Rudi Walujo Prastianto

Stress concentration factor distribution of inclined brace in multiplanar offshore tubular double kt joints

The majority of tubular joints commonly found in offshore structures are in the form of multi-planar tubular joints, but very few investigations have been reported due to the complexity and high cost involved. The majority of research have been focused on the study of stress distribution at certain position such as saddle and crown points, and the hot spot stress (HSS) at other position along the weld toe of brace/chord intersection have been ignored. In this paper a 60° two-planar double KT (DKT) tubular joint is modelled as a finite element model from an offshore jacket platform. The effect of dimensionless geometrical parameters on the geometrically stress distribution and SCF distribution along the weld toe of inclined brace in axially loaded on the joint are investigated. Non-dimensional parameters that are varied include β, τ, γ and θ. Validation of the finite element model shown a good agreement to the global structural analysis results. The results of parametric studies show that the increase of the β leads to decrease of SCF. While the increase of the τ, γ and θ leads to increase of SCF. The peak SCF mostly occurs at the outer saddle point. The effect of parameters β, γ and θ on the SCF are greater than the effect of parameters τ.

On Offshore Engineering Rules for Designing Floating Structure of Tidal Current Energy Conversion System

Offshore engineering rules have been important part in supporting industrial development of tidal current energy conversion (TCEC) systems. The rules have been considered as guidelines for design of fixed type of TCEC systems, particularly those provided by European Marine Energy Centre (EMEC). However, for floating type of TCEC system, this is not the case. In fact, floating systems have a potential application for particular area of interests, for example in the area with strong currents at the seawater surface or in that with minimal infrastructure for installation support. In future, floating TCEC systems might be installed at the offshore area, even though the current application is commonly at the nearshore. Therefore, it may be beneficial to adopt relevant aspects of the offshore engineering rules for the floating structure design to support TCEC systems. This paper identifies elemental rules which may be suitable for application in the design of this type of floating structure. It includes choice of configurations, dynamic response analysis, material selection, mooring-water depth analyses and removal. This work is an important part of the whole big effort in supporting the development of ocean renewable energy industries.

An Analytical Approach to Modeling of Motion-Response of Floating Structure for Ocean Renewable Energy Conversion System

Ocean renewable energy research has been progressing well. Supporting structures are needed to convert energy from the sea. This paper discusses the response of the floating structure for ocean renewable energy conversion system by providing a simple design of floating structure. Due to its function, the system is limited for the pitching motion. By using the Lagrange formula, the equation of motion of the system can be obtained. In the analysis, there are three variations of wave period to determine the response of floating structure motion. The result shows the trend where the larger wave periods induce larger intersection angle (larger response) of the structure. The floating structure configuration for the ocean energy converter should be determined in such a way that have the most stable motion-response in any condition. The stability of floating structure will affect the current forces in the rotated turbine. It needs a specific design to hold the stability of floating structure.

Experimental Study on Two Flexible Hanging-off Circular Cylinders undergoing Wake Interference

This paper presents experimental results of three different configurations of two flexible circular cylinders were towed in still water. Each cylinder has length-to-diameter ratio of 34.4 with low mass ratio of 1.24. The cylinders were submerged partially into the still water from towing carriage as hanging vertical cantilever and towed by various speeds that give Reynolds number of 1.08 times 104 up to 3.78 times 104. For side-by-side arrangement, two distinct center-to-center distances between the two cylinders were considered, while for the tandem arrangement the relative position of the cylinders is only 4D. For staggered arrangement, a distance between upstream and downstream cylinders (LUD) was fixed by 4D, and the position of the downstream cylinder in transverse direction (LT) was varied by 1D, 1.5D, 2D, and 2.5D, respectively. Measurement of the hydrodynamics forces in two, in-line (drag force) and transverse (lift force) directions are conducted simultaneously with two- component load cells. For all test cases, the characteristics of the time-dependent forces are strongly dictated by the reduced velocity (Ur) parameter. Frequency of the drag force was found approximately twice the corresponding lift force frequency at the related Ur. For all cases, the CD and CL values lie in the range of approximately 0.03 up to 0.25. The tandem case became a very special case due to an extreme drop of the CD for the downstream cylinder compared with all other cases. In addition, for staggered configuration, the wake interference only has strong influence on the forces fluctuation until the LT = 1D, especially for the downstream cylinder.