Classification Society Rules Research Articles

Innerbottom Design Problems in Double-Hull Tankers

OPA '90 and parallel IMO rules are driving a phased changeover in tanker design from single-hull to double-hull construction. This paper describes field observations and analyses of two of the more persistent innerbottom design problems: the joint between frame vertical stiffeners and longitudinals, and panel cracks along the innerbottom/longitudinal seams. Potential shortcomings in applicable classification society rules are addressed, and possible solutions at both the design and repair stage are offered.

Hydrodynamic Pressure Distribution for Fatigue Analysis of Large Ships in Waves

As for the recent structural design of a ship, direct strength calculations are approved in classification society's rules, and wave loads for the calculation are given. However, such wave loads may be taken on the premise that the buckling or collapse strength of a ship will be checked by the direct strength calculation. In consequence, it may be questionable to apply such wave loads to the investigation of fatigue strength of a ship. In fatigue analysis of a ship, it is most important to estimate accurate pressure fluctuations in time and space. With the use of the pressure fluctuations, the stress fluctuation can be calculated.In the present paper, the fluctuation in time and space of pressures acting on a bulk carrier in waves were investigated. Time histories of the pressure along ship's hull were calculated by Boundary Element Method. Surveying the pressures, distribution patterns along the ship's hull of the pressure fluctuation were classified ; 4 typical patterns of pressure distribution were introduced. With the use of these pressure distributions, structural analyses were performed for 1/2 hold spans fore and aft part of a bulkhead in port side of the ship by Finite Element Method. The stress distributions on the inner bottom plate and the bilge hopper tank plate were investigated. Finally, design loads for fatigue analysis of a large ship are discussed.

Fracture toughness of steel plate from MV Kowloon Bridge

Chemical analysis, tensile, Charpy, DW NDT and fracture mechanics toughness data are presented for a grade A steel plate from the Kowloon Bridge, a sister ship of Derbyshire. The plate is shown to have poor toughness under dynamic loading conditions. The results leave open the possibility that brittle fracture could have contributed to a structural failure in the Derbyshire even at the high temperature of +30°C which is reported to have existed at the time of the ship's disappearance. The results are felt to support the proposition that present classification society rules need tightening to reduce the risk of brittle fracture in ships.

Nonlinearity of Sagging Moment of Fine Ships

Rational design of ship's longitudinal strength should, be based on accurate evaluation of bending moment and shearing force. The nonlinear strip theory and model experiments reveal that the internal force by waves in rough seas differ from the ones obtained by the linear theory. Rules of classification societies are based on the long term prediction of structural responses, which is performed under the assumption of linearity in response and uses of the linear superposition method. According to the recent studies, the effect of nonlinearity becomes to be taken into consideration in the rules of classification societies.In the present paper, calculations are performed for a fine container ship and for a fullbodied bulk carrier using the nonlinear strip theory. Numerical results are obtained for regular waves of various wave height, wave length and wave encounter angle and for irregular waves of ISSC spectra by the nonlinear strip theory, and are compared with the result of O. S. M. : the linear theory. Results obtained are as follows : 1) Sagging moment increases as wave height increases by the effect of nolinearities, and the moment is about 170% of the one obtained by O. S. M. at the wave height 8 m in regular head sea for the container ship.2) On the contrary, the effect of nonlinearity in hogging moment is not so significant as in sagging moment. Therefore, long term prediction of hogging moment is obtained appropriately by the linear theory.3) Approximate prediction of long term response of bending moment is performed taking into account of the nonlinearity, and compared with the present rules.

Veritas'' Role In Offshore Certification

Abstract What is DnV? It is an independent self-financed society or, "foundation" created in 1864 in Norway. It has no shareholders. Its main objective is to safeguard life, property and the environment both at sea and on land. This has involved the establishing of Rules and Guidelines regarding classification, quality assurance and certification of sea-going vessels, structures and other installations. DnV is now operating in more than 100 countries with a world-wide staff of over 3,000, including research teams. What is Certification? As used by DnV, it implies that a structure or an item of equipment has been reviewed against a certain set of requirements and furthermore that a document is issued stating that the requirements have been complied with. Certification has evolved from such events as disasters at sea and pressure vessel explosions. In recent years, there has been a growing clamour for improved protection of life, equipment and resources which has been reflected in ever tighter surveillance and inspections by certifying societies such as DnV.A typical Certification Program will include some or all of the following:Evaluation and review of design parameters and design,Inspection during all phases of construction,Surveying of marine operations,Survey of testing and commissioning,In-service inspection during the lifetime of the project. Inspection during fabrication and installation is intended to be additional to and not a replacement of the control activities of the operator/owner, designer or contractor. It is to ensure that these activities are carried out according to the design and specifications under independent supervision. In a new offshore theatre where existing regulations and codes/standards are difficult to apply, manageable regulations are essential. DnV believes that governmental regulations must tailor themselves to basic requirements such as:Protection of the public interest,Minimum standards that give adequate levels of safety and reasonable protection to the environment,Implementation and practice so that they do not form any undue hindrance in the executi9n of work and are in keeping with "state-of-the-art" advances. Classification societies claim right of ownership to their rules in a certification/ approval system. At the same time, regulations of government bodies always supersede the rules of classification societies relating to offshore certification. The design of fixed steel platforms is commonly based on National Regulations, Standards or Building Codes and the rules of societies such as DnV. Offshore rules and guidelines have been set down by those bodies most closely involved (e.g. API). Canadian offshore activities are governed by regulatory authorities such as COGLA, Canadian Coast Guard, Newfoundland/Labrador Government (Petroleum Directorate). This includes the various statutes on regulatory matters. Safety Approaches in A Certification Scheme Safety and reliability of offshore installations depend on a combination of: environmental phenomena, structural response, strength capacity, efficiency and quality of topside facilities, fitness of instrumentation and last but not least, the capabilities of the personnel staffing the project. Technological activities always have a certain element of risk and this can never be eliminated.

On the Effectiveness of Panting Stringers and Web Frames of a Ship (2nd Report)

In the first report, the author studied the “Effectiveness of Panting Stringers and Web Frames of A Ship”, and showed that the stringers with web frames whose sizes were determined by the Rules of Classification Societies are not strong enough to support side frames. Recently, however, strong stringers with web frames are often adopted, which is known as “Web and Stringer System”. This paper gives the result of an analysis made to the structure of panting zone of a 8, 750 G. T. cargo ship which has been strengthened in such a way as stated above and shows that the effectiveness of “Web and Stringer System” is practically sufficient in this case.