Flutter Analysis of a Morphing Wing Considering Fluid–Thermal–Structure Coupling

Aiming at improving the range of wing-body combination aircraft at hypersonic flow conditions and exploring the application of morphing technology in hypersonic aircraft, morphing aircrafts with different morphing modes have been proposed. The aerodynamic characteristics and wing efficiency of morphing aircraft with different morphing modes have been studied for a further application. In order to verify the significance of morphing technology on the trajectory, the trajectory of the glide phase has been optimized through multiobjective optimization method. Through a 3 degree-of-freedom dynamic model and a heat flux model, the range of glide trajectory and the total heat of the leading edge of the wing are calculated and selected as optimization objectives in the multiobjective optimization problem. The optimization variables include the Mach numbers when the aircraft is morphing (morphing timing) and the angle of attack of different phases. Based on the multiobjective evolutionary algorithm based on decomposition, the multiobjective trajectory optimization problem is solved and a uniform Pareto Front is obtained, and through the analysis of typical solutions, it can be seen that a compromise is made to balance the two objectives. Through the comparison of morphing and non-morphing aircraft, morphing aircraft can fly further with a smaller total heat of the leading edge of the wing. Also, it seems that the variable sweep wing morphing mode has a better overall performance. The result in this paper is a verification of the application prospects of the morphing technology under hypersonic environment, which will provide a reference for further application of morphing technology in hypersonic aircraft.

The aim of this paper is to investigate the free vibration of single-cracked nanomaterials beams under thermal axial load. The beam model is Euler-Bernoulli. The well-known nonlocal elasticity theory is used for analyzing the nanomaterial beams in which the size effect nonlocal parameter is considered. Crack is modeled as a rotational spring that connects the beam segments with each other. The thermal load acts as an axial force on the nanomaterial beam. The effect of the thermal load, the crack location, the crack severity, and the nonlocal parameter are examined in this paper. Two cases of the non-cracked nanomaterial beam and the single-cracked nanomaterial beam are analyzed for three different types of the boundary conditions as simply supported (SS), clamped-clamped (CC), and clamped-simply supported (CS). The results show that when the crack severity is increased the natural frequencies are decreased but in some cases in which the nonlocal parameter value is high, the reverse phenomenon occurs. The temperature changes have a great effect on the frequencies as the temperature is decreased to a value lower than the room temperature, the natural frequencies for all modes decrease and when the temperature is increased to a value higher than the room temperature, the all mode frequencies increase.

Investigations on structural intensity in nanoplates with thermal load

The effect of severe cyclic thermal loading on the plastic and creep deformation of shell structures may be understood through the use of shakedown theory and its extension to time dependent material properties. The paper discusses methods of estimating shakedown limits, deformation in excess of shakedown, and steady state creep strain rates using solution technique based on this theory with the objective of forming a broad understanding of the material and structural phenomena involved. The incentive for this work arises from problems associated with the structural design of the U.K. Commercial Sodium Cooled Fast-Breeder Reactors.

Design, modeling, and control of morphing aircraft: A review

Morphing aircraft can adaptively regulate their aerodynamic layout to meet the demands of varying flight conditions, improve their aerodynamic efficiency, and reduce their energy consumption. The design and fabrication of high-performance, lightweight, and intelligent morphing structures have become a hot topic in advanced aircraft design. This paper discusses morphing aircraft development history, structural characteristics, existing applications, and future prospects. First, some conventional mechanical morphing aircraft are examined with focus on their morphing modes, mechanisms, advantages, and disadvantages. Second, the novel applications of several technologies for morphing unmanned aerial vehicles, including additive manufacturing for fabricating complex morphing structures, lattice technology for reducing structural weight, and multi-mode morphing combined with flexible skins and foldable structures, are summarized and categorized. Moreover, in consideration of the further development of active morphing aircraft, the paper reviews morphing structures driven by smart material actuators, such as shape memory alloy and macro-fiber composites, and analyzes their advantages and limitations. Third, the paper discusses multiple challenges, including flexible structures, flexible skins, and control systems, in the design of future morphing aircraft. Lastly, the development and application of morphing structures in the aerospace field are discussed to provide a reference for future research and engineering applications.

ABSTRACTEmploying the variational differential quadrature (VDQ) method, the effects of initial thermal loading on the vibrational behavior of embedded single-walled carbon nanotubes (SWCNTs) based on the nonlocal shell model are studied. According to the first-order shear deformation theory and considering Eringen's nonlocal elasticity theory, the energy functionality of the system is presented and discretized using the VDQ method. The effects of thermal loading and elastic foundation are simultaneously taken into account. The use of the numerical discretization technique in the context of variational formulation reduces the order of differentiation in the governing equations and consequently improves the convergence rate. The accuracy of the present model is first checked by comparison with molecular dynamics simulation results and those of other methods. The effects of involved parameters are then investigated on the fundamental frequencies of thermally preloaded embedded SWCNTs. The results imply that the thermal loading has a significant effect on the vibration analysis of embedded SWCNTs.

Impact of thermal loads on interfacial debonding in FRP strengthened beams

The mechanical response of energy pile groups in layered cross-anisotropic soils under vertical loadings

Under the repeated action of traffic and thermal loads, a cement concrete pavement slab may partially lose contact with its base course, and voids may develop underneath the slab. Such distress will greatly impact the pavement performance. To fill the voids and restore the base support to the slab, the technology of polymer grouting has been increasingly adopted in recent years due to its advantages of quick application and high efficiency. There is, however, a lack of research on the mechanistic responses and performance of such a repaired rigid pavement under coupled influences of thermal and traffic loads. Existing literature has mainly focused on normal cement concrete pavement structures (i.e., without polymer grouted voids). This study intends to fill the research gap by investigating the time-domain characteristics of thermal stress response of a cement concrete pavement with underlying voids filled with polymer grout, along with design traffic loads. The finite element method was adopted with a 3-dimensional nonlinear temperature field within the pavement. A program module was developed in the Abaqus FEA software environment for temperature effect analysis. It was found that under the coupling action of thermal and traffic loads, thermal stress had a greater influence on the critical slab stress at the slab corner than those at other slab locations. Through the comparative analysis before and after polymer grouting repair, the critical tensile stress at the slab corner under the vehicle and thermal loads can be effectively reduced. The polymer performance is stable after three years.

The geometric nonlinearity due to static and thermal load can significantly alter the vibration response of structures. This study presents a semi-analytical approach to illustrate the nonlinear vibration of clamped-clamped beams under static and thermal loads. The von Karman strain and Hamilton’s principle are employed to derive the nonlinear static equilibrium equation and nonlinear governing equation. The vibration equation’s coefficient is variable. The transfer-matrix method and local homogenization are used to solve the equation. The proposed method’s accuracy is validated by commercial software and literature. The numerical results indicate that uniform stress caused by thermal load only reduces the structural mode frequencies. The geometric nonlinearity of the structural static deformation affects both the mode frequencies and mode shapes. And the mode shapes cannot be approximated by harmonic functions. When the static deformation is significant, the structure’s local RMS response is substantially affected. The combined loads have a more significant impact on the acceleration response than the superposition of individual load effects.

With the change of external environmental factors, thermal loads are changing and causing fluctuating thermal stresses in critical fatigue details of steel bridges, which contribute to fatigue damage cumulation significantly. This paper proposed two fatigue evaluation methods considering the coupling effects of traffic load and thermal load: (1) Evaluation based on vehicular fatigue load model (VFLM) and thermal fatigue load model (TFLM). (2) Evaluation based on measurements of thermal load and traffic load. The analytical approach for obtaining the thermal fatigue load model was introduced, and the concept of the coupling stress model of ‘wave-surfer model’ was set up according to the mechanism of fatigue damage cumulation. Taking a steel box girder bridge as a case study, the collections of temperature data and traffic information were carried out. The two evaluation methods based on different load information were applied to two typical fatigue details, and the corresponding fatigue damage was calculated, which demonstrates that thermal effects should be taken into account for fatigue evaluation.

The effect of a transient thermal load on an interface crack in adhesively bonded dissimilar materials was experimentally studied by using photothermoelasticity. It is determined that the effect of the thermal load is to cause mostly shearing deformations at the crack tip. For two configurations, a horizontal crack (normal to the heat flow direction) and a vertical crack (parallel to the heat flow direction), it is shown that increasing the adhesive thickness results in steady-state and maximum transient strain-energy release rates and stress-intensity factors of smaller magnitudes. It is also found that the ratio of mode I to mode II stressintensity factors for the vertical crack is larger than the one for the horizontal crack.

Active development of mechanical metamaterials has currently led to the widespread application of auxetic structures in various applications with differing loading conditions. This research explores thermomechanical behaviour of novel in-plane cylindrical auxetic lattice structures by studying the correlation between their deformational characteristics and the coefficient of thermal expansion (CTE) of the material. Unlike traditional auxetic cylinders, the plane of auxeticity in the developed models is oriented perpendicular to the cylinder axis, which defines their specific behavior. To understand the behavior of auxetic lattices under combined thermal and mechanical loads, computational experiments were conducted based on the finite element method (FEM). Deformations of both rectangular and cylindrical lattice structures were investigated. The relationships between transverse deformation and CTE were obtained and compared. The influence of CTE on the structural Poisson's ratio of rectangular auxetic lattices was assessed, which is a key parameter characterizing the auxetic behavior of the structure under thermomechanical loading. The feasibility of modeling the mechanical behavior of auxetic cylinders using an orthotropic mechanical model with effective material properties was verified. The constants for defining such a material model were obtained by simulating a numerical experiment on tensile and shear testing of the rectangular auxetic lattices along coordinate axes. Using an example with artificial material properties, it was demonstrated that the predominant deformation mechanism, caused by the opposing effects of mechanical and thermal loads, can be controlled by selecting a material with an appropriate CTE. This allows for regulating the structural response to changes in temperature and mechanical load. Such results can be utilized for creating cylindrical auxetic lattice structures subjected to mechanical and thermal deformations in applications requiring controlled thermomechanical responses.

This study examines the aeroelastic interactions of triangular steel flags in tandem configuration for flow speed (U) up to 9.0 m/s, with inter-flag gap (Gf) ranging from 0.1 to 5 times the leading flag's characteristic length (L). The leading flag is subjected to both streamlined and vortex-induced flows (VIFs). Wind tunnel experiments reveal a subcritical bifurcation route to limit cycle oscillations (LCOs) under streamlined flow, while VIF alters the bifurcation to a supercritical route. First, the identical flags with a natural frequency of 3.59 Hz (first bending mode) and a flutter speed near 7.4 m/s are tested in tandem under streamlined flow. The leading flag's dynamics remains largely unchanged compared to its standalone dynamics, while the trailing flag's response is highly sensitive to its position in the wake of the leading flag. Phase dynamics, including frequency locking and bounded phase differences, emerges at different flow regimes depicting synergistic and destructive coherence. For closely spaced flags (Gf = 0.1L), trailing flag LCO amplitudes are suppressed by up to 50%, while at larger gaps, amplitudes increase by up to 1.5 times. For a non-identical trailing flag with much higher natural frequency (5.48 Hz) and flutter onset speed (U> 9.0 m/s), the flutter onset is advanced and matches that of the leading flag. The non-identical trailing flag oscillates close to its natural dynamics across a wide range of inter-flag gaps and flow speeds but exhibits small-amplitude LCOs driven by the leading flag at very low speeds. Finally, the identical tandem flags are placed downstream of a cylindrical bluff body to examine the impact of VIF conditions. Small-amplitude aperiodic oscillations are observed in the leading flag much below its critical flutter speed, which, in turn, induce a sufficiently strong wake to trigger LCOs in the trailing flag. The leading flag dynamics transitions to periodic oscillations at higher speeds, while the trailing flag exhibits strongly aperiodic oscillations, with one frequency locked to that of the leading flag. The comprehensive nonlinear aeroelastic analysis of tandem flags presented in the study can be utilized for enhancing multi-flag energy harvesting, fluid mixing, and heat transfer.