Water entry of marine structures has long been an important problem in ocean engineering. Among the different techniques to predict fluid-structure interactions during water entry, smoothed particle hydrodynamics (SPH) method gradually becomes a promising method that is able to solve the impact pressure and the splashing fluid jets simultaneously. However, for three-dimensional (3D) problems, SPH method is computationally expensive due to the huge number of particles that are needed to resolve the local impact pressure accurately. Therefore, in this work an axisymmetric SPH model is applied to solve different water entry problems with axisymmetric structures including spheres and cones with different deadrise angles. Importantly, the Volume Adaptive Scheme (VAS) is added to guarantee the homogeneousness of particle volumes during the simulation. The axisymmetric SPH model with VAS scheme will be introduced in detail and the numerical results will be sufficiently validated with experimental data to demonstrate the high robustness and accuracy of the SPH model for solving 3D axisymmetric water entry problems in an efficient way.

The taut mooring system using synthetic fiber ropes has overcome the shortcomings such as the large self-weight of the mooring lines and provides better mooring performance for the floating structures. The polyester rope has attracted much attention among numerous synthetic fiber rope materials due to its lightweight, low price, corrosion resistance, and high strength. Thus, the mooring characteristics of it are worth studying. Polyester mooring lines are flexible in deep water, when a marine structure is moored by them, the geometric nonlinearity such as large displacement, large stretch, and large bending deformation, and the material nonlinearity like viscoelastic of the polyester ropes become complex integrated problems to be studied. Considering the nonlinear phenomenon, the simulation and calculation of a polyester line were carried out by the absolute nodal coordinate formulation (ANCF) in this paper since the ANCF method has advantages in dealing with the significant deformation problems of the flexible structures. In addition, a chain mooring line was also simulated for comparison, and the results show that the polyester ropes reduce the self-weight of the mooring lines and provide sufficient mooring strength at the same time, and the nonlinear phenomenon of the polyester ropes is different from that of the chain mooring lines.

A supercavitating projectile is launched underwater with supersonic speed, and then, the speed decreases to transonic and subsonic conditions orderly because of the drag coming from surrounding water. The flow regime and hydrodynamic characteristics are significantly influenced by the flying speed, the influence laws in supersonic, transonic, and subsonic regions are totally different. These issues aren’t well studied. A numerical model consisting of VOF model, moving frame method and state equation of liquid is established to calculate the compressible supercavitation flow field, and validated by comparing with a published result. The influences of water compressibility and Mach number on supercavity shape and hydrodynamic characteristics are quantitatively summarized. The results show that the flying speed of supercavitating projectiles exerts significant influences on the flow regime, supercavity shape and hydrodynamic characteristics for the transonic and supersonic conditions. With the decrease of flying speed, the drag coefficient decreases gradually, and the dimensions of the supercavity near supercavitating projectiles significantly increases in the high-speed conditions. An underwater bow shock is numerically observed before the disk cavitator in supersonic condition. However, no obvious changes are found for the incompressible water cases with different speeds. For supersonic conditions, the supercavity near supercavitating projectiles of compressible water is smaller than that of incompressible water, the drag coefficient is larger, and the relative difference significantly increases with the flying speed. For the case of Ma 1.214, the relative difference of supercavity diameter at the tail section 3.98%, and the difference of the drag coefficient is 23.90%.

This paper investigated the resistance performance of a submersible surface ship (SSS) in different working cases and scales to analyze the hydrodynamic performance characteristics of an SSS at different speeds and diving depths for engineering applications. First, a hydrostatic resistance performance test of the SSS was carried out in a towing tank. Second, the scale effect of the hydrodynamic pressure coefficient and wave-making resistance was analyzed. The differences between the three-dimensional real-scale ship resistance prediction and numerical methods were explained. Finally, the advantages of genetic algorithm (GA) and neural network were combined to predict the resistance of SSS. Back propagation neural network (BPNN) and GA-BPNN were utilized to predict the SSS resistance. We also studied neural network parameter optimization, including connection weights and thresholds, using K-fold cross-validation. The results showed that when a SSS sails at low and medium speeds, the influence of various underwater cases on resistance is not obvious, while at high speeds, the resistance of water surface cases increases sharply with an increase in speed. After improving the weights and thresholds through K-fold cross-validation and GA, the prediction results of BPNN have high consistency with the actual values. The research results can provide a theoretical reference for the optimal design of the resistance of SSS in practical applications.

Following developments in artificial intelligence and big data technology, the level of intelligence in intelligent vessels has been improved. Intelligent vessels are being developed into unmanned surface vehicles (USVs), which have widely interested scholars in the shipping industry due to their safety, high efficiency, and energy-saving qualities. Considering the current development of USVs, the types of USVs and applications domestically and internationally are being investigated. USVs emerged with technological developments and their characteristics show some differences from traditional vessels, which brings some problems and advantages for their application. Certain maritime regulations are not applicable to USVs and must be changed. The key technologies in the current development of USVs are being investigated. While the level of intelligence is improving, the protection of cargo cannot be neglected. An innovative approach to the internal structure of USVs is proposed, where the inner hull can automatically recover its original state in case of outer hull tilting. Finally, we summarize the development status of USVs, which are an inevitable direction of development in the marine field.

The current design philosophy for submarine hulls, in the preliminary design stage, generally considers as governing limit states material yielding along with various buckling modes. It is common belief that, beyond the design pressure, material yielding of the shell plating should occur first, eventually followed by local buckling, while global buckling currently retains the highest safety factor. On the other hand, in the aeronautical field, in some cases structural components are designed in such a way that local instability may occur within the design loads, being the phenomena inside the material elastic range and not leading to a significant drop in term of stiffness. This paper is aimed at investigating the structural response beyond a set of selected limit states, using nonlinear FE method adopting different initial imperfection models, to provide the designers with new information useful for calibrating safety factors. It was found that both local and global buckling can be considered as ultimate limit states, with a significant sensitivity towards initial imperfection, while material yielding and tripping buckling of frames show a residual structural capacity. In conclusion, it was found that the occurrence of local buckling leads to similar sudden catastrophic consequences as global buckling, with the ultimate strength capacity highly affected by the initial imperfection shape and amplitude.

To control the vibration level of ships under construction, MSC Software’s Patran & Nastran modeling solutions can be used to establish a detailed finite element model of a new manned submersible support mother ship based on a line drawing, including the deck layout, bulkhead section, and stiffener distribution. After a comprehensive analysis of the ship simulation conditions, boundaries, and excitation forces of the main operating equipment, modal analysis and calculation of the ship vibration can be conducted. In this study, we calculated and analyzed the vibration response of key points in the stern area of the ship’s main deck and the submersible warehouse area under design loading working conditions. We then analyzed the vibration response of typical decks (including the compass deck, steering deck, captain’s deck, forecastle deck, and main deck) under the main excitation forces and moments (such as the full swing pod and generator sets). The analysis results showed that under DESIDEP working conditions, the vibration of each deck and key areas of the support mother ship could meet the vibration code requirements of the ship’s preliminary design (using the pod excitation and generator sets). Similarly, the vibration response of a scientific research ship under other loading conditions also met the requirements of the code and provided data support for a comprehensive understanding of the ship’s vibration and noise levels. Using actual vibration measurements, the accuracy of the vibration level simulations using finite element modeling was verified, the vibration of each area of the ship comfortably meeting the requirements of the China Classification Society.

In this paper, the mechatronic design and maneuverability analysis of a novel robotic shark are presented. To obtain good maneuverability, a barycenter regulating device is designed to assist the posture adjustment at low speeds. Based on the Newton-Euler approach, an analytical dynamic model is established with particular consideration of pectoral fins for three-dimensional motions. The hydrodynamic coefficients are computed using computational fluid dynamics (CFD) methods. Oscillation amplitudes and phases are determined by fitting an optimized fish body wave. The performance of the robotic shark is estimated by varying the oscillation frequency and offset angle. The results show that with oscillation frequency increasing, the swimming speed increases linearly. The robotic shark reaches the maximum swimming speed of 1.05 m/s with an oscillation frequency of 1.2 Hz. Furthermore, the turning radius decreases nonlinearly as the offset angle increased. The robotic shark reaches the minimum turning radius of 1.4 times the body length with 0.2 Hz frequency and 12° offset angle. In the vertical plane, as the pectoral fin angle increases, the diving velocity increases nonlinearly with increase rate slowing down.

In this study, the performance of a twin-screw propeller under the influence of the wake field of a fully appended ship was investigated using a coupled Reynolds-averaged Navier-Stokes (RANS)/boundary element method (BEM) code. The unsteady BEM is an efficient approach to predicting propeller performance. By applying the time-stepping method in the BEM solver, the trailing vortex sheet pattern of the propeller can be accurately captured at each time step. This is the main innovation of the coupled strategy. Furthermore, to ascertain the effect of the wake field of the ship with acceptable accuracy, a RANS solver was developed. A finite volume method was used to discretize the Navier-Stokes equations on fully unstructured grids. To simulate ship motions, the volume of the fluid method was applied to the RANS solver. The validation of each solver (BEM/RANS) was separately performed, and the results were compared with experimental data. Ultimately, the BEM and RANS solvers were coupled to estimate the performance of a twin-screw propeller, which was affected by the wake field of the fully appended hull. The proposed model was applied to a twin-screw oceanography research vessel. The results demonstrated that the presented model can estimate the thrust coefficient of a propeller with good accuracy as compared to an experimental self-propulsion test. The wake sheet pattern of the propeller in open water (uniform flow) was also compared with the propeller in a real wake field.

A high-efficiency propeller can enable a long mission duration for autonomous underwater vehicles (AUVs). In this study, a new method with OpenProp coupled with computational fluid dynamics was developed to design a propeller for an Explorer100 AUV. The towed system simulation of the AUV was used to measure the nominal wake, and a self-propulsion simulation was used to measure the effective wake at the disc plane just in front of a propeller. Two propellers referring to the nominal wake (propeller 1) and effective wake (propeller 2) were designed with OpenProp and appended with the AUV for self-propulsion simulations, respectively. Through the numerical simulation of the AUV self-propulsion tests, the cruising velocity of AUV was obtained. The flow characteristics of the self-propulsion in pressure and velocity contours were also analyzed. The propeller designed with an effective wake improved the thrust, velocity, and efficiency by approximately 11.3%, 6.7%, and 2.5%, respectively, as compared with those with a nominal wake. The cruising velocity of the final designed propeller for the Explorer100 AUV improved by 21.8%, as compared to that of the original propeller from the AUV free-running tests.

A corrosion defect is recognized as one of the most severe phenomena for high-pressure pipelines, especially those served for a long time. Finite-element method and empirical formulas are thereby used for the strength prediction of such pipes with corrosion. However, it is time-consuming for finite-element method and there is a limited application range by using empirical formulas. In order to improve the prediction of strength, this paper investigates the burst pressure of line pipelines with a single corrosion defect subjected to internal pressure based on data-driven methods. Three supervised ML (machine learning) algorithms, including the ANN (artificial neural network), the SVM (support vector machine) and the LR (linear regression), are deployed to train models based on experimental data. Data analysis is first conducted to determine proper pipe features for training. Hyperparameter tuning to control the learning process is then performed to fit the best strength models for corroded pipelines. Among all the proposed data-driven models, the ANN model with three neural layers has the highest training accuracy, but also presents the largest variance. The SVM model provides both high training accuracy and high validation accuracy. The LR model has the best performance in terms of generalization ability. These models can be served as surrogate models by transfer learning with new coming data in future research, facilitating a sustainable and intelligent decision-making of corroded pipelines.

In this paper, the influence of geometric parameters on the stress concentration factors due to three different types of axial loading on 81 TY tubular structures is studied. Our results reveal that, geometric parameters have a considerable impact on the variation of stress concentration factors on tubular TY-joints under axial loads. Thus, the highest stress concentration factor values are observed on the vertical brace than on the inclined one. The finite element results of the tubular structures were verified by parametric equations and experimental data. A parametric study was carried out by analyses using the non-linear regression method to obtain parametric equations. These equations are used to calculate stress concentration factors and to analyse the fatigue resistance of TY-joints due to axial loads.

The efficiency of a Mewis propeller duct by the analysis of ship operational data is examined. The analysis employs data collected with high frequency for a three-year period for two siter vessels, one of them fitted with a Mewis type duct. Our approach to the problem of identifying improvements in the operational performance of the ship equipped with the duct is two-fold. Firstly, we proceed with the calculation of appropriate Key Performance Indicators to monitor vessels performance in time for different operational periods and loading conditions. An extensive pre-processing stage is necessary to prepare a dataset free from datapoints that could impair the analysis, such as outliers, as well as the appropriate preparations for a meaningful KPI calculation. The second approach concerns the development of multiple linear regression problem for the prediction of main engine fuel oil consumption based on operational and weather parameters, such as ship’s speed, mean draft, trim, rudder angle and the wind speed. The aim is to quantify reductions due to the Mewis duct for several scenarios. Key results of the studies reveal a contribution of the Mewis duct mainly in laden condition, for lower speed range and in the long-term period after dry-docking.

An actuator is a machine or component installed on the top of an industrial valve for automatically moving and controlling the valve. The performance of a valve is largely dependent on its actuator. An actuator can be hydraulic, pneumatic, or electrical. This paper focuses on hydraulic actuators, which are common for large size and high-pressure class ball valves. Hydraulic actuators can be either single-acting (spring return) or double-acting. Single-acting actuators return to safe mode in case of failure. However, double-acting actuators have a fail-as-is function and cannot keep the valves open or closed in case of failure. This research used a combination of theoretical and experimental approaches. The paper discusses two case studies in offshore industry projects in which double-acting hydraulic actuators were selected instead of single-acting, and possible design impacts are discussed. A theoretical review is given in three papers about operating torque for ball valves, optimization of shutdown valve actuator weight, and design and analysis of hydraulic actuators. These three papers were selected for review to connect the valve required torque with actuator sizing and selection, finding practical approaches to optimize the actuator weight as well as develop a theoretical model to calculate the actuator thickness and dimensions for the 38" CL1500 ball valve in the Johan Sverdrup project. The proposed formulas and calculations used for sizing the 38" CL1500 ball valves were validated through a finite element analysis model.

In the shipbuilding industry, market competition is currently operating in an intense state. To be able to strive in the global market, the shipbuilders must able to produce ships that are more efficient and can be constructed in a relatively short amount of time. The piping layouts in the engine room requires a lot of time for the designer to design the best possible route and in a way are not the most efficient route. This paper presents an automatic piping support system in the ship’s engine room based on the Dijkstra’s algorithm of pathfinding method. The proposed method is focused on finding the shortest possible route with a consideration of the following things:cost of the bend pipe, cost of the crossing pipe, cost reduction by pipe support, restriction on piping, reduction of calculation time, and design procedure of piping route. Dijkstra’s shortest path algorithm is adopted to find the shortest path route between the start and goal point that is determined based on the layout of the ship’s engine room. Genetic algorithm is adopted to decide the sequence of the pipe execution. The details of the proposed method are explained in this paper. This paper also discusses the application of the proposed method on an actual ship and evaluates its effectiveness.

This paper presents an original probabilistic model of a hybrid underwater wireless sensor network (UWSN), which includes a network of stationary sensors placed on the seabed and a mobile gateway. The mobile gateway is a wave glider that collects data from the underwater network segment and retransmits it to the processing center. The authors consider the joint problem of optimal localization of stationary network nodes and the corresponding model for bypassing reference nodes by a wave glider. The optimality of the network is evaluated according to the criteria of energy efficiency and reliability. The influence of various physical and technical parameters of the network on its energy efficiency and on the lifespan of sensor nodes is analyzed. The analysis is carried out for networks of various scales, depending on the localization of stationary nodes and the model of bypassing the network with a wave glider. As a model example, the simulation of the functional characteristics of the network for a given size of the water area is carried out. It is shown that in the case of a medium-sized water area, the model of "bypassing the perimeter" by a wave glider is practically feasible, energy efficient and reliable for hourly data measurements. In the case of a large water area, the cluster bypass model becomes more efficient.

Cooperative jamming (CJ) is one of the important methods to solve security problems of underwater acoustic sensor networks (UASNs). In this paper, we propose a Cooperative Jamming Scheme based on Node Authentication for UASNs to improve the effect of CJ by selecting suitable jamming source for found illegal nodes. In the node authentication, all nodes will be identified by their trust value (TV). TV is calculated according to three types of evidence:channel-based trust evidence, behavior-based trust evidence and energy-based trust evidence. Besides, to deal with cases where legal nodes may be suspected, the historical TV and trust redemption will be considered when calculating TV. In cooperative jamming, according to the link quality, several nodes are selected to jam illegal nodes. Both simulation and field experiment show that the proposed scheme can accurately find the illegal nodes in the time-vary channel and improve the security of the network.

Fluidization mechanism of liquefiable cargo is similar to that of sand liquefaction. But the cargo is subjected to more complex external loads during sea transportation. Based on two different constitutive models, numerical predictions were conducted in this study. And the effects of ship motions including motion acceleration, frequency and relative density of cargo on fluidization was investigated. By comparing with available the experimental data, validation is carried out. Results show that the roll motion is the most important one related to cargo fluidization. When the motion acceleration increases, the possibility of cargo fluidization increases. The higher of the cargo density the lower of the possibility of cargo fluidization. The effect of frequency on cargo fluidization is not unique, and it exists a critical value. The fluidization behavior of cargo could be described both by UBCSAND and FINN models. And the comparisons were discussed and summed up.