Pub Date : 2026-04-30Epub Date: 2026-02-18DOI: 10.1016/j.oceaneng.2026.124609
Xu Zhang , Yu Cao , Hexiong Zhou , Baoheng Yao , Lian Lian , Zhihua Mao
This paper presents an adaptive dense sampling strategy for thermocline observation using an underwater glider (UG). The sampling strategy includes an efficient planning algorithm that dynamically adjusts the gliding angle based on a historical temperature gradient profile, enabling targeted dense sampling within regions of strong thermal stratification, which is tailored to the sawtooth gliding motion of UGs. To accurately execute the planned trajectories under boundary constraints and external disturbances, a fixed-time non-singular terminal sliding mode control scheme is employed, ensuring rapid and robust convergence. The proposed computationally efficient algorithm is readily deployable on the UG’s embedded system. Both numerical simulations and preliminary pool trials demonstrate the effectiveness of the proposed strategy. The results show that our method achieves enhanced spatial sampling density within the thermocline and outperforms conventional sliding mode control and finite-time sliding mode control in tracking accuracy. The main contribution of this work is the development of a practical and easily deployable planning and control framework that enables UGs to autonomously conduct efficient thermocline observations.
{"title":"Adaptive dense sampling planning and fixed-time trajectory tracking control for thermocline observation with an underwater glider","authors":"Xu Zhang , Yu Cao , Hexiong Zhou , Baoheng Yao , Lian Lian , Zhihua Mao","doi":"10.1016/j.oceaneng.2026.124609","DOIUrl":"10.1016/j.oceaneng.2026.124609","url":null,"abstract":"<div><div>This paper presents an adaptive dense sampling strategy for thermocline observation using an underwater glider (UG). The sampling strategy includes an efficient planning algorithm that dynamically adjusts the gliding angle based on a historical temperature gradient profile, enabling targeted dense sampling within regions of strong thermal stratification, which is tailored to the sawtooth gliding motion of UGs. To accurately execute the planned trajectories under boundary constraints and external disturbances, a fixed-time non-singular terminal sliding mode control scheme is employed, ensuring rapid and robust convergence. The proposed computationally efficient algorithm is readily deployable on the UG’s embedded system. Both numerical simulations and preliminary pool trials demonstrate the effectiveness of the proposed strategy. The results show that our method achieves enhanced spatial sampling density within the thermocline and outperforms conventional sliding mode control and finite-time sliding mode control in tracking accuracy. The main contribution of this work is the development of a practical and easily deployable planning and control framework that enables UGs to autonomously conduct efficient thermocline observations.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"353 ","pages":"Article 124609"},"PeriodicalIF":5.5,"publicationDate":"2026-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387094","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-30Epub Date: 2026-02-23DOI: 10.1016/j.oceaneng.2026.124795
Yuxin Wu, Hao Chen, Junquan Chen
To address the challenges of target dynamic drift and environmental factor coupling in maritime search and rescue (SAR) missions, this study proposes a path planning method for unmanned surface vehicles (USVs) based on a multimodal information deep Q-network (MDQN). An innovative target probability evolution model driven by ocean currents and sea winds is constructed, utilizing a dynamic diffusion matrix and probabilistic decay mechanism in the search process to characterize the spatiotemporal changes in target distribution. Additionally, a dual-branch architecture MDQN algorithm is designed, employing a convolutional neural network (CNN) to extract spatial features from nautical charts, and integrating multimodal information such as USV's position and energy consumption to optimize decision-making. A double Q-network (DDQN) mechanism is also introduced to enhance training stability. Simulation experiments show that when USV energy consumption is constrained, the MDQN-planned path achieves a probability of success (POS) superior to that of swarm intelligence algorithms such as genetic algorithms (GA) and ant colony optimization (ACO) in both obstacle-free and obstacle-laden environments, improving by nearly 10% compared to traditional algorithms. Especially in dispersed multi-target scenarios, this algorithm demonstrates stronger global exploration capabilities and significantly better training stability than traditional DDQN algorithms. This study provides a reinforcement learning (RL)-based multimodal fusion framework for path planning in maritime environments with dynamic blurred targets.
{"title":"A path planning method for USV in maritime SAR missions based on improved deep Q-network","authors":"Yuxin Wu, Hao Chen, Junquan Chen","doi":"10.1016/j.oceaneng.2026.124795","DOIUrl":"10.1016/j.oceaneng.2026.124795","url":null,"abstract":"<div><div>To address the challenges of target dynamic drift and environmental factor coupling in maritime search and rescue (SAR) missions, this study proposes a path planning method for unmanned surface vehicles (USVs) based on a multimodal information deep Q-network (MDQN). An innovative target probability evolution model driven by ocean currents and sea winds is constructed, utilizing a dynamic diffusion matrix and probabilistic decay mechanism in the search process to characterize the spatiotemporal changes in target distribution. Additionally, a dual-branch architecture MDQN algorithm is designed, employing a convolutional neural network (CNN) to extract spatial features from nautical charts, and integrating multimodal information such as USV's position and energy consumption to optimize decision-making. A double Q-network (DDQN) mechanism is also introduced to enhance training stability. Simulation experiments show that when USV energy consumption is constrained, the MDQN-planned path achieves a probability of success (<em>POS</em>) superior to that of swarm intelligence algorithms such as genetic algorithms (GA) and ant colony optimization (ACO) in both obstacle-free and obstacle-laden environments, improving by nearly 10% compared to traditional algorithms. Especially in dispersed multi-target scenarios, this algorithm demonstrates stronger global exploration capabilities and significantly better training stability than traditional DDQN algorithms. This study provides a reinforcement learning (RL)-based multimodal fusion framework for path planning in maritime environments with dynamic blurred targets.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"353 ","pages":"Article 124795"},"PeriodicalIF":5.5,"publicationDate":"2026-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387117","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-30Epub Date: 2026-02-20DOI: 10.1016/j.oceaneng.2026.124757
Xiaoxu Sun , Xiufeng Yue , Yan Zhao
This paper presents a consistent co-rotational method for the dynamic analysis of two-dimensional (2D) slender flexible structures in marine environments, effectively handling arbitrarily distributed loads and realizing fluid-structure interaction (FSI) analysis within the co-rotational framework. First, the beam element motion and deformation are described based on the co-rotational framework, and consistent tangent stiffness and mass matrices are derived via the variational method. Second, combining the principle of virtual work, the consistent load equivalence formulation for concentrated and distributed loads is derived using identical shape functions, and the fluid load model is established based on the Morison equation. Finally, the FSI equations of motion are established, and the nonlinear system is solved efficiently using the HHT method with a modified Newton-Raphson strategy. Numerical examples of 2D flexible beams in air and water analyze static and dynamic responses under different discretizations. Results compared with commercial software verify the method's correctness and effectiveness. Furthermore, dynamic analysis of a top-tensioned riser under uniform current indicates that the proposed method maintains high accuracy and computational efficiency even with fewer elements.
{"title":"A consistent co-rotational method for fluid-structure interaction dynamic analysis of 2D flexible beams","authors":"Xiaoxu Sun , Xiufeng Yue , Yan Zhao","doi":"10.1016/j.oceaneng.2026.124757","DOIUrl":"10.1016/j.oceaneng.2026.124757","url":null,"abstract":"<div><div>This paper presents a consistent co-rotational method for the dynamic analysis of two-dimensional (2D) slender flexible structures in marine environments, effectively handling arbitrarily distributed loads and realizing fluid-structure interaction (FSI) analysis within the co-rotational framework. First, the beam element motion and deformation are described based on the co-rotational framework, and consistent tangent stiffness and mass matrices are derived via the variational method. Second, combining the principle of virtual work, the consistent load equivalence formulation for concentrated and distributed loads is derived using identical shape functions, and the fluid load model is established based on the Morison equation. Finally, the FSI equations of motion are established, and the nonlinear system is solved efficiently using the HHT method with a modified Newton-Raphson strategy. Numerical examples of 2D flexible beams in air and water analyze static and dynamic responses under different discretizations. Results compared with commercial software verify the method's correctness and effectiveness. Furthermore, dynamic analysis of a top-tensioned riser under uniform current indicates that the proposed method maintains high accuracy and computational efficiency even with fewer elements.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"353 ","pages":"Article 124757"},"PeriodicalIF":5.5,"publicationDate":"2026-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147387264","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-30Epub Date: 2026-02-18DOI: 10.1016/j.oceaneng.2026.124665
Maolin Dai , Liang Cao , Guoqing Huang , Xuhong Zhou , Jiepeng Liu , Y. Frank Chen
The mooring cable serves a critical function in connecting floating platforms to the seabed in offshore floating wind turbines. Its dynamic response under complex ocean current conditions significantly influences overall system performance, yet remains challenging to analyze effectively. This paper proposes an efficient dynamic model that incorporates hydrodynamic effects within a finite difference framework. The governing equations are first simplified into a first-order partial differential equation using the perturbation method, then discretized through the Keller-box scheme. To address the sensitivity to initial conditions and enhance computational efficiency, the Bisection method is employed for parameter determination. Numerical simulations demonstrate that the proposed approach achieves substantial improvements in computational efficiency while maintaining accuracy under wave and current loading. Systematic parametric analysis further reveals that cable stiffness and node discretization density markedly affect dynamic response, whereas other parameters exhibit comparatively minor influence. These findings provide valuable insights for optimizing mooring system design in floating offshore wind turbine applications.
{"title":"Dynamic response analysis of mooring cables for floating offshore wind turbines under ocean currents using a perturbation-based finite difference method","authors":"Maolin Dai , Liang Cao , Guoqing Huang , Xuhong Zhou , Jiepeng Liu , Y. Frank Chen","doi":"10.1016/j.oceaneng.2026.124665","DOIUrl":"10.1016/j.oceaneng.2026.124665","url":null,"abstract":"<div><div>The mooring cable serves a critical function in connecting floating platforms to the seabed in offshore floating wind turbines. Its dynamic response under complex ocean current conditions significantly influences overall system performance, yet remains challenging to analyze effectively. This paper proposes an efficient dynamic model that incorporates hydrodynamic effects within a finite difference framework. The governing equations are first simplified into a first-order partial differential equation using the perturbation method, then discretized through the Keller-box scheme. To address the sensitivity to initial conditions and enhance computational efficiency, the Bisection method is employed for parameter determination. Numerical simulations demonstrate that the proposed approach achieves substantial improvements in computational efficiency while maintaining accuracy under wave and current loading. Systematic parametric analysis further reveals that cable stiffness and node discretization density markedly affect dynamic response, whereas other parameters exhibit comparatively minor influence. These findings provide valuable insights for optimizing mooring system design in floating offshore wind turbine applications.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"353 ","pages":"Article 124665"},"PeriodicalIF":5.5,"publicationDate":"2026-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386707","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-30Epub Date: 2026-02-21DOI: 10.1016/j.oceaneng.2026.124727
Sang-Do Lee , Gi-Seon Jeong
This study presents a systematic, full-scale offshore experimental validation of an unmanned aerial vehicle (UAV)-derived L1 guidance law for a very large container ship (VLCS). The innovation of the study lies in demonstrating the law's unique dual capability: enabling precise trajectory tracking while simultaneously executing adaptive aggressive maneuvers in the presence of environmental disturbances. A combination that has not been previously verified. This study provides a complete low-cost methodology for maritime autonomous surface ship model design, integration, and sea trials, with superior circular-path performance analogous to the “tight maneuvers” of the Anderson turn for search and rescue activities. The experiments offer a novel solution for the ship chase maneuvers, resembling the short-range tactical maneuvers of missiles, in a cluttered sea environment. The energy efficiency is high in the curved path compared with the UAV case and existing ships. The method is also beneficial for a high-speed ship attempting to arrive at a specific point with a narrowing spiral path within a confined sea. The combination of Pixhawk® 4, PX4 firmware, and QGroundControl, which most UAVs possess, was applied to marine vessels. The experimental model was a VLCS at 1/320 scale of the existing 20,000 TEU COSCO Shipping Gemini. The test site was the coastal sea of Yeosu, South Korea, where the winds, waves, and tidal currents vary. The experiments quantified the speed-dependent effects on tracking accuracy, overshoot, and coursekeeping under dynamic ocean conditions. This study is based on a test organized on the March 16, 2025.
{"title":"Maritime autonomous surface ship for experimental trajectory tracking in the ocean","authors":"Sang-Do Lee , Gi-Seon Jeong","doi":"10.1016/j.oceaneng.2026.124727","DOIUrl":"10.1016/j.oceaneng.2026.124727","url":null,"abstract":"<div><div>This study presents a systematic, full-scale offshore experimental validation of an unmanned aerial vehicle (UAV)-derived L1 guidance law for a very large container ship (VLCS). The innovation of the study lies in demonstrating the law's unique dual capability: enabling precise trajectory tracking while simultaneously executing adaptive aggressive maneuvers in the presence of environmental disturbances. A combination that has not been previously verified. This study provides a complete low-cost methodology for maritime autonomous surface ship model design, integration, and sea trials, with superior circular-path performance analogous to the “tight maneuvers” of the Anderson turn for search and rescue activities. The experiments offer a novel solution for the ship chase maneuvers, resembling the short-range tactical maneuvers of missiles, in a cluttered sea environment. The energy efficiency is high in the curved path compared with the UAV case and existing ships. The method is also beneficial for a high-speed ship attempting to arrive at a specific point with a narrowing spiral path within a confined sea. The combination of Pixhawk® 4, PX4 firmware, and QGroundControl, which most UAVs possess, was applied to marine vessels. The experimental model was a VLCS at 1/320 scale of the existing 20,000 TEU COSCO Shipping <em>Gemini</em>. The test site was the coastal sea of Yeosu, South Korea, where the winds, waves, and tidal currents vary. The experiments quantified the speed-dependent effects on tracking accuracy, overshoot, and coursekeeping under dynamic ocean conditions. This study is based on a test organized on the March 16, 2025.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"353 ","pages":"Article 124727"},"PeriodicalIF":5.5,"publicationDate":"2026-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147386764","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-15Epub Date: 2026-02-14DOI: 10.1016/j.oceaneng.2026.124674
Ming Zhao , Qin Zhang , Bing Ren , Heath Palmer , Adnan Munir , Vatsal Dhamelia , Helen Wu
Focusing wave energy on an oscillatory wave column (OWC) is an effective way to enhance its energy harvesting efficiency, which is quantified by the capture width ratio (CWR). A properly designed rectangular OWC can achieve a maximum CWR greater than 100% because of its inherent ability of wave focusing. For an infinite row of OWC devices under perpendicularly incident waves, the hydrodynamic efficiency of each OWC device is affected by two factors: wave focusing and possible transverse sloshing. Due to symmetry, this configuration is equivalent to one OWC device within a wave flume. This study uses numerical simulations to investigate the impact of wave focusing and transverse sloshing on the performance of an OWC device in a wave flume. The peak CWR is found to decrease with a decrease in the flume width. It reduces from 1.402 to 0.946 as the flume-width-to-OWC-width ratio decreases from 5 to 1.05. Through wave ray visualization, this paper found that the fundamental mechanism of transverse sloshing that causes minimum values of CWR is the multiple reflection of the waves between the flume side wall and the centre line of the OWC.
{"title":"Impact of wave focusing and transverse sloshing on the wave energy harvesting of an oscillating water column (OWC) in a wave flume","authors":"Ming Zhao , Qin Zhang , Bing Ren , Heath Palmer , Adnan Munir , Vatsal Dhamelia , Helen Wu","doi":"10.1016/j.oceaneng.2026.124674","DOIUrl":"10.1016/j.oceaneng.2026.124674","url":null,"abstract":"<div><div>Focusing wave energy on an oscillatory wave column (OWC) is an effective way to enhance its energy harvesting efficiency, which is quantified by the capture width ratio (CWR). A properly designed rectangular OWC can achieve a maximum CWR greater than 100% because of its inherent ability of wave focusing. For an infinite row of OWC devices under perpendicularly incident waves, the hydrodynamic efficiency of each OWC device is affected by two factors: wave focusing and possible transverse sloshing. Due to symmetry, this configuration is equivalent to one OWC device within a wave flume. This study uses numerical simulations to investigate the impact of wave focusing and transverse sloshing on the performance of an OWC device in a wave flume. The peak CWR is found to decrease with a decrease in the flume width. It reduces from 1.402 to 0.946 as the flume-width-to-OWC-width ratio decreases from 5 to 1.05. Through wave ray visualization, this paper found that the fundamental mechanism of transverse sloshing that causes minimum values of CWR is the multiple reflection of the waves between the flume side wall and the centre line of the OWC.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"352 ","pages":"Article 124674"},"PeriodicalIF":5.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146172177","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-15Epub Date: 2026-02-12DOI: 10.1016/j.oceaneng.2026.124462
Sang-seok Han , Ho-won Lee , Saishuai Dai , Momchil Terziev
Traditional ship resistance models often assume uniform hull surface roughness, potentially misrepresenting the heterogeneous fouling patterns observed in real-world operations. To address this limitation, we investigate the hydrodynamic impact of spatially non-uniform roughness on a KRISO Container Ship (KCS) hull using Computational Fluid Dynamics (CFD) simulations.
Seven hull surface conditions were investigated, including a smooth baseline and six types of roughness distributions: uniform, linear gradient, non-linear gradient, random, direct-shear, and inverse-shear. All cases were designed to have the same arithmetic mean hull surface roughness, allowing isolation of the effects of spatial roughness distribution. Among the tested configurations, the linear gradient distribution exhibited the most favourable resistance characteristics, whereas the shear-based and random distributions showed relatively minor differences from the uniform case.
Spatial roughness patterns significantly influenced boundary layer growth and wake development. Uniform, random, and shear-based distributions induced thicker boundary layers and delayed wake recovery, whereas the linear gradient case resulted in weaker momentum loss and faster wake recovery.
These findings indicate that even under identical arithmetic mean roughness conditions, the spatial distribution of hull surface roughness can significantly affect resistance characteristics. Explicit modelling of roughness patterns is therefore essential for accurate performance prediction and motivates further experimental validation and integration with propeller-hull interaction and free surface effects.
{"title":"Beyond uniform roughness: Ship resistance with spatially non-uniform hull surface conditions","authors":"Sang-seok Han , Ho-won Lee , Saishuai Dai , Momchil Terziev","doi":"10.1016/j.oceaneng.2026.124462","DOIUrl":"10.1016/j.oceaneng.2026.124462","url":null,"abstract":"<div><div>Traditional ship resistance models often assume uniform hull surface roughness, potentially misrepresenting the heterogeneous fouling patterns observed in real-world operations. To address this limitation, we investigate the hydrodynamic impact of spatially non-uniform roughness on a KRISO Container Ship (KCS) hull using Computational Fluid Dynamics (CFD) simulations.</div><div>Seven hull surface conditions were investigated, including a smooth baseline and six types of roughness distributions: uniform, linear gradient, non-linear gradient, random, direct-shear, and inverse-shear. All cases were designed to have the same arithmetic mean hull surface roughness, allowing isolation of the effects of spatial roughness distribution. Among the tested configurations, the linear gradient distribution exhibited the most favourable resistance characteristics, whereas the shear-based and random distributions showed relatively minor differences from the uniform case.</div><div>Spatial roughness patterns significantly influenced boundary layer growth and wake development. Uniform, random, and shear-based distributions induced thicker boundary layers and delayed wake recovery, whereas the linear gradient case resulted in weaker momentum loss and faster wake recovery.</div><div>These findings indicate that even under identical arithmetic mean roughness conditions, the spatial distribution of hull surface roughness can significantly affect resistance characteristics. Explicit modelling of roughness patterns is therefore essential for accurate performance prediction and motivates further experimental validation and integration with propeller-hull interaction and free surface effects.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"352 ","pages":"Article 124462"},"PeriodicalIF":5.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146172273","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-15Epub Date: 2026-02-11DOI: 10.1016/j.oceaneng.2026.124486
Chuanzhen Bai, Peng Liu, Yuhua Lyu, Siqi Wang
The caudal fin is a major propulsive organ in most fish, and its flexible oscillatory motion offers high efficiency, good maneuverability, and low noise. In current studies on caudal-fin propulsion performance, flexible deformation is often prescribed through active deformation patterns or obtained from fluid–structure interaction simulations assuming a single uniform stiffness, which makes it difficult to capture the true passive deformation of real caudal fins with non-uniform stiffness. In this study, the caudal fin is simplified as a rectangular flexible plate. Its motion is decomposed into macroscopic periodic oscillation and passive deformation induced by fluid loading, and this process is simulated using a two-way fluid–structure interaction algorithm. The results show that plates with medium stiffness produce the highest mean thrust, whereas plates with lower stiffness achieve higher propulsion efficiency. A segmented non-uniform stiffness distribution provides more balanced hydrodynamic performance, achieving high thrust while maintaining excellent efficiency. This study clarifies how overall stiffness and spatial stiffness distribution influence thrust generation and propulsion efficiency. By appropriately adjusting global stiffness and its distribution, bio-inspired robotic fish can meet performance requirements in confined, high-maneuverability tasks and long-distance, high-efficiency cruising.
{"title":"Effect of variable stiffness characteristics on the propulsion performance of biomimetic caudal fin flexible plates","authors":"Chuanzhen Bai, Peng Liu, Yuhua Lyu, Siqi Wang","doi":"10.1016/j.oceaneng.2026.124486","DOIUrl":"10.1016/j.oceaneng.2026.124486","url":null,"abstract":"<div><div>The caudal fin is a major propulsive organ in most fish, and its flexible oscillatory motion offers high efficiency, good maneuverability, and low noise. In current studies on caudal-fin propulsion performance, flexible deformation is often prescribed through active deformation patterns or obtained from fluid–structure interaction simulations assuming a single uniform stiffness, which makes it difficult to capture the true passive deformation of real caudal fins with non-uniform stiffness. In this study, the caudal fin is simplified as a rectangular flexible plate. Its motion is decomposed into macroscopic periodic oscillation and passive deformation induced by fluid loading, and this process is simulated using a two-way fluid–structure interaction algorithm. The results show that plates with medium stiffness produce the highest mean thrust, whereas plates with lower stiffness achieve higher propulsion efficiency. A segmented non-uniform stiffness distribution provides more balanced hydrodynamic performance, achieving high thrust while maintaining excellent efficiency. This study clarifies how overall stiffness and spatial stiffness distribution influence thrust generation and propulsion efficiency. By appropriately adjusting global stiffness and its distribution, bio-inspired robotic fish can meet performance requirements in confined, high-maneuverability tasks and long-distance, high-efficiency cruising.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"352 ","pages":"Article 124486"},"PeriodicalIF":5.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146154092","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-15Epub Date: 2026-02-11DOI: 10.1016/j.oceaneng.2026.124559
Ningge Fan , Gong Chen , Shunhua Chen , Yingying Lin , Di Wang
During the water entry stage, a free-fall lifeboat experiences strong impact and complex two-phase flow, which exposes occupants to injury risk. Existing assessments often rely on combined acceleration response (CAR), a global evaluation standard, for quick screening. However, occupant head injuries during lifeboat impact with the water surface can be fatal, while CAR lacks the precision needed for head-specific assessment. To address this limitation, a partitioned coupling framework for accurate occupant head injury evaluation subjected to water entry impact of a free-fall lifeboat is developed. The fluid and lifeboat motion are solved utilizing a fluid-rigid body interaction manner, in which the fluid is discretized with the finite volume method (FVM). The occupant response is then computed with the dynamic explicit finite element method (FEM) with the aid of a one-way coupling strategy, which improves computational efficiency while maintaining high accuracy. A standardized data interface links the two solvers and transfers displacement and orientation histories from the matched-node region. Occupant head injury is evaluated with the head injury criterion (HIC) using an occupant-seat-restraint finite element model that includes a Hybrid III 50th percentile dummy, a shell seat, and a four-point safety belt. The accuracy and effectiveness of the developed framework are well demonstrated, including a comparison with the 35 mph sled test data. Finally, a parametric study is conducted to examine the influence of vertical velocity, horizontal velocity, and pitch angle on the dynamic response and head injury of an occupant subjected to water entry impact, where the results are compared with those computed via CAR. The proposed framework provides reliable head acceleration histories efficiently, enabling occupant head injury assessment over a wide range of water-entry conditions.
{"title":"A partitioned coupling framework for occupant head injury assessment under water entry impact of a free-fall lifeboat","authors":"Ningge Fan , Gong Chen , Shunhua Chen , Yingying Lin , Di Wang","doi":"10.1016/j.oceaneng.2026.124559","DOIUrl":"10.1016/j.oceaneng.2026.124559","url":null,"abstract":"<div><div>During the water entry stage, a free-fall lifeboat experiences strong impact and complex two-phase flow, which exposes occupants to injury risk. Existing assessments often rely on combined acceleration response (CAR), a global evaluation standard, for quick screening. However, occupant head injuries during lifeboat impact with the water surface can be fatal, while CAR lacks the precision needed for head-specific assessment. To address this limitation, a partitioned coupling framework for accurate occupant head injury evaluation subjected to water entry impact of a free-fall lifeboat is developed. The fluid and lifeboat motion are solved utilizing a fluid-rigid body interaction manner, in which the fluid is discretized with the finite volume method (FVM). The occupant response is then computed with the dynamic explicit finite element method (FEM) with the aid of a one-way coupling strategy, which improves computational efficiency while maintaining high accuracy. A standardized data interface links the two solvers and transfers displacement and orientation histories from the matched-node region. Occupant head injury is evaluated with the head injury criterion (HIC) using an occupant-seat-restraint finite element model that includes a Hybrid III 50th percentile dummy, a shell seat, and a four-point safety belt. The accuracy and effectiveness of the developed framework are well demonstrated, including a comparison with the 35 mph sled test data. Finally, a parametric study is conducted to examine the influence of vertical velocity, horizontal velocity, and pitch angle on the dynamic response and head injury of an occupant subjected to water entry impact, where the results are compared with those computed via CAR. The proposed framework provides reliable head acceleration histories efficiently, enabling occupant head injury assessment over a wide range of water-entry conditions.</div></div>","PeriodicalId":19403,"journal":{"name":"Ocean Engineering","volume":"352 ","pages":"Article 124559"},"PeriodicalIF":5.5,"publicationDate":"2026-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146154121","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-04-15Epub Date: 2026-02-12DOI: 10.1016/j.oceaneng.2026.124566
Jingyuan Zhang , Hailong Li , Zhifan Zhang , Jie Yan , Longkan Wang , Guiyong Zhang
The landing of the deep-sea floor drill rig is a crucial step in its underwater deployment prior to operation. However, traditional Kelvin models fail to accurately describe the rheological behaviors of sediments during the landing impact process. To address this limitation, this paper proposes an improved contact force model that innovatively incorporates the Zener model—capable of characterizing rheological phenomena such as relaxation and creep effects of sediments. The validity of the proposed model is verified through comparison with experimental data, and the maximum fitting error is reduced by 80.45% compared with the traditional Kelvin model. A dynamic model of the deep-sea floor drill rig under rheological contact forces is established using MATLAB. The dynamic interaction (including loading, unloading, and rebound) between the drill rig and the seabed is characterized by defining the motion cycle and three force-bearing phases. This enables the prediction of the drill rig's dynamic parameters under rheological contact forces and resolves the dynamic calculation challenge associated with its landing process. Finally, the effects of landing velocity and drill rig mass on the dynamic parameters and the duration proportion of the three phases are investigated. In addition, the influence of rheological sediment parameters on the extreme dynamic values of the drill rig is analyzed, and it is found that sediment stiffness exerts the most significant effect on these extreme values. Then, Two-factor analysis of variance (ANOVA) is employed to evaluate the drill rig's dynamic behavior under the combined influence of landing velocity and mass, and the safe landing parameter range is determined. This study provides a theoretical reference for the structural design and safety validation of deep-sea floor drill rigs.
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