Francisco Ayuga

Assessment of the visual impact made on the landscape by new buildings: a methodology for site selection

Geographical information systems (GIS) are excellent tools for landscape modelling and three-dimensional analysis. They allow easy digitalisation of geographical information and coverage structure, as well as facilitating graphical representation. The aim of this research, using a new computer programme which makes use of GIS, was to analyse the location of rural constructions in order to improve their integration into the countryside. Logical routines were employed to study planning variables (physical, social, economic and legal) and the visual impact of buildings on the landscape. These routines can be used for analysis and decision-making in environmental administration, and are useful to planners and designers attempting to choose locations where new rural buildings will best integrate into the landscape. Finally, a public survey was conducted on visual impact of rural buildings, in order to endorse the proposed methodology.

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.

MECHANICAL PROPERTIES OF GRANULAR AGRICULTURAL MATERIALS

The use of numerical methods in the design of silos requires properties that describe the behavior of materials that are commonly stored in silos. Variations in the values of these parameters can result in the risk of failures in this type of structure. Because of the lack of existing data in the literature, the goal of this research was to: (1) provide different testing methods for determining these properties, and (2) determine values of the mechanical properties that can be used in either traditional or more recent silo design methods.

Three dimensional discrete element models for simulating the filling and emptying of silos: Analysis of numerical results

Abstract The discrete element method (DEM) is a promising technique that allows the mechanical behaviour of the material stored in silos and hoppers to be studied. The present work analyses the numerical results obtained by two three-dimensional DEM models that simulate the filling and discharge of a silo for two materials: glass beads or maize grains. The aim of the present work was to assess the capacity of these models to predict the behaviour of the studied materials. To guarantee the maximum representativeness of the results, many of the simplifications usually used in DEM models were avoided. The results analysed included the vertical distributions of the normal pressure, tangential pressure and mobilised friction, the horizontal distribution of normal pressure, velocity profiles and the spatial distribution of the bulk density. The results of this analysis highlight the potential of DEM models for studying the behaviour of granular materials in silos and hoppers, provided that simplifications are minimized.

MECHANICAL PROPERTIES OF GRANULAR AGRICULTURAL MATERIALS, PART 2

Traditionally, the design of silos was carried out using classical theories. Hence, it is possible to find data on many granular agricultural materials for all the material properties considered in these theories. Nevertheless, the application of numerical methods to silo design is relatively recent. With these methods, new material properties are needed, in addition to the ones considered in classical theories, in order to estimate grain loads inside silos. As there is a lack of these new parameters in the existing literature, the goal of this research was to provide values of all material properties needed in silo design for several granular agricultural materials. These values can be applied to the design of silos using numerical methods.

Simulation of the Filling Pressures of Cylindrical Steel Silos with Concentric and Eccentric Hoppers Using 3-Dimensional Finite Element Models

This work presents the simulated filling of two cylindrical silos, one with a concentric hopper and the other with an eccentric hopper, both with flexible walls supported on columns. The results showed that, for both types of hopper, the presence of columns led to local increases in pressure just above the junction of the cylinder and hopper, and decreases in pressure below this point. The combination of columns and eccentric hopper led to notable differences in the stresses on the upper and lower faces of the silo wall, which generated deformations towards the interior of the vertical wall when they coincided with the reinforcing columns and deformations towards the exterior in the other zones of the wall. In the silo equipped with an eccentric hopper, there appeared combinations of zones below the cylinder/hopper interface where the wall was alternately deformed both inwardly and outwardly.

DISCHARGE FROM CYLINDRICAL SLENDER STEEL SILOS: FINITE ELEMENT SIMULATION AND COMPARISON WITH EUROCODE 1

This study presents a model for the analysis of silo discharge with the finite element method. The proposed model incorporates the Drucker-Prager plasticity model, a metal wall, and surface-to-surface contact using a dynamic analysis. This study reports the results obtained for discharge from a silo with a flexible wall and compares these results with the new version of Eurocode 1. The mean overpressure coefficients obtained were 1.23 on the vertical wall and 1.28 on the hopper. The analysis of different silo geometries reveals a strong dependence of the value of the overpressure coefficient on silo height. A study of the relative rigidity of the wall and the grain showed that rigidity did not affect the dynamic pressures clearly.

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.

Experimental tests to validate numerical models in silos design

The main objective of the research project described in this paper is to provide information about the behaviour of silos in order to improve their safety and their economic design. Hence, an installation of full-scale silos has been designed and performed for this purpose. Different experimental tests have been proposed to be carried out in these silos. Therefore, the experimental results will be compared to those obtained with numerical models developed in a commercial Finite Element (FE) software. The construction of a FE model requires the determination of mechanical properties for the stored material to obtain accurate results. In consequence triaxial, direct-shear or oedometer tests have been carried out in some common agricultural materials to determine their main mechanical parameters. In addition, ignitiability and explosibility properties of different agricultural materials have been also determined due to the existing lack of data. It may contribute to the understanding of dust explosions and propagation of flames in silos. The aforementioned installation consists of three smooth steel silos where normal and frictional wall pressures were measured during the filling, storage and emptying of the silo. The experimental silos have a cylindrical bin and a conical hopper. The cylindrical bin has an aspect ratio of 2.50 (height 5.00 m; diameter 2.00 m). The hopper is 1.54 m height and the outlet has a diameter of 0.32 m. The outlet eccentricity is the only difference between the three silos, whose values are 0%, 50% and 100%.

Determination of Mechanical Properties of Agricultural Powder Materials and Sugar to be Used in Silos Design

Powder agricultural materials are usually stored inside silos. However, there is a lack of data in the literature about mechanical properties of these materials. Numerical methods are commonly used for the analysis of the behavior of the agricultural materials stored in silos. Nevertheless, the accuracy and efficiency of the results obtained when using these methods depend on the values of the material properties. A methodology previously used for granular agricultural materials is proposed in this research for powder materials. Thus, mechanical properties for some of these materials can be determined. Triaxial, direct shear and oedometer tests among others were carried out for determining different parameters such as Poisson’s ratio, dilatancy angle and elasticity modulus. The materials tested were sugar and five types of flour, confectioners’ sugar, barley, corn, soya and wheat.