1,721,009 research outputs found
Implicit preconditioned numerical schemes for the simulation of three-dimensional barotropic flows
Full text linkA 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
Adhesion mechanisms inspired by octopus suckers
No full textAbstractNature offers many interesting adhesion mechanisms where attachment forces can be generated in a binary on/off state. Some biological systems (e.g. octopus, sea urchins, starfishes, etc.) take benefit from amazing features that endow movement in different terrains, concurrently to reliable and energetically advantageous attachment and detachment strategies. From an engineering point of view, the study of efficient attachment and detachment mechanisms is extremely interesting and deserves attention for the development of new artificial strategies in robotics.This work describes an adhesion solution inspired by the octopus suckers, starting by a deep investigation of the biological features that allow octopus to perform a variety of complex movements [1]. The final goal is to identify specifications and physical principles useful to conceive innovative bio-inspired adhesion mechanisms [2]. With this approach in mind, we propose a study to fully understand the adhesion natural phenomenon in octopus, which is still not completely clear
Exact solution to the inverse Womersley problem for pulsatile flows in cylindrical vessels, with application to magnetic particle targeting
No full textAn exact solution to the inverse Womersley problem was derived for the fully-developed, laminar pulsatile flow of a viscous Newtonian fluid, within a circular cylindrical vessel with rigid walls. In particular, given an arbitrary, time-periodic flow rate, the axisymmetric velocity profile was obtained by means of two neat and computable maps relating the corresponding Fourier coefficients. The study of such an inverse problem is motivated by the fact that flow rate is the main physical quantity which can be actually measured in many practical situations. The hypothesis of a fully-developed flow was deliberately introduced, in order to obtain an analytical solution (otherwise hardly achievable). Despite the intrinsic simplifications associated with the adopted position (which restrict the applicability of our results to 3D finite-length complex domains, and non-Newtonian fluids), the obtained solution provides a benchmark – and at the same time an approximation – for the inverse problem of pulsatile flows, it may serve as a debugging tool for more ambitious numerical approaches based on realistic data, and can also be used as an improved source of boundary data. As expected, the main advantage of our analytical solutions (compared to fully numerical approaches) resides in computational efficiency; this was quantitatively assessed through numerical tests. Moreover, the proposed solution was applied in the context of magnetic particle targeting, to highlight some peculiar effects on particle trajectories and capture efficiency due to pulsatility. Such a transport problem is increasingly drawing the attention of an interdisciplinary community, ranging from physicians to biomedical engineers, physicists and roboticists, thanks to its potential for targeted therapy, up to remote guidance of intravascular devices. More in general, the obtained benchmark solution holds potential for effectively exploitation in an interdisciplinary context
Removing vascular obstructions: a challenge, yet an opportunity for interventional microdevices
No full text
Shape estimation based on Kalman filtering: Towards fully soft proprioception
No full textAn innovative methodology to realize a sensing system able to estimate the shape of a soft robot arm without hampering 'softness' is presented. The system is based on a low-cost plastic optical fiber (POF) used as curvature sensor and on a simplified steady-state model, both integrated in an Adaptive Extended Kalman Filter (AEKF). Sensory feedback was obtained through accelerometers and it was used as quantitative benchmark for the AEKF. The AEKF estimation turned out to be more accurate (RMS error < 5°) than the model prediction alone and the soft sensor alone, thus supporting the proposed fully soft proprioception strategy
Preliminary Assessment of Accurate Motion Detection via Magnetic Tracking towards Wearable Technologies
Full text linkTracking permanent magnets represents a low-footprint and passive approach to monitoring objects or human motion by attaching or embedding magnets therein. Recent tracking techniques achieved high-bandwidth detection considering a simplified model for the magnetic sources, i.e. The dipole model. Nonetheless, such a model can lead to inaccurate results any time a non-spherical magnet approaches the sensor array. Here, we present a novel tracking algorithm based on an analytical model for permanent magnet cylinders with uniform arbitrary magnetization. By means of a physical system mounting 20 magnetometers, we compared the tracking accuracy obtained with our algorithm vs. results obtained by using the dipole model and with respect to a ground-truth reference. With a single magnetic target, our algorithm can significantly lower position (up to 0.68 mm) and orientation errors (up to 2.5°) while enabling online tracking (computation time below 19 ms). We also accurately tracked two magnets, by obtaining a reduction in position error (up to 0.92 mm) vs. The dipole-based algorithm. These findings broaden the applicability of accurate magnetic tracking to real-time applications, facilitating the tracking of multiple magnetic targets in proximity of the magnetic sensors. This advancement opens avenues for applications in wearable devices, advancing the field of motion detection beyond traditional inertial measurement units
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