Effects and Prospects of the Vibration Isolation Methods for an Atomic Interference Gravimeter

An atomic interference gravimeter (AIG) is of great value in underwater aided navigation, but one of the constraints on its accuracy is vibration noise. For this reason, technology must be developed for its vibration isolation. Up to now, three methods have mainly been employed to suppress the vibration noise of an AIG, including passive vibration isolation, active vibration isolation and vibration compensation. This paper presents a study on how vibration noise affects the measurement of an AIG, a review of the research findings regarding the reduction of its vibration, and the prospective development of vibration isolation technology for an AIG. Along with the development of small and movable AIGs, vibration isolation technology will be better adapted to the challenging environment and be strongly resistant to disturbance in the future.

Active Vibration Control on a Smart Composite Structure using Modal-Shaped Sliding Mode Control

This paper proposes an active modal vibration control method based on a modal sliding mode controller applied to a smart material composite structure with integrated piezoelectric transducers as actuators and sensors. First, the electromechanical coupled system is identified using a modal reduced-order model. The sliding surface is based on the modal-filtered states and designed using a general formulation allowing the control of multiple vibration modes with multiple piezoelectric sensors and actuators. The performance and stability of the nonlinear controller are addressed and confirmed with the experimental results on a composite smart spoiler-shaped structure. The nonlinear switching control signal, based on the modal-shaped sliding surface improves the performances of the linear part of the control while maintaining not only stability but also robustness. The attenuation level achieved on the target modes on all piezoelectric sensors starts from -14dB up to -22dB, illustrating the strong potential of nonlinear switching control methods in active vibration control.

Foundation forces caused by dynamic air gap torques of converter driven induction motors influenced by active vibration control: a theoretical analysis

In the paper, a theoretical analysis regarding foundation forces caused by dynamic air gap torques of converter-driven induction motors, influenced by active vibration control, is shown. Based on a plane model, where actuators are placed between the motor feet and steel frame foundation and where the vertical motor feet accelerations are controlled, a mathematical description in the time domain, Laplace domain, and Fourier domain is presented, as well as a block diagram for numerical simulation. A numerical example is shown, where a 2-pole induction motor (2 MW) is analyzed for different cases—motor directly mounted on a steel frame foundation (case 1), actuators between motor feet and foundation, operating passively (case 2) and actively (case 3). It could be shown, that with the presented active vibration control concept the foundation forces due to dynamic air gap torques can be clearly reduced.

Magnetorheological Elastomer based torsional vibration isolator for application in a prototype drilling shaft

Smart materials properties are altered using external stimuli such as temperature, pressure and magnetic field. Magnetorheological Elastomer (MRE) is a type of smart composite material consisting of a polymer matrix embedded with ferromagnetic particles. In the presence of an external magnetic field, its mechanical properties, such as stiffness, change due to the interaction between the magnetic particles, which have applications in vibration isolation. Unwanted vibration in machines can cause severe damage and machine breakdown. In this work, a semi-active vibration isolator using MRE is proposed for a potential application in a drilling system to isolate the torsional vibration. The MRE was fabricated with a 35% mass fraction (MF) consisted of silicon rubber and iron particles. It was fitted with aluminium couplers and attached to the shaft (drill string) to study its efficiency in vibration isolation under a magnetic field. Two tests were conducted on the drilling prototype setup used in this work; the first test was a hammer impact test. The torsional transfer function TTF analysis showed that the system’s natural frequency has shifted from 13.9 Hz to 17.5 Hz by the influence of increasing magnetic field around the MRE. The results showed that the continuous rotational vibration amplitude of the prototype is attenuated by more than 40%.