فهرست مطالب

Applied and Computational Mechanics - Volume:6 Issue: 3, 2020
  • Volume:6 Issue: 3, 2020
  • تاریخ انتشار: 1398/11/29
  • تعداد عناوین: 25
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  • Wenlong Zhang *, Ala Tabiei Pages 373-382
    The phase field method integrates the Griffith theory and damage mechanics approach to predict crack initiation, propagation, and branching within one framework. No crack tracking topology is needed, and complex crack shapes can be captures without user intervention. In this paper, a detailed description of how the phase field method is implemented with explicit dynamics into LS-DYNA is provided. The displacement field and the damage field are solved in a staggered approach and the phase field equation is solved every Nth time step (N is refered to as calculation cycle) to save computational time. An N value smaller than 1/400 of the total time step numbers is suggested. Several simulations are presented to demonstrate the feasibility of this solving scheme.
    Keywords: Phase field method, Calculation cycle, LS-DYNA, Explicit time integration
  • Farzad Pashmforoush * Pages 383-393
    An effort is made to gain insight on the effect of carbon nanotubes (CNTs) on the impact response of carbon fiber reinforced composites (CFRs) under low velocity impact. Certain amount of CNTs could lead improvements in mechanical properties of composites. In the present investigation, ABAQUS/Explicit finite element code (FEM) is employed to investigate various damages modes of nano composites including matrix cracking, fiber damage and delamination by employing Hashin’s criterion and cohesive zone modeling. The obtained results for 0, 0.5, 1, 2 and 4% CNTs demonstrate that by including CNTs in composite plates, damage could be reduced. However, adding further CNTs causes sudden reduction of impact tolerance capability of the composite plates, particularly, damage due to delamination.
    Keywords: Nano-composites, Impact behavior, Finite element analysis, Damage mechanisms, Carbon nanotubes
  • R.P. Shimpi, P.J. Guruprasad, K.S. Pakhare * Pages 394-415
    In this paper, a displacement-based, variationally consistent, two variable refined theory for shear deformable beams is presented. The beam is assumed to be of linearly elastic, homogeneous, isotropic material and has a uniform rectangular cross-section. In this theory, the beam axial displacement and beam transverse displacement consist of bending components and shearing components. The assumed displacement field of this theory is such that, bending components do not take part in the cross-sectional shearing force, and shearing components do not take part in the cross-sectional bending moment. This theory utilizes linear strain-displacement relations. The displacement functions give rise to the beam transverse shear strain (and hence to the beam transverse shear stress) which varies quadratically through the beam thickness and maintains transverse shear stress-free beam surface conditions. Hence the shear correction factor is not required. Hamilton’s principle is utilized to derive governing differential equations and variationally consistent boundary conditions. This theory involves only two governing differential equations of fourth-order. These governing equations are only inertially coupled for the case of dynamics and are decoupled for the case of statics. This theory is simple and has a strong resemblance with the Bernoulli-Euler beam theory. To demonstrate the efficacy of the present theory, illustrative examples pertain to the static bending and free vibrations of shear deformable isotropic rectangular beams are presented.
    Keywords: Refined beam theory, Two variable, Shear deformation theory
  • Mohsen Rahmani, Younes Mohammadi *, Farshad Kakavand, Hamed Raeisifard Pages 416-432
    Vibration behavior of different types of porous functionally graded (FG) conical sandwich shells are investigated based on a modified high order sandwich shells theory for the first time. Sandwich shell includes FG face sheets covering a homogeneous core and the second one includes homogeneous face sheets and a FG core. Power law rule modified by considering two types of porosity distributions is used to model the functionally graded materials. All materials are temperature dependent and uniform, linear and nonlinear temperature distributions are used to model the effect of the temperature variation in the sandwiches. Governing equations are obtained by the Hamilton's energy principle and solved with Galerkin method. To verify the results, they are compared with ones achieved by finite element method obtained by Abaqus software for special cases with the results in literatures.
    Keywords: Conical sandwich shell, Porosity, FG core, Temperature Dependent, Vibration
  • Akinbowale T. Akinshilo *, Adeleke Ilegbusi, Hafiz M. Ali, Abdul Jalil Surajo Pages 433-444

    In this paper, flow and heat transfer of nanofluid through a converging or diverging channel with porous medium is investigated. The fluid constantly flows under the effect of magnetic field through the channel. The diverging/converging fluid motion is modeled using the momentum and energy equations. The influence of some parameters such as opening channel angle, Reynolds number and Darcy’s number when the nanofluid flows through the non-parallel plates are studied. It is seen that high Reynolds number enhances the fluid viscosity while decreases velocity. Similarly, heat transfer reduces at high Darcy’s number owing to decreased flow consequently internal friction reduces. The obtained results in comparison with the similar studies in the literatures show satisfactory agreement.

    Keywords: Jeffery Hamel, Nanofluid, Diverging, Converging plates, Porous medium, HPM
  • Ahmed Abouelregal * Pages 445-456
    In the present work, a modified model of heat conduction including higher order of time derivative is derived by extending Green and Naghdi theory without energy dissipation. We introduce two phase lag times to include the thermal displacement gradient and the heat flux in the heat conduction and depict microscopic responses more precisely. The constructed model is applied to study thermoelastic waves in a homogeneous and isotropic perfect conducting unbounded solid body containing a spherical cavity. We use the Laplace transform method to analyze the problem. The solutions for the field functions are obtained numerically using the numerical Laplace inversion technique. The results are analyzed in different tables and graphs and compared with those obtained earlier in the contexts of some other theories of thermoelasticity.
    Keywords: Thermoelasticity, Green-Naghdi model II, Phase-lags, Higher-order, Spherical cavity
  • Wei Ren Chen *, Chun Sheng Chen, Heng Chang Pages 457-470

    Thermal buckling behavior of functionally graded Euler-Bernoulli beams in thermal conditions is investigated analytically. The beam with material and thermal properties dependent on the temperature and position is considered. Based on the transformed-section method, the functionally graded beam is considered as an equivalent homogeneous Euler-Bernoulli beam with an effective bending rigidity under an eccentric thermal load. Then, the thermal elastic buckling equation associated with the bending deflection about the neutral axis is established. The easily usable closed-form solutions for the critical thermal buckling temperature of functionally graded beams under uniform and non-linear temperature rise are obtained and used to calculate the thermal buckling temperature. Some results are evaluated and compared with those by other investigators to validate the accuracy of the presented method. The effects of material compositions, temperature-dependent material properties, slenderness ratios and restraint conditions on thermal buckling behaviors are discussed. It is believed that the proposed model provides engineers and designers an easy and useful method to investigate the effects of various parameters affecting the thermal buckling characteristics of functionally graded beams.

    Keywords: Thermal buckling, Euler-Bernoulli beam, Transformed-section method, Functionally graded beam, Buckling temperature
  • Yonghui Park * Pages 471-479
    In this study, dynamic behavior of a mooring line in a floating system is analyzed by probability approaches. In dynamics, most researches have shown the system model and environments by mathematical expression. We called this process as the forward dynamics. However, there is a limit to define the exact environments because of uncertainty. To consider uncertainty, we introduce the redundancy in flexible system, mooring line. For verifying the effectiveness and stability of the mooring line, criterion of axial breaking load of the mooring line is applied to joint reaction forces according to the various path of the mooring line. To cover the limits for defining the non-linearity of the environments, various responses of the mooring line along the redundancy that is used in Robotics, are derived by probability distribution. By using the Newton-Euler formulation, the inverse kinematics and the linear acceleration theorem to get joint displacements, velocities and accelerations, the joint reaction forces and moments are calculated and probability distribution of the mooring about stability and compatibility is investigated. Lastly, we simulate the flexible systems in various null motions, calculated each joint torque and force, and evaluated failure probabilities using the Monte-Carlo method.
    Keywords: Structural Analysis, Mooring line, Dynamics, Newton-Euler formulation, Redundancy
  • Arash Bahari Kordabad *, Mehrdad Boroushaki Pages 480-492
    During the milling process, one of the most important factors in reducing tool life expectancy and quality of workpiece is the chattering phenomenon due to self-excitation. The milling process is considered as a MIMO strongly coupled nonlinear plant with time delay terms in cutting forces. We stabilize the plant using two independent Emotional Learning-based Intelligent Controller (ELIC) in parallel. Control inputs are considered as forces Ux and Uy in two directions x and y, which are applied by the piezoelectrics. The ELIC consists of three elements; Critic, TSK controller and the learning element. The results of the ELIC have been compared with a Sliding Mode Controller (SMC). The simulation for the nominal plant shows better performance of the ELIC in IAE and ITSE values at least 86% in the x-direction and 79% in the y-direction. Similar simulation for an uncertain plant also shows an improvement of at least 89% in the x-direction and 97% in the y-direction.
    Keywords: Emotional learning, Intelligent control, Peripheral milling, nonlinear MIMO, Time-delay, Sliding mode
  • Fazilay Abbès, Boussad Abbès *, Rim Benkabou, Aïssa Asroun Pages 493-504
    This paper aims to develop a numerical multiscale homogenization method for prediction of elasto-viscoplastic properties of a high performance concrete (HPC). The homogenization procedure is separated into two-levels according to the microstructure of the HPC: the mortar or matrix level and the concrete level. The elasto-viscoplastic behavior of individual microstructural phases of the matrix are identified from nanoindentation data using an inverse identification method. The micromechanical results are then used as input parameters for numerical elasto-viscoplastic homogenization at microscale. The mortar level is analyzed with numerical homogenization by using the finite element simulation to predict the overall elasto-viscoplastic properties of HPC. The results are compared with macroscopic experimental and analytical results from the literature showing a good agreement.
    Keywords: Homogenization, Nanoindentation, Finite element simulation, Elasto-viscoplastic model, Multiscale modeling, High performance concrete
  • Jean Baptiste Sauvage, Pierre Chalandon, Dominique Poquillon, Michel Nardin, Maëlenn AUFRAY * Pages 505-516

    An elastic finite element analysis was conducted to evaluate the stress distribution in the initiation zone of the adhesive rupture during the 3-point bending test. This test is used to measure the adherence between a polyepoxy adhesive and aluminum alloy with different surface treatments. The purpose is to compare, in the high stress concentration areas, the stress fields calculated using finite element method with the experimental data obtained in different configurations. Focusing on the load level at crack initiation, on the localization and the size of adhesive failure initiation, a local criterion for adhesive fracture is proposed based on the value of the stress normal to the interface.

    Keywords: 3-point bending, Adhesive failure, Initiation test, FEM, Stress, strain distribution
  • Raju Kumhar *, Santimoy Kundu, Shishir Gupta Pages 517-530
    The present article is devoted to a theoretical study on Love wave vibration in a pre-stressed fluid-saturated anisotropic porous viscoelastic medium embedded over an inhomogeneous isotropic half-space influenced by gravity. The expression of dispersion has been achieved with the help of mathematical tools such as variable separable method and Whittaker’s function’s expansion under certain boundary conditions. After that, the obtained result has been coincided with the pre-established classical equation of Love wave, as shown in the section of particular case and validation. The substantial influence of various affecting factors like gravity, initial stress, porosity, viscosity and inhomogeneity on dispersion curves of Love wave has been investigated extensively by means of graphical depictions and discussions accomplished by numerical results.
    Keywords: Love waves, porous, Viscoelastic, Gravity, Whittaker’s function
  • P. Naga Santoshi *, G.V. Ramana Reddy, P. Padma Pages 531-542
    This study presents the computational analysis of three dimensional Casson and Carreau nanofluid flow concerning the convective conditions. To do so, the flow equations are modified to nonlinear system of ODEs after using appropriate self-similarity functions. The solution for the modified system is evaluated by numerical techniques. The results show the impacts of involving variables on flow characteristics and the outcomes of the friction factors are evaluated as well. In this study, the outcomes to local Nusselt number and Sherwood numbers are evaluated. Favourable comparison is performed with previously available outcomes. The achieved results are similar to solutions obtained by other researchers. The results are presented for flow characteristics in the case of Casson and Carreau fluids. Velocities are reduced for the growing values of permeability and velocity slip parameters in case of Casson and Carreau nanofluids. Temperature field enhances with the hike in the estimations of thermophoresis parameter and the thermal Biot number in case of Casson and Carreau nanofluids. Enhancing values of velocity slip parameter results in decrease in the skin friction coefficients and the rate of heat transfer, and rise in the rate of mass transfer in case of Casson and Carreau nanofluids.
    Keywords: Steady flow, Three dimensional flow, Casson Fluid, Carreau Fluid, Nano fluid, stretching Sheet, Convective condition
  • Liping Tang *, Wei He, Xiaohua Zhu, Yunlai Zhou Pages 543-553
    The sealing performance of end fittings is very important for offshore oil and gas pipelines. To investigate the sealing behavior of a ring-shaped wedge seal, global and local numerical models of the ring–pipe interaction have been developed based on the finite-element method. First, the sealing process of the ring under pressure is simulated. Second, a criterion for the penetration of fluid pressure is applied in these models to assess how the sealing capacity changes along the contact surface. Finally, the contact magnitude of interference and the shape of the sawtooth heaves on the sealing ring are predicted and compared. The results show an interesting concentration of von Mises stress in the sealing ring and also that the peak contact pressure appears in the sealing zone. However, the penetration of fluid pressure has obvious effects on the distributions of von Mises stress and contact pressure. The best sealing performance is when the axial displacement of the sealing ring is 1.4 mm and the contact magnitude of interference is 0.3 mm. Given the sawtooth heave of sealing ring, semicircular heave gives the better sealing capacity compared with trapezoidal heave.
    Keywords: Marine unbonded flexible pipe, Sealing performance, Finite-element method, Pressure penetration, Contact pressure
  • J. Stephen Leon *, V. Jayakumar Pages 554-563
    In friction stir welding frictional heat is generated by the rotating tool, sliding over the stationary plate along the weld centre. Tool being the only source of heat producing member, its geometrical design influences the heat generation rate. In this present work, effects of variation in tool shoulder and tool pin taper angles on thermal history during joining are analysed. Tools with triangular and hexagonal tool pins are used to understand the influence of tool pin shape on process temperature. An analytical heat input model is developed for tools with non-circular tool pins and a comparative study is carried out between the hexagonal and triangular tool pins on temperature distribution using a three dimensional Matlab model. Proposed model is validated through experimental analysis. Apart from this, regression model based comparative study is carried out on the variation in temperature response to the change in tool pin shape, tool shoulder and tool pin taper angle.
    Keywords: Tool design, Thermal analysis, Friction stir welding, Non-circular tool pin
  • J.V. Ramana Reddy, D. Srikanth * Pages 564-581
    The analysis of solute and thermal dispersion in pulsatile flow through the stenotic tapered blood vessel is presented. The present problem is an extension of the work done by Ramana et al. who considered the time-invariant arterial wall. In the present model, the flexible nature of the arterial wall through the obstruction (called stenosis) is considered and it is achieved with the help of period trigonometric function. In the present study, the impact of the time-dependent arterial wall on the blood flow dynamics is discussed in details. The rheology of the blood is modeled as a couple stress fluid. The proposed fluid model is the isothermal inclusion of temperature-sensitive drug coated Titanium dioxide Nano-particles in the couple stress fluid for examining the concentration and temperature dispersion. The effects of the catheter and permeability of the stenosis are considered in the model. Care has been taken to model the thermo-physical properties of the fluid with the immersed nanoparticle, e.g., TiO2, Ag and Cu. The modeled non-linear and coupled equations are solved by using the Homotopy Perturbation Method. The temperature and concentration dispersion effects are in the flexible stenotic arterial vessel under the pulsatile physiological pressure gradient are studied and reported in details. The alterations in the axial velocity, resistance to the flow, and wall shear stress are studied and found out that the high intense vortex regions are identified in the stenotic region. The model has direct applications in the pharmaceutical industry in design and developing the drug to treat stenotic conditions.
    Keywords: Flexible arterial wall, Couple stress nano fluid, Homotopy perturbation method, Temperature dispersion, Drug delivery, Impedance, Wall shear stress
  • Mohammad Hasan Taheri *, Nematollah Askari, Mohammad Hadi Mahdavi Pages 582-592
    This paper focuses on using the numerical finite volume method (FVM) and artificial neural network (ANN) in order to propose a correlation for computing the entrance length of laminar magnetohydrodynamics (MHD) channels flow. In the first step, for different values of the Reynolds (Re) and Hartmann (Ha) numbers (600<ReL increases.
    Keywords: Artificial neural network, Channel, Magnetohydrodynamics, MHD entrance length, Numerical simulation
  • Fereydoon Omidinasab *, Vahid Goodarzimehr Pages 593-604
    A new hybrid algorithm of Particle Swarm Optimization and Genetic Algorithm (PSOGA) is presented to get the optimum design of truss structures with discrete design variables. The objective function chosen in this paper is the total weight of the truss structure, which depends on upper and lower bounds in the form of stress and displacement limits. The Particle Swarm Optimization basically modeled the social behavior of birds on the basis of the fact that Individual birds exchange information about their position, velocity, fitness, and on the basis that the behavior of the flock is then influenced to increase the probability of migration to other regions with high fitness. One of the problems of PSO is that it is easily trapped at the local point due to its non-uniform movement. The present study uses the mutation, random selection, and reproduction to reach the best genetic algorithm with the operators of natural genetics. Therefore, only identical chromosomes or particles can be converged. In other words, PSO and GA algorithm goes from one point in the search space to another point, interacting with each other. In this way, this helps them to find the optimum design by means of deterministic and probabilistic rules. The present study merged the two algorithms together in order to design several benchmark truss structures, and then the results of the new algorithm compared to those of other evolutionary optimization methods.
    Keywords: Particle Swarm Optimization, Genetic Algorithm, Size optimization, Structural optimization, Discrete variables
  • D. Dastagiri Babu *, S. Venkateswarlu, E. Keshava Reddy Pages 605-616
    An analysis is suggested to study the impact of Hall currents in Jeffrey fluid which is chemically reactive through a porous medium limited by a semi-infinite vertical permeable plate within the existence of heat generation. An evenly distributed magnetic field turns vertically on the porous surface which absorbs the Jeffrey fluid with a changed suction velocity with time. The analytical expressions are solved by means of three terms harmonic and non-harmonic functions. Statistical calculations are carried out for the point of resultant outcomes which are shown graphically and the impacts of the parameters velocity, temperature and concentration are listed. In addition, the results of skin-friction coefficient (τ), Nusselt number (Nu) and Sherwood number (Sh) are taken in to consideration. It is revealed that the impact of the Hall parameter on the channel velocities and skin friction coefficient is subjected to the estimation of the wall suction parameter.
    Keywords: MHD flows, Jeffrey fluid flow, Porous medium, Unsteady flows
  • K.N.V. Chandrasekhar *, V. Bhikshma, S. Abdul Mohi Pages 617-639
    The need of polygonal elements to represent the domain is gaining interest among structural engineers. The objective is to perform static analysis and topology optimization of a given continuum domain using the rational fraction type shape functions of six node hexagonal elements. In this paper, the main focus is to perform the topology optimization of two-dimensional plate structures using Evolutionary Swarm Intelligence Firefly Algorithms (ESIFA) and three-dimensional shell structures using optimality criteria. The optimization of plates carrying in plane loading is performed with minimum weight as objective. Two different types of shell structures are optimized using maximum strain energy as criteria. The optimal distribution of the material in the design domain obtained using six node hexagon elements is compared with the optimal distribution of material obtained using quadrilateral elements. A few problems from the literature have been solved and this study has proved that hexagon element gives better results over traditional quadrilateral elements.
    Keywords: Six node hexagon, Topology, Shells, Firelfy algorithms, Strain energy optimization, Weight optimization
  • A. Patra, M.K. Nayak *, Ashok Misra Pages 640-652
    In the present investigation, the magnetohydrodynamic Falkner-Skan flow of tangent hyperbolic nanofluids over a stretching/shrinking wedge with variable suction, internal heat generation/absorption and chemical reaction with activation energy have been scrutinized. Nanofluid model is composed of “Brownian motion’’ and “Thermophoresis’’. Transformed non-dimensional coupled non-linear equations are solved by adopting the fourth-order R-K method along with the shooting technique. A comprehensive analysis of nanofluid velocity, the relative temperature, and its concentration profiles has been addressed. The major outcomes of the current study include that augmentation in the Weissenberg parameter, Hartmann number along with suction impede fluid flow and the shrinkage of the related boundary layer while internal heating develops an ascending thermal boundary layer for static and moving (stretching/shrinking) wedge. An increment in reaction rate undermines the nanoparticle concentration while that of activation energy exhibits a reverse trend.
    Keywords: Falkner-Skan MHD Flow, Tangent Hyperbolic Nanofluid, Stretching, shrinking wedge, Variable Suction, Chemical Reaction with activation energy, Heat generation, absorption
  • Chandra Shekar Balla *, Ramesh Alluguvelli, Kishan Naikoti, Oluwole Daniel Makinde Pages 653-664
    In this paper, the bioconvective flow in a porous square cavity containing oxytactic microorganism in the presence of chemical reaction is investigated. The bioconvection flow and heat transfer in porous media are formulated based on the Darcy model of Boussinesq approximation. The governing partial differential equations are solved using the Galerkin finite element method. The computational numerical results are exhibited by the streamlines, isotherms, isoconcentrations of oxygen, isoconcentrations of microorganisms, average Nusselt number, average Sherwood numbers of oxygen concentration and microorganisms. The effects of key parameters such as bioconvection Rayleigh number (Rb), chemical reaction parameter (Kr) and thermal Rayleigh number (Ra) are presented and analyzed. It can be deduced that the chemical reaction reduces the strength of isoconcentrations of both oxygen and microorganisms. It has been revealed that the chemical reaction has a greater effect on the swimming of the microorganisms, average Nusselt number, and average density number.
    Keywords: thermo-bioconvection, oxytactic microorganisms, porous square cavity, Chemical reaction, Finite element method
  • George C. Tsiatas *, Ioannis N. Tsiptsis, Antonis G. Siokas Pages 665-683
    In this work, the nonlinear buckling and post-buckling behavior of shallow arches made of Shape Memory Alloy (SMA) is investigated. Arches are susceptible to large deflections, due to their slenderness, especially when the external load exceeds the serviceability limit point. Beyond this, loss of stability may occur, the famous snap-through buckling. For this reason, curved beams can be used in passive vibration control devices for seismic response mitigation, and the geometrically nonlinear analysis is needed for the accurate prediction of their response. Thus, in this research effort, the assumptions of the Euler-Bernoulli beam theory are considered, and the Von Karman strain field is employed to account for large deflections. The formulation of the problem is displacement-based regarding the axial (tangential) and transverse (normal) displacements, while the two governing equations are coupled and nonlinear. In order to introduce the SMA constitutive law, the stress-strain experimental curves described in the literature are employed together with a fiber approach at specific control cross-sections along the beam. The numerical solution of the longitudinal problem is achieved using the Analog Equation Method (AEM), a Boundary Element Method (BEM) based technique, and the iterative procedure is based on a Newton-Raphson scheme by using a displacement control algorithm to trace the fully nonlinear equilibrium path and overcome the limit points. Several representative examples are studied, not only to validate the proposed model but also to investigate the nonlinear buckling and post-buckling of SMA shallow arches.
    Keywords: Shallow arches, Shape Memory Alloys, Buckling, Nonlinear Analysis, Fiber Approach
  • Huitzilín Yépez Martínez, José Francisco Gómez Aguilar * Pages 684-698

    A universal approach by Laplace transform to the variational iteration method for fractional derivatives with the nonsingular kernel is presented; in particular, the Caputo-Fabrizio fractional derivative and the Atangana-Baleanu fractional derivative with the non-singular kernel is considered. The analysis elaborated for both non-singular kernel derivatives is shown the necessity of considering the modified Caputo-Fabrizio fractional derivative and the analogous modifications for the Atangana-Baleanu fractional derivative with non-singular Mittag-Leffler kernel in order to satisfy the initial conditions for some fractional differential equations.

    Keywords: Variational iteration method, Fractional calculus, Laplace transform, Modified Caputo-Fabrizio fractional derivative, Modified Atangana-Baleanu fractional derivative
  • Dhananjay Yadav * Pages 699-712
    In this study, a numerical examination of the significance of rotation and changeable gravitational field on the start of nanofluid convective movement in an anisotropic porous medium layer is shown. A model that accounts for the impact of Brownian diffusion and thermophoresis is used for nanofluid, while Darcy’s law is taken for the porous medium. The porous layer is subjected to uniform rotation and changeable downward gravitational field which fluctuates with the height from the layer by linearly or parabolic. The higher-order Galerkin technique is applied to obtain the numerical solutions. The outcomes demonstrate that the rotation parameter TD, the thermal anisotropy parameterh and the gravity variation parameter λ slow the beginning of convective motion, whereas the mechanical anisotropy parameter ξ, the nanoparticle Rayleigh-Darcy number Rnp, the modified diffusivity ratio NAnf and the modified nanofluid Lewis number Lenf quick the start of convective motion. For instance, by rising the gravity variation parameterfrom zero to 1.4, the critical nanofluid thermal Rayleigh-Darcy number Rnf,c and the critical wave numberboost maximum around 133% and 7%, respectively for linear variation of the gravity field, while it were 47% and 2.8% for parabolic variation of the gravity field. It is also observed that the system is more unstable for the parabolic variation of the gravity field.
    Keywords: Nanofluids, Convective instability, Rotation, Variable gravity, Anisotropic porous medium