Drilling risers are regularly deployed in deep water (over 1500 m) with large sections covered in buoyancy modules. The smooth cylindrical shape of these modules can result in significant vortex-induced vibration (VIV) response, causing an overall amplification of drag experienced by the riser. Operations can be suspended due to the total drag adversely affecting top and bottom angles. Although suppression technologies exist to reduce VIV (such as helical strakes or fairings), and therefore reduce VIV-induced amplification of drag, only fairings are able to be installed onto buoyancy modules for practical reasons, and fairings themselves have significant penalties related to installation, removal, and reliability. An innovative solution has been developed to address this gap; LGS (Longitudinally Grooved Suppression)1. Two model testing campaigns were undertaken; small scale (sub-critical Reynolds Number flow), and large scale (post-critical Reynolds Number flow) to test and confirm the performance benefits of LGS. The testing campaigns found substantial benefits measured in hydrodynamic performance that will be realized when LGS modules are deployed by operators for deepwater drilling operations.

Drilling risers are regularly deployed in deep water (over 1500 m) with large sections covered in buoyancy modules. The smooth cylindrical shape of these modules can result in significant vortex-induced vibration (VIV) response, causing an overall amplification of drag experienced by the riser. Operations can be suspended due to the total drag adversely affecting top and bottom angles. Although suppression technologies exist to reduce VIV (such as helical strakes or fairings), and therefore reduce VIV-induced amplification of drag, only fairings are able to be installed onto buoyancy modules for practical reasons, and fairings themselves have significant penalties related to installation, removal, and reliability. An innovative solution has been developed to address this gap: longitudinally grooved suppression (LGS). Two model testing campaigns were undertaken: small scale (subcritical Reynolds number flow), and large scale (postcritical Reynolds number flow) to test and confirm the performance benefits of LGS. The testing campaigns found substantial benefits measured in hydrodynamic performance that will be realized when LGS modules are deployed by operators for deepwater drilling operations.

Counter-rotating vortices form from the opposite edges of lifting surfaces, and gradually move laterally and dissipate as they travel downstream (as seen in a wing-fixed reference frame). Under ground effect conditions, the vortex from a lifting wing -such as that used in an aircraft application -moves laterally outboard from the wingtip as it progresses downstream; for a downforce wing in ground effect -such as that used in an automotive application -the vortex moves laterally inboard. An interesting case is the situation where the inboard moving vortices become in close proximity to each other. The objective of the present study was to investigate counter-rotating vortices produced from a low aspect ratio downforce wing operating in ground effect. The pair of vortices move towards each other and mutually induce an upwards directed motion which in turn reduces the inboard movement driven by the ground effect. Experimental data gained from three-dimensional Laser Doppler Anemometry in a moving ground wind-tunnel was used to validate a Large Eddy Simulation computational result.

2017-280 Abstract This paper describes the development of a Decision Support Tool (DST) for response planning associated with aerial operations for offshore oil spills. The research program was formulated to include characterization of dispersant spray drift through numerical modeling to generate a database of drift response for a range of airframes and environmental conditions. The drift of aerial dispersants is dependent on a number of different influences including airframe shape and aerodynamics, environmental effects, flight conditions and aerial dispersant make up. As with agricultural spraying, oil spill response spraying has the potential of spray drift to impact upon ecologically sensitive regions and/or areas occupied by people or marine mammals surfacing in the spill area. The development of the DST included an evaluation of existing regulatory models, investigating their application to the offshore environment. It was found that, due to inherent limitations and simplifications, particularly for the larger airframes considered, the existing models were under conservative in comparison with Computational Fluid Dynamics (CFD) models in the near field wake regions for offshore spraying purposes. To address these issues, a combination of scaling factors and the use of inviscid vortex transport and particle dispersion models were adopted for inclusion in the DST. It is envisaged that, once validated further, the DST will become an invaluable tool for Oil Spill Response Operators (OSROs) and decision planners in both the operational mode of providing information to aid in establishing setback distances and in the planning mode to assist with the identification of windows of opportunity conducive to spraying operations.

Irregular seabed bathymetry around subsea pipelines can lead to the formation of pipeline free spans. When exposed to on-bottom currents these free spans can be subject to Vortex-Induced Vibration (VIV), with consequential effects on the fatigue life of the pipeline. Traditional VIV suppression technologies such as strakes and fairings present installation challenges and durability concerns due to the significant increase in overall diameter associated with the geometric profiles of strakes and fairings. Longitudinally Grooved Suppression (LGS) technology was developed from a concept stage through to field deployment on active drilling risers (Johnstone et. al., OMAE 2017) [1]. The low profile and VIV suppression abilities of LGS present an opportunity for a more effective and operationally beneficial VIV suppression solution for pipeline free spans. Based on existing Class guidance for assessing pipeline free spans, a simplified framework for assessing free spans with LGS under a response based approach is presented. The simplified assessment implied a suppression efficiency (reduction in vibration amplitude) of up to 80%. An alternative comparative analysis using a force based approach was also performed in SHEAR7 of a bare pipeline and a LGS-wrapped pipeline. The requirements for qualification of new VIV mitigation technologies are also addressed and an example of an actual field installation of the device is presented, on an existing pipeline free span with low seabed clearance.