Implicit preconditioned numerical schemes for the simulation of three-dimensional barotropic flows

A numerical method for simulating three-dimensional, generic barotropic flows on unstructured grids is developed. Space and time discretizations are separately considered. A finite volume compressible approach, based on a suitable Roe numerical flux function, is proposed and the accuracy of the resulting semi-discrete formulation for nearly-incompressible flows is ensured by ad hoc preconditioning. Moreover, a linearized implicit time-advancing technique is proposed, only relying on the algebraic properties of the Roe flux function and therefore applicable to a variety of problems. This implicit strategy is extended so as to incorporate the aforementioned preconditioning. The considered numerical ingredients are firstly defined in a one-dimensional context; after validation, they are extended to three-dimensional non-rotating as well as rotating frames. Finally, the resulting numerical method is validated by considering complex industrial flows, namely the water flow around a hydrofoil (for which specific experimental data are available) and the water flow around a rotating turbo-pump inducer. By starting from a particular industrial problem (namely the numerical simulation of propellant flows around an axial inducer belonging to the feed turbo-pump system of a liquid propellant rocket engine), a numerical method which can be applied to generic barotropic flows is defined. Along the way, a constructive procedure for solving the 1D Riemann problem associated with a generic convex barotropic state law is proposed. This solution, also exploited for defining a Godunov numerical flux suitable for incorporation into finite volume schemes, is systematically used in order to define exact benchmarks for the quantitative validation of the proposed one-dimensional numerical methods

A Preconditioned implicit Roe's scheme for barotropic flows: towards simulation of cavitation phenomena

The discretisation of the Euler equations for a barotropic state law is considered. An upwind scheme based on the definition of a Roe's type matrix is first obtained for this particular hyperbolic problem. A low Mach number asymptotic study is performed both in the continuous and discrete case showing that the discrete solution admits pressure fluctuations in space much larger than those of the exact one. This is the same kind of behaviour observed for the case of a polytropic state law. A preconditioning is then applied such that the obtained discrete formulation has an asymptotic behaviour in agreement with the continuous case. A linearised implicit scheme is defined using the properties of the Roe matrix instead of the first-order homogeneity of the flux function which is not satisfied here. The implicit formulation is also extended to the preconditioned scheme. All the proposed ingredients are validated in the case of a quasi 1-D nozzle flow of a cavitating liquid

Plant-like hooked miniature machines for on-leaf sensing and delivery

New sustainable strategies for preserving plants are crucial for tackling environmental challenges. Bioinspired soft and miniature machines have the potential to operate in forests and agricultural fields by adapting their morphology to plant organs like leaves. However, applications on leaf surfaces are limited due to the fragility and heterogeneity of leaves, and harsh outdoor conditions. Here, we exploit the strong shear-dependent leaf-attachment of the hook-climber Galium aparine to create miniature systems that enable precision anchoring to leaf tissues via multifunctional microhooks. We first study the anchoring forces of the microhooks and then fabricate a soft wireless multiparameter sensor to monitor the leaf proximity and degradable hooks for in-plant molecular delivery to the vascular tissues of the leaves. In addition, we use a soft robotic proof-of-concept demonstrator to highlight how our hooks enable ratchet-like motion on leaves. This research showcases opportunities for specifically designing multifunctional machines for targeted applications in plant ecosystems

A 3D Real-Scale, Biomimetic, and Biohybrid Model of the Blood-Brain Barrier Fabricated through Two-Photon Lithography

The investigation of the crossing of exogenous substances through the blood-brain barrier (BBB) is object of intensive research in biomedicine, and one of the main obstacles for reliable in vitro evaluations is represented by the difficulties at the base of developing realistic models of the barrier, which could resemble as most accurately as possible the in vivo environment. Here, for the first time, a 1:1 scale, biomimetic, and biohybrid BBB model is proposed. Microtubes inspired to the brain capillaries were fabricated through two-photon lithography and used as scaffolds for the co-culturing of endothelial-like bEnd.3 and U87 glioblastoma cells. The constructs show the maturation of tight junctions, good performances in terms of hindering dextran diffusion through the barrier, and a satisfactory trans-endothelial electrical resistance. Moreover, a mathematical model is developed, which assists in both the design of the 3D microfluidic chip and its characterization. Overall, these results show the effective formation of a bioinspired cellular barrier based on microtubes reproducing brain microcapillaries to scale. This system will be exploited as a realistic in vitro model for the investigation of BBB crossing of nanomaterials and drugs, envisaging therapeutic and diagnostic applications for several brain pathologies, including brain cancer

Neuromorphic tactile sensor array based on fiber Bragg gratings to encode object qualities

Emulating the sense of touch is fundamental to endow robotic systems with perception abilities. This work presents an unprecedented mechanoreceptor-like neuromorphic tactile sensor implemented with fiber optic sensing technologies. A robotic gripper was sensorized using soft and flexible tactile sensors based on Fiber Bragg Grating (FBG) transducers and a neuro-bio-inspired model to extract tactile features. The FBGs connected to the neuron model emulated biological mechanoreceptors in encoding tactile information by means of spikes. This conversion of inflowing tactile information into event-based spikes has an advantage of reduced bandwidth requirements to allow communication between sensing and computational subsystems of robots. The outputs of the sensor were converted into spiking on-off events by means of an architecture implemented in a Field Programmable Gate Array (FPGA) and applied to robotic manipulation tasks to evaluate the effectiveness of such information encoding strategy. Different tasks were performed with the objective to grant fine manipulation abilities using the features extracted from the grasped objects (i.e., size and hardness). This is envisioned to be a futuristic sensor technology combining two promising technologies: optical and neuromorphic sensing

Flexible Over-the-Tube Device for Soft-Tethered Colonoscopy

Soft-tethered colonoscopes were proposed for safe and effective colon navigation, yet the deployment of front-wheel actuated colonoscopes is hindered by contact interactions with the lumen along the entire soft tether. To mitigate this problem, this study introduces an over-the-tube flexible device aimed to assist colonoscope deployment. The device is composed of three pneumatically driven actuators devised to repeatedly perform a two-phase operation: (phase I) to advance along the tether up to a working position relatively close to the colonoscope’s tip; (phase II) to clamp and drag the tether forward, upon anchoring to colonic wall. This way, a distal tether portion is freed, thus reducing the aforementioned limitations and fostering effective front-wheel navigation. Considering anatomical/clinical constraints and a 2N resistive force, we designed and prototyped a system with an inner and outer diameter of 12 and 26 mm, respectively, a length of 91 mm, and operating pressures equal to 150, 50 and 15 kPa for clamping the tether, elongating the device and safely anchoring to the colonic wall, respectively. The device was successfully tested, achieving locomotion speeds up to 4.9 and 2.2 mm/s, and tether freeing rates up to 2.9 and 1.8 mm/s, in tabletop conditions and in a colon phantom, respectively

Wireless Robotic Capsule for Releasing Bioadhesive

A novel, miniature wireless robotic capsule for releasing bioadhesive patches in the gastrointestinal (GI) tract was designed, fabricated, and preliminarily tested. In particular, the assembled prototype was successfully navigated in a GI phantom, up to a target site where the release mechanism was verified. Then, deployment of a bioadhesive patch onto ex vivo porcine tissue was accomplished, and patch adhesion strength was verified. The main application of the present system is the deployment of anchoring patches for miniature robotic modules to be operated in the targeted anatomical domain. Such an innovative application stems from the wise blend of robotics and bioadhesion. Obtained results, which are consistent with previous investigations by the group, confirm the viability of the adopted bioadhesives for the envisaged anchoring tasks. The present feasibility study complies with the spirit of minimally invasive, wireless diagnosis, and therapy, and provides a preliminary contribution for their advancement