Hydrodynamic Study on Water Column Oscillation of Varying Cross-Sectional Moonpool and Its Effect on Resistance of a Drill Ship

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Sivabalan Ponnappan ◽  
Surendran Sankunny
Keyword(s):  
Ship Motion ◽  
Floating Platform ◽  
Empirical Formulas ◽  
Cross Sectional ◽  
Calm Water ◽  
Vertical Opening ◽  
Vessel Response ◽  
Hydrodynamic Study ◽  
Different Shapes ◽  
Piston Mode

A moonpool is meant for access to the underwater part of the ship from onboard. It is a vertical opening along the depth having an effect on the performance of the floating platform. Inside the moonpool, water motions in horizontal plane is called sloshing and in vertical planes it is called piston mode. Moonpool causes deck wetness and sometimes results in the downtime of the platform. It is the necessity of the operator to be at the safe conditions of platform facing varied environmental conditions. In the present study, vessel response in the region of moonpool resonance was investigated with different shapes of moonpool and comparison is made with Molin's (2001, “On the Piston and Sloshing Modes in Moonpools,” J. Fluid Mech., 430, pp. 27–50.) theoretical and Fukuda's (1977, “Behavior of Water in Vertical Well With Bottom Opening of Ship and Its Effects on Ship-Motion,” J. Soc. Nav. Archit. Jpn., 1977(141), pp. 107–122.) empirical formulas. It is seen that there is a shift in the frequency of resonance based on moonpool shapes. The effect of moonpool on the ship motion with forward speed is also attempted in this paper. Proven packages are used to calculate the calm water resistance of the ship with moonpool of various cross section. Wave making coefficient of the ship is modified due to opening to accommodate the moonpool. The openings to accommodate moonpool causes further entry of water both zero and nonzero Froude number especially in the presence of waves.

Hydrodynamic Study on Water Column Oscillation of Varying Cross-Section Moonpool and its Effect on Resistance of a Drill Ship

2016 ◽  
Author(s):  
Sivabalan Ponnappan ◽  
Surendran Sankunny ◽  
Rajesh Reguram Balakrishnan
Keyword(s):  
Cross Sections ◽  
Water Resistance ◽  
Floating Platform ◽  
Empirical Formulas ◽  
Calm Water ◽  
Vertical Opening ◽  
Vessel Response ◽  
Hydrodynamic Study ◽  
Different Shapes ◽  
Piston Mode

A moonpool is meant for access to the underwater part of the ship from onboard. It is a vertical opening along the depth having an effect on the performance of the floating platform. Inside the moonpool, water motions in horizontal plane is called sloshing and in vertical planes it is called piston mode. Moonpool causes deck wetness and sometimes result in the downtime of the platform. It is the necessity of the operator to be at the safe conditions of platform facing varied environmental conditions. In the present study, vessel response in the region of moonpool resonance was investigated with different shapes of moonpool and comparison is made with Molin’s (2001) theoretical and Fukuda’s (1977) empirical formulas. It is seen that there is a shift in the frequency of resonance based on moonpool shapes. The effect of moonpool on the ship motion with forward speed is also attempted in this paper. Proven packages are used to calculate the calm water resistance of the ship with moonpool of various cross-sections. Wave making coefficient of the ship is modified due to opening to accommodate the moonpool. The openings to accommodate moonpool causes further entry of water both zero and non-zero Froude number especially in the presence of waves.

scholarly journals Wave interaction with Floating platform of different shapes and supports using BEM approach

2017 ◽  
Vol 14 (2) ◽  
pp. 115-133
Author(s):  
Anoop I. Shirkol ◽  
Nasar Thuvanismail
Keyword(s):  
Numerical Model ◽  
Elastic Plate ◽  
Wave Interaction ◽  
Wave Force ◽  
Ocean Waves ◽  
Wave Forces ◽  
Thin Elastic Plate ◽  
Floating Platform ◽  
Floating Elastic Plate ◽  
Different Shapes

Wave interaction with a floating thin elastic plate which can be used as floating platform is analyzed using Boundary Element Method (BEM) for different shapes such as rectangular, circular and triangular. Different support conditions are considered and the performance of the floating platform under the action of ocean waves is explored. The study is performed under the assumption of linearized water wave theory and the floating elastic plate is modelled based on the Euler-Bernoulli beam theory. Using Galerkin’s approach, a numerical model has been developed and the hydrodynamic loading on the floating elastic plate of shallow draft (thickness) is investigated. The wave forces are generated by the numerical model for the analysis of the floating plate. The resulting bending moment and optimal deflection due to encountering wave force is analysed. The present study will be helpful in design and analysis of the large floating platform in ocean waves.

Dynamic Behavior of a Novel Heave-Compensated Floating Platform for Well Interventions

2020 ◽  
Author(s):  
Marcelo A. Jaculli ◽  
Bernt J. Leira ◽  
Sigbjørn Sangesland ◽  
Celso K. Morooka ◽  
José Ricardo P. Mendes
Keyword(s):  
Dynamic Behavior ◽  
Small Diameter ◽  
Floating Platform ◽  
Floating Structure ◽  
Cross Sectional ◽  
Platform Design ◽  
The North ◽  
The North Sea ◽  
Heave Motion ◽  
Intervention Costs

Abstract A new type of floating platform design has been investigated. It consists of a relatively small semi-submersible floating structure with an air chamber that aims to keep a constant buoyancy, thus effectively reducing heave motion and enabling its use under harsh environmental conditions such as in the North Sea. It aims to provide an alternative solution compared to large floating structures, such as drillships and semi-submersible platforms, in terms of time availability, drilling costs and operational flexibility. One recent focus has been on the application of this platform for reducing well intervention costs. A small diameter (workover) riser may be used for installing the well control stack on the wet Christmas tree and for performing well intervention through the riser using a wireline cable. Alternatively, the operation can take place without a riser; this operation is termed riserless well intervention (RLWI). In this work, we investigate the dynamic behavior of this system, which is attached either to a wireline — for RLWI — or to a small-sized riser for well service through the riser. By modeling this system — which acts similarly to a passive heave compensation system — we have verified that this new platform indeed experiences smaller displacements when compared to conventional platform. The reduction observed varies depending on the platform design; in some cases, it reduces the displacement by a factor of two. A relatively heavier platform with a small cross sectional water plane area is found to be the best design option, but a lighter platform might be preferable for increased flexibility, as long as its dynamic behavior is satisfactory for safe operations.

Thorough Verification and Validation of CFD Simulation for FPSO Roll Damping

2019 ◽  
Author(s):  
Donghwan Lee ◽  
Zhenjia (Jerry) Huang
Keyword(s):  
Numerical Modeling ◽  
Cfd Simulation ◽  
Development Project ◽  
Model Tests ◽  
Design Tool ◽  
Verification And Validation ◽  
Empirical Formulas ◽  
Roll Damping ◽  
Calm Water ◽  
Offshore Industry

Abstract For floating production platform such as FPSO and FLNG, it is important to use confidently estimated roll damping coefficients in the prediction of its motions in waves since in many cases the roll response is mainly contributed from resonance. Traditionally roll damping prediction was made through model tests or empirical formulas. As computing power and numerical modeling techniques have been improved during last a few decades, offshore industry starts to consider CFD as an alternative engineering and design tool complementary and/or supplementary to physical model tests. This paper presents our verification and validation work of modeling practices with commercially available CFD software for engineering applications for FPSO roll decay damping in calm water. The numerical modeling followed a recommended modeling practice developed by a Joint Development Project – TESK JDP [1].

scholarly journals Introducing a particular mathematical model for predicting the resistance and performance of prismatic planing hulls in calm water by means of total pressure distribution

2015 ◽  
Vol 12 (2) ◽  
pp. 73-94 ◽  
Author(s):  
P. Ghadimi ◽  
S. Tavakoli ◽  
M. A. Feizi Chekab ◽  
A. Dashtimanesh
Keyword(s):  
Mathematical Model ◽  
Pressure Distribution ◽  
Total Pressure ◽  
Center Of Gravity ◽  
Governing Equations ◽  
Calm Water ◽  
Hydrodynamic Study ◽  
Pass Through ◽  
And Performance

Mathematical modeling of planing hulls and determination of their characteristics are the most important subjects in hydrodynamic study of planing vessels. In this paper, a new mathematical model has been developed based on pressure distribution. This model has been provided for two different situations: (1) for a situation in which all forces pass through the center of gravity and (2) for a situation in which forces don not necessarily pass through the center of gravity. Two algorithms have been designed for the governing equations. Computational results have been presented in the form of trim angle, total pressure, hydrodynamic and hydrostatic lift coefficients, spray apex and total resistance which includes frictional, spray and induced resistances. Accuracy of the model has been verified by comparing the numerical findings against the results of Savitsky's method and available experimental data. Good accuracy is displayed. Furthermore, effects of deadrise angle on trim angle of the craft, position of spray apex and resistance have been investigated.

scholarly journals Prevalence of Different Types of Apical Root Canal Morphology and their Treatment Recommendations in an Institute

2018 ◽  
Vol 56 (210) ◽  
pp. 616-620 ◽  
Author(s):  
Sushmita Shrestha ◽  
Smriti Karki ◽  
Navin Agrawal ◽  
Mannu Vikram ◽  
Vimmi Singh ◽  
...  
Keyword(s):  
Root Canal ◽  
Sampling Technique ◽  
Cross Sectional Study ◽  
Cross Sectional ◽  
Root Canals ◽  
Rotary Instruments ◽  
Root Canal Morphology ◽  
Different Shapes ◽  
Diamond Disc

  Introduction: Canals can be of different shapes in cross section including round canals, oval canals, long oval canals or ribbon shaped canals. Recesses of nonround canals may not be included in the round preparation created by rotary instruments and thus they remain unprepared. The aim of this study included determination of shape and taper of the apical root canal based on diameter at different levels. Methods: This was a cross sectional study which used convenient sampling technique to determine the sample size. Seventy extracted teeth were sectioned horizontally at one, two and three millimeter from the apex using the diamond disc which was observed under trinocular research microscope for the determination of diameter of root canal under 10x magnification. Results: The most common canal configuration was oval. The taper of the canals was 25% in mesial root and 20% in distal in bucco-lingual orientation and 14% in mesial root and 15% in distal in mesio-distal orientation. Conclusions: The most prevalent canal configuration in this study was non round, however, most of the rotary instruments tend to prepare root canals into round shape making their use questionable. The taper of the root canals was found to be higher in our study than what most of the shaping instruments have to offer. So it would be advisable to consider this fact while selecting instruments and preparing these non-round canals as far as the Nepalese subpopulation is considered.

scholarly journals Experimental Research on Water Column Oscillations in Moonpool of a Drillship in Downtime Period

2019 ◽  
Vol 8 (4) ◽  
pp. 7152-7155
Keyword(s):  
Weather Condition ◽  
Green Water ◽  
Measuring Instruments ◽  
Water Motion ◽  
Vertical Opening ◽  
Drilling Operations ◽  
Sloshing Mode ◽  
Propulsion Unit ◽  
Piston Mode ◽  
Keel Plate

A drillship is a kind of merchant vessel with a self-propulsion unit and drilling equipment used for oil exploration. The major difference with the merchant vessel is the moonpool. A moonpool is a vertical opening from the continuous deck to the keel plate of the vessel for drilling operations and other applications like the launching of measuring instruments. This moonpool opening allowing the entry of water into the vessel. The water motion within the moonpool is mostly related to the encountering wave frequency, the geometry of the moonpool and the draft condition of the vessel. The major amplitude of the water particle motion within the moonpool, either may be in the sloshing mode or in piston mode. This water motion leads to the entry of green water on the deck during the rough weather condition. This is known as the downtime period of a drillship, during this time the operation of the drillship is in off-mode. This paper presents the study about the downtime period of drillship experimentally with rectangular moonpool.

Influence of the Geometric Imperfection on the Buckling Behavior of Floating Platform Column Under Axial Load

2007 ◽  
Author(s):  
Tiago P. Estefen ◽  
Daniel S. Werneck ◽  
Segen F. Estefen
Keyword(s):  
Progressive Failure ◽  
Correlation Study ◽  
Gas Production ◽  
Small Scale ◽  
Failure Behavior ◽  
Floating Platform ◽  
Cross Sectional ◽  
Geometric Imperfection ◽  
Stiffened Panels ◽  
Buckling Behavior

The present work focuses on the design of the new generation of semi-submersible platforms for oil&gas production offshore that is based on column square cross-sectional area. The platform column is based on an arrangement of stiffened flat panels having their ultimate strength characterized by buckling under in-plane compressive loading. Distortions induced by fabrication have considerable influence on the buckling behavior and are discussed in order to provide design recommendations. The aim of the paper is to study a segment of the column structural arrangement between robust transverse frames to analyze the failure behavior of the stiffened panels. Previous research demonstrated the strong influence of both mode and magnitude of the geometric imperfection distribution, as well as the boundary conditions. Numerical and experimental simulations for small scale isolated panels are carried out in order to perform a correlation study to adjust the numerical model for further use in more complex numerical simulations of the structural failure of the column arrangement. The stiffened panels are analyzed to identify the buckling initiation on a particular panel and then the interaction between plates, longitudinal stiffeners and the robust transverse frames during the progressive failure of the whole column.

scholarly journals Review and uncertainty assessment of size-resolved scavenging coefficient formulations for below-cloud snow scavenging of atmospheric aerosols

2013 ◽  
Vol 13 (19) ◽  
pp. 10005-10025 ◽  
Author(s):  
L. Zhang ◽  
X. Wang ◽  
M. D. Moran ◽  
J. Feng
Keyword(s):  
Atmospheric Aerosols ◽  
Atmospheric Aerosol ◽  
Collection Efficiency ◽  
Aerosol Particles ◽  
Empirical Formulas ◽  
Cross Sectional ◽  
Atmospheric Aerosol Particles ◽  
Order Of Magnitude ◽  
Snow Particle ◽  
Scavenging Coefficient

Abstract. Theoretical parameterizations for the size-resolved scavenging coefficient for atmospheric aerosol particles scavenged by snow (Λsnow) need assumptions regarding (i) snow particle–aerosol particle collection efficiency E, (ii) snow-particle size distribution N(Dp), (iii) snow-particle terminal velocity VD, and (iv) snow-particle cross-sectional area A. Existing formulas for these parameters are reviewed in the present study, and uncertainties in Λsnow caused by various combinations of these parameters are assessed. Different formulations of E can cause uncertainties in Λsnow of more than one order of magnitude for all aerosol sizes for typical snowfall intensities. E is the largest source of uncertainty among all the input parameters, similar to rain scavenging of atmospheric aerosols (Λrain) as was found in a previous study by Wang et al. (2010). However, other parameters can also cause significant uncertainties in Λsnow, and the uncertainties from these parameters are much larger than for Λrain. Specifically, different N(Dp) formulations can cause one-order-of-magnitude uncertainties in Λsnow for all aerosol sizes, as is also the case for a combination of uncertainties from both VD and A. Assumptions about dominant snow-particle shape (and thus different VD and A) will cause an uncertainty of up to one order of magnitude in the calculated scavenging coefficient. In comparison, uncertainties in Λrain from N(Dp) are smaller than a factor of 5, and those from VD are smaller than a factor of 2. As expected, Λsnow estimated from empirical formulas generated from field measurements falls in the upper range of, or is higher than, the theoretically estimated values, which can be explained by additional processes/mechanisms that influence field-derived Λsnow but that are not considered in the theoretical Λsnow formulas. Predicted aerosol concentrations obtained by using upper range vs. lower range of Λsnow values (a difference of around two orders of magnitude in Λsnow) can differ by a factor of 2 for just a one-centimetre snowfall (liquid water equivalent of approximately 1 mm). Based on the median and upper range of theoretically generated Λsnow and Λsnow values, it is likely that, for typical rain and snow events, the removal of atmospheric aerosol particles by snow is more effective than removal by rain for equivalent precipitation amounts, although a firm conclusion requires much more evidence.

Sign in / Sign up

Export Citation Format

Share Document