Pub Date : 2024-10-15DOI: 10.1016/j.jfluidstructs.2024.104201
Pavan Kumar Yadav, Himalaya Sarkar, Subhankar Sen
<div><div>Undamped transverse-only flow-induced vibrations (FIV) of an elliptic cylinder of mass ratio, <span><math><mrow><msup><mrow><mi>m</mi></mrow><mrow><mo>∗</mo></mrow></msup><mo>=</mo><mn>10</mn></mrow></math></span> at 45° incidence are investigated via two-dimensional computations at Reynolds numbers, <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>100</mn></mrow></math></span> and 200. Using quasi-steady theory, it is illustrated that the asymmetric oscillator does not gallop at <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>100</mn></mrow></math></span> and 200. Resolution of hysteresis-free solutions at <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>100</mn></mrow></math></span> is a novel finding. As compared to <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>100</mn></mrow></math></span>, response at <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>200</mn></mrow></math></span> is associated with additional branches: a lower branch, a terminal branch and a third regime of desynchronization. Assuming harmonic lift and response, mathematical expressions are obtained for modified dimensionless circular frequency, <span><math><msup><mrow><msup><mrow><msub><mrow><mi>ω</mi></mrow><mrow><mi>N</mi></mrow></msub></mrow><mrow><mo>∗</mo></mrow></msup></mrow><mrow><mn>2</mn></mrow></msup></math></span> and modified damping. The variation of <span><math><msup><mrow><msup><mrow><msub><mrow><mi>ω</mi></mrow><mrow><mi>N</mi></mrow></msub></mrow><mrow><mo>∗</mo></mrow></msup></mrow><mrow><mn>2</mn></mrow></msup></math></span> with reduced speed, <span><math><msup><mrow><mi>U</mi></mrow><mrow><mo>∗</mo></mrow></msup></math></span> reveals excellent collapse with predicted dynamic response. For FIV at <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>200</mn></mrow></math></span> and not at <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>100</mn></mrow></math></span>, a second regime of significant vibrations develops in the neighbourhood of <span><math><mrow><msup><mrow><mi>U</mi></mrow><mrow><mo>∗</mo></mrow></msup><mo>=</mo><mn>8</mn></mrow></math></span> in addition to the first one around <span><math><mrow><msup><mrow><mi>U</mi></mrow><mrow><mo>∗</mo></mrow></msup><mo>=</mo><mn>4</mn></mrow></math></span>. The period doubling bifurcation occurring around <span><math><mrow><msup><mrow><mi>U</mi></mrow><mrow><mo>∗</mo></mrow></msup><mo>=</mo><mn>8</mn></mrow></math></span> is an 1:2 sub-harmonic synchronization; it halves the oscillation frequency that in turn closely approaches reduced natural frequency of the cylinder. In this regime, the wake mode is found to be 2(2S). Leontini et al. (2018) resolved periodic doubling bifurcation for FIV of an inclined elliptic cylinder using a low <span><math><msup><mrow><mi>m</mi></mrow><mrow><mo>∗</mo></mrow></msup></math></span> of unity. The occurrences of second lock-in and period doubling therefore appear not to be a function of <span><math><msup><mrow><mi>m</mi></mrow><mrow><mo
{"title":"Flow past a freely vibrating elliptic cylinder at 45∘ incidence","authors":"Pavan Kumar Yadav, Himalaya Sarkar, Subhankar Sen","doi":"10.1016/j.jfluidstructs.2024.104201","DOIUrl":"10.1016/j.jfluidstructs.2024.104201","url":null,"abstract":"<div><div>Undamped transverse-only flow-induced vibrations (FIV) of an elliptic cylinder of mass ratio, <span><math><mrow><msup><mrow><mi>m</mi></mrow><mrow><mo>∗</mo></mrow></msup><mo>=</mo><mn>10</mn></mrow></math></span> at 45° incidence are investigated via two-dimensional computations at Reynolds numbers, <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>100</mn></mrow></math></span> and 200. Using quasi-steady theory, it is illustrated that the asymmetric oscillator does not gallop at <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>100</mn></mrow></math></span> and 200. Resolution of hysteresis-free solutions at <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>100</mn></mrow></math></span> is a novel finding. As compared to <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>100</mn></mrow></math></span>, response at <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>200</mn></mrow></math></span> is associated with additional branches: a lower branch, a terminal branch and a third regime of desynchronization. Assuming harmonic lift and response, mathematical expressions are obtained for modified dimensionless circular frequency, <span><math><msup><mrow><msup><mrow><msub><mrow><mi>ω</mi></mrow><mrow><mi>N</mi></mrow></msub></mrow><mrow><mo>∗</mo></mrow></msup></mrow><mrow><mn>2</mn></mrow></msup></math></span> and modified damping. The variation of <span><math><msup><mrow><msup><mrow><msub><mrow><mi>ω</mi></mrow><mrow><mi>N</mi></mrow></msub></mrow><mrow><mo>∗</mo></mrow></msup></mrow><mrow><mn>2</mn></mrow></msup></math></span> with reduced speed, <span><math><msup><mrow><mi>U</mi></mrow><mrow><mo>∗</mo></mrow></msup></math></span> reveals excellent collapse with predicted dynamic response. For FIV at <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>200</mn></mrow></math></span> and not at <span><math><mrow><mi>R</mi><mi>e</mi><mo>=</mo><mn>100</mn></mrow></math></span>, a second regime of significant vibrations develops in the neighbourhood of <span><math><mrow><msup><mrow><mi>U</mi></mrow><mrow><mo>∗</mo></mrow></msup><mo>=</mo><mn>8</mn></mrow></math></span> in addition to the first one around <span><math><mrow><msup><mrow><mi>U</mi></mrow><mrow><mo>∗</mo></mrow></msup><mo>=</mo><mn>4</mn></mrow></math></span>. The period doubling bifurcation occurring around <span><math><mrow><msup><mrow><mi>U</mi></mrow><mrow><mo>∗</mo></mrow></msup><mo>=</mo><mn>8</mn></mrow></math></span> is an 1:2 sub-harmonic synchronization; it halves the oscillation frequency that in turn closely approaches reduced natural frequency of the cylinder. In this regime, the wake mode is found to be 2(2S). Leontini et al. (2018) resolved periodic doubling bifurcation for FIV of an inclined elliptic cylinder using a low <span><math><msup><mrow><mi>m</mi></mrow><mrow><mo>∗</mo></mrow></msup></math></span> of unity. The occurrences of second lock-in and period doubling therefore appear not to be a function of <span><math><msup><mrow><mi>m</mi></mrow><mrow><mo","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"130 ","pages":"Article 104201"},"PeriodicalIF":3.4,"publicationDate":"2024-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142442877","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 : 2024-10-14DOI: 10.1016/j.jfluidstructs.2024.104194
Christiana Mavroyiakoumou , Silas Alben
We study the large-amplitude flutter of rectangular membranes in 3-D inviscid flows. The membranes’ deformations vary significantly in both the chordwise and spanwise directions. Many previous studies used 2D flow models and neglected spanwise variations, so here we focus on cases with significant spanwise nonuniformity. We determine when such cases occur and how the dynamics vary over the parameter space of membrane mass and pretension for two sets of boundary conditions and two values of both the Poisson ratio and the membrane aspect ratio. With spanwise symmetric and asymmetric initial perturbations, the motions differ for long times but eventually reach the same steady state in most cases.
At large times, spanwise symmetric and asymmetric oscillations are seen, with the latter more common. Oscillations are often in the form of “side-to-side” and other standing wave motions along the span, as well as traveling wave motions, particularly with free side-edges. Motions are generally nonperiodic and more spatially complex with a large membrane mass, and sometimes periodic at small-to-moderate membrane mass. A large Poisson ratio gives somewhat smoother spatial and temporal features in the dynamics at a given pretension. Increasing the aspect ratio makes the deflection more uniform along the span. With different chordwise and spanwise pretensions we find motions that are qualitatively similar to cases with isotropic pretensions between the anisotropic values.
{"title":"Spanwise variations in membrane flutter dynamics","authors":"Christiana Mavroyiakoumou , Silas Alben","doi":"10.1016/j.jfluidstructs.2024.104194","DOIUrl":"10.1016/j.jfluidstructs.2024.104194","url":null,"abstract":"<div><div>We study the large-amplitude flutter of rectangular membranes in 3-D inviscid flows. The membranes’ deformations vary significantly in both the chordwise and spanwise directions. Many previous studies used 2D flow models and neglected spanwise variations, so here we focus on cases with significant spanwise nonuniformity. We determine when such cases occur and how the dynamics vary over the parameter space of membrane mass and pretension for two sets of boundary conditions and two values of both the Poisson ratio and the membrane aspect ratio. With spanwise symmetric and asymmetric initial perturbations, the motions differ for long times but eventually reach the same steady state in most cases.</div><div>At large times, spanwise symmetric and asymmetric oscillations are seen, with the latter more common. Oscillations are often in the form of “side-to-side” and other standing wave motions along the span, as well as traveling wave motions, particularly with free side-edges. Motions are generally nonperiodic and more spatially complex with a large membrane mass, and sometimes periodic at small-to-moderate membrane mass. A large Poisson ratio gives somewhat smoother spatial and temporal features in the dynamics at a given pretension. Increasing the aspect ratio makes the deflection more uniform along the span. With different chordwise and spanwise pretensions we find motions that are qualitatively similar to cases with isotropic pretensions between the anisotropic values.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"130 ","pages":"Article 104194"},"PeriodicalIF":3.4,"publicationDate":"2024-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142432760","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 : 2024-10-13DOI: 10.1016/j.jfluidstructs.2024.104204
Hongjun Zhu , Jiawen Zhong , Ze Shao , Tongming Zhou , Md. Mahbub Alam
The flow-induced vibration (FIV) of three tandem circular cylinders is numerically investigated using OpenFOAM based on the finite-volume method. The one-degree-of-freedom dynamic response of three tandem circular cylinders with a spacing ratio ranging from 2 to 6 is analysed at a low Reynolds number of 150 over a reduced velocity range of 2–16. The results of hydrodynamic coefficients, response amplitude, vibration frequency, wake structure, and decomposition of vorticity are discussed in this study. Although the streamwise spacing ratio is constant, the dynamic evolution of the crossing angles among three cylinders leads to the switching of wake interference mode. The two-layered vortices are merged into secondary vortices in the far wake, and the energy of secondary vortices is higher than the two-layered vortices. The upstream cylinder exhibits a similar trend as an isolated cylinder in terms of the variations of hydrodynamic coefficients and response amplitude with the reduced velocity. In contrast, the middle and downstream cylinders experience a significantly lower drag due to the shielding effect. Particularly at small spacing ratios, the drag on the middle cylinder becomes negative. At the same time, the lift coefficient and response amplitude are higher than those of an isolated cylinder at high reduced velocities. The three tandem cylinders intermittently form a triangular configuration during the oscillation.
{"title":"Fluid-structure interaction among three tandem circular cylinders oscillating transversely at a low Reynolds number of 150","authors":"Hongjun Zhu , Jiawen Zhong , Ze Shao , Tongming Zhou , Md. Mahbub Alam","doi":"10.1016/j.jfluidstructs.2024.104204","DOIUrl":"10.1016/j.jfluidstructs.2024.104204","url":null,"abstract":"<div><div>The flow-induced vibration (FIV) of three tandem circular cylinders is numerically investigated using OpenFOAM based on the finite-volume method. The one-degree-of-freedom dynamic response of three tandem circular cylinders with a spacing ratio ranging from 2 to 6 is analysed at a low Reynolds number of 150 over a reduced velocity range of 2–16. The results of hydrodynamic coefficients, response amplitude, vibration frequency, wake structure, and decomposition of vorticity are discussed in this study. Although the streamwise spacing ratio is constant, the dynamic evolution of the crossing angles among three cylinders leads to the switching of wake interference mode. The two-layered vortices are merged into secondary vortices in the far wake, and the energy of secondary vortices is higher than the two-layered vortices. The upstream cylinder exhibits a similar trend as an isolated cylinder in terms of the variations of hydrodynamic coefficients and response amplitude with the reduced velocity. In contrast, the middle and downstream cylinders experience a significantly lower drag due to the shielding effect. Particularly at small spacing ratios, the drag on the middle cylinder becomes negative. At the same time, the lift coefficient and response amplitude are higher than those of an isolated cylinder at high reduced velocities. The three tandem cylinders intermittently form a triangular configuration during the oscillation.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"130 ","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142426890","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 : 2024-10-10DOI: 10.1016/j.jfluidstructs.2024.104196
Runqing Cao , Dilong Ma , Wei Chen , Mingwu Li , Huliang Dai , Lin Wang
The present study newly found multistable dynamic characteristics of cantilevered curved pipes conveying fluid due to the gravity. These multistable behaviors of the pipe offer a promising avenue for the development and deployment of fluid actuators. Three configurations of curved pipes, namely, one-quarter circular, semi-circular, and three-quarter circular, are considered. A nonlinear dynamic theoretical model is established based on the geometrically exact model to investigate the large deformation behaviors of the curved pipe conveying subcritical fluid flows. The theoretical model for predicting large deformations of the curved pipe is validated through the finite element method (FEM). Afterwards, linear dynamic characteristics for three configurations of curved pipes are explored. Strangely, the discontinuity phenomenon for natural frequencies of the curved pipe occurs with increasing the flow velocity, which has never been reported before. Meanwhile, it is demonstrated that the gravity parameter has a significant effect on the critical velocity for flutter. Large deformation responses of the curved pipe in three configurations are further investigated, multistable dynamic behaviors are detected for all considered curved pipes. It displays that for different gravity parameters, the dynamic behavior of curved pipe is varying from a single state to multiple states with increasing the flow velocity. Results indicate that when the dimensionless gravity parameter and fluid velocity are 15 and 2.5, the curved pipe exhibits three distinct displacements due to static deformations. These three displacements are in three equilibrium states, which helps to explain the interesting phenomenon of frequency discontinuity.
{"title":"Multistable dynamic behaviors of cantilevered curved pipes conveying fluid","authors":"Runqing Cao , Dilong Ma , Wei Chen , Mingwu Li , Huliang Dai , Lin Wang","doi":"10.1016/j.jfluidstructs.2024.104196","DOIUrl":"10.1016/j.jfluidstructs.2024.104196","url":null,"abstract":"<div><div>The present study newly found multistable dynamic characteristics of cantilevered curved pipes conveying fluid due to the gravity. These multistable behaviors of the pipe offer a promising avenue for the development and deployment of fluid actuators. Three configurations of curved pipes, namely, one-quarter circular, semi-circular, and three-quarter circular, are considered. A nonlinear dynamic theoretical model is established based on the geometrically exact model to investigate the large deformation behaviors of the curved pipe conveying subcritical fluid flows. The theoretical model for predicting large deformations of the curved pipe is validated through the finite element method (FEM). Afterwards, linear dynamic characteristics for three configurations of curved pipes are explored. Strangely, the discontinuity phenomenon for natural frequencies of the curved pipe occurs with increasing the flow velocity, which has never been reported before. Meanwhile, it is demonstrated that the gravity parameter has a significant effect on the critical velocity for flutter. Large deformation responses of the curved pipe in three configurations are further investigated, multistable dynamic behaviors are detected for all considered curved pipes. It displays that for different gravity parameters, the dynamic behavior of curved pipe is varying from a single state to multiple states with increasing the flow velocity. Results indicate that when the dimensionless gravity parameter and fluid velocity are 15 and 2.5, the curved pipe exhibits three distinct displacements due to static deformations. These three displacements are in three equilibrium states, which helps to explain the interesting phenomenon of frequency discontinuity.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"130 ","pages":"Article 104196"},"PeriodicalIF":3.4,"publicationDate":"2024-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142426886","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 : 2024-10-07DOI: 10.1016/j.jfluidstructs.2024.104198
Novi Andria , Lavi Rizki Zuhal , Pramudita Satria Palar , Duong Viet Dung , Leonardo Gunawan , Hari Muhammad
The current study aims to investigate the fluid–structure interaction (FSI) of flexible thin structures undergoing large displacements using numerical simulations. The primary case of interest is the self-induced inverted flag problem, which exhibits a rich set of coupled fluid–structure behavior and flapping dynamics. To achieve this, a new FSI algorithm is proposed via a partitioned approach. The proposed algorithm uses the remeshed-Vortex Particle Method (VPM) to resolve the flow and a finite element method-based elastodynamics solver to evaluate the response of the flexible structure. The remeshed-VPM algorithm is modified and extended in this study with new developments to enhance its applicability for complex FSI simulations of thin flexible structures. A multiresolution scheme is developed and applied in combination with the iterative Brinkman penalization method for remeshed-VPM. A new force formulation is introduced that is based on corrected penalization velocity, which can generate distributed body forces for the iterative Brinkman penalization method. Finally, the fully 3D remeshed-VPM is applied in conjunction with corotational beam formulation for FSI simulations of the inverted flag system. The FSI solver is utilized to conduct a series of simulations on the 2D and 3D inverted flag model, aiming to gain insights into the intricate dynamics of these fluid–structure interactions.
{"title":"Numerical study on three-dimensional self-induced inverted flag","authors":"Novi Andria , Lavi Rizki Zuhal , Pramudita Satria Palar , Duong Viet Dung , Leonardo Gunawan , Hari Muhammad","doi":"10.1016/j.jfluidstructs.2024.104198","DOIUrl":"10.1016/j.jfluidstructs.2024.104198","url":null,"abstract":"<div><div>The current study aims to investigate the fluid–structure interaction (FSI) of flexible thin structures undergoing large displacements using numerical simulations. The primary case of interest is the self-induced inverted flag problem, which exhibits a rich set of coupled fluid–structure behavior and flapping dynamics. To achieve this, a new FSI algorithm is proposed via a partitioned approach. The proposed algorithm uses the remeshed-Vortex Particle Method (VPM) to resolve the flow and a finite element method-based elastodynamics solver to evaluate the response of the flexible structure. The remeshed-VPM algorithm is modified and extended in this study with new developments to enhance its applicability for complex FSI simulations of thin flexible structures. A multiresolution scheme is developed and applied in combination with the iterative Brinkman penalization method for remeshed-VPM. A new force formulation is introduced that is based on corrected penalization velocity, which can generate distributed body forces for the iterative Brinkman penalization method. Finally, the fully 3D remeshed-VPM is applied in conjunction with corotational beam formulation for FSI simulations of the inverted flag system. The FSI solver is utilized to conduct a series of simulations on the 2D and 3D inverted flag model, aiming to gain insights into the intricate dynamics of these fluid–structure interactions.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"130 ","pages":"Article 104198"},"PeriodicalIF":3.4,"publicationDate":"2024-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142426888","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 : 2024-10-07DOI: 10.1016/j.jfluidstructs.2024.104199
Elijah Hao Wei Ang, Bing Feng Ng
In this paper, a genetic algorithm linear quadratic Gaussian controller (GA-LQG) and an artificial neural network (ANN) controller are implemented for gust response alleviation of lightweight flying wings undergoing body-freedom oscillations. A state–space aeroelastic model has been formulated by coupling the unsteady vortex lattice method for aerodynamics with finite-element based structural dynamics. The model is subsequently reduced using balanced truncation to improve computational efficiency during controller synthesis. Open-loop simulations show that the flying wing experiences large changes in pitching angles during gusts. For GA-LQG controller, the LQG weights are optimised using a genetic algorithm, maximising a defined fitness function. Generally, the GA-LQG controller reduces the plunge displacements by up to 94.2% while damping out wingtip displacements for discrete and continuous gusts. Similarly, the ANN controller effectively regulates both the plunge displacements and wingtip displacements, including gust cases that are not presented during the ANN training phase. The ANN controller is more effective in correcting wingtip displacements during discrete gusts than the GA-LQG controller, while the opposite is true for the continuous gust cases. The ANN controller offers several advantages over the GA-LQG controller, including the elimination of the need for a Kalman filter for full state estimation and offers a non-linear control solution.
{"title":"Genetic algorithm LQG and neural network controllers for gust response alleviation of flying wing unmanned aerial vehicles","authors":"Elijah Hao Wei Ang, Bing Feng Ng","doi":"10.1016/j.jfluidstructs.2024.104199","DOIUrl":"10.1016/j.jfluidstructs.2024.104199","url":null,"abstract":"<div><div>In this paper, a genetic algorithm linear quadratic Gaussian controller (GA-LQG) and an artificial neural network (ANN) controller are implemented for gust response alleviation of lightweight flying wings undergoing body-freedom oscillations. A state–space aeroelastic model has been formulated by coupling the unsteady vortex lattice method for aerodynamics with finite-element based structural dynamics. The model is subsequently reduced using balanced truncation to improve computational efficiency during controller synthesis. Open-loop simulations show that the flying wing experiences large changes in pitching angles during gusts. For GA-LQG controller, the LQG weights are optimised using a genetic algorithm, maximising a defined fitness function. Generally, the GA-LQG controller reduces the plunge displacements by up to 94.2% while damping out wingtip displacements for discrete and continuous gusts. Similarly, the ANN controller effectively regulates both the plunge displacements and wingtip displacements, including gust cases that are not presented during the ANN training phase. The ANN controller is more effective in correcting wingtip displacements during discrete gusts than the GA-LQG controller, while the opposite is true for the continuous gust cases. The ANN controller offers several advantages over the GA-LQG controller, including the elimination of the need for a Kalman filter for full state estimation and offers a non-linear control solution.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"130 ","pages":"Article 104199"},"PeriodicalIF":3.4,"publicationDate":"2024-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142426887","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 : 2024-10-04DOI: 10.1016/j.jfluidstructs.2024.104192
Junchen Tan, Zhijin Wang, Ismet Gursul
Stall delay and lift enhancement play a crucial role in modern aircraft performance. This is commonly achieved by devices such as slats or flaps located at the leading edge or trailing edge of an aircraft's wing. In this paper, we report a feasibility study of using light-weight compliant surfaces for novel high lift devices. The effects of compliant flags with one end fixed or both ends fixed near the leading edge and trailing edge of an airfoil were studied by force, flag deformation, and flow field measurements in a wind tunnel. When a flag is placed near the leading edge, the excitation of the separated shear layer from the leading edge is the main mechanism in increasing the lift at the post-stall angles of attack. In contrast, the trailing-edge flag with an excess length and both ends fixed could increase the effective camber and the circulation around the airfoil in a time-averaged sense. The mechanism is similar to that of the conventional Gurney flap effect, and equally effective at pre-stall and post-stall angles of attack. When used together, the compliant flags can delay stall angle by 8° and increase the maximum lift coefficient by 67% in the parameter range tested presently. Compliant surfaces require no external power as a passive method. If they are to be used as active methods, they are light weight, and can be stored and deployed easily.
{"title":"High lift devices using compliant surfaces","authors":"Junchen Tan, Zhijin Wang, Ismet Gursul","doi":"10.1016/j.jfluidstructs.2024.104192","DOIUrl":"10.1016/j.jfluidstructs.2024.104192","url":null,"abstract":"<div><div>Stall delay and lift enhancement play a crucial role in modern aircraft performance. This is commonly achieved by devices such as slats or flaps located at the leading edge or trailing edge of an aircraft's wing. In this paper, we report a feasibility study of using light-weight compliant surfaces for novel high lift devices. The effects of compliant flags with one end fixed or both ends fixed near the leading edge and trailing edge of an airfoil were studied by force, flag deformation, and flow field measurements in a wind tunnel. When a flag is placed near the leading edge, the excitation of the separated shear layer from the leading edge is the main mechanism in increasing the lift at the post-stall angles of attack. In contrast, the trailing-edge flag with an excess length and both ends fixed could increase the effective camber and the circulation around the airfoil in a time-averaged sense. The mechanism is similar to that of the conventional Gurney flap effect, and equally effective at pre-stall and post-stall angles of attack. When used together, the compliant flags can delay stall angle by 8° and increase the maximum lift coefficient by 67% in the parameter range tested presently. Compliant surfaces require no external power as a passive method. If they are to be used as active methods, they are light weight, and can be stored and deployed easily.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"130 ","pages":"Article 104192"},"PeriodicalIF":3.4,"publicationDate":"2024-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142426885","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 : 2024-09-30DOI: 10.1016/j.jfluidstructs.2024.104191
I.A. Carvalho , G.R.S. Assi
We numerically investigate the attribute of omnidirectionality of the flow-control system comprised of a large circular cylinder equipped with eight spinning rods of smaller diameter, subject to an incoming flow that adopts different angles of attack. Detached-eddy simulations are employed to compute hydrodynamic loads and to provide flow topology at a Reynolds number of 1000. Two cases are assessed regarding the rods angular velocities. In case 0, all rods spun with the same angular velocity. In case 1, velocities were inspired by potential-flow theory. The two systems have the same input kinetic energy in common. To assess the system response, the velocities were increased proportionally. Both cases succeeded in reducing the mean drag. However, while case 1 proved to become ever “more omnidirectional” with increasing angular velocities, case 0 demonstrated to be prone to the angle of attack as it was unable to suppress vortex shedding for sufficiently large slopes of the incoming flow, and in such circumstances, unable to reduce hydrodynamic forces. We verify that the lift is mitigated in case 1, in contrast to case 0. Even for a vortex-free downstream flow resulting from configurations of high velocities and high angle of attack, the latter produces asymmetric recirculation regions downstream of the system that drive a pressure imbalance. The different outcomes of the two systems are also explored from the viewpoint of power consumption, and it is revealed that the omnidirectionality of case 1 is intrinsically related to the emphasis imposed on rotation rates of a subset of the eight rods.
{"title":"Omnidirectional control of the wake of a circular cylinder with spinning rods subject to a turbulent flow","authors":"I.A. Carvalho , G.R.S. Assi","doi":"10.1016/j.jfluidstructs.2024.104191","DOIUrl":"10.1016/j.jfluidstructs.2024.104191","url":null,"abstract":"<div><div>We numerically investigate the attribute of omnidirectionality of the flow-control system comprised of a large circular cylinder equipped with eight spinning rods of smaller diameter, subject to an incoming flow that adopts different angles of attack. Detached-eddy simulations are employed to compute hydrodynamic loads and to provide flow topology at a Reynolds number of 1000. Two cases are assessed regarding the rods angular velocities. In case 0, all rods spun with the same angular velocity. In case 1, velocities were inspired by potential-flow theory. The two systems have the same input kinetic energy in common. To assess the system response, the velocities were increased proportionally. Both cases succeeded in reducing the mean drag. However, while case 1 proved to become ever “more omnidirectional” with increasing angular velocities, case 0 demonstrated to be prone to the angle of attack as it was unable to suppress vortex shedding for sufficiently large slopes of the incoming flow, and in such circumstances, unable to reduce hydrodynamic forces. We verify that the lift is mitigated in case 1, in contrast to case 0. Even for a vortex-free downstream flow resulting from configurations of high velocities and high angle of attack, the latter produces asymmetric recirculation regions downstream of the system that drive a pressure imbalance. The different outcomes of the two systems are also explored from the viewpoint of power consumption, and it is revealed that the omnidirectionality of case 1 is intrinsically related to the emphasis imposed on rotation rates of a subset of the eight rods.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"130 ","pages":"Article 104191"},"PeriodicalIF":3.4,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142357914","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 : 2024-09-27DOI: 10.1016/j.jfluidstructs.2024.104193
S. Michele , S. Zheng , E. Renzi , J. Guichard , A.G.L. Borthwick , D.M. Greaves
We present a theoretical model to analyse the hydrodynamics of wave energy converters (WECs) comprised of three-dimensional, rigid, floating, compound rectangular plates in the open sea. The hydrodynamic problem is solved by means of Green’s theorem and a free-surface Green’s function. Plate motion is predicted through decomposition into rigid natural modes. We first analyse the case of a single rectangular plate and validate our model against experimental results from physical model tests undertaken in the COAST laboratory at the University of Plymouth. Then we extend our theory to complex shapes and arrays of plates and examine how the geometry, incident wave direction and power take-off (PTO) coefficient affect the response of the platform and the consequent absorbed energy.
{"title":"Wave energy extraction from rigid rectangular compound floating plates","authors":"S. Michele , S. Zheng , E. Renzi , J. Guichard , A.G.L. Borthwick , D.M. Greaves","doi":"10.1016/j.jfluidstructs.2024.104193","DOIUrl":"10.1016/j.jfluidstructs.2024.104193","url":null,"abstract":"<div><div>We present a theoretical model to analyse the hydrodynamics of wave energy converters (WECs) comprised of three-dimensional, rigid, floating, compound rectangular plates in the open sea. The hydrodynamic problem is solved by means of Green’s theorem and a free-surface Green’s function. Plate motion is predicted through decomposition into rigid natural modes. We first analyse the case of a single rectangular plate and validate our model against experimental results from physical model tests undertaken in the COAST laboratory at the University of Plymouth. Then we extend our theory to complex shapes and arrays of plates and examine how the geometry, incident wave direction and power take-off (PTO) coefficient affect the response of the platform and the consequent absorbed energy.</div></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"130 ","pages":"Article 104193"},"PeriodicalIF":3.4,"publicationDate":"2024-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142326325","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：