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Vortex-Induced Vibration (VIV) has emerged as a crucial problem that may arise during a drilling operation, which could result in riser failure. Engineers focus on drilling riser's flow characteristics and controls with the intention of improving the drilling environment. Auxiliary lines or control rods are usually placed around the main drilling riser to suppress the VIV. However, the issue related to the flow past drilling riser system with auxiliaries has yet to be resolved. The flow characteristics around a riser system with auxiliaries were analysed in this research. The simulations were conducted using Computational Fluid Dynamics (CFD) software, Altair AcuSolve. This work focuses on the influence of various gap ratios (G/D) and diameter ratios (d/D) on the vortex interaction. A main cylinder with six auxiliary lines was modelled with G/D of 0 to 2.0 and d/D of 0.10 to 0.60 to simulate the riser system. The simulations were carried out at Reynold Number of 200 in the laminar flow regime. The results revealed that the hydrodynamic forces decreased when d/D and G/D increased. The vortex shedding was significantly reduced for auxiliary lines with G/D between 0.3 and 1.4. The numerical simulation results indicated that the vortex interaction in the wake region was, and the hydrodynamic forces were reduced due to the auxiliary lines configurations. The findings of this study are intended to contribute a new CFD simulation result for a better prediction of VIV on a drilling riser with auxiliary lines.

Prediction of ship’s total resistance of a pusher-barge system has become enormous complexity involving nonlinear-hydrodynamic flows behaviour along their hull forms. Both of empirical and simplified numerical solutions may still lead into inaccurate results due to presence of nonlinear characteristics of the pressure and viscous resistances. The use of a more sophisticated method would obviously necessitate to solve the above problem. This paper presents a Computational Fluid Dynamics (CFD) approach to predict the total ship’s resistance of a pusher-barge system at various barge’s configurations. To achieve such objective, four different configurations of the barge models incorporated with various Froude numbers have been taken into account in the computational simulation. In general, the results revealed that the increase of Froude number (Fr = 0.182 to 0.312) was proportional to the magnitude of RT, RP and RV. Regardless of the various Froude number, the pusher-barge system with a 13BP configuration provides the highest resistance compared to the 12BP and 11BP. In addition, the arrangement of barges in the longitudinal (12BP) and lateral (21BP) configurations produced a significant effect with increases in RT, RP and RV values of 110%, 167.5% and 77.6%, respectively. The possible reason for this is that the increase of the total wetted surface area for 21BP has produced to a proportionally higher amount of the pressure and viscous resistance. Overall study, the numerical results were presented and analysed based on few aspects involved the total resistance and resistance coefficient in terms of pressure and viscous resistance of the pusher-barge system. This analysis provides very valuable information on choosing the most reliable arrangement of pusher-barge system. This analysis provides very valuable information on choosing the most reliable arrangement of pusher-barge system

Platform decommissioning activities have been increasing due to unproductive fields and unstable oil prices. One of the decommissioning methods used by the oil and gas companies is by converting the platform into an artificial reef through the rigs-to-reef (R2R) programme. The programme benefits the marine life and increases the marine productions. In this study, the dynamic responses and flow characteristics of jacket platforms were investigated using computational fluid dynamics (CFD) analysis. Three jacket structures with different sizes were used to investigate the suitability of the structure as a potential artificial reef. The pressure exerted on the structure as well as the back eddies and upwelling phenomenon were also investigated. This is to ensure the settlement of the coral larvae and attract marine life to inhabit around the artificial reef. The results show that the platform size and configurations are the significant criteria to design any artificial reef. The pressure on the jacket member is in the acceptable range. Higher efficiency index of back eddy and upwelling could also be obtained by smaller jacket structures.

The current study improved the predictive capability of the biological reefing viability index (BRVI) calibrated using local data. The prediction capability of the BRVI improved from 61% to 76% accuracy out of the 181 locations where the underwater videos available for verification. The BRVI includes corals larvae density, age of larvae at site, sea current, sea temperature, chlorophyll-a, water depth and sediment type to predict biological productivity of an area. Among the parameters, corals larvae density and age of the larvae are the most critical parameters that influent establishment of new biological ecosystem. The BRVI uses settlement of corals larvae as the precursors for the establishment of new habitats in the offshore environment because scleractinian corals is known to be able to form backbone of a new habitat in the environment. In this approach, the BRVI focuses on habitat creation instead of just being a fish aggregating device (FAD) when an artificial reef is deployed in an area. The BRVI can be used as a rapid screening tool to identified potential area for deployment of artificial reefs. The BRVI could reduce the chances of artificial reefs deployment that failed to address its objectives and intended outcomes.

In Malaysia, numerous offshore oil and gas platforms are approaching the end of their operational lifespans and will soon be scheduled for decommissioning. Traditional decommissioning typically involves the complete removal of the platform from the seabed, consequently resulting in the destruction of the established marine life communities present on the structure. A Rigs-to-Reefs strategy provides an alternative to the complete removal of obsolete, non-productive offshore oil and gas platforms, by converting the platform into a permanent artificial reef by utilizing one of the following three methods: partial removal or topple-in-place (in-situ), or tow and place (ex-situ). In-situ reefing provides a means of conserving the marine communities found on the platform by decommissioning the platform jacket in place as an artificial reef. However, not all platforms are good candidates for a Rigs-to-Reef conversion. Thus, pre-decommissioning biological assessments should be undertaken to determine the most appropriate decommissioning strategy on a case-by-case basis. In this study, a biological assessment was developed to catalog the marine life assemblages present on two offshore oil and gas platforms in Malaysia using remotely operated vehicles. Given the limited amount of biological data available on the marine ecosystems found on Malaysia’s platforms, this data may be useful for minimizing adverse impacts of platform removal, while enhancing benefits to the marine environment.

Floating structures, such as Spar platform, are likely to experience significant motions while operation due to Vortex-induced Motion (VIM). The main features of VIM include aspect ratio and mass r...

Overtopping breakwater for energy conversion (OBREC) is integration between breakwater and wave energy converter (WEC) that allows incoming waves to be stored in the reservoir. The higher the overtopping amount collected in a reservoir, the greater the energy generated will be. Hence, most of the overtopping concept has attempted to maximize the inclusion of water in the reservoir by optimizing geometrical parameters, particularly the ramp angle. However, the studies corresponding to ramp shapes geometries have not been adequately reviewed. Most studies only focused on the usage of linear overtopping ramp shape. There is still limited knowledge on the influence of different ramp shape parameters towards the overtopping wave. Thus, this paper aimed to push the border of available knowledge by investigating the influence of the ramp shape parameters to the overtopping wave discharge through simulation and experimenting approaches. Seven different ramp shapes have been tested under Malaysia&rsquo, s wave condition and a new ramp shape parameter allowing for maximized overtopping wave on OBREC is presented.

Decommissioning of the offshore platform as an artificial reef, known as Rigs-to-Reefs (R2R), has become a sustainable approach for oil companies. The platform was reused to serve the underwater ecosystem as an artificial reef for a new marine ecosystem which helps to tackle food security issue. This paper presents the findings of the formulation of the reefing viability index to recognize an offshore region that can be used for R2R projects within the South China Sea. The combined effects of spatial data, numerical modelling, and geographic system (GIS) are proposed to study the relationship of spawning ground coral reefs, diversity, and planula larvae in the process of colonization to establish a map of the reef potential environment. Coral connectivity and spawning behaviour were studied to determine the possible source of coral seedling released during the spawning season, twice a year. A geographic reef viability index was established consisting of seven parameters which are coral larval density, pelagic larval length, sea currents, temperature, chlorophyll-a, depth, and substrate availability. The ocean hydrodynamic model was designed to resemble the pattern of larval scattering. By using the simulations and rankings, there were 95 (21%) sites which could probably be used for in situ reefing, whereas 358 (79%) sites were likely ideal for ex situ reefing. Validation of the viability index was carried out using media footage assessment of remotely operated vehicle (ROV).

Reefing of Oil and Gas structure has become as one of the emerging options for decommissioning of an O&G Structure offshore and requires expert input beyond engineering such as biomarine and environmental sciences. This paper will present the interdisciplinary collaborative effort by industries with academia in Malaysia in developing a reef viability index as the first high level screening to assess the suitability of decommissioning using the reefing option in the region. The results of the reef viability index formulation to identify an offshore area that potential to be used for Rigs-to-Reefs (RTR) program in the South China Sea. The integration of data collection, numerical modelling and Geographic Information System (GIS) aims to review the relationship of coral reefs spawning ground, diversity and planula larvae in the colonization process which to produce a reefing area map. Coral connectivity and spawning behaviour were investigated to reveal the potential source of coral seedling as well as the number of coral larvae based on different taxa released during the spawning seasons. A spatial reef viability index was developed based on seven parameters, i.e. coral larval density, pelagic larval duration, sea currents, temperature, chlorophyll-a, depth, and substrate availability. Hydrodynamic model was developed to emulate the pattern of larval scattering. Based on the simulation and rankings, there were 95 (21%) sites that are most likely for in-situ reefing while the remaining 358 (79%) sites were probably suitable for ex-situ reefing or decommissioning. Validation of the viability index was done using Remotely Operated Vehicle (ROV) media footage assessment.

This research aims to investigate the influence of soil engineering properties on the corrosion dynamic and to classify these properties according to the power law constants k and v. Fieldwork and laboratory tests were carried out to measure the metal loss influenced by soil properties. Results from fieldwork indicated moisture content as the most influential factor on metal loss. Principal component analysis classified moisture content into constant k, while plasticity index and particle size are grouped into constant v. Similar findings were also observed for laboratory tests. As a conclusion, this research has identified moisture content as the most significant governing factor on constant k, while other soil properties have strong to modest influence on constant v. This research also reveals the existence of an optimum value of soil properties that influence the highest measured corrosion rate. This finding is significant and may change the way researcher model corrosion behaviour.

For offshore structures, especially jacket supported structure such as fixed platform and offshore wind turbine, the underwater area provides an ideal site for corrosion formation and marine fouling. In this marine environment, the structures are exposed to particularly aggressive corrosion and colonized by marine organisms involving a diversity of species. In this paper, a number of cases are conducted where an existing fixed platform is subjected to uniform corrosion. Furthermore, the platform is also subjected to marine fouling. The platform is assessed to investigate the effects of corrosion and marine fouling on its structural strength by determining the Reserve Strength Ratio (RSR) value. It is found the platform is limited to at least 50 years of service life when subjected to average corrosion. However, the platform is no longer considered as safe after 37 years when subjected to severe corrosion. Moreover, there is an RSR loss of 38% when marine fouling is introduced at the first 5 years which is detrimental to the overall safety of the platform. On the other hand, there is minimum RSR loss of only 5% for most cases when marine fouling is introduced but still detrimental to the overall safety of the platform. The obtained outcomes were documented and will be useful information to conduct condition assessment (or structural health monitoring) of aged fixed jacket structures.

In presence of complex-hydrodynamic interaction between water wave and moving structure, a reliable method that can analyse nonlinear phenomena is necessarily required. This paper presents numerical investigation of a moored floating breakwater using computational fluid dynamic (CFD) approach. The mathematical model is based on the extended Reynolds Average Navier-Stokes (RANS) solver for solid-porous obstacle. A high amplitude wave with several wave periods were deliberately considered in the simulation to allow nonlinear wave effects on the floating structure such as wave breaking, overtopping, including viscous friction. Here, the two fluid calculation method for interface boundary between water and air is proposed to capture the complex free surface changes. In addition, the fractional average volume obstacle representation (FAVOR) using partial cell treatment method is employed to simulate the motion of breakwater boundary on the free surface. Approximations and validations on the hydrodynamic properties of the structure have been carried out which include wave transmission coefficient, sway, heave, pitch, and mooring forces. The results show that the CFD model can fairly simulate well on hydrodynamics of the floating breakwater. The discrepancies between numerical and experimental data can be partly attributed to the nonlinearity in the incident wave definition.

Offshore structures are exposed to random wave loading in the ocean environment, and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. In most cases, the dominant load on offshore structures is due to wind-generated random waves where the ocean surface elevation is defined using appropriate ocean wave energy spectra. Several spectral models have been proposed to describe a particular sea state that is used in the design of offshore structures. These models are derived from analysis of observed ocean waves and are thus empirical in nature. The spectral models popular in the offshore industry include Pierson-Moskowitz spectrum and JONSWAP spectrum. While the offshore industry recognizes that different methods of simulating ocean surface elevation lead to different estimation of design wave height, no systematic investigation has been conducted. Hence, the aim of this study is to investigate the effects of predicting the 100-year responses from various wave spectrum models. In this paper, the Monte Carlo time simulation (MCTS) procedure has been used to compare the magnitude of the 100-year extreme responses derived from different spectral models. Additionally, the linear random wave theory (LRWT) was implemented to simulate the offshore structural responses due to random wave loading. The models have been tested for three different environmental conditions represented by Hs = 15m, 10m and 5m respectively. The accuracy of the predictions of the 100-year responses from Pierson-Moskowitz and JONSWAP spectrums will then be investigated.

Subsea pipelines used for oil and gas production in deepwater are exposed to harsh environment involving corrosion, high internal pressure, high temperature, and bending moment. Failure of subsea pipelines can cause serious problems, including oil/gas spill, hydrocarbon explosion and fires, production downtime, and maintenance and repair. Hence, it is of paramount importance to prevent failure of subsea pipelines. The aim of the present study is to investigate the residual strength characteristics of corroded subsea pipelines under combined internal pressure and bending moment. ANSYS non-linear finite element method was applied to examine the residual strength characteristics of subsea pipelines by varying the corrosion damage and the loading ratio of internal pressure and bending moment, where the size of the corrosion damage was also varied. The ultimate strength interaction relationships of subsea pipelines between the internal pressure and bending moment with various corrosion damages were also develo...

This paper presents a computational fluid dynamics (CFD) study of vortex-induced vibration (VIV) for different aspect ratio (L/D) cylinder. Of particular interest was to measure hydrodynamic forces and numerically investigate the wake behaviour of VIV while varying the aspect ratio. The simulation models represented the actual experimental conditions with idealised free-surface boundary condition to capture the responses from fluid-structure interaction phenomenon. The simulations were performed in the subcritical flow region (7.4×103 < Re < 2×105), corresponding to a range of reduced velocity (Ur) from 2 to 14. The results of the cases studied were discussed and compared with the experimental data to verify the accuracy and validity of the present simulation. The comparisons have shown a similar curved-shape drag coefficient plot, and however underestimated the value of the drag coefficients over the reduced velocity. Additionally, the simulations seemed to capture a higher lift force response compared w...

Accurately assessing the reliability of ageing structures is essential, especially in the oil and gas industry where inaccurate predictions of structural performance may have significant hazardous consequences. This study aims to develop a time-dependent pit depth corrosion model for subsea gas pipelines. This model is formulated with the parameters as function of age using the 3-parameter Weibull distribution function. The developed model gives the prediction of the pit depth of a gas pipeline at any given age by changing the scale, shape and location parameters. Measurement data for gas pipeline corrosion pit depth were collected and the statistical characteristics were quantified by statistical analysis in terms of gas pipeline age. The results and outcomes of the present study will be useful for predicting the corrosion pit depth of gas pipeline structures and can be used in the design stage of a new gas pipeline structure.

Precise evaluation of the performance of aging structures is particularly essential in the oil and gas industry, where inaccurate predictions of structural performance may lead to significantly hazardous consequences. It is also important to accurately predict the corrosion behavior of pipeline structures used in the production of gas in subsea areas. The effects of pipeline failure due to a significant reduction in burst strength make it hard for pipeline operators to maintain pipeline serviceability. Therefore, the serviceability of ongoing subsea gas pipelines should be assessed according to their burst strength capacities, which should not exceed the maximum allowable operating pressure (MAOP). In this study, the critical part of the corrosion along a 2.4 km pipeline was evaluated using two approaches: an empirical design codes formula and Ansys numerical analysis. The future integrity of the aging pipeline was then assessed to predict its remaining years of service. The results and outcomes of this study will be useful in evaluating pipeline integrity and predicting the remaining service life of aging pipeline structures.

Precisely evaluation of the reliability of aging structure is essential, particularly in the oil gas industry where inaccurate predictions of structural performance may have significant hazardous consequences. Related to this issue, it is important to predict the corrosion behavior of the gas pipeline structure used in the production of gas in subsea area. As corrosion is concerned, the effects of pipeline failure due to significant reduction of burst strength will make it hard for the pipeline operator to maintain the serviceability of pipelines. Therefore related to this problem, the resistance service of the pipeline is assessed by means of burst strength capacity. In this study, the critical part of the corrosion along 2.4 km pipeline is assessed using two approaches; empirical design codes formula and ANSYS numerical analysis. The future integrity of the pipeline is then assessed to predict the remaining year in service for the aging pipeline. The results and outcomes of the present study will be useful for evaluating the pipeline integrity as well as the prediction of the remaining life of in service aging pipeline structures.Copyright © 2013 by ASME

This study compares the Residual ultimate longitudinal strength – grounding Damage index (R-D) diagrams produced by two analysis methods: the ALPS/HULL Intelligent Supersize Finite Element Method (ISFEM) and the design formula (modified Paik and Mansour) method – used to assess the safety of damaged ships. The comparison includes four types of double-hull oil tankers: Panamax, Aframax, Suezmax and VLCC. The R-D diagrams were calculated for a series of 50 grounding scenarios. The diagrams were efficiently sampled using the Latin Hypercube Sampling (LHS) technique and comprehensively analysed based on ship size. Finally, the two methods were compared by statistically analysing the differences between their grounding damage indices and ultimate longitudinal strength predictions. The findings provide a useful example of how to apply the ultimate longitudinal strength analysis method to grounded ships.