Eutiquio Gallego

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.

Simulation of silo filling and discharge using ANSYS and comparison with experimental data

Experimental tests have been conducted in bin-hopper silos.Results of Finite Element Models (FEMs) are close to the experimental values.The FEM predicts higher peak pressures than the experimental values.The FEM predicts that the peak pressure is located closer to the transition. Silos are structures widely used in the industrial and agricultural sectors. Despite the advances in research during the last century, many uncertainties still remain. Some of the still unresolved questions in silos are the knowledge about the laws which control the behavior of materials stored in silos or the phenomena produced during the discharge process, when the highest thrust forces exerted by the stored materials on the walls appear.Numerical methods have been extensively employed for the understanding of these complex structures. Among them, the Finite Element Method is a suitable technique to determine the stresses and displacements appeared on the walls or the bulk solid both for filling and discharge of the silo. However, numerical models must be validated by experimental assays. Due to the high investment required, there are very few experimental installations in the world with full-scale silos for determining the actions produced by the stored materials. Therefore, very few assays can be found in the literature.In this article, it has been accomplished a comparison of the results obtained in several assays conducted using an experimental cylindrical silo with those calculated using a Finite Element Model (FEM) developed by using ANSYS software package. A mid-scale test silo was used to carry out the assays, which is equipped to measure the normal wall pressures and the friction forces. The numerical pressures predicted by the FEM are quite close of those experimentally obtained, both for filling and discharge. In addition, the mean vertical pressure obtained at transition is the same for both sets of results during the filling process. Some differences appear during the initial instants of the discharge, when the numerical model predicts higher mean vertical pressures at transition than those experimentally measured. The FEM predicts higher peak pressures than the experimental ones measured, and at a location closer to the transition than the real position of the sensor placed in the hopper to detect this peak.

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%.

How many hours of instruction are needed for students to become competent in engineering subjects

The aim of this work was to compare the curricula of three different agricultural engineering courses and to determine the competence of graduating students in three subject areas in order to identify possible shortfalls in the number of hours of instruction (HI) required for full competence to be attained. A total of 132 students sat a voluntary examination in the final year of their studies to determine their competence in three subject areas: electrical facilities, machinery and construction. The degree courses completed by these students are meant to provide them with the legal standing required to undertake infrastructure projects in agricultural installations. This work detected significant differences in the competence of graduates in the mentioned subjects, depending on the number of HI they had received. Students who had received under 120 HI in these subjects were found to be significantly less competent than those who had received more.

Use of the labour-intensive method in the repair of a rural road serving an indigenous community in Jocotán (Guatemala).

This paper reports the results obtained in an aid project designed to improve transport in the municipal area of Jocotán (Guatemala). The rural road network of an area occupied by indigenous people was analysed and a road chosen for repair using the labour-intensive method–something never done before in this area. The manpower required for the project was provided by the population that would benefit from the project; the involvement of outside contractors and businesses was avoided. All payment for labour went into the pockets of the local people. The small earth movements made and the use of local materials guaranteed the project’s environmental sustainability, while the on-site training of the local community prepared its members for the continued maintenance of the road, thus investing the project with social sustainability.

Discrete Element Modeling of a 3D Scale Silo With Hopper

The discrete element method (DEM) is a numerical technique widely used to study the behavior of granular materials. It has proven to be reliable and effective in simulating many flow scenarios as well as the interaction between granular materials and the physical elements of the machinery or the physical system where they are contained.

Some Practical Features in Modelling Silos with Finite Elements

Studies have shown significant variability exists in pressure predictions in silos using finite element models. Such pressure predictions must be reliable if designers can use them with confidence. This technical note explains why some differences may occur as a result of small changes in reasonable assumptions when modelling contacts in finite element models of silos. The influence of Poisson´s ratio on the lateral pressures expected in silo walls is analyzed in this paper by comparing the values obtained with two commercial finite element packages, ANSYS and ABAQUS. The interaction between the silo wall and the stored solid is a critical point in the development of finite element models. Finite element models developed with commercial software like ANSYS require the adjustment of many parameters involved in contact simulation. The influence on lateral pressures of the contact stiffness factor and the algorithm method in two materials has been carried out with ANSYS.

Effects of different snow load arrangements on steel silo roof structures

Large diameter steel silos usually require a beam structure to support rooftop inspection gangways and resist loads derived from the snow and wind actions. The existence of localized overloads caused by drifted snow on roofs as a consequence of the wind action has been reported in the literature. European standard EN 1991-1-3 also considers the need of taking into account asymmetric patterns for snow loads calculation. However, conical roofs are not included in the specific list of cases considered by this standard. The present work compares the normal stresses and displacements produced in a conical steel silo roof structure by applying balanced loads distributed on the whole roof and unbalanced loads applied on a roof sector. Experimental measurements and a three-dimensional beam model developed by the authors have been used to predict the stresses and vertical displacements of a metal silo roof structure measuring 18.34 m in diameter. The results show that the existence of an asymmetric load pattern produces higher normal stresses (up to 23%) and vertical displacements (up to 50%) than those derived from balanced loads, for any similar load per beam considered.

The "threads" of biosystems engineering

The core concepts, or threads, of Biosystems Engineering (BSEN) are variously understood by those within the discipline, but have never been unequivocally defined due to its early stage of development. This makes communication and teaching difficult compared to other well established engineering subjects. Biosystems Engineering is a field of Engineering which int egrates engineering science and design with applied biological, environmental and agricultural sciences. It represents an evolution of the Agricultural Engineering discipline applied to all living organisms not including biomedical applications. The basic key element for the emerging EU Biosystems Engineering program of studies is to ensure that it offers essential minimum fundamental engine ering knowledge and competences . A core curriculum developed by Erasmus Thematic Networks is used as benchmark for Agr icultural and Biosystems Engineering studies in Europe. The common basis of the core curriculum for the discipline across the Atlantic , including a minimum of competences comprising the Biosystems Engineering core competencies, has been defined by an Atlan tis project , but this needs to be taken further by defining the threads linking courses together. This paper presents a structured approach to define the Threads of BSEN . The definition of the mid-level competences and the associated learning outcomes has been one of the objectives of the Atlantis programme TABE.NET. The mid-level competences and learning outcomes for each of six specializations of BSEN are defined while the domain-specific knowledge to be acquired for each outcome is proposed. Once the proposed definitions are adopted, these threads will be available for global development of the BSEN.

Repair Costs of Low Volume Roads in Spain

Low volume roads play an essential role in the development of rural areas in Spain. They provide access to farms and food industries, and they also provide services traditionally assumed by major roads, e.g., the connection of small towns or their use by emergency services. The construction of most part of the Spanish low volume roads network took place during the second half of the 20th century by using different techniques. The current condition of low volume roads is generally quite poor. However, some differences appear depending on the year of construction and the materials used for the pavement. The authors selected 41 low volume roads throughout Spain to calculate the budget required for their repair in order to analyze the influence of the pavement materials and the period of construction. This paper describes the repair works considered for calculating the budget required by each low volume road.