Wave Impact Pressures Research Articles

Gas flow dynamics over a plunging breaking wave prior to impact on a vertical wall

We present an experimental study on the gas flow field development over a plunging breaking wave prior to impact on a vertical wall. The variability of wave impact pressure over repeated measurements is well known (Bagnold, 1939). The formation of instabilities on the wave crest are postulated to be the main source of impact pressure variability (Dias and Ghidaglia, 2018). However, the mechanism that results in wave impact pressure variability and the influence of the gas phase in particular are relatively unknown. The velocity field of the gas phase is measured with particle image velocimetry, while simultaneously the local free surface is determined with a stereo-planar laser-induced fluorescence technique. The bulk velocity between the wave crest tip and the impact wall deviates from the mass conservation estimate based on the velocity profile between the wave crest and the impact wall. This is caused by a significant increase of the local gas velocity near the wave crest tip. The non-uniformities in the seeding concentration accumulate near the wave crest tip and reduce the accuracy of the velocity measurements. However, the bulk velocity estimate is significantly improved with a fit of the velocity profile that is based on a potential flow over a bluff body. Additionally, the development of vortex is observed and quantified for two typical measurements with either a disturbance on the wave crest or a smooth wave crest. The circulation development is comparable to the formation and separation of a vortex ring, which results in a saturated vortex that separates from the wave crest (Gharib et al., 1998). Furthermore, the impact location of the wave tip is altered by the formation of secondary vortices. The secondary vortex enhances the lift locally and alters the trajectory of the wave crest tip, which may result in additional variability of the wave impact pressure.

Experimental investigations on wave impact pressures under the deck and global wave forces and moments on offshore jacket platform for partial and full green water conditions

The wave induced dynamic pressures under the deck and the global wave forces and moments on an offshore platform model were measured for three different model orientations and for partial and full green water conditions in random wave fields of different energy levels. It is found that for partial and full green water conditions, the global vertical wave force dominates when compared to horizontal wave forces. The orientation of the structure to wave direction has some effect, only for 22.5° orientation of the deck to wave direction. Shoreward maximum wave force can reach 3 times the maximum seaward wave force. For zero air gap condition, the highest value of normalized peak vertical force can reach a value of 42, which is 5 times higher than the normalized significant uplift force value. The normalized downward peak force value can reach as high as 8 for full green water condition due to the weight of overrunning water staying on the top of deck slab. For zero air gap condition, the normalized peak impact pressure under the deck can reach as high as 13.2 and 21.5 near the leading and trailing bottom side of the deck.

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

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.

Experimental study of freak wave impacts on a tension-leg platform

This study investigates the freak wave impinging on a tension-leg platform through wave flume experiments. The freak waves are generated using the focused wave theory. By adjusting the wave focusing location, different incident wave scenarios at the structure location are produced. Simultaneous measurements of wave shape evolutions upon impingement, wave impact pressures on the platform deck, platform motions and tether forces are carried out for synchronized analyses of the wave kinematics/dynamics and structural responses. The variation of these parameters with the incident wave profile is studied. It is found that although applying less intensive local impact pressures as compared to the highly-breaking freak wave, the slightly-breaking or non-breaking freak wave imposes the same level of adverse effect on the platform's global stability in terms of motions and tether forces. In addition, the high-crest freak wave causes violent motions of the floating platform, which are likely to induce snap loads of large amplitude and high occurrence frequency in tethers. The published results would provide useful benchmarks for validating numerical and analytical models.

Hydroelasticity effects on water-structure impacts

Local and global loadings, which may cause the local damage and/or global failure and collapse of offshore structures and ships, are experimentally investigated in this study. The research question is how the elasticity of the structural section affects loading during severe environmental conditions. Two different experiments were undertaken in this study to try to answer this question: (i) vertical slamming impacts of a square flat plate, which represents a plate section of the bottom or bow of a ship structure, onto water surface with zero degree deadrise angle; (ii) wave impacts on a truncated vertical wall in water, where the wall represents a plate section of a hull. The plate and wall are constructed such that they can be either rigid or elastic by virtue of a specially designed spring system. The experiments were carried out in the University of Plymouth’s COAST Laboratory. For the cases considered here, elasticity of the impact plate and/or wall has an effect on the slamming and wave impact loads. Here the slamming impact loads (both pressure and force) were considerably reduced for the elastic plate compared to the rigid one, though only at high impact velocities. The total impact force on the elastic wall was found to reduce for the high aeration, flip-through and slightly breaking wave impacts. However, the impact pressure decreased on the elastic wall only under flip-through wave impact. Due to the elasticity of the plates, the impulse of the first positive phase of pressure and force decreases significantly for the vertical slamming impact tests. This significant effect of hydroelasticity is also found for the total force impulse on the vertical wall under wave impacts.Graphic abstractHydroelasticity effects on water-structure impacts: a impact pressures on dropped plates; b impact forces on dropped plates; c, d, e, f wave impact pressures on the vertical walls; g wave impact forces on the vertical walls; h wave force impulses on the vertical walls: elastic wall 1 vs. rigid wall (filled markers); elastic wall 2 vs. rigid wall (empty markers)

Continuous Measurement and Automatic Processing of In-situ Wave Impact Pressure Data

d'Amico, D.; Larroque, B.; Luthon, F.; Poncet, P.A., and Abadie, S., 2020. Continuous measurement and automatic processing of in-situ wave impact pressure data. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 214-219. Coconut Creek (Florida), ISSN 0749-0208.Although wave impact has been extensively studied in laboratories, field studies are comparatively rare. However, as real wave impacts are influenced by numerous environmental factors, complementing physical studies with in-situ data is necessary to better understand the processes at stake and provide reliable tools for coastal engineers. One of the main reasons for the lack of field data is the extreme conditions usually met on site. Nowadays, technology allows to set up stations able to resist those conditions and record data over long periods. In this context, the so-called Artha breakwater, in the French Basque coast, was equipped with an in-situ laboratory to record wave impact pressures. This station enables to collect long term wave impact pressure data therefore covering any weather conditions. In the present paper, the use of computer engineering based methods to process the large amount of wave impact data is described. It involves signal pre-processing, impact automatic segmentation, automatic computation of impact parameters, and artificial intelligence to classify the impacts. Impact automatic segmentation allows to have a big database of impacts available. This database has been used to make a first classification of the strongest impacts. The classification was performed thanks to the parameters automatically computed for each impact. As preliminary results for the classification, several wave impact pressure classes have been established. The approach is encouraging since the obtained results can be compared with the existing laboratory classification. However, the results can still be improved by computing other impact parameters and considering all impacts.

Experimental study of vertical wave-in-deck force and pressure on a thin plate due to regular and focused waves

Offshore platforms and ocean structures endure wave impact loads due to transient steep waves, including wave breaking events during their design life. The present study aims to understand the nature of the impact pressure and vertical wave-in-deck impact force on a horizontal deck under the action of the regular and breaking waves through experimental investigations. The model details, wave simulation, vertical wave-in-deck load, and pressure variation along the wave direction on a thin plate are presented in the present paper. The maximum breaking wave impact pressure on the plate increases with the air gap up to about one-eighth of the maximum wave height and further decreases with an increase in the air gap.

Blast resistance of steel plate shear walls designed for seismic loading

Since a blast loading or explosion can create nonlinear wave action and impact pressure on a structure, it necessary to construct a structure to resist blast loading as like other loads. In this study the nonlinear behaviour of a blast loading is simulated by calculating the pressure diagram with respect to time under the guidance of IS 4991 – 1968, code for “Criteria for Blast Resistant Design of Structures for Explosions above Ground”. The study carried out for different charge weight (100kg TNT, 200kg TNT and 400kg TNT) and standoff distances of 20metre. Nonlinear behaviour of a Blast loading to steel structures with shear plates of thickness 6 mm, 8 mm and 10 mm are modelled in ETABS and the analysis is carried out to obtain base shear, story displacement, story deformation pattern, column forces, etc.

MPS-FEM Coupled Method for Study of Wave-Structure Interaction

Nowadays, an increasing number of ships and marine structures are manufactured and inevitably operated in rough sea. As a result, some phenomena related to the violent fluid-elastic structure interactions (e.g., hydrodynamic slamming on marine vessels, tsunami impact on onshore structures, and sloshing in liquid containers) have aroused huge challenges to ocean engineering fields. In this paper, the moving particle semi-implicit (MPS) method and finite element method (FEM) coupled method is proposed for use in numerical investigations of the interaction between a regular wave and a horizontal suspended structure. The fluid domain calculated by the MPS method is dispersed into fluid particles, and the structure domain solved by the FEM method is dispersed into beam elements. The generation of the 2D regular wave is firstly conducted, and convergence verification is performed to determine appropriate particle spacing for the simulation. Next, the regular wave interacting with a rigid structure is initially performed and verified through the comparison with the laboratory experiments. By verification, the MPS-FEM coupled method can be applied to fluid-structure interaction (FSI) problems with waves. On this basis, taking the flexibility of structure into consideration, the elastic dynamic response of the structure subjected to the wave slamming is investigated, including the evolutions of the free surface, the variation of the wave impact pressures, the velocity distribution, and the structural deformation response. By comparison with the rigid case, the effects of the structural flexibility on wave-elastic structure interaction can be obtained.

Pressures induced by regular waves on a large scale OWC

The traditional function of coastal structures is the protection of the land from the sea. Such a function has been often carried out by breakwaters which dissipate part of the incident wave energy.Recently, the ongoing climate changes and their related issues have moved the attention toward new kinds of coastal structures which can protect the land and human activities and at the same time harvest part of the available wave energy. Such an energy source is alternative to non renewable ones like oil and gas, it is covered by the incentives of the renewable energy sector and it is subjected to an increasing interest of the international community.In such a framework, the present challenge of the coastal engineering is to design hybrid Wave Energy Coverters (WECs) which are: (i) effective in protecting the land, (ii) efficient in extracting wave energy, (iii) economically competitive with the conventional structures, (iv) structurally reliable.In comparison to other WECs, the Oscillating Water Column (OWC) breakwaters are considered among the most promising, therefore it is needed to investigate their design characteristics appropriately. Indeed, the durability of hybrid OWC breakwaters is strongly related to their response to wave action. In particular, the most critical point is the front lip, which is subjected to external wave impact and internal pressures within the chamber, at the same time.The complexity of wave-OWC interactions is studied here by means of a large scale physical model, which has been tested under regular wave conditions. The Power Take Off (PTO) characteristics are replaced here by a circular orifice, whose section has been varied. Such variations of the orifice section cause different types of response of the air inside the pneumatic chamber to external wave forcing.The response of the device under regular waves has been monitored by means of wave gauges and pressure sensors located both at the OWC and along the flume. First, the time evolution of the air pressure signal is analyzed. This is strongly affected by the air compressibility which is the key parameter in this analysis, since it controls the air-water interaction and it influences the whole OWC dynamics.The spectral analyses of the signals of pressure and free surface elevation provide insights on the relationship between water column oscillations and pressures inside and outside the chamber, in terms of both amplitudes and phase lags. It is found that the relation between inner and outer pressures is shown to be related to the resonance coefficient, which is a function of the lag between the flow across the OWC and the forcing outer pressure.

An experimental and numerical study of plunging wave impact on a box-shape structure

The plunging wave impacts on a box-shape structure are investigated experimentally and numerically, focusing on three typical scenarios with distinct features, i.e. the wave impact occurs after, upon and before wave breaking. In the experiments, the plunging wave is generated by a piston-type wave maker whose motion is governed by the focused wave theory. The fixed box-shape structure mimics the offshore platform structures. Measured are the wave elevations at typical positions, the wave impact pressures on the front and bottom (violent impact is very likely to occur) of the platform, and the wave profiles of the transient wave impact process. The experiment identifies the pressure maximums both on the front and bottom walls under three different wave impacts. The pressure oscillation along the front wall is observed and analyzed by examining the evolution of air cavity. The experimental parameters and dimensions including the actual wave maker motion signal were inputted into the numerical model to reproduce the same case. Numerical simulations using an improved immersed boundary method are compared with the experimental results with roughly good agreements being achieved. Besides, numerical pressure distributions along the front and bottom walls are presented to find different modes of wave impact. Finally, the maximal pressures on the front wall of the box-shape structure are normalized by two approaches and compared with the documented maximal pressure ranges.

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

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.

Wave impact pressure and kinematics due to breaking wave impingement on a monopile

Breaking wave impact on a vertical cylinder in shallow waters is investigated numerically with the two-phase flow computational fluid dynamics model REEF3D. The model is based on the incompressible Reynolds-Averaged Navier-Stokes (RANS) equations together with the level set method (LSM) and k−ω turbulence model. The spatial and time development of the maximum wave impact pressure and the associated velocity components are examined. Further, the breaking wave characteristics and geometric properties are evaluated with two-dimensional simulations. Comparisons of numerical results and experimental data indicate good agreement for free surface elevations and the characteristics at breaking and the breaking wave forces. A total of 9 two-dimensional and 27 three-dimensional simulations are performed to investigate the influence of the incident wave characteristics, wave impact conditions and breaker types on the maximum wave impact pressure and kinematics. The factors influencing the spatial and temporal variability of the vertical distribution for the maximum impact pressure and kinematics are investigated. Three impact conditions are considered in this study: (1) the wave with a vertical front breaks at the cylinder, (2) the broken wave hits the cylinder with a moderately developed overturning wave crest, and (3) the broken wave impacts the cylinder with a fully developed overturning wave crest. Further, the vertical and longitudinal variations of the maximum impact pressure during the breaking wave impact on the monopile are assessed. The numerically simulated free surface deformations during the wave impact are also presented and discussed. Finally, the total breaking wave force and the maximum impact pressure are analyzed for spilling and plunging breakers under different wave impact conditions.

Numerical modelling of tsunami bore impact on low-rise residential buildings using SPH

The resilience of buildings subject to tsunami bore impact can be improved by reducing tsunami-induced lateral hydrodynamic pressure by allowing part of the tsunami bore to pass through the buildings via openings and break-away walls. This research investigated the reduction of lateral pressure caused by tsunami bore impact on a low-rise residential building with openings proposed as the prototype of tsunami-resistant house. Numerical method using smoothed particle hydrodynamic (SPH)- based software called DualSPHysics was used to create simulation in numerical boundary in the form of a water tank. The tsunami-like bore simulations were generated based on dam-break analogy and were validated against experimental results. Four simulation cases were conducted in this study: Case 1 and Case 2 were dealing with the parameter sensitivity of reservoir height and distance between reservoir and building, while Case 3 and Case 4 were related to the effectiveness of openings and the base elevation of building in reducing wave impact pressures. The numerical modelling results show that the presence of openings and building’s base elevation significantly reduced the lateral hydrodynamic pressures on buildings up to 50% and this could become an effective strategy for improving the resilience of low-rise residential buildings under tsunami bore impact.

Effect of Venting Holes to Relieve Wave Impact Pressures on Flood Gates with Overhangs

Flood gates in storm surge barriers or outlet sluices can be prone to violent wave impacts. When an obstruction is present at the sea side above the gate, confinement of the incoming waves can lead to impulsive wave loads, even when the waves are non-breaking. The large loads can increase the stresses in the gate and structure considerably. One of the measures that is often discussed to relieve the pressures of these impacts is to apply small openings in the gates. In this paper the potential effect of these venting holes on the wave impact loads is determined. The decrease in impact pressure impulse is determined for a range of venting hole geometries is determined by numerical 2D and 3D solutions of a schematized wave impact. In this model the pressure impulse P (integral of the local pressure over the small impact duration) is determined directly by the so-called pressure impulse theory. The potential decrease in pressure impulse due to wave impacts is presented. Moreover, some initial CFD modelling is applied, and the applicability of the pressure impulse theory is discussed.

Wave Impact Pressures on Stepped Revetments

The wave impacts on horizontal and vertical step fronts of stepped revetments is investigated by means of hydraulic model tests conducted with wave spectra in a wave flume. Wave impacts on revetments with relative step heights of 0.3 < Hm0/Sh < 3.5 and a constant slope of 1:2 are analyzed with respect to (1) the probability distribution of the impacts, (2) the time evolution of impacts including a classification of load cases, and (3) a special distribution of the position of the maximum impact. The validity of the approved log-normal probability distribution for the largest wave impacts is experimentally verified for stepped revetments. The wave impact properties for stepped revetments are compared with those of vertical seawalls, showing that their impact rising times are within the same range. The impact duration for stepped revetments is shorter and decreases with increasing step height. Maximum horizontal wave impact loads are about two times larger than the corresponding maximum vertical wave impact loads. Horizontal and vertical impact loads increase with a decreasing step height. Data are compared with findings from literature for stepped revetments and vertical walls. A prediction formula is provided to calculate the maximum horizontal wave impact at stepped revetments along its vertical axis.

In-situ Measurements of Wave Impact Pressure on a Composite Breakwater: Preliminary Results

Larroque, B.; Arnould P.; Luthon F.; Poncet, P.A.; Rahali, A., and Abadie, S., 2018. In-situ measurements of wave impact pressure on a composite breakwater: preliminary results. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1086–1090. Coconut Creek (Florida), ISSN 0749-0208.A detached horizontally composite breakwater protecting the Saint Jean de Luz bay (French Basque Coast, Bay of Biscay, France) has been equipped with two pressure sensors displayed vertically onto the vertical wall. The two sensors recorded wave impact pressure in ten minute burst each hour at 10 kHz. In parallel, incoming waves were also recorded about 1 km off the structure with a directional wave buoy giving access to spectral wave parameters as well as raw data. Finally water level, wind magnitude and direction were also acquired. The whole dataset covers winter 2015–2016 from January to March.The results show first the statistical distribution of the measured parameters confirming preceding similar studies in which significantly lower impact pressure values were obtained compared to physical experiments or numerical simulations. A linear multivariate model has then been adjusted showing the overwhelming influence of wave heights to explain maximum pressure variability, followed by water level. Nevertheless this result has still to be confirmed for data reduced to impulsive impacts. Finally, interesting events supposedly corresponding to, or approaching flip-through impact type, have been identified and need further investigations.

Embedded Sensors in Coastal Structures for On-Site Wave Impact Pressure Monitoring

The climate change induces heavy storms that impact coastal environments. In order to predict such events or to adapt coastal structures in the future, it is desirable to be able to monitor the action of waves. Thanks to new technologies, one can embed sensors on dykes and have access remotely and continuously to field data measurements. In this paper, an in situ system, installed in September 2014, to measure the wave impact pressure is described. Additionally, the preliminary results of data processing are given.

Shared-Memory parallelization of consistent particle method for violent wave impact problems

A shared-memory parallelization is implemented to the recently developed Consistent Particle. Method (CPM) for violent wave impact problems. The advantages of this relatively new particle method lie in four key aspects: (1) accurate computation of Laplacian and gradient operators based on Taylor series expansion, alleviating spurious pressure fluctuation and being able to model two-phase flows characterized by large density difference, (2) a thermodynamics-based compressible solver for modelling compressible air that eliminates the need of determining artificial sound speed, (3) seamless coupling of the compressible air solver and incompressible water solver, and (4) parallelization of the numerical model based on Open Multi-Processing (OpenMP) and a parallel direct sparse solver (Pardiso) to significantly improve computational efficiency. Strong and weak scaling analyses of the parallelized CPM are conducted, showing an efficiency speedup of 100 times or more depending on the size of simulated problem. To demonstrate the accuracy of the developed numerical model, three numerical examples are studied including the benchmark study of wave impact on seawall, and our experimental studies of violent water sloshing under rotational excitations and sloshing impact with entrapped air pocket. CPM is shown to accurately capture highly deformed breaking waves and violent wave impact pressure including pressure oscillation induced by air cushion effect.

Development of a Shipboard Remote Control and Telemetry Experimental System for Large-Scale Model's Motions and Loads Measurement in Realistic Sea Waves.

Wave-induced motion and load responses are important criteria for ship performance evaluation. Physical experiments have long been an indispensable tool in the predictions of ship’s navigation state, speed, motions, accelerations, sectional loads and wave impact pressure. Currently, majority of the experiments are conducted in laboratory tank environment, where the wave environments are different from the realistic sea waves. In this paper, a laboratory tank testing system for ship motions and loads measurement is reviewed and reported first. Then, a novel large-scale model measurement technique is developed based on the laboratory testing foundations to obtain accurate motion and load responses of ships in realistic sea conditions. For this purpose, a suite of advanced remote control and telemetry experimental system was developed in-house to allow for the implementation of large-scale model seakeeping measurement at sea. The experimental system includes a series of technique sensors, e.g., the Global Position System/Inertial Navigation System (GPS/INS) module, course top, optical fiber sensors, strain gauges, pressure sensors and accelerometers. The developed measurement system was tested by field experiments in coastal seas, which indicates that the proposed large-scale model testing scheme is capable and feasible. Meaningful data including ocean environment parameters, ship navigation state, motions and loads were obtained through the sea trial campaign.