• International Journal of Railway
• /
• v.6 no.4
• /
• pp.155-159
• /
• 2013

The purpose of this study was to develop a theoretical model to analyze the vibration of finite railways forced by distributed moving loads. The vibration characteristics of compliantly supported beam utilizing compressional damping model were investigated through the Rayleigh-Ritz method. The distributed moving load was analyzed as the cross correlation function on railways. This allowed the use of statistical characteristics for simulation of the moving train wheels on the rail. The results showed there is a critical velocity inducing resonant vibration of the rail. The mass spring resonance from the rail fastening systems exhibited significant influence on the resulting vibration response. In particular, the effect of the viscoelastic core damping was investigated as an efficient method for minimizing rail vibration. The decrease of the averaged vibration and rolling noise generation by the damping core was maximized at the mass-stiffness-mass resonance frequency.

• Steel and Composite Structures
• /
• v.17 no.6
• /
• pp.803-824
• /
• 2014

The dynamic characterization is important in making accurate predictions of the seismic response of the hybrid structures dominated by different damping mechanisms. Different damping characteristics arise from the construction of the tower with different materials: steel for the upper part; reinforced concrete for the lower main part and interaction with supporting soil. The process of modeling damping matrices and experimental verification is challenging because damping cannot be determined via static tests as can mass and stiffness. The assumption of classical damping is not appropriate if the system to be analyzed consists of two or more parts with significantly different levels of damping, such as steel/concrete mixed structure - supporting soil coupled system. The dynamic response of structures is critically determined by the damping mechanisms, and its value is very important for the design and analysis of vibrating structures. An analytical approach capable of evaluating the equivalent modal damping ratio from structural components is desirable for improving seismic design. Two approaches are considered to define and investigate dynamic characteristics of hybrid tower of cable-stayed bridges: The first approach makes use of a simplified approximation of two lumped masses to investigate the structure irregularity effects including damping of different material, mass ratio, frequency ratio on dynamic characteristics and modal damping; the second approach employs a detailed numerical step-by step integration procedure in which the damping matrices of the upper and the lower substructures are modeled with the Rayleigh damping formulation.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 1997.10a
• /
• pp.126-131
• /
• 1997

Recently, the ground motion occurred by vehicles or trains has been recognized one of the major factors of damage of structures nearly the motion source. To isolate the environments from ground motions, it is necessary to understand the wave propagation in half spaces. Especially, Rayleigh wave is the primary concern because it transmits a major portion of the total source energy and decays the energy more slowly with response to distance than the other waves. In this study, the preliminary data(wave length and damping effect) to design the isolating system are obtained. For this, a field dynamic test is performed, using the exciter which can generate the 100kN vertical cyclic load in the range of 1-60 Hz is used. The fifteen accelerometers to measure the ground response are set up in 3 radial direction at intervals of 10 meters in each row. The wave lengths are calculated using the distance and the phase between the measuring points. The damping effects of the Rayleigh-wave are also observed from the experiments.

• Journal of the Korean Society of Industry Convergence
• /
• v.20 no.5
• /
• pp.431-439
• /
• 2017

Since the power transmission line(PTL) passes through the high mountain and heavy snowfall region, it is necessary to keep the stability of the PTL. In this study, PTL is modeled as a mass-spring-damper system by using RecurDyn. The lumped mass model is verified by calculated from the simulation comparing the deflection analysis according to the sag and tension. In order to analyze the dynamic behavior of PTL, a damping coefficient for a multi-body model is derived by using the free vibration test and Rayleigh damping theory. Sleet jump simulation according to the region is performed. The maximum jump height, icing sag and amount of jump are confirmed. Also, the amount of jump and the reaction force at the supporting point according to the tension and load of ice are analyzed, respectively. As a result, it is noted that the amount of jump and reaction force are influenced more by the load of ice than by the tension of PTL.

• Proceedings of the KSME Conference
• /
• 2007.05a
• /
• pp.578-583
• /
• 2007

Many papers have studied computer-aided simulations of elastic bodies undergoing large deflections and large deformations. But there have been few attempts to validate their numerical formulations used in these studies. The main aim of this paper is to validate the absolute nodal coordinate formulation (ANCF) by comparing the results to experimental measurements on beams. Physical experiments with a high-speed camera were carried out to capture the large displacement of the beam and to verify the results of computer simulations. To consider the damping forces, the Rayleigh's damping and quadratic damping are employed and compared to the experimental results, respectively. Numerical results obtained from computer simulations were compared with the results from the physical experiments according to the $1^{st}$ mode and the $2^{nd}$ mode of the beam, respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.05a
• /
• pp.430-433
• /
• 2003

This paper presents a system identification (SI) scheme in time domain using measured acceleration data. The error function is defined as the time integral of the least square errors between the measured acceleration and the calculated acceleration by a mathematical model. Damping parameters as well as stiffness properties of a structure are considered as system parameters. The structural damping is modeled by the Rayleigh damping in SI. The regularization technique is applied to alleviate the ill-posed characteristics of inverse problems. The validity of the proposed method is demonstrated by an experimental study on a shear building model.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.27 no.1
• /
• pp.9-18
• /
• 2023

The purpose of this paper is to review the appropriateness of the application method for the value of the damping ratio suggested in the current design standards and evaluation guidelines when evaluating the seismic performance of concrete dams and to suggest improvements. As a result of the study, for the magnitude of the damping ratio in the dynamic elastic analysis, it is necessary to refer to the case of a similar dam in which the magnitude of the earthquake load is similar and the reproducibility of the damping ratio has been verified. Considering this, it is necessary to apply a low damping ratio and consider adding hysteresis damping in case of nonlinear behavior. In addition, since the concrete dam body located on the rock has insignificant radiation attenuation effect, it is not reasonable to increase the damping ratio of the concrete dam body to reflect the radiation damping. Therefore, in order to evaluate the realistic seismic performance of concrete dams, it is necessary to revise the damping ratio-related contents contained in the current dam design standards and evaluation guidelines.

• Proceedings of the KSME Conference
• /
• 2004.11a
• /
• pp.1146-1151
• /
• 2004

Measurements of OH chemiluminescence in an atmospheric pressure, laboratory-scale dump combustor at equivalence ratios ranging from 0.63 to 0.89 were reported. The signal from the first electronically excited state of OH to ground state was detected through a band-pass filter with an ICCD. The objectives of this study are two: One is to see the effects of equivalence ratio on global heat release rate and local Rayleigh index distribution. To get the local Rayleigh index distribution, the line-of-sight images were inverted by tomographic method, such as Abel de-convolution. Another aim is to investigate the validity of using OH chemiluminescence acquired with an ICCD as a qualitative measure of local heat release. For constant inlet velocity and temperature, the overall intensities of OH emission acquired at different equivalence ratio showed periodic and higher value at high equivalence ratio. OH intensity averaged over one period of pressure increased exponentially with equivalence ratio. Local Rayleigh index distribution clearly showed the region of amplifying or damping the combustion instability as equivalence ratio increased. It could provide an information/insights on active control such as secondary fuel injection. Finally, local heat release rate derived from reconstructed OH images were presented for typical locations.

• Steel and Composite Structures
• /
• v.51 no.4
• /
• pp.457-471
• /
• 2024

In this research, for the first time the instability boundaries for a spinning shaft reinforced with graphene nanoplatelets undergone the principle parametric resonance are determined and examined taking into account the gyroscopic effect. In this respect, the extracted equations of motion in our previous research (Ref. Asadi et al. (2023)) are implemented and efficiently upgraded. In the upgraded discretized equations the effect of the Rayleigh's damping and the varying spinning speed is included that leads to a different dynamical discretized governing equations. The previous research was about the free vibration analysis of spinning graphene-based shafts examined by an eigen-value problem analysis; while, in the current research an advanced mechanical analysis is addressed in details for the first time that is the dynamics instability of the aforementioned shaft subjected to the principal parametric resonance. The spinning speed of the shaft is considered to be varied harmonically as a function of time. Rayleigh's damping effect is applied to the governing equations in order to regard the energy loss of the system. Resorting to Bolotin's route, Floquet theory and β-Newmark method, the instability region and its accompanied boundaries are defined. Accordingly, the effects of the graphene nanoplatelet on the instability region are elucidated.

• Structural Engineering and Mechanics
• /
• v.23 no.6
• /
• pp.691-711
• /
• 2006

This paper uses the finite element method to simultaneously consider the coupled cable-deck vibrations and the parametric vibrations of stay cables in dynamic analysis of a cable-stayed bridge. The stay cables are represented by some cable finite elements, which can consider the parametric vibration of the cables. In addition to modeling stay cables using multiple link cable elements, a procedure for removing the self-weight term of cable element is proposed. A eigenvalue analysis process using dynamic condensation method for sorting out the natural modes of the girder-tower vibrations and the Rayleigh damping considering element damping for damping matrix are also proposed for dynamic analyses of cable-stayed bridges. The possibilities of using cable elements and of using global and local vibrations to evaluate the parametric vibrations of stay cables in a cable-stayed bridge are confirmed, respectively.