Semi-active control systems

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. 

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... 

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

As a final example of a MR fluid controlled adaptronic system, the smart prosthesis knee developed by Biedermann Motech GmbH [178-181] is presented. This system shown in Fig. 6.91 is a complete artificial knee that automatically adapts and responds in real-time to changing conditions to provide the most natural gait possible for above-knee amputees. The heart of this system is a small magnetorheological fluid damper that is used to semi-actively control the motion of the knee based on inputs from a group... 

Magnetorheological fluid actuators provide technology that enables effective semi-active control in a number of real-world applications. Automotive applications of MR fluid are significant and growing rapidly. Annual production of MR fluid is now on the order of hundreds of tons. It is estimated that more than one hundred thousand MR fluid devices are presently in use. This number is expected to rise into the millions as more automotive platforms adopt MR fluid based real-time controlled motion control systems. Due to their simplicity, low power, and inherent robustness, MR fluid devices have proven themselves in a wide variety of commercial applications. 

In addition to the trend to increasingly use soft active engine mounts there is an increasing importance to optimize the NVH-characteristics of the chassis. An example for a semi-active mechatronic system for chassis control based on electrohydraulics was investigated in [160], whereas different active systems recently focussed on AVC within convertibles [151]. The latter will be discussed below. 

Semi-Active (Adaptive-Passive) Systems Refer to an adjustable passive vibration control scheme, that is, the passive treatment can adjust itself in response to changes in the structure. For example, the stiflfiiess, damping coefficient or other variables of the passive control scheme can change automatically so that optimal vibration mitigation is induced. These variable components, also known as tunable parameters of the control system, are re-tailored via a properly developed semi-active control algorithm. Being more versatile than passive control techniques and more affordable (in terms of cost and energy consumption) than active control schemes, has made semi-active control methods very popular. 

The main objective of this chapter is to find the optimal values of the base isolation system as a kind of passive control device, and that of the STMD system as a kind of semi-active control device using genetic algorithms (GAs) and fuzzy logic to simultaneously minimize the buildings selected responses. A comprehensive literature review of these systems is provided in the main relevant sections of each system. 

Gluck, J., Ribakov, Y. (2000). Semi-active friction system with amplifying braces for control of MDOF structures. Structural Design of Tall Buildings, 10(2), 107-120. doi 10.1002/tal.l68... 

Leitmarm, G. (1994). Semi-active control for vibration attenuation. Journal of Intelligent Material Systems and Structures, 5, 841-846. doi 10.1177/1045389X9400500616... 

A semi-active control device cannot inject energy into the controlled system (structure and device) but has properties that can be varied in real time in order to reduce the response of a structural system (Housner et al. 1997). Changes in mechanical properties of the device are based on feedback from measured response and/or ground excitation. Therefore, in contrast to active control devices, semi-active ones do not destabilize the structural system. They offer... 

Actively and Semi-actively Controlled Structures Under Seismic Actions Modeling and Analysis, Fig. 8 Simplified diagram of DUOX control system... 

Base isolation systems are passive systems, and they do not have the ability to adapt and change their properties in different external excitation (e.g., near- or far-fault excitation). With the addition of an active or semi-active control device to a base-isolated structure, a higher level of performance can be achieved without a substantial increase in the cost. This thought has led to another type of hybrid control system, referred to as hybrid seismic isolation, consisting of active or semi-active devices introduced in base-isolated structures (see Fig. 9). Although base isolation has the ability to reduce interstory drifts and structural accelerations, it increases base displacement, hence the need for an active or semi-active device. In addition, a semi-active friction-controllable fluid bearing has been employed in parallel with a seismic isolation system (Feng and Shinozuka 1992 Sriram et al. 2003). 

Makris N, Hill D, Burton S, Jordan M (1995) Electrorheological fluid damper for seismic protection of structures. In Proceedings of the smart stmctures and materials, San Diego, pp 184—194 Martin RC, Soong TT (1976) Modal control of multistory structures. ASCE J Eng Mech 102 613-623 Nagarajaiah S, Mate D (1998). Semi-active control of continuously variable stiffness system. In Proceedings of the 2nd world conference on structural control, Kyoto, vol 1, pp 397 105... 

LOPA is a semi-quantitative tool for analyzing and assessing risk. This method includes simplified methods to characterize the consequences and estimate the frequencies. Various layers of protection are added to a process, for example, to lower the frequency of the undesired consequences. The protection layers may include inherently safer concepts the basic process control system safety instrumented functions passive devices, such as dikes or blast walls active devices, such as relief valves and human intervention. This concept of layers of protection is illustrated in Figure 11-16. The combined effects of the protection layers and the consequences are then compared against some risk tolerance criteria. 

The prime contractor is Raytheon Co, and it is powered by the Hercules Mark 58 Mod 0 solid proplnt rocket motor. The airframe is a slim cylindrical body with a pointed ogive nose. Pivoted cruciform delta wings are mid-way along the body, indexed in line with cruciform delta tail fins. Guidance is a Raytheon semi-active Doppler radar homing system, with control by movable wings... 

The TBS utilises both a passive radiator cooling system and a semi-active system comprising heaters and thermal sensors that are controlled and managed by the Thermal Control Unit (TCU). MLI is used to thermally decouple the experiment from deep space and solar effects. Thermal screens consisting of Kapton foil (X-Ray transparent) are interposed in the telescopes field of... 

Innovative seismic control systems belongs to the world of the vibration control techniques of structures, which includes passive, semi-active, active and hybrid systems (Housner et al., 1997 Spencer, 2003 Christopoulos and Filiatrault, 2007). The experiences acquired during experimental activities and worldwide apvplications have indicated the passive control techniques as the most suitable solutions for the seismic protection of structures. These systems modify the stiffness and/or the dissipative properties of the structure, favoring the reduction of the dynamic response to seismic actions. They can be classified on the basis of... 

Interest in MR fluids stems from the benefits they enable in mechatronic systems. Much of the current interest in MR fluids can be traced directly to the need for a simple, robust, fast-acting valve necessary to enable semiactive vibration control systems [148 150]. Such a valve was the holy grail of semi-active vibration-control technology for nearly two decades beginning in... 

S5mians, M. D., Kelly, S. W. (1999). Fuzzy logic control of bridge structures using intelligent semi-active seismic isolation systems. Earthquake Engineering Structural Dynamics, 25(1), 37-60. doi 10.1002/(SICI) 1096-9845(199901)28 K37 AID-EQE803>3.0.CO 2-Z... 

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