Janusz Kozak

Selected problems on application of steel sandwich panels to marine structures

Selected problems on application of steel sandwich panels to marine structures The paper presents a view on selected problems concerning application of steel sandwich panels to marine structures. Such problems connected with specificity of thin- skin laserwelded structure are varying in topics beginning from micro-scale properties of laser- welded T-joint through the joining of sandwich structures together up to connection and integration of such structures with a classical single-skin structure.

Problems Of Determination Of Welding Angular Distortions Of T - Fillet Joints In Ship Hull Structures

Abstract Ship hull structure elements are usually joined by welding. Welding distortions may cause many problems during manufacturing process. In the literature a wide spectrum of suggestions has been proposed for correct estimation of welding deformation, particularly angular ones, in the fillet welded T-joints. In this work a verification of certain methods selected from the literature is presented basing upon the results of the laboratory measurements. To this end, values determined on the basis of engineering hypotheses have been compared with those obtained from the laboratory tests.

Variant Designing in the Preliminary Small Ship Design Process

Abstract Ship designing is a complex process, as the ship itself is a complex, technical multi-level object which operates in the air/water boundary environment and is exposed to the action of many different external and internal factors resulting from the adopted technical solutions, type of operation, and environmental conditions. A traditional ship design process consists of a series of subsequent multistage iterations, which gradually increase the design identification level. The paper presents problems related to the design of a small untypical vessel with the aid of variant methodology making use of optimisation algorithms. The computer-aided design methodology has been developed which does not need permanent reference to already built real ships and empirical-statistical relations. Possibilities were indicated for integrating together early design stages, and parallel designing of hull shape and parameters.

Design Methodology for Small Passenger Ships On the Example of the Ferryboat Motława 2 Driven by Hybrid Propulsion System

Abstract Dynamic development in practically all fields of science and engineering has not passed over shipbuilding. In last years, engineers got to their use computer software which makes it possible to perform strength and hydrodynamic calculations as well as to visualize design projects in 3 D space [1-4]. At their disposal they have full spectrum of modern solutions associated with the use of advanced materials and technologies [5-7]. More and more attention is also paid to impact onto the natural environment [8,9]. Every new object must influence the environment as low as possible, beginning from building phase through its service life up to final utilization - such approach is called „green-shipping“. However, not only practical reasons are important. Clients, i.e. ship owners and passengers of ships paid more and more attention to image of floating units. During decision taking on that from whom a transport service has to be ordered, the most modern ships of an attractive image matching with place and time, are often taken into consideration. Such situation has become a basis for an idea of working out a concept of a new ferryboat for National Maritime Museum. As the ferry has to navigate in „the heart of the town“, then, apart from strictly marine and engineering aspects, an important factor of its designing is its expected image - a set of significant meanings and emotions written in architecture language. The new ferryboat, like its historical predecessors, will never leave urban water routes.

Comparison of strain results at a laser weld notch obtained by numerical calculations and experimental measurements

In the development of ship structures applying new materials and it’s purposeful placement play an important role. During the last years, especially in a construction of ro-ro type vessels, the usage of novel sandwich structures in cargo decks is profitable. Steel sandwich panel is an innovative solution which at a todays state of development can be used for the construction of any members not taking part in a global bending of a hull. The one important reason for this is a lack of knowledge and experience in the fatigue assessment. The problem of fatigue assessment of the steel sandwich structures arises from no typical welds connecting its structural components. The joints are fabricated by the use of laser welding technique, or hybrid welding. Standard methodology for the fatigue analysis is local stress approach or local strain approach. In both methods the crucial aspect is determination of a maximum values of strains and stresses. The most effective technique to designate these values is numerical modelling with the use of Finite Element Method or Boundary Element Method. In this paper the comparison of local stresses at a weld notch obtained by two independent methods is presented. The results calculated by the Finite Element Analysis are being compared with the experimental one measured by the use of laser extensometer grid technique. The goal of this comparison is verification of the main numerical modelling assumptions.

The Influence of Modelling Material Zones on Strains and Stresses at Weld Toe Notch

The latest development in the field of welding technology enabled prefabrication of thinwalled sandwich structures in an industrial scale. Sandwich structures fabricated of steel, or aluminium alloy plates and stiffeners are welded with the use of hipower CO2 lasers. Strength analysis of such structures with the use of finite element method needs proper material modelling. In this paper the material model of steel sandwich panel tee-joint is analysed. The influence of including different material zones on strains and stresses at the weld notch area is presented. The analysis shows that material changes outside the weld notch area do not influence the results of strains and stresses. The impact of the geometrical notch is very local and it does not interfere with material property changes at neighbouring weld zones. For the purpose of determination of maximum values of stresses and strains at weld toe notch, the analysed laser weld can be modelled with the use of one material property for all weld zones.

Influence of the Notch Rounding Radius on Estimating the Elastic Notch Stress Concentration Factor in a Laser Welded Tee Joint

In recent years an increased interest of industry in sandwich-type metal structures can be observed. These structures consist of thin plates of 2.5 mm in thickness separated by stiffeners of different shapes and forms. Welds joining the plates and stiffeners are made on the outer side of the plates using laser welding technique. A locally focused source of heat causes the plate to melt creating a very narrow and elongated joint. As a result, sharp geometric notches are formed on the side of the root of a weld – a place which is inaccessible and cannot be checked. Geometries of individual welded joints vary, sometimes considerably, and this makes their analysis even more complicated. Additionally, the use of laser welding technique influences the formation of untypical distribution of changes in material properties in weld zones. The effect is a joint whose behaviour under load is significantly different from the behaviour of a welded tee joint made with the use of classical methods. Fatigue strength calculations for this type of joints can be conducted based on local stress values in notches, which can be determined with the use of Finite Element Method (FEM). This article analyses the influence of the notch rounding radius on the elastic notch stress concentration factor Kt The aim of the analysis is to evaluate the notch stress concentration according to local notch stress approach.

Elastic protection coatings for ship fuel tanks, intended for the increasing of environment protection level

Elastic protection coatings for ship fuel tanks, intended for the increasing of environment protection level Small closed sea shipping regions (such as the Baltic Sea) are specially vulnerable to consequences of ecological disasters due to spills of fuel oil used for ship propulsion and carried in single-plating double-bottom tanks. An alternative solution (against the recommended double- plating structure) was proposed. It consists in applying the second, elastic protection barrier to decrease risk of oil spills resulting from loss of tightness of ship plating in consequence of e.g. collision or grounding.

The Effect of Numerical 2D and 3D Fem Element Modelling on Strain and Stress Distributions at Laser Weld Notches in Steel Sandwich Type Panels

Abstract Like other means of transport, merchant ships face the problem of increasing requirements concerning the environment protection, which, among other issues, implies the reduction of fuel consumption by the ship. Here, the conventional approach which consists in making use of higher strength steels to decrease the mass of the ship hull can be complemented by the use of new steel structures of sandwich panel type. However, the lack of knowledge and experience concerning, among other issues, fatigue strength assessment of thin-walled sandwich structures makes their use limited. Untypical welds imply the need for individual approach to the fatigue analysis. The article presents the effect of numerical FEM modelling with the aid of two-dimensional (2D) and three-dimensional (3D) elements on the results of strain and stress distributions in the areas of toe and root notches of the analysed laser weld. The presented results of computer simulation reveal that modelling of strain and stress states in 2D (instead of full 3D) affects only the results in close vicinity of the notch, and the observed differences rapidly disappear at a distance of 0.05 mm from the bottom of the notch. The obtained results confirm the possibility of use of numerically effective 2D strain and stress state models for analysing the fatigue strength of laser weld according to local approach.

Numerical Model of Plastic Destruction of Thick Steel Structural Elements

Abstract In the shipbuilding industry, the risk of brittle fracture of the structure is limited by using certified materials with specified impact strength, determined by the Charpy method (for a given design temperature) and by supervising the welding processes (technology qualification, production supervision, non-destructive testing). For off-shore constructions, classical shipbuilding requirements may not be sufficient. Therefore, the regulations used in the construction of offshore structures require CTOD tests for steel and welded joints with a thickness greater than 40 mm in the case of high strength steel and more than 50 mm in the case of other steels. Classification societies do not accept CTOD test results of samples with a thickness less than the material tested. For this reason, the problem of theoretical modeling of steel structure destruction process is a key issue, because laboratory tests for elements with high thickness (in the order of 100 mm and more) with a notch are expensive (large samples, difficulties in notching), and often create implementation difficulties due to required high load and range of recorded parameters. The publication will show results and conclusions from numerical modeling of elastic properties for steel typical for offshore applications. Calculations were carried out at the Academic Computer Centre in Gdańsk.