Offshore Construction Research Articles

수중시공현장 적용을 위한 위치 획득 신호 주기와 인식 방법에 관한 연구

With the increase in the research on marine IoT in recent years, the demand for enhanced mission performance in marine construction and civil engineering is increasing. Accordingly, various equipment have been introduced in the field. However, recognizing the location of the equipment is difficult because of the underwater environmental characteristics (e.g., radiated noise and turbidity). As a result, studies have been conducted on underwater positioning methods that combine technologies such as GPS (Global Positioning System)and IMU (Inertial Measurement Unit).However, the problem of intermittent disconnection persists due to radiated noise and turbidity generated in offshore construction environments. To solve this problem, we proposed the method of using a KF(Kalman Filter) in underwater construction environments. To verify the proposed method, we conducted an experiment on land at the speed used in offshore construction. In the experiment, the signal acquisition cycle was varied, and the usable cycle in the field was checked. The experimental results demonstrated the applicability of the proposed underwater positioning system.

A System-Theory and Complex Network-Fused Approach to Analyze Vessel–Wind Turbine Allisions in Offshore Wind Farm Waters

Given the national goal of “emission peaking and carbon neutralization”, China has become the largest country in the world for offshore wind farm construction. At the same time, navigational safety problems in offshore wind farm waters have become increasingly frequent. Owing to the complexity of offshore wind farm waters and the small number of accident data samples available for reference, the system theory method is more suitable for selection than the traditional method. Based on causal analysis based on system theory (CAST) and a complex network (CN), in this study, a qualitative and quantitative accident analysis model, CAST-CN, is constructed to analyze a complete case of vessel and wind turbine allision in offshore wind farm waters. The results show that, at the micro level, in addition to the master, crew, shipping company, and typhoon Hato, the maritime safety administration and the wind farm operation management department have a certain impact on the development of the accident discussed in this study. At the macro level, internal and external factors leading to the lack of system safety are identified, and measures and suggestions for system safety improvement are proposed based on analysis. This study can fill the research gap in the systematic analysis of traffic accidents in offshore wind farm waters and provide support for the safety assessment and decision-making of government management departments and research institutes.

Study on Horizontal Loading of Large Diameter Single Pile of Offshore Fan on Soft Clay Seabed Foundation


 Vigorously developing offshore wind power is an important measure to achieve China's "dual carbon" goal. For offshore wind turbines, the foundation embedded in the seabed is directly related to the safety and stability of the wind turbine, and is the most important part of wind power design. At present, in the offshore wind power construction within 40 m, large diameter single pile foundation is the most widely used foundation form. For the design of single pile foundation, it is necessary to ensure that the ultimate load of foundation can withstand the most extreme external load. Secondly, it is necessary to ensure that during the 25-year service period of the fan, the cumulative deformation of a single pile at the mud surface under the cyclic load of wind and waves does not exceed the value specified in the code; Finally, it is necessary to ensure that the wind power structure does not occur fatigue damage under the action of reciprocating dynamic load. Such strict design criteria, coupled with the soft clay seabed with poor mechanical properties widely distributed in the sea area of China's wind farms, bring severe challenges to the design of single piles.

Design, local structural stress, and global dynamic response analysis of a steel semi-submersible hull for a 10-MW floating wind turbine

Platforms for floating wind turbines cannot be designed using conventional procedures like other offshore constructions. The design of floating wind turbine platforms must consider the significant nonlinearity of the fully coupled aero-hydro-servo-elastic dynamics, which necessitates a time-domain load transfer for structural stress analysis. This article presents and verifies an effective yet practical design method for floating wind turbine platforms, which can provide reasonable internal stress for design checks. A robust design process is proposed. Following the proposed method and procedure of a 10-MW wind turbine, a steel semi-submersible platform is developed with the criterion for the steel platform’s design checks, intact stability analysis, natural period analysis, and buckling analysis executed. A tangible concept is established, along with fully coupled numerical models of the 10-MW wind turbines supported on the steel structure. The dynamic behavior of the steel platform is evaluated by accessing and comparing the dynamic performances of the concrete- and steel-support wind turbine numerical models. The key findings and conclusions from the steel platform’s design and numerical study are summarized below. In addition, future design and analysis ideas are proposed, expanding the engineering practice and research on floating wind turbine platforms.

Assessing the liquefaction potential of seabed soils based on ocean ambient noise in the Yellow River Delta

Seabed soils can undergo liquefaction under cyclic loading, resulting in a rapid decrease in strength and stiffness, which may lead to the destruction of offshore structures. Therefore, the assessment of seabed soil liquefaction will become an important factor in disaster prevention and risk analysis in coastal and offshore engineering construction. In this study, the ocean ambient noise with low-frequency, long-wavelength, and wide-band characteristics was used to conduct and analysis noise based on the horizontal-to-vertical spectral ratio method. The shear wave velocity of the seabed soil was obtained by inverting the ocean ambient noise dataset. Then, we proposed a shear wave velocity threshold that can be used for liquefaction assessment of Holocene unconsolidated fine-grained soils by statistical analysis, and the liquefaction potential of the soils was evaluated according to 1-D shear wave velocity structures and 2-D shear wave velocity profiles. The results showed that the distribution of the shear wave velocity obtained by inverting ocean ambient noise was generally consistent with the measured shear wave velocity in the field, indicating that the inversion results have a certain degree of accuracy. A shear wave velocity threshold of 200 m/s was proposed for liquefaction assessment, determining that the soils within 0-10 m depth in the coastal area of Yellow River Delta have liquefaction potential. This result is in accordance with the assessment based on the critical shear wave velocity, indicating that this threshold is applicable to the assessment of seabed soil liquefaction in the Yellow River Delta. The in-situ observations of ocean ambient noise provide a more convenient, economical, and environmentally friendly method, which can help to investigate marine geology disasters and serve marine engineering construction.

Offshore construction using gravity-base foundations indicates no long-term impacts on dolphins and harbour porpoise

There are concerns about the short- and long-term effects on cetaceans from offshore construction using pile-driving. Gravity-base foundations and anchored floating turbines are alternative installation methods that may have less impact on cetaceans. In this study, we investigated the response of dolphins (Tursiops truncatus and Lagenorhynchus albirostris) and harbour porpoise (Phocoena phocoena) to the construction of wind turbines using gravity-base foundations off Blyth, Northumberland, United Kingdom using cetacean echolocation recorders (C-PODs). Data were collected at nine sites across 3 years (2016–2018) before, during and after construction. Generalised additive mixed models were used to investigate temporal, environmental, and anthropogenic drivers of dolphin and porpoise occurrence from 143,215 h (5967 days) of C-POD data. The models explained 27% and 30% of the deviance in dolphin and porpoise occurrence, respectively. Overall, the results showed no long-term effect on the dolphin occurrence from the construction of the gravity-base wind turbine array. In contrast, porpoise occurrence increased by 32% and 75%, respectively, in the years during and after construction, compared to the before-construction year. Other predictors of dolphin and porpoise occurrence included month, hour of day, tidal currents and vessel sonar activity. Our findings indicate that wind turbine installation using gravity-base foundations had no long-term effects on the occurrence of dolphins or porpoise and may represent an offshore construction methodology that is less impactful to dolphins and harbour porpoise than impact pile-driven turbine installation methods. These results are important for future offshore energy developments; however, further studies are recommended to investigate potential species and location variations.

Identification of 4D-BIM Barriers in Offshore Construction Projects Using Fuzzy Structural Equation Modeling

Planners face many obstacles during the planning phase of any new project, especially project scheduling due to the numerous details and complexity of each uniquely designed project; previous experience in similar projects and traditional scheduling methods are not sufficient. The 4D-BIM schedule is the best solution, as it can be integrated with other modern technologies such as UAS, which improves project scheduling by allowing the project team to access project plans, details, and time-related information to simulate construction sequences. Despite the benefits of using 4D-BIM, planners prefer traditional planning and scheduling methods because of the barriers to using modern technologies. This research proposes a structural equation model focusing on estimating the weights of BIM barriers in offshore construction projects, including: the investigation of barriers keeping the construction industry standing at 3D-BIM; the relationships between them; and the evaluation of the probability and impact of each, using fuzzy theory. To validate the proposed model, a case study of an offshore project was conducted. The most important latent variables were awareness, risk, demand, and management, while the most prominent observed variables were the uncertainty of the return on investment and the lack of experienced users. This research guides project managers on actions that can be taken for each key variable to enhance and develop the use of 4D-BIM in project scheduling.

Distribution of boulders in coastal waters of Western Pomerania, German Baltic Sea

This study contributes to a better understanding of geogenic reef distribution in the southern Baltic Sea and highlights the implications of survey-related factors on automated boulder classification when utilizing data from multiple surveys. The distribution of hard grounds and reefs is needed as a baseline for geological and biological studies, but also for offshore construction, navigation and coastal management. In this study we provide maps of the distribution of geogenic reefs for about 750 km2 in the southern Baltic Sea, at the sites Wismar Bay, Darss Sill and Plantagenet Ground. The maps are based on full-coverage backscatter surveys with different side scan sonar and multibeam echo sounder systems. The distribution and number of boulders in the backscatter maps was determined using a convolutional neural network combined with quality control by human experts. The extent of the geogenic reefs was calculated on the basis of the number of boulders in 50 m x 50 m grid cells. We compare the results with previous reef maps based on point sampling, which show reefs of either biogenic or geogenic origin. According to the earlier maps, 11% of the Plantagenet Ground seabed was classified as reef habitat type. This is similar to the result of our study (12%), although we only considered reefs of geogenic origin. In the Darss Sill, geogenic reefs are larger in this study than in previous maps (30% versus 23%). In both regions, the spatial distribution of reefs differs significantly between old and new maps. For Wismar Bay, previous maps classify 3% of the seafloor as habitat type reef, whereas this study classifies 35% as geogenic reef. The use of automated classification during seafloor mapping allowed large areas to be interpreted in a few days. It also provided more information on the distribution of boulders within the geogenic reef. However, the boulder distribution maps show the negative effects of survey geometry, frequency and environmental conditions on automated boulder classification when data from different surveys are combined.

Gaidai-Xing reliability method validation for 10-MW floating wind turbines

In contrast to well-known bivariate statistical approach, which is known to properly forecast extreme response levels for two-dimensional systems, the research validates innovative structural reliability method, which is particularly appropriate for multi-dimensional structural responses. The disadvantage of dealing with large system dimensionality and cross-correlation across multiple dimensions is not a benefit of traditional dependability approaches that deal with time series. Since offshore constructions are built to handle extremely high wind and wave loads, understanding these severe stresses is essential, e.g. wind turbines should be built and operated with the least amount of inconvenience. In the first scenario, the blade root flapwise bending moment is examined, whereas in the second, the tower bottom fore-aft bending moment is examined. The FAST simulation program was utilized to generate the empirical bending moments for this investigation with the load instances activated at under-rated, rated, and above-rated speeds. The novel reliability approach, in contrast to conventional reliability methods, does not call for the study of a multi-dimensional reliability function in the case of numerical simulation. As demonstrated in this work, it is now possible to assess multi-degree-of-freedom nonlinear system failure probability, in the case when only limited system measurements are available.

Study on dynamic properties of ultrasoft clay based on large amplitude oscillatory shear tests

In offshore engineering, the dynamic properties of ultrasoft clay in the seabed could affect the stability of offshore construction under dynamic loading. The typical rheological response of ultrasoft clay is studied based on the test results from large amplitude oscillatory shear tests with a rheometer. The ultrasoft clay undergoes three phases: the solid phase, transition phase and liquid phase, under dynamic loading. Modulus overshoot is observed when a phase transition occurs. The shear modulus and damping ratio of ultrasoft clay are studied based on the relationship between rheological parameters and dynamic parameters. The results show that the maximum shear modulus of ultrasoft clay could be expressed as a function of water content. Compared with general clay, the normalized shear modulus of ultrasoft clay decreases, and the damping ratio rapidly increases with increasing shear strain. Models describing the change in the normalized shear modulus and damping ratio with the shear strain of ultrasoft clay are suggested based on our test results. This study could aid in the evaluation of the stability of submarine structures at the seabed level under dynamic loading.

Experimental and analytical research on seismic performance of ECC-filled high-strength double skin steel tubular columns with out-of-code D/t ratios

Against the offshore construction requirement on light weight and high performance, using high-strength (HS) steel in concrete-filled double skin steel tubular (CFDST) members usually results in out-of-code diameter-to-thickness (D/t) ratios and performance uncertainty. A quasi-static cyclic loading test was therefore conducted to investigate the seismic performance of circular-in-circular ECC-filled high-strength double skin steel tubular (EFHDST) columns with out-of-code D/t ratios. Typical failure mode, hysteretic curves, bearing capacity and ductility were analyzed. Subsequently, the finite element (FE) model incorporating material damage effect was established and verified to conduct further parametric study. Influence of geometric parameters (e.g., wall thickness and hollow ratio), material strength and axial compression level was discussed in detail. Finally, a simplified restoring force model was developed to predict the seismic behavior of EFHDST columns. The result indicates that: the EFHDST columns fail by the ECC crushing, steel fracture and local buckling of double-skin tubes; the steel yield strength and thickness of outer tube, axial compression level and hollow ratio obviously affect the hysteretic performance (e.g., the bearing capacity and ductility) through the test and FE analysis, e.g., increasing hollow ratio from 0.54 to 0.82 the bearing capacity and ductility coefficient of test respectively decrease by 11.20% and 26.61%; the dimensionless skeleton curve, unloading stiffness degradation and hysteretic rule are proposed to form the restoring force model, where a strength model considering effect of ECC tension strength is included, and the reasonable agreement is achieved by the comparison results. The displayed research on EFHDST columns can provide significant references to its engineering applications.

Impact Dynamic Analysis of Suspended Marine Cables

Objective: It is often impossible to avoid collisions between marine cables, the impact dynamic response of the collisions between marine cable needs to be obtained. Methods: In this paper, we derive the lumped mass method based on the bending moment and torque; using the lumped parameter method, the suspended cable is discretized into lumped mass models, and the impact force of the suspended cable is considered in the dynamic analysis; the impact dynamics model of the suspension cable is developed by referring to the specific parameters of the suspension cable and combining them with offshore construction processes. Results: There is a relationship between the impact force and the tension of the cable. The tension and impact force are related in cable collisions. While the maximum effective tension occurs at the upper end of the vertical cable and at the collision point, the horizontal cable's tension at the collision position is minimal. The distribution of curvature mutates at the collision point, causing bending deformation. The horizontal cable experiences greater bending change at the collision position than the vertical cable. Conclusion: In summary, collision of different parts of vertical cable is not obvious, while horizontal cable is more prone to self-collision and collision with vertical cable. Collision impact on horizontal cable is greater, with minimum tension occurring at collision point. Maximum velocity for horizontal cable appears at collision position, and for vertical cable at bottom. Maximum acceleration for both cables occurs at collision zone.

Bond durability between BFRP bars and seawater coral aggregate concrete under seawater corrosion environments

The combination of fiber-reinforced polymer (FRP) composites with seawater coral aggregate concrete (CAC) in offshore construction contributes to reduced construction costs and avoids the corrosion problems related to steel-reinforced concrete structures. However, the durability for FRP-reinforced CAC members during service in marine environments is not well understood, which greatly hinders their application in offshore construction. In this paper, accelerated aging tests were employed for investigating the bond performance between the basalt-FRP (BFRP) bars and the CAC under seawater drying-wetting cycle and immersion environments. The effects of various exposure temperatures and exposure times on bond characteristics were considered, and scanning electron microscopy (SEM) was adopted to characterize microstructure changes at the cross-section of BFRP bars subjected to seawater exposure environments. The experimental results revealed that after being exposed to seawater corrosion conditions, the slope in the rising stage of the curves (i.e., initial bond stiffness) appeared to increase somewhat due to the hygroscopic expansion effect of the FRP bars, but the bond strength and its corresponding slip value demonstrated a gradual decrease. After being subjected to seawater drying-wetting cycle conditions at 45 °C and 60 °C for 12 months, the bond strength of BFRP bars in CAC declined by approximately 6.5 % and 12.0 %, respectively. This deterioration in the bond strength was related to the degradations in the mechanical properties of the FRP bars and the CAC, as well as the interfacial performance between the FRP bars and the CAC.

Response of harbor porpoises (Phocoena phocoena) to different types of acoustic harassment devices and subsequent piling during the construction of offshore wind farms

Before piling of offshore wind farm foundations, acoustic harassment devices (AHDs) are used to drive harbor porpoises out of the area where they could suffer injuries. Until 2017, a combination of pingers and seal scarer devices (usually SPL = 174-193 dB re 1 μPa (rms) @ 1m at 1 to 20 kHz depending on the device) was prescribed for mitigation purposes in Germany. However, seal scarers led to decreased porpoise detection rates in much larger distances than intended, when 750 m is usually rendered sufficient to avoid injuries. Therefore, devices specifically designed for mitigation purposes were developed and are prescribed since then. These acoustic porpoise deterrents (APDs; e.g. FaunaGuard Porpoise Module; SPL = 172 dB re 1 μPa (rms) @ 1m at 60 to 150 kHz) aim to keep the animals away from offshore construction sites but should not lead to large-scale disturbance as caused by a seal scarer. Although project-specific evaluations indicated that APDs are effective, a cross-project analysis and a comparison with data from previous piling procedures employing seal scarers were still pending. The present study aimed to fill this gap. Between March 2018 and April 2019, harbor porpoise detection rates were monitored acoustically in four offshore wind farm projects using CPODs before, during and after piling at different distances up to 10 km from piling. APD operation led to a significant decrease in detection rates in the vicinity of the device, indicating the displacement of the animals from a small-scale area. Depending on the wind farm, detection rates during APD operation decreased by 30 to 100% at 750 m distance compared to 6 hours before APD operation. Furthermore, reduced detection rates during APD operation were only observed up to about 2.5 km distance even when the APD was switched on for over 40 minutes. Given that the extent of disturbance to harbor porpoises is lower when using an acoustic porpoise deterrent compared to the seal scarer, we consider that preferential use of an acoustic porpoise deterrent is an improvement to mitigation strategies and an important step forward to a less harmful piling procedure.

Feasibility of ice sheet conservation using seabed anchored curtains.

Sea level rise is expected to be rapid and extremely damaging to coastal communities and infrastructure, with unavoidable losses and coastal protection costs in the tens of billions per year. Retreat of the Thwaites and Pine Island Glaciers is likely already in an unstable regime as their oceanic fronts are ablated by deep intruding layers of relatively warm seawater. Warm water can be blocked from reaching the grounding line by thin flexible buoyant curtains anchored to the seabed. The consequent reduction in ice shelf melting could result in increased ice sheet buttressing as the shelf makes contact with seabed highs. Flexible curtains are less costly than solid artificial barriers, more robust against iceberg collisions, and easier to repair or remove in the event of unforeseen side effects. We illustrate the technical viability of this approach by considering curtain design concepts that should withstand oceanographic forces, and feasible methods of installation. Suitable materials are commonly available. Installation of a seabed curtain in temperate ocean waters would be entirely within the capabilities of existing offshore and deep ocean construction techniques. Installing in polar waters presents severe challenges from icebergs, harsh weather, and brief working seasons, which can however, be overcome with present-day technology. An 80 km long curtain installed in 600 m deep waters on alluvial sediments could help stabilize Pine Island and Thwaites glaciers over the next few centuries at much lower cost ($40-80 billion + $1-2 billion/yr maintenance) than the global coastline protection (∼$40 billion/yr) needed due to their collapse.

Full participation flat closed-loop safety management method for offshore wind power construction sites

This study aims to develop a full participation flat closed-loop (FPFCL) safety management method for offshore wind power (OWP) construction sites. People participation in safety management is improved by giving rewards based on evolutionary game theory. The method avoids management deficiencies due to information loss by reducing redundant management hierarchies and establishing point-to-point communication. The closed-loop mechanism ensures that a safety hazard is timely rectified. Meanwhile, an OWP safety management system (OWPsafety) is developed based on the social media platform (WeChat). The functions of the system include safety hazard report, processing center, and personal center. The software runs on smartphones and allows all stakeholders to participate in safety management, leveraging the advantages of social media in the sharing of knowledge. The benefits of this systematic approach include the elimination of time and space isolation, the interconnection between different construction parties, and the promotion of participation. The proposed method and system were applied to four OWP construction sites. The monthly rectification rate of safety hazards is maintained at more than 91%. Successful on-site tests demonstrated that the method and system can effectively solve the safety management challenges in OWP projects.

An underwater stable superhydrophobic surface for robust ultra-long-lasting biofouling resistance

An underwater stable superhydrophobic surface that displays a very low affinity to water and microorganisms is urgently required in marine engineering and offshore constructions. In this study, we demonstrated an underwater stable superhydrophobic surface with pressure resistance, chemical stability, biocompatibility, and biofouling resistance. The surface demonstrated superhydrophobicity under a water pressure of 13.72 kPa for up to 27 days. To examine the anti-biofouling property of the surface, the as-prepared samples were submerged in a natural lake for 50 days. The surface could withstand water flush and biological attacks for more than 35 days. The mechanical stability of the surface was evaluated by a sandpaper scratching test. An abrasion length of 12 m would not decrease the water contact angle of the surface, which is superior over the state-of-the-art coatings based on candle soot networks. The stable long-lasting underwater superhydrophobic surface is of great importance to marine applications.

Advances in Marine Engineering: Geological Environment and Hazards

With the continuous advancement of coastal, offshore, and deep-sea engineering construction (e [...]

Calcium carbide sludge activated fly ash mixture for offshore construction and its crack repair using seawater-mixed bioslurry cement

This paper reports a mixture based on the calcium carbide sludge (CCS) activation of fly ash. The formed calcium silicate hydrate (C–S–H) gel binds sands and gravel particles to synthesize pozzolanic-lime mortars and concretes. In both seawater and tap water, Ca(CO3), Ca(OH)2, and C–S–H were the main phases of hydration, as determined by powder X-ray diffraction. The optimal mixture was obtained using a CCS to FA ratio of 0.8 and curing time of 14 d. The surface morphology of spherical FA in the tap water mixed pozzolanic-lime materials had relatively loose rod-like, flower-like, and block structures, which were different from the irregular and dense block structure in the seawater mixed pozzolanic-lime mixture. For the fiber-reinforced mortar, the optimal content of polypropylene fiber was 0.1%. The surfaces of the fiber reinforced pozzolanic-lime mortars prepared using seawater were more compact than those prepared using tap and distilled water. The strengths of the fiber-reinforced specimens soaked in both seawater and tap water were maintained after 14, 28, 60, 90, and 120 d. The water permeability of pozzolanic-lime mixture with cracks was effectively reduced by spraying a seawater-mixed bioslurry cement. This work demonstrates the potential of a seawater-mixed pozzolanic-lime mortar as an offshore road base material and a bioslurry cement as its crack repairing material.

Non-uniform corrosion characteristics of the steel pipe pile exposed to marine environments

Steel pipe piles are commonly used as structural members in offshore construction steel trestles, and they may be imposed with serious corrosion threats. This study examines the corrosion characteristics of steel pipe piles which have been existing in the East China Sea for about five years. Nine samples were collected from the splash, tidal, and immersion zones, and cleaned and scanned by a laser scanner. Then they were reverse-modelled, 3D coordinates of the surfaces were generated, and the remaining thickness was calculated. Based on the surface height data, the waviness component was filtered while the roughness component was retained for each surface, and the topographic parameters were calculated and compared. The results reveal that the remaining thickness and the roughness of the steel pipe pile both showed non-uniform features. The steel pipe pile experienced double-sided corrosion in the splash and tidal zones, whilst it only experienced one-sided corrosion on the outer surface in the immersion zone. The severest corrosion damage was observed in the splash zone. Besides, the extreme value analysis results indicated that the minimal values of the remaining thickness in all zones conformed to the generalized extreme value distribution.