Marek Klisinski

Finite element simulation of granular material flow in plane silos with complicated geometry

A model with few material parameters is proposed for finite element simulation of the transient flow of cohesionless granular materials in silos. The constitutive model used is essentially a fluid model and, consequently, it is best established in the Eulerian format. The model allows the simulation of initial stress transients at the beginning of the discharging process. After long time, when the solution approaches steady state, the flow pattern that is developed represents either a mass or funnel flow situation. Numerical examples of transient stress fields are given, and the flow patterns in advanced silo geometries are studied. The numerical results are in good agreement with analytical solutions and experiments known from the literature.

FE-studies on rapid flow of bulk solids in silos

Abstract This paper contains results of numerical modelling of the onset of silo flow for granular material in a model silo with convergent walls. The calculations were performed with a finite element method based on a polar elasto-plastic constitutive relation by Mühlhaus. It differs from the conventional theory of plasticity by the presence of Cosserat rotations and couple stresses using a mean grain diameter as a characteristic length. The characteristic length causes that numerical results do not depend upon the mesh discretisation. The model tests on rapid silo flow of glass beads performed by Renner in a glass hopper with a large wall inclination from the bottom were numerically simulated. The FE-calculations were performed for plane strain by taking into account inertial forces and linear viscous damping. A satisfactory agreement between numerical and experimental results was obtained. In addition, the FE-calculations were performed for very rough walls. Advantages and limitations of a continuum approach for simulations of rapid silo flow were outlined.

A METHOD TO CORRECT YIELD SURFACE DRIFT IN SOIL PLASTICITY UNDER MIXED CONTROL AND EXPLICIT INTEGRATION

SUMMARY When applying an explicit integration algorithm in e.g. soil plasticity, the predicted stress point at the end of an elastoplastic increment of loading might not be situated on the updated current yield surface. This so-called yield surface drift could generally be held under control by using small integration steps. Another possibility, when circumstances might demand larger steps, is to adopt a drift correction method. In this paper, a drift correction method for mixed control in soil plasticity, under drained as well as undrained conditions, is proposed. By simulating triaxial tests in a Constitutive Driver, the capability and eƒciency of this correction method, under di⁄erent choices of implementation, have been analysed. It was concluded that the proposed drift correction method, for quite marginal additional computational cost, was able to correct successfully for yield surface drift giving results in close agreement to those obtained with a very large number of integration steps. ( 1997 by John Wiley & Sons, Ltd.

On constitutive equations for arbitrary stress-strain control in multi-surface plasticity

The structure of incremental constitutive equations in multi-surface plasticity is discussed with respect to different choices of state and control variables. The state and control variables can co ...

On a constitutive driver as a useful tool in soil plasticity

Abstract A mathematical basis for the development of Constitutive Drivers in soil plasticity has recently been proposed by the authors. A Constitutive Driver is here understood as a computer program, containing a number of selected constitutive models, in which different laboratory and field tests can be simulated and model parameters optimised. As a pilot study of the mathematical concept, a Constitutive Driver for soils, in the form of a PC-program, has been developed. The paper discusses this particular program, i.e. its structure, the mathematical basis, included soil models and some application examples, to give an idea of how a general and user-friendly Constitutive Driver can be designed. Such a program can be used for practical, research and educational purposes. In fact, it is believed that so many important applications for Constitutive Drivers exist that it would be beneficial if such programs were easily accessible as complementary programs in commercial software.

Implementation of 3D frictional contact condition

This chapter deals with the formulation and implementation of frictional boundary conditions. The presented method excludes the necessity of usage of interface elements. The key point of the presented contact algorithm is the choice of a local coordinate system that allows it to establish uniquely, the states of slip and stick. This is done by applying at the contact point a conical coordinate system in which the total contact force vector lies on the meridian of the cone. The algorithm is formulated in incremental form and the slipstick conditions are checked in implicit manner. The Coulomb friction law is taken into account. The presented method is the direct extension of the developments concerning 2D problem presented in. The algorithm is implemented into an Eulerian finite element program simulating the 3D flow of a bulk material. In addition, the presented description is also applicable to simulation of other problems—for example, metal forming processes, where the friction prevails. Numerical examples illustrating the correctness of the presented method are provided.

Numerical simulation of 3D iron ore flow

This chapter deals with the simulation of three-dimensional silo flow of a bulk material. Most of the numerical simulations of the flow in silos are usually done in two dimensions what cannot fully reflect all effects observed in real silos. The goal of this chapter is to provide an effective numerical tool to analyze this type of silos including different types of silos including various inserts. The description of the problem is Eulerian and Drucker-Prager type yield function is used. The solution consists of the following three steps: elastic initial stage, creep state and the flow. All of the stages are nonlinear because friction between the flowing material and the walls is considered. The constitutive equations governing the material behavior are solved implicitly and the algorithmic tangent moduli are used. The 4 and 10 nodes tetrahedral elements are used. A finite element program based on the aforementioned assumptions is being developed. This program is the 3D extension of a program described in. Numerical examples of complex geometry silo showing the current capabilities of the program developed are presented.