Introduction to ANSYS Mechanical Offshore

Mechanical Offshore is a 2-day training course designed to introduce the process required to carry out the analysis of fixed marine (jacket type) structures.
The course is based on ANSYS Mechanical
A brief introduction to basic analysis and geometry creation with Design Modeler is given.
This is followed by offshore structure specific topics.
Reference will be made to the necessary Mechanical APDL, ASAS commands, and documentation where needed.

The analysis process required for offshore structures is the same as any other analysis – Pre processing,
Solution and Post processing.
The particular requirements for offshore structures are:
Modeling – The finite element model needs to be created using PIPE elements in Mechanical.
Loading: Dedicated methods for wave and current loading are needed with APDL commands.
Pile Analysis – may be needed to model foundations.
Post Processing – Design checks for ultimate states and fatigue is considered with specific tools (Design Assessment).

This training course covers the basics of using ANSYS Mechanical in performing structural analyses of fixed marine structures.
It is intended for all new or occasional
ANSYS Mechanical users, regardless of the CAD software used.
Course Objectives:
General understanding of the user interface, geometry import, meshing, application of loads, supports, and postprocessing.
Procedure for performing FEA simulations, application of wave loads (in-place analysis), soil-pile interactions, code checking and fatigue analysis.
Utilizing parameters for ‘what-if’ scenarios.
Training Courses are also available covering the use of other Workbench applications (e.g. DesignModeler, Design Exploration, etc.)

General Preprocessing
A. Geometry
B. Contact
C. Remote Boundary Conditions
D. Coordinate Systems
E. Named Selections
F. Selection Information
G. Workshop 2 “Jacket Structure”

Working in Design Modeler
Direct modeling vs history based modeling
Concept of Planes & Sketches
Concept Modeling
Create line bodies
Cross Sections (definition, alignment, offset)

Ocean Loading
Various pipe elements have been present in ANSYS Mechanical for many years:
PIPE16: elastic straight pipe
PIPE17: elastic pipe tee
PIPE18: elastic curved pipe (elbow)
PIPE20: plastic straight pipe
PIPE59: immersed pipe (wave loading)
PIPE60: plastic curved pipe (elbow)
The capabilities, namely elastic vs. plastic behavior as well as ocean loading,were dependent upon the element selection
The user needed to select the pipe element type based on whether plasticity or hydrodynamic loads were present

Pile Analysis
– There are a number of methods that can be used to analyze piled foundations in ANSYS Mechanical:
SPLINTER (a standalone nonlinear solver that was originally developed as part of the ASAS suite)
Matrix definition (MAT27)
Spring definition (COMBIN14)
Direct Definition of P-Y and T-Z curves (COMBIN39)

Design Assessment
– Design Assessment (DA), provides a framework for customized post-processing of Mechanical solutions.
Designed to facilitate the incorporation of industrial codes and return results in Workbench
– Includes both direct and user customizable features
– ANSYS provides some licensed tools that make use of this framework (BEAMCHECK and FATJACK), but the primary benefit is the ability to define customized results

Fatigue Analysis
– This lecture provides only the basic ideas of fatigue. Some discussion of the background to the checking methods is included as well.
– The main purpose of this lecture is to demonstrate the implementation of ANSYS technology in studying fatigue in fixed marine structures.
– Joint fatigue assessment (FATJACK) is included in Design Assessment and can be connected to Static Structural, Transient Structural and Harmonic Response analyses.
– In order to use FATJACK in the most efficient way, global models are often studied first. Although such models contain approximations, they have the benefit of giving a good insight into the structural behaviour. At a later stage local models may need to be solved (see submodeling).

Submodeling
FE Technique where the actual structure is analysed as a series of smaller structures. Also known as
substructuring or cut-boundary displacement method.

Reduced sized matrices are created where the reduced matrices are only defined in terms of the
connection freedoms.
The reduced matrices are assembled and displacements are found along common boundaries.
Boundary displacements are fed back to the individual component(s) to assess the response.

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