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This addendum addresses the assessment of offshore wind power based on observed mean wind speed statistics from 11 sites in the North Sea and the North Atlantic. The wind gust and the ambient turbulence level are also estimated by adopting a wind gust spectrum. The sea surface roughness is specified using a recently published sea surface drag coefficient given in terms of the spectral bandwidth of ocean waves. The results are supplementary to those in a recent paper published by the present authors using the same mean wind speed statistics and wind gust spectrum, but with a different sea surface roughness formula depending on significant wave height and spectral wave steepness. It is demonstrated how the spectral bandwidth affects the assessment of the offshore wind power and the ambient turbulence level. Thus, since the spectral bandwidth is a frequently used parameter to characterize wave conditions the results should be useful.

The paper provides a simple and analytical method which can be used to give estimates of the wave-induced bottom shear stress for very rough beds and mud beds in shallow water based on wind statistics in deep water. This is exemplified by using long-term wind statistics from the northern North Sea, and by providing examples representing realistic field conditions. Based on, for example, global wind statistics, the present results can be used to make estimates of the bottom shear stress in shallow water.

In the present study, breaking solitary waves over a sloping seabed and breaking wave forces on a vertically mounted cylinder are simulated with the three-dimensional CFD model REEF3D. The numerical model uses the Reynolds-Averaged Navier–Stokes (RANS) equations together with the level set method (LSM) for the free surface and the $$k-\omega $$ k-ω for the turbulence. The numerical model is validated for simulating breaking solitary waves and breaking wave forces against the experimentally measured free surface profiles and vertical and horizontal velocities by Mo et al. (Ocean Eng 74:48–60, 2013) and the experimentally measured free surface elevation and breaking wave force by Chakrabarti et al. (Appl Ocean Res 19:113–140, 1997). The main purpose of the paper is to examine the effects of the breaking characteristics, the geometric properties, the relative cylinder positions and the incident wave heights on the breaking wave force characteristics. A total of 21 simulations are performed to investigate the characteristics and the geometric properties of solitary waves breaking over a slope and the associated breaking wave forces on a cylinder. First, the characteristics and geometric properties of breaking solitary waves are investigated with two-dimensional simulations. Further, the study explores the effect of the relative distance between the breaking point and the cylinder on breaking wave forces. Finally, the study examines breaking solitary wave forces for different incident waves. This also includes the analysis of breaking wave force characteristics such as the impact duration and rise time, the peak force, the average slamming coefficient and the force impulse. The results of the numerical simulations show that the relative distance between the cylinder and the breaking point plays an important role in obtaining the maximum force. In addition, the numerical model is capable of representing the most important physical flow features related to the breaking solitary waves and the interaction with the vertical slender cylinder.