Analysis of wind generated wave characteristics by SWAN model in Balikpapan Bay

The initiative to relocate the capital of the Republic of Indonesia from Jakarta to Penajam Paser Utara requires research from various sectors in the area. Since Penajam Paser Utara is located in the coastal zone of Balikpapan Bay, it requires careful preparation. This research aims to examine the characteristics of wind-generated waves in the Balikpapan Bay area from 2016 to 2018. Bathymetry data from BATNAS with a resolution of 0.00166666° and Wind data (U10 wind velocity and direction) from the European Center for Medium-Range Weather Forecasts (ECMWF) with a resolution of 0.25° × 0.25° were utilized as input data in this study during three years (2016-2018). This research used the SWAN Model to model wind-produced waves to get significant wave values in spatial and time series form and monthly and seasonal wave energy spectrum characteristics. Based on this research, it can be concluded that significant wave height values are strongly correlated with wind speed. The highest wind speed is found in the DJF (Transition I) season. Maximum Hs (wave height) is found in DJF season, while Hs tends to be high in SON (Transition II) as well as DJF (Western Season), and Hs tends to be weak in MAM (Transition I) season.

Reconstructing Sea-States in the Southern Ocean Using Ship Motion Data

Sea state conditions can be estimated from the motion of a moving ship by converting its response to incident waves through the response amplitude operator. The method is applied herein to ship motion data from the icebreaker R/V Akademik Tryoshnikov and recorded during the Antarctic Circumnavigation Expedition across the Southern Ocean during the Austral summer 2016–17. The response amplitude operator of the vessel was estimated using two boundary element method models, namely NEMOH and HydroSTAR. An inter-comparison of model performance is discussed. The accuracy of the reconstructed sea states is assessed against concurrent measurements of the wave energy spectrum, which were acquired during the expedition with the marine radar WaMoS-II. Results show good agreement between reconstructed sea states (wave spectrum as well as integrated parameters) and direct observations. Model performances are consistent. Nevertheless, NEMOH produces slightly more accurate wave parameters when quantitatively compared against HydroSTAR.

ASSESSING UNCERTAINTY IN THE MODELING OF RUNUP AND SWASH MORPHODYNAMICS USING XBEACH

Phase-resolving numerical models are frequently used tools to investigate short and long wave transformation, nonlinear wave interactions, and wave runup. Moreover, nearshore morphodynamics can be explored with the recent advancement of the models and computational resources. Sea surface elevation time series that force phase-resolving models at the offshore boundary are often unavailable. Therefore, time series are usually recreated from wave energy-frequency spectra through the superposition of harmonics. The wave phases of the harmonics are unknown and therefore assumed to be randomly distributed. This implies that an infinite number of time series with different sequencing of waves can be recreated from a single wave-energy spectrum and, for that reason, recreated time series are a source of uncertainty in model predictions. This intrinsic uncertainty has been found to cause variability in wave overtopping of structures (e.g., Pearson et al, 2002; Williams et al., 2014; Romano et al., 2015) and in setup and runup at beaches (McCabe et al., 2011; Torres-Freyermuth et al., 2019). Torres-Freyermuth et al. (2019) investigated the effect of intrinsic uncertainty on runup at planar beaches for different wave conditions and beach slopes and suggested that uncertainty is especially important under dissipative conditions. Yet unknown is the effect of intrinsic uncertainty on bed evolution. Here we assess the effect of intrinsic uncertainty on inner surf and swash zone evolution at three beaches with different beach morphology.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/w3zi3Yoo170

Generation of 3-hr Long-Crested Waves of Extreme Sea States With HOS-NWT Solver

The accurate control of wave fields generated in experiments and numerical simulations is of great interest for the ocean engineering community. In the context of wave-structure interactions, the recommended practices of classification societies are indeed based on the definition of a wave spectrum, that needs to be reproduced. The present work intends to address this problem from the numerical point of view, using a Numerical Wave Tank equipped with a wavemaker and an absorbing beach, based on the High-Order Spectral method (HOS-NWT). The challenging case of the generation of 3-hours long-crested extreme sea states is studied in details. An iterative procedure to reproduce a target wave spectrum at a given distance from the wavemaker is proposed. The quality of the sea state obtained is evaluated using several criteria defined from spectral quantities. A validation is first performed with a highly nonlinear but non-breaking sea-state. Statistical crest distributions obtained are compared with the Forristall and Huang distributions [1,2]. Then, the Gulf of Mexico 1,000 Year Return Period wave condition is generated. This corresponds to an extreme sea state with significant wave breaking occurrence. The numerical solver needs to be able to account for this phenomenon [3]. The Tian breaking model [4, 5] is calibrated to realistically reproduce the dissipation due to breaking, with particular attention paid to the spatial discretization, enlightening its significant effect on breaking model actions. Consequences on the iterative correction process are studied. The computed statistical quantities appear to be significantly different changing the spatial discretization, while the wave energy spectrum stands the same. It questions the relevance of the characterization of a sea state with the sole wave energy spectrum.

Springing Analysis of a Passenger Ship in Waves

Traditionally, the evaluation of global loads experienced by passenger ships has been based on closed-form Classification Society Rule formulae or quasi direct analysis procedures. These approaches do not account for the combined influence of hull flexibility, slenderness, and environmental actions on global dynamic response. This paper presents a procedure for the prediction of the global wave-induced loads of a medium-size passenger ship using a potential flow Flexible Fluid Structure Interaction (FFSI) model. The study compares results from direct long-term hydro-structural computations against Classification Society Rules. It is demonstrated that for the specific vessel under consideration: (a) the elastic contributions of the responses on loads are negligible as springing effects occur outside of the wave energy spectrum, (b) deviations of the order of 28% arise by way of amidships when comparing direct hydrodynamic analysis predictions encompassing IACS UR S11A hog/sag nonlinear correction factors and the longitudinal strength standard, and (c) the interpretation of the wave scatter diagram influences predictions by approximately 20%. Based on these indications, it is recommended that further parametric studies over a range of passenger ship designs could help draw unified conclusions on the total influence of global and local hydrodynamic actions on passenger ship loads and dynamic response.

Lyapunov Function based Criteria for Ship Rolling in Random Beam Seas

The aim of this study is to present a Lyapunov function which can be used to derive an intact stability criterion for a ship in random beam seas. First, the mathematical model of the rolling motion of ships in random beam seas is introduced. The random wave excitation is described by a spectrum which is depended on the wave energy spectrum and the amplitude of the moment of roll. This spectrum is generated by a second order linear filter. Second, the methodology of creating a Lyapunov function is explained briefly. Then, there is outlined the way by which Lyapunov function can be used as the intact stability criterion for a ship. The proposed criterion is derived by considering the weather criteria for German naval vessels. Finally, the coherence of the boundary of safe basin obtained by Lyapunov function with the numerical results obtained by Euler-Maruyama Method is presented. From the results it can be deduced that the Lyapunov function can be used to define an intact stability criterion.

Diffusion of inertia-gravity waves by geostrophic turbulence

The scattering of inertia-gravity waves by large-scale geostrophic turbulence in a rapidly rotating, strongly stratified fluid leads to the diffusion of wave energy on the constant-frequency cone in wavenumber space. We derive the corresponding diffusion equation and relate its diffusivity to the wave characteristics and the energy spectrum of the turbulent flow. We check the predictions of this equation against numerical simulations of the three-dimensional Boussinesq equations in initial-value and forced scenarios with horizontally isotropic wave and flow fields. In the forced case, wavenumber diffusion results in a $k^{-2}$ wave energy spectrum consistent with as-yet-unexplained features of observed atmospheric and oceanic spectra.

Effect of Wave-Current Interaction on Strong Tidal Current

We consider the influence of wave-current interactions (WCI) on the tidal energy resource through changes in the velocity field of tidal currents. In order to investigate this, we have run three models: SWAN (stand-alone), ROMS (stand-alone) and COAWST (two-way coupled ROMS and SWAN model). The research area of our studies is Alderney Race, France, an area with strong currents, which has a strong potential for tidal turbine deployment. The time period used for the simulations was March 2008, when a strong storm hit the Alderney Race area and produced significant wave heights (Hs) of up to 7 m and a Stokes drift near the surface close to 0.3 m/s. Furthermore, in order to see the extent of the influence of large waves on current parameters, two virtual storms with larger waves have been generated by magnifying the wave energy spectrum and changing the frequency of the spectrum of the real storm in March 2008. The 3D and the barotropic velocity field were analysed in order to see if the WCI in the waters of Alderney Race during storm conditions can cause a significant increase or decrease of the current speed and through which mechanisms. This study also investigates the Turbulent Kinetic Energy (TKE) in order to portray the turbulent conditions in the area of interest which are important for resource characterisation and device design.