SIMLA - Simulation of Pipelaying

SIMLA is MARINTEK’s newly developed computer tool for analysis of offshore pipelines in deep waters and rough environments. Currently available functionality include pipe laying and inspection of free spans.

The initial version of SIMLA was developed by MARINTEK for Norsk Hydro ASA, with Ceetron GLview AS and Systems in Motion as sub-contractors on 3D visualization.

Background

In the last years many pipelines have been installed in rough seabed areas, e.g. in landfalls, and the operating temperatures have increased. This tendency is continuing also when looking at new field developments.

In order to design cost effective solutions at high temperatures and rough seabeds, the design procedure has to be optimized. Instead of performing rock dumping to avoid snaking behaviour as a result of the temperature/pressure gradient, utilizing more sophisticated analysis tools in combination with strain based design is believed to bring significant cost savings particularly related to the installation phase. This means that remedial action is performed only when needed based on the observations made with respect to snaking behaviour. In addition, the pipeline strength may be utilized into the plastic range of material behaviour.

Based on the uncertainties related to the loading conditions, and when taking into account the fact that new pipeline technology will also be applied in new field developments, it is believed that new procedures, tools and techniques are needed for some of the planned field developments to be able to select the most optimal pipeline route, and to take proper care of other design and safety issues.

The initial objective of the SIMLA development was to develop a software tool to simulate the structural response of a pipe during laying, and to be able to inspect the result of this operation by 3D graphical visualization of the laid pipe on the 3D sea-bottom, including pipe details with analysis results. The simulator, including visualization, is available on desktop computers.

SIMLA has been implemented as a real-time client-server infrastructure, as illustrated below.

A special purpose finite element solver has been developed to calculate the structural response of the pipe being laid.

Analysis engine for calculation of pipeline response

The special purpose finite element solver is based on integrating several levels of response resolution into one object, including the following features:

• Catenary solution
• Stiffened catenary solution
• 2D FEM solution both 4 dofs and 6 dofs per element, linear and elastoplastic material model
• 3D FEM solution both 8 dofs and 12 dofs per element, linear and elastoplastic material model

The 12 dofs representation is shown below. The multi-level solver approach has been chosen to allow for different levels of detail in the analysis, including efficient generation of inital pipe configuration.

The active number of dofs is configureable to allow for optimalization of computer time if necessary in order to obtain the requested computation speed.

The input to the numerical module is based on engineering terms for pipe laying, as used e.g. in alignment sheets.

The principle of the analysis module is to only handle the pipe from the touchdown point to the vessel, including also the necessary (affected) part of the pipe resting on the seabed, as illustrated below. Hence, the pipe response for the already laid pipe not affected by the current pipe configuration will be stored in a result database for later use (result plots, restart analyses, etc).

Visualization

The SIMLA visualization module automatically adjusts the graphical resolution of both the pipe and the seabed depending on viewpoint. Hence, when inspecting a laying scenario from some distance the actual pipe will be rendered as a line (colored if analysis results are included). However, when closing up to e.g. the touchdown point the pipe will be rendered with polygons (colored if analysis results are included) representing the pipe outer surface, and the resolution of the 3D seabed will increase.

The SIMLA graphical user interface is built as a Windows application with pull-down menus, toolbars and graphics in order to visualize large terrain models and the pipe laying process including ship, pipe, and structural response.

The user may move freely around in the selected project scenario, e.g. by utilizing a joystick controlled ROV:

At any time the laid pipeline may be inspected visually, and free span details, such as length, height, pipe support volume, … etc, may be aquired by a single point-and-click:

Contact person at MARINTEK: Egil Giertsen

Further references: DEEPLINE – Design, Installation and Operation of Deepwater Pipelines