On Friday, 24. October 2025 at 2:30 PM, Nicola Gottardi will presented his doctoral theses with the title "Real-time Structural Health Assessment of Segmental Tunnel Linings".

Abstract:
The underground network has been constantly expanding, and one of the challenges is ensuring safety, operability, and durability of tunnels throughout their service life. In this context, structural health monitoring (SHM) plays a crucial role for the evaluation of the tunnel lining performance and safety. Tunnel lining health assessment faces unique challenges due to limited accessibility to critical areas and a sparse availability of measurement data compared to the complexity of the structural system. The objective of this thesis was to develop a framework to accomplish comprehensive SHM of segmental tunnel linings, by leveraging the benefits of computational and surrogate models to accommodate a limited monitoring of the structure. Numerical simulations are employed to generate synthetic data, which are used to train surrogate models capable of reconstructing the lining structural state, accounting for possible damage, and its loading conditions based on limited measurements. The SHM framework proposed in this thesis, validated on experiments and a tunnel project, represents a flexible approach adaptable to various monitoring configurations, enabling real-time evaluations of the structural health of segmental linings to ensure tunnel operability and safety in a cost-effective manner.

The lecture dates for the winter term 2025/2026 are online:

On Friday, 12. September 2025 at 10 AM, Simon Peters presented his doctoral theses with the title "Computational Multiscale Modeling of Low-Carbon Concretes at Elevated Temperatures".

Dear Simon, congratulations on your successful PhD! We wish you all the best for your future and continued success!




Abstract:
Despite decades of research, the underlining mechanism of explosive concrete spalling at elevated temperatures remains unknown. This thesis proposes a fully coupled numerical chemo-thermo-hygro-mechanical model, advanced through a micromechanical framework, providing a deeper understanding of the multiphysical nature of explosive spalling.

Key contributions include the development and validation of the micromechanical framework to analyze the binder-specific dehydration behavior, chemically induced material evolution and microstructure. This framework enhances applicability and reduces experimental calibration requirements for the well-established multiphysical macroscale model, particularly for concretes based on CO2-reduced cements.

By means of virtual parametric studies, the main findings of the thesis are: i) The binder-specific dehydration behavior of CO2-reduced cement pastes is not the primary driving mechanism behind fire-induced concrete spalling. ii) Aggregates characterized by high thermal conductivity can lead to a significant increase (even more than 35%) in pore pressure when compared to aggregates with lower thermal conductivity. iii) The dense microstructure is the primary factor driving the susceptibility of concretes containing CO2-reduced cements to fire-induced concrete spalling compared to ordinary concretes. iv) The moisture clog theory is not supported.

Written by Roger A. Sauer the new Open access publication "A curvilinear surface ALE formulation for self-evolving Navier-Stokes manifolds – stabilized finite element formulation" is published now in the journal 'Computer Methods in Applied Mechanics and Engineering' by Elsevier.

Abstract:
This work presents a stabilized finite element formulation of the arbitrary Lagrangian-Eulerian (ALE) surface theory for Navier-Stokes flow on self-evolving manifolds developed in Sauer [1] . The formulation is physically frame-invariant, applicable to large deformations, and relevant to fluidic surfaces such as soap films, capillary menisci and lipid membranes, which are complex and inherently unstable physical systems. It is applied here to area-incompressible surface flows using a stabilized pressure-velocity (or surface tension-velocity) formulation based on quadratic finite elements and implicit time integration. The unknown ALE mesh motion is determined by membrane elasticity such that the in-plane mesh motion is stabilized without affecting the physical behavior of the system. The resulting three-field system is monolithically coupled, and fully linearized within the Newton-Rhapson solution method. The new formulation is demonstrated on several challenging examples including shear flow on self-evolving surfaces and inflating soap bubbles with partial inflow on evolving boundaries. Optimal convergence rates are obtained in all cases. Particularly advantageous are C1-continuous surface discretizations, for example based on NURBS.

'A curvilinear surface ALE formulation for self-evolving Navier–Stokes manifolds: general theory and analytical solutions' is a new open-access paper written by Roger A. Sauer. It is published in the 'Journal of Fluid Mechanics' by Cambridge University Press.

Abstract:
A new arbitrary Lagrangian–Eulerian (ALE) formulation for Navier–Stokes flow on self-evolving surfaces is presented. It is based on a general curvilinear surface parameterisation that describes the motion of the ALE frame. Its in-plane part becomes fully arbitrary, while its out-of-plane part follows the material motion of the surface. This allows for the description of flows on deforming surfaces using only surface meshes. The unknown fields are the fluid density or pressure, the fluid velocity and the surface motion, where the latter two share the same normal velocity. The corresponding field equations are the continuity equation or area-incompressibility constraint, the surface Navier–Stokes equations and suitable surface mesh equations. Particularly advantageous are mesh equations based on membrane elasticity. The presentation focuses on the coupled set of strong and weak form equations, and presents several manufactured steady and transient solutions. These solutions are used together with numerical simulations to illustrate and discuss the properties of the proposed new ALE formulation. They also serve as basis for the development and verification of corresponding computational methods. The new formulation allows for a detailed study of fluidic membranes such as soap films, capillary menisci and lipid bilayers.