Axial Degrees Of Freedom Research Articles

Experimental Validation of a Novel Concept to Reduce Optical Surface Wave Front Errors by Using Deformable Bushes at Opto-Mechanical Interfaces

One of the major objectives of the optomechanics is to support large optics required for the purpose and also to maintain high dynamic stability in operation. This requirement calls for more number of supports, to support large optics. While addressing this issue, the mounting system tends to become non-kinematic and distorts the optical surface and leads to poor image quality. The distorted optical surfaces bring in increased RMS surface wavefront errors which will result in poor image quality. In this context, a new concept is proposed in our previous publication ( Nagabhushana et al., 2021 ) which involves introduction of deformable bushes at the optomechanical interfaces. These are deformed by applied clamping forces and also enabling all degrees of freedom (DOF) to be arrested. This also ensures that the clamping force in axial DOF is limited to a minimal value. This technique enables to arrest of axial DOF without exerting the clamping force on the optomechanical assembly there by reduces optical aberrations and improves the mounting system’s dynamic stability. This is because deformable bushes absorb all the clamping forces and the strain has no impact on the mount and therefore does not lead deformation of the optical surface. The clamping forces are simulated by Finite Element (FE) methods. Further, in this paper, the concept is verified and validated by experiments. The simulation results are observed to be in close correlation with experiment results. Improved stability is also observed by additional constraints introduced to optomechanical mounts with no compromise in wavefront errors.

A Novel Approach to Reduce Optical Aberrations by using Deformable Bushes at Opto-Mechanical Interfaces

There is a continuous need to enhance the aperture size of telescopes by astronomers to explore the space much deeper by getting better resolutions and high image quality. Supporting large optics and maintaining high dynamic stability involves more number of constraints. This renders optical surface more distorted and results in poor image quality, since the image quality deteriorates with increase in RMS surface error. A new approach is proposed to introduce deformable bushes at the interfaces. These are tuned to deform under specific clamping force and thus arrests all Degrees of Freedom (DOF). This limits the clamping force exerted by an axial DOF ([Formula: see text]) to an insignificant value. This approach helps to arrest [Formula: see text] without imposing clamping stress on the opto-mechanical mount and brings down optical aberrations and enhances dynamic stability of the mounting system. This due to the fact that all clamping forces are taken by deformable bushes and the stress is not transferred to mount and thus does not contribute to non-uniformity of the optical surface. The non-uniformity of the optical surfaces influenced by clamping forces is simulated by Finite Element (FE) techniques. The use of deformable bush approach in minimizing optical aberrations and stability enhanced by additional constraints to opto-mechanical mounts are demonstrated by simulations.

Response of a High Damping Rubber Bearing to Multiaxial Excitation

Abstract A high damping rubber bearing fabricated as part of a seismic isolation system was tested at the Caltrans Seismic Response Modification Device Test Facility at the University of California, San Diego. The purpose of the test program, which consisted of 33 tests, was to assess the impact of multiaxial excitation and input rate on the response of the bearing. The test protocol consisted of unique tests, including testing the bearing in all six degrees of freedom (uncoupled and coupled) and testing the bearing dynamically to failure. This article examines the hysteretic response and resulting performance parameters of the bearing to the different tests. The most notable impacts on the bearing’s hysteretic response were the axial loading and coupling the lateral degrees of freedom, while the rotational degrees of freedom had minimal impact on the bearing’s response. The bearing’s hysteretic response to coupling input in the rotational degrees of freedom with lateral and axial degrees of freedom was consistent with the expected performance from superimposing the response to input from individual degrees of freedom. The bearing failed at almost three times the design shear strain and at a shear force over five times the shear force at the design shear strain during the dynamic test to failure.

Controllable two-dimensional Kerr and Raman–Kerr frequency combs in microbottle resonators with selectable dispersion

We report a broadband two-dimensional (2D) Kerr and Raman–Kerr frequency comb generation in a silica bottle resonator accounting for azimuthal and axial degrees of freedom and pioneer a method that allows for controlled and reversible switching between a four wave mixing (FWM) state and a stimulated Raman scattering state. The repetition rate of the Raman–Kerr comb is not an integer number of the free spectral range, which spans more than 242 nm with hundreds of teeth. We show that, experimentally and numerically, multiple 2D comb regimes can be selectively accessed via dispersion engineering by exciting different orders of axial modes or modifying the curvature of the axial profile, involving cascaded FWM, Raman lasing, and Raman-assisted FWM. The effect of axial curvature on dispersion is associated with the axial mode number in bottle resonators. Our approach enables dispersion and spectral engineering flexibility in any resonator with localized axial modes.

Suspension force analysis of six-pole radial-axial magnetic bearing for energy storage flywheel

This paper proposes a six-pole radial-axial hybrid magnetic bearing (RAHMB) used in a flywheel system. The radial and axial bias fluxes are generated by one permanent magnet and the radial control coils are driven by a three-phase converter. So, it has the advantages of compact structure, low power consumption and simple driver. First, the work principle is introduced. Then, the mathematical model is built. The force-current characteristics with different eccentricities, the coupling between radial two degrees of freedom (DOF) and the coupling between radial and axial DOF are analyzed based on the analytical model. Finally, the analyses are validated by 3D finite element analysis in the Maxwell software. The results have shown that the coupling between radial and axial DOF is very small. However, the force-current curves of radial two DOFs turn out to be nonlinear and coupled with the increase of rotor eccentricity.

Two-dimensional nonlinear modes and frequency combs in bottle microresonators.

We theoretically investigate frequency comb generation in a bottle microresonator accounting for the azimuthal and axial degrees of freedom. We first identify a discrete set of the axial nonlinear modes of a bottle microresonator that appear as tilted resonances bifurcating from the spectrum of linear axial modes. We then study azimuthal modulational instability of these modes and show that families of two-dimensional (2D) soliton states localized both azimuthally and axially bifurcate from them at critical pump frequencies. Depending on detuning, 2D solitons can be stable, form persistent breathers or chaotic spatio-temporal patterns, or exhibit collapse-like evolution.

Investigation on the effect of coulomb friction on nose landing gear shimmy

Landing gear shimmy remains a challenge in aircraft design despite abundant advances in aircraft engineering in the past few decades. Accurate shimmy prediction is closely tied to availability of dynamic models with all relevant types of motions and key nonlinear elements, a matter which has been accomplished in the present study through including rotational, lateral, longitudinal, and axial degrees of freedom and tire, shock absorber, and Coulomb friction nonlinearities. Using multi-body dynamic simulations, stability of the nose landing gear is studied as a function of key system parameters. Influences of nonlinearities are investigated in isolation, with a more in-depth look at the Coulomb friction effect, which is modeled as a function of the shock absorber stroke rate and rotational shimmy speed. It is found that Coulomb friction is a key factor in determining the onset and type of shimmy. The effect of friction parameters is then studied using nonlinear sensitivity analyses, and witnessed trends are utilized to draw design recommendations.

HIGAMod: A Hierarchical IsoGeometric Approach for MODel reduction in curved pipes

Abstract In computational hemodynamics we typically need to solve incompressible fluids in domains given by curved pipes or network of pipes. To reduce the computational costs, or conversely to improve models based on a pure 1D (axial) modeling, an approach called “Hierarchical Model reduction” (HiMod) was recently proposed. It consists of a diverse numerical approximation of the axial and of the transverse components of the dynamics. The latter are properly approximated by spectral methods with a few degrees of freedom, while classical finite elements were used for the main dynamics to easily fit any morphology. However affine elements for curved geometries are generally inaccurate. In this paper we conduct a preliminary exploration of IsoGeometric Analysis (IGA) applied to the axial discretization. With this approach, the centerline is approximated by Non Uniform Rational B-Splines (NURBS). The same functions are used to represent the axial component of the solution. In this way we obtain an accurate representation of the centerline as well as of the solution with few axial degrees of freedom. This paper provides preliminary promising results of the combination of HiMod with IGA - referred to as HIGAMod approach - to be applied in any field involving computational fluid dynamics in generic pipe-like domains.

Progress on electrodynamic passive magnetic bearings for rotor levitation

Electrodynamic suspension exploits repulsive forces due to eddy currents to produce positive stiffness by passive means, without violating the Earnshaw stability criterion. Systems employing this principle to levitate a rotor radial and/or axial degrees of freedom are called electrodynamic bearings (EDBs). Since the eddy currents can be induced either by using alternating current supplied electromagnets or by the relative motion between a conductor and a constant magnetic field, the research on EDBs has developed many different configurations. The present paper reviews the literature on electrodynamic passive magnetic bearings to analyze the evolution of this technology toward completely passive, stable, rotor levitation, and to compare the EDBs performance with other common magnetic bearing technologies. Radial and axial EDB technologies are reviewed attempting to create an organized connection between the works and to discuss some critical issues that still preclude the use of EDBs in industrial applications.

Entanglement generation in planar Penning traps

We investigate the generation of entanglement between the axial degrees of freedom of electrons confined in separated locations in planar Penning traps. We show that there are two different sources of entanglement: one is related with the mechanism of switching on and off the electrical coupling between the two electrons, and the other is due to the two-quanta-transition term of the coupling interaction. We show that the degree of entanglement can be controlled by adjusting the strength of the coupling between the traps and the time of interaction. We show that the coupled electrons behave as a temporal active interferometer.

The Rotor Dynamic Coefficients of Eccentric Mechanical Face Seals

Abstract The Reynolds equation is extended to include the effects of radial deflection in a seal with two flexibly mounted rotors. The resulting pressures are used to obtain the forces and moments introduced in the axial and angular modes by the inclusion of eccentricity in the analysis. The rotor dynamic coefficients relating the forces and moments in these modes to the axial and angular deflection are shown to be the same as those presented in the literature for the concentric case. Additional coefficients are obtained to express the dependence of these forces and moments upon the radial deflections and velocities. The axial force is shown to be decoupled from both the angular and radial modes, but the angular and radial modes are coupled to one another by the dependence of the tilting moments upon the radial deflections. The shear stresses acting upon the element faces are derived and used to obtain the radial forces acting upon the rotors. These forces are used to obtain rotor dynamic coefficients for the two radial degrees of freedom of each rotor. The additional rotor dynamic coefficients can be used to obtain the additional equations of motion necessary to include the radial degrees of freedom in the dynamic analysis. These coefficients introduce additional coupling between the angular and radial degrees of freedom, but the axial degrees of freedom remain decoupled.