Numerical Simulation of Fluid Resonance in Narrow Gap of Two Bodies in Close Proximity

2014 ◽  
Author(s):  
Nima Moradi ◽  
Tongming Zhou ◽  
Liang Cheng
Keyword(s):  
Free Surface ◽  
Wave Height ◽  
Incident Wave ◽  
Flow Theory ◽  
Wave Generation ◽  
Numerical Results ◽  
Wave Frequency ◽  
Computational Domain ◽  
Narrow Gap ◽  
Wave Flume

The resonant behavior of the fluid trapped in the narrow gap between a floating LNG and an LNG carrier in a side-by-side offloading operation is investigated in this study employing a numerical wave flume. The wave flume is based on the finite volume solution of the Navier-Stokes equations to account for the viscous dissipation. The waveFoam toolbox, a modified version of the standard OpenFOAM multiphase flow solver interFoam developed by Jacobson et al (2011) has been used for the purpose of wave generation and relaxation inside the computational domain. This method has a quite high efficiency as it takes advantage of the potential flow theory for wave generation purpose and the viscous flow theory for inside the wave tank, respectively. The volume of fluid (VOF) method first introduced by Hirt and Nichols (1981) is used to capture the free surface oscillations at the air and water interface. Water waves are generated at a reasonable distance from the inlet boundary and two rectangular relaxation zones at the inlet and outlet boundaries of the domain have been implemented to suppress wave reflection at the outer boundaries as well as waves reflected internally in the computational domain. The influence of incident wave frequency on resonance wave height and frequency is examined. Numerical results of free surface evolution at different incident wave frequency seem to agree well with the experimental results of Saitoh et al (2006) and numerical results of Lu et al (2008). In order to justify the effect of bilge keels on flow separation at the bottom corner of the ship, four different corner configurations have been investigated and compared to the base sharp edged case. It is observed that the magnitude of the free surface elevation at the resonance frequency increases significantly by about 10 times the incoming wave height while the peak of resonant frequency curves shifts to higher frequencies in the higher curvature modes compared with the base case.

Calculation of Wave Height Dependent Force RAO’s on Submerged Bodies in Close Proximity to the Free Surface

2013 ◽  
Author(s):  
Ivan van Winsen ◽  
Job S. Bokhorst ◽  
René H. M. Huijsmans
Keyword(s):  
Free Surface ◽  
Wave Height ◽  
High Water ◽  
Wave Frequency ◽  
Parameter Study ◽  
Submerged Body ◽  
Close Proximity ◽  
Submerged Cylinder ◽  
Water Elevations ◽  
Water Elevation

Diffraction calculations overpredict motion RAO’s and force RAO’s in cases where a small layer of water is present on top of a submerged body. This was observed after conducting model tests on a free floating SSCV Thialf and a captive submerged cylinder. A parameter study is done to get a better understanding of why diffraction calculations overpredict the forces in heave direction. From this study it was observed that unrealistically high water elevations existed on top of the cylinder causing the heave forces to be overestimated. A damping lid is therefore implemented to decrease this water elevation. On top of that, a new method is developed to be able to capture the dependency of the force RAO on the wave height. This method uses the instantaneous submergence height (the height of water on top of the submerged body) to determine the time averaged force RAO for a given wave height and wave frequency.

Modeling the sloshing problem in a rectangular tank with submerged incomplete baffles

2016 ◽  
Vol 26 (3/4) ◽  
pp. 722-744 ◽  
Author(s):  
Marcela A. Cruchaga ◽  
Carlos Ferrada ◽  
Nicolás Márquez ◽  
Sebastián Osses ◽  
Mario Storti ◽  
...  
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Wave Height ◽  
Numerical Study ◽  
Free Surface Flows ◽  
Numerical Results ◽  
Surface Evolution ◽  
Content Type ◽  
Near Resonance ◽  
Wave Heights

Purpose – The present work is an experimental and numerical study of a sloshing problem including baffle effects. The purpose of this paper is to assess the numerical behavior of a Lagrangian technique to track free surface flows by comparison with experiments, to report experimental data for sloshing at different conditions and to evaluate the effectiveness of baffles in limiting the wave height and the wave propagation. Design/methodology/approach – Finite element simulations performed with a fixed mesh technique able to describe the free surface evolution are contrasted with experimental data. The experiments consist of an acrylic tank of rectangular section designed to attach baffles of different sizes at different distance from the bottom. The tank is filled with water and mounted on a shake table able to move under controlled horizontal motion. The free surface evolution is measured with ultrasonic sensors. The numerical results computed for different sloshing conditions are compared with the experimental data. Findings – The reported numerical results are in general in good agreement with the experiments. In particular, wave heights and frequencies response satisfactorily compared with the experimental data for the several cases analyzed during steady state forced sloshing and free sloshing. The effectiveness of the baffles increases near resonance conditions. From the set of experiments studied, the major reduction of the wave height was obtained when larger baffles were positioned closer to the water level at rest. Practical implications – Model validation: evaluation of the effectiveness of non-massive immersed baffles during sloshing. Originality/value – The value of the present work encompass the numerical and experimental study of the effect of immersed baffles during sloshing under different imposed conditions and the comparison of numerical results with the experimental data. Also, the results shown in the present work are a contribution to the understanding of the role in the analysis of the proposed problem of some specific aspects of the geometry and the imposed motion.

Effect of Free Surface Nonlinear and Fluid Viscosity on Fluid Resonance in the Narrow Gap

2017 ◽  
Author(s):  
Sheng-chao Jiang ◽  
Li Zou ◽  
Tie-zhi Sun ◽  
Chang-feng Liu
Keyword(s):  
Free Surface ◽  
Energy Dissipation ◽  
Resonant Frequency ◽  
Incident Wave ◽  
Wave Amplitude ◽  
Relative Energy ◽  
Dominant Factor ◽  
Fluid Viscosity ◽  
Narrow Gap ◽  
Resonant Amplitude

Numerical simulations are carried out for gap resonance problem between two side-by-side non-identical boxes. The linear potential model over-predicts the resonant amplitude in the narrow gap because it not only neglects the energy dissipation due to vortical motion, but also neglect the nonlinearity due to free surface. More relative energy are reflected with the increase of incident wave amplitude, leading to the decrease of relative resonant amplitude and relative energy dissipation in the narrow gap at resonant frequency. When the incident wave frequency is outside a little band to resonant frequency, relative energy dissipation becomes the dominant factor for the decrease of relative wave amplitude in the narrow gap with the increase of incident wave amplitudes. In a word, both the free surface nonlinearity and fluid viscosity play the important, but different, roles on wave resonances in the narrow gap.

Performance Analysis of a Semicircular Free Surface Ocean Structure under the Different Water Depths

2011 ◽  
Vol 90-93 ◽  
pp. 2782-2789
Author(s):  
Gang Jun Zhai ◽  
Zhe Ma ◽  
Hee Min Teh ◽  
Vengatesan Venugopal
Keyword(s):  
Free Surface ◽  
Wave Height ◽  
Incident Wave ◽  
Wave Attenuation ◽  
Hydrodynamic Characteristics ◽  
Irregular Wave ◽  
Surface Ocean ◽  
Semicircular Breakwater ◽  
Water Depths ◽  
Structure Width

The increasing importance of the sustainability challenge in o engineering has led to the development of free surface ocean structure of various configurations. In this study, the hydrodynamic characteristics of a perforated free surface, semicircular breakwater (SCB) are investigated for irregular wave conditions under the different water depths. The performance of the breakwaters was evaluated in the form of coefficients of transmission (CT), reflection (CR) and energy dissipation (CL). The measured wave modification in front of the structure and in the structure’s chamber were quantified and presented in the form of a ratio relative to the incident wave height, respectively, which are then presented as a function of the relative immersion depth (D/d) and the relative structure width (B/Lp), where D = the depth of immersion, d = the water depth, B = the structure width and Lp = the wavelength corresponding to the peak wave period. The measured wave modification in front of the structure and in the breakwater’s chamber were quantified and presented in the form of a ratio relative to the incident wave height, respectively. It is found that the wave attenuation ability of the SCB model improves with the increase of D/d and B/Lp. The SCB performs better as an energy dissipater than as a wave reflector.

Computational Fluid Dynamics Simulations of Regular and Irregular Waves Past a Horizontal Semi-Submerged Cylinder

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Shengnan Liu ◽  
Muk Chen Ong ◽  
Charlotte Obhrai ◽  
Sopheak Seng
Keyword(s):  
Free Surface ◽  
Numerical Simulations ◽  
Wave Height ◽  
Stokes Equations ◽  
Wave Force ◽  
Numerical Results ◽  
Irregular Waves ◽  
Wave Forces ◽  
Regular Waves ◽  
Peak Period

Two-dimensional (2D) numerical simulations have been performed to investigate both regular and irregular waves past a fixed horizontally semisubmerged circular cylinder. The 2D simulations are carried out by solving Navier–Stokes equations discretized by finite volume method. Volume of fluid (VOF) method is employed to capture the free surface in the numerical wave tank (NWT). Validation studies have been performed by comparing the numerical results of free surface waves past the cylinder with the published experimental and numerical data. The present numerical results are in good agreement with both the experimental and the other numerical results in terms of hydrodynamic forces and free surface elevation. Subsequently, the effects of the wave height and the wavelength on wave–structure interaction are investigated by conducting numerical simulations on the regular and the irregular waves past a semisubmerged cylinder at different wave heights and the wavelengths. The averaged and maximum vertical wave forces on the cylinder increase with the increasing wave height. The numerical results for the irregular waves are compared with those induced by the regular waves in terms of the maximum and averaged vertical wave forces. When the significant wave height and the spectral peak period of the irregular waves are equal to the wave height and the wave period of the regular waves, the maximum vertical wave force induced by the irregular waves is larger than that induced by the regular waves, meanwhile, the average vertical wave forces have the contrary relationship.

Numerical Simulations of Tsunami Wave Generation by Submarine and Aerial Landslides Using RANS and SPH Models

2009 ◽  
Author(s):  
Kaushik Das ◽  
Ron Janetzke ◽  
Debashis Basu ◽  
Steve Green ◽  
John Stamatakos
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Numerical Simulations ◽  
Tsunami Wave ◽  
Wave Generation ◽  
Numerical Results ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Tsunami Waves ◽  
Time Histories

Tsunami wave generation by submarine and aerial landslides is examined in this paper. Two different two-dimensional numerical methods have been used to simulate the time histories of fluid motion, free surface deformation, shoreline movement, and wave runup from tsunami waves generated by aerial and submarine landslides. The first approach is based on the Navier-Stokes equation and the volume of fluid (VOF) method: the Reynolds Averaged Navier-Stokes (RANS)-based turbulence model simulates turbulence, and the VOF method tracks the free surface locations. The second method uses Smoothed Particle Hydrodynamics (SPH)—a numerical model based on a fully Lagrangian approach. In the current work, two-dimensional numerical simulations are carried out for a freely falling wedge representing the landslide and subsequent wave generations. Numerical simulations for the landslide-driven tsunami waves have been performed with different values of landslide material densities. Numerical results obtained from both approaches are compared with experimental data. Simulated results for both aerial and submerged landslides show the complex flow patterns in terms of the velocity field, shoreline evolution, and free-surface profiles. Flows are found to be strongly transient, rotational, and turbulent. Predicted numerical results for time histories of free-surface fluctuations and the runup/rundown at various locations are in good agreement with the available experimental data. The similarity and discrepancy between the solutions obtained by the two approaches are explored and discussed.

Numerical Simulation of Irregular Wave Forces on a Horizontal Cylinder

2016 ◽  
Author(s):  
Ankit Aggarwal ◽  
Mayilvahanan Alagan Chella ◽  
Arun Kamath ◽  
Hans Bihs ◽  
Øivind Asgeir Arnsten
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Numerical Model ◽  
Circular Cylinder ◽  
Wave Generation ◽  
Numerical Results ◽  
Irregular Waves ◽  
Wave Forces ◽  
Ghost Cell ◽  
Irregular Wave

In the present study, the irregular wave forces on a fully submerged circular cylinder are investigated using the open-source computational fluid dynamics (CFD) model REEF3D. A complete three dimensional representation of the ocean waves requires the consideration of the sea surface as an irregular wave train with the random characteristics. The numerical model uses the incompressible Reynolds-averaged Navier-Stokes (RANS) equations together with the continuity equation to solve the fluid flow problem. Turbulence modeling is carried out using the two equation k-ω model. Spatial discretization is done using an uniform Cartesian grid. The level set method is used for computing the free surface. For time discretization, third-order total variation diminishing (TVD) Runge Kutta scheme is used. Ghost cell boundary method is used for implementing the complex geometries in the numerical model. MPI is used for the exchange of the value of a ghost cell. Relaxation method is used for the wave generation. The numerical model is validated for the irregular waves for a wave tank without any structure. Further, the numerical model is validated by comparing the numerical results with the experimental data for a fully submerged circular cylinder under regular waves and irregular waves. The numerical results are in a good agreement with the experimental data for the regular and irregular wave forces. The JONSWAP spectrum is used for the wave generation. The free surface features and kinematics around the cylinder is also presented and discussed.

scholarly journals Performance of rigidly interconnected multiple floating pontoons

1970 ◽  
Vol 1 (1) ◽  
pp. 3-17 ◽  
Author(s):  
Shafiuddin Amer Syed ◽  
JS Mani
Keyword(s):  
Free Surface ◽  
Wave Height ◽  
Incident Wave ◽  
Inviscid Fluid ◽  
Relative Width ◽  
Theoretical Formulation ◽  
Direction Parallel ◽  
Floating Breakwater ◽  
Floating System ◽  
Free Surface Oscillations

A floating system consisting of three pontoons equispaced, rigidly interconnected and taut moored to act as a single unit is analyzed. The theoretical formulation of the problem is based on the assumptions of irrotational fluid flow, an inviscid fluid, and small incident waves. The breakwater is assumed to be long and uniform in the direction parallel to the incident wave crests. The diffracted and the scattered potentials are obtained from the solution of boundary value problem using Green's identity method. The potentials and hence the free surface oscillations in between the spacing are also determined. The results of parametric study of varying space and drafts of the pontoons have been presented as a function of relative width of breakwater (Ratio of width of the breakwater to the wavelength) .It is evident from the results that the spaces between the pontoons have a definite effect on transmission and reflection characteristics of a floating breakwater system. As the draft of the floating breakwater increases the bandwidth of incident wave frequencies for which Kt (Ratio of transmitted wave height to incident wave height) is less than 0.2, also increases, thus ensuring a wider spectrum of operation. In addition the paper discusses on forces, oscillations in the interspaces and reflection coefficient. Keywords: breakwater, pontoon, taut moored, free surface oscillations. doi: 10.3329/jname.v1i1.2031 Journal of Naval Architecture and Marine Engineering 1(2004) 3-17

Prediction of Ship Motions Via a Three-Dimensional Time-Domain Method Following a Quad-Tree Adaptive Mesh Technique

2020 ◽  
Vol 27 (1) ◽  
pp. 29-38
Author(s):  
Teng Zhang ◽  
Junsheng Ren ◽  
Lu Liu
Keyword(s):  
Free Surface ◽  
Incident Wave ◽  
Time Domain ◽  
Three Dimensional ◽  
Adaptive Mesh ◽  
Wave Profile ◽  
Time Domain Method ◽  
Ship Motions ◽  
Quad Tree ◽  
Mesh Technique

AbstractA three-dimensional (3D) time-domain method is developed to predict ship motions in waves. To evaluate the Froude-Krylov (F-K) forces and hydrostatic forces under the instantaneous incident wave profile, an adaptive mesh technique based on a quad-tree subdivision is adopted to generate instantaneous wet meshes for ship. For quadrilateral panels under both mean free surface and instantaneous incident wave profiles, Froude-Krylov forces and hydrostatic forces are computed by analytical exact pressure integration expressions, allowing for considerably coarse meshes without loss of accuracy. And for quadrilateral panels interacting with the wave profile, F-K and hydrostatic forces are evaluated following a quad-tree subdivision. The transient free surface Green function (TFSGF) is essential to evaluate radiation and diffraction forces based on linear theory. To reduce the numerical error due to unclear partition, a precise integration method is applied to solve the TFSGF in the partition computation time domain. Computations are carried out for a Wigley hull form and S175 container ship, and the results show good agreement with both experimental results and published results.

An implicit scheme for simulation of free surface non-Newtonian fluid flows on dynamically adapted grids

2021 ◽  
Vol 36 (3) ◽  
pp. 165-176
Author(s):  
Kirill Nikitin ◽  
Yuri Vassilevski ◽  
Ruslan Yanbarisov
Keyword(s):  
Free Surface ◽  
Numerical Model ◽  
Newtonian Fluid ◽  
Viscoelastic Fluid ◽  
Fluid Flows ◽  
Numerical Results ◽  
Implicit Scheme ◽  
New Approach

Abstract This work presents a new approach to modelling of free surface non-Newtonian (viscoplastic or viscoelastic) fluid flows on dynamically adapted octree grids. The numerical model is based on the implicit formulation and the staggered location of governing variables. We verify our model by comparing simulations with experimental and numerical results known from the literature.

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