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SUMMARYAn Enhanced Energy Conserving Algorithm (EECA) formulation for time integration of frictionless contact-impact problems is presented. In it the energy, linear and angular momentum are conserved for every contact using an enhanced Penalty method. Previous formulations for these problems have shown that the total bodies' energy decreases for contact due to an artificial energy transfer between the penalty spring and the contacting bodies. Consequently, they are not able to reproduce a physical response after a single contact, introducing errors in trajectories and velocities.Through the conserving balance equations, EECA computes a physical response by inserting for every contact an additional amount of linear momentum and contact force. The structure of these equations defines the additional linear momentum to restore the energy and the enhanced Penalty method based on a spring and a dashpot. This method approximately enforces the first and second Kuhn-Tucker conditions.The new algorithm has been applied to several frictionless rigid problems using the Discrete Element Method. The first two problems consist of the simulation and analytical comparison of the Newton's Cradle and Carom problems (billiard pool problem). The last two are the hopper filling process and the breaking of a pool ball's triangular arrangement, both of which involve a medium number of contacts. Application of this formulation will be straightforward to elastic and general-shaped bodies using the Finite Element Method.

We introduce a numerical method for incipient sediment transport past bedforms. The approach is based on the discrete element method (DEM) (Pérez-Aparicio and Bravo (2006)), simulating the micro-mechanics of the landform as an aggregate of rigid spheres interacting by contact and friction. A continuous finite element approximation ) predicts the boundary shear stress field due to the fluid flow, resulting in drag and lift forces acting over the particles. Numerical experiments verify the method by reproducing results by Shields (1936) and other authors for the initiation of motion of a single grain. A series of experiments for sediments with varying compacity and constituting piles yields enhanced relationships between threshold shear stress and friction Reynolds number, to define incipient sediment transport criterion for flows over small-scale bed morphologies.

The structural use of timber coming from fast growing and low-grade species such as poplar is one of the current challenges in the wood value chains, through the development of engineering products. In this work, a qualitative comparison of the behavior of mixed glued laminated timber made of pine in their outer layers and of poplar in their inner layers is shown and discussed. Single-species poplar and pine laminated timber have been used as control layouts. The investigation includes destructive four-point bending tests and three non-destructive methodologies: finite elements numerical model; semi-analytical model based on the Parallel Axes theorem and acoustic resonance testing. An excellent agreement between experimental and numerical results is obtained. Although few number of samples have been tested, the results indicate that the use of poplar as a low-grade species in the inner layers of the laminated timber can be a promising technology to decrease the weight of the timber maintaining the good mechanical properties of pine. Likewise, the need for the use of the shear modulus in both experimental measurements and numerical analysis is suggested, as well as the need to reformulate the vibration methodology for non-destructive grading in the case of mixed timber.

The main objective of the present work is to develop and prove a theoretical explanation based on the Extended Non-Equilibrium Thermodynamics (ENET) for the hysteretical thermoelectric behavior observed in certain thinfilm photovoltaic materials. The ENET introduces dissipative fluxes in the entropy balance that could explain this behavior. To verify this explanation from a numerical point of view, results are generated using a Finite Element (FE) formulation based on the ENET and already developed in previous publications by the authors. In addition, an identification Inverse Problem (IP) is formulated; a cost function is defined as the quadratic difference between experimental and numerical results and the IP is solved minimizing the cost function using genetic algorithms. The conclusion is that the loop-like distributions are due to energy dissipation introduced by dissipative fluxes that are closely related with relaxation times. Also, the FE-IP combination permits to find an approximated characterization of properties for several materials from single experimental curves. Finally, several numerical simulations are proposed for laboratory experiments to further validate