Results Of Wave Forces Research Articles

ANALYSIS OF THE IMPACT PROCESS AT DIKES WITH CROWN WALLS AND PARAPETS

This paper is focused on the analysis of the impact process at dikes with crown walls and parapets under breaking and non-breaking waves. A small-scale laboratory campaign was performed at the Hydraulic Laboratory of Bologna. The experiments were aimed to analyze the vertical pressure distribution along the crown wall and the resulting wave forces, by varying geometrical and hydraulic parameters. The tested configurations included different off-shore slopes, dike crest widths, crown-wall heights, dike crest freeboards and the inclusion of the parapet. The measurements were combined with the image analysis of the run-up and of the wave impact process. A sub-set of the experiments was numerically reproduced, with the openFOAM modelling suite, to support and to extend the experimental results. The results confirmed the link between the air content, the shape and the magnitude of the pressures according to the breaker type, already observed for larger-scale experiments.

Dynamic response of spar-type floating offshore wind turbine in freak wave considering the wave-current interaction effect

In this paper, the dynamic responses of a Spar-type floating offshore wind turbine (FOWT) are simulated and analyzed under the scenarios with freak wave superimposed a uniform current. The wave-current interaction is considered in the process of freak wave generation. An improved phase modulation algorithm is used to generate the free surface profile of the freak wave. Compared with the deterministic wave modeling method, this method can realize the randomness of the sea state and also achieve high efficiency. The effect of the presence of current on the wave energy spectra is firstly investigated. Then the OC3 Hywind Spar-type FOWT in the parked condition is chosen as an example to study the dynamic responses under the extreme wave scenarios. An in-house MATLAB code based on a nonlinear aero-hydro-mooring coupled model is adopted to perform these numerical investigations. The simulations are conducted in the time domain and then the results of wave forces and platform motions in the surge, heave and pitch are summarized and analyzed considering the presence of current with different velocities. The results of mooring lines tension and the acceleration at nacelle are also investigated. Through the simulation results, we can have a clear understanding of the mechanism of the wave-current interaction phenomenon for extremely high waves in Gaussian seas. Furthermore, it also allows identifying the severest wave conditions which are important for the analysis of the floating structure ultimate design conditions.

Simplified algorithm for evaluating the hydrodynamic performance of very large modular semi-submersible structures

This paper develops a simplified algorithm for evaluating the hydrodynamic performances of mobile offshore bases (MOBs) in the preliminary design stage based on the following reasonable assumptions: no navigational velocity exists, and marine environment loads only consider the random and irregular wave forces at high sea states. MOBs are a representative structural style for very large modular semi-submersible structures in deep-sea areas. Simplified formulas for different parameters in the dynamic equations of MOBs are derived, including added mass, restoring force, and the constraint forces of connectors. The revised Morison equation is used to estimate the wave forces on MOBs because the components of MOBs can be treated as small-scale components by comparing them to the wavelengths at high sea states. During this process, the shielding effects of the interactions between multiple components of MOBs are considered to estimate the effects of wave diffraction and other fluid-structure interactions on the results of wave forces. A 3-module numerical MOB model at high sea states is considered as a case study. The hydrodynamic responses of the MOB modules are calculated under random and irregular wave conditions with different wave angles. The statistical results obtained using this simplified algorithm in the time domain exhibit close agreement with the results of experiments reported in the literature and obtained using the potential flow theory (PFT) method. Additionally, the relative errors among the 3 methods fall within the permitted range for practical engineering, which adequately validates the accuracy, feasibility and reliability of the methodologies developed in this paper. The statistical results of the hydrodynamic responses among 3 adjacent MOB modules under the same sea state are also compared. Finally, this paper discusses the response spectra associated with the time-domain results of MOB module. This study provides significant support for the evaluation of the hydrodynamic performances of very large modular semi-submersible structures.

Breaking wave interaction with a vertical cylinder and the effect of breaker location

The open-source CFD model REEF3D is used to simulate plunging breaking wave forces on a vertical cylinder. The numerical results are compared with data from the experiments carried out at the Large Wave Channel, Hannover, Germany to validate the model. Further, the location of the cylinder is changed so that the breaking wave impacts the cylinder at different stages of wave breaking and the resulting wave forces are evaluated. The different locations for the cylinder placement based on the breaker location are determined from the results obtained for the wave breaking process in a two-dimensional numerical wave tank. Maximum wave forces are found to occur when the breaking wave tongue impacts the cylinder just below the wave crest in all the cases simulated and the lowest wave forces are generally obtained when the wave breaks behind the cylinder. Several wave features such as the splashing on impact, the splitting and rejoining of the wave around the cylinder resulting in a chute-like jet formation are identified. The model provides a good representation of the breaking wave process and can be a useful tool to evaluate breaking wave forces on structures.

Wave pressures and forces on slotted vertical wave barriers

Vertical slotted barriers are cost effective energy-dissipating structures. The design of such barriers requires an accurate estimation of dynamic pressures and resulting wave forces. Herein, a physical model study is carried out to assess the wave forces acting on a single and twin wave barriers of various porosities under a wide range of wave conditions. The study provides explicit data on how dynamic pressures vary vertically from the seabed to the still water surface and on the resulting forces, both seaward and shoreward. In particular, the experimental results indicate that porosity affects dynamic pressures significantly especially near the free surface, but less so closer to the seabed. Further, resultant horizontal wave forces seaward are 20–25% less than shoreward forces. Forces on the front panel in the twin wave barrier cases are 20–25% more than those on a single porous wall while the forces on the rear or second barrier is always 20–25% less than the single wave-barrier case under identical test conditions. These and other results presented in the study can be useful in designing wave dissipaters, especially for inner harbors and vertical sea walls.

Experimental investigation on rogue waves and their impacts on a vertical cylinder using the Peregrine breather model

This paper presents an experimental investigation on the rogue waves and the corresponding wave forces acting on a vertical cylinder. The waves are modelled using the Peregrine breather solution of the third-order nonlinear Schrödinger equation. The experimental wave elevations are compared with the theoretical solutions, and the behaviours of wave energy distribution and evolution are calculated using the fast Fourier transformation and wavelet transform (WT) methods. The resulting wave forces acting on the vertical cylinder are compared with the numerical results based on potential flow calculations. Moreover, coherence analyses are conducted for the rogue waves and their impact forces acting on the cylinder based on the WT.

Second order wave diffraction forces and runup by finite—infinite element method

This paper presents a finite-infinite element method for solving the second order wave diffraction problem. The formulation of the problem is based on the inhomogeneous far field condition and its corresponding higher order asymptotic solutions for the second order diffracted potential suggested by Li 9 , and follows the finite-infinite element method as used by Lau and Ji 18 . The interpolation in the infinite element along the radial direction has a far field decay rate compatible diffraction by a vertical surface-piercing circular cylinder. Numerical solutions of the second order diffracted potential, satisfying all the governing and boundary conditions as well as the inhomogeneous far field condition, are obtainable with the method. Numerical tests of the method give very good results of wave forces and runup profiles when compared with those published by other researchers.

Wave Forces on Wall

Revised criteria is presented for wave shoaling after breaking on a plane beach and for resulting wave forces on a wall landward of the still-water line. Existing criteria is based on the assumption that the wave height above still water will remain constant between the point of wave breaking and the shoreline. A review of experiments carried out by several different researchers shows a marked reduction in wave height following breaking; and the assumption used in existing criteria will overestimate wave heights by a factor of four and wave forces by a factor of 16. New criteria is presented that more accurately predicts the height of a broken wave. Revised equations are given for calculating resulting wave forces.

DYNAMIC FORCES DUE TO WAVES BREAKING AT VERTICAL COASTAL STRUCTURES

In the past 20 years, considerable effort has been devoted to replacing the widely used approaches of HIROI, MINIKIN, NAGAI, PLAKIDA and others /1,2,3,4/, for the design of vertical breakwaters under the impact of breaking waves, with improved and more exact calculation methods. However, almost all new theoretical and empirical approaches lacked the support of prototype measurements or test results from model measurements at a larger scale. The difference between the proposed design criteria and classical approaches is sometimes so great that engineers do not have a reliable method for the design of a vertical or composite breakwater. Figure 1 shows the resulting wave forces per unit width due to different theories as a function of the design wave height H.

Probabilistic Model of Wave Forces on Cylindrical Pile

Based upon the Mellin Transformation technique, a probabilistic model of wave forces on cylindrical pile is developed which incorporates the random nature of wave property as well as the uncertainty of force coefficients. The solutions have the advantage that all the moments of the probability distributions can be determined exactly. In addition, the solutions are simple and can accommodate a wide range of distribution functions. Specific types of distribution functions are proposed for the wave properties and the force coefficients. Solutions are then obtained for both the inertia force and the drag force on the basis of these distribution functions. The effect of the randomness of the input parameters and the statistical significance of the resulting wave forces are examined.

Second-Order Directional Seas and Associated Wave Forces

Abstract Most methods for wave force computation incorporate either the nonlinearities of the ocean surface for a single fundamental component or the random and/or directional characteristics using superposition of linear wave components. One exception is the intuitive "hybrid" method1 which combines elements of linear and nonlinear waves. This paper describes and applies a method correct to the second order in wave height for calculating waves and wave forces caused by a directional wave spectrum on an offshore structure. Starting with a prescribed linear spectrum of directional waves, a set of random phases is generated and the second-order spectrum computed with phases defined by all contributing pairs of first-order components. Thus, with one realization of the spectrum complete up to the second order, the wave profile and water particle kinematics can be simulated in the time domain. The wave forces also are computed in the time domain, taking full account of their nonlinear and directional properties. The resulting wave forces at any level vary in direction and magnitude. The total wave forces summed over all piling of a structure are less than those for a unidirectional train of waves with the same one-dimensional spectrum. Several examples are presented to illustrate reductions in maximum wave forces caused by the directional distribution of waves. We found that for a single piling the maximum force decreases by a factor ranging from 1.0 to 0.61 as the directional spread increases from unidirectional to uniformity over a half plane. For a four-pile group on a square array of 300-ft (91.4-m) spacing, the corresponding decrease in the factor is 1.0 to 0.51 for a Bret-schneider spectrum with a peak period of approximately 12 seconds. The results of this complete model are compared with the more intuitive and approximate hybrid method and are found to agree quite well. Force spectra are presented and discussed for the inline and transverse directions.