Breaking Wave Impact on a Platform Column: An Introductory CFD Study

2011 ◽  
Author(s):  
Csaba Pakozdi ◽  
Timothy E. Kendon ◽  
Carl-Trygve Stansberg
Keyword(s):  
Model Test ◽  
Breaking Waves ◽  
Wave Profile ◽  
Scale Model ◽  
Computational Time ◽  
Breaking Wave ◽  
Wave Impact ◽  
Time Step ◽  
Test Setup ◽  
Wave Maker

The slamming of breaking waves on the legs of large volume offshore platforms has received increased attention over recent years. To investigate this problem, MARINTEK’s Wave Impact Loads JIP has, in one of its sub-tasks, focused towards an idealised model test setup of a rectangular cylinder in breaking waves. The model consists of a vertical column with a fragment of a horizontal deck attached. The model is fixed at a distance L ahead of the wave maker. Physical scale model test experiments of the block in regular waves and in wave groups have been carried out in Phase 1 of the JIP (2008). The objective of this study is the CFD simulation of a long crested breaking wave and its impact on the aforementioned cylinder and deck structure in order to find out the feasibility of the numerical reconstruction of such events. The commercial CFD tool Star-CCM+ V5.03.0056 (www.cd-adapco.com) is used in this study. This paper considers results from the test setup, and compares the measured wave elevation against results from the CFD code. The position of the cylinder in relation to the breaking wave front is investigated in the numerical simulation in order to analyze its effect on the slamming force. Use of an unsteady wave boundary condition, matching the exact motion history of the wave-maker with the measured free surface elevation at the wave maker gives an almost exact matching between the computed wave profile and the measured wave profile. The improvement in the numerical tool of Star-CCM+ which makes it possible to use higher order time integration scheme for VOF significantly decreases the numerical diffusion of the wave propagation. This new scheme also enables the use of a time step 10 times larger than the first order scheme which reduces the computational time. Because a large time step can be chosen it is important that the time step is small enough to capture the correct time evolution of the physical phenomena of interest. Capturing the pressure evolution at a slamming event demands very high spatial resolution. Spatially averaged slamming pressures look fairly similar to the model test observations, while further work is needed for a more detailed comparison.

scholarly journals Influence of the Spatial Pressure Distribution of Breaking Wave Loading on the Dynamic Response of Wolf Rock Lighthouse

2021 ◽  
Vol 9 (1) ◽  
pp. 55
Author(s):  
Darshana T. Dassanayake ◽  
Alessandro Antonini ◽  
Athanasios Pappas ◽  
Alison Raby ◽  
James Mark William Brownjohn ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Pressure Distribution ◽  
Distinct Element ◽  
Breaking Waves ◽  
Breaking Wave ◽  
Wave Loading ◽  
Wave Impact ◽  
Pressure Distributions ◽  
Impact Area ◽  
The Impact

The survivability analysis of offshore rock lighthouses requires several assumptions of the pressure distribution due to the breaking wave loading (Raby et al. (2019), Antonini et al. (2019). Due to the peculiar bathymetries and topographies of rock pinnacles, there is no dedicated formula to properly quantify the loads induced by the breaking waves on offshore rock lighthouses. Wienke’s formula (Wienke and Oumeraci (2005) was used in this study to estimate the loads, even though it was not derived for breaking waves on offshore rock lighthouses, but rather for the breaking wave loading on offshore monopiles. However, a thorough sensitivity analysis of the effects of the assumed pressure distribution has never been performed. In this paper, by means of the Wolf Rock lighthouse distinct element model, we quantified the influence of the pressure distributions on the dynamic response of the lighthouse structure. Different pressure distributions were tested, while keeping the initial wave impact area and pressure integrated force unchanged, in order to quantify the effect of different pressure distribution patterns. The pressure distributions considered in this paper showed subtle differences in the overall dynamic structure responses; however, pressure distribution #3, based on published experimental data such as Tanimoto et al. (1986) and Zhou et al. (1991) gave the largest displacements. This scenario has a triangular pressure distribution with a peak at the centroid of the impact area, which then linearly decreases to zero at the top and bottom boundaries of the impact area. The azimuthal horizontal distribution was adopted from Wienke and Oumeraci’s work (2005). The main findings of this study will be of interest not only for the assessment of rock lighthouses but also for all the cylindrical structures built on rock pinnacles or rocky coastlines (with steep foreshore slopes) and exposed to harsh breaking wave loading.

scholarly journals NON-BREAKING AND BREAKING WAVE LOADS ON A COOLING WATER OUTFALL

1978 ◽  
Vol 1 (16) ◽  
pp. 148
Author(s):  
G.R. Mogridge ◽  
W.W. Jamieson
Keyword(s):  
Water Level ◽  
Cooling Water ◽  
High Water ◽  
Breaking Waves ◽  
Irregular Waves ◽  
Scale Model ◽  
Breaking Wave ◽  
Wave Loads ◽  
Eastern Canada ◽  
Spilling Breakers

Cooling water from a power generating station in Eastern Canada is pumped to an outfall and distributed into the ocean through discharge ports in the sidewalls of a diffuser cap. The cap is essentially a shell-type structure consisting of a submerged circular cylinder 26.5 ft in diameter and 14 ft high. It is located in 25 ft of water at low water level and 54 ft at high water level. Horizontal forces, vertical forces and overturning moments exerted by waves on a 1:36 scale model of the diffuser cap were measured with and without cooling water discharging from the outfall. Tests were run with regular and irregular waves producing both non-breaking and breaking wave loads on the diffuser cap. The overturning moments measured on the diffuser cap were up to 150 percent greater than those on a solid submerged cylinder sealed to the seabed. Unlike sealed cylinders, all of the wave loads measured on the relatively open structure reached maximum values at approximately the same time. The largest wave loads were measured on the diffuser structure when it was subjected to spilling breakers at low water level. For a given wave height, the spilling breakers caused wave loads up to 100 percent greater than those due to non-breaking waves.

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.

A Virtual Piston-Type Wave Maker Based on OpenFOAM

2017 ◽  
Vol Vol 159 (A2) ◽  
Author(s):  
J Yao
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Procedure ◽  
Finite Amplitude ◽  
Wave Profile ◽  
Piston Motion ◽  
Time Step ◽  
Simulation Accuracy ◽  
Wave Maker ◽  
Permanent Form

OpenFOAM is an open source CFD (Computational Fluid Dynamics) toolbox and recently attracts many researchers to develop codes based on it for their own applications. In order to numerically generate waves based on the wave-maker theory for a piston motion, numerical improvements have been done on the base of OpenFOAM by the author. In gen-eral, the present new tool can be employed to simulate wave generation as long as the piston motion is given. This paper presents the related computational procedure and simulations for generating relatively long finite-amplitude waves ac-cording to Madsen’s second-order wave-maker theory. The sensitivities of the computed incident wave profile to grid density and time step are investigated for the case of generating a wave with permanent form. The simulation accuracy is validated by comparison with the analytical solution and available experimental data.

A VIRTUAL PISTON-TYPE WAVE MAKER BASED ON OPENFOAM

2021 ◽  
Vol 159 (A2) ◽  
Author(s):  
J Yao
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Procedure ◽  
Finite Amplitude ◽  
Wave Profile ◽  
Piston Motion ◽  
Time Step ◽  
Simulation Accuracy ◽  
Wave Maker ◽  
Permanent Form

OpenFOAM is an open source CFD (Computational Fluid Dynamics) toolbox and recently attracts many researchers to develop codes based on it for their own applications. In order to numerically generate waves based on the wave-maker theory for a piston motion, numerical improvements have been done on the base of OpenFOAM by the author. In gen- eral, the present new tool can be employed to simulate wave generation as long as the piston motion is given. This paper presents the related computational procedure and simulations for generating relatively long finite-amplitude waves ac- cording to Madsen’s second-order wave-maker theory. The sensitivities of the computed incident wave profile to grid density and time step are investigated for the case of generating a wave with permanent form. The simulation accuracy is validated by comparison with the analytical solution and available experimental data.

Discus Buoy Stability and the Spectrum of Steep Waves

1980 ◽  
Vol 24 (03) ◽  
pp. 190-202
Author(s):  
John H. Nath ◽  
Theodore Chester ◽  
Robert E. Bunney ◽  
David M. Brooks
Keyword(s):  
Joint Probability ◽  
Ocean Waves ◽  
Breaking Waves ◽  
Wave Climate ◽  
Laboratory Scale ◽  
Scale Model ◽  
Probability Density Distribution ◽  
Breaking Wave ◽  
Random Waves ◽  
Model Studies

Thick discus buoys are used in the ocean as platforms from which oceanographic and meteorological measurements are made and reported to shore. The stability of these buoys is sensitive to steep breaking waves, and a few have capsized in the ocean from large breaking waves. This occurrence can be simulated in laboratory scale-model studies. Generally, in the laboratory, the buoys will not capsize for a breaking wave that is small relative to buoy diameter. The problem is predicting the probability of capsizing for engineering planning purposes. This paper describes how first approximations can be made from a combination of laboratory scale-model testing of buoy capsizings in random waves, a few reported occurrences of buoy capsizings in the open ocean, and the statistics of ocean waves. An estimate of the joint probability density distribution function of a wave steepness parameter and a wave height parameter is made from buoy motion measurements. It is found that in the northeastern Pacific Ocean the wave climate is quite severe and includes a large percentage of relatively large breaking waves. Under such circumstances, buoy diameters of 10 m have a relatively low reliability. The reliability increases rapidly as buoy diameter increases.

Column Slamming Loads on a TLP From Steep and Breaking Waves

2017 ◽  
Author(s):  
Tone M. Vestbøstad ◽  
Ole David Økland ◽  
Gunnar Lian ◽  
Terje Peder Stavang
Keyword(s):  
Model Test ◽  
Limit State ◽  
Breaking Waves ◽  
Complex Problem ◽  
Load Level ◽  
Special Focus ◽  
Ultimate Limit State ◽  
Wave Impact ◽  
Design Loads ◽  
Ultimate Limit

Previous model test campaigns of various large-volume platforms indicate that wave impact loads on vertical platform columns can become high in extreme sea states. Column slamming is a highly non-linear and complex problem and reliable estimation1 of Ultimate Limit State (ULS) and Accidental Limit State (ALS) design loads is a challenge. Previous measurements indicate ALS pressures of about 3 MPa acting on an area of typically 50m2 in North Sea and Norwegian Sea wave conditions. The corresponding ULS loads were in the range 1.5–2.0 MPa for the same impact area. Such high predictions for ULS and ALS impact pressures may be critical for both steel and concrete platforms, and accurate predictions of design loads is therefore crucial to establish the correct level of safety. A model test campaign dedicated to investigate column slamming has been performed on the Heidrun platform, a large concrete Tension Leg Platform (TLP). The column diameter is 31 m. The test campaign was performed in 2013 at Marintek (now Sintef Ocean), at a model scale of 1:55. The main objective of the test campaign was to estimate the characteristic slamming loads, defined as the q-annual extreme 3-hour slamming load level of 10−2 for the Ultimate Limit State (ULS) and 10−4 for the Accidental Limit State (ALS). To ascertain that the test campaign would result in reliable load estimates, a pre-study on column slamming was performed, involving a selected expert group with participants from several organizations. Review of previous work, identification of governing parameters for wave impact and assessment of model uncertainties and extreme value prediction of slamming loads was performed. It was concluded that two challenges were to be specifically addressed during the planning and execution of the test: 1) the localized nature and short duration of the slamming loads and 2) the large statistical variability of the slamming loads. To address the first challenge, special focus was given to the extent and quality of the instrumentation capturing the slamming loads. Comprehensive documentation of the instrumentation was also performed using hammer testing, structural analysis and drop tests. The second challenge was addressed with a carefully planned test strategy. The resulting model test campaign set a new standard for model testing of such loads, using over 80 slamming panels with a sampling frequency of 19.2 kHz, and over 300 sea state realizations. This paper presents the planning and execution of the model test campaign, including the instrumentation and model set-up, the test matrix, main challenges, findings and results.

The Dynamic Response of an Offshore Wind Turbine With Realistic Flexibility to Breaking Wave Impact

2011 ◽  
Author(s):  
Erik Jan de Ridder ◽  
Pieter Aalberts ◽  
Joris van den Berg ◽  
Bas Buchner ◽  
Johan Peeringa
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Breaking Waves ◽  
Impulsive Loading ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Breaking Wave ◽  
Extreme Waves ◽  
Wave Impact ◽  
Pilot Model

The effects of operational loads and wind loads on offshore monopile wind turbines are well understood. For most sites, however, the water depth is such that breaking or near-breaking waves will occur causing impulsive excitation of the monopile and consequently considerable stresses and displacements in the monopile, tower and turbine. To investigate this, pilot model tests were conducted with a special model of an offshore wind turbine with realistic flexibility tested in (extreme) waves. This flexibility was considered to be necessary for two reasons: the impulsive loading of extreme waves is very complex and there can be an interaction between this excitation and the dynamic response of the foundation and tower. The tests confirmed the importance of the topic of breaking waves: horizontal accelerations of more than 0.5g were recorded at nacelle level in extreme cases.

Experimental Investigations of Breaking Wave Impact Forces on a Monopile Substructure for Offshore Wind Turbines Under Regular Breaking Waves

2017 ◽  
Author(s):  
Vipin Chakkurunni Palliyalil ◽  
Panneer Selvam Rajamanickam ◽  
Mayilvahanan Alagan Chella ◽  
Vijaya Kumar Govindasamy
Keyword(s):  
Circular Cylinder ◽  
Wind Turbines ◽  
Breaking Waves ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Breaking Wave ◽  
Wave Impact ◽  
Offshore Wind Turbines ◽  
Impact Forces ◽  
The Impact

The main objective of the paper is to investigate wave impact forces from breaking waves on a monopile substructure for offshore wind turbine in shallow waters. This study examines the load assessment parameters relevant for breaking wave forces on a vertical circular cylinder subjected to breaking waves. Experiments are conducted in a shallow water flume and the wave generation is based on piston type wave maker. The experiments are performed with a vertical circular cylinder with diameter, D = 0.20m which represents a monopile substructure for offshore wind turbines with regular waves of frequencies around 0.8Hz. The experimental setup consists of a 1/10 slope followed by a horizontal bed portion with a water depth of 0.8m. Plunging breaking waves are generated and free surface elevations are measured at different locations along the wave tank from wave paddle to the cylinder in order to find the breaking characteristics. Wave impact pressures are measured on the cylinder at eight different vertical positions along the height of the cylinder under breaking waves for different environmental conditions. The wave impact pressures and wave surface elevations in the vicinity of the cylinder during the impact for three different wave conditions are presented and discussed.

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