Kazuaki Itoh

Experimental Study on a Self Standing Hybrid Riser System Throughout Tests on a Deep-Sea Model Basin

The present paper introduces a concept of a hybrid riser, Self Standing Hybrid Riser (SSHR), particularly in development for ultra deepwater around 3000 meters. Main problems faced in the initial definitions for design of such risers in the described scenario are discussed. Unique laboratory test with reduced model carried out in waves, current and riser top oscillation experiments in a very deepwater wave tank is shown. And, experimental results are shown and discussed, especially considering difficulties faced to carry out this experiment. Discussions are addressed in terms of vortex induced vibration (VIV) around buoyancy can, riser line pipe and flexible jumper.Copyright

Behavior Characteristics of Hang Off Riser That Considers Oscillation of Floating Structure

A riser system has been used widely as the progress of ocean developments. The vibration is one of the most important problems from the safety aspect of a riser system. In this paper, we conducted the model experiment of a hang-off riser at the Deep-Sea Basin in the National Maritime Research Institute of Japan. Translational and rotational motions of the upper floating structure are simulated by the forced-oscillation device. The motion of the riser was measured using 3D video tracking system. Numerical analysis program for simulating the behavior of riser was also developed. This program used the improved Morison’s equation as a method of evaluating hydrodynamic force. The validity of this calculation method was verified through the comparison with the experiment results.Copyright

Full depth ROV “ABISMO” and its transponder

The Japan Agency for Marine-earth Science and Technology is now developing an automatic bottom inspection and sampling mobile, ABISMO, which is a full depth rating remotely operated vehicle for conducting research at the deepest sea bottom, observing the area with a camera, and sampling the bottom layer.

Strain Measurement on Riser Pipe Compared With Model Test and Calculation

For pumping up deep ocean water, a SPAR type floating structure with a steel riser pipe was installed in Sagami Bay, Japan, in 2003. The riser pipe, which is 175 m long and 1.0 m in diameter, was connected to the floating structure by two mooring chains. At the middle height of the riser pipe, strain gages were attached on the pipe surface so that they faced to 8 directions at equal angles. The authors measured not only strains but also motions of the floating structure and wave and current conditions from 2003 to 2005. From these measured results in actual sea, it was found that the strains (or stresses) of the riser pipe are mostly concerned with motions of the floating structures, more than wave and current conditions. In order to make clear this phenomenon, the authors carried out forced oscillation tests by using a reduced riser pipe model in the Deep-sea Basin in National Maritime Research Institute, along with some numerical simulations based on FEM. In this paper, we show the results of the model tests and numerical simulations compared with the measured results in actual sea.Copyright