title: Speed control with low armature loss for very small sensorless brushed DC motors

authors: Scott, Jonathan B.

subjects: DC motor drives

abstract: A method for speed control of brushed dc motors is presented. It is particularly applicable to motors with armatures of less than 1 cm3. Motors with very small armatures are difficult to control using the usual pulsewidth-modulation (PWM) approach and are apt to overheat if so driven. The technique regulates speed via the back electromotive force but does not require current-discontinuous drives. Armature heating in small motors under PWM drive is explained and quantified. The method is verified through simulation and measurement. Control is improved, and armature losses are minimized. The method can expect to find application in miniature mechatronic equipment.

text: Speed control with low armature loss for very small sensorless brushed DC motors A method for speed control of brushed dc motors is presented. It is particularly applicable to motors with armatures of less than 1 cm3. Motors with very small armatures are difficult to control using the usual pulsewidth-modulation (PWM) approach and are apt to overheat if so driven. The technique regulates speed via the back electromotive force but does not require current-discontinuous drives. Armature heating in small motors under PWM drive is explained and quantified. The method is verified through simulation and measurement. Control is improved, and armature losses are minimized. The method can expect to find application in miniature mechatronic equipment.

year: 2009

title: Wave dissipation by flexible vegetation

authors: Riffe, Kassi C.

subjects: wave

abstract: Dissipation of waves propagating through natural salt marsh vegetation was about half the dissipation expected for rigid vegetation. This low dissipation was predicted by a theoretical model that accounts for bending of vegetation by wave motions. A transect of 3 pulse-coherent Acoustic Doppler Current Profilers recorded water velocity and pressure (at 8 Hz) within the dense (650 stems/m²) canopy of semi-flexible single-stem vegetation (Schoenoplectus americanus). Most wave energy (56 - 81%) was dissipated within 19 m of the marsh edge. Two dissipation models, the first assuming rigid vegetation, and the second simulating wave-forced vegetation motion using the theory for bending of linearly-elastic beams, were tested. After choosing optimal drag coefficients, both models yielded a good fit to the observed dissipation (skill score = 0.95 - 0.99). However, fitted drag coefficients for the rigid model (0.58 - 0.78) were below the range (0.98 - 2.2) expected for the observed Reynolds numbers (13 - 450) and canopy densities (accounting for interactions between stem wakes), whereas drag coefficients for the flexible model (0.97 - 1.6) were nearer the expected range, indicating that prediction of wave dissipation was improved by simulating vegetation motion.

text: Wave dissipation by flexible vegetation Dissipation of waves propagating through natural salt marsh vegetation was about half the dissipation expected for rigid vegetation. This low dissipation was predicted by a theoretical model that accounts for bending of vegetation by wave motions. A transect of 3 pulse-coherent Acoustic Doppler Current Profilers recorded water velocity and pressure (at 8 Hz) within the dense (650 stems/m²) canopy of semi-flexible single-stem vegetation (Schoenoplectus americanus). Most wave energy (56 - 81%) was dissipated within 19 m of the marsh edge. Two dissipation models, the first assuming rigid vegetation, and the second simulating wave-forced vegetation motion using the theory for bending of linearly-elastic beams, were tested. After choosing optimal drag coefficients, both models yielded a good fit to the observed dissipation (skill score = 0.95 - 0.99). However, fitted drag coefficients for the rigid model (0.58 - 0.78) were below the range (0.98 - 2.2) expected for the observed Reynolds numbers (13 - 450) and canopy densities (accounting for interactions between stem wakes), whereas drag coefficients for the flexible model (0.97 - 1.6) were nearer the expected range, indicating that prediction of wave dissipation was improved by simulating vegetation motion.

year: 2011

title: Māori language interfaces

authors: Keegan, Te Taka Adrian Gregory

abstract: This paper considers the usability of the interface and the ramifications for te reo Māori if the interface language, the messages displayed in those text boxes, is written in te reo Māori.

text: Māori language interfaces This paper considers the usability of the interface and the ramifications for te reo Māori if the interface language, the messages displayed in those text boxes, is written in te reo Māori.

year: 2017