scholarly journals Responses of Multiple Nonlinear Tuned Vibration Absorbers under Harmonic Excitation

Author(s):  
Abdullah S. Alsuwaiyan
2006 ◽  
Vol 06 (02) ◽  
pp. 269-284 ◽  
Author(s):  
SUNNY K. GEORGE ◽  
K. SHANKAR

The distribution of vibrational energy in members of a complex structure with tuned absorbers attached at the joints and subjected to dynamic loading is studied. The concept of power flows through the structure is used to determine the time-averaged energy levels of each member in the structure. The power flows are calculated using the time-averaged product of force and velocity at the input and coupling points (joints) of a general structure made of axially vibrating rods. The receptance approach is used to calculate the coupling forces and velocities in the structure. By balancing the input power against the dissipated powers, the time-averaged energy levels in members are determined. The main criteria studied here is the reduction in the frequency-averaged vibrational energy level of a member when an absorber is attached, expressed as a percentage compared to the case where there are no absorbers. The concept is first illustrated with a simple model of 2 axially vibrating rods with an absorber attached to the joint. Next, a more complex structure comprising 8 rods with arbitrary orientations and several absorbers attached to junctions is studied. The effect of activating absorbers at various locations on reducing the energy levels of certain members is examined. It is possible to estimate the usefulness of the absorber with respect to any member by determining the percentage reduction of energy level for that member.


Author(s):  
Neil D. Sims ◽  
Ashan Amarasinghe ◽  
Keith Ridgway

It is well known that the chatter stability of a machining process can be improved by increasing the structural damping of the system. To date this approach has been effectively used on various components of the machining system, for example boring bars, milling tools, and the machine structure itself. Various damping treatments have been proposed, including tuned vibration absorbers, active methods, and impact dampers. However, to date there has been little or no work to investigate the issue of particle dampers for this application. This special class of damper comprises a container of thousands of small granular particles which dissipate energy by friction and impact when the container vibrates. The resulting behaviour is highly nonlinear but can provide very high levels of damping across a wide frequency range. In the present study, particle dampers were applied to a workpiece to mitigate chatter during milling, and the limiting critical depth of cut was increased by an order of magnitude. This article gives an overview of the particle damper’s behaviour and key design parameters. Cutting trials employing the device are then described.


Author(s):  
Brian J. Olson ◽  
Steve W. Shaw ◽  
Christophe Pierre

This paper investigates the use of order-tuned absorbers to attenuate vibrations of flexible blades in a bladed disk assembly subjected to engine order excitation. The blades are modeled by a cyclic chain of N oscillators, and a single vibration absorber is fitted to each blade. These absorbers exploit the centrifugal field arising from rotation so that they are tuned to a given order of rotation, rather than to a fixed frequency. A standard change of coordinates based on the cyclic symmetry of the system essentially decouples the governing equations of motion, yielding a closed form solution for the steady-state response of the overall system. These results show that optimal reduction of blade vibrations is achieved by tuning the absorbers to the excitation order n, but that the resulting system is highly sensitive to small perturbations. Intentional detuning (meaning that the absorbers are slightly over- or under-tuned relative to n) can be implemented to improve the robustness of the design. It is shown that by slightly undertuning the absorbers there are no system resonances near the excitation order of interest and that the resulting system is robust to mistuning (i.e., small random uncertainties in the system parameters) of the absorbers and/or blades. These results offer a basic understanding of the dynamics of a bladed disk assembly fitted with order-tuned vibration absorbers, and serve as a first step to the investigation of more realistic models, where, for example, imperfections and nonlinear effects are considered, and multi-DOF and general-path absorbers are employed.


2009 ◽  
Vol 16 (5) ◽  
pp. 467-480 ◽  
Author(s):  
Nader Vahdati ◽  
Mehdi Ahmadian

Passive fluid mounts are used in the fixed wing applications as engine mounts. The passive fluid mount is placed in between the engine and the fuselage to reduce the cabin's structure- borne noise and vibration generated by the engine.To investigate the benefits of passive fluid mounts used in conjunction with tuned vibration absorbers (TVA), a simple mathematical model is developed. This mathematical model includes the mathematical model of a passive fluid mount, a TVA, and a spring representing the fuselage structure. The simulation results indicate that when passive fluid mounts are used in conjunction with TVAs, an active suspension system behavior is nearly created.


Author(s):  
Mark Holdhusen ◽  
Kenneth A. Cunefare

A state-switched absorber (SSA) is a device capable of instantaneously changing its stiffness, thus it can switch between resonance frequencies, increasing its effective bandwidth as compared to classical tuned vibration absorbers for vibration control. Previous numerical work has shown that an optimized SSA outperforms an optimized TVA at controlling vibrations of both a beam and a plate. This paper details the experimental validation of these simulation results. An SSA was realized by employing magneto-rheological elastomers to achieve a stiffness change. The stiffness of these elastomers is a function of the magnetic field put across them. Experiments were conducted on both a cantilever beam and a square plate clamped on all sides. Each system was excited by several two-frequency component excitations. For each forcing combination, several tuning configurations of the SSA were applied and the kinetic energy of the system was found. This observed performance was compared to the performance found through numerical simulations of a system with a similar tuning and excitation configuration. It was found that the observed performance follows closely with results found through numerical simulation.


2004 ◽  
Vol 10 (2) ◽  
pp. 163-174 ◽  
Author(s):  
Jeong-Hoi Koo ◽  
Mehdi Ahmadian ◽  
Mehdi Setareh ◽  
Thomas Murray

The main purpose of this study is to identify a suitable control method for semi-active tuned vibration absorbers (TVAs) in structural vibration applications. Four control policies are considered. The semi-active control schemes include the following: velocity-based, on-off groundhook control (on-off VBG); velocity-based, continuous groundhook control (continuous VBG); displacement-based, on-off groundhook control (on-off DBG); and displacement-based, continuous groundhook control (continuous DBG). A force-excited model that can be representative of many structural systems is adapted as the baseline model for our analysis. Each of the control policies is applied to the baseline model coupled with a TVA. In order to equally evaluate the control policies, the TVA parameters are optimized according to each policy using numerical optimization techniques. The optimal design parameters are obtained based on minimization of peak transmissibility. The performances of each of the optimized cases are then compared along with the equivalent passive model using the peak transmissibility criteria. The results indicate that all of the semi-active peak transmissibilities are lower than those of the passive, implying that the semi-active TVAs are more effective in reducing vibration levels. The results further indicate that on-off DBG performs the best among the considered control polices.


Author(s):  
Jeong-Hoi Koo ◽  
Fernando Goncalves ◽  
Hong Zhang

The primary objective of this paper is to bridge the theory of tuned vibration absorbers (TVA) with the practice of implementing TVAs in systems. Often, the practice of implementing TVAs in systems is a far departure from the theory expressed in many textbooks. These departures are often required in practice to account for the less than ideal conditions that the TVAs will be operating under. Many retrofitted TVAs use “smart” or active materials along with various control techniques to improve the performance of the traditional TVA proposed in textbooks. The intent of the current paper is to demonstrate several of these modern methods of implementing retrofitted TVAs to undergraduate students. The first author introduced the methods in a junior level vibrations course, and is developing a laboratory experiment. Teaching these advanced TVAs to undergraduate engineering students will help them understand how theories learned in class are used in real world problems, and motivate them to explore new fields of research. After introducing a “textbook” vibration absorber theory, this paper describes principles and operations of a new class of vibration absorbers. In reviewing conventional TVAs, students are introduced to many of the engineering challenges encountered in the implementation of TVAs. One such challenge is inevitable off-tuning caused by system parameter changes with time. After identifying many of the challenges associated with the implementation of TVAs, the students are introduced to many modern solutions to these problems. Many of these solutions involve the use of smart materials, such as piezoceramics, magnetorheological fluids, magnetorheological elastomers, shape memory alloys, etc. Through this experience, students are introduced to many smart materials and have the opportunity to see how these smart materials can provide solutions to many engineering challenges and improve existing technologies.


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