When a ship with a wide immersed transom stern runs on a deeper draft than its design draft, forward-oriented wave breaking often occurs just behind the transom stern. The phenomenon accompanies large momentum loss and accordingly large hull resistance. The bottom profile form of the transom stern is one of the most important factors which affect the phenomenon, though not so much attention must has been paid to the part in many ships just by the reason that the part is only a limited local part of a hull. In this paper, model tests on typical bottom profile forms are conducted at first and then the effect of the bottom profile form on stern wave resistance is discussed based on the results of the model tests. As a result, characteristics and amount of the effect and the relation between the bottom profile form and the stern wave resistance are clarified.
Using flat plate ships of up to 50m in length in a 400m-long towing tank, we carried out experiments on the scale effect of microbubbles, the aim being to apply microbubbles to full-scale ships. The scale effect was studied to determine how a model ship's size affects microbubbles' ability to reduce skin friction. By understanding the scale effect we can determine the performance of microbubbles in reducing skin friction in full-scale ships. The experiments showed that in the area covered with microbubbles, frictional drag was reduced by as much as 22%, and measurements using skin friction sensors indicated that even at the downstream end of the 50m-long ship the friction was reduced by about 2%. We also measured the local void ratio distribution using a suction tube method, and found that there was a strong correlation between the skin friction reduction and the local void ratio near the ship's bottom wall. These confirm the possibility of using microbubbles in full-scale ships. We verified the reliability of the measured data by comparing it with data obtained in separate towing tanks and by checking the data itself.
In order to clarify correlation between properties of coating on ship hull surfaces and frictional resistance, experimental studies were carried out. A rotating cylinder type dynamometer was newly developed. It is possible to measure frictional resistance acts on coatings in higher Reynolds number flow similar to it around a actual ship. Measuring the frictional resistance and the change of its roughness of cylinders coated with self-polishing type paint or water repellent paints, correlation between properties of coatings and frictional resistance were investigated. Further, a simple method base on these experimental results was proposed, to estimate the frictional resistance acting on the surface of the actual ship hull.
Low-level noise propellers with a higher propulsion performance are required lower incipient cavitation number of tip vortex cavitation and even if tip vortex cavitation is developed, to depress the underwater noise level. In this study, the author provided some highly skewed propellers that were modified propeller geometry to influence low-noise performance and then the incipient cavitation numbers and the underwater noise were measured at a cavitation tunnel by using the propeller models. From the results, we find that the propeller with lower incipient cavitation number does not always have low-level underwater noise even if the cavitation is generated. Also the author shows a guideline in design of low-level noise propellers by referring to the results from the measurements and CFD analysis.
This paper presents a new friction coefficient of flat plate in wide Raynols number range. The main purpose of this study is to present a verification data for CFD calculation, which will be applied to predict ship performance in full scale Reynols number. The friction coefficient is calculated by solving a differential equation without approximation that is based on momentum equation and Coles' wall-wake law. The parameters used in Coles' wall-wake law for the assumption of the velocity profile in turbulent boundary layer are determined based on reliable experimental data by Osaka et al. The calculated results of flat plate friction resistance, local frictional resistance and velocity profile in turbulent boundary layer agree well with experimental ones. However, few experimental data avoid to verify the results at high Reynols number, therfore the research should be continued focusing on the behavior of wake function at high Reynols number.
Experimental investigation to reduce friction drag of ship by means of air lubrication is presented. Tanker form model ship with four air injection devices on flat bottom is used. Resistance tests were carried out both in calm water and in waves. This paper also presents a method to estimate full scale ship performance with air lubrication. This method takes model experiments under full scale ship speed into account. By this method, it is estimated that about 8% energy will be saved by air lubrication in case of VLCC.
The propulsion performance of actual ship at sea tends to deteriorate mainly due to the fouling of hull and propeller. It is important, therefore, to monitor the present situation of ship propulsion performance in order to make an optimum operation and maintenance planning for cost saving. The monitoring method of propulsion performance by the use of Logbook data has been to analyze the consumption and/or ship velocity, which is just variation of overall propulsion performance. This paper proposes a new analyzing method of Logbook data, which could make it possible to investigate the surface fouling effects on hull resistance and propeller performance individually. At first, the surface roughness effects on propeller performance are calculated using the numerical estimation method developed by the authors in the previews paper, and the validity of estimate are conformed by the experimental results of model and actual propellers. Next the behaviors of propeller torque and thrust coefficient change due to surface fouling is investigated, and it is revealed that is a certain relation between the changes of torque and thrust coefficient ΔKQ and ΔKT. The paper suggests that is possible to predict simply ΔKT from ΔKQ by the use of relation instead of carrying out the numerical calculation. Finally, based on the above results, the paper indicates the possibility of a new useful monitoring method of ship propulsion performance at sea, which can analyze the recitation of hull resistance and propeller performance individually.
The authors had developed a component-type mathematical model of hydrodynamic forces acting on a ship hull in steering motion that is deduced from the simplified vortex model. This mathematical model describes the hydrodynamic forces X, Y and N with small to large drift angles, and it is also applicable to changing trim and loaded condition of a ship. This paper describes a prediction method of ship maneuvering hydrodynamic forces with small to large drift angles by oblique hydrodynamic forces and the estimated results of the steering motion using the hydrodynamic forces expressed by the component-type mathematical model. On this estimation, the expressions proposed in this paper to estimate some hydrodynamic characteristic constants are used. Through these investigation, it has been found that the component-type mathematical model can predict hydrodynamic forces with small to large drift angles and the steering motion only through oblique hydrodynamic forces. This method will be useful to predict maneuvering behavior at initial design stage or in the case of few of sea trial data available.
In order to clarify availability of the so-called cross-flow model, some model experiments on longitudinal distribution of lateral force on a ship hull were carried out with the segmented model. Lateral forces on each of the segments were measured for the hull in turning motion. Here, it is assumed that lateral force on each segment can be expressed by a formula consisting of linear and second order terms. Nonlinear derivatives due to yaw angular velocity for each segment are determined through the procedure described above. A comparison is made between the nonlinear derivatives and those predicted using the cross-flow model. In this report, a correction factor is introduced to modify the nonlinear derivatives obtained from the cross-flow model. As a result, it is indicated that the correction factor largely depends on ship's longitudinal position. Moreover, it is found that generally speaking the value of the correction factor increases where the segmented element is closer to midship. Development of prediction procedure of the correction factor is left as a future problem.
Numerical simulation of progressive waves and floating body's motions with particle method (MPS method) are examined. Availability of the particle method for wave problems is considered through calculated examples of progressive waves with MPS method. Some numerical examples of floating body's motions, which is under very complicated situation like a damaged case, are demonstrated.
The purpose of this paper is to clarify the cause of occurrence of Bow-Diving for planing craft. First, measurements of Bow-Diving using a scale model of planing craft are carried out and they confirm that Bow-Diving occurs in calm water and waves. From this experiment result, the relative position of the hull to the water surface at Bow-Diving occurring is shown. Next, the hydrodynamic forces acting on the model are measured by fully captive model tests with wide range of attitude including the running attitude at Bow-Diving occurring to obtain the restoring forces acting on the model, and the characteristic of them are investigated. Consequently, it is shown that the restoring forces play an important role to Bow-Diving occurring and a method of obtaining the criteria of Bow-Diving occurring based on the restoring forces is proposed. Furthermore, the diagnoses of Bow-Diving occurring are proposed.
In the present study, a methodology for selection and evaluation of advanced marine transportation systems is proposed, which consists of three steps. The first step is selection of preferable marine transportation systems. In the selection, firstly, a planning method for selection of the optimum solution as an advanced marine transportation system from many alternatives is deduced. Using the planning method, index value of each alternative is determined using a Priority model for filtering the alternatives. Then, the most highest index values are selected as preferable marine transportation systems. In the second step, the selected preferable marine transportation systems are evaluated using a Life Cycle Value Chain model from three different points of view, which are life cycle profit for companies, life cycles business and environmental impacts on societies. In the last step, an economical-environmental index is introduced for evaluation of the selected preferable marine transportation systems from societies' viewpoint. Using the present methodology, a feasibility study on a Liquefied Natural Gas(LNG) carrier operating in Arun, Indonesia-Osaka, Japan route is carried out, and the results are discussed.
A theoretical study on the psyche of a captain operating in confined sea is made from the view point of thermodynamic analogy. A relationship which corresponds to the PVT system in thermodynamics is found among P the narrowness of sea area, V the volume of ship action and T the temperature of volition in sense of menace. The feeling of efficacy of a captain is defined effectively by thermodynamic work. A model of psycho-engine in a captain is proposed keeping the conservation law of psychological energy. The psycho-engine works by using his volition energy in order to change his motivation energy into his feeling of efficacy. The psycho-entropy law which represents the quality of motivation degenerates out is applied obtain a equilibrium velocity in operation in a straight narrow canal. The obtained velocity is proportional to square root of the width of the canal. Equilibrium distance and velocity of two ships marching in a single file is obtained by applying the psycho-entropy law with a deadlocked condition.
The circular plastic window (we call it as acoustic window) at the bottom of a large ocean observation ship was broken sometimes. This window is a cover of the downward hole of the recess of the ADCP (Acoustic Doppler Current Profiler) of this ship. This paper report about the reason of the damage of this plastic window through the simple model tests and simple theoretical calculations. Through this considerations, the importance of the concept of the pressure by the incompressible fluid in acceleration motion is stressed.
July 27, 2015 There had been a system trouble (from July 26‚ 2015 15:25 to July 27‚ 2015 1:00 (GMT)). The service has been back to normal.
July 15, 2015 A new online journal "Mechanical Engineering Letters" has been launched by The Japan Society of Mechanical Engineers (JSME). This publication of such a letter journal is not only a new experience but also a tremendous challenge for the mechanical engineering society.
May 01, 2015 Please note the "spoofing mail" that pretends to be J-STAGE.