Title:

The good, the bad, and the beautiful: Leonardo’s studies of turbulence

Abstract:

Aspects of fluid dynamics appear often in Leonardo da Vinci's notebooks: sketches of water flow, plans for flying machines, studies of bird flight.

He seemed fascinated by the eddying movement of water, and designed ingenious experiments to try and understand the causes of these complex motions. He lacked the advanced mathematical tools required to study this subject properly, however, and his attempts to use geometrical reasoning for the analysis of fluid flows were unsuccessful.

This limitation is reflected in many of the machines he designed, which we now know cannot work. His observational powers, however, allowed him to make some exceptionally perceptive remarks that foreshadow techniques used today, both in the experimental and the theoretical analysis of flow problems, observations illustrated by striking drawings and sketches. In this talk, some of Leonardo's reflections on turbulence will be discussed, vis a vis the present understanding of this captivating but baffling subject, perhaps the last unsolved problem in classical physics.

Title:

Turbomachinery Design for Industrial Decarbonization Technologies

Abstract:

Industrial decarbonization is driving the demand for advanced technologies capable of improving energy efficiency, recovering waste heat, and supporting the electrification of industrial processes. Over the last four decades, Turboden has developed an extensive experience in Organic Rankine Cycle (ORC) systems and has recently expanded its technology portfolio to include Industrial Heat Pumps (IHPs), gas expanders, and Mechanical Vapor Recompression (MVR) systems.

The design of new machines is based on the iterative evaluation of different technical solutions, including different cycle layouts, working fluids, and economic drivers. The performance and cost of key components, such as heat exchangers and turbomachines, strongly influence the selection of the optimal configuration. For this reason, Turboden is currently introducing automated design methodologies, transforming internal know-how into structured corporate knowledge, while enabling faster and more reliable design workflows.

Turbomachinery design is based on a digital twin approach, integrating several simulation tools with different levels of accuracy accordingly to the specific design phases. Accurate and reliable numerical simulation are extensively used for the evaluation of aerodynamic performance, structural and thermal integrity, and rotordynamics, which are mandatory for designing high-performance and reliable systems.

To support this process, Turboden is investing in advanced numerical and optimization methods, such as high-order CFD solvers and adjoint-based techniques. These tools are being developed to supports the design of more efficient, reliable, and flexible turbomachines for the next-generation ORC and IHP systems, aiming to drastically reduce the environmental footprint of energy-intensive industrial processes.

Title:

Dealing with the Devil: In-Silico Experiments Across the Scales to Design Better Engineering Interfaces

Abstract:

Small, surface-level features dictate the overall function/failure of a material and control the behaviour of critical interfaces. Being able to tame the “devilish" (chaotic/unpredictable) nature of surfaces is key to design better products. The talk will cover recent advances in modelling aspects of a variety of problems where the behaviour of moving interfaces controls the performance of several engineering systems. It will start with an overview of the modelling tools developed to predict interfacial phenomena across the scales, and will then move onto demonstrating how in-silico experiments can be used to shed light on physical, chemical and mechanical phenomena that affect frictional interactions and engineering performance in several applications in the energy sector, including electric vehicles (EVs) and triboelectric nanogenerators (TENGs), biomedical applications, consumer goods, and functionalized and hierarchical materials and surfaces.

Many of the components undergoing contact in the presence of relative motion are strongly affected by the design and evolution of their surfaces.  Of particular interest for the talk will be the importance of capturing the effect of surface features across the many length scales that they span.  Examples will be provided to demonstrate how multiscale modelling can be used to simulate how molecular and surface roughness interactions across different scales affect frictional behaviour.  These will cover dry contact interactions, where thermal effects and materials transformation can play an extremely important role in the system response, and lubricated interfaces, with the investigation of the interplay between molecules, multiscale roughness and fluid-solid interactions in both conventional mechanical components and soft lubricated contacts, such as those found in biomechanics and soft robotics.

It will be shown how machine learning tools, combined with accurate physics-based modelling techniques, can be used to significantly accelerate simulations of surface evolution almost in real time, leading to the perspective development of digital twins that can capture and monitor the evolution of surfaces and improve the design, efficiency and reliability of many mechanical systems.

Title:

Rearrangeable matter: multiscale mechanics in engineered and biological structures

Abstract:

Many engineered and biological materials function by allowing internal microstructures to rearrange under loading while preserving macroscopic integrity. Describing this interplay between sub-microscopic reorganization and overall mechanical response is still a key challenge in modern mechanics.

This lecture illustrates a unified multiscale framework originated through Structured Deformations and Elasticity with Disarrangements, which jointly capture smooth deformations and submacroscopic slips, rotations, separations, switching, and reconfigurations. These tools connect geometry, kinematics, and energetics across scales within a rigorous continuum setting.

Examples from lipid monolayers and bilayers, and architected solids illustrate how microstructural rearrangements drive macroscopic instabilities, relaxation, shear localization, folding, and pattern formation. By linking theory with experimental observations, the framework provides predictive insight into materials whose effective behavior emerges from internal structural mobility, offering a common language for understanding and designing rearrangeable matter.

Title:

Constitutive Modeling in Nonlinear Elasticity: History, Pitfalls, and Perspectives

Abstract:

This lecture presents a critical overview of constitutive modeling in nonlinear elasticity, with particular emphasis on isotropic incompressible materials. Starting from the historical foundations of the Italian school and the seminal contributions of Rivlin, the talk revisits the motivations behind invariant-based strain-energy functions and their experimental interpretation.

The widespread proliferation of constitutive models is discussed in relation to several recurring pitfalls, including over-parameterization, identifiability issues, and an excessive reliance on analyticity. Special attention is devoted to Ogden-type models, whose remarkable descriptive capabilities are contrasted with their well-known limitations in predictive reliability.

By reconsidering classical experimental data and multiscale arguments, alternative modeling perspectives are outlined, with the aim of clarifying the principles that should guide constitutive choices in nonlinear elasticity and their applications to soft materials and biomechanics.

Title:

Numerical Modeling of Structural Nonlinearities with COMSOL Multiphysics®

Abstract:

The COMSOL Multiphysics® environment provides a comprehensive FEM framework for analyzing the mechanical behavior of solid structures across engineering and research fields. Its features, including shell and beam elements, dynamic and vibration modeling, and contact analysis, are applied across numerous fields, including civil, mechanical, and biomechanical engineering, geomechanics, and MEMS design.

This presentation explores COMSOL Multiphysics® capabilities in handling structural nonlinearities, including geometric nonlinearity, contact, and material nonlinearities. While geometric linearity is often tacitly assumed, it becomes unsuitable in cases of large rotations, significant deflections, or stress stiffening.

Structural contact modeling is a highly nonlinear problem; available methods and practical approaches for both static and dynamic analyses are briefly discussed.

Material nonlinearities are also critical, as many materials exhibit nonlinear stress–strain behavior at higher stress and strain levels. Nonlinear Structural Materials Module and Geomechanics Module include numerous built-in models and supports the customization of constitutive laws. Parameter identification for nonlinear material models requires the use of extensive experimental datasets, and COMSOL Multiphysics® enables calibration through nonlinear least-squares parameter estimation techniques and efficient gradient-based optimization solvers.

Under large strains, several material models have regions where the material is unstable, indicating use beyond their validity range and potentially causing convergence issues. COMSOL Multiphysics® provides dedicated tools to test material models in advance, ensuring more reliable simulations.