Fluid damper

A torsional spring of stiffness K, a mass of moment of inertia / and a fluid damper with damping coefficient C are connected together as shown in Figure 3.25. The angular displacement of the free end of the spring is 0 ( ) and the angular displacement of the mass and damper is 6a t). 

This High Intelligence Prosthesis for the knee uses an MR fluid damper to provide motion that closely duplicates the naturai movement of the knee joint. 

Yang G (2001) Large-scale magnetorheological fluid damper for vibration mitigation modeling, testing and control. Ph.D. Dissertation. University of Notre Dame, Notre Dame, IN, 2001... 

An example of a simple valve-mode device is the RD-1005-3 linear damper by Lord Corporation shown in Fig. 6.77 [152]. As in the vast majority of all commercial MR fluid dampers, these dampers have an internal, axi-symmetric valve with an annular flow path. In this case the damper is a single-ended, mono-tube style having an internal rod volmne accumulator pressurized with nitrogen. As indicated in the Fig. 6.77, downward motion of the piston causes MR fluid to flow up through the annular flow channel. Application of current to the coil creates a magnetic field that interacts with the MR fluid in two regions where the magnetic flux crosses the flow channel. 

The range of force control that is possible with a valve-mode MR fluid damper is illustrated in Fig. 6.78. Here the force/velocity character that is typical of a passive hydraulic damper is compared to the range of forces possible with a MR damper. With appropriate control based on displacement, velocity or acceleration, any force profile between the upper and lower bounds can be realized. Unlike passive viscous dampers, with the MR damper it is easy to achieve large force at very low speed. 

Fig. 6.77. Basic MR fluid damper with axi-symmetric valve geometry Force...

Fig. 6.78. Controllable force range possible with MR fluid damper Direct-Shear Mode...

In another civil engineering application, MR fluid dampers have been used to mitigate potentially damaging wind-induced cable vibrations in a cable-... 

Fig. 6.89. MR fluid dampers used control wind-induced cable vibrations on Dong ting Lake cable-stayed bridge in central China...

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... 

Fig. 6.91. Above-knee prosthesis with real-time control provided MR fluid damper...

Fig. 6.93. Algorithm for controlling the MR fluid damper in the artiflcial knee...

Gandhi, F. Wang, K.W. and Xia, L. Magnethorheological fluid damper feedback linearization control for helicopter rotor application. Smart Mater. Struct., 10 (2001), pp. 96-103... 

Numerous dampers have been developed to release seismic forces such as soft steel damper, friction damper, magneto-rheological (MR) damper, viscous fluid damper, etc. In this study, the relative mature viscous fluid damper is applied. The force of damper varying with the relative velocity can be formed as ... 

The tuned mass damper (TMD) system is a typical form of control devices including a mass, spring, and a viscous fluid damper, which can be attached to the main structure at one of its degrees offreedom. This system is one ofthe well-accepted devices to control flexible structures, particularly, tall buildings. In this passive control system, if its damping ratio or stiffness of the spring changes with time, then it is called a semi-active tuned mass damper (STMD). 

Passive control devices are devices that do not require power to operate. Examples of passive devices are base isolation, tuned mass dampers (TMD), tuned liquid dampers (TLD), metallic yield dampers, viscous fluid dampers, and... 

Examples of such devices include variable orifice fluid dampers, controllable friction devices, variable stiffness devices, controllable liquid dampers, and controllable fluid dampers (Figs. 6 and 7). A variable orifice fluid damper uses an electromechanically variable orifice to alter the resistance to flow of a conventional hydraulic fluid (Feng and Shinozuka 1992 Constantinou et al. 1993). 

The discovery of both ER and MR fluids dates back to the late 1940s (Winslow 1947). ER fluid dampers have been developed, modeled, and tested for civil engineering applications (Erhrogott and Marsi 1992, 1993 Makris et al. 1995). Work on MR devices have been done by Spencer et al. (1997), Soong and Spencer (2002), Spencer and Nagarajaiah (2003), Carlson et al. (1995), and Dyke et al. (1996c-f). 

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... 

Blind Identification of Output-Only Systems and Structural Damage via Sparse Representations, Fig. 2 The experimental highly-damped 3-story steel fiame and the zoomed fluid damper... 

---