Thomas Lykke Andersen

• MSc, PhD
• Professor (Associate) at Aalborg University

The influence of directional spreading of waves is significant for wave-induced loads, wave breaking and nonlinearity of the waves. For physical model testing performed at test facilities such as the Ocean and Coastal Engineering Laboratory at Aalborg University, it is crucial to validate if the test conditions match the target sea states by measur...

The stability formula for rock slopes under wave attack was revised in Van der Meer (2021), replacing the mean period Tm with the spectral period Tm-1,0. This rewritten formula closely resembles the Modified Van der Meer formula as in the Rock Manual (2007), with differences primarily in coefficients and the use of H2% in the Rock Manual and H1/3 i...

Monopiles are often the preferred foundation concept for an offshore wind turbine. The interaction between extreme waves and the large diameter monopile will in some cases result in a vertical jet of water uprush on the monopile (i.e., wave run-up) which subsequently may lead to large slamming loads on monopile appurtenances like the external worki...

The influence of directional spreading of waves is significant for wave-induced loads, wave breaking and nonlinearity of the waves. For physical model testing performed at test facilities such as the Ocean and Coastal Engineering Laboratory at Aalborg University, it is crucial to validate if the test conditions match the target sea states by measur...

The typical approach for generating nonlinear waves in physical models involves employing first- or second-order wave theory, requiring a large water depth at the wavemaker. When the prototype bathymetry shows a gentle slope, a large facility is required. However, practical constraints often make this unfeasible, leading to the use of steep transit...

In hydraulic model tests, it is common practice to relate the response of the tested structure to the incident wave parameters at the toe. Estimation of the incident wave parameters at the toe is thus an essential part of the analysis of hydraulic model testing. In many cases, the design conditions at the toe are given by waves that are highly nonl...

The present paper deals with overtopping prediction for berm breakwaters in line with the EurOtop methodology. The basis for the paper is the recent advances proposed for EurOtop for conventional breakwaters with respect to the influence of the wave steepness and the crest width. New model tests have been performed to investigate the applicability...

This paper investigates the influence of a crown wall on wave overtopping on rubble mound breakwaters. Existing data is used to modify the EurOtop overtopping formula updated by Eldrup et al. (2022) to cover the influence of the crown wall. The effect of raising the wall above the armour crest (elevated wall) or lowering the wall below the armour c...

New data was collected in the wave flumes of Ghent University and Aalborg University on wave overtopping discharges over rubble mound structures, focusing on the influence of (large) crest width and surface roughness in combination with wave period. Combining these new data with existing data, analysis has led to the improvement of the guidance for...

In Van der Meer (2021) the stability formula for rock slopes under wave attack has been rewritten to remove the mean period Tm and to include the spectral period Tm-1,0. This formula is now identical to the Modified Van der Meer formula in the Rock Manual (2007 – Eqs 5.139 and 5.140), except for its coefficients and the use of H2 percent in the Roc...

For design validation of offshore structures and conceptualisation of wave energy converters, physical model testing performed in wave basin laboratories is often applied. In such cases, knowledge about the wave conditions is of great significance. For validation of the wave condition in such tests, different methods for estimation of the direc...

In this paper existing guidelines to predict wave overtopping on rubble mound breakwaters and coastal structures are modified and improved with respect to the influence of the roughness and crest width. Data from recently made model tests and existing data are combined to demonstrate the need for modifying these formulations in EurOtop. A new reduc...

The present paper deals with separation of long-crested regular waves into incident and reflected components. Such methods have been available for several decades for linear waves, but has recently been extended to cover nonlinear waves over horizontal foreshores. The overall goal of the present paper is to extend the separation method for nonlinea...

The main objective of this research is to present an improved and more accurate formula to estimate the reflection coefficient (KR) for rubble mound breakwaters. Physical model tests were performed for this purpose and existing data was also considered. The evaluation of existing prediction formulas for KR based on the Iribarren number (ξ) shows th...

The design of large diameter monopiles (8–10 m) at intermediate to deep waters is largely driven by the fatigue limit state and mainly due to wave loads. The scope of the present paper is to assess the mitigation of wave loads on a monopile by perforation of the shell. The perforation design consists of elliptical holes in the vicinity of the splas...

Numerical tests are performed to investigate wave transformations of nonlinear nonbreaking regular waves with normal incidence to the shore in decreasing and increasing water depth. The wave height transformation (shoaling) of nonlinear waves can, just as for linear waves, be described by conservation of the mechanical energy flux. The numerical te...

In the present paper, the experimental data on wave run-up on slender monopiles from recently published small and large scale tests are reanalyzed using different methods for the wave analysis. The hypothesis is that the post processing has an impact on the results, due to depth limited and highly nonlinear waves in many of the tests. Thus, the ide...

Existing active absorption systems do not take into account the spurious waves caused by the segmentation of the wavemaker. Thus, the theoretical estimated performance curves for oblique waves are only valid for infinitely narrow segments. In the present paper, it is demonstrated that by ignoring the spurious waves, an unstable system might be desi...

The authors wish to make the following corrections to this paper [...]

Burcharth et al. (2014) studied different upgrade solutions for a typical shallow water revetment and found that the most economical solution was to add an extra layer of armour rocks to the existing two layers. Because none of the existing design formulae for armour stability and overtopping cover designs with armour consisting of three layer of r...

The present paper presents new formulae for hydraulic stability of the main armour layer on rock armoured conventional rubble mound structures. In the present study, new stability tests were performed covering both mild (1:100) and steep (1:30) foreshores. The tests covered nonbreaking and breaking waves on the foreshore and also waves of very low...

The Van der Meer [1] formulae for quarry rock armor stability are commonly used in breakwater design. The formulae describe the stability as a function of the wave characteristics, number of waves, front slope angle and rock material properties. The latter includes a so-called notional permeability factor characterizing the permeability of the stru...

Methods for the separation of long-crested linear waves into incident and reflected waves have existed for more than 40 years. The present paper presents a new method for the separation of nonlinear bichromatic long-crested waves into incident and reflected components, as well as into free and bound components. The new method is an extension of a r...

Generation of high-quality waves is essential when making numerical or physically model tests. When using a wavemaker theory outside the validity area, spurious waves are generated. In order to investigate the validity of different wave generation methods, new model test results are presented where linear and nonlinear wave generation theories are...

In the present paper, the performance of active absorption systems based on nearfield surface elevation measurements is studied. Based on linear wavemaker theory the performance of such systems can easily be calculated for linear waves. A recent study demonstrated that bound superharmonics in regular waves is also well absorbed by such system and h...

In model tests, the wave overtopping discharge is typically measured at the rear corner of the armour crest. So far, all overtopping formulae have been calibrated to predict this specific overtopping discharge. The EurOtop Manual however proposed a formula to include also the discharge trough the permeable armour crests. The total overtopping inclu...

Most existing methods for separation of two-dimensional (long-crested) waves into incident and reflected components are based on linear wave theory. Recently, a new method for separation of incident and reflected nonlinear regular waves was presented including separation of bound and free superharmonics. The present paper extends this method to irr...

Monopiles are the most common type of foundation used for bottom-fixed offshore wind turbines. This investigation concerns the influence of uncertainty related to soil–structure interaction models used to represent monopile–soil systems. The system response is studied for a severe sea state. Three wave-load cases are considered: (i) irregular waves...

The present paper presents new overtopping results for permeable and impermeable rock armoured rubble mound breakwaters. The new tests show that EurOtop II and similar type of formulae underpredicts the overtopping for long waves and especially for structures with a permeable core. A new method is proposed to include the effect from long waves whic...

This paper presents initial results from an on-going study on the influence from wave nonlinearity on the wave height distribution in deep- and depth-limited nonlinear wave conditions. A fully nonlinear VOF model, IH-2VOF, is applied to model the propagation of irregular waves on a sloping sea bed from deep to shallow water, including the effects o...

The Overtopping BReakwater for Energy Conversion (OBREC) is an overtopping type wave energy converter, totally embedded into traditional rubble mound breakwaters. The device consists of a reinforced concrete front reservoir designed with the aim of capturing the wave overtopping in order to produce electricity. The energy is extracted through low h...

The present report presents results from a two-dimensional model test study carried out at Aalborg University in December 2016 with the proposed trunk section for the new western breakwater in Port of Hanstholm. The objectives of the model tests were to study the stability of the armour layer, toe erosion, overtopping and transmission. The scale us...

Knowledge of the incident and reflected waves present in laboratory experiments is a key issue in order to correctly assess the behaviour of the tested structure. Usual applied reflection separation algorithms are based on linear wave theory. These linear methods might result in unreliable estimates of the incident and reflected waves in case the w...

The present paper presents a new active absorption method for wavemakers in physical models based on digital filtering of signals from wave gauges in the nearfield. Such system is needed to maintain control of the waves when performing model tests where reflections from the models are significant. Similar systems have been described earlier, but in...

A reliable set of tools for prediction of low-exceedance design waves is of high importance when designing coastal protection structures. The significant wave parameters are typically obtained from buoys or numerical wave propagation models and design values are found by extreme analysis. Statistical wave height distributions are used to transform...

Engineering solutions are widely used for the mitigation of flood and erosion risks and have new challenges because of the expected effects induced by climate change in particular sea level rise and increase of storminess.This chapter describes both active methods of mitigation based on the reduction of the incident wave energy, such as the use of...

This paper deals with stability of hardly (or partly) reshaping berm breakwaters. A simple physical argument is used to derive a new stability formula based on the assumption that the maximum wave force causing damage of armor layer is proportional to the maximum wave momentum flux near the structure toe. The main goal of the present paper is to pr...

The present report presents results from a three-dimensional model test study carried out at Aalborg University in the period June 2015 – August 2015. The objectives of the model tests were to study the stability of the Xbloc armoured breakwaters at Punta Catalina under short-crested wave attack as well as the overtopping and the wave agitation beh...

Existing coastal management and defense approaches are not well suited to meet the challenges of climate change and related uncertanities. Professionals in this field need a more dynamic, systematic and multidisciplinary approach. Written by an international group of experts, Coastal Risk Management in a Changing Climate provides innovative, multid...

This paper deals with a case study on the wave height reduction behind floating Wave Dragon wave energy converters in Santander Bay, Spain. The study is performed using the MIKE21 Boussinesq model from DHI. The Wave Dragon transmission characteristics in the numerical wave propagation model are based on previously performed physical model tests in...

Stability of hardly reshaping berm breakwaters has been investigated in this paper, mainly focusing on exposure to long waves. The study continues previous work by Aalborg University, which suggested that stability of berm breakwaters follow the plunging equation of the Van der Meer stability formula also in the surging domain. Different combinatio...

This paper intends contributing to the development of an economically and environmentally sustainable coastal infrastructure, which combines rubble mound breakwaters with Wave Energy Converters (WEC). The energy is produced by collecting wave overtopping in a front reservoir, which is returned to the sea through turbines. Wave loadings and average...

The paper presents a design exercise of upgrading a typical rock armoured revetment by modifying the structure profile and adding structure elements. Several concepts of upgrading are examined. A sea level rise corresponding to the mean of the IPCC 2007 predictions is used together with a slight increase in long-term wind/wave conditions as predict...

The Limfjord is the largest Danish estuary and is connected to both the North Sea in the west and the Kattegat in the east. The connection to the North Sea was formed in 1825 by a storm surge, and has since been kept open partly artificially. The debate about the climate changes and thereby the increased risk of flooding in the estuary has revitali...

This paper contributes to a better knowledge on the distribution of individual wave overtopping volumes in shallow-water wave conditions. Results from new two-dimensional physical model tests on typical rubble-mound breakwater geometries indicate that the formulae by Besley (1999) are underestimating the number of individual overtopping waves in no...

This paper puts forward a new method to determine horizontal wave loads on rubble mound breakwater crown walls with specific exceedance probabilities based on the formulae by Nørgaard et al. (2013) as well as presents a new modified version of the wave run-up formula by Van der Meer & Stam (1992). Predictions from the method are compared to measure...

In this paper, the investigation of overtopping on rubble mound breakwaters for low steepness waves in both deep and shallow-water conditions are presented. The existing formulae provide quite different results for long waves for both conventional and berm breakwaters. Therefore, new model tests with focus on long waves have been performed for both...

This paper evaluates the formulae by Nørgaard et al. (2013) for predicting wave loads on rubble mound breakwater crown walls on new model tests. The formulae are tested outside their validation area by means of waves with a low wave steepness and low run-up height compared to the armour freeboard height. Furthermore, both a permeable and an imperme...

This note presents wave flume experiments, carried out at Aalborg University, measuring the horizontal sliding distance of a vertical breakwater in 1:40 scale. Horizontal and uplift wave induced pressures were accurately measured simultaneously with the caisson movements. Caissons of different weight and same geometries are tested under regular and...

In this paper data has been collected on berm breakwater stability from several laboratories. The total database contains more than 1500 model test data on berm recession. The data has been compared to five existing recession formulae and most of the existing recession formulae provide good estimates within the validation area of the formula. The L...

The semi-empirical formulae by Pedersen (1996) for wave loads on vertical front faces of stiff crown walls are based on model tests with deep and intermediate water wave conditions. A new series of model tests performed at the same test facility as used by Pedersen has revealed that the formulae by Pedersen overpredict the loads in shallow water wa...

Dike resilience against wave overtopping has gained more and more attention in recent years due to the effect of expected future climate changes. The overtopping flow velocities and flow depths on dikes have recently been studied in 2D small-scale experiments. This has led to semi-empirical formulae for the estimation of flow depths and flow veloci...

An experimental large scale study on wave run-up generated loads on entrance platforms for offshore wind turbines was performed. The experiments were performed at Grosser Wellenkanal (GWK), Forschungszentrum Küste (FZK) in Hannover, Germany. The present paper deals with the run-up heights determined from high speed video recordings. Based on the me...

Any kind of Wave Energy Converter (WEC) requires information on reliability of technology and on time required for the return of the investment (reasonable payback). The structural response is one of the most important parameters to take in to account for a consistent assessment on innovative devices. This paper presents results on wave loading act...

One of the greatest challenges of coastal engineering today is the need for coastal protection in the changing climate scenario. Places which are nowadays protected will demand upgraded defences and more sites will require security; in all cases a large amount of resources will be needed to ensure beach maintenance and coastal safety. This may be a...

This paper intends contributing to an economically and environmentally sustainable development of coastal infrastructures by investigating the possibility of combining together breakwaters and Wave Energy Converters (WEC). The latter change the wave energy to electricity, which may serve both the rubble mound breakwaters and seawalls related activi...

This paper evaluates the validity of a simple one-dimensional dynamic analysis as well as a Finite-Element model to determine the sliding of a rubble-mound breakwater crown-wall. The evaluation is based on a case example with real wave load time-series and displacements measured from two-dimensional physical model tests. The outcome is a more relia...

The present paper deals with stability of berm breakwaters designed to be hardly or sometimes partly reshaping. Burcharth (2008, 2011) showed by comparison to the performance of a prototype berm breakwater that the Van der Meer formulae for stability of conventional rock armour including low crests could predict the deformations of the front slope...

CFD models are promising in predicting non-linear wave loads on fixed and floating offshore structures. The NS3 model is described in this paper and it has been validated by means of model test such as wave run-up on monopiles in regular waves. The goal for the use of the NS3 model is to make a detailed investigation of the effect of 2D waves on th...

This paper focuses on the calibration of the MIKE21BW model against the measured wave height reduction behind a 24 kW/m Wave Dragon (WD) wave energy converter. A numerical model is used to determine the wave transmission through the floating WD in varying wave conditions. The transmission obtained from the MIKE21BW model is compared to results from...

The modelling of swash zone (SZ) sediment transport and the resulting morphodynamics have been areas of active research over the last decade. However, many details are still to be understood, whose knowledge will be greatly advanced by the collection of high-quality data under the controlled large-scale laboratory conditions. The research describes...

Report on Risk Assessment in the Study Sites – Appendices

This paper deals with the development of scour holes in time and space around individual offshore monopiles. It is based on physical flume tests of a model-scale pile subjected to current and/or irregular water waves. The main focus is on backfilling, i.e. the wave-induced or current-wave-induced deposition of sediment into holes that have been pre...

Wave run-up on foundations is a very important factor in the design of entrance platforms for offshore wind turbines. When the Horns Reef 1 wind turbine park in Denmark was designed the vertical wave run-up phenomenon was not well known in the industry, hence not sufficiently considered in the design of Horns Reef 1. As a consequence damage was obs...

Many breakwaters are, due to functional requirements, designed for small wave overtopping discharges. From the EC-research projects OPTICREST and CLASH it is known that overtopping discharges determined from conventional Froude scale models of rubble mound breakwaters are smaller than measured in corresponding prototypes. The present study examines...

The present paper deals with loads on wind turbine access platforms. The many planned new wind turbine parks together with the observed damages on platforms in several existing parks make the topic very important. The paper gives an overview of recently developed design formulae for different types of entrance platforms. Moreover, the paper present...

The paper presents a comparison of the stability of concrete cube armour and Cubipod armour in a breakwater roundhead with slope 1:1.5, exposed to both 2-D (long-crested) and 3-D (short-crested) waves. The model tests were performed at the Hydraulics and Coastal Engineering Laboratory at Aalborg University, Denmark. The model tests showed that Cubi...

Wave loads are important in problems related to offshore structure, such as wave run-up, slamming. The computation of such wave problems are carried out by CFD models. This paper presents one model, NS3, which solve 3D Navier-Stokes equations and use Volume of Fluid (VOF) method to treat the free surface. NS3 is used to simulate the wave run-up due...

Based on recent experiments carried out in wave basin on breakwaters with armour layer of rocks and cubes, this paper examines the dependence of the reflection coefficient on wave directional spreading and obliquity. Results suggest that long-crested and short-crested waves give similar reflection. The reflection coefficient is markedly dependent o...

The front slope stability of breakwaters with a homogeneous berm was studied in a large number of two dimensional model tests at Aalborg University, Denmark. The results are presented together with a new formula for prediction of the berm recession which is the most important parameter for describing the reshaping. The formula has also been calibra...

Wave slamming on vertical breakwaters cause a sudden, impulsive load that may cause a caisson to slide on its foundation. Alternatively, geotechnical failure may occur in the subsoil. This paper investigates whether simple analytical solutions, accounting only for the sliding along the caisson–foundation interface, can be utilized to properly deter...

This paper analyses wave reflection from permeable structures with a berm, including reshaping cases. Data are obtained from recent wave flume experiments and from 2DV numerical simulations performed with the COBRAS-UC code. The objectives of this research were to identify the proper representation of the average structure slope to be included in t...

To study the influence of wave obliquity and directional spreading on wave overtopping of rubble mound breakwaters a total of 736 three-dimensional model tests were carried out at Aalborg University. The results of these tests are presented and analysed in this paper yielding a new empirical reduction factor to describe the influence of wave obliqu...

This paper discusses the influence of wave load sampling frequency on calculated sliding distance in an overall stability analysis of a monolithic caisson. It is demonstrated by a specific example of caisson design that for this kind of analyses the sampling frequency in a small scale model could be as low as 100 Hz in model scale. However, for des...

Experiences have shown that the vertical run-up generated by waves meeting the offshore wind turbine foundations, can result in rather vigorous loads on appurtenances and platform structures. This study aims to provide a qualitative method of determining run-up height and the following loads depending on the wave parameters in the area in question....

This paper describes development of the mathematical model simulating ocean performance of an offshore wave energy point absorber device-AquaBuOY. The AquaBuOY is the next generation of the technology, based on the IPS point absorber system and the hose pump, both of Sweden. AquaEnergy Group Ltd., USA, is developing the system in cooperation with R...

The paper deals with forces generated by a stationary jet on different types of gratings and a solid plate. The force reduction factors for the different gratings compared to the solid plate mainly depend on the porosity of the gratings, but the geometry of the grating is also of some importance. The derived reduction factors are expected to be app...

The SSG (Sea Slot-cone Generator) is a wave energy converter of the overtopping type. The structure consists of a number of reservoirs one on the top of each others above the mean water level, in which the water of incoming waves is stored temporary. In each reservoir, expressively designed low head hydro- turbines are converting the potential ener...