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.
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 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.
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 ⩽ Ur ⩽ 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.