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Manufacturing Shock Interactions for Innovative Nanoscale Processes

Periodic Reporting for period 4 - NANOSHOCK (Manufacturing Shock Interactions for Innovative Nanoscale Processes)

Reporting period: 2020-06-01 to 2020-11-30

The project “Nanoshock – Manufacturing Shock Interactions for Innovative Nanoscale Processes” investigates 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 interventions with unprecedented precision can be generated. At the other extreme of the application range, improving combustion by enhanced mixing of fuels, shockwave interactions can serve to destabilize interfaces 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 have developed 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.
Main methodological accomplishment is a new advanced numerical-simulation framework that is capable of predicting highly complex interface interaction mechanisms with discontinuous flow states. The accuracy and level of detail that is achieved with high-fidelity simulations allows to complement and enhance experimental investigations by the ability for non-invasive quantitative data analysis and targeted parameter studies. With the help of highly resolved numerical simulations, we have been able to identify new interface deformation mechanisms (e.g. new aerobreakup mechanisms, previously unkown phenomena during the collapse of triple-emulsion structures). We are currently further exploring the wealth of new findings and the new opportunities opened by their understanding for future technical and medical applications.
"During the Nanoshock project, we have developed and improved the versatile advanced multi-resolution computational environment “ALPACA”. This framework is designed for large-scale simulations with novel numerical methods to describe compressible multiphase flows. The use of low-dissipation high-resolution schemes with shock-capturing allows to accurately simulate liquid and gas flows with strong gradients or discontinuities, like present at phase interfaces or at compression shocks. Since November 2020, ALPACA is publically available under open-source license and offers a “state-of-the-art and beyond” tool to the scientific community.

As of flow-physics investigations with ALPACA, we have studied fundamentals of shock-induced bubble collapse dynamics near biomaterial-surrogate gelatin interfaces. This ongoing research helps to understand perforation of living cells, as it occurs e.g. during sonoporation (transient increase of cell permeability with improved drug uptake). Within the last reporting period we have identified a novel flow focusing mechanism that can be technically exploited for non-invasive surgery on cell level or enhanced drug-delivery. Shock-driven interface breakup, surface cleaning, high-viscosity micro-jetting, and liquid-drop explosion phenomena have been investigated with ALPACA revealing an unprecedented level of detail. Results corroborated experimental finding, revealed much of hidden insight, and also falsified erroneous experimental claims. The high quality level of resulting publications demonstrates the value of numerical simulations to the scientific community.

In order to reduce simulation costs of complex flow problems, we have been developing approaches towards the inverse problem. Here, the idea is to understand the sensitivity of the simulation result on the input parameter to define a specific initial setting for a desirable outcome. With these methods, shock-bubble interactions can be manufactured, e.g. to control the peak pressures at a given location in time for complex configurations where explicit numerical simulations would be tedious, if not infeasible.

To reach out to the broader public and to literally visualize our simulation results, we have developed a transformation of flow simulation data to Virtual Reality in collaboration with the Centre for Virtual Reality and Visualization (V2C, LRZ Garching). We can offer now to ""experience"" three-dimensional simulation results, for instance by fly-through of a collapsing helium bubble in air."
The highly advanced numerical methods implemented in 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. We have pushed beyond the state-of-the-art of numerical schemes by merging adaptive multi-resolution, multi-physics, and nonlinear high-resolution and low-dissipation schemes into a high-performance parallel simulation environment. Moreover, we have been embedding the tool into an effective multi-fidelity co-Kriging framework for model inversion.

We have discovered previously unknown breakup mechanisms during the shock – interaction of a triple-phase emulsion drop, which mimics a layered-capsule / nanoparticle as used in modern medical applications. The resulting highly focused and shielded micro-jet of the inner material could be very useful for future targeted drug delivery. The investigation of droplet breakup under extreme conditions has demonstrated the potential of numerical simulations for complementing experimental investigations. With the help of a novel Knudsen-front Riemann solver for the conservative interface-interaction method (level set method), we have been able to simulate phase transition through rapid evaporation for a laser-induced shock-driven explosion of an isolated liquid drop.
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.