Wave Impact Loads on Offshore Gravity Based Structure

2015 ◽  
Author(s):  
Ben de Sonneville ◽  
Bas Hofland ◽  
Amund Mowinckel ◽  
Bo Terp Paulsen
Keyword(s):  
Measurement Techniques ◽  
Inertial Force ◽  
Breaking Waves ◽  
Power Converter ◽  
Air Gap ◽  
Wave Loads ◽  
Wave Impact ◽  
Large Wave ◽  
Resonant Wave ◽  
Set Up

Aibel is developing an offshore power converter platform concept. Its foundation is gravity-based and consists of four columns interconnected by a ring-shaped pontoon at the seabed. The platform is intended for water depths in the order of 20 to 40m. In these waters, breaking waves typically cause large wave loads on the foundation that need to be accounted for in the design. The slamming loads, pressures and air gap at the platform were investigated with a combined approach of physical and numerical modeling. This paper summarizes the set-up, test program, measurement techniques, results and analysis of the physical model tests. The tests showed that reflection and diffraction patterns caused a significant steepening of the waves between the columns, reducing the air gap and increasing the slamming frequency and magnitude on the downstream columns and underside of the deck. Excitation of resonant wave modes was identified for certain wave frequencies. Although the global wave loads were primarily governed by inertia, largest loads occurred under slamming impacts on the upstream columns, in phase with the inertial force.

Numerical Modeling of Breaking Wave Kinematics and Wave Impact Pressures on a Vertical Slender Cylinder

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Mayilvahanan Alagan Chella ◽  
Hans Bihs ◽  
Dag Myrhaug ◽  
Øivind Asgeir Arntsen
Keyword(s):  
Free Surface ◽  
Breaking Waves ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Breaking Wave ◽  
Total Force ◽  
Wave Loads ◽  
Wave Impact ◽  
Large Wave ◽  
Surface Deformations

Wave loads from breaking waves on offshore wind turbine (OWT) substructures in shallow waters still remain uncertain. The interaction of breaking waves with structures is characterized by complex free surface deformations, instantaneous impact of the water mass against the structure, and consequently large wave forces on the structures. The main objective of the paper is to investigate wave impact pressures and kinematics during the interaction of breaking waves with a vertical cylinder using the open-source computational fluid dynamics (CFD) model REEF3D. The model is based on the Reynolds-averaged Navier–Stokes (RANS) equations coupled with the level set method and k–ω turbulence model. Three wave impact conditions are considered in this study. The numerically simulated free surface deformations around the cylinder during the breaking wave interaction are also presented for different wave impact conditions. For three wave impact conditions, the wave impact pressure and the horizontal and vertical components of the particle velocity are computed in front of the cylinder and analyzed. The pressure and velocity profile at their maximum values are also examined and discussed. In addition, the total force is calculated for three breaking conditions and they are correlated with the pressure and kinematics during the interaction.

Loads and Dynamic Response of a Floating Wave Energy Converter due to Regular Waves From CFD Simulations

2016 ◽  
Author(s):  
Anna Büchner ◽  
Thomas Knapp ◽  
Martin Bednarz ◽  
Philipp Sinn ◽  
Arndt Hildebrandt
Keyword(s):  
Dynamic Response ◽  
Boundary Conditions ◽  
Wave Energy ◽  
Single Point ◽  
Breaking Waves ◽  
Wave Energy Converter ◽  
Wave Loads ◽  
Regular Waves ◽  
Energy Converter ◽  
Set Up

The commercial CFD code ANSYS Fluent is used for the three-dimensional estimation of wave loads and the dynamic response of a floating single point wave energy converter of the SINN Power wave power plant due to non-breaking and unidirectional waves in coastal waters. The VoF method is used to model the free surface and wave theories to set up the boundary conditions at the inlet for regular waves. The wave induced vertical motions of the floating module are computed by a sixDoF solver. Preliminary 2D and 3D studies to set up boundary conditions, mesh densities and solver settings were performed. The numerical results were compared to analytical solutions in form of water surface elevations and wave kinematics which showed good agreement. The paper presents the dynamic response of the floating module for different load cases in terms of non-breaking waves. The resulting horizontal and vertical forces at the floating module will be presented and explained by the flow dynamics. Time and space depending velocities and pressure distributions including details on vortex separation will be given, which reveal valuable insights on the contribution of inertia and drag forces leading to the dynamic structural response of the floating devices.

Deterministic Simulation of Breaking Wave Impact and Flexible Response of a Fixed Offshore Wind Turbine

2015 ◽  
Author(s):  
Tim Bunnik ◽  
Joop Helder ◽  
Erik-Jan de Ridder
Keyword(s):  
Numerical Model ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Breaking Waves ◽  
Model Tests ◽  
Offshore Wind Turbine ◽  
Breaking Wave ◽  
Wave Loads ◽  
Wave Impact ◽  
Flexible Response

The effects of operational wave loads and wind loads on offshore mono pile 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 mono pile and consequently considerable stresses, displacements and accelerations in the mono pile, tower and turbine. Model tests with a flexible mono pile wind turbine were carried out to investigate the effect of breaking waves. In these model tests the flexibility of the turbine was realistically modelled. These model tests were used for validation of a numerical model for the flexible response of wind turbines due to breaking waves. A focusing wave group has been selected which breaks just aft of the wind turbine. The numerical model consists of a one-way coupling between a CFD model for breaking wave loads and a simplified structural model based on mode shapes. An iterative wave calibration technique has been developed in the CFD method to ensure a good match between the measured and simulated incoming wave profile. This makes a deterministic comparison between simulations and measurements possible. This iteration is carried out in a 2D CFD domain (long-crested wave restriction) and is therefore relatively cheap. The calibrated CFD wave is then simulated in a (shorter) 3D CFD domain including a (fixed) wind turbine. The resulting wave pressures on the turbine have been used to compute the modal excitation and subsequently the modal response of the wind turbine. The horizontal accelerations resulting from this one-way coupling are in good agreement with the measured accelerations.

scholarly journals HAVE IMPACT PRESSURES ON COMPOSITE BREAKWATERS

1980 ◽  
Vol 1 (17) ◽  
pp. 111 ◽  
Author(s):  
G.R. Mogridge ◽  
W.W. Jamieson
Keyword(s):  
Solid Wall ◽  
Probability Distributions ◽  
Relative Effectiveness ◽  
Breaking Waves ◽  
Cumulative Probability ◽  
Breaking Wave ◽  
Wave Loads ◽  
Wave Impact ◽  
Pressure Transducers ◽  
Perforated Breakwater

Wave impact pressures and forces on composite breakwaters have been measured in the laboratory. A solid wall breakwater and a perforated breakwater were instrumented with small pressure transducers in a study designed to estimate the relative effectiveness of perforated breakwaters in reducing impact loads caused by breaking waves. Experimental results of maximum pressures and forces measured on the breakwater walls are presented as cumulative probability distributions. It is concluded that the perforated breakwater experiences significantly lower breaking wave loads although local impact pressures may be as high as those measured on the solid wall breakwater. Further studies are required on the perforated breakwater and alternative designs to determine the most suitable caisson type for the reduction of wave impact forces.

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.

Computation of Wave Impact Pressures and Kinematics During Plunging Breaking Wave Interaction With a Vertical Cylinder Using CFD Modelling

2017 ◽  
Author(s):  
Mayilvahanan Alagan Chella ◽  
Hans Bihs ◽  
Dag Myrhaug ◽  
Øivind Asgeir Arntsen
Keyword(s):  
Free Surface ◽  
Vertical Cylinder ◽  
Wave Interaction ◽  
Breaking Waves ◽  
Offshore Wind Turbine ◽  
Breaking Wave ◽  
Total Force ◽  
Wave Impact ◽  
Large Wave ◽  
Surface Deformations

Wave loads from breaking waves on offshore wind turbine (OWT) substructures in shallow waters still remain uncertain. The interaction of breaking waves with structures is characterized by complex free surface deformations, instantaneous impact of the water mass against the structure and consequently large wave forces on the structures. The main objective of the paper is to investigate wave impact pressures and kinematics during the interaction of breaking waves with a vertical cylinder using the open-source CFD model REEF3D. The model is based on the Reynolds-Averaged Navier-Stokes (RANS) equations coupled with the level set method (LSM) and k-ω turbulence model. Three wave impact conditions are considered in the present study. The numerically simulated free surface deformations around the cylinder during the breaking wave interaction are also presented for different wave impact conditions. For three wave impact conditions, the wave impact pressure and the horizontal and vertical components of the particle velocity are computed in front of the cylinder and analyzed. The pressure and velocity profile at their maximum values are also examined and discussed. In addition, the total force is calculated for three breaking conditions and they are correlated with the pressure and kinematics during the interaction.

scholarly journals EMC Component Modeling and System-Level Simulations of Power Converters: AC Motor Drives

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1568
Author(s):  
Bernhard Wunsch ◽  
Stanislav Skibin ◽  
Ville Forsström ◽  
Ivica Stevanovic
Keyword(s):  
Power Converters ◽  
Filter Design ◽  
Magnetic Coupling ◽  
Power Converter ◽  
System Level ◽  
Noise Propagation ◽  
Ac Motor ◽  
Input Side ◽  
Indispensable Tool ◽  
Set Up

EMC simulations are an indispensable tool to analyze EMC noise propagation in power converters and to assess the best filtering options. In this paper, we first show how to set up EMC simulations of power converters and then we demonstrate their use on the example of an industrial AC motor drive. Broadband models of key power converter components are reviewed and combined into a circuit model of the complete power converter setup enabling detailed EMC analysis. The approach is demonstrated by analyzing the conducted noise emissions of a 75 kW power converter driving a 45 kW motor. Based on the simulations, the critical impedances, the dominant noise propagation, and the most efficient filter component and location within the system are identified. For the analyzed system, maxima of EMC noise are caused by resonances of the long motor cable and can be accurately predicted as functions of type, length, and layout of the motor cable. The common-mode noise at the LISN is shown to have a dominant contribution caused by magnetic coupling between the noisy motor side and the AC input side of the drive. All the predictions are validated by measurements and highlight the benefit of simulation-based EMC analysis and filter design.

A CFD Study of Focused Extreme Wave Impact on Decks of Offshore Structures

2014 ◽  
Author(s):  
Xin Lu ◽  
Pankaj Kumar ◽  
Anand Bahuguni ◽  
Yanling Wu
Keyword(s):  
Real World ◽  
Offshore Structures ◽  
Air Gap ◽  
Irregular Waves ◽  
Linear Wave ◽  
Extreme Wave ◽  
Wave Impact ◽  
Loading Test ◽  
Wide Range ◽  
Wave Maker

The design of offshore structures for extreme/abnormal waves assumes that there is sufficient air gap such that waves will not hit the platform deck. Due to inaccuracies in the predictions of extreme wave crests in addition to settlement or sea-level increases, the required air gap between the crest of the extreme wave and the deck is often inadequate in existing platforms and therefore wave-in-deck loads need to be considered when assessing the integrity of such platforms. The problem of wave-in-deck loading involves very complex physics and demands intensive study. In the Computational Fluid Mechanics (CFD) approach, two critical issues must be addressed, namely the efficient, realistic numerical wave maker and the accurate free surface capturing methodology. Most reported CFD research on wave-in-deck loads consider regular waves only, for instance the Stokes fifth-order waves. They are, however, recognized by designers as approximate approaches since “real world” sea states consist of random irregular waves. In our work, we report a recently developed focused extreme wave maker based on the NewWave theory. This model can better approximate the “real world” conditions, and is more efficient than conventional random wave makers. It is able to efficiently generate targeted waves at a prescribed time and location. The work is implemented and integrated with OpenFOAM, an open source platform that receives more and more attention in a wide range of industrial applications. We will describe the developed numerical method of predicting highly non-linear wave-in-deck loads in the time domain. The model’s capability is firstly demonstrated against 3D model testing experiments on a fixed block with various deck orientations under random waves. A detailed loading analysis is conducted and compared with available numerical and measurement data. It is then applied to an extreme wave loading test on a selected bridge with multiple under-deck girders. The waves are focused extreme irregular waves derived from NewWave theory and JONSWAP spectra.

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.

Leakage Flow Investigations on a Through-Wall Crack Related to Thermal Fatigue of Nuclear Power Plant Piping

2017 ◽  
Author(s):  
Stefan Schmid ◽  
Rudi Kulenovic ◽  
Eckart Laurien
Keyword(s):  
Experimental Data ◽  
Nuclear Power ◽  
Numerical Models ◽  
Measurement Techniques ◽  
Experimental Investigations ◽  
Leakage Flow ◽  
Test Rig ◽  
Reduced Pressure ◽  
Flow Rates ◽  
Set Up

For the validation of empirical models to calculate leakage flow rates in through-wall cracks of piping, reliable experimental data are essential. In this context, the Leakage Flow (LF) test rig was built up at the IKE for measurements of leakage flow rates with reduced pressure (maximum 1 MPA) and temperature (maximum 170 °C) compared to real plant conditions. The design of the test rig enables experimental investigations of through-wall cracks with different geometries and orientations by means of circular blank sheets with integrated cracks which are installed in the tubular test section of the test rig. In the paper, the experimental LF set-up and used measurement techniques are explained in detail. Furthermore, first leakage flow measurement results for one through-wall crack geometry and different imposed fluid pressures at ambient temperature conditions are presented and discussed. As an additional aspect the experimental data are used for the determination of the flow resistance of the investigated leak channel. Finally, the experimental results are compared with numerical results of WinLeck calculations to prove specifically in WinLeck implemented numerical models.

Sign in / Sign up

Export Citation Format

Share Document