scholarly journals An Analytical Approach for the Two-Dimensional Plunging Breaking Wave Impact on a Vertical Wall with Air Entrapment

Fluids ◽  
2020 ◽  
Vol 5 (2) ◽  
pp. 58
Author(s):  
Theodosis D. Tsaousis ◽  
Ioannis K. Chatjigeorgiou
Keyword(s):  
Free Surface ◽  
Velocity Potential ◽  
Mixed Boundary ◽  
Dimensional Space ◽  
Vertical Wall ◽  
Breaking Wave ◽  
Linear Potential ◽  
Two Dimensional ◽  
Wave Impact ◽  
Air Pocket

This study investigates an idealized formulation of the two-dimensional impact of a breaking wave on a vertical impermeable wall. An overturning-like wave is assumed, which is close to the concept of a plunging breaker. It is assumed that during the collision an air pocket is entrapped between the wave and the wall. The air pocket width is assumed to be negligible and the compression effects are omitted. The problem is considered in the two-dimensional space (2D) using linear potential theory along with the small-time approximation. We use a perturbation method to cope with the linearized free-surface kinematic and dynamic boundary conditions. We impose the complete mixed boundary value problem (bvp) and we solve for the leading order of the velocity potential. The problem derived involves dual trigonometrical series and is treated analytically. The main assumption made is that, within the air pocket, the pressure is zero. Results are presented for the velocity potential on the wall, the velocity, and the free-surface elevation.

Plunging Wave Impact on a Wall

2008 ◽  
Author(s):  
Jian-Jun Shu
Keyword(s):  
Free Surface ◽  
Vertical Wall ◽  
Rigid Wall ◽  
Small Time ◽  
Breaking Wave ◽  
Wave Impact ◽  
Third Order ◽  
Offshore Engineering ◽  
Surface Profiles ◽  
Engineering Industries

The intention of this paper is to study impact force of an oblique-angled slamming wave acting on a rigid wall. In the present study the analytical approach is pursued based on a technique proposed by the author. A nonlinear theory in the context of potential flow is presented for determining accurately the free-surface profiles immediately after an oblique breaking wave impingement on the rigid vertical wall that suddenly starts from rest. The small-time expansion is taken as far as necessary to include the accelerating effect. The analytical solutions for the free-surface elevation are derived up to the third order. The results derived in this paper are of particular interest to the marine and offshore engineering industries, which will find the information useful for the design of ships, coastal and offshore.

On the Validity and Sensitivity of CFD Simulations for a Deterministic Breaking Wave Impact on a Semi Submersible

2018 ◽  
Author(s):  
Henry Bandringa ◽  
Joop A. Helder
Keyword(s):  
Free Surface ◽  
Absorbing Boundary Conditions ◽  
Implicit Time ◽  
Breaking Wave ◽  
Computational Domain ◽  
Wave Impact ◽  
Time Step ◽  
Cfd Simulations ◽  
Detailed Model ◽  
Run Up

To assess the integrity and safety of structures offshore, prediction of run-up, green water, and impact loads needs to be made during the structure’s design. For predicting these highly non-linear phenomena, most of the offshore industry relies on detailed model testing. In the last couple of years however, CFD simulations have shown more and more promising results in predicting these events, see for instance [1]–[4]. To obtain confidence in the accuracy of CFD simulations in the challenging field of extreme wave impacts, a proper validation of such CFD tools is essential. In this paper two CFD tools are considered for the simulation of a deterministic breaking wave impact on a fixed semi submersible, resulting in flow phenomena like wave run-up, horizontal wave impact and deck impacts. Hereby, one of the CFD tools applies an unstructured gridding approach and implicit free-surface reconstruction, and uses an implicit time integration with a fixed time step. The other CFD tool explicitly reconstructs the free surface on a structured grid and integrates the free surface explicitly in time, using a variable time step. The presented simulations use a compact computational domain with wave absorbing boundary conditions and local grid refinement to reduce CPU time. Besides a typical verification and validation of the results, for one of the CFD tools a sensitivity study is performed in which the influence of small variations in the incoming breaking wave on the overall results is assessed. Such an analysis should provide the industry more insight in the to-be-expected sensitivity (and hence uncertainty) of CFD simulations for these type of applications. Experiments carried out by MARIN are used to validate all the presented simulation results.

On the Hydrodynamic Interaction Between Ship and Free-Surface Motions on Vessels With Moonpools

2019 ◽  
Author(s):  
Senthuran Ravinthrakumar ◽  
Trygve Kristiansen ◽  
Babak Ommani
Keyword(s):  
Free Surface ◽  
Flow Separation ◽  
Coupling Effect ◽  
Three Dimensional ◽  
Dimensional Case ◽  
Navier Stokes ◽  
Linear Potential ◽  
Two Dimensional ◽  
Sloshing Mode ◽  
Vessel Motion

Abstract Coupling between moonpool resonance and vessel motion is investigated in two-dimensional and quasi three-dimensional settings, where the models are studied in forced heave and in freely floating conditions. The two-dimensional setups are with a recess, while the quasi three-dimensional setups are without recess. One configuration with recess is presented for the two-dimensional case, while three different moonpool sizes (without recess) are tested for the quasi three-dimensional setup. A large number of forcing periods, and three wave steepnesses are tested. Boundary Element Method (BEM) and Viscous BEM (VBEM) time-domain codes based on linear potential flow theory, and a Navier–Stokes solver with linear free-surface and body-boundary conditions, are implemented to investigate resonant motion of the free-surface and the model. Damping due to flow separation from the sharp corners of the moonpool inlets is shown to matter for both vessel motions and moonpool response around the piston mode. In general, the CFD simulations compare well with the experimental results. BEM over-predicts the response significantly at resonance. VBEM provides improved results compared to the BEM, but still over-predicts the response. In the two-dimensional study there are significant coupling effects between heave, pitch and moonpool responses. In the quasi three-dimensional tests, the coupling effect is reduced significantly as the moonpool dimensions relative to the displaced volume of the ship is reduced. The first sloshing mode is investigated in the two-dimensional case. The studies show that damping due to flow separation is dominant. The vessel motions are unaffected by the moonpool response around the first sloshing mode.

Large Scale Experimental Wave Impact on Walls in the Québec Coastal Physics Laboratory

2015 ◽  
Author(s):  
Jannette B. Frandsen ◽  
Francis Bérubé
Keyword(s):  
Large Scale ◽  
Peak Pressure ◽  
Vertical Wall ◽  
Test Series ◽  
Vertical Force ◽  
Wave Impact ◽  
Physics Laboratory ◽  
Air Pocket ◽  
Jet Velocity ◽  
Plunging Breaker

The present tests are conducted in the new Québec Coastal Physics Laboratory, Canada. The flume has a depth and a width of 5 m and is 120 m long. This paper presents large scale experiments of water wave impact on a vertical wall following wave runup on a mixed sand-gravel-cobble beach. This present study is concerned with advancing knowledge on rapidly varying pressure magnitude and distributions on different types of sea/river/harbor walls. Protection against extreme events and subsequent coastal erosion is a key theme of application. Herein is presented preliminary test series which has focus on forces on vertical walls. Specifically, 27 pressure sensors are mounted on the vertical wall with a total test area of 1.2 m wide and 2.4 m high and is a stiffened aluminum plate. The outer regions of the wall are made of steel to span the entire width of the tank. The wall is designed to behave as a rigid plate. The geometric model to full scale is about 1:4. The incoming waves evolve on a flat bed to climb the final 25 m on a beach with slope with constant slope of 1:10. A small regular wave train forms the basis for investigations of force patterns on the wall. Herein, our preliminary findings reported are based on selected 6 test series (18 impacts out of 150 impacts). In general, wall pressures greater than 1 MPa and 10 m run-up are easily developed even with moderate amplitude waves at the inlet. We will discuss some details of the underlying mechanism of various types of breaking and impact on the wall. The peak pressure identified on the wall with the mixed gravel beach surface was 1.23 million N/m2 occurring in 0.2 milli seconds. It was cuased by a plunging breaker with a relatively large air pocket (∼0.11 m2). It was further identified that the maximum pressure on the wall does not necessarily give the maximum jet velocity (equivalent to vertical force considered in design of on parapets). They are independent quantities in these very random rapid processes. The maximum jet velocity was in the order of 35 m/s but could higher on a different beach surface. Further, it was found that the maximum waves are not necessarily the most critical ones as the waves break and therefore dissipates its energy before reaching the wall. A plunging breaker with a relatively large airpocket with a crest tip located at the top part of the wall resulted in max. peak wall pressure. One impact case caused a near simultaneous double peak pressure generated by a plunging breaker with two relatively small airpockets (0.003 m2 and 0.01 m2). This was the impact case responsible for the max. vertical jet velocity. We further found that the max. peak water pressure of the plunging breakers had a similar order of magnitude as the max. pressure within an air pocket.

Incipient breaking of steady waves in the presence of surface wakes

1999 ◽  
Vol 383 ◽  
pp. 285-305 ◽  
Author(s):  
MATTHEW MILLER ◽  
TOBIAS NENNSTIEL ◽  
JAMES H. DUNCAN ◽  
ATHANASSIOS A. DIMAS ◽  
STEPHAN PRÖSTLER
Keyword(s):  
Free Surface ◽  
Wave Height ◽  
Flow Characteristics ◽  
Breaking Wave ◽  
Maximum Height ◽  
Two Dimensional ◽  
Mean Flow ◽  
Experimental Findings ◽  
Drift Layer ◽  
Surface Drift

The effect of free-surface drift layers on the maximum height that a steady wave can attain without breaking is explored through experiments and numerical simulations. In the experiments, the waves are generated by towing a two-dimensional fully submerged hydrofoil at constant depth, speed and angle of attack. The drift layer is generated by towing a plastic sheet on the water surface ahead of the hydrofoil. It is found that the presence of this drift layer (free-surface wake) dramatically reduces the maximum non-breaking wave height and that this wave height correlates well with the surface drift velocity. In the simulations, the inviscid two-dimensional fully nonlinear Euler equations are solved numerically. Initially symmetric wave profiles are superimposed on a parallel drift layer whose mean flow characteristics match those in the experiments. It is found that for large enough initial wave amplitudes a bulge forms at the crest on the forward face of the wave and the vorticity fluctuations just under the surface in this region grow dramatically in time. This behaviour is taken as a criterion to indicate impending wave breaking. The maximum non-breaking wave elevations obtained in this way are in good agreement with the experimental findings.

scholarly journals Breaking Wave Impact Pressure on a Vertical Wall

2010 ◽  
Vol 1 (3-4) ◽  
pp. 155-166 ◽  
Author(s):  
C. Rajasekaran ◽  
S.A. Sannasiraj ◽  
V. Sundar
Keyword(s):  
Vertical Wall ◽  
Impact Pressure ◽  
Breaking Wave ◽  
Wave Impact

Simulation Study on the Characteristics of Flow Field in the Process of Wave Impact

2012 ◽  
Vol 212-213 ◽  
pp. 1172-1176
Author(s):  
Jin Feng
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Flow Field ◽  
Simulation Study ◽  
Numerical Models ◽  
Two Dimensional ◽  
Regular Wave ◽  
Wave Impact ◽  
Distribution Rule ◽  
Wave Slamming

In order to study the characteristics of flow field in the process of wave impact, two-dimensional regular wave numerical models were established based on the software FLUENT. RANS equations were adopted. The standard equations were used to close the Reynolds equations. VOF method was used to reconstruct the free surface. After three typical cases of wave slamming on open-piled structures were reproduced, the models were verified by experimental data and the flow field surrounding the structure was displayed visually. Then the processes of wave impact under various wave height, period and over height were simulated. The influences of the three parameters on the distribution of vertical velocities were analyzed, which shows that the distribution rule of the vertical velocities is similar to the wave impact pressures.

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