This paper is intended to reconcile the stress-based and strain-based formulations for material failure criteria, where a longstanding and deep division is present. The two approaches do not naturally agree with each other, and they not genuinely complement each other, either. Most popular criteria are stress-based when originally proposed, including the maximum stress, Tresca, von Mises, Raghava-Caddell-Yeh and the Mohr criteria. Their formulations are unique and self-consistent, i.e., capable of reproducing the input data. Their strain-based counterparts, with the maximum strain criterion being considered as the strain-based counterpart of the maximum stress criterion, are neither unique nor necessarily self-consistent. It has been proven that the self-consistent ones reproduce their respective stress-based counterparts identically in effect with a disadvantage of requiring an additional material property to apply, without a single benefit. For the Mohr criterion as a special case, a strain-based counterpart is simply infeasible in general. All undesirable features of strain-based criteria are rooted in a single source: The failure strains can only be measured under a uniaxial stress state, which corresponds to a combined strain state in general, not a uniaxial strain state! Given the arguments presented, the reconciliation proves to be biased completely towards the stress-based side if mathematics, logic and common sense prevail over perception and prejudice.
Mechanical metamaterials are engineered materials with unconventional mechanical behavior that originates from artificially programmed microstructures along with intrinsic material properties. With tremendous advancement in computational and manufacturing capabilities to realize complex microstructures over the last decade, the field of mechanical metamaterials has been attracting wide attention due to immense possibilities of achieving unprecedented multi-physical properties which are not attainable in naturally-occurring materials. One of the rapidly emerging trends in this field is to couple the mechanics of material behavior and the unit cell architecture with different other multi-physical aspects such as electrical or magnetic fields, and stimuli like temperature, light or chemical reactions to expand the scope of actively programming on-demand mechanical responses. In this article, we aim to abridge outcomes of the relevant literature concerning mechanical and multi-physical property modulation of metamaterials focusing on the emerging trend of bi-level design, and subsequently highlight the broad-spectrum potential of mechanical metamaterials in their critical engineering applications. The evolving trends, challenges and future roadmaps have been critically analyzed here involving the notions of real-time reconfigurability and functionality programming, 4D printing, nano-scale metamaterials, artificial intelligence and machine learning, multi-physical origami/kirigami, living matter, soft and conformal metamaterials, manufacturing complex microstructures, service-life effects and scalability.
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.
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.
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
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.
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.
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.
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 Re = 2.85 × 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 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
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.
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.
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
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.
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.
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, _1 and _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, ω = _2/ _1 , the instability has maximum at a finite frequency _1 while for the low and high fresquencies stabilizing effect is observed. The decrease of the superimposed acceleration amplitudes has also a stabilizing effect.
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≤ Ri≤ 10) , Reynolds number (50≤ Re≤ 500) , thermal conductivity ratios (0.1≤ K≤ 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.
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.
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.
