Use of SIMA in a static and dynamic analysis of a spool piece installation

Abstract

A new modeling environment for marine operations, SIMA, has been used to perform a spool piece installation analysis. Spool design and installation analyses have formerly been done in two separate operations. STAAD Pro has been used for the structural strength verification, while SIMO has been used to simulate the installation and to set the operational criteria. In the SIMO analysis, the spool is modeled as a rigid body. This is not optimal. One of the targets has been to test if it is possible to set up analyses in SIMA, which can cover both structural verification and operational criteria.

An introduction to the basic dynamics involved in this analysis has been made, along with response calculation of a simple degree of freedom system. The background theory for static finite element analysis and dynamic time domain analysis has been presented. Different iteration methods and numerical time integration methods are described.

The properties and the SIMO input file for a 26 inch spool piece installed at the Skarv developement in 2010, has been provided by Subsea7. The spool is modeled with flexible slender elements, and all the modeling is done within the SIMA modeling environment. The spool is connected to the Skandi Acergy cranetip, and follows the ship motion. The first order motion transfer function for Skandi Acergy is given. Three load cases are investigated: spool located in air, in the splash zone and submerged. Static analyses are done to find the equilibrium, and dynamic response analyses are performed for eight different sea states. The post-processing is done in MATLAB by exporting binary result files from SIMA.

The maximum and minimum dynamic rigging tension occurred when the spool was located in the splashing zone, and the significant wave height was three meters and the peak period four seconds. The maximum sling stress was 179 MPa, while the minimum sling stress was -15.9 MPa. The latter one indicates that snap-loads may occur. Stress time series are presented in the appendix. Spool element utilization has been checked, and the elements located at the end of the gooseneck experienced the highest utilizations.

SIMA has proven to be an easily learned software, even for a beginner. This indicates that an analyst with experience within RIFLEX or any of the other in-built solvers will have no problem using this software. The user interface is clearly and practical, and the 3D view works perfectly for model verification. If the post-processing part is improved, SIMA will become a powerful engineering tool for marine operations.