@misc{BorciaRichterBorciaetal., author = {Borcia, Ion-Dan and Richter, Sebastian and Borcia, Rodica and Sch{\"o}n, Franz-Theo and Harlander, Uwe and Bestehorn, Michael}, title = {Wave propagation in a circular channel: sloshing and resonance}, series = {The European Physical Journal Special Topics}, volume = {Vol. 232}, journal = {The European Physical Journal Special Topics}, number = {4}, issn = {1951-6401}, doi = {10.1140/epjs/s11734-023-00790-z}, pages = {461 -- 468}, abstract = {Surface wave resonance of a liquid (water) layer confined in a circular channel is studied both experimentally and numerically. For the experiment, eight unevenly distributed ultrasonic distance sensors measure the local height of the wave surface. The resonance curves show maxima only for odd multiples of the fundamental resonance frequency . We explained this behavior using a simple intuitive "ping-pong" like model. Collision of wave fronts can be observed for higher frequencies. Also, the wave reflection on the walls can be treated as wave collision with itself. The non-linearity seems to be weak in our study so the delay in the wave propagation before and after the collision is small. Time-space plots show localized propagating waves with high amplitudes for frequencies near resonance. Between the peaks low amplitude and harmonic patterns are observed. However, for higher frequencies, the frequency band for localized waves becomes wider. In the Fourier space-time plane, this can be observed as a point for the harmonic patterns or a superposition of two lines: one line parallel to wave-vector k axis corresponding to the excitation frequency and a second line with inclination given by wave propagation velocity . For planned future work, this result will help us to reconstruct the whole water surface elevation using time-series from only a few measurement points}, language = {en} } @misc{HarlanderSukhanovskiiAbideetal., author = {Harlander, Uwe and Sukhanovskii, Andrei and Abide, St{\´e}phane and Borcia, Ion-Dan and Popova, Elene and Rodda, Costanza and Vasiliev, Andrei and Vincze, Miklos}, title = {New Laboratory Experiments to Study the Large-Scale Circulation and Climate Dynamics}, series = {Atmosphere}, volume = {14}, journal = {Atmosphere}, number = {5}, doi = {10.3390/atmos14050836}, pages = {19}, abstract = {The large-scale flows of the oceans and the atmosphere are driven by a non-uniform surface heating over latitude, and rotation. For many years scientists try to understand these flows by doing laboratory experiments. In the present paper we discuss two rather new laboratory experiments designed to study certain aspects of the atmospheric circulation. One of the experiments, the differentially heated rotating annulus at the Brandenburg University of Technology (BTU) Cottbus, has a cooled inner cylinder and a heated outer wall. However, the structure of the atmospheric meridional circulation motivates a variation of this "classical" design. In the second experiment described, operational at the Institute of Continuous Media Mechanics (ICMM) in Perm, heating and cooling is performed at different vertical levels that resembles more the atmospheric situation. Recent results of both experiments are presented and discussed. Differences and consistencies are highlighted. Though many issues are still open we conclude that both setups have their merits. The variation with heating and cooling at different levels might be more suited to study processes in the transition zone between pure rotating convection and the zone of westerly winds. On the other hand, the simpler boundary conditions of the BTU experiment make this experiment easier to control.}, language = {en} } @misc{HarlanderBorciaVinczeetal., author = {Harlander, Uwe and Borcia, Ion-Dan and Vincze, Miklos and Rodda, Costanza}, title = {Probability Distribution of Extreme Events in a Baroclinic Wave Laboratory Experiment}, series = {Fluids}, volume = {7}, journal = {Fluids}, number = {8}, issn = {2311-5521}, doi = {10.3390/fluids7080274}, abstract = {Atmospheric westerly jet streams are driven by temperature differences between low and high latitudes and the rotation of the Earth. Meandering jet streams and propagating Rossby waves are responsible for the variable weather in the mid-latitudes. Moreover, extreme weather events such as heat waves and cold spells are part of the jet stream dynamics. For many years, a simple analog in the form of a simplified laboratory experiment, the differentially heated rotating annulus, has provided insight into the dynamics of the meandering jet stream. In the present study, probability density distributions of extreme events from a long-term laboratory experiment are studied and compared to the atmospheric probability density distributions. Empirical distributions of extreme value monthly block data are derived for the experimental and atmospheric cases. Generalized extreme value distributions are adjusted to the empirical distributions, and the distribution parameters are compared. Good agreement was found, but the distributions of the experimental data showed a shift toward larger extreme values, and some explanations for this shift are suggested. The results indicate that the laboratory model might be a useful tool for investigating changes in extreme event distributions due to climate change. In the laboratory context, the change can be modeled by an increase in total temperature accompanied by a reduction in the radial heat contrast.}, language = {en} } @misc{LeGalHarlanderBorciaetal., author = {Le Gal, Patrice and Harlander, Uwe and Borcia, Ion-Dan and Le Diz{\`e}s, St{\´e}phane and Chen, J. and Favier, Benjamin}, title = {Instability of vertically stratified horizontal plane Poiseuille flow}, series = {Journal of Fluid Mechanics}, volume = {907}, journal = {Journal of Fluid Mechanics}, number = {R1}, issn = {1469-7645}, doi = {10.1017/jfm.2020.917}, pages = {1 -- 14}, language = {en} } @misc{VinczeBozokiHereinetal., author = {Vincze, Miklos and Boz{\´o}ki, Tam{\´a}s and Herein, M{\´a}ty{\´a}s and Borcia, Ion-Dan and Harlander, Uwe and Horics{\´a}nyi, Attila and Nyerges, Anita and Rodda, Costanza and P{\´a}l, Andr{\´a}s and P{\´a}lfy, J{\´o}zsef}, title = {The Drake Passage opening from an experimental fluid dynamics point of view}, series = {SScientific Reports}, volume = {11}, journal = {SScientific Reports}, issn = {2045-2322}, doi = {10.1038/s41598-021-99123-0}, pages = {11}, language = {en} } @misc{BorciaBorciaXuetal., author = {Borcia, Ion-Dan and Borcia, Rodica and Xu, Wenchao and Bestehorn, Michael and Richter, Sebastian and Harlander, Uwe}, title = {Undular bores in a large circular channel}, series = {European Journal of Mechanics - B/Fluids}, volume = {79}, journal = {European Journal of Mechanics - B/Fluids}, issn = {0997-7546}, doi = {10.1016/j.euromechflu.2019.09.003}, pages = {67 -- 73}, abstract = {An experimental device previously developed for studying rotating baroclinic flows has been used to investigate undular bores formation, propagation and collision. Up to our knowledge this is the first experimental study of undular bores in a circular channel. For a setup without barriers, this geometry accomplishes in a natural way the periodic lateral boundary conditions, very often used in numerical simulations. An excellent agreement between the experiment and simulation has been achieved. The spatio-temporal structure of bores is well reproduced for the first few reflections or collisions.}, language = {en} } @misc{HarlanderBorciaKrebs, author = {Harlander, Uwe and Borcia, Ion-Dan and Krebs, Andreas}, title = {Nonnormality increases variance of gravity waves trapped in a tilted box}, series = {Geophysical \& Astrophysical Fluid Dynamics}, volume = {113}, journal = {Geophysical \& Astrophysical Fluid Dynamics}, number = {5/6}, issn = {1029-041}, doi = {10.1080/03091929.2018.1549660}, pages = {602 -- 622}, language = {en} } @misc{RoddaBorciaLeGaletal., author = {Rodda, Costanza and Borcia, Ion-Dan and Le Gal, Patrice and Vincze, Miklos and Harlander, Uwe}, title = {Baroclinic, Kelvin and inertia-gravity waves in the barostrat instability experiment}, series = {Geophysical \& Astrophysical Fluid Dynamics}, volume = {112}, journal = {Geophysical \& Astrophysical Fluid Dynamics}, number = {3}, issn = {1029-0419}, doi = {10.1080/03091929.2018.1461858}, pages = {175 -- 206}, language = {en} } @misc{VinczeBorciaHarlander, author = {Vincze, Mikl{\´o}s and Borcia, Ion-Dan and Harlander, Uwe}, title = {Temperature fluctuations in a changing climate: an ensemble-based experimental approach}, series = {Scientific Reports}, volume = {7}, journal = {Scientific Reports}, issn = {2045-2322}, doi = {10.1038/s41598-017-00319-0}, pages = {254}, language = {en} } @misc{BorciaBorciaHelbigetal., author = {Borcia, Rodica and Borcia, Ion-Dan and Helbig, Markus and Meier, Martin and Egbers, Christoph and Bestehorn, Michael}, title = {Dancing drops over vibrating substrates}, series = {The European Physical Journal Special Topics}, volume = {226}, journal = {The European Physical Journal Special Topics}, number = {6}, issn = {1951-6355}, doi = {10.1140/epjst/e2016-60202-6}, pages = {1297 -- 1306}, language = {en} } @misc{KleinSeeligKurganskyetal., author = {Klein, Marten and Seelig, Torsten and Kurgansky, Michael V. and Ghasemi, Abouzar and Borcia, Ion-Dan and Will, Andreas and Schaller, Eberhard and Egbers, Christoph and Harlander, Uwe}, title = {Inertial wave excitation and focusing in a liquid bounded by a frustum and a cylinder}, series = {Journal of Fluid Mechanics}, journal = {Journal of Fluid Mechanics}, number = {vol. 751}, issn = {1750-6859}, doi = {10.1017/jfm.2014.304}, pages = {255 -- 297}, abstract = {The mechanism of localized inertial wave excitation and its efficiency is investigated for an annular cavity rotating with Ω0 . Meridional symmetry is broken by replacing the inner cylinder with a truncated cone (frustum). Waves are excited by individual longitudinal libration of the walls. The geometry is non-separable and exhibits wave focusing and wave attractors. We investigated laboratory and numerical results for the Ekman number E ≈ 10-6. inclination α = 5.71◦ and libration amplitudes ε 0.2 within the inertial wave band 0 < ω < 2Ω0 . Under the assumption that the inertial waves do not essentially affect the boundary-layer structure, we use classical boundary-layer analysis to study oscillating Ekman layers over a librating wall that is at an angle α = 0 to the axis of rotation. The Ekman layer erupts at frequency ω = f∗, where f∗ ≡ 2Ω0 sin α is the effective Coriolis parameter in a plane tangential to the wall. For the selected inclination this eruption occurs for the forcing frequency ω/Ω0 = 0.2. For the librating lids eruption occurs at ω/Ω0 = 2. The study reveals that the frequency dependence of the total kinetic energy Kω of the excited wave field is strongly connected to the square of the Ekman pumping velocity wE (ω) that, in the linear limit, becomes singular when the boundary layer erupts. This explains the frequency dependence of non-resonantly excited waves. By the localization of the forcing, the two configurations investigated, (i) frustum libration and (ii) lids together with outer cylinder in libration, can be clearly distinguished by their response spectra. Good agreement was found for the spatial structure of low-order wave attractors and periodic orbits (both characterized by a small number of reflections) in the frequency windows predicted by geometric ray tracing. For 'resonant' frequencies a significantly increased total bulk energy was found, while the energy in the boundary layer remained nearly constant. Inertial wave energy enters the bulk flow via corner beams, which are parallel to the characteristics of the underlying Poincar{\´e} problem. Numerical simulations revealed a mismatch between the wall-parallel mass fluxes near the corners. This leads to boundary-layer eruption and the generation of inertial waves in the corners.}, language = {en} }