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Article type: Cover
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Published: March 30, 1985
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Article type: Index
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Published: March 30, 1985
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Article type: Appendix
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Published: March 30, 1985
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Takeshi FUWA, Tadashi NIMURA
Article type: Article
Pages
1-7
Published: March 30, 1985
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Semi-captive model test technique, which is possible by means of quite simple equipments and measurement in a towing tank, to identify the maneuvering characteristics of ships is proposed. Using a container ship model, an experiment is carried out in the No.3 Experimental Tank of SRI, and methods of experiment and analysis are examined. A self-running ship model is captured by a towing block set on a towing carriage of the tank. Surge, sway and roll motions are constrained, and surge force and sway force are measured by a force gage on the ship model. The towing block has a vertical rod, around which yawing motion of the ship model is free, and the yawing is measured by a potentiometer. Heave and pitch are also free but not measured. During the model is running in the towing tank, ship motion is induced as a response to the steering of the rudder. Propeller thrust, rudder angle and normal force on the rudder are also measured and recorded. Analysing these measured data, coefficients of equations of maneuvering motion of the ship model are identified. Several methods of analysis are examined. In combination with oblique towing test and rudder angle test, sinusoidal steering test with the semi-captive test device gives rotatory derivatives. Therefore a role of PMM test can be played by this newly proposed experimental technique. More precise measurements by further improved device and comparision of the resulsdts with those of the free-running model test or captive model test are expected to confirm the validity of the method and utility for practical ship design.
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Naoya UMEDA
Article type: Article
Pages
9-17
Published: March 30, 1985
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When ships run at the high speed, the variation of the sinkage and trim cannot be ignored. Recently the Froude number of small fishing boats becomes larger and larger. So we must consider the running attitude to predict the seakeeping quality and manoeuvrability of high-speed fishig boats. This study dealed with this problem from the hydrodynamic point of view. Theoretical calculation based on the slender body approximation was applied to typical high-speed fishing boats. The two dimensional boundary value problem of the slender body theory was solved by using the integral equation method. The three dimensional correction involved the free surface effect. The calculated results are compared with the corresponding experimental values. Both calculated and experimental values indicate the drastic increase of trim (F_n=0.4∼0.5) and the floating tendency (F_n>0.5). And further, the slender body theory made it clear that these phenomena are caused by the free surface effect.
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Tsugukiyo HIRAYAMA, Yoshifumi YAMASHITA
Article type: Article
Pages
19-30
Published: March 30, 1985
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The authors already examined the ship capsizing in irregular waves probabilistically, but the capsizing in relatively large breaking waves was left un-examined. This is because that the controll of occurence of breaking wave is difficult inirregular waves. So,in this paper, we investigated the ship capsizing process (fishing vessel of 300 ton class) deterministially in deterministic breaking waves by adopting the so called concentration phenomena of Transient Water Waves. Here we used newly introduced remote sensing technique (position Sensor Device, P.S.D) by Prof. S.Takezawa. Furthermore, to confirm our experimental technique, we conducted a digital simulation by introducing an equation of motion which can describe the capsizing including sway, roll and heave mode. In this simulation, as external force, we mainly considered Froude-Krylov force from linear velocity potential of Transient Water Wave by integrating pressure along the ship surface up to the crossing points with wave surface of finite elevation. On the other hand, the breaking wave effect was represented by adding a pulse like force on the ship. From these experiments and simulations, the following conclusions are obtained. Namely, the minimum impact force generating capsizing, when considered as rectangular pulse, for actual ship of this study is estimated about 135ton and its duration is about 1.0 sec with wave height of about 7.5m. Time to complete capsize is about 10 sec. Furthermore, the direction of this impact force is about 25 degrees upwards, the net mass of impact water is about 210ton and the speed of breaking wave front is about 16m/sec. Finally it was shown that the boundary values, like impact strength and GM etc, generating capsizing seems to be estimated using this simulation.
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Norio TANAKA, Yoshiho IKEDA
Article type: Article
Pages
31-37
Published: March 30, 1985
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Effect of skeg and hard-chine on roll damping of small fishing vessels are investigated experimentally and theoretically. Experimental results show that they make the roll damping increase owing to the eddies creating at chine part and the skeg. In some cases, however, the increase of the roll damping due to the skeg is unexpectedly small. This is because that the negative damping due to the pressure acting on the bottom surface created by the eddies cancels the damping due to the pressure acting on the skeg surface. Prediction methods for the roll damping due to skeg and hard-chine are proposed.
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Yutaka MASUYAMA
Article type: Article
Pages
39-47
Published: March 30, 1985
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A method of numerical simulation to analyse the motions of a hydrofoil system was proposed. The method has been developed by applying non-linear equations with six-degree-of-freedom for calculation of the motions in arbitrary wave conditions. The simulation results were compared with those of towing tank test. The hydrofoil system investigated was made up of two surface-piercing dihedral foils with an inverted "T" foil. The towing experiments were performed in both head and following regular waves using the model in which the motions have two-freedom of heave and pitch, and the motions have three-freedom of heave, pitch and surge. In head wave condition,the simulation results of the motions in heave, pitch and surge, were in broad agreement with the experimental results.On the other hand, in following wave condition, the numerical simulation was a slight under-estimation of the experimental results but succeeded to show their tendency. The motion in surge, however, the comparison between the simulation and the experimental results was not available because of experimental limitations due to a resonant motion with wave.
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Masami HAMAMOTO
Article type: Article
Pages
49-58
Published: March 30, 1985
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In order to obtain an analytical solution of the lift acting on a ship hull running with the drift angle, slender bpdy theory is reviewed and extended for analizing the flow around a slender body with wake. As a result, a new flow model is presented to calculate the linear and nonlinear terms of the lift analytically. In this flow model, the wake is represented with a vortex pair behind the transverse section of the slender body and then, the strength of it is determined by making an assumption to keep it on the Fopple line, so that the so called Lagally force acting on the body is equal to zero. Therefore, we can obtain the differential lift from the change of momentum in each section of the slender body. Finally, the comparison between the lifts calculated by present theory and the experimental results of model tests are shown to confirm its usefullness and accuracy. It seems to be fairly good.
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Kiyoshi NEMA, Tetsuro IKEBUCHI, Yoshio YAMAGAMI
Article type: Article
Pages
59-69
Published: March 30, 1985
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In our previous paper, we carried out calculations of linear hydrodynamic forces and moment on vertical body of revolution considering its property of axisymmetry. Then we confirmed the accuracy of this calculation method from the comparison of the results of the calculation with those of the experiment. In this paper, first, we made the calculation of 2nd-order steady forces and moment on the basis of the method presented in the previous paper and compared the results with model tests in regular waves. The calculation method adopted in this study is based on the regular perturbation method, and steady forces and moment are calculated by the integration of hydrodynamic pressure over the wetted surface of body. The calculation results showed good agreement with the experimental results. Secondly, we carried out the motion tests in irregular waves using a bottle type model with long natural periods of heave and pitch. Long period motions of heave and pitch were observed in the model tests as we have expected. We calculated spectra of the slowly varying forces by Pinkster's method, estimated long period motions of heave and pitch and compared the calculation results with those of the model test. By the comparison, good agreement was obtained.
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Yasushi HIGO, Ichiro NAKAMURA
Article type: Article
Pages
71-78
Published: March 30, 1985
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In this paper, the non-linear hydrodynamic forces acting on a two-dimensional body moving laterally are discussed. The numerical calculations are made for a circular cylinder swaying with large amplitude on a free surface. The procedure of the calculation is based on the theory; it is assumed that the free surface elevation is small and that the interval of impulsive motions are small enough, so that the impulse response function can be used which have been already applied to the heaving motion in the previous report (1). The hydrodynamic forces are obtained from forced swaying tests and then these experimental results are compared with the calculations. For the most part, good agreements are observed. Additionally, applying this method, the wave resistance of a submerged circular cylinder is also obtained and compared with the calculated results of the report (5).
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Yoshiho IKEDA, Hiroshi HORIE, Norio TANAKA
Article type: Article
Pages
79-87
Published: March 30, 1985
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Interference effect between two oscillating circular cylinders in still water is experimentally investigated. The array of two circular cylinders with the same diameter is placed at the angle of 0゜,30゜,45°and 90゜ to the direction of motion. The spacing between the cylinder centers was varied from 1.2 diameters to 7 diameters. Drag and added mass coefficients, which are analyzed the experimental data by Fourier Analysis, are presented as the functions of the K_c number and the spacing of two circular cylinders. Lift coefficient and its frequency in occurrence are also obtained to show that the lift force decreases a little with decreasing the spacing and that the lift frequency is independent of the spacing.
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Yukio KOSHIBA, Takayuki SASAKI, Ichiro TANAKA, Toshio SUZUKI
Article type: Article
Pages
89-96
Published: March 30, 1985
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It is well known that the stern form plays an important role in the propulsive performance and the vibration problems induced by a propeller. This paper presents a design procedure based on the theoretical calculations to improve the stern form. The procedure is composed of the potential calculation, the boundary layer calculation and the thrust deduction calculation, which were already published. Through these calculations, the viscous resistance, the tendency of the wake pattern and the thrust deduction factor are predicted respectively to judge the total performance of the ship. Firstly, the accuracy of each calculation method is investigated to compare the predicted results with those of experiments for three models with different sterns and same forebody. Next, an example is shown to apply the design procedure to improve the stern form together with the confirmation test results. As a result of examination, it is found that the design procedure has a fairly good accuracy and is useful for the improvement of the stern form at initial design stage.
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Ryusuke HOSODA, Yutaka YAMAUCHI, Katashi TAGUCHI
Article type: Article
Pages
97-111
Published: March 30, 1985
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Cross-bi-spectral analysis method, the second order spectral analysis method, is applied to the analysis of response characteristics of added resistance in waves. The method was firstly developed by Dalzell under an assumption that resistance of ships in waves can be represented by a functional polynominal truncated upto second order terms with respect to incident wave height. By making use of results of resistance tests in irregular head waves, cross-bi-spectra and response characteristics are analyzed for two ship models. An analytical method is developed after Dalzell and Kim in order to analyze the response characteristics of added resistance in bi-frequency domain. Experimental and numerical results are compared with each other, and as the results of the study, it can be said that the cross-bi-spectral analysis method. is applicable to the analysis of added resistance of ships in waves.
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Soon-Kap KIM, Shigeru NAITO, Shoichi NAKAMURA
Article type: Article
Pages
113-126
Published: March 30, 1985
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Recently, there is a tendency to design the large full ships with lower-powered engine as the means for energy saving in ship's navigation at seas. Such a lower-powered ship is anticipated to show the different propulsive performance in rough seas, because the fluctuation of main engine load of lower-powered ship is relatively large as compared with higher-powered ship. The fluctuation of propeller load is nonlinear at racing condition in waves. It is due to the variation of inflow velocity into propeller, the propeller immersion and the characteristics of engine governor. In this paper, the theoretical calculation of the nominal speed loss and the numerical simulation for the nonlinear load fluctuation of lower speed ship in rough seas are carried out. From the results of calculatiion, the followings are discussed. (1) The ratio of nominal speed loss to the speed in still water. (2) The manoeuvring ability of ship and the operational ability of main engine in a seaway. (3) A method of the evaluation for the fluctuation of propeller torque and revolution on the engine characteristics plane. (4) The effect of engine governor characteristics on the propeller load fluctuation.
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Masatoshi BESSHO, Yoji HIMENO
Article type: Article
Pages
127-135
Published: March 30, 1985
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In the preceding paper the authors made an attempt to obtain optimum profiles with minimum drag in two-dimensional Stokes flow, using an inverse method for optimization developed by Bessho. The present analysis is an application of the same method to three-dimensional Stokes flow. The elementary optimum shape with a prescribed volume which is obtained by the present computation, is found to be entirely similar to the result by Bourot. Other optimum shapes with various restrictions are also obtained. It is found that the optimum shape in the present analysis is quite similar to other cases based on flow models like boundary layer flow and two-dimensional Stokes flow.
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Keiji SUEMITSU, Norihiro MATSUMOTO
Article type: Article
Pages
137-146
Published: March 30, 1985
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A prediction method of motion basd on a simulated calculation in the time domain is usually adopted to design and evaluate dynamic positioning capabilities of offshore structures under varying environmental conditions. In this paper, the prediction method of dynamic positioning motion using hydrodynamic forces and moments obtained from captive model tests was proposed. In addition to this, the sea tria1 of the semi-submersible drilling platform was carried out, and from the acquired data, the dynamic response characterstics of motion to the thruster output were calculated. Comparing the results of the sea trial with the predicted results by the present method, the validity of this prediction method was verified. Then, some simulated calculations concerning the dynamic positioning characteristics under combined environmental conditions of current, wind and waves were carried out. It was shown from the power spectra of motion and thruster output that the wave filtering technique was important for reducing the useless operation of thrusters.
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Katsuji TANIZAWA
Article type: Article
Pages
147-154
Published: March 30, 1985
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The boundary element method is applied to the analysis of two-dimensional self-similar wedge entry problem, assuming that fluid is incompressible and inviscid, gravitational effects are negligible and impact velocity is constant. In order to solve the problem exactly, formation of splash is taken into consideration. The calcuration is carried out for cases of dead rise angle β=45°,30°,20°,15°,10°,8°,6°and4°. The shape of free surface with splash, the impact pressure distribution over the wedge and velocity vectors of the flow arround the wedge are calcurated and compared with Wagner's theoretical results and Hughes's numerical results as well as experimental results. It is concluded that the splash should not be neglected to estimate pressure distribution over the wedge correctly.
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Tamaji IKEDA, Mitsuo YAMAMOTO, Yozo SHIBATA, Tetsuji YUASA, Yoichiro I ...
Article type: Article
Pages
155-160
Published: March 30, 1985
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As the new type of underwater electric cable system used for deep submergence research vehicles and deep sea equipments, pressure compensated, oil-filled cable system is being developed. In contrast with the usual underwater cable system which requires hard adhesion between connector's shell and cable sheath by molding rubber, the oil-filled cable system is anticipated to solute any probrem caused by water leakage through deteriorated adhesion surface, because no chemical adhesives is required. It is expected too as the other merit that the operation effeciecy of wiring work under construction and repairs will improve, for it is easy to separate and connect individual hardwares of oil-filled cable system. On this development, oil-filled cable and connectors were manufactured for trial and tested successfully, therefore fair prospect of oil-filled cable system operated at 6,000m depth has been confirmed. From now, the durability of oil-filled cable and connectors will be tested finaly and underwater wiring junction box will be manufactured and tested through continual development. In this paper, the contents of enforced development of oil-filled cable and connectors is reported.
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Mitsuo KISHI, Yoshisada MUROTSU, Yoshinori MINAMI, Katashi TAGUCHI
Article type: Article
Pages
161-167
Published: March 30, 1985
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The optimum design pocedure is proposed for offshore platforms minimizing the expected total cost which is composed of the structural cost and the expected maintenance cost. The design variables are the geometrical dimensions of the structure while its configuration and the materials to be used are given. Structural failure is disregarded in the present study since its probability is generally much smaller than the partial failure probabilities and the cost induced by structural failure is difficult to evaluate. The design is performed for the platforms subjected to wave loads. The optimum design problem contains many parameters which are difficult to estimate exactly, and thus the optimum solution may not be absolute. However, the failure probability corresponding to the optimum solution could be used as an index for specifying the allowable failure probability in probabilistically design problem. Numerical examples for a jacket-type offshore platform are provided to illustrate the applicability of the proposed method.
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Sakito KAMEI, Masahiro SUDO, Junichi IKEDA, Shojiro HATO
Article type: Article
Pages
169-175
Published: March 30, 1985
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Recently, heavy cargo ships are apt to have peculiar hull structures to speed up loading and unloading heavy cargoes. The ship dealt with in this report is one of these ships, and has a unsymmetrical hull section with extraordinary large hatch openings. Owing to the peculiar hull structures as mentioned above, the following problems are apprehended. (1) Stress distributions in each side structure due to vertical bending moment are different from one another because of a unsymmetrical hull section. (2) Warpings and warping stresses of the hull due to torsional moment become larger because of large hatch openings. In order to clarify the problems, the whole hull structural analyses using 3-dimen-sional FEM model and full-scale measurements are carried out. The main results are as follows, (1) The results of stress distribution of the hull using the beam theory have good agreements with those of the 3-D analysis. (2) The differences of stress distribution in each side structure are negligibly small provided the scantlings of each side structure has same inertia. (3) A notable shear lag phenomenon is observed in side shells under the horizontal bending moment, however not observed in bottom shells under the vertical bending moment.
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[in Japanese]
Article type: Article
Pages
177-178
Published: March 30, 1985
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[in Japanese]
Article type: Article
Pages
179-184
Published: March 30, 1985
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Article type: Appendix
Pages
185-186
Published: March 30, 1985
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Article type: Appendix
Pages
187-191
Published: March 30, 1985
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Article type: Appendix
Pages
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Article type: Appendix
Pages
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Published: March 30, 1985
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Article type: Appendix
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Published: March 30, 1985
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Article type: Appendix
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Article type: Appendix
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Article type: Appendix
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Article type: Appendix
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Article type: Appendix
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Article type: Cover
Pages
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Published: March 30, 1985
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Article type: Cover
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