OFFSHORE ENGINEERING
Mega-Float
1. Introduction
The Mega-Float research project was already described in the preceding issue (March 1999). The report is updated here as the scheduled research work has now been almost completed.
The first three-year period (Phase 1) of this research attempt, launched in 1995, was spent on elemental technologies needed for Mega-Float construction, and they were successfully established. It was followed by Phase 2 (from 1998) in which application technologies for the construction of a Mega-Float airport were worked out, and the whole project will be completed in March 2001. All the experiments involved have already been finished, and the 1,000-meter long airport model, then the world's largest floating structure (registered with Guinness World Records), began to be dismantled in November 2000, when the experiments ended, and by December it had disappeared. The disassembled blocks are scheduled for use as medium- or small-sized floating structures to serve as a disaster prevention base, parking lot, pier, floating park and so forth. This article is a report on the fruits of the Phase 2 research.
2. Fruits of Phase 2 Research
2.1 Outline of Research
The Phase 2 research, under the theme of "Corroborative Research on the Use of Mega-Float as Airport," was planned to involve building of an airport model officially qualified as a temporary airport and use of the model mainly for various verification experiments on airport functions.
In April 1998, fabrication of modular units and mooring equipment of the experimental airport model was started in the factories of a number of participating companies, and from June 1999 onward the mooring equipment was installed and the units were joined in the location for installation until the completion of the model in August. In this way, by fully utilizing the elemental technologies established in Phase 1, the airport model was brought to completion in about 17 months. The 300-meter long model built in Phase 1 was converted and used as part of the new model.
After preliminary work was finished, verification experiments using real aircraft were started in September 1999, and an approximately 13-month series of experiments were finished at the end of October 2000.
Principal dimensions of the airport model are as follows, and its general shape is shown in the photograph of Fig. 1.
Length ... About 1,000 m
Breadth ... 60 m (121 m in some part)
Depth ... 3 m
Draft ... About 1 m
Total area ... About 8.5 ha
The following five themes were selected for the Phase 2 research after careful consideration: (1) verification test of the landing facilities, (2) comprehensive aircraft takeoff / landing test, (3) development of an airport function simulation program, (4) research on airport equipment and (5) environmental assessment. Findings of the research are outlined below.
2.2 Verification Test of Landing Facilities
An ordinary airport has an instrument landing system (ILS) for electronically informing the incoming aircraft of the direction and angle of approach it should take, and precision approach pass indicators (PAPI) for visually indicating the angle of approach. These landing guidance devices for informing the aircraft of the right approach course may have serious adverse effects at a long distance if their positions of installation deviate, even only slightly, either vertically or laterally. The ILS has a localizer (ILS / LLZ) indicating the direction and a glide slope (ILS / GS) indicating the angle of approach, and both were checked for proper performance. The ILS / GS notifies the aircraft of the right approach course by utilizing the phase difference between an electric wave directly transmitted from an antenna and another that is once reflected by the ground (the upper deck in this experiment). The behavior of this reflected electric wave was one of the major unknown factors because a floating structure is materially different from the ground and its surface undulates, if only slightly, over the sea waves.
A research on the next generation landing navigation system now under development was also carried out.
(1) Research on landing equipment
Various items of aircraft equipment which were likely to be affected by the behavior of the floating body were checked by using airplanes of the Ministry of Transport for testing purposes. The tests were conducted by low pass flights, in which the aircraft took a landing attitude and rose again after the performances of these landing devices were checked, and by level flights. The low pass flying is shown in Fig. 2. For the flight tests, the MOT's YS-11 and Beachcraft 99 and a Dornier plane of the Science and Technology Agency were used.
The flight tests were carried out in a number of rounds for 25 days in total, involving some 350 flight checks altogether.
During the experiment, electric waves and light rays were measured with testing machines, and at the same time the vertical motions and the angles of inclination of the floating model were measured to determine the relationships between the electronic / optical aspects and the behavior of the model. The sea was relatively calm during the tests, even the highest wave being no more than about 0.5 m (insignificant wave height), when the floating model moved up and down by about 4 cm. All the test results were satisfactory, with no particular problem reported.
(2) Test with deformed GS reflective face
As the waves were insignificant during the tests, the model body, i.e. the GS reflective face, was deliberately deformed by filling ballast tanks with water. While the extent of deformation was about 30 cm, no change was observed in the GS electric wave.
(3) Research on future air navigation system (FANS)
FANS is a system which informs an aircraft of its accurate position including the altitude and the direction according to information from satellites. It is an integrated air navigation system now under development, having a landing guidance function as well. Since this system for use in a floating airport would have to be able to take account of vertical shifts due to tidal fluctuations, its basic functions were checked, and necessary modifications were studied. This aspect of research was entrusted to the MOT's Electronic Navigation Research Institute, a specialized body in this field, which arrived at a conclusion through theoretical research and flight tests that there would be no technical problem.
