Analysis of impact loads on a self-elevating unit during jacking operation

[+] Author and Article Information
Jonas W. Ringsberg

ASME Member Chalmers University of Technology Department of Shipping and Marine Technology Division of Marine Technology SE-412 96 Gothenburg SWEDEN

Viktor Daun

SSPA Sweden AB P O Box 24001 SE-400 22 Göteborg SWEDEN

Fredrik Olsson

SSPA Sweden AB P O Box 24001 SE-400 22 Göteborg SWEDEN

1Corresponding author.

ASME doi:10.1115/1.4035996 History: Received August 11, 2016; Revised February 09, 2017


A method is presented that enables the analysis of weather window assessments for the installation and retrieval phases of a self-elevating unit (SEU). The method takes site-specific parameters, defined as soil type and water depth, into account in addition to vessel-specific and environmental parameters. The inclusion of site-specific parameters is the novel contribution compared to assessment methodologies used today. A simulation model is presented that incorporates a coupled non-linear time-domain analysis of vessel motion and soil-structure interaction. Soil deformation behaviour during impact is described by resistance curves based on a bearing capacity theory. A structural evaluation criterion against which impact forces are compared is used for weather window assessments. The simulation model is applied on a case study utilizing different soil types to study impact forces and the capacity of the structure for withstanding such impacts and eventually performing a weather window assessment. The results show that the jacking operation can be divided into two phases when it comes to loads on the spudcan: a phase dominated by vertical forces followed by a phase dominated by horizontal forces. It is found that including soil deformation behaviour is of paramount importance to the magnitude of the resulting impact forces and that class-recommended practice does indeed produce rather large force estimates. Thus, assessments where site-specific parameters are incorporated could definitely increase the operable weather window for SEUs, and, consequently, increase the economic competitiveness of, for example, the offshore wind industry.

Copyright (c) 2017 by ASME
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