Nippon Kaiji Kyokai (一般財団法人日本海事協会, Ippan-zaidan-hōjin Nippon Kaiji Kyōkai) is a ship classification society.It is also known by the brand name “ClassNK” or often in the industry as just “NK”. ClassNK is a non profitable non governmental organization dedicated to ensure the safety of life and property at sea, and the prevention of pollution of the marine environment.The principal work of the Society's expert technical staff is to undertake surveys to ensure that the rules which it has developed, are applied to both newly built and existing ships in order to ensure the safety of these vessels. The rules cover not only hull structures, but also safety equipment, cargo handling gear, engines, machinery, and electrical and electronic systems among others.By the end of December 2007, the Society had 6793 ships totaling 152.22 million gross tons under class. This figure represents approximately 20 percent of the world merchant fleet currently under class. Although based in Japan, ClassNK has worldwide representation through a network of exclusive surveyor offices. ClassNK's surveyors work in shipbuilding and repair yards and at ports across the world, wherever they may be called upon to examine the condition of a ship so that all of the Society's services are available worldwide. On November 15, 1999, Nippon Kaiji Kyokai celebrated the centenary of its foundation.On 28 May 2012, ClassNK officially announced that its register had surged past the 200 million gross ton mark becoming the world’s first class society in history to have more than 200 million gross tons on its register..
A benchmark study of 10 different numerical methods for ship motion and load assessment is presented. Pitch motions and midship vertical bending moments are compared to model test results for a containership at zero speed in head regular waves. The wave steepness is varied from 2.1% to 10.5%. The model tests show that pitch and the vertical bending moment (VBM) display nonlinear behavior even for low-steepness waves. It is demonstrated that computational fluid dynamics (CFD) methods can reproduce the ship responses with good accuracy, even in very steep waves, involving green water and parts of the ship going in and out of water. Weakly nonlinear potential-theory methods tend to overestimate the pitch motions and the sagging moments as the wave steepness increases. For the vertical bending moment in steep waves, the 3D panel methods did not give significantly better results than those obtained with the nonlinear strip theories.
This study aimed to demonstrate the susceptibility of 5% Ni steel to stress corrosion cracking, SCC, in anhydrous liquid ammonia. SCC tests using four-point bend specimens cut from welds in SPV315, HT780 and 5% Ni steel were carried out in anhydrous liquid ammonia with 5wt% NH 4 CO 2 NH 2 and 0.1MPa O 2 at +2.0V, which is an accelerated SCC test condition. No SCC was observed in SPV315, whose strength is within the allowable strength of IGC code 17.12, but SCC was observed in the HAZ of HT780, whose strength is higher than the upper limit of IGC code 17.12. Furthermore, SCC was recognized in the HAZ and base metal of 5% Ni steel, whose nickel content is higher than the upper limit of IGC code 17.12, and this suggests that 5% Ni steel is susceptible to SCC in anhydrous liquid ammonia.
This study develops a novel class of queueing game to explain a common practice in cargo shipping "Sail Fast, Then Wait" (SFTW), and demonstrates that resolving information asymmetry among ships can deconcentrate port arrival times. We formulate a competitive navigating environment as an incomplete information game where players strategically decide their arrival time within heterogeneous feasible sets under First-Come, First-Served port policy. Our results show that in incomplete information settings, SFTW emerges as the unique symmetric equilibrium. Conversely, under complete information, the set of equilibria expands, allowing for slower and more environmentally friendly actions without compromising service order. We further quantitatively evaluate the effect of information enrichment based on empirical data. Our findings suggest that the prevalence of technologies enabling ships to infer others' private information can effectively reduce SFTW and enable more energy-efficient and environmentally sustainable operations.
Hot-rolled 5083-O aluminum alloy has emerged as a strong candidate for use in storage tanks for liquefied hydrogen (LH₂) marine transport, owing to its performance under extreme cryogenic conditions. This study aims to investigate the micromechanisms and critical conditions for the formation of split cracks in 5083-O aluminum alloy at cryogenic temperatures. Tensile tests on smooth and notched round bar specimens and L–T direction C(T) tests were conducted at 293 K, 223 K, 123 K, and 4 K, while an S–L direction C(T) test was performed at 77 K. The fracture locus at each temperature was obtained by combining the results of notched round bar tests with finite element (FE) analyses. The results showed that the fracture locus of 5083-O is temperature-independent. Among the round bar specimens, split cracks were observed only in those tested at 4 K and in the R1 notched specimen at 123 K. For the C(T) specimens, split cracks occurred only in the 4 K tests. Furthermore, a three-stage model was established for the formation process of split cracks. To calibrate the model for 5083-O, FE analyses were conducted to determine the critical conditions for each stage at various temperatures. The results predicted by the developed model were compared with the C(T) test results at temperatures ranging from 123 to 293 K.
Concern for descriptions of the ocean environment, especially with respect to wave, current and wind, in deep and shallow waters, and ice, as a basis for the determination of environmental loads for structural design. Attention shall be given to statistical description of these and other related phenomena relevant to the safe design and operation of ships and offshore structures. The committee is encouraged to cooperate with the corresponding ITTC committee.
