The steering quality indices (K: The index of turning ability, T: The index of stability on course and quickness in responding to steering) are normally obtained by fitting time histories of steerage and heading angle into Nomoto's 1st order equation for maneuver. The drift angle, on the other hand, is sure to arise when a ship turns. If any analysis method for the steering indices and the drift angle is found out, it will make it easier to understand how large a ship laterally deviates especially in the stern. The focus on this paper is how to analyze the steering indices and the drift angle under the restriction of constant velocity and small heading angle. SR108 container ship is supposed as the analysis object ship and the steerage is considered to be closer to a practical maneuver rather than zig-zag one. The time histories of heading angle and trajectory are computed by the steerage supposed. The technical interest is whether the indices and drift angle could be calculated inversely from the time histories computed. The indices, in general, are obtained under the condition the steerage is known, but in this study, they are computed also in the condition it is unknown. The verification summaries that the indices are calculated inversely well if the steerage is known and even if it is unknown, trends of them can be grasped.
Various energy-saving technologies have been developed because improved fuel consumption contributes. Pre-swirl fins, which consist of multiple fins installed in front of a propeller, swirl inflow to the propeller in the opposite direction of the propeller rotation to recover the waste energy of a propelled ship. The propeller mast be designed in consideration of pre-swirl inflow, because velocity distributions flowing into the propeller are changed by pre-swirl fin. This paper describes a propeller optimization method in consideration of pre-swirl inflow using real-coded genetic algorithm. A propeller was designed by utilizing the present method. Propeller tests in which influence of pre-swirl inflow of the original and improved propellers were carried out.
In order to design a floating OWC (Oscillating Water Column)-type wave energy converter such as Backward Bent Duct Buoy (BBDB) optimally, it is necessary to develop a numerical method to make clear an optimal hull shape which maximizes the generating electrical energy.
In this paper, a two-dimensional numerical method in time domain to estimate the primary conversion efficiency of a floating OWC-type wave energy converter with arbitrary cross section is proposed. The fluid motion in water waves is calculated by using vortex method which can consider viscosity of the fluid, vortex generation from the floating body surface and diffusion of the vortex into the fluid. For air flow in air chamber, equations of state, conservation of mass and energy with the assumption of air being the perfect gas are used. From these equations, motions of floating body, air pressure and free surface elevation in air chamber and primary conversion efficiency etc. are calculated. Wave tank tests are also carried out for BBDB in regular waves. Numerical results are compared with experimental results.
Recently enormous amount of data can be obtained from running ships, so that the needs of the analysis of the data are increasing. For the analysis, the relationship among ship speed, engine revolution and engine power in calm sea is important. In order to estimate the relationship accurately, data in calm sea distributed widely in terms of ship speed are necessary, but ship speed does not change much in some voyages. In the paper, The method of correction for the displacement using Admiralty coefficient and weather correction method is explained to obtain more accurate relationship among ship speed, engine revolution and engine power in calm sea. Using the methods, the voyages of different displacements are investigated and the range of application of Admiralty coefficient is revealed.
For the accurate evaluation of the ship performance in actual seas, the relation among ship speed, engine revolution and engine power in calm sea is important. The relation is to be expressed by a numerical model for the application to the analysis for the aging deterioration and the biological fouling. Conventionally these relations are obtained by fitting of the onboard measurement data in calm sea. However when the data in calm sea is few and not distributed in wide speed range, the fitting curve is not appropriate in many cases. And in the case of the evaluation of the ship performance in actual seas for the different displacement, the relation among ship speed, engine revolution and engine power is to be corrected for the displacement.
In the paper, a numerical model for the relation among ship speed, engine revolution and engine power in calm sea and the application of the model to the different displacement are proposed and evaluated by onboard measurement data.
When a ship is carried out speed/power trials in shallow water, the measured power is larger than that in deep water. To correct the effect the method is recommended by ITTC and standardized by ISO.
In ITTC a method by Raven, which corrects viscous resistance considering the squat effect is proposed to alter the method by Lackenby which corrects the speed.
In order to evaluate the shallow water performance, resistance and propulsion tests were carried out using a tank which can perform the tests in both deep and shallow waters. The engine power estimated by the results of the tank tests, Lackenby method and Raven method have been compared and evaluated.
From the evaluation it is clarified that Raven method shows lower engine power than Lackenby method and can be applied for the shallow water correction by means of conservative correction.
The prediction of the propeller load fluctuations in waves, which can cause great fluctuations of engine power and revolutions, is important for ship operations. Recently the prediction of free running model advancing in waves with real rotating propeller and rudder can be done by Computational Fluid Dynamics (CFD) technique. However, the validation of these methods is not enough and it requires huge mesh density and long computational time. The new propeller body-force prediction model (OU propeller model) was proposed in particular to make the computation of free running condition easier and applied for many problems. The present work is conducted to validate the capability of OU propeller model for the condition that propeller exists near free surface in waves. For the simulations, the Reynolds Averaged Navier-Stokes (RANS) solver CFDSHIP-IOWA V4.5 is used. The propeller loads are predicted, and validated against the existing experimental data and the experiments conducted in Osaka University towing tank. The results showed that the OU propeller model works well for moderate loadings and high expanded blade area ratios.
Wing-In-Ground Effect (WIG) / Wing-In-Surface Effect Ship (WISES) is an unconventional aircraft/ship which utilizes the high lift-to-drag ratio in the ground effect. It is expected to be one of the fast-sea transportations between ships and airplanes. Up to now, many kinds of WIG crafts are developed. The authors have also designed a canard-configuration WIG taken over the concept of Kubo and Akimoto. In this paper, the steady aerodynamic properties and the aerodynamic interaction effect between wings are investigated by applying the theoretical calculation based on the potential theory and the wind tunnel experiment. The aerodynamic interaction effect due to propulsor are also made clear by activating the ducted fans mounted on the main wing in the wind tunnel experiment. Through the comparison between the calculations and experiments, the steady aerodynamic properties of the canard-configuration WIG are estimated well by the present theoretical calculation and it is useful as a preliminary design tools for the WIG crafts.
To study the influence of the vortical flow around a ship on the hydrodynamic forces and maneuvering performance, PMM test are simulated by CFD with local grid refinement method. It is confirmed that the local grid refinement method is effective for computing the detail of vortical flow and also the refined grid gives slightly better hydrodynamic forces than the original grid. All hydrodynamic derivatives and hydrodynamic interaction factors are calculated from the present CFD results and simulations of zigzag test and turning circle test are performed by the MMG model with the obtained derivatives and interaction factors. The simulation results show reasonable agreement with the experimental data. In order to improve the accuracy of maneuvering simulations, it is considered that discrepancies of some hydrodynamic derivatives and hydrodynamic interaction factors between CFD and experiments must be reduced. Further investigations on the local grid refinement method will enable the practical applications of simulation based maneuvering performance evaluations.
This paper proposes a method to simultaneously measure wave profiles and particle velocity on a wave surface by stereo imaging. About 100 markers are used as floats in the measurement. The motion of the markers is tracked by stereo cameras. From the position of the markers, the wave profile and the particle velocity on the wave surface are estimated.
Experiments were carried out in a wave tank (50m in length, 8m in width and 4.5m in depth) to validate the stereo imaging measurement method. Regular waves with the wavelength λ = 3(m) and wave height H = 3 ～ 20(cm) were generated in the tank and measured by the stereo imaging method. The wave height, crest height, particle velocity on the wave surface and distance between zero-crossing points estimated by the stereo imaging were compared with those measured by capacitance wave gauges or Stokes' wave theory. The comparison revealed that the errors in the 2nd-order drift velocity were less than 10% and those in other measurement items were less than 4% when the wave height is larger than 10cm.
These days ship designers make efforts to improve the ship propulsive performance in actual seas. To reduce added resistance due to waves the bow shape above water is important factor. Some ships install the bolsters at the bow, however, it is thought that waves acting on the bolsters affect the propulsive performance in actual seas. Thus tank tests in waves using a model ship with two types of the bolsters and without bolsters were carried out and the influence of bolsters on the propulsive performance was examined.
As a result, it is found that the increment of added resistance in waves is not so large since the bolster interfered with the waves reflected by the hull.
Water waves generated by the forced oscillation of a 3D non-wall-sided structure are analyzed based on the fully nonlinear potential-flow theory. In order to track an exact position of the free surface, Arbitrary Lagrangian-Eulerian (ALE) scheme is used in the computation. The feature of ALE scheme is that by introducing a prescribed path (curve) for each fluid marker on the free surface, the movement of fluid marker representing the deformation of free surface is confined along a path. With properly-designed configuration of those paths, this scheme brings about several advantages compared with the Mixed Eulerian-Lagrangian scheme and the Semi-Lagrangian scheme which are extensively used. In the computation, a higher-order boundary element method (HOBEM) and the 4th-order Runge-Kutta method are adopted as the solver of an initial boundary value problem (BVP). In the validation, the radiated waves generated by a truncated circular cylinder with flare oscillating in heave or surge are studied. Regarding the calculation of hydrodynamic forces, the temporal derivative of the velocity potential (ϕt) is evaluated in an exact but simple manner, i.e. ϕt is obtained by solving a reconstructed BVP without evaluating second-order derivatives of the velocity potential. Besides hydrodynamic forces, wave profiles at specific points and wave run-ups are also computed. Comparisons of the present results against published results of corresponding computations are made. To evaluate capability of the proposed ALE scheme, bodies with curved large flare are used in the computation.
A simulation method to examine under-film corrosion of epoxy coated free edges in ship's Water Ballast Tanks (WBT) has been developed, and the corrosion behavior on the longitudinal member's free edges made of conventional steel and Corrosion Resistant Steel (CRS) in VLOC's WBTs, which was measured by Shiotani and Tachibana (2016), are simulated. The simulations are performed by using the two-dimensional cellular automaton developed in the previous report (Osawa et al., 2016). In order to emulate the point coating defect's corrosion incubation on edges, a 'spattering' model is developed. The onboard exposure tests of the scribed coated steel panels examined in the previous report were performed in the WBTs in which the edge corrosion was measured. The cellular automaton parameters determined in the previous report are adopted for intact coated cells. The determination techniques of automaton parameters for thin film regions (edge) and point coating defects are developed. Those parameters are determined from the measured stochastic characteristics of corroded spot length on free edges. The effectiveness of the proposed spattering model and the parameter determination technique are examined by comparing simulated and measured stochastic characteristics of corroded spot length. Based upon these simulation results, CRS's resistance improvement mechanisms are discussed.
This paper is the third followed by the two companion papers dealing with ultimate longitudinal strength analysis of container ships considering effects of bottom local loads. The major causes of reduction of ultimate hull girder strength due to local loads were discussed based on the finite element analysis of a hold model in the Part 1. The extended Smith's method was developed in Part 2, which is a practical method of progressive collapse analysis of a hull girder under combined longitudinal bending moment and bottom local loads. The objective of this paper is to develop a simplified estimation method of ultimate longitudinal bending strength of a hull girder which can consider the effect of bottom local loads. The proposed method uses an ultimate strength interaction formula on basis of first failure of hull girder. The first failure in compression may be occurred at outer bottom plate near a partial bulk head or inner bottom plate near a water tight bulkhead depending on the deformation of double bottom. The effect of first failure location on hull girder collapse behavior is investigated by the finite element analysis, and it is found that the outer bottom collapse is a direct cause to the hull girder collapse even if the collapse precedes at inner bottom plate. Therefore, the proposed method targets the case of first compressive failure at outer bottom plate. The ultimate longitudinal strength estimated by proposed method is compared with that by finite element method in order to validate its estimation accuracy.
A technique for motion estimation of a tether cable of an observation class ROV is proposed in this paper. A simulation procedure based on the lumped mass method is adopted for the motion and shape estimation of the cable. Deployment of the tether cable from a starting point is approximately treated locating the mass points at the starting point. These mass points are deployed and follow the leading part of the cable. The simulation results are compared with results from tank experiments and the validity of the simulation technique is confirmed. Examples of path planning for the inspection of a pontoon type floating structure is also shown.
Tidal currents have two types of intrinsic long-term fluctuations. The one is single tidal constituent such as Ssa and the other one is interferences between tidal constituents. The effect of the long-term fluctuation of tides on the resource assessment for tidal current energy generation system near Japan has been described based on the predictions using data-assimilative global barotropic tide model results. It is shown that monthly mean tidal energy flux varies by more than 20% over a year in the most of the prospective areas. The result indicates the intrinsic long-term fluctuations need to be considered in the resource assessment of tidal current power generation system.
The importance of transportation has been recognized when a city function is destroyed by natural disasters, such as the Great East Japan Earthquake or Kumamoto Earthquakes, etc. Sea transportation accounts for more than 95 percents of logistic cargos. It is also required to operate ships more efficiently and environment-friendly. This might relates to the fact that few weather database there than in the subtropical zone or the Northern Hemisphere. This study shows three measured results of rough sea navigations of 28,000DWT class bulk carrier in the Southern Hemisphere. Waves and winds are numerically computed by different models, and the computed results are validated with measured data. Moreover, the validation on ship motions is carried out using response functions. The possibility of wave estimation in the Southern Hemisphere is shown from measured and simulated results.
In deciding which IoT technologies should be introduced in the maritime industry, it is important to quantitatively compare their diverse functions. In this research, an evaluation method using a parametric ship operation simulator is proposed. The simulator consists of three models, shipping, loading and docking, with the shipper's QCD (safety, economy and delivery reliability) as evaluation criteria. The effect of introducing IoT technologies is evaluated by changing input parameter value. As a case study, evaluation of various kinds of actual IoT technologies was conducted. The Result showed that the proposed method can quantitatively compare each IoT technology considering technology's maturity levels.
When tsunami attacks a harbor, the vessels moored at the wharf are exposed to a risk. For example, the following damages are assumed; breaking the mooring tether, grounding on a wharf, drifting to land areas and destroying buildings. In the previous report, the motion analysis of mooring vessels in tsunamis and the usefulness of tsunami protection measures by the install more mooring tethers (IMMT) was described using the MPS method. The incident wave angles of tsunami were used the 0 degrees (longitudinal wave) and 90 degrees (Transverse wave). For any incident angles, IMMT was effective. However, in the case of transverse wave of wave height 6.0m or more, it is possible to prevent the break of the mooring tethers, but it was confirmed that the vessels damaged by the grounding on a wharf. In the case of longitudinal wave, IMMT confirmed that it did not affect in some cases. It is influenced by the direction the mooring tether pulls. When the vessel moves, there are mooring tethers that are pulled or slacked. As a result, the mooring force does not act equally on the mooring tethers. Also, as an issue of existing papers, studies on oblique waves were not done. It is important to solve these issues.
In this present paper, the influence of the oblique wave is studied. The extent of damage of longitudinal waves, transverse waves and oblique waves are compared through a numerical simulation method, the 3D MPS method. The 3D MPS method is used for numerical simulation. In this paper, quaternion is applied to the algorithm of rotational motion of the floating model. Furthermore, a more effective mooring method for longitudinal wave is proposed, and its effectiveness is demonstrated.
In recent years, the increase in container ship sizes is progressing prominently due to the expansion of worldwide economy, accompanied by usage of materials of higher strength. These changes cause relatively smaller hull girder rigidity, posing concerns on the increased hull girder whipping response and its influence on the hull girder ultimate strength. Moreover, the increase in container ship sizes caused greater ship breadths and more flexible double bottom structure, which also affects the hull girder ultimate strength. In this paper, the authors investigated ‘influence of the hull girder flexibility to the whipping response’ and ‘the correlation factors between the double bottom bending and the hull girder bending’ in irregular waves through a combined numerical simulation method, comprising ship motion and wave load analysis based on Rankine source method and subsequent 3-dimensional whole ship finite element analysis based on Newmark-β method.