The riser is a typical structural type used in the offshore construction. They are slender and compliant structures that rely on vertical prestressing for lateral stability. Risers are subjected to gravity waves, their own dead weight, lateral buoyancy and prescribed harmonic motions at the top during a storm. During the storm, the riser is considered to be in either a connected position and subjected to lateral motion or in the hangoff (disconnected) position for severe storm and subjected to both vertical and horizontal motions. The vertical motion represents a critical design condition especially for deep water risers. The riser’s behavior may be nonlinear in the connected position because of the relatively large motions prescribed. Nonlinearities may exist for the hangoff condition due to the changing P-Delta stiffnesses that are caused by the riser’s axial vibration. Further, the loading is nonlinear due to Morison’s equation. Since the structure is slender and nonlinear, sound analysis methods are required to predict solutions that are representative of field conditions.
Our objective was to develop a software package specifically conceived for educational or research purposes with emphasis on : 1) graphical I/O interfaces, 2) automatic data generation, and 3) graphical display of computed results. The software needed to be highly interactive on all design parameters and allow the student/researcher to investigate the effects in key parameters and alternative design solutions. Our goal was not geared towards self-paced instruction, but instead focused on enabling the student to gain insight into the behavior of a physical system.
Course compression often precludes or discourages use of valuable lecture time to explain input guides, options, etc.; therefore, an overriding consideration was to make the program’s use as intuitive and natural as possible. Once the student understands the underlying principles and theories presented in the classroom, he/she could then investigate various design parameters affecting the problem. Ideally, one strives for a situation where this could be accomplished with little or no sacrifice in lecture time.
Sequence of Program Development: In this project four versions of the program were developed. The first was for Macintosh SE30 because of its graphics and its availability during the early stages of the project. The second version was written for a DECstation 3100 workstation using DecWindows for designing the interface. The third version was similar to the first but utilized the larger screen of the Macintosh II. The final version, which is described in this report, was developed on an IBM RISC 6000 workstation using Motif for the interface design. During the course of the project, Motif has emerged as the defacto industry standard and for this reason it will be the version maintained and upgraded, because of the wider and more portable platform. This version can easily be adapted to any workstation that supports X Windows and Motiff. The workstation version is also considerably more effective because of the larger screen and faster computation.