This paper presents a numerical optimization method to improve propeller performance using real-coded genetic algorithm. In the method presented, UNDX (Unimodal Normal Distribution Crossover) and MGG (Minimal Generation Gap) models are used as crossover operator and generation-alternation models, respectively. Propeller performance is evaluated by a simple surface panel method “SQCM” in the optimization process. The blade section of the original propeller is replaced by the NACA66 a=0.8 section. However, original chord, skew, rake and maximum blade thickness distributions in the radial direction are unchanged. Pitch and maximum camber distributions in the radial direction and the position of maximum camber in the chord wise direction are selected as the design variables. Optimization is conducted to maximize the propeller efficiency while keeping the target thrust coefficient constant. Cavitation performance is also considered as a constraint condition. Propellers for a product tanker and a cargo ship were improved by utilizing the present method. Propeller open tests and cavitation tests of the original and improved propellers were carried out. It was confirmed that both improved propellers had higher efficiencies compared to those of the original propellers. It was also found that both cavitation performances of the improved propellers are permissible.
This paper discusses the feasibility of high-performance NHV propeller whose blade area is decreased by 20％ compared to a normal NHV propeller without the risk of cavitation erosion and increasing pressure fluctuations, and presents the results of experiments and numerical computations of an NHV propeller with the smallest blade area (SBA-NHV propeller) and an equipped conventional propeller for a 749GT chemical tanker. In recent studies conducted by the authors, a propeller with a blade area 20% smaller than that of aconventional propeller offered an improvement of about 2% in propeller efficiency with an almost equivalent risk of cavitation erosion and pressure fluctuations in model tests. In order to improve propeller efficiency by decreasing the propeller blade area, four propellers were designed whose blade areas were decreased systematically. An SBA-NHV propeller with a blade area 20% smaller than that of the conventional propeller was designed. Three four-bladed propeller models including the conventional propeller, the above-mentioned SBA-NHV propeller, and the propeller with each blade having a different blade area ratio were manufactured. Propeller open tests and self propulsion tests were carried out in the towing tank and cavitation observations were made with a high speed video camera, erosion paint tests and fluctuating pressure measurements were carried out in the cavitation tunnel using these three propeller models. The SBA-NHV propeller attained improvements of about 1.3% and about 3% in the propeller efficiency and in the propulsive efficiency, respectively, compared with those of the conventional propeller. The effects of decreasing the blade area ratio on the risk of cavitation erosion and the pressure fluctuations were confirmed and the SBA-NHV propeller demonstrated an almost equivalent performance with that of the conventional propeller. To validate existing numerical tools, propeller efficiencies and cavitation patterns were numerically simulated by a lifting surface theory (LST) and a Reynolds-Averaged Navier-Stokes solver (RANS). The LST and RANS need to be modified to predict the effect of the blade area ratio etc. on the propeller efficiency. Meanwhile, these are found useful as design tools to evaluate the risk of cavitation erosion even though further improvements are still necessary.
Our mission is to manufacture optimum products using provided design data. Thanks to analysis tools brought in recently, the design of more efficient propellers have become possible. To manufacture propellers with maximum design efficiency, a high level manufacturing technology is essential. The Tamashima Works, is a specialized facility for manufacturing large-sized fixed pitch propellers. Manufacturing size ranges from 5 meters up to a maximum of 12 meters in diameter, and a maximum weight of 150 tons. Here, we succeeded in developing special facilities, the only one of its kind in the world, such as the blade milling machine which can control 5 axis at the same time, the balancing machine, and the propeller overturning facility. These special facilities resulted in higher machining accuracy.
IHI Marine United Inc. (IHIMU) has developed an environmental-friendly and economically efficient diesel-electric propulsion system with CRP designated as “IHIMU-CRP Electric Propulsion System (IHIMU-CEPS)”. Several vessels with the IHIMU-CEPS have already been delivered and their significant fuel savings have been verified in sea trials. This paper presents an outline of the IHIMU-CEPS and its inherent hydrodynamic performance especially those which are manifested through the self-propulsion factors of the CRP system.
The authors have developed an advanced propulsion system, called the Overlapping Propellers System (OLP), which utilizes bilge vortices to obtain high propulsive performance. A pair of bilge vortices symmetric about the hull centerline occurs around the propeller disk, which has an inward rotational component. OLP fully utilizes the rotational component of bilge vortices because the center of each propeller is close to that of the bilge vortex and the turning direction is outward, opposite to the rotational direction of bilge vortices. In OLP, since the center of each propeller is close to the hull centerline and about half of each propeller closely overlaps, the added resistance due to the shaft bracket and so on is negligibly small. The hydrodynamic characteristics of OLP, in which the propellers are in the vicinity of each other, are especially important in designing a ship with OLP. The authors have designed OLPs for various types of ships such as large LNG carriers with various propeller inflow improving devices. Energy savings by OLP were proven to be over 10 %, compared with single screw ships. This paper describes the hydrodynamic characteristics of the propulsive performance, the cavitation behavior, the propeller excited hull pressure pulses and the shaft bearing force variations of OLP.
While there are many advantages with electric propulsion vessels, energy loss is considered as its most significant disadvantage. Therefore, the minimization of energy loss and the improvement of the ship’s propulsion efficiency are important elements. There are two conceivable elements to improve propulsion efficiency, one is to decrease hull resistance, and the other is to increase the propeller efficiency. Contra-Rotating Propeller (CRP) is one of the solutions to improve the efficiency of propulsion systems, and the tandem type CRP, which is an azimuth pod propeller installation behind the CPP, is considered as an example of practical application. In this paper, an electric propulsion system with the tandem CRP is introduced. By designing a hybrid CRP system that operates a CPP driven by a diesel engine and an azimuth pod propeller driven by an electric motor, the reduction of the percentage of energy loss and the minimization of fuel consumption were made possible. Nakashima’s pod propulsion system is based on CPP’s and side thrusters’ technology. Propeller pitch was determined using an NMRI1) CRP program. Since the azimuth pod propulsion system can be used as a stern thruster as well, with this propulsion system, not only an improvement in propulsion efficiency, but also an improvement in maneuverability can be expected. 1): National Maritime Research Institute
In this study, the authors conducted mechanical property tests and the vibration characteristic tests of CFRP (carbon fiber reinforced plastics) specimens that can be adopted as new marine propeller materials. CFRP materials exhibited higher strength than NAB (nickel aluminum bronze casting) which is conventionally used as material for marine propellers. The damping ratio of CFRP materials was four times larger or more than that of NAB. In field tests using a small fishing boat, two types of CFRP propellers were manufactured by using CF-prepreg. One propeller was laminated with CF-Fabric and another with CF-UD, to obtain a quasi-isotropic composite. These are the so-called “built-up type” as three CFRP blades were assembled in an NAB boss. An NAB propeller of the so-called “mono-block type” was also manufactured to facilitate comparison with CFRP propellers. Analyses of field test results are ongoing. In vibration tests, the damping ratios of the both types of CFRP propellers were about ten times larger than that of the NAB propeller. Cavitation which can cause erosion on the surface is a severe problem for FRP propellers. Therefore, we cavitation erosion resistances for eight kinds of FRP and an NAB were evaluated in cavitation tests using a magnetostriction ultrasonic transducer. The cavitation erosion resistance of the NAB was much superior to that of FRP materials. However, it was found that aramid fibers on the surface of FRP can improve the erosion resistance. In order to improve the erosion resistance of FRP materials to the same level as that of NAB, the further research is necessary.
The concept of Zero Emission Ultimate Ship (ZEUS) concept is an idea of promising future vessels which utilize several key technologies such as a hybrid diesel electric propulsion system, a reaction pod and an extremely wide twin skeg hull form. This paper mainly deals with the reaction pod propulsion system and propeller design that is well adapted to this new concept.
Currently, there are more than 1,800 vessels that are equipped with PBCF (Propeller Boss Cap Fins), a trustworthy energy saving device which contributes not only to fuel oil consumption savings, but also to the reduction of greenhouse gas emissions. The PBCF mainly recovers the energy loss at the propeller hub vortex downstream of the propeller, and lowers fuel consumption by 5% at constant speed operation, or boost speed by 2% with the same fuel consumption. In the earlier section of this paper, the basic hydrodynamic mechanism of the PBCF as an energy saving device is described. Then, outline of the recent R&D efforts carried out in the past few years to improve the PBCF’s fuel saving effect are described. Although it is still ongoing, the geometric shape of the existing PBCF is being improved by taking into account knowledge of the hydrodynamic mechanism obtained through Computational Fluid Dynamics (CFD) analysis. The effectiveness of improvements made was confirmed by the model tests. Finally, in the later section, the possible direction of PBCF improvements necessary for it to be a more effective energy saving device is explained.
Numerical simulation has become a practical tool for marine propeller designers. However, compared with experiments, the management and evaluation of the accuracy is generally more difficult. Especially when cavitation is involved, reliability of CFD is still much lower than that of experiments conducted in a cavitation tunnel. Uncertainty in CFD arises mainly from the approximation used in the mathematical model and discretization of the model. To clarify the sources of uncertainty and improve accuracy, it is necessary to carry out careful investigations through comparisons with reliable experimental data. In this study, numerical simulations of non-cavitating and cavitating propellers in various conditions were performed and the results were compared with experimental data.
This paper discusses the application of CFD (Computational Fluid Dynamics) to cavitating flow around marine propellers operating in the ship wake. Emphasis was put especially on the tip vortex cavitation and the erosive cavitation around the trailing edge. This research found that adaptive mesh refinement methodology is effective for improving the resolution of tip vortex cavitation. Next, Full cavitation model(Singhal et al. 2002) was validated, and it showeda qualitative agreement with experimental results. Finally, four simple cavitation erosion indexes were applied to estimate erosion risk.One index showed good agreement with experimental results. It is concluded that the RANS (Reynolds-Averaged Navier-Stokes) CFD provides valuable information for judging erosion risks although its presumption’s accuracy and numerical stability need to be improved.
Japan Railway Construction, Transport and Technology Agency (JRTT) has developed three types of SES for domestic coastal ships and promoted their wide use under the support of the Ministry of Land, Infrastructure, Transport and Tourism. These three types of SES, the Line Shaft CRP type, the Tandem Hybrid type and the Twin POD type were developed in cooperation with shipbuilding companies and marine equipment manufacturing companies. In total, 17 SES type ships have been delivered and currently three more SES ships are under construction. JRTT, research organizations and engineering and manufacturing companies are now jointly promoting the development project of Twin-propeller type SES as a new type of SES in addition to the three existing SES. Twin-propeller type SES is expected to give higher performance and lower building costs in comparison with the other SES and all other similar type of ships.
There are different ways of hybridization of ships. Previously, the authors have reported on the hybridization of a fishing boat and a training ship. In this paper, the authors propose the hybridization of a large car ferry boat plying between the cities of Osaka and Kita Kyushu. This ferry boat lies in port during the day and sails overnight. The hybridization method of collecting heat from the engine exhaust gas during the ship’s voyage through some thermoelectric elements supplies battery power to some electric loads at standby when a ship enters or leaves port and during lay days.
The steady combustion of coal fuel was successfully conducted in a laboratory scale combustion furnace, and the formation of particulate matter was investigated. Combustion resulted in a high concentration of particulate matter. To reduce the formation of particulates, secondary combustion was proposed. An afterburner made from stainless steel pipe with a diameter of 300 mm was placed between the second and third stages from the burner. Holes at the pipe were 1.5 mm in diameter. Secondary combustion influenced both combustion and particulate formation. As a result, the concentration of particulate matter in the exhaust gas was reduced.
A wrong TDC position leads to incorrect cylinder pressure-crank angle phasing, and has been recognized as a major source of error in thermodynamic calculation results such as indicated mean effective pressure, heat release rate, or thermal and mechanical efficiencies. One of the most convenient ways to determine TDC is to use measured cylinder pressure obtained from a pressure transducer under non-firing conditions. However, it is impossible to determine TDC precisely because the thermodynamic loss angle is unknown. In the paper a new method for TDC determination based on a measured non-fired cylinder pressure versus time diagram has been presented. In this method there is no need to know the details of the heat transfer formula, heat transfer coefficients or the properties of working gas in the engine . The method is applied to a four stroke high-speed marine diesel engine successfully. This method is distinguished for its high accuracy and is also probably applicable to large two stroke diesel engines.
Effects of the split injection pattern on combustion and emission characteristics of a D.I. Diesel engine with a common-rail injection system were investigated. While keeping the injection pressure and total injection quantity constant, the ratio of amounts of fuel injected between two injection pulses and the injection interval were varied, and the emissions and performance of a D. I. Diesel engine with a common-rail injection system were measured. The concentration distributions of the vapor and liquid phases in the splitting fuel spray injected into a high-pressure / high-temperature vessel were measured by means of the laser absorption scattering (LAS) technique. The results account for the effects of the split injection pattern on the combustion and emission characteristics.
In this research, particulate emissions from a marine diesel engine were measured using a dilution system according to JIS B 8008 and the soluble organic fraction (SOF) in the particulate matter (PM) was extracted by a Soxhlet extractor. Then, the SOF was analyzed by a thermo-gravimetric analyzer to determine its origin. Total hydrocarbon (THC) concentrations in the upstream and downstream of the dilution system were also measured using a hydrocarbon analyzer to evaluate how much THC passes through the PM collection filter of the dilution system. The relationship between SOF and THC were investigated. The results show that: 1) SOF consists of higher boiling point constituents of the fuel oil and lubricant; and the ratios of the former to the latter is influenced by engine operating conditions, 2) several tens of percent of THC in the exhaust gas pass through the PM collection filter, 3) there was no close correlation between SOF and THC in the engine operating conditions studied.
Observations were made of the elastohydrodynamic lubrication of stern-tube bearings on the propeller shaft with the stern-tube bearing in an inclined state. The force generated by the propeller can be neglected based on the assumption that the propeller shaft has a low rotation frequency. The magnitudes of the inclination and deflection of the propeller shaft were calculated under these conditions, and numeric values for the approximate range of inclination and deflection were measured. The magnitudes of inclination and deflection calculated under these conditions were used as parameters to calculate the elastohydrodynamic lubrication characteristics under various conditions. The relationship between oil film pressure distribution and deflection mode of the bearings was also calculated.