Flutter Control Research Articles

Controlling flutter of a cable-stayed bridge with output feedback driven winglets

Active control of flutter of a long span cable-stayed bridge is considered in this study. The control action is provided by winglets actuated using constant/variable gain output feedback controllers. Two FE modeling schemes are adopted, namely one element cables, and multi-element cables with each stay-cable discretized into multiple elements to consider the cable vibration effect. Cable discretization results in additional closely spaced modes. Rational function approximation of flat plate flutter derivatives is considered to model aeroelastic forces on deck and winglets. The output feedback controller yields the desired winglet rotation by using vertical and torsional displacements of the deck. Controllability Gramian and response indices are used to obtain the optimal location of winglets, while the best sensor location is obtained based on a combined index. This yields around 40% increase in the stability limit with winglets covering 12% of the central span, and eight measured outputs for feedback. Response indices reduce substantially if a shift from constant to variable gain is performed at a certain wind speed. Controller design based on the one-element model, when applied to the more realistic multi-element model, results in substantially lesser response attenuation. Hence, cable vibration needs to be consider for the controller design. Keywords: Flutter, Cable-stayed bridge, Winglet, Rational function approximation, Variable gain output feedback, Cable vibration.

Observer-based sliding mode control for piezoelectric wing bending-torsion coupling flutter involving delayed output

An observer-based sliding mode control scheme is proposed for suppressing bending-torsion coupling flutter motions of a wing aeroelastic system with delayed output by using the piezoelectric patch actuators. The wing structure is modeled as a thin-walled beam, and the aerodynamics on the wing are computed by the strip theory. For the implementation of the control algorithm, the piezoelectric patch is bonded on the top surface of the beam to act as the actuator. Ignoring the effect of piezoelectric actuators on structural dynamics, only considering the bending moments induced by piezoelectric effects, the corresponding dynamic motion equation is established by using the Lagrange method with the assumed mode method. The flutter speed and frequency of the closed-loop system with time delay are obtained by solving a polynomial eigenvalue problem. An observer-based controller that does not dependent on time delay is developed for suppressing the flutter, and the corresponding gain matrices are obtained by solving linear matrix inequalities. The sufficient condition for the asymptotic stability of the closed-loop system is derived in terms of linear matrix inequalities. The simulation results demonstrate that the proposed control strategy based on the piezoelectric actuator is effective in wing bending-torsion coupling flutter system with a delayed output.

Aeroelastic Flutter and Sliding Mode Control of Wind Turbine Blade

Flutter is an important form of wind turbine blade failure. Based on damping analysis, synthetically considering aeroelastic vibration instability of the blade and using the parameter fitting method, the aeroelastic flutter model of the pretwisted blade is built, with the simulation and emulation of flap and lead-lag directions flutter of the 2D dangerous cross section realized. Through the construction of two controllers, modular combinatorial sliding mode controller and sliding mode controller based on LMI for parameterized design suppress blade aeroelastic flutter. The results show that a better control effect can be achieved on the premise of the design of the precise parameters of the controller: the proposed sliding mode control algorithm based on LMI can effectively act on the aeroelastic system of the blade, significantly reduce the vibration frequency, and make the aeroelastic system converge to an acceptable static difference in a short time, which proves the effectiveness of sliding mode control in suppressing high-frequency vibration under high wind speed.

Flutter mitigation of a superlong-span suspension bridge with a double-deck truss girder through wind tunnel tests

As flutter is a very dangerous wind-induced vibration phenomenon, the mitigation and control of flutter are crucial for the design of long-span bridges. In the present study, via a large number of section model wind tunnel tests, the flutter performance of a superlong-span suspension bridge with a double-deck truss girder was studied, and a series of aerodynamic and structural measures were used to mitigate and control its flutter instability. The results show that soft flutter characterized by a lack of an evident divergent point occurred for the double-deck truss girder. Upper central stabilizers on the upper deck, lower stabilizers below the lower deck, and horizontal flaps installed beside the bottoms of the sidewalks are all effective in suppressing flutter for this kind of truss girder. By combining the structural design with aerodynamic optimizations, a redesigned truss girder with widened upper carriers and sidewalks, and double lower stabilizers combined with the inspection vehicle rails is identified as the optimal flutter mitigation scheme. It was also found that the critical flutter wind speed increases with the torsional damping ratio, indicating that the dampers may be efficient in controlling soft flutter characterized by single-degree-of-freedom torsional vibration. This study aims to provide a useful reference and guidance for the flutter design optimization of long-span bridges with double-deck truss girders.

Improved fault diagnosis for aircraft flap control system based on bond graph

PurposeThis paper aims to improve the fault detection adaptive threshold of aircraft flap control system to make the system fault diagnosis more accurate.Design/methodology/approachAccording to the complex mechanical–electrical–hydraulic structure and the multiple fault modes of the aircraft flap control system, the advanced fault diagnosis method based on the bond graph (BG) model is presented, and based on the system diagnostic BG model, the parameter uncertainty intervals are estimated and a new adaptive threshold is constructed by linear fraction transformation.FindingsTo construct a more reasonable and accurate adaptive threshold range to more accurately detect system failures, some typical failure modes’ diagnosis process are selected and completed for verification; the simulation results show that the proposed method is effective and feasible for complex systems’ fault diagnosis.Practical implicationsThis study can provide a theoretical guidance and technical support for fault diagnosis of complex systems, which avoid misdiagnosis and missed diagnosis.Originality/valueThis study enables more accurate fault detection and diagnosis of complex systems when considering factors such as parameter uncertainty.

Short-Term Response of a Bridge-Winglet Sectional Model under Active Flutter Control

Active winglets, with a manually controlled attitude angle, can take advantage of the self-excited force to suppress the flutter tendency of a bridge girder. Previous studies mostly focused on the effectiveness and robustness under long-term closed-loop control. However, the deck-winglet system’s short-term response, due to the memory effect of the aerodynamic force, is of concern. A bridge sectional model with active winglets was developed to investigate this problem. Experiments with different phase shifts between the members of the winglet pair were carried out in a wind tunnel. We found that the influence residue of an instantaneous change of the control pattern lasted about three pitching cycles, indicating that a large control interval was acceptable for practical applications. A theoretical relationship between the control effect and control phase was derived to explain the results of the open-loop control. The system responses under different control intervals were analyzed by the closed-loop control, demonstrating that a large control interval was acceptable if some time-consuming algorithms are used in a practical bridge’s flutter control operation.

Flutter control of a streamlined box girder with active flaps

Flutter control is necessary in the design of a long-span bridge. With the help of active flaps, flutter control can suppress flutter vibration and increase aerodynamic stability. This study aims to build a theoretical framework for active flutter control using a system consisting of a streamlined box girder with adjacently mounted active flaps (noted as a “deck–flap system”). An adaptive expression was proposed for the system’s self-excited forces, and an identification method was established for obtaining the system flutter derivatives in consideration of the bluff characteristics of the bridge deck and the aerodynamic interactions between the bridge girder and flaps. Then, the suboptimal control algorithm was implemented into the deck–flap system to simultaneously stabilize the divergent oscillation at the designed wind speed. Based on the proposed approach, numerical simulations were conducted to investigate the system flutter derivatives and the effectiveness of the control law. A comparison between the critical speeds of the two-dimensional flutter analysis and a fluid–structure interaction simulation showed a satisfactory performance from the theoretical model and the reliability of the identification method. The vibrations of the deck–flap system were successfully suppressed by the controlled motions of the active flaps under the application of the suboptimal control algorithm. This study provides a reliable framework for conducting an analysis of active control for bridge flutter and for significantly increasing the flutter stability of a deck–flap system.

Evaluation of platelet-rich plasma gel as an angiogenesis-inducing agent in canineadvancement skin flaps

ABSTRACT: This work aimed to evaluate the effect of platelet-rich plasma (PRP) on advancement skin flaps in dogs regarding improvement of vascularization, with focus on increasing its viable area, since there are reports that it is a potential angiogenesis stimulator. The experimental group was composed of eight adult bitches, in which two advancement skin flaps were made in the ventral abdominal region. No product was applied in the control flap (CF), while PRP was used in the contralateral flap, called treated flap (TF). The areas were clinically evaluated every two days until the 7th postoperative day regarding skin color and presence of necrosis. At 10 days, both flaps were removed and submitted to histological examination and blood vessel morphometry. The vessels counted in each group were statistically analyzed by the F-test at 1% probability. Results showed no significant difference in macroscopic changes in the wound, or CF and TF vascularization, thus suggesting that PRP gel did not improve advancement skin flap angiogenesis in bitches under the experimental conditions in which this research was developed.

Active flutter control of thin walled wing-engine system using piezoelectric actuators

In the present study, control of a Thin Walled Beam (TWB) wing-engine system is examined applying piezoelectric actuators to enhance the performance of aeroelastic response. The composite piezoelectric governing equations of motion including the structure and electric effects are derived applying Hamilton's principle. Piezoelectric composite plate equations are added to the composite host wing-engine governing system of equations. The incompressible aerodynamic model based on Wagner's function is applied and the Ritz based solution methodology is employed. As a passive control approach, the effects of piezoelectric fiber angles are studied on the time domain response of the high-aspect-ratio wing-engine system. The linear quadratic Gaussian (LQG) control algorithm is applied as a closed-loop active control strategy to enhance the flutter response characteristics of the composite wing-engine system. Numerical results firstly, demonstrate the effectiveness of the active control strategy based on piezocomposite actuator on suppressing the flutter response of the composite wing-engine system and secondly, prove the effect of piezocomposite actuator location and fiber angle orientation on the closed-loop control performance.

Aerodynamic Countermeasure Schemes of Super Long-Span Suspension Bridges with Various Aspect Ratios

The purpose of this study is to investigate the flutter control scheme of super long-span bridges with various aspect ratios (e.g. width to height (B/H)) using passive aerodynamic countermeasures. Through a series of wind tunnel testing and theoretical analysis, three types of passive aerodynamic countermeasures, i.e. vertical central stabilizer (VCS), wind barrier and inspection rail, were investigated for five typical aspect ratios of a closed-box girder bridge. The results show that both the aspect ratio and flutter critical wind speed generally increase with the decrease of the ratio of torsional and vertical frequencies of the bridge. In the case of an aspect ratio of 8.9, a downward VCS (DVCS) has a much better flutter performance than that of an upward VCS (UVCS) because aerodynamic damping of Part A and Part D could produce a higher heaving degree of freedom (DOF) participation level. Furthermore, the position variation of wind barriers is superior to their shape variation for the bridge with an aspect ratio of 8.3, and the flutter performance of the girder with a combination of the wind barrier (WB3P3) and UDVCS with 0.3[Formula: see text]h/H DVCS appears to be better than that without countermeasures. In addition, the installation of an inspection rail near the bottom point of an inclined-web (IR3) has the best flutter control effect among four positions of inspection rails.

LO08: A randomized, controlled comparison of electrical versus pharmacological cardioversion for emergency department patients with atrial flutter

Acute atrial flutter has one-tenth the prevalence of acute atrial fibrillation in the emergency department (ED) but shares many management strategies. Our aim was to compare conversion from acute atrial flutter to sinus rhythm between pharmacological cardioversion followed by electrical cardioversion (Drug-Shock), and electrical cardioversion alone (Shock-Only). We conducted a randomized, blinded, placebo-controlled comparison of attempted pharmacological cardioversion with IV procainamide followed by electrical cardioversion if necessary, and placebo infusion followed by electrical cardioversion. We enrolled stable patients with a primary diagnosis of acute acute atrial flutter at 11 academic EDs. The primary outcome was conversion to normal sinus rhythm. From July 2013 to October 2018, we enrolled 76 patients, and none were lost to follow-up. Comparing the Drug-Shock to the Shock-Only group, conversion to sinus rhythm occurred in 33 (100%) versus 40 (93%) (absolute difference 7.0%; 95% CI -0.6 to 14.6; P = 0.25). Median time to conversion from start of infusion in the Drug-Shock group was 24min (IQR 21-82) but only 9 (27%) cases were converted with IV procainamide. Patients in both groups had similar outcomes at 14days; there were no strokes or deaths. This trial found that the Drug-Shock strategy is potentially superior but that either approach to immediate rhythm control in the ED for patients with acute acute atrial flutter is highly effective, rapid, and safe in restoring sinus rhythm and allowing patients to go home and return to normal activities. Unlike the case of atrial fibrillation, we found that IV procainamide alone was infrequently effective.

8 th Symposium on Mechanics of Slender Structures 2019 (MoSS2019)

8 th Symposium on Mechanics of Slender Structures 2019 (MoSS2019)

Aeroelastic flutter control of a bridge using rotating mass dampers and winglets

Flutter control of a bridge deck section using a combination of aerodynamic and mechanical measures, that is controllable winglets and rotating mass dampers, is considered. Deck and winglets are considered as flat plates for their aerodynamics. Self-excited wind forces are represented in the time domain using the Scanlan–Tomko model with Roger’s rational function approximation for flutter derivatives. Winglet rotation relative to the deck is the control input generated by the variable-gain output feedback controller that uses vertical and torsional displacements of the deck as measured outputs. Control using winglets enhances the critical speed to twice the uncontrolled flutter speed. Further attenuation of vertical response is obtained by using rotating mass dampers configured to provide only a resultant vertical force due to counter-rotating unbalanced masses. The rotors are driven at a constant angular speed, and start–stop criteria are applied. This generates additional vertical force on the deck that is mostly out of phase with its vertical velocity. It yields better control than the damper operated in a continuous rotation mode for a fixed number of cycles. A maximum reduction of 15% in root mean square vertical response is obtained when compared with control using winglets only.

Modeling, Design, and Flight Testing of Three Flutter Controllers for a Flying-Wing Drone

Three flutter-suppression designs for a flexible flying-wing research drone are discussed, along with the modeling and flight-test results. The drone, with wing span of 10 feet, aspect ratio of almost 9, and control surfaces along the entire wing trailing edges, was developed for flight research into the modeling and control of highly elastic aircraft. The low-speed vehicle was designed to exhibit body-freedom flutter in its flight envelope. The all-important dynamic modeling of the vehicle, used for analysis and control design, is based on a mean-axis formulation and quasi-steady aerodynamics, with the nondimensional aerodynamic/aeroelastic coefficients updated from flight tests. Flutter-modeling results were found to agree with those from NASTRAN and flight tests. The three different flutter-suppression approaches include both fairly classical and multivariable methods, all fixed gains but with different architectures. The primary control-design objective was to augment the damping of the eventual flutter mode at a design condition below the open-loop flutter speed, for safety of flight, and to achieve a closed-loop flutter speed at least as high as the open-loop flutter speed. Analysis and flight tests revealed that all three designs achieved these design goals. In addition, two of these designs actually expanded the flutter boundary. The theoretical stability robustness of all three controllers at the design flight condition is quite good, but there are differences in controller complexity. Research is currently underway to further expand the flutter boundary using all three design approaches.

Steady-Suction-Based Flow Control of Flutter of Long-Span Bridge

The present wind tunnel study focuses on the effects of the steady-suction-based flow control method on the flutter performance of a 2DOF bridge deck section model. The suction applied to the bridge model was released from slots located at the girder bottom. The suction rates of all slots along the span were equal and constant. A series of test cases with different combinations of suction slot positions, suction intervals, and suction rates were studied in detail for the bridge deck model. The experimental results showed that the steady-suction-based flow control method could improve the flutter characteristics of the bridge deck with a maximal increase in the critical flutter speed of up to 10.5%. In addition, the flutter derivatives (FDs) of the bridge deck with or without control were compared to investigate the fundamental mechanisms of the steady-suction-based control method. According to the results, installing a suction control device helps to strengthen aerodynamic damping, which is the primary cause for enhanced flutter performance of bridge decks.

Passive flutter suppression of damaged smart laminated composite plate using active fiber composite layer

This research addresses the effect of damage on flutter characteristics of laminated composite plate and passive control of flutter with active fiber composite (AFC) layer bonded over the substrate. A finite element model coupled with MSC.Nastran is developed to calculate the flutter characteristics of smart laminated composite plate. The damage characterized based on anisotropic damage formulation is incorporated through the finite element model. The effect of orientation and location of damage on flutter characteristics of laminated plate is studied. Further AFC layer with interdigitated electrode, which is more adaptive and efficient than conventional monolithic piezoelectric, is considered over the top of substrate layer to act as actuator. The enhancement of the flutter characteristics lost due to damage, is investigated by activating AFC layer with applied voltage. The AFC layer is observed to have great potential to regain the flutter strength of composite plate. Communicated by Chandrika Prakash Vyasarayani.

Tympanomeatal flap creation in endoscopic stapedotomy: cautery vs. cold instrumentation.

Bleeding is one of the most challenging issues for surgeons performing endoscopic stapedotomy. During creation and elevation of the tympanomeatal flap (TMF) prevention or control of bleeding greatly facilitates the safety and comfort in the next steps of the surgery. The aim of this study was to compare the effects of cautery versus cold instrumentation during creation of TMF at endoscopic stapedotomy surgery. We investigated 15 patients TMF created with cautery and 14 patients with cold instrument, and compared bleeding scores, operation time, postoperative hearing, pain and complications between groups. The mean bleeding score was significantly lower in cautery incised patients compared to cold instrument patients (1.2 ± 0.9 vs. 2.3 ± 1, p = 0.005). Mean duration of surgery was also significantly shorter in cautery used patients (35.3 ± 6.8 vs. 48.8 ± 9.2min, p < 0.001). There was no significant difference between postoperative pain, complications, wound healing, and auditory outcomes. Cautery may be a better choice for the creation of TMF in endoscopic stapedotomy surgery due to reduced bleeding, shorter operation time and increased comfort without causing any complications.

Flutter and Thermal Buckling Properties and Active Control of Functionally Graded Piezoelectric Material Plate in Supersonic Airflow

This paper is devoted to investigate the flutter and thermal buckling properties of the functionally graded piezoelectric material (FGPM) plate in supersonic airflow, and the active flutter control is carried out under different temperature fields. The piezoelectric material component of the FGPM plate has gradient changes along the thickness, such as piezoelectricity and dielectric coefficients. The supersonic piston theory is used to evaluate the aerodynamic pressure. Based on the first-order shear deformation theory and Hamilton’s principle with the assumed mode method, the equation of motion of the structural system is deduced. The effect of aerodynamic pressure on the frequency and damping ratio of the FGPM plate is analyzed. Moreover, the flutter and thermal buckling properties of the FGPM and pure metal plates are compared to show the superior aerothermoelastic properties of the FGPM plates. The influences of volume fraction exponent and temperature on the flutter and thermal buckling properties of the FGPM plate are also examined in detail. The LQR controller is adopted to achieve active flutter control. The simulation results show that the present control method can largely improve dynamic stability of the FGPM plate in supersonic airflow and high-temperature environment.

Flutter Fault-Tolerant Control with Observer Considering Actuator Faults and Time Delay

To suppress airfoil flutter, a lot of control methods have been proposed, such as classical control methods and optimal control methods. However, these methods did not consider the influence of actuator faults. We designed a new finite-time H∞ adaptive fault-tolerant flutter controller by radial basis function neural network technology and adaptive fault-tolerant control methods, taking into account actuator faults, actuator saturation, modeling uncertainties and external disturbances. The theoretical section of this paper is about airfoil flutter dynamic modeling and the design of adaptive fault-tolerant controller. Lyapunov function and linear matrix inequality are employed to prove the stability of the proposed control method of this paper. The numeral simulation section further proves the effectiveness and robustness of the proposed control algorithm of this paper.

Comparative Effectiveness of Different Interventions of Perivascular Hyaluronidase.

Soft-tissue necrosis caused by vascular compromise is a frequent and troublesome complication of hyaluronic acid filler injection. Hyaluronidase has been proposed as a treatment for this condition. This study aimed to determine the effective dose and administration interval of hyaluronidase injection in a skin necrosis animal model. New Zealand rabbits were used to simulate the hyaluronic acid-associated vascular occlusion model. Hyaluronic acid filler (0.1 ml) was injected into the central auricular artery to create an occlusion. Three rabbit auricular flaps were injected with 500 IU of hyaluronidase once (group A) and three flaps each were injected at 15-minute intervals with 250 IU of hyaluronidase twice (group B), 125 IU of hyaluronidase four times (group C), 100 IU of hyaluronidase five times (group D), and 75 IU of hyaluronidase seven times (group E), all at 24 hours after occlusion. No intervention was administered after occlusion in the control group. Flap fluorescence angiography was performed immediately after hyaluronidase injection and on postoperative days 2, 4, and 7. Flap necrotic areas were analyzed. All control and experimental flaps demonstrated total occlusion after hyaluronic acid injection. The average total survival rate (positive area/total area ×100 percent) of control flaps was 37.61 percent. For experimental groups, the average total survival rates were 74.83 percent, 81.49 percent, 88.26 percent, 56.48 percent, and 60.69 percent in groups A through E, respectively. A better prognosis can be obtained by administering repeated doses rather than a single high dose of hyaluronidase.