Very Large Crude Carrier Research Articles

Circulation-controlled wind-assisted ship propulsion: Technical innovations for future shipping industry decarbonization

Amidst mandatory policies aimed at energy savings and emission reductions in the shipping industry, wind-assisted ship propulsion technology has gained prominence for its immediate practicality in promoting environmental sustainability. Wing-sails possess favorable aerodynamic characteristics and adjustable capabilities, yet their efficiency is impeded by flow separation at high angles of attack. This study addressed the challenge of mitigating delayed separation and enhancing lift at large angles of attack for wing-sails through technical solutions involving trailing-edge circulation control and leading-edge boundary layer control. Three-dimensional steady-state flow fields of conventional and circulation-controlled wing-sails were accurately modeled using a Generalized k-ω (GEKO) model across angles of attack ranging from 0° to 30°. Under moderate jet strength conditions with a velocity ratio of 5, the stall angle of attack of the circulation-controlled wing-sail was delayed by approximately 6°. Furthermore, compared to a conventional wing-sail, the circulation-controlled variant exhibited a 111 % increase in maximum lift coefficient and a 120 % rise in maximum resultant force coefficient. The energy-saving and emission reduction benefits of implementing this innovative technology were quantified using the Energy Efficiency Design Index (EEDI) on a real very large crude carrier (VLCC). The circulation-controlled wing-sail demonstrated a 10.38 % reduction in EEDI under optimal operating conditions with medium jet strength, compared to an unassisted vessel. Moreover, this reduction was enhanced by 77.55 % compared to incorporating a conventional wing-sail. These discoveries signify an advancement in wind-assisted ship propulsion technology on an innovative frontier, promising greater energy utilization and reduced fuel consumption, thereby facilitating the achievement of stringent green ship standards.

Evaluating long-term operational data of a Very Large Crude Carrier: Assessing the diesel engines waste heat potential for integrating ORC systems

Given the spotlight on waste heat recovery (WHR) technologies for decarbonizing the shipping industry, critically assessing waste heat from propulsion and auxiliary engines using actual data is crucial for accurately predicting fuel and carbon savings. This paper addresses this by applying advanced data processing, considering voyage characteristics, and developing methods for mapping waste heat from main engine (ME) and diesel gensets (DGs) operations using long-term operational data from a Very Large Crude Carrier (VLCC) case study. Two methods predict unrecorded air mass flows by implementing heat balance: one using measured temperature values and the other estimating exhaust gas mass flow rates based on fuel oil consumption. Within the main objectives of this study is to examine the impacts of employing the exhaust gases of both ME and DGs to evaporate recuperative ORC working fluid on power output and vessel annual carbon savings, with the formed diesel engines operational profiles serving as inputs. Simulations show a power output of 530 kW using ME exhaust gases, increasing to 653 kW and 741 kW with DGs integration for R245fa and R1233zd(E) as the selected ORC working fluids, respectively. The proposed solutions can reduce annual CO2 emissions by 4 % to 7 %.

A Quantitative Model of the Oil Tanker Market in the Arabian Gulf

Using a novel dataset, we develop a structural model of the Very Large Crude Carrier (VLCC) market between the Arabian Gulf and the Far East. We study how fluctuations in oil tanker rates, oil exports, shipowner profits, and bunker fuel prices are determined by shocks to the supply and demand for oil tankers, to the utilization of tankers, and to the cost of operating tankers, including bunker fuel costs. Our analysis shows that time charter rates are largely unresponsive to tanker cost shocks. In response to higher costs, voyage profits decline, as cost shocks are only partially passed on to round-trip voyage rates. Oil exports from the Arabian Gulf also decline, reflecting lower demand for VLCCs. Positive utilization shocks are associated with higher profits, a slight increase in time charter rates and lower fuel prices and oil export volumes. Tanker supply and tanker demand shocks have persistent effects on time charter rates, round-trip voyage rates, the volume of oil exports, fuel prices, and profits with the expected sign.

A Study on the Viability of Fuel Cells as an Alternative to Diesel Fuel Generators on Ships

This study investigates methods for reducing air pollution in the shipping sector, particularly in port areas. The study examines the use of fuel cells as an alternative to diesel generators. Environmental pollution at ports remains a critical issue, so using fuel cells as an alternative to conventional energy systems warrants further research. This study compares commercial fuel cell types that can be used on a case study very large crude carrier (VLCC) vessel specifically, although the technology is applicable to other vessels and requirements. Seven different fuel cell types were ranked based on five criteria to accomplish this. The proton-exchange membrane cell type was found to be the most suitable fuel cell type for the case study vessel. Based on the input fuel, ammonia-based hydrogen storage has been identified as the most promising option, along with using an ammonia reforming unit to produce pure hydrogen. Furthermore, this study provides an integrated fuel cell module and highlights the economic, environmental, and maintenance aspects of implementing the proton-exchange membrane fuel cell module for this case study. It also calculates the required space as a crucial constraint of implementing fuel cell technology at sea.

Longitudinal strength of high block coefficient merchant ships in irregular waves

In this work, a method is developed to calculate the instantaneous shear force and bending moment of the ship in waves using point clouds. The force at each station is calculated by computing the hydrostatic and hydrodynamic pressure at each panel and the area of each panel at that station. This gives the variation of hydrostatic and hydrodynamic force in the vertical direction along the ship's length. The hydrostatic and hydrodynamic force acting on the ship is used to calculate the heave and pitch motion of the ship in waves. The weight distribution at each station is estimated by adding different components like lightship, cargo, machineries and outfit weight. The weight distribution is determined using the exact geometrical layout of the cargo/water ballast/fuel and fresh water tanks inside the ship. The longitudinal strength of a bulk carrier and Very Large Crude Carrier (VLCC) at zero forward speed in the head wave is investigated. The investigation shows that the shear force and bending moment of a ship can be accurately estimated using the proposed method. The bending moment in an irregular wave shows the Rayleigh distribution. One of the applications of this procedure is fatigue strength analysis of ships.

Leakage Fault Diagnosis of Lifting and Lowering Hydraulic System of Wing-Assisted Ships Based on WPT-SVM

Wing-assisted technology is an effective way to reduce emissions and promote the decarbonization of the shipping industry. The lifting and lowering of wing-sail is usually driven by hydraulic system. Leakage, as an important failure form, directly affects the safety as well as the functioning of hydraulic system. To increase the system reliability and improve the wing-assisted effect, it is essential to conduct leakage fault diagnosis of lifting and lowering hydraulic system. In this paper, an AMESim simulation model of lifting and lowering hydraulic system of a Very Large Crude Carrier (VLCC) is established to analyze the operation characteristics of the hydraulic system. The effectiveness of the model is verified by the operation data of the actual hydraulic system. On this basis, a wavelet packet transform (WPT)-based sensitive feature extracting method of leakage fault for the hydraulic system is proposed. Subsequently, a support vector machine (SVM)-based multi-classification model and diagnosis method of leakage fault are proposed. The study results show that the proposed method has an accuracy of as high as 97.5% for six leakage fault modes. It is of great significance for ensuring the reliability of the wing-sail operation and improving the utilization rate of the offshore wind resources.

Life Cycle Greenhouse Gas Emission Assessment for Using Alternative Marine Fuels: A Very Large Crude Carrier (VLCC) Case Study

The International Maritime Organization (IMO) has set decarbonisation goals for the shipping industry. As a result, shipowners and operators are preparing to use low- or zero-carbon alternative fuels. The greenhouse gas (GHG) emission performances are fundamental for choosing suitable marine fuels. However, the current regulations adopt tank-to-wake (TTW) emission assessment methods that could misrepresent the total climate impacts of fuels. To better understand the well-to-wake (WTW) GHG emission performances, this work applied the life cycle assessment (LCA) method to a very large crude carrier (VLCC) sailing between the Middle East and China to investigate the emissions. The life cycle GHG emission impacts of using alternative fuels, including liquified natural gas (LNG), methanol, and ammonia, were evaluated and compared with using marine gas oil (MGO). The bunkering site of the VLCC was in Zhoushan port, China. The MGO and LNG were imported from overseas, while methanol and ammonia were produced in China. Four production pathways for methanol and three production pathways for ammonia were examined. The results showed that, compared with MGO, using fossil energy-based methanol and ammonia has no positive effect in terms of annual WTW GHG emissions. The emission reduction effects of fuels ranking from highest to lowest were full solar and battery-based methanol, full solar and battery-based ammonia, and LNG. Because marine ammonia-fuelled engines have not been commercialised, laboratory data were used to evaluate the nitrous oxide (N2O) emissions. The GHG emission reduction potential of ammonia can be exploited more effectively if the N2O emitted from engines is captured and disposed of through after-treatment technologies. This paper discussed three scenarios of N2O emission abatement ratios of 30%, 50%, and 90%. The resulting emission reduction effects showed that using full solar and battery-based ammonia with 90% N2O abatement performs better than using full solar and battery-based methanol. The main innovation of this work is realising the LCA GHG emission assessment for a deep-sea ship.

Longitudinal Strength Analysis Considering the Cargo Load on Very Large Crude Carrier (VLCC)

The ultimate strength of the Very Large Crude Carrier (VLCC) is an important aspect that must be analyzed. The purpose of this study was to analyze the ultimate strength of the VLCC ship in terms of deformation under hogging and sagging conditions on the deck and bottom. Deformation is a change in the shape or size of a material due to a workforce that is applied to you. In this case, the deformation in question arises due to the working moment. This deformation analysis was carried out using the Non-Linear Finite Element Analysis (NLFEA) method. This analysis is carried out by presenting the support or Multi-Point Constraints (MPC) in the cross-section, as well as moments of 6.52 × 1012 for hogging conditions and -5.5 × 1012 for slack conditions.

Mechanical behavior assessment of FPSO mid-ship repaired stiffened corroded side panels under combined loading

Hull plating thickness reduction due to corrosion generates a significant decrease in the structure ultimate load capacity, which may compromise the vessel’s integrity. In offshore oil and gas production units demobilization to a shipyard is unfeasible, so reparation must be performed locally and efficiently. This article presents an experimental - numerical investigation to assess the performance of an alternative in situ repair methodology for FPSO mid-ship corroded side panels subjected to common types of loads. The repair technique consists in the inclusion, with a single-pass welding, of an intermediate light longitudinal steel stiffener on the plating exposed to considerable thickness reduction, to reestablish the load carrying capacity, thus extending its operational life. A set of nine mid-ship panels of a VLCC (very large crude carrier) converted into an FPSO (floating production storage and offloading) platform, on a scale of 1:3.5, are fabricated and subjected to uniaxial compression. The panels portray the corrosion free intact condition, two levels of thickness reduction (25% and two with 58%) and two repair light stiffener profile dimensions for each level of thickness loss. A finite element model (FEM) is developed and firstly employed to compare and validate the experimental results for uniaxial compression. The FEM is subsequently employed to evaluate other typical loading combinations encountered in hull structures, including lateral pressure, uniaxial compression and shear stresses. The results show that the inclusion of an intermediate light longitudinal steel stiffener may satisfactorily restore the plate and consequently the panel load carrying capacity, allowing additional hull plating thickness reduction.

Experimental Parametric Investigation to Reduce Drag of a Scaled Model of Bulk Carrier Using BDR/ALS Technique

Abstract The shipping business expects to develop energy-saving and drag-reducing techniques addressing the cost of shipping and environmental problems. It has been reported that for slow-moving vessels, frictional resistance accounts for up to 80% of the total resistance, needing urgent attention to reduce the same. To reduce frictional resistance, the air has been used as lubricant, which is injected below the moving body known as Bubble Drag Reduction or the Air Lubrication System. In this article, results obtained from experimental investigations into drag reduction of a 1:23 scaled model of an 8000-ton deadweight bulk carrier by injecting air bubbles below it are presented. Investigations were carried out for a speed range of 6–10 knots, and for each speed, the effect of six injection flow rates of .5–3.0 CFM were investigated. To investigate the effect of different sizes of injection holes, two types of injector units have been used: one with injection holes of 1 mm diameter and the other with injection holes of 2 mm diameter. The study carried out has many practical implications because it is easier to create bigger size holes which will reduce the power required to inject air, thereby increasing the efficiency of the entire technique. Introduction It is projected that crude oil prices will continue to increase in the future, forcing marine businesses to rely on researchers to develop energy-saving devices (ESD) and drag-reducing technologies. It has been reported that for slow-moving vessels such tankers, bulk carriers, very large crude carrier (VLCC), and ultra large crude carrier (ULCC), frictional resistance accounts for up to 80% of the total resistance, needing urgent attention to reduce the same (Lewis n.d.; Larsson & Raven 2010). Numerous technologies have been studied and applied in reducing the frictional drag (Brostow 2008; Abdulbari et al. 2013; Luo et al. 2015; Mohammad & Mousavi 2015; Sindagi et al. 2016). Based on further studies Sindagi et al. (2018a, 2018b, 2018c, 2018d) and Sindagi and Vijayakumar (2020), it is concluded that air lubrication has additional advantages over other technologies, such as it is environmentally friendly, the operation is quite easy, and it results in low operating costs and high energy savings. Moreover, with air lubrication, an 80% reduction in the drag of the flat plate was achieved by Merkle et al. (1983) and Madavan et al. (1984, 1985).

An investigation on the solvent based carbon capture and storage system by process modeling and comparisons with another carbon control methods for different ships

This study investigates the effects of hydraulic design parameters of separation columns on the effectiveness of the solvent-based carbon capture and storage (CCS) systems and performs the cost analyses of CCS systems for different ships. The CCS and power systems of ships are simulated by using process modeling with Aspen HYSYS. A very large crude carrier (VLCC) tanker and three different sizes of liquefied natural gas (LNG) carriers (Q-Max, Q-Flex, and conventional LNG carrier) are considered. The study also employs different carbon control methods such as speed reduction and LNG usage. These methods are compared in terms of their CO2 emission reduction effectiveness and costs. Comparisons between the speed reduction, LNG usage, and the CCS system show that the speed reduction is the best cost-oriented and easiest solution for ships with low freight values like crude oil tankers. However, for ships with high speed and freight values like Q-Max and Q-Flex LNG carriers, it is shown that the CCS is more cost-effective than other compared CO2 control methods. The results show that the CCS system is a promising and feasible method for reducing CO2 emissions of ships.

EKF-DRNN autopilot for VLCC heading hybrid control

An online Extended Kalman Filter (EKF)-Dynamic Recurrent Neural Network (DRNN) autopilot implementation strategy for Very Large Crude Carrier (VLCC) heading hybrid control with uncertain dynamics is designed in this paper. The autopilot scheme is based on a DRNN control model, which learns VLCC dynamic characteristics, while the VLCC heading control is estimated by the EKF to minimize squared course error. The online EKF-DRNN autopilot provides optimal control on the basis of fuel-saving evaluation criteria using the heading deviation and rudder angle. Therefore, the autopilot output is guaranteed to converge to the desired VLCC trajectory asymptotically. The proposed strategy is evaluated by applying it to VLCC Yuan Kun Yang from COSCO Shipping, and works excellently under different loads, speed and weather conditions. The VLCC heading hybrid controller is also assessed by ‘Z’ manoeuvring and turning test, and the superiority of the online EKF-DRNN autopilot is demonstrated. The remote online monitoring of Yuan Kun Yang’s main navigation data shows that it improved fuel-saving properties despite worsening weather conditions causing increased yawing.

Ship service life extension considering ship condition and remaining design life

Reliable and continuous operation of ships is vitally important to the decision-makers. Driven by the rising cost of newbuilding ships, maintenance actions are needed on existing ships to ensure safe and enduring service beyond their initial design life. Extending ship service life can provide economic operating profit and promote sustainability. Meanwhile, ships during their extended service life may involve higher failure risk and additional maintenance expenditure. Therefore, a cost-benefit evaluation is imperative for determining the optimal duration of service life extension (SLE) and the associated maintenance actions. In this paper, a novel method for this purpose is proposed. Two cost-benefit indicators, benefit-cost ratio (BCR) and net present value (NPV) are used to optimize the duration of SLE. Using Bayesian updating, information on the remaining design life and the structural condition at the SLE decision is incorporated into the optimization process to better inform SLE decision-making. The proposed method is illustrated by a fatigue-sensitive very large crude carrier (VLCC) at both structural component and structural system levels.

Comparison of the Economic Performances of Three Sulphur Oxides Emissions Abatement Solutions for a Very Large Crude Carrier (VLCC)

Ship-source air pollutants, especially sulphur oxides (SOx), have a major impact on human health, the marine environment and the natural resources. Therefore, control of SOx emissions has become a main concern in the maritime industry. The International Maritime Organization (IMO) has set a global limit on sulphur content of 0.50% m/m (mass by mass) in marine fuels which has entered into effect on 1 January 2020.To comply with the sulphur limits, ship owners are facing the need to select suitable abatement solutions. The choice of a suitable solution is a compromise among many issues, but the economic performance offers the basis for which ones are attractive to ship owners. Currently, there are three technologically feasible SOx abatement solutions that could be used by ships, namely, liquified natural gas (LNG) as a fuel (Solution A), scrubbers (Solution B) and low-sulphur fuel oil (LSFO) (Solution C). To compare the economic performances of the mentioned three solutions for a newbuilding very large crude carrier (VLCC), this paper proposes a voyage expenses-based method (VEM). It was found that, within the initial target payback period of 6 years, Solution A and C are more expensive than Solution B, while Solution C is more competitive than Solution A. Five scenarios of target payback years were assumed to compare the trends of the three proposed solutions. The results show that Solution B maintains its comparative advantage. As the assumed target payback years becomes longer, the economy of Solution A gradually improves and the economics of Solution B and C gradually decline. A comparison between Solution A and C shows 6.5 years is a turning point. The advantage of Solution A is prominent after this payback period. In addition, the performance of a certain solution in terms of adaptability to the IMO greenhouse gas (GHG) emissions regulations is also a factor that ship owner need to consider when making decisions. In conclusion, when the IMO air pollutant regulations and GHG regulations are considered simultaneously, the advantages of using LNG are obvious.

Synthesis, design and operation optimization of a combined cycle integrated energy system including optimization of the seasonal speed of a VLCC

The study of an integrated energy system is presented in this article that will cover all types of energy loads (mechanical, electrical, thermal) on a Very Large Crude Carrier (VLCC) with the maximum technically possible and economically feasible exploitation of fuel energy, thus reducing the operating cost and environmental footprint of the ship. There may be a large variety of configurations, design specifications and operating states that can cover the loads, making it necessary to apply synthesis, design and operation optimization of the system. The net present value of the system is selected as the objective function. For this purpose, a superconfiguration of the system is considered, which includes a number of Diesel engines adapted for possible operation in a combined Diesel and Rankine cycle, heat recovery steam generators producing high and low pressure steam, steam turbines that can contribute to propulsion and/or to the electricity production, an exhaust gas boiler and auxiliary boilers, as well as Diesel-generator sets. The synthesis of the system, that is, the components that will finally exist in the system, and their interconnections, the design specification of the components and the operating properties at characteristic operating states of the ship are not predetermined, but they are the result of formal, mathematical optimization. In addition, the speed of the vessel in each state, an important operational variable that has a crucial effect on the propulsion power and thus on the fuel consumption, is also determined by the optimization. The hull characteristics, the loading condition and the weather state are taken into account for the calculation of the propulsion power. For the optimization, proper models of the various components have been developed and the optimization problem is solved by addressing the three levels (synthesis, design, and operation) at a single computational step. The benefits of optimization, as well as the conditions that make the combined cycle economically justified, are demonstrated through an application example. The numerical solution is obtained for various values of fuel price and freight rate, so that the effects of these two crucial parameters on the optimal solution are assessed.

A Quantitative Model of the Oil Tanker Market in the Arabian Gulf

Using a novel dataset, we develop a structural model of the Very Large Crude Carrier (VLCC) market between the Arabian Gulf and the Far East. We study how fluctuations in oil tanker rates, oil exports, shipowner profits, and bunker fuel prices are determined by shocks to the supply and demand for oil tankers, to the utilization of tankers, and to the cost of operating tankers, including bunker fuel costs. Our analysis shows that time charter rates are largely unresponsive to tanker cost shocks. In response to higher costs, voyage profits decline, as cost shocks are only partially passed on to round-trip voyage rates. Oil exports from the Arabian Gulf also decline, reflecting lower demand for VLCCs. Positive utilization shocks are associated with higher profits, a slight increase in time charter rates and lower fuel prices and oil export volumes. Tanker supply and tanker demand shocks have persistent effects on time charter rates, round-trip voyage rates, the volume of oil exports, fuel prices, and profits with the expected sign.

Risk-based decision-making on corrosion delay for ship hull tankers

Corrosion addition, as defined by the International Association of Classification Societies (IACS), is a proactive design measure against corrosion-induced structural deterioration. In conjunction with regular dry-docking maintenance (e.g., coating and steel renewal), corrosion addition is aimed to sustain the intended functionality of a corroding ship toward the end of its service life. It is expected that corrosion addition can improve hull strength and save the lifetime maintenance cost. However, the benefit of upfront steel investment in corrosion addition on the ship’s life-cycle cost, including construction, dry-docking maintenance, and failure consequence, remains unclear. Obtaining such knowledge is very helpful in ship design and lifetime dry-docking planning. This paper presents a risk-based approach to study the most economically optimal corrosion addition. The method is illustrated on a very large crude carrier (VLCC) and the benefit analysis takes into account different magnitudes of the construction, dry-docking, steel renewal, and failure costs. The results show that corrosion addition by IACS may not be economically optimal; the reduction in the life-cycle cost through corrosion addition and the optimal corrosion addition achieving the maximum benefit varies with the item costs specified.

A Quantitative Model of the Oil Tanker Market in the Arabian Gulf

Using a novel dataset, we develop a structural model of the Very Large Crude Carrier (VLCC) market between the Arabian Gulf and the Far East. We study how fluctuations in oil tanker rates, oil exports, shipowner profits, and bunker fuel prices are determined by shocks to the supply and demand for oil tankers, to the utilization of tankers, and to bunker fuel costs. Our analysis shows that time charter rates respond only slightly to fuel cost shocks. In response to higher fuel costs, voyage profits decline, as cost shocks are only partially passed on to round-trip voyage rates. Oil exports from the Arabian Gulf also decline, reflecting lower demand for VLCCs. Positive utilization shocks are associated with higher profits, a slight increase in time charter rates and slightly lower fuel prices and oil export volumes. Tanker supply and tanker demand shocks have persistent effects on time charter rates, round-trip voyage rates, the volume of oil exports, fuel prices, and profits with the expected sign.

A Quantitative Model of the Oil Tanker Market in the Arabian Gulf

Using a novel dataset, we develop a structural model of the Very Large Crude Carrier (VLCC) market between the Arabian Gulf and the Far East. We study how fluctuations in oil tanker rates, oil exports, shipowner profits, and bunker fuel prices are determined by shocks to the supply and demand for oil tankers, to the utilization of tankers, and to bunker fuel costs. Our analysis shows that time charter rates respond only slightly to fuel cost shocks. In response to higher fuel costs, voyage profits decline, as cost shocks are only partially passed on to round-trip voyage rates. Oil exports from the Arabian Gulf also decline, reflecting lower demand for VLCCs. Positive utilization shocks are associated with higher profits, a slight increase in time charter rates and slightly lower fuel prices and oil export volumes. Tanker supply and tanker demand shocks have persistent effects on time charter rates, round-trip voyage rates, the volume of oil exports, fuel prices, and profits with the expected sign.

Simulation study of approach manoeuvre in lightering and reverse lightering operations

Generally, there exists a case wherein a laden service ship approaches a partially loaded very large crude carrier (VLCC) for cargo transfer. This process is called ‘reverse lightering operation’. The manoeuvrability of these nearly fully loaded ships under interaction loads should be understood for the operation safety. In this study, we presented at first a practical method to simulate the approach manoeuvre, taking the interaction loads estimated by a 3D panel method and other hydrodynamic loads based on experiments into consideration. A standard approach manoeuvre of an Aframax tanker to a VLCC was simulated, and the difference in the behaviour of conventional lightering operation and reverse lightering operation was discussed. One result indicated that the service ship might experience difficulty in keeping the heading angle in parallel with the VLCC at the final phase of the approach manoeuvre in the reverse lightering operation. This would be caused by the increase of interaction loads. • A standard approach manoeuvre of an Aframax tanker to a VLCC was studied. • Both lightering and reverse lightering operations were simulated. • Interaction loads between hulls were estimated by a 3D panel method. • The difference in the behaviour between different operations was discussed.