Gemi yapı elemanlarının boyutlandırılması için gerilme analizi
Stress analysis for the determination of scantlings of ship structures
- Tez No: 46514
- Danışmanlar: PROF.DR. MESUT SAVCI
- Tez Türü: Doktora
- Konular: Gemi Mühendisliği, Marine Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1995
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 63
Özet
ÖZET Bu çalışmada, hafıza kapasiteleri, büyük bilgisayar sistemleri ile karşılaştırıldığında daha az olan fakat, endüstride yaygın olarak kullanılan kişisel bilgisayarlardan yararlanılması hedeflenmiş, bu amaçla gemi bünyesinde yapısal analiz yapabilmek için bir model geliştirilmiştir. Böylelikle bu çalışmanın endüstride kullanılabilmesi amaçlanmıştır. Geliştirilen modelde gemi dip yapısı ızgara sistem, dip üzerindeki gemi yapısı da çerçeveler halinde düşünülmüştür. Bu tür yaklaşımlarda daha önce yapılandan farklı olarak gemi bünyesini oluşturan her iki yapısal alt grubun birbirlerine etkilerinin de göz önüne alındığı bir çalışma yapılmış ve bu amaca uygun bir bilgisayar programı hazırlanmıştır. Gemi bünyesini oluşturan elemanlar, enine ve boyuna elemanlar olarak iki grup altında sınıflanmış ve sınır şartları gemi mukavemetinde kullanılan kabullere uygun olarak seçilmiş ve de direkt Matris Deplasman yöntemi ile çözüm yapılmıştır. Yapılan modellemeye uygun olarak hazırlanan bilgisayar programı inşa edilmiş örnek bir gemi üzerinde uygulanmıştır. Gemi bünyesine etkiyen dış yükler olarak Türk Loydu'nun vermiş olduğu değerler kullanılmıştır. Gemi bünyesinde yapılan gerilme analizi sonucunda elde edilen değerler yine Türk Loydu'nun vermiş olduğu değerlerle karşılaştırılmıştır.
Özet (Çeviri)
Recent developments in computing technology in terms of capacity and speed have enabled the use of numerical methods widely for the stress analysis of the ship structures compared to the conventional calculation methods. The classification societies, in addition to the determination -of the dimensions of the structural elements carried out according to their rule book based on the semi- empirical methods, have started accepting the results of the calculations obtained from the numerical procedures performed by taking into account the design loads and the allowed stresses specified in their codes. This situation encouraged the use of the numerical methods for the ship structural design. These computer aided studies started at the end of the 1950' s. In this period, ship sections located between the two bulkheads were studied and the stress distribution on the structural elements was investigated by using the grillage system modelling. This type of numerical local stress analysis of the ship structure was also supported by the experimental studies. Furthermore, in the same time period the structural design techniques for the ship transverse strength were developed utilising the frame and the grillage structural modelling where the two-dimensional structural representation of the ship section was assumed to be independent of the longitudinal effects. The developments in the computer technology, increased memory capacities and precision have lead the way to the possibility of solving larger systems of equations. The three or four noded shell elements were used instead of one-dimensional beam elements in later periods. With continuing development, three-dimensional stress analysis began replacing the two-dimensional versions and the results obtained were compared with those of the extensively built prototypes. In those studies, incorporating highly advanced numerical methods, several commercially developed finite element programs were employed.Advances in the ship production technology, broad variety of the cargo and the emergence of the environmental pollution prevention as an important design parameter reformed the classical ship structure. Consequently, new ship types were developed. During the design process of these new ships, not much help could possibly be obtained from the experience and the rule books of the classification societies. As a result, the significance of the numerical studies as ship structural design tools explained in the previous paragraphs increased sharply. The present work aims to utilize, in structural design of ships, the personal computers which have found extensive use in shipbuilding industry, although their memory capacities are limited when compared to the mainframe systems. A model is developed to perform the structural analysis of the ship's hull for this purpose. ît is intended that the tools developed in this study can be employed during the design stage in shipbuilding industry. The model considers the ship's inner-bottom as a grillage system with a frame structure located on this base. This model differs from the previously developed approaches since the interaction between the double-bottom and frames is fully into consideration. In this study, the existing finite element packages are not used, but instead, a computer program is developed to meet the exact requirements of the theoretical and the related numerical' model proposed. The direct matrix displacement method is employed for the numerical solution which is described in detail in Chapter 2. As a general rule, the strength calculations of a structural system are performed to obtain the stress distributions in the elements of the structure due to the external loads, together with the deformations and displacements at various locations of importance in the structure. The fundamental purpose of the matrix methods is to evaluate the extreme stress and strain values associated with the elements forming the structure, hence, providing the designer a full solution of the system. In order to perform the stress analysis calculations mentioned above, the following conditions must be satisfied: i. static equilibrium conditions, ii. geometric compatibility conditions, iii. stress-strain relations. In the direct matrix displacement method, firstly, the boundary conditions of the system are expressed as the linearcombination of the end displacements which are independent of each other and satisfy the appropriate geometric compatibility condition. Then, the unknown coefficients, which are equal in numbers as the degrees of freedom of the system, are evaluated with the help of the equilibrium conditions and the stress-strain relations. viiFinally, the end displacements of the system are determined. Next, the previously found end displacements are used together with the equilibrium conditions and the stress-strain relations to calculate the stress values of the system. In the matrix notation of the matrix displacement method, the solutions of the unknown coefficients are obtained from: where [K] is the NxN square stiffness matrix of the system for N unknowns, [D] is the unknown vector of end displacements, [P] is the external load vector of the system. It is essential to construct a dedicated model for the type of the strength calculations considered for the ship hull. The stress calculations for the hull structure may be performed under two fundamental titles; global and local analyses. In the global ship strength calculations, the ship is considered as a beam under external loading and a general stress analysis, static or dynamic in nature, is performed. For the local ship strength calculations, more emphasize is given to the individual elements in the ship hull structure and a static or dynamic stress analysis is performed for the structural sub-systems. In this study, for the structural elements that form the ship hull, a static stress analysis is carried out. The ship structural elements are grouped as transverse and longitudinal members and the assumptions are made according to the properties of the elements. The ship double-bottom is modelled as a grillage system which consists of the transverse solid floors, the longitudinal central beam and various side girders. At the points where the frames meet the side walls, the simple support assumption is employed and a built-in support is assumed to exist where the longitudinal elements join with the transverse bulkheads, in line with the conventional assumptions of the ship structural engineering. The external loads acting on the bottom structure are applied on the longitudinal elements and the loads are specified asthose recommended by the Turkish Lloyd. The double -bottom of the ship hull is modelled as a frame structure and the boundary conditions are determined with respect to the assumptions explained above. Here, again, the external loads specified by the Turkish Lloyd are taken as reference. The solution is carried out by taking into account of the interaction between the two separate structural sub-systems. VlllThe end points of the ship bottom structural elements, which are modelled on the whole as a grillage system, are thought to have three degrees of freedom, consisting of one for the linear displacement and two for the rotation. At the end points of the other structural sub-systems modelled as frames have also three degrees of freedom, somewhat different from those of the grillage system, consisting of two linear displacements and one rotation. Firstly, the frame problem is solved by employing the developed numerical procedure for five elements and the results were compared with those of the Cross method. Next, a grillage system of two- longitudinal and four- transverse elements is worked out. The results obtained from the use of 22 elements are then compared with the solution by the displacement method. Finally, the stress analysis for the two adjacent sections of a reai ship hull, using the numerical model explained above is carried out and the results for the three cases are presented by graphical illustrations. The input data required for the first and the second cases and the results are presented in the form of tables. The interpretation of the calculated results and the discussion of the numerical modelling should. surely be carried out by comparison with the experimental findings. Unfortunately, within the time period of this work, an experimental study could not be realised and this discussion could not be put forward. Therefore, to be able to reach a sound general conclusion, the data from the hull of a ship in operation is used and the results are discussed in detail. Additionally, a simple ship frame and a grillage system are worked out and the results are compared with those of the well known solution methods. A highly satisfactory correlation between the results is achieved. The results of the stress analysis for the real ship hull are examined and discussed by referring to the specifications of the Turkish Lloyd as reference. The greatest stress values for the bottom structure are observed where the longitudinal elements cross the transverse bulkheads and in the central regions of the cargo holds. When a similar analysis was made for the ship sections modelled as frames, the greatest stresses were observed at the transverse frames of the hatch openings and at the pointswhere the hold frame and the double-bottom joins. For the transverse frames that are located between two hatch openings, the positions where the hold frame joins the double -bottom and the mid-points of the decks have the largest stress values. The stresses at those critical positions were compared with the allowable stress values specified by the Turkish Lloyd and it was observed that the calculated stresses were lower than the specified ones. As a result of these investigations, it is suggested that the numerical model is capable of predicting the behaviour of the ship structure under external loading and ixit can be used during the design process. In conclusion, it is observed that the calculated stress values are found to be lower than the values given by the classification societies. Accordingly, it may be possible to decrease the dimensions of some of the structural elements in the ship hull and therefore, cost savings may be achieved due to a lighter ship hull. Since the developed computer program for the model presented in this thesis can be run on personal computers, the shipyards and the design bureaus will also be able to make use of it as a tool for designing lighter ships, without any compromise from the fundamental concept of achieving structurally safe ships.
Benzer Tezler
- Ultimate limit state design assessment and recommendation comments for offshore crane foundation
Açık deniz kreyn fandeyşını için nihai limit durum tasarımı değerlendirmesi ve tavsiye açıklamaları
MUHAMMET CÜNEYT SAKÖNDER
Yüksek Lisans
İngilizce
2019
Deniz Bilimleriİstanbul Teknik ÜniversitesiGemi ve Deniz Teknoloji Mühendisliği Ana Bilim Dalı
DOÇ. DR. ÖZGÜR ÖZGÜÇ
- Hidrostatik basınç altındaki denizaltı mukavim teknesinin sonlu elemanlar metodu ile optimum yapısal tasarımı
Optimum structural design of a submarine pressure hull under hydrostatic pressure with finite element method
BURAK EYİLER
Yüksek Lisans
Türkçe
2022
Gemi Mühendisliğiİstanbul Teknik ÜniversitesiGemi İnşaatı ve Gemi Makineleri Mühendisliği Ana Bilim Dalı
DOÇ. DR. ERTEKİN BAYRAKTARKATAL
- Gemilerin yapısal tasarımı ve yapı analiz yöntemlerinin incelenmesi
Ship structural design and investigation of structural analysis methods
HASAN ÖLMEZ
Yüksek Lisans
Türkçe
2008
Deniz BilimleriKaradeniz Teknik ÜniversitesiMakine Mühendisliği Bölümü
DOÇ. DR. ERCAN KÖSE
- Fonksiyonel derecelendirilmiş gözenekli sandviç kirişlerin statik ve serbest titreşim analizi
Static and free vibration analysis of functionally graded porous sandwich beams
SURA KAREEM ABBAS AL ITBI
Yüksek Lisans
Türkçe
2023
İnşaat Mühendisliğiİstanbul Gelişim Üniversitesiİnşaat Mühendisliği Ana Bilim Dalı
DR. ÖĞR. ÜYESİ AHMAD RESHAD NOORI
- Darbe hasarlı filaman sargılı kompozit yapı elemanlarının basma kuvveti altındaki mekanik özelliklerinin belirlenmesi ve hasar analizi
Determination of the mechanical properties of filament wound composite structural elements under compressive force with impact damage and damage analysis
ZEYNEP KÜBRA GÜVEN
Yüksek Lisans
Türkçe
2021
İnşaat MühendisliğiNecmettin Erbakan Üniversitesiİnşaat Mühendisliği Ana Bilim Dalı
DR. ÖĞR. ÜYESİ EMRAH MADENCİ
DOÇ. DR. LOKMAN GEMİ