Pub Date : 2024-12-12DOI: 10.1016/j.jfluidstructs.2024.104248
Sahand Najafpour, Majid Bahrami
Inverted flags have captivated the attention of researchers due to their distinct behavior and post-divergence dynamics. In this study, we focused on the instability and post-divergence dynamics of an inverted flag attached to a tube in a flow impinging on its free end. A new model is proposed which captures the instability of an arbitrary aspect-ratio inverted flag attached to a tube and is validated with experimental data collected in our lab. An asymptotic approach is adopted to cover a wide range of aspect ratios and tube radius to flag length ratios. Generally, the tube increases the critical flow speed by decelerating the flow speed in the vicinity of the flag. Our experimental measurements also showed the flapping frequency increases and reaches a maximum value with increasing flow speed for the case where the tube is absent. However, the frequency remained relatively constant at the onset of flapping or declined consistently for a flag affixed to a tube. Additionally, an earlier transition to the fully deflected mode was observed in the presence of a tube.
{"title":"Investigating stability and dynamics of inverted flags attached to a cylindrical tube","authors":"Sahand Najafpour, Majid Bahrami","doi":"10.1016/j.jfluidstructs.2024.104248","DOIUrl":"10.1016/j.jfluidstructs.2024.104248","url":null,"abstract":"<div><div>Inverted flags have captivated the attention of researchers due to their distinct behavior and post-divergence dynamics. In this study, we focused on the instability and post-divergence dynamics of an inverted flag attached to a tube in a flow impinging on its free end. A new model is proposed which captures the instability of an arbitrary aspect-ratio inverted flag attached to a tube and is validated with experimental data collected in our lab. An asymptotic approach is adopted to cover a wide range of aspect ratios and tube radius to flag length ratios. Generally, the tube increases the critical flow speed by decelerating the flow speed in the vicinity of the flag. Our experimental measurements also showed the flapping frequency increases and reaches a maximum value with increasing flow speed for the case where the tube is absent. However, the frequency remained relatively constant at the onset of flapping or declined consistently for a flag affixed to a tube. Additionally, an earlier transition to the fully deflected mode was observed in the presence of a tube.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104248"},"PeriodicalIF":3.4,"publicationDate":"2024-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143141265","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 : 2024-12-09DOI: 10.1016/j.jfluidstructs.2024.104231
Jordan D. Thayer , Matthew J. Kronheimer , Rohit Deshmukh , Jack J. McNamara , Datta V. Gaitonde
Accurate and efficient prediction of high-speed aeroelastic behavior is greatly hampered by insufficient understanding of the role of multi-scale fluid features on structural dynamics. In this work, we use a combination of scale-resolving and modeled simulations to evaluate the significance of capturing coupling with the broadband turbulent pressure fluctuations on prediction of the aeroelastic response. A Mach 2 turbulent flow separating from a cantilever plate is considered at nondimensional dynamic pressures of and 150. The fully coupled Large-Eddy Simulations (LES) predict sustained oscillations, with larger amplitudes and modal coalescence for the higher and shock-induced separation on the cantilever top surface. The significance of capturing dynamic feedback between the broadband turbulence and structural compliance is highlighted through aeroelastic response prediction comparisons between LES and URANS. Here, wall pressure fluctuations are extracted from LES data about undeformed and time-mean deflected states of the cantilever and separately added to coupled URANS simulations. The results indicate that key aspects of the aeroelastic behavior can be recovered by URANS in conjunction with an uncoupled turbulent load. However, clear differences in response frequency and instantaneous amplitude remain present compared to LES, suggesting missing coupled phenomena from the URANS prediction.
{"title":"Role of turbulence on high-speed aeroelastic behavior of a cantilever plate","authors":"Jordan D. Thayer , Matthew J. Kronheimer , Rohit Deshmukh , Jack J. McNamara , Datta V. Gaitonde","doi":"10.1016/j.jfluidstructs.2024.104231","DOIUrl":"10.1016/j.jfluidstructs.2024.104231","url":null,"abstract":"<div><div>Accurate and efficient prediction of high-speed aeroelastic behavior is greatly hampered by insufficient understanding of the role of multi-scale fluid features on structural dynamics. In this work, we use a combination of scale-resolving and modeled simulations to evaluate the significance of capturing coupling with the broadband turbulent pressure fluctuations on prediction of the aeroelastic response. A Mach 2 turbulent flow separating from a cantilever plate is considered at nondimensional dynamic pressures of <span><math><mrow><mi>λ</mi><mo>=</mo><mn>100</mn></mrow></math></span> and 150. The fully coupled Large-Eddy Simulations (LES) predict sustained oscillations, with larger amplitudes and modal coalescence for the higher <span><math><mi>λ</mi></math></span> and shock-induced separation on the cantilever top surface. The significance of capturing dynamic feedback between the broadband turbulence and structural compliance is highlighted through aeroelastic response prediction comparisons between LES and URANS. Here, wall pressure fluctuations are extracted from LES data about undeformed and time-mean deflected states of the cantilever and separately added to coupled URANS simulations. The results indicate that key aspects of the aeroelastic behavior can be recovered by URANS in conjunction with an uncoupled turbulent load. However, clear differences in response frequency and instantaneous amplitude remain present compared to LES, suggesting missing coupled phenomena from the URANS prediction.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104231"},"PeriodicalIF":3.4,"publicationDate":"2024-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143141311","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 : 2024-12-05DOI: 10.1016/j.jfluidstructs.2024.104232
Inga Prüter , Felix Spröer , Kara Keimer , Oliver Lojek , Christian Windt , David Schürenkamp , Hans Bihs , Ioan Nistor , Nils Goseberg
Submerged vegetation is becoming more and more relevant as a nature-based solution for coastal protection schemes, counteracting the effects of climate change and sea level rise. The numerical model REEF3D has been used to simulate the motion of and forces exerted on flexible vegetation under unidirectional currents. This study emphasizes the critical need for accurate solutions obtained by numerical models to investigate the complex ecosystem services, adopting a direct forcing approach using the immersed boundary method. The fluid–structure interaction capability within the finite difference model is comprehensively evaluated for the simulation of stem motions and forces exerted on flexible vegetation under varying unidirectional flows. Thresholds for numerical parameters, including a minimum number of 25 rigid elements composing the stem, are identified for accurate solutions. The necessity of using large eddy simulations and a Smagorinsky constant of 0.1 to simulate the turbulent flow is demonstrated. The study confirms the accuracy of the implemented fluid–structure interaction model to replicate stem bending (less than 10 % deviation relative to the stem length) and forces across varying hydrodynamic conditions.
{"title":"A comprehensive numerical study on the current-induced fluid–structure interaction of flexible submerged vegetation","authors":"Inga Prüter , Felix Spröer , Kara Keimer , Oliver Lojek , Christian Windt , David Schürenkamp , Hans Bihs , Ioan Nistor , Nils Goseberg","doi":"10.1016/j.jfluidstructs.2024.104232","DOIUrl":"10.1016/j.jfluidstructs.2024.104232","url":null,"abstract":"<div><div>Submerged vegetation is becoming more and more relevant as a nature-based solution for coastal protection schemes, counteracting the effects of climate change and sea level rise. The numerical model REEF3D has been used to simulate the motion of and forces exerted on flexible vegetation under unidirectional currents. This study emphasizes the critical need for accurate solutions obtained by numerical models to investigate the complex ecosystem services, adopting a direct forcing approach using the immersed boundary method. The fluid–structure interaction capability within the finite difference model is comprehensively evaluated for the simulation of stem motions and forces exerted on flexible vegetation under varying unidirectional flows. Thresholds for numerical parameters, including a minimum number of 25 rigid elements composing the stem, are identified for accurate solutions. The necessity of using large eddy simulations and a Smagorinsky constant of 0.1 to simulate the turbulent flow is demonstrated. The study confirms the accuracy of the implemented fluid–structure interaction model to replicate stem bending (less than 10<!--> <!-->% deviation relative to the stem length) and forces across varying hydrodynamic conditions.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104232"},"PeriodicalIF":3.4,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143141302","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}
This study presents an experimental investigation into the vortex-induced vibrations (VIV) of a single circular cylinder supported by various nonlinear springs. Unlike previous studies focused on systems satisfying the Duffing equation, this study explores a realistic scenario with nonlinear restoring forces derived from different magnet configurations. Experiments were conducted in a low-speed circulating water flume across a Reynolds number range of Re = 232-20930, a mass ratio (m*) ranging from 3.39 to 5.55, and a nonlinear strength coefficient (λ) from -1.48 to 1.70. The results demonstrated that predicted nonlinear VIV amplitudes using linear VIV data align well with experimental observations, validating the applicability of the prediction theory (Mackowski and Williamson, PoF, 2013) to general nonlinear systems. An equivalent reduced velocity (Ueq) was introduced to rescale vibration responses, effectively collapsing the envelopes for linear and hardening nonlinear systems, although shifts to higher Ueq values were observed for softening systems. A detailed analysis of the nonlinear coefficient's impact on VIV characteristics, including amplitude, frequency, phase lag, and displacement history, identified four distinct VIV response groups: softening, weak hardening, intermediate hardening, and strong hardening nonlinear VIV. A notable finding is the presence of two lock-in regions in nonlinear VIV responses, characterized by superharmonic synchronization, and multiple-value sections and gaps in vibration envelopes at specific transitions. These behaviors are attributed to variations in the natural frequency (fn(A*)) with vibration amplitude. This study provides valuable insights into the complex dynamics of general nonlinear VIV, offering a foundation for future research and practical applications.
{"title":"Experimental study on vortex-induced vibrations of a circular cylinder elastically supported by realistic nonlinear springs: Vibration response","authors":"Yawei Zhao , Zhimeng Zhang , Chunning Ji , Weilin Chen , Jiahang Lv , Hanghao Zhao","doi":"10.1016/j.jfluidstructs.2024.104233","DOIUrl":"10.1016/j.jfluidstructs.2024.104233","url":null,"abstract":"<div><div>This study presents an experimental investigation into the vortex-induced vibrations (VIV) of a single circular cylinder supported by various nonlinear springs. Unlike previous studies focused on systems satisfying the Duffing equation, this study explores a realistic scenario with nonlinear restoring forces derived from different magnet configurations. Experiments were conducted in a low-speed circulating water flume across a Reynolds number range of <em>Re</em> = 232-20930, a mass ratio (<em>m*</em>) ranging from 3.39 to 5.55, and a nonlinear strength coefficient (<em>λ</em>) from -1.48 to 1.70. The results demonstrated that predicted nonlinear VIV amplitudes using linear VIV data align well with experimental observations, validating the applicability of the prediction theory (Mackowski and Williamson, PoF, 2013) to general nonlinear systems. An equivalent reduced velocity (<em>U<sub>eq</sub></em>) was introduced to rescale vibration responses, effectively collapsing the envelopes for linear and hardening nonlinear systems, although shifts to higher <em>U<sub>eq</sub></em> values were observed for softening systems. A detailed analysis of the nonlinear coefficient's impact on VIV characteristics, including amplitude, frequency, phase lag, and displacement history, identified four distinct VIV response groups: softening, weak hardening, intermediate hardening, and strong hardening nonlinear VIV. A notable finding is the presence of two lock-in regions in nonlinear VIV responses, characterized by superharmonic synchronization, and multiple-value sections and gaps in vibration envelopes at specific transitions. These behaviors are attributed to variations in the natural frequency (<em>f<sub>n</sub></em>(<em>A*</em>)) with vibration amplitude. This study provides valuable insights into the complex dynamics of general nonlinear VIV, offering a foundation for future research and practical applications.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104233"},"PeriodicalIF":3.4,"publicationDate":"2024-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142759307","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 : 2024-12-01DOI: 10.1016/j.jfluidstructs.2024.104223
Yahya Modarres-Sadeghi
{"title":"Editorial for the “Special Issue in Honor of Emmanuel de Langre”","authors":"Yahya Modarres-Sadeghi","doi":"10.1016/j.jfluidstructs.2024.104223","DOIUrl":"10.1016/j.jfluidstructs.2024.104223","url":null,"abstract":"","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"131 ","pages":"Article 104223"},"PeriodicalIF":3.4,"publicationDate":"2024-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143136244","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 : 2024-12-01DOI: 10.1016/j.jfluidstructs.2024.104227
Jingge Quan , Sijia Zhang , Chuanqiang Gao , Zhengyin Ye , Weiwei Zhang
Potential frequency lock-in vibration can frequently occur in aircraft flying at separated flow conditions during take-off and landing stages, severely threatening the safety of the aircraft. A deeper understanding of the lock-in phenomenon in pre-stall (steady separated flow) conditions is necessary to improve aircraft reliability and safety. In this paper, a reduced-order model (ROM) for the pitching NACA0012 airfoil in steady separated flow is established. A linear aeroelastic model is then obtained by coupling the ROM with the structural dynamical equation with the pitching degree of freedom, and it is verified by the computational fluid dynamics/computational structural dynamics (CFD/CSD) simulation. Next, the mechanism of frequency lock-in vibration is revealed by the ROM-based aeroelastic model of different structural natural frequencies. Results from the complex eigenvalue analysis indicate that the instability can be divided into two patterns. At high frequencies, the flutter frequency locked onto the natural frequency of the structure, and it is dominated by the instability of structural mode. At low frequencies, the flutter frequency follows the fluid characteristic frequency, which is dominated by the instability of the fluid mode. Finally, the effects of the angle of attack and mass ratio are investigated. The damping of dominant fluid mode decreases with the increase of angle of attack, which affects the structural mode through coupling effects. Therefore, the angle of attack influences the upper boundary of the coupling system’s instability (high frequency boundary). On the contrary, the mass ratio mainly influences the lower boundary of instability (low frequency boundary), because fluid mode becomes unstable at low frequencies merely when the mass ratio is relatively low.
{"title":"On the mechanism of frequency lock-in vibration of airfoils during pre-stall conditions","authors":"Jingge Quan , Sijia Zhang , Chuanqiang Gao , Zhengyin Ye , Weiwei Zhang","doi":"10.1016/j.jfluidstructs.2024.104227","DOIUrl":"10.1016/j.jfluidstructs.2024.104227","url":null,"abstract":"<div><div>Potential frequency lock-in vibration can frequently occur in aircraft flying at separated flow conditions during take-off and landing stages, severely threatening the safety of the aircraft. A deeper understanding of the lock-in phenomenon in pre-stall (steady separated flow) conditions is necessary to improve aircraft reliability and safety. In this paper, a reduced-order model (ROM) for the pitching NACA0012 airfoil in steady separated flow is established. A linear aeroelastic model is then obtained by coupling the ROM with the structural dynamical equation with the pitching degree of freedom, and it is verified by the computational fluid dynamics/computational structural dynamics (CFD/CSD) simulation. Next, the mechanism of frequency lock-in vibration is revealed by the ROM-based aeroelastic model of different structural natural frequencies. Results from the complex eigenvalue analysis indicate that the instability can be divided into two patterns. At high frequencies, the flutter frequency locked onto the natural frequency of the structure, and it is dominated by the instability of structural mode. At low frequencies, the flutter frequency follows the fluid characteristic frequency, which is dominated by the instability of the fluid mode. Finally, the effects of the angle of attack and mass ratio are investigated. The damping of dominant fluid mode decreases with the increase of angle of attack, which affects the structural mode through coupling effects. Therefore, the angle of attack influences the upper boundary of the coupling system’s instability (high frequency boundary). On the contrary, the mass ratio mainly influences the lower boundary of instability (low frequency boundary), because fluid mode becomes unstable at low frequencies merely when the mass ratio is relatively low.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"133 ","pages":"Article 104227"},"PeriodicalIF":3.4,"publicationDate":"2024-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142759302","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}
Vortex-induced vibration (VIV) has been addressed in the literature mostly for quasi-streamlined and shallow π-deck sections, typical of long-span bridges, since the latter are particularly prone to wind-induced oscillations. In contrast, although full-scale observations demonstrate that even steel-box girder bridges, usually characterized by a shorter span length if compared to suspension and cable-stayed bridges, can experience a violent VIV response, systematic studies for these bluffer cross-section geometries are less frequent. In addition, the aerodynamic optimization of non-structural additions (barriers, screens, fairings) is rarely carried out for this bridge typology. Therefore, a wind tunnel investigation is conducted on a non-streamlined box-girder sectional model (inspired by the Volgograd Bridge, Russia) equipped with two typologies of traffic barriers giving rise to a large ratio of barrier height to deck width. A realistic range of angles of attack (from −3° to 3°) are considered, and static forces, aeroelastic vibrations and wake velocity fluctuations are measured. A large and even unexpected variability in the vibration amplitude and lock-in curve pattern is found, emphasizing the possible existence of competing excitation mechanisms. Indeed, low-porosity barriers can alter the characteristics of vortex shedding, in particular creating a cavity on the upper side of the deck, which is known to foster the impinging-shear-layer instability, as in H-shaped sections. This vortex-shedding mechanism may co-exist with Kármán-vortex shedding and may be responsible for significant anticipation of the VIV onset compared to the predictions based on the Strouhal number measured during static tests. The intensity of a secondary excitation mechanism and its interaction with the dominant mechanism strongly depend on the angle of attack and is largely responsible for profound changes in the VIV bridge response, both in terms of qualitative pattern and peak amplitude. In some cases, the tracks of these competing vortex-shedding mechanisms are even clearly visible in the VIV response curves of the tested bridge model. Finally, the wind tunnel results are also reconsidered based on the quasi-steady theory, highlighting some, even qualitative, discrepancies.
{"title":"VIV mechanisms of a non-streamlined bridge deck equipped with traffic barriers","authors":"Bernardo Nicese , Antonino Maria Marra , Gianni Bartoli , Claudio Mannini","doi":"10.1016/j.jfluidstructs.2024.104195","DOIUrl":"10.1016/j.jfluidstructs.2024.104195","url":null,"abstract":"<div><div>Vortex-induced vibration (VIV) has been addressed in the literature mostly for quasi-streamlined and shallow π-deck sections, typical of long-span bridges, since the latter are particularly prone to wind-induced oscillations. In contrast, although full-scale observations demonstrate that even steel-box girder bridges, usually characterized by a shorter span length if compared to suspension and cable-stayed bridges, can experience a violent VIV response, systematic studies for these bluffer cross-section geometries are less frequent. In addition, the aerodynamic optimization of non-structural additions (barriers, screens, fairings) is rarely carried out for this bridge typology. Therefore, a wind tunnel investigation is conducted on a non-streamlined box-girder sectional model (inspired by the Volgograd Bridge, Russia) equipped with two typologies of traffic barriers giving rise to a large ratio of barrier height to deck width. A realistic range of angles of attack (from −3° to 3°) are considered, and static forces, aeroelastic vibrations and wake velocity fluctuations are measured. A large and even unexpected variability in the vibration amplitude and lock-in curve pattern is found, emphasizing the possible existence of competing excitation mechanisms. Indeed, low-porosity barriers can alter the characteristics of vortex shedding, in particular creating a cavity on the upper side of the deck, which is known to foster the impinging-shear-layer instability, as in H-shaped sections. This vortex-shedding mechanism may co-exist with Kármán-vortex shedding and may be responsible for significant anticipation of the VIV onset compared to the predictions based on the Strouhal number measured during static tests. The intensity of a secondary excitation mechanism and its interaction with the dominant mechanism strongly depend on the angle of attack and is largely responsible for profound changes in the VIV bridge response, both in terms of qualitative pattern and peak amplitude. In some cases, the tracks of these competing vortex-shedding mechanisms are even clearly visible in the VIV response curves of the tested bridge model. Finally, the wind tunnel results are also reconsidered based on the quasi-steady theory, highlighting some, even qualitative, discrepancies.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"132 ","pages":"Article 104195"},"PeriodicalIF":3.4,"publicationDate":"2024-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142702048","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 : 2024-11-25DOI: 10.1016/j.jfluidstructs.2024.104230
Yiwen He , Aiming Shi , Earl H. Dowell , Shengxi Zhou
This paper investigates the aeroelastic stability and nonlinear aeroelastic behavior of a two-dimensional heated panel in irregular shock reflection and extends prior work to include the effects of viscoelasticity. The aeroelastic model is formulated using the von Kármán large deflection plate theory and the Kelvin–Voigt damping model, accompanied by the quasi-steady thermal stress theory. The unsteady aerodynamic pressure is evaluated through the piston theory and the compressibility-corrected potential theory. The Galerkin approach is used to discretize the governing equation. The Lyapunov indirect method is applied to conduct theoretical analysis, obtaining the aeroelastic stability boundary. Also, the nonlinear aeroelastic response is numerically simulated via the fourth-order Runge–Kutta method. The proper orthogonal decomposition is applied to the panel deflection to manifest the influence of various system parameters. It is demonstrated that the shock wave aggravates the aerodynamic heating, lowering the critical buckling temperature. The viscoelastic damping restricts the impact of shock impingement location and shock strength on the stability boundary and also transforms the chaotic motions into periodic LCOs.
{"title":"Nonlinear aeroelastic behavior of a two-dimensional heated panel by irregular shock reflection considering viscoelastic damping","authors":"Yiwen He , Aiming Shi , Earl H. Dowell , Shengxi Zhou","doi":"10.1016/j.jfluidstructs.2024.104230","DOIUrl":"10.1016/j.jfluidstructs.2024.104230","url":null,"abstract":"<div><div>This paper investigates the aeroelastic stability and nonlinear aeroelastic behavior of a two-dimensional heated panel in irregular shock reflection and extends prior work to include the effects of viscoelasticity. The aeroelastic model is formulated using the von Kármán large deflection plate theory and the Kelvin–Voigt damping model, accompanied by the quasi-steady thermal stress theory. The unsteady aerodynamic pressure is evaluated through the piston theory and the compressibility-corrected potential theory. The Galerkin approach is used to discretize the governing equation. The Lyapunov indirect method is applied to conduct theoretical analysis, obtaining the aeroelastic stability boundary. Also, the nonlinear aeroelastic response is numerically simulated via the fourth-order Runge–Kutta method. The proper orthogonal decomposition is applied to the panel deflection to manifest the influence of various system parameters. It is demonstrated that the shock wave aggravates the aerodynamic heating, lowering the critical buckling temperature. The viscoelastic damping restricts the impact of shock impingement location and shock strength on the stability boundary and also transforms the chaotic motions into periodic LCOs.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"132 ","pages":"Article 104230"},"PeriodicalIF":3.4,"publicationDate":"2024-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142702049","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 : 2024-11-22DOI: 10.1016/j.jfluidstructs.2024.104203
Daiki Sato , Razelle Dennise A. Soriano , Alex Shegay , Kou Miyamoto , Jinhua She , Kazuhiko Kasai
Time-history analyses are usually performed to design and examine the performance of tall structures subjected to strong wind loading. An accurate estimate of the time history of wind forces is required to carry out time-history analysis. However, previous studies conducted to estimate the time-history of wind forces require a lot of priori information, such as complete structural parameters and wind-induced responses, which are generally not available in actual conditions. This work addresses the estimation of the time-history of wind forces acting on each story of a ten degree-of-freedom model under the assumption that only the mass and acceleration responses measured on three stories are known. First, cubic spline interpolation is used to determine the unknown acceleration responses and frequency domain integration is used to obtain the velocity and displacement responses. Then, unknown structural parameters (particularly stiffness and damping) are estimated by the Frequency Domain Decomposition method. Finally, the obtained responses and structural parameters are used to estimate the wind forces using the equation of motion. It is demonstrated that the proposed methodology can accurately estimate the input wind forces on the structure.
{"title":"Estimation of wind force time-history using limited floor acceleration responses by modal analysis","authors":"Daiki Sato , Razelle Dennise A. Soriano , Alex Shegay , Kou Miyamoto , Jinhua She , Kazuhiko Kasai","doi":"10.1016/j.jfluidstructs.2024.104203","DOIUrl":"10.1016/j.jfluidstructs.2024.104203","url":null,"abstract":"<div><div>Time-history analyses are usually performed to design and examine the performance of tall structures subjected to strong wind loading. An accurate estimate of the time history of wind forces is required to carry out time-history analysis. However, previous studies conducted to estimate the time-history of wind forces require a lot of priori information, such as complete structural parameters and wind-induced responses, which are generally not available in actual conditions. This work addresses the estimation of the time-history of wind forces acting on each story of a ten degree-of-freedom model under the assumption that only the mass and acceleration responses measured on three stories are known. First, cubic spline interpolation is used to determine the unknown acceleration responses and frequency domain integration is used to obtain the velocity and displacement responses. Then, unknown structural parameters (particularly stiffness and damping) are estimated by the Frequency Domain Decomposition method. Finally, the obtained responses and structural parameters are used to estimate the wind forces using the equation of motion. It is demonstrated that the proposed methodology can accurately estimate the input wind forces on the structure.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"132 ","pages":"Article 104203"},"PeriodicalIF":3.4,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142702011","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 : 2024-11-22DOI: 10.1016/j.jfluidstructs.2024.104224
Lucas Berthet , Philippe Blais , Bernd Nennemann , Christine Monette , Frederick P. Gosselin
High-head turbine runners are subject to multiple sources of excitation. Coupled with the added mass of water, rotation induces a mode split in the natural frequencies of runners, where co-rotating and counter-rotating waves travel through the runner at different relative speeds. Disks, by displaying a similar behavior, can be used as a geometrically simpler model. Mode split is characterized for a rotating disk in dense fluid but, in high-head turbines, the runner and the compliant confinement are coupled through the axial gap fluid. In this article, we develop an analytical model of coupled stationary and rotating disks to analyze the effect of their interaction on the mode split phenomenon. First, we apply the potential flow theory, considering the fluid as irrotational, inviscid and incompressible. We assume that the modeshapes of the disk in a dense fluid are similar to their shapes in vacuum. We then derive the potential flows that respect the no-penetration boundary conditions. One after the other, each disk is considered flexible while the other one is rigid. By applying the superposition principle, we then couple the two obtained fluid flows through the structural equations of motion. A finite-element vibro-acoustic modal analysis was developed to verify the analytical model and propose a fast numerical tool for hydraulic turbine design. Analytical results show that rotation induces a split of the coupled rotor–stator frequencies as for a lone rotor, while the ratio of their amplitudes varies slightly. A change in the relative thickness of the rotor and stator affects their individual frequencies in vacuum, and in turn their coupling by the fluid, with a potential shift in dominance.
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