• Title/Summary/Keyword: Volume of fluid method

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Dynamic characteristics and response analysis of accelerating underwater structures

  • Liu, Zhengxing;Williams, F.W.;Jemah, A.K.
    • Structural Engineering and Mechanics
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    • v.6 no.6
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    • pp.613-632
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    • 1998
  • A coupling system for a structure accelerating through a fluid is considered which is composed of the structure and the fluid in a finite surrounding volume. Based on the variational principle, the finite element equations of hydrodynamic pressure and structural elastic vibration are deduced. A numerical method is given for the dynamic character and response of the structure which takes the coupled fluid into account. The effect of axial inertial forces on the dynamic character and response of rapidly accelerating structures is also considered.

Prediction of the turning and zig-zag maneuvering performance of a surface combatant with URANS

  • Duman, Suleyman;Bal, Sakir
    • Ocean Systems Engineering
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    • v.7 no.4
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    • pp.435-460
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    • 2017
  • The main objective of this study is to investigate the turning and zig-zag maneuvering performance of the well-known naval surface combatant DTMB (David Taylor Model Basin) 5415 hull with URANS (Unsteady Reynolds-averaged Navier-Stokes) method. Numerical simulations of static drift tests have been performed by a commercial RANS solver based on a finite volume method (FVM) in an unsteady manner. The fluid flow is considered as 3-D, incompressible and fully turbulent. Hydrodynamic analyses have been carried out for a fixed Froude number 0.28. During the analyses, the free surface effects have been taken into account using VOF (Volume of Fluid) method and the hull is considered as fixed. First, the code has been validated with the available experimental data in literature. After validation, static drift, static rudder and drift and rudder tests have been simulated. The forces and moments acting on the hull have been computed with URANS approach. Numerical results have been applied to determine the hydrodynamic maneuvering coefficients, such as, velocity terms and rudder terms. The acceleration, angular velocity and cross-coupled terms have been taken from the available experimental data. A computer program has been developed to apply a fast maneuvering simulation technique. Abkowitz's non-linear mathematical model has been used to calculate the forces and moment acting on the hull during the maneuvering motion. Euler method on the other hand has been applied to solve the simultaneous differential equations. Turning and zig-zag maneuvering simulations have been carried out and the maneuvering characteristics have been determined and the numerical simulation results have been compared with the available data in literature. In addition, viscous effects have been investigated using Eulerian approach for several static drift cases.

Air Compressibility Effect in CFD-based Water Impact Analysis (CFD 기반 유체충격 해석에서 공기 압축성 효과)

  • Tran, Huu Phi;Ahn, Hyung-Taek
    • Journal of the Society of Naval Architects of Korea
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    • v.48 no.6
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    • pp.581-591
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    • 2011
  • This paper describes the air compressibility effect in the CFD simulation of water impact load prediction. In order to consider the air compressibility effect, two sets of governing equations are employed, namely the incompressible Navier-stokes equations and compressible Navier-Stokes equations that describe general compressible gas flow. In order to describe violent motion of free surface, volume-of-fluid method is utilized. The role of air compressibility is presented by the comparative study of water impact load obtained from two different air models, i.e. the compressible and incompressible air. For both cases, water is considered as incompressible media. Compressible air model shows oscillatory behavior of pressure on the solid surface that may attribute to the air-cushion effect. Incompressible air model showed no such oscillatory behavior in the pressure history. This study also showed that the CFD simulation can capture the formation of air pockets enclosed by water and solid surface, which may be the location where the air compressibility effect is dominant.

Dynamic stress, strain and deflection analysis of pipes conveying nanofluid buried in the soil medium considering damping effects subjected to earthquake load

  • Abadi, M. Heydari Nosrat;Darvishi, H. Hassanpour;Nouri, A.R. Zamani
    • Computers and Concrete
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    • v.24 no.5
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    • pp.445-452
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    • 2019
  • In this paper, dynamic stress, strain and deflection analysis of concrete pipes conveying nanoparticles-water under the seismic load are studied. The pipe is buried in the soil which is modeled by spring and damper elements. The Navier-Stokes equation is used for obtaining the force induced by the fluid and the mixture rule is utilized for considering the effect of nanoparticles. Based on refined two variables shear deformation theory of shells, the pipe is simulated and the equations of motion are derived based on energy method. The Galerkin and Newmark methods are utilized for calculating the dynamic stress, strain and deflection of the concrete pipe. The influences of internal fluid, nanoparticles volume percent, soil medium and damping of it as well as length to diameter ratio of the pipe are shown on the dynamic stress, strain and displacement of the pipe. The results show that with enhancing the nanoparticles volume percent, the dynamic stress, strain and deflection decrease.

Experimental study and numerical modeling of liquid sloshing damping in a cylindrical container with annular and sectorial baffles

  • Mohammadi, Mohammad Mahdi;Moosazadeh, Hamid
    • Advances in aircraft and spacecraft science
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    • v.9 no.4
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    • pp.349-366
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    • 2022
  • The ability of baffles in increasing the sloshing damping is investigated in this study by theoretical, numerical, and experimental methods. Baffles Installed as separators in containers, can change the dynamic properties of sloshing. The main purpose of this study is to investigate the effect of baffle placement.The main purpose of this study is to investigate the effect of placing baffles in order to provide appropriate frequencies and damping and to present a practical baffle arrangement in the design ofsloshing. In this regard, an experimental setup is designed to study the fluid sloshing behavior and damping properties in cylindrical tanks filled up to an arbitrary depth. A new combination of annular and sectorial baffles is employed to evaluate fluid sloshing in the tank. The results show that the proposed baffle arrangement has a desired effect on the damping and fluid sloshing frequencies and optimally satisfies the anticipated design requirements. In addition, the theoretical frequencies exceed empirical frequencies at the points far from baffles, while at the points close to baffles, the empirical ones are higher than theoretical ones. Also, at the depths near the bottom of container sloshing frequencies are not affected by sectorial baffles, although the theoretical curve predicts a reduction in the fundamental frequency of sloshing. Finally, the results of finite volume and finite element methods which compared with experimental data, indicated a good agreement between different approaches.

Finite Element Analysis of Transient Viscous Flow with Free Surface using Filling Pattern Technique (형상 충전 기법을 이용한 자유표면의 비정상 점성 유동장의 유한 요소 해석)

  • Kim, Ki-Don;Jeong, Jun-Ho;Yang, Dong-Yol
    • Proceedings of the KSME Conference
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    • 2001.11b
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    • pp.551-556
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    • 2001
  • The filling pattern technique based on the finite element method and Eulerian mesh advancement approach has been developed to analyze incompressible transient viscous flow with free surfaces. The governing equation for flow analysis is Navier-Stokes equation including inertia and gravity effects. The penalty and predictor-corrector methods are used effectively for finite element formulation. The flow front surface and the volume inflow rate are calculated using the filling pattern technique to select an adequate pattern among four filling patterns at each triangular control volume. Using the proposed numerical technique, the collapse of a dam has been analyzed to predict flow phenomenon of fluid and the predicted front positions versus time have been compared with the reported experimental result.

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Simulation of dynamic fracture and fluid-structure interaction in solid propellant rockets : Part 1 (theoretical aspects) (고체추진로켓 내부에서 발생하는 동적 파괴 현상과 유체-고체 상호작용의 시뮬레이션 - Part 1 (이론적 측면))

  • Hwang, Chan-Gyu
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.9 no.2
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    • pp.286-290
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    • 2008
  • This paper summarizes the components of an explicit aeroelastic solver developed especially for the simulation of dynamic fracture events occurring during the flight of solid propellant rockets. The numerical method combines an explicit Arbitrary Lagrangian Eulerian (ALE) version of the Cohesive Volumetric Finite Element (CVFE) scheme, used to simulate the spontaneous motion of one or more cracks propagating dynamically through a domain with regressing boundaries, and an explicit unstructured finite volume Euler code to follow the flow field during the failure event. A key feature of the algorithm is the ability to adaptively repair and expand the fluid mesh to handle the large geometrical changes associated with grain deformation and crack motion.

A Volume Grid Deformation Code for Computational fluid Dynamics of Moving Boundary Problems (이동경계문제의 전산유체역학을 위한 체적격자변형코드)

  • Ko, Jin-Hwan;Kim, Jee-Woong;Byun, Do-Young;Park, Soo-Hyung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.36 no.11
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    • pp.1049-1055
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    • 2008
  • Modern multidisciplinary computational fluid dynamics often incorporates moving boundaries, as would be required in the applications such as design optimization, aeroelasticity, or forced boundary motion. It is challenging to develop robust, efficient grid deformation algorithms when large displacement of the moving boundaries is required. In this paper, a volume grid deformation code is developed based on the finite macro-element and the transfinite Interpolation, and then interfaces to a structured multi-block Navier-Stokes in-house code. As demonstrated by an airfoil with pitching motion, the hysteresis loops of lift, drag and moment coefficients of the developed method are shown to be in good agreement with those of experimental data.

Performance of a hydrofoil operating close to a free surface over a range of angles of attack

  • Ni, Zao;Dhanak, Manhar;Su, Tsung-chow
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.13 no.1
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    • pp.1-11
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    • 2021
  • Performance of a NACA 634-021 hydrofoil in motion under and in close proximity of a free surface for a large range of angles of attack is studied. Lift and drag coefficients of the hydrofoil at different submergence depths are investigated both numerically and experimentally, for 0° ≤ AoA ≤ 30° at a Reynolds number of 105. The results of the numerical study are in good agreement with the experimental results. The agreement confirms the new finding that for a submerged hydrofoil operating at high angles of attack close to a free surface, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil results in mitigation of the flow separation characteristics on the suction side of the foil and delay in stall, and improvement in hydrofoil performance. In comparing with a baseline case, results suggest a 55% increase in maximum lift coefficient and 90% average improvement in performance for, based on the lift-to-drag ratio, but it is also observed significant decrease of lift-to-drag ratio at lower angles of attack. Flow details obtained from combined finite volume and volume of fluid numerical methods provide insight into the underlying enhancement mechanism, involving interaction between the hydrofoil and the free surface.

Cavitation Characteristics of a Pump-turbine Model by CFD Analysis

  • Singh, Patrick Mark;Chen, Chengcheng;Chen, Zhenmu;Choi, Young-Do
    • The KSFM Journal of Fluid Machinery
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    • v.18 no.4
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    • pp.49-55
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    • 2015
  • The pumped storage plant operates with quick change of the discharge as well as quick changes between pump mode and turbine mode. This study focuses on the cavitation analysis of a pump-turbine model because in turbo-machinery, cavitation can reduce the performance and shorten service life. The pump-turbine model system consists of 7 blades, 20 stay vanes (including tongue) and 20 guide vanes. This study adopts the Rayleigh-Plesset model as a cavitation model, which illustrates cavitation by using the air volume fraction method. The pump mode and turbine mode at the operating condition of partial loading, normal and excessive loading are analyzed to investigate the cavitation performance of the pump-turbine. It was observed that this pump-turbine design showed very good cavitation characteristics with no cavitation bubbles in all operating conditions. Overall value of air volume fraction of both mode at different operating condition are lower than 1, which confirms low possibility of cavitation occurrence at current situation.