İkiz teknelerin toplam direnç açısından form optimizasyonu
İkiz teknelerin toplam direnç açısından form optimizasyonu
Dosyalar
Tarih
1997
Yazarlar
Danışman, Bülent
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Fen Bilimleri Enstitüsü
Özet
Son yıllarda büyük güverte alanı gerektiren yüksek süratli deniz taşımacılığı türlerinde -örneğin yolcu taşımacılığı, feribotlar, balıkçı gemileri vs-, ikiz teknelere gittikçe daha çok ilgi duyulmaktadır. Bunun nedeni bu tip teknelerin tekne boyutlarından bağımsız yüksek stabiliteye sahip olmaları ve alışılmadık direnç karakteristiklerinin olmasıdır. Yüksek süratli teknelerde yüksek güç gereksinimi, tekne direncinin ortaya makul bir dizayn koyabilmek için.dizayner tarafından bir iyileştirmeye tabii tutulmasını zorunlu kılar. Bu çalışmada gittikçe yaygınlaşmakta olan bir yüksek süratli tekne tipi olarak ikiz teknelerin direnç karakteristikleri incelenmiş ve verilen kısıtlar altında minimum toplam dirence sahip formlar matematik programlama yöntemiyle bulunmaya çalışılmıştır. îkiz tekne toplam direnci, sürtünme ve dalga dirençlerinin toplamı olarak modellenmiş ve optimizasyon çalışması için amaç fonksiyonu bu şekilde teşkil edilmiştir. Sürtünme direnci ITTC-1957 formülüyle hesaplanırken dalga direnci, Michell integralinin Lunde(1951) tarafından ikiz tekneler için geliştirilmiş şekliyle hesaplanmaktadır. Bu integralin girişim terimini ifade eden ve integrantı hızla salınan kısmı, tek tekne halinden farklı olarak özel bir algoritma kullanılarak "SIDI(1982), çözülebilmiş ve hesaplara katılmıştır. Optimizasyon çalışmalarında kuadratik programlama kullanılmış Wolfe algoritması uygulanmıştır. Sayısal hesaplamalar için iki adet bilgisayar programı geliştirilmiştir. Bu programlardan birincisi ikinci programa giriş datası teşkil edecek olan sürtünme ve dalga direnç matrislerini oluşturmaktadır. Formulasyonun ayrıklaştırılmasında; gemi yüzeyi çadır fonksiyonları kullanılarak modellenmiştir. Form optimizasyonu değişik tekne aralıkları ve Froude sayıları için denenmiştir. Fakat bunların içinde bu tip bir teknenin çalışma rejimine uygun olan Froude sayısı 0.60 ve tekneler arası mesafenin tekne boyuna oranı 0.3 durumu optimizasyon için hedef seçilmiştir. Optimizasyon sonucunda kayda değer sonuçlar veren formlar incelemeye alınmıştır. Bu inceleme sonucunda elde edilen yeni formun direnci sayısal, olarak yeniden hesaplanmış ve böylelikle model imalatı için optimal form belirlenmeye çalışılmıştır. Sayısal ve deneysel inceleme için simetrik ikiztekneler için oldukça uygun olan NPL serisi seçilmiş, başlangıç ve optimal formların modelleri imal edilip direnç deneyleri yapılmıştır. Deneylerin sonucu sayısal çalışma ile bulduğumuz direnç kazançlarını kanıtlamaktadır. Böylelikle bu optimizasyon prosedürünün yüksek süratli ikiz teknelere de başarıyla uygulanabileceği gösterilmiş olur.
Recently the demand for high-speed ships have increased in passenger boat market. Various hull forms have been tried to satisfy the design criteria of such vessels. But except them catamaran ships should have been taken into consideration because of its large deck area, strong transverse stability, and its unusual resistance characteristics. So these type of ships can be used for passenger ferries, container-carriers, oil- drilling platforms and fishing vessels. Generally the total resistance of catamaran is greater than that of a monohull with the same length draft and displacement. In low Froude number region the frictional resistance is predominant. However in high Froude number region wave resistance becomes more prevailing. Since these ships have been considered as high speed crafts wave resistance becomes more important. Wave resistance can be minimized by well-chosen twin hull spacing which can produce a favorable wave interference effect. The interference effect depends not only on the hull spacing but also on the demihull geometry and Froude number. In this study an analytical procedure was developed to determine optimal hull forms for minimum total resistance by using the quadratic programming method. Lunde (1 95 1) studied the wave resistance of a ship moving parallel to a rigid wall. It was the basic theoretical approach for catamarans wave resistance. In that study the solution was obtained by distribution of simple sources on the center-plane of demihull and linear wave theory was applied. However if the demihull is sufficiently thin and straight and if the values of he ratio of beam/hull-spacing become sufficiently small the thin-ship approximation with center-plane sources distribution give a useful solution for practical applications. The general approach in optimization in engineering is to write down a proper objective function and to reduce it into one of the standard forms of mathematical programming. In this study the objective function chosen is the sum of frictional resistance and wave resistance. Frictional resistance is calculated by the ITTC - 1957 formula for equivalent flat plate resistance. Wave resistance calculations are done by utilizing the Michell integral which is developed for catamarans by Lunde(1951). In these calculations the ship hull is characterized by the tent functions. Following the same formulation given by Hsiung(1981) the coordinate system is chosen as in figure 1 and ship hull function is defined as: n = f&q The variables Ç, r\, and Ç are non dimensionalized by the length L, beam B, and the draft T of the ship to give -1 n -£ X~ L ' y~{BI2) ' Z~T Vll Therefore nondimensonalized hull form expressed as: /M =~F($>c) K \ M. (A.P.) H-!,,-i (F.P.>.j+1 Figure 1 Figure 2 In order to make use of tent functions, the ship's center-plane meshed as shown in figure 2. The first station is the for-perpendicular of the ship and the first waterline is the base line. The last station may be chosen as the aft-perpendicular and the waterline should be loaded waterline. The station and waterlines are not necessarily equally spaced. Then the unit tent function at the grid point (xj,Zj) is given as: k (<../) (*..-) Xi~Xi-\J Xi ~ Xi-\ J Xi Xi+l J z - Z ? i 7 7-1 z ? - Z ? i 7 7-1 1 X;~X Xi Xi+l J 1- ZJ~Z ZJ~ZJ+l ;xi_l<x<="" if2="" (u2="" 2="" du="" as.="" calculations="" some="" after="" functions,="" tent="" interms="" into="" taken="" integral="" i"="" ix i="" dxdz="" +1)2="" +l)exp[2ro|(z-l)(«2="" 3="JpA.(x,z)2S(2/ox)(«2" w="" <z<x<z0 Two computer programs are developed. One for calculating wave and frictional resistance and generating the resistance matrix and the other for finding optimum half-breadths by using Wolfe's algorithm with the help of output of first program. To calculate the wave resistance of catamaran by employing Michell integral a special integration technique,SIDI (1982), is used because of the highly oscillatory integrant due to the interference effect between demihulls. In this study a parent catamaran form is generated by using CB=0.40 and L/B=10 of NPL series. Different hull spacings are taken into consideration to find an optimal form which has minimum total resistance. Constraints mostly used in the present optimization study are : 1. All the known offsets are less then or equal to the half beam: II The waterline slope is less than or equal to tanG, such as; 2Z III The block coefficient of the forebody volume is increased: CBF=m*C$ m>l I V The waterline area coefficient is kept constant: C\VL = C\VL ° V The origina offsets of the initial ship may be taken as the lower bound for the unknown offsets: v.. > yio) Sij -Sij Depending on the specific problems of the design procedure, some costraints can be added, and some constraints may be altered to obtain a realistic hull. The forebody volume of the initial hull to be optimized was chosen as the volume between bow profile and the 8th station. The half-breadths on stations A, 10, 91/2, 9, 8 being described by 7 waterlines were the unknowns in the optimization study. The resistance matrices were computed different Froude numbers and different twin-hull spacings. Model tests validated our the theoretical computations which gives 13 percent reduction in total resistanece at Froude number 0.425 and 5 percent reduction at Froude number 0.60, for the ratio of twin-hull spacing / length 0.3. By model tests wave pattern resistance is analyzed and effect of protruding bulb on interference wave resistance is observed. The test results shows us the bulbous bow can reduce the interference effect. As well as an observation for the ratio of twin-hull spacing / length 0.2 for Froude number 0.70 a jet-like spray is observed between twin-hulls of parent hull But at the same condition there is no spray observed between twin-hulls of optimal catamaran hulls. XI h is shown by the help of the model test mathematical programming with a proper set of constraints can substantially reduce the total resistance of catamarans by using protruding bulbs. The choice of initial hull form and the set of constraints are important for the success of optimization procedure. The procedure removes guess work on hull form improvements even for high-speed catamarans and can find optimum solutions having commercial significance.</x
Recently the demand for high-speed ships have increased in passenger boat market. Various hull forms have been tried to satisfy the design criteria of such vessels. But except them catamaran ships should have been taken into consideration because of its large deck area, strong transverse stability, and its unusual resistance characteristics. So these type of ships can be used for passenger ferries, container-carriers, oil- drilling platforms and fishing vessels. Generally the total resistance of catamaran is greater than that of a monohull with the same length draft and displacement. In low Froude number region the frictional resistance is predominant. However in high Froude number region wave resistance becomes more prevailing. Since these ships have been considered as high speed crafts wave resistance becomes more important. Wave resistance can be minimized by well-chosen twin hull spacing which can produce a favorable wave interference effect. The interference effect depends not only on the hull spacing but also on the demihull geometry and Froude number. In this study an analytical procedure was developed to determine optimal hull forms for minimum total resistance by using the quadratic programming method. Lunde (1 95 1) studied the wave resistance of a ship moving parallel to a rigid wall. It was the basic theoretical approach for catamarans wave resistance. In that study the solution was obtained by distribution of simple sources on the center-plane of demihull and linear wave theory was applied. However if the demihull is sufficiently thin and straight and if the values of he ratio of beam/hull-spacing become sufficiently small the thin-ship approximation with center-plane sources distribution give a useful solution for practical applications. The general approach in optimization in engineering is to write down a proper objective function and to reduce it into one of the standard forms of mathematical programming. In this study the objective function chosen is the sum of frictional resistance and wave resistance. Frictional resistance is calculated by the ITTC - 1957 formula for equivalent flat plate resistance. Wave resistance calculations are done by utilizing the Michell integral which is developed for catamarans by Lunde(1951). In these calculations the ship hull is characterized by the tent functions. Following the same formulation given by Hsiung(1981) the coordinate system is chosen as in figure 1 and ship hull function is defined as: n = f&q The variables Ç, r\, and Ç are non dimensionalized by the length L, beam B, and the draft T of the ship to give -1 n -£ X~ L ' y~{BI2) ' Z~T Vll Therefore nondimensonalized hull form expressed as: /M =~F($>c) K \ M. (A.P.) H-!,,-i (F.P.>.j+1 Figure 1 Figure 2 In order to make use of tent functions, the ship's center-plane meshed as shown in figure 2. The first station is the for-perpendicular of the ship and the first waterline is the base line. The last station may be chosen as the aft-perpendicular and the waterline should be loaded waterline. The station and waterlines are not necessarily equally spaced. Then the unit tent function at the grid point (xj,Zj) is given as: k (<../) (*..-) Xi~Xi-\J Xi ~ Xi-\ J Xi Xi+l J z - Z ? i 7 7-1 z ? - Z ? i 7 7-1 1 X;~X Xi Xi+l J 1- ZJ~Z ZJ~ZJ+l ;xi_l<x<="" if2="" (u2="" 2="" du="" as.="" calculations="" some="" after="" functions,="" tent="" interms="" into="" taken="" integral="" i"="" ix i="" dxdz="" +1)2="" +l)exp[2ro|(z-l)(«2="" 3="JpA.(x,z)2S(2/ox)(«2" w="" <z<x<z0 Two computer programs are developed. One for calculating wave and frictional resistance and generating the resistance matrix and the other for finding optimum half-breadths by using Wolfe's algorithm with the help of output of first program. To calculate the wave resistance of catamaran by employing Michell integral a special integration technique,SIDI (1982), is used because of the highly oscillatory integrant due to the interference effect between demihulls. In this study a parent catamaran form is generated by using CB=0.40 and L/B=10 of NPL series. Different hull spacings are taken into consideration to find an optimal form which has minimum total resistance. Constraints mostly used in the present optimization study are : 1. All the known offsets are less then or equal to the half beam: II The waterline slope is less than or equal to tanG, such as; 2Z III The block coefficient of the forebody volume is increased: CBF=m*C$ m>l I V The waterline area coefficient is kept constant: C\VL = C\VL ° V The origina offsets of the initial ship may be taken as the lower bound for the unknown offsets: v.. > yio) Sij -Sij Depending on the specific problems of the design procedure, some costraints can be added, and some constraints may be altered to obtain a realistic hull. The forebody volume of the initial hull to be optimized was chosen as the volume between bow profile and the 8th station. The half-breadths on stations A, 10, 91/2, 9, 8 being described by 7 waterlines were the unknowns in the optimization study. The resistance matrices were computed different Froude numbers and different twin-hull spacings. Model tests validated our the theoretical computations which gives 13 percent reduction in total resistanece at Froude number 0.425 and 5 percent reduction at Froude number 0.60, for the ratio of twin-hull spacing / length 0.3. By model tests wave pattern resistance is analyzed and effect of protruding bulb on interference wave resistance is observed. The test results shows us the bulbous bow can reduce the interference effect. As well as an observation for the ratio of twin-hull spacing / length 0.2 for Froude number 0.70 a jet-like spray is observed between twin-hulls of parent hull But at the same condition there is no spray observed between twin-hulls of optimal catamaran hulls. XI h is shown by the help of the model test mathematical programming with a proper set of constraints can substantially reduce the total resistance of catamarans by using protruding bulbs. The choice of initial hull form and the set of constraints are important for the success of optimization procedure. The procedure removes guess work on hull form improvements even for high-speed catamarans and can find optimum solutions having commercial significance.</x
Açıklama
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1997
Anahtar kelimeler
optimizasyon,
ikiz tekneler,
optimization,
twin vessels