Ocean Engineering Applications Research Articles

Comparison of wave modeling methods in CFD solvers for ocean engineering applications

Numerical wave tanks rely on specific models to generate realistic wave condition, propagate accurately the waves in the domain, and absorb the reflected waves at the boundaries. In this paper, three wave modeling methods for two-phase CFD solvers are compared, including the Internal Wave Generator method, the Relaxation Zone method, and the Spectral Wave Explicit Navier Stokes Equations (SWENSE) method. The first two methods consist in generating and absorbing the waves in specific regions of the domain, while the third achieves a potential/viscous coupling in the entire domain. These methods, implemented either in OpenFOAM or in ISIS-CFD are compared by simulating a fixed Catenary Anchor Leg Mooring (CALM) buoy in regular waves. The simulation results are compared with available experimental data obtained by a model test in the Ocean Engineering Tank of Ecole Centrale de Nantes. The comparison shows the efficiency and the accuracy of these waves modeling methods. A problem related to the turbulence modeling in two-phase flow is also remarked.

Inversion of HF Radar Doppler Spectra Using a Neural Network

For a number of decades, coastal HF radar has been used to remotely measure ocean surface parameters, including waves, at distances exceeding 100 km. The information, which has value in many ocean engineering applications, is obtained using the HF radar cross-section, which relates the directional ocean spectrum to the received radar signal, through a nonlinear integral equation. The equation is impossible to solve analytically, for the ocean spectrum, and a number of numerical methods are currently used. In this study, a neural network is trained to infer the directional ocean spectrum from HF radar Doppler spectra. The neural network is trained and tested on simulated radar data and then validated with data collected off the coast of Cornwall, where there are two HF radars and a wave buoy to provide the sea-truth. Key ocean parameters are derived from the estimated directional spectra and then compared with the values measured by both the wave buoy and an existing inversion method. The results are encouraging; for example, the RMSE of the obtained mean wave direction decreases from 20.6° to 15.7°. The positive results show that neural networks may be a viable solution in certain situations, where existing methods struggle.

Numerical investigation of inflatable structures filled with hydrogel beads

Utilizing deployable morphing structures in ocean engineering applications is a practice in its infancy. We propose an inflatable tubular beam using a hydrogel bead's ability to absorb water to achieve the desired structural shape and strength. It is therefore essential to know the strength of the morphed structure. The first step is to study the strength of the simple structural element. This paper focuses on the numerical modelling of bending tests on inflatable tubular structures filled with hydrogel beads to elucidate the various deformations of multiple compositions of bead/tube structures using the discrete element method. The properties of the tubes and beads were obtained, then calibrations of the micro numerical parameters were conducted. Twenty-four cases of bending tests were simulated. The results show that the degree to which the beads are filled, along with the bead's radius, have a direct effect on the composite structure's strength against deformation.

Generalized Extreme Value-Pareto Distribution Function and Its Applications in Ocean Engineering

In this paper, we establish a generalized extreme Value-Pareto distribution model and derive an analytical expression of Weibull–Pareto distribution model. Based on a data sample of 26-year wave height, we adopt the new model to estimate the design wave height for 500, 700 and 1000-year return periods. Results show that the design wave height from Weibull–Pareto distribution is between that of the Weibull distribution and that of the Pearson-III distribution. For the 500-year return period design wave height, the results from the new model is 1.601% lower than those from the Weibull distribution and 1.319% higher than those from the Pearson-III distribution. The Weibull–Pareto distribution innovatively considers the fractal features, extreme-value statistics and the truncated data in the derivation process. Therefore, it is a more holistic and practical model for estimating the design parameters in marine and coastal environments.

Significant Wave Height Prediction with the CRBM-DBN Model

AbstractIn recent years, deep learning technology has been gradually used for time series data prediction in various fields. In this paper, the restricted Boltzmann machine (RBM) in the classical deep belief network (DBN) is substituted with the conditional restricted Boltzmann machine (CRBM) containing temporal information, and the CRBM-DBN model is constructed. Key model parameters, which are determined by the particle swarm optimization (PSO) algorithm, are used to predict the significant wave height. Observed data in 2016, which are from nearshore and offshore buoys (i.e., 42020 and 42001) belonging to the National Data Buoy Center (NDBC), are taken to train the model, and the corresponding data in 2017 are used for testing with lead times of 1–24 h. In addition, we trained the data of 42040 in 2003 and tested the data in 2004 in order to investigate the prediction ability of the CRBM-DBN model for the extreme event. The prediction ability of the model is evaluated by the Nash–Sutcliffe coefficient of efficiency (CE) and root-mean-square error (RMSE). Experiments demonstrate that for the short-term (≤9 h) prediction, the RMSE and CE for the significant wave height prediction are <10 cm and >0.98, respectively. Moreover, the relative error of the short-term prediction for the maximum wave height is less than 26%. The excellent short-term and extreme events forecasting ability of the CRBM-DBN model is vital to ocean engineering applications, especially for designs of ocean structures and vessels.

Quasi-static indentation and impact in glass-fibre reinforced polymer sandwich panels for civil and ocean engineering applications

Sandwich structures comprising glass-fibre reinforced polymer faces and low-density core constitute an efficient and versatile constructive system for civil and ocean engineering structures. However, being multilayered with relatively soft core materials, they are particularly susceptible to damage under concentrated loads. Whilst numerous studies exist on the indentation and impact behaviour of sandwich composites, the great majority considers the thin-skinned laminates used by the aeronautical industry. To mitigate the lack of studies on the significantly thicker and more robust civil and ocean engineering sandwich laminates, the quasi-static indentation and low-velocity impact behaviour of such panels is experimentally studied. Three types of core materials (polyurethane and polyethylene terephthalate foams and end-grain balsa) and five different indenters, of varying shape (hemispherical versus flat) and diameter (10, 20 and 30 mm), are considered. Flat and larger indenters required higher loads and energies for first damage and perforation. The first damage and peak resistance values of the polyethylene terephthalate panels were, respectively, 15 and 8% higher than in the polyurethane panels; for the balsa panels, such figures were 20 and 10%. The polyurethane panels showed the highest energy absorption capacity. Predictions of first damage resistance given by two analytical models (for flat and hemispherical indenters) were assessed against the gathered experimental data. The obtained predictions were reasonably accurate, but indicate a need for further calibration, mainly concerning the effects of core material.

A CONSISTENT DESCRIPTION OF THE SPATIAL DISTRIBUTION OF WIND GENERATED WAVES WITHIN HURRICANES

In tropical and sub-tropical regions, hurricanes (or tropical cyclones or typhoons) represent the most extreme meteorological systems. The complex vortex structure of the winds in such storms also represent a demanding test of the physics of numerical models. Despite the apparent complexity of these systems, the fact that the intense low pressure systems are well formed means that the wind field can be parameterized with surprising accuracy. This feature of the wind field, together with extensive insitu buoy and remote sensing measurements means that a detailed understanding of the spatial distribution of the waves and the form of the directional spectrum is emerging. This paper will summarize the various data sets available and present a consistent description of the hurricane wave field suitable for coastal and ocean engineering applications.

Concentrators for Water Waves

By introducing concepts from transformation optics to the manipulation of water waves, we design and experimentally demonstrate two annular devices for concentrating waves, which employ gradient depth profiles based on Fabry-Pérot resonances. Our measurements and numerical simulations confirm the concentrating effect of the annular devices and show that they are effectively invisible to the water waves. We show that transformation optics is thus an effective framework for designing devices to improve the efficiency of wave energy collection, and we expect potential applications in coastline ocean engineering.

An alternative method for computing hydrostatic performances of a floating body with arbitrary geometrical configurations

In the fields of naval architecture and ocean engineering applications, floating platforms or multi-hull vessels with very different geometrical appearance have been designed to meet their mission requirements. Many objects were built by composing a number of sub-objects in an arbitrary way because of the high flexibility available for the construction work. Because the composition of the sub-objects normally are not arranged along a certain direction in a fixed sequence, it could be sometimes troublesome for computing the hydrostatic data of such objects. In order to facilitate this computation more easily and flexibly, a method has been developed in this paper, which was derived from the simple principles of an exact pressure integration over triangles for getting the total buoyancy force vector and the static equilibrium condition between the buoyancy force and the weight of the floating object. The triangles thereby were generated by triangulation of the surfaces representing a whole floating object. Finally, applications on a high-speed trimaran hull and a floating Kuroshio current turbine were conducted for demonstrating the merit of this method. The placement of water compartments and free surface effects were further analysed to evaluate the changing ballast conditions for hydrostatic and transitional stabilities.

Numerical Uncertainty Analysis in Regular Wave Modeling

In recent decades, the use of computational fluid dynamics (CFD) in many areas of engineering as a research and development tool has seen remarkable growth. Recently, an increasing concern with the assessment of the quality of CFD results has been observed. Wave modeling is an important task in many ocean engineering applications. Although numerical modeling studies of waves can be found in the literature for many applications, it is hard to find studies that present the numerical uncertainties of the results. In this study, the numerical uncertainties in mean wave parameters simulated using a viscous model were estimated using a procedure based on grid/time refinement studies and power series expansions. starccm+ software was used to simulate wave propagation. The computational domain was discretized using a trimmer mesh. The results obtained for a regular wave with a wave steepness (H/L) equal to 0.025 are presented. The numerical uncertainties in mean wave height and mean wave period were estimated along the computational domain. The results indicate that the convergence properties of the mean wave parameters with the grid refinement depended on both position in the domain and the selected wave parameter.

On the state-of-the-art of particle methods for coastal and ocean engineering

ABSTRACTThe article aims at providing an up-to-date review on several latest advancements related to particle methods with applications in coastal and ocean engineering. The latest advancements corresponding to accuracy, stability, conservation properties, multiphase multi-physics multi-scale simulations, fluid-structure interactions, exclusive coastal/ocean engineering applications and computational efficiency are reviewed. The future perspectives for further enhancement of applicability and reliability of particle methods for coastal/ocean engineering applications are also highlighted.

Error control and adjustment method for underwater wireless sensor network localization

Underwater sensor position information is very important in Underwater Wireless Sensor Networks (UWSNs). The sensor collected information is only meaningful with the correct positions. While current method only processes underwater nodes individually, which causes the localization precision for each nodes varying severely. This problem is very common in both centralized network and distributed network. The varying localization precision causes real trouble especially in data fusion, aided navigation, and signal processing. To solve this problem and achieve a consistent localization precision in the network, we propose an error control and adjustment method to make all the sensor localization precision refined. We use the distance information between nodes to establish a network error adjustment model, which can improve the localization precision and make the network localization error consistent. The simulation and actual experiment proves that this method can make all the node positioning more precise, the localization precision can be lower than decimetres. This method can be widely used in UWSNs and show a favourable potential in ocean engineering applications.

Estimation of the probability density function of transmission loss in the ocean using area statistics

Predictions of acoustic transmission loss (TL) in the ocean and its uncertainty are useful for a variety of ocean and naval engineering applications. Previously, an ad-hoc technique, area statistics (AS), was developed as a computationally efficient method to estimate the probability density function (PDF) of TL in any uncertain ocean environment from a single range-depth TL-field calculation in that environment. Here, the performance of AS is reported for ten ocean environments having uncertain sound speed profile, bathymetry, and seabed properties. In each environment, a parabolic-equation-based prediction of TL from a point source was generated as a function of range and depth at frequencies of 100, 200, and 300 Hz using the most probable values of the uncertain environmental parameters. From these calculations, AS was used to estimate the PDF of TL at more than 3000 locations within the ten environments. These estimated PDFs are then quantitatively compared, via an L1-error norm, to PDFs generated from traditional Monte Carlo techniques for the same locations and frequencies. Current results show that the L1-error of the AS PDF is less than 0.5, indicating 75% or greater overlap between the AS and Monte Carlo PDFs, at 90% of the test locations. [Sponsored by ONR.]

In situ preparation of graphene/polypyrrole nanocomposite via electrochemical co-deposition methodology for anti-corrosion application

Graphene has attracted much attention and triggered extensive anti-corrosion applications due to its excellent electrochemical stability and robust barrier for molecules and ions. In this paper, a novel polypyrrole/reduced graphene oxide (PPy/rGO) nanocomposite was successfully prepared on carbon steel as an efficient protective coating for improving the anti-corrosion property. Graphene oxide (GO) was deposited onto carbon steel via potentiostatic technique, and PPy was obtained simultaneously by oxidation polymerization. Scanning cyclic voltammetry method was adopted to reduce GO into rGO to form PPy/rGO nanocomposite coating. Due to the synergistic effect of PPy and rGO, excellent anti-corrosion performance for carbon steel in simulated seawater was obtained. Impressively, the PPy/rGO-coated carbon steel showed 7.05 times higher corrosion resistance than that of bare carbon steel and revealed the excellent protection efficiency above 95.9%. The anti-corrosion mechanism of the PPy/rGO coating was also proposed. Our results suggested that the PPy/rGO composite coatings could serve as effectively protectors for anti-corrosion of seawater, therefore, they could envision potential applications in naval architecture and ocean engineering.

Numerical investigation and dynamic behavior of pipes conveying fluid based on isogeometric analysis

Dynamic analysis and design of slender structures subject to different types of applied forces is of considerable practical interest in ocean engineering and aerospace applications. In this paper, the stability of pipes subjected to influences induced by fluid flow is investigated by using IsoGeometric Analysis (IGA). IGA aims to use the exact Computer-Aided Design (CAD) geometry and reduce the geometrical errors introduced by approximation of the physical domain of the problem. It uses B-Splines and Non-Uniform Rational B-Splines (NURBS) as basis functions and provides several advantages, which make it suitable for efficient and accurate simulations. The mathematical formulation of the problem is developed based on the Euler-Bernoulli beam theory (EBT) and the plug-flow model for the fluid forces. Both divergence and flutter instabilities are investigated. The numerical results are compared with those obtained by other available methods and it is shown that the results are in good agreement with lesser number of degrees of freedom, which is a fundamental criterion for the computational cost of an analysis. It is also confirmed that the IGA as described in the present paper, can be used efficiently to predict the possibility of divergence and coupled-mode flutter in dynamic analysis of pipes conveying fluid.

Global changes of extreme coastal wave energy fluxes triggered by intensified teleconnection patterns

AbstractIn this study we conducted a comprehensive modeling analysis to identify global trends in extreme wave energy flux (WEF) along coastlines in the 21st century under a high emission pathway (Representative Concentration Pathways 8.5). For the end of the century, results show a significant increase up to 30% in 100 year return level WEF for the majority of the coastal areas of the southern temperate zone, while in the Northern Hemisphere large coastal areas are characterized by a significant negative trend. We show that the most significant long‐term trends of extreme WEF can be explained by intensification of teleconnection patterns such as the Antarctic Oscillation, El Niño–Southern Oscillation, and North Atlantic Oscillation. The projected changes will have broad implications for ocean engineering applications and disaster risk management. Especially low‐lying coastal countries in the Southern Hemisphere will be particularly vulnerable due to the combined effects of projected relative sea level rise and more extreme wave activities.

On the selection of bivariate parametric models for wind data

The joint modelling of wind speed and direction in an area is important for wind energy projects and a variety of ocean engineering applications. In the context of wind resource assessment, the analytical description of wind climate is usually confined to the description of wind speed; however, the accurate joint description of the directional and linear wind characteristics is also essential at the candidate sites for wind farm development. In this work, three families of models for the joint probabilistic description of wind speed and wind direction are examined and thoroughly evaluated, namely Johnson-Wehrly and two families of copulas, Farlie-Gumbel-Morgenstern and Plackett families. These models are applied on long-term wind data obtained by different measuring devices (five oceanographic buoys and one meteorological mast) for six different locations of the Greek and Spanish waters in the Mediterranean Sea. The proposed bivariate models are theoretically sound and tractable, since they are defined by closed relations and are constructed by considering the marginal (univariate) distributions of wind speed and wind direction along with an appropriate dependence structure of the involved variables. In the univariate case, wind speed modelling is based on a wide range of conventional and mixture distributions, while wind direction is modelled through finite mixtures of von Mises distributions. The evaluation of the bivariate models is based on seven bin-specific goodness-of-fit criteria, namely root mean square error, relative root mean square error, mean absolute error, index of agreement, chi-square statistic, adjusted coefficient of determination and normalized deviation. The obtained results suggest that the performance of the Johnson-Wehrly model is rather superior, since it provides better fits compared to the other two families of bivariate distributions for the overwhelming majority of the examined cases and criteria. The most efficient bivariate models are then implemented to estimate the detailed structure of wind power density at three selected locations.

Investigation on the dynamics of air-gun array bubbles based on the dual fast multipole boundary element method

The air-gun array has important applications in ocean engineering. In this work, new dynamic behaviors of the air-gun array bubbles were investigated. The new adaptive fast multipole boundary element method (FMBEM) was implemented to accelerate the calculation of large scale moving boundary problems. The dual boundary integral equation (BIE) with an optimal linear combination of the regular BIE and the gradient BIE was used to facilitate a faster convergent FMBEM. It has been verified that the accuracy of the present numerical model was satisfactory for the dynamic simulation and the overall computational cost was scaled to O(N1.1) with N being the number of unknowns, which surpassed the conventional BEM largely. The behavior of air-gun array bubbles was studied for different distribution forms of the air-guns with the gravity effect considered. By increasing the dimensions of the bubble array, it can be seen that the “shield effect” of outer bubbles on inner bubbles was more evident. Pressure gradient was the dominant factor that determined the re-entrant jet's direction. The period of bubble array was longer if array scale increased. The distance between bubbles versus the intensity of interaction effect has been studied. In addition, the evolutions and the movements of the bubbles are quite different in this kind of large scale problem.

The Hydrodynamic Nonlinear Schrödinger Equation: Space and Time

The nonlinear Schrödinger equation (NLS) is a canonical evolution equation, which describes the dynamics of weakly nonlinear wave packets in time and space in a wide range of physical media, such as nonlinear optics, cold gases, plasmas and hydrodynamics. Due to its integrability, the NLS provides families of exact solutions describing the dynamics of localised structures which can be observed experimentally in applicable nonlinear and dispersive media of interest. Depending on the co-ordinate of wave propagation, it is known that the NLS can be either expressed as a space- or time-evolution equation. Here, we discuss and examine in detail the limitation of the first-order asymptotic equivalence between these forms of the water wave NLS. In particular, we show that the the equivalence fails for specific periodic solutions. We will also emphasise the impact of the studies on application in geophysics and ocean engineering. We expect the results to stimulate similar studies for higher-order weakly nonlinear evolution equations and motivate numerical as well as experimental studies in nonlinear dispersive media.

Current achievements and future perspectives for projection-based particle methods with applications in ocean engineering

The paper aims at providing a comprehensive and up-to-date review on the latest achievements made in the context of particle methods, in particular the projection-based ones, with applications in ocean engineering. The latest achievements corresponding to stability, accuracy, energy conservation and boundary condition enhancements as well as advancements related to improved simulations of multiphase flows, surface tension and fluid–structure interactions are reviewed. The future perspectives for enhancement of applicability and reliability of these methods for ocean engineering applications are also highlighted.