Ocean Engineering Applications Research Articles

Coupling characteristics of bubbles with a free surface initially disturbed by water waves

The interactions between bubbles and water waves have important applications in ocean engineering, and their coupling characteristics are strongly associated with the wave phase angle, wavelength, and wave amplitude. Based on the assumption that the liquid is inviscid and incompressible, the coupling characteristics between bubbles and water waves are solved by the Euler equations with the finite volume method, and the bubble surface and water wave surface are tracked by the front tracking method. The accuracy of the numerical method is verified by comparison with a spark-generated bubble experiment. Compared with the bubble near the initially plane free surface, the rising height of the water spike is reduced by water waves in the crest state, where a concave shape forms on the falling water wave during bubble contraction when the wavelength λ≤ 4.00 and the wave amplitude h≥ 0.364. The rising height of the water spike is significantly strengthened by water waves in the trough state with smaller wavelengths and larger wave amplitudes, which produce a thinner and higher water spike. The bubble cycle is shortened by water waves in the crest state with smaller wavelengths and prolonged by water waves in the trough state with smaller wavelengths and larger wave amplitudes. The results presented in this paper provide guidance for the study of underwater explosions in complex water wave environments.

Tailoring the Local Design of Deep Water Composite Risers to Minimise Structural Weight

Following the rising technological advancements on composite marine structures, there is a corresponding surge in the demand for its deployment as ocean engineering applications. The push for exploration activities in deep waters necessitates the need for composite marine structures to reduce structural payload and lessen weights/loads on platform decks. This gain is achieved by its high strength–stiffness modulus and light-in-weight attributes, enabling easier marine/offshore operations. Thus, the development of composite marine risers considers critical composite characteristics to optimize marine risers’ design. Hence, an in-depth study on composite production risers (CPR) is quite pertinent in applying composite materials to deep water applications. Two riser sections of 3 m and 5 m were investigated under a 2030 m water depth environment to minimise structural weight. ANSYS Composites ACP was utilized for the CPR’s finite element model (FEM) under different load conditions. The choice of the material, the fibre orientation, and the lay-up configurations utilised in the modelling technique have been reported. In addition, the behaviour of the composite risers’ layers under four loadings has been investigated under marine conditions. Recommendations were made for the composite tubular structure. Results on stresses and weight savings were obtained from different composite riser configurations. The recommended composite riser design that showed the best performance is AS4/PEEK utilising PEEK liner, however more work is suggested using global design loadings on the CPR.

Multidimensional Maximum Entropy Model and Its Application in Ocean Engineering

Multidimensional Maximum Entropy Model and Its Application in Ocean Engineering

A truncated, translated Weibull distribution for shallow water sea states

Reliable probabilistic information of the long-term ocean wave climate is important in many coastal and ocean engineering applications such as the design of marine and coastal structures. There is therefore a need to establish accurate models for the long-term distribution of relevant metocean variables. One of the most important wave parameters in marine design is the significant wave height, which is a measure of the severity of the sea state, and wave loads are typically described in terms of this and other variables. Hence, a lot of effort has been put on the proper probabilistic modelling of significant wave height. However, probability distributions proposed to model significant wave height have mostly focused on deep water conditions and less efforts have been put on shallow water conditions. This paper proposes a truncated, translated Weibull distribution for the long-time distribution of significant wave height in shallow waters and demonstrates that the model fit shallow water data quite well. In particular, the proposed model describes shallow-water wave data better than the commonly used 3-parameter Weibull distribution, which is often the preferred distribution for deep water locations.

An accurate and robust axisymmetric SPH method based on Riemann solver with applications in ocean engineering

The present work develops an accurate and robust axisymmetric SPH method by introducing the Riemann solver into the framework of axisymmetric SPH. To reduce numerical dissipations caused by the intrinsic numerical viscosity of the Riemann solver, PVRS Riemann solver with MUSCL reconstruction is embedded into the scheme of the axisymmetric Riemann SPH. In addition, in order to maintain the uniformity of particle distributions, the volume adaptive scheme and the particle shifting technique are applied in this work. The advantage of the present axisymmetric Riemann SPH method is that it can consider the real compressibility of the air, which allows a larger stable time step in the simulation of the strongly-compressible flows. Through the three benchmark tests, including the Sod shock tube test, the Sedov point explosion test and the blast wave problem test, the accuracy of the present axisymmetric Riemann SPH method is verified. Then this method is applied to the simulations of some practical issues in ocean engineering, including the shockwave propagation of the underwater explosion, the water entry of the sphere and the coalescence of an oscillating bubble pair.

Simultaneous short-term significant wave height and energy flux prediction using zonal multi-task evolutionary artificial neural networks

The prediction of wave height and flux of energy is essential for most ocean engineering applications. To simultaneously predict both wave parameters, this paper presents a novel approach using short-term time prediction horizons (6h and 12h). Specifically, the methodology proposed presents a twofold simultaneity: 1) both parameters are predicted by a single model, applying the multi-task learning paradigm, and 2) the prediction tasks are tackled for several neighbouring ocean buoys with such single model by the development of a zonal strategy. Multi-Task Evolutionary Artificial Neural Network (MTEANN) models are applied to two different zones located in the United States, considering measurements collected by three buoys in each zone. Zonal MTEANN models have been compared in a two-phased procedure: 1) against the three individual MTEANN models specifically trained for each buoy of the zone, and 2) against some state-of-the-art regression techniques. Results achieved show that the proposed zonal methodology obtains not only better performance than the individual MTEANN models, but it also requires a lower number of connections. Besides, the zonal MTEANN methodology outperforms state-of-the-art regression techniques. Hence, the proposed approach results in an excellent method for predicting both significant wave height and flux of energy at short-term prediction time horizons.

Deep Learning Approach for Submerged Image Enhancement

Abstract: Because of underwater pictures application in ocean engineering, ocean research, marine biology, and marine archaeology to name a few, underwater picture enhancement was widely publicized in the last several years. Underwater photos frequently upshot in low contrast, blurred, color distortion, hazy, poor visible images. This is because of light attenuation, absorption, scattering (forward scattering and backward scattering), turbidity, floating particles. As a result, effective underwater picture solution must be developedin order to improve visibility, contrast, and color qualities for greater visual quality and optical attractiveness. Many underwater picture enhancing approaches have been proposed to overcome these challenges; however they all failed to produce accurate results. Hence for this we first undertook a large scale underwater image dataset which is trained by convolution neural network (CNN) and then we have studied and implemented a deep learning approach called very deep super resolution (VDSR) model for improving the color, contrast, and brightness of underwater photos by using different algorithms such as white balance, histogram equalization, and gamma correction respectively. Moreover, our method is compared with the existing method which reveals that our method surpassesthe existing methods Keywords: CNN, gamma correction, histogram equalization, underwater image enhancement, VDSR, white balance

Nonlinear time‐domain wave‐structure interaction: A parallel fast integral equation approach

AbstractWe report on the development and validation of a new numerical wave tank (NWT) solving fully nonlinear potential flow (FNPF) equations, as a more efficient variation of Grilli et al.'s NWT [Grilli et al., A fully nonlinear model for three‐dimensional overturning waves over arbitrary bottom. Int J Numer Methods Fluids. 2001; 35:829‐867], which was successful at modeling many wave phenomena, including landslide‐generated tsunamis, rogue waves, and the initiation of wave breaking over slopes. This earlier NWT combined a three dimensional MII (mid‐interval interpolation) boundary element method (BEM) to an explicit mixed Eulerian–Lagrangian time integration. The latter was based on second‐order Taylor series expansions for the mesh geometry and Dirichlet free surface boundary condition for the potential, requiring high‐order derivatives to be computed in space and time. Here, to be able to solve large scale wave‐structure interaction problems for surface‐piercing bodies of complex geometry, of interest for ocean engineering and naval hydrodynamics applications, the NWT is reformulated to use cubic B‐spline meshes and the BEM solution is accelerated with a parallelized fast multipole method (FMM) based on ExaFMM, one of the fastest open source FMM to date. The NWT accuracy, convergence, and scaling are first assessed for simple cases, by comparing results with those of the earlier MII‐NWT as a function of mesh size and other model parameters. The relevance of the new NWT for solving the targeted applications is then demonstrated for surface piercing fixed cylinders, for which we show that results agree well with theoretical and experimental data for wave elevation and hydrodynamic forces.

Experimental and numerical simulation on dynamics of a moored semi-submersible in various wave directions.

A moored floating platform has great potential in ocean engineering applications because the mooring system is necessary to keep a floating platform in the station. It relates directly to operational efficiency and safety of a floating platform. This study presents a comprehensive assessment of the dynamics of a moored semi-submersible in waves by performing model test and numerical simulation. First, a three-dimensional panel method was used to estimate the motion of a moored semi-submersible in waves. A semi-submersible is modelled as a rigid body with six degrees-of-freedom (6DOF) motion. Dynamic response analysis of a semi-submersible is performed in regular wave and irregular wave. Second, the model test is performed in various wave directions. An Optical-based system is used to measure 6DOF motion of a semi-submersible. Numerical results are compared with the experimental results in various wave directions. Wavelength and wave direction showed significant effects on the motion response of a semi-submersible in regular wave. Third, to obtain a better understanding of response frequencies, the time histories of motion responses in irregular wave are converted from the time domain to the frequency domain. Effects of the wave frequency component on motion responses and mooring dynamics are analyzed. Motion spectrum in irregular wave has a strong response to the natural frequency of a moored semi-submersible and the peak of wave frequency. Finally, exceedance probability is estimated to predict probable extreme values of motion responses of a moored semi-submersible as well as mooring dynamics.

Review on the local weak form-based meshless method (MLPG): Developments and Applications in Ocean Engineering

This paper reviews the developments and applications of meshfree method based on MLPG (Meshless Local Petrov Galerkin) in ocean engineering, primarily from the work carried out at IIT Madras and City, University of London, UK. Apart from discussing the various stages in the model development, this paper will also reports its applications to small amplitude waves, wave overtopping and breaking, porous layers, long wave run-up, vegetation, floating bodies in waves, wave interaction with elastic structure and two phase flow modelling. Generally, the Navier – Stokes equation will lead to numerical dissipation for long distance propagations and increase in computational time. In order to avoid this, one needs to look for a physics based approach. One of the successfully implemented approaches in MLPG was by coupling with fully nonlinear potential flow theory (FNPT), either one-way or two-way. In this paper, we bring out the advantages and implementation issues of MLPG. The paper also discuss the relationship with ISPH/MPS methods and some concepts that are adopted in both formulations. The paper ends with the key challenges and future directions in the development of the numerical method.

Probabilistic characterization of the effect of transient stochastic loads on the fatigue-crack nucleation time

The rainflow counting algorithm for material fatigue is both simple to implement and extraordinarily successful for predicting material failure times. However, it neglects memory effects and time-ordering dependence, and therefore runs into difficulties dealing with highly intermittent or transient stochastic loads with heavy tailed distributions. Such loads appear frequently in a wide range of applications in ocean and mechanical engineering, such as wind turbines and offshore structures. In this work we employ the Serebrinsky–Ortiz cohesive envelope model for material fatigue to characterize the effects of load intermittency on the fatigue-crack nucleation time. We first formulate efficient numerical integration schemes, which allow for the direct characterization of the fatigue life in terms of any given load time-series. Subsequently, we consider the case of stochastic intermittent loads with given statistical characteristics. To overcome the need for expensive Monte-Carlo simulations, we formulate the fatigue life as an up-crossing problem of the coherent envelope. Assuming statistical independence for the large intermittent spikes and using probabilistic arguments we derive closed expressions for the up-crossing properties of the coherent envelope and obtain analytical approximations for the probability mass function of the failure time. The analytical expressions are derived directly in terms of the probability density function of the load, as well as the coherent envelope. We examine the accuracy of the analytical approximations and compare the predicted failure time with the standard rainflow algorithm for various loads. Finally, we use the analytical expressions to examine the robustness of the derived probability distribution for the failure time with respect to the coherent envelope geometrical properties.

Particle methods in ocean and coastal engineering

This paper aims at providing a state-of-the-art review on the applications of particle methods in hydrodynamics-related problems in ocean and coastal engineering. The problems are placed into three categories according to their physical characteristics, namely, wave hydrodynamics and corresponding mass (air, oil, etc.) transport, wave-structure interaction, and wave-current-sediment interaction. For the first category, particle-based simulations of wave generation, propagation, breaking, as well as the associated turbulence production and dissipation, air entrainment, and mass transport, are reviewed. For wave-structure interaction, extensive structural types are considered that include fixed and moving (floating) structures, rigid and deformable structures, impermeable and porous structures, etc. For the third category, the latest advances of particle methods in wave/current interaction with sediments, i.e., sediment transport and coastal morphological changes, are outlined. This article also reviews the latest developments of particle methods with respect to enhancement of numerical stability, accuracy, efficiency and consistency in order to handle the multi-physics and multi-scale problems emerging from coastal and ocean engineering practices. Finally, the future perspectives of extending particle methods to a wider range of ocean and coastal engineering applications are highlighted.

A study of the shallow water waves with some Boussinesq-type equations

In this paper, analytic solutions and dynamic properties of a variety of Boussinesq-type equations are established via the complete discrimination system for polynomial method. All the existing single traveling wave solutions to these equations as well as some new solutions are shown, and the Hamiltonian and topological properties to these equations are also presented. Considering the significance of the Boussinesq-type equations, our results would have wide applications in ocean engineering and fluid mechanics, like describing and predicting the solitary and periodic waves in various shallow water models.

Enhancement of δ-SPH for ocean engineering applications through incorporation of a background mesh scheme

The improved Smoothed Particle Hydrodynamics (SPH) method with numerical diffusive terms, which is referred to as δ-SPH, has been widely applied into the studies of engineering problems, especially in the fields of ocean and coastal engineering. Nonetheless, there are still some drawbacks associated with δ-SPH model as in case of other particle methods. These drawbacks correspond to presence of unphysical pressure noise as well as imprecise satisfaction of dynamic free-surface boundary condition in numerical simulations. Through derivation and implementation of a so-called Background Mesh (BM) scheme and enforcing the spatial continuity of calculated source term of pressure equation (Equation of State; EOS), we present enhancements for δ-SPH in providing a more accurate pressure field as well as a more precise reproduction of free-surface. The enhancing effects of the newly proposed δ-SPH+BM are portrayed through several ocean engineering-related test cases including dam break and violent sloshing flows in both two and three dimensions. The incorporation of BM scheme is shown to result in enhanced calculation of pressure field as well as improved satisfaction of dynamic free-surface boundary condition as a consequence of enhanced density and pressure fields.

Operational Wave Forecast Selection in the Atlantic Ocean Using Random Forests

The existence of multiple wave forecasts leads to the question of which one should be used in practical ocean engineering applications. Ensemble forecasts have emerged as an important complement to deterministic forecasts, with better performances at mid-to-long ranges; however, they add another option to the variety of wave predictions that are available nowadays. This study developed random forest (RF) postprocessing models to identify the best wave forecast between two National Centers for Environmental Protection (NCEP) products (deterministic and ensemble). The supervised learning classifier was trained using National Data Buoy Center (NDBC) buoy data and the RF model accuracies were analyzed as a function of the forecast time. A careful feature selection was performed by evaluating the impact of the wind and wave variables (inputs) on the RF accuracy. The results showed that the RF models were able to select the best forecast only in the very short range using input information regarding the significant wave height, wave direction and period, and ensemble spread. At forecast day 5 and beyond, the RF models could not determine the best wave forecast with high accuracy; the feature space presented no clear pattern to allow for successful classification. The challenges and limitations of such RF predictions for longer forecast ranges are discussed in order to support future studies in this area.

A high-performance three-dimensional lattice Boltzmann solver for water waves with free surface capturing

The lattice Boltzmann method (LBM) is a numerical method with high parallel computational efficiency. However, currently few 3D numerical wave model based on LBM can be widely applied to water wave simulations in coastal engineering due to several problems related to numerical instability and numerical accuracy. To develop a high-performance 3D LBM solver for water wave simulations with free surface capture, a new 3D collision operator with sufficient numerical stability for wave simulation is first proposed. Then, wave generation and active wave absorption methods for the volume of fluid coupled with LBM are implemented in the solver to ensure accurate wave motion. The performances of this solver and other popular numerical wave solvers are analyzed and compared. The parameters of the numerical model are tested and determined to simulate wave transformation around structures. Through the comparison with three benchmark physical experiments, the accuracy of the presented solver proves that the present model is a promising tool for wave propagation and transformation simulation in practice. Benchmark tests and comparisons with the IHFoam and SPHysics solvers prove that the 3D LBM solver developed in this paper has a very good computational efficiency and parallel scalability. Overall, the work in this paper provides a new high-performance 3D solver for water wave simulations with free surface capturing for coastal and ocean engineering applications.

Building Suitable Datasets for Soft Computing and Machine Learning Techniques from Meteorological Data Integration: A Case Study for Predicting Significant Wave Height and Energy Flux

Meteorological data are extensively used to perform environmental learning. Soft Computing (SC) and Machine Learning (ML) techniques represent a valuable support in many research areas, but require datasets containing information related to the topic under study. Such datasets are not always available in an appropriate format and its preparation and pre-processing implies a lot of time and effort by researchers. This paper presents a novel software tool with a user-friendly GUI to create datasets by means of management and data integration of meteorological observations from two data sources: the National Data Buoy Center and the National Centers for Environmental Prediction and for Atmospheric Research Reanalysis Project. Such datasets can be created using buoys and reanalysis data through customisable procedures, in terms of temporal resolution, predictive and objective variables, and can be used by SC and ML methodologies for prediction tasks (classification or regression). The objective is providing the research community with an automated and versatile system for the casuistry that entails well-formed and quality data integration, potentially leading to better prediction models. The software tool can be used as a supporting tool for coastal and ocean engineering applications, sustainable energy production, or environmental modelling; as well as for decision-making in the design and building of coastal protection structures, marine transport, ocean energy converters, and well-planned running of offshore and coastal engineering activities. Finally, to illustrate the applicability of the proposed tool, a case study to classify waves depending on their significant height and to predict energy flux in the Gulf of Alaska is presented.

Study on bubble collapse near a solid wall under different hypergravity environments

Bubble has significant applications in ocean engineering. Aiming at the difficulty of conducting the underwater explosion bubble experiment with large charge in deep water, this paper adopts a new way to deal with this problem. On the basis of similarity theory, it is found that by considering the scaling relationship of gravitational acceleration, the explosion bubble with small charge in shallow water can satisfy the similar relationship with the explosion bubble with large charge in deep water. Therefore, the dynamic characteristics of the explosion bubble with large charge in deep water can be realized by changing the gravitational acceleration. With the assumption that the liquid is inviscid and incompressible, the bubble dynamics are solved by the Euler equations with the finite volume method, and the motion of the bubble interface is tracked by the front tracking method. Based on this model, the bubble collapse characteristics near a solid wall under different hypergravity environments are studied systematically. The results show that the bubble motion, the formation position of the bubble jet, the liquid jet velocity, and the pressure induced by the bubble will change significantly under different hypergravity environments.

Intercomparison of Three Open-Source Numerical Flumes for the Surface Dynamics of Steep Focused Wave Groups

NewWave-type focused wave groups are commonly used to simulate the design wave for a given sea state. These extreme wave events are challenging to reproduce numerically by the various Numerical Wave Tanks (NWTs), due to the high steepness of the wave group and the occurring wave-wave interactions. For such complex problems, the validation of NWTs against experimental results is vital for confirming the applicability of the models. Intercomparisons among different solvers are also important for selecting the most appropriate model in terms of balancing between accuracy and computational cost. The present study compares three open-source NWTs in OpenFOAM, SWASH and HOS-NWT, with experimental results for limiting breaking focused wave groups. The comparison is performed by analysing the propagation of steep wave groups and their extracted harmonics after employing an accurate focusing methodology. The scope is to investigate the capabilities of the solvers for simulating extreme NewWave-type groups, which can be used as the “design wave” for ocean and coastal engineering applications. The results demonstrate the very good performance of the numerical models and provide valuable insights to the design of the NWTs, while highlighting potential limitations in the reproduction of specific harmonics of the wave group.

Mechanical behavior and durability of coral aggregate concrete and bonding performance with fiber-reinforced polymer (FRP) bars: A critical review

Utilization of coral aggregates (CAs) for concrete production can effectively resolve the shortage of raw materials for construction in remote islands and reduce the energy consumption due to the shipping from the mainland. However, the porous nature of CAs and contained salt will affect the mechanical and durability performance of the concrete. This study aims to first summarize the characteristics of CAs and properties of coral aggregate concrete (CAC) and then propose future research needs based on the identified knowledge gaps. The previous studies indicate that the utilization of CAs in concrete can lead to significant strength loss and the elastic modulus of CAC is generally lower than that of ordinary concrete (OC). The workability of concrete at the fresh stage can also be reduced by the added porous CAs. To resolve these issues, the pre-treatment protocols were proposed to enhance the performance of CAC, including acid washing, surface coating, and utilization of alternative cementitious materials. However, the influence of CAs on the durability performance of concrete has not been fully understood, including drying shrinkage and carbonation resistance. The corrosion issue is also a serious threat to the durability performance of reinforced CAC. It is expected that using the non-corrosive fiber-reinforced polymer (FRP) bars can effectively resolve the corrosion issues, but the related investigations are quite limited. The research needs on the durability performance of CAC and the evaluation of FRP bars reinforced CAC are then proposed for further investigation. This study can serve as a solid base for future investigation on CAC and promote its application in ocean engineering. • The effects of coral aggregates on the properties of concrete are discussed. • Many effective measures to improve the performance of coral aggregate concrete are summarized. • The combination of fiber reinforced polymer bars and coral aggregate concrete is attractive.