In this paper, air entrapment during slamming is an investigation subjected to an experimental method of inquiry, analysed alongside a theoretical approach obtained from previous attempts to address similar matters. The experiment consisted of assembling three different sizes and depths of artificially created pockets underneath the 1:75 deck model of a 76 m x 76 m prototype to encourage air entrapment and study how this entrapped air affects local and global loads. A parametric study is ultimately conducted on the geometry of the pocket, altering area and depth to observe the response to the pressure. Air entrapment effects were observed to reduce the magnitudes of impact pressure inside the pocket while slightly altering the force time histories in x and z-directions. Force magnitudes for global forces are significantly close to the smooth deck results. However, horizontal force data are slightly higher than their corresponding smooth deck due to additional surfaces inside the pocket. In addition, a parametric study of the depth and size of the pocket reveals that pocket depth is the dominant parameter that affects the impact pressure inside a pocket.

This paper investigates wave-in-deck loads on a fixed offshore deck structure at three scales (1:75, 1:100, and 1:125 of a 76 m × 76 m prototype). Various wave conditions and air gap variations were examined, aiming to measure global forces and pressure at twelve specific points under each model. Froude's similitude law was applied for scaling, considering model dimensions, wave height, wave period, and air gap. Results show reasonable wave scaling, but force and pressure measurements exhibited discrepancies due to minor wave characteristic differences, emphasizing challenges in achieving precise scaling. Even slight variations in wave crest, height, and period led to notable differences in recorded loads. This study underscores the complexities of achieving perfect scaling for wave-in-deck loads on fixed offshore structures, citing wave behaviour and measurement uncertainties as contributing factors. It provides insights into scaling effects and emphasizes the need to consider these factors in experimental analyses, highlighting the challenges associated with achieving accurate scaling in such investigations.

An experimental investigation has been undertaken to determine the effects of fatigue on the high strain-rate material properties of high-performance steel used in modern naval vessel structures. A novel methodology to conduct tensile testing at low and high strain-rates on fatigued specimens was developed. A bespoke Split Hopkinson's Tension Bar clamping arrangement was designed to undertake the necessary high strain-rate testing of flat dog-bone specimens. Analysis of the microstructure of the specimens was performed alongside a comparison on the strain-rate sensitivity of the tested DH36 steel against other literature sources. Testing revealed no statistically significant effect of high cycle fatigue at high strain-rate as determined by a two-sample t-test, but revealed a possible effect on quasi-static material properties. The findings of this novel comparison between fatigued and virgin material properties of shipbuilding steel provides decision-makers and researchers with an understanding on the effect of fatigue on high strain-rate material properties.

When a ship enters service it has an implied or calculated design fatigue life. Factors including construction quality, loads, material performance, and operational profile are assumed. However, these factors vary through life. Failure of structural items due to fatigue cracking can lead to increased cost of ownership and reduced capability. Therefore, to allow informed decision-making, it is necessary to monitor the variables that influence a ship's fatigue life. This paper presents a new method whereby in-service data, fleet maintenance reports, and Finite Element Analysis are incorporated to predict the fatigue life and hence support the management of the remaining service life of a ship. The method is applied to a naval High Speed Light Craft to demonstrate its merit. The fatigue lives of different welded details are predicted using a practical implementation of the S-N curve approach, employed with strain and operational data acquired from an on-board hull monitoring system.

Modern warships are often constructed from aluminium alloys or high tensile steel, and their increasing range of operational roles indicates exposure to harsh seaway loads including slamming. These factors can lead to fatigue cracking, which can reduce operational availability. The objective of the present study is to improve understanding of the influence of variables in the fatigue analysis of a weight-optimised warship. The objective is met by analysing hull monitoring data acquired from a 56 m naval aluminium patrol boat, to determine the long-term importance of slamming and the correlation between the hourly number of slams, ship speed, and fatigue damage at two structural details. It was found that the effect of the ship’s speed on the fatigue damage is not statistically significant. In addition, a sizable proportion of the fatigue damage accumulated at low to moderate ship speed, when the patrol boat experienced slamming, rather than at higher speeds. This may be due to voluntary and/or involuntary speed reduction, which is not typically taken into account in numerical fatigue analysis. That is, the use of long-term distributions of the wave environment and ship speed may mask the effects of voluntary and/or involuntary speed reduction on slamming occurrence and the fatigue damage. This finding can lead to improved requirements setting and through-life structural management of weight-optimised warships.

Prediction of the hydrodynamic efficiency of a Wave Energy Converter (WEC) device is crucial to evaluate the design and the concept of the device. Experimental and numerical techniques are the main tools currently available for WEC designers; however, these techniques are still costly and too time expensive to be used for optimisation and commercial purposes. It is, therefore, important to develop an efficient and cost/time-effective technique in order to investigate the hydrodynamic characteristics of WEC devices. In this work, an Adaptive Neuro-Fuzzy Inference System (ANFIS) technique was developed to predict the hydrodynamic efficiency of WEC devices. ANFIS models were designed, trained and tested using published experimental datasets for the hydrodynamic efficiency of fixed Oscillating Water Column (OWC) devices, and different types of membership functions were examined to develop the best accurate model. ANFIS technique was found to provide good estimates in comparison with experimental results and can be used to predict the hydrodynamic efficiency of WEC devices during the early stages of design.

Increasing attention has recently been paid to the effects of localised pitting corrosion on the ultimate strength of marine structures. In this paper, an adaptive neuro-fuzzy inference system (ANFIS) method was developed to predict the ultimate strength reduction of steel plates with pitting corrosion subjected to uniaxial in-plane compressive loads. Published ultimate strength data-sets for unstiffened plates affected by pitting corrosion were used to train and test a series of ANFIS models composed of several input variables. To develop the best accurate model, rule-based fuzzy sets were used for mapping the inputs to the output using seven different types of membership functions. The two-sided Gaussian-type function was found to be more effective and less sensitive to the sample size than other functions tested. The developed method provided good estimates (maximum RMSE of 0.019) in comparison with published results obtained using the finite element and artificial neural network methods.

This paper presents results of two-phase flow numerical simulations of the dynamic behaviour of a Tension Leg Platform (TLP). The Computational Fluid Dynamics (CFD) simulations were based on the volume of fluid (VOF) method implemented in the CFD code STAR-CCM+. The TLP’s rigid body motions and the effect of tendons were simulated by means of an overset grid and massless spring lines, respectively. The global response and tendon tensions computed by the CFD code were found to be in good agreement with experimental measurements. CFD tools provided detailed results of the effect of wave impact including wave-in-deck loads and were able to predict some rare features such as tendon slackness and ringing response.

Model testing was conducted to investigate the feasibility of a Tension Leg Platform concept for an Oscillating Water Column (TLP-OWC) wave energy converter device. The tested TLP-OWC model was loosely based on a previously tested fixed OWC model modified to accommodate a tension leg mooring system. The designed experimental set-up allowed for the measurements of wave elevation in-phase to the model and inside the OWC chamber, OWC chamber air-pressure, impact wave pressure acting on the front wall, tendon dynamic response and the motion response. The Response Amplitude Operators (RAO’s) were employed in the analysis of the maximum motion response and tendon dynamic response of the model. From the attained results, the experimental investigation determined that the TLP-OWC is a promising concept in pushing OWC wave energy converters offshore. However, further hydrodynamic testing is required to test the global performance of the TLP-OWC in irregular wave conditions.

Marine and offshore structures constructed with stainless steel are regarded as having high corrosion resistance due to their superior self-passivating properties. However, they are equally susceptible to environmental degradation, especially due to pitting corrosion in highly corrosive marine environments. Pitting immersion tests performed on 304 austenitic stainless steel specimens using ASTM G48 presented significant challenges. Some of the issues encountered during these tests included unspecified experimental factors that control the pitting process such as pH, specimen size limitations, materials’ properties, and the variation on the quality of the test solution. To overcome these challenges, the effect of surface finishes and aeration of the test solution on the corrosion behavior of 304 stainless steel specimens in 6% ferric chloride were examined and compared. The result shows that an aerated solution has much lower concentrations of pits compared to quiescent solutions. Controlled aeration eliminates unwanted crevice corrosion background noise. Subsequently, to suit larger specimens, the ASTM G48 was modified. This study presents the modified ASTM G48 procedure. A series of pitting corrosion tests on stainless steel specimen with different thickness were conducted and data were statistically evaluated. The generalized extreme value distribution, such as Weibull, provides adequate statistical descriptions of the pit depth and pit diameter distributions. The modified ASTM G48 offered advantages in the extraction and interpretation of the data for pit characteristics in the accelerated pitting corrosion test simulating actual marine environment.

Model tests were conducted to investigate the global response of a conventional tension leg platform (TLP) due to wave-in-deck loads associated with extreme wave events in irregular long-crested waves of a cyclonic sea state. The experimental setup was designed to allow for the simultaneous measurement of wave surface elevations, rigid body motions, tendon tensions, as well as the pressure distribution at the model's deck underside. The obtained results demonstrated the variability of all the measurements and provided insights into the effect of wave-in-deck loads on the platform behaviour, tendon tensions and slamming pressures and showed qualitative correlations between these parameters. Based on the repeated tests in several events with different wave parameters, general observations and conclusions were made with respect to the platform dynamics during the deck impact, tendon tensions, slack tendon situations, tendon ringing and local impact pressures. The results of this study could be used for calibrating computational fluid dynamics (CFD) tools.

Modeling depth of long-term pitting corrosion is of interest for engineers in predicting the structural longevity of ocean infrastructures. Conventional models demonstrate poor quality in predicting the long-term pitting corrosion depth. Recently developed phenomenological models provide a strong understanding of the pitting process; however, they have limited engineering applications. In this study, a novel probabilistic model is developed for predicting the long-term pitting corrosion depth of steel structures in marine environment using Bayesian network (BN). The proposed BN model combines an understanding of corrosion phenomenological model and empirical model calibrated using real-world data. A case study, which exemplifies the application of methodology to predict the pit depth of structural steel in long-term marine environment, is presented. The result shows that the proposed methodology succeeds in predicting the time-dependent, long-term anaerobic pitting corrosion depth of structural steel in different environmental and operational conditions.

Ship structures are prone to fatigue cracking due to fluctuating loads caused by the seaway. This is especially the case for high-speed craft (HSC), as the slamming loads and associated response are known to significantly impact the stress magnitudes experienced by the structure. Therefore, slamming may have a considerable influence on the fatigue life of HSC when compared to accounting for the global wave induced stresses alone. This paper presents an investigation into various methods for identifying slams for structural response analysis. Measurements of hull girder stresses of an aluminium high-speed patrol boat are utilised to explore the characteristics of slam events. The approach to analyse full-scale time records, decomposition of the wave-induced and impact components of stress, and definition and detection of slam events are discussed. With respect to fatigue life, identification of slam events enables the evaluation of the influence of slamming and the associated whipping response in a range of speeds, headings and sea states. Such knowledge supports informed decision-making in regards to the sustainability and maintainability of the vessel.

This paper presents an experimental and numerical investigation into the magnitude and distribution of the hydrodynamic loads affecting a fixed multicolumn offshore platform (rigidly mounted tension leg platform) when subjected to extreme wave events. All wave load components, including wave-in-deck slamming pressures, were predicted using a commercial computational fluid dynamics (CFD) code STAR-CCM+ and compared against experimental measurements. Slamming pressures were calculated using both data obtained locally at discrete points and globally averaged over the whole exposed area of the deck. In all simulated cases, the deck area exposed to a wave-slamming event was found to be in contact with a water-air mixture with a significant proportion of air phase. It was concluded that the slamming pressure data for the exposed area provided better insights into the pressure changes due to air compressibility and its content.

This article describes a series of model tests conducted to examine extreme wave events associated with tropical cyclonic conditions and their impacts on an offshore deck structure. Extreme waves of a representative cyclonic sea state were examined in a towing tank within long-crested irregular wave trains. Experimental results presented include global forces and localised slamming pressures acting on a rigidly mounted box-shaped deck, which represents a simplified topside structure of a tension leg platform. The effect of static set-down on the still-water air gap was investigated by applying an equivalent reduction for the deck clearance. It was found that a small reduction of 20mm (2.5m full scale) in the original deck clearance can lead to a doubling of the magnitude of the horizontal force and the vertical upward-directed force components, as well as significantly increased slamming pressures in many locations on the deck underside.

Abstract The commercial Computational Fluid Dynamics (CFD) code STAR-CCM+ was used to simulate the dynamic behaviour of a tension leg platform in extreme weather conditions. The numerical results of surge motions and tendon tensions were compared against the measurements acquired in model tests. The full-scale CFD simulations were then conducted on the basis of the settings performed in modelscale simulations. Both model- and full-scale surge motions and tendon tensions predicted by CFD were in good agreement with the measurements. Using CFD results, it was revealed that the component of the vertical wave-in-deck force caused a slam force on the platform followed by tendon slack situations in the down-wave tendons.

Numerical simulations of an extreme wave impact on a topside deck structure were conducted to ascertain the effect of air content and its compressibility on the magnitude of the wave-indeck impact (slam) pressure. The topside deck was investigated as both a fixed structure and as a topside structure of a typical Tension Leg Platform (TLP) exposed to unidirectional regular waves. The volume of fluid model implemented in STAR-CCM+ was used to capture the free surface interface. CFD results were validated using different levels of mesh resolution against 1:125 model-scale experiments. In all simulated cases, the deck area exposed to a wave slam event was found to be in contact with a water-air mixture with a significant proportion of air, which revealed that two-phase models are necessary to accurately simulate wave-in-deck problems.

This paper describes a series of model tests of a rigidly mounted tension leg platform (TLP) subjected to extreme wave events corresponding to long-crested irregular wave trains of a 10,000-year cyclonic sea state. The experimental setup was instrumented to simultaneously measure wave surface elevations in the vicinity of the model, global wave impact forces and local pressure distribution on the underside of the model's topside deck. Model accelerations were also monitored for each wave impact event so that the inertial force due to structural dynamic response could be identified. The deck-column intersection areas were found to experience large wave-in-deck slamming pressures, in particular around the aft columns. A reduction of the deck clearance was found to increase the magnitude of the global horizontal forces; however, the global vertical forces and local wave-in-deck slamming pressures did not follow this trend.

Corrosion is a major cause of structural deterioration in marine and offshore industries. It affects the life of process equipment and pipelines resulting in structural failure, leakage, product loss, environmental pollution and the loss of life. Pitting corrosion is regarded as one of the most hazardous forms of corrosion in marine and offshore structures. Hence reliability assessments of these structures are crucial. The empirical and statistical degradation models are developed by either fitting field or lab data. However, these models are only useful for specific site or operating conditions and still carry a high degree of uncertainty. Other modeling approaches used for assessing rate of pitting corrosion in industry is phenomenological model which is based on corrosion scientific principles. These models provide strong understanding of corrosion process but are often hard to test in engineering applications. This paper presents a novel methodology for predicting the pitting corrosion rate of structural steel in long-term marine environment. The proposed methodology combines a multi-phase phenomenological and empirical model with calibrated real-world data using the Bayesian Network (BN) approach. A case study is presented which exemplifies the application of this methodology to predict the long-term pitting corrosion rate in marine environment. The result shows that the proposed BN based methodology is successful in predicting the time-dependent pitting corrosion rate for steel structures in different environmental conditions.

Numerical simulations of a conventional tension leg platform (TLP) were generated to investigate its response to wave-in-deck-loads under extreme wave conditions. The model was setup as a fixed body and as a floating body connected to a fixed boundary by flexible mooring cables. The overset mesh technique was utilised to account for large platform motions in the floating body CFD simulations. The validity of the CFD simulations was extensively studied using 1:125 model-scale experiments. Special attention was given to ensure the accuracy of the simulated wave profile, global and local loads on the fixed structure as well as motions and global loads on the moored floating structure. The global horizontal wave impact loads and motions were found to agree well between simulations and experiments.