Approximation of Surge and Pitch Loads on Truncated Vertical Cylinders

2003 ◽  
Author(s):  
Keyvan Sadeghi ◽  
Atilla Incecik ◽  
Martin Downie ◽  
Hoi-Sang Chan
Keyword(s):  
Computer Program ◽  
Deep Water ◽  
Parametric Study ◽  
Unit Length ◽  
Diffraction Theory ◽  
Circular Cylinders ◽  
Offshore Platforms ◽  
Vertical Cylinders

Truncated vertical circular cylinders are used to make deep water floating offshore platforms like Truss Spars. When the draft of the cylindrical hull is not deep enough, prediction of the surge and pitch diffraction loads by integration of McCamy and Fuchs expression of the force per unit length over the cylinder draft causes an error which is not negligible. Using hydrodynamic arguments the approximated surge and pitch loads by McCamy and Fuchs diffraction theory are modified. The modified results are compared with the results of a parametric study using the computer program WaMIT 4.01 based on the linear diffraction theory, reported by Weggel [1].

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.

Near-field mean flow dynamics of a cylindrical canopy patch suspended in deep water

2018 ◽  
Vol 858 ◽  
pp. 634-655 ◽  
Author(s):  
Jian Zhou ◽  
Subhas K. Venayagamoorthy
Keyword(s):  
Deep Water ◽  
Near Field ◽  
Flow Dynamics ◽  
Flow Diversion ◽  
Circular Cylinders ◽  
Published Data ◽  
Global Flow ◽  
Mean Flow ◽  
Near Wake ◽  
Local Flow

The time-averaged flow dynamics of a suspended cylindrical canopy patch with a bulk diameter of $D$ is investigated using large-eddy simulations (LES). The patch consists of $N_{c}$ constituent solid circular cylinders of height $h$ and diameter $d$, mimicking patchy vegetation suspended in deep water ($H/h\gg 1$, where $H$ is the total flow depth). After validation against published data, LES of a uniform incident flow impinging on the canopy patch was conducted to study the effects of canopy density ($0.16\leqslant \unicode[STIX]{x1D719}=N_{c}(d/D)^{2}\leqslant 1$, by varying $N_{c}$) and bulk aspect ratio ($0.25\leqslant AR=h/D\leqslant 1$, by varying $h$) on the near-wake structure and adjustment of flow pathways. The relationships between patch geometry, local flow bleeding (three-dimensional redistribution of flow entering the patch) and global flow diversion (streamwise redistribution of upstream undisturbed flow) are identified. An increase in either $\unicode[STIX]{x1D719}$ or $AR$ decreases/increases/increases bleeding velocities through the patch surface area along the streamwise/lateral/vertical directions, respectively. However, a volumetric flux budget shows that a larger $AR$ causes a smaller proportion of the flow rate entering the patch to bleed out vertically. The global flow diversion is found to be determined by both the patch geometrical dimensions and the local bleeding which modifies the sizes of the patch-scale near wake. While loss of flow penetrating the patch increases monotonically with increasing $\unicode[STIX]{x1D719}$, its partition into flow diversion around and beneath the patch shows a non-monotonic dependence. The spatial extents of the wake, the flow-diversion dynamics and the bulk drag coefficients of the patch jointly reveal the fundamental differences of flow responses between suspended porous patches and their solid counterparts.

Stochastic analysis of explosion risk for ultra-deep-water semi-submersible offshore platforms

2019 ◽  
Vol 172 ◽  
pp. 844-856 ◽  
Author(s):  
Jihao Shi ◽  
Yuan Zhu ◽  
Depeng Kong ◽  
Fasial Khan ◽  
Jingde Li ◽  
...  
Keyword(s):  
Deep Water ◽  
Stochastic Analysis ◽  
Offshore Platforms ◽  
Explosion Risk

Strength and Fatigue Performance of Steel Lazy Wave Risers With Change in Configuration Parameters

2019 ◽  
Author(s):  
Mayank Lal ◽  
Feng Wang ◽  
Xiaohua Lu ◽  
Abhilash Sebastian
Keyword(s):  
Deep Water ◽  
Parametric Study ◽  
Fatigue Performance ◽  
Design Criteria ◽  
Cost Assessment ◽  
Fatigue Design ◽  
Design Variables ◽  
Steel Catenary Risers ◽  
Normative Cost ◽  
The Impact

Abstract Steel Lazy wave risers are being increasingly used for deep water applications due to better strength and fatigue performance in the touchdown zone compared to steel catenary risers. Several parameters govern the design of steel lazy wave risers including the length of the catenary from hang-off to start of buoyancy section and the length of the buoyancy section. In this paper, a parametric study is performed to investigate the trends in strength and fatigue performance of steel lazy wave risers with change in configuration parameters. A normative cost assessment is also performed to show the impact of these design variables on overall cost of the system. Dynamic analysis is performed to check the change in strength and fatigue performance of steel lazy wave risers as the configuration parameters are changed. The results from the parametric study will assist in designing steel lazy wave risers which satisfy the strength and fatigue design criteria.

scholarly journals SCOUR BEHIND CIRCULAR CYLINDERS IN DEEP WATER

1982 ◽  
Vol 1 (18) ◽  
pp. 93
Author(s):  
Jorg Imberger ◽  
Des Alach ◽  
John Schepis
Keyword(s):  
Test Data ◽  
Deep Water ◽  
Vertical Cylinder ◽  
Shear Velocity ◽  
Circular Cylinders ◽  
Marginal Value ◽  
Flume Test ◽  
Cylinder Diameter ◽  
Ocean Sediment

Flume test data is presented for the depth of scour in deep water near a vertical cylinder placed in a uniform sand and a fine calcareous ocean sediment. The ratio of the depth of scour to the cylinder diameter at equilibrium is shown to depend only on the ratio of the shear velocity to the critical shear velocity at which bed motion is initiated. Protection against scour by placing collars around the cylinder is shown to be of marginal value.

Parametric study and geomechanical design of Ultra-deep-water Offshore Salt Caverns for Carbon Capture and Storage in Brazil

2020 ◽  
Vol 131 ◽  
pp. 104354
Author(s):  
Pedro Vassalo Maia da Costa ◽  
Alvaro Maia da Costa ◽  
Julio R. Meneghini ◽  
Kazuo Nishimoto ◽  
Claudio M. Sampaio ◽  
...  
Keyword(s):  
Deep Water ◽  
Parametric Study ◽  
Carbon Capture ◽  
Carbon Capture And Storage ◽  
Salt Caverns ◽  
And Storage

Anchor Deployment Planning Using Simulated Annealing

2002 ◽  
Author(s):  
Oscar Brito Augusto
Keyword(s):  
Simulated Annealing ◽  
Objective Function ◽  
Deep Water ◽  
Simulated Annealing Algorithm ◽  
Production Systems ◽  
Offshore Platforms ◽  
Additional Advantage ◽  
Floating System ◽  
Deployment Planning ◽  
Planning Methodology

In this work a planning methodology for deep-water anchor deployment of anchor lines for offshore platforms and floating production systems aiming at operational resources optimization is explored, by minimizing a multi criteria objective function. A Simulated Annealing Algorithm was used to optimize the objective function. As an additional advantage, inherited from the proposed methodology, the planning automation is achieved. Planning automation overcomes the traditional way based on trial error exercise, where an engineer using an anchoring application, decides how much of work wire and anchoring line must be paid out from both the floating system and the supply boat and additionally which horizontal force must be applied to the line trying settle the anchor on a previously defined target in the ocean floor. Some cases, from anchor deployment of some MODUs operating in deep-water oil fields in Brazil, are shown demonstrating some potentialities of the proposed model.

On the Occurrence of Mathieu Instabilities of Vertical Cylinders

2008 ◽  
Author(s):  
Marcelo A. S. Neves ◽  
Sergio H. Sphaier ◽  
Bruno M. Mattoso ◽  
Claudio A. Rodri´guez ◽  
Alberto L. Santos ◽  
...  
Keyword(s):  
Vertical Cylinder ◽  
Design Parameters ◽  
Offshore Platforms ◽  
Spar Platforms ◽  
Motion Responses ◽  
Theoretical Investigations ◽  
Series Of Experiments ◽  
Vertical Cylinders ◽  
Metacentric Height ◽  
Limited Motion

Large offshore platforms with vertical circular cylindrical hull shapes have been designed and employed in recent times. Classical spar platforms and mono-column concepts are just two examples of designs with such simple configuration, supposed to perform limited motion responses in waves. Reports on investigations on the occurrence of parametric resonance of spar platforms have been published recently in which the relevance of Mathieu amplifications have been assessed making use of different mathematical models. However, some uncertainties still remain on the influence of crucial design parameters as, for instance, metacentric height, draft/diameter ratio, associated damping and mooring system. In an attempt to clarify some of these aspects, in this paper the dynamic stability of a vertical cylinder in regular waves is investigated theoretically and experimentally. A coupled non-linear mathematical model is employed to model and simulate the coupled heave, roll and pitch motions. Theoretical aspects related to the development of resonant motions are discussed. In addition to the numerical and theoretical investigations, an extensive series of experiments with a model of a typical mono-column have been recently conducted at LabOceano. The findings of these investigations are compared and summarized.

Viscous Free-Surface Flow Past Twin Vertical Cylinders

2003 ◽  
Author(s):  
Tong Chen ◽  
Allen T. Chwang
Keyword(s):  
Free Surface ◽  
Large Scale ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Circular Cylinders ◽  
Small Scale ◽  
The Finite Element Method ◽  
Suction Force ◽  
Large Scale Vortex ◽  
Vertical Cylinders

The laminar flow behaviors around two vertical circular cylinders (in a tandem arrangement) that pierce a free surface are investigated by the finite element method in this paper. The computational results exhibit two major free-surface effects: the presence of a free surface allows the occurrence of small-scale Kelvin-Helmholtz instabilities, but suppresses the onset of large-scale vortex alternating behavior. It is also found that the vorticity will expand in a necklace shape adjacent to the free surface. The second cylinder may experience a persisting suction force due to “trapped” vortices in the gap between the two cylinders, which may not happen in the absence of a free surface.

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