scholarly journals LOSS FACTORS OF STRUCTURAL CABLES FOR MODAL DAMPING EVALUATION

2006 ◽  
Vol 62 (2) ◽  
pp. 279-287
Author(s):  
Yoshihiro HAMAZAKI ◽  
Toru OKADA ◽  
Hiroki YAMAGUCHI ◽  
Yozo FUJINO
Keyword(s):  
Modal Damping ◽  
Structural Cables ◽  
Loss Factors

Loss Factors Of Damping Treated Structural Cables

1994 ◽  
Vol 176 (4) ◽  
pp. 487-495 ◽  
Author(s):  
H. Yamaguchi ◽  
R. Adhikari
Keyword(s):  
Structural Cables ◽  
Loss Factors

The Effect of Visco-Elastic Core Thickness on Modal Loss Factors of a Thick Three-Layer Cylinder

2007 ◽  
Author(s):  
Hamid R. Hamidzadeh
Keyword(s):  
Elastic Moduli ◽  
Natural Frequencies ◽  
Middle Layer ◽  
Constrained Layer Damping ◽  
Governing Equations ◽  
Modal Damping ◽  
Core Thickness ◽  
Elastic Cylinders ◽  
Thick Layers ◽  
Loss Factors

Free vibration of damped three-layer sandwich cylinders with thick layers is considered. In particular, the effect of the different thicknesses for the middle layer on the overall natural frequencies and modal damping factors are studied. The constrained layer damping is accomplished by sandwiching a linear visco-elastic material between two isotropic elastic cylinders with the same properties. The governing equations are derived using the theory of elasto-dynamic, by employing complex elastic moduli for the sandwiched layer. Dimensionless natural frequencies and modal loss-factors for the first three thickness modes associated with wave numbers of n = 0, 1, 2, 3, and 4 are tabulated for a range of thicknesses for the middle visco-elastic layer while keeping the thicknesses of inner and outer layers unchanged.

Effect of Modes Inside or Outside the Studied Band on Accuracy of Decay Rate Method in Vibration Damping Test

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Banghui Yin ◽  
Minqing Wang
Keyword(s):  
Decay Rate ◽  
Frequency Band ◽  
Vibration Damping ◽  
Response Data ◽  
Modal Damping ◽  
Element Simulation ◽  
Positive Variation ◽  
Energy Leakage ◽  
Rate Method ◽  
Loss Factors

The band-averaged damping is determined by modal damping of the modes inside/outside the frequency band. In this paper, the effect of modes inside/outside a frequency band on the accuracy of the decay rate method (DRM) in vibration damping test was studied. First, to study the effect of modes inside a frequency band on the accuracy of DRM, the relationship between the damping loss factors (DLFs) from DRM and that from statistical energy analysis (SEA) was deduced theoretically. As shown from the analytical results, the DLF from DRM is close to that from SEA when the differences of the modal loss factors of the modes in the band are small; while the DLF from DRM is much less than that from the SEA if the differences of the modal loss factors in the band are large. Second, the influence of energy leakage from modes outside a frequency band on damping test results was studied numerically. The study reveals that when there is no mode in a frequency band, the effect of the mode outside the band on the decay rate (DR) of DRM is only related with the DR of the mode instead of the location of the mode; while when the band contains modes, the DR of DRM is influenced by the DR, amplitude, and location of the modes outside the band and the influence has a positive variation with DR, amplitude, and distance from the mode to the band. Finally, plate's transient impact response data from finite element simulation were used to verify the relevant conclusions.

Effect of Bass Bar Tension on Modal Parameters of a Violin's Top Plate

2015 ◽  
Vol 39 (1) ◽  
pp. 145-149 ◽  
Author(s):  
Ewa B. Skrodzka ◽  
Bogumił B.J. Linde ◽  
Antoni Krupa
Keyword(s):  
Modal Analysis ◽  
Experimental Modal Analysis ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Normal Value ◽  
Modal Damping

Abstract Experimental modal analysis of a violin with three different tensions of a bass bar has been performed. The bass bar tension is the only intentionally introduced modification of the instrument. The aim of the study was to find differences and similarities between top plate modal parameters determined by a bass bar perfectly fitting the shape of the top plate, the bass bar with a tension usually applied by luthiers (normal), and the tension higher than the normal value. In the modal analysis four signature modes are taken into account. Bass bar tension does not change the sequence of mode shapes. Changes in modal damping are insignificant. An increase in bass bar tension causes an increase in modal frequencies A0 and B(1+) and does not change the frequencies of modes CBR and B(1-).

scholarly journals Dynamic mechanical behaviors of epoxy resin/hollow polymeric microsphere composite foams under forced non-resonance and forced resonance

2021 ◽  
Vol 30 ◽  
pp. 263498332110081
Author(s):  
Rui Li ◽  
Guisen Fan ◽  
Xiao Ouyang ◽  
Guojun Wang ◽  
Hao Wei
Keyword(s):  
Mechanical Properties ◽  
Epoxy Resin ◽  
Second Order ◽  
Polymer Microspheres ◽  
Hollow Glass Microsphere ◽  
Dynamic Mechanical ◽  
First Order ◽  
Composite Foams ◽  
Prepared Composite ◽  
Loss Factors

Composite foams with 10–50 vol% hollow polymeric microspheres were prepared using bisphenol A epoxy resin and polyetheramine curing agent as the matrix. The results demonstrated that the density, hardness, and static mechanical properties of the epoxy resin/hollow polymer microsphere composite foams, as well as their dynamic mechanical properties under forced non-resonance, were similar to those of polymer/hollow glass microsphere composite foams. At 25°C and under 1–100 Hz forced resonance, the first-order and second-order resonance frequencies of the composite foams shifted to the low-frequency region as the volume fraction of hollow polymer microspheres increased. Meanwhile, the first-order and second-order loss factors of the as-prepared composite foams were improved by 41.7% and 103.3%, respectively, compared with the pure epoxy resin. Additionally, the first-order and second-order loss factors of the as-prepared composite foams reached a maximum at 40 vol% and 30 vol% hollow polymer microspheres, respectively. This research helps us to expand the application range of composite foam materials in damping research.

scholarly journals Topology Optimization of Hard-Coating Thin Plate for Maximizing Modal Loss Factors

Coatings ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 774
Author(s):  
Haitao Luo ◽  
Rong Chen ◽  
Siwei Guo ◽  
Jia Fu
Keyword(s):  
Topology Optimization ◽  
Objective Function ◽  
Composite Plates ◽  
Optimization Method ◽  
Hard Coating ◽  
Design Variables ◽  
Coating Composite ◽  
Damping Materials ◽  
Topology Optimization Method ◽  
Loss Factors

At present, hard coating structures are widely studied as a new passive damping method. Generally, the hard coating material is completely covered on the surface of the thin-walled structure, but the local coverage cannot only achieve better vibration reduction effect, but also save the material and processing costs. In this paper, a topology optimization method for hard coated composite plates is proposed to maximize the modal loss factors. The finite element dynamic model of hard coating composite plate is established. The topology optimization model is established with the energy ratio of hard coating layer to base layer as the objective function and the amount of damping material as the constraint condition. The sensitivity expression of the objective function to the design variables is derived, and the iteration of the design variables is realized by the Method of Moving Asymptote (MMA). Several numerical examples are provided to demonstrate that this method can obtain the optimal layout of damping materials for hard coating composite plates. The results show that the damping materials are mainly distributed in the area where the stored modal strain energy is large, which is consistent with the traditional design method. Finally, based on the numerical results, the experimental study of local hard coating composites plate is carried out. The results show that the topology optimization method can significantly reduce the frequency response amplitude while reducing the amount of damping materials, which shows the feasibility and effectiveness of the method.

A validated robust and automatic procedure for vibration analysis of bridge structures using MEMS accelerometers

2020 ◽  
Vol 14 (3) ◽  
pp. 327-354
Author(s):  
Mohammad Omidalizarandi ◽  
Ralf Herrmann ◽  
Boris Kargoll ◽  
Steffen Marx ◽  
Jens-André Paffenholz ◽  
...  
Keyword(s):  
Vibration Analysis ◽  
Damping Ratio ◽  
Fem Analysis ◽  
Cost Effective ◽  
Analysis Procedure ◽  
Modal Parameters ◽  
Bridge Structure ◽  
Modal Damping ◽  
Mems Accelerometers ◽  
Better Than

AbstractToday, short- and long-term structural health monitoring (SHM) of bridge infrastructures and their safe, reliable and cost-effective maintenance has received considerable attention. From a surveying or civil engineer’s point of view, vibration-based SHM can be conducted by inspecting the changes in the global dynamic behaviour of a structure, such as natural frequencies (i. e. eigenfrequencies), mode shapes (i. e. eigenforms) and modal damping, which are known as modal parameters. This research work aims to propose a robust and automatic vibration analysis procedure that is so-called robust time domain modal parameter identification (RT-MPI) technique. It is novel in the sense of automatic and reliable identification of initial eigenfrequencies even closely spaced ones as well as robustly and accurately estimating the modal parameters of a bridge structure using low numbers of cost-effective micro-electro-mechanical systems (MEMS) accelerometers. To estimate amplitude, frequency, phase shift and damping ratio coefficients, an observation model consisting of: (1) a damped harmonic oscillation model, (2) an autoregressive model of coloured measurement noise and (3) a stochastic model in the form of the heavy-tailed family of scaled t-distributions is employed and jointly adjusted by means of a generalised expectation maximisation algorithm. Multiple MEMS as part of a geo-sensor network were mounted at different positions of a bridge structure which is precalculated by means of a finite element model (FEM) analysis. At the end, the estimated eigenfrequencies and eigenforms are compared and validated by the estimated parameters obtained from acceleration measurements of high-end accelerometers of type PCB ICP quartz, velocity measurements from a geophone and the FEM analysis. Additionally, the estimated eigenfrequencies and modal damping are compared with a well-known covariance driven stochastic subspace identification approach, which reveals the superiority of our proposed approach. We performed an experiment in two case studies with simulated data and real applications of a footbridge structure and a synthetic bridge. The results show that MEMS accelerometers are suitable for detecting all occurring eigenfrequencies depending on a sampling frequency specified. Moreover, the vibration analysis procedure demonstrates that amplitudes can be estimated in submillimetre range accuracy, frequencies with an accuracy better than 0.1 Hz and damping ratio coefficients with an accuracy better than 0.1 and 0.2 % for modal and system damping, respectively.

Sign in / Sign up

Export Citation Format

Share Document