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|Title alternative ||:||Studies on Measures against Typhoon for Horicultural Facilities in the Southwest Islands|
|Authors ||:||玉城, 麿|
|Authors alternative ||:||Tamaki, Maro|
|Issue Date ||:||Mar-2011 |
本研究では南西諸島における農産物の安定供給体制の構築に寄与するため，台風対策技術の高度化に取り組んだ。農業関係者や生産現場からは，耐風性に優れ，かつ低価格で導入できるような園芸施設が求められている。これらの要望に応えるために，既存施設の問題点やこれまでの台風被害状況を調査，分析し，その結果を踏まえて新たな園芸施設の開発，防風施設の遮風効果の検証，園芸施設の風観測システムの高度化に関する技術開発を行った。まず，沖縄県の園芸施設の特徴として，台風来襲時の風荷重軽減を目的に被覆材に網を利用することがあげられる。しかし，これらの網の通風特性は明確でなく，使用時の選定基準も曖昧であることから，網の圧力損失，圧力損失係数を測定した。その結果，沖縄で利用される網の通風特性には，開口比が影響することを明らかにした(2 章)。ネット式鋼管施設と角形鋼管プラスチックハウスの台風による倒壊事例から，これらの倒壊要因を解析した。また，南西諸島における園芸施設に関する台風被害の特徴を明らかにし，既存の園芸施設の弱点や課題について考察した(3 章)。次に，既存の園芸施設よりも耐風性に優れた2 種類の園芸施設を開発した。一つは農業従事者の農業所得を考慮して開発した小型園芸施設である。最大瞬間風速50m/s の風荷重に耐えるように設計を行った結果，実証試験においても耐風性を確認できた。本施設は沖縄県内で広く利用されている。もう一方は，トラス構造を特徴とした大型園芸施設である。高コストとなるトラス構造を農業用ハウスに採用するために，コスト削減と軽量化について検討した。そして，重量が大きく，高額なトラスの接合部中核部材の代替品として，安価で高強度な樹脂製ボールジョイント(特許第4576488 号)を開発した(4 章)。近年は地球温暖化により台風の大型化が懸念されることから，台風対策の強化に資する防風施設の遮風効果についても検証した。防風施設の風洞実験による研究事例は多いが，現地実証試験事例はほとんどない。試験には九州地域で普及が見込まれる2列型防風ネットを用いた。検証の結果，防風施設の設置による平均風速の低減，すなわち，遮風効果を確認できた。また，現場観測においては，地形条件を無視できないため，遮風効果を検討するためには，防風ネットを設置する前の風速分布を考慮する必要があることが明らかになった。これらの現地試験は，電力の確保やケーブル配線が困難な離島や遠隔地での実施が想定される。そのため，太陽光パネルを利用したワイヤレス型の観測システムを開発した。本システムは3日間の連続観測が可能であり，実用化の目処をつけた(5章)。本研究では，農業従事者の期待に応えられる園芸施設を開発し，台風対策に必要な防風施設や網の特性について新たな知見を得ることができた。そして，成果の一部は実践的な台風対策技術として実用化された。これらの成果は国内のみならず，東南アジアなどの島嶼地域における風害対策の一助となることが期待できる。
The gardening facility is essential for the progress of the agriculture in the southwest islands. It contributes greatly to the stable crop production not only for the typhoon damage protection but also for the pest management and the temperature management. In Okinawa prefecture, 42% of the gardening facilities are steel plastic houses as a countermeasure against potential typhoon damages. The steel plastic house requires high cost and it seems difficult to set up the facilities without subvention. In this study, the gardening facility to resist wind with low cost has been developed by the improved technology against typhoon in the southwest islands. In Chapter 1, researches on the gardening facilities and windbreak facilities have been reviewed. Moreover, the status of using the gardening facilities in Okinawa Prefecture was described in detail. In Chapter 2, the airflow characteristics of eleven anti-insect screens used in the southwest islands were evaluated by means of a wind tunnel. The thread diameter of anti-insect screens ranged from 0.17 to 0.29 mm, and the porosity ranged from 0.25 to 0.68. Wind tunnel experiments indicated that the pressure loss through the screens was a function of porosity. Specifically, the pressure loss increased when the porosity decreased, even if the pores were approximately the same size. For instance, the pressure loss increased to 1.6 times when the porosity decreased by 18%. It is recommended to examine the porosity, not the pore size, for the airflow characteristics of the anti-insect screens. The pressure loss through a screen was found to be a quadratic function of its porosity for a constant airflow velocity through the screen. In Chapter 3, Typhoon 0314 attacked Miyako Island on September 10-11, 2003. The maximum instantaneous wind speed of 74.1 m/s was recorded and this is the seventh record in Japan. The damages of commercial greenhouses by the typhoon were investigated in sixteen locations. The damages were categorized into 1) cracked the concrete foundation, 2) breaking of end plate for the base of column, 3) breaking or looseness of the bolt which joint beam and doorjamb, and 4）broken weld zone. These damages caused by the strong winds have not been reported in the past in Okinawa. The collapse patterns of the greenhouses covered with only insect screens were similar to other greenhouses, the bases on the windward gable end of which were pulled out. The Analysis showed that the bases could be pulled out at a wind speed of 46.4 m/s or higher because of the weak resistance against the wind forces to be pulled upward. Moreover, the analysis showed that the weld zone of eaves of a square steel pipe plastic house was fractured by the side load caused by wind speed of 37.5m/s or higher. In Chapter 4, many greenhouses in Okinawa islands are frequently damaged by hitting of large-scale typhoons in these years. These damages caused by the strong wind loads have not been reported in the past in Okinawa. In order to improve the strength and reliability of greenhouses for Okinawa horticultural farmers, the new greenhouse that endure the load by the gusts of up to 50m/s was developed based on the analysis of the damage.
The greenhouse allows opening and closing of the vinyl sheet for temperature management of the inside of the greenhouse, and is designed to withstand typhoon gusts in the closing state of the vinyl sheet. To prevent deformation of greenhouse beams, the reinforcement method with wire rope was proposed. In recent years, the intensity of typhoons has increased causing great damage to gardening facilities in not only Okinawa but also the mainland of Japan. Through the truss structure to large - scale green houses were tried to apply to wind – resistant houses, the introduction of such a structure involves very high costs. For implementation in agriculture, it is necessary to reduce the cost of introducing such a structure. In this study, a large size greenhouse with the truss structure at low cost using resin joints, which are light weight and inexpensive has been developed. In Chapter 5, performance of the uneven dual-screen windbreak (UDSW) to protect agricultural products from the strong wind was tested when the typhoon 0310 attacked Okinawa. The test area surrounded by the UDSW was located on a plateau near a cliff. Wind speed was measured by ultrasonic anemometers at 6m high from the ground at the outside of the test area and 3m and 6m high at the inside. The relations between the distance from the cliff edge and the average wind speed were indicated a quadratic function of the distance in the range of 400m from the edge. These calculated data by a quadratic function were compared with the measured data. The wind speed at 28m leeward from the UDSW was reduced by 25% at a height of 6m, and that at 90m leeward was reduced by 17%. The wind speed ratio at a height of 3m to 6m was increased with distance from the UDSW about 0.83 to 0.92. In this study, the multipoint observation system using wireless transmission was developed to observe the strong wind during the typhoon raid, and the feature of the sonic anemometer was examined from the comparison with the wind mill anemometer. It was shown that sonic anemometer is able to measure the strong wind during the storm. This system can be used enough range more than 300m. Moreover, this system can synchronize the data from 11 sonic anemometers by up to 50Hz sampling rate. This system can be available even in the field where the electric power cannot be supplied. Two solar cells and two deep cycle batteries were used for the power supply on the client side. As a result, the system can be operated continuously about 3 days. Subject for a further study is a quantitative research to evaluate a wind resistance of the facilities covered by net. Moreover, it is necessary to research economic efficiency such as initial construction and maintenance costs. The research about maintenance technique for long-term used of the gardening facilities are also important. These studies contribute greatly to the development of agricultural industry in the southwest islands.
|Type Local ||:||学位論文|
|Appears in Collections||:||Doctoral Dissertation (Graduate School of Engineering and Science)|
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