Reducing velocity error and its consequences by an iterative feedback immersed boundary method

The immersed boundary method (IBM) has attracted growing interest in the computational fluid dynamics (CFD) research community due to its simplicity in dealing with moving boundaries in fluid-structure interaction (FSI) systems. We present a study on streamline penetration, velocity error and consequences of a FSI solver based on an iterative feedback IBM. In the FSI, the fluid flows are solved by the lattice Boltzmann method; the solid structure deformation is solved by the finite difference method, and an iterative feedback IBM is used to realize the interaction between fluid and structure. The iteration can improve the no-slip and no-penetration boundary conditions at the fluid-solid interface. Four benchmark cases are simulated to study the reduced velocity error and its consequences: a uniform flow over a flapping foil, flow-induced vibration of a flexible plate attached behind a stationary cylinder in a channel, flow through a two-dimensional asymmetric stenosis and a one-sided collapsible channel. Results show that the iterative IBM can suppress the boundary-slip error and spurious flow penetration on the solid wall. While the iterative IBM does not have significant effect on the force production and structure deformation for external flows, it significantly improves the prediction of the force distribution and structure deformation for internal flows. The increased computational cost incurred by the iteration can be largely reduced by increasing the feedback coefficient. This study will provide a better understanding of the feedback IBM and a better option for the CFD community

Test methods for on-site corrosion rate measurement of steel reinforcement in concrete by means of the polarization resistance method

  This recommendation covers the description of non-destructive electrochemical test methods for the estimation in large size concrete structures of the instantaneous corrosion current densiti, icor, expressed in gA/cm2, by means of the so called Polarization Resistance technique, Rp, in order to asses the condition of embedded Steel reinforcement related to its corrosion. The values of icor, can be used to assess the rate of degradation of concrete structures affected by reinforcement corrosión. However, the cannot give information on the actual loss in steel cross section which, at present, only can be assessed by means of direct visual observation.   Values of the free corrosión potential or half-cell potential, Ecorr [V], of the embedded reinforcing Steel and of the electrical concrete resistance, Re [f)], are obtained as preliminary steps of the Rp measurements. Values of the concrete resistivity, P [~m], can be calculated from Re values providing the geometrical arrangement of the electrodes enables this calculation. Both parameters, Ecorr and Re (or P) may be used to complement the reliability of the ico~r measurements

Tool development based on FAST for performing design optimization of offshore wind turbines: FASTLognoter

The new engineering FASTLognoter software is presented. This code is essentially the result of the integration of two tools, along with some additional features. Thefirst basis tool is FAST (developed by NREL), a comprehensive aeroelastic simulator code for wind turbines. The second basis tool is Lognoter (developed by CompassIS), a general-purpose commercial software for managing and creating engineering forms. The integration of FAST and Lognoter gives a useful, comprehensive and versatile toolkit, which is verified in this work by means of bibliographic documented cases. An important advantage of the tool presented is the parametric design capability, allowing the user of FAST/AeroDyn/HydroDyn codes to analyze a massive group of cases; therefore, optimal design can be carried out

Enhanced goal-oriented error assessment and computational strategies in adaptive reduced basis solver for stochastic problems

This work focuses on providing accurate low-cost approximations of stochastic ¿nite elements simulations in the framework of linear elasticity. In a previous work, an adaptive strategy was introduced as an improved Monte-Carlo method for multi-dimensional large stochastic problems. We provide here a complete analysis of the method including a new enhanced goal-oriented error estimator and estimates of CPU (computational processing unit) cost gain. Technical insights of these two topics are presented in details, and numerical examples show the interest of these new developments.Postprint (author's final draft

Size-dependent nonlinear elastic scaling of multiwalled carbon nanotubes

We characterize through large-scale simulations the nonlinear elastic response of multi-walled carbon nanotubes (MWNCNTs) in torsion and bending. We identify a unified law consisting of two distinct power-law regimes in the energy-deformation relation. This law encapsulates the complex mechanics of rippling and is described in terms of elastic constants, a critical length-scale and an anharmonic energy-deformation exponent. The mechanical response of MWCNTs is found to be strongly size-dependent, in that the critical strain beyond which they behave nonlinearly scales as the inverse of their diameter. These predictions are consistent with available experimental observations