• Nuclear Engineering and Technology
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• 제41권3호
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• pp.355-364
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• 2009

Circular plates with holes are extensively used in mechanical components. The existence of a hole in a circular plate results in a significant change in the natural frequencies and mode shapes of the structure. Especially if the hole is located eccentrically, the vibration behavior of these structures is expected to deviate significantly from that of a plate with a concentric hole. In addition, if the plate is in contact with or submerged in fluid, the situation is more complex. Therefore, in this study, an analytical method to determine the modal characteristics of a plate submerged in fluid is developed based on the finite Fourier-Bessel series expansion and Rayleigh-Ritz method and is verified by the finite element analysis using a commercial program. Also, the relationship between parameter variations and vibration modes is investigated. These results can be used as guidance for the modal analysis and damage detection of a circular plate with a hole.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 춘계 학술대회논문집
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• pp.219-222
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• 2005

A compressible two-fluid two-phase flow computation model using the stiffened-gas equation of state is formulated. Since the conservation equation system is of mixed type, it gives complex eigenvalues. The sonic speeds obtained from the individual single phase have been simply used in the literature for the fastest wave speeds necessary in the HLL scheme. This method has worked fine but proved to be quite diffusive according to our test. To improve the accuracy, we here propose to utilize the analytic eigenvalues evaluated from an approximate Jacobian matrix lot the fastest wave speeds. The interfacial transfer terms were dropped in constituting the Jacobian matrix for this purpose. The present scheme proved efficient, robust and accurate in comparison with other existing methods. We solved the cavitating flow problem using the present scheme. The result shows more detailed wave structure in the cavitating process caused by the strong expansion waves.

• Tribology and Lubricants
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• 제27권1호
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• pp.34-39
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• 2011

In this study, finite element analysis of particle-surface collision using 2-dimensional elements was performed to observe the effects of abrasive size and impact angle. The result of the simulation on the change in abrasive size revealed that larger abrasive particle induced larger contact stress due to force transfer through slurry fluid as the particle moved and pushed the fluid. This observation brought an important finding that the slurry fluid could make the workpiece surface soften and then change the mechanical properties of the surface layer such as elastic modulus and yield strength. As for the impact angle, it was found that the contact stress increased with the angle of impact and jumped up at a specific angle. Such result would be attributed to the complex effects of the impact velocity and angle.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.813-816
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• 2006

Complex pressure pulsation phenomenon in fuel rails is generated by rapid opening and closing of injectors and it commonly causes undesirable noise. In this study, fluid-structure interaction analyses based on CFD and FEM have been conducted to examine the pulsation damping characteristics for different shapes of fuel rails. It is shown from the present results that the fuel rail with a high aspect ratio rectangular cross section seems to be best in order to reduce the pressure pulsations. It also agrees well with the previous experimental test by Mizuno, K. et al.

• Structural Engineering and Mechanics
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• 제16권4호
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• pp.423-440
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• 2003

Arbitrary Lagrangian Eulerian finite element methods gain interest for the capability to control mesh geometry independently from material geometry, the ALE methods are used to create a new undistorted mesh for the fluid domain. In this paper we use the ALE technique to solve fuel slosh problem. Fuel slosh is an important design consideration not only for the fuel tank, but also for the structure supporting the fuel tank. "Fuel slosh" can be generated by many ways: abrupt changes in acceleration (braking), as well as abrupt changes in direction (highway exit-ramp). Repetitive motion can also be involved if a "sloshing resonance" is generated. These sloshing events can in turn affect the overall performance of the parent structure. A finite element analysis method has been developed to analyze this complex event. A new ALE formulation for the fluid mesh has been developed to keep the fluid mesh integrity during the motion of the tank. This paper explains the analysis capabilities on a technical level. Following the explanation, the analysis capabilities are validated against theoretical using potential flow for calculating fuel slosh frequency.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.784-788
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• 2004

A visualization study of shock formation of the supersonic jet nozzle using a Shadowgraph Method (SM) was carried out to investigate the effect of the longitudinal variation of coaxial pipe end tip position inside the supersonic nozzle. The experiment was performed for the Mach number range from 1.1 to 1.2 at nozzle exit. The well known shock cell structure was shown with the pipe end located deep inside the nozzle for the studied Mach number. With the pipe end approaches nozzle exit, it was found that the shock cell structure disappeared and turned into complex formation. In order to understand the mechanism of the shock structural change, computational simulation was carried out using the Navier-Stokes solver, FLUENT. Topological sketch was added with an aid of the visualization and the numerical simulation.

• Bulletin of the Korean Chemical Society
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• 제18권9호
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• pp.965-972
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• 1997

An approximate molecular theory of classical fluids based on the nonrandom lattice statistical-mechanical theory is presented. To obtain configurational Helmholtz free energy and equation of state (EOS), the lattice-hole theory of the Guggenheim combinatorics is approximated by introducing the nonrandom two-fluid theory. The approximate nature in the derivation makes the model possible to unify the classical lattice-hole theory and to describe correctly the configurational properties of real fluids including macromolecules. The theory requires only two molecular parameters for a pure fluid. Results obtained to date have demonstrated that the model correlates quantitatively the first- and second-order thermodynamic properties of real fluids. The basic simplicity of the model can readily be generalized to multicomponent systems. The model is especially relevant to (multi) phase equilibria of systems containing molecularly complex species.

• 한국산업융합학회 논문집
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• 제21권5호
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• pp.191-195
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• 2018

By using an ANSYS product suite (CFX, Ansys Multiphysics), which is a powerful tool for multiphysics analysis of complicated physical phenomena, we performed a structural stress analysis based on fluid flow and heat transfer phenomena within a quick connect/disconnect (QC/DC) bellows system. Considering the extremely low temperatures in the QC/DC environment, an approach to the problem based on complex multi-physics phenomena, where different phenomena interact with each other, is crucial. Therefore, we use a numerical analysis technique where fluid-thermal-structural interactions are combined. In conclusion, when low temperature fluids flow inside bellows, the expected service life is conspicuously reduced due to the thermal stress caused by heat transfer. Therefore, in future research, a structure with considerably reduced thermal stress by robust design optimization will be derived.

• Wind and Structures
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• 제29권1호
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• pp.55-64
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• 2019

The effect of vortex impingement on the fluid dynamics around a cylinder submerged in the wake of another of different diameters is numerically investigated at a Reynolds number Re = 200. While the diameter (D) of the downstream cylinder is fixed, impinging vortices are produced from the upstream cylinder diameter (d) varied as d/D = 0.24, 0.4, 0.6, 0.8 and 1.0, with a spacing ratio L=5.5d, where L is the distance between the center of the upstream cylinder to the front stagnation point of the downstream cylinder. Two-dimensional simulations are carried out using the finite volume method. Fluid forces acting on the two cylinders are correlated with impinging vortices, vortex shedding, and wake structure. Different facets of wake formation, wake structure, and flow separation and their connections to fluid forces are discussed.

• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3390-3397
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• 2022

Among the different techniques available, nuclear methods, including gamma-gamma logging tools, are of special importance. Though the real environment which surrounds the drilled borehole is a complex fractured medium which the fluid can flow through the porosities, simulation studies generally use the traditional model of a homogeneous mixture of formation and the liquid. Considering a previously published study, which shows that modeling of fluid flow in fractured reservoirs and simulating the formation as an inhomogeneous fractured medium leads to different results compared with those of homogeneous mixture, here we study the effect of the presence of drilling fluid (mudcake) on the response of the detectors in both the models. To study this effect, a typical gamma-gamma logging tool was modeled by using the MCNPX Monte Carlo code. The results show that the responses of the detectors in the mixture model in the presence of various thicknesses of mudcake are sensitive to the density of the formation material. However, this effect is not notable in the inhomogeneous fractured medium. These results emphasize the importance of the model employed for simulation of the medium in gamma-gamma well-logging.