Tank Model Tests Research Articles

Development of wave power generators

The Japan Marine Science and Technology Center (JAMSTEC) started a study on “Wave Power Generator” in 1974. After two years of water tank experiments, the ship type buoy model seemed to be the best compared to the other models with respect to converting efficiency of wave energy into air output, easy construction and safe mooring. JAMSTEC has ordered a prototype of the system which is a massive floating structure, 80 m in length, 12 m in width, 5 m in height and 500 tons in weight. The structure consists of buoyancy rooms and air rooms, and the bottom of the air room is opened to the sea water. When a wave passes through an air room, air is pushed out of the room and sucked into the air, as the water levels rises and falls. Thus electric power is generated with the air turbine generator by the air motion in and out of the air room. The output power of the generated electricity is assumed to be about 2,000 kW, in case of 3 m wave height and 6 sec wave period, according to our theoretical calculation. The system is moored with a chain to the seabed. We have prepared many anchors and a 94-mm chain for the main mooring line of a safety load of 650 tons. A 1/10 scale model test in the water tank showed that the drag force was not so large, and it was about 100 tons to the full scale structure in the rough sea. The first open sea test will be carried out in 1978.

Dynamic Responses of Floating Structures

Theoretical and experimental studies were conducted to investigate wave loadings on, and structural responses of, floating platforms. Strip theory is applied to calculate wave forces on the structure. The wave forces, the interaction between waves and the structure, and the resulting inertia forces are then applied to the structure, as external forces, to calculate member stresses. The structure is treated as a space frame for stress calculations. Typical characteristics of dynamic stresses resulting from wave loading are considered. A wave tank model test program was conducted to collect strain data. The model test program, measurements, and correlation of measured data with theoretical calculations are considered. Satisfactory agreement was found between theoretical stress calculation and measured data.

Statistics of Ocean Wave Groups

Abstract Statistical parameters are derived that describe the occurrence probability for the number and height of consecutive waves in as group, which are large compared with the average wave height. Such wave groups can create extreme forces in mooring lines of large vessels. All the parameters that describe the statistics of wave groups can be derived from the energy spectrum representing the sea state, if the energy spectrum is assumed to contain only a narrow band of wave frequencies. Good agreement was found between the theoretical expression derived in this paper and actual wave data. Introduction It has been shown by Hsu and Blenkarn that be long-period sway motion and peak mooring-line force observed in a model study of a barge resulted from the combined action of a sequence of consecutive high waves in the random wave train. Such a sequence of waves will be referred to as a wave group. Independent model-tank tests conducted by Remery and Hermans substantiated the findings presented in Ref. 1. it is anticipated that the presented in Ref. 1. it is anticipated that the action of wave groups may also be important in other types of ocean engineering systems that are subjected to horizontal motions with periods much longer than the period of individual waves. Such systems could include dynamically positioned vessels. In the analysis and design of such systems it would be prudent to check whether the action of wave groups could subject the systems to motions beyond those calculated on the basis of individual waves. As a basis to perform such a check, one can use either recorded wave groups measured in the sea, or wave groups generated in a model tank. There are also available electronic and numerical methods to simulate ocean waves. However, to make proper engineering decisions, one would need to know whether the occurrence of such wave groups is a common or a rare event. More specifically, one would require a probabilistic description of the basic characteristics of wave groups in order to assess whether a system is likely to survive. The purpose of this paper is to develop tools with which one can characterize the statistics of wave groups in terms of occurrence probabilities. No attempt is made here to illustrate how such statistical tools could be used in practical engineering. Rational procedures for utilizing such tools for specific problems can best be developed by individual users. Theoretical Derivations In this paper a wave group will be defined in terms of the envelopes of wave crests and troughs as shown in Fig. 1. The distance between the crest envelope and the trough envelope will be called the height envelope, whereas the distance between the crest envelope and the mean water surface will be called the amplitude envelope. The height envelope indicates the change of wave heights. Similarly, the amplitude envelope indicates the change of wave amplitude. In reality, ocean waves are not symmetrical as is implied by the term "amplitude". Measured from mean water level, the distance to the crest of a wave is generally greater than the distance to the trough. However, in order to use the theoretical methods developed by Rice, we shall assume that the wave amplitude is half the wave height. As one can see from Fig. 1, the height envelope has the characteristics of a wave with a much longer period than the individual waves. period than the individual waves.

A Study of Motion and Strength of Floating Marine Structure in Waves

Many floating marine structures of various kinds have been constructed for varied purposes ; however, researches and technical experiences for such structures, some of which are quite different from conventional ships, are not so exhaustive and comprehensive, as those for the ships, and many problems still remain unsolved.Taking an opportunity of construction of newly developed iron ore loading station with submersible, column stabilized, catamaran hulls, a systematic study was made on the motion and strength of the structure in waves. Theoretical analysis of the motion and strength of the structure was carried out first. Secondly, the theoretical results of its motion in waves were compared with that of model tank test. Thirdly, in order to check the theoretical calculation the stress measurements were made at the time of launching. Finally, during the ocean towage of the structure from Japan to India, comprehensive measurements of motion of and stress in the structure in waves were conducted simultaneously with the accurate measurements of waves by means of a clover-leaf buoy.Conclusions of the present study are summerized as follows : 1) Motions of floating marine structure with catamaran hulls in irregular waves can be estimated with sufficient accuracy for engineering purpose by the spectral computations of responses utilizing the linear superposition principle using the response functions which are obtained by the strip method usually used for ship motions in oblique waves and are corrected by the results of model tank test.2) Longitudinal stress of the structure can be estimated with fairly good accuracy, by the finite element method using the response function of longitudinal bending moment in waves which is also calculated by the strip method.

THEORETICAL AND EXPERIMENTAL EVALUATION OF OIL SPILL CONTROL DEVICES1

ABSTRACT This paper describes the first phases of a program aimed at providing a means for evaluation of existing oil containment devices (booms, barriers, etc) and for improving basic design through variation of geometric and physical parameters. A mathematical/computer model is derived that describes the behavior (forces and motions) of a spill-control device in given environmental conditions of wind, current, and waves, and specified deployment configuration. The results of evaluating 14 booms in terms of probability of mechanical (structural) and spill-control failure are discussed in general terms as are the results of model-tank tests aimed at obtaining data for comparative evaluation of booms and for validating and improving the analytical model A more definitive statement of results awaits the completion of at-sea experiments and data analysis which are presently being carried out.

Study Of Boundary Layer Turbulence Stimulations Of Ship Models Tested In A Towing Tank

The parer present result of theoretical and experimental investigation of the natural and artificial turbulence timulation of the boundary layer on ship model by towing tank tests. A dependence of the extent of the laminar and transition regions in a boundary layer upon the model hull form is shown. Some practical tips are recommended both for the choice of trip wire and for the correction introduced in the results of model basin test for laminar region of the boundary layer near the trip wire and for its parasite resistance. Introduction of the proposed corrections brings about an essential increase of reliability of ship resistance data derived from the result of model test in the towing tank. Results of this study have been reported at the XII International Towing Tank Conference, Rome, 1969, [1].

An extended use of model tank test data

An extended use of model tank test data

Modern Improvement of the “Straight-Side System” of Hull Form

This paper describes the idea of improvement of the author's straight side hull form, which was explained in his paper “two patent systems of simplified hull forms”, read at the autumn meeting of this society in the year 1938. The new -system claims that it can be applied to the designs of any sea going vessels of ordinary proportions and fineness, and advantage may be taken in lower construction cost, easier, more rapid and more acculate hull construction work.Although with the earlier system its application has been somehow limited in scope for fine lined vessels, the present system has no such limitation. The results of model tank tests comparing the performances of the models of this system and of an ordinary good form are shown in the accompanying graphs. It will thereby be understood that the hull form of the new system is at least as good as an ordinary good form in relation to the question of economical propulsion.