Dr Arman Khoshghalb
The Next Generation of Numerical Modelling
Dr Arman Khoshghalb is a senior lecturer in geotechnical engineering at the School of Civil and Environmental Engineering (CVEN) and is a member of the Centre for Infrastructure Engineering and Safety (CIES).
In partnership with Professor Nasser Khalili and Dr Bernhard Schrefler, Dr Khoshghalb was recently awarded a substantial Australia Research Council (ARC) grant to investigate mitigation techniques for those recurring geotechnical problems of failure and instability. The research outcome will be a computational model that works as a reliable predictive tool for civic structures such as dams and embankments. This project aims to create new knowledge in the area of strain localisation in unsaturated soils and slope failures involving large deformations.
Arman’s main area of research for the last ten years has been a fundamental investigation into the efficiency of numerical modelling for geotechnical problems. “Every engineering project uses modelling. If we can improve our numerical methods, we can improve our work.” He, ultimately, aims to create a next generation tool for geotechnical simulation that significantly improves the efficiency of the current methods. “In the next 10 years my vision is to be able to simulate slope failures more efficiently using state-of-the-art tools.”
To model any engineering problem, the first step is to work out the governing equations of that problem. Due to difficulty and complexity of these governing equations, particularly when the soil is unsaturated, they are often solved approximately. Currently, the most widely used method is the Finite Element Method (FEM). To approximate the unknown, FEM divides the domain into smaller elements and, through the meshing of the domain, formulates simpler equations for these elements, assembling them into a larger system that models the whole domain.
“FEM is accurate and efficient most of the time, but it is not well suited to solve some problems, for example, those including large deformations or cracks.”
Recently, numerous methods have been developed to address this problem. Arman Khoshghalb is one of a select group of international academics working on a cluster of approaches referred to as Meshfree Methods. “I am working on a particular group of Meshfree methods called the Smooth Point Interpolation Methods (SPIMs). The idea is to relax the heavy reliance of the FEM on the mesh and make a method that is more flexible. SPIMs adjust strain definition in each of the finite elements to yield a more accurate and flexible numerical model.”
“My main research goal is to develop accurate and efficient techniques for modelling slope failures through practical application of the S-PIMs. Current computational methods for modelling soil movement down a slope are cumbersome and expensive. S-PIMs have the potential to improve efficiency by achieving the modelling in only a fraction of the time.”
“SPIMs were first developed in late 2000s in the field of mechanical engineering. The application of SPIMs in the field of geotechnical engineering has, however, been limited so far, mainly due to the complexities of the technique.”
Arman was one of the first engineers to apply SPIMs to geotechnical engineering problems. His innovation has inspired others to adopt this approach. “Academics working in this field constantly use each other’s findings.” However, the paucity of publications in this area reveals just how nascent and innovative this research is. There have also been some roadblocks to the widespread adoption of SPIMs. “They are complicated methods compared to the standard FEM. This level of complexity has made industry, and many academics, reluctant to adopt these innovations. I have to emphasise that although, at first, they are difficult to understand and code, once that understanding comes, codes based on SPIMs are easy to develop and efficient to use. Currently, most industrial software is based on FEM, so uptake must involve will, cost and patience.”
As industry moves toward adoption, the resilience of the SPIMs will be revealed. It has the potential to become the overarching method, with an efficiency and a flexibility that includes but supersedes FEM. “It is like an umbrella method, that has several methods underneath its cover, including FEM.”
Geotechnical industries are booming in Australia. As Engineering Australia states: “more and more, society requires to know the risk to which people, property and the environment are exposed. The role of the geotechnical engineering profession should increasingly be reducing exposure to threats, reducing risk and protecting people.”
For the last 20 years industry has largely relied on two main modelling software packages: PLAXIS and FLAC. “While these packages are very powerful and well developed, the core of these systems has not changed for years and there is industry talk about the need for revision, rejuvenation and improvement. While we cannot expect companies to completely change their software to one based on a relatively new technique, what I am hoping to see is that SPIMs become an option within these programs. Change must be paced to deal with risk.”
These types of additions have already happened in other fields: “ABAQUS has adopted certain meshfree methods for example.” It is the right time for action, change and growth.
Arman will continue to refine his SPIM research and code, discovering any weak points and addressing them now, so that by the time industry is ready for a more full-scale adoption, the method will be mature and safe. “Applying this technique to a wide variety of cases (including unsaturated soils), assessing suitability and comparing the SPIM efficiency to FEM will prepare solid ground for full practical application. Most of my publications currently reflect this comparison.”
Dr Khoshghalb believes that SPIMs represent the future of computational modelling. This is a lasting, long-term investment, driving geotechnical engineering forward.