Aframax Tanker Research Articles

Fatigue Life Analysis on The Local Construction Near the Chain Stopper Area of Papa Terminal Floating Storage Offloading (FSO) With 4X2 Chain Line Spread Mooring Configuration

This research aims to determine the fatigue life of the structure near the chain stopper of a storage tanker using the spectral fatigue analysis method. The wave spectrum is developed based on six significant wave height and period variations from the site wave scatter data using a modified spectrum of JONSWAP. The stress analysis is carried out using finite element analysis software. It can then be processed into Stress RAO from each loading direction. The response spectra are generated from the wave spectrum, multiplying with the square of the Stress RAO. These response spectra will determine the stochastic values of each stress range variation in obtaining the number of cycles that occur in each variation (nL). The accumulation of each ratio obtained from all existing variations will produce a fatigue index value (D). The American Bureau of Shipping’s S-N curve D-Class is used in this fatigue life analysis. The Gamkonora Aframax tanker operated as a temporary storage tanker at Papa’s field area is used as the case of this study.

Selection of mooring system configuration of a FSO using multi-criteria methods

In order to maintain and restrain the movement of a temporary storage tanker during the loading and offloading process, it is necessary to design a mooring system that is safe and reliable for its operation needs. The main problem that must be solved in this research is choosing the appropriate mooring system configuration for the temporary storage tanker equipped with a catenary mooring configuration that can be used for oil loading operations from the storage tanker to a transport tanker using the ship to ship method. This research focusses in the selection of mooring system configurations based on the strength of the anchor chain. There are nine alternatives configurations and predetermined criteria that were carried out in the study. Each alternative configuration will provide a different value of tension in each mooring line and ship movement. The analysis of the mooring tension is carried out using dynamic method with time domain approach. There are many criteria to be considered in the selection of the alternatives. The analytical hierarchical process (AHP) method is used in the selection of the best configuration based on multi criteria conditions. As case study of the study is a temporary storage tanker at Papa Field in Pertamina (Persero) ONWJ operation area as temporary storage taker is an Aframax tanker size.

A novel objective oriented methodology for marine engine–turbocharger matching

The matching of the turbocharging system with a marine engine is an essential undertaking due to the turbocharger effects on the engine performance, emissions and response, whilst the limited data availability during the ship design phase renders it challenging. This study aims at developing a novel methodology for the matching of a single turbocharger and multiple turbochargers connected in parallel with marine engines. This methodology employs a compressor parametric modelling tool and a zero-dimensional engine model, whilst taking into account the engine operational profile and the turbocharger components flow limitations. The compressor parametric tool is used for the generation of a database with compressor families that can be investigated during the matching procedure. The model of one engine cylinder block is used for mapping the engine performance parameters at a wide engine operating envelope by developing response surfaces. The developed methodology is implemented for the case study of the turbocharger matching with the propulsion engine of an Aframax tanker. The annual fuel consumption and the engine load diagram upper limit are employed as the main objectives for the selection the turbocharging system. The derived results demonstrate that the effective turbocharger matching results in reducing the engine brake specific fuel consumption up to 5%. The identified turbochargers led to the reduction of the ship annual fuel consumption in the range 1.3%–5.3% compared to the reference engine, whilst providing a more expanded load diagram. This study overcomes the limitations of the manual engine turbocharger–matching process providing decision support on the effective turbocharger matching to satisfy contradictory objectives.

OPTIMUM INSPECTION INTERVAL FOR TANKER IN UNIFIED INSPECTION REGIME

Inspections on board tankers contribute to the prevention of accidents, which can have a significant impact to humans and environment. Therefore a high amount of tanker inspections is performed by various stakeholders. This practice could be made more efficient by introducing unified inspection regime, which covers existing areas of inspection, eliminates overlapping and has the potential to improve safety. In this paper an important aspect in defining inspection regime, inspection interval, is determined considering contradictory goals: lowering the costs of inspection and increasing useful service life of tanker structure and equipment, without compromising safety. A probabilistic approach has been applied to establish inspection schedule, which fulfils a range of requirements. Due to the many varieties of tanker types, their conditions, range of size and age span, the paper focuses on the 10 years AFRAMAX tanker. Results indicate that optimal inspection interval in the unified inspection regime for that tanker should be 3 months. Using modified input parameters, similar approach could be used for other tanker types.

Numerical Method to Simulate Self-Propulsion of Aframax Tanker in Irregular Waves

With the implement of ship energy efficiency design index (EEDI), computational fluid dynamics (CFD) technique has become an effective method to predict the ship performance and further guide the designers to optimize hull lines. However, due to the complexity of the propeller-hull interactions and the ship’s complex motions in waves, accurately predicting the speed-power performance of a self-propelled ship in actual seaway remains a challenge. In the present work, firstly, the resistance and self-propulsion experiments of Aframax model in waves are carried out at FORCE towing tank. Then, the CFD model and method are adopted to investigate the resistance and thrust under the conditions of regular and irregular waves in a three-dimensional numerical wave tank created by commercial software Star-CCM+. Therein, Reynolds-Averaged Navier–Stokes (RANS) equations and k-ε turbulent models were used for modeling the turbulent flow, and volume of fluid (VOF) method was applied to track the location and shape of transit-free surface. Based on the numerical method, the added resistance caused by regular waves was firstly investigated, and the self-propulsion of propeller in irregular waves was further performed. Furthermore, in order to simulate the rotation of the propeller, both the sliding mesh technique and overset mesh technique were discussed. Finally, compared with the experimental data, the numerical solutions have been validated, which shows potential to provide theoretical guidance and technical support for the self-propulsion performance of Aframax tanker in waves.

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.

Application of the Design of Experiments and Computational Fluid Dynamics to Bow Design Improvement

Techniques of the design of experiments (DOE) and computational fluid dynamics (CFD) were applied for improving the bow shape of a tanker hull. Through this, a hull that could reduce the added resistance in waves was derived. The key design elements of the bow shape were selected as parameters for design optimization and added resistance in the short-wavelength region was interpreted through CFD considering the operational condition of the full scale ship. For design parameter changes, the number of analyses was minimized by applying DOE. The regression equation for calculating added resistance was derived using bow-shape design parameters by applying the response surface method and regression analysis to obtain the optimal hull with minimal added resistance was derived. The methodology was applied to an Aframax tanker hull form, and the derived added resistance regression equation and the added resistance value obtained through CFD analysis showed a difference of approximately 1%. The model test results of the improved hull form showed that the added resistance was reduced by 52% in comparison to that obtained for the original hull form.

Periodicity of world crude oil maritime transportation: Case analysis of Aframax Tanker market

The oil tanker shipping market always presents periodicity following varied laws in different periods. However, most of the studies on the tanker freight rate market are short-term projections, while those on its long-term periodicity characteristics are mostly qualitative ones. In order to study the periodic variation law of the tanker market, this paper uses quantitative methods to figure out the cycle duration and amplitude of different scales of Aframax tanker's freight, and predicts the long-term variation trend of freight rate on that basis. This paper selects the one-year charter freight rate of Aframax tankers (110,000 DWT D/H) to comprehensively analyze the Aframax tanker freight market variation law, and further divides the cycle into three major categories. With the help of wavelet analysis, this paper quantifies the periodic volatility of the Aframax tanker shipping market, and figures out a quarterly cycle of 11.2 months, a short-term cycle of 3.7 years, and a medium-to-long-term cycle of 11.9 years. Based on the cycle characteristics, the paper predicts the market cycle trend to the next medium-to-long-term cycle and further to the year 2030, so as to offer some reference to oil tanker shipping market players for better decision-making.

Spectral fatigue analyses comparison study: Suez Canal vs. Cape of Good Hope Arab Academy for Science, Technologies and Maritime Transport (AASTMT)

ABSTRACT Suez Canal is one of the shortest navigational routes between east and west. Vessels that transit the Canal should normally save distance, time and operating cost. During the current economic recession and low fuel prices, longer shipping routes may be chosen to avoid the Canal transit fees. Harsh weather conditions may be encountered along these lengthy routes resulting in higher stresses and structural fatigue damage on ship’s hull, which would impact structural safety and affects the cost of ship maintenance. This paper quantifies ship structural fatigue damage along the routes: Suez Canal transit versus the Cape of Good Hope. Several voyages of an Aframax tanker along these routes are selected and evaluated for fatigue damage using a route-specific spectral fatigue damage assessment approach. Fatigue accumulation during the tanker lifetime, for each trade route, is computed as the sum of all the encountered sea states having caused fatigue damage along that route. Results are presented as fatigue damage and fatigue life for each trade route. Results show that in addition to saving in distance and time, less accumulated fatigue is achieved along the Suez Canal route.

Maneuverability of a combined two-ship unit engaged in underway transfer

Ship-to-ship transfer operations, primarily used to transfer crude oil, petroleum, and other chemical products between ocean going ships (i.e., lightering operations), are commonly conducted worldwide because a deep draft of a large ship limits its access to ports. In areas where the water depth is too great for anchoring, cargo is transferred to another rigidly moored ship running slowly. This operation is called “underway transfer.” During this process, the maneuvering service ship (SS) approaches and berths from the port side to the starboard side of the large ship to be lightered (STBL). After mooring, the SS stops its engine and behaves as a towed ship. Meanwhile, the STBL maintains its steerage on a steady course, responsible for all maneuvers. To reduce the possibility of accidents, the maneuverability of this unique combined two-ship unit should be further investigated.In this study, a very-large crude carrier (VLCC) and an Aframax tanker are used as the STBL and SS. Two scenarios are considered for the two-ship unit: the full-load STBL with the ballasted SS, and the half-load STBL with the full-load SS. These are assumed to be different stages of the cargo transfer process. Free-running model tests and captive model tests are conducted, and a mathematical model for maneuvering simulation of such a front-back and left-right asymmetric two-ship unit is presented. Additionally, full-scale simulations are performed. Based on the results of experiments and simulations, the change in maneuverability, according to the progress of the cargo transfer, is assessed. The combined two-ship unit needs a large advance and transfer when turning to port, especially in the case of the half-load STBL with the full-load SS. The difference of left- and right-turning abilities is significant. In terms of the directional stability, the combined unit condition during underway transfer would be preferable to running alone.

Potential power setups, fuels and hull designs capable of satisfying future EEDI requirements

Maritime emission regulations set limits for SOx and NOx emissions for health and environmental reasons, and for CO2, through the Energy Efficiency Design Index (EEDI), with the general aim of mitigating global warming. EEDI verification is performed at the vessel's design speed and design loads, under calm-water conditions. This, although calm seas are the exception in shipping, and that even with calm-water conditions, ships usually operate at lower speeds than their design speed. A major challenge, if greenhouse gases (GHG) reduction targets are to be met through the EEDI, will be to identify EEDI-compliant solutions that reduce energy consumption and GHG emissions under realistic operational conditions, from lying idle at berth in port to when full power is required in critical situations at sea. In view of all the above, we use the Aframax tanker class to illustrate how such an assessment can be performed, and to display the differences in costs and benefits of options, all of which meet the requirements of the EEDI.

대형 캐비테이션 터널 내 선박 모형의 3차원 선체 반류 계측을 위한 레이저 유속계 개발

Large Cavitation Tunnel (LCT) of KRISO enables us to conduct cavitation tests of the propeller attached to a ship model. As the ship model tests are done at rather high Reynolds number of 107~108, flow measurement system such as pitot tube cannot be employed because of structural safety problems in its system and difficulties in installing it within the test section. Thus, KRISO has developed new 3-D LDV system used in large test section of LCT. There are several difficulties in using 3-D LDV, which did not allow efficient operation of it. The first trouble was the calibration using the conventional pin hole. To make the focus with same laser-beam waists at the wanted position, the high spatial resolution CCD is utilized in the calibration procedure for 3-D LDV. The off-axis configuration provides two velocity components in the horizontal plane and on-axis configuration gives third velocity component in the vertical plane. The horizontal velocity components are also obtained in the coincidence mode, which prevents any misleading results in the off-axis configuration. The nominal wake of Aframax tanker model is measured by the developed 3-D LDV system. The measured hull wake showed good agreement with that obtained by CFD calculation.

Ultimate Strength of the Buoy Structure due to the Loads Arise from the Tanker and Mooring Lines

A study was conducted to evaluate the ultimate strength of a 40 ton buoy induced by the dynamic loads arising from a 120,000 DWT Aframax tanker and mooring lines. The buoy is operated at Bangka Strait offshore oil terminal. The eva­luation was commen­ced by analyzing the motion characteristics of the buoy and tanker due to environmental excitations, both in free floating conditions. This is continued by the simulation and time-domain analysis of con­nected buoy and tanker to observe the hawsers and mooring line tension intensities. The correspon­ding results show the largest tension occurs in the in-line configu­ration with the tanker in ballast condi­tion, where hawsers tension reaches 1282.58 kN with a safety factor of 2.23 and mooring line tension 1974.18 kN with a safety factor of 3.20. The resulting tensions were further applied as input data for structural modeling using FEM to find out the stresses develop on the buoy structure. Results of this modeling reveal the maximum value of stress experienced by the buoy structure is approaching 184.28 MPa, which is below allowable stress of 200 MPa. Following this, the ultimate stress of 450 MPa will be violated by 143% incremental load above the maximum, namely 3,116.67 kN and 4,797.26 kN due to the hawsers and mooring line. This fact suggests that the structure is unlikely to experience ultimate failure if merely operated in the current operational site.

Safety and CO2 emissions: Implications of using organic fluids in a ship’s waste heat recovery system

This paper considers the practical application of exhaust gas waste heat recovery from the main engines of merchant ships. A water-based Rankine Cycle is used as a baseline and this is compared with five organic Rankine cycle systems using benzene, heptane, hexamethyldisiloxane, toluene and R245fa. The thermodynamic model of the waste heat recovery system is described. This is then applied in a case study utilising an Aframax tanker. The case study allows the comparison of the different waste heat recovery systems in more realistic scenarios. The efficiency of the different systems is compared as well as their potential to reduce CO2 emissions, ship impact, and economic viability are also discussed. The paper closes with consideration of the safety and regulatory issues associated with the use of organic fluids in the marine environment.

Simulation and optimisation of cargo handling operations of AFRAMAX tankers

This article focuses on the optimisation of cargo handling operations of tankers. A combined hydraulic-energy model has been developed and adapted to the design characteristics of AFRAMAX tankers, allowing the simulation of a tanker’s cargo discharging procedures, while monitoring all related ship parameters, like characteristics of pumps/manifolds, piping system, flow rates, pressures, ship responses, etc. A preference-based multi-criteria optimisation methodology has been additionally applied to the modelled simulation procedure, which results in practical guidelines for the optimisation of discharging procedure in terms of energy–fuel consumption and discharging time. These guidelines have proven very valuable in the decision-making process during cargo handling operations.

Experimental Results of Ship-To-Ship Lightering Operations Applied Velocity Information GPS

A ship-to-ship (STS) lightering operation takes place in order to transfer cargo (e.g. crude oil or petroleum products) between an ocean-going ship and a service ship alongside it. Instrumental measurements to accurately determine the relative speeds and distances during the approach between the vessels would benefit the operational safety and efficiency. A velocity information GPS (VI-GPS) system, which uses the instantaneous velocity measures from carrier-phase Doppler measurement, has been applied in a field observation onboard a service ship (Aframax tanker) approaching a ship-to-be-lightered (VLCC) in open waters. This article proposes to apply VI-GPS as the input sensor to a guidance and decision-support system aiming to provide accurate velocity information to the officer in charge of an STS operation. A method for precise velocity measurement using VI-GPS was described and the measurement results were compared each other with the results of Voyage Data Recorder (VDR) and VI-GPS that showed the concept of a guidance and decision-support system applying VI-GPS with the field test results during STS operations. Also, it turned out that VI-GPS has sufficient accuracy to serve as an input sensor from the field test results.

An economic evaluation of operating expenditures for LNG fuel gas supply systems onboard ocean-going ships considering availability

This paper proposes a methodology for economic evaluations of liquefied natural gas fuel gas supply (LNG–FGS) systems. To evaluate the economics of various LNG–FGS systems, expected operating expenditures during long-term voyages were compared, including the loss from venting boil-off gas (BOG) to prevent overpressurisation of the fuel tank, penalties for venting BOG, expenses for consuming marine diesel oil when LNG–FGS systems are unavailable, and expenses for electricity consumption. A secondary objective was to compare the economics of various LNG–FGS systems for large-sized ships. An analysis demonstrated that the comparative operational expenditures vary considerably within various design options. Three LNG–FGS systems were compared. As a case study, an Aframax tanker (a highly popular crude carrier) was chosen, and the actual voyage scenario between Ulsan and Antwerp was used for calculating expenses. The results indicated that group FP-P (fully pressurised-type storage tank with cryogenic pump) provides a profit of approximately 7 MUS$ per 25 yrs compared to group UP-P (unpressurised-type storage tank with cryogenic pump); conversely, group FP-P incurs a loss of approximately 5.4 MUS$ per 25 yrs compared to group FP-N (fully pressurised-type storage tank with vapour-generating unit). Nevertheless, group FP-N is valuable for small-sized tanks because the vapour-generating unit requires high energy consumption during an extended initial time to raise pressure. In conclusion, group FP-P is the most economical system if it can compensate for approximately 5.4 MUS$ in capital expenditure and maintenance costs. The proposed methodology reflects the availability of necessary equipment and the results of process dynamic simulation in an actual voyage scenario.

東北地方太平洋沖地震津波来襲時の桟橋係留大型石炭船の挙動再現について

The 2011 Tohoku earthquake and tsunami at 14:46 JST on March 11, 2011 affected large areas of the eastern and northern part of Japan, and many sea disasters against vessels moored along terminal inside harbor basins occurred. The authors conducted surveys upon sea disasters of a Very Large Crude Carriers (VLCC) at S-Port and an Aframax tanker at O-Port. There was also a severe disaster of large coal carrier at H-Port, which encountered a tsunami of tsunami wave height beyond 10 meters and damaged mooring equipment such as fenders and mooring lines, and unloader of coal, entirely. In this paper, the authors have also tried to reproduce the ship's behavior and analyze the mooring loads during the tsunami through a numerical simulation of tsunami and ship motion.

東北地方太平洋沖地震動によるドルフィン振動に伴う係留船舶の動揺および係留索切断に関する一考察

Many sea disasters of vessels moored along the terminals occurred during the 2011 Tohoku Earthquake Tsunami. We conducted surveys of the sea disasters for two large crude oil carriers moored at dolphin terminals. The mooring lines breakages happened not only in the tsunami attack but also in the seismic vibrations. In this study, we have composed a time domain model to estimate the moored ship behavior due to oscillations of dolphins during earthquake, and investigated the Aframax tanker behavior moored at dolphins during the seismic vibration which was actually recorded at the harbor. It is clarified that there is a possibility to push out the tanker and induce the mooring line breakage due to oscillations of dolphins during earthquake.

東北地方太平洋沖地震津波における大型原油タンカーの係留避泊実態

The 2011 off the Pacific Coast of Tohoku Earthquake Tsunami at 14:46 JST, 11 March 2011 affected the large areas of eastern and northern part of Japan. Many sea disasters of vessels moored along the terminals such as ship drifting and grounding, and damages to the mooring facilities and equipment were occurred. Recently several reports such as questionnaires of the sea disasters have been reported. Among the sea disasters, there was a successful example of safe mooring harborage of an Aframax tanker (100kDWT class crude oil carrier) during the tsunami. In this study, we have carried out a survey of the mooring harborage by a hearing investigation to the crews, and tried to reproduce the ship behaviors during the tsunami by the numerical simulation methods on ship motions and tsunami to find out the causes of the safe harborage.