This paper summarizes the results of experiments performed to investigate pore pressure generation in the subsoil underneath a breakwater foundation model inducted by rocking-motion excitation. The foundation was placed either on the surface or embedded in the soil. The main experiments were conducted with a fixed foundation, i.e., it could not move downward during the test. Further tests were carried out to observe sinking of the plate in liquefied soil during rocking motion. The excess of pore-water pressure induced by rocking motion was measured, and the susceptibility of subgrade to liquefaction was analyzed. The wide range period and amplitude values of rocking motion on liquefaction of seabed were considered, and the extensive experimental database was presented. It was found that the effect of the period on the maximum excess pore pressure was very significant, but the amplitude did not have a major impact here. The sequences of the liquefaction process were also analyzed. In this case, the build-up of pore pressure, liquefaction, and dissipation time were a strong function of the amplitude.

This paper presents the results of an experimental study on seabed liquefaction under progressive waves. To analyze the potential of the soil to liquefy, the position of the critical state line (CSL) was determined in a series of monotonic triaxial shear tests that were carried out on soil samples, which were characterized by different initial states that correspond to contractive and dilative behavior. Based on these results, the main experiments in the wave flume were designed. They were performed to investigate the effect of wave height and wave period on the possibility of soil liquefaction. Pore water pressures were measured at different depths of the subsoil. The correlation between the wave parameters and the susceptibility of the soil subgrade to liquefaction was analyzed. A three-dimensional (3D) analysis of the effect of the wave height and period on the variation in the maximum excess pore pressure and the sequences in the liquefaction process was performed. The experimental results show that the level of the maximum excess pore pressure and sequence of the liquefaction process are strongly affected by the wave height and period.

Sea surface displacement (SSD) is a crucial parameter in environmental engineering. The measurements of SSD are susceptible to the failure of instruments and equipment, data losses, and other unpredictable events. In this study, we developed an innovative nonlinear regression trees (NRT) technique to retrieve the missing data of SSD. The model was used on the record of SDD for the ADCPs deployed in the Gdansk Gulf along the Vistula Lagoon. The NRT suggests using a nonlinear machine learning algorithm instead of linear regression at the end nodes of a tree. Two different NRT models were developed. One of them is based on the support vector regression (SVR) and the other on adaptive neuro-fuzzy inference system (ANFIS). The performance of both models was validated by comparing their results with the state-of-the-art algorithms. The models were trained using four input parameters, including the pressure and SDD of two other ADCPs, which recorded complete time series data. The analysis shows that NRT methods, with an average RMSE of 0.019 m, provide about 71.13% more accurate prediction than random forest (RF). Among all models, the NRT-SVR, with the lowest RMSE of 0.009 m and MAE of 0.002 m, and the highest R2 of 0.997, NSE of 0.997, and IA of 0.999, is ranked as the most accurate model. The simplicity, as well as the high efficiency of the developed NRT models, enable us to apply them for pattern recognition of other environmental and engineering problems.

Wave-induced liquefaction results in significant seabed dynamics and can lead to a complete loss of the bearing capacity of the soil. With the increasing use of marine space for energy harnessing, geotechnical challenges move into focus during the development and planning of such installations. To date, a lack of comprehensive modelling tools for wave-induced liquefaction around marine structures has been observed. This paper documents the efforts in the framework of the NuLIMAS project to provide such a modelling tool. In particular, this paper presents a numerical implementation of the hydrogeotechnical processes together with a detailed overview of the calibration and validation strategy employing small- and large-scale experimental data, respectively.

The horizontal elements of maritime structures are susceptible to both wave impact and resulting vibrations. These vibrations can lead to a partial or complete failure of structures and require detailed investigations. To address this issue, laboratory experiments were conducted in a wave flume. The aim of this study was to investigate the problem of standing wave impact underneath a horizontal deck. The main focus was on the effect of the wave-induced vertical forces on the global response of the structure. The physical model of the deck was installed above a still water level in front of a vertical barrier. The model was supported by a system of strings and springs. The mechanical system had one degree of freedom corresponding to a small rotational displacement around rear deck edge. Among other physical parameters, the impact pressure generated under the structure due to wave impact was measured. The high sampling frequency of the data acquisition system allowed to capture momentary slamming pressure. The systems of accelerometers and displacement gauges were installed to measure induced vibrations. Thorough analysis of the influence of wave parameters and the deck clearance on the structure response was performed based on the measurements. The rapid slamming force increase, recorded at the moment of impact is not revealed in the dynamic response of the plate.

The purpose of the study was to collect experimental data on the vertical structure of sediment fluxes during the wave crest and trough phase. The first stage of the experimental work included measurements of these fluxes using the particle image method, while in the second stage, measurements of sediment transport rates and granulometric distributions of sediments were collected in the traps on both sides of the initial area. The experimental data were compared with the results of a theoretical analysis based on a three-layer model of graded sediment transport. The comparison of the calculations with the measurements was conducted separately for fluxes of fine and very fine fractions in the diameter range d(i) < 0.20 mm, coarse, and total fractions all outgoing in the crest and trough phase from the initial area and deposited in adjacent control areas. As this model did not take into account both the effects of vertical mixing and the phase-lag effects related to the presence of fine and very fine fractions, a modification of this model was proposed that was based on four coefficients that corrected for fluxes. The consistency of the sediment transport calculations according to the modified model with measurements was achieved within plus/minus a factor of 2 of the measurements.

This paper presents the results of an experimental study of seabed liquefaction under progressive waves. Firstly, during preliminary tests, the physical and mechanical parameters of the soil selected as the subgrade material were determined. A series of monotonic triaxial shear tests were carried out at different initial void ratios and mean effective stresses. The susceptibility of soil samples to liquefaction was estimated. The results were used to design experiments in a wave flume. Their main purpose was to study the effect of wave height on wave-induced liquefaction. The experiments were carried out in a wave flume that is 64.1 m long, 0.6 m wide, and 1.4 m high, in a specially built experimental stand located 5.0 m from the wave generator below the flume bottom. Wave propagation was conducted over constant water depth which was equal h = 0.5 m. The wave surface elevation was measured by resistance type wave gauges. The pore-water pressure was measured by transducers located in the middle of the sediment pit, at four different soil depths. Parametric studies were carried out to investigate the influence of wave height on the liquefaction process. The results of experiments shown that pressure buildup is a strong function of the wave height and increases with increasing its value.

The liquefaction around marine structures can lead to severe structural failure and the susceptibility of seabed soil to liquefaction at a specific installation site of, e.g., floating offshore wind turbines should be included within the design process and site evaluation. To that end, advanced prediction tools based on numerical modelling can provide valuable insight into the hydro-geotechnical processes. However, due to the complex interaction of the underlying physics, developing a holistic modelling framework for seabed liquefaction is a challenging task. The NuLIMAS research project (Numerical modelling of seabed liquefaction around marine structures) aims at the development of such a numerical model of seabed liquefaction implemented in the OpenFOAM® framework. This paper provides an overview of the NuLIMAS project, laying out the current state of the art of experimental and numerical modelling approaches for seabed liquefaction and presenting some initial results.

The paper presents the experimental test setup and measurement method of hydrodynamic force generated on the rotating cylinder (rotor) under uniform flow including the free surface effect. The experimental test setup was a unique construction installed in the flume tank equipped with advanced flow generating and measuring systems. The test setup consisted of a bearing mounted platform with rotor drive and sensors measuring the hydrodynamic force. The low length to diameter ratio cylinders were selected as models of bow rotor rudders of a shallow draft river barge. The rotor dynamics was tested for the rotational speeds up to 550 rpm and water current velocity up to 0.85 m/s. The low aspect ratio of the cylinder and free surface effect had significant impacts on the phenomena influencing the generated hydrodynamic force. The effects of the rotor length to diameter ratio, rotational velocity to flow velocity ratio, and the Reynolds number on the lift force were analyzed. The validation of the computational model against experimental results is presented. The results show a similar trend of results for the simulation and experiment.

A theoretical approach was applied to investigate the impact of nonlinear standing waves underneath a horizontal deck. A solution was achieved by applying a boundary element method. The model was applied to predict impact pressure underneath a deck. The results show that the wave impact is a very complex momentary process. The influence of initial boundary conditions, wave parameters and deck clearance on impact pressure are analysed. The analysis shows that purely sinusoidal waves of very small amplitude may cause an impact pressure several orders of magnitude higher than a pressure arising from typical applications of a linear wave theory. The analysis shows that all these non-intuitive outcomes arise from the complexity of a wave impact process and its enormous sensitivity to initial conditions what indicates serious difficulties in a reliable prediction of a wave impact for complex wave fields or other structures. Laboratory experiments were conducted to validate theoretical results.

A novel approach to assess vulnerability to erosion for the Arctic coastline is proposed and a concept of a Polar Coastal Risk Index (PCRI) is introduced. This original concept is applied in the present study to the Arctic coastline. The PCRI is calculated by applying data from the DIVA and ACD databases. The investigations are supported by the open water season data obtained from satellite images of the European Organization for the Exploitation of Meteorological Satellites. The derived concept seems to be a better method of determining vulnerability to erosion for polar coastal regions than previous approaches.