A weakly compressible SPH scheme has been used to describe the evolution of viscous flows around blunt bodies at Reynolds numbers ranging from 10 to 2400. The simulation of such a wide range, rarely ...addressed to in the SPH literature, has been possible thanks to the use of a proper ghost-fluid technique and to an accurate enforcement of the boundary conditions along the solid boundaries. In this context, a new numerical technique based on previous works by Takeda et al. (1994) 48, Marrone et al. (2011) 28 and De Leffe et al. (2011) 16 has been proposed, along with a new method for the evaluation of the global loads on bodies. Particular care has been taken to study the influence of the weakly-compressibility assumption and of different ghost-fluid techniques on the numerical results. An in-depth validation of the model has been performed by comparing the numerical outcome with experimental data from the literature and other numerical references. The influence of the domain size has been discussed in order to avoid wall side effects and, at the same time, to limit the computational costs. The convergence of the numerical solutions has been checked on both global and local quantities by choosing appropriate Reynolds-cell number.
The flux of cosmic ray antiprotons is a powerful tool for indirect detection of dark matter. The sensitivity is limited by the uncertainty on the predicted antiproton flux from scattering of primary ...rays on the interstellar medium. This is, in turn, limited by the knowledge of production cross‐sections, notably in p–He scattering. Thanks to its internal gas target, the LHCb experiment performed the first measurement of antiproton production from collisions of LHC proton beams on He nuclei at rest. The results and prospects are presented.
The present paper proposes a novel algorithm to detect the free-surface in particle simulations, both in two and three dimensions. Since the proposed algorithms are based on SPH interpolations their ...implementation does not require complex geometrical procedures. Thus the free-surface detection can be easily embedded in SPH solvers, without a significant increase of the CPU time. Throughout this procedure accurate normal vectors to the free-surface are made available. Then it is possible to define a level-set function algorithm which is presented in detail. The latter allows in-depth analyses of three-dimensional free-surface simulations by using standard visualization tools, including internal features of the flow. The algorithms proposed for detecting free-surface particles and defining the level-set function are validated on simple and complex two- and three-dimensional flow simulations. The usefulness of the proposed procedures to post-process and analyze complex flows are illustrated on realistic examples.
Aquatic locomotion of a deformable body from rest up to its asymptotic speed is given by the unsteady motion which is produced by a series of periodic reactions dictated by the body configuration and ...by the style of swimming. The added mass plays a crucial role, not only for the initial burst, but also along each manoeuvre, to accelerate the surrounding fluid for generating the kinetic energy and to enable vortex shedding in the wake. The estimate of these physical aspects has been largely considered in most theoretical models, but not sufficiently deepened in many experimental and numerical investigations. As a motivation, while the vortical structures are easily detectable from the flow field, the added mass, on the contrary, is usually embedded in the overall forcing terms. By the present impulse formulation, we are able to separate and to emphasize the role of the added mass and vorticity release to evaluate in a neat way their specific contributions. The precise identification of the added mass is also instrumental for a well-posed numerical problem and for easily readable results. As a further point, the asymptotic speed is found to be guided either by the phase velocity of the prescribed undulation and by the unavoidable recoil motion induced by the self-propelled swimming. The numerical results reported in the present paper concern simplified cases of non-diffusing vorticity and two-dimensional flow.
δ-SPH model for simulating violent impact flows Marrone, S.; Antuono, M.; Colagrossi, A. ...
Computer methods in applied mechanics and engineering,
03/2011, Letnik:
200, Številka:
13
Journal Article
Recenzirano
A smoothed particle hydrodynamics model with numerical diffusive terms, hereinafter referred to as
δ-SPH
1 is used to analyze violent water flows. The boundary conditions on solid surfaces of ...arbitrary shape are enforced with a new technique based on
fixed ghost particles. The violent impacts studied result from dam-break water flows striking obstacles of different shapes. The numerical results are validated against experimental data from the literature and solutions from a Navier–Stokes Level-Set solver. Predicted impact pressures are also compared with analytical solutions. The proposed scheme thus proves to be accurate and robust for the prediction of global and local loads of impact flows on structures.
In this paper two dimensional free vorticity dynamics is studied using two different particle methods. The first one is a Diffused Vortex Hydrodynamics (DVH) and the second one is a Smoothed Particle ...Hydrodynamics (SPH) method. These two methods present some similarities linked to their meshless nature but they are based on different numerical approaches. In this work advantages and drawbacks are highlighted by testing the particle methods on selected test-cases and by performing heuristic convergence measurements. The DVH method discussed in this work is characterized by the use of a regular distribution of points to perform the vorticity diffusion process. This redistribution avoids excessive clustering or rarefaction of the vortex particles providing robustness and high accuracy of the method.
Oscillatory swimming of a fishlike body, whose motion is essentially promoted by the flapping tail, has been studied almost exclusively in axial mode under an incoming uniform stream or, more ...recently, self-propelled under a virtual body resistance. Obviously, both approaches do not consider the unavoidable recoil motions of the real body which have to be necessarily accounted for in a design procedure for technological means. Actually, once combined with the prescribed kinematics of the tail, the recoil motions lead to a remarkable improvement on the resulting swimming performance. An inviscid impulse model, linear in both potential and vortical contributions, is a proper tool to obtain a deeper comprehension of the physical events with respect to more elaborated flow interaction models. In fact, at a first look, the numerical results seem to be quite entangled, since their trends in terms of the main flapping parameters are not easy to be identified and a fair interpretation is obtained by means of the model capability to separate the effects of added mass and vortex shedding. Specifically, a prevailing dependence of the potential contribution on the heave amplitude and of the vortical contribution on the pitch amplitude is instrumental to unravel their combined action. A further aid for a proper interpretation of the data is provided by accounting separately for a geometrical component of the recoil which is expected to follow from the annihilation of any spurious rigid motion in case no fluid interactions occur. The above detailed decomposition of the recoil motions shows, through the numerical results, how the single components are going to influence the main flapping parameters and the locomotion performance as a guide for the design of biomimetic swimmers.
New anti-telomere strategies represent important goals for the development of selective cancer therapies. In this study, we reported that uncapped telomeres, resulting from pharmacological ...stabilization of quadruplex DNA by RHPS4 (3,11-difluoro-6,8,13-trimethyl-8H-quino4,3,2-klacridinium methosulfate), trigger specific recruitment and activation of poly-adenosine diphosphate (ADP) ribose polymerase I (PARP1) at the telomeres, forming several ADP-ribose polymers that co-localize with the telomeric repeat binding factor 1 protein and are inhibited by selective PARP(s) inhibitors or PARP1-specific small interfering RNAs. The knockdown of PARP1 prevents repairing of RHPS4-induced telomere DNA breaks, leading to increases in chromosome abnormalities and eventually to the inhibition of tumor cell growth both in vitro and in xenografts. More interestingly, the integration of a TOPO1 inhibitor on the combination treatment proved to have a high therapeutic efficacy ensuing a complete regression of the tumor as well as a significant increase in overall survival and cure of mice even when treatments started at a very late stage of tumor growth. Overall, this work reveals the unexplored link between the PARP1 and G-quadruplex ligands and demonstrates the excellent efficacy of a multi-component strategy based on the use of PARP inhibitors in telomere-based therapy.
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