Time-dependent linearisation of bottom friction for storm surge modelling in the Wadden Sea

The nonlinear nature of bottom friction in shallow flow complicates its analysis, particularly in idealised models. For tidal flows, Lorentz’ linearisation has been widely applied, using an energy criterion to specify the friction coefficient. Here we propose an extension of this approach to storm surges, leading to a friction coefficient that may gradually vary over a storm event. The derivation is provided along with first results for a single channel

Downward-going tau neutrinos as a new prospect of detecting dark matter

Dark matter trapped in the Sun produces a flux of all flavors of neutrinos, which then reach the Earth after propagating out of the Sun and oscillating from the production point to the detector. The typical signal which is looked at refers to the muon neutrino component and consists of a flux of up-going muons in a neutrino detector. We propose instead a novel signature: the possibility of looking at the tau neutrino component of the dark matter signal, which is almost background-free in the downward-going direction, since the tau neutrino amount in atmospheric neutrinos is negligible and in the down-going baseline atmospheric muon-neutrinos have no time to sizably oscillate. We analyze the prospects of studying the downward-going tau neutrinos from dark matter annihilation (or decay) in the Sun in Cherenkov detectors, by looking at hadronic showers produced in the charged-current tau neutrino interactions and subsequent tau decay. We discuss the various sources of background (namely the small tau neutrino component in atmospheric neutrinos, both from direct production and from oscillations; tau neutrinos from solar corona interactions; the galactic tau neutrino component) as well as sources of background due to misidentification of electron and muon events. We find that the downward-going tau neutrinos signal has potentially very good prospects for Mton scale Cherenkov detectors, the main limitation being the level of misidentification of non-tau events, which need to be kept at level of percent. Several tens of events per year (depending on the dark matter mass and annihilation/decay channel) are potentially collectible with a Mton scale detector, and a 5 sigma significance discovery is potentially reachable for dark matter masses in the range from 20 to 300 GeV with a few years of exposure on a Mton detector.Comment: 24 pages, 10 figures. Version published in JHEP. Figures revisited with inclusion of galactic neutrino background. Main results and conclusions unchange

Laughing waves in ancient Greek

The unattributed ἀκύματος πορθμὸς γελᾷ, Aeschylus’ κυμάτων γέλασμα, Plato’s κῦμα ἐκγελῶν, Pseudo-Aristotle’s τὸ κῦμα ἐπιγελᾷ, and Strabo’s στόματα ἐπιγελῶντα imply images of waves as laughing, spanning centuries in the ancient Greek canon. A linguistically and physically consistent analysis clarifies prior uncertainties and flaws in their interpretation. The analogy with human laughter is at the heart of the ancient Greek vocabulary for wave motions; shoaling waves broke into figurative laughter. Our reanalysis reveals the wordplay preparing the third wave in Respublica 5, the Peripatetics’ study of the swell life cycle in Problemata 23, and an appropriate site description in Geographica 11

Dam break flow benchmarks: quo vadis?

SPH has widened the scope of simulations of dam-break flows beyond the primary focus on impact loads. The flow complexity – involving boundary layers, air phase, surface tension, bubble and droplet formation, nonstationary, inhomogeneous and anisotropic turbulence – still imposes a piecemeal modelling approach to both two- and three-dimensional studies. Here, two-dimensional simulations provide fresh insights into the capability of SPH to reproduce vortical and acoustic features after increasing the sole spatial resolution. A dam-break flow on a dry floor and impacting a vertical wall has been resolved up to Re eff = 256,000. The array of spatial resolutions d/∆x = 800, 1600, 3200, 6400 shows the emergence by nonlinearity of progressively smaller flow scales. Fluid particles can populate the viscous sublayer and resolve boundary layer separations. Also, in the stages of chaotic motion, the intricate soundscape of acoustic waves and pulses supported by the weakly compressible fluid is resolved cleanly. The frequency bands in the pattern-bearing spectra of pressure signals help diagnose both causal and spurious flow events occurred during a simulation. The efficacy of density diffusion and viscosity in abating disturbances below the scale of the kernel diameter is apparent. Experiments are needed to address all flow stages and validate highly resolved 2D and 3D simulations of dam breaks. The available measurements do not cover the agitated stages, while pressure loads regard only the impingement stages. The configuration of new apparatuses could be optimized for a high return of relevant detail from the compute elements (SPH particles), so that simulations can produce densely informative datasets