*********** +++++++++++++++++++++ 120294B.ENG + Source: ONR Asia + *********** +++++++++++++++++++++ Country: Japan From: Techno-Ocean '94 Proceedings Volumes International Symposium 26-29 October 1994 Kobe, Japan KEYWORDS: With each item Part II/XIII 5 Items Item 1 V. I, p. 33-44 Text in English FAILURE MODES AND PROBABILISTIC STRENGTH EVALUATION OF OFFSHORE STRUCTURES Yoshiyasu WATANABE, Ship Research Institute, Tokyo, Japan Masahiko FUJIKUBO, Hiroshima University, Hiroshima, Japan KEYWORDS: Offshore risk, Failure mode, ReliabilitY analysis, Strength model Buckling strength, Ultimate strength, Offshore foundation strength ABSTRACT A review of the present states of risks and failure modes of offshore structures and that of the probabilistic modeling of component strength associated with typical failure modes are reported. The present state of the risks of offshore structures, is first described by comparing with thore of merchant ships, commercial aviations and so on, and failure modes of offshore structures sudi as semi-submersible platforms, jack-up platforms and fixed platfortm are made clear based on offshore accident data base. It is shown that the primary failure modes of the ofeshore structures are a fatigue failure at member joints and a budding/plastic collapse of bracing members mainly due to collision, contact and foundation failures. A structural reliability analysis considering uncertainties of strength and load effects gives a rational measure of safety of offshore structurer, against there failures. In the second part of the paper, the uncertainties of component strength concerned with some typical failure modes and their probabilistic modeling are described. The buckling strength of columns and stiffened shells, the ultimate capacity of simple tubular joints and the offshore soil strength are considered, with an emphasis on the evaluation of modeling uncertainty caused in the formulation of the strength model. 5. CONCLUSIONS In this paper, the failure modes of offshore structures and the probabilistic strength modeling concerning some of typical failure modes were reported. It may be concluded that: (1) According to the offshore accident data base, the primary failure modes of offshore structures are a fatigue failure at member joints and a buckling/plastic collapse of bracing members causm by collision, contact and foundation failures. (2) Many efforts have been made to develop rational strength models for buckling/plastic collapse of offshore @l members and foundation failures. However, there still exist significant bias and scatter between predicted and tested strengths. A modeling uncertainties shown in the study must be taken into account in the evaluation of a failure probability and a failure risk. (3) Offshore foundation strength generally has larger uncer- tainties than steel member strengths, resulting from a difficulty in the estimates of spatial distribution of in- situ strength and in the correlation of test and in-situ strengths. REFERENCES 1) Sharples, B.P.M., Bennett, W.T. and Hickey,J.C.: Risk Analysis of Jackup Rigs, J. Marine Structures, Vol.2, 1989. 2) Eftliymioul M. and Graham, C.G: Environmental Loading oti Fixed OfFshore Platforms, SUT Inti Conf., Environmental Forces on Offshore Structures and their Prediction, London Engineer, 1992. 3) Tien, H.W, Tang, W.H., Sangrey, D.A. and Bamher, G.B.: Reliability of Offshore Foundations-State of the Art, ASCE, J. of Geotechincal Engineering, Vol.115, no.2, 1989. 4) Fukumoto, Y. and Itoh, Y.: Evaluation of Multiple Column Curves using the Experimental Data-Base Approach, J. Const. Steel Rearchch, Vol.3, No.3, 1983. 5) Frieze, P.A.: Lessons Learnt from Reliability Analysis Studies of Offshore Platforms, OMAE'86 Tokyo, Japan, Vol.2, 1986. 6) Warwick, D.M. and Faulkner, D.: Strength of Tbbular Members in Offshore Structures, Report NAOE-88-36, Glasgow University, 1988. 7) Faulkner, D.: Development of a Reliability Design Code for the Structure of Tension Leg Platforms, OTC 4648, 1983. 8) Cho, S.R. and Frieze, P.A.: Strength Formulation for Ring- Stiffened Cylinders under Combined Axial Loading and Radial Pressure, J. Const. Steel Research, 1988, Vol 9. 9) Faulkner, D., Chen, Y.N. and DeOliveira, J.G.: Limit State Design Criteria for Stiffened Cylinders of Offshore Structures, ASME, 4th National Congress of Preinure and Piping Technology, 1983. 10) Yura, J-A., Zettlemoyer, N and Edwards, F.: Ultimate Capacity Equation for Tbbular Joints, OTC 3690, 1980. 11) API, Recommended Practice for Planning, Design and Constructing Fixed Ofrsitore Platforms - Load and Resistance Factor Design, API RP2A-LRFD, 1st Edition, 1993. 12) Hoadley, P.W., Clarkson. U. and Yura, J.A.: Ultimate Strength of tubular Joints Subjected to Combined Loads, OTC 4854, 1985. 13) Matsuo, M: Foundation Engineering, Gihodo, 1984. 14) Matsuo, M. et al.: Probability models of undrained strength of marine clay layer, Soils and Foundations, Vol. 17, No.3, 1977. 15) Matsuo, M et al.: A Stochastic Study on Some Properties and Failure Probability for Unsaturated Soils, Proc. JSCE, No.208, 1972. 16) Horiuchi, H. et al.: Probabilistic Nature of Soils for Re. liability Design, Tsuti-to-Kiso, Vol.25, No.11, 1977, 17) Wu, T.H. et al.: Probabilistic Analysis of Offshore Site Exploration, J. @tech. Engrg., ASCE, Vol.112, No.11, 1986. 18) Wu, T.H- et al.: Uncertainties in Evaluation of Strength of Marine Sand, J. Geotech. Engrg., ASCE, Vol-113, No.7, 1987. 19) Barlow, R.E.: The Bayesian Approach in Risk Anal@, ASCE Specialty Conference on Probabilistic Mechanics and Structural Reliability, Berkeley, Calif., 1984. 20) Ingra, T.S. et al.: Uncertainty in @ing Capacity of Sands, J. Geotech. Engrg., ASCE, Vol-109, No-7, 1983. 21) Tang, W.H.: Offshore Axial Pail Reliability, Research Report for Project PRAC 86-29B, sponsored by API, 1988. 22) Tang, W.H. et a].: Performance Reliability of OfFshore Piles, OTC6379, 1990. 23) API, Recommended Practice for Planning, Design and Constructing Fixed Ofrshore Platforim, API RP2A, 16th Edition, 1986. 24) Tang, W.H. et al.: Offshore Lateral Pile Design Reliability, Research Report for Project PRAC 87-29, sponsored by API, 1990. 25) API, Recommended Practice for Planning, Design and Constructing Fixed Offshore Platforms, API R.P 2A, 17th Edition, 1987. 26) Matlock, H: Correlations for Design of Laterally Loaded Piles in Soft Clay, OTC1204, 1970. 27) Reese, L.C. et al.: Field Testing and Analysis of Laterally Loaded Piles in Stiff Clay, OTC2312, 1976. 28) Reese, L.C. et al.: Analysis of Laterally Loaded Piles in Sand, OTC2080, 1974. +++++ Item 2 V. I, p. 41-46 Text in Japanese ACTIVE CONTROL OF UNDERWATER ELASTIC STRUCTURES AND ITS PROSPECT Hideyuki SUZUKI, Koichiro YOSHIDA Department of Naval Architecture & Ocean Engineering University of Tokyo, JAPAN KEYWORDS: Elastic Structure, Active Control, Deepsea Installation, Elastic Response ABSTRACT Construction of underwater structures in deepsea is accompanied by much difficulty. Lowering of components and construction of structures on the sea bed is no longer efficient, because the operation from the sea surface depends on weather condition. Precise positioning with suspension wire becomes much more difficult in deepsea. Another choice is to install onshore fabricated larger components or completed structure. In this operation, structures must be protected from excessive deformation and dynamic responses. One key technology in the near future will be a remotely operated or autonomous installation and mating of large underwater structures in the deesea or on the sea bed. The structures are launched at the sea surface and towed to the installation site by the thrusters attached on the structure and installed. During this operation the attitude and structural response are controlled. If the structural responses are controlled properly and structures are protected from excessive responses, the structures can be designed much lighter, flexible and neutrally buoyant, at least during installation for the sake of efficiency. This paper is concerned with active control of elastic and rigid body response of structures. handling of complicated coupled motion of elastic and rigid body response of a structure is discussed. Possible effect of active control on structural design is examined. REFERENCES (in English) [2] Suzuki, H. and Yoshida.K. :"Controlled Installation of Deep Water TLP Tendons", Ilth International Symposium on Offshore Mechanics and Arctic Engineering, Vol.1 -part B, 1992, pp-549- 556. [6] Y.Ohkami, T.Kida and I.Yamaguchi :"Dynamics, Modeling and Order Reduction of LSS". Journal of the Society of Instrument and Control Engineers, Vol.26. No.10(1987). pp.845-854. [7] Y.Ohkami and II.Fujii :"Dynamics Modeling of Flexible Spacecraft - Hybrid System and Truncation". Journal of the Japan Society for Aeronautical and Space Sciences, Vol.32, No- 364(1984). pp.263-274. [8] M.J Balas :"Active Control of Flexible Systems", Journal of Optimization Theory and Application, Vol-25, No.3(1987). pp.415- 436. [9] H. Ohta, T.Aoki and F.Kainuma :"The Implementation of Modal Filters for Spillover Reduction". Journal of the Society of Instrument and Control Engineers, Vol.25, No.11(1986). pp-1015- 1022. [10] L.Meirovitch and H.Baruh : "The Implementation of Modal Filters for Control of Structures', Journal of Guidance and Control, Vol.8, No-6 (1985). pp-707-716. [11] L. Meirovitch and H.Oz : "Modal Space Control of Large Flexible Spacecraft Possessing Ignorable Coordinate". Journal of Guidance and Control, Vol.3, No.6 (1980), pp-569-577. [12]K.Tsuchiya, T.Kashivase and S.Manabe: "Attitude Control of Flexible Spacecraft". Journal of the Society of Instrument and Control Engineers, Vol.24, No.5(1985), pp.410-416. [13]M.J.Balas :"Feedback Control of Flexible System", IEEE Trans., AC23(1978). pp-673-679. +++++ Item 3 V. I, p. 57-62 Text in Japanese DEVELOPMENT OF FLAPBOARD BREAKWATER Yuzo SUZUKI, Yosinobu NISIMIRA, Toshikazu UTO Kobe Investigation and Design Office The 3rd District Port Construction Bureau Ministry of Transport KEYWORDS: Flapboard breakwater, Wave dissipation by elastic boards ABSTRACT Flapboard breakwater is a newly developed structure made up of rows of elastic boards with high rigidity. Reducing the energy of the incoming waves due to reaction forces and swing of the elastic boards,this breakwater creates calm sea area. The 3rd District Port Construction Bureau is now carrying out fundaaental hydraulic model tests to examine the functions and characteristics of this newly developed breakwater. This paper reports the hydraulic property of this flapboard breakwater obtained through the hydraulic model tests. +++++ Item 4 V. I, p. 63-67 Text in Japanese HYDRAULIC CHARACTERISTICS OF SUBMERGED TRAPEZOIDAL BREAKWATER TOPPED WITH A ROW OF ROUGHNESS CAISSONS Shigeru YOSHIDA Nagaoka College of Technology Norio HAYAKAWA Nagaoka University of Technology KEYWORDS: Submerged Breakwater-Wave Breaking-Energy Dissipation ABSTRACT An experimental study is conducted with a laboratory wave tank 14 m long, in which a trapezoidally shaped breakwater topped with a row of roughness caissons is placed. It is expected that to place the roughness caissons in one to five rows would enhance dissipation of wave energy while allowing passage of certain amount of water over the breakwater. A careful measurement of the incident, reflected and transmitted waves is carried out and the energy dissipation rate is obtained for a variety of number of rows of roughness caissons, submerged depth and wave period. The result is exhibited in figures and it is noted that the energy dissipation rate is expressible as a parabolic function of the ratio of the submerged depth to the breakwater height Parameters of the parabolic function are analyzed to give an empirical formula of the energy dissipation as a function of the ratio of the submerged depth to the breakwater height, number of rows of roughness caissons and wave period. +++++ Item 5 V. 1, p. 69-74 Text in English OCEAN ENVIRONMENTAL CHANGE DUE TO AN OFFSHORE -AIRPORT IN ARLAKE BAY Yusaku KYOZUKA* Kazutoyo YOKOYAMA** * Dept. Earth System Sci. & Tech., Kyushu Univ. ** Sumoto Public Works Bureau, Hyogo Prefecture ABSTRACT An assessment of the ocean environment is presented for an airport in Ariake Bay, which is well known for its large tides and vast tidal marsh. A newly developed ADI method including the ettects of moving boundaries on the tidal marsh is applied for calculating the tides and currents in the bay. Moving boundaries on the tidal marsh are treated by a quasi-static approximation at every time step in the calculations. Assessment functions for the changes in tides and currents are defined by the ocean area which would be aitected by the construction of an &irport in the bay. Three locations for an island airport and an approaximated floating airport are compared in the assessment functions. Diffusion of COD from four rivers is also simulated and the distribution patterns of COD density after 30 tides are compared. It is found that the location of the airport has great impact on the ocean environment, especially near the coast where tidal marsh exists. The results are presented graphically. +++++ END Part II/XIII ************** END Msg. B.ENG **************