At-Sea Experiment of Floating Platform "POSEIDON"

At-Sea Experiment of Floating Platform "POSEIDON" At-sea experiment using the prototype floating platform "POSEIDON" has finished in summer of 1990. The main objective of this field measurement is to validate the design methodology of floating offshore structures based on the model experiments and on the theoretical approaches. 1 Floating Platform "POSEIDON" The POSEIDON means Platform for Ocean Space Exploitation. The structure of POSEIDON are shown in Fig.l. It consists of 12 legs with footings which support the upper structure. The upper structure is mainly composed of the box-type girders around four sides. The instrumentation house is arranged on the upper deck for power supply and data aquisition. Data Acquisition Room

2 Location of test area The location of test area is about 3 km offshore Yura port, Tsuruoka City, Yamagata Prefecture, southwestern part of Japan Sea as shown in Fig.2. The sea depth is about 41 m. We have constantly severe sea conditions due to the strong seasonal wind in winter. The POSEIDON was constructed at Naruto, Tokushima Prefecture. After an inclining and free decaying test were carried out at there, it was towed by a tag boat from Naruto port to Yura port, about 800 miles over 9 days, and instaued in the test area of Yura port in July, 1986. The POSEIDIN was sla<;kly moored by six chain Unes as shown in Fig.3. The forward direction of the POSEIDON was WNW, which corresponds to the dominant direction of seasonal wind and waves in winter. l4tcna 15ton» / / / Utoni /\ / POSEIDOM \loconi ( ] Fig.2 Location test area Fig.3 Arrengetnent of chain lines

3 Measuring items and devices The POSEIDON has many measuring items. They can be categorized as follows: Enviroimaental conditions(wind,waves and current etc.) Motions Structirre strength Mooring hne tensions Corrosion and paints Table 1. Measuring Items and Devices ITEMS No. Devices and Remarks Wind 2 Ultrasonic, 3 axes, 19.5m above W.L. Ultrasonic, 1 axes, 10.0m above W.L. Waves 3 Ultrasonic, sea floor of 180 m offehore of POSEIDON line array Current 1 Impeller type, under 10 m below W.L. Temparature air 1 Resistance temparature type, on the top of house Temparatuie water surface 1 Semiconductor type, at the footing Temparature bottom 1 Semiconductor type, on the sea floor Humidity 1 Thin film capacitive type, on the top of house Solar radiation 1 Thermopile type, on the top of the house Temparature deck plate 1 Resistance temparature device Temparature house wall 1 Resistance temparature device Relative water level 1 Ultrasonic, at the centre column of offshore side Impact pressure 3 Strain type, lm,3m and 6m above W.L. on the center column of offshore side Wind pressure 2 Semiconductor sensor, difference of wind pressures on fore & aft side of upperstructure and starboad fc port side of upperstructure Acceleration 5 servo type, surge, sway and heave (center, fore and aft) Roll 1 Vertical gyroscope Pitch 1 Vertical gyroscope Yaw 1 Directional gyroscope Slow drift motion 6 Ultrasonic, 2 transmitters on the footings and 3 receivers on the sea floor Mooring line tension 8 Load cell type, strain gauge type Strain 12 Strain gauge installed indirectly

The three ultrasonic wave probes were installed as a line array on the bottom of 180 m offshore of the POSEIDON. They were used to estimate the directional wave spectra. The measuring system of slow drift motion consists of two ultrasonic transmitters attached on the footings and three receivers on the sea floor. 4 Data Aquisition System Fourty eight items are automatically recorded by a personal computer at every six hours. One record time was 34 minites and 8 seconds. The sampling interval was 0.5 sec. thus 4096 data are recorded for each items. In order to record a long duration data, another recording system is also used. The system is that the lond duration measurement can be started by a cormnand sent from the beach by means of a telemeter system. In this case, the sampling interval was 1.0 sec. The recorded data were store on boad into the hard disc of 40 MB. 4

r The list of the papers about the at-sea experiment <Outlitie of the at-sea experiment> 1. Hara Shohichi et. al; A Field Tests of Proto-Type Floating Offshore Structure POSEIDON, Proc of OCEANS '89 (1989) at Washington 2. Ohmatsu Shigeo et.al; At-Sea Experiment of Floating Platform POSEIDON. Proc. of OMAE (1989) at Hague 3. Kitaraura fumitoshi et.al; At-Sea Experiment of Floating Offshore Structure POSEIDON. Proc. of Techno-Ocean ' 90 (1990) at Kobe 4. Ohkawa Yutaka et.al; A Field Measurement of Floating Platform POSEIDON, Proc. of IMSDC (1991) at Kobe 5. Ohkawa Yutaka et al.; Results of the Field Experiment of the Floating Offshore Platform POSEIDON, UJNR 1991 Meeting (1991) at Tokyo 6. Ohmatsu Shigeo; At-Sea Experiment of Floating Offshore Structure - Environmental Conditions responses of Structure -. Proc. of Techno-Ocean ' 92 (1992) at Yokohama <Environinental condition> 1. Ohmatsu Shigeo et.al; Wind. Waves and Currents at the Test Field of Floating Platform POSEIDON, Proc. of OMAE (1990) at Hague 2. Yoshimoto Hirofumi et.al; Characteristics of Directional Wave Spectra Measured at Japan Sea. Proc. of OMAE (1992) at Calgary 3. Kato Shunji et.al; At-Sea Experiment of a Floating Offshore Structure Part 1. Wind Characteristics of the Test Field, Jour, of SNAJ Vol. 167 (1990) ( in Japanese and English ) 4. Ando Sadao et, al; At-Sea Experiment of a Floating Offshore Structure Part 2. On the Distribution of Temperature by Solar Radiation for Experimental Structure, Jour, of SNAJ Vol.167 (1990) (in Japanese ) 5. Yoshiraoto Hirofumi et.al; At-Sea Experiment of a Floating Offshore Structure Part 3. Characteristics of Directional Wave Spectra at the Test Field. Jour, of SNAJ Vol.168 (1990) (in Japanese and English ) 5. Yoshimoto Hirofumi et.al; On the Statistical Properties of Waves Measured at the Japan Sea, OCEANS' 93 ( to be submitted ) <Motions of structure> 1. Ohmatsu Shigeo et.al; Motion Responses in Directional Waves of Prototype Floating Platform "POSEIDON", Proc. of OMAE (1992) at Galgary 2. Ohmatsu Shigeo et.al; At-Sea Experiment of a Floating Offshore Structure Part 4.Motion Response in Directional Spectra Waves, Jour, of SNAJ Vol.169 (1991) ( in Japanese ) 3. Saitoh Masakatsu et.al; At-Sea Experiment of a Floating Offshore Structure Part 8. Analysis of free Decaying Test. Jour, of SNAJ Vol.171 (1992) ( in Japanese ) 4. Kato Shunji et.al; At-Sea Experiment of a Floating Offshore Structure Part 9. Time Domain Simulation and Statistical Predictions of Slow Drift Motion, Jour, of SNAJ Vol.172 (1992)

<Mooring systeb> 1. Ohmatsu Shigeo et.al; On the Tensions of Mooring Lines of Floating Platform POSEIDON, Proc. of OMAE (1991) at Stavanger 2. Omata Sadao et. al; At-Sea Experiment of a Floating Offshore Structure Part 7. Characteristics of mooring line Tension, Jour, of SNAJ Vol.171 (1992) ( in Japanese ) <Strength of structure> 1. Yago Kiyokazu et.al; At-Sea Experiment of a Floating Offshore Structure Part 5. Measurement of Stress Range Distribution for Fatigue Analysis, Jour, of SNAJ Vol. 170 (1991) ( in Japanese ) 2. Hoshino Kunihiro et.al; At-Sea Experiment of a Floating Offshore Structure Part 6. Deforma tion and stress of Structure due to the Ununiformity of the Temperature Distribution, Jour, of SNAJ Vol. 171 (1992) ( in Japanese ) OMAE : Offshore mechanics and Arctic Engineering IMSDC : International Marine System Design Conference UJNR : United States/Japan Cooperative Program in Natural Resources SNAJ : Society of Naval Architects of Japan