The author proposed "vertically movable tension leg mooring system" in the previous paper for the purpose that an offshore floating body subject to comparatively large static horizontal loads for its scale is moored so that the occupied plane area of the mooring system may become as small as possible. And its static mooring characteristics were discussed with model calculations to demonstrate the advantages compared with the conventional tension leg mooring or the catenary mooring. In this paper, the response of the floating body and the mooring system to waves is studied to investigate the dynamic effect of the massive template hung from the floating body in the proposed system. As a result, it is demonstrated that the dynamic effect of the mooring system on the wave exciting motions of the floating body is quite small when the system is properly designed. And it is found that the tension fluctuation could generate the slack and taut repetition in the windward side mooring chain which connects the sea floor anchor and the template hung from the floating body. Finally, some guidelines to reduce such phenomenon are shown based on the parametric case study.
In this research, the numerical analysis method which can predict the residual stress distribution after tempering with sufficient accuracy was established. First, residual stress distribution of the cylinders test material after quenching and tempering was measured. Next, the creep test was done using the material after quenching, and the formula which predicts the creep strain of each material was clarified. Finally, comparison and examination of the experimental and numerical analysis value of the residual stress distribution after tempering was performed using the formula which predicts creep strain drawn from the experiment. By using the linear expansion coefficient, the yield stress of heating and cooling process of tempering, and the formula which predicts the creep strain, the residual stress distribution after tempering can be predicted with sufficient accuracy by numerical analysis. Moreover, reduction of the stress by tempering has the great influence by the fall of yield stress and creep strain, and the influence of strain resulting from a deposit of the carbide which arises in the heating process of tempering hardly affects residual stress distribution.
In this paper, we have an aim developing the next-generation-type airship for resolving airworthiness problems especially for mooring condition. For this purpose, we propose the TORUS-TYPE AIRSHIP. The torus-type airship will have the advanced characteristics of airworthiness especially at mooring condition, and have advanced maneuverability especially for movement of any direction(forward, backward, left, right, rotation), but some instability at flight condition are considered.At first, we designed a simplified torus-type airship model, and carried out towing experiments about aerodynamic characteristics of the model in upper water space of our huge towing tank instead of carrying out experiments in a wind tunnel. By introducing torus-type airship, we will be able to minimize the mooring area, reduce the maximum mooring forces, and in the result prevent the body damage at mooring. In the second, we developed a 3D Flight-simulation program using the data from the experiment. By using the numerical simulation, we can evaluate the performance of the torus-type airship from various viewpoints including mooring.
Automatic designing of piping layout is challenging since it is composed of several numerical and/or combinational optimization problems, e.g., routing problems of pipes including branches, and arrangement problems of equipments. This paper presents a new approach based on a simple idea that the branches of pipes are considered to be a variety of equipment. Accordingly, the pipe routing problems are fairly simplified by removing the branches, and it derives a lot of efficient algorithms to solve the pipe arrangement problems. One is a multi-objective genetic algorithm (MOGA) in which the gene represents both the locations of the equipments and the arrangement of the pipes. And a new simple and efficient crossover operation which appropriately merges two different piping layouts (but of course the PID is the same) is proposed. In order to provide a fairly good initial population for the MOGA, a new heuristics making use of self-organization techniques to arrange equipments is proposed. The efficiency of the proposed approach is demonstrated through two experiments, one is a designing problem including five valves, one pump, and five branches, and the other includes seven valves, one pump, and six branches. The objective of the optimization in the experiments is to minimize the length of the pipes, the number of elbows, and the valve operability cost. The algorithms are programmed using Java language. Although the automatic arrangement system used in the experiments is academic, the concept of the proposed approach will be accepted in practical systems.
It is clarified that fatigue crack propagation rate of the optimum ferrite-bainite (F/B) steel shows superior resistance in comparison with conventional ferrite-pearlite (F/P) steel. In this study, fatigue crack propagation properties of both F/P steel and the F/B steel are investigated in consideration of opening/closure of fatigue crack tip. Fatigue crack propagation tests have been carried out under various loading conditions ( constant amplitude cyclic loading, block amplitude cyclic loading and constant amplitude cyclic loading and a few static large spike loads ) for acceleration, retardation and non-propagation of crack growth rate. From the results of this study, fatigue crack propagation phenomena are shown in hysteresis loop for fatigue crack tip, and fatigue crack growth retardation and non-propagation bring long tail of hysteresis loop for fatigue crack tip. And effects of retardation in the F/B steel are larger than that in F/P steel.
Navigating in two layers is a common case for ships. It's reported the rigid bed of shallow water areas, such as ports, navigation channels, harbors and river estuaries, is often covered by a mud layer which consists of a dense mixture of water and particles of sand, clay and etc1). Additionally, it's well known the density stratification occurs in Norwegian fiords and ice-rimmed seas. It's due to the variation in salinity and temperature with depth. When navigating at a low speed in such sites, a ship accidentally experiences the large drag mainly due to the wave-making on the interface. Understanding the ship hydrodynamics in two layers is a must for her safe navigation. However there apparently has been not so many experimental and theoretical works so far.This paper proposes a new method to solve the ship steady wave-making problem in two layers. A Green function which satisfies the linearized interface condition and the rigid bottom surface condition was newly derived and used for the expression of the velocity potentials. In this method, the hull shape and the interaction between the free surface and the interface can be considered more exactly so that the ship wave-making in two layers can be discussed more correctly. First, the wave patterns generated by a single source and the wave-making resistance of a submerged spheroid were calculated to prove the validity of the proposed method. Second, Wigley hull was used for calculations and it was numerically confirmed that the sharp increase of the wave-making resistance occurred when navigating close at the critical velocity of the internal waves. The proposed method succeeded to capture the waves both on the free surface and interface properly through a series of calulations.
It is significant to predict ductile fracture initiation in plastic forming of metal materials. Tube hidroforming (THF) is attracting general attention.THFprocess requires the control of internal liquid pressure and axial compression. In this case a ductile fracture may occur under stress triaxiality lower than that for uniaxial tension loading. In this report, combined longitudinal tensile and compression to thickness direction tests using thin plate specimens inA5083-Oaluminum alloy to obtain low stress triaxiality were carried out. On the basis of observations of ductile fracture processes it was founded that ductile fracture was shear type fracture controlled by a nucleation of micro-voids in this test. It is seemed that the local inclusion-matrix interfacial stress was constant independently of any stress ratio of tension and compression. Additionally, THFtests for SPFH590 tubes were performed. It was confirmed that the critical interfacial stress obtained using FE analysis forTHFtest was constant.
In various contexts of the shipbuilding industry as well as in the marine transportation industry, the relocation of objects such as steel plates, containers, etc. by using cranes is a common task. In these operations, crane operators are faced with the problem of starting with a given distribution of objects and restacking them in order to achieve a desired distribution using the least possible effort or movement of the crane. This type of problem involves a practically infinite number of solutions, since the possible combinations of operational order are so numerous. Therefore, it is difficult for the operator to determine the optimal sequence from the candidate processes, and it also is difficult to present a general method that can solve this problem with high degrees of efficiency and reliability. As a result, in practical situations the crane operators on site usually decide the sequence according to their experience and intuition. However, sometimes the planning of the crane operation process is very troublesome and time consuming and is thought to be not necessarily suitable for human beings.In this study we apply a genetic algorithm (GA) that excels at finding solutions to combinatory problems. The sequence of a crane's operation is represented in string expression and with the merit of a population search (i.e., a simultaneous multi-point search) of the GA, excellent operations were efficiently obtained for the practical examples shown in the paper.
We verified the applicability of a fiber-optic sensor to deformation monitoring of the seal equipped with an air cushion vehicle such as a surface effect ship (SES). The seal is a membrane structure made of an elastomeric material. It is difficult to measure deformation or vibration of the membrane structures by using a sensor which is fixed on it. In laboratory tests, we could measure strain-rate of the seal material subjected to cyclic loading by using the fiber-optic sensor adhered to it. Then, in monitoring tests of a small model of the seal with the sensors, frequency or amplitude of vibration was changed according to the velocity of water flow or the length of the bottom in water. In this paper, we described the results of these tests and showed the good applicability of the fiber-optic sensor to measure the response of membrane structures which have elastomeric properties.
The present paper proposes a method to classify objects' surfaces by analyzing relative spectrum of an ultrasonic echo with respect to the spectrum of an echo from a flat plane. Time-of-flight is obtained from linear phase shift between the reference echo and the echo from the object. Distance between two planes separated along longitudinal direction is obtained from frequency dips in the echo spectrum. Surface features such as an edge of a prism can be recognized by a decrease of power in higher frequencies and constant phase shift with respect to the reference echo. It is also shown that phase spectrum is useful for determining arrival time of an echo coming from an oblique surface with respect to the center axis. The theoretical analysis and some experimental data are presented.
A numerical simulation scheme has been developed for the vortex induced vibration response of flexible risers and has been validated by experimental results. In the experiments, a riser model was forced to surge by fixing the top end of the model to a forced oscillating apparatus in an experimental towing tank. To measure the three-dimensional motion of the model, six CCD cameras were used for each direction, horizontal and vertical. A numerical simulation scheme for three-dimensional dynamics of the flexible risers considering the VIV effects has been developed which is based on the ‘Hamilton's principle’and mode expansion method. The numerical simulation method was validated by comparing with experimental results and showed a good agreement.
At the design stage of a ship, the engine output is determined by taking into consideration of a lowering of performance. The lowering is mainly caused by winds, waves, aging deterioration and biological fouling. To keep the speed in actual seas, the output is appended to a proper ratio, which is called sea margin.The component of sea margin divides into two groups. One is a weather effect and the other is a deterioration effect which progresses with time. For the estimation of the weather effect, weather forecasting data of 8 years were applied. Also, for the estimation of the deterioration effect, roughness increase of the hull was taken into account.In this paper, the desirable sea margin is derived rationally. As an example, for a coastal chemical tanker, Shinko Maru No.28, performance estimation and voyage data analysis were carried out.By comparison with the estimated and analyzed sea margin, it made clear that the estimated sea margin agrees with the analyzed one. Consequently the physical meaning of sea margin is explained as a function of wave, wind and time.
In developing large-scale products, it is important to review the design of products from multiple perspectives and to prevent inconsistency in design. Web-based information sharing is very promising for realizing efficient design reviews. In this paper, we propose a design review system based on 3D models shared on the Web. We call comments and locations defined on a 3D model as annotations. In our system, annotations on 3D models are stored in a client-server framework, and can be shared among the design team. We propose four types of annotation methods, which consist of billboards, direct 3D painting, 2D drawing on a snapshot, and feature extraction. Since all of them are defined using 2D strokes and transformation matrices, they can be very easily and interactively specified by reviewers. These annotated regions are associated with comments, and are shared by designers through network. We implemented our review system and applied it to 3D models represented in the VRML format.
Japan Marine Science and Technology Center (JAMSTEC) has been engaged in research and development of ocean-wave energy extraction technology for many years now. In particular, work began in 1987 an offshore floating type wave power device called “Mighty Whale”. Theoretical investigations and model tests led to an understanding of the hydrodynamic behavior of device, and provided information of constructing for the prototype of Mighty Whale. The open sea tests were started on the 10th of September 1998. Tests were conducted until March 2002. In this paper, firstly, the characteristics of hydrodynamics with “Mighty Whale” have been examined comparing with the results of experiments and calculations approving a numerical method being developed. Secondly, using developed numerical analyze method, the displacements of water level inside air chambers of “Mighty Whale” have been calculated. The generating outputs of “Mighty Whale” have been estimated using these results, the efficiency of primary conversion and the efficiency of secondary conversion of “Mighty Whale” getting through the experiments that had been carried out.
The purpose of this study is to investigate the effect of pitting corrosion on local strength of hold frames of bulk carriers. In the present study, a series of 4-point bend tests with structural models which consist of web, shell and face plates has been conducted. Artificial pitting was made on the web plate. In these tests, two equal concentrated loads has been applied at the one third points of simply supported models so that compression load would act on the face plate. In this testing condition, lateral-distortional buckling occurred before ultimate load was reached and local buckling of the face plate was observed after the ultimate load. It has been revealed that the effect of pitting on the web plate on lateral-distortional buckling load was small but ultimate load decreases with the increase of area ratio of pitting. As a result of FE-Analysis, the ultimate load of the structural models where pitting prevailed uniformly on the web plates was found to be almost the same as that of the structural models where the web plates have uniform corrosion corresponding to the average thickness loss.
In this paper we propose a Galerkin's method for the hydroelastic problem of a rectangular plate on shallow water in waves. The bi-directional complex Fourier series are adopted as a displacement function of the rectangular plate, which complex conjugates are adopted as weighting functions. The weighted residual method leads to the weak form to be solved. On the plate boundary, the weak form should be combined with Boundary Element Method. A boundary element, in which two nodes are arranged at two Gauss-Legendre integral points, is proposed to obtain the same results as 3rd order polynomial interpolation. Present Galerkin's method can calculate large ratio of plate length and incident wavelength quickly.
The purpose of this study is to investigate the effect of pitting corrosion on local strength of hold frames of bulk carriers. A series of 4-point bend tests with structural models which consist of web, shell and face plates has been conducted. Artificial pitting was made on the web plate and bending moment has been applied so that tensile load would act on the face plate. In the case of the long-span model, when pitting concentrated on the web plate near the face plate, cracks were initiated at the bottom of the pits. In the case of the short-span model, local buckling of the web plate occurred near the shell plate and the deformation behavior was strongly affected by the existence of pitting.Following the experiment, an elasto-plastic analysis has been carried out to simulate the deformation behavior and buckling behavior observed in the experiment in order to verify the method of modeling members with pitting corrosion.
The first report dealt with the investigation of pitting corrosion observed on hold frames of a 14 year old bulk carrier. Tensile strength and buckling strength of actual members taken from the bulk carrier were also investigated.In the present study, a series of tensile tests and compression (buckling) tests has been conducted using test specimens with artificial pitting under a wide variety of testing conditions to investigate the effect of pitting corrosion on the strength in more details. The following results have been obtained;- Tensile strength decreases gradually and total elongation decreases drastically with the increase of thickness loss. The reduction of tensile strength and total elongation is large when the original thickness is small.- In general, ultimate strength of pitted members under compressive loading is smaller than that of uniformly corroded members in terms of average thickness loss.Following the experiment, an elasto-plastic analysis has been carried out to simulate the buckling behavior observed in the compression test in order to verify the method of modeling members with pitting corrosion.
The objective of this study is to investigate the effect of pitting corrosion on local strength of hold frames of bulk carriers. In the present study, a series of 3-point bend tests with structural models which consist of web, shell and face plates has been conducted. Artificial pitting was made on the web plate. In these tests, a concentrated load has been applied at the center of simply supported models so that compression load would act on the face plate. In this testing condition, local buckling occurred just after ultimate load was reached. It has been revealed that ultimate load decreases with the increase of area ratio of pitting. As a result of FE-Analysis, the ultimate load of the structural models where pitting prevailed uniformly on the web plates was found to be almost the same as that of the structural models where the web plates have uniform corrosion corresponding to the average thickness loss.
