Armor Layer Research Articles

Assessment of the variation of failure probability of upgraded rubble-mound breakwaters due to climate change

The effects of climate change on coastal areas are expected to significantly influence the risk for port operations. In the present work, a novel methodology for the quantitative assessment of the performances of upgraded rubble-mound breakwaters under a changing climate is proposed. For each considered upgrading option, the failure probability related to a certain limit state is calculated through the implementation of Monte Carlo (MC) simulations, using the factor of change (FoC) method to include the projected future climate. Three indexes are defined for the immediate and intuitive interpretation of the results: i) the ratio between the calculated and the maximum acceptable failure probability during lifetime (r); ii) the rate of the growth of the failure probability during lifetime (s); iii) the coefficient of variation of the failure probability due to both the intrinsic uncertainty of the MC simulation and the variability of future climate (v). The methodology was applied to the case study of the Catania harbor breakwater, considering the failure of different upgrading solutions due to the collapse of the outer armor layer and to excessive mean overtopping discharge. The results revealed the acceptability of the structural and hydraulic performances of all the tested configurations, under both present and future climate. Moreover, a high climate-related variability of the future failure probability was found. The usefulness of the proposed indexes for designer and decision-makers was also demonstrated. In particular, r gives direct information about the acceptability of the structure performances, enabling the immediate comparison between different configurations and climate scenarios. The index s is fundamental to calculate the appropriate times to implement repair interventions during the structure lifetime. Finally, v allows the identification of those situations which requires the design of highly flexible maintenance plans, able to adapt to a very variable climate avoiding excessive costs.

Hydrodynamic analysis of floating tunnel with submerged rubble mound breakwater

The wave interaction with a Submerged Floating Tunnel (SFT) of two different shapes (rectangular and circular) in the presence of a submerged rubble mound breakwater (SRMB) is analyzed using Multi-Domain Boundary Element Method (MDBEM). Furthermore, three typical SFT cross-sections (rectangular, trapezoidal, and circular) of equal area and structural height in the presence of SRMB under similar operating conditions are investigated as comparative study to analyse the influence of SFT shape on hydrodynamic performance. The performance of the tunnel configurations is analyzed as a (a) measurement in terms of hydrodynamic efficiency and (b) criterion for tunnel structure safety. In both shallow and intermediate water depth regions, the critical wave number and the critical angle of incidence followed by resonant wave reflection are identified, and suitable structural parameters of SRMB such as structural porosity in the armour layer, relative crest width, relative gap width between the SFT and the SRMB, structural width and position (relative draft of tunnel structure measured from the free water surface) of SFT are investigated. The present parametric investigation of SFT with SRMB reveals an improved wave transformation properties for a specific range of water depth. The coupling of SRMB has resulted not only in a reduction of wave-induced force acting on SFTs, but also in improved performance in wave transformation characteristics as a coastal protection structure, which is substantially determined by SRMB structural properties. Due to the presence of SRMB, the SFT's safety is improved, which may also add stability to the SFT. A comparative study of different distinct cross-sections of SFTs indicates that, due to its shape, the circular SFT has a reduced reflection capability and lower wave-induced force with nearly the same wave transmission as the rectangular and trapezoidal SFT. The study performed on the coupled SFT and rubble mound breakwater may be useful in determining the suitability of breakwaters not only for maintaining shore dynamics but also for protecting important floating structures for underwater transit.

A novel helix contact model for predicting hysteretic behavior of unbonded flexible pipes

This paper presents novel equivalent layered contact numerical and analytical models to predict the bending hysteretic behavior of unbonded flexible pipes. A double helix contact beam model, instead of surface-to-surface contact algorithm, is proposed to simulate normal contact and tangential friction behavior between tensile armor tendons and supporting layers. The spatial beam distance is evaluated based on Hertz contact theory. The proposed model is validated through comparison with bending moment-curvature relations obtained from experimental data, a full layered finite element model, and existing analytical models considering or not shear interactions. The shear stiffness is determined by accounting steel armor layers as boundary conditions. The initial contact pressure is introduced into analytical models by accounting residual stress in cylindrical layers and residual strain in helical layers. The bending stresses and relative slip displacements of tensile armor tendons are cross validated between the proposed model and available data. The results show that the proposed model could give consistent bending hysteretic consequences, while shorten simulation time due to significantly reduction of total elements. Sensitivity studies including definition of helix contact beams, equivalent material properties of inner core layer and tangential stick stiffness between layers are performed to validate feasibility of the proposed model.

Microstructure Characteristics and Corrosion Behavior of Low‐Alloy High‐Strength Steel used for Armor Layer under Exposure to H2S‐Saturated Solution

The corrosion behavior of low‐alloy steel exposed to saturated H2S solution is systematically studied using electron backscattered diffraction, scanning electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, and electron probe microanalysis. The experimental results suggest that the corrosion rate decreases with prolonged immersion time because more corrosion products are formed on the steel surface. The corrosion products consist of mackinawite, greigite, and molybdenite regardless of the corrosion time. The structure of the corrosion products transforms from a single layer into two layers with increasing corrosion time. The Cr content in the corrosion products is similar to that in the steel substrate. The corrosion products are rich in molybdenum owing to the formation of molybdenite.

Hydraulic Stability of BPPT – lock on Breakwater Head

Breakwater is one of the coastal buildings built by humans to protect coastal areas such as ports, settlements, and tourist attractions from wave attacks. This test aims to determine the condition damage of BPPT – lock in one- and two-layers placements in the head of the rubble mound breakwater. The method used to conduct this research was physical model test and carried out at laboratory of Balai Teknologi Infrastruktur Pelabuhan dan Dinamika Pantai (BTIPDP) Yogyakarta – Indonesia. The armour unit model used BPPT–locks were 66.048 grams or equivalent to 2.268 tons in prototype and tested in various wave heights, starting from 7.5 cm, 9.2 cm, and 11.4 cm with period 1.5 S or equal to 4 meters of wave height in the prototype. Based on the laboratory results of testing, installing a double armour layer was recommended because the percentage of damage of the double armour layer was lower, and the coefficient of damage was higher.

Experimental and analytical fretting characterisation of pressure armour nub-groove contact in flexible marine risers

This paper presents the development of a test rig for the characterisation of fretting in the nub-groove contacts of pressure armour layers in flexible marine risers and an analytical design tool called EASY-FRET (Engineering Analysis SYstem for FRETting) for fretting wear, fatigue and stress analysis of fretting contacts. The test rig characterisation includes both partial and gross slip fretting regimes under representative three-dimensional crossed-cylinder contact pressure and slip fretting loading conditions, identified from finite element global-local modelling of the complex geometrical-loading configuration. The analytical design tool simulates wear and associated fretting fatigue indicator parameters. The ability to predict the fretting wear and fretting fatigue in flexible marine risers will allow for less conservative design.

Study on Induced Voltage and Circulation Current of Metal Layer in Single-Core Cable of High-Speed Railway Power Transmission Line

The metal shield and metal armor layers of single-core cables on high-speed railroad power penetration lines are usually grounded by common equipment protectors. This grounding method brings a continuous circulating current between the metal shield and metal armor layer compared to the subequipment protection grounding. In order to quantitatively study the circulating current condition of the through line and its influence on the reliability of the railroad power through line, the induced electric potential and circulating current generation mechanism of the single-core cable of the through line and its influencing factors were firstly analyzed in depth. Then, based on the cross-sectional structure of the single-core cable and the location of the traction network and cable in the roadbed section, a traction power supply model was established and simulated for the interlayer-induced potentials and circulating currents due to the two grounding protection methods under no load, single train operation, and heavy load four-train operation of the line. Finally, three actual sections of the Shanghai–Kunming and Nan–Kunming high-speed railroads in China were selected to collect and analyze the loop flow data with no load and with vehicles passing through, and finally the loop flow law of single-core cable for railroad electric through traffic was derived. The analysis shows that when the metal sheath of a single-core cable is grounded by ordinary equipment, the circulating current generated does not exceed 1% of the core current, which meets the relevant safety standards, but the induced voltage in the case of large loads will exceed 50 V safety voltage.

High‐Performance Polyimide Nanofiber Membrane for Progressive and Safe Lithium‐Ion Batteries Guarded by a Zirconia Armor Layer

Superior separator: A flexible zirconia nanoshell@polyimide (ZrO2@PI) composite separator with a core-shell structure is prepared via an in situ absorption complexation and hydrolysis strategy for high-performance and safe lithium-ion batteries. This separator combines the advantages of the PI nanofiber and the ceramic ZrO2, exhibiting excellent flame retardance, wettability, and thermal stability, far better than commercial Celgard-2400 separator. Batteries assembled with this ZrO2@PI composite separator display a higher rate capability and capacity retention rate.

Armor Layer Uniformity and Thickness in Stationary Conditions with Steady Uniform Flow

The continuous movement of riverbed particles due to turbulent flow determines the stability of non-cohesive riverbeds and banks during riverbed and bank erosion and sedimentation. This study emulated the stable channel design by deriving the low maintenance cost of the channel through bed protection by an armor layer. The study investigated the effects of shear stress and grain size uniformity to determine the minimum non-cohesive armor layer thickness for the stability of riverbeds under steady uniform flow conditions. Experiments were conducted with four different discharges, five armor material gradations, and five bed-slope variations in a full-scale flume. We observed and recorded the behaviors of the five gradations of armor materials for given discharges and bed slopes. Eighty data points were recorded and analyzed. The hydraulic analysis of the flow along with the soil mechanics analysis of the armor materials was done. The soil mechanic analysis was particularly focused on the uniformity coefficient of the armor layer, Cu, to derive the armor layer equation. However, for the manageability of the study, we set the limit of the Cu between 3.0 and 6.0. From the viewpoint of non-erodibility, a wider Cu value indicated a thinner armor layer. Variables that govern the armor layer thickness and the layer thickness itself were derived and proposed. The variables, namely Cu, shear stress (t0 and tc), and mean diameter of the bed load and armor materials (Db50 and Da50). Our results show that these variables governed the thickness of the armor layer, and this is expected to contribute to the design of stable natural channels, which can minimize the cost of irrigation canal maintenance and development. Doi: 10.28991/CEJ-2022-08-06-01 Full Text: PDF

Offshore wind farms contribute to epibenthic biodiversity in the North Sea

The North Sea was once abundantly covered with hard substrates such as oyster beds, coarse peat banks and glacial erratics, providing habitat to a rich community of marine species. Most of these habitats were destroyed by bottom-trawl fisheries over the past century, and today, the seabed hosts a relatively poor species community. Emerging offshore windfarms include the re-introduction of hard substrate by means of scour protection around the foundation of wind turbines. It is assumed that the new habitat will contribute to marine biodiversity, and this study aims to demonstrate that. Video data were collected using a Remotely Operated Vehicle in four wind farms in the southern North Sea. A quantitative assessment was made to determine the effect of scour protection on community structure. The assessment revealed distinct community clusters for geographic location and seabed type. Windfarms closely located to each other had a more similar epibenthic community compared to those further away. The epibenthic community at the rocky armour layer of the scour protection had a different species composition and a higher species abundance than the one at the sandy seabed surrounding it. Species diversity by means of richness, evenness and the Shannon diversity index was not consistently higher or lower for the communities at the different seabed types.This study shows that marine life inhabits scour protection in offshore wind farms and that it is different from the community living at the surrounding seabed. Knowing the potential epibenthic community structure at and around a scour protection supports the development of new wind farms that include components to enhance their ecological value. Herewith, our study contributes to efforts to restore biodiversity in the North Sea.

Stress corrosion cracking susceptibility of armour layers in CO2 annulus environments – SSRT experimental simulation

Flexible wires present wet occluded spaces where corrosion induces supersaturation of ferrous ions and precipitation of FeCO3. Localized corrosion is possible due to discontinuities of the precipitated FeCO3. This work aims to investigate the Stress Corrosion Cracking susceptibility of armour layer in FeCO3 supersaturated seawater, addressing the influence of CO2 partial pressure and strain rate, at 25 °C and at 40 °C, using the Slow Strain Rate Test. The results were expressed by ASTM G129 standard parameters. The material showed loss of ductility under all experimental conditions. The most aggressive conditions were at 25 °C, 10 bar, under 10-7 s−1 and 10-6 s-1strain rates, respectively. The results showed that fracture mechanism is related to hydrogen embrittlement, suggested by the presence of internal secondary cracks on the fracture surface. These secondary cracks suggest the interference of delamination. From the results it was possible to rank the severity of experimental conditions imposed.

A global-local approach for dynamic stress evaluation of lazy wave flexible risers subjected to random wave and vessel motion

ABSTRACT With the increasingly severe marine environment, the safety reliability of unbonded flexible risers under service conditions is closely related to its dynamic stress response. In this paper, a systematic approach for riser dynamic stress evaluation subjected to random wave and vessel motion is developed to explore the influencing factors. This methodology proposes a global model to acquire the riser global dynamic response under random wave and vessel motion, considering the effects of nonlinear bend stiffener (BS) constraint and nonlinear bending behaviour of flexible pipes. Then, an axisymmetric load model and bending load model are employed to convert the forces and curvatures obtained from the global model into the dynamic stresses of the tensile armour layers. The findings show that BS and riser top angle can affect the dynamic curvature for the riser top-end region, however, has little influence on the effective tension and bending curvature for the other regions.

Monitoring the slip of helical wires in a flexible riser under combined tension and bending

When a flexible pipe is subjected to combined tension and bending, the helical wires in the external tension armour layer are most failure prone. Understanding the true relative slippage of helical wires is very important to accurately predict the mechanical behaviour of flexible risers under complex loads. This study proposes a monitoring method for the relative slippage of helical wires in flexible risers under combined tension and bending, using three-dimensional digital image correlation technology. For the flexible riser test specimen with an internal diameter of 8 inches, a four-point quasi-static test was carried out, and full-field displacement vectors of helical wires marked by a range of scattered spots were accurately monitored. Thereafter, the relative slip character of the helical wires is obtained by processing the measurement data. The results indicate that the measured relative slip vectors are essentially tangential to the surface of the internal cylinder, while the measured total slip distances and angles are compared with the results from the existing theoretical model and the good agreement is achieved, thus verifying the correctness of the measurement method. Additionally, the laws of slip responses, such as the total slip distance, slip direction, and slip components along the axial and lateral wire directions, of helical wires in flexible risers are investigated, and the slip responses of the helical wire under different axial tensions are discussed.

Prediction Method and Validation Study of Tensile Performance of Reinforced Armor Layer in Marine Flexible Pipe/Cables

Marine flexible pipe/cables, such as umbilicals, flexible pipes and cryogenic hoses, are widely adopted in ocean engineering. The reinforcing armor layer in these pipe/cables is the main component for bearing loads, which is a typical multi-layer helically wound slender structure with different winding angles for different devices. There has been no general theoretical methodology to describe the tensile performance of these flexible pipe/cables. This paper first introduces a theory to solve the tensile mechanical behavior of a helically wound structure. Based on the curved beam theory, a solution of the tensile stress of a helically wound slender is derived. Then, the deformation mechanism of the marine flexible pipe/cables structure with different winding angles is studied. Through comparing theoretical and numerical results, the deformation characteristic of the helically wound slender structure is further explained. It is found that a sectional torsional deformation generates when the structure with a larger winding angle is under tension condition, while the sectional deformation of the structure with a smaller winding angle is mainly tension. Finally, a couple types of marine flexible pipe/cables under the tension condition are provided to analyze the mechanical performance and compare the difference between different theoretical models. The research conclusion from this paper provides a useful reference for the structural analysis and design of marine flexible pipe/cables.

Assessment of Coastal Revetment: Case study of Rosetta Revetment

Coastal structures have been affected after the climate changes that lead to sea-level rise so their functional efficiency has been reduced because of increasing deterioration and failure rates. Efforts and studies must be directed to solve this problem to adapt to the surrounding environmental phenomena. Hence, monitoring of the coastal structure must be executed frequently. This study assesses the deterioration and failure of Rosetta Revetment and gives proposed solutions to solve this problem. Laboratory tests and monitoring programs have been executed during the period from 2011 to 2020 to investigate the deterioration and collapse rates. The results have shown that the deterioration rate within the Revetment armour layer increases dramatically within the last seven years and the fracture rate of units exceeded 10% of the total units. This study can be used for serving the future assessments of Rosetta Revetment. Removing the visible part of the steel hook, treating the units that had a leg fracture, and replacing the fracture units with another one or adding extra units within the revetment armour layer are some recommendations to develop the efficiency of the Revetment.

Simplified Method for Estimation of Mean Residual Life of Rubble-mound Breakwaters

A simplified model using the lifetime distribution has been presented to estimate the Mean Residual Life (MRL) of rubble-mound breakwaters, which is not like a stochastic process model based on time-dependent history data to the cumulative damage progress of rubble-mound breakwaters. The parameters involved in the lifetime distribution can be easily estimated by using the upper and lower limits of lifetime and their likelihood that made a judgement by several experts taking account of the initial design lifetime, the past sequences of loads, and others. The simplified model presented in this paper has been applied to the rubble-mound breakwater with TTP armor layer. Wiener Process (WP)-based stochastic model also has been applied together with Monte-Carlo Simulation (MCS) technique to the breakwater of the same condition having time-dependent cumulative damage to TTP armor layer. From the comparison of lifetime distribution obtained from each models including Mean Time To Failure (MTTF), it has found that the lifetime distributions of rubble-mound breakwater can be very satisfactorily fitted by log-normal distribution for all types of cumulative damage progresses, such as exponential, linear, and logarithmic deterioration which are feasible in the real situations. Finally, the MRL of rubble-mound breakwaters estimated by the simplified model presented in this paper have been compared with those by WP stochastic process. It can be shown that results of the presented simplified model have been identical with those of WP stochastic process until any ages in the range of MTT F regardless of the deterioration types. However, a little of differences have been seen at the ages in the neighborhood of MTTF, specially, for the linear and logarithmic deterioration of cumulative damages. For the accurate estimation of MRL of harbor structures, it may be desirable that the stochastic processes should be used to consider properly time-dependent uncertainties of damage deterioration. Nevertheless, the simplified model presented in this paper can be useful in the building of the MRL-based preventive maintenance planning for several kinds of harbor structures, because of which is not needed timedependent history data about the damage deterioration of structures as mentioned above.

Stability of high density cube armoured breakwaters

The performance of high-density cubes in the armor layer of a breakwater was investigated through an experimental study. For this purpose, two different cross-sections, one with a conventional cross-section and one with a berm, were modelled in a wave flume. A total of ten tests were performed for both cross-sections. Different concrete densities of cubes and different placement methods were applied. The dimensions of the cubes with two different densities were the same for all tests to avoid potential scale effects caused by the dimensions of HD cubes. The experimental study showed that HD cubes were more stable than ND cubes; the characteristic wave height for HD cubes was 1.5 times higher than that of the ND cubes. The use of HD cubes may provide economic efficiency and enables a significant reduction of the concrete volume, transportation of material, and reduction of required construction area for manufacturing, etc. HD cubes in a single layer turned out to be very stable. However, only using HD cubes in a part of the armor layer or only used on the second (upper) layer caused a decrease in the stability of the armor layer, especially in comparison to the armor layers that fully consist of HD cubes. The performance of HD cubes was also evaluated by comparing the experimental results with the Van der Meer (1988) formula and the suitability of the stability number for HD cubes was discussed.

Application of calcium-rich mineral under nonwoven fabric mats and sand armor as cap layer for interrupting N and P release from river sediments.

This work investigates the applicability of thermally treated calcium-rich minerals (CRMs), such as sepiolite (SPL), attapulgite (ATT), and dolomite (DLM) to hinder the nitrogen (N) and phosphorus (P) release from river sediments. A non-woven fabric mat (NWFM) or a sand layer were also capped as armor layers, i.e., placed over CRMs to investigate the capping impact on the N/P release. The capping efficiency was evaluated in a cylindrical reactor, consisting of CRMs, armor layers, sediments, and sampled water. We monitored N/P concentrations, dissolved oxygen (DO), oxidation reduction potential, pH, and electric conductivity in overlying water over 70days. The DO concentrations in the uncapped and capped conditions were preserved for 30days and 70days (until the end of experiment duration), respectively. ATT showed higher efficiency for NH4-N and T-N than the other two materials, and the capping efficiency of NH4-N was measured as 96.4%, 93.7%, and 61.6% when capped with 2-cm sand layer, 1-cm sand layer, and NWFM layer, respectively. DLM showed a superior rejection capability of PO4-P to ATT and SPL, reported as 97.2% when capped with 2-cm sand armor. The content of weakly adsorbed-P was lower in the uncapped condition than in the capping condition. It can be concluded that ATT and DLM can be used as capping agents to deactivate N and P, respectively, to reduce water contamination from sediments of the eutrophic river.

Carbon armor-layer decorated Li3V2(PO4)3 core-shell cathode materials derived from nitrogen doped lignin waste liquor for robust lithium ion batteries

Simultaneous boosting the lithium ions extraction/insertion kinetics and improving the structural stability of Li3V2(PO4)3 (LVP) cathode material highly determine the capacity and lifespan of lithium-ion batteries (LIBs). Herein, terminal oxygen-containing functional groups enriched carbonaceous layer from N doped lignin waste liquor is successfully demonstrated as the armor layer to decorate LVP with core-shell structures for robust LIBs. To the best of our knowledge, it is the first exploration using N doped lignin waste liquor as carbon source in synthesizing high-performance LVP cathode materials. More importantly, owing to the facilitated reversible V3+/V4+ redox couple induced by oxygen-containing functional groups aligning with the promoted Li+ kinetic behaviors, the champion device delivered a high initial discharge capacity of 126.9 mA h g−1 (∼95% of the theoretical capacity) at 0.5C. Furthermore, the optimized battery displays superior capacity retention of 88.9% after 1000 cycles at a high rate of 10C because of the suppressed crystallization expand and transition metal dissolution.

Experimental Investigation of Wave Force on the Pavement behind Crown Wall of Rubble Mound Seawall

Physical experiments were conducted to establish an empirical formula that predicts the wave force on the upside of the pavement behind crown wall of rubble mound seawall due to wave overtopping as well as the uplift force on the downside of the pavement. The experiments were performed by different conditions of the parapet, water depth, relative freeboard, and thickness of the armour layer. Then, the wave force on the upside and downside of the pavement behind the crown wall was analyzed. The parameters that affect the wave overtopping force and the uplift force were identified and empirical formulae were suggested for evaluating the forces on the pavement.