In the present paper, the minimum wave resistance problem based on the low speed theory is investigated by means of the nonlinear programming. In case of the low speed theory, the variational approach is of no use, because the formula of wave resistance is highly nonlinear. In order to reduce the computer time, the simplified formula is employed, and the wall-sided hull of equal waterline is assumed. Several approximate numerical treatments are also used in the optimization process. The fairing constraint is included in the problem to obtain the stable shape of hull as in the previous reports.
Numerical examples are given and compared with former theories and design data. Optimum coefficients of fineness obtained by the present method show the similar tendency to those based on the series model tests carried out by Taylor.

抄録全体を表示

A new formulation of the slender body theory for a ship with constant forward speed is developed. It is based on an asymptotic expression for the Kelvin source and may be regarded as a substitute for the Neumann-Kelvin approximation. Wave patterns of a point source in a uniform stream are computed by the original formula of the Kelvin source and by the asymptotic formula. Wave patterns of a submerged body which is represented by a source distribution along the longitudinal axis are also computed by both methods. They agree well near the longitudinal axis. Then computation of the wave pattern for a model of Series 60, C_B=0.6 is carried out, and the result is compared with measurement. It is concluded that the present theory is useful as an approximate method of prediction of ship waves near the hull.

抄録全体を表示

A new version of the TUMMAC method, which is a modified marker-and-cell method, is developed in order to analyse nonlinear wave making in the near-field of forebodies of ships of arbitrary waterline advancing steadily in deep water. The 3-D Navier-Stokes equations are solved by a finite-difference scheme under boundary conditions which are improved so that they suit to the problem of ships of arbitrary waterline. Numerical tests are conducted with a wedge model and some forebodies of ships of arbitrary waterline.

抄録全体を表示

The two-dimensional finite-difference method TUMMAC-III developed in the first report is applied to three problems of steep regular waves interacting with obstacles, i.e., run-up on a beach, deformation and breaking on a sandbar and diffraction by a rectangular floating body. Experiments are undertaken for these problems and the wave profiles and pressures on the body are compared with the computation. The agreement is satisfactory as far as the waves before breaking are concerned.

抄録全体を表示

A numerical method for two-dimensional stern wave problems is developed by use of a time-dependent stream function. Fully nonlinear dynamic and kinematic free surface conditions are employed. The governing equations and the boundary conditions are expressed in finite-difference forms in a boundary-fitted curvilinear coordinate system. Present method has potentiality to explain viscous effects on the stern waves by including vorticity.
Preliminary computational tests are carried out in order to refine the computational scheme. Some computed results of the potential flow past a semi-infinite flat-bottomed body with a transom stern are presented and the viscous effect is discussed by comparing the calculated inviscid results with the measured.

抄録全体を表示

A finite-difference method is developed for the explanation of the characteristics of nonlinear bow and stern waves generated by a 2-D floating body of rectangular configuration advancing steadily in deep water. The generation of bow waves of steep slope and stern waves in vortical flow are explained. The effects of viscosity and shear flow near the free surface are simulated to know the detailed structure of nonlinear waves.

抄録全体を表示

The present paper describes an attempt to minimize the viscous resistance of two-dimensional bodies and three-dimensional full form ships under certain design constraints. The minimization was made by means of Hooke and Jeeves' direct search method with an external penalty function. Frictional and viscous pressure resistances are calculated by integrating shear stress and pressure over the hull surface, respectively, which are obtained by the boundary layer calculations based on a higher order theory. In the case of two-dimensional bodies, the boundary layer calculations were made assuming that the boundary layer is laminar from the leading edge to the transition point and is fully turbulent downstream of the transition point. On the other hand, in the case of ship hulls the turbulent boundary layer calculations were started near the fore end.
Optimum shapes were determined first for two-dimensional symmetric bodies. The optimum shapes obtained at Reynolds number of 10⁶ and 10⁷ are similar to a conventional wing section and a laminar wing section, respectively. Next, the optimum stern forms for conventional ship form were determined by the same manner.

抄録全体を表示

A simple integral-type boundary-layer calculation method is applied to the prediction of ship viscous resistance. A calculation method for the vortex resistance due to the stern bilge vortex is evaluated from the energy-loss concept using the crossflow quantities in the stern boundary layer. The ship viscous resistance thus consists both of the streamwise momentum loss and of the crossflow energy loss. A regression analysis of the resistance shows a fairly good agreement between the theory and experiments.
The local development of the viscous resistance components near stern is also discussed in terms of the boundary layer quantities. The potential-flow quantities like pressure gradient and streamline convergences are related to the boundary layer development and then the viscous resistance. The present method can be applied to ship-stern form improvement for reducing viscous resistance.

抄録全体を表示

The scale effects of the boundary layer and wake distribution of ships with bilge vortices are investigated as an extension of the author's previous paper on the same problem without bilge vortices. It is assumed that the flow consists of the ordinary wake portion without bilge vortices and the vortex wake. The characteristics of the latter are discussed firstly with the main purpose of investigating the Reynolds number effects on the location of the vortex center, circulation, velocity and vorticity distributions. Secondly a method of correlating the model and ship's wake is proposed.

抄録全体を表示

In this paper, Unsymmetrical Propellers are proposed in order to reduce the fluctuating pressure at blade frequency induced by a cavitating propeller. The idea behind the unsymmetrical spacing of blade is to give rise to a suitable phase lag between the fluctuating pressures transmitted from each individual blade. Pressure fluctuations can be roughly estimated in terms of the blade spacing by using Fourier expansions. In order to obtain the suitable blade spacing, an iterative calculation procedure is adopted.
Finally five model propellers with non-uniform spacing of blades were designed. Experiments were performed with these five propellers and the one with uniform spacing.
Comparing these results, the reduction of fluctuating pressure amplitude due to unsymmetrical propellers were verified.

抄録全体を表示

In a previous paper, the authors proposed a nonlinear theory for a partially cavitating hydrofoil and showed that the cavity shapes obtained from this theory agreed well with the experimental ones.
In this paper, pressure distribution on the hydrofoil surface and velocity distribution in its wake were measured using the same foil section as before. Experimental lift and drag coefficients were calculated from the pressure distribution and the momentum loss of the wake. From these results, following conclusions were obtained.
(1) The results obtained from this theory agree well with the experimental ones if the viscous effects are considered. However, when the cavity becomes unstable, the experimental pressure distribution on the suction side does not agree with the theoretical one.
(2) The wake in cavitating case is wider than that in noncavitating case. This result shows that the occurence of cavity causes the velocity loss in the wake.

抄録全体を表示

By prescribing a certain surface pressure distribution, a new foil section is designed to give less cavitation and higher lift-drag ratio in comparison to a MAU type one. Using the cavity flow theory proposed by the authors in a previous paper, it is predicted that cavitation performance of the new foil section is better than that of the MAU type one.
Experiments were performed in order to verify these facts, using both foil sections. It was found that the difference of cavitation performance between the two foil sections was more than predicted, because for the MAU type section the predicted cavity was smaller than the experimental one.

抄録全体を表示

The propeller load varying test method, which has been developed in the S. R. I. to investigate into the propulsive performance of ships, has broad applications in the field of ship's performance problems. The basic idea of it is to study the propulsive performance in the wide range of the propeller load from T=0 to the thrust far beyond ship point. The self-propulsion factors are given as the functions of propeller thrust.
In this paper the author mentions how the data from the method can be utilized in the estimation of the propulsive performance of a ship affected by the external force such as wave exiting drag and wind thrust or drag. He also shows the effectiveness of the method in the investigation of the effect of reaction rudder.

抄録全体を表示

In the previous reports, theoretical investigations were given for various aspects of wave devouring propulsion. The ideal wave devouring propulsion efficiency was discussed, and, when an oscillatory hydrofoil was used as a wave devouring propulsor, the importance of free surface effect and that of the optimization of foil motion were shown.
In the present paper, the thrust generation through absorption of wave energy by a passive-type hydrofoil propulsor is verified experimentally by using a specially designed testing device, and the amount of the thrust is also measured. Some theoretical studies are conducted to obtain the theoretical estimations for the free running or self-propulsion speed, foil motions and generated thrust etc. on the basis of Wu's theory for an unsteady hydrofoil in waves.

抄録全体を表示

When a ship is travelling in a following sea, the frequency of encounter is reduced to be very low. In this case, however, the so-called strip theory can not evaluate the wave exciting force correctly, because it does not take the lift component into consideration.
In the present paper, a theoretical method is described for calculating the diffraction force. It is based on the generalized unsteady lifting-surface theory; thus the lift force is taken into account, and the free-surface effects in the high speed as well as low frequency range can be also incorporated. Numerical computations using the present theory are carried out, and then the results are represented as a function of U/C, where U denotes ship speed and C phase velocity of a wave. Furthermore, corresponding experiments are conducted for a flat plate and a Wigley ship model.
Through the comparison between computed and measured values, it is confirmed that the effect of encounter frequency on the diffraction force in following seas can be explained in terms of the present theory.

抄録全体を表示

Accurate estimation of wave loads acting on a ship is a long-lasting task for naval architects. Recently, a new approach for the investigation of non-linear characteristics of wave loads was introduced; namely, combination of experiments using “elastic model” and non-linear digital simulation.
In this paper, at first, possible construction techniques of “elastic model” are examined. Adopting “backbone model” composed of segmented hulls and a metal backbone representing ship's longitudinal rigidity, two series of model experiments were carried out for a high-speed cargo vessel with different values of backbone's rigidity.
Application of “backbone model” makes it easy to change model's longitudinal rigidity. Using as high rigidity backbone as possible, vibration response components can be reduced and responses almost as a rigid body can be measured. Replacing the backbone with the one having corresponding rigidity to the full scale ship, approximate responses of the ship can be measured.
By the examination of dynamic characteristics of the model, vibration modes and modal damping coefficients were obtained, and the damping coefficients were found to be very close to those of full scale ships. It means that close correspondence between model experiments and full scale phenomena can be obtained.
A digital simulation program was developed for the estimation of nonlinear heave and pitch motions, vertical bending moment and shearing force. Compared with the results measured through the model test, calculated results seem to predict non-linear characteristics fairly well.

抄録全体を表示

In this paper, the authors investigate into vertical motions of a high-speed boat travelling in head sea and wave loads acting on it, taking account of the effects of non-linear hydrodynamic forces and dynamic lift in waves. A series of tests was carried out to measure heave and pitch, bow acceleration, vertical bending moment and shearing force at the midship section of a segmented model. The experimental results were compared with theoretical values predicted in the following three different ways : (A) linear calculation, that is to say, the Ordinary Strip Method applied to the running condition at travelling in a calm water, (B) non-linear calculation in which the effects of time-varying sectional hydrodynamic forces were taken into account, and (C) non-linear calculation taking account of the effects of planing at a high-speed as well as the effects of time-varying sectional hydrodynamic forces. As the result of comparison, it was shown that vertical motions and wave loads of high-speed boats can be evaluated by the method presented in this paper with accuracy enough for practical use, and that the method may be applied to the case of travelling at a higher speed than that considered in this paper if the sectional hydrodynamic forces will be appropriately evaluated when travelling at that speed.

抄録全体を表示

It is clear that capsizing in rough seas is probabilistic phenomenon. But the probabilistic treatment by theoretical consideration only is very difficult.
So, in this study, the probability of capsizing in short term sea condition is examined by experiments.
In the first, the definition of capsizing probability is made and the distribution function of the time to capsizing (t_c) is assumed to become Gamma distribution.
This can be obtained by the analogy of the failure of mechanical system.
And the next, capsizing experiments are conducted and the above assumption is confirmed. Some examples of the probability of capsizing are obtained as shown in Fig.14. This probability is also shown by using he Weibull distribution.
At the same time it is shown that those parameters representing Gamma distribution have closer relation to the significant wave height (H_1/3) and metacentric height (GM) or dynamical stability (D_st) as shown in Fig. 10.

抄録全体を表示

The mineral concentrate cargo which has high moisture contents may shift owing to liquefaction when the ship is exposed to rough weather. This may result in a dangerous heel of ship and eventually capsize.
In this paper, the characteristics of liquefaction of barite, pyrite, and lead concentrates are investigated on the basis of the cyclic triaxial test. It is shown that the relation between the volume of liquefied concentrate and duration of ship motion can be calculated with the use of experimental data and the linear stress analysis. The results of simulation test with barite concentrate show good agreement with analytical results.
The advantage of the use of shifting board is examined with the proposed method. It is shown that the shifting board with appropriate depth and rigidity prevents considerable amount of mass of concentrate from liquefaction.

抄録全体を表示

In the foregoing reports, the theoretical and experimental studies are carried out on the behavior and the maximum tension of mooring chain which is anchored in the slack condition and is forced to oscillate vertically at its upper end. In this paper, the maximum tension of chain forced to oscillate horizontally and the minimum tension which is related to the snap generating condition are investigated.
At first the oscillation of the mooring chain is idealized as a single-degree-of-freedom motion of a lumped mass and the dynamical equation of motion is solved over a broad range of amplitudes and periods. The values of the maximum and minimum tensions of chain calculated by this method coincide with those of experiments fairly well. Secondly the mechanisms which generate the snap tension of mooring line are discussed and the snap generating conditions are derived analytically and are verified experimentally. Finally the method for calculating the dynamic tension of slack mooring chain are summarized for the practical use.

抄録全体を表示

Appearance of recent complicated mooring lines demands the development of new method, which is able to be applied for the analysis of dynamic behavior of various types of mooring lines including the deep sea mooring line. In this paper, two-dimensional lumped mass method which was originally developed by Walton and Polachek (1959) have been extended to the three-dimensional method. The present paper also shows the alternative method which is able to include elastic deformation without lengthy procedure of computer simulation. The time histories of dynamic tensions of three-dimensional problem as well as the motions of the line are obtained by the present methods and are compared with the experimental records with excellent agreement.

抄録全体を表示

The first report proposed quite a new floating breakwater, the multi-body-type floating breakwater, of which transmission coefficient was proved experimentally very small compared with conventional one's. The mechanism of absorbing wave power by this breakwater was made clear by a mathematical model. Its drift force due to waves was shown small, too. So it is expected that mooring tension is also small, when it is moored by slack chains or ropes. This paper shows how small it is, comparing with conventional types. In order to estimate the mooring tension and a surging displacement of the breakwater, model experiments were carried out in irregular waves and their extreme values and others were examined and compared with theoretical calculations.

抄録全体を表示

In this paper the authors investigate the wave-power absorbing performance of ship utilizing the anti-rolling tank (A. R. T.). In the first part, an ordinary-ship model is examined on the performance both by the experiments and by the theoretical calculations. The wave power absorbability is, however, found to be poor, but the design procedure is proved to be useful.
In the second part, the effect of the floating-body shape on the performance is investigated basically, which shows that the deep draft and low center-of-gravity type is advantageous. Its remarkable characteristic is the easy adaptability to the variation of the sea condition by changing the c. g. position. This is also proved by the experiments.
Finally, the basic design of the A. R. T. wave power absorber is proposed and estimated. The theoretical evaluation shows that the significant mass of tank water makes the wave-power absorbing response effectively wide by shifting the A. R. T. up and/or down according to the sea condition.

抄録全体を表示

In this paper, model experiments were conducted in regular and irregular waves for the twin-hull-type floating wave energy converter equipped with some electric generators.
The results of generated electric power, motion of the converter and transmitting wave obtained by the experiments were compared with the ones predicted by theoretical method.
It was found that the results obtained by the experiments were in agreement with the predicted values.
Further, the average values of generated electric power and the rate of operation of the full scale wave energy converter (Δ=1, 430 ton) were estimated by using the experimental data and actual wave data for some coastal areas of Japan. The average electric power and the rate of operation were respectively estimated to have about 40 kW and 97 percent throughout the year at Habu, which was located on the Pacific side of Japan.

抄録全体を表示

Three type of offshore structure on which an Ocean Thermal Energy Conversion (OTEC) power plant will be constructed are now available; that is, land based (on shore) type, bottom mounted (offshore) type and floating type. Among them, the floating type offshore structure is popular and examined extensively in Japan. As one of the typical and practical applications of the “SUNSHINE PROJECT”, “Study of the Ocean Thermal Energy Conversion (OTEC) Power Generation System” has been commenced.
In studying this system, actually using a floating type pilot plant provided with a water intaking device, various experiments are scheduled to conduct. Since the power plant site is often a sea area where might be well visited by a typhoon.
In order to protect such offshore structures from the above disasters, it is required to provide the structure with sufficient strength that is bearable against severe sea conditions (such as wave, wind etc.) after analyzing the dynamic response.
So, we have studied the calculation method of a fluid force acting on the floating platforms and Cold Water Pipe (CWP), and a formulation of the mathematical models for the coupled platforms and CWP systems, as well as the equivalent linealized treatment of nonlinear fluid force. Then we have carried out the tank test by using 1/50 scale model of the OTEC plant which was designed in the “SUNSHINE PROJECT” for the experiment at sea, and compared the experimental results with the theoretical calculation, there by a reasonable agreement of both has been confirmed.
This work was supported by Agency of Industrial Science and Technology under the contract of the “SUNSHINE PROJECT”.

抄録全体を表示

The supposed wave condition has the most significant effect on the result of the statistical estimation of the wave induced variable of a ship. It is the general case of the theoretical estimation of the wave induced variable of a ship in a given sea zone to suppose the observed wave statistics of the weather ships or voluntary ships in the sea zone.
Authors researched the data of wave observation of 62 voluntary ships in the North Pacific Ocean during 3 years (1976-78). It was clarified that the wave conditions encountered by them had remarkably wide scatter band in comparison with that of random samples from the same population.
To investigate the cause of the wide scatter band, authors research statistical character of wave and wind conditions observed on 35 voluntary ships in the above sea zone during 6 years (197681), wave condition on 9 weather ships in the North Atlantic Ocean for 18 years, and records wind measurement at 5 weather stations in Japan for 20 years.
From the above statistical study, it is made clear that the newly analysed wave and wind records have also the similar wider scatter band. Authors deduced from the result that such variable as wave-and wind in ocean have the basic character in which the sample distribution shows a different distribution from that of random samples from usual population having a given distribution with constant parameters.
Authors study on the probabilistic model of population which can describe this special sample distribution, and introduce a population having a complex distribution with parameters which are not constant but stochastic variables, too. The distribution of the above observed wave heights is described by assuming them as sample values from the population with a complex log-normal distribution with a constant standard deviation and a mean which is described by a normal distribution.
From the study of the sample distribution of wave conditions encounterd by ships, it is evaluated that the coefficient of variation of the extreme wave condition encountered by a ship during her life time in a given sea zone may be nearly 15% in maximum, and the value for larger ship will increase. This means the coefficient of the extreme value of wave induced variables of the ship has also nearly the same value. This value is larger than that usualy supposed in the case of reliability of strength of ship structure.

抄録全体を表示

In the previous paper, the authors introduced a concept of 'mission-effectiveness' for evaluating the effect of seakeeping performance on ship system capability. They also showed that the short-term mission-effectiveness could be estimated easily by applying a simple method proposed.
In the present paper, they show the importance of long-term mission-effectiveness and propose two methods for estimating long-term mission-effectiveness. One is the statistical prediction method which estimates long-term availability of the ship system for a single mission, and the other the simulation method which gives the overall mission-effectiveness for a combined mission as well as a single mission.
They discuss the long-term mission-effectiveness of patrol boats which are assumed to be operated for the mission “Salvage”.

抄録全体を表示

Turbulence measurements in a circulating water channel are made by an X-type hot film probe. From three components of velocity fluctuations turbulence intensities, Reynolds shear stresses and turbulent kinetic energies are obtained. By stern longitudinal vortices formed in the wake the values of turbulence quantities are influenced appreciably. In the surface condition of a model the turbulence intensities of vertical component w and shear stresses -uw are intensely suppressed due to the existence of free water surface. The value of every turbulence quantity takes the maximum value near the vortex center.

抄録全体を表示

A new method to predict near wake flow is proposed where the time dependent vorticity transport equation and the boundary layer equation are used as governing equations. The flow field is supposed to be that made by a sudden move of a body to which a vorticity layer is attached. The attached vorticity layer is equivalent to the steady boundary layer. The flow field is solved by the time marching method. The two-equations model is invoked for the turbulent closure. The wakes of three 2-dimensional elliptic cylinders are calculated which are significantly separated and recirculating. The wake flow of a flat plate is calculated, in advance, to make sure the propriety of the present method. As far as the near wake flows are concerned, satisfactory results are obtained within a reasonable computing time. Recirculating and fluctuating flow fields are nicely simulated. The viscous drag is also calculated by making use of the results of wake calculations.

抄録全体を表示

Nonlinearity in normal force for a slender body with small incidence to flow is discussed by the asymptotic expansion method under the usual assumptions, 1>>ε>>1/√Rn and k=β/ε=O (1), where ε is a slenderness parameter, β an angle of attack, k relative angle of attack, and R_n Reynolds number. The main purpose of the present paper is to develop the method to determine the separation line and the strength of the vortex sheet separating from there. The near field is composed of continuous vortex sheet whose complex potential is expressed with the circulation as a parameter, which is measured from the end point of vortex sheet to the point considered. Kutta's condition to be used to determine the strength density of the vortex sheet near the separation line is proposed by investigating the characteristics of the governing equation of vortex sheet shape. It is shown that this condition is consistent with the vortex conservation law. A method is proposed to solve simultaneously potential stream-lines and boundry layer parameters including the effects of the vortex sheet by only one marching downstream. The shape of the vortex sheet and the separation line are calculated and the normal force coefficient is compared with experimental results.

抄録全体を表示

It is well known that at the single point mooring or anchoring the slewing motion of a ship is caused by action of the wind or the current. During the slewing, the extraordinary tension occurs in the mooring line when the ship's yaw angle becomes nearly maximum, and incurs, as the case may be, the breakdown of mooring lines or unforeseen drift of anchors. However, there exist only a few published papers related to the slewing motion, and theoretical predictions of slewing motions and tension of mooring lines do not agree well with the observed ones.
In this paper, a new mathematical model is proposed to describe the current forces acting on a ship under the slewing motion, and validity of the proposed model is examined through comparing the ship motions and the tension of mooring line predicted by the present method with those measured at the model experiment performed in the water basin.
Prior to advent of the mathematical model proposed in this paper, the current force acting on a ship during the slewing was experimentally determined in the wind tunnel or the water basin as functions of relative inflow angle of the current.
As the result of examining the prediction through the present method, it is verified that the method proposed in this paper is of a great practical use compared with the previous method, because the proposed method enables us to evaluate various effects of changing the mooring conditions such as ship's displacement, ship's trim, the length of mooring line, current speed, etc. on the slewing motion with ease and with accuracy.

抄録全体を表示

This paper describes a new method to calculate the lateral hydrodynamic forces acting on a ship during manoeuvring motions. On the slender body assumption, the fluid motion around a three dimensional body is approximated by unsteady two dimensional flow in a space-fixed plane normal to the longitudinal axis of the body. Consequently, the hydrodynamic lateral forces acting on the slender body is obtained through integrating two dimensional lateral force over the whole length of the body.
The two dimensional flow in infinite region is substituted by that in finite region bounded by an artificial open-boundary on which Sommerfeld's radiation condition is imposed. Making use of Orlanski's method to deal with Sommerfeld's radiation condition, two dimensional Laplace equation is solved by Boundary Element Method and Finite Differences Method, and then two dimensional hydrodynamic lateral force is calculated by differentiating the fluid momentum with respect to time.
As an application of the method described above, the hydrodynamic lateral forces acting on a flat plate with aspect ratio equal to 0.2 are calculated and compared with the experimental results. In consequence, it is shown that the stability derivatives predicted by the present method agree well with those measured at oblique towing, CMT, and PMM tests, and that the predicted stability derivatives of a flat plate with aspect ratio equal to 0.05 are in good agreement with the stability derivatives measured by a Series 60 model with a realistic hull form.

抄録全体を表示

Traffic flow in the crossing points is the important factor for the traffic capacity as well as the safety of navigation. In order to improve the capacity and safety, the time sheared control were studied at the parallel route crossing. Two control system were considered, one is the priority in order of arrival (first come first service system), the other is the signal system.
In the previous report, the authors have assumed that ships navigate in a line (single line navigation), this report treated with navigating two or three abreast (parallel navigation) in the fairway.
As, the arrival time distribution of large ships have a great influence on the traffic flow in the crossing points (a number of large ship arrive to control area in a short time, traffic volume exceed the crossing capacity), pre-scheduling for large ships before arriving to the control area was considered in this report.
Some results of Digital Simulation are shown;
(1) The effectiveness of parallel navigation are shown in the case of priority system, unallocatable ships decrease to 1/10 compared with single line navigation.
(2) Pre-scheduling of large ships is very practical and useful control. In the priority system, number of unallocatable ships reduces to 1/5.
(3) Priority system with pre-scheduling for large ship is most useful control. If the maximum permissible limit of unallocatable ship rate are assumed 2%, the traffic capacity of crossing point has more than 420 (ships/day/crossing point) within 10 min. mean delay time under condition of DA =10, 000 m.

抄録全体を表示

This paper presents a numerical method capable of analyzing vibration problems of a plate, which has damped one-degree-of-freedom absorber systems. Lagrange's equations of motion will be employed based on the kinematic, strain and dispersive energies for the plate and damped absorber systems. The deformation of the plate will be approximated as a continuous system by using. Ritz method.
The present authors will also carry out the experimental work in order to study the interactive effects between the plate and mass-spring systems, and also verify the validity of the proposed numerical method.
The vibration of deck loaded with cars in pure car carrier will be considered as a typical example of interactive vibration of plate and mass-spring systems. By applying the proposed numerical method, the present author will investigate characteristics of vibration of car deck in the steady state, and transitional behaviors of deck during the slamming.

抄録全体を表示

In this paper, a method to calculate the natural vibration of rectangular and trapezoid stiffened shell is presented. Several numerical calculations using present method are carried out, and following conclusions are obtained.
(1) The natural vibrations of rectangular stiffened shell calculated by present method have a good agreement with the experimental results. Then it can be said that the propriety of present method is confirmed.
(2) The relationship between the reinforcement method of shell and natural vibration is analytically investigated. If the stiffeners are arranged to the same direction that the curveture is small, the reinforcement with stiffeners is not effective to the increment of natural frequency. On the other hand, if the stiffeners are arranged to the direction of large curveture, the natural frequencies increase by the multiplication effect of the increments of rigidity due to curveture and stiffeners.
(3) The effect of the shape and magnitude of initial deflection to the natural frequencies is also investigated choosing the actual deck structure of pure car carrier as a subject of investigation. And it is seen that in the case of complex initial deflection and higher order vibration, a little initial deflection is causative of the increment of natural frequency.
(4) According to the calculated results for the trapezoid stiffened shell, because of the relationship between the strain energy due to membrane force and that of bending moment, the natural frequencies decrease as upper side-lower side ratio c/a becomes large in the case of small initial deflection or small c/a. But the natural frequencies increase conversely in the case of large initial deflection and large c/a.

抄録全体を表示

The relation between radius-to-thickness ratios and non-axisymmetric plastic buckling patterns for axially compressed circular cylindrical shells was investigated from both analytical and experimental viewpoints. The obtained results are summarized as follows :
(1) The lower bound value (R/t) _el (eq. (6)) of the radius-to-thickness ratios which produce the non-axisymmetric buckling pattern with n circumferential waves was determined by applying the elastic buckling theory, and its validity was confirmed through comparison with the experimental data given by Horton et al.
(2) Numerical calculations of non-axisymmetric buckling stresses were carried out by using the simulator with 9 degrees of freedom which was composed of 6 rigid elements idealizing the periodic unit area of Yoshimura buckle pattern, and the value of (R/t) _pl (Table 1 and Table 2) was obtained corresponding to the circumferential wave number n.
(3) It was certified that the value of (R/t) _pl can be almost considered as the lower bound to each circumferential wave number by conducting the compression tests for mild steel circular cylinders (Fig.10), however, more experimental data will be needed in order to establish the above conclusion.

抄録全体を表示

In general, a deck plate of a box girder such as ship hull is subjected to inplane tensile and/or compressive load due to longitudinal bending. A deck plate is a main strength member of a box girder, and is stiffened by stiffeners and girders in the longitudinal and transverse directions to prevent overall buckling under compressive load. When the strength of a deck plate is considered, the plate elements subdivided by stiffeners and girders play an important role, and the precise evaluation of their compressive strength is necessary.
In this paper, as a series of research, the compressive ultimate strength of a rectangular plate is theoretically investigated as follows.
(1) The mode of initial deflection is measured on 33 deck panels of Bulk Carrier and Pure Car Carrier, and the coefficients of components of initial deflection are calculated.
(2) A series of elastic-plastic large deflection analysis is performed assuming the measured mode of initial deflection. According to the results of calculation, it is due to the effect of large deflection that inplane rigidity reduces in the middle part of the plate in the case of thin plate, while it is due to the local plastification by bending in the case of thick plate.
(3) Based on the results of calculation, deflection method and curveture method are proposed to predict the compressive ultimate strength of thin plate and thick plate, respectively. In both methods, a rectangular plate with uni-modal initial deflection is considered which is equivalent in behavior to the actual panel. It is demonstrated that these methods predict the compressive ultimate strengths which have good relations with calculated ones.
(4) Effective coefficient of initial deflection is more precisely evaluated, and its simple formula is proposed.

抄録全体を表示

In this paper, a method to calculate the necessary thickness of a right-angled triangular corner bracket proposed in the previous paper is extended to more general case. First, the effect of a flange attached to the bracket is considered from a viewpoint of the buckling and ultimate strength of the bracket, and the simple formula is proposed to calculate the necessary breadth of the flange which ensures the maximum buckling and ultimate strengths. Then, more precise method is proposed which is applicable to a triangular bracket of an arbitrary shape with a flange to calculate its necessary thickness.
The procedure of calculation is as follows : (1) to calculate the plastic collapse load of a beam with brackets, (2) to determine the stress distribution in the bracket at the plastic collapse of the beam, (3) to calculate the elastic buckling strength for thinner plate or the ultimate strength for thicker plate of the bracket, and (4) to determine the necessary thickness of the bracket from the condition that the bracket reaches to its elastic buckling or ultimate strength when the beam collapses. In extending the previous method, the more precise stress distribution is assumed in the bracket.
Elastic-plastic large deflection analysis is performed on several cases, and it is confirmed that the necessary thickness calculated by the proposed method is the optimum one. Furthermore, the weight of brackets are examined with and without flange.

抄録全体を表示

It is important to estimate the ultimate longitudinal strength of a ship hull girder, because it is the real resistant value to the wave bending moment. The ultimate bending moment of its cross-section was calculated by the in-plane strength of stiffened plates. The author's 3 rd report presented two approximate formulas to estimate the ultimate strength of the typical stiffened plates. These formulas took into account the influence of initial imperfection. In this report, a simple method using these formulas is proposed for an estimation of the ultimate bending moment. Experiments were carried out by using nine box girder models under pure bending loading. The calculated ultimate bending moment agrees well with the experimental results and have confirmed efficiency in first design stage.
The ultimate bending moments of the cross-section at the midship are calculated by this method and the characters are studied. It is found that the ultimate bending moment is strongly relative to the ultimate strength of the deck plate or bottom plate under compressive loading.

抄録全体を表示

Submarine pipelines which transport oil and gas are now being installed or planed for more, and more deep waters. It was reported that planed crossing includes a Norweigian Trench crossing with depth to 350 m and trans-Mediterranean crossing with depth to 2, 000 m. Submarine pipelines to be installed at such depths will require the utmost care in engineering design.
During a pipelaying operation, the pipe is subjected to the combined loads of bending, tension and external pressure. Considering the fact that bending stress during installation often reach the yield range, even though DNV Rules allow 0.2% residual longitudinal strain, it implies that this bending may become a collapse initiator. Furthermore, it should be considered that initial deformation reduce the resistance of pipeline against collapse, especially in deep water.
A rigorous analytical treatment of the collapse strength of pipeline during installation is very complicated, because it is a function of loading conditions as well as D/t ratios, material properties, and initial deformation.
In this paper a simplified analytical method, which was proposed by authors for evaluating the ultimate strength of stiffend plate, is extended in order to estimate the collapse strength of pipeline under the action of combined bending, axial force and external pressure, including the effect of initial out-of-roundness.
The present method is compound of two parts. One is elastic analysis based on energy method, and the other is plastic analysis in which collapse mechanism is assumed. In both analysis large deformation is considerd.
The following conclusions are obtained.
1) Theoretical results are checked with available published data. It is confirmed that this proposed method is fairly efficient one.
2) Since this proposed method is an analytical one that the complicated collapse strength of a pipe with out-of-roundness under combined loads can easily be estimated comparing with other numerical methods.
3) Analytical results indicate that there exist two different collapse modes for pipelines under combined bending and external pressure. One of them is circumferential flattening of pipe cross section (circumferential collapse) and the other is so-called Brazier's type of failure (bending collapse).
4) Analytical results show that both bending moment and axial tension considerably reduce the external pressure-bearing capacity.

抄録全体を表示

Collapsing of the circular cylindrical shell under external pressure can be divided into three modes, namely, shell buckling, axisymmetrical collapse (or stress failure) and general instability.
In this paper, the load carrying capacity and the behaviors of the shell were investigated when the shell failed in the axisymmetrical collapse. Thirty four models with three bays and twelve models with five bays were tested. Those models were fabricated with machine tools on a mandrel having out side diameter 113 mm, and had the dimensions and the mechanical properties shown in the Table 1. The collapsing pressure of those models obtained from the experiment are shown in Table 2, but twelve models of those resulted in the general instability.
On the other hand, the theoretical collapsing pressure of the tested models were calculated by finite element method, and the collapsing pressure of the shell varying systematically these characteristics were calculated.
The following conclusion were obtained from the experimental result and the calculation.
(1) The collapsing pressure of the cylindrical shell under external pressure can be predicted from Fig. 13.
(2) The average of the ratio between the experimental result and the theoretical value on the collapsing pressure is 95 percent.
(3) The axisymmetrical collapsing pressure is in proportion to yield strength of the material.

抄録全体を表示

Most of actual service loads for real structures are random in general and, moreover, are stationary processes in many cases. It is essential for the structural engineer to be able to estimate fatigue strength of structural members under the effect of such randomness in service loading on the basis of the conventional fatigue test data. Engineers are sometimes confronted with the necessity of prompt relevant action on cracks discovered by inspection in service or in fabrication.
A number of investigations on estimating methods for fatigue crack growth under random loading have been carried out, but most of them are based on the assumption that the random loading can appropriately be replaced by so-called “block loading”. Experimental investigations on the comparison between fatigue behaviors under purely random loading and block loading and/or constant amplitude loading are quite limited.
In this paper, the authors have conducted fatigue crack propagation tests using a computer aided testing system, where random process required was generated by micro-computer, as well as block loading and constant amplitude tests. Experimentally obtained features and comparative discussion based on the experimental data are given.

抄録全体を表示

To obtain a fundamental information about fatigue properties of materials, hysteresis loop data obtained from the fatigue tests conducted on austenitic stainless steels of SUS 304 and 316 at 288°C, and a nuclear vessel material of SFVV 3 at room temperature, were analysed. And then the cyclic characteristics of hysteresis loops at room temperature and 288°C were compared.
The main conclusions obtained are as follows :
(1) In the first few cycles at 288°C, austenitic stainless steels SUS 304 and 316 exhibit cyclic hardening and then they transfer to cyclic softening stages after showing the maximum true stress amplitude at approximately 50 cycles.
(2) The ratio of plastic strain hysteresis energy per cycle ΔW to the product of true stress range and plastic strain range decreases gradually with increasing number of repetition of strain cycling.
(3) The fatigue toughness W_f (kgf · mm/mm³) versus N_c or N_f curves were obtained for some groupes of structural steels at room temperature and austenitic steels at 288°C.
(4) The relation between the constants a₀, and n in the n-th power strain hardening formulae at one half of crack initiation life or failure life are expressed by semilogarithmic formula as follows :
log a₀=2.406 (1/n) -1.828

抄録全体を表示

The cyclic stress-strain response and the fatigue property of spiral ropes under constant and variable amplitude axial loadings were investigated. The effects of a construction of wire rope and sea water environment on pulsating tension fatigue strength were also examined.
Pulsating tensile load fatigue tests of 1×7 wire ropes of 7 mm in diameter were carried out by changing stress ratio. An analysis of test results showed that the zero-to-tension fatigue strength at 4 x 10⁵ to 2 × 10⁶ cycles is about 30% of breaking load, and that the fatigue strength under any stress ratio can be predicted by an elliptic line drawn through the zero- to-tension fatigue strength on the ordinate of stress amplitude and the ultimate strength on the abscissa of mean stress.
Though the cyclic creep phenomena were observed, the axial strain ranges were kept nearly constant in each stress level. Then, the cyclic stress-strain relations were almost independent on both of stress ratio and stress history.
Pulsating tensile load fatigue tests were also carried out in air and in sea water environments on a 1 × 37 wire rope of 20 mm in diameter consisting of 37 galvanized steel wires, showing that the fatigue strength in air is lower than that of 1 × 7 wire rope in air. Furthermore, it was shown that the sea water environment operates not only detrimental corrosive effect, but also beneficial effect upon the fatigue life due to decrease in the internal wear among wires.
The results of random and p-distribution block loadings fatigue tests in air on 1×7 wire ropes showed a valid applicability of linear cumulative damage hypothesis to the estimation of fatigue life for engineering purpose.

抄録全体を表示

It is well known that Miner's cumulative damage sum at fracture is widely scattered and reason for the scatter of damage sum is not yet made clear. But, at present, Miner's rule is used in most cases to analyze fatigue strength of structural components under random loading conditions in spite of existence of uncertainty for application of the rule.
The purpose of this investigation is to find the above reason and to get the suitable value for critical damage sum at failure.
To achieve the above purpose, the following experiments were performed on plane specimens of mild steel in life range of about 3 × 10⁴ cycles. The experiments are axial reversed fatigue test with a minimum amplitude larger than fatigue limit, and loading conditions are constant loading amplitude, load and strain controlled random loading with exponential and uniform density. The relationship between Miner's cumulative damage sum and the stress-strain response under random loading was discussed.
As a result, it became clear that there existed good correlation between the critical cumulative damage value and the following parameter (σ_YR' k_R n_R) / (σ_Yc' k_c n_c), where σY_c' and σ_YR'are yield stresses, and k_c, n_c, and k_R, n_R are coefficients in stress-strain response (_a/σ_Y) =k (ε_a/ε_Y) ⁿ, S_a, ε_a : stress and strain amplitude, σ_Y, ε_Y : yield stress and strain, under constant amplitude and random amplitude loading respectively.

抄録全体を表示

The effect of strain rate and low temperature on the critical COD (δ_c) of structural steels has been experimentally investigated. The materials tested are 20 mm thick ordinary mild steel (KAS ; yield stress 28 kgf/mm²) and 60 kgf/mm² class high tensile steel (HW 45; yield stress 56 kgf/mm²). The 3-point bend COD testings were carried out at temperatures from -150°C to -10°C with crosshead speeds varied from 0.05 mm/min to 500 mm/min. For highest strain rate test, drop weight impact load was applied.
The results of the investigation are summarized as follows. Values of δ_c for KAS and HW 45 decrease with increase in strain rate. Particularly, the decrease in δ_c for both materials is remarkable at temperature below -50°C and at crosshead speed (strain rate) above 50 mm/min. The data plot of δ_c against rate-temperature parameter, Tln (A/ε) showed rather wide scatter band for both tested steels.

抄録全体を表示

A computer program has been developed by the present authors for the curved crack path prediction. We consider the proportional loading condition, and the loading parameter is increased or decreased in such a manner that the brittle crack is quasi-statically growing along the curved trajectory. Although dynamic behavior including inertia effects and dynamic material properties is beyond the scope of the present prediction, we expect that some of the essential features of the curved crack paths observed in actual brittle fracture or fatigue crack propagation can be obtained by the method.
The computational prediction is performed by the step-by-step method in cooperation with the stress analysis ahead of the crack tip and the determination of the curved increment of the crack growth. The stress distribution around the crack tip is first calculated by the method of the superposition of analytical and finite-element solutions proposed by Yamamoto et al., where the finite element data generation due to the crack growth process is to a certain extent carried out by automatical mesh rearrangement and nodal renumbering. Then a highly accurate asymptotic representation of the curved crack path, which is introduced in our first report assuming the locally symmetric deformation ahead of the crack tip, is employed for the path prediction.
Numerical examples are given for the crack path prediction in DCB type specimen, which was numerically and experimentally investigated in our previous report from the view point of crack path stability. After few steps of numerical calculation unstable crack curving is obtained, and the predicted paths show extremely good agreements with the experimentally measured crack paths. It is also observed that the Mode II stress intensity factor K_II is actually very small during the entire curved crack growth. Application of the present prediction method to more complicated problems, i. e. crack curving in structural elements, the growth of interacting cracks and etc, will be made in subsequent works.

抄録全体を表示

Jack-up type oil rigs are consisted of legs and platforms. The number of redundancies of legs are generally smaller than those of platforms. As a structure becomes less redundant, reserved strength after the initial yielding tends to decrease. So it is important to clarify the ultimate strengths of tubular joints which are leading causes of overall failures of the legs.
In the present paper, the authors carried out theoretical and experimental investigations into the local strengths of T-joints of circular tube.
Main conclusions obtained are as follows;
1) For the theoretical elastic-plastic analysis, the plastic node method was applied and its effectiveness was demonstrated.
2) Effects of the thickness and yield stress of the leg plate, diameters of brace and chord, stiffening ribs, leg guide, axial force exerted on chord and clearance between chord and leg guide upon the local strength of T-joints were clarified.
3) Simple formula was proposed for the ultimate carrying capacity of T-joints.

抄録全体を表示

A method of three dimensional elastic-plastic analysis of frame structures consisted of main transverse and longitudinal members like web frames, girders, side shells and longitudinal bulkheads etc. of oil tanker or are carrier etc. which are subjected to transverse extreme loads is presented.
The purpose of this paper is to predict development of plastic strain, generation of plastic hinge, local or single span buckling in the framed members and collapse load of the whole frame structure based on elastic-plastic analysis of transverse frame rings which are supported by longitudinal members like longitudinal girders, longitudinal bulkheads or side shells etc. elastically, providing that those longitudinal members are assumed to be supported by trans- verse bulkheads.
This theory is applied to analyze the experiments for models of the plane frame structure conducted by authors and the three dimensional structural models of are carriers conducted by T. Suhara et al. Good agreement of the results between each of them is shown.

抄録全体を表示

Recently, modern long stroke marine diesel engines are adopted for energy saving. While this type of slow running diesel engine with small cylinder number has the advantage of shortenning of engine room length and simpler maintenance, vibration of the engine column should be considered. A longitudinal vibration has been observed on the engine column of 5-cylinder long stroke diesel engine which is installed in 80, 000 DWT oil tanker built at Mitsubishi Nagasaki ship yard.
In this paper, the characteristics of engine vibration is studied as a first report. The longitudinal vibration of engine column can be calculated by FEM and mode synthesis. Calculated results show good agreement with the measured frequency. The parametric study is carried out by mode synthesis and simplified equation for frequency calculation is derived.

抄録全体を表示