Operation Characteristics of Steady-State, Applied Field, Rectangular Magnetoplasmadynamics (MPD) Thruster

2015 ◽  
Vol 63 (2) ◽  
pp. 37-44 ◽  
Author(s):  
Daisuke ICHIHARA ◽  
Shota HARADA ◽  
Hisashi KATAOKA ◽  
Shigeru YOKOTA ◽  
Akihiro SASOH
Keyword(s):  
Steady State ◽  
Applied Field ◽  
Operation Characteristics

Nonlinear electrohydrodynamics of slightly deformed oblate drops

2015 ◽  
Vol 774 ◽  
pp. 245-266 ◽  
Author(s):  
Javier A. Lanauze ◽  
Lynn M. Walker ◽  
Aditya S. Khair
Keyword(s):  
Steady State ◽  
Electric Field ◽  
Surface Charge ◽  
Time Scale ◽  
Applied Field ◽  
Major Axis ◽  
Boundary Integral ◽  
Numerical Results ◽  
Transient Deformation ◽  
Leaky Dielectric

The transient deformation of a weakly conducting (‘leaky dielectric’) drop under a uniform DC electric field is computed via an axisymmetric boundary integral method, which accounts for surface charge convection and a finite relaxation time scale over which the drop interface charges. We focus on drops that attain an ultimate oblate (major axis normal to the applied field) steady-state configuration. The computations predict that as the time scale for interfacial charging increases, a shape transition from prolate deformation (major axis parallel to the applied field) to oblate deformation occurs at intermediate times due to the slow buildup of charge at the surface of the drop. Convection of surface charge towards the equator of the drop is shown to weaken the steady-state oblate deformation. Additionally, convection results in sharp shock-like variations in surface charge density near the equator of the drop. Our numerical results are then compared with an experimental system consisting of a millimetre-sized silicone oil drop suspended in castor oil. Agreement in the transient deformation is observed between our numerical results and experimental measurements for moderate electric field strengths. This suggests that both charge relaxation and charge convection are required, in general, to quantify the time-dependent deformation of leaky dielectric drops. Importantly, accurate prediction of the observed modest deformation requires a nonlinear model. Discrepancies between our numerical calculations and experimental results arise as the field strength is increased. We believe that this is due to the observed onset of rotation and three-dimensional flow at such high electric fields in the experiments, which an axisymmetric boundary integral formulation naturally cannot capture.

Steady-State Spatial Screening Solitons in Photorefractive Materials with External Applied Field

1994 ◽  
Vol 73 (24) ◽  
pp. 3211-3214 ◽  
Author(s):  
Mordechai Segev ◽  
George C. Valley ◽  
Bruno Crosignani ◽  
Paolo DiPorto ◽  
Amnon Yariv
Keyword(s):  
Steady State ◽  
Applied Field ◽  
Photorefractive Materials ◽  
Screening Solitons

Robot torque and position control using an electrorheological actuator

1998 ◽  
Vol 212 (3) ◽  
pp. 229-238 ◽  
Author(s):  
D J Brookfield ◽  
Z B Dlodlo
Keyword(s):  
Steady State ◽  
Applied Field ◽  
Position Control ◽  
Open Loop ◽  
Settling Time ◽  
Time Varying ◽  
Control Loop ◽  
Loop Transfer Function ◽  
Non Linear ◽  
State Error

An electrorheological (ER) clutch driven from a constant speed motor provides a steady torque independent of shaft angle and can be controlled by control of the applied field. Such an actuator avoids the ‘cogging’ variation in torque observed in d.c. servo-motors and is thus well suited to robot control applications, particularly in view of the very rapid time response of ER clutches (≍ 10−3 s). However, the relationship between applied field and torque is difficult to model, being both non-linear and time varying. Whereas the non-linearity can be shown to be relatively small, the time-varying characteristic has remained a problem. In most controlled plants, a non-linear or time-varying characteristic can be mitigated by providing a closed control loop around the plant. A PID (proportional plus integral plus derivative)-based torque controller was developed and tested. This was shown to be stable with at least critical damping and to exhibit low steady state error. Design of the controller was facilitated by the identification of the open-loop transfer function of the ER actuator. The ER actuator with torque feedback was used to position a small robot link. A second PID control loop responding to the error in the link position and tuned using the standard Ziegler and Nichols method was designed and tested. A steady state error of less than 0.75 mm was achieved with a 2 per cent settling time of 2.0 s. Finally, the link position was controlled using a single-loop controller with no torque feedback and a similar steady state error achieved with a 2 per cent settling time of 1.4 s. It is argued that the ER torque actuator is ideally suited to the actuation of robot joints where precise smooth movement is required.

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