scholarly journals A New Semisubmersible Design for Improved Heave Motion, Vortex-Induced Motion and Quayside Stability

2011 ◽  
Author(s):  
Qi Xu
Keyword(s):  
Floating Platform ◽  
Natural Period ◽  
Suppression Effect ◽  
Structural Rigidity ◽  
Hull Design ◽  
Induced Motion ◽  
Steel Catenary Risers ◽  
The Difference ◽  
Touchdown Point ◽  
Heave Motion

Recently the semisubmersible has become a favorable choice as a wet-tree floating platform supporting steel catenary risers (SCRs), mainly due to its capability of quayside topside integration and cost-effectiveness. However, it is still a challenge for a conventional semisubmersible to support SCRs, particularly large ones, in harsh environment and relatively shallow water due to its large heave motion. To answer this challenge, a new semisubmersible design has been developed at Technip as a wet-tree floater which achieves significantly improved heave motion and vortex-induced-motion (VIM) performance through hull form optimization while maintaining the simplicity of a conventional semisubmersible design. The difference between the NexGen semi-submersible design and a conventional semi-submersible design is in the blisters attached to the columns, distribution of pontoon volume, and pontoon cross section shape. In the NexGen semi-submersible design, the pontoon volume is re-distributed to minimize heave loading while maintaining sufficient structural rigidity, a long heave natural period and adequate quayside buoyancy. The blisters attached to the columns effectively break the vortex shedding coherence along the column length and therefore suppresses VIM. The blisters also provide much needed stability at quayside and during the hull deployment process, making the hull design less sensitive to topside weight increase. In the present paper the hydrodynamic aspects of this new design are discussed in detail. A benchmark case is presented in which the new design is compared against a more conventional design with the same principal dimensions. It is shown that the heave response in extreme sea states (100-yr hurricane) at the platform center of gravity is reduced by about 30–40%, and at the SCR hang-off locations by about 25–30%. Due to the reduced heave motion, SCRs experience about one third less stress at the touchdown point. A qualitative VIM analytical model is used to predict the VIM suppression effect of the new design. A highlight of a VIM model test for the proposed design is also presented. The reduced heave and VIM significantly improve the riser stress and fatigue near the touchdown point. This new design makes the semisubmersible a more robust wet-tree floater concept, and even a potentially good candidate as a dry-tree host concept in relatively benign environment.

Model Tests With the HVS Semisubmersible for Dry Tree Application

2014 ◽  
Author(s):  
Johyun Kyoung ◽  
Chan-Kyu Yang ◽  
Kostas Lambrakos ◽  
Jim O’Sullivan
Keyword(s):  
Model Tests ◽  
Base Case ◽  
Natural Period ◽  
Depth Limit ◽  
Wave Basin ◽  
Induced Motion ◽  
Motion Performance ◽  
Heave Motion ◽  
Keel Plate ◽  
Measured Response

The global hull motion performance of the HVS semisubmersible for dry tree application is investigated with model tests. The HVS semisubmersible, which has been validated for low heave motion and VIM (Vortex Induced Motion) response, was modified for dry tree application. As a base case, the modification includes a keel plate with riser keel guides at the level of the pontoons. The keel plate is optimally designed to increase the hull heave period to compensate for the heave period reduction in the HVS semisubmersible due to the riser tensioners for the dry tree application. The plate also provides additional viscous damping that decreases the heave response at the heave natural period. The model tests were performed to investigate the in-place hull motion performance for the Gulf of Mexico environmental conditions. The pneumatic riser tensioners were modeled using a spring with dual stiffness. Because of the water depth limit in the wave basin, a truncated mooring was used to simulate the full scale prototype mooring system. An alternate modification to the HVS semisubmersible that includes pontoon plates was also tested and the measured response was compared to the response of the base case. The measured hull responses were correlated with MLTSIM, a Technip in-house nonlinear time-domain 6-DOF motion analysis program.

A Comparison Study of Improved SCR Response for HVS Semisubmersible

2013 ◽  
Author(s):  
Xiaoning Jing ◽  
Roger Qian ◽  
Yongming Cheng ◽  
Kostas Lambrakos ◽  
Jim O’Sullivan ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Comparison Study ◽  
Floating Platform ◽  
Sea State ◽  
Strength Performance ◽  
Compression Load ◽  
Deep Waters ◽  
Induced Motion ◽  
Heave Motion ◽  
Wave Induced

A new deep draft semisubmersible HVS (Heave and VIM Suppressed) has been developed at Technip as another wet-tree floating platform option, which achieves significantly improved heave motion and Vortex-Induced-Motion (VIM) performance as compared to conventional semisubmersible concepts. This paper presents results from a study that compares the strength and fatigue performance of a gas export (20 inch) SCR that is supported by either the HVS semi or a comparable conventional semi in 4000 ft or 6000 ft of water depth. Both floaters are designed for the central Gulf of Mexico, and have comparable hull principal dimensions and mooring configurations. For the HVS semisubmersible in an extreme sea state (100-yr hurricane), the reduced heave motion significantly improves SCR strength performance at the Touch Down Zone (TDZ) and effectively eliminates the compression load at the sag bend region. The assessment of SCR fatigue responses indicates that most damage near the TDZ results from wave induced motion fatigue and hull VIM fatigue. The suppressed VIM response of the HVS semisubmersible due to the unique blisters attached to the four hull columns significantly enhances the SCR fatigue life near the critical TDZ. The results from this study confirm HVS as a SCR-friendly wet tree host concept for the deep waters in GoM.

scholarly journals Mechanical analysis of deepwater drilling riser system based on multibody system dynamics

2020 ◽  
Author(s):  
Xiu-Quan Liu ◽  
He-Xiang Sun ◽  
Meng-Ru Yu ◽  
Na Qiu ◽  
Yan-Wei Li ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Multibody System ◽  
Stress Amplitude ◽  
Three Dimensional ◽  
Mechanical Analysis ◽  
Floating Platform ◽  
Suppression Effect ◽  
Deepwater Drilling ◽  
Gas Drilling ◽  
Heave Motion

Abstract A multibody system including a drilling riser system, tensioners and a floating platform is key equipment for offshore oil and gas drilling. Most of the previous studies only focus on the drilling riser system rather than the multibody system. Mechanical characteristics of the deepwater drilling riser system cannot be analyzed accurately in a simplified model. Therefore, a three-dimensional multibody analysis program is developed. The static and dynamic characteristics of the deepwater drilling riser system under different platform motions are analyzed based on the developed program. The results show that the static displacement of the riser system with tensioners is smaller than that without tensioners, which means the tensioners can suppress the deformation of the riser system. Under surge and sway motions of the platform, the dynamic displacement of the riser system with tensioners is also smaller than that without tensioners due to the tensioner suppression effect. Besides, the heave motion induces a uniform axial vibration of the riser system, while roll and pitch motions excite the riser system to vibrate laterally. Compared with the stress amplitude due to surge and sway motions, the stress amplitude of the riser system due to heave, roll and pitch motions is relatively small but cannot be neglected.

Study of Numerical Modeling of Moonpool as Minimization Device of Monocolumn Hull

2004 ◽  
Author(s):  
Fernando G. S. Torres ◽  
Marcos Cueva ◽  
Edgard Borges Malta ◽  
Kazuo Nishimoto ◽  
Marcos Donato Ferreira
Keyword(s):  
Wave Spectrum ◽  
Oil Field ◽  
Oil Fields ◽  
Natural Period ◽  
Section Area ◽  
New Type ◽  
Steel Catenary Risers ◽  
Heave Motion ◽  
Bilge Keel ◽  
Geographical Characteristics

The steel catenary risers (SCR) have been studied to be used in ultra-deep oil fields. In Brazil, the oil field is going to deeper water. The geographical characteristics impose this type of production risers, and the necessity of these risers is real. However, in order to avoid risers fatigue problems, some premises related to low vertical motions have to be respected. To reach the necessary good seakeeping responses, new type of hull shape has been proposed, the monocolumn hull, to which some motion minimization devices have been developed. There are several conceptions of monocolumn type hull, but the concept presented in this paper is different from the existing monocolumn hull. To have good seakeeping capability, three main minimization devices were proposed: the structural skirt, the inclined wall, and the moonpool. The inclined wall, a variation of a section area near the water-plane, works together with the skirt, an enlarged bilge keel at the bottom of the platform, modifying the effect of damping, added mass and inertia. The moonpool is the old tank usually found in drilling units, properly modified to work as a motion minimization system. It works as a passive heave motion reduction system, shifting the natural period far from the wave spectrum. Some numerical analyses were made to present the effects obtained from these devices. These numerical results from WAMIT® were compared to experimental showing to be according to them.

The Dynamic Response of a Simple Elastic System to Antisymmetric Forcing Functions Characteristic of Airplanes in Unsymmetric Landing Impact

1949 ◽  
Vol 16 (3) ◽  
pp. 310-316
Author(s):  
Joseph B. Woodson
Keyword(s):  
Dynamic Response ◽  
Sine Wave ◽  
Response Curves ◽  
Response Factors ◽  
Natural Period ◽  
Wave Pulse ◽  
Pulse Disturbance ◽  
Landing Impact ◽  
Forcing Functions ◽  
The Difference

Abstract This paper presents an analysis of the dynamic response of an undamped mechanical system with one degree of freedom subjected to disturbances which are described by antisymmetric forcing functions. The analysis was undertaken to throw light on the effect on the vibration of the wings caused by unsymmetric landing impact of an airplane. Two types of disturbances are considered; a full-sine-wave pulse, and a pulse which is the difference between two overlapping half sine waves. The results are presented in the form of dynamic-response curves and dynamic-response-factor curves. The numerically greatest dynamic-response factors, approximately 3.24 and −3.26, resulted for a full-sine-wave pulse disturbance with a ratio of duration of impact to natural period, Ti/T ≅ 1.11. When Ti/T is in the neighborhood of 1, the first positive peak of dynamic response is numerically less than the negative and positive peaks which follow it. For much of the range, the positive and negative dynamic-response factors are numerically approximately equal. The analysis was confined to values of Ti/T between 0.33 and 12. As Ti/T increases without limit, the positive and negative dynamic-response factors tend to 1 and −1, respectively.

scholarly journals The Impact of China’s Low-Carbon Initiative on the Location Expansion of International SPA Enterprises

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Zhaoyang Zhao ◽  
Chong Ye
Keyword(s):  
Economic Development ◽  
Product Life Cycle ◽  
Large Scale ◽  
High Energy ◽  
Inhibitory Effect ◽  
Low Carbon ◽  
Suppression Effect ◽  
Carbon Neutrality ◽  
The Difference ◽  
The Impact

“Fast fashion” represents a short product life cycle, and international SPA enterprises are therefore criticised as representatives of high energy consumption, pollution, and emissions, which is contrary to China’s goal of achieving carbon neutrality. In the context of China’s shift to a low-carbon economic development model, how should SPA enterprises breakthrough in the face of China’s large-scale market advantage and domestic demand potential? Based on the statistics of 277 prefecture-level cities from 2010 to 2018, this article selects 5 leading international SPA enterprises and uses the difference-in-differences (DID) method to explore the impact of low-carbon initiative on the location expansion of international SPA enterprises. The results suggest that the quantity of location expansions of SPA enterprises in the pilot cities is significantly lower by approximately 0.418 units compared with the nonpilot cities, implying that the low-carbon initiative has a significant inhibitory effect on the location expansion of SPA enterprises. After a series of robustness tests, the conclusion is valid. The results of the heterogeneity test suggest that the suppression effect is mainly found in the subsample of central cities and cities with medium and low levels of economic development. This article proposes that SPA enterprises should reduce their carbon emissions and gradually explore a green and sustainable development path.

Sensitivity Study of Critical Parameters Influencing the Uncertainty of Fatigue Damage in Steel Catenary Risers

2010 ◽  
Author(s):  
Feng Zi Li ◽  
Ying Min Low
Keyword(s):  
Fatigue Damage ◽  
Cost Effective ◽  
Sensitivity Study ◽  
Structural Safety ◽  
Critical Parameters ◽  
Design Parameters ◽  
Steel Catenary Riser ◽  
Bending Stresses ◽  
Steel Catenary Risers ◽  
Touchdown Point

The most challenging aspect of a deepwater development is the riser system, and a cost-effective choice is the Steel Catenary Riser (SCR). Fatigue is often a governing design consideration, and it is usually most critical at the touchdown point (TDP) where static and dynamic bending stresses are highest. Unfortunately, it is also at this region that uncertainty is the maximum. The increased uncertainty casts doubt on the applicability of generic safety factors recommended by design codes, and the most consistent way of ensuring the structural safety of the SCR is to employ a reliability-based approach, which has so far not received attention in SCR design. As the number of basic random variables affects the complexity of a reliability analysis, these variables should be selected with caution. To this end, the aim of this paper is to draw up a comprehensive list of design parameters that may contribute meaningfully to the uncertainty of the fatigue damage. From this list, several parameters are selected for sensitivity studies using the commercial package Orcaflex. It is found that variations in seabed parameters such as soil stiffness, soil suction and seabed trench can have a pronounced influence on the uncertainty of the fatigue damage at the touchdown point.

Vortex Induced Motion of TLP With Consideration of Appurtenances

2014 ◽  
Author(s):  
Jaime Hui Choo Tan ◽  
Yih Jeng Teng ◽  
Allan Magee ◽  
Benedict Toong Heng Ly ◽  
Shankar Bhat Aramanadka
Keyword(s):  
Cfd Simulation ◽  
Scale Effects ◽  
Floating Platform ◽  
Steel Catenary Riser ◽  
Aspect Ratios ◽  
Significant Difference ◽  
Helical Strakes ◽  
Induced Motion ◽  
Set Up ◽  
Comparison Of The Results

Offshore floating platform configurations often consist of geometrically simple and symmetrical shapes which are made complicated by the presence of appurtenances such as helical strakes, tendon porches, steel catenary riser (SCR) porches, pipes, chains, fairleads and anodes on the surface of the hull. Previous studies mainly on spars show that these hull external features affect the Vortex Induced Motion (VIM) performance of the platform significantly. This is to be expected since VIM is controlled by the flow separation on the hull surface and the resulting vortex shedding patterns. Scale effects may also play a role in model tests for bare cylinders or hulls with bare cylindrical columns, whereas previous studies have shown less Reynolds dependence when appurtenances are modelled. This study investigates the effect of hull appurtenances on VIM of a multi-column floating platform, i.e. a Tension Leg Platform (TLP) designed for Southeast Asian environment. Significant difference in VIM behaviors is expected between spars and TLPs since the column aspect ratios are very different and TLPs do not have helical strakes that are commonly fitted on spars. Model testing and Computational Fluid Dynamics (CFD) simulation are used in this VIM study, with the former being the emphasis of this paper. Descriptions of the respective experimental and numerical methodologies are presented and the comparison of the results is made. Further work required to improve the model test set-up and the CFD simulation are suggested. From this study, it is shown that the effect of appurtenances on TLP VIM simulation is important and must be taken into account to obtain realistic results.

Development of semi-submersible production vessels and its application to Australian waters

2008 ◽  
Vol 48 (1) ◽  
pp. 241
Author(s):  
Hilde Engelsen ◽  
Henrik Hannus
Keyword(s):  
North Sea ◽  
Environmental Conditions ◽  
Oil And Gas ◽  
Gas Production ◽  
Oil And Gas Production ◽  
The North ◽  
Hull Design ◽  
Steel Catenary Risers ◽  
Drilling Rigs ◽  
In The Beginning

Semi-submersible platforms have a long history in the North Sea. In the beginning they were used mainly as mobile offshore drilling units, but in the last two decades the permanently moored semi-submersible production vessels have become widely used both as gas processing units and combination oil and gas production vessels. The design of production semi-submersibles evolved from that of drilling rigs, but there have since been significant improvements to the design of the hull and the topside configuration in relation to operational requirements and construction processes. The design methods have also been successfully adapted to areas with different environmental conditions, in combination with steel catenary risers and polyester mooring systems. On recent designs, simplifications of the hull systems are being implemented, which ease operation and enhance the passive safety. Finally, the semi-submersible production vessel’s application to Australian waters is discussed with focus on topside layout, hull design and mooring system design. Environmental conditions offshore northwest Australia are compared to North Sea and Gulf of Mexico conditions, along with vessel class and regulatory requirements.

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