Low Speed Aerodynamics

Ship-shaped offshore units are some of the more economical systems for the development of offshore oil and gas, and are often preferred in marginal fields These systems are especially attractive to develop oil and gas fields in deep and ultra-deep water areas and remote locations away from existing pipeline infrastructures Recently, the ship-shaped offshore units have been applied to near shore oil and gas terminals This 2007 text is an ideal reference on the technologies for design, building and operation of ship-shaped offshore units, within inevitable space requirements The book includes a range of topics, from the initial contracting strategy to decommissioning and the removal of the units concerned Coverage includes both fundamental theory and principles of the individual technologies This book will be useful to students who will be approaching the subject for the first time as well as designers working on the engineering for ship-shaped offshore installations

Ship-Shaped Offshore Installations : Design, Building, and Operation

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Foundations Of Potential Theory

Shape optimisation of floating wave energy converters for a specified wave energy spectrum

A geometrical optimization method applied to a heaving point absorber wave energy converter

Numerical study on the trajectory of dropped cylindrical objects

The paper reports on the continuous development of an automated optimization procedure for the design of offshore structure hulls. Advanced parametric design algorithms, numerical analysis of wave-body interaction, and formal multi-objective optimization are integrated into a computer aided design system that produces hull shapes with superior seakeeping qualities. By allowing multiple objectives in the procedure naval architects may pursue concurrent design objectives, e.g., minimizing heave motion while simultaneously maximizing deck load. The system develops a Pareto frontier of the best design alternatives for the user to choose from. Constraints are directly considered within the optimization algorithm, thus eliminating infeasible or unfit designs. The paper summarizes the new developments in the shape generation, illustrates the optimization procedure, and presents results of the multi-objective hull shape optimization.

Application of Constrained Multi-Objective Optimization to the Design of Offshore Structure Hulls

The paper presents improved methods and new results on the introduction of formal optimization strategies into the design of offshore structures. The hull design stage is singled out from the overall design process and automated by introducing parametric shape generation, numeric hydrodynamic analysis and assessment tools as well as Nonlinear Programming algorithms for process control. The investigation compares the performance of three different optimization algorithms within a shape optimization framework. The classical deterministic Sequential Quadratic Programming method competes with two so called global optimization algorithms: The popular Genetic Algorithm and the more exotic Adaptive Simulated Annealing. The applications show that significant improvements of seakeeping qualities are obtained in either case. As expected, the global methods require definitely more computation time than the deterministic algorithm. Furthermore the global methods do not always produce better results, which makes a careful choice of the optimization algorithm mandatory. Guidelines for an efficient application are given in the conclusions.Copyright © 2004 by ASME

Practical Application of Global Optimization to the Design of Offshore Structures

Dropped objects are among the top ten causes of fatalities and serious injuries in the oil and gas industry (DORIS, 2016). Objects may accidentally fall down from platforms or vessels during lifting or any other offshore operation. Proper planning of lifting operations requires the knowledge of the risk-free zone on the sea bed to protect underwater structures and equipment. To this end a three-dimensional (3D) theory of dynamic motion of dropped cylindrical object is expanded to also consider ocean currents. The expanded theory is integrated into the authors\' Dropped Objects Simulator (DROBS). DROBS is utilized to simulate the trajectories of dropped cylinders falling through uniform currents originating from different directions (incoming angle at 0o, 90o, 180o, and 270o). It is found that trajectories and landing points of dropped cylinders are greatly influenced by the direction of current. The initial conditions after the cylinders have fallen into the water are treated as random variables. It is assumed that the corresponding parameters orientation angle, translational velocity, and rotational velocity follow normal distributions. The paper presents results of DROBS simulations for the case of a dropped cylinder with initial drop angle at 60 through air-water columns without current. Then the Monte Carlo simulations are used for predicting the landing point distributions of dropped cylinders with varying drop angles under current. The resulting landing point distribution plots may be used to identify risk free zones for offshore lifting operations.

http://www.techno-press.org/download.php?journal=ose&volume=6&num=4&ordernum=5

Risk free zone study for cylindrical objects dropped into the water

Dropped objects are among the top ten causes of fatalities and serious injuries in the oil and gas industry (DORIS, 2016). Objects may accidentally fall down from platforms or vessels during lifting or any other offshore operation. The accurate prediction of the landing points of the dropped objects may protect underwater structures and equipment from being damaged. In this paper, the authors propose a three-dimensional (3D) theory to numerically simulate the dynamic motion of a dropped cylindrical object under the water and to investigate the influence of the longitudinal center of gravity (LCG) on the motion. A numerical tool called Dropped Objects Simulator (DROBS) has been further developed on the basis of this 3D theory. It is initially applied to a dropped cylinder with its center of gravity at the center of volume (cylinder #1, LCG = 0) falling from the surface through calm water. The calculated trajectories match very well with both the experimental and numerical results published in Aanesland (1987). Then DROBS is further utilized to simulate two dropped cylinders with positive LCG (cylinder #2) and negative LCG (cylinder #3), respectively. The simulated results from DROBS show better agreement with the measured data than the numerical results given in Chu et al. (2005). This comparison again validates and indicates the effectiveness of the DROBS program. Finally, the simulation is applied to investigate the effects of varying LCGs on the trajectory and landing points. The newly developed DROBS program can be used to simulate the distribution of the landing points of dropped cylindrical objects in order to predict risk-free zones for offshore operations.

Lothar Birk

Papers

Numerical study on the trajectory of dropped cylindrical objects

Application of Constrained Multi-Objective Optimization to the Design of Offshore Structure Hulls

Practical Application of Global Optimization to the Design of Offshore Structures

Risk free zone study for cylindrical objects dropped into the water

Study of the Trajectory and Landing Points of Dropped Cylindrical Object with Different Longitudinal Center of Gravity