Imperial College London

Dr Ado Farsi

Faculty of EngineeringDepartment of Earth Science & Engineering

Research Associate
 
 
 
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Contact

 

ado.farsi Website CV

 
 
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Location

 

4.94Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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14 results found

Farsi A, Xiang J, Latham J-P, Carlsson M, Stitt H, Marigo Met al., 2021, Packing simulations of complex-shaped rigid particles using FDEM: An application to catalyst pellets, Powder Technology, Vol: 380, Pages: 443-461, ISSN: 0032-5910

A new component of the combined finite-discrete element method (FDEM) is employed to estimate the effects of geometrical features, friction and energy dissipation parameters on the bulk properties of rigid pellet packs. This work constitutes the first systematic validation of the Solidity FDEM code for rigid particles. The experimental and numerical axial and radial packing density profiles and orientation distributions have been compared, confirming that the numerical simulations of packing of cylindrical catalyst supports, glass beads and trilobe pellets deposited in a cylindrical container match the corresponding emergent bulk properties obtained from X-Ray CT scans. The presented results are a first confirmation of the applicability of FDEM based methods to the simulation of this class of multi-body problems. The assessment of the accuracy of the simulated topology of the pellet pack that is established in this work is encouraging for further investigations of the multi-physical engineering systems of interest for catalyst pellets involving hydro-thermo-mechanical, fracturing and fragmentation interactions using coupled FDEM formulations.

Journal article

Farsi A, Bedi A, Latham JP, Bowers Ket al., 2020, Simulation of fracture propagation in fibre-reinforced concrete using FDEM: an application to tunnel linings, Computational Particle Mechanics, Vol: 7, Pages: 961-974, ISSN: 2196-4378

The application of the combined finite-discrete element method (FDEM) to simulate fracture propagation in fibre-reinforced-concrete (FRC)-lined tunnels has been investigated. This constitutes the first attempt of using FDEM for the simulation of fracture in FRC structures. The mathematical implementations of the new FDEM joint-element constitutive model are first introduced, and the numerical model is then validated comparing the results for plain and FRC beams with three-point bending experimental data. The code has also been applied to two practical tunnel design case studies, showing different behaviours depending on the type of concrete and shape of tunnel section. The FDEM simulations of the linings are also compared with results from a finite element code that is commonly used in the engineering design practise. These results show the capabilities of FDEM for better understanding of the fracture mechanics and crack propagation in FRC tunnels. A methodology for directly inferring the numerical parameters from three-point bending tests is also illustrated. The results of this research can be applied to any FRC structure.

Journal article

Latham J-P, Xiang J, Farsi A, Joulin C, Karantzoulis Net al., 2020, A class of particulate problems suited to FDEM requiring accurate simulation of shape effects in packed granular structures, Computational Particle Mechanics, Vol: 7, Pages: 975-986, ISSN: 2196-4378

In many granular material simulation applications, DEM capability is focused on the dynamic solid particulate flow properties and on systems in which millions of particles are involved. The time of relevance is many seconds or even minutes of real time. Simplifying assumptions are made to achieve run completion in practical timescales. There are certain applications, typically involving manufactured particles, where a representative pack is of the order of a thousand particles. More accurate capturing of the influence of complex shape is then often possible. Higher accuracies are necessary to model the topology of the void space, for example, for further CFD simulation and optimisation of fluid flow properties. Alternatively, the accuracy may be critical for structural performance and the force or stress transmission through the contact points is to be controlled to avoid material damage and poor function. This paper briefly summarises methods for simulation of shape effects on packing structures in the granular community and narrows the scope to problems where shape effects are of overriding concern. Two applications of mono-sized, mono-shaped packing problems are highlighted: catalyst support pellets in gas reforming and concrete armour units in breakwater structures. The clear advantages of FDEM for complex-shaped particle interactions in packed systems with relatively few particles are discussed. A class of particulate problems, ‘FDEM-suited’ problems, ones that are ideal to be solved by FDEM rather than by DEM, is proposed for science and engineering use.

Journal article

Farsi A, Xiang J, Latham JP, Carlsson M, Stitt EH, Marigo Met al., 2020, Strength and fragmentation behaviour of complex-shaped catalyst pellets: A numerical and experimental study, Chemical Engineering Science, Vol: 213, Pages: 1-18, ISSN: 0009-2509

The effects of catalyst support shapes on their final strength and fragmentation behaviour are investigated. Uniaxial compression tests by diametrical loading of solid and four-holed discs with high-speed video recordings are employed to investigate strengths and pellet crushing behaviours. The combined finite-discrete element method (FDEM) is employed to simulate the effects of geometrical features and loading orientation on the pre- and post-failure behaviour of catalysts. A comparison with experimental results is also presented and the remarkable agreement in failure evolution and mode is discussed. A methodology to derive representative fragment size distributions from defined pellet shapes and material properties is introduced, providing a further tool to understand the strength and fragmentation behaviour of catalyst supports. The results suggest that fixed-bed reactors made with solid cylindrical catalysts will be more likely to be affected by pressure drops caused by the choking effect of a significant portion of fines than if it was made with catalyst supports with four holes. Two designs of four-hole catalyst supports sintered with different porosities have also been studied, showing different fragment size distributions and fines production. Characterisation of fines production for different catalyst support designs will improve prediction of reactor clogging and pressure drops.

Journal article

Latham J-P, Farsi A, Xiang J, Clark E, Bakker Ret al., 2019, Numerical modelling of the influence of in-situ stress, rock strength and hole-profile geometry on the stability of Radial Water Jet Drill (RJD) boreholes, American Rock Mechanics Association

Conference paper

Latham JP, Farsi A, Xiang J, Clark E, Bakker RRet al., 2019, Numerical modelling of the influence of in-situ stress, rock strength and hole-profile geometry on the stability of Radial Water Jet Drill (RJD) boreholes

Radial water jet drilling (RJD) is a method of enhancing heat recovery by accessing and connecting to high permeable zones within geothermal reservoirs. The wall rock geometry behind an advancing water jet borehole under in-situ conditions is largely unknown. Water jet drilling tests were performed on 300 mm cubical blocks of weak porous sandstone under true-triaxial boundary stress conditions at the Delft Technical University (DTU) rock mechanics laboratory. Some of these tests showed distinct breakout features depending on the applied stress field. Geometries of resulting boreholes are recovered using X-Ray CT scans, and are analysed using segmentation software (Avizo). The code Solidity, using a combined finite-discrete element method with a cohesive zone fracture model, simulates stress take-up and wall shearing giving breakouts comparable to the experiments. The results lead to the suggestion that criteria based on Kirsch solutions would be suitable to provide general guidance on in-situ stress and rock strength conditions free of breakouts. FEMDEM models appear well-suited to examine geometries and dimensions that can be sustained by given strengths under deeper in-situ conditions. Wall-rock failure and a process of jet-hole enlargement together with the potential benefits of greater heat recovery arising from larger holes is also briefly discussed.

Conference paper

Farsi A, Xiang J, Latham JP, Carlsson M, Stitt EH, Marigo Met al., 2017, Does shape matter? FEMDEM estimations of strength and post failure behaviour of catalyst supports, 5th International Conference on Particle-Based Methods

Conference paper

Farsi A, 2017, Numerical and experimental investigations of particle stress and fracture for complex-shaped pellets

Reactors with fixed beds of cylindrical particles have a wide application in the chemical industry. Ceramic particles are pelletized and fired to produce high porosity catalyst pellets of complex shapes. These pellets fill cylindrical reactor columns with particulate packing structures that are key to the in-service performance, but will suffer breakages, which impact on catalyst performance. The combined Finite-Discrete Element Method (FEMDEM) implemented in the Solidity code would appear to be ideally suited to capturing both the multi-body pellet interactions and pellet fracture and fragmentation. However, to put to use the Solidity code for this purpose and establish its capabilities and limitations required a substantive research programme, as reported in this PhD thesis. Laboratory experiments were performed to evaluate the elastic and fracture properties of reference ceramic samples, as required for input parameters for computer simulation and to investigate code capability to describe fracture in such high strength and porous media for which no previous such simulations had been reported. Each set of specimens was characterised by means of micro- and nano-indentations, ultrasonic and strength tests. Standard laboratory rigs are generally too compliable for capturing the deformations of stiff and tiny ceramic specimens. For this reason, a novel digital image correlation methodology was developed to obtain both strength and stiffness from three-point bending tests on alumina bars which would have been otherwise impossible.The effects of the catalyst support shapes on their final strength and fragmentation behaviour were investigated through controlled experiments and predominantly 2D plane stress simulations on single pellet shapes. Uniaxial compression tests and high-speed video recordings were employed to estimate the strength and fragment size respectively. The Solidity FEMDEM code was employed to simulate the effects of geometrical features and loading or

Thesis dissertation

Farsi A, Pullen AD, Latham JP, Bowen J, Carlsson M, Stitt EH, Marigo Met al., 2017, Full deflection profile calculation and Young's modulus optimisation for engineered high performance materials, Scientific Reports, Vol: 7, Pages: 1-13, ISSN: 2045-2322

New engineered materials have critical applications in different fields in medicine, engineering and technology but their enhanced mechanical performances are significantly affected by the microstructural design and the sintering process used in their manufacture. This work introduces (i) a methodology for the calculation of the full deflection profile from video recordings of bending tests, (ii) an optimisation algorithm for the characterisation of Young’s modulus, (iii) a quantification of the effects of optical distortions and (iv) a comparison with other standard tests. The results presented in this paper show the capabilities of this procedure to evaluate the Young’s modulus of highly stiff materials with greater accuracy than previously possible with bending tests, by employing all the available information from the video recording of the tests. This methodology extends to this class of materials the possibility to evaluate both the elastic modulus and the tensile strength with a single mechanical test, without the need for other experimental tools.

Journal article

Xiang J, Latham JP, Farsi A, 2017, Algorithms and capabilities of solidity to simulate interactions and packing of complex shapes, DEM 7, Pages: 139-149, ISSN: 0930-8989

© Springer Science+Business Media Singapore 2017. A number of numerical algorithms for simulation of particle packing have been proposed and used in a wide range of industries: mining, chemical engineering, pharmaceuticals, agriculture and food handling, etc. However, most of them can only deal with simple and regular shapes due to the complex and expensive numerical algorithms needed to simulate complex shapes. In this paper, a FEMDEM code, Solidity, is used to more accurately capture the influence of complex shape. It combines deformable fracturing arbitrary-shaped particle interactions modelled by FEM with discrete particulate motion modelled by DEM. This paper will cover recent code optimisation for the contact force calculation with arbitrary body shape, parallelisation performance and discussion of results showing both deformable and rigid body versions of the code in different application scenarios. Solidity also provides post-processing tools to analyse the particle packing structure in terms of local porosity and orientation distributions, contact forces, and coordination number, etc. Some examples of Platonic and Archimedean body packs are presented.

Conference paper

Farsi A, Xiang J, Latham JP, Carlsson M, Stitt EH, Marigo Met al., 2016, Simulation and characterisation of packed columns for cylindrical catalyst supports and other complex-shaped bodies, Proceedings of the 7th International Conference on Discrete Element Methods, Publisher: Springer Singapore, Pages: 397-406, ISBN: 978-981-10-1926-5

Catalyst pellets are packed in reactor beds and the shape and mechanicalproperties have a major influence on the reactor performance by virtue of (i)the detailed topology of the void space and grain surface area and (ii) the fragility of the pack to withstand in-service stresses within the solid skeleton – often through thermal and cyclic stressing. The paper highlights the features of the FEMDEM code used to simulate these performance-related properties of the pack. The local porosity, packing structure, bulk porosity and orientation distributions of the resulting bodies making up the pack of pellets will be presented. The generic methodology illustrated is shown to be suitable for shape optimisation of industrial packing processes.

Book chapter

Latham JP, Xiang J, Farsi A, 2016, Accurate modelling of particle shape effects in packed granular structures: a class of particulate problems solved by FEMDEM, 7th International Conference on Discrete Element Methods

Conference paper

Farsi A, Xiang J, Latham J, Pullen A, Carlsson M, Stitt EH, Marigo Met al., 2015, An application of the finite-discrete element method in the simulation of ceramic breakage: methodology for a validation study for alumina specimens, IV International Conference on Particle-based Methods, Publisher: International Center for Numerical Methods in Engineering (CIMNE), Pages: 921-932

ABSTRACT: Alumina (aluminum oxide, Al 2 O 3) particles are pelletised and fired to produce high porosity catalyst pellets of complex shapes. These pellets fill cylindrical reactor columns with particulate packing structures that are key to the in-service performance, but will suffer breakages which impact on catalyst performance. The combined Finite-Discrete Element Method (FEMDEM) is ideally suited to the simulation of both the multi-body pellet dynamic packing and quasi-static interactions as well as the stress field of each individual pellet, its deformations and fragmentation. The application of FEMDEM fracture modelling to a fine-grained brittle and porous material is novel. This paper presents a methodology for a validation study through comparison with three point-bending and Brazilian tests and discusses FEMDEM's potential in modelling multi-body fragile systems.

Conference paper

Farsi A, 2013, Inverse analysis procedures and possible applications in drilling operations

The purpose of this dissertation is to define a new experimental methodology to identify the information that can be obtained during drilling operations that can be used in different fields of application. The points that will be addressed are an outline of the different phases of the experiment and of the simulation, and a description of the methodologies of inverse analysis relevant to parameter identification. Different specific applications will need different numerical models to perform parameters identification: the computational model that describes the behaviour of concrete, for instance, is obviously very different from the one needed to describe multiphase geological material. This made it necessary to focus on a specific application: the diagnostic of structures subjected to structural deterioration, such as concrete dams. A numerical model that best represented the experiment for this specific application has been studied, and through that model the experimental equipment has been optimised, by comparing computational simulations. Through the experimental phases that will be defined and the process of inverse analysis, the elastic parameters, state of stress before the excavation, the plastic and fracture parameter of the structure can be evaluated.

Thesis dissertation

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