• Nuclear Engineering and Technology
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• v.49 no.7
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• pp.1513-1523
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• 2017

Improvement of numerical analysis methods has been required to solve complicated phenomena that occur in nuclear facilities. Particularly, fluid-structure interaction (FSI) behavior should be resolved for accurate design and evaluation of complex reactor vessel internals (RVIs) submerged in coolant. In this study, the FSI effect on dynamic characteristics of RVIs in a typical 1,000 MWe nuclear power plant was investigated. Modal analyses of an integrated assembly were conducted by employing the fluid-structure (F-S) model as well as the traditional added-mass model. Subsequently, structural analyses were carried out using design response spectra combined with modal analysis data. Analysis results from the F-S model led to reductions of both frequency and Tresca stress compared to those values obtained using the added-mass model. Validation of the analysis method with the FSI model was also performed, from which the interface between the upper guide structure plate and the core shroud assembly lug was defined as the critical location of the typical RVIs, while all the relevant stress intensities satisfied the acceptance criteria.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.3
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• pp.241-257
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• 2014

The modern development in design of airships and aerostats has led to unconventional configurations quite different from the classical ellipsoidal and spherical ones. This new class of air-vehicles presents a mass-to-volume ratio that can be considered very similar to the density of the fluid displaced by the vehicle itself, and as a consequence, modeling and simulation should consider the added masses in the equations of motion. The concept of added masses deals with the inertia added to a system, since an accelerating or decelerating body moving into a fluid displaces a volume of the neighboring fluid. The aim of this paper is to provide designers with the added masses matrix for more than twenty Lighter Than Air vehicles with unconventional shapes. Starting from a CAD model of a given shape, by applying a panel-like method, its external surface is properly meshed, using triangular elements. The methodology has been validated by comparing results obtained with data available in literature for a known benchmark shape, and the inaccuracies of predictions agree with the typical precision required in conceptual design. For each configuration, a CAD model and a related added masses matrix are provided, with the purpose of assisting the practitioner in the design and flight simulation of modern airships and scientific balloons.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.04a
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• pp.81-88
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• 2000

Unlike structures in the air, the vibration analysis of a submerged or floating structure such as offshore structures or ships is possible only when the fluid-structure interaction is understood, as the whole or part of the structure is in contact with water. Specially, the importance of the added mass is not necessary to say like the submerged vehicle, all of the hull body, is positioned in the water. This paper introduce two method to find natural frequency in consideration of fluid-structure modal coupled vibration analysis. The purpose of this study is to analyze of the vibration characteristic of submerged vehicle to obtain the anti-vibration design data, which could be used in the preliminary design stage data. Underwater pressure hull of submerged vehicle is used as the model of this study. The F.E.M model is meshed by shell and beam element. Also, considering of the inner hull weight, mass element is distributed in the direction of hull length. Numerical calculations are accomplished using the commercial B.E.M code. The characteristics of natural frequency(eigenvalues), mode shape(eigenvectors) and frequency-displacement response are analyzed. The results of this study will be used as the useful design data in preliminary anti-vibration design stage.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.349-354
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• 2011

Tuned mass damper is widely used in many applications of industry. The main advantage of tuned mass damper is that it can increase the damping ratio of system and reduce the vibration amplitude. Meanwhile, the natural frequency of system will be divided by two peaks, and the peak speeds are closely related to the mass and the stiffness of auxiliary mass system added. In addition, the damping ratio will also affect the peak frequency of the dynamic response. In the present research, the nonlinear mechanical characteristics of rubber is investigated and put into use, since it is usually manufactured as the spring element of tuned mass damper. By the sense of the nonlinear stiffness as well as the damping ratio which can be changed by preload applied on, the shape memory alloy is proposed to control the auxiliary mass system by self-optimizing. Supported by the experiment data of rubber, the 1 DOF theoretical model and finite element model based on computer simulation are implemented to perform the feasibility of the proposed semi-active tuned mass damper working on the drive shaft.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.1
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• pp.1-7
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• 2013

The high-skewed and/or composite propellers of current interests to reduce the ship vibration and to increase the acoustic performance are likely to be exposed to the unexpected structural problems. One typical example is that the added mass effect on the propellers working in the non-uniform wake field reduces the natural frequency of the propeller leading to the resonance with the low-frequency excitation of the external forces. To avoid this resonance problem during the design stage, the technique of fluid-structure interaction has been developed, but the higher-order effect of the blade geometry deformation is not yet considered in evaluating the added mass effects. In this paper the fluid boundary-value problem is formulated by the potential-based panel method in the inviscid fluid region with the velocity inflow due to the body deformation, and the structural response of the solid body under the hydrodynamic loading is solved by applying the finite element method which implements the 20-node iso-parametric element model. The fluid-structure problem is solved iteratively. A basic fluid-sturcture interaction study is performed with the simple rectangular plates of thin thickness with various planform submerged in the water of infinite extent. The computations show good correlation with the experimental results of Linholm, et al. (1965).

• Journal of Institute of Convergence Technology
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• v.7 no.2
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• pp.25-30
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• 2017

This paper presents the effects of a virtual mass with a low-pass filter on the stability boundary of a virtual spring in the haptic system. In general, a haptic system consists of a haptic device, a sampler, a virtual impedance model and zero-order-hold. The virtual impedance is modeled as a virtual spring and a virtual mass. However the high-frequency noise due to the sampling time and the quantization error of sampled data may be generated when an acceleration is measured to compute the inertia force of the virtual mass. So a low-pass filter is needed to prevent the unstable behavior due to the high-frequency noise. A finite impulse response (FIR) filter is added to the measurement process of the acceleration and the effects on the haptic stability are simulated. According to the virtual mass with the FIR filter and the sampling time, the stability boundary of the virtual spring is analyzed through the simulation. The maximum available stiffness to guarantee the stable behavior is reduced, but simulation results still show that the stability boundary of the haptic system with the virtual mass is larger than that of the haptic system without the virtual mass.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.2
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• pp.109-116
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• 2010

It is important to make a mechanical structure precisely and reasonably in predicting the dynamic characteristics, controlling the vibration, and designing the structure dynamics. In finite element analysis model updating is appropriate as the design parameter is used to analyze the dynamic system. The errors can be contained from the physical parameters and the element modeling. From the dynamic test, more precise dynamic characteristics can be obtained. In this paper, model updating algorithm is developed using frequency difference between experiment and calculation. Modal frequencies are obtained by experiment and finite element analysis for beams with various cross section and shapes which have added masses and holes in the middle. For plates with and without groove, experiment and analyses are carried out by applying free boundary conditions as well. Mass and stiffness matrices are updated by comparing test and analytical modal frequencies. The result shows that the updated frequencies become closer to the test frequencies in case that both matrices are updated. An improved analytical model is obtained by changing model parameters such that the discrepancy between test and finite element frequencies is minimized. For beam and plate models updating of mass and stiffness matrices can improve the dynamical behavior of the model by acting on the physical parameters such as masses and stiffness.

• Environmental and Resource Economics Review
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• v.11 no.2
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• pp.321-333
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• 2002

Approximating bottled water consumption distribution is complicated by zero observations in the sample. To deal with the zero observations, a mixture model of bottled water consumption distributions is proposed and applied to allow a point mass at zero. The bottled water consumption distribution is specified as a mixture of two distributions, one with a point mass at zero and the other with full support on the positive half of the real line. The model is empirically verified for household bottled water consumption survey data. The mixture model can easily capture the common bimodality feature of the bottled water consumption distribution. In addition, when covariates were added to the model, it was found that the probability that a household has non-consumption significantly varies with some variables.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.1
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• pp.271-281
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• 2005

The effects of radiation damping is used to compensate the truncated boundary which is relatively close to the structure-fluid interface in the fluid element surrounding the submerged structures. An efficient ring element is presented to model the shell and fluid element which fully utilizes the characteristics of the axisymmetry. The computational model uses the technique which separate the meridional shape and circumferential wave mode and gets similar result with the exact solution in the eigenvalues and the earthquake analysis. The fluid-structure interaction techniques is developed in the finite element analysis of two dimensional problems using the relations between pressure, nodal unknown acceleration and added mass assuming the fluid to be invicid, incompressible and irrotational. The effectiveness and efficiency of the technique is demonstrated by analyzing the free vibration and seismic analysis using the added mass matrix considering the structural deformation effect.

• Structural Engineering and Mechanics
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• v.52 no.5
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• pp.997-1017
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• 2014

According to the structure characteristics of the non-uniform beam bridge, a practical model for calculating the vibration equation of the non-uniform beam bridge is given and the application scope of the model includes not only the beam bridge structure but also the non-uniform beam with added masses and elastic supports. Based on the Bernoulli-Euler beam theory, extending the application of the modal perturbation method and establishment of a semi-analytical method for solving the vibration equation of the non-uniform beam with added masses and elastic supports based is able to be made. In the modal subspace of the uniform beam with the elastic supports, the variable coefficient differential equation that describes the dynamic behavior of the non-uniform beam is converted to nonlinear algebraic equations. Extending the application of the modal perturbation method is suitable for solving the vibration equation of the simply supported and continuous non-uniform beam with its arbitrary added masses and elastic supports. The examples, that are analyzed, demonstrate the high precision and fast convergence speed of the method. Further study of the timesaving method for the dynamic characteristics of symmetrical beam and the symmetry of mode shape should be developed. Eventually, the effects of elastic supports and added masses on dynamic characteristics of the three-span non-uniform beam bridge are reported.