ObjectivesThis study seeks to address the low-frequency limitations in the computation of hydrodynamics for slender ships using strip theory, and develops an efficient method for calculating hydrodynamics over a wider frequency range for slender ships using a simplified approach. MethodsBased on the unified theory of strip theory and ordinary slender body theory, the added mass and damping coefficients of a prolate spheroid, slender, modified Wigley model and S60 ship are calculated programmatically. A comparison is made between the calculated results using the unified theory and experimental data, as well as results obtained from strip theory, 3D translating and pulsating source Green's function method and other methods. The computational characteristics and advantages of the unified theory are then analyzed. ResultsThe results indicate that the unified theory based on 2D sections produces results under zero-speed conditions that are consistent with those obtained by the 3D panel method. For conditions involving ship speed, the calculated results exhibit consistent variations with those obtained from the 3D translating and pulsating source Green's function method. ConclusionsThe proposed unified theory is capable of reflecting 3D effects in the low-frequency region, which gives it greater efficiency and simplicity compared to 3D methods, and thus significant practical value.

ObjectivesThis study seeks to explore the influence of water depth on the drag reduction effect and optimal drag reduction height of an interceptor. Based on the numerical solution approach of the RANS equations, the flow field around a high-speed monohull ship with various height interceptors is numerically simulated. MethodsFirst, the validity of the numerical method is verified by a DTMB 5415 high-speed ship. Next, the flow field around a high-speed monohull ship is numerically simulated under different interceptor heights and water depths. Based on the numerical results, the resistance, navigation state and flow field characteristics under different working conditions are analyzed. ResultsThe results show that the drag reduction effect of the interceptor has an obvious shallow water effect. The optimal drag reduction height and reduction of trim angle of the interceptor is unchanged with the change in water depth. The interceptor has a certain effect on reducing wave-making behind the ship, but the effect decreases with the decrease in water depth. ConclusionsThis study has certain practical reference value for the application of interceptors in shallow water.

ObjectiveA local dynamic collision avoidance algorithm based on an improved fast-marching square (IFMS) method is proposed to solve the multi-vessel collision avoidance problem of unmanned sailboats in open water. MethodsConsidering the uncontrollable speed of a sailboat, its collision avoidance behavior is transformed into a heading control problem, with the direction of the total potential field gradient decreasing as the desired collision avoidance heading. When sailing without risk of collision or downwind, a temporal potential field is constructed to avoid all stationary irregular obstacles and reach the target point. When the sailboat has sailing constraints, Gaussian likelihood functions are designed for specific encounter situations to dynamically construct obstacle potential fields according to the convention on the international regulations for preventing collisions at sea (COLREGS), while the local wind potential field is introduced to consider the dead zone of a sailboat and realize the application requirements of combining dynamic collision avoidance with a zigzag sailing strategy. ResultsThe results show that the proposed algorithm can enable an unmanned sailboat to successfully achieve collision avoidance operations with other sailboats and restricted motor vessels in various encounter situations, while complying with collision avoidance rules and avoiding navigational dead zones. Compared with the original fast-marching square (FMS) algorithm, the upwind sailing time is significantly reduced and the planned collision avoidance trajectory is safer and more reasonable.ConclusionThe proposed method complies with the characteristics of sailboat motion and collision avoidance rules, has high safety and robustness in complex environments, and possesses scientific value regarding the development of autonomous obstacle avoidance technology for unmanned sailboats.

ObjectivesThis study calculates and analyzes the flow field around the hull of a 210 000 DWT bulk carrier in order to perform hull line optimization with resistance and wake non-uniformity as the optimization objectives. MethodsComputational Fluid Dynamics (CFD) is used to evaluate the initial hull lines, calculate the flow field around the ship and obtain flow field characteristics such as the wave pattern, pressure distribution, velocity distribution, etc. According to the CFD calculation results, an optimization strategy is constructed to form the modified hull lines. CFD calculation is then carried out on the modified lines to evaluate the optimization effects on resistance and wake non-uniformity. Finally, a model test of the optimized hull form's power delivery performance is carried out to verify the optimization effects. ResultsThe CFD calculation results show that compared with the initial hull form, the effective power of the modified hull form is reduced by 2.46% and the wake non-uniformity is reduced by 8.48%, while the model test results show that compared with the initial hull form, the delivered power of the modified hull form is reduced by 3.49%.ConclusionsThe proposed optimization method can obtain hull lines with excellent resistance performance and good wake field uniformity, giving it strong engineering applicability.

ObjectivesThis study takes a typical pressure hull segment of an unmanned underwater vehicle (UUV) as the object and explores its load bearing capacity law based on lightweight design technology. MethodsFirst, several typical materials are analyzed using the mechanical properties of the pressure hull, load law and optimal critical load design value (stress strength failure and stability failure occur concurrently). The bearing properties of a typical pressure hull with varying depths are then discussed further in terms of the specific engineering requirements. ResultsThe failure mode of the shell gradually transitions from stability failure to strength failure as the depth increases, and the optimal critical load design value is proportional to the qualities of the material. Taking bearing efficiency and other factors into consideration, aluminum alloy shells should be selected within the 300 m depth range, titanium alloy and glass fiber composite shells within the 300-600 m depth range, and titanium alloy and carbon fiber composite shells within the 600-1 000 m depth range. In the 1 000-3 000 m depth range, a carbon fiber and boron fiber composite shell is the ideal solution. ConclusionsThe findings of this study can be used to guide the design of pressure hulls for UUVs made of various materials.

ObjectivesWith the continuous development of larger scale and more complex ships, the number of finite element model elements required to model hull structures at the cabin structure level and above is increasing dramatically, resulting in collision, impact, contact and other large-scale non-linear mechanical problems which are difficult to solve. To this end, a simplified method for the deformation of two-way stiffened plate structures based on orthotropic equivalent theory is proposed in order to simplify the modeling of ship structures.MethodsFirst, the current well-established simplification method for the plane stress of one-way stiffened plates is extended to the more complex plane bending problem of two-way stiffened plates. The ratio of the total moment of inertia of stiffened plates to the moment of inertia of plates in the orthogonal direction is introduced to reflect the structural orthotropism. Next, the moment of inertia ratios are substituted into the equivalent constitutive equation for the plane bending of stiffened plates to achieve the transformation to physical orthotropism, thereby taking into account both the deformation resistance of the structure and the influence of the membrane forces generated by shifting the neutral surface at the mechanical level. Finally, finite element calculations are used to classify the deformation modes of the four-sided fixed stiffened plates according to different displacement distributions, and the actual results of the stiffened plates are analyzed in terms of error comparisons with the equivalent results of this method and the traditional method.ResultsThe result comparison shows that the proposed method can reduce the number of elements in two-way stiffened plates by up to 84%, and the equivalent errors in all three deformation modes can be controlled within 6%, which is much lower than those of the two traditional methods.ConclusionsWith high precision, a wide application range and greatly reduced calculation resources, the proposed method can provide a direct modeling and simulation calculation solution to address the nonlinear mechanical problems of large hull structures for practical engineering applications.

ObjectivesIn this paper, an orthogonal braided glass fiber composite sandwich panel with a PVC foam core and dimensions of 150 mm×100 mm×26 mm is selected as the research object in order to study the impact mechanical properties of composite sandwich panels. The dynamic response and residual compressive strength of the panel under single-point low-velocity impact are then analyzed.MethodsFirst, a series of drop hammer impact tests are conducted to study the failure mode, impact force-displacement response and energy absorption characteristics of the panel under different impact energies. Next, quasi-static compression experiments are conducted to investigate the maximum compression load capacity and residual compressive strength under impact damage.ResultsThere are significant differences in the failure modes and impact force-displacement characteristics of the sandwich panel under different impact energies. The core mainly absorbs impact energy through compression deformation. As the impact energy increases, the maximal impact force, dent depth and absorbed energy of panel gradually increase, while the maximum compression load capacity and residual strength decrease after impact. The damage degree of the impacted composite sandwich panel determines its residual compressive strength. ConclusionThe findings of this study can provide valuable references for the impact resistance design of naval ship structures.

ObjectiveThis study aims to investigate the complex welding residual stress of high-strength steel thick plate with multi-pass welding, and examines the influence of such stress on the fracture behavior of welded joints. MethodsTaking 75 mm thick Q690 high-strength steel thick plate as the research object, multi-pass butt welding and a corresponding welding experiment are carried out, and the longitudinal residual stress on the middle cross section is then measured by the contour method after cooling. Based on effective thermal elastic-plastic FE computation, properties such as the thermal cycle and microstructure evolution during the multi-pass welding of thick steel plate are represented. The uniaxial tension test and GTN damage model are combined to obtain the parameters of GTN model for Q690 high-strength steel plate, which are then used to examine the fracture behavior and stress-strain curves of the base metal and welded joint specimens.ResultsThe predicted shape of the weld pool and the content of the metallographic phase show good agreement with the measured data. After considering the solid phase transformation during welding and initial stress due to rolling, the longitudinal and transverse residual stresses are in good agreement with the measured results. Moreover, the fracture behavior of the welded joints is also investigated while considering welding micro defects and transverse residual stress, and the mechanical mechanism of welding residual stress is clarified.ConclusionThe results of this study can provide valuable references for the evaluation of the residual stress and fracture behavior of welded joints in high-strength steel thick plate .

Marine renewable energy has broad application prospects. Compared with the single energy utilization device, the floating multi-energy combined power generation device can better realize the optimal allocation of resources and reduce the development cost of energy. In order to fully understand the development prospects of multi-energy combined power generation devices, this paper starts with the multi-energy combined power generation integration scheme, analyzes the differences between different types of combined power generation devices, and summarizes their technical characteristics. Next, the research progress of each module analysis method and multi-module coupling dynamics analysis method of the floating multi-energy combined power generation device is clarified and summarized in such aspects as theoretical research and simulation. Finally, the applicable scenarios of the various methods are analyzed and the development trends, problems, and challenges of floating multi-energy combined power generation devices are discussed, aiming to provide references for the subsequent construction of economically feasible floating multi-energy combined power generation devices.

The vigorous development of wind power generation technology is the core path for the country to promote the low-carbon energy transformation and realize the "dual-carbon" (carbon peaking and carbon neutrality) goals. With the gradual saturation of the development of onshore and offshore wind power resources, wind power development from the near-shore to the distant deep sea is the inevitable trend of the future development of the wind power industry. The research and development and optimization of floating offshore wind turbine (FOWT) platforms is the key to promoting the development of offshore wind power in distant deep sea areas. Based on an analysis of the current development status of FOWT platforms at home and abroad, this paper further analyzes the current research status of aerodynamic loads, hydrodynamic loads, mooring systems, coupling analysis methods and commonly used numerical simulation tools in the design of FOWT platforms, and focuses on sorting out the key technological ideas and constitutive features of FOWT platforms that are driven by the enhancement of structural stability and the reduction of costs. By summarizing the current research status of FOWT platform optimization, we can forecast the problems and challenges in the design of FOWT platforms with a view to providing technical references for researchers in related fields.

Metal hydride hydrogen storage is a hydrogen storage method based on the principle of chemical absorption. Featuring high volumetric hydrogen storage density and high safety, its potential applications in the field of hydrogen storage on ships have attracted significant attention. Against this background, there is a series of issues to be studied, such as material properties, reactor performance, thermal management systems, cost, etc. This paper categorizes metal hydride hydrogen storage technology, summarizes its working principle and research progress on its material properties, and introduces its applications on ships. Next, combined with the application environment and demands of hydrogen ships, the paper analyzes the technological and economic feasibility of the application of metal hydride hydrogen storage technology on ships. To meet the requirements of hydrogen ships for hydrogen storage capacity and release rate, research on marine metal hydride hydrogen storage systems is introduced, including hydrogen storage system performance research, hydrogen storage reactor structure, reactor structure optimization and design ideas for thermal management systems coupled with marine fuel cell and hydrogen storage systems. Finally, the research direction of marine metal hydride hydrogen storage systems is predicted and summarized.

The application of offshore wind power gangways ensures the normal operation of offshore wind turbines and provides reliable support for optimizing the boarding process, improving the operation and maintenance efficiency, and reducing the cost of wind power projects. This paper provides an overview of the development history and technological progress of gangways, and analyzes the main equipment in this field and its performance at home and abroad, as well as discussing the key technologies of offshore wind turbine gangways in such aspects as motion sensing and data analysis, compensation control and execution, structural design and reliability, and composite material application. It is pointed out that the parallel platform is the mainstream offshore gangway actuator; wave compensation is the core of equipment performance and the source of competitiveness; and advanced wave compensation technology depends on the development of sensor technology, artificial intelligence technology and other multidisciplinary development. This paper makes a comprehensive analysis for researchers and practitioners in the field of offshore wind power gangways, providing valuable references for subsequent technology exploration.

ObjectivesThis paper investigates the impact of shared lines with different materials on the dynamic response of floating wind farms in order to design a rational shared mooring system. MethodsFirst, shared mooring and traditional (without shared cables) mooring systems are designed for floating wind farms. The dynamic response and economic cost of the two mooring systems are then compared to validate the feasibility of the shared mooring system design. Second, the influence of the two types of shared mooring systems on the mooring response of floating wind farms is studied. Finally, an analysis is made of the influence of load direction and line material on the tension of the shared lines.ResultsThe results indicate that floating wind farms with shared mooring systems using different materials have nearly identical blade tension. However, there are differences in the impact of the two types of shared mooring systems on wind turbine displacement and the mean tension of mooring lines. In addition, the environmental load direction and line material affect wind turbine displacement and shared line tension.ConclusionsThis study provides useful references for selecting material for shared lines in the mooring systems of floating wind farms.

ObjectivesA new Spar-type floating wind turbine platform design scheme is proposed for a 15 MW floating wind turbine, and its performance is analyzed. MethodsBased on potential flow theory, the frequency domain hydrodynamic calculation of the platform is carried out and the wave loads and motion response characteristics of the platform under different wave directions are analyzed. The blade element momentum method is applied to calculate the aerodynamic load of the impeller and make it equivalent to the wind coefficient in order to calculate the time-domain response of the platform under the combined effect of wind, waves and currents under different working conditions, while also analyzing the force situation of the mooring lines. ResultsThe results show that the heave, roll, and pitch of the platform have peak points at the natural frequency of its motion, and the positions of occurrence are all far from the main energy region of the waves. Under the action of wind, waves and currents, compared to the working conditions, the maximum pitch angle of the platform under extreme conditions is smaller, but the amplitude of maximum surge, heave and mooring tension are greater than the working conditions. ConclusionsThe newly designed Spar-type floating wind turbine platform has good stability and hydrodynamic performance. Under the designed environmental loads, its response and mooring force can meet the requirements of the specifications, ensuring the safety and stability of the wind turbine.

ObjectivesIn order to fully leverage electricity and seawater resources, this paper carries out the thermodynamic analysis and optimization design of an alkaline water electrolysis（AWE） hydrogen production system for offshore wind power. The focus comprises the impacts of operating pressure, temperature and lye flow rate on the operational characteristics of the system. MethodsThermodynamic, kinetic and flux balance analyses are carried out to develop a thermodynamic equilibrium model for hydrogen production by alkaline water electrolysis using Aspen Plus software, which is then validated in comparison with the experimental results.ResultsThe optimum working pressure and temperature of the alkaline water electrolysis hydrogen production system are 9 bar and 70 °C respectively, and the optimum lye flow rate is 1600 t/h. The system energy loss and exergy loss increase with the increase of input current density. When the alkaline water electrolysis input current density reaches 3000 A/m2, the system energy efficiency and exergetic efficiency are 63.58% and 57.27% respectively, and the system energy loss accounts for 26% of the total energy input, of which the exergy loss of the electrolyzer is the highest, accounting for 93.39% of the total exergy loss of the system.ConclusionsThrough this parametric optimization method, a suitable range of operating parameters can be obtained, providing useful references for the selection of offshore wind power hydrogen production parameters.

ObjectiveTo improve the safety of wet-towing transportation for offshore wind power multi-bucket jacket foundations, it is necessary to explore the stability and dynamic response during the wet-towing transportation.MethodsA hydrodynamic model was constructed based on the offshore engineering analysis software MOSES, and frequency-domain analysis and time-domain analysis were performed on the wet-towing process. Quantitative analysis was also conducted on the influence of parameters such as wave loads and towing modes on the towing characteristics of the three-bucket jacket foundation.ResultsComputational results show that the three-bucket jacket foundation has good wet-towing stability, and its upright floating state can meet the intact stability checking within a draft of 8-10 m. The amplitudes of towing force, pitching angle, heaving acceleration and air pressure in the bucket of the three-bucket jacket foundation are directly proportional to the wave height, have a linear relationship with draft, and show less influence. The amplitudes of towing force and air pressure in the bucket have no obvious relationship with the wave period, but the wave period will affect the amplitudes of pitching and heaving responses the foundation. The towing force is approximately proportional to the speed squared. The pitching motion of the three-bucket jacket foundation under the conditions of the stern sea is more severe than that under the cross sea. ConclusionThe research results have important guiding significance for improving the safety of wet-towing transportation of multi-bucket jacket foundations.

Objective The paper aims to solve the problem of the overall stability of the ship's power system being reduced due to the use of grid-following (GFL) control for grid connection in existing solar ship photovoltaic (PV) power generation systems.MethodsBased on the characteristics and operational characteristics of marine power systems, four inverter control methods, including GFL PQ control and grid-forming (GFM) droop control, as well as virtual synchronous generator (VSG) control and virtual oscillator control (VOC), were selected to construct photovoltaic grid-connected control strategies for solar-powered marine power systems. Finally, Matlab/Simulink is used to establish a simulation model of a solar ship power system in order to verify the effectiveness of the GFM control concepts and ideas.ResultsCompared to the GFL control strategy, the utilization of GFM under load switching conditions can lead to an average reduction of 26.86% in frequency fluctuation amplitude and 37.85% in voltage regulation time. ConclusionsThe utilization of the GFM control strategy is capable of effectively mitigating the stability deterioration of the ship's power system triggered by the grid-connected photovoltaic system. This approach enables the PV system to proactively uphold the stability of the power parameters of the ship's power system while fulfilling the energy supply, resulting in the substantial enhancement of the power system's stability.

ObjectivesThe purpose of this paper is to investigate the control and optimization of the power output system for a multi-body floating wave energy converter (MBFWEC) with wave protection effects.MethodsTo study the interaction of the multi-body floating WEC with waves, a numerical wave flume is constructed using OpenFOAM software. The experiment simulates the interaction between the WEC and waves under different power take-off (PTO) strategies, namely linear, constant, linear spring, velocity-squared and snap through PTO systems, then compares the energy capture efficiency and wave dissipation performance of the WEC under each.ResultsThe results show that the wave energy capture efficiency of the MBFWEC can reach up to 52.6%. The linear spring and snap through PTO systems, which are based on the optimization of linear PTO, have a certain degree of influence on the WEC and its wave dissipation effects. However, linear PTO is more advantageous than linear spring and snap through when considering both wave energy capture and wave dissipation effects.ConclusionsThis study identifies the advantageous wave intervals of PTO systems such as constant damping and velocity-squared damping, and can provide useful references for optimizing PTO system settings for MBFWECs.

ObjectivesA life cycle carbon emission assessment method is proposed to comprehensively evaluate the carbon emission reduction capacity of hydrogen-electric hybrid ships. MethodsFirst, an energy flow model of the power system is established using the Matlab/Simulink software platform. Hydrogen consumption and electricity consumption under actual operating conditions are then calculated, and the life cycle carbon emissions are obtained. Finally, sensitivity analysis is performed on carbon emissions from different power sources and hydrogen sources.ResultsThe results of an inland river ferry show that compared with the traditional diesel engine power system, the hydrogen-electric hybrid system can reduce carbon emissions by 30.24% in one operation cycle. The sensitivity analysis results show that the carbon emissions of the hydrogen-electric hybrid system are not necessarily better than those of the traditional diesel power system, so it is recommended to use renewable energy for hydrogen production and power generation to significantly reduce carbon emissions (up to 94.2%).ConclusionsThe results of this study can provide references for the power system design of green ships.

ObjectiveTo improve the combustion, performance and emissions of high-power marine engines, diesel fuel micro-injection with methanol ignition is adopted to study the in-cylinder combustion and emission characteristics. MethodsA three-dimensional simulation model of a diesel micro-injection pilot-ignition methanol engine is established on the basis of an ACD320 high-power marine medium-speed diesel engine in order to study the effects of injector parameters (nozzle number and methanol spray angle γ) on the combustion performance and emission characteristics of a marine large-bore methanol engine.ResultsWith the increase in the number of nozzle, the in-cylinder methanol atomization improves and the in-cylinder work mass mixing becomes more adequate, leading to the advancement of CA50 and the shortening of the combustion duration. While this yields higher indicated thermal efficiency（ITE） and a better equivalent indicated specific fuel consumption (EISFC), as well as contributing to the reduction of soot emissions, it also causes the elevation of NOx emissions. Moreover, as the methanol spray angle increases, the ITE increases, obtaining better fuel economy and lower soot emissions. With the optimal methanol spray angle (γ = 60°), the methanol spray is located in front of the diesel spray injection point, the flame propagation speed in the cylinder is faster, the indicated thermal efficiency is at its maximum and the fuel combustion is fuller, thereby obtaining the lowest soot emissions and most optimal EISFC.ConclusionThe results of this analysis can provide a theoretical basis for engine injector parameters.

Objectives Aiming to address the existing challenges in the power capacity configuration of island and reef hybrid power generation systems, this paper proposes an optimization method based on the adaptive ant colony algorithm (ACA). MethodsAn ACA is used as the core optimization tool to configure the power capacity of an island and reef hybrid power generation system. The process of ants foraging is simulated by employing the ACA and using the power generation of renewable energy as dynamic pheromones in the search space. The optimal solution is then found through global search, achieving the full utilization of renewable energy. Taking Wai Lingding Island as the target island, a 'wind-solar-diesel-storage' microgrid hybrid power generation system model is constructed, and the ACA is used to optimize its capacity configuration. ResultsThe simulation results of the algorithm indicate that, compared to the improved Grey Wolf algorithm and Artificial Bee Colony algorithm, the ACA can effectively reduce the operational costs and environmental pollution of the microgrid hybrid power generation system, while ensuring the stability of the power supply. ConclusionsThe results of this study can effectively increase the power supply stability of the microgrid hybrid power generation system, reduce operating costs and environmental pollution, and thus achieve efficient utilization of energy resources.

ObjectivesA multi-objective optimization algorithm is proposed to address the problem of the complex operating conditions of large horizontal axis hydraulic turbine blades. MethodsAn airfoil optimization model is established based on the multi-island genetic algorithm, the airfoil is parametrically fitted using the class shape function transformation (CST) function method, and the whole optimization process is integrated on the Isight platform to achieve automatic optimization. ResultsUsing the above method, NACA 63813/63815/63816 airfoils are selected as the initial airfoils for multi-objective optimization, CFD numerical validation is carried out on the obtained airfoils using the Fluent turning model, and the lift-to-drag ratios and lifting forces at the airfoil attack angle of 5° are selected as the optimization objectives, resulting in the optimized airfoils gaining increased lift coefficients of 14%, 15% and 20%, and increased lift-to-drag ratios of 14%, 16% and 28%, respectively. ConclusionsNumerical validation shows that the lift-to-drag ratios of the optimized airfoil is higher than those of the original airfoils with the same thickness under several operating conditions, and the structural strength of the blade is improved while ensuring good aerodynamic performance, making it more suitable than conventional airfoils for large-scale tidal current energy horizontal axis hydraulic turbines.

ObjectiveTo optimize the energy capture efficiency of a rocker-type wave energy converter, the effects of the platform pillar wave diversion scheme and shape of finned floats on energy capture are studied.MethodsFirst, a hydrodynamic model of float motion is established. Next, the hydrodynamic characteristics of different finned floats are calculated using AQWA software and analyzed under different platform pillar wave diversion schemes, different frequency domain parameters such as added mass, radiation damping, wave excitation force and response amplitude operator (RAO), and different time domain parameters such as displacement, velocity, acceleration and excitation force. Finally, the energy-capture width ratios of different finned floats under different platform pillar wave diversion schemes are investigated.ResultsThe results show that different platform pillar wave diversion schemes have little effect on the frequency domain parameters of the finned floats or the float motion displacement of time domain parameters, but a large effect on the motion period. Energy capture is optimal at a fin angle of 100° under the double-pillar wave diversion scheme.ConclusionsBased on the proposed numerical simulation model, the hydrodynamic response of multi-degree-of-freedom finned floats in wave motion can be simulated accurately, providing useful references for the optimized design of the float shape for oscillating float-type wave energy generation platforms.

ObjectiveThis study uses the structural load inversion method to conduct a dynamic response state analysis of a floating wind turbine tower under wave action. MethodBased on a semi-submersible wind turbine, the measurement data is simulated in the time domain, and the mass-normalized modes of the tower are calculated using a frequency-domain simulation model of the floating wind turbine. Both are used as inputs to a joint input-state estimation (JIS) algorithm to conduct the structural load inversion and real-time state analysis of the floating wind turbine tower. ResultsThe results show that when using the simulated data of tower nodes as inputs to the JIS algorithm, the estimated tower root loads and node responses agree well with the simulated results, achieving high-precision inversion. ConclusionThe inversion results verify that the JIS algorithm is effective and can be used for the real-time state analysis of floating wind turbines to ensure their long-term safe and stable operation.

ObjectivesWhen assessing the safety of the connectors of a multi-module offshore floating power generation platform, in order to compensate for the inability to carry out the real-time monitoring of the structural stress field across the whole domain due to a limited numbers of sensor, a digital twin method based on a simulation database is proposed that can rapidly predict the platform's stress field. MethodsBy downgrading the three-dimensional physical model of the connectors to a one-dimensional digital model, the stress field data is interpolated and deduced in digital space, thereby achieving the rapid prediction of the structural stress field across the whole domain and its visual display.ResultsThe results show that the simulation model is in good agreement with the test results, with a maximum absolute error of 8.61%; for the interpolation of data under different loading angles, when the interpolation step of the loading angle is 10°, the aver-age absolute error of stress is 1.98%; and for the interpolation of data under different loads, when the interpolation step of the load is 10 t, the average absolute error of stress is 1.28%, achieving the rapid prediction and visualization of the connectors' stress field distribution. Conclusions The digital twin-based model of connectors can provide useful references for the rapid dynamic perception and scientific prediction of the structural strength of offshore floating power generation platforms.

ObjectiveThis study aims to explore the structural strength deterioration mechanism of pipelines with corrosion defects in hydrogen-blended environments.MethodsBased on the experimental data, an analysis is made of the load bearing performance of X52 steel under different levels of hydrogen blending , and the structural strength failure mechanism of an X52 hydrogen-blended natural gas pipeline under different corrosion defects is described using the nonlinear finite element method. ResultsWhen the hydrogen blend level increases to 50.0%, under a combined load, the pipeline reaches minimum displacement failure at 2.58 mm, and the structural toughness deteriorates to a greater degree; at a hydrogen blend level of 25.0%, the defect depth is greater and the degree of structural failure more serious; comparing square and circular defects, the maximum stress of the square defects is higher than that of the circular defects. ConclusionsThe material property-based defective pipeline model can realize the assessment of the structural bearing capacity deterioration of natural gas pipelines under different hydrogen-blending conditions, providing engineering suggestions for the design and health monitoring of new energy pipelines.

ObjectivesThis paper integrates the finite element method (FEM) with the discrete-module-beam (DMB) method and improves the derivation of the lumped-mass stiffness matrix in order to efficiently apply the DMB method to complex and compound very large floating structures (VLFS). MethodsFirst, 3D potential flow theory is introduced to the DMB method to establish the hydroelastic equation. FEM theory is then introduced to discretize each macro-submodule into micro beam elements, and the lumped-mass matrix is then derived on the basis of the sub-structure approach and matrix manipulation. In dealing with complex boundary conditions, the cross-zeros-set-one approach or adding an additional constraint into the total stiffness matrix is adopted. In dealing with complex interconnections, the node numbering is first altered and then an additional constraint stiffness matrix is added to the total stiffness matrix. ResultsWhen the FEM+DMB method is applied to VLFS with fixed/spring-damped boundary conditions and hinged/rigid/spring-damped interconnections, good agreement is shown with the results from the direct method. ConclusionsThe proposed FEM+DMB method can analyze the hydroelasticity of VLFS in complex engineering scenarios with enhanced speed and accuracy.

ObjectiveThis paper proposes a novel structure that combines an offshore wind turbine jacket and aquaculture net cage, and its hydrodynamic characteristics are investigated. Methods Experimental tests are carried out to analyze the horizontal loads on the pile foundations of the combined structure, and the tension in the connection between the jacket and net cage, while considering the effects of water depth, wave height, wave period, wave direction, current velocity and direction, and other parameters. ResultsFor 0-degree regular wave conditions, the maximum horizontal load on the pile foundations is 30.2 N. For 45-degree regular wave conditions, the maximum horizontal load on the pile foundations is 27.5 N. Thus, the maximum horizontal load on the pile foundations under 0-degree regular wave conditions is 9.5% greater than that under 45-degree regular wave conditions. ConclusionsUnder regular wave conditions, the net cage has little influence on the horizontal load on the pile foundations when the wave period is small, while under pure current conditions, the net cage will cause a significant increase in the horizontal load on the pile foundations of the combined structure.

ObjectiveTo overcome the problem of the limitation of working bandwidth due to the phase ambiguity caused by the carrier frequency's variation in conventional time-modulated direction finding, a single-channel direction finding method with nonuniform time modulation is proposed in this paper.MethodsBy modulating the signals received by different antenna elements at the same time with nonuniform periods, the amplitude information can be separately mapped to the corresponding modulated frequency without aliasing. With the amplitude ratio independently extracted from the harmonics, single-channel direction finding for the incident signal can be achieved using the lookup table method. ResultsThe feasibility of the proposed method is verified on the basis of the numerical simulation results. Meanwhile, a wideband non-uniform time modulation system available for 2.4 GHz and 5.8 GHz is constructed and its effectiveness demonstrated, with the results showing that the mean of direction finding absolute error is 0.21° and 0.18° respectively. ConclusionsThe proposed method can effectively improve the working bandwidth and has such advantages as a simple structure, low cost, low signal processing complexity and wideband direction finding.

ObjectiveThis paper analyzes and models the core logic of a strike chain in terms of time sensitivity, reconfiguration and coverage, thereby providing model and method support for improving the dynamic management ability of naval combat resources under confrontation conditions. MethodsFirst, the typical combat platforms and elements related to the cross-domain cooperative combat of naval battlefields, such as escort ships, UAVs and unmanned boats, are abstracted into four types of resource nodes, namely detection, processing, decision-making and strike. Next, taking the shortest delay as the goal and considering constraints such as wide battlespace, low transmission rate between nodes and limited communication distance, the dynamic integration optimization mathematical model of the strike chain is established. A typical air defense scenario is then designed to demonstrate the shortest delay analysis of the strike chain and the destruction reconstruction analysis under the absence or attack of nodes, and quantitatively describe the changes of the shortest delay and sector coverage index of the reorganized strike chain under countermeasure conditions. Finally, based on a typical combat example of a Ukrainian unmanned cluster attack on the Black Sea Fleet, the ability of the fleet to resist the attack is analyzed on basis of the strike chain model. ResultsThe simulation results show that the model can be used to generate multiple strike chains with the shortest delays, and the responsibility division of each strike chain can be optimized, forming a multi-target killing network at sea. The destruction reconstruction of the strike chain often needs to pay such costs as increased delay and decreased sector coverage. The model can also be used to test anti-saturation attack ability under different formations.ConclusionsThis paper studies and validates the feasibility of analyzing the naval warfare system based on the strike chain model, and can provide theoretical model support for the subsequent design of future naval joint combat systems oriented to the killing network.