Magnitude Of Control Force Research Articles

Research on Instability Boundaries of Control Force for Trajectory Correction Projectiles

The balance of stability and maneuverability is the foundation of the trajectory correction projectile. For the terminal correction projectile without an attitude feedback loop, a larger control force is expected which may cause an instability. This paper proposes a novel method to derive instability boundaries for the control force magnitude. No additional coordinate system is needed in this method. By introducing the concept of angular compensation matrix, the exterior ballistic linearized equations considering control force are established. The necessary prerequisite for a stable flight under control is given by the Routh stability criterion. The instability boundaries for the control force magnitude are derived. The results of example flights are 13.5% more accurate compared with that in relevant research. Numerical simulations demonstrate that if the control force magnitude lies in the unstable scope derived in this paper, the projectile loses its stability. Furthermore, the effects of the projectile pitch, velocity, and roll rate on flight stability during correction are investigated using the proposed instability boundaries.

Nonlinear Controllers for Active Composite Tuned Mass Dampers

This paper considers nonlinear control of buildings utilizing composite tuned mass dampers subject to earthquake. Basically composite tuned mass dampers are tuned mass dampers having two dampers connected in series, where auxiliary mass dampers as satellite damper is attached on the first dampers. The properties of composite tuned mass dampers are optimized before they are used in the structures. Active control systems are then applied to the composite tuned mass dampers. Because the magnitude of control force is not unlimited, the maximum energy to be supplied to the building should be bounded within the actuator's capacity. Several combinations of active control locations are investigated, i.e., two controllers at both dampers, one controller at first damper only, and one controller at the second damper only. Continuous bounded control algorithms utilizing continuous function are used as the control algorithms in this paper. From the numerical simulations, it is found that the best result is obtained when both control forces are applied to the mass dampers. In the case that only one actuator is used, better performance is achieved when the control force is applied at the first (bottom) damper.

Control mechanism strategies for spin-stabilized projectiles

Spin-stabilized artillery munitions were originally designed to provide precise ballistic fire on long-range targets. Today, the challenge is to use these ballistic munitions in urban operations where significantly higher levels of precision are required to minimize collateral damage. One strategy is to retrofit these munitions with some level of low-cost precision. Unique challenges arise when munitions designed to be ballistically precise are guided. Projectile flight is often stabilized by a high spin rate, which induces complex dynamics. Flight mechanics are further aggravated by adding a control mechanism. The goal of this study was to provide a fundamental understanding of various control mechanism strategies for spin-stabilized projectiles. Flight control systems were developed and executed in a six-degree-of-freedom simulation. Formulating a generalized model of a control mechanism allowed us to investigate parameters such as control force magnitude, control axial location, control lift-to-drag ratio, and control force duration for a spin-stabilized projectile. Results show that control authority linearly relates to control force magnitude. Maximal control authority was obtained by placing the control mechanism at the rear of the projectile. The variation with axial location was also determined since these results are valuable, for instance, when the control is unable to be located near the projectile base. A lower lift-to-drag ratio of the control mechanism decreased control authority and maximum range. Lastly, the trade-offs associated with continuous and pulsed flight control systems were quantified. Physical explanations for the simulation results are provided.

Semi-active MR dampers for seismic control of structures

Magnotorheological (MR) dampers have been demonstrated to be more effective in reducing the structural response due to earthquakes using only a small amount of external power. The performance of MR damper depends upon type of control law used and the damper force is directly depends on the input command voltage. The purpose of this study is to evaluate the effectiveness of input command voltage on MR damper system against recently proposed control laws under different earthquakes. The magnitude of control force increases with the increase in the input command voltage of MR damper, however for the different damper locations and configurations maximum command voltage to the current driver may not always effective in reducing the structural responses. To investigate the effective performance of the MR dampers, different control algorithms with multiple MR damper locations are considered in this study. A phenomenological model of a shear- mode MR damper, based on a Bouc–Wen element, is employed in the analysis of the controlled building. The control algorithms are tested on a five-story framed building and parametric study on variation in the input command voltage is conducted for different real earthquake ground motions. The numerically evaluated optimum parametric values are considered for the analysis of the different damper locations in the building in order to reduce the displacement, acceleration and the base shear of the building. It is shown numerically that the performance of the MR damper has a great potential in suppressing structural vibrations over a wide range of seismic inputs by selecting appropriate optimum input command voltages.

Taking into account the influence of elastic elements of a free structure on the accuracy of its stabilization under a bang-bang control

We consider the problem of stabilization with respect to a prescribed position for the translational motion of a rigid body with interior material points connected with each other and with the exterior body by linear viscoelastic constraints. The motion occurs under the action of a constant exterior perturbation and a bang-bang control force that are directed along the line of motion. We assume that the bang-bang force control channel has a fixed delay, so that arbitrarily frequent switchings are impossible. We suggest a positional control ensuring the solution of this problem. We estimate the amplitude of the rigid body vibrations about the center of mass of the entire structure and the accuracy of stabilization of the prescribed position of the rigid body depending on the mechanical characteristics of the system and the control force magnitude. We also consider the problem of maximizing the stabilization accuracy depending on the control parameters. By way of example, we consider the controlled motion of a two-mass oscillatory system. This work is closely related to [1–3] and continues the studies of the guaranteed optimal bang-bang controllers with delay in the control channel [4–9]. The dynamics of a rigid body with elastic and dissipative elements was studied in [10] under the assumption that the period of natural vibrations and their decay time are small compared with the characteristic time of motion.

A study on interaction control for seismic response of parallel structures

A structure response control approach which uses controlled interactions between two parallel structures (a primary structure and an auxiliary structure) to reduce the seismic response of the primary structure (P-structure) during earthquake excitation, is proposed. Three strategies of the control approach, including optimal passive control, semi-active control, and active control are examined. The optimum passive-coupling elements between two parallel structures under different circumstances are firstly investigated. Then, emphasis has been placed on the derivation of a simple effective algorithm for semi-active control which guarantees the power absorption of the required control force from the P-structure at every time step. Finally, numerical results in the frequency and time domains are presented to demonstrate the effectiveness of these proposed control strategies. The comparison of the structure response time histories when subjected to El Centro 1940 ground excitation with different control methods also illustrates that the semi-active control based on optimum passive coupling element can achieve improvement in reducing the response of P-structure compared to the passive control and is almost comparable to the active control system with the same degree of magnitude of control force, and that the proposed instantaneous power absorption semi-active control algorithm is always superior to conventional linear control law.

Sliding mode fuzzy control: Theory and verification on a benchmark structure

A sliding mode fuzzy control (SMFC) algorithm is presented for vibration reduction of large structures. The rule base of the fuzzy inference engine is constructed based on the sliding mode control, which is one of the non-linear control algorithms. In general, fuzziness of the controller makes the control system robust against the uncertainties in the system parameters and the input excitation, and the non-linearity of the control rule makes the controller more effective than linear controllers. For verification of the present algorithm, a numerical study is carried out on the benchmark problem initiated by the ASCE Committee on Structural Control. To achieve a high level of realism, various aspects are considered such as actuator–structure interaction, sensor noise, actuator time delay, precision of the A/D and D/A converters, magnitude of control force, and order of control model. Performance of the SMFC is examined in comparison with those of other control algorithms such as Hmixed 2/∞, optimal polynomial control, neural networks control, and SMC, which were reported by other researchers. The results indicate that the present SMFC is efficient and attractive, since the vibration responses of the structure can be reduced very effectively and the design procedure is simple and convenient. Copyright © 2000 John Wiley & Sons, Ltd.

Active control of non-linearly coupled TLP response under wind and wave environments

This paper deals with an active control strategy to check the non-linearly coupled response of a tension leg platform (TLP), a deep water semi-submersible type compliant offshore structure moored by vertical taut cables called tendons or tethers. The effects of potential non-linearities together with coupling of various degrees of freedom are studied. Low-frequency viscous drift force has also been taken into account with first-order wave forces. Simulation techniques have been employed to incorporate the random sea and fluctuating wind characteristics. Corrective control force is generated to alleviate the undesirable motion characteristics. The Riccati equation is used to determine the optimal control force. Response time histories and power spectra are generated for long crested random sea along with drift and wind forces. These responses are compared with the same under control. The present study aims at an efficient method of determination of the control force magnitude to design a control strategy for serviceability and survival of tension leg platforms in hostile ocean environments.

Robust tracking controller for a seeker scan loop

This paper deals with the problem of designing a robust tracking controller for a seeker scan loop where the plant model contains uncertainty. The goal is to have the seeker accurately track specific scan patterns in the presence of system uncertainty. Two scan patterns, the circular and the rosette, are generated as reference models and used in the simulation to test the robustness of the controllers. Results from H/sup /spl infin// control theory for full state feedback and output feedback are used to design the controllers. Furthermore, to limit the control force magnitude to satisfy physical constraints, a special filtering procedure is introduced. For both scan patterns, it is shown that robust controllers can be determined so that the scan loop accurately tracks the scan patterns even with model uncertainty up to 100%.

Analysis of a nonlinear control system for stabilizing a missile

An autopilot with attitude and rate feedback, representative system lags, and a two-way relay servo with inherent hysteresis is considered for roll control of a missile with peripheral, tangentially operating jets. This type of control system is shown to produce a steady-state oscillation. Missile dynamics in the presence of this hunting are developed and the relationships governing angular position and rates are found to be functions of the oscillation frequency, control force magnitude, and missile constants (geometry and weight). The describing function technique is utilized to determine graphically the relationship among frequency, hysteresis band, and system time delays. A comparison is made between the root locus and amplitude-phase presentation. An analog computer study of system behavior is presented to illustrate the agreement between the analysis and system performance.