Advances in Mechanics

In recent years, graphite-epoxy materials have been widely used in the space industry due to their ability to satisfy design demands (minimum weight and high structural rigidity). However, radiation resulting from the space environment can create imperfections in these structures. The ultrasonic non-destructive testing by guided wave presents an alternative for the detection of these defects. The knowledge of the dispersion curves is an essential step in order to know the adequate frequencies susceptible to propagate in our material for a successful control. In this manuscript, we present a hybrid analytical method to plot the dispersion curves of a graphite-epoxy composite material. The advantage of this method over the classical analytical methods has been studied. The accuracy of the obtained results is controlled using the DISPERSE software. Next, the profiles of the displacements and stresses normalized by the acoustic power flow of the fundamental modes are plotted at a given frequency. A discussion of the vibratory states of the plate is established.

This work presents the dynamics and AVC of a non-uniform FGM beam. The beam is equipped with four layers of piezoelectric sensors/actuators, on different finite elements to see the influence of its location on the dynamics and AVC. In this study, the classical EB theory combined with FEM is applied to a beam dividing it into a finite number of elements. Principle of Hamilton is applied to generate the equation of motion. The structure is modeled analytically then numerically and the simulation results are presented at the end.

The tubular metal constructions find their applications in the following industrial sectors: metal tanks, industrial hangars, metal bridges, commercial buildings, pipelines, support for oil platforms etc. The phenomenon of stress concentration, born in the welded zones, contributes to the damage of these structure.

In the literature, the semi-parametric formulas give information about the stress concentration factor value, but gives no idea about its distribution.

In this study, three different Y-joints have been studied. A finite element modeling was used to show the inclination brace effect (θ = 45°, θ = 60° and θ = 90°) on the distribution of stress concentration factor SCF and on the tubular Y-joint strength under deflected bending loads.

In this work, we are interested in combining the method of fundamental solutions (MFS) with the domain decomposition technique for solving Laplace equations. This coupling allows a good control of the resulting system generated by the MFS. Our main objective is to stabilize numerically the MFS by controlling the ill-conditioning of the system matrices. Several examples are considered to analyse the robustness and efficiency of this coupling.

A high-order algorithm to compute elastoplastic structures in large deformation . We will asses the robustness of this algorithm by studying four loading processes and and we will check the quality of the solution with the help of the residual curve.

In this paper, a semi-analytical solution for the dynamic behavior of the multilayered piezoelectric beams is derived. The beam is assumed to be simply supported and the interfaces between the layers are considered perfect. In each layer of the beams, the pseudo-Stroh formalism is developed and the set of partial differential equations is reduced to a system of second order ordinary equation of time. To solve that equation in time domain, the time interval is divided into several sub-intervals having equal length. In each sub-interval of time, the Lagrange polynomials have been used and a discrete eigenvalue problem is then obtained. The solutions are therefore constructed and interpolated in the time domain. Those solutions have been propagated throughout the thickness direction of beams using the propagator matrix method. In the computation process, the elastic material graphite epoxy (named E) and the piezoelectric material BaTiO₃ (named B) are used. The layering effect and the surfaces boundary conditions effect on the dynamic response of the three-layered piezoelectric beams are clearly illustrated. The obtained results can be helpful as benchmark.

The objective of this study is to investigate the effect of endurance and takeoff distance on the result of an adapted pre-sizing of an unmanned aerial vehicle (uav). Pre-sizing methods aim to define an initial geometry of the uav that necessitates little modifications in the next phase of uav design: detailed dimensioning. Endurance and takeoff distance are two important parameters, among others, that the end user wishes to control. The non-linear formulas and equations used in pre-sizing do not give a direct relation between these two parameters and the initial geometry. In this work, a summary presentation of an adapted pre-sizing method is given. A parametric study is then conducted of the effect of endurance and takeoff distance in two cases, an uav with one engine and one with two engines. The results will help to quantify and control the effect of the required parameters on the geometry at early stages of an uav design project and assist designers when they must choose one or two motors to better meet the end user's expectations.

We review several infiltration phenomena and modeling approaches for unsaturated porous media. First, we present a recent extension of the piston flow model of Green & Ampt, called Moving Multi-Front (MMF), which propagates vertically a discrete number of “fronts” or pressure iso-values. Secondly, based on the general Richards PDE governing variably saturated flow, we analyze several infiltration phenomena like capillary barrier phenomena due to heterogeneities in 1D (vertically discontinuous water contents) and in 2D (perched water over a clay lens in vertical cross-section). Thirdly, we present previously unpublished modeling and analyses of the 2D/3D dynamics of moisture plumes and ponded zones during localized infiltration from point sources and line sources (drip irrigation).

In this work, a mesh-free indicator is proposed to detect the bifurcation points of incompressible viscous fluid flow in a 2D sudden expansion. This indicator is mainly based on the high order mesh-free algorithm (HO-MFA) to solve the nonlinear problems obtained from the linear stability analysis. The Padé approximants are then used to improve the validity range of the HO-MFA and to determinate the roots of the indicator. The combination of these mathematical tools allows us to determine the zero of the indicator corresponding to the critical point. The Lyapunov-Schmidt reduction is used to search all the bifurcated branches from the critical point. To show the accuracy of our model, comparisons of the obtained results with those of the literature are made.

In this work, a novel drag reduction device applied to the Ahmed body is presented. This consists of perforating a rectangular conduit in the body. The purpose of this conduit is leading part of the airflow from the front and inject it in the recirculation region behind the body. Three–dimensional simulations have been carried out, at a Reynolds number of \({\text{Re}} = 2.85 \times 10^{6}\), with the software of computational fluid dynamics ANSYS FLUENT. The influence of changing the conduit dimensions and its position from the lower slant edge on drag coefficient is presented. This study is a continuation of the two–dimensional numerical study of this drag reduction technique.

The minimum oil film thickness, at a given load, is calculated in this paper for Magneto-elastohydrodynamic (MEHD) parabolic slider bearings lubricated with non-Newtonian couple stress fluid. The modified MHD Reynolds equation of finite and infinite geometries is developed. It is discretized by finite difference technique and the resulting algebraic equations are iteratively solved using the Gauss–Seidel method. In particular, the value of minimum oil film thickness is decreasing with that of the load.

In this paper, the linear hydrodynamic stability analysis of a viscoelastic fluid in a plane channel flow driven by a constant pressure gradient is investigated numerically. A nonlinear eigenvalue problem for the perturbed state is obtained from a generalized Orr-Sommerfeld equation. The Chebyshev spectral collocation method with expansions in Lagrange’s polynomials are used for the numerical calculation. The complex wave speed, the critical Reynolds and wavenumber numbers are calculated for different parameters. We mainly examine the combined effects of relaxation time (via the Deborah number) and delay time (via the elasticity number) on the onset of instability. Results show that the relaxation time has a destabilizing effect and the retardation time has a stabilizing effect, with a displacement towards the long-wave region. Moreover, an important feature occurs when the Reynolds number is equal to the ratio of both characteristic times, the Jeffrey’s fluid model behaves like the Newtonian model.

We investigate the Faraday instability with an air-liquid interface in a Hele-Shaw cell subjected to a periodic vertical oscillation with two commensurate frequencies, \(\varOmega _1\) and \(\varOmega _2\). The linear stability formulation allows to reduce the governing equations to a damped Mathieu equation describing the evolution of the interface amplitude. Thereafter, spectral methods are used to establish the marginal stability curves in terms of reduced critical forcing amplitude as a function of wavenumber, which allows us to examine the effects of frequency ratios, the amplitudes of the excitations, and the effect of phase shift of the two superimposed accelerations. The instability diagrams are presented in the form of tongues which are resonances that can be harmonic or sub-harmonic with the existence of several bi-critical points. We show that the phase shift has a stabilizing effect. Also, for each frequency ratio, \(\omega =\frac{\varOmega _2}{\varOmega _1}\), the instability has maximum at a finite frequency \(\varOmega _1\) while for the low and high fresquencies stabilizing effect is observed. The decrease of the superimposed acceleration amplitudes has also a stabilizing effect.

Solar energy is currently the most abundant and cleanest source of renewable energy, making it a good substitute for increasing efficiency. Solar water heaters can significantly reduce the cost of electricity consumption and help reduce greenhouse gas emissions. The solar heat exchanger, a phase-change heat storage system, is designed in this work. A numerical analysis was carried out to examine the impact of various cooling temperatures on the solidification thermal cycle of the phase change material. Phase Change Material (PCM) can be used to effectively regulate temperature. Depending on the PCM and its storage capacity, the temperature of the produced water is controlled. Through the tubes, a fluid used for heat transfer from the solar collector transfers heat from the sun’s rays to the PCM. During the discharge phase, the heat that has been stored in the PCM is then transferred to the water, heating it up. In order to quantitatively evaluate the thermal performance of the latent heat storage unit, a numerical simulation using the finite volume method was developed. To determine the best design, several simulations were carried out for the different types of PCM (Paraffin, n-eicosane and Rubitherm Paraffin) and also to improve their discharge time.

The partial substitution of petroleum coke with alternative solid fuels, such as biomass, is advantageous for mitigating greenhouse gases and energy consumption in cement production. This study evaluates the effect of using two alternative biomass-type fuels, olive pomace powder and crushed almond shells, on the cement rotary kiln’s combustion performance by comparing the two particles’ co-combustion behavior to the case of combustion of petroleum coke alone using the Ansys Fluent Computational Fluid Dynamics (CFD) software. According to the results, the maximal temperatures achieved by the co-combustion of olive pomace and almond shells are lower than the temperature of coke combustion alone. However, on the other hand, it has noticed a difference in combustion behavior in terms of the char particle fractions.

Improvement of the efficiency of thermoelectric modules requires the improvement of their performance. Thus, an optimisation method will be studied in this paper, as well as the analysis of the management of the operating conditions. By reversing the flow of hot and cold heat transfer fluids, we can reduce the temperature rise at the cold junctions and improve the performance. Water is the heat transfer fluid we have chosen for this study. The hot heat transfer fluid will flow in a channel to heat the hot junctions, and the cold heat transfer fluid will flow in a channel to cool the cold junctions. In the first case, the flows of the two heat transfer fluids are in the same direction. Subsequently, a second study will be carried out by opposing the flow direction of the heat transfer fluids. The results obtained show that by opposing the flow direction of the cold heat transfer fluid, we obtain a greater generated power than that obtained in the case of a flow in the same direction, which will allow us to have a better efficiency.

The fundamental problem of the steady convection-diffusion in potential flow around a heated circular cylinder with uniform heat flux is solved both analytically and numerically. The analytical solution is derived in closed form by using the method of Green’s function and presented as an integral. This solution is useful to validate the numerical codes of several others more complex problems considering Neumann boundary condition. It is thereby used to check the present numerical solution with potential flow. The asymptotic solution, at a great distance in the thermal wake region behind the cylinder is also obtained. It divulges the existence of singularities which lead to a deterioration of the accuracy of the numerical solution. An accurate numerical solution is then obtained by solving efficiently theses singularities. Its validity and its accuracy are supported by a comparison with the results derived from the exact analytical solution with relative error less than 0.1%, notably for the thermal characteristics. A useful correlation formula giving the overall Nusselt number as function of Péclet number is also proposed.

In this work, we examined numerically the heat transfer by mixed convection coupled with surface thermal radiation in a square cavity with a moving wall, using the Lattice Boltzmann method. The cavity is discretely heated from its left and lower walls with a hot temperature and cooled from its right wall, while the upper wall is adiabatic and moves from left to right at a constant velocity. The cooling medium is assumed to be air, which modeled as a radiatively transparent medium. The critical parameters in this study are the emissivity of the surfaces, ε, which varies between 0 and 1, and the number of Richardson, Ri, which varies from 0.1 to 10. The latter varies by varying the Reynolds number, Re, with a Rayleigh number, Ra = 10⁵. The results obtained indicate that the dynamic structure is monocellular, which illustrated by the existence of a large cell generated by the combined effects of shear and buoyancy. In addition, it should be noted that the increase of the emissivity of the surfaces enhances the radiative heat exchange, reduces convective effect and improves the total heat exchange. Additionally, it is discovered that an increase in Ri causes a significant decrease in convective and global heat exchange, while just slight increase in radiative heat transfer.

This article studies an exact solve for 2-D thermal conduction through cylinders with orthotropic properties, subjected to a prescribed temperature on both end sections and longitudinally varying heat flux over the whole lateral surface. The method of separation of variables is employed to integrate the orthotropic equation along with the boundary conditions, temperature continuity, and flux at the interface between the two mediums. The effectiveness of the obtained results is examined through the ratio of the principal thermal conductivity and the radial ratio of the thermal conductivity between the two mediums. The analysis demonstrates that the radial and axial profiles of temperature and flux are influenced by the specific values of the given problem data.

The work consists of a numerical study of a forced convection of an incompressible, laminar flow of a Newtonian fluid within a channel with symmetrical wavy walls of semi-infinite length.

The temperature profile and the distribution of the local Nusselt number are determined numerically using the Alternating Direction Implicit method. We present the effect of certain parameters on the radial and axial temperature profiles and on the Nusselt number.

The building sector is one of the most energy-intensive fields in the world. Hence, enhancing the production techniques of traditional materials seems to offer a viable solution for tackling this challenge effectively. However, plaster is considered one of the most used construction substances thanks to its advantageous characteristics such as its aesthetic aspect, its fire resistance and its thermo-acoustic insulation qualities. The present paper includes in its entirety an experimental study aiming to evaluate the effect of the mixing water ratio on the thermo-physical properties, and the thermal behavior of the plaster matrix. Otherwise four blending proportions were investigated (0.5, 0.6, 0.7 and 0.8). The obtained results showed that increasing the water quantity used during the preparation process allows reducing simultaneously the plaster thermal conductivity from 0.415 to 0.359 W/m.K and its density from 1398.4 to 1096.4 kg/m\(^3\). Furthermore, an appreciable improvement of the thermal behavior has been noted. Thus gains of approximately 24.47 and 15.68% were achieved for the time lag and the temperature attenuation factor, respectively. On the other hand, this process has adversely affected the mechanical performance of plaster. Therefore, by transitioning from a water-to-mix ratio of 0.5 to 0.8, the mechanical strength decreases from 5.8 to 2.1 MPa, respectively.

This work aims to investigate the complex phenomenon of mixed convection in a vented cavity containing a circular heat-generating cylinder, which holds significant relevance for electronic device cooling applications. To achieve this objective, a comprehensive numerical study is conducted using the finite volume technique. The mathematical model is discretized, and the resulting equations are solved numerically employing a dedicated numerical code based on the SIMPLE algorithm. In this study, the effects of various parameters on the flow and thermal field are examined. These parameters include the Richardson number \((0.1\le Ri\le 10)\), Reynolds number \((50\le Re\le 500)\), thermal conductivity ratios \((0.1\le K\le 100)\), and cylinder position. The Prandtl number is fixed at 0.71, and the cylinder diameter is set at 0.4. It is found that the Reynolds number plays a significant role in influencing the flow patterns. Increasing the Reynolds number leads to enhanced cooling effectiveness of the circular cylinder. This suggests that higher flow rates contribute to better heat transfer and improved cooling performance. Additionally, the investigation demonstrates that an increase in thermal conductivity ratios yields substantial improvements in the overall performance of the cooling system.

The construction industry is a large consumer of cement which is used in concrete and mortar manufacture. Cement substitution would reduce its economic and environmental cost. This work is part of the local materials development such as cement and residual ash from thermal power plants. Our objective is to study the effect of ash fineness and replacement rate on the thermomechanical characteristics of mortar. For this reason, the ash was ground into two different fineness values of 4500 cm²/g and 6500 cm²/g and used as replacement rate ranging from 10 up to 50% by weight of cement. In a first step, the thermal properties of ash mortars have been experimentally determined in terms of thermal conductivity and diffusivity using the box method, subsequently, thermomechanical characterizations were performed using the H10KL bench to estimate the ash mortars mechanical parameters. Test results show that the use of ash in the mortar resulted in a significant improvement in thermomechanical properties and a substantial decrease in water absorption. This subsequently contributes to the reduction of building energy consumption, CO₂ emissions in the atmosphere and annual quantities of ash produced by thermal power stations.