Frequency Tunable Isolator Based on Shape Memory Alloy for Effective Shock and Vibration Suppression

2013 ◽  
Author(s):  
Ho-Kyeong Jeong ◽  
Juho Lee ◽  
Jae-Hung Han
Keyword(s):  
Natural Frequency ◽  
Structural Integrity ◽  
Frequency Tuning ◽  
Dynamic Pressure ◽  
Excitation Frequency ◽  
Low Frequency ◽  
Design Procedure ◽  
Shock Attenuation ◽  
Exciting Frequency ◽  
Frequency Tunable

A Shock and vibration isolator is widely used due to its simplicity and effectiveness. It attenuates vibration energy when the external excitation frequency is more than about 2 times its natural frequency, while the vibration around its natural frequency is generally amplified. However, an exciting frequency often varies so that it is difficult to avoid the vibration amplification. In particular, when these amplification phenomena occur in the low frequency domain, induced large vibration displacements degrade the structural integrity. This paper introduces a novel frequency tunable isolator proposed by the present authors. The isolator uses SMA wires as actuator as well as the isolation materials. The isolator material is a compressed mesh washer isolator using the pseudoelasticity of SMA. Frequency tune of the isolator can be easily achieved through a simple electric circuit. Thus, this isolator can be widely applied to various vibration and shock environments such as in aircrafts and motor vehicles. Particularly, the detail design procedure is presented here for the adaptive shock isolator for launch vehicle in order to achieve both shock attenuation performance and avoidance of the vibration amplification. Launch vehicles experience severe dynamic environment during the flight phase. Specially, pyroshock generated from the several separation events could result in malfunctions of electric components and low frequency vibration below 100 Hz at the maximum dynamic pressure phase could reduce the structural integrity of payload. The resonant frequency of the isolator is selectively controlled in two modes by using an adaptive mechanical system with compressing the isolation materials. The isolator was successfully designed and various test results with frequency tuning are presented, in this paper.

scholarly journals Bursting Oscillations in Shimizu-Morioka System with Slow-Varying Periodic Excitation

2018 ◽  
Vol 2018 ◽  
pp. 1-11
Author(s):  
Xindong Ma ◽  
Shuqian Cao
Keyword(s):  
Natural Frequency ◽  
Coupling Effect ◽  
Excitation Frequency ◽  
Time Interval ◽  
Periodic Excitation ◽  
Bursting Oscillations ◽  
Fold Bifurcation ◽  
Exciting Frequency ◽  
Bursting Oscillation ◽  
Parameter Condition

The coupling effect of two different frequency scales between the exciting frequency and the natural frequency of the Shimizu-Morioka system with slow-varying periodic excitation is investigated. First, based on the analysis of the equilibrium states, homoclinic bifurcation, fold bifurcation, and supercritical Hopf bifurcation are observed in the system under a certain parameter condition. When the exciting frequency is much smaller than the natural frequency, we can regard the periodic excitation as a slow-varying parameter. Second, complicated dynamic behaviors are analyzed when the slow-varying parameter passes through different bifurcation points, of which the mechanisms of four different bursting patterns, namely, symmetric “homoclinic/homoclinic” bursting oscillation, symmetric “fold/Hopf” bursting oscillation, symmetric “fold/fold” bursting oscillation, and symmetric “Hopf/Hopf” bursting oscillation via “fold/fold” hysteresis loop, are revealed with different values of the parameterbby means of the transformed phase portrait. Finally, we can find that the time interval between two symmetric adjacent spikes of bursting oscillations exhibits dependency on the periodic excitation frequency.

Investigating the Feasibility of Tuning the Natural Frequency of an Electromagnetically-Transduced Energy Harvester Using Passively-Controlled Inductance

2014 ◽  
Author(s):  
Brennan E. Yamamoto ◽  
A. Zachary Trimble
Keyword(s):  
Energy Harvesting ◽  
Natural Frequency ◽  
Energy Harvester ◽  
Frequency Tuning ◽  
Excitation Frequency ◽  
Energy Output ◽  
Vibration Energy ◽  
Vibration Energy Harvesting ◽  
Mechanical Spring ◽  
Energy Harvesting System

As the required power for wireless, low-power sensor systems continues to decrease, the feasibility of a fully self-sustaining, onboard power supply, has increased interest in the field of vibration energy harvesting — where ambient kinetic energy is scavenged from the surrounding environment. Current literature has produced a number of harvesting techniques and transduction methods; however, they are all fundamentally similar in that, the harmonic excitation frequency must fall within the resonant bandwidth frequency of the harvesting mechanism to maintain acceptable energy output. The purpose of this research is to investigate the potential for natural frequency tuning by means of passive electrical components, that is, using an imposed electrical inductance to adjust the equivalent stiffness, and resulting resonant frequency of a vibration energy harvester. In past literature, it was concluded that an “active” frequency tuning mechanism would be infeasible, as the power required by an equivalent “stiffening transducer” would require more power to maintain the system at resonance, than the system would actually produce as a result of maintaining resonance, i.e., a net energy loss (Roundy and Zhang 2005). It is believed that the model used in this conclusion can be improved by directly modeling changes in system stiffness as an equivalent mechanical spring, instead of an external inertial loading. Due to the conservative nature of the harmonic spring, the compliance of a harvesting mechanism can be theoretically altered without energy losses, whether the actuation is applied using “active” or “passive” means. This revised model departs from the traditional, base excitation model in most vibration energy harvesting systems, and includes additional stiffness, and damping elements, representative of induced mechanical spring, and related losses. We can validate the feasibility of this technique, if it can be shown that the natural frequency of an energy harvester can be altered, and still maintain energy output similar to its “untuned” natural frequency. If feasible, this tuning method would provide a viable alternative to other bandwidth-increasing techniques in literature, e.g., wideband harvesting, bandwidth normalizing, high-damping, etc. In this research, a change in natural frequency of the experimental energy harvesting system of 0.5 Hz was demonstrated, indicating that adjusting the natural frequency of a vibration energy harvesting system is possible; however, there are many new challenges associated with the revised energy harvesting model, related to the new introduced losses to the system, as well as impedance matching between the mechanical and electrical domains. Further research is required to better quantitatively characterize the relationship between natural frequency shift, and imposed electrical inductance.

Experimental Study of the Variable Stiffness Vibration Isolator

2011 ◽  
Vol 328-330 ◽  
pp. 2129-2133 ◽  
Author(s):  
Zhi Jun Shuai ◽  
Tie Jun Yang ◽  
Zhuo Liang Zhou ◽  
Zhi Gang Liu
Keyword(s):  
Natural Frequency ◽  
Vibration Isolation ◽  
Excitation Frequency ◽  
Low Frequency ◽  
Variable Stiffness ◽  
Resonance Problem ◽  
Vibration Isolator ◽  
Isolation System ◽  
Vibration Isolation System ◽  
Passive Vibration Isolation

The traditional passive vibration isolation system can reduce the vibration transmission greatly while the excitation frequency is times higher than its natural frequency. As the external excitation approach its natural frequency, vibration isolator system is invalid. In this paper, a new variable stiffness vibration isolator was designed to solve the low-frequency resonance problem of the traditional isolator by combining toothed electromagnetic spring with passive isolator. Theoretical analysis and experimental results illustrate that this isolator met the design requirements and obtained the no resonance operating characteristic at the low frequency.

Direct Fixation Fastener (DFF) Spacing and Stiffness Design

2011 ◽  
Author(s):  
Nazmul Hasan
Keyword(s):  
Natural Frequency ◽  
Frequency Ratio ◽  
Vibration Isolation ◽  
Design Procedure ◽  
Past Performance ◽  
Spring Rate ◽  
Exciting Frequency ◽  
Noise Vibration ◽  
Mass Spring ◽  
Track Modulus

Direct fixation fasteners are one of the most important elements in trackwork design. Elastomeric pads are incorporated in the fastener to provide vertical and horizontal flex and they assist in the reduction of noise, vibration and impact. The spring rate in DFF is often adjusted to mitigate ground borne vibration, that adjustment then affects the track modulus. Currently no industry-wide specifications exist for the design, definition or procurement of direct fixation fasteners. A thorough examination of the characteristics and past performance of available fasteners, as well as the characteristics of the proposed transit vehicle should be undertaken prior to fastener selection for any specific application. In this paper a procedure is suggested to calculate the spacing and desirable (vertical) stiffness of DFF that would mitigate noise, vibration and impact. There are two issues to consider enabling proper vibration isolation. The dominant issue is spring rate and the secondary issue is damping constant. Both are considered. Rail can be defined as a beam supported by DFF, directly fixed to a concrete slab. Usually light mass-spring ballast less track systems have a natural frequency varying from 12 Hz up to 18 Hz. Firstly a natural frequency for the direct Fixation Track is chosen. This choice must conform to the fact that exciting frequency such as train passing frequency should not go close to the natural frequency level so as to avoid resonance. Using a load-deflection formula for the track, a formula for natural frequency of a mass-spring system, a DFF passing frequency formula and relation between track modulus and characteristic length, DFF stiffness can be calculated. The design of stiffness and spacing of DFF does not lead to a unique value. There will always be a range of value depending on the choice of frequency ratio, r. It is found that spacing and stiffness are strongly correlated with R2 = 0.991. At the end a discussion follows on how to choose the value of natural frequency, fn stiffness amplification factor, R and the frequency ratio, r. Finally an application of the proposed design procedure is shown.

Effect of different magnets and iron-platelets on the low frequency performance of membrane sound absorber

2021 ◽  
Vol 263 (6) ◽  
pp. 342-347
Author(s):  
Junjuan Zhao ◽  
Liying Zhu ◽  
Xinyun Li ◽  
Yueyue Wang ◽  
Wenjiang Wang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Sound Absorption ◽  
Tuning Range ◽  
Frequency Tuning ◽  
Low Frequency ◽  
Cavity Depth ◽  
Sound Absorber ◽  
Frequency Tunable ◽  
Compact Design ◽  
Frequency Properties

To achieve a compact design for low frequency tunable sound absorption, a membrane sound absorber (MSA) with nonlinear magnetic field is proposed in this paper. By employing a central iron platelet on the membrane, the MSA can be easily tuned by introducing a magnet at a distance from the platelet that can be adjusted. To investigate the low frequency properties of MSA with different magnets and iron-platelets, a series of impedance tube experiments are conducted in detail. The sample absorber has a rear cavity depth of 30 mm, three different magnets were used inside, tested results real that using a strong magnetic field can help broaden the frequency tuning range. Then, results from the MSA with five different sizes of iron plates tuned by one magnet show that the low-frequency tuning range moves to lower with the increase of the area of iron plates.

Frequency Tuning of a Nonlinear Electromagnetic Energy Harvester

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Longhan Xie ◽  
Ruxu Du
Keyword(s):  
Magnetic Field ◽  
Permanent Magnets ◽  
Energy Harvester ◽  
Frequency Tuning ◽  
Nonlinear Behavior ◽  
Stretch Ratio ◽  
Electromagnetic Energy ◽  
Elastic Strings ◽  
Simulation And Experiment ◽  
Frequency Tunable

This paper investigates a frequency-tunable nonlinear electromagnetic energy harvester. The electromagnetic harvester mainly consists of permanent magnets supported on the base to provide a magnetic field, and electrical coils suspended by four even-distributed elastic strings to be an oscillating object. When the base provides external excitation, the electrical coils oscillate in the magnetic field to produce electricity. The stretch length of the elastic strings can be tuned to change their stretch ratio by tuning adjustable screws, which can result in a shift of natural frequency of the harvester system. The transverse force of the elastic strings has nonlinear behavior, which broadens the system's frequency response to improve the performance of the energy harvester. Both simulation and experiment show that the above-discussed electromagnetic energy harvester has nonlinear behavior and frequency-tunable ability, which can be used to improve the effectiveness of energy harvesting.

Optimally Sensitive and Efficient Compact Loudspeakers for Low Audio Frequencies

2007 ◽  
Vol 38 (7) ◽  
pp. 11-17
Author(s):  
Ronald M. Aarts
Keyword(s):  
Optimality Criterion ◽  
Low Frequency ◽  
Audio Signal ◽  
Design Procedure ◽  
Frequency Range ◽  
Force Factor ◽  
Low Frequencies ◽  
Limited Frequency ◽  
The Cost ◽  
Higher Sensitivity

Conventionally, the ultimate goal in loudspeaker design has been to obtain a flat frequency response over a specified frequency range. This can be achieved by carefully selecting the main loudspeaker parameters such as the enclosure volume, the cone diameter, the moving mass and the very crucial “force factor”. For loudspeakers in small cabinets the results of this design procedure appear to be quite inefficient, especially at low frequencies. This paper describes a new solution to this problem. It consists of the combination of a highly non-linear preprocessing of the audio signal and the use of a so called low-force-factor loudspeaker. This combination yields a strongly increased efficiency, at least over a limited frequency range, at the cost of a somewhat altered sound quality. An analytically tractable optimality criterion has been defined and has been verified by the design of an experimental loudspeaker. This has a much higher efficiency and a higher sensitivity than current low-frequency loudspeakers, while its cabinet can be much smaller.

Mechanisms and Mitigation of 3D Coupled Vibrations in Drilling with PDC Bits

2021 ◽  
Author(s):  
Shilin Chen ◽  
Chris Propes ◽  
Curtis Lanning ◽  
Brad Dunbar
Keyword(s):  
Torsional Oscillation ◽  
Excitation Frequency ◽  
Low Frequency ◽  
Coupled Vibration ◽  
Stick Slip ◽  
Rock Interaction ◽  
Bottom Hole ◽  
New Type ◽  
Design Characteristics ◽  
Axial Resonance

Abstract In this paper we present a new type of vibration related to PDC bits in drilling and its mitigation: a vibration coupled in axial, lateral and torsional directions at a high common frequency (3D coupled vibration). The coupled frequency is as high as 400Hz. 3D coupled vibration is a new dysfunction in drilling operation. This type of vibration occurred more often than stick-slip vibration. Evidences reveal that the coupled frequency is an excitation frequency coming from the bottom hole pattern formed in bit/rock interaction. This excitation frequency and its higher order harmonics may excite axial resonance and/or torsional resonance of a BHA. The nature of 3D coupled vibration is more harmful than low frequency stick-slip vibration and high frequency torsional oscillation (HFTO). The correlation between the occurrence of 3D coupled vibration and bit design characteristics is studied. Being different from prior publications, we found the excitation frequency is dependent on bit design and the occurrence of 3D coupled vibration is correlated with bit design characteristics. New design guidlines have been proposed to reduce or to mitigate 3D coupled vibration.

A Frequency-Tunable Comb Resonator Using Spring Tension and Compression Effects

2004 ◽  
Author(s):  
Ki Bang Lee ◽  
Albert P. Pisano ◽  
Liwei Lin
Keyword(s):  
Resonant Frequency ◽  
Bias Voltage ◽  
Frequency Tuning ◽  
Electrostatic Force ◽  
Voltage Change ◽  
Tension And Compression ◽  
Frequency Tunable ◽  
Frequency Changes ◽  
Compression Effects ◽  
First Time

A 2μm-thick frequency-tunable microresoantor capable of either increasing or decreasing its resonant frequency by a combination of Joule heating and electrostatic force has been successfully demonstrated for the first time. For the heating voltage increase from 0 to 2V under fixed bias voltage of 40V, the resonant frequency changes from 22.2kHz to 16.2kHz, resulting in the 27% reduction in the resonant frequency. For the bias voltage change from 20V to 40V under the heating voltage of 0V, the resonant frequency increase from 19.0kHz to 23.6kHz, resulting in the 24.2% increase in the resonant frequency. As such, this surface-micromachined microactuator could assist complicated frequency tuning for applications of microsensors and microactuators.

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