Marine Propulsion Research Articles

Experimental study of dynamic response of passive flapping hydrofoil in regular wave

The hydrofoil harnesses wave energy and converts it into thrust. In this paper, we present the results of the first experimental study investigating the dynamic behavior of a fully passive foil with spring-loaded pitch and heave in regular waves. Our study shows that the real-time load signal is multi-harmonic with strong superposition, directly proving the robust energy harvesting performance due to the restoring springs. By interpreting the hydrofoil's pose and path from an image sequence captured underwater, we conclude the dynamic evolution of the fully passive hydrofoil interacting with regular waves. The hydrofoil's dynamics exhibit asymmetric surge, pitch, and heave in a motion cycle. Furthermore, we employ a pixel capturing algorithm with self-correction utility to quantify the hydrofoil's forward displacement from the image sequence of the moving carriage. These findings provide valuable insight into the performance and potential of hydrofoils for marine propulsion.

Analysis and Comparison of Main Steam Turbines from Four Different Thermal Power Plants

This paper presents an analysis and comparison of four steam turbines and their cylinders from four different power plants (marine, conventional, ultra-supercritical and nuclear power plants). The main goal was to find which steam turbine and their cylinders show the best performances, the highest efficiencies, the lowest specific steam consumption and which turbine is the lowest influenced by the ambient temperature change. The highest efficiencies, both isentropic and exergy, are observed in the steam turbine and their cylinders from the ultra-supercritical power plant (whole turbine from ultra-supercritical power plant has an isentropic efficiency equal to 88.36% and exergy efficiency equal to 91.05%). Also, this turbine has the lowest specific steam consumption (7.32 kg/kWh) and exergy parameters of this turbine are the lowest influenced by the ambient temperature change. The worst performance (the lowest efficiencies, high specific steam consumption and the highest sensitivity to the ambient temperature change) show the cylinders and whole turbine from marine propulsion power plant. The same analysis and comparison are also performed for several other steam turbines from four mentioned power plants, so the presented relations and dominant conclusions have general validity. It can be concluded that steam turbines in ultra-supercritical power plants show the best performances in comparison to steam turbines from any other power plant.

Healthy marine diesel engine threshold characterisation with probability density functions and ANNs

The condition-based maintenance of marine propulsion systems is attracting increasing interest in safety-related, financial, and environmental terms. Many researchers have studied different marine diesel engine models and fault identification techniques. However, the thresholds between a healthy and a faulty engine have not been thoroughly analysed. Thus, this study aims to determine healthy engine threshold values for multiple parameters of a marine diesel engine. To this end, an operative commercial fishing vessel was considered, and multiple engine performance variables were measured through 2020 and the first half of 2021, totalling 5181 operating hours of the main engine without any fault occurrence. Preliminary correlation and relative deviation studies suggested the analysis of some constant trend parameters with alternative modelling techniques. Hence, probability density functions (PDFs) were used to establish confidence intervals for such parameters with data from the entire year of 2020. The parameters with the highest correlation and deviation were alternatively modelled using artificial neural networks (ANNs). Four different ANNs were trained, validated, and tested with data from 2020, calculating the mean absolute percentage errors for all the predicted parameters. Finally, data from 2021 were used to validate both the PDF and ANN modelled parameter thresholds set in 2020. For the 2021 data, the confidence interval set with the PDF showed a maximum failure rate of 1.21%. Alternatively, the ANN model parameters exhibited maximum percentage errors of 1.1%, 1.22%, and 1.95% for the engine performance, cooling, and cylinder subsystems, respectively. Finally, all the obtained thresholds were summarised, providing a good source for establishing faulty engine threshold values in future fault detection studies.

Characteristics and dynamics of electrolyzed bubbles in magnetohydrodynamic bubbly jet

BackgroundThe magnetohydrodynamics (MHD) are highly relevant to practical applications, including marine propulsion and hydrogen production etc. For better implementation to applications, typical characteristics of the MHD bubbly jet, such as the size distribution and motion of oxygen and hydrogen bubbles, need to be well realized. MethodsThe MHD bubbly jet generated by high current density associated with strong permanent magnet is experimentally investigated. Two fields of view are taken to analyze the details of micro-sized bubbles and the whole pattern of bubbly jet. To couple the magnetoelectric effects and bubble dynamics, the Reynolds number based on the Lorentz force ReL is applied in the parametric analysis. FindingsDependence of the mean size of bubble on the current density is generally verified. Two regimes regarding the bubble sizes are distinguished. The proposed mechanisms of these two regimes are supported by the pattern of bubbly jet. For ReL≤2000, size of bubble monotonically increases with current density, so that referred to as the electrochemistry regime. Nevertheless, the size of bubble remains nearly unchanged for ReL>2000, referred to as the flow regime in which the turbulent breakup of the bubbly jet core starts to evolve.

Review of Biofuel Effect on Emissions of Various Types of Marine Propulsion and Auxiliary Engines

The International Maritime Organization aims to reduce the maritime industry’s carbon emissions by 40% in the next two decades and has introduced measures to control CO2 emissions. These have significantly increased interest regarding biofuels, which can be used immediately on existing vessels, reducing their carbon footprint. The most common variant is B30, a blend of 70% crude oil and 30% biodiesel. Concerns exist for the potential effect on engine performance and NOx emissions. Scientific works on the subject are limited for two-stroke marine engines, while some studies are available for four-stroke ones, usually auxiliaries. To increase information availability on the subject, in this work, we review the results of testing on multiple marine engine types, two-stroke propulsion and four-stroke auxiliary units using B30 and conventional fuels. The effect on emissions and fuel efficiency is examined and cross-referenced with the available literature. A small increase in specific fuel consumption was observed for B30 use that varied with engine type. The increase was on average 1% for two-stroke and 2.5% for four-stroke engines. The effect of B30 on NOx emissions was low but varied between engines. For low-speed two-stroke engines, NOx increase was on average 4% compared to crude oil, and 2.4% for four-stroke auxiliary units, albeit with higher variance. For some four-stroke units, a decrease in emissions was found. All previous results were in line with other published studies. Overall, it was found that while biofuel effect can vary considerably between applications, 30% biodiesel blends can be used with no concerns regarding emissions and fuel efficiency.

Simultaneous and Global Optimizations of LNG-Fueled Hybrid Electric Ship for Substantial Fuel Cost, CO2, and Methane Emission Reduction

Natural gas (NG) is a promising low-carbon fuel to replace diesel for heavy-duty marine propulsion with prominent fuel cost and carbon dioxide equivalent (CDE) emissions reduction potential. However, using NG in compression ignition (CI) engines presents several inherent drawbacks. This research addresses the central issue of an NG-diesel CI engine with increased methane emissions, resulting in minor CDE emission reduction. The hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NOx) emissions are minimized in addition to fuel consumption and carbon dioxide emission reduction as in the current practice. The simultaneous optimizations of powertrain component sizes and the NG-engine hybrid electric propulsion control are introduced to minimize NG fuel consumption and CDE emissions globally. The top-level powertrain component sizing and bottom-level optimal power control and energy management are conducted simultaneously to achieve global optimization with balanced fuel cost and CDE emissions reductions. The new method reduced the fuel cost by about 75 percent and well-to-wake CDE emissions by about 40 percent over the traditional diesel-mechanical propulsion for the test ferry running under an actual operation profile. The research opened a new path to the global design and control optimization of the NG-diesel CI engine-powered hybrid electric marine propulsion system.

Выбор методов постоянного мониторинга крутильных колебаний в судовых машинно-движительных комплексах

The article considers the problem of the continuing emergency damages to the elements of ship engine-propulsion systems with fatigue failures of shaft pipelines. The classification societies require to analyze and measure the dangerous torsional vibrations in ship power plants. There is given an overview and comparison of methods of measuring torsional vibrations in order to determine the most promising ones for constant monitoring and diagnostics of the technical condition of the elements of marine propulsion systems. In the course of analysis of scientific and technical literature there have been identified the main methods of measuring torsional vibrations, which formed the basis for developing the national and foreign measuring software and hardware complexes. The marine conditions surely require the appropriate design and operating principles from the monitoring systems, therefore, such methods as strain measurement, using laser and optical sensors with reflective tape, inductive sensors with gears are defined as promising. There is illustrated a diagram of the measuring bridge of four load cells, given an example of the design and positioning of the IVC Technologies strain gauge system on the shaft, considered the Geislinger systems with a spring damper and measuring gears. There are presented the illustrations of the OROS measuring system, the Konsberg system, the RT-660 radiotorsiograph, the SCAN optical torsiograph developed by JSC Central Research and Design Institute of the Marine Fleet (TsNIIMF), the TNK-1 sensor, the BAGS-4M measuring complex and others. The results of the study will be used to develop experimental samples of a monitoring system with the selected methods for measuring torsional vibrations and conducting tests in the laboratory and on board a ship.

Пружинные демпферы крутильных колебаний в составе современных судовых дизелей: преимущества и недостатки

The article presents analysis of the advantages and disadvantages in assembling the spring dampers of torsional vibrations in modern marine diesel engines. There are considered the urgent problems of using spring dampers in the marine propulsion systems: lack of the systematized scientific data about the spring damper design, statistics of their prevalence in the marine diesel engines, analysis of breakdowns. It has been stated that today there is no methodology for assessing the technical condition of spring dampers, except for the methods recommended by the Russian Maritime Register of Shipping in relation to the silicone dampers. Disassembly diagnostics of the technical condition of spring dampers is extremely difficult and costly for a shipowner. Most of the vessels that are currently being operated in Russia are found obsolete, and there has started a gradual process of modernization and replacement 
 of morally and physically obsolete main engines G60,G70 (6CPH 36/45), SKL NVD, 6ChH18/22, 3D6 (6ChH 15/18) etc. by new foreign diesel engines manufactured by Wartsila (Finland), Caterpillar (USA), Volvo - Penta (Sweden), Scania (Sweden), Henan Diesel Engine Industry Co., Ltd (China) etc., which have new dampers of such companies as Geislinger (Germany), Hasse & Wrede (Germany), STE - Schwingungstechnik (Germany), Holset (England), Caterpillar (USA) etc. Diagnostics of dampers of modern diesel engines is a new direction for the domestic marine industry; it requires a revision of both the technological processes of working with such equipment and training the qualified specialists. The study of the structural and operational features of spring dampers of modern diesel engines will allow to accumulate the necessary amount of scientific and technical information to create in Russia the foundations of production of efficient structures and the development of engine building in general.

Termodinamička analiza i usporedba dviju propulzijskih parnih turbina

This paper presents thermodynamic (energy and exergy) analysis and comparison of two different marine propulsion steam turbines based on their operating parameters from exploitation. The first turbine did not possess steam reheating and had only two cylinders (high-pressure and low-pressure cylinders), while the second turbine possesses steam reheating and has one additional cylinder (intermediate-pressure cylinder). In the literature at the moment, there cannot be found a direct and exact comparison of these two marine steam turbines and their cylinders based on real exploitation conditions. Along with energy and exergy analyses, the research it is investigated the sensitivity of exergy parameters to the ambient temperature change for both turbines and each cylinder. It is also presented the influence of the steam reheating process on the energy and exergy efficiency of the entire power plant. For both observed turbines and their cylinders it is valid that relative losses and efficiencies (both energy and exergy) are reverse proportional. The operation of an intermediate pressure cylinder from a steam turbine with reheating is the closest to optimal. Due to the different origins of losses considered in energy and exergy analyses, each analysis detects different turbine cylinders as the most problematic ones. The steam reheating process decreases losses and increases efficiencies (both energy of each turbine cylinder and the whole turbine. The whole turbine with reheating has an energy efficiency equal to 81.46% and an exergy efficiency equal to 86.48%, while the whole turbine without reheating has energy and exergy efficiencies equal to 76.47% and 80.94%, respectively. Exergy parameters of a steam turbine without reheating as well as its cylinders are much more influenced by the ambient temperature change in comparison to the steam turbine with reheating and its cylinders. The steam reheating process will increase the efficiency of the whole power plant in real exploitation conditions between 10% and 12%.

A real-time shaft alignment monitoring method adapting to ship hull deformation for marine propulsion system

Shaft alignment states are strictly stipulated in the marine propulsion system. However, there are relatively limited studies on shaft alignment monitoring and control considering the effects of ship hull deformation (SHD). SHD can be caused by wave load, loading, depth, speed, etc., and leads to various relative displacements at different shaft supporting points between the ship foundation and the support bearings of the propulsion system. It leads to shaft misalignment, increases shaft vibration and noise, and even endangers the safety of shaft system during the operation stages. To overcome this problem, a real-time shaft alignment monitoring method based on laser displacement sensors (SAMM/LDS) is proposed. Firstly, the defects of a present shaft alignment monitoring method based on eddy current displacement sensors (SAMM/ECDS) are analyzed when considering the effects of SHD. The structure and working principle of a shaft alignment monitoring system adapted to SHD (SAMS/SHD) are proposed. It consists of three sub-systems: the shaft alignment monitoring sub-system adapting to SHD (SAMSS/SHD), the present shaft alignment monitoring sub-system (SAMSS/P), and the shaft alignment correcting sub-system (SACSS). Based on SHD data-driven, SAMS/SHD can not only take advantage of SAMSS/P for long-time operations but also reflect SHD by exploiting the advantages of SAMSS/SHD. Secondly, SAMM/LDS is deduced. Two laser displacement sensors (LDS) are placed on the driving shaft and the driven shaft to reflect the spatial relative displacement and attitude information affected by SHD. Therefore, two reference coordinate systems are fixed at the center of LDS, and the coordinate expressions of their imaging points are derived using a 4 × 4 homogeneous coordinate transformation matrix. For reducing computing complexity in engineering applications, a simplified monitoring model is proposed for very small rigid-body rotational angularities. Finally, the effectiveness and testing accuracy of the SAMM/LDS is verified on a five-DOF platform which can simulate the effects of SHD. The SAMM/LDS can be used to realize real-time and high-precision shaft alignment monitoring for marine propulsion system which can adapt to the effects of SHD and so on. Based on the foundation of this research, compensation control algorithms to solve the misalignment effects deduced by SHD will be studied for marine propulsion system with resilient mounts in the next few years.

Interphase Mechanical Energy Transfer of Gas-Liquid Flow in Variable Cross-Section Tubes

The use of gas energy includes a wide range of applications to directly accelerate the liquid in a pipeline without the aid of mechanical equipment, such as marine gas-liquid jet propulsion. To clarify the characteristics of energy transfer by interphase forces for gas-liquid flows in variable cross-section tubes, two-fluid models of annular flow, bubbly flow and homogeneous flow were adopted, respectively, along with four newly elaborated coefficients, which are the work factor of gas fg, reflecting the relative ability of gas to power liquid, the interface work transfer coefficient kg (representing the relative magnitude of mechanical work received by liquid from gas), the interphase work-to-energy conversion coefficient kl (denoting the capability of energy transfer through work performed by interphase forces) and the interphase mechanical efficiency ηw. The results reveal the interphase work transfer is strongly influenced by the structural parameters of the tubes (or nozzles), and an optimized design is necessary to improve the performance. The higher the degree of gas dispersion in the liquid, the more advantageous the conversion of gas work into the liquid’s mechanical energy. Of these three flow patterns, annular flow has the lowest kl and ηw (kl = 0.0797, ηw = 0.9885 in present example), while homogeneous flow displays the limit of interphase mechanical energy conversion because the gas-liquid momentum coupling reaches the maximum (kl = 0.9979, ηw = 1).

Frictional vibration behaviors of a new piezo-damping composite under water-lubricated friction

Water-lubricated bearings have become an important component of marine propulsion systems due to the requirements of environmental friendliness and concealability. However, water-lubricated bearings are often subjected to bending stress, additional stress, frictional resistance and other multi-factor effects, resulting in boundary friction or even dry friction on the friction interfaces when encountering unique working conditions such as engine start-stop, steering, low-speed, and heavy-load. The severe frictional processes often induce vibration behaviors and generate frictional noise, which seriously weakens the sound concealment performance and service life of marine propulsion systems. Therefore, it is urgent to improve the vibration and sound pressure behaviors of the composite bearings under water-lubricated conditions. In this study, novel barium titanate/carbon black/polyurethane composites (BaTiO3/CB/PU) are fabricated and then explored the damping capacities and tribological properties of the new polymers. The results showed that the BaTiO3 concentrated on transforming the mechanical energy generated by frictional vibration into electrical energy which generates the thermal energy. The water cooled the frictional heat and the piezo-damping heat. This energy dissipation method increased the damping capacity to reduce the vibration and noise behaviors induced by friction. The composite with 3.0 wt% BaTiO3 performed the highest loss factor under the operating temperatures and presented the best frictional vibration reduction properties. The knowledge obtained in this study is useful not only to explore a new piezo-damping composite, but also to provide a theoretical basis for developing higher performance polymer-based water-lubricated bearing.

A study on interaction among hull, diesel engine and propellers of a twin-screw ship during turning circle maneuver

A marine propulsion plant will experience power fluctuations during ship maneuvers. In the turning circle maneuver, the propulsive load increases significantly, and the power required by the two shafts of a twin-screw ship may be completely inconsistent. To protect the propulsion plant, the interaction between the engine and the propellers should be studied in depth. In this paper, the twin-screw ONRT ship and the 16PA6-STC diesel engine are selected as the study objects. A series of captive model tests are simulated by using CFD method to obtain the hydrodynamic derivatives and hull-propeller-rudder interaction coefficients in the MMG model. The effective wake fraction is computed under the maneuvering conditions. Turning circle maneuver of the ship is predicted by using the established MMG model, and the predicted ship maneuvering characteristics show good agreement with the available experimental results, which verifies the CFD-based modeling method. Finally, a dynamic model of hull-engine-propeller system is established on the simulation platform for evaluating the operating characteristics of propulsion plant. The propeller loads are predicted and the interaction among hull, engine and propellers is investigated. This study helps to provide a deeper insight into the engine operation behaviors during turning circle maneuver of a ship.

The Impact of Slow Steaming on Fuel Consumption and CO2 Emissions of a Container Ship

Modern marine propulsion systems must be reliable, energy efficient, environmentally friendly, and economical. Efforts to reduce fuel costs and carbon dioxide (CO2) emissions per nautical mile have a significant impact on the choice of propulsion system. Considering that there is no alternative for maritime transport, various technical and technological solutions are being considered that aim to improve efficiency and reduce the negative impact on the environment. One of the ways to achieve this goal is slow steaming, which reduces fuel consumption and CO2 emissions. The designed speed of the vessel has a significant impact on the efficiency of slow steaming. Slow steaming is particularly suitable for large container ships with a design speed of more than 20 knots. In this paper, the effects of slow steaming are analyzed using the example of a container ship with diesel-engine propulsion. Propulsion systems with low-speed and medium-speed marine diesel engines with mechanical power transmission are investigated. Data on the required engine power and propeller speed were used for the study, obtained from calculations during testing of the ship’s hull model. The effects of speed reduction on specific fuel consumption and emission reduction were analyzed using numerical models of two-stroke and four-stroke diesel engines. The models were calibrated and validated using data provided by the engine manufacturers. The paper analyses four different cases where one or two low-speed diesel engines, or three or four medium-speed diesel engines, are used for propulsion. The analysis concludes that slow steaming can effectively reduce fuel consumption and CO2 emissions, but the choice of the optimal propulsion system is highly dependent on maritime market conditions in maritime transportation. The choice of propulsion system affects the potential of slow steaming.

Advancement of biodiesel fuel quality and NOx emission control techniques

Sustainable waste derived biodiesel can substitute significant amount of fossil-based fuels currently used for marine propulsion, agricultural processes, small scale power generation, and in heavy goods vehicles. However, biodiesel fuel quality varies depending on the feedstock type, production method and storage conditions. Meeting biodiesel standards and reduction of NOx emissions are two main challenges when biodiesels are being used in the internal combustion engines. This study aims to address these two challenges by using biodiesel-biodiesel blending and various NOx reduction techniques. Biodiesels produced from waste resources and inedible plant seed oils are investigated. Fuel properties, biodiesels standards, and engine test results are reviewed. It was found that blends of animal fat biodiesels and vegetable oil biodiesels are likely to improve fuel properties and combustion characteristics. The biodiesel-biodiesel blends also help to reduce exhaust pollutants. The saturation level of the biodiesel fuel is increased through this technique. Animal fat biodiesels are composed of saturated fatty acid methyl esters, and vegetable oil biodiesels are composed of unsaturated fatty acids. The NOx gas emission reduction techniques are investigated and categorised under three sub-groups, fuel treatment, engine adjustment and exhaust after-treatment. Based on the state of art review, scopes for future R&D topics are presented for researchers and relevant industries.

Intelligent Adaptive PID Control for the Shaft Speed of a Marine Electric Propulsion System Based on the Evidential Reasoning Rule

To precisely and timely control the shaft speed for a marine electric propulsion system under normal sea conditions, a new shaft speed control technique combining the evidential reasoning rule with the traditional PID controller was proposed in this study. First, an intelligent adaptive PID controller based on the evidential reasoning rule was designed for a marine electric propulsion system to obtain the PID parameters KP, KI, and KD. Then, a local iterative optimization strategy for model parameters was proposed. Furthermore, the parameters of the adaptive PID controller model were optimized in real time by using the sequential linear programming algorithm, which enabled the adaptive adjustment of KP, KI, and KD. Finally, the performance of the adaptive PID controller regarding the shaft speed control was compared with that of other controllers. The results showed that the adaptive PID controller designed in this study had better control performance, and the shaft speed control method based on the adaptive PID controller could better control the shaft speed of the marine electric propulsion system.

Numerical assessment of the effect of length, angle of attack, and type of ducts on hydrodynamic parameters of a linear-jet propulsion system

Achieving noble and more practical propulsion systems is still a major concern for engineers and researchers. Accordingly, many researchers have strived to opt for better and suitable system for the targeted vessels. One of the marine propulsion systems is linear-jet propulsion which includes rotor and stator. In this paper, the effects of geometrical shape of the duct in the form of different length and angle of attack for two types of the accelerating and decelerating ducts are comprehensively explored. Furthermore, section of rotor from Kaplan series are selected and the geometrical shape effects of the rotor on hydrodynamic performance of linear-jet propulsion system are also investigated. Therefore, to obtain the effects of the expressed parameters on the hydrodynamic characteristics of this propulsion system, Ansys-CFX software has been used. The governing equations of the studied problem are RANS equations and SST k-omega turbulent model is utilized. The obtained results are presented in the form of dimensionless coefficients of the forces applied on the propulsion system. The existing data for a ducted propeller are used to validate the numerical solution. Based on the results of the numerical solution, it is concluded that use of a decelerating duct increases the efficiency of the linear-jet system. On the other hand, the use of accelerating ducts reduces the hydrodynamic efficiency of the linear jet, so the performance is not desirable at high advance ratio. Therefore, the use of decelerating ducts in the linear-jet system is found to be the appropriate choice. Results further illustrate that, if the duct length increases, the generated thrust by the rotor increases. It is also concluded that, by increasing the angle of attack of the decelerating duct, the overall efficiency of the linear-jet propulsion system decreases.

Application of the stiffness method to the optimization analysis of a marine propulsion shaft system

Application of the stiffness method to the optimization analysis of a marine propulsion shaft system

The ENBIS‐21 quality and reliability engineering international special issue

The ENBIS-21 Quality and Reliability Engineering International Special Issue is related to the contributions to the 21st Annual Conference of the European Network for Business and Industrial Statistics (ENBIS) held online from 13 to 15 September, 2021. The topics covered by the 12 papers included in this special issue fall within the scope of ENBIS, whose ultimate goal is to bridge the gap between methodology and application in the field of business and industrial statistics and foster networking between statisticians in academic and commercial settings. It becomes evident from the papers on this issue that classical methods of industrial statistics are still having a wide range of applications and expansions towards complex and big data structures as well as they are increasingly cross-fertilized by artificial intelligence and machine learning perspectives and approaches. The issue is opened by the contribution of Yang et al.1 in the Statistical Process Monitoring (SPM) of data in the form of tensors. The authors develop a hierarchical in-situ process monitoring approach for anomaly detection, which is applied to thermal video streams acquired during a metal additive manufacturing process for highly complex parts. A more traditional SPM approach based on generalized likelihood ratio (GLR) control charts is elaborated by Rizzo and Di Bucchianico2 to set up tailor-made monitoring for high-purity (high-quality) processes and deals with issues arising in GLR control charts for discrete processes. Along the line of developing statistical methods for complex data structures, Gril et al.3 set up a tensor-on-tensor regression model able to dynamically predict repetitive human motions helpful in avoiding unwanted collisions at the interface with robots in industrial assembly tasks. Chuquin et al.4 present a straightforward extension of the K-means clustering to spatially correlated functional data, with an application in the analysis of the normalized difference vegetation index in a large region of Ecuador. From a more general perspective, Vanacore et al.5 address the problem of assessing prediction performance in the multi-class classification of imbalanced data sets. In the optimal Design of Experiments (DoE) Pesce et al.6 offer new results that are oriented to bias reduction in large datasets and protection against confounders. Whereas, Kirchhoff et al.7 use DoE as the initial solution for the optimization of shift planning in high-bay warehouse operations based on Gaussian process models with low-rank correlation kernels. Risk assessment and management is the topic of the following three papers. Testik and Unlu8 compare traditional and fuzzy failure modes and effect analysis to rank risks in different areas of testing and calibration laboratories. Meynaoui et al.9 deal with an accidental scenario in a sodium-cooled fast nuclear reactor by means of a global sensitivity analysis of the input parameter distribution used in numerical simulator outputs to model physical phenomena. Lai and Zwetsloot10 offer a data-driven ensemble ranking system of product quality, which is validated in the identification of high-risk manufacturers in a solar industry case study. The final two papers are devoted to the Reliability and Maintenance of repairable systems. El-Aroui and Gaudoin11 propose a general goodness-of-fit test for imperfect repair models that has the favorable property of being asymptotically distribution-free for renewal and power law processes. Fouladirad et al.12 develop a new bounded transformed gamma process model to describe and predict degradation phenomena by relaxing the typical assumption that the degradation level can grow indefinitely, which is often unrealistic for technological units. The proposed model is also applied to a set of wear measures of cylinder liners that equip a diesel engine for marine propulsion. We are deeply grateful to the journal staff for their professional assistance in the editorial process, as well as to the anonymous referees for the time and effort spent to provide careful and constructive comments, and to all the authors, who made revisions on a very tight timescale.

The Relationship Between Marine Propulsion Power and Heat Transfer with Constructal Law

Yapısal Gelişim Teorisi 1996 yılında literatüre kazandırılmış olup tabiattaki ve mühendislikteki tasarım prensiplerini açıklar. Teori, yeryüzündeki akış sistemlerini bütüncül bir şekilde ele alır. Akışın (hareketin) olmadığı yerde çoğu zaman canlılıktan bahsetmemiz dahi mümkün olmamaktadır. Akış sistemlerinin çözümünde anahtar davranış biçimi bu sistemlerin minimum dirençli yol ile hareketini sürdürmesidir. Belli bir zaman dilimi için minimum direnç ile hareket eden sistem zaman geçtikçe kendine yeni yollar (kanallar) bulmakta ya da bazı yolları hiç kullanmayarak yönünü değiştirmektedir. Yapısal Gelişim Teorisi ise hayati öneme sahip olan akış sistemlerinin fiziksel arka planını ortaya koymaktadır. Bu makalede özellikle mühendislik çözümlerinin başında gelen akış sistemlerinin yapısı (gemilerde kurulu ana makine gücü ve ısı transferi örnekleri özelinde) ve Yapısal Gelişim Teorisi’ne göre ilişkisi araştırılmıştır. Bunun için 1085 adet petrol tankeri için DWT ile bu tankerler için gerekli olan güç ilişkisi nonlineer regresyon ile analiz edilmiştir. Sonuç olarak gemilerdeki genel gelişimin ve ısı transferinin yapısal gelişim prensiplerine uygun şekilde gerçekleştiği gösterilmiştir.