Sören Ehlers

Technische Universität Hamburg | TUHH

The International Maritime Organization (IMO) aims to reduce the annual greenhouse gas emissions from international shipping by at least 50 % by 2050, compared to 2008. To this end, the organization has adopted a set of regulations, including the Energy Efficiency Design Index (EEDI), the Energy Efficiency eXisting ship Index (EEXI), and the Carbon...

Digital twins (DTs) are being increasingly considered in the maritime industry for the purposes of system design, monitoring, control, optimization, operational planning, maintenance, fault detection, and life cycle management. A system simulation can be utilized to enable many of these functionalities. Co-simulation based on the Functional Mock-up...

Fatigue and fracture are important design criteria for marine structures subjected to static and cyclic loading [...]

To enhance the safety of ship structure design, this study evaluated time-dependent hull girder ultimate strength considering thick corrosion and the inclination conditions of stiffened panels. The hull girder ultimate strength was calculated using incremental–iterative methods based on IACS-CSR in a bulk carrier hull model. The corrosion effect wa...

Integration of renewable energies into existing grids must be safe and reliable including the subsea power-transmission cables. Therefore, this paper determines the purely mechanical ultimate strength of a DC and an AC power transmission cable under axial load. Aspects concerning the electrical functionality of these cables are outside the scope of...

Combining several additive manufactured (AM) parts to larger parts by welding may be required due the limited building volume of powder bed AM methods. Laser powder bed fusion (LPBF) has a great potential because it enables the production of nearly full-density components through AM processes; however, additional residual stresses and production de...

Coating systems protect maritime structures from corroding; nevertheless, coatings have a high probability to fail preferentially at highly stressed elements, i.e. welds, due to their exposure to cyclic loading. The increasing trend of installing offshore platforms, the aimed level of safety on ships and offshore structures, and the need of reducin...

Welded joints have a large variation of their geometry and is one important reason for the comparable large scatter regarding their fatigue life. This study presents and tests an approach for the probabilistic fatigue assessment of welded joints based on their individual local geometry. This approach is adopted from the IBESS research cluster and c...

The microstructure‐properties relations and strengthening mechanisms of additively manufactured 316L stainless steel is comprehensively investigated in this work. The orientation dependency and the strain hardening are studied by tensile testing of as‐built specimens fabricated by laser‐based powder bed fusion (LPBF) in different directions. The re...

Corrosion is mostly considered as homogeneous thickness reduction in construction guidelines of the maritime industry. Several studies concluded that besides a homogeneous thickness reduction the corroded non-uniform surface morphology is affecting the strength and strain behavior of steel. However, the effects of non-uniform corrosion on the behav...

Thermal cut edges can be found in most maritime structures, e.g. in window openings or hatch corners on ships. It is very common to treat free plate edges by grinding or sandblasting due to fatigue and coating requirements. The aim of this study is to review the fatigue behavior of typical treatment methods. Within this study several fatigue tests...

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...

Ships and offshore structures operating in ice-covered sea areas have to withstand ice loads. In particular, the distribution of ice pressure in the contact area is critical. The pressure distribution changes temporally and spatially and depends on the ice failure behaviour. Experimental measurements of ice pressures are possible with pressure mapp...

The climate crisis results in a rapid sea ice decline, making shipping routes accessible for longer durations throughout the year and therefore increasing maritime traffic. At the same time, ice-structure interaction is known to cause damage to ships and structures. In this context, the flexural strength is a key property of the ice. It is also an...

_ The aim of this paper is to investigate the relationship between design and operational ship parameters with respect to radiated underwater noise and to develop a semiempirical noise prediction model that includes the dominant noise contributors present on merchant vessels. The model is based on Dietrich Wittekind’s prediction model and on underw...

Experimental Methods, Scaling Laws, DIC (Digital Image Correlation), Hydrodynamic of Flexible Structures, Wave-in-deck, Hybride model testing, Vibrations, Fatigue testing, Large scale impact testing, Corrosion testing, Full-scale iced load measurements, Health monitoring model, Digital twin model

The aim of this paper is to introduce a fully nonlinear numerical finite element solver for the simulation of nonlinear wave processes in the presence of a solid ice sheet. In this study, solid ice cover referred to the size of the ice sheet and denoted that the length of the ice sheet was many times larger than the longest relevant wavelength. The...

Support structures for offshore wind turbines and the corresponding transformer platforms are highly susceptible to corrosion. In particular, the phenomenon of pitting is crucial, as it leads to local stress concentrations and thus affects the fatigue life of structures. Despite corrosion protection systems, corrosion cannot be completely avoided,...

Building and using ice-related models is challenging due to the complexity of the material. A common issue, shared by both material models and (semi-)empirical approaches, is estimating unknown input parameters such as compressive strength. This is often done with additional empirical formulas which have drawbacks, e.g., they are based on a limited...

In order to ensure high weld qualities and structural integrity of engineering structures, it is crucial to detect areas of high stress concentrations along weld seams. Traditional inspection methods rely on visual inspection and manual weld geometry measurements. Recent advances in the field of automated measurement techniques allow virtually unre...

Fixed offshore wind turbines are increasingly developed for high latitude areas where not only wind and wave loads need to be considered, but also moving sea ice. Current structural design rules do not adequately consider the effect of ice loading on fatigue life, due to missing studies on fatigue strength of welded joints under combined wind, wave...

Climate change provides for a stronger wave climate and the open water area in this region will increase. The increase in open water area allows for an increase in higher energy surface waves than previously. In addition, human activities are much more complex in this zone, called Marginal Ice Zone, compared to the open ocean, so that there is an i...

Ships and offshore structures operating in ice-covered sea areas have to withstand ice loads. In particular, the distribution of ice pressure in the contact area is critical. The pressure distribution changes temporally and spatially and depends on the ice failure behaviour. Experimental measurements of ice pressures are possible with pressure mapp...

Abstract: Ships and offshore structures in Arctic waters are exposed to sub-zero temperatures. While the effects of high temperatures on material behavior are considered in international standards and guidelines, there is at present no basis for evaluating fatigue strength at sub-zero temperatures, as there is limited data on the fatigue strength o...

Building and using ice-related models is challenging due to the complexity of the material. A common issue, shared by both material models and (semi-)empirical approaches, is estimating unknown input parameters such as compressive strength. This is often done with additional empirical formulas which have drawbacks, e.g., they are based on a limited...

Shipping accounts for about 3% of global CO2 emissions. In order to achieve the target set by the Paris Agreement, IMO introduced their GHG strategy. This strategy envisages 50% emission reduction from international shipping by 2050, compared with 2008. This target cannot be fulfilled if conventional fuels are used. Amongst others, hydrogen is cons...

Due to the limited building volume of powder bed additive manufactured (AM) methods, combining several AM parts for a larger part through a welding joint may be required. Through AM processes, Laser powder bed fusion (LPBF) has a great potential because it enables the production of nearly full-density components. But the residual stresses are still...

Due to the limited building volume of powder bed additive manufactured (AM) methods, combining several AM parts for a larger part through a welding joint may be required. Through AM processes, Laser powder bed fusion (LPBF) has a great potential because it enables the production of nearly fulldensity components. But the residual stresses are still...

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 elements of ships are subjected to a high number of cyclic loads, which are critical to fatigue life. Especially for ultra-large container ships the cutting of thick steel plates with high finishing quality and good fatigue life is important, e.g. located at openings in walls and decks of ships. This study presents a series of fatigue te...

In recent years, there has been a growing interest in exploring the resources of the Arctic regions and an increase in shipping in regions with seasonal sub-zero temperatures. Such low temperatures impose challenging requirements for the structural integrity of steel structures and their weldments. Hence, specific knowledge of the behavior of mater...

The formation and propagation of cracks occur through irreversible dislocation movements at notches, material defects, and grain boundaries. Since this process is partly thermally controlled, the resistance to dislocation movements at low temperatures increases. This slows both fatigue initiation and fatigue crack propagation. From recent experimen...

The paper presents a procedure for numerically modeling the surface of corroded specimens. A 3D laser scan is utilized to derive surface morphology and corrosion pit depth distribution. This corrosion depth is analyzed with a probability model to assess the morphology difference and the characteristic of the corrosion pit depth at a particular volu...

A lower pitting severity produces a shallower corrosion pit shape on a corroded ballast tank. Pit distributions of corroded specimens have a probability model for the non-Gaussian surface. Therefore, the present work focuses on the numerical study of stress distribution within the corrosion pit area, while considering different corrosion pit geomet...

The formation and propagation of cracks occurs through irreversible dislocation movements at notches, material defects and grain boundaries. Since this process is partly thermally controlled, the resistance to dislocation movements at low temperatures increases. This slows both fatigue initiation and fatigue crack propagation. From recent experimen...

Fixed offshore wind turbines continue to be developed for high latitude areas where not only wind and wave loads need to be considered but also moving sea ice. Current rules and regulations for the design of fixed offshore structures in ice-covered waters do not adequately consider the effects of ice loading and its stochastic nature on the fatigue...

Repeated wet–dry cycle exposure to seawater during ballasting processes hastens the surface corrosion rate. Moreover, the larger volumetric changes of corroded ballast tanks generate lower pitting severity. This paper models the pitting severity of corroded ballast tanks of varying roughness and volumes. Seven rectangular finite elements models wit...

Ships are operating in ice-covered waters and level ice interaction represents one of the relevant interaction scenarios. Furthermore, level ice is the standard ice condition for testing and performance assessment. Therefore, various approaches exist to obtain relevant loads for this interaction type. While limitations of existing numerical approac...

Butt-welded joints are common in many industries. The fatigue behavior of such joints depends on numerous factors, e.g. load level, local weld geometry, or parent material strength. To make things worse, these factors often interact, yet mutual influence can hardly be quantified by multivariate studies, i.e. varying one factor at a time out of many...

Raw data of the temperature measurements on the ship structure of RV Polarstern during the MOSAiC expedition

H-adaptivity is an effective tool to introduce local mesh refinement in the FEM-based numerical simulation of crack propagation. The implementation of h-adaptivity could benefit the numerical simulation of fatigue or accidental load scenarios involving large structures, such as ship hulls. Meanwhile, in engineering applications, the element deletio...

A methodology for risk analysis applicable to shipping in arctic waters is introduced. This methodology uses the Bowtie relationship to represent an accident causes and consequences. It is further used to quantify the probability of a ship accident and also the related accident consequences during navigation in arctic waters. Detailed fault trees f...

Commonly, to evaluate the influence of the local weld geometry in fatigue test, small-scale specimens are used, assuming those represent a longer weld adequately. In this study, a comparison between short specimens and a long weld is performed. A method is developed for the statistical evaluation of weld toe radii and angles, stress concentration f...

Fixed offshore wind turbines continue to be developed for high latitude areas where not only wind and wave loads need to be considered, but also moving sea ice. Current rules and regulations for the design of fixed offshore structures in ice-covered waters do not adequately consider effects of ice loading and its stochastic nature on fatigue life o...

While some post-weld treatment techniques increase the fatigue life mainly due to induced compressive residual stress others are trying to create a smooth transition at weld toes. One of the latter is weld profiling. This study investigates the effect of weld profiling for four different steel types from S355 to S900 including one duplex stainless-...

H-adaptivity is an effective tool to introduce local mesh refinement in FEM-based numerical simulation of crack propagation. The implementation of h-adaptivity could benefit the numerical simulation of fatigue or accidental load scenarios involving large structures such as ship hulls. In engineering applications, the element deletion method is freq...

Additively manufactured components typically contain process-related defects on and near surfaces that have to be removed by surface post-treatment. Various studies show that post-treatment can achieve a similar fatigue strength as in conventionally manufactured components. To this day, however, hardly any studies are known on the fatigue strength...

While some post-weld treatment techniques increase the fatigue life mainly due to induced compressive residual stress others are trying to create a smooth transition at weld toes. One of the latter is weld profiling. This study investigates the effect of weld profiling for four different steel types from S355 to S900 including one duplex stainless-...

Fatigue strength of welded joints is typically independent of the parent material static strength; however, there are two exceptions from this rule—post-weld treated joints and high-quality joints. The reason for both is the absence of sharp weld transitions. Thus, fatigue life is not fully governed by fatigue crack propagation but also by fatigue...

This paper presents a finite element model for the simulation of ice-structure interaction problems, which are dominated by crushing. The failure mode of ice depends significantly on the strain rate. At low strain rates the ice behaves ductile, whereas at high strain rates ice reacts in brittle mode. This paper focuses on the brittle mode, which is...

The size of the fully developed process zone (FDPZ) is needed for the arrangement of displacement sensors in fracture experiments and choosing element size in numerical models using the cohesive element method (CEM). However, the FDPZ size is generally not known beforehand. Analytical solutions for the exact FDPZ size only exist for highly idealise...

Commonly, to evaluate the influence of the local weld geometry in fatigue test, small-scale specimens are used, assuming those represent a longer weld adequately. In this study, a comparison between short specimens and a long weld is performed. A method is developed for the statistical evaluation of weld toe radii and angles, stress concentration f...

Additive manufacturing (AM) enables the cost‐effective production of complex components, many of which are traditionally manufactured using costly subtractive processes. During laser‐based powder bed fusion of metals (PBF‐LB/M), internal pores and rough surfaces are typically inevitable, reducing fatigue and corrosion resistance compared to traditi...

In the FATICE project we have addressed the fatigue damage on fixed offshore structures exposed to drifting ice. This is an important challenge in the development of energy production from offshore wind in the Baltic and involves at least five element: a) define ice statistics, b) predict the structural response (ice-structure interaction simulatio...

This paper presents a finite element model for the simulation of ice-structure interaction problems, which are dominated by crushing at low and medium confinement ratios. The failure mode of ice depends significantly on the strain rate. At very low impact velocities the ice behaves ductile, whereas at high velocities the ice reacts in brittle mode....

Additive manufacturing (AM) enables the cost-effective production of complex components, many of which are traditionally manufactured using costly production steps among other processes. One widely applied AM process is Laser-based Powder Bed Fusion of Metals (PBF-LB/M); however, internal pores and rough surfaces are typically inevitable with PBF-L...

The surface morphology of the ballast tank has changed due to years of exposure to seawater corrosion. Hence, the severity of pitting corrosion and the random shapes of corrosion pits may affect the remaining life of the ballast tank. Therefore, this paper presents the difference in surface morphologies of corroded ballast tank and its correlation...

The problem of typical stress-based fatigue assessment methods is that additional influencing factors like temperature effects do not directly influence the respective stress and can thus only be incorporated via modification factors. The stress averaging approach is expected to account for effects that influence the support around notches via the...

Strain gauges are commonly used for the instrumentation of ship structures to measure ice loads on the basis of shear strain differences. Finite Element Analysis (FEA) is used to determine the load–strain relation of the instrumented area by calculating an Influence Coefficient Matrix (ICM). However, the accuracy of the measurement method and the i...

It is well known that material properties undergo significant changes with temperature. In order to meet extreme environmental requirements for ships and offshore structures operating in Arctic regions, the effect of temperature on material behavior needs to be considered. In recent studies, significantly higher fatigue strength was observed for ba...

Prioritizing effects for material modeling of natural materials such as ice and rock is mostly done based on a subjective mix of knowledge, model purpose, and experimental studies limited to that purpose. This risks overlooking effects or interaction of effects, and limits transferability of material models to other scenarios. We compiled a large i...

Ice ridges represent a major threat to ships and offshore structures in areas with sea ice but no icebergs, since they frequently determine and govern the structural design loads. This work focuses on the development of environmental contours for first-year sea ice ridge statistics, which are able to represent the key parameters that will influence...

For the evaluation of the structural response in accidental scenarios like ship collisions, the simulation of tensile failure initiation is inevitable. Here, one difficulty is that the process of failure initiation is a very local process, which cannot be simulated in its details at present due to the computing effort which would be required. Howev...

Additive Fertigung wie z.B. selektives Laserschmelzen (SLM) ermöglicht die kostengünstige Produktion komplexer Bauteile, die mit anderen Verfahren oftmals mehrere aufwendige Fertigungsschritte umfassen. Allerdings können beim SLM Verfahren prozessbedingt Poren und raue Oberflächen entstehen, welche zu einer geringeren Schwingfestigkeit dieser Struk...

The size of the Fully Developed Process Zone (FDPZ) is needed for the arrangement of displacement sensors in fracture experiments and choosing element size in numerical models using the cohesive element method (CEM). However, the FDPZ size is generally not known beforehand. Analytical solutions for the exact FDPZ size only exist for highly idealise...

Most merchant ships operating in the cold regions are not able to break ice themselves, they can only navigate in the broken ice, the so-called brash ice channels. Today’s standard requires a model test in real brash ice conditions to be carried out and realistic additional resistances to be estimated from this. The problem is that they can only be...

Ships and offshore structures operating in Artic regions face specific challenges such as ice loads and seasonal low temperatures. In order to meet these extreme environmental requirements, the effect of temperature on material behaviour needs to be considered. It is well known that static material properties (yield strength, fracture toughness etc...

This paper presents the capabilities of a ship-ice interaction simulator developed at the Hamburg University of Technology for the ship operation in level ice. Besides a brief introduction of the fundamentals of the simulator and the full availability of the source code, the capabilities of the simulator in terms of the following are presented: sim...

Within stress‐based fatigue assessment concepts, causes that do not influence the fatigue stress parameters, such as temperature, can only be accounted for by means of modification factors. The strain energy density (SED) method allows to account for changing material support effects and Young's modulus with temperature directly. Thus, in this stud...

The global demand in energy resources is moving the petroleum industry to the Arctic with its huge resource potential. The lack of infrastructure onshore increases the role of the Arctic marine shipping and the importance of the Northern Sea Route (NSR). Shipping within NSR waters is associated with challenges and risks, including environmental one...

Several studies have found significant increase in the fatigue strength of welded joints of structural steels at sub-zero temperatures. This study addresses the research by investigating the applicability of local fatigue assessment methods to welded joints exposed to sub-zero temperatures. For this purpose, fatigue test results of two fillet weld...

Ships operating in ice-covered waters may experience structural damage due to ice-induced loads. This can occur even though the ship structure is designed according to rules considering ice loading. The basis of these design rules can be empirical, e.g. measured loads from full-scale trials and observed damages or energy based, which is known as th...