727 research outputs found

    Solution of Coupled Thermoelasticity Problem in Rotating Disks

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    The main purpose of this dissertation is to study coupled thermoelastic behaviors in disks subjected to thermal shock loads based on the generalized and classic theories of coupled thermoelasticity. To this end, this research has been carried out in two stages. In the first stage, thermoelasticity problems in an axisymmetric rotating disk with constant thickness made of a homogeneous isotropic material are analytically solved and closed-form formulations are presented for temperature and displacement fields. Since, the analytical solution is not always feasible, the finite element (FE) method can be employed for more sophisticated coupled thermoelasticity problems. Accordingly, in the second stage of the research, a novel refined 1D finite element approach with 3D-like accuracies are developed for theories of coupled thermoelasticity. Then, the developed FE models are applied for a 3D solution of the dynamic generalized coupled thermoelasticity problem in disks. Use of the reduced models with low computational costs may be of interest in a laborious time history analysis of the dynamic problems. The obtained analytical and numerical solutions are in good agreement with the results available in the literature. It is further shown that the proposed analytical and FE methods are quite efficient with very high rate of convergence

    An unconditionally stable algorithm for generalized thermoelasticity based on operator-splitting and time-discontinuous Galerkin finite element methods

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    An efficient time-stepping algorithm is proposed based on operator-splitting and the space–time discontinuous Galerkin finite element method for problems in the non-classical theory of thermoelasticity. The non-classical theory incorporates three models: the classical theory based on Fourier’s law of heat conduction resulting in a hyperbolic–parabolic coupled system, a non-classical theory of a fully-hyperbolic extension, and a combination of the two. The general problem is split into two contractive sub-problems, namely the mechanical phase and the thermal phase. Each sub-problem is discretized using the space–time discontinuous Galerkin finite element method. The sub-problems are stable which then leads to unconditional stability of the global product algorithm. A number of numerical examples are presented to demonstrate the performance and capability of the method

    Development of an integrated BEM approach for hot fluid structure interaction

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    The progress made toward the development of a boundary element formulation for the study of hot fluid-structure interaction in Earth-to-Orbit engine hot section components is reported. The convective viscous integral formulation was derived and implemented in the general purpose computer program GP-BEST. The new convective kernel functions, in turn, necessitated the development of refined integration techniques. As a result, however, since the physics of the problem is embedded in these kernels, boundary element solutions can now be obtained at very high Reynolds number. Flow around obstacles can be solved approximately with an efficient linearized boundary-only analysis or, more exactly, by including all of the nonlinearities present in the neighborhood of the obstacle. The other major accomplishment was the development of a comprehensive fluid-structure interaction capability within GP-BEST. This new facility is implemented in a completely general manner, so that quite arbitrary geometry, material properties and boundary conditions may be specified. Thus, a single analysis code (GP-BEST) can be used to run structures-only problems, fluids-only problems, or the combined fluid-structure problem. In all three cases, steady or transient conditions can be selected, with or without thermal effects. Nonlinear analyses can be solved via direct iteration or by employing a modified Newton-Raphson approach

    Fully coupled peridynamic thermomechanics

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    This study concerns the derivation of the coupled peridynamic (PD) thermomechanics equations based on thermodynamic considerations. The generalized peridynamic model for fully coupled thermomechanics is derived using the conservation of energy and the free-energy function. Subsequently, the bond-based coupled PD thermomechanics equations are obtained by reducing the generalized formulation. These equations are also cast into their nondimensional forms. After describing the numerical solution scheme, solutions to certain coupled thermomechanical problems with known previous solutions are presented

    Development of an integrated BEM approach for hot fluid structure interaction

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    A comprehensive boundary element method is presented for transient thermoelastic analysis of hot section Earth-to-Orbit engine components. This time-domain formulation requires discretization of only the surface of the component, and thus provides an attractive alternative to finite element analysis for this class of problems. In addition, steep thermal gradients, which often occur near the surface, can be captured more readily since with a boundary element approach there are no shape functions to constrain the solution in the direction normal to the surface. For example, the circular disc analysis indicates the high level of accuracy that can be obtained. In fact, on the basis of reduced modeling effort and improved accuracy, it appears that the present boundary element method should be the preferred approach for general problems of transient thermoelasticity

    Finite element simulation of a gradient elastic half-space subjected to thermal shock on the boundary

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    The influence of the microstructure on the macroscopical behavior of complex materials is disclosed under thermal shock conditions. The thermal shock response of an elastic half-space subjected to convective heat transfer at its free surface from a fluid undergoing a sudden change of its temperature is investigated within the context of the generalized continuum theory of gradient thermoelasticity. This theory is employed to model effectively the material microstructure. This is a demanding initial boundary value problem which is solved numerically using a higher-order finite element procedure. Simulations have been performed for different values of the microstructural parameters showing that within the gradient material the thermoelastic pulses are found to be dispersive and smoother than those within a classical elastic solid, for which the solution is retrieved as a special case. Energy type stability estimates for the weak solution have been obtained for both the fully and weakly coupled thermoelastic systems. The convergence characteristics of the proposed finite element schemes have been verified by several numerical experiments. In addition to the direct applicative significance of the obtained results, our solution serves as a useful benchmark for modeling more complicated problems within the framework of gradient thermoelasticity

    Development of BEM for ceramic composites

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    It is evident that for proper micromechanical analysis of ceramic composites, one needs to use a numerical method that is capable of idealizing the individual fibers or individual bundles of fibers embedded within a three-dimensional ceramic matrix. The analysis must be able to account for high stress or temperature gradients from diffusion of stress or temperature from the fiber to the ceramic matrix and allow for interaction between the fibers through the ceramic matrix. The analysis must be sophisticated enough to deal with the failure of fibers described by a series of increasingly sophisticated constitutive models. Finally, the analysis must deal with micromechanical modeling of the composite under nonlinear thermal and dynamic loading. This report details progress made towards the development of a boundary element code designed for the micromechanical studies of an advanced ceramic composite. Additional effort has been made in generalizing the implementation to allow the program to be applicable to real problems in the aerospace industry
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