A finite element framework is presented for the analysis of crack-tip phenomena in an elastic material containing a single edge crack under compressive stretch. The mechanical response of the material is modeled by a nonlinear constitutive relationship that algebraically relates stress to linearized strain. This approach serves to mitigate non-physical strain singularities and ensures that the crack-tip strains don't grow, unlike singular stresses. A significant advancement is thus achieved in the formulation of boundary value problems (BVPs) for such complex scenarios. The governing equilibrium equation, derived from the balance of linear momentum and the nonlinear constitutive model, is formulated as a second-order, vector-valued, quasilinear elliptic BVP. A classical traction-free boundary condition is imposed on the crack face. The problem is solved using a robust numerical scheme in which a Picard-type linearization is combined with a continuous Galerkin finite element method for the discretization. Analyses are performed for both an isotropic and a transversely isotropic elastic solid containing a crack subjected to compressive stretch. The primary crack-tip variables-stress, strain, and strain energy density-are examined in detail. It is demonstrated that while high concentrations of compressive stress and strain energy density are observed at the crack tip, the growth of strain is substantially lower than that of stress. These findings are shown to be consistent with the predictions of linear elastic fracture mechanics, but a more physically meaningful representation of the crack-tip field is provided by the nonlinear approach. A rigorous basis is thus established for investigating fundamental processes like crack propagation and damage in anisotropic, strain-limiting solids under various loading conditions, including compression.

In this study, linear instability and nonlinear stability analyses are performed to investigate double-diffusive convection driven by radiation absorption and magnetic field effects. The Rayleigh-B & eacute;nard configuration with realistic rigid boundaries is considered, in which the fluid layer is heated and salted from below. The mathematical model comprises the Navier-Stokes equation for an incompressible fluid, incorporating a Kelvin-Voigt term that describes viscoelasticity, and is coupled with convection-diffusion equations for energy and solute concentration. Linear instability thresholds are determined using the Fourier mode approach, while nonlinear stability analysis is carried out by using the energy method. The resulting eighth-order differential eigenvalue problems from both linear and nonlinear theories are solved using the Chebyshev Collocation Method. The nonlinear analysis produces critical Rayleigh numbers that closely match those obtained from linear instability theory. However, the discrepancy between linear and nonlinear stability thresholds indicates the existence of a subcritical instability region. The Kelvin Voigt and Hartmann numbers are found to exert a stabilizing influence, whereas radiation absorption significantly destabilizes the onset of convection.

This paper presents a finite element model for the analysis of crack-tip fields in a transversely isotropic strain-limiting elastic body. A nonlinear constitutive relationship between stress and linearized strain characterizes the material response. This algebraically nonlinear relationship is critical as it mitigates the physically inconsistent strain singularities that arise at crack tips. These strain-limiting relationships ensure that strains remain bounded near the crack tip, representing a significant advancement in the formulation of boundary value problems (BVPs) within the context of first-order approximate constitutive models. For a transversely isotropic elastic material containing a crack, the equilibrium equation, derived from the balance of linear momentum under a specified nonlinear constitutive relation, is shown to reduce to a second-order, vector-valued, quasilinear elliptic BVP. A robust numerical method is introduced, integrating Picard-type linearization with a continuous Galerkin-type finite element procedure for spatial discretization. Numerical results, obtained for tensile loading conditions and two distinct material fiber orientations, illustrate that the evolution of crack-tip strains occurs significantly slower than that of the stresses. However, the strain-energy density is most pronounced near the crack tip, consistent with observations from linearized elasticity theory. It is demonstrated that the framework investigated herein can serve as a basis for formulating physically meaningful and mathematically well-defined BVPs, which are essential for exploring crack evolution, damage, nucleation, and failure in anisotropic strain-limiting elastic materials.

This paper presents a comprehensive computational framework for investigating thermo-elastic fracture in transversely isotropic materials, where classical linear elasticity fails to predict physically realistic behavior near stress concentrations. We address the challenge of unphysical strain singularities at crack tips by employing a strain-limiting theory of elasticity. This theory is characterized by an algebraically nonlinear constitutive relationship between stress and strain, which intrinsically enforces a limit on the norm of the strain tensor. This approach allows the development of very large stresses, as expected near a crack tip, while ensuring that the corresponding strains remain physically bounded. A loosely coupled system of linear and nonlinear partial differential equations governing the response of a thermo-mechanical transversely isotropic solid is formulated. We develop a robust numerical solution based on the finite element method, utilizing a conforming finite element discretization within a continuous Galerkin framework to solve the two-dimensional boundary value problem. The model is applied to analyze the stress and strain fields near an edge crack under severe thermo-mechanical loading. Our numerical results reveal a significant departure from classical predictions: while stress concentrates intensely at the crack tip, the strain grows at a substantially slower rate and remains bounded throughout the domain. This work validates the efficacy of the strain-limiting model in regularizing thermo-elastic crack-tip fields and establishes a reliable computational foundation for the predictive modeling of thermally driven crack initiation and evolution in advanced anisotropic materials.

Crack-tip fields within a transversely isotropic strain-limiting elastic body are investigated under the influence of piecewise linear slope boundary loads. The mechanical response is characterized via a nonlinear constitutive framework relating the Cauchy stress to the linearized strain, by which non-physical strain singularities at the crack tip are eliminated. The governing system is formulated as a quasi-linear elliptic boundary value problem in terms of the displacement field and is solved utilizing a continuous Galerkin finite element method coupled with a Picard linearization scheme. Boundary conditions are prescribed such that the vertical displacement varies piecewise linearly along the top and bottom edges, exhibiting opposite slopes on each half of the boundary. Numerical results are derived for two distinct fiber orientations. It is demonstrated that piecewise slope loads provide a flexible and realistic configuration for elucidating the interplay between strain-limiting behavior and crack-tip mechanics in transversely isotropic media.

This study investigates the stability analysis of Rayleigh-B & eacute;nard configuration fora viscoelastic fluid subject to thermorheological effects, using the D-2-Chebyshev-r method. The fluid is modeled as a third-order viscoelastic fluid. This study accentuates how salting the fluid layer affects the thresholds for the onset of instability in a fluid of third order encompassing physically realistic rigid boundaries. The dynamic model incorporates advection-diffusion of temperature and solute concentration and a modified Navier-Stokes equation. We determine instability thresholds for the complex non-Newtonian fluid by analyzing the linear stability of the steady-state conduction solution. Our analysis proves the strong form of the principle of exchange of stabilities, demonstrating that convective motions can only occur through stationary motion. Additionally, a nonlinear stability analysis using the energy method is performed, deriving an unconditional nonlinear stability criterion. The results provide a comprehensive understanding of how variable viscosity and viscoelasticity impact system stability. Both the viscosity parameter and the third-grade fluid parameter exhibit stabilizing effects. Notably, we observe a discrepancy between the linear and global nonlinear stability results, indicating the presence of a subcritical instability region. This study contributes to the understanding of complex fluid dynamics in non-linear mechanical systems, with potential applications in various industrial and natural processes.

The stability of Darcy-Brinkman-B & eacute;nard model for Kelvin-Voigt fluids is investigated using a local thermal non-equilibrium (LTNE) configuration. The study considers physically realistic rigid surfaces, with the lower surface heated from below. The effects of spatially varying gravitational force and constant magnitude Lorentz force on the onset of convection are investigated. A systematic analysis is conducted on two porous materials: Sander sandstone and aluminum metallic foam (AL1050). Our mathematical model comprises the Kelvin- Voigt-Navier-Stokes equation, coupled with a two-equation, thermal non-equilibrium model of energy. The Fourier modes technique is used for linear instability analysis, while the energy method is applied for nonlinear stability analysis. The differential eigenvalue problems arising from linear and nonlinear theories are solved using the Spectral Collocation-QZ method. We determine the critical conditions for the onset of convection, examining the impact of the Darcy number, Darcy-Hartmann number, and inter-phase heat transport parameter. The results reveal a notable disparity between linear and nonlinear stability thresholds, with the latter being consistently lower. This discrepancy indicates the existence of a subcritical instability region. Our findings demonstrate that increased magnitudes of Lorentz and gravitational forces postpone the initiation of convective motion, thereby stabilizing the fluid system. This stabilization is reflected in higher Darcy-Rayleigh numbers, which potentially contribute to enhanced heat transfer rates. Similarly, an increase in the Darcy number leads to elevated Darcy-Rayleigh numbers, potentially improving thermal stability and heat transfer efficiency. Furthermore, we found that the subcritical instability regime expands significantly when both porosity and gravity field intensity reaches sufficiently high levels.

A finite element framework is presented for analyzing crack-tip phenomena in transversely isotropic, strain-limiting elastic materials. Mechanical response is characterized by an algebraically nonlinear constitutive model, relating stress to linearized strain. Non-physical strain singularities at the crack apex are mitigated, ensuring bounded strain magnitudes. This methodology significantly advances boundary value problem (BVP) formulation, especially for first-order approximate theories. For a transversely isotropic elastic solid with a crack, the governing equilibrium equation, derived from linear momentum balance and the nonlinear constitutive model, is reduced to a second-order, vector-valued, quasilinear elliptic BVP. This BVP is solved using a robust numerical scheme combining Picard-type linearization with a continuous Galerkin finite element method for spatial discretization. Numerical results are presented for various loading conditions, including uniform tension, non-uniform slope, and parabolic loading, with two distinct material fiber orientations. It is demonstrated that crack-tip strain growth is substantially lower than stress growth. Nevertheless, strain-energy density is found to be concentrated at the crack tip, consistent with linear elastic fracture mechanics principles. The proposed framework provides a robust basis for formulating physically meaningful, rigorous BVPs, critical for investigating fundamental processes like crack propagation, damage, and nucleation in anisotropic, strain-limiting elastic solids under diverse loading conditions.

The linear and nonlinear stability analyses of thermosolutal convection in a non-Newtonian Navier-Stokes-Voigt fluid, considering Soret and Ekman damping effects, are conducted analytically. Instability thresholds are determined for thermosolutal convection within a viscoelastic fluid of the Kelvin-Voigt type, wherein a dissolved salt field exists. Two scenarios are examined: one where the fluid layer is heated from the bottom and concurrently salted bottom, and the other where the fluid layer is heated from the bottom and concurrently salted top. The governing partial differential equations system includes conservation laws of mass, momentum, energy, and salt concentration. Using the nonlinear energy method, the disturbances to the fluid system is shown to decay exponentially. Analytical expressions are developed for the eigenvalue as a function of Soret, Lewis, Prandtl, Kelvin-Voigt, and Rayleigh friction numbers. The study illustrates the shift from a stationary mode of convection to an oscillatory mode and provides thresholds that indicate these transitions. It is found that the viscoelastic property of the fluid acts as a stabilizing agent for oscillatory mode convection. Rayleigh friction substantially controls the convection threshold. Upon comparing threshold values between linear and nonlinear theories, a subcritical instability region is observed in the heating bottom-salting bottom case (case-1), whereas such a region is absent in the heating bottom-salting top case (case-2).

The influence of Rayleigh friction and chemical reaction on the onset of double‐diffusive convection in a Navier–Stokes–Voigt (NSV) fluid layer is investigated by conducting linear instability and nonlinear stability analyses. The fluid layer is subjected to isothermal conditions and chemical equilibrium at the boundaries. The solubility of the dissolved component exhibits a linear dependency on temperature. The analysis is conducted for two distinct cases: the fluid layer is heated and salted from the bottom ( case‐1 ), and the fluid layer is heated from the bottom and salted from the top ( case‐2 ). Analytical expressions for the thermal Rayleigh number are obtained for both linear and nonlinear theories, and these expressions depend on Kelvin–Voigt, Rayleigh friction, solutal Rayleigh, Lewis, Prandtl, and Damkohler numbers. Including the Rayleigh friction term in the NSV fluid model improves the stability of the system and hence instability occurs with less ease. For lower solutal Rayleigh numbers, convection commences in the stationary mode and subsequently transitions to the traveling wave mode occurred in case‐1 . The Damkohler number plays a significant role in the linear instability thresholds. It is also found that the Kelvin–Voigt number acts as a stabilizing factor for oscillatory mode convection. The comparison between linear and nonlinear thresholds unveils the region characterized by subcritical instability.

In this paper, the finite element solutions of crack-tip fields for an elastic porous solid with density-dependent material moduli are presented. Unlike the classical linearized case in which material parameters are globally constant under a small strain regime, the stiffness of the model presented in this paper can depend upon the density with a modeling parameter. The proposed constitutive relationship appears linear in the Cauchy stress and linearized strain independently. From a subclass of the implicit constitutive relation, the governing equation is bestowed via the balance of linear momentum, resulting in a quasi-linear partial differential equation (PDE) system. Using the classical damped Newton’s method, the sequence of linear problems is then obtained, and the linear PDEs are discretized through a bilinear continuous Galerkin-type finite element method. We perform a series of numerical simulations for material bodies with a single edge-crack subject to a variety of loading types (i.e. the pure mode-I, II, and mixed-mode). Numerical solutions demonstrate that the modeling parameter in our proposed model can control preferential mechanical stiffness with its sign and magnitude along with the change of volumetric strain. This study can provide a mathematical and computational foundation to further model the quasi-static and dynamic evolution of cracks, utilizing the density-dependent moduli model and its modeling framework.

In this article, a finite element model is implemented to analyze hydro-thermal convective flow in a porous medium. The mathematical model encompasses Darcy's law for incompressible fluid behavior, which is coupled with a convection-diffusion-type energy equation to characterize the temperature in the porous medium. The current investigation presents an efficient, stable, and accurate finite element discretization for the hydro-thermal convective flow model. The well-posedness of the proposed discrete Galerkin finite element formulation is guaranteed due to the decoupling property and the linearity of the numerical method. Computational experiments confirm the optimal convergence rates for a manufactured solution. Several numerical results are obtained for the variations of the hydraulic resistivity and thermal diffusivity. In the present study, the bottom wall is maintained at a constant higher hot temperature while side vertical walls are thermally insulated and the top wall is maintained at a constant cold temperature. Heat transfer rates at the heated bottom wall are presented in terms of local Nusselt number. A linear variation in hydraulic resistivity and a quadratic variation in thermal diffusivity show an increase in the heat transfer rate.

A study of the rheological and heat transport characteristics in cone–disk systems finds relevance in many applications such as viscometry, conical diffusers, and medical devices. Therefore, a three‐dimensional axisymmetric flow with heat transport of a magnetized nanofluid in a cone–disk system subjected to Hall current and thermal radiation effects is investigated. The simplified Navier–Stokes (NS) equations for the cone–disk system given by Sdougos et al. [18] Journal of Fluid Mechanics, 138, 379–404 are solved by using the asymptotic expansion method for the four different models, such as rotating cone with static disk (Model I), rotating disk with static cone (Model II), co‐rotating cone and disk (Model III), and counter‐rotating cone and disk (Model IV). The Khanafer–Vafai–Lightstone (KVL) model along with experimental data‐based properties of 37 nm Al 2 O 3 –H 2 O nanofluid is considered. To obtain the transformations leading to self‐similar equations from the Navier–Stokes (NS) and energy conservation equations, the Lie group technique is used. The self‐similar nonlinear problem is solved numerically to examine the effects of physical parameters. There are critical values of the power exponent at which no heat transport from the disk surface occurs. Nanoparticles significantly enhance heat transport when both the cone and disk rotate in the same or opposite directions. The centrifugal force and thermal radiation improve the heat transport in cone–disk systems.

In this chapter, a theoretical study of the Falkner–Skan flow and heat transport of a Newtonian ethylene glycol containing MWCNT-MgO hybrid nanoparticles on a wedge-shaped surface using the modified Buongiorno nanofluidic model (MBNM) is performed. The mechanisms of Brownian motion (BM) and microscopic thermophoresis (MT) of solid nanoparticles are implicitly included together with the thermophysical properties. The effects of thermal radiation, the Lorentz force, and Joule heating are examined. The passive control of the nanoparticles and the thermal jump boundary conditions are considered. The governing equations are modeled using the conservation of mass, the Navier–Stokes equation, the conservation of energy, and the conservation of nanoparticle volume fraction. The Prandtl boundary layer and Rosseland heat flux approximations were used. The velocity, temperature, and volume fraction of nanoparticles behaviors are analyzed for various parameters. It is determined that the temperature of the hybrid nanofluid increased due to the presence of Joule heating, radiative heat flux, Brownian motion, and thermophoresis aspects in the system. Furthermore, a hybrid nanoliquid exhibits a higher heat transfer rate than mono nanoliquid and base fluid.

A fully developed laminar steady flow of an incompressible, viscous fluid in a horizontal cylindri-cal pipe is considered here. Flow patterns for an incompressible, viscous fluid for both Newtonian and non-Newtonian fluids such as shear-thinning, shear-thickening and Bingham plastic fluids are analyzed in this study. Assuming that the flow is only due to the wall shear stress and the pressure drop, the velocity component in the axial direction for these cases is derived. Computational results of the velocity profiles for various cases are obtained using MATLAB and presented in graphical forms. It is observed that the velocity profile is parabolic for Newtonian fluid whereas it is flatter for a shear-thinning fluid and sharper for a shear-thickening fluid. For a Bingham fluid, the velocity reaches a constant value known as the plug velocity in the central plug flow region, and it decreases gradually to zero at the pipe wall.

Linear stability and weakly nonlinear stability analyses are developed for Rayleigh–Bénard convection in water near 3.98 °C subject to isothermal boundary conditions. The density–temperature relationship (equation of state) is approximated by a cubic polynomial, including linear, quadratic, and cubic terms. The continuity equation, the Navier–Stokes momentum equation, the equation of state, and the energy equation constitute the governing system. Linear stability analysis is used to investigate how the maximum density property of water affects the onset of convective instability and the choice of unstable wave number for four different types of boundary conditions. Then, a weakly nonlinear stability study is done using the spectral Fourier method for isothermal tangential stress-free boundary conditions to quantify the heat transport of the system and demonstrate the transition from regular/periodic convection to chaotic convection. A Stuart-Ginzburg–Landau equation is obtained using the multiscale expansion method. Streamlines and isotherms are presented and analyzed. The influence of maximum density has been shown to delay the onset of instability and is, therefore, a stabilizing mechanism for thermal instability. Due to the maximum density, the onset of chaotic convection is also delayed. Among four different boundaries, the impermeable rigid boundaries require the highest Rayleigh number for instability to begin. Increasing boundary temperatures advance the onset of chaotic convection and improve the heat transport situation.

The classical Boussinesq approximation (linear density-temperature variation) is valid for small temperature differences in the system. However, density varies with temperature nonlinearly in various applications, such as heat exchangers, solar collectors, and nuclear reactors. Therefore, unsteady nonlinear mixed convection (quadratic density-temperature variation) in a nanofluid on a vertical plate due to impulsive motion is investigated. Modified Nield and Kuznetsov nanofluid model is incorporated that considers physical realistic boundary conditions. Unsteady flow is governed by the conservation of mass, momentum, energy, and the continuity equation of nanoparticles. Williams-Rhyne transformations are used to parameterize and reduce the infinite time domain to a finite time domain. Subsequent nonlinear differential equations system is solved by using the Finite Difference Method (FDM) based routine. Rayleigh and Hiemenz type equations are obtained respectively in an initial-unsteady and final-steady state. The Response Surface Method (RSM) and Central Composite Design (CCD) are used for the simultaneous optimization of the friction factor and the rate of heat transport. It is found that the quadratic density-temperature variation significantly affects the flow fields. The friction factor has the highest and positive sensitivity toward the thermal buoyancy number. The heat transport rate has the highest and negative sensitivity toward the thermo-migration of nanoparticles.

Heat and mass transfer rates play a significant role in achieving a high-efficiency, low-cost wire coating process. Therefore, the flow analysis of molten polymer (polyvinyl chloride) carrying nanoparticles inside a pressure-type die is presented. The third-grade liquid model is used for the constitutive equation of the polyvinyl chloride (PVC), while the non-homogeneous biphasic model is used for nanoparticles. The properties of PVC are temperature-dependent. The melt flow is governed by the modified Navier-Stokes equation for the third-grade fluid, energy conservation, and nanoparticles' continuity equation. The finite difference method-based routine is applied to solve the nonlinear differential equations that include nine physical parameters. The Response Surface Method (RSM) is implemented to optimize the heat/mass transfer rate coated wire's eminence depends on the coating material's rheological characteristics of PVC. Full quadratic correlation models for heat/mass transfer rate of melt are proposed through central-composite-design (CCD). The optimal level of third-grade fluid factor and nanofluid factors was determined to achieve an optimum heat/mass transfer rate of the melt. The rheological characteristics of PVC have been improved due to the temperature-dependent viscosity and shear thickening/thinning property of the melt. The nanofluid factors improve the thermal field and subsequently reduce the Nusselt number. Maximum heat transfer occurs for a low level of Brownian factor, a high level of thermophoresis factor, and a third-grade fluid factor of 0.2177, also reaching the maximum mass transfer simultaneously.

In this paper, we study the preferential stiffness and the crack-tip fields for an elastic porous solid of which material properties are dependent upon the density. Such a description is necessary to describe the failure that can be caused by damaged pores in many porous bodies such as ceramics, concrete and human bones. To that end, we revisit a new class of implicit constitutive relations under the assumption of small deformation. Although the constitutive relationship \textit{appears linear} in both the Cauchy stress and linearized strain, the governing equation bestowed from the balance of linear momentum results in a quasi-linear partial differential equation (PDE) system. For the linearization and obtaining a sequence of elliptic PDEs, we propose the solution algorithm comprise a \textit{Newton's method} coupled with a bilinear continuous Galerkin-type finite elements for the discretization. Our algorithm exhibits an optimal rate of convergence for a manufactured solution. In the numerical experiments, we set the boundary value problems (BVPs) with edge crack {under different modes of loading (i.e., the pure mode-I, II, and the mixed-mode). From the numerical results, we find that the density-dependent moduli model describes diverse phenomena that are not captured within the framework of classical linearized elasticity. In particular,numerical solutions clearly indicate that the nonlinear \textit{modeling} parameter depending on its sign and magnitude can control preferential mechanical stiffness along with the change of volumetric strain; larger the parameter is in the positive value}, the responses are such that the strength of porous solid gets weaker against the tensile loading while stiffer against the in-plane shear (or compressive) loading, which is vice versa for the negative value of it.

The cone–disk apparatus consists of a cone that touches the disk at its apex and is used in medical evices, viscosimeters, conical diffusers, etc. Theoretically, a three-dimensional flow of a nanofluid in a conical gap of a cone–disk apparatus is studied for four different physical configurations. Buongiorno nanofluid model, consisting of thermophoresis and Brownian diffusion mechanisms, is used to describe the convective heat transport of the nanofluid. The continuity equation, the Navier–Stokes momentum equation, the heat equation, and the conservation of nanoparticle volume fraction equation constitute the governing system for the flow of nanofluids. The Lie group approach is used to obtain self-similar equations. Solutions are computed for an appropriate rotational Reynolds number and four different gap angles to examine flow, mass, and heat transport features. The skin friction coefficients and torque are computed and analyzed. Multivariate nonlinear regression analysis is also performed. A co-rotating disk and cone configuration has been shown to produce less torque due to the increased centrifugal force. Of the four cone–disk apparatus configurations, the maximum heat/mass transport occurs for a rotating disk with a static cone for all selected gap angles, and the least drag in the radial direction is attained for a rotating cone with a static disk. In addition, there is a minimal drag along the tangential direction for the counter-rotating disk and cone configuration. Brownian diffusion and thermophoresis of the nanoparticles lead to a higher fluid temperature and, thus, lower Nusselt numbers are obtained.