# lec1 - AE 383 SYSTEM DYNAMICS A system is considered as an...

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1 AE 383 SYSTEM DYNAMICS A system is considered as an assemblage of components or elements . Dynamics refers to situations which change with time. System Dynamics: i. Deals with entire operating machines and processes rather than isolated components. ii. Examines the dynamic behavior of mechanical, electrical, fluid, thermal and “mixed” systems. iii. Emphasizes the behavioral similarity between systems that differ physically and develops general analysis and design tools useful for all kinds of physical systems. iv. Develops universal lab test methods for characterizing component behavior. v. Serves as a common unifying foundation for many later courses and practical application areas, such as vibration, measurement systems, control systems, circuit analysis, acoustics, vehicle dynamics. vi. Has a wide variety of computer software to implement its methods of analysis and design. Input-Output Representation of Systems Inputs may be thought of as those entities which cause a system to respond with some sort of action or output: that is, there is a cause and effect relation between the inputs and the outputs. In system dynamics the concept of cause-effect relation is formalized and represented mathematically by differential equations and transfer functions. In a “block diagram” representation of a system inputs and outputs are shown as arrows and the system is shown as a block with the mathematical operation performed on the input signal. The signals are in the direction of the arrows. Signals: In the context of this course a signal is a phenomenon that represents information and may be described quantitatively . Examples: Voltage in an electrical circuit, elevator deflection of an aircraft. Transfer Function G(s) Input Signal Output Signal

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2 Classification of Inputs and Systems It is useful to classify the inputs and systems. When inputs and the system are defined the output is determined. System Inputs Initial Energy Storage External Driving Kinetic Potential Deterministic Random Initial velocity, Compressed spring Fluid flow Charged capacitor Transient Periodic Stationary Nonstationationary A transient input can have any desired shape but exists only for a certain time. Periodic inputs repeat a certain wave form over again. (Good models for constant- speed operation of many processes. )
3 Random inputs are more realistic input models. They cannot be formulated as functions of time but their statistical properties can be specified such as average value, mean square value etc. If the statistical properties are not changing with time then the signal is stationary , otherwise it is non stationary. Mathematical Modeling of Dynamic Systems Mathematical modeling implies the description of the important system characteristics by sets of equations. By applying the physical laws, it may be possible to develop a mathematical model that describes the dynamics of the system. The parameters required by the physical laws are usually obtained from actual tests.

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## This note was uploaded on 10/24/2011 for the course AEE 463 taught by Professor Melin during the Spring '11 term at Middle East Technical University.

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lec1 - AE 383 SYSTEM DYNAMICS A system is considered as an...

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