Search

Production risers as well as drilling risers are often subjected to Vortex-induced vibrations (VIV) when exposed to ocean currents. VIV have been observed in the field and can cause fatigue failure and excessive drag on the riser. In order to suppress VIV and reduce drag, fairings are often used. This paper presents hydrodynamic qualification tests for two types of fairings: the short crab claw (SCC) and a tapered dual fin design. The short crab claw fairing design is a novel design that was developed by the Norwegian Deepwater Programme (NDP). As will be detailed in this paper, the SCC design offers very low drag, completely suppresses VIV and reduces riser interference. In 2012, a model test campaign was undertaken to understand and qualify the hydrodynamic performance of fairings at prototype conditions. The program consisted of testing the three fairing geometries and a strake to understand the stand-alone performance in VIV and the performance in interference. This was accomplished by utilizing a single pipe setup for the standalone test and a two-pipe setup for the interference tests. The paper reports the results of the program and draws conclusions on the hydrodynamic performance of the VIV suppression devices tested. Overall, all VIV suppression devices tested were able to suppress VIV with the SCC fairing being the most effective. In all cases tested, the downstream fairings / strakes were very effective in suppressing VIV in an interference scenario where a fairing was placed upstream. Contrary to the well-documented case of two strakes in tandem, in this case the upstream fairings did not reduce the effectiveness of the downstream fairings/strakes.

The objective of this paper is to investigate the predictive capabilities of an anisotropic turbulence model for Helideck turbulence studies on offshore platforms and also to discuss the challenges in fulfilling the regulations and demands from the authorities for ensuring a safe helideck design. A Computational Fluid Dynamics (CFD) study is performed on a Front End Engineering Design (FEED) phase offshore platform geometry using unsteady Reynolds Stress model (RSM) [1] and the mean flow conditions for safe helideck operations are evaluated. The results are compared with an isotropic turbulence model using the realizable-kEpsilon (RKE) model [2] to establish if there is any gain or added merits in using computationally intensive RSM versus RKE model. The result comparison shows that for the skewed wind angles, flow separation from the platform outer edges will develop a swirl that starts to rise towards the helideck areas. This is well captured in the RSM model when compared to RKE model. In addition to numerical prediction, operational experience from pilots and their reactions to turbulence has also been documented in this paper. An open source software tool OpenFOAM is used in this study for the numerical analysis. As a part of this study, OpenFOAM has also been tested for canonical flows and the results are compared with experimental studies. Guidelines for evaluating helideck flow conditions and potential design modifications for safe helideck operations are also discussed in this paper.Copyright © 2015 by ASME

Buoyancy modules are widely used in offshore and subsea fields, such as on pipelines, risers, umbilicals, and ROVs, etc. in operation and installation. Accidental release of subsea buoyancy modules due to broken or damaged parts may pose a potential risk and hazard to offshore vessels, floating platforms and risers & surrounding umbilicals. A released buoyancy module rises and may collide with any floating structures or pipes above it. For offshore and subsea field development, it is important to assess such potential risk to offshore vessels, floating platforms, and risers & umbilicals around them. Accurate prediction of the trajectory and the impact speed of the released buoyancy module is the key component for risk assessment in offshore and subsea field development. This paper presents a Computational Fluid Dynamics (CFD) solution for prediction of the trajectory and velocity of the released buoyancy modules from subsea. Six Degree of Freedom (DOF) rigid body motion of buoyancy module is modeled using an efficient moving mesh approach in transient CFD simulation. The effect of ocean currents at different water depths is considered in the motion of buoyancy modules. This methodology has potential applications in many areas, such as, offshore vessel and floating platform protection, riser and umbilical protection, offshore and subsea field planning and layout, etc. This transient CFD approach has been successfully implemented on typical buoyancy modules and demonstrated effect of ocean currents on the trajectory of the buoyancy modules. Hydrostatic forces, 6DOF motion and the velocities of the buoyancy module were predicted with different ocean current velocities. The approach proposed in this paper captures the physics of released buoyance module in transient CFD and provides a practical tool for determining the trajectory and velocity of the released buoyancy modules from subsea and quantifying the risk for such an event. It can potentially be used for assessing the risk to offshore vessels and floating platforms, risers and umbilicals, as well as for offshore and subsea field planning and layout.

Some drilling operators have experienced a loss of pressure from drilling riser auxiliary lines during operations. In some instances the loss of pressure has been as a result of auxiliary line seals experiencing excessive wear at the pin-box connection. In the case described within this paper, the failure was investigated and attributed to Vortex Induced Vibration of the main drilling riser. The rigid interface between the main riser and the outer auxiliary lines results in transfer of main drilling riser dynamic curvature motions directly into vertical axial motions at the pin-box connection. In the case considered, a high degree of VIV excitation was experienced through the drilling campaign which resulted in excessive wearing and ultimately failure of the pin-box seal. This paper presents a methodology to compute the auxiliary line axial displacement resulting from the drilling riser displacement and curvature. This methodology provides a means of estimating the relative axial motion of the pin-box connection when the main drilling riser is under VIV lock-in. It will also assist in identifying if excessive seal wear will be a concern during a drilling campaign. In this case it suggested that the limiting condition for the drilling riser was not fatigue of the main drilling riser, but wear of the pin-box seal. As a consequence of this investigation, it is recommended to include checks for excessive relative axial motion in general analysis methodology for deepwater drilling risers. As with VIV fatigue issues, the issue may be mitigated through VIV suppression.

The roll motion of ships operating in a seaway is often limiting operations. These limits could be due to, e.g. maximum acceleration, green water, capsize risk or just comfort. Therefore additional roll damping is desired to prevent uncontrolled roll motion. Different means are available to decrease the roll motion of a ship, amongst other these include bilge keels, active fin stabilizers (either for forward or zero speed) and U-shape or free surface anti-roll tanks (ART). The amplitude and phase of the roll opposing moment resulting from the water that moves inside the ART are a function of the geometry of the tank and especially its internal damping. Due to the complex and non-linear nature of this flow, the use of Computational Fluid Dynamics (CFD) was chosen to analyse the details of the flow inside the tank and its anti-roll performance. The present paper focuses on the sensitivity and validation of the anti-roll performances of passive U-type ART using CFD. For this, the incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) code ReFRESCO was used. The sensitivity on the results for the U-tank is analysed by varying the grid resolution and the numerical time step. The two-dimensional (2D) full-scale and Froude based model-scale ReFRESCO results are compared to 2D and 3D full-scale CFD results of Delaunay (2012) [1] and Thanyamanta and Molyneux (2012) [2] and validated with model-scale experimental results of Field and Martin (1975) [3] and MARIN experimental results by Gunsing et al. (2014) [4]. This paper shows the influence of the convective scheme for capturing the free-surface interface and provides recommendations for a time step and grid resolution to effectively calculate the roll damping of an ART.

In the offshore drilling, during emergency disconnect scenario the drilling operation must not be maintained and forced LMRP disconnect procedure takes place [1,2]. Such procedure allows drilling mud to interact with seawater. The paper presents hydrodynamic behavior of a drilling riser when mud is retained and not interacted with seawater. A two-way coupled fluid-structure interaction (FSI) model between a simplified drilling riser structure and mud fluid was studied through techniques of computational fluid dynamics (CFD). The volume of fluid (VOF) hydrodynamics model was used with commercially available software STAR-CCM+ [3]. A 3D finite element (FE) model of a drilling riser was created in FE software ABAQUS [4] to determine the stress and deflection of structural parts of the model due to hydrodynamic loads. In the model, the compressibility [5] and non-linear behavior of the mud was included. The dynamic frequencies of the two domains and possible resonance of the coupled system were investigated. The aim of the study was to verify the dynamic behavior of a riser system with a drilling mud enclosed within the system. The authors of this paper know no similar study of such a problem.Copyright © 2014 by ASME

The vortex-induced motions (VIM) of offshore platforms stand as an intriguing and challenging engineering problem, drawing attention from industry, universities and research institutes. Field observations, model tests and calculations have extensively showed that the complex fluid-structure interaction can result in appreciable motions and increased fatigue of mooring and risers. It is thus a very relevant issue from the engineering standpoint. A large volume of experimental research has been carried out, mainly to verify designs and characterize the occurrence of VIM. Conversely, the numerical investigations applying CFD tools have shown to be a more flexible approach enabling better understanding of the physics at play due to the possibility of investigating the effects of different parameters upon the vortex induced motions of floating platforms. Moreover, the CFD calculations enable investigation of the full-scale behavior of the platforms under VIM, a very controversial issue presently. Bearing upon these issues, the VIM Joint Industry Project aims at increasing physical insight of this phenomenon by means of investigating the influence of geometric design variations, flow conditions and scale effects with the objective of improving practical knowledge that can be applied in the design stage of floating platforms. In this paper, we present some of the CFD studies, results and observations carried out within the JIP, regarding the VIM of a semi-submersible with circular columns in 0 and 45 degrees and over a wide range of reduced velocities. It is confirmed that the 0 degree incidence results in larger motions than the 45 degrees-incidence case, in contrast to the VIM behavior of a semi-submersible with square columns. The tests campaign carried out at the University of São Paulo for the same platform agree with these results. Within the lock-in range, the frequency synchronization of the lift forces on columns and pontoons cause large net transverse forces. Appreciable sway motions thus result. For larger reduced velocities, synchronization of the flow around the columns cease, but the forces on the pontoons then largely contribute to the total force. In this high-reduced velocity range, the phasing between total force and motion is such that energy transfer from the fluid to the body occurs, causing the amplification of the motions.

Drillships have specific features which make ship resistance and propulsion characteristics difficult to predict with simple empirical methods. In this paper, RANSE CFD was used to optimize the hull and appendages of a drillship for speed or fuel consumption. An innovative thruster arrangement was initially designed for dynamic positioning and its performance in transit was verified with the use of CFD. Furthermore a special hydrodynamically shaped moonpool has been developed to eliminate moonpool sloshing during transit, further reducing resistance and increasing safety on board. CFD was also used to determine the propulsion efficiencies of the vessel. An innovative way to use an actuator disc approach was used to calculate effective wake factors. The various CFD calculations and the resulting design modifications are verified and confirmed with calm water resistance and self-propulsion tests. The bow shape modifications reduce the bare hull resistance by 12% and the headbox modifications reduce the added headbox resistance by 26% of the bare hull resistance. The Callirrhoe moonpool design reduces the added moonpool resistance by 37% compared to a conventional moonpool while at the same time eliminates sloshing in transit. The propulsion efficiency is above 60% when the aft thrusters are used, which is deemed high for such a vessel.

Breaking wave-induced loads on offshore structures can be extremely severe. The air entrainment mechanism during the breaking process plays a not well-known role in the exerted forces. This paper present a CFD solver, developed in the Open-FOAM environment, capable of simulating the wave breaking-induced air entrainment. Firstly the model was validated against a bubble column flow. Then it was employed to compute the inline force exerted by a spilling breaking wave on a vertical cylinder in a 3D domain at a laboratory scale. Results showed that the entrained bubbles affected the magnitude of the force partially. Further analyses on the interaction of the bubble plume with the flow around the cylinder are needed.

Marine drilling riser is subject to complicated environmental loads which include top motions due to Mobile Offshore Drilling Unit (MODU), wave loads and current loads. Cyclic dynamic loads will cause severe fatigue accumulation along the drilling riser system, especially at the subsea well head (WH). Statoil and BP have carried out a comprehensive model test program on drilling riser in MARINTEK’s Towing Tank in February 2015. The objective is to validate and verify software predictions of drilling riser behaviour under various environmental conditions by use of model test data. Six drilling riser configurations were tested, including different components such as Upper Flex Joint (UFJ), tensioner, marine riser, Lower Marine Riser Package (LMRP), Blow-Out Preventer (BOP), Lower Flex Joint (LFJ), buoyancy elements and seabed boundary model. The drilling riser models were tested in different load conditions: 1. Forced top motion tests 2. Regular wave test 3. Combined regular wave and towing test 4. Irregular wave test 5. Combined irregular wave and towing test 6. Towing test (VIV) Measurements were made of micro bending strains and accelerations along the riser in both In-Line (IL) and Cross-Flow (CF) directions. Video recordings were made both above and under water. In this paper, the test set-up and test program are presented. Comparisons of results between model test and RIFLEX simulation are presented on selected cases. Preliminary results show that the drilling riser model tests are able to capture the typical dynamic responses observed from field measurement, and the comparison between model test and RIFLEX simulation is promising.

The Steel Lazy Wave Riser (SLWR) configuration is considered as one of the favorable solutions for deepwater applications. This is due to the SLWR’s capability to effectively absorb the dynamic motions from the vessel and the relatively lower cost that it offers. However, the application of SLWRs has its own challenges when it comes to fatigue due to Vortex-Induced Vibrations (VIV). The buoyancy section and the touchdown area may be critical to VIV due to curvature and current exposure onto the area. Furthermore, there is only limited previous research on VIV responses of a SLWR configuration. This paper presents a parametric study of VIV responses of various SLWR systems. The study location is the deeper area of the Norwegian Continental Shelf. The main parametric variations are water depth, the length of the buoyancy section, the dimension of the buoyancy modules and the hydrocarbon content. These variations result in different lazy wave configurations, which give different trends of VIV responses. The analysis works are performed using the computer programs Riflex and VIVANA. The observation results show that, for the type of current used in this study, riser configurations at the same water depth tend to have the same level of fatigue life. In addition, risers in shallower water have a lower fatigue life compared to risers in deeper water due to the current profiles used in this study and the higher system stiffness of the risers at shallower water. The results also show that the buoyant section has only little to modest influence on the VIV-fatigue life. The influence will only become apparent when the buoyancy section creates a sufficiently high arch shape in the lazy wave configuration. The riser’s selfweight mainly affects the riser’s fatigue life at the upper catenary part of the riser. Although the upper catenary part of the riser generally has sufficient VIV-fatigue lifetime, a riser with lighter content has a lower fatigue life at this part compared to a riser with heavier content.

New discoveries of petroleum reservoirs in ultra deep-water depths, like Pre-salt fields in Santos Basin, are demanding new riser systems concepts. In this scenario, the Free-Standing Hybrid Riser (FSHR) system is a viable choice. A submersible buoy connected by rigid and flexible risers constitutes this riser system. The sea current can cause the Vortex-Induced Motion (VIM) of the buoy, which can increase significantly the riser fatigue damage. Although the VIM phenomenon is similar to Vortex-Induced Vibration (VIV), it generally occurs in rigid bodies with low aspect ratio, where end effects causes tridimensional flow behavior. Therefore, the vortex wake characteristics and the hydrodynamics coefficients found for VIV is no longer valid for VIM. In this context, wake oscillator models used for VIV prediction in actual form is not adequate for the VIM prediction of the buoys. In this paper, a VIV wake oscillator model is calibrated for VIM, through hydrodynamic coefficients found in the technical literature. In order to verify accuracy, the VIM calibrated wake oscillator model is used to reproduce some FSHR reduced model tests. The results of amplitude and frequency of oscillation against the reduced velocity obtained from the numerical simulation are compared with the experimental results. The numerical results presented the same trend with some differences in amplitude. The amplitude deviation could be related to the hydrodynamics coefficients used in the calibration of the wake oscillator model.

The VIV oscillations of marine risers are known to increase drag, and lead to structural fatigue. One proven method of suppressing this vibration is the use of fairings and strakes. These coverings essentially modify the flow along the cylinder, tripping the production of Karman vortices so that they act less coherently or far enough downstream so they interact less with the body. The Norwegian Deepwater Programme (NDP) has conducted a project with the objective to develop and qualify effective low drag fairing concepts with respect to VIV mitigation and galloping. Furthermore, emphasis is put on easy handling and installation. This paper describes the work and findings in an early phase of the development. This includes small scale model test campaigns. In addition to the bare riser for reference, the behaviour and performance of a total of 10 different fairing concepts are evaluated. Free oscillation tests are performed in a towing tank, where 2D fairings were tested in a pendulum set-up. The set-up enables free vibrations in up to 3 DOF (in-line and cross-flow vibrations and yaw). Fix tests with the purpose of establishing hydrodynamic coefficients for the various fairings have been performed in a large cavitation tunnel. Clear differences in performance have been noticed; particular for drag and galloping responses. Based on the results from the 2D tests, a screening of the fairing designs has been performed and the findings have set the course for further development of the most promising candidates for real life applications.

In order to design a drilling riser system that meets the operational requirements, it is industry practice to use analytical tools to predict the riser and wellhead fatigue damage. This paper focuses on the comparison between the analysis and field measurements for both the drilling riser and wellhead vortex induced vibration (VIV) fatigue damage, during a recent loop current event in the Gulf of Mexico. The field data, which includes the drilling riser configuration, riser tensioner setting, and loop current data, were considered in this comparison. As one of the key contributors to VIV fatigue, the loop current, was measured from a survey vessel in the field during the blowout preventer (BOP) latched and retrieval period. The analysis utilized the VIV program SHEAR7 V4.6 to calculate the fatigue damage for both the drilling riser and wellhead system. The field measured acceleration data from the installed monitoring system was converted to the fatigue damage by transfer function methods. Key findings and conclusions are summarized to improve future analysis predictions of drilling riser and wellhead fatigue damage.Copyright © 2015 by ASME

The design of semi-submersible platforms for offshore oil and gas operations requires an iterative process between early-stage design, numerical simulation, measurements, and full-scale design. Early stage designs are evaluated using numerical simulations, which are typically validated using measurements of a scaled model tested in a wave tank. Full-scale semi-submersibles present a unique challenge, because of the sheer size of the structure. Since VIV measurements of full scale structures are not possible, numerical simulation plays an important role for evaluating vortex-induced vibration (VIV) effects in the appropriate physical regime. The quantification of error in numerical simulation results is limited to verification-type studies, in which the error is reduced by converging the solution on the computational grid. The importance of grid convergence studies in this field cannot be understated, since it is the only way to judge solution accuracy in the absence of measurement data at the full scale. In this paper, a method for a grid convergence study of vortex-induced vibration (VIV) of a model scale semi-submersible platform is presented, in which solutions are obtained using the ANSYS Fluent CFD solver. Five levels of grid refinement are used, with the finest mesh acting as the reference solution for the coarser four levels. Qualitative results of vorticity, pressure and Q-criterion (vortex identification) are presented. Quantitative results such as the nominal amplitude (A/D) of the sway motion are used for judging the convergence of the solution as the grid is refined.Copyright © 2015 by ASME

Mesh and domain optimization strategies for a RANS solver to accurately estimate the open water propulsive characteristics of fixed pitch propellers are proposed based on examining the effect of different mesh and computation domain parameters. The optimized mesh and domain size parameters were selected using Design of Experiments (DoE) methods enabling simulations to be carried out in a limited memory environment, and in a timely manner; without compromising the accuracy of results. A Reynolds-Averaged Navier Stokes solver is used to predict the propulsive performance of a fixed pitch propeller. The predicted thrust and torque for the propeller were compared to the corresponding measurements. A total of six meshing parameters were selected that could affect the computational results of propeller open water performance. A two-level fractional factorial design was used to screen out parameters that do not significantly contribute to explaining the dependent parameters: namely simulation time, propeller thrust and propeller torque. A total of 32 simulations were carried out only to find out that the selected six meshing parameters were significant in defining the response parameters. Optimum values of each of the input parameters were obtained for the DOE technique and additional simulations were run with those parameters. The simulation results were validated using open water experimental results of the same propeller. It was found that with the optimized meshing arrangement, the propeller opens simulation time was reduced by at least a factor of 6 as compared to the generally popular meshing arrangement. Also, the accuracy of propulsive characteristics was improved by up to 50% as compared to published simulation results. The methodologies presented in this paper can be similarly applied to other simulations such as calm water ship resistance, ship propulsion to systematically derive the optimized meshing arrangement for simulations with minimal simulation time and maximum accuracy. This investigation was carried out using STAR-CCM+, a commercial CFD package; however the findings can be applied to any RANS solver.

Most deepwater tubulars experiencing high currents frequently require vortex-induced vibration (VIV) suppression to maintain an acceptable fatigue life. Helical strakes and fairings are the most popular VIV suppression devices in use today. Marine growth can significantly affect the VIV of a bare riser, often within just a few weeks or months after riser installation. Marine growth can have a strong influence on the performance of helical strakes and fairings on deepwater tubulars. This influence affects both suppression effectiveness as well as the drag forces on the helical strakes and fairings. Unfortunately, many VIV analyses and suppression designs fail to account for the effects of marine growth at all, even on a bare riser. This paper utilizes results from both high and low Reynolds number VIV test programs to provide some design considerations for managing marine growth for VIV suppression devices.

Vortex Induced Vibrations (VIV) may cause fatigue damage to subsea jumpers that are exposed to bottom currents. ExxonMobil Upstream Research Company (URC) has been conducting research on VIV of subsea jumpers since 2011. Model tests conducted on an “M” shaped jumper in 2012 showed that VIV can occur in subsea jumpers over a wide range of bottom current speeds and directions [1]. Presently, there is no well-established industry practice for assessing subsea jumper VIV and determining the need for its suppression. In this paper, we present two different methods for characterizing jumper VIV response based on the model test data described in [1]. Specifically, these methods consist of spectral analysis of local response and modal scalar analysis of global response. These methods are used to analyze measured response over a wide range of towing speeds and towing directions. A brief summary of the findings are provided and some general conclusions are drawn.Copyright © 2015 by ASME

This paper present results from numerical simulations and laboratory experiments investigating the flow around a riser with fairings at Reynolds number of 5000. We present fully resolved direct numerical simulations (DNS), large eddy simulations (LES) and compare the results with flowfields obtained from particle image velocimetry (PIV) experiments in a circulating water tunnel. The DNS and LES results do agree very well on surface integral quantities such as drag and lift force, but there are discrepancies in first order statistical flow parameters such as recirculation length. This indicate that a comparison of force coefficients is not sufficient to validate this type of bluff body wake flows. Comparing the simulation data with the experimental PIV data, also reveals significant discrepancies in the mean flow field, although the Strouhal number agrees between DNS and PIV results.Copyright © 2015 by ASME

This paper reports calculations of three dimensional (3D) unsteady cross flow over two ship sections in close proximity and compares the results with measurements. The ship sections have different breadth and draft, and represent typical situations in a ship-to-ship marine operation in a cross current. The behavior of the vortex-shedding around the two different ship hull sections is investigated numerically by CFD methods and experiments. For the two sections, simulations are done for several Reynolds numbers by using the dynamic Smagorinsky Large Eddy Simulation (LES) turbulence model. Finally the cross flow past the ship sections in side-by-side position is simulated and vortex interaction between the sections is found by using the software (Ansys) FLUENT. The numerical predictions are compared with PIV results taken in a circulating water tunnel.Copyright © 2014 by ASME

In recent years, the study of flow-induced erosion phenomena has gained interest as erosion has a direct influence on the life, reliability and safety of equipment. Particularly significant erosion can occur inside the drilling tool components caused by the low particle loading ( A finite-volume based CFD-erosion model was developed using a commercially available CFD code. The CFD model involves fluid flow and turbulence modeling, particle tracking, and application of existing empirical erosion models. All parameters like surface velocity, particle concentration, particle volume fraction, etc., used in empirical erosion equations are obtained through CFD analysis. CFD modeling parameters like numerical schemes, turbulence models, near-wall treatments, grid strategy and discrete particle model parameters were investigated in detail to develop guidelines for erosion prediction. As part of this effort, the effect of computed results showed good qualitative and quantitative agreement for the benchmark case of flow through an elbow at different flow rates and particle sizes. This paper proposes a new/modified erosion model. The combination of an improved CFD methodology and a new erosion model provides a novel computational approach that accurately predicts the location and magnitude of erosion. Reliable predictive methodology can help improve designs of downhole equipment to mitigate erosion risk as well as provide guidance on repair and maintenance intervals. This will eventually lead to improvement in the reliability and safety of downhole tool operation.

Nowadays, discoveries of petroleum reservoirs are located in ultra deep-water depths. In this scenario, risers systems generally demand submersible buoys to support the riser, in order to reduce weight in floating platform and riser tensioners. Usually, these buoys are installed below 200 meters depth to avoid the wave forces. However, in this condition the sea current cause the Vortex-Induced Motion (VIM) of the buoys, which can increase significantly the riser fatigue damage. Although the VIM phenomenon is similar to Vortex-Induced Vibration (VIV), it generally occurs in rigid bodies with low aspect ratio, where end effects causes tridimensional flow behavior. Therefore, the vortex wake characteristics and the hydrodynamics coefficients found for VIV is no longer valid for VIM. It makes complex the prediction of VIM in buoys. In this paper, a semi-empirical model using hydrodynamic coefficients found for low aspect ratio cylinders are presented. In order to verify accuracy of numerical simulations, results are compared with experimental data presented in the literature and a good agreement is found.Copyright © 2014 by ASME

Recent advances in computers and software have enabled the direct simulation of the vortex induced vibrations of long risers. Most of the problems solved to date have focused on bare or straked risers with a mild catenary shape. However fielded risers often make use of large buoyancy elements and may have a very general “lazy wave” shape. These features introduce new problems of solution stability and run time. In this paper we address some of these issues. We develop efficient meshing strategies for risers with buoyancy modules. The models are tested against published laboratory experiments. The CFD solutions show the same effects of changing excitation frequencies with changing buoyancy coverage and other effects as seen in the experiments. A general approach is proposed to build large problems with an L/D of 10,000 and a lazy wave shape. This approach demonstrated with an example problem.Copyright © 2014 by ASME

The overset grid method has been implemented in the open source code OpenFOAM. The purpose of this work is to validate the overset code in OpenFOAM and demonstrate the capability and flexibility of overset grid approach to solve complex situations. Ship motions of KCS in head waves with and without rotating propeller are investigated using overset grid method in this paper. Two conditions are conducted. The first case involves the model without propeller advancing at a speed of 1.701 m/s, corresponding to Fr = 0.26 and Re = 6.82×106. Incident regular wave of wave length λ = 1.15Lpp and wave height Hw = 0.084m is adopted. A grid convergence study is conducted for the validation of overset grid method. In the second case, a rotating propeller is installed on the KCS model. The seakeeping characteristics of KCS model with rotating propeller in head waves are investigated numerically. The motion responses and propeller thrust and torque are analyzed and compared with experimental data.Copyright © 2014 by ASME

Ships are typically designed for a life cycle of about 20–25 years, with a specific transportation task, that suits the instant or estimated requirements of the owner or operator. Anyhow the business model might change due to a multitude of reasons and force the owner to buy new ships or modify the existing. Such an event took place in the year 2008 with the beginning of the financial crisis and the resulting recession, which lead to a drastic decrease of the global volume of cargo. This paper describes the re-design of the propulsion system of an existing post pan-max container vessel to suit the new economical boundary conditions.Copyright © 2014 by ASME

This paper presents a multiphysics approach for characterizing flow-induced vibrations in a subsea jumper subject to pressure fluctuation due to downstream slugging and external vortex shedding effects due to ocean current. In this study the associated fluid properties, phase behavior, and slugging dynamics were all characterized at subsea condition using PVTSIM and OLGA programs, respectively; the outcomes were then applied to a two-way fluid-structure interaction analysis (FSI) to quantify the vibration response. To mitigate the resonant phenomenon, detailed modal analysis was also conducted to check the modal shapes and natural frequencies. Therefore, this study integrated the best practices in flow assurance study (OLGA and PVTSim), computational fluid dynamics simulation (CFD), and computational structure analysis (FEA), and provided a complete solution to the fluid-structure interaction involved in a subsea jumper. It is revealed that both the slugging flow and the external ocean current induce vibration response in a subsea jumper. Compared to the vortex-induced vibration due to the external current and the flow-induced vibration due to the internal flow, the pressure fluctuation due to the slug plays a dominant role in generating excessive vibration and fatigue failure of a subsea jumper. Although this study focused on a subsea jumper only, the same approach can be applied to subsea flowline, subsea riser, and other subsea structures.

In general, the speed power performance of ships is optimized for design speed and draught in accordance with the contract condition. But, the contract condition may not be always the same as the actual operating condition. Therefore, in order to reduce the fuel consumption practically, it is necessary to optimize the performance under various conditions considering the actual voyage. This is the reason that the trim optimization covering various operating profiles becomes the main issue in reducing fuel oil consumption. In this paper, a numerical study is carried out to optimize trim conditions through the computational evaluation system called SoLuTion developed by Samsung Heavy Industries Co. (SHI) with variation in draught, ship speed and voyage trim. In order to get more accurate results in resistance and self-propulsion performance, the Reynolds-Averaged Navier-Stokes (RANS) equations including Volume of the Fluid (VOF) method by Hirt and Nichols (1981) for free-surface boundary condition and moving mesh technique for propeller rotation effect are employed as governing equations. Reynolds Stresses Model (RSM) with the wall function is applied as a turbulence model for turbulent flow computation. Through this study, the followings are the main three factors to be considered in evaluation of the quantitatively accurate speed performance by varying the draught, speed and voyage trim. First, the distance from hull surface to the first grid point should be adjusted to eliminate the effects of frictional resistance. Second, the grid system should be generated to avoid the grid dependency on variation of draught. Finally, the running trim and sinkage of the voyage conditions should be considered. The results of the trim optimization performed numerically are well-matched with the towing test results conducted at Samsung Ship Model Basin(SSMB). As the results of this study, it is confirmed that SoLuTion is a useful and efficient tool for trim optimization and the provided optimum trim will be able to contribute to fuel savings under the operating conditions. From trim optimization study, it is found that there is certain level of effects due to the bulb and transom immersion to find the optimum trim condition. Also SoLuTion is applicable not only to trim optimization but also to parametric studies in optimum shape of the ships considering the actual operating profile.