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Unformatted text preview: MIT OpenCourseWare http://ocw.mit.edu 2.004 Dynamics and Control II Spring 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms . L L 8 = > I i n d i c a t e s t h a t w e a s s u m e L > L > = = > . I i n d i c a t e s t h a t w e a s s u m e t h e c u r r e n t f l o w i n t h e d i r e c t i o n o f t h e a r r o w o r t h a t t h e s o u r c e a c t s t o m o v e n o d e = i n t h e p o s i t i v e r e f e r e n c e d i r e c t i o n i n a m e c h a n i c a l s y s t e m Massachusetts Institute of Technology Department of Mechanical Engineering 2.004 Dynamics and Control II Spring Term 2008 Lecture 16 1 Reading: Class Handout- Modeling Part 3: Two-Port Energy Transducing Elements 1 Arrow Conventions on Ideal Sources To this point we have simply told you to draw the arrows on source elements (a) In the direction of the assumed across-variable drop for across-variable sources (voltage and velocities), (b) in the direction of the assumed through-variable direction for through-variable sources (currents and forces) When we draw a branch on a graph we make the assumption that P > 0, that is that power is owing into the element. There are in fact two arrows implicit on each branch: one representing the assumed across-variable drop, and a second representing the assumed through-variable direction. If P > (power is owing into the element), the two arrows are in the same direction. For example, consider a capacitor 1 copyright c D.Rowell 2008 161 S y s t e m 1 I a c r o s s - v a r i a b l e d r o p t h r o u g h - v a r i a b l e d i r e c t i o n 4 d r o p +- E 4 d r o p E Z Z Z v = s V 1 2 F s 1 2 3 L o o p 1 : v + v - V = 0 Z 1 s Z 2 L o o p 2 : v - v = 0 Z 3 Z 2 + L > L = E + d r o p L + = > E + L + = > v o l t a g e d r o p a n d c u r r e n t i n t h e s a m e d i r e c t i o n v o l t a g e d r o p a n d c u r r e n t i n t h e o p p o s i t e d i r e c t i o n P = v c i c > when either P = v c i c < when either 1. v c > and i c > 0,or 1. v c > and i c < 0,or On 2. v c < and i c < 0. 2. v c < and i c > 0....
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lecture_16 - MIT OpenCourseWare http://ocw.mit.edu 2.004...

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