Hyper-Damping Behavior of Stiff and Stable Oscillators with Embedded Statically Unstable Stiffness Elements

2017 ◽  
Vol 17 (05) ◽  
pp. 1740008 ◽  
Author(s):  
Ioannis A. Antoniadis ◽  
Konstantinos J. Kyriakopoulos ◽  
Evangelos G. Papadopoulos
Keyword(s):  
Equilibrium Point ◽  
Damping Ratio ◽  
Resonance Phenomenon ◽  
Static Stiffness ◽  
Sdof System ◽  
Damping Behavior ◽  
System Equilibrium ◽  
Elastic Forces ◽  
Unstable Equilibrium Point ◽  
Novel Concept

A novel concept of a nonlinear oscillator is proposed, based on a bistable element, which operates around an unstable equilibrium point. Contrary to the Quasi-Zero Stiffness oscillators, a totally different redistribution of the stiffness elements is followed, so that any level required static stiffness for the entire system can be maintained. This oscillator is designed to present the same overall (static) stiffness around the system equilibrium point, the same mass and to use the same damping element as a reference classical linear SDOF oscillator. Once such an oscillator is optimally designed, it is shown to exhibit an extraordinary apparent damping ratio, which is several orders of magnitude higher than that of the original SDOF system, especially in cases where the original damping of the SDOF system is extremely low. This damping behavior is not a result of a novel additional extraordinary energy dissipation mechanism, but a result of the phase difference between the positive and the negative stiffness elastic forces; this is in turn a consequence of the proper redistribution of the stiffness and the damping elements. This fact ensures that an adequate level of elastic forces exists throughout the entire frequency range, able to counteract the inertial and the external excitation forces. Consequently, a resonance phenomenon, which is inherent in the original linear SDOF system, cannot emerge in the proposed oscillator.

Damping Analysis of Asymmetrical Comb Accelerometer

2007 ◽  
Vol 353-358 ◽  
pp. 2597-2600 ◽  
Author(s):  
Wei Ping Chen ◽  
Zhen Gang Zhao ◽  
Xiao Wei Liu ◽  
Yu Min Lin
Keyword(s):  
Damping Ratio ◽  
Resonance Phenomenon ◽  
Damping Coefficient ◽  
Anodic Bonding ◽  
Squeeze Film ◽  
Frequency Bandwidth ◽  
Vibration Method ◽  
Capacitive Accelerometer ◽  
Squeeze Film Damping

The resonance phenomenon is suppressed by adjusting the damping of the comb accelerometer structure to widen the frequency bandwidth of the capacitive accelerometer. The capacitive accelerometer with asymmetrical combs, fabricated with DRIE and anodic bonding, is presented. The damping category of the accelerometer is introduced, in which the squeeze-film damping coefficient and the damping ratio factor are detailed. The damping ratio factor of the accelerometer, measured by a vibration method, is 0.17. The damping ratio factor of the optimized structure is calculated of 0.15 to 0.18 with the change of experiential modulus C from 25 to 30, theoretically.

Contribution of carbon nanotubes to vibration damping behavior of epoxy and its carbon fiber composites

2020 ◽  
Vol 39 (7-8) ◽  
pp. 311-323
Author(s):  
Esma Avil ◽  
Ferhat Kadioglu ◽  
Cevdet Kaynak
Keyword(s):  
Mechanical Properties ◽  
Carbon Nanotubes ◽  
Carbon Fiber ◽  
Damping Ratio ◽  
Vibration Damping ◽  
Matrix Composites ◽  
Fiber Reinforced ◽  
Damping Behavior ◽  
Continuous Carbon Fiber ◽  
Carbon Fiber Reinforced

The main objective of this study was to investigate contribution of the non-functionalized multi-walled carbon nanotubes on the vibration damping behavior of first neat epoxy resin and then unidirectional and bidirectional continuous carbon fiber reinforced epoxy matrix composites. Epoxy/carbon nanotubes nanocomposites were produced by ultrasonic solution mixing method, while the continuous carbon fiber reinforced composite laminates were obtained via resin-infusion technique. Vibration analysis data of the specimens were evaluated by half-power bandwidth method; and the mechanical properties of the specimens were determined with three-point bending flexural tests, including morphological analyses under scanning electron microscopy. It was generally concluded that when even only 0.1 wt% carbon nanotubes were incorporated into neat epoxy resin, they have contributed not only to the mechanical properties (flexural strength and modulus), but also to the vibration behavior (damping ratio) of the epoxy. When 0.1 or 0.5 wt% carbon nanotubes were incorporated into continuous carbon fiber reinforced epoxy matrix composites, although they have no additional contribution to the mechanical properties, their contribution in terms of damping ratio of the composites were significant.

scholarly journals A Four-Zone Model and Nonlinear Dynamic Analysis of Solution Multiplicity of Buoyancy Ventilation in Underground Building

Complexity ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-24
Author(s):  
Yuxing Wang ◽  
Chunyu Wei
Keyword(s):  
Differential Equations ◽  
Equilibrium Point ◽  
Equilibrium Points ◽  
Underground Structure ◽  
Unstable Equilibrium ◽  
Phase Portraits ◽  
Zone Model ◽  
Unstable Equilibrium Point ◽  
Index 2 ◽  
The Stability

The solution multiplicity of natural ventilation in buildings is very important to personnel safety and ventilation design. In this paper, a four-zone model of buoyancy ventilation in typical underground building is proposed. The underground structure is divided to four zones, a differential equation is established in each zone, and therefore, there are four differential equations in the underground structure. By solving and analyzing the equilibrium points and characteristic roots of the differential equations, we analyze the stability of three scenarios and obtain the criterions to determine the stability and existence of solutions for two scenarios. According to these criterions, the multiple steady states of buoyancy ventilation in any four-zone underground buildings for different stack height ratios and the strength ratios of the heat sources can be obtained. These criteria can be used to design buoyancy ventilation or natural exhaust ventilation systems in underground buildings. Compared with the two-zone model in (Liu et al. 2020), the results of the proposed four-zone model are more consistent with CFD results in (Liu et al. 2018). In addition, the results of proposed four-zone model are more specific and more detailed in the unstable equilibrium point interval. We find that the unstable equilibrium point interval is divided into two different subintervals corresponding to the saddle point of index 2 and the saddle focal equilibrium point of index 2, respectively. Finally, the phase portraits and vector field diagrams for the two scenarios are given.

Experimental Study on the Performance of the Laminated Steel Isolators

2013 ◽  
Vol 423-426 ◽  
pp. 1603-1607
Author(s):  
Yao Guo Xie ◽  
Ping He ◽  
Xian Qiang Qu ◽  
Hong Bin Cui
Keyword(s):  
Experimental Study ◽  
Vibration Isolation ◽  
Dynamic Stiffness ◽  
Damping Ratio ◽  
Dynamic Performance ◽  
Performance Testing ◽  
Stiffness Ratio ◽  
Static Stiffness ◽  
Comparison Of The Results

Through the analysis and comparison of the results of static and dynamic performance testing of a series of laminated steel pieces isolators used in the vibration isolation of warships, in the number and thickness of laminated steel pieces of the same circumstances, laminated steel arc and preload of test samples had a certain impact on the values ​​of static stiffness, dynamic stiffness, damping ratio as well as dynamic and static stiffness ratio.

The Effects of Fiber Volume Fraction on the Vibration Damping Characteristics of Three-Layer-Connected Biaxial Weft Knitted Fabric Reinforced Composite Materials

2012 ◽  
Vol 602-604 ◽  
pp. 49-52
Author(s):  
Jing Xue Liu ◽  
Jia Lu Li
Keyword(s):  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Damping Ratio ◽  
Vibration Damping ◽  
Knitted Fabric ◽  
Vibration Modes ◽  
Fiber Volume ◽  
Damping Behavior ◽  
Weft Knitted Fabric ◽  
Vibration Parameters

The paper presents an analysis of the vibration damping properties of three-layer-connected biaxial weft knitted fabric (TBWK), which are constituted of carbon fibers as inserted yarns and polyester yarns as knitted yarns impregnated in an epoxy matrix with resin transfer molding (RTM) technique. Damping parameters were investigated using beam test specimens and an impulse technique. Several vibration parameters were varied to characterize the damping behavior in different amplitudes, natural frequencies and vibration modes. The results obtained show that the damping ratio of TBWK composites decreases with the increasing of fiber volume fraction in all the three vibration modes. The vibration test also indicates that the natural frequency of the TBWK composites increases with the increasing of fiber volume fraction (Vf) in all the three modes.

Local Control of Chaotic Systems — A Lyapunov Approach

1998 ◽  
Vol 08 (07) ◽  
pp. 1565-1573 ◽  
Author(s):  
Hendrik Richter ◽  
Kurt J. Reinschke
Keyword(s):  
Equilibrium Point ◽  
Local Control ◽  
Chaotic Systems ◽  
Basin Of Attraction ◽  
Design Procedure ◽  
Control Action ◽  
Unstable Equilibrium Point ◽  
Linear State ◽  
Time Systems ◽  
The Basin Of Attraction

In this paper a method for local control of an unstable equilibrium point in chaotic systems is presented. Linear state feedback to stabilize the equilibrium is employed which is only active in a bounded region around the desired point: the area of control action. Size and shape of the area of control action are determined by a Lyapunov function of the controlled chaotic system such that it belongs to the basin of attraction of the equilibrium point. We give the design procedure for both continuous-time and discrete-time systems.

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