Pub Date : 2025-02-12DOI: 10.1016/j.jfluidstructs.2025.104274
Gustavo R.S. Assi
An experimental investigation performed at moderate Reynolds numbers was set to study how a pair of tandem cylinders can be excited into flow-induced vibrations by different interference mechanisms as a function of longitudinal spacings varying from 2 to 10 diameters. Results showed that the downstream cylinder could develop vortex-induced vibration (VIV) caused by its own vortex shedding, wake-induced vibration (WIV) caused by a developed wake formed in the gap, and gap-flow-switching. A combination of these mechanisms appeared for cases under close proximity. For a specific spacing of 3 diameters, the vibration of the downstream cylinder was able to synchronize the vortex shedding from the upstream, fixed body. We call this mechanism “retro lock-in” since the vortex-formation process of a bluff body was governed by the dynamics of another body located further downstream.
{"title":"Retro lock-in in the wake-induced vibration of a pair of tandem cylinders in close proximity","authors":"Gustavo R.S. Assi","doi":"10.1016/j.jfluidstructs.2025.104274","DOIUrl":"10.1016/j.jfluidstructs.2025.104274","url":null,"abstract":"<div><div>An experimental investigation performed at moderate Reynolds numbers was set to study how a pair of tandem cylinders can be excited into flow-induced vibrations by different interference mechanisms as a function of longitudinal spacings varying from 2 to 10 diameters. Results showed that the downstream cylinder could develop vortex-induced vibration (VIV) caused by its own vortex shedding, wake-induced vibration (WIV) caused by a developed wake formed in the gap, and gap-flow-switching. A combination of these mechanisms appeared for cases under close proximity. For a specific spacing of 3 diameters, the vibration of the downstream cylinder was able to synchronize the vortex shedding from the upstream, fixed body. We call this mechanism “retro lock-in” since the vortex-formation process of a bluff body was governed by the dynamics of another body located further downstream.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104274"},"PeriodicalIF":3.4,"publicationDate":"2025-02-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143388302","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 : 2025-02-07DOI: 10.1016/j.jfluidstructs.2025.104276
Xuehan Gao , Shun He , Yingsong Gu
Mesh deformation is an important element of CFD/CSD coupled time marching simulation. A mode shape-based Radial Basis Functions interpolation (M-RBF) approach is proposed to improve the efficiency of mesh deformation in the time marching simulation. Inspired by the modal expansion theorem in vibration theory, a set of interpolation nodes is pre-selected according to the mode shapes, rather than the physical displacements at each individual time step. The data reduction scheme of the forward-backward greedy algorithm is developed to select an optimum set of interpolation nodes. The AGARD 445.6 wing, a benchmark model for transonic flutter prediction, and the Goland+ wing with a tip store, which presents complexities in both aerodynamic configuration and mode shapes, are employed to validate the accuracy, efficiency, and capability of the M-RBF approach. The results show that the optimum set of interpolation nodes can achieve the desired interpolation accuracy while having little effect on the mesh quality at all time steps. The traditional RBF mesh deformation (T-RBF) and the RBF mesh deformation method via forward greedy algorithm (G-RBF) method spent majority of CPU time on the linear system solution (approximately 99% and 77.6%, respectively) and the selection of interpolation nodes (about 87.7% and 91.9%, respectively) in the case of AGARD 445.6 and Goland+ wing. However, by eliminating the need for repeated node selections, our M-RBF approach can improve the efficiency of mesh deformation by 2 to 3 orders of magnitude compared to the T-RBF method and 1 to 2 orders of magnitude compared to the G-RBF approach. The comparison of selected interpolation nodes by the M-RBF approach to the structural grid and CFD mesh indicates that the importance of nodes on the deforming boundary may be related to their distances from the structural grid.
{"title":"An efficient mode shape-based RBF mesh deformation approach via forward-backward greedy algorithm in CFD/CSD coupled simulation","authors":"Xuehan Gao , Shun He , Yingsong Gu","doi":"10.1016/j.jfluidstructs.2025.104276","DOIUrl":"10.1016/j.jfluidstructs.2025.104276","url":null,"abstract":"<div><div>Mesh deformation is an important element of CFD/CSD coupled time marching simulation. A mode shape-based Radial Basis Functions interpolation (M-RBF) approach is proposed to improve the efficiency of mesh deformation in the time marching simulation. Inspired by the modal expansion theorem in vibration theory, a set of interpolation nodes is pre-selected according to the mode shapes, rather than the physical displacements at each individual time step. The data reduction scheme of the forward-backward greedy algorithm is developed to select an optimum set of interpolation nodes. The AGARD 445.6 wing, a benchmark model for transonic flutter prediction, and the Goland+ wing with a tip store, which presents complexities in both aerodynamic configuration and mode shapes, are employed to validate the accuracy, efficiency, and capability of the M-RBF approach. The results show that the optimum set of interpolation nodes can achieve the desired interpolation accuracy while having little effect on the mesh quality at all time steps. The traditional RBF mesh deformation (T-RBF) and the RBF mesh deformation method via forward greedy algorithm (G-RBF) method spent majority of CPU time on the linear system solution (approximately 99% and 77.6%, respectively) and the selection of interpolation nodes (about 87.7% and 91.9%, respectively) in the case of AGARD 445.6 and Goland+ wing. However, by eliminating the need for repeated node selections, our M-RBF approach can improve the efficiency of mesh deformation by 2 to 3 orders of magnitude compared to the T-RBF method and 1 to 2 orders of magnitude compared to the G-RBF approach. The comparison of selected interpolation nodes by the M-RBF approach to the structural grid and CFD mesh indicates that the importance of nodes on the deforming boundary may be related to their distances from the structural grid.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104276"},"PeriodicalIF":3.4,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143345777","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 : 2025-02-07DOI: 10.1016/j.jfluidstructs.2025.104271
Matthew J. Kronheimer, Jordan D. Thayer, Jack J. McNamara, Datta V. Gaitonde
The fluid-structural coupling between an impinging Mach 4 shock boundary layer interaction (SBLI) and a flexible panel is investigated using wall-resolved implicit large-eddy simulation (ILES). Since the prediction of fluctuating wall pressure remains a challenge in aeroelastic configurations with large flow separation regions, an exposition of the coupling processes associated with the difference in the wall pressure fields between the coupled and uncoupled interaction is sought. The distinction between the time-mean pressure, induced coherent fluctuations, and inherent pressure fluctuations is formalized using a triple decomposition. Further, the role of the time-mean aeroelastic condition is considered to delineate predominantly static and dynamic coupling mechanisms between the fluid and structure. This is achieved by computing the fluid solution over the time-mean panel deformation of the coupled interaction. The impinging shock induces a large, highly unsteady separation region, the mean and fluctuating quantities of which are augmented by the imposed aeroelastic state. The use of the time-mean aeroelastic condition as a static structural deformation in a fluid-only simulation is found to capture the mean wall pressure of the coupled condition and some, but not all, of the increased flow unsteadiness. A local piston theory model is then implemented over a portion of the panel to assess the degree of flow unsteadiness associated with classical quasi-steady fluid-structural coupling between the supersonic ensemble-mean flow and the structural dynamics. It is found that, after the flow reattachment point, the coherent, dynamically induced pressure can be linearly superimposed with the statically coupled pressure field to predict the coupled wall pressure fluctuations to a reasonable degree.
{"title":"Assessment of aeroelastic coupling between a shock boundary layer interaction and a flexible panel","authors":"Matthew J. Kronheimer, Jordan D. Thayer, Jack J. McNamara, Datta V. Gaitonde","doi":"10.1016/j.jfluidstructs.2025.104271","DOIUrl":"10.1016/j.jfluidstructs.2025.104271","url":null,"abstract":"<div><div>The fluid-structural coupling between an impinging Mach 4 shock boundary layer interaction (SBLI) and a flexible panel is investigated using wall-resolved implicit large-eddy simulation (ILES). Since the prediction of fluctuating wall pressure remains a challenge in aeroelastic configurations with large flow separation regions, an exposition of the coupling processes associated with the difference in the wall pressure fields between the coupled and uncoupled interaction is sought. The distinction between the time-mean pressure, induced coherent fluctuations, and inherent pressure fluctuations is formalized using a triple decomposition. Further, the role of the time-mean aeroelastic condition is considered to delineate predominantly static and dynamic coupling mechanisms between the fluid and structure. This is achieved by computing the fluid solution over the time-mean panel deformation of the coupled interaction. The impinging shock induces a large, highly unsteady separation region, the mean and fluctuating quantities of which are augmented by the imposed aeroelastic state. The use of the time-mean aeroelastic condition as a static structural deformation in a fluid-only simulation is found to capture the mean wall pressure of the coupled condition and some, but not all, of the increased flow unsteadiness. A local piston theory model is then implemented over a portion of the panel to assess the degree of flow unsteadiness associated with classical quasi-steady fluid-structural coupling between the supersonic ensemble-mean flow and the structural dynamics. It is found that, after the flow reattachment point, the coherent, dynamically induced pressure can be linearly superimposed with the statically coupled pressure field to predict the coupled wall pressure fluctuations to a reasonable degree.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104271"},"PeriodicalIF":3.4,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143345775","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 : 2025-02-07DOI: 10.1016/j.jfluidstructs.2025.104275
Xu Dong , Lin Zhao , Xu Chen , Shikui Huang , Mao Chen
The investigation was physically and numerically conducted aiming at wind load distribution patterns and structural effects of a super large reinforced concrete cooling tower (SLRCCT) subjected to tornado-like vortices, and the influence of swirl ratios and the central distances between the SLRCCT and the tornado vortex core (TVC) were studied. The tornado-induced loads on the SLRCCT were firstly obtained based on rigid pressure measurement tests. Subsequently, tornado-induced structural displacement and internal force responses were analysed. It is revealed that the swirl ratios and the central distance between the SLRCCT and TVC significantly determine the tornado-induced load distributions and structural performances of the SLRCCT. Finally, an equivalent static wind load mode suitable for tornado resistance design of the SLRCCTs was proposed. Specifically, an empirical polynomial was suggested to fit the critical net wind pressure coefficient envelope. Wind vibration factor based on the evaluation criterion of time-variant dynamic reinforcement ratios was proposed to consider the fluctuating effects of the tornado, and the maximum tangential speed could be used to estimate the intensity influence of the tornado acting on the SLRCCT. This paper aims to contribute to a better understanding of the wind-related effects and the wind-resistant design of the SLRCCTs exposed to disaster-causing non-synoptic winds, particularly tornadoes.
{"title":"Tornado-induced load distribution patterns and structural effects of a super large cooling tower","authors":"Xu Dong , Lin Zhao , Xu Chen , Shikui Huang , Mao Chen","doi":"10.1016/j.jfluidstructs.2025.104275","DOIUrl":"10.1016/j.jfluidstructs.2025.104275","url":null,"abstract":"<div><div>The investigation was physically and numerically conducted aiming at wind load distribution patterns and structural effects of a super large reinforced concrete cooling tower (SLRCCT) subjected to tornado-like vortices, and the influence of swirl ratios and the central distances between the SLRCCT and the tornado vortex core (TVC) were studied. The tornado-induced loads on the SLRCCT were firstly obtained based on rigid pressure measurement tests. Subsequently, tornado-induced structural displacement and internal force responses were analysed. It is revealed that the swirl ratios and the central distance between the SLRCCT and TVC significantly determine the tornado-induced load distributions and structural performances of the SLRCCT. Finally, an equivalent static wind load mode suitable for tornado resistance design of the SLRCCTs was proposed. Specifically, an empirical polynomial was suggested to fit the critical net wind pressure coefficient envelope. Wind vibration factor based on the evaluation criterion of time-variant dynamic reinforcement ratios was proposed to consider the fluctuating effects of the tornado, and the maximum tangential speed could be used to estimate the intensity influence of the tornado acting on the SLRCCT. This paper aims to contribute to a better understanding of the wind-related effects and the wind-resistant design of the SLRCCTs exposed to disaster-causing non-synoptic winds, particularly tornadoes.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104275"},"PeriodicalIF":3.4,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143345776","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 : 2025-02-04DOI: 10.1016/j.jfluidstructs.2025.104272
Pooria Akbarzadeh , Michael Krieger , Dominik Hofer , Maria Thumfart , Philipp Gittler
This study provides further investigation on parallel water entry of pairings of hydrophobic-hydrophilic spheres. In a prior publication by the current authors (Akbarzadeh et al., 2023), a distinct phenomenon termed “second pinch-off” was observed for certain scenarios of parallel water entry of equally-sized hydrophobic-hydrophilic spheres. This experimental study examines this event more comprehensively. Experiments with differently-sized spheres are also conducted and analyzed. In the equally-sized cases, two spheres with a diameter of , positioned in a lateral distance of 1.5 times the diameter, are released simultaneously from heights ranging from 25 to 55cm. This corresponds to impact velocities of . In these configurations, the vortex shedding behind the hydrophilic sphere significantly influences the air cavity produced by the hydrophobic sphere. A high-speed photography system, coupled with an image processing technique, is employed to analyze the event dynamics. Additionally, a Particle Image Velocimetry system is utilized to capture the flow field, extracting both velocity and vorticity fields. The analysis demonstrates that a vortex ring forms behind the hydrophilic sphere and causes some waviness in the cavity interface. This vortex ring is shed and migrates towards the cavity wall causing an indentation which grows over time and finally completely severs the air cavity (second pinch-off). Furthermore, the results highlight that the second pinch-off time, in non-dimensional form, correlates linearly with the impact Weber number. The findings for the case of differently-sized spheres ( and in diameter), reveal that a second pinch-off event can also be observed in pairings where the smaller sphere is hydrophilic.
{"title":"Parallel water entry of hydrophobic-hydrophilic sphere pairings: particle image velocimetry and High-Speed camera analysis","authors":"Pooria Akbarzadeh , Michael Krieger , Dominik Hofer , Maria Thumfart , Philipp Gittler","doi":"10.1016/j.jfluidstructs.2025.104272","DOIUrl":"10.1016/j.jfluidstructs.2025.104272","url":null,"abstract":"<div><div>This study provides further investigation on parallel water entry of pairings of hydrophobic-hydrophilic spheres. In a prior publication by the current authors (Akbarzadeh et al., 2023), a distinct phenomenon termed “second pinch-off” was observed for certain scenarios of parallel water entry of equally-sized hydrophobic-hydrophilic spheres. This experimental study examines this event more comprehensively. Experiments with differently-sized spheres are also conducted and analyzed. In the equally-sized cases, two spheres with a diameter of <span><math><mrow><mn>20</mn><mtext>mm</mtext></mrow></math></span>, positioned in a lateral distance of 1.5 times the diameter, are released simultaneously from heights ranging from 25 to 55cm. This corresponds to impact velocities of <span><math><mrow><mn>2.21</mn><mo>∼</mo><mn>3.328</mn><mspace></mspace><mi>m</mi><msup><mrow><mi>s</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math></span>. In these configurations, the vortex shedding behind the hydrophilic sphere significantly influences the air cavity produced by the hydrophobic sphere. A high-speed photography system, coupled with an image processing technique, is employed to analyze the event dynamics. Additionally, a Particle Image Velocimetry system is utilized to capture the flow field, extracting both velocity and vorticity fields. The analysis demonstrates that a vortex ring forms behind the hydrophilic sphere and causes some waviness in the cavity interface. This vortex ring is shed and migrates towards the cavity wall causing an indentation which grows over time and finally completely severs the air cavity (second pinch-off). Furthermore, the results highlight that the second pinch-off time, in non-dimensional form, correlates linearly with the impact Weber number. The findings for the case of differently-sized spheres (<span><math><mrow><mn>12</mn><mtext>mm</mtext></mrow></math></span> and <span><math><mrow><mn>20</mn><mtext>mm</mtext></mrow></math></span> in diameter), reveal that a second pinch-off event can also be observed in pairings where the smaller sphere is hydrophilic.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104272"},"PeriodicalIF":3.4,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143141273","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-02-03DOI: 10.1016/j.jfluidstructs.2024.104259
J. McNaughton , F. Zilic de Arcos , C.R. Vogel , R.H.J. Willden
This paper investigates the dynamic loading of two side-by-side 1.2 m diameter tidal stream turbines tested experimentally in currents with regular waves. By towing the turbines through a tank against head waves we explore the influence of tip-speed ratio, wave amplitude and wave frequency, on the mean and unsteady rotor and blade loads. Turbine mean power and thrust coefficients in waves agree well with the steady flow coefficients recorded without waves. The dynamic power and thrust coefficients describe paths forming hysteresis loops around mean values when presented against tip-speed ratio defined based on instantaneous rotor-averaged flow speed. Single frequency harmonic fits provide reasonable fits to rotor loads enabling the assessment of loading phase with respect to incident waves. Rotor fluctuating loads increase with wave amplitude and tip-speed ratio, but decrease with wave frequency, with rotor torque showing greater sensitivity to wave conditions than thrust. Analysis of blade root bending moments as a function of wave phase and blade azimuth reveals that flapwise and edgewise load maxima and minima occur in advance of the crests and troughs of the approaching waves, but that the azimuthal locations at which blades experience maxima and minima are functions of wave frequency. Contrary to expectations blade loading is found to be maximum when blades are approximately horizontal which we attribute to spanwise correlation of wave orbital kinematics along blades. As wave frequency is increased, blade load maxima and minima occur closer to top dead centre due to increased vertical decay of wave orbitals. Peak flapwise and edgewise blade loads are found to occur on blade upstrokes and downstrokes respectively which we attribute to the contribution of the vertical component of wave orbitals and rotor-rotor interference. Differences in blade loads of the side-by-side turbines are attributed to hydrodynamic interactions due to the close quarter-diameter spacing between rotors.
{"title":"Dynamic loading of two side-by-side tidal stream turbines in regular waves","authors":"J. McNaughton , F. Zilic de Arcos , C.R. Vogel , R.H.J. Willden","doi":"10.1016/j.jfluidstructs.2024.104259","DOIUrl":"10.1016/j.jfluidstructs.2024.104259","url":null,"abstract":"<div><div>This paper investigates the dynamic loading of two side-by-side 1.2<!--> <!-->m diameter tidal stream turbines tested experimentally in currents with regular waves. By towing the turbines through a tank against head waves we explore the influence of tip-speed ratio, wave amplitude and wave frequency, on the mean and unsteady rotor and blade loads. Turbine mean power and thrust coefficients in waves agree well with the steady flow coefficients recorded without waves. The dynamic power and thrust coefficients describe paths forming hysteresis loops around mean values when presented against tip-speed ratio defined based on instantaneous rotor-averaged flow speed. Single frequency harmonic fits provide reasonable fits to rotor loads enabling the assessment of loading phase with respect to incident waves. Rotor fluctuating loads increase with wave amplitude and tip-speed ratio, but decrease with wave frequency, with rotor torque showing greater sensitivity to wave conditions than thrust. Analysis of blade root bending moments as a function of wave phase and blade azimuth reveals that flapwise and edgewise load maxima and minima occur in advance of the crests and troughs of the approaching waves, but that the azimuthal locations at which blades experience maxima and minima are functions of wave frequency. Contrary to expectations blade loading is found to be maximum when blades are approximately horizontal which we attribute to spanwise correlation of wave orbital kinematics along blades. As wave frequency is increased, blade load maxima and minima occur closer to top dead centre due to increased vertical decay of wave orbitals. Peak flapwise and edgewise blade loads are found to occur on blade upstrokes and downstrokes respectively which we attribute to the contribution of the vertical component of wave orbitals and rotor-rotor interference. Differences in blade loads of the side-by-side turbines are attributed to hydrodynamic interactions due to the close quarter-diameter spacing between rotors.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104259"},"PeriodicalIF":3.4,"publicationDate":"2025-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143097243","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-29DOI: 10.1016/j.jfluidstructs.2025.104268
Yanru Wu , Chenyang Ma , Pengyong Miao , Xiaotong Han , Yan Liu
Long-span truss roof structures are significantly susceptible to wind loads due to their inherent properties of being lightweight, small stiffness, and exhibiting high flexibility. The objective of this study is to evaluate the wind-induced response of a long-span truss roof structure under both closed and different open working states. This will be achieved through the utilization of pressure measurement wind-tunnel tests, finite element modelling, and dynamic response analysis. The present study conducts a statistical analysis on the influence of opening rate and opening position on wind load characteristics and wind response. The Welch method and Frequency method are employed to investigate the spectral characteristics of fluctuating wind pressure and the spatial correlation evolution of wind pressure in the low-frequency range. The findings indicate that the introduction of ventilation openings leads to a notable reduction in mean wind load. The presence of these openings, however, leads to an increase in localized wind pressure fluctuations due to the generated prominent turbulence. Secondly, the friction generated during the opening process primarily dissipates low-frequency large-scale vortex energy, thereby leading to a higher frequency distribution of fluctuating wind pressure spectrum. The time-averaged wind response, fluctuating wind response, dynamic response spectrum characteristics, and probability density distribution characteristics of the roof structure are statistically analyzed based on this premise. The results indicate that the variation in wind-induced response of the roof structure aligns with the fluctuation in wind load as a function of opening rate. When the frequency is lower than the dominant frequency, opening ventilation mitigates wind-induced vibration response of the structure; conversely, opening ventilation will amplify wind-induced vibration response of the structure. The windward area of the long-span truss roof structure experiences buffeting. The structural aerodynamic instability occurs in both the rooftop and wake region due to the presence of non-Gaussian, non-self-excited aerodynamic forces and modal vibrations.
{"title":"Influence of opening rate and opening position on wind load and aerodynamic stability of long-span truss roof structure","authors":"Yanru Wu , Chenyang Ma , Pengyong Miao , Xiaotong Han , Yan Liu","doi":"10.1016/j.jfluidstructs.2025.104268","DOIUrl":"10.1016/j.jfluidstructs.2025.104268","url":null,"abstract":"<div><div>Long-span truss roof structures are significantly susceptible to wind loads due to their inherent properties of being lightweight, small stiffness, and exhibiting high flexibility. The objective of this study is to evaluate the wind-induced response of a long-span truss roof structure under both closed and different open working states. This will be achieved through the utilization of pressure measurement wind-tunnel tests, finite element modelling, and dynamic response analysis. The present study conducts a statistical analysis on the influence of opening rate and opening position on wind load characteristics and wind response. The Welch method and Frequency method are employed to investigate the spectral characteristics of fluctuating wind pressure and the spatial correlation evolution of wind pressure in the low-frequency range. The findings indicate that the introduction of ventilation openings leads to a notable reduction in mean wind load. The presence of these openings, however, leads to an increase in localized wind pressure fluctuations due to the generated prominent turbulence. Secondly, the friction generated during the opening process primarily dissipates low-frequency large-scale vortex energy, thereby leading to a higher frequency distribution of fluctuating wind pressure spectrum. The time-averaged wind response, fluctuating wind response, dynamic response spectrum characteristics, and probability density distribution characteristics of the roof structure are statistically analyzed based on this premise. The results indicate that the variation in wind-induced response of the roof structure aligns with the fluctuation in wind load as a function of opening rate. When the frequency is lower than the dominant frequency, opening ventilation mitigates wind-induced vibration response of the structure; conversely, opening ventilation will amplify wind-induced vibration response of the structure. The windward area of the long-span truss roof structure experiences buffeting. The structural aerodynamic instability occurs in both the rooftop and wake region due to the presence of non-Gaussian, non-self-excited aerodynamic forces and modal vibrations.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104268"},"PeriodicalIF":3.4,"publicationDate":"2025-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143141300","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}
The present work contributes to the ever growing literature on the modelling of flow-induced vibrations in pipes conveying fluid. A three-dimensional nonlinear mathematical model is obtained for a pipe conveying fluid subjected to an external torsional moment. Bending, axial and torsional dynamics are included in the model and nonlinearities up to the cubic order are retained in the equations of motion. The dynamics of the pipe is formulated around the axial and torsional static solutions. The effects of the external torsional moment on the stability of the pipe are characterized as functions of the magnitude and location of the moment. It is shown that there is a critical magnitude, which depends on the location, above which a static instability occurs. Regardless of the magnitude of the torsional moment, it always reduces the critical flow velocity for flutter. While the stability of pipes conveying lighter fluids is shown to be more sensitive to torsional moments applied at the free end, applications at the middle point are more critical for pipes conveying heavier fluids. Depending on the system parameters, divergence and flutter may either coexist, or the system is stabilized over a range of flow velocities before it loses stability again, at higher flow velocities, by flutter. By numerically integrating the nonlinear equations of motion in the time domain, it is also shown that the presence of torsional moments induce three-dimensional motions, even when two-dimensional initial conditions are given.
{"title":"A model for the axial-bending-torsional dynamics of pipes conveying fluid","authors":"Vitor Schwenck Franco Maciel , Guilherme Vernizzi , Mojtaba Kheiri , Guilherme Rosa Franzini","doi":"10.1016/j.jfluidstructs.2024.104260","DOIUrl":"10.1016/j.jfluidstructs.2024.104260","url":null,"abstract":"<div><div>The present work contributes to the ever growing literature on the modelling of flow-induced vibrations in pipes conveying fluid. A three-dimensional nonlinear mathematical model is obtained for a pipe conveying fluid subjected to an external torsional moment. Bending, axial and torsional dynamics are included in the model and nonlinearities up to the cubic order are retained in the equations of motion. The dynamics of the pipe is formulated around the axial and torsional static solutions. The effects of the external torsional moment on the stability of the pipe are characterized as functions of the magnitude and location of the moment. It is shown that there is a critical magnitude, which depends on the location, above which a static instability occurs. Regardless of the magnitude of the torsional moment, it always reduces the critical flow velocity for flutter. While the stability of pipes conveying lighter fluids is shown to be more sensitive to torsional moments applied at the free end, applications at the middle point are more critical for pipes conveying heavier fluids. Depending on the system parameters, divergence and flutter may either coexist, or the system is stabilized over a range of flow velocities before it loses stability again, at higher flow velocities, by flutter. By numerically integrating the nonlinear equations of motion in the time domain, it is also shown that the presence of torsional moments induce three-dimensional motions, even when two-dimensional initial conditions are given.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104260"},"PeriodicalIF":3.4,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143097236","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 : 2025-01-21DOI: 10.1016/j.jfluidstructs.2025.104269
Dheeraj Tripathi , Mehdi Ghommem , Abdessattar Abdelkefi , Lotfi Romdhane , George C. Bourantas
This study explores the aeroelastic performance of a slender steel flag positioned in the wake of bluff bodies with different cross-sectional shapes, namely, C, inverted C (IC), and U shaped cut cylinders — with radial cavities cut at angles of 60° and 120° for each shape, and 180° for U shape. The flag is positioned at varying gap distances () from the bluff body. This distance varies from 0.5 to 9, where represents the diameter of the bluff body. A preliminary numerical analysis using the immersed boundary method reveals distinct wake patterns for each configuration. Subsequent wind tunnel experiments align with these findings, showing a range of instability regimes. For the “C-type” bluff body, flutter in flag occurs at gap distances between 3 and 9, while no limit cycle oscillations (LCOs) are observed for closer distances (0.5 to 2). In contrast, for the “IC-type” bluff body, the cut angle strongly influences the flag flutter dynamics, with the 60° cut cylinder exhibiting the most pronounced instability. As the cut angle increases, the instability regime narrows. The “U-type” bluff body results in asymmetric wake interaction, allowing the flag to flutter even in closer gap distances ( = 0.5 - 2), with a subcritical bifurcation observed at = 0.5, which is not observed elsewhere. The onset of the flutter is notably advanced under the wake of “U-type” bluff body as compared to other bluff body shapes at higher gap distances ( = 3 to 9). Overall, this study underscores the combined role of the bluff body shape and the gap distance on aeroelastic behavior of the flag, offering insights for designing efficient flutter-based energy harvesters at low Reynolds numbers.
{"title":"Dynamic aeroelastic response of a slender triangular flag behind bluff bodies of varying shapes","authors":"Dheeraj Tripathi , Mehdi Ghommem , Abdessattar Abdelkefi , Lotfi Romdhane , George C. Bourantas","doi":"10.1016/j.jfluidstructs.2025.104269","DOIUrl":"10.1016/j.jfluidstructs.2025.104269","url":null,"abstract":"<div><div>This study explores the aeroelastic performance of a slender steel flag positioned in the wake of bluff bodies with different cross-sectional shapes, namely, C, inverted C (IC), and U shaped cut cylinders — with radial cavities cut at angles of 60° and 120° for each shape, and 180° for U shape. The flag is positioned at varying gap distances (<span><math><mi>G</mi></math></span>) from the bluff body. This distance varies from 0.5<span><math><mi>d</mi></math></span> to 9<span><math><mi>d</mi></math></span>, where <span><math><mi>d</mi></math></span> represents the diameter of the bluff body. A preliminary numerical analysis using the immersed boundary method reveals distinct wake patterns for each configuration. Subsequent wind tunnel experiments align with these findings, showing a range of instability regimes. For the “C-type” bluff body, flutter in flag occurs at gap distances between 3<span><math><mi>d</mi></math></span> and 9<span><math><mi>d</mi></math></span>, while no limit cycle oscillations (LCOs) are observed for closer distances (0.5<span><math><mi>d</mi></math></span> to 2<span><math><mi>d</mi></math></span>). In contrast, for the “IC-type” bluff body, the cut angle strongly influences the flag flutter dynamics, with the 60° cut cylinder exhibiting the most pronounced instability. As the cut angle increases, the instability regime narrows. The “U-type” bluff body results in asymmetric wake interaction, allowing the flag to flutter even in closer gap distances (<span><math><mi>G</mi></math></span> = 0.5<span><math><mi>d</mi></math></span> - 2<span><math><mi>d</mi></math></span>), with a subcritical bifurcation observed at <span><math><mi>G</mi></math></span> = 0.5<span><math><mi>d</mi></math></span>, which is not observed elsewhere. The onset of the flutter is notably advanced under the wake of “U-type” bluff body as compared to other bluff body shapes at higher gap distances (<span><math><mi>G</mi></math></span> = 3<span><math><mi>d</mi></math></span> to 9<span><math><mi>d</mi></math></span>). Overall, this study underscores the combined role of the bluff body shape and the gap distance on aeroelastic behavior of the flag, offering insights for designing efficient flutter-based energy harvesters at low Reynolds numbers.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104269"},"PeriodicalIF":3.4,"publicationDate":"2025-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143097242","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 : 2025-01-21DOI: 10.1016/j.jfluidstructs.2025.104270
Caiping Jin , Jingxin Zhang
Aquatic flexible vegetation is widespread in rivers, lakeshores, harbors, and coastal areas and plays an important role in the riverine and coastal ecosystems. The flow with flexible vegetation is difficult to simulate due to the complex motions of flexible vegetation and fluid. This work proposes and validates a semi-resolved numerical model coupling the computational fluid dynamics (CFD) and flexible rod dynamics (FRD) using a promoted two-way domain expansion method. The governing equations in the FRD model are solved by the finite element method (FEM), and the CFD is implemented by the finite volume method (FVM). The vegetation effect is added by introducing body forces into the Reynolds-averaged Navier-Stokes equations as point source terms. To mimic the flexible vegetation stem with the anisotropic cross-section, a named distributed virtual body forces method (DVBFM) was first proposed to model the fluid-solid body coupling. A test case of flow around a single flexible plate was first designed to strictly validate the numerical scheme. The model was then further validated by experimental results of flow with a gently undulating patch of flexible plates. Finally, the test case of flow through a wavy patch of flexible vegetation, mimicked by the plates, was used as a benchmark to validate the usability of the model for flexible vegetation flow simulation in a practical engineering sense.
{"title":"Numerical strategy of modelling flexible vegetation flows using a semi-resolved numerical model by means of distributed virtual body forces","authors":"Caiping Jin , Jingxin Zhang","doi":"10.1016/j.jfluidstructs.2025.104270","DOIUrl":"10.1016/j.jfluidstructs.2025.104270","url":null,"abstract":"<div><div>Aquatic flexible vegetation is widespread in rivers, lakeshores, harbors, and coastal areas and plays an important role in the riverine and coastal ecosystems. The flow with flexible vegetation is difficult to simulate due to the complex motions of flexible vegetation and fluid. This work proposes and validates a semi-resolved numerical model coupling the computational fluid dynamics (CFD) and flexible rod dynamics (FRD) using a promoted two-way domain expansion method. The governing equations in the FRD model are solved by the finite element method (FEM), and the CFD is implemented by the finite volume method (FVM). The vegetation effect is added by introducing body forces into the Reynolds-averaged Navier-Stokes equations as point source terms. To mimic the flexible vegetation stem with the anisotropic cross-section, a named distributed virtual body forces method (DVBFM) was first proposed to model the fluid-solid body coupling. A test case of flow around a single flexible plate was first designed to strictly validate the numerical scheme. The model was then further validated by experimental results of flow with a gently undulating patch of flexible plates. Finally, the test case of flow through a wavy patch of flexible vegetation, mimicked by the plates, was used as a benchmark to validate the usability of the model for flexible vegetation flow simulation in a practical engineering sense.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104270"},"PeriodicalIF":3.4,"publicationDate":"2025-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143141272","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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