scholarly journals Influence of Structural Stiffness and Loss Factor on Railroad Vehicle Comfort

2021 ◽  
Vol 11 (19) ◽  
pp. 9273
Author(s):  
Publio Pintado ◽  
Carmen Ramiro ◽  
Eduardo Palomares ◽  
Angel L. Morales ◽  
Antonio J. Nieto ◽  
...  
Keyword(s):  
Loss Factor ◽  
Complex Modulus ◽  
Railway Vehicle ◽  
Structural Stiffness ◽  
Structural Damping ◽  
Elastic Supports ◽  
First Approximation ◽  
Rigid Body Modes ◽  
New Formulation ◽  
Railroad Vehicle

This paper presents a new formulation for analyzing a beam on elastic supports traveling on irregular profiles. The model is a first approximation of a passenger railway vehicle car body. The main difference with previous works is the use of a complex modulus to represent structural damping rather than relying on equivalent viscous terms. The formulation groups rigid body modes with flexible modes and proposes a matrix form that is easy to interpret and solve in the frequency domain. Comfort indexes are readily obtained from weighted response spectral densities. The model is used to assess the influence of structural damping and stiffness on comfort. It will be shown that the evolution of comfort with stiffness is non-monotonic and, therefore, comfort does not always improve as stiffness increases.

Measurement of Structural Stiffness and Damping Coefficients in a Metal Mesh Foil Bearing

2009 ◽  
Vol 132 (3) ◽  
Author(s):  
Luis San Andrés ◽  
Thomas Abraham Chirathadam ◽  
Tae-Ho Kim
Keyword(s):  
Loss Factor ◽  
Copper Wire ◽  
Mechanical Energy ◽  
Excitation Frequency ◽  
Viscous Damping ◽  
Structural Stiffness ◽  
Metal Mesh ◽  
Equivalent Viscous Damping ◽  
Damping Coefficients ◽  
Stiffness And Damping

Engineered metal mesh foil bearings (MMFBs) are a promising low cost bearing technology for oil-free microturbomachinery. In a MMFB, a ring shaped metal mesh provides a soft elastic support to a smooth arcuate foil wrapped around a rotating shaft. This paper details the construction of a MMFB and the static and dynamic load tests conducted on the bearing for estimation of its structural stiffness and equivalent viscous damping. The 28.00 mm diameter 28.05 mm long bearing, with a metal mesh ring made of 0.3 mm copper wire and compactness of 20%, is installed on a test shaft with a slight preload. Static load versus bearing deflection measurements display a cubic nonlinearity with large hysteresis. The bearing deflection varies linearly during loading, but nonlinearly during the unloading process. An electromagnetic shaker applies on the test bearing loads of controlled amplitude over a frequency range. In the frequency domain, the ratio of applied force to bearing deflection gives the bearing mechanical impedance, whose real part and imaginary part give the structural stiffness and damping coefficients, respectively. As with prior art published in the literature, the bearing stiffness decreases significantly with the amplitude of motion and shows a gradual increasing trend with frequency. The bearing equivalent viscous damping is inversely proportional to the excitation frequency and motion amplitude. Hence, it is best to describe the mechanical energy dissipation characteristics of the MMFB with a structural loss factor (material damping). The experimental results show a loss factor as high as 0.7 though dependent on the amplitude of motion. Empirically based formulas, originally developed for metal mesh rings, predict bearing structural stiffness and damping coefficients that agree well with the experimentally estimated parameters. Note, however, that the metal mesh ring, after continuous operation and various dismantling and re-assembly processes, showed significant creep or sag that resulted in a gradual decrease in its structural force coefficients.

Flutter stability analysis of a perforated damping blade for large wind turbines

2017 ◽  
Vol 21 (3) ◽  
pp. 973-989
Author(s):  
Da-Gang Sun ◽  
Jin-Jun Guo ◽  
Yong Song ◽  
Bi-juan Yan ◽  
Zhan-Long Li ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Turbine Blades ◽  
Time Integration ◽  
Response Analysis ◽  
Damping Factor ◽  
Deformation Model ◽  
Structural Stiffness ◽  
Structural Damping ◽  
Comparison Results

The flutter stability of wind turbine blades is one of the important contents in the research of wind turbines. The bending stiffness of blades has decreased with the development of large-sized wind turbines. To achieve damping flutter-suppressing on the long spanwise blades, perforated damping blade was proposed under the consideration of the structural damping factor and the structural stiffness in this paper. Through the study of the unit cell, the deformation model was established and the structural loss factor of the perforated damping blade was derived. The undamped blade and the perforated damping blade, combined with the relevant parameters of a 1500 kW wind turbine blade, were established to simulate the flutter-suppressing abilities and the structural stability. The dynamic response analysis was accomplished with the large deformation theory, and the MPC algorithm was used to realize grid mobile and data delivery, according to the Newmark time integration method. The comparison results show that the perforated damping blade has both a higher structural damping factor and a better structural stiffness.

scholarly journals Examining the movement differences in the behavior of normal and rack railway vehicle

2019 ◽  
Vol 4 (1) ◽  
pp. 96-103
Author(s):  
Andor Nagy ◽  
István Lakatos
Keyword(s):  
Mechanical Model ◽  
Railway Vehicle ◽  
Vehicle System ◽  
The Many ◽  
Movement Differences ◽  
Railroad Vehicle

The rack railway is a special type of railroad. There weren”t much built worldwide, and their number is decreasing. Now, in Budapest, there is a possibility to create an interoperable vehicle, based upon the experience gained from the previously operated line, and all the research regarding its unique characteristics. One from the many important sector of its operation, is the rail/rack/vehicle system. Its mechanical model is far more complex than a traditional railroad vehicle. We will demonstrate its behaviorial differences from a traditional railroad vehicle.

Measurement of Structural Stiffness and Damping Coefficients in a Metal Mesh Foil Bearing

2009 ◽  
Author(s):  
Luis San Andre´s ◽  
Thomas Abraham Chirathadam ◽  
Tae-Ho Kim
Keyword(s):  
Loss Factor ◽  
Copper Wire ◽  
Mechanical Energy ◽  
Excitation Frequency ◽  
Viscous Damping ◽  
Structural Stiffness ◽  
Metal Mesh ◽  
Equivalent Viscous Damping ◽  
Damping Coefficients ◽  
Stiffness And Damping

Engineered Metal Mesh Foil Bearings (MMFB) are a promising low cost bearing technology for oil-free microturbomachinery. In a MMFB, a ring shaped metal mesh (MM) provides a soft elastic support to a smooth arcuate foil wrapped around a rotating shaft. The paper details the construction of a MMFB and the static and dynamic load tests conducted on the bearing for estimation of its structural stiffness and equivalent viscous damping. The 28.00 mm diameter, 28.05 mm long bearing, with a metal mesh ring made of 0.3 mm Copper wire and compactness of 20%, is installed on a test shaft with a slight preload. Static load versus bearing deflection measurements display a cubic nonlinearity with large hysteresis. The bearing deflection varies linearly during loading, but nonlinearly during the unloading process. An electromagnetic shaker applies on the test bearing loads of controlled amplitude over a frequency range. In the frequency domain, the ratio of applied force to bearing deflection gives the bearing mechanical impedance, whose real part and imaginary part give the structural stiffness and damping coefficients, respectively. As with prior art published in the literature, the bearing stiffness decreases significantly with the amplitude of motion and shows a gradual increasing trend with frequency. The bearing equivalent viscous damping is inversely proportional to the excitation frequency and motion amplitude. Hence, it is best to describe the mechanical energy dissipation characteristics of the MMFB with a structural loss factor (material damping). The experimental results show a loss factor as high as 0.7 though dependent on the amplitude of motion. Empirically based formulas, originally developed for metal mesh rings, predict bearing structural stiffness and damping coefficients agreeing well with the experimentally estimated parameters. Note, however, that the metal mesh ring, after continuous operation and various dismantling and reassembly processes, showed significant creep or sag that resulted in a gradual decrease of its structural force coefficients.

The role of wake stiffness on the wake-induced vibration of the downstream cylinder of a tandem pair

2013 ◽  
Vol 718 ◽  
pp. 210-245 ◽  
Author(s):  
G. R. S. Assi ◽  
P. W. Bearman ◽  
B. S. Carmo ◽  
J. R. Meneghini ◽  
S. J. Sherwin ◽  
...  
Keyword(s):  
Vortex Structure ◽  
Fluid Dynamic ◽  
Dynamic Effect ◽  
Structural Stiffness ◽  
Structure Interaction ◽  
Tandem Cylinders ◽  
First Approximation ◽  
Linear Spring ◽  
Series Of Experiments

AbstractWhen a pair of tandem cylinders is immersed in a flow the downstream cylinder can be excited into wake-induced vibrations (WIV) due to the interaction with vortices coming from the upstream cylinder. Assi, Bearman & Meneghini (J. Fluid Mech., vol. 661, 2010, pp. 365–401) concluded that the WIV excitation mechanism has its origin in the unsteady vortex–structure interaction encountered by the cylinder as it oscillates across the wake. In the present paper we investigate how the cylinder responds to that excitation, characterising the amplitude and frequency of response and its dependency on other parameters of the system. We introduce the concept of wake stiffness, a fluid dynamic effect that can be associated, to a first approximation, with a linear spring with stiffness proportional to $\mathit{Re}$ and to the steady lift force occurring for staggered cylinders. By a series of experiments with a cylinder mounted on a base without springs we verify that such wake stiffness is not only strong enough to sustain oscillatory motion, but can also dominate over the structural stiffness of the system. We conclude that while unsteady vortex–structure interactions provide the energy input to sustain the vibrations, it is the wake stiffness phenomenon that defines the character of the WIV response.

Dynamic Rheological Behaviors of the Bone Scaffold Reinforced by Chitin Fibres

2005 ◽  
Vol 475-479 ◽  
pp. 2387-2390 ◽  
Author(s):  
X.M. Li ◽  
Qing Ling Feng
Keyword(s):  
Viscoelastic Properties ◽  
Loss Factor ◽  
Complex Modulus ◽  
Loss Modulus ◽  
Complex Viscosity ◽  
Materials Processing ◽  
Bone Scaffold ◽  
Rheological Behaviors ◽  
Wide Range ◽  
Yielding Behavior

In this study, a novel bioabsorbable porous bone scaffold reinforced by chitin fibres was prepared, the porosity of which is about 90 % and the pore size is approximately 200µm. The Advanced Rheological Enlarged System (ARES) was used to study the dynamic rheological behaviors of the ropy materials which would be made into the reinforced scaffold. The increase of the fibres’ volume content (Cf) enhanced the complex modulus (G*) and complex viscosity (h*) of the materials, the reason of which is that the fibres formed networks in the materials. When Cf increased from 35 % to 45 %, the storage modulus (G’) and loss modulus (G’’) curve showed obvious yielding behavior, which indicates that G’ and G’’ of the materials are hardly variable in a wide range. When Cf was more than 35 %, the loss factor (tand) was obviously lower than 1 and the materials exhibited viscoelastic properties, which result in a disadvantage for materials’ processing.

scholarly journals Identification of Loss Factor of Fiber-Reinforced Composite Based on Complex Modulus Method

2017 ◽  
Vol 2017 ◽  
pp. 1-13 ◽  
Author(s):  
Hui Li ◽  
Yi Niu ◽  
Chao Mu ◽  
Bangchun Wen
Keyword(s):  
Loss Factor ◽  
Complex Modulus ◽  
Damping Ratio ◽  
Fiber Reinforced ◽  
Identification Procedure ◽  
Fiber Reinforced Composite ◽  
Modal Damping Ratio ◽  
Reinforced Composite ◽  
Modal Damping ◽  
Modulus Method

The identification of the loss factor of fiber-reinforced composite based on complex modulus method is presented. Firstly, the damping model of fiber-reinforced composite plate is established, and the relation between each loss factor and modal damping ratio is deduced based on the complex modulus method. Then, the least square relative error function is formed by using the modal damping ratio obtained in the experimental test, and the appropriate step-size is selected in the range of 0~10% to calculate the loss factor. Next, the identification procedure of loss factor of such composite material is summarized, and the corresponding identification procedure is realized based on self-designed MATLAB program. Finally, TC300 carbon/epoxy composite plate is taken as an example to carry out a case study, and its loss factors along the longitudinal, transverse, and shear direction are identified by the complex modulus method. By comparing the measured damping results obtained in this paper and the calculated damping results based on the Adams-Bacon model with the same loss factor, it is found that the corresponding maximum deviation between them is less than 15%, so the correctness of such identification method has been verified indirectly, which can be used to identify loss factor of fiber-reinforced composite with high precision and efficiency.

An Approach of Constrained Damping Design and Application for the Fine Stage

2011 ◽  
Vol 52-54 ◽  
pp. 1788-1793
Author(s):  
Ling Fei Gao ◽  
Ming Zhang ◽  
Yu Zhu ◽  
Jing Wang
Keyword(s):  
Experimental Verification ◽  
Dynamic Property ◽  
Loss Factor ◽  
High Stability ◽  
Structural Damping ◽  
Stage Design ◽  
High Dynamic ◽  
Constrained Damping ◽  
Design And Application

High dynamic property is a major object in fine stage design, as well as high stability. To raise structural damping is a feasible and effective method. In this paper, an approach is advanced by choosing parameters of structural damping for fine stage, via analysis of the loss factor of the structure. Through the experimental verification, this method could double the damping ratios, and be applicable to the same structures without changing the original interface.

Comparison of damping parameters based on the half-power bandwidth methods of viscous and hysteretic damping models

2021 ◽  
pp. 107754632110546
Author(s):  
Panxu Sun ◽  
Dongwei Wang
Keyword(s):  
Loss Factor ◽  
Damping Ratio ◽  
Relative Difference ◽  
Structural Damping ◽  
Application Condition ◽  
Comparison Results ◽  
First Choice ◽  
Hysteretic Damping ◽  
Approximate Relationship ◽  
Half Power

The half-power bandwidth method is usually used to calculate structural damping parameters by frequency response function (FRF). In this note, the half-power bandwidth methods for the displacement FRF, the velocity FRF, and the acceleration FRF are proposed based on viscous and hysteretic damping models, respectively. Comparison results show that the application conditions of half-power bandwidth methods for the displacement and acceleration FRFs are limited. They can only be used to calculate the small damping ratio/loss factor. The application condition of half-power bandwidth method for the velocity FRF is not limited. It can be used to calculate the large or small damping ratio/loss factor, which should be the first choice for calculating damping parameters. Besides, when the damping ratio is less than 0.2546 or the loss factor is less than 0.5658, the relative difference between the loss factor and twice the damping ratio is less than 10%. With the increase of the damping ratio or loss factor, the relative difference will increase rapidly, and the approximate relationship is no longer applicable.

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