PURPOSE: To prevent 4-fold wrinkles from being produced at the time of expansion of a cover so as to make it difficult for a film to be broken by an installation of a curved and columnar formed film body inside the cover at the jointing portion of a slope part to the body of the cover in a mobile dam by a cover made of a flexible film and the like.
CONSTITUTION: A curved air column film body 5 and the like is stuck with half of its circumference on the inside of a cover 4 at the jointing portion of a slope part 1 to a body 2 of the cover 4 made of a flexible film. At the time of expansion of the cover body 2, air is filled into the air column film body 5 by a blower 14 or 15. By doing so, sharp 4-fold wrinkles are not produced but gentle two fold wrinkles are only produced on the cover 4 of the dam film and the like to prevent breakages of the dam film against waves and so on.
MATSUOKA HARUHIKO
MARUYAMA ICHIROU
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