Artykuły w czasopismach: „Flutter Margin”

1

Abbasi, A. A., i J. E. Cooper. "Statistical evaluation of flutter boundaries from flight flutter test data". Aeronautical Journal 113, nr 1139 (styczeń 2009): 41–51. http://dx.doi.org/10.1017/s0001924000002761.

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AbstractA methodology is described that determines the statistical confidence bounds on the results from flight flutter tests: modal parameter estimates, flutter margin values and flutter speed estimates, without the need for Monte-Carlo simulation. The approach is based on least squares statistics and eigenvalue perturbation theory applied to the various stages of the analysis process, starting with frequency and damping estimation through to the flutter margin calculations. The technique is demonstrated upon a number of data sets from aeroelastic simulations of flight flutter tests.

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Zafari, E., MM Jalili i A. Mazidi. "Analytical nonlinear flutter and sensitivity analysis of aircraft wings subjected to a transverse follower force". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, nr 4 (1.02.2018): 1503–15. http://dx.doi.org/10.1177/0954410017754171.

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In the present study, the nonlinear aeroelastic and sensitivity analysis of high aspect ratio wings subjected to a transverse follower force are discussed. A nonlinear structural model of wings is extracted and coupled with an incompressible unsteady aerodynamic model. The governing equations of motions are obtained via Hamilton’s principle and Galerkin method. Utilizing the method of multiple-scales, analytical approximate flutter response of the system is obtained. For validation, the analytical solution is compared with numerical solution and good agreement is observed. The time history of the tip displacement and tip twist solution are plotted for different airspeeds. Effects of follower force and its spanwise location and also the wing geometric characteristics on the flutter margin are discussed. Moreover, flutter margin sensitivity to different design parameters is analyzed. Results indicate that increasing the wing chord makes the system unstable. Furthermore, according to the analytical solution, effects of the wing chord and mass per unit length on the flutter margins are more important than the other system parameters.

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3

Niblett, LL T. "The fundamentals of body-freedom flutter". Aeronautical Journal 90, nr 899 (listopad 1986): 373–77. http://dx.doi.org/10.1017/s0001924000015979.

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SummaryThe object of this paper is to uncover the nature of the destabilising coupling that is the major cause of body-freedom flutter and to see whether a simple cure for the flutter can be found. To do this frequency-coalesence theory is applied to a simple aircraft. It is shown that the aircraft is liable to flutter if it has a sweptforward wing and a positive ‘tail-off’ cg margin or a sweptback wing and a negative cg margin but a simple cure for the flutter does not appear to exist.

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Sudha, U. P. V., G. S. Deodhare i K. Venkatraman. "A comparative assessment of flutter prediction techniques". Aeronautical Journal 124, nr 1282 (27.10.2020): 1945–78. http://dx.doi.org/10.1017/aer.2020.84.

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ABSTRACTTo establish flutter onset boundaries on the flight envelope, it is required to determine the flutter onset dynamic pressure. Proper selection of a flight flutter prediction technique is vital to flutter onset speed prediction. Several methods are available in literature, starting with those based on velocity damping, envelope functions, flutter margin, discrete-time Autoregressive Moving Average (ARMA) modelling, flutterometer and the Houbolt–Rainey algorithm. Each approach has its capabilities and limitations. To choose a robust and efficient flutter prediction technique from among the velocity damping, envelope function, Houbolt–Rainey, flutter margin and auto-regressive techniques, an example problem is chosen for their evaluation. Hence, in this paper, a three-degree-of-freedom model representing the aerodynamics, stiffness and inertia of a typical wing section is used(1). The aerodynamic, stiffness and inertia properties in the example problem are kept the same when each of the above techniques is used to predict the flutter speed of this aeroelastic system. This three-degree-of-freedom model is used to generate data at speeds before initiation of flutter, during flutter and after occurrence of flutter. Using these data, the above-mentioned flutter prediction methods are evaluated and the results are presented.

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Yang, Zhi Chun, i Ying Song Gu. "Robust Flutter Analysis of an Airfoil with Flap Freeplay Uncertainty". Advanced Materials Research 33-37 (marzec 2008): 1247–52. http://dx.doi.org/10.4028/www.scientific.net/amr.33-37.1247.

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Modern robust flutter method is an advanced technique for flutter margin estimation. It always gives the worst-case flutter speed with respect to potential modeling errors. Most literatures are focused on linear parameter uncertainty in mass, stiffness and damping parameters, etc. But the uncertainties of some structural nonlinear parameters, the freeplay in control surface for example, have not been taken into account. A robust flutter analysis approach in μ-framework with uncertain nonlinear operator is proposed in this study. Using describing function method the equivalent stiffness formulation is derived for a two dimensional wing model with freeplay nonlinearity in its flap rotating stiffness. The robust flutter margin is calculated for the two dimensional wing with flap freeplay uncertainty and the results are compared with that obtained with nominal parameter values. It is found that by considering the perturbation of freeplay parameter more conservative flutter boundary can be obtained, and the proposed method in μ-framework can be applied in flutter analysis with other types of concentrated nonlinearities.

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6

Torii, Hiroshi, i Yuji Matsuzaki. "Flutter Margin Evaluation for Discrete-Time Systems". Journal of Aircraft 38, nr 1 (styczeń 2001): 42–47. http://dx.doi.org/10.2514/2.2732.

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MATSUDAIRA, Yasuaki, Hiroyuki NAKAGAWA, Hikaru YOSHIDA i Hiromichi OBARA. "Supercavitation Hydrofoil Performance and Torsional Flutter Margin." Transactions of the Japan Society of Mechanical Engineers Series B 66, nr 648 (2000): 2079–86. http://dx.doi.org/10.1299/kikaib.66.648_2079.

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Corpas, J. L. Casado, i J. López Díez. "Flutter margin with non-linearities: Real-time prediction of flutter onset speed". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 222, nr 6 (czerwiec 2008): 921–29. http://dx.doi.org/10.1243/09544100jaero251.

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Saputra, Angga Dwi, i R. Wibawa Purabaya. "Prediction of Flutter Boundary Using Flutter Margin for The Discrete-Time System". Journal of Physics: Conference Series 1005 (kwiecień 2018): 012019. http://dx.doi.org/10.1088/1742-6596/1005/1/012019.

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Price, S. J., i B. H. K. Lee. "Evaluation and Extension of the Flutter-Margin Method for Flight Flutter Prediction". Journal of Aircraft 30, nr 3 (maj 1993): 395–402. http://dx.doi.org/10.2514/3.56887.

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Casado Corpas, JL, A. Sanz-Lobera, I. González-Requena i L. Sevilla. "A revision of the flutter margin method to predict in real-time the limit cycle oscillations onset speed with structural freeplay present in the plunge axis". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 231, nr 1 (6.08.2016): 124–42. http://dx.doi.org/10.1177/0954410016638867.

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Computational fluid dynamic and order reducing methods have been extensively applied to predict the flutter onset speed of several types of aircrafts. However, the accuracy required by certification standards still ascribes flight testing as the only method available that safely validates the flight envelope of an aircraft. In particular, free-flutter conditions must be demonstrated in the target flight envelope, and several methods have been developed to determine the flutter onset speed in real-time when expanding the envelope during flight testing. Among the methods, the damping versus velocity technique combined with a flutter margin implementation remains the most common technique used for envelope expansion. Even with the popularity and “easy to implement” characteristics of this method, several shortcomings can adversely affect the identification of non-stable conditions during envelope expansion. Notably, the limit cycle oscillations conditions, distinct from flutter, cannot be accurately identified. This study proposes to apply a similar methodology to the flutter margin to anticipate limit cycle oscillations associated with freeplay in the plunge axis of a bi-dimensional airfoil that is aeroelastically representative of the tested aircraft. Analytical considerations are conducted to support this new approach, and a computer model is used to validate the proposed methodology.

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12

Poirel, Dominique, Shane Dunn i Jay Porter. "Flutter-Margin Method Accounting for Modal Parameters Uncertainties". Journal of Aircraft 42, nr 5 (wrzesień 2005): 1236–43. http://dx.doi.org/10.2514/1.7778.

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Roizner, Federico, i Moti Karpel. "Parametric Flutter Margin Method for Aeroservoelastic Stability Analysis". AIAA Journal 56, nr 3 (marzec 2018): 1011–22. http://dx.doi.org/10.2514/1.j056514.

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Baldelli, Dario H., Hirobumi Ohta, Hiroshi Matsushita, Masataka Hashidate i Kenichi Saitoh. "Flutter margin augmentation synthesis using normalized coprime factors approach". Journal of Guidance, Control, and Dynamics 18, nr 4 (lipiec 1995): 802–11. http://dx.doi.org/10.2514/3.21462.

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Khalil, Mohammad, Dominique Poirel i Abhijit Sarkar. "Bayesian analysis of the flutter margin method in aeroelasticity". Journal of Sound and Vibration 384 (grudzień 2016): 56–74. http://dx.doi.org/10.1016/j.jsv.2016.07.016.

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Lu, P. J., i S. K. Chen. "Evaluation of Acoustic Flutter Suppression for Cascade in Transonic Flow". Journal of Engineering for Gas Turbines and Power 124, nr 1 (1.11.2000): 209–19. http://dx.doi.org/10.1115/1.1365933.

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Flutter suppression via actively excited acoustic waves is a new idea proposed recently. The high flutter frequency (typically 50–500 Hz for a fan blade) and stringent space constraint make conventional mechanical type flutter suppression devices difficult to implement for turbomachines. Acoustic means arises as a new alternative which avoids the difficulties associated with the mechanical methods. The objective of this work is to evaluate numerically the transonic flutter suppression concept based on the application of sound waves to two-dimensional cascade configuration. This is performed using a high-resolution Euler code based on a dynamic mesh system. The concept has been tested to determine the effectiveness and limitations of this acoustic method. In a generic bending-torsion flutter study, trailing edge is found to be the optimal forcing location and the control gain phase is crucial for an effective suppression. The P&W fan rig cascade was used as the model to evaluate the acoustic flutter suppression technique. With an appropriate selection of the control logic the flutter margin can be enlarged. Analogous to what were concluded in the isolated airfoil study, for internal excitation, trailing-edge forcing was shown to be optimal since the trailing-edge receptivity still works as the dominant mechanism for generating the acoustically induced airloads.

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17

MATSUDAIRA, Yasuaki, i Naoto OKAZAKI. "Fluid Force and Flutter Margin of a Pitching Hydrofoil in Subcavitation Region." Transactions of the Japan Society of Mechanical Engineers Series B 63, nr 613 (1997): 2938–44. http://dx.doi.org/10.1299/kikaib.63.2938.

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Schildkamp, Roderick, Jing Chang, Jurij Sodja, Roeland De Breuker i Xuerui Wang. "Incremental Nonlinear Control for Aeroelastic Wing Load Alleviation and Flutter Suppression". Actuators 12, nr 7 (9.07.2023): 280. http://dx.doi.org/10.3390/act12070280.

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This paper proposes an incremental nonlinear control method for an aeroelastic system’s gust load alleviation and active flutter suppression. These two control objectives can be achieved without modifying the control architecture or the control parameters. The proposed method has guaranteed stability in the Lyapunov sense and also has robustness against external disturbances and model mismatches. The effectiveness of this control method is validated by wind tunnel tests of an active aeroelastic parametric wing apparatus, which is a typical wing section containing heave, pitch, flap, and spoiler degrees of freedom. Wind tunnel experiment results show that the proposed nonlinear incremental control can reduce the maximum gust loads by up to 46.7% and the root mean square of gust loads by up to 72.9%, while expanding the flutter margin by up to 15.9%.

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19

Pizzoli, Marco, Francesco Saltari i Franco Mastroddi. "Linear and Nonlinear Reduced Order Models for Sloshing for Aeroelastic Stability and Response Predictions". Applied Sciences 12, nr 17 (31.08.2022): 8762. http://dx.doi.org/10.3390/app12178762.

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This paper makes use of sloshing reduced-order models to investigate the effects of sloshing dynamics on aeroelastic stability and response of flying wing structure. More specifically, a linear frequency-domain operator derived by an equivalent mechanical model is used to model lateral (linear) sloshing dynamics whereas data-driven neural-networks are used to model the vertical (nonlinear) sloshing dynamics. These models are integrated into a formulation that accounts for both the rigid and flexible behavior of aircraft. A time domain representation of the unsteady aerodynamics is achieved by rational function approximation of the fully unsteady aerodynamics obtained via the doublet lattice method. The case study consists of the so called Body Freedom Flutter research model in two different configurations with one or two tanks partially filled with liquid with a mass comprising 25% of the aircraft structure. The results show that linear sloshing dynamics are able to change the stability margin of the aircraft in addition to having non-negligible effects on rigid body dynamics. On the other hand, vertical sloshing acts as a nonlinear damper and eventually provides limit cycle oscillations after flutter onset.

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20

Ueda, Takeo. "AEROELASTIC ANALYSIS CONSIDERING STRUCTURAL UNCERTAINTY". Aviation 9, nr 1 (31.03.2005): 3–7. http://dx.doi.org/10.3846/16487788.2005.9635889.

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Uncertainties in aero elastic analysis are investigated. In aero elastic analysis, we usually find divergence speed or flutter speed by using deterministic equations of motion for elastic wings of aircraft. If any parameter in these equations is sensitive to the critical speed, we should treat it carefully since inaccuracy is inevitable in the production process. Tragic failure may occur if the margin is small. Therefore, it is important to know in the analysis the effects of uncertainties of the critical values when they play a critical role in the design. The sensitivity of parameters in aero elastic analysis is not simple even in linear analysis. It is not always possible to have an analytic form of the sensitivity of uncertainty. In order to evaluate the structural sensitivity of aero elastic phenomena, we have to resort to numerical calculations with uncertain parameters having some random deviations, i.e. the so‐called Monte Carlo simulation. In the present study, the divergence speed and flutter speed of a typical wing section with structural uncertainties are discussed, and some results of calculations with scattering parameters in Gaussian distribution will be presented.

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21

Rahme, Marc M., Elise Jalil, Martin Laflamme i Teresa Kus. "Effect of autonomic neurotransmitters on excitable gap composition in canine atrial flutter". Canadian Journal of Physiology and Pharmacology 79, nr 1 (1.01.2001): 13–17. http://dx.doi.org/10.1139/y00-109.

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Atrial arrhythmias are believed to be influenced by autonomic nervous system tone. We evaluated the effects of sympathetic and parasympathetic activation on atrial flutter (AFl) by determining the effects of norepinephrine (NE) and acetylcholine (ACh) on the composition of the excitable gap. A model of reentry around the tricuspid valve was produced in 17 chloralose anesthetized dogs using a Y-shaped lesion in the intercaval area that extended to the right atrial appendage. Excitable gap characteristics were determined during AFl by scanning diastole with a single premature extrastimulus at progressively shorter coupling intervals to define the reset-response curve. Measurements were made during a constant infusion of NE (15 µg/min) into the right coronary artery and repeated during ACh infusion (2 µg/min) following a 15 min recovery period. The excitable gap (27 ± 1 ms) was significantly (P < 0.001) increased by NE (34 ± 1 ms) and ACh (50 ± 2 ms). The fully excitable portion (7 ± 1 ms) was also significantly (P < 0.001) increased by NE (17 ± 1 ms) and ACh (43 ± 2 ms). We conclude that both neurotransmitters increase the safety margin of full excitability ahead of the wavefront, demonstrating that parasympathetic and sympathetic activation can facilitate the persistence of this refractory atrial arrhythmia.Key words: atrial flutter, acetylcholine, norepinephrine, excitable gap.

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22

Piche´, R. "On the Symmetrizability of Structural Control Systems With Noncolocated Sensors and Actuators". Journal of Dynamic Systems, Measurement, and Control 112, nr 2 (1.06.1990): 249–52. http://dx.doi.org/10.1115/1.2896132.

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In problems of active vibration control of elastic structures, it is known that systems with symmetric feedback matrices (realized using colocated dual sensor/actuator pairs) possess many desirable properties, including real eigenvalues, infinite gain margin, no flutter instability, and the lower-bound character of Rayleigh estimation formulas. In this paper, we consider systems with nonsymmetric feedback matrices which may be transformed, via a similarity transformation, into symmetric systems. We propose constructive conditions to recognize a-priori which systems are symmetrizable. It is shown that lumped-mass structures are not symmetrizable. The results are applied in an example showing how to place sensors and actuators on a structure in such locations that the system remains symmetrizable.

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23

Parafes’, S. G. "About revising the computational dynamic scheme of an unmanned aerial vehicle based on the results of ground-based modal test operations in the aeroelasticity problems". Civil Aviation High Technologies 25, nr 3 (29.06.2022): 73–85. http://dx.doi.org/10.26467/2079-0619-2022-25-3-73-85.

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The problem of revising the computational dynamic scheme of an unmanned aerial vehicle (UAV), based on the results of ground-based modal test operations, in order to study the UAV flutter and to assess the aeroelastic stability of an UAV with an automatic control system (ACS), is considered. It is noted that at the design stage, when there is no UAV prototype or its units yet, the determination of modal characteristics, specifically natural frequencies, modes and generalized masses, is carried out using the computational dynamic scheme developed according to the design documentation. However, the similar computations, performed even with the use of modern finite-element software systems, do not give sufficiently precise values of the parameters of the UAV design elastic-mass schematization. In this regard, it is relevant and important to specify the parameters of the design schematization in conformity with data of ground test operations for UAV prototypes. The provisions, allowing us to achieve satisfactory results when revising the UAV computational dynamic scheme, are made. The criteria of revising are considered. The features of revising the computational dynamic scheme, while studying the flutter and aeroelastic stability of the ACS-fitted UAV, are presented. It is noted that along with the provisions that are universal for dynamic aeroelasticity problems, specifically for flutter, and related to compensating of natural frequencies, modes and coefficients of structural damping for the UAV model according to the results of ground modal tests. In the problems of aeroelastic stability study of the UAV equipped with the ACS, it is also crucial to correct the UAV body transfer function from the section, corresponding to the axis of controls rotation, to the section where ACS sensors are installed. This is because the UAV hull is an integral part of the UAV stabilization loop and significantly affects its stability margin. The example of revising the computational dynamic scheme of a maneuverable cruciform UAV is given.

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24

Xie, Chang Chuan, Jia Zhen Leng i Chao Yang. "Geometrical Nonlinear Aeroelastic Stability Analysis of a Composite High-Aspect-Ratio Wing". Shock and Vibration 15, nr 3-4 (2008): 325–33. http://dx.doi.org/10.1155/2008/957561.

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A composite high-aspect-ratio wing of a high-altitude long-endurance (HALE) aircraft was modeled with FEM by MSC/NASTRAN, and the nonlinear static equilibrium state is calculated under design load with follower force effect, but without load redistribution. Assuming the little vibration amplitude of the wing around the static equilibrium state, the system is linearized and the natural frequencies and mode shapes of the deformed structure are obtained. Planar doublet lattice method is used to calculate unsteady aerodynamics in frequency domain ignoring the bending effect of the deflected wing. And then, the aeroelastic stability analysis of the system under a given load condition is successively carried out. Comparing with the linear results, the nonlinear displacement of the wing tip is higher. The results indicate that the critical nonlinear flutter is of the flap/chordwise bending type because of the chordwise bending having quite a large torsion component, with low critical speed and slowly growing damping, which dose not appear in the linear analysis. Furthermore, it is shown that the variation of the nonlinear flutter speed depends on the scale of the load and on the chordwise bending frequency. The research work indicates that, for the very flexible HALE aircraft, the nonlinear aeroelastic stability is very important, and should be considered in the design progress. Using present FEM software as the structure solver (e.g. MSC/NASTRAN), and the unsteady aerodynamic code, the nonlinear aeroelastic stability margin of a complex system other than a simple beam model can be determined.

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25

Iannelli, Andrea, Mark Lowenberg i Andrés Marcos. "On the effect of model uncertainty on the Hopf bifurcation of aeroelastic systems". Nonlinear Dynamics 103, nr 2 (styczeń 2021): 1453–73. http://dx.doi.org/10.1007/s11071-020-06169-2.

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AbstractThis paper investigates the effect of model uncertainty on the nonlinear dynamics of a generic aeroelastic system. Among the most dangerous phenomena to which these systems are prone, Limit Cycle Oscillations are periodic isolated responses triggered by the nonlinear interactions among elastic deformations, inertial forces, and aerodynamic actions. In a dynamical systems setting, these responses typically emanate from Hopf bifurcation points, and thus a recently proposed framework, which address the problem of robustness from a nonlinear dynamics viewpoint, is employed. Briefly, the notion of robust bifurcation margin extends the concept of $$\mu $$ μ analysis technique from the robust control theory. The main contribution of this article is a systematic investigation of the numerous scenarios arising in the study of nonlinear flutter when uncertainties in the model are accounted for in the analyses. The advantages of adopting this framework include the possibility to: quantify relevant information for the determination of the nonlinear stability envelope; gain a more in-depth understanding of the physical mechanisms triggering subcritical and supercritical Hopf bifurcations; and reveal properties of the nominal system by identifying isolated branches not straightforward to detect with conventional numerical approaches.

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Roizner, Federico, Daniella E. Raveh i Moti Karpel. "Safe Flutter Tests Using Parametric Flutter Margins". Journal of Aircraft 56, nr 1 (styczeń 2019): 228–38. http://dx.doi.org/10.2514/1.c035045.

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Li, H. D., i L. He. "Toward Intra-Row Gap Optimization for One and Half Stage Transonic Compressor". Journal of Turbomachinery 127, nr 3 (10.01.2005): 589–98. http://dx.doi.org/10.1115/1.1928934.

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Multistage effects on both aerodynamics and aeromechanics have been identified as significant. Thus, design optimizations for both aerodynamic performance and aeromechanical stability should be done in the unsteady multistage environment. The key issue preventing such a procedure to be carried out is the enormous computing time cost of multistage unsteady simulations. In this paper, a methodology based on the single-passage shape-correction method integrated with an interface disturbance truncation technique has been developed. The capability, efficiency, and accuracy of the developed methodology have been demonstrated for a one and a half stage quasi-three-dimensional transonic compressor with realistic blade counts. Furthermore, the interface disturbance truncation technique enables us to separate multirow interaction effects from the upstream and the downstream, which makes it possible to superimpose different rotor upstream gap effects and rotor downstream gap effects on the middle row rotor aerodynamic damping. In addition, a gap influence coefficient approach has been developed for investigation of all the possible gap spacing combinations of M upstream stator-rotor gaps and N downstream rotor-stator gaps. Then the number of cases that need to be computed has been reduced from M×N to M+N, which saved substantial computing time. The optimization analysis shows significant damping variation (∼300%) within the chosen intrarow gap design space. The intrarow gap spacing could have either stabilizing or destabilizing effects so that the stabilizing axial spacing could be utilized to increase flutter-free margin in aeromechanical designs. The current approach also can be used for setting aeromechanical constraints for aerodynamic performance optimizations.

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Travaglini, Lorenzo, Sergio Ricci i Giampiero Bindolino. "PyPAD: a multidisciplinary framework for preliminary airframe design". Aircraft Engineering and Aerospace Technology 88, nr 5 (5.09.2016): 649–64. http://dx.doi.org/10.1108/aeat-02-2015-0061.

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Purpose The purpose of this paper is to describe the development of an integrated framework suitable for preliminary airframe design, called PyPAD (Python module for Preliminary Aircraft Design), providing the capability to define models to compute loads and to perform the structural sizing. Design/methodology/approach The modules developed until now allow for the definition of multi-fidelity aero-structural models starting from a Common Parametric Aircraft Configuration Schema (CPACS) input file and to compute static loads (trim) and flutter margin with minimum user effort. PyPAD take advantages of Abaqus-CAE, and the main functions are developed in Python, to take advantages of the simplicity in terms of software development and maintenance, but the core routines are developed in Fortran, taking advantages of parallel programming to get the best performances. Findings A complete test case, starting from the CPACS input and ending with the definition of structural, aerodynamic and aero-elastic models, with the computation of different design loads, is reported. An example will show that the framework developed is able to handle different problematics of the preliminary projects using quite complex global models. Practical implications All the tools developed in the framework, and the ones currently under development, could be a valid help during the preliminary design of a new aircraft, speeding up the iterative process and improving the design solution. Originality/value PyPAD is the first framework developed around Abaqus-CAE for the preliminary aircraft design and is one of the few tools looking at the different problematics involved in a preliminary airframe design: design, loads and aero-elasticity, sizing and multi-disciplinary optimization.

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Cipolla, Vittorio, Andri Dine, Andrea Viti i Vincenzo Binante. "MDAO and Aeroelastic Analyses of Small Solar-Powered UAVs with Box-Wing and Tandem-Wing Architectures". Aerospace 10, nr 2 (20.01.2023): 105. http://dx.doi.org/10.3390/aerospace10020105.

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The market of solar-powered Unmanned Aerial Vehicles (UAVs) for defence purposes and drone services is expected to grow by a factor of more than 2 in the next decade. From an aircraft design perspective, the main challenge is the scalability of the proposed architectures, which is needed to increase the payload capabilities. Beside some successful examples of wing-tail UAVs, some newcomers are developing prototypes with tandem-wing architectures, hence enlarging the possible design. The present paper aims to introduce a further step in this direction, taking also the box-wing architecture into account to show how the presence of wing tip joiners can provide benefits from the aeroelastic point of view. UAVs with take-off mass within 25 kg are considered and the main tools adopted are presented. These are an in-house developed Multi-Disciplinary Analysis and Optimization (MDAO) code called SD2020 and the open source aeroelastic code ASWING, both presented together with an assessment of their accuracy by means of higher fidelity numerical results. SD2020 results are presented for the case of small box-wing solar UAVs optimized to achieve the longest endurance, focusing on the strategy implemented to achieve feasible solutions under an assigned set of constraints. Further results are presented for comparable box-wing and tandem-wing UAVs from both the aerodynamic and aeroelastic standpoints. Whereas the aerodynamic advantages introduced by the box-wing are marginal, significant advantages result from the aeroelastic analyses which indicate that, if the joiners are removed from the box-wing configuration, safety margin from flutter speed is halved and the bending-torsion divergence occurs at relatively low speed values.

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30

Lind, Rick. "Flutter Margins for Multimode Unstable Couplings with Associated Flutter Confidence". Journal of Aircraft 46, nr 5 (wrzesień 2009): 1563–68. http://dx.doi.org/10.2514/1.40328.

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Roizner, Federico, i Moti Karpel. "Sensitivity of Aeroservoelastic Stability Characteristics Using Parametric Flutter Margins". Journal of Aircraft 56, nr 4 (lipiec 2019): 1387–97. http://dx.doi.org/10.2514/1.c035286.

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Acree, C. W., R. J. Peyran i Wayne Johnson. "Rotor Design Options for Improving Tiltrotor Whirl-Flutter Stability Margins". Journal of the American Helicopter Society 46, nr 2 (1.04.2001): 87–95. http://dx.doi.org/10.4050/jahs.46.87.

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Lind, Rick, i Marty Brenner. "Flutterometer: An On-Line Tool to Predict Robust Flutter Margins". Journal of Aircraft 37, nr 6 (listopad 2000): 1105–12. http://dx.doi.org/10.2514/2.2719.

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Karpel, M. "Sensitivity derivatives of flutter characteristics and stability margins for aeroservoelastic design". Journal of Aircraft 27, nr 4 (kwiecień 1990): 368–75. http://dx.doi.org/10.2514/3.25281.

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Lind, Rick, i Marty Brenner. "Robust Flutter Margins of an F/A-18 Aircraft from Aeroelastic Flight Data". Journal of Guidance, Control, and Dynamics 20, nr 3 (maj 1997): 597–604. http://dx.doi.org/10.2514/2.4082.

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Lewy, Zeev. "The function of the ammonite fluted septal margins". Journal of Paleontology 76, nr 1 (styczeń 2002): 63–69. http://dx.doi.org/10.1017/s0022336000017352.

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The fluted margins of ammonite septa were thought to resist the hydrostatic pressure upon the phragmocone while the ammonoid dived. However, ammonoids probably did not dive deeper than the extant nautilids, whose conchs, with the simple septa, sustain pressure correlative to depth of about 800 m. The backward and forward stretching lobes and saddles actually provide resistance to pressure perpendicular to the septum. Ammonoids lived for about three to five years, and septa were precipitated in intervals of nearly two weeks to two days, which explain the small dimensions of the scars of the adductor muscles, which were periodically detached and reattached. The weak hold between these small muscles and the buoyant conch was compensated for by the backward branching and expanding folds (forming the sutural lobes), into which the soft tissue penetrated and stiffened for a required period to firmly anchor the body to the conch throughout its whole circumference. The greater the complexity of the septa marginal fluting, the better the ammonoid could withstand the dragging force between the body and the buoyant conch, and hence the more aggressively the ammonoid predated and competed with other creatures.

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LEWY, ZEEV. "THE FUNCTION OF THE AMMONITE FLUTED SEPTAL MARGINS". Journal of Paleontology 76, nr 1 (styczeń 2002): 63–69. http://dx.doi.org/10.1666/0022-3360(2002)076<0063:tfotaf>2.0.co;2.

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Iannelli, Andrea, Mark Lowenberg i Andrés Marcos. "An extension of the structured singular value to nonlinear systems with application to robust flutter analysis". CEAS Aeronautical Journal 11, nr 4 (9.09.2020): 1057–69. http://dx.doi.org/10.1007/s13272-020-00469-4.

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Abstract The paper discusses an extension of $$\mu$$ μ (or structured singular value), a well-established technique from robust control for the study of linear systems subject to structured uncertainty, to nonlinear polynomial problems. Robustness is a multifaceted concept in the nonlinear context, and in this work the point of view of bifurcation theory is assumed. The latter is concerned with the study of qualitative changes of the steady-state solutions of a nonlinear system, so-called bifurcations. The practical goal motivating the work is to assess the effect of modeling uncertainties on flutter, a dynamic instability prompted by an adverse coupling between aerodynamic, elastic, and inertial forces, when considering the system as nonlinear. Specifically, the onset of flutter in nonlinear systems is generally associated with limit cycle oscillations emanating from a Hopf bifurcation point. Leveraging $$\mu$$ μ and its complementary modeling paradigm, namely linear fractional transformation, this work proposes an approach to compute margins to the occurrence of Hopf bifurcations for uncertain nonlinear systems. An application to the typical section case study with linear unsteady aerodynamic and hardening nonlinearities in the structural parameters will be presented to demonstrate the applicability of the approach.

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Taylor, N. V., C. B. Allen, A. Gaitonde i D. P. Jones. "A structure-coupled CFD method for time-marching flutter analysis". Aeronautical Journal 108, nr 1086 (sierpień 2004): 389–401. http://dx.doi.org/10.1017/s0001924000000208.

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AbstractAeroelastic analysis is a critical area of the aircraft design process, as a good understanding of the dynamic behaviour of the wing structure is essential to safe operation of the vehicle. The inevitable inaccuracies present in the modelling of such phenomena impose mass penalties, as large safety margins are necessitated, which in turn lead to overly stiff designs. In an effort to reduce the uncertainty in analysis methods, fully coupled CFD and structural models are under widespread development. This paper describes the results produced by such a system for a series of test cases based on the AGARD445.6 and MDO wings. Results relating to the latter are of particular interest, as significant variations were found to be produced by the different methodologies used in previous studies, the precise cause of which could not be isolated. In an effort to provide this isolation, a detailed description of the method used is given, including the interpolation scheme between the structural model and the aerodynamic surface, and particular attention is given to the issue of aerofoil shape preservation.

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Clark, Jathan, Mark Murray-Flutter i Tyler Berger. "Book Reviews". Armax: The Journal of Contemporary Arms VIII, nr 2 (31.01.2023): 103–8. http://dx.doi.org/10.52357/armax98640.

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Kunstoffe: A Collector’s Guide to German World War II Plastics and Their Markings Reviewed by: Jathan Clark W. Darrin Weaver. Atglen: Schiffer Military, 2008. ISBN 978-0-7643-2923-4. 176 pp., numerous col. & b. & w. illus. $40. Sniping Rifles in World War I Reviewed by: Mark Murray-Flutter Martin Pegler. Oxford: Osprey Publishing, 2022. ISBN 978-1-4728-5076-8. 80 pp., numerous col. and b. & w. illus. £14.99 (paperback). Gun Barons: The Weapons That Transformed America and the Men Who Invented Them Reviewed by: Tyler Berger John Bainbridge, Jr. New York: St. Martin’s Press, 2022. ISBN 978-1-250-26686-6. 352 pp., 23 non-col. illus. $29.99 (hardcover).

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Prabhu, L., i J. Srinivas. "Modeling of flutter stability margins in an aerofoil cantilever wing with multiple engines mounts under inherent structural nonlinearities". Engineering Science and Technology, an International Journal 21, nr 5 (październik 2018): 1034–46. http://dx.doi.org/10.1016/j.jestch.2018.07.001.

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Le Heron, D. P., P. Dietrich, M. E. Busfield, C. Kettler, S. Bermanschläger i B. Grasemann. "Scratching the surface: Footprint of a late Carboniferous ice sheet". Geology 47, nr 11 (23.09.2019): 1034–38. http://dx.doi.org/10.1130/g46590.1.

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Abstract Field observations in conjunction with aerial images from an unmanned aerial vehicle were used to create the first map of a glacial unconformity underlying the late Carboniferous Dwyka Group of South Africa. Crosscutting relationships reveal that the glacial unconformity at Oorlogskloof, in which flutes, grooves, and striae were ploughed into unconsolidated sand, formed in a three-phased process charting a periodic shift in the locus of subglacial erosion. The unconformity formed by a periodically decoupled ice sheet in a probable tidewater setting. This model contrasts with earlier views that the structures simply record progressive ice-margin liftoff during transgression, and they provide unique insight into the complex temporal development of a 300 Ma subglacial environment.

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Polyak, Leonid, Dennis A. Darby, Jens F. Bischof i Martin Jakobsson. "Stratigraphic constraints on late Pleistocene glacial erosion and deglaciation of the Chukchi margin, Arctic Ocean". Quaternary Research 67, nr 2 (marzec 2007): 234–45. http://dx.doi.org/10.1016/j.yqres.2006.08.001.

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AbstractAt least two episodes of glacial erosion of the Chukchi margin at water depths to ∼ 450 m and 750 m have been indicated by geophysical seafloor data. We examine sediment stratigraphy in these areas to verify the inferred erosion and to understand its nature and timing. Our data within the eroded areas show the presence of glaciogenic diamictons composed mostly of reworked local bedrock. The diamictons are estimated to form during the last glacial maximum (LGM) and an earlier glacial event, possibly between OIS 4 to 5d. Both erosional events were presumably caused by the grounding of ice shelves originating from the Laurentide ice sheet. Broader glaciological settings differed between these events as indicated by different orientations of flutes on eroded seafloor. Postglacial sedimentation evolved from iceberg-dominated environments to those controlled by sea-ice rafting and marine processes in the Holocene. A prominent minimum in planktonic foraminiferal δ18O is identified in deglacial sediments at an estimated age near 13,000 cal yr BP. This δ18O minimum, also reported elsewhere in the Amerasia Basin, is probably related to a major Laurentide meltwater pulse at the Younger Dryas onset. The Bering Strait opening is also marked in the composition of late deglacial Chukchi sediments.

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Le Heron, Daniel Paul, Christoph Kettler, Bethan J. Davies, Lars Scharfenberg, Lukas Eder, Michael Ketterman, Gerit E. U. Griesmeier i in. "Rapid geomorphological and sedimentological changes at a modern Alpine ice margin: lessons from the Gepatsch Glacier, Tirol, Austria". Journal of the Geological Society 179, nr 3 (28.10.2021): jgs2021–052. http://dx.doi.org/10.1144/jgs2021-052.

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The Gepatsch Glacier in Tirol (Austria) is a rapidly retreating valley glacier whose host valley and forefield reveal subglacial, proglacial, and reworked sediment–landform assemblages. Structures include roches moutonées develop on gneiss, compound bedrock-sediment bedforms (crag and tail structures), flutes, and small diamicton ridges. The glacial sediments and landforms are undergoing incision and terrace development by meltwater streams. Glacial geomorphological and surface geological maps, in concert with elevation models of difference between July 2019 and July 2020 highlight considerable changes to the forefield over a 12-month time period. Till exposed within the last 20 years has undergone substantial mass wasting and re-deposition as subaerial mass flows, or reworked into stream deposits. The lee sides of many roches moutonées completely lack subglacial sediment, and instead contain a sand and gravel deposit interpreted to result from glaciofluvial deposition. Thus, insights into the rates of erosion and deposition in a complex, proglacial setting, allow some of these processes to be quantified for the first time. Repeated monitoring of glacier forefields is expected to yield a better understanding of the preservation potential of proglacial sedimentary facies, and hence their preservation potential in Earth's sedimentary record.Supplementary material: A comparison of 3D model parameters for 2019 and 2020 data is available at https://doi.org/10.6084/m9.figshare.c.5664299

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COBOS-VILLAGRÁN, AURORA, TANIA RAYMUNDO, ROSA PAULINA CALVILLO-MEDINA i RICARDO VALENZUELA. "Rhytidhysteron mexicanum sp. nov. (Dothideomycetes, Ascomycota) from the Sierra of Guadalupe, Trans Mexican Volcanic Belt". Phytotaxa 479, nr 3 (13.01.2021): 275–86. http://dx.doi.org/10.11646/phytotaxa.479.3.4.

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A novel dothideomycete species, Rhytidhysteron mexicanum, is described and illustrated supported by morphological and cultural characters and a phylogenetic analysis (rDNA nucleotide data set). The new species is characterized when immature by boat-shaped hysterothecia (2–4 mm long × 1.5–2.5 mm wide). In mature stage, 2.5–4 mm apothecia with fluted margins remain the same when dry. The epithecium is yellowish green to pistachio green, becoming ocher in the presence of 10% KOH. Ascospores are 34–40(–44) × 10–12(–15) µm, and reddish brown. The morphology of R. mexicanum is compared with other Rhytidhysteron species. A dichotomous key is provided to the five species of Rhytidhysteron known from Mexico.

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Hu, Zhengwen, Baoqiang Zhang i Jing Yang. "A Two-Phase Monte Carlo Simulation/Non-Intrusive Polynomial Chaos (MSC/NIPC) Method for Quantification of Margins and Mixed Uncertainties (QMMU) in Flutter Analysis". IEEE Access 8 (2020): 118773–86. http://dx.doi.org/10.1109/access.2020.3005289.

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Sutherland, James, i Anubhav Datta. "Fabrication, Testing, and 3D Comprehensive Analysis of Swept-Tip Tiltrotor Blades". Journal of the American Helicopter Society 68, nr 1 (1.01.2023): 1–17. http://dx.doi.org/10.4050/jahs.68.012002.

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This paper covers the design, fabrication, testing, and modeling of a family of Froude-scale tiltrotor blades. They are designed with the objective of gaining a fundamental understanding of the impact of a swept tip on tiltrotor whirl flutter. The goal of this paper is to describe the development of the blades needed for this purpose. The rotor is three bladed with a diameter of 4.75 ft. The blades have a VR-7 profile, chord of 3.15 inches, and linear twist of –37° per span. The swept-tip blades have a sweep of 20° starting at 80% R. The blade properties are loosely based on the XV-15 design. A CATIA and Cubit-based high-fidelity three-dimensional (3D) finite element model is developed. It accurately represents the fabricated blade and is analyzed with X3D. Experiments in a vacuum chamber were carried out to demonstrate the structural integrity of the blades. Measured frequencies and strains were validated with X3D predictions proving the fidelity of the 3D model. Thus, even though the wind tunnel facilities were closed due to COVID-19, hover and forward flight calculations for the blade stress could be performed using the high-fidelity 3D structural model. The results prove the blades have sufficient structural integrity and stress margins to allow for wind tunnel testing.

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Marques, Fernando Araújo dos Santos, Carlos Antônio Ferreira, Eliana Tiba Gomes Grande, Maria Gláucia Dourado Furquim i José Carlos de Sousa Júnior. "Desenvolvimento de um aplicativo multilateral de gerenciamento de negócios para microempreendedores individuais do setor de estética". Research, Society and Development 11, nr 16 (14.12.2022): e453111636898. http://dx.doi.org/10.33448/rsd-v11i16.36898.

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O marketing é uma ferramenta primordial nas relações de troca e venda do meio comercial. Para um melhor relacionamento com o público-alvo é necessário conhecer suas necessidades e trazer uma melhor experiência nos serviços e produtos que são adquiridos pelo consumidor final. A proposta deste artigo é fundamentar e propor um aplicativo de serviços de estética que em conjunto com o composto dos 4 P's estratégicos do marketing auxiliará microempreendedores individuais do ramo de estética a gerenciar os pedidos de agendamento, a abrangência da marca e o relacionamento com o público-alvo. Nesse sentido, o presente trabalho se classifica como pesquisa científica aplicada, sendo para tanto adotado para a construção do aplicativo para as plataformas móveis Android e iOS, o framework de desenvolvimento de aplicativos Flutter e a metodologia de arquitetura Clean Architecture idealizado por Robert C. Martin. A proposta avança em relação ao segmento de cliente atendido, seguindo um conceito padrão de desenvolvimento de aplicativos mobile, uma vez que a arquitetura do aplicativo foi construída de modo a facilitar a otimização e futuras modificações caso surjam novas demandas técnicas, além de atender solicitações de mudanças com base no comportamento e exigências dos prestadores e consumidores. Assim o desenvolvedor responsável pelo aplicativo poderá aplicar correções e atualizações no menor tempo possível de acordo com a demanda levantada.

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Laws, Catherine. "Beckett in New Musical Composition". Journal of Beckett Studies 23, nr 1 (kwiecień 2014): 54–72. http://dx.doi.org/10.3366/jobs.2014.0086.

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The musical legacy of Samuel Beckett is evident in the large number of compositions inspired by his work. Moreover, Beckett's influence has endured beyond the associations with musical modernism from the 1960s onwards. How, then, do the approaches of younger composers relate to and differ from those working during Beckett's lifetime, and what are the implications for performance? This article explores these questions in relation to two recent compositions: Damien Harron's what is the word (2011) for flute, percussion, piano and electronics, and Martin Iddon's head down among the stems and bells (2009) for amplified prepared piano.

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Ebbestad, Jan Ove R., i Juan Carlos Gutiérrez-Marco. "Phragmolites (Gastropoda) from the Late Ordovician of the Peruvian Altiplano". Journal of Paleontology 94, nr 2 (22.10.2019): 255–65. http://dx.doi.org/10.1017/jpa.2019.79.

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AbstractPhragmolites lissoni new species is described from 11 specimens found in the Sandbian Calapuja Formation near Calapuja in Peru. The deposits are part of the Central Andean Basin. This is the hitherto only systematically described Ordovician gastropod from Peru. The species is from a brachiopod-dominated siliciclastic sequence and is associated with bryozoans. Most specimens are preserved as external molds, but latex casts yield excellent details of shell ornamentation and are used as a basis for evaluating this feature in the genus. The characteristic ornamentation of Phragmolites should be called corrugated lamellae, and the individual elements on these should be referred to as flutes. A descriptive terminology for these is suggested. The development and shape of the corrugated lamellae and flutes could be biomechanical process. A second component in lamellar formation is the alternation between regular incremental growth and formation of a lamella. Phragmolites is mainly found in shallow-water carbonate facies from tropical latitudes in the Sandbian and a mid-latitude presence in Peru is unexpected. Brachiopods from the same section in Calapuja show affinities with faunas of the Mediterranean margin of Gondwana but also weak links with Avalonia. Phragmolites is found abundantly in deeper-water facies in Laurentia, and a broad tolerance to facies and temperature and possible planktotrophy might have allowed a wide geographical dispersal of the genus. The scant record of Ordovician gastropods in the Central Andean Basin precludes comparison with the disparate record of the Ordovician gastropod taxa from the Precordillera, which do not include Phragmolites.UUID: http://zoobank.org/References/fbd7a43e-a610-42fd-a31d-b1a16fa69c9b

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