The present paper describes development and demonstration of CFD-based optimal design method for Energy Saving Devices (ESD), which are installed near the stern of commercial ship. Focus here is implementation of the two state-of-the-art numerical approaches, i.e., the overset grid technique and the nonlinear programing (NP) theory. Through our investigations, combination of the two is very effective in application to optimal ESD design. For the former, a practical geometry modeling method to yield new designs is successfully demonstrated in the present study. The latter is a well-validated NP numerical scheme, i,e., Successive Quadratic Programming (SQP), coded in a form of parallel architecture based on message passing interface (MPI) protocol. Together with the asynchronous evaluator model proposed in this work, the present approach offers significant advantages over other serial mode algorithms for high computational efficiency that is an apparently demanded feature for basically very time consuming CFD-based optimization problem. In the following, an overview of the present method is given, and results are presented and discussed for the twofold aims: first, to assess accuracy of the present overset grid technique through comparison with detailed experimental data; and next, to evaluate and state the effectiveness of the present approach for ESD optimal design. Finally, future prognoses and conclusion are given.
We present a new method determining a form factor from resistance test results. The total resistance coefficient is approximated by a straight line and a polynomial expression in the present method. The straight line and the polynomial expression represent a viscous resistance and a wave-making resistance, respectively. It is shown that existing flat plate friction formulae are expressed as straight lines, and its inclination is only a function of the form factor. We determine the inclination (form factor) and coefficients of the polynomial expression by means of a linear least-squares method. The features of the present method are that: the form factor is decided without extrapolation; all measured data of resistance testing can be used in this analysis, although low-speed range data should be selected in the Prohaska's method. Using the ITTC57 correlation line, the values of the form factors obtained by the present method are almost the same as by Prohaska's method. It is found that the influence of the unreliable extra low-speed range data in the present method is less than in the Prohaska's method.
This is the second report of hull form optimization to minimize Brake Horse Power (BHP). In the previous report, two hull form optimization techniques, Sequential Quadratic Programming (SQP) and Surrogated-Based Optimization (SBO), for minimizing BHP were proposed, and it was shown that the optimization methods are effective for obtaining high performance hull forms. Recently most of ships are equipped Energy Saving Device (ESD) to improve their performance. Some ESDs have energy saving effect of over 5%. However their effect is strongly dependent of a shape of a main hull. Similarly dimensions of a propeller are dependent of a shape of a main hull. Therefore hull form optimization considering ESD effect and propeller design is necessary for total BHP reduction.
In this paper, hull form optimization method with a stern duct and propeller design is suggested. The stern duct is one of the ESDs whose effect is affected by the change of stern hull form. The result of VLCC hull form optimization with the duct is presented. Then the result is compared with the optimum result without the ESD effect, and efficiency of the hull optimization with ESD is discussed.
Wake adapted propellers have been studied to improve propeller performance behind a ship hull for a long time. In the beginning, they were designed by adjusting pitch distribution based on the optimum circulation distribution. In recent years, propeller shape optimization considering wake distribution at a propeller position or nteraction between a hull and a propeller is also studied. Most of these studies adopt a panel method based on potential flow for estimating propeller performance in order to save CPU time. There have been few optimization cases using CFD because CFD needs longer computational time than a panel method for obtaining performance. As CPU time becomes shorter than before due to the improved computer performance, CFD-based propeller shape optimization applications are increasing. However, these approaches generally do not consider design conditions such as rotational speed or horse power determined from the engine specifications.
The ultimate goal of the present study is to establish a propeller shape optimization method with practical design conditions. For the first step, a propeller shape optimization system using CFD is presented and the system is applied to the optimization in given design conditions with a uniform inflow. Performance of the optimized propeller is confirmed by a propeller open test. In the second stage, the propeller design optimization in a non-uniform wake field is carried out and the performance of the obtained design is verified by the self-propulsion test. Thus, the practical capability of the system is demonstrated.
The present paper describes a development of hull-form database which can comprehensively include propulsive performances, dead weights, gross tonnages and general arrangement plans, and a verification of the effectiveness of the database for hull-form design. The present database focuses on 749GT-type domestic general cargos, which are subject to restrictions on the gross tonnage by a domestic law. The collaborative work with the shipyard had made the database more practical and more competitive than before. The towing tank test result shows the high performance of the developed standard hull-form which reaches design speed of 12.00 knots at about 61% MCR, even installed about 20% smaller main engine than the conventional one.
Firstly, the design space of the database was carefully determined by the construction record of 749GT-type domestic general cargos, which have 3 design parameters with ship length, breadth and draft. 463 hull-forms were generated by hull-form blending (morphing) technique based on 8 basic hull-form. To reduce the wave resistances of its hull-forms effectively, CB and LCB of 8 basic hull-forms, which define the shapes of the sectional area curves, are formulated by the 3 design parameters.
The relationships between CB and wave resistance, form factor and self-propulsion factor, respectively were discussed based on the evaluated results of propulsive performances in the view of the effect of increasing the diameter depending on draft. After the 51 hull-forms were selected by the practicality of propulsive performance, we evaluated dead weights and gross tonnages. The integrated evaluation of propulsive performance and dead weight indicates the trade-off relationship to the optimum ship length and breadth.
To solve this problem more designer-friendly, we propose integrated hull-form database and an example of visualization (visualization useful for design), which enables multifaceted and quantitative design discussion. The advantage of this method over the multi-objective optimization methods is the capability to provide multifaced and highly effective information for decision making in the design process. The design verification about practical design discussion on the trade-off problem is shown the effectiveness of the integrated hull-form database.
Maneuvering simulations for full hull ships were conducted by the MMG model, which is one of a maneuvering simulation method, based on the hydrodynamic force characteristics obtained in the captive model tests presented in previous paper1), and compared with the free-running model test results. The purpose of this study is to investigate the applicability of the MMG model to the full hull ships with very large block coefficient. We found that the original formula for longitudinal velocity component to rudder (uR) in the MMG model is not well working in case that the block coefficient (Cb) is very large as Cb = 0:87. To settle the problem, an improved formula of uR proposed by Yoshimura et al.3) was used and it was confirmed that the formula can capture the behavior of the rudder normal force just after steering better. Turning and course keeping performances in fullscale ships become worse comparing to those in ship model due to the worse rudder force performance comes from smaller propeller load in fullscale. Although the level of the worse turning performance is not so serious in fullscale, there is a possibility that overshoot angle of zig-zag maneuvers is over the IMO regulation for the present ship with Cb = 0.87.
Semi-submersible type offshore floating structures are expected to be used in the Japanese coastal area and at sea off Japan for promoting resource exploitation and development in near future. As the moored offshore floating structures are suffered from current, Vortex-induced Motion (VIM) effect should be assessed in an appropriate manner since the VIM causes fatigue damage of the floating structure's mooring lines. VIM phenomenon on semi-submersible type floating structures, however, is not clear, and its comprehension is insufficient since there are only small number of open studies with lack specifications of the structures. Then this paper represents the results of VIM measurement test using many forms of semi-submersible floating structure models to investigate the effects of column-column interval and lower hull volume for VIM amplitude, and shows the trends of VIM amplitude depending on current velocity and lower hull volume ratio for the first time. Moreover, using these results of the VIM amplitude for the models, fatigue damage of mooring lines is investigated using one sample semi-submersible offshore floating structure.
This paper provides the rational explanation of influence of liquid sloshing on the FLNG motion using spring-mass type mechanical model to represent the liquid cargo behavior and the coupling effects on the FLNG motion. The mechanical model of sloshing was originally developed in the mid-1960s and used to represent the coupling effects on the spacecraft motion for predicting and controlling the spacecraft behavior and stability. Authors believe that the mechanical model is a useful tool for better understanding the interaction of liquid cargo and the floating body motion. Firstly, the concept and associated formula of the mechanical model are explained and the parameters of the mechanical model for a rectangular tank are obtained analytically. Secondly, the equation of floating body motion and the mechanical model are coupled. Next, the numerical demonstration is performed and compared to the experiment and the calculation by other means. Finally, a rational explanation of the influence of liquid sloshing on the FLNG motion is provided.
Logistics hub project, i.e. transportation of marine operation workers from the base on the land to the offshore platform using a logistics hub, high Speed vessel and helicopters, was led by J-DeEP (Japan offshore Design and Engineering Platform) as the Japanese National project (2014~15). NMRI (National Maritime Research Institute) had joined this project and conducted both experimental and numerical analyses for the feasibility study of this concept. Model test and numerical simulation of the fast tug system, i.e. docking operation of the high speed vessel to the stern of the logistic hub using winches equipped each side of the hub and constant thrusts of the vessel, were conducted to survey the feasibility of this tug system. There are some assessment points in this system. One is tension acting on each tug lines. The other is development of the tension control system and confirmation of the effect acting on those lines. Through the experiment, snapping load acted on those lines were confirmed. Tension control algorithm was mounted in the winch control systems to reduce this load. As a result, decrease in standard deviation of the tension was confirmed. In addition to this, some simulation models were developed to simulate tension of the line and motion of the vessel and good coincidence was confirmed between experimental results and simulation ones at oblique wave conditions. Additional survey was conducted in order to understand effect of the amount of the constant thrust generated by the vessel for holding its orientation using these simulation models. Though the survey, the most suitable thrust range was specified considering maximum value of tension, tension balance and standard deviation of yaw.
This report concerns a numerical calculation procedure for global ship motions of a LNG carrier considering LNG liquid dynamic effect in wave conditions. Both a frequency-domain and a time-domain analysis procedures of the ship motions are developed. The velocity potential of the liquid is obtained in the methods, based on the artificial damping on the free water surface of the liquid. The value of the damping factor is determined by model tests. The response amplitude operators of the hydrodynamic force of the tank are derived and the maximum value of the apparent transverse acceleration of the tank to design is predicted based on the long term distribution of the tank force. The estimated maximum value is almost equal to a conventional design chart method.
In this research, we examined a simple method for maximum loads corresponding to long-term probability of exceedance Q=10-8 due to sloshing of a spherical LNG tank and new type tank. Tank excitation test using large scale tank model was carried out and the characteristics of sloshing load was confirmed. Regarding to the sloshing load in the excitation direction, the tank load becomes large near the tank natural frequency. The mode transition to the swirling occurs when the excitation amplitude increases and the tank load responds nonlinearly against the excitation amplitude. We proposed a formula for the long-term maximum load considering with the characteristics of sloshing load by means of specifying the wave condition based on the severest wave condition method. It can be estimated accurately compared with the conventional long-term prediction method. By using a simplified formula, we have made it possible to reduce a large number of test conditions (amplitude and frequency) required in the conventional method to once.
Numerical simulation method for the fatigue crack propagation in the case that the initial defect surface closes by the compressive loading is proposed. Previous fatigue crack opening / closing model based on the strip yield model proposed by Toyosada et al. is improved to consider the closure effect on the initial defect surfaces. This improved numerical simulation procedure for the fatigue crack propagation was verified by comparing with measured fatigue crack propagation histories under various superimposed stress histories.
In addition, numerical case studies were performed to investigate the influence of appearance degree of superimposed stress for the fatigue crack propagation history by applying our improved numerical simulation procedure. These simulation results are suggested that safe side evaluation for the fatigue crack propagation could be obtained by replacing the superimposed stress into the stress with enveloping the superimposed stress.
For the cruciform welded joints between corrugated bulkhead of duplex stainless steel plate and inner bottom of stainless (SUS) clad steel plate which have misalignment between the vertical steel plates under uniaxial and biaxial tensile loading conditions, numerical analysis of finite element method were performed with variable parameters of the loading condition, amount of misalignment, weld size and welding condition of penetration. The stress concentration factor on each weld toe of the cruciform welded joint was evaluated and the relations between the stress concentration factor and relative positional difference of weld toes on both side of inner bottom are investigated. As results, with misalignment, geometrical symmetry between weld leg shapes on both side of inner bottom is also desirable to avoid high stress concentration. In addition, for misalignment due to vertical alignment with mold line between vertical steel plates with difference in plate thicknesses, deep penetration welding is desirable to suppress stress concentration increased by its misalignment from comparison with fillet welding.
Most of large frame-based welded structures are subjected to multiaxial cyclic loadings with different phases under in-service condition. However, the fatigue performance of these structures are evaluated according to the design codes based on theoretical and experimental investigations under a uniaxial loading condition. Most of these codes are based on the S-N curves approach. On the other hand, authors proposed the numerical simulation method of fatigue crack propagation histories of a cracked plate subjected in-plane biaxial loadings with phase difference of each loading component. Fracture mechanics approach was applied to establish our method. In this study, fatigue crack growth behaviour of an out-of-plane gusset welded joint under in-plane biaxial loading with two different phase conditions are investigated. The phase difference effect for fatigue crack shape evolution under in-plane biaxial loading is confirmed by measured ones. Besides, the numerical simulation method of fatigue crack growth is proposed and confirmed this method by comparisons of measured crack evolution with the numerical simulation results.
Recently, the awareness regarding environmental issues is increasing all over the world. Natural gas is an attractive energy option because of its environmental performance. Regarding its transportation, Moss type tank, a spherical tank, is one of the most used cargo containment systems. In this research, the behavior of the partially filled spherical tank of LNG carriers is examined. The motions of the liquid inside the tank are divided into four types in this study, i.e., planar wave, sloshing, steady-state swirling and non-steady-state swirling. Sloshing and swirling are easy to occur as the excitation amplitude becomes larger. The force and the pressure on the tank wall are also studied by both model experiments and numerical simulations. The non-dimensional force becomes smaller as the excitation amplitude becomes larger because of its nonlinearity. Regarding the pressure, each motion type has its own characteristic time history. For example, the pressure history has two peaks when the excitation frequency is high. The effect of the position of the rotation center is also examined. Considering the sloshing effect on the spherical tank, the results show that the rotation center located close to the center of the tank is advantageous.
An experiment was carried out to measure sloshing pressures and forces in a prismatic chamfered tank. The tank was excited laterally for regular and irregular excitation and the results were compared with numerical computations based on a Finite difference method. The tank has a Length to breadth ratio near 1, and especially in intermediate filling levels, at around the tank's 1st mode sloshing frequency, the occurrence of a rotational flow, i.e. swirling, was observed. Based on the results from both model experiment and numerical simulations, there are cases where swirling loads can be significant and therefore cannot be neglected. After checking the tank dimensions of real LNG carriers, it was noted that many actual designs have tank with the length to breadth ratio near 1 and therefore the problem can be relevant. The rotational flow characteristics and its occurrence is investigated and its pressure distribution is compared with the 1st mode sloshing, finally, considerations about the tank safety are inferred concerning the swirling problem.
Scientific drilling vessel Chikyu faced drill pipe failure during offshore commissioning of drilling control and instrumentation system upgrade work. The failure occurred with cyclic bending stress which was enough low to prevent fatigue failure according to S-N curve obtained from full-scale fatigue tests. Material tests and observation of a remaining part of the failed drill pipe, investigation of onboard data observed and measured during the operation, and fatigue analysis based on the material tests data and stress amplitude determined by both the onboard observation and the simulation of drill pipe motion are examined to investigate the cause of the failure. All three examinations provide that the number of cycles of bending stress to fail is in the order of 104. The examinations also provide an evidence of cause of initiating cracks. This study presents the results of examinations and discusses the cause of drill pipe failure by verifying and complementing the results. It finally concludes that micro cracks were initiated owing to heat and stress, then cracks grew with cyclic stress, and it consequently reached to failure owing to the drill pipe motion including Magnus effect.
In this study, an experimental method predicting for fatigue crack initiation lives of welded structures is proposed. Fatigue test specimens were extracted from the welded structures containing embedded defects detected with a time-of-flight diffraction technique by electric discharge machining. The fatigue test conditions were set to be equal to the operating conditions of the welded structures. The validity of the operation conditions was confirmed by finite element analysis.
The fatigue tests found a good correlation between a stress intensity factor range and a number of cycles to fatigue crack initiation life within a factor of 2 scatter bands. This correlation of the stress intensity factor range was more accurate than one of a net cross-sectional stress range. Using the correlation, the fatigue crack initiation lives of the welded structures are predicted within the factor of 2 scatter bands by calculating the stress intensity factor ranges of the embedded defects.
To mitigate global warming, it is necessary to reduce the large volume of CO2 released into the atmosphere. Carbon capture and storage technology is a promising means of achieving this purpose. Those who inject and store CO2 in sub-seabed geological formations may be legally required to monitor CO2 leakage, even when the likelihood of such an event is very low. In the case that the leaked CO2 is monitored by limited numbers of CO2 censors set on the sea bottom, it is required to elucidate the leakage location and rate immediately, in order to evaluate its impacts on the marine ecosystems and to minimize the impacts. In this study, we developed a numerical method to predict the location and rate of a contaminant seeping from the seafloor, using the adjoint marginal sensitivity method, based on the data monitored by limited numbers of sensors. A time-reversed numerical test was successfully conducted, using information obtained by the time-forward simulation of tidal current and contaminant dispersion.
In recent years it has become evident that ocean data in time and space is required to make predictions of environmental changes on earth. As one method of acquiring data, we propose a virtual mooring system using an underwater glider, and have developed a prototype vehicle called “BOOMERANG” which can glide back and forth between the sea surface and the seabed collecting ocean data. In this paper, the research on course control of a disk type underwater glider is shown for improvement in the performance of virtual mooring.
Modal shift helps not only to reduce greenhouse gas but also to mitigate labor shortage problem because transportation means used in modal shift can carry more cargos with fewer people. Recently shortage of truck driver becomes more and more serious. Among various factors, problems of long work hours and low wage are significant. It can be observed that some cargos shift their routes to marine transport for retention of drivers and improvement of their treatment. We add new functions to the existing cargo transportation simulation system which uses generalized cost model expanded with correction terms to estimate cargo transportation route and achieved highly accurate transportation reproduction although the simulation model is precise. The new functions are driver operation scheduling, detailed truck cost evaluation, considering backhaul cargo, automatic parameter tuning and so on. With the system, we analyze how the improvement of truck driver treatment (pay increase and improvement of labor hours) effects on modal shift. The result shows that there is possibility of noticeable modal shift progress on large lot size cargos.
The International Maritime Organization (IMO) has been discussing about amendment of required subdivision index ‘R’ of passenger ships and some amendments of R has been proposed. It is important to consider the amendment of R from not only one aspect such as technical feasibility but also the view point of cost-effectiveness. Therefore, Cost-Benefit Assessment (CBA) on Formal Safety Assessment (FSA) was carried out for ‘R’ of Japan’s proposal in this study. In general, FSA is conducted for a generic model, i.e. for an individual ship, however, in this study, we proposed that FSA was carried out for the fleet by considering the distribution of the number of Persons on Board (PoB). As the result, the distribution of Gross Cost of Averting a Fatality (GCAF), which is an index for CBA in FSA, was obtained. The impact of amendment of the rule will be able to be considered deeper by using the method presented in this paper.
A data compression method applicable to position data in AIS (Automatic Identification System) like system is proposed, in which MSBs (Most Significant Bits, higher bits) of position data are dropped from data to be exchanged. The MSB dropping technique has had a problem which comes from the nature that the distance corresponding to a degree longitude becomes smaller in the high latitude region than on the equator. This problem is solved by splitting region according to latitudes and dropping LSBs (Least Significant Bits, lower bits) in high latitude regions instead of dropping MSBs. In addition, a sample protocol is designed according to real AIS data. With the designed protocol, the data size of position data in the AIS is decreased by 20%.
Countermeasures of ships for tsunamis became a major concern for ship operators after the Great East Japan Earthquake in 2011. Evacuation from ports is generally recommended to avoid tsunami disasters. However staying in port with enhancement of mooring lines could be another option. In this study, a dedicated model experiment to tow a quay wall and a ship model together was conducted to estimate hydrodynamic forces acting on a containership alongside a quay wall under tsunami attack, to discuss the required strength of mooring against tsunami flows. Finally, a simple conversion formula was proposed based on the experimental results, to estimate the wind speed equivalent to the tsunami-induced hydrodynamic forces.
In numerical simulation, the bow flare slamming phenomenon is often treated as the wedge impact to water surface. Up to now, in many numerical simulation, the impact pressure under bow flare slamming has been firstly calculated by CFD in which the structure have been assumed to be rigid, and then the structural response has been calculated utilizing FEA under the pressure obtained by CFD. But, the impact pressure is possible to be influenced by structural rigidity. Therefore, in order to calculate the impact pressure and structural response accurately, the coupling analysis of structure and fluid under the bow flare slamming load must be performed. In this paper, in order to establish the assessment procedure of the structural response under bow flare slamming load, the general purpose FEM software; LS-DYNA, which can simulate the structure-fluid coupling behavior by ALE, is applied for the impact problem of elastic wedge. The parametric calculations are performed to obtain the pressure and the structural response by changing the attacking angle of wedge to water surface. And, the effect of structural rigidity on impact load and structural response are investigated by series of calculation.