• Computers and Concrete
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• v.22 no.2
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• pp.161-166
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• 2018

This paper deals with the instability analysis of concrete pipes conveying viscous fluid-nanoparticle mixture. The fluid is mixed by $AL_2O_3$ nanoparticles where the effective material properties of fluid are obtained by mixture rule. The applied force by the internal fluid is calculated by Navier-Stokes equation. The structure is simulated by classical cylindrical shell theory and using energy method and Hamilton's principle, the motion equations are derived. Based on Navier method, the critical fluid velocity of the structure is calculated and the effects of different parameters such as fluid velocity, volume percent of nanoparticle in fluid and geometrical parameters of the pipe are considered. The results present that with increasing the volume percent of nanoparticle in fluid, the critical fluid velocity increase.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.6
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• pp.873-879
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• 2009

The steady breakers at an infant stage are investigated through the numerical simulation. The appearing condition and characteristics of the sub-breaking waves are reviewed by analysing bow waves. The instability analysis is possibly done through the relationship between the free-surface curvature and circumferential force, which is obtained from the momentum equations. Navier-Stokes equations are solved by a finite difference method where the body-fitted coordinate system, the wall function and the advanced mesh system are invoked. The numerical result shows that the gradient of M/$U_s$ is greatly influenced by the Froude number and the decrease of M/$U_s$ indicates that the flows are unstable. Additionally flows with plunging or spilling are simulated successfully, but the application of breakers to the severely broken wave still remains to be settled in the future.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.1000-1002
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• 2017

Here, the unsteady Navier-Stokes solver has been developed using implicit dual time stepping method. The implicit dual time stepping method introduced the pseudo time step for solving the new residual including the steady state residual and real time derivative. For the validation of code, Stokes 2nd problem, the laminar flow on the oscillating flat plate was selected and compare the calculating results with analytic solutions. The calculating velocity profile and skin friction has a good agreement with analytic solutions.

• Ocean Systems Engineering
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• v.9 no.3
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• pp.241-259
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• 2019

This paper presents a fully three-dimensional numerical approach for analyzing deepwater drilling riser-conductor system vortex-induced vibrations (VIV) including nonlinear soil-structure interactions (SSI). The drilling riser-conductor system is modeled as a tensioned beam with linearly distributed tension and is solved by a fully implicit discretization scheme. The fluid field around the riser-conductor system is obtained by Finite-Analytic Navier-Stokes (FANS) code, which numerically solves the unsteady Navier-Stokes equations. The SSI is considered by modeling the lateral soil resistance force according to nonlinear p-y curves. Overset grid method is adopted to mesh the fluid domain. A partitioned fluid-structure interaction (FSI) method is achieved by communication between the fluid solver and riser motion solver. A riser-conductor system VIV simulation without SSI is firstly presented and served as a benchmark case for the subsequent simulations. Two SSI models based on a nonlinear p-y curve are then applied to the VIV simulations. Also, the effects of two key soil properties on the VIV simulations of riser-conductor systems are studied.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.164-169
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• 2009

Study on swimming of microorganisms like, sperm motility, cilia beating, bacterial flagellar propulsion has found immense significance in the field of biological fluiddynamics. Because of the complexity involved, it is challenging for the researchers to model such problems. Immersed boundary method has proved its efficacy in the field of biological fluiddynamics, The present work aims at performing a numerical study on the microorganism locomotion using the immersed boundary method proposed by Peskin[1]. A two-dimensional model of the microorganism is modeled as thin elastic filament described as a sine wave. The neutrally buoyant organism undergoing deformations is immersed in a viscous and incompressible fluid. The fluid quantities are described using Eulerian coordinates and the immersed body is represented by Lagrangian coordinates. The Eulerian and Lagrangian variables are connected by the Dirac delta function. The Navier-Stokes equations governing the fluid flow are solved using the fractional step method on a staggered Cartesian grid system. The developed numerical code in FORTRAN will be validated by comparing the numerical results with the available results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.11
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• pp.1-8
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• 2006

A steady prediction method is presented to compute dynamic damping coefficients for axisymmetric projectiles. Viscous flow analysis is essential to the steady method using a zero-spin coning motion in the inertial coordinate frame. The present method is applied to compute the pitching moment and the pitch-damping moment coefficients for the Army-Navy Spinning Rocket. The results are in good agreement with the parabolized Navier-Stokes data, range data, and unsteady prediction data. Predictions for Secant-Ogive-Cylinder configurations are performed to investigate effects of afterbody geometries. To investigate the geometrical effect and flow physics, the longitudinal developments of the coefficients are examined in detail.

• Aerospace Engineering and Technology
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• v.3 no.2
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• pp.248-255
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• 2004

In this study, aerodynamic shape design of airfoils was performed by using RSM(response surface method) and two-dimensional Navier-Stokes solver. Numerical experiment points were determined by D-optimal method and quadratic response surfaces were constructed by using JMP. For the validations of design method, NACA 64621 airfoil was inversely designed to have aerodynamic characteristics of Bell airfoil. The design method was applied to the aerodynamic design of both smart UAV wing airfoil and low Reynolds rotor-blade airfoil for unmanned helicopter. The optimized airfoils showed improved performance with various constraint conditions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.3
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• pp.185-194
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• 1984

The finite analytic method is extended to solve the steady two dimensional Navier-Stokes equation of stream functions and vorticity in polar coordinate system. The method is applied to calculate laminar flows in a sector cavity where the motion is induced by the rotation of the outer wall. Numerical solutions are obtained in the range of Reynolds number 0 to 5000 and aspect ratios 0.50, 1.20, 1.60 and 1.92. The finite analytic method is verfied to be accurate and fast convergent at high Reynolds numbers. It is promising as a numerical method of viscous flows and heat transfer. Flows in sector cavities show different flow structures and formation of secondary vortex with aspect ratios and Reynolds numbers in comparison with rectangular cavities.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.4
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• pp.17-23
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• 2002

The present paper describes the optimum inverse design of 2-D linear cascade airfoil. The pressure coefficient of an airfoil surface is taken as the objective function, and non-orthogonal incompressible Navier-Stokes equation is applied to calculate the pressure coefficient. Both of steepest descent and conjugate gradient method have been used to make the objective function go to zero. The 1st order finite differential method is applied to the searching direction and the golden section method is used to compute the searching distance. As a result of the present work, a good convergence to the target airfoil has been obtained.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.1
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• pp.63-70
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• 1994

The three-dimensional incompressible clavier-Stokes equations are solved to simulate the flow field around a Wigley model with free-surface. The IAF(Implicit Approximate Factorization) method is used to show a good success in reducing the computing time. The CPU time is almost an half of that if the IAF method were used. The present method adopts the local linearization and Euler implicit scheme without the pressure-gradient terms for the artificial viscosity. Calculations are carried out at the Reynolds number of $10^6$ and the Froude numbers are 0.25, 0.289 and 0.316. For the approximations of turbulence, the Baldwin-Lomax model is used. The resulting free-surface wave configurations and the velocity vectors are compared with those by the explicit method and experiments.