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The hydrodynamic pressures due to random waves around a pipeline near a rigid bed of slope 1:10 have been measured. The tests were performed for pipelines normal and parallel to the wave direction. These tests were carried out for three gap ratios of the pipeline from the sloping bed. The pressures were resolved in the horizontal and vertical directions and integrated for the force time history in the respective directions. The effects of relative clearance of pipe from the bed and wave steepness on the probability distribution of the forces on the pipeline are reported. The average statistical force ratios as a function of scattering parameter and the variation of the force coefficients as a function of Keulegan–Carpenter number are also presented. The details of the model setup, experimental procedure, analysis of results and discussion are reported in this paper.

Wave flume experiments investigating the cross-shore transport and accumulation patterns of non-buoyant microplastic particles under irregular waves propagating, shoaling and breaking on a live sediment bed are considered. Eighteen microplastic particle groups having variable shape, density and size are tested. The experiments considered a pre-developed singly-barred profile, reasonably representative of field conditions. Four different microplastic accumulation hotspots are identified: (1) the offshore toe of the breaker bar, (2) at the breaker bar, (3) the plateau region between the breaker bar and beach, and (4) the beach. The accumulation patterns primarily fall within three different particle Dean number regimes (ratio of the characteristic wave height to the product of the settling velocity and characteristic wave period). For the parameter space tested, the dominant transport direction generally depends on the importance of offshore-driving gravitational effects and onshore-driving effects associated with nonlinear wave shapes. Particle position relative to the jet of plunging breaking waves likewise plays a key role in determining the net transport direction, especially near the breaker bar. These results help to improve understanding of the transport mechanisms and accumulation patterns of microplastic particles in e.g. nearshore coastal environments is required, as a prerequisite to any successful management or mitigation strategies.

This paper presents a wave flume investigation of beaching times for buoyant microplastic particles dropped at various distance from the shoreline. The beaching times are used to quantify the cross-shore Lagrangian transport velocities of the microplastic particles. Results show that prior to breaking, there is little dependence on particle characteristics (e.g. their rise velocity), and the particles travel onshore with a velocity close to the Lagrangian fluid particle velocity. In the surf zone the Lagrangian transport velocities of the microplastic particles increase significantly, becoming closer to the wave celerity. Additionally, particle characteristics become important, as particles with low Dean numbers (high rise velocity) have a greater tendency to be captured by surface rollers relative to particles with larger Dean numbers (lower rise velocity). An empirical relation is formulated for predicting the cross-shore Lagrangian transport velocities of buoyant microplastic particles. The expression matches the present experiments well and is valid for both non-breaking and breaking irregular waves. These findings help in understanding the accumulation of microplastics at beaches due to the surf-zone processes, especially for buoyant particles.

The present paper investigates breaking wave processes (transient wave package) in a laboratory wave flume using a high speed camera and the particle imaging velocimetry (PIV) technique. This specific measurement device assists to examine the entire breaking process in depth without the necessity to repeat experiments. Variability of essential kinematics among experimental runs is thus eliminated. Full review of analytical formulations on net mass-transport velocities beneath nonlinear waves is given and considered in respect to transient, breaking waves. Calculations of magnitude and direction of water particle motions beneath breaking waves and time-dependent, depth-resolving mass-transport velocities are exposed. Furthermore, detailed studies at arbitrarily chosen cross-sections are carried out and information about net transport before, during and after breaking are given. Significant divergence with existing analytical theories of mass transport formulations beneath water waves is elucidated.

Transient breaking waves exceeding a critical steepness are investigated by means of numerical simulations based on the Reynolds-averaged Navier-Stokes equations. For the approximation of Reynolds stresses four different closure models are used: the first order standard k-ε-model, RNG k-ε-model and SST k-ω-model and a second order Reynolds stress model. Up to the breaking point the influence of turbulence models is insignificant and the numerical results agree very well with laboratory PIV measurements. The turbulence quantities like turbulent kinetic energy and turbulent viscosity that develop during the breaking and post breaking process are investigated and the influence of the different turbulence models is analyzed.

Time series of regular and irregular water surface elevations from various experimental configurations are examined with time series analysis methods and Fourier analysis techniques in a laboratory wave flume concerning the hydrodynamic wave damping performance of an artificial reef. The decomposition phenomenon of nonlinear wave trains passing over an artificial reef has been investigated experimentally. It is demonstrated for monocomponent wave trains that the spectral energy distributions and the total amount of energy within the spectra is significantly dependent on the position of a wave gage in the wake of the reef since all Fourier based analysis techniques are incapable to identify nonstationary processes. The Hilbert-Huang Transformation (HHT) is chosen to operate as a more appropriate tool to demonstrate the nonlinear processes of the transmitted transient waves induced by the presence of the artificial reef. Results of this technique are shown and prove that the nonstationary sea states behind the structure are essentially composed of individual dispersive waves which are phase shifted in the wake of the struture and propagating individually to generate a beat effect. Further experiments with irregular waves (JONSWAP) are also carried out and analysed with the HHT.

An experimental study on the flow patterns around a submerged plate under a propagating bore is presented. Vortices and velocity magnitudes are determined by the PIV method. Parameters are calculated by the open-source code MatPIV and validated by numerical simulations via FLOW-3D with the classical k-ε and the RNG turbulence model on the one hand and a Large Eddy Simulation on the other hand. Furthermore, the influence of the wave period, the wave height and the submersion depth is described.