Normal Sea Research Articles

On the Development of a Near-Shore Pivoting Wave Energy Converter

Numerous offshore wave energy converter (WEC) designs have been invented; however, none has achieved full commercialization so far. The primary obstacle impeding WEC commercialization is the elevated levelized cost of energy (LCOE). Consequently, there exists a pressing need to innovate and swiftly diminish the LCOE. A critical challenge faced by WECs is their susceptibility to extreme wave loads during storms. Promising concepts must demonstrate robust design features to ensure resilience in adverse conditions, while maintaining efficiency in harnessing power under normal sea states. It is anticipated that the initial commercial endeavors will concentrate on near-shore WEC technologies due to the cost advantages associated with proximity to the coastline, facilitating more affordable power transmission and maintenance. In response, this manuscript proposes a pioneering near-shore WEC concept designed with a survivability mode that is engineered to mitigate wave loads during severe sea conditions. Moreover, prior investigations have highlighted favorable resonance properties of this novel concept, enhancing wave power extraction during recurrent energetic sea states. This study employs numerical and physical modelling techniques to evaluate wave loads on the proposed WEC. The results indicate a remarkable 65% reduction in wave loads on the moving floater of the WEC during a range of sea states under the implemented survivability mode.

Experimental and Numerical Study of Suspended Inter-Array Cable Configurations for Floating Offshore Wind Farm

The present study evaluates the feasibility of using a fully suspended inter-array cable system for an offshore wind farm. It includes both numerical simulations and a scaled-down experiment, conducted at a 1:49 scale, to validate the numerical results. To achieve the goal, a 15 MW floating offshore wind turbine (FOWT) and a floating offshore substation (FOSS) are involved to simulate the wind farm array. This study incorporates the 50-year return period conditions of the Taiwan Hsinchu offshore area, which has a water depth of about 100 m, to validate the specifications related to the platform motion and mooring line tension. Additionally, an analysis of the tension, curvature, and fatigue damage of the dynamic cable system is discussed in this research. Because a fully suspended cable is a relatively new concept and may be more frequently considered in a deeper water depth area, numerical simulation software Orcina Orcaflex 11.4 has been chosen to conduct the fully coupled simulation, determining whether the fully suspended cable system could effectively withstand the challenges posed by extreme sea conditions. This is due to the reason that a fully suspended cable would occupy a larger space in the ocean, which may pose a risk by influencing the navigation of the vessels. Therefore, the cable laying depth under normal sea states is also discussed to evaluate the influence over vessel navigation. This study also collects the long-term environmental data from the Central Weather Bureau, Taiwan, to calculate the accumulative cable fatigue damage under different sea states. To integrate the results, this research applies fitness parameters to evaluate the feasibility of each cable configuration. Covering the cable performance under extreme sea states and regular operating sea states offers valuable insights for applications in ocean engineering.

Evaluation of in situ observations on Marine Weather Observer during Typhoon Sinlaku

Abstract. The mobile ocean weather observation system, named Marine Weather Observer (MWO), developed by the Institute of Atmospheric Physics (IAP), consists of a fully solar-powered, unoccupied vehicle and meteorological and hydrological instruments. One of the MWOs completed a long-term continuous observation, actively approaching the center of Typhoon Sinlaku from 24 July to 2 August 2020, over the South China Sea. The in situ and high-temporal-resolution (1 min) observations obtained from MWO were analyzed and evaluated through comparison with the observations made by two types of buoys during the evolution of Typhoon Sinlaku. First, the air pressure and wind speed measured by MWO are in good agreement with those measured by the buoys before the typhoon, reflecting the equivalent measurement capabilities of the two methods under normal sea conditions. The sea surface temperature (SST) between MWO and the mooring buoys is highly consistent throughout the observation period, indicating the high stability and accuracy of SST measurements from MWO during the typhoon evolution. The air temperature and relative humidity measured by MWO have significant diurnal variations, generally lower than those measured by the buoys, which may be related to the mounting height and sensitivity of sensors. When actively approaching the typhoon center, the air pressure from MWO can reflect some drastic and subtle changes, such as a sudden drop to 980 hPa, which is difficult to obtain by other observation methods. As a mobile meteorological and oceanographic observation station, MWO has shown its unique advantages over traditional observation methods, and the results preliminarily demonstrate the reliable observation capability of MWO in this paper.

A revision of Silurian corals (Anthozoa: Heliolitoidea) from the collection of the National Museum of Natural History, NAS of Ukraine (Kyiv)

The collection of Silurian heliolitoid corals revised in this study has been assembled by the first author (V.G.) for four decades. The material was collected predominantly from Silurian outcrops and borehole cores in the Middle Dnister area. Some of the specimens were found in Belarus and Moldova during field works and field trips. The scientific works were part of the projects elaborated by a collective of scientists from the Institute of Geological Sciences, NAS of Ukraine and Taras Shevchenko National University of Kyiv. The working group consisted of geologists who graduated from the university in 1965 to 1970. Professors M. M. Klushnikov and O. L. Einor were our advisors. P. D. Tsegelnjuk was the oldest and the leader of the group. The collecting of specimens started in 1966 and now is ready to summarise the results. In the last fifty years, a large collection of fossil cnidarians from Silurian deposits has been assembled in the course of long-term geological field expeditions organised to study outcrops, cores of boreholes, and collect fossils. More than fifty outcrops and one hundred boreholes were studied in the territory of the Podillian region and the west slope of the Ukrainian Shield from Volyn to Snake Island. The collection comprises nearly ten thousand samples and 6000 thin sections of cnidarians. The total number of the studied samples belonging to Heliolitoidea is 139, of which 19 came from 9 outcrops and 120 from cores of 37 boreholes. The described samples represent 3 orders, 1 superfamily, 8 families, 2 subfamilies, 16 genera, 20 species (9 new), and 1 new subspecies. The authors consider that all the remains belong to fossil cnidarians. Fossil cnidarians are especially important from a facial point of view. The remains primarily indicate normal sea conditions in warm subtropical and tropical zones. In some cases, the identification of fossil cnidarians is easy, but usually we need to use the oriented thin sections. In the paper, only a small part of the collection is described following the system of Heliolitoidea developed by Olga Bondarenko. A studied collection is deposited in the Geological Department of the National Museum of Natural History, NAS of Ukraine under the number GD-1986.

Изотопный состав и условия образования фаменских карбонатолитов Центрально-Хорейверского вала (Хорейверская впадина, Печорская плита)

The article presents results of the distribution of the isotopic composition of 13C and 18O (119 samples) across four facies zones to substantiate the conditions of Famennian carbonation accumulation. The Lower Famennian carbonates of the shoal zone showed values of 13C (1.5 ± 0.15 %), 18O (25.01 ± 0.29 %) reflecting evaporative processes in a shallow basin in a warm and dry climate. For the rocks of the microbial mounds zone, the values of 13C (2.47 ± 1.12 %) and 18O (23.51 ± 1.12 %) reflect an increase in bioproductivity and some fluctuation in water salinity. In the limestones of the zone of transition to depression, the variations of isotopic composition are more distinct in the section. Thus, the Early Famennian is characterized by the average values of 13C (0.94 ± 0.59 %) and 18O (23.73 ± 2.18 %) for marine carbonates. The transition to the Middle Famennian is accompanied by isotopic weighting of 13C (1.30 ± 0.47%) and 18O (24.52 ± 1.45%), which shows an increase in evaporation processes under aridization conditions. In the Late Famennian, the isotopic composition abruptly lightens by 13C (–1.05 ± 0.66 %), which is associated with desalination under conditions of climate humidification. At the same time, the value of 18O (25.75 ± 0.31 %) corresponds to the average values for carbonates of the Devonian. The values of 13C (1.04 ± 0.89 %) and 18O (26.01 ± 0.99 %) in the carbonates of the zone slope of the carbonate bank towards the shallow shelf reflect the conditions of the normal sea basin with a slight increase in the evaporation regime during climate aridization. The obtained results indicate that the Famennian sedimentation basin characterized by fluctuations in sea level, facies, water hydrochemistry and climate.

Influence of Six-Degree-of-Freedom Motion of a Large Marine Data Buoy on Wind Speed Monitoring Accuracy

In order to quantitatively analyze the data measurement accuracy of ocean buoys under normal and extreme sea conditions, in this study, we simulated the six-degree-of-freedom motion response of self-designed ocean buoys under different sea conditions based on a separated vortex simulation and the fluid volume method and analyzed the impact of the unsteady motion of buoys on data measurement. The results indicate that under normal sea conditions, the deviation between the numerical method used in this paper and the experimental results is less than 10%. The heaving motion of a buoy is most sensitive to changes in wave conditions. The fluctuation intensity of buoy motion is modulated by the height and wavelength of waves. When the wave height and wavelength are similar to the overall geometric size of a buoy, the wave characteristics of the buoy’s heave, yaw, and pitch motion are significant. In addition, under extreme sea conditions, the movement of the buoy can also cause a deviation in the measured velocity in the transverse flow direction, but the overall deviation is less than 10%. In extreme sea conditions, the wind speed measurement results should be corrected to improve the measurement accuracy of a buoy.

Turbidity buffers coral bleaching under extreme wind and rainfall conditions

Coral reefs in turbid waters have been hypothesized to be a refuge from climate change. These naturally occurring communities were brought into the spotlight because some of their species exhibited record levels of resistance to marine heatwaves (MHWs) by disturbance-tolerant corals. However, long-term monitoring data on the drivers of coral bleaching in these extreme reef habitats are scarce. Here, we describe the population structure and bleaching rates of a widespread and resilient coral (Siderastrea stellata). We examine the links between environmental factors, namely, rainfall, wind speed, turbidity, solar irradiance, sea surface temperature, MHWs, and coral bleaching status under the worst recorded drought cycle in the Tropical South Atlantic (2013–2015). We examined 2880 colonies, most of which (∼93%) fit in the size group of 2–10 cm, with a small number (∼1%) of larger and older colonies (>20 cm). The results indicated the absence of MHWs and normal sea surface temperature variations (between 26.6 °C and 29.3 °C), however, we detected an extreme rainfall deficit (30–40% less annual volume precipitation). In general, a high proportion (44–84%) of bleached colonies was found throughout the months when turbidity decreased. Siderastrea is the only reef-building coral that comprises this seascape with encrusting and low-relief colonies. During drought periods, cloudiness is reduced, turbidity and wind speed are reduced, and solar irradiance increase, driving coral bleaching in turbid reefs. However, episodic rainfall and higher wind speeds increase turbidity and decrease coral bleaching. Our hypothesis is that turbidity decreases during drought periods which increases bleaching risk to corals even without thermal stress. Our results suggest that turbidity may have related to wind and rainfall to provoke the coral bleaching phenomenon.

Cloning and expression characterization of elongation of very long-chain fatty acids protein 6 (elovl6) with dietary fatty acids, ambient salinity and starvation stress in Scylla paramamosain.

Introduction: Elongation of very long-chain fatty acids protein 6 (ELOVL6) played crucial roles in regulating energy expenditure and fatty acid metabolism. Many studies have performed to investigate the physiological roles and regulatory mechanisms of elovl6 in fish and animals, while few studies were reported in crustaceans. Methods: Here we reported on the molecular cloning, tissue distribution and expression profiles in response to dietary fatty acids, ambient salinity and starvation stress in Scylla paramamosain by using rapid amplification of cDNA ends (RACE) and quantitative real-time PCR. Results: Three elovl6 isoforms (named elovl6a, elovl6b and elovl6c) were isolated from S. paramamosain in the present study. The complete sequence of elovl6a was 1345 bp, the full-length sequence of elovl6b was 1419 bp, and the obtained elovl6c sequence was 1375 bp in full length. The elovl6a, elovl6b and elovl6c encoded 287, 329 and 301 amino acids respectively, and exhibited the typical structural features of ELOVL protein family members. Phylogenetic analysis showed that the ELOVL6a from S. paramamosain clustered most closely to ELOVL6 from Portunus trituberculatus and Eriocheir sinensis, while the ELOVL6b and ELOVL6c from S. paramamosain gathered alone into a single branch. Quantitative real-time PCR exhibited that the relatively abundant expression of elovl6b was observed in intestine and stomach, and the elovl6a and elovl6c were highly expressed in hepatopancreas. In addition, studies found that replacing fish oil with soybean oil could significantly increase the transcriptional levels of three elovl6 in hepatopancreas of S. paramamosain, and the expression of elovl6a and elovl6c in hepatopancreas were more sensitive to dietary fatty acids than the elovl6b. Compared with the normal sea water group (27‰), the expression of sterol-regulatory element binding protein1c (srebp-1), elovl6a, elovl6b and elovl6c were upregulated in the low salinity groups, particularly in 7‰. On the contrary, the starvation stress suppressed the expression of srebp-1, elovl6a, elovl6b and elovl6c. Discussion: These results may contribute to understand the functions of elovl6 in fatty acid synthesis and regulatory mechanisms in crustaceans.

Fore Poppet Design and Optimization to Apply on Norway type Trawler Fishing Ships

In the classical sea landing methods of ships, aquaplaning and slipway support systems are used. In Norwegian Type Trawler Fishing vessels, the outer shell surface geometry is very delicate. Therefore; the incoming forces are extreme and the use of wooden poppets by these forces in normal sea landings is insufficient. This work; It includes two different steel fore poppet designs and analyzes for the Norwegian type trawler fishing vessel, which cannot be launched with conventional slipway support systems after landing calculations. Within the scope of this study, two different steel fore poppets were designed. After the analyzes and examinations, it was decided that the Norwegian type trawler fishing vessel, which is the subject of the article, with which steel fore poppet design will be launched without any problems. Studies carried out in this context; Two different steel fore poppet designs were made using the Rhinoceros analysis program, which is a 3D design program.Rhinoceros Scan & Solve analysis was performed and simulation was run by applying forces to the designed steel fore poppets. A force of 3e+06N, including gravity, was applied to both designed structures. As a result of this; In the first steel fore poppet structure, a maximum displacement of 1.18611mm occurred. In structures designed under a force of 3e+06N; In the first structure, the maximum Von Mises Stress value was found to be 505.761MPa. In the second structure, the maximum Von Mises Stress value was found to be 163.142MPa.

Course keeping control for very large ship using hyperbolic tangent function based on nonlinear decoration technique

To solve the problems of difficult course keeping, high energy output, and large wear of very large ships under different sea conditions, a robust controller combining the closed-loop gain shaping algorithm and nonlinear decoration is proposed in this paper. Firstly, a linear controller is designed by using the third-order closed-loop gain shaping algorithm and takes the hyperbolic tangent function as the nonlinear decoration of the controller output, and the robustness of the system is proved by H∞ robust control theory. Secondly, taking ‘Vale Brasil’, an ore carrier with a displacement of 400,000 tons, as the test plant. The nonlinear Nomoto model and nonlinear Norrbin model were established, which were compared with the control effect from the existing controller. Thirdly, simulation experiments were carried out under normal sea state and heavy sea state to prove the effectiveness. The results indicate that the proposed control strategy can achieve the required course faster, and enhances the smoothness of rudder angle actuation compared with the existing controller. It can maintain good control ability under different sea conditions. The proposed controller has the advantages of simple parameter adjustment, better robustness, less energy consumption, and reduced rudder angle. It is more in line with engineering practice and increases ship operation benefits.

Intelligent Adaptive PID Control for the Shaft Speed of a Marine Electric Propulsion System Based on the Evidential Reasoning Rule

To precisely and timely control the shaft speed for a marine electric propulsion system under normal sea conditions, a new shaft speed control technique combining the evidential reasoning rule with the traditional PID controller was proposed in this study. First, an intelligent adaptive PID controller based on the evidential reasoning rule was designed for a marine electric propulsion system to obtain the PID parameters KP, KI, and KD. Then, a local iterative optimization strategy for model parameters was proposed. Furthermore, the parameters of the adaptive PID controller model were optimized in real time by using the sequential linear programming algorithm, which enabled the adaptive adjustment of KP, KI, and KD. Finally, the performance of the adaptive PID controller regarding the shaft speed control was compared with that of other controllers. The results showed that the adaptive PID controller designed in this study had better control performance, and the shaft speed control method based on the adaptive PID controller could better control the shaft speed of the marine electric propulsion system.

The Mechanism Driving a HAB-Induced SST Warming Anomaly: A Case Study in the Beibu Gulf

Water temperature is one of the most important factors that affect the occurrence of harmful algal blooms (HABs). Characteristics of sea surface temperature (SST) variability related to a Noctiluca scintillans bloom were analyzed with Himawari-8 data in the Beibu Gulf during mid-February 2021. An SST warming anomaly was found around the bloom area from 10:00 to 19:00 local time, with a peak temperature of 24.3 °C at 15:00, which was 2.9 °C higher than the surrounding normal sea water. The possible formation mechanism of the HAB-induced SST anomaly was studied in this work by integrating meteorological, ocean dynamics, and ecological processes. During the HAB event, the sea surface was covered by biological mucilage. A model that considered the net heat flux, heat capacity, density of seawater, and temperature variation was established to estimate the thickness changes (Δ H ) in the marine heating layer during the HAB event. The model results show that the heating layer thickness of the HAB area (Δ H between 0.76 m and 0.91 m) was smaller than that of the non-HAB area (Δ H > 1.19 m). The SST anomaly in this study might be caused by a thinner and warmer marine heating layer that is related to the biological mucilage on the surface of the HAB area.

Green energy-saving robust control for ship course-keeping system based on nonlinear switching feedback

To further save energy and reduce carbon emissions, a simple and robust green energy-saving control algorithm was proposed under the premise that the ship achieved an excellent course-keeping effect. To this end, the controller is designed by employing the third-order closed-loop gain shaping algorithm, and the final control law is obtained via the nonlinear switching feedback technique. The robustness of the system is proved by the Nyquist stability criterion. An evaluation model is carefully established for energy-saving and carbon-reduction of the course-keeping controller. The nonlinear Nomoto and Norrbin models for MV “Yukun” are implemented for simulating and further assessing under normal and heavy sea conditions. Compared with the nonlinear decoration controller, the proposed controller enhances the ship's course-keeping accuracy, shortens the delay time and settling time of the controller, lessens the steering angle and steering frequency of the rudder, increases the robustness of the system, and reduces the comprehensive energy-saving index by 26.1% under normal sea conditions. Meanwhile, good controller performance and green energy-saving effects are more in line with the requirements of navigation practice, which is essential for ships to achieve safe, economical, green, and low-carbon navigation.

Impact of hydrodynamic drag coefficient uncertainty on 15 MW floating offshore wind turbine power and speed control

The main objective of this study is to analyse the impact of the drag coefficient uncertainty on large floating offshore wind turbines with respect to the power performance and generator speed control. In order to do so, the recently published IEA 15 MW reference wind turbine mounted on two different floating platform types (semi-submersible UMaine VolturnUS-S and spar WindCrete) has been selected. The platforms have been divided by components (columns, heave plates and pontoons) and the drag coefficient uncertainty has been quantified for each component, using a range of values from the literature that is representative for normal sea state conditions. Dynamic simulations have been performed for both floating platforms operating in a variety of environmental conditions (wind and waves), with a range of drag coefficients to account for the variability. Then, operating variables (generated power, generator speed, blade pitch angle.), platform motions and hydrodynamic forces have been analysed, to determine how large the impact due to the variations of the drag coefficient is. Results have shown that the considered range of drag coefficient uncertainty, although being quite large, has negligible impact on the performance of the wind turbine control response, irrespective of the floating platform type.

Field Study of Longshore Sediment Transport Rate Estimation over the Newly-Developed Coastline of Northern Oman Sea

Estimations of sediment transport rate is the prerequisite of coastal development and management studies, as accretion and erosion are among main controlling considerations for port planning. The Iranian coastline of the Oman Sea, which is so-called Makran Coastline, has a complex morpho-dynamic behavior and should be considered from both scientific importance and its high potential for development in the next decade. It is while morpho-dynamic perspective of the area is not well studied so far. On the other hand, the wave climate of the area is affected by different regimes: monsoon waves, normal seas, swells coming from the Indian Ocean and tropical cyclones. There are limited researches on the contribution of each regime on the longshore sediment transport with considering the sensitivity to deep water wave direction variability. This study aims to put different pieces of knowledge together, including field measurements, numerical modeling and Geographic Information System-based (GIS-based) analysis of multi-year cross-shore profile data, to obtain a more realistic estimation of Longshore Sediment Transport (LST) rate along the undeveloped Makran Coastline. The focus of this paper is mostly on the accurate wave and sediment transport modeling, verified against available field data and morphological evidences. The major challenge in this regard has been the lack of long-term data availability, as the coastline has been remained undeveloped. This has been overcome by adopting satellite imagery as a complementary source to the available periodic hydrography data, as well as data science methods for improving wave data accuracy. A numerical model is applied for simulating the transportation process of sediments along Makran Coastline. The existing extracted shoreline changes around Makran Coastline through GIS analysis of satellite images were used to assess the general morphological changes in the study area. All the simulation and coastline change analysis results are adopted for obtaining an integrated conclusion in Zarabad Port as the case study of this research. The obtained results were in fair agreement with observations and this is why the model setup and study methodology can be applied for LST rate estimations over Makran Coastline.

Seasonal prediction of summer extreme precipitation over the Yangtze River based on random forest

The 2020 summer extreme precipitation event over the Mid-Lower Reaches of Yangtze River in China caused widespread socioeconomic impacts, with a death toll of hundreds and direct economic loss of half billion CNY. Seasonal prediction of summer extreme precipitation event over this region, however, has long been a challenge, due to the underlying interactions among various atmospheric and oceanic factors. Based on the random forest (RF), a classical machine learning method, a series of predictive models are trained and tested on the samples during 1951–2019, with 14 preceding atmospheric and oceanic indices as potential predictors. It is found that the model based on 3 indices has optimal performance in terms of the distinguishing capacity between extreme and non-extreme events. For the 2020 summer extreme event, the model predicts a large probability far beyond the climatological mean level, indicating a very likely extreme event. Interpretation of the decision trees in the RF model reveals 3 main decision paths leading to an extreme precipitation event over this region. The first one is driven by a strong eastern tropical Pacific (EP) El Niño which starts to decay in spring but does not totally disappear in summer. The second one results from the combined effect of an EP La Niña and normal sea surface temperature over the North Indian Ocean (NIO). The last one is also associated with a decaying EP El Niño, but the EP El Niño here is much weaker than that in the first path. Both the Pacific-El Niño-independent warming of NIO and cooling in the eastern tropical western Pacific in spring play important roles. The RF integrates different nonlinear physical mechanisms in a model and discovers weak signals which are easily omitted by traditional linear methods. The trained model can self-improve with increasing samples and serve as a reference for operational prediction of extreme precipitation events in the region.

Characterization of the Impacts of Living at High Altitude in Taif: Oxidative Stress Biomarker Alterations and Immunohistochemical Changes.

At high elevations, the human body experiences a number of pathological, physiological, and biochemical changes, all of which have adverse impacts on human health and organ vitality. This study aimed to investigate the alterations in the liver and kidney biomarkers, oxidative stress markers, gene expression, and cellular histology of rats maintained at high altitudes and normal sea level. A total of twenty male Wistar rats at 2 months of age were randomly assigned to two groups. The rats in group A were maintained at normal sea level in Jeddah, whereas rats in group B were maintained in an area in Taif 2600 m above sea level. After 2 months of housing, orbital blood samples were collected for the analysis of significant biochemical indicators of oxidative stress biomarkers of the liver and kidneys. Liver and kidney tissues from both groups were taken to examine the hepatorenal changes occurring at the biochemical, histological, immunohistochemical, and genetic levels. The results revealed substantial increases in the serum levels of liver and kidney biomarkers (GPT, GOT, urea, and creatinine) and decreases in the serum levels of antioxidant biomarkers (SOD, catalase, GSH, and NO). In parallel, the levels of the malondialdehyde (MDA) tissue damage marker and inflammatory cytokines (IL-1β, TNF-α, and IFN-γ) were increased in the high-altitude group compared to the normal sea level group. In addition, there were significant alterations in the oxidative and inflammatory status of rats that lived at high altitude, with considerable upregulation in the expression of hepatic VEGF, type 1 collagen, Cox-2, TNF-α, and iNOS as well as renal EPASI, CMYC, HIF-α, and EGLN-2 genes in the high-altitude group compared with controls housed at normal sea level. In conclusion, living at high altitude induces hepatorenal damage and biochemical and molecular alterations, all of which may serve as critical factors that must be taken into account for organisms living at high altitudes.

The 1:20 scaled hydraulic model test and field experiment of barge-type floating offshore wind turbine system

Objective of this study is to develop a barge-type floating offshore wind turbine (FOWT) in order to face extreme environmental conditions in western Taiwan offshore water area. The prototype of FOWT considered here consists of (1) NERL 5 MW wind turbine, (2) a single steel column with a hub height of 90 m above sea level, (3) a square barge-type floating platform equipped with a damping pool and heave plate to improve the stability of the floating foundation, (4) catenary mooring system using anchor chain, and installation at a water depth of 70 m in the western Taiwan offshore water area.In order to verify the feasibility of the concept, a 1/20 scale model of the FOWT prototype was used by conducting hydraulic model tests in the large flume (300m × 5m× 5m) at Tainan Hydraulics Laboratory (THL), National Cheng Kung University (NCKU) and field experiments at the Anping Harbor. Hydraulic model tests include (1) regular wave test, with normal wave period from 5.7sec to 8.9sec, and long wave period from 9 s to 14sec. (2) irregular wave test, including normal sea condition, northeast monsoon sea condition, ten-year return period typhoon wave condition, and 50-year return period typhoon wave condition. Moreover, investigation of wind speed, wind direction, wave height, dynamic motion of FOWT, mooring tension, and rotor speed were conducted in the field experiment.After examining the motion of the barge-type offshore floating wind turbine, it was found that the pitch and the roll motions could satisfy the DNV standard. The tension of the mooring line did not exceed the minimum breaking load (MBL), which indicating the good stability of the barge-type FOWT proposed by this study.

Research on navigation risk of the Arctic Northeast Passage based on POLARIS

AbstractThe complex sea ice conditions in Arctic waters has different impacts on the legs of the Arctic passage, and ships of specific ice classes face different navigation risks. Therefore, the quantitative analysis of the navigation risks faced in different legs has important practical significance. Based on the POLARIS introduced by IMO, the sea ice condition data from 2011 to 2020 was used to quantify the navigation risk of the Arctic Northeast passage. The risk index outcome (RIO) of the Arctic Northeast Passage were calculated. The navigable windows of the route for ice class 1A ships sailing independently under different sea ice conditions in the last decade were determined, with a navigable period of 91 days under normal sea ice conditions, approximately 175 days under light sea ice conditions and only week 40 close to navigation under severe sea ice conditions. The three critical waters affecting the safety of ships were identified. Combined with the navigable windows and critical waters, recommendations on ship's navigation and manipulation and recommendations for stakeholders were given. The method and results provided reference and support for the assessment of the navigation risk of ships in the Northeast Passage and safety navigation and operations of ships, and satisfied the needs of relevant countries and enterprises to rationally arrange shipment dates and sailing plans based on different ice classes of ships.

An Investigation on the Vortex Effect of a CALM Buoy under Water Waves Using Computational Fluid Dynamics (CFD)

Floating offshore structures (FOS) must be designed to be stable, to float, and to be able to support other structures for which they were designed. These FOS are needed for different transfer operations in oil terminals. However, water waves affect the motion response of floating buoys. Under normal sea states, the free-floating buoy presents stable periodic responses. However, when moored, they are kept in position. Mooring configurations used to moor buoys in single point mooring (SPM) terminals could require systems such as Catenary Anchor Leg Moorings (CALM) and Single Anchor Leg Moorings (SALM). The CALM buoys are one of the most commonly-utilised type of offshore loading terminal. Due to the wider application of CALM buoy systems, it is necessary to investigate the fluid structure interaction (FSI) and vortex effect on the buoy. In this study, a numerical investigation is presented on a CALM buoy model conducted using Computational Fluid Dynamics (CFD) in ANSYS Fluent version R2 2020. Some hydrodynamic definitions and governing equations were presented to introduce the model. The results presented visualize and evaluate specific motion characteristics of the CALM buoy with emphasis on the vortex effect. The results of the CFD study present a better understanding of the hydrodynamic parameters, reaction characteristics and fluid-structure interaction under random waves.