Numerical Prediction of Spar Motions Considering Top Tension Riser Stiffness

2004 ◽  
Author(s):  
Cheng-Yo Chen ◽  
Prahoro Nurtjahyo
Keyword(s):  
Gulf Of Mexico ◽  
Model Test ◽  
Pitch Angle ◽  
Motion Prediction ◽  
Test Results ◽  
Proposed Model ◽  
Comparison Results ◽  
Truss Spar ◽  
Righting Moment ◽  
Delta Model

Spar motions are often predicted without explicitly considering the stiffness effect of the buoyancy can of top tension risers (TTRs). This may result from the inability of most motion prediction programs to take this effect into consideration. The forces exerted by the TTR buoyancy can on the spar provide a net beneficial righting moment. Hence, neglecting the effect of TTR stiffness could produce excessive predicted spar motions, particularly maximum pitch angle. The derived spar configurations based on such predicted motions are likely to be conservative and not optimal. This paper proposes a simple “Linearized P-Delta” model to account for the effect of TTR stiffness on spar motions. The predicted motions using the proposed model are compared with the model test results for a production truss spar in the Gulf of Mexico. The comparison results indicate that the proposed model is quite rigorous and correlates reasonably well with the model test results.

Improving the Motions of a Semi by the Addition of Heave Plates

2008 ◽  
Author(s):  
Cheng-Yo Chen ◽  
Yun Ding ◽  
Trevor Mills ◽  
John Murray
Keyword(s):  
Gulf Of Mexico ◽  
Model Test ◽  
Cost Effective ◽  
Analytical Prediction ◽  
Test Results ◽  
Effective Manner ◽  
Truss Spar ◽  
Heave Plate ◽  
Motion Characteristics ◽  
Plate System

Similar to the manner in which heave plates provide a Truss Spar with low global motions, a heave plate system can be used to significantly mitigate the motions of a conventional semi-submersible. This paper will focus on the global performance of a conventional semi-submersible that has been properly configured with heave plates. The design case is a Gulf of Mexico deepwater environment similar to that for a Spar located in 5,600 feet of water. The system has eight top-tensioned risers (TTR) supported on the top of the semi hull with tensioners, a spread mooring and a 10,000-ton operating payload. Extensive global motion analyses and comprehensive model testing have been carried out to validate the in-place behavior of such a solution. This paper presents the validation results from the analytical prediction and the model test. A semi-submersible with properly configured heave plates can be used as a viable deepwater dry-tree floating solution in such harsh environments as in the Gulf of Mexico. Because of its superior motion characteristics, this solution is also more SCR friendly and can be a better wet-tree application as compared to conventional semi-submersibles. The analytical and model test results demonstrate that the excitation of a semi-submersible hull by wind, wave and current can be adequately mitigated by the proper placement and sizing of a heave plate system. The analysis and testing also indicates that to achieve suitable motions in a cost effective manner requires incorporating fabrication and installation issues into the heave plate system. The in-place behavior of this solution has been validated and thus proving the concept provides a viable cost effective dry-tree floating solution for deepwater developments.

Improved Strake Design for Vortex Induced Motions of Spar Platforms

2005 ◽  
Author(s):  
Mehernosh Irani ◽  
Lyle Finn
Keyword(s):  
Model Test ◽  
Model Tests ◽  
Test Results ◽  
Test Program ◽  
Test Set ◽  
Test Methodology ◽  
Spar Platforms ◽  
Truss Spar ◽  
Set Up

An extensive model test program was conducted to explore the effectiveness of alternate strake designs to reduce Truss Spar VIV response. Different strake configurations were tested to minimize VIV response. The paper presents results of the model tests. The model test set-up is described, important parameters that are modeled (including hull and truss geometry, strake configuration, mass and mooring properties) and considerations of instrumentation and test methodology are discussed. The paper also describes the analysis of the test results and shows the effectiveness of new strake design. The present results are compared with VIV response of existing Truss Spars with conventional strake design.

The Effect of Mooring System and Sheared Currents on Vortex Induced Motions of Truss Spars

2003 ◽  
Author(s):  
Radboud R. T. van Dijk ◽  
Arjan Voogt ◽  
Paul Fourchy ◽  
Saadat Mirza
Keyword(s):  
Gulf Of Mexico ◽  
Mooring System ◽  
Test Results ◽  
Current Profile ◽  
Scaled Model ◽  
Production Platform ◽  
Helical Strakes ◽  
Truss Spar ◽  
Set Up ◽  
Program Show

Since 1996 Spars have been used as production platform in the Gulf of Mexico. Spar Vortex Induced Motions (VIM) in strong currents like the hurricane and loop currents are an important consideration for the design of the mooring system and risers. This is important for the extreme offsets as well as fatigue in risers and the mooring system. This paper compares the VIM behavior of a truss Spar in sheared currents, like the Hurricane current in the Gulf of Mexico, with tow test results. Experiments have been carried out on a scaled model in both a complete mooring system and in a towing set-up with a simplified horizontal mooring. The Spar model consists of a hard tank with removable helical strakes, a truss section and a square soft tank. The results of this model test program show that both the choice of the mooring system and current profile have a significant influence on the VIM response of the Spar. The paper discusses the results of this research and also addresses important issues and considerations for VIM model tests.

Motion Comparison Between a Conventional Deep Draft Semi-Submersible and a Dry Tree Semi-Submersible

2009 ◽  
Author(s):  
Anis Hussain ◽  
Edwin Nah ◽  
Rain Fu ◽  
Apurva Gupta
Keyword(s):  
Gulf Of Mexico ◽  
Model Test ◽  
Significant Influence ◽  
Extreme Environments ◽  
Test Results ◽  
Numerical Computations ◽  
Deep Waters ◽  
Second Tier ◽  
Motion Characteristics ◽  
Heave Motion

One of the major requirements for a floating vessel designed to support top tensioned risers is to have the heave response within a minimum specified range in extreme environments. The heave has a significant influence on the riser stroke. Usually floater designs aim to use conventional riser tensioners, available commercially, which typically have a maximum stroke range in the order of 30 to 35ft. One of the limitations of traditional Semi-submersible designs to support dry trees is that the heave ranges seen in central Gulf of Mexico (GoM) are outside the range that can apply a conventional tensioner. The Extendable Semi-submersible (E-Semi) utilizes a retractable Second Tier Pontoon (STP) to suppress heave motions and reduce its heave motion in order to support top tensioned risers in central GoM ultra deep waters. The design is based on an established deep draft Semi-submersible with the STP attached. This paper presents a comparison between motion characteristics of the deep draft Semi-submersible with and without the STP attached. The comparison is based on numerical computations to predict the responses together with model test results in the same environments. The analysis essentially shows the effectiveness of the STP is suppressing the heave motion.

Model Testing for Vortex Induced Motions of Spar Platforms

2004 ◽  
Author(s):  
Mehernosh Irani ◽  
Lyle Finn
Keyword(s):  
Gulf Of Mexico ◽  
Model Test ◽  
State Of The Art ◽  
Model Testing ◽  
Model Tests ◽  
The State ◽  
Test Results ◽  
Test Set ◽  
Vortex Induced Vibrations ◽  
Set Up

The state-of-the art in model testing for Vortex Induced Vibrations (VIV) of Spars is presented. Important issues related to Spar VIV model testing are highlighted. The parameters that need to be modeled including hull geometry, strake configuration, mass and mooring properties and, considerations of test set-up and instrumentation are discussed. Results are presented from model tests of an as-built Spar deployed in the Gulf of Mexico. It is shown that the model test results compare well with the VIV responses measured in the field.

The State of Dry-Tree Semi-Submersible Platforms for Deepwater Gulf of Mexico

2014 ◽  
Author(s):  
Ming-Yao Lee ◽  
Jack Zeng ◽  
Philip Poll
Keyword(s):  
Gulf Of Mexico ◽  
Technology Acceptance ◽  
Model Test ◽  
Water Depth ◽  
Technology Development ◽  
Cost Effective ◽  
Test Results ◽  
Scaled Model ◽  
Size Limits ◽  
Long Stroke

The use of semi-submersible platforms has become increasingly popular due to its ability to carry large topsides and the possibility for quayside integration. With recent exploration successes in ultra-deepwater fields of the Gulf of Mexico, major oil and engineering companies are keen to look for a safe, reliable and cost-effective dry-tree option to maximize the value of deepwater field developments. Dry-tree semi-submersible (DTS) emerges as such an option to overcome the water depth and size limits imposed by TLP and Spar, respectively, and enables the platform to carry a large well array and payloads in ultra-deep water. This paper presents the offshore industry’s multi-year efforts to mature two promising semi-submersible platform concepts that can accommodate long-stroke dry-tree risers and have large drilling and production capabilities. Results of technology development and qualification will be highlighted with details on hull performance and hull/riser interfaces. Key structural, mooring and riser analyses and scaled model test results including the long-stroke riser tensioning system will be presented. Remaining challenges that need to be overcome to advance the DTS concepts from “technology acceptance” to “project readiness” will also be discussed.

Float Over Installation Method—Comprehensive Comparison Between Numerical and Model Test Results

2006 ◽  
Vol 128 (3) ◽  
pp. 256-262 ◽  
Author(s):  
Arcandra Tahar ◽  
John Halkyard ◽  
Atle Steen ◽  
Lyle Finn
Keyword(s):  
West Africa ◽  
Gulf Of Mexico ◽  
Model Test ◽  
Test Results ◽  
Sea State ◽  
Numerical Predictions ◽  
Single Piece ◽  
Heavy Lift ◽  
Compliant Tower ◽  
Comprehensive Comparison

Installing a large deck onto a platform, such as a spar, using the floatover method is gaining popularity. This is because the operational cost is much lower than other methods of installation, such as modular lifts or a single piece installation by a heavy lift barge. Deck integration can be performed on land, at quay side and will not depend on a heavy lift barge. A new concept for a floatover vessel has been developed for operations in the Gulf of Mexico and West Africa. In this application sea state conditions are essential factors that must be considered in the Gulf of Mexico, especially for transportation. In West Africa, swell conditions will govern floatover deck (FOD) installation. Based on these two different environmental conditions, Technip Offshore, Inc. developed the FOD installation concept using semi-submersible barge type vessels. A significant amount of development work and model testing has been done on this method in recent years on spar floatover. These tests have validated our numerical methods. Another test was conducted to investigate the feasibility of a deck float-over operation onto a compliant tower for a West Africa project. The project consists of a compliant tower supporting a 25,401metricton(28,000s.ton) integrated deck. This paper will describe comparisons between model test data and numerical predictions of the compliant tower floatover operation.

scholarly journals An extended super/subloading surface model for soft rock considering structure degradation

PLoS ONE ◽  
2021 ◽  
Vol 16 (10) ◽  
pp. e0258813
Author(s):  
Kai Cui ◽  
Bin Hu ◽  
Aneng Cui ◽  
Jing Li ◽  
Erjian Wei ◽  
...  
Keyword(s):  
Yield Surface ◽  
Soft Rock ◽  
Yield Function ◽  
Surface Shape ◽  
Surface Model ◽  
Test Results ◽  
Structure Degradation ◽  
Proposed Model ◽  
Comparison Results ◽  
Cam Clay

The strain-softening and dilatancy behavior of soft rock is affected by the loading history and the development of structure. This study regards soft rock as a structured and overconsolidated soil and develops a new elastoplastic model based on the classical super yield surface Cam-clay model. The proposed model is capable of capturing the effect of yield surface shape on the mechanical behavior of soft rock by introducing a new yield function. The proposed model is validated against the triaxial test results on different types of soft rocks under drained condition. The comparison results indicate that the proposed model is suitable for describing the constitutive behavior of soft rock.

On Roll Hydrodynamics of FPSO’s Fitted With Bilge Keels and Riser Balcony

2011 ◽  
Author(s):  
R. van ’t Veer ◽  
F. Fathi ◽  
J. G. Kherian
Keyword(s):  
Model Test ◽  
Potential Flow ◽  
Model Tests ◽  
Continuous Operation ◽  
Motion Prediction ◽  
Roll Motion ◽  
Test Results ◽  
Site Location ◽  
Cfd Simulations ◽  
Roll Damping

The topic of this paper is the roll motion prediction of ship-shaped FPSO’s, designed for continuous operation at site location. The maximum roll amplitude is a critical operability parameter which is difficult to predict accurately due to the nonlinear roll damping associated with the appendages. This paper contributes to the understanding of roll damping physics through model test results, CFD simulations and potential flow predictions. The model tests discussed concern two different Floating Production, Storage and Offloading (FPSO) units, designed by SBM as spread-moored units for operation offshore Brazil. The relevant roll damping appendages are the bilge keels on both sides and the submerged riser balcony on one side of the vessel. In particular the riser balcony complicates the motion prediction and was a main reason for the model tests and CFD investigation. The results presented focus on roll motion prediction in the frequency domain.

scholarly journals Modeling Local Bond Stress–Slip Relationships of Reinforcing Bars Embedded in Concrete with Different Strengths

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3701
Author(s):  
Chao-Wei Tang ◽  
Chiu-Kuei Cheng
Keyword(s):  
Prediction Models ◽  
Concrete Strength ◽  
Bond Stress ◽  
Analytical Models ◽  
Test Results ◽  
Reinforcing Bars ◽  
Model Code ◽  
Steel Bar ◽  
Proposed Model ◽  
Comparison Results

Although many different analytical models of local bond stress–slip have been proposed, considering the possible differences between materials in different countries, their applicability needs to be further explored. In this paper, the local bond stress–slip characteristics of reinforcing bars embedded in concrete with different strengths were experimentally studied. The experimental variables included the concrete strength (20, 40, and 60 MPa) and deformed rebar size (#4, #6, and #8). The experimental results of the bond stress–slip relationship were compared with the Euro-International Concrete Committee (CEB-Comité Euro-International du Béton)-International Federation for Prestressing (FIP-Fédération Internationale de la Précontrainte) Model Code and prediction models found in the literature. In addition, based on the test results, an empirical model of the bond stress–slip relationship was proposed. The evaluation and comparison results show that, regardless of the concrete strength grades, the predicted value calculated using the CEB-FIP Model Code will underestimate the bond strength of the specimens with different steel bar diameters. From this perspective, it is more conservative. In contrast, the proposed model can predict the test results with a reasonable accuracy.

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