Subsea Engineering

Course — SUBS 6320: Riser Design

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Term: 

Usually offered in the Fall Semester.

Description: 

This class will review the various types of riser systems used today on offshore floating platforms. The student will gain an understanding of standard products used in these systems and the design and selection of such components. A thorough study of the analysis of riser systems will include global riser analysis methods, strength capacity calculations and fatigue life estimation. The major topics that will be covered in this class include pipe mechanics, ocean environmental loading, vessel dynamics, vortex induced vibration, riser analysis software, analysis process, and reporting. Other topics include upper space-out considerations, stroke estimation, top tension requirements, fluid/structure hydrodynamics, and environmental design conditions.

The objectives of the course will be to:

  • Impart an understanding in the function, technology, design of riser systems.
  • Introduce tools and methodologies required for global riser analysis.
  • Review basic pipe mechanics and summarize standard fatigue analysis methods.
  • Describe ocean environment, wave models, and vessel motions.
  • Provide understanding of riser response and vortex induced vibration.

Topics Covered: 

Introduction to Riser Systems: The purpose of this unit is to provide a review of the function and types of risers. A riser system will be described at the component level. The basic design issues will be discussed. The main topics of this unit will be wellhead connectors, specialty riser joints, standard riser joints, materials considerations, connectors, and surface equipment.

Interfaces to the Rig: In this unit, the main interfaces to the rig will be reviewed. In particular, the analytical method of sizing of the upper riser joints will be laid out. The causes and categories of vessel motions will be provided along with their impact on the performance of the riser system. The mathematical description of vessel motions will be reviewed. Tensioning systems will be discussed and the analytical methods to estimate the required stroke of the tensioners will be shown.

Pipe Mec​hanics: This unit will discuss the basic structural analysis methods to calculate the stress in a pipe that is subjects to internal pressure, external pressure, tension, and bending.

Hanging Weight Ca​lculations: This unit will discuss the mathematical methods to calculate air weight, wet weight, internal fluid weight, and buoyancy effects. The weight calculations will be used to estimate the strength requirements of the tensioner.

Current and W​ave Loading: The purpose of this unit is to present the basic engineering methods behind fluid structure hydrodynamics. The drag forces caused by external flow over pipes will be reviewed. The ocean environments will be described including basic ocean loads such as current and waves. The analysis methods to calculate current and wave forces will be presented. The basic understanding of vortex induced vibrations will be covered along with basic analytical prediction methods.

Fatigue Analysis: The analytical methods to estimate fatigue and fracture will be presented in this unit.

Global Riser Analysis Software: The commercially available software packages to conduct global riser analysis will be shown in this unit. Global riser analysis software includes Flexcom, Riflex, OrcaFlex, and Staris. 

Simulation Software Tools: 

DeepRiser will be used during the course project to design and analyze drilling riser and top-tensioned riser systems. Final project evaluation will cover interpretation of graphical output of all results variables, statistics, stress snapshots and time result histories.

Course Grading: 

The course grade will be based on homework, project, quizzes and final exam.

Project: 

Each student will be completing a project in this course. Students will conduct a strength and fatigue analysis of a riser system using DeepRiser. Each student will size the riser components based on a set of input conditions. Since several answers may satisfy the set of input conditions, it is expected that students will develop different solutions. Outputs for this project shall include global riser analysis model, pipe hoop pressure calculations, hanging weight calculations, current loading and fatigue calculation worksheet.