Bachelor-, project- and master theses

We always appreciate your interest in executing a bachelor’s, project or master’s theses at our institute. As part of our ongoing research, we are offering the following topics. Topics other than those listed here can be discussed and assigned with the employees at short notice. Please contact Prof. Sören Ehlers or Prof. Alexander Düster for further information. It is also possible to find suitable thesis topics in cooperation with out national and international partners.

Bachelor and project theses:

Berechnung der Ermüdungsfestigkeit von geschweißten und korrodierten Proben

Tragstrukturen für Offshore-Windenergieanlagen (OWEAn) werden überwiegend aus Stahl gefertigt und sind unter maritimen Umweltbedingungen stark korrosionsgefährdet. Daher werden besondere Anforderungen an den Korrosionsschutz von OWEAn gestellt. Als Korrosion wird ein durch die Umgebung bedingter, zerstörerischer Prozess eines Metalls durch elektrochemische Reaktionen bezeichnet. Trotz Korrosionsschutzmaßnahmen kann Korrosion nicht vollständig ausgeschlossen werden. Die Hersteller von Korrosionsschutzsystemen gewährleisten einen Schutz über eine Lebensdauer von ca. 20 Jahren. Es besteht großes Interesse seitens der Betreiber von Windparks, die OWEA auch nach Schädigung des Korrosionsschutzsystems weiter zu betreiben. Eine vollständige Neubeschichtung auf See ist nicht wirtschaftlich. Daher ist es im Interesse der Betreiber, die Restlebensdauer unter freier Korrosion zu ermitteln.

Dazu sind geschweißte Stahlproben in künstlichem Meerwasser eingelagert und sollen mittels Versuchen auf ihre Ermüdungsfestigkeit untersucht werden.

Mehr Informationen bei christian.woitzik(at)tuhh.de

Development of Latex Coated Poraver®Particles via Fluidised Spray Granulation Process

The aim is to investigate the use of fluidised spray granulation as a method for generating latex coated particles. The fluidised spray granulation process involves suspending particles in a fluidized bed, and then spraying a liquid coating onto the particles. The resulting coated particles can be used in a variety of applications, such as in the cavity of a ship’s double hull which leads to improved
crashworthiness. Expanded glass granules (Poraver) have been found to be particularly suitable due to their chemical and physical properties. However, the absorbed energy needs to be improved and optimised by means of a latex coating layer.

The objectives are to:
Develop a method for generating latex coated particles using fluidised spray granulation.
Characterize the properties of the resulting coated particles, including size distribution, morphology, and coating thickness.
Conduct single and multi particle tests to evaluate the performance of the coated particles in different applications.

More information here.

For further information, contact us at:
Wasif Safdar, M.Sc., wasif.safdar(at)tuhh.de, 040 / 42878 – 6185
Sonja Rotter, M.Sc., sonja.rotter(at)tuhh.de, 040 / 42878 – 4764

 

Vergleichende Untersuchung einer quasi-statischen Verformung mit LS-DYNA und OpenRadioss

Sehr schnelle und/oder hochgradig nichtlineare Probleme der Festkörpermechanik werden mit Hilfe der expliziten Berechnungsmethoden gelöst. Anschauliche Beispiele solcher Berechnungen sind Crash- oder Umformsimulationen.
Momentan existieren auf dem Markt einige wenige Anbieter propriäterer Software, die explizite Solver entwickeln und vertreiben. Diese sind robust und validiert. Parallel dazu werden von der Open Source Community freie Alternativen entwickelt.
In dieser Arbeit soll eine vergleichende Untersuchung zwischen einem Vertreter der kommerziellen Software und Open Source auf Basis eine Umformsimulation erstellt werden. Als kommerzielle Software dient dem Projekt LS-DYNA und auf der Seite von Open Source OpenRadioss.

Mehr informationen gibt es hier.
Oder bei alexander.duester(at)tuhh.de

Modelling of a container with FE with measured material data for the simulation of bearing capacity and damages

The loss of containers is a significant problem for the global merchant fleet as well as other marine operators that might accidentally hit floating containers. Some container losses are associated with structural damages of the containers which lead to a collapse of a container stack. In order to investigate the bearing capacity a numerical finite element model of a container is to be built in LS-Dyna. Material properties from specimen tests conducted in our laboratory are available and need to be incorporated.
One major challenge is the modelling of the container doors which is one of the most important parts in this study. The bearing capacity of a container door and its contribution to the global strength is different than of a wall, but the question is how. The objective is to model this in a simplified way and to evaluate the modelling approach.

Hence, this project is based on the following tasks:  

  • Reading and analysis of the state of the art
  • FE Modelling of a container where experimental data can be incorporated
  • Assessment of the modelling of the doors (including a parameter study)
  • Validation of the container model with experiments and / or simulations from the literature.

20” Containers that are need to be modeled

Thesis supervisor: Franz von Bock und Polach (franz.vonBock@tuhh.de)

Prediction of fatigue failure of welded joints based on machine learning algorithm 

Fatigue behaviour of welded joints depends on a number of factors, such as local weld geometry, macro-geometric misalignment, loading type, etc. Due to the complexity of this topic, machine learning techniques offer a possibility to assess the mutual influence of these aspects. In this study, different machine learning techniques, i.e. decision tree, boosted trees, and artificial neural network are utilised to to predict fracture locations and fatigue life of welded joints.

Please send an email to moritz.br(at)tuhh.de

Correlation between local weld geometry and fatigue strength of butt-welded joints 

It is a well-known fact that weld geometry influences fatigue resistance of welded connection, weld toe shape being of particular importance. Geometrical features of a weld can be generally described by size of weld toe undercut, radius and angle, as well as weld height and width.

Industry standards regulate size of some of these features and thereby define quality class of the weld and to ensure fatigue performance. Usually measurements of weld features are performed manually by means of templates. This method is not very efficient and obviously subject to individual inspector’s judgment. Many industries are more and more looking into 3D scanning as an inspection method which bears potential for automation and offers high repeatability. Scanned surfaces of welds can then be subject to geometric evaluation with regard to size of their features more reliably. Hence, this project deals with the correlation of local weld geometries and fatigue crack initiation locations.

Please send an email to moritz.br(at)tuhh.de

Fatigue strength of flush ground butt-welded joints

The post-weld treatment of butt-welded joints enables a significant increase in fatigue strength. Especially the use of high-strength steels allows a significant increase compared to the condition after welding. In many codes, the determination of fatigue strength of post-welded joints does not yet take into account the higher yield strength and the associated improved fatigue strength, although this is associated with design disadvantages.
Within the scope of this work, the fatigue strength behaviour of welded joints with optimised butt-welded joints is to be investigated and evaluated. For this purpose, literature data and test results from previous work are to be statistically evaluated.
The aim of this work is to improve the design of post-treated welded joints by highlighting the effect of post-treatment with regard to material strength and other influencing factors.

Please send an email to moritz.br(at)tuhh.de

Application of the strain energy density method to butt-welded joints

To this day many different local fatigue assessment methods have been proposed and are still being developed. Each of them has benefits and downsides for particular problems.

The most common local fatigue assessment method in ship and offshore industry is the structural hot-spot stress approach. One of the more sophisticated methods is based on the integration of the averaged strain energy density (SED) in a small volume surrounding for example the notch at a weld toe. In different studies the accuracy of the method has proven to be eminent; however, the computational effort is still high, due to particular requirements on the finite element mesh used for calculation of the SED.

In order to improve the applicability of the method for fatigue assessment of larger structures like ships or offshore structures it is necessary to decrease the computational effort of this method and to verify its accuracy based on different scenarios. Thus, this thesis aims at comparing different approaches for SED-based assessment of butt-welded joints.

Please send an email to moritz.br(at)tuhh.de

Fatigue assessment of steel specimens subjected to an accelerated corrosion test 

Steel structures exposed in maritime environments are highly susceptible to corrosion. To guarantee operational safety, the integrity of the structure has to be ensured. The remaining fatigue life of steel structures in a corrosive environment is difficult to predict. According to DNV, the service life can be verified with the nominal stress concept using S-N curves. Different curves considering the environmental condition can be applied, such as “air” or “free corrosion”.

Within the scope of this work, the S-N curves for round steel specimens are to be investigated and evaluated. In order to account for corrosion, an accelerated corrosion procedure has to be implemented – based on given literature – before testing the specimens.

The aim of this work is to determine the S-N curves for the given specimens and compare the results with respect to the corrosive media. Furthermore, the validity of the data obtained by the accelerated corrosion test has to evaluated.

Please send an email to christian.woitzik(at)tuhh.de

Finite element modeling of the triaxial test

In this project, the triaxial test as one of the important characterizing tests for powder materials shall be simulated using the finite element method (FEM). This approach can help to study the behavior of discrete materials in two different ways. It may consider all particles together as a continuum and discretize it with finite elements. Here, some constitutive models like the Mohr-Coulomb or the Drucker-Prager model may be used. The other way is using the multi-particle finite element method (MPFEM) where each particle is modeled separately and discretized by finite elements. For this study, it is required to carry out a parametric study using the commercial software Ansys and prepare the corresponding macro scripts (APDL). Comparing the results of two above mentioned approaches and a scientific discussion is also expected.  

      Schematic view of the triaxial test

Interested applicants are asked to contact Sonja Rotter : sonja.rotter(at)tuhh.de

Experimentele und numerische Untersuchung poröser Materialien

Im Rahmen des Graduiertenkollegs, Prozesse in natürlichen und technischen Partikel-Fluid-Systemen (PintPFS), werden zum Thema ”Identifikation von kontinuumsmechanischen Materialparametern granularer Materialien mit Hilfe von Partikelmethoden” Bachelor-, Projekt- und Masterarbeiten sowie Hiwi-Stellen vergeben.

Der aktuelle Schwerpunkt des Projekts ist die experimentelle und numerische Untersuchung von Multi-Partikel Systemen mit hilfe unixialer Drucktests. Hierfür sollen im Rahmen einer studentischen Arbeit oder Hiwi-Stelle Experimente mit unterschiedlicher Anzahl an Partikeln sowie mehreren Gescheindigkeiten durchgeführt werden. Im nächsten Schritt werden diese Experimente numerisch simuliert um weitere Einblicke über die wechselwirkung der Partikel zu erlangen.

Matlab Kenntnisse zur Auswertung der Experimente sind von Vorteil.

Kontakt: sonja.kraus(at)tuhh.de

Application of DEM-BPM to simulate the mechanical behaviour of coated particles

As part of the project “Optimisation of kinetic energy of coated particles for improved kinetic energy absorption” in the research training group “Processes in natural and technical particle-fluid systems” (PintPFS), HiWis, Bachelor, Project and Master theses are offered.

Current work involves the numerical modelling of coated particles using the Discrete Element Method (DEM). The difficulty lies in the correct determination of large number of structural and material parameters for the numerical model. Since there is more than one coating material, a robust methodology needs to be developed for parameter identification that can be validated against experimental results from single and/or multi particle tests. The validated numerical model will be used to simulate a collision scenario with a particle filled double hull to determine the extent of kinetic energy absorbing capabilities of coated particles. In this context, different topics can be developed.

More information here.

Knowledge of MATLAB is required for the evaluation of results. For further information, contact us at:
Wasif Safdar, M.Sc., wasif.safdar(at)tuhh.de, 040 / 42878 – 6185
Sonja Rotter, M.Sc., sonja.rotter(at)tuhh.de, 040 / 42878 – 4764
 
 

Application of FEM to simulate the mechanical behaviour of particles

As part of the research training group “Processes in natural and technical particle-fluid systems” (PintPFS), HiWis, Bachelor, Project and Master theses are offered.

For the FEM modelling of particles, a continuum approach needs to be adopted. Previous work has been done using Mohr-Coloumb and hypoplastic material model to simulate the breakage of Poraver particles. Experiments were carried out to validate the simulations. However, the results were not reliable in areas with large deformation where the particles are crushed by contact with the bulbous bow. Therefore, the work needs to be repeated and extended by using other material models. In this context, different topics can be developed.

More information here.

Knowledge of MATLAB is required for the evaluation of results. For further information, contact us at:
Wasif Safdar, M.Sc., wasif.safdar(at)tuhh.de, 040 / 42878 – 6185
Sonja Rotter, M.Sc., sonja.rotter(at)tuhh.de, 040 / 42878 – 4764
 
 

Master Theses:

Development of Latex Coated Poraver®Particles via Fluidised Spray Granulation Process

The aim is to investigate the use of fluidised spray granulation as a method for generating latex coated particles. The fluidised spray granulation process involves suspending particles in a fluidized bed, and then spraying a liquid coating onto the particles. The resulting coated particles can be used in a variety of applications, such as in the cavity of a ship’s double hull which leads to improved
crashworthiness. Expanded glass granules (Poraver) have been found to be particularly suitable due to their chemical and physical properties. However, the absorbed energy needs to be improved and optimised by means of a latex coating layer.

The objectives are to:
Develop a method for generating latex coated particles using fluidised spray granulation.
Characterize the properties of the resulting coated particles, including size distribution, morphology, and coating thickness.
Conduct single and multi particle tests to evaluate the performance of the coated particles in different applications.

More information here.

For further information, contact us at:
Wasif Safdar, M.Sc., wasif.safdar(at)tuhh.de, 040 / 42878 – 6185
Sonja Rotter, M.Sc., sonja.rotter(at)tuhh.de, 040 / 42878 – 4764

Vergleichende Untersuchung einer quasi-statischen Verformung mit LS-DYNA und OpenRadioss

Sehr schnelle und/oder hochgradig nichtlineare Probleme der Festkörpermechanik werden mit Hilfe der expliziten Berechnungsmethoden gelöst. Anschauliche Beispiele solcher Berechnungen sind Crash- oder Umformsimulationen.
Momentan existieren auf dem Markt einige wenige Anbieter propriäterer Software, die explizite Solver entwickeln und vertreiben. Diese sind robust und validiert. Parallel dazu werden von der Open Source Community freie Alternativen entwickelt.
In dieser Arbeit soll eine vergleichende Untersuchung zwischen einem Vertreter der kommerziellen Software und Open Source auf Basis eine Umformsimulation erstellt werden. Als kommerzielle Software dient dem Projekt LS-DYNA und auf der Seite von Open Source OpenRadioss.

Mehr informationen gibt es hier.
Oder bei alexander.duester(at)tuhh.de

Modelling of a container with FE with measured material data for the simulation of bearing capacity and damages

The loss of containers is a significant problem for the global merchant fleet as well as other marine operators that might accidentally hit floating containers. Some container losses are associated with structural damages of the containers which lead to a collapse of a container stack. In order to investigate the bearing capacity a numerical finite element model of a container is to be built in LS-Dyna. Material properties from specimen tests conducted in our laboratory are available and need to be incorporated.
One major challenge is the modelling of the container doors which is one of the most important parts in this study. The bearing capacity of a container door and its contribution to the global strength is different than of a wall, but the question is how. The objective is to model this in a simplified way and to evaluate the modelling approach.

Hence, this project is based on the following tasks:  

  • Reading and analysis of the state of the art
  • FE Modelling of a container where experimental data can be incorporated
  • Assessment of the modelling of the doors (including a parameter study)
  • Validation of the container model with experiments and / or simulations from the literature.

20” Containers that are need to be modeled

Thesis supervisor: Franz von Bock und Polach (franz.vonBock@tuhh.de)

Predicting Ship structural responses to enable Autonomous Shipping: Fluid-Structure-Interaction and Machine Learning

Autonomous ships are seen by the maritime industry as key to improve shipping efficiency and safety in the future. The full realization of the benefits of autonomous shipping requires significant developments within ship design, navigation and control systems technology and operational modes combined with the ability to assess and verify the safety and performance in a credible manner. The aim of the work is to develop a digital twin approach to address one aspect of the very complex overall problem – ship hydrodynamics in waves and the associated structural consequences based on near field information.

simon.haberl@tuhh.de

3D enrichment for extended finite element modeling

Numerical modeling of problems with singularities, such as cracks or V-notches, exhibits poor results near the singularity. One of the methods to overcome this is the extended finite element method (XFEM), which makes use in enrichment functions to capture the singularity. Current works on XFEM make use only in the first terms of the 2D eigen-expansion near the singularity, even when describing complex 3D crack geometries. This thesis aims at implementing high-order terms of the 3D eigen-expansion as enrichment functions in the context of the finite cell method (Cartesian grids).
For further information please contact:

mahan.gorji(at)tuhh.de or yaron.schapira(at)tuhh.de

Prediction of fatigue failure of welded joints based on machine learning algorithm 

Fatigue behaviour of welded joints depends on a number of factors, such as local weld geometry, macro-geometric misalignment, loading type, etc. Due to the complexity of this topic, machine learning techniques offer a possibility to assess the mutual influence of these aspects. In this study, different machine learning techniques, i.e. decision tree, boosted trees, and artificial neural network are utilised to to predict fracture locations and fatigue life of welded joints.

Please send an email to moritz.br(at)tuhh.de

Implementing new integration methods in the Finite Cell Method (FCM)

Mesh generation is usually the most time-consuming process in using the standard FEM for applications with complex geometry. It may be difficult for a FE mesh to accurately follow the complex shape of the physical domain. The issues of mesh generation problems can be addressed by using the FCM. The FCM combines the benefits of higher order finite elements with the idea of fictitious domain methods. The essential idea of FCM is to simplify the mesh generation step by separating the approximation of the analytical solution from the physical domain as shown in the following picture.

With this definition, there are three types of elements in FCM: 1) elements that are fully inside the physical domain, 2) elements that are fully outside the physical domain and 3) trimmed element. Integration over trimmed elements can be done using different methods such as Quad/Octree, moment fitting, etc. In your project, you will work on a new integration method, which is based on adaptive fitting of trimming points using parametric functions. With this method, the positions and weights of standard Gaussian points will be recalculated to be adapted to the conditions of trimmed cells (See below picture)

Interested students should have the initial knowledge of programming with MATLAB and/or C++ to develop and implement new concepts into two/three dimensional FCM problems. For further information please contact:

farhad.hosseini(at)tuhh.de

Weld toe and root failure transition in load-carrying cruciform joints

It is well known that there is an inherent risk in load-carrying fillet welded joints for fatigue fracture from the weld root. This is usually avoided by large throat thicknesses, which reduced the nominal stress in the cross-section of the fillet weld. However, the reason for weld root failure is not only governed by throat thickness, but also by other parameters like loading type, leg length and so on. Assessment of the risk of root failure can be either empirically or numerically. For the later, different methods are permitted by industry standards and or are still under development.

In recent years, attempts have been made to simplify these approaches and to find a method that is most suitable for fatigue assessment based on finite element method. Although, differences between the different approaches have been proven, it is sometimes believed that some of the methods are directly comparable. However, recent studies found differences in the estimating whether cracks will initiate from the weld toe or root for different methods. Hence, this project is concerned with the investigation of weld toe or root transition for load-carrying cruciform joints. For this purpose, finite element simulations will be applied.

Please send an email to moritz.br(at)tuhh.de

Topics related to fatigue strength of 3D printed materials

Additive manufacturing as a new production process offers great advantageous for certain applications compared to classical processes; however, additively manufactured components are known to have poor surface quality after production. These surfaces can contain defects, from which fatigue cracks can be initiated. Possibilities to improve the fatigue strength included post-production methods like heat treatment or hybrid production processes (e.g. machining of the surface). In current projects the fatigue behavior of 316L specimens produced by selective laser melting and wire and arc additive manufactured are investigated. Topics for project and master thesis include:

• Fatigue strength of welded 3D printed materials
• Fatigue strength of wire and arc additive manufactured (WAAM) materials
• Hybrid additive manufacturing

Please send an email to moritz.br(at)tuhh.de

Fatigue assessment of welded joints under consideration of notch acuity, material strength, and crack initiation behaviour

In recent years there has been a trend towards steels of higher and higher strength in various industrial sectors. In order to be able to use the advantages of greater strength constructively, high demands are placed on the quality of weld seams. The estimation of the fatigue strength according to the classification regulations of DNV GL etc. As a result, no high-strength materials are currently being considered in welded joints. Within the scope of this thesis, the fatigue strength behavior of butt weld joints shall be investigated and evaluated. For this purpose, fatigue strength evaluations are to be carried out under consideration of notch acuity, material strength, and crack initiation behaviour. The aim of this study is an estimation of the fatigue strength based on the aforementioned properties and an estimation of the constructional possibilities by the use of high-strength steels in shipbuilding.

Please send an email to moritz.br(at)tuhh.de

Fatigue assessment of post-weld treated joints for high-speed sailing yachts

The keels of high-performance sailing yachts are increasingly made of high-strength steels with yield strengths above the usual strengths of ship structural steel. The constructions of these keels consist of both milled profiles and welded hollow chamber profiles which are often post-weld treated. However, the assessment of the fatigue strength according to the DNV GL regulations does not currently include consideration for high-strength materials in welded joints and the effect of post-weld treatment. Within the scope of this project thesis, the fatigue behaviour of high-strength steels will be investigated and evaluated. For this purpose, fatigue tests are carried out for different steel grades and production methods. Herein welded joints in as-welded state and after grinding are considered. In addition, the effect of notches in the base material due to milling of the structure will be investigated. To secure and validate the test results, the sample series should be analysed with the aid of the finite element method.

Please send an email to moritz.br(at)tuhh.de

Investigation of temperature effect on fatigue crack growth in welded structures

The fatigue life of structures can be divided in two stages. While the crack initiation stages can occupy up to 90% of the lifetime of smooth specimen (Clark and Knott, 1975), the fatigue life of welded structures is generally propagation-dominated. Crack growth is usually influenced by temperature effects and since more ship and offshore structures are employed in arctic environments these effects need to be analysed.

Recommendations for using material data for fatigue crack growth analysis in failure assessment procedures and codes like BS 7910:1999 or API 579-1, are usually given regardless of the service conditions like temperature. However, fatigue assessment based on crack growth simulation is a difficult procedure due to many influencing factors. Hence, this project is concerned with the investigation of temperature effects on fatigue crack growth in welded joints under low temperatures. For this purpose, finite element simulations will be applied.

Please send an email to moritz.br(at)tuhh.de

A comparative study of deformation and crushing behavior of particles using DEM and MPFEM

The Poraver expanded glass granules may be used as filler material in the void spaces between two walls in double hull vessels. Recent studies demonstrated that this filler material has improved crashworthiness and energy absorption of ship structures during collision.

To model discrete materials like powder, sand, soil, rock, etc., two techniques, i.e. the finite element method (FEM) and the discrete element method (DEM) are mainly used. In DEM, for each particle the equation of motion is solved, considering contact with its neighbors. On the other hand, FEM considers all particles together as a continuum and discretizes it with finite elements. Now, if each particle is modeled separately and discretized by finite elements, we have the multi-particle finite element method (MPFEM). Both DEM and MPFEM may be used for modeling of breakage and crushing behavior of Poraver granules. For DEM, an open source code is available, and for MPFEM, the commercial software Ansys may be employed. In this project, the Poraver particles are under quasi-static compressive loading, and the particles crushing behavior is investigated using these two techniques. It is also expected to have a comparative study on the theory and different aspects of each technique.

Interested applicants are asked to contact DR. Amir Atrian: amir.atrian(at)tuhh.de

Simulation des Bruchverhaltens poröser Materialien mit der Diskrete-Elemente Methode

Im Rahmen des Graduiertenkollegs, Prozesse in natürlichen und technischen Partikel-Fluid-Systemen (PintPFS), werden zum Thema ”Identifikation von kontinuumsmechanischen Materialparametern granularer Materialien mit Hilfe von Partikelmethoden” Bachelor-, Projekt- und Masterarbeiten vergeben.

Der aktuelle Schwerpunkt des Projekts liegt in der Simulation und Auswertung verschiedener Experimente wie z.B. dem Oedometertest, mit deren Hilfe das Bruchverhalten von Partikeln untersucht werden kann. Die Simulationen werden mit einer Diskrete-Elemente Methode durchgeführt. Die Partikel werden dabei als Agglomeratebestehend aus Primärpatikeln und verbindenden Feststoffbrücken dargestellt. Durch das Versagen der Feststoffbrücken kann das Brechen der Partikel simuliert werden.expected.

Weitere Informationen hier

Kontakt: sonja.kraus(at)tuhh.de

Fluid-structure interaction of ships and offshore structures

Coupled simulation of a floating offshore windturbine.

Fluid-structure interaction plays an important role, especially in marine applications, where the loads acting on possibly deformable structures are mainly determined by the fluid around them.
In the past, we have considered several applications, such as ships in sea waves in order to simulate the landing maneuver of service ships to an offshore wind turbine plant as shown in the figure below.
It also includes snapshots of simulations of flexible marine propellers and floating offshore wind turbine plants.

In all of these applications, the interaction of fluid and structure must be considered to predict the structural integrity or the performance accurately.
This leads to a coupled problem, where loads have to be transferred from the fluid subproblem to the structural subproblem and where displacements of the structure have to be sent in the other direction.
For both subproblems, dedicated solvers already exist. It is therefore desired to reuse existing software and modify it such that coupling can be realized between two solvers instead of developing a new code that can handle both problems simultaneously.

Accordingly, we pursue a partitioned approach to solve the coupled problem rather than a monolithic approach. Through a third software, a coupling manager, the data exchange between the fluid and the structural solver (and possibly between any number of solvers for a variety of different problem types) is managed. A major field of research in our group is the development of new coupling algorithms and so-called convergence acceleration schemes inside our coupling manager comana. You can find below a list of publications around these topics.

In your thesis, you may work more on the application side and participate in one of our research projects, e.g. the acoustic behavior of flexible marine propellers or the simulation of a wave energy converter. Alternatively, topics which are less related to applications (e.g. about coupling algorithms and novel discretization schemes) are available.

Interested applicants are asked to contact:

Dr.-Ing. Lars Radtke, Prof. Alexander Düster

Cardiovascular fluid-structure interaction

The simulation of blood flow (hemodynamics) requires the simulation of a fluid-structure interaction problem such that it is very possible for this biomedical application to join forces with the simulation of flexible marine structures.
One of the main applications for blood flow simulations is the optimization of implants like stents, bypass-grafts or stent-grafts as well as external cardiovascular devices.
In recent years, we have developed a simulation approach that allows for investigations, e.g. of the hemodynamic in the connection by arteries and bypass-grafts, so-called anastomoses, as shown in the figure below.

Coupled simulation of the hemodynamics in an end-to-side anastomosis.

In order to solve the coupled fluid-structure interaction problem, we reuse existing software for the structure and the fluid subproblem and couple them using a third software, our coupling manager comana.
In such a partitioned solution approach for coupled problems, the so-called added mass effect can lead to instabilities in the simulations. In biomedical applications, where the density of the fluid and the structure are almost equal this effect is especially problematic (as opposed to engineering applications considering, e.g. steel and water). While we can achieve stable simulations with novel stabilization methods from literature, we constantly work on improving and fine-tuning these. Theses focusing on these rather theoretical aspects may only perform larger simulations in an exemplary spirit and mainly work with academic test cases.

In an active research project, we currently use mathematical shape optimization methods in combination with the coupled simulation approach. Using the so-called adjoint method, our goal is to find optimal shapes. e.g. for anastomoses, that minimize or maximize clinically relevant hemodynamic factors associated, e.g. with the development of atherosclerosis or hemolysis.

Interested applicants are asked to contact:

Dr.-Ing. Lars Radtke, M.Sc. Jorrid Lund, Prof. Alexander Düster

Numerical investigation of cable structures

Cables are slender and long structures that are used in many areas of our daily life as well as in numerous industrial applications. With the growing electrification, the increasing digitalisation and automation of (industrial) processes, the demands and requirements with regard to cables are becoming more and more important. Cables can serve as structural elements (e.g. in bridges and ski lifts), electrical conductors to transmit energy or signals, or feed lines in maritime applications to name only a few examples.
It is our aim to advance and study the numerical simulation of cables, given their complex and challenging structure: several layers of different materials like metallic wires, dielectric layers, polymer insulations, or conducting sheaths among various other types of materials are used. Throughout their lifetime cycle, cables can be exposed to various loading situations like tension, torsion, bending or contact deformations, which can lead to large local deformations.
Also, geometrical aspects like reordering of the inner parts and friction between the parts must be considered, posing a serious challenge to numerical simulations.
In our approach, high-order hexahedral elements with an anisotropic ansatz space [1] are used to model the cables as slender structures. The geometric characteristics of the slender structure facilitate the choice of an advantageous and efficient ansatz for each loading situation [2]. The complex inner structure is approximated by a single material that is anisotropic in both the elastic and elastoplastic regime [3]. Thereby, the elastoplasticity covers the inelastic phenomena arising from the contact of the inner parts.

[1] Düster, A., Bröker, H. & Rank., E., 2001. The p-version of the finite element method for threedimensional curved thin walled structures. International Journal for Numerical Methods in Engineering, 52(7), 673-703.
[2] Hildebrandt, A., & Düster, A. (2022). Numerical Investigation of High-Order Solid Finite Elements for Anisotropic Finite Strain Problems. International Journal of Computational Methods, 2250007.
[3] Sansour, C., Karšaj, I., & Sorić, J., 2006. A formulation of anisotropic continuum elastoplasticity at finite strains. Part I: Modellin
g. International journal of plasticity, 22(12), 2346-2365.  
[4] Dörlich, V., Linn, J., Scheffer, T., & Diebels, S., 2016. Towards viscoplastic constitutive models for cosserat rods. Archive of Mechanical Engineering, 215-230.

In the scope of the project, master and project thesis are possible. Next to the listed topics we can discuss your own ideas as well or find an interesting topic together.

  1. Topic: Parameter identification for anisotropic material parameters of cables
    Possible tasks:
    1. Identify loading/deformation states that correspond to specific material parameters
    2. Analyse the influence of the loading/unloading path
    3. Define different parameter identification methods of interest and compare their
      performance on virtual experiments
    4. Optionally: Create and train a machine learning algorithm to identify parameters for a
      defined set of input values
  2. Topic: Create an ABAQUS model of a fully resolved cable structure
    Possible tasks:
    1. Research and choose one or several cable structures that are created
    2. Create a mesh in ABAQUS resolving the inner parts of the cable (wires, insulation, etc.)
      and include part specific materials
    3. Add contact between the inner parts (ideally with friction)
    4. Analyse the behaviour under defined loading situations with varying material parameters
    5. Optionally: Create a mesh, that is composed of layers without resolving the single wires
      and identify effective parameters for the layers
    6. Optionally: Compare the behaviour for different cable cross-sections.

If you are interested, please contact André Hildebrandt .

Application of DEM-BPM to simulate the mechanical behaviour of coated particles

As part of the project “Optimisation of kinetic energy of coated particles for improved kinetic energy absorption” in the research training group “Processes in natural and technical particle-fluid systems” (PintPFS), HiWis, Bachelor, Project and Master theses are offered.

Current work involves the numerical modelling of coated particles using the Discrete Element Method (DEM). The difficulty lies in the correct determination of large number of structural and material parameters for the numerical model. Since there is more than one coating material, a robust methodology needs to be developed for parameter identification that can be validated against experimental results from single and/or multi particle tests. The validated numerical model will be used to simulate a collision scenario with a particle filled double hull to determine the extent of kinetic energy absorbing capabilities of coated particles. In this context, different topics can be developed

More information here

Knowledge of MATLAB is required for the evaluation of results. For further information, contact us at:
Wasif Safdar, M.Sc., wasif.safdar(at)tuhh.de, 040 / 42878 – 6185
Sonja Rotter, M.Sc., sonja.rotter(at)tuhh.de, 040 / 42878 – 4764

Application of FEM to simulate the mechanical behaviour of particles

As part of the research training group “Processes in natural and technical particle-fluid systems” (PintPFS), HiWis, Bachelor, Project and Master theses are offered.

For the FEM modelling of particles, a continuum approach needs to be adopted. Previous work has been done using Mohr-Coloumb and hypoplastic material model to simulate the breakage of Poraver particles. Experiments were carried out to validate the simulations. However, the results were not reliable in areas with large deformation where the particles are crushed by contact with the bulbous bow. Therefore, the work needs to be repeated and extended by using other material models. In this context, different topics can be developed.

More information here.

Knowledge of MATLAB is required for the evaluation of results. For further information, contact us at:
Wasif Safdar, M.Sc., wasif.safdar(at)tuhh.de, 040 / 42878 – 6185
Sonja Rotter, M.Sc., sonja.rotter(at)tuhh.de, 040 / 42878 – 4764