scholarly journals A New Small Drifter for Shallow Water Basins: Application to the Study of Surface Currents in the Muggia Bay (Italy)

2016 ◽  
Vol 2016 ◽  
pp. 1-5 ◽  
Author(s):  
Carmelo Nasello ◽  
Vincenzo Armenio
Keyword(s):  
Free Surface ◽  
Shallow Water ◽  
Coriolis Force ◽  
Surface Current ◽  
Meteorological Conditions ◽  
Water Current ◽  
Surface Currents ◽  
Water Basin ◽  
Surface Circulation ◽  
The City

A new small drifter prototype for measuring current immediately below the free surface in a water basin is proposed in this paper. The drifter dimensions make it useful for shallow water applications. The drifter transmits its GPS location via GSM phone network. The drifter was used to study the trajectory of the surface current in the Muggia bay, the latter containing the industrial harbor of the city of Trieste (Italy). The analysis has been carried out under a wide variety of wind conditions. As regards the behavior of the drifter, the analysis has shown that it is well suited to detect the water current since its motion is marginally affected by the wind. The study has allowed detecting the main features of the surface circulation within the Muggia bay under different meteorological conditions. Also, the study has shown that the trajectory of the surface current within the bay is weakly affected by the Coriolis force.

The action of a surface current used as a breakwater

1955 ◽  
Vol 231 (1187) ◽  
pp. 466-478 ◽  
Keyword(s):  
Surface Current ◽  
Water Current ◽  
Air Bubbles ◽  
Surface Currents ◽  
Mean Velocity ◽  
Uniform Velocity ◽  
Sea Bottom ◽  
The Mean ◽  
Perforated Tube ◽  
A Current

The conditions under which an outward-flowing surface current can prevent the passage of waves coming in from the sea are investigated mathematically. Two types of current are considered: ( a ) a current with uniform velocity extending to a depth h ; ( b ) a current with velocity decreasing uniformly and vanishing at depth h . They have very similar effects. The mean velocity required to stop waves of given frequency is rather greater in case ( a ) than in case ( b ). The water current produced by a curtain of air bubbles from a perforated tube on the sea bottom is investigated theoretically on the assumption that the bubbles are very small. Evans (1955) has measured the surface currents produced in a tank by a bubble curtain and finds them smaller than predicted. The discrepancy is partly due to the fact that the bubbles were not very small.

Use of a Stem Device for VIV Mitigation on a Dry Tree Semi-Submersible

2009 ◽  
Author(s):  
Apurva Gupta ◽  
John Murray ◽  
Bin Li ◽  
Harish Mukundan ◽  
Anis Hussain
Keyword(s):  
Gulf Of Mexico ◽  
Fatigue Damage ◽  
Production Systems ◽  
High Surface ◽  
Surface Current ◽  
Water Current ◽  
Surface Currents ◽  
Offshore Industry ◽  
Viv Suppression ◽  
Tree Production

The offshore industry is devoting considerable effort to develop a dry tree production Semi-submersible with motion characteristics similar to a Spar but with the functionality of a Tension Leg Platform (TLP) or a Semi-submersible in terms of fabrication, installation and commissioning. Installation of these Semi-submersibles in the Gulf of Mexico environment exposes the risers to high surface current which result in high fatigue damage due to Vortex Induced Vibration (VIV). In the existing dry tree production systems, the Spar shields the riser from the high velocity surface currents in depths to approximately 600 ft. In the dry tree Semi-submersible the upper sections of the risers are exposed to surface currents. In addition, most dry tree Semi-submersibles designs have to support Keel Joints similar to a Spar. Thus, installing and replacing conventional VIV mitigation devices like the fairings and strakes could become difficult. In comparison, the TLP has no keel guides making it easier to install risers with strakes or fairings to improve the riser’s response to currents in terms of VIV. There are two basic proven techniques to reduce VIV damage on a riser. These involve application of standard fairings or strakes and direct protection of an exposed riser to currents. This paper discusses a methodology for VIV suppression using a riser stem. This mechanism does not reduce the VIV directly on the riser, but it in fact shields the riser from the surface currents, and thus reduces the fatigue damage on risers. This riser is shielded inside a conduit section called a stem which extends from the deck of the Semi-submersible to the keel. The paper quantifies and discusses the reduction in fatigue damage when the stem is used. The analysis is based on typical deep water current conditions for the Gulf of Mexico.

Viscous interface instability supporting free-surface currents in a hydromagnetic rotating fluid column

2001 ◽  
Vol 65 (1) ◽  
pp. 1-28 ◽  
Author(s):  
YUSRY O. EL-DIB
Keyword(s):  
Magnetic Field ◽  
Free Surface ◽  
Angular Velocity ◽  
Current Density ◽  
Surface Current ◽  
Surface Currents ◽  
Rotating Fluid ◽  
Field Frequency ◽  
Surface Current Density ◽  
Azimuthal Magnetic Field

The stabilization of a viscous interface stressed by an oscillating magnetic field is investigated. Account is taken of the influence of free-surface currents on the effective solidly rotating fluid column. Only azimuthal modes are considered in the linear perturbation. The dispersion relation with or without free-surface currents is obtained in the form of a linear Mathieu equation with complex coefficients. It is found that there is a nonlinear relation between the surface current density and both the stratified viscosity and the stratified azimuthal magnetic field. The surface currents disappear on the interface of the fluid column when the stratified magnetic field has the value of unity. At this value, a coupled parametric resonance occurs in the absence of angular velocity. The magnetic field plays a stabilizing role. This role increases with increasing surface currents. The angular velocity plays a destabilizing role, while the field frequency plays a stabilizing role and acts against the angular velocity. The stratified viscosity plays a damping role in the presence of the surface current density, while, in the absence of a surface current, it plays two opposite roles corresponding to the presence or absence of the field frequency. A set of graphs are used to illustrate the relation between the presence of free-surface currents and both the viscosity and the azimuthal magnetic field.

scholarly journals Meteorological conditions, ozone concentration and leaf age affect gas exchange in Psidium guajava ‛Palumaʼ

Hoehnea ◽  
2017 ◽  
Vol 44 (2) ◽  
pp. 236-245 ◽  
Author(s):  
Juliana Moreno Pina ◽  
Sérgio Tadeu Meirelles ◽  
Regina Maria de Moraes
Keyword(s):  
Gas Exchange ◽  
Ozone Concentration ◽  
Leaf Age ◽  
Psidium Guajava ◽  
Meteorological Conditions ◽  
Gas Exchanges ◽  
Mature Leaves ◽  
Young Leaves ◽  
Entire Experiment ◽  
The City

ABSTRACT This study aimed to investigate the importance of leaf age, meteorological conditions and ozone concentration (O3) on gas exchange of Psidium guajava ‛Paluma'. Saplings were grown and exposed in standard conditions in the city of São Paulo, in six periods of three months with weekly measurements in young and mature leaves. Gas exchanges were higher in young leaves for almost the entire experiment. Mature leaves showed greater reduction in gas exchange. The multivariate analysis of biotic and abiotic variables indicated that vapor pressure deficit (VPD), O3 concentration and radiation were the main variables associated with gas exchange decrease in young leaves. In mature leaves the influence of VPD is lower, but the temperature importance is higher. Moreover, the opposition between assimilation and O3 is more evident in mature leaves, indicating their greater sensitivity to O3.

A layer-integrated approach for shallow water free-surface flow computation

2007 ◽  
Vol 24 (12) ◽  
pp. 1699-1722
Author(s):  
Meng-Chi Hung ◽  
Te-Yung Hsieh ◽  
Tung-Lin Tsai ◽  
Jinn-Chuang Yang
Keyword(s):  
Free Surface ◽  
Shallow Water ◽  
Free Surface Flow ◽  
Integrated Approach ◽  
Surface Flow ◽  
Flow Computation

scholarly journals WAVETRISK-2.1: an adaptive dynamical core for ocean modelling

2021 ◽  
Author(s):  
Nicholas Keville-Reynolds Kevlahan ◽  
Florian Lemarié
Keyword(s):  
Free Surface ◽  
Shallow Water ◽  
Time Integration ◽  
Ocean Model ◽  
Mesh Adaptivity ◽  
Time Step ◽  
Vertical Coordinate ◽  
Slip Boundary ◽  
Modelling Framework ◽  
Atmosphere Model

Abstract. This paper introduces WAVETRISK-2.1 (i.e. WAVETRISK-OCEAN), an incompressible version of the atmosphere model wavetrisk-1.x with free-surface. This new model is built on the same wavelet-based dynamically adaptive core as wavetrisk, which itself uses DYNANICO's mimetic vector-invariant multilayer rotating shallow water formulation. Both codes use a Lagrangian vertical coordinate with conservative remapping. The ocean variant solves the incompressible multilayer shallow water equations with inhomogeneous density layers. Time integration uses barotropic--baroclinic mode splitting via an semi-implicit free surface formulation, which is about 34–44 times faster than an unsplit explicit time-stepping. The barotropic and baroclinic estimates of the free surface are reconciled at each time step using layer dilation. No slip boundary conditions at coastlines are approximated using volume penalization. The vertical eddy viscosity and diffusivity coefficients are computed from a closure model based on turbulent kinetic energy (TKE). Results are presented for a standard set of ocean model test cases adapted to the sphere (seamount, upwelling and baroclinic turbulence). An innovative feature of wavetrisk-ocean is that it could be coupled easily to the wavetrisk atmosphere model, thus providing a first building block toward an integrated Earth-system model using a consistent modelling framework with dynamic mesh adaptivity and mimetic properties.

scholarly journals Characteristic Mode Analysis of surface current distributions on metallic structures exposed to HIRF- and DCI-excitations

2020 ◽  
Vol 18 ◽  
pp. 33-41
Author(s):  
Jan Ückerseifer ◽  
Frank Gronwald
Keyword(s):  
Three Dimensional ◽  
Surface Current ◽  
Resonance Region ◽  
Mode Analysis ◽  
Surface Currents ◽  
Characteristic Mode ◽  
Metallic Structures ◽  
Current Distributions ◽  
Characteristic Modes ◽  
Physical Quantities

Abstract. This paper treats Characteristic Mode Analyses of three-dimensional test objects in the context of EMC. Based on computed Characteristic Modes and mode-specific physical quantities, series expansions for HIRF- and DCI-induced surface currents are deduced. The contribution of single Characteristic Modes to surface currents at different test frequencies is analyzed. HIRF- and DCI-excitations are compared with regard to their surface current distributions in their resonance region determined by Characteristic Mode Analysis.

scholarly journals Evaluating the surface circulation in the Ebro delta (northeastern Spain) with quality-controlled high-frequency radar measurements

Ocean Science ◽  
2015 ◽  
Vol 11 (6) ◽  
pp. 921-935 ◽  
Author(s):  
P. Lorente ◽  
S. Piedracoba ◽  
J. Soto-Navarro ◽  
E. Alvarez-Fanjul
Keyword(s):  
High Frequency ◽  
Marine Protected Area ◽  
Accuracy Assessment ◽  
Surface Current ◽  
Radar Data ◽  
Western Mediterranean ◽  
Hf Radar ◽  
Ebro Delta ◽  
Ebro River ◽  
Surface Circulation

Abstract. The Ebro River delta is a relevant marine protected area in the western Mediterranean. In order to promote the conservation of its ecosystem and support operational decision making in this sensitive area, a three-site standard-range (13.5 MHz) CODAR SeaSonde high-frequency (HF) radar was deployed in December 2013. The main goal of this work is to explore basic features of the sea surface circulation in the Ebro deltaic region as derived from reliable HF radar surface current measurements. For this aim, a combined quality control methodology was applied: firstly, 1-year long (2014) real-time web monitoring of nonvelocity-based diagnostic parameters was conducted to infer both radar site status and HF radar system performance. The signal-to-noise ratio at the monopole exhibited a consistent monthly evolution, although some abrupt decreases (below 10 dB), occasionally detected in June for one of the radar sites, impacted negatively on the spatiotemporal coverage of total current vectors. It seemed to be sporadic episodes since radar site overall performance was found to be robust during 2014. Secondly, a validation of HF radar data with independent in situ observations from a moored current meter was attempted for May–October 2014. The accuracy assessment of radial and total vectors revealed a consistently high agreement. The directional accuracy of the HF radar was rated at better than 8°. The correlation coefficient and root mean square error (RMSE) values emerged in the ranges [0.58–0.83] and [4.02–18.31] cm s−1, respectively. The analysis of the monthly averaged current maps for 2014 showed that the HF radar properly represented basic oceanographic features previously reported, namely, the predominant southwestward flow, the coastal clockwise eddy confined south of the Ebro delta mouth, or the Ebro River impulsive-type freshwater discharge. The EOF analysis related the flow response to local wind forcing and confirmed that the surface current field evolved in space and time according to three significantly dominant modes of variability.

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