Patrick Kaeding

Application of the idealized structural unit method for ultimate strength analyses of stiffened plate structures

ABSTRACT To assess the safety of ship structures, the determination of the ultimate hull girder strength is of essential importance. The idealized structural unit method (ISUM) is a simplified method to perform progressive collapse analyses of large structural systems with less computational efforts compared to non-linear finite element analyses (FEA). In this paper, the basic concept and the applicability of ISUM are demonstrated for a stiffened plate panel under lateral pressure and inplane thrust. Ship structures are subjected to global bending moments and lateral pressure loads. To simulate the collapse behaviour of such complex structural systems, a box-girder specimen in bending is investigated. Appropriate numerical models are presented and the corresponding ultimate strength values are validated against experimental results. To simulate combined load cases with lateral pressure loads acting on the bottom of the box-girder specimen, the corresponding ultimate strength values determined with ISUM are compared with non-linear FEA results.

Investigations on the influence of shear and lateral loads on the collapse behaviour of plate structures under inplane thrust

ABSTRACT The design of stiffened plate structures is of essential importance to prevent an ultimate strength failure of ship hull girders under extreme loads. Progressive collapse analyses are necessary to determine the buckling/plastic collapse behaviour of structural components. In this paper, plates, stiffened plates and larger panels of different plate slenderness ratios are investigated by nonlinear finite element analyses (FEA). The progressive collapse behaviour is determined for load cases of pure longitudinal and transverse thrust as well as for combined loads of lateral pressure and shear. The influence of preloads due to lateral pressure and shear on the remaining load carrying capacity of steel plate structures under inplane thrust is demonstrated. The effect of two different configurations of essential boundary conditions for shear load applications is discussed. The ultimate strength results delivered by separate models for continuous plates, stiffened plates and stiffened plate panels are compared.

Validation of Twistlocks in Modular Offshore Platform Designs for the Arctic

The University of Rostock has generated dimensioning equations to calculate the strength of twistlock systems under non-standard loading conditions on offshore platforms in the POLAR project in the last years. These dimensioning equations have been presented on previous OMAE conferences. In this paper ultimate strength analyses are conducted to assess the safety margin between elastic design and final rupture. The validation of the local system is shown and the results of the experiment and the simulation are analyzed and compared. In these experiments twistlock systems are subjected to cyclic loads, long-term tensile load at design level and ultimate loads. The experiments are conducted with a heavy duty hydraulic test rig. The results show agreement between experiment and simulation with regard to the rupture behavior and the force-displacement relationship.Copyright

Simulations of Mountings on Offshore Platforms in Arctic Regions

In the arctic offshore industry auxiliary systems are required for adequate living and working conditions. These systems comprise pipes and service modules on LNG ships as well as work and accommodation modules on offshore platforms. The object of this paper is an overview about the approach to simulate the different mounting systems on offshore/ship-structures in arctic regions: Which assumptions are made in the simulations? Which forces act on the systems? How are the results accomplished — by parameter studies, sub-model-technique? Where are the challenges located in the simulation? How can the runtime of the simulations be reduced?In the case of pipe mountings, two different phases — installation and operation mode — as well as the cooling down of the insulating material between the two phases are considered. The result of this research topic is an automatic and parametric FE-Analysis of the structural limit state in these modes. The analysis of the twistlock system has been presented the last two years at OMAE. These systems are used to mount living and working modules on offshore platforms. The existing and new results will be discussed and evaluated. The accommodation modules are located in a containment — the so-called housing — attached to the deck. The required connection between this housing and the deck is analyzed. This analysis comprises welded and bolted connections. According to the stress results of the simulations the adequate connection is selected. These analyses are performed with the sub-model-technique in ANSYS.Copyright

Dimensioning of Twistlocks in Modular Offshore Platform Designs for Arctic Regions

To mount service modules in a flexible manner on offshore platforms twistlock systems are used. If the application is not in accordance with standard conditions the existing regulations are not sufficient. Therefore new regulations with appropriate dimensioning equations must be generated. The results of the OMAE 2013 paper “Assessment of Container Mountings in Modular Offshore Platform Designs for Arctic Regions” are applied in this paper to reach such equations.The stress on twistlocks which mount standard containers to the offshore platform deck in arctic regions depends on roll angle of the offshore platform and friction coefficient — depending on temperature — and is analyzed by regression analysis in this paper. The results show that a local twistlock system can be used to simplify the calculation.Also the application of a crane module is simulated. The regression analysis is divided into two parts — the cone and the base of the twistlock: these parts take most of the load again depending on roll angle and friction coefficient.The result of this paper consists of dimensioning equations for these two different applications of twistlock systems in arctic regions.Copyright

Assessment of Container Mountings in Modular Offshore Platform Designs for Arctic Regions

Regularly the twistlock system is used to mount containers on container vessels or on offshore platforms as service containers in normal climate regions. In this paper the twistlock system is analyzed with respect to mounting auxiliary systems as well as accommodation and service modules to the deck of offshore platforms in arctic regions. When the twistlock systems are used in harsh environment it is also important that the twistlocks withstand the acting forces without great displacements and without exceeding the elastic range. But in arctic regions the mountings must resist additional forces due to ice interaction, cold temperatures and small friction coefficients. Because the existing rules do not include regulations how to analyze the strength of these mountings in arctic regions the influence of the friction coefficients and the Young’s modulus were of interest in this study. This paper summarizes some numerical works on these new discoveries. The results of the computations show that the Young’s modulus has no influence on the stress and the displacement of the bodies. However, the friction coefficient has influence on the stress specified in the simulations for large roll angles.Copyright

Thick Plate Rolling—a Numerical Approach in Comparison with Analytics and Experimental Data

Today, wind turbines are mostly made of glass or carbon fibre. The manufacturing process leads to high precision and quality of the final product. Nevertheless, this fabrication method of rotor blades is very cost intensive and its production technology is not the best in terms of recyclability. In addition to its good recyclability, the handling of steel is well known and its fabrication is inexpensive. Due to these facts an idea of foils to be produced from steel arose. In cooperation with a metal forming company the 3‐Dimensional rolling concept came up. Initially, rolling experiments with cold lead plates in a scale of 1:4 are made to simulate the later on used hot steel plates. Such an approach has to be accompanied by fundamental research. This paper sketches the lead rolling experiment and gives an assessment if it is applicable for a hot rolling process with steel. For this purpose, the lead test data are interpreted, the numerical model is explained and results are presented. Furthermore, an anal...