CFD Simulations of Spilling Breaking Waves and Steep Waves Past a Monopile Structure at Different KC Numbers

2018 ◽  
Author(s):  
Shengnan Liu ◽  
Muk Chen Ong ◽  
Charlotte Obhrai
Keyword(s):  
Breaking Waves ◽  
Numerical Results ◽  
Navier Stokes ◽  
Wave Forces ◽  
Time Step ◽  
Two Phase ◽  
Secondary Load ◽  
Turbulence Effects ◽  
Sst Turbulence Model ◽  
Steep Waves

A 3D numerical two-phase flow model based on solving Unsteady Reynolds-averaged Navier-Stokes (URANS) equations has been used to simulate spilling breaking waves and steep waves past a monopile structure at a 1:10 slope. The volume of fluid (VOF) method is employed to capture the free surface and the k–ω Shear-Stress Transport (k–ω SST) turbulence model is used to simulate the turbulence effects. Mesh and time-step refinement studies have been conducted. The numerical results of wave forces on the structure are compared with the experimental data from Irschik et al. (2004) to validate the numerical model, and the numerical results are in good agreement with the measured data. The wave forces on the structure at different KC numbers are discussed in terms of the generation of the slamming force. The secondary load cycles are observed after the wave front past the structure. The pressure and velocity distribution, as well as the characteristics of the vortices around the structure at four important instants, are studied.

Numerical Simulations of Breaking Waves and Steep Waves Past a Vertical Cylinder at Different Keulegan–Carpenter Numbers

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Shengnan Liu ◽  
Muk Chen Ong ◽  
Charlotte Obhrai
Keyword(s):  
Dynamic Pressure ◽  
Vertical Cylinder ◽  
Breaking Waves ◽  
Numerical Results ◽  
Wave Forces ◽  
Breaking Wave ◽  
Wave Loads ◽  
Time Step ◽  
Two Phase ◽  
Steep Waves

A three-dimensional (3D) numerical two-phase flow model based on solving unsteady Reynolds-averaged Navier–Stokes (URANS) equations has been used to simulate breaking waves and steep waves past a vertical cylinder on a 1:10 slope. The volume of fluid (VOF) method is employed to capture the free surface and the k–ω shear–stress transport (k–ω SST) turbulence model is used to simulate the turbulence effects. Mesh and time-step refinement studies have been conducted. The numerical results of wave forces on the structure are compared with the experimental data (Irschik et al., 2004, “Breaking Wave Loads on a Slender Pile in Shallow Water,” Coastal Engineering, Vol. 4, World Scientific, Singapore, pp. 568–581) to validate the numerical model, and the numerical results are in good agreement with the measured data. The wave forces on the structure at different Keulegan–Carpenter (KC) numbers are discussed in terms of the slamming force. The secondary load cycles are observed after the wave front past the structure. The dynamic pressure and velocity distribution, as well as the characteristics of the vortices around the structure at four important time instants, are studied.

Fully Lagrangian Modeling of Two-Phase Impulse Microjets

2013 ◽  
Author(s):  
Natalia Lebedeva ◽  
Alexander Osiptsov ◽  
Sergei Sazhin
Keyword(s):  
Carrier Phase ◽  
Stokes Equations ◽  
Order System ◽  
Navier Stokes ◽  
Time Step ◽  
Particle Trajectories ◽  
Two Phase ◽  
Novel Approach ◽  
Mesh Free ◽  
Lagrangian Modeling

A new fully Lagrangian approach to numerical simulation of 2D transient flows of viscous gas with inertial microparticles is proposed. The method is applicable to simulation of unsteady viscous flows with a dilute admixture of non-colliding particles which do not affect the carrier phase. The novel approach is based on a modification and combination of the full Lagrangian method for the dispersed phase, proposed by Osiptsov [1], and a Lagrangian mesh-free vortex-blob method for Navier-Stokes equations describing the carrier phase in the format suggested by Dynnikova [2]. In the combined numerical algorithm, both these approaches have been implemented and used at each time step. In the first stage, the vortex-blob approach is used to calculate the fields of velocity and spatial derivatives of the carrier-phase flow. In the second stage, using Osiptsov’s approach, particle velocities and number density are calculated along chosen particle trajectories. In this case, the problem of calculation of all parameters of both phases (including particle concentration) is reduced to the solution of a high-order system of ordinary differential equations, describing transient processes in both carrier and dispersed phases. The combined method is applied to simulate the development of vortex ring-like structures in an impulse two-phase microjet. This flow involves the formation of local zones of particle accumulation, regions of multiple intersections of particle trajectories, and multi-valued particle velocity and concentration fields. The proposed mesh-free approach enables one to reproduce with controlled accuracy these flow features without excessive computational costs.

scholarly journals Transport due to Transient Progressive Waves

2019 ◽  
Vol 49 (9) ◽  
pp. 2323-2336
Author(s):  
Juan M. Restrepo ◽  
Jorge M. Ramirez
Keyword(s):  
Breaking Waves ◽  
Stokes Drift ◽  
Lagrangian Model ◽  
Navier Stokes ◽  
Lagrangian Description ◽  
Transient Waves ◽  
Two Phase ◽  
Transient Transport ◽  
The Mean ◽  
Progressive Waves

AbstractMaking use of a Lagrangian description, we interpret the kinematics and analyze the mean transport due to numerically generated transient progressive waves, including breaking waves. The waves are packets and are generated with a boundary-forced, air–water, two-phase Navier–Stokes solver. These transient waves produce transient transport, which can sometimes be larger than what would be estimated using estimates developed for translationally invariant progressive waves. We identify the critical assumption that makes our standard notion of the steady Stokes drift inapplicable to the data and explain how and in what sense the transport due to transient waves can be larger than the steady counterpart. A comprehensive analysis of the data in the Lagrangian framework leads us to conclude that much of the transport can be understood using an irrotational approximation of the velocity, even though the simulations use Navier–Stokes fluid simulations with moderately high Reynolds numbers. Armed with this understanding, it is possible to formulate a simple Lagrangian model that captures the mean transport and variance of transport for a large range of wave amplitudes. For large-amplitude waves, the parcel paths in the neighborhood of the free surface exhibit increased dispersion and lingering transport due to the generation of vorticity. We examined the wave-breaking case. For this case, it is possible to characterize the transport very well, away from the wave boundary layer, and approximately using a simple model that captures the unresolved breaking dynamics via a stochastic parameterization.

scholarly journals Numerical Simulation of Breaking Wave Loading on Standing Circular Cylinders with Different Transverse Inclined Angles

2020 ◽  
Vol 10 (4) ◽  
pp. 1347
Author(s):  
Sen Qu ◽  
Shengnan Liu ◽  
Muk Chen Ong ◽  
Shuzheng Sun ◽  
Huilong Ren
Keyword(s):  
Experimental Data ◽  
Vertical Cylinder ◽  
Wave Force ◽  
High Order ◽  
Numerical Results ◽  
Circular Cylinders ◽  
Wave Forces ◽  
Breaking Wave ◽  
Time Step ◽  
Inclined Angle

The purpose of this paper is to numerically simulate the breaking wave past a standing cylinder with different transverse inclined angles. The numerical simulations are carried out by solving the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations with the k − ω S S T turbulence model. The air–water interface is captured using the Volume of Fluid (VOF) method. The convergence studies on the grid and time-step are performed by examining the total horizontal breaking wave forces on the vertical cylinder. The present numerical results have been validated with the published experimental data. A good agreement is obtained between the present numerical results and the experimental data in terms of the surface elevation and the horizontal breaking wave force. Moreover, the total horizontal breaking wave force is decomposed into low-order and high-order wave forces through Fast Fourier Transform (FFT). It is observed that the free surface elevations in front of the cylinder and the normalized high-order wave force have a minimum value when the transverse inclined angle of the cylinder is 45°. The secondary load causing the higher-harmonic ringing motion of structures is not observed when the cylinder is placed with the transverse inclined angles of 30° and 45°.

On the Occurrence of Strong Higher Harmonic Wave Forces and Induced Ringing Loads on Vertical Cylinders

2002 ◽  
Author(s):  
John Grue ◽  
Morten Huseby
Keyword(s):  
Harmonic Wave ◽  
Vertical Cylinder ◽  
Offshore Structures ◽  
Load Cycle ◽  
Wave Forces ◽  
Wave Elevation ◽  
Secondary Load ◽  
Steep Waves ◽  
Acceleration Of Gravity ◽  
Vertical Cylinders

Experimental observations of a secondary load cycle in the force acting on a vertical cylinder exposed to long and steep waves are discussed. A complementary discussion of the occurrence of ringing of models of offshore structures is given. The height of the secondary load cycle is typically up to about 0.1–0.15 times the peak to peak force on the cylinder. The load cycle is observed for a nondimensional wavenumber kR in the range 0.1–0.33 and for a Froude number Fr = ωζm/gD exceeding about 0.4. Pronounced ringing occurs for the same parameter range. (k the wavenumber, R the cylinder radius, ω the wave frequency, ζm the maximal wave elevation, g the acceleration of gravity, D = 2R.)

scholarly journals Numerical simulation of compressible cavitating two-phase flows with a pressure-based solver

2017 ◽  
Author(s):  
Marco Cristofaro ◽  
Wilfried Edelbauer ◽  
Manolis Gavaises ◽  
Phoevos Koukouvinis
Keyword(s):  
Stokes Equations ◽  
Navier Stokes ◽  
Test Case ◽  
Time Step ◽  
Two Phase ◽  
Navier Stokes Equations ◽  
Liquid Phases ◽  
Flow Features ◽  
Liquid Evaporation ◽  
Semi Empirical

This work intends to study the effect of compressibility on throttle flow simulations with a pressure–based solver.The simple micro throttle geometry allows easier access for obtaining experimental data compared to a real injector, but still maintaining the main flow features. For this reasons it represents a meaningful and well reported benchmark for validation of numerical methods developed for cavitating injector flows.An implicit pressure–based compressible solver is used on the filtered Navier–Stokes equations. Thus, no stability limitation is applied on the time step. A common pressure field is computed for all phases, but different velocity fields are solved for each phase, following the multi–fluid approach. The liquid evaporation rate is evaluated with a Rayleigh–Plesset equation based cavitation model and the Coherent Structure Model is adopted as closure for the sub–grid scales in the momentum equation.The aim of this study is to show the capabilities of the pressure–based solver to deal with both vapor and liquid phases considered compressible. A comparison between experimental results and compressible simulations is presented. Time–averaged vapor distribution and velocity profiles are reported and discussed.  The distribution of pressure maxima on the surface and the results from a semi–empirical erosion model are in good agreement with the erosion locations observed in the experiments. This test case aims to represent a benchmark for furtherapplication of the methodology to industrial relevant cases.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4629

scholarly journals VALIDATION OF A BUOYANCY-MODIFIED TURBULENCE MODEL BY NUMERICAL SIMULATIONS OF BREAKING WAVES OVER A FIXED BAR

2018 ◽  
pp. 71
Author(s):  
Brecht Devolder ◽  
Peter Troch ◽  
Pieter Rauwoens
Keyword(s):  
Numerical Simulations ◽  
Wave Breaking ◽  
Surf Zone ◽  
Breaking Waves ◽  
Navier Stokes ◽  
Two Phase ◽  
Numerical Wave Flume ◽  
Wave Flume ◽  
Nearshore Sediment Transport ◽  
Run Up

The surf zone dynamics are governed by important processes such as turbulence generation , nearshore sediment transport , wave run-up and wave overtopping at a coastal structure. During field observations , it is very challenging to measure and quantify wave breaking turbulence . Complementary to experimental laboratory studies in a more controlled environment , numerical simulations are highly suitable to understand and quantify surf zone processes more accurately. In this study, wave propagation and wave breaking over a fixed barred beach profile is investigated using a two­ phase Navier-Stokes flow solver. We show that accurate predictions of the turbulent two-phase flow field require special attention regarding turbulence modelling. The numerical wave flume is implemented in the open­ source OpenFOAM library. The computed results (surface elevations , velocity profiles and turbulence levels) are compared against experimental measurements in a wave flume (van der A et al., 2017) .

Numerical simulation of wave interaction with a pair of fixed large tandem cylinders subjected to regular non-breaking waves

2021 ◽  
pp. 1-34
Author(s):  
Mohammad Mohseni ◽  
Carlos Guedes Soares
Keyword(s):  
Circular Cross Section ◽  
Wave Interaction ◽  
Breaking Waves ◽  
Navier Stokes ◽  
Two Phase ◽  
Wave Amplification ◽  
Vof Model ◽  
Stokes Waves ◽  
Truncated Cylinders ◽  
Fifth Order

Abstract This paper presents the application of a two-phase Computational Fluid Dynamics (CFD) model to carry out a detailed investigation of nonlinear wave field surrounding a pair of columns placed in the tandem arrangement in the direction of wave propagation and corresponding harmonics. The numerical analysis is conducted using the Unsteady Reynolds-Averaged Navier-Stokes/VOF model based on the OpenFOAM framework combined with the olaFlow toolbox for wave generation and absorption. For the simulations, the truncated cylinders are assumed vertical and surface piercing with a circular cross-section subjected to regular, non-breaking fifth-order Stokes waves propagating with moderate steepness in deep water. Primarily, the numerical model is validated with experimental data for a single cylinder. Future, the given simulations are conducted for different centre-to-centre distances between the tandem large cylinders. The results show the evolution of a strong wave diffraction pattern and consequently, high wave amplification harmonics around cylinders are apparent.

Current generation by deep-water breaking waves

2016 ◽  
Vol 803 ◽  
pp. 275-291 ◽  
Author(s):  
N. E. Pizzo ◽  
Luc Deike ◽  
W. Kendall Melville
Keyword(s):  
Wave Field ◽  
Water Column ◽  
Deep Water ◽  
Stokes Equations ◽  
Laboratory Data ◽  
Breaking Waves ◽  
Navier Stokes ◽  
Mean Flow ◽  
Two Phase ◽  
Navier Stokes Equations

We examine the partitioning of the energy transferred to the water column by deep-water wave breaking; in this case between the turbulent and mean flow. It is found that more than 95 % of the energy lost by the wave field is dissipated in the first four wave periods after the breaking event. The remaining energy is in the coherent vortex generated by breaking. A scaling argument shows that the ratio between the energy in this breaking generated mean current and the total energy lost from the wave field to the water column due to breaking scales as $(hk)^{1/2}$, where $hk$ is the local slope at breaking. This model is examined using direct numerical simulations of breaking waves solving the full two-phase air–water Navier–Stokes equations, as well as the limited available laboratory data, and good agreement is found for strong breaking waves.

scholarly journals URANSE-Based Numerical Prediction for the Free Roll Decay of the DTMB Ship Model

2021 ◽  
Vol 9 (5) ◽  
pp. 452
Author(s):  
Adham Bekhit ◽  
Florin Popescu
Keyword(s):  
Experimental Data ◽  
Stokes Equations ◽  
Flow Characteristics ◽  
Roll Angle ◽  
Navier Stokes ◽  
Special Focus ◽  
Time Step ◽  
Two Phase ◽  
Ship Model ◽  
Richardson Extrapolation Method

In the present study, Computational Fluid Dynamics (CFD) is used to investigate the roll decay of the benchmark surface combatant DTMB-5512 ship model appended with bilge keels, sailing in calm water at different speeds (Fr = 0.0, 0.138, 0.2, 0.28 and 0.41) and with different initial roll angles. The numerical simulations are carried out using the viscous flow solver ISIS-CFD of the FINETM/Marine software provided by NUMECA. The solver uses the finite volume method to build the spatial discretization of the transport equation to solve the unsteady Reynolds-Averaged Navier–Stokes equations. Two-phase flow approach is applied to model the air–water interface, where the free surface is captured using the volume of fluid method. The closure to turbulence is achieved by making use of the blended Menter shear stress transport and the explicit algebraic Reynolds stress models. First, a systematic validation against the experimental data at medium speed and initial roll angle of 10° are performed; then, the effect of the initial roll angle and ship speed is later studied. Numerical errors and uncertainties are assessed using grid and time step convergence study based on Richardson Extrapolation method. A special focus on the flow in the vicinity of the bilge keels during the simulation is also investigated and presented in the form of velocity contours and vortical structure formations. The resemblance between the CFD results and experimental data for roll motion and flow characteristics are within a satisfactory congruence; however, some discrepancies are recorded for the over predicted roll amplitudes in the second and, sometimes, the third roll cycle, which appeared mostly in the cases with high initial roll angles.

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