scholarly journals A Comparative Study of Breaking Wave Loads on Cylindrical and Conical Substructures

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 924
Author(s):  
Eirinaios Chatzimarkou ◽  
Constantine Michailides
Keyword(s):  
Comparative Study ◽  
Pressure Distribution ◽  
Dynamic Pressure ◽  
Load Ratio ◽  
Navier Stokes ◽  
Breaking Wave ◽  
Wave Loads ◽  
Wave Loading ◽  
Wave Load ◽  
Sst Turbulence Model

In the present paper, a comparative study of different cylindrical and conical substructures was performed under breaking wave loading with the open-source Computational Fluid Dynamics (CFD) package OpenFoam capable of the development of a numerical wave tank (NWT) with the use of Reynolds-Averaged Navier–Stokes (RANS) equations, the k-ω Shear Stress Transport (k-ω SST) turbulence model, and the volume of fluid (VOF) method. The validity of the NWT was verified with relevant experimental data. Then, through the application of the present numerical model, the distributions of dynamic pressure and velocity in the x-direction around the circumference of different cylindrical and conical substructures were examined. The results showed that the velocity and dynamic pressure distribution did not change significantly with the increase in the substructure’s diameter near the wave breaking height, although the incident wave conditions were similar. Another important aspect of the study was whether the hydrodynamic loading or the dynamic pressure distribution of a conical substructure would improve or deteriorate under the influence of breaking wave loading compared to a cylindrical one. It was concluded that the primary wave load in a conical substructure increased by 62.57% compared to the numerical results of a cylindrical substructure. In addition, the secondary load’s magnitude in the conical substructure was 3.39 times higher and the primary-to-secondary load ratio was double compared to a cylindrical substructure. These findings demonstrate that the conical substructure’s performance will deteriorate under breaking wave loading compared to a cylindrical one, and it is not recommended to use this type of substructure.

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.

Efficient Computations of Second-Order Low-Frequency Wave Load

2009 ◽  
Author(s):  
Xiao-Bo Chen ◽  
Fla´via Rezende
Keyword(s):  
Low Frequency ◽  
Second Order ◽  
Wave Loads ◽  
Wave Loading ◽  
Wave Load ◽  
Frequency Wave ◽  
New Developments ◽  
Novel Method ◽  
The Difference ◽  
New Formulation

As the main source of resonant excitations to most offshore moored systems like floating LNG terminals, the low-frequency wave loading is the critical input to motion simulations which are important for the design. Further to the analysis presented by Chen & Duan (2007) and Chen & Rezende (2008) on the quadratic transfer function (QTF) of low-frequency wave loading, the new formulation of QTF is developed by the series expansion of the second-order wave loading with respect to the difference-frequency upto the order-2. It provides a novel method to evaluate the low-frequency second-order wave loads in a more accurate than usual order-0 approximation (often called Newman approximation) and more efficient way comparing to the computation of complete QTF. New developments including numerical results of different components of QTF are presented here. Furthermore, the time-series reconstruction of excitation loads in the motion simulation of mooring systems is analyzed and a new efficient and accurate scheme is demonstrated.

Estimating Iceberg-Wave Companion Loads Using Probabilistic Methods

2015 ◽  
Author(s):  
Mark Fuglem ◽  
Paul Stuckey ◽  
Somchat Suwan
Keyword(s):  
Hydrodynamic Pressure ◽  
Offshore Structures ◽  
Probabilistic Methods ◽  
Wave Loads ◽  
Wave Loading ◽  
Wave Load ◽  
Sea State ◽  
Load Factors ◽  
Induced Velocity ◽  
The Impact

Many challenges arise when designing offshore structures for iceberg loads in arctic and subarctic regions. To help the designer, the ISO 19906:2010 standard provides guidance for the calculation of design ice loads using both deterministic and probabilistic approaches. In determining design loads for different environmental factors, both principal and companion actions must be taken into account; an example is iceberg actions and companion wave actions. ISO 19906 allows the designer to calculate the companion wave action as a specified fraction (combination factor) of the extreme level (EL) design wave load. Alternatively, the designer can calculate appropriate companion wave loads explicitly. A methodology has been developed at C-CORE in which representative iceberg actions are determined using a software package, the Iceberg Load Software (ILS). This is a probabilistic tool which uses Monte Carlo simulation to obtain a distribution of global impact forces based on the expected range of iceberg and environmental conditions that a structure would likely encounter. The software provides a reasonably accurate representation of the iceberg loading situation, following the provisions of ISO 19906:2010, without introducing unnecessary conservatism in the design load. In the software, the influence of waves on the iceberg actions are considered, but companion wave loads must be calculated and added externally to the software, The software accounts for the probability of different sea state conditions and the influence of the sea state on the probability and severity of iceberg impact, given the correlations between the sea state, iceberg management effectiveness and iceberg drift and wave-induced velocity. The additional hydrodynamic pressure due to the wave during the period of the impact; is not considered. This wave loading will be complicated by the influence that the presence the iceberg and structure have on the local sea state. In this paper, brief descriptions are provided of background studies on companion wave loading and the application of companion load factors in ISO 19906. The companion load factors allow the designer to apply the design wave load, which is calculated for situations with no iceberg present, to the case of iceberg impacts. In this study, a methodology is presented for determining companion wave loads based on the distribution of sea states expected during an iceberg impact. These sea states are significantly less severe than that associated with the design wave load as iceberg impacts are rare events. The companion wave loads are determined without accounting for the influence of the iceberg; this is thought to be quite conservative. An example application of the methodology is presented for a hypothetical platform located on the Grand Banks, off the east coast of Newfoundland. Iceberg actions, wave actions and combined iceberg-wave actions are estimated using the described methodology. Comparisons are provided for the resulting companion loads and those based on ISO 19906:2010 companion load factors applied to the extreme level wave load.

Evaluation of Tsunami Wave Loads Acting on Walls of Confined-Masonry-Brick and Concrete-Block Houses

2014 ◽  
Vol 9 (6) ◽  
pp. 976-983 ◽  
Author(s):  
Gaku Shoji ◽  
◽  
Hirofumi Shimizu ◽  
Shunichi Koshimura ◽  
Miguel Estrada ◽  
...  
Keyword(s):  
Pressure Distribution ◽  
Structural Damage ◽  
Failure Modes ◽  
Tsunami Wave ◽  
Concrete Block ◽  
Wave Loads ◽  
Wave Load ◽  
Confined Masonry ◽  
Wave Pressure ◽  
Horizontal Wave

Damage to confined-masonry-brick or concrete-block house was assessed for being subjected to a tsunami wave load. This study was prompted by recent three tsunamis – one during 2001 on the Near Coast of Peru, one in 2009 in the Samoa Islands, and one in 2010 in Maule, Chile. We analyzed 13 damaged walls from 10 single-storey houses located near the coastline. We focused on evaluating the tsunami wave pressure distribution on house walls. Based on the formula proposed by Asakura et al. (2000) to evaluate tsunami wave pressure distribution on a structural component located on land behind on-shore structures, which is used for designing a tsunami evacuation building, we identify the values of horizontal wave pressure indexain Asakura’s formula for walls and discuss the boundary value ofaat which a wall presents structural damage, such as in collapse and cracking failure modes.

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.

Numerical Reproduction of Extreme Wave Loads on a Gravity Wind Turbine Foundation

2006 ◽  
Author(s):  
H. Bredmose ◽  
J. Skourup ◽  
E. A. Hansen ◽  
E. D. Christensen ◽  
L. M. Pedersen ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Wave Climate ◽  
Irregular Waves ◽  
Navier Stokes ◽  
Wave Loads ◽  
Load History ◽  
Wave Load ◽  
Extreme Wave ◽  
Run Up ◽  
A Current

A fully nonlinear 3D Navier Stokes solver with VOF (Volume of Fluid) treatment of the free surface is used to reproduce two extreme laboratory wave impacts on a gravity wind turbine foundation. The wave climate is irregular waves with a current. Numerical results for inline force, overturning moment and run-up are compared to measurements. The extreme wave loads for the two events are associated with slamming onto the under side of a horizontal platform placed 9.1m above the still water level. For such impacts, the computed wave loads are strongly sensitive to the shape of the incoming waves. A comparison with a Morison-type estimation of the wave loads shows that this much simpler approach can reproduce the overall trend of the wave load history, but not the extreme moment.

Transfer of Boussinesq Waves to a Navier-Stokes Solver: Application to Wave Loads on an Offshore Wind Turbine Foundation

2009 ◽  
Author(s):  
Erik Damgaard Christensen ◽  
Henrik Bredmose ◽  
Erik Asp Hansen
Keyword(s):  
Wind Turbine ◽  
Shallow Water ◽  
Offshore Wind ◽  
Navier Stokes ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Cfd Model ◽  
Wave Load ◽  
Boussinesq Model ◽  
Run Up

Wave load and wave run-up is a very important issue to offshore wind turbine foundations. These are often installed in relatively shallow water on for instance sand banks. Therefore the non-linear shoaling and subsequently the force and run-up are important to address. The paper presents a method to combine a Boussinesq model with a CFD model. This gives an accurate tool to estimate wave loads on the foundations at acceptable computational times.

Adaptive Stretching of Dynamic Pressure Distribution in Long- and Short-Crested Sea States

2009 ◽  
Author(s):  
Gu¨nther Clauss ◽  
Sascha Kosleck ◽  
Florian Sprenger ◽  
Florin Boeck
Keyword(s):  
Pressure Distribution ◽  
Dynamic Pressure ◽  
Load Condition ◽  
Wave Structure ◽  
Wave Theory ◽  
Offshore Structures ◽  
Fast Fourier Transformation ◽  
Wave Loads ◽  
Sea State ◽  
Precise Knowledge

During their lifetime, marine structures and ships are frequently exposed to severe weather and rough, sometimes extreme sea states. To ensure survival, the precise knowledge of global and local loads is an inevitable integral prerequisite for the design of safe offshore structures and marine vessels. Wave-structure interaction and the associated pressure induced wave loads are key parameters for the definition of design load cases. Once the complete surrounding sea state for the identified load condition is known, the pressure induced loads can be computed by calculating the pressure distribution along the hull, using an appropriate wave theory. As 1st-order AIRY-Theory as well as 2nd- and 3rd-order STOKES-Theory excessively overestimate the dynamic pressure above still water level, especially in high wave crests, a variety of stretching terms has been applied to common wave theories to correct the pressure distribution. This paper presents a second-order stretching approach to describe the distribution of the dynamic pressure in regular wave crests. In combination with FFT (Fast Fourier Transformation), the applicability of this method can be extended to irregular sea states and even extreme waves. Calculations for several regular and irregular sea states are shown and compared to calculations with existing stretching methods. The results are validated by measurements conducted in a wave tank at the Technical University Berlin. The paper concludes with an example for the calculation of the wave induced pressure field along a ship hull operating in a short-crested, multidirectional sea state.

Impact of New Slamming Wave Design Method on the Structural Dynamics of a Classic, Modern and Future Offshore Wind Turbine

2017 ◽  
Author(s):  
Johan M. Peeringa ◽  
Koen W. Hermans
Keyword(s):  
Wind Turbine ◽  
Wave Train ◽  
Breaking Waves ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Breaking Wave ◽  
Wave Loads ◽  
Wave Load ◽  
Wave Impact ◽  
The Impact

In the WiFi-JIP project, the impact of steep (and breaking) waves on a monopile support structure was studied. Observations during model tests showed that large tower top accelerations occur due to a slamming wave. Using experiments and simulations results, a new formulation of the design load for a slamming wave was developed. Instead of the embedded stream function, as applied in industry, the wave train is generated with the nonlinear potential flow code Oceanwave3D. On the wave train a set of conditions is applied to find the individual waves, that are closest to the prescribed breaking wave and most likely cause a slamming impact. To study the effect of the new slamming load formulation on different sized offshore wind turbines, aero-hydroelastic simulations were performed on a classic 3MW wind turbine, a modern 4MW wind turbine and a future 10MW wind turbine. The simulations are performed with and without a slamming wave load. The slamming has a clear effect on the tower top acceleration. Accelerations due to the wave impact are highest for the 3MW model at the tower top and at 50m height. A serious tower top acceleration of almost 7m/s2 due to wave slamming is found for the 3MW turbine. This is an increase of 474% compared with the case of Morison wave loads only.

scholarly journals Assessment of Numerical Methods for Plunging Breaking Wave Predictions

2021 ◽  
Vol 9 (3) ◽  
pp. 264
Author(s):  
Shanti Bhushan ◽  
Oumnia El Fajri ◽  
Graham Hubbard ◽  
Bradley Chambers ◽  
Christopher Kees
Keyword(s):  
Solitary Wave ◽  
Wave Breaking ◽  
Large Scale ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Wave Crest ◽  
Breaking Wave ◽  
Rans Turbulence Models ◽  
Run Up ◽  
Better Than

This study evaluates the capability of Navier–Stokes solvers in predicting forward and backward plunging breaking, including assessment of the effect of grid resolution, turbulence model, and VoF, CLSVoF interface models on predictions. For this purpose, 2D simulations are performed for four test cases: dam break, solitary wave run up on a slope, flow over a submerged bump, and solitary wave over a submerged rectangular obstacle. Plunging wave breaking involves high wave crest, plunger formation, and splash up, followed by second plunger, and chaotic water motions. Coarser grids reasonably predict the wave breaking features, but finer grids are required for accurate prediction of the splash up events. However, instabilities are triggered at the air–water interface (primarily for the air flow) on very fine grids, which induces surface peel-off or kinks and roll-up of the plunger tips. Reynolds averaged Navier–Stokes (RANS) turbulence models result in high eddy-viscosity in the air–water region which decays the fluid momentum and adversely affects the predictions. Both VoF and CLSVoF methods predict the large-scale plunging breaking characteristics well; however, they vary in the prediction of the finer details. The CLSVoF solver predicts the splash-up event and secondary plunger better than the VoF solver; however, the latter predicts the plunger shape better than the former for the solitary wave run-up on a slope case.

Sign in / Sign up

Export Citation Format

Share Document