The presence and danger of microplastics in the oceans

Since the environmental pollution by microplastics is a relatively new area of research, the main problem is the lack of appropriate rules, regulations and parameters globally. Therefore, the sources of primary and secondary microplastics particles vary from source to source, and due to this the difference in the division of microplastic particles by size arises too. Moreover, various techniques and technologies are used when testing seawater and sediment as well. Ultimately, with different qualities of the obtained results, it leads to difficult and/or inadequate comparison. Furthermore, the research has been mainly conducted on smaller marine organisms, which needs to be extended to other larger organisms as well as to the human population to create a complete image of the negative effects of contamination of the marine food chain and the marine environment with microplastic particles in general.

Risk assessment and exemption approval procedure for the semi-closed seas according to the International Convention for the Control and Management of Ships’ Ballast Water and Sediments, 2004

The paper analyses statutory foundations applicable to ships requiring to be exempted from the mandatory installation of the ballast water management system. In particular, it deals with ships sailing on regular international lines but within the semi-closed seas, such as the Adriatic Sea. The legal framework is set out in the International Convention for the Control and Management of Ships’ Ballast Water and Sediments (BWM, 2004), the IMO Guidelines for Risk Assessment A-4 (G7), and the Croatian Ordinance on Ballast Water Control and Management, 2012 [Pravilnik o upravljanju i nadzoru balastnih voda]. The paper presents the model procedure to be followed by main stakeholders, mainly national maritime administrations and shipping companies. The paper outlines the main advantages and disadvantages of the whole process and analyses several cases of good practice. Furthermore, the main stakeholders in the approval procedure and their responsibilities are described, available risk assessment models are analysed, with the particular emphasis on the species-specific risk assessment method as the most preferred method. Finally, the need for cooperation between the involved states and their maritime administrations is considered. It is concluded that bilateral and regional cooperations are an essential element in preserving the marine environment of any sea area. In that respect, the proposed model of the BWM system exemption approval in closed and semi-closed seas, such as the Adriatic Sea, is essential for shipping companies connecting ports in different countries on regular routes. Although demanding in respect of efforts and time, a procedure is viable and may be carried out in due time and with satisfactory outcomes.

Evaluation of port workers’ general awareness of dangerous cargo transport

The International Maritime Dangerous Goods (IMDG) Code training is mandatory for all shore-side personnel involved in the handling and transport of dangerous cargoes by sea. This study aims to measure and evaluate the port workers’ dangerous cargo transport general awareness level. For this purpose, the “Dangerous Cargo Transport General Awareness Questionnaire” was developed and applied to trained 100 port workers face-to-face. The questionnaire was proven to be valid and reliable by content validity, construct validity, internal consistency reliability, and test-retest reliability analyses. Four factors were determined as a result of Explanatory Factor Analysis. Discriminant analyses were performed using the Student’s t-test and One Way ANOVA test. Pearson correlation analysis was carried out to determine the relationship between factors. Simple linear regression analysis was used for modeling the relationship between factors. SPSS 24.0 was utilized to conduct the analyses. According to analysis results, port workers’ dangerous cargo transport general awareness does not differ depending on age, position, and education. There is a weak positive or a moderate positive correlation between factors. Port workers have an average and above-average level of general awareness. It is highlighted that increasing this level is possible by increasing the frequency of dangerous cargo transport training. Suggestions are offered for more effective training.

Methodology for composite materials shrinkage definition for use in shipbuilding and marine technology

Deformations of steel material in shipbuilding and marine technology applications as a result of mechanical or temperature influences are a well-known problem. However, in the modern shipbuilding industry, the application of alternative materials, especially composite materials, in the structure and for the equipment of the ship is increasingly represented. Consequently, there is a need to determine the deformation and change of characteristics of such composite materials as a result of various mechanical, and especially temperature influences that cause the so-called shrinkage. The basic composite production process involves connecting the matrix with a catalyst and accelerators that create temperature, then the material shrinks by cooling when it can change its dimensions and characteristics. Also, in order to achieve the best possible mechanical properties, composite materials are specially heated and then cooled according to strictly defined processes and curves. The ability to predict the characteristics and parameters of such deformations is important in the context of the application of composite materials. To define such deformations, different methods are used within individual numerical solvers, whose results can differ significantly from each other. Therefore, the authors in this paper present an established methodology for predicting mechanical and temperature deformations, and modelling of composite materials, based on the analysis of analytical methods and numerical solvers with the aim of defining the most accurate numerical solver. By applying the presented methodology, it is expected to raise the level of accuracy and quality of composite materials production as well as to raise the quality of design solutions and efficiency of production procedures during shipbuilding in particular, but also within different marine technology applications and during the product’s life cycle.

2D Ship-Like Section Slamming Pressure Numerical Analysis by Conformal Mapping

In this paper, a method to predict slamming pressures and pressure distribution at the time of water entry for 2D sections is presented. The mathematical model is based on the Schwarz-Christoffel conformal mapping method. This conformal mapping technique has been used to calculate slamming loads during water entry. The pile-up of water during motion is also considered and an alternative pile-up coefficient is assumed against Wagner’s generalized method. A simplified and accurate method is presented, which does not include non-linear terms and jet flow in the calculated pressure distribution on monotonically increasing 2D sections like wedge shapes. Comparison with real ship sections has been done to show accuracy of the results. Finally, a simple yet powerful method is obtained to aid the initial design stage of ships.

Operational failure assessment of Remotely Operated Vehicle (ROV) in harsh offshore environments

For an effective integrity assessment of marine robotic in offshore environments, the elements’ failure characteristics need to be understood. A structured probabilistic methodology is proposed for the operational failure assessment (OFA) characteristics of ROV. The first step is to assess the likely failure mode of the ROV system and its support systems. This captures the interaction and failure induced events during operation. The identified potential failure modes are further developed into logical connectivity based on the cause-effect relationship. The logical framework is modeled using the fault tree analysis technique to predict the ROV operational failure probability in an uncertain harsh environment. The fault tree analysis captured the logical relationship between the primary, intermediate, and top events probability. The importance measure criteria were adopted to identify the most probable events, links, and their importance on the failure propagation. The model was demonstrated with an ROV for deep arctic water subsea operations. The result identified the control system, communication linkages, human factor, among others, as most critical in the ROV operational failure. The methodology’s application provides core information on the Mean time between failure (MTBF) of the ROV system that could aid integrity management and provides a guide on early remedial action against total failure.

Determining residuary resistance per unit weight of displacement with Symbolic Regression and Gradient Boosted Tree algorithms

Determining the residuary resistance per unit weight of displacement is one of the key factors in the design of vessels. In this paper, the authors utilize two novel methods – Symbolic Regression (SR) and Gradient Boosted Trees (GBT) to achieve a model which can be used to calculate the value of residuary resistance per unit weight, of displacement from the longitudinal position of the center of buoyancy, prismatic coefficient, length-displacement ratio, beam-draught ratio, length-beam ratio, and Froude number. This data is given as results of 308 experiments provided as a part of a publicly available dataset. The results are evaluated using the coefficient of determination (R2) and Mean Absolute Percentage Error (MAPE). Pre-processing, in the shape of correlation analysis combined with variable elimination and variable scaling, is applied to the dataset. The results show that while both methods achieve regression results, the result of regression of SR is relatively poor in comparison to GBT. Both methods provide slightly poorer, but comparable results to previous research focussing on the use of “black-box” methods, such as neural networks. The elimination of variables does not show a high influence on the modeling performance in the presented case, while variable scaling does achieve better results compared to the models trained with the non-scaled dataset.

Analysis of image compression methods based on wavelet transforms for maritime applications

The purpose of the article is to develop recommendations for choosing image compression method based on wavelet transformation, depending on image type, quality and compression requirements. Among the wavelet image compression methods, Embedded Zerotree Wavelet coder (EZW) and Set Partition In Hierarchical Trees (SPIHT) are considered, and the Haar wavelet and wavelet transformation in the oriented basis with the first, third, fifth and seventh decomposition levels is used as the base wavelet transform. These compression methods were compared with each other and with the standard JPEG method on the following parameters: mean square error, maximum error, peak to noise ratio, number of bits per pixel, compression ratio, and image size. The proposed methods can be successfully applied in the transmission of seabed relief images obtained from satellites or sea buoys.

Deviations and errors review on measuring and calculating heavy fuel oil consumption and fuel stock onboard vessels equipped with volumetric fuel consumption flowmeters

A common way of measuring heavy fuel oil consumption on board a vessel is to use volumetric fuel flow meters installed at fuel systems inlets for each of the major fuel consumers. At each stage of the fuel processing cycle, certain mass fuel losses or deviations and calculation errors occur that are not counted accurately into fuel consumption figures. The goal of this paper is to identify those fuel mass losses and measuring/calculating errors and perform their quantitative numerical analysis based on actual data. Fuel mass losses defined as deviations identified during the fuel preparation process are evaporation of volatile organic compounds, water drainage, fuel separation, and leakages while errors identified are flow meter accuracy and volumetric/mass flow conversion accuracy. By utilizing statistical analysis of obtained data from engine logbook extracts from three different ships numerical models were generated for each fuel mass loss point. Measuring errors and volumetric/mass conversion errors are numerically analyzed based on actual equipment and models used onboard example vessels. By computational analysis of the obtained models, approximate percentage losses and errors are presented as a fraction of fuel quantity on board or as a fraction of fuel consumed. Those losses and errors present between 0,001% and 5% of fuel stock or fuel consumption figures for each identified loss/error point. This paper presents a contribution for more accurate heavy fuel oil consumption calculation and consequently accurate declaration of remaining fuel stock onboard. It also presents a base for possible further research on the possible influence of fuel grade, fuel water content on the accuracy of consumption calculation.

A multi-objective integrated procurement, production, and distribution problem of supply chain network under fuzziness uncertainties

In this paper, we devoted a design under uncertainty of a four-echelon supply chain network including multiple suppliers, multiple plants, multiple distributors and multiple customers. The proposed model is a bi-objective mixed integer linear programming which considers several constraints and aims to minimize the total costs including the procurement, production, storage and distribution costs as well as to maximize on-time deliveries (OTD). To bring the model closer to real-world planning problems, the objective function coefficients (e.g. procurement cost, production cost, inventory holding and transport costs) and other parameters (e.g., demand, production capacity and safety stock level), are all considered triangular fuzzy numbers. Besides, a hybrid mathematical model-based on credibility approach is constructed for the problem, i.e., expected value and chance constrained models. Moreover, to build the crisp equivalent model, we use different property of the credibility measure. The resulted crisp equivalent model is a bi-objective mixed integer linear programs (BOMILP). To transform this crisp BOMILP into a single objective mixed integer linear programs (MILP) model, we apply three different aggregation functions. Finally, numerical results are reported for a real case study to demonstrate the efficiency and applicability of the proposed model.