“Bigfoot” Direct Vertical Access Semisubmersible Model Tests and Comparison With Numerical Predictions

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Stergios Liapis ◽  
Yile Li ◽  
Haining Lu ◽  
Tao Peng
Keyword(s):  
Model Tests ◽  
Attractive Alternative ◽  
Force Measurements ◽  
Numerical Predictions ◽  
Order Of Magnitude ◽  
Drilling Operations ◽  
Computational Fluid Dynamics Cfd ◽  
Project Model ◽  
Production Host ◽  
Motion Characteristics

The Bigfoot direct vertical access (DVA) semisubmersible is a novel floating drilling and production host that provides an attractive alternative to the spar. This concept utilizes heave plates (big feet) that improve the motion characteristics of a semisubmersible in all mild environments (Southeast Asia, West Africa, and Brazil). Bigfoot offers riser-friendly motions that enable top-tensioned risers, which is often a project requirement. This floater works in all water depths, in particular ultra-deepwater (5000 + ft) where a tension leg platform (TLP) is not an option, supports top-tensioned risers, and enables drilling and workover operations. The Bigfoot has several advantages over a spar. These include: (1) quayside topsides integration. This eliminates offshore topsides integration, a significant issue for all spar projects in terms of cost, safety, and schedule, (2) a more open deck layout compared to a spar, and (3) no fabrication location restrictions as it can be built by many yards worldwide potentially offering local content to a project. Model tests were undertaken at the Shanghai Jiao Tong University (SJTU) Offshore Basin to assess the dynamic response of the Bigfoot in waves, swell, wind, and current. Five mild non-Gulf of Mexico (GOM) environments were considered. In all the cases, the floater motions are an order of magnitude smaller than those of a conventional semisubmersible for similar deck payload, thus enabling drilling operations and top-tensioned production risers. In a parallel effort, a cosmos numerical model of the Bigfoot was developed for coupled motion analysis. The experimental results and the cosmos numerical predictions are in close agreement. In addition to measuring global motions, two heave plates were instrumented with load cells to measure forces and moments. The force measurements from the model tests are in good agreement with numerical predictions using computational fluid dynamics (CFD).

“Bigfoot” DVA Semi-Submersible Model Tests and Comparison With Numerical Predictions

2015 ◽  
Author(s):  
Stergios Liapis ◽  
Yile Li ◽  
Haining Lu ◽  
Tao Peng
Keyword(s):  
Model Tests ◽  
Attractive Alternative ◽  
Force Measurements ◽  
Numerical Predictions ◽  
Order Of Magnitude ◽  
Drilling Operations ◽  
Computational Fluid Dynamics Cfd ◽  
Production Host ◽  
Motion Characteristics ◽  
Good Agreement

The Bigfoot direct vertical access (DVA) semisubmersible is a novel floating drilling and production host that provides an attractive alternative to the spar. This concept utilizes heave plates (big feet) that improve the motion characteristics of a semisubmersible in all mild environments (S.E. Asia, W. Africa and Brazil). Bigfoot offers direct-vertical access (DVA) which is often a project requirement. This floater works in all water depths, in particular ultra-deepwater (5000+ ft) where a tension leg platform (TLP) is not an option, supports top tensioned risers and enables drilling and workover operations. The Bigfoot has several advantages over a spar. These include: 1) Quayside topsides integration. This eliminates offshore topsides integration, a significant issue for all spar projects in terms of cost, safety and schedule. 2) A more open deck layout compared to a spar, 3) No fabrication location restrictions as it can be built by many yards worldwide potentially offering local content to a project. Model tests were undertaken at the Shanghai Jiao Tong University (SJTU) Offshore Basin to assess the dynamic response of the Bigfoot in waves, swell, wind and current. Five mild (non-Gulf of Mexico) environments were considered. In all cases, the floater motions are an order of magnitude smaller than those of a conventional semisubmersible for similar deck payload thus enabling drilling operations and top-tensioned production risers. In a parallel effort, a COSMOS numerical model of the Bigfoot was developed for coupled motion analysis. The experimental results and the COSMOS numerical predictions are in close agreement. In addition to measuring global motions, two heave plates were instrumented with load cells to measure forces and moments. The force measurements from the model tests are in good agreement with numerical predictions using computational fluid dynamics (CFD).

Model Tests for the Validation of Extreme Roll Motion Predictions

2002 ◽  
Author(s):  
Walter L. Kuehnlein ◽  
K.-E. Brink
Keyword(s):  
Practical Knowledge ◽  
Rapid Development ◽  
Model Tests ◽  
Design Stage ◽  
Roll Motion ◽  
Ministry Of Education ◽  
Following Seas ◽  
Early Design Stage ◽  
Shaped Container ◽  
Motion Characteristics

At present common stability criteria are based on practical knowledge gained from the operation of ships. Therewith the assessment of ship safety against capsizing is partly determined by long-term statistics of accidents. Regulations like the IMO-Resolution A 167 do not rate the typical seakeeping characteristics of different hull form geometries. Therefore strictly speaking, these criteria are just applicable for ships of similar types as included in statistics. Rapid development in ship design calls for the determination of ship and cargo safety in regard of extreme roll motions or capsizing during early design stage. Within the ROLL-S project, which was founded by the German Federal Ministry of Education and Research, dynamic stability tests with a box shaped Container Ship and a RO-RO vessel have been performed. The performance of model tests, which are intended to serve for the validation of numerical simulation methods, put high demands on test and data acquisition techniques. The data of the waves encountered, course and position, as well as the response of the model had to be determined by model tests in order to use these data for the validation of numerical ship motion simulations. During the tests extreme roll motions of the two considered vessels could be observed in head seas and in following seas. Besides critical motion characteristics in following seas, like broaching, parametric induced roll motion effects were investigated in head sea condition. Remark: This paper should be read in conjunction with paper OMAE 2002-28297 which describes generation and transformation of the used waves.

Truss Spar Vortex Induced Motions: Benchmarking of CFD and Model Tests

2006 ◽  
Author(s):  
John Halkyard ◽  
Sampath Atluri ◽  
Senu Sirnivas
Keyword(s):  
Fluid Dynamics ◽  
Best Practices ◽  
Turbulence Modeling ◽  
Production Systems ◽  
Model Tests ◽  
The Past ◽  
Helical Strakes ◽  
Truss Spar ◽  
Computational Fluid Dynamics Cfd ◽  
Riser Design

Spar production systems are subject to Vortex Induced Motions (VIM) which may impact mooring and riser design. Helical strakes are employed to mitigate VIM. Model tests are typically required to validate the performance of the strakes. This paper will report on the results of benchmarking studies that have been conducted over the past few years to compare model tests with computational fluid dynamics (CFD). The paper discusses comparisons of CFD with model tests, “best practices” for the use of CFD for these classes of problems and issues related to turbulence modeling and meshing of problems at large Reynold’s numbers. This work is ongoing.

Numerical Modeling of Static and Rotordynamic Characteristics for Three Types of Helically Grooved Liquid Annular Seals

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Zhigang Li ◽  
Zhi Fang ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Perturbation Method ◽  
Navier Stokes ◽  
Force Coefficients ◽  
Numerical Predictions ◽  
Curve Fit ◽  
Annular Seal ◽  
Frequency Independent ◽  
Computational Fluid Dynamics Cfd ◽  
Multiple Reference ◽  
Annular Seals

Abstract This paper deals with numerical predictions of the leakage flowrates, drag power, and rotordynamic force coefficients for three types of helically grooved liquid annular seals, which include a liquid annular seal with helically grooved stator (GS/SR seal), one with helically grooved rotor (SS/GR seal), and one with helical grooves on stator and rotor (GS/GR seal). A novel transient computational fluid dynamics (CFD)-based perturbation method was proposed for the predictions of the leakage flowrates, drag power, and rotordynamic force coefficients of helically grooved liquid annular seals. This method is based on the unsteady Reynolds-averaged Navier–Stokes (RANS) solution with the mesh-deformation technique and the multiple reference frame theory. The time-varying fluid-induced forces acting on the rotor/stator surface were obtained as a response to the time-dependent perturbation of the seal stator surface with the periodic motion, based on the multiple-frequency elliptical-orbit stator whirling model. The frequency-independent rotordynamic force coefficients were determined using curve fit and fast Fourier transform (FFT) in the frequency domain. The CFD-based method was adequately validated by comparisons with the published experiment data of leakage flowrates and fluid response forces for three types of helically grooved liquid annular seals. Based on the transient CFD-based perturbation method, numerical results of the leakage flowrates, drag powers, and rotordynamic force coefficients were presented and compared for three types of helically grooved liquid annular seals at five rotational speeds (n = 0.5 krpm, 1.0 krpm, 2.0 krpm, 3.0 krpm, and 4.0 krpm), paying special attention to the effective stiffness coefficient and effective damping coefficient.

CFD Simulations of the Cold Neutron Source at the OPAL Reactor

2020 ◽  
Author(s):  
James L Spedding ◽  
Mark Ho ◽  
Weijian Lu
Keyword(s):  
Neutron Source ◽  
Cold Neutron ◽  
Operating Conditions ◽  
Convergence Time ◽  
Cfd Model ◽  
Cfd Simulations ◽  
Cold Neutron Source ◽  
Order Of Magnitude ◽  
Computational Fluid Dynamics Cfd ◽  
Polyhedral Mesh

Abstract The Open Pool Australian Light-water (OPAL) reactor Cold Neutron Source (CNS) is a 20 L liquid deuterium thermosiphon system which has performed consistently but will require replacement in the future. The CNS deuterium exploits neutronic heating to passively drive the thermosiphon loop and is cryogenically cooled by forced convective helium flow via a heat exchanger. In this study, a detailed computational fluid dynamics (CFD) model of the complete thermosiphon system was developed for simulation. Unlike previous studies, the simulation employed a novel polyhedral mesh technique. Results demonstrated that the polyhedral technique reduced simulation computational requirements and convergence time by an order of magnitude while predicting thermosiphon performance to within 1% accuracy when compared with prototype experiments. The simulation model was extrapolated to OPAL operating conditions and confirmed the versatility of the CFD model as an engineering design and preventative maintenance tool. Finally, simulations were performed on a proposed second-generation CNS design that increases the CNS moderator deuterium volume by 5 L, and results confirmed that the geometry maintains the thermosiphon deuterium in the liquid state and satisfies the CNS design criteria.

Interfacing Virtual Reality, CFD and the Internet

1997 ◽  
Author(s):  
David J. Freeman
Keyword(s):  
Fluid Dynamics ◽  
Virtual Reality ◽  
The Internet ◽  
Parallel Processor ◽  
Computing Power ◽  
Numerical Predictions ◽  
Computational Fluid Dynamics Cfd ◽  
Software And Hardware ◽  
Time Required ◽  
The Cost

Computational Fluid Dynamics (CFD) is a valuable tool for the process and petroleum industries. CFD reduces development timescales and costs by replacing expensive and lengthy laboratory investigation with numerical predictions of processes. However, there are several reasons why some companies are unwilling to use CFD. These include the cost of the software and hardware, the need for in-house CFD expertise and the time required to solve complex simulations. CHAM has developed a solution to these problems, in the form of a Virtual Reality Interface linked via the Internet to powerful parallel-processor computers. Virtual reality makes CFD accessible to non-CFD experts and allows the engineer to concentrate on the solution of his problem. Remote computing makes it possible to access from a PC the necessary computing power to solve the problem. Several examples will be shown, demonstrating the application and benefits of the PHOENICS-VR interface and the advantages of remote computing to the process and petroleum industries.

Fuel Flexible Biomass Reburn Technology

2009 ◽  
Author(s):  
Guang Xu ◽  
Wei Zhou ◽  
Larry Swanson
Keyword(s):  
Particle Size ◽  
Bituminous Coal ◽  
Nox Reduction ◽  
Unburned Carbon ◽  
Gas Temperature ◽  
Mean Particle Size ◽  
High Volatility ◽  
Order Of Magnitude ◽  
Char Reactivity ◽  
Computational Fluid Dynamics Cfd

Biomass reburn is a low NOx alternative to cofiring that effectively uses the high volatility and high char reactivity of biomass for NOx reduction. In this paper, computational fluid dynamics (CFD) and thermal modeling, and a NOx prediction model were used to evaluate the impacts of sawdust/coal reburn on the performance of a 250 MW opposed-fired boiler burning bituminous coal as the primary fuel. The results showed that the reburn system maintained overall boiler performance with a 50 – 70 °F reduction in the furnace exit gas temperature. Predicted losses in thermal efficiency were caused by the lower biomass fuel heating value (similar to biomass cofiring) and increase in unburned carbon. The higher unburned carbon emissions were attributed to an order of magnitude larger biomass mean particle size relative to bituminous coal. Thus, LOI emissions can be improved significantly by reducing the biomass mean particle size. The NOx predictions showed that for reburn rates above about 19%, adding dry sawdust biomass to a coal reburn system can improve NOx reduction; i.e., using pure dry sawdust as reburn fuel at 30% of the total heat input can lead to NOx levels about 30% less than those for pure coal reburn under for similar firing conditions.

Green Sea and Water Impact on FPSO: Numerical Predictions Validated Against Model Tests

2002 ◽  
Author(s):  
C. T. Stansberg ◽  
O̸. Hellan ◽  
J. R. Hoff ◽  
V. Moe
Keyword(s):  
Structural Integrity ◽  
Design Method ◽  
Model Tests ◽  
Random Wave ◽  
Simplified Approach ◽  
Irregular Wave ◽  
Wave Kinematics ◽  
Numerical Predictions ◽  
Statistical Sense ◽  
Local Pressures

A recently developed numerical design method for analysis of green sea events and resulting impact loads on deck structures of FPSO’s, is validated against model test data. Steep irregular wave conditions are considered, and numerical time series reconstructions are made using the measured wave as input. A second-order numerical random wave description is combined with standard 3D wave diffraction and related vessel motions to predict the relative wave kinematics. A modified shallow water formulation is applied for the prediction of the propagation on deck, and resulting local pressures on the deck-house are estimated by a similarity solution. From this an analysis of the structural integrity can be made. Comparisons to the experiments are made for the relative wave amplitudes, water propagation on deck, and the resulting deck-house loads. A reasonably good agreement is observed for the reconstructions, in a statistical sense, but also for individual events. Thus selected green sea events are investigated in detail, and characteristics identified. The agreement with the model tests is promising especially on the background of the simplified approach used, as well as the expected statistical scatter.

scholarly journals Feeling the Force: Measurements of Platelet Contraction and Their Diagnostic Implications

2018 ◽  
Vol 45 (03) ◽  
pp. 285-296 ◽  
Author(s):  
Evelyn Williams ◽  
Oluwamayokun Oshinowo ◽  
Abhijit Ravindran ◽  
Wilbur Lam ◽  
David Myers
Keyword(s):  
Mechanical Properties ◽  
Heart Disease ◽  
Ischemic Heart Disease ◽  
Material Properties ◽  
Blood Cells ◽  
Ischemic Heart ◽  
Force Measurements ◽  
Blood Clots ◽  
Order Of Magnitude

AbstractIn addition to the classical biological and biochemical framework, blood clots can also be considered as active biomaterials composed of dynamically contracting platelets, nascent polymeric fibrin that functions as a matrix scaffold, and entrapped blood cells. As platelets sense, rearrange, and apply forces to the surrounding microenvironment, they dramatically change the material properties of the nascent clot, increasing its stiffness by an order of magnitude. Hence, the mechanical properties of blood clots are intricately tied to the forces applied by individual platelets. Research has also shown that the pathophysiological changes in clot mechanical properties are associated with bleeding and clotting disorders, cancer, stroke, ischemic heart disease, and more. By approaching the study of hemostasis and thrombosis from a biophysical and mechanical perspective, important insights have been made into how the mechanics of clotting and the forces applied by platelets are linked to various diseases. This review will familiarize the reader with a mechanics framework that is contextualized with relevant biology. The review also includes a discussion of relevant tools used to study platelet forces either directly or indirectly, and finally, concludes with a summary of potential links between clotting forces and disease.

Analysis of Semi-Submersible Under Combined High Waves and Current Conditions Compared With Model Tests

2018 ◽  
Author(s):  
Limin Yang ◽  
Arne Nestegård ◽  
Erik Falkenberg
Keyword(s):  
Simulation Model ◽  
Low Frequency ◽  
Model Tests ◽  
Wave Forces ◽  
Viscous Effects ◽  
Numerical Predictions ◽  
Wave Drift ◽  
Zero Current ◽  
Frequency Excitation ◽  
Wave Drift Forces

Viscous effects on the low-frequency excitation force on column based platforms are significant in extreme waves. The wave drift force as calculated by a zero-current potential flow radiation/diffraction code becomes negligible for such waves. In the present study, the effect of current and viscous contributions on the slowly varying wave forces are adjusted by a formula developed in the Exwave JIP, see e.g. [1], which is validated against model test results. This paper presents numerical predictions of low frequency horizontal motions of a semi-submersible in combined high waves and current condition. In the simulation model, frequency dependent wave drift forces from radiation/diffraction code are modified by the formula. Static current forces and viscous damping are modelled by the drag term in Morison load formula using relative velocity between current and floater and with force coefficients as recommended by DNVGL-RP-C205 [2]. Low frequency surge responses calculated by the simulation model are compared with model tests for waves only and for combined collinear and noncollinear wave and current conditions.

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