Active control systems

Although many engineers provide only the minimum adequate vessel design to minimize costs, it is inherently safer to minimize the use of safety interlocks and administrative controls by designing robust equipment. Passive hardware devices can be substituted for active control systems. For example, if the design pressure of the vessel system is higher than the maximum expected pressure, an interlock to trip the system on high pressure or temperatures may be unnecessary. 

Active perimeter gas control systems control off-site gas migration with the use of an active control system to alter pressure gradients and paths of gas movement by mechanical means. Three or four major components are required in active perimeter gas control systems ... 

The efficacy of the active control system for soot reduction was demonstrated in both open and enclosed combustion systems using gaseous fuels. 

Langhorne, P. J., A. P. Dowling, and N. Hooper. 1990. Practical active control system for combustion oscillations. J. Propulsion Power 6 324-30. 

Lee, J. G., and D. A. Santavicca. 1998. Application of flame evolution imaging to the optimization of an active control system for suppressing combustion instability. 27th Symposium (International) on Combustion Proceedings. Pittsburgh, PA The Combustion Institute. 

When Ei differs sufficiently from E%, then with the change in pH two wave appear on polarographic curves. Furthermore, if n = n%, the change in the wave-heights is similar to that shown in Fig. 2. The difference between the thermodynamic and activation-controlled systems is that in the region in which the two waves are observed for the equilibrium case, described in Chapter 2.1, both waves are diffusion-controlled, whereas for the activation-controlled system discussed here, the more positive wave at i <0.15 ia possesses a kinetic character. 

Biological materials are, almost by definition, selfassembling—which generally also implies that there are active control systems to provide self-repair, self-reinforcement, and disassembly when needed. Self-assembly has become an objective of much of materials chemistry for example, in the formation of mesoporous silica and of colloidal crystals with potential uses in photonic tech-... 

Active Vibration Reduction. An active vibration control system consists of a hydraulic or electrodynamic actuator, vibration sensor, and electronic controller designed to maintain the seat pan stationary irrespective of the motion of the seat support. Such a control system must be capable of reproducing the vehicle motion at the seat support, which will commonly possess large displacement at low frequencies, and supply a phase-inverted version to the seat pan to counteract the vehicle motion in real time. This imposes a challenging performance requirement for the control system and vibration actuator. Also, the control system must possess safety interlocks to ensure it does not erroneously generate harmful vilxation at the seat pan. While active control systems have been employed commercially to adjust the static stiffness or damping of vehicle suspensions, to improve the ride comfort on different road surfaces, there are currently no active seat suspensions. 

Conventional dynamic vibration absorbers are composed of a mass, spring, and damper. Although dynamic vibration absorbers do not have sensors or controllers, they can provide vibration mitigation similar to that of actively controlled systems with a complicated sensor, control, and actuator system. Since an absorbers mass/spring/damper forms a single degree of freedom (DOF) vibration system, it consequently has a single resonant frequency and can exhibit an amplified response at this frequency. Dynamic absorbers behave similar to a system with a sensor to detect the specific frequency and a controller to amplify the vibration. Therefore, the absorbers natural frequency should be carefully tuned to a specific frequency for which the vibration amplitude of the host structure is to be reduced. The tuned frequency usually corresponds to natural modes and harmonically excited vibrations of a system. 

Tamura, K. Technology of active control systems for structured vibration. Int. Post-SMiRT Conf. Seminar, Capri (1993)... 

To spoil the neutron economy to increase leakage to give up on internal conversion ratio and go to active control systems to compensate bum-up reactivity loss or... 

The dynamic response of civil engineering structures subjected to earthquake excitation can be reduced by using passive control systems such as energy dissipation devices (e.g. viscous dampers, etc.). The advantage of these systems with respect to active and semi-active control systems consist in the fact that they don t require any power supply, therefore are quite reliable and they require least maintenance. 

An active control system may be defined as a system which typically requires a large power source for operation of electrohydraulic or electro-... 

S5mians, M. D., Constantinou, M. C. (1999). Semi-active control systems for seismic protection of structures A state-of-the-art review. Engineering Structures, 21, 469-487. doi 10.1016/ S0141-0296(97)00225-3... 

Many state of the art publications on control applications are published. These publications provide a review of base isolation systems (Kelly, 1986), active control (Soong, 1988, 1990, 1994, Datta, 2003), structural control concepts and strategies (Housner, 1997, Spencer, 2003), etc. Inmost cases active control systems are designed based on the linear quadratic regulator (LQR) theory or... 

Analysis of the amplification and active controlled devices placement on efficiency of a control system was performed. A twenty-story fi-amed structure with active control systems including different dampers configurations was simulated. The response of the structure to an artificial white noise ground motion was simulated in order to find the optimal locations of control devices. Behavior of the structure was further investigated under natural earthquake excitations. 

The main advantage of passive compensation systems is not to require an active control system to reduce the load or the damage caused by the earthquake. This makes them a favourite in cases where the electric energy supply may fail and destruction of even small parts of the edifice would be equivalent to a total economic loss. 

These systems behave similarly to passive ones but, instead of inert devices, there are highly powered mechanisms (actuators) that are able to push the structure to counteract the input effect. Hydraulic cylinders driven by servo-valves are examples of actuators. An active control system is composed of a set of sensors to measure on-line the response of the structure (mostly displacements and accelerations), the actuators, a source or reservoir of eneigy to power the actuators and a controller (typically a computer) that decides the amounts of forces to be exerted by the actuators. 

Figure 1. Example of active (or semi-active) control system (active mass damper)...

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