Mihkel Kõrgesaar

Tallinn University of Technology | TTU · Estonian Maritime Academy

Equivalent Single Layer (ESL) approach is extended to model ultimate strength of stiffened panels under a combination of in-plane compression and shear. Ultimate strength under this combined loading depends on the loading path and could be lower than for only uni-axial compression since shear load can produce axial forces. Thus, to account for this...

The objective of this paper is to present the application of equivalent single layer (ESL) approach for the ultimate strength assessment of ship hull girder in the context of numerical finite element (FE) simulations. In the ESL approach, the stiffened panel is replaced with a single plate, which has the equivalent stiffness of the original panel....

The interaction of sea ice with offshore structures is an important engineering concern in ice-infested areas. This paper presents a procedure to evaluate ice loads acting at the sloping offshore wind turbines in the Estonian territorial waters at the Baltic Sea, where the waters are seasonally covered by ice. Region-specific characterization of ic...

Arctic shipping is growing driven by a demand for natural resources, climate change, and technological development, among other factors. While this provides many benefits for society, it also entails risks for people, the environment, and property. The purpose of this article is to assist ship designers, operators, owners, and other stakeholders in...

Committee Mandate Concern for accidental limit states (ALS) of ships and offshore structures and their structural components under accidental conditions. Types of accidents considered shall include collision, grounding, dropped objects, explosion, and fire. Attention shall be given to hazard identification, accidental loads and nonlinear structural...

While society benefits from Arctic shipping, it is necessary to recognize that ship operations in Arctic waters pose significant risks to people, the environment, and property. To support the management of those risks, this article presents a comprehensive approach addressing both short-term operational risks, as well as risks related to long-term...

Structural integrity analysis of ships in collisions and groundings requires a realistic idealization of environmental and operational conditions within computational models. In essence, the problems are solved as Fluid-Structure-Interaction problems in which structural mechanics has an important role by modeling the contact. The accuracy of struct...

Steel stiffened panels are widely used in engineering design and construction. However, numerical modeling and analysis effort for a three-dimensional (3D) stiffened panel may be notable, especially for the ultimate limit state of ship structures. Therefore, a homogenization method is outlined that transforms 3D stiffened panel into an Equivalent S...

This paper presents CFD (Computational Fluid Dynamics) simulations of the performance of a planing hull in a calm-water condition, aiming to evaluate similarities and differences between results of different CFD models. The key differences between these models are the ways they use to compute the turbulent flow and simulate the motion of the vessel...

Analysis of the dynamic response of ships in accident scenarios requires a realistic idealisation of environmental and operational conditions by multi-physics models. This paper presents a procedure that simulates the influence of strongly coupled FSI effects on the dynamic response of ships involved in typical collision and grounding events. Our m...

This paper presents a benchmark study on grounding simulations. The objective was to compare key parameters in modelling techniques and assumptions for finite element (FE) analysis. Five contributors participated in the benchmark study by performing numerical simulations, and results were compared with available results from experimental tests. Goo...

This paper re-evaluates recently published quasi-static tests on laser-welded thin-walled steel structures in order to discuss the fundamental challenges in collision simulations based on finite element analysis. Clamped square panels were considered, with spherical indenter positioned at the mid-span of the stiffeners and moved along this centerli...

The paper presents a method for the assessment of residual strength of a ship hull damaged in a grounding accident. The strength assessment is based on a coupled beam (CB) method that allows time-efficient analysis. As a case study the method is applied to a double hull tanker. Three grounding damages are defined based on IACS guidelines and with a...

The analysis of dynamic response of ships in accident scenarios requires realistic idealization of the environmental actions for different ship operational conditions. This paper presents a procedure for fluid structure interaction (FSI) modelling of ships involved in typical collision and grounding events. The method implements LSDYNA / MCOL model...

This paper focuses on the bending deformation experienced by metallic materials and its characterization during the crash analysis of ship structures. These analyses are conducted with plane stress shell elements for computational reasons. The inherent nature of through thickness plane stress poses restrictions on how the bending associated stress...

Planing hulls are quite well known for their wide application in coastal seas. These vessels can reach high-speeds using the hydrodynamic pressure acting on the wetted area, which tends to raise the bow of the vessel thereby decreasing wave-making resistance. However, operation at super high-speeds necessitates accurate performance prediction of th...

An analytical procedure is presented based on the perturbation technique to solve the governing equations of the reactant gas flow in the gas channels of a PEMFC draft angle. The equations are solved in both the anode and cathode gas channels with conveniently defined perturbation parameters to achieve the velocity, species concentration and temper...

The climate change has made the transit through Arctic area more feasible, which demands reliable methods to evaluate ship performance. Ship performance in ice is a cross-scale problem, where the desired output such as ship speed lies in larger scale while the actual ship-ice interaction happens in smaller scale. Due to insufficient knowledge in ic...

Present paper gives an overview of the factors that affect the strength and structural design of advanced thin-walled marine structures with reduced plate thickness or alternative topologies to those used today in marine industry. Due to production-induced initial deformations and resulting geometrical non-linearity, the classical division between...

Spray rails, as well as the whole topic of spray sheet deflection, have been generally disregarded since the 1960s. Therefore, a series of model tests has been conducted with a 19 m craft configured with different spray rail arrangements (operating in a range of Froude numbers Fr = 0.77…1.35). The model test series comprises five spray rail configu...

This paper investigates the influence of the strain rate and element size on the fracture of steel plates presented in marine structures undergoing grounding when modeled by the finite element method. Three different experimental tests (tensile, tearing and perforation tests), performed at different velocities, are used in the study. These tests ar...

In accidental limit state analysis of ship structures and their components, the common assumption is that failure takes place in the plate field under multi-axial tension, thus most advancements in developing fracture criteria have focused on that region. In contrast, failure in low stress triaxialities is relatively unexplored territory in the con...

Spray rails and deflectors are appendages that are attached to the hull of a vessel in order to detach the spray from the bottom panels above the stagnation line. This reduces the frictional resistance caused by the spray, and thus makes the operation more efficient. Spray rails, as well as the whole topic of spray sheet deflection, have been gener...

Present paper gives an overview of the factors that affect the strength and structural design of advanced thin-walled marine structures with reduced plate thickness or alternative topologies to those used today in marine industry. Due to production-induced initial deformations and resulting geometrical non-linearity, the classical division between...

This paper presents a benchmark study on collision simulations that was initiated by the MARSTRUCT Virtual Institute. The objective was to compare assumptions, finite element models, modelling techniques and experiences between established researchers within the field. Fifteen research groups world-wide participated in the study. An experiment invo...

Overload response of the stiffening frames in ship side structure due to ice loading is an important design consideration for ships operating in ice infested waters. By overload, we mean loads that are larger than assumed by the rules. Therefore, the response of ice strengthened grillage frames is investigated under a range of idealized rectangular...

Selection of suitable ice class for ships operation is an important but not simple task. The increased exploitation of the Polar waters, both seasonal periods and geographical areas, as well as the introduction of new international design standards such as Polar Code, reduces the relevancy of using existing experience as basis for the selection, an...

This paper investigates the influence of material non-linearity on load carrying mechanism and strain path in stiffened panel. First, clamped stiffened panel with dimensions of 1.2 x 1.2 m was penetrated with rigid indenter until fracture took place. Second, panel material was characterized with standard tensile tests using flat test coupons extrac...

Ductile fracture in large structures is often resolved with non-linear finite element (FE) simulations employing structural shell elements which are larger than localization zone. This makes solution element size dependent and calibration of material parameters complex. Therefore, the paper explores the ability of numerical simulations to capture t...

Groundings are among the most common and destructive maritime accidents. Sea bottom shape influences greatly what kind of damage the ship structure suffers and whether this leads to loss of water tightness. Sormunen et al. [21] presented and statistically compared rock models used in grounding damage analysis with detailed bottom shape data from tw...

Current design standards for ships operating in ice-covered waters involve great deal of uncertainty in the associated risk level. The main reason for this uncertainty is the stochastic nature of ice failure process during ice-structure interaction, which means that the load imposed by ice on structures cannot be accurately defined. Therefore, rule...

All-metal sandwich panels with a low weight-to-stiffness ratio provide the means to develop cost and energy efficient large-scale thin-walled structures such as ships. However, the modeling and computational effort for a three-dimensional (3-D) sandwich structures may be significant especially in the limit state analysis of ship structures. This ca...

Element size sensitivity of shell elements employed in the non-linear finite element (NLFE) crash simulations of large structures has been one of the key issues in the accidental limit state analysis lately because of its strong effect on simulation accuracy. Recently it was found that scaling the failure strain based on the combined effect of elem...

This paper presents improvements to the simplified ship grounding resistance and damage opening model for double bottom tankers of Heinvee et al. (2013) by in-cluding the effect of longitudinal and transverse bulk-heads. The study is based on numerical simulations of 90 grounding scenarios. The scenarios were constructed for three different size ta...

This paper contributes to the physical understanding of stress states in different element sizes during uniaxial tension. For this purpose, the results of uniaxial tension tests with the dog-bone sheet speci- mens are re-analysed to determine the stress state in the material during deformation and the equivalent plas- tic strain to failure. Failure...

Large-scale thin-walled structures with a low weight-to-stiffness ratio provide the means for cost and energy efficiency in structural design. However, the design of such structures for crash and impact resistance requires reliable FE simulations. Large shell elements are used in those simulations. Simulations require the knowledge of the true stre...

In this investigation, ductile fracture in stiffened and unstiffened panels is simulated employing the fracture criterion, which depends on the mesh size, stress state and damage induced softening. The aim of the study is to show that employed fracture criterion removes mesh size effects more efficiently than traditional fracture criteria adjusted...

Recently, various novel steel sandwich structures have been proposed as they promise increased energy absorbing capabilities during impact or collision. The amount of energy absorbed during impact depends on the sandwich core geometry. Therefore, in this study, two different sandwich core geometries (X- and Y-core) are optimized for crashworthiness...

There is a wide range of fracture criteria available in the literature to simulate the ductile fracture in large structures. Almost all criteria depend in some form on the mesh size and some criteria also account the effect of the stress state on the fracture ductility. Furthermore, a material model employed could considerably influence the analysi...

In this study, fracture propagation in large shell elements is modelled with the softening law. This law is given in a general form, enabling investigations of different softening behaviours to be conducted. The final fracture is simulated by removing elements. The softening parameters are derived using the energy-based representative volume elemen...

A Ship collision accident represents a daily threat for vessels operating in dense traffic zones. The collision consequences may include loss of life or severe injuries if passengers are on board. The latter would be the case for ROPAX vessels, which are fairly dominant in the Baltic Sea connecting various member states. Furthermore, their routes t...

In this paper a procedure is presented for the conceptual design of a crashworthy side structure of a liquefied natural gas (LNG) tanker. The crashworthiness of an LNG tanker is assessed taking into account the deformation restrictions of the containment system. A particle swarm algorithm is used for the structure optimisation. The classification s...