• 대한수학회보
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• 제53권3호
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• pp.843-852
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• 2016

A vortex sheet is susceptible to the Kelvin-Helmhotz instability, which leads to a singularity at finite time. The vortex blob model provided a regularization for the motion of vortex sheets in an inviscid fluid. In this paper, we consider the blob model for viscous vortex sheets and present a linear stability analysis for regularized sheets. We show that the diffusing viscous vortex sheet is unstable to small perturbations, regardless of the regularization, but the viscous sheet in the sharp limit becomes stable, when the regularization is applied. Both the regularization parameter and viscosity damp the growth rate of the sharp viscous vortex sheet for large wavenumbers, but the regularization parameter gives more significant effects than viscosity.

• Coupled systems mechanics
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• 제12권1호
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• pp.21-40
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• 2023

In thisstudy, the vibration problem ofthermo elastic carbon nanotubes conveying pulsating viscous nano fluid subjected to a longitudinal magnetic field is investigated via Euler-Bernoulli beam model. The controlling partial differential equation of motion is arrived by adopting Eringen's non local theory. The instability domain and pulsation frequency of the CNT is obtained through the Galerkin's method. The numerical evaluation of thisstudy is devised by Haar wavelet method (HWM). Then, the proposed model is validated by analyzing the critical buckling load computed in presentstudy with the literature. Finally, the numerical calculation ofsystem parameters are shown as dispersion graphs and tables over non local parameter, magnetic flux, temperature difference, Knudsen number and viscous parameter.

• 한국해양공학회지
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• 제14권2호
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• pp.112-116
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• 2000

To determine a preliminary hull form with a minimum viscous resistance this study considers the systematic variations of full form and calculations of the viscous resistance for varied hull forms. A preliminary hull form can be determined from a parametric study of viscous resistance.

• Ocean Systems Engineering
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• 제2권2호
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• pp.99-113
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• 2012

Steel Catenary Risers (SCR) are the simplest and often the most economic solution compared to other riser types such as flexible pipe, riser towers, top tensioned risers, etc. The top of a SCR is connected to the host platform riser porch. The other end of the SCR connects to flowlines from subsea wells. The riser touchdown point (TDP), which is the location along the riser where contact with the sea floor first occurs, exhibits complex behaviors and often results in compression and fatigue related issues. Heave dynamic responses of semisubmersibles in extreme and operating sea states are crucial for feasibility of SCR application. Recent full field measurement results of a deep draft semisubmersible in Hurricane Gustav displayed the considerable discrepancies in heave responses characteristics between the measured and the simulated results. The adequacy and accuracy of the simulated results from recognized commercial software should be examined. This finding raised the awareness of shortcomings of current commercial software and potential risk in mega investment loss and environmental pollutions due to SCR failures. One main objective of this paper is to attempt to assess the importance and necessity of accounting for viscous effects during design and analysis by employing indicator of viscous parameter. Since viscous effects increase with nearly third power of significant wave height, thus newly increased metocean criteria per API in central Gulf of Mexico (GoM) and even more severe environmental conditions in Western Australia (WA) call for fundamental enhancements of the existing analysis tools to ensure reliable and robust design. Furthermore, another aim of this paper is to address the impacts of metocean criteria and design philosophy on semisubmersible hull sizing in WA and GoM.

• 천문학논총
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• 제18권1호
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• pp.21-24
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• 2003

The problem of the collapse of a self gravitating disk is here considered. We show self-similar solutions for the above problem under a modified viscous parameter. Surface density depends on r$^m$ in the inner region, where m is -1.6. Therefore growing central mass goes on without mass inflow to the system.

• Korean Chemical Engineering Research
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• 제53권1호
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• pp.91-102
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• 2015

Analytical solutions for the forced convection heat transfer of viscoelastic fluids obeying the Giesekus model are obtained in a concentric annulus under laminar flow for both thermal and hydrodynamic fully developed conditions. Boundary conditions are assumed to be (a) constant fluxes at the walls and (b) constant temperature at the walls. Temperature profiles and Nusselt numbers are derived from dimensionless energy equation. Subsequently, effects of elasticity, mobility parameter and viscous dissipation are discussed. Results show that by increasing elasticity, Nusselt number increases. However, this trend is reversed for constant wall temperature when viscous dissipation is weak. By increasing viscous dissipation, the Nusselt number decreases for the constant flux and increases for the constant wall temperature. For the wall cooling case, when the viscous dissipation exceeds a critical value, the generated heat overcomes the heat which is removed at the walls, and fluid heats up longitudinally.

• 천문학논총
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• 제20권1호
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• pp.37-42
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• 2005

The problem for the collapse of isothermal and rotational self-gravitational viscous disk is considered. We derive self-similar solutions for the cases in the inner and outer regions of the self-gravitational viscous disk. We show that surface density depends on ${\sigma}_0/r$ in the outer region of the disk using a slow accretion approximation. The ratio of a modified viscous parameter in the outer region of the disk to that in the inner region is 0.042. We resorted to numerical solutions of governing equations of the self-gravitational disk to find out profiles of ${\sigma}$, u and ${\upsilon}$ in terms of x. Their profiles were rapidly changed around the innermost region of the self-gravitational disk. It indicates that a new object was formed in the most inner region of the disk.

• Earthquakes and Structures
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• 제24권3호
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• pp.165-181
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• 2023

The effectiveness of fluid viscous dampers (FVDs) on dynamic response mitigation of coupled two adjacent structures was investigated, considering soil-structure interaction (SSI) effects under earthquake excitation. A numerical procedure was employed to evaluate system response. The finite elements were used for the numerical treatment of the adjacent buildings and soil region. Viscous boundary conditions were used as special non-reflecting boundaries on the edges of finite soil region. According to the results, the FVDs were found to be very effective for dynamic response mitigation of the adjacent buildings, even if considering the soil medium. The results showed that the most affecting parameter on the system response was found to be soil type. It was also concluded that when adjacent structures coupled by FVDs, the maximum values of the roof displacements, the base shear forces, and the base bending moments could decrease up to around 50%. Changing in lateral stiffness of the one building has minor effects on the effectiveness of viscous dampers.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제20권4호
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• pp.309-332
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• 2016

Finite element method has been applied to solve the fundamental governing equations of natural convective, electrically conducting, incompressible fluid flow past an infinite vertical plate surrounded by porous medium in presence of thermal radiation, viscous dissipation, Soret and Dufour effects. In this research work, the results of coupled partial differential equations are found numerically by applying finite element technique. The sway of significant parameters such as Soret number, Dufour number, Grashof number for heat and mass transfer, Magnetic field parameter, Thermal radiation parameter, Permeability parameter on velocity, temperature and concentration evaluations in the boundary layer region are examined in detail and the results are shown in graphically. Furthermore, the effect of these parameters on local skin friction coefficient, local Nusselt number and Sherwood numbers is also investigated. A very good agreement is noticed between the present results and previous published works in some limiting cases.

• Smart Structures and Systems
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• 제21권5호
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• pp.669-675
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• 2018

Under braking forces of a freight train, there are great longitudinal structural responses of a large freight railway cable-stayed bridge. To alleviate such adverse reactions, viscous dampers are required, whose parametric selection is one of important and arduous researches. Based on the longitudinal dynamics vehicle model, responses of a cable-stayed bridge are investigated under various cases. It shows that there is a notable effect of initial braking speeds and locations of a freight train on the structural responses. Under the most unfavorable braking condition, the parameter sensitivity analyses of viscous dampers are systematically performed. Meanwhile, a mixing method called BPNN-NSGA-II, combining the Back Propagation neural network (BPNN) and Non-Dominated Sorting Genetic Algorithm With Elitist Strategy (NSGA-II), is employed to optimize parameters of viscous dampers. The result shows that: 1. the relationships between the parameters of viscous dampers and the key longitudinal responses of the bridge are high nonlinear, which are completely different from each other; 2. the longitudinal displacement of the bridge main girder significantly decreases by the optimized viscous dampers.