A state-of-the-art review is presented of mathematical manoeuvring models for surface ships and parameter estimation methods that have been used to build mathematical manoeuvring models for surface ships. In the first part, the classical manoeuvring models, such as the Abkowitz model, MMG, Nomoto and their revised versions, are revisited and the model structure with the hydrodynamic coefficients is also presented. Then, manoeuvring tests, including both the scaled model tests and sea trials, are introduced with the fact that the test data is critically important to obtain reliable results using parameter estimation methods. In the last part, selected papers published in journals and international conferences are reviewed and the statistical analysis of the manoeuvring models, test data, system identification methods and environmental disturbances used in the paper is presented.

Extreme waves may considerably impact crucial coastal and marine engineering structures. The First Scientific Assessment Report on Ocean and Climate Change of China and The Fourth Assessment Report on Climate Change of China were published in 2020 and 2022, respectively. However, no concrete results on the long-term trends in wave changes in China have been obtained. In this study, long-term trends in extreme wave elements over the past 55 years were investigated using wave data from five in situ observation sites (i.e., Lao Hu Tan, Cheng Shan Tou, Ri Zhao, Nan Ji, Wei Zhou) along the coast of China. The five stations showed different trends in wave height. Results show a general downward trend in wave heights at the LHT and CST stations, reaching -0.78 and -1.44 cm/a, respectively, in summer at middle and high latitudes. NJI stations at middle-to-low latitudes are influenced by the winter monsoon and summer tropical cyclones, showing a substantial increase in extreme wave heights (0.7 cm/a in winter and 2.68 cm/a in summer). The cumulative duration of H_1/10 ≥ 3 m at NJI and RZH has grown since 1990.

Flow characteristics around a wall-mounted square cylinder have been numerically simulated at aspect ratios (AR) ranging from 4 to 7 at Re = 10 000. Four turbulence models have been compared in terms of drag coefficient (C_D). The closest result has been provided by two turbulence models, namely, k-ε Realizable and k-ε Shear Stress Transport (SST). Hence, these models were utilized to present the flow patterns of pressure distributions, turbulent kinetic energy values, velocity magnitude values with streamlines, streamwise velocity components, cross-stream velocity components and spanwise velocity components on different planes. Flow stagnation has been attained in front of the cylinder. Pressure values peaked for the upstream region. Over the cylinders, the tip vortex structure was dominant owing to the influence of the free end. Flow separation from the top front edge of the body has been obtained. The dividing streamline affected by the flow separation was highly effective in the wake region and moved nearer to the body when the aspect ratio was decreased; the reason was the wake shrinkage owing to the decreasing aspect ratio. Upwash and downwash have been seen in the cylinder wake. These two models presented similar flow patterns and drag coefficients. These drag coefficients are in good agreement with those in previous studies.

Pulsating flow is a common condition for underwater manipulators in Bohai Bay. This study aimed to investigate the effects of pulsation frequency and amplitude on the hydrodynamic characteristics of an underwater manipulator with different postures using the user-defined function (UDF) method. The lift coefficient (C_L), drag coefficient (C_D), and vortex shedding of the underwater manipulator in single- and dualarm forms were obtained. Results indicated that the maximum increase in the lift and drag coefficients subjected to the pulsation parameters was 24.45% and 28%, respectively, when the fluid flowed past a single arm. Compared with the single arm, the lift and drag coefficients of the arms were higher than those of the single arm when arm 2 was located upstream. Additionally, the pulsation frequency had no obvious effect on the manipulator, but the C_L and C_D of arm 2 showed an obvious increasing trend with an increase in pulsation amplitude. Meanwhile, when arm 2 was located downstream, the C_L and C_D of arm 2 were reduced by 16.38% and 1.15%, respectively, with an increase in the pulse frequency, and the maximum increase in the lift and drag coefficients was 33.33% and 16.78%, respectively, with increasing pulsation amplitude. Moreover, the downstream wake morphology changed significantly, and a combined vortex phenomenon appeared. Finally, a theoretical basis for examining the hydrodynamic characteristics of marine engineering equipment was established to aid future marine resource exploitation.

Clarifying the gas ingestion mechanism in the turbine disc cavity of marine gas turbines is crucial for ensuring the normal operation of turbines. However, the ingestion is influenced by factors such as the rotational pumping effect, mainstream pressure asymmetry, rotor-stator interaction, and unsteady flow structures, complicating the flow. To investigate the impact of rotor-stator interaction on ingestion, this paper decouples the model to include only the mainstream. This research employs experiments and numerical simulations to examine the effects of varying the flow coefficient through changes in rotational speed and mainstream flow rate. The main objective is to understand the influence of different rotor-stator interactions on the mainstream pressure field, accompanied by mechanistic explanations. The findings reveal inconsistent effects of the two methods for changing the flow coefficient on the mainstream pressure field. Particularly, the pressure distribution on the vane side primarily depends on the mainstream flow rate, while the pressure on the blade side is influenced by the mainstream flow rate and the attack angle represented by the flow coefficient. A larger angle of attack angle can increase pressure on the blade side, even surpassing the pressure on the vane side. Assessing the degree of mainstream pressure unevenness solely based on the pressure difference on the vane side is insufficient. This research provides a basis for subsequent studies on the influence of coupled real turbine rotor-stator interaction on gas ingestion.

In designing modern vessels, calculating the propulsion performance of ships in ice is important, including propeller effective thrust, number of revolutions, consumed power, and ship speed. Such calculations allow for more accurate prediction of the ice performance of a designed ship and provide inputs for designers of ship power and automation systems. Preliminary calculations of ship propulsion and thrust characteristics in ice can enable predictions of full-scale ice resistance without measuring the propeller thrust during sea trials. Measuring propeller revolutions, ship speed, and the power delivered to propellers could be sufficient to determine the propeller thrust of the vessel. At present, significant difficulties arise in determining the thrust of icebreakers and ice-class ships in ice conditions. These challenges are related to the fact that the traditional system of propeller/hull interaction coefficients does not function correctly in ice conditions. The wake fraction becomes negative and tends to minus infinity starting from a certain value of the propeller advance coefficient. This issue prevents accurate determination of the performance characteristics, thrust, and rotational speed of the propulsors. In this study, an alternative system of propeller/hull interaction coefficients for ice is proposed. It enables the calculation of all propulsion parameters in ice based on standard hydrodynamic tests with self-propulsion models. An experimental method is developed to determine alternative propeller/hull interaction coefficients. A prediction method is suggested to determine propulsion performance in ice based on the alternative interaction coefficient system. A case study applying the propulsion prediction method for ice conditions is provided. This study also discusses the following issues of ship operation in ice: the scale effect of icebreaker propellers and the prospects for introducing an ice interaction coefficient.

As an important part of offshore wind turbine support and fixed units, the multibucket jacket foundation bears large loads and a complex marine environment. In this paper, the horizontal bearing characteristics of the four-bucket jacket foundation of offshore wind power in sandy soil are studied. Through model tests and numerical simulations, the influence of bucket foundation sealing properties, load application speed, and loading direction on foundation-bearing capacity are discussed. The results show that the horizontal ultimate bearing capacity of the foundation in the nonsealing condition is decreased by 51.3% compared with the sealing condition; therefore, after the foundation penetration construction is completed, the bucket sealing must be ensured to increase the load-bearing performance of the structure. At a loading speed of 3.25 mm/s, the horizontal ultimate bearing capacity of the foundation is increased by 9.4% over the working condition of 1.85 mm/s. The bearing capacity of the foundation is maximized in the loading direction α =45° and is the smallest when α =0°. That is, the foundation can maximize its load-bearing performance under the condition of single-bucket compression/tension. During the design process, the main load of the structure should be loaded in the 45° direction. The contrast error of the experiment and numerical simulation does not exceed 10%. The research results have important guiding importance for designing and constructing the jacket foundation and can be used as a reference for the stable operation and sustainable development of offshore wind power systems.

Long-term responses of floating structures pose a great concern in their design phase. Existing approaches for addressing long-term extreme responses are extremely cumbersome for adoption. This work aims to develop an approach for the long-term extreme-response analysis of floating structures. A modified gradient-based retrieval algorithm in conjunction with the inverse first-order reliability method (IFORM) is proposed to enable the use of convolution models in long-term extreme analysis of structures with an analytical formula of response amplitude operator (RAO). The proposed algorithm ensures convergence stability and iteration accuracy and exhibits a higher computational efficiency than the traditional backtracking method. However, when the RAO of general offshore structures cannot be analytically expressed, the convolutional integration method fails to function properly. A numerical discretization approach is further proposed for offshore structures in the case when the analytical expression of the RAO is not feasible. Through iterative discretization of environmental contours (ECs) and RAOs, a detailed procedure is proposed to calculate the long-term response extremes of offshore structures. The validity and accuracy of the proposed approach are tested using a floating offshore wind turbine as a numerical example. The long-term extreme heave responses of various return periods are calculated via the IFORM in conjunction with a numerical discretization approach. The environmental data corresponding to N-year structural responses are located inside the ECs, which indicates that the selection of design points directly along the ECs yields conservative design results.

The water curtain spray system of the ship helps reduce surface thermal load and lowers thermal infrared radiation, notably enhancing the stealth and survivability of naval ships. The performance of the water curtain spray system is largely influenced by the density of the nozzles and their installation height. Therefore, a test platform was established to investigate these critical influencing factors, employing an orthogonal design methodology for the experimental study. Specifically, the study evaluated the effects of varying distances to the steel plate target and different injection heights on the cooling performance of the system. Results demonstrate that using one nozzle per 4 square meters of the ship’s surface area effectively lowers the surface temperature, bringing it closer to the ambient background temperature. This nozzle configuration creates irregular infrared heat patterns, which complicate the task for infrared detectors to discern the ship’s outline, thus enhancing its infrared stealth. Additionally, maintaining the nozzle installation height within 0.6 m to prevent the temperature difference between the steel plate and the background temperature from exceeding 4 K. Moreover, as the infrared imaging distance increases from 3 to 9 m, the temperature difference measured by the thermocouple and the infrared imager increases by 141.27%. Furthermore, with the increase in infrared imaging distance, the infrared temperature of the target steel plate approaches the background temperature, indicating improved detectability. These findings have significantly enhanced the stealth capabilities of naval ships, maximizing their immunity to infrared-guided weapon attacks. Moreover, their importance in improving the survivability of ships on the water surface cannot be underestimated.

A numerical simulation analysis is conducted to examine the unsteady hydrodynamic characteristics of vortex-induced vibration (VIV) and the suppression effect of helical strakes on VIV in subsea pipelines. The analysis uses the standard k-ε turbulence model for 4.5- and 12.75-inch pipes, and its accuracy is verified by comparing the results with large-scale hydrodynamic experiments. These experiments are designed to evaluate the suppression efficiency of VIV with and without helical strakes, focusing on displacement and drag coefficients under different flow conditions. Furthermore, the influence of important geometric parameters of the helical strakes on drag coefficients and VIV suppression efficiency at different flow rates is compared and discussed. Numerical results agree well with experimental data for drag coefficient and vortex-shedding frequency. Spring-pipe self-excited vibration experimental tests reveal that the installation of helical strakes substantially reduces the drag coefficient of VIV within a certain flow rate range, achieving suppression efficiencies exceeding 90% with strake heights larger than 0.15D. Notably, the optimized parameter combination of helical strakes, with a pitch of 15D, a fin height of 0.2D, and 45° edge slopes, maintains high suppression efficiency, thereby exhibiting superior performance. This study provides a valuable reference for the design and application of helical strakes and VIV suppression in subsea engineering.

To improve the efficiency of ship traffic in frequently traded sea areas and respond to the national “dual-carbon” strategy, a multi-objective ship route induction model is proposed. Considering the energy-saving and environmental issues of ships, this study aims to improve the transportation efficiency of ships by providing a ship route induction method. Ship data from a certain bay during a defined period are collected, and an improved backpropagation neural network algorithm is used to forecast ship traffic. On the basis of the forecasted data and ship route induction objectives, dynamic programming of ship routes is performed. Experimental results show that the routes planned using this induction method reduce the combined cost by 17.55% compared with statically induced routes. This method has promising engineering applications in improving ship navigation efficiency, promoting energy conservation, and reducing emissions.

Path planning for recovery is studied on the engineering background of double unmanned surface vehicles (USVs) towing oil booms for oil spill recovery. Given the influence of obstacles on the sea, the improved artificial potential field (APF) method is used for path planning. For addressing the two problems of unreachable target and local minimum in the APF, three improved algorithms are proposed by combining the motion performance constraints of the double USV system. These algorithms are then combined as the final APF-123 algorithm for oil spill recovery. Multiple sets of simulation tests are designed according to the flaws of the APF and the process of oil spill recovery. Results show that the proposed algorithms can ensure the system’s safety in tracking oil spills in a complex environment, and the speed is increased by more than 40% compared with the APF method.

Biodiesel is a clean and renewable energy, and it is an effective measure to optimize engine combustion fueled with biodiesel to meet the increasingly strict toxic and CO₂ emission regulations of internal combustion engines. A suitable-scale chemical kinetic mechanism is very crucial for the accurate and rapid prediction of engine combustion and emissions. However, most previous researchers developed the mechanism of blend fuels through the separate simplification and merging of the reduced mechanisms of diesel and biodiesel rather than considering their cross-reaction. In this study, a new reduced chemical reaction kinetics mechanism of diesel and biodiesel was constructed through the adoption of directed relationship graph (DRG), directed relationship graph with error propagation, and full-species sensitivity analysis (FSSA). N-heptane and methyl decanoate (MD) were selected as surrogates of traditional diesel and biodiesel, respectively. In this mechanism, the interactions between the intermediate products of both fuels were considered based on the cross-reaction theory. Reaction pathways were revealed, and the key species involved in the oxidation of n-heptane and MD were identified through sensitivity analyses. The reduced mechanism of n-heptane/MD consisting of 288 species and 800 reactions was developed and sufficiently verified by published experimental data. Prediction maps of ignition delay time were established at a wide range of parameter matrices (temperature from 600 to 1 700 K, pressure from 10 bar to 80 bar, equivalence ratio from 0.5 to 1.5) and different substitution ratios to identify the occurrence regions of the cross-reaction. Concentration and sensitivity analyses were then conducted to further investigate the effects of cross-reactions. The results indicate temperature as the primary factor causing cross-reactivity. In addition, the reduced mechanism with cross-reactions was more accurate than that without cross-reactions. At 700-1 000 K, the cross-reactions inhibited the consumption of n-heptane/MD, which resulted in a prolonged ignition delay time. At this point, the elementary reaction, NC₇H₁₆+OH<=>C₇H₁₅-2+H₂O, played a dominant role in fuel consumption. Specifically, the contribution of the MD consumption reaction to ignition decreased, and the increased generation time of OH, HO₂, and H₂O₂ was directly responsible for the increased ignition delay.

Knowing the optimal operating parameters of Stirling engines is important for efficient combustion through adaptability to changed pressures and oxygen atmospheres. In this study, the optimum operating conditions for efficient combustion in a singular Stirling engine combustor at different oxygen atmospheres were investigated and determined. Numerical simulations were performed to investigate the effects of ejection ratio and pressure on combustion performance. In an oxygen/carbon dioxide atmosphere, the results show that increasing the ejection ratio substantially alters the flame distribution in the Stirling engine combustor, increasing heat transfer and external combustion efficiency. In contrast, increasing the ejection ratio reduces the average and maximum temperatures of the Stirling engine combustor. Increased pressure affects the flame distribution in the Stirling engine combustor and impedes the flow and convective heat transfer in the combustor, reducing the overall external combustion efficiency at pressures above 6.5 MPa. In an air/carbon dioxide atmosphere, an increased ejection ratio reduces the average and maximum temperatures in the Stirling engine combustor. However, the overall flame distribution does not change substantially. The external combustion efficiency tends to increase and then decrease because of two opposing factors: the increase in the convective heat transfer coefficient and the decrease in the temperature difference. Increasing pressure inhibits forced convection heat transfer in the Stirling engine combustor, reducing external combustion efficiency, which drops from 78% to 65% when pressure increases from 0.2 MPa to 0.5 MPa.

A finite element and boundary element model of the 100 m X-BOW polar exploration cruise ship is established. The vibrated velocity-excited force admittance matrix is calculated by frequency response analysis, and the vibrated velocity in the stern plate and main engine foundations is tested during the trial trip. Then, the excited force of the propeller and main engine is derived using the vibrated velocity and admittance matrix. Based on the excited force, the cabin-simulated vibrated velocity is compared with the tested vibrated velocity, and the tolerance is within the allowable scope in engineering. Loading the excited forces on the boundary element model, the distribution characteristics of sound level underwater are analyzed. Then, forces excited by the main engine and propeller are loaded on the model, and the contribution ratio of excitation sources to underwater acoustic radiation is analyzed. The result provides a reference for vibration assessment in the early stage and control in the late stage.