Effect of Geometric Shape of Periodic Cavities in Attenuating Baseframe Vibration

2020 ◽  
Author(s):  
S. N. Das ◽  
Kachita Kohli ◽  
Ayush Kumar ◽  
G. R. Sabareesh
Keyword(s):  
Stop Band ◽  
Rotating Machinery ◽  
Vibration Level ◽  
Structural Vibrations ◽  
Frequency Bands ◽  
Natural Modes ◽  
Vibration Attenuation ◽  
Specific Frequency ◽  
Different Shapes ◽  
Air Cavities

Abstract Vibration attenuation is an important factor while designing rotating machinery since frequency lying in the range corresponding to natural modes of structures can result in resonance and ultimately failure. Damping dissipates energy in the system, which reduces the vibration level. The mitigation of vibrations can be achieved by designing the base frame with periodic air holes. The periodicity in air holes result in vibration attenuation by providing a stop band. A finite element-based approach is developed to predict the modal and frequency response. The analysis is carried out with different shapes of periodic cavities in order to study the effectiveness of periodic stop bands in attenuating vibrations. The amount of mass removed due to the periodic cavities is kept constant. It is seen that better attenuation is obtained in case of periodic cavities compared to a uniform base frame. Among the different geometries tested, rectangular cavities showed better results than circular and square cavities. As a result, it is seen that waves propagate along periodic cells only within specific frequency bands called the “Pass bands”, while these waves are completely blocked within other frequency bands called the “Stopbands”. The air cavities filter structural vibrations in certain frequency bands resulting in effective attenuation.

Damping and Bandgap Characteristics of a Viscoelastic Tensegrity Damper

2021 ◽  
pp. 1-47
Author(s):  
Mohamed Raafat ◽  
Amr Baz
Keyword(s):  
Mathematical Model ◽  
Material Characterization ◽  
Structural Vibrations ◽  
New Class ◽  
Structural Applications ◽  
Theoretical Predictions ◽  
Specific Frequency ◽  
The Mathematical Model ◽  
Theory And Experiments

Abstract A theoretical and experimental investigation of a new class of a tensegrity-based structural damper is presented. The damper is not only capable of attenuating undesirable structural vibrations, as all conventional dampers, but also capable of completely blocking the transmission of vibration over specific frequency bands by virtue of its periodicity. Such dual functionality distinguishes the tensegrity damper over its counterparts of existing structural dampers. Particular emphasis is placed here in presenting the concept and developing the mathematical model of the dynamics of a unit cell the damper. The model is then coupled with a Floquet-Bloch analysis in order to identify the bandgap characteristics of the damper. The predictions of the mathematical model are validated experimentally using a prototype of the damper which is built using 3D printing. A comprehensive material characterization of the damper is performed followed by a detailed extraction of the static and dynamic behavior of the damper in order to validate the theoretical predictions. Close agreement is observed between theory and experiments. The developed theoretical and experimental techniques provide invaluable means for the design of this new class of dampers particularly for critical structural applications.

scholarly journals Experimental and Numerical Study on Dynamics of Two Footbridges with Different Shapes of Girders

2020 ◽  
Vol 10 (13) ◽  
pp. 4505 ◽  
Author(s):  
Anna Banas ◽  
Robert Jankowski
Keyword(s):  
Natural Vibration ◽  
Numerical Study ◽  
Numerical Results ◽  
Vibration Exciter ◽  
Structural Vibrations ◽  
Impulse Load ◽  
Different Shapes ◽  
Comfort Criteria ◽  
Good Agreement

The paper presents the experimental and numerical results of the dynamic system identification and verification of the behavior of two footbridges in Poland. The experimental part of the study involved vibration testing under different scenarios of human-induced load, impulse load, and excitations induced by vibration exciter. Based on the results obtained, the identification of dynamic parameters of the footbridges was performed using the peak-picking method. With the impulse load applied to both structures, determination of their natural vibration frequencies was possible. Then, based on the design drawings, detailed finite element method (FEM) models were developed, and the numerical analyses were carried out. The comparison between experimental and numerical results obtained from the modal analysis showed a good agreement. The results also indicated that both structures under investigation have the first natural bending frequency of the deck in the range of human-induced excitation. Therefore, the risk of excessive structural vibrations caused by pedestrian loading was then analysed for both structures. The vibration comfort criteria for both footbridges were checked according to Sétra guidelines. In the case of the first footbridge, the results showed that the comfort criteria are fulfilled, regardless of the type of load. For the second footbridge, it was emphasized that the structure meets the assumptions of the guidelines for vibration severability in normal use; nevertheless, it is susceptible to excitations induced by synchronized users, even in the case of a small group of pedestrians.

Passive Periodic Engine Mount

2008 ◽  
Author(s):  
Ling Zheng ◽  
Woojin Jung ◽  
Zheng Gu ◽  
A. Baz
Keyword(s):  
Spectral Width ◽  
Shear Mode ◽  
Effective Width ◽  
Frequency Bands ◽  
Automotive Engine ◽  
New Class ◽  
Mechanical Filter ◽  
Transfer Matrix Approach ◽  
Specific Frequency ◽  
Engine Mount

The transmission of automotive engine vibrations to the chassis is isolated using a new class of mounts which rely in their operation on optimally designed and periodically distributed viscoelastic inserts. The proposed mount acts as mechanical filter for impeding the propagation of vibration within specific frequency bands called the ‘Stop Bands’. The spectral width of these bands is enhanced by making the viscoelastic inserts operate in a shear mode rather than compression mode. The theory governing the operation of this class of periodic mounts is presented using the theory of finite elements combined with the transfer matrix approach. The predictions of the performance of the mount are validated against the predictions of the commercial finite element code ANSYS and against experimental results obtained from prototypes of plain and periodic mounts. The obtained results demonstrate the feasibility of the shear mode periodic mount as an effectiveness means for blocking the transmission of vibration over a broad frequency band. Extending the effective width of the operating frequency bands of this class of mount through active control means is the ultimate goal of this study.

scholarly journals A Multiband Printed Log-Periodic Dipole Array for Wireless Communications

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Giovanni Andrea Casula ◽  
Paolo Maxia
Keyword(s):  
Wireless Communications ◽  
Radiation Pattern ◽  
Frequency Band ◽  
Stop Band ◽  
Operating Frequency ◽  
Frequency Bands ◽  
Operating Frequency Band ◽  
Input Matching ◽  
Compact Size ◽  
Cst Microwave Studio

A multiband printed Log-periodic dipole array (LPDA) antenna for wireless communications is presented. The antenna has been designed starting from Carrel’s theory, optimized using CST Microwave Studio 2012, and then realized. The comparison between simulated and measured results shows that the proposed antenna can be used for wireless communications both in the S (2.4–3 GHz) and in the C (5.2–5.8 GHz) frequency bands, with very good input matching and a satisfactory end-fire radiation pattern. Moreover, it has a compact size, is very easy to realize, and presents an excellent out-of-band rejection, without the use of stop-band filters, thus avoiding interference out of its operating frequency band.

Field Study on Pump Vibration and ISO’s New Criteria

1999 ◽  
Vol 121 (4) ◽  
pp. 798-803 ◽  
Author(s):  
Toshiyuki Osada ◽  
Takashi Kawakami ◽  
Tadashi Yokoi ◽  
Yoshinobu Tsujimoto
Keyword(s):  
Rotational Speed ◽  
Work Group ◽  
Field Measurements ◽  
Rotating Machinery ◽  
International Organization ◽  
Vibration Level ◽  
Term Operation ◽  
New Criteria

ISO 10816-3 (a new standard of International Organization for Standardization) was established as vibration criteria for industrial rotating machinery based on the bearing housing vibration in situ. The appropriateness of the application of the proposed vibration criteria to pumps was discussed and studied by a work group in Japan. For the assessment, the data of vibration level in field were measured, and the effects of driver output, rotational speed, and pump type were studied. This paper describes the applicability of the new ISO criteria to the evaluation of vibration level of pumps, based on the results of the field measurements. It was found that the new boundaries of evaluation zones, which are acceptable for unrestricted long-term operation of pumps, are quite appropriate and satisfactory.

Experimental Evaluation of Vibration Effects Induced by Planed Railway Line on Surrounding Historic Tower

2014 ◽  
Vol 501-504 ◽  
pp. 861-866
Author(s):  
Yuan Tian ◽  
Nan Zhang ◽  
Wei Guo Yang ◽  
Jia Ming Niu
Keyword(s):  
Field Experiments ◽  
Dominant Frequency ◽  
Vibration Velocity ◽  
Vibration Source ◽  
Vibration Level ◽  
Frequency Range ◽  
Structural Vibrations ◽  
Upward Trend ◽  
Railway Line ◽  
Different Types

Using field experiments, the vibration effects of historic tower induced by planed railway line are estimated. The vibrations include the construction vibration and the traffic-induced vibration. The results show that the blasting construction leads to the significant increase in vertical velocity and acceleration. There is no difference between the background vibration of field and foundation of tower. Different types of the sites soil around the tower cause little change. Each measurement time showed an upward trend of vibration level with the increase of frequency. The closer the tower is to the vibration source, the larger the structural vibrations would be. The dominant frequency range for highway-induced vibration is 10-20Hz. For train-induced vibration, the dominant frequency range is more than 40Hz. Surface waves will result in amplification phenomenon of vibration velocity of ancient structures within a certain range.

scholarly journals Mathematical model of the impact assessment of roughness and waviness deviations of races surfaces of rolling bearings on the level of generated vibration

Mechanik ◽  
2019 ◽  
Vol 92 (1) ◽  
pp. 35-37
Author(s):  
Paweł Zmarzły
Keyword(s):  
Mathematical Model ◽  
Mathematical Models ◽  
Impact Assessment ◽  
Ball Bearings ◽  
Vibration Level ◽  
Rolling Bearings ◽  
Shape Deviations ◽  
Specific Frequency ◽  
The Impact ◽  
Dominant Influence

The article presents mathematical models allowing to describe the level of vibration generated by ball bearings 6304-2z type depending on the value of roughness and waviness deviations of inner and outer bearings races. This models will allow to estimate what type of shape deviations have dominant influence on the vibration level generated in specific frequency ranges.

scholarly journals Information Decomposition in the Frequency Domain: a New Framework to Study Cardiovascular and Cardiorespiratory Oscillations

2020 ◽  
Author(s):  
Luca Faes ◽  
Riccardo Pernice ◽  
Gorana Mijatovic ◽  
Yuri Antonacci ◽  
Jana Cernanova Krohova ◽  
...  
Keyword(s):  
Time Series ◽  
Spectral Measures ◽  
Short Term ◽  
Information Theoretic ◽  
Frequency Bands ◽  
Information Measures ◽  
Head Up Tilt ◽  
Specific Frequency ◽  
Domain Information ◽  
New Framework

SummaryWhile cross-spectral and information-theoretic approaches are widely used for the multivariate analysis of physiological time series, their combined utilization is far less developed in the literature. This study introduces a framework for the spectral decomposition of multivariate information measures, which provides frequency-specific quantifications of the information shared between a target and two source time series and of its expansion into amounts related to how the sources contribute to the target dynamics with unique, redundant and synergistic information. The framework is illustrated in simulations of linearly interacting stochastic processes, showing how it allows to retrieve amounts of information shared by the processes within specific frequency bands which are otherwise not detectable by time-domain information measures, as well as coupling features which are not detectable by spectral measures. Then, it is applied to the time series of heart period, systolic and diastolic arterial pressure and respiration variability measured in healthy subjects monitored in the resting supine position and during head-up tilt. We show that the spectral measures of unique, redundant and synergistic information shared by these variability series, integrated within specific frequency bands of physiological interest, reflect the mechanisms of short term regulation of cardiovascular and cardiorespiratory oscillations and their alterations induced by the postural stress.

scholarly journals Design and optimization of left-handed materials with specific frequency bands

2012 ◽  
Vol 61 (5) ◽  
pp. 054103
Author(s):  
Gao Ren-Jing ◽  
Wang Guo-Ming ◽  
Liu Shu-Tian ◽  
Tang Zhen-An
Keyword(s):  
Frequency Bands ◽  
Design And Optimization ◽  
Left Handed ◽  
Specific Frequency
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