Browse Category: Numerical Modelling

Papers, papers…


Much is happening at Aalto and I have been late with much what should be posted. Just to update things quickly, recently SMJ Seyedan has published a paper detailing a small strain enhancement for constitutive models for soils. The paper is here (open access). The idea is to have a thermodynamically consistent enhancement in the initial part of the stress-strain curve, which can be applied to any model using constant shear modulus. We tested it for Mohr-Coulomb and Modified Cam Clay, but it should work for other constitutive models too. Unfortunately, we have no such neat way to adjust the bulk modulus yet, but hopefully in the future… The paper comes with a Matlab code, so it is easy to try it out!


On another front, QA Tran has published a paper related to the null space errors in the Material Point Method. The paper is here and is also open access. The paper discusses null space errors and show how to filter them out efficiently. Such filtering is recommended when we have a problem with large deformations, in which number of material points in some grid cells increases above the initial value. That creates a problem when the data is tranferred from the nodes back to the material points – we have less nodes than the points and as such the transfer uses extra assumptions leading to errors. For example, having 4 nodes transferring data to 9 points, we need to create 9 values at the points from 4 values at the node – that is impossible without extra assumptions which may lead to errors.
The same paper also shows that use of a generalised-alpha integration scheme in the Material Point Method helps to damp out high frequency vibrations, without affecting the total energy and total momentum balance much. Very useful when we need a solution without high frequency noise – and much better than using an overall damping coefficient which alters the solution significantly.

References:
S. Seyedan and W. T. Sołowski, “Enhancing Constitutive Models for Soils: Adding the Capability to Model Nonlinear Small Strain in Shear,” Advances in Civil Engineering, vol. 2019, Article ID 6016350, 11 pages, 2019. https://doi.org/10.1155/2019/6016350.
Tran, Q‐A, Sołowski, W. Temporal and null‐space filter for the material point method. Int J Numer Methods Eng. 2019; 1– 33. https://doi.org/10.1002/nme.6138

MPM 2019 Conference in Cambridge and presentation at Imperial College London

We have attended the 2019 MPM conference in Cambridge in numbers. I had a presentation on Uintah software and a keynote, while other members of the research group presented their research. You can find the proceedings here: http://mpm2019.eu/papers

In particular there are some presentations available:

And the conference papers:

On the way back, I have been given opportunity to present my research at Imperial College London. In particular, you can download the abridged presentation related to our research with Dr Abed in project THEBES: THMC Behaviour of the Swelling Clay Barriers

New Journal Paper: GIMP modelling of large deformation problems including strain-rate effects – Application to penetration and progressive failure problems

Quoc Anh Tran, doctoral student working in the Academy of Finland project on landslide modelling, managed to get a journal paper published in Computers & Geotechnics. The paper shows number of improvements in landslides modelling with the Material Point Method. Those include strain rate dependent, structure dependent Mohr-Coulomb model for undrained analysis. We also  used a simple non-local formulation for the shear-band thickness (Pinyol et al. 2017), which reduces mesh dependence. After validation, the paper shows some – I dare to say – rather nice simulation of a Saint-Monique landslide.

The paper is open access, download it from here:

https://www.sciencedirect.com/science/article/pii/S0266352X18302738

Enjoy!

Conferences, conferences…

Last several months have been really busy, with me having really no time to catch my breath (but well, we have now 5 journal papers under review, keep fingers crossed). Recently, SeyedMohammadJavad Seyedan presented in the beautiful city of Porto in the NUMGE 2018 conference. He was explaining how to enrich the constitutive model for soil with capability to model the small strain shear nonlinearity. It is a neat expansion, which has also thermodynamical consistency (note: full paper under review)…   Then, Dr Ayman Abed presented on chemical coupling (download paper) in UNSAT Conference in Hong Kong. That is a nice effort with cooperation from UPC BarcelonaTech. Finally, I have been presenting in Vienna Dr Yang Xiujuan paper on water retention behaviour of MX-80 bentonite, when partially saturated with saline solution, as unfortunately Xiujuan could not come to Vienna.

Hong Kong – photo from the conference dinner (yay, my new camera)

Paper published and available for download!

The new paper in Computers & Geotechnics:

 A study on how to couple thermo-hydro-mechanical behaviour of unsaturated soils: Physical equations, numerical implementation and examples

 is now on-line!

For the paper please follow https://authors.elsevier.com/a/1VXgy,63b~gd8H  to get the free copy (link valid until 30th of September). Afterwards, please contact me for the copy if you need one… The paper is summing up the developments of the coupled Finite Element code for the THEBES project at Aalto.

 
Thanks for reading!