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Yüksek süratli teknelerde aynakıçın tekne performansına etkileri

Başlık çevirisi mevcut değil.

  1. Tez No: 66680
  2. Yazar: KAYA TÜMER
  3. Danışmanlar: DOÇ. DR. MUSTAFA İNSEL
  4. Tez Türü: Yüksek Lisans
  5. Konular: Gemi Mühendisliği, Marine Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1997
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Gemi İnşaatı Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 137

Özet

ÖZET Günümüzde donanmalarda savaş gemilerinin büyük bir çoğunluğu ile yüksek süratli teknelerin önemli bir kısmında kıç formu olarak aynakıç kullanılmaktadır. Aynakıçın; iç yerleştirmede kullanılabilir alanı arttırmak suretiyle dizayn kolaylıkları sağlaması, şekli sebebiyle ucuz ve kolay inşa edilmesi ve yüksek süratlerde az direnç oluşturması gibi bir takım avantaj lan vardır, buna rağmen düşük ve orta hızlarda, birtakım direnç sorunları yaratmaktadır. Yüksek süratli teknelerde, aynakıç formu teknenin direnç özelliklerini etkilemektedir. Düşük hızlarda (Fnt < 0.4)aynakıç 'ıslak aynakıç' adı verilen girdaplı bir akımı, yüksek hızlarda (F»ı > 0.5) ise 'kuru aynakıç' olarak adlandırılan akımı ve kıçtan ayrılan horoz kuyruğu adı verilen bir dalga sistemi meydana getirir. Bu iki hız rejimi arasında da geçiş bölgesi olarak adlandırılan yarı-ıslak aynakıç oluşmaktadır. Ayna kıçta oluşan bu akım değişikliği ile beraber tekne, geçiş bölgesinde tekne kıça trimlenmekte ve dinamik kaldırma kuvvetlerinin etkisi altına girmektedir. Tekne triminin optimum hale getirilmesi ve kıçtaki akımda oluşan girdapların yönetilmesi için aynakıç altında“trim kanatlan”kullanılmaktadır. Aynakıçtaki akım oluşumu, kuru ıslak rejimlerin geçerli olduğu hızlar konusunda literatürde büyük bir eksiklik bulunmaktadır. Bu tez çalışması değişik aynakıç formlan ve trim kanatlarının oluşan dalga sistemini ve aynakıçtaki basınç dağılımı üzerine etkisini incelemeyi amaçlamaktadır. Bu çalışmada 5 adet farklı“su altındaki aynakıç alanı / maksimum en kesit alanı”oranlarında (Ar/Ax= 0.0, 0.286, 0.572, 0.786, 1.0) yuvarlak karinalı NPL serisi model üretilmiştir. Üretilen bu modellerin deneyleri sirkülasyon kanalı ünitesinde boy Froude sayısının 0.2 ile 0.7 değerleri arasındaki hız rejimlerinde yapılmış. Bu deneylerde toplam direnç, operasyon sırasındaki trim, batma ve aynakıştaki su yüksekliği ölçülmüştür. Deneylerde kullanılmak amacıyla beş delikli bir pitot tüpü dizayn edilerek, yine bu deneyler için dizayn edilen ve y-z eksenlerinde otomatik hareket edebilen bir düzenek yardımıyla aynakıç arkasındaki basınç dağılımları ölçülmüş ve bu datalardan modellere ve hız rejimlerine göre aynakıç akımlannın değişimleri belirlenmiş ve viskoz travers dalga direnci elde edilmiştir. xviii

Özet (Çeviri)

SUMMARY Transom stern is a feature found on many naval surface combatants and nearly ali of the high speed passenger/car ferries. The transom stern offers several advantages över the craiser stern for these crafts. it facilitates internal arrangements and, because of its simple shape, is easier and cheaper to fabricate. More importantly, it generates less resistance at high speeds than would a craiser stern, thus allowing high speed craft to attain such speeds with lower propulsive power. The reduced high- speed resistance of a transom-sterned ship is accompanied by a reduction in the amount of trim by the stern relative to a cruiser-sterned hull. However, at low to moderate speeds, there is a resistance penalty caused by the transom. Notice that, transom stern has detrimental effect on the resistance characteristics of a high speed craft. The stern is wet and the flow has vortices at low speeds (F,,/ < 0.4). in contrast, the stern is dry, i.e. water separates from the stern, and flow forms a complex wave system called rooster tail for higher speeds (F»ı > 0.5). There is a transition regime between wet and dry regimes, which is partly wetted. The hull is trimmed by the stern and hydrodynamic lifting force becomes noticeable by the change of flow at the stern. Trim flaps are used for optimizing trim angle and cleaning the stern from the vortices. There has been little systematic research concerning the effect of various physical transom characteristics on ship resistance. There are several reasons for this. First, designing a systematic series of ships in order to isolate the effects of any single geometric change -transom shape in this case- is difficult. in addition, the resulting differences in model resistance for such a systematic series have been too small to be measured accurately by available dynamometry and data acquisition systems. Finally, and most importantly, systematic series design and testing are tedious and expensive. Because of these reasons, there is a lack of knowledge on.the understanding of transom stern flow and the transition speed. Wet and dry transom stern have effect on both wave and viscous resistance features. Therefore, A project has been performed which aimed at investigating the wave system due to transom flow and trim flaps and pressure distribution. A series of high speed forms consisting of five models derived from NPL round bilge series were designed and fabricated in different“transom area-maximum section area”coeffıcients that are (AT/AX) 0.0, 0.286, 0.572, 0.786, 1.0. xixThe effect of changing transom shape can be seen for some distance forvvard of the transom. it was decided to fair the entire aft form of each model form its point of maximum sectional area to the transom. AH hull forms were faired into the same maximum cross section shape. The afterbodies were ali of the same length and were terminated vertically at the after perpendicular. The shape of each afterbody was designed to provide a smooth transition from the common maximum section to each of the fıve transom shapes. Displacement, length, maximum waterline beam and draft were held constant for the models and change other geometrical characteristics vvere minimized. The characteristics of each model are given in the table below. Table l The characteristics of modelsModeli (E) Model2 (D) ModeB (C) Model4 (B) ModelS (A) AT / Amax 0.0000.2860.5720.7861.000 LBP(meters) 0.960.960.960.960.96D (meters) 0.1210.1210.1210.1210.121 B (meters) 0.1240.1240.1240.1240.124 BT (meters) 0.1240.1140.1050.0820.063 T (meters) 0.0640.0640.0640.0640.064 A (tones) 3.433.23.02.662.36CBj 0.45j 0.420.40.350.31Ali of the models were buut using high-density closed-cell foam. Foam was chosen över wood because it is easier to shape to shape and is heavier. The foam models \vere coated with Lake Paste and then Polyester Paste before final fairing. Ali models were faired entirely by hand. Three coat of dye were sprayed över the models. Then ali models were coated with polish to provide smoothness. Ali five models were tested in a circulation channel at Ytanbul Technical University Ata Nutku Ship Model Test Laboratory. The same model dynamometry and signal conditioning equipment were used for ali tests in order to achieve the highest possible consistency of acquired data. The description of this tank is shovvn as Figüre 5.1. The fresh water depth for ali tests were 0.7 m. Blockage was not considered a problem. XXThe coordinate system for circulation channel is given as picture belovv. Sirkülasyon kanalı,>x Figüre l The coordinate system of circulation channel Turbulent flow simulation was provided by studs placed parallel to, and aft of, the stem approximately at a distance of 2 percent of the model length (20 mm). The studs \vere right circular cylinders having a diameter of 2.5 mm, a height of 2.5 mm, spaced every 25 mm around the model girth. The water speed in the channel was measured by a static - total pitot tube combined to a differential pressure transducer was calibrated statically by submerging in the channel. The dynamics calibration of the tube was performed in the towing tank by towing in predetermined speeds. The velocity distribution in the channel was measured by transversing pitot tube across the channel. The wave formation in the channel was reduced by two parallel plates in the entrance. Even these case at wave formation and reduction of water depth near the exit were observed. This free surface of channel without the model was measured by wave elevation measurement system developed during this study. According to the calibrations1 datum; the PC controlled rake can be positioned the measurement instruments to the measurement points within a 0.0053 mm accuracy for y axis and 0.0038 mm accuracy for z axis. The five hole pitot tube can be used to measure the pressures less then 0.046 m/s error at x direction, 0.032 m/s at y and z directions. The circulation channel's pitot tube can be used to measure channel vvater velocity within 0.075 m/s error. xxiWave system behind the transom were measured for the same configurations by use of an automated pointer, and characteristics of the rooster tail were determined by the change of speed and transom area. A five hole pitot tube was designed and used to measure the pressure distribution behind of the transom. Cross sections were taken by use of automated, stepper motor driven Y-Z table, at several distances from the stern to determine the change of flow for all the models, speed range and transom flap configurations. Viscous wake traverse resistance were derived from the measurements. A series of cross sections have been measured by transversing the five hole pitot tube from the lowest point of wake to the free surface and between the end points of wake on the free surface. The sections were between transom to two model lengths behind transom. Pressure distribution in each section have been plotted by contours to investigate the head loss and viscous resistance. All the pressure transducers, wave probes and LVDT measurements were amplified by special purpose amplifiers and then sampled by computerized data acquisition systems. A sampling frequency of 50 Hz have been used for a time of 10 seconds and then averages have been utilized. Planned that; total drag, operating trim angle, sinkage and water height at transom stern were measured for a range of Froude number from 0.2 to 0.7 and tests were conducted for 0.86 m/s, 1.25 m/s, 1.62 m/s water speeds. Because of the the problem in the circulation channel system - that was the heating problem in a coil that burnt - we had to finished the tests in an early stage. Until that problem the tests were performed with two model for one x section that was one model length far behind the amidships. For model A wave pattern tests and three dimensional pressure tests were performed all channel water speeds and for model C only wave pattern tests were performed in two channel water speeds. That was because that we have some datum to explain the physical behaviors of the transom stern at a high speed craft, but they are not enough to obtain general results for transom sterns. As a recommendations of this thesis, some items are given below: Firstly, these tests were had to finish in early stage, that was because, these tests will be completed and then transom flap measurements in different angles can be added in these tests. XXIIIn addition to this; with the experiences that we gained during this thesis, on model production with high-density closed-cell foam, new models in other projects will be fabricated with this material, because of the low costs. Furthermore; step motors in the PC controlled rake will be used for new experiment systems, as examples; maneuverability test systems and fin tests systems. Moreover; lots of new three dimensional pressure measurement tests will be conducted on different types of vessels in both circulation channel and big towing tank with five hole pitot tube that produced in this thesis. Finally physical explanations of the transom stern flow at one x section that is a model length far behind were given as graphics. xxm

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