Variations Of Wave Parameters Research Articles

Deep gated recurrent unit networks for time-domain long-term fatigue analysis of mooring lines considering wave directionality

Mooring lines are a crucial component of offshore mooring systems, and long-term fatigue damage assessment is a challenging task in mooring line design and structural health monitoring. Traditional methods require a large number of structural time-domain simulations. Because the sea state varies over time, the variations in wave parameters (e.g., wave heights, periods, and directions) must be considered in long-term fatigue damage assessment. Wave directions have usually been ignored in previous studies, while the wave direction sensitive analysis conducted in this study showed that the wave directions could not be neglected in the long-term fatigue damage assessment of mooring lines. Recent deep neural network (DNN) methods have shown great potential in mooring line/riser response prediction for offshore structures. However, the utilization of float responses as input data in these DNNs restricts their applicability during the structure design phase. To address this issue, a gated recurrent unit (GRU) network is proposed for mooring line tension modeling. The proposed GRU network surrogate models are capable of accurately predicting the mooring line tension using wave elevation components or float motion responses. The rain-flow counting algorithm, T-N approach, and Miner's rule were employed to estimate the structural fatigue damage. The results showed that the proposed method could replace the heavy cost numerical computation, assess the long-term fatigue damage with high accuracy and alleviate the data dependency of DNN methods.

Numerical Modelling of Wave Attenuation in Pile Breakwater

Pile breakwater is an artificial coastal structure consisting of closely spaced piles. Its benefits are similar to other coastal structures by attenuating the energy of the incoming wave. In this paper, the wave attenuation caused by the pile structure is investigated using a numerical model, namely the SWASH model. The model allows for simulating non-hydrostatic phenomena in coastal waters as driven by waves. The model setup is conducted in a rectangular wave flume with paddles to produce monochromatic waves on the left and the wave absorber on the other side. Several scenarios were carried out to determine the effect of variations in wave parameters. To deal with the efficiency of numerically modelled pile breakwater, we also investigate the transmission coefficient. We compare the result of the numerical model with experimental data, which took place in a wave flume at Balai Penelitian dan Pengembangan Pantai, Buleleng, Bali, Indonesia. The validation results demonstrate the capability of the SWASH Model to approximate the incident and transmitted wave height with good accuracy compared to experimental data.

Wave characteristics in the nearshore waters of Sanmen bay

The wave characteristics in the bay of central coast of Zhejiang are studied based on the AWAC-measured data for 1 year off Sanmen at 7.5 m water depth. The observed wave parameters are analyzed by statistical analysis and linear regression analysis, and moreover the variations of wave parameters and wave spectra in Sanmen Bay under the influence of typhoon are discussed. The results show that: The dominant wave direction and the strong wave direction are both E due to the topography of Sanmen Bay, while the one-tenth wave height (H1/10) is mainly under 0.8 m with a typical Rayleigh distribution of wave height. Due to the influence of typhoon Talim, the maximum wave height (Hmax) of 2.71 m was observed on 14 September 2017. The wave spectra estimated during typhoon Talim are mainly double-peaked, and the sea waves are mixed waves consisting of swells and wind-seas, when the low frequency swells about 0.08 Hz are in a dominant position and the high frequency wind-seas about 0.3 Hz are relatively weak. This study will be important as reference in the design of offshore structures as well as for disaster prevention and mitigation.

Assessment of wave characteristics and resource variability at a 1/4-scale wave energy test site in Galway Bay using waverider and high frequency radar (CODAR) data

This research presents an assessment of wave characteristics at the 1/4 scale wave energy test site in Galway Bay based on (1) data from a waverider buoy from 2009 to 2013 and (2) data from a high frequency radar system (CODAR) from 2011 to 2013. The main objective of this research is to provide an assessment of annual and seasonal wave characteristics and resource variability at a wave energy site. Such assessments are extremely important for wave energy test sites so as to inform the design, optimisation and maintenance of wave energy converters. An approach for classifying operational, high and extreme wave events is presented. The approach is based on percentage of occurrences of particular wave events and can be applied to any site and any wave parameter. In the present research it is separately applied to wave height and wave power. An additional objective is the validation of CODAR wave data for use in assessment of wave height characteristics; this was achieved by comparing CODAR data with waverider data. The research shows that the authors characterisation methodology is easy to apply and unambiguous to interpret. Due to the significant variation in wave parameters at the site from season to season and year to year, operational, high and extreme conditions are presented for the 5-year measurement period, individual years and individual seasons. The research also shows that wave heights determined from CODAR show good agreement with those from a waverider buoy and may be relied upon for accurate site characterisation.

Waves on the Water Surface — Mathematical Models — Part 1

The work presents new expressions related to wave energy density and flux based on Stokes and cnoidal waves theories. It shows that as progressive waves of finite amplitude propagate a compensatory reverse flow is formed within the bottom fluid layers. The existence of such flow was experimentally confirmed. Modified mathematical models for surface waves over a non-uniform bottom and of a free plane configuration are suggested. A method of calculating the wave transformation and the currents in the surf zone is proposed. Computations made over a wide range of variations in wave parameters are presented.

Co-existence of wind seas and swells along the west coast of India during non-monsoon season

Abstract. An attempt has been made to understand the co-existence of wind seas and swells along the west coast of India during non-monsoon season. Wave data were collected in different years during non-monsoon season (off Goa during May 2005, off Ratnagiri during January–February 2008 and off Dwarka during December 2007–January 2008), which is fairly a calm weather season along these regions. Diurnal variation in wave parameters is noticeable along the central west coast of India (off Goa and Ratnagiri), which is due to the interaction of multidirectional waves (both wind seas and swells) of varying magnitudes and frequencies. Swells are predominantly mature (91%) and old (88%) during late pre-monsoon and post-monsoon seasons, respectively. Sea Swell Energy Ratio quantifies wind sea, swell and mixed seas prevailing in these regions during non-monsoon season. Intermodal distance (ID) between the energy peaks is moderately separated during non-monsoon season, whereas, during the shamal events, energy peaks are very close to each other (ID ∼ 0). However, pure wind seas (ID ∼ 1) are weakly present and found to co-exist with the swells almost all the time during non-monsoon season. Wind sea growth has been found while the swell propagates opposite to the direction of the wind and wind sea. Wind seas have minimum angular spreads in multimodal state. Under low winds, the interaction between wind sea and swell dominates and thereby the multimodal state reduces to unimodal state. The fetch available for the evolution of the wind sea spectrum has been estimated, and it is found to be less than 150 km. For the fetch limited condition, a non-dimensional empirical relation has been derived relating the significant wind sea height in terms of wind speed and peak wind sea period, and this relation fits for the west coast of India.

Spatiotemporal variations in the statistical parameters of the shear wave splitting from local events beneath Eastern Hokkaido

Statistical analysis is carried out of the distribution of the fast Swave $$(\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\frown}$}}{\phi } )$$ , polarization azimuths, time delays between the split shear waves $$(\delta \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\frown}$}}{t} )$$ and the dominant frequencies of P waves $$(\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\frown}$}}{f} _P )$$ from weak seismic events that hit Eastern Hokkaido during the period of 1998–2003, which also includes strong events with M > 6 and the strong Tokachi-oki earthquake (M8.0) of September 26, 2003. The analysis revealed oscillatory pattern of variations in wave parameters along Eastern Hokkaido. In the rigid crustal blocks beneath the Tokachi and Kushiro Plains, stability is observed in the fast azimuth orientation and unstable behavior of $$\delta \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\frown}$}}{t}$$ and $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\frown}$}}{f} _P$$ in the interval of periods 0.5–2.5 years. In the weakened zones beneath the Hidaka Range and the Nemuro Peninsula, periodical alternation of $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\frown}$}}{\phi }$$ along orthogonal directions is revealed. It is found that the parameters of the waves coming from the seismic events originating in different depth intervals experience anomalous changes before strong earthquakes. These anomalies reflect depth changes in the type of deformation of the medium. Active deformation is observed beneath the Hidaka Range. Dynamic changes in beneath the stations on either side of the range (ERM, MYR), their antiphase pattern, and the discrepancies in the behavior of the parameters from the events that originate in different depths indicate that these regions act as active buffers in the redistribution of stresses in the Kuril-Japan arc-arc junction zone. The onset of instability that develops before the Tokachi-oki earthquake is marked by gradual shortening of the period of oscillations in $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\frown}$}}{\phi }$$ and transition to the north and east azimuths as well as by the decreasing of $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\frown}$}}{f} _P$$ from the intermediate-depth events starting from middle 2002, and for deep events, starting from 2000. The acceleration of the process begins in the middle of 2003 and is recognized by a noticeable increase in and a decrease in $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\frown}$}}{f} _P$$ beneath almost all stations.

Study on the wave climate variation to the renewable wave energy assessment

To reduce the dependence on fossil fuel and imported energy resources, Taiwan has ever-increasing needs of renewable energy. With the rapid development of the technologies of wave energy converter, the wave energy source will be able to meet parts the demand. The Energy Research Laboratories of the Industrial Technology Research Institute, Taiwan (2005), based on the statistic of one-year wave data, stated that the mean wave energy at the northeast coast of Taiwan reaches 11.56 kW/m, giving it the potential of wave power utilization. However, one of the major obstacles with the wave energy utilization is lack of long-term ocean wave measurements. The long-term variations in wave parameters impose changes in wave energy converter outputs. Lack of long-term data makes it difficult to assess the cost-benefit of wave energy conversion projects for the policy and decision makers. The present study aims to quantitatively evaluate the wave climate variations of the northwestern Pacific and the Taiwan Waters based on long-term wave data base. Wave observations around Taiwan have been performed since 1998, thus, earlier data of wave climate are not available. This study reconstructs the wave data of the northwest Pacific over the past three decades based on the SWAN numerical wave model that driven by NECP global reanalysis wind fields. The simulation results are compared and validated with measured data. The results show that the long-term wave climate variations around Taiwan consist of oscillations of three different periods, i.e. the seasonal, inter-annual and decade oscillations. The seasonal oscillation has significant amplitude that leads the wave energy one order magnitude greater in winter than in summer. In addition to seasonal changes, the wave energy features inter-annual variations, which are highly related to the El Nino and La Nina phenomena. In the La Nina years, the annual averaged wave energy could be double than in El Nino years. Finally, this study adopted the Man-Kendall Non-Parametric Test and the Hilbert Huang EMD method to analyze the long-term wave variation trends. The results showed that the wave height experienced climbing trends during 1976–1985 and 1997–2006, and a descending trend during 1985–1997. The reasons for wave climate oscillations in the decadal variation should be further investigation.

Response Sensitivity for Probabilistic Damage Assessment of Coastal Bridges under Surge and Wave Loading

The susceptibility of coastal bridges to damage during hurricane-induced storm surge has been illustrated along the U.S. Gulf Coast in several hurricane events. This factor poses a significant threat to the safety of nationwide transportation systems, effectiveness of postevent emergency response and recovery activities, and socioeconomic stability further afforded by functioning transportation infrastructure. Nationwide risk and loss assessment packages currently lack any reliable input models of bridge fragility to assess the risk to the transportation infrastructure posed by hurricane-induced storm surge and wave. However, these tools are essential for comparing the vulnerability of different bridge types, conducting regional risk assessment or loss estimates, and supporting decision making on risk mitigation activities. As a first step in the development of probabilistic models of bridge vulnerability subjected to hurricane scenarios, sensitivity studies are conducted to assess the significance of varying hazard and bridge parameters on the dynamic response of coastal bridges. Three-dimensional nonlinear finite element models are used to assess these demands under varying input modeling parameters, and an analysis of variance is conducted to evaluate the significance of each parameter. The sensitivity study reveals that the potential variation in wave parameters has the most statistically significant impact on the response of the bridge. Additionally, a second-level sensitivity study reveals that the most critical structural parameter is the deck mass followed by connection modeling parameters. The results of this study provide insight into modeling parameters that should receive careful treatment in probabilistic analysis of bridge vulnerability.

SIMULATION OF WAVE PRESSURE ON A VERTICAL WALL BASED ON 2-D NAVIER-STOKES EQUATIONS

This paper applies and develops a numerical model based on the two-dimensional vertical Navier-Stokes equations to simulate the temporal and spatial variations of wave parameters in front of vertical walls. A non-uniform grids system is performed in the numerical solution of the model by transforming a variable physical domain to a fixed computational domain. Through present model, beside some basic hydrodynamic problems of water waves such as wave profile and water particle velocities, standing wave pressures at the wall are examined. Numerical results of the present model are compared with laboratory data and with existing empirical and theoretical models. The comparisons show that the model can simulate reasonably the wave processes of the waves in front of vertical walls as well as the wave pressures on the wall.

A Numerical Study of Wave Refraction in Shallow Tidal Waters

Wave observations taken at two shallow water sites off the coast of south-west Wales, U.K. are examined. The buoys are located in a region of strong semi-diurnal tides and the observations show significant variation, at semi-diurnal frequencies, in period, amplitude and direction. The interaction between tides and waves is studied using linear theory of wave refraction by slowly varying currents and depths. It is shown that quasi-steady analytical models fail to reproduce the tidally-induced variations in wave parameters. A linear ray-tracing model, including the effects of both spatial and temporal variations in the tidal currents and elevations, improves the simulation of the observed modification of the waves. Short period waves respond to variations in current refraction over a tidal cycle; long period waves are more influenced by variations in water depth over a tidal cycle.

Group velocity of anisotropie waves—Part II: Conservative properties

It has been argued in Part I that traditional expression of multidimensional group velocity used in meteorology is only applicable for isotropic waves. While for anisotropic waves, it cannot manifest propagation of waves group along the trajectory of a reference wave point, and varies with rotation of coordinates. The general mathematical expression of group velocity which may be used also for anisotropic waves has been derived in Part I. It will be proved that the mean wave energy, momentum and wave action density are all conserved as a wave group propagates at the general group velocity. Since general group velocity represents the movement of a reference point in either isotropic or anisotropic wave trains, it may be used to define wave rays. The variations of wave parameters along the rays in a slowly varying environment are represented by ray-tracing equations. Using the general group velocity, we may derive the anisotropic ray-tracing equations, which give the traditional ray-tracing equations for isotropic waves.

Nonlinear beam waves in inhomogeneous media

Nonlinear potential space charge waves, caused by particle beam propagation in statistically inhomogeneous resistive media, are considered. Variations of wave parameters caused by the fluctuation are obtained. Complete analogy with the corresponding linear case is stated. All calculations are carried out in the hydrodynamic approximation.

Conceptual Model of Coarse Clastic Barrier Formation from Multiple Sediment Sources

Conceptual Model of Coarse Clastic Barrier Formation from Multiple Sediment Sources

Waves over the Arabian Sea during the southwest monsoon

A study of waves over the Arabian Sea was undertaken mainly for the operational purpose of giving wave forecasts for Bombay High area where oil drilling and production has been going on. For the southwest monsoon season of 1976 to 1978 daily observations from the rigs in Bombay High area were available. Thus three years' data have been analysed to study variations of wave parameters with time during monsoon. After the re-opening of Suez canal, the number of ships moving over the Arabian Sea has increased considerably. Moreover, large quantity of data has been collected by the Soviet Research vessels during the Monsoon-1977 experiment. All ships observations for 1977 have been analysed to get an idea of the space variations of wave parameters over the Arabian Sea.