International technical-science conference dedicated to the memory of prof. Yu.L. Vorobyov take place at ONMU
International technical-science conference "Actual problems of shipping, shipbuilding and shiprepairing" dedicated to the memory of prof. Yuriy L. Vorobyov take place at Odessa State Maritime University (ONMU) on 20-21.10.2016. Conference was a part of celebrating of 85th Anniversary of Odessa Marine Fleet Engineers (ONMU now).
Reports of different themes were introduced during plenary session from history of shipbuilding science development till current tendencies of shipbuilding and marine fleet evolution. Set of reports included "Participation of Yu.L. Vorobyov into shipbuilding science" (A.V. Demidyuk, G.V. Egorov, C.V. Rudenko are authors), "Mathematical model of coast guard vessel's function" (A.V. Bondarenk, V.A. Nekrasov are authors), etc.
Totally 31 reports (including sectional ones) have been made by specialists from ONMU, National Shipbuilding University (Nikolaev), Ukraine Hydromechanics Institute, National Technical University "Kiev Polytechnic Institute", Kiev State Water Transport Academy.
During sectional work, colleagues from Strength department of Marine engineering Bureau introduced several reports:
1. Analyze of strength criteria evolution for hull of marine cargo vessels (V.V. Kozlyakov, bureau's scientific consultant, prof., Sc. Dr. is author).
Development of requirements of Classification Societies Regulations to the general and local strength of marine cargo vessels has long empirical history and is actively going on now on the basis of modern statistical, physical and technic-economical base.
In the report comparison of the requirements of the Regulations and Norms of different Classification Societies to section modulus of the hull girder is carried out for last 100 years. Real modern vessels 0f 100 - 400 m length built from different grade steel were accepted as investigation objects.
Outstanding role in this process have posed complex computation-design system for vessel's constructions that was created by prof. I.G Bubnov in 1908. It was brightly realized during design and construction of vessels of many types and was widely used by domestic shipbuilders till the end of the 1960s.
Later on ideas and results of this work were kept, significantly developed and improved by domestic ship structural mechanics society headed by Yu.A. Shimanskiy and P.F. Papkovich.
Carried out comparison doesn't show clear tendency of requirements' evolution because of wide difference of structure and values of accepted outer impacts and general strength criteria used. However, tendency of relative decreasing of general strength requirements (especially for vessel's length increasing) may be strictly pointed; but this isn't in accord with last years' investigations.
Available ways for enhancement of Regulation and Norms are examined in the report; they are based onto 3 statistical criteria: of general limit plastic strength, fragile strength and fracture strength of marine cargo vessels' hull. These criteria should be combined together with technical-economical grounding of breakage normative probability and safety factor, that is defined with accounting of wearing and initial defects of technological and operational nature.
When formulating the criterion of limit plastic strength, it is reasonable to take into consideration the IACS recommendations that differ significantly from domestic ones. Also simultaneously impact from several wave loadings with high correlation factor has to be considered particularly for interchangeable holds' loading.
Statistical criteria of fracture strength should be improved by accounting of bi-linearity of fracture curves and modern fracture and crack-resistance characteristics of typical hull constructions.
Despite of existing underestimation of practical importance of limit fragile strength criterion, it is reasonable to use for design of vessels intended for navigation in high latitudes of the World Ocean. Probability of the fragile breakage should be defined as probability of conjunction of 3 independent events:
• operational temperature of the tensioned part of hull is smaller than critical value;
• impact stress in the tensioned part of hull is bigger than critical value;
• summarized tension stress are bigger than the critical value.
It is important to consider that fragile breakage (cracks) grow very fast and are the mostly dangerous; they depend on vessel's dimensions, constructions' condition and level of energy in them.
General plastic breakage of hull is also very dangerous. After buckling failure of the compressed strake of the hull girder, corrugation quickly spreads towards the tensioned strake of the hull girder and is accompanied by catastrophic falling of the limit bending moment that is usually concentrated within single web frame space.
For improving all 3 pointed strength criterion, a lot of efforts are required: to increase significantly precision of definition for parameters of long-term distribution of wave, impact, vibration and temperature loadings at the all parts of the World Ocean; systemize and develop additional characteristics of reliability for typical hull's components, especially for quasi-static and impact tension at lower temperature.
Special attention was put for the analysis of influence of indirect (non-monetary) economical prejudice (from damages and all kind of navigation accidents) onto optimal normative safety factors. Also attention was spread onto corresponding normative probabilities based on minimization of summarized expenses for construction, operation and repairing of vessels, including indirect economical prejudice caused by their unreliability (due to ecology or human life hazard) which can be learned from operational experience of vessels build according to regulation of Classification Societies with actual high and low reliability.
2. Specific of hull design for single-hold dock-type vessels (N.F. Butenko, head of Strength Department is author).
Dock-type feeder lighter carriers have no hatch covers due to excess free board. They are equipped with aft gate-ramp which. They are characterized by pivoting (free) bearing of the main longitudinal girders at the aft end of the cargo hold and rigid anchorage of these girders at the fore end of the hold. Also these vessels have relatively high double bottom with all transverse frames made as braces-less trusses (except those that coincide with rare transverse bulkheads of ballast compartments).
More general approximate methodic for the cargo 3D compartment is provided; it means design of every main longitudinal girder as separate girder on the elastic foundation. The elastic foundation is formed by main direction girders as "Ï"-shape frame braces-less trusses; rigidity and strength estimation for these trusses is carried out concerning to composite bar theory with additional accounting of shear deformation. As a result, practical rigidity and strength definition of every part of the trusses' composite bars became elementary.
In order to validate this approximate methodic, rigidity and strength was defined for frame of m/v "P. Antokolskiy" by bar and plate idealizations of FEM. FEM calculations were enhanced by additional stresses estimation by analytical formulae for general longitudinal and transverse bending of the middle frame of 3D compartment as well as for other elements of the complex 3D structure. Methodic was validated finely.
3. Accidents' analyze for hull of river and river-sea vessels (V.A. Nilva is author).
The analysis of statistical data of vessels' casualties of the internal and river-sea going vessels' types for the period of1991-2012 is carried out in the article. More detailed classification of hull damages that takes into consideration damage localization along the vessel is proposed. Such classification does not damages of gears, systems and mechanisms of the vessel. By the received results it is possible to make a conclusion that the most probable types of damage of inland waterways vessels are: the fires and explosions, groundings and ice damages.