scholarly journals Optomechanics of a stable diffractive axicon light sail

2020 ◽  
Vol 135 (7) ◽  
Author(s):  
Prateek R. Srivastava ◽  
Grover A. Swartzlander
Keyword(s):  
Stability Analysis ◽  
Numerical Integration ◽  
Linear Stability ◽  
Radiation Pressure ◽  
Linear Stability Analysis ◽  
Diffraction Grating ◽  
Equations Of Motion ◽  
Longitudinal Force ◽  
Longitudinal Acceleration ◽  
Diffractive Axicon

Abstract Beamed propulsion of a light sail based on radiation pressure benefits from a passively self-stabilizing “beam riding” diffractive film. We describe the optomechanics of a rigid non-spinning light sail that mitigates catastrophic sail walk-off and tumbling by use of a flat axicon diffraction grating. A linear stability analysis and numerical integration of the coupled translational and rotational equations of motion are examined. Stability is traded against longitudinal acceleration. The examined system achieves 90% of the theoretical longitudinal force limit and stability against a relative sail translation up to 30% of the sail radius when the payload is attached to a long boom.

scholarly journals Dynamical properties of forced shear layers in an annular geometry

2000 ◽  
Vol 402 ◽  
pp. 255-289 ◽  
Author(s):  
K. BERGERON ◽  
E. A. COUTSIAS ◽  
J. P. LYNOV ◽  
A. H. NIELSEN
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Initial Conditions ◽  
Landau Equation ◽  
Equations Of Motion ◽  
Reynolds Numbers ◽  
Radius Of Curvature ◽  
Simulation Code ◽  
Annular Geometry

Results of numerical simulations of a forced shear flow in an annular geometry are presented. The particular geometry used in this work reduces the effects of centrifugal and Coriolis forces. However, there are still a large number of system parameters (shear width, shear profile, radius of curvature, initial conditions, etc.) to characterize. This set of variables is limited after the code has been validated with experimental results (Rabaud & Couder 1983; Chomaz et al. 1988) and with the associated linear stability analysis. As part of the linear stability characterization, the pseudo-spectrum for the associated Orr–Sommerfeld operator for plane, circular Couette flow is calculated, and it is found to be insensitive to perturbations.The numerical simulation code is a highly accurate de-aliased spectral method which utilizes banded operators to increase the computational efficiency. Viscous dissipation terms enter the code directly from the equations of motion. The results from the simulation code at low Reynolds numbers are compared with the results from linear stability analysis and are used to give predictions for the coefficients of the Landau equation describing the saturation behaviour near the critical Reynolds number. Numerical results at higher Reynolds numbers demonstrate the effects of spin-up and spin-down, including the experimentally observed hysteresis. The properties of two- dimensional shears at high Reynolds numbers, at which temporal states are formed, are also addressed.

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