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155 APPENDIX J DEVELOPMENT OF DYNAMIC-MOTIONS-BASED STABILITY ANALYSIS The Need and Development of Dynamic-Motions-Based Stability Criteria Ship stability criteria are focused on avoiding capsizing, which can occur in extreme weather accompanied by large nonlinear vessel motions in random seas. The existing static stability criteria are at best an approximation that considers a greatly simplified and idealized model of the actual physics. Existing criteria explicitly and even implicitly ignore the dynamics, the damping, and the randomness of the seas. Research efforts to improve the approximations inherent to existing ship stability criteria in order to consider a more accurate physical model are ongoing worldwide and could be promoted within the United States. It seems generally understood that any dynamic-based regulations would need to be simplified from the complexity of trying to duplicate precisely the physics of extreme conditions, but they could be supported by an understanding of the underlying physics (e.g., complicated physical modeling, nonlinear dynamics, and randomness of the environment) and the approximations inherent in the simplified practical criteria. An early development in the United States of industry-supported physics-based vessel stability criteria was the American Bureau of Shippingâs (ABSâs) response-based mobile offshore drilling units (MODUs) stability criteria (Shark et al, 1994). In the aftermath of the highly publicized capsizing of two major offshore units (i.e., Ocean Ranger and Alexander Killeen) ABS organized a series of joint industry projects with various interested parties. These efforts resulted in its MODU response-based criteria. However, these criteria were solely applicable for column-stabilized units and did incorporate a spectral representation of the environment, direct time domain motion simulation, and validation with physical model testing.
156 They were subsequently submitted to the International Maritime Organization (IMO) and exist as an alternative to the traditional prescriptive criteria of comparing area under the righting arm to area under the wind heeling arm. The ABS/IMO response-based MODU stability criteria and ABS efforts in this area represent a leadership role by classification societies in vessel stability criteria. There are many specific issues associated with MODU stability and the UK Health and Safety Executive (HSE) described many of these in a recent study (HSE, 2006). Another group that has contributed to our understanding of the unique aspects of offshore platform stability is the American Petroleum Institute expert committee, which updated their guide Recommended Practice for Planning, Designing, and Constructing Tension Leg Platforms (API, 2010) to reflect the unique mechanics associated with the tension leg platform (TLP). This became particularly important following the total loss of the TLP Typhoon during Hurricane Rita in 2005. The investigation of the effect of waves on the time-varying roll-restoring moment had begun at least as far back as the 1950s in Germany (see, e.g., Grim, 1952). However, work in the United States commenced soon after that (see, e.g., Kerwin, 1955). Analytical work then continued into the early 1960s with Paulling (1961) and was followed by an extensive research program supported by the U.S. Coast Guard (USCG), which included the development of a computer program to accurately simulate parametric resonance. This research program also included scale model testing in a protected part of the San Francisco Bay of several vessel types, including a fishing vessel and a cargo ship (see, e.g., Oakley et al, 1974). Interest in parametric roll was mainly restricted to academic researchers until the U.S. container ship APL China experienced a large motion event in 1998, which resulted in significant cargo loss (France et al, 2003). This accident occurred due to the hull form of modern container vessels, which have
157 extreme flare at the bow and overhanging sterns. These vessels are particularly prone to parametric resonance, and an ABS internal and sponsored research effort resulted in a classification guide on methods to assess parametric resonance in hull design (ABS, 2004/2008). Much of the ABS work, along with the investigations of other international researchers, has been incorporated into the proposed IMO Second Generation Stability criteria, and parametric resonance is one of the five vulnerabilities considered. Based on the inherent danger of high seas fishing (National Research Council, 1991) and the fact that most fishing vessels are not regulated and even those that are have been involved in casualties, the United Kingdom and others have sponsored major research projects in this subject area. These research efforts include the United Kingdomâs Marine Directorate Department of Transportâs so-called âSafeship project,â which applied mathematical stability theory and stochastic dynamics to analyze the nonlinear and stochastic ship stability problem. This project began in the late 1970s and continued through the 1980s (see, e.g., RINA, 1982, 1986). Many high-profile research projects were part of this effort and numerous publications describing various advanced approaches were issued. These efforts continued into the 1990s, although in a more diverse form (see, e.g., Thompson, 1997). These early fundamental studies form the basis of much of the current, ongoing international research in this area, and have contributed greatly to the better understanding of the ship stability problem. References ABS. Guide for the Assessment of Parametric Roll Resonance in the Design of Container Carriers. 2004 (updated 2008). American Petroleum Institute. Recommended Practice for Planning, Designing, and Constructing Tension Leg Platforms, 3rd ed., Rp-2T., 2010.
158 France, W. N., M. Levadou, T. W. Treakle, J. R. Paulling, R. K. Michel, and C. Moore. An investigation of head-sea parametric rolling and its influence on Container Lashing Systems. Mar Technol., Vol. 40:1 Jan. 1, 2003, p. 19. Grim, O. StabilitÃ¤t und Sicherheit im Seegang. Schiffstechnik, Vol. 1, 1952, pp. 10â21. Health and Safety Executive, UK. Review of Issues Associated with the Stability of Semi- Submersibles. Research Report 473, 2006. International Maritime Organization, Subcommittee on Ship Design and Construction. Report to the Maritime Safety Committee. SDC 5/15, Section 6, Feb.15, 2018. Kerwin, J. E. Notes on Rolling in Longitudinal Waves, International Shipbuilding Progress, Vol. 2, 1955, pp. 597â614. National Research Council. Fishing Vessel Safety. National Academy Press, Washington, DC, 1991. Oakley, O. H., J. R. Paulling, and P. D. Wood. Ship motions and capsizing in Astern Seas. Proceedings of Tenth Office on Naval Research Symposium on Naval Hydrodynamics, 1974. Paulling, J. R. The transverse stability of a ship in a longitudinal Seaway. Journal of Ship Research, Vol. 4:4, 1961. Royal Institution of Naval Architects. Safeship Seminar. Proceedings of a Seminar held March 4, 1982. Royal Institution of Naval Architects. The Safeship Project: Ship Stability and Safety. International Conference, June 9â10, 1986. Shark, G., Y. S. Shin, J.S. Spencer. Dynamic-Response-Based Intact and Residual Stability Criteria for Semisubmersible Units. SNAME Transactions, Vol. 97, 1989, pp. 213â242. Thompson, J. M. T. Designing Against Capsize in Beam Seas: Recent Advances and New Insights. Appl. Mech. Review, Vol. 50(5), May 1, 1997, pp. 307â325.