This chapter begins with a short discussion of the concept of semi-active control (passive devices with variable properties which can be changed with little energy). Next, the magneto-rheological (MR) fluids are described, and their modelling is briefly discussed (the simple Bingham model is sufficient in many applications); the operating modes (valve, shear, pinch modes) are described. It is followed by a discussion of various MR devices: MR shock absorber, MR brake, MR engine mount. Next, a quarter-car semi-active suspension model is analyzed and it is shown how the so-called “semi-active sky-hook” is prone to chatter, exciting higher frequencies.
KeywordsSemi-active control Magneto-rheological fluid (MR) Electro-rheological fluid (ER) Shock absorber MR brake Engine mount Bingham model
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