Offshore structures towed to a job site must be launched and upended (see Fig. 1). 1), 2) In relatively shallow water, a structure is upended by hoisting it with a derrick crane. In deep water, however, a structure (usually large and heavy) is often self-upended without the aid of a crane, through buoyancy adjustment.
There are two important factors involved in upending procedures: the stability of the structure being upended, and the time-dependent change in the attitude of the structure.
A computer program was developed to systematically analyze the stability of a structure being upended. The upending of a hydraulically unstable structure was analyzed by this program and, as a result, a safe upending procedure has been determined.
A flooding analysis method has been developed for the time-dependent attitude change. This method analyzes the time-dependent change in the surface of water flooded into a structure's flood tanks. An actual jacket structure was analyzed by the method, and the analytical results are reported in this paper.