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168

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## Publications

Publications (168)

A novel monolithic approach for simulating vessels in waves with granular cargo is presented using a Finite Volume framework. This model integrates a three-phase Volume of Fluid method to represent air, water, and cargo, coupled with a granular material model. The approach incorporates vessel dynamics by assuming rigid-body motion for the vessel's...

A quantum algorithm for simulating multidimensional scalar transport problems using a time-marching strategy is presented. After discretization, the explicit time-marching operator is separated into an advection-like component and a corrective shift operator. The advection-like component is mapped to a Hamiltonian simulation problem and is combined...

Granular flow problems characterized by large deformations are widespread in various applications, including coastal and geotechnical engineering. The paper deals with the application of a rigid‐perfectly plastic two‐phase model extended by the Drucker–Prager yield criterion to simulate granular media with a finite volume flow solver (FV). The mode...

This talk presents an approximation approach for shape sensitivities in hydrodynamic applications based on the discontinuous Galerkin method (DGM). The DGM is used to compute the primal and the adjoint Navier-Stokes equations and numerical experiments are carried out to investigate the solver performance.

The accuracy of global circulation models partly relies on understanding the dynamics at the coupled atmosphere-ocean interface. Related current research efforts focus on a range of aspects, including the quantification of energy budgets, an understanding of wave growth mechanisms as well as other processes relating to the interaction between waves...

The paper presents a variational quantum algorithm to solve initial-boundary value problems described by second-order partial differential equations. The approach uses hybrid classical/quantum hardware that is well suited for quantum computers of the current noisy intermediate-scale quantum era. The partial differential equation is initially transl...

This article investigates the effect of the cuff size of arterial bypass grafts and the flow conditions on the hemodynamics in the anastomosis (connection) to the artery, using numerical simulations. We consider a fluid-structure interaction problem which is solved based on a partitioned scheme. Additionally, we employ computational fluid dynamics...

The paper is concerned with the minimal drag problem in shape optimization of merchant ships exposed to turbulent two-phase flows. Attention is directed to the solution of Reynolds Averaged Navier-Stokes equations using a Finite Volume method. Central aspects are the use of a p-Laplacian relaxed steepest descent direction and the introduction of cr...

In the last decade, parameter-free approaches to shape optimization problems have matured to a state where they provide a versatile tool for complex engineering applications. However, sensitivity distributions obtained from shape derivatives in this context cannot be directly used as a shape update in gradient-based optimization strategies. Instead...

This article discusses the derivation and numerical implementation of an adjoint system, to the primal Navier–Stokes equations, for the computation of shape sensitivities of ducted blood flows considering non‐Newtonian fluid properties. The ever‐growing advancements in blood flow simulations are, naturally, accompanied by an increased interest in t...

The paper is devoted to two-phase flow simulations and investigates the ability of a diffusive interface Cahn–Hilliard volume-of-fluid model to capture the dynamics of the air–sea interface at geophysically relevant Reynolds numbers. It employs a hybrid filtered/averaging improved detached eddy simulation method to model turbulence and utilizes a c...

The contribution is devoted to combined shape- and mesh-update strategies for parameter-free (CAD-free) shape optimization methods. Three different strategies to translate the shape sensitivities computed by adjoint shape optimization procedures into simultaneous updates of both the shape and the discretized domain are employed in combination with...

Quantum computing uses the physical principles of very small systems to develop computing platforms which can solve problems that are intractable on conventional supercomputers. There are challenges not only in building the required hardware but also in identifying the most promising application areas and developing the corresponding quantum algori...

The talk presents the application of a novel ADMM-based approach for approximating the direction of the steepest descent in W-1-infinity topology. Numerical experiments compare the presented approach with a p-harmonic steepest descent approximation and a Hilbert space approach.

In the last decade, parameter-free approaches to shape optimization problems have matured to a state where they provide a versatile tool for complex engineering applications. However, sensitivity distributions obtained from shape derivatives in this context cannot be directly used as a shape update in gradient-based optimization strategies. Instead...

The paper presents a strategy to construct an incremental Singular Value Decomposition (SVD) for time-evolving, spatially 3D discrete data sets. A low memory access procedure for reducing and deploying the snapshot data is presented. Considered examples refer to Computational Fluid Dynamic (CFD) results extracted from unsteady flow simulations, whi...

The operation of fluid engineering systems is usually governed by a wide range of different parameters. Investigations of the entire parameter spectrum using classical, first-principle based CFD methods are costly with regards to CPU and wall-clock time. Therefore, a near real-time assessment of complex flows using CFD to support the operation is d...

The paper is devoted to two-phase flow simulations and investigates the ability of a diffusive interface Cahn-Hilliard Volume-of-Fluid model to capture the dynamics of the air-sea interface at geophysically relevant Reynolds numbers. It employs a hybrid filtered/averaging Improved Detached Eddy Simulation method to model turbulence, and utilizes a...

This technical paper outlines the predictive performance of a recently published dynamic cumulant lattice Boltzmann method (C-LBM) to model turbulent shear flows at all resolutions.
Emphasis is given to a simple strategy that avoids a frequently observed velocity overshoot phenomenon near rigid walls when combining the C-LBM with an all-resolution...

Quantum computing uses the physical principles of very small systems to develop computing platforms which can solve problems that are intractable on conventional supercomputers. There are challenges not only in building the required hardware, but also in identifying the most promising application areas and developing the corresponding quantum algor...

The paper is concerned with a node-based, gradient-driven, continuous adjoint two-phase flow procedure to optimize the shapes of free-floating vessels and discusses three topics. First, we aim to convey that elements of a Cahn–Hilliard formulation should augment the frequently employed Volume-of-Fluid two-phase flow model to maintain dual consisten...

The paper reports the assessment of a modified cumulant lattice Boltzmann method in turbulent channel flows. The suggested approach is of interest for its resolution-spanning capabilities, which are scrutinized for grid resolutions between 4 and 430 wall units. With the emphasis on a recently published parameterized cumulant collision operator, we...

The paper is concerned with the minimal drag problem in shape optimization of merchant ships exposed to turbulent two-phase flows. Attention is directed to the solution of Reynolds Averaged Navier-Stokes equations using a Finite Volume method. Central aspects are the use of a p-Laplacian relaxed steepest descent direction and the introduction of cr...

In many applications, free surface flow through rigid porous media has to be modeled. Examples refer to coastal engineering applications as well as geotechnical or biomedical applications. Albeit the frequent applications, slight inconsistencies in the formulation of the governing equations can be found in the literature. The main goal of this pape...

This work develops an algorithm for PDE-constrained shape optimization based on Lipschitz transformations. Building on previous work in this field, the $p$-Laplace operator is utilized to approximate a descent method for Lipschitz shapes. In particular, it is shown how geometric constraints are algorithmically incorporated avoiding penalty terms by...

The paper is concerned with the assessment of a cumulant lattice Boltzmann method in wall‐bounded, separated turbulent shear flows. The approach is of interest for its resolution‐spanning success in turbulent channel flows without using a specific turbulence treatment. The assessment focuses upon the flow over a periodic hill, which offers a rich b...

This Technical Note outlines an adjoint complement to a critical building block of pressure-based Finite-Volume (FV) flow solvers that employ a collocated variable arrangement to simulate virtually incompressible fluids. The focal point is to strengthen the adjoint pressure-velocity coupling by using an adjoint Momentum-Weighted Interpolation (MWI)...

The paper is concerned with a node-based, gradient-driven, continuous adjoint two-phase flow procedure to optimize the shapes of free-floating vessels and discusses three topics. First, we aim to convey that elements of a Cahn-Hilliard formulation should augment the frequently employed Volume-of-Fluid two-phase flow model to maintain dual consisten...

The paper is devoted to an adjoint complement to the universal Law of the Wall (LoW) for fluid dynamic momentum boundary layers. The latter typically follows from a strongly simplified, unidirectional shear flow under a constant stress assumption. We first derive the adjoint companion of the simplified momentum equation, while distinguishing betwee...

We introduce a novel method for the implementation of shape optimization for non-parameterized shapes in fluid dynamics applications, where we propose to use the shape derivative to determine deformation fields with the help of the $$p-$$ p - Laplacian for $$p > 2$$ p > 2 . This approach is closely related to the computation of steepest descent dir...

This paper reports on the derivation and implementation of a shape optimization procedure for the minimization of hemolysis induction in blood flows through biomedical devices. Despite the significant progress in relevant experimental studies, the ever-growing advances in computational science have made computational fluid dynamics an indispensable...

In many applications free surface flow through rigid porous media has to be modeled. Examples refer to coastal engineering applications as well as geotechnical or biomedical applications. Albeit the frequent applications, slight inconsistencies in the formulation of the governing equations can be found in the literature. The main goal of this paper...

The paper is concerned with an adjoint complement to the Volume-of-Fluid (VoF) method for immiscible two-phase flows, e.g. air and water, which is widely used in marine engineering due to its computational efficiency. The particular challenge of the primal and the corresponding adjoint VoF-approach refers to the sharp interface treatment featuring...

We introduce a novel method for the implementation of shape optimziation in fluid dynamics applications, where we propose to use the shape derivative to determine deformation fields with the help of the $p-$ Laplacian for $p > 2$. This approach is closely related to the computation of steepest descent directions of the shape functional in the $W^{1...

The paper is devoted to the simulation of maritime two-phase flows of air and water. Emphasis is put on an extension of the classical Volume-of-Fluid (VoF) method by a diffusive contribution derived from a Cahn-Hilliard (CH) model and its benefits for simulating immiscible, incompressible two-phase flows. Such flows are predominantly simulated with...

This manuscript is concerned with a continuous adjoint complement to two-dimensional, incompressible, first-order boundary-layer equations for a flat plate boundary layer. The text is structured into three parts. The first part demonstrates that the adjoint complement can be derived in two ways, following either a first simplify then derive or a fi...

This paper reports on the derivation and implementation of a shape optimization procedure for the minimization of hemolysis induction in biomedical devices. Hemolysis is a blood damaging phenomenon that may occur in mechanical blood-processing applications where large velocity gradients are found. An increased level of damaged blood can lead to det...

This paper reports on the derivation and implementation of a shape optimization procedure for the minimization of hemolysis induction in biomedical devices. Hemolysis is a blood damaging phenomenon that may occur in mechanical blood-processing applications where large velocity gradients are found. An increased level of damaged blood can lead to det...

The paper is devoted to an adjoint complement to the universal Law of the Wall (LoW) for fluid dynamic momentum boundary layers. The latter typically follows from a strongly simplified, unidirectional shear flow under a constant stress assumption. We first derive the adjoint companion of the simplified momentum equation, while distinguishing betwee...

The manuscript is concerned with a continuous adjoint complement to two-dimensional, incompressible, first-order boundary-layer equations for a flat plate boundary-layer. The text is structured into three parts. The first part demonstrates, that the adjoint complement can be derived in two ways, either following a first simplify then derive or a fi...

The paper is concerned with an adjoint complement to the Volume-of-Fluid (VoF) method for immiscible two-phase flows, e.g. air and water, which is widely used in marine engineering due to its computational efficiency. The particular challenge of the primal and the corresponding adjoint VoF-approach refers to the sharp interface treatment featuring...

This paper presents numerical simulations of the natural laminar-turbulent transition in a flat plate boundary layer. Natural transition occurs in low disturbance environments and is triggered by the growth of boundary layer instabilities or disturbances. This contribution specifically aims at investigating the interaction of multiple disturbances...

The paper is devoted to the simulation of maritime two-phase flows of air and water. Emphasis is put on an extension of the classical Volume-of-Fluid (VoF) method by a diffusive contribution derived from a Cahn-Hilliard (CH) model and its benefits for simulating immiscible, incompressible two-phase flows. Such flows are predominantly simulated with...

The paper outlines the predictive capabilities of lattice Boltzmann methods (LBM) in turbulent shear flows. Attention is devoted to a specific collision operator which relaxes the distribution functions in cumulant space. The study highlights the benefits of a carefully defined discrete collision operator by scrutinizing the numerical stability and...

This paper focuses on consistency issues caused by truncated kernels and irregular particle distributions in Smoothed-Particle-Hydrodynamics (SPH). The analysis starts from the kernel-based approximations inherent to the SPH method. An explicit kernel correction is proposed, which approximately achieves first-order consistency. The suggested approa...

The increasing activities in arctic sea areas over the last years have led to a rising demand for numerical tools to design and evaluate ice-going ships. Numerical simulation of ship-ice
interaction can be a suitable method for engineers to evaluate ship designs in early development phases. We present an efficient method to evaluate local and globa...

This contribution outlines the capabilities of an enhanced GPU-accelerated Lattice Boltzmann method (LBM) for the simulation of ice-going Voith Schneider propelled (VSP) ships. Reported results cover a collaboration between an academic and an industrial partner, i.e. TUHH and Voith, within a joint research project to assess the ice-induced loads fo...

The paper is concerned with the simulation of grounding of gravity foundations for wind turbines and the installation process of jack-up rigs in seaway. They are of particular interest for offshore wind parks, where numerical investigations can support the safety margins of an operation. The computational focus of the present study is to supplement...

We discuss exterior and classical interior alternatives for evaluating fluid flow induced forces on bodies. The discussion aims at a reduction of the total shape derivative, achieved through a decoupling of control and objective in the exterior approach. In this case, geometric as well as convective contributions to the shape derivative vanish. Con...

The present research project comprises the development of innovative hydrodynamic design methods for ice-going ships for the investigation and optimization of the propulsion efficiency. It can be stated that there is an urgent need for rational simulation-based techniques in order to reliably analyze the ship motions in ice-covered areas that have...

This paper is devoted to the hydrodynamic interplay of rigid bodies in direct proximity. Emphasis is given to proximity influences on inertia and resistance forces. The numerical study employs an overset grid procedure, which accounts for the mechanical contact of rigid bodies, to investigate contact simulations of a circular cylinder and a sphere...

This paper presents a new and efficient algorithm for the calculation of sub-grid distances in the context of a lattice Boltzmann method (LBM). LBMs usually operate on equidistant Cartesian grids and represent moving geometries by either using immersed boundary conditions or dynamic fill algorithms in combination with slip or no-slip boundary condi...

This paper deals with two frequently reported issues of SPH, i.e. errors related to truncated kernels or irregular particle distributions and the aim to reduce the computational cost associated with homogeneous particle resolution. An attempt was made to increase the consistency of the SPH gradient approximation of functions, while also dealing wit...

The paper is concerned with simulation-based shape optimisation in marine engineering flows. Attention is devoted to the derivation of an adjoint complement to two-phase flow finite-volume procedures. The strategy refers to an extension of a hybrid continuous/discrete adjoint method for volume-of-fluid (VoF) approaches. The study outlines means to...

The paper deals with the mass conservation and geometry intersection of overset grid coupling strategies. The interpolation based grid coupling of the overset procedure violates the inherent mass conservation of finite-volume methods. This is problematic since incompressible finite-volume solvers directly use the mass defect when solving for the pr...

Focus of this work is set in the field of Consistency and Adaptivity. The study addresses two frequently reported issues of SPH, i.e. errors related to truncated kernels or irregular particle distributions and the aim to reduce the computational cost associated to homogeneous particle resolution. The novelty of the present approach refers to the co...

Focus of this work is set in the field of Computational Fluid Dynamics and starting point are the kernel based approximations, on which the Smoothed Particle Hydrodynamics (SPH) method is based. The study addresses two frequently reported issues of SPH, i.e. errors related to truncated kernels or irregular particle distributions as well as the aim...

The paper is concerned with the simulation of mechanically coupled bodies in seaway. While the applications of such cases are very wide, they are of particular interest for offshore operations, e.g. towing and boat landing. The focus of the present study is to supplement a viscous flow solver by appropriate mechanical models to analyse the hydrodyn...

The paper reports on the predictive performance of Lattice Boltzmann methods in turbulent channel flows. Attention is confined to model-free (direct) numerical simulations at ReTau=180 using essentially different collision models, i.e. the Bhatnagar-Gross-Krook (BGK), the Multiple-Relaxation-Time (MRT) and the Cumulant model. The three approaches a...

It is inevitable that commercial shipping and oil and gas resource exploitation activities in the Arctic will increase due to decreasing sea ice extent caused by global climate changes. Significantly more demanding and at the same time less well known environmental conditions create a need for reliable methods to assess icebreaking performance guar...

The contribution is devoted to a novel grid refinement technique for GPU-accelerated Lattice Boltzmann Method (LBM) dedicated to free surface flow simulations in marine applications. LBM implementations are mostly based on homogeneous isotropic Cartesian discretizations of the computational domain. Challenges occur when a refined spatial and tempor...

This paper reports on the adaptation of a Lattice Boltzmann based free surface flow solver to the simulation of complex fluid-ship-ice interactions in marine engineering. The analysis is restricted to the interaction of already broken ice floes and the ship hull, aiming at the optimization of a ship hull’s capability to clear the ice and keep it aw...

This work concerns the development of a meshfree semi-implicit numerical scheme based on the Smoothed Particle Hydrodynamics (SPH) method, here applied to free surface hydrodynamic problems governed by the shallow water equations. In explicit numerical methods, a severe limitation on the time step is often due to stability restrictions imposed by t...

This paper reports on the challenges of using an overset grid approach when simulating incompressible flows with a cell-centred finite-volume solver. The focal point is on the grid coupling approach. Usually, overset grid methods for unstructured three-dimensional grids apply a local interpolation of field values onto the partner grid as a coupling...

An L1-penalty term is inserted in the cost functional of an optimal control problem in order to promote a sparse distribution of the control variable. The non-differentiable L1-regularization term is approximated by differentiable Huber functions. The approach is validated by generic fluid-dynamic test cases and applied to a cabin air outlet of an...

This contribution presents a GPU-accelerated simulation tool for turbulent flows. The tool is based on LBM implementations on Cartesian grids with local grid refinement. The turbulent characteristics of the under-resolved high Reynolds number flows are either modeled by Large Eddy models, e.g. Smagorinsky LES, or by the LBM collision operator itsel...

The Poster was presented on the 13th International Conference for Mesoscopic Methods in Engineering and Science in Hamburg. It gives an overview of a research project on the numerical simulation of ship-ice interaction under consideration of ice breaking.

A numerical model to predict the interaction between floating objects and the surrounding level ice is presented. Attention is restricted to breaking of level ice due to bending. Emphasis is given to modeling the process by contact forces between floating objects, i.e. the vessel, the level ice and the ice floes, in the framework of a physics engin...

This contribution addresses the efficient numerical simulation of wave impact on the side walls of two-dimensional containers. For the flow field calculations, an efficient Lattice Boltzmann Method (LBM) is used. Whilst modeling essentially similar physics as classical continuum mechanics procedures, LBM features a number of performance-related adv...

The paper presents the development of a cavitation erosion prediction method. The approach is tailored to marine applications and embedded into a VoF-based procedure for the simulation of turbulent flows. Supplementary to the frequently employed Euler-Euler models, Euler-Lagrange approaches are employed to simulate cavitation. The study aims to con...

Investigations of flow characteristics around ship hulls at large drift angle are very important for understanding the motion behavior of ships during maneuvers. At large drift angles, the flow is dominated by strong vortical structures and complex three-dimensional separations. An accurate prediction of these flow structures is still a challenge f...

This paper advocates the benefits of consistent kernel-based filter functions dedicated to the filtering of shape sensitivities obtained from CAD-free adjoint hydrodynamic shape optimisation procedures. Emphasis is given to explicit corrections of truncated Gaussian filters in discrete space subjected to first-order consistency constraints. The nat...

Real-time rendering in the realm of computational fluid dynamics (CFD) in particular and scientific high performance computing (HPC) in general is a comparably young field of research, as the complexity of most problems with practical relevance is too high for a real-time numerical simulation. However, recent advances in HPC and the development of...

This contribution is dedicated to demonstrating the high potential and manifold applications of state-of-the-art computational fluid dynamics (CFD) tools for free-surface flows in civil and environmental engineering. All simulations were performed with the academic research code elbe (efficient lattice boltzmann environment, http://www.tuhh.de/elbe...

Dive deep into the fascinating world of real-time computational fluid dynamics. We present details of our GPU-accelerated flow solver for the simulation of non-linear violent flows in marine and coastal engineering. The solver, the efficient lattice boltzmann environment elbe, is accelerated with recent NVIDIA graphics hardware and allows for three...

This paper reports on the applicability of the Lattice Boltzmann based free surface flow solver elbe to the simulation of complex ship-ice interactions in marine engineering. In order to model the dynamics of these colliding rigid multi-body systems, elbe is coupled to the ODE physics engine. First, basic validations of the ODE collision and fricti...

This paper presents a fast surface voxelization technique for the mapping of tessellated triangular surface meshes to uniform and structured grids that provide a basis for CFD simulations with the lattice Boltzmann method (LBM). The core algorithm is optimized for massively parallel execution on graphics processing units (GPUs) and is based on a un...