Manuel Guaita

Numerical simulation of wall pressure during discharge of granular material from cylindrical silos with eccentric hoppers

Abstract One of the main causes for failure in grain silos is due to the excessive pressures exerted on the silo wall during discharge. Within traditional theories, several attempts have been made to obtain mathematical expressions reflecting the overpressures produced due to eccentric discharge. These start from the calculation of pressures in a concentric static condition, making the corrections needed due to outlet eccentricity and then applying majoration coefficients in the discharging condition. A new research possibility appears now with the application of the finite element method to present-day engineering. This method is used worldwide by many teams for silo design. In this work, an elasto-plastic constitutive law is applied to cylindrical silos with eccentric hoppers and rigid walls, using the Drucker–Prager criterion. In this model, the distribution of plastic areas according to eccentricity is analysed. The study of the influence on static pressures of the internal friction angle combined with the variation of the hopper eccentricity is also carried out. The results obtained are compared to elastic behaviour. For the development of this work, the commercial programme ANSYS 5.5 has been used, and it has been necessary to develop the analysis in three dimensions.

Determination of the mechanical properties of Castanea sativa Mill. using ultrasonic wave propagation and comparison with static compression and bending methods

The goal of this paper was to analyse the mechanical properties of Castanea sativa determined using an ultrasonic wave method. The results were compared with those obtained using the traditional static compression and bending methods with the same sample. The results were also compared with expected values for this species, and relationships between properties were determined to verify whether there were differences between the results and the expected behaviour of the wood. The elastic constants determined using ultrasound did not reveal statistically significant differences compared with the static methods, and the results were generally within the expected range for this species. This result makes ultrasound a powerful method for determining the elastic constants of wood, in addition to its feasibility and low cost. Future studies regarding optimisation of the specimen are important to improve the results of the Poisson’s ratios.

The analytical influence of all types of knots on bending

The influence of different types of knots and fiber deviations on the bending of wood, as managed using visual grading standards, was analytically discussed in this research by means of the finite element method. The effect of each geometrical variable on the strength and stress distribution has been studied individually. This was accomplished after validating a previously presented finite element model that accounted for the three-dimensional shape of the knots and fiber deviations. The simulated sizes and positions were those commonly managed by the standards for strength grading. The research presents the effect of: (1) the size and position of cylindrical face knots; (2) size and position of truncated conical face knots; (3) size and position of shallow conical face knots; (4) size and position of conical edge knots; (5) inclination of face knots. In each case, the analytical predictions of the modulus of rupture and stress distribution are detailed. Seven characteristic positions with distinct mechanical behavior were found, which should be accounted for in order to improve the wood grading efficiency.

Simulation of discharging processes in metallic silos

This paper presents a new dynamic model for silo discharge using the Drucker-Prager plasticity model, surface-to-surface contact and flexible wall. Results were compared with Eurocode 1 – part 4 actions in silos and tanks, which is the standard used in the European Union. Overpressure coefficients due to discharge were obtained in all cases. The results of critical time were evaluated in different parts of the silo. In order to know the behaviour of the model the results of principal major stresses were achieved. A parametric study were developed to know the influence of the flexibility of the wall and the internal coefficient.

Parametric study of the pressures of cylindrical silos with rigid wall

The objective of this work was to perform an analysis of pressure distributions in grain silos both for the discharge and for static conditions. To this end a model based on the finite element method (FEM) was employed. In this paper, we present results for a cylindrical silo with rigid wall, Drucker- Prager material criterion and surface-to-surface contact. The model was employed in a parametric study of the influence of Poisson ratio, friction coefficient and hopper opening of a silo with a hopper with an inclination of 60o, a radius of 2 m, a height of 12 m and an outlet radius of 0.6 m.