Karol Niklas

Search for optimum geometry of selected steel sandwich panel joints

Search for optimum geometry of selected steel sandwich panel joints Application of steel sandwich panels to ship structures requires many problems to be solved. Joints between the panels as well as those between the panels and other structures is one of the more difficult problems associated with the structures in question. This paper presents the searching for process of optimum geometry of a panel-to-panel joint of longitudinal arrangement, performed by means of the ANSYS software. A configuration was searched for of parameters which can ensure as-low-as possible values of geometrical stress concentration coefficients at acceptable mass and deformations of the structure. Analysis of the obtained results made it possible to propose the optimum geometry of the considered joint.

Strength Analysis of a Large-Size Supporting Structure for an Offshore Wind Turbine

Abstract The offshore wind power industry is the branch of electric energy production from renewable sources which is most intensively developed in EU countries. At present, there is a tendency to install larger-power wind turbines at larger distances from the seashore, on relatively deep waters. Consequently, technological solutions for new supporting structures intended for deeper water regions are undergoing rapid development now. Various design types are proposed and analysed, starting from gravitational supports (GBS), through monopiles and 3D frame structures (jackets, tripods), and ending with floating and submerged supports anchored to the seabed by flexible connectors, including TLP type solutions. The article presents the results of examination of an untypical large-size gravitational support intended for waters with the depth of up to 40 m. Firstly, a general concept of the new design is presented, while the next basic part of the article describes the support design in detail and provides its strength analysis. The examined support has the form of a large steel container consisting of conical segments. The strength analysis was conducted using the finite element method (FEM), in accordance with the standard DNVGL-ST-0126. Modifications introduced to the most heavily loaded structural node of the support, which was the set of base bottom trusses, is also included. The results of the performed analysis prove that the presented concept of supporting structure for a 7MW turbine meets fundamental strength criteria. The nonlinear buckling analysis was performed to evaluate the critical force acting on the support, which turned out to be 1.44 times as large as the maximum load of the wind turbine. Potentially important issues for further analyses have been identified as those resulting from the asymmetry of basic loads acting on the support.

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.

Numerical calculations of behaviour of ship double-bottom structure during grounding

Numerical calculations of behaviour of ship double-bottom structure during grounding The idea of the CORET project consists in adding, to the existing construction, special polymer-concrete coatings intended for the increasing of ships capability against losing structural tightness during collision or grounding. In order to correctly design the protective barriers, to perform relevant numerical simulations is necessary. The elaborating of numerical models of ship structure behaviour during collision is very complicated and requires auxiliary simulations (on submodels) to be performed. This paper is devoted to elaborating a numerical model of a fragment of ship double-bottom structure. On the basis of experimental tests it was possible to verify and calibrate the numerical model which may be used in further design work aimed at the increasing of crashworthiness of structure during collision.

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.

FEM modelling of stress and strain distribution in weld joints of steel sandwich panels

The development of laser welding technology has enabled the mass production of thin-walled structures, including steel sandwich panels. The technology of joining plating panels with stiffeners by welding allows us to create joints with a specific geometry and material properties. In comparison with other types of joints, laser welds are characterized by their specific behaviour under cyclic load and, as a consequence, a different model of fatigue damage. The basis of fatigue analysis of laser-welded joints was the determination of stress concentrations in the notches. For this purpose, a numerical finite element method model of a laser-welded joint was created. The article presents the main aspects of the numerical model and the results concerning the influence of the modelling method on the strain and stress distribution in the notches. For the weld root notch, the theoretical results have been compared with experimental data of strain distributions obtained by the laser extensometry grid technique.