A tabular optimisation technique for steel lazy wave riser

Abstract

Steel lazy wave riser (SLWR) is derived from the simple catenary riser (SCR) by the installation of buoyancy modules on its section. Infinite SLWR configurations are possible, and this poses difficulties in determining the best configuration. However, it is possible to capture some suitable configurations which satisfy some given design criteria specific to a project. We referred to these as the optimum configurations for the problem. Several advanced optimization tools and techniques for engineering optimization are available. In this paper, we present a 2D tabular optimization method for SLWR, which is an index-based optimization technique. The approach reduces a multidimensional problem to a 2D type providing a significant reduction in the required computational resources. It combines the design variables in pairs and assigns indices to the resulting design points (configurations) for each combination. The optimum design points are then tracked through index matching using techniques such as data sorting and intersection operations. In the application of the technique to SLWR design, we set the number of design variable for the problem to three. This results in three pair of combinations of the design variables. The design variables are the apparent mass ratio, the sag bend elevation, and the arc height. The output variables of interest to be optimized include the SLWR hanging length, the smeared buoyancy section length, the smeared buoyancy thickness, the riser hang-off tension, the stress utilization and fatigue damage around the bends. Selected optimum SLWR configurations from the optimization process are subjected to an irregular wave simulation to demonstrate the suitability of the approach for such optimisation problems.

The Performance of KH and KG Flexible Riser with Distributed Buoyancy Modules Configuration

“…The static analysis [1] is considered to be the foundation of subsequent dynamic analyses and aims to establish the equilibrium configuration of the riser system due to weight, buoyancy, tension and current. In this analysis, Finite Element Analysis was conducted in Orcaflex based on provided flexible data and hang-off / tie-in locations which were modelled as fix.…”

“…In the offshore oil and gas production process, exploited hydrocarbon resources are delivered from sea well to the offshore floating storage station called Floating Production Storage and Offloading (FPSO) [1]. This storage critically connected with flexible risers equipped with buoyancy module, which highly vulnerable and complex in terms of technical or even environmental risks which may lead to higher economic cost.…”

“…The configuration of flexible riser could be seriously determined by the selection of its buoyancy system that maintain riser to be "float" at mid-water level [1,2]. Utilization of Distributed Buoyancy Module (DBM) becomes one of the alternatives to generate efficient risers yet simple configuration with simple installation procedure and simple equipment involved [2,3].…”

“…Utilization of Distributed Buoyancy Module (DBM) becomes one of the alternatives to generate efficient risers yet simple configuration with simple installation procedure and simple equipment involved [2,3]. The use of buoyancy modules not only to assist in achieving desired configurations and shape but also to achieve optimal performance of structural strength against topside or tension loads of the deepwater flexible risers [1,4]. One of common preferred configuration is Lazy Wave riser configuration, which is known to its better resistance against dynamic condition in comparison with conventional Steel Catenary Riser (SCR) [1].…”

“…The use of buoyancy modules not only to assist in achieving desired configurations and shape but also to achieve optimal performance of structural strength against topside or tension loads of the deepwater flexible risers [1,4]. One of common preferred configuration is Lazy Wave riser configuration, which is known to its better resistance against dynamic condition in comparison with conventional Steel Catenary Riser (SCR) [1]. The high stress and fatigue damage responses induced by dynamic condition of particular riser configuration could be determined and analysed by an aid by several design engineering simulation.…”