Geotechnical sampling in deep water using a tensioned conductor pipe-casing and weighted footblock

1984 ◽  
Vol 21 (1) ◽  
pp. 92-99
Author(s):  
H. T. Yan
Keyword(s):  
Deep Water ◽  
Concrete Block ◽  
Vertical Movement ◽  
The Self ◽  
Wave Forces ◽  
Secondary Effects ◽  
Marine Riser ◽  
Grand Banks ◽  
Riser Pipe ◽  
Axial Tension

A drilling system is described for geotechnical exploration and soil sampling in the seabed, modelled after the concept of the marine riser pipe. The system derives its stability from a "tensioning weight," in the form of a cylindrical concrete block at the bottom, which keeps the conductor pipe in tension at all times. The axial tension from the tensioning weight and the self-weight of the conductor pipe substantially reduce the bending effects in the conductor pipe resulting from current and wave forces, as well as from the drift of the drilling vessel. The lateral reaction required to keep the pipe in place at the sea floor is provided by a concrete footblock. The bottom end of the conductor pipe slides into the footblock, which has a doughnut-shaped cross section that allows for the vertical movement or heave of the drilling vessel. The Hermitian equation is used to solve for the secondary effects due to the deformation of the flexible conductor under wave or current forces and the self-weight of the conductor pipe. The system has been used successfully on the Grand Banks in 122 m of water. Keywords: geotechnical exploration, sampling, deep water drilling, marine riser analogy, tensioning weight.

scholarly journals Distribution of deep-water corals of the Flemish Cap, Flemish Pass, and the Grand Banks of Newfoundland (Northwest Atlantic Ocean): interaction with fishing activities

2010 ◽  
Vol 68 (2) ◽  
pp. 319-332 ◽  
Author(s):  
F. J. Murillo ◽  
P. Durán Muñoz ◽  
A. Altuna ◽  
A. Serrano
Keyword(s):  
Atlantic Ocean ◽  
Continental Slope ◽  
Deep Water ◽  
Coral Species ◽  
Habitat Mapping ◽  
Bottom Trawl ◽  
Soft Corals ◽  
Northwest Atlantic ◽  
Grand Banks ◽  
Black Corals

Abstract Murillo, F. J., Durán Muñoz, P., Altuna, A., and Serrano, A. 2011. Distribution of deep-water corals of the Flemish Cap, Flemish Pass, and the Grand Banks of Newfoundland (Northwest Atlantic Ocean): interaction with fishing activities. – ICES Journal of Marine Science, 68: 319–332. The distribution of deep-water corals of the Flemish Cap, Flemish Pass, and the Grand Banks of Newfoundland is described based on bycatch from Spanish/EU bottom trawl groundfish surveys between 40 and 1500 m depth. In all, 37 taxa of deep-water corals were identified in the study area: 21 alcyonaceans (including the gorgonians), 11 pennatulaceans, 2 solitary scleractinians, and 3 antipatharians. The greatest diversity of coral species was on the Flemish Cap. Corals were most abundant along the continental slope, between 600 and 1300 m depth. Soft corals (alcyonaceans), sea fans (gorgonians), and black corals (antipatharians) were most common on bedrock or gravel, whereas sea pens (pennatulaceans) and cup corals (solitary scleractinians) were found primarily on mud. The biomass of deep-water corals in the bycatches was highest in previously lightly trawled or untrawled areas, and generally low in the regularly fished grounds. The information derived from bottom-trawl bycatch records is not sufficient to map vulnerable marine ecosystems (VMEs) accurately, but pending more detailed habitat mapping, it provides a valuable indication of the presence/absence of VMEs that can be used to propose the candidate areas for bottom fishery closures or other conservation measures.

Focused Plunging Breaking Waves Impact on Cylinder Group in Deep Water

2021 ◽  
Author(s):  
Ting Cui ◽  
Arun Kamath ◽  
Weizhi Wang ◽  
Lihao Yuan ◽  
Duanfeng Han ◽  
...  
Keyword(s):  
Free Surface ◽  
Deep Water ◽  
Breaking Waves ◽  
Surface Elevation ◽  
Relative Distance ◽  
Structural Safety ◽  
Wave Forces ◽  
Free Surface Elevation ◽  
Single Cylinder ◽  
Numerical Wave

Abstract The correct estimation of wave loading on a cylinder in a cylinder group under different impact scenarios is essential to determine the structural safety of coastal and offshore structures. This scenario differs from the interaction of waves with a single cylinder but not a lot of studies focus on cylinder groups under different arrangements. In this study, the interaction between plunging breaking waves and cylinder groups in deep water is investigated using the two-phase flow model in REEF3D, an open-source computational fluid dynamics program. The Reynolds-averaged Navier-Stokes equation with the two equation k–Ω turbulence model is adopted to resolve the numerical wave tank, with free surface calculated using the level set method. In this study, focused waves in deep water were modeled with a fixed wave steepness method. Wave breaking occurs when the steepness of the wave crest front satisfies the breaking criteria. The model is validated by comparing the numerical wave forces and free surface elevation with measurements from experiments. The computational results show fairly good agreement with experimental data for both free surface elevation and wave forces. Four cases are simulated to investigate the interaction of breaking waves with a cylinder group with different relative distance, number of cylinders and arrangement. Results show that breaking wave forces on the upstream cylinder are smaller than on a single cylinder with a relative distance of one cylinder diameter. The wave forces on cylinders in the pile group are effected by the relative distance between cylinders. The staggered arrangement has a significant influence on the wave forces on the first and second cylinder. The interaction inside a cylinder group mostly happens between the neighbouring cylinders. These interactions are also effected by the relative distance and the numbers of the neighbouring cylinders.

Linear Stability Control of Offshore Wind Turbines

2010 ◽  
Author(s):  
Christine A. Mecklenborg ◽  
Philipp Rouenhoff ◽  
Dongmei Chen
Keyword(s):  
Wind Turbines ◽  
Deep Water ◽  
Fossil Fuels ◽  
Wind Farms ◽  
Stability Control ◽  
Offshore Wind ◽  
Wave Forces ◽  
Offshore Wind Farms ◽  
Offshore Wind Turbines ◽  
Strong Winds

Offshore wind farms in deep water are becoming an attractive prospect for harnessing renewable energy and reducing dependence on fossil fuels. One area of major concern with offshore wind turbines is stability control. The same strong winds that give deep water turbines great potential for energy capture also pose a threat to stability, along with potentially strong wave forces. We examine development of state space controllers for active stabilization of a spar-buoy floating turbine. We investigate linear state feedback with a state observer and evaluate response time and disturbance rejection of decoupled SISO controllers.

Geotechnical aspects of seabed pits in the Grand Banks area

1988 ◽  
Vol 25 (3) ◽  
pp. 448-454 ◽  
Author(s):  
J. I. Clark ◽  
J. Landva
Keyword(s):  
Strength Properties ◽  
Soil Parameters ◽  
Wave Forces ◽  
Grand Banks ◽  
Pit Formation ◽  
Deep Pit ◽  
Ice Loads ◽  
Sufficient Magnitude ◽  
Pit Depth ◽  
Almost All

Ice-created seabed pits found on the Grand Banks of Newfoundland can be analysed in terms of probable range of soil strength properties and failure mechanisms to determine the ice loads transmitted to the seabed. Almost all pits are less than 3 m deep; their existence can be explained by indentation failures caused by rolling icebergs. About 3.5% of the pits are more than 5 m deep and cannot be explained by iceberg impact. This paper presents a possible mechanism for their formation consisting of two actions: (1) the hard grounding of an iceberg, such that the keel becomes embedded in the seabed, and (2) the passive failure of the soil after the grounding event, predominantly caused by the loads associated with wave forces on the iceberg at the time of grounding or shortly thereafter. A 10 m deep pit located in the Hibernia area is analysed with respect to its configuration and soil parameters. Calculations have shown that, though waves in the Grand Banks area cause forces on the iceberg of a sufficient magnitude to create pits of the order of 10 m deep or more in the stiff Grand Banks soils, the controlling factor of pit depth is the ability of the iceberg keel to deliver these loads to the soil. Key words: iceberg pits, iceberg scour, pit formation, ice–seabed interaction.

The Study on Vibration of Marine Riser under Deep Water

2010 ◽  
Vol 97-101 ◽  
pp. 2816-2819
Author(s):  
Chun Jie Han ◽  
Tie Yan
Keyword(s):  
Water Depth ◽  
Deep Water ◽  
Wave Loads ◽  
Lateral Vibration ◽  
Actual Situation ◽  
Marine Riser ◽  
Drilling Engineering ◽  
Set Up

With the development of deep water drilling engineering, marine riser has become the important equipment. With the increase in water depth, the failure of marine riser is very serious, the vibration is the main reason. According to the actual situation, the model of marine is set up, the rule of lateral vibration is obtained. The result is helpful to avoid the phenomena of resonance of marine riser under wave loads.

scholarly journals Horizontal Forces Due to Waves Acting on Large Vertical Cylinders in Deep Water

1972 ◽  
Vol 94 (4) ◽  
pp. 862-866
Author(s):  
E. R. Johnson
Keyword(s):  
Deep Water ◽  
Large Diameter ◽  
Wave Force ◽  
Circular Cylinders ◽  
Wave Forces ◽  
Typical Application ◽  
Model Studies ◽  
Horizontal Wave ◽  
Horizontal Wave Force ◽  
Vertical Cylinders

The special case of horizontal wave forces on large vertical cylinders in deep water is considered. The typical application for such a case is the calculation of horizontal forces on column stabilized floating ocean platforms. Existing literature discussing horizontal wave forces on cylinders does not generally agree on how to predict these forces. Since for large diameter cylinders in deep water the maximum force is completely inertial, the problem of deriving a solution is considerably simplified. In this study, an expression for the maximum horizontal wave force on large diameter circular cylinders mounted vertically in deep water has been analytically derived. Experimental model studies were also conducted and the resulting measured forces were within 20 percent of predicted forces. An example of how to predict horizontal wave forces using the methods of this report is given.

Fatigue Assessment on Reverse–Balanced Flange Connections In Offshore Floating Wind Turbine Towers

2021 ◽  
Author(s):  
Tao Zou ◽  
Wenjie Liu ◽  
Mingxin Li ◽  
Longbin Tao
Keyword(s):  
Wind Turbine ◽  
Fatigue Damage ◽  
Deep Water ◽  
Wind Loading ◽  
Wave Forces ◽  
Local Geometry ◽  
Elastic Analysis ◽  
Wind Turbine Towers ◽  
Welding Joints ◽  
Offshore Floating Wind Turbine

Abstract Offshore floating wind turbines (FWTs) in deep water experience cyclic loadings from both environment and mechanical operations. For FWTs, the upper turbine and tower are mainly subjected to wind loading; and the floater is subjected to wave forces. It has been widely accepted that there is a strong coupling between the floater motions and the turbine forces. As the tower is placed between the upper wind turbine and the floater, both wind and wave loadings affect the cyclic forces on the tower. The construction of towers makes use of prefabricated segments. These prefabricated segments are bolted together with flanges at either end. The paper aims to investigate the axial hotspot stress on FWT’s tower base and analyze its induced fatigue damage at the welding joints around the flanges. A coupled aero-hydro-servo-elastic analysis is conducted to simulate the motion of FWTs. Then, the local welding joint along the reverse-balanced flange connection is modeled to consider the influence of local geometry. At last, the hourly fatigue damages at four locations over the tower base section are compared.

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