Oceangoing ships may encounter rarely occurring waves like freak waves during their operational lifespan, which largely affects the safety of ships. In this paper a two-way CFD-FEM fluid-structure coupled method is adopted to simulate ship motions and wave load responses in three-dimensional (3D) freak waves. First, in-house code using MATLAB is developed to generate wave parameters which are used for generating short-crested waves and 3D freak waves in the CFD solver. The simulated freak waves are examined and the evolution of freak waves during propagation process is analyzed. Then, ship motions and wave loads considering hydroelastic response in 3D short-crested waves and in 3D freak waves are analyzed. The increase in motions and load responses when ship encountering freak waves is studied quantitatively. This study provides some insights into ship extreme dynamic responses in realistic seaways and in extreme freak waves.
{"title":"Numerical simulation of ship hydroelastic responses in 3D realistic ocean waves with occurrence of freak waves","authors":"Jialong Jiao , Zhenwei Chen , Yuanming Chen , Shuai Chen , Caixia Jiang","doi":"10.1016/j.jfluidstructs.2025.104448","DOIUrl":"10.1016/j.jfluidstructs.2025.104448","url":null,"abstract":"<div><div>Oceangoing ships may encounter rarely occurring waves like freak waves during their operational lifespan, which largely affects the safety of ships. In this paper a two-way CFD-FEM fluid-structure coupled method is adopted to simulate ship motions and wave load responses in three-dimensional (3D) freak waves. First, in-house code using MATLAB is developed to generate wave parameters which are used for generating short-crested waves and 3D freak waves in the CFD solver. The simulated freak waves are examined and the evolution of freak waves during propagation process is analyzed. Then, ship motions and wave loads considering hydroelastic response in 3D short-crested waves and in 3D freak waves are analyzed. The increase in motions and load responses when ship encountering freak waves is studied quantitatively. This study provides some insights into ship extreme dynamic responses in realistic seaways and in extreme freak waves.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"140 ","pages":"Article 104448"},"PeriodicalIF":3.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145475028","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 : 2026-01-01Epub Date: 2025-11-22DOI: 10.1016/j.jfluidstructs.2025.104461
John T. Antolik , Eli A. Silver , Jesse L. Belden , Daniel M. Harris
We present the CyberDiver, an untethered robotic impactor capable of actively modulating the fluid physics during high-speed water entry. First, we utilize the CyberDiver to extend our understanding of the water entry of passively flexible systems, designing a high-bandwidth controller that enables the CyberDiver to operate as a cyber–physical system that permits an arbitrary programmable structural coupling to be experimentally tested. Onboard sensors record the body acceleration during impact and reveal that the introduction of damping or a nonlinear force-versus-displacement structural law can significantly reduce impact loading as compared to a linear elastic case, with implications for damage mitigation in aerospace and naval applications. Next, by operating the CyberDiver in a displacement control mode, we demonstrate that the splash size can be dramatically altered depending on the parameters of an active maneuver, laying a groundwork for better understanding the techniques of human competitive divers.
{"title":"CyberDiver: An untethered robotic impactor for water-entry experiments","authors":"John T. Antolik , Eli A. Silver , Jesse L. Belden , Daniel M. Harris","doi":"10.1016/j.jfluidstructs.2025.104461","DOIUrl":"10.1016/j.jfluidstructs.2025.104461","url":null,"abstract":"<div><div>We present the CyberDiver, an untethered robotic impactor capable of actively modulating the fluid physics during high-speed water entry. First, we utilize the CyberDiver to extend our understanding of the water entry of passively flexible systems, designing a high-bandwidth controller that enables the CyberDiver to operate as a cyber–physical system that permits an arbitrary programmable structural coupling to be experimentally tested. Onboard sensors record the body acceleration during impact and reveal that the introduction of damping or a nonlinear force-versus-displacement structural law can significantly reduce impact loading as compared to a linear elastic case, with implications for damage mitigation in aerospace and naval applications. Next, by operating the CyberDiver in a displacement control mode, we demonstrate that the splash size can be dramatically altered depending on the parameters of an active maneuver, laying a groundwork for better understanding the techniques of human competitive divers.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"140 ","pages":"Article 104461"},"PeriodicalIF":3.5,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145623940","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 : 2025-12-01Epub Date: 2025-09-25DOI: 10.1016/j.jfluidstructs.2025.104422
Sina Kazemipour, Peng Zhang
Mid- and large-size road vehicles are responsible for high levels of green-house gas emissions, due to their poor aerodynamic designs. To alleviate this environmental and health risk, we propose a low-cost, noninvasive morphing vehicle design toward improved aerodynamic efficiency and reduced emissions. Using a generic pickup truck as the base geometry, morphing is accomplished by retrofitting a flexible structure over its cargo bed region, enabling active deformation and interaction with the airflow. The shape morphing process is optimized through a combined parametric genetic algorithm – computational fluid dynamics framework, enabling continuous morphing across a range of driving speeds. The optimal structural shapes lead to a reduction in the aerodynamic drag force between 8.7% and 10.1%. Analysis of the airflow physics reveals that the morphing structure compresses the size of the circulation bubble and reduces the strength of the counter-rotating flow structures in the wake, resulting in increased wake pressure and decreased drag force. Remarkably, the morphing structure not only reduces the drag on the base vehicle geometry but also elicits a negative drag force on itself. This non-invasive morphing vehicle design concept could transform the automotive industry by enhancing fuel economy and reducing emissions for existing vehicle models.
{"title":"A low-cost morphing vehicle design for enhanced aerodynamic performance","authors":"Sina Kazemipour, Peng Zhang","doi":"10.1016/j.jfluidstructs.2025.104422","DOIUrl":"10.1016/j.jfluidstructs.2025.104422","url":null,"abstract":"<div><div>Mid- and large-size road vehicles are responsible for high levels of green-house gas emissions, due to their poor aerodynamic designs. To alleviate this environmental and health risk, we propose a low-cost, noninvasive morphing vehicle design toward improved aerodynamic efficiency and reduced emissions. Using a generic pickup truck as the base geometry, morphing is accomplished by retrofitting a flexible structure over its cargo bed region, enabling active deformation and interaction with the airflow. The shape morphing process is optimized through a combined parametric genetic algorithm – computational fluid dynamics framework, enabling continuous morphing across a range of driving speeds. The optimal structural shapes lead to a reduction in the aerodynamic drag force between 8.7% and 10.1%. Analysis of the airflow physics reveals that the morphing structure compresses the size of the circulation bubble and reduces the strength of the counter-rotating flow structures in the wake, resulting in increased wake pressure and decreased drag force. Remarkably, the morphing structure not only reduces the drag on the base vehicle geometry but also elicits a negative drag force on itself. This non-invasive morphing vehicle design concept could transform the automotive industry by enhancing fuel economy and reducing emissions for existing vehicle models.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"139 ","pages":"Article 104422"},"PeriodicalIF":3.5,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145159583","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 : 2025-12-01Epub Date: 2025-10-22DOI: 10.1016/j.jfluidstructs.2025.104442
Arthur Haudeville , Xavier Amandolese , Boris Lossouarn , Christophe Giraud-Audine , Olivier Thomas
The present work investigates the ability of a reduced-order fluid–structure model to estimate the vortex-induced vibrations (VIV) of marine lifting surface under hydrodynamic flow, such as hydrofoils. A particular VIV area is scrutinized, for which a hydrodynamic excitation mechanism due to a Kármán-type vortex wake organization successively locks the first twisting and second bending mode of a cantilever truncated hydrofoil. Coupling two structural oscillators with a Van der Pol wake oscillator satisfactorily reproduces the amplitude response and the lock-in frequency. This work also investigates the ability of a piezo-elasto-hydrodynamic model to anticipate the vibration amplitude of the hydrofoil when mitigated thanks to a resonant piezoelectric shunt. Composed of an inductance in series with a resistance connected to a piezoelectric patch, the passive shunt was tuned to minimize the vibration amplitude in the frequency lock-in range. The proposed semi-empirical models are fitted to experimental results in order to reproduce the coupled system’s dynamic.
{"title":"Low-order coupled model for vortex-induced vibrations mitigation by resonant piezoelectric shunt","authors":"Arthur Haudeville , Xavier Amandolese , Boris Lossouarn , Christophe Giraud-Audine , Olivier Thomas","doi":"10.1016/j.jfluidstructs.2025.104442","DOIUrl":"10.1016/j.jfluidstructs.2025.104442","url":null,"abstract":"<div><div>The present work investigates the ability of a reduced-order fluid–structure model to estimate the vortex-induced vibrations (VIV) of marine lifting surface under hydrodynamic flow, such as hydrofoils. A particular VIV area is scrutinized, for which a hydrodynamic excitation mechanism due to a Kármán-type vortex wake organization successively locks the first twisting and second bending mode of a cantilever truncated hydrofoil. Coupling two structural oscillators with a Van der Pol wake oscillator satisfactorily reproduces the amplitude response and the lock-in frequency. This work also investigates the ability of a piezo-elasto-hydrodynamic model to anticipate the vibration amplitude of the hydrofoil when mitigated thanks to a resonant piezoelectric shunt. Composed of an inductance in series with a resistance connected to a piezoelectric patch, the passive shunt was tuned to minimize the vibration amplitude in the frequency lock-in range. The proposed semi-empirical models are fitted to experimental results in order to reproduce the coupled system’s dynamic.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"139 ","pages":"Article 104442"},"PeriodicalIF":3.5,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145363700","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 : 2025-12-01Epub Date: 2025-10-03DOI: 10.1016/j.jfluidstructs.2025.104431
Guangrui Zhang, Yanbin Wang, Deli Gao
Air injection and discharge pipes play an essential role in the deep-sea mining airlift process, and their influence on the flow field and riser vortex-induced vibration (VIV) is not fully investigated. In this study, the discrete vortex method is modified to incorporate the influence of multiple solid domains, and the flow field evolution in the presence of auxiliary pipes is simulated. Based on the assumption that the vortex structure is constant within a certain spanwise length, an analytical model is established by strip theory and a weakly coupled fluid-structure interaction approach to investigate riser VIV in the cross-flow direction. The results show that the auxiliary pipes will interfere with the vortex shedding of the main riser and inhibit the formation of a stable wake pattern, which leads to a reduction in both the amplitude and frequency of the lift force. The VIV exhibits a mixed behavior of standing and travelling waves, and multi-mode responses induced by temporal drift of the frequency can be observed. In addition, the auxiliary pipes suppress the VIV by disturbing vortex shedding and increasing the bending stiffness of the riser. Moreover, the effects of inflow angle, current velocity, and vessel navigational motion on the VIV response and power region distribution are investigated. Specifically, a 45° inflow angle provides optimal VIV suppression and leads to the narrowest power-in region, while vessel motion in either the upstream or downstream direction aggravates VIV and significantly alters the power region distribution.
{"title":"Numerical analysis of vortex-induced vibration of deep-sea mining riser with auxiliary pipes based on discrete vortex method","authors":"Guangrui Zhang, Yanbin Wang, Deli Gao","doi":"10.1016/j.jfluidstructs.2025.104431","DOIUrl":"10.1016/j.jfluidstructs.2025.104431","url":null,"abstract":"<div><div>Air injection and discharge pipes play an essential role in the deep-sea mining airlift process, and their influence on the flow field and riser vortex-induced vibration (VIV) is not fully investigated. In this study, the discrete vortex method is modified to incorporate the influence of multiple solid domains, and the flow field evolution in the presence of auxiliary pipes is simulated. Based on the assumption that the vortex structure is constant within a certain spanwise length, an analytical model is established by strip theory and a weakly coupled fluid-structure interaction approach to investigate riser VIV in the cross-flow direction. The results show that the auxiliary pipes will interfere with the vortex shedding of the main riser and inhibit the formation of a stable wake pattern, which leads to a reduction in both the amplitude and frequency of the lift force. The VIV exhibits a mixed behavior of standing and travelling waves, and multi-mode responses induced by temporal drift of the frequency can be observed. In addition, the auxiliary pipes suppress the VIV by disturbing vortex shedding and increasing the bending stiffness of the riser. Moreover, the effects of inflow angle, current velocity, and vessel navigational motion on the VIV response and power region distribution are investigated. Specifically, a 45° inflow angle provides optimal VIV suppression and leads to the narrowest power-in region, while vessel motion in either the upstream or downstream direction aggravates VIV and significantly alters the power region distribution.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"139 ","pages":"Article 104431"},"PeriodicalIF":3.5,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145221834","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 : 2025-12-01Epub Date: 2025-10-04DOI: 10.1016/j.jfluidstructs.2025.104435
David Quero
A frequency-domain flutter solver for rotary-wing aeroelasticity is presented. The method applies to linear time-periodic (LTP) aeroelastic systems, including helicopters in forward flight, propellers with yaw angle, and wind energy turbines. It assumes a frequency-domain representation of the aerodynamic model, using the aerodynamic harmonic transfer function (HTF), denoted here as the harmonic generalized aerodynamic force (GAF) matrix. This accounts for the effects of harmonics of the fundamental or forcing frequency. The harmonic GAF exhibits a nonlinear dependence on the Laplace variable, and after coupling with the structural model, the relevant subset of Floquet exponents is determined by solving a nonlinear eigenvalue problem.
This method extends the conventional flutter solvers used in fixed-wing aeroelasticity, which are based on a linear time-invariant (LTI) system. Specifically, it introduces harmonic extensions of the p-k and g flutter solvers, termed the h-p-k and h-g solvers, making them applicable to rotary-wing aeroelasticity. When applied to an LTI system, the method naturally reduces to the standard p-k and g flutter solvers used in fixed-wing aeroelasticity.
The proposed method is demonstrated on a two-degree-of-freedom rotor blade section in forward flight, incorporating an unsteady aerodynamic model based on potential flow theory. It accurately predicts the same advance ratio for flutter onset as the Floquet method while eliminating the need to construct the monodromy matrix. Furthermore, it enables stability analysis even when the aerodynamic model is not available in state-space form, allowing for the use of nonparametric aerodynamic representations.
{"title":"A frequency-domain flutter solver for rotary-wing aeroelasticity","authors":"David Quero","doi":"10.1016/j.jfluidstructs.2025.104435","DOIUrl":"10.1016/j.jfluidstructs.2025.104435","url":null,"abstract":"<div><div>A frequency-domain flutter solver for rotary-wing aeroelasticity is presented. The method applies to linear time-periodic (LTP) aeroelastic systems, including helicopters in forward flight, propellers with yaw angle, and wind energy turbines. It assumes a frequency-domain representation of the aerodynamic model, using the aerodynamic harmonic transfer function (HTF), denoted here as the harmonic generalized aerodynamic force (GAF) matrix. This accounts for the effects of harmonics of the fundamental or forcing frequency. The harmonic GAF exhibits a nonlinear dependence on the Laplace variable, and after coupling with the structural model, the relevant subset of Floquet exponents is determined by solving a nonlinear eigenvalue problem.</div><div>This method extends the conventional flutter solvers used in fixed-wing aeroelasticity, which are based on a linear time-invariant (LTI) system. Specifically, it introduces harmonic extensions of the <em>p-k</em> and <em>g</em> flutter solvers, termed the <em>h-p-k</em> and <em>h-g</em> solvers, making them applicable to rotary-wing aeroelasticity. When applied to an LTI system, the method naturally reduces to the standard <em>p-k</em> and <em>g</em> flutter solvers used in fixed-wing aeroelasticity.</div><div>The proposed method is demonstrated on a two-degree-of-freedom rotor blade section in forward flight, incorporating an unsteady aerodynamic model based on potential flow theory. It accurately predicts the same advance ratio for flutter onset as the Floquet method while eliminating the need to construct the monodromy matrix. Furthermore, it enables stability analysis even when the aerodynamic model is not available in state-space form, allowing for the use of nonparametric aerodynamic representations.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"139 ","pages":"Article 104435"},"PeriodicalIF":3.5,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145269133","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 : 2025-12-01Epub Date: 2025-09-18DOI: 10.1016/j.jfluidstructs.2025.104412
Daniele Vivaldi, Roxan Pulicani
Fluid–structure numerical simulations of an experimental campaign by Cioncolini et al. of a cantilever rod in water axial flow were performed. The experimental configuration aims at representing a nuclear fuel rod, in terms of hydraulic diameter. Water velocity profiles and structure vibrations were measured experimentally. Two of the experimental tests were simulated numerically, one at Re=1.5104 and one at Re=1.9104. Different CFD approaches were tested, using code_Saturne: a wall-resolved two-equation linear viscosity model (k--SST), two wall-modeled Reynolds stress models (SSG and LRR), a wall-resolved Reynolds stress model (EBRSM) and a wall-resolved hybrid URANS/LES model (DDES). The structure was simulated through a one-dimensional finite element Euler–Bernoulli beam model. A 2-way coupling was implemented between the two solvers, with an Arbitrary Lagrangian Eulerian approach. Unexpectedly, wall-modeled Reynolds-stress models were found to calculate higher amplitudes of vibration than the higher-resolution EBRSM and DDES. The frequency domain analysis allowed to identify high energy flow velocity and flow-induced force harmonics at relatively low frequency calculated by LRR and SSG, not present in the EBRSM and DDES results, which explain the numerical results in terms of vibration response. This specific behavior of LRR and SSG seems to be linked to the wall function boundary condition. LRR and SSG calculate a rms amplitude of vibration close to the experiments, whereas EBRSM and DDES underestimate them by a factor of 2.5. A hypothetical small permanent deformation (4% of the hydraulic diameter) of the rod was simulated and found to increase the calculated vibration amplitudes by a factor of 2. 1-way coupling was also tested to assess the influence of damping and added mass on the results.
{"title":"Coupled fluid–structure simulations of a cantilever rod in water turbulent axial flow with different CFD approaches","authors":"Daniele Vivaldi, Roxan Pulicani","doi":"10.1016/j.jfluidstructs.2025.104412","DOIUrl":"10.1016/j.jfluidstructs.2025.104412","url":null,"abstract":"<div><div>Fluid–structure numerical simulations of an experimental campaign by Cioncolini et al. of a cantilever rod in water axial flow were performed. The experimental configuration aims at representing a nuclear fuel rod, in terms of hydraulic diameter. Water velocity profiles and structure vibrations were measured experimentally. Two of the experimental tests were simulated numerically, one at Re=1.5<span><math><mi>⋅</mi></math></span>10<sup>4</sup> and one at Re=1.9<span><math><mi>⋅</mi></math></span>10<sup>4</sup>. Different CFD approaches were tested, using code_Saturne: a wall-resolved two-equation linear viscosity model (k-<span><math><mi>ω</mi></math></span>-SST), two wall-modeled Reynolds stress models (SSG and LRR), a wall-resolved Reynolds stress model (EBRSM) and a wall-resolved hybrid URANS/LES model (DDES). The structure was simulated through a one-dimensional finite element Euler–Bernoulli beam model. A 2-way coupling was implemented between the two solvers, with an Arbitrary Lagrangian Eulerian approach. Unexpectedly, wall-modeled Reynolds-stress models were found to calculate higher amplitudes of vibration than the higher-resolution EBRSM and DDES. The frequency domain analysis allowed to identify high energy flow velocity and flow-induced force harmonics at relatively low frequency calculated by LRR and SSG, not present in the EBRSM and DDES results, which explain the numerical results in terms of vibration response. This specific behavior of LRR and SSG seems to be linked to the wall function boundary condition. LRR and SSG calculate a rms amplitude of vibration close to the experiments, whereas EBRSM and DDES underestimate them by a factor of 2.5. A hypothetical small permanent deformation (4% of the hydraulic diameter) of the rod was simulated and found to increase the calculated vibration amplitudes by a factor of 2. 1-way coupling was also tested to assess the influence of damping and added mass on the results.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"139 ","pages":"Article 104412"},"PeriodicalIF":3.5,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145107825","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 : 2025-12-01Epub Date: 2025-10-03DOI: 10.1016/j.jfluidstructs.2025.104433
Patrick F. Musgrave , Charles M. Tenney
This study establishes the role of higher resonant frequencies on the swimming performance of flexible bio-inspired propulsors. Biological and bio-inspired swimmers typically swim at or near their first resonance to achieve high efficiency and thrust. These swimmers also have higher resonances that could yield the same performance benefits; however, the role of these higher resonances is not well understood. This study experimentally identifies the thrust, kinematics, and power performance of flexible propulsors across resonances and uncovers the fluid-structural mechanism that governs the performance. We experimentally test multiple propulsors that share a simplified design consisting of a constant cross-section beam excited by piezoelectric actuators in quiescent water and with stiffnesses in the range of biological swimmers. Our results demonstrate that higher resonances significantly improve the performance compared to the fundamental resonance yielding a increase in thrust to power ratio, up to increase in absolute thrust, while requiring of the displacement amplitude.
While the higher resonances yield better overall performance, we show that higher resonances are less effective at converting tail velocity into thrust since the thrust coefficient depends on the mode shape. We determine that higher resonances engage less fluid mass, and show that the effective aspect ratio (wavelength normalized by width) is a predictor of performance across resonances. These results indicate that higher resonances could be a viable swimming option to improve the thrust and efficiency of stiffer bodied swimmers while yielding smaller displacement amplitudes that improve operation near obstacles.
{"title":"Higher resonances improve the swimming performance of flexible bio-inspired propulsors","authors":"Patrick F. Musgrave , Charles M. Tenney","doi":"10.1016/j.jfluidstructs.2025.104433","DOIUrl":"10.1016/j.jfluidstructs.2025.104433","url":null,"abstract":"<div><div>This study establishes the role of higher resonant frequencies on the swimming performance of flexible bio-inspired propulsors. Biological and bio-inspired swimmers typically swim at or near their first resonance to achieve high efficiency and thrust. These swimmers also have higher resonances that could yield the same performance benefits; however, the role of these higher resonances is not well understood. This study experimentally identifies the thrust, kinematics, and power performance of flexible propulsors across resonances and uncovers the fluid-structural mechanism that governs the performance. We experimentally test multiple propulsors that share a simplified design consisting of a constant cross-section beam excited by piezoelectric actuators in quiescent water and with stiffnesses in the range of biological swimmers. Our results demonstrate that higher resonances significantly improve the performance compared to the fundamental resonance yielding a <span><math><mrow><mn>2</mn><mo>×</mo></mrow></math></span> increase in thrust to power ratio, up to <span><math><mrow><mn>11</mn><mo>×</mo></mrow></math></span> increase in absolute thrust, while requiring <span><math><mrow><mo><</mo><mn>25</mn><mtext>%</mtext></mrow></math></span> of the displacement amplitude.</div><div>While the higher resonances yield better overall performance, we show that higher resonances are less effective at converting tail velocity into thrust since the thrust coefficient depends on the mode shape. We determine that higher resonances engage less fluid mass, and show that the effective aspect ratio (wavelength normalized by width) is a predictor of performance across resonances. These results indicate that higher resonances could be a viable swimming option to improve the thrust and efficiency of stiffer bodied swimmers while yielding smaller displacement amplitudes that improve operation near obstacles.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"139 ","pages":"Article 104433"},"PeriodicalIF":3.5,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145221832","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 : 2025-12-01Epub Date: 2025-09-27DOI: 10.1016/j.jfluidstructs.2025.104429
Xuepu Yan , Shuai Sun , Mo Zhu , Tengfei Xu , Pengfei Liu , Zeqing Guo
An investigation into the transient fluid-structure interactions during the high-speed (600 m/s) shallow-angle (8°) water entry of cylindrical projectiles with varying densities (2.7-16.1 g/cm³) is presented. The fundamental mechanisms governing cavity dynamics and projectile stability are revealed using three-dimensional computational fluid dynamics (CFD) simulations, which are validated by synchronized high-speed imaging. The key findings demonstrate that asymmetric wetting of the cylinder’s head during the early stage of water entry induces a critical head-down moment that governs subsequent hydrodynamic behavior. Three distinct fluid dynamic mechanisms are identified: 1) Delayed upper cavity formation accompanied by asymmetric cavity expansion; 2) Splash convergence producing distinct upward and downward jets, with the latter inducing localized cavity collapse upon impacting the wall; and 3) Pressure redistribution at the head end caused by variations in angle of attack, which generates restoring moments through asymmetric flow patterns. Density-dependent kinematic analysis reveals that within the same range of horizontal displacement, low-density cylinders (ρ≤4.1 g/cm³) undergo multiple tail slaps, whereas high-density cylinders (ρ≥7.2 g/cm³) achieve rotational stabilization through head-end restoring moments prior to tail slap initiation. Quantitative analysis shows that increasing the density from 2.7 to 16.1 g/cm³ reduces the maximum angular deflection by 89.43 % and the accumulated trajectory curvature by 42.83 %. These findings establish material density as the primary control parameter for ricochet prevention during shallow-angle water entry.
{"title":"Study on the high-speed shallow-angle water entry of cylinders with varying densities","authors":"Xuepu Yan , Shuai Sun , Mo Zhu , Tengfei Xu , Pengfei Liu , Zeqing Guo","doi":"10.1016/j.jfluidstructs.2025.104429","DOIUrl":"10.1016/j.jfluidstructs.2025.104429","url":null,"abstract":"<div><div>An investigation into the transient fluid-structure interactions during the high-speed (600 m/s) shallow-angle (8°) water entry of cylindrical projectiles with varying densities (2.7-16.1 g/cm³) is presented. The fundamental mechanisms governing cavity dynamics and projectile stability are revealed using three-dimensional computational fluid dynamics (CFD) simulations, which are validated by synchronized high-speed imaging. The key findings demonstrate that asymmetric wetting of the cylinder’s head during the early stage of water entry induces a critical head-down moment that governs subsequent hydrodynamic behavior. Three distinct fluid dynamic mechanisms are identified: 1) Delayed upper cavity formation accompanied by asymmetric cavity expansion; 2) Splash convergence producing distinct upward and downward jets, with the latter inducing localized cavity collapse upon impacting the wall; and 3) Pressure redistribution at the head end caused by variations in angle of attack, which generates restoring moments through asymmetric flow patterns. Density-dependent kinematic analysis reveals that within the same range of horizontal displacement, low-density cylinders (<em>ρ</em>≤4.1 g/cm³) undergo multiple tail slaps, whereas high-density cylinders (<em>ρ</em>≥7.2 g/cm³) achieve rotational stabilization through head-end restoring moments prior to tail slap initiation. Quantitative analysis shows that increasing the density from 2.7 to 16.1 g/cm³ reduces the maximum angular deflection by 89.43 % and the accumulated trajectory curvature by 42.83 %. These findings establish material density as the primary control parameter for ricochet prevention during shallow-angle water entry.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"139 ","pages":"Article 104429"},"PeriodicalIF":3.5,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145221835","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 : 2025-12-01Epub Date: 2025-10-17DOI: 10.1016/j.jfluidstructs.2025.104437
Wenyu Chen , Con Doolan , Danielle Moreau
A finite-length circular cylinder mounted to a wall serves as a simplified model for bluff bodies encountering flow, with a wide range of relevant applications, including aircraft landing gear, automobile appendages, and wind turbine masts. In the present study, finite wall-mounted circular cylinders with different spanwise aspect ratios ( where is the length of the cylinder and is its diameter) of 3.2, 6.5, 12.9 and 22.6 are examined at a Reynolds number of based on the cylinder diameter. The incoming boundary layer thickness on the wall to which the cylinder is mounted is . Large Eddy Simulation (LES) is employed to simulate the turbulent flow, and the Ffowcs Williams–Hawkings equations are solved simultaneously to predict the far-field noise. The acoustic spectrum of the circular FWMCs is characterized by tonal peaks for aspect ratios = 3.2, 12.9, and 22.6 in which a primary tonal peak (P1) and lower frequency secondary peak (P2) are identified. The transition from dipole to quadrupole in the three-dimensional time-averaged vortical structures is also summarized. Notably, suppression of vortex shedding is observed for the cylinder with , while cellular vortex shedding is observed in longer cylinders. The shedding cells near the junction and free tip exhibit lower shedding frequencies compared to the mid-span cell. Wake structures in-phase to the acoustic pressure are examined, confirming both the tip and mid-span related vortex shedding noise of the circular FWMCs. Furthermore, the in-phase structures associated with the primary (P1) peak are characterized by vertical vortex tubes that are well-organized downstream and exhibit strong consistency with Kármán vortex tubes shedding from the mid-span. The coherent structures corresponding to the secondary (P2) peak are found to be concentrated to the free end and are inclined in the downstream direction.
固定在壁上的有限长圆柱体是钝体遇到气流的简化模型，在飞机起落架、汽车附件、风力涡轮机桅杆等领域有着广泛的应用。在本研究中，在雷诺数Re=12,000的条件下，基于圆柱体直径，研究了不同展向纵横比（AR=L/D，其中L为圆柱体长度，D为圆柱体直径）分别为3.2、6.5、12.9和22.6的有限壁挂圆柱体。圆柱体所处壁面的来面层厚度为δ/D=0.83。采用大涡模拟（Large Eddy Simulation， LES）方法模拟紊流，同时求解Ffowcs williams - hawkins方程来预测远场噪声。在宽高比为AR = 3.2、12.9和22.6时，圆形fwmc的声谱特征为一个主音峰（P1）和一个低频次峰（P2）。总结了三维时均涡结构中偶极子向四极子的转变过程。值得注意的是，在AR=6.5的圆柱体中观察到涡脱落的抑制，而在更长的圆柱体中观察到细胞涡脱落。与跨中单元相比，靠近结和自由尖端的脱落单元表现出较低的脱落频率。研究了与声压相一致的尾迹结构，证实了圆形fwmc的尖端和跨中相关的涡脱落噪声。此外，与初级峰（P1）相关的同相结构以垂直涡管为特征，这些垂直涡管在下游组织良好，与Kármán涡管从跨中脱落具有很强的一致性。次级（P2）峰对应的相干结构集中在自由端，并向下游倾斜。
{"title":"Flow-induced noise of circular finite wall-mounted cylinders","authors":"Wenyu Chen , Con Doolan , Danielle Moreau","doi":"10.1016/j.jfluidstructs.2025.104437","DOIUrl":"10.1016/j.jfluidstructs.2025.104437","url":null,"abstract":"<div><div>A finite-length circular cylinder mounted to a wall serves as a simplified model for bluff bodies encountering flow, with a wide range of relevant applications, including aircraft landing gear, automobile appendages, and wind turbine masts. In the present study, finite wall-mounted circular cylinders with different spanwise aspect ratios (<span><math><mrow><mi>A</mi><mi>R</mi><mo>=</mo><mi>L</mi><mo>/</mo><mi>D</mi></mrow></math></span> where <span><math><mi>L</mi></math></span> is the length of the cylinder and <span><math><mi>D</mi></math></span> is its diameter) of 3.2, 6.5, 12.9 and 22.6 are examined at a Reynolds number of <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>12</mn><mo>,</mo><mn>000</mn></mrow></math></span> based on the cylinder diameter. The incoming boundary layer thickness on the wall to which the cylinder is mounted is <span><math><mrow><mi>δ</mi><mo>/</mo><mi>D</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>83</mn></mrow></math></span>. Large Eddy Simulation (LES) is employed to simulate the turbulent flow, and the Ffowcs Williams–Hawkings equations are solved simultaneously to predict the far-field noise. The acoustic spectrum of the circular FWMCs is characterized by tonal peaks for aspect ratios <span><math><mrow><mi>A</mi><mi>R</mi></mrow></math></span> = 3.2, 12.9, and 22.6 in which a primary tonal peak (P1) and lower frequency secondary peak (P2) are identified. The transition from dipole to quadrupole in the three-dimensional time-averaged vortical structures is also summarized. Notably, suppression of vortex shedding is observed for the cylinder with <span><math><mrow><mi>A</mi><mi>R</mi><mo>=</mo><mn>6</mn><mo>.</mo><mn>5</mn></mrow></math></span>, while cellular vortex shedding is observed in longer cylinders. The shedding cells near the junction and free tip exhibit lower shedding frequencies compared to the mid-span cell. Wake structures in-phase to the acoustic pressure are examined, confirming both the tip and mid-span related vortex shedding noise of the circular FWMCs. Furthermore, the in-phase structures associated with the primary (P1) peak are characterized by vertical vortex tubes that are well-organized downstream and exhibit strong consistency with Kármán vortex tubes shedding from the mid-span. The coherent structures corresponding to the secondary (P2) peak are found to be concentrated to the free end and are inclined in the downstream direction.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"139 ","pages":"Article 104437"},"PeriodicalIF":3.5,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145321322","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}
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