Three-dimensional numerical simulation of wind-induced barotropic circulation in the Gulf of Patras   总被引：1，自引：0，他引：1  

Nikolaos Th. Fourniotis 《Ocean Engineering》2010,37(4):355-364

The barotropic, wind-induced circulation, which develops in the Gulf of Patras in Western Greece during the winter, is studied using three-dimensional numerical simulations. The simulations are performed using the numerical code MIKE 3 FM (HD). The Gulf's basin is bracketed between two sills, one on the west at the opening with the Ionian Sea and the other on the east at the Straits of Rio-Antirio at the opening with the Gulf of Corinth. The simulations show that the wind-induced flow creates strong currents near the coasts, which determine the sense of rotation of the gyres that develop in the Gulf. Strong currents are also created at the Rio-Antirio Straits. The wind-induced, barotropic currents do not seem to contribute to the direct replenishment of bottom waters, which recirculate between the two sills. Depending on the wind-speed forcing of the flow, the residence time of the waters in the Gulf of Patras is estimated to range from one week to one month.  相似文献   

Detection of water leaks in supply pipes using continuous wave sensor operating at 2.45 GHz     

Matthaios Bimpas  Angelos Amditis  Nikolaos Uzunoglu 《Journal of Applied Geophysics》2010,70(3):226-236

An innovative sensor technique has been developed to detect water leaks in supply pipes, especially in cases where the existing prevailing methods do not offer reliable solution, such as in PVC pipelines or for minor leaks. The presented system uses a Continuous Wave (CW) Doppler sensing unit operating at 2.45 GHz, consisting of a low power transmitter, a homodyne receiver and a digital signal processing unit. The operation principle is the detection of the Doppler frequency shift of the reflected electromagnetic wave by slightly moving water that leaks out of a pipe. A first prototype has already been developed and tested in test sites as well as in real water leaking conditions. The system has additionally been compared to the commercially available water leaking methods, verifying its reliability and accuracy in the detection of water leaks.  相似文献   

Modelling the Gibraltar Strait/Western Alboran Sea ecohydrodynamics     

Nikolaos Skliris  Jean-Marie Beckers 《Ocean Dynamics》2009,59(3):489-508

The ecohydrodynamics of the Gibraltar Strait and the Western Alboran Sea is investigated using a 3-D, two-way nested, coupled hydrodynamic/plankton ecosystem model, exploiting the MEDATLAS climatological database. A high-resolution model (~1 km) of the Gibraltar/Western Alboran region embedded within a coarse-resolution model of the West Mediterranean (~5 km) is implemented. The model seasonal climatology of the 3-D circulation and the flow characteristics at the Gibraltar Strait and the Alboran Sea are discussed, and their impact on the plankton ecosystem evolution is explored. An important ecohydrodynamic feature produced by the model is a permanent upwelling zone in the northwestern part of the Alboran Sea in agreement with observations. Model results show that both horizontal and vertical current intensity of the Atlantic Jet increases progressively at the strait to obtain maximum values in the northeastern Mediterranean entrance, inducing an upward displacement of the nitracline. The nutrient-rich water transport through the strait along with the generation of cyclonic vorticity in the northwestern Alboran Sea result in the accumulation of nutrients there and thus induce a permanent fertilisation of this area.  相似文献   

A reach‐scale biogeochemical model for temporary rivers     

Ourania Tzoraki  Nikolaos P. Nikolaidis  Anna Rosa Trancoso  Frank Braunschweig  Ramiro Neves 《水文研究》2009,23(2):272-283

The RS‐tempQ Model ( r each– s cale t emporary flow biogeochemical model) is a conceptual model that can describe the hydrologic, sediment transport and biogeochemical processes of temporary rivers at the reach scale. The model takes into account the expansion–contraction of the inundated area of the river. It simulates the sediment transport and the nutrient fluxes that are transferred to the coastal area due to the first flash flood and during extreme rain events. The RS‐tempQ Model simulates the in‐stream processes during the wet and dry cycles as the river corridor expands and contracts. The model was used to assess and quantify the hydrologic and geochemical processes occurring in a temporary river reach (Krathis River) in Greece. Since the conventional gauging techniques cannot measure the flow in rivers that are split into small braided streams, discharge measurements could not be obtained in order to calibrate and verify the model. Other field measurements such as infiltration losses and sediment accumulation were used for model calibration. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Eccentricity generation in hierarchical triple systems with coplanar and initially circular orbits   总被引：1，自引：0，他引：1  

Nikolaos Georgakarakos 《Monthly notices of the Royal Astronomical Society》2002,337(2):559-566

  相似文献   

Eccentricity generation in hierarchical triple systems: the planetary regime     

Nikolaos Georgakarakos 《Monthly notices of the Royal Astronomical Society》2006,366(2):566-574

In previous papers, we developed a technique for estimating the inner eccentricity in hierarchical triple systems, with the inner orbit being initially circular. We considered systems with well-separated components and different initial setups (e.g., coplanar and non-coplanar orbits). However, the systems we examined had comparable masses. In the present paper, the validity of some of the formulae derived previously is tested by numerically integrating the full equations of motion for systems with smaller mass ratios (from 10⁻³ to 10³, i.e. systems with Jupiter-sized bodies). There is also discussion about HD 217107 and its planetary companions.  相似文献   

Eccentricity Generation in Hierarchical Triple Systems with Non-coplanar and Initially Circular Orbits     

Nikolaos Georgakarakos 《Celestial Mechanics and Dynamical Astronomy》2004,89(1):63-82

In a previous paper, we developed a technique for estimating the inner eccentricity in coplanar hierarchical triple systems on initially circular orbits, with comparable masses and with well-separated components, based on an expansion of the rate of change of the Runge-Lenz vector. Now, the same technique is extended to non-coplanar orbits. However, it can only be applied to systems with I ₀ < 39.23° or I ₀ > 140.77°, where I is the inclination of the two orbits, because of complications arising from the so-called ‘Kozai effect’. The theoretical model is tested against results from numerical integrations of the full equations of motion. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Non-linear pulsations in differentially rotating neutron stars: mass-shedding-induced damping and splitting of the fundamental mode     

Nikolaos Stergioulas  Theocharis A. Apostolatos  José A. Font 《Monthly notices of the Royal Astronomical Society》2004,352(4):1089-1101

  相似文献   

Fractionation of grain size in terrestrial sediment routing systems          下载免费PDF全文

Philip A. Allen  Nikolaos A. Michael  Mitchall D’Arcy  Duna C. Roda‐Boluda  Alexander C. Whittaker  Robert A. Duller  John J. Armitage 《Basin Research》2017,29(2):180-202

Sediment is fractionated by size during its cascade from source to sink in sediment routing systems. It is anticipated, therefore, that the grain size distribution of sediment will undergo down‐system changes as a result of fluvial sorting processes and selective deposition. We assess this hypothesis by comparing grain size statistical properties of samples from within the erosional source region with those that have undergone different amounts of transport. A truncated Pareto distribution describes well the coarser half of the clast size distribution of regolith, coarse channel bed sediment and proximal debris flows (particularly their levees), as well as the coarser half of the clast size distribution of gravels that have undergone considerable amounts of transport in rivers. The Pareto shape parameter a evolves in response to mobilization, sediment transport and, importantly, the selective extraction of particles from the surface flow to build underlying stratigraphy. A goodness of fit statistic, the Kolmogorov–Smirnov vertical difference, illustrates the closeness of the observed clast size distributions to the Pareto, Weibull and log‐normal models as a function of distance from the depositional apex. The goodness of fit of the particle size distribution of regolith varies with bedrock geology. Bedload sediment at catchment outlets is fitted well by the log‐normal and truncated Pareto models, whereas the exponential Weibull model provides a less good fit. In the Eocene Escanilla palaeo‐sediment routing system of the south‐central Pyrenees, the log‐normal and truncated Pareto models provide excellent fits for distances of up to 80 km from the depositional apex, whereas the Weibull fit progressively worsens with increasing transport distance. A similar trend is found in the Miocene–Pliocene gravels of the Nebraskan Great Plains over a distance of >300 km. Despite the large fractionation in mean grain size and gravel percentage from source region to depositional sink, particle size distributions therefore appear to maintain log‐normality over a wide range of transport distance. Use of statistical models enables down‐system fractionation of sediment released from source regions to be better understood and predicted and is a potentially valuable tool in source‐to‐sink approaches to basin analysis.  相似文献   

Torsional oscillations of magnetized relativistic stars     

Neophytos Messios  Demetrios B. Papadopoulos  Nikolaos Stergioulas 《Monthly notices of the Royal Astronomical Society》2001,328(4):1161-1168

Strong magnetic fields in relativistic stars can be a cause of crust fracturing, resulting in the excitation of global torsional oscillations. Such oscillations could become observable in gravitational waves or in high-energy radiation, thus becoming a tool for probing the equation of state of relativistic stars. As the eigenfrequency of torsional oscillation modes is affected by the presence of a strong magnetic field, we study torsional modes in magnetized relativistic stars. We derive the linearized perturbation equations that govern torsional oscillations coupled to the oscillations of a magnetic field, when variations in the metric are neglected (Cowling approximation). The oscillations are described by a single two-dimensional wave equation, which can be solved as a boundary-value problem to obtain eigenfrequencies. We find that, in the non-magnetized case, typical oscillation periods of the fundamental     torsional modes can be nearly a factor of 2 larger for relativistic stars than previously computed in the Newtonian limit. For magnetized stars, we show that the influence of the magnetic field is highly dependent on the assumed magnetic field configuration, and simple estimates obtained previously in the literature cannot be used for identifying normal modes observationally.  相似文献