The authors verified an energy saving effect of an air lubrication system for the domestic service ferry which was one of slender body ships. The energy saving effect was evaluated by the engine output reduction rate of system ON and OFF at speed-trial test. As the result, a net energy saving effect of about 3.7% was confirmed.
After that, long-term voyage monitoring had been conducted since the ship was in service. At the same time, monitoring had been conducted about same type of sister ship without air lubrication system, in service on the same route.
The investigation result of the energy saving effect by comparison of fuel consumption of both ships, a net effect of about 3.13% was confirmed. According to these results, the effectiveness of an air lubrication system for slender body ships was proved; therefore, scope of an air lubrication system as energy saving system of ships had expanded.
The Reynolds number effect on the open water characteristics of a propeller with a laminar type blade section has been studied by CFD and compared with the experiment. At a Reynolds number of model tests, the boundary layer flow over the blade is mostly laminar, while it becomes almost fully turbulent at a full scale Reynolds number. Because of this fact, the Reynolds number effect is very complicated. When the Reynolds number is increased from the model scale to the full scale, the open water efficiency first increases, and then start to decrease because of the transition of the boundary layer. As the boundary layer becomes almost fully turbulent, the open water efficiency again increases with increasing Reynolds number. It has been also shown that the transition Reynolds number of a propeller with laminar type blade section is higher than that of a propeller with MAU type blade section.
The open water efficiency of a model test at a sufficiently high Reynolds number is close to that at a full scale Reynolds number. However, because the open water efficiency of model tests is significantly dependent on the Reynolds number, the selection of the Reynolds number in model tests is of critical importance.
This paper addresses effect of the Reynolds number on the optimum diameter and optimum efficiency of propellers with laminar flow blade section (N propellers) in comparison with those of MAU propellers.
A series of propeller open water tests (POT) were performed at a high Reynolds number by using N4-50 propellers (number of blades 4, expanded area ratio 0.50), of which results show that the optimum diameter and optimum efficiency of N propellers are respectively 2～5% larger and 5～7% higher than those of MAU propeller design charts. The effect of different Reynolds number is included in these differences. Considering the effect of different Reynolds number between POT of N propellers and MAU propeller design charts, it may be said that the optimum diameter and optimum efficiency of N propellers are respectively almost same as and 2～3% higher than those of MAU propellers.
Next, CFD calculations were performed on open water characteristics of N4-50 propellers at model and full scale conditions, of which results show that the optimum diameter and optimum efficiency of N propellers are respectively 0～1.5% larger and about 1% higher at the full scale condition than at the model scale condition.
Finally, it is confirmed that 5% diameter deviation from the optimum diameter leads to about 1% efficiency down and the efficiency down is not almost affected by the propeller type nor the Reynolds number in case of small deviation from the optimum diameter.
Fins are often installed on submerged parts of a floating structure to reduce its motion in waves. It is expected that its kinetic energy is reduced by vortex generated from fins because its energy is converted into vortex energy around fins. To utilize this method, numerical analysis method for viscous fluid is required to decide the optimum shape and installation position of these fins. For this problem, authors proposed 2D numerical analysis method in time domain, using vortex method that can consider the fluid viscosity and calculated motions and primary conversion efficiency of a floating OWC-type wave energy converter in waves. In this method, unknown quantities are vorticity and stream function. As a next step, vortex method should be expanded to 3D problem so that it will be applied to actual design for floating structure, however its method can't be applied because stream function isn't defined in 3D problem. Therefore, development of vortex method using vorticity and velocity as unknown quantities is required. In this paper, by restricting to 2D problem, the vortex method using these unknown quantities is applied to flow field around a 2D cylinder in uniform flow and a forced oscillation problem of a submerged plate under the free surface. We carry out the comparison between calculation and experimental results, confirming its effectivity and reliability.
In order to satisfy the EEDI regulation introduced by IMO, ships tend to select a lower output engine, which might be dangerous in safety in adverse sea condition. Thus the assessment of load fluctuation in ship's main engine in waves is important, for which improvement in ship motion prediction, especially for surge motion, may be a key in enhancement of the prediction of load fluctuation in waves of ship's main engine. The strip method has been a robust and practical tool to estimate the seakeeping performance of a ship, but hydrodynamic radiation and diffraction forces for surge have been ignored in conventional strip methods, because the longitudinal-direction component of the normal vector on the ship hull surface (denoted as nx) is regarded as higher order, due to the assumption of slender ship hull. However, by retaining nx-related terms in the formulation for hydrodynamic forces, we can expect improvement in the estimation accuracy not only in the surge motion but also in the other longitudinal motions.
In this study, a strip theory including the effects of nx is proposed. First, the formulation for the radiation, diffraction, and restoring forces is presented, and then transformation of the forces and motion equations to those in another coordinate system is explained. Next, the effects of nx-term in the diffraction problem are investigated by applying three conventional methods (NSM, STFM and the method by Mizoguchi and Watanabe). Calculated results by this proposed method are validated through comparison with model test results and numerical results by the conventional strip method. Furthermore, as a study on the load fluctuation of the ship main engine in waves, the results of surge motion computed with nx-related terms are used in calculation of propeller effective inflow velocity in waves, and discussion is made for validation on the effects of the nx-related terms.
Regarding the added resistance in waves, research on head waves was mainly performed for a long time, mainly because of the restrictions of test facility which allows only test in head waves, and also it has been considered that heaving and pitching motion seems to be dominant and the influence of lateral motion is relatively small. Recently, Valanto and Hong 6) reported that each motion of six degrees affect great on added resistance in oblique waves based on the test results. Therefore, it seems necessary to investigate the influence of ship motion of 6 degrees of freedom on the added resistance in waves again.
In this paper, measurement of ship motions and added resistance for large blunt ship in oblique and beam waves were carried out and experimentally showed that rolling motion has a very large influence on the resistance increase in waves in the vicinity of its natural period. In addition, qualitative consideration will be given to the mechanism that the added resistance in the beam wave increases by the influence of the rolling motion.
Osawa et al. (2016) developed a two-dimensional cellular automaton (CA) for under-film corrosion analysis and succeeded in consistent analysis of coating film deterioration and corrosion depletion. In this study, epoxy coated steels with and without inorganic zinc primer were prepared, and the panels having one scribe were subjected to cyclic corrosion test (CCT). And the influence of inorganic zinc primer on CA parameters was investigated from the corrosion surface profiles. In the CCT, corrosion depth became unaffected by zinc as CCT test time passed. However, progress of corrosion in perpendicular direction from the scribe was greatly increased by absence of zinc. As a result of identifying the CA parameters, the increase of coating film deterioration acceleration rate A0, the decrease of shielding duration TS and the increase of acceleration factor of bare material fbare were required by the specification change from zinc coating to no zinc coating. In order to understand the change of these parameters value, the mechanism of corrosion and blistering of epoxy coated steels with and without inorganic zinc primer was discussed. And the validity of difference in value of CA parameters with zinc coating and no zinc coating was shown based on the mechanism.
In recent years, container ships become larger and larger to increase the transport efficiency. The torsional rigidity of a container ship is lower than other type of ships, because the container ship has the large deck opening and large flare structure. Therefore, it is important to calculate the longitudinal ultimate strength with considering the torsional moment for the design of ships.
In the 1st report, the structure model test was carried out to clarify the effect of the torsional moment on the ultimate longitudinal strength of a container ship with deck opening. The 3D-FEA (Finite Element Analysis) were also carried out and the collapse behavior of the model was investigated in detail. But it requires large computational effort and cost to conduct 3D-FEA. Therefore, the simple and fast analysis to calculate the ultimate longitudinal strength with considering the torsional moment is needed. Thus, in the 2nd report, a new method of the progressive collapse analysis to calculate the ultimate longitudinal strength considering the torsional moment was developed by connecting the beam elements, of which the collapse of cross section is simulated by the Smith method, in the direction of ship length. The effect of the torsional moment was considered in the warping stresses and the yield strength of material. The effectiveness of the method was verified through comparison with the 3D-FEA of the test model.
In the present study, the calculation method for the torsional constant in consideration of the effect of bulkheads and side structures is proposed. The transverse bulkheads and the side structures prevent torsional deformation of ship's hull girder. Therefore, in this method, the original torsional constant is modified by considering the strain energy of the transverse bulkheads and the side structures. Finally, 3D-LFEA (Linear Finite Element Analysis) for the model with the U-shaped cross-section subjected to the torsional moment
is carried out to clarify the validity of the 1D-LFEA considering the effect of the bulkhead and side structure.
Up to now, wear estimation method for mooring chain of floating facilities has not been established, and it currently relies on empirical methods. In this research, numerical analysis combining 1) wear analysis between links by finite element method and 2) response analysis of mooring system was performed to establish a method for estimating wear amount of mooring chain during operation. The validity of the proposed method was confirmed by comparing with the actual measurement value in the actual sea area. As a result, it was found that the wear amount estimated by our proposed method is generally close to the measured value. However, it was also confirmed that the estimated wear amount at the touchdown point between the seabed and mooring chain was considerably overestimated. That result could be attributed to insufficient consideration of the effects caused between the links ( e.g. snap load, elastic deformation and friction), the behavior of the links ( e.g. sticking, rolling and non-contact) and the external forces ( e.g. wind and current ).
“YUMEIRUKA" is an AUV that Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has developed and is operating. A seabed resource exploration is carried out by two-set simultaneous operation with AUV “JINBEI" developed by JAMSTEC. “YUMEIRUKA" towing a sensor cable, and the cable is oscillated by the AUV. The up-and-down oscillation of the sensor has a bad influence on the exploration result. Therefore, in order to perform accurate seabed resource exploration, it is necessary to comprehend the motion of the sensor cable and to optimize it. In this paper, motion simulations of a sensor cable towed by X rudder AUV “YUMEIRUKA" are shown.
The Japan Agency for Marine–Earth Science and Technology (JAMSTEC) has been developing “YUMEIRUKA", an autonomous underwater vehicle (AUV) with a fore X-rudder and an aft X-rudder. The vehicle can change its submersion depth by controlling the pitch angle using the two-sets X-rudder system. It is said that the advantage of X-rudder is that the motion control performance at the time of trouble is excellent. In this paper, the motion control performance of “YUMEIRUKA" having broken X rudders is verified by simulations. LQI controller is adopted to control the motion of the vehicle in simulations.
It is important to understand and predict fish behavior to assess the impacts of coastal development on ecosystem or to conduct appropriate fishery management. In order to collect information for understanding fish behavior, we measured the environmental factors and the distribution of fish simultaneously by using fishing boats. The memory-type sensors were attached to the fishing gear of the small trawling boats in Ise Bay, through which the water temperature, dissolved oxygen, and depth were measured as well as position information by GPS. At the same time, fish catch of each haul by trawling were recorded to grasp the fish distribution. The obtained data provides much more information for temporal and spatial distribution of water qualities than conventional monitoring. We tried to predict resource distributions by artificial neural network using the obtained data. It is found that the environmental factor affecting the behavior of conger eel varies with respect to the months. The developed neural network could predict the horizontal distribution of the conger eel fairly well.
Ultra-deep ocean drilling is expected to develop to deeper and deeper fields. Such drilling has some problems. One of them is that weight on bit (WOB) can not be measured in real time, that is important for drilling operation. Therefore, simulation models estimating WOB are needed. However, previous studies have shown insufficient accuracy of physics-based models. In this research, we introduced a black box model with recurrent neural networks for WOB estimation. We revealed such black box model has applicability to ultra-deep ocean drilling systems, but it has low adaptability to extrapolation. In order to compensate a black box model and a physics-based model, by combining both of them we created a new model called grey box model. This grey box model was revealed to have high accuracy. This research is expected to be a guideline of grey box model with neural networks.
To study the influence of the CO2 on the cutting performance, the heat input due to preheating flame qG, and that due to the combustion of the material being cut qB are estimated by performing a three-dimensional nonlinear heat conduction analysis that considers the temperature dependence of the thermomechanical properties. Spot heating tests are performed to identify the heat input parameters of the preheating gases H2 and H2-CO2. Gas cutting tests are performed to identify the characteristics of the cutting groove shape while employing the selected preheating gases. Based on the information of the spot heating, and the gas cutting tests, a three-dimensional heat conduction analysis is performed to identify the temperature fields along the thickness direction of the workpiece. A new technique for the estimation of the temperature fields considering inclined cutting-fronts based on Matsuyama’s theory is proposed. The role of the preheating heat input and the material combustion heat input for the selected gases is examined. Based on the simulation results of this study, CO2 deterioration mechanism on the cutting performance is discussed. From the study, the following results were obtained: (1) A new procedure for the kerf temperature estimation throughout the plate thickness based on the two-dimensional analysis of Matsuyama is established. The procedure allows a smooth and continuous temperature distribution through the plate thickness direction. (2) By applying the proposed procedure, it is possible to estimate the three-dimensional kerf temperature distribution on thick plates and allows the consideration of inclined cutting fronts. (3) By evaluating the preheating, and the material combustion heat input, it is observed a substantial declined in qG when employing CO2 while qB remains unchanged regardless of the employed preheating gas.
Building the technologies to commercialize the mining of seafloor polymetallic sulfides which is promising mineral resource is necessary. Based on the both the Basic Plan on Ocean Policy (approved by the cabinet on April 26, 2013) and the Plan for the Development of Marine Energy and Mineral Resources (formulated by Ministry of Economy, Trade and Industry (METI)), METI and JOGMEC (Japan Oil, Gas and Metals National Corporation) started the national seafloor polymetallic sulfides developing project and planed to demonstrate the pilot test in actual sea to validate the technologies for especially excavating and ore lifting, which is the first test in the world. Usually testing in actual sea is not safety and economical because the marine condition is severe for the operation. Therefore three years studies to ensure both safe and availability were conducted which led the pilot test to succeed. This paper shows our procedure of the availability analysis for the pilot test with the results of numerical simulation, model experiments and operational window analysis. To investigate the accuracy of the numerical simulation and confirm the effectiveness of the operational window analysis, the comparison with the measurements in the actual sea is also shown.
Crowdsourcing using low-cost measurement sensors is becoming a possible option for environmental sciences. This study describes the development and demonstration experiment of a prototype of the low-cost observation system for wind over the ocean. A validation experiment of the low-cost anemometer showed calibration is necessary to use the sensor for the field measurement. The sensor is next attached to the floating buoy and deployed to the harsh environment of the sea. The deployed system measured the wind over the coastal ocean in Sagami-bay for ten days consecutively. A good correlation for both measured wind speed and wind direction is found based on the comparison with results from a wind station at the coast. Issues related to the increase in the number of low-cost sensors are discussed.
This paper numerically investigates motion and power production characteristics of a point absorber type wave energy converter (WEC) using a model predictive control (MPC). The MPC is able to maximize power production while handling hard constraints, such as maximum motion, control force and so on. Motion and power production characteristics of the MPC were compared with two conventional control methods, the approximate complex-conjugate control with considering the copper loss (ACL) and the resistive loading control (RLC), under the sea condition of Japanese typical joint probability distribution based on a 21-year high-resolution hindcast dataset. From the numerical simulation, it was found that motion and power production characteristics of the MPC were comparable to these of the ACL if the wave height was low enough not to activate the MPC's constraints. As the wave height increased, the two conventional control methods, excluding the MPC, couldn't keep the WEC's motion constraint. Moreover, the sea conditions in which the WEC with the MPC can operate as the power production mode was broadened compared with the two conventional control methods. Through the numerical simulations, it can be said that the WEC with the MPC is feasible in the sea condition around Japanese coast.