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Manufacturing Shock Interactions for Innovative Nanoscale Processes

Periodic Reporting for period 3 - NANOSHOCK (Manufacturing Shock Interactions for Innovative Nanoscale Processes)

Reporting period: 2018-12-01 to 2020-05-31

Within the project “Nanoshock – Manufacturing Shock Interactions for Innovative Nanoscale Processes”, we want to investigate the potential of shockwaves for in situ control of fluid processes with surgical precision. Shockwaves are discontinuities in the macroscopic fluid state that can lead to extreme temperatures, pressures and concentrations of energy. Applications of such shock interactions range from kidney-stone lithotripsy and drug delivery to advanced aircraft design. With the use of properly focused shockwaves on tissue material, e.g. , lesions with unprecedented surgical precision can be generated. Alternatively, improving combustion by enhanced mixing of fuels, shockwave interactions can help to further destabilize and atomize spray droplets. Our overall objective is to understand and predict the formation and control of shocks in complex environments such as living organisms using computational methods. The fundamental knowledge of shock generation and its dynamics is essential to unravel the path to technical solutions and leveraging the enormous potential of manufactured shocks in situ. For this purpose, we develop advanced numerical tools that have the capability to simulate accurately multi-physics problems of compressible fluid dynamics giving access to breakthrough innovations and high-impact technologies, ranging from shock-driven nanoparticle reactors to non-invasive shock-mediated low-impact cancer therapies.

Our mission is to offer tools that help to understand and improve medical treatments and nanoparticle generation based on cavitation effects.

Our vision are new strategies for improving targeted medication and for tailoring efficient bioactive nanoparticles.
"During the first period of the research project, we concentrated our efforts on the development of a versatile advanced multi-resolution computational environment for large-scale simulations with novel numerical methods including low-dissipative shock-capturing (WENO and TENO schemes) and advanced level-set interface tracking with conservative interface interactions for multiple materials. Using MPI communication, our code framework is designed for large-scale simulations on modern high-performance architectures such as the SuperMUC at the Leibniz-Rechen-Zentrum in Garching. We have demonstrated that unprecedentedly high resolution with the multi-resolution environment for physically very complex flow can be achieved. The simulation environment is unique in terms of the advanced level of numerical models and possible physical complexity. It is our main work horse for performing our physical experiments through simulation.

The computational cost of numerical fluid simulations is determined by the necessary spatial resolution of the smallest relevant flow structures and, concurrently, by the large amount of time-integration steps due to small time-increments. Enabling technology for the planned numerical simulation are adaptive local time-stepping that ensures stability of the method at maximum possible time-step sizes and a parallel-efficient spatial multi-resolution formulation. For the complex interactions, a multi-region level set method was developed and implemented to handle efficiently multiple phases. Going beyond the limitations of the original level set method, this technique allows for handling more than two phases. We have demonstrated the validity of the approach for foam-like problems dealing with more than 100 different phases.

Our first contribution to the fundamental exploration of cavitation effects in organisms is the detailed investigation of bubble collapse near a gelatin interface using fluid material models as surrogate for the biomaterial. A quantification of pressure peaks and the so-called reentrant-jet penetrating into the gelatin phase reveals the dependence of penetration evolution on the initial bubble configuration. The considered generic setup thus outlines the research directions for the ongoing investigations of the perforation of living cells, as it occurs e.g. during sonoporation (transient increase of cell permeability with improved drug uptake). For this purpose, a realistic bio-material model is currently in development to replace the gelatin surrogate.

Complex interactions of reactive bubble gas mixtures with an impinging shock, which ignites the gas mixture, have been investigated by two- and three-dimensional direct numerical simulations. This work has been published in two journal publications (Combustion and Flames) and is a precursor study towards shock-driven chemically reacting flows. This research line is currently extended towards considering shock-driven nanoparticle generation by laser ablation, for which the underlying physical mechanisms are very similar to shock-bubble interactions. The very localized deposition of high energies in liquids can generate vapor bubbles that eventually collapse and emit shockwaves. We have extended our level-set interface-interaction simulation framework to reproduce a laser-induced cavity formation and have simulated the subsequent so-called liquid drop explosion. Our results reveal for the first time a very detailed insight of the cavity formation. On one hand they agree very well with recent experimental data, on the other hand they rectify some critical elements of the mechanism that was put forward based on the experimental observations alone, demonstrating the value of numerical simulations for such highly complex processes.

We aim at reaching out with our research to a broader public and, therefore, improve the visualization of scientic results for non-experts. In collaboration with the Centre for Virtual Reality and Visualisation (V2C, Leibnitz Supercomputing Centre of the Bavarian Academy of Sciences and Humanities) we can offer now to ""experience"" three-dimensional numerical simulation results, e.g. a fly-through of a collapsing helium bubble in air.

Up to now, the scientific results of our work have resulted in three journal publications and three conference proceedings. Additionally, we have presented our work to the scientific community in 10 presentations at international conferences.

"The highly advanced numerical methods employed by our simulation environment allow for very detailed direct numerical simulations of interface interactions in fluid flows resolving all inertial, acoustic, diffusive and capillary mechanisms at unprecedented accuracy. The fully MPI-parallelized simulation environment enables large-scale simulations to investigate realistic physical problems. The simulation environment ""ALPACA"" is publically available under an open-source license. Other research groups are invited to use this code and to contribute to the further development to improve future simulation capabilities.

The multi-region level set method enables multiphase simulations beyond the state of the art taking large numbers of different phases (>100) into account. Besides the planned activities and expected results, we have synthesized the simulation capabilities achieved so far and initiated new research directions towards direct-simulation of phase-change processes in additive manufacturing.
A near-wall bubble collapse generates a microjet that penetrates the material.
"""Liquid drop explosion"": Slice through expanding drop due to laser-induced cavitation."
Science meets Virtual Reality - a 3D fly-through of a collapsing helium bubble in air.