Bubbles play crucial roles in various fields, including naval and ocean engineering, chemical engineering, and biochemical engineering. Numerous theoretical analyses, numerical simulations, and experimental studies have been conducted to reveal the mysteries of bubble motion and its mechanisms. These efforts have significantly advanced research in bubble dynamics, where theoretical study is an efficient method for bubble motion prediction. Since Lord Rayleigh introduced the theoretical model of single-bubble motion in incompressible fluid in 1917, theoretical studies have been pivotal in understanding bubble dynamics. This study provides a comprehensive review of the development and applicability of theoretical studies in bubble dynamics using typical theoretical bubble models across different periods as a focal point and an overview of bubble theory applications in underwater explosion, marine cavitation, and seismic exploration. This study aims to serve as a reference and catalyst for further advancements in theoretical analysis and practical applications of bubble theory across marine fields.

Researchers have achieved notable advancements over the years in exploring ship damage and stability resulting from underwater explosions (UNDEX). However, numerous challenges and open questions remain in this field. In this study, the research progress of UNDEX load is first reviewed, which covers the explosion load during the shock wave and bubble pulsation stages. Subsequently, the research progress of ship damage caused by UNDEX is reviewed from two aspects: contact explosion and noncontact explosion. Finally, the research progress of ship navigation stability caused by UNDEX is reviewed from three aspects: natural factors, ship’s internal factors, and explosion factors. Analysis reveals that most existing research has focused on the damage to displacement ships caused by UNDEX. Meanwhile, less attention has been paid to the damage and stability of non-displacement ships caused by UNDEX, which are worthy of discussion.

Understanding the behaviour of composite marine propellers during operating conditions is a need of the present era since they emerge as a potential replacement for conventional propeller materials such as metals or alloys. They offer several benefits, such as high specific strength, low corrosion, delayed cavitation, improved dynamic stability, reduced noise levels, and overall energy efficiency. In addition, composite materials undergo passive deformation, termed as “bend-twist effect”, under hydrodynamic loads due to their inherent flexibility and anisotropy. Although performance analysis methods were developed in the past for marine propellers, there is a significant lack of literature on composite propellers. This article discusses the recent advancements in experimental and numerical modelling, state-of-the-art computational technologies, and mutated mathematical models that aid in designing, analysing, and optimising composite marine propellers. In the initial sections, performance evaluation methods and challenges with the existing propeller materials are discussed. Thereafter, the benefits of composite propellers are critically reviewed. Numerical and experimental FSI coupling methods, cavitation performance, the effect of stacking sequence, and acoustic measurements are some critical areas discussed in detail. A two-way FSI-coupled simulation was conducted in a non-cavitating regime for four advanced ratios and compared with the literature results. Finally, the scope for future improvements and conclusions are mentioned.

This study investigates the hydrodynamic process of a cylinder ejected from the water’s surface through high-speed camera experiments. Using digital image processing methods, the images obtained through experiments are processed and analyzed. Although the dynamics of rising buoyant cylinders have been thoroughly investigated, the pop-up height of the cylinders has not been extensively explored. Statistical analysis of the kinematic and dynamic data of cylinders is conducted. Research has shown that after the cylinder rises, it pops out of the water’s surface. Within the experimental range, the pop-up height of the cylinder is related to the release depth. Furthermore, the pop-up height and release depth of the cylinder vary linearly under vertical release conditions. Under horizontal release conditions, the relationship between pop-up height and release depth shows irregular changes mainly because of the unstable shedding of the wake vortex.

Semisubmersible naval ships are versatile military crafts that combine the advantageous features of high-speed planing crafts and submarines. At-surface, these ships are designed to provide sufficient speed and maneuverability. Additionally, they can perform shallow dives, offering low visual and acoustic detectability. Therefore, the hydrodynamic design of a semisubmersible naval ship should address at-surface and submerged conditions. In this study, Numerical analyses were performed using a semisubmersible hull form to analyze its hydrodynamic features, including resistance, powering, and maneuvering. The simulations were conducted with Star CCM+ version 2302, a commercial package program that solves URANS equations using the SST k-ω turbulence model. The flow analysis was divided into two parts: at-surface simulations and shallowly submerged simulations. At-surface simulations cover the resistance, powering, trim, and sinkage at transition and planing regimes, with corresponding Froude numbers ranging from 0.42 to 1.69. Shallowly submerged simulations were performed at seven different submergence depths, ranging from D/L_OA = 0.063 5 to D/L_OA = 0.635, and at two different speeds with Froude numbers of 0.21 and 0.33. The behaviors of the hydrodynamic forces and pitching moment for different operation depths were comprehensively analyzed. The results of the numerical analyses provide valuable insights into the hydrodynamic performance of semisubmersible naval ships, highlighting the critical factors influencing their resistance, powering, and maneuvering capabilities in both at-surface and submerged conditions.

This study experimentally investigates the hydrodynamic characteristics, geometric configurations, fluttering motions of the codend, and the instantaneous flow fields inside and around the codend, with and without a liner, under varying catch sizes and inflow velocities. A proper orthogonal decomposition method is employed to extract phase-averaged mean properties of unsteady turbulent flows from flow measurement data obtained using an electromagnetic current velocity meter inside and around the codend. The results reveal that as catch size increases, the drag force, codend motion, Reynolds number, and codend volume increase while the drag coefficient decreases. Owing to the codend shape and pronounced motion, a complex fluid-structure interaction occurs, demonstrating a strong correlation between drag force and codend volume. The oscillation amplitudes of the hydrodynamic forces and codend motions increase with increasing catch size, and their oscillations mainly involve low-frequency activity. A significant reduction in the flow field occurs inside and around the unlined codend without a catch. The flow field is 5.81%, 14.39%, and 27.01% lower than the unlined codend with a catch, the codend with a liner but without a catch, and the codend with both a liner and a catch, respectively. Fourier analysis reveals that the codend motions and hydrodynamic forces are mainly characterized by low-frequency activity and are synchronized with the unsteady turbulent flow street. Furthermore, the proper orthogonal decomposition results reveal the development of unsteady turbulent flow inside and around the codend, driven by flow passage blockage caused by the presence of the liner, intense codend motions, and the catch. Understanding the hydrodynamic characteristics and flow instabilities inside and around the codend, particularly those associated with its fluttering motions, is crucial for optimizing trawl design and improving trawl selectivity.

This study employed a computational fluid dynamics model with an overset mesh technique to investigate the thrust and power of a floating offshore wind turbine (FOWT) under platform floating motion in the wind-rain field. The impact of rainfall on aerodynamic performance was initially examined using a stationary turbine model in both wind and wind-rain conditions. Subsequently, the study compared the FOWT’s performance under various single degree-of-freedom (DOF) motions, including surge, pitch, heave, and yaw. Finally, the combined effects of wind-rain fields and platform motions involving two DOFs on the FOWT’s aerodynamics were analyzed and compared. The results demonstrate that rain negatively impacts the aerodynamic performance of both the stationary turbines and FOWTs. Pitch-dominated motions, whether involving single or multiple DOFs, caused significant fluctuations in the FOWT aerodynamics. The combination of surge and pitch motions created the most challenging operational environment for the FOWT in all tested scenarios. These findings highlighted the need for stronger construction materials and greater ultimate bearing capacity for FOWTs, as well as the importance of optimizing designs to mitigate excessive pitch and surge.

This paper reports an experimental investigation on the flow of a water entry cavity formed with a water jet cavitator. To investigate the formation characteristics, systematic water entry experiments were conducted in a water tank under different water jet rates, entry velocities, entry angles, and nozzle diameters. The formation mechanism of the water entry cavity was also analyzed. Results indicate that before the model impacts the water surface for water entry with a water jet cavitator, a gas bubble is created, and its width increases as the model approaches the water surface. Moreover, the length of the water jet gradually reduces to zero due to the increase in the static pressure of the water. The formation of the cavity is directly correlated with the location of the stagnation point moving downstream from the far field of the water jet to the exit of the water jet nozzle with the increasing entry depth. The dominant parameter is the momentum ratio of the water jet and quiescent water.

The present study focuses on simulating supercavitating projectile tail-slaps with an analytical method. A model of 3σ-normal distribution tail-slaps for a supercavitating projectile is established. Meanwhile, the σ-κ equation is derived, which is included in this model. Next, the supercavitating projectile tail-slaps are simulated by combining the proposed model and the Logvinovich supercavity section expansion equation. The results show that the number of tail-slaps depends on where the initial several tail-slaps are under the same initial condition. If the distances between the initial several tail-slap positions are large, the number of tail-slaps will considerably decrease, and vice versa. Furthermore, a series of simulations is employed to analyze the influence of the initial angular velocity and the centroid. Analysis of variance is used to evaluate simulation results. The evaluation results suggest that the projectile’s initial angular velocity and centroid have a major impact on the tail-slap number. The larger the value of initial angular velocity, the higher the probability of an increase in tail-slap number. Additionally, the closer the centroid is to the projectile head, the less likely a tail-slap number increase. This study offers important insights into supercavitating projectile tail-slap research.

As intelligent sensors for marine applications rapidly advance, there is a growing emphasis on developing efficient, low-cost, and sustainable power sources to enhance their performance. With the continuous development of triboelectric nanogenerators (TENGs), known for their simple structure and versatile operational modes, these devices exhibit promising technological potential and have garnered extensive attention from a broad spectrum of researchers. The single-electrode mode of TENGs presents an effective means to harness eco-friendly energy sourced from flowing water. In this study, the factors affecting the output performance were investigated using different structures of single-electrode solidliquid TENGs placed in a circulating water tank. In addition, the solid-liquid contact process was numerically simulated using the COMSOL Multiphysics software, and significant potential energy changes were obtained for the solid-liquid contact and liquid flow processes. Finally, the energy generated is collected and converted to power several light-emitting diodes, demonstrating that solid-liquid TENGs can generate effective electrical power in a flowing water environment. Through several experimental investigations, we finally determined that the flow rate of the liquid, the thickness of the friction electrode material, and the contact area have the most significant effect on the output efficiency of TENGs in the form of flowing water, which provides a guide for improving their performance in the future.

The novel structural reliability methodology presented in this study is especially well suited for multidimensional structural dynamics that are physically measured or numerically simulated over a representative timelapse. The Gaidai multivariate reliability method is applied to an operational offshore Jacket platform that operates in Bohai Bay. This study demonstrates the feasibility of this method to accurately estimate collapse risks in dynamic systems under in situ environmental stressors. Modern reliability approaches do not cope easily with the high dimensionality of real engineering dynamic systems, as well as nonlinear intercorrelations between various structural components. The Jacket offshore platform is chosen as the case study for this reliability analysis because of the presence of various hotspot stresses that synchronously arise in its structural parts. The authors provide a straightforward, precise method for estimating overall risks of operational failure, damage, or hazard for nonlinear multidimensional dynamic systems. The latter tool is important for offshore engineers during the design stage.

To explore the relationship between dynamic characteristics and wake patterns, numerical simulations were conducted on three equal-diameter cylinders arranged in an equilateral triangle. The simulations varied reduced velocities and gap spacing to observe flow-induced vibrations (FIVs). The immersed boundary-lattice Boltzmann flux solver (IB-LBFS) was applied as a numerical solution method, allowing for straightforward application on a simple Cartesian mesh. The accuracy and rationality of this method have been verified through comparisons with previous numerical results, including studies on flow past three stationary circular cylinders arranged in a similar pattern and vortex-induced vibrations of a single cylinder across different reduced velocities. When examining the FIVs of three cylinders, numerical simulations were carried out across a range of reduced velocities (3.0 ≤ U_r ≤ 13.0) and gap spacing (L = 3D, 4D, and 5D). The observed vibration response included several regimes: the desynchronization regime, the initial branch, and the lower branch. Notably, the transverse amplitude peaked, and a double vortex street formed in the wake when the reduced velocity reached the lower branch. This arrangement of three cylinders proved advantageous for energy capture as the upstream cylinder’s vibration response mirrored that of an isolated cylinder, while the response of each downstream cylinder was significantly enhanced. Compared to a single cylinder, the vibration and flow characteristics of this system are markedly more complex. The maximum transverse amplitudes of the downstream cylinders are nearly identical and exceed those observed in a single-cylinder set-up. Depending on the gap spacing, the flow pattern varied: it was in-phase for L = 3D, antiphase for L = 4D, and exhibited vortex shedding for L = 5D. The wake configuration mainly featured double vortex streets for L = 3D and evolved into two pairs of double vortex streets for L = 5D. Consequently, it well illustrates the coupling mechanism that dynamics characteristics and wake vortex change with gap spacing and reduced velocities.

Currently, the cranes used at sea do not have enough flexibility, efficiency, and safety. Thus, this study proposed a floating multirobot coordinated towing system to meet the demands for offshore towing. Because of the flexibility of rope-driven robots, the one-way pulling characteristics of the rope, and the floating characteristics of the base, towing robots are easily overturned. First, the spatial configuration of the towing system was established according to the towing task, and the kinematic model of the towing system was established using the coordinate transformation. Then, the dynamic model of the towing system was established according to the rigid-body dynamics and hydrodynamic theory. Finally, the stability of the towing system was analyzed using the stability cone method. The simulation experiments provide a reference for the practical application of the floating multirobot coordinated towing system, which can improve the stability of towing systems by changing the configuration of the towing robot.