Active vibration reduction

Active Vibration Reduction. An active vibration control system consists of a hydraulic or electrodynamic actuator, vibration sensor, and electronic controller designed to maintain the seat pan stationary irrespective of the motion of the seat support. Such a control system must be capable of reproducing the vehicle motion at the seat support, which will commonly possess large displacement at low frequencies, and supply a phase-inverted version to the seat pan to counteract the vehicle motion in real time. This imposes a challenging performance requirement for the control system and vibration actuator. Also, the control system must possess safety interlocks to ensure it does not erroneously generate harmful vilxation at the seat pan. While active control systems have been employed commercially to adjust the static stiffness or damping of vehicle suspensions, to improve the ride comfort on different road surfaces, there are currently no active seat suspensions. 

Despite the reduction in symmetry, no additional bands have ever been unambiguously assigned to internal fullerene active vibrations. For multiple addition adducts, the severe disruption to the cage structure results in a markedly different spectrum. 

Structural materials of the ultraprecision machine tools require low thermal expansion, high Young s modulus, and low density. In order to meet such requirements, various kinds of ceramics are widely applied to the machine tool structure, such as the bed, columns, top beams, and nano-motion system. Various remedies for reduction of thermal error (Shinno 2010) are also important. In addition, the main frame structure is constructed on an active vibration isolation system installed inside a temperature-controlled enclosure. 

Monner, H. P. 2005. Smart materials for active noise and vibration reduction. Proceedings of the Novem - Noise and Vibration Emerging Methods, Saint-Raphael, France. 

Fig. 2.4. MD 900 helicopter hingeless blade displaying the planned trim tab for in-flight tracking and active control flap for noise and vibration reduction [10]...

Another space related topic is the reduction of noise impacts on pay-loads through active noise control using technologies such as an acoustic foam with embedded PVDF material, distributed active vibration absorbers (DAVA) made from acoustic foam hnked to a metallic plate and in a latest version even added by a very small electrodjmamic shaker that allows to cover lower frequencies [103]. This sandwich of acoustic foam, PVDF and electrodynamic shakers is then used as an active coating on the fairings of space vehicles. 

Active vibration control (AVC) Increased passengers comfort, reduced load/stress level, extended lifetime, weight reduction... 

One adaptronic approach to reduce torsional vibrations was to integrate actuators within the diagonal stiffening struts of the car underbody (Fig. 8.24) [150,151]. Different actuators have been investigated, piezoceramic stacks, hydraulic cylinders and hydraulic muscles. Control approaches like adaptive feed-forward and feedback were implemented and significant vibration reductions were achieved (Fig. 8.24). To commercialize this affirmative active concept system cost, size, complexity and power consumption must be further reduced. 

Fig. 8.24. AVC-application within a convertible a convertible and concept of active struts, b achievable vibration reduction...

For vibration reduction of panels mostly, semi-active vibration damping systems based on piezoelectric transducers have been studied. The piezos are attached to the structure and electrically shunted with resistor-inductor circuits. By proper tuning of the circuit elements, effects compared to the application of mechanical vibration absorbers can be observed, however only laboratory experiments have been performed yet [147]. 

Thomaier, M. Atzrodt, H. Herold, S. Mayer, D. Melz, D. Simulation of a Complete System Using the Example of an Active Interface for Vibration Reduction. Proc. Virtual Product Development in Automotive Eng., Miirzzuschlag / Austria (2005)... 

Semi-active tuned mass dampers are similar to TMDs, but with the capability of varying then-level of damping. They are mainly used for wind vibration reduction. Another type of semi-active TMD is the semi-active variable stiffness tuned mass damper (SAIVS-TMD), where the stiffness is also controllable. Their performance is similar to that of AMDs but with less power consumption. 

The paper gives an overview of effects occurring or acoustic treatment of dissolved and molten polymers. Emphasis is made on acoustic cavitation discovered recently not only in low-viscous fluids but also in molten polymers. Major guidelines have been specified for practical utilization of acoustic treatment of flowable polymers in molding intensification of extrusion processes, reduction in thickness of produced films, directed mechanical destruction, chemical activation of melts, etc. Efficiency of overlapping high-frequency vibrations in molding of molten thermoplastics is discussed in terms of power consumption. 

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