With the aim of overcoming the shortcomings of traditional approaches, in this paper, an exponential Weibull distribution for fitting the significant wave height data is proposed in order to calculate more accurately the sea-state parameter distribution tails and to extrapolate well. This proposal is applied in predicting the probability distribution tails of a measured ocean wave dataset, and its accuracy is clearly demonstrated. The proposal is subsequently utilised in combination with Monte Carlo sampling to form a new environmental contour method for deriving a 50 year contour line based on the aforementioned measured ocean wave dataset. The derived environmental contour line is compared with that predicted by using a traditional contour line approach. Additionally, the engineering significance of using a more reliable environmental contour line, such as the one derived using the proposed new method for predicting the long-term design force values for an ocean sustainable energy system is highlighted. In conclusion, the newly proposed environmental contour method is recommended to be used when predicting the extreme dynamic response values for the safe and successful design of ocean sustainable energy systems.

A hybrid random-forest-based subset simulation (RFSS) method for probabilistic assessment of scour around pile groups under waves is proposed. In the RFSS, a random forest is used to replace the true limit state function (LSF); it is updated based on design samples in the first and last levels of the subset simulation method. For modelling, 127 laboratory datasets collected from the literature were used. First, an existing equation for predicting the scour depth around piles was modified using a metaheuristic approach. The performance of the modified equation was compared with existing equations and models. The modified equation was found to be more accurate than the existing formulas and AI-based models. A probabilistic model based on the RFSS was then developed by considering the modified formula as the LSF of scour depth. Solving two numerical problems, one hydraulic engineering problem and one scour problem validated the robustness and accuracy of the structural reliability method. The results showed that the RFSS is a robust and efficient method for solving high-dimensional real-world problems. Furthermore, compared to the Monte Carlo simulation, the RFSS was able to estimate the reliability index with less computational cost and the same accuracy.

This paper describes the dynamic behaviour of offshore structures modelled as discrete dynamic systems with the installation of innovative smart-tuned liquid column dampers (TLCDs). The use of advanced nano-fluids enhances the mechanical properties of the TLCD and allows the conventional passive system to be modified into a semi-active damping system. The magnetic force is modelled as an additional non-linear stiffness applied on the main structure once the magnetic field is activated. This new approach brings novel perspectives in reducing structural vibrations with respect to conventional TLCD systems. The aim of the study is to present a numerical investigation of the parameters involved in the dynamic behaviour of these systems subjected to random forces. In particular, a comprehensive analysis of a simplified structural model as a two-degrees-of-freedom system is given. Mathematical details and procedures using magneto-rheological-TLCD dampers without the need for commercial frameworks are presented. The present coupled system of ordinary differential equations is solved in a Matlab environment by using the built-in Runge–Kutta implementations for the solution of non-linear equations. This allows engineers and designers to obtain an initial estimation of the structural behaviour prior to in-depth simulations and analysis.

The Amalia lander is a modular gravity-based structure capable of executing different tasks in subsea conditions such as monitoring, surveillance and docking autonomous underwater vehicles, and could work as a platform for validating coatings, damage at foundations and scour protections and integrity of new materials, among other applications. This lander has a unique complex geometry and is made of the eco-friendly material polyoxymethylene, a high-performance thermoplastic of low cost, low density and high stiffness. This paper elaborates on the latest design developments of Amalia, including in situ material characterisation and numerical modelling activities, which focus on fulfilling the rising needs of the blue economy in the subsea engineering field. Material characterisation included tensile and Charpy impact experimental tests. The experimental curve was used to improve the numerical models (Ansys software). Full-scale data, obtained at Berlenga Grande Island, were used to compile design information on loads and boundary conditions in order to set numerical and experimental trials used to study Amalia's structural reliability. The Amalia lander was studied and its design was upgraded, the details of which are presented here. Further research showed that both the interface between the rod and the ballast weight and the bearing connection between the cage and the sphere fork can be improved.

A proper description of the ocean wave climate is of great importance for coastal and ocean engineering design and operation. Marine structures must be designed and constructed so they can withstan...

The dynamic performance of a work ship with a mooring line failure was studied. A fully coupled dynamic analysis program (Ansys Aqwa) was applied to simulate ship motions and mooring line dynamics. The first- and second-order wave excitation forces were calculated using the three-dimensional diffraction/radiation theory, and the behaviours of the mooring lines were analysed using a non-linear finite-element method. Under the combined environmental loads of waves and wind, one mooring line was intentionally disconnected at a certain moment. Then, the dynamic response after the mooring line breaks, the energy distribution characteristics in the motion response spectrum and the mean tension variation of the remaining mooring lines were assessed. The results showed that sudden failure of the mooring line significantly affected the performance of the ship. Therefore, to ensure the structural integrity of the ship system and the safety of personnel on deck, the influence of a mooring line failure on a ship should be investigated in advance.

This paper investigates the dynamic recovery policies for liner shipping services with the consideration of buffer time allocation and uncertainties. The aim of this study was to allocate the buffer time at the tactical level and then determine optimal options of actions, including speed optimisation strategy, port skipping and acceleration rate choice, for recovering from disruptions due to various uncertainties or random adverse events, which cause vessel delays. To achieve this, an attempt was made to obtain the optimal balance among economic, environmental and service reliability objectives. A novel mathematical formulation is introduced to solve the robust vessel scheduling problem with short- and long-term decisions. Furthermore, two heuristics were tested to solve the proposed model. Experiments on a container liner shipping service showed the validity of the model and a set of managerial insights were gained from them.

An experimental model of an Icelandic-berm breakwater has been set up in the hydraulic laboratory of Tarbiat Modares University using irregular waves. Experimental model tests have been carried out using a wide range of sea-state conditions and geometrical parameters to measure different parameters, such as the eroded area (Ae), the berm recession (Rec) and the depth of the intersection point of initial and reshaped profiles (hf). A stability formula is proposed to establish the relationship between the damage parameter of the Icelandic-berm breakwater (Sd) and the non-dimensional form of Rec and hf. The application of the given formula for estimating the berm recession in the phenomenon and practical cases was evaluated employing the Sirevåg berm breakwater. The results of the evaluation highlight the appropriate estimation of berm recession. Moreover, some recommendations are suggested to consider berm parameters, such as the berm width, the berm elevation from still water level and the height of class I stones, as an Icelandic-type berm breakwater design criterion for future engineers. Eventually, taking all the proposed formulae and recommendations into consideration, a design tool for engineers in berm design of berm breakwaters has been provided.

Offshore structures have a long service life and involve high cost. However, the working environment of offshore structures is harsh. When an accident occurs, it causes an adverse social impact and economic loss. Therefore, in the design process of offshore structures, in order to enhance their safety, this is an important problem that needs attention. Reliability-based design and optimisation (RBDO) using saddlepoint approximation (SA) is a powerful method to enhance the reliability of offshore structures. The SA utilises a cumulant generating function and saddlepoint to approximately express the probability density function and cumulative distribution function of a limit-state function. To further improve the accuracy of reliability evaluation in RBDO with SA, in this study, a mean-value second-order SA (MVSOSA) is introduced. A RBDO with MVSOSA strategy is proposed for the design problem of a wellhead platform. An engineering case study illustrates the application of the proposed method.

A depth-averaged two-dimensional (2D) numerical model was developed to investigate hydrodynamics in estuaries. The Qiantang estuary is taken as a demonstrative case study. The Qiantang estuary is f...

The sustainability of the planet is a burning issue that has affected all areas of life. The port sector is also affected by this increasing focus on protecting the environment and making efficient and intelligent use of the available resources. The search for sustainable policies in the Spanish port system is a priority. A detailed analysis of the sustainability of the Spanish port system is presented here, through use of a graphic tool that is a pioneer in the port field: the business observation tool (BOT). The aim of this research study was to identify the minimum elements to be considered when formulating the concept of sustainability linked to Spanish ports, allowing the reality of the conditions of the port environment to be known and establishing possible scenarios to evolve beyond the observed reality, towards harmonious and balanced growth by means of an observation model through the BOT. This pioneering and innovative project in the application of this strategy has required research considered as approximate through analysis of the current condition of the Spanish port system and the study of adjacent ports as examples. The paper concludes with the fundamental idea of the need to promote the implementation of increasing measures towards intelligent ports.

This paper addresses the random wave-induced current in shallow water based on deep-water wind and wave statistics, where the wave-induced current is expressed in terms of the deep-water seastate wave parameters, significant wave height and mean zero-crossing wave period. The average statistical properties of the random wave-induced current in shallow water expressed in terms of the mean value and the standard deviation are presented. The results are exemplified by using long-term wind statistics from the northern North Sea and long-term wave statistics from the same ocean area. Overall, it appears that there is an agreement between the results based on these inputs from wind and wave statistics. The presented analytical method should be useful for making preliminary estimates of the random wave-induced drift in shallow water within seastates using either available deep-water wind statistics or deep-water wave statistics, which enhances the possibilities for assessing further the wave-induced current in, for example, near-coastal zones.

This paper deals with state of the art in structural health monitoring (SHM) methods in offshore and marine structures. Most SHM methods have been developed for onshore infrastructures. Few studies are available to implement SHM technologies in offshore and marine structures. This paper aims to fill this gap and highlight the challenges in implementing SHM methods in offshore and marine structures. The present work categorises the available techniques for establishing SHM models in oil rigs, offshore wind turbine structures, subsea systems, vessels, pipelines and so on. Additionally, the capabilities of proposed ideas in recent publications are classified into three main categories: model-based methods, vibration-based methods and digital twin methods. Recently developed novel signal processing and machine learning algorithms are reviewed and their abilities are discussed. Developed methods in vision-based and population-based approaches are also presented and discussed. The aim of this paper is to provide guidelines for selecting and establishing SHM in offshore and marine structures.

The reinforced concrete (RC) caissons, code-named Phoenix, still visible off the coast of Arromanches, France, have been exposed to marine immersion, tidal, splash and atmospheric conditions since 1944. Little evidence of corrosion of the steel reinforcement was observed during inspections in 2011, 2015 and 2019, although there was much structural damage. Archival material from the Second World War reveals the caissons were designed to low safety margins, without consideration of durability and constructed at a very fast rate mostly with unskilled labour, minimal material usage, without additives and no restrictions on adding water to aid concrete workability. Analysis of data that has recently become available indicates the concretes had a high cement content and were made with calcareous aggregates. It is concluded that these factors contributed to the high strength, low permeability and high remaining alkalinity of the concretes and hence to the very low evidence of reinforcement corrosion. When interpreted using recent experimental observations, these observations have implications for the design of new RC structures in marine exposures and for the prediction of the remaining life of older marine-exposed RC structures.

This paper outlines the evolution of joint probability methods in the design and assessment of sea defence structures in the UK, together with the key drivers for these different methods. It highli...

Despite efforts to maintain supply chains unaltered as a result of the Covid-19 pandemic, statistics published after the second quarter (Q2) of 2020 have confirmed a drop in maritime traffic in European ports. Furthermore, the evolution of the pandemic indicates that stabilisation of traffic at levels prior to the Q1 of 2020 may take years. Port authorities in Europe, in an overall context of landlord port governance, are already being challenged, due to the need to ensure the provision of port technical services (mooring, pilotage and towage). In addition, the cost adaptability of these services to the current situation could be confronted by the European legal framework that demands transparency and proportionality in port rates in order to provide an effective cost of services. This paper analyses the impacts of Covid-19 on European ports, first by quantifying traffic drop after Q2 of 2020 and then calculating its effects on the cost of port technical services, in a general context of lack of flexibility in the cost structures of private providers. Due to this ongoing situation, a rise in rates, allowed by the port authorities, could mean that the prices of port services are not aligned with effective costs, along with loss of competitiveness.

The collaborative design of maritime structures involves not only multiple disciplines, but also uncertainty of information. Collaborative optimisation (CO) is a powerful multidisciplinary design and optimisation strategy known for its two-layer structure. In the original mathematical formulation of system-level optimisation, the second-level compatibility constraints are utilised. However, this makes a system-level CO algorithm have additional non-linear characteristics. Furthermore, during design optimisation considering uncertainty, the introduction of uncertainty quantisation increases complexity. Overall, the approach can reduce accuracy and efficiency. To solve these problems, a decoupling strategy called sequential optimisation and reliability assessment is proposed in this paper together with a collaborative uncertainty design and optimisation model. Three examples are provided to show how this hierarchical strategy can be applied to modern distributed maritime engineering design processes.

The decomposition of gas hydrates releases gas and water at volumes much larger than the original volume. The gas escapes violently, which destroys seabed sediments and can even cause geological disasters. To explore the effect of natural gas hydrate decomposition on underwater slopes, laboratory experiments were conducted to observe the features of slope failure. Aeration was used to model the gas that was produced by hydrate decomposition, and the results were as follows. (a) Once air filled into the bottom of the underwater slope, the pore pressure at the slope was altered, which eventually caused the slope to fail. (b) The formation of pockmarks corresponded to the variations in the pore-water pressure. (c) The theoretical analysis results showed that the sedimentation rate of fine particles (d < 0.4 mm) was lower than the water flow velocity, indicating that these particles were carried away with the air–liquid two-phase flow, which eventually caused the pockmarks to develop into craters.

Wind effects on wave overtopping over a fully impermeable vertical sea wall were studied numerically using the open-source computational fluid dynamics library OpenFoam. A pressure gradient correction term was incorporated in the momentum equations. In recent studies, it was found that, in the absence of wind, an increase in wave steepness results in a reduction of wave overtopping. This is related to the instability of the standing wave formed at the front of a vertical structure. Such instability was noticed in the range of steepness 0.285–0.443 from previous physical experiments for a regular wave interacting with a vertical structure. The existence of this regime was confirmed in the current study. It was also found that the stability of the standing wave determines the shape and volume of the overshooting jet, which has a strong effect on wave overtopping. When the wind is relatively weak (e.g. a wind speed of 10 m/s) it is unable to alter the overshooting jet very much, meaning a weak wind effect on wave overtopping. When the wind is strong (e.g. a wind speed of 30 m/s) it completely deforms the overshooting jet resulting in overtopping discharge almost three times that without wind.