Marine Structure Research Articles

Marine redox stratification on the earliest Cambrian (ca. 542–529 Ma) Yangtze Platform

In order to explore the marine redox structure on the earliest Cambrian (ca. 542–529 Ma) Yangtze Platform, South China, new Fe-Mo-C-S geochemical data from the slope Xugongping section for the Liuchapo and the base of Niutitang Formation are reported here. Integrated Fe speciation and Mo abundance data from the Xugongping section, in combination with previously published data from slope-basinal Longbizui section and others, suggest oxic surface waters and ferruginous deep waters coexisting with occasional mid-depth euxinic waters during the Fortunian Stage, and with widespread euxinic waters during the early Stage 2 marine transgression. A compilation of new and published sulfur isotope data of pyrite for the Liuchapo and the base of Niutitang Formations presents high isotopic values (mostly >+10‰) and distinctly different spatiotemporal gradient characteristics during the Fortunian Stage and the beginning of the Stage 2. We propose that redox stratification developed in the earliest Cambrian protected basin, and eustatic change and the connectivity of the protected basin with the open ocean controlled the materials supply from riverine input and open ocean reservoir and thus spatiotemporal variability of ocean chemistry.

Fatigue Magnification Factors of Arc-Soft-Toe Bracket Joints

Arc-soft-toe bracket (ASTB), as a joint structure in the marine structure, is the hot spot with significant stress concentration, therefore, fatigue behavior of ASTBs is an important point of concern in their design. Since macroscopic geometric factors obviously influence the stress flaws in joints, the shapes and sizes of ASTBs should represent the stress distribution around cracks in the hot spots. In this paper, we introduce a geometric magnification factor for reflecting the macroscopic geometric effects of ASTB crack features and construct a 3D finite element model to simulate the distribution of stress intensity factor (SIF) at the crack endings. Sensitivity analyses with respect to the geometric ratio H t /L b , R/L b , L t /L b are performed, and the relations between the geometric factor and these parameters are presented. A set of parametric equations with respect to the geometric magnification factor is obtained using a curve fitting technique. A nonlinear relationship exists between the SIF and the ratio of ASTB arm to toe length. When the ratio of ASTB arm to toe length reaches a marginal value, the SIF of crack at the ASTB toe is not influenced by ASTB geometric parameters. In addition, the arc shape of the ASTB slope edge can transform the stress flowing path, which significantly affects the SIF at the ASTB toe. A proper method to reduce stress concentration is setting a slope edge arc size equal to the ASTB arm length.

Seismic Forces in Ancillary Components Supported on Piers and Wharves

This paper presents a simple procedure to estimate seismic forces in ancillary components (secondary systems) supported on marine structures such as piers, wharves, and marine oil terminals (primary systems). Since many such marine structures can be idealized as single-degree-of-freedom (SDOF) systems, this study uses a simple linear-elastic model with two DOF, one representing the marine structure and the other representing the ancillary component. This study shows that acceleration at the base of the secondary system is approximately equal to spectral acceleration at the fundamental period of the primary system. It also proposes a formula, which is an improvement over current ASCE 7-10 recommendations, to estimate acceleration amplification in the secondary system due to its flexibility when mass and period ratios of the secondary and primary systems are known. The procedure in this paper is strictly applicable to marine structures for which primarily a single mode contributes to seismic response.

Vertical and Seasonal Patterns Control Bacterioplankton Communities at Two Horizontally Coherent Coastal Upwelling Sites off Galicia (NW Spain).

Analysis of seasonal patterns of marine bacterial community structure along horizontal and vertical spatial scales can help to predict long-term responses to climate change. Several recent studies have shown predictable seasonal reoccurrence of bacterial assemblages. However, only a few have assessed temporal variability over both horizontal and vertical spatial scales. Here, we simultaneously studied the bacterial community structure at two different locations and depths in shelf waters of a coastal upwelling system during an annual cycle. The most noticeable biogeographic patterns observed were seasonality, horizontal homogeneity, and spatial synchrony in bacterial diversity and community structure related with regional upwelling-downwelling dynamics. Water column mixing eventually disrupted bacterial community structure vertical heterogeneity. Our results are consistent with previous temporal studies of marine bacterioplankton in other temperate regions and also suggest a marked influence of regional factors on the bacterial communities inhabiting this coastal upwelling system. Bacterial-mediated carbon fluxes in this productive region appear to be mainly controlled by community structure dynamics in surface waters, and local environmental factors at the base of the euphotic zone.

Peridynamic Analysis of Marine Composites under Shock Loads by Considering Thermomechanical Coupling Effects

Nowadays, composite materials have been increasingly used in marine structures because of their high performance properties. During their service time, they may be exposed to extreme loading conditions such as underwater explosions. Temperature changes induced by pure mechanical shock loadings cannot to be neglected especially when smart composite materials are employed for condition monitoring of critical systems in a marine structure. Considering this fact, both the thermal loading effect on deformation and the deformation effect on temperature need to be taken into consideration. Consequently, an analysis conducted in a fully coupled thermomechanical manner is necessary. Peridynamics is a newly proposed non-local theory which can predict failures without extra assumptions. Therefore, a fully coupled thermomechanical peridynamic model is developed for laminated composites materials. In this study, numerical analysis of a 13 ply laminated composite subjected to an underwater explosion is conducted by using the developed model. The pressure shocks generated by the underwater explosion are applied on the top surface of the laminate for uniform and non-uniform load distributions. The damage is predicted and compared with existing experimental results. The simulation results obtained from uncoupled case are also provided for comparison. Thus the coupling term effects on crack propagation paths are investigated. Furthermore, the corresponding temperature distributions are also investigated.

Vibration-response due to thickness loss on steel plate excited by resonance frequency

The degradation of steel structure due to corrosion is a common problem found especially in the marine structure due to exposure to the harsh marine environment. In order to ensure safety and reliability of marine structure, the damage assessment is an indispensable prerequisite for plan of remedial action on damaged structure. The main goal of this paper is to discuss simple vibration measurement on plated structure to give image on overview condition of the monitored structure. The changes of vibration response when damage was introduced in the plate structure were investigated. The damage on plate was simulated in finite element method as loss of thickness section. The size of damage and depth of loss of thickness were varied for different damage cases. The plate was excited with lower order of resonance frequency in accordance estimate the average remaining thickness based on displacement response obtain in the dynamic analysis. Significant reduction of natural frequency and increasing amplitude of vibration can be observed in the presence of severe damage. The vibration analysis summarized in this study can serve as benchmark and reference for researcher and design engineer.

Integration of tidal range energy with undersea pumped storage

Abstract The deployment of tidal technology is affected by the general bottlenecks associated with all new renewables in respect of finance and integration with the grid. In this research, a development strategy is defined for tidal range projects based on geodynamics, civil engineering, and economics with the aim of assisting policy makers and industry. Criteria related to hydrodynamics, bathymetry, marine structure safety and cost recovery apply to relevant sites and to real data power prices. The case study described is that of the Bay of Bourgneuf on the French Atlantic coast, where a tidal range power plant of 900 MW could optimally be built with respect to sedimentation, water depth, and tidal coefficients. It has been determined that a 30 m-high artificial dam could maximise the harvestable energy (3 TWh). Numerical simulations show that a tidal plant sized at just 700 MW would be cost-efficient, due to the constraints of the grid and to high power curtailment rates (30%). The expected value of the Levelised Cost of Electricity would be around 200€2016/MWh. Integration into the grid could be improved through addition of an innovative underwater energy storage system, rated to one third of the size of the tidal plant. The economics would improve (the LCOE would drop to 170€2016/MWh) due to lower curtailment and to price arbitrage opportunities. Issues related to missing investor money (>3Bln€2016) and unquantifiable positive externalities such as flood protection, energy independency, and clean energy provision are discussed, underpinning the need for regulator support.

A robust risk assessment methodology for safety analysis of marine structures under storm conditions

Accidents involving vessels and/or offshore structures (henceforth referred to as marine structures) may pose high financial, environmental and fatality risk. To effectively manage these risks a methodical approach is required to model accident load and the stochastic behaviour of the marine structure that are arising from storm effects. This paper introduces a proactive framework that identifies and considers all the initial relevant risks. Compared to the conventional approaches that rely on precursor data for accident modelling, the developed methodology utilizes the critical stochastic variables directly from the hydrodynamic analysis of the floating structure. For this purpose, a novel numerical model is proposed to replicate a storm based on Endurance Wave Analysis (EWA) method. This approach reduces the computational cost (time and load) of the simulations. The critical stochastic variables are subsequently used in Bayesian Network (BN) to develop the risk model. The EWA and BN based integrated methodology assists in better understanding of accident causation and associated risk in changing operational conditions. The application of the methodology is demonstrated through a Floating Storage Unit (FSU) experiencing capsizing scenario.

Experimental investigation on dynamic failure of carbon/epoxy laminates under underwater impulsive loading

The dynamic response and failure modes of carbon/epoxy laminates subjected to underwater impulsive loading are experimentally investigated in this work. The effects of impulse intensity and fluid-structure interaction (FSI) on the failure modes of the clamped laminates were also assessed. A lab-scale underwater explosive simulator was utilized to impart the controlled impulsive loading with three different decay times on the laminates. The 3D Digital Image Correlation method with high speed photography was used to capture the dynamic response of the laminates. A series of microscopic examinations was conducted to analyze the failure mechanism of the laminates. The results show that the composite laminates provided higher blast resistance than aluminum plates in the same thickness. The fiber breakage, delamination and matrix crack were the main failure modes of the laminates subjected to underwater impulsive loading. The fiber breakage occurring at the center and the boundary of the plate was mainly caused by the stretching and shear-off, respectively. The damage extent of the laminates was increased with the impulsive loading increasing or FSI parameter decreasing. The results obtained in this study provide a potential application guidance for laminates in marine structure lightweight design.

Advancing assessment of marine phytoplankton community structure and nutritional value from fatty acid profiles of cultured microalgae

AbstractThe dual function of fatty acids as both biomarkers of phytoplankton community structure and proxies of their nutritional value is becoming increasingly recognized as a substantial complement to elemental stoichiometry studies in aquatic ecology and aquaculture. Despite information on fatty acid composition of marine microalgae being more abundant, phytoplankton fatty acid reviews as well as information on their nutritional quality and effects in food webs are far more frequent for freshwater species. Here, 683 fatty acid profiles of 115 genera of marine microalgae belonging to 17 classes from eight phyla and cultured under nonstressful conditions were compiled. Data analysis allowed establishment of fatty acid reference values that can be used to quantitatively determine marine phytoplankton community structure with an unprecedented descriptive level. Fatty acids also served to generate the first microalgae nutritional index adapted to requirements of consumers and their trophic upgrading capabilities. Fatty acid profile allowed taxonomically differentiating among marine microalgae within a group comprising 14 classes and the Bacillariophyta phylum. Phylogeny was the strongest driving force of fatty acid variation, whereas the marine or freshwater origin of microalgae contributed <1%. Nutritionally, marine microalgae were more homogeneously arranged at the phylum level, with the Dinophyta separately scoring the maximum nutritional value. The phylum Chlorophyta comprised strictly marine classes and other classes also present in freshwaters and showed the highest within‐phylum nutritional quality variability. Such variability is relevant and recommends using specific taxonomic terminology for green lineage microalgae regarding their nutritional value.

A simulation study on the interaction between sloping marine structure and level ice based on cohesive element model

The interaction between sloping marine structure and level ice is a complex process, which contains local crushing and flexural failure. The ice fragments fallen from ice sheet will continuously experience rotation, sliding and accumulation processes. These processes interfere with each other and give rise to difficulty to determine accurately the ice loads on structure. The issue is solved by using cohesive element model (CEM) in this paper. In the condition of a cone icebreaking against level ice, the elastoplastic linear softening constitutive model is introduced to the regular tri-prism bulk elements to present the microscopic crushing of ice sheet, while the bending failure of ice sheet is caused by the failure of cohesive elements. The proposed models are incorporated into the LS-DYNA finite element code. The mesh dependency study and a series of parametric analysis on the main parameters of models are conducted. The numerical results are compared with available model test data in literature, and good agreements are achieved. Then a series of simulations in terms of invasion velocity, cone angle and cone waterline diameter are performed. Effects of these parameters on the ice loads and contributions of breaking module are discussed.

Scatter and error estimates in ice loads – Results from virtual experiments

This paper analyses peak ice loads on an inclined, rigid marine structure by using data from 2D combined finite-discrete element method simulations. The aim is look for answers to the questions: what type of distributions do peak ice loads follow, what type of data is needed for their analysis, and how should the data on peak ice loads be collected? In the simulations, an initially continuous ice sheet, modeled as a floating beam, breaks into smaller ice blocks as the sheet is pushed against the structure. Statistical tools were used to analyse the peak ice load distributions, error estimates, and peak ice load occurrences. Load distributions appeared to be right-skewed and thus non-normal. Gumbel distribution appeared to describe the data well. The results show that the large scatter in the ice load data is due to the ice-structure interaction process itself. Due to the scatter, a large number of observations are needed for studying peak ice load statistics: To reliably observe a 15% difference in peak loads due to a single parameter would require more than 80 observations in total. The results showed that high peak loads may occur even in the early stage of the ice-structure interaction process.

Investigation of impact phenomena on the marine structures: Part I - On the behaviour of thin-walled double bottom tanker during rock-structure interaction

Predicted loads, such as crew, cargo, and structure have been applied as main inputs during ship design and analysis. However, unexpected events on the sea has high possibility to deliver remarkable losses for ship, industry, and environment. Previous oil spill incident by the Exxon Valdez in Alaska is the perfect example which an environmental damage and industry loss are initiated by an impact phenomenon on the ship, i.e. grounding. Even though hull arrangement has adopted double hull system, grounding may threaten ship safety in various scenarios. This situation pushes society to demand sustainable investigation for impact phenomena on water transportation mode to update understanding in the phenomenon and ensure structural safety during ship operation. This work aimed to study structural behaviour of chemical tanker as a marine structure under impact, namely ship grounding. Bottom raking case was considered to be calculated by virtual experiment. The study was performed using nonlinear finite element (FE) method and an idealised geometry of seabed rock would be deployed to be hard obstruction. Observation on the selected crashworthiness criteria, i.e. internal energy and crushing force indicated that as advanced penetration occurred on the ship structure, the absorbed strain energy continued to increase, while major fluctuation appeared during the initial contact between obstruction and ship happened. Damage extent of several structural members during the crushing process was shown, which concluded that the bottom plating had the largest severity in forms of tearing mode among of all members on the bottom structure.

Natural Products from Marine Invertebrates and Microorganisms in Brazil between 2004 and 2017: Still the Challenges, More Rewards

The Brazilian marine biodiversity represents a unique, yet underexplored resource of biologically active compounds. This review provides an analysis of the development of marine natural products chemistry in Brazil within the period comprised between 2004 and 2017. Emphasis is directed towards marine invertebrate and marine microorganisms metabolites, including isolation, structure analysis, biosynthesis, bioactivities and total synthesis. An overview of the research on marine natural products by Brazilian researchers is also discussed, as well as perspectives for the development of the chemistry of marine natural products in Brazil.

QSAR and Structure Based Modeling of Marine Derived Anticancer Hymenialdisine Compounds

Drug discovery research based on marine organisms is a big challenge. However, lack of facilities and competent human resources stand as a barrier on the way of research. More in-depth study especially on deep-sea natural products needs to be carried out to solidify the research on the potential for marine organisms to contribute to the future of drug discovery. The total drug discovery processes including collection of marine organisms, extraction, isolation, structure elucidation, biological assay and experimental screening as well as clinical trials is a very long journey and big challenge. Therefore, researchers pay a big attempt to design and discovery of synthetic congeneric leads by derivatizing the natural potent compounds. Therefore, In-silico High throughput screening based on QSAR and molecular docking has been attempted in the present study for the design and discovery of promising anticancer compounds considering existed marine sponge-derived hymenialdisine analogs which are protein kinase inhibitors having nanomolar activities against CDKs, Mek1, GSK 3β and CK1. It may crystallize crucial features for the design and discovery of promising anticancer HMD compounds which could be proposed for further synthesis and testing. QSAR and molecular docking analysis of HMD analogs are being carried out by freely accessible open source software which are very economical and potential in drug discovery attempt.

Crashworthiness assessment of double-hull tanker structures under ship grounding actions

Ship grounding is considered as a serious maritime accident which highly contributes to environmental pollution. This impact phenomenon attracts audiences to be studied and assessed since in an instantaneous moment, oil or waste from the damaged bottom tank can spill and contaminate wide water territory. In this study, grounding scenario is modelled as hard grounding where a rock geometry is chosen as representative of oceanic obstruction. The contribution of several main parameters, such as target component and oceanic obstruction are evaluated. The method is to apply a virtual experiment by nonlinear finite element (FE) method to conduct a simulation. A chemical tanker is taken as representative of a marine structure which is subjected to impact load on its bottom structure during interaction with the obstruction. The results indicate that the space between girders provides less resistance in the crushing process. The internal energy in this work is presented to estimate the strength capability of the impacted component, which is followed by the deformation pattern on the lower part of the bottom structure. Finally, the effect of the obstruction on failure sequences in grounding is summarised.

Numerical Prediction of Chloride Penetration in Concrete Exposed to a Marine Environment at Tide

Reinforced concrete structures under cyclic exposure to the corrosive environment such as the tidal zone as a part of marine structure entail the higher risk of steel corrosion. In this paper, chloride penetration in concrete exposed to the tidal zone was predicted using a combined moisture and chloride transport model. For the analysis of moisture transport, pore size distribution in concrete was determined from the experimental observation and used to determine the moisture permeability and degree of saturation. Then, the chloride profile through nonsaturated concrete cover was calculated by applying the moisture distribution along the penetration depth to the chloride convection and diffusion model. To assess sensitivity of the service life to the environment and concrete mix conditions, this study used three types of tide levels and water to cement ratios in the simulation. Under 10 years of tidal exposure condition, the minimum required cover depth at which the threshold chloride concentration reaches on the steel embedment increases only about 1.13 times as the tide level increases from the minimum to the highest while that for the w/c ratio increases about 1.69 times.

Motion and dynamic responses of a semisubmersible in freak waves

The present research aims at clarifying the effects of freak wave on the motion and dynamic responses of a semisubmersible. To reveal the effects of mooring stiffness, two mooring systems were employed in the model tests and time-domain simulations. The 6-DOF motion responses and mooring tensions have been measured and the 3-DOF motions of fairleads were calculated as well. From the time series, trajectories and statistics information, the interactions between the freak wave and the semisubmersible have been demonstrated and the effects of mooring stiffness have been identified. The shortage of numerical simulations based on 3D potential flow theory is presented. Results show that the freak wave is likely to cause large horizontal motions for soft mooring system and to result in extremely large mooring tensions for tight mooring system. Therefore, the freak wave is a real threat for the marine structure, which needs to be carefully considered at design stage.

Partial safety factors for berthing velocity and loads on marine structures

Design methods for marine structures have evolved into load and resistance factor design, however existing partial safety factors related to berthing velocity and loads have not been verified and validated by measurement campaigns. In this study, field observations of modern seagoing vessels berthing in Bremerhaven, Rotterdam and Wilhelmshaven were used to evaluate partial safety factors for berthing energy and berthing impact loads. Various types of vessels and navigation conditions were statistically examined. The results show that characteristic values of berthing velocity with a return period of 50 years are in line with design recommendations in literature. Design values of berthing velocity are sensitive to the number of berthing operations during the lifetime of a marine structure. Typical partial safety factors for sheltered and exposed navigation conditions were derived by extrapolating distribution fits and applying extreme value theory. Differences in structural response due to soil stiffness and the type of berthing system installed influence partial safety factors for berthing impact loads. The probability of an uncontrolled berthing event was higher for exposed navigation conditions (strong tidal currents). In these circumstances, higher partial safety factors for berthing velocity should be considered in the design of marine structures. When berthing aid systems are used, the probability of extreme berthing velocities is lower, resulting in lower partial safety factors. The key findings of this study could be beneficial for the structural design of new and lifetime extension of existing marine structures.

Ice loads on inclined marine structures - Virtual experiments on ice failure process evolution

Failure of level ice against an inclined marine structure has been simulated using a two-dimensional finite-discrete element method. The simulation model is deterministic, but very sensitive to initial conditions. This allowed us to create ice load data and to study the evolution of the ice failure process. The mean load, the standard deviation, and the maximum load increased during the ice failure process. Ice thickness had a strong effect on the ice load and also the plastic limit of ice had an effect, especially when the ice was thick. The coefficient of variation of the ice load was initially high and then continuously decreased during the ice failure process. This suggests that the ice failure process did not reach a stationary stage, showed high probability of extreme peak loads, and that distributions with a constant coefficient of variation should not be used for this kind of ice loading processes. Extreme value analysis, with the assumption that the ice load follow a log-normal distribution on each time step, fitted the data well and suggested that the maximum ice load increases with sample size. Further, it appears that the peak ice loads are bounded by the crushing capacity of the ice even in the case of an inclined structure. The statistical analysis of simulated ice load data further suggests that observations from short interaction processes, or with small sample sizes, may lead to very inaccurate ice load estimates.