Wave Impact Forces Research Articles

PROBABILITY MODEL OF WAVE IMPACT LOAD ON THE ELEVATED PILE CAP FOR SEA-CROSSING BRIDGES

Elevated pile cap is one of the foundation types that are commonly used to support sea-crossing bridges. However, the large weight and small lateral stiffness make it sensitive to wave impact loads. The horizontal dynamic response of the elevated pile cap induced by extreme wave is obviously larger than that calculated by the static method, which will seriously threaten the safety of the structure. Moreover, traditional calculation methods of wave impact loading seldom consider the time-varying and random characteristics of wave impact loading. This paper focuses on the wave impact force on an elevated pile cap. The time history of the horizontal component of the wave impact load was obtained from the wave flume testing of the extreme wave impact on the scale model of elevated pile cap. The time history of the horizontal component of the wave impact load was obtained from the wave flume testing of the extreme wave impact on the scale model of an elevated pile cap. A wave flume test of the extreme wave impact on the scale model of an elevated pile cap is carried out. By analyzing the normalized wave impact load time history, the time history model is established. Impact maxima and rising time of the wave impact load are analyzed with probability method. The marginal distribution of impact maxima and the rising time of the wave impact load and their joint distribution form based on Copula were finally developed.

Computational Fluid Dynamics Investigations of Breaking Focused Wave-Induced Loads on a Monopile and the Effect of Breaker Location

Abstract The design of new offshore structures requires the calculation of the wave-induced loads. In this regard, the computational fluid dynamics (CFD) methodology has shown to be a reliable tool, in the case of breaking waves especially. In this paper, two CFD models are tested in the reproduction of the experimental spilling waves impacting a circular cylinder for four different wave impact scenarios for focused waves. The numerical and experimental free surface elevations at different locations around the cylinder are also compared to verify the both numerical models. The numerical results from the models are shown together with the experimental measurements. Both CFD models are able to model the impact forces with a reasonable accuracy. When the cylinder is placed at a distance of 0.7 m from the wave breaking point, the value of the measured wave impact forces is highest due to the overturning wave crest and air entrainment. The wave-induced impact forces decrease, when the monopile is placed at distances further away from the breaking location.

Numerical and laboratory analysis of post-overtopping wave impacts on a storm wall for a dike-promenade structure

The problem of predicting the wave impact forces on walls and buildings, located at the crest of coastal defence structures with a smooth dike and a nearly horizontal promenade, is considered in this paper, using dedicated numerical computations and by re-analysis of available experimental data. The limit of previous studies on this important engineering problem, is that the geometries of the coastal defences structures considered are all very similar. Design methods (i.e. prediction formulae for the wave forces on the wall) are therefore developed within the specific ranges of wave and structural geometrical parameters considered in the experimental campaigns. In this paper, to partially overcome this limitation, the numerical model IH2VOF is applied to study the wave impacts on the specific structural layout introduced. First, validation is provided by means of comparison with available, mid scale, physical laboratory tests. Then, the model is applied to carry out parametric tests, to investigate the dependency of the phenomenon under much wider variations of the wave (mainly concentrating on the wave period) and structural (i.e. the length of the promenade, the height of the wall, the water depth at the toe) parameters than those considered so far.Finally, on the basis of the available experimental and numerical datasets a new empirical design formula is developed and presented.

A 3D numerical analysis of wave-induced seabed response around a monopile structure

ABSTRACT Despite the numerous ideas concept for an offshore wind turbine foundation, the monopile foundation is the most widely adopted concept in engineering practices. In this paper, a 3-dimensional integrated numerical model is established to study the wave-induced oscillatory seabed responses around a monopile foundation by adopting the Reynolds-Average Navier-Stokes (RANS) equation with turbulence closure model for the mean flow and the Biot’s consolidation equation for porous seabed as the governing equations respectively. The present wave and seabed sub-models in this studies are verified with physical experimental results and an analytical solution, while for the monopile structure, the wave impact force exerted on it are calculated and verified with physical experimental data to show that the present model has the ability to simulate the wave-seabed-pile structure interaction (WSSI-PILE). The numerical investigations on the monopile foundation indicated that the wave impact force on the pile structure and the seabed foundation has a very significant impact on horizontal displacement of the monopile within the seabed and the pile rocking motion. Parametric studies analysis on the effect of wave height, seabed permeability and pile structure diameter also indicated significant influence on the oscillatory wave-induced dynamic response .

Numerical and Experimental Evaluation of Sloshing Wave Force Caused by Dynamic Loads in Liquid Tanks

Proper evaluation of forces exerted on a solid boundary by liquid sloshing is difficult. If the free board in a liquid storage tank is insufficient, the sloshing waves caused by seismic excitation will collide with the tank roof and may cause major damage. The current study investigated the sloshing wave impact force (SWIF) in full-scale liquid storage tanks using numerical simulation based on the lattice Boltzmann method (LBM). Several shaking table tests have been conducted on a small-scale rectangular tank to validate the numerical model. The results of a standard dam break test have been used to express the validity of the proposed numerical model. This comparison confirms the validity of the numerical strategy for simulating the effect of sloshing. After validating the numerical model, it has been applied to a practical parametric study of SWIF in full-scale liquid tanks. The results of numerical simulation indicate that the simplified method recommended by related codes and standards for calculating SWIF in liquid tanks significantly underestimates the sloshing force. This confirms that the dynamic nature of sloshing should be considered in the design process of liquid storage tanks.

Effect of bed roughness on tsunami-like waves and induced loads on buildings

Tsunami, impulse-waves and dam-break waves afflict humanity with casualties and damages. An insight into the flow mechanisms of these waves is important to provide safety and reduce reconstruction costs. This experimental study focuses on the effect of bed roughness on the main hydrodynamic properties of surges propagating on dry bed. In addition, the resulting wave impact forces on buildings with and without openings are studied. Results pointed out that dry bed surges on a rough bed had a lower front celerity and a higher flow depth, resulting into inundation depths during the impact around 20% higher as compared to the smooth bed. Furthermore, a rough bed induced a lower momentum flux during wave propagation, resulting into lower impact forces exerted on the building. The rough bed configuration also caused shorter impact durations, leading to lower impulse values transferred to the building. Results pointed out that even on rough bed, openings within the buildings linearly reduced impact forces, thus providing some helpful information for the design of safer coastal structures.

Use of impulses to determine the reaction force of a hydraulic structure with an overhang due to wave impact

This paper describes a method of determining the reaction forces of a vertical structure with an overhang to impulsive wave impacts. The aim is to develop a method to design a hydraulic structure exposed to the impulsive wave impact. At present, there is a lack of guidelines on the designing and verification with such a purpose. The impulse of the impact is taken as the primary design variable to estimate the impulsive reaction force instead of peak impact forces. By using extreme value analysis (EVA), the characteristic impulse (e.g., Iim,0.1%) can be determined. Then a simple structure model is used for obtaining reaction forces to the characteristic impact impulse. The sum of the impulsive reaction force and the quasi-steady wave force could represent the total reaction force, which can be used as a design load on the structure. The advantage of using the impact impulse could give an approach in which several aspects of the impulsive wave impact force can be incorporated better, like determining the exceedance probability of a certain load, incorporating the flexibility of the structure and correcting possible scale effects in small scale hydraulic models. The proposed method based on the characteristic value of the Iim,0.1% is applied to forces measured in a small scale model of the Afsluitdijk discharge sluice, and compared well to a full-time domain solution. The results indicate the initial assumption that using the impact impulse of the impact as the primary design variable, it is possible to estimate the dynamic response of the structure.

Behavior of a steel bridge with large caisson foundations under earthquake and tsunami actions

The main focus of this study is to numerically investigate the influence of strong earthquake and tsunami-induced wave impact on the response and behavior of a cable-stayed steel bridge with large caisson foundations, by assuming that the earthquake and the tsunami come from the same fault motion. For this purpose, a series of numerical simulations were carried out. First of all, the tsunami-induced flow speed, direction and tsunami height were determined by conducting a twodimensional (2D) tsunami propagation analysis in a large area, and then these parameters obtained from tsunami propagation analysis were employed in a detailed three-dimensional (3D) fluid analysis to obtain tsunami-induced wave impact force. Furthermore, a fiber model, which is commonly used in the seismic analysis of steel bridge structures, was adopted considering material and geometric nonlinearity. The residual stresses induced by the earthquake were applied into the numerical model during the following finite element analysis as the initial stress state, in which the acquired tsunami forces were input to a whole bridge system. Based on the analytical results, it can be seen that the foundation sliding was not observed although the caisson foundation came floating slightly, and the damage arising during the earthquake did not expand when the tsunami-induced wave impact is applied to the steel bridge. It is concluded that the influence of tsunami-induced wave force is relatively small for such steel bridge with large caisson foundations. Besides, a numerical procedure is proposed for quantitatively estimating the accumulative damage induced by the earthquake and the tsunami in the whole bridge system with large caisson foundations.

Study on Wave Impact force measurement by using piezoelectric polymer

Study on Wave Impact force measurement by using piezoelectric polymer

2D OVERTOPPING AND IMPACT EXPERIMENTS IN SHALLOW FORESHORE CONDITIONS

This paper introduces the 2D experiments conducted for the CREST project in the wave flume of Ghent University. The experiments focus on wave interactions with low-crested sea dikes fronted by a shallow foreshore and mildly to steeply sloping beaches, which is a very typical situation along the Belgian coast. Foreshore slopes of 1/20, 1/35, 1/50 and 1/80 were tested for a range of low to high energy wave conditions, a variation in wave steepness and two water levels. The main goal was to obtain a dataset in which the effects of the infragravity waves on the wave-structure interactions (i.e. wave overtopping and impact forces) can be studied. The tests included high spatial resolution surface elevation measurement tests, which is new for beaches including a dike in the inner surf zone. From the first results it became clear that the foreshore slope influences the wave transformation up to the dike toe. The influence is apparent comparing to existing (semi-) empirical models for prediction of the spectral wave period at the dike toe and wave overtopping at the dike crest. The high spatial resolution data show a steep increase in infragravity significant wave height in the very shallow area in front of the dike.

Hydrodynamic flow characteristics of tsunami waves impact on bearing wall layout

Coastal zones management of a tsunami-prone area should be implemented with an effective and eco-friendly layout of near-shoreline structures. Eco-friendly layout term in this study means the layout produced a minimal bed scouring at the bottom of the structures. In this research, we studied the hydrodynamic flow caused by tsunami wave’s propagation on the bearing walls in coastal area. This flow which occur in 2 (two) bearing wall layout variations were analysed using the Computational Fluid Dynamic (CFD) modelling program. The data and condition of the simulation are utilizing the bathymetric and topographic data of coastal area in the south of Yogyakarta, Java Island Indonesia. The simulation result shows that wave propagation reduction of square bearing wall 45° and 0° layout are 52,99% and 59%, respectively. The square bearing wall 0° is not recommended to be applied due to its highest tsunami wave impact force on the wall structure. The square bearing wall of 0° has a higher shear force and lateral force. This forces can caused an unstable structure wall. The wave impact forces on wall structure area and layout is important parameter for changing the scouring parameter influenced.

Inverse Estimation of Local Slamming Loads on a Jacket Structure

Slamming loads from plunging breaking waves feature a high impulsive force and a very short duration. It is difficult to measure these loads directly in experiments due to the dynamics of the structures. In this study, inverse approaches are investigated to estimate the local slamming loads on a jacket structure using hammer test and wave test data from a model scale experiment. First, a state-of-the-art approach is considered. It uses two deconvolution techniques to first determine the impulse response functions and then to reconstruct the wave impact forces. Second, an easier applicable approach is proposed. It uses linear regression with the ordinary least square technique for the force estimation. The results calculated with these two approaches are highly identical. The linear regression approach can be extended to account for the loads transferred among different locations. This leads to lower and theoretically more accurate estimation of the loads compared to the previous two approaches. For the investigated case, the total impulse due to the wave is 22% lower. The estimated forces by the extended approach have a resolution at the millisecond level, which provides detailed information on the shape of the forces. The approach is an important tool for statistical investigations into the local slamming forces, and further on for the development of a reliable engineering model of the forces.

Impacts on a storm wall caused by non-breaking waves overtopping a smooth dike slope

Will coastal towns survive the rising pressure, or better, the rising sea level in future decades? Waves overtop dikes, and the overtopping flow on the crest of the dike can cause damage. Wave impacts from these overtopping flows already became of interest in coastal engineering the past few years, but very little literature and almost no design formulae are available yet for irregular waves. This paper gives such design formulae for practical use. Experimental modeling at three different scales (small, middle and large scale) has been carried out to measure such impacts. The tested geometry was a smooth sloping dike (only non-breaking waves) with a promenade at crest level and a storm wall at the end of this promenade.The outcome of this paper are three methodologies to a) calculate wave impact forces on such a storm wall as a function of the hydraulic parameters; b) determine the (Weibull) distribution of all impacts in one test, with the shape and scale parameters also linked to the hydraulic parameters; and c) to provide an indirect approach to calculate the impact forces on the storm wall. In this last approach, the (distribution of the) individual overtopping waves are linked to the (distribution of the) overtopping flow parameters, which are then linked to the (distribution of the) impact forces.Finally, the empirical formulae from the aforementioned three methodologies are compared; analogies and differences are discussed, and guidance is provided to design storm walls against post overtopping impact forces.Results show that forces from waves overtopping the dikes are in the order of 20 to 40kN/m prototype scale in the dimensionless freeboard (Rc/Hm0) range of 1 to 2. This is (much) lower compared to impact forces on vertical walls as calculated by the Shore Protection Manual.

Numerical and Experimental Investigation of Breaking Wave Interaction with a Vertical Slender Cylinder

Offshore wind turbine substructures consisting of cylindrical members are exposed to highly non-linear and breaking waves in shallow waters [1]. Those structures experience extreme impulsive loads of short duration from breaking waves that can cause permanent structural damage[2]. The main purpose of the present paper is to investigate the wave impact forces on a slender cylinder from plunging breaking waves in shallow waters both experimentally and numerically. The present study consists of two major parts: laboratory measurements and numerical simulations. The laboratory experiments are performed with regular waves. Plunging breaking waves are generated and free surface elevations are measured around the cylinder. Next, numerical simulations are carried out in the three-dimensional numerical wave tank REEF3D. The model is based on the incompressible Reynolds-averaged Navier-Stokes equations together with the k − ω for turbulence and the level set method for free surface. The numerical results are compared with the laboratory measurements in order to validate the numerical model. A good agreement between the computed results and the experimental data is seen for the breaking wave properties. Further, the breaking wave forces and the free surface deformations during the interaction of plunging breaking waves with a vertical cylinder are investigated and they are reasonably well represented in the numerical simulations.

Variability of breaking wave characteristics and impact loads on offshore wind turbines supported by monopiles

Most existing and planned offshore wind turbines (OWTs) are located in shallow water where the possibility of breaking waves impacting the structure may influence design. Breaking waves and their associated impact loads are challenging to model because the breaking process is a strongly non-linear phenomenon with significant statistical scattering. Given the challenges and uncertainty in modeling breaking waves, there is a need for comparing existing models with simultaneous environmental and structural measurements taken from utility-scale OWTs exposed to breaking waves. Overall, such measurements are lacking; however, one exception is the Offshore Wind Turbines at Exposed Sites project, which recorded sea state conditions and associated structural loads for a 2.0 MW OWT supported by a monopile and located at the Blyth wind farm off the coast of England. Measurements were recorded over a 17 month campaign between 2001 and 2003, a period that included a storm that exposed the instrumented OWT to dozens of breaking waves. This paper uses the measurements from this campaign to categorize and identify breaking waves and quantify the variability of their impact loads. For this particular site and turbine, the distribution of measured mudline moments due to breaking waves has a mean of 8.7 MN-m, a coefficient of variation of 26% and a maximum of 14.9 MN-m. The accuracy of several breaking wave limits and impact force models is compared with the measurements, and the impact force models are shown to represent the measurements with varying accuracy and to be sensitive to modeling assumptions. Copyright © 2015 John Wiley & Sons, Ltd.

Investigation of random wave impact on highly pervious pipe breakwaters

The main cause of damage to offshore structures is the wave impact force. Protective structures such as submerged breakwaters, screen breakwaters, and various piles are often designed to provide additional attenuation (reduction) of the impact force. In this study, reduction of the wave impact force and wave pressure on an embankment with highly pervious pipe breakwaters is investigated through physical experiment. The process of wave impact is rather complicated, involving strongly nonlinear and transient effects. Coastal structures are often partially damaged by the strong intensity of the wave impact force; therefore, the effect of the wave impact force is one of the important factors to be considered for the safety and/or destruction of coastal structures. This study addresses the use of highly pervious dense pipes with small apertures, which can be beneficial for convection and interchange of seawater within the harbor district and, furthermore, perform wave absorption effectively. This study investigated the performance of a pervious pipe screen breakwater installed in front of a seawall in terms of reducing the wave impact force and wave pressure. The physical experiments were performed by considering regular and irregular waves under various conditions. The experimental results indicated that pervious pipe obstacles placed vertically in front of an embankment can effectively mitigate and reduce the wave impact forces by over 70%.

Experimental investigation of extreme wave impacts on a rigid TLP model in cyclonic conditions

This paper describes a series of model tests of a rigidly mounted tension leg platform (TLP) subjected to extreme wave events corresponding to long-crested irregular wave trains of a 10,000-year cyclonic sea state. The experimental setup was instrumented to simultaneously measure wave surface elevations in the vicinity of the model, global wave impact forces and local pressure distribution on the underside of the model's topside deck. Model accelerations were also monitored for each wave impact event so that the inertial force due to structural dynamic response could be identified. The deck–column intersection areas were found to experience large wave-in-deck slamming pressures, in particular around the aft columns. A reduction of the deck clearance was found to increase the magnitude of the global horizontal forces; however, the global vertical forces and local wave-in-deck slamming pressures did not follow this trend.

岸壁設置式OWC型波力発電装置のMPS法による数値シミュレーションに関する基礎的研究

This research investigates applicability of the two-phase flow MPS (Moving Particle Semi-implicit) method to performance analysis of the OWC (Oscillating Water Column) type WEC (Wave Energy Converter). Estimating detail behavior of an OWC type WEC under any sea state including heavy weather is important for evolution of development of OWC type WECs. Basic applicability and effectiveness of the present method is indicated by numerical simulation of reproducing a coastline OWC type WEC model against a large wave. In addition, arrangement of air particles for setting computational domain is examined. Numerical results about wave impact force analysis by the simulation that air particles are arranged small agree well with the results by the simulation that air particles are arranged full. The result indicates that the present method with pseudo air pressure can reduce computational costs. The full arrangement simulation indicates effectiveness to response analysis of OWC type WECs in the severe wave by the present results including numerical results of response in the chamber. In case of carrying out the small arrangement simulation, suitable boundary condition is required at the end of duct for improving calculation accuracy of response analysis in the air chamber.

Variability of breaking wave characteristics and impact loads on offshore wind turbines supported by monopiles

AbstractMost existing and planned offshore wind turbines (OWTs) are located in shallow water where the possibility of breaking waves impacting the structure may influence design. Breaking waves and their associated impact loads are challenging to model because the breaking process is a strongly non‐linear phenomenon with significant statistical scattering. Given the challenges and uncertainty in modeling breaking waves, there is a need for comparing existing models with simultaneous environmental and structural measurements taken from utility‐scale OWTs exposed to breaking waves. Overall, such measurements are lacking; however, one exception is the Offshore Wind Turbines at Exposed Sites project, which recorded sea state conditions and associated structural loads for a 2.0 MW OWT supported by a monopile and located at the Blyth wind farm off the coast of England. Measurements were recorded over a 17 month campaign between 2001 and 2003, a period that included a storm that exposed the instrumented OWT to dozens of breaking waves. This paper uses the measurements from this campaign to categorize and identify breaking waves and quantify the variability of their impact loads. For this particular site and turbine, the distribution of measured mudline moments due to breaking waves has a mean of 8.7 MN‐m, a coefficient of variation of 26% and a maximum of 14.9 MN‐m. The accuracy of several breaking wave limits and impact force models is compared with the measurements, and the impact force models are shown to represent the measurements with varying accuracy and to be sensitive to modeling assumptions. Copyright © 2015 John Wiley & Sons, Ltd.

The effect of dynamic amplification due to a structure׳s vibration on breaking wave impact

In this paper, breaking wave impact forces on vertical and inclined piles are studied by using a 3D numerical model. A method for obtaining net breaking wave impact forces from the measured response time history is also investigated. The computed forces are compared with the results of hydraulic model tests. However, because the piles installed in the numerical model are modeled as rigid objects, it is not possible to make a direct comparison between the CFD (Computational Fluid Dynamic) results and the experimental data. A force separation procedure is used for the experimental data. A low pass filter and EMD (Empirical Mode Decomposition) are employed for removing the effect of dynamic amplification in the experimental data, and the filtered results are compared with the numerical results. Based on the results, DAFs (Dynamic Amplification Factor) are estimated for these particular structures. Moreover, Duhamel integral is used to reproduce dynamic breaking wave forces (i.e., net breaking wave force+the force which is the amplified component due to the structure׳s vibration) based on the breaking wave forces calculated by the CFD model. The reproduced results are compared with the unfiltered experimental data for the verification of the method stated above.