tailieunhanh - Crc Press Mechatronics Handbook 2002 By Laxxuss Episode 1 Part 5

Tham khảo tài liệu 'crc press mechatronics handbook 2002 by laxxuss episode 1 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | fs Thermal port a Resistive Causality f R e bR f Conductive Causality e f -1 f b FIGURE a Resistive bond graph element. b Resistive and conductive causality. F F . a V1 F3 O V3 F1 F3 F2 F 11----0-------- H1 F3 V R b FIGURE a Two sliding surfaces. b Bond graph model with causality implying velocities as known inputs. and entropy flow rate fs is the flow variable. To compute heat generated by the R element compose the calculation as Q heat in watts T f X ei fị over the n ports. The system attached to a resistive element through a power bond will generally determine the causality on that bond since resistive elements generally have no preferred causal Two possible cases on a given R-element port are shown in Fig. b . A block diagram emphasizes the computational aspect of causality. For example in a resistive case the flow . velocity is a known input so power dissipated is Pd e f F f f. For the linear damper F b V so Pd F V by2 W . In mechanical systems many frictional effects are driven by relative motion. Hence identifying how a dissipative effect is configured in a mechanical system requires identifying critical motion variables. Consider the example of two sliding surfaces with distinct velocities identified by 1-junctions as shown in Fig. a . Identifying one surface with velocity V1 and the other with V2 the simple construction shown in Fig. b shows how an R element can be connected at a relative velocity V3. Note the relevance of the causality as well. Two velocities join at the 0-junction to form a relative velocity which is a causal input to the R. The causal output is a force F3 computed using the constitutive relation F F V . The 1-junction formed to represent V3 can be eliminated when there is only a single element attached as shown. In this case the R would replace the 1-junction. When the effort-flow relationship is linear the proportionality constant is a resistance and in mechanical systems these quantities are typically