A numerical analysis of mixed convection in a vertical channel filled with metal foam partially heated at uniform heat flux is studied numerically. Local thermal non-equilibrium and Brinkman-Forchheimer-extended Darcy model are assumed. Boussinesq approximation with constant thermophysical proprieties are considered. Results are carried out for an aluminium foam with 10 pore per inch (PPI) and ε=0.909, the fluid is air. Results, for different Reynolds numbers and geometrical aspect ratios, are given in terms of solid and fluid temperatures, at heated walls and inside the channel at several heights, velocity profile along the channel, local and average Nusselt numbers. Results show that diffusive effect resulted lower temperature values inside the solid and the fluid temperatures are higher in all considered cases. For heated channel with smaller aspect ratios, an average Nusselt number increase is found for solid and fluid phases.

In the present paper, simulation for shell and tube heat exchanger investigated using CFD techniques. Numerical simulations of the turbulent, three-dimensional fluid flow and heat transfer are performed using Ansys Fluent 6.3. The effect of friction characteristics on the model of heat exchanger is discussed. A RNG κ-ε turbulence model with non-equilibrium wall function and 2 nd order upwind is used. The present model is validated with the experimental literature and show a good agreement. The numerical results of the present study predict reasonably agree well with available correlations. Finally the present study model can be used to model a shell and tube heat exchanger with a satisfactory accuracy level in predictions.

This work presents a closed form investigation on the effect of temperature gradient on the buckling resistance of functionally graded material (FGM) shallow arches. The constituents are assumed to vary smoothly through the thickness of the arch according to the power law distribution and they are assumed to be temperature dependent. The arches subjected to the both uniform distributed radial load and central concentrated load and both boundary supports are supposed to be pinned. The temperature field is approximated by one-dimensional linear gradient through the thickness of the arch and the displacement field approximated by classical arches model. Also, Donnell type kinematics is utilized to extract the suitable strain-displacement relations for shallow arches. Adjacent equilibrium criterion is used to buckling analysis, and, critical bifurcation load is obtain in the complete presence of pre-buckling deformations. Results discloses the usefulness of using the FGM shallow arches in thermal environment because the temperature gradient enhances the buckling resistance of these structures when they are subjected to a lateral mechanical load.

In this study non-linear thermal buckling of circular shallow arches made of functionally graded materials subjected to a linear temperature gradient is investigated. For this purpose, a functionally graded circular shallow arch is considered that its strain-displacement relation follows the Donnells nonlinear shallow shell theory. The material properties are varied smoothly through the arch thickness according to the power law distribution of the volume fraction of constituent materials. Also, material properties are considered temperature-dependent. The classical single layer theory assumptions that are reasonable for slender arches are implemented. To investigate the large deformations of such arch, the von-Karman type geometrical nonlinearity is utilized that is suitable for moderately large class of rotations. The virtual displacement principle and calculus of variation are employed to derive the governing equilibrium equations and complete set of boundary conditions of the FGM arch. The adjacent equilibrium criterion is employed for the stability analysis of the FGM arch. An analytical approach is accomplished and a closed-forms solution for thermal bifurcation points of the FGM shallow arches is presented. Also critical bifurcation loads corresponding to the critical temperatures with the presence of non-linear pre-buckling deformations is obtained. Illustrative results examine the effect of various involved parameters such as power law index, opening angle, geometric parameter (or otherwise length to thickness ratio). Obtained numerical results represent that, in most cases, thermal bifurcation for the FGM arches occurs in the high temperatures and the critical buckling temperatures are approximately high even for slender FGM arches. Also effective of ceramic or metal rich area at the bottom surface of the FGM arch is investigated and results are presented for both cases and are compared together. Varieties between this two cases due to contrast between material and structural stretching-bending coupling effect. Results presented illustrative the ceramic rich area at the bottom surface cause the higher critical buckling temperatures for the FGM arches.

Graded materials, also known as functionally graded materials (FGMs), are multiphase composites mainly composed of a ceramic and a metal; thus, they exploit the heat, oxidation and corrosion resistance typical of ceramics, and the strength, ductility and toughness typical of metals. These materials are mainly used as heat barriers. In addition, many of the present and potential applications of FGMs involve contact problems. On the other hand, the production process of FGMs is somewhat complex and leaves some defects in the produced structure. One of the most important defects in such structures is surface cracks. Here, the combination of the contact and crack problems is investigated in a functionally graded rectangular plate containing a semi–elliptic surface crack indented by a frictionless rigid spherical indenter. The plate is simply supported and the crack is located in the middle of the plate surface in the tension part. The crack surface is parallel to one of the plate edges. The gradient of mechanical properties variation is considered through the thickness of the plate and the volume fraction distribution of the constituting phases is modeled by a polynomial function and the Poisson’s ratio is kept constant. The analyzing of the problem is divided into two steps. At the first step, for an uncracked plate the equations of equilibrium are derived in terms of the displacement field and are solved numerically to find the contact rule. As the second step in studying the problem, the contact problem of a cracked plate is modeled by using ABAQUS finite element package. The aim of this step is to find the effect of the presence of the crack on the contact rule. The optimum mesh for the ABAQUS model is found by using the results of the first step. In order to do so, an ABAQUS model is created for the uncracked plate. The analytical results and the obtained results from ABAQUS for specified plate and indenter dimensions and material properties are compared. After finding the optimum mesh, a crack is added to the ABAQUS model of the plate under contact loading. The effects of gradient changes and indenter dimensions on the contact rule and stress distribution at the crack tip are then investigated by using the obtained ABAQUS model. The acquired results show that the influence of the material nonhomogeneity on the stress distribution around the crack tip and in the plate (uncracked and cracked) and contact rule can be quite significant. In general, increasing the overall volume fraction of the metal phase increases the load carrying capacity in an uncracked plate. In a cracked plate, the changes in material distribution as well as the changes of the indenter diameter does not affect the results that much.

For the simplified linear hypersonic air-breathing propulsion model, aiming at the safety boundaries existing during the working progressing, this paper considers the output regulation/ safety protection switching control problem. Several comments are given to the minimum control switching strategy studied in our previous work, and to make the designing of the switching controller more systematic, a novel command switching strategy is proposed, where discontinuous controllers are adapted. The protected output will be forced to escape from the safety boundary once the danger comes. The asymptotic tracking problem is transformed into the asymptotic stability problem of the linear switched and impulsive systems or that of the switched systems whose subsystems have different equilibrium points. The design of the dynamical output feedback controllers and the switching laws can be finished separately, and the principles guaranteeing asymptotic tracking are given, the decline of the candidate Lyapunov function can be checked by solving an optimal problem. Finally, simulations verify the effectiveness of the given results, which also indicate that the commands switching control can improve both the safety margin of the protected output and the tracking performance of the regulated output, the ability of tracking commands safely and quickly is thus enhanced.

This paper presents the development of Meshless Methods based on Moving Least Square Approximation (MLSA) [3][10][14]. In the case of solid mechanics, the shape displacement functions are computed for each node with a centered scheme approximation [3][12] associated with a specific weight function [10]. Both interpolated and approximated weight functions are studied [10][9][15]. We propose to build a new C 1 weight function based on a 2d boundary line. The Galerkin Method is used to solve the mechanical equilibrium balance problems [14]. A 2-dimensional example is presented to validate the Meshless Method.

We propose to incorporate a Response Surface (RS) approximation of variables over a parametric domain into a weak form of parametric Partial Differential Equations (PDEs). Hence a multidimensional model-reduction can be achieved. We propose a multidimensional a priori model reduction method to generate or to enrich RSs. It is coined multidimensional because the fields to forecast are defined over an augmented domain in term of dimension. They are functions of both space variables and parameters that simultaneously evolve in time. This changes the functional space related to the weak form of the PDEs and the definition of the reduced bases. It has a significant impact on the proposed model reduction method. In particular, a new point of view on interpolation of variables has to be addressed. A Multidimensional Reduced Integration Domain (MRID) is proposed to reduce the complexity of the reduced formulation. A multidimensional Hyper-Reduction method extract from the MRID truncated equilibrium equations, truncated residuals and a truncated error indicator.

Cadaveric experiments and computer simulations have shown that the tendon network of the fingers performs logic computation to preferentially change torque production capabilities. Distribution of input tensions in the tendon network itself regulates how tensions propagate to the finger joints, acting like the switching function of a logic gate. The tendon network as proposed by Winslow (1669–1760) is responsible for this phenomenon; and that a certain switching behavior is exhibited, depending upon the input tension loading. This work explores how this switching behavior varies with different static postures of the finger and under different loading conditions on input tendon terminals. Experimental setup is designed and developed to study this switching behavior, comprising of a bio-mimetic model of middle finger, designed and developed. Winslow’s tendon network as proposed by Winslow is employed over it. Force sensors based on strain gauges are designed and developed in order to measure the tension at the proximal and terminal slips of network. Experiments have been carried out to understand the switching behavior exhibited by rhomboidal tendon network and how it varies under different loading conditions. Its variation with different pre-configured postures under static equilibrium is observed. Results show that indeed the rhomboidal tendon network of Winslow exhibits switching behavior and that they vary under different loads and postures of the finger.

The paper is devoted to the analysis of robotic manipulator behavior under internal and external loadings. The main contributions are in the area of stability analysis of manipulator configurations corresponding to the loaded static equilibrium. In contrast to other works, in addition to usually studied the end-platform behavior with respect to the disturbance forces, the problem of configuration stability for each kinematic chain is considered. The proposed approach extends the classical notion of the stability for the static equilibrium configuration that is completely defined the properties of the Cartesian stiffness matrix only. The advantages and practical significance of the proposed approach are illustrated by several examples that deal with serial kinematic chains and parallel manipulators. It is shown that under the loading the manipulator workspace may include some specific points that are referred to as elastostatic singularities where the chain configurations become unstable.

In this paper, the buckling analysis of conical shell under transverse pressure or axial compression is studied using the Differential Quadrature Method (DQM) for various boundary conditions. Based on the Donnell theory of shell, the equilibrium equations are obtained using Hamilton’s principle. The adjacent equilibrium criterion is employed to defining the stability equations of conical shell subjected to lateral pressure and axial compression. Then the stability equations are solved numerically using DQM and employing the concept of extra degrees of freedom. The acquired results in special cases are compared with the results in literature for the accuracy evaluation of the method and a good agreement can be seen. The non-dimensional critical buckling loads are tabulated for different vertex angles, some thickness-radius ratios and various combinations of boundary conditions. Also, the effects of the vertex angle, boundary conditions, length-radius ratio and thickness-length ratio on the buckling behavior of the conical shell are investigated in details.

This paper analytically investigates the effect of fiber arrangements on stress distribution around a pin joint in a laminated composite. It is assumed that all fibers lie in one direction while loaded by a force p o at infinity. According to the shear lag model, equilibrium equations are derived for two types of fiber arrangements. In the first model, a square arrangement is selected for the fibers, while in the second; a hexagonal arrangement is used to deduce the equilibrium equations. Upon proper use of boundary and boundness conditions, stress and displacement fields are derived within the laminate and their peak values are determined on the compressive side of the pin periphery. The effect of pin diameter on stress concentration around the pin is well examined. The presence of the pin on shear stress distribution in the laminate is also examined for various pin diameters. According to the results, a square arrangement of fibers results in smaller values of stress concentrations around the pin, as compared to those of a hexagonal arrangement. The pin position and its diameter shows to have noticeable effect on both normal and shear stresses developed within the laminate, as well as pin surrounding.

In the present article, the buckling analysis of thin functionally graded rectangular plates resting on elastic foundation is presented. According to the classical plate theory, (Kirchhoff plate theory) and using the principle of minimum total potential energy, the equilibrium equations are obtained for a functionally graded rectangular plate. It is assumed that the plate is rested on elastic foundation, Winkler and Pasternak elastic foundations, and is subjected to in-plane loads. Since the plate is made of functionally graded materials (FGMs), there is a coupling between the equations. In order to remove the existing coupling, a new analytical method is introduced where the coupled equations are converted to decoupled equations. Therefore, it is possible to solve the stability equations analytically for special cases of boundary conditions. It is assumed that the plate is simply supported along two opposite edges in x direction and has arbitrary boundary conditions along the other edges (Levy boundary conditions). Finally, the critical buckling loads for a functionally graded plate with different boundary conditions, some aspect ratios and thickness to side ratios, various power of FGM and foundation parameter are presented in tables and figures. It is concluded that increasing the power of FGM decreases the critical buckling load and the load carrying capacity of plate increases where the plate is rested on Pasternak in comparison with the Winkler type.

The discrete ordinates method (DOM) for the solution of radiative heat transfer problems have received significant attention and development owing to their good compromise between accuracy, flexibility and moderate computational requirement. However, the DOM suffers from the ray effects related to the discretization of the angular distribution of the radiation intensity. The modified discrete ordinate method (MDOM) proved to significantly mitigate ray effects originated from discontinuities or abrupt changes of the wall temperature. This article presents blocked-off region treatment of irregular geometries using a modified discrete ordinates method in Cartesian coordinates. The Cartesian based 2D algorithm can be used to solve radiative heat transfer in irregular geometries by dividing the region into active and inactive regions. It is easier and convenient way of handling 2D irregular geometries than to write an algorithm in curvilinear coordinates. It is capable of handling participating (absorbing, emitting and isotropic or anisotropic scattering) or non participating gray media enclosed by gray diffuse walls. Both radiative and non-radiative equilibrium situations are considered. The walls of the enclosures can have either heat flux or temperature boundary conditions. Cases with curved and obstacle and radiation shield are considered. Some test problems are considered and results are validated with the available results in the literature. Results are found to be accurate for all kinds of situations.

In this research, a new approach for stability analysis of drill string is investigated. To this goal, the potential energy of drill string for axial and lateral vibrations is written in an integral equation. In this equation, the effect of geometrical shortening, which causes nonlinear coupling between axial and lateral vibration, is considered. The work done by WOB force and weight of drill string is calculated. The finite element method is employed to convert the integral potential energy of the continuous system to a discrete one. The effects of stabilizers are modeled by dropping the nodes coincided with them. Dropping and considering third and fourth order tensor of potential energy lead to linear and nonlinear stability analysis, respectively. Taking the first order derivative of discrete potential energy, the equilibrium position of drill string can be found. Taking second order derivative, the stability of the equilibrium position can be analyzed. Illustrated results demonstrate that as the length of hole is increased, the differences between linear and nonlinear cases become larger. This analysis shows the working condition of drill string is stable or not. These results can be used to obtain safe working conditions in drilling progress.

Performance data obtained from measurements of process variables usually do not obey material and energy conservation laws. This is why a data reconciliation process, that is, the adjustment of measured data to obey the conservation laws and other constraints is necessary in order to characterize the real performance of equipment, processes, or the whole plant. The information on the partial load and off-design operation performance of absorption chillers is scarce. Real operation of these units do not always coincides with the expected performance according to the data provided by the manufacturer due to site specific conditions. On the other hand the data reconciliation procedure has been extensively applied mainly only for open cycles with a moderate number of recycle streams. The objective of this work is the development and application of the data reconciliation technique to analyse the performance of absorption chillers using rigorous thermodynamic properties for the calculation of the P-V-T equilibrium properties and enthalpies. We present in this paper the preliminary test results for one of the absorption chiller components, the evaporator.

Hydrogen as the most abundant element on Earth is viewed to be a promising energy carrier. For transmission, hydrogen stored as metal hydrides is a potent candidate for its advantages in safe and reliability and being able to offer high energy density compared to the conventional ways such as high pressure gas and liquefaction. Metal hydriding is basically an exothermic process. The heat released will cause an increase in temperature and raise the absorption equilibrium pressure as high as that of the supplied hydrogen gas, which may in turn stop the hydriding process. On the other hand, metal dehydriding is an endothermic process. A temperature decrease can retard desorption and even bring down the dissociation equilibrium pressure as low as the back pressure to stop dehydriding. Therefore, reducing thermal resistance of the storage vessels and enhancing heat transfer of the storage system have become a critical issue for the success of hydrogen storage using metal hydrides. This work models the metal hydriding/dehydriding process in order to assess the vessel design on heat transfer enhancement to improve the performance of hydrogen storage with metal hydrides. First of all, the thermal-fluid behavior of hydrogen storage was modeled including gas flow and energy equations. The vessel is considered to be equipped with an air pipe at the centre line with internal fins. Detailed theoretical models that describe force convection of the heat exchange pipe and natural convection at the lateral wall are constructed. Results from the simulation show that the addition of a concentric heat exchanger pipe with fins can enhance the reaction rates. The work demonstrates how computer aided engineering can be applied to evaluate the performance of hydrogen storage designs, and help reduce experimental efforts in developing the hydrogen storage systems.

Exergy analysis provides useful information for the system optimization. An exergy analysis identifies the sources of thermodynamic inefficiencies by evaluating the exergy destruction within each system component. The present work is an attempt to compare the effect of variations of species concentrations of the combustion process in a simple gas turbine system. Therefore, using a Complete combustion model and an Equilibrium combustion program model, the exergetic evaluation is carried out for a simple gas turbine system with a rated output power of 30 MW. The Complete combustion involves O 2 , N 2 , CO 2 , H 2 O and Equilibrium combustion model involves N 2 , O 2 , CO 2 , H 2 O, CO, H 2 , H, O, OH, N, NO as the species of combustion products. In this work, Equilibrium combustion products were calculated using Olikara and Borman method. Also, a principle of division of chemical availability (exergy) into oxidation availability, reduction availability and diffusion availability has been investigated in these models. Expression involving the variables for exergetic efficiency, exergy destruction, and chemical availability in the components of the gas turbine cycle are derived. The exergy losses and efficiencies of components based on both Complete combustion and Equilibrium combustion models are evaluated. The exergetic efficiencies of the plant based on Complete combustion and Equilibrium combustion are determined to be 28.11% and 28.16%, respectively. It is found that, variation of species has negligible effect on the system main parameters. It is also concluded that chemical exergy in Equilibrium combustion is a little more than that of Complete combustion. Because of additional species involved in Equilibrium combustion, reduction availability and oxidation availability are defined in this modeling beside diffusion availability and it increases chemical exergy of equilibrium combustion modeling. The results obtained here show that in the analysis of the power plant cycles, a simple combustion model (i.e. Complete combustion model) is in good agreement with a complex combustion model considering various species (i.e. Equilibrium combustion model). As a result, there is negligible difference between results of the mentioned combustion models and the simple Complete combustion model facilitates the analysis of such processes.

Thermoeconomic analyses of any thermal system design are always based on the economic objectives. However, knowledge of economic optimization may not be sufficient for decision making process, since solutions with higher thermodynamic efficiency, in spite of small increases in total costs, may result in much more interesting designs due to changes in the energy market prices or in the energy policies. In this paper a multi-objective optimization scheme is developed and applied for an Integrated Solar Combined Cycle System (ISCCS) that produces 400 MW of electricity to find solutions that simultaneously satisfy exergetic as well as economic objectives. This corresponds to search for a set of Pareto optimal solutions with respect to the two competing objectives. The optimization process is carried out by a particular class of search algorithms known as multi-objective evolutionary algorithms (MOEAs). For such MOEAs, an example of decision-making is presented and a final optimal solution has been introduced. The final optimal solution that is selected in this analysis belongs to the region of Pareto Frontier with significant sensitivity to the costing parameters. However, the region with lower sensitivity to the costing parameter is not reasonable for the final optimum solution due to a weak equilibrium of Pareto Frontier in which a small changes in exergetic efficiency of plant due to variation of operating parameters may lead to the danger of increasing the cost rate of product, drastically. The analysis shows that optimization process leads to 3.2% increasing in the exergetic efficiency and 3.82% decreasing of the rate of product cost. Also optimization leads to the 2.73% reduction on the fuel exergy, 5.71% reductions in the total exergy destruction and also 3.46% and 7.32% reductions in the fuel cost rate and cost rate relating to the exergy destruction, respectively.

The present study investigates static analyses of moderately thick FG plates. Using the First Order Shear Deformation Theory (FSDT), functionally graded plates subjected to transversely distributed loading with various boundary conditions are studied. Effective mechanical properties which vary from one surface of the plate to the other assumed to be defined by a power law form of distribution. Different ceramic-metal sets of materials are studied. Solution of the governing equations, including five equilibrium and eight constitutive equations, is obtained by the Extended Kantorovich Method (EKM). The system of thirteen Partial Differential Equations (PDEs) in terms of displacements, rotations, force and moment resultants are considered as multiplications of separable function of independent variables x and y . Then by successful utilization of the EKM these equations are converted to a double set of ODE systems in terms of x and y . The obtained ODE systems are then solved iteratively until final convergence is achieved. Closed form solution is presented for these ODE sets. It is shown that the method is very stable and provides fast convergence and highly accurate predictions for both thin and moderately thick plates. Comparison of the normal stresses at various points of rectangular plates and deflection of mid-point of the plate are presented and compared with available data in the literature. The effects of the volume fraction exponent n on the behavior of the normalized deflection, moment resultants and stresses of FG plates are also studied. To validate data for analysis fully clamped FG plates, another analysis was carried out using finite element code ANSYS. Close agreement is observed between predictions of the EKM and ANSYS.