Diatoms in Arctic Shallow Seas Sediments

1989 ◽  
pp. 481-496 ◽  
Author(s):  
E. I. Polyakova
Keyword(s):  
Shallow Seas

Nonlinear stationary internal and surface waves in shallow seas

Tellus ◽  
1979 ◽  
Vol 31 (2) ◽  
pp. 150-160 ◽  
Author(s):  
A. I. Leonov ◽  
Yu. Z. Miropolsky ◽  
R. E. Tamsalu
Keyword(s):  
Surface Waves ◽  
Shallow Seas

scholarly journals Performance of an Advanced Intelligent Control Strategy in a Dynamic Positioning (DP) System Applied to a Semisubmersible Drilling Platform

2021 ◽  
Vol 9 (4) ◽  
pp. 399
Author(s):  
Mohamad Alremeihi ◽  
Rosemary Norman ◽  
Kayvan Pazouki ◽  
Arun Dev ◽  
Musa Bashir
Keyword(s):  
Oil And Gas ◽  
Weather Conditions ◽  
Dynamic Positioning ◽  
System Failures ◽  
Oil Drilling ◽  
System A ◽  
Advanced Control ◽  
Safety And Reliability ◽  
Drilling Operations ◽  
Shallow Seas

Oil drilling and extraction platforms are currently being used in many offshore areas around the world. Whilst those operating in shallow seas are secured to the seabed, for deeper water operations, Dynamic Positioning (DP) is essential for the platforms to maintain their position within a safe zone. Operating DP requires intelligent and reliable control systems. Nearly all DP accidents have been caused by a combination of technical and human failures; however, according to the International Marine Contractors Association (IMCA) DP Incidents Analysis, DP control and thruster system failures have been the leading causes of incidents over the last ten years. This paper will investigate potential operational improvements for DP system accuracy by adding a Predictive Neural Network (PNN) control algorithm in the thruster allocation along with a nonlinear Proportional Integral derivative (PID) motion control system. A DP system’s performance on a drilling platform in oil and gas deep-water fields and subject to real weather conditions is simulated with these advanced control methods. The techniques are developed for enhancing the safety and reliability of DP operations to improve the positioning accuracy, which may allow faster response to a critical situation during DP drilling operations. The semisubmersible drilling platform’s simulation results using the PNN strategy show improved control of the platform’s positioning.

Provenance Tracing of Indicative Minerals in Sediments of the Yalu River Estuary and its Adjacent Shallow Seas

2013 ◽  
Vol 290 ◽  
pp. 1227-1235 ◽  
Author(s):  
Yue Liu ◽  
Yan Cheng ◽  
Huixiang Li ◽  
Jingwei Liu ◽  
Chunpeng Zhang ◽  
...  
Keyword(s):  
River Estuary ◽  
Yalu River ◽  
Shallow Seas

Analysis of the interannual variability in satellite gravity solutions : impact of climate modes on water mass displacements across continents and oceans

2021 ◽  
Author(s):  
Julia Pfeffer ◽  
Anny Cazenave ◽  
Anne Barnoud
Keyword(s):  
Climate Variability ◽  
Mass Transport ◽  
Interannual Variability ◽  
North Atlantic ◽  
North Pacific ◽  
Water Mass ◽  
Water Cycle ◽  
Satellite Gravity ◽  
Climate Modes ◽  
Shallow Seas

<p>The acquisition of time-lapse satellite gravity measurements during the GRACE and GRACE Follow On (FO) missions revolutionized our understanding of the Earth system, through the accurate quantification of the mass transport at global and regional scales. Largely related to the water cycle, along with some geophysical signals, decadal trends and seasonal cycles dominate the mass transport signals, constituting about 80 % of the total variability measured during GRACE (FO) missions. We focus here on the interannual variability, constituting the remaining 20 % of the signal, once linear trends and seasonal signals have been removed. Empirical orthogonal functions (EOFs) highlight the most prominent signals, including short-lived signals triggered by major earthquakes, interannual oscillations in the water cycle driven by the El Nino Southern Oscillation (ENSO) and significant decadal variability, potentially related to the Pacific Decadal Oscillation (PDO). The interpretation of such signals remains however limited due to the arbitrary nature of the statistical decomposition in eigen values. To overcome these limitations, we performed a LASSO (Least Absolute Shrinkage and Selection Operator) regression of eight climate indices, including ENSO, PDO, NPGO (North Pacific Gyre Oscillation), NAO (North Atlantic Oscillation), AO (Arctic Oscillation), AMO (Atlantic Multidecadal Oscillation), SAM (Southern Annular Mode) and IOD (Indian Ocean Dipole). The LASSO regularization, coupled with a cross-validation, proves to be remarkably successful in the automatic selection of relevant predictors of the climate variability for any geographical location in the world. As expected, ENSO and PDO impact the global water cycle both on land and in the ocean. The NPGO is also a major actor of the global climate, showing similarities with the PDO in the North Pacific. AO is generally favored over NAO, especially in the Mediteranean Sea and North Atlantic. SAM has a preponderant influence on the interannual variability of ocean bottom pressures in the Southern Ocean, and, in association with ENSO, modulates the interannual variability of ice mass loss in West Antarctica. AMO has a strong influence on the interannual water cycle along the Amazon river, due to the exchange of moisture in tropical regions. IOD has little to no impact on the interannual water cycle. All together, climate modes generate changes in the water mass distribution of about 100 mm for land, 50 mm for shallow seas and 15 mm for oceans. Climate modes account for a secondary but significant portion of the total interannual variability (at maximum 60% for shallow seas, 50 % for land and 40% for oceans). While such processes are insufficient to fully explain the complex nature of the interannual variability of water mass transport on a global scale, climate modes can be used to correct the GRACE (FO) measurements for a significant part of the natural climate variability and uncover smaller signals masked by such water mass transports.</p>

scholarly journals Ambient noise in shallow seas: Propagation issues

1993 ◽  
Vol 94 (3) ◽  
pp. 1824-1825
Author(s):  
Ira Dyer
Keyword(s):  
Ambient Noise ◽  
Shallow Seas

Path Replanning Method for an AUV in Natural Hydrothermal Vent Fields: Toward 3D Imaging of a Hydrothermal Chimney

2014 ◽  
Vol 48 (3) ◽  
pp. 104-114 ◽  
Author(s):  
Yoshiki Sato ◽  
Toshihiro Maki ◽  
Ayaka Kume ◽  
Takumi Matsuda ◽  
Takashi Sakamaki ◽  
...  
Keyword(s):  
Hydrothermal Vent ◽  
Autonomous Underwater Vehicles ◽  
Visual Observation ◽  
Color Information ◽  
High Coverage ◽  
Human Control ◽  
Kagoshima Bay ◽  
Sufficient Energy ◽  
Shallow Seas ◽  
Limited Coverage

AbstractAutonomous underwater vehicles (AUVs) can operate without the need for human control or tether cables as long as there is sufficient energy. AUVs have recently been used for seafloor imaging. Visual observation by AUVs provides high-resolution color information of the seafloor. However, conventional observation techniques that follow a prespecified path offer limited coverage because it is impossible for operators to build a suitable path in unknown rough terrain. A flawed prespecified path will produce incomplete observation. If unobserved areas are found during postprocessing, another dive is necessary, which increases the total cost. To overcome this problem, the authors have proposed a path replanning method to realize high-coverage observation in one dive. With this method, the AUV evaluates unobserved areas after the first prespecified observation; if unobserved areas are found, the AUV recreates an appropriate path to cover what was missed. The validity of the proposed method was previously evaluated using an artificial target in a tank and in shallow seas at a depth of approximately 35 m. In this study, the feasibility of the method was validated in a more challenging setting: experimental data were taken from a hydrothermal vent field in Kagoshima Bay, Japan.

scholarly journals HYDRODYNAMIC MODELLING OF THE SOUTHERN NORTH SEA

1978 ◽  
Vol 1 (16) ◽  
pp. 65
Author(s):  
David Prandle
Keyword(s):  
North Sea ◽  
Three Dimensional ◽  
Flood Routing ◽  
Hydrodynamic Modelling ◽  
One Dimensional ◽  
Southern North Sea ◽  
Tidal Propagation ◽  
Modelling Studies ◽  
Residual Flows ◽  
Shallow Seas

Numerical modelling of rivers, estuaries and shallow seas has attracted increasing interest over the last two decades. The models have developed from one dimensional (ID) applications to tidal propagation and flood routing through two and, finally, three dimensional applications to motions ranging from "pseudo-turbulence" to annual mean residual flows. The present account describes the development, over the last five years, of the modelling studies carried out by the author concerning the hydrodynamics of the southern North Sea and River Thames. The objective is to identify those major points which have emerged that may have a wider significance.

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