Journal of Applied and Computational Mechanics
Volume:6 Issue: 1, winter 2020

This paper proposes a new adaptive extended Kalman filter (AEKF) for a class of nonlinear systems perturbed by noise which is not necessarily additive. The proposed filter is adaptive against the uncertainty in the process and measurement noise covariances. This is accomplished by deriving two recursive updating rules for the noise covariances, these rules are easy to implement and reduce the number of noise parameters that need to be tuned in the extended Kalman filter (EKF). Furthermore, the AEKF updates the noise covariances to enhance filter stability. Most importantly, in the worst case, the AEKF converges to the conventional EKF. The AEKF performance is determined based on the mean square error (MSE) performance measure and the stability is proven. The results illustrate that the proposed AEKF has a dramatic improved performance over the conventional EKF, the estimates are more stable with less noise.

A sequential implicit numerical scheme is proposed for a system of partial differential equations defining the transport of heat and mass in the channel flow of a variable-viscosity fluid. By adopting the backward difference scheme for time derivative and the central difference scheme for the spatial derivatives, an implicit finite difference scheme is formulated. The variable-coefficient diffusive term in each equation is first expanded by differentiation. The next step of the sequential approach consists of providing a solution of the temperature and concentration, before providing a solution for the velocity. To verify the numerical scheme, the results are compared with those of a Matlab solver and a good agreement are found. We further conduct a numerical convergence analysis and found that the method is convergent. The numerical results are investigated against the model equations by studying the time evolution of the flow fields and found that the data, such as the boundary conditions, are perfectly verified. We then study the effects of the flow parameters on the flow fields. The results show that the Solutal and thermal Grashof numbers, as well as the pressure gradient parameter, increase the flow, while the Prandtl number and the pollutant injection parameter both decrease the flow. The conclusion of the study is that the sequential scheme has high numerical accuracy and convergent, while a change in the pollutant concentration leads to a small change in the flow velocity due to the opposing effects of viscosity and momentum source.

This study analyzes the unsteady Rivlin-Ericksen fluid and irreversibility of exponentially temperature dependent variable viscosity of hydromagnetic two-step exothermic chemical reactive flow along the channel axis with walls convective cooling. The non-Newtonian Hele-Shaw flow of Rivlin-Erickson fluid is driven by bimolecular chemical kinetic and unvarying pressure gradient. The reactive fluid is induced by periodic changes in magnetic field and time. The Newtons law of cooling is satisfied by the constant heat coolant convection exchange at the wall surfaces with the neighboring regime. The dimensionless non-Newtonian reactive fluid equations are numerically solved using a convergent and consistence semi-implicit finite difference technique which are confirmed stable. The response of the reactive fluid flow to variational increase in the values of some entrenched fluid parameters in the momentum and energy balance equations are obtained. A satisfying equations for the ratio of irreversibility, entropy generation and Bejan number are solved with the results presented graphically and discussed quantitatively. From the study, it was obtained that the thermal criticality conditions with the right combination of thermo-fluid parameters, the thermal runaway can be prevented. Also, the entropy generation can minimize at low dissipation rate and viscosity.

This research presents, buckling and free vibration analysis of fiber metal-laminated (FML) plates on a total and partial elastic foundation using the generalized differential quadrature method (GDQM). The partial foundation consists of multi-section Winkler and Pasternak type elastic foundation. Taking into consideration the first-order shear deformation theory (FSDT), FML plate is modeled and its equations of motion and boundary conditions are derived using Hamilton's principle. The formulations include Heaviside function effects due to the nonhomogeneous foundation. The novelty of this study is considering the effects of partial foundation and in-plane loading, in addition to considering the various boundary conditions of FML plate. A computer program is written using the present formulation for calculating the natural frequencies and buckling loadings of composite plates without contacting with elastic foundation and composite plates resting on partial foundations. The validation is done by comparison of continuous element model with available results in the literature. The results show that the constant of total or partial spring, elastic foundation parameter, thickness ratio, frequency mode number and boundary conditions play an important role on the critical buckling load and natural frequency of the FML plate resting on partial foundation under in-plane force.

The roll of melting heat transfer on magnetohydrodynamic natural convection in a square enclosure with heating of bottom wall is examined numerically in this article. The dimensionless governing partial differential equations are transformed into vorticity and stream function formulation and then solved using the finite difference method (FDM). The effects of thermal Rayleigh number (Ra), melting parameter (M) and Hartmann number (Ha) are graphically illustrated. As melting parameter and Rayleigh number increase, the rate of fluid flow and temperature gradients also increase. And in the presence of magnetic field, the temperature gradient reduces and hence, the conduction mechanism is dominated for larger Ha. Greater heat transfer rate is observed in the case of uniform heating compared with non-uniform case. The average Nusselt number reduces with increasing magnetic parameter in the both cases of heating of bottom wall.

In this study, the small scale effect on the linear free-field vibration of a nano-circular plate has been investigated using nonlocal elasticity theory. The formulation is based on the classical theory and the linear strain in cylindrical coordinates. To take into account the small scale and the linear geometric effects, the governing differential equation based on the nonlocal elasticity theory was extracted from Hamilton principle while the inertial effect, as well as the shear stresses effect was ignored. Effect of nonlocal parameter is investigated by solving the governing equation using Adomian decomposition method (ADM) for the clamped and simply supported boundary conditions. By using this method, the first five axisymmetric natural frequencies and displacements of nano-circular plate are obtained one at a time and some numerical results are given to illustrate the influence of nonlocal parameters on the natural frequencies and displacements of the nano-circular plate. For the purpose of comparison, the linear equations were solved by the analytical method. Excellent agreements were observed between the two methods. This indicates that the latter method can be applied to seek the linear solution of nano-circular plates with high accuracy while simplifying the problem.

During the homogeneous-heterogeneous autocatalytic chemical reaction in the dynamics of micropolar fluid, relaxation of heat transfer is inevitable; hence Cattaneo-Christov heat flux model is investigated in this report. In this study, radiative heat flux through an optically thick medium is treated as nonlinear due to the fact that thermal radiation at low heat energy is distinctly different from that of high heat energy, hence classical approach of using Taylor series for simplification is ignored and implicit differentiation is used leading to temperature parameter. Uniqueness of the present analysis is the consideration of cubic autocatalytic chemical reaction between the homogeneous bulk fluid and two species of catalyst at the wall. Application of similarity analysis enabled us to recast the flow equations into a set of coupled nonlinear ODEs. The resulting equations along with the appropriate conditions are solved computationally. Graphical illustrations of the effect of pertinent parameters on momentum, heat and mass boundary layers are presented and discussed. The concentration of the homogeneous bulk fluid with microstructures and catalyst at the surface decreases and increases with diffusion ratio, respectively. Buoyancy has a decreasing effect on temperature distribution.

In this article, the problem of time-dependent stress redistribution of a piezomagnetic rotating thick-walled cylinder under an axisymmetric hygro-thermo-magneto-electro-mechanical loading is analyzed analytically for the condition of plane strain. Using the constitutive equations, a differential equation is found in which there are creep strains. Primarily, eliminating creep strains, an analytical solution for the primitive electric and magnetic potential in addition to stresses is obtained. Then, creep strains are kept and creep stress rates are found by utilizing Norton’s law and Prandtl-Reuss equations for steady-state hygrothermal boundary condition. Lastly, the history of stresses and radial displacement as well as magnetic and potential fields during the time is obtained using an iterative method.  In the numerical examples, the effect of angular velocity, hygrothermal loading and thermal and moisture concentration dependency of elastic constants is investigated comprehensively.

In this research, a numerical algorithm is employed to investigate the classical Blasius equation which is the governing equation of boundary layer problem. The base of this algorithm is on the development of RCW (Rahmanzadeh-Cai-White) method. In fact, in the current work, an attempt is made to solve the Blasius equation by using the sum of Taylor and Fourier series. While, in the most common numerical methods, the answer is considered only as a Taylor series. It should be noted that in these algorithms which use Taylor expansion, the values of the truncation error are considerable. However, adding the Fourier series to the Taylor series leads to reduce the amount of the truncation error. Nevertheless, the results of this research show the RCW method has the ability to achieve the accuracy of analytical solution. Moreover, it is well illustrated that the accuracy of RCW method is higher than the Runge-Kutta one.

One of the most important structures in the ports is the wharf. The most common one is the pile-supported wharf. This type of wharf is consisted of a number of piles and one deck which placed on the piles. In addition to the conventional loads that this structure should withstand, in seismic areas, pile-supported wharfs should have the necessary capacity and strength against seismic excitations. There are some approaches to increase the seismic capacity of the berth. One of these methods is to control the vibrations of the pile-supported wharf against earthquake loads using a damper. In this research, for the first time, a new semi-active damper called the semi active liquid column gas damper (SALCGD), was used to reduce the response of pile supported wharf under seismic loads. In the first step by applying different records of the earthquake, the most important parameter of this damper - the optimal opening ratio of the horizontal column- was obtained for this particular structure. In the following, the performances of this damper and its comparison with the tuned liquid column gas damper (TLCGD) were discussed. This study showed that the use of this semi-active damper (SALCGD) reduces the displacement of the pile-supported wharf by 35% and reduces the acceleration of the structure by 50% on average. In contrast, the passive damper (TLCGD) reduces the displacement of about 20 percent and the acceleration of about 30 percent. Therefore, it was observed that the semi-activation of the damper (SALCGD) had a significant improvement in its performance in controlling the vibrations of pile-supported wharf.

This paper develops a computational model for nonlinear bending analysis of functionally graded (FG) plates using a four-node quadrilateral element SQ4T within the context of the first order shear deformation theory (FSDT). In particular, the construction of the nonlinear geometric equations are based on Total Lagrangian approach in which the motion at the present state compared with the initial state is considered to be large. Small strain-large displacement theory of von Kármán is used in nonlinear formulations of the quadrilateral element SQ4T with twice interpolation strategy (TIS). The solution of the nonlinear equilibrium equations is obtained by the iterative method of Newton-Raphson with the appropriate convergence criteria. The present numerical results are compared with the other numerical results available in the literature in order to demonstrate the effectiveness of the developed element. These results also contribute a better knowledge and understanding of nonlinear bending behaviors of these structures.

In this article, a time dependent partial differential equation is used to model the nonlinear boundary value problem describing heat transfer through a radial porous moving fin with rectangular profile. The study is performed by applying a numerical solver in MATLAB (pdepe), which is a centered finite difference scheme. The thermal conductivity and fin surface emissivity are linearly dependent on temperature while the heat transfer coefficient is given by power law function of temperature. The effects of thermo-physical parameters, such as the Peclet number, surface emissivity coefficient, power index of heat transfer coefficient, convective-conductive parameter, radiative-conductive parameter and non-dimensional ambient temperature on temperature are studied.

The implementation of high-order (spectral) approximations associated with FEM is an approach to overcome the difficulties encountered in the numerical analysis of complex problems. This paper proposes the use of the spectral finite element method, originally developed for computational fluid dynamics problems, to achieve improved solutions for these types of problems. Here, the interpolation nodes are positioned in the zeros of orthogonal polynomials (Legendre, Lobatto, or Chebychev) or equally spaced nodal bases. A comparative study between the bases in the recovery of solutions to 1D and 2D elastostatic problems are performed. Examples are evaluated, and a significant improvement is observed when the SFEM, particularly the Lobatto approach, is used in comparison to the equidistant base interpolation.

Additive Manufacturing describes the technologies that can produce a physical model out of a computer model with a layer-by-layer production process. Additive Manufacturing technologies, as compared to traditional manufacturing methods, have the high capability of manufacturing the complex components using minimum energy and minimum consumption. These technologies have brought about the possibility to make small pieces of raw materials in the shortest possible time without the need for a mold or tool. One of the technologies used to make pieces of the layer-by-layer process is the Gas Metal Arc Welding (GMAW). One of the basic steps in this method of making parts is the prediction of bead geometry in each pass of welding. In this study, taking into account the effective parameters on the geometry of weld bead, an empirical study has been done in this field. For this purpose, three parameters of voltage, welding speed and wire feeding rate are considered as effective parameters on the welding geometry of the process. Width and height of the bead are also determined by the parameters of the geometry of the weld according to the type and application of the research as output parameters are considered. In this paper, an adaptive neuro-fuzzy inference system (ANFIS) is used to create an adaptive model between input process data and parameters of weld bead geometry. The least squares mean error is used to evaluate the model. The predicted results by the model have a good correlation with the experimental data.

The present work illustrates the variable viscosity of dust nanofluid runs over a permeable stretched sheet with thermal radiation. The problem has been modelled mathematically introducing the mixed convective condition and magnetic effect. Additionally analysis of entropy generation and Bejan number provides the fine points of the flow. The of model equations are transformed into non-linear ordinary differential equations which are then transformed into linear form using the spectral quasi-linearization method (SQLM) for direct Taylor series expansions that can be applied to non-linear terms in order to linearize them. The spectral collocation approach is then applied to solve the resulting linearized system of equations. The validity of our model is established using relative entropy generation analysis. A convergence schematic was obtained graphically. Consequence of various parameters on flow features have been delivered via graphs. Some important findings reported in this study that entropy generation analysis have significant impact in controlling the rate of heat transfer in the boundary layer region. The paper acquires realistic numerical explanations for rapidly convergent solutions using the Spectral quasi-linearization method. Convergence of the numerical solutions was monitored using the convergence graph. The initial guess values are automatically satisfied the boundary conditions. The resulting equations are then integrated using the Spectral quasi-linearization methods. The influence of radiation, heat and mass parameters on the flow are made appropriately via graphs. The effects of varying certain physical parameters of interest are examined and presented.