Human aortas are subjected to large mechanical stresses because of blood flow pressurization and through contact with the surrounding tissue. It is essential that the aorta does not lose stability by buckling with deformation of the cross-section (shell-like buckling) (i) for its proper functioning to ensure blood flow and (ii) to avoid high stresses in the aortic wall. A numerical bifurcation analysis employs a refined reduced-order model to investigate the stability of a straight aorta segment conveying blood flow. The structural model assumes a nonlinear cylindrical orthotropic laminated composite shell composed of three layers representing the tunica intima, media and adventitia. Residual stresses because of pressurization are evaluated and included in the model. The fluid is formulated using a hybrid model that contains the unsteady effects obtained from linear potential flow theory and the steady viscous effects obtained from the time-averaged Navier-Stokes equations. The aortic segment loses stability by divergence with deformation of the cross-section at a critical flow velocity for a given static pressure, exhibiting a strong subcritical behaviour with partial or total collapse of the inner wall. Preliminary results suggest directions for further study in relation to the appearance and growth of dissection in the aorta.

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Nonlinear vibrations of rectangular laminated composite plates with different boundary conditions are studied by using different nonlinear plate theories. In particular, numerical results for (i) the classical Von Kárman theory, (ii) the first-order shear deformation theory (SDT), and (iii) the third-order SDT are compared. The nonlinear response to harmonic excitation in the frequency neighborhood of the fundamental mode is investigated. Numerical investigation is carried out by using pseudo-arclength continuation method and bifurcation analysis. The boundary conditions of the plates are: simply supported with movable edges, simply supported with immovable edges, and clamped (CL) edges. For thick plates (thickness ratio 0.1), the strongest hardening nonlinear behavior is observed for CL plates, while the simply supported movable plates are the ones with the weakest nonlinearity among the three different boundary conditions studied here. Differences among the three nonlinear plate theories are large for thick laminated plates. For all the other cases, the first-order SDT, with shear correction factor [Formula: see text], and the higher-order SDT give almost coincident results.

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The NEAMS program aims to develop an integrated multi-physics simulation capability "pelletto-plant" for the design and analysis of future generations of nuclear power plants. In particular, the Reactor Product Line code suite's multi-resolution hierarchy is being designed to ultimately span the full range of length and time scales present in relevant reactor design and safety analyses, as well as scale from desktop to petaflop computing platforms. In particular the NEAMS program is supporting the development of novel thermal-hydraulic codes.