Acta Mechanica最新文献

The present research investigates the convective and radiative heat transfer characteristics of a moving longitudinal porous fin. The study incorporates the influence of a magnetic field as a driving force for enhancing heat transfer in the system. To optimize heat transfer efficiency, a novel ternary hybrid nanofluid consisting of Ag, MgO and Au nanoparticles dispersed in water is utilized. The analysis employs the Adomian decomposition sumudo transfer method (ADSTM) as the semi-analytical approach, complemented by the numerical method of Runge–Kutta Fehlberg 4–5th (RKF-45) order for comparative analysis. Moreover, the application of fractional order ADSTM is explored to address non-dimensionalized ordinary differential equations (ODEs), and the findings are visually represented through graphical plots, showcasing the impact of various parameters on heat transfer performance and the superiority of the proposed ADSTM technique. The results show that trihybrid nanofluid outperforms both single-component and binary hybrid nanofluids in terms of temperature distribution and thermal efficiency. Importantly, the use of trihybrid nanofluid leads to a significant enhancement in the fin performance. The current findings indicate that a 400% increase in the Peclet number (Pe) leads to a 1.67% rise in the temperature from the base to the tip. Additionally, increasing the Hartmann number ((H)) by 400% results in a 16.34% decrease in the temperature from the base to the tip. This study holds significance for various engineering applications, enabling more efficient heat transfer in porous fin systems with potential for future advancements in the field.

The aim of this study is to present an alternative way to deduce the equations of motion of general (i. e. also nonlinear) nonholonomic constrained systems starting from the d’Alembert principle and proceeding by an algebraic procedure. The two classical approaches in nonholonomic mechanics – ({check{textrm{C}}})etaev method and vakonomic method – are treated on equal terms, avoiding integrations or other steps outside algebraic operations. In the second part of the work, we compare our results with the standard forms of the equations of motion associated with the two method and we discuss the role of the transpositional relation and of the commutation rule within the question of equivalence and compatibility of the ({check{textrm{C}}})etaev and vakonomic methods for general nonholonomic systems.

In the current paper, a new first-order Timoshenko’s theory (N-FSDBT) based on the indefinite integral is proposed to examine the vibrational behavior of power-law (P-FG), sigmoid (S-FG), and exponential (E-FG) functionally graded beams. The developed formulation takes into consideration the effect of the transverse shear deformation. During the manufacturing process, faults, such as the presence of micro voids or porosities in FGMs, structural imperfections may arise in the material. For this purpose, this research has focused on the modification of the mixture rules including the porosity volume fraction. To illustrate the porosity variation throughout the body of the structures, the uniform, nonuniform and mass-density porosity distribution are considered in the present examination. Mathematical approach is used to simplify the FG beam governing equation based on classical beam theory (CBT) and new-FSDBT frame works for free vibration. The resultant equations of motion are solved using the Navier’s technique, for simply supported FG beams. To validate the results, a parameter study was presented to analyze the impact of the types of volume fraction (FG beam-type), the effects of porosity distribution, material exponent parameter, slenderness ratio, and porosity index on the dynamic behavior of imperfect FG beams.

Radial ribs are important supporting parts of umbrella antenna, and its shape is a crucial factor affecting the overall reflector accuracy. Considering the difficulty of in-orbit shape sensing, a fiber-optic shape sensing (FOSS) method for the radial rib is presented in this paper, then on the basis of FOSS a shape active control method for the radial rib driven by Macro-Fiber Composite actuators is proposed. Firstly, combining the deformation characteristics of the radial rib structure, an improved Ko displacement algorithm is proposed for its shape sensing using distributed fiber-optic. Then, establish the shape active control model with the Influence-Coefficient-Matrix method, and propose a closed-loop shape active control method with FOSS as feedback for the radial rib. In this paper, the optimization problem of solving control voltage is established by using the Least-Square method, and Root-Mean-Square error is taken as the convergence condition. Finally, numerical simulation and experiment show that the relative error of the shape sensing with fiber-optic is less than 5%, and the shape accuracy of radial rib after control is improved by more than 90% to reach submillimeter level, which verifies the effectiveness of the radial rib shape active control method based on FOSS.

The propagation of a wave packet in a discontinuous medium, one of them with absorption of energy, has been studied analytically. We examined an electromagnetic pulse starting in a free medium and moving toward a dissipative one. In the first medium, the wave is free-moving governed by the wave equation, while in the second medium, the wave is affected by the Joule effect governed by the telegrapher’s equation. We solved the motion at the discontinuity using the Fourier representation for a wave packet in the formalism of a wave attenuated approach. This allowed us to calculate a reflection amplitude in analogy with the ordinary definition at a discontinuity in a medium without dissipation but with different velocities in each medium.

In this paper, the dynamic characteristics of inhomogeneous three-layer spheres under spherical wave induced by cyclic pressure are studied. The density is assumed to have a square of inverse proportional function distribution along the radius. Firstly, on the basis of Lamb decomposition and variable separation method, the analytical expression of spherical wave is conducted, which satisfies the stress equilibrium on the outer and inner surfaces of the sphere, and the Euler equation is obtained due to inhomogeneity. Next, algebraic equations with respective boundary conditions are composed and solved by effective truncation techniques. Finally, a comparison and discussion are conducted between the model presented in this article and the homogeneous model obtained by the Legendre polynomial expansion. Obtained results enable to reveal the influence on the dynamic stress concentration factor intensity under proper conditions. The conclusions of this article are verified by comparing the analytical solutions to the ones obtained by finite element method. This paper can provide a theoretical method for the analysis of mechanical properties of inhomogeneous multilayered spherical structure under dynamic loading.

In this paper, a fractional constitutive model is constructed to link the rate-dependent loading and relaxation stages. As for strain rate effects, an inverse relationship between relaxation time and strain rate is established with assuming fractional order following the microbial growth curve in the loading stage. The anomalous stress relaxation behaviors of glassy polymers under various strain rates are successfully characterized by establishing the relationship between model parameters and initial stress. The proposed model is validated by numerical results applied to various strain rates and initial relaxation strains. Compared with the existing model, the proposed fractional model presents higher accuracy.

The dynamic response of a double-layered circular region under anti-plane linear loads is investigated using the complex function method. The scattering wave functions for each layer are provided, and the total wave field functions for each layer are formulated through the superposition principle. By establishing an infinite linear equation system with unknown coefficients based on the boundary conditions, finite term truncation is performed to obtain the dynamic stress concentration coefficient of the circular hole defect. Furthermore, a specific example is presented to discuss both the validity of the theory and numerical results regarding this factor.

This work aims to develop a mathematical model for Love-type wave (LTW) propagation in non-planar non-homogeneous nearly incompressible elastic layered structure with imperfect and sliding interfaces following a geometrical model. Concretely, the geometrical model constitutes two unlike non-homogeneous nearly incompressible elastic materials forming a combination of stratum and substrate, which in turn involve imperfectness at the interface and non-planar boundaries (NPBs). With aid of applicable mathematical techniques, the expressions of displacement components (DCs) of LTW have been determined for both planar boundaries (PBs) and NPBs with imperfect interface. As a special case of the study, the expressions of DCs of LTW have also been deduced for both PBs and NPBs with sliding interface. Further, as an offshoot of the current study, dispersion relations (DRs) of LTW propagating in non-homogeneous and homogeneous nearly incompressible as well as isotropic elastic structures having imperfect, perfect and sliding interfaces have been established and validated with the results present in the literature. For graphical delineation, numerical computation of the DCs and phase velocity (PV) of LTW has been performed. The influences of non-homogeneity parameters, curvature parameters, interfacial parameter and wave number on DCs and PV of LTW have been figured out. It has been revealed that the presence of non-homogeneity in structure has substantial effect on the DCs and PV of LTW. Moreover, a comparative approach has been brought in to study the DCs and PV of LTW in non-homogeneous and homogeneous cases of nearly incompressible elastic structure (NIES) having imperfect and sliding interfaces.

In this work, we study some qualitative properties arising in the solution of a thermoelastic problem with heat radiation. The so-called Moore–Gibson–Thompson equation is used to model the heat conduction. By using the logarithmic convexity argument, the uniqueness and instability of solutions are proved without imposing any condition on the elasticity tensor. Then, the existence of solutions is obtained assuming that the elastic tensor is positive definite applying the theory of linear semigroups, and the exponential energy decay is shown in the one-dimensional case. Finally, we consider the one-dimensional quasi-static version and we assume that the elastic coefficient is negative. The existence and decay of solutions are proved, and a justification of the quasi-static approach is also provided.