scholarly journals Experimental investigations on tension based tension leg platform (TBTLP)

2014 ◽  
Vol 11 (2) ◽  
pp. 105-116
Author(s):  
D. S. Bhaskara Rao ◽  
R. Panneer Selvam ◽  
Nagan Srinivasan
Keyword(s):  
Degrees Of Freedom ◽  
Experimental Investigations ◽  
Regular Waves ◽  
Tension Leg Platform ◽  
Scaled Model ◽  
Deep Waters ◽  
Offshore Industry ◽  
Motion Characteristics ◽  
Heave Motion ◽  
Water Depths

Tension Leg Platforms (TLPs) are one of the reliable structures for offshore industry in deep waters because of its motion characteristics in heave, roll and pitch degrees of freedom. Heave motion is very important in offshore facilities and have to kept as minimum as possible. As the water depth increases TLPs suffers from some limitations and hence has to be modified to cater to deeper waters. One such concept proposed is Tension Based Tension Leg Platform (TBTLP). In this paper, experimental investigations carried out on a scaled model of a Tension Based Tension Leg Platform in regular waves are reported. This is the first ever experiments that was carried out on a scaled model of the new concept. To investigate the effect of Tension Base, experiments were also conducted on the TLP (without Tension Base) in two different water depths. RAOs have been compared for surge and heave dof of TLP and TBTLP. Numerical modeling of the TLP and TBTLP responses using ANSYS AQWA software are included as well for comparisons.DOI: http://dx.doi.org/10.3329/jname.v11i2.17341

Riser Analysis for a Dry Tree Semi-Submersible

2008 ◽  
Author(s):  
Apurva Gupta ◽  
Chan K. Yang ◽  
John Murray ◽  
Guoan Shen ◽  
Anis Hussain ◽  
...  
Keyword(s):  
Wave Zone ◽  
Tension Leg Platform ◽  
Non Linear ◽  
Heave Plate ◽  
Second Tier ◽  
Offshore Industry ◽  
Motion Characteristics ◽  
Main Components ◽  
Water Depths ◽  
Tree Production

There is currently ongoing interest in the offshore industry to develop a dry tree production semi submersible that has motion characteristics similar as a Spar, but with the functionality of a Tension Leg Platform (TLP) or a Semi in terms of fabrication, installation and commissioning. It has been proposed that the required motions can been achieved by adding a heave plate to an existing deep draft semi with external extendable columns supporting the heave plate. The ESEMI II is such a concept with telescopic structure to lower the Second Tier Pontoon (STP). The riser technology presently used on Spars can be ported to a dry tree semi design assuming the motions are similar. These designs consist of a tensioning system using either buoyancy cans or hydraulic/pneumatic tensioners. The main components of the risers for such a semi-submersible are similar to those of the Spar including Keel Joints and stress joints, where the heave plate on the dry tree semi replaces the soft tank on the Spar. The Top Tensioned Risers (TTR), however, can not be tensioned using simple buoyancy cans and have to be tensioned by non-linear pneumatic tensioners because of exposure in the wave zone. The stroke of the risers in the dry tree semi is estimated to be similar to that of the Spar. The heave plate connectors have to be designed considering not only the hydrodynamic loadings but also horizontal riser loads at the keel as well, which would give enormous moments at the keel and stress joints. The stroke of the riser should also be considered while designing the heave plate connectors. The riser, unlike a Spar, will not be shielded in the hull area, and will be subjected to high currents, and hence the Vortex Induced Vibration (VIV) effects may also be significant. This paper discusses a methodology for riser and VIV analysis, and mitigations, on a dry tree semi-submersible for two water depths.

Analytical investigation of nonlinear heave-coupled response of tension leg platform

2018 ◽  
Vol 233 (3) ◽  
pp. 699-713
Author(s):  
Mohammad Reza Tabeshpour ◽  
Reza Hedayatpour
Keyword(s):  
Degrees Of Freedom ◽  
Structural Response ◽  
Wave Theory ◽  
Equation Of Motion ◽  
Analytical Investigation ◽  
Response Analysis ◽  
Wave Forces ◽  
Tension Leg Platform ◽  
Heave Motion ◽  
Diffraction Effects

Having deep view in structural response of tension leg platform is important issue not only for response analysis but also for engineering design. Coupling between surge and heave motions of tension leg platform is such a problem. Here, tension leg platform motions are considered only in surge and heave degrees of freedom without pitch effect. The coupled term of heave is a nonlinear differential equation. Because the focus of this article is on this term, therefore, Duffing equation of motion in the surge direction is linearized. The wave forces are calculated using Airy’s wave theory and Morison’s equation, ignoring the diffraction effects. Current force also can be very important in dynamic analysis of tension leg platform. Because it affects the term of heave that is coupled with surge. It is shown that the effect of surge motion coupling on heave motion is very important in large displacement of surge motion in many sea states. The main result is that the coupling effects appeared in some frequencies such as heave and surge frequency, twice the frequency of wave, twice the natural surge frequency, and summation and difference of frequency of wave and surge frequency.

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.

Hydrodynamic Analysis of Tension Based Tension Leg Platform

2012 ◽  
Author(s):  
D. S. Bhaskara Rao ◽  
R. Panneer Selvam ◽  
Nagan Srinivasan
Keyword(s):  
Water Depth ◽  
Vertical Plane ◽  
Hydrodynamic Analysis ◽  
Response Characteristics ◽  
Deep Waters ◽  
Economical Design ◽  
Motion Responses ◽  
Offshore Industry ◽  
Response Amplitude Operators ◽  
Water Depths

Tension Leg Platforms (TLPs) are one of the best options for offshore industry in deep waters due to proven motion response characteristics. These are water depth sensitive structures and the motion responses in vertical plane motions (heave, roll and pitch) are critical for a TLP. Tension Based TLP (TBTLP) is a new concept and finds application in much deeper waters. A provision of a tension base at mid-depth results in an economical design of TLP. In fact, the TLP installed at a certain depth without any modifications can be made to be deployed in much deeper water depths by means of a tension base. In this paper, the concept of TBTLP is highlighted and hydrodynamic analysis of the chosen platform has been carried out using ANSYS AQWA package. The motion responses in terms of Response Amplitude Operators (RAOs) of TBTLP with one Tension Base in surge, heave and pitch have been obtained and compared with a TLP without a tension base.

Experimental Studies on Dynamic Response Behavior of Multi-Legged Articulated Tower

2010 ◽  
Author(s):  
Srinivasan Chandrasekaran ◽  
K. Bhaskar ◽  
Mohammed Hashim
Keyword(s):  
Dynamic Response ◽  
Experimental Studies ◽  
Experimental Investigations ◽  
Random Waves ◽  
Response Behavior ◽  
Scaled Model ◽  
Response Characteristics ◽  
Sea Bed ◽  
Motion Characteristics ◽  
Stress Variations

Articulated towers consist of surface piercing columns pinned to sea floor and have increased applications in deep water oil exploration. Vital component is the buoyant shaft connected to sea bed through a universal joint. Design methodologies of these towers ensure reduced motion characteristics with less deck acceleration while loads at the articulated joint are kept to minimum; this is required to establish sufficient stability under working conditions. A Scaled model of a multi-legged articulated tower is experimentally investigated under regular and random waves. Influence of different parameters on the tower response, namely, deck load and wave approach angle are examined in detail. Apart from having increased deck area, multi-legged articulated towers showed controlled dynamic response behavior under environmental loads. Conclusions drawn from the study bring a detailed insight to the design of such platforms. Though few observations inferred from the study are not new, important dynamic response characteristics like bending stress variations are quantified through experimental investigations.

Heave and Pitch Response of an Offshore Platform With Air Cushion Support in Shallow Water

2004 ◽  
Author(s):  
K. P. Thiagarajan ◽  
M. T. Morris-Thomas ◽  
A. Spargo
Keyword(s):  
Linear Wave ◽  
Test Results ◽  
Regular Waves ◽  
Long Wavelength ◽  
Air Cushion ◽  
Decay Tests ◽  
Heave Motion ◽  
The University ◽  
Scaled Models ◽  
Water Depths

Model tests were conducted on two 1:100 scaled models of a typical concrete gravity substructure at the University of Western Australia. The two models had dimensions 0.5m length × 0.5m width with the first model being a sealed closed bottom box of height 0.1m and the second model being an open bottom box with skirt length of 0.1m. The open bottom model had the capacity to hold an air cushion with dimensions 0.49m width × 0.49m length × 0.08m height. Each model was floated at a constant draft of 0.1m and tested in water depths ranging between 0.03m (shallow) and 0.8m (deep). The environment comprised of regular waves with periods ranging between 0.6s and 3.5s and amplitude of 0.08m–0.02m. To quantify the dynamic response the heave and pitch motion of each model were measured. The model test results were compared with a theoretical solution based on long wavelength, linear wave assumptions applied to a box shaped floating vessel without an internal free surface. Results show that experimental trends compare reasonably well with analytical solution. Added mass values were predicted from heave and pitch decay tests. The results show that introducing air cushion support into a CGS increases the pitch response, while having little effect of the heave motion. The theory is also used to delineate regions of safe and unsafe tow-out operations of the air cushion structure.

scholarly journals Comparative Framework Linking Some Capabilities of Small Array Dispositions of Generic Points Absorbers

2017 ◽  
Author(s):  
Lorenzo Baños Hernandez
Keyword(s):  
Degrees Of Freedom ◽  
Radiation Force ◽  
Domain Model ◽  
Irregular Waves ◽  
Wave Direction ◽  
Regular Waves ◽  
Wave Regime ◽  
Variable Distance ◽  
Motion Characteristics ◽  
Generic Points

This thesis completion works it out to deepen into diverse modeling techniques for Point Absorbers. A combined frequency-time domain model is conceived, designed and developed in Matlab with Fortran as a base, leading to obtain physical variables of primary importance, namely position, velocity and power to energy net balance relationships of absorption. Integration of different degrees of freedom with heave as main executable leads in turn to a single buoy motion focus. Acquisition of the needed hydrodynamic coefficients is provided through application of NEMOH \& BEMIO solvers due to the Boundary Element Methodology. Initially, this Wave-to-motion model is validated by comparison with previous experimental results for a floating cone cylinder shape (Buldra-FO3). A single, generic, vertical floating cylinder is contemplated then, that responds to the action of the passing regular waves excitation. Later, two equally sized vertical floating cylinders aligned with the incident wave direction are modeled for a variable distance between the bodies. For both unidirectional regular and irregular waves as an input in deep water, we approximate the convolutive radiation force function term through the Prony method. By changing the spatial disposition of the axisymmetric buoys, using for instance triangular or rectangular shaped arrays of three and four bodies respectively, the study delves into motion characteristics for regular waves. The results highlight efficient layouts for maximizing the energy production whilst providing important insights into their performance, revealing displacement amplification- and capture width-ratios, while deriving in possible interpretations of scenarios related to the the known park effect. These terms are encompassed by the novelty of a new conceptual Post-Processing methodology in the field, which leads to obtain an optimal distance for the separated bodies with effective energy absorption in a regular wave regime. In conclusion, this computational excursion envisions and proposes potential fields of study, which will surely enhance new connections and link this renewable energy form.

Deep Water Current Observations in Lankahuasa Area in the Mexican Gulf of Mexico

2006 ◽  
Author(s):  
C. Garcia Govea ◽  
Juan Jose´ Corte´s Romero ◽  
O. Valle Molina
Keyword(s):  
Water Column ◽  
Deep Water ◽  
Oil Industry ◽  
Water Current ◽  
Current Profile ◽  
The North ◽  
Deep Waters ◽  
Offshore Industry ◽  
Near Future ◽  
Water Depths

In preparation for the near future deep-water exploitation in the Mexican oil industry, the Mexican Petroleum Institute and Pemex carried out the first oceanographic sub-surface mooring installation in deep waters, in Lankahuasa area in 1500 m water depth. The aim of this project is to supply the necessary water column information for planning, installation, development and production activities for the Mexican offshore industry. Parameters measured include, current velocities, current direction, internal waves as well as traditional water quality measurements. Profiles of conductivity, temperature and Depth (CTD) from 100 m up to 2,500 m water depths were obtained from cruises where samples were taken over a wide area during January and February 2005. Salinity and density are calculated from CTD data. Oceanographical parameters were measured by 3 ADCP (Acoustic Doppler Current Profile) and by 2 current meters in the entire water column. The oceanographic situation during the deployment was characterized by the presence of an anticyclonic (clockwise rotating) eddy and a cyclonic one in the area, located to the north of 21° N. Both eddies were slowly propagating in a general southward direction.

scholarly journals Computational Investigation on Various Small Array Dispositions of Generic Points Absorbers

2017 ◽  
Author(s):  
Lorenzo Baños Hernandez
Keyword(s):  
Degrees Of Freedom ◽  
Radiation Force ◽  
Domain Model ◽  
Irregular Waves ◽  
Wave Direction ◽  
Regular Waves ◽  
Wave Regime ◽  
Variable Distance ◽  
Motion Characteristics ◽  
Generic Points

This thesis completion works it out to deepen into diverse modeling techniques for Point Absorbers. A combined frequency-time domain model is conceived, designed and developed in Matlab with FoRtran as a base., leading to obtain physical variables of primary importance, namely position, velocity and power to Energy net balance relationships of absorption. Integration of different degrees of freedom with heave as main executable leads in turn to a single buoy motion focus. Acquisition of the needed hydrodynamic coefficients is provided though application of NEMOH & BEMIO solvers due to the Boundary Element Methodology. Initially, this Wave-to-motion model is validated through comparison with previous experimental results for a floating cone cylinder shape (Buldra-FO3). A single, generic, vertical floating cylinder is contemplated then, that responds to the action of the passing regular waves excitation. Later, two equally sized vertical floating cylinders aligned with the incident wave direction are modeled for a variable distance between the bodies. For both unidirectional regular and irregular waves as an input in deep water, we approximate the convolutive radiation force function term through the Prony method. By changing the spatial disposition of the axisymmetric buoys, using for instance triangular or rectangular shaped arrays of three and four bodies respectively, the study delves into motion characteristics for regular waves. The results highlight efficient layouts for maximizing the energy production whilst providing important insights into their performance, revealing displacement amplification- and capture width-ratios, while deriving in possible interpretations of scenarios related to the the known park effect. These terms are encompassed by the novelty of a new conceptual Post-Processing methodology in the field, which leads to obtain an optimal distance for the separated bodies with effective energy absorption in a regular wave regime. In conclusion, this computational excursion envisions and proposes potentials fields of study, which will surely enhance new connections and link this renewable energy form.

scholarly journals Surge Motion Passive Control of TLP with Double Horizontal Tuned Mass Dampers

2021 ◽  
Vol 26 (1) ◽  
pp. 4-8
Author(s):  
Mohammad Reza Tabeshpour ◽  
Ebrahim Malayjerdi
Keyword(s):  
Degrees Of Freedom ◽  
Passive Control ◽  
Vertical Direction ◽  
Horizontal Displacement ◽  
Regular Waves ◽  
Tuned Mass Dampers ◽  
Six Degrees Of Freedom ◽  
Mass Damper ◽  
And Performance ◽  
Heave Motion

The tension leg platform (TLP) is comprised of a buoyant hull that holds the platform's topside. A group of tendons under the columns connect the TLP to the foundation. The TLP is displaced in six degrees of freedom due to environmental loads. Tendons moor the TLP in vertical direction (heave and pitch). Surge amplitude (horizontal displacement) of TLP is greater than other degrees of freedom. Also heave motion is coupled with surge one. Therefore, it is important to introduce and implement a method to control and reduce displacement of the TLP in horizontal direction. In this paper, a passive control system (double horizontal tuned mass damper (TMD)) is used to mitigate the surge motion of TLP that is under regular waves. Also the efficiency and performance of double horizontal TMD and single horizontal TMD in reduction of surge response is compared.

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