CFD Analysis of a LNGC Carrier in Waves

2012 ◽  
Author(s):  
Emmanuel Guilmineau ◽  
Alban Leroyer ◽  
Michel Visonneau ◽  
Emmanuel Ory
Keyword(s):  
Oil And Gas ◽  
Model Tests ◽  
Product Line ◽  
Irregular Waves ◽  
Head Wave ◽  
Linear Potential ◽  
Cfd Simulations ◽  
Wave Condition ◽  
Numerical Predictions ◽  
Cfd Method

Single Buoy Moorings (SBM) Offshore is a pioneer in the offshore and gas industry. Its product line is the supply of facilities and services for the development and production of offshore oil and gas fields as well as the systems relevant to the mooring technology at large. SBM is currently developing various concepts aimed at offloading LNG (Liquefied Natural Gas) carriers offshore. These concepts whether they assume tandem or side-by-side offloading have in common a building block: the LNG carrier. Owing to its unusual shape (shallow draft, non wall sided hull at the waterline with a flared bow and a transom stern and the presence of a bulb just below the sea surface) at least compared to standard VLCCs (Very Large Crude Carrier), difficulties arise when performing diffraction calculations and when comparing model test results in monochromatic, bi-chromatic and irregular waves with numerical time domain simulations. The main objective is to identify whether differences between model tests and standard numerical predictions based on linear potential theory can be bridged in increasingly complex wave fields by resorting to CFD simulations. The CFD software used is ISIS-CFD, developed by the Numerical Modelling Group of the Fluid Mechanics Laboratory of Ecole Centrale de Nantes and distributed as commercial software by NUMECA International under the name FINE/Marine. CFD simulations have been performed in monochromatic head wave condition with and without the 4-line mooring system to prevent the LNG carrier from drifting away. The CFD method is described and a comparison between model tests and simulations is presented. CFD shows that it is able to predict the motions measured in model tests. In addition, both the wave frequency and the natural frequency of the mass spring system are correctly linked with the frequencies of the predicted motions.

Resonant Vibrations of Riser Guide Tubes Due to Wave Impact

2004 ◽  
Author(s):  
Arne Nestega˚rd ◽  
Arve Johan Kalleklev ◽  
Kjell Hagatun ◽  
Yu Lin Wu ◽  
Sverre Haver ◽  
...  
Keyword(s):  
High Frequency ◽  
Rapid Change ◽  
Ocean Basin ◽  
Model Tests ◽  
Slender Body ◽  
Irregular Waves ◽  
Resonant Vibrations ◽  
Wave Impact ◽  
Numerical Predictions ◽  
Steep Waves

The Kristin platform is a catenary moored semi-submersible production vessel (SSPV) intended for production of gas at the Kristin field at Haltenbanken. Kristin has 24 riser guide tubes for tie in of flexible risers, umbilicals and electric cables to the riser balcony. The riser guide tubes (RGT) provide the necessary guiding, support and protection for risers and cables. The guide tubes run vertically from the deck and through the extended east pontoon. The guide tubes are welded to the pontoon and horizontally supported at the underside of the balcony deck. During model tests of the Kristin platform performed in the Ocean Basin laboratory at Marintek, high frequency in-line vibrations of the RGTs were observed during passage of steep waves. The resonance period for the individual RGTs is 0.3 sec. To mitigate the vibration problem, a vibration suppression arrangement of stiff rods was introduced between the guide tubes. Model tests were performed with respect to extreme- and fatigue loads in regular and irregular waves, with and without the suppression arrangement. The model included the floating framework representing the hull and the 24 RGTs with correct diameter and resonance period. The model was suspended in a horizontal mooring system, giving resonance periods in surge and sway close to the prototype platform. A load-response model for the interaction between large steep waves and vertical flexible cylinders has been developed. A slender body load model derived from Morison’s equation is shown to be able to excite the resonant vibrations. The dominant part of the loading comes from the rapid change of added mass momentum, giving rise to an additional slamming term in the load formulation. The structural response is calculated from a recognized non-linear slender body response program. Numerical simulations have been carried out and compared with model tests for both regular and irregular waves. The numerical predictions confirm the effect observed in the model tests; i.e. connecting the tubes generally leads to a reduction of the high frequency response amplitudes.

scholarly journals Experimental Investigation of Wave-Induced Hydroelastic Vibrations of Trimaran in Oblique Irregular Waves

2016 ◽  
Vol 2016 ◽  
pp. 1-17 ◽  
Author(s):  
Haoyun Tang ◽  
Huilong Ren ◽  
Hui Li ◽  
Qi Zhong
Keyword(s):  
Longitudinal Vibration ◽  
Model Tests ◽  
Irregular Waves ◽  
Wave Impact ◽  
Wave Condition ◽  
Strength Assessment ◽  
Irregular Wave ◽  
Hydroelastic Vibrations ◽  
Structural Parts ◽  
Wave Induced

The irregular wave condition, especially the oblique irregular wave condition, is the actual circumstances when trimaran is sailing in sea. In order to identify the characteristic of the wave-induced hydroelastic vibration in irregular waves, as well as investigate the change of vibration in different oblique irregular wave conditions, trimaran model tests were conducted to measure vibrations, wave impact, and motion under different azimuth and wave height. The vibration on main hull, side hull, and cross-desk is measured and analyzed separately to observe the influence of irregular wave in different structural parts. The longitudinal vibration, transverse vibration, and torsion are also included in the model tests measurement to investigate the relationship between these vibration deformation components and parameters of the irregular waves. The wave-induced hydroelastic vibrations and whipping effect is extracted and analyzed to find influence of whipping and springing on the total vibration. Based on the analysis, the dangerous positions and the critical waves condition is introduced to ensure that the subsequent structural strength assessment is more reliable.

CFD Analysis of Waves Over a Submerged Cylinder in Close Proximity of the Free Surface

2014 ◽  
Author(s):  
Harald Ottens ◽  
Alessio Pistidda ◽  
Radboud van Dijk
Keyword(s):  
Inviscid Flow ◽  
Wave Force ◽  
Model Tests ◽  
Irregular Waves ◽  
Ship Motions ◽  
Wave Forces ◽  
Cfd Simulations ◽  
Submerged Body ◽  
Submerged Cylinder ◽  
Water Elevation

Diffraction programs using potential theory are a quick and effective method in calculating wave forces and ship motions. However in cases where a small layer of water is present on top of a submerged body diffraction calculations overpredict motion and wave force RAOs. This shortcoming of diffraction programs is observed after conducting model tests on a captive submerged cylinder and a free floating SSCV. Unrealistic high wave elevations were predicted by diffraction programs on top of the submerged body. In a previous study a damping lid is implemented [1], to decrease the water elevation to realistic values. In this study CFD is used to simulate the captive submerged cylinder in regular waves with different wave heights, wave periods and different submerged drafts. In addition irregular waves are used in the simulation matching the wave spectra used in the model tests. The simulations are transient and require high CPU usage, therefore the influence of numerical settings on wave propagation is investigated. Turbulent, laminar and inviscid flow are applied to evaluate which flow phenomena are important. The forces in heave and surge direction are validated with model test data of the captive cylinder. The numerical water elevation on top of the captive cylinder will be used to gain insight in the fluid flow and can be used as a guideline for the use of damping lids in diffraction programs. This paper will focus on the CFD simulations and the validation with available forces obtained by model tests of the captive submerged cylinder. It will address the use of regular and irregular waves constructing the force RAO for this non-linear phenomenon. Lessons learnt to improve the CFD simulations as well as limitations of constructing RAOs using CFD from an engineering perspective will be addressed as well.

scholarly journals A Comparative Analysis Between Optimized and Baseline High Pressure Compressor Stages Using Tridimensional Computational Fluid Dynamics

2016 ◽  
Vol 6 (4) ◽  
pp. 1103-1108 ◽  
Author(s):  
V. Dragan ◽  
I. Malael ◽  
B. Gherman
Keyword(s):  
Oil And Gas ◽  
Pressure Ratio ◽  
Oil And Gas Industry ◽  
Successful Implementation ◽  
Cfd Simulations ◽  
Current Case ◽  
Gas Industry ◽  
High Pressure Compressor ◽  
Cfd Method

Re-vamping of industrial turbo-machinery is commonplace in the oil and gas industry in applications where subterranean combustion is used for oil extraction. The current case study refers to such an industrial compressor re-vamping, using a state of the art 3D fully viscous CFD methodology coupled with artificial neural networks (ANNs) and genetic algorithms (GA). The ANN is used to establish correlations within a database of CFD simulations of geometrical variations of the original rotor and the GA uses those correlations to estimate an optimum. The estimate is then tested with the same CFD method and the results are fed back into the database, increasing the accuracy of the ANN correlations. The process is reiterated until the optimum estimated by the GA is confirmed with the CFD simulations. The resulting geometry is superior to the original in terms of efficiency and pressure ratio as well as the range of stabile operation, as confirmed by the successful implementation in the field. In this paper we present an analysis of why the optimized geometry achieves superior performances to the original one. Further work will present comparison between the detailed experimental data and CFD.

scholarly journals Two-phase CFD simulation of the monodyspersed suspension hydraulic behaviour in the tank apparatus from a circulatory pipe

2008 ◽  
Vol 10 (1) ◽  
pp. 22-27 ◽  
Author(s):  
Roch Plewik ◽  
Piotr Synowiec ◽  
Janusz Wójcik
Keyword(s):  
Cfd Simulation ◽  
Fluidised Bed ◽  
Cfd Simulations ◽  
Two Phase ◽  
Hydraulic Behaviour ◽  
Hydraulic Conditions ◽  
The One ◽  
Cfd Method ◽  
Multi Phase ◽  
The Ideal

Two-phase CFD simulation of the monodyspersed suspension hydraulic behaviour in the tank apparatus from a circulatory pipe The hydrodynamics in fluidized-bed crystallizers is studied by CFD method. The simulations were performed by a commercial packet of computational fluid dynamics Fluent 6.x. For the one-phase modelling (15), a standard k-ε model was applied. In the case of the two-phase flows the Eulerian multi-phase model with a standard k-ε method, aided by the k-ε dispersed model for viscosity, has been used respectively. The collected data put a new light on the suspension flow behaviour in the annular zone of the fluidised bed crystallizer. From the presented here CFD simulations, it clearly issues that the real hydraulic conditions in the fluidised bed crystallizers are far from the ideal ones.

Numerical and Experimental Analysis of the Tensile and Bending Behaviour of CFRP Cables

2017 ◽  
Vol 25 (9) ◽  
pp. 643-650
Author(s):  
Eduardo Antonio Wink de Menezes ◽  
Laís Vasconcelos da Silva ◽  
Carlos Alberto Cimini Junior ◽  
Felipe Ferreira Luz ◽  
Sandro Campos Amico
Keyword(s):  
Analytical Model ◽  
Oil And Gas ◽  
Steel Wire ◽  
Small Diameter ◽  
Oil And Gas Industry ◽  
Small Radius ◽  
Tensile Behaviour ◽  
Specific Strength ◽  
Numerical Predictions ◽  
Bending Behaviour

Due to their high fatigue life, specific strength and specific stiffness in comparison with steel, carbon-fibre reinforced polymer (CFRP) cables have attracted the infrastructure industry interest in recent years, primarily for use as structural tendons. Particularly the oil and gas industry showed interest for application in offshore platform anchorage systems, because of their exceptional corrosion and creep/relaxation behaviour. In such applications, the cables need to be tensioned in service and to be bent around relatively small-diameter spools for transportation and maintenance. Therefore, their tensile and bending behaviour is a subject of great concern. The aim of this work was to perform a test program on 1 × 19 CFRP cables in two different situations: tensile loading and four-point bending loading. Finite element models were developed to simulate both conditions, including frictional contact between the cable wires. A simplified analytical model was also used to predict the cable behaviour in tension. Numerical predictions were compared to experimental data showing relatively good accuracy, unlike the verified analytical model. CFRP cables presented outstanding tensile behaviour, but bending over small radius spools could not reach the performance of steel wire ropes. Furthermore, simulation could only fairly predict bending below strains of μ1,000 μe for the external rods, beyond which the cable presented highly non-linear behaviour that could not be simulated by the numerical model.

Guidelines for CFD Simulations of Spar VIM

2013 ◽  
Author(s):  
Charles Lefevre ◽  
Yiannis Constantinides ◽  
Jang Whan Kim ◽  
Mike Henneke ◽  
Robert Gordon ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Test Data ◽  
Model Test ◽  
Model Tests ◽  
Full Scale ◽  
Mooring System ◽  
Time Step ◽  
Cfd Simulations ◽  
Scaled Model ◽  
Sway Motion

Vortex-Induced Motion (VIM), which occurs as a consequence of exposure to strong current such as Loop Current eddies in the Gulf of Mexico, is one of the critical factors in the design of the mooring and riser systems for deepwater offshore structures such as Spars and multi-column Deep Draft Floaters (DDFs). The VIM response can have a significant impact on the fatigue life of mooring and riser components. In particular, Steel Catenary Risers (SCRs) suspended from the floater can be sensitive to VIM-induced fatigue at their mudline touchdown points. Industry currently relies on scaled model testing to determine VIM for design. However, scaled model tests are limited in their ability to represent VIM for the full scale structure since they are generally not able to represent the full scale Reynolds number and also cannot fully represent waves effects, nonlinear mooring system behavior or sheared and unsteady currents. The use of Computational Fluid Dynamics (CFD) to simulate VIM can more realistically represent the full scale Reynolds number, waves effects, mooring system, and ocean currents than scaled physical model tests. This paper describes a set of VIM CFD simulations for a Spar hard tank with appurtenances and their comparison against a high quality scaled model test. The test data showed considerable sensitivity to heading angle relative to the incident flow as well as to reduced velocity. The simulated VIM-induced sway motion was compared against the model test data for different reduced velocities (Vm) and Spar headings. Agreement between CFD and model test VIM-induced sway motion was within 9% over the full range of Vm and headings. Use of the Improved Delayed Detached Eddy Simulation (IDDES, Shur et al 2008) turbulence model gives the best agreement with the model test measurements. Guidelines are provided for meshing and time step/solver setting selection.

scholarly journals OPTIMIZATION OF THE WAVECAT WAVE ENERGY CONVERTER

2012 ◽  
Vol 1 (33) ◽  
pp. 5 ◽  
Author(s):  
Hernan Fernandez ◽  
Gregorio Iglesias ◽  
Rodrigo Carballo ◽  
Alberte Castro ◽  
Marcos Sánchez ◽  
...  
Keyword(s):  
Physical Model ◽  
Wave Energy ◽  
Model Tests ◽  
Irregular Waves ◽  
Intermediate Water ◽  
Plan View ◽  
Santiago De Compostela ◽  
Wave Energy Converters ◽  
Physical Model Tests ◽  
The Difference

The development of efficient, reliable Wave Energy Converters (WECs) is a prerequisite for wave energy to become a commercially viable energy source. Intensive research is currently under way on a number of WECs, among which WaveCat©—a new WEC recently patented by the University of Santiago de Compostela. In this sense, this paper describes the WaveCat concept and its ongoing development and optimization. WaveCat is a floating WEC intended for operation in intermediate water depths (50–100 m). Like a catamaran, it consists of two hulls—from which it derives its name. The difference with a conventional catamaran is that the hulls are not parallel but convergent; they are joined at the stern, forming a wedge in plan view. Physical model tests of a 1:30 model were conducted in a wave tank using both regular and irregular waves. In addition to the waves and overtopping rates, the model displacements were monitored using a non-intrusive system. The results of the physical model tests will be used to validate the 3D numerical model, which in turn will be used to optimize the design of WaveCat for best performance under a given set of wave conditions.

Numerical Predictions and Verifications for Hydrodynamic Performance of Bidirectional Tidal Stream Turbine

2012 ◽  
Vol 229-231 ◽  
pp. 2478-2480
Author(s):  
Bin Guo ◽  
Da Zheng Wang ◽  
Jun Wei Zhou
Keyword(s):  
Hydrodynamic Performance ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Numerical Predictions ◽  
Ansys Cfx ◽  
Tidal Stream ◽  
Cfd Method ◽  
Tidal Stream Turbine ◽  
Bem Theory ◽  
Blade Element

In this paper, the tidal stream turbine blade is designed by using blade element momentum (BEM) theory. The bidirectional airfoil is created derived from NACA airfoil. Ansys-CFX is used to predict the hydrodynamic performance of this bidirectional airfoil, and it turns out that the bidirectional airfoil works well at both of the tidal current directions. A test turbine named rotor 2 is used, and a comparison is made between experimental results of the test turbine and numerical prediction results to prove the correctness of the numerical method. The power coefficient of bidirectional tidal stream turbine obtained by CFD method is 39.36% at the design tip speed ratio.

Experimental Assessment of the Performance of CECO Wave Energy Converter in Irregular Waves

2018 ◽  
Author(s):  
Claudio A. Rodríguez ◽  
F. Taveira-Pinto ◽  
P. Rosa-Santos
Keyword(s):  
Wave Energy ◽  
Transfer Functions ◽  
Nonlinear Effects ◽  
Model Tests ◽  
Experimental Results ◽  
Irregular Waves ◽  
Scale Model ◽  
Experimental Assessment ◽  
Simplified Approach ◽  
Wave Basin

A new concept of wave energy device (CECO) has been proposed and developed at the Hydraulics, Water Resources and Environment Division of the Faculty of Engineering of the University of Porto (FEUP). In a first stage, the proof of concept was performed through physical model tests at the wave basin (Rosa-Santos et al., 2015). These experimental results demonstrated the feasibility of the concept to harness wave energy and provided a preliminary assessment of its performance. Later, an extensive experimental campaign was conducted with an enhanced 1:20 scale model of CECO under regular and irregular long and short-crested waves (Marinheiro et al., 2015). An electric PTO system with adjustable damping levels was also installed on CECO as a mechanism of quantification of the WEC power. The results of regular waves tests have been used to validate a numerical model to gain insight into different potential configurations of CECO and its performance (López et al., 2017a,b). This paper presents the results and analyses of the model tests in irregular waves. A simplified approach based on spectral analyses of the WEC motions is presented as a means of experimental assessment of the damping level of the PTO mechanism and its effect on the WEC power absorption. Transfer functions are also computed to identify nonlinear effects associated to higher waves and to characterize the range of periods where wave absorption is maximized. Furthermore, based on the comparison of the present experimental results with those corresponding to a linear numerical potential model, some discussions are addressed regarding viscous and other nonlinear effects on CECO performance.

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