built a tensile test machine capable of mN-level force measurements and nm-level displacement measurements, with a view to the study of structural linear joining technology at the lower limit of its resolution. The tester is composed of a moving table that is supported by six flexured legs and a test specimen cantilevered off the table to ground. Three vertical legs contain piezoactuators allowing changes in length up to 200 microns while generating axial load and bending moments. Displacements between ground and table are measured by means of three laser-interferometric channels.
The effectiveness of a tangential slot blowing concept for generating lateral control forces on an aircraft forebody is analyzed using computational fluid dynamics. The flow about a fighter forebody is computed using a multiple-zone, thin-layer Navier-Stokes code. Tangential slot blowing is modeled by the use of an actuator plane. The effects of slot location and slot length on the efficiency of the system are analyzed. Results of the study indicate that placement of the slot near the nose of the aircraft greatly enhances the efficiency of the system, while the length and circumferential location of the slot are of secondary importance. Efficiency is defined by the amount of side force or yawing moment obtained per unit blowing coefficient. The effect of sideslip on the system is also analyzed. The system is able to generate incremental changes in forces and moments in flows with sideslip angles up to 10 deg comparable to those obtained at zero sideslip. These results are used to determine a baseline configuration for an experimental study of the tangential slot blowing concept.
This paper presents a computational investigation of a tangential slot blowing concept for generating lateral control forces on an aircraft fuselage forebody. The effects of varying both the jet width and jet exit velocity for a fixed location slot are analyzed. This work is aimed at aiding researchers in designing future experimental and computational models of tangential slot blowing. The primary influence on the resulting side force of the forebody is seen to be the jet mass flow rate. This influence is sensitive to different combinations of slot widths and jet velocities over the range of variables considered. Both an actuator plane and an overset grid technique are used to model the tangential slot. The overset method successfully resolves the details of the actual slot geometry, extending the generality of the numerical method. The actuator plane concept predicts side forces similar to those produced by resolving the actual slot geometry.
An experimental study has been undertaken to investigate the possibility of using tangential blowing to provide control forces and moments on a delta wing-forebody combination at high angles of attack. The present model can utilize the blowing separately on the wing and forebody. This research emphasizes the effect of blowing on the aerodynamics of the state of the art model by using: (1) flow visualization (smoke-flow visualization using a laser sheet), and (2) force and moment measurements. Experiments revealed that the effect of the blowing on a body-wing combination differs in several respects compared to that of wing alone or body alone. Force and moment measurements on the present model showed that the asymmetric blowing from the fuselage creates larger side force, rolling and yawing moments compared to blowing from the wing. In the presence of the forebody, the effectiveness of the rolling moment generated by blowing from the wing is reduced.