• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.454-460
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• 1998

The vibration behavior of fuel rods has been analyzed by FEM in consideration of axial force and support spring constants. The axial compression force on the fuel rod in reactor decreases with the fuel rod burnup, and its decrease makes the natural frequencies of fuel rod considerably increase. The change of support spring constant can contribute to the remarkable change of the mode shapes, but not greatly to the natural frequencies. The reaction forces of support springs are obtained from normalizing the lst mode with the max. 0.2 mm displacement. The calculated reaction forces are larger than the previous results obtained by disregarding the deflections of the support springs.

• Structural Monitoring and Maintenance
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• v.5 no.1
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• pp.15-38
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• 2018

Negative stiffness dampers (NSDs) have been proven an efficient solution to vibration control of stay cables. Although previous studies usually assumed a linear negative stiffness behavior of NSDs, many negative stiffness devices produce negative stiffness with nonlinear behavior. This paper systematically evaluates the impact of nonlinearity in negative stiffness on vibration control performance for stay cables. A linearization method based on energy equivalent principle is proposed, and subsequently, the impact of two types of nonlinear stiffness, namely, displacement hardening and softening stiffness, is evaluated. Through the Hilbert transform (HT) of free vibration responses, the effects of nonlinear stiffness of an NSD on the modal frequencies, damping ratios and frequency response functions of a stay cable is also investigated. The HT analysis results validate the accuracy of the linearization method.

• Advances in materials Research
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• v.8 no.4
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• pp.313-335
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• 2019

The objective of the present paper is to investigate the bending and free vibration behavior of functionally graded material (FGM) sandwich rectangular plates using an efficient and simple higher order shear deformation theory. Unlike other theories, there are only four unknown functions involved, as compared to five in other shear deformation theories. The most interesting feature of this theory is that it does not require the shear correction factor. Two common types of FGM sandwich plates are considered, namely, the sandwich with the FGM facesheet and the homogeneous core and the sandwich with the homogeneous facesheet and the FGM core. The equation of motion for the FGM sandwich plates is obtained based on Hamilton's principle. The closed form solutions are obtained by using the Navier technique. A static and free vibration frequency is given for different material properties. The accuracy of the present solutions is verified by comparing the obtained results with the existing solutions.

• Structural Engineering and Mechanics
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• v.74 no.4
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• pp.559-565
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• 2020

This paper intends to progress models to accurately estimate the behavior of fresh concrete under vibration using artificial neural networks (ANNs). To this end, behavior of a full scale precast concrete mold was investigated numerically. Experimental study was carried out under vibration with the use of a computer-based data acquisition system. In this study measurements were taken at three points using two vibrators. Transducers were used to measure time-dependent lateral displacements at these points on mold while both mold is empty and full of fresh concrete. Modeling of empty and full mold was made using ANNs. Benefiting ANNs used in this study for modeling fresh concrete, mold design can be performed. For the modeling of ANNs: Experimental data were divided randomly into two parts such as training set and testing set. Training set was used for ANN's learning stage. And the remaining part was used for testing the ANNs. Finally, ANN modeling was compared with measured data. The comparisons show that the experimental data and ANN results are compatible.

• Earthquakes and Structures
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• v.19 no.2
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• pp.91-101
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• 2020

This work presents an efficient and original hyperbolic shear deformation theory for the bending and dynamic behavior of functionally graded (FG) beams resting on Winkler - Pasternak foundations. The theory accounts for hyperbolic distribution of the transverse shear strains and satisfies the zero traction boundary conditions on the surfaces of the beam without using shear correction factors. Based on the present theory, the equations of motion are derived from Hamilton's principle. Navier type analytical solutions are obtained for the bending and vibration problems. The accuracy of the present solutions is verified by comparing the obtained results with the existing solutions. It can be concluded that the present theory is not only accurate but also simple in predicting the bending and vibration behavior of functionally graded beams.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1334-1339
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• 2006

Dynamic response of buried pipelines both in the axial and the transverse directions on concrete pipe and steel pipe, FRP pipe were investigated through a forced vibration analysis. The dynamic behavior of the buried pipelines for the forced vibration is found to exhibit two different forms, a transient response and a steady state response, depending on the time before and after the transfer of a seismic wave on the end of the buried pipeline. The former is identified by a slight change in its behavior before the sinusoidal-shaped seismic wave travels along the whole length of the pipeline whereas the latter by the complete form of a sinusoidal wave when the wave travels throughout the pipeline. The transient response becomes insignificant as the wave speed increases. From the results of the dynamic responses at the many points of the pipeline, we have found that the responses appeared to be dependent critically on the boundary end conditions. Such effects are found to be most prominent especially for the maximum values of the displacement and the strain and its position.

• Structural Engineering and Mechanics
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• v.57 no.3
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• pp.425-439
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• 2016

This paper deals with the behavior of fresh concrete that is under vibration using mass-spring model (MSM). To this end, behaviors of two different full scale precast concrete molds were investigated experimentally and theoretically. Experiments were performed under vibration with the use of a computer-based data acquisition system. Transducers were used to measure time-dependent lateral displacements at some points on mold while mold is empty and full of fresh concrete. Analytical modeling of molds used in experiments were prepared by three dimensional finite element method (3D FEM) using software. Modeling of full mold, using MSM, was made to solve the problem of dynamic interaction between fresh concrete and mold. Numerical displacement histories obtained from time history analysis were compared with experimental results. The comparisons show that the measured and computed results are compatible.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.900-910
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• 2000

This study have been performed to investigate the dynamic behavior of the Korean High Speed Train(KHST) during the conceptual design process. This study gets a focus on the analysis of the rigid model, for which the yaw damper layout is modified in a nonlinear limit cycle analysis. In this study, influences of the system parameters such as stiffness of suspension and connection elements as well as damping coefficients were studied and an optimized parameter set is achieved. Throughout the dynamic calculation of KHST on the straight and the curved track, vibration accelerations in car body, ride comforts and wheel rail forces are investigated. Finally the vibration characteristics from rigid car body are compared with those due to the influence of elastic car body.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1871-1874
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• 2000

It is impossible to predict accurately the dynamic behavior of turbine-generator system because bearing, and rotor characteristics are nonlinear and different from temperature, load, operation speed and bearing lubricant oil property. Especially, the characteristics of turbine hoods affect much the entire vibration characteristics of turbine. As the dynamic stiffness of turbine hoods are changed, the critical speeds of rotor are shifted. In this paper, the vibration behavior of turbine-generator is analyzed by using component mode synthesis and the critical speeds measured during shut-down are compared with the analytic results. It is confirmed that the 1st natural frequency and the mode shape are well in agreement with actual measured data.

• Smart Structures and Systems
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• v.26 no.5
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• pp.631-640
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• 2020

In this paper, nonlinear vibration behaviors of multi-phase Magneto-Electro-Elastic (MEE) doubly-curved nanoshells have been studied employing Jacobi elliptic function method. The doubly-curved nanoshell has been modeled by using nonlocal elasticity and classic shell theory. An exact estimation of nonlinear vibrational behavior of smart doubly-curved nanoshell has been obtained via Jacobi elliptic function method. This method can incorporate the influences of higher order harmonics leading to an exact estimation of nonlinear vibration frequency. It will be indicated that nonlinear vibrational frequency of doubly-curved nanoshell relies on nonlocal effect, material composition, curvature radius, center deflection and electro-magnetic field.