The friction force for aircraft landing is mainly provided by the texture of runway surfaces. The mechanism underlying friction force generation is the energy dissipation of tire rubber materials ...during random excitation induced by asperities. However, the runway surface texture is deteriorated by cyclic loading and environmental effects during the service life of a runway, leading to loss of braking force and extension of landing distance. Additionally, when an aircraft lands on a wet runway at a high velocity, the hydrodynamic force causes the tires to detach from the runway surface, which is risky and may lead to the loss of aircraft control and runway excursion. Worn-out surfaces along with wet conditions increase the risk of poor control during aircraft landing. Accordingly, this study investigated three types of asphalt runways (SMA-13, AC-13, and OGFC-13). Surface texture deterioration was simulated using a surface texture wear algorithm. Kinematic friction models were established based on the viscoelastic property of rubber materials, power spectrum density, and statistics of surface textures. A finite element model was developed by considering a real rough runway surface and different water film depths (3, 7, and 10 mm). A comparison of hydroplaning speed was conducted between numerical simulation and former experiments. The effects of different factors, such as velocity, wear ratio, runway type, water film depth, and slip ratio, on the skid resistance of the runway were analyzed.
•Runway surface texture deterioration was considered in FEM simulation based on a surface texture wear algorithm.•The friction coefficient between tire rubber and runway was calculated based on surface texture and tread rubber property.•The effect of surface texture deterioration and wet conditions were considered simultaneously in finite element model.
Piezoelectric vibration energy harvesters have demonstrated the potential for sustainable energy generation from diverse ambient sources in the context of low-powered micro-scale systems. However, ...challenges remain concerning harvesting more power from low-frequency input excitations and broadband random excitations. To address this, here we propose a purely mechanical approach by employing inertial amplifiers with cantilever piezoelectric vibration energy harvesters. The proposed mechanism can achieve inertial amplification amounting to orders of magnitude under certain conditions. Harmonic, as well as broadband random excitations, are considered. Two types of harvesting circuits, namely, without and with an inductor, have been employed. We explicitly demonstrate how different parameters describing the inertial amplifiers should be optimally tuned to maximise harvested power under different types of excitations and circuit configurations. It is possible to harvest five times more power at a 50% lower frequency when the ambient excitation is harmonic. Under random broadband ambient excitations, it is possible to harvest 10 times more power with optimally selected parameters.
The purpose of this study is to investigate and propose a vibration isolation system with a negative stiffness structure (NSS) for driver seats in low frequency vibration conditions. In this paper, ...the nonlinear stiffness characteristic of the system is presented. The relationship between the configurative parameters and the stiffness of the elastic element, for which the dimensionless nonlinear stiffness of the proposed system ranges from zero to one and the range of the displacement of the isolation equipment (mass) is the maximum without exceeding a desired value of stiffness, will be obtained. An experimental apparatus is subsequently configured to examine the characteristic of the vibration transmissibility of the system according to various values of the configurative parameters. Next, the time responses to the multiple frequency and random base excitations are also investigated. In addition, the dynamic responses of the system with and without the negative stiffness structure are considered. The results show that the proposed system has a wide frequency range of isolation, especially since the resonance phenomenon almost does not occur.
► A vibration isolation system using negative stiffness structure (NSS) for vehicle seat is presented. ► Nonlinear stiffness characteristics of this NSS is clearly explained. ► Time responses with respect to multi frequency and random base excitations are also investigated. ► The isolation performance by the proposed system was verified to be very effective.
•A unified solution for the stationary/nonstationary stochastic vibration problems of the composite laminated plate with thermal and aerodynamic loads is proposed.•The modified Fourier method ...combined with pseudo excitation method (PEM) is adopted to obtain the solutions for the cases with classical and elastic boundary conditions.•An experiment study concerning random vibration of the composite plate under acoustic loads is performed.•The effects of the boundary condition, thermal load, fiber orientation and aerodynamic pressure on the random vibration behaviors of the composite laminated plate in supersonic airflow are clearly figured out.
This paper investigates the stationary/nonstationary stochastic responses of composite laminated plates under thermal and aerodynamic loads, where the point random excitation, distributed random excitation and base acceleration random excitation can be considered. The effects of the thermal stress and aerodynamic pressure are taken into account by employing the thermo-elastic theory and supersonic piston theory, respectively. The Hamilton's principle is used to formulate the governing equations of the system, and the solutions for the dynamic problems of cases having classical and non-classical (elastic) boundary conditions are obtained by the modified Fourier method combined with pseudo excitation method (PEM). To validate the proposed formulation, a sufficient number of numerical and experimental studies are conducted for the free vibration, flutter and stochastic response analysis of composite laminated plates with various boundary conditions. Satisfactory agreements are shown between the computed results and those from the finite element method (FEM), published literature and experiments. Finally, the effect of boundary condition, thermal load, fiber orientation and aerodynamic pressure on the random vibration behaviors of composite laminated plates is also presented.
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This study presents the experiments, modeling and numerical simulations of an industrial aeronautical structure subjected to vibroacoustic excitation. In flight, especially during atmospheric ...re-entry, an aeronautical structure is exposed to major pressure fluctuations on its external surface. These fluctuations are described as a dynamic excitation which generates structural vibrations of the outer surface and of the components inside the aeronautical structure. Due to some of these internal components such as joints, the assembly may exhibit a nonlinear vibration response. The simulation of these nonlinear vibrations requires reliable modeling of the wall pressure fluctuations and a nonlinear vibration simulation method adapted to the nonlinear modeling of the structure. In this study, a modeling and simulation method is developed to compute the nonlinear vibration response of an industrial assembly to such a surface, random, correlated dynamic excitation. More specifically, numerical simulations are performed by proposing an extension of the well-known Harmonic Balance Method for nonlinear mechanical systems subjected to complex vibroacoustic excitation. The method is validated using a dedicated ground experiment. A metallic industrial assembly representing a ballistic vehicle and including friction joints is used. This structure is subjected to controlled vibroacoustic excitation: diffuse acoustic loading in a reverberant chamber. The structure exhibits a nonlinear vibration response due to friction. The finite element model is validated through an experimental modal analysis with an electrodynamic shaker. The vibroacoustic modeling of the excitation is then validated through a test-simulation comparison using diffuse acoustic field testing at low excitation level. Then the global nonlinear simulation process is validated using diffuse acoustic field testing at increasing excitation levels. Test and simulation results exhibit the same nonlinear behavior: increase of dissipation and softening effect at the main resonances. This work thus represents a new step towards the use of nonlinear vibration simulation methods with real industrial structures and real-life loading.
•Experimental and numerical analysis of a ballistic vehicle subjected to vibroacoustic excitation.•Modeling of a real industrial structure with friction joints and real-life loading.•Extension of the Harmonic Balance Method for solving a nonlinear problem with vibroacoustic excitation.
•The FBEH owns a variable potential energy function.•The threshold of snap-through for FBEH is much lower than that of BEH.•The FBEH could realize snap-through more easily and create large output ...voltages.
In this paper, aim at improving the performance of bi-stable energy harvester (BEH), we proposed a flexible bi-stable energy harvester (FBEH). The FBEH is composed of two elastic beams: one is the piezoelectric cantilever beam with a tip magnet and the other is the clamped-clamped beam with a mid-magnet. The dynamic behavior of FBEH was studied, and the results show that the FBEH owning a variable potential energy function is beneficial for snap-through. The governing equations of FBEH are derived by energy principles. Then its dynamic response under random excitation was studied. The results prove that the FBEH not only has a smaller threshold for snap-through, but also can generate a larger power output for the excitation intensity larger than the critical one. Validation experiments were designed and carried out. The experimental results are in good agreement with the simulation ones.
We study the problem of capsizing of a rolling ship in harmonic and random beam seas, by means of the Melnikov method and safe basin calculations. In the random excitation case, we consider an ...integro-differential Cummins-type model equation that takes into account the hydrodynamic memory. The non-linear restoring moment is modeled by a high-order polynomial and the Melnikov criteria are evaluated numerically. We also examine a variant of the classical Melnikov method in which the damping terms are incorporated into the unperturbed system and the perturbation takes a modified form. We compare the theoretical predictions with direct (Monte-Carlo) simulations of the safe basins for two existing ships. In the random excitation case, we quantify the erosion by means of a mean integrity index. For weak damping, the classical and modified Melnikov curves coincide and are in good agreement with the onset of the safe basin erosion. As damping increases the Melnikov curves become less and less conservative with respect to the onset of erosion. Finally, the potential of the Melnikov method to provide a ship classification tool is discussed.
•Melnikov method with high-order restoring polynomial and hydrodynamic memory.•Safe-basin simulations with hydrodynamic memory using a fourth-order scheme.•Melnikov-based criteria in good agreement with the onset of erosion of the safe basin•Criteria become less conservative as damping increases•Application to ship classification.
•A distributed model of a tri-stable energy harvester (TEH) is established.•The TEH with asymmetric potential wells extended the working bandwidth.•The asymmetric TEH realizes snap-through at weak ...excitations.•The superiority of an asymmetric TEH is experimentally verified.
Scavenging energy from ambient vibration by tri-stable energy harvesters (TEHs) has been focused in recent years. Generally, classical TEHs adopt a design of symmetric potential wells. To improve the harvesting efficiency, a TEH with a staircase-shaped potential well (TEH-SSP) is proposed. This staircase-shaped potential well is established by adjusting the distances from the fixed magnets to the axis of symmetry. The distributed model of the proposed energy harvester is established, and the dynamical equations are derived by using the energy approach method. The nonlinear characteristics are explored theoretically and validated by experiments. Compared with the classical TEH with symmetric potential (TEH-SP), the proposed TEH-SSP could execute snap-through from a low frequency, and can obviously enlarge the frequency bandwidth of snap-through. Thus it can create a more dense high output voltages under weak random excitation. Both the theoretical analysis and experimental results prove the effectiveness of the proposed asymmetric design and vindicate that it is very beneficial for harvesting energy from the ambient vibration excitation. This work may serve as a novel insight into the design of more efficient harvesters with a broad bandwidth.
In this study, vibration analysis of a cantilever pipe conveying fluid under distributed random excitation was performed using stochastic approach. The equation of motion was first discretized by ...means of the Galerkin method. Next, the classic flutter analysis of the pipe conveying fluid was performed in absence of random excitation. Then, the random load was taken into account as a white noise excitation. Spectral density of response and response variance were calculated versus the velocity of internal flow in the pipe. The velocity of the maximum of the response variance in case of white noise excitation was regarded as flutter speed. The effects of viscoelastic dissipation, mass ratio and damping ratio of surrounding environment were investigated for the pipe under random excitation and results showed a good agreement with other studies. The spectral density of response was used to obtain the flutter frequency. Random time history and probability density function were exploited to study the pipe’s random behavior near the flutter speed. This novel approach for pipe conveying fluid was also used to investigate all possible flutter speeds. The results provided a better understanding of dynamical behavior of pipes conveying fluid under random excitation.
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