Wave Impact Forces Research Articles

A quasi-three-phase flow simulation of the interactions between solitary waves and a vertical seawall installed on a sandy beach

Local scour and wave loading are two key factors that affect the safety of seawalls under tsunami attacks. In this study, the scouring process at the toe of and wave impact force on a vertical seawall under consecutive solitary wave attacks are simulated using a quasi-three-phase (air, water, and sediment) flow model, which models the air and water as a fluid mixture phase and sediment as a solid phase. The air and water interface is modeled by a VOF method and the sediment–fluid interaction is modeled using the Eulerian two-phase flow method. A comparison between the beach profiles with and without the seawall shows that, with a seawall, a deeper scour hole is generated at the toe of the seawall. Besides, the presence of the seawall causes the eroded sediment to be deposited further offshore. The numerical results are then analyzed in detail regarding the flow field and sediment transport process to reveal the mechanisms of the above eroding/depositing patterns. The wave impact force on the seawall is also analyzed to understand the effect of scouring on the wave loading. It is shown that the wave impact force, despite being stochastic for a specific wave, increases in general with the deepening of the scour hole because the latter increases the exposure of the seawall to wave slamming.

Investigation into the relationship between wave forces and characteristic velocity during wave impact on the deck structures

Deck structures, whose safety is threatened by catastrophic waves, are widely used in offshore and coastal engineering. This study aims to enhance the understanding of the impact of waves on deck structures through a combined approach of hydrodynamic experimentation and numerical simulations. In this study, the wave impact forces and pressure on a deck structure, which was simplified as a rectangular box model, were experimentally measured. The numerical model based on smoothed particle hydrodynamics was validated using experimental data due to its capacity to compute the wave force exerted on the box structure accurately. A characteristic velocity parameter was defined to explore the relationship between the wave-slamming forces and the wave velocity field. It was found that the characteristic velocity was highly correlated with the wave impact forces, which could be fitted using a negative exponential curve. In addition, the characteristic velocity can be roughly calculated using Stokes’ second wave theory, which offers a preliminary method for estimating wave impact loads on deck structures.

3D SPH analysis of focused waves interacting with a floating structure

In recent years, the number of offshore floating structures has been growing and is expected to continue growing. Due to climate change, the frequency and severity of extreme waves are increasing. Numerical models can be a strategic tool in the reliable design and optimization of marine structures. However, the number of numerical parameters to be tuned plays a crucial role, as they could limit the model’s applicability and reliability. Furthermore, there are many challenges in modelling wave-structure interaction. Among these challenges, the simulation of one-dimensional tethers is of great concern when dealing with moored floating structures. In this study, a 3D numerical model is developed based on the Smoothed Particle Hydrodynamics (SPH) technique. This hydrodynamic model is coupled with a multi-body solver for the dynamic analysis of moorings and structures. In a three-dimensional numerical flume, focused ocean waves are generated with a piston-type wave-maker and propagated until impact with the floating structure. The developed model predicts the wave profile, impact forces, and structural dynamics, and is validated by comparing numerical results against experimental data.

Wave-impact forces and moments due to random waves on a jacket-type platform for different relative submergence of the deck

Force and moment measurements due to wave impacts were conducted on a jacket platform model under six distinct relative deck submergence conditions. The water depth was carefully chosen to facilitate scenarios ranging from sufficient deck air gaps to partial and complete submergence. For the purpose of our analysis, we focused on peak and average peak wave force and moment values. The study uncovers that the peak wave force towards the shore can escalate to 1.5 times the peak wave force towards the sea. Moreover, the ratio of the peak shoreward force to the average peak shoreward force fluctuates between 3 and 4, contingent upon the relative water level at the deck base and the prevailing wave condition. Remarkably, the peak upward wave force on the deck can reach 5 to 7 times the peak inline wave force. A review of existing guidelines suggests a significant need to enhance research regarding the air gap between the deck and the still water level (SWL), as well as its effect on global and local wave forces and moments on the structures. Our finding establishes that the relative water level from the base of the deck is a crucial parameter in the design process of these structures. This study presents a more in-depth understanding of the physical mechanisms at play by utilizing a realistic jacket platform model. It serves as an initial exploration into the influence of air gap and relative water depth on wave-impact forces and moments. The results obtained from this study shed light on optimal design strategies for jacket-type offshore drilling platforms, considering green water effects. This understanding will enhance the life expectancy and survivability of such platforms.

Required test durations for converged short-term wave and impact extreme value statistics–Part 2: Deck box dataset

In the assessment of wave-in-deck loads for new and existing maritime structures typically model tests are carried out. To determine the most critical conditions and measure sufficient impact loads, a range of sea states and various seeds (realisations) for each sea state are tested. Based on these measurements, probability distributions can be derived and design loads determined. In air gap model testing usually only few, if any, impact loads occur per 3-hour seed. This can make it challenging to derive reliable probability distributions of the measured loads, especially when only a few seeds are generated. In addition wave impact forces, such as greenwater loading, slamming, or air gap impacts are typically strongly non-linear, resulting in a large variability of the measured loads. This results in the following questions: How many impacts are needed to derive a reliable distribution? How is the repeatability of individual events affecting the overall distribution? To answer these questions wave-in-deck model tests were carried out in 100 x 3-hour realisations of a 10,000 year North Sea sea state. The resulting probability distributions of the undisturbed wave measurements as well as the measured wave-in-deck loads are presented in this paper with focus on deriving the number of seeds and exposure durations required for a reliable estimate of design loads.The presented study is Part 2 of a combined study on guidance for the convergence and variability of wave crests and impact loading extreme values. The data set of Part 1 ([1]) is based on greenwater loads on a sailing ferry and the data set of Part 2 on wave-in-deck loads on a stationary deck box.

Required test durations for converged short-term wave and impact extreme value statistics — Part 1: Ferry dataset

For the design of maritime structures in waves, the extreme values of responses such as motions and wave impact loads are required. Waves and wave-induced responses are stochastic, so such responses should always be related to a probability. This information is not easy to obtain for strongly non-linear responses such as wave impact forces. Usually class rules or direct assessment via experiments or numerical simulations are applied to obtain extreme values for design. This brings up questions related to the convergence of extreme values: how long do we need to test in order to obtain converged statistics for the target duration? Or, vice versa: given testing data, what is the uncertainty of the associated statistics? Often the test or simulation duration is cut up in ‘seeds’ or ‘realisations’, with an exposure duration of one or three hours based on the typical duration of a steady environmental condition at sea, or the time that a ship sails a single course. The required number of seeds for converged results depends on the type of structure and response, the exposure duration, and the desired probability level. The present study provides guidelines for the convergence of most probable maximum (MPM) wave crest heights and MPM green water wave impact forces on a ferry. Long duration experiments were done to gain insight into the required number of seeds, and the effect of fitting. The present paper presents part 1 of this study; part 2 [1] presents similar results for wave-in-deck loads on a stationary deck box.

Vessel Wake Impact Forces on Marsh Scarps

Priestas, A.M.; Styles, R., and Bain, R., 2023. Vessel wake impact forces on marsh scarps. Journal of Coastal Research, 39(2), 207–220. Charlotte (North Carolina), ISSN 0749-0208. A common morphological feature of high-energy coastal plain salt marshes is an erosive scarp separating the marsh platform from the abutting tidal flat. A noted deficiency in the understanding of scarp erosion is a lack of direct wave impact measurements to better constrain the physical processes driving material loss. To measure wave impact forces, load cells were embedded into a scarp face along the Intracoastal Waterway in northern Florida, which is frequented by shallow-draft vessels. The largest impact forces occurred when the mean water surface elevation was just below the midpoint of the scarp and decayed as the mean depth either increased or decreased. Early wave breaking around low tide reduced the direct impact on the scarp, whereas wave reflection around high tide reduced wave breaking and the associated maximum impact force. The sensitivity of impact force to tidal stage suggests that wave energetics (breaking vs. reflection) and scarp morphology (ramp vs. near-vertical surface) combine to produce a force pattern that favors maximum impact around midtide. Regression analysis indicated that the impact pressures were positively correlated with wave power and dynamic pressure, which are primary metrics used to model shoreline erosion. This study argues that the critical threshold for erosion may be refined by evaluating the relationship between impact pressures and marsh resistance, since wave exposure alone does not necessarily initiate erosion.

Digital Filter Design for Force Signals from Eulerian–Lagrangian Analyses of Wave Impact on Bridges

Finite element (FE) models that simulate wave–superstructure interactions with the coupled Eulerian–Lagrangian (CEL) technique provide a viable and economical solution to estimate wave impact forces on bridge superstructures. One of the main drawbacks of CEL FE models is that they produce solutions distorted by numerical artifacts with very high frequencies that make it difficult to quantify the magnitude of hydrodynamic forces on superstructures. This paper investigated digital filter parameters for horizontal forces extracted from CEL FE models. The optimal filter configuration was evaluated by comparing unfiltered and filtered horizontal force signals with experimentally measured values from a reduced-scale superstructure specimen tested at the O.H. Hinsdale Wave Research Laboratory at Oregon State University. It was found that digital filters with cutoff frequencies below the fundamental frequency of the superstructure produced the best results and that optimizing Eulerian–Lagrangian surface interactions significantly improved the quality of the calculated force signals.

Extratropical cyclone damage to the seawall in Dawlish, UK: eyewitness accounts, sea level analysis and numerical modelling

The February 2014 extratropical cyclonic storm chain, which impacted the English Channel (UK) and Dawlish in particular, caused significant damage to the main railway connecting the south-west region to the rest of the UK. The incident caused the line to be closed for two months, £50 million of damage and an estimated £1.2bn of economic loss. In this study, we collate eyewitness accounts, analyse sea level data and conduct numerical modelling in order to decipher the destructive forces of the storm. Our analysis reveals that the disaster management of the event was successful and efficient with immediate actions taken to save lives and property before and during the storm. Wave buoy analysis showed that a complex triple peak sea state with periods at 4–8, 8–12 and 20–25 s was present, while tide gauge records indicated that significant surge of up to 0.8 m and wave components of up to 1.5 m amplitude combined as likely contributing factors in the event. Significant impulsive wave force of up to 286 KN was the most likely initiating cause of the damage. Reflections off the vertical wall caused constructive interference of the wave amplitudes that led to increased wave height and significant overtopping of up to 16.1 m3/s/m (per metre width of wall). With this information and our engineering judgement, we conclude that the most probable sequence of multi-hazard cascading failure during this incident was: wave impact force leading to masonry failure, loss of infill and failure of the structure following successive tides.

Numerical investigation of wave run-up and impact forces on large offshore jacket platforms

This paper focuses on wave interactions with large deep-sea jacket platforms. A numerical wave tank is designed and developed to simulate the wave-structure interactions, and the accuracy and precision of this numerical wave tank are verified by the theoretical values and LWI experimental tests. Then the processes of wave run-up along with the legs and impact the lower deck of a large deep-sea jacket platform located at the South China Sea are simulated, analyzed, and discussed. The results show that the greater the wave steepness, the stronger the wave run-up ability. The wave run-up processes are mainly concentrated within a radius R around the legs, and the maximum wave run-up ratio reaches 1.56 on the front side of leg 1 when the wave steepness is 0.03. Due to the interference, reflection, and superposition effects, all the legs show different wave run-up characteristics, and additional high-frequency side wave peaks are observed around the legs, which are mainly focused on 0–0.6 Hz in the frequency domain. With the increase of wave steepness λ, the wave drag forces increase significantly during the wave run-up processes. Especially, when the waves impact the lower deck under case 3, it will cause huge vertical wave impact loads, and the maximum value reaches 46.59 MPa, which will cause further attenuation to the vertical and lateral resistance of the jacket platform.

Numerical investigation of wave impact forces on coastal deck structures with girders along the West Coast of India in changing climate

ABSTRACT Coastal structural damage has been a serious issue in the past decades due to changes in various ocean environmental parameters and increased frequency of extreme events. The present study focuses on the estimation of wave impact forces on typical deck structures at Indian port locations in a changing climate scenario. The effect of climate change has been investigated by applying the future ocean climate characteristics, such as future wave height conditions and sea-level rise by the year 2100 using RCP 4.5 scenario obtained from the recent studies. The numerical investigations were carried out by generating solitary waves in a numerical wave tank modelled using an open-source CFD model REEF3D. Comparison of peak wave impact force and pressure distribution due to climate change on a model and prototype deck structure in the elevated condition is carried out to investigate the scale effects. Overall, the study concluded that there is a significant change in both vertical and horizontal forces on coastal deck structures due to climate change, where the percentage change varies with varying airgaps and geographical locations. Investigation on prototype scale deck shows that the model scale overestimates the positive horizontal impact force to a larger extent than the vertical impact force.

A Study on the Calculation Method of Wave Crest Height and Panel Wave Force of a New Barrel-Pile Foundation Composite Structure Wharf

Due to the depletion of near-shore resources and the complex environment of offshore deep-water open port construction, a new barrel-pile foundation composite structure wharf is proposed. In order to provide technical support for the engineering design and application of the new structure, research is carried out on a physical model. Through setting up a series of group tests, on the basis of fully understanding the wave impact characteristics of the wharf panel of the new structure: (1) the relationship between the wave crest height, impact force, and various influence factors is established; (2) a calculation method and formula are put forward (compared with the physical model test data, the calculation formula results have good accuracy); (3) according to the formulas of wave crest height and panel impact force, a determination method for the wharf surface elevation of the new structure is given. In addition, due to the limitations of the test conditions, it is suggested that the physical model should be further verified for a complex transverse and longitudinal beam structure or extreme sea conditions, such as traveling wave breaking and wave inundation of the wharf.

Wave Impact Loads on Vertical Seawalls: Effects of the Geometrical Properties of Recurve Retrofitting

This study investigates the variation of wave impact loads with the geometrical configurations of recurve retrofits mounted on the crest of a vertical seawall. Physical model tests were undertaken in a wave flume at the University of Warwick to investigate the effects of the geometrical properties of recurve on the pressure distribution, overall force, and overturning moment at the seawall, subject to both impulsive and non-impulsive waves. Additionally, the wave impact and quasi-static loads on the recurve portion of the retrofitted seawalls are investigated to understand the role of retrofitting on the structural integrity of the vertical seawall. Detailed analysis of laboratory measurements is conducted to understand the effects of overhang length and height of the recurve wall on the wave loading. It is found that the increase in both recurve height and overhang length lead to the increase of horizontal impact force at an average ratio of 1.15 and 1.1 times larger the reference case of a plain vertical wall for the tested configurations. The results also show that the geometrical shape changes in recurve retrofits, increasing the overturning moment enacted by the wave impact force. A relatively significant increase in wave loading (both impact and quasi-static loads) are observed for the higher recurve retrofits, while changes in the overturning moment are limited for the retrofits with longer overhang length. The data generated from the physical modelling measurements presented in this study will be particularly helpful for a range of relevant stakeholders, including coastal engineers, infrastructure designers, and the local authorities in coastal regions. The results of this study can also enable scientists to design and develop robust decision support tools to evaluate the performance of vertical seawalls with recurve retrofitting.

Verification and Validation of Transient Body Force in GOTHIC for Spent Fuel Pool Response to Seismic Events and Other Applications

Post Fukushima the U.S. Nuclear Regulatory Commission issued an Order on Spent Fuel Instrumentation (EA-12-051) requiring all U.S. nuclear plants to install spent fuel pool (SFP) water level monitoring instrumentation and ensure the instrument would remain functional following a safe shutdown earthquake (SSE). The structural integrity analysis requires an assessment of the hydrodynamic loads and wave impact forces that the instrument is subjected to during an SSE. Modeling and simulation of the SFP response to an SSE can provide this type of information if the simulation tool is able to capture the important physical phenomena, such as seismic acceleration, surface wave formation, fluid velocities, and multidimensional effects. This paper describes the capabilities of GOTHICTM that can be used to simulate the sloshing surface waves and subsurface fluid motion of an SFP in response to an earthquake. GOTHIC is a versatile, general-purpose, thermal-hydraulic software package for multiphase flow that is a hybrid between traditional system thermal-hydraulic and computational fluid dynamics codes. It includes a transient, variable body force capability to simulate multi-axis acceleration, and is therefore applicable to seismic events; movement experienced on ships, airplanes, or spacecraft; and other events with system acceleration. Also, since the gravitational constant can be adjusted, GOTHIC can model systems placed outside the Earth’s atmosphere (e.g., spacecraft, space station, the Moon, or other extraterrestrial bodies). The variable body force capability makes GOTHIC well suited to model the hydrodynamic response of an SFP to a seismic event. This paper describes the governing equations that are solved by GOTHIC as they pertain to accelerating systems. A series of benchmarks covering a range of experiments for surface wave dynamics, acceleration-induced motion, and other important phenomena are presented to demonstrate the verification and validation of GOTHIC for these types of applications. Finally, results from a sample application of GOTHIC for SFP hydrodynamic response are presented that provide the necessary inputs for a structural integrity analysis.

Three Dimensional Cellular Automata Sand Castle construction Model Based on Step Factor

It seems that everyone has the experience of making sandcastles on the leisure beach. In order to know how to build a beautiful and sturdy beach castle, this article simulates and analyzes the process of sand castles being eroded by water, and obtains some factors that extend the life of sand castles. First, we model the waves. Simplify the waves into a sine wave. Using calculus and fluid mechanics, the water wave impact force on a particle on the sand castle was calculated. Second, we model the sandcastle. Discretizing time, space, and state, we innovatively introduce the concepts of friction and impact into the model, and propose a new Three-dimensional Cellular Automaton model combined with step factors. We consider each gravel or water molecule as a cell, and simultaneously introduce the moving probability and collision probability to describe the moving trend and collision between the gravel cells, respectively. In order to effectively describe the loss of sand castles in the waves, the gravel cells that are in direct contact with the water cells will receive an impact force calculated by the first model. According to the law of large numbers, we use enough cells to simulate the erosion of sandcastles by the waves. It was found that within a certain range, the farther from the ocean and the more the total gravel, the stronger the anti-erosion ability of the sand castle.

Rocking of offshore lighthouses under extreme wave impacts: Limit analysis, analytic formulations and distinct element method

This study describes the structural response of historic lighthouses to extreme wave impacts. Located offshore on exposed rocks, 19th Century lighthouses were built with large interlocked granite blocks and have survived weathering for nearly two centuries. Under extreme wave impacts, lighthouses of this structural typology may uplift and rock, whereas sliding is prevented by the vertical interlocking. The uplift and sliding thresholds calculated with the limit analysis method reveal why this structural system is capable of bearing extreme wave impacts without failure. The ingenious vertical keying is proven to be a major characteristic that contributes to the resilience of these lighthouses. The structural response is explained with the use of analytic formulations of the rocking motion. Detailed analysis of the response to wave impact is conducted with reference to Wolf Rock lighthouse. The impact wave corresponding to a 250-year effective return period is identified using non-stationary Bayesian extreme analysis. Moreover, wave flume tests on a scaled cylindrical structure were performed to identify the wave impact force time-history shapes. Based on two waves: a theoretical time-history based on existing models in the literature and the measured time-histories from small-scale experiments, a series of synthetic force time-history sequences are generated for the purposes of a parametric analysis. This parametric analysis, with the Distinct Element Method, using the commercial software 3DEC, reveals the influence of the duration and shape of the force time-history function. For impacts with the same impulse values, shorter time impacts produce the most intense opening of joints, despite causing smaller horizontal displacements. Furthermore, variability in the structural response is revealed even for impacts of the same impulse, duration and maximum force but different shape of the force time-history.

Wave-in-deck experiments with focussed waves into a solid deck

This paper examines impact forces resulting from wave-in-deck processes from two separate series of experiments: one with a generic solid deck model, and the other with a combined jacket and deck model, both were conducted with and without an I-beam grillage in-place below the solid deck. A range of inundation levels from 2.1 to 7.1 cm at 1:80 scale is considered. The focus is on global impact forces, which are considered more relevant for integrity assessment of overall bottom-founded structures when survivability is in question and local slamming is not addressed. The objective is to characterise the resultant impact forces as well as to investigate whether there is any interaction between the flows through the jacket and hitting the deck. Focussed wave groups were generated to impinge on the models which were suspended from a carriage over a towing tank. The motion of the support carriage mimics uniform current in-line with the incident waves. Both undisturbed surface elevations as well as impact force time histories were measured. From the first series of tests, a large increase in peak forces as well as high frequency oscillations (force spikes) is observed with the grillage in-place. As soon as the jacket model is in-place for the second series of tests, albeit with a different mounting support arrangement, such a large difference vanishes, which could likely be due to the effect of frequency-dependent transfer functions. We provide experimental evidence of the presence of the jacket in modifying the wave impact on the deck through a significant reduction in the total horizontal impulse. The effects of current on the wave impact forces are also investigated. A simple analytical model based on a momentum argument is used to describe the scaling of horizontal peak force with currents and inundation levels. Finally, the importance of the short duration force spikes as well as vertical impact loads on a real structure at full-scale is discussed based on the same analytical model.

Reduction of Wave Overtopping and Force Impact at Harbor Quays Due to Very Oblique Waves

Physical model experiments were conducted in a wave tank at Flanders Hydraulics Research, Antwerp, Belgium, to characterize the wave overtopping and impact force on vertical quay walls and sloping sea dike (1:2.5) under very oblique wave attack (angle between 45° and 80°). This study was triggered by the scarce scientific literature on the overtopping and force reduction due to very oblique waves since large reduction is expected for both when compared with the perpendicular wave attack. The study aimed to compare the results from the experimental tests with formulas derived from previous experiments and applicable to a Belgian harbor generic case. The influence of storm return walls and crest berm width on top of the dikes has been analyzed in combination with the wave obliqueness. The results indicate significant reduction of the overtopping due to very oblique waves and new reduction coefficients were proposed. When compared with formulas from previous studies the proposed coefficients indicate the best fit for the overtopping reduction. Position of the storm return wall respect to the quay edge rather than its height was found to be more important for preventing wave induced overtopping. The force reduction is up to approximately 50% for the oblique waves with respect to the perpendicular wave impact and reduction coefficients were proposed for two different configurations a sea dike and vertical quay wall, respectively.

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)

Numerical investigation of monochromatic wave interaction with a vertical seawall located on a reef flat

Existing design codes for coastal defense structures built on coral reefs are scarce compared to those for traditional sandy or muddy beaches. A three-dimensional numerical wave flume is developed to investigate monochromatic wave interaction with a vertical seawall located on the reef flat. The Navier-Stokes equations for two-phase incompressible flow, combining with methods of Large Eddy Simulation (LES) for turbulence closure and Volume of Fluid (VOF) for tracking the free surface, are solved. A set of large-scale laboratory experiments are performed to validate the adopted model in terms of free surface, velocity, dynamic pressure as well as overtopping discharge around the seawall. The model is first applied to examine the cross-shore evolution of waves and flows associated with breaking wave interaction with the seawall. Subsequently, a series of numerical simulations are implemented to study the impacts of different hydrodynamic (incident wave height, incident wave period, and reef-flat wave level) as well as reef and seawall morphological factors (fore-reef slope, seawall position and seawall crest width) on the overtopping discharge over the seawall as well as the cross-shore wave impact force acting on the seawall. Finally, new empirical formulas are proposed, respectively, to predict the overtopping discharge and the wave force.