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TYPES OF SYSTEMS, PROBLEMS, AND STRATEGIES 3 TYPES OF DYNAMICAL SYSTEMS, CONTROL PROBLEMS AND CONTROL STRATEGIES The field of controls is very broad. Even when it’s restricted to dynamical systems, it still applies to a very wide range of problems. It applies to mechanical systems, aerospace systems, civil systems, to mention a few. The systems are commercial products, systems found in manufacturing lines, processing facilities, and systems used in laboratories settings. The control problems appear to vary widely, but they exhibit important characteristics that are independent of the application. Both the systems and the control objectives exhibit common features that dictate shared control strategies. In this introductory section, we describe the properties of dynamical systems that are pertinent to their control, the control objectives that are sought, and the control strategies that are adopted to meet the control objectives. 1. Applications This section introduces in broad terms the themes treated in detail later in the notes. To keep the MAE 461: DYNAMICS AND CONTROLS
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discussion concrete, we start by describing three familiar areas of application: the automotive vehicle, the building structure, and the aircraft vehicle. Then, we look at what they have in common in terms of their dynamics, the control objectives, and the control strategies. The Automotive Vehicle Control systems are used in automotive vehicles for braking, cruising, and for producing a comfortable ride. Anti-lock brake control systems prevent skidding, cruise control regulates speed, springs and shocks produce a comfortable ride, and the suspension system produces good handing qualities. The anti-lock brake is a balanced, rigid disk that has one rotational degree-of-freedom acted on by a moment produced by a friction force reaction exerted on the wheel by the road and by a control moment produced by a sliding disk contact. Cruise control regulates the vehicle’s speed, functioning as a gas pedal that either increases or decreases a torque delivered to wheels. Four springs and four shocks control stiffness and damping of vehicle vibration caused by road disturbances. The suspension system controls vehicle motion for handling during turns and it controls the distribution of wheel loads on each end of an axle, thereby controlling wheel traction. The Building Structure Control systems are found in long-span bridges and tall towers to prevent them from swaying during earthquakes and hurricanes. Control systems found in off-shore towers prevent swaying resulting from ocean swells. Earthquakes, hurricanes, and ocean swells occur infrequently, but when they occur they cause deformations that in turn produce unacceptably high stresses, ultimately resulting in failure. Reducing the deformations by heavily reinforcing a structure can multiply the cost of a structure by a factor of ten or more, which is a high cost to pay to prevent an MAE 461: DYNAMICS AND CONTROLS
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This note was uploaded on 09/17/2009 for the course MAE 469 taught by Professor Silverberg during the Fall '08 term at N.C. State.

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