EFFECT OF DOUBLE BOTTOM HEIGHT ON THE STRUCTURAL BEHAVIOUR OF BULK CARRIERS

This is the first of a series of companion papers that the authors propose to present on the effect that the new CSR Rules will have on the design of bulk carriers. Our initial focus will be on the new design framework established for the inner bottom height of such vessels, a parameter critical to their structural integrity. It examines the effect that double bottom height reduction has on the reliability of the bulk carrier structure, by applying a finite element 3D - 3 hold analysis of varying double bottom heights to a typical current Panamax bulk carrier design. The results are compared to pre and post IACS CSR[2] requirements. The conclusion reached is that the establishing of the double bottom height should not be left to direct calculations. A minimum acceptable height should be established in order to maintain a minimum level of structural reliability and safety.

LIFE-CYCLE CO2 EMISSIONS OF BULK CARRIERS: A COMPARATIVE STUDY

In order to maintain shipping capacity to serve seaborne trade, new ships have to be built to replace those scrapped. The cost of building, manning, operating, maintaining and repairing a ship throughout its life is borne by society at large through market mechanisms. Gratsos and Zachariadis (2005) had investigated through a cost/benefit analysis how the average annual cost of ship transport varies with the corrosion additions elected at the design stage. The results of that paper clearly indicated that ships built with sufficient corrosion allowances, truly adequate for the ship’s design life, have a lower life cycle cost per annum despite the fact that such ships would carry a slightly smaller quantity of cargo. Furthermore the safety and environmental benefits due to the reduced repairs and extended lifetime of such ships were briefly discussed. The debate of how “robust” a ship should be was also transferred to IMO in the context of Goal Based Standards following a submission by Japan which stated that the increased steel weight of a more robust ship will result in increased CO2 emissions due to a reduced cargo carrying capacity. Greece replied by submitting a summary of the aforementioned paper and preliminary estimations on Life cycle CO2 emissions disputing the Japanese contentions. However, taking onboard the challenge, an update is provided in the present paper, using the final Common Structural Rules (CSR) of the International Association of Classification Societies (IACS) bulk carrier corrosion margins and taking into account the major environmental implications of the heavier ship scantlings for two bulk carrier size brackets, Panamax and Handymax. The results show that the more robust ships would produce less CO2 emissions over their lifetime.

STUDY ON THE ASSESSMENT OF IMPACT FORCE BETWEEN SHIP AND BRIDGE PIER

The bridge crossing water way is in the risk of impact by vessel, and thus it is very important to estimate the collision force for the safety of bridge. The impact force between bridge pier and vessel is investigated by numerical simulation and various empirical formulae. The collision response between a 5000t DWT bulk carrier with bulb bow and rigid bridge pier is simulated in the explicit finite element code of ANSYS LS-DYNA. The difference of the impact force between the empirical formulae and FE analysis are discussed. Based on the comparison of the results, the coefficient in the formulae is suggested for obtaining more accurate assessment of impact force.

CHANGE OF STEEL’S YIELD STRESS OVER SHIP’S SERVICE LIFE AND ITS EFFECT ON THE FIRST YIELD HULL GIRDER BENDING MOMENT

The publication deals with the decrease of the yield and tensile stress of high tensile shipbuilding steel AH-32 over ship’s service life and its effect on the first yield bending moment as a representative of the hull girder capacity. An example is given for a sample 25K DWT (25 thousand tons deadweight) bulk carrier. The probability of failure is calculated as the probability of the total hull girder bending moment exceeding the first yield bending moment. The probabilistic distributions of yield and tensile stress are obtained from laboratory test of the specimen of AH-32 steel (corroded plates of a 20 year old ship). It is found that although the decrease of yield stress may not be great, the increase of the probability of failure (i.e., the probability yield bending moment) could be substantial.

A FUZZY NEURAL NETWORK MODEL FOR ANALYZING BALTIC DRY INDEX IN THE BULK MARITIME INDUSTRY

Baltic Dry Index (BDI) is one of the important indexes in the dry bulk shipping market. BDI analysis and forecasting is one of important activities of shipowners, charterers, shipping carriers, importers and exporters, and banks in the dry bulk shipping market. Based on the accurate BDI analysis and forecasting , the shipowners, charterers, shipping carriers, importers and exporters, and banks in the bulk shipping market could make many important decisions of shipping operation, management and financial invest such as building a new bulk carrier, chartering-in or chartering-out a second-hand bulk carrier, demolishing an old bulk carrier, and providing funding for shipowners. Thus, this paper adopts a fuzzy neural network model to analyze the relationship between the BDI in the international bulk shipping market and the major economic indexes in the global financial market. Finally, the proposed fuzzy neural network model is tested by empirical data during the period of 2000-2015. The results show that the fuzzy neural network model has high accuracy of forecasting. The fuzzy neural network model in this study seems to be promising and the model could help the shipowners, charterers, shipping carriers, importers and exporters, and banks forecast future BDI points in the bulk shipping market, and then make important decisions and operation strategies of shipping operation, management and financial invest.

Bulk Cargo Marine Transportation Industry

Bulk cargo is being transported in large parcels to reduce transportation cost calculated per unit of cargo. Its main categories are: liquid cargo, dry bulk cargo and special bulk cargo. The deadweight of the fleet of ships carrying bulk cargo by sea increased 3.4 times in 1990-2020. Dry carriers account for 55% of the fleet and their deadweight increased 4.4 times during the same period. The Oil and oil products tankers account for 37% of the deadweights which has been increased by 2.4 times. The majority of the oil tanker tonnage (over 98%) comes from VLCC, Suezmax and Aframax type vessels. 60% of this is 200 thousands tankers sized more than dwt. The oil tanker freight market in 2002-2019 was characterized by a high level of volatility. VLCC tanker time-charter equivalent ranged from $ 8.7-95.2 thousand in 2002-2019. The variability of time-charter rates in other oil tanker categories was similar. The major part of the tonnage of product tankers (more than 90%) is derived from from LR2, LR1 and MR2 type of vessels. 43% of these are LR2 tankers. This segment of the freight market was also highly variable. LR2 tanker time-charter equivalent ranged from $ 7.5-28.8 thousand in 2011-2019 years. The main part of the tonnage of dry cargo vessels (over 69%) comes from Capesize, Panamax and Supramax type vessels. This segment of the freight market has been declining and highly volatile in recent years. The capesize-type ship time charter equivalent ranged from $ 3.5-30.8 thousands in 2011-2019. Keywords: bulk cargo, oil tanker, bulk carrier, gas carrier, chemical tanker, time charter equivalent.

Atmospheric Emissions in Ports Due to Maritime Traffic in Mexico

Atmospheric emissions from vessels at 38 Pacific and Gulf-Caribbean Mexican ports were determined for nitrogen oxides, sulfur dioxide, particulates, carbon monoxide, non-methane volatile organic compounds, and carbon dioxide. The emissions have been estimated using a bottom-up methodology in the maneuver and hoteling phases, by vessel type, from 2005 to 2020. Maritime traffic in Mexico’s Pacific zone contributes approximately with 60% of the country’s total ship emissions, with the remaining 40% in Gulf-Caribbean ports. The highest atmospheric emissions were found at the Manzanillo and Lázaro Cárdenas ports on the Pacific coast, as well as the Altamira and Veracruz ports on the Gulf-Caribbean coast. The contribution of the atmospheric emissions by vessel type at Pacific ports was Container 67%, Bulk Carrier 32%, Tanker 0.8%, and RoRo 0.4%. For Gulf-Caribbean ports it was Container 76%, Bulk Carrier 19%, Tanker 3%, and RoRo 2%. This study incorporates the International Maritime Organization implementations on reductions of sulfur content in marine fuel, from 4.5% mass by mass from 2005 to 2011, to 3.5% from 2012 to 2019, to 0.5% beginning in 2020. Overall, sulfur dioxide emissions were reduced by 89%.

Local flow assessment of the Japan Bulk Carrier using different turbulence models

Ship resistance and powering represent the most important aspects in the initial design stage of the ship. Based on their estimation the basic milestone for selecting the main engine and the propulsion system is established. The majority of ships in the international fleet nowadays rely on the screw propeller working in the wake zone behind the ship. The wake flow of the ship has a direct impact on the propeller performance and the propulsion efficiency. Accurate prediction of the nominal and effective wake is crucially important to provide a proper understanding of the flow where the propeller will perform. From this point of view, the wake flow of the Capesize Japan Bulk Carrier (JBC) is assessed using a viscous flow Computational Fluid Dynamics (CFD) method. Numerical simulations are performed to predict the nominal and effective wake of the ship by making use of the viscous flow solver ISIS_CFD of the FINETM/Marine software provided by NUMECA. The solver is based on the finite volume method to build the spatial discretization of the transport equation to resolve the Reynolds-Averaged Navier-Stokes (RANS) equations. Closure to turbulence is achieved using different turbulence models in order to investigate their accuracy in predicting the complex wake flow of the ship. Two-phase flow approach is used to model the air-water interface where the Volume of Fluid method is implemented to capture the free-surface. The results for both nominal and effective wake are assessed against the experimental data provided by the National Maritime Research Institute (NMRI) and Yokohama National University in Japan that were presented in the seventh Workshop on CFD in ship hydrodynamics (Tokyo2015). The results validation showed a reasonable agreement compared to the experimental data for both nominal and effective wake. As it was expected, some turbulence models showed to be more accurate in predicting ship wake, especially the Shear Stress Transport (K-ω SST) and Explicit Algebraic Reynolds Stress (EASM) Models. A special investigation of the flow vortices is also taken into consideration.