h n g k y -center https://ntrs.nasa.gov/search.jsp? R=19870011944 2018-05-09T17:43 energy release rates for the 'bare' interface laminate, i.e. one without the resin layer, and for the laminate with the resin showed that the 'bare' interface models are a very good approximation for the resin case if the delamination tip elements were one-quarter to one-half of the ply thickness.
SUMMARYA new method for analysing plate and shell structures with two or more independently modelled finite element subdomains is presented, assessed, and demonstrated. This method provides a means of coupling local and global finite element models whose nodes d o not coincide along their common interface. In general, the method provides a means of coupling structural components (e.g., wing and fuselage) which may have been modelled by different analysts. In both cases, the need for transition modelling, which is often tedious and complicated, is eliminated. The coupling is accomplished through an interface for which three formulations are considered and presented. These formulations are: collocation, discrete least-squares, and hybrid variational. Several benchmark problems are analysed and it is shown that the hybrid variational formulation provides the most accurate solutions.
SUMMARYAn assumed-stress hybrid/mixed 4-node quadrilateral shell element is introduced that alleviates most of the deficiencies associated with such elements. The formulation of the element is based on the assumed-stress hybrid/mixed method using the Hellinger-Reissner variational principle. The membrane part of the element has 12 degrees of freedom including rotational or 'drilling' degrees of freedom at the nodes. The bending part of the element also has 12 degrees of freedom. The bending part of the element uses the Reissner-Mindlin plate theory which takes into account the transverse shear contributions. The element formulation is derived from an 8-node isoparametric element by expressing the midside displacement degrees of freedom in terms of displacement and rotational degrees of freedom at corner nodes. The element passes the patch test, is nearly insensitive to mesh distortion, does not 'lock', possesses the desirable invariance properties, has no hidden spurious modes, and for the majority of test cases used in this paper produces more accurate results than the other elements employed herein for comparison.
Slip flow in ducts and porous media is simulated using lattice-Boltzmann method incorporated with interfacial force models. The dependence of the results on the viscosity, LBM scheme (D3Q15 and D3Q19) and the relaxation time model (single or multi-relaxation time) is investigated. The severity of spurious velocities (arisen from classic and advanced interfacial force models) is discussed that leads to entirely non-physical results for whole flow rates (0.027 < Re < 10.7). A simple method based on superposition of solutions is proposed to fully rehabilitate the simulations. We validate the method by showing the simulations versus analytical solution of slip flow through circular ducts. The validity of the rehabilitated results for porous media applications are also tested through two approaches: First, we show that the rehabilitation method is independent to the force scheme used, i.e., the rehabilitated results are identical in both pore and macro-scales for different force schemes with different distributions of spurious velocities. Second, using an analogy based on the Kozeny-Carman model, we show that the permeability variation in porous media resulted from the flow slippage obtained from rehabilitated simulations is reliable. We argue that to obtain correct results, it is necessary to use the rehabilitation method whenever interfaical force models are used in LB simulations. The results reveal that the permeability of porous media may increase or decrease with positive or negative slippage (repulsive and attractive interfaces), respectively. The permeability enhancement rate increases as the system becomes simpler in its interfaces, i.e., for the same positive slippage of flow, (κ κ N S) parallel plates > (κ κ N S) square ducts > (κ κ N S) porous media (where κ is the permeability and N S denotes no-slip).
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